Grain Structure Evolution in 6013 Aluminum Alloy during High Heat-Input Friction-Stir Welding

This work was undertaken to evaluate the influence of friction-stir welding (FSW) under a high-heat input condition on microstructural evolution. Given the extreme combination of deformation conditions associated with such an FSW regime (including the highest strain, temperature, and strain rate), it was expected to result in an unusual structural response. For this investigation, a commercial 6013 aluminum alloy was used as a program material, and FSW was conducted at a relatively high spindle rate of 1100 rpm and an extremely low feed rate of 13 mm/min; moreover, a Ti-6Al-4V backing plate was employed to reduce heat loss during welding. It was found that the high-heat-input FSW resulted in the formation of a pronounced fine-grained layer at the upper weld surface. This observation was attributed to the stirring action exerted by the shoulder of the FSW tool. Another important issue was the retardation of continuous recrystallization. This interesting phenomenon was explained in terms of a competition between recrystallization and recovery at high temperatures. Specifically, the activation of recovery should reduce dislocation density and thus retard the development of deformation-induced boundaries.

On the Degree of Plastic Strain during Laser Shock Peening of Ti-6Al-4V

Laser shock peening (LSP) is an innovative technique that is used to enhance the fatigue strength of structural materials via the generation of significant residual stress. The present work was undertaken to evaluate the degree of plastic strain introduced during LSP and thus improve the fundamental understanding of the LSP process. To this end, electron backscatter diffraction (EBSD) and nano-hardness measurements were performed to examine the microstructural response of laser-shock-peened Ti-6Al-4V alloy. Only minor changes in both the shape of α grains/particles and hardness were found. Accordingly, it was concluded that the laser-shock-peened material only experienced a small plastic strain. This surprising result was attributed to a relatively high rate of strain hardening of Ti-6Al-4V during LSP.

External and gastrointestinal parasites of the black-faced ibis Theristicus melanopis (Pelecaniformes: Threskiornithidae) in the Los Ríos region, southern Chile

The black-faced ibis, Theristicus melanopis, is considered a useful bird species for agricultural activity because it preys upon various invertebrate and vertebrate pests. Although it is a common species in Chile, limited information is available regarding its parasites. The main objective of this study was to recover the diversity of ectoparasites and gastrointestinal helminths in black-faced ibises living in the communes of Valdivia and Panguipulli, Los Ríos region. A total of 74 specimens were received for examination from the Centro de Rehabilitación de Fauna Silvestre at the Universidad Austral de Chile (CEREFAS-UACh), Valdivia, in 2011-2015. Black-faced ibises were externally inspected for ectoparasites by direct examining of the plumage, and necropsies were performed to examine digestive and respiratory organs in search of endoparasites. For each taxon, prevalence, mean intensity, mean abundance, and range of parasites per bird were estimated. Five species of ectoparasites and six species of helminths were identified. A total of 298 lice (Insecta: Phthiraptera) belonging to four species were collected: Ardeicola melanopis (13.51%), Colpocephalum trispinum (20.27%), Ibidoecus fissisignatus (4.05%), and Plegadiphilus mamillatus (9.46%). In addition, one feather mite species, Diodochaetus melanopis (Acari: Pterolichoidea) (17.56%), was isolated. In 48 black-faced ibis (64.86%), a total of 1229 gastrointestinal helminths were found: two nematodes, Porrocaecum heteropterum (55.41%) and Baruscapillaria obsignata (24.32%); one tapeworm Eugonodaeum nasuta (20.27%); two digeneans, Echinoparyphium recurvatum (1.35%) and Strigea bulbosa (6.76%); and the acanthocephalan Sphaerirostris sp. (1.35%). The findings of the following parasites present new host-parasite associations: P. mamillatus, D. melanopis, B. obsignata, E. recurvatum, S. bulbosa, and Sphaerirostris sp. Additionally, the louse P. mamillatus, feather mite D. melanopis, platyhelminths E. nasuta, E. recurvatum and S. bulbosa, and the acanthocephalan Sphaerirostris sp. are new records for the fauna of Chile.

Measuring the variability of local characteristics in complex networks: Empirical and analytical analysis

We examine the dynamics for the average degree of a node's neighbors in complex networks. It is a Markov stochastic process, and at each moment of time, this quantity takes on its values in accordance with some probability distribution. We are interested in some characteristics of this distribution: its expectation and its variance, as well as its coefficient of variation. First, we look at several real communities to understand how these values change over time in social networks. The empirical analysis of the behavior of these quantities for real networks shows that the coefficient of variation remains at high level as the network grows. This means that the standard deviation and the mean degree of the neighbors are comparable. Then, we examine the evolution of these three quantities over time for networks obtained as simulations of one of the well-known varieties of the Barabási-Albert model, the growth model with nonlinear preferential attachment (NPA) and a fixed number of attached links at each iteration. We analytically show that the coefficient of variation for the average degree of a node's neighbors tends to zero in such networks (albeit very slowly). Thus, we establish that the behavior of the average degree of neighbors in Barabási-Albert networks differs from its behavior in real networks. In this regard, we propose a model based on the NPA mechanism with the rule of random number of edges added at each iteration in which the dynamics of the average degree of neighbors is comparable to its dynamics in real networks.

Effect of Tempforming on Strength and Toughness of Medium-Carbon Low-Alloy Steel

The effect of tempforming on the strength and fracture toughness of 0.4%C-2%Si-1%Cr-1%Mo-VNb steel was examined. Plate rolling followed by tempering at the same temperature of 600 °C increases yield stress by 25% and the Charpy V-notch impact energy by a factor of ~10. Increasing rolling reduction leads to the reorientation and elongation of grains toward the rolling direction (RD) and the development of a strong {001} <110> (rotated cube) texture component that highly enhances fracture toughness. A lamellar structure with a spacing of 72 nm between boundaries and a lattice dislocation density of ~10¹⁵ m^-2 evolves after tempforming at 600 °C with a total strain of 1.4. Two types of delamination were found, attributed to crack branching and the propagation of secondary cracks along the rolling plane perpendicular to the propagation direction of the primary crack. Delamination toughness is associated with the nucleation of secondary cracks in RD and their propagation over a large distance. The critical condition for delamination toughness is the propagation of primary cracks by the ductile fracture mechanism and the propagation of secondary cracks by the brittle quasi-cleavage mechanism.

Small-scale fluctuations of laser beam fluence at the large B-integral in ultra-high intensity lasers

Analytical expressions for the spatial spectrum of fluence fluctuations of a laser pulse propagating in a medium with Kerr nonlinearity have been obtained. It is shown that inhomogeneities with a spatial scale much larger than the critical scale of self-focusing grow insignificantly even at large values of the B-integral. Experiments using BK7 glass and a KDP crystal as a nonlinear medium confirm the obtained theoretical results. This may be interesting for pulse post-compression, frequency doubling, and other experiments using transmission optical elements in ultra-high intensity lasers.

Dissimilar Friction Stir Welding of AA2519 and AA5182

In this study, the friction-stir welding (FSW) technique was successfully applied for joining of AA2519 to AA5181 alloy. Microstructure and mechanical properties of dissimilar FSW joints were investigated by optical microscopy, microhardness, and tensile testing. The deformation behaviour of the welded joints was elucidated via the digital image correlation technique. After welding, the ultimate tensile strength of joints was ~300 MPa and ductility was ~16%. The microhardness values observed at the stir zone were higher than those in the base material AA5182. The produced welds demonstrate nearly 100% (based on AA5182) joint efficiency.

Tailoring of Dissimilar Friction Stir Lap Welding of Aluminum and Titanium

An approach was proposed to optimize dissimilar friction stir lap welding of aluminum and titanium alloys. The basic concept of the new technique included (i) the plunging of the welding tool solely into the aluminum part (i.e., no direct contact with the titanium side) and (ii) the welding at a relatively high-heat input condition. It was shown that sound welds could be readily produced using an ordinary cost-effective tool, with no tool abrasion and no dispersion of harmful titanium fragments within the aluminum side. Moreover, the intermetallic layer was found to be as narrow as ~0.1 µm, thus giving rise to excellent bond strength between aluminum and titanium. On the other hand, several important shortcomings were also revealed. First of all, the high-heat input condition provided significant microstructural changes in the aluminum part, thereby resulting in essential material softening. Furthermore, the new approach was not feasible in the case of highly alloyed aluminum alloys due to the relatively low rate of self-diffusion in these materials. An essential issue was also a comparatively narrow processing window.

Improving focusability of post-compressed PW laser pulses using a deformable mirror

The use of the post-compression technique ensures gain in laser pulse peak power but at the same time degrades beam focusability due to the nonlinear wavefront distortions caused by a spatially nonuniform beam profile. In this paper a substantial focusability improvement of a post-compressed laser pulse by means of adaptive optics was demonstrated experimentally. The Strehl ratio increase from 0.16 to 0.43 was measured. Simulations showed that the peak intensity in this case reaches 0.52 of the theoretical limit.

Helminth and ectoparasitic faunas of the Harris's hawk, Parabuteo unicinctus (Accipitriformes: Accipitridae), in Chile: new data on host-parasite associations for Neotropical raptors

Birds of prey harbor a wide spectrum of various parasites, mostly with a heteroxenous life cycle. However, most reports on their parasites come from Europe. Although the Harris's hawk (Parabuteo unicinctus) is a widespread species in America, parasitological surveys on this hawk are mostly focused on coprological findings and ectoparasites, with poor attention paid to helminths. The aim of this study was to gather new and additional data on host-parasite associations for the Harris's hawk. Twenty-nine birds from central and southern Chile were necropsied. Further, nine birds from a rehabilitation center and 22 museum specimens were inspected for ectoparasites. Sixty-eight percent of birds hosted at least one parasite species. Four lice species, one mite species and eight helminth species (five nematodes, two platyhelminthes and one acanthocephalan) were recorded. Parasitic lice Colpocephalum nanum and Nosopon chanabense, and a nematode Cyathostoma (Hovorkonema) americana were recorded for the first time in raptors from the Neotropics. A feather mite, Pseudalloptinus sp., nematodes, Physaloptera alata and Microtetrameres sp., and a trematode Neodiplostomim travassosi, were recorded for the first time in Chile. The presence of diverse heteroxenous helminths reported here in the Harris's hawk could be explained by the generalist diet of this raptor.

533 Human Case Characterizations of Skin Burn Using Novel Multi-Spectral Short Wave Infrared Imaging

Introduction

Determining the depth of skin burns in patients is critical for surgical decision making, but currently lacks accuracy in clinical practice. Short-wave infrared (SWIR) light penetrates tissue more than visual or near-infrared light and is very sensitive to water content. We have shown in animal models that imaging of skin burns in the SWIR range distinguishes between superficial and deep tissue necrosis. Here we present the first 2 cases of multi-spectral SWIR imaging of human burn injury as a first step toward a non-invasive, label-free, technique for burn depth determination.

Methods

Two subjects admitted for mixed depth, thermal, 6% and 7% total body surface area (TBSA), burns were studied. Prior to burn excision, a novel system, based on a specialized camera, imaged the burn areas and normal skin at 4 different SWIR bands. Standard photographs from imaged areas were collected and presented for 5 independent, blinded, surgeons’ assessments. In SWIR images, 3-5 regions of interest (ROIs) were selected in burned and adjacent normal skin and the reflected light intensity in each ROI was averaged.

Results

Visual and SWIR images were collected for 9 burn areas in the hands, arms, and shoulder of 2 patients (Panel A). Fifty ROIs from the burn areas were assessed by the surgeons and 30 (60%) ROIs were agreed as being superficial or superficial partial thickness (n=5), deep partial thickness (n=11), or full thickness (n=14) burns by a majority (60% or above consensus together with a possible disagreement only between deep partial and full thickness burn). In Panel B the cumulative SWIR reflectance intensity at the 4 SWIR bands for the 3 burn groups, determined by expert surgeon evaluation, and normal skin are compared. The reflectance from superficial and superficial partial thickness burns (yellow) were 102.7±1.2%, 102.3±0.7% and 103.4±1.4% of the normal skin reflectance for 1200, 1650 and 1940 nm, respectively. On the other hand, the reflectance from deep partial thickness burns (grey) were 96.7±0.1% and 94.7±0.1%, and for full thickness burn (red) were 96.1±1.4% and 93.7±1.6% of normal skin reflectance for 1650 and 1940 nm, respectively.

Conclusions

We present the first human SWIR study demonstrating a distinct reflectance intensity of SWIR wavelengths for different burn depths based on surgeon assessments. The results motivate further studies of SWIR imaging of burns in the hope to non-invasively and accurately identify operative versus non-operative burns.

Compact pulse shaper based on a tilted volume Bragg grating

A compact optical layout of a pulse shaper for strongly chirped laser pulses of nanosecond time scale exploiting a tilted chirped volume Bragg grating and a programmable spatial light modulator is proposed. The setup has a non-zero frequency dispersion; thus it may be used for stretching or compressing the pulse and controlling its shape simultaneously. The feasibility of spectral shaping with a resolution of 0.16 nm, corresponding to a time resolution of 150 ps, and a contrast ratio of 10² is demonstrated experimentally.

Ectoparasites of Columbina passerina insularis (Columbiformes) in the National Zoological Park, Havana, Cuba

Ectoparasites of 18 free-living Cuban Ground Doves, Columbina passerina insularis (Columbiformes: Columbidae), captured in the National Zoological Park, Havana, Cuba, were identified. The collected ectoparasites included two species of lice (Phthiraptera: Ischnocera): Columbicola passerinae (77.1%), and Physconelloides eurysema (50%), as well as four species of feather mites (Astigmata: Falculiferidae): Pterophagus lomatus (83.3%), Byersalges talpacoti (50%), Byersalges phyllophorus (72.2%), and Hyperaspidacarus tridentatus (27.7%). Pterophagus lomatus, B. phyllophorus, and H. tridentatus represent new records for Cuba.

11 fs, 1.5 PW laser with nonlinear pulse compression

The PEARL laser output pulse with a duration of 60-70 fs was compressed to 11 fs after passing through a 5-mm thick silica plate and reflecting from two chirping mirrors with a total dispersion of -250 fs². The experiments were carried out for the B-integral values up to 19 without damage of the optical elements, which indicates that small-scale self-focusing was suppressed. The results obtained show the possibility of further nonlinear compression scaling to multipetawatt power in pulses with duration commensurate with the field period.

Parasitic fauna of the invasive house sparrow (Passer domesticus) from Ñuble region, Chile: an example of co-introduced parasites

Invasive species impact native wildlife in several ways, as they compete for resources and may transmit their specific pathogens. However, the potential consequences of co-introduced parasites are not fully understood. While the house sparrow (Passer domesticus) was introduced in Chile about a century ago, no data are available regarding its parasites. Thus, the aim of the present study was to determine the parasitic fauna of this avian invader and to determine whether there are co-introduced/co-invasive parasites shared with native birds. One hundred and eight birds were collected from three different localities in the Ñuble region of Chile, and a complete parasitic necropsy was performed in the laboratory. Twenty-three (21.3%) were parasitized by six arthropod species and four (3.7%) were parasitized by two helminth species. Four out of eight taxa are reported for the first time in Chile; among them, three arthropod parasites and the tapeworm, Anonchotaenia globate, are considered as co-introduced parasites. Only A. globata is a potential co-invasive parasite given its low degree specificity in terms of its definitive hosts. Future research should examine whether additional co-introduced/co-invasive parasites have been brought by the house sparrow, and what their potential consequences might be on the health of native birds in Chile.

Discovering and documenting Acari: the first twenty years in Zootaxa

Acari represent the most diverse group within the arachnids with some 60,000 described species. It is generally believed that most species of mites are waiting to be discovered and described. Zootaxa was the most important journal for mite taxonomy during the last twenty years (2001 to 2020). It published 1305 papers by 1057 authors during these two decades, with descriptions of 3271 new taxa/names, which account for 24.4% of the total indexed in Zoological Record. The numbers of new synonyms of Acari in Zootaxa (334) also accounted for nearly a quarter (24.9%) of the total published during this period. These data indicate that Zootaxa has been an important and leading journal for acarologists to document the diversity of mites and ticks in the world.

Spin-orbit coupling suppression and singlet-state blocking of spin-triplet Cooper pairs

An inhomogeneous magnetic exchange field at a superconductor/ferromagnet interface converts spin-singlet Cooper pairs to a spin-polarized triplet state. Although the decay envelope of triplet pairs within ferromagnetic materials is well studied, little is known about their decay in nonmagnetic metals and superconductors and, in particular, in the presence of spin-orbit coupling (SOC). Here, we investigate devices in which singlet and triplet supercurrents propagate into the s-wave superconductor Nb. In the normal state of Nb, triplet supercurrents decay over a distance of 5 nm, which is an order of magnitude smaller than the decay of spin-singlet pairs due to the SOC. In the superconducting state of Nb, triplet supercurrents are not able to couple with the singlet wave function and are thus blocked by the absence of available equilibrium states in the singlet gap. The results offer insight into the dynamics between s-wave singlet and s-wave triplet states.

Detection of Drug-Induced Torsades de Pointes Arrhythmia Mechanisms Using hiPSC-CM Syncytial Monolayers in a High-Throughput Screening Voltage Sensitive Dye Assay

We validated 3 distinct hiPSC-CM cell lines-each of different purity and a voltage sensitive dye (VSD)-based high-throughput proarrhythmia screening assay as a noncore site in the recently completed CiPA Myocyte Phase II Validation Study. Blinded validation was performed using 12 drugs linked to low, intermediate, or high risk for causing Torsades de Pointes (TdP). Commercially sourced hiPSC-CMs were obtained either from Cellular Dynamics International (CDI, Madison, Wisconsin, iCell Cardiomyoyctes2) or Takara Bio (CLS, Cellartis Cardiomyocytes). A third hiPSC-CM cell line (MCH, Michigan) was generated in house. Each cell type had distinct baseline electrophysiological function (spontaneous beat rate, action potential duration, and conduction velocity) and drug responsiveness. Use of VSD and optical mapping enabled the detection of conduction slowing of sodium channel blockers (quinidine, disopyramide, and mexiletine) and drug-induced TdP-like activation patterns (rotors) for some high- and intermediate-risk compounds. Low-risk compounds did not induce rotors in any cell type tested. These results further validate the utility of hiPSC-CMs for predictive proarrhythmia screening and the utility of VSD technology to detect drug-induced APD prolongation, arrhythmias (rotors), and conduction slowing. Importantly, results indicate that different ratios of cardiomyocytes and noncardiomyocytes have important impact on drug response that may be considered during risk assessment of new drugs. Finally, we present the first blinded CiPA hiPSC-CM validation results to simultaneously detect drug-induced conduction slowing, action potential duration prolongation, action potential triangulation, and drug-induced rotors in a proarrhythmia assay.

Antimicrobial resistance in Clostridioides (Clostridium) difficile derived from humans: a systematic review and meta-analysis

Background

Clostridioides (Clostridium) difficile is an important pathogen of healthcare- associated diarrhea, however, an increase in the occurrence of C. difficile infection (CDI) outside hospital settings has been reported. The accumulation of antimicrobial resistance in C. difficile can increase the risk of CDI development and/or its spread. The limited number of antimicrobials for the treatment of CDI is matter of some concern.

Objectives

In order to summarize the data on antimicrobial resistance to C. difficile derived from humans, a systematic review and meta-analysis were performed.

Methods

We searched five bibliographic databases: (MEDLINE [PubMed], Scopus, Embase, Cochrane Library and Web of Science) for studies that focused on antimicrobial susceptibility testing in C. difficile and were published between 1992 and 2019. The weighted pooled resistance (WPR) for each antimicrobial agent was calculated using a random- effects model.

Results

A total of 111 studies were included. The WPR for metronidazole and vancomycin was 1.0% (95% CI 0–3%) and 1% (95% CI 0–2%) for the breakpoint > 2 mg/L and 0% (95% CI 0%) for breakpoint ≥32 μg/ml. Rifampin and tigecycline had a WPRs of 37.0% (95% CI 18–58%) and 1% (95% CI 0–3%), respectively. The WPRs for the other antimicrobials were as follows: ciprofloxacin 95% (95% CI 85–100%), moxifloxacin 32% (95% CI 25–40%), clindamycin 59% (95% CI 53–65%), amoxicillin/clavulanate 0% (0–0%), piperacillin/tazobactam 0% (0–0%) and ceftriaxone 47% (95% CI 29–65%). Tetracycline had a WPR 20% (95% CI 14–27%) and meropenem showed 0% (95% CI 0–1%); resistance to fidaxomicin was reported in one isolate (0.08%).

Conclusion

Resistance to metronidazole, vancomycin, fidaxomicin, meropenem and piperacillin/tazobactam is reported rarely. From the alternative CDI drug treatments, tigecycline had a lower resistance rate than rifampin. The high-risk antimicrobials for CDI development showed a high level of resistance, the highest was seen in the second generation of fluoroquinolones and clindamycin; amoxicillin/clavulanate showed almost no resistance. Tetracycline resistance was present in one fifth of human clinical C. difficile isolates.

On the Fatigue Performance of Friction-Stir Welded Aluminum Alloys

This work was undertaken in an attempt to ascertain the generic characteristics of fatigue behavior of friction-stir welded aluminum alloys. To this end, different alloy grades belonging to both the heat-treatable and non-heat-treatable types in both the cast and wrought conditions were studied. The analysis was based on the premise that the fatigue endurance of sound welds (in which internal flaws and surface quality are not the major issues) is governed by residual stress and microstructure. Considering the relatively low magnitude of the residual stresses but drastic grain refinement attributable to friction-stir welding, the fatigue performance at relatively low cyclic stress was deduced to be dictated by the microstructural factor. Accordingly, the fatigue crack typically nucleated in relatively coarse-grained base material zone; thus, the fatigue strength of the welded joints was comparable to that of the parent metal. At relatively high fatigue stress, the summary (i.e., the cyclic-plus residual-) stress may exceed the material yield strength; thus, the fatigue cracking should result from the preceding macro-scale plastic deformation. Accordingly, the fatigue failure should occur in the softest microstructural region; thus; the fatigue strength of the welded joint may be inferior to that of the original material.

Parasites of the Shiny Cowbird, Molothrus bonariensis, and the Austral Blackbird, Curaeus curaeus, (Passeriformes: Icteridae) in Chile

Comparative studies of parasites in sympatric bird species have been generally scarce. Parasitic infection/transmission can be spread in a number of ways that suggests possible direct and indirect, horizontal transmission between avian hosts. In order to determine whether two sympatric icterids from Central and Southern Chile share their parasite fauna (ecto- and endoparasites), we examined parasites of 27 Shiny Cowbirds, Molothrus bonariensis, and 28 Austral Blackbirds, Curaeus curaeus, including individuals captured in the wild and carcasses. We found that Shiny Cowbirds were infected with the chewing lice Brueelia bonariensis, Philopterus sp. 1, the feather mites Amerodectes molothrus, Proctophyllodes spp. (species 1 and 2), and the helminths Mediorhynchus papillosus, Plagiorhynchus sp., Dispharynx nasuta and Tetrameres paucispina, while Austral Blackbirds had the chewing lice Myrsidea sp., Philopterus sp. 2, the feather mites Proctophyllodes sp. 3, Amerodectes sp., and three helminths: Anonchotaenia sp., Capillaria sp. and M. papillosus. The flea Dasypsyllus (Neornipsyllus) cteniopus was found only on the Austral Blackbird. The only parasite species shared by both icterids was the acanthocephalan M. papillosus, possibly due to their feeding on the same intermediate insect hosts. With the exception of B. bonariensis and Philopterus sp. 1 found on the Shiny Cowbird, all species reported in this study represent new parasite-host associations and new records of parasite diversity in Chile.

Dental anomalies in people living in radionuclide-contaminated regions

The 1986 accident at the Chernobyl Nuclear Power Plant led to large-scale changes in the environmental situation. The purpose of our study was to conduct a comparative analysis of the morphological states of the dentition of individuals living in regions exposed to radiation to determine the groups at risk for the main classes of dental anomalies. We believe our results will support the development of a differentiated system for dental rehabilitation and follow-up of individuals exposed to radiation. The prevalence rate of dental anomalies was studied in 1,889 patients of both sexes divided by age in accordance with dentition formation stages and by regions of residence in accordance with the ¹³⁷Cs soil-contamination level. A statistically significant decrease was observed in the number of patients with normal dentition for their age among those who had been exposed to prenatal radiation. A sharp increase in combined dental anomalies was revealed in patients who lived in regions with a¹³⁷Cs soil-contamination level ranging from 555 to 1665 GBq/km²; concomitantly, multidirectional fluctuations were observed in the numbers of tooth and occlusion anomalies. Among the examined population, the most severe pathology of the oral organs was found in prenatally irradiated patients (born between April 26, 1986, and April 30, 1987). The prevalence of dental anomalies is interrelated not only with the level of radioactive contamination in the soil of the dwelling area, but also with the age of the surveyed individuals at the moment of the accident.

Short-wave infrared light imaging measures tissue moisture and distinguishes superficial from deep burns

Existing clinical approaches and tools to measure burn tissue destruction are limited resulting in misdiagnosis of injury depth in over 40% of cases. Thus, our objective in this study was to characterize the ability of short-wave infrared (SWIR) imaging to detect moisture levels as a surrogate for tissue viability with resolution to differentiate between burns of various depths. To accomplish our aim, we constructed an imaging system consisting of a broad-band Tungsten light source; 1,200-, 1,650-, 1,940-, and 2,250-nm wavelength filters; and a specialized SWIR camera. We initially used agar slabs to provide a baseline spectrum for SWIR light imaging and demonstrated the differential absorbance at the multiple wavelengths, with 1,940 nm being the highest absorbed wavelength. These spectral bands were then demonstrated to detect levels of moisture in inorganic and in vivo mice models. The multiwavelength SWIR imaging approach was used to diagnose depth of burns using an in vivo porcine burn model. Healthy and injured skin regions were imaged 72 hours after short (20 seconds) and long (60 seconds) burn application, and biopsies were extracted from those regions for histologic analysis. Burn depth analysis based on collagen coagulation histology confirmed the formation of superficial and deep burns. SWIR multispectral reflectance imaging showed enhanced intensity levels in long burned regions, which correlated with histology and distinguished between superficial and deep burns. This SWIR imaging method represents a novel, real-time method to objectively distinguishing superficial from deep burns.

Mechanisms by Which Ranolazine Terminates Paroxysmal but Not Persistent Atrial Fibrillation

BACKGROUND

Ranolazine inhibits Na⁺ current (I_Na), but whether it can convert atrial fibrillation (AF) to sinus rhythm remains unclear. We investigated antiarrhythmic mechanisms of ranolazine in sheep models of paroxysmal (PxAF) and persistent AF (PsAF).

METHODS

PxAF was maintained during acute stretch (N=8), and PsAF was induced by long-term atrial tachypacing (N=9). Isolated, Langendorff-perfused sheep hearts were optically mapped.

RESULTS

In PxAF ranolazine (10 μmol/L) reduced dominant frequency from 8.3±0.4 to 6.2±0.5 Hz (P<0.01) before converting to sinus rhythm, decreased singularity point density from 0.070±0.007 to 0.039±0.005 cm^-2 s^-1 (P<0.001) in left atrial epicardium (LA_epi), and prolonged AF cycle length (AFCL); rotor duration, tip trajectory, and variance of AFCL were unaltered. In PsAF, ranolazine reduced dominant frequency (8.3±0.5 to 6.5±0.4 Hz; P<0.01), prolonged AFCL, increased the variance of AFCL, had no effect on singularity point density (0.048±0.011 to 0.042±0.016 cm^-2 s^-1; P=ns) and failed to convert AF to sinus rhythm. Doubling the ranolazine concentration (20 μmol/L) or supplementing with dofetilide (1 μmol/L) failed to convert PsAF to sinus rhythm. In computer simulations of rotors, reducing I_Na decreased dominant frequency, increased tip meandering and produced vortex shedding on wave interaction with unexcitable regions.

CONCLUSIONS

PxAF and PsAF respond differently to ranolazine. Cardioversion in the former can be attributed partly to decreased dominant frequency and singularity point density, and prolongation of AFCL. In the latter, increased dispersion of AFCL and likely vortex shedding contributes to rotor formation, compensating for any rotor loss, and may underlie the inefficacy of ranolazine to terminate PsAF.

External and intestinal parasites of the Austral thrush Turdus falcklandii (Aves, Turdidae) in central Chile

A total of thirty Austral thrushes Turdus falcklandii Quoy & Gaimard, 1824 (Turdidae) carcasses were brought to the Departamento de Ciencia Animal, Facultad de Ciencias Veterinarias, Universidad de Concepción, to be examined for ecto- and endoparasites. Ectoparasites were found on 20% (6/30) of the thrushes and belonged to species Brueelia magellanica Cichino, 1986 (Phthiraptera), Menacanthus eurysternus Burmeister, 1838 (Phthiraptera) and Tyrannidectes falcklandicus Mironov & González-Acuña, 2011 (Acari). Endoparasites were isolated from 26.6% (8/30) of the birds and identified as Lueheia inscripta Westrumb, 1821 (Acanthocephala), Plagiorhynchus cylindraceus Goeze, 1782 (Acanthocephala), Wardium sp. sensu Mayhew, 1925 (Cestoda), Dilepis undula (Cestoda) Schrank, 1788, and Zonorchis sp. (sensu Travassos, 1944) (Trematoda). To our knowledge, all endoparasites collected in this study are new records in T. falcklandii and expand their distributional range to Chile.

Heterogeneity of the action potential duration is required for sustained atrial fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia and accounts for substantial morbidity and mortality. Recently, we created a mouse model with spontaneous and sustained AF caused by a mutation in the NaV1.5 channel (F1759A) that enhances persistent Na+ current, thereby enabling the investigation of molecular mechanisms that cause AF and the identification of novel treatment strategies. The mice have regional heterogeneity of action potential duration of the atria similar to observations in patients with AF. In these mice, we found that the initiation and persistence of the rotational reentrant AF arrhythmias, known as spiral waves or rotors, were dependent upon action potential duration heterogeneity. The centers of the rotors were localized to regions of greatest heterogeneity of the action potential duration. Pharmacologically attenuating the action potential duration heterogeneity reduced both spontaneous and pacing-induced AF. Computer-based simulations also demonstrated that the action potential duration heterogeneity is sufficient to generate rotors that manifest as AF. Taken together, these findings suggest that action potential duration heterogeneity in mice and humans is one mechanism by which AF is initiated and that reducing action potential duration heterogeneity can lessen the burden of AF.

Theory of Magnetic Domain Phases in Ferromagnetic Superconductors

Recently discovered superconducting P-doped EuFe_{2}As_{2} compounds reveal the situation when the superconducting critical temperature substantially exceeds the ferromagnetic transition temperature. The main mechanism of the interplay between magnetism and superconductivity occurs to be an electromagnetic one, and a short-period magnetic domain structure was observed just below Curie temperature [V. S. Stolyarov et al., Sci. Adv. 4, eaat1061 (2018)SACDAF2375-254810.1126/sciadv.aat1061]. We elaborate a theory of such a transition and demonstrate how the initial sinusoidal magnetic structure gradually transforms into a solitonlike domain one. Further cooling may trigger a first-order transition from the short-period domain Meissner phase to the self-induced ferromagnetic vortex state, and we calculate the parameters of this transition. The size of the domains in the vortex state is basically the same as in the normal ferromagnet, but with the domain walls which should generate the set of vortices perpendicular to the vortices in the domains.

Unexpected bird-feather mite associations revealed by DNA metabarcoding uncovers a dynamic ecoevolutionary scenario

The high relevance of host-switching for the diversification of highly host-specific symbionts (i.e., those commonly inhabiting a single host species) demands a better understanding of host-switching dynamics at an ecological scale. Here, we used DNA metabarcoding to study feather mites on passerine birds in Spain, sequencing mtDNA (COI) for 25,540 individual mites (representing 64 species) from 1,130 birds (representing 71 species). Surprisingly, 1,228 (4.8%) mites from 84 (7.4%) birds were found on host species that were not the expected to be a host according to a recent bird-feather mite associations catalog. Unexpected associations were widespread across studied mite (40.6%) and bird (43.7%) species and showed smaller average infrapopulation sizes than typical associations. Unexpected mite species colonized hosts being distantly related to the set of their usual hosts, but with similar body size. The network of bird-mite associations was modular (i.e., some groups of bird and mite species tended to be more associated with each other than with the others), with 75.9% of the unexpected associations appearing within the module of the typical hosts of the mite species. Lastly, 68.4% of mite species found on unexpected hosts showed signatures of genetic differentiation, and we found evidence for reproduction or the potential for it in many of the unexpected associations. Results show host colonization as a common phenomenon even for these putatively highly host-specific symbionts. Thus, host-switching by feather mites, rather than a rare phenomenon, appears as a relatively frequent phenomenon shaped by ecological filters such as host morphology and is revealed as a fundamental component for a dynamic coevolutionary and codiversification scenario.

Towards wormhole beyond Horndeski

We address the issue of whether a no-go theorem for static, spherically symmetric wormholes, proven in Horndeski theories, can be circumvented by going beyond Horndeski. We show that the ghost instabilities which are at the heart of the no-go theorem, can indeed be avoided. The wormhole solutions with the latter property are, however, strongly fine tuned, and hence it is likely that they are unstable. Furthermore, it remains unclear whether these solutions have other pathologies, like gradient instabilities along angular and radial directions.

Cosmological bounce in Horndeski theory and beyond

We discuss the stability of the classical bouncing solutions in the general Horndeski theory and beyond Horndeski theory. We restate the no-go theorem, showing that in the general Horndeski theory there are no spatially flat non-singular cosmological solutions which are stable during entire evolution. We show the way to evade the no-go in beyond Horndeski theory and give two specific examples of bouncing solutions, whose asymptotic past and future or both are described by General Relativity (GR) with a conventional massless scalar field. Both solutions are free of any pathologies at all times.

Enabling large-scale feather mite studies: an Illumina DNA metabarcoding pipeline

Feather mites are among the most common and diverse ectosymbionts of birds, yet basic questions such as the nature of their relationship remain largely unanswered. One reason for feather mites being understudied is that their morphological identification is often virtually impossible when using female or young individuals. Even for adult male specimens this task is tedious and requires advanced taxonomic expertise, thus hampering large-scale studies. In addition, molecular-based methods are challenging because the low DNA amounts usually obtained from these tiny mites do not reach the levels required for high-throughput sequencing. This work aims to overcome these issues by using a DNA metabarcoding approach to accurately identify and quantify the feather mite species present in a sample. DNA metabarcoding is a widely used molecular technique that takes advantage of high-throughput sequencing methodologies to assign the taxonomic identity to all the organisms present in a complex sample (i.e., a sample made up of multiple specimens that are hard or impossible to individualise). We present a high-throughput method for feather mite identification using a fragment of the COI gene as marker and Illumina Miseq technology. We tested this method by performing two experiments plus a field test over a total of 11,861 individual mites (5360 of which were also morphologically identified). In the first experiment, we tested the probability of detecting a single feather mite in a heterogeneous pool of non-conspecific individuals. In the second experiment, we made 2 × 2 combinations of species and studied the relationship between the proportion of individuals of a given species in a sample and the proportion of sequences retrieved to test whether DNA metabarcoding can reliably quantify the relative abundance of mites in a sample. Here we also tested the efficacy of degenerate primers (i.e., a mixture of similar primers that differ in one or several bases that are designed to increase the chance of annealing) and investigated the relationship between the number of mismatches and PCR success. Finally, we applied our DNA metabarcoding pipeline to a total of 6501 unidentified and unsorted feather mite individuals sampled from 380 European passerine birds belonging to 10 bird species (field test). Our results show that this proposed pipeline is suitable for correct identification and quantitative estimation of the relative abundance of feather mite species in complex samples, especially when dealing with a moderate number (> 30) of individuals per sample.

Gastrointestinal and ectoparasites of plumbeous rail, Pardirallus sanguinolentus (Aves: Rallidae) in Central Chile

With the aim to identify the parasite fauna of plumbeous rail, Pardirallus sanguinolentus (Aves: Rallidae) in Chile, 26 carcasses were parasitologically necropsied. The present study revealed the presence of 14 species of parasites (inverse Simpson index = 4.64; evenness = 0.332), including ectoparasites: feather mites: Analloptes megnini , Grallobia sp., Grallolichus sp., Megniniella sp., and Metanalges sp.; the feather lice Pseudomenopon meinertzhageni, Rallicola andinus, and Fulicoffula sp.; and six species of gastrointestinal helminths: Heterakis psophiae, Porrocaecum ardeae, Tetrameres sp., Capillaria sp., Diorchis sp., and Plagiorhynchus sp. The relatively high parasite richness that was found could be attributed to the highly favorable conditions of wetlands for parasite development. All parasites found, except feather lice, are new records for plumbeous rail. A checklist of parasites for plumbeous rail is presented.

Parasites of the Southern silvery grebe Podiceps occipitalis (Aves, Podicipedidae) in Chile

A total of 97 southern silvery grebes (Podiceps occipitalis), which died as the result of an oil spill on the coast of central Chile, were examined for ecto- and endoparasites. Two lice species including Aquanirmus rollandii (Philopteridae) and Pseudomenopon dolium (Menoponidae) were found from 6.2% (6/97) of birds. In 91.7% (89/97) of cases, grebes were infected with some kind of helminths. Three species of gastrointestinal helminths were detected: Eucoleus contortus (Nematoda), Profilicollis bullocki (Acanthocephala), and Confluaria sp. (Cestoda). In addition, Pelecitus fulicaeatrae (Nematoda) was removed from the tibiotarsal-tarsometatarsal articulation in 13.4% (13/97) of the specimens examined. To our knowledge, these are the first records of A. rollandii, E. contortus, and Confluaria sp. as parasites of P. occipitalis. In addition, these findings expand the distributional range of A. rollandii, E. contortus, P. fulicaeatrae, and Confluaria sp. to Chile.

Gastrointestinal and external parasitism in the Magellanic Horned Owl Bubo magellanicus (Strigiformes: Strigidae) in Chile

Abstract To describe the parasitic community of the Magellanic Horned Owl, Bubo magellanicus (Aves, Strigiformes), 19 carcasses from central Chile were analyzed. Ectoparasites were collected through plumage inspection, while endoparasites were collected through traditional techniques of parasitological necropsy. Sixteen owls were infected with at least one species of ectoparasite (84.21%) or endoparasite (31.58%). Eleven of 19 birds (57.89%) harbored feather mites of the three species Pandalura cirrata (42.11%), Glaucalges attenuatus (47.37%), and Kramerella sp. (10.53%), whereas 16 individuals (84.21%) harbored the chewing louse Strigiphilus chilensis. Only six birds (31.58%) were infected with helminths; the nematodes Capillaria tenuissima (26.32%) and Dispharynx nasuta (5.26%); the acanthocephalan Centrorhynchus spinosus (5.26%); and the trematode Neodiplostomum sp. (5.26%). Apart from S . chilensis, all parasites comprised new records for B . magellanicus.

Causality analysis of leading singular value decomposition modes identifies rotor as the dominant driving normal mode in fibrillation

Cardiac fibrillation is a major clinical and societal burden. Rotors may drive fibrillation in many cases, but their role and patterns are often masked by complex propagation. We used Singular Value Decomposition (SVD), which ranks patterns of activation hierarchically, together with Wiener-Granger causality analysis (WGCA), which analyses direction of information among observations, to investigate the role of rotors in cardiac fibrillation. We hypothesized that combining SVD analysis with WGCA should reveal whether rotor activity is the dominant driving force of fibrillation even in cases of high complexity. Optical mapping experiments were conducted in neonatal rat cardiomyocyte monolayers (diameter, 35 mm), which were genetically modified to overexpress the delayed rectifier K⁺ channel I_Kr only in one half of the monolayer. Such monolayers have been shown previously to sustain fast rotors confined to the I_Kr overexpressing half and driving fibrillatory-like activity in the other half. SVD analysis of the optical mapping movies revealed a hierarchical pattern in which the primary modes corresponded to rotor activity in the I_Kr overexpressing region and the secondary modes corresponded to fibrillatory activity elsewhere. We then applied WGCA to evaluate the directionality of influence between modes in the entire monolayer using clear and noisy movies of activity. We demonstrated that the rotor modes influence the secondary fibrillatory modes, but influence was detected also in the opposite direction. To more specifically delineate the role of the rotor in fibrillation, we decomposed separately the respective SVD modes of the rotor and fibrillatory domains. In this case, WGCA yielded more information from the rotor to the fibrillatory domains than in the opposite direction. In conclusion, SVD analysis reveals that rotors can be the dominant modes of an experimental model of fibrillation. Wiener-Granger causality on modes of the rotor domains confirms their preferential driving influence on fibrillatory modes.

From a reversible code to the quantum one: R-matrix

This research has been carried out in collaboration with D.Melnikov, A.Mironov, A.Morozov and An.Morozov. We study the relation between quantum programming and knot theory. The general idea is that knot theory provides a special basis for unitary matrices. We suggest to use R-matrices of knot theory as universal gates in quantum code. We also examine basic operations in reversible programming.

hiPSC-CM Monolayer Maturation State Determines Drug Responsiveness in High Throughput Pro-Arrhythmia Screen

Human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) offer a novel in vitro platform for pre-clinical cardiotoxicity and pro-arrhythmia screening of drugs in development. To date hiPSC-CMs used for cardiotoxicity testing display an immature, fetal-like cardiomyocyte structural and electrophysiological phenotype which has called into question the applicability of hiPSC-CM findings to the adult heart. The aim of the current work was to determine the effect of cardiomyocyte maturation state on hiPSC-CM drug responsiveness. To this end, here we developed a high content pro-arrhythmia screening platform consisting of either fetal-like or mature hiPSC-CM monolayers. Compounds tested in the screen were selected based on the pro-arrhythmia risk classification (Low risk, Intermediate risk, or High risk) established recently by the FDA and major stakeholders in the Drug Discovery field for the validation of the Comprehensive In vitro Pro-Arrhythmia Assay (CiPA). Here we show that maturation state of hiPSC-CMs determines the absolute pro-arrhythmia risk score calculated for these compounds. Thus, the maturation state of hiPSC-CMs should be considered prior to pro-arrhythmia and cardiotoxicity screening in drug discovery programs.

External and gastrointestinal parasites of the rufous-collared sparrow Zonotrichia capensis (Passeriformes, Emberizidae) in Chile

Abstract A total of 277 rufous-collared sparrows, Zonotrichia capensis Müller, 1776 (Emberizidae), were examined for external parasites. The birds were captured using mist nets in seven locations in northern and central Chile. Additionally, seven carcasses from central Chile (the Biobío region) were necropsied to evaluate the presence of endoparasite infection. Ectoparasites were found on 35.8% (99/277) of the examined birds and they were represented by the following arthropods: feather mites Amerodectes zonotrichiae Mironov and González-Acuña, 2014 (Analgoidea: Proctophyllodidae), Proctophyllodes polyxenus Atyeo and Braasch, 1966 (Analgoidea: Proctophyllodidae), and Trouessartia capensis Berla, 1959 (Analgoidea: Trouessartiidae); a louse Philopterus sp. (Phthiraptera: Ischnocera); and ticks Amblyomma tigrinum Koch, 1844 (Acari: Ixodidae) and Ixodes auritulus Neumann, 1904 (Acari: Ixodidae). Two of the seven necropsied carcasses were infected with the acanthocephalan Mediorhynchus papillosus Van Cleave, 1916 (Gigantorhynchida: Gigantorhynchidae). To our knowledge, this study reports P. polyxenus, Philopterus sp., A. tigrinum, and M. papillosus for the first time for Z. capensis and expands the distributional range for T. capensis to Chile.

Parasite biodiversity faces extinction and redistribution in a changing climate

Climate change is a well-documented driver of both wildlife extinction and disease emergence, but the negative impacts of climate change on parasite diversity are undocumented. We compiled the most comprehensive spatially explicit data set available for parasites, projected range shifts in a changing climate, and estimated extinction rates for eight major parasite clades. On the basis of 53,133 occurrences capturing the geographic ranges of 457 parasite species, conservative model projections suggest that 5 to 10% of these species are committed to extinction by 2070 from climate-driven habitat loss alone. We find no evidence that parasites with zoonotic potential have a significantly higher potential to gain range in a changing climate, but we do find that ectoparasites (especially ticks) fare disproportionately worse than endoparasites. Accounting for host-driven coextinctions, models predict that up to 30% of parasitic worms are committed to extinction, driven by a combination of direct and indirect pressures. Despite high local extinction rates, parasite richness could still increase by an order of magnitude in some places, because species successfully tracking climate change invade temperate ecosystems and replace native species with unpredictable ecological consequences.

Spontaneous Currents in Superconducting Systems with Strong Spin-Orbit Coupling

We show that Rashba spin-orbit coupling at the interface between a superconductor and a ferromagnet should produce a spontaneous current in the atomic thickness region near the interface. This current is counterbalanced by the superconducting screening current flowing in the region of the width of the London penetration depth near the interface. Such a current-carrying state creates a magnetic field near the superconductor surface, generates a stray magnetic field outside the sample edges, changes the slope of the temperature dependence of the critical field H_{c3}, and may generate the spontaneous Abrikosov vortices near the interface.

Ectoparasites of the black-chinned siskin Spinus barbatus (Passeriformes: Fringillidae) in Chile

Despite being a bird with a broad and extensive distribution in Chile, the black-chinned siskin, Spinus barbatus Molina, 1782 is not well studied in relation to its parasites. This paper aims to describe the ectoparasite fauna of S. barbatus in central and southern Chile. A total of 125 individuals caught with mist nets were examined alive; a total of 22 parasites were found dead and were exposed to parasit autopsy. The extracted parasites were preserved in 70% alcohol for subsequent mounting and identification. Ectoparasites were found in 56 black-chinned siskins (38%); 48 of them (33%) had 870 mites - 680 feather mites (Astigmata: Analgoidea) were identified as Proctophyllodes spini, 167 as Knemidokoptes jamaicensis, 19 as Strelkoviacarus critesi, and one as Analges passerinus. Moreover, three mites were chiggers belonging to the tribe Schoengastiini (Prostigmata: Trombiculidae). In 21 birds (14%), 54 lice were found, 21 of which were identified as Philopterus roehreri, 18 as Myrsidea serini, and 15 as Ricinus carolynae. Endoparasites were not found in the necropsied individuals. All of the parasites that were found represent new records for Chile, and they also serve as new records of host-parasite associations for S. barbatus.

Global associations between birds and vane-dwelling feather mites

Understanding host-symbiont networks is a major question in evolutionary ecology. Birds host a great diversity of endo- and ectosymbiotic organisms, with feather mites (Arachnida: Acariformes: Analgoidea, Pterolichoidea) being among the most diverse of avian symbionts. A global approach to the ecology and evolution of bird-feather-mite associations has been hampered because of the absence of a centralized data repository. Here we present the most extensive data set of associations between feather mites and birds. Data include 12 036 records of 1887 feather mite species located on the flight feathers of 2234 bird species from 147 countries. Feather mites typically located inside quills, on the skin, or on downy body feathers are not included. Data were extracted from 493 published sources dating from 1882 to 2015. Data exploration shows that although most continents and bird families are represented, most bird species remain unexplored for feather mites. Nevertheless, this is the most comprehensive data set available for enabling global macroecological analyses of feather mites and their hosts, such as ecological network analyses. This metadata file outlines the structure of these data and provides primary references for all records used.

Deficient cMyBP-C protein expression during cardiomyocyte differentiation underlies human hypertrophic cardiomyopathy cellular phenotypes in disease specific human ES cell derived cardiomyocytes

AIMS

Mutations of cardiac sarcomere genes have been identified to cause HCM, but the molecular mechanisms that lead to cardiomyocyte hypertrophy and risk for sudden death are uncertain. The aim of this study was to examine HCM disease mechanisms at play during cardiac differentiation of human HCM specific pluripotent stem cells.

METHODS AND RESULTS

We generated a human embryonic stem cell (hESC) line carrying a naturally occurring mutation of MYPBC3 (c.2905 +1 G >A) to study HCM pathogenesis during cardiac differentiation. HCM-specific hESC-derived cardiomyocytes (hESC-CMs) displayed hallmark aspects of HCM including sarcomere disarray, hypertrophy and impaired calcium impulse propagation. HCM hESC-CMs presented a transient haploinsufficiency of cMyBP-C during cardiomyocyte differentiation, but by day 30 post-differentiation cMyBP-C levels were similar to control hESC-CMs. Gene transfer of full-length MYBPC3 during differentiation prevented hypertrophy, sarcomere disarray and improved calcium impulse propagation in HCM hESC-CMs.

CONCLUSION(S)

These findings point to the critical role of MYBPC3 during sarcomere assembly in cardiac myocyte differentiation and suggest developmental influences of MYBPC3 truncating mutations on the mature hypertrophic phenotype.

Extracellular Matrix-Mediated Maturation of Human Pluripotent Stem Cell-Derived Cardiac Monolayer Structure and Electrophysiological Function

BACKGROUND

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) monolayers generated to date display an immature embryonic-like functional and structural phenotype that limits their utility for research and cardiac regeneration. In particular, the electrophysiological function of hPSC-CM monolayers and bioengineered constructs used to date are characterized by slow electric impulse propagation velocity and immature action potential profiles.

METHODS AND RESULTS

Here, we have identified an optimal extracellular matrix for significant electrophysiological and structural maturation of hPSC-CM monolayers. hPSC-CM plated in the optimal extracellular matrix combination have impulse propagation velocities ≈2× faster than previously reported (43.6±7.0 cm/s; n=9) and have mature cardiomyocyte action potential profiles, including hyperpolarized diastolic potential and rapid action potential upstroke velocity (146.5±17.7 V/s; n=5 monolayers). In addition, the optimal extracellular matrix promoted hypertrophic growth of cardiomyocytes and the expression of key mature sarcolemmal (SCN5A, Kir2.1, and connexin43) and myofilament markers (cardiac troponin I). The maturation process reported here relies on activation of integrin signaling pathways: neutralization of β1 integrin receptors via blocking antibodies and pharmacological blockade of focal adhesion kinase activation prevented structural maturation.

CONCLUSIONS

Maturation of human stem cell-derived cardiomyocyte monolayers is achieved in a 1-week period by plating cardiomyocytes on PDMS (polydimethylsiloxane) coverslips rather than on conventional 2-dimensional cell culture formats, such as glass coverslips or plastic dishes. Activation of integrin signaling and focal adhesion kinase is essential for significant maturation of human cardiac monolayers.

Constitutive Intracellular Na+ Excess in Purkinje Cells Promotes Arrhythmogenesis at Lower Levels of Stress Than Ventricular Myocytes From Mice With Catecholaminergic Polymorphic Ventricular Tachycardia

Supplemental Digital Content is available in the text.

Background—

In catecholaminergic polymorphic ventricular tachycardia (CPVT), cardiac Purkinje cells (PCs) appear more susceptible to Ca²⁺ dysfunction than ventricular myocytes (VMs). The underlying mechanisms remain unknown. Using a CPVT mouse (RyR2^{R4496C+/Cx40eGFP}), we tested whether PC intracellular Ca²⁺ ([Ca²⁺]_i) dysregulation results from a constitutive [Na⁺]_i surplus relative to VMs.

Methods and Results—

Simultaneous optical mapping of voltage and [Ca²⁺]_i in CPVT hearts showed that spontaneous Ca²⁺ release preceded pacing-induced triggered activity at subendocardial PCs. On simultaneous current-clamp and Ca²⁺ imaging, early and delayed afterdepolarizations trailed spontaneous Ca²⁺ release and were more frequent in CPVT PCs than CPVT VMs. As a result of increased activity of mutant ryanodine receptor type 2 channels, sarcoplasmic reticulum Ca²⁺ load, measured by caffeine-induced Ca²⁺ transients, was lower in CPVT VMs and PCs than respective controls, and sarcoplasmic reticulum fractional release was greater in both CPVT PCs and VMs than respective controls. [Na⁺]_i was higher in both control and CPVT PCs than VMs, whereas the density of the Na⁺/Ca²⁺ exchanger current was not different between PCs and VMs. Computer simulations using a PC model predicted that the elevated [Na⁺]_i of PCs promoted delayed afterdepolarizations, which were always preceded by spontaneous Ca²⁺ release events from hyperactive ryanodine receptor type 2 channels. Increasing [Na⁺]_i monotonically increased delayed afterdepolarization frequency. Confocal imaging experiments showed that postpacing Ca²⁺ spark frequency was highest in intact CPVT PCs, but such differences were reversed on saponin-induced membrane permeabilization, indicating that differences in [Na⁺]_i played a central role.

Conclusions—

In CPVT mice, the constitutive [Na⁺]_i excess of PCs promotes triggered activity and arrhythmogenesis at lower levels of stress than VMs.

Gastrointestinal and external parasites of Enicognathus ferrugineus and Enicognathus leptorhynchus (Aves, Psittacidae) in Chile

Abstract Parasite species are important components of biodiversity, as they provide valuable information about host health, evolutionary relationships, population structures, trophic interactions, the existence of environmental stresses, and climatic conditions. With the aim of describing the parasites associated with parrots of the genus Enicognathus Gray 1840 from central Chile, thirteen austral parakeets, Enicognathus ferrugineus, and five slender-billed parakeets, E. leptorhynchus, were examined between September 2007 and March 2014. The prevalence of ectoparasites and endoparasites was 88.9% and 22.2%, respectively. On eleven of the E. ferrugineus (84.6%) analyzed, and on all of the E. leptorhynchus analyzed (100%), five feather mite species (Pararalichus hastifolia, Genoprotolichus major, Protonyssus sp., Fainalges sp., and Eurydiscalges sp.) were collected. On ten E. ferrugineus (76.9%) and two E. leptorhynchus (40%), the chewing lice Heteromenopon macrurum, Psittacobrossus patagoni, and Paragoniocotes enicognathidis were collected. The nematode Capillaria plagiaticia was collected from three E. ferrugineus (23.1%), and the nematode Ascaridia hermaphrodita was found in one E. leptorhynchus (20%). The presence of C. plagiaticia, Protonyssus sp., Fainalges sp., and Eurydiscalges sp. from the two Enicognathus spp. are new records for Chile and represent new parasite-host associations.

Gastrointestinal and external parasites of the white-crested elaenia Elaenia albiceps chilensis (Aves, Tyrannidae) in Chile

The objective of this study is to evaluate the ectoparasites and helminths of the white-crested elaenia, Elaenia albiceps chilensis. Feather mites Anisophyllodes elaeniae, Trouessartia elaeniae, and Analges sp. were detected in 51% of birds (n=106), whereas 24% were infected with lice (Tyranniphilopterus delicatulus, Menacanthus cfr. distinctus, and Ricinus cfr. invadens). Helminths Viguiera sp. and Capillaria sp. were found in five of the birds that were necropsied (n=20). With the exception of A. elaeniae, T. elaeniae, and T. delicatulus, all parasites represented new records found for the white-crested elaenia, and therefore for the Chilean repertoire of biodiversity.

DNA barcoding and minibarcoding as a powerful tool for feather mite studies

Feather mites (Astigmata: Analgoidea and Pterolichoidea) are among the most abundant and commonly occurring bird ectosymbionts. Basic questions on the ecology and evolution of feather mites remain unanswered because feather mite species identification is often only possible for adult males, and it is laborious even for specialized taxonomists, thus precluding large-scale identifications. Here, we tested DNA barcoding as a useful molecular tool to identify feather mites from passerine birds. Three hundred and sixty-one specimens of 72 species of feather mites from 68 species of European passerine birds from Russia and Spain were barcoded. The accuracy of barcoding and minibarcoding was tested. Moreover, threshold choice (a controversial issue in barcoding studies) was also explored in a new way, by calculating through simulations the effect of sampling effort (in species number and species composition) on threshold calculations. We found one 200-bp minibarcode region that showed the same accuracy as the full-length barcode (602 bp) and was surrounded by conserved regions potentially useful for group-specific degenerate primers. Species identification accuracy was perfect (100%) but decreased when singletons or species of the Proctophyllodes pinnatus group were included. In fact, barcoding confirmed previous taxonomic issues within the P. pinnatus group. Following an integrative taxonomy approach, we compared our barcode study with previous taxonomic knowledge on feather mites, discovering three new putative cryptic species and validating three previous morphologically different (but still undescribed) new species.