Validating silicon polytrodes with paired juxtacellular recordings: method and dataset

Cross-validating new methods for recording neural activity is necessary to accurately interpret and compare the signals they measure. Here we describe a procedure for precisely aligning two probes for in vivo "paired-recordings" such that the spiking activity of a single neuron is monitored with both a dense extracellular silicon polytrode and a juxtacellular micropipette. Our new method allows for efficient, reliable, and automated guidance of both probes to the same neural structure with micrometer resolution. We also describe a new dataset of paired-recordings, which is available online. We propose that our novel targeting system, and ever expanding cross-validation dataset, will be vital to the development of new algorithms for automatically detecting/sorting single-units, characterizing new electrode materials/designs, and resolving nagging questions regarding the origin and nature of extracellular neural signals.

Growth of asteroids, planetary embryos, and Kuiper belt objects by chondrule accretion

Chondrules are millimeter-sized spherules that dominate primitive meteorites (chondrites) originating from the asteroid belt. The incorporation of chondrules into asteroidal bodies must be an important step in planet formation, but the mechanism is not understood. We show that the main growth of asteroids can result from gas drag-assisted accretion of chondrules. The largest planetesimals of a population with a characteristic radius of 100 km undergo runaway accretion of chondrules within ~3 My, forming planetary embryos up to Mars's size along with smaller asteroids whose size distribution matches that of main belt asteroids. The aerodynamical accretion leads to size sorting of chondrules consistent with chondrites. Accretion of millimeter-sized chondrules and ice particles drives the growth of planetesimals beyond the ice line as well, but the growth time increases above the disc lifetime outside of 25 AU. The contribution of direct planetesimal accretion to the growth of both asteroids and Kuiper belt objects is minor. In contrast, planetesimal accretion and chondrule accretion play more equal roles in the formation of Moon-sized embryos in the terrestrial planet formation region. These embryos are isolated from each other and accrete planetesimals only at a low rate. However, the continued accretion of chondrules destabilizes the oligarchic configuration and leads to the formation of Mars-sized embryos and terrestrial planets by a combination of direct chondrule accretion and giant impacts.

The 67P/Churyumov-Gerasimenko observation campaign in support of the Rosetta mission

We present a summary of the campaign of remote observations that supported the European Space Agency's Rosetta mission. Telescopes across the globe (and in space) followed comet 67P/Churyumov-Gerasimenko from before Rosetta's arrival until nearly the end of the mission in September 2016. These provided essential data for mission planning, large-scale context information for the coma and tails beyond the spacecraft and a way to directly compare 67P with other comets. The observations revealed 67P to be a relatively 'well-behaved' comet, typical of Jupiter family comets and with activity patterns that repeat from orbit to orbit. Comparison between this large collection of telescopic observations and the in situ results from Rosetta will allow us to better understand comet coma chemistry and structure. This work is just beginning as the mission ends-in this paper, we present a summary of the ground-based observations and early results, and point to many questions that will be addressed in future studies.This article is part of the themed issue 'Cometary science after Rosetta'.

Microstructural Characterization of TiC-White Cast-Iron Composites Fabricated by In Situ Technique

High-chromium white cast-iron specimens locally reinforced with TiC–metal matrix composites were successfully produced via an in situ technique based on combustion synthesis. Powder mixtures of Ti, Al, and graphite were prepared and compressed to fabricate green powder compacts that were inserted into the mold cavity before the casting. The heat of the molten iron causes the ignition of the combustion reaction of the reactant powders, resulting in the formation of the TiC by self-propagating high-temperature synthesis. The microstructure of the resultant composites and the bonding interfaces was characterized by scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The microstructural results showed a good adhesion of the composite, suggesting an effective infiltration of the metal into the inserted compact, yet a non-homogeneous distribution of the TiC in the martensite matrix was observed. Based on the results, the in situ synthesis appears to be a great potential technique for industrial applications.

Identification of potential Leishmania chagasi superoxide dismutase allosteric modulators by structure-based computational approaches: homology modelling, molecular dynamics and pharmacophore-based virtual screening

The visceral form of Leishmaniasis, also known as kala-azar, caused by Leishmania chagasi is the main etiological agent of this form in Brazil responsible for 30,000 annual deaths. Despite its epidemiological impact, treatment of the disease is limited by resistance, species-dependent efficacy and serious adverse effects. The application of computational tools to prioritize potential bioactive molecules based on 3D structural of biological target is a viable alternative. Among the L. chagasi validated targets, Fe + 2 superoxide dismutase B2 (LcFeSODB2) is the first parasite enzyme against oxidative stress and it is involved in essential metabolic processes for its survival. Due to substrate binding-site volume (superoxide ion) and consequent difficulty in its active site modulation for small molecules, the search for allosteric sites at LcFeSODB2 3D structure is a promising strategy. As there are no 3D structures of LcFeSODB2, comparative modeling was applied to build 3D models by SWISS-MODEL and MODELLER version 9.19. Next, the best 3D model was used in molecular dynamics (MD) routines with multiple probes on GROMACS version 5.1.2. In addition, potential allosteric sites predicted by FTMap and Metapocket web servers were used with probe occupancy maps from MD to select an allosteric binding site and propose a pharmacophore model. Next, it was used as a template in virtual screening by UNITY^® module available on SYBYL-X version 2.1.1 at Sigma-Aldrich CPR™ subset of ZINC12 database. The pharmacophore-based virtual screening resulted in the selection of two potential allosteric LcFeSOD compounds with partial pharmacophoric requirements, drug-like properties and commercial availability for enzymatic assays. Communicated by Ramaswamy H. Sarma.

Production and Characterization of Austenitic Stainless Steel Cast Parts Reinforced with WC Particles Fabricated by Ex Situ Technique

In this work, austenitic stainless steel specimens were locally reinforced with WC particles. The reinforcements were fabricated via an ex situ technique based on powder technology. Mixtures of WC, Fe, and M0101 binder were cold-pressed to obtain powder compacts. After debinding and sintering, the porous WC–Fe inserts were fixed in a mold cavity, where they reacted with liquid metal. Microstructural analysis was conducted for characterization of the phases constituting the produced reinforcement zone and the bonding interface. The results revealed that the reinforcement is a graded material with compositional and microstructural gradients throughout its thickness. The zone nearest to the surface has a ferrous matrix with homogeneously distributed WC particles and (Fe,W,Cr)₆C and (Fe,W,Cr)₃C carbides, formed from the liquid metal reaction with the insert. This precipitation leads to austenite destabilization, which transforms into martensite during cooling. A vast dissolution of the WC particles occurred in the inner zones, resulting in more intense carbides formation. Cr-rich carbides ((Fe,Cr,W)₇C₃, and (Fe,Cr,W)₂₃C₆) formed in the interdendritic regions of austenite; this zone is characterized by coarse dendrites of austenite and a multi-phase interdendritic network composed of carbides. An interface free of discontinuities and porosities indicates good bonding of the reinforcement zone to stainless steel.

Preparation and Microstructural Characterization of a High-Cr White Cast Iron Reinforced with WC Particles

High-chromium white cast iron (WCI) specimens locally reinforced with WC-metal matrix composites were produced via an ex situ technique: powder mixtures of WC and Fe cold-pressed in a pre-form were inserted in the mold cavity before pouring the base metal. The microstructure of the resulting reinforcement is a matrix of martensite (α') and austenite (γ) with WC particles evenly distributed and (Fe,W,Cr)₆C carbides that are formed from the reaction between the molten metal and the inserted pre-form. The (Fe,W,Cr)₆C precipitation leads to the hypoeutectic solidification of the matrix and the final microstructure consists of martensite, formed from primary austenite during cooling and eutectic constituent with (Fe,Cr)₇C₃ and (Fe,W,Cr)₆C carbides. The presence of a reaction zone with 200 µm of thickness, between the base metal and the composite should guarantee a strong bonding between these two zones.

Anoxia Effects in Asphyxiated Green Sea Turtles (Chelonia mydas) Caught in an Artisanal Fishing Net on the Coast of Brazil

Among studies of drowning in green sea turtles (Chelonia mydas), none have associated drowning with injuries of organs other than the lung. We describe the gross and microscopical findings in 23 green sea turtles found dead in a fishing net. Deprived of air, these animals experienced hypoxia and anoxia before dying, which caused congestion, hydropic degeneration and necrosis in several organs. There was no evidence of an alternative cause of death. These findings demonstrate a pattern characteristic of death by asphyxia caused by drowning.

Adaptive cross-country optimization strategies in thermal soaring birds

Thermal soaring enables birds to perform cost-efficient flights. Although aerodynamic rules dictate the costs of flight, soaring species vary strongly in their morphologies and behavioral strategies. To quantify morphology-related differences in behavioral cross-country strategies, we analyzed a large dataset consisting of over a hundred individuals from 12 soaring species recorded with high-frequency tracking devices. We quantified their performance during thermalling and gliding flights and their overall cross-country behavior. Our results confirmed aerodynamic theory across the species; species with higher wing loading typically flew faster and consequently turned on a larger radius than lighter ones. Furthermore, the combination of circling radius and minimum sink speed determines the maximum benefits soaring birds obtain from thermals. Notably, we observed a spectrum of strategies regarding the adaptivity to thermal strength and uncovered a universal rule for cross-country strategies for all analyzed species which can provide inspiration for technical applications, like autopilot for robotic gliders.

Blood group antigen profile predicted by molecular biology-use of real-time polymerase chain reaction to genotype important KEL, JK,RHD, and RHCE alleles

The most clinically important blood group systems in transfusion medicine, excluding the ABO system, are the RH, Kell, and Kidd systems. Alloantibodies to antigens of these systems may be produced following blood transfusion or during pregnancy and can result in serious hemolytic transfusion reactions and hemolytic disease of the newborn. We developed rapid and robust techniques for RHD, RHCE, KEL, and JK genotyping with the use of a real-time polymerase chain reaction instrument. Two fluorescence-based methods for the detection of amplification products were used: for KEL1/KEL2, JK1/JK2, and RHE/RHe (exon 5) we used the hybridization probes protocol; for RHC/RHc the analysis was done in sequences of exon 1 for RHC and exon 2 for RHc; and for RHD, analysis was done in sequences of intron 4, exon 7, and exon 4 pseudogene using the SYBR Green I protocol. The genotyping tests were validated with samples from 85 Caucasian Portuguese and 15 Black European blood donors. Complete phenotype-genotype correlations were obtained. The potential use of the presented methods can be predicted in clinical transfusion medicine, allowing appropriate monitoring, early intervention, and improved care. When blood group genotyping techniques are necessary, this methodology is highly competitive for a routine laboratory.

Rapid genotyping of the major alleles at the Duffy (FY) blood group locus using real-time fluorescence polymerase chain reaction

The Duffy blood group system has clinical importance due to involvement in transfusion reactions and hemolytic disease of the newborn. Recently, the molecular basis of the two alleles, FY*A and FY*B (125G>A), and the mutation situated in the promoter region of the FY gene (-33T>C), have been elucidated. In order to develop an accurate, easy, and rapid genotyping method, we describe a procedure using the LightCycler. Samples from 53 Caucasian Portuguese blood donors and 7 black, healthy, European individuals were phenotyped with commercial antisera. DNA was extracted from blood samples and the relevant sequences were amplified with the same cycling conditions, using real-time polymerase chain reaction. The melting point of the FY*A allele was 63 degrees C and of the FY*B allele, 55 degrees C. The allele without mutation at the promoter region had a melting point at 64 degrees C and the FY*B silent allele at 58 degrees C. The results in Caucasian individuals were similar to those found in European and American populations. When FY genotyping techniques are necessary, the methodology described is preferable to conventional methods as it is reliable, high speed, and uses small volumes, providing a highly competitive technology for use by a routine laboratory.

Towards development of new antimalarial compounds through in silico and in vitro assays

Malaria is one of most widespread infectious disease in world. The antimalarial therapy presents a series of limitations, such as toxicity and the emergence of resistance, which makes the search for new drugs urgent. Thus, it becomes necessary to explore essential and exclusive therapeutic targets of the parasite to achieve selective inhibition. Enoyl-ACP reductase is an enzyme of the type II fatty acid biosynthetic pathway and is responsible for the rate-limiting step in the fatty acid elongation cycle. In this work, we use hierarchical virtual screening and drug repositioning strategies to prioritize compounds for phenotypic assays and molecular dynamics studies. The molecules were tested against chloroquine-resistant W2 strain of Plasmodium falciparum (EC50 between 330.05 and 13.92 µM). Nitrofurantoin was the best antimalarial activity at low micromolar range (EC50 = 13.92 µM). However, a hit compound against malaria must have a biological activity value below 1 µM. A large number of molecules present problems with permeability in biological membranes and reaching an effective concentration in their target's microenvironment. Nitrofurantoin derivatives with inclusions of groups which confer increased lipid solubility (methyl groups, halogens and substituted and unsubstituted aromatic rings) have been proposed. These derivatives were pulled through the lipid bilayer in molecular dynamics simulations. Molecules 14, 18 and 21 presented lower free energy values than nitrofurantoin when crossing the lipid bilayer.

A Study on a Cast Steel Reinforced with WC-Metal Matrix Composite

This study seeks to investigate the local reinforcement of low carbon cast steel specimens with WC-metal matrix composites (WC-MMCs), to obtain a new material effective in competing with hard alloy steels. For this purpose, a powder compact of tungsten carbide (WC) and iron (Fe) was prepared and placed in the mold cavity before casting. The reactions that occurred with the molten steel led to the formation of the WC-MMC and, consequently, to the local reinforcement of the steel. The microstructure of the WC-MMC reinforcement was characterized by scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD). The results showed a microstructural variation throughout the depth of the reinforcement. In the surface region, most of the original WC particles retain their polygonal morphology, but towards the base metal, the dissolution of the WC particles increased with the formation of (Fe,W)₆C carbides. Closer to the base metal, dendritic eutectic carbides of (Fe,W)₆C and fine (Fe,W)₂₃C₆ precipitates in a matrix of martensite were formed. The mechanical properties of the reinforcement were evaluated by hardness and ball-cratering abrasion tests. The results revealed a significant increase in hardness, being three times harder than the base metal, and a decrease of 39% in the wear rate.