Acute Hypotension after High-Intensity Interval Exercise in Metabolic Syndrome Patients

The purpose of this study was to compare the magnitude of post-exercise hypotension (PEH) after a bout of cycling exercise using high-intensity interval training (HIIT) in comparison to a bout of traditional moderate-intensity continuous exercise (CE). After supine rest 14 obese (31±1 kg·m−2) middle-age (57±2 y) metabolic syndrome patients (50% hypertensive) underwent a bout of HIIT or a bout of CE in a random order and then returned to supine recovery for another 45 min. Exercise trials were isocaloric and compared to a no-exercise trial (CONT) of supine rest for a total of 160 min. Before and after exercise we assessed blood pressure (BP), heart rate (HR), cardiac output (Q), systemic vascular resistance (SVR), intestinal temperature (TINT), forearm skin blood flow (SKBF) and percent dehydration. HIIT produced a larger post-exercise reduction in systolic blood pressure than CE in the hypertensive group (−20±6 vs. −5±3 mmHg) and in the normotensive group (−8±3 vs. −3±2 mmHg) while HIIT reduced SVR below CE (P<0.05). Percent dehydration was larger after HIIT, and post-exercise TINT and SKBF increased only after HIIT (all P<0.05). Our findings suggest that HIIT is a superior exercise method to CE to acutely reduce blood pressure in MSyn subjects.

7 INFLUENCE OF ESTRUS EXPRESSION AND TREATMENT WITH GnRH ON PREGNANCY RATES IN BEEF CATTLE SYNCHRONIZED WITH PROGESTERONE DEVICES AND ESTRADIOL AND INSEMINATED AT A FIXED-TIME

We have previously shown that expression of oestrus significantly influences the time of ovulation and pregnancy rates to timed-AI (P/TAI) in beef cattle synchronized with progesterone devices and oestradiol (Bó et al. 2016 Theriogenology 86, 388–396). Furthermore, delaying TAI from 48 h to 54–58 h after device removal improved P/TAI of those animals not showing oestrus by 48 h. The objective of the present study was to determine whether the administration of GnRH to those animals not showing oestrus by 48 h after device removal had an impact on P/TAI. Non-lactating and suckled beef cows and heifers (Bonsmara, Brangus, and Braford; n = 868), with a corpus luteum (CL) or a follicle ≥8 mm in diameter detected by ultrasonography (Mindray DP 30 Vet, 7.5 MHz, China) and body condition score 2 to 4 (1 to 5 scale) were synchronized in 3 replicates. On Day 0, animals received a progesterone device (DIB 0.5 g, Zoetis, Argentina) and 2 mg of oestradiol benzoate (Von Franken, Argentina). On Day 8, DIB were removed and cows received 0.150 mg of D+cloprostenol (Río de Janeiro, Argentina) plus 0.5 mg oestradiol cypionate (Cipiosyn, Zoetis). In addition, all cows were tail-painted on the sacrococcygeal area (CeloTest, Biotay, Argentina) at DIB removal and were observed to determine the expression of oestrus, according to the percentage of paint loss (PL) 48 h later. The animals that showed oestrus (PL > 30%) were recorded and TAI at that time while those with PL ≤ 30% (not in oestrus) were randomly allocated to receive 100 μg of gonadorelin (GnRH; Gonasyn, Zoetis) or no treatment and TAI between 54 to 58 h after DIB removal. Pregnancy was diagnosed by ultrasonography at 45 days after TAI, and data were analysed by logistic regression. There were no significant differences among replicates, inseminators, semen source or animal class (dry cows, suckled cows or heifers; P > 0.11). However, animals showing oestrus by 48 h after DIB removal had higher P/TAI (371/666; 55.7; P < 0.04) than those that did not show oestrus (96/202; 47.5%). Within animals not showing oestrus at 48 h, those that were in oestrus by the TAI at 54 to 58 h had higher P/TAI (71/124, 57.3%; P < 0.01) than those that did not show oestrus within that period (27/78; 34.6%). In addition, P/TAI was higher (P < 0.01) in animals that received GnRH (66/113; 58.4%) than in those that did not receive GnRH (30/89; 33.7%). In conclusion, the expression of oestrus significantly affected P/TAI in beef cattle synchronized with progesterone devices and oestradiol. Furthermore, treatment of animals not showing oestrus by 48 h after DIB removal with GnRH resulted in improved P/TAI performed 6 to 10 h later.

104 FACTORS AFFECTING PREGNANCY RATES AND EMBRYO/FETAL LOSSES IN RECIPIENTS RECEIVING IN VITRO-PRODUCED EMBRYOS BY FIXED-TIME EMBRYO TRANSFER

A retrospective analysis evaluated pregnancy rates and embryo losses with in vitro-produced embryos in a commercial embryo transfer program on 15 different beef farms. Recipients were beef cows and heifers (n = 1841) that were synchronized with 5 different protocols and transferred at a fixed-time (FTET). Recipients were examined by ultrasonography on Day 0, and those with a corpus luteum (CL) or a follicle ≥8 mm in diameter and with body condition score 2 to 4 (1 to 5 scale) were synchronized. The synchronization treatments were as follows. (T1) Recipients received an intravaginal device with 0.5 g of progesterone plus 2 mg of oestradiol benzoate on Day 0; device removal, plus 500 μg of cloprostenol (prostaglandin F2α), 400 IU of eCG, and 0.5 mg of oestradiol cypionate on Day 8; and FTET on Day 17. (T2) This treatment was similar to T1 but 1 mg of oestradiol cypionate was injected at device removal instead of 0.5 mg of oestradiol cypionate. (T3) This treatment was similar to T1 except that animals were tail-painted on Day 8 and observed on Day 10. Those with the tail-paint intact on Day 10 received 100 μg of gonadorelin (gonadotropin-releasing hormone) and all recipients were FTET on Day 17. (T4) Recipients received a progesterone device on Day 0; device removal, prostaglandin F2α, and eCG on Day 5; gonadotropin-releasing hormone on Day 8; and FTET on Day 15. (T5) Recipients received a progesterone device and 2 mg of oestradiol benzoate on Day 0; device removal, prostaglandin F2α, and eCG on Day 6; gonadotropin-releasing hormone on Day 9; and FTET on Day 16. On the day of FTET all recipients with CL ≥18 mm in diameter (G1), ≥16 and <18 mm in diameter (G2), and ≥14 mm and <16 mm in diameter (G3) received in vitro-produced fresh embryos. Pregnancy was diagnosed by ultrasonography at 30 and 60 days of gestation, and data were analysed by logistic regression. The overall proportion of recipients synchronized that were FTET was 80.8% (1487/1841), with a 30-day pregnancy rate to FTET (P/FTET) of 45.6% (678/1487) and the rate of 30- to 60-day embryo/fetal loses on the 528 recipients that were re-checked at 60 days was 12.8% (68/528). There were no significant differences in P/FTET among operators, animal category, time of the year, embryo stage, or body condition score; however, there was a significant effect of farm (P < 0.001) and CL diameter (P < 0.05), but no interaction between CL diameter and farm or treatment (P > 0.1). Recipients with G1 (443/953, 46%) and G2 (221/462, 47%) CL had higher pregnancy rates than those with G3 CL (23/71, 32%). There was a significant effect of synchronization treatment on the proportion of recipients transferred and on P/FTET (P < 0.01) that was highly influenced by farm (farm by treatment interaction P < 0.01). The proportions of recipients selected for embryo transfer were as follows: T1: 386/486, 79.4%; T2: 233/331, 70.3%; T3: 342/377, 90.7%; T4: 126/160, 78.7%; and T5: 400/487, 82.1%. The P/FTET were as follows: T1: 190/386, 49.2%; T2: 96/233, 41.2%; T3: 175/342, 51.1%; T4: 49/126, 38.8%; and T5: 168/400, 42.0%. Although 30- to 60-day embryo/fetal losses were not influenced by synchronization treatments, they were highly influenced by farm (P < 0.001) and ranged from 0 to 34.5%. In conclusion, P/FTET in a commercial program with beef in vitro-produced embryos was influenced by factors related to the recipient (CL diameter) and the environment (farm), whereas embryo/fetal losses were influenced by farm but not treatment or recipient factors.

Infection of Internal Umbilical Remnant in Foals by Clostridium sordellii

Omphalitis and the resulting septicemia contribute to perinatal mortality in several animal species. In foals, the most important causes of omphalitis are Escherichia coli and Streptococcus zooepidemicus. However to date, no information has been published about the role of Clostridium sordellii in these infections. In this paper, we describe 8 cases of perinatal mortality in foals associated with internal umbilical remnant infection by C. sordellii. The foals studied were between 12 and 21 days old at the time of death, and various breeds were represented in the group. Five of the foals were male and 3 were female. The diagnosis was established on the basis of the detection of C. sordellii by 3 methods (culture, fluorescent antibody test, and immunohistochemistry) and on gross and histopathologic findings. All foals had acute peritonitis, and the internal umbilical remnant was thickened by edema, hemorrhage, and fibrosis. A moderate amount of serosanguinous fluid with fibrin strands was present in the pericardial sac and pleural cavity. Histopathologically, the urachus and umbilical arterial walls were thickened by edema and exhibited hemorrhage, fibrin, and leukocytic infiltration. Gram-positive bacterial rods were observed in subepithelial areas of the urachus, the adventicia of umbilical arteries, and interstitium of the internal umbilical remnant. On the basis of these findings, we suggest that C. sordellii should be considered in the differential diagnosis for infections of the internal umbilical remnant in foals.

Kinetic behavior of light emission in cholesteric liquid crystal lasers: An experimental study

Some dynamical aspects of fluorescence and lasing have been studied in a dye-doped cholesteric liquid crystal by measuring the response of the material to nanosecond optical pumping. It has been found that as the pumping energy is increased the fluorescence pulse duration decreases, reaching a minimum at the lasing threshold. Above the threshold the temporal profiles are irregular and consist of a set of narrow pulses whose measured duration is limited by the detector risetime (1 ns). The results are interpreted in terms of a recently proposed model [JETP, 118, 822 (2014)] that makes use of rate equations to account for the laser generation in cholesteric liquid crystals. The prediction of such equations for an experimental configuration appropriate for fluorescence lifetime measurements is analyzed.

Ultrafast Atomic Diffusion Inducing a Reversible (2sqrt[3]×2sqrt[3])R30°↔(sqrt[3]×sqrt[3])R30° Transition on Sn/Si(111)∶B

Dynamical phase transitions are a challenge to identify experimentally and describe theoretically. Here, we study a new reconstruction of Sn on silicon and observe a reversible transition where the surface unit cell divides its area by a factor of 4 at 250 °C. This phase transition is explained by the 24-fold degeneracy of the ground state and a novel diffusive mechanism, where four Sn atoms arranged in a snakelike cluster wiggle at the surface exploring collectively the different quantum mechanical ground states.

Thermally induced light-scattering effects as responsible for the degradation of cholesteric liquid crystal lasers

We have studied the degradation process of the laser emission in a cholesteric liquid crystal laser. We have found that there exists a negative correlation between the laser efficiency and the amount of light scattered by the liquid-crystal sample in the illuminated area. The growth of scattering is attributed to the appearance of small imperfections generated in the sample as a result of certain thermal processes that involve the dye molecules. The scattering implies an increase of the coefficient of distributed losses, which is the main response of the rise of the laser threshold.

The role of charge transfer in the energy level alignment at the pentacene/C60 interface

Understanding the mechanism of energy level alignment at organic-organic interfaces is a crucial line of research to optimize applications in organic electronics. We address this problem for the C60-pentacene interface by performing local-orbital Density Functional Theory (DFT) calculations, including the effect of the charging energies on the energy gap of both organic materials. The results are analyzed within the induced density of interface states (IDIS) model. We find that the induced interface potential is in the range of 0.06-0.10 eV, in good agreement with the experimental evidence, and that such potential is mainly induced by the small, but non-negligible, charge transfer between the two compounds and the multipolar contribution associated with pentacene. We also suggest that an appropriate external intercompound potential could create an insulator-metal transition at the interface.

Indocyanine green plasma disappearance rate: a new tool for the classification of paediatric patients with acute liver failure

BACKGROUND & AIMS

Pediatric acute liver failure is a rare disorder which results in death or the need for liver transplantation in 25-50% of cases. The adults scores are unable to predict survival without liver transplantation of pediatric patients. The present study assessed the use the of indocyanine green plasma disappearance rate as a tool to predict the evolution of pediatric patients with acute liver failure.

PATIENTS AND METHODS

All patients met the criteria of acute liver failure according to the Pediatric Acute Liver Failure Study Group. King's College, Clichy's criteria and ICG-PDR were obtained on admission or when acute liver failure was diagnosed and repeated every 12-24 hours, respectively.

RESULTS

Thirteen out of 48 patients suffered an irreversible liver damage. Seven of them underwent a liver transplantation and 6 died on the waiting. A total of 154 ICG-PDR measurements were taken during the study (Median 12.4 %/min, r:6.2 - 26.3). The ICG-PDR was significantly lower in patients who suffered irreversible liver damage compared with those who survived without liver transplantation (median ICG-PDR 4.1 %/min; r:4.0 - 5.7 vs median ICG-PDR 20.3 %/min; r: 9.1 - 30.1; respectively. P < 0.001). Using a ROC curve the cutoff of ICG-PDR for assessing the need for liver transplantation was set at 5.9 %/min (sensitivity 92.3%, specificity 97.1%). Sensitivity, specificity, PPV, NPV and DA for ICG-PDR were higher than the King's College and Clichy's criteria.

CONCLUSIONS

ICG-PDR is a powerful tool that would improve the categorization of patients with pediatric acute liver failure.

Low plasma levels of antithrombin III in the early post-operative period following pediatric liver transplantation: should they be replaced? A single-center pilot study

eHAT after LT remains a life-threatening complication. In the majority of anticoagulation protocols, heparin is used to prevent thromboses. Our study aimed to monitor AT-III levels in the early post-LT period to assess the need for the administration of AT-III concentrate to ensure the effectiveness of heparin. We monitored coagulation daily by measuring INR, APTT, fibrinogen, platelets, and AT-III. Anticoagulation therapy consisted of LMWH, AT-III, and dipyridamole. AT-III concentrate was administered when AT-III activity was ≤60%. DUS was performed daily for the first five post-operative days or whenever vascular thrombosis was suspected. Between October 2007 and October 2011, 39 LT were performed in our center. The median age was 26 months (6-196) with a median weight of 9 kg (5.5-49). AT-III activity was ≤60% in 27 patients. Lower levels were particularly observed in partial grafts and recipients weighing less than 10 kg. Patent arterial flow was present in all 39 LT during the first five post-operative days. AT-III levels were low in 70% of pediatric patients following LT, thereby risking heparin ineffectiveness. These results may implicate low AT-III levels in the etiology of eHAT post-LT. However, this is a small single-center pilot study and further larger prospective trials are required to confirm these results.

Spontaneous and field-induced mesomorphism of a silyl-terminated bent-core liquid crystal as determined from second-harmonic generation and resonant X-ray scattering

The polarity and structure of the phases of a liquid crystal constituted by thiophene-based bent-core molecules is investigated by means of optical second-harmonic generation (SHG), and resonant and conventional X-ray diffraction. The material studied is representative of a wide family of mesogens that contain silyl groups at the ends of the chains. These bulky terminal groups have been reported to give rise to smectic phases showing ferroelectric switching. However, the analysis of the SHG signal before and after application of electric fields has allowed us to establish unambiguously that the reported ferroelectricity is not intrinsic to the material but stabilized by the cell substrates once an electric field has been applied. In addition, the results obtained from resonant X-ray diffraction indicate that virgin samples have antiferroelectric undulated synclinic smectic structures.

On the organic energy gap problem

In conjugated organic molecules, the difference between the HOMO and LUMO Kohn-Sham eigenvalues is significantly smaller than the transport gap measured experimentally. We discuss here, within a local-orbital formulation of DFT, how this problem can be corrected using appropriate hybrid potentials, that add a fraction of Hartree-Fock exchange interaction in the DFT calculation. We illustrate this approach presenting calculations for two simple systems: H(2) and C(6)H(6); then, we discuss how to implement this hybrid approach in a general local-orbital calculation, adjusting the hybrid contribution to yield the correct experimental HOMO/LUMO energy gap for the molecule. We also consider the case of an organic molecule on a metal and analyze the effect of the molecule-metal interaction on the organic energy gap. In particular, we discuss how to introduce in this hybrid-potential scheme the effect of the image potential, and present results for the organic molecules PTCDA, TTF, benzene and pentacene on the metal surfaces Au(111), Ag(111) and Cu(111).

Brain lesions associated with clostridium perfringens type D epsilon toxin in a Holstein heifer calf

A 6-month-old dairy heifer calf with no premonitory signs was acutely down after the morning feeding and could not rise. On presentation, the heifer was in right lateral recumbency and moribund with opisthotonus and left hind limb paddling. Following euthanasia, gross examination of the brain revealed multifocal loss of gray-white matter distinction and extensive petechiae throughout the brainstem. On histopathological examination, there was striking white matter edema and marked perivascular proteinaceous edema surrounding many arterioles and venules (microangiopathy), mainly in the white matter of the internal capsule, thalamus, midbrain, cerebellum, and cerebellar peduncles. The perivascular neuropil was strongly positive for Alzheimer precursor protein A4. Clostridium perfringens epsilon toxin was detected in the intestinal contents. This is the first report of microangiopathy in postneonatal cattle associated with the detection of epsilon toxin in the intestinal contents.

Prediction equations for Warner-Bratzler shear force using principal component regression analysis in Brahman-influenced Venezuelan cattle

A database consisting of 331 beef animals (Brahman-crossbred) was used to determine the multivariate relationships between carcass and beef palatability traits of Venezuelan cattle and to develop prediction equations for Warner-Bratzler shear force (WBSF). The first three principal components (PC) explained 77.53% of the standardized variance. Equations were obtained for each sex class and the total variability observed in WBSF could be explained by its orthogonal regression with carcass weight (CW), fat cover (FC), fat thickness (FT), and skeletal maturity (SM). Prediction equations were: WBSF(steers)=3.566+0.003(CW)-0.033(FC)-0.015(FT)+0.0004(SM); WBSF(heifers)=4.824+0.002(CW)-0.229(FC)+0.096(FT)-0.064(SM); WBSF(bulls)=3.516+0.009(CW)+0.154(FC)-0.129(FT)-0.006(SM). A higher proportion of the variation was explained by the PC when variables of greater weight were selected to define each PC. The equation set presented herein could become an important tool to improve the Venezuelan carcass grading system.

Second-harmonic generation in a laterally azo-bridged trimer ferroelectric liquid crystal: phase matching in the presence of a helicoidal structure

Optical second-harmonic generation (SHG) has been studied in a trimer smectic C* liquid crystal especially designed for nonlinear optical applications. The molecule has a long conjugated donor-acceptor unit that transversally links three parallel rod-shaped moieties. A strong SHG signal has been observed at a fundamental wavelength of 1369 nm even in the presence of the spontaneous helicoidal structure of the smectic C* phase. This unusual behavior has been interpreted as due to the existence of phase matching, in which the wave vector mismatch is compensated by the wave vector of the helix. This point has been confirmed by the study of the SHG intensity versus sample thickness and light polarization characteristics. The main coefficient of the second-order susceptibility tensor of the material has been estimated to be d(22) = 28 pm/V.

Dynamical screening of the van der Waals interaction between graphene layers

The interaction between graphene layers is analyzed combining local orbital DFT and second order perturbation theory. For this purpose we use the linear combination of atomic orbitals-orbital occupancy (LCAO-OO) formalism, that allows us to separate the interaction energy as the sum of a weak chemical interaction between graphene layers plus the van der Waals interaction (Dappe et al 2006 Phys. Rev. B 74 205434). In this work, the weak chemical interaction is calculated by means of corrected-LDA calculations using an atomic-like sp(3)d(5) basis set. The van der Waals interaction is calculated by means of second order perturbation theory using an atom-atom interaction approximation and the atomic-like-orbital occupancies. We also analyze the effect of dynamical screening in the van der Waals interaction using a simple model. We find that this dynamical screening reduces by 40% the van der Waals interaction. Taking this effect into account, we obtain a graphene-graphene interaction energy of 70 ± 5 meV/atom in reasonable agreement with the experimental evidence.

Improvement of scanning tunneling microscopy resolution with H-sensitized tips

Recent scanning tunneling hydrogen microscopy (STHM) experiments on PTCDA (perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride)/Au(111) have shown unprecedented intramolecular and intermolecular spatial resolution. The origin of this resolution is studied using an accurate STHM theoretical simulation technique that includes a detailed description of the electronic structure of both the tip and sample. Our results show that H2 molecules are dissociated on the Au tip; the adsorbed H atoms change the density of states at the Fermi level (E(F)) of the tip, increasing its p-orbital character and reducing the s-orbital contribution. Also, due to the interaction with the H-decorated tip, E(F) is shifted to the middle of the PTCDA lowest unoccupied molecular orbital peak, increasing dramatically the density of states of the sample at E(F). These effects give rise to the enhanced STHM resolution.

Non–invasive sampling of endangered neotropical river otters reveals high levels of dispersion in the Lacantun River System of Chiapas, Mexico

Patterns of genetic dispersion, levels of population genetic structure, and movement of the neotropical river otter (Lontra longicaudis) were investigated by screening eight polymorphic microsatellites from DNA extracted from fecal samples, collected in a hydrologic system of the Lacandon rainforest in Chiapas, Mexico. A total of 34 unique genotypes were detected from our surveys along six different rivers, and the effect of landscape genetic structure was studied. We recovered 16 of the 34 individuals in multiple rivers at multiple times. We found high levels of dispersion and low levels of genetic differentiation among otters from the six surveyed rivers (P > 0.05), except for the pairwise comparison among the Lacantún and José rivers (P < 0.05). We recommend that conservation management plans for the species consider the entire Lacantún River System and its tributaries as a single management unit to ensure the maintenance of current levels of population genetic diversity, because the population analyzed seems to follow a source–sink dynamic mainly determined by the existence of the major river.

Decreased prevalence of diabetes in marijuana users: cross-sectional data from the National Health and Nutrition Examination Survey (NHANES) III

OBJECTIVE

To determine the association between diabetes mellitus (DM) and marijuana use.

DESIGN

Cross-sectional study.

SETTING

Data from the National Health and Nutrition Examination Survey (NHANES III, 1988-1994) conducted by the National Center for Health Statistics of the Centers for Disease Control and Prevention.

PARTICIPANTS

The study included participants of the NHANES III, a nationally representative sample of the US population. The total analytic sample was 10 896 adults. The study included four groups (n=10 896): non-marijuana users (61.0%), past marijuana users (30.7%), light (one to four times/month) (5.0%) and heavy (more than five times/month) current marijuana users (3.3%). DM was defined based on self-report or abnormal glycaemic parameters. We analysed data related to demographics, body mass index, smoking status, alcohol use, total serum cholesterol, high-density lipoprotein, triglyceride, serum 25-hydroxy vitamin D, plasma haemoglobin A1c, fasting plasma glucose level and the serum levels of C reactive protein and four additional inflammatory markers as related to marijuana use.

MAIN OUTCOME MEASURES

OR for DM associated with marijuana use adjusted for potential confounding variables (ie, odds of DM in marijuana users compared with non-marijuana users).

RESULTS

Marijuana users had a lower age-adjusted prevalence of DM compared to non-marijuana users (OR 0.42, 95% CI 0.33 to 0.55; p<0.0001). The prevalence of elevated C reactive protein (>0.5 mg/dl) was significantly higher (p<0.0001) among non-marijuana users (18.9%) than among past (12.7%) or current light (15.8%) or heavy (9.2%) users. In a robust multivariate model controlling for socio-demographic factors, laboratory values and comorbidity, the lower odds of DM among marijuana users was significant (adjusted OR 0.36, 95% CI 0.24 to 0.55; p<0.0001).

CONCLUSIONS

Marijuana use was independently associated with a lower prevalence of DM. Further studies are needed to show a direct effect of marijuana on DM.

Giant alkali-metal-induced lattice relaxation as the driving force of the insulating phase of alkali-metal/Si(111):B

Ab initio density-functional theory calculations, photoemission spectroscopy (PES), scanning tunneling microscopy, and spectroscopy (STM, STS) have been used to solve the 2sqrt[3]×2sqrt[3]R30 surface reconstruction observed previously by LEED on 0.5 ML K/Si:B. A large K-induced vertical lattice relaxation occurring only for 3/4 of Si adatoms is shown to quantitatively explain both the chemical shift of 1.14 eV and the ratio 1/3 measured on the two distinct B 1s core levels. A gap is observed between valence and conduction surface bands by ARPES and STS which is shown to have mainly a Si-B character. Finally, the calculated STM images agree with our experimental results. This work solves the controversy about the origin of the insulating ground state of alkali-metal/Si(111):B semiconducting interfaces which were believed previously to be related to many-body effects.

Electric-field-induced phase transitions in bent-core mesogens determined by x-ray diffraction

The changes in the x-ray diffraction diagram induced by an electric field have been studied in four bent-core liquid crystals. Two of the compounds present columnar B1 phases and the other two show dark conglomerate (DC) structures. In the B1 materials the electric field gives rise to switchable phases whose diffraction pattern is that of the smectic C polar (SmCP) phase. In the DC structures the positions of the Bragg reflections remain essentially unaltered, but in one of the compounds the peaks become narrower under field, indicating that the correlation length of the smectic order increases. A slight enhancement of the smectic spacing is found in the DC phases upon field application.

Polarization periodicity in the B(1) columnar phase determined by resonant x-ray scattering

We report structural results that evidence the polarization distribution of the blocks in the columnar phase of an achiral bent-core liquid crystal. The study was performed using resonant x-ray diffraction at the sulfur K edge on oriented samples aligned on substrates. The extra periodicity is revealed through the violation of the systematic extinction rule of the structural symmetry group along the experimentally accessible diffraction direction. Further data obtained from the polarization analysis of a resonant reflection give information concerning the transition mechanism between B(1) and B(2) phases.