Lehmann rotation of cholesteric droplets subjected to a temperature gradient: role of the concentration of chiral molecules

International audienceWe present a systematic study of the Lehmann rotation of cholesteric droplets subjected to a temperature gradient when the concentration of chiral molecules is changed. The liquid crystal chosen is an eutectic mixture of 8CB and 8OCB doped with a small amount of the chiral molecule R811. The angular velocity of the droplets strongly depend on their size and on the concentration of chiral molecules. The Lehmann coefficient is estimated by using three different methods. Our results are consistent with a Lehmann coefficient proportional to the concentration of chiral molecules. We additionally show the existence of a critical size of the droplets below which they change texture and stop rotating

Electric-field-induced nematic-cholesteric transition and 3-D director structures in homeotropic cells

We study the phase diagram of director structures in cholesteric liquid crystals of negative dielectric anisotropy in homeotropic cells of thickness d which is smaller than the cholesteric pitch p. The basic control parameters are the frustration ratio d/p and the applied voltage U. Fluorescence Confocal Polarising Microscopy allows us to directly and unambiguously determine the 3-D director structures. The results are of importance for potential applications of the cholesteric structures, such as switchable gratings and eyewear with tunable transparency based.Comment: Will be published in Physical Review

Body Mass Index in Multiple Sclerosis modulates ceramide-induced DNA methylation and disease course.

abstract Background: Multiple Sclerosis (MS) results from genetic predisposition and environmental variables, including elevated Body Mass Index (BMI) in early life. This study addresses the effect ofBMI on the epigenome ofmono- cytesand diseasecourseinMS. Methods: Fifty-four therapy-naive Relapsing Remitting (RR)MS patientswith high and normal BMI received clin- ical andMRI evaluation. Blood samples were immunophenotyped, and processed for unbiased plasma lipidomic profiling and genome-wide DNA methylation analysis of circulating monocytes. The main findings at baseline were validated in an independent cohort of 91 therapy-naïve RRMS patients. Disease course was evaluated by a two-year longitudinal follow up and mechanistic hypotheses tested in human cell cultures and in animal models ofMS. Findings: Higher monocytic counts and plasma ceramides, and hypermethylation of genes involved in negative regulation ofcell proliferationwere detected in the high BMI group ofMSpatients compared to normal BMI. Cer- amide treatment of monocytic cell cultures increased proliferation in a dose-dependent manner and was prevented by DNA methylation inhibitors. The high BMI group ofMS patients showed a negative correlation be- tween monocytic counts and brain volume. Those subjects at a two-year follow-up showed increased T1 lesion load, increased disease activity, and worsened clinical disability. Lastly, the relationship between body weight, monocytic infiltration, DNA methylation and disease course was validated in mouse models ofMS. Interpretation: High BMI negatively impacts disease course in Multiple Sclerosis by modulating monocyte cell number through ceramide-induced DNA methylation of anti-proliferative genes

Control over phase separation and nucleation using a laser-tweezing potential

Control over the nucleation of new phases is highly desirable but elusive. Even though there is a long history of crystallization engineering by varying physicochemical parameters, controlling which polymorph crystallizes or whether a molecule crystallizes or forms an amorphous precipitate is still a poorly understood practice. Although there are now numerous examples of control using laser-induced nucleation, the absence of physical understanding is preventing progress. Here we show that the proximity of a liquid–liquid critical point or the corresponding binodal line can be used by a laser-tweezing potential to induce concentration gradients. A simple theoretical model shows that the stored electromagnetic energy of the laser beam produces a free-energy potential that forces phase separation or triggers the nucleation of a new phase. Experiments in a liquid mixture using a low-power laser diode confirm the effect. Phase separation and nucleation using a laser-tweezing potential explains the physics behind non-photochemical laser-induced nucleation and suggests new ways of manipulating matter

Body Mass Index in Multiple Sclerosis modulates ceramide-induced DNA methylation and disease course

Background: Multiple Sclerosis (MS) results from genetic predisposition and environmental variables, including elevated Body Mass Index (BMI) in early life. This study addresses the effect of BMI on the epigenome of monocytes and disease course in MS. Methods: Fifty-four therapy-naive Relapsing Remitting (RR) MS patients with high and normal BMI received clinical and MRI evaluation. Blood samples were immunophenotyped, and processed for unbiased plasma lipidomic profiling and genome-wide DNA methylation analysis of circulating monocytes. The main findings at baseline were validated in an independent cohort of 91 therapy-na\uefve RRMS patients. Disease course was evaluated by a two-year longitudinal follow up and mechanistic hypotheses tested in human cell cultures and in animal models of MS. Findings: Higher monocytic counts and plasma ceramides, and hypermethylation of genes involved in negative regulation of cell proliferation were detected in the high BMI group of MS patients compared to normal BMI. Ceramide treatment of monocytic cell cultures increased proliferation in a dose-dependent manner and was prevented by DNA methylation inhibitors. The high BMI group of MS patients showed a negative correlation between monocytic counts and brain volume. Those subjects at a two-year follow-up showed increased T1 lesion load, increased disease activity, and worsened clinical disability. Lastly, the relationship between body weight, monocytic infiltration, DNA methylation and disease course was validated in mouse models of MS. Interpretation: High BMI negatively impacts disease course in Multiple Sclerosis by modulating monocyte cell number through ceramide-induced DNA methylation of anti-proliferative genes. Fund: This work was supported by funds from the Friedman Brain Institute, NIH, and Multiple Sclerosis Society

The Period Changes of the Cepheid RT Aurigae

Observations of the light curve for the 3.7-day Cepheid RT Aur both before and since 1980 indicate that the variable is undergoing an overall period increase, amounting to +0.082 +-0.012 s/yr, rather than a period decrease, as implied by all observations prior to 1980. Superposed on the star's O-C variations is a sinusoidal trend that cannot be attributed to random fluctuations in pulsation period. Rather, it appears to arise from light travel time effects in a binary system. The derived orbital period for the system is P = 26,429 +-89 days (72.36 +-0.24 years). The inferred orbital parameters from the O-C residuals differ from those indicated by existing radial velocity data. The latter imply the most reasonable results, namely a1 sin i = 9.09 (+-1.81) x 10^8 km and a minimum secondary mass of M2 = 1.15 +-0.25 Msun. Continued monitoring of the brightness and radial velocity changes in the Cepheid are necessary to confirm the long-term trend and to provide data for a proper spectroscopic solution to the orbit.Comment: Accepted for publication in PASP (November 2007

Estimation du sexe fœtal à partir de l’ilium

La détermination du sexe est une des problématiques les plus fréquemment rencontrées en anthropologie médico-légale. Chez l’adulte, cette détermination est essentiellement basée sur l’os iliaque et autorise un très fort taux de classification correcte, tandis que chez le fœtus, les études sont beaucoup moins nombreuses et conduisent à des résultats souvent contradictoires.Nous avons recherché sur 83 paires d’ilia fœtaux de la collection ostéologique hongroise de Fazekas et Kosa quels étaient les critères métriques qui décrivaient le mieux le dimorphisme sexuel, en évaluant les différentes méthodes proposées sur l’ilium fœtal et en adaptant certaines de celles proposées chez l’adulte. Nous avons pour cela établi et validé un protocole de prise de clichés photographiques et une méthode de mesure sur image numérisée à partir du logiciel Adobe Photoshop 6‚.Certains des paramètres retenus dans l’étude – principalement ceux qui ont été relevés sur l’échancrure ischiatique – présentant de fortes corrélations avec le sexe, nous avons établi une régression logistique estimant la probabilité d’appartenir à l’un ou l’autre des deux sexes. Le faible pourcentage de discrimination sexuelle obtenu avec cette formule nous a amené à tenir compte de l’âge : nous avons donc structuré notre échantillon en différents groupes d’âge et avons établi une formule permettant de déterminer correctement le sexe dans plus de 85 % des cas (sur l’échantillon qui a servi à l’établir) pour les fœtus dont l’âge est inférieur à 26 semaines d’aménorrhée.Sex estimation is one of the most frequently encountered issues in forensic medicine. While in the case of adults this determination is essentially based on iliac bones and provides a rather reliable classification, there are fewer studies conducted on fetuses and the results are often contradictory.Therefore, we examinated 83 pairs of fetal iliac bones in the Hungarian collection of Fazekas and Kosa and searched for metric criteria that can the best be applied for determining sexual dimorphism. During this research, we tested the different methods proposed for fetal iliac bones and adapted some others used particularly in the case of adults.For this reason, we set up and validated a protocol of taking photographs, as well as a measurement technique developed for numeric pictures with the help of a software program, Adobe Photoshop 6‚.During this study, we selected certain parameters, principally the ones taken on the great sciatic notch, which showed a strong correlation with sex, and we established a logistic regression for estimating the probability of belonging to one sex or the other.The weak percentage of sexual differentiation obtained by this formula led us to take into account age: we organised our sample in different age groups and established a formula that permits correct sex determination in more than 85% of cases (in our sample) for fetuses that are less than 24 gestational weeks old

Location and function of TDP-43 in platelets, alterations in neurodegenerative diseases and arising considerations for current plasma biobank protocols

The TAR DNA Binding Protein 43 (TDP-43) has been implicated in the pathogenesis of human neurodegenerative diseases and exhibits hallmark neuropathology in amyotrophic lateral sclerosis (ALS). Here, we explore its tractability as a plasma biomarker of disease and describe its localization and possible functions in the cytosol of platelets. Novel TDP-43 immunoassays were developed on three different technical platforms and qualified for specificity, signal-to-noise ratio, detection range, variation, spike recovery and dilution linearity in human plasma samples. Surprisingly, implementation of these assays demonstrated that biobank-archived plasma samples yielded considerable heterogeneity in TDP-43 levels. Importantly, subsequent investigation attributed these differences to variable platelet recovery. Fractionations of fresh blood revealed that ≥ 95% of the TDP-43 in platelet-containing plasma was compartmentalized within the platelet cytosol. We reasoned that this highly concentrated source of TDP-43 comprised an interesting substrate for biochemical analyses. Additional characterization of platelets revealed the presence of the disease-associated phosphoserine 409/410 TDP-43 proteoform and many neuron- and astrocyte-expressed TDP-43 mRNA targets. Considering these striking similarities, we propose that TDP-43 may serve analogous functional roles in platelets and synapses, and that the study of platelet TDP-43 might provide a window into disease-related TDP-43 dyshomeostasis in the central nervous system