64 research outputs found
Shear induced instabilities in layered liquids
Motivated by the experimentally observed shear-induced destabilization and
reorientation of smectic A like systems, we consider an extended formulation of
smectic A hydrodynamics. We include both, the smectic layering (via the layer
displacement u and the layer normal p) and the director n of the underlying
nematic order in our macroscopic hydrodynamic description and allow both
directions to differ in non equilibrium situations. In an homeotropically
aligned sample the nematic director does couple to an applied simple shear,
whereas the smectic layering stays unchanged. This difference leads to a finite
(but usually small) angle between n and p, which we find to be equivalent to an
effective dilatation of the layers. This effective dilatation leads, above a
certain threshold, to an undulation instability of the layers. We generalize
our earlier approach [Rheol. Acta, vol.39(3), 15] and include the cross
couplings with the velocity field and the order parameters for orientational
and positional order and show how the order parameters interact with the
undulation instability. We explore the influence of various material parameters
on the instability. Comparing our results to recent experiments and molecular
dynamic simulations, we find a good qualitative agreement.Comment: 15 pages, 12 figures, accepted for publication in PR
Possible Associations of NTRK2 Polymorphisms with Antidepressant Treatment Outcome: Findings from an Extended Tag SNP Approach
Background: Data from clinical studies and results from animal models suggest an involvement of the neurotrophin system in the pathology of depression and antidepressant treatment response. Genetic variations within the genes coding for the brain-derived neurotrophic factor (BDNF) and its key receptor Trkb (NTRK2) may therefore influence the response to antidepressant treatment.
Methods: We performed a single and multi-marker association study with antidepressant treatment outcome in 398 depressed Caucasian inpatients participating in the Munich Antidepressant Response Signature (MARS) project. Two Caucasian replication samples (N = 249 and N = 247) were investigated, resulting in a total number of 894 patients. 18 tagging SNPs in the BDNF gene region and 64 tagging SNPs in the NTRK2 gene region were genotyped in the discovery sample; 16 nominally associated SNPs were tested in two replication samples.
Results: In the discovery analysis, 7 BDNF SNPs and 9 NTRK2 SNPs were nominally associated with treatment response. Three NTRK2 SNPs (rs10868223, rs1659412 and rs11140778) also showed associations in at least one replication sample and in the combined sample with the same direction of effects ( = .018, = .015 and = .004, respectively). We observed an across-gene BDNF-NTRK2 SNP interaction for rs4923468 and rs1387926. No robust interaction of associated SNPs was found in an analysis of BDNF serum protein levels as a predictor for treatment outcome in a subset of 93 patients.
Conclusions/Limitations: Although not all associations in the discovery analysis could be unambiguously replicated, the findings of the present study identified single nucleotide variations in the BDNF and NTRK2 genes that might be involved in antidepressant treatment outcome and that have not been previously reported in this context. These new variants need further validation in future association studies
Simple scoring system to predict in-hospital mortality after surgery for infective endocarditis
BACKGROUND:
Aspecific scoring systems are used to predict the risk of death postsurgery in patients with infective endocarditis (IE). The purpose of the present study was both to analyze the risk factors for in-hospital death, which complicates surgery for IE, and to create a mortality risk score based on the results of this analysis.
METHODS AND RESULTS:
Outcomes of 361 consecutive patients (mean age, 59.1\ub115.4 years) who had undergone surgery for IE in 8 European centers of cardiac surgery were recorded prospectively, and a risk factor analysis (multivariable logistic regression) for in-hospital death was performed. The discriminatory power of a new predictive scoring system was assessed with the receiver operating characteristic curve analysis. Score validation procedures were carried out. Fifty-six (15.5%) patients died postsurgery. BMI >27 kg/m2 (odds ratio [OR], 1.79; P=0.049), estimated glomerular filtration rate 55 mm Hg (OR, 1.78; P=0.032), and critical state (OR, 2.37; P=0.017) were independent predictors of in-hospital death. A scoring system was devised to predict in-hospital death postsurgery for IE (area under the receiver operating characteristic curve, 0.780; 95% CI, 0.734-0.822). The score performed better than 5 of 6 scoring systems for in-hospital death after cardiac surgery that were considered.
CONCLUSIONS:
A simple scoring system based on risk factors for in-hospital death was specifically created to predict mortality risk postsurgery in patients with IE
Influence of screw dislocations on the orientation of a sheared lamellar phase
We have investigated the role of screw dislocations defects in a
lyotropic lamellar phase of the mixed DMPC/\chem{C_{12}E_5}/water system
using microscopy and scattering techniques. Several of the usual
shear-induced orientations of the lamellar phase were observed as
a function of temperature and shear rate. It is suggested that
the corresponding dynamical transitions are consistent with a
variation in size of the defects
Lamellar phase under shear : SANS measurements
The static properties of lyotropic lamellar phases have been investigated for a long time. Recently, we studied the dynamic properties and more specifically the effect of shear on these phases. Using different techniques (conoscopy, light, neutron and X-ray scattering, microscopy and rheology), the different stationary orientation states of a lamellar phase (in a quaternary mixture water-SDS-pentanol-dodecane) have been analyzed ; in this paper we describe the analysis of the oriented state of these lamellar phase at high shear rates ; we consider a Gaussian distribution to define the mosaicity of this orientation where the normal of the membrane is parallel to the velocity gradient
Lamellar-to-nematic phase transition in a lipid-surfactant mixture
A lyotropic system, consisting of a lecithin (DMPC) and a
non-ionic surfactant (C12E5) in water was studied. The
system exhibits a lamellar-to-nematic phase transition. The nematic
phase appears as the temperature is decreased and only exists in a
very limited temperature and concentration range, for specific
lipid-to-surfactant ratios. While a lamellar phase is found at
higher temperatures in both mixed and pure C12E5
systems, the transition to the nematic phase at lower temperatures
coincides with a micellar phase in the pure C12E5
system. The transition appears to be driven by the strong
temperature dependence of the surfactant film spontaneous
curvature. The structural properties of the lamellar phase close to
the lamellar-to-nematic boundary have been studied by polarised
light microscopy and small-angle neutron and X-ray scattering
experiments. The signature of a helical defect with Burgers vector
of magnitude 2 is apparent in our data, close to the
lamellar-to-nematic phase transition. The proliferation of screw
dislocations in the lamellar phase might be a plausible mechanism
for driving this transition
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