High resolution mass spectrometric suspect screening, wide-scope target analysis of emerging contaminants and determination of legacy pollutants in adult black-tailed godwit Limosa limosa limosa in the Netherlands - A pilot study

The Dutch breeding population of the black-tailed godwit Limosa limosa limosa has declined substantially over recent decades; the role of contaminants is unknown. We analysed liver samples from 11 adult birds found dead on their breeding grounds in SW Friesland 2016-2020, six from extensive, herb-rich grasslands, five from intensive grasslands. We carried out LC and GC wide-scope target analysis of more than 2400 substances, LC suspect screening for more than 60,000 substances, target analysis for Cd, Hg, Ni and Pb, organo-phosphate flame retardants (OPFRs), dechlorane plus compounds and selected polybrominated diphenyl ether flame retardants (PBDEs), and bioassay for polybrominated dibenzo-p-dioxins and dibenzofurans (PBDDs/PDBFs) and dioxin-like polychlorinated biphenyls (dl-PCBs). Residues of 29 emerging contaminants (ECs) were determined through wide-scope target analysis. Another 20 were tentatively identified through suspect screening. These contaminants include industrial chemicals (personal care products, surfactants, PAHs and others), plant protection products (PPPs) and pharmaceuticals and their transformation products. Total contaminant load detected by wide-scope target analysis ranged from c. 155 to c. 1400 ng g^-1 and was generally lower in birds from extensive grasslands. Heatmaps suggest that birds from intensive grasslands have a greater mix and higher residue concentrations of PPPs, while birds from extensive grasslands have a greater mix and higher residue concentrations of per- and polyfluoroalkyl substances (PFAS). All four metals and two OPFRs were detected. All tested PBDEs were below the respective LODs. Bioassay revealed presence of PBDDs, PBDFs and dl-PCBs. Further research is required to elucidate potential health risks to godwits and contaminant sources.

Role of an oscillatory electric field on the Lehmann rotation of cholesteric droplets

This paper deals with the Lehmann rotation of banded cholesteric droplets subjected to a temperature gradient when they coexist with their own isotropic liquid. I show that their angular rotation velocity increases --in absolute value-- when they are subjected to an additional AC electric field in the conducting regime. This velocity increase is correlated with a prolate distortion of the droplets and the probable presence of electrohydrodynamical toroidal circulation flows inside and outside the droplets. I propose that the coupling between these flows and the director field is responsible for the increase of the angular velocity of the texture. The origin of these flows is discussed qualitatively in the framework of the leaky dielectric model by taking into account the generation of charges both in the bulk via a Carr-Helfrich mechanism (Tarasov, Krekhow and Kramer model) and at the surface of the droplet (Taylor-Melcher model).

Lehmann rotation of cholesteric droplets driven by Marangoni convection

We show experimentally and theoretically that the Lehmann effect recently observed by Yoshioka and Araoka (Nat. Commun., 2018, 9, 432) in emulsified cholesteric liquid crystal droplets under temperature gradients is due to Marangoni flows rather than to the thermomechanical or chemomechanical couplings often invoked to explain the phenomenon. Using colloidal tracers we visualize convection rolls surrounding stationary cholesteric droplets in vertical temperature gradients, while a shift in the position of internal point defects reveals the corresponding inner convection in nematic droplets thermomigrating in a horizontal temperature gradient. We attribute these phenomena to the temperature dependence of the surface tension at the interface between these partially-miscible liquids, and justify their absence in the usual case of purely lyophobic emulsions. We perform a theoretical analysis to help validate this hypothesis, demonstrating the strong dependence of the precession velocity on the configuration of the cholesteric director field.

Dislocations dynamics during the nonlinear creep of a homeotropic sample of smectic-A liquid crystal

New creep experiments under sinusoidal compression/dilation deformation of a homeotropic sample of smectic-A liquid crystal (8CB) show that its response is nonlinear at very small amplitude of deformation. This behavior is explained by taking into account the crossing between the edge dislocations that climb parallel to the layers and the screw dislocations joining the two surfaces limiting the sample. The activation energy of the crossing process and the density of the screw dislocations as a function of the sample thickness are estimated experimentally.

Drag of a Cottrell atmosphere by an edge dislocation in a smectic-A liquid crystal

In a recent letter (P. Oswald et al., EPL 103, 46004 (2013)), we have shown that a smectic-A phase hardens in compression normal to the layers when the liquid crystal is doped with gold nanoparticles. This is due to the formation of Cottrell clouds nearby the core of the edge dislocations and the appearance of an additional drag force that reduces their mobility. We theoretically calculate the shape of the Cottrell cloud and the associated drag force as a function of the climb velocity of the dislocations. The main result is that the drag force depends on velocity and vanishes when the temperature tends to the smectic-A-to-nematic transition temperature. The role of the diffusion anisotropy is also evaluated.

[Clinical characteristics among forensic inpatients: A special case, the establishment of social defense "Les Marronniers" in Tournai (Belgium)]

BACKGROUND

In Belgium, the law of "social defense" stipulates that an accused "which is either in a state of dementia or in a serious state of mental disturbance or mental deficiency, incapable of controlling his actions" can be interned. The establishment of social defense (ESD) in Tournai (Belgium) hosts 350 inmates.

OBJECTIVES

In collaboration with the Centre for research in social defense, we organized a systematic assessment of patients interned in ESD. This is the first study evaluating prospectively this population.

METHODS

Of the total, 229 patients signed informed consent. Different scales of assessment (MINI, WAIS-III, SCID II) were used. Descriptive analyzes were applied (SPSS version 12).

RESULTS

We show that 48.8 % of our participants had committed a sexual offense (rape or attempted rape, indecent assault, public outrage or mixed). The average intelligence quotient is 71.4. According to the MINI, 33.2 % of participants showed no psychiatric disorder. Among psychiatric disorders, psychotic disorders are the most represented (37.4 %). According to the SCID, personality disorders were absent in 26.8 % of our participants. Most of the axis II disorders are represented personality disorders related to cluster B (57.3 %) mainly with antisocial personality disorder (37.9 %).

CONCLUSION

These data demonstrate the significant heterogeneity of our sample and the need for the establishment of specific care routes to each subpopulation.

Microscopic vs. macroscopic origin of the Lehmann effect in cholesteric liquid crystals

In a recent letter (EPL 97, 36006 (2012)), we have shown that the Leslie thermomechanical coupling cannot alone explain the Lehmann effect (namely the rotation of cholesteric droplets when they are subjected to a temperature gradient). This result was obtained by measuring in a compensated cholesteric mixture the "Lehmann coefficient" as a function of temperature both below and at the transition to the isotropic liquid. In this article, we detail these experiments and present new ones performed with other compensated mixtures and a diluted cholesteric mixture. The new results confirm the macroscopic origin of the Lehmann effect, in contrast to the Leslie thermomechanical effect that is clearly of microscopic origin.

Elasto- and electro-capillary instabilities of a nematic-isotropic interface: Experimental results

Recently, we have shown the existence of an electro-capillary instability of a nematic-isotropic interface stabilized by a temperature gradient (P. Oswald, EPL 90, 16005 (2010)). This instability results from a competition between the destabilizing action of the electric Maxwell stress and the stabilizing action of the thermal and capillary forces. The control parameters are the temperature gradient G , the applied voltage V and the thickness h of the nematic layer. In this paper, we present new experimental results on this instability in both the linear and nonlinear regimes. In particular, very rich phase diagrams are mapped out in the (h, V) plane for three different values of G . The divergence of the growth time close to the onset of instability is also studied in detail. In addition, we show the existence at low voltages of another instability of the de Gennes type, where the elastic Ericksen stress is responsible for the destabilization. In this case, a hill-and-valley structure or a square array of umbilics develop at the interface depending on the values of h , V and G .

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

We 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.

Lehmann effect in a compensated cholesteric liquid crystal: experimental evidence with fixed and gliding boundary conditions

In a recent letter (Europhys. Lett. 80, 26001 (2007)), we have shown that a compensated cholesteric liquid crystal (in which the macroscopic helix completely unwinds) may be subjected to a thermomechanical torque (the so-called Lehmann effect), in agreement with previous findings of Eber and Jánossy (Mol. Cryst. Liq. Cryst. Lett. 72, 233 (1982)). These results prove that one must take into account the chirality of the molecules and the absence of inversion symmetry at the macroscopic scale when deriving the constitutive equations of the phase at the compensation temperature. In this paper, we present the details of our experimental work and a new experiment performed in a sample treated for planar gliding anchoring. The latter experiment, coupled with a numerical simulation, supports the existence of a thermomechanical coupling in a compensated cholesteric.

Does the electric Lehmann effect exist in cholesteric liquid crystals?

Experiments have shown that cholesteric droplets or cholesteric fingers may be put into motion by the action of an electric field. The former rotate whereas the latter drift perpendicularly to their axes. In all cases, the texture moves without visible material transport. The electric Lehmann effect was initially used to interpret these observations but, recently, alternative explanations were found, based on electrohydrodynamics. Another experiment in this area was that of Padmini and Madhusudana (Liq. Cryst. 14, 497 (1993)). Performed in 1993 with a compensated cholesteric liquid crystal under fixed planar boundary conditions, it was also explained in terms of electric Lehmann effect. We conducted the same experiment and extended it to a pi -twisted planar geometry. Although our experimental results agree with those of Padmini and Madhusudana, we demonstrate that they are incompatible with an electric Lehmann effect. By contrast, an explanation based on flexoelectricity allows us to interpret the whole data set obtained in both geometries. The consequence is that there is at the moment no clear experimental evidence of the electric Lehmann effect.

Surface tension and capillary waves at the nematic-isotropic interface in ternary mixtures of liquid crystal, colloids, and impurities

In mixtures of thermotropic liquid crystals with spherical poly(methyl methacrylate) particles, self-supporting networklike structures are formed during slow cooling past the isotropic-to-nematic phase transition. Experimental results support the hypothesis that a third component, alkane remnants slowly liberated from the particles, plays a crucial role. A theoretical model, based on the phenomenological Landau-de Gennes, Carnahan-Starling, and hard-sphere crystal theories, is developed to describe the continuous phase separation in a ternary nematic-impurity-colloid mixture. The interfacial tension and the dispersion relation of the surface modes of the nematic-isotropic interface are determined. The colloids decrease the interfacial tension and the damping rate of surface waves, whereas impurities act in an opposite way. This should strongly influence the formation of abovementioned networklike structures and could help explain some of their rheological properties.

Collapse dynamics of smectic-A bubbles

The collapse dynamics of smectic-A bubbles are analyzed experimentally and theoretically. Each bubble is expanded from a flat film stretched at the end of a hollow cylinder and deflated through a pressure release by means of a capillary tube. Its total collapse time can be varied between 0.1s and 20s by suitably choosing the length and the internal diameter of the capillary. This experiment allowed us to show that the collapse takes place in two steps: an initial one, which lasts a fraction of a second, where the meniscus destabilizes and fills up with focal conics, followed by a much longer period during which the bubble collapses and exchanges material with the meniscus. By measuring simultaneously the Laplace pressure and the internal pressure inside the bubble, we were able to fully characterize the shear-thinning behavior of the smectic phase within the meniscus. We emphasize that this method is generic and could be applied as well to other systems such as soap bubbles, on condition that inertial effects are negligible.

Faceting and stability of smectic A droplets on a solid substrate

It is shown that a smectic A droplet deposited on a solid substrate treated for strong homeotropic anchoring is faceted at the top in spite of the fact that there are no steps at the free surface, but instead edge dislocations in the bulk. The radius of the facet and the full profile of the curved part of the droplet are determined as a function of the temperature in the vicinity of a nematic-smectic A phase transition. It is shown that the observed profiles do not correspond to the actual equilibrium shape, but to metastable configurations close to their point of marginal stability. In addition, we predict that the profiles must be different for a given temperature depending on whether the droplet has been heated or cooled down to reach this temperature. Finally, we discuss the problem of the formation of giant dislocations in big droplets (Grandjean terraces).

Zigzag instability of a chi disclination line in a cholesteric liquid crystal

We studied the formation of chi disclination lines in planar cholesteric samples placed in a temperature gradient near the cholesteric to smectic A phase transition. We observed that the first simple line which forms close to the smectic-cholesteric front zigzags when it is perpendicular to the direction of planar anchoring and is straight for other orientations. This instability is similar to Herring instability for crystalline surfaces. We show numerically that it originates from a strong increase of the elastic anisotropy close to the transition. In addition, we propose a new method to measure the pitch divergence at the smectic to cholesteric phase transition.

Growth below and above the spinodal limit: the cholesteric-nematic front

In classical crystal growth, the solid propagates into its metastable liquid, even in the fast-dynamics regime in which kinetic effects dominate the diffusive effects. In usual experiments, the liquid is always very far from its spinodal limit below which it becomes unstable. For that reason, very little is known about crystal growth just below and above the spinodal limit of the liquid. In order to tackle this problem, we have performed an experiment about the propagation of the cholesteric-nematic front in directional melting. We show experimentally that, in this system, it is possible to reach and pass the spinodal limit. We show the existence of many morphological transitions at increasing velocities which lead to the formation of metastable or unstable phases. A complete phase diagram is drawn up as a function of the front velocity and the sample thickness. In particular, the crossing of the spinodal limit is clearly identified by comparison with the morphologies observed in free growth (i.e., at a homogeneous temperature). We show that this passage is accompanied by a reversal (pi rotation) of the structure in thin samples only. This spectacular effect resembles a "cell-to-dendrite" transition and is chirality induced. The importance of the first-order character of the transition is also emphasized.

Direct measurement of the permeability of the meniscus bordering a free-standing smectic-A film

A smectic-A free-standing film is always connected by a meniscus to the frame on which it has been stretched. The meniscus acts as a dissipative reservoir and is characterized by its permeability. We propose a method to measure directly this quantity by equilibrating two menisci in correspondence with the same free-standing film. The permeability is shown to depend on the film thickness, in full agreement with previous indirect measurements obtained by analyzing the growth dynamics of dislocation loops. An improved model of the meniscus is proposed to interpret all the data.

A major SNP haplotype of the arginine vasopressin 1B receptor protects against recurrent major depression

Increasing amounts of data suggest that affective disorders might be related to dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, one of the stress-response systems. Arginine vasopressin (AVP) influences several symptoms, relevant to affective disorders, notable memory processes, pain sensitivity, synchronization of biological rhythms and the timing and quality of REM sleep. We examined whether genetic variations in the AVP receptor 1b gene (AVPR1b) could be associated with increased susceptibility to affective disorders using a gene-based association analysis of single-nucleotide polymorphisms (SNPs). Five SNPs were identified in AVPR1b and genotyped in two well-diagnosed samples of patients with recurrent major depression and matched controls. In the Swedish sample, we observed significant allele (P=0.02) and genotype (P=0.01) association with SNP AVPR1b-s3, and in the Belgian sample, a borderline significant association with SNP AVPR1b-s5 (P=0.04). In both patient-control samples, the haplotype defined by alleles A-T-C-A-G for the AVPR1b-s SNPs s1-s2-s3-s4-s5 was significantly over-represented in controls compared to patients. Our data support a protective effect of this major haplotype for recurrent major depression.

Dislocation loop dynamics in freestanding smectic films: the role of the disjoining pressure and of the finite permeability of the meniscus

When a dislocation loop nucleates in a freestanding film, it collapses or grows depending on whether its radius r is smaller or larger than a critical radius r(c). In this paper, we analyze the growth dynamics of a dislocation loop in the limit of r>>r(c). Experiments with pure octylcyanobiphenyl show that the dislocation velocity is constant in thick films (more than 100 layers) regardless of their thicknesses, and only depends on the pressure in the meniscus. At intermediate thickness (between 100 and 15 layers), the velocity is no longer constant and tends to decrease in time on account of the finite permeability of the meniscus. In very thin films (less than 15 layers), the dislocations move faster than in thick films, although their velocities continue to decrease in time. The thinner the film, the larger the global acceleration is. This effect is linked to a supplementary force acting on the dislocations caused by the attraction between the free surfaces (where the smectic order parameter is enhanced). The progressive deceleration is due to the finite permeability of the meniscus.

Waves at the nematic-isotropic interface: the role of surface tension anisotropy, curvature elasticity, and backflow effects

Recently, a theoretical description of waves at the nematic-isotropic interface has been proposed using a generalized dynamical Landau-Ginzburg-de Gennes theory [V. Popa-Nita and T. J. Sluckin, Phys. Rev. E 66, 041703 (2002)]. This calculation assumed an isotropic surface tension, i.e., independent of the director orientation at the interface and neglected all coupling between the director and the hydrodynamic flow. As a consequence, the director was assumed to keep a fixed orientation and do not couple with the oscillations of the interface. These assumptions are rather crude in real nematics where surface tension anisotropy may be as large as 20% and where hydrodynamic coupling with the director is known to be important. In this paper we propose to take into account these two effects: as a result, interface oscillations couple with the director field via hydrodynamic flows and backflow effects. We analyze how these phenomena change the dispersion relation. Finally, we review experiments on the nematic-isotropic interface and discuss how to measure experimentally the dispersion relation.

Determination of the interconversion energy barrier of enantiomers by separation methods

Separation methods have become versatile tools for the determination of kinetic activation parameters and energy barriers to interconversion of isomers and enantiomers in the last 20 years. New computer-aided evaluation systems allow the on-line determination of these data after separating minute amount of pure compounds or mixture of isomers or enantiomers, respectively. Both dynamic interconversion during the separation process as well as static stopped-flow techniques have been applied to determine the kinetic activation parameters and interconversion energy barriers by separation methods. The use of (1) combinations of batchwise kinetic studies with enantioselective separations, (2) a continuous flow model, (3) a comparison of real chromatograms with simulated ones, (4) stopped-flow techniques, (5) stochastic methods, (6) approximation functions and (7) deconvolution methods, for the determination of interconversion energy barriers by separation methods is summarized in detail.

Optical filter architecture for approximating any 2 X 2 unitary matrix

A new optical filter architecture and a new design methodology are presented for approximating any frequency-dependent 2 x 2 unitary matrix that consists of two coupled phase and amplitude responses. Design examples are provided for the compensation of polarization mode dispersion (PMD) by approximating the inverse of a synthesized fiber's Jones matrix. Compensation of the channel PMD over the signal bandwidth is demonstrated, as required for demultiplexing channels in a polarization-multiplexed system.

Controlled nucleation of point defects on a disclination line near a free surface during smectic-A-to-nematic directional melting

A disclination line populated with point defects that break the translational symmetry forms near a free nematic (N) interface in a confined geometry. The disclination line is, however, absent in the smectic-A phase (SmA). We use this fact to control the formation of point defect distributions on a disclination line by directional melting of the SmA phase in a temperature gradient. A threshold velocity ( v(th)) exists below which a defect-free disclination line is formed. The frequency of nucleation of point defects increases steadily for v > v(th) and exhibits a remarkable regularity. We derive an empirical scaling for v(th) in terms of the experimental tuning parameters. We propose a simple model that allows to understand the formation of the point defects.

Phase-field model for front propagation in a temperature gradient: selection and competition between the correlation and the thermal lengths

A phase-field model is presented to study the propagation and the selection of a front in directional growth. The phase transition can be first or second order and is described by a nonconserved order parameter. In general, the thermal length l(u) (inversely proportional to the temperature gradient) is much larger than the correlation length l(phi), which gives the width of the front, and there is no direct competition between them (epsilon =l(phi)/l(u)<<1). In this paper, we consider a situation where these two lengths can be of the same order of magnitude (epsilon =l(phi)/l(u) close to 1). This happens in liquid crystals at the nematic-cholesteric phase transition. The problem of the front selection is solved theoretically by first performing an asymptotic analysis of the governing equations in the limit epsilon-->0, and then by solving the equations numerically. The main result is that the front is selected in a single way (no continuum of solutions) as long as epsilon not equal 0, whatever the velocity and the order of the phase transition. Finally, we show that the order parameter profile and the front temperature can change significantly when epsilon approaches 1.

Evaluation of reversible and irreversible models for the determination of the enantiomerization energy barrier for N-(p-methoxybenzyl)-1,3,2-benzodithiazol-1-oxide by supercritical fluid chromatography

It has been found that the interconversion of enantiomers on a chromatographic column during the separation process can be studied by the first-order kinetic equations derived both for reversible and irreversible reactions in a stationary system if the extent of interconversion is not too high. The equation derived for irreversible reactions gives, however, results also for higher degrees of enantiomerization while that derived for reversible interconversion failed. The irreversible equation was used to determine the enantiomerization barrier of N-(p-methoxybenzyl)-l,3,2-benzodithiazol-l-oxide enantiomers by supercritical fluid chromatography. The racemate of N-(p-methoxybenzyl)-l,3,2-benzodithiazol-l-oxide was separated by supercritical fluid chromatography on the (R,R)-Whelk-Ol column with supercritical carbon dioxide containing 20% methanol as a mobile phase. Peak areas of enantiomers prior to and after the separation used for the calculation of the enantiomerization barrier were determined by computer-assisted peak deconvolution of peak clusters registered on chromatograms using commercial software.

Formation and distribution of point defects on a disclination line near a free nematic interface

Point defects of opposite signs can alternately nucleate on the -1/2 disclination line that forms near the free surface of a confined nematic liquid crystal. We show the existence of metastable configurations consisting of periodic repetitions of such defects. These configurations are characterized by a minimal interdefect spacing that is seen to depend on sample thickness and on an applied electric field. The time evolution of the defect distribution suggests that the defects attract at small distances and repel at large distances.

Disjoining pressure and thinning transitions in smectic-A liquid crystal films

The contact angle between a free standing film of a smectic-A liquid crystal and its meniscus is different from zero. It increases independently of the meniscus size when the film thickness decreases. This angle provides a very precise measurement of the film tension and of the interactions between the two free surfaces. This interaction is attractive and can be qualitatively explained within the framework of the de Gennes theory of the presmectic state. According to this model, the attraction is caused by an increase of the smectic order parameter at the free surface. This phenomenon also explains the metastability of very thin smectic films above the bulk smectic-A-nematic phase transition. The temperatures T(N) of spontaneous thinning from N layers to N-1 layers is measured in the smectic phase of the liquid crystal 8CB (octylcyanobiphenyl).

Edge dislocation in a vertical smectic-A film: line tension versus temperature and film thickness near the nematic phase

The line tension of a dislocation is measured in a vertical smectic-A film as a function of temperature and film thickness. There are two contributions to the line tension: a bulk contribution that corresponds to the energy of the dislocation in an infinite medium and a surface correction that accounts for interactions with the two free surfaces. Both terms are measured in pure 8CB (octylcyanobiphenyl) as a function of temperature when the bulk nematic-smectic-A transition temperature T(c) is approached.

Diffusion coefficients in a lamellar lyotropic phase: evidence for defects connecting the surfactant structure

We measure diffusion coefficients in the lamellar phase of the nonionic binary system C(12)EO(6)/H(2)O using fluorescence recovery after photobleaching. The diffusion coefficient across the lamellae shows an abrupt increase upon approaching the lamellar-isotropic phase transition. We interpret this feature in terms of defects connecting the surfactant structure. An estimation of the defect density and of the variation in defect energy close to the transition is given in terms of a simple model.

[Swiss registry for patients with cystic fibrosis: design, programming, implementation and first examples of use]

The Swiss Registry for Cystic Fibrosis (SRCF) was designed to collect demographic, clinical and therapeutic data from patients with cystic fibrosis (CF) in Switzerland. It was designed, programmed and implemented for standalone application in Swiss cystic fibrosis centres. It is part of the European Registry for Cystic Fibrosis (ERCF), which has been implemented in Europe to collect data on the use and safety of dornase alpha (Pulmozyme) in the treatment of cystic fibrosis. At the time of first evaluation 245 cystic fibrosis patients are registered, their mean age is 13 years, and 17% are over 18. In larger databases in Germany or North America we observe comparable demographic data, similar degrees of severity and similar therapeutic approaches to those in Swiss cystic fibrosis patients. The aim of the Swiss Registry is to cover the maximum possible number of cystic fibrosis patients from this country.

Coupling between meniscus and smectic-A films: circular and catenoid profiles, induced stress, and dislocation dynamics

In this paper we discuss the formation and shape of the meniscus between a free-standing film of a smectic-A phase and a wall (in practice the frame that supports the film). The wall may be flat or circular, and the system with or without a reservoir of particles. The formation of the meniscus is always an irreversible thermodynamic process, since it involves the creation of dislocations in the bulk (therefore it involves friction). The four basic shapes of meniscus discussed are the following: exponential, algebraic (x(3/2)), circular, and catenoid. Three principal regions of the whole meniscus must be distinguished: close to the wall with a high density of dislocations, away from the wall with medium density of dislocations, and far from the wall (i.e., close to the film) with a low density of dislocations (vicinal regime). The region with medium density of dislocations is observable using a microscope, and is determined by the competition between surface tension, energy of dislocations, and pressure difference set by the mass of the meniscus or by the reservoir. Its profile is circular as observed in recent experiments [J.-C. Geminard, R. Holyst, and P. Oswald, Phys. Rev. Lett. 78, 1924 (1997)]. By contrast, the vicinal regime with low density of dislocations is never observable with an optical microscope. In the regime with a high density of dislocations, the reasons why the dislocations tend to gather by forming giant dislocations and rows of focal conics are discussed. Finally, we discuss the stability of a smectic film with respect to the formation of a dislocation loop. We show experimentally that the critical radius of the loop is proportional to the curvature radius of the meniscus in its circular part, in agreement with the theory. In addition, we show that the mobility of edge dislocations measured in thick films is in agreement with that found in bulk samples from a creep experiment. This result confirms again our model of the meniscus.

Growth and melting of the nematic phase: sample thickness dependence of the mullins-sekerka instability

In this article we report our systematic studies of the dependence on the sample thickness of the onset parameters of the instability of the nematic-isotropic interface during directional growth and melting, in homeotropic or planar anchoring.

On the calculation of Gibbs energy corresponding to enantioselective interactions at a direct HRGC separation of enantiomers

A novel procedure is proposed for the calculation of Gibbs energy corresponding to enantiospecific interactions of 2-(2, 4-dinitrophenoxy)-, 2-phenoxy-, and 2-halogen-n-pentane enantiomers with a beta-cyclodextrin (ChirasilDex) stationary phase under gas chromatographic conditions. This energy is calculated from retention data as a difference between the Gibbs energy of an enantiomer and its corresponding achiral congener. The procedure for the determination of 2-(2,4-dinitrophenoxy)-, 2-phenoxy- and 2-halogen- n-pentane achiral congener retention data is discussed in detail.

Effect of the electric conductivity on the drift velocity of the cholesteric fingers of the second type in confined geometry

We show that the drift velocity of the cholesteric fingers of the second species in ac electric field strongly depends on the conductivity of the liquid crystal chosen and exponentially vanishes above a cutoff frequency we found to be equal (within a numerical factor close to 1) to the charge relaxation frequency of the sample. We further show that the drift velocity is proportional to the applied electric field, provided that the confinement ratio is kept constant.

Looped finger transformation in frustrated cholesteric liquid crystals

Localized structures named "fingers" form in the vicinity of the unwinding transition of a cholesteric liquid crystal subjected to an electric field and to homeotropic boundary conditions. Several types of fingers exist, with different static and dynamic properties. For instance, cholesteric fingers of the second species (CF-2) can drift perpendicular to their axes and form spirals in ac electric fields, whereas fingers of the first species (CF-1) crawl along their axes. In this article we show that CF-2's are much easier to nucleate in thick samples (with respect to the pitch) than in thin ones and may form loops like the CF-1's, with or without defects. We show that looped CF-1's always collapse in thick samples at increasing voltage, whereas they can form cholesteric bubbles in thin samples. By contrast, we never observe the formation of a bubble from a loop of a CF-2 except when it possesses a point defect. We also recall that CF-1 segments always collapse at increasing voltage, whereas CF-2 segments systematically give cholesteric bubbles in similar conditions. To qualitatively explain these transformations, we use a simplified representation on the unit sphere S2 of the director field within the fingers. While the CF-1's are described within the standard model of Press and Arrot, we use for the CF-2's a recent model of Gil and Gilli, which we prove to explain most observations. We also describe the growth and collapse dynamics of a loop of a CF-2 in close connection with the spiral dynamics. Finally, we show experimentally and numerically that the CF-2's get abruptly thinner when the electric field exceeds the spinodal limit of the CF-1's. This transformation is reversible, but strongly hysteretic.

Liver positive enhancement after injection of superparamagnetic nanoparticles: respective role of circulating and uptaken particles

Superparamagnetic nanoparticles have both high r1 and r2 relaxivities responsible for positive or negative enhancement properties. The aim of this study was to investigate to what extent perfusion (circulating particles) and uptake (clustered particles) mechanisms contribute to liver positive or negative enhancement using two different particles, superparamagnetic iron oxides (ferumoxides, AMI 25) and ultrasmall superparamagnetic iron oxides (ferumoxtran, AMI-227). Uptake kinetics were studied after intravenous injection of 20 micromol Fe/kg ferumoxtran on a washout liver model. Livers of 82 rats were surgically isolated and washed with saline infusion. Imaging was performed ex vivo at 0.5T with T1- and T2-weighted sequences. Enhancement kinetics of the liver were studied in vivo using MRI up to 180 min post injection of 20 micromol Fe/kg ferumoxtran (time response study) or 10, 20, 40 micromol Fe/kg ferumoxtran and 20 micromol Fe/kg ferumoxides (dose response study.) Particle uptake occurred early and resulted in a negative enhancement of the washed livers 15 min after injection of both T1 and T2 sequences. In vivo, a positive enhancement was only seen during the first five min with the lowest dose of ultrasmall superparamagnetic iron oxides and the T1 sequence. Uptake and clustering of the particles induced a negative liver enhancement. During the first minutes after injection, when uptake has not significantly occurred, perfusion imaging of the liver at a dose of 10 micromol Fe/kg results in a positive enhancement with T1-weighted sequences.

[Endovascular treatment of hemorrhagic renal angiomyolipoma with platinum microcoils]

Haemorrhage is the major complication of renal angiomyolipoma and is classically treated surgically, but embolization constitutes an alternative treatment. Improvement of catheters and embolization materials now allows highly selective embolization. The authors present a case in which the use of a variable stiffness catheter and platinum microcoils allowed highly selective embolization of a haemorrhagic renal angiomyolipoma while preserving the functional renal parenchyma.

[Hepatosplenic silicosis]

A case of hepatosplenic silicosis complicating a pulmonary silicosis is reported. Numerous calcified splenic nodules seen with conventional radiology, ultrasound or computed tomography, hepatic microcalcifications and "egg shell" abdominal lymph nodes best seen with computed tomography represent the radiologic signs. However, hepatosplenic silicosis can only be confirmed by pathological examination of liver biopsies showing birefringent particles within hyalinized nodules.