Genetic variability among and within domestic Old and New World camels at the α-lactalbumin gene (LALBA) reveals new alleles and polymorphisms responsible for differential expression.

α-Lactalbumin (α-LA), which is encoded by the LALBA gene, is a major whey protein that binds to Ca2+ and facilitates lactose synthesis as a regulatory subunit of the synthase enzyme complex. In addition, it has been shown to play central roles in immune modulation, cell-growth regulation, and antimicrobial activity. In this study, a multitechnical approach was used to fully characterize the LALBA gene and its variants in both coding and regulatory regions for domestic camelids (dromedary, Bactrian camel, alpaca, and llama). The gene analysis revealed a conserved structure among the camelids, but a slight difference in size (2,012 bp on average) due to intronic variations. Promoters were characterized for the transcription factor binding sites (11 found in total). Intraspecies sequence comparison showed 36 SNPs in total (2 in the dromedary, none in the Bactrian camel, 22 in the alpaca, and 12 in the llama), whereas interspecies comparison showed 86 additional polymorphic sites. Eight SNPs were identified as trans-specific polymorphisms, and 2 of them (g.112A>G and g.1229A>G) were particularly interesting in the New World camels. The first creates a new binding site for transcription factor SP1. An enhancing effect of the g.112G variant on the expression was demonstrated by 3 independent pGL3 gene reporter assays. The latter is responsible for the p.78Ile>Val AA replacement and represents novel allelic variants (named LALBA A and B). A link to protein variants has been established by isoelectric focusing (IEF), and bioinformatics analysis revealed that carriers of valine (g.1229G) have a higher glycosylation rate. Genotyping methods based on restriction fragment length polymorphism (PCR-RFLP) were set up for both SNPs. Overall, adenine was more frequent (0.54 and 0.76) at both loci. Four haplotypes were found, and the AA and GA were the most common with a frequency of 0.403 and 0.365, respectively. Conversely, a putative biological gain characterizes the haplotype GG. Therefore, opportunities for rapid directional selection can be realized if this haplotype is associated with favorable milk protein properties. This study adds knowledge at the gene and protein level for α-LA (LALBA) in camelids and importantly contributes to a relatively unexplored research area in these species.

Anisotropy of spatiotemporal decorrelation in electrohydrodynamic turbulence.

Nonlinear straining and random sweeping spatiotemporal decorrelation properties, originally introduced as the main processes for turbulent fluctuations decorrelation in usual fluid flows, have been observed experimentally in anisotropic electroconvective turbulence generated in a nematic liquid crystal under the action of an external oscillating electric field. A transition between both processes occurs when the instability is driven toward states of increasing complexity, thus showing that decorrelation mechanisms in turbulent media are more universal than naively expected. A model for both decorrelation mechanisms is introduced, its comparison with experimental results providing an estimate of the characteristic sweeping velocity.

Thermo-recurrent nematic random laser.

This experimental work is aimed to investigate the thermal behavior of random laser action in dye doped nematic liquid crystals. The study evidenced an important temperature dependence of the random lasing characteristics in the nematic phase and in close proximity of the nematicisotropic (N-I) phase transition. A lowering of the laser emission intensity as the temperature increases is strictly related to the shift of the lasing threshold as function of the temperature even though the pump energy is kept fixed. The optical losses increasing owing to the thermal fluctuation enhanced scattering drive the input-output smoother behavior until the system stops to lase, because below threshold. The unexpected reoccurrence of random lasing at higher temperature, in proximity of N-I transition is found to be related to a different scattering mechanism, the micro-droplets nucleation and critical opalescence.

Dielectric characterization of doped M5.

We analyze the dielectric properties of the liquid crystal M5 used to investigate the electrohydrodynamics instability in nematic liquid crystals. We show that the spectra of the electrical impedance of doped samples of M5 with several concentrations of salt and of acid can be interpreted by assuming the doped liquid crystal as a dispersion of ions in a dielectric liquid. The analysis has been performed by considering the electrodes as blocking. From the best fit of the experimental data relevant to the real and imaginary parts of the electrical impedance of the cells, we derive the diffusion coefficients for the positive and negative ions and their bulk density. According to our analysis, in the limit of small concentrations of doping substance, the effective dielectric constant of the resulting liquid is, practically, independent of the doping.

Random lasing and weak localization of light in dye-doped nematic liquid crystals.

The first observation of random laser action in a partially ordered, optically anisotropic nematic liquid crystal with long-range dielectric tensor fluctuations is reported. Above a given pump power the fluorescence curve collapses and the typical narrowing and explosion effect leads to discrete sharp peaks. The unexpected surviving of interference effects in recurrent multiple scattering provide the required optical feedback for lasing in nematics. Coherent backscattering of light waves in orientationally ordered nematic liquid crystals manifests a weak localization of light which strongly supports diffusive laser action in presence of gain medium. Intensity fluctuations of the speckle-like emission pattern indicate the typical spatio-temporal randomness of diffusive laser emission. A comparison of the laser action is reported for systems with different order degree: fully disordered semiconductor powders, self-ordered cholesterics and partially ordered nematic liquid crystals.

Influence of the bias-voltage on the anchoring energy for nematic liquid crystals.

The influence of the bias-voltage on the anisotropic part of the nematic surface energy is analyzed. The experimental data show a strong dependence of the anchoring strength on the bias-voltage when the electrodes of the nematic cell are covered with WO3. The observed dependence can be interpreted taking into account the ions dissolved in the liquid crystal. We propose a model in which the effect of the bias-voltage is to collect the ions near the electrodes, in a surface layer whose thickness is of the order of the Debye's screening length. The surplus of electric field due to this ions confinement gives rise to an electrostatic contribution to the total energy that can be considered as a surface energy. The proposed model is in good agreement with the experimental data. The model is used to interpret the observed independence of the anchoring strength on the bias-voltage when the (indium-tin-oxide) electrode is covered with a film of polyimide, or it is without any covering. The influence of a charge emission from the electrodes under the bias voltage on the anchoring energy is also analyzed. Possible applications of the observed phenomenon are discussed.

Liquid-crystal-electrochromic-material interface: a p-n-like electro-optic junction.

A liquid crystal (LC) cell has been made by using a standard sandwich configuration with one of the indium tin oxide (ITO) electrodes covered by a thin layer of tungsten trioxide (WO3). In this kind of cell optical polarization switching (observed under a crossed polarizer microscope) occurs for only one of the two polarities of an ac external applied electric field, while in the usual liquid crystal cells the electro-optic response does not depend on the sign of the field. The inhibiting switching configuration corresponds to anodic polarization of the tungsten trioxide film in which the deintercalation of cations occurs. Here we present the time behavior of charge and discharge for both the anodic and cathodic currents. A model based on charge carrier exchange between the ITO-WO3 and WO3-LC interfaces and also electrochemical processes is reported. Our model is also capable of explaining the electric and electro-optic asymmetric responses of the cell. Numerical calculations confirm the model.

Turbulence to turbulence transition in homeotropically aligned nematic liquid crystals.

In this paper, a study of the electrically driven turbulent-turbulent transition in a homeotropically oriented nematic sample is reported. The transition has the characteristics of a nucleation process, and its threshold has been experimentally determined. The nucleation rate and the growth velocity of the new turbulent nuclei are also reported.

Electrical and electro-optical investigations of liquid crystal cells containing WO3 thin films

An interesting application of the fast ion transport properties of tungsten trioxide is presented, when it is inserted as an electrode in nematic liquid crystal (NLC) cells. In a standard sandwichlike cell the nematic liquid crystal, confined between two transparent plane electrodes of purely electronic conductors [indium tin oxide (ITO)], undergoes a molecular reorientation under the action of an external electric field E. This electrically controlled birefringence (electro-optical switching) is proportional to E2, thus polarity insensitive [L. M. Blinov and V. G. Chigrinov, Electrooptic Effects in Liquid Crystal Materials (Springer-Verlag, New York, 1994)]. When a thin film of tungsten trioxide is deposited by magnetron sputtering onto one of the transparent ITO electrodes, and a NLC cell is assembled with such asymmetry, the electro-optical response becomes polarity sensitive [G. Strangi et al., Appl. Phys. Lett. 74, 534 (1999)]. The analysis of this response suggests the occurrence of a reverse internal electric field, associated with the ionic diffusion process of protons always present in these sputtered WO3 films [E. Cazzanelli et al., Electrochim. Acta 44, 3101 (1999)]. By using an opportune voltage waveform it is possible to evaluate such an internal field. Impedance and cyclic voltammetry measurements were carried out on these cells, comparing "as-deposited" and "annealed" tungsten trioxide electrodes. These studies confirm that an important ionic diffusion process is involved in the establishment of an internal electric field, which modifies the electro-optical response of the nematic liquid crystal cell.

Photopolarimetric characterization of the transition between two turbulent states in a nematic liquid crystal film.

This work was aimed at the photopolarimetric characterization of the transition between two dynamic scattering modes that take place in a planarly aligned nematic liquid crystal sample, under the effect of an external low-frequency electric field. The time evolution of the degree of polarization and the behavior of the radiation entropy of the transmitted light allow us to interpret the transition between two turbulent states, or dynamic scattering modes, as a decay from a two-dimensional (2D) to a (3D) turbulence.