The photocurrent response of human cones is fast and monophasic

Background  

The precise form of the light response of human cone photoreceptors in vivo has not been established with certainty. To investigate the response shape we compare the predictions of a recent model of transduction in primate cone photoreceptors with measurements extracted from human cones using the paired-flash electroretinogram method. As a check, we also compare the predictions with previous single-cell measurements of ground squirrel cone responses.     

On the definition of a Monte Carlo model for binary crystal growth

We show that consistency of the transition probabilities in a lattice Monte Carlo (MC) model for binary crystal growth with the thermodynamic properties of a system does not guarantee the MC simulations near equilibrium to be in agreement with the thermodynamic equilibrium phase diagram for that system. The deviations remain small for systems with small bond energies, but they can increase significantly for systems with large melting entropy, typical for molecular systems. These deviations are attributed to the surface kinetics, which is responsible for a metastable zone below the liquidus line where no growth occurs, even in the absence of a 2D nucleation barrier. Here we propose an extension of the MC model that introduces a freedom of choice in the transition probabilities while staying within the thermodynamic constraints. This freedom can be used to eliminate the discrepancy between the MC simulations and the thermodynamic equilibrium phase diagram. Agreement is achieved for that choice of the transition probabilities yielding the fastest decrease of the free energy (i.e., largest growth rate) of the system at a temperature slightly below the equilibrium temperature. An analytical model is developed, which reproduces quite well the MC results, enabling a straightforward determination of the optimal set of transition probabilities. Application of both the MC and analytical model to conditions well away from equilibrium, giving rise to kinetic phase diagrams, shows that the effect of kinetics on segregation is even stronger than that predicted by previous models.     

Fractal dimension and localization of DNA knots

The scaling properties of DNA knots of different complexities were studied by atomic force microscope. Following two different protocols DNA knots are adsorbed onto a mica surface in regimes of (i) strong binding, that induces a kinetic trapping of the three-dimensional (3D) configuration, and of (ii) weak binding, that permits (partial) relaxation on the surface. In (i) the radius of gyration of the adsorbed DNA knot scales with the 3D Flory exponent nu approximately 0.60 within error. In (ii), we find nu approximately 0.66, a value between the 3D and 2D (nu=3/4) exponents. Evidence is also presented for the localization of knot crossings in 2D under weak adsorption conditions.     

Comparison of hydrodistillation and headspace solid-phase microextraction techniques for antibacterial volatile compounds from the fruits of Seseli libanotis

The volatile compounds from the fruits of Seseli libanotis, wild-growing in Poland, were obtained by hydrodistillation (HD) and headspace solid-phase microextraction techniques (HS-SPME) and analyzed using GC-MS. A total of 58 components were identified. The most abundant compounds were sabinen and beta-phellandrene. MIC (minimal inhibitory concentration) and MBC (minimal bactericidal concentration) values for the essential oil against reference bacterial strains and clinical S. aureus isolates were determined. The essential oil showed better antibacterial activity against the Gram-positive bacteria (MICs between 0.15 to 1.25 mg/mL) when compared with Gram-negative bacteria (MICs between 1.25 to 2.5 mg/mL). The low values of the MBC/MIC ratio suggest that the examined oil behaved as a bactericidal agent.     

Explaining the length threshold of polyglutamine aggregation

The existence of a length threshold, of about 35 residues, above which polyglutamine repeats can give rise to aggregation and to pathologies, is one of the hallmarks of polyglutamine neurodegenerative diseases such as Huntington's disease. The reason why such a minimal length exists at all has remained one of the main open issues in research on the molecular origins of such classes of diseases. Following the seminal proposals of Perutz, most research has focused on the hunt for a special structure, attainable only above the minimal length, able to trigger aggregation. Such a structure has remained elusive and there is growing evidence that it might not exist at all. Here we review some basic polymer and statistical physics facts and show that the existence of a threshold is compatible with the modulation that the repeat length imposes on the association and dissociation rates of polyglutamine polypeptides to and from oligomers. In particular, their dramatically different functional dependence on the length rationalizes the very presence of a threshold and hints at the cellular processes that might be at play, in vivo, to prevent aggregation and the consequent onset of the disease.     

Theoretical models of the negative ionization of hydrogen on clean tungsten,cesiated tungsten and cesium surfaces at low energies

The formation of negative hydrogen ions by scattering protons from a metal surface is described with two models: a probability model and an amplitude model. In both models the electron motion is described quantum mechanically and the nuclear motion classically. However, in the probability model the time evolution of the ionization probability is considered, while in the amplitude model the time evolution of the corresponding wave function amplitude is considered. The electron affinity level of an atom close to the metal is lowered by means of image forces and broadened due to resonant transition of an electron between te conduction band of the metal and the valence shell of the atom. The calculated position of the affinity level and the transition rate in both models give rise to maximum negative ionization efficiencies of 4% on W(110), 40% on cesiated tungsten and 15% on cesium.     

Emission cross sections of balmer-α,β,γ radiation for electrons (0–2000 eV) on H2 and D2

Absolute emission cross sections (σ_em) of Balmer-α,β, γ radiation have been measured in the case of electrons (0–2000 eV) incident on H₂ and D₂. The H Balmer σ_em's are larger than the corresponding D Balmer σ_em's for every electron impact energy. It has been found that this isotope effect varies strongly as a function of the incident electron energy below 100 eV. The isotope effect will be interpreted using the H₂ and D₂ potential energy curves.     

Neutral scattering and vibrational excitation in K+Br2 Collisions

Differential cross sections are presented for neutral scattering of K atoms in collisions with Br₂ molecules in the energy range from 20 to 150 eV. In addition energy-loss spectra for the scattered K atoms are shown. The differential cross sections show a large peak near the forward direction. The energy-loss spectra point to considerable vibrational excitation at small angles. The results are attributed to reneutralization from an ion-pair state formed during the collision. In some cases this process can involve three potential surface crossings. The experimental results can be reproduced in simple trajectory calculations on diabatic potential surfaces. The calculations show that the forward scattering is rainbow scattering, caused by the internal motion of the Br₂^? molecular ion during the collision. There is no analog to this rainbow in atom-atom scattering. The internal moti is also responsible for the observed vibrational excitation.     

Contribution of milk to daily intakes of iodine and bromine in northwestern Ukraine

Summary The concentration of stable iodine and bromine in Ukrainian milk has been determined in relation to the effect of the Chernobyl nuclear power plant accident. The geometric mean of iodine and bromine concentration was 31.0mg/kg and 2.57 mg/kg, respectively. Compared with Japanese milk, it was statistically lower. Bromine concentrations in Ukrainian and Japanese milk were not significantly different. Contribution of milk to daily intake of iodine and bromine in Ukrainian adults has been estimated to 88% and 94%.