Superfluid drag of two-species Bose-Einstein condensates in optical lattices

We study two-species Bose-Einstein condensates in quasi two-dimensional optical lattices of varying geometry and potential depth. Based on the numerically exact Bloch and Wannier functions obtained using the plane-wave expansion method, we quantify the drag (entrainment coupling) between the condensate components. This drag originates from the (short range) inter-species interaction and increases with the kinetic energy. As a result of the interplay between interaction and kinetic energy effects, the superfluid-drag coefficient shows a non-monotonic dependence on the lattice depth. To make contact with future experiments, we quantitatively investigate the drag for mass ratios corresponding to relevant atomic species.Comment: 6 pages, 4 figures. Accepted in its original form but minor changes have been don

Electron-phonon coupling in crystalline organic semiconductors: Microscopic evidence for nonpolaronic charge carriers

We consider electron(hole)-phonon coupling in crystalline organic semiconductors, using naphthalene for our case study. Employing a first-principles approach, we compute the changes in the self-consistent Kohn-Sham potential corresponding to different phonon modes and go on to obtain the carrier-phonon coupling matrix elements (vertex functions). We then evaluate perturbatively the quasiparticle spectral residues for electrons at the bottom of the lowest-unoccupied- (LUMO) and holes at the top of the highest-occupied (HOMO) band, respectively obtaining $Z_e\approx 0.74$ and $Z_h\approx 0.78$. Along with the widely accepted notion that the carrier-phonon coupling strengths in polyacenes decrease with increasing molecular size, our results provide a strong microscopic evidence for the previously conjectured nonpolaronic nature of band-like carriers in these systems.Comment: final, published versio

Inflationary RSII Model with a Matter in the Bulk and Exponential Potential of Tachyon Field

In this paper we study a tachyon cosmological model based on dynamics of a 3-brane in the second Randall-Sundrum (RSII) model extended to include matter in the bulk. The presence of matter in the bulk changes warp factor which leads to modification of inflationary dynamics. The additional brane behaves effectively as a tachyon. We calculate numerically observation parameters of inflation: the scalar spectral index ($n_s$) and the tensor-to-scalar ratio ($r$) for the exponential potential of tachyon field.Comment: 9 pages, 1 figure, will be published in the Special Issue of Facta Universitatis, Series: Physics, Chemistry and Technology devoted to the SEENET-MTP Balkan Workshop BSW2018 (3-14 June 2018

Numerical Calculation of Hubble Hierarchy Parameters and Observational Parameters of Inflation

We present results obtained by a software we developed for computing observational cosmological inflation parameters: the scalar spectral index ($n_s$) and the tensor-to-scalar ratio ($r$) for a standard single field and tachyon inflation, as well as for a tachyon inflation in the second Randall-Sundrum model with an additional radion field. The calculated numerical values of observational parameters are compared with the latest results of observations obtained by the Planck Collaboration. The program is written in C/C++. The \textit{GNU Scientific Library} is used for some of the numerical computations and R language is used for data analysis and plots.Comment: 8 pages, 5 figures, based on talk presented at The 10th Jubilee Conference of the Balkan Physical Union (BPU10), 26-30 August 2018 (Sofia, Bulgaria

Incommensurate superfluidity of bosons in a double-well optical lattice

We study bosons in the first excited Bloch band of a double-well optical lattice, recently realized at NIST. By calculating the relevant parameters from a realistic nonseparable lattice potential, we find that in the most favorable cases the boson lifetime in the first excited band can be several orders of magnitude longer than the typical nearest-neighbor tunnelling timescales, in contrast to that of a simple single-well lattice. In addition, for sufficiently small lattice depths the excited band has minima at nonzero momenta incommensurate with the lattice period, which opens a possibility to realize an exotic superfluid state that spontaneously breaks the time-reversal, rotational, and translational symmetries. We discuss possible experimental signatures of this novel state.Comment: 4 pages, 5 figures

Quantum simulation of small-polaron formation with trapped ions

We propose a quantum simulation of small-polaron physics using a one-dimensional system of trapped ions acted upon by off-resonant standing waves. This system, envisioned as an array of microtraps, in the single-excitation case allows the realization of the anti-adiabatic regime of the Holstein model. We show that the strong excitation-phonon coupling regime, characterized by the formation of small polarons, can be reached using realistic values of the relevant system parameters. Finally, we propose measurements of the quasiparticle residue and the average number of phonons in the ground state, experimental probes validating the polaronic character of the phonon-dressed excitation.Comment: accepted for publication in Phys. Rev. Let

Polymers Based on Renewable Raw Materials – Part II

A short review of biopolymers based on starch (starch derivatives, thermoplastic starch), lignin and hemicelluloses, chitin (chitosan) and products obtained by degradation of starch and other polysaccharides and sugars (poly(lactic acid), poly(hydroxyalkanoates)), as well as some of their basic properties and application area, are given in this part. The problem of environmental and economic feasibility of biopolymers based on renewable raw materials and their competitiveness with polymers based on fossil raw materials is discussed. Also pointed out are the problems that appear due to the increasing use of agricultural land for the production of raw materials for the chemical industry and energy, instead for the production of food for humans and animals. The optimistic assessments of experts considering the development perspectives of biopolymers based on renewable raw materials in the next ten years have also been pointed out.At the end of the paper, the success of a team of researchers gathered around the experts from the company Bayer is indicated. They were the first in the world to develop a catalyst by which they managed to effectively activate CO - and incorporate it into polyols, used for the synthesis of polyurethanes in semi-industrial scale. By applying this process, for the first time a pollutant will be used as a basic raw material for the synthesis of organic compounds, which will have significant consequences on the development of the chemical industry, and therefore the production of polymers

Rat duodenal motility in vitro: Prokinetic effects of DL-homocysteine thiolactone and modulation of nitric oxide mediated inhibition

Homocysteine is a significant but modifiable risk factor for vascular diseases. As gastrointestinal smooth musculature is similar to blood vessel muscles, we investigated how elevated homocysteine levels affect nitric oxide-mediated neurotransmission in the gut. There is accumulated evidence that a dysfunction of NO neurons in the myenteric plexus may cause various diseases in the gastrointestinal tract such as achalasia, diabetic gastroparesis and infantile hypertrophic pyloric stenosis. In the present study, we aimed to assess the effects of homocysteine on NO-mediated responses in vitro, and to examine the effects of DL-homocysteine thiolactone on the spontaneous motility of rat duodenum and nitrergic neurotransmission. DL-homocysteine thiolactone concentration of 10 μmol/L leads to the immediate increase in tone, amplitude and frequency of spontaneous movements in isolated rat duodenum. L-NAME (30 μmol/L) leads to an increase in basal tone, amplitude and frequency of spontaneous contractions. The relaxations induced by EFS were significantly reduced in duodenal segments incubated in DL-homocysteine thiolactone compared with the control group. EFS-induced relaxations were inhibited by L-NAME in both experimental and control groups. These results suggest that a high level of homocysteine causes an important impairment of non-adrenergic non-cholinergic innervation of the rat duodenum. [Projekat Ministarstva nauke Republike Srbije, br. 175043

Study on a standard for grounding systems realization

Grounding systems of objects inside power facilities are very often realized as structures consisting of protective electrodes’ system placed in the object foundation, and neutral electrodes’ system placed at a specified distance from the object. Official standards and publications recommend a minimal value for the distance between the protective and the neutral part of grounding structures, so that the influence of one on another can be neglected. We analyze several practical implementations of grounding structures and demonstrate that the minimal distance is actually much smaller than that recommended by the standards