Dissipative Dynamics of a Heavy Impurity in a Bose Gas in the Strong Coupling Regime.

We study the motion of a heavy impurity in a one-dimensional Bose gas. The impurity experiences the friction force due to scattering off thermally excited quasiparticles. We present detailed analysis of an arbitrarily strong impurity-boson coupling in a wide range of temperatures within a microscopic theory. Focusing mostly on weakly interacting bosons, we derive an analytical result for the friction force and uncover new regimes of the impurity dynamics. Particularly interesting is the low-temperature T^{2} dependence of the friction force obtained for a strongly coupled impurity, which should be contrasted with the expected T^{4} scaling. This new regime applies to systems of bosons with an arbitrary repulsion strength. We finally study the evolution of the impurity with a given initial momentum. We evaluate analytically its nonstationary momentum distribution function. The impurity relaxation towards the equilibrium is a realization of the Ornstein-Uhlenbeck process in momentum space.

Workplace stress of occupational safety specialists in Croatia and Serbia.

BACKGROUND: Numerous studies have shown that work often causes stress in employees and even in occupational safety experts. Occupational stress can lead to serious health consequences for employees. As the job of occupational safety experts is very responsible, they are more exposed to workplace stress and more vulnerable to its consequences. This study resulted with expertise on the work related stress of safety experts in Croatia and Serbia. OBJECTIVE: This study examined workplace stress of occupational safety experts in Croatia and Serbia. METHODS: Surveys were used to collect original data and statistical methods were used for data processing and analysis. RESULTS: There was a correlation between the level of stress on safety expert's jobs and stress levels related to the status of safety experts as dependent variables and the organization profile related with safety experts' employment as independent variables. Stress of safety experts related to activities and the status of safety experts were of medium level. CONCLUSION: There is a need for preventive protection from stress in this profession. Continuous education of safety experts plays a key role in stress prevention, not only for the safety experts but it also plays a key role in stress management throughout the organization.

Educational needs of employees in work-related stress management.

BACKGROUND: Dynamic and intense socio-economic, scientific and technological development has both positive and negative effects on the business world. Due to increasing problems of work-related stress, the issue of stress management has arisen. Primary stress management and proactive interventions in work-related stress prevention are specifically activated. In this regard, the issue of educational needs of employees for the prevention of work-related stress is of particular importance. OBJECTIVE: The basic concern that has drawn our attention is whether employees generally show the desire and need to adopt the knowledge in the field of work-related stress prevention and relief and whether they are supported by the management of their business organization. METHODS: We used several methods to conduct this research: survey, scaling and comparative method. The comparative method was used for the analysis of legal documents in the field of occupational safety and health in six Balkan countries with the aim of determining the legal obligations of employers in managing workplace stress. The research population consisted of employees in small and medium-sized enterprises in the city of Kraljevo (the Republic of Serbia), while the research sample was determined by a random sampling method and included 450 respondents. RESULTS: Despite the recommendations of international organizations, the employers in most countries are not legally bound to deal with work-related stress management. The results have shown that there is a correlation between work-related risks/stressors and educational needs of employees for learning or acquiring knowledge in the field of work-related stress prevention. Employees express the desire to become acquainted with the possibilities of overcoming work-related stress. CONCLUSION: Employees' education and training have an invaluable role and considerable importance in primary, work-related stress management. The knowledge about the causes and mechanisms of work-related stress development is an important step towards its prevention. The research has shown that employees express the need for acquiring knowledge to prevent stress at work. In this regard, it is necessary to provide legally binding support of the manager in order to undertake the activities of work-related stress management. Interventions should target work-related stress at its source with a focus on prevention rather than an individual approach whose long-term benefits are uncertain.

Exact Results for the Boundary Energy of One-Dimensional Bosons.

We study bosons in a one-dimensional hard-wall box potential. In the case of contact interaction, the system is exactly solvable by the Bethe ansatz, as first shown by Gaudin in 1971. Although contained in the exact solution, the boundary energy in the thermodynamic limit for this problem is only approximately calculated by Gaudin, who found the leading order result at weak repulsion. Here we derive an exact integral equation that enables one to calculate the boundary energy in the thermodynamic limit at an arbitrary interaction. We then solve such an equation and find the asymptotic results for the boundary energy at weak and strong interactions. The analytical results obtained from the Bethe ansatz are in agreement with the ones found by other complementary methods, including quantum Monte Carlo simulations. We study the universality of the boundary energy in the regime of a small gas parameter by making a comparison with the exact solution for the hard rod gas.

Spectrum of Elementary Excitations in Galilean-Invariant Integrable Models.

The spectrum of elementary excitations in one-dimensional quantum liquids is generically linear at low momenta. It is characterized by the sound velocity that can be related to the ground-state energy. Here we study the spectrum at higher momenta in Galilean-invariant integrable models. Somewhat surprisingly, we show that the spectrum at arbitrary momentum is fully determined by the properties of the ground state. We find general exact relations for the coefficients of several terms in the expansion of the excitation energy at low momenta and arbitrary interaction and express them in terms of the Luttinger liquid parameter. We apply the obtained formulas to the Lieb-Liniger model and obtain several new results.

Dynamics of a Mobile Impurity in a One-Dimensional Bose Liquid.

We develop a microscopic theory of a quantum impurity propagating in a one-dimensional Bose liquid. As a result of scattering off thermally excited quasiparticles, the impurity experiences the friction. We find that, at low temperatures, the resulting force scales either as the fourth or the eighth power of temperature, depending on the system parameters. For temperatures higher than the chemical potential of the Bose liquid, the friction force is a linear function of temperature. Our approach enables us to find the friction force in the crossover region between the two limiting cases. In the integrable case, corresponding to the Yang-Gaudin model, the impurity becomes transparent for quasiparticles and thus the friction force is absent. Our results could be further generalized to study other kinetic phenomena.

Levels of interleukin-6 in tears before and after excimer laser treatment.

BACKGROUND/AIM: Immune response and consequent inflammatory process which originate on ocular surface after a trauma are mediated by cytokines. Photoablation of corneal stroma performed by excimer laser causes surgically induced trauma. Interleukin-6 (IL-6) is mostly known as a proinflammatory cytokine. However, it also has regenerative and anti-inflammatory effects. It is supposed that this cytokine is likely to play a significant role in the process of corneal wound healing response after photoablation of stroma carried out by laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) methods. The aim of this study was to determine and compare the levels of IL-6 in tears before and after treatment with LASIK and PRK methods. METHODS: The study included 68 shortsighted eyes up to -3.0 diopter sphere, i.e. 198 samples of tears (per three samples taken from each of the eyes), divided into two groups according to the kind of excimer laser intervention performed: the group 1--eyes treated by LASIK method (n=31), and the group 2--eyes treated by the PRK method (n=37). The samples of tears were taken from each eye at the following time points: before excimer laser treatment (0 h, the control group), 1 h after the treatment (1 h) and 24 h after the treatment (24 h). The patients did not use anti-inflammatory therapy 24 h after the intervention. Tear samples were collected using microsurgical sponge. Level of IL-6 in tear fluid was determined by the flow cytometry method, applying a commercial test kit which allowed cytokine detection from a small sample volume. Results. The values of IL-6 were detectable in 16% of samples before LASIK treatment and in 30% of samples before PRK treatment. One h after the treatment IL-6 was detectable in 29% of samples for the LASIK group and 43% of samples for the PRK group, and 24 h after the treatment it was detectable in 19% of samples for the LASIK group and in 57% of samples for the PRK group. When we analyzed the dynamics of IL76 production in particular groups, we noticed that both in the LASIK and PRK group the number of samples with increased values of IL-6 after 1 h, and after 24 h, was con- siderably larger than the number of samples with decreased values of IL-6 after the intervention. Analyzing the dynamics of IL-6 concentration changes in the 1 h samples vs. 24 h samples there was a statistically significant increase in the number of samples with IL-6 concentration decline in the LASIK group, while at the same time no considerable changes occurred in the PRK group. Comparing average IL-6 values between the two treatment groups in all tear samples at 0 h, 1 h and 24 h after intervention a significantly higher level in the PRK group 24 h after procedure (p = 0.0031) was detected. CONCLUSION: IL-6 level in tears increases 1 h and 24 h after LASIK and PRK treatments. This increment is significantly larger 24 h after the treatment with the PRK method than with the LASIK method. Changes of IL-6 production levels in tears after excimer laser treatment indicate that this cytokine takes part in the corneal recovery process after stromal photoablation.

Pairing fluctuation ac conductivity of disordered thin films.

We study temperature T and frequency ω dependence of the in-plane fluctuation conductivity of a disordered superconducting film above the critical temperature. Our calculation is based on the nonlinear sigma model within the Keldysh technique. The fluctuation contributions of different physical origin are found and analyzed in a wide frequency range. In the low-frequency range, ω ≪ T, we reproduce the known leading terms and find additional subleading ones in the Aslamazov-Larkin and the Maki-Thompson contributions to the ac conductivity. We also calculate the density of states ac correction. In the dc case these contributions logarithmically depend on the Ginzburg-Landau rate and are considerably smaller that the leading ones. However, in the ac case an external finite-frequency electromagnetic field strongly suppresses the known Aslamazov-Larkin and Maki-Thompson ac contributions, while the corresponding new terms and the density of states contribution are weakly suppressed and therefore become relevant at finite frequencies.

Phase transition of interacting disordered bosons in one dimension.

Interacting bosons generically form a superfluid state. In the presence of disorder it can get converted into a compressible Bose glass state. Here we study such a transition in one dimension at moderate interaction using bosonization and renormalization group techniques. We derive the two-loop scaling equations and discuss the phase diagram. We find that the correlation functions at the transition are characterized by universal exponents in a finite region around the fixed point.

Distribution of velocities and acceleration for a particle in Brownian correlated disorder: inertial case.

We study the motion of an elastic object driven in a disordered environment in presence of both dissipation and inertia. We consider random forces with the statistics of random walks and reduce the problem to a single degree of freedom. It is the extension of the mean-field Alessandro-Beatrice- Bertotti-Montorsi (ABBM) model in presence of an inertial mass m. While the ABBM model can be solved exactly, its extension to inertia exhibits complicated history dependence due to oscillations and backward motion. The characteristic scales for avalanche motion are studied from numerics and qualitative arguments. To make analytical progress, we consider two variants which coincide with the original model whenever the particle moves only forward. Using a combination of analytical and numerical methods together with simulations, we characterize the distributions of instantaneous acceleration and velocity, and compare them in these three models. We show that for large driving velocity, all three models share the same large-deviation function for positive velocities, which is obtained analytically for small and large m, as well as for m=6/25. The effect of small additional thermal and quantum fluctuations can be treated within an approximate method.

Order and creep in flux lattices and charge density wave pinned by planar defects.

The influence of randomly distributed point impurities and planar defects on the order and transport in type-II superconductors and related systems is considered theoretical. For random planar defects of identical orientation, the flux line lattice exhibits a new glassy phase with diverging shear and tilt modulus, a transverse Meissner effect, large sample to sample fluctuations of the susceptibility, and an exponential decay of translational long range order. The flux creep resistivity for currents J parallel to the defects is p(J) to approximately exp-(J0/J)mu with mu = 3/2. Strong disorder enforces an array of dislocations to relax shear

Absence of the Mott glass phase in 1D disordered fermionic systems.

We study the competition between the Mott and the Anderson insulating state in a one-dimensional disordered fermionic system. The notorious difficulties associated with strong coupling phases are avoided by using a new description in terms of the kink energies (or instanton surface tension) of the electronic displacement pattern. The approach has some similarities to the description of the flat phase of surfaces undergoing a roughening transition. Tracing back both a finite compressibility and a nonzero ac conductivity to vanishing kink energy we exclude the existence of an intermediate Mott-glass phase in systems with short range interaction only. In systems with long range interaction the Anderson insulating phase exhibits the features of a Mott glass however. The phase diagram is constructed from combining the information from the renormalization group flow, the kink energy, and simple rescaling analysis.

Acute ethanol treatment increases level of progesterone in ovariectomized rats.

To determine whether an increased level of progesterone in adult female rats after acute ethanol treatment, described previously in our study, is the result of activation of adrenal glands, we analyzed adrenal cortex morphologically and measured serum levels of corticosterone and progesterone in ovariectomized rats. In addition, a possible involvement of the opioid system in an observed phenomenon was tested. Adult female Wistar rats were ovariectomized, and 3 weeks after surgery they were treated intraperitoneally with (a) ethanol (4 g/kg), (b) naltrexone (5 mg/kg), followed by ethanol (4 g/kg) 45 min later, and (c) naltrexone (5 mg/kg), followed by saline 45 min later. Untreated and saline-injected rats were used as controls. The animals were killed 0.5 h after ethanol administration. Morphometric analysis was carried out on paraffin sections of adrenal glands, stained with hematoxylin-eosin, and the following parameters were determined: absolute volume of the zona glomerulosa, the zona fasciculata, and the zona reticularis; numerical density, volume, and the mean diameter of adrenocortical cells and of their nuclei; and mean diameter and length of capillaries. The results showed that acute ethanol treatment significantly increased absolute volume of the zona fasciculata and length of its capillaries but did not alter other stereological parameters. Also, serum levels of corticosterone and progesterone were enhanced. Pretreatment with naltrexone had no effect on ethanol-induced changes. These findings are consistent with our previous hypothesis that an ethanol-induced increase of the progesterone level in adult female rats originates from the adrenal cortex.