Dynamical lattice instability versus spin liquid state in a frustrated spin chain system

The low-dimensional s=1/2 compound (NO)[Cu(NO3)3] has recently been suggested to follow the Nersesyan-Tsvelik model of coupled spin chains. Such a system shows unbound spinon excitations and a resonating valence bond ground state due spin frustration. Our Raman scattering study demonstrates phonon anomalies as well as the suppression of a broad magnetic scattering continuum for temperatures below a characteristic temperature, T<T*=100K. We interpret these effects as evidence for a dynamical interplay of spin and lattice degrees of freedom that might lead to a further transition into a dimerized or structurally distorted phase at lower temperatures.Comment: 5 pages, 6 figure

Epidemiology of Schistosoma mansoni infection in Ituri Province, north-eastern Democratic Republic of the Congo

BACKGROUND: Schistosomiasis, caused by Schistosoma mansoni, is of great significance to public health in sub-Saharan Africa. In the Democratic Republic of Congo (DRC), information on the burden of S. mansoni infection is scarce, which hinders the implementation of adequate control measures. We assessed the geographical distribution of S. mansoni infection across Ituri province in north-eastern DRC and determined the prevailing risk factors. METHODS/PRINCIPAL FINDINGS: Two province-wide, community-based studies were conducted. In 2016, a geographical distribution study was carried out in 46 randomly selected villages across Ituri. In 2017, an in-depth study was conducted in 12 purposively-selected villages, across the province. Households were randomly selected, and members were enrolled. In 2016, one stool sample was collected per participant, while in 2017, several samples were collected per participant. S. mansoni eggs were detected using the Kato-Katz technique. In 2017, a point-of-care circulating cathodic S. mansoni antigen (POC-CCA) urine test was the second used diagnostic approach. Household and individual questionnaires were used to collect data on demographic, socioeconomic, environmental, behavioural and knowledge risk factors. Of the 2,131 participants in 2016, 40.0% were positive of S. mansoni infection. Infection prevalence in the villages ranged from 0 to 90.2%. Of the 707 participants in 2017, 73.1% were tested positive for S. mansoni. Prevalence ranged from 52.8 to 95.0% across the health districts visited. Infection prevalence increased from north to south and from west to east. Exposure to the waters of Lake Albert and the villages' altitude above sea level were associated with the distribution. Infection prevalence and intensity peaked in the age groups between 10 and 29 years. Preschool children were highly infected (62.3%). Key risk factors were poor housing structure (odds ratio [OR] 2.1, 95% 95% confidence interval [CI] 1.02-4.35), close proximity to water bodies (OR 1.72, 95% CI 1.1-2.49), long-term residence in a community (OR 1.41, 95% CI 1.11-1.79), lack of latrine in the household (OR 2.00, 95% CI 1.11-3.60), and swimming (OR 2.53, 95% CI 1.20-5.32) and washing (OR 1.75, 95% CI 1.10-2.78) in local water bodies. CONCLUSIONS/SIGNIFICANCE: Our results show that S. mansoni is highly endemic and a major health concern in Ituri province, DRC. Infection prevalence and intensity, and the prevailing socioeconomic, environmental, and behavioural risk factors in Ituri reflect intense exposure and alarming transmission rates. A robust plan of action is urgently needed in the province

Correlation Between the Resistance to Stress Corrosion Cracking of Steel Tubes of Gas Pipelines with Their Layerwise Texture Inhomogeneity

In the present work, the influence of the tubes texture layering on their resistance to stress-corrosion cracking (SCC) is demonstrated by the example of several main gas pipelines (MGP) constructed of X70 steel tubes of different manufactures and operated under various exploitation conditions. X-ray studies of crystallographic texture and structural characteristics were implemented for external and internal layers of various tubes sections, which were cut out from MGP zones with fixed SCC defects and without them. Correlation between the depth of corrosion cracks and the thickness of the surface layer with sharply differing texture parameters is established. The system data analysis also shows that the presence of the texture component {110} &lt;001&gt; in the tubes surface layers can increase their resistance to the SCC. Keywords: crystallographic texture, structure, texture layering, electron backscattered diffraction, stress corrosion cracking, main gas pipeline, hot rolling

Point-contact spectroscopy of the antiferromagnetic superconductor HoNi2B2C in the normal and superconducting state

Point-contact (PC) spectroscopy measurements on antiferromagnetic (AF) (T_N=5.2K) HoNi2B2C single crystals in the normal and two different superconducting (SC) states (T_c=8.5K and $T_c^*=5.6K) are reported. The PC study of the electron-boson(phonon) interaction (EB(P)I) spectral function reveals pronounced phonon maxima at 16, 22 and 34meV. For the first time the high energy maxima at about 50meV and 100meV are resolved. Additionally, an admixture of a crystalline-electric-field (CEF) excitations with a maximum near 10meV and a `magnetic` peak near 3meV are observed. The contribution of the 10-meV peak in PC EPI constant \lambda_PC is evaluated as 20-30contribution of the high energy modes at 50 and 100meV amounts about 10each maxima, so the superconductivity might be affected by CEF excitations. The SC gap in HoNi2B2C exhibits a standard single-band BCS-like dependence, but vanishes at$T_c^*=5.6K<T_c, with 2\Delta/kT_c^*=3.9. The strong coupling Eliashberg analysis of the low-temperature SC phase with T_c^*=5.6K =T_N, coexisting with the commensurate AF structure, suggests a sizable value of the EPI constant \lambda_s=0.93. We also provide strong support for the recently proposed by us ''Fermi surface (FS) separation'' scenario for the coexistence of magnetism and superconductivity in magnetic borocarbides, namely, that the superconductivity in the commensurate AF phase survives at a special (nearly isotropic) FS sheet without an admixture of Ho 5d states. Above T_c^* the SC features in the PC characteristics are strongly suppressed pointing to a specific weakened SC state between T_c* and T_c.Comment: 11 pages, 8 figs, to be published in PRB, Vol.75, Iss.2

Strongly anisotropic magnetocaloric effect in a dipolar magnet LiGdF4_4

We report the detailed study of the magnetocaloric effect (MCE) in a dipolar-Heisenberg magnet LiGdF$_4$ using magnetization measurements performed on a single crystal sample. Entropy variation on isothermal demagnetization from the magnetic field up to 3 T is determined in the temperature range 2-10 K for two principal directions of the applied field (parallel and perpendicular to the tetragonal $c$-axis of the crystal). The MCE is found to be highly anisotropic, with the cooling efficiency being up to twice higher at $H\parallel c$. The results are nicely interpreted in the frame of a conventional molecular field approach taking into account considerable anisotropy of the paramagnetic Curie-Weiss temperature. These results are compared to earlier studies of MCE in powder samples of LiGdF$_4$ [T. Numazawa et al., AIP Conf. Proc. 850, 1579 (2006)] as well as with analogous data for other well known magnetocaloric materials. Our findings may open new possibilities to enhance the efficiency of magnetic refrigeration in the liquid helium-4 temperature range.Comment: 4 pages, 3 figure

Strong-coupling effects in the relaxation dynamics of ultracold neutral plasmas

We describe a hybrid molecular dynamics approach for the description of ultracold neutral plasmas, based on an adiabatic treatment of the electron gas and a full molecular dynamics simulation of the ions, which allows us to follow the long-time evolution of the plasma including the effect of the strongly coupled ion motion. The plasma shows a rather complex relaxation behavior, connected with temporal as well as spatial oscillations of the ion temperature. Furthermore, additional laser cooling of the ions during the plasma evolution drastically modifies the expansion dynamics, so that crystallization of the ion component can occur in this nonequilibrium system, leading to lattice-like structures or even long-range order resulting in concentric shells

NMR and X-ray diffraction studies of the influence of adsorbed molecule nature on phase transitions in a ZSM-5 silicalite

Pulsed NMR and X-ray diffraction analysis are employed to study the influence of adsorbed toluene, p-xylene, acetone, and di(ethylene glycol) (DEG) molecules on phase transitions in a ZSM-5 silicalite. In the region of phase transitions, times T1 and T2 of longitudinal and transverse magnetic relaxation of apolar molecules adsorbed in silicalite micropores increase and decrease in a jumpwise manner, respectively, with a rise in the total content of the liquid. Such changes in T1 and T 2 occur for hexane, decane, toluene, and p-xylene molecules. Qualitatively different concentration dependences of T1 and T 2 are observed for polar acetone and DEG molecules, because these liquids do not cause a rearrangement in the crystal lattice of silicalite; this is confirmed by the X-ray diffraction data. © 2004 MAIK "Nauka/Interperiodica"