An electron paramagnetic resonance study of the tetragonally distorted [Formula: see text] ion in [Formula: see text] and [Formula: see text

Chromium-doped [Formula: see text] and [Formula: see text] have been studied by both EPR and ENDOR spectroscopy. [Formula: see text] ions enter the fluorite structure in distorted substitution cation sites. In both matrices the distortion observed is tetragonal. X- and Q-band EPR measurements at temperatures between 4 and 300 K allowed us to determine the ion symmetry and the following spin-Hamiltonian parameters: [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] for [Formula: see text]; and [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] for [Formula: see text]. For [Formula: see text], the weak superhyperfine interaction of [Formula: see text] with the surrounding [Formula: see text] ions has been studied by both EPR and ENDOR techniques for [Formula: see text]. No ENDOR signals were detected for [Formula: see text]. The results are tentatively explained in terms of a Jahn - Teller effect corresponding to [Formula: see text] coupling strongly stabilized by lattice stresses, although other possible origins for the distortion cannot be completely ruled out.     

Anomalies in the ion transport of phosphoric acid in water and heavy-water environments

This paper presents the experimentally determined precise transport data - (tracer) diffusion coefficients in both water and heavy-water environments, together with molar conductivity and viscosity of (ortho)phosphoric acid in water over an extended concentration range at [Formula: see text]. The concentration (c) dependence of the diffusion coefficients (D), viscosity [Formula: see text] and molar conductivity [Formula: see text] have been analysed. An anomalous depression in the D - [Formula: see text] curve for both [Formula: see text] - [Formula: see text] and [Formula: see text] - [Formula: see text] systems in the neighbourhood of 0.8 M is observed, which is complementary to the sudden sharp rise observed in the [Formula: see text] curve in the neighbourhood of 0.8 M. Although the occurrence of such an anomaly could be inferred from the earlier conductance, e.m.f. and diffusion data, it was never conclusively inferred earlier. This new set of diffusion and viscosity data clearly delineates anomalies in the ion transport of phosphoric acid.     

Regional and temporal variability of the isotope composition (O, S) of atmospheric sulphate in the region of Freiberg, Germany, and consequences for dissolved sulphate in groundwater and river water

The isotope composition of dissolved sulphate and strontium in atmospheric deposition, groundwater, mine water and river water in the region of Freiberg was investigated to better understand the fate of these components in the regional and global water cycle. Most of the isotope variations of dissolved sulphates in atmospheric deposition from three locations sampled bi- or tri-monthly can be explained by fractionation processes leading to lower [Formula: see text] (of about 2-3‰) and higher [Formula: see text] (of about 8-10‰) values in summer compared with the winter period. These samples showed a negative correlation between [Formula: see text] and [Formula: see text] values and a weak positive correlation between [Formula: see text] and [Formula: see text] values. They reflect the sulphate formed by aqueous oxidation from long-range transport in clouds. However, these isotope variations were superimposed by changes of the dominating atmospheric sulphate source. At two of the sampling points, large variations of mean annual [Formula: see text] values from atmospheric bulk deposition were recorded. From 2008 to 2009, the mean annual [Formula: see text] value increased by about 5‰; and decreased by about 4‰ from 2009 to 2010. A change in the dominating sulphate source or oxidation pathways of SO(2) in the atmosphere is proposed to cause these shifts. No changes were found in corresponding [Formula: see text] values. Groundwater, river water and some mine waters (where groundwater was the dominating sulphate source) also showed temporal shifts in their [Formula: see text] values corresponding to those of bulk atmospheric deposition, albeit to a lower degree. The mean transit time of atmospheric sulphur through the soil into the groundwater and river water was less than a year and therefore much shorter than previously suggested. Mining activities of about 800 years in the Freiberg region may have led to large subsurface areas with an enhanced groundwater flow along fractures and mined-refilled ore lodes which may shorten transit times of sulphate from precipitation through groundwater into river water.     

Measurements of the strong-interaction widths of the kaonic (3)He and (4)He 2p levels

The kaonic (3)He and (4)He X-rays emitted in the [Formula: see text] transitions were measured in the SIDDHARTA experiment. The widths of the kaonic (3)He and (4)He 2p states were determined to be [Formula: see text], and [Formula: see text], respectively. Both results are consistent with the theoretical predictions. The width of kaonic (4)He is much smaller than the value of [Formula: see text] determined by the experiments performed in the 70's and 80's, while the width of kaonic (3)He was determined for the first time.     

Ferroelastic domain freezing and low-frequency elastic behaviour of [Formula: see text] (ALHS)

In this work elastic measurements on [Formula: see text] (ALHS) which were carried out in the low-frequency range between 1 and 50 Hz are presented. The temperature dependence of the inverse elastic compliance [Formula: see text] has been determined between 90 K and 420 K. Distinct anomalies have been found in the temperature dependence of [Formula: see text], which are connected to the motion of domain walls in the ferroelastic phase below [Formula: see text]. Around [Formula: see text] a (partial) ferroelastic `domain freezing' phenomenon has been observed. To the knowledge of the authors this is the first time that pure ferroelastic domain freezing has been reported. However, below [Formula: see text] the domain walls seem to retain a certain vibrational degree of freedom which could be responsible for an additional anomaly of the loss modulus which was observed. The elastic behaviour of a crystal of ALHS is dependent on the `history' of the given sample. During temperature cycling [Formula: see text] shows differences between the first run of heating and cooling and later runs. Finally, some basic insights concerning the domain wall motion were obtained; it was found that the domain wall mobility decreases by three orders of magnitude in the temperature region 170 - 230 K.     

Thermodynamic behaviour of two-dimensional vesicles revisited

We study pressurised self-avoiding ring polymers in two dimensions using Monte Carlo simulations, scaling arguments and Flory-type theories, through models which generalise the model of Leibler, Singh and Fisher (Phys. Rev. Lett. 59, 1989 (1987)). We demonstrate the existence of a thermodynamic phase transition at a non-zero scaled pressure [Formula: see text] , where [Formula: see text] = Np/4[Formula: see text] , with the number of monomers N [Formula: see text] ∞ and the pressure p [Formula: see text] 0 , keeping [Formula: see text] constant, in a class of such models. This transition is driven by bond energetics and can be either continuous or discontinuous. It can be interpreted as a shape transition in which the ring polymer takes the shape, above the critical pressure, of a regular N -gon whose sides scale smoothly with pressure, while staying unfaceted below this critical pressure. Away from these limits, we argue that the transition is replaced by a sharp crossover. The area, however, scales with N(2) for all positive p in all such models, consistent with earlier scaling theories.     

The effect of Co doping on antiferromagnetic correlations in the Kondo semi-metal CeNiSn

Single-crystal neutron scattering experiments have been performed to study magnetic excitations in [Formula: see text], in which the pseudo-gap of CeNiSn is suppressed by the doping. In CeNiSn there are two inelastic excitation peaks at [Formula: see text] and 4 meV, which correspond to dynamic antiferromagnetic correlations. In [Formula: see text] the 2 meV peak is smeared out, whereas the 4 meV peak becomes very weak and broad, but preserves the same quasi-one-dimensional character as that for CeNiSn. These results suggest the strong relation between the antiferromagnetic correlations and the pseudo-gap formation.     

Physical properties of [Formula: see text] polymer electrolytes: nuclear magnetic resonance investigation and comparison with [Formula: see text

The physical properties of the ionic conductor [Formula: see text], obtained by dissolution of lithium trifluoromethanesulphonylimide in poly(propylene oxide), have been investigated for several values of n. The glass transition temperature [Formula: see text] has been established from both DSC and NMR techniques. The diffusion coefficients of [Formula: see text]-containing species have been determined by the pulsed magnetic field gradient technique. The behaviour of the proton relaxation time [Formula: see text] versus temperature and concentration has been correlated to the glass temperature. The behaviour of the proton transverse relaxation function, obtained by the spin-echo technique, has been interpreted using a simple model in which two regimes and consequently two transverse relaxation times coexist and are assigned to the `entangled' and `non-entangled' parts of the high-molecular-weight polymer chains investigated.     

The electronic structure of liquid silver chalcogenides: a tight-binding approach

We present a computational study of the electronic structure of the stoichiometric liquid zero-gap semiconductors [Formula: see text], [Formula: see text] and [Formula: see text]. The geometry of the fluids is described by the primitive model of charged hard spheres; the electronic structure is modelled using a tight-binding Hamiltonian. The density of states is computed considering the Madelung potential fluctuations and the topological disorder characteristic of an ionic fluid. Only the introduction of nonzero tight-binding hopping matrix elements - equivalent to the formation of chemical bonds - induces a pseudogap between the chalcogenide conduction band and the silver valence band. The Fermi level can be located in a region of a small density of states; eigenstates at [Formula: see text] are likely to exhibit disorder-induced localization.     

Final-state effects in neutron Compton scattering measurements on zirconium deuteride and beryllium

We report inelastic neutron scattering measurements of the neutron Compton profile, J(y), for Be and for D in polycrystalline [Formula: see text] over a range of momentum transfers, q between 27 and [Formula: see text]. The measurements were performed using the inverse geometry spectrometer eVS which is situated at the UK pulsed spallation neutron source ISIS. We have investigated deviations from impulse approximation (IA) scattering which are generically referred to as final-state effects (FSEs) using a method described by Sears. This method allows both the magnitude and the q dependence of the FSE to be studied. Analysis of the measured data was compared with analysis of numerical simulations based on the harmonic approximation and good agreement was found for both [Formula: see text] and Be. Finally we have shown how [Formula: see text], where V is the interatomic potential, can be extracted from the antisymmetric component of J(y).     

Magnetic properties of charged spin-1 Bose gases with ferromagnetic coupling

The magnetic properties of a charged spin-1 Bose gas with ferromagnetic interactions are investigated within mean-field theory. It is shown that a competition between paramagnetism, diamagnetism and ferromagnetism exists in this system. It is shown that diamagnetism, being concerned with spontaneous magnetization, cannot exceed ferromagnetism in a very weak magnetic field. The critical value of reduced ferromagnetic coupling of the paramagnetic phase to ferromagnetic phase transition [Formula: see text] increases with increasing temperature. The Landé-factor g is introduced to describe the strength of the paramagnetic effect which comes from the spin degree of freedom. The magnetization density [Formula: see text] increases monotonically with g for fixed reduced ferromagnetic coupling [Formula: see text] as [Formula: see text]. In a weak magnetic field, ferromagnetism makes an immense contribution to the magnetization density. On the other hand, at a high magnetic field, the diamagnetism tends to saturate. Evidence for condensation can be seen in the magnetization density at a weak magnetic field.     

Pressure dependence of the melting temperature of rare-gas solids

According to Lindemann's law and the Debye model and with the assumption that the volume derivative [Formula: see text] of the Grüineisen parameter [Formula: see text] is a constant depending on the material, we present a new expression for the analysis of the experimental data for the melting temperature of solids under a high pressure. The test on rare-gas solids (Ne, Ar, Kr and Xe) shows that the calculated results are in good agreement with the corresponding experimental data.     

3D-QSAR and molecular docking analysis of biphenyl amide derivatives as p38α mitogen-activated protein kinase inhibitors

The p38α mitogen-activated protein (MAP) kinase plays a vital role in treating many inflammatory diseases such as rheumatoid arthritis, inflammatory bowel disease, Crohn's disease and psoriasis. Herein, we have performed 3D-QSAR and molecular docking analysis on a novel series of biphenyl amides to design potent p38 MAP kinase inhibitors. This study correlates the p38 MAP kinase inhibitory activities of 80 biphenyl amide derivatives to several stereochemical parameters representing steric, electrostatic, hydrophobic, hydrogen bond donor and acceptor fields. The resulting model from CoMFA and CoMSIA exhibited excellent [Formula: see text] values of 0.979 and 0.942, and [Formula: see text] values of 0.766 and 0.748, respectively. CoMFA predicted [Formula: see text] of 0.987 and CoMSIA predicted [Formula: see text] of 0.761 showed that the predicted values were in good agreement with experimental values. Glide (5.5) program gave the path for binding mode exploration between the inhibitors and p38α MAP kinase. We have accordingly designed novel p38α MAP kinase inhibitors by utilizing LeapFrog and predicted with excellent activity in the developed models.     

Search for heavy long-lived particles that decay to photons at CDF II

We present the first search for heavy, long-lived particles that decay to photons at a hadron collider. We use a sample of gamma + jet + missing transverse energy events in pp[over] collisions at square root[s] = 1.96 TeV taken with the CDF II detector. Candidate events are selected based on the arrival time of the photon at the detector. Using an integrated luminosity of 570 pb(-1) of collision data, we observe 2 events, consistent with the background estimate of 1.3+/-0.7 events. While our search strategy does not rely on model-specific dynamics, we set cross section limits in a supersymmetric model with [Formula: see text] and place the world-best 95% C.L. lower limit on the [Formula: see text] mass of 101 GeV/c(2) at [Formula: see text].     

Theoretical and experimental study of the nanoparticle-driven blue phase stabilisation

We have studied theoretically and experimentally the effects of various types of nanoparticles (NPs) on the temperature stability range [Formula: see text] T (BP) of liquid-crystalline (LC) blue phases. Using a mesoscopic Landau-de Gennes type approach we obtain that the defect core replacement (DCR) mechanism yields in the diluted regime [Formula: see text] T (BP)(x) [Formula: see text] 1/(1 - xb) , where x stands for the concentration of NPs and b is a constant. Our calculations suggest that the DCR mechanism is efficient if a local NP environment resembles the core structure of disclinations, which represent the characteristic property of BP structures. These predictions are in line with high-resolution ac calorimetry and optical polarising microscopy experiments using the CE8 LC and CdSe or aerosil NPs. In mixtures with CdSe NPs of 3.5nm diameter and hydrophobic coating the BPIII stability range has been extended up to 20K. On the contrary, the effect of aerosil silica nanoparticles of 7.0nm diameter and hydrophilic coating is very weak.     

Bulk modulus calculations based on perturbation self-consistency

We propose a method for bulk modulus calculations of solids based on perturbation self-consistency within the local density functional. The essential assumption is that a finite scaling is applied to the one-electron wavefunction when the solid adjusts to a new distorted structure under pressure. Thus the one-electron potential of a deformed structure near equilibrium can be obtained by performing a scaling transformation to charge density directly. The method is formulated within the linear muffin-tin orbital method in the atomic sphere approximation and applied to the calculation of bulk moduli of [Formula: see text], FCC Al, BCC Li, [Formula: see text] and an ordered FCC [Formula: see text] superlattice. The bulk modulus calculated from a single self-consistency is in reasonably good agreement with that of a full self-consistent calculation. Our results for Al - Li systems confirm that the addition of lithium to FCC Al causes the bulk modulus to decrease.     

Evolution of the commensurate and incommensurate magnetic phases of the S = 3/2 kagome staircase Co?V?O? in an applied field

Single crystal neutron diffraction studies have been performed on the S = 3/2 kagome staircase compound Co(3)V(2)O(8) with a magnetic field applied along the magnetization easy-axis ([Formula: see text]). Previous zero-field measurements (Chen Y et al 2006 Phys. Rev. B 74 014430) reported a rich variety of magnetic phases, with a ferromagnetic ground state as well as incommensurate, transversely polarized spin density wave (SDW) phases (with a propagation vector of [Formula: see text]) interspersed with multiple commensurate lock-in transitions. The magnetic phase diagram with [Formula: see text] adds further complexity. For small applied fields, μ(0)H ≈ 0.05 T, the commensurate lock-in phases are destabilized in favor of the incommensurate SDW ones, while slightly larger applied fields restore the commensurate lock-in phase with δ = 1/2 and yield a new commensurate phase with δ = 2/5. For measurements in an applied field, higher-order scattering is observed that corresponds to the second harmonic.     

Application of fast amplitude-modulated pulse trains for signal enhancement in static and magic-angle-spinning 47,49Ti-NMR spectra

It is demonstrated that the use of fast amplitude-modulated RF pulse trains with constant (FAM-I) and incremented pulse durations (SW-FAM) leads to considerable sensitivity enhancement for the central-transition signal (via spin population transfer from the satellite transitions) for solid-state NMR spectra of titanium, 47Ti (I = [Formula: see text] and 49Ti (I = [Formula: see text]. For the magic-angle spinning spectra of TiO2 and BaTiO3, the intensity of the 49Ti central-transition line was more than doubled compared to simple Hahn-echo acquisition, while for the static case, enhancement factors of 1.6 (TiO2) and 1.8 (BaTiO3) were obtained. No lineshape distortions are observed in either MAS or static spectra of both compounds. Employment of the FAM and SW-FAM sequences should be useful in the routine acquisition of 47,49Ti spectra, as the NMR signal can be detected much faster.     

The phase diagram and hidden order for generalized spin ladders

We investigate the phase diagram of antiferromagnetic spin ladders with additional exchange interactions on diagonal bonds by variational and numerical methods. These generalized spin ladders interpolate smoothly between the [Formula: see text] chain with competing nn and nnn interactions, the [Formula: see text] chain with alternating exchange and the antiferromagnetic (AF) S = 1 chain. The Majumdar - Ghosh ground states are formulated as matrix product states and are shown to exhibit the same type of hidden order as the AF S = 1 chain. Generalized matrix product states are used for a variational calculation of the ground state energy and the spin and string correlation functions. Numerical (Lanczos) calculations of the energies of the ground state and of the low-lying excited states are performed, and compare reasonably with the variational approach. Our results support the hypothesis that the dimer and Majumdar - Ghosh points are in the same phase as the AF S = 1 chain.     

Temperature-dependent Raman scattering study of the defect pyrochlores RbNbWO6 and CsTaWO6

Lattice dynamics calculations and temperature-dependent Raman scattering experiments were performed on RbNbWO(6) and CsTaWO(6) pyrochlore oxides. The observed bands were assigned to the respective motions of atoms in the unit cell. The spectra showed the presence of additional Raman bands not allowed for by the [Formula: see text] cubic structure. We have shown that these bands appear due to both substitutional disorder in the 16c sites and displacive disorder of the A ions. Raman studies also revealed the presence of an additional 80?cm(-1) band at room temperature for RbNbWO(6), not observed for CsTaWO(6). The presence of this band has been attributed to off-center displacement of the Nb and W ions due to structural phase transition into a tetragonal ferroelectric phase. The temperature evolution of the 80?cm(-1) band intensity revealed that it disappeared at a much higher temperature (about 650?K) than the reported phase transition temperature (about 360?K). This behavior is reminiscent of chemically disordered perovskite ferroelectrics, including relaxor ferroelectrics, and was attributed to the presence of small polar regions with local tetragonal distortion embedded in the paraelectric matrix of the [Formula: see text] structure.