31P NMR study of Na2CuP2O7: a S=1/2 two-dimensional Heisenberg antiferromagnetic system

The magnetic properties of Na2CuP2O7 were investigated by means of 31P nuclear magnetic resonance (NMR), magnetic susceptibility, and heat capacity measurements. We report the 31P NMR shift, the spin-lattice 1/T1, and spin-spin 1/T2 relaxation-rate data as a function of temperature T. The temperature dependence of the NMR shift K(T) is well described by the S=1/2 square lattice Heisenberg antiferromagnetic (HAF) model with an intraplanar exchange of J/k_B \simeq 18\pm2 K and a hyperfine coupling A = (3533\pm185) Oe/mu_B. The 31P NMR spectrum was found to broaden abruptly below T \sim 10 K signifying some kind of transition. However, no anomaly was noticed in the bulk susceptibility data down to 1.8 K. The heat capacity appears to have a weak maximum around 10 K. With decrease in temperatures, the spin-lattice relaxation rate 1/T1 decreases monotonically and appears to agree well with the high temperature series expansion expression for a S = 1/2 2D square lattice.Comment: 12 pages, 8 figures, submitted to J. Phys.: Cond. Ma

Synthesis, Structure and Properties of Tetragonal Sr2M3As2O2 (M3 = Mn3, Mn2Cu and MnZn2) Compounds Containing Alternating CuO2-Type and FeAs-Type Layers

Polycrystalline samples of Sr2Mn2CuAs2O2, Sr2Mn3As2O2, and Sr2Zn2MnAs2O2 were synthesized. Their temperature- and applied magnetic field-dependent structural, transport, thermal, and magnetic properties were characterized by means of x-ray and neutron diffraction, electrical resistivity rho, heat capacity, magnetization and magnetic susceptibility measurements. These compounds have a body-centered-tetragonal crystal structure (space group I4/mmm) that consists of MO2 (M = Zn and/or Mn) oxide layers similar to the CuO2 layers in high superconducting transition temperature Tc cuprate superconductors, and intermetallic MAs (M = Cu and/or Mn) layers similar to the FeAs layers in high-Tc pnictides. These two types of layers alternate along the crystallographic c-axis and are separated by Sr atoms. The site occupancies of Mn, Cu and Zn were studied using Rietveld refinements of x-ray and neutron powder diffraction data. The temperature dependences of rho suggest metallic character for Sr2Mn2CuAs2O2 and semiconducting character for Sr2Mn3As2O2 and Sr2Zn2MnAs2O2. Sr2Mn2CuAs2O2 is inferred to be a ferrimagnet with a Curie temperature TC = 95(1) K. Remarkably, we find that the magnetic ground state structure changes from a G-type antiferromagnetic structure in Sr2Mn3As2O2 to an A-type ferrimagnetic structure in Sr2Mn2CuAs2O2 in which the Mn ions in each layer are ferromagnetically aligned, but are antiferromagnetically aligned between layers.Comment: 18 pages, 16 figures, 6 tables; submitted to Phys. Rev.

Magnetic and thermal properties of the S = 1/2 zig-zag spin-chain compound In2VO5

Static magnetic susceptibility \chi, ac susceptibility \chi_{ac} and specific heat C versus temperature T measurements on polycrystalline samples of In2VO5 and \chi and C versus T measurements on the isostructural, nonmagnetic compound In2TiO5 are reported. A Curie-Wiess fit to the \chi(T) data above 175 K for In2VO5 indicates ferromagnetic exchange between V^{4+} (S = 1/2) moments. Below 150 K the \chi(T) data deviate from the Curie-Weiss behavior but there is no signature of any long range magnetic order down to 1.8 K. There is a cusp at 2.8 K in the zero field cooled (ZFC) \chi(T) data measured in a magnetic field of 100 Oe and the ZFC and field cooled (FC) data show a bifurcation below this temperature. The frequency dependence of the \chi_{ac}(T) data indicate that below 3 K the system is in a spin-glass state. The difference \Delta C between the heat capacity of In2VO5 and In2TiO5 shows a broad anomaly peaked at 130 K. The entropy upto 300 K is more than what is expected for S = 1/2 moments. The anomaly in \Delta C and the extra entropy suggests that there may be a structural change below 130 K in In2VO5.Comment: 6 pages, 7 figures, 1 tabl

Helicoidal magnetic order in a clean copper oxide spin chain compound

We report susceptibility, specific heat, and neutron diffraction measurements on NaCu$_2$O$_2$, a spin-1/2 chain compound isostructural to LiCu$_2$O$_2$, which has been extensively investigated. Below 13 K, we find a long-range ordered, incommensurate magnetic helix state with a propagation vector similar to that of LiCu$_2$O$_2$. In contrast to the Li analogue, substitutional disorder is negligible in NaCu$_2$O$_2$. We can thus rule out that the helix is induced by impurities, as was claimed on the basis of prior work on LiCu$_2$O$_2$. A spin Hamiltonian with frustrated longer-range exchange interactions provides a good description of both the ordered state and the paramagnetic susceptibility.Comment: 4 pages, 4 figures Improved Fig.1 and 4. Minor rephrasing. Reference adde

Results from a phase II proof of concept trial of VSN16R to treat multiple sclerosis related spasticity

BACKGROUND: VSN16R is an opener of neural, big-conductance, calcium-activated, potassium channels. We report the results of a phase 2a trial of twice daily oral tablet therapy in people with spasticity due to multiple sclerosis (MS). METHODS: Subjects had confirmed diagnosis of MS, spasticity reported as 4 on the spasticity numerical rating scale (NRS) and modified Ashworth scale 2 in 2 or more lower limb muscle groups. Participants entered (i) a hospital-based, placebo-controlled, single ascending dose (SAD) group (100mg, 200mg, 400mg and 800mg) to assess pharmacokinetics (n=10), safety and drug tolerability (n=53) and (ii) a second group (Total n=156) to receive either a maximum-tolerated dose or up to 400mg BID of VSN16R capsules or matching placebo. The primary end-point was reduction of spasticity as measured by the NRS, with secondary-outcomes including reduction of modified Ashworth and Tardieu Spasticity Scales, Penn spasm scale and 10m walk following treatment. RESULTS: Pharmacokinetics and relative lack of adverse events in the SAD safety phase were consistent with phase I safety studies in healthy individuals and all people tolerated the single 800mg dose. Therefore, all people were assigned to 400mg BID during the efficacy arm. Among the people who received VSN16R (n=77) the change in the NRS was -0.9 ± 1.50 in the VSN16R 400mg BID group and -1.1 ± 1.52 in the placebo group (n=79), giving a non-significant treatment difference of +0.20 (95% CI: -0.2 to +0.7, p=0.3434). There was no significant effect on the secondary endpoints. However, post-hoc analysis of people who responded (>30% inhibition of the NRS) to the 800mg dose in the SAD phase (n=10) demonstrated a significant (p< 0.02) inhibition in the NRS compared those receiving placebo during the multiple dosing arm. The drug was not associated with any sedation. Reported adverse effects were inconsistent and generally mild. CONCLUSION: VSN16R at the dose 400mg BID did not show activity in reducing spasticity in MS patients. The single dose of 800 mg showed activity in comparison to placebo in the dose escalation phase. VSN16R has a very good safety profile. Due to a short half-life of VSN16R further studies with higher doses and slow-release formulation may be warranted. (ClinicalTrials.gov number NCT02542787. EU trials register Number: 2014-004412-11)

Electronic correlations in FeGa3 and the effect of hole doping on its magnetic properties

We investigate signatures of electronic correlations in the narrow-gap semiconductor FeGa 3 by means of electrical resistivity and thermodynamic measurements performed on single crystals of FeGa 3 , Fe 1−x Mn x Ga 3 , and FeGa 3−y Zn y , complemented by a study of the 4d analog material RuGa 3 . We find that the inclusion of sizable amounts of Mn and Zn dopants into FeGa 3 does not induce an insulator-to-metal transition. Our study indicates that both substitution of Zn onto the Ga site and replacement of Fe by Mn introduces states into the semiconducting gap that remain localized even at highest doping levels. Most importantly, using neutron powder diffraction measurements, we establish that FeGa 3 orders magnetically above room temperature in a complex structure, which is almost unaffected by the doping with Mn and Zn. Using realistic many-body calculations within the framework of dynamical mean field theory (DMFT), we argue that while the iron atoms in FeGa 3 are dominantly in an S=1 state, there are strong charge and spin fluctuations on short-time scales, which are independent of temperature. Further, the low magnitude of local contributions to the spin susceptibility advocates an itinerant mechanism for the spin response in FeGa 3 . Our joint experimental and theoretical investigations classify FeGa 3 as a correlated band insulator with only small dynamical correlation effects, in which nonlocal exchange interactions are responsible for the spin gap of 0.4 eV and the antiferromagnetic order. We show that hole doping of FeGa 3 leads, within DMFT, to a notable strengthening of many-body renormalizations

Analysis of and workarounds for element reversal for a finite element-based algorithm for warping triangular and tetrahedral meshes

We consider an algorithm called FEMWARP for warping triangular and tetrahedral finite element meshes that computes the warping using the finite element method itself. The algorithm takes as input a two- or three-dimensional domain defined by a boundary mesh (segments in one dimension or triangles in two dimensions) that has a volume mesh (triangles in two dimensions or tetrahedra in three dimensions) in its interior. It also takes as input a prescribed movement of the boundary mesh. It computes as output updated positions of the vertices of the volume mesh. The first step of the algorithm is to determine from the initial mesh a set of local weights for each interior vertex that describes each interior vertex in terms of the positions of its neighbors. These weights are computed using a finite element stiffness matrix. After a boundary transformation is applied, a linear system of equations based upon the weights is solved to determine the final positions of the interior vertices. The FEMWARP algorithm has been considered in the previous literature (e.g., in a 2001 paper by Baker). FEMWARP has been succesful in computing deformed meshes for certain applications. However, sometimes FEMWARP reverses elements; this is our main concern in this paper. We analyze the causes for this undesirable behavior and propose several techniques to make the method more robust against reversals. The most successful of the proposed methods includes combining FEMWARP with an optimization-based untangler.Comment: Revision of earlier version of paper. Submitted for publication in BIT Numerical Mathematics on 27 April 2010. Accepted for publication on 7 September 2010. Published online on 9 October 2010. The final publication is available at http://www.springerlink.co

Hepatitis C virus exploits cyclophilin A to evade PKR

Counteracting innate immunity is essential for successful viral replication. Host cyclophilins (Cyps) have been implicated in viral evasion of host antiviral responses, although the mechanisms are still unclear. Here, we show that hepatitis C virus (HCV) co-opts the host protein CypA to aid evasion of antiviral responses dependent on the effector protein kinase R (PKR). Pharmacological inhibition of CypA rescues PKR from antagonism by HCV NS5A, leading to activation of an interferon regulatory factor-1 (IRF1)-driven cell intrinsic antiviral program that inhibits viral replication. These findings further the understanding of the complexity of Cyp-virus interactions, provide mechanistic insight into the remarkably broad antiviral spectrum of Cyp inhibitors, and uncover novel aspects of PKR activity and regulation. Collectively, our study identifies a novel antiviral mechanism that harnesses cellular antiviral immunity to suppress viral replication

Magnetic, Thermal, and Transport Properties of Layered Arsenides BaRu2As2 and SrRu2As2

The magnetic, thermal and transport properties of polycrystalline BaRu2As2 and SrRu2As2 samples with the ThCr2Si2 structure were investigated by means of magnetic susceptibility chi(T), electrical resistivity rho(T), and heat capacity Cp(T) measurements. The temperature (T) dependence of rho indicates metallic character for both compounds with residual resistivity ratios rho(310 K)/rho(2 K) of 17 and 5 for the Ba and Sr compounds, respectively. The Cp(T) results reveal a low-T Sommerfeld coefficient gamma = 4.9(1) and 4.1(1) mJ/mol K^2 and Debye temperature \Theta_D = 271(7) K and 271(4) K for the Ba and Sr compounds, respectively. The chi (T) was found to be diamagnetic with a small absolute value for both compounds. No transitions were found for BaRu2As2 above 1.8 K. The chi(T) data for SrRu2As2 exhibit a cusp at \sim 200 K, possibly an indication of a structural and/or magnetic transition. We discuss the properties of BaRu2As2 and SrRu2As2 in the context of other ThCr2Si2-type and ZrCuSiAs-type transition metal pnictides.Comment: 6 pages, 6 figures; v2: additional discussion of the relationship with FeAs-type materials and the importance of Stoner enhancement of the susceptibilit

Survival on Renal Replacement Therapy: Data from the EDTA Registry

Extensive survival data are presented from the EDTA Registry's files for patients who started renal replacement therapy in 1970-1974 compared to 1980-1984. The contribution of the different treatment modalities (haemodialysis, continuous peritoneal dialysis, and transplantation) to the survival of patients according to geographical region is also shown. Survival on renal replacement therapy, irrespective of treatment modality and of primary renal disease, was best in the 10-14-year-old patients, with 58% at 10 years and 52% at 15 years, and decreased with rising age to 28% at 10 years and 16% at 15 years in patients aged 45-54 when they commenced therapy in 1970-1974. When comparing the 0-4-year-old with the 10-14-year-old cohort of the paediatric patients, 5-year survival rates for patients starting renal replacement therapy in the early eighties declined from 85% to 70% with decreasing age. Treatment policy, as reflected by the proportion of patients on different modes of therapy, varied markedly between European regions but affected survival to a small extent only. The large population with diabetic nephropathy incurred annual mortality rates 2-3 times greater than those observed in patients with ‘standard' primary renal diseases. Haemodialysis and continuous peritoneal dialysis, although not comparable because of important differences in selection policy, yielded similar survival rates. Patient and graft survival rates have improved markedly when comparing patients starting renal replacement therapy in the early seventies with the eighties; particularly for cadaveric transplantation. Patient survival after second grafting was similar to that after first grafting, with 83% at 5 years after second cadaveric grafting in the 15-44-year-old cohort, vs 85% after first cadaver transplantation in 1980-1984. Second cadaveric graft survival was superior to average first-graft survival for those recipients whose first graft had been functioning for more than 1 year. However, second-graft survival in rapid rejectors of a first graft as well as third cadaveric graft survival were curtailed by the large number of early losses, with only 52% of third grafts functioning at 1 year. For living related donor transplantation, parents were mostly used in children whilst identical siblings predominated in adults older than 45. In the early eighties, patient survival was 92% at 5 years for recipients younger than 15, 87% for the 15-45 year old cohort and 72% for those aged 45 or older. From the overall survival rates on renal replacement therapy obtained at 5 years in the early eighties, it appears safe to predict that at least 65% of young adults and 25% of patients aged 55-64 will be surviving at 10 years after starting therap