Sr2V3O9 and Ba2V3O9: quasi one-dimensional spin-systems with an anomalous low temperature susceptibility

The magnetic behaviour of the low-dimensional Vanadium-oxides Sr2V3O9 and Ba2V3O9 was investigated by means of magnetic susceptibility and specific heat measurements. In both compounds, the results can be very well described by an S=1/2 Heisenberg antiferromagnetic chain with an intrachain exchange of J = 82 K and J = 94 K in Sr2V3O9 and Ba2V3O9, respectively. In Sr2V3O9, antiferromagnetic ordering at T_N = 5.3 K indicate a weak interchain exchange of the order of J_perp ~ 2 K. In contrast, no evidence for magnetic order was found in Ba2V3O9 down to 0.5 K, pointing to an even smaller interchain coupling. In both compounds, we observe a pronounced Curie-like increase of the susceptibility below 30 K, which we tentatively attribute to a staggered field effect induced by the applied magnetic field. Results of LDA calculations support the quasi one-dimensional character and indicate that in Sr2V3O9, the magnetic chain is perpendicular to the structural one with the magnetic exchange being transferred through VO4 tetrahedra.Comment: Submitted to Phy. Rev.

CPT Pharmacometrics Syst Pharmacol

We modeled the viral dynamics of 13 untreated patients infected with SARS-CoV-2 to infer viral growth parameters and predict the effects of antiviral treatments. In order to reduce peak viral load by more than 2 logs, drug efficacy needs to be greater than 90% if treatment is administered after symptom onset; an efficacy of 60% could be sufficient if treatment is initiated before symptom onset. Given their pharmacokinetic/pharmacodynamic properties, current investigated drugs may be in a range of 6-87% efficacy. They may help control virus if administered very early, but may not have a major effect in severe patients

Clinical applicability of current pharmacokinetic models: Splanchnic elimination of 5-fluorouracil in cancer patients

What can be inferred from limited clinical data by using current models of hepatic elimination? We examined this question by analyzing previously published data on the steady-state uptake of the anticancer agent 5-fluorouracil (5-FU) in seven cancer patients in terms of the venous equilibration model, the undistributed and distributed forms of the sinusoidal perfusion model, and the convection-dispersion model. Because of appreciable extrasplanchnic removal of 5-FU, the value of the steady infusion rate was not used in our analysis. When the data from all patients were pooled by plotting the measured hepatic venous concentration against the measured hepatic arterial concentration, the high concentration data fell on a limiting straight line of slope 1, indicating that at high dose rates elimination of 5-FU in both the liver and gastrointestinal tract was close to saturation. The intercept of this line gave a model-independent estimate of V max /Q= 48.0± 11.6 (SD) μM for the pooled data set, where V max is the maximum splanchnic elimination rate of 5-FU, and Q is the hepatic blood flow. The low concentration data points fell on a limiting straight line through the origin, from which model-dependent values of the Michaelis constant were determined. The venous equilibration model gave K m =9.4 μM , while the undistributed sinusoidal perfusion model gave K m * =26,5 μM. With these values of K m , both models fit the pooled data equally well. These methods were applied to analyses of the five individual data sets which contained sufficiently high concentration data points. The resulting mean values were V max /Q=41.0±5.1 (sem) μM, K m =8.4±1.3μM and K m * =23.2±3.2 μM. However, the splanchnic region is a highly heterogeneous organ system, for which an undistributed analysis provides no more than an upper bound on the Michaelis constant K m + ( K m + ⩽ K m * ). A perfusion model distributed to represent total splanchnic elimination is developed in the Appendix. Using previous estimates of the degree of functional heterogeneity in the liver alone, this model yields K m + values for individual patients which have a mean of 20.3±2.8 μM .Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45038/1/10928_2005_Article_BF01062135.pd

Structural investigation of composite phases Ba1+x[(NaxMn1-x)O-3] with x similar or equal to 2/7, 5/17 and 1/3; exotic Mn4.5+ valence

International audienceStructural models are proposed for three composite compounds of chemical formula Ba1+x[(NaxMn1-x)O-3] (x similar or equal to 2/7, 5/17 and 1/3) by single crystal X-ray diffraction; superspace formalism is used to obtain an unified description of the three phases. The modulation affecting Ba atoms can be easily designed but the competition "occupational/displacive" modulations relating to the Mn/Na metallic columns were particularly difficult to modelize. However, the large amplitude of the displacive modulation affecting the oxygen atoms (similar or equal to +/- 0.7 angstrom) in comparison with that observed for related compounds (similar or equal to +/- 0.3 angstrom) makes it a direct consequence of the Na+ alkali insertion inside the trigonal prisms. Owing to this insertion, the Mn atoms exhibit, in the three phases, an "exotic" oxidation state of about +4.5. In addition, even if the sequence between face sharing MnO6 octahedra and NaO6 trigonal prisms can be analytically deduced from the x value, it is clear that the Na/Mn contrasts play in favour of its accurate determination through the XRD single crystal refinement