A Variational Principle for the Asymptotic Speed of Fronts of the Density Dependent Diffusion--Reaction Equation

We show that the minimal speed for the existence of monotonic fronts of the equation $u_t = (u^m)_{xx} + f(u)$ with $f(0) = f(1) = 0$, $m >1$ and $f>0$ in $(0,1)$ derives from a variational principle. The variational principle allows to calculate, in principle, the exact speed for arbitrary $f$. The case $m=1$ when $f'(0)=0$ is included as an extension of the results.Comment: Latex, postcript figure availabl

Erosion waves: transverse instabilities and fingering

Two laboratory scale experiments of dry and under-water avalanches of non-cohesive granular materials are investigated. We trigger solitary waves and study the conditions under which the front is transversally stable. We show the existence of a linear instability followed by a coarsening dynamics and finally the onset of a fingering pattern. Due to the different operating conditions, both experiments strongly differ by the spatial and time scales involved. Nevertheless, the quantitative agreement between the stability diagram, the wavelengths selected and the avalanche morphology reveals a common scenario for an erosion/deposition process.Comment: 4 pages, 6 figures, submitted to PR

Thermal and electrical transport in the spin density wave antiferromagnet CaFe4_{4}As3_{3}

We present here measurements of the thermopower, thermal conductivity, and electrical resistivity of the newly reported compound CaFe4As3. Evidence is presented from specific heat and electrical resistivity measurements that a substantial fraction of the Fermi surface survives the onset of spin density wave (SDW) order at the Neel temperature TN=88 K, and its subsequent commensurate lockin transition at T2=26.4 K. The specific heat below T2 consists of a normal metallic component from the ungapped parts of the Fermi surface, and a Bardeen-Cooper- Schrieffer (BCS) component that represents the SDW gapping of the Fermi surface. A large Kadowaki-Woods ratio is found at low temperatures, showing that the ground state of CaFe4As3 is a strongly interacting Fermi liquid. The thermal conductivity of CaFe4As3 is an order of magnitude smaller than those of conventional metals at all temperatures, due to a strong phonon scattering. The thermoelectric power displays a sign change from positive to negative indicating that a partial gap forms at the Fermi level with the onset of commensurate spin density wave order at T2=26.4 K. The small value of the thermopower and the enhancements of the resistivity due to gap formation and strong quasiparticle interactions offset the low value of the thermal conductivity, yielding only a modest value for the thermoelectric figure of merit Z < 5x10^-6 1/K in CaFe4As3. The results of ab initio electronic structure calculations are reported, confirming that the sign change in the thermopower at T2 is reflected by a sign change in the slope of the density of states at the Fermi level. Values for the quasiparticle renormalization are derived from measurements of the specific heat and thermopower, indicating that as T->0, CaFe4As3 is among the most strongly correlated of the known Fe-based pnictide and chalcogenide systems.Comment: 8 pages with 5 figure

Relationship between self-efficacy and patient knowledge on adherence to oral contraceptives using the Morisky Medication Adherence Scale (MMAS-8)

BackgroundPreconception care, including family planning, is a vital component of healthcare for women of reproductive age. An average female spends the majority of her reproductive life trying to prevent a pregnancy. In order to prevent unintended pregnancy, women often rely on the use of hormonal contraceptives. In the United States, the majority of hormonal contraceptive users are prescribed oral contraceptive pills (OCPs). Reduced adherence to OCPs decreases their ability to prevent pregnancy. The study aimed to measure OCP adherence among female college students, and explore the relationship between OCP adherence, knowledge, and self-efficacy. MethodsThis cross-sectional study recruited a random sample of female college students to participate in an online survey. OCP adherence was based on the 8-item Morisky Medication Adherence Scale (MMAS-8). Secondary reporting of medication adherence included participant reports of the number of missed OCP doses in the previous month and typical month of use. ResultsOf the 5000 invited, 1559 (31.3%) completed the survey. Of those responding, 670 (41.3%) reported use of OCPs. A total of 293 (44.3%) OCP users met criteria for low adherence, 241 (36.4%) met criteria for medium adherence, and 128 (19.3%) met criteria for high adherence. Those with high adherence had higher self-efficacy (P \u3c 0.001) and perceived knowledge (p \u3c 0.001). After controlling for other factors, self-efficacy (b = .37) and perceived knowledge (b = .09) remained associated with OCP adherence. ConclusionLess than 20% of respondents met the criteria for high adherence to OCPs. Self-efficacy and knowledge were associated with higher OCP adherence. Targeted interventions from healthcare providers, health educators, and other adherence related media to increase the knowledge and self-efficacy of patients using OCPs may improve adherence rates. Additional research is needed to evaluate the impact of innovative interventions focused on social and behavioral patient factors, like knowledge and self-efficacy, on adherence to OCPs

Neutron, electron and X-ray scattering investigation of Cr1-xVx near Quantum Criticality

The weakness of electron-electron correlations in the itinerant antiferromagnet Cr doped with V has long been considered the reason that neither new collective electronic states or even non Fermi liquid behaviour are observed when antiferromagnetism in Cr$_{1-x}$V$_{x}$ is suppressed to zero temperature. We present the results of neutron and electron diffraction measurements of several lightly doped single crystals of Cr$_{1-x}$V$_{x}$ in which the archtypal spin density wave instability is progressively suppressed as the V content increases, freeing the nesting-prone Fermi surface for a new striped charge instability that occurs at x$_{c}$=0.037. This novel nesting driven instability relieves the entropy accumulation associated with the suppression of the spin density wave and avoids the formation of a quantum critical point by stabilising a new type of charge order at temperatures in excess of 400 K. Restructuring of the Fermi surface near quantum critical points is a feature found in materials as diverse as heavy fermions, high temperature copper oxide superconductors and now even elemental metals such as Cr.Comment: 6 pages, 6 figures. Accepted to Physical Review