Search

A new Ba2CuO4-y superconductor with critical temperature (Tc) exceeding 70 K was discovered. The X-ray absorption measurement gives evidence that this cuprate resembles La2CuO4 but is doped with a fairly large amount of holes, while in contrast to the so far known hole-doped high-Tc cuprates, the new cuprate possesses a much shorter local apical oxygen distance as well as much expanded in-plane Cu–O bond, leading to unprecedented compressed local octahedron. In compressed local octahedron, the Cu3d3z2–r2 orbital level will be lifted above the Cu3dx2-y2 orbital level with more three-dimensional features, implying that pairing symmetry may carry admixtures from more than one gap, suggesting that Ba2CuO4-y composed of alkaline earth copper oxides that are the essential elements to form cuprate superconductors may belong to a new branch of cuprate superconductors.

High-pressure electrical resistivity measurements reveal that the mechanical deformation of ultra-hard WB

With ${T}_{c}\ensuremath{\sim}9.6\phantom{\rule{0.16em}{0ex}}\mathrm{K}, {\mathrm{Be}}_{22}\mathrm{Re}$ exhibits one of the highest critical temperatures among Be-rich compounds. We have carried out a series of high-pressure electrical resistivity measurements on this compound to 30 GPa. The data show that the critical temperature ${T}_{c}$ is suppressed gradually at a rate of $d{T}_{c}/dP=\ensuremath{-}0.05\phantom{\rule{0.16em}{0ex}}\mathrm{K}/\mathrm{GPa}$. Using density functional theory (DFT) calculations of the electronic and phonon density of states (DOS) and the measured critical temperature, we estimate that the rapid increase in lattice stiffening in ${\mathrm{Be}}_{22}\mathrm{Re}$ overwhelms a moderate increase in the electron-ion interaction with pressure, resulting in the decrease in ${T}_{c}$. High-pressure x-ray diffraction measurements show that the ambient pressure crystal structure of ${\mathrm{Be}}_{22}\mathrm{Re}$ persists to at least 154 GPa.

The mechanism of superconductivity in cuprates remains one of the big challenges of condensed matter physics.High Tc cuprates crystallize into layered perovskite structure featuring copper oxygen octahedral coordination. Due to the Jahn Teller effect in combination with the strong static Coulomb interaction, the octahedra in high Tc cuprates are elongated along the c axis, leading to a 3dx2-y2 orbital at the top of the band structure wherein the doped holes reside.This scenario gives rise to two dimensional characteristics in high Tc cuprates that favor d wave pairing symmetry. Here we report superconductivity in a cuprate Ba2CuO4-y wherein the local octahedron is in a very exceptional compressed version.The Ba2CuO4-y compound was synthesized at high pressure at high temperatures, and shows bulk superconductivity with critical temperature Tc above 70 K at ambient conditions. This superconducting transition temperature is more than 30 K higher than the Tc for the isostructural counterparts based on classical La2CuO4. X-ray absorption measurements indicate the heavily doped nature of the Ba2CuO4-y superconductor. In compressed octahedron the 3d3z2-r2 orbital will be lifted above the 3dx2-y2 orbital, leading to significant three dimensional nature in addition to the conventional 3dx2-y2 orbital. This work sheds important new light on advancing our comprehensive understanding of the superconducting mechanism of high Tc in cuprate materials., Comment: Total 28 pages incuding 9 Figures

UBe13 was the second discovered heavy fermion superconductor, and numerous pieces of evidence exist that imply that it is an unconventional (non-BCS, non-s wave pairing symmetry) superconductor. Exhibiting even more signs of unconventional superconductivity, Th-doped UBe13 is perhaps the most puzzling of any of the unconventional superconductors. This review considers both the parent, undoped compound as well as the more interesting Th-doped UBe13. After summarizing the rather thorough characterization, which because of the interest in these compounds has continued from their discovery in 1983 and 1984 to date, these properties are compared with a recent template for determining whether a superconductor is unconventional. Finally, further experiments are suggested., accepted review to appear in Journal of Low Temperature Physics

Ammonia assimilation has been followed in ectomycorrhizal roots of Fagus sylvatica. The absorption of ammonium ions was associated with a rapid synthesis of free amino acids in mycorrhizal tissues, glutamine being the most prominent. In the presence of [

Several previous reports on undoped $AE\mathrm{}{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$ ($AE=$ alkaline earth metal) point to drops in resistivity indicative of possible superconductivity and some degree of Meissner effect in the magnetic susceptibility. Also, based on both resistivity and magnetic susceptibility measurements, controlled exposure to water vapor has been shown to induce superconductivity in $AE{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$. In our study, $\mathrm{Ba}{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$ single crystals grown using the self-flux method showed a full resistive drop around 22 K and magnetic shielding, when exposed to fluorine gas postgrowth. Our measurements indicate electron (donor) doping via atomic substitution of F for As is concurrent with the observed superconductivity, which sheds light on the likely effect of exposure to water vapor in previous work. Like doping experiments (such as substitution of Co for Fe, P for As, or K for Ba) in $AE{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$ to date, the present work is consistent with suppression of the spin density wave transition coincident with the appearance of ${T}_{c}$. In addition to answering the puzzle of superconductivity in undoped or water vapor exposed $AE{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$, our results also represent a fast (20 min exposure to 5% F in He) and reliable method suitable for inducing superconductivity in thin films of $AE{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$. Some supportive work on $\mathrm{Ba}{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$ exposed to ${\mathrm{Cl}}_{2}$ is also presented.

The authors show that antiferromagnetism can be stabilized when a small amount of Fe is intercalated in the van der Waals gap of 1T-TaS${}_{2}$. When they compare the temperature-pressure phase diagram of Fe-intercalated 1T-TaS${}_{2}$ with that of pristine 1T-TaS${}_{2}$, they conclude that the antiferromagnetic region is close to, but decoupled from, the Mott insulating phase of pristine 1T-TaS${}_{2}$.

Two-dimensional triangular-lattice materials with spin-1/2 are perfect platforms for investigating quantum frustrated physics with spin fluctuations. Here we report the structure, magnetization, heat capacity, and inelastic neutron scattering (INS) results on cesium ytterbium diselenide, ${\mathrm{CsYbSe}}_{2}$. There is no long-range magnetic order down to 0.4 K at zero field. The temperature-dependent magnetization, $M(T)$, reveals an easy-plane magnetic anisotropy. A maximum is found in $M(T)$ around $T\ensuremath{\approx}1.5$ K when magnetic field $H$ is applied in the $ab$ plane, indicating the short-range interaction. The low-temperature isothermal magnetization $M(H)$ shows a one-third plateau of the estimated saturation moment, which is characteristic of a two-dimensional (2D) frustrated triangular lattice. Heat capacity shows field-induced long-range magnetic order for both $H||c$ and $H||ab$ directions. The broad peak in heat capacity and highly damped INS magnetic excitation at $T=2$ K suggests strong spin fluctuations. The dispersive in-plane INS, centered at the (1/3 1/3 0) point, and the absence of dispersion along the $c$ direction suggest ${120}^{\ensuremath{\circ}}$ noncollinear 2D-like spin correlations. All these results indicate that the two-dimensional frustrated material ${\mathrm{CsYbSe}}_{2}$ can be in proximity to the triangular-lattice quantum spin liquid. We propose an experimental low-temperature $H\text{\ensuremath{-}}T$ phase diagram for ${\mathrm{CsYbSe}}_{2}$.

In this paper we report the synthesis, magnetization, and heat capacity of the frustrated magnets $A{\mathrm{ErSe}}_{2}$($A=\mathrm{Na},\mathrm{K}$) which contain perfect triangular lattices of ${\mathrm{Er}}^{3+}$. The magnetization data suggests no long-range magnetic order exists in $A{\mathrm{ErSe}}_{2}$($A=\mathrm{Na},\mathrm{K}$), which is consistent with the heat capacity measurements. Large anisotropy is observed between the magnetization within the $ab$ plane and along the $c$ axis of both compounds. When the magnetic field is applied along the $ab$ plane, anomalies are observed at 1.8 ${\ensuremath{\mu}}_{B}$ in ${\mathrm{NaErSe}}_{2}$ at 0.2 T and 2.1 ${\ensuremath{\mu}}_{B}$ in ${\mathrm{KErSe}}_{2}$ at 0.18 T. Unlike ${\mathrm{NaErSe}}_{2}$, a plateaulike field-induced metamagnetic transition is observed for $\mathrm{H}\ensuremath{\parallel}c$ below 1 K in ${\mathrm{KErSe}}_{2}$. Two broad peaks are observed in the heat capacity below 10 K indicating possible crystal electric field (CEF) effects and magnetic entropy released under different magnetic fields. All results indicate that $A{\mathrm{ErSe}}_{2}$ are strongly anisotropic, frustrated magnets with field-induced transition at low temperature. The lack of signatures for long-range magnetic order implies that these materials are candidates for hosting a quantum spin liquid ground state.

Predicting the critical temperature ${T}_{c}$ of new superconductors is a notoriously difficult task, even for electron-phonon paired superconductors, for which the theory is relatively well understood. Early attempts to obtain a simple ${T}_{c}$ formula consistent with strong-coupling theory, by McMillan and by Allen and Dynes, led to closed-form approximate relations between ${T}_{c}$ and various measures of the phonon spectrum and the electron-phonon interaction appearing in Eliashberg theory. Here we propose that these approaches can be improved with the use of machine-learning algorithms. As an initial test, we train a model for identifying low-dimensional descriptors using the ${T}_{c}l10$ K dataset by Allen and Dynes, and show that a simple analytical expression thus obtained improves upon the Allen-Dynes fit. Furthermore, the prediction for the recently discovered high-${T}_{c}$ material ${\mathrm{H}}_{3}\mathrm{S}$ at high pressure is quite reasonable. Interestingly, ${T}_{c}$'s for more recently discovered superconducting systems with a more two-dimensional electron-phonon coupling, which do not follow Allen and Dynes's expression, also do not follow our analytic expression. Thus, this machine-learning approach appears to be a powerful method for highlighting the need for a new descriptor beyond those used by Allen and Dynes to describe their set of isotropic electron-phonon coupled superconductors. We argue that this machine-learning method, and its implied need for a descriptor characterizing Fermi-surface properties, represents a promising approach to superconductor materials discovery which may eventually replace the serendipitous discovery paradigm begun by Kamerlingh Onnes.

The early work on superconductivity in layered transition metal dichalcogenides, the prototypical two-dimensional material, at Stanford in the Geballe group is reviewed. Specific heat played an important role as a characterization tool.

A15 Nb$_3$Si is, until now, the only high temperature superconductor produced at high pressure (~110 GPa) that has been successfully brought back to room pressure conditions in a metastable condition. Based on the current great interest in trying to create metastable-at-room-pressure high temperature superconductors produced at high pressure, we have restudied explosively compressed A15 Nb$_3$Si and its production from tetragonal Nb$_3$Si. First, diamond anvil cell pressure measurements up to 88 GPa were performed on explosively compressed A15 Nb$_3$Si material to trace Tc as a function of pressure. Tc is suppressed to ~ 5.2 K at 88 GPa. Then, using these Tc (P) data for A15 Nb$_3$Si, pressures up to 92 GPa were applied at room temperature (which increased to 120 GPa at 5 K) on tetragonal Nb$_3$Si. Measurements of the resistivity gave no indication of any A15 structure production, i.e., no indications of the superconductivity characteristic of A15 Nb$_3$Si. This is in contrast to the explosive compression (up to P~110 GPa) of tetragonal Nb$_3$Si, which produced 50-70% A15 material, Tc = 18 K at ambient pressure, in a 1981 Los Alamos National Laboratory experiment. Our theoretical calculations show that A15 Nb$_3$Si has an enthalpy vs the tetragonal structure that is 0.07 eV/atom smaller at 100 GPa, implying that the accompanying high temperature (1000 deg C) caused by explosive compression is necessary to successfully drive the reaction kinetics of the tetragonal -> A15 Nb$_3$Si structural transformation. Annealing experiments on the A15 explosively compressed material reaching time scales of 39 years are consistent with this viewpoint., 6 figures

Adolescence methamphetamine use is an issue of considerable concern due to its correlation with later delinquency, divorce, unemployment and health problems. Understanding how adolescents initiate methamphetamine abuse is important in developing effective prevention programs. We formulate a mathematical model for the spread of methamphetamine abuse using nonlinear ordinary differential equations. It is assumed that susceptibles are recruited into methamphetamine use through imitation. An epidemic threshold value, $${\mathcal {R}}_a$$ , termed the abuse reproduction number, is proposed and defined herein in the drug-using context. The model is shown to exhibit the phenomenon of backward bifurcation. This means that methamphetamine problems may persist in the population even if $${\mathcal {R}}_a$$ is less than one. Sensitivity analysis of $${\mathcal {R}}_a$$ was performed to determine the relative importance of different parameters in methamphetamine abuse initiation. The model is then fitted to data on methamphetamine users less than 20 years old reporting methamphetamine as their primary substance of abuse in the treatment centres of Cape Town and parameter values that give the best fit are chosen. Results show that the proportion of methamphetamine users less than 20 years old reporting methamphetamine as their primary substance of abuse will continue to decrease in Cape Town of South Africa. The results suggest that intervention programs targeted at reducing adolescence methamphetamine abuse, are positively impacting methamphetamine abuse.

Here we report a quasi-one-dimensional $S=1$ chain compound ${\mathrm{NiTe}}_{2}{\mathrm{O}}_{5}$. From the comprehensive study of the structure and magnetic properties on high-quality single-crystalline ${\mathrm{NiTe}}_{2}{\mathrm{O}}_{5}$, it is revealed that ${\mathrm{NiTe}}_{2}{\mathrm{O}}_{5}$ undergoes a transition into an intriguing long-range antiferromagnetic order at ${T}_{\mathrm{N}}=30.5\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, in which longitudinal magnetic moments along the chain direction are ferromagnetically ordered, while their transverse components have an alternating ferromagnetic-antiferromagnetic coupling. Even though the temperature dependence of magnetic susceptibility represents an archetypal anisotropic antiferromagnetic order, we found that critical behavior of unconventional nature with ${\ensuremath{\alpha}}^{\ensuremath{'}}\ensuremath{\sim}0.25$ and $\ensuremath{\beta}\ensuremath{\sim}0.18$ is accompanied by the temperature evolution of the antiferromagnetic order parameter.

The abuse of drugs is now an epidemic globally whose control has been mainly through rehabilitation. The demand for drug abuse rehabilitation has not been matched with the available capacity resulting in limited placement of addicts into rehabilitation. In this paper, we model limited rehabilitation through the Hill function incorporated into a system of nonlinear ordinary differential equations. Not every member of the community is equally likely to embark on drug use, risk structure is included to help differentiate those more likely (high risk) to abuse drugs and those less likely (low risk) to abuse drugs. It is shown that the model has multiple equilibria, and using the centre manifold theory, the model exhibits the phenomenon of backward bifurcation whose implications to rehabilitation are discussed. Sensitivity analysis and numerical simulations are performed. The results show that saturation in rehabilitation will in the long run lead to the escalation of drug abuse. This means that limited access to rehabilitation has negative implications in the fight against drug abuse where rehabilitation is the main form of control. This suggests that increased access to rehabilitation is likely to lower the drug abuse epidemic.

We present direct evidence for an enhanced superconducting $T_c$ on the surface of cleaved single crystals of Ba(Fe$_{0.95}$Co$_{0.05}$)$_2$As$_2$. Transport measurements performed on samples cleaved in ultra high vacuum (UHV) show a significantly enhanced superconducting transition when compared to equivalent measurements performed in air. Deviations from the bulk resistivity appear at 21K, well above the 10K bulk $T_c$ of the underdoped compound. We demonstrate that the excess conductivity above the bulk $T_c$ can be controllably suppressed by application of potassium ions on the cleaved surface, indicating that the enhanced superconductivity is strongly localized to the sample surface. Additionally, we find that the effects of the potassium surface dosing are strongly influenced by the presence of residual gas absorbates on the sample surface, which may prevent effective charge transfer from the potassium atoms to the FeAs plane. This is further support for the conclusion that the effects of the dosing (and enhanced superconductivity) are localized within a few layers of the surface., Comment: 11 pages, 3 figures

We report studies on the Ba2CuO4- y superconductor (1) with features including compressed local coordination and extreme over-doping level, etc.; while such behaviors are not favorable for superconductivity in previous cuprates (2), Yamamoto (3) raises an inquiry on one of these features: The compressed local octahedron. We have solid evidence to show that what we discussed in our paper has nothing to do with his speculation. There are 2 types of “214” structures with a CuO2 plane, i.e., the T phase based on La2CuO4 and the T′ phase based on Nd2CuO4 due to the different charge reservoir substructures, the rock-salt type for the former and the fluorite type for the latter. The relative strong Coulomb attraction interaction in the rock-salt layer over … [↵][1]1To whom correspondence may be addressed. Email: Jin{at}iphy.ac.cn. [1]: #xref-corresp-1-1

Drug dependence is a ‘chronic disease’ treatable through rehabilitation. Many drug addicts progress through a series of rehabilitation and relapsing episodes. In this paper, we formulate a mathematical model with n-alternate stages of rehabilitation and relapsing. The dynamics of drug abuse are treated as an infectious disease that spreads through a population. The model analysis shows that the model has two equilibria, the drug free equilibrium and the drug persistent equilibrium, that are both globally stable when the threshold $${\mathcal {R}}_{0}1$$ respectively. The model is fitted to data on individuals under repeated rehabilitation and parameter values that give the best fit chosen. The projections carried out the long term trends of proportions for repeated rehabilitants. The relative impact for each subgroup is determined to find out which population subgroup is responsible for a disproportionate number of initiations. The results have huge implications to designing policies aligned to rehabilitation processes.

Conventional superconductivity, as used in this review, refers to electron-phonon coupled superconducting electron-pairs described by BCS theory. Unconventional superconductivity refers to superconductors where the Cooper pairs are not bound together by phonon exchange but instead by exchange of some other kind, e. g. spin fluctuations in a superconductor with magnetic order either coexistent or nearby in the phase diagram. Such unconventional superconductivity has been known experimentally since heavy fermion CeCu2Si2, with its strongly correlated 4f electrons, was discovered to superconduct below 0.6 K in 1979. Since the discovery of unconventional superconductivity in the layered cuprates in 1986, the study of these materials saw Tc jump to 164 K by 1994. Further progress in high temperature superconductivity would be aided by understanding the cause of such unconventional pairing. This review compares the fundamental properties of 9 unconventional superconducting classes of materials - from 4f-electron heavy fermions to organic superconductors to classes where only three known members exist to the cuprates with over 200 examples, with the hope that common features will emerge to help theory explain (and predict!) these phenomena. In addition, three new emerging classes of superconductors (topological, interfacial [e. g. FeSe on SrTiO3], and H2S under high pressure) are briefly covered, even though their conventionality is not yet fully determined., accepted for publication in Advances in Physics; comparison of 9 unconventional superconducting classes of materials, plus 3 emerging classes of superconductors whose conventionality is still under discussion; 30 figures, 13 tables, 712 references. This version has minor typographical errors fixed

Nitrogen relations of natural and disturbed tropical plant communities in northern Australia (Kakadu National Park) were studied. Plant and soil N characteristics suggested that differences in N source utilisation occur at community and species level. Leaf and xylem sap N concentrations of plants in different communities were correlated with the availability of inorganic soil N (NH4+ and NO3-). In general, rates of leaf NO3- assimilation were low. Even in communities with a higher N status, including deciduous monsoon forest, disturbed wetland, and a revegetated mine waste rock dump, levels of leaf nitrate reductase, xylem and leaf NO3 levels were considerably lower than those that have been reported for eutrophic communities. Although NO3- assimilation in escarpment and eucalypt woodlands, and wetland, was generally low, within these communities there was a suite of species that exhibited a greater capacity for NO3- assimilation. These high-NO3- species were mainly annuals, resprouting herbs or deciduous trees that had leaves with high N contents. Ficus, a high-NO3- species, was associated with soil exhibiting higher rates of net mineralisation and net nitrification. Low-NO3- species were evergreen perennials with low leaf N concentrations. A third group of plants, which assimilated NO3- (albeit at lower rates than the high-NO3- species), and had high-N leaves, were leguminous species. Acacia species, common in woodlands, had the highest leaf N contents of all woody species. Acacia species appeared to have the greatest potential to utilise the entire spectrum of available N sources. This versatility in N source utilisation may be important in relation to their high tissue N status and comparatively short life cycle. Differences in N utilisation are discussed in the context of species life strategies and mycorrhizal associations.

Although the pairing mechanism of Fe-based superconductors (FeSCs) has not yet been settled with consensus with regard to the pairing symmetry and the superconducting (SC) gap function, the vast majority of experiments support the existence of spin-singlet sign-changing s-wave SC gaps on multi-bands ([Formula: see text]-wave state). This multi-band [Formula: see text]-wave state is a very unique gap state per se and displays numerous unexpected novel SC properties, such as a strong reduction of the coherence peak, non-trivial impurity effects, nodal-gap-like nuclear magnetic resonance signals, various Volovik effects in the specific heat (SH) and thermal conductivity, and anomalous scaling behaviors with a SH jump and condensation energy versus T

Although the pairing mechanism of the Fe-based superconductors (FeSCs) has not yet been settled with a consensus, as to the pairing symmetry and the superconducting (SC) gap function, the abundant majority of experiments are supporting for the spin-singlet sign-changing s-wave SC gaps on multibands ($s^{\pm}$-wave state). This multiband $s^{\pm}$-wave state is a very unique gap state {\it per se} and displays numerous unexpected novel SC properties such as a strong reduction of the coherence peak, non-trivial impurity effects, nodal-gap-like nuclear magnetic resonance (NMR) signals, various Volovik effects in the specific heat (SH) and thermal conductivity, and anomalous scaling behaviors with the SH jump and the condensation energy vs. $T_c$, etc. In particular, many of these non-trivial SC properties can be easily mistaken as evidence for a nodal gap state such as a d-wave gap. In this review, we provide detailed explanations of theoretical principles for the various non-trivial SC properties of the $s^{\pm}$-wave pairing state, and then critically compare the theoretical predictions with the experiments of the FeSCs. This will provide a pedagogical overview of how much we can coherently understand the wide range of different experiments of the FeSCs within the $s^{\pm}$-wave gap model., Comment: 82 pages, 51 figures

The transition metal dichalcogenide 1T-TaS$_2$ is well known to harbor a rich variety of charge density wave (CDW) distortions which are correlated with underlying lattice atom modulations. The long range CDW phases extend throughout the whole crystal and terminate with charge displacements at the crystal boundaries. Here we report on the transport properties and capacitance characteristics of the interface between freshly exfoliated flakes of 1T-TaS$_2$ in intimate van der Waals contact with \textit{n}-type GaAs substrates. The extracted barrier parameters (ideality, barrier height and built-in potential) experience pronounced changes across the Mott-CDW transition in the 1T-TaS$_2$. The CDW-induced changes in barrier properties are well described by a bond polarization model which upon decreasing temperature gives rise to an increased potential drop across the interfacial region due to the localization of carriers and a decreased dielectric constant., Comment: 17 Pages, 6 figures, Accepted by Applied Physics Letters

Single crystals of Li(Fe1−xCox)As (x = 0.00, 0.02, 0.04, 0.06, 0.08 and 0.1) were grown by the Sn-flux method and their resistivity behaviors were investigated. As the Co concentration x increased, the superconducting transition temperature Tc as well as the residual resistivity ratio systematically decreased, indicating a monotonic doping of electron carriers. Upon the analysis of the Fermi-liquid behavior of the resistivity and by using the Kadowaki–Woods relation, the T2 coefficient of the resistivity A and the Sommerfeld coefficient γN were found to increase abruptly near x = 0.06. This is the point in the phase diagram at which the density of states at the Fermi energy (proportional to γN) is expected to be enhanced due to the collapse of the small hole-pockets. This result suggests that the Li(Fe1−xCox)As series at least up to x = 0.08 remain as compensated metals and their transport properties are determined by multi-band effects.

Unsafe injecting practices, blood exchange, the use of nonsterile needles, and other cutting instruments for tattooing are common in correctional institutions, resulting in a number of blood transmitted infections. A mathematical model for assessing the dynamics of HCV and HIV coinfection within correctional institutions is proposed and comprehensively analyzed. The HCV-only and HIV-only submodels are first considered. Analytical expressions for the threshold parameter in each submodel and the cointeraction are derived. Global dynamics of this coinfection shows that whenever the threshold parameter for the respective submodels and the coinfection model is less than unity, then the epidemics die out, the reverse condition implies disease persistence within correctional institutions. Numerical simulations using a set of plausible parameter values are provided to support analytical findings.

At ambient pressure, BiTeI is the first material found to exhibit a giant Rashba splitting of the bulk electronic bands. At low pressures, BiTeI undergoes a transition from trivial insulator to topological insulator. At still higher pressures, two structural transitions are known to occur. We have carried out a series of electrical resistivity and AC magnetic susceptibility measurements on BiTeI at pressure up to ~40 GPa in an effort to characterize the properties of the high-pressure phases. A previous calculation found that the high-pressure orthorhombic P4/nmm structure BiTeI is a metal. We find that this structure is superconducting with Tc values as high as 6 K. AC magnetic susceptibility measurements support the bulk nature of the superconductivity. Using electronic structure and phonon calculations, we compute Tc and find that our data is consistent with phonon-mediated superconductivity., Comment: 7 pages, 7 figures

One of the goals in understanding any new class of superconductors is to search for commonalities with other known superconductors. The present work investigates the superconducting condensation energy, $U$, in the iron based superconductors (IBSs), and compares their $U$ with a broad range of other distinct classes of superconductor, including conventional BCS elements and compounds and the unconventional heavy fermion, $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ru}{\mathrm{O}}_{4},\phantom{\rule{0.16em}{0ex}}\mathrm{L}{\mathrm{i}}_{0.1}\mathrm{ZrNCl},\phantom{\rule{0.16em}{0ex}}\ensuremath{\kappa}{\text{-(BEDT-TTF})}_{2}\mathrm{Cu}(\mathrm{NCS}{)}_{2}$, and optimally doped cuprate superconductors. Surprisingly, both the magnitude and ${T}_{c}$ dependence $(U\ensuremath{\propto}{T}_{c}^{3.4\ifmmode\pm\else\textpm\fi{}0.2})$ of $U$ are---contrary to the previously observed behavior of the specific heat discontinuity at ${T}_{c}$, $\ensuremath{\Delta}C$---quite similar in the IBS and BCS materials for ${T}_{c}g1.4$ K. In contrast, the heavy fermion superconductors' $U$ vs ${T}_{c}$ are strongly (up to a factor of 100) enhanced above the IBS/BCS while the cuprate superconductors' $U$ are strongly (factor of 8) reduced. However, scaling of $U$ with the specific heat \ensuremath{\gamma} (or $\mathrm{\ensuremath{\Delta}}C$) brings all the superconductors investigated onto one universal dependence upon ${T}_{c}$. This apparent universal scaling $U/\phantom{\rule{0.0pt}{0ex}}\ensuremath{\gamma}\ensuremath{\propto}{T}_{c}^{2}$ for all superconductor classes investigated, both weak and strong coupled and both conventional and unconventional, links together extremely disparate behaviors over almost seven orders of magnitude for $U$ and almost three orders of magnitude for ${T}_{c}$. Since $U$ has not yet been explicitly calculated beyond the weak coupling limit, the present results can help direct theoretical efforts into the medium and strong coupling regimes.

Background Dependence on methamphetamine remains one of the major health and social problem in the Western Cape province of South Africa. We consider a mathematical model that takes into account two forms of rehabilitation, namely; inpatient and outpatient. We examine the trends of these two types of rehabilitation. We also seek to investigate the global dynamics of the developed methamphetamine epidemic model. Methods The model is designed by likening the initiation process to an infection that spreads in a community through interactions between methamphetamine users and non-users. We make use of Lyapunov functions obtained from a suitable combination of common quadratic and Volterra-type functions to establish the global stability of the methamphetamine-persistent steady state. The least squares curve fit routine (lsqcurvefit) in Matlab with optimization is used to estimate the parameter values. Results The model analysis shows that the model has two equilibria, the methamphetamine free equilibrium and the methamphetamine persistent equilibrium, that are both globally stable when the threshold \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathcal {R}_a1$$\end{document}Ra>1, respectively. Upon fitting the model to data on drug users under rehabilitation, parameter values that give the best fit were obtained. The projections carried out the long term trends of these forms of rehabilitation. Conclusion The results suggest that inpatient rehabilitation programs have an increased potential of enhancing the chances of recovery for methamphetamine addicts.

Kamihara and coworkers' report of superconductivity at Tc = 26 K in fluorine-doped LaFeAsO inspired a worldwide effort to understand the nature of the superconductivity in this new class of compounds. These iron pnictide and chalcogenide (FePn/Ch) superconductors have Fe electrons at the Fermi surface, plus an unusual Fermiology that can change rapidly with doping, which lead to normal and superconducting state properties very different from those in standard electron-phonon coupled 'conventional' superconductors. Clearly superconductivity and magnetism/magnetic fluctuations are intimately related in the FePn/Ch - and even coexist in some. Open questions, including the superconducting nodal structure in a number of compounds, abound and are often dependent on improved sample quality for their solution. With Tc values up to 56 K, the six distinct Fe-containing superconducting structures exhibit complex but often comparable behaviors. The search for correlations and explanations in this fascinating field of research would benefit from an organization of the large, seemingly disparate data set. This review attempts to provide an overview, using numerous references, with a focus on the materials and their superconductivity., Comment: 30 figures, 4 tables, approximately 600 references; to appear in Rev. Mod. Phys

The specific heat of single crystal hole-doped Ca0.33Na0.67Fe2As2, T-c(onset) = 33.7 K, was measured from 0.4 to 40 K. The discontinuity in the specific heat at T-c, Delta C, divided by T-c is 105 +/- 5 mJ/mol K-2, consistent with values found previously for hole-doped Ba0.6K0.4Fe2As2 and somewhat above the general trend for Delta C/T-c vs T-c for the iron based superconductors established by Bud'ko, Ni and Canfield. The usefulness of measured values of Delta C/T-c, as an important metric for the quality of samples is discussed. (C) 2014 Elsevier Ltd. All rights reserved.

Recent superconducting transition temperatures (Tc) over 100 K for monolayer FeSe on SrTiO3 have renewed interest in the bulk parent compound. In KCl:AlCl3 flux-transport-grown crystals of FeSe0.94Be0.06, FeSe0.97Be0.03 and, for comparison, FeSe, this work reports doping of FeSe using Be, among the smallest of possible dopants, corresponding to an effective chemical pressure. According to lattice parameter measurements, 6% Be doping shrank the tetragonal FeSe lattice equivalent to a physical pressure of 0.75 GPa. Using this flux-transport method of sample preparation, 6% of Be was the maximum amount of dopant achievable. At this maximal composition of FeSe0.94Be0.06, the lattice unit cell shrinks by 2.4%, Tc - measured in the bulk via specific heat - increases by almost 10%, the Tc vs pressure behavior shifts its peak Tconset downwards by ~1 GPa, the high temperature structural transition around TS = 89 K increases by 1.9 K (in contrast to other dopants in FeSe which uniformly depress TS), and the low temperature specific heat gamma increases by 10 % compared to pure FeSe. Also, upon doping by 6% Be the residual resistivity ratio, rho(300K)/rho(T->0), increases by almost a factor of four, while rho(300K)/rho(T=Tc+) increases by 50%., accepted by Journal of Physics: Condensed Matter

Specific heat of flux-grown single crystals of YbIr2 in zero and applied magnetic field indicates a more complicated magnetic behavior than was inferred from earlier magnetic susceptibility measurements. The possibility of defect-induced Kondo behavior mixed together with some sort of antiferromagnetic local order is discussed.

We report on X-ray powder diffraction, magnetic susceptibility, electrical resistivity, and specific heat measurements on samples of Ce1-xLaxPt3Si and CePt3Si1+δ in order to better understand this unusual heavy Fermion superconductor’s normal and superconducting state properties. By suppressing the antiferromagnetic transition, TN = 2.2 K, using La-doping on the Ce-site in CePt3Si, we find that in Ce1-xLaxPt3Si, x ≥ 0.8, ρ, χ, and C/T show non-Fermi liquid temperature dependences. C/T ~ Tα with α ~ 1 for the temperature range of 0.3–3 K while low-temperature (2–20 K) susceptibility data follow 1/χ−1/χ0 = aTη behavior with η = 0.36. In addition, χ and C/T exhibit single-ion behavior in this composition range (x ≥ 0.8), i.e. the measured values expressed per Ce-mole are independent of x. Via doping the Si-site with a small excess—2–4—of Si, we present specific heat data for the bulk superconducting transition at Tc ~ 0.8 K showing that this excess sharpens the transition, obviating the need for annealing. Measurements of the X-ray diffraction patterns, ρ, χ, and C/T of these CePt3Si1+δ samples, when compared to similar measurements on annealed CePt3Si samples, indicate that the microscopic mechanism for the strengthening and sharpening of ΔC(Tc) with Si-excess may be similar to that responsible in the annealed material.

Previous research has found that the pairing symmetry in the iron-based superconductor Ba1-xKxFe2As2 changes from nodeless s-wave near optimally doped, x≈0.4-0.55 and Tc>30 K, to nodal (either d-wave or s-wave) at the pure endpoint, x=1 and Tc

Co-doped BaFe2As2 has been previously shown to have an unusually significant improvement of Tc (up to 2 K, or almost 10%) with annealing 1-2 weeks at 700 or 800 C, where such annealing conditions are insufficient to allow significant atomic diffusion. While confirming similar behavior in optimally Co-doped SrFe2As2 samples, the influence on Tc of strain induced by grinding to ~50 micron sized particles, followed by pressing the powder into a pellet using 10 kbar pressure, was found to increase the annealed transition width of 1.5 K by approximately a factor of ten. Also, the bulk discontinuity in the specific heat at Tc, deltaC, on the same pellet sample was completely suppressed by grinding. This evidence for a strong sensitivity of superconductivity to strain was used to optimize single crystal growth of Co-doped BaFe2As2. This strong dependence (both positive via annealing and negative via grinding) of superconductivity on strain in these two iron based 122 structure superconductors is compared to the unconventional heavy Fermion superconductor UPt3, where grinding is known to completely suppress superconductivity, and to recent reports of strong sensitivity of Tc to damage induced by electron-irradiation-induced point defects in other 122 structure iron-based superconductors, Ba(Fe0.76Ru0.24)2As2 and Ba1-xKxFe2As2. Both the electron irradiation and the introduction of strain by grinding are believed to only introduce non-magnetic defects, and argue for unconventional superconducting pairing.

The cubic A15 structure metals, with over 60 distinct member compounds, held the crown of highest Tc superconductor starting in 1954 with the discovery of Tc=18 K in Nb3Sn. Tc increased over the next 20 years until the discovery in 1973 of Tc = 22.3 K (optimized to approximately 23 K a year later) in sputtered films of Nb3Ge. Attempts were made to produce - via explosive compression - higher (theorized to be 31-35 K) transition temperatures in not stable at ambient conditions A15 Nb3Si. However, the effort to continue the march to higher Tc values in A15 Nb3Si only resulted in a defect-suppressed Tc of 19 K by 1981. Focus in superconductivity research partially shifted with the advent of heavy Fermion superconductors (CeCu2Si2, UBe13, and UPt3 discovered in 1979, 1983 and 1984 respectively) and further shifted away from A15 superconductors with the discovery of the perovskite structure cuprate superconductors in 1986 with Tc=35 K. However, the A15 superconductors, and specifically doped Nb3Sn, are still the material of choice today for most applications where high critical currents (e. g. magnets with dc persistent fields up to 21 T) are required. Thus, this article discusses superconductivity, and the important physical properties and theories for the understanding thereof, in the A15 superconductors which held the record Tc for the longest time (32 years) of any known class of superconductor since the discovery of Tc=4.2 K in Hg in 1911. The discovery in 2008 of Tc=38 K at 7 kbar in A15 Cs3C60 (properly a member of the fullerene superconductor class), which is an insulator at 1 atm pressure and otherwise also atypical of the A15 class of superconductors, will be briefly discussed., Comment: contribution to the special issue on Superconductivity and Its Applications in Physica C, Volume 514

The editors have dedicated this special issue on superconducting materials "to Ted Geballe in honor of his numerous seminal contributions to the field of superconducting materials over more than 60 years, on the year of his 95th birthday." Here, as an executive summary, are just a few highlights of his research in superconductivity, leavened with some anecdotes, and ending with some of Teds general insights and words of wisdom., Comment: Contribution to the special issue on Superconductivity and Its Applications in Physica C, volume 514

In the approximately four years since the first review on this subject appeared, a large amount of additional work---both experimental and theoretical---has been accomplished in the field. In an effort to keep the original review experimentally current, the compilation of resistivity, susceptibility, and specific-heat data that was presented in the original ten-page Table II is herein updated with approximately 60 new systems and 70 new references, adding eight new pages to the compilation. It is worth noting that approximately 15% of these new entries in fact predate the original review's publication; certainly the literature searches employed for this update will also have missed work worthy of inclusion.

The question of whether the temperature dependences of the magnetic susceptibility and the electrical resistivity of UCu5−xNix near, and away from, the QCP where TN is suppressed to T = 0 are due to intrinsic fluctuations or are dominated by disorder effects is addressed. The interesting ρ ∝ log T behavior below 2 K present for 0.75 ⩽ x ⩽ 1.1 is analyzed and discussed.

Using double-hit hot compression tests, the softening behavior of 304 H stainless steel was studied during unloading. The prestrains used were associated with the initiation of dynamic recrystallization (DRX) (e c), the peak strain (e p), 1/2 (e c+e p), the strain at maximum softening rate (e i), and the onset of steady state flow (e s). The following conditions of deformation were used: T=1000 °C, 1050 °C, and 1100 °C, $$\dot \varepsilon $$ =0.01 and 0.1 s−1, and delay times of 0.3 to 1000 seconds. To define the above important strains, single-hit hot compression tests were performed over a wider range of deformation conditions than the double-hit ones—i.e., 900 °C to 1100 °C and $$\dot \varepsilon $$ =0.01 to 1 s−1. The results show that a transition strain (e*) separates the strain-dependent range of postdynamic softening from the strain-independent range. At strains between e c and e*, both metadynamic and static recrystallization contribute to interhit softening. The value of e* obtained in this work was e*=4/3 e p. It was also found that the strain hardening rate was identical at all the critical strains (e*) and took the value −22 MPa.

We report the low-temperature specific heats of NpCu 5-x Pd x (x = 0, 0.5, 1.0, and 1.5), the "plus one f-electron" analogs to the well-studied non-Fermi liquid (nFl) system UCu 5-x Pd x . The Np materials were shown to form in the same AuBe 5 structure type as the U pseudobinary alloys. A number of differences between the Np and U materials are found. The magnetic transition at 15 K in the U system is evidently suppressed to lower temperatures in the Np analog, and the low-temperature C/T values are strongly enhanced in the NpCu 5-x Pd x (x = 1.0 and 1.5) alloys vs. their U counterparts. Finally, NpCu 4 Ni appears to show non-Fermi liquid behavior similar to that of the NpCu 5-x Pd x system, just as UCu 4 Ni is quite similar to UCu 4 Pd in its nFl behavior.

The Upper North Bosque River (UNBR) watershed is under a total maximum daily load (TMDL) mandate to reduce loading of soluble phosphorus (P) in impaired river segments. To address these problems, Texas A&M University researchers have developed a Best Management Practice (BMP) that removes excess nutrients from impaired watersheds through turfgrass sod. Harvest of manure-grown sod removes a thin layer of topsoil along with any residual P in this soil layer. In order to assess the impact of the turfgrass BMP on a watershed scale, the Soil and Water Assessment Tool (SWAT) was used to predict water quality changes among four scenarios in the UNBR watershed. The SWAT model was modified to incorporate turfgrass harvest routines for simulation of manure and soil P export during harvest of turfgrass sod. SWAT simulations of the four BMP scenarios predicted reductions of 20% to 36% for instream P loads in the UNBR depending on manure P rate and areas allotted to sod. In addition, total N load was reduced on average by 31% and sediment load declined on average 16.7% at the watershed outlet. The SWAT model predicted up to 176 kg/ha P was removed per harvest of sod top-dressed with 100 kg manure P/ha. Export increased to 258 kg/ha of P per harvest for the manure P application rate of 200 kg/ha. Depending on the implementation scenario, simulations indicated the turfgrass BMP could export between 262 and 784 metric tons of P out of the UNBR watershed every year.