Structural origins of electronic conduction in amorphous copper-doped alumina

We perform an {\it ab initio} modeling of amorphous copper-doped alumina (a-Al$_2$O$_3$:Cu), a prospective memory material based on resistance switching, and study the structural origin of electronic conduction in this material. We generate molecular dynamics based models of a-Al$_2$O$_3$:Cu at various Cu-concentrations and study the structural, electronic and vibrational properties as a function of Cu-concentration. Cu atoms show a strong tendency to cluster in the alumina host, and metallize the system by filling the band gap uniformly for higher Cu-concentrations. We also study thermal fluctuations of the HOMO-LUMO energy splitting and observe the time evolution of the size of the band gap, which can be expected to have an important impact on the conductivity. We perform a numerical computation of conduction pathways, and show its explicit dependence on Cu connectivity in the host. We present an analysis of ion dynamics and structural aspects of localization of classical normal modes in our models

Ballistic magnon heat conduction and possible Poiseuille flow in the helimagnetic insulator Cu2_2OSeO3_3

We report on the observation of magnon thermal conductivity $\kappa_m\sim$ 70 W/mK near 5 K in the helimagnetic insulator Cu$_2$OSeO$_3$, exceeding that measured in any other ferromagnet by almost two orders of magnitude. Ballistic, boundary-limited transport for both magnons and phonons is established below 1 K, and Poiseuille flow of magnons is proposed to explain a magnon mean-free path substantially exceeding the specimen width for the least defective specimens in the range 2 K $<T<$ 10 K. These observations establish Cu$_2$OSeO$_3$ as a model system for studying long-wavelength magnon dynamics.Comment: 10pp, 9 figures, accepted PRB (Editor's Suggestion

Strain-controlled band engineering and self-doping in ultrathin LaNiO3_3 films

We report on a systematic study of the temperature-dependent Hall coefficient and thermoelectric power in ultra-thin metallic LaNiO$_3$ films that reveal a strain-induced, self-doping carrier transition that is inaccessible in the bulk. As the film strain varies from compressive to tensile at fixed composition and stoichiometry, the transport coefficients evolve in a manner strikingly similar to those of bulk hole-doped superconducting cuprates with varying doping level. Density functional calculations reveal that the strain-induced changes in the transport properties are due to self-doping in the low-energy electronic band structure. The results imply that thin-film epitaxy can serve as a new means to achieve hole-doping in other (negative) charge-transfer gap transition metal oxides without resorting to chemical substitution

Heat capacity, thermal expansion and heat transport in the Han Blue (BaCuSi 4 O 10 ): Observation of structural phase transitions

a b s t r a c t Structural phase transitions at 87 K and 103 K are reported for single-crystalline Han Blue (BaCuSi 4 O 10 ) by means of high-resolution thermal-expansion, thermal conductivity and heat capacity measurements. The phase transition at 103 K results in differing lengths of the a and b lattice parameters, and thus a lowering of the crystallographic symmetry. Negative thermal-expansion coefficients are observed perpendicular to the c-axis over a wide temperature range The thermal conductivity is small, and decreases with temperature, both of which suggest strong scattering of heat-carrying phonons. The principle Grüneisen parameter within the plane and perpendicular to it was determined to be γ 1 ¼ À1.09 and γ 3 ¼1.06 at room temperature; the bulk Grüneisen parameter is γ¼0.10. The results are consistent with the presence of low-energy vibrations associated with the collective motions of CuO 4 and Si 4 O 10 polyhedral subunits

Magnetic-field dependence of low-energy magnons, anisotropic heat conduction, and spontaneous relaxation of magnetic domains in the cubic helimagnet ZnCr2Se4

Anisotropic low-temperature properties of the cubic spinel helimagnet ZnCr2Se4 in the single-domain spin-spiral state are investigated by a combination of neutron scattering, thermal conductivity, ultrasound velocity, and dilatometry measurements. In an applied magnetic field, neutron spectroscopy shows a complex and nonmonotonic evolution of the spin-wave spectrum across the quantum-critical point that separates the spin-spiral phase from the field-polarized ferromagnetic phase at high fields. A tiny spin gap of the pseudo-Goldstone magnon mode, observed at wave vectors that are structurally equivalent but orthogonal to the propagation vector of the spin helix, vanishes at this quantum critical point, restoring the cubic symmetry in the magnetic subsystem. The anisotropy imposed by the spin helix has only a minor influence on the lattice structure and sound velocity but has a much stronger effect on the heat conductivities measured parallel and perpendicular to the magnetic propagation vector. The thermal transport is anisotropic at T < 2 K, highly sensitive to an external magnetic field, and likely results directly from magnonic heat conduction. We also report long-time thermal relaxation phenomena, revealed by capacitive dilatometry, which are due to magnetic domain motion related to the destruction of the single-domain magnetic state, initially stabilized in the sample by the application and removal of magnetic field. Our results can be generalized to a broad class of helimagnetic materials in which a discrete lattice symmetry is spontaneously broken by the magnetic order.Comment: 13 pages, 8 figures + Supplemental Materia

Challenges in diabetes mellitus type 2 management in Nepal: a literature review

BACKGROUND AND OBJECTIVES: Diabetes has become an increasingly prevalent and severe public health problem in Nepal. The Nepalese health system is struggling to deliver comprehensive, quality treatment and services for diabetes at all levels of health care. This study aims to review evidence on the prevalence, cost and treatment of diabetes mellitus type 2 and its complications in Nepal and to critically assess the challenges to be addressed to contain the epidemic and its negative economic impact. DESIGN: A comprehensive review of available evidence and data sources on prevalence, risk factors, cost, complications, treatment, and management of diabetes mellitus type 2 in Nepal was conducted through an online database search for articles published in English between January 2000 and November 2015. Additionally, we performed a manual search of articles and reference lists of published articles for additional references. RESULTS: Diabetes mellitus type 2 is emerging as a major health care problem in Nepal, with rising prevalence and its complications especially in urban populations. Several challenges in diabetes management were identified, including high cost of treatment, limited health care facilities, and lack of disease awareness among patients. No specific guideline was identified for the prevention and treatment of diabetes in Nepal. CONCLUSIONS: We conclude that a comprehensive national effort is needed to stem the tide of the growing burden of diabetes mellitus type 2 and its complications in Nepal. The government should develop a comprehensive plan to tackle diabetes and other non-communicable diseases supported by appropriate health infrastructure and funding

White Paper: Shifting the goal post - from high impact journals to high impact data

The purpose of this white paper is to provide an overview of the ongoing initiatives at center level to respond to changing public expectations and to the challenge of improving the conduct of science by making research data widely available. We also attempt to provide a framework for implementing open access for research data to maximize CGIAR’s impact on development. The remainder of this paper proceeds as follows; firstly a summary of the diversity of research data produced by the centers is given, followed by an overview of the existing infrastructure for data management for each Center. Secondly, some of the limitations and barriers faced by the centers in their process to mainstream research data publishing are addressed. The paper concludes with recommendations for how these limitations and barriers can be tackled

Graphene Transistor as a Probe for Streaming Potential

We explore the dependence of electrical transport in a graphene field effect transistor (GraFET) on the flow of the liquid within the immediate vicinity of that transistor. We find large and reproducible shifts in the charge neutrality point of GraFETs that are dependent on the fluid velocity and the ionic concentration. We show that these shifts are consistent with the variation of the local electrochemical potential of the liquid next to graphene that are caused by the fluid flow (streaming potential). Furthermore, we utilize the sensitivity of electrical transport in GraFETs to the parameters of the fluid flow to demonstrate graphene-based mass flow and ionic concentration sensing. We successfully detect a flow as small as~70nL/min, and detect a change in the ionic concentration as small as ~40nM.Comment: 6 pages, 4 figure