Conductivity and Structure of Superionic Composite (AgI)0.6(NaPO3)0.4

Superionic conductors are of considerable interest from both application and fundamental points of view. Superionic solid electrolytes can be used for batteries, fuel cells and sensors. We have used melt quenching to make a new superionic composite (AgI)0.6(NaPO3)0.4 which exhibits an ionic conductivity of about 2 x 10-4 S/cm at ambient temperature. The conductivity of crystalline AgI and NaPO3 glass are lower of orders of magnitude. (AgI)0.6(NaPO3)0.4 is a composite material containing both crystalline and glass phases. The paper presents the conductivity as a function of temperature measured by impedance spectroscopy and the crystal structure performed by a high resolution powder diffractometer, VEGA at the Neutron Science Laboratory (KENS), KEK, Japan

Conductivity and Structure of Superionic Composite (AgI)0.6(NaPO3)0.4

Superionic conductors are of considerable interest from both application and fundamental points of view. Superionic solid electrolytes can be used for batteries, fuel cells and sensors. We have used melt quenching to make a new superionic composite (AgI)0.6(NaPO3)0.4 which exhibits an ionic conductivity of about 2 x 10-4 S/cm at ambient temperature. The conductivity of crystalline AgI and NaPO3 glass are lower of orders of magnitude. (AgI)0.6(NaPO3)0.4 is a composite material containing both crystalline and glass phases. The paper presents the conductivity as a function of temperature measured by impedance spectroscopy and the crystal structure performed by a high resolution powder diffractometer, VEGA at the Neutron Science Laboratory (KENS), KEK, Japan

Covering problems in edge- and node-weighted graphs

This paper discusses the graph covering problem in which a set of edges in an edge- and node-weighted graph is chosen to satisfy some covering constraints while minimizing the sum of the weights. In this problem, because of the large integrality gap of a natural linear programming (LP) relaxation, LP rounding algorithms based on the relaxation yield poor performance. Here we propose a stronger LP relaxation for the graph covering problem. The proposed relaxation is applied to designing primal-dual algorithms for two fundamental graph covering problems: the prize-collecting edge dominating set problem and the multicut problem in trees. Our algorithms are an exact polynomial-time algorithm for the former problem, and a 2-approximation algorithm for the latter problem, respectively. These results match the currently known best results for purely edge-weighted graphs.Comment: To appear in SWAT 201

Synthesis and Characterization of Stoichiometric Spinel-LiMn2O4

In this study, spinel LiMn2O4 powder was synthesized from LiOH.H2O and MnOx by conventional and mechanical alloying (MA) methods, followed by heat treatment at 800 °C in O2 for four hours with cooling to room temperature in the furnace at 60 °C/h. It is found that both samples do not show phase transition in low temperature, and this occurred for different reasons. In the MA sample, the presence of Fe as contamination increased the Mn valence and hindered the occurrence of phase transition. The conventional sample does not show phase transition at low temperature due to stoichiometric content, without any contamination. In general, the absence of phase transition occurred due to synthesis condition employed in this study

Crystallography and magnetism of the heavy-fermion compound YbBiPt

The super-heavy-fermion compound YbBiPt has the largest known linear specific-heat coefficient γ=8 J mol−1 K−2, and the source of this enormous ‘‘electronic’’ specific heat is of great current interest. Here we describe neutron-diffraction studies that indicate its previously reported crystallographic structure to be incorrect. We find that the Pt atom is on the unique site and can be thought of as an interstitial in a fictitious rock-salt structure YbBi, which can in turn be thought of as an ordered form of elemental bismuth. We find no evidence of disorder between sites, occupancy on the nominally vacant site, nor for any tetragonal or rhombohedral distortions or displacements. Furthermore, any ordered magnetic moment at low temperature must be less than 0.25μB. The sample contains 8.1 wt. % elemental Bi, and if this is typical of other samples, the previously published values for molar susceptibilities and specific heats should be scaled up by this amount to obtain the intrinsic properties of YbBiPt alone

Doping Dependence of Spin-Lattice Coupling and Two-Dimensional Ordering in Multiferroic Hexagonal Y₁₋ₓLuₓMnO₃ (0 ≤ x ≤ 1)

We have examined a complete phase diagram of Y1-x Lu xMnO3 with 0≤x≤1 by using bulk measurements and neutron-diffraction studies. With increasing Lu concentration, Curie-Weiss temperature and Neel temperature are found to increase continuously while the two-dimensional nature of short-range magnetic correlation persists even in the paramagnetic phase throughout the entire doping range. At the same time, the lattice constants and the unit-cell volume get contracted with Lu doping, i.e., chemical pressure effect. This decrease in the lattice constants and the unit-cell volume then leads naturally to an increased magnetic exchange interaction as found in our local spin-density approximation band calculations. We also discover that there is strong correlation in the temperature dependence of a volume anomaly at TN and the magnetic moments

Magnetism and Ion Diffusion in Honeycomb Layered Oxide K2_2Ni2_2TeO6_6: First Time Study by Muon Spin Rotation & Neutron Scattering

In the quest of finding novel and efficient batteries, a great interest has raised in K-based honeycomb layer oxide materials both for their fundamental properties and potential applications. A key issue in the realization of efficient batteries based on such compounds, is to understand the K-ion diffusion mechanism. However, investigation of potassium-ion (K$^+$) dynamics in materials using magneto-spin properties has so far been challenging, due to its inherently weak nuclear magnetic moment, in contrast to other alkali ions such as lithium and sodium. Spin-polarised muons, having a high gyromagnetic ratio, make the muon spin rotation and relaxation ($\mu$+SR) technique ideal for probing ions dynamics in weak magneto-spin moment materials. Here we report the magnetic properties and K+ dynamics in honeycomb layered oxide material of the K$_2$Ni$_2$TeO$_6$ using $\mu$+SR measurements. Our low-temperature $\mu$+SR results together with, with complementary magnetic susceptibility, find an antiferromagnetic transition at 26 K. Further $\mu$+SR studies performed at higher temperatures reveal that potassium ions (K$^+$) become mobile above 250 K and the activation energy for the diffusion process is Ea = 121(13) meV. This is the first time that K+ dynamics in potassium-based battery materials has been measured using $\mu$+SR. Finally our results also indicate an interesting possibility that K-ion self diffusion occurs predominantly at the surface of the powder particles. This opens future possibilities for improving ion diffusion and device performance using nano-structuring.Comment: 12 pages, 12 figure

Left-sided appendicitis in a patient with congenital gastrointestinal malrotation: a case report

<p>Abstract</p> <p>Background</p> <p>While appendicitis is the most common abdominal disease requiring surgical intervention seen in the emergency room setting, intestinal malrotation is relatively uncommon. When patients with asymptomatic undiagnosed gastrointestinal malrotation clinically present with abdominal pain, accurate diagnosis and definitive therapy may be delayed, possibly increasing the risk of morbidity and mortality. We present a case where CT was crucial diagnostically and helpful for pre-surgical planning in a patient presenting with an acute abdomen superimposed on complete congenital gastrointestinal malrotation.</p> <p>Case presentation</p> <p>A 46-year-old previously healthy male with four days of primarily left-sided abdominal pain, low-grade fevers, nausea and anorexia presented to the Emergency Department. His medical history was significant for poorly controlled diabetes and dyslipidemia. His white blood count at that time was elevated. Initial abdominal plain films suggested small bowel obstruction. A CT scan of the abdomen and pelvis was performed with oral and IV contrast to exclude diverticulitis, revealing acute appendicitis superimposed on congenital intestinal malrotation. Following consultation with the surgical team for surgical planning, the patient went on to laparoscopic appendectomy and did well postoperatively.</p> <p>Conclusion</p> <p>Atypical presentations of acute abdominal conditions superimposed on asymptomatic gastrointestinal malrotation can result in delays in delivery of definitive therapy and potentially increase morbidity and mortality if not diagnosed in a timely manner. Appropriate imaging can be helpful in hastening diagnosis and guiding intervention.</p