Charge-orbital density wave and superconductivity in the strong spin-orbit coupled IrTe2:Pd

Using transmission electron microscopy, the anomalies in resistivity and magnetic susceptibility at ~262 K in IrTe2 are found to accompany the superlattice peaks with q[over q=(1/5,0,-1/5). The wave vector is consistent with our theoretical calculation for the Fermi surface nesting vector, indicating that the ~262 K transition is of the charge-orbital density wave (DW) type. We also discovered that both Pd intercalation and substitution induce bulk superconductivity with T(c) up to ~3 K, which competes with DW in a quantum critical pointlike manner.     

Nanoparticle collisions in the gas phase in the presence of singular contact potentials

Collisional growth and ionization is commonplace for gas phase nanoparticles (i.e., in aerosols). Nanoparticle collisions in atmospheric pressure environments occur in the mass transfer transition regime, and further attractive singular contact potentials (which arise when modeling nanoparticles as condensed matter and for which the potential energy approaches -∞ when two entities contact) often have a non-negligible influence on collision processes. For these reasons collision rate calculations for nanoparticles in the gas phase are not straightforward. We use mean first passage time calculations to develop a simple relationship to determine the collision rate in the gas phase, accounting for the influences of both the transition regime and singular contact potentials (specifically the non-retarded van der Waals and image potentials). In the presented analysis, methods to determine the degree of enhancement in collision rate due to attractive singular potentials in the continuum (diffusive) regime, η(C), and the degree of enhancement in the free molecular (ballistic) regime, η(FM), are first reviewed. Accounting for these enhancement factors, with mean first passage time calculations it is found that the collision rate for gas phase nanoparticles with other gas phase entities can be determined from a relationship between the dimensionless collision rate coefficient, H, and the diffusive Knudsen number, Kn(D), i.e., the ratio of the mean collision persistence distance to the collision length scale. This coincides with the H(Kn(D)) relationship found to appropriately describe collisions between entities interacting via a hard-sphere potential, but with η(C) and η(FM) incorporated into the definitions of both H and Kn(D), respectively. The H(Kn(D)) relationship is compared to the predictions of flux matching theory, used prevalently in prior work for collision rate calculation, and through this comparison it is found that at high potential energy to thermal energy ratios, flux matching theory predictions underestimate the true collision rate. Finally, a series of experimental measurements of nanoparticle-nanoparticle collision rates are compared to the determined H(Kn(D)) expression, considering that nanoparticles interact via non-retarded van der Waals potentials. Very good agreement is found with collision rates inferred from experiments, with almost all measured values from four separate studies within 25% of model predictions.     

Factors influencing the QMF resolution for operation in stability zones 1 and 3

This study uses a computer model to simulate a quadrupole mass filter (QMF) instrument under different operating conditions for Mathieu stability zones 1 and 3. The investigation considers the factors that limit the maximum resolution (R_max), which can be obtained for a given QMF for a particular value of scan line. Previously, QMF resolution (R) has been found to be dependent on number (N) of radio frequency (rf) cycles experienced by the ions in the mass filter, according to R = N ⁿ /K, where n and K are the constants. However, this expression does not predict the limit to QMF resolution observed in practice and is true only for the linear regions of the performance curve for QMF operation in zone 1 and zone 3 of the stability diagram. Here we model the saturated regions of the performance curve for QMF operation in zone 1 according to R = q(1 – 2c ^N )/∆q, where c is a constant and ∆q is the width of the intersection of the operating scan line with the stability zone 1, measured at q-axis of the Mathieu stability diagram. Also by careful calculations of the detail of the stability tip of zone 1, the following relationship was established between R_max and percentage U/V ratio: R _max   = q/(0.9330-0.00933U/V). For QMF operation in zone 3 the expression R = a – bc ^N simulates well the linear and saturated regions of the performance curve for a range of operational conditions, where a, b, and c are constants.     

An Analogue of Slepian Vectors on Boolean Hypercubes

Journal of Fourier Analysis and Applications - Analogues of Slepian vectors are defined for finite-dimensional Boolean hypercubes. These vectors are the most concentrated in neighborhoods of the...     

Quantitative Estimation: One, Two, or Three Abilities?

The mathematics education literature refers to 3 types of quantitative estimation skill: numerosity, measurement, and computational estimation. The psychometric literature includes a confusing array of tests intended to define quantitative estimation. This study examined relations among tests for numerosity, measurement, and computational estimation, and recognized tests for numerical facility and quantitative reasoning using principal components analysis. 2 components were identified. The first component aligned computational estimation with numerical facility and general quantitative reasoning. The second component included the tests of numerosity and measurement estimation. It was suggested that this second component might be related to spatial ability. Implications for mathematics education and assessment are discussed.     

Asymptotic symmetries in general relativity

In the context of a recent reformulation of the theory of gravitational radiation from bounded sources in which both shearing and shear-free radiation is manifestly present, we derive the asymptotic symmetry group of the spacetime. The group we obtain contains the Bondi-Metzner-Sachs group as a subgroup. This observation is relevant to the problem of the mysterious role of shear-free radiation in the Bondi-Sachs approach to the theory of gravitational radiation from bounded sources.     

The mathematical miscellany (1836–1839)

Charles Gill (1805–1855), who immigrated to the United States from England in 1830, began to edit The Mathematical Miscellany (1836–1839) while teaching on Long Island (New York, U.S.A.). Most of America's best mathematicians of the day were contributors, including Benjamin Peirce, Theodore Strong, and William Lenhart. The contents of the journal and the correspondence between Gill and its contributors, as well as the journal's troubles, give insights into American mathematics in the middle of the 19th century.     

The maximum reliability location problem and α-reliablep-center problem: Derivatives of the probabilistic location set covering problem

In the last several years, the modeling of emergency vehicle location has focussed on the temporal availability of the vehicles. Vehicles are not available for service when they are engaged in earlier calls. To incorporate this dynamic aspect into facility location decisions, models have been developed which provide additional levels of coverage. In this paper, two new models are derived from the probabilistic location set covering problem. These models allow the examination of the relationships between the number of facilities being located, the reliability that a vehicle will be available, and a coverage standard. In addition, these models incorporate sectoral specific estimates of the availability of the vehicles. Solution of these models reveals that the use of sectoral estimates leads to facility locations which are distributed to a greater spatial extent over the region to be serviced.     

Profiling isoflavonoids found in legume root extracts using capillary electrophoresis

Legumes such as alfalfa (Medicago sativa L.), barrel medic (Medicago truncatula), white sweet clover (Melilotus alba) and fenugreek (Trigonella graecum), normally accumulate (-)-medicarpin and its malonated glucose conjugate as natural inhibitors of fungal pathogens. These plants also accumulate the biosynthetic precursor formononetin as well as the malonated glycoside. We were interested in developing a robust high-throughput method to quantitate the levels of these two isoflavonoids, both free and conjugated, in legume root extracts, for use in screening for mutant plants accumulating altered levels of these compounds. Capillary electrophoresis was examined as an alternative to current high-performance liquid chromatography (HPLC) methods to generate isoflavonoid profiles. The developed assay used micellar electrokinetic capillary chromatography (MEKC) to provide the required selectivity in complex root extracts. The addition of 1,2-hexanediol to the sodium dodecyl sulfate (SDS) electrolyte provided improved resolution of adjacent isoflavonoids. We examined the role of several factors including sample preparation, buffer composition, buffer pH, and organic component in the injected sample. The use of capillaries with longer path lengths were also examined to increase sensitivity. A comparison of results obtained using MEKC and HPLC showed good correlation in the relative amounts of the isoflavonoids studied.