Crystal structures and freezing of dipolar fluids

We investigate the crystal structure of classical systems of spherical particles with an embedded point dipole at T=0. The ferroelectric ground state energy is calculated using generalizations of the Ewald summation technique. Due to the reduced symmetry compared to the nonpolar case the crystals are never strictly cubic. For the Stockmayer (i.e., Lennard-Jones plus dipolar) interaction three phases are found upon increasing the dipole moment: hexagonal, body-centered orthorhombic, and body-centered tetragonal. An even richer phase diagram arises for dipolar soft spheres with a purely repulsive inverse power law potential $\sim r^{-n}$. A crossover between qualitatively different sequences of phases occurs near the exponent $n=12$. The results are applicable to electro- and magnetorheological fluids. In addition to the exact ground state analysis we study freezing of the Stockmayer fluid by density-functional theory.Comment: submitted to Phys. Rev.

Modeling of electron emission processes accompanying Radon-α\alpha-decays within electrostatic spectrometers

Electrostatic spectrometers utilized in high-resolution beta-spectroscopy studies such as in the Karlsruhe Tritium Neutrino (KATRIN) experiment have to operate with a background level of less than 10^(-2) counts per second. This limit can be exceeded by even a small number of Rn-219 or Rn-220 atoms being emanated into the volume and undergoing alpha-decay there. In this paper we present a detailed model of the underlying background-generating processes via electron emission by internal conversion, shake-off and relaxation processes in the atomic shells of the Po-215 and Po-216 daughters. The model yields electron energy spectra up to 400 keV and electron multiplicities of up to 20 which are compared to experimental data.Comment: 7 figure

Exploring Race, Culture, and Identity Among Chinese Adoptees: “China Dolls,” “Bananas,” and “Honorary Whites”

When exploring culture, race, and identity, Chinese adoptees in the United States often can face numerous emotions, ranging from confusion, to curiosity, to celebratory. From honoring Chinese holidays, to wearing American-style clothing, to being called a banana , adoptees have a unique set of experiences when trying to navigate what it means to be Chinese, Chinese-American, and American. Through a series of interviews conducted with ten adult female Chinese adoptees within the U.S., this study investigates key themes related to cultural and racial identity formation. Key themes included exploring the different aspects of Chinese culture participants were exposed to, instances of racism participants faced, and discussions with their parents about various race issues both within the family and on a societal level. It was found that adoptees were exposed to a wide range of aspects related to Chinese culture, ranging from celebrating Chinese holidays, to learning Chinese language and dance, to simply eating at Chinese restaurants. It was also observed that the adoptees not only faced multiple forms of racism, especially microaggressions and stereotyping, but that having discussions surrounding racism and other race issues with their parents were mostly absent. The majority of the findings within the study were congruent with previous literature and research; however, it is strongly recommended that more research about the Chinese adoptee population should be continued in order to develop better resources for adoptees, their families, and others within the community

A critical review of modern approaches for multidimensional energy poverty measurement

Recent efforts to measure energy poverty more comprehensively attempt to redress the shortcomings of binary metrics that remain in common use. However, significant challenges remain both with the construction of the new measurement frameworks and their application. The paper presents an analysis of recent multidimensional measurement approaches and applications to draw inferences on the implications of applying these for the measurement of energy access and in informing policies aimed at improving it. The assessment suggests that despite progress having been made in capturing the multidimensional nature of energy poverty, the new measures are currently too complex to operationalize at the global level and too prescriptive to gain acceptance in diverse national contexts. Further efforts are thus required to consolidate and simplify the new frameworks for global tracking purposes, and to adapt and modify these to specific country contexts to inform national policy and planning. A subset of key energy poverty dimensions and uniform set of indicators need to be shortlisted for the purposes of global comparisons, while specific national tracking efforts can apply dimensions and thresholds most suited to accurately capture energy poverty and its drivers in a given context

You are what you measure! But are we measuring it right? An empiric analysis of energy access metrics based on a multi-tier approach in Bangladesh

Measuring energy access through binary indicators is insufficient, and often, even misleading. In this work, the SE4ALL global tracking framework, and the recently introduced ESMAP multi-tier approach, is critically discussed analyzing questionnaire based primary data from rural Bangladesh. The performance of different energy interventions is evaluated using the new tier framework. The challenges in its application lie in reliable data collection, adequate gradation of indicators, and an effective algorithm for the tier assignment based on the specified set of attributes. The study showcases very high sensitivities to parameter changes, different algorithms, and data requirements. The results reveal a clear trade-off between capturing the multi-dimensionality of energy access and the simplicity of an easy to use global framework. Suggestions to improve the measuring approach are made and conclusions are drawn for possible implications of the tier framework for different energy service offers in the market. Strengths and weaknesses of the present measurement scheme are discussed and country specific results interpreted through targeted gap analysis for future policy advice

Particle dynamics of a cartoon dune

The spatio-temporal evolution of a downsized model for a desert dune is observed experimentally in a narrow water flow channel. A particle tracking method reveals that the migration speed of the model dune is one order of magnitude smaller than that of individual grains. In particular, the erosion rate consists of comparable contributions from creeping (low energy) and saltating (high energy) particles. The saltation flow rate is slightly larger, whereas the number of saltating particles is one order of magnitude lower than that of the creeping ones. The velocity field of the saltating particles is comparable to the velocity field of the driving fluid. It can be observed that the spatial profile of the shear stress reaches its maximum value upstream of the crest, while its minimum lies at the downstream foot of the dune. The particle tracking method reveals that the deposition of entrained particles occurs primarily in the region between these two extrema of the shear stress. Moreover, it is demonstrated that the initial triangular heap evolves to a steady state with constant mass, shape, velocity, and packing fraction after one turnover time has elapsed. Within that time the mean distance between particles initially in contact reaches a value of approximately one quarter of the dune basis length

Atomistic modeling of grain boundary behavior under shear conditions in magnesium and magnesium-based binary alloys

In this study, the structure, the energetic, and the strength of a symmetric tilt grain boundary in magnesium and magnesium binary alloys were analyzed in the framework of (semi-)empirical potentials. Following a systematic investigation of the transferability and accuracy of the interatomic potentials, atomistic calculations of the grain boundary energy, the grain boundary sliding energy, and the grain boundary strength were performed in pure magnesium and in binary MgX alloys (X = Al, Ca, Gd, Li, Sn, Y, Ag, Nd, and Pb). The data gained in this study were analyzed to identify the most critical material parameters controlling the strength of the grain boundary, and their consequence on atomic shuffling motions occurring at the grain boundary. From the methodology perspective, the role of in-plane and out-of plane relaxation on the grain boundary sliding energy curves was investigated. In pure magnesium, the results showed that in-plane relaxation is critical in activating twinning dislocation resulting in grain boundary migration. In the alloy systems, however, grain boundary migration was disabled as a consequence of the pinning of the grain boundary by segregated elements. Finally, while the grain boundary energy, the shape of the grain boundary sliding energy curves, and the grain boundary sliding energy are critical parameters controlling the grain boundary strength in pure magnesium, only the grain boundary energy and the segregation energy of the alloying elements at the grain boundary were identified as critical material parameters in the alloys system