Low-energy, planar magnetic defects in BaFe2As2: nanotwins, twins, antiphase and domain boundaries

In BaFe2As2, structural and magnetic planar defects begin to proliferate below the structural phase transition, affecting descriptions of magnetism and superconductivity. We study using density-functional theory the stability and magnetic properties of competing antiphase and domain boundaries, twins and isolated $nano$twins (twin nuclei) - spin excitations proposed and/or observed. These nanoscale defects have very low surface energy ($22$-$210$~$m$Jm$^{-2}$), with twins favorable to the mesoscale. Defects exhibit smaller moments confined near their boundaries -- making a uniform-moment picture inappropriate for long-range magnetic order in real samples. {\it{Nano}}twins explain features in measured pair distribution functions, so should be considered when analyzing scattering data. All these defects can be weakly mobile and/or have fluctuations that lower assessed "ordered" moments from longer spatial and/or time averaging, and should be considered directly.Comment: 6 pages, 6 figures, 1 tabl

Estimation of losses for adobe buildings in Pakistan

Adobe buildings are vulnerable to seismic forces. Large scale destructions and casualties have been caused due to the collapse of adobe buildings during the past earthquakes. A significant number of adobe structures exist in different parts of Pakistan, similar to other parts of the world. Since Pakistan lies in a seismic active region, it is necessary to assess the level of vulnerability of these buildings in order to estimate associated losses during a seismic event. This paper presents the results of a study which was conducted to quantify damages to adobe buildings based on their fragility curves. The adobe buildings were found to be highly vulnerable to low intensity earthquakes. The vulnerability of these buildings has been compared with the European adobe buildings. It was noted that Pakistani adobe buildings were slightly less resistant to earthquakes as compared to similar buildings in Europe. Retrofitting solutions were suggested in order to increase the seismic capacity of adobe buildings in Pakistan

Interplay of chemical pressure and hydrogen insertion effects in CeRhSn {\bf CeRhSn} from first principles

Investigations within the local spin density functional theory (LSDF) of the intermetallic hydride system ${\rm CeRhSnH_x}$ were carried out for discrete model compositions in the range $0.33 \leq x_H \leq 1.33$. The aim of this study is to assess the change of the cerium valence state in the neighborhood of the experimental hydride composition, ${\rm CeRhSnH_{0.8}}$. In agreement with experiment, the analyses of the electronic and magnetic structures and of the chemical bonding properties point to trivalent cerium for $1 \leq x_H \leq 1.33$. In contrast, for lower hydrogen amounts the hydride system stays in an intermediate-valent state for cerium, like in ${\rm CeRhSn}$. The influence of the insertion of hydrogen is addressed from both the volume expansion and chemical bonding effects. The latter are found to have the main influence on the change of Ce valence character. Spin polarized calculations point to a finite magnetic moment carried by the Ce $4f$ states; its magnitude increases with $x_H$ in the range $1 \leq x_H \leq 1.33$

Band heterotopia

Band heterotopias are one of the rarest groups of congenital disorder that result in variable degree of structural abnormality of brain parenchyma. Band of heterotopic neurons result from a congenital or acquired deficiency of the neuronal migration. MRI is the examination of choice for demonstrating these abnormalities because of the superb gray vs. white matter differentiation, detail of cortical anatomy and ease of multiplanar imaging. We report a case of band heterotopia that showed a bilateral band of gray matter in deep white matter best demonstrated on T2 Wt. and FLAIR images

Experimental determination of the state-dependent enhancement of the electron-positron momentum density in solids

The state-dependence of the enhancement of the electron-positron momentum density is investigated for some transition and simple metals (Cr, V, Ag and Al). Quantitative comparison with linearized muffin-tin orbital calculations of the corresponding quantity in the first Brillouin zone is shown to yield a measurement of the enhancement of the s, p and d states, independent of any parameterizations in terms of the electron density local to the positron. An empirical correction that can be applied to a first-principles state-dependent model is proposed that reproduces the measured state-dependence very well, yielding a general, predictive model for the enhancement of the momentum distribution of positron annihilation measurements, including those of angular correlation and coincidence Doppler broadening techniques

Assessment of seismic performance of adobe structures in Pakistan and Portugal

Adobe buildings exist in different parts of the world. The construction of these buildings can be carried out economically, using locally available materials and skills that do not require use of modern machinery. Therefore, adobe buildings provide an economic housing option. The construction of adobe structures is carried out based on traditional construction practices which vary from region to region. This paper presents the results of a study which was conducted to study the construction practices of adobe buildings in Pakistan and Portugal in the context of their seismic vulnerability. The adobe buildings in both these countries were found to be subjected to seismic hazard levels which, although is low in some regions, may cause significant damages. Lack of essential elements or details for the adequate seismic performance was found in the adobe buildings in both regions

Current-Voltage Characteristics of Long-Channel Nanobundle Thin-Film Transistors: A Bottom-up Perspective

By generalizing the classical linear response theory of stick percolation to nonlinear regime, we find that the drain current of a Nanobundle Thin Film Transistor (NB-TFT) is described under a rather general set of conditions by a universal scaling formula ID = A/LS g(LS/LC, rho_S * LS * LS) f(VG, VD), where A is a technology-specific constant, g is function of geometrical factors like stick length (LS), channel length (LC), and stick density (rho_S) and f is a function of drain (VD) and gate (VG) biasing conditions. This scaling formula implies that the measurement of full I-V characteristics of a single NB-TFT is sufficient to predict the performance characteristics of any other transistor with arbitrary geometrical parameters and biasing conditions

Dark energy and dark matter from cosmological observations

The present status of our knowledge about the dark matter and dark energy is reviewed. Bounds on the content of cold and hot dark matter from cosmological observations are discussed in some detail. I also review current bounds on the physical properties of dark energy, mainly its equation of state and effective speed of sound.Comment: 12 pages, 4 figures, to appear in Lepton-Photon 2005 proceedings, added figure and typos correcte