Configurations, and parallelograms associated to centers of mass

The purpose of this article is to \begin{enumerate} \item define $M(t,k)$ the $t$-fold center of mass arrangement for $k$ points in the plane, \item give elementary properties of $M(t,k)$ and \item give consequences concerning the space $M(2,k)$ of $k$ distinct points in the plane, no four of which are the vertices of a parallelogram. \end{enumerate} The main result proven in this article is that the classical unordered configuration of $k$ points in the plane is not a retract up to homotopy of the space of $k$ unordered distinct points in the plane, no four of which are the vertices of a parallelogram. The proof below is homotopy theoretic without an explicit computation of the homology of these spaces. In addition, a second, speculative part of this article arises from the failure of these methods in the case of odd primes $p$. This failure gives rise to a candidate for the localization at odd primes $p$ of the double loop space of an odd sphere obtained from the $p$-fold center of mass arrangement. Potential consequences are listed.Comment: 11 page

Point defect dynamics in bcc metals

We present an analysis of the time evolution of self-interstitial atom and vacancy (point defect) populations in pure bcc metals under constant irradiation flux conditions. Mean-field rate equations are developed in parallel to a kinetic Monte Carlo (kMC) model. When only considering the elementary processes of defect production, defect migration, recombination and absorption at sinks, the kMC model and rate equations are shown to be equivalent and the time evolution of the point defect populations is analyzed using simple scaling arguments. We show that the typically large mismatch of the rates of interstitial and vacancy migration in bcc metals can lead to a vacancy population that grows as the square root of time. The vacancy cluster size distribution under both irreversible and reversible attachment can be described by a simple exponential function. We also consider the effect of highly mobile interstitial clusters and apply the model with parameters appropriate for vanadium and $\alpha-$iron.Comment: to appear in Phys. Rev.

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

Broadband Antireflection and Light Extraction Enhancement in Fluorescent SiC with Nanodome Structures

We demonstrate a time-efficient and low-cost approach to fabricate Si3N4 coated nanodome structures in fluorescent SiC. Nanosphere lithography is used as the nanopatterning method and SiC nanodome structures with Si3N4 coating are formed via dry etching and thin film deposition process. By using this method, a significant broadband surface antireflection and a considerable omnidirectional luminescence enhancement are obtained. The experimental observations are then supported by numerical simulations. It is believed that our fabrication method will be well suitable for large-scale production in the future

The role of defects in fluorescent silicon carbide layers grown by sublimation epitaxy

Donor-acceptor co-doped SiC is a promising light converter for novel monolithic all-semiconductor white LEDs due to its broad-band donor-acceptor pair luminescence and potentially high internal quantum efficiency. Besides sufficiently high doping concentrations in an appropriate ratio yielding short radiative lifetimes, long nonradiative lifetimes are crucial for efficient light conversion. The impact of different types of defects is studied by characterizing fluorescent silicon carbide layers with regard to photoluminescence intensity, homogeneity and efficiency taking into account dislocation density and distribution. Different doping concentrations and variations in gas phase composition and pressure are investigated

Expression of transient receptor potential channel vanilloid (TRPV) 1–4, melastin (TRPM) 5 and 8, and ankyrin (TRPA1) in the normal and methimazole-treated mouse olfactory epithelium

Conclusion: It is suggested that TRPV1, 2, 3, and 4, TRPM5 and 8, and TRPA1 may play several roles in the olfactory epithelium (OE), contributing to olfactory chemosensation, olfactory adaptation, olfactory-trigeminal interaction, and OE fluid homeostasis. In patients with olfactory disturbance, TRPV1 and TRPM8 may be closely related to a high rate of recognition of curry and menthol odors, while TRPV2 may also play a crucial role in the regeneration of olfactory receptor neurons. Objective: Expression of TRPV1–4, TRPM5 and 8, and TRPA1 in the normal and methimazole-treated mouse OE was analyzed. Methods: The localization of TRPV1–4, TRPM5 and 8, and TRPA1 in the OE of normal and methimazole-treated CBA/J mice was investigated by immunohistochemistry. Results: Normal OE showed a positive immunofluorescent reaction to TRPV1–4, TRPM5 and 8, and TRPA1. In lamina propria, the nerve fibers displayed TRPV 1, 2, and 3, TRPM8 and TRPA1. In the pathological condition, the expression of TRPV3, TRPV4, TRPM5, and TRPA1 was markedly reduced and took a long time to recover. In contrast, expression of TRPM8 was scarcely affected, even in the pathological condition, while TRPV1 and TRPV2 showed early recovery following methimazole treatment