Optical properties of Mn4+ ions in GaN:Mn codoped with Mg acceptors

The optical properties of Mn-Mg codoped epitaxial GaN were studied. Addition of Mg acceptors quenches the weak manganese-related photoluminescence (PL) band at 1.3 eV in GaN:Mn and a series of sharp PL peaks are observed at 1 eV in codoped epilayers. The change in PL spectra indicates that Mg addition stabilizes the Mn4+ charge state by decreasing the Fermi level. The 1 eV PL peaks are tentatively attributed to intra center transitions involving Mn4+ ions. Spin allowed 3d-shell 4T2-4T1 transitions and their phonon replicas are involved. The relative intensities of the sharp peaks are strongly dependent on the excitation wavelength, indicating the optically active Mn4+ centers involved in the separate peaks are different. The temperature dependence of the PL spectrum suggests the presence of at least three distinct Mn4+ complex centers.Comment: 14 pages, 3 figures, 1 table, accepted by Appl. Phys. Let

Group classification of the Sachs equations for a radiating axisymmetric, non-rotating, vacuum space-time

We carry out a Lie group analysis of the Sachs equations for a time-dependent axisymmetric non-rotating space-time in which the Ricci tensor vanishes. These equations, which are the first two members of the set of Newman-Penrose equations, define the characteristic initial-value problem for the space-time. We find a particular form for the initial data such that these equations admit a Lie symmetry, and so defines a geometrically special class of such spacetimes. These should additionally be of particular physical interest because of this special geometric feature.Comment: 18 Pages. Submitted to Classical and Quantum Gravit

Association of ABCB1, 5-HT3B receptor and CYP2D6 genetic polymorphisms with ondansetron and metoclopramide antiemetic response in Indonesian cancer patients treated with highly emetogenic chemotherapy.

Our study shows that in Indonesian cancer patients treated with highly cytostatic emetogenic, carriership of the CTG haplotype of the ABCB1 gene is related to an increased risk of delayed chemotherapy-induced nausea and vomiting

Optical investigation of electronic states of Mn4+ ions in p-type GaN

The electronic states of manganese in p-type GaN are investigated using photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies. A series of sharp PL lines at 1.0 eV is observed in codoped GaN and attributed to the intra d-shell transition 4T2(F)-4T1(F) of Mn4+ ions. PLE spectrum of the Mn4+ [4T2(F)-4T1(F)] luminescence reveals intra center excitation processes via the excited states of Mn4+ ions. PLE peaks observed at 1.79 and 2.33 eV are attributed to the intra-d-shell 4T1(P)-4T1(F) and 4A2(F)-4T1(F) transitions of Mn4+, respectively. In addition to the intra shell excitation processes, a broad PLE band involving charge-transfer transition of the Mn4+/3+ deep level is observed, which is well described by the Lucovsky model. As determined from the onset of this PLE band, the position of the Mn4+/3+ deep level is 1.11 eV above the valence band maximum, which is consistent with prior theory using ab initio calculations. Our work indicates 4+ is the predominant oxidation state of Mn ions in p-type GaN:Mn when the Fermi energy is lower than 1.11 eV above the valence band maximum.Comment: 7 pages, 3 figures, To be publised in Appl. Phys. Let

A compensation procedure for multiprogramming queues

Abstract. In this paper we study a multiprogramming system consisting of an input-output unit (10 unit) and a central processor (CP). This system can be represented by a continuous time Marlmv process with states (m. n). where m and n denote the number of jobs at the CP and the 10 unit respectively. The computation of the equilibrium distribution {Pm,n} of this Markov process is the purpose of the analysis in this paper. The analysis consists of two parts. In the first Part. we use a compensation procedure to show that the equilibrium distribution {Pm,n} in those states (m. n) for which m+n is not too small. can be expressed as an infinite linear combination of product forms. Explicit formulae are given for the product forms and the coefficients of this infinite linear combination. In the second part of the analysis. we pay attention to some numerical aspects of the computation of the equilibrium distribution. For the computation of the equilibrium probabilities that can be expressed as infinite linear combinations of product forms. we derive bounds for the errors caused by cutting off these infinite linear combinations, and after that we present numerically stable formulae to compute one by one the remaining equilibrium probabilities

Wall-Fluid and Liquid-Gas Interfaces of Model Colloid-Polymer Mixtures by Simulation and Theory

We perform a study of the interfacial properties of a model suspension of hard sphere colloids with diameter $\sigma_c$ and non-adsorbing ideal polymer coils with diameter $\sigma_p$. For the mixture in contact with a planar hard wall, we obtain from simulations the wall-fluid interfacial free energy, $\gamma_{wf}$, for size ratios $q=\sigma_p/\sigma_c=0.6$ and 1, using thermodynamic integration, and study the (excess) adsorption of colloids, $\Gamma_c$, and of polymers, $\Gamma_p$, at the hard wall. The interfacial tension of the free liquid-gas interface, $\gamma_{lg}$, is obtained following three different routes in simulations: i) from studying the system size dependence of the interfacial width according to the predictions of capillary wave theory, ii) from the probability distribution of the colloid density at coexistence in the grand canonical ensemble, and iii) for statepoints where the colloidal liquid wets the wall completely, from Young's equation relating $\gamma_{lg}$ to the difference of wall-liquid and wall-gas interfacial tensions, $\gamma_{wl}-\gamma_{wg}$. In addition, we calculate $\gamma_{wf}, \Gamma_c$, and $\Gamma_p$ using density functional theory and a scaled particle theory based on free volume theory. Good agreement is found between the simulation results and those from density functional theory, while the results from scaled particle theory quantitatively deviate but reproduce some essential features. Simulation results for $\gamma_{lg}$ obtained from the three different routes are all in good agreement. Density functional theory predicts $\gamma_{lg}$ with good accuracy for high polymer reservoir packing fractions, but yields deviations from the simulation results close to the critical point.Comment: 23 pages, 10 figures, REVTEX. Fig 5a changed. Final versio

Spatial models of cell distribution in human lumbar dorsal root ganglia

Dorsal root ganglia (DRG), which contain the somata of primary sensory neurons, have increasingly been considered as novel targets for clinical neural interfaces, both for neuroprosthetic and pain applications. Effective use of either neural recording or stimulation technologies requires an appropriate spatial position relative to the target neural element, whether axon or cell body. However, the internal three- dimensional spatial organization of human DRG neural fibers and somata has not been quantitatively described. In this study, we analyzed 202 cross- sectional images across the length of 31 human L4 and L5 DRG from 10 donors. We used a custom semi- automated graphical user interface to identify the locations of neural elements in the images and normalize the output to a consistent spatial reference for direct comparison by spinal level. By applying a recursive partitioning algorithm, we found that the highest density of cell bodies at both spinal levels could be found in the inner 85% of DRG length, the outer- most 25- 30% radially, and the dorsal- most 69- 76%. While axonal density was fairly homogeneous across the DRG length, there was a distinct low density region in the outer 7- 11% radially. These findings are consistent with previous qualitative reports of neural distribution in DRG. The quantitative measurements we provide will enable improved targeting of future neural interface technologies and DRG- focused pharmaceutical therapies, and provide a rigorous anatomical description of the bridge between the central and peripheral nervous systems.Dorsal root ganglia (DRG) are novel targets for neural interface technologies that treat neurological disorders, such as chronic pain and spinal cord injury. The three- dimensional cellular anatomy of DRG are not well- mapped, particularly in humans, limiting the effectiveness of neurotechnology. We developed a semi- automated algorithm to quantify the three- dimensional distribution of neural elements in histologically- processed tissue. We applied this algorithm to sequential NF200- stained histology slices obtained from human lumbar DRG and demonstrated that cell bodies typically congregate around the dorsal edge of the ganglia. These results are crucial to the development of safe and effective clinical neural interface technologies.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155471/1/cne24848_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155471/2/cne24848.pd

Is there a reentrant glass in binary mixtures?

By employing computer simulations for a model binary mixture, we show that a reentrant glass transition upon adding a second component only occurs if the ratio $\alpha$ of the short-time mobilities between the glass-forming component and the additive is sufficiently small. For $\alpha \approx 1$, there is no reentrant glass, even if the size asymmetry between the two components is large, in accordance with two-component mode coupling theory. For $\alpha \ll 1$, on the other hand, the reentrant glass is observed and reproduced only by an effective one-component mode coupling theory.Comment: 4 pages, 3 figure

COSY-11: an experimental facility for studying meson production in free and quasi-free nucleon-nucleon collisions

The COSY-11 experimental setup is an internal facility installed at the COoler SYnchrotron COSY in Juelich. It allows to investigate meson production in free and quasi-free nucleon-nucleon collisions, eg. pp --> pp meson and pd --> p_sp np meson reactions. Drift chambers and scintillators permit to measure outgoing protons, separated in magnetic field of COSY-11 dipole. Neutrons are registered in the neutron modular detector installed downstream the beam. Recently, the experimental setup has been extended with spectator detector, deuteron drift chamber and polarization monitoring system, and since then meson production can be investigated also as a function of spin and isospin of colliding nucleons.Comment: Presented at LEAP05: International conference on Low Energy Antiproton Physics, Bonn - Juelich, Germany, May 16-22, 200