Titania/alumina bilayer gate insulators for InGaAs metal-oxide-semiconductor devices

We describe the electrical properties of atomic layer deposited TiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> bilayer gate oxides which simultaneously achieve high gate capacitance density and low gate leakage current density. Crystallization of the initially amorphous TiO<sub>2</sub> film contributes to a significant accumulation capacitance increase (∼33%) observed after a forming gas anneal at 400 °C. The bilayer dielectrics reduce gate leakage current density by approximately one order of magnitude at flatband compared to Al<sub>2</sub>O<sub>3</sub> single layer of comparable capacitance equivalent thickness. The conduction band offset of TiO<sub>2</sub> relative to InGaAs is 0.6 eV, contributing to the ability of the stacked dielectric to suppress gate leakage conduction

Measuring energy dependent polarization in soft gamma-rays using Compton scattering in PoGOLite

Linear polarization in X- and gamma-rays is an important diagnostic of many astrophysical sources, foremost giving information about their geometry, magnetic fields, and radiation mechanisms. However, very few X-ray polarization measurements have been made, and then only mono-energetic detections, whilst several objects are assumed to have energy dependent polarization signatures. In this paper we investigate whether detection of energy dependent polarization from cosmic sources is possible using the Compton technique, in particular with the proposed PoGOLite balloon-experiment, in the 25-100 keV range. We use Geant4 simulations of a PoGOLite model and input photon spectra based on Cygnus X-1 and accreting magnetic pulsars (100 mCrab). Effective observing times of 6 and 35 hours were simulated, corresponding to a standard and a long duration flight respectively. Both smooth and sharp energy variations of the polarization are investigated and compared to constant polarization signals using chi-square statistics. We can reject constant polarization, with energy, for the Cygnus X-1 spectrum (in the hard state), if the reflected component is assumed to be completely polarized, whereas the distinction cannot be made for weaker polarization. For the accreting pulsar, constant polarization can be rejected in the case of polarization in a narrow energy band with at least 50% polarization, and similarly for a negative step distribution from 30% to 0% polarization.Comment: 11 pages, 12 figures; updated to match version accepted for publication in Astroparticle Physics (only minor changes

J/ψJ/\psi suppression in the threshold model at RHIC and LHC energy

In the QGP based threshold model \cite{Blaizot:2000ev,Blaizot:1996nq}, in addition to the normal nuclear absorption, $J/\psi$'s are subjected to an 'anomalous' suppression such that above a threshold density $n_{J/\psi}$, all the $J/\psi$'s are melted. In the threshold model we have analysed the recent PHENIX data on the centrality dependence of $J/\psi$ suppression in Au+Au collisions at RHIC. Feedback from decay of the state $\chi$ is accounted for. $J/\psi$'s are anomalously suppressed above a threshold density, $n_{J/\psi}=3.57\pm 0.17$ $fm^{-2}$. Threshold density for anomalous suppression of the state $\chi$ is uncertain to a large extent, $n_\chi=0.32 \pm 0.32$ $fm^{-2}$. The fraction $F$ of the state $\chi$ can not be determined unambiguously, depending on the nuclear absorption, it can vary from 20% to 40%. We have also predicted for the suppression in Pb+Pb collisions at LHC energy. In central Pb+Pb collisions, $J/\psi$'s are suppressed by a factor of 3-4. Suppression pattern is rather similar to that in Au+Au collisions, if not slighty less in central collisions. Using the PHENIX data on the participant number dependence of the Bjorken energy density, we have also estimated the QGP formation time. For critical temperature $T_c$=192 MeV, estimated QGP formation time ranges between 0.07-0.09 fm/c.Comment: 9 pages, 9 figure

Recent Heavy-Flavor results at STAR

We present the recent results on non-photonic electron (NPE) yields from RHIC run8 p+p collisions. The $e/\pi$ ratio as a function of $p_T$ in run8 with a factor of 10 reduction of the inner detector material at STAR is found to be consistent with those results from run3 taking into account the NPE from charm leptonic decay and the difference of photonic electron yield from photon conversion in detector material. \Jpsi spectra in \pp and \cucu collisions at \sNN = 200 GeV with high sampled luminosity \Jpsi spectrum at high-\pT follows $x_T$ scaling, but the scaling is violated at low \pT. $J/\psi$-hadron correlations in \pp collisions are studied to understand the \Jpsi production mechanism at high $p_T$. We observed an absence of charged hadrons accompanying \Jpsi on the near-side, in contrast to the strong correlation peak in the di-hadron correlations. This constrains the $B$-meson contribution and jet fragmentation to inclusive \Jpsi to be ${}^{<}_{\sim}17$. Yields in minimum-bias \cucu collisions are consistent with those in \pp collisions scaled by the underlying binary nucleon-nucleon collisions in the measured \pT range. Other measurements and future projects related to heavy-flavors are discussed.Comment: 8 pages 4 figures, proceedings of the International Conference on Strangeness in Quark Matter 2008 - Beijing, China, Oct. 6-10, 200

ASCA Detection of Pulsed X-ray Emission from PSR J0631+1036

ASCA's long look at the 288 millisecond radio pulsar, PSR J0631+1036, reveals coherent X-ray pulsation from this source for the first time. The source was first detected in the serendipitous Einstein observation and later identified as a radio pulsar. Possible pulsation in the gamma-ray band has been detected from the CGRO EGRET data (Zepka, et al. 1996). The X-ray spectrum in the ASCA band is characterized by a hard power-law type emission with a photon index of about 2.3, when fitted with a single power-law function modified with absorption. An additional blackbody component of about 0.14 keV increases the quality of the spectral fit. The observed X-ray flux is 2.1e-13 ergs/s/cm2 in the 1-10 keV band. We find that many characteristics of PSR J0631+1036 are similar to those of middle-aged gamma-ray pulsars such as PSR B1055-52, PSR B0633+17 (Geminga), and PSR B0656+14.Comment: To appear in ApJ Letter

Strict Limit on CPT Violation from Polarization of Gamma-Ray Bursts

We report the strictest observational verification of CPT invariance in the photon sector, as a result of gamma-ray polarization measurement of distant gamma-ray bursts (GRBs), which are brightest stellar-size explosions in the universe. We detected the gamma-ray polarization of three GRBs with high significance, and the source distances may be constrained by a well-known luminosity indicator for GRBs. For the Lorentz- and CPT-violating dispersion relation E_{\pm}^2=p^2 \pm 2\xi p^3/M_{Pl}, where \pm denotes different circular polarization states of the photon, the parameter \xi is constrained as |\xi|<O(10^{-15}). Barring precise cancellation between quantum gravity effects and dark energy effects, the stringent limit on the CPT-violating effect leads to the expectation that quantum gravity presumably respects the CPT invariance.Comment: 4 pages; accepted for publication in Physical Review Letters; redshift estimates of GRBs changed (i.e z=0.382 was wrong for GRB 110721A) and calculations of \xi limit improved from the previous versio

Development of a Time Projection Chamber Using Gas Electron Multipliers (GEM-TPC)

We developed a prototype time projection chamber using gas electron multipliers (GEM-TPC) for high energy heavy ion collision experiments. To investigate its performance, we conducted a beam test with 3 kinds of gases (Ar(90%)-CH4(10%), Ar(70%)-C2H6(30%) and CF4). Detection efficiency of 99%, and spatial resolution of 79 $\mu$m in the pad-row direction and 313 $\mu$m in the drift direction were achieved. The test results show that the GEM-TPC meets the requirements for high energy heavy ion collision experiments. The configuration and performance of the GEM-TPC are described.Comment: 18 pages, 12 figures, published online in Nucl. Instr. and Meth.

Novel DNA Microarray System for Analysis of Nascent mRNAs

Transcriptional activation and repression are a key step in the regulation of all cellular activities. The development of comprehensive analysis methods such as DNA microarray has advanced our understanding of the correlation between the regulation of transcription and that of cellular mechanisms. However, DNA microarray analysis based on steady-state mRNA (total mRNA) does not always correspond to transcriptional activation or repression. To comprehend these transcriptional regulations, the detection of nascent RNAs is more informative. Although the nuclear run-on assay can detect nascent RNAs, it has not been fully applied to DNA microarray analysis. In this study, we have developed a highly efficient method for isolating bromouridine-labeled nascent RNAs that can be successfully applied to DNA microarray analysis. This method can linearly amplify small amounts of mRNAs with little bias. Furthermore, we have applied this method to DNA microarray analysis from mouse G2-arrested cells and have identified several genes that exhibit novel expression profiles. This method will provide important information in the field of transcriptome analysis of various cellular processes