Modeling Changes in Measured Conductance of Thin Boron Carbide Semiconducting Films Under Irradiation

Semiconducting, p-type, amorphous partially dehydrogenated boron carbide films (a-B10C2+x:Hy) were deposited utilizing plasma enhanced chemical vapor deposition (PECVD) onto n-type silicon thus creating a heterojunction diode. A model was developed for the conductance of the device as a function of perturbation frequency (��) that incorporates changes of the electrical properties for both the a-B10C2+x:Hy film and the silicon substrate when irradiated. The virgin model has 3 independent variables (R1, C1, R3), and 1 dependent variable (��). Samples were then irradiated with 200 keV He+ ions, and the conductance model was matched to the measured data. It was found that initial irradiation (0.1 displacements per atom (dpa) equivalent) resulted in a decrease in the parallel junction resistance parameter from 6032 Ω to 2705 Ω. Further irradiation drastically increased the parallel junction resistance parameter to 39000 Ω (0.2 dpa equivalent), 77440 Ω (0.3 dpa equivalent), and 190000 Ω (0.5 dpa equivalent). It is believed that the initial irradiation causes type inversion of the silicon substrate changing the original junction from a p-n to a p-p+ with a much lower barrier height leading to a lower junction resistance component between the a-B10C2+x:Hy and irradiated silicon. Additionally, it was found that after irradiation, a second parallel resistor and capacitor component is required for the model, introducing 2 additional independent variables (R2, C2). This is interpreted as the junction between the irradiated and virgin silicon near ion end of range

Competing Quantum Orderings in Cuprate Superconductors: A Minimal Model

We present a minimal model for cuprate superconductors. At the unrestricted mean-field level, the model produces homogeneous superconductivity at large doping, striped superconductivity in the underdoped regime and various antiferromagnetic phases at low doping and for high temperatures. On the underdoped side, the superconductor is intrinsically inhomogeneous and global phase coherence is achieved through Josephson-like coupling of the superconducting stripes. The model is applied to calculate experimentally measurable ARPES spectra.Comment: 5 pages, 4 eps included figure

Variations in the spin period of the radio-quiet pulsar 1E 1207.4-5209

The X-ray source 1E 1207.4-5209 is a compact central object in the G296.5+10.0 supernova remnant. Its spin period of 424 ms, discovered with the Chandra X-ray Observatory, suggests that it is a neutron star. The X-ray spectrum of this radio-quiet pulsar shows at least two absorption lines, first spectral features discovered in radiation from an isolated neutron star. Here we report the results of timing analysis of Chandra and XMM-Newton observations of this source showing a non-monotonous behavior of its period. We discuss three hypotheses which may explain the observational result. The first one assumes that 1E 1207.$-5209 is a glitching pulsar, with frequency jumps of \Delta f > 5 \muHz occurring every 1-2 years. The second hypothesis explains the deviations from a steady spin-down as due to accretion, with accretion rate varying from \sim 10^{13} to >10^{16} g s^{-1}, from a disk possibly formed from ejecta produced in the supernova explosion. Finally, the period variations could be explained assuming that the pulsar is in a wide binary system with a long period, P_orb \sim 0.2-6 yr, and a low-mass companion, M_2 < 0.3 M_\odot.Comment: 20 pages, 5 figures, accepted for publications in ApJ. 2004 ApJ, in pres

Rapidly variable Fe Kα\alpha line in NGC 4051

We present a detailed analysis on the variability of the Fe K emission line in NGC 4051 using ASCA data. Through simple Gaussian line fits, we find not only obvious Fe K line variability with no significant difference in the X-ray continuum flux between two ASCA observations which were separated by $\sim$ 440 days, but also rapid variability of Fe K line on time scales $\sim 10^4$ s within the second observation. During the second observation, the line is strong (EW = 733$^{+206}_{-219}$ eV) and broad ($\sigma = 0.96^{+0.49}_{-0.35}$ keV) when the source is brightest, and become weaker (EW = 165$^{+87}_{-86}$ eV) and narrower ($\sigma<0.09$ keV) whilst the source is weakest. The equivalent width of Fe K line correlates positively with the continuum flux, which shows an opposite trend with another Seyfert 1 galaxy MCG --6-30-15.Comment: 12 pages with 5 figures, to appear in ApJ Vol. 516, L6

Alternate cyclin D1 mRNA splicing modulates P27\u3csup\u3eKlP1\u3c/sup\u3e binding and cell migration

Cyclin D1 is an important cell cycle regulator but in cancer its overexpression also increases cellular migration mediated by p27KlP1 stabilization and RhoA inhibition. Recently, a common polymorphism at the exon 4-intron 4 boundary of the human cyclin D1 gene within a splice donor region was associated with an altered risk of developing cancer. Altered RNA splicing caused by this polymorphism gives rise to a variant cyclin D1 isoform termed cyclin D1b, which has the same N-terminus as the canonical cyclin D1a isoform but a distinct C-terminus. In this study we show that these different isoforms have unique properties with regard to the cellular migration function of cyclin D1. Whereas they displayed little difference in transcriptional co-repression assays on idealized reporter genes, microarray cDNA expression analysis revealed differential regulation of genes including those that influence cellular migration. Additionally, while cyclin D1a stabilized p27KIP1 and inhibited RhoA-induced ROCK kinase activity, promoting cellular migration, cyclin D1b failed to stabilize p27KIP1 or inhibit ROCK kinase activity and had no effect on migration. Our findings argue that alternate splicing is an important determinant of the function of cyclin D1 in cellular migration

A spatially shifted beam approach to subwavelength focusing

Although negative-refractive-index metamaterials have successfully achieved subwavelength focusing, image resolution is limited by the presence of losses. In this Letter, a metal transmission screen with subwavelength spaced slots is proposed that focuses the near-field beyond the diffraction limit and furthermore, is easily scaled from microwave frequencies to the optical regime. An analytical model based on the superposition of shifted beam patterns is developed that agrees very well with full-wave simulations and is corroborated by experimental results at microwave frequencies.Comment: 5 pages, 7 figures. Content updated following reviewer comments to match final published pape

Involutive orbits of non-Noether symmetry groups

We consider set of functions on Poisson manifold related by continues one-parameter group of transformations. Class of vector fields that produce involutive families of functions is investigated and relationship between these vector fields and non-Noether symmetries of Hamiltonian dynamical systems is outlined. Theory is illustrated with sample models: modified Boussinesq system and Broer-Kaup system.Comment: LaTeX 2e, 10 pages, no figure

Phase I dose-escalation and pharmacokinetic study of dasatinib in patients with advanced solid tumors

PURPOSE: To determine the maximum tolerated dose, dose-limiting toxicity (DLT), and recommended phase II dose of dasatinib in metastatic solid tumors refractory to standard therapies or for which no effective standard therapy exists. &lt;br&gt;&lt;/br&gt; EXPERIMENTAL DESIGN: In this phase I, open-label, dose-escalation study, patients received 35 to 160 mg of dasatinib twice daily in 28-day cycles either every 12 hours for 5 consecutive days followed by 2 nontreatment days every week (5D2) or as continuous, twice-daily (CDD) dosing. &lt;br&gt;&lt;/br&gt; RESULTS: Sixty-seven patients were treated (5D2, n = 33; CDD, n = 34). The maximum tolerated doses were 120 mg twice daily 5D2 and 70 mg twice daily CDD. DLTs with 160 mg 5D2 were recurrent grade 2 rash, grade 3 lethargy, and one patient with both grade 3 prolonged bleeding time and grade 3 hypocalcemia; DLTs with 120 mg twice daily CDD were grade 3 nausea, grade 3 fatigue, and one patient with both grade 3 rash and grade 2 proteinuria. The most frequent treatment-related toxicities across all doses were nausea, fatigue, lethargy, anorexia, proteinuria, and diarrhea, with infrequent hematologic toxicities. Pharmacokinetic data indicated rapid absorption, dose proportionality, and lack of drug accumulation. Although no objective tumor responses were seen, durable stable disease was observed in 16% of patients.&lt;br&gt;&lt;/br&gt; CONCLUSION: Dasatinib was well tolerated in this population, with a safety profile similar to that observed previously in leukemia patients, although with much less hematologic toxicity. Limited, although encouraging, preliminary evidence of clinical activity was observed. Doses of 120 mg twice daily (5D2) or 70 mg twice daily (CDD) are recommended for further studies in patients with solid tumors.&lt;br&gt;&lt;/br&gt