Exploring the validity and limitations of the Mott-Gurney law for charge-carrier mobility determination of semiconducting thin-films

Using drift-diffusion simulations, we investigate the voltage dependence of the dark current in single carrier devices, typically used to determine charge-carrier mobilities. For both low and high voltages, the current increases linearly with the applied voltage. Whereas the linear current at low voltages is mainly due to space charge in the middle of the device, the linear current at high voltage is caused by charge-carrier saturation due to a high degree of injection. As a consequence, the current density at these voltages does not follow the classical square law derived by Mott and Gurney, and we show that for trap-free devices, only for intermediate voltages, a space-charge-limited drift current can be observed with a slope that approaches two. We show that, depending on the thickness of the semiconductor layer and the size of the injection barriers, the two linear current-voltage regimes can dominate the whole voltage range, and the intermediate Mott-Gurney regime can shrink or disappear. In this case, which will especially occur for thicknesses and injection barriers typical for single-carrier devices used to probe organic semiconductors, a meaningful analysis using the Mott-Gurney law will become unachievable, because a square-law fit can no longer be achieved, resulting in the mobility being substantially underestimated. General criteria for when to expect deviations from the Mott-Gurney law when used for analysis of intrinsic semiconductors are discussed

The effect of lower body negative pressure on phase 1 cardiovascular responses at exercise onset in healthy humans

We tested the hypothesis that vagal withdrawal and increased venous return interact in determining the rapid cardiac output response (Phase I) at exercise onset. We used lower body negative pressure (LBNP) to increase blood dislocation to the heart by muscle pump action and simultaneously reduce resting vagal activity. At exercise start, we expected larger response amplitude for stroke volume and smaller for heart rate at progressively stronger LBNP levels, so that the cardiac output response would remain unchanged. Ten subjects performed 50 W exercise supine in Control condition and during -45 mmHg LBNP exposure. On single beat basis, we measured heart rate (HR), stroke volume (SV), and we calculated cardiac output (CO). We computed Phase I response amplitudes (A1) using an exponential model. SV A1 was higher under LBNP than in Control (p < 0.05). Conversely, the A1 of HR, was 23 ± 56 % lower under LBNP than in Control (although NS). Since these changes tended to compensate each other, the A1 for CO was unaffected by LBNP. The rapid SV kinetics at exercise onset is compatible with an effect of increased venous return, whereas the vagal withdrawal conjecture cannot be dismissed for HR kinetics. The rapid CO response may indeed be the result of two independent yet parallel mechanisms, as hypothesized, one acting on SV, the other on H

Hypernuclear spectroscopy with K−^- at rest on 7^7Li, 9^9Be, 13^{13}C and 16^{16}O

The FINUDA experiment collected data to study the production of hypernuclei on different nuclear targets. The hypernucleus formation occurred through the strangeness-exchange reaction K^-_{stop} + \; ^AZ \rightarrow \; ^A_{\Lambda}Z + \pi^-. From the analysis of the momentum of the emerging $\pi^-$, binding energies and formation probabilities of $^7_{\Lambda}$Li, $^9_{\Lambda}$Be, $^{13}_{\Lambda}$C and $^{16}_{\Lambda}$O have been measured and are here presented. The behavior of the formation probability as a function of the atomic mass number A is also discussed.Comment: Accepted for publication in PL

The A(Kstop−,π±Σ∓)A′A(K^-_{stop},\pi^\pm\Sigma^\mp)A' reaction on p-shell nuclei

This letter is concerned with the study of the $K^-_{stop}A\rightarrow \pi^\pm\Sigma^\mp A'$ reaction in p-shell nuclei, i.e., $^{6,7}Li$, $^9Be$, $^{13}C$ and $^{16}O$. The $\pi^\pm\Sigma^\mp / K^-_{stop}$ emission rates are reported as a function of $A$. These rates are discussed in comparison with previous findings. The ratio $\pi^-\Sigma^+/\pi^+\Sigma^-$ in p-shell nuclei is found to depart largely from that on hydrogen, which provides support for large in-medium effects possibly generated by the sub-threshold $\Lambda(1405)$. The continuum momentum spectra of prompt pions and free sigmas are also discussed as well as the $\pi^\pm\Sigma^\mp$ missing mass behavior and the link with the reaction mechanism. The apparatus used for the investigation is the FINUDA spectrometer operating at the DA$\Phi$NE $\phi$-factory (LNF-INFN, Italy).Comment: 14 pages, 5 figures, accepted for publication in Phys. Lett.

CAT rs1001179 Single Nucleotide Polymorphism Identifies an Aggressive Clinical Behavior in Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is characterized by an extremely variable clinical course. Although several parameters have been shown to be associated with clinical outcomes in patients with CLL, there remains substantial intragroup clinical heterogeneity in otherwise molecularly and staging homogeneous CLL subgroups. We have recently shown that high catalase (CAT) expression identifies patients with an aggressive clinical course and that higher CAT expression is associated with the presence of the rs1001179 single nucleotide polymorphism (SNP) T allele in the CAT promoter. Herein, we genotyped CLL patients for CAT rs1001179 SNP in an exploratory study (n = 235) and in a sequential independent validation study (n = 531). Time-to-event modeling analyses for time-to-first-treatment (TTFT) from the two patients' cohorts showed that TT genotype was associated with a shorter TTFT, independently of other currently used prognostic parameters in CLL. Moreover, the TT genotype identifies CLL patients with a faster clinical progression even within subgroups of patients with low-risk biological and clinical hallmarks. In conclusion, our data show that the TT genotype identifies CLL patients with a shorter TTFT, pointing to this SNP as a possible prognostic factor, which can improve patients' risk stratification leading to better patient management and personalized therapeutic choices

Annihilation of low energy antiprotons in silicon

The goal of the AE$\mathrm{\bar{g}}$IS experiment at the Antiproton Decelerator (AD) at CERN, is to measure directly the Earth's gravitational acceleration on antimatter. To achieve this goal, the AE$\mathrm{\bar{g}}$IS collaboration will produce a pulsed, cold (100 mK) antihydrogen beam with a velocity of a few 100 m/s and measure the magnitude of the vertical deflection of the beam from a straight path. The final position of the falling antihydrogen will be detected by a position sensitive detector. This detector will consist of an active silicon part, where the annihilations take place, followed by an emulsion part. Together, they allow to achieve 1$$ precision on the measurement of $\bar{g}$ with about 600 reconstructed and time tagged annihilations. We present here, to the best of our knowledge, the first direct measurement of antiproton annihilation in a segmented silicon sensor, the first step towards designing a position sensitive silicon detector for the AE$\mathrm{\bar{g}}$IS experiment. We also present a first comparison with Monte Carlo simulations (GEANT4) for antiproton energies below 5 MeVComment: 21 pages in total, 29 figures, 3 table

Prospects for measuring the gravitational free-fall of antihydrogen with emulsion detectors

The main goal of the AEgIS experiment at CERN is to test the weak equivalence principle for antimatter. AEgIS will measure the free-fall of an antihydrogen beam traversing a moir\'e deflectometer. The goal is to determine the gravitational acceleration g for antihydrogen with an initial relative accuracy of 1% by using an emulsion detector combined with a silicon micro-strip detector to measure the time of flight. Nuclear emulsions can measure the annihilation vertex of antihydrogen atoms with a precision of about 1 - 2 microns r.m.s. We present here results for emulsion detectors operated in vacuum using low energy antiprotons from the CERN antiproton decelerator. We compare with Monte Carlo simulations, and discuss the impact on the AEgIS project.Comment: 20 pages, 16 figures, 3 table

Incidence of thrombotic complications in patients with haematological malignancies with central venous catheters : A prospective multicentre study

This prospective, observational and multicentre study assessed the incidence of, and risk factors for, symptomatic venous thrombotic complications after central venous catheter (CVC) positioning in patients with haematological malignancies. A total of 458 consecutive CVC insertions were registered in 416 patients (81-2% of whom had severe thrombocytopenia). Over the observation period (3 months or up to catheter removal), the incidence of events was: CVC-related deep vein thrombosis (DVT), 1.5%; lower limb DVT, 0.4%; pulmonary embolism (PE), 1.3%; fatal PE, 0.6%; CVC-related superficial thrombophlebitis, 3.9%; CVC-occlusion/malfunction of thrombotic origin, 6.1%; major arterial events, 1.1%. Severe bleeding and CVC-related infections were observed in 3.5% and 4.6% of cases respectively. A composite end point (any venous thromboembolism or superficial thrombophlebitis or CVC occlusion/malfunction) was defined in order to consider venous thrombotic events with a significant impact on clinical practice. With this criterion, the overall incidence was 12.0% (2.54 cases/1000 catheter days). No factor helped to predict venous thrombotic complications: only thrombocytopenia was associated with a weak trend for a reduced risk (odds ratio 0.52; 95% confidence interval 0.26-1.07). No severe bleeding was observed in those patients who received antithrombotic prophylaxis. This study shows that the impact on clinical practice of symptomatic CVC-related thrombotic complications is not negligible in patients with haematological malignancies. (copyright) 2005 Blackwell Publishing Ltd

An improved determination of the two--nucleon induced non mesonic weak decay of Λ\Lambda-hypernuclei

The decay of $\Lambda$-hypernuclei without pion emission, known as Non Mesonic Weak Decay (NMWD), gives an effective tool to investigate $\Delta$S=1 four-baryon interactions. It was theoretically suggested that the two-nucleon induced mechanism could play a substantial role in reproducing the observed NMWD decay rates and nucleon spectra, but at present no direct evidence of such a mechanism has been obtained. The FINUDA experiment, exploiting the possibility to detect both charged and neutral particles coming from the hypernucleus decay, has allowed us to deduce the relative weight of the two nucleon induced decay rate to the total NMWD rate. The value of $\Gamma_{2N}$/$\Gamma_{NMWD}$=0.24$\pm$${0.03_{stat}}^{+0.03_{sys}}_{{-{0.02_{sys}}}}$ has been deduced, with an error reduced by a factor more than two compared with the previous assessment.Comment: 10 pages, 3 figure