Photoluminescence properties of 4,5-dimethyl-4′,5′-di(methylamido) tetrathiafulvalene thin film grown by thermal evaporation

In this paper, a temperature dependence study of photoluminescence spectra of vacuum-deposited organic donor tetrathiafulvalene: 4,5-dimethyl-4′,5′-di(methylamido) tetrathiafulvalene thin layers is presented. The investigated layers were deposited in a high vacuum (2 × 10−6 Torr) using molecular beam deposition (MBD) technique on n-doped (1 1 1) oriented silicon substrates. The photoluminescence studies were carried out in the temperatures range [13 K–325 K]. Under a 325 nm wavelength light excitation and at low-temperature a broad luminescence emission peak was observed in the UV–Visible and 2 peaks in the near infrared region. The photoluminescence spectra exhibit temperature dependence with a maximum emission at 180 K. Furthermore, an enhancement of the photoluminescence signal under a continuous excitation was observed at room temperature

Hubbard model versus t-J model: The one-particle spectrum

The origin of the apparent discrepancies between the one-particle spectra of the Hubbard and t-J models is revealed: Wavefunction corrections, in addition to the three-site terms, should supplement the bare t-J. In this way a quantitative agreement between the two models is obtained, even for the intermediate-$U$ values appropriate for the high-Tc cuprate superconductors. Numerical results for clusters of up to 20 sites are presented. The momentum dependence of the observed intensities in the photoemission spectra of Sr2CuO2Cl2 are well described by this complete strong-coupling approach.Comment: 4 two-column RevTeX pages, including 4 Postscript figures. Uses epsf. Accepted for publication in Physical Review B, Rapid Communicatio

Processing optimization with parallel computing for the J-PET tomography scanner

The Jagiellonian-PET (J-PET) collaboration is developing a prototype TOF-PET detector based on long polymer scintillators. This novel approach exploits the excellent time properties of the plastic scintillators, which permit very precise time measurements. The very fast, FPGA-based front-end electronics and the data acquisition system, as well as, low- and high-level reconstruction algorithms were specially developed to be used with the J-PET scanner. The TOF-PET data processing and reconstruction are time and resource demanding operations, especially in case of a large acceptance detector, which works in triggerless data acquisition mode. In this article, we discuss the parallel computing methods applied to optimize the data processing for the J-PET detector. We begin with general concepts of parallel computing and then we discuss several applications of those techniques in the J-PET data processing.Comment: 8 page

Spatial Structure of Spin Polarons in the t-J Model

The deformation of the quantum Neel state induced by a spin polaron is analyzed in a slave fermion approach. Our method is based on the selfconsistent Born approximation for Green's and the wave function for the quasiparticle. The results of various spin-correlation functions relative to the position of the moving hole are discussed and shown to agree with those available from small cluster calculations. Antiferromagnetic correlations in the direct neighborhood of the hole are reduced, but they remain antiferromagnetic even for J as small as 0.1 t. These correlation functions exhibit dipolar distortions in the spin structure, which sensitively depend on the momentum of the quasiparticle. Their asymptotic decay with the distance from the hole is governed by power laws, yet the spectral weight of the quasiparticles does not vanish.Comment: 12 pages, 2 postscipt files with figures; uses REVTeX, to be published in Phys. Rev. B, Feb. 199

Structures of Cu-Based Glass Forming System Doped with Iron

The effects of iron additions on the structure of (Cu0.47Ti0.34Zr0.11Ni0.08)100−xFex (x = 0, 1.5, 3, 6) glass forming system are presented. The alloys were synthesized by arc melting of high purity elements and melt spun to form rapidly quenched ribbons. X-ray diffraction studies showed the amorphous structure of the base and Fe-containing alloys, confirmed by the presence of exothermic peaks on differential scanning calorimetry curves. Bulk samples in the form of rods (Φ3 × 55 mm) were cast using a suction casting unit attached to the arc melter. Structural investigations revealed partial crystallization of the base Cu47Ti34Zr11Ni8 alloy. Iron additions significantly decreased the glass forming ability of the alloy, leading to primary crystallization of dendrites

Incretin treatment and risk of pancreatitis in patients with type 2 diabetes mellitus : systematic review and meta-analysis of randomised and non-randomised studies

Objective To investigate the risk of pancreatitis associated with the use of incretin-based treatments in patients with type 2 diabetes mellitus. Design Systematic review and meta-analysis. Data sources Medline, Embase, the Cochrane Central Register of Controlled Trials (CENTRAL), and ClinicalTrials.gov. Eligibility criteria Randomised and non-randomised controlled clinical trials, prospective or retrospective cohort studies, and case-control studies of treatment with glucagon-like peptide-1 (GLP-1) receptor agonists or dipeptidyl peptidase-4 (DPP-4) inhibitors in adults with type 2 diabetes mellitus compared with placebo, lifestyle modification, or active anti-diabetic drugs. Data collection and analysis Pairs of trained reviewers independently screened for eligible studies, assessed risk of bias, and extracted data. A modified Cochrane tool for randomised controlled trials and a modified version of the Newcastle-Ottawa scale for observational studies were used to assess bias. We pooled data from randomised controlled trials using Peto odds ratios, and conducted four prespecified subgroup analyses and a post hoc subgroup analysis. Because of variation in outcome measures and forms of data, we describe the results of observational studies without a pooled analysis. Results 60 studies (n=353 639), consisting of 55 randomised controlled trials (n=33 350) and five observational studies (three retrospective cohort studies, and two case-control studies; n=320 289) were included. Pooled estimates of 55 randomised controlled trials (at low or moderate risk of bias involving 37 pancreatitis events, raw event rate 0.11%) did not suggest an increased risk of pancreatitis with incretins versus control (odds ratio 1.11, 95% confidence interval 0.57 to 2.17). Estimates by type of incretin suggested similar results (1.05 (0.37 to 2.94) for GLP-1 agonists v control; 1.06 (0.46 to 2.45) for DPP-4 inhibitors v control). Analyses according to the type of control, mode, duration of treatment, and individual incretin agents suggested no differential effect by subgroups, and sensitivity analyses by alternative statistical modelling and effect measures did not show important differences in effect estimates. Three retrospective cohort studies (moderate to high risk of bias, involving 1466 pancreatitis events, raw event rate 0.47%) also did not suggest an increased risk of pancreatitis associated with either exenatide (adjusted odds ratios 0.93 (0.63 to 1.36) in one study and 0.9 (0.6 to 1.5) in another) or sitagliptin (adjusted hazard ratio 1.0, 0.7 to 1.3); a case-control study at moderate risk of bias (1003 cases, 4012 controls) also suggested no significant association (adjusted odds ratio 0.98, 0.69 to 1.38). Another case-control study (1269 cases, 1269 controls) at moderate risk of bias, however, suggested that the use of either exenatide or sitagliptin was associated with significantly increased odds of acute pancreatitis (use within two years v no use, adjusted odds ratio 2.07, 1.36 to 3.13). Conclusions The available evidence suggests that the incidence of pancreatitis among patients using incretins is low and that the drugs do not increase the risk of pancreatitis. Current evidence, however, is not definitive, and more carefully designed and conducted observational studies are warranted to definitively establish the extent, if any, of increased risk

Feasibility studies of the polarization of photons beyond the optical wavelength regime with the J-PET detector

J-PET is a detector optimized for registration of photons from the electron-positron annihilation via plastic scintillators where photons interact predominantly via Compton scattering. Registration of both primary and scattered photons enables to determinate the linear polarization of the primary photon on the event by event basis with a certain probability. Here we present quantitative results on the feasibility of such polarization measurements of photons from the decay of positronium with the J-PET and explore the physical limitations for the resolution of the polarization determination of 511 keV photons via Compton scattering. For scattering angles of about 82 deg (where the best contrast for polarization measurement is theoretically predicted) we find that the single event resolution for the determination of the polarization is about 40 deg (predominantly due to properties of the Compton effect). However, for samples larger than ten thousand events the J-PET is capable of determining relative average polarization of these photons with the precision of about few degrees. The obtained results open new perspectives for studies of various physics phenomena such as quantum entanglement and tests of discrete symmetries in decays of positronium and extend the energy range of polarization measurements by five orders of magnitude beyond the optical wavelength regime.Comment: 10 pages, 14 figures, submitted to EPJ

Electron momentum distribution in underdoped cuprates

We investigate the electron momentum distribution function (EMD) in a weakly doped two-dimensional quantum antiferromagnet (AFM) as described by the t-J model. Our analytical results for a single hole in an AFM based on the self-consistent Born approximation (SCBA) indicate an anomalous momentum dependence of EMD showing 'hole pockets' coexisting with a signature of an emerging large Fermi surface. The position of the incipient Fermi surface and the structure of the EMD is determined by the momentum of the ground state. Our analysis shows that this result remains robust in the presence of next-nearest neighbor hopping terms in the model. Exact diagonalization results for small clusters are with the SCBA reproduced quantitatively.Comment: 5 pages, submitted to PR

Bilayer manganites: polarons in the midst of a metallic breakdown

The exact nature of the low temperature electronic phase of the manganite materials family, and hence the origin of their colossal magnetoresistant (CMR) effect, is still under heavy debate. By combining new photoemission and tunneling data, we show that in La{2-2x}Sr{1+2x}Mn2O7 the polaronic degrees of freedom win out across the CMR region of the phase diagram. This means that the generic ground state is that of a system in which strong electron-lattice interactions result in vanishing coherent quasi-particle spectral weight at the Fermi level for all locations in k-space. The incoherence of the charge carriers offers a unifying explanation for the anomalous charge-carrier dynamics seen in transport, optics and electron spectroscopic data. The stacking number N is the key factor for true metallic behavior, as an intergrowth-driven breakdown of the polaronic domination to give a metal possessing a traditional Fermi surface is seen in the bilayer system.Comment: 7 pages, 2 figures, includes supplementary informatio