Surface-acoustic-wave driven planar light-emitting device

Electroluminescence emission controlled by means of surface acoustic waves (SAWs) in planar light-emitting diodes (pLEDs) is demonstrated. Interdigital transducers for SAW generation were integrated onto pLEDs fabricated following the scheme which we have recently developed. Current-voltage, light-voltage and photoluminescence characteristics are presented at cryogenic temperatures. We argue that this scheme represents a valuable building block for advanced optoelectronic architectures

Atmospheric circulation patterns, cloud-to-ground lightning, and locally intense convective rainfall associated with debris flow initiation in the Dolomite Alps of northeastern Italy

The Dolomite Alps of northeastern Italy experience debris flows with great frequency during the summer months. An ample supply of unconsolidated material on steep slopes and a summer season climate regime characterized by recurrent thunderstorms combine to produce an abundance of these destructive hydro-geologic events. In the past, debris flow events have been studied primarily in the context of their geologic and geomorphic characteristics. The atmospheric contribution to these mass-wasting events has been limited to recording rainfall and developing intensity thresholds for debris mobilization. This study aims to expand the examination of atmospheric processes that preceded both locally intense convective rainfall (LICR) and debris flows in the Dolomite region. 500 hPa pressure level plots of geopotential heights were constructed for a period of 3 days prior to debris flow events to gain insight into the synoptic-scale processes which provide an environment conducive to LICR in the Dolomites. Cloud-to-ground (CG) lightning flash data recorded at the meso-scale were incorporated to assess the convective environment proximal to debris flow source regions. Twelve events were analyzed and from this analysis three common synoptic-scale circulation patterns were identified. Evaluation of CG flashes at smaller spatial and temporal scales illustrated that convective processes vary in their production of CF flashes (total number) and the spatial distribution of flashes can also be quite different between events over longer periods. During the 60 min interval immediately preceding debris flow a majority of cases exhibited spatial and temporal colocation of LICR and CG flashes. Also a number of CG flash parameters were found to be significantly correlated to rainfall intensity prior to debris flow initiation

Acoustic charge transport in n-i-n three terminal device

We present an unconventional approach to realize acoustic charge transport devices that takes advantage from an original input region geometry in place of standard Ohmic input contacts. Our scheme is based on a n-i-n lateral junction as electron injector, an etched intrinsic channel, a standard Ohmic output contact and a pair of in-plane gates. We show that surface acoustic waves are able to pick up electrons from a current flowing through the n-i-n junction and steer them toward the output contact. Acoustic charge transport was studied as a function of the injector current and bias, the SAW power and at various temperatures. The possibility to modulate the acoustoelectric current by means of lateral in-plane gates is also discussed. The main advantage of our approach relies on the possibility to drive the n-i-n injector by means of both voltage or current sources, thus allowing to sample and process voltage and current signals as well.Comment: 9 pages, 3 figures. Submitted to Applied Physics Letter

Determination of the s-wave Scattering Length of Chromium

We have measured the deca-triplet s-wave scattering length of the bosonic chromium isotopes $^{52}$Cr and $^{50}$Cr. From the time constants for cross-dimensional thermalization in atomic samples we have determined the magnitudes $|a(^{52}Cr)|=(170 \pm 39)a_0$ and $|a(^{50}Cr)|=(40 \pm 15)a_0$, where $a_0=0.053nm$. By measuring the rethermalization rate of $^{52}$Cr over a wide temperature range and comparing the temperature dependence with the effective-range theory and single-channel calculations, we have obtained strong evidence that the sign of $a(^{52}Cr)$ is positive. Rescaling our $^{52}$Cr model potential to $^{50}$Cr strongly suggests that $a(^{50}Cr)$ is positive, too.Comment: v3: corrected typo in y-axis scaling of Figs. 3 and

Tailoring symmetry groups using external alternate fields

Macroscopic systems with continuous symmetries subjected to oscillatory fields have phases and transitions that are qualitatively different from their equilibrium ones. Depending on the amplitude and frequency of the fields applied, Heisenberg ferromagnets can become XY or Ising-like -or, conversely, anisotropies can be compensated -thus changing the nature of the ordered phase and the topology of defects. The phenomena can be viewed as a dynamic form of "order by disorder".Comment: 4 pages, 2 figures finite dimension and selection mechanism clarifie

Epidemiologic aspects of closed-globe trauma

Purpose: To describe the epidemiologic aspects of closed-globe injury with contusion and its alterations. Methods: Forty patients with closed-globe injury, were analyzed prospectively between January 1998 and February 1999. They were attended at the Ocular Trauma Outpatient Clinic of the Department of Ophthalmology of the Escola Paulista de Medicina-Federal University of São Paulo. A complete ophthalmologic examination was performed in all patients and they were classified according to the new classification proposed by Pieramici et al (1997). Results: Sixty-seven and a half percent (67.5%) of the studied patients were less than 30 years old. The main causes were: accidents at home and acts of violence with 32.5% each. In relation to visual acuity, with best correction, 60.0% of the patients did not achieve 20/100 visual acuity. Seventy-five per cent (75.0%) showed improvement in visual acuity during follow-up and most in less than 1 month. Fifty-two and a half percent (52.5%) were classified as zone III. Fifty percent (50%) of the patients developed hyphema and 67.5% had some grade of angle recession, higher than 180° in 30.0%. Conclusions: In relation the patients attended at the Ocular Trauma Outpatient Clinic of the Universidade Federal de São Paulo (UNIFESP), Escola Paulista de Medicina (EPM), more than 13 years old, males, with closed-globe injury we may conclude: 1. it is more prevalent in adults; 2. the main causes were domestic accidents and violence (32.5% each); 3. it presents good visual acuity recovery, except for zone III patients; 4. fifty per cent developed hyphema; 5. more than a half had angle recession (67.5%) and 30.0% had angle recession over 180°.Objetivo: Descrever os aspectos epidemiológicos do traumatismo ocular fechado com contusão e suas alterações. Métodos: Foram avaliados, prospectivamente, 40 olhos de 40 pacientes, com idade superior a 13 anos, do sexo masculino, com traumatismo ocular fechado contuso, no período de janeiro de 1998 a fevereiro de 1999, atendidos no Ambulatório de Trauma Ocular do Departamento de Oftalmologia da Escola Paulista de Medicina-Universidade Federal de São Paulo (UNIFESP). Todos foram submetidos a exame oftalmológico completo e classificados de acordo com a nova classificação proposta por Pieramici et al. (1997). Resultados: Sessenta e sete e meio por cento (67,5%) dos pacientes tinham menos de 30 anos. As principais causas de traumatismo ocular contuso foram acidentes domésticos e violência com 32,5% cada. Em relação à acuidade visual, medida com a melhor correção, 60,0% apresentaram acuidade menor que 20/100 e 75,0% melhora da acuidade visual durante o acompanhamento, sendo que a maioria evoluiu com melhora em menos de 1 mês. Cinqüenta e dois e meio por cento (52,5%) foram classificados como zona III. Cinqüenta por cento (50%) dos pacientes evoluíram com hifema e 67,5% com algum grau de recessão angular, sendo 30% maior que 180°. Conclusões: Em relação aos pacientes atendidos no Ambulatório de Trauma Ocular da Universidade Federal do Estado de São Paulo - Escola Paulista de Medicina com idade menor de 13 anos e sexo masculino, com traumatismo ocular contuso podemos concluir que: 1. apresentou maior prevalência no adulto jovem; 2. as principais causas foram: acidentes domésticos e violência (32,5% cada); 3. apresenta boa recuperação da acuidade visual, exceto os pacientes zona III; 4. cinqüenta por cento evoluiu com hifema; 5. mais da metade, 67,5% apresentaram algum grau de recessão angular, sendo 30,0% maior que 180°.UNIFESP Departamento de OftalmologiaUNIFESP Departamento de Oftalmologia setor de Pronto Socorro e Trauma OcularUNIFESP, Depto. de OftalmologiaUNIFESP, Depto. de Oftalmologia setor de Pronto Socorro e Trauma OcularSciEL

Multichannel quantum-defect theory for ultracold atom-ion collisions

We develop an analytical model for ultracold atom-ion collisions using the multichannel quantum-defect formalism. The model is based on the analytical solutions of the r^-4 long-range potential and on the application of a frame transformation between asymptotic and molecular bases. This approach allows the description of the atom-ion interaction in the ultracold domain in terms of three parameters only: the singlet and triplet scattering lengths, assumed to be independent of the relative motion angular momentum, and the lead dispersion coefficient of the asymptotic potential. We also introduce corrections to the scattering lengths that improve the accuracy of our quantum-defect model for higher order partial waves, a particularly important result for an accurate description of shape and Feshbach resonances at finite temperature. The theory is applied to the system composed of a 40Ca+ ion and a Na atom, and compared to numerical coupled-channel calculations carried out using ab initio potentials. For this particular system, we investigate the spectrum of bound states, the rate of charge-transfer processes, and the collision rates in the presence of magnetic Feshbach resonances at zero and finite temperature.Comment: 39 pages, 21 figure

U3+/LiYF4, a promising IR laser

Under reducing conditions, single crystal of LiYF4 doped with 762 ppm of U3+ were obtained. Absorption and fluorescence spectra of this system are presented as well as the energy level scheme of the lasing transition. Oscillator strength and laser cross section between Stark levels of the [MATH] transition are calculated

IMPACT OF AGRICULTURAL MANAGEMENT ON COMMUNITIES OF ORIBATIDA, GAMASINA AND COLLEMBOLA IN ITALIAN AND FRENCH VINEYARDS

Quantitative and qualitative analyses among the soil microarthropods can be used in biomonitoring as tools in multi-disciplinary approach to characterize soil quality. Three groups of microarthropods - Collembola and Oribatida as detrivores and Gamasina as predators - were selected to evaluate the impact of different management treatments adopted to recover degraded soil in organic. Differences in arthropod populations between French and Italian sites were registered. In Italy, after two years of recovering treatments, an increase of the abundances of all groups, particularly detritivores in degraded plots, was observed. The population of gamasids increased, in all sites, only in non degraded plots. Soil invertebrates of similar trophic groups, like collembolans and oribatids, seem to differently respond to treatments: the collembolans were more affected by some agronomic practices enhancing soil fertility

A major electronics upgrade for the H.E.S.S. Cherenkov telescopes 1-4

The High Energy Stereoscopic System (H.E.S.S.) is an array of imaging atmospheric Cherenkov telescopes (IACTs) located in the Khomas Highland in Namibia. It consists of four 12-m telescopes (CT1-4), which started operations in 2003, and a 28-m diameter one (CT5), which was brought online in 2012. It is the only IACT system featuring telescopes of different sizes, which provides sensitivity for gamma rays across a very wide energy range, from ~30 GeV up to ~100 TeV. Since the camera electronics of CT1-4 are much older than the one of CT5, an upgrade is being carried out; first deployment was in 2015, full operation is planned for 2016. The goals of this upgrade are threefold: reducing the dead time of the cameras, improving the overall performance of the array and reducing the system failure rate related to aging. Upon completion, the upgrade will assure the continuous operation of H.E.S.S. at its full sensitivity until and possibly beyond the advent of CTA. In the design of the new components, several CTA concepts and technologies were used and are thus being evaluated in the field: The upgraded read-out electronics is based on the NECTAR readout chips; the new camera front- and back-end control subsystems are based on an FPGA and an embedded ARM computer; the communication between subsystems is based on standard Ethernet technologies. These hardware solutions offer good performance, robustness and flexibility. The design of the new cameras is reported here.Comment: Proceedings of the 34th International Cosmic Ray Conference, 30 July- 6 August, 2015, The Hague, The Netherland