Repository UNSAP (Universitas Sebelas April)
Not a member yet
1145 research outputs found
Sort by
Application of machine learning techniques at the CERN Large Hadron Collider
No full textMachine learning techniques have been used extensively in several domains of Science and Engineering for decades. These powerful tools have been applied also to the domain of high-energy physics, in the analysis of the data from particle collisions, for years already. Accelerator physics, however, has not started exploiting machine learning until very recently. Several activities are flourishing in this domain, in view of providing new insights to beam dynamics in circular accelerators, in different laboratories worldwide. This is, for instance, the case for the CERN Large Hadron Collider, where since a few years exploratory studies are being carried out. A broad range of topics have been addressed, such as anomaly detection of beam position monitors, analysis of optimal correction tools for linear optics, optimisation of the collimation system, lifetime and performance optimisation, and detection of hidden correlations in the huge data set of beam dynamics observables collected during the LHC Run 2. Furthermore, very recently, machine learning techniques are being scrutinised for the advanced analysis of numerical simulations data, in view of improving our models of dynamic aperture evolution
Large-k exciton dynamics in GaN epilayers: Nonthermal and thermal regimes
No full textWe present a detailed investigation performed at low temperature (T < 50 K) concerning the exciton dynamics in GaN epilayers grown on c-plane sapphire substrates, focusing on the exciton formation and the transition from the nonthermal to the thermal regime. The time-resolved kinetics of longitudinal-optical-phonon replicas is used to address the energy relaxation in the excitonic band. From picosecond time-resolved spectra, we bring evidence for a long lasting nonthermal excitonic distribution, which accounts for the first 50 ps. Such a behavior is confirmed in different experimental conditions when both nonresonant and resonant excitations are used. At low excitation power density, the exciton formation and their subsequent thermalization are dominated by impurity scattering rather than by acoustic phonon scattering. The estimate of the average energy of the excitons as a function of delay after the excitation pulse provides information on the relaxation time, which describes the evolution of the exciton population to the thermal regime. DOI: 10.1103/PhysRevB.87.075202LASP
Recruiting new neurons from the subventricular zone to the rat postnatal cortex: an organotypic slice culture model
No full textThe neurogenic subventricular zone (SVZ) of the lateral ventricle is a potential source for neuronal replacement in the postnatal or adult neocortex after injury. Here we present a novel model system to directly explore the cellular mechanisms of this process. In order to visualize directed migration from the SVZ towards the cortex, we transplanted green fluorescent protein-labeled progenitor/stem cells into the SVZ of newborn rats. At 2 days after transplantation, we generated organotypic slice cultures and applied fluorescent time-lapse imaging to explore directly the migration and integration of donor cells into the host tissue for up to 2 weeks. Our studies revealed that subventricular grafts provide a significant number of immature neurons to neocortical regions. In the cortex, immature neurons first migrate radially towards the pial surface and then differentiate into GABAergic interneurons. We conclude that our model system presents a novel and effective experimental paradigm to evaluate the recruitment of SVZ-derived neurons into the postnatal cortex, a phenomenon that may represent a potential route for cortical repair.S
Blue monolithic AlInN-based vertical cavity surface emitting laser diode on free-standing GaN substrate
No full textWe report on III-nitride based blue vertical cavity surface emitting lasers using defect-free highly reflective AlInN/GaN distributed Bragg reflectors grown on c-plane free-standing GaN substrates. Lasing is demonstrated at room temperature under pulsed electrical injection. The high lasing threshold current density still prevents devices from continuous wave lasing because of large self-heating. The reasons for such a high threshold are discussed and we show that it mainly comes from large light absorption in the indium tin oxide current spreading layer. Properly tuning both its thickness and its position with respect to the electrical field could remarkably decrease the threshold. © 2012 American Institute of Physics.LASP
Solar disinfection of viruses (SODIS): inactivation of coliphages MS2 and phiX174, human adenovirus and echovirus in water from Switzerland and India
No full textAccess to safe drinking water remains a challenge in many regions of the world. New methods to treat drinking water are constantly developped and improved in both in industrialised countries and in developing countries. SODIS is an interesting household-level disinfection technique that simply consists of pouring water into a PET bottle and exposing it to sunlight for at least 6 hours. Bacteria are efficiently inactivated by sunlight during SODIS, but the efficiency of SODIS on virus removal is much less studied. In this work, the inactivation of bacteriophages MS2 and phiX174, and human echovirus and adenovirus was studied in three different waters, two from India and one from Switzerland. Good removal (4 logs in 6 hours at 22°C and a fluence rate of 600 1.34 kJ/cm2) of MS2 was achieved in Swiss tap water, while less efficient inactivation was achieved in both Indian waters for MS2 and echovirus (1 log in 6 hours at 22°C and a fluence rate of 1.34 kJ/cm2). Both phiX174 and adenovirus were much more resistant to SODIS disinfection and less than 1 log of inactivation was obtained in Swiss tap water for phiX174. However, inactivation was not significantly different from the dark control in Indian water and for all experiments with adenovirus. Echovirus was inactivated similarly than MS2 and adenovirus was equally slow as phiX174. An increased temperature during SODIS enhanced inactivation substantially; 6 logs in 6 hours could be expected at 45 °C and with a fluence rate of 1.34 kJ/cm2. Indirect-solar inactivation was responsible for the MS2 removal, while direct inactivation via sunlight absorption of genome was not occurring during SODIS. We argue that iron could be responsible for the formation of reactive oxygen species which react with the viruses and yield their inactivation. The slower inactivation in Indian waters was probably due to the quenching effect of the higher concentration of organic matter. Removal of echoviruses during SODIS could be sufficient (4 logs in 6 hours) particularly at higher temperatures and for water with a low organic matter content. In contrast, SODIS may not be effective to remove Adenoviruses.LEVSIE-
