Resistive plate chambers for time-of-flight measurements

The applications of Resistive Plate Chambers (RPCs) have recently been extended by the development of counters with time resolution below 100 ps sigma for minimum ionising particles. Applications to HEP experiments have already taken place and many further applications are under study. In this work we address the operating principles of such counters along with some present challenges, with emphasis on counter aging.Comment: Presented at "PSD6 - 6th International Conference on Position Sensitive Detectors", 9-13 September 2002, Leicester, UK. Submitted to Nuclear Instruments and Methods

Diffusion of Hydrogen in Pd Assisted by Inelastic Ballistic Hot Electrons

Sykes {\it et al.} [Proc. Natl. Acad. Sci. {\bf 102}, 17907 (2005)] have reported how electrons injected from a scanning tunneling microscope modify the diffusion rates of H buried beneath Pd(111). A key point in that experiment is the symmetry between positive and negative voltages for H extraction, which is difficult to explain in view of the large asymmetry in Pd between the electron and hole densities of states. Combining concepts from the theory of ballistic electron microscopy and electron-phonon scattering we show that H diffusion is driven by the $s$-band electrons only, which explains the observed symmetry.Comment: 5 pages and 4 figure

Rotation of Hot Horizontal Branch Stars in the Globular Clusters NGC 1904, NGC 2808, NGC 6093 and NGC 7078

We present high resolution UVES+VLT spectroscopic observations of 56 stars in the extended horizontal branch (EHB) of the Galactic globular clusters NGC 1904, NGC 2808, NGC 6093, and NGC 7078. Our data reveal for the first time the presence in NGC 1904 of a sizable population of fast (vsini > 20 km/s) horizontal branch (HB) rotators, confined to the cool end of the EHB, similar to that found in M13. We also confirm the fast rotators already observed in NGC 7078. The cooler stars (Teff < 11,500 K) in these three clusters show a range of rotation rates, with a group of stars rotating at ~ 15 km/s or less, and a fast rotating group at ~ 30 km/s. Apparently, the fast rotators are relatively more abundant in NGC 1904 and M13, than in NGC 7078. No fast rotators have been identified in NGC 2808 and NGC 6093. All the stars hotter than Teff ~ 11,500 K have projected rotational velocities vsini < 12 km/s, but less than 20% have vsini < 2 km/s. The connection between photometric gaps in the HB and the change in the projected rotational velocities is not confirmed by the new data. However, our data are consistent with a relation between this discontinuity and the HB jump. We discuss a number of possibilities for the origin of the stellar rotation distribution along the HB. We conclude that none of them can yet provide a satisfactory explanation of the observations.Comment: 12 pages, 3 figures, ApJ Letter, accepte

Improving count rate capability of timing RPCs by increasing the detector working temperature

This communication describes test beam results, focusing on detection efficiency and timing precision, of common float glass timing Resistive Plate Chambers (tRPCs) exposed to a $2.7$~GeV proton beam and operated at above ambient temperature in order to increase the count rate capability of the chambers, by exploiting the reduction in the resistivity of the glass electrodes. Results suggest that the count rate capability can be extended at least up to $1500~Hz/cm^2$ when the detector is operated at $40.6^{\circ}$C without noticeable loss of efficiency or timing precision degradation with values of $90\%$ and $100$~ps, respectively, for this specific timing RPC arrangement.Comment: to be published in Proceedings of 15th Pisa Meeting on Advanced Detector

Identification of defects originated during the filling of cast pieces through particles modelling

In casting processes, strong recirculation zones may trap air, gases and strip particles of sand off the mold affecting seriously the quality of the cast pieces. Especially during the filling of molten pieces with large surfaces, several faults were detected which are responsible of considerable economic losses in such casting processes. The aim of this work is focused on the correct identification of these physical phenomena, through Computational Fluid Dynamics (CFD). A fully experimental work correlating a saline solution with similar properties than the liquid alloy was carried out in order to guess the flow behavior inside the mold. Different parameters such as filling time, temperature and velocity of the liquid alloy together with the geometrical design of the mold were taken into account. The simulated evolution profiles and propagation speeds were compared with the laboratory experiments showing good agreement, validating thus the numerical model. Through an advanced particles modeling feature from a commercial package, the potential to predict and later correct some casting defects was demonstrated. As a conclusion, the mold together with supply channels need to be carefully optimized in order to control the correct direction of solidification avoiding the appearance of oxides but also to prevent stripping the sand off the walls

Brane Bremsstrahlung in DBI Inflation

We consider the effect of trapped branes on the evolution of a test brane whose motion generates DBI inflation along a warped throat. The coupling between the inflationary brane and a trapped brane leads to the radiation of non-thermal particles on the trapped brane. We calculate the Gaussian spectrum of the radiated particles and their backreaction on the DBI motion of the inflationary brane. Radiation occurs for momenta lower than the speed of the test brane when crossing the trapped brane. The slowing down effect is either due to a parametric resonance when the interaction time is small compared to the Hubble time or a tachyonic resonance when the interaction time is large. In both cases the motion of the inflationary brane after the interaction is governed by a chameleonic potential,which tends to slow it down. We find that a single trapped brane can hardly slow down a DBI inflaton whose fluctuations lead to the Cosmic Microwave Background spectrum. A more drastic effect is obtained when the DBI brane encounters a tightly spaced stack of trapped branes.Comment: 20 pages, 1 figur

Search and characterization of viral antigens able to stimulate a protective immune response against CMV infection for vaccine design

Motivation: Despite improvements in detection and treatment, human cytomegalovirus (CMV) infection is the main cause of morbi-mortality in solid organ transplant (SOT) recipients. Several efforts have been made to develop a vaccine to prevent CMV infection. However, no vaccine had been licenced to date. Efforts are necessary to identify antigens able to stimulate an immune response to protect against CMV infection.Methods: We used serum (from SOT recipients with previous CMV infection and neutralizing antibody titers &gt;480) as primary antibody to identify proteins from CMV-infected cell lysates, not recognized by the serum from the same patient with no neutralizing antibodies or in the mock-infected lysate. The identified bands were sequenced by mass spectrometry. The gene of the identified candidates was amplified by PCR using specific primers and cloned into the expression plasmids PTYB21 (fused to intein tail to purify the recombinant protein) and into pCDNA plasmid (for DNA vaccine). The PTYB21 construct was transformed into the E. coli BL21 Rosetta strain for protein expression. Protein purification was performed using the IMPACT kit (BioLabs) using a chitin affinity column. The pcDNA construct was transformed into the E. coli TOP-10 strain. All constructs were sequenced. Protein antigenicity was analyzed using VAxiJen informatic tool (threshold 0.4).Results: We identified three proteins with 135, 70 and 50 kDa approximately. The 48 kDa candidate predicted to be from the tegument and with an antigenicity score of 0.520 was selected. A 1200pb band corresponding to the predicted size of the gene was amplified. Due to difficulties of blunt ligations we introduced a dephosphorylation step of the insert before ligation. We obtained 3 positive clones with the following pattern: a band of 1280 bp corresponding to the insert and a 7514 bp for the PTYB21 plasmid and 5400 bp for the pCDNA plasmid. Sequencing of positive clones showed a 100% homology. The 48 kDa protein had the highest expression using 0.5 mM IPTG for 6 hours, and was isolated in the insoluble fraction. We are in the process of optimizing the conditions for protein purification.Conclusions:The use of patient sera is an optimal approach to identify proteins that induce an specific immune response against CMV that may be candidates for vaccine design. The process for protein purification must be optimized for each candidate since depends on multiple factors such as size and solubility