No abstract available

[en] The requirements of large dynamic range, 40 MHz readout and 4 T magnetic field of the CMS Hadronic calorimeter have led to the development of a custom Hybrid PhotoDiode (HPD). In the last 5 years many improvements have been made in cooperation with DEP and Canberra to the basic HPD concept to improve the performance. A 200-μm thick 19-channel PIN diode array with various surface treatments has been developed to ensure fast pulse behavior and low optical and capacitive crosstalk

[en] Full text of publication follows: Hydrogen is a clean fuel that will be used in automotive transport when the problem of storage will be solved. The difficulties of H₂ storage (available space, security and performance, etc...) require a material that can store 5 weight % of hydrogen. Research is focused on new materials that can assume the constraints imposed by the automotive applications. Among these materials, the nano-structured carbons (nano-fibers and single walled carbon nano-tubes) were claimed to be promising by numerous authors [1-3]. The more promising carbon materials for hydrogen adsorption are those having micropores (i. e. single walled carbon nano-tubes and activated carbon), for which the energy of sorption of hydrogen molecules is theoretically higher [7- 8]. Presently, the best performance of hydrogen adsorption was found in super-activated micro-porous carbons sorbing 5 weight % at 77 K, and almost 0.5 % at room temperature and 6 MPa [9]. Up to now, the performance of these materials can still be improved as the known mechanism of sorption in these carbon materials: physisorption controlled by Van der Waals attractive forces through London interaction is efficient at cryogenic temperatures (77 K) where the interaction between adsorbent and adsorbate becomes stronger. One way to improve the attractive interaction between adsorbent and molecule is to increase the forces due to the interaction of electrical field and induced dipole of the molecule. This can be theoretically tailored in carbon materials through the electron charge transfer by electron donors who can provide an increase in the electrical field al the surface of the adsorbent. Then, the doping of carbon substrates, appearing to be a promising method to increase the energy of adsorption has been proposed in recent papers as a solution to obtain good hydrogen adsorption properties at appropriate temperatures close to room temperatures [10-12]. Thus, we have studied the adsorption properties of doped microporous carbons (SWNTs and activated carbons). The raw nano-structured carbon materials are microporous activated carbons (BET specific surface area: 1600 m²/g), electric-arc closed-end single-walled carbon nano-tubes (SWNTs), and HiPCO SWNTs. They have been doped in the vapor phase by K, and Li (in order to obtain KC₇, KC₁₀, LiC₁₈ SWNTs and LiC₆, LiC₁₈, KC₂₄ activated carbons). The hydrogen adsorption-desorption isotherms of the doped activated carbons were obtained at room temperature and at 77 K, up to 3 MPa, by a volumetric method. The adsorption of D₂ was studied in situ on doped nano-tubes and filaments by neutron diffraction on DIB experiment (ILL), at λ = 2.52 Angstroms, as a function of temperature [300-20 K] and pressure. Simultaneously the adsorption isotherms were recorded in the range 0-0.1 MPa [13]. Doping of microporous carbon by Li or K leads to an increase in the energy of adsorption of H₂ or D₂ molecules. Thus, the room temperature sorption capacities (at P≤3 MPa) can be higher than that of the raw materials after slight doping. However, the maximum H₂ (or D₂) storage measured at T≤ 77 K is lower than the one of pristine materials as the sites of adsorption are occupied by alkali ions inserted in the micropores [14]. The microporous adsorption sites of doped single-walled carbon nano-tubes, identified by neutron diffraction, are both the interstitial voids (in electric-arc or HiPCO tubes) in between the tubes and the central canals of the tubes (only in HiPCO tubes) [15]. We have also prepared nano-structured porous doped carbons by ball-milling carbon host materials with some dopant, such as alkali or alkaline earth metal. The new nano-porous carbons obtained by this method have been characterised and tested for their hydrogen-adsorption properties. [1] A. Chambers et al, J. Phys. Chem. B, 102, 4253, 1998; [2] A. C. Dillon et al, Nature, 386, 377, 1997; [3] J. Conard, Ann. Chim. Sci. Mat 26, 107, 2001; [4] A. Zuttel et al, Int J. Hydrogen Energy, 27, 203, 2002; [5] G. G. Tibbetts et al, Carbon 39, 2291, 2001; [6] C. C. Ahn et al, Appl. Phys. Lett, 73, 3378, 1998; [7] M. Rzepka, et al, J. Phys. Chem. B, 702 10894, 1998; [8] M. Shiraisly et al, Chem. Phys. Lett., 367 633, 2003; [9] P. Benard et al, Langmuir, 17 1950, 2001; [l0] G. E. Froudakis, Nanoletters 1, 531 2001; [11] 0. Maresca, et al, accepted in Journal of Chemical Physics, 2004; [12] W.-Q. Deng et al, Phys. Rev Letters 92, 166103-1,2004; [13] S. Challet et al, Chemical Physics Letters, 377, 544 2003; [14] S. Challet et al, Journal of Physics and Chemistry of Solids, 65, 541 2004; [15] S. Los et al, accepted in Ann. Chim. Sci. Mat., 2005. (authors)

[en] The readout electronics designed for the D null Muon Upgrade are described. These electronics serve three detector subsystems and one trigger system. The front-ends and readout hardware are synchronized by means of timing signals broadcast from the D null Trigger Framework. The front-end electronics have continuously running digitizers and two levels of buffering resulting in nearly deadtimeless operation. The raw data is corrected and formatted by 16- bit fixed point DSP processors. These processors also perform control of the data buffering. The data transfer from the front-end electronics located on the detector platform is performed by serial links running at 160 Mbit/s. The design and test results of the subsystem readout electronics and system interface are discussed

[en] Polycrystalline or single-crystal ferroelectric materials present dielectric dispersion in the frequency range 100 MHz-1 GHz that has been attributed to a dispersive (relaxation-like) mechanism as well as a resonant mechanism. Particularly in 'normal' ferroelectric materials, a dielectric response that is indistinguishable from dispersion or a resonance has been reported. Nevertheless, the reported results are not conclusive enough to distinguish each mechanism clearly. A detailed study of the dielectric dispersion phenomenon has been carried out in PbTiO₃-based ferroelectric ceramics, with the composition Pb_1-xLa_xTiO₃ (x = 0.15), over a wide range of temperatures and frequencies, including microwave frequencies. The dielectric response of La-modified lead titanate ferroelectric ceramics, in 'virgin' and poled states, has been investigated in the temperature and frequency ranges 300-450 K and 1 kHz-2 GHz, respectively. The results revealed that the frequency dependence of the dielectric anomalies, depending on the measuring direction with respect to the orientation of the macroscopic polarization, may be described as a general mechanism related to an 'over-damped' resonant process. Applying either a uniaxial stress along the measurement field direction or a poling electric field parallel and/or perpendicular to the measuring direction, a resonant response of the real and imaginary components of the dielectric constant is observed, in contrast to the dispersion behavior obtained in the absence of the stress, for the 'virgin' samples. Both results, resonance and/or dispersion, can be explained by considering a common mechanism involving a resonant response (damped and/or over-damped) which is strongly affected by a ferroelastic-ferroelectric coupling, contributing to the low-field dielectric constant

[en] A volumetric method was applied to study an adsorption coefficient of hydrogen molecules in a gas phase on super activated carbon surface. The investigations were focused on getting the best possible materials for the energy storage. Several treatments on raw samples were used to improve adsorption properties. The biggest capacities were obtain after high temperature treatment at reduced atmosphere. The adsorption coefficient at 77 K and 2 MPa amounts to 3.158 wt.%. The charge transfer between lithium and carbon surface groups via the doping reaction enhanced the energy of adsorption. It was also found that is a gradual decrease in the adsorbed amount of H₂ molecules due to occupation active sites by lithium ions. (author)

No abstract available

[en] This paper reports the results of a dielectric investigation of deuterated glass D-RADA, x = 0.39. The shape of the temperature dependence of the imaginary part of the permittivity ε'' was analyzed. Analysis of the shape of the temperature dependence of ε''(T, ν) proved the existence of two phases of different mechanisms of relaxation, forming among the antiferroelectric domains. One of these mechanisms can be described by the Vogel-Fulcher equation with the parameters T₀ = 25.7 K, E_c = 105.6 K (9.1 meV) and ν₀ = 1.16 x 10⁸ Hz, and is typical for clusters with short-range order characteristic of proton (deuteron) glass. The other relaxational mechanism is the thermally activated Arrhenius dipolar reorientation with activation energy E_c = 1105 K (95.2 meV) and frequency ν₀ = 1.44 x 10¹² Hz. It is related to free dipoles which have been released from the melting long-range ordering but have not managed to form a cluster yet. (orig.)

[en] Thermal conductivity of the improper ferroic Tb₂(MoO₄)₃ was measured in the range 0.3 K-100 K by the method of the stationary heat flow. An additional maximum in thermal conductivity observed at 0.45 K is due to the anomaly of specific heat corresponding to the antiferromagnetic phase transition. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] We describe here the outlines of research undertaken by Fermilab into timing characteristics of photodetectors. We describe our experimental method and give benchtop results on the timing resolution of micro-channel plate photomultipliers (MCP-PMT) and silicon photomultipliers (SiPM). In addition, we describe results of various configurations of these detectors, along with quartz radiators, in particle test beams at Fermilab. Results for timing of scintillator light using the DRS4 high speed digitizer are also presented. (author)