249 research outputs found
Vacuum high-temperature refining of carbon materials using NaCl vapors as a transport and reaction medium
One of the main requirements to carbon materials is their purity. The authors have proposed and experimentally tested a new method for vacuum-thermal refining of carbon materials using NaCl vapor as an activator. It is experimentally confirmed that this method allows increasing the refining process efficiency and decreasing the energy consumption. The proposed method can be an alternative to modern methods of chlorine- and fluorine thermal refining that permits to exclude the use of hazardous reagents.Однією з основних вимог до вуглецевих матеріалів є їх чистота. В роботі представлена та експериментально перевірена нова методика вакуумно-термічної рафінації вуглецевих матеріалів з використанням в якості активатора NaCl. Експериментально підтверджено, що використання такої методики дозволяє підвищити ефективність та зменшити енергоємність процесів рафінації. Запропонована методика може стати альтернативою сучасним методам хлор- та фтортермічної рафінації, тим самим дозволить виключити використання шкідливих та небезпечних реагентів.Одним из основных требований к углеродным материалам является их чистота. В работе представлена и экспериментально проверена новая методика вакуумно-термической рафинации углеродных материалов с использованием в качестве активатора NaCl. Экспериментально подтверждено, что использование такой методики позволяет повысить эффективность и уменьшить энергоемкость процессов рафинации. Предложенная методика может стать альтернативой современным методам хлор- и фтортермической рафинации, тем самым позволит исключить использование вредных и опасных реагентов
Performance of a fine-sampling electromagnetic calorimeter prototype in the energy range from 1 to 19 GeV
The fine-sampling electromagnetic calorimeter prototype has been
experimentally tested using the 1-19 GeV/c tagged beams of negatively charged
particles at the U70 accelerator at IHEP, Protvino. The energy resolution
measured by electrons is Delta{E}/E=2.8%/\sqrt{E} + 1.3%. The position
resolution for electrons is Delta{x}=3.1 + 15.4/sqrt{E} mm in the center of the
cell. The lateral non-uniformity of the prototype energy response to electrons
and MIPs has turned out to be negligible. Obtained experimental results are in
a good agreement with Monte-Carlo simulations.Comment: Article is prepared for pdflatex using the class elsart. 13 pages, 9
figures in 11 PDF file
Azimuthal anisotropy and correlations in p+p, d+Au and Au+Au collisions at 200 GeV
We present the first measurement of directed flow () at RHIC. is
found to be consistent with zero at pseudorapidities from -1.2 to 1.2,
then rises to the level of a couple of percent over the range . The latter observation is similar to data from NA49 if the SPS rapidities
are shifted by the difference in beam rapidity between RHIC and SPS.
Back-to-back jets emitted out-of-plane are found to be suppressed more if
compared to those emitted in-plane, which is consistent with {\it jet
quenching}. Using the scalar product method, we systematically compared
azimuthal correlations from p+p, d+Au and Au+Au collisions. Flow and non-flow
from these three different collision systems are discussed.Comment: Quark Matter 2004 proceeding, 4 pages, 3 figure
Azimuthal anisotropy: the higher harmonics
We report the first observations of the fourth harmonic (v_4) in the
azimuthal distribution of particles at RHIC. The measurement was done taking
advantage of the large elliptic flow generated at RHIC. The integrated v_4 is
about a factor of 10 smaller than v_2. For the sixth (v_6) and eighth (v_8)
harmonics upper limits on the magnitudes are reported.Comment: 4 pages, 6 figures, contribution to the Quark Matter 2004 proceeding
Partonic flow and -meson production in Au+Au collisions at = 200 GeV
We present first measurements of the -meson elliptic flow
() and high statistics distributions for different
centralities from = 200 GeV Au+Au collisions at RHIC. In
minimum bias collisions the of the meson is consistent with the
trend observed for mesons. The ratio of the yields of the to those of
the as a function of transverse momentum is consistent with a model
based on the recombination of thermal quarks up to GeV/,
but disagrees at higher momenta. The nuclear modification factor () of
follows the trend observed in the mesons rather than in
baryons, supporting baryon-meson scaling. Since -mesons are
made via coalescence of seemingly thermalized quarks in central Au+Au
collisions, the observations imply hot and dense matter with partonic
collectivity has been formed at RHIC.Comment: 6 pages, 4 figures, submit to PR
Strange Resonance Production in p+p and Au+Au Collisions at RHIC Energies
Resonance yields and spectra from elementary p+p and Au+Au collisions at
200 GeV from the STAR experiment at RHIC are presented
and discussed in terms of chemical and thermal freeze-out conditions. Thermal
models do not adequately describe the yields of the resonance production in
central Au+Au collisions. The approach to include elastic hadronic interactions
between chemical freeze-out and thermal freeze-out suggests a time of 5 fm/c.Comment: 4 pages, 7 figures, proceedings of the Quark Matter 2004, in Oakland,
California, to be published in Journal of Physics G: Nuclear and Particle
Physic
Identified particles at large transverse momenta in STAR in Au+Au collisions @ sqrt(s_NN) = 200 GeV
We report measurements of the ratios of identified hadrons (pi,K,p,Lambda) in
Au+Au collisions at sqrt(s_NN) = 200 GeV as a function of both collision
centrality and transverse momentum (p_T). Ratios of anti-baryon to baryon
yields are independent of p_T within 2<p_T <6 GeV/c indicating that, for such a
range, our measurements are inconsistent with theoretical pQCD calculations
predicting a decrease due to a stronger contribution from valence quark
scattering. For both strange and non-strange species, a strong baryon
enhancement relative to meson yields is observed as a function of collision
centrality in this intermediate p_T region, leading to p/pi and Lambda/K ratios
greater than unity. The nuclear modification factor, R_cp (central relative to
peripheral collisions), is used to illustrate the interplay between jet
quenching and hadron production. The physics implications of these measurements
are discussed with reference to different theoretical models.Comment: 5 pages, 4 figures. Proceedings of Quark Matter 2004 Conference, Jan
2004, Oakland, USA. Submitted to Journal of Physics
High- electron distributions in d+Au and p+p collisions at RHIC
We present preliminary measurements of electron and positron spectra in d+Au
and p+p collisions at GeV for GeV/c.
These measurements were carried out using the STAR Time Projection Chamber
(TPC) and the Barrel Electromagnetic calorimeter (EMC). Overall hadron
rejection factors in the range of have been achieved. In this work we
describe the measurement technique used to discriminate electrons from hadrons
and compare the results for single electron spectra with Pythia based pQCD
calculations for electrons from heavy-quark semi-leptonic decays.Comment: Quark Matter 2004 conference proceeding
Plasma Wakefield Acceleration with a Modulated Proton Bunch
The plasma wakefield amplitudes which could be achieved via the modulation of
a long proton bunch are investigated. We find that in the limit of long bunches
compared to the plasma wavelength, the strength of the accelerating fields is
directly proportional to the number of particles in the drive bunch and
inversely proportional to the square of the transverse bunch size. The scaling
laws were tested and verified in detailed simulations using parameters of
existing proton accelerators, and large electric fields were achieved, reaching
1 GV/m for LHC bunches. Energy gains for test electrons beyond 6 TeV were found
in this case.Comment: 9 pages, 7 figure
The energy dependence of angular correlations inferred from mean- fluctuation scale dependence in heavy ion collisions at the SPS and RHIC
We present the first study of the energy dependence of angular
correlations inferred from event-wise mean transverse momentum
fluctuations in heavy ion collisions. We compare our large-acceptance
measurements at CM energies $\sqrt{s_{NN}} =$ 19.6, 62.4, 130 and 200 GeV to
SPS measurements at 12.3 and 17.3 GeV. $p_t$ angular correlation structure
suggests that the principal source of $p_t$ correlations and fluctuations is
minijets (minimum-bias parton fragments). We observe a dramatic increase in
correlations and fluctuations from SPS to RHIC energies, increasing linearly
with $\ln \sqrt{s_{NN}}$ from the onset of observable jet-related
fluctuations near 10 GeV.Comment: 10 pages, 4 figure
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