213 research outputs found
A continuous isotropic-nematic liquid crystalline transition of F-actin solutions
The phase transition from the isotropic (I) to nematic (N) liquid crystalline
suspension of F-actin of average length m or above was studied by local
measurements of optical birefringence and protein concentration. Both
parameters were detected to be continuous in the transition region, suggesting
that the I-N transition is higher than 1st order. This finding is consistent
with a recent theory by Lammert, Rokhsar & Toner (PRL, 1993, 70:1650),
predicting that the I-N transition may become continuous due to suppression of
disclinations. Indeed, few line defects occur in the aligned phase of F-actin.
Individual filaments in solutions of a few mg/ml F-actin undergo fast
translational diffusion along the filament axis, whereas both lateral and
rotational diffusions are suppressed.Comment: 4 pages with 4 figures. Submitted to Physical Review Letter
Materialized View Selection in XML Databases
Materialized views, a rdbms silver bullet, demonstrate its
efficacy in many applications, especially as a data warehousing/decison support system tool. The pivot of playing materialized views efficiently is view selection. Though studied for over thirty years in rdbms, the
selection is hard to make in the context of xml databases, where both the semi-structured data and the expressiveness of xml query languages add challenges to the view selection problem. We start our discussion on producing minimal xml views (in terms of size) as candidates for a given workload (a query set). To facilitate intuitionistic view selection, we present a view graph (called vcube) to structurally maintain all generated views. By basing our selection on vcube for materialization, we propose two view selection strategies, targeting at space-optimized and space-time tradeoff, respectively. We built our implementation on
top of Berkeley DB XML, demonstrating that significant performance improvement could be obtained using our proposed approaches
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
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
Measurement of Transverse Single-Spin Asymmetries for Di-Jet Production in Proton-Proton Collisions at GeV
We report the first measurement of the opening angle distribution between
pairs of jets produced in high-energy collisions of transversely polarized
protons. The measurement probes (Sivers) correlations between the transverse
spin orientation of a proton and the transverse momentum directions of its
partons. With both beams polarized, the wide pseudorapidity () coverage for jets permits separation of Sivers functions for the valence
and sea regions. The resulting asymmetries are all consistent with zero and
considerably smaller than Sivers effects observed in semi-inclusive deep
inelastic scattering (SIDIS). We discuss theoretical attempts to reconcile the
new results with the sizable transverse spin effects seen in SIDIS and forward
hadron production in pp collisions.Comment: 6 pages total, 1 Latex file, 3 PS files with figure
System size dependence of associated yields in hadron-triggered jets
We present results on the system size dependence of high transverse momentum
di-hadron correlations at = 200 GeV as measured by STAR at
RHIC. Measurements in d+Au, Cu+Cu and Au+Au collisions reveal similar jet-like
correlation yields at small angular separation (,
) for all systems and centralities. Previous measurements have
shown that the away-side yield is suppressed in heavy-ion collisions. We
present measurements of the away-side suppression as a function of transverse
momentum and centrality in Cu+Cu and Au+Au collisions. The suppression is found
to be similar in Cu+Cu and Au+Au collisions at a similar number of
participants. The results are compared to theoretical calculations based on the
parton quenching model and the modified fragmentation model. The observed
differences between data and theory indicate that the correlated yields
presented here will provide important constraints on medium density profile and
energy loss model parameters.Comment: 12 pages, 5 figure
The energy dependence of p\u3csub\u3et\u3c/sub\u3e angular correlations inferred from mean-p\u3csub\u3et\u3c/sub\u3e fluctuation scale dependence in heavy ion collisions at the SPS and RHIC
We present the first study of the energy dependence of pt angular correlations inferred from event-wise mean transverse momentum pt fluctuations in heavy ion collisions. We compare our large-acceptance measurements at CM energies , 62.4, 130 and 200 GeV to SPS measurements at 12.3 and 17.3 GeV. pt angular correlation structure suggests that the principal source of pt 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 from the onset of observable jet-related pt fluctuations near 10 GeV
Direct Observation of Dijets in Central Au+Au Collisions at √sNN=200 GeV
The STAR Collaboration at the Relativistic Heavy Ion Collider reports measurements of azimuthal correlations of high transverse momentum (pT) charged hadrons in Au+Au collisions at higher pT than reported previously. As pT is increased, a narrow, back-to-back peak emerges above the decreasing background, providing a clear dijet signal for all collision centralities studied. Using these correlations, we perform a systematic study of dijet production and suppression in nuclear collisions, providing new constraints on the mechanisms underlying partonic energy loss in dense matter
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