2,875 research outputs found
Bounded Gaps Between Products of Distinct Primes
Let be an integer. We adapt the Maynard-Tao sieve to produce the
asymptotically best-known bounded gaps between products of distinct primes.
Our result applies to positive-density subsets of the primes that satisfy
certain equidistribution conditions. This improves on the work of Thorne and
Sono
Effects of initial flow velocity fluctuation in event-by-event (3+1)D hydrodynamics
Hadron spectra and elliptic flow in high-energy heavy-ion collisions are
studied within a (3+1)D ideal hydrodynamic model with fluctuating initial
conditions given by the AMPT Monte Carlo model. Results from event-by-event
simulations are compared with experimental data at both RHIC and LHC energies.
Fluctuations in the initial energy density come from not only the number of
coherent soft interactions of overlapping nucleons but also incoherent
semi-hard parton scatterings in each binary nucleon collision. Mini-jets from
semi-hard parton scatterings are assumed to be locally thermalized through a
Gaussian smearing and give rise to non-vanishing initial local flow velocities.
Fluctuations in the initial flow velocities lead to harder transverse momentum
spectra of final hadrons due to non-vanishing initial radial flow velocities.
Initial fluctuations in rapidity distributions lead to expanding hot spots in
the longitudinal direction and are shown to cause a sizable reduction of final
hadron elliptic flow at large transverse momenta.Comment: 17 pages in RevTex, 18 figures, final version published in PR
Equilibrium states of a test particle coupled to finite size heat baths
We report on numerical simulations of the dynamics of a test particle coupled
to competing Boltzmann heat baths of finite size. After discussing some
features of the single bath case, we show that the presence of two heat baths
further constraints the conditions necessary for the test particle to
thermalize with the heat baths. We find that thermalization is a spectral
property in which the oscillators of the bath with frequencies in the range of
the test particle characteristic frequency determine its degree of
thermalization. We also find an unexpected frequency shift of the test particle
response with respect to the spectra of the two heat baths. Finally, we discuss
implications of our results for the study of high-frequency nanomechanical
resonators through cold damping cooling techniques, and for engineering
reservoirs capable of mitigating the back-action on a mechanical system.Comment: Strongly related to arXiV:0810.3251 (appeared in European Physical
Journal B 61, 271 (2008
Reactions of C({\it a}) with selected saturated alkanes: A temperature dependence study
We present a temperature dependence study on the gas phase reactions of the
C({\it a}) radical with a selected series of saturated alkanes
(CH, CH, n-CH, i-CH, and n-CH) by
means of pulsed laser photolysis/laser-induced fluorescence technique. The
bimolecular rate constants for these reactions were obtained between 298 and
673 K. A pronounced negative temperature effect was observed for n-CH,
i-CH, and n-CH and interpreted in terms of steric hindrance
of the more reactive secondary or tertiary C-H bonds by less reactive CH
groups. Detailed analysis of our experimental results reveals quantitatively
the temperature dependence of reactivities for the primary, secondary, and
tertiary C-H bonds in these saturated alkanes and further lends support to a
mechanism of hydrogen abstraction.Comment: 26 pages, 8 figures, 1 table, 30 references; accepted to JC
A Two-Dimensional CA Traffic Model with Dynamic Route Choices Between Residence and Workplace
The Biham, Middleton and Levine (BML) model is extended to describe dynamic
route choices between the residence and workplace in cities. The traffic
dynamic in the city with a single workplace is studied from the velocity
diagram, arrival time probability distribution, destination arrival rate and
convergence time. The city with double workplaces is also investigated to
compared with a single workplace within the framework of four modes of urban
growth. The transitional region is found in the velocity diagrams where the
system undergoes a continuous transition from a moving phase to a completely
jamming phase. We perform a finite-size scaling analysis of the critical
density from a statistical point of view and the order parameter of this
jamming transition is estimated. It is also found that statistical properties
of urban traffic are greatly influenced by the urban area, workplace area and
urban layout.Comment: 18 pages, 13 figure
Neutrino Emission From Direct Urca Processes in Pion Condensed Quark Matter
We study neutrino emission from direct Urca processes in pion condensed quark
matter. In compact stars with high baryon density, the emission is dominated by
the gapless modes of the pion condensation which leads to an enhanced
emissivity. While for massless quarks the enhancement is not remarkable, the
emissivity is significantly larger and the cooling of the condensed matter is
considerably faster than that in normal quark matter when the mass difference
between - and -quarks is sizable.Comment: 12 pages,6 figures, published versio
Modulation of Mitochondrial Bioenergetics in the Isolated Guinea Pig Beating Heart by Potassium and Lidocaine Cardioplegia: Implications for Cardioprotection
Mitochondria are damaged by cardiac ischemia/reperfusion (I/R) injury but can contribute to cardioprotection. We tested if hyperkalemic cardioplegia (CP) and lidocaine (LID) differently modulate mitochondrial (m) bioenergetics and protect hearts against I/R injury. Guinea pig hearts (n = 71) were perfused with Krebs Ringer\u27s solution before perfusion for 1 minute just before ischemia with either CP (16 mM K+) or LID (1 mM) or Krebs Ringer\u27s (control, 4 mM K+). The 1-minute perfusion period assured treatment during ischemia but not on reperfusion. Cardiac function, NADH, FAD, m[Ca2+], and superoxide (reactive oxygen species) were assessed at baseline, during the 1-minute perfusion, and continuously during I/R. During the brief perfusion before ischemia, CP and LID decreased reactive oxygen species and increased NADH without changing m[Ca2+]. Additionally, CP decreased FAD. During ischemia, NADH was higher and reactive oxygen species was lower after CP and LID, whereas m[Ca2+] was lower only after LID. On reperfusion, NADH and FAD were more normalized, and m[Ca2+] and reactive oxygen species remained lower after CP and LID. Better functional recovery and smaller infarct size after CP and LID were accompanied by better mitochondrial function. These results suggest that mitochondria may be implicated, directly or indirectly, in protection by CP and LID against I/R injury
Optimal design of nonuniform FIR transmultiplexer using semi-infinite programming
This paper considers an optimum nonuniform FIR transmultiplexer design problem subject to specifications in the frequency domain. Our objective is to minimize the sum of the ripple energy for all the individual filters, subject to the specifications on amplitude and aliasing distortions, and to the passband and stopband specifications for the individual filters. This optimum nonuniform transmultiplexer design problem can be formulated as a quadratic semi-infinite programming problem. The dual parametrization algorithm is extended to this nonuniform transmultiplexer design problem. If the lengths of the filters are sufficiently long and the set of decimation integers is compatible, then a solution exists. Since the problem is formulated as a convex problem, if a solution exists, then the solution obtained is unique and the local solution is a global minimum
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