5,942 research outputs found
Degrees of freedom and the phase transitions of two flavor QCD
We study two effective models for QCD, the Nambu-Jona-Lasinio -model and the
linear sigma model extended by including a Polyakov loop potential, which is
fitted to reproduce pure gauge theory thermodynamics, and a coupling between
the chiral fields and the Polyakov loop. Thus the resulting models have as
relevant degrees of freedom the Polyakov loop and chiral fields. By comparing
the extended models with the bare chiral models we can conclude that the
addition of the Polyakov loop is necessary in order to obtain both
qualitatively and quantitatively correct results at finite temperatures. These
results are extended to finite net quark densities, several thermodynamical
quantites are investigated in detail and possible applications and consequences
for relativistic heavy ion collision phenomenology are discussed
Periodic variations in the colours of the classical T Tauri star RW Aur A
The classical T Tauri star RW Aur A is an irregular variable with a large
amplitude in all photometric bands. In an extended series of photometric data
we found small-amplitude periodic variations in the blue colours of the star,
with a period of 2.64 days. The period was relatively stable over several
years. The amplitude of the periodic signal is 0.21 mag in U-V, 0.07 mag in
B-V, and about 0.02 mag in V-R and V-I. No periodicity was found in the V
magnitude. The relevance of this photometric period to the recently discovered
periodicity in spectral features of the star is discussed, and the hypothesis
of a hot spot is critically considered.Comment: 5 pages, 8 figures, uses new aa.cls, accepted for publication in
Astronomy and Astrophysic
Confinement and Chiral Symmetry
We illustrate why color deconfines when chiral symmetry is restored in gauge
theories with quarks in the fundamental representation, and while these
transitions do not need to coincide when quarks are in the adjoint
representation, entanglement between them is still present.Comment: 4 pages, 1 figure, proceedings of Quark Matter 200
Halogen bonding enhances nonlinear optical response in poled supramolecular polymers
We demonstrate that halogen bonding strongly enhances the nonlinear optical response of poled supramolecular polymer systems. We compare three nonlinear optical chromophores with similar electronic structures but different bond-donating units, and show that both the type and the strength of the noncovalent interaction between the chromophores and the polymer matrix play their own distinctive roles in the optical nonlinearity of the systems
Measurement of Magnetization Dynamics in Single-Molecule Magnets Induced by Pulsed Millimeter-Wave Radiation
We describe an experiment aimed at measuring the spin dynamics of the Fe8
single-molecule magnet in the presence of pulsed microwave radiation. In
earlier work, heating was observed after a 0.2-ms pulse of intense radiation,
indicating that the spin system and the lattice were out of thermal equilibrium
at millisecond time scale [Bal et al., Europhys. Lett. 71, 110 (2005)]. In the
current work, an inductive pick-up loop is used to probe the photon-induced
magnetization dynamics between only two levels of the spin system at much
shorter time scales (from ns to us). The relaxation time for the magnetization,
induced by a pulse of radiation, is found to be on the order of 10 us.Comment: 3 RevTeX pages, including 3 eps figures. The paper will appear in the
Journal of Applied Physics as MMM'05 conference proceeding
Incoherent dynamics of vibrating single-molecule transistors
We study the tunneling conductance of nano-scale quantum ``shuttles'' in
connection with a recent experiment (H. Park et al., Nature, 407, 57 (2000)) in
which a vibrating C^60 molecule was apparently functioning as the island of a
single electron transistor (SET). While our calculation starts from the same
model of previous work (D. Boese and H. Schoeller, Europhys. Lett. 54,
66(2001)) we obtain quantitatively different dynamics. Calculated I-V curves
exhibit most features present in experimental data with a physically reasonable
parameter set, and point to a strong dependence of the oscillator's potential
on the electrostatics of the island region. We propose that in a regime where
the electric field due to the bias voltage itself affects island position, a
"catastrophic" negative differential conductance (NDC) may be realized. This
effect is directly attributable to the magnitude of overlap of final and
initial quantum oscillator states, and as such represents experimental control
over quantum transitions of the oscillator via the macroscopically controllable
bias voltage.Comment: 6 pages, LaTex, 6 figure
Decoherence in circuits of small Josephson junctions
We discuss dephasing by the dissipative electromagnetic environment and by
measurement in circuits consisting of small Josephson junctions. We present
quantitative estimates and determine in which case the circuit might qualify as
a quantum bit. Specifically, we analyse a three junction Cooper pair pump and
propose a measurement to determine the decoherence time .Comment: 4 pages, 4 figure
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