2,354 research outputs found
Northward field excursions in Saturn’s magnetotail and their relationship to magnetospheric periodicities
We present results from an investigation of Cassini encounters with Saturn’s magnetotail current sheet, using magnetic field and plasma data. In the first of two intervals shown, small periodic changes in the north-south component of the magnetic field are matched by periodic density enhancements associated with the plasma sheet center. In the second interval, a large plasmoid signature is observed set against a background of small-scale current sheet motions. We interpret the quasi-periodic small field deflections and density enhancements as large-scale wave-like motion of the current sheet. We stress that plasmoid signatures are of a clearly different character and occur much less frequently
Non-equilibrium melting of colloidal crystals in confinement
We report on a novel and flexible experiment to investigate the
non-equilibrium melting behaviour of model crystals made from charged colloidal
spheres. In a slit geometry polycrystalline material formed in a low salt
region is driven by hydrostatic pressure up an evolving gradient in salt
concentration and melts at large salt concentration. Depending on particle and
initial salt concentration, driving velocity and the local salt concentration
complex morphologic evolution is observed. Crystal-melt interface positions and
the melting velocity are obtained quantitatively from time resolved Bragg- and
polarization microscopic measurements. A simple theoretical model predicts the
interface to first advance, then for balanced drift and melting velocities to
become stationary at a salt concentration larger than the equilibrium melting
concentration. It also describes the relaxation of the interface to its
equilibrium position in a stationary gradient after stopping the drive in
different manners. We further discuss the influence of the gradient strength on
the resulting interface morphology and a shear induced morphologic transition
from polycrystalline to oriented single crystalline material before melting
Expression of connexins in human preimplantation embryos in vitro
Intercellular communication via gap junctions is required to coordinate developmental processes in the mammalian embryo. We have investigated if the connexin (Cx) isoforms known to form gap junctions in rodent preimplantation embryos are also expressed in human embryos, with the aim of identifying species differences in communication patterns in early development. Using a combination of polyA PCR and immunocytochemistry we have assessed the expression of Cx26, Cx31, Cx32, Cx40, Cx43 and Cx45 which are thought to be important in early rodent embryos. The results demonstrate that Cx31 and Cx43 are the main connexin isoforms expressed in human preimplantation embryos and that these isoforms are co-expressed in the blastocyst. Cx45 protein is expressed in the blastocyst but the protein may be translated from a generally low level of transcripts: which could only be detected in the PN to 4-cell embryos. Interestingly, Cx40, which is expressed by the extravillous trophoblast in the early human placenta, was not found to be expressed in the blastocyst trophectoderm from which this tissue develops. All of the connexin isoforms in human preimplantation embryos are also found in rodents pointing to a common regulation of these connexins in development of rodent and human early embryos and perhaps other species
Randomized clinical trial of adenosine 5'-triphosphate in patients with advanced non-small-cell lung cancer
BACKGROUND: Extracellular adenosine 5'-triphosphate (ATP) is involved in
the regulation of a variety of biologic processes, including
neurotransmission, muscle contraction, and liver glucose metabolism, via
purinergic receptors. In nonrandomized studies involving patients with
different tumor types including non-small-cell lung cancer (NSCLC), ATP
infusion appeared to inhibit loss of weight and deterioration of quality
of life (QOL) and performance status. We conducted a randomized clinical
trial to evaluate the effects of ATP in patients with advanced NSCLC
(stage IIIB or IV). METHODS: Fifty-eight patients were randomly assigned
to receive either 10 intravenous 30-hour ATP infusions, with the infusions
given at 2- to 4-week intervals, or no ATP. Outcome parameters were
assessed every 4 weeks until 28 weeks. Between-group differences were
tested for statistical significance by use of repeated-measures analysis,
and reported P values are two-sided. RESULTS: Twenty-eight patients were
allocated to receive ATP treatment and 30 received no ATP. Mean weight
changes per 4-week period were -1.0 kg (95% confidence interval [CI] =
-1.5 to -0.5) in the control group and 0.2 kg (95% CI = -0.2 to +0.6) in
the ATP group (P =.002). Serum albumin concentration declined by -1.2 g/L
(95% CI= -2.0 to -0.4) per 4 weeks in the control group but remained
stable (0.0 g/L; 95% CI = -0.3 to +0.3) in the ATP group (P =.006). Elbow
flexor muscle strength declined by -5.5% (95% CI = -9.6% to -1. 4%) per 4
weeks in the control group but remained stable (0.0%; 95% CI= -1.4% to
+1.4%) in the ATP group (P =.01). A similar pattern was observed for knee
extensor muscles (P =.02). The effects of ATP on body weight, muscle
strength, and albumin concentration were especially marked in cachectic
patients (P =.0002, P =.0001, and P =. 0001, respectively, for ATP versus
no ATP). QOL score changes per 4-week period in the ATP group showed
overall less deterioration than in the control group-physical scores
(-0.2% versus -2.4%; P =. 0002); functional scores (+0.4% versus -5.5%; P
=.02); psychologic scores (-0.7% versus -2.4%; P =.11); overall QOL score
(+0.1% versus -3.5%; P =.0001). CONCLUSIONS: This randomized trial
demonstrates that ATP has beneficial effects on weight, muscle strength,
and QOL in patients with advanced NSCLC
Properties of the Intermediate Mass Fragment Emission Source in the 270 MeV 3-He + 232-Th Reaction
This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440
Fractal Structures and Scaling Laws in the Universe: Statistical Mechanics of the Self-Gravitating Gas
Fractal structures are observed in the universe in two very different ways.
Firstly, in the gas forming the cold interstellar medium in scales from 10^{-4}
pc till 100 pc. Secondly, the galaxy distribution has been observed to be
fractal in scales up to hundreds of Mpc. We give here a short review of the
statistical mechanical (and field theoretical) approach developed by us. We
consider a non-relativistic self-gravitating gas in thermal equilibrium at
temperature T inside a volume V. The statistical mechanics of such system has
special features and, as is known, the thermodynamical limit does not exist in
its customary form. Moreover, the treatments through microcanonical, canonical
and grand canonical ensembles yield different results.We present here for the
first time the equation of state for the self-gravitating gas in the canonical
ensemble. We find that it has the form p = [N T/ V] f(eta), where p is the
pressure, N is the number of particles and \eta \equiv {G m^2 N \over V^{1/3}
T}. The N \to\infty and V \to\infty limit exists keeping \eta fixed. We compute
the function f(\eta) using Monte Carlo simulations and for small eta
analytically. We compute the thermodynamic quantities of the system as free
energy, entropy, chemical potential, specific heat, compressibility and speed
of sound. We reproduce the well-known gravitational phase transition associated
to the Jeans' instability. Namely, a gaseous phase for eta < eta_c and a
condensed phase for eta > eta_c. Moreover, we derive the precise behaviour of
the physical quantities near the transition. In particular, the pressure
vanishes as p \sim(eta_c-eta)^B with B \sim 0.2 and eta_c \sim 1.6 and the
energy fluctuations diverge as \sim(eta_c-eta)^{B-1}. The speed of sound
decreases monotonically and approaches the value sqrt{T/6} at the transition.Comment: Invited paper to the special issue of the `Journal of Chaos, Solitons
and Fractals': `Superstrings, M, F, S...theory', M. S El Naschie and C.
Castro, Editors. Latex file, 16 pages plus three .ps figure
The discontinuous nature of chromospheric activity evolution
Chromospheric activity has been thought to decay smoothly with time and,
hence, to be a viable age indicator. Measurements in solar type stars in open
clusters seem to point to a different conclusion: chromospheric activity
undergoes a fast transition from Hyades level to that of the Sun after about 1
Gyr of main--sequence lifetime and any decaying trend before or after this
transition must be much less significant than the short term variations.Comment: 6 pages, 1 figure, to be published in Astrophysics and Space Scienc
Boost-Invariant Running Couplings in Effective Hamiltonians
We apply a boost-invariant similarity renormalization group procedure to a
light-front Hamiltonian of a scalar field phi of bare mass mu and interaction
term g phi^3 in 6 dimensions using 3rd order perturbative expansion in powers
of the coupling constant g. The initial Hamiltonian is regulated using momentum
dependent factors that approach 1 when a cutoff parameter Delta tends to
infinity. The similarity flow of corresponding effective Hamiltonians is
integrated analytically and two counterterms depending on Delta are obtained in
the initial Hamiltonian: a change in mu and a change of g. In addition, the
interaction vertex requires a Delta-independent counterterm that contains a
boost invariant function of momenta of particles participating in the
interaction. The resulting effective Hamiltonians contain a running coupling
constant that exhibits asymptotic freedom. The evolution of the coupling with
changing width of effective Hamiltonians agrees with results obtained using
Feynman diagrams and dimensional regularization when one identifies the
renormalization scale with the width. The effective light-front Schroedinger
equation is equally valid in a whole class of moving frames of reference
including the infinite momentum frame. Therefore, the calculation described
here provides an interesting pattern one can attempt to follow in the case of
Hamiltonians applicable in particle physics.Comment: 24 pages, LaTeX, included discussion of finite x-dependent
counterterm
Influence of thermal fluctuations on quantum phase transitions in one-dimensional disordered systems: Charge density waves and Luttinger liquids
The low temperature phase diagram of 1D weakly disordered quantum systems
like charge or spin density waves and Luttinger liquids is studied by a
\emph{full finite temperature} renormalization group (RG) calculation. For
vanishing quantum fluctuations this approach is amended by an \emph{exact}
solution in the case of strong disorder and by a mapping onto the \emph{Burgers
equation with noise} in the case of weak disorder, respectively. At \emph{zero}
temperature we reproduce the quantum phase transition between a pinned
(localized) and an unpinned (delocalized) phase for weak and strong quantum
fluctuations, respectively, as found previously by Fukuyama or Giamarchi and
Schulz.
At \emph{finite} temperatures the localization transition is suppressed: the
random potential is wiped out by thermal fluctuations on length scales larger
than the thermal de Broglie wave length of the phason excitations. The
existence of a zero temperature transition is reflected in a rich cross-over
phase diagram of the correlation functions. In particular we find four
different scaling regions: a \emph{classical disordered}, a \emph{quantum
disordered}, a \emph{quantum critical} and a \emph{thermal} region. The results
can be transferred directly to the discussion of the influence of disorder in
superfluids. Finally we extend the RG calculation to the treatment of a
commensurate lattice potential. Applications to related systems are discussed
as well.Comment: 19 pages, 7 figure
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