1,659 research outputs found
High-resolution alternating-field technique to determine the magnetocaloric effect of metals down to very low temperatures
The magnetocaloric effect or "magnetic Gr\"uneisen ratio"
quantifies the cooling or heating of a material when
an applied magnetic field is changed under adiabatic conditions. Recently this
property has attracted considerable interest in the field of quantum
criticality. Here we report the development of a low-frequency alternating
field technique which allows to perform continuous temperature scans of
on small single crystals with very high precision and down to
very low temperatures. Measurements on doped YbRhSi show that
can be determined with this technique in a faster and much more
accurate way than by calculation from magnetization and specific heat
measurements
Dispersion forces in macroscopic quantum electrodynamics
The description of dispersion forces within the framework of macroscopic
quantum electrodynamics in linear, dispersing, and absorbing media combines the
benefits of approaches based on normal-mode techniques of standard quantum
electrodynamics and methods based on linear response theory in a natural way.
It renders generally valid expressions for both the forces between bodies and
the forces on atoms in the presence of bodies, while showing very clearly the
intimate relation between the different types of dispersion forces. By
considering examples, the influence of various factors like form, size,
electric and magnetic properties, or intervening media on the forces is
addressed. Since the approach based on macroscopic quantum electrodynamics does
not only apply to equilibrium systems, it can be used to investigate dynamical
effects such as the temporal evolution of forces on arbitrarily excited atoms.Comment: 112 pages, 7 figures, 4 tables, extended versio
Shareholding Networks in Japan
The Japanese shareholding network existing at the end of March 2002 is
studied empirically. The network is constructed from 2,303 listed companies and
53 non-listed financial institutions. We consider this network as a directed
graph by drawing edges from shareholders to stock corporations. The lengths of
the shareholder lists vary with the companies, and the most comprehensive lists
contain the top 30 shareholders. Consequently, the distribution of incoming
edges has an upper bound, while that of outgoing edges has no bound. The
distribution of outgoing degrees is well explained by the power law function
with an exponential tail. The exponent in the power law range is gamma=1.7. To
understand these features from the viewpoint of a company's growth, we consider
the correlations between the outgoing degree and the company's age, profit, and
total assets.Comment: 10 pages, 4 figures, International Conference Science of Complex
Networks: from Biology to the Internet and WWW (CNET2004
On the Prompt Signals of Gamma Ray Bursts
We introduce a new model of gamma ray burst (GRB) that explains its observed
prompt signals, namely, its primary quasi-thermal spectrum and high energy
tail. This mechanism can be applied to either assumption of GRB progenitor:
coalescence of compact objects or hypernova explosion. The key ingredients of
our model are: (1) The initial stage of a GRB is in the form of a relativistic
quark-gluon plasma "lava"; (2) The expansion and cooling of this lava results
in a QCD phase transition that induces a sudden gravitational stoppage of the
condensed non-relativistic baryons and form a hadrosphere; (3) Acoustic shocks
and Alfven waves (magnetoquakes) that erupt in episodes from the epicenter
efficiently transport the thermal energy to the hadrospheric surface and induce
a rapid detachment of leptons and photons from the hadrons; (4) The detached
and form an opaque, relativistically hot leptosphere, which
expands and cools to , or 0.5 MeV, where and
its reverse process becomes unbalanced, and the GRB photons are finally
released; (5) The "mode-conversion" of Alfven waves into electromagnetic waves
in the leptosphere provides a "snowplow" acceleration and deceleration that
gives rise to both the high energy spectrum of GRB and the erosion of its
thermal spectrum down to a quasi-thermal distribution. According to this model,
the observed GRB photons should have a redshifted peak frequency at where is the
Lorentz factor of the bulk flow of the lava, which may be determined from the
existing GRB data.Comment: 8 pages, 1 figur
- …