60,590 research outputs found
Calculation of the microcanonical temperature for the classical Bose field
The ergodic hypothesis asserts that a classical mechanical system will in
time visit every available configuration in phase space. Thus, for an ergodic
system, an ensemble average of a thermodynamic quantity can equally well be
calculated by a time average over a sufficiently long period of dynamical
evolution. In this paper we describe in detail how to calculate the temperature
and chemical potential from the dynamics of a microcanonical classical field,
using the particular example of the classical modes of a Bose-condensed gas.
The accurate determination of these thermodynamics quantities is essential in
measuring the shift of the critical temperature of a Bose gas due to
non-perturbative many-body effects.Comment: revtex4, 10 pages, 1 figure. v2: updated to published version. Fuller
discussion of numerical results, correction of some minor error
Energy Efficient Engine: Flight propulsion system final design and analysis
The Energy Efficient Engine (E3) is a NASA program to create fuel saving technology for future transport engines. The Flight Propulsion System (FPS) is the engine designed to achieve E3 goals. Achieving these goals required aerodynamic, mechanical and system technologies advanced beyond that of current production engines. These technologies were successfully demonstrated in component rigs, a core engine and a turbofan ground test engine. The design and benefits of the FPS are presented. All goals for efficiency, environmental considerations, and economic payoff were met. The FPS has, at maximum cruise, 10.67 km (35,000 ft), M0.8, standard day, a 16.9 percent lower installed specific fuel consumption than a CF6-50C. It provides an 8.6 percent reduction in direct operating cost for a short haul domestic transport and a 16.2 percent reduction for an international long distance transport
Magnifying superlens in the visible frequency range
In this communication we introduce a new design of the magnifying superlens
and demonstrate it in the experiment.Comment: 3pages, 1 figur
Limits of sympathetic cooling of fermions: The role of the heat capacity of the coolant
The sympathetic cooling of an initially degenerate Fermi gas by either an
ideal Bose gas below or an ideal Boltzmann gas is investigated. It is
shown that the efficiency of cooling by a Bose gas below is by no means
reduced when its heat capacity becomes much less than that of the Fermi gas,
where efficiency is measured by the decrease in the temperature of the Fermi
gas per number of particles evaporated from the coolant. This contradicts the
intuitive idea that an efficient coolant must have a large heat capacity. In
contrast, for a Boltzmann gas a minimal value of the ratio of the heat
capacities is indeed necessary to achieve T=0 and all of the particles must be
evaporated.Comment: 5 pages, 3 figure
Vacuum Decay on a Brane World
The bubble nucleation rate for a first order phase transition occurring on a
brane world is calculated. Both the Coleman-de Luccia thin wall instanton and
the Hawking-Moss instanton are considered. The results are compared with the
corresponding nucleation rates for standard four-dimensional gravity.Comment: 5 page
- …