16,381 research outputs found
Airship economics
Projected operating and manufacturing costs of a large airship design which are considered practical with today's technology and environment are discussed. Data and information developed during an 18-month study on the question of feasibility, engineering, economics and production problems related to a large metalclad type airship are considered. An overview of other classic airship designs are provided, and why metalclad was selected as the most prudent and most economic design to be considered in the 1970-80 era is explained. Crew operation, ATC and enroute requirements are covered along with the question of handling, maintenance and application of systems to the large airship
Discrete Self-Similarity in Type-II Strong Explosions
We present new solutions to the strong explosion problem in a non-power law
density profile. The unperturbed self-similar solutions discovered by Waxman &
Shvarts describe strong Newtonian shocks propagating into a cold gas with a
density profile falling off as , where (Type-II
solutions). The perturbations we consider are spherically symmetric and
log-periodic with respect to the radius. While the unperturbed solutions are
continuously self-similar, the log-periodicity of the density perturbations
leads to a discrete self-similarity of the perturbations, i.e. the solution
repeats itself up to a scaling at discrete time intervals. We discuss these
solutions and verify them against numerical integrations of the time dependent
hydrodynamic equations. Finally we show that this method can be generalized to
treat any small, spherically symmetric density perturbation by employing
Fourier decomposition
Honey bee colony losses
No description supplie
Relative momentum for identical particles
Possible definitions for the relative momentum of identical particles are
considered
The microcanonical thermodynamics of finite systems: The microscopic origin of condensation and phase separations; and the conditions for heat flow from lower to higher temperatures
Microcanonical thermodynamics allows the application of statistical mechanics
both to finite and even small systems and also to the largest, self-gravitating
ones. However, one must reconsider the fundamental principles of statistical
mechanics especially its key quantity, entropy. Whereas in conventional
thermostatistics, the homogeneity and extensivity of the system and the
concavity of its entropy are central conditions, these fail for the systems
considered here. For example, at phase separation, the entropy, S(E), is
necessarily convex to make exp[S(E)-E/T] bimodal in E. Particularly, as
inhomogeneities and surface effects cannot be scaled away, one must be careful
with the standard arguments of splitting a system into two subsystems, or
bringing two systems into thermal contact with energy or particle exchange. Not
only the volume part of the entropy must be considered. As will be shown here,
when removing constraints in regions of a negative heat capacity, the system
may even relax under a flow of heat (energy) against a temperature slope. Thus
the Clausius formulation of the second law: ``Heat always flows from hot to
cold'', can be violated. Temperature is not a necessary or fundamental control
parameter of thermostatistics. However, the second law is still satisfied and
the total Boltzmann entropy increases. In the final sections of this paper, the
general microscopic mechanism leading to condensation and to the convexity of
the microcanonical entropy at phase separation is sketched. Also the
microscopic conditions for the existence (or non-existence) of a critical
end-point of the phase-separation are discussed. This is explained for the
liquid-gas and the solid-liquid transition.Comment: 23 pages, 2 figures, Accepted for publication in the Journal of
Chemical Physic
Optimal Covariant Measurement of Momentum on a Half Line in Quantum Mechanics
We cannot perform the projective measurement of a momentum on a half line
since it is not an observable. Nevertheless, we would like to obtain some
physical information of the momentum on a half line. We define an optimality
for measurement as minimizing the variance between an inferred outcome of the
measured system before a measuring process and a measurement outcome of the
probe system after the measuring process, restricting our attention to the
covariant measurement studied by Holevo. Extending the domain of the momentum
operator on a half line by introducing a two dimensional Hilbert space to be
tensored, we make it self-adjoint and explicitly construct a model Hamiltonian
for the measured and probe systems. By taking the partial trace over the newly
introduced Hilbert space, the optimal covariant positive operator valued
measure (POVM) of a momentum on a half line is reproduced. We physically
describe the measuring process to optimally evaluate the momentum of a particle
on a half line.Comment: 12 pages, 3 figure
Designing Dirac points in two-dimensional lattices
We present a framework to elucidate the existence of accidental contacts of
energy bands, particularly those called Dirac points which are the point
contacts with linear energy dispersions in their vicinity. A generalized
von-Neumann-Wigner theorem we propose here gives the number of constraints on
the lattice necessary to have contacts without fine tuning of lattice
parameters. By counting this number, one could quest for the candidate of Dirac
systems without solving the secular equation. The constraints can be provided
by any kinds of symmetry present in the system. The theory also enables the
analytical determination of k-point having accidental contact by selectively
picking up only the degenerate solution of the secular equation. By using these
frameworks, we demonstrate that the Dirac points are feasible in various
two-dimensional lattices, e.g. the anisotropic Kagome lattice under inversion
symmetry is found to have contacts over the whole lattice parameter space.
Spin-dependent cases, such as the spin-density-wave state in LaOFeAs with
reflection symmetry, are also dealt with in the present scheme.Comment: 15pages, 9figures (accepted to Phys. Rev. B
XMM-Newton observations of the Coma cluster relic 1253+275
Using XMM Newton data, we investigate the nature of the X-ray emission in the
radio relic 1253+275 in the Coma cluster. We determine the conditions of the
cluster gas to check current models of relic formation, and we set constraints
on the intracluster magnetic field. Both imaging and spectral analysis are
performed, and the X-ray emission is compared with the radio emission. We found
that the emission is of thermal origin and is connected to the sub-group around
NGC 4839. The best-fit gas temperature in the region of the relic and in its
vicinity is in the range 2.8 - 4.0 keV, comparable to the temperature of the
NGC 4839 sub-group. We do not detect any high temperature gas, resulting from a
possible shock in the region of the Coma relic. We therefore suggest that the
main source of energy for particles radiating in the radio relic is likely to
be turbulence. From the X-ray data, we can also set a flux upper limit of 3.2 x
10e-13 erg/cm^2 s, in the 0.3 - 10 keV energy range, to the non-thermal
emission in the relic region. This leads to a magnetic field B > 1.05 microG.Comment: 4 pages, 2 figures, Accepted for publication in A&A Letter
A computerized Langmuir probe system
For low pressure plasmas it is important to record entire single or double Langmuir probe characteristics accurately. For plasmas with a depleted high energy tail, the accuracy of the recorded ion current plays a critical role in determining the electron temperature. Even for high density Maxwellian distributions, it is necessary to accurately model the ion current to obtain the correct electron density. Since the electron and ion current saturation values are, at best, orders of magnitude apart, a single current sensing resistor cannot provide the required resolution to accurately record these values. We present an automated, personal computer based data acquisition system for the determination of fundamental plasma properties in low pressure plasmas. The system is designed for single and double Langmuir probes, whose characteristics can be recorded over a bias voltage range of ±70 V with 12 bit resolution. The current flowing through the probes can be recorded within the range of 5 nA–100 mA. The use of a transimpedance amplifier for current sensing eliminates the requirement for traditional current sensing resistors and hence the need to correct the raw data. The large current recording range is realized through the use of a real time gain switching system in the negative feedback loop of the transimpedance amplifier
A Lévy-Ciesielski expansion for quantum Brownian motion and the construction of quantum Brownian bridges
We introduce "probabilistic" and "stochastic Hilbertian structures". These seem to be a suitable context for developing a theory of "quantum Gaussian processes". The Schauder system is utilised to give a Lévy-Ciesielski representation of quantum (bosonic) Brownian motion as operators in Fock space over a space of square summable sequences. Similar results hold for non-Fock, fermion, free and monotone Brownian motions. Quantum Brownian bridges are defined and a number of representations of these are given
- …