11,800 research outputs found
Two lighter than air systems in opposing flight regimes: An unmanned short haul, heavy load transport balloon and a manned, light payload airship
Lighter Than Air vehicles are generally defined or categorized by the shape of the balloon, payload capacity and operational flight regime. Two balloon systems that are classed as being in opposite categories are described. One is a cable guided, helium filled, short haul, heavy load transport Lighter Than Air system with a natural shaped envelope. The other is a manned, aerodynamic shaped airship which utilizes hot air as the buoyancy medium and is in the light payload class. While the airship is in the design/fabrication phase with flight tests scheduled for the latter part of 1974, the transport balloon system has been operational for some eight years
Coherent photon manipulation in interacting atomic ensembles
Coupling photons to Rydberg excitations in a cold atomic gas yields
unprecedentedly large optical nonlinearities at the level of individual light
quanta, where the formation of nearby dark-state polaritons is blocked by the
strong interactions between Rydberg atoms. This blockade mechanism, however,
realizes an inherently dissipative nonlinearity, which limits the performance
of practical applications. In this work, we propose a new approach to strong
photon interactions via a largely coherent mechanism at drastically suppressed
photon losses. Rather than a polariton blockade, it is based on an interaction
induced conversion between distinct types of dark-state polaritons with
different propagation characteristics. We outline a specific implementation of
this approach and show that it permits to turn a single photon into an
effective mirror with a robust and continuously tuneable reflection phase. We
describe potential applications, including a detailed discussion of achievable
operational fidelities
Two-step rocket engine bipropellant valve Patent
Solenoid two-step valve for bipropellant flow rate control to rocket engin
Two-step rocket engine bipropellant valve concept
Initiating combustion of altitude control rocket engines in a precombustion chamber of ductile material reduces high pressure surges generated by hypergolic propellants. Two-step bipropellant valve concepts control initial propellant flow into precombustion chamber and subsequent full flow into main chamber
Nonthermal THz to TeV Emission from Stellar Wind Shocks in the Galactic Center
The central parsec of the Galaxy contains dozens of massive stars with a
cumulative mass loss rate of ~ 10^{-3} solar masses per year. Shocks among
these stellar winds produce the hot plasma that pervades the central part of
the galaxy. We argue that these stellar wind shocks also efficiently accelerate
electrons and protons to relativistic energies. The relativistic electrons
inverse Compton scatter the ambient ultraviolet and far infrared radiation
field, producing high energy gamma-rays with a roughly constant luminosity from
\~ GeV to ~ 10 TeV. This can account for the TeV source seen by HESS in the
Galactic Center. Our model predicts a GLAST counterpart to the HESS source with
a luminosity of ~ 10^{35} ergs/s and cooling break at ~ 4 GeV. Synchrotron
radiation from the same relativistic electrons should produce detectable
emission at lower energies, with a surface brightness ~ 10^{32} B^2_{-3}
ergs/s/arcsec^2 from ~ THz to ~ keV, where B_{-3} is the magnetic field
strength in units of mG. The observed level of diffuse thermal X-ray emission
in the central parsec requires B < 300 micro-G in our models. Future detection
of the diffuse synchrotron background in the central parsec can directly
constrain the magnetic field strength, providing an important boundary
condition for models of accretion onto Sgr A*.Comment: submitted to ApJ Letter
Energy Conversion Alternatives Study (ECAS), General Electric Phase 1. Volume 2: Advanced energy conversion systems. Part 3: Direct energy conversion cycles
For abstract, see N76-23680
Conversion of relativistic pair energy into radiation in the jets of active galactic nuclei
It is generally accepted that relativistic jet outflows power the nonthermal
emission from active galactic nuclei (AGN). The composition of these jets --
leptonic versus hadronic -- is still under debate. We investigate the
microphysical details of the conversion process of the kinetic energy in
collimated relativistic pair outflows into radiation through interactions with
the ambient interstellar medium. Viewed from the coordinate system comoving
with the pair outflow, the interstellar protons and electrons represent a
proton-electron beam propagating with relativistic speed in the pair plasma. We
demonstrate that the beam excites both electrostatic and low-frequency
magnetohydrodynamic Alfven-type waves via a two-stream instability in the pair
background plasma, and we calculate the time evolution of the distribution
functions of the beam particles and the generated plasma wave turbulence power
spectra. For standard AGN jet outflow and environment parameters we show that
the initial beam distributions of interstellar protons and electrons quickly
relax to plateau-distributions in parallel momentum, transferring thereby
one-half of the initial energy density of the beam particles to electric field
fluctuations of the generated electrostatic turbulence. On considerably longer
time scales, the plateaued interstellar electrons and protons will isotropise
by their self-generated transverse turbulence and thus be picked-up in the
outflow pair plasma. These longer time scales are also characteristic for the
development of transverse hydromagnetic turbulence from the plateaued electrons
and protons. This hydromagnetic turbulence upstream and downstream is crucial
for diffusive shock acceleration to operate at external or internal shocks
associated with pair outflows.Comment: A&A in pres
Eigenfunctions of transfer operators and automorphic forms for Hecke triangle groups of infinite covolume
We develop cohomological interpretations for several types of automorphic forms for Hecke triangle groups of infinite covolume. We then use these interpretations to establish explicit isomorphisms between spaces of automorphic forms, cohomology spaces and spaces of eigenfunctions of transfer operators. These results show a deep relation between spectral entities of Hecke surfaces of infinite volume and the dynamics of their geodesic flows
DNA loop statistics and torsional modulus
The modelling of DNA mechanics under external constraints is discussed. Two
analytical models are widely known, but disagree for instance on the value of
the torsional modulus. The origin of this embarassing situation is located in
the concept of writhe. This letter presents a unified model for DNA
establishing a relation between the different approaches. I show that the
writhe created by the loops of DNA is at the origin of the discrepancy. To take
this into account, I propose a new treatment of loop statistics based on
numerical simulations using the most general formula for the writhe, and on
analytic calculations with only one fit parameter. One can then compute the
value of the torsional modulus of DNA without the need of any cut-off.Comment: 8 pages, 1 figure. Accepted by Europhysics Letter
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