4,204 research outputs found
Precision laser range finder system design for Advanced Technology Laboratory applications
Preliminary system design of a pulsed precision ruby laser rangefinder system is presented which has a potential range resolution of 0.4 cm when atmospheric effects are negligible. The system being proposed for flight testing on the advanced technology laboratory (ATL) consists of a modelocked ruby laser transmitter, course and vernier rangefinder receivers, optical beacon retroreflector tracking system, and a network of ATL tracking retroreflectors. Performance calculations indicate that spacecraft to ground ranging accuracies of 1 to 2 cm are possible
Nuclear burst plasma injection into the magnetosphere and resulting spacecraft charging
The passage of debris from a high altitude ( 400 km) nuclear burst over the ionospheric plasma is found to be capable of exciting large amplitude whistler waves which can act to structure a collisionless shock. This instability will occur in the loss cone exits of the nuclear debris bubble, and the accelerated ambient ions will freestream along the magnetic field lines into the magnetosphere. Using Starfish-like parameters and accounting for plasma diffusion and thermalization of the propagating plasma mass, it is found that synchronous orbit plasma fluxes of high temperature electrons (near 10 keV) will be significantly greater than those encountered during magnetospheric substorms. These fluxes will last for sufficiently long periods of time so as to charge immersed bodies to high potentials and arc discharges to take place
A novel laser ranging system for measurement of ground-to-satellite distances
A technique was developed for improving the precision of laser ranging measurements of ground-to-satellite distances. The method employs a mode-locked laser transmitter and utilizes an image converter tube equipped with deflection plates in measuring the time of flight of the laser pulse to a distant retroreflector and back. Samples of the outgoing and returning light pulses are focussed on the photocathode of the image converter tube, whose deflection plates are driven by a high-voltage 120 MHz sine wave derived from a very stable oscillator. From the relative positions of the images produced at the output phosphor by the two light pulses, it is possible to make a precise determination of the fractional amount by which the time of flight exceeds some large integral multiple of the period of the deflection sinusoid
Towards Sustainable Rural Development in South Africa through Passive Solar Housing Design
Rural low-cost housing in South Africa is characterised by poor thermal performance, as these houses are designed with no consideration of utilising ambient weather conditions for indoor thermal comfort. Hence, a prototype low-cost energy efficiency house was built based on the principle of passive solar design to avert the energy burden faced by low-cost house dwellers. Passive solar design in this context is the strategic selecting and locating of building envelope components to utilise the ambient weather factor of a house to enhance indoor thermal comfort. The aim of this study is to analyse the thermal performance of the passive solar house. To this effect, the indoor and weather conditions of the house which include air temperature, relative humidity, and solar radiation were monitored. The thermal contribution of the windows was determined from the measured data. In summer, 49% of the whole building air temperature and approximately 85% of its corresponding relative humidity were found within the thermal comfort. Only 23% temperature and 78% relative humidity distributions of the whole building were in the thermal comfort zone in the winter season. The daily cumulative heat contribution of the clerestory windows with no shading material was higher than that of the south-facing windows by 1.08 kWh/m2/windows in summer and 4.45 kWh/m2/windows in winter
Correlational Origin of the Roton Minimum
We present compelling evidence supporting the conjecture that the origin of
the roton in Bose-condensed systems arises from strong correlations between the
constituent particles. By studying the two dimensional bosonic dipole systems a
paradigm, we find that classical molecular dynamics (MD) simulations provide a
faithful representation of the dispersion relation for a low- temperature
quantum system. The MD simulations allow one to examine the effect of coupling
strength on the formation of the roton minimum and to demonstrate that it is
always generated at a sufficiently high enough coupling. Moreover, the
classical images of the roton-roton, roton-maxon, etc. states also appear in
the MD simulation spectra as a consequence of the strong coupling.Comment: 7 pages, 4 figure
Measurement of 0.25-3.2 GeV antiprotons in the cosmic radiation
The balloon-borne Isotope Matter-Antimatter Experiment (IMAX) was flown from Lynn Lake, Manitoba, Canada on 16–17 July 1992. Using velocity and magnetic rigidity to determine mass, we have directly measured the abundances of cosmic ray antiprotons and protons in the energy range from 0.25 to 3.2 GeV. Both the absolute flux of antiprotons and the antiproton/proton ratio are consistent with recent theoretical work in which antiprotons are produced as secondary products of cosmic ray interactions with the interstellar medium. This consistency implies a lower limit to the antiproton lifetime of ∼10 to the 7th yr
Corrections to the universal behavior of the Coulomb-blockade peak splitting for quantum dots separated by a finite barrier
Building upon earlier work on the relation between the dimensionless interdot
channel conductance g and the fractional Coulomb-blockade peak splitting f for
two electrostatically equivalent dots, we calculate the leading correction that
results from an interdot tunneling barrier that is not a delta-function but,
rather, has a finite height V and a nonzero width xi and can be approximated as
parabolic near its peak. We develop a new treatment of the problem for g much
less than 1 that starts from the single-particle eigenstates for the full
coupled-dot system. The finiteness of the barrier leads to a small upward shift
of the f-versus-g curve at small values of g. The shift is a consequence of the
fact that the tunneling matrix elements vary exponentially with the energies of
the states connected. Therefore, when g is small, it can pay to tunnel to
intermediate states with single-particle energies above the barrier height V.
The correction to the zero-width behavior does not affect agreement with recent
experimental results but may be important in future experiments.Comment: Title changed from ``Non-universal...'' to ``Corrections to the
universal...'' No other changes. 10 pages, 1 RevTeX file with 2 postscript
figures included using eps
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