17,544 research outputs found
Regulated high efficiency, lightweight capacitor-diode multiplier dc to dc converter
A voltage multiplier having a capacitor-diode voltage multiplying network is disclosed which is fed with voltage pulses from a dc source through a first switching means. Pulses of a second polarity are also supplied through a second switching means to the input of the capacitor-diode voltage multiplier from a second dc source whose voltage is adjustable to change the voltage of the pulses of second polarity. The switching means are alternately rendered conducting by signals from a control circuit. The second dc source may be controlled by a voltage comparator which compares the output voltage of the capacitor-diode voltage multiplier to the reference source
Medium power voltage multipliers with a large number of stages
Voltage multiplier techniques are extended at medium power levels to larger multiplication ratios. A series of dc-dc converters were built, with from 20 to 45 stages and with power levels up to 100 watts. Maximum output voltages were about 10,000 volts
High performance dc-dc conversion with voltage multipliers
The voltage multipliers using capacitors and diodes first developed by Cockcroft and Walton in 1932 were reexamined in terms of state of the art fast switching transistors and diodes, and high energy density capacitors. Because of component improvements, the voltage multiplier, used without a transformer, now appears superior in weight to systems now in use for dc-dc conversion. An experimental 100-watt 1000-volt dc-dc converter operating at 100 kHz was built, with a component weight of about 1 kg/kW. Calculated and measured values of output voltage and efficiency agreed within experimental error
Efficiency and weight of voltage multiplier type ultra lightweight dc-dc converters
An analytical and experimental study was made of a capacitor-diode voltage multiplier without a transformer which offers the possibility of high efficiency with light weight. The dc-dc conversion efficiencies of about 94 percent were achieved at output powers of 150 watts at 1000 volts using 8x multiplication. A detailed identification of losses was made, including forward drop losses in component, switching losses, reverse junction capacitance charging losses, and charging losses in the main ladder capacitors
Autonomous RPRV Navigation, Guidance and Control
Dryden Flight Research Center has the responsibility for flight testing of advanced remotely piloted research vehicles (RPRV) to explore highly maneuverable aircraft technology, and to test advanced structural concepts, and related aeronautical technologies which can yield important research results with significant cost benefits. The primary purpose is to provide the preliminary design of an upgraded automatic approach and landing control system and flight director display to improve landing performance and reduce pilot workload. A secondary purpose is to determine the feasibility of an onboard autonomous navigation, orbit, and landing capability for safe vehicle recovery in the event of loss of telemetry uplink communication with the vehicles. The current RPRV approach and landing method, the proposed automatic and manual approach and autoland system, and an autonomous navigation, orbit, and landing system concept which is based on existing operational technology are described
From finite nuclei to the nuclear liquid drop: leptodermous expansion based on the self-consistent mean-field theory
The parameters of the nuclear liquid drop model, such as the volume, surface,
symmetry, and curvature constants, as well as bulk radii, are extracted from
the non-relativistic and relativistic energy density functionals used in
microscopic calculations for finite nuclei. The microscopic liquid drop energy,
obtained self-consistently for a large sample of finite, spherical nuclei, has
been expanded in terms of powers of A^{-1/3} (or inverse nuclear radius) and
the isospin excess (or neutron-to-proton asymmetry). In order to perform a
reliable extrapolation in the inverse radius, the calculations have been
carried out for nuclei with huge numbers of nucleons, of the order of 10^6. The
Coulomb interaction has been ignored to be able to approach nuclei of arbitrary
sizes and to avoid radial instabilities characteristic of systems with very
large atomic numbers. The main contribution to the fluctuating part of the
binding energy has been removed using the Green's function method to calculate
the shell correction. The limitations of applying the leptodermous expansion to
actual nuclei are discussed. While the leading terms in the macroscopic energy
expansion can be extracted very precisely, the higher-order, isospin-dependent
terms are prone to large uncertainties due to finite-size effects.Comment: 13 pages revtex4, 7 eps figures, submitted to Phys. Rev.
Initial Data for Black Holes and Black Strings in 5d
We explore time-symmetric hypersurfaces containing apparent horizons of black
objects in a 5d spacetime with one coordinate compactified on a circle. We find
a phase transition within the family of such hypersurfaces: the horizon has
different topology for different parameters. The topology varies from to
. This phase transition is discontinuous -- the topology of the
horizon changes abruptly. We explore the behavior around the critical point and
present a possible phase diagram.Comment: 4 pp, 3 figs. v3: Discussion extended including know variouse choices
of the source. The value of , errors and typos are corrected.
Conclusions clarified but ain't changed. More references added. Accepted for
publication in PR
J0316+4328: a Probable "Asymmetric Double" Lens
We report a probable gravitational lens J0316+4328, one of 19 candidate
asymmetric double lenses (2 images at a high flux density ratio) from CLASS.
Observations with the Very Large Array (VLA), MERLIN and the Very Long Baseline
Array (VLBA) imply that J0316+4328 is a lens with high confidence. It has 2
images separated by 0.40", with 6 GHz flux densities of 62 mJy and 3.2 mJy. The
flux density ratio of ~19 (constant over the frequency range 6-22 GHz) is the
largest for any 2 image gravitational lens. High resolution optical imaging and
deeper VLBI maps should confirm the lensing interpretation and provide inputs
to detailed lens models. The unique configuration will give strong constraints
on the lens galaxy's mass profile.Comment: Accepted to MNRAS Letters. 5 pages, 6 figures, 3 table
Optical control of internal electric fields in band-gap graded InGaN nanowires
InGaN nanowires are suitable building blocks for many future optoelectronic
devices. We show that a linear grading of the indium content along the nanowire
axis from GaN to InN introduces an internal electric field evoking a
photocurrent. Consistent with quantitative band structure simulations we
observe a sign change in the measured photocurrent as a function of photon
flux. This negative differential photocurrent opens the path to a new type of
nanowire-based photodetector. We demonstrate that the photocurrent response of
the nanowires is as fast as 1.5 ps
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