27,925 research outputs found
The Ranger 4 Flight Path and Its Determination from Tracking Data
The ranger iv flight path and its determination from tracking dat
The space shuttle launch vehicle aerodynamic verification challenges
The Space Shuttle aerodynamics and performance communities were challenged to verify the Space Shuttle vehicle (SSV) aerodynamics and system performance by flight measurements. Historically, launch vehicle flight test programs which faced these same challenges were unmanned instrumented flights of simple aerodynamically shaped vehicles. However, the manned SSV flight test program made these challenges more complex because of the unique aerodynamic configuration powered by the first man-rated solid rocket boosters (SRB). The analyses of flight data did not verify the aerodynamics or performance preflight predictions of the first flight of the Space Transportation System (STS-1). However, these analyses have defined the SSV aerodynamics and verified system performance. The aerodynamics community also was challenged to understand the discrepancy between the wind tunnel and flight defined aerodynamics. The preflight analysis challenges, the aerodynamic extraction challenges, and the postflight analyses challenges which led to the SSV system performance verification and which will lead to the verification of the operational ascent aerodynamics data base are presented
Remarks on the extension of the Ricci flow
We present two new conditions to extend the Ricci flow on a compact manifold
over a finite time, which are improvements of some known extension theorems.Comment: 9 pages, to appear in Journal of Geometric Analysi
Piezoelectric rotator for studying quantum effects in semiconductor nanostructures at high magnetic fields and low temperatures
We report the design and development of a piezoelectric sample rotation
system, and its integration into an Oxford Instruments Kelvinox 100 dilution
refrigerator, for orientation-dependent studies of quantum transport in
semiconductor nanodevices at millikelvin temperatures in magnetic fields up to
10T. Our apparatus allows for continuous in situ rotation of a device through
>100deg in two possible configurations. The first enables rotation of the field
within the plane of the device, and the second allows the field to be rotated
from in-plane to perpendicular to the device plane. An integrated angle sensor
coupled with a closed-loop feedback system allows the device orientation to be
known to within +/-0.03deg whilst maintaining the sample temperature below
100mK.Comment: 8 pages, 5 figure
Non-ancient solution of the Ricci flow
For any complete noncompact Khler manifold with nonnegative and
bounded holomorphic bisectional curvature,we provide the necessary and
sufficient condition for non-ancient solution to the Ricci flow in this paper.Comment: seven pages, latex fil
Local light-ray rotation
We present a sheet structure that rotates the local ray direction through an
arbitrary angle around the sheet normal. The sheet structure consists of two
parallel Dove-prism sheets, each of which flips one component of the local
direction of transmitted light rays. Together, the two sheets rotate
transmitted light rays around the sheet normal. We show that the direction
under which a point light source is seen is given by a Mobius transform. We
illustrate some of the properties with movies calculated by ray-tracing
software.Comment: 9 pages, 6 figure
Two decades of pulsar timing of Vela
Pulsar timing at the Mt Pleasant observatory has focused on Vela, which can
be tracked for 18 hours of the day. These nearly continuous timing records
extend over 24 years allowing a greater insight into details of timing noise,
micro glitches and other more exotic effects. In particular we report the
glitch parameters of the 2004 event, along with the reconfirmation that the
spin up for the Vela pulsar occurs instantaneously to the accuracy of the data.
This places a lower limit of about 30 seconds for the acceleration of the
pulsar to the new rotational frequency. We also confirm of the low braking
index for Vela, and the continued fall in the DM for this pulsar.Comment: Isolated Neutron Stars conference, London, April 24-28 200
Enhanced Zeeman splitting in Ga0.25In0.75As quantum point contacts
The strength of the Zeeman splitting induced by an applied magnetic field is
an important factor for the realization of spin-resolved transport in
mesoscopic devices. We measure the Zeeman splitting for a quantum point contact
etched into a Ga0.25In0.75As quantum well, with the field oriented parallel to
the transport direction. We observe an enhancement of the Lande g-factor from
|g*|=3.8 +/- 0.2 for the third subband to |g*|=5.8 +/- 0.6 for the first
subband, six times larger than in GaAs. We report subband spacings in excess of
10 meV, which facilitates quantum transport at higher temperatures.Comment: [Version 2] Revtex4, 11 pages, 3 figures, accepted for publication in
Applied Physics Letter
Toward a Transboundary Monitoring Network: A Continuing Binational Exploration. Proceedings of a Workshop. Vol. 1
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