29,721 research outputs found
Orbiter Landing Loads Math Model Description and Correlation with ALT Flight Data
Results of the space shuttle approach and landing test are examined in order to assess landing gear characteristics and performance and verify landing dynamic analyses. The landing gears were instrumented with load-calibrated strain gages, a wheel-speed sensor, and strut stroke measurement devices. The mathematical procedure used in predicting the shuttle touchdown loads and dynamics is presented together with the comparisons between measured flight data and the analytical predictions. Conclusions from these data are also presented
The Generalized Ricci Flow for 3D Manifolds with One Killing Vector
We consider 3D flow equations inspired by the renormalization group (RG)
equations of string theory with a three dimensional target space. By modifying
the flow equations to include a U(1) gauge field, and adding carefully chosen
De Turck terms, we are able to extend recent 2D results of Bakas to the case of
a 3D Riemannian metric with one Killing vector. In particular, we show that the
RG flow with De Turck terms can be reduced to two equations: the continual Toda
flow solved by Bakas, plus its linearizaton. We find exact solutions which flow
to homogeneous but not always isotropic geometries
Design of the Annular Suspension and Pointing System (ASPS) (including design addendum)
The Annular Suspension and Pointing System is an experiment pointing mount designed for extremely precise 3 axis orientation of shuttle experiments. It utilizes actively controlled magnetic bearing to provide noncontacting vernier pointing and translational isolation of the experiment. The design of the system is presented and analyzed
The effect of low-energy ion-implantation on the electrical transport properties of Si-SiO2 MOSFETs
Using silicon MOSFETs with thin (5nm) thermally grown SiO2 gate dielectrics,
we characterize the density of electrically active traps at low-temperature
after 16keV phosphorus ion-implantation through the oxide. We find that, after
rapid thermal annealing at 1000oC for 5 seconds, each implanted P ion
contributes an additional 0.08 plus/minus 0.03 electrically active traps,
whilst no increase in the number of traps is seen for comparable silicon
implants. This result shows that the additional traps are ionized P donors, and
not damage due to the implantation process. We also find, using the room
temperature threshold voltage shift, that the electrical activation of donors
at an implant density of 2x10^12 cm^-2 is ~100%.Comment: 11 pages, 10 figure
The measurement of lubricant-film thickness using ultrasound
Ultrasound is reflected from a liquid layer between two solid bodies. This reflection depends on the ultrasonic frequency, the acoustic properties of the liquid and solid, and the layer thickness. If the wavelength is much greater than the liquid-layer thickness, then the response is governed by the stiffness of the layer. If the wavelength and layer thickness are similar, then the interaction of ultrasound with the layer is controlled by its resonant behaviour. This stiffness governed response and resonant response can be used to determine the thickness of the liquid layer, if the other parameters are known.
In this paper, ultrasound has been developed as a method to determine the thickness of lubricating films in bearing systems. An ultrasonic transducer is positioned on the outside of a bearing shell such that the wave is focused on the lubricant-film layer. The transducer is used to both emit and receive wide-band ultrasonic pulses. For a particular lubricant film, the reflected pulse is processed to give a reflection-coefficient spectrum. The lubricant-film thickness is then obtained from either the layer stiffness or the resonant frequency.
The method has been validated using fluid wedges at ambient pressure between flat and curved surfaces. Experiments on the elastohydrodynamic film formed between a sliding ball and a flat surface were performed. Film-thickness values in the range 50-500 nm were recorded, which agreed well with theoretical film-formation predictions. Similar measurements have been made on the oil film between the balls and outer raceway of a deep-groove ball bearing
Electrically-detected magnetic resonance in ion-implanted Si:P nanostructures
We present the results of electrically-detected magnetic resonance (EDMR)
experiments on silicon with ion-implanted phosphorus nanostructures, performed
at 5 K. The devices consist of high-dose implanted metallic leads with a square
gap, into which Phosphorus is implanted at a non-metallic dose corresponding to
10^17 cm^-3. By restricting this secondary implant to a 100 nm x 100 nm region,
the EDMR signal from less than 100 donors is detected. This technique provides
a pathway to the study of single donor spins in semiconductors, which is
relevant to a number of proposals for quantum information processing.Comment: 9 pages, 3 figure
Nuclear Model of Binding alpha-particles
The model of binding alpha-particles in nuclei is suggested. It is shown good
(with the accuracy of 1-2%) description of the experimental binding energies in
light and medium nuclear systems. Our preliminary calculations show enhancement
of the binding energy for super heavy nuclei with Z~120.Comment: 4 pages, 2 figures, Will be puplished in World Scientific as Procs.
Int. Symposium on Exotic Nuclei, "EXON - 2004", July 5 - 12, 2004, Peterhof,
Russi
A compactness theorem for complete Ricci shrinkers
We prove precompactness in an orbifold Cheeger-Gromov sense of complete
gradient Ricci shrinkers with a lower bound on their entropy and a local
integral Riemann bound. We do not need any pointwise curvature assumptions,
volume or diameter bounds. In dimension four, under a technical assumption, we
can replace the local integral Riemann bound by an upper bound for the Euler
characteristic. The proof relies on a Gauss-Bonnet with cutoff argument.Comment: 28 pages, final version, to appear in GAF
Ricci flows, wormholes and critical phenomena
We study the evolution of wormhole geometries under Ricci flow using
numerical methods. Depending on values of initial data parameters, wormhole
throats either pinch off or evolve to a monotonically growing state. The
transition between these two behaviors exhibits a from of critical phenomena
reminiscent of that observed in gravitational collapse. Similar results are
obtained for initial data that describe space bubbles attached to
asymptotically flat regions. Our numerical methods are applicable to
"matter-coupled" Ricci flows derived from conformal invariance in string
theory.Comment: 8 pages, 5 figures. References added and minor changes to match
version accepted by CQG as a fast track communicatio
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