606 research outputs found
Onorbit IMU alignment error budget
The Star Tracker, Crew Optical Alignment Sight (COAS), and Inertial Measurement Unit (IMU) from a complex navigation system with a multitude of error sources were combined. A complete list of the system errors is presented. The errors were combined in a rational way to yield an estimate of the IMU alignment accuracy for STS-1. The expected standard deviation in the IMU alignment error for STS-1 type alignments was determined to be 72 arc seconds per axis for star tracker alignments and 188 arc seconds per axis for COAS alignments. These estimates are based on current knowledge of the star tracker, COAS, IMU, and navigation base error specifications, and were partially verified by preliminary Monte Carlo analysis
Orbit IMU alignment: Error analysis
A comprehensive accuracy analysis of orbit inertial measurement unit (IMU) alignments using the shuttle star trackers was completed and the results are presented. Monte Carlo techniques were used in a computer simulation of the IMU alignment hardware and software systems to: (1) determine the expected Space Transportation System 1 Flight (STS-1) manual mode IMU alignment accuracy; (2) investigate the accuracy of alignments in later shuttle flights when the automatic mode of star acquisition may be used; and (3) verify that an analytical model previously used for estimating the alignment error is a valid model. The analysis results do not differ significantly from expectations. The standard deviation in the IMU alignment error for STS-1 alignments was determined to the 68 arc seconds per axis. This corresponds to a 99.7% probability that the magnitude of the total alignment error is less than 258 arc seconds
A Comparison of the Ovulation Method With the CUE Ovulation Predictor in Determining the Fertile Period
The purpose of this study was to compare the CUE Ovulation Predictor with the ovulation method in determining the fertile period. Eleven regularly ovulating women measured their salivary and vaginal electrical resistance (ER) with the CUE, observed their cervical-vaginal mucus, and measured their urine for a luteinizing hormone (LH) surge on a daily basis. Data from 21 menstrual cycles showed no statistical difference (T= 0.33, p= 0.63) between the CUE fertile period, which ranged from 5 to 10 days (mean = 6.7 days, SD = 1.6), and the fertile period of the ovulation method, which ranged from 4 to 9 days (mean = 6.5 days, SD = 2.0). The CUE has potential as an adjunctive device in the learning and use of natural family planning methods
Transport properties of heterogeneous materials derived from Gaussian random fields: Bounds and Simulation
We investigate the effective conductivity () of a class of
amorphous media defined by the level-cut of a Gaussian random field. The three
point solid-solid correlation function is derived and utilised in the
evaluation of the Beran-Milton bounds. Simulations are used to calculate
for a variety of fields and volume fractions at several different
conductivity contrasts. Relatively large differences in are observed
between the Gaussian media and the identical overlapping sphere model used
previously as a `model' amorphous medium. In contrast shows little
variability between different Gaussian media.Comment: 15 pages, 14 figure
Deformation of a nearly hemispherical conducting drop due to an electric field: theory and experiment
We consider, both theoretically and experimentally, the deformation due to an electric field of a pinned nearly-hemispherical static sessile drop of an ionic fluid with a high conductivity resting on the lower substrate of a parallel plate capacitor. Using both numerical and asymptotic approaches we find solutions to the coupled electrostatic and augmented Young–Laplace equations which agree very well with the experimental results. Our asymptotic solution for the drop interface extends previous work in two ways, namely to drops that have zero-field contact angles that are not exactly π/2 and to higher order in the applied electric field, and provides useful predictive equations for the changes in the height, contact angle and pressure as functions of the zero-field contact angle, drop radius, surface tension and applied electric field. The asymptotic solution requires some numerical computations, and so a surprisingly accurate approximate analytical asymptotic solution is also obtained
Low-Frequency Crossover of the Fractional Power-Law Conductivity in SrRuO\u3csub\u3e3\u3c/sub\u3e
We combine the results of terahertz time-domain spectroscopy with far-infrared transmission and reflectivity to obtain the conductivity of SrRuO 3 over an unprecedented continuous range in frequency, allowing us to characterize the approach to zero frequency as a function of temperature. We show that the conductivity follows a simple phenomenological form, with an analytic structure fundamentally different from that predicted by the standard theory of metals
Magnetic field induced charge and spin instabilities in cuprate superconductors
A d-wave superconductor, subject to strong phase fluctuations, is known to
suffer an antiferromagnetic instability closely related to the chiral symmetry
breaking in (2+1)-dimensional quantum electrodynamics (QED3). On the basis of
this idea we formulate a "QED3 in a box" theory of local instabilities of a
d-wave superconductor in the vicinity of a single pinned vortex undergoing
quantum fluctuations around its equilibrium position. As a generic outcome we
find an incommensurate 2D spin density wave forming in the neighborhood of a
vortex with a concomitant "checkerboard" pattern in the local electronic
density of states, in agreement with recent neutron scattering and tunneling
spectroscopy measurements.Comment: 4 pages REVTeX + 2 PostScript figures included in text. Version to
appear in PRL (minor stylistic changes, references updated). For related work
and info visit http://www.physics.ubc.ca/~fran
Phase-fluctuation induced reduction of the kinetic energy at the superconducting transition
Recent reflectivity measurements provide evidence for a "violation" of the
in-plane optical integral in the underdoped high-T_c compound
Bi_2Sr_2CaCu_2O_{8+\delta} up to frequencies much higher than expected by
standard BCS theory. The sum rule violation may be related to a loss of
in-plane kinetic energy at the superconducting transition. Here, we show that a
model based on phase fluctuations of the superconducting order parameter can
account for this change of in-plane kinetic energy at T_c. The change is due to
a transition from a phase-incoherent Cooper-pair motion in the pseudogap regime
above T_c to a phase-coherent motion at T_c.Comment: 5 pages, 3 eps-figure
The superfluid density in cuprate high-Tc superconductors - a new paradigm
The doping dependence of the superfluid density, r_s, of high-Tc
superconductors is usually considered in the context of the Uemura relation,
namely Tc proportional to rs, which is generally assumed to apply in the
underdoped regime. We show that a modified plot of Tc/Do versus rs, where Do is
the maximum d-wave gap at T=0, exhibits universal features that point to an
alternative interpretation of the underlying physics. In the underdoped region
this plot exhibits the canonical negative curvature expected when a
ground-state correlation competes with superconductivity (SC) by opening up a
gap in the normal-state DOS. In particular rs is suppressed much faster than
Tc/Do or indeed Tc. The pseudogap is found to strongly modify the SC ground
state.Comment: 9 pages, 5 figures, submitted Phys. Rev. Let
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