16,902 research outputs found
Measuring Hospital Performance: The Importance of Process Measures
Evaluates the effectiveness of Hospital Quality Alliance standards, and identifies specific activities hospitals can work on to improve performance and deliver higher quality health care
Evidence for an intermediate mass black hole and a multi-zone warm absorber in NGC 4395
We report on the results of an analysis in the X-ray band of a recent long
ASCA observation of NGC 4395, the most variable low-luminosity AGN known. A
relativistically-broadened iron line at ~6.4 keV is clearly resolved in the
time-averaged spectrum, with an equivalent width of 310^{+70}_{-90} eV.
Time-resolved spectral analysis of the heavily absorbed soft X-ray band
confirms the existence of a variable, multi-zone warm absorber in this source,
as proposed in a previous analysis of a shorter ASCA observation. The light
curve of the source is wildly variable on timescales of hours or less, and a
factor of nearly 10 change in count-rate was recorded in a period of less than
2000 s. The long observation and variability of the source allowed the power
density spectrum (PDS) to be constructed to an unprecedented level of detail.
There is evidence for a break in the PDS from a slope of \alpha~1 to \alpha~1.8
at a frequency of around 3 \times 10^{-4} Hz. The central black hole mass of
NGC 4395 is estimated to be approximately 10^4-10^5 solar masses using the
break in the PDS, a result consistent with previous analyses using optical and
kinematical techniques.Comment: 8 pages, 6 figures, accepted for publication in MNRA
System dynamic simulation of precision segmented reflector
A joint effort was undertaken on a Precision Segmented Reflector (PSR) Project. The missions in which the PSR is to be used will use large (up to 20 m in diameter) telescopes. The essential requirement for the telescopes is that the reflector surface of the primary mirror must be made extremely precise to allow no more than a few microns of errors and, additionally, this high surface precision must be maintained when the telescope is subjected to on-orbital mechanical and thermal disturbances. Based on the mass, size, and stability considerations, reflector surface formed by segmented, probably actively or passively controlled, composite panels are regarded as most suitable for future space based astronomical telescope applications. In addition to the design and fabrication of composite panels with a surface error of less than 3 microns RMS, PSR also develops related reflector structures, materials, control, and sensing technologies. As part of the planning effort for PSR Technology Demonstration, a system model which couples the reflector, consisting of panels, support truss and actuators, and the optical bench was assembled for dynamic simulations. Random vibration analyses using seismic data obtained from actual measurements at the test site designated for PSR Technology Demonstration are described
Rapid optimization of working parameters of microwave-driven multi-level qubits for minimal gate leakage
We propose an effective method to optimize the working parameters (WPs) of
microwave-driven quantum logical gates implemented with multi-level physical
qubits. We show that by treating transitions between each pair of levels
independently, intrinsic gate errors due primarily to population leakage to
undesired states can be estimated accurately from spectroscopic properties of
the qubits and minimized by choosing appropriate WPs. The validity and
efficiency of the approach are demonstrated by applying it to optimize the WPs
of two coupled rf SQUID flux qubits for controlled-NOT (CNOT) operation. The
result of this independent transition approximation (ITA) is in good agreement
with that of dynamic method (DM). Furthermore, the ratio of the speed of ITA to
that of DM scales exponentially as 2^n when the number of qubits n increases.Comment: 4pages, 3 figure
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