11,852 research outputs found
Ion yields and erosion rates for Si1−xGex(0x1) ultralow energy O2+ secondary ion mass spectrometry in the energy range of 0.25–1 keV
We report the SIMS parameters required for the quantitative analysis of Si1−xGex across the range of 0 ≤ x ≤ 1 when using low energy O2+ primary ions at normal incidence. These include the silicon and germanium secondary ion yield [i.e., the measured ion signal (ions/s)] and erosion rate [i.e., the speed at which the material sputters (nm/min)] as a function of x. We show that the ratio Rx of erosion rates, Si1−xGex/Si, at a given x is almost independent of beam energy, implying that the properties of the altered layer are dominated by the interaction of oxygen with silicon. Rx shows an exponential dependence on x. Unsurprisingly, the silicon and germanium secondary ion yields are found to depart somewhat from proportionality to (1−x) and x, respectively, although an approximate linear relationship could be used for quantification across around 30% of the range of x (i.e., a reference material containing Ge fraction x would give reasonably accurate quantification across the range of ±0.15x). Direct comparison of the useful (ion) yields [i.e., the ratio of ion yield to the total number of atoms sputtered for a particular species (ions/atom)] and the sputter yields [i.e., the total number of atoms sputtered per incident primary ion (atoms/ions)] reveals a moderate matrix effect where the former decrease monotonically with increasing x except at the lowest beam energy investigated (250 eV). Here, the useful yield of Ge is found to be invariant with x. At 250 eV, the germanium ion and sputter yields are proportional to x for all x
The FAA: A Tombstone Agency? Putting the Nickname to the Test
The purpose of this research was to investigate Federal Aviation Administration (FAA) activity before and after six catastrophic airline accidents to examine the alleged reactive policysetting reputation of the FAA. Actions reviewed were regulatory, inspection, and enforcement activities. The study revealed that change in agency activity does occur following an accident. The location of the event appears to influence the direction of change. When accidents occurred within the United States, FAA activity increased following the accident. The opposite occurred for airline accidents outside the U.S. The increase in FAA activity following U.S. based events, supports the reactive, tombstone agency reputation the FAA has acquired.
In addition, the research revealed nine FAA activities judged by industry experts as having the ability to improve safety in the airline industry. Inspections and certificate actions are considered activities that will improve safety. Regulatory actions, fines, warning notices, and letters of correction were judged as non-safety enhancing activities. The result of this research was an increased understanding of how the FAA responds to airline accidents and the consequences of the response
Conducting Measurement Invariance Tests with Ordinal Data: A Guide for Social Work Researchers
Objective: The validity of measures across groups is a major concern for social work researchers and practitioners. Many social workers use scales, or sets of questionnaire items, with ordinal response options. However, a review of social work literature indicates the appropriate treatment of ordinal data in measurement invariance tests is rare; only 3 of 57 articles published in 26 social work journals over the past 12 years used proper testing procedures. This article synthesizes information from the literature and provides recommendations for appropriate measurement invariance procedures with ordinal data. Method: We use data from the Cebu Longitudinal Health and Nutrition Survey to demonstrate applications of invariance testing with ordinal data. Using a robust weighted least squares estimator and polychoric correlation matrix, we examine invariance of a 10-item Perceived Stress Scale (PSS) across 2 young adult groups defined by health status. We describe 2 competing approaches: a 4-step approach, in which factor loadings and thresholds are tested and constrained separately; and a 3-step approach, in which loadings and thresholds are tested and constrained in tandem. Results: Both approaches lead to the same conclusion that the 2 dimensions of the PSS are noninvariant across health status. In the absence of invariance, mean scores on the PSS factors cannot be validly compared across groups, nor should latent variables be used in the hypothesis testing across the 2 groups. Readers are directed to online resources. Conclusions: Careful examination of social work scales is likely to reveal fit or noninvariance problems across some groups. Use of appropriate methods for invariance testing will reduce misuse of measures in practice and improve the rigor and quality of social work publications
Biased EPR entanglement and its application to teleportation
We consider pure continuous variable entanglement with non-equal correlations
between orthogonal quadratures. We introduce a simple protocol which equates
these correlations and in the process transforms the entanglement onto a state
with the minimum allowed number of photons. As an example we show that our
protocol transforms, through unitary local operations, a single squeezed beam
split on a beam splitter into the same entanglement that is produced when two
squeezed beams are mixed orthogonally. We demonstrate that this technique can
in principle facilitate perfect teleportation utilising only one squeezed beam.Comment: 8 pages, 5 figure
Bunches of misfit dislocations on the onset of relaxation of SiGe/Si(001) epitaxial films revealed by high-resolution x-ray diffraction
The experimental x-ray diffraction patterns of a SiGe/Si(001)
epitaxial film with a low density of misfit dislocations are modeled by the
Monte Carlo method. It is shown that an inhomogeneous distribution of
60 dislocations with dislocations arranged in bunches is needed to
explain the experiment correctly. As a result of the dislocation bunching, the
positions of the x-ray diffraction peaks do not correspond to the average
dislocation density but reveal less than a half of the actual relaxation
Teleportation of continuous variable polarisation states
This paper discusses methods for the optical teleportation of continuous
variable polarisation states. We show that using two pairs of entangled beams,
generated using four squeezed beams, perfect teleportation of optical
polarisation states can be performed. Restricting ourselves to 3 squeezed
beams, we demonstrate that polarisation state teleportation can still exceed
the classical limit. The 3-squeezer schemes involve either the use of quantum
non-demolition measurement or biased entanglement generated from a single
squeezed beam. We analyse the efficacies of these schemes in terms of fidelity,
signal transfer coefficients and quantum correlations
Crystal truncation rods in kinematical and dynamical x-ray diffraction theories
Crystal truncation rods calculated in the kinematical approximation are shown
to quantitatively agree with the sum of the diffracted waves obtained in the
two-beam dynamical calculations for different reflections along the rod. The
choice and the number of these reflections are specified. The agreement extends
down to at least of the peak intensity. For lower intensities,
the accuracy of dynamical calculations is limited by truncation of the electron
density at a mathematically planar surface, arising from the Fourier series
expansion of the crystal polarizability
An experimental investigation of criteria for continuous variable entanglement
We generate a pair of entangled beams from the interference of two amplitude
squeezed beams. The entanglement is quantified in terms of EPR-paradox [Reid88]
and inseparability [Duan00] criteria, with observed results of and , respectively. Both results clearly beat the standard quantum
limit of unity. We experimentally analyze the effect of decoherence on each
criterion and demonstrate qualitative differences. We also characterize the
number of required and excess photons present in the entangled beams and
provide contour plots of the efficacy of quantum information protocols in terms
of these variables.Comment: 4 pages, 5 figure
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