13,793 research outputs found
Electric-field Manipulation of the Lande' g Tensor of Holes in In0.5Ga0.5As/GaAs Self-assembled Quantum Dots
The effect of an electric field on spin precession in In0.5Ga0.5As/GaAs
self-assembled quantum dots is calculated using multiband real-space
envelope-function theory. The dependence of the Lande' g tensor on electric
fields should permit high-frequency g tensor modulation resonance, as well as
direct, nonresonant electric-field control of the hole spin. Subharmonic
resonances have also been found in g tensor modulation resonance of the holes,
due to the strong quadratic dependence of components of the hole g tensor on
the electric field.Comment: 4 pages, 2 figure
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Some Lessons from the New Public Finance
Stiglitz and Boskin provide us with lessons from the new public finance
GraphX: Unifying Data-Parallel and Graph-Parallel Analytics
From social networks to language modeling, the growing scale and importance
of graph data has driven the development of numerous new graph-parallel systems
(e.g., Pregel, GraphLab). By restricting the computation that can be expressed
and introducing new techniques to partition and distribute the graph, these
systems can efficiently execute iterative graph algorithms orders of magnitude
faster than more general data-parallel systems. However, the same restrictions
that enable the performance gains also make it difficult to express many of the
important stages in a typical graph-analytics pipeline: constructing the graph,
modifying its structure, or expressing computation that spans multiple graphs.
As a consequence, existing graph analytics pipelines compose graph-parallel and
data-parallel systems using external storage systems, leading to extensive data
movement and complicated programming model.
To address these challenges we introduce GraphX, a distributed graph
computation framework that unifies graph-parallel and data-parallel
computation. GraphX provides a small, core set of graph-parallel operators
expressive enough to implement the Pregel and PowerGraph abstractions, yet
simple enough to be cast in relational algebra. GraphX uses a collection of
query optimization techniques such as automatic join rewrites to efficiently
implement these graph-parallel operators. We evaluate GraphX on real-world
graphs and workloads and demonstrate that GraphX achieves comparable
performance as specialized graph computation systems, while outperforming them
in end-to-end graph pipelines. Moreover, GraphX achieves a balance between
expressiveness, performance, and ease of use
Single photon production by rephased amplified spontaneous emission
The production of single photons using rephased amplified spontaneous
emission is examined. This process produces single photons on demand with high
efficiency by detecting the spontaneous emission from an atomic ensemble, then
applying a population-inverting pulse to rephase the ensemble and produce a
photon echo of the spontaneous emission events. The theoretical limits on the
efficiency of the production are determined for several variants of the scheme.
For an ensemble of uniform optical density, generating the initial spontaneous
emission and its echo using transitions of different strengths is shown to
produce single photons at 70% efficiency, limited by reabsorption. Tailoring
the spatial and spectral density of the atomic ensemble is then shown to
prevent reabsorption of the rephased photon, resulting in emission efficiency
near unity
Poster 156 Musculoskeletal Injuries in Dancers
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147106/1/pmr2s223.pd
Optical Tweezers as an Effective Tool for Spermatozoa Isolation from Mixed Forensic Samples
A single focus optical tweezer is formed when a laser beam is launched through a high numerical aperture immersion objective. This objective focuses the beam down to a diffraction-limited spot, which creates an optical trap where cells suspended in aqueous solutions can be held fixed. Spermatozoa, an often probative cell type in forensic investigations, can be captured inside this optical trap and dragged one by one across millimeter-length distances in order to create a cluster of cells which can be subsequently drawn up into a capillary for collection. Sperm cells are then ejected onto a sterile cover slip, counted, and transferred to a tube for DNA analysis workflow. The objective of this research was to optimize sperm cell collection for maximum DNA yield, and to determine the number of trapped sperm cells necessary to produce a full STR profile. A varying number of sperm cells from both a single-source semen sample and a mock sexual assault sample were isolated utilizing optical tweezers and processed using conventional STR analysis methods. Results demonstrated that approximately 50 trapped spermatozoa were required to obtain a consistently full DNA profile. A complete, single-source DNA profile was also achieved by isolating sperm cells via optical trapping from a mixture of sperm and vaginal epithelial cells. Based on these results, optical tweezers are a viable option for forensic applications such as separation of mixed populations of cells in forensic evidence
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