1,458 research outputs found
Spatial Distribution of Lead in Sacramento, California, USA
Chronic exposure to lead remains a health concern in many urban areas; Sacramento, California is one example, with state surveillance data showing nearly 3% of screened children reported with blood lead levels over 4.5 μg/dL in 2009. To investigate the environmental exposure, 91 soil samples were collected and analyzed by ICP-AES and ICP-MS for 14 elements. An additional 28 samples were collected from areas of focus and analyzed by hand-held X-ray fluorescence spectrometry for Pb and Zn. Analysis of the metals data revealed non-normal distributions and positive skewness, consistent with anthropogenic input. In addition, high correlation coefficients (≥0.75) of metal concentrations in Cd-Pb, Cd-Zn, Pb-Zn, and Sb-Sn pairs suggest similarities in the input mechanisms. Semivariograms generated from Pb and associated metals reveal these metals to exhibit spatial correlation. A prediction map of lead concentrations in soil was generated by ordinary kriging, showing elevated concentrations in soil located in the central, older area of Sacramento where historic traffic density and industrial activity have been historically concentrated. XRF analysis of Pb and Zn from additional samples verifies elevated concentrations in the central areas of Sacramento as predicted
MATCH: a new industry-focused approach to medical device development
MATCH (Multidisciplinary Assessment of Technology Centre for
Healthcare) is a new collaboration in the UK that aims to support the healthcare sector by creating methods to assess the value of medical devices from concept through to mature product. A major aim of MATCH is to encourage the inclusion of the user throughout the product lifecycle in order to achieve devices that truly meet the requirements of their users. A review of the published literature indicates that user requirements are mainly collected during the design and evaluation stage of the product lifecycle whilst other areas, including the concept stage, have less user involvement. Complementing the literature review is an in-depth consultation with the medical device industry, which has identified a number of barriers encountered by companies when attempting to capture user requirements. These will be addressed by a number of case study projects, performed in collaboration with our industrial partners,
that will examine the application and utility of different approaches to collecting and analysing data on user requirements. MATCH is focused on providing advice to device developers on how to select and apply methods that have maximum theoretical strength, practical application,
cost-effectiveness and likelihood of wide sector acceptance. Feedback will be sought in order to ensure that the needs of the diverse medical device sector are met
Fully broadband vAPP coronagraphs enabling polarimetric high contrast imaging
We present designs for fully achromatic vector Apodizing Phase Plate (vAPP)
coronagraphs, that implement low polarization leakage solutions and achromatic
beam-splitting, enabling observations in broadband filters. The vAPP is a pupil
plane optic, inducing the phase through the inherently achromatic geometric
phase. We discuss various implementations of the broadband vAPP and set
requirements on all the components of the broadband vAPP coronagraph to ensure
that the leakage terms do not limit a raw contrast of 1E-5. Furthermore, we
discuss superachromatic QWPs based of liquid crystals or quartz/MgF2
combinations, and several polarizer choices. As the implementation of the
(broadband) vAPP coronagraph is fully based on polarization techniques, it can
easily be extended to furnish polarimetry by adding another QWP before the
coronagraph optic, which further enhances the contrast between the star and a
polarized companion in reflected light. We outline several polarimetric vAPP
system designs that could be easily implemented in existing instruments, e.g.
SPHERE and SCExAO.Comment: 11 pages, 5 figures, presented at SPIE Astronomical Telescopes and
Instrumentation 201
High-performance 3D waveguide architecture for astronomical pupil-remapping interferometry
The detection and characterisation of extra-solar planets is a major theme
driving modern astronomy, with the vast majority of such measurements being
achieved by Doppler radial-velocity and transit observations. Another technique
-- direct imaging -- can access a parameter space that complements these
methods, and paves the way for future technologies capable of detailed
characterization of exoplanetary atmospheres and surfaces. However achieving
the required levels of performance with direct imaging, particularly from
ground-based telescopes which must contend with the Earth's turbulent
atmosphere, requires considerable sophistication in the instrument and
detection strategy. Here we demonstrate a new generation of photonic
pupil-remapping devices which build upon the interferometric framework
developed for the {\it Dragonfly} instrument: a high contrast waveguide-based
device which recovers robust complex visibility observables. New generation
Dragonfly devices overcome problems caused by interference from unguided light
and low throughput, promising unprecedented on-sky performance. Closure phase
measurement scatter of only has been achieved, with waveguide
throughputs of . This translates to a maximum contrast-ratio
sensitivity (between the host star and its orbiting planet) at
(1 detection) of (when a conventional
adaptive-optics (AO) system is used) or (for typical
`extreme-AO' performance), improving even further when random error is
minimised by averaging over multiple exposures. This is an order of magnitude
beyond conventional pupil-segmenting interferometry techniques (such as
aperture masking), allowing a previously inaccessible part of the star to
planet contrast-separation parameter space to be explored
Extracting dynamical equations from experimental data is NP-hard
The behavior of any physical system is governed by its underlying dynamical
equations. Much of physics is concerned with discovering these dynamical
equations and understanding their consequences. In this work, we show that,
remarkably, identifying the underlying dynamical equation from any amount of
experimental data, however precise, is a provably computationally hard problem
(it is NP-hard), both for classical and quantum mechanical systems. As a
by-product of this work, we give complexity-theoretic answers to both the
quantum and classical embedding problems, two long-standing open problems in
mathematics (the classical problem, in particular, dating back over 70 years).Comment: For mathematical details, see arXiv:0908.2128[math-ph]. v2: final
version, accepted in Phys. Rev. Let
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Comparison of Molecular Dynamics and Binary Collision Approximation Simulations for Atom Displacement Analysis
Molecular dynamics (MD) and binary collision approximation (BCA) computer simulations are employed to study surface damage by single ion impacts. The predictions of BCA and MD simulations of displacement cascades in amorphous and crystalline silicon and BCC tungsten by ion bombardment are compared. Single ion impacts are studied at angles of from normal incidence. Four parameters for BCA simulations have been optimized to obtain the best agreement of the results with MD. For the conditions reported here, BCA agrees with MD simulation results at displacements larger than for amorphous Si, whereas at small displacements a difference between BCA and MD arises due to a material flow component observed in MD simulations but absent from a regular BCA approach due to the algorithm limitations. MD and BCA simulation results for crystalline W are found to be in a good agreement even at small displacements, while in crystalline Si there is some difference due to displacements in amorphous pockets.Engineering and Applied Science
High flux cold Rubidium atomic beam for strongly coupled Cavity QED
This paper presents a setup capable of producing a high-flux continuous beam
of cold rubidium atoms for cavity QED experiments in the regime of strong
coupling. A 2 MOT, loaded by rubidium getters in a dry film coated vapor
cell, fed a secondary moving-molasses MOT (MM-MOT) at a rate of 1.5 x
atoms/sec. The MM-MOT provided a continuous beam with tunable velocity. This
beam was then directed through the waist of a 280 m cavity resulting in a
Rabi splitting of more than +/- 10 MHz. The presence of sufficient number of
atoms in the cavity mode also enabled splitting in the polarization
perpendicular to the input. The cavity was in the strong coupling regime, with
parameters (g, , )/2 equal to (7, 3, 6)/ 2 MHz.Comment: Journal pape
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