966 research outputs found
Structure and energetics of Si(111)-(5x2)-Au
We propose a new structural model for the Si(111)-(5x2)-Au reconstruction.
The model incorporates a new experimental value of 0.6 monolayer for the
coverage of gold atoms, equivalent to six gold atoms per 5x2 cell. Five main
theoretical results, obtained from first-principles total-energy calculations,
support the model. (1) In the presence of silicon adatoms the periodicity of
the gold rows spontaneously doubles, in agreement with experiment. (2) The
dependence of the surface energy on the adatom coverage indicates that a
uniformly covered phase is unstable and will phase-separate into empty and
covered regions, as observed experimentally. (3) Theoretical scanning tunneling
microscopy images are in excellent agreement with experiment. (4) The
calculated band structure is consistent with angle-resolved photoemission
spectra; analysis of their correspondence allows the straightforward assignment
of observed surface states to specific atoms. (5) The calculated activation
barrier for diffusion of silicon adatoms along the row direction is in
excellent agreement with the experimentally measured barrier.Comment: 11 pages, 7 figures, also available with higher-resolution figures
from http://cst-www.nrl.navy.mil/users/erwin/ausi111.v5.pd
The late positive potential: a neural marker of the regulation of emotion-based approach-avoidance actions?
Could stool collection devices help increase uptake to bowel cancer screening programmes?
Objective: We aimed to understand the usage and acceptability of a faecal collection device (FCD) amongst participants of the NHS Bowel Cancer Screening Programme in order to influence future uptake.
Setting: Men and women completing faecal occult blood test (FOBt) retests as part of the routine Bowel Cancer Screening Programme in Eastern England.
Methods: A FCD and questionnaire was sent to all potential retest participants during a 1 month period collecting information on prior stool collection methods and ease of use and usefulness of the enclosed FCD.
Results: Of 1087 invitations to participate, 679 (62.5%) participants returned their questionnaire. Of these 429 (63.2%) trialled the FCD at least once. 163 (38.4%) found the device made collecting their sample easier than previously, with 189 (44.6%) finding it made collection more difficult and 72 (17.0%) feeling it made no difference. Similar numbers reported finding that the FCD made collecting the sample more pleasant (130, 31.5%), less pleasant (103, 25.0%) and no different (179, 43.4%) compared to previous collection without a FCD.
Conclusion: Although a small proportion of participants found the FCD helpful a considerable majority did not or did not use it at all. Offering FCDs is unlikely to produce a substantial increase in bowel cancer screening uptake
Evaluating the performance of ionic liquid coatings for mitigation of spacecraft surface charges
To reduce the impact of charging effects on satellites, cheap and lightweight
conductive coatings are desirable. We mimic space-like charging environments in
ultra-high vacuum (UHV) chambers during deposition of charges via the electron
beam of a scanning electron microscope (SEM). We use the charge induced
signatures in SEM images of a thin ionic liquid (IL) film on insulating
surfaces such as glass, to assess the general performance of such coatings. In
order to get a reference structure in SEM, the samples were structured by
nanosphere lithography and coated with IL. The IL film (we choose BMP DCA, due
to its beneficial physical properties) was applied ex situ and a thickness of
10 to 30 nm was determined by reflectometry. Such an IL film is stable under
vacuum conditions. It would also only lead to additional mass of below 20
mg/m. At about 5 A/m e/(sm), a typical
sample charging rate in SEM, imaging is possible with no noticeable contrast
changes over many hours; this electron current density is already 6 orders of
magnitudes higher than "worst case geosynchronous environments" of
A/m. Measurements of the surface potential are used for
further insights in the reaction of IL films to the electron beam of a SEM.
Participating mechanisms such as polarization or reorientation will are
discussed.Comment: Submitted to Proceedings of the 14th IAA Symposium on Small
Satellites for Earth System Observatio
State-related electroencephalographic deviances in attention deficit hyperactivity disorder
The dynamic security region (DSR) of bulk power system has been accepted more and more in recent years for providing plenty of security information and good prospect in online application. This paper compares three linear approximations for the dynamic security region of network-reduction power systems. The three linear approximations are the Q-linear approximation based on the quadratic approximation of stability region, the L-linear approximation based on the linear approximation of stability region and the L0-linear approximation based on the invariant assumption of the normal vector for the boundary of the stability region corresponding to different control variable. The three linear approximations are all obtained with a same critical point lying just on the boundary of dynamic security region. The critical point is searched with numerical simulation. The accuracy of the three linear approximations is compared, using the linear approximation obtained with the curve fitting approach or the actual boundary of DSR searched as the benchmark. Simulation results in IEEE 3-machine 9-bus system and 10-machine 39-bus New England system show that all the three linear approximations display fairly accurate estimation. Furthermore, from the computational viewpoint, the L-linear and the L0-linear method are two alternative choices to approximate the dynamic security region.link_to_subscribed_fulltex
Readout for intersatellite laser interferometry: Measuring low frequency phase fluctuations of HF signals with microradian precision
Precision phase readout of optical beat note signals is one of the core
techniques required for intersatellite laser interferometry. Future space based
gravitational wave detectors like eLISA require such a readout over a wide
range of MHz frequencies, due to orbit induced Doppler shifts, with a precision
in the order of at frequencies between
and . In this paper, we present phase
readout systems, so-called phasemeters, that are able to achieve such
precisions and we discuss various means that have been employed to reduce noise
in the analogue circuit domain and during digitisation. We also discuss the
influence of some non-linear noise sources in the analogue domain of such
phasemeters. And finally, we present the performance that was achieved during
testing of the elegant breadboard model of the LISA phasemeter, that was
developed in the scope of an ESA technology development activity.Comment: submitted to Review of Scientific Instruments on April 30th 201
Reaction time variability in children with ADHD symptoms and/or dyslexia.
Reaction time (RT) variability on a Stop Signal task was examined among children with attention deficit hyperactivity disorder (ADHD) symptoms and/or dyslexia in comparison to typically developing (TD) controls. Children's go-trial RTs were analyzed using a novel ex-Gaussian method. Children with ADHD symptoms had increased variability in the fast but not the slow portions of their RT distributions compared to those without ADHD symptoms. The RT distributions of children with dyslexia were similar to those of TD-controls. It is argued that variability in responding may be underpinned by impairments in response preparation or timing during Stop Signal tasks
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