15,311 research outputs found
The structure of atomic nitrogen adsorbed on Fe(100)
Nitrogen atoms adsorbed on a Fe(100) surface cause the formation of an ordered c(2 × 2) overlayer with coverage 0.5. A structure analysis was performed by comparing experimental LEED I–V spectra with the results of multiple scattering model calculations. The N atoms were found to occupy fourfold hollow sites, with their plane 0.27 Å above the plane of the surface Fe atoms. In addition, nitrogen adsorption causes an expansion of the two topmost Fe layers by 10% (= 0.14 Å). The minimum r-factor for this structure analysis is about 0.2 for a total of 16 beams. The resulting atomic arrangement is similar to that in the (002) plane of bulk Fe4N, thus supporting the view of a “surface nitride” and providing a consistent picture of the structural and bonding properties of this surface phase
Quantum interference by two temporally distinguishable pulses
We report a two-photon interference effect, in which the entangled photon
pairs are generated from two laser pulses well-separated in time. In a single
pump pulse case, interference effects did not occur in our experimental scheme.
However, by introducing a second pump pulse delayed in time, quantum
interference was then observed. The visibility of the interference fringes
shows dependence on the delay time between two laser pulses. The results are
explained in terms of indistinguishability of biphoton amplitudes which
originated from two temporally separated laser pulses.Comment: two-column, 4pages, submitted to PRA, minor change
Characteristic Length Scale of Electric Transport Properties of Genomes
A tight-binding model together with a novel statistical method are used to
investigate the relation between the sequence-dependent electric transport
properties and the sequences of protein-coding regions of complete genomes. A
correlation parameter is defined to analyze the relation. For some
particular propagation length , the transport behaviors of the coding
and non-coding sequences are very different and the correlation reaches its
maximal value . and \omax are characteristic values for
each species. The possible reason of the difference between the features of
transport properties in the coding and non-coding regions is the mechanism of
DNA damage repair processes together with the natural selection.Comment: 4 pages, 4 figure
Digging Deeper for New Physics in the LHC Data
In this paper we describe a novel, model-independent technique of
"rectangular aggregations" for mining the LHC data for hints of new physics. A
typical (CMS) search now has hundreds of signal regions, which can obscure
potentially interesting anomalies. Applying our technique to the two CMS
jets+MET SUSY searches, we identify a set of previously overlooked excesses. Among these, four excesses survive tests of inter- and
intra-search compatibility, and two are especially interesting: they are
largely overlapping between the jets+MET searches and are characterized by low
jet multiplicity, zero -jets, and low MET and . We find that resonant
color-triplet production decaying to a quark plus an invisible particle
provides an excellent fit to these two excesses and all other data -- including
the ATLAS jets+MET search, which actually sees a correlated excess. We discuss
the additional constraints coming from dijet resonance searches, monojet
searches and pair production. Based on these results, we believe the
wide-spread view that the LHC data contains no interesting excesses is greatly
exaggerated.Comment: 31 pages + appendices, 14 figures, source code for recasted searches
attached as auxiliary materia
An Update on the LHC Monojet Excess
In previous work, we identified an anomalous number of events in the LHC
jets+MET searches characterized by low jet multiplicity and low-to-moderate
transverse energy variables. Here, we update this analysis with results from a
new ATLAS search in the monojet channel which also shows a consistent excess.
As before, we find that this "monojet excess" is well-described by the resonant
production of a heavy colored state decaying to a quark and a massive invisible
particle. In the combined ATLAS and CMS data, we now find a local (global)
preference of 3.3 (2.5) for the new physics model over the
Standard Model-only hypothesis. As the signal regions containing the excess are
systematics-limited, we consider additional cuts to enhance the
signal-to-background ratio. We show that binning finer in and requiring
the jets to be more central can increase by a factor of .Comment: 5 pages, 5 figures, source for analysis code used in this paper in
attached Ancillary file
Cornering Natural SUSY at LHC Run II and Beyond
We derive the latest constraints on various simplified models of natural SUSY
with light higgsinos, stops and gluinos, using a detailed and comprehensive
reinterpretation of the most recent 13 TeV ATLAS and CMS searches with fb of data. We discuss the implications of these constraints for
fine-tuning of the electroweak scale. While the most "vanilla" version of SUSY
(the MSSM with -parity and flavor-degenerate sfermions) with 10% fine-tuning
is ruled out by the current constraints, models with decoupled valence squarks
or reduced missing energy can still be fully natural. However, in all of these
models, the mediation scale must be extremely low ( TeV). We conclude by
considering the prospects for the high-luminosity LHC era, where we expect the
current limits on particle masses to improve by up to TeV, and discuss
further model-building directions for natural SUSY that are motivated by this
work.Comment: v2: added tree level- parton shower matching, fixed bug in Delphes,
main results unchanged. 24 pages, 7 figures, plus appendi
GRID3D-v2: An updated version of the GRID2D/3D computer program for generating grid systems in complex-shaped three-dimensional spatial domains
In order to generate good quality systems for complicated three-dimensional spatial domains, the grid-generation method used must be able to exert rather precise controls over grid-point distributions. Several techniques are presented that enhance control of grid-point distribution for a class of algebraic grid-generation methods known as the two-, four-, and six-boundary methods. These techniques include variable stretching functions from bilinear interpolation, interpolating functions based on tension splines, and normalized K-factors. The techniques developed in this study were incorporated into a new version of GRID3D called GRID3D-v2. The usefulness of GRID3D-v2 was demonstrated by using it to generate a three-dimensional grid system in the coolent passage of a radial turbine blade with serpentine channels and pin fins
Understanding Rates of Marijuana Use and Consequences Among Adolescents in a Changing Legal Landscape.
Purpose of Review:There is not one answer to address whether marijuana use has increased, decreased, or stayed the same given changes in state legalization of medical and non-medical marijuana in the USA. Recent Findings:Evidence suggests some health benefits for medical marijuana; however, initiation of marijuana use is a risk factor for developing problem cannabis use. Though use rates have remained stable over recent years, about one in three 10th graders report marijuana use, most adolescents do not view the drug as harmful, and over 650,000 youth aged 12 to 17 struggle with cannabis use disorder. Summary:Although the health benefits of medical marijuana are becoming better understood, more research is needed. Intervention and prevention programs must better address effects of marijuana, acknowledging that while there may be some benefits medically, marijuana use can affect functioning during adolescence when the brain is still developing
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