1,297 research outputs found
A hybrid method for determining particle masses at the Large Hadron Collider with fully identified cascade decays
A new technique for improving the precision of measurements of SUSY particle
masses at the LHC is introduced. The technique involves kinematic fitting of
events with two fully identified decay chains. We incorporate both event ETmiss
constraints and independent constraints provided by kinematic end-points in
experiment invariant mass distributions of SUSY decay products. Incorporation
of the event specific information maximises the information used in the fit and
is shown to reduce the mass measurement uncertainites by ~30% compared to
conventional fitting of experiment end-point constraints for the SPS1a
benchmark model.Comment: 10 pages, 2 .eps figures, JHEP3 styl
Spectral signatures of photosynthesis I: Review of Earth organisms
Why do plants reflect in the green and have a 'red edge' in the red, and
should extrasolar photosynthesis be the same? We provide: 1) a brief review of
how photosynthesis works; 2) an overview of the diversity of photosynthetic
organisms, their light harvesting systems, and environmental ranges; 3) a
synthesis of photosynthetic surface spectral signatures; 4) evolutionary
rationales for photosynthetic surface reflectance spectra with regard to
utilization of photon energy and the planetary light environment. Given the
surface incident photon flux density spectrum and resonance transfer in light
harvesting, we propose some rules with regard to where photosynthetic pigments
will peak in absorbance: a) the wavelength of peak incident photon flux; b) the
longest available wavelength for core antenna or reaction center pigments; and
c) the shortest wavelengths within an atmospheric window for accessory
pigments. That plants absorb less green light may not be an inefficient legacy
of evolutionary history, but may actually satisfy the above criteria.Comment: 69 pages, 7 figures, forthcoming in Astrobiology March 200
Technological Devices in the Archives: A Policy Analysis
Doing research in the archive is the cornerstone of humanities scholarship.
Various archives institute policies regarding the use of technological
devices, such as mobile phones, laptops, and cameras in their reading rooms.
Such policies directly affect the scholars as the devices mediate the nature of
their interaction with the source materials in terms of capturing, organizing,
note taking, and record keeping for future use of found materials. In this paper,
we present our analysis of the policies of thirty archives regarding the use of
technology in their reading rooms. This policy analysis, along with data from
interviews of scholars and archivists, is intended to serve as a basis for developing
mobile applications for assisting scholars in their research activities. In this
paper we introduce an early prototype of such a mobile application—
AMTracker.Informatio
Supersymmetric particle mass measurement with invariant mass correlations
The kinematic end-point technique for measuring the masses of supersymmetric
particles in R-Parity conserving models at hadron colliders is re-examined with
a focus on exploiting additional constraints arising from correlations in
invariant mass observables. The use of such correlations is shown to
potentially resolve the ambiguity in the interpretation of quark+lepton
end-points and enable discrimination between sequential two-body and three-body
lepton-producing decays. The use of these techniques is shown to improve the
SUSY particle mass measurement precision for the SPS1a benchmark model by at
least 20-30% compared to the conventional end-point technique.Comment: 29 pages, 23 .eps figures, JHEP3 style; v2 adds some references and
small clarifications to text; v3 adds some more clarifications to the tex
Using Subsystem MT2 for Complete Mass Determinations in Decay Chains with Missing Energy at Hadron Colliders
We propose to use the MT2 concept to measure the masses of all particles in
SUSY-like events with two unobservable, identical particles. To this end we
generalize the usual notion of MT2 and define a new MT2(n,p,c) variable, which
can be applied to various subsystem topologies, as well as the full event
topology. We derive analytic formulas for its endpoint MT2{max}(n,p,c) as a
function of the unknown test mass Mc of the final particle in the subchain and
the transverse momentum pT due to radiation from the initial state. We show
that the endpoint functions MT2{max}(n,p,c)(Mc,pT) may exhibit three different
types of kinks and discuss the origin of each type. We prove that the subsystem
MT2(n,p,c) variables by themselves already yield a sufficient number of
measurements for a complete determination of the mass spectrum (including the
overall mass scale). As an illustration, we consider the simple case of a decay
chain with up to three heavy particles, X2 -> X1 -> X0, which is rather
problematic for all other mass measurement methods. We propose three different
MT2-based methods, each of which allows a complete determination of the masses
of particles X0, X1 and X2. The first method only uses MT2(n,p,c) endpoint
measurements at a single fixed value of the test mass Mc. In the second method
the unknown mass spectrum is fitted to one or more endpoint functions
MT2{max}(n,p,c)(Mc,pT) exhibiting a kink. The third method is hybrid, combining
MT2 endpoints with measurements of kinematic edges in invariant mass
distributions. As a practical application of our methods, we show that the
dilepton W+W- and tt-bar samples at the Tevatron can be used for an independent
determination of the masses of the top quark, the W boson and the neutrino,
without any prior assumptions.Comment: 47 pages, 9 figures. revised version, published in JHEP. Major
addition: a new appendix with the complete set of formulas for the MT2
endpoints as functions of the upstream transverse momentum pT and test mass
M
Influence of intensive melt shearing on the microstructure and mechanical properties of an Al-Mg alloy with high added impurity content
The official published version can be accessed from the link below - Copyright @ The Minerals, Metals & Materials Society and ASM International 2011We have investigated the influence of melt conditioning by intensive shearing on the mechanical behavior and microstructure of Al-Mg-Mn-Fe-Cu-Si alloy sheet produced from a small book mold ingot with high added impurity content. The melt conditioned ingot has fine grains throughout its cross section, whereas a conventionally cast ingot, without melt shearing, has coarser grains and shows a wider variation of grain size. Both needle-shaped and coarse Chinese script iron bearing intermetallic particles are found in the microstructure at the center of the conventionally processed ingot, but for the melt conditioned ingot, only fine Chinese script intermetallic particles are observed. In addition to the iron bearing intermetallics, Mg2Si particles are also observed. The ingots were rolled to thin sheet and solution heat treated (SHT). During rolling, the iron-based intermetallics and Mg2Si particles are broken and aligned along the rolling direction. Yield strength (YS), ultimate tensile strength (UTS), and elongation of the intensively melt sheared and processed sheet are all improved compared to the conventionally cast and processed sheet. Fractographic analysis of the tensile fracture surfaces shows that the clustered and coarse iron bearing intermetallic particles are responsible for the observed reduction in mechanical properties of the conventionally cast sheet. We have shown that by refining the initial microstructure of the ingot by intensive shear melt conditioning, it is possible to achieve improved mechanical properties at the final sheet gage of an AlMgMn alloy with a high content of impurities.This study is under the Technology
Strategy Board funded REALCAR projec
High-efficiency p-i-n photodetectors on selective-area-grown ge for monolithic integration
We demonstrate normal incidence p-i-n photodiodes on selective-area-grown Ge using multiple hydrogen annealing for heteroepitaxy for the purpose of monolithic integration. An enhanced efficiency in the near-infrared regime and the absorption edge shifting to longer wavelength is achieved due to 0.14% residual tensile strain in the selective-area-grown Ge. The responsivities at 1.48, 1.525, and 1.55 μ are 0.8, 0.7, and 0.64 A/W, respectively, without an optimal antireflection coating. These results are promising toward monolithically integrated on-chip optical links and in telecommunications. © 2009 IEEE
Altered levels of blood proteins in Alzheimer\u27s disease longitudinal study: Results from Australian Imaging Biomarkers Lifestyle Study of Ageing cohort
Introduction A blood-based biomarker panel to identify individuals with preclinical Alzheimer\u27s disease (AD) would be an inexpensive and accessible first step for routine testing. Methods We analyzed 14 biomarkers that have previously been linked to AD in the Australian Imaging Biomarkers lifestyle longitudinal study of aging cohort. Results Levels of apolipoprotein J (apoJ) were higher in AD individuals compared with healthy controls at baseline and 18 months (P =.0003) and chemokine-309 (I-309) were increased in AD patients compared to mild cognitive impaired individuals over 36 months (P =.0008). Discussion These data suggest that apoJ may have potential in the context of use (COU) of AD diagnostics, I-309 may be specifically useful in the COU of identifying individuals at greatest risk for progressing toward AD. This work takes an initial step toward identifying blood biomarkers with potential use in the diagnosis and prognosis of AD and should be validated across other prospective cohorts. © 2017 The Author
Pilot testing the feasibility of a game intervention aimed at improving help seeking and coping among sexual and gender minority youth: protocol for a randomized controlled trial
Background: Sexual and gender minority youth (SGMY; e.g., lesbian, gay, bisexual, and transgender youth) experience myriad substance use and mental health disparities compared with their cisgender (non-transgender) heterosexual peers. Despite much research showing these disparities are driven by experiences of bullying and cyberbullying victimization, few interventions have aimed to improve the health of bullied SGMY. One possible way to improve the health of bullied SGMY is via an online-accessible game intervention. Nevertheless, little research has examined the feasibility of using an online-accessible game intervention with SGMY. Objectives: To describe the protocol for a randomized controlled trial (RCT) pilot testing the feasibility and limited-efficacy of a game-based intervention for increasing help-seeking-related knowledge, intentions, self-efficacy, and behaviors, productive coping skills use, and coping flexibility, and reducing health risk factors and behaviors among SGMY. Methods: We enrolled 240 SGMY aged 14-18 years residing in the United States into a two-arm prospective RCT. The intervention is a theory-based, community-informed, computer-based, role playing game with three primary components: (1) encouraging help-seeking behaviors; (2) encouraging use of productive coping; and (3) raising awareness of online resources. SGMY randomized to both the intervention and control conditions will receive a list of SGMY-inclusive resources covering a variety of health-related topics. Control condition participants received only the list of resources. Notably, all study procedures are conducted online. We conveniently sampled SGMY using online website advertisements. Study assessments occur at enrollment, 1 month after enrollment, and 2 months after enrollment. The primary outcomes of this feasibility study include implementation procedures, game demand, and game acceptability. Secondary outcomes include help-seeking intentions, self-efficacy, and behaviors; productive coping strategies and coping flexibility; and knowledge and use of online resources. Tertiary outcomes include bullying and cyberbullying victimization; loneliness; mental health issues; substance use; and internalized sexual and gender minority stigma. Results: From April through July 2018, 240 participants were enrolled and randomized. Half of the enrolled participants (n=120) were randomized into the intervention condition, and half (n=120) into the control condition. At baseline, 52% of participants identified as gay or lesbian, 27% as bisexual, 24% as queer, and 12% as another non-heterosexual identity. Nearly half (47%) of participants were a gender minority, 37% were cisgender boys, and 16% were cisgender girls. There were no differences in demographic characteristics between intervention and control condition participants. Data collection is anticipated to end in November 2018. Conclusions: Online-accessible game interventions overcome common impediments of face-to-face interventions and present a unique opportunity to reach SGMY and improve their health. This trial will provide data on feasibility and limited-efficacy that can inform future online studies and a larger RCT aimed at improving health equity for SGMY. Trial Registration: ClinicalTrials.gov NCT03501264; https://clinicaltrials.gov/ct2/show/NCT03501264 (Archived by WebCite at http://www.webcitation.org/72HpafarW
Sparticle Spectra and LHC Signatures for Large Volume String Compactifications
We study the supersymmetric particle spectra and LHC collider observables for
the large-volume string models with a fundamental scale of 10^{11} GeV that
arise in moduli-fixed string compactifications with branes and fluxes. The
presence of magnetic fluxes on the brane world volume, required for chirality,
perturb the soft terms away from those previously computed in the dilute-flux
limit. We use the difference in high-scale gauge couplings to estimate the
magnitude of this perturbation and study the potential effects of the magnetic
fluxes by generating many random spectra with the soft terms perturbed around
the dilute flux limit. Even with a 40% variation in the high-scale soft terms
the low-energy spectra take a clear and predictive form. The resulting spectra
are broadly similar to those arising on the SPS1a slope, but more degenerate.
In their minimal version the models predict the ratios of gaugino masses to be
M_1 : M_2 : M_3=(1.5 - 2) : 2 : 6, different to both mSUGRA and mirage
mediation. Among the scalars, the squarks tend to be lighter and the sleptons
heavier than for comparable mSUGRA models. We generate 10 fb^{-1} of sample LHC
data for the random spectra in order to study the range of collider
phenomenology that can occur. We perform a detailed mass reconstruction on one
example large-volume string model spectrum. 100 fb^{-1} of integrated
luminosity is sufficient to discriminate the model from mSUGRA and aspects of
the sparticle spectrum can be accurately reconstructed.Comment: 42 pages, 21 figures. Added references and discussion for section 3.
Slight changes in the tex
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