4,087 research outputs found
Non-perturbative QCD effects in spectra of Drell-Yan and -boson production
The factorization theorems for transverse momentum distributions of
dilepton/boson production, recently formulated by Collins and
Echevarria-Idilbi-Scimemi in terms of well-defined transverse momentum
dependent distributions (TMDs), allows for a systematic and quantitative
analysis of non-perturbative QCD effects of the cross sections involving these
quantities. In this paper we perform a global fit using all current available
data for Drell-Yan and -boson production at hadron colliders within this
framework. The perturbative calculable pieces of our estimates are included
using a complete resummation at next-to-next-to-leading-logarithmic accuracy.
Performing the matching of transverse momentum distributions onto the standard
collinear parton distribution functions and recalling that the corresponding
matching coefficient can be partially exponentiated, we find that this
exponentiated part is spin-independent and resummable. We argue that the
inclusion of higher order perturbative pieces is necessary when data from lower
energy scales are analyzed. We consider non-perturbative corrections both to
the intrinsic nucleon structure and to the evolution kernel and find that the
non-perturbative part of the TMDs could be parametrized in terms of a minimal
set of parameters (namely 2-3). When all corrections are included the global
fit so performed gives a and a very precise
prediction for vector boson production at the Large Hadron Collider (LHC).Comment: 24 pages, 11 figures. v2: new subsection added, discussion on the
stability of the calculations and on higher order contributions improved,
results unchange
Masses and decay constants of mesons with twisted mass fermions
We present a preliminary lattice determination of the masses and decay
constants of the pseudoscalar and vector mesons and . Our analysis
is based on the gauge configurations produced by the European Twisted Mass
Collaboration with flavors of dynamical quarks. We simulated
at three different values of the lattice spacing and with pion masses as small
as 210 MeV. Heavy-quark masses are simulated directly on the lattice up to
times the physical charm mass. The physical b-quark mass is reached
using the ETMC ratio method. Our preliminary results are: MeV, MeV, and .Comment: 7 pages, 3 figures, 1 table; contribution to the proceedings of the
XXXVI Int'l Workshop on Lattice Field Theory (LATTICE2018), July 22-28, 2018,
East Lansing, Michigan State University (Michigan, USA
Consistency in motion event encoding across languages
Syntactic templates serve as schemas, allowing speakers to describe complex events in a systematic fashion. Motion events have long served as a prime example of how different languages favor different syntactic frames, in turn biasing their speakers towards different event conceptualizations. However, there is also variability in how motion events are syntactically framed within languages. Here we measure the consistency in event encoding in two languages, Spanish and Swedish. We test a dominant account in the literature, namely that variability within a language can be explained by specific properties of the events. This event-properties account predicts that descriptions of one and the same event should be consistent within a language, even in languages where there is overall variability in the use of syntactic frames. Spanish and Swedish speakers (N=84) described 32 caused motion events. While the most frequent syntactic framing in each language was as expected based on typology (Spanish: verb-framed, Swedish: satellite-framed, cf. Talmy, 2000), Swedish descriptions were substantially more consistent than Spanish descriptions. Swedish speakers almost invariably encoded all events with a single syntactic frame and systematically conveyed manner of motion. Spanish descriptions, in contrast, varied much more regarding syntactic framing and expression of manner. Crucially, variability in Spanish descriptions was not mainly a function of differences between events, as predicted by the event-properties account. Rather, Spanish variability in syntactic framing was driven by speaker biases. A similar picture arose for whether Spanish descriptions expressed manner information or not: Even after accounting for the effect of syntactic choice, a large portion of the variance in Spanish manner encoding remained attributable to differences among speakers. The results show that consistency in motion event encoding starkly differs across languages: Some languages (like Swedish) bias their speakers towards a particular linguistic event schema much more than others (like Spanish). Implications of these findings are discussed with respect to the typology of event framing, theories on the relationship between language and thought, and speech planning. In addition, the tools employed here to quantify variability can be applied to other domains of language
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Stretching Method-Based Operational Modal Analysis of An Old Masonry Lighthouse.
We present in this paper a structural health monitoring study of the Egyptian lighthouse of Rethymnon in Crete, Greece. Using structural vibration data collected on a limited number of sensors during a 3-month period, we illustrate the potential of the stretching method for monitoring variations in the natural frequencies of the structure. The stretching method compares two signals, the current that refers to the actual state of the structure, with the reference one that characterizes the structure at a reference healthy condition. For the structure under study, an 8-day time interval is used for the reference quantity while the current quantity is computed using a time window of 24 h. Our results indicate that frequency shifts of 1% can be detected with high accuracy allowing for early damage assessment. We also provide a simple numerical model that is calibrated to match the natural frequencies estimated using the stretching method. The model is used to produce possible damage scenarios that correspond to 1% shift in the first natural frequencies. Although simple in nature, this model seems to deliver a realistic response of the structure. This is shown by comparing the response at the top of the structure to the actual measurement during a small earthquake. This is a preliminary study indicating the potential of the stretching method for structural health monitoring of historical monuments. The results are very promising. Further analysis is necessary requiring the deployment of the instrumentation (possibly with additional instruments) for a longer period of time
Social media and youth political engagement: Preaching to the converted or providing a new voice for youth?
Amidst concern about declining youth political engagement, it is often suggested that social media can provide a solution to this challenge. In this article, however, we argue that these online tools have not thus far mobilised a new audience to become engaged in either institution-oriented activities or political expression. Instead, we found that some young people are far more engaged in using social media for political purposes than others, and that a substantial proportion of young adults never use social media for this purpose. Using latent class analysis (LCA) of a unique web survey of young Britons aged 22–29, we show that the principal driver of online political engagement is political interest (even after controlling for socio-demographic characteristics). On this basis, we conclude that social media may be providing a new outlet for some young adults; it is not re-engaging the young adults who have already lost interest in politics
High temperature NASP engine seal development
Key to the development of advanced hypersonic engines such as those being considered for the National Aerospace Plane (NASP) is the development and evaluation of high temperature, flexible seals that must seal the many feet of gaps between the articulating and stationary engine panels. Recent seal progress made at NASA-Lewis is reviewed in the areas of seal concept maturation, test rig development, and performance tests. A test fixture was built at NASA capable of subjecting candidate 3 ft long seals to engine simulated temperatures (up to 1500 F), pressures (up to 100 psi), and engine wall distortions (up to 0.15 in only 18 in span). Leakage performance test results at high temperatures are presented for an innovative high temperature, flexible ceramic wafer seal. Also described is a joint Pratt and Whitney/NASA planned test program to evaluate thermal performance of a braided rope seal under engine simulated heat flux rates (up to 400 Btu/sq ft s), and supersonic flow conditions. These conditions are produced by subjecting the seal specimen to hydrogen oxygen rocket exhaust that flows tangent to the specimen
Robust seismic velocity change estimation using ambient noise recordings
We consider the problem of seismic velocity change estimation using ambient
noise recordings. Motivated by [23] we study how the velocity change estimation
is affected by seasonal fluctuations in the noise sources. More precisely, we
consider a numerical model and introduce spatio-temporal seasonal fluctuations
in the noise sources. We show that indeed, as pointed out in [23], the
stretching method is affected by these fluctuations and produces misleading
apparent velocity variations which reduce dramatically the signal to noise
ratio of the method. We also show that these apparent velocity variations can
be eliminated by an adequate normalization of the cross-correlation functions.
Theoretically we expect our approach to work as long as the seasonal
fluctuations in the noise sources are uniform, an assumption which holds for
closely located seismic stations. We illustrate with numerical simulations and
real measurements that the proposed normalization significantly improves the
accuracy of the velocity change estimation
Detailed compositional analysis of the heavily polluted DBZ white dwarf SDSS J073842.56+183509.06: A window on planet formation?
We present a new model atmosphere analysis of the most metal contaminated
white dwarf known, the DBZ SDSS J073842.56+183509.06. Using new high resolution
spectroscopic observations taken with Keck and Magellan, we determine precise
atmospheric parameters and measure abundances of 14 elements heavier than
helium. We also report new Spitzer mid-infrared photometric data that are used
to better constrain the properties of the debris disk orbiting this star. Our
detailed analysis, which combines data taken from 7 different observational
facilities (GALEX, Gemini, Keck, Magellan, MMT, SDSS and Spitzer) clearly
demonstrate that J0738+1835 is accreting large amounts of rocky
terrestrial-like material that has been tidally disrupted into a debris disk.
We estimate that the body responsible for the photospheric metal contamination
was at least as large Ceres, but was much drier, with less than 1% of the mass
contained in the form of water ice, indicating that it formed interior to the
snow line around its parent star. We also find a correlation between the
abundances (relative to Mg and bulk Earth) and the condensation temperature;
refractory species are clearly depleted while the more volatile elements are
possibly enhanced. This could be the signature of a body that formed in a lower
temperature environment than where Earth formed. Alternatively, we could be
witnessing the remains of a differentiated body that lost a large part of its
outer layers.Comment: 16 pages, 17 figures, accepted for publication in The Astrophysical
Journa
Muscle fatty infiltration in rotator cuff tears: Descriptive analysis of 1688 cases
SummaryIntroductionFatty infiltration (FI) is an important prognosis factor in the anatomical and functional outcomes of rotator cuff repairs. The objective of this study was to analyze the natural history of muscle FI and better evaluate its onset and aggravation time frame.Material and methodsA total of 1688 medical charts of patients operated on for rotator cuff tear and whit a preoperative CT arthrogram (82%) or an MRI (18%) were reviewed. Surgery was performed between 1988 and 2005. The FI of each muscle was assessed as minimal (in Goutallier's stages 0 and 1), intermediate (in stage 2), and severe (in stages 3 and 4). Regarding supraspinatus, we retained the mean FI observed in the sagittal, coronal, and axial planes; for the infraspinatus and the subscapularis, we retained the observed mean on two views at the upper and lower levels of the glenoid in the axial plane.ResultsWe found a statistically significant correlation (p<0.0005) between FI, the type of tendon lesion, and patient age for the supraspinatus, the infraspinatus, and the subscapularis. Statistically, the FI significantly increased (p<0.0005) with time elapsed for the supraspinatus and the infraspinatus but not significantly for the subscapularis. The mean time to tendon rupture observed for intermediate FI was three years for the supraspinatus and 2.5 years for the infraspinatus and the subscapularis when their tendons ruptured. The mean time observed to severe FI was five, four, and three years for the supraspinatus, the infraspinatus, and the subscapularis, respectively.Discussion and conclusionThe more extensive the lesion, the longer the time following rupture, and the older the patient is, the more severe the FI is. The objective of surgery is to intervene before intermediate FI sets in, which means irreversible functional loss.Level of evidence: Level IV. Diagnostic Retrospective Study
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