1,253 research outputs found
Charm Production in Deep Inelastic Scattering from Threshold to High $Q^{2}
Charm final states in deep inelastic scattering constitute of the
inclusive cross-section at small as measured at HERA. These data can reveal
important information on the charm and gluon structure of the nucleon if they
are interpreted in a consistent perturbative QCD framework which is valid over
the entire energy range from threshold to the high energy limit. We describe in
detail how this can be carried out order-by-order in PQCD in the generalized
\msbar formalism of Collins (generally known as the ACOT approach), and
demonstrate the inherent smooth transition from the 3-flavor to the 4-flavor
scheme in a complete order calculation, using a Monte Carlo
implementation of this formalism. This calculation is accurate to the same
order as the conventional NLO calculation in the limit . It includes the resummed large logarithm contributions of the 3-flavor
scheme (generally known in this context as the fixed-flavor-number or FFN
scheme) to all orders of . For the inclusive structure
function, comparison with recent HERA data and the existing FFN calculation
reveals that the relatively simple order- (NLO) 4-flavor () calculation can, in practice, be extended to rather low energy scales,
yielding good agreement with data over the full measured range. The Monte
Carlo implementation also allows the calculation of differential distributions
with relevant kinematic cuts. Comparisons with available HERA data show
qualitative agreement; however, they also indicate the need to extend the
calculation to the next order to obtain better description of the differential
distributions.Comment: 22 pages (LATEX), 8 figures (EPS); A few clarifying changes made;
version published in JHE
Bohler´s angle and the crucial angle of Gissane in paediatric population
Bohler angle and the crucial angle of Gissane are used on the evaluation of calcaneus fractures. However, few authors have described the variation of the angles when the calcaneus is growing. In this study, Bohler angle and the crucial angle of Gissane in paediatric population were measured using lateral foot radiographs of 429 patients, from 0 to 16 years of age. The control group was composed of 70 adult patients. The sample had a mean Bohler angle of 35.4° ± 5.9° and a mean crucial angle of Gissane of 110.5° ± 7.4°. The greater mean difference was identified for Bohler angle (8°) in the age group of 5 to 8 years (39.6° ± 5.7°) and for the crucial angle of Gissane (5°-6°) in the age group of 0 to 4 years (115.8° ± 7.3) (P < .05). The influence of the ossification centres on the geometry of the calcaneus across age groups makes Bohler angle and the crucial angle of Gissane higher in young children. The increase in Bohler angle points out the relative development of the posterior facet in young children and the importance of the reconstruction of the posterior facet height in the intra-articular calcaneus fractures
Open Heavy Flavor Production in QCD -- Conceptual Framework and Implementation Issues
Heavy flavor production is an important QCD process both in its own right and
as a key component of precision global QCD analysis. Apparent disagreements
between fixed-flavor scheme calculations of b-production rate with experimental
measurements in hadro-, lepto-, and photo-production provide new impetus to a
thorough examination of the theory and phenomenology of this process. We review
existing methods of calculation, and place them in the context of the general
PQCD framework of Collins. A distinction is drawn between scheme dependence and
implementation issues related to quark mass effects near threshold. We point
out a so far overlooked kinematic constraint on the threshold behavior, which
greatly simplifies the variable flavor number scheme. It obviates the need for
the elaborate existing prescriptions, and leads to robust predictions. It can
facilitate the study of current issues on heavy flavor production as well as
precision global QCD analysis.Comment: 13 pages, 10 figures, Proceedings of Ringberg Workshop: New Trends in
HERA Physics 2001, Munich, German
Temporal perception deficits in schizophrenia: integration is the problem, not deployment of attentions
Patients with schizophrenia are known to have impairments in sensory processing. In order
to understand the specific temporal perception deficits of schizophrenia, we investigated and determined to what extent impairments in temporal integration can be dissociated from attention deployment using Attentional Blink (AB). Our findings showed that there was no evident deficit in the deployment of attention in patients with schizophrenia. However, patients showed an increased temporal integration deficit within a hundred-millisecond timescale. The degree of such integration dysfunction was correlated with the clinical manifestations of schizophrenia. There was no difference between individuals with/without schizotypal personality disorder in temporal integration. Differently from previous studies using the AB, we did not find a significant impairment in deployment of attention in schizophrenia. Instead, we used both theoretical and empirical approaches to show
that previous findings (using the suppression ratio to correct for the baseline difference) produced a systematic exaggeration of the attention deficits. Instead, we modulated the perceptual difficulty of the task to bring the baseline levels of target detection between the groups into closer alignment. We found that the integration dysfunction rather than deployment of attention is clinically relevant, and thus should be an additional focus of research in schizophrenia
Heart Rate Variability and Non-Linear Dynamics in Risk Stratification
The time-domain measures and power–spectral analysis of heart rate variability (HRV) are classic conventional methods to assess the complex regulatory system between autonomic nervous system and heart rate and are most widely used. There are abundant scientific data about the prognostic significance of the conventional measurements of HRV in patients with various conditions, particularly with myocardial infarction. Some studies have suggested that some newer measures describing non-linear dynamics of heart rate, such as fractal measures, may reveal prognostic information beyond that obtained by the conventional measures of HRV. An ideal risk indicator could specifically predict sudden arrhythmic death as the implantable cardioverter-defibrillator (ICD) therapy can prevent such events. There are numerically more sudden deaths among post-infarction patients with better preserved left ventricular function than in those with severe left ventricular dysfunction. Recent data support the concept that HRV measurements, when analyzed several weeks after acute myocardial infarction, predict life-threatening ventricular tachyarrhythmias in patients with moderately depressed left ventricular function. However, well-designed prospective randomized studies are needed to evaluate whether the ICD therapy based on the assessment of HRV alone or with other risk indicators improves the patients’ prognosis. Several issues, such as the optimal target population, optimal timing of HRV measurements, optimal methods of HRV analysis, and optimal cutpoints for different HRV parameters, need clarification before the HRV analysis can be a widespread clinical tool in risk stratification
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