5,395 research outputs found
EFFICIENT ANALYTIC COMPUTATION OF HIGHER-ORDER QCD AMPLITUDES
We review techniques simplifying the analytic calculation of one-loop QCD
amplitudes with many external legs, for use in next-to-leading-order
corrections to multi-jet processes. Particularly useful are the constraints
imposed by perturbative unitarity, collinear singularities and a
supersymmetry-inspired organization of helicity amplitudes. Certain sequences
of one-loop helicity amplitudes with an arbitrary number of external gluons
have been obtained using these constraints.Comment: Talk given at Beyond the Standard Model IV, December 13-18 1994, Lake
Tahoe, CA. Latex, 4 pages, no figures
Aspirated capacitor measurements of air conductivity and ion mobility spectra
Measurements of ions in atmospheric air are used to investigate atmospheric
electricity and particulate pollution. Commonly studied ion parameters are (1)
air conductivity, related to the total ion number concentration, and (2) the
ion mobility spectrum, which varies with atmospheric composition. The physical
principles of air ion instrumentation are long-established. A recent
development is the computerised aspirated capacitor, which measures ions from
(a) the current of charged particles at a sensing electrode, and (b) the rate
of charge exchange with an electrode at a known initial potential, relaxing to
a lower potential. As the voltage decays, only ions of higher and higher
mobility are collected by the central electrode and contribute to the further
decay of the voltage. This enables extension of the classical theory to
calculate ion mobility spectra by inverting voltage decay time series. In
indoor air, ion mobility spectra determined from both the novel voltage decay
inversion, and an established voltage switching technique, were compared and
shown to be of similar shape. Air conductivities calculated by integration
were: 5.3 +- 2.5 fS/m and 2.7 +- 1.1 fS/m respectively, with conductivity
determined to be 3 fS/m by direct measurement at a constant voltage.
Applications of the new Relaxation Potential Inversion Method (RPIM) include
air ion mobility spectrum retrieval from historical data, and computation of
ion mobility spectra in planetary atmospheres.Comment: To be published in Review of Scientific Instrument
Cardiovascular disease and air pollution in Scotland: no association or insufficient data and study design?
<p><b>Background:</b>
Coronary heart disease and stroke are leading causes of mortality and ill health in Scotland, and clear associations have been found in previous studies between air pollution and cardiovascular disease. This study aimed to use routinely available data to examine whether there is any evidence of an association between short-term exposure to particulate matter (measured as PM10, particles less than 10 micrograms per cubic metre) and hospital admissions due to cardiovascular disease, in the two largest cities in Scotland during the years 2000 to 2006.</p>
<p><b>Methods:</b> The study utilised an ecological time series design, and the analysis was based on overdispersed Poisson log-linear models.</p>
<p><b>Results:</b> No consistent associations were found between PM10 concentrations and cardiovascular hospital admissions in either of the cities studied, as all of the estimated relative risks were close to one, and all but one of the associated 95% confidence intervals contained the null risk of one.</p>
<p><b>Conclusions:</b> This study suggests that in small cities, where air quality is relatively good, then either PM10 concentrations have no effect on cardiovascular ill health, or that the routinely available data and the corresponding study design are not sufficient to detect an association.</p>
Is the Scottish population living dangerously? Prevalence of multiple risk factors: the Scottish Health Survey 2003
<b>Background:</b>
Risk factors are often considered individually, we aimed to investigate the prevalence of combinations of multiple behavioural risk factors and their association with socioeconomic determinants.<p></p>
<b>Methods:</b>
Multinomial logistic regression was used to model the associations between socioeconomic factors and multiple risk factors from data in the Scottish Health Survey 2003. Prevalence of five main behavioural risk factors - smoking alcohol, diet, overweight/obesity, and physical inactivity, and the odds in relation to demographic, individual and area socioeconomic factors.<p></p>
<b>Results:</b>
Full data were available on 6,574 subjects (80.7% of the survey sample). Nearly the whole adult population (97.5%) reported to have at least one behavioural risk factor; while 55% have three or more risk factors; and nearly 20% have four or all five risk factors. The most important determinants for having four or five multiple risk factors were low educational attainment which conferred around a 3-fold increased odds compared to high education; and residence in the most deprived communities (relative to least deprived) which had greater than 3-fold increased odds.<p></p>
<b>Conclusions:</b>
The prevalence of multiple behavioural risk factors was high and the prevalence of absence of all risk factors very low. These behavioural patterns were socioeconomically determined. Policy to address factors needs to be joined up and better consider underlying socioeconomic circumstances.<p></p>
Simplifying Algebra in Feynman Graphs, Part III: Massive Vectors
A T-dualized selfdual inspired formulation of massive vector fields coupled
to arbitrary matter is generated; subsequently its perturbative series modeling
a spontaneously broken gauge theory is analyzed. The new Feynman rules and
external line factors are chirally minimized in the sense that only one type of
spin index occurs in the rules. Several processes are examined in detail and
the cross-sections formulated in this approach. A double line formulation of
the Lorentz algebra for Feynman diagrams is produced in this formalism, similar
to color ordering, which follows from a spin ordering of the Feynman rules. The
new double line formalism leads to further minimization of gauge invariant
scattering in perturbation theory. The dualized electroweak model is also
generated.Comment: 39 pages, LaTeX, 8 figure
Is bronchiectasis really a disease?
The definition of a disease requires that distinguishing signs and symptoms are present that are common, and that the constellation of signs and symptoms differentiate the condition from other causes. In bronchiectasis, anatomical changes, airways inflammation and airway infection are the distinguishing features that are common to this disease. However, bronchiectasis is a heterogenous disease: signs and symptoms are shared with other airway diseases, there are multiple aetiologies and certain phenotypes of bronchiectasis have distinct clinical and laboratory features that are not common to all people with bronchiectasis. Furthermore, response to therapeutic interventions in clinical trials is not uniform. The concept of bronchiectasis as a treatable trait has been suggested, but this may be too restrictive in view of the heterogeneity of bronchiectasis. It is our opinion that bronchiectasis should be defined as a disease in its own right, but one that shares several pathophysiological features and âtreatable traitsâ with other airway diseases. These traits define the large heterogeneity in the pathogenesis and clinical features and suggest a more targeted approach to therapy
Eye Changes in Disseminated Sclerosis
What is probably the first written account of the clinical features of disseminated sclerosis is contained in the diary of Augustus D'Este, the illegitimate son of Prince Augustus Frederick, and grandson of George III. The first manifestations of the disease in his case, as m some 30% of all such patients, were referable to the eyes. In 1822, we read, he journeyed to visit a much-loved relative; On my arrival I found him dead. I attended hisfuneral-there being many persons present I struggled violently not to weep, I was however unable to prevent myself so doing; shortly after I was obliged to have my letters read to me and their answers written for me, as my eyes were so attacked that when fixed upon minute objects, indistinctness of vision was the consequence. Until I attempted to read or cut my pen, I was not aware of my eyes being in the least attacked. Soon after I went to Ireland, and without anything having been done to my eyes they completely recovered their strength, and distinctness of vision."3 It is interesting to note the temporal relationship of the onset of symptoms in this case, to a period of emotional stress, a relationship which has been much discussed in connection with disseminated sclerosis, but which has little statistical evidence in its support
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