12 research outputs found
Analytic continuation and physical content of the gluon propagator
The analytic continuation of the gluon propagator is revised in the light of
recent findings on the possible existence of complex conjugated poles. The
contribution of the anomalous pole must be added when Wick rotating, leading to
an effective Minkowskian propagator which is not given by the trivial analytic
continuation of the Euclidean function. The effective propagator has an
integral representation in terms of a spectral function which is naturally
related to a set of elementary (complex) eigenvalues of the Hamiltonian, thus
generalizing the usual K\"allen-Lehmann description. A simple toy model shows
how the elementary eigenvalues might be related to actual physical
quasiparticles of the non-perturbative vacuum.Comment: Editorially accepted version, with an entirely new introduction, a
figure on Wick rotation and many more reference
Submillimeter Polarimetry with PolKa, a reflection-type modulator for the APEX telescope
Imaging polarimetry is an important tool for the study of cosmic magnetic
fields. In our Galaxy, polarization levels of a few up to 10\% are
measured in the submillimeter dust emission from molecular clouds and in the
synchrotron emission from supernova remnants. Only few techniques exist to
image the distribution of polarization angles, as a means of tracing the
plane-of-sky projection of the magnetic field orientation. At submillimeter
wavelengths, polarization is either measured as the differential total power of
polarization-sensitive bolometer elements, or by modulating the polarization of
the signal. Bolometer arrays such as LABOCA at the APEX telescope are used to
observe the continuum emission from fields as large as \sim0\fdg2 in
diameter. %Here we present the results from the commissioning of PolKa, a
polarimeter for Here we present PolKa, a polarimeter for LABOCA with a
reflection-type waveplate of at least 90\% efficiency. The modulation
efficiency depends mainly on the sampling and on the angular velocity of the
waveplate. For the data analysis the concept of generalized synchronous
demodulation is introduced. The instrumental polarization towards a point
source is at the level of \%, increasing to a few percent at the
db contour of the main beam. A method to correct for its effect in
observations of extended sources is presented. Our map of the polarized
synchrotron emission from the Crab nebula is in agreement with structures
observed at radio and optical wavelengths. The linear polarization measured in
OMC1 agrees with results from previous studies, while the high sensitivity of
LABOCA enables us to also map the polarized emission of the Orion Bar, a
prototypical photon-dominated region
Non-Zeeman circular polarization of CO rotational lines in SNR IC 443
Context. We study interstellar magnetic fields by measuring the polarization in molecular spectral lines and thermal emission of dust.
Aims. We report detection of non-Zeeman circular polarization and linear polarization levels of up to 1% in the ^(12)CO spectral line emission in a shocked molecular clump around the supernova remnant (SNR) IC 443. We examine our polarization results to confirm that the circular polarization signal in CO lines is caused by a conversion of linear to circular polarization, consistent with anisotropic resonant scattering. In this process background, linearly polarized CO emission interacts with similar foreground molecules aligned with the ambient magnetic field and scatters at a transition frequency. The difference in phase shift between the orthogonally polarized components of this scattered emission can cause a transformation of linear to circular polarization.
Methods. We compared linear polarization maps from the dust continuum, which were obtained with PolKa at APEX, and ^(12)CO (J = 2 → 1) and (J = 1 → 0) from the IRAM 30-m telescope. We found no consistency between the two sets of polarization maps. We then reinserted the measured circular polarization signal in the CO lines across the source to the corresponding linear polarization signal to test whether the linear polarization vectors of the CO maps were aligned with those of the dust before this linear to circular polarization conversion.
Results. After the flux correction for the two transitions of the CO spectral lines, the new polarization vectors for both CO transitions aligned with the dust polarization vectors, establishing that the non-Zeeman CO circular polarization is due to a linear to circular polarization conversion
Seasonal pattern of peptic ulcer hospitalizations: analysis of the hospital discharge data of the Emilia-Romagna region of Italy
BACKGROUND:
Previous studies have reported seasonal variation in peptic ulcer disease (PUD), but few large-scale, population-based studies have been conducted.
METHODS:
To verify whether a seasonal variation in cases of PUD (either complicated or not complicated) requiring acute hospitalization exists, we assessed the database of hospital admissions of the region Emilia Romagna (RER), Italy, obtained from the Center for Health Statistics, between January 1998 and December 2005. Admissions were categorized by sex, age ( or = 75 yrs), site of PUD lesion (stomach or duodenum), main complication (hemorrhage or perforation), and final outcome (intended as fatal outcome: in-hospital death; nonfatal outcome: patient discharged alive). Temporal patterns in PUD admissions were assessed in two ways, considering a) total counts per single month and season, and b) prevalence proportion, such as the monthly prevalence of PUD admissions divided by the monthly prevalence of total hospital admissions, to assess if the temporal patterns in the raw data might be the consequence of seasonal and annual variations in hospital admissions per se in the region. For statistical analysis, the chi2 test for goodness of fit and inferential chronobiologic method (Cosinor and partial Fourier series) were used.
RESULTS:
Of the total sample of PUD patients (26,848 [16,795 males, age 65 +/- 16 yrs; 10,053 females, age 72 +/- 15 yrs, p or = 75 yrs of age. There were more cases of duodenal (DU). (89.8%) than gastric ulcer (GU) (3.6%), and there were 1,290 (4.8%) fatal events. Data by season showed a statistically difference with the lowest proportion of PUD hospital admissions in summer (23.3%) (p < 0.001), for total cases and rather all subgroups. Chronobiological analysis identified three major peaks of PUD hospitalizations (September-October, January-February, and April-May) for the whole sample (p = 0.035), and several subgroups, with nadir in July. Finally, analysis of the monthly prevalence proportions yielded a significant (p = 0.025) biphasic pattern with a main peak in August-September-October, and a secondary one in January-February.
CONCLUSIONS:
A seasonal variation in PUD hospitalization, characterized by three peaks of higher incidence (Autumn, Winter, and Spring) is observed. When data corrected by monthly admission proportions are analyzed, late summer-autumn and winter are confirmed as higher risk periods. The underlying pathophysiologic mechanisms are unknown, and need further studies. In subjects at higher risk, certain periods of the year could deserve an appropriate pharmacological protection to reduce the risk of PUD hospitalization
PolKa: a Polarimeter for Submillimeter Bolometer Arrays
Starting from measurements of the linear polarization of the radiation emitted by celestial objects it is possible to estimate some physical parameters of the source. For example, magnetic field intensities and directions or, when the magnetic field is already known, the processes producing the polarization. A new concept of polarimeter has been designed to be used together with the arrays of bolometers developed in the Bolometer Group at the Max-Planck-Institut fuer Radioastronomie in Bonn. The new polarimeter has the unique characteristic of being tunable over a wide range of wavelengths and of producing a negligible absorption. It has been used at the Heinrich Hertz telescope in Arizona, to measure the linear polarization of some quasars and of some extended sources inside our galaxy. Some results are presented. We detected polarization on the quasars 3C279 and 1633+382. On 3C279 we also detected polarization variability on a time scale of a week. Three maps of extended sources are presented: - the BN/KL complex in Orion OMC-1, - a filament cloud in Orion OMC-3 and - the massive star forming region IRAS 05358+3543. The first map shows the polarization pattern in OMC-1 over an extended sky area with high signal-to-noise and accurate detection of the position angle. The filament in OMC-3 was observed for a short integration time and is presented here only to show the agreement with published data even under conditions of a weak signal-to-noise. The third map is the first detection of polarization in the high-mass star forming region IRAS 05358+3543. The polarimeter has low spurious polarization and a good efficiency and the tests at the telescope show that it is well suited to become a permanent facility