267 research outputs found
Exclusive photo- and electroproduction at HERA as a possible probe of the odderon singularity in QCD
Theory and phenomenology of the eta_c photo- and electroproduction is
developed from the point of view of probing the odderon singularity in QCD
which corresponds to the three gluon exchange mechanism. This mechanism leads
to the cross-sections which are independent of W^2 for the exchange of three
non-interacting gluons or exhibit increase with increasing W^2 (or 1/x) for the
odderon intercept above unity. The \eta_c electroproduction in the three gluon
exchange mechanism is shown to be entirely controlled by the transversely
polarised virtual photons. The magnitude of the eta_c photoproduction
cross-section is estimated to be around 11-45pb. The t-dependence of the
differential cross-section is also discussed.Comment: 9 pages, LaTeX, uses epsfig.sty; Numerical error corrected. A factor
of 1/3 missing in amplitude in Eq.(8) added. Obtained gamma p -> eta_c p
cross-section smaller by a factor of 9 than in the original version of the
paper. Figures 4 and 5 changed accordingl
Nuclear Attenuation of high energy two-hadron system in the string model
Nuclear attenuation of the two-hadron system is considered in the string
model. The two-scale model and its improved version with two different choices
of constituent formation time and sets of parameters obtained earlier for the
single hadron attenuation, are used to describe available experimental data for
the -dependence of subleading hadron, whereas satisfactory agreement with
the experimental data has been observed. A model prediction for
-dependence of the nuclear attenuation of the two-hadron system is also
presented.Comment: 8 page
Agreement between prospective diary data and retrospective questionnaire report of abdominal pain and stooling symptoms in children with irritable bowel syndrome
BACKGROUND:
In functional gastrointestinal disorders, patient recall of symptoms drives diagnostic decisions and evaluation of treatment response, and research conclusions about potential treatments. In pediatrics, parent report also impacts assessment and care. Hence, identifying methods for accurately capturing patient and parent report of irritable bowel syndrome (IBS) symptoms is important. This study evaluated correspondence between retrospective questionnaire (parent and child report) and prospective diary data for children and adolescents with IBS.
METHODS:
Participants included 50 children/adolescents with IBS per Rome III criteria. Children completed a 2-week pain and stool diary. Children and parents subsequently completed a 2-week recall questionnaire, reporting number of pain days, maximum pain, days without bowel movement, and days with diarrhea during the diary interval. Intraclass correlation coefficients and Bland-Altman plots assessed agreement.
KEY RESULTS:
For pain and days without bowel movement, overall agreement between child recall questionnaire and child diary was strong, although under conditions likely to facilitate agreement and with individual variation observed. Parent recall and child diary were less concordant, and agreement about diarrhea was poor for parent and child. Age did not significantly correlate with agreement.
CONCLUSIONS & INFERENCES:
Child questionnaire with short recall interval may be a reasonable approximation for diary data, although this varies by individual and replication/investigation of lengthier recall are needed. Relying on parent questionnaire does not appear a suitable proxy, and recall of stool form by both parent and child appears more problematic. These results combined with existing literature support use of diary data whenever possible
The impact of pulsed electric field on the extraction of bioactive compounds from beetroot
Beetroot is a root vegetable rich in different bioactive components, such as vitamins, minerals, phenolics, carotenoids, nitrate, ascorbic acids, and betalains, that can have a positive effect on human health. The aim of this work was to study the influence of the pulsed electric field (PEF) at different electric field strengths (4.38 and 6.25 kV/cm), pulse number 10\u201330, and energy input 0\u201312.5 kJ/kg as a pretreatment method on the extraction of betalains from beetroot. The obtained results showed that the application of PEF pre-treatment significantly (p < 0.05) influenced the efficiency of extraction of bioactive compounds from beetroot. The highest increase in the content of betalain compounds in the red beet\u2019s extract (betanin by 329%, vulgaxanthin by 244%, compared to the control sample), was noted for 20 pulses of electric field at 4.38 kV/cm of strength. Treatment of the plant material with a PEF also resulted in an increase in the electrical conductivity compared to the non-treated sample due to the increase in cell membrane permeability, which was associated with leakage of substances able to conduct electricity, including mineral salts, into the intercellular space
The Process gamma* + p -> eta_c + X: A Test for the Perturbative QCD Odderon
The rates of inclusive photo- and electroproduction of the eta_c meson:
gamma* + p -> eta_c + X are calculated in the triple Regge region, integrated
over the diffractive mass X. For the Regge exchanges we use the hard Pomeron
and Odderon, both being calculated in the framework of perturbative QCD. The
integrated cross-section depends upon the coupling of the BFKL pomeron to two
odderons, and it is found to be of the order 60 pb for photoproduction
and 1.5 pb at Q^2=25 GeV^2.Comment: 19 pages, latex, 7 eps figure
CALIBRATION AND APPLICATION OF NUCLEAR TRACK DETECTORS FOR HIGH-TEMPERATURE PLASMA DIAGNOSTICS
Abstract The paper reports on features of so-called solid-state nuclear track detectors (SSNTDs), their calibration measurements performed with known ion beams, and their different applications for detailed studies of charged particle emissions from various high-temperatures plasma facilities
Estimate of the Collins fragmentation function in a chiral invariant approach
We predict the features of the Collins function, which describes the
fragmentation of a transversely polarized quark into an unpolarized hadron, by
modeling the fragmentation process at a low energy scale. We use the chiral
invariant approach of Manohar and Georgi, where constituent quarks and
Goldstone bosons are considered as effective degrees of freedom in the
non-perturbative regime of QCD. To test the approach we calculate the
unpolarized fragmentation function and the transverse momentum distribution of
a produced hadron, both of which are described reasonably well. In the case of
semi-inclusive deep-inelastic scattering, our estimate of the Collins function
in connection with the transversity distribution gives rise to a transverse
single spin asymmetry of the order of 10%, supporting the idea of measuring the
transversity distribution of the nucleon in this way. In the case of e+ e-
annihilation into two hadrons, our model predicts a Collins azimuthal asymmetry
of about 5%.Comment: 12 pages, 15 figures. Figs. 11-14 changed, minor changes in
discussion, few typos fixed and some references added. Final version to
appear in PR
Polycyclic aromatic hydrocarbon processing in a hot gas
Context: PAHs are thought to be a ubiquitous and important dust component of
the interstellar medium. However, the effects of their immersion in a hot
(post-shock) gas have never before been fully investigated. Aims: We study the
effects of energetic ion and electron collisions on PAHs in the hot post-shock
gas behind interstellar shock waves. Methods: We calculate the ion-PAH and
electron-PAH nuclear and electronic interactions, above the carbon atom loss
threshold, in H II regions and in the hot post-shock gas, for temperatures
ranging from 10^3 to 10^8 K. Results: PAH destruction is dominated by He
collisions at low temperatures (T < 3x10^4 K), and by electron collisions at
higher temperatures. Smaller PAHs are destroyed faster for T < 10^6 K, but the
destruction rates are roughly the same for all PAHs at higher temperatures. The
PAH lifetime in a tenuous hot gas (n_H ~ 0.01 cm^-3, T ~ 10^7 K), typical of
the coronal gas in galactic outflows, is found to be about thousand years,
orders of magnitude shorter than the typical lifetime of such objects.
Conclusions: In a hot gas, PAHs are principally destroyed by electron
collisions and not by the absorption of X-ray photons from the hot gas. The
resulting erosion of PAHs occurs via C_2 loss from the periphery of the
molecule, thus preserving the aromatic structure. The observation of PAH
emission from a million degree, or more, gas is only possible if the emitting
PAHs are ablated from dense, entrained clumps that have not yet been exposed to
the full effect of the hot gas.Comment: 16 pages, 11 figures, 3 tables, typos corrected and PAH acronym in
the title substituted with full name to match version published in Astronomy
and Astrophysic
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