92 research outputs found
A Solution to the Decompactification Problem in Chiral Heterotic Strings
We present a solution to the decompactification problem of gauge thresholds
in chiral heterotic string theories with two large extra dimensions, where
supersymmetry is spontaneously broken by the Scherk-Schwarz mechanism. Whenever
the Kaluza-Klein scale is much lower than the string scale, the infinite towers
of heavy states contribute non-trivially to the renormalisation of gauge
couplings, which typically grow linearly with the large volume of the internal
space and invalidate perturbation theory. We trace the origin of the
decompactification problem to properties of the six dimensional theory obtained
in the infinite volume limit and show that thresholds may instead exhibit
logarithmic volume dependence and we provide the conditions for this to occur.
We illustrate this mechanism with explicit string constructions where the
decompactification problem does not occur.Comment: 26 pages, 1 figur
A rare case of ascending colon actinomycosis mimicking cancer
BACKGROUND: Actinomycosis is a rare inflammatory disease caused by an anaerobic bacterium that can rarely affect the large intestine. CASE PRESENTATION: We present a rare case of a cecum and ascending colon actinomycosis in a 72 years old woman, mimicking clinically a malignant inflammatory tumor of the right colon. The patient complained of right lower quadrant pain. Although our first thought was a peri-appendiceal abscess, CT scan suggested a right colon tumor. The patient underwent a right colectomy and the histological examination of the specimen revealed colon actinomycosis. CONCLUSIONS: Preoperative diagnosis in colon actinomycosis is difficult to achieve. Treatment of choice is antibiotics administration. A review of the possible pathogenesis and therapeutic modalities is also presented
Teaching perspectives of the Frobenius coin problem of two denominators
Let be positive, relatively prime, integers. Our goal is to
characterize, in an elementary way, all positive integers that can be
expressed as a linear combination of with non-negative integer
coefficients and discuss the teaching perspectives of our methods.Comment: 10 pages, 2 figure
An inductive proof of the Frobenius coin problem of two denominators
Let be positive, relatively prime, integers. We prove, using induction,
that for every there exist , such that
.Comment: 5 page
Three-Generation Super No-Scale Models in Heterotic Superstrings
We derive the conditions for the one-loop contribution to the cosmological
constant to be exponentially suppressed in a class of heterotic string
compactifications with three generations of chiral matter, where supersymmetry
is spontaneously broken \`a la Scherk-Schwarz. Using techniques of partial
unfolding based on the Hecke congruence subgroup of the modular
group to extract the leading asymptotics, we show that the super no-scale
condition between the degeneracies of massless bosons and
fermions in the full string spectrum is necessary but not sufficient, and
needs to be supplemented by additional conditions which we identify. We use
these results to construct three-generation Pati-Salam models with interesting
phenomenological characteristics.Comment: 17 pages, 2 figure
Notions about the nature of Geometry
In this paper we discuss, from a historical and philosophical point of view,
a variation of the meaning of the five postulates in Euclidean Geometry and we
make a short reference to D. Hilberts formalism. We examine, throughout the
ages, the question what is Geometry by studying the segmentation and the
unification of various geometries, been introduced by F. Kleins Erlangen
Program. We concisely present three out of nine Cayley-Klein geometries and
then we conclude with some didactic perspectives.Comment: 20 pages, in Greek languag
Worldwide research productivity in critical care medicine
INTRODUCTION: The number of publications and the impact factor of journals are accepted estimates of the quantity and quality of research productivity. The objective of the present study was to assess the worldwide scientific contribution in the field of critical care medicine. METHOD: All research studies published between 1995 and 2003 in medical journals that were listed in the 2003 Science Citation Index (SCI(®)) of Journal Citation Reports under the subheading 'critical care' and also indexed in the PubMed database were reviewed in order to identify their geographical origin. RESULTS: Of 22,976 critical care publications in 14 medical journals, 17,630 originated from Western Europe and the USA (76.7%). A significant increase in the number of publications originated from Western European countries during the last 5 years of the study period was noticed. Scientific publications in critical care medicine increased significantly (25%) from 1995 to 2003, which was accompanied by an increase in the impact factor of the corresponding journals (47.4%). Canada and Japan had the better performance, based on the impact factor of journals. CONCLUSION: Significant scientific progress in critical care research took place during the period of study (1995–2003). Leaders of research productivity (in terms of absolute numbers) were Western Europe and the USA. Publications originating from Western European countries increased significantly in quantity and quality over the study period. Articles originating from Canada, Japan, and the USA had the highest mean impact factor.. Canada was the leader in productivity when adjustments for gross domestic product and population were made
Toxicity after prolonged (more than four weeks) administration of intravenous colistin
BACKGROUND: The intravenous use of polymyxins has been considered to be associated with considerable nephrotoxicity and neurotoxicity. For this reason, the systemic administration of polymyxins had been abandoned for about 20 years in most areas of the world. However, the problem of infections due to multidrug-resistant (MDR) Gram-negative bacteria such us Pseudomonas aeruginosa and Acinetobacter baumanniii has led to the re-use of polymyxins. Our objective was to study the toxicity of prolonged intravenous administration of colistin (polymyxin E). METHODS: An observational study of a retrospective cohort at "Henry Dunant" Hospital, a 450-bed tertiary care center in Athens, Greece, was undertaken. Patients who received intravenous colistin for more than 4 weeks for the treatment of multidrug resistant Gram-negative infections were included in the study. Serum creatinine, blood urea, liver function tests, symptoms and signs of neurotoxicity were the main outcomes studied. RESULTS: We analyzed data for 19 courses of prolonged intravenous colistin [mean duration of administration (± SD) 43.4 (± 14.6) days, mean daily dosage (± SD) 4.4 (± 2.1) million IU, mean cumulative dosage (± SD) 190.4 (± 91.0) million IU] in 17 patients. The median creatinine value increased by 0.25 mg/dl during the treatment compared to the baseline (p < 0.001) but returned close to the baseline at the end of treatment (higher by 0.1 mg/dl, p = 0.67). No apnea or other evidence of neuromuscular blockade was noted in any of these patients who received prolonged treatment with colistin. CONCLUSIONS: No serious toxicity was observed in this group of patients who received prolonged intravenous colistin. Colistin should be considered as a therapeutic option in patients with infections due to multidrug resistant Gram-negative bacteria
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