79 research outputs found
The Lake Baikal neutrino experiment
We rewiew the present status of the Baikal Neutrino Project and present the
results of a search for high energy neutrinos with the detector intermediate
stage NT-96.Comment: 3 pages, 2 figures, to appear in the Proceedings of Sixth
International Workshop on Topics in Astroparticle and Underground Physics
(TAUP99), September 6-10, 1999, Pais, Franc
Search for diffuse neutrino flux from astrophysical sources with MACRO
Many galactic and extragalactic astrophysical sources are currently
considered promising candidates as high energy neutrino emitters. Astrophysical
neutrinos can be detected as upward-going muons produced in charged-current
interactions with the medium surrounding the detector. The expected neutrino
fluxes from various models start to dominate on the atmospheric neutrino
background at neutrino energies above some tens of TeV. We present the results
of a search for an excess of high energy upward-going muons among the sample of
data collected by MACRO during ~5.8 years of effective running time. No
significant evidence for this signal was found. As a consequence, an upper
limit on the flux of upward-going muons from high-energy neutrinos was set at
the level of 1.7 10^(-14) cm^(-2) s^(-1) sr^(-1).
The corresponding upper limit for the diffuse neutrino flux was evaluated
assuming a neutrino power law spectrum. Our result was compared with
theoretical predictions and upper limits from other experiments.Comment: 19 pages, 8 figures, 2 table
Activation of DNA-PK by Ionizing Radiation Is Mediated by Protein Phosphatase 6
DNA-dependent protein kinase (DNA-PK) plays a critical role in DNA damage repair, especially in non-homologous end-joining repair of double-strand breaks such as those formed by ionizing radiation (IR) in the course of radiation therapy. Regulation of DNA-PK involves multisite phosphorylation but this is incompletely understood and little is known about protein phosphatases relative to DNA-PK. Mass spectrometry analysis revealed that DNA-PK interacts with the protein phosphatase-6 (PP6) SAPS subunit PP6R1. PP6 is a heterotrimeric enzyme that consists of a catalytic subunit, plus one of three PP6 SAPS regulatory subunits and one of three ankyrin repeat subunits. Endogenous PP6R1 co-immunoprecipitated DNA-PK, and IR enhanced the amount of complex and promoted its import into the nucleus. In addition, siRNA knockdown of either PP6R1 or PP6 significantly decreased IR activation of DNA-PK, suggesting that PP6 activates DNA-PK by association and dephosphorylation. Knockdown of other phosphatases PP5 or PP1γ1 and subunits PP6R3 or ARS-A did not reduce IR activation of DNA-PK, demonstrating specificity for PP6R1. Finally, siRNA knockdown of PP6R1 or PP6 but not other phosphatases increased the sensitivity of glioblastoma cells to radiation-induced cell death to a level similar to DNA-PK deficient cells. Our data demonstrate that PP6 associates with and activates DNA-PK in response to ionizing radiation. Therefore, the PP6/PP6R1 phosphatase is a potential molecular target for radiation sensitization by chemical inhibition
High-energy Neutrino Astronomy: The Cosmic Ray Connection
This is a review of neutrino astronomy anchored to the observational fact
that Nature accelerates protons and photons to energies in excess of
and eV, respectively.
Although the discovery of cosmic rays dates back close to a century, we do
not know how and where they are accelerated. Basic elementary-particle physics
dictates a universal upper limit on their energy of eV, the
so-called Greisen-Kuzmin-Zatsepin cutoff; however, particles in excess of this
energy have been observed by all experiments, adding one more puzzle to the
cosmic ray mystery. Mystery is fertile ground for progress: we will review the
facts as well as the speculations about the sources including gamma ray bursts,
blazars and top-down scenarios.
The important conclusion is that, independently of the specific blueprint of
the source, it takes a kilometer-scale neutrino observatory to detect the
neutrino beam associated with the highest energy cosmic rays and gamma rays. We
also briefly review the ongoing efforts to commission such instrumentation.Comment: 83 pages, 18 figures, submitted to Reports on Progress in Physic
Paracetamol in therapeutic dosages and acute liver injury: causality assessment in a prospective case series
Background: Acute liver injury (ALI) induced by paracetamol overdose is a well known cause of emergency hospital admission and death. However, there is debate regarding the risk of ALI after therapeutic dosages of the drug. The aim is to describe the characteristics of patients admitted to hospital with jaundice who had previous exposure to therapeutic doses of paracetamol. An assessment of the causality role of paracetamol was performed in each case. Methods: Based on the evaluation of prospectively gathered cases of ALI with detailed clinical information, thirty-two cases of ALI in non-alcoholic patients exposed to therapeutic doses of paracetamol were identified. Two authors assessed all drug exposures by using the CIOMS/RUCAM scale. Each case was classified into one of five categories based on the causality score for paracetamol. Results: In four cases the role of paracetamol was judged to be unrelated, in two unlikely, and these were excluded from evaluation. In seven of the remaining 26 cases, the RUCAM score associated with paracetamol was higher than that associated with other concomitant medications. The estimated incidence of ALI related to the use of paracetamol in therapeutic dosages was 0.4 per million inhabitants older than 15 years of age and per year (99%CI, 0.2-0.8) and of 10 per million paracetamol users-year (95% CI 4.3-19.4). Conclusions:Our results indicate that paracetamol in therapeutic dosages may be considered in the causality assessment in non-alcoholic patients with liver injury, even if the estimated incidence of ALI related to paracetamol appears to be low
Astrophysical Origins of Ultrahigh Energy Cosmic Rays
In the first part of this review we discuss the basic observational features
at the end of the cosmic ray energy spectrum. We also present there the main
characteristics of each of the experiments involved in the detection of these
particles. We then briefly discuss the status of the chemical composition and
the distribution of arrival directions of cosmic rays. After that, we examine
the energy losses during propagation, introducing the Greisen-Zaptsepin-Kuzmin
(GZK) cutoff, and discuss the level of confidence with which each experiment
have detected particles beyond the GZK energy limit. In the second part of the
review, we discuss astrophysical environments able to accelerate particles up
to such high energies, including active galactic nuclei, large scale galactic
wind termination shocks, relativistic jets and hot-spots of Fanaroff-Riley
radiogalaxies, pulsars, magnetars, quasar remnants, starbursts, colliding
galaxies, and gamma ray burst fireballs. In the third part of the review we
provide a brief summary of scenarios which try to explain the super-GZK events
with the help of new physics beyond the standard model. In the last section, we
give an overview on neutrino telescopes and existing limits on the energy
spectrum and discuss some of the prospects for a new (multi-particle)
astronomy. Finally, we outline how extraterrestrial neutrino fluxes can be used
to probe new physics beyond the electroweak scale.Comment: Higher resolution version of Fig. 7 is available at
http://www.angelfire.com/id/dtorres/down3.html. Solicited review article
prepared for Reports on Progress in Physics, final versio
Faculty collaboration in teaching global business, MBA teaching process
This presentation stems from global business teaching and ongoing research of an interactive group of professors working together in the service delivery of online MBA education at University of Maryland University College . A model for collaborative teaching by delocated professors who literally span the globe – from Australia to Canada, including the United Kingdom, both coasts of the USA, China and Dubai - is offered, underscoring the enormous mobility of knowledge and knowledge workers. Working together as a collaborating team, it was found that the "whole is greater than the sum of the parts". The teachers became more than a teaching team, they became a collaborating operation as they worked together in the sharing and development of materials, insights and knowledge. The model demonstrates how the teaching of global business in an MBA environment is really an exercise in the management of global service operations.<br /
Tapping global human resources in an MBA teaching team : insights with implications for management education worldwide
It is found that geographic diversity, respect for differing beliefs, encouraging feedback, active participation and interaction with the students, and techniques such as active listening, contribute an architecture and atmosphere to student learning, teacher effectiveness and program excellence in virtual education. One functioning teaching team in University of Maryland University College’s online MBA program provides the action research foundation underpinning the findings. A widely dispersed team of academics and assistants have documented the ways they enhance educational information for students in the program. Assessment activities, supplementary communications and biographical information contribute to student perception of the quality of management education in the program. Mechanisms for effectively tapping a global faculty team are discussed and are informative for administrators and academics alike
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