390 research outputs found
BAIKAL experiment: status report
We review the present status of the Baikal Neutrino Project and present the
results obtained with the deep underwater neutrino telescope NT-200.Comment: 4 pages, 3 figures. Presented at TAUP 2001 (7th international
workshop on Topics in Astroparticle and Underground Physics), Sep. 2001,
Laboratori Nazionali del Gran Sasso, Assergi, Ital
The Lake Baikal neutrino experiment: selected results
We review the present status of the lake Baikal Neutrino Experiment and
present selected physical results gained with the consequetive stages of the
stepwise increasing detector: from NT-36 to NT-96. Results cover atmospheric
muons, neutrino events, very high energy neutrinos, search for neutrino events
from WIMP annihilation, search for magnetic monopoles and environmental
studies. We also describe an air Cherenkov array developed for the study of
angular resolution of NT-200.Comment: 25 pages, 12 figures. To appear in the Procrrdings of International
Conference on Non-Accelerator New Physics, June 28 - July 3, 1999, Dubna,
Russi
The optical module of the Baikal deep underwater neutrino telescope
A deep underwater Cherenkov telescope has been operating since 1993 in stages
of growing size at 1.1 km depth in Lake Baikal. The key component of the
telescope is the Optical Module (OM) which houses the highly sensitive
phototube QUASAR-370. We describe design and parameters of the QUASAR-370, the
layout of the optical module, the front-end electronics and the calibration
procedures, and present selected results from the five-year operation
underwater. Also, future developments with respect to a telescope consisting
from several thousand OMs are discussed.Comment: 30 pages, 24 figure
Optical Properties of Deep Ice at the South Pole - Absorption
We discuss recent measurements of the wavelength-dependent absorption
coefficients in deep South Pole ice. The method uses transit time distributions
of pulses from a variable-frequency laser sent between emitters and receivers
embedded in the ice. At depths of 800 to 1000 m scattering is dominated by
residual air bubbles, whereas absorption occurs both in ice itself and in
insoluble impurities. The absorption coefficient increases approximately
exponentially with wavelength in the measured interval 410 to 610 nm. At the
shortest wavelength our value is about a factor 20 below previous values
obtained for laboratory ice and lake ice; with increasing wavelength the
discrepancy with previous measurements decreases. At around 415 to 500 nm the
experimental uncertainties are small enough for us to resolve an extrinsic
contribution to absorption in ice: submicron dust particles contribute by an
amount that increases with depth and corresponds well with the expected
increase seen near the Last Glacial Maximum in Vostok and Dome C ice cores. The
laser pulse method allows remote mapping of gross structure in dust
concentration as a function of depth in glacial ice.Comment: 26 pages, LaTex, Accepted for publication in Applied Optics. 9
figures, not included, available on request from [email protected]
MRI-based contrast clearance analysis shows high differentiation accuracy between radiation-induced reactions and progressive disease after cranial radiotherapy
BACKGROUND: Pseudoprogression (PsP) or radiation necrosis (RN) may frequently occur after cranial radiotherapy and show a similar imaging pattern compared with progressive disease (PD). We aimed to evaluate the diagnostic accuracy of magnetic resonance imaging-based contrast clearance analysis (CCA) in this clinical setting. PATIENTS AND METHODS: Patients with equivocal imaging findings after cranial radiotherapy were consecutively included into this monocentric prospective study. CCA was carried out by software-based automated subtraction of imaging features in late versus early T1-weighted sequences after contrast agent application. Two experienced neuroradiologists evaluated CCA with respect to PsP/RN and PD being blinded for histological findings. The radiological assessment was compared with the histopathological results, and its accuracy was calculated statistically. RESULTS: A total of 33 patients were included; 16 (48.5%) were treated because of a primary brain tumor (BT), and 17 (51.1%) because of a secondary BT. In one patient, CCA was technically infeasible. The accuracy of CCA in predicting the histological result was 0.84 [95% confidence interval (CI) 0.67-0.95; one-sided P = 0.051; n = 32]. Sensitivity and specificity of CCA were 0.93 (95% CI 0.66-1.00) and 0.78 (95% CI 0.52-0.94), respectively. The accuracy in patients with secondary BTs was 0.94 (95% CI 0.71-1.00) and nonsignificantly higher compared with patients with primary BT with an accuracy of 0.73 (95% CI 0.45-0.92), P = 0.16. CONCLUSIONS: In this study, CCA was a highly accurate, easy, and helpful method for distinguishing PsP or RN from PD after cranial radiotherapy, especially in patients with secondary tumors after radiosurgical treatment
The AMANDA Neutrino Telescope and the Indirect Search for Dark Matter
With an effective telescope area of order 10^4 m^2, a threshold of ~50 GeV
and a pointing accuracy of 2.5 degrees, the AMANDA detector represents the
first of a new generation of high energy neutrino telescopes, reaching a scale
envisaged over 25 years ago. We describe its performance, focussing on the
capability to detect halo dark matter particles via their annihilation into
neutrinos.Comment: Latex2.09, 16 pages, uses epsf.sty to place 15 postscript figures.
Talk presented at the 3rd International Symposium on Sources and Detection of
Dark Matter in the Universe (DM98), Santa Monica, California, Feb. 199
The AMANDA Neutrino Telescope
With an effective telescope area of order m for TeV neutrinos, a
threshold near 50 GeV and a pointing accuracy of 2.5 degrees per muon
track, the AMANDA detector represents the first of a new generation of high
energy neutrino telescopes, reaching a scale envisaged over 25 years ago. We
describe early results on the calibration of natural deep ice as a particle
detector as well as on AMANDA's performance as a neutrino telescope.Comment: 12 pages, Latex2.09, uses espcrc2.sty and epsf.sty, 13 postscript
files included. Talk presented at the 18th International Conference on
Neutrino Physics and Astrophysics (Neutrino 98), Takayama, Japan, June 199
The AMANDA Neutrino Telescope: Principle of Operation and First Results
AMANDA is a high-energy neutrino telescope presently under construction at
the geographical South Pole. In the Antarctic summer 1995/96, an array of 80
optical modules (OMs) arranged on 4 strings (AMANDA-B4) was deployed at depths
between 1.5 and 2 km. In this paper we describe the design and performance of
the AMANDA-B4 prototype, based on data collected between February and November
1996. Monte Carlo simulations of the detector response to down-going
atmospheric muon tracks show that the global behavior of the detector is
understood. We describe the data analysis method and present first results on
atmospheric muon reconstruction and separation of neutrino candidates. The
AMANDA array was upgraded with 216 OMs on 6 new strings in 1996/97
(AMANDA-B10), and 122 additional OMs on 3 strings in 1997/98.Comment: 36 pages, 23 figures, submitted to Astroparticle Physic
Population genomics provide insights into the global genetic structure of Colletotrichum graminicola, the causal agent of maize anthracnose
Understanding the genetic diversity and mechanisms underlying genetic variation in pathogen populations is crucial to the development of effective control strategies. We investigated the genetic diversity and reproductive biology of Colletotrichum graminicola isolates which infect maize by sequencing the genomes of 108 isolates collected from 14 countries using restriction site-associated DNA sequencing (RAD-seq) and whole-genome sequencing (WGS). Clustering analyses based on single-nucleotide polymorphisms revealed three genetic groups delimited by continental origin, compatible with short-dispersal of the pathogen and geographic subdivision. Intra- and intercontinental migration was observed between Europe and South America, likely associated with the movement of contaminated germplasm. Low clonality, evidence of genetic recombination, and high phenotypic diversity were detected. We show evidence that, although it is rare (possibly due to losses of sexual reproduction- and meiosis-associated genes) C. graminicola can undergo sexual recombination. Our results support the hypotheses that intra- and intercontinental pathogen migration and genetic recombination have great impacts on the C. graminicola population structure
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