Cosmic-ray positrons: are there primary sources?     

Stphane Coutu  Steven W. Barwick  James J. Beatty  Amit Bhattacharyya  Chuck R. Bower  Christopher J. Chaput  Georgia A. de Nolfo  Michael A. DuVernois  Allan Labrador  Shawn P. McKee  Dietrich Müller  James A. Musser  Scott L. Nutter  Eric Schneider  Simon P. Swordy  Gregory Tarl  Andrew D. Tomasch  Eric Torbet 《Astroparticle Physics》1999,11(4):208-435

Galactic cosmic rays consist of primary and secondary particles. Primary cosmic rays are thought to be energized by first order Fermi acceleration processes at supernova shock fronts within our Galaxy. The cosmic rays that eventually reach the Earth from this source are mainly protons and atomic nuclei, but also include electrons. Secondary cosmic rays are created in collisions of primary particles with the diffuse interstellar gas. They are relatively rare but carry important information on the Galactic propagation of the primary particles. The secondary component includes a small fraction of antimatter particles, positrons and antiprotons. In addition, positrons and antiprotons may also come from unusual sources and possibly provide insight into new physics. For instance, the annihilation of heavy supersymmetric dark matter particles within the Galactic halo could lead to positrons or antiprotons with distinctive energy signatures. With the High-Energy Antimatter Telescope (HEAT) balloon-borne instrument, we have measured the abundances of positrons and electrons at energies between 1 and 50 GeV. The data suggest that indeed a small additional antimatter component may be present that cannot be explained by a purely secondary production mechanism. Here we describe the signature of the effect and discuss its possible origin.  相似文献   

Stochastic behaviour and scaling laws in geoelectrical signals measured in a seismic area of southern Italy     

Vincenzo Cuomo  Vincenzo Lapenna  Maria Macchiato  Carmine Serio  & Luciano Telesca 《Geophysical Journal International》1999,139(3):889-894

We explore the inner dynamics of daily geoelectrical time series measured in a seismic area of the southern Apennine chain (southern Italy). Autoregressive models and the Higuchi fractal method are applied to extract maximum quantitative information about the time dynamics from these geoelectrical signals. First, the predictability of the geoelectrical measurements is investigated using autoregressive models. The procedure is based on two forecasting approaches: the global and the local autoregressive approximations. The first views the data as a realization of a linear stochastic process, whereas the second considers the data points as a realization of a deterministic process, which may be non-linear. Comparison of the predictive skills of the two techniques allows discrimination between low-dimensional chaos and stochastic dynamics. Our findings suggest that the physical systems governing electrical phenomena are characterized by a very large number of degrees of freedom and can be described only with statistical laws. Second, we investigate the stochastic properties of the same geoelectrical signals, searching for scaling laws in the power spectrum. The spectrum fits a power law P (  f )∝  f  ^−α , with the scaling exponent α a typical fingerprint of fractional Brownian processes. In this analysis we apply the Higuchi method, which gives a linear relationship between the fractal dimension D _Σ and the spectral power law scaling index α : D _Σ=(3− α )/2. This analysis highlights the stochastic nature of geoelectrical signals recorded in this seismic area of southern Italy.  相似文献   

Old, Low-Mass, Metal-Rich (SMR) Stars     

G. Cayrel de Strobel  Y. Lebreton  C. Soubiran  E.D. Friel 《Astrophysics and Space Science》1999,265(1-4):345-352

The authors of this paper try to disentangle the many problems arisen from a new enlarged sample of nearby low-mass,metal-rich-stars. These stars have reliable absolute magnitudes, deduced from Hipparcos parallaxes, precise bolometric corrections, effective temperatures and metal abundances from high resolution detailed spectroscopic analyses. Their ages have been derived from a grid of isochrones calculated with up to date physics. The main goal of this paper is to determine the ages of the slightly evolved SMR stars. Among those with well determinated ages about 80% of them have intermediate ages of (2 to 5 Gyr), but only 20% have ages of 8 Gyr or more. Nevertheless, the existence of very old metal-rich stars is confirmed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

白刺不同果实性状的遗传力估计及优良亲本选择   总被引：8，自引：1，他引：7  

高志海  崔建国 《中国沙漠》1999,19(1):82-85

亲子回归法研究白刺果实不同性状遗传力的结果表明,果径、果形、果色、果味、核形和果实出肉率等性状指标的遗传力较高,说明这些性状变异的遗传贡献较大,可作为白刺果实类型划分的主要指标,其中果径、果味和出肉率可作为白刺果实品质评价和优良亲本选择的主要依据。以果径和出肉率为指标,用家系选择法选择优良亲本可获得较大的遗传增益,且两指标选择的亲本一致,选择效果满意。  相似文献   

环境场对边界层低空急流形成的影响   总被引：1，自引：1，他引：0  

罗德海 《热带气象学报》1987,(3):227-232

本文利用两层流的浅水波模式,讨论了环境场对边界层低空急流形成的影响,并得到了边界层低空急流的特征宽度为L₀=(ρ₂-ρ₁)/(ν₂ρ₂-ρ₁ν₁)L₀*C₀*,式中C₀*=√gh₂, L₀*=C₀*/f为Rossby变形半径,ρ₁,p₂和v₁,v₂分别为上下两层大气的密度和大尺度经向地转风,H₂为低层大气的厚度,g为重力加速度,f为柯氏参数,当高低层大气中的大尺度经向地转风的垂直切变越强时,所形成的中尺度边界层低空急流就越强;当低层大气中的温度增高和湿度增大、并且低层大气中的大尺度经向地转风越强、高度越低时,越有利于形成边界层低空急流。   相似文献   

VSOP/global VLBI observations of 2021+614: Detection of hotspot advance     

W. Tschager  R. T. Schilizzi  I. A. G. Snellen  A. G. de Bruyn  G. K. Miley  H. J. A. Rttgering  H. J. van Langevelde  C. Fanti  R. Fanti 《New Astronomy Reviews》1999,43(8-10)

We have analysed VSOP and global VLBI data at 5 GHz and VLBA + Effelsberg data at 15 GHz for 2021+614. By identifying the core as being between two bright hotspots, we show that 2021+614 is a compact symmetric object of size 40 pc. From comparison with earlier observations we deduce an apparent age of 375 yr for 2021+614. This provides additional support for the contention that compact symmetric radio objects associated with galaxies are in fact young radio sources and the possible precursors of the classical FR I or FR II radio galaxies.  相似文献   

Major neotectonic features of eastern Marmara region,Turkey: development of the Adapazarı–Karasu corridor and its tectonic significance     

Erdi&#x;n Yi&#x;i&#x;tba  Ali&#x; Elmas  Ati&#x;lla Sefun  Nai&#x;de zer 《Geological Journal》2004,39(2):179-198

Eastern Marmara region consists of three different morphotectonic units: Thrace–Kocaeli Peneplain (TKP) and Çamdağ–Akçakoca Highland (ÇAH) in the north, and Armutlu–Almacık Highland in the south of the North Anatolian Fault Zone (NAFZ). The geologic‐morphologic data and seismic profiles from the Sakarya River offshore indicate that the boundary between the TKP in the west and ÇAH in the east is a previously unrecognized major NNE–SSW‐trending strike‐slip fault zone with reverse component. The fault zone is a distinct morphotectonic corridor herein named the Adapazarı–Karasu corridor (AKC) that runs along the Sakarya River Valley and extends to its submarine canyon along the southern margin of the Black Sea in the north. It formed as a transfer fault zone between the TKP and ÇAH during the Late Miocene; the former has been experiencing extensional forces and the latter compressional forces since then. East–West‐trending segments of the NAFZ cuts the NE–SW‐trending AKC and their activity has resulted in the formation of a distinct fault‐bounded morphology, which is characterized by alternating E–W highlands and lowlands in the AKC. Furthermore, this activity has resulted in the downward motion of an ancient delta and submarine canyon of the Sakarya River in the northern block of the NAFZ below sea level so that the waters of the Black Sea invaded them. The NE–SW‐trending faults in the AKC were reactivated with the development of the NAFZ in the Late Pliocene, which then caused block motions and microseismic activities throughout the AKC. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Movement and Home Ranges of Dugongs Around the Lease Islands, East Indonesia   总被引：1，自引：0，他引：1  

Hans H. de  Iongh  Paul  Langeveld Mark  van der Wal 《Marine Ecology》1998,19(3):179-193

Abstract. Four individual dugongs Dugong dugong , MÜLLER, 1776 were tracked with buoyant, tethered. conventional and satellite radio transmitters. The dugongs three adult females and one immature male were encircled with a net at a catch site near Haruku Island, East Indonesia, and tracked for between 41 and 285 days. The animals showed individualistic patterns of movement, moving between 2 and 3 core areas, travelling between 17 and 65 km from the site of capture. One adult female spent most of the time at two distinct inshore seagrass beds separated by about 17 km; she made five trips between the two sites. Two other females made separate trips to two distinct sites, one of them returning to the catch site at Haruku Island. The immature male journeyed between two areas about 65 km apart. completing the journey in four days. The patterns of movement confirmed a practice of regular recropping of restricted grazing swards by small, loose feeding assemblages rather than fixed herds with a strong social bond. Mean home ranges covered 4.1 km² 50% harmonic mean and 43.4 km² 95% harmonic mean.  相似文献   

Responses of marine phytoplankton in iron enrichment experiments in the northern North Sea and northeast Atlantic Ocean     

Klaas R. Timmermans  Martha Gledhill  Rob F. Nolting  Marcel J. W. Veldhuis  Hein J. W. de Baar  Constant M. G.van den Berg 《Marine Chemistry》1998,61(3-4)

Short-term iron enrichment experiments were carried out with samples collected in areas with different phytoplankton activity in the northern North Sea and northeast Atlantic Ocean in the summer of 1993. The research area was dominated by high numbers of pico-phytoplankton, up to 70,000 ml⁻¹. Maximum chlorophyll a concentrations varied from about 1.0 μg l⁻¹ in a high-reflectance zone (caused by loose coccoliths, remnants from a bloom of Emiliania huxleyi) and about 3.5 μg l⁻¹ in a zone in which the phytoplankton were growing, to about 0.5 μg l⁻¹ in the northeast Atlantic Ocean. From the high-reflectance zone to the northeast Atlantic Ocean, nitrate concentrations increased from 0.5 μM to 6.0 μM. Concentrations of reactive iron in surface water showed an opposite trend and decreased from about 2.6 nM in the high-reflectance zone to <1.0 nM in the northeast Atlantic Ocean. In the research area, no signs of true iron deficiency were found, but iron enrichments in the high-reflectance zone, numerically dominated by Synechococcus sp., resulted in increased nitrate uptake. Ammonium uptake was hardly affected. Strong support for the effect of Fe on cell physiology is given by the increase in the f-ratio. Net growth rates of the phytoplankton (changes in cell numbers over 24 h) were almost unchanged. Phytoplankton collected from the northeast Atlantic Ocean, did not show changes in the nitrogen metabolism upon addition of iron. Net growth rates in these incubations were low or negative, with only slightly higher values with additional iron.  相似文献   

A GPS-Supported Gravity Survey in the Amazon of Ecuador   总被引：1，自引：0，他引：1  

Mamadou Balde  Jeremy Fishman  Carlos L. V. Aiken  Mohamed Abdel-Salam  Mauricio F. de la Fuente 《GPS Solutions》1999,2(3):3-17

The growing importance and effectiveness of the Global Positioning System (GPS) in positioning geophysical surveys is now well established. In Ecuador's Amazon basin the use of GPS was the determining factor in the successful completion of a gravity survey carried out in 1994. Over 500 gravity stations, spaced from 1 to 5 km apart and positioned by GPS, were collected in the jungle environment in the country's southeast, where the preexisting data, of variable and unknown quality, were mostly confined to areas along the major rivers. This station densification, which includes the reoccupation of selected points, contributed to increase the gravity coverage; it also allowed us to evaluate and correct 1100 preexisting data points in the area, so that the different surveys can be merged. The composite data set is used for a geologic analysis of the study area, where previously unknown structures are discovered. ? 1999 John Wiley & Sons, Inc.  相似文献