Search for supernova neutrino bursts with the AMANDA detector     

《Astroparticle Physics》2002,16(4):119-359

The core collapse of a massive star in the Milky Way will produce a neutrino burst, intense enough to be detected by existing underground detectors. The AMANDA neutrino telescope located deep in the South Pole ice can detect MeV neutrinos by a collective rate increase in all photo-multipliers on top of dark noise. The main source of light comes from positrons produced in the CC reaction of anti-electron neutrinos on free protons . This paper describes the first supernova search performed on the full sets of data taken during 1997 and 1998 (215 days of live time) with 302 of the detector's optical modules. No candidate events resulted from this search. The performance of the detector is calculated, yielding a 70% coverage of the galaxy with one background fake per year with 90% efficiency for the detector configuration under study. An upper limit at the 90% c.l. on the rate of stellar collapses in the Milky Way is derived, yielding 4.3 events per year. A trigger algorithm is presented and its performance estimated. Possible improvements of the detector hardware are reviewed.  相似文献   

The mass of helium in white dwarf stars and the formation and evolution of hydrogen-deficient post-AGB stars     

T. M. Lawlor  J. MacDonald 《Monthly notices of the Royal Astronomical Society》2006,371(1):263-282

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Synthetic stellar populations: single stellar populations, stellar interior models and primordial protogalaxies     

Raul Jimenez  James MacDonald  James S. Dunlop  Paolo Padoan  John A. Peacock 《Monthly notices of the Royal Astronomical Society》2004,349(1):240-254

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Magnetic fields in massive stars: dynamics and origin     

James MacDonald  D. J. Mullan 《Monthly notices of the Royal Astronomical Society》2004,348(2):702-716

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Solar Wind Statistics at 1 AU: Alfven Speed and Plasma Beta     

D. J. Mullan  C. W. Smith 《Solar physics》2006,234(2):325-338

The phenomenon of MHD wave refraction is useful in interpreting the properties of the magnetic fluctuations in certain parcels of solar wind. In the physics of MHD wave refraction, variations in the Alfvén speed V_Alf play a dominant role. Here, we compile statistics of the 1-min averages of V_Alf at the location of the ACE spacecraft during its first 5 years of operation. We find that monthly distributions of V_Alf are close to log-normal, with standard deviations σ_V as small as 0.11 in the logarithm. Variations in the monthly mean V_Alf are correlated significantly with sunspot number. We also compile monthly distributions of the plasma β parameter. The distributions of both V_Alf and β are significantly narrower than they would be if the various solar wind parameters were statistically independent. In the T_p–V_Alf plane, we find a zone of avoidance at low V_Alf: for V_Alf ≤10 – 15 km/s, there are no samples in the 1-min data that are cooler than T_p = 10 000 – 15 000 K. This feature can be understood in the context of MHD wave refraction, although other explanations are also possible.  相似文献   

Comparison of model predictions of the anisotropic plasticity of Lower Cromer Till     

《Computers and Geotechnics》2015

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Progress and opportunities for monitoring greenhouse gases fluxes in Mexican ecosystems: the MexFlux network     

R. Vargas  E.A. Yépez  J.L. Andrade  G. Ángeles  T. Arredondo  A.E. Castellanos  J. Delgado-Balbuena  J. Garatuza-Payán  E. González Del Castillo  W. Oechel  J.C. Rodríguez  A. Sánchez-Azofeifa  E. Velasco  E.R. Vivoni  C. Watts 《Atmósfera》2013,26(3):325-336

Understanding ecosystem processes from a functional point of view is essential to study relationships among climate variability, biogeochemical cycles, and surface-atmosphere interactions. Increasingly during the last decades, the eddy covariance (EC) method has been applied in terrestrial, marine and urban ecosystems to quantify fluxes of greenhouse gases (e.g., CO₂, H₂O) and energy (e.g., sensible and latent heat). Networks of EC systems have been established in different regions and have provided scientific information that has been used for designing environmental and adaptation policies. In this context, this article outlines the conceptual and technical framework for the establishment of an EC regional network (i.e., MexFlux) to measure the surface-atmosphere exchange of heat and greenhouse gases in Mexico. The goal of the network is to improve our understanding of how climate variability and environmental change influence the dynamics of Mexican ecosystems. First, we discuss the relevance of CO₂ and water vapor exchange between terrestrial ecosystems and the atmosphere. Second, we briefly describe the EC basis and present examples of measurements in terrestrial and urban ecosystems of Mexico. Finally, we describe the conceptual and operational goals at short-, medium-, and long-term scales for continuity of the MexFlux network.  相似文献   

Trophic Links in the Plankton in the Low Salinity Zone of a Large Temperate Estuary: Top-down Effects of Introduced Copepods     

Joanna K. York  George B. McManus  Wim J. Kimmerer  Anne M. Slaughter  Toni R. Ignoffo 《Estuaries and Coasts》2014,37(3):576-588

We investigated trophic relationships involving microzooplankton in the low salinity zone of the San Francisco Estuary (SFE) as part of a larger effort aimed at understanding the dynamics of the food web supporting the endangered delta smelt, Hypomesus transpacificus. We performed 14 cascade experiments in which we manipulated the biomass of a copepod (Limnoithona tetraspina, Pseudodiaptomus forbesi, or Acartiella sinensis) and quantified responses of lower trophic levels including bacterioplankton, phytoplankton, and microzooplankton. Microzooplankton comprised a major food source for copepods; 9 out of 14 experiments showed removal of at least one group of microzooplankton by copepods. In contrast, the impact of copepods on phytoplankton was indirect; increased copepod biomass led to greater growth of phytoplankton in 3 of 14 experiments. Estimated clearance rates on microzooplankton were 4 mL day^?1 for L. tetraspina and 2–6 mL day^?1 for P. forbesi, whereas A. sinensis consumed mainly copepod nauplii. Complex trophic interactions, including omnivory, among copepods, microzooplankton, and different components of the phytoplankton likely obscured clear trends. The food web of the SFE is probably less efficient than previously thought, providing poor support to higher trophic levels; this inefficient food web is almost certainly implicated in the continuing low abundance of fishes, including the delta smelt that use the low salinity zone of the San Francisco Estuary.  相似文献   

Testing and modeling of the state-dependent behaviors of rockfill material     

《Computers and Geotechnics》2014

Dense Tacheng rockfill material (TRM) exhibits strain softening and dilation during drained triaxial tests, and therefore, an adapted Rowe’s stress–dilatancy equation was proposed for TRM. This equation incorporates an internal state index related to the density and pressure, as well as the coefficient of particle breakage and rotation. The adapted Rowe’s stress–dilatancy equation indicates that the relationship between stress and dilatancy is not constant, but varies with density and pressure. This result is in agreement with TRM test data. A state-dependent model was established for TRM using generalized plasticity theory combined with the adapted Rowe’s stress–dilatancy equation. The model includes twelve constants calibrated using TRM test data from Group A, and this model was used to predict the strain softening and dilatancy behaviors of dense TRM. Furthermore, the model predictions were validated using test data from Group B. In summary, the model accurately represented the stress–strain and dilatancy behaviors of TRM over a wide range of densities and pressures.  相似文献   

Controls on seasonal variations of silicate weathering and CO2 consumption in two river catchments on the NE Tibetan Plateau     

《Journal of Asian Earth Sciences》2013

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