COBE observations of the microwave counterpart of GRBs     

R. K. Schaefer  S. Ali  M. Limon  L. Piccirillo 《Astrophysics and Space Science》1995,231(1-2):331-334

We have used the data from the COBE satellite to search for delayed microwave emission (31 - 90 GHz) from Gamma Ray Bursts (GRBs). The large 7° beam of COBE is well matched to the large positional uncertainties in the GRB locations, although it also means that fluxes from (point source) GRB objects will be diluted. In view of this we are doing a statistical search of the GRBs which occurred during the currently released COBE DMR data (years 1990 and 1991), which overlap 200 GRBs recorded by GRO. Here we concentrate on just the top 10 GRBs (in peak counts/second). We obtain the limits on the emission by comparing the COBE fluxes before and after the GRB at the GRB location. Since it is thought that the microwave emission should lag the GRB event, we have searched the GRB position for emission in the few months following the GRB occurrence.  相似文献   

Determination of the Electrochemical Properties of a Soluble Aqueous FeS Species Present in Sulfidic Solutions     

Stephen M. Theberge  George W. Luther III 《Aquatic Geochemistry》1997,3(3):191-211

Field and laboratory data are presented that show a soluble FeS species(FeS_aq) exists in sulfidic seawater solutions, and is observedwhen the IAP exceeds the K_sp of amorphous FeS. TheFeS_aq yields a discrete signal (double peak) using square-wavevoltammetry and two one-electron waves in sampled DC polarographyexperiments at the Hg electrode. The aqueous FeS species reacts irreversiblyat the electrode as a single FeS subunit and not as a polymeric entity. Thepeak potential of FeS_aq occurs at -1.1 V whereas the peakpotential of Fe occurs at-1.45 V; the positive shift for Fe²⁺ reduction inFeS_aq indicates a change in geometry for Fe²⁺from octahedral to tetrahedral. The kinetics of electron transfer at theelectrode are determined to be similar for both Fe²⁺ andFeS_aq. Molecular orbital energy diagrams, further indicatethat Fe(II) does change from octahedral to tetrahedral geometry in solution.First, Fe(II) exists as octahedralFe in solution whichundergoes a substitution reaction of bisulfide for water. The resultingcomplex, Fe(H₂O)₅(HS)⁺, thentransforms to a tetrahedral complex on further addition of sulfide. Thisgeometry change is consistent with the formation of amorphous FeS thatconverts to mackinawite which has tetrahedral Fe(II). The process is entropydriven because of the water loss that occurs. The overall sequence can berepresented as: Soluble FeS species are important asreactants in the formation of iron-sulfide minerals including pyrite.  相似文献   

Managing marine invasive species through public participation: Lionfish derbies as a case study     

《Marine Policy》2016

The management of invasive species can be facilitated by public participation. The drivers of public involvement and success at invasive removal in tournaments (derbies) to catch Indo-Pacific lionfish (Pterois volitans/miles) in the Western Atlantic were examined. Information on 69 lionfish derbies held in the wider Caribbean region from 2010 to 2015 was compiled. Derbies attended mainly by artisanal fishers reported lower catches but higher participation than derbies dominated by recreational divers or attended by a mixed public. As predicted, the number of lionfish caught increased with effort and with time since lionfish were established in an area. In contrast, participation was best predicted by national wealth (GDP per capita) and number of local dive shops. From the point of view of public engagement, derbies should therefore be held in areas where lionfish are well established, and where the pool of potential participants is large. However, if the management goal is instead to slow the invasion, early detection is critical. The focus should then shift to areas where no or very few lionfish have been detected, and the derby approach modified to a more frequent or continuous, monitoring-like incentive scheme.  相似文献   

Surfzone currents, by D.R. Basco     

James T. Kirby  Robert A. Dalrymple 《Coastal Engineering》1984,8(4):387-389

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Water waves past abrupt channel transitions     

Robert A. Dalrymple 《Applied Ocean Research》1989,11(4):170-175

Small amplitude water waves propagating from a narrow rectangular channel into a wider rectangular channel are examined to determine the reflection coefficients and the diffraction patterns associated with the channel transition. An eigenfunction expansion method is used for the full range of channel transitions, while a variational solution is developed for the case when only planar waves are reflected in the upwave channel. Significant reflections occur when the wavelength of the waves in the wider channel corresponds to multiples of the channel width.  相似文献   

The generating mechanisms of the August 17, 1999 İzmit bay (Turkey) tsunami: Regional (tectonic) and local (mass instabilities) causes     

《Marine Geology》2006,225(1-4):311-330

The M_W = 7.4 earthquake that affected the northwestern part of Turkey on August 17, 1999, and in particular the gulf of İzmit, had dramatic consequences also as regards tsunami generation. The main cause of the earthquake was a dextral strike-slip rupture that took place along different segments of the western part of the North Anatolian Fault (WNAF). The rupture process involved not only a number of distinct strike-slip fault segments, but also dip-slip ancillary faults, connecting the main transcurrent segments. The general picture was further complicated by the occurrence of subsidence and liquefaction phenomena, especially along the coasts of the İzmit bay and in the Sapanca Lake. Tsunami effects were observed and measured during post-event surveys in several places along both the northern and the southern coasts of the bay. The run-up heights in most places were reported to lie in the interval 1–3 m: but in the small town of Değirmendere, where a local slump occurred carrying underwater buildings and gardens of the waterfront sector, eyewitnesses reported water waves higher than 15 m.The purpose of this work is to investigate on the causes of the tsunami by means of numerical simulations of the water waves. We show that the tsunami was a complex event consisting at least of the combination of a regional event due to tectonic causes and of a local event associated with the mass failure. As to the first, we are able to demonstrate that the observed tsunami cannot be explained only in terms of the sea bottom dislocation produced by the main right-lateral dislocation, but that the prominent contribution comes from the displacement associated with the secondary shallow normal faults. Furthermore, the large waves and effects seen in Değirmendere can be explained as the consequence of the slump. By means of a stability analysis based on an original method making use of the limit equilibrium concept, we show that the slump was highly stable before the earthquake and that it was triggered by seismic waves. Simulation of the tsunami induced by the slump was carried out by a two-step numerical code that computes the landslide motion first, and then the generated water wave propagation. It is shown that the computed local tsunami matches the experimental data.  相似文献   

Discussion of ‘Study on the action of the active earth pressure by variational limit equilibrium method’ by Li Xinggao and Liu Weining,International Journal for Numerical and Analytical Methods in Geomechanics 2010; 34:991–1008     

Farshid Vahedifard 《国际地质力学数值与分析法杂志》2011,35(10):1185-1188

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Swash–groundwater dynamics in a sandy beach laboratory experiment     

《Coastal Engineering》2013

Experiments are carried out in a wave basin in order to study the swash–groundwater interaction. A set of wave gages and pressure sensors are used to monitor the free surface and groundwater dynamics. The study is based on the comparison of two selected cases which differ by the gravity and infragravity forcing conditions, the features of wave breaking in the surf zone, the presence of a standing wave attached to the beach face and the wave setup at the shoreline. Significant differences are observed in the response of the swash–groundwater system. The water table overheight appears to be controlled by the amount of infragravity energy available at the shore. Cyclic beach drainage processes can be observed when the water table is low. Significant time-averaged and time-resolved flows are observed into the sand, depending on the swash hydrodynamics. The presence of a gravity standing wave modulation attached to the shore is shown to affect swash and groundwater dynamics. Most of the pressure gradients observed under the swash zone are related to infiltration flows and are thus related to moderate increase of the sediment relative weight.  相似文献   

Are gamma-ray bursts the sources of ultra-high energy cosmic rays?     

《Astroparticle Physics》2015

We reconsider the possibility that gamma-ray bursts (GRBs) are the sources of the ultra-high energy cosmic rays (UHECRs) within the internal shock model, assuming a pure proton composition of the UHECRs. For the first time, we combine the information from gamma-rays, cosmic rays, prompt neutrinos, and cosmogenic neutrinos quantitatively in a joint cosmic ray production and propagation model, and we show that the information on the cosmic energy budget can be obtained as a consequence. In addition to the neutron model, we consider alternative scenarios for the cosmic ray escape from the GRBs, i.e., that cosmic rays can leak from the sources. We find that the dip model, which describes the ankle in UHECR observations by the pair production dip, is strongly disfavored in combination with the internal shock model because (a) unrealistically high baryonic loadings (energy in protons versus energy in electrons/gamma-rays) are needed for the individual GRBs and (b) the prompt neutrino flux easily overshoots the corresponding neutrino bound. On the other hand, GRBs may account for the UHECRs in the ankle transition model if cosmic rays leak out from the source at the highest energies. In that case, we demonstrate that future neutrino observations can efficiently test most of the parameter space – unless the baryonic loading is much larger than previously anticipated.  相似文献   

A Flume Experiment on the Adjustment of the Mean and Turbulent Statistics to a Transition from Short to Tall Sparse Canopies     

Anthony Seraphin  Philippe Guyenne 《Boundary-Layer Meteorology》2008,129(1):47-64

Water-flume experiments are conducted to study the structure of turbulent flow within and above a sparse model canopy consisting of two rigid canopies of different heights. This difference in height specifies a two-dimensional step change from a rough to a rougher surface, as opposed to a smooth-to-rough transition. Despite the fact that the flow is in transition from a rough to a rougher surface, the thickness of the internal boundary layer scales as x ^4/5, consistent with smooth-to-rough boundary layer adjustment studies, where x is the downstream distance from the step change. However, the analogy with smooth-to-rough transitions no longer holds when the flow inside the canopy and near the canopy top is considered. Results show that the step change in surface roughness significantly increases turbulence intensities and shear stress. In particular, there is an adjustment of the mean horizontal velocity and shear stress as the flow passes over the rougher canopy, so that their vertical profiles adjust to give maximum values at the top of this canopy. We also observe that the magnitude and shape of the inflection in the mean horizontal velocity profile is significantly affected by the transition. The horizontal and vertical turbulence spectra compare well with Kolmogorov’s theory, although a small deviation at high frequencies is observed in the horizontal spectrum within the canopy. Here, for relatively low leaf area index, shear is found to be a more effective mechanism for momentum transfer through the canopy structure than vortex shedding.  相似文献