3.8-μm photometry during the secondary eclipse of the extrasolar planet HD 209458b     

Drake Deming †  L. Jeremy Richardson  Joseph Harrington 《Monthly notices of the Royal Astronomical Society》2007,378(1):148-152

We report infrared photometry of the extrasolar planet HD 209458b during the time of secondary eclipse (planet passing behind the star). Observations were acquired during two secondary eclipses at the NASA Infrared Telescope Facility (IRTF) in 2003 September. We used a circular variable filter (1.5 per cent bandpass) centred at 3.8 μm to isolate the predicted flux peak of the planet at this wavelength. Residual telluric absorption and instrument variations were removed by offsetting the telescope to nearby bright comparison stars at a high temporal cadence. Our results give a secondary eclipse depth of 0.0013 ± 0.0011, not yet sufficient precision to detect the eclipse, whose expected depth is  ∼0.002 –0.003  . We here elucidate the current observational limitations to this technique, and discuss the approach needed to achieve detections of hot Jupiter secondary eclipses at 3.8 μm from the ground.  相似文献   

QED can explain the non-thermal emission from SGRs and AXPs: variability     

Jeremy S. Heyl 《Astrophysics and Space Science》2007,308(1-4):101-107

Owing to effects arising from quantum electrodynamics (QED), magnetohydrodynamical fast modes of sufficient strength will break down to form electron-positron pairs while traversing the magnetospheres of strongly magnetised neutron stars. The bulk of the energy of the fast mode fuels the development of an electron-positron fireball. However, a small, but potentially observable, fraction of the energy (～10³³ erg) can generate a non-thermal distribution of electrons and positrons far from the star. This paper examines the cooling and radiative output of these particles. Small-scale waves may produce only the non-thermal emission. The properties of this non-thermal emission in the absence of a fireball match those of the quiescent, non-thermal radiation recently observed non-thermal emission from several anomalous X-ray pulsars and soft-gamma repeaters. Initial estimates of the emission as a function of angle indicate that the non-thermal emission should be beamed and therefore one would expect this emission to be pulsed as well. According to this model the pulsation of the non-thermal emission should be between 90 and 180 degrees out of phase from the thermal emission from the stellar surface.  相似文献   

Simple models of fluid flow at the core surface derived from geomagnetic field models     

Jeremy Bloxham 《Geophysical Journal International》1989,99(1):173-182

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Special features of cyclotron radiation in anisotropic plasmas     

P. C. W. Fung  P. L. Leung 《Astrophysics and Space Science》1987,137(1):33-62

We analyze the special features of cyclotron radiation in four different modes radiated by a mildly relativistic electron current in an anisotropic plasma, taking into consideration that the radiation is transmitted along the group velocity, rather than the wave normal direction. A systematic series of numerical analysis is carried out, to demonstrate the characteristics of the focussing effect and Doppler effect of the radiation, arising from anisotropy. The parameters used pertain to plasmas and radiators of the types encountered in the terrestrial upper atmosphere and the solar corona.  相似文献   

Towfish orientation and position estimation     

Kirlin  R.L. Lu  W.S. Hedstrom  B. Leung  C.M. 《Oceanic Engineering, IEEE Journal of》1993,18(3):319-326

The towfish location and orientation problems that arise in using side-scan sonar to detect objects on the sea bottom are treated separately. Data which locate the towfish relative to the ship are usually deteriorated by multipath receptions and other effects. In order to overcome this serious degradation in the location measurements, a modified Kalman filter is proposed. An estimate of the state transition matrix for this filter is derived, and a means of switching between two Kalman gains is suggested. The feasibility of the proposed filter is justified by a case study. Improved estimates of towfish pitch and heading measurements are obtained by a separate system employing model identification and subsequent Kalman filtering. Application of these methods to data from similar towed side-scan sonar systems should yield significant gains in object location accuracy  相似文献   

Numerical solutions for flow in porous media     

J.G. Wang  C.F. Leung  Y.K. Chow 《国际地质力学数值与分析法杂志》2003,27(7):565-583

A numerical approach is proposed to model the flow in porous media using homogenization theory. The proposed concept involves the analyses of micro‐true flow at pore‐level and macro‐seepage flow at macro‐level. Macro‐seepage and microscopic characteristic flow equations are first derived from the Navier–Stokes equation at low Reynolds number through a two‐scale homogenization method. This homogenization method adopts an asymptotic expansion of velocity and pressure through the micro‐structures of porous media. A slightly compressible condition is introduced to express the characteristic flow through only characteristic velocity. This characteristic flow is then numerically solved using a penalty FEM scheme. Reduced integration technique is introduced for the volumetric term to avoid mesh locking. Finally, the numerical model is examined using two sets of permeability test data on clay and one set of permeability test data on sand. The numerical predictions agree well with the experimental data if constraint water film is considered for clay and two‐dimensional cross‐connection effect is included for sand. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Self-gravity and quasi-stellar object discs     

Jeremy Goodman 《Monthly notices of the Royal Astronomical Society》2003,339(4):937-948

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Metallothioneins and trace metals in the dogwhelk Nucella lapillus (L.) collected from Icelandic coasts     

Leung KM  Dewhurst RE  Halldórsson H  Svavarsson J 《Marine pollution bulletin》2005,51(8-12):729-737

Different sizes of the dogwhelk Nucella lapillus were collected from eight locations along the southwest and north coasts of Iceland. Concentrations of total metallothioneins (MTs) and heavy metals (Cd, Cu, Cr, Mn, Ni, and Zn) were analysed using the silver saturation method and inductively coupled plasma-atomic emission spectrometry. The level of tributyltin (TBT) contamination was also assessed using imposex indices, the vas deferens stage index (VDSI) and relative penis size index (RPSI). Gufunes N. lapillus presented the highest values of VDSI (4.0) and RPSI (11.1), followed by Grenivík individuals (VDSI = 3.0; RPSI = 0.9), while the Strandakirkja population showed the lowest VDSI (0.3) and zero RPSI. At a standardised size (0.25 g dry soft-body weight), Grenivík N. lapillus exhibited significantly higher concentrations of all metals whereas overall metal concentrations were significantly lower in individuals from Strandakirkja and Garðskagi compared to other study sites. Partial correlation analyses with size correction indicated that MT concentrations were better correlated with Cd and Cu concentrations than with other metals. At the standard size, the pattern of MT concentrations in N. lapillus from different sites was, however, very different from those of metal profiles. Such discrepancies between the patterns of MT and metals in N. lapillus might be explained by the fact that MT induction could be influenced by various factors such as temperature, dietary metal intake, growth rate and co-existence of other MT-inducing chemicals.  相似文献   

Toxicity of antifouling biocides to the intertidal harpacticoid copepod Tigriopus japonicus (Crustacea, Copepoda): effects of temperature and salinity   总被引：2，自引：0，他引：2  

Kwok KW  Leung KM 《Marine pollution bulletin》2005,51(8-12):830-837

Intertidal harpacticoid copepods are commonly used in eco-toxicity tests worldwide. They predominately live in mid-high shore rock pools and often experience a wide range of temperature and salinity fluctuation. Most eco-toxicity tests are conducted at fixed temperature and salinity and thus the influence of these environmental factors on chemical toxicity is largely unknown. This study investigated the combined effect of temperature and salinity on the acute toxicity of the copepod Tigriopus japonicus against two common biocides, copper (Cu) and tributyltin (TBT) using a 2 × 3 × 4 factorial design (i.e. two temperatures: 25 and 35 °C; three salinities: 15.0‰, 34.5‰ and 45.0‰; three levels of the biocide plus a control). Copper sulphate and tributyltin chloride were used as the test chemicals while distilled water and acetone were utilised as solvents for Cu and TBT respectively. 96h-LC50s of Cu and TBT were 1024 and 0.149 μg l⁻¹ respectively (at 25 °C; 34.5‰) and, based on these results, nominal biocide concentrations of LC0 (i.e. control), LC30, LC50 and LC70 were employed. Analysis of Covariance using ‘concentration’ as the covariate and both ‘temperature’ and ‘salinity’ as fixed factors, showed a significant interaction between temperature and salinity effects for Cu, mortality increasing with temperature but decreasing with elevated salinity. A similar result was revealed for TBT. Both temperature and salinity are, therefore, important factors affecting the results of acute eco-toxicity tests using these marine copepods. We recommend that such eco-toxicity tests should be conducted at a range of environmentally realistic temperature/salinity regimes, as this will enhance the sensitivity of the test and improve the safety margin in line with the precautionary principle.  相似文献   

Toward an expert system for identification of minerals in thin section     

Jeremy West 《Mathematical Geology》1985,17(7):743-753

Minerals may be identified by optical inspection and x-ray diffraction analysis. Full and correct identification, however, requires experience and extensive knowledge of mineral characteristics and association. Computer systems designed to approach levels of human expertise in similarly complex identification tasks have become increasingly effective with the application and refinement of various Artificial Intelligence (AI) techniques. These knowledge-based systemsuse the skills, knowledge, and rules of thumb that distinguish the expert from the knowledgeable layman to emulate human expertise. They also may be modified to serve a tutorial role whereby a nonexpert's approach to the task may be compared with that of the expert (system), and criticized accordingly. Such a knowledge-based system capable of identifying minerals from their optical characteristics is being developed at the University of Reading.  相似文献