Co60γ射线对海带幼孢子体的影响

近几年来,有关X射线对海带配子体和幼孢子体的影响以及Co60γ射线对海带配子体的影响都有过报导。本实验在于观察Co60γ射线对海带幼孢子体的影响和目前条件下可能看到的作用机制。正如Gray(1959)所指出：尽管X射线对活细胞的作用问题已有60多年的研究,但对有关的机制还是所知极少。本实验所能探讨的只是一些可见的、也就是属于细胞水平的机制。     

A Late Pleistocene submarine slide on the Bear Island Trough Mouth Fan

A large submarine slide on the southern flank of the Bear Island Trough Mouth Fan, southwestern Barents Sea continental slope, has a run-out distance of about 400 km, a total volume of about 1100 km³, and is younger than 330 ka. Three seismic units, comprising mainly hemipelagic sediments has partly filled the slide scar. An increased sedimentation rate on the Bear Island Trough Mouth Fan from Late Pliocene time, probably in combination with abundant earthquakes, is the most likely cause of the slide. Based on these and previous studies, we suggest that large-scale slides were important sediment transport processes during Plio-Pleistocene.     

Optical interferometric observations of a transient event of 1986 March 13 in the coma of Comet Halley

During the recent apparition of Comet Halley in 1985-86 a transient ionic event in the form of a blob of H₂ O⁺ emission was recorded in thecoma at ～ 0^h UT on 1986 March 13. Observations were carried out using a special IHW filter for H₂ O⁺ emission at 7000 å/175 å, a 35 cm telescope, a Fabry-Perot interferometer and an image intensifier camera from Gurushikhar, Mt Abu. (24?39’N,72? 47’E). A Fabry-Perot inter-ferogram in Ha taken a few minutes later at the same location reveals strong hydrogen emission (Hα) associated with the blob. The velocity field in the blob is structured with relative velocities upto ～ 35km s^?1. The event is interpreted as arising due to the sector boundary crossing of the interplanetary magnetic field by the comet     

The University of Durham Southern Hemisphere VHE gamma ray telescope

The design of very high energy (VHE) gamma ray telescopes is discussed and it is shown that a triple-mirror telescope operating in threefold fast coincidence provides an effective instrument. The design, construction and operation of a large VHE gamma ray telescope with an energy threshold of 300 GeV (at the zenith) and incorporating several novel features is described. The use of a coincidence guard ring technique is shown to result in the rejection of about 50% of the off-source (proton) events which form a high background and limit the sensitivity of such telescopes.     

Radiometry of near-earth asteroids

We report 10 micrometers infrared photometry for 22 Aten, Apollo, and Amor asteroids. Thermal models are used to derive the corresponding radiometric albedos and diameters. Several of these asteroids appear to have surfaces of relatively high thermal inertia due to the exposure of bare rock or a coarse regolith. The Apollo asteroid 3103, 1982 BB, is recognized as class E. The Jupiter-crossing Amor asteroid 3552, 1983 SA, is confirmed as class D, but low albedos remain rare for near-Earth asteroids.     

External radiation field in Rayleigh-Cabannes atmospheres with constant and linear sources

The external field of radiation in Rayleigh-Cabannes atmospheres with constant and linear sources is found using the resolvent matrix approach. If the internal sources are constant the external field may be described by theX-, Y-, andH-matrices. For the case with linear sources we need the derivatives of these matrices with respect to angular variable. The respective scheme for their determination is given.A set of integro-differential equations for theX- andY-matrices is derived and solved numerically. Some relations between the moments of theH-matrix are given and a sample of results for external fields are provided.     

Radio observations of the M8.1 solar flare of 23 June, 1988: Evidence for energy transport by thermal processes

The Very Large Array (VLA) and the frequency agile interferometer at the Owens Valley Radio Observatory (OVRO) were used to observe the M8.1 flare of 23 June, 1988. The VLA obtained images prior to and during the flare at 333 MHz, and at 1.5 and 4.7 GHz. The frequency agile interferometer at Owens Valley obtained interferometer amplitude and total power spectra of the flare at 45 frequencies between 1 and 18 GHz. The observations were supplemented by radiometer measurements made by the USAF RSTN network site at Palehua, HI, by GOES soft X-ray observations, by USAF SOON H filtergrams, and by a KPNO photospheric magnetogram.The radio data reveal a wide variety of phenomena, including: (i) a multiply impulsive microwave burst that is essentially thermal in character; (ii) stationary discrete components at 1.5 GHz, associated temporally and spatially with distant brightenings in Ha; (iii) a dynamical component at 1.5 GHz associated with hot plasma moving subsonically into the corona; (iv) the appearance of intense, short-lived, decimetric burst activity near the lead sunspot in the active region at 1.5 GHz, indicative of a high degree of inhomogeneity in the source.The unusually complete radio coverage allows us to investigate the transport of energy from the initial site to sites of distant H brightenings. The transport of energy appears to be most consistent with slow, thermal processes, rather than rapid transport by nonthermal electron beams.     

Solution of the equation of transfer for coherent scattering in an exponential atmosphere by the method of discrete ordinates

A solution of the transfer equation for coherent scattering in stellar atmosphere with Planck's function as a nonlinear function of optical depth, viz., $$B_v (T) = b_0 + b_1 {\text{ }}e^{ - \beta \tau } $$ is obtained by the method of discrete ordinates originally due to Chandrasekhar.     

The center-to-limb variations of four Ca i lines in the photospheric spectrum at λ6500

We study the center-limb (CL) variation of the average profiles of four Ca i lines near 6500 and compare these observations with synthetic data obtained from several line formation models having different thermal structures, line parameters, LTE and non-LTE conditions, and micro and macroturbulence values, to assess the formation characteristics of our Ca i lines in the solar photosphere.Comparison of numerical results with observations indicates that non-LTE is indispensable to fit the CL variation of the central residual intensity for the line 6493, and anisotropic microturbulence is indispensable to improve the CL behavior of the equivalent widths for all lines. The Ca i line analysis favors a cool photospheric model, but this cannot be disentangled clearly from the effects of non-LTE and small-scale velocity fields on the grounds of the present line formation models.     

Bianchi type-II,VIII, and IX in certain new theories of gravitation

Bianchi type-II, VIII, and IX models have been investigated in scalar-tensor theories developed by Saez (1985), Saez and Ballester (1985), and Lau and Prokhovnik (1986) (under the assumption of a certain relationship between the cosmological term and the scalar field ). The dynamical behaviour of these models has been studied.