We describe the initial results of a programme to detect and identify extended X-ray sources found serendipitously in XMM-Newton observations. We have analyzed 186 EPIC-PN images at high galactic latitude with a limiting flux of 1 × 10−14 erg cm−2 s−1 and found 62 cluster candidates. Thanks to the enhanced sensitivity of the XMM-Newton telescopes, the new clusters found in this pilot study are on the average fainter, more compact, and more distant than those found in previous X-ray surveys. At our survey limit the surface density of clusters is about 5 deg−2. We also present the first results of an optical follow-up programme aiming at the redshift measurement of a large sample of clusters. The results of this pilot study give a first glimpse on the potential of serendipitous cluster science with XMM-Newton based on real data. The largest, yet to be fulfilled promise is the identification of a large number of high-redshift clusters for cosmological studies up to z = 1 or 1.5. 相似文献
Superrotation on Venus is discussed in the context of comparative planetary atmospheres. In our planetary system, the rigid shell component (global average) of superrotation is ubiquitous (Jupiter, Saturn, Earth, Venus, Mars, Titan). The largest equatorial values of the component are between 25 and 150 m/sec. We present a simplified, heuristic analysis, utilizing mixing length theory to describe the small scale non-linear advections of energy and angular momentum, thereby providing a closure of the dynamic system. This leads to the conjecture that the zonal velocity may be crudely estimated by , approximating the observed planetary trends; with c the speed of sound, the parameter a being 1 or 2 for geostrophic or cyclostrophic conditions respectively, Pα an effective Prandtl number which becomes less than one when radiative cooling is important, So the average stability, Γ the adiabatic lapse rate and γ the ratio of specific heats. 相似文献
The results of experiments with the DAKON-M convection sensor onboard the Russian orbital segment of the International Space Station are described. A comparison of the sensor measurements with the results of calculation of the quasistatic microacceleration component at the point of installation is made. For this comparison we have used three measurement intervals of the experiments in 2009, during which spacecraft were docked with the station, undocked from it, and actuation of jet engines of the attitude control system took place. When calculating microacceleration, we use the measurement data of the low-frequency MAMS accelerometer, installed on the American segment, and the telemetry data on the ISS rotational motion. This information allowed one to convert the MAMS measurements to the point of installation of the DAKON-M convection sensor. A comparison of sensor measurements with calculated microaccelerations showed sufficiently accurate coincidence between the calculated and measured data. 相似文献
The electronic communication technology available today offers the possibility of changing many patterns of information transfer in urban areas. There are three major trends which are converging to make this change possible. These are: 1) the technology to permit wideband information transfer manifested in the existing 2300/CATV/Cable System and in modification of the Bell network for wideband services; 2) the potential demand for a vast range of new services to persons operating in the urban areas; 3) the increasing demands for meeting mobile information transfer needs in the urban areas through radio systems operating in the 100 to 1000 MHz part of the spectrum. The extent to which these trends are allowed to converge will be a function of the quality of telecommunication policy formulation and execution. In order to formulate policy, it is necessary to have a vision of the future toward which to work. This paper will discuss the types of services possible with the technology presently available, which will have impact on future policy decisions. 相似文献
The application of a highly parallel computer known as PEPE (Parallel Element Processing Ensemble) to radar data processing is described. The PEPE computer consists of a large number of identical processing elements which operate in parallel and are controlled by a common control unit. Each of the processing elements is assigned to a particular radar target such that many targets can be tracked in parallel. PEPE is designed to augment a conventional computer rather than to stand alone. The total data processing load associated with a radar tracking system is distributed between PEPE and the sequential machine in a manner than maximizes the overall system efficiency and desensitizes the system performance to fluctuations in traffic levels. The use of PEPE provides very high data processing throughput potential to a radar data processing system. 相似文献
Gravity may influence different aspects of plant activity. The present report deals with two questions: gravity as an ecological factor determining spatial orientation of plant growth; and second, a possible requirement for gravity in the process of normal growth, morphogenesis and generative development of plants. 相似文献
Understanding the effects of single-particles from conventional radiation biology experiments is problematic due to the stochastics of particle tracks. This complicates the determinations of risk associated with low doses. We have developed a charged particle microbeam, which allows individually counted particles to be delivered to precise cellular locations. The system is capable of delivering a single charged particle with > 99% efficiency. Of these particles 90% are delivered with a resolution of +/- 2 micrometers and 96% with a resolution of +/- 5 micrometers. We have carried out preliminary studies in Chinese hamster V79 cells to monitor the effectiveness of low energy protons at inducing cytological damage. We have used the micronucleus assay as a measure of predominantly lethal chromosome damage. The effects of a single 3.2 MeV proton delivered individually to cells could be measured, with less than 2% of the exposed cells producing micronuclei 24 hours later. The yield of micronuclei formation was essentially linear up to the highest dose (30 particles per cell nucleus) delivered. Ultimately, the ability to target particles to different parts of the cell nucleus may start to impact on models available for chromosome aberration formation and chromosomal Organisation and mechanisms underlying genomic instability. 相似文献
The time-domain transient response of a thin dipole antenna is discussed in terms of element lengths and the surge impedances of the transmission line and element terminals. Theory and measurements show that, unlike symmetric configurations, asymmetry in the element lengths, together with appropriate mismatch of the transmission line, produces radiation proportional to the first time derivative of the signal voltage, and replica reception proportional to the incoming field. 相似文献