Acquisition of S-Band Telemetry Data during Spacecraft Launch Phases

Whenever one sets out to write a paper dealing with space exploration, the temptation is strong to try to cover everything, from the philosophy of why we are in the space business, to the detailed component description of our own favorite spacecraft . It is therefore, worth while to define the limits of the topic of this paper. The object is to compare the problems encountered in the acquisition of S-band telemetry data from spacecraft during the launch phases, with those encountered in the deep space phases. The paper is also limited to a discussion of the Pioneer, Mariner and Surveyor missions. In the discussion of telemetry mission support, the point of primary concern is data quality, which is directly related to the system signalto- noise ratio (S/N). It is primarily from this point of view that this paper discusses support problems. There were some valid reasons for transferring some telemetry link frequencies from the 215 to 260 MHz band to the 2200 to 2300 MHz band . Of primary importance was the lower noise environment at S-band. Also of importance was the improvement in overall antenna system gain for a given size directional antenna on the ground and on the spacecraft . If you consider system antenna gain as the sum of the transmitting and receiving antenna gains, fixed parabolic sizes will give an increase in system gain proportional to the square of the cormnunication frequency. During launch, an omni-directional spacecraft antenna nrust be used since the spacecraft may not be stabilized and the aspect angles from the multiple ground stations vary widely. Any improvement in system antenna gain with increase in frequency due to the ground antenna alone , is cancelled by the increase in free space attenuation. Even though the transition to S-band improved system performance in the deep space mode, during the launch phases, it did nothing but complicate the acquisition problem with narrower beam widths . For example, the beamwidth of the 85\u27 antennas on the Range decrease from 4 degrees at 230 MHz to 0 . 4 degrees at 2300 .MHz

Evolution of the eyes of vipers with and without infrared-sensing pit organs

We examined lens and brille transmittance, photoreceptors, visual pigments, and visual opsin gene sequences of viperid snakes with and without infrared-sensing pit organs. Ocular media transmittance is high in both groups. Contrary to previous reports, small as well as large single cones occur in pit vipers. Non-pit vipers differ from pit vipers in having a twotiered retina, but few taxa have been examined for this poorly understood feature. All vipers sampled express rh1, sws1 and lws visual opsin genes. Opsin spectral tuning varies but not in accordance with the presence/absence of pit organs, and not always as predicted from gene sequences. The visual opsin genes were generally under purifying selection, with positive selection at spectral tuning amino acids in RH1 and SWS1 opsins, and at retinal pocket stabilization sites in RH1 or LWS (and without substantial differences between pit and nonpit vipers). Lack of evidence for sensory trade-off between viperid eyes (in the aspects examined) and pit organs might be explained by the high degree of neural integration of vision and infrared detection; the latter representing an elaboration of an existing sense with addition of a novel sense organ, rather than involving the evolution of a wholly novel sensory system

Post weaning diarrhea in pigs: risk factors and non‑colistin‑based control strategies

Post-weaning diarrhea (PWD) is one of the most serious threats for the swine industry worldwide. It is commonly associated with the proliferation of enterotoxigenic Escherichia coli in the pig intestine. Colistin, a cationic antibiotic, is widely used in swine for the oral treatment of intestinal infections caused by E. coli, and particularly of PWD. However, despite the effectiveness of this antibiotic in the treatment of PWD, several studies have reported high rates of colistin resistant E. coli in swine. Furthermore, this antibiotic is considered of very high importance in humans, being used for the treatment of infections due to multidrug-resistant (MDR) Gram-negative bacteria (GNB). Moreover, the recent discovery of the mcr-1 gene encoding for colistin resistance in Enterobacteriaceae on a conjugative stable plasmid has raised great concern about the possible loss of colistin effectiveness for the treatment of MDR-GNB in humans. Consequently, it has been proposed that the use of colistin in animal production should be considered as a last resort treatment only. Thus, to overcome the economic losses, which would result from the restriction of use of colistin, especially for prophylactic purposes in PWD control, we believe that an understanding of the factors contributing to the development of this disease and the putting in place of practical alternative strategies for the control of PWD in swine is crucial. Such alternatives should improve animal gut health and reduce economic losses in pigs without promoting bacterial resistance. The present review begins with an overview of risk factors of PWD and an update of colistin use in PWD control worldwide in terms of quantities and microbiological outcomes. Subsequently, alternative strategies to the use of colistin for the control of this disease are described and discussed. Finally, a practical approach for the control of PWD in its various phases is proposed