Investigations of laser pumped gas cell atomic frequency standard

The performance characteristics of a rubidium gas cell atomic frequency standard might be improved by replacing the standard rubidium discharge lamp with a single mode laser diode. Aspects of the laser pumped gas cell atomic clock studied include effects due to laser intensity, laser detuning, and the choice of the particular atomic absorption line. Results indicate that the performance of the gas cell clock may be improved by judicious choice of the operating parameters of the laser diode. The laser diode also proved to be a valuable tool in investigating the operation of the conventional gas cell clock. Results concerning linewidths, the light shift effect and the effect of isotopic spin exchange in the conventional gas cell clock are reported

Automated Classification of 2000 Bright IRAS Sources

An Artificial Neural Network (ANN) has been employed using a supervised back-propagation scheme to classify 2000 bright sources from the Calgary database of IRAS (Infrared Astronomy Satellite) spectra in the wavelength region of 8-23 microns. The data base has been classified into 17 pre-determined classes based on spectral morphology. We have been able to classify more than 80 percent of the 2000 sources correctly at the first instance. The speed and robustness of the scheme will allow us to classify the whole of LRS database, containing more than 50,000 sources in the future.Comment: 26 pages, To appear in ApJS after July 200

Lamp reliability studies for improved satellite rubidium frequency standard

In response to the premature failure of Rb lamps used in Rb atomic clocks onboard NAVSTAR GPS satellites experimental and theoretical investigations into their failure mechanism were initiated. The primary goal of these studies is the development of an accelerated life test for future GPS lamps. The primary failure mechanism was identified as consumption of the lamp's Rb charge via direct interaction between Rb and the lamp's glass surface. The most effective parameters to accelerate the interaction between the Rb and the glass are felt to be RF excitation power and lamp temperature. Differential scanning calorimetry is used to monitor the consumption of Rb within a lamp as a function of operation time. This technique yielded base line Rb consumption data for GPS lamps operating under normal conditions

Laser induced asymmetry and inhomogeneous broadening of the microwave lineshape of a gas cell atomic frequency standard

The possibility of replacing the RF discharge lamp in a rubidium gas cell clock with a single mode laser diode is addressed. Since the short term stability of the rubidium frequency standard is limited by the shot noise of the photodetector, an increased signal-to-noise ratio due to more efficient laser diode optical pumping might improve the short term performance. Because the emission wavelength of the laser diode can be tuned, improved long term performance could be gained through the control of the light shift effect. However, due to the nature of the gas cell frequency standard, various physical phenomena are strongly coupled in their effect on the frequency output, and thus careful consideration must be given to any change in one parameter because of its interrelation with other parameters. Some investigations concerning the coupled effect of the optical and microwave fields in the rubidium atomic clock are reported. It is shown that this type of coupling is an important consideration for any attempt to incorporate a laser diode into a gas cell clock

Development of learning objectives for neurology in a veterinary curriculum: part I: undergraduates

Background With an increasing caseload of veterinary neurology patients in first opinion practice, there is a requirement to establish relevant learning objectives for veterinary neurology encompassing knowledge, skills and attitudes for veterinary undergraduate students in Europe. With help of experts in veterinary neurology from the European College of Veterinary Neurology (ECVN) and the European Society of Veterinary Neurology (ESVN) a survey of veterinary neurologic learning objectives using a modified Delphi method was conducted. The first phase comprised the development of a draft job description and learning objectives by a working group established by the ECVN. In the second phase, a quantitative questionnaire (multiple choice, Likert scale and free text) covering 140 learning objectives and subdivided into 8 categories was sent to 341 ESVN and ECVN members and a return rate of 62% (n = 213/341) was achieved. Results Of these 140 learning objectives ECVN Diplomates and ESVN members considered 42 (30%) objectives as not necessary for standard clinical veterinary neurology training, 94 (67%) were graded to be learned at a beginner level and 4 (3%) at an advanced level. The following objectives were interpreted as the most important day one skills: interpret laboratory tests, perform a neurological examination and establish a neuroanatomical localization. In this survey the three most important diseases of the central nervous system included epilepsy, intervertebral disc disease and inflammatory diseases. The three most important diseases of the peripheral nervous system included polyradiculoneuritis, myasthenia gravis and toxic neuropathies. Conclusions The results of this study should help to reform the veterinary curriculum regarding neurology and may reduce the phenomenon of “Neurophobia”.</p

Species Matrix for New York State

Species selection is an important step in the design of effective and efficient living snow fences. A species matrix assists in the plant selection process for living snow fences by providing a pallete of suitable species, and a summary of relevant plant traits to compare and contrast species. Recent research at SUNY ESF has built on previous research (Tabler, 2003) and identified key plant traits for living snow fences. Twenty-eight species that possess the traits relevant to living snow fences have been identified and included in this plant matrix. These species are tolerant to a variety of roadside conditions across New York State, and possess the traits necessary to achieve adequate snow trapping and snow storage capabilities. Every plant species is unique, and this matrix is therefore intended as a selection tool to compare and contrast a variety of plants for living snow fences within the context of design goals and site conditions

ПРОБЛЕМИ РАЦІОНАЛЬНОГО ПРИРОДОКОРИСТУВАННЯ НА ТЕРИТОРІЯХ АГРОМЕЛІОРАТИВНИХ ЛАНДШАФТІВ ЗОНИ ПОЛІССЯ УКРАЇНИ

The article presents the problems of rational nature use in theterritories of agromeliorative landscapes in Ukrainian part of Polissiaregion and ways to solve themВ статье представлены проблемы рационального природопользования на территориях агромелиоративных ландшафтов зоны Полесья Украины и пути их решения.У статті представлено проблеми раціонального природокористування на територіях агромеліоративних ландшафтів зони Полісся України та шляхи їх вирішення