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

The Evidence Behind the Treatment of Canine Idiopathic Epilepsy

Oral phenobarbital and imepitoin in particular, followed by potassium bromide and levetiracetam are likely to be effective for the treatment of canine idiopathic epilepsy. There is strong evidence supporting the use of oral phenobarbital and imepitoin as ‘first line’ medications. However, there remains a lack of evidence for targeted treatment for the various individual epileptic phenotypes and quite limited evidence on direct comparisons of the efficacy between various anti-epileptic drugs

The Evidence Behind the Diagnostic Investigation of Canine Idiopathic Epilepsy

<p><strong>Clinical bottom line</strong></p><p>There remains until recently an overall lack of clarity for the practical criteria for the diagnosis of canine idiopathic epilepsy. Signalment and an interictal neurological examination are vital for the diagnosis of idiopathic epilepsy. Despite the current insufficient evidence, the emerge of new diagnostic methods, such as cerebrospinal fluid and/or serum biomarkers, advanced functional neuroimaging techniques and electroencephalography, is likely to change the diagnostic approach in canine epilepsy in the near future.</p

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

Reflection-plane tests of spoilers on an advanced technology wing with a large Fowler flap

Wind tunnel experiments were conducted to determine the effectiveness of spoilers applied to a finite-span wing which utilizes the GA(W)-1 airfoil section and a 30% chord full-span Fowler flap. A series of spoiler cross sectioned shapes were tested utilizing a reflection-plane model. Five-component force characteristics and hinge moment measurements were obtained. Results confirm earlier two-dimensional tests which showed that spoilers could provide large lift increments at any flap setting, and that spoiler control reversal tendencies could be eliminated by providing a vent path from lower surface to upper surface. Performance penalties due to spoiler leakage airflow were measured

Physiological reactivity to spontaneously occurring seizure activity in dogs with epilepsy and their carers

There is a complex bidirectional relationship between stress and epilepsy. Stressful stimuli and subsequent cortisol release act as a trigger for seizure activity in some individuals with epilepsy, and seizure activity itself may act as a stressor to the affected individual. Epilepsy is the most common chronic neurological condition in domestic dogs and requires chronic management by their human carers, impacting upon the quality of life of both dog and carer. Seizures occur unpredictably and may be stressful for carers to witness and manage. In the present study we investigated the role of seizure activity as a stressor, measuring the effect of spontaneously occurring seizure activity in dogs with epilepsy upon their own cortisol levels and that of their carers. Furthermore, we tested whether individual differences in HPA reactivity were associated with owner personality characteristics and the quality of the dog carer relationship. Saliva samples were obtained from sixteen dog carer dyads in the home setting 20 and 40 minute post-seizure, and at time-matched points on the following (non-seizure) day. Significant differences in cortisol levels were found in dogs at 40 minute post-seizure (265.1% increase), and at 20 minute post-seizure in their carers (40.5% increase). No associations were found between cortisol reactivity and the strength of the dog-carer bond. Carers with higher neuroticism scores exhibited higher cortisol levels at both post-seizure sampling points. As there was a gender bias in the carer sample (15/16 were female), and there are known sex differences in cortisol reactivity in response to psychological stress, the conclusions of this study may be limited to female carers. These findings are the first to objectively demonstrate the acutely stressful effects of seizures in dogs with epilepsy and their carers

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

Constraints on Cold Dark Matter in the Gamma-ray Halo of NGC 253

A gamma-ray halo in a nearby starburst galaxy NGC 253 was found by the CANGAROO-II Imaging Atmospheric Cherenkov Telescope (IACT). By fitting the energy spectrum with expected curves from Cold Dark Matter (CDM) annihilations, we constrain the CDM-annihilation rate in the halo of NGC 253. Upper limits for the CDM density were obtained in the wide mass range between 0.5 and 50 TeV. Although these limits are higher than the expected values, it is complementary important to the other experimental techniques, especially considering the energy coverage. We also investigate the next astronomical targets to improve these limits.Comment: 13 pages, 5 figures, aastex.cls, natbib.sty, To appear in ApJ v596n1, Oct. 10, 200

Gamma Rays from Clusters and Groups of Galaxies: Cosmic Rays versus Dark Matter

Clusters of galaxies have not yet been detected at gamma-ray frequencies; however, the recently launched Fermi Gamma-ray Space Telescope, formerly known as GLAST, could provide the first detections in the near future. Clusters are expected to emit gamma rays as a result of (1) a population of high-energy primary and re-accelerated secondary cosmic rays (CR) fueled by structure formation and merger shocks, active galactic nuclei and supernovae, and (2) particle dark matter (DM) annihilation. In this paper, we ask the question of whether the Fermi telescope will be able to discriminate between the two emission processes. We present data-driven predictions for a large X-ray flux limited sample of galaxy clusters and groups. We point out that the gamma ray signals from CR and DM can be comparable. In particular, we find that poor clusters and groups are the systems predicted to have the highest DM to CR emission at gamma-ray energies. Based on detailed Fermi simulations, we study observational handles that might enable us to distinguish the two emission mechanisms, including the gamma-ray spectra, the spatial distribution of the signal and the associated multi-wavelength emissions. We also propose optimal hardness ratios, which will help to understand the nature of the gamma-ray emission. Our study indicates that gamma rays from DM annihilation with a high particle mass can be distinguished from a CR spectrum even for fairly faint sources. Discriminating a CR spectrum from a light DM particle will be instead much more difficult, and will require long observations and/or a bright source. While the gamma-ray emission from our simulated clusters is extended, determining the spatial distribution with Fermi will be a challenging task requiring an optimal control of the backgrounds.Comment: revised to match resubmitted version, 35 pages, 16 figures: results unchanged, some discussion added and unnecessary text and figures remove