Satellite gravitational orbital perturbations and the gravitomagnetic clock effect

In order to detect the gravitomagnetic clock effect by means of two counter-orbiting satellites placed on identical equatorial and circular orbits around the Earth with radius 7000 km their radial and azimuthal positions must be known with an accuracy of delta r =10^{-1} mm and delta phi =10^{-2} mas per revolution. In this work we investigate if the radial and azimuthal perturbations induced by the dynamical and static parts of the Earth' s gravitational field meet this requirements. While the radial direction is affected only by harmonic perturbations with periods up to some tens of days, the azimuthal location is perturbed by a secular drift and very long period effects.It results that the present level of accuracy in the knowledge both of the Earth solid and ocean tides, and of the static part of the geopotential does not allow an easy detection of the gravitomagnetic clock effect, at least by using short arcs only.Comment: 18 pages, 4 figures. Submitted to Int. Journal of Mod. Phys.

A Gravitomagnetic Effect on the Orbit of a Test Body due to the Earth's Variable Angular Momentum

The well known general relativistic Lense-Thirring drag of the orbit of a test particle in the stationary field of a central slowly rotating body is generated, in the weak-field and slow-motion approximation of General Relativity, by a gravitomagnetic Lorentz-like acceleration in the equations of motion of the test particle. In it the gravitomagnetic field is due to the central body's angular momentum supposed to be constant. In the context of the gravitational analogue of the Larmor theorem, such acceleration looks like a Coriolis inertial term in an accelerated frame. In this paper the effect of the variation in time of the central body's angular momentum on the orbit of a test mass is considered. It can be shown that it is analogue to the inertial acceleration due to the time derivative of the angular velocity vector of an accelerated frame. The possibility of detecting such effect in the gravitational field of the Earth with LAGEOS-like satellites is investigated. It turns out that the orbital effects are far too small to be measured.Comment: LaTex2e, 1 table, no figures, 7 page

MEASURING GRAVITOMAGNETIC EFFECTS BY MEANS OF RING LASERS

Light is a good probe for general relativistic effects. Exploiting the asymmetry of the propagation in the vicinity of a central rotating mass it is possible to use a ring laser in order to measure the frame dragging of the reference frames by the gravitational field of the Earth (Lense-Thirring effect). I shall present the G-GranSasso experiment whose objective is precisely to measure the Lense-Thirring and the de Sitter effects in a terrestrial laboratory. The experimental apparatus will be made of a set of at least three, differently oriented, ring lasers rigidly attached to a central "monument". The signal will be in the form of the beat frequency produced in the annular cavity of each laser by the rotational anisotropy. The laboratory will be located underground in the Laboratori Nazionali del Gran Sasso facility, in Italy. The required sensitivity is just one order of magnitude below the performance of the best existing instruments and the new design will attain i

Can Solar System observations tell us something about the cosmological constant?

In this note we show that the latest determinations of the residual Mercury's perihelion advance, obtained by accounting for almost all known Newtonian and post-Newtonian orbital effects, yields only very broad constraints on the cosmological constant. Indeed, from \delta\dot\omega=-0.0036 + - 0.0050 arcseconds per century one gets -2 10^-34 km^-2 < Lambda < 4 10^-35 km^-2. The currently accepted value for Lambda, obtained from many independent cosmological and large-scale measurements, amounts to almost 10^-46 km^-2.Comment: Latex2e, 4 pages, 2 table, no figures, 11 references. Table 2 added, typos in the units of Lambda correcte

External Factors Affecting the Performance of Micro and Small Enterprises (MSES): a Study on Selected MSEs in Bedele Town

The study was designed to assess the external factors affecting the performance of Micro and Small Enterprises (MSEs) in Bedele town. A sample of 297 operators or owners of the enterprises engaged in five sectors was taken for the study using stratified random sampling technique. The head of Bedele micro and small enterprises development agency was purposely selected for the interview. From the distributed 297 questionnaires 269 were returned. The data collected through questionnaire is analyzed using both descriptive and inferential analysis (Pearson's product moment correlation coefficient and Multiple Linear Regression Model). Besides, the interview questions were analyzed using descriptive narrations. The empirical finding elucidated that factors affect the performance of MSEs which include; accessibility of external source of finance, accessibility of business development services and marketing factors are significantly affect the performance of micro and small enterprises in Bedele town. While, government policy and bureaucracy and infrastructure are found to be insignificantly explaining the performance of MSEs. The finding further indicate that, the existence of linear and positive significant, ranging from weak to strong relationship was found between independent variables and dependent variable. Based on the findings recommendations to stakeholders, to operators of MSEs and suggestions for further researchers are forwarded.Jimma Universit

Gravitomagnetic time delay and the Lense-Thirring effect in Brans-Dicke theory of gravity

We discuss the gravitomagnetic time delay and the Lense-Thirring effect in the context of Brans-Dicke theory of gravity. We compare the theoretical results obtained with those predicted by general relativity. We show that within the accuracy of experiments designed to measure these effects both theories predict essentially the same result.Comment: 10 pages Typeset using REVTE

Glaciation in Montana

Glacial deposits are increasingly entering into consideration in engineering projects, soil surveys, ground-water supply, sources for industrial materials, and other economic enterprises. In the field of en­gineering, glacial deposits if present must be consider­ed in connection with reservoir sites, dam or bridge abutments, road building, and other types of construction work

Personal reflection in medical education

Medical doctors are nowadays expected to be able to reflect in both a scientific and a personal manner in order to be an excellent doctor. However, more precise knowledge is needed about the construct of personal reflection, as applied in the daily practice, and about the related educational strategies. Personal reflection is defined as: the careful exploration and appraisal of experience, thus clarifying and creating meaning for the benefit of balanced conduct, learning and development, and the well-being of the doctor. An educational model for medical educators, using the angler’s float as a metaphor, is described. The ‘behaviour’ of the reflective practitioner is visible above the water level; beneath the surface are cognitive-affective levels of thinking: ‘clinical reasoning’, ‘scientific reflection’, ‘personal reflection’ and ‘unconscious thinking’. A new scale to measure personal reflection, the Groningen Reflection Ability Scale (GRAS), was developed and validated. The GRAS proved to yield reliable data that contribute to valid inferences about the personal reflection ability of medical students and doctors. The expectation that ‘experiential learning’ is an effective educational method for encouragement of reflection was tested. We could conclude that enhanced experiential learning has a positive effect on the development of personal reflection of undergraduate medical students. A conceptual framework was described, for a more precise understanding of personal reflection in order to identify, use, and encourage it. Reflection was defined as a competence for the medical education continuum. Artsen moeten tegenwoordig wetenschappelijk èn persoonlijk kunnen reflecteren om een excellente arts te worden en te blijven. Beide soorten reflectie zijn in gelijke mate nodig om evenwichtig te functioneren. Dat is van belang voor de kwaliteit van de medische zorg, het ontwikkelen van allround vakmanschap en professionaliteit, inter-professionele samenwerking en ook voor hun eigen welbevinden. Dit proefschrift richt zich op persoonlijk reflecteren. Artsen die persoonlijk kunnen reflecteren zijn in staat met aandacht te functioneren richting patiënten en collega’s. Zij zijn zich bewust van en leren van hun praktijkervaringen en hun emoties/gevoelens, lichamelijke gewaarwordingen, gedachten en beelden. En zij weten de door reflectie opgedane inzichten te gebruiken voor de verbetering van hun functioneren en de medische behandeling. Dit proefschrift rapporteert over verschillende projecten. Er is een onderwijskundig model ontwikkeld, ‘het dobbermodel’, waarmee persoonlijke reflectie concreet gemaakt kan worden voor medische docenten. Boven water steekt het zichtbare gedrag. Onder water bevinden zich de verschillende lagen van denken: klinisch redeneren, wetenschappelijk reflecteren, persoonlijk reflecteren en onbewust denken. Er is een instrument, de Groningen Reflection Ability Scale (GRAS), ontwikkeld en gevalideerd waarmee het persoonlijke reflectievermogen van medische studenten kan worden gemeten. Het effect van de methode van ervaringsleren op de groei van het reflectievermogen van eerstejaars medische studenten is onderzocht. Er is een positief effect vastgesteld. Verder is een conceptueel raamwerk gemaakt om wetenschappelijke en persoonlijke reflectie beter te kunnen begrijpen en in de praktijk te kunnen gebruiken en bevorderen. Tot slot is reflectie als competentie voor het medisch onderwijs gedefinieerd.

Trajectory of test particle around a slowly rotating relativistic star emitting isotropic radiation

We explored the motion of test particles near slowly rotating relativistic star having a uniform luminosity. In order to derive the test particle's equations of motion, we made use of the radiation stress-energy tensor first constructed by Miller and Lamb \cite{ML96}. From the particle's trajectory obtained through the numerical integration of the equations of motion, it is found that for sufficiently high luminosity, "suspension orbit" exists, where the test particle hovers around at uniform angular velocity in the same direction as the star's spin. Interestingly, it turned out that the radial position of the "suspension orbit" was determined by the luminosity and the angular momentum of the star alone and was independent of the initial positions and the specific angular momentum of the particle. Also found is that there exist not only the radiation drag but also "radiation counter-drag" which depends on the stellar radius and the angular momentum and it is this radiation counter-drag that makes the test particle in the "suspension orbit" to hover around at uniform angular velocity which is greater than that induced by the Lense-Thirring effect (i.e., general relativistic dragging of inertial frame).Comment: 23 pages, 7 figures, to appear in Phys. Rev. D