3,836 research outputs found
Charged Particle Dynamics in the Field of a Slowly Rotating Compact Star
We study the dynamics of a charged particle in the field of a slowly rotating
compact star in the gravitoelectromagnetic approximation to the geodesic
equation . The star is assumed to be surrounded by an ideal, highly conducting
plasma (taken as a magnetohydrodynamic fluid) with a stationary, axially
symmetric electromagnetic field. The general relativistic Maxwell equations are
solved to obtain the effects of the background spacetime on the electromagnetic
field in the linearized Kerr spacetime. The equations of motion are then set up
and solved numerically to incorporate the gravitational as well as the
electromagnetic effects. The analysis shows that in the slow rotation
approximation the frame dragging effects on the electromagnetic field are
absent. However the particle is directly effected by the rotating gravitational
source such that close to the star the gravitational and electromagnetic field
produce contrary effects on the particle's trajectory.Comment: 10 pages, 6 figures in B & W PostScript Forma
A post-Keplerian parameter to test gravito-magnetic effects in binary pulsar systems
We study the pulsar timing, focusing on the time delay induced by the
gravitational field of the binary systems. In particular, we study the
gravito-magnetic correction to the Shapiro time delay in terms of Keplerian and
post-Keplerian parameters, and we introduce a new post-Keplerian parameter
which is related to the intrinsic angular momentum of the stars. Furthermore,
we evaluate the magnitude of these effects for the binary pulsar systems known
so far. The expected magnitude is indeed small, but the effect is important per
se.Comment: 6 pages, RevTeX, 1 eps figure, accepted for publication in Physical
Review D; references adde
Doppler Effects from Bending of Light Rays in Curved Space-Times
We study Doppler effects in curved space-time, i.e. the frequency shifts
induced on electromagnetic signals propagating in the gravitational field. In
particular, we focus on the frequency shift due to the bending of light rays in
weak gravitational fields. We consider, using the PPN formalism, the
gravitational field of an axially symmetric distribution of mass. The zeroth
order, i.e. the sphere, is studied then passing to the contribution of the
quadrupole moment, and finally to the case of a rotating source. We give
numerical estimates for situations of physical interest, and by a very
preliminary analysis, we argue that analyzing the Doppler effect could lead, in
principle, in the foreseeable future, to the measurement of the quadrupole
moment of the giant planets of the Solar System.Comment: 16 pages, 2 EPS figures; to appear in the International Journal of
Modern Physics
The Ground CO2 Mapper. An innovative tool for the rapid and precise mapping of CO2 leakage distribution
The recently developed Ground CO2 Mapper (“Mapper” for short) is an inexpensive, light, robust, and
low power consuming tool for determining the distribution of CO2 at the soil-atmosphere contact as
an indicator of CO2 leakage. The basic premise behind the Mapper is that the contact between the
ground surface and the atmosphere represents an interval where CO2 leaking from the subsurface
can accumulate in anomalous concentrations due to two mechanisms, the higher density of CO2 with
respect to air and the tendency of wind speed (and thus mixing) to approach zero near the ground
surface due to frictional drag. Because of its measurement target and the tool’s very rapid response
time, Mapper surveys can be conducted very quickly at a high sampling density, yielding accurate
maps of CO2 spot anomalies. The unit can be used by anyone and deployed within only 5-10 minutes
after sensor and GPS signal warm-up. Here we describe the Mapper and present results from a site
of natural diffuse CO2 degassing in central Italy
Gravitomagnetism and the Speed of Gravity
Experimental discovery of the gravitomagnetic fields generated by
translational and/or rotational currents of matter is one of primary goals of
modern gravitational physics. The rotational (intrinsic) gravitomagnetic field
of the Earth is currently measured by the Gravity Probe B. The present paper
makes use of a parametrized post-Newtonian (PN) expansion of the Einstein
equations to demonstrate how the extrinsic gravitomagnetic field generated by
the translational current of matter can be measured by observing the
relativistic time delay caused by a moving gravitational lens. We prove that
measuring the extrinsic gravitomagnetic field is equivalent to testing
relativistic effect of the aberration of gravity caused by the Lorentz
transformation of the gravitational field. We unfold that the recent Jovian
deflection experiment is a null-type experiment testing the Lorentz invariance
of the gravitational field (aberration of gravity), thus, confirming existence
of the extrinsic gravitomagnetic field associated with orbital motion of
Jupiter with accuracy 20%. We comment on erroneous interpretations of the
Jovian deflection experiment given by a number of researchers who are not
familiar with modern VLBI technique and subtleties of JPL ephemeris. We propose
to measure the aberration of gravity effect more accurately by observing
gravitational deflection of light by the Sun and processing VLBI observations
in the geocentric frame with respect to which the Sun is moving with velocity
30 km/s.Comment: 16 pages, no figure
[The role of endoscopy in gastroenteropancreatic neuroendocrine tumors].
[The role of endoscopy in gastroenteropancreatic
neuroendocrine tumors].
[Article in Italian]
Magno L, Sivero L, Napolitano V, Ruggiero S, Fontanarosa G, Massa S.
Source
Dipartmento di Chirurgia Generale, Geriatrica ed Endoscopia Diagnostica ed Geriatrica, Universitá
degli Studi, Federico II di Napoli.
Abstract
Versione italiana Riassunto: Il ruolo dell'endoscopia nei tumori neuroendocrini
gastroenteropancreatici. L. Magno, L. Sivero, V. Napolitano, S. Ruggiero, G.
Fontanarosa, S. Massa I tumori neuroendocrini (NET) gastro-entero-pancreatici (GEP)
sono neoplasie rare che originano dalle cellule neuroendocrine del tubo digerente e
del pancreas. L'endoscopia digestiva e l'ecoendoscopia rivestono un ruolo importante
nella diagnosi, stadiazione e sorveglianza dei pazienti con NET. Inoltre, in casi
selezionati, le tecniche endoscopiche operative consentono il trattamento di queste
neoplasie in fase precoce. English version Summary: The role of endoscopy in
gastroenteropancreatic neuroendocrine tumors. L. Magno, L. Sivero, V. Napolitano, S.
Ruggiero, G. Fontanarosa, S. Massa Gastroenteropancreatic (GEP) neuroendocrine
tumors (NET) are rare neoplasia arisen from neuroendocrine cells present in the gut
mucosa and pancreas. Digestive endoscopy and endoscopic ultrasonography play a
relevant role in NET diagnosis, stadiation and surveillance. Moreover, in selected
patients, surgical endoscopy allows the tratment of these cancers at an early stage
Non-volcanic CO2 and CH4 degassing in an actively extending orogen, southern Apennines, Italy
The southern Apennines fold and thrust belt has been undergoing post-orogenic extension since ca. 700
kyr. Crustal extension controls active tectonics and seismogenesis in the mountain chain [1], with
seismicity being characterized by low to moderate magnitude events punctuated by strong earthquakes
[2]. Effective decoupling between deep and shallow structural levels is related to the strong rheological
contrast produced by a fluid-saturated, clay-rich mélange zone interposed between buried
autochthonous carbonates – continuous with those exposed in the Apulian foreland – and the
allochthonous units. This mélange zone also acts as a seal preventing the migration of deep-seated
aqueous fluids – as well as oil in the Basilicata region, which hosts the largest Europe’s onshore oil fields
– towards the surface.
On the other hand, the mountain belt is characterized by substantial gas flow, recorded as both
distributed soil gas emissions and vigorous gas vents, associated with active faults at the surface. We
measured a CO2 flux up to 34000 g/m-2 per day at a gas vent, as well as large amounts of He (up to 52
ppm), Rn (up to 228 kBq/m3) and CH4 (up to 5000 ppm).
Overpressured CO2, which has been proposed as triggering normal fault earthquakes in the Apennines,
has been interpreted as mostly of mantle origin. However, our new results from isotope analyses carried
out on the carbon contained in both CO2 and CH4 indicate a dominant thermogenic origin for these
gases, probably associated with the emplacement of magmatic sills within the lower section of the thick
carbonate platform succession occurring at the base of the sedimentary cover in the southern
Apennines. Our results bear major implication concerning the postulated occurrence of crustal faults
allowing fluids to migrate directly from mantle depths to the surface
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