2,674 research outputs found
Impedance and loss factor of a coaxial liner with many holes: effect of the attenuation
In the framework of the modified Bethe's diffraction theory, we study the energy lost by a relativistic particle beam traveling in a coaxial liner with many holes, including the effect of attenuation in the coaxial region. The interference among the holes is the main source of losses and is affected by the attenuation in the coaxial only over sufficiently long distances. We derive analytical formulas for all the interesting quantities and particular attention is given to clarifying the physical meaning of the results; numerical examples are considered using LHC-like parameters. (17 refs)
On the time delay in binary systems
The aim of this paper is to study the time delay on electromagnetic signals
propagating across a binary stellar system. We focus on the antisymmetric
gravitomagnetic contribution due to the angular momentum of one of the stars of
the pair. Considering a pulsar as the source of the signals, the effect would
be manifest both in the arrival times of the pulses and in the frequency shift
of their Fourier spectra. We derive the appropriate formulas and we discuss the
influence of different configurations on the observability of gravitomagnetic
effects. We argue that the recently discovered PSR J0737-3039 binary system
does not permit the detection of the effects because of the large size of the
eclipsed region.Comment: 7 pages, 2 eps figures, RevTex, to appear in Physical Review
On the possibility of measuring the Earth's gravitomagnetic force in a new laboratory experiment
In this paper we propose, in a preliminary way, a new Earth-based laboratory
experiment aimed to the detection of the gravitomagnetic field of the Earth. It
consists of the measurement of the difference of the circular frequencies of
two rotators moving along identical circular paths, but in opposite directions,
on a horizontal friction-free plane in a vacuum chamber placed at South Pole.
The accuracy of our knowledge of the Earth's rotation from VLBI and the
possibility of measuring the rotators'periods over many revolutions should
allow for the feasibility of the proposed experiment.Comment: Latex2e, 8 pages, no figures, no tables, accepted for publication by
Classical and Quantum Gravity. Typo corrected in the formula of the error in
the difference of the orbital period
A stochastic-hydrodynamic model of halo formation in charged particle beams
The formation of the beam halo in charged particle accelerators is studied in
the framework of a stochastic-hydrodynamic model for the collective motion of
the particle beam. In such a stochastic-hydrodynamic theory the density and the
phase of the charged beam obey a set of coupled nonlinear hydrodynamic
equations with explicit time-reversal invariance. This leads to a linearized
theory that describes the collective dynamics of the beam in terms of a
classical Schr\"odinger equation. Taking into account space-charge effects, we
derive a set of coupled nonlinear hydrodynamic equations. These equations
define a collective dynamics of self-interacting systems much in the same
spirit as in the Gross-Pitaevskii and Landau-Ginzburg theories of the
collective dynamics for interacting quantum many-body systems. Self-consistent
solutions of the dynamical equations lead to quasi-stationary beam
configurations with enhanced transverse dispersion and transverse emittance
growth. In the limit of a frozen space-charge core it is then possible to
determine and study the properties of stationary, stable core-plus-halo beam
distributions. In this scheme the possible reproduction of the halo after its
elimination is a consequence of the stationarity of the transverse distribution
which plays the role of an attractor for every other distribution.Comment: 18 pages, 20 figures, submitted to Phys. Rev. ST A
Renal health after long-term exposure to tenofovir disoproxil fumarate (TDF) in HIV/HBV positive adults in Ghana
Objectives: The study assessed markers of renal health in HIV/HBV co-infected patients receiving TDF- containing antiretroviral therapy in Ghana.
Methods: Urinary protein-to-creatinine ratio (uPCR) and albumin-to-protein ratio (uAPR) were measured cross-sectionally after a median of four years of TDF. At this time, alongside extensive laboratory testing, patients underwent evaluation of liver stiffness and blood pressure. The estimated glomerular filtration rate (eGFR) was measured longitudinally before and during TDF therapy.
Results: Among 101 participants (66% women, median age 44 years, median CD4 count 572 cells/mm 3 ) 21% and 17% had detectable HIV-1 RNA and HBV DNA, respectively. Overall 35% showed hypertension, 6% diabetes, 7% liver stiffness indicative of cirrhosis, and 18% urinary excretion of Schistosoma antigen. Tubular proteinuria occurred in 16% of patients and was independently predicted by female gender and hypertension. The eGFR declined by median 1.8 ml/min/year during TDF exposure (IQR −4.4, −0.0); more pronounced declines ( ≥5 ml/min/year) occurred in 22% of patients and were associated with receiv-ing ritonavir-boosted lopinavir rather than efavirenz. HBV DNA, HBeAg, transaminases, and liver stiffness were not predictive of renal function abnormalities.
Conclusions: The findings mandate improved diagnosis and management of hypertension and suggest targeted laboratory monitoring of patients receiving TDF alongside a booster in sub-Saharan Africa
Wakefields due to surface waves in a beam pipe with a periodic rough surface
The problem of the wakefields generated by an ultrarelativistic particle traveling in a long beam tube with a periodic rough surface has been revisited by means of a standard theory based on the hybrid modes excited in a periodically corrugated rectangular waveguide. Slow surface waves synchronous with the particle can be excited in the structure, producing wakefields whose frequency and amplitude depend on the depth of the corrugation. We apply our results to the case of the CERN Large Hadron Collider beam screen and the Linac Coherent Light Source undulator. (19 refs)
Gravito-electromagnetism versus electromagnetism
The paper contains a discussion of the properties of the gravito-magnetic
interaction in non stationary conditions. A direct deduction of the equivalent
of Faraday-Henry law is given. A comparison is made between the
gravito-magnetic and the electro-magnetic induction, and it is shown that there
is no Meissner-like effect for superfluids in the field of massive spinning
bodies. The impossibility of stationary motions in directions not along the
lines of the gravito-magnetic field is found. Finally the results are discussed
in relation with the behavior of superconductors.Comment: 13 Pages, LaTeX, 1 EPS figure, to appear in European Journal of
Physic
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