Particle motion in a rotating dust spacetime: the Bonnor solution

We investigate the geometrical properties, spectral classification, geodesics, and causal structure of the Bonnor's spacetime [Journal of Physics A Math. Gen., \textbf{10}, 1673 (1977)], i.e., a stationary axisymmetric solution with a rotating dust as a source. This spacetime has a directional singularity at the origin of the coordinates (related to the diverging vorticity field of the fluid there), which is surrounded by a toroidal region where closed timelike curves (CTCs) are allowed, leading to chronology violations. We use the effective potential approach to provide a classification of the different kind of orbits on the symmetry plane as well as to study the motion parallel to the symmetry axis. In the former case we find that as a general feature test particles released from a fixed space point and directed towards the singularity are repelled and scattered back as soon as they approach the CTC boundary, without reaching the central singularity.Comment: 11 pages, 5 figures (10 eps files

Design of high gradient, high repetition rate damped C-band rf structures

The gamma beam system of the European Extreme Light Infrastructure–Nuclear Physics project foresees the use of a multibunch train colliding with a high intensity recirculated laser pulse. The linac energy booster is composed of 12 traveling wave C-band structures, 1.8 m long with a field phase advance per cell of 2π=3 and a repetition rate of 100 Hz. Because of the multibunch operation, the structures have been designed with a dipole higher order mode (HOM) damping system to avoid beam breakup (BBU). They are quasiconstant gradient structures with symmetric input couplers and a very effective damping of the HOMs in each cell based on silicon carbide (SiC) rf absorbers coupled to each cell through waveguides. An optimization of the electromagnetic and mechanical design has been done to simplify the fabrication and to reduce the cost of the structures. In the paper, after a review of the beam dynamics issues related to the BBU effects, we discuss the electromagnetic and thermomechanic design criteria of the structures. We also illustrate the criteria to compensate the beam loading and the rf measurements that show the effectiveness of the HOM damping

Limitations of Radar Coordinates

The construction of a radar coordinate system about the world line of an observer is discussed. Radar coordinates for a hyperbolic observer as well as a uniformly rotating observer are described in detail. The utility of the notion of radar distance and the admissibility of radar coordinates are investigated. Our results provide a critical assessment of the physical significance of radar coordinates.Comment: 12 pages, revtex and pictex macros, 3 pictex figures, 1 eps figure. Expanded versio

High-pressure vibrational properties of polyethylene

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A null frame for spacetime positioning by means of pulsating sources

We introduce an operational approach to the use of pulsating sources, located at spatial infinity, for defining a relativistic positioning and navigation system, based on the use of four-dimensional bases of null four-vectors, in flat spacetime. As a prototypical case, we show how pulsars can be used to define such a positioning system. The reception of the pulses for a set of different sources whose positions in the sky and periods are assumed to be known allows the determination of the user's coordinates and spacetime trajectory, in the reference frame where the sources are at rest. We describe our approach in flat Minkowski spacetime, and discuss the validity of this and other approximations we have considered.Comment: 19 pages, revised to match the version accepted for publication in Advances in Space Researc

Corrigendum to a new neurocognitive interpretation of shoulder position sense during reaching:unexpected competence in the measurement of extracorporeal space

[This corrects the article DOI: 10.1155/2016/9065495.

Correlates of spinal deforming index (SDI) in HIV-positive patients naive and on treatment

Methods HIV-infected subjects naive or on stable HAART were included. Vertebral deformities were identified using SDI (according to semiquantitative method by Genant), calculated by summing the deformity grades of all vertebrae (T4 to L4); pathological deformities are defined as follow: grade 1 between 20–25%, grade 2 between 26–40%, and grade 3 > >40%. According to WHO criteria, osteopenia and osteoporosis were diagnosed in patients having spine BMD calculated as -1 << T-score << -2.5 and T-score ≤≤2.5, respectively. The correlation between SDI and spine BMD was evaluated by univariate and multivariate linear regression. [Other variables considered: gender, age, current CD4 count, CD4 nadir, BMI, lipid parameters, alcohol intake, smoking habit, physical activity, family history for bone fracture, months of ARV exposure, and co-infection with hepatitis viruses; only the variables with p <<0.2 in univariate analyses were included in the final model.

Proteome analysis of breast cancer cells (8701-BC) cultured from primary ductal infiltrating carcinoma: relation to correspondent breast tissues

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A new neurocognitive interpretation of shoulder position sense during reaching: unexpected competence in the measurement of extracorporeal space

Background.The position sense of the shoulder joint is important during reaching. Objective. To examine the existence of additional competence of the shoulder with regard to the ability to measure extracorporeal space, through a novel approach, using the shoulder proprioceptive rehabilitation tool (SPRT), during reaching. Design. Observational case-control study. Methods. We examined 50 subjects: 25 healthy and 25 with impingement syndrome with a mean age [years] of 64.52 +/− 6.98 and 68.36 +/− 6.54, respectively. Two parameters were evaluated using the SPRT: the integration of visual information and the proprioceptive afferents of the shoulder (Test 1) and the discriminative proprioceptive capacity of the shoulder, with the subject blindfolded (Test 2). These tasks assessed the spatial error (in centimeters) by the shoulder joint in reaching movements on the sagittal plane. Results. The shoulder had proprioceptive features that allowed it to memorize a reaching position and reproduce it (error of 1.22 cm to 1.55 cm in healthy subjects). This ability was lower in the impingement group, with a statistically significant difference compared to the healthy group ( < 0.05 by Mann–Whitney test). Conclusions. The shoulder has specific expertise in the measurement of the extracorporeal space during reaching movements that gradually decreases in impingement syndrome