Simultaneity as an Invariant Equivalence Relation

This paper deals with the concept of simultaneity in classical and relativistic physics as construed in terms of group-invariant equivalence relations. A full examination of Newton, Galilei and Poincar\'e invariant equivalence relations in $\R^4$ is presented, which provides alternative proofs, additions and occasionally corrections of results in the literature, including Malament's theorem and some of its variants. It is argued that the interpretation of simultaneity as an invariant equivalence relation, although interesting for its own sake, does not cut in the debate concerning the conventionality of simultaneity in special relativity.Comment: Some corrections, mostly of misprints. Keywords: special relativity, simultaneity, invariant equivalence relations, Malament's theore

MIMO noise radar - matched filters and coarrays

Copyright © 2008 IEEEThe noise radar concept can be extended to an array of K transmit antenna and M receive antenna. When independent noise sources are transmitted from each antenna the approach may be viewed as a special case of MIMO radar and matched filters may be derived. In this contribution statistical properties of matched filters for MIMO noise radar are derived. For any array the concepts of the sum and difference coarrays are useful and important tools for understanding an arraypsilas beamforming properties particularly for sparse arrays. Element space matched filters are shown to be related to the concept of the sum coarray and some examples of the advantages of this for sparse transmit/receive array geometry are provided. A variation of this result for beam space matched filters is also presented.Douglas A Gray, Amerigo Capri

Reconfigurable radar transmitter based on photonic microwave signal generation

In this paper we propose a photonic technique for a reconfigurable microwave signal generation based on the beating in a photodiode of two laser modes from a regenerative Fiber Mode-Locked Laser (FMLL). The excellent performance of this kind of pulsed laser guarantees high stability to the generated microwave signal even at ultra high frequencies (up to W band). Therefore, by using the proposed architecture, the performance of a reconfigurable full digital coherent radar system can be enhanced in terms of Moving Target Indicator (MTI) improvement factor. Moreover, thanks to the achievable high repetition rates and the coherence properties of the FMLL, this laser scheme has also been proposed for digitizing the received signal by electro-optical sampling. Thus the advantage of using just one device for signal generation in both the transmitter and receiver chain, makes the proposed solution a cost effective architecture for microwave signal generation. Differently from the microwave synthesizers, whose performance strongly deteriorate with increasing frequencies, the photonic radio frequency generation always shows an excellent spectral purity. The results show excellent spectral purity above 5 KHz for the proposed technique compared to a state of the art Agilent synthesizer even though the timing jitter increases for integration time greater than 10 msec. In order to achieve the same stability performance at both high and low frequencies a Phase Locked Loop between the laser and a synthesizer could be used

Peripheral neurological disturbances, autonomic dysfunction, and antineuronal antibodies in adult celiac disease before and after a gluten-free diet

Thirty-two consecutive adult celiac disease (CD) patients (pts), complaining of peripheral neuropathy (12 pts), autonomic dysfunction (17 pts), or both (3 pts), were evaluated to assess the presence of neurological damage (by clinical neurological evaluation and electrophysiological study) and antineuronal antibodies and to assess the effect of a gluten-free diet (GFD) on the course of the neurological symptoms and on antineuronal antibodies. At entry, 12 of 32 (38%) pts showed signs and symptoms of neurological damage: 7 of 12 (58%), peripheral neurological damage; 3 of 12 (25%), autonomic dysfunction; and 2 (17%), both peripheral neurological damage and autonomic dysfunction. The overall TNS score was 105 at entry. Anti-GM1 antibodies were present in 5 of 12 (42%) pts: 3 showed peripheral neurological damage and 2 showed both peripheral neurological damage and autonomic dysfunction. One year after the GFD was started, histological lesions were still present in only 10 of 12 (83%) pts. TNS score was 99, 98, 98, and 101 at the 3rd, 6th, 9th, and 12th month after the GFD was started, so it did not improve throughout the follow-up. None of the pts showed disappearance of antineuronal antibodies throughout the follow-up. We conclude that adult CD patients may show neurological damage and presence of antineuronal antibodies. Unfortunately, these findings do not disappear with a GFD

Locality hypothesis and the speed of light

The locality hypothesis is generally considered necessary for the study of the kinematics of non-inertial systems in special relativity. In this paper we discuss this hypothesis, showing the necessity of an improvement, in order to get a more clear understanding of the various concepts involved, like coordinate velocity and standard velocity of light. Concrete examples are shown, where these concepts are discussed.Comment: 23 page

Variations in the amount of water ice on Ceres' surface suggest a seasonal water cycle.

The dwarf planet Ceres is known to host a considerable amount of water in its interior, and areas of water ice were detected by the Dawn spacecraft on its surface. Moreover, sporadic water and hydroxyl emissions have been observed from space telescopes. We report the detection of water ice in a mid-latitude crater and its unexpected variation with time. The Dawn spectrometer data show a change of water ice signatures over a period of 6 months, which is well modeled as ~2-km2 increase of water ice. The observed increase, coupled with Ceres' orbital parameters, points to an ongoing process that seems correlated with solar flux. The reported variation on Ceres' surface indicates that this body is chemically and physically active at the present time

First mineralogical maps of 4 Vesta

Before Dawn arrived at 4 Vesta only very low spatial resolution (~50 km) albedo and color maps were available from HST data. Also ground-based color and spectroscopic data were utilized as a first attempt to map Vesta’s mineralogical diversity [1-4]. The VIR spectrometer [5] onboard Dawn has ac-quired hyperspectral data while the FC camera [6] ob-tained multi-color data of the Vestan surface at very high spatial resolutions, allowing us to map complex geologic, morphologic units and features. We here re-port about the results obtained from a preliminary global mineralogical map of Vesta, based on data from the Survey orbit. This map is part of an iterative map-ping effort; the map is refined with each improvement in resolution

Mesosiderites on Vesta: A Hyperspectral VIS-NIR Investigation

The discussion about the mesosiderite origin is an open issue since several years. Mesosiderites are mixtures of silicate mineral fragments or clasts, embedded in a FeNi metal matrix. Silicates are very similar in mineralogy and texture to howardites [1]. This led some scientists to conclude that mesosiderites could come from the same parent parent asteroid of the howardite, eucrite and diogenite (HED) meteorites [2, 3]. Other studies found a number of differences between HEDs and mesosiderite silicates that could be explained only by separate parent asteroids [4]. Recently, high precision oxygen isotope measurements of m esosiderites silicate fraction were found to be isotopically identical to the HEDs, requiring common parent body, i.e. 4 Vesta [5]. Another important element in favor of a common origin was given by the identification of a centimeter-sized mesosiderite clast in a howardite (Dar al Gani 779): a metal-rich inclusion with fragments of olivine, anorthite, and orthopyroxene plus minor amounts of chromite, tridymite, and troilite [6]. The Dawn mission with its instruments, the Infrared Mapping Spectrometer (VIR) [7], the Framing Camera [8] and the Gamma-Ray and Neutron Detector (GRaND) [9] confirmed that Vesta has a composition fully compatible with HED meteorites [10]. We investigate here the possibility to discern mesosiderite rich locations on the surface of Vesta by means of hyperspectral IR images