On lattice chiral gauge theories

The Smit-Swift-Aoki formulation of a lattice chiral gauge theory is presented. In this formulation the Wilson and other non invariant terms in the action are made gauge invariant by the coupling with a nonlinear auxilary scalar field, omega. It is shown that omega decouples from the physical states only if appropriate parameters are tuned so as to satisfy a set of BRST identities. In addition, explicit ghost fields are necessary to ensure decoupling. These theories can give rise to the correct continuum limit. Similar considerations apply to schemes with mirror fermions. Simpler cases with a global chiral symmetry are discussed and it is shown that the theory becomes free at decoupling. Recent numerical simulations agree with those considerations

Gamma-Ray Astronomy around 100 TeV with a large Muon Detector operated at Very High Altitude

Measurements at 100 TeV and above are an important goal for the next generation of high energy gamma-ray astronomy experiments to solve the still open problem of the origin of galactic cosmic rays. The most natural experimental solution to detect very low radiation fluxes is provided by the Extensive Air Shower (EAS) arrays. They benefit from a close to 90% duty cycle and a very large field of view (about 2 sr), but the sensitivity is limited by their angular resolution and their poor cosmic ray background discrimination. Above 10 TeV the standard technique for rejecting the hadronic background consists in looking for "muon-poor" showers. In this paper we discuss the capability of a large muon detector (A=2500 m2) operated with an EAS array at very high altitude (>4000 m a.s.l.) to detect gamma-ray fluxes around 100 TeV. Simulation-based estimates of energy ranges and sensitivities are presented.Comment: 4 pages, proceedings of the 30th ICRC, Merida, Mexico, 200

Mars Observer Radar Altimeter Radiometer (MORAR)

The Mars Observer Project will permit the advancement of the state of the topographic and hypsometric knowledge of Mars to a level of 10 m or better over the surface of the planet Mars, the measurement of microwave surface brightness temperature of Mars with an accuracy of 15 to 20 K over 24 hours, and the measurement, globally, of surface returned power related to radar cross section with an accuracy of 1 dB and a repeatability of .5 dB. The MORAR Hardware Development, Ground Data Processing, and the Mission Operations will allow the accomplishment of these scientific objectives to define globally the topography of Mars at sufficient vertical resolution and spatial scale to address both large-scale geophysical and small-scale geologic problems, and to obtain global surface electrical and scattering properties of the upper several centimeters of the Martian surface for assessment of the composition, physical state, and volatile distribution of the surface

Transmission Power Measurements for Wireless Sensor Nodes and their Relationship to the Battery Level

In this work we focus on the new generation EYESIFXv2 [1] wireless sensor nodes by carrying out experimental measurements on power related quantities. In particular, our aim is to characterize the relationship between the level of the battery and the transmission power radiated by the node. The present results point out the non linear and non trivial effects due to the output potentiometer which can be used to tune the transmission power. It shall be observed that a thorough study of how battery and/or potentiometer settings translate to actual transmitted power levels is crucial to e.g. design correct power control algorithms, which can effectively operate under any operational condition of the wireless sensor device

Coherent phenomena in semiconductors

A review of coherent phenomena in photoexcited semiconductors is presented. In particular, two classes of phenomena are considered: On the one hand the role played by optically-induced phase coherence in the ultrafast spectroscopy of semiconductors; On the other hand the Coulomb-induced effects on the coherent optical response of low-dimensional structures. All the phenomena discussed in the paper are analyzed in terms of a theoretical framework based on the density-matrix formalism. Due to its generality, this quantum-kinetic approach allows a realistic description of coherent as well as incoherent, i.e. phase-breaking, processes, thus providing quantitative information on the coupled ---coherent vs. incoherent--- carrier dynamics in photoexcited semiconductors. The primary goal of the paper is to discuss the concept of quantum-mechanical phase coherence as well as its relevance and implications on semiconductor physics and technology. In particular, we will discuss the dominant role played by optically induced phase coherence on the process of carrier photogeneration and relaxation in bulk systems. We will then review typical field-induced coherent phenomena in semiconductor superlattices such as Bloch oscillations and Wannier-Stark localization. Finally, we will discuss the dominant role played by Coulomb correlation on the linear and non-linear optical spectra of realistic quantum-wire structures.Comment: Topical review in Semiconductor Science and Technology (in press) (Some of the figures are not available in electronic form