Narrow Results

WWW, its interfaces and tools, can represent a big opportunity to solve some historical problems of the astronomers. After a description of the state of the Italian Astronomy and Astrophysics environment, with special emphasis to the network usage and to the development of two challenging new technology telescopes, some of the more important (for us) topics are discussed. Several of the major points described in this paper have been outlined and exposed by several authors during a recent Workshop devoted to the first experiments with WWW in the Italian Astronomical Observatories. The application to a very promising field, the astronomical archives, and its fall-out on the organization of the work in observational astronomy is finally discussed.

Non-baryonic, or "dark", matter is believed to be a major component of the total mass budget of the Universe. We review the candidates for particle dark matter and discuss the prospects for direct detection (via interaction of dark matter particles with laboratory detectors) and indirect detection (via observations of the products of dark matter self-annihilations), focusing in particular on the Galactic center, which is among the most promising targets for indirect detection studies. The gravitational potential at the Galactic center is dominated by stars and by the supermassive black hole, and the dark matter distribution is expected to evolve on sub-parsec scales due to interaction with these components. We discuss the dominant interaction mechanisms and show how they can be used to rule out certain extreme models for the dark matter distribution, thus increasing the information that can be gleaned from indirect detection searches.

We discuss the most recent developments in our understanding of the acceleration and propagation of cosmic rays up to the highest energies. In particular we specialize our discussion to three issues: (a) developments in the theory of particle acceleration at shock waves; (b) the transition from galactic to extragalactic cosmic rays; (c) implications of up-to-date observations for the origin of ultra high energy cosmic rays (UHECRs).

We review the latest attempts to determine the accretion geometry in radio-loud active galactic nuclei (AGN). These objects, which comprise ~ 10–20% of the AGN population, produce powerful collimated radio jets that can extend thousands of parsecs from the center of the host galaxy. Recent multiwavelength surveys have shown that radio-loudness is more common in low-luminosity AGN than in higher luminosity Seyfert galaxies or quasars. These low-luminosity AGN have small enough accretion rates that they are most likely accreting via a geometrically thick and radiatively inefficient accretion flow. In contrast, X-ray spectroscopic observations of three higher luminosity broad-line radio galaxies (3C 120, 4C+74.26 and PG 1425+267) have found evidence for an untruncated thin disk extending very close to the black hole. These tentative detections indicate that, for this class of radio-loud AGN, the accretion geometry is very similar to their radio-quiet counterparts. These observations suggest that there are three conditions to jet formation that must be satisfied: the presence of a rapidly spinning black hole, an accretion flow with a large H/r ratio, and a favorable magnetic field geometry.

Beyond spatial anisotropy and polarization, a third type of structure in the Cosmic Microwave Background radiation, that of deviations in the overall absolute intensity versus frequency spectrum from a blackbody form, encodes additional important cosmological and astrophysical information, and remains inconclusively studied. This article discusses the ARCADE 2 project, the current balloon-based experimental effort to measure the absolute radiometric temperature of the CMB and Galactic microwave emission in the range from 3 to 90 GHz.

This paper presents a new model using optimization approach for efficient prediction of load in real-life environment. Monte Carlo simulation and Schrödinger equations provide the effective number of solutions. This technique is useful in representation of relationships between different models. The proposed algorithm is verified and validated with various state-of-the-art approaches for solving economic load power dispatch problem to demonstrate its efficiency. Experimental results signify that the proposed algorithm is more precise than existing competing models.

Dynamical equations of asymmetric thin shell wormholes connecting two different spacetimes by applying the cut and paste technique are constructed. The linear stability with variable modified generalized Chaplygin gas (VMGCG) equation of state, where the pressure will be a function of both radius and density, is investigated. This formalism is applied to two specific cases of asymmetric wormhole of a Schwarzschild connected to Reissner–Nordström spacetime and Reissner–Nordström connected to Schwarzschild–De Sitter (SDS) spacetime.

Gamma-ray astrophysics in the energy range between 30 MeV and 30 GeV is in desperate need of arcminute angular resolution and source monitoring capability. The AGILE Mission planned to be operational in 2004-2006 will be the only space mission entirely dedicated to gamma-ray astrophysics above 30 MeV. The main characteristics of AGILE are the simultaneous X-ray and gamma-ray imaging capability (reaching arcminute resolution) and excellent gamma-ray timing (10-100 microseconds). AGILE scientific program will emphasize a quick response to gamma-ray transients and multiwavelength studies of gamma-ray sources.

The Sudbury Neutrino Observatory is a 1000 T D₂O Cerenkov detector that is sensitive to ⁸B and hep solar neutrinos. Both Charged Current and Neutral Current interaction rates on deuterons as well as the Elastic Scattering interaction rate on electrons can be measured simultaneously. Assuming an undistorted ⁸B neutrino spectrum, the total flux measured with the NC reaction is , which is consistent with solar models. The ν_e component of the ⁸B solar flux is for a kinetic energy threshold of 5 MeV. The non-ν_e component is , which is 5.3σ greater than zero, giving strong evidence for solar ν_e flavor transformation. The Day-Night Asymmetry for the Charged Current interaction is . If the total flux of active neutrinos is additionally constrained to have no asymmetry, the ν_e asymmetry is found to be . Combined with other solar neutrino data, a global MSW oscillation analysis strongly favors the Large Mixing Angle (LMA) solution.

The aim of the lectures in this paper is to introduce some basic problems arising in gravitation and modern cosmology. All along the discussion the guiding theme is provided by the phenomenological and theoretical properties of the Cosmic Microwave Background (CMB). These lectures have been prepared for a regular PhD course of the University of Milan-Bicocca.

In this paper we develop a simple analytic model for the steady state of self-gravitating incompressible nonswirling gas in three dimensions with axial symmetry which is based on the hydrodynamic equations for stratified fluid. These equations are then reduced to a system of two equations for the mass density and the gravitational field. Numerical solutions of these equations under different modeling assumptions (with special attention to the isothermal case) are then used to study the patterns of the resulting steady state of the fluid.

The process of neutrino production of electron–positron pairs in a magnetic field of arbitrary strength, where electrons and positrons can be created in the states corresponding to excited Landau levels, is analyzed. The mean value of the neutrino energy loss due to the process ν → νe^-e⁺ is calculated. The result can be applied for calculating the efficiency of the electron–positron plasma production by neutrinos in the conditions of the Kerr black hole accretion disk considered by experts as the most possible source of a short cosmological gamma burst. The presented research can also be useful for further development of the calculation technique for an analysis of quantum processes in external active medium, and in part in the conditions of moderately strong magnetic field, when taking account of the ground Landau level appears to be insufficient.

The tree-level two-point amplitudes for the transitions j f → j′ f′, where f is a fermion and j is a generalized current, in a constant uniform magnetic field of an arbitrary strength and in charged fermion plasma, for the j f f interaction vertices of the scalar, pseudoscalar, vector and axial-vector types have been calculated. The generalized current j could mean the field operator of a boson, or a current consisting of fermions, e.g. the neutrino current. The particular cases of a very strong magnetic field, and of the coherent scattering off the real fermions without change of their states (the "forward" scattering) have been analyzed. The contribution of the neutrino photoproduction process, , to the neutrino emissivity has been calculated with taking account of a possible resonance on the virtual electron.

We consider application of our development of Zeldovich’s ideas, presented in Ref. 1, for measurement of the cosmological angular diameter distance (ADD) in the Friedmann Universe. To make a comparison with $\mathrm{\Lambda }$CDM we analyze ADD measurement in $\varphi$CDM model responsible for the later inflation (present accelerated expansion of the Universe). We also analyze a small deviation from equality in the distance duality relation induced by the fullness (by matter) of the cone of light rays (CLR) which is used for the ADD measurement method.

In this paper, a novel astrophysics-based approach is proposed for automatically finding the clusters and features simultaneously. A novel agent encoding scheme is used to encode both the number of clusters and features. A novel dynamic threshold technique is proposed for an efficient searching. The validation of proposed technique is tested on eight real-life data sets. The statistical significance of proposed technique is attributed by statistical tests. It is also applied on solving image segmentation and microarray data analysis problems. Experimental results reveal that the proposed technique outperforms the other competitive approaches.

In this paper, a novel astrophysics-based prediction framework is developed for estimating the binding affinity of a glucose binder. The proposed framework utilizes the molecule properties for predicting the binding affinity. It also uses the astrophysics-learning strategy that incorporates the concepts of Kepler’s law during the prediction process. The proposed framework is compared with 10 regression algorithms over ZINC dataset. Experimental results reveal that the proposed framework provides 99.30% accuracy of predicting binding affinity. However, decision tree provides the prediction with 97.14% accuracy. Cross-validation results show that the proposed framework provides better accuracy than the other existing models. The developed framework enables researchers to screen glucose binder rapidly. It also reduces computational time for designing small glucose binding molecule.

This study investigates an astrophysics-based Transit search optimization algorithm (TSOA) for solving a challenging engineering problem. This innovative strategy uses the fundamentals of physics to improve the accuracy and efficacy of problem solving techniques. Harmonic distortions in power systems have become a massive challenge because of the nonlinear loads associated with the electrical power distribution system. Overheating of the equipment, motor failure, capacitor failure, and improper power metering are all issues caused by harmonic distortion. A new examination of the causes and consequences of these issues, as well as the status of hardware and software available for harmonic evaluation, is necessary in light of the unprecedented advancements in power electronic devices and their integration at all levels in the power and energy system. In order to estimate phase and amplitude simultaneously with a specified frequency, an objective function of power system harmonics is created. Keeping in mind the adverse effects of harmonics, parameter estimation is carried out under various conditions by taking different particle sizes and signal-to-noise ratios. TSOA proved its efficacy for both phase and amplitude parameters under different situations and precisely estimated the harmonics signal up to an accuracy of 1.1648E–15. Two harmonic signals were taken in this research work, and the best MSE values achieved are 9.748E–4, 8.287E–07, 6.157E–10, and 1.165E–15 for 30, 60, 90, and 150 dB noise, respectively, under case study 1 while varying the particle size from 50 to 450. The results for case study 2 proved to be best up to 7.373E–16, and no significant change occurred by increasing the generations above 500. The proposed study would be a step further in developing a more accurate and robust computing platform for robust estimation of harmonics arising in power and energy systems.

This study presents an astrophysics-inspired transit search optimization (TSO) algorithm based on exoplanet search divided into five phases: galaxy phase, star phase, transit phase, neighbor phase and exploitation phase for effective parameter estimation of fractional Hammerstein control autoregressive (Fr-HCAR) systems. Various physical phenomena and real processes can be modeled with Fr-HCAR systems and estimating the Fr-HCAR parameters becomes a vital task. The mean-square error (MSE)-based criterion function is developed, and efficacy of the TSO for Fr-HCAR identification is deeply analyzed for different fractional orders, disturbance levels and degrees of freedom. The TSO remained accurate, convergent, robust and stable for all variations in Fr-HCAR but the accuracy level degrades a little bit for high disturbance and increased degrees of freedom. The reliability and trustworthiness of the TSO for Fr-HCAR identification are endorsed through statistical analyses conducted on sufficient autonomous executions of the scheme.

Cosmology, high-energy physics and astrophysics are today converging to the study of large scale magnetic fields. While the experimental evidence for the existence of large scale magnetization in galaxies, clusters and super-clusters is rather compelling, the origin of the phenomenon remains puzzling especially in light of the most recent observations. The purpose of the present review is to describe the physical motivations and the open theoretical problems related to the existence of large scale magnetic fields.

I present a non-technical and necessarily biased and incomplete overview of our present understanding of the physical universe and its constituents, emphasizing what we have learned from the explosive growth in cosmological and astrophysical data acquisition and some of the key open questions that remain. The topics are organized under the labels space, time, and matter. Most bibliographical references are for the non-expert.