The Dynamics of Vehicular Networks in Urban Environments

Vehicular Ad hoc NETworks (VANETs) have emerged as a platform to support intelligent inter-vehicle communication and improve traffic safety and performance. The road-constrained, high mobility of vehicles, their unbounded power source, and the emergence of roadside wireless infrastructures make VANETs a challenging research topic. A key to the development of protocols for inter-vehicle communication and services lies in the knowledge of the topological characteristics of the VANET communication graph. This paper explores the dynamics of VANETs in urban environments and investigates the impact of these findings in the design of VANET routing protocols. Using both real and realistic mobility traces, we study the networking shape of VANETs under different transmission and market penetration ranges. Given that a number of RSUs have to be deployed for disseminating information to vehicles in an urban area, we also study their impact on vehicular connectivity. Through extensive simulations we investigate the performance of VANET routing protocols by exploiting the knowledge of VANET graphs analysis.Comment: Revised our testbed with even more realistic mobility traces. Used the location of real Wi-Fi hotspots to simulate RSUs in our study. Used a larger, real mobility trace set, from taxis in Shanghai. Examine the implications of our findings in the design of VANET routing protocols by implementing in ns-3 two routing protocols (GPCR & VADD). Updated the bibliography section with new research work

System Estimates of Cyclical Unemployment and Cyclical Output in the 15 European Union Member-States, 1961-1999

The purpose of this paper was to estimate cyclical unemployment and cyclical output in the 15 European Union member-states using a system of Phillips curve and Okun’s law equations. Treating both the NAIRU and the potential output growth rate as time varying unobserved stochastic processes, a state-space maximum likelihood estimation method - using Kalman filter where the state variables were random walks - was followed in order to estimate the 15 systems of equations. Overall, the estimated with the new approach systems of conditional equations suggested that the extent and direction of changes of cyclical unemployment and cyclical output over the period 1961-1999 is mixed across the 15 EU member states. The paper concludes that the application of “common” policies across the 15 EU member states may be questionable because of the different expected effects of these policies on the various economies.Phillips curve, Okun’s law, Kalman filter, Cyclical unemployment, Potential output growth rate, NAIRU, Europe

Tracking Quintessence and Cold Dark Matter Candidates

We study the generation of a kination-dominated phase in the context of a quintessential model with an inverse-power-law potential and a Hubble-induced mass term for the quintessence field. The presence of kination is associated with an oscillating evolution of the quintessence field and the barotropic index. We find that, in sizeable regions of the parameter space, a tracker scaling solution can be reached sufficiently early to alleviate the coincidence problem. Other observational constraints originating from nucleosynthesis, the inflationary scale, the present acceleration of the universe and the dark-energy-density parameter can be also met. The impact of this modified kination-dominated phase on the thermal abundance of cold dark matter candidates is investigated too. We find that: (i) the enhancement of the relic abundance of the WIMPs with respect to the standard paradigm, crucially depends on the hierarchy between the freeze-out temperature and the temperature at which the extrema in the evolution of the quintessence field are encountered, and (ii) the relic abundance of e-WIMPs takes its present value close to the temperature at which the earliest extremum of the evolution of the quintessence field occurs and, as a consequence, both gravitinos and axinos arise as natural cold dark matter candidates. In the case of unstable gravitinos, the gravitino constraint can be satisfied for values of the initial temperature well above those required in the standard cosmology.Comment: Final versio

Comments on SUSY inflation models on the brane

In this paper we consider a class of inflation models on the brane where the dominant part of the inflaton scalar potential does not depend on the inflaton field value during inflation. In particular, we consider supernatural inflation, its hilltop version, A-term inflation, and supersymmetric (SUSY) D- and F-term hybrid inflation on the brane. We show that the parameter space can be broadened, the inflation scale generally can be lowered, and still possible to have the spectral index $n_s=0.96$.Comment: 7 page

Quintessential Kination and Leptogenesis

Thermal leptogenesis induced by the CP-violating decay of a right-handed neutrino (RHN) is discussed in the background of quintessential kination, i.e., in a cosmological model where the energy density of the early Universe is assumed to be dominated by the kinetic term of a quintessence field during some epoch of its evolution. This assumption may lead to very different observational consequences compared to the case of a standard cosmology where the energy density of the Universe is dominated by radiation. We show that, depending on the choice of the temperature T_r above which kination dominates over radiation, any situation between the strong and the super--weak wash--out regime are equally viable for leptogenesis, even with the RHN Yukawa coupling fixed to provide the observed atmospheric neutrino mass scale ~ 0.05 eV. For M< T_r < M/100, i.e., when kination stops to dominate at a time which is not much later than when leptogenesis takes place, the efficiency of the process, defined as the ratio between the produced lepton asymmetry and the amount of CP violation in the RHN decay, can be larger than in the standard scenario of radiation domination. This possibility is limited to the case when the neutrino mass scale is larger than about 0.01 eV. The super--weak wash--out regime is obtained for T_r << M/100, and includes the case when T_r is close to the nucleosynthesis temperature ~ 1 MeV. Irrespective of T_r, we always find a sufficient window above the electroweak temperature T ~ 100 GeV for the sphaleron transition to thermalize, so that the lepton asymmetry can always be converted to the observed baryon asymmetry.Comment: 13 pages, 8 figure

Experimental performance evaluation of a multi-diaphragm pump of a micro-ORC system

Abstract The performance of micro-scale ORC systems strongly depends on the performance of their key components. While the heat exchangers and expander have been extensively investigated, the pump has only received limited attention. The main purpose of this work is the experimental characterization of a multi-diaphragm positive displacement pump, integrated in an experimental ORC system with a rated power output of 4kWel. The study focuses on the experimental evaluation of the pump performance and on cavitation phenomena. A detailed presentation of the experimental procedure and results is supplied. A great effort has been spent in calculating the global and volumetric pump efficiencies for a wide range of operational conditions, which reach maximum values around 45-48% and 95%, respectively. With regards to cavitation issues, the effect of the available Net Positive Suction Head at the pump inlet has been deeply investigated both at partial and full load to obtain guidelines for stable operation. Finally, an extensive dataset of steady-state operating points has been used to calibrate an improved version of a semi-empirical model previously developed for positive displacement ORC pumps. Special attention has been given to the ability of the model to accurately predict the behaviour and performance of the pump at different, properly chosen, steady-state conditions. Relative errors in between 0.5%, for the outlet temperature, and 10%, for the electric power consumption, are achieved

Mutated hybrid inflation in f(R,□R)f(R,{\Box}R)-gravity

A new hybrid inflationary scenario in the context of $f(R,{\Box}R)$-gravity is proposed. Demanding the waterfall field to 'support the potential from below' [unlike the original proposal by Stewart in Phys. Lett. B345, 414 (1995)], we demonstrate that the scalar potential is similar to that of the large-field chaotic inflation model proposed by Linde in Phys. Lett. B129, 177 (1983). Inflationary observables are used to constrain the parameter space of our model; in the process, an interesting limit on the number of e-folds N is found.Comment: 9 pages, 2 figures, LaTeX2e, v2: Sec.3 expanded and improved, 1 Fig. added, a new result included, some Eqs. corrected, 2 References adde

Colliders as a simultaneous probe of supersymmetric dark matter and Terascale cosmology

Terascale supersymmetry has the potential to provide a natural explanation of the dominant dark matter component of the standard lambda-CDM cosmology. However once we impose the constraints on minimal supersymmetry parameters from current particle physics data, a satisfactory dark matter abundance is no longer prima facie natural. This Neutralino Tuning Problem could be a hint of nonstandard cosmology during and/or after the Terascale era. To quantify this possibility, we introduce an alternative cosmological benchmark based upon a simple model of quintessential inflation. This benchmark has no free parameters, so for a given supersymmetry model it allows an unambiguous prediction of the dark matter relic density. As a example, we scan over the parameter space of the CMSSM, comparing the neutralino relic density predictions with the bounds from WMAP. We find that the WMAP--allowed regions of the CMSSM are an order of magnitude larger if we use the alternative cosmological benchmark, as opposed to lambda-CDM. Initial results from the CERN Large Hadron Collider will distinguish between the two allowed regions.Comment: 14 pages, 8 figure