The luminosity evolution over the EQuiTemporal Surfaces in the prompt emission of Gamma-Ray Bursts

Due to the ultrarelativistic velocity of the expanding "fireshell" (Lorentz gamma factor \gamma \sim 10^2 - 10^3), photons emitted at the same time from the fireshell surface do not reach the observer at the same arrival time. In interpreting Gamma-Ray Bursts (GRBs) it is crucial to determine the properties of the EQuiTemporal Surfaces (EQTSs): the locus of points which are source of radiation reaching the observer at the same arrival time. In the current literature this analysis is performed only in the latest phases of the afterglow. Here we study the distribution of the GRB bolometric luminosity over the EQTSs, with special attention to the prompt emission phase. We analyze as well the temporal evolution of the EQTS apparent size in the sky. We use the analytic solutions of the equations of motion of the fireshell and the corresponding analytic expressions of the EQTSs which have been presented in recent works and which are valid for both the fully radiative and the adiabatic dynamics. We find the novel result that at the beginning of the prompt emission the most luminous regions of the EQTSs are the ones closest to the line of sight. On the contrary, in the late prompt emission and in the early afterglow phases the most luminous EQTS regions are the ones closest to the boundary of the visible region. This transition in the emitting region may lead to specific observational signatures, i.e. an anomalous spectral evolution, in the rising part or at the peak of the prompt emission. We find as well an expression for the apparent radius of the EQTS in the sky, valid in both the fully radiative and the adiabatic regimes. Such considerations are essential for the theoretical interpretation of the prompt emission phase of GRBs.Comment: 11 pages, 5 figures, in the Proceedings of the 1st Galileo-Xu GuangQi Meeting, October 26-30, 2009, Shangha

THREE ESSAYS ON CREDIT MARKETS AND THE MACROECONOMY

Historically, credit market conditions have been shown to impact economic activity, at times severely. For instance, in the late 2000s, the United States experienced a financial crisis that seized domestic and foreign credit markets. The ensuing lack of access to credit brought about a steep decline in output and a sluggish recovery. Accordingly, policymakers commonly take steps to mitigate the effects of adverse credit market conditions and, at times, conduct unconventional monetary policy once traditional policy tools become ineffective. This dissertation is a collection of essays regarding monetary policy, the flow of credit, financial crises, and the macroeconomy. Specifically, I describe monetary policy’s impact on the allocation of credit in the U.S. and analyze the role of upstream and downstream credit conditions and financial crises on international trade in a global supply chain. The first chapter assesses the impact of monetary policy shocks on credit reallocation and evaluates the importance of theoretical transmission mechanisms. Compustat data covering 1974 through 2017 is used to compute quarterly measures of credit flows. I find that expansionary monetary policy is associated with positive long-term credit creation and credit reallocation. These impacts are larger for long-term credit and for credit of financially constrained firms and firms that are perceived as risky to the lender. This is predicted by the balance sheet channel of monetary policy and mechanisms that reduce lenders’ risk perceptions and increase the tendency to search for yield. Furthermore, I find that, on average, the largest increases in credit creation resulting from monetary expansion are to firms that exhibit relatively low investment efficiency. These estimation results suggest that expansionary monetary policy may have a negative impact on future economic growth. The second chapter evaluates the quantitative effects of unconventional monetary policy in the late 2000s and early 2010s. This was a period when the traditional monetary policy tool (the federal funds rate) was constrained by the zero lower bound. We compute credit flow measures using Compustat data, and we employ a factor augmented vector autoregression to analyze unconventional monetary policy’s impact on the allocation of credit during the zero lower bound period. By employing policy counterfactuals, we find that unconventional monetary policy has a positive and simultaneous impact on credit creation and credit destruction and these impacts are larger in long-term credit markets. Applying this technique to analyze the flows of financially constrained and non-financially constrained borrowing firms, we find that unconventional monetary policy operates through the easing of collateral constraints because these effects are larger for small firms or those with high default probabilities. During the zero lower bound period, we also find that unconventional monetary policy brings about increases in credit creation for firms of relatively high investment efficiency. The third chapter pertains to the global trade collapse of the late 2000s. This collapse was due, in part, to strained credit markets and the vulnerability of exporters to adverse credit market conditions. The chapter evaluates the impact of upstream and downstream credit conditions and the differential effects of financial crises on bilateral trade. I find that upstream and downstream sectors’ needs for external financing is negatively associated with trade flows when the exporting or importing country’s cost of credit is high. However, I find that this effect is dampened for downstream sectors. I also find that downstream sectors’ value of collateral is positively associated with trade when the cost of credit is high in the importing country. High downstream trade credit dependence coupled with high costs of credit in the importing country also cause declines in imports. There are amplifying effects of credit costs for sectors that are highly dependent on external financing when the importing or exporting country is in financial crisis. Further, the magnitude is larger when the exporting country is in financial crisis. Finally, I find that these effects on trade flows are large when the exporting country is a developed economy, but they are muted for developing economies

On the physical processes which lie at the bases of time variability of GRBs

The relative-space-time-transformation (RSTT) paradigm and the interpretation of the burst-structure (IBS) paradigm are applied to probe the origin of the time variability of GRBs. Again GRB 991216 is used as a prototypical case, thanks to the precise data from the CGRO, RXTE and Chandra satellites. It is found that with the exception of the relatively inconspicuous but scientifically very important signal originating from the initial ``proper gamma ray burst'' (P-GRB), all the other spikes and time variabilities can be explained by the interaction of the accelerated-baryonic-matter pulse with inhomogeneities in the interstellar matter. This can be demonstrated by using the RSTT paradigm as well as the IBS paradigm, to trace a typical spike observed in arrival time back to the corresponding one in the laboratory time. Using these paradigms, the identification of the physical nature of the time variablity of the GRBs can be made most convincingly. It is made explicit the dependence of a) the intensities of the afterglow, b) the spikes amplitude and c) the actual time structure on the Lorentz gamma factor of the accelerated-baryonic-matter pulse. In principle it is possible to read off from the spike structure the detailed density contrast of the interstellar medium in the host galaxy, even at very high redshift.Comment: 11 pages, 5 figure

Effects of Littlest Higgs model in rare D meson decays

A tree-level flavor changing neutral current in the up-like quark sector appears in one of the variations of the Littlest Higgs model. We investigate the effects of this coupling in the D+ -> pi+ l+ l- and D0 -> rho0 l+ l- decays, which are the most appropriate candidates for the experimental studies. However, the effects are found to be too small to be observed in the current and the foreseen experimental facilities. These decays are still dominated by the standard model long-distance contributions, which are reevaluated based on the new experimental input.Comment: 13 pages, 3 figures; new constraint on scale f taken into account and effects on charm meson decays recalculate

The EMBH model in GRB 991216 and GRB 980425

This is a summary of the two talks presented at the Rome GRB meeting by C.L. Bianco and R. Ruffini. It is shown that by respecting the Relative Space-Time Transformation (RSTT) paradigm and the Interpretation of the Burst Structure (IBS) paradigm, important inferences are possible: a) in the new physics occurring in the energy sources of GRBs, b) on the structure of the bursts and c) on the composition of the interstellar matter surrounding the source.Comment: 8 pages, 3 figures, in the Proceedings of the "Third Rome Workshop on Gamma-Ray Bursts in the Afterglow Era", 17-20 September 2002, M. Feroci, F. Frontera, N. Masetti, L. Piro (editors

Updated constraints on new physics in rare charm decays

Motivated by recent experimental results on charm physics we investigate implications of the updated constraints of new physics in rare charm meson decays. We first reconsider effects of the MSSM in $c\to u \gamma$ constrained by the recent experimental evidence on $\Delta m_D$ and find, that due to the dominance of long distance physics, $D \to V \gamma$ decay rates cannot be modified by MSSM contributions. Then we consider effects of the extra heavy up vector-like quark models on the decay spectrum of $D^+ \to \pi^+ l^+ l^-$ and $D_s^+ \to K^+ l^+ l^-$ decays. We find a possibility for the tiny increase of the differential decay rate in the region of large dilepton mass. The R-parity violating supersymmetric model can also modify short distance dynamics in $c \to u l^+ l^-$ decays. We constrain relevant parameters using current upper bound on the $D^+ \to \pi^+ l^+ l^-$ decay rate and investigate impact of that constraint on the $D_s^+ \to K^+ l^+ l^-$ differential decay dilepton distribution. Present bounds still allow small modification of the standard model differential decay rate distribution.Comment: 15 pages, 4 figure

Integrazione della fotomodellazione nel processo di rilievo. Applicazioni alle costruzioni alpine tradizionali in pietra

This contribute shows the most significant results of the Interreg-AlpStone research in relation to the methods of survey for stone constructions. The Alpine territory located in the area between Italy and Switzerland presents a rich architectural heritage which has an important value both from the cultural (for the local traditions) and real-estate (for touristic and residential aims) points of view. In order to recover these typical buildings it needs in primis to find the survey methodology that best fits the goal. The buildings realized with stone materials are characterized, for their nature, by a high degree of irregularity, which is still more evident in abandoned buildings. This irregularity can't be ignored because it could affect several aspects of the redevelopment (seismic and thermal renovation, space management,…). Techniques of survey with laser scanner and photomodelling have been tested. Photomodelling turned out to be a convenient technique because of its cheapness, its facility of use and its practicality in territories such as the Alpine ones, with impervious paths. The degree of detail of the photomodelling is lower than the one of laser scanner. Nevertheless, for the recovery, the survey based on the multi-images correlation turned out to be largely sufficient for a careful critical analysis of instabilities, deformations and inflections of the building components. The only inconveniences are the time employed for the photos snapshots and the difficulty in modeling the natural context near the architectural heritag

Is acting prosocially beneficial for the credit market?

This article argues that behaving prosocially implies more transparent information during the negotiation process of a financial contract and more cooperation among the parties to respect the terms of the contract. For this reason this work considers interest rate on loans and insolvency rate functions of prosocial behaviour along with the traditional socio-economic and financial collaterals. The context of study is Italy and the analysis is developed at a cross-regional level. We collect data from the two reports on “Relatives and Safety Net” produced by the Italian Centre Bureau of Statistics (ISTAT) in 1998 and 2003 and from the reports on “Regional Economics” produced by the Bank of Italy in the same years. A two-period panel model shows two interesting outcomes. Firstly, regions with a higher proportion of prosocial individuals report lower interest rates on loans and insolvency rates. Secondly, when we include the efficiency of legal enforcement, evidence supports the idea that a more efficient legal framework can act as a more reliable transmission mechanism of institutional norms and facilitate the internalisation of social norms

Building bone tissue: matrices and scaffolds in physiology and biotechnology

Deposition of bone in physiology involves timed secretion, deposition and removal of a complex array of extracellular matrix proteins which appear in a defined temporal and spatial sequence. Mineralization itself plays a role in dictating and spatially orienting the deposition of matrix. Many aspects of the physiological process are recapitulated in systems of autologous or xenogeneic transplantation of osteogenic precursor cells developed for tissue engineering or modeling. For example, deposition of bone sialoprotein, a member of the small integrin-binding ligand, N-linked glycoprotein family, represents the first step of bone formation in ectopic transplantation systems in vivo. The use of mineralized scaffolds for guiding bone tissue engineering has revealed unexpected manners in which the scaffold and cells interact with each other, so that a complex interplay of integration and disintegration of the scaffold ultimately results in efficient and desirable, although unpredictable, effects. Likewise, the manner in which biomaterial scaffolds are "resorbed" by osteoclasts in vitro and in vivo highlights more complex scenarios than predicted from knowledge of physiological bone resorption per se. Investigation of novel biomaterials for bone engineering represents an essential area for the design of tissue engineering strategies

Steel Reinforcement Influence on the Dynamic Behaviour of Bituminous Pavement

It has been investigated the theoretical dynamic response of a bituminous pavement subject to dynamic loads with harmonic variation. The study, developed through a FEM mathematical model, has allowed to underline that the strain rate generally dependent, beyond that on the intensity of the load, on his frequency and on the bituminous concrete own damping. The bituminous concrete has been modelled like elastoplastic material. The results show that when the load frequency is close to the resonance frequencies, high stresses are induced. In these cases the internal damping of the bituminous concrete reduces the stress amplification. High stiff reinforcement can produce, in some cases, the same effect with higher reduction. Also cracks propagation in presence of stiff reinforcement has been investigated. A remarkable increase of load repetition has been obtained to have, for a reinforced paving, the same crack propagation. The analysis has been developed particularly with reference to the metallic reinforcement Road Mesh, manufactured and commercialized by Officine Maccaferri Spa