Oscillations above the barrier in the fusion of 28Si + 28Si

Fusion cross sections of 28Si + 28Si have been measured in a range above the barrier with a very small energy step (DeltaElab = 0.5 MeV). Regular oscillations have been observed, best evidenced in the first derivative of the energy-weighted excitation function. For the first time, quite different behaviors (the appearance of oscillations and the trend of sub-barrier cross sections) have been reproduced within the same theoretical frame, i.e., the coupled-channel model using the shallow M3Y+repulsion potential. The calculations suggest that channel couplings play an important role in the appearance of the oscillations, and that the simple relation between a peak in the derivative of the energy-weighted cross section and the height of a centrifugal barrier is lost, and so is the interpretation of the second derivative of the excitation function as a barrier distribution for this system, at energies above the Coulomb barrier.Comment: submitted to Physics Letters

Credit, asset prices and monetary policy

The developments in asset markets have influenced researchersto focus on the interaction between monetary policy and the financial system. In Chapter I we provide an overview of the role of the financial system for the whole economy. We show the importance of this sector in transmitting the monetary policy actions. The aim of this research is twofold; firstly we want to investigate how important the amount of credit for the whole economy is. To accomplish this objective, in Chapter 2 we make use of the VAR technique to study the monetary transmission mechanism. In particular we are interested in explaining why previous empirical research has found that prices show an increase after monetary tightening. We investigate how an unanticipated movement in the risk free interest rate affects all those variables responsible for the transmission of a monetary shock. Our results suggest that the immediate increase in prices is not due to some form of econometric misspecification, but rather, to the change in the composition of firms' source of finance. Prices rise because the need for external funds increases thus firms' costs of production increase. Another important issue that we want to tackle is the contribution of external finance to the 1990 economic recession. In Chapter 3 we show that the increased level of indebtedness as one of the forces at the root of the economic downturn. We argue that the crisis could be explained on the basis of Minsky's financial instability hypothesis. In the remaining part of this research we tackle the second aim of this research: we focus our attention on the link between asset prices and monetary policy. Asset prices, in fact, can give an indication of future consumers' and firms' decisions on spending and, therefore, might be indicators of future economic activity. Wealth deriving from gains in these markets tends t o increase the level of consumption and investment. A t the same time, sharp movements in asset prices could signal imbalances in the economy; developments of this kind can threaten financial stability. In Chapter 4 we argue there might be a trade-off between financial stability and monetary stability when these are the main objectives of the monetary authorities. First we explore the possibility that the demand equation is affected positively by changes in asset prices, secondly empirical findings suggest that for the period 1992: 10-2003: 1 monetary policy in the UK can be better represented by a rule which takes into consideration movements in house prices and stock prices. The empirical evidence provided in Chapter 4 brings us in Chapter 5 to construct a macroeconomic model where the asset prices enter indirectly into the Central Bank's loss function. We model the aggregate demand of the economy so that output is determined, among other variables, by the wealth effect. The optimal interest rate rule is obtained by optimising intertemporally a loss function that includes inflation and output variance. We find that the optimal policy in the presence of wealth effects not only depends upon inflation and output but also it depends on financial imbalances, as represented by asset price misalignments from fundamentals. The response to asset price deviations from fundamentals becomes more aggressive as wealth effects build up, while the reaction to inflation and the output gap becomes less pronounced.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A new study of 25^{25}Mg(α\alpha,n)28^{28}Si angular distributions at EαE_\alpha = 3 - 5 MeV

The observation of $^{26}$Al gives us the proof of active nucleosynthesis in the Milky Way. However the identification of the main producers of $^{26}$Al is still a matter of debate. Many sites have been proposed, but our poor knowledge of the nuclear processes involved introduces high uncertainties. In particular, the limited accuracy on the $^{25}$Mg($\alpha$,n)$^{28}$Si reaction cross section has been identified as the main source of nuclear uncertainty in the production of $^{26}$Al in C/Ne explosive burning in massive stars, which has been suggested to be the main source of $^{26}$Al in the Galaxy. We studied this reaction through neutron spectroscopy at the CN Van de Graaff accelerator of the Legnaro National Laboratories. Thanks to this technique we are able to discriminate the ($\alpha$,n) events from possible contamination arising from parasitic reactions. In particular, we measured the neutron angular distributions at 5 different beam energies (between 3 and 5 MeV) in the \ang{17.5}-\ang{106} laboratory system angular range. The presented results disagree with the assumptions introduced in the analysis of a previous experiment.Comment: 9 pages, 9 figures - accepted by EPJ

REPRESENTAÇÕES SOCIAIS DA SURDEZ

The aim of this study was to understand the social representations and the impact of the deafness in the daily life of families with deaf children. Methods : To reach this aim, qualitative methodology was adopted using interviews with open-ended questions as tool to collect data.Fifteen parents of deaf children who attended a rehabilitation center were interviewed. Results: The deafness was represented as a “weight”, “a suffering”, “a upset”, “a overload”, producing guilty conscience and difficulty of acceptance by these families, while rehabilitation refer to ideas like “socialization”, “respect” and “acceptance” in the social environment..Conclusion: The knowledge of the representations and expectations of the deaf people parents, brought back information to formulate new ways of assistance to them. Moreover, the living together with the deafness and other deaf people made possible to them share their feelings, doubts and expectations.O objetivo deste estudo foi conhecer as representações sociais e o impacto da surdez no cotidiano de familiares de crianças surdas. Métodos: Nesta investigação adotou-se a metodologia qualitativa utilizando-se entrevistas com questões abertas como ferramenta de coleta de dados. A amostra contou com 15 familiares (pais ou mães) de crianças surdas atendidas em um serviço de reabilitação. Resultados : A surdez foi representada como “um fardo”, “sofrimento”, “transtorno”, “sobrecarga” gerando “sentimento de culpa”, e dificuldade de aceitação por parte da família, enquanto a reabilitação remete à idéias de “socialização”, “respeito’ e “aceitação” no meio social.  Conclusão : O conhecimento das representações e expectativas dos pais trouxe subsídios para novas ações que incluam maior atenção às famílias, incentivo à participação em grupos de pais, visando a troca de experiências

Regional Interest Rate Pass-Through in Italy

Regional interest rate pass-through in Italy, Regional Studies. This paper estimates the pass-through and speed of adjustment of Italian regional interest rates to changes in the money market rate for the period 1998Q1–2009Q4. The main findings suggest that the mark-ups for the lending rates that banks charge are generally higher in the South than in the North. Moreover, the empirical results indicate that the pass-through tends to be longer in Southern regions. Furthermore, little support is found for the hypothesis that regional banks react asymmetrically when adjusting their loan rates when these are above or below equilibrium levels, but some evidence supporting an upward rigidity in the regional deposit rates is detected

Recent experimental results in sub- and near-barrier heavy ion fusion reactions

Recent advances obtained in the field of near and sub-barrier heavy-ion fusion reactions are reviewed. Emphasis is given to the results obtained in the last decade, and focus will be mainly on the experimental work performed concerning the influence of transfer channels on fusion cross sections and the hindrance phenomenon far below the barrier. Indeed, early data of sub-barrier fusion taught us that cross sections may strongly depend on the low-energy collective modes of the colliding nuclei, and, possibly, on couplings to transfer channels. The coupled-channels (CC) model has been quite successful in the interpretation of the experimental evidences. Fusion barrier distributions often yield the fingerprint of the relevant coupled channels. Recent results obtained by using radioactive beams are reported. At deep sub-barrier energies, the slope of the excitation function in a semi-logarithmic plot keeps increasing in many cases and standard CC calculations over-predict the cross sections. This was named a hindrance phenomenon, and its physical origin is still a matter of debate. Recent theoretical developments suggest that this effect, at least partially, may be a consequence of the Pauli exclusion principle. The hindrance may have far-reaching consequences in astrophysics where fusion of light systems determines stellar evolution during the carbon and oxygen burning stages, and yields important information for exotic reactions that take place in the inner crust of accreting neutron stars.Comment: 40 pages, 63 figures, review paper accepted for EPJ

Terrestrial laser scanning and low magnetic field digitization yield similar architectural coarse root traits for 32-year-old Pinus ponderosa trees

Background Understanding how trees develop their root systems is crucial for the comprehension of how wildland and urban forest ecosystems plastically respond to disturbances such as harvest, fire, and climate change. The interplay between the endogenously determined root traits and the response to environmental stimuli results in tree adaptations to biotic and abiotic factors, influencing stability, carbon allocation, and nutrient uptake. Combining the three-dimensional structure of the root system, with root morphological trait information promotes a robust understanding of root function and adaptation plasticity. Low Magnetic Field Digitization coupled with AMAPmod (botAnique et Modelisation de l’Architecture des Plantes) software has been the best-performing method for describing root system architecture and providing reliable measurements of coarse root traits, but the pace and scale of data collection remain difficult. Instrumentation and applications related to Terrestrial Laser Scanning (TLS) have advanced appreciably, and when coupled with Quantitative Structure Models (QSM), have shown some potential toward robust measurements of tree root systems. Here we compare, we believe for the first time, these two methodologies by analyzing the root system of 32-year-old Pinus ponderosa trees Results In general, at the total root system level and by root-order class, both methods yielded comparable values for the root traits volume, length, and number. QSM for each root trait was highly sensitive to the root size (i.e., input parameter PatchDiam) and models were optimized when discrete PatchDiam ranges were specified for each trait. When examining roots in the four cardinal direction sectors, we observed differences between methodologies for length and number depending on root order but not volume. Conclusions We believe that TLS and QSM could facilitate rapid data collection, perhaps in situ, while providing quantitative accuracy, especially at the total root system level. If more detailed measures of root system architecture are desired, a TLS method would benefit from additional cans at differing perspectives, avoiding gravitational displacement to the extent possible, while subsampling roots by hand to calibrate and validate QSM models. Despite some unresolved logistical challenges, our results suggest that future use of TLS may hold promise for quantifying tree root system architecture in a rapid, replicable manner

Breakup of 17^{17}F on 208^{208}Pb near the Coulomb barrier

Angular distributions of oxygen produced in the breakup of $^{17}$F incident on a $^{208}$Pb target have been measured around the grazing angle at beam energies of 98 and 120 MeV. The data are dominated by the proton stripping mechanism and are well reproduced by dynamical calculations. The measured breakup cross section is approximately a factor of 3 less than that of fusion at 98 MeV. The influence of breakup on fusion is discussed.Comment: 7 pages, 8 figure

Fusion of 28Si + 28Si: oscillations above the barrier and the behavior down to 1μb

Fusion excitation functions of light heavy-ion systems show oscillatory structures above the Coulomb barrier, caused by resonances or due to the penetration of successive centrifugal barriers well separated in energy. In heavier systems, the amplitude of oscillations decreases and the peaks get nearer to each other. This makes the measurements very challenging. We have performed a first experiment for 28Si + 28Si, by measuring fusion cross sections (σ) in an energy range of ≃15 MeV above the barrier, with a small ΔElab = 0.5 MeV step. Three regular oscillations are clearly observed, which are best revealed by plotting the energy-weighted derivative of the excitation function. The excitation function has been recently measured down to cross sections ≤1μb with larger energy steps. Coupled-channel (CC) calculations based on a shallow potential in the entrance channel are able to reproduce the oscillations. A further analysis will provide a stringent test for the calculations, in particular for the choice of the ion-ion potential, because the subbarrier excitation function has to be reproduced as well. Coupled-channel (CC) calculations based on a shallow potential in the entrance channel are able to reproduce the oscillations. A further analysis will provide a stringent test for the calculations, in particular for the choice of the ion-ion potential, because the subbarrier excitation function has to be reproduced as well