Enhanced shot noise in carbon nanotube field-effect transistors

We predict shot noise enhancement in defect-free carbon nanotube field-effect transistors through a numerical investigation based on the self-consistent solution of the Poisson and Schrodinger equations within the non-equilibrium Green functions formalism, and on a Monte Carlo approach to reproduce injection statistics. Noise enhancement is due to the correlation between trapping of holes from the drain into quasi-bound states in the channel and thermionic injection of electrons from the source, and can lead to an appreciable Fano factor of 1.22 at room temperature.Comment: 4 pages, 4 figure

Shot noise suppression in quasi one-dimensional Field Effect Transistors

We present a novel method for the evaluation of shot noise in quasi one-dimensional field-effect transistors, such as those based on carbon nanotubes and silicon nanowires. The method is derived by using a statistical approach within the second quantization formalism and allows to include both the effects of Pauli exclusion and Coulomb repulsion among charge carriers. In this way it extends Landauer-Buttiker approach by explicitly including the effect of Coulomb repulsion on noise. We implement the method through the self-consistent solution of the 3D Poisson and transport equations within the NEGF framework and a Monte Carlo procedure for populating injected electron states. We show that the combined effect of Pauli and Coulomb interactions reduces shot noise in strong inversion down to 23 % of the full shot noise for a gate overdrive of 0.4 V, and that neglecting the effect of Coulomb repulsion would lead to an overestimation of noise up to 180 %.Comment: Changed content, 7 pages,5 figure

Endogenous Bubbles in Derivatives Markets: The Risk Neutral Valuation Paradox

This paper highlights the role of risk neutral investors in generating endogenous bubbles in derivatives markets. We find that a market for derivatives, which has all the features of a perfect market except completeness and has some risk neutral investors, can exhibit extreme price movements which represent a violation to the Gaussian random walk hypothesis. This can be viewed as a paradox because it contradicts wide-held conjectures about prices in informationally efficient markets with rational investors. Our findings imply that prices are not always good approximations of the fundamental values of derivatives, and that extreme price movements like price peaks or crashes may have endogenous origin and happen with a higher-than-normal frequency.Comment: 21 pages. The second version presents the following upgrades: improved precision in the definition of agents and their behaviour; simplification in the notation of the probability measure; simplification in section 4.1; addition of caveats in the conclusions. The results of the second version remain unchange

China and the BRI: Challenges and Opportunities for Southeast Asia

Since Xi Jinping’s unveiling, in 2013, the Belt and Road Initiative (BRI) has drawn remarkable global attention, raising polarized judgements about China’s ambitions. A number of countries and institutions enthusiastically considered the BRI as a valuable infrastructural and economic contribution that would enhance connectivity among Eurasian countries; on the other hand, critics viewed the BRI as part of Beijing’s effort to gain global influence, especially within its neighborhood. Chinese policymakers have considered Southeast Asia as a critical region for the success of the BRI, mainly because of the geographical proximity as well as the strong economic ties with both individual states and the ASEAN. In Southeast Asian states’ view, however, the BRI still presents a mixed picture of opportunities and challenges. Despite the clear appeal the BRI has to both democratic and authoritarian leaders in the region, especially at a time of economic uncertainty—fueled by unhelpful actions by the United States (withdrawal from the TPP and the trade war against Beijing)—concerns remain. Potential overdependence on China, the BRI’s financial sustainability and negative popular perceptions about Beijing within certain Southeast Asian countries, all contribute to nurture caution in the region. The paper aims at showing how the implementation of the BRI will likely enhance China’s influence in Southeast Asia. Against this backdrop, whereas the establishment of a renovated Sinocentric system is far from certain, this study sheds light on the challenges and opportunities the BRI is determining upon Southeast Asian countries and their relationship with Beijing

Lithuanian pension system’s reforms transformations and forecasts

The aim of this article is to describe the Lithuanian pension system, its reform process and its long-term financial sustainability. We define therefore the current reforms in the public pension system, influenced by the last economic crisis and social challenges. Also, we forecast the financial dynamics of the public pension system, in the light of raising social expenses (due to second pillar pension reforms) and of demographic trends (like ageing society and low fertility). Results reveal the long-term sustainability of the system, albeit at a cost of initial negative balances to be covered with public budget. Policy solutions could improve sustainability by encouraging and extending employment (especially for the disadvantaged) and by building trust in both public and private pension systems

Drift velocity peak and negative differential mobility in high field transport in graphene nanoribbons explained by numerical simulations

We present numerical simulations of high field transport in both suspended and deposited armchair graphene nanoribbon (A-GNR) on HfO2 substrate. Drift velocity in suspended GNR does not saturate at high electric field (F), but rather decreases, showing a maximum for F=10 kV/cm. Deposition on HfO2 strongly degrades the drift velocity by up to a factor of 10 with respect to suspended GNRs in the low-field regime, whereas at high fields drift velocity approaches the intrinsic value expected in suspended GNRs. Even in the assumption of perfect edges, the obtained mobility is far behind what expected in two-dimensional graphene, and is further reduced by surface optical phonons.Comment: 4 pages, 4 figure

The Ecology of defensive medicine and malpractice litigation

Using an evolutionary game, we show that patients and physicians can interact with predator-prey relationships. Litigious patients who seek compensation are the ‘predators’ and physicians are their ‘prey’. Physicians can adapt to the risk of being sued by performing defensive medicine. We find that improvements in clinical safety can increase the share of litigious patients and leave unchanged the share of physicians who perform defensive medicine. This paradoxical result is consistent with increasing trends in malpractice claims in spite of safety improvements, observed for example in empirical studies on anesthesiologists. Perfect cooperation with neither defensive nor litigious behaviors can be the Pareto-optimal solution when it is not a Nash equilibrium, so maximizing social welfare may require government intervention

La Crisi dei mutui <i>subprime</i> e le sue implicazioni nella gestione e regolamentazione del rischio

We expose a historical and theoretical framework for the concepts of probability, risk and financial bubbles. Then, we focus on the subprime mortgage crisis in the United States and we provide: a comparison with similar past crises, an analysis of the causes and consequences, a review of the Basel Accords on banking capital regulations in the light of reform proposals. In appendix, a martingale model for bubbles in financial markets is finally provided

Precise optical timing of PSR J1023+0038, the first millisecond pulsar detected with Aqueye+ in Asiago

We report the first detection of an optical millisecond pulsar with the fast photon counter Aqueye+ in Asiago. This is an independent confirmation of the detection of millisecond pulsations from PSR J1023+0038 obtained with SiFAP at the Telescopio Nazionale Galileo. We observed the transitional millisecond pulsar PSR J1023+0038 with Aqueye+ mounted at the Copernicus telescope in January 2018. Highly significant pulsations were detected. The rotational period is in agreement with the value extrapolated from the X-ray ephemeris, while the time of passage at the ascending node is shifted by $11.55 \pm 0.08$ s from the value predicted using the orbital period from the X-rays. An independent optical timing solution is derived over a baseline of a few days, that has an accuracy of $\sim 0.007$ in pulse phase ($\sim 12$ $\mu$s in time). This level of precision is needed to derive an accurate coherent timing solution for the pulsar and to search for possible phase shifts between the optical and X-ray pulses using future simultaneous X-ray and optical observations.Comment: 6 pages, 4 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society Letter