1,759 research outputs found
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
Lie-Group Modeling and Numerical Simulation of a Helicopter
Helicopters are extraordinarily complex mechanisms. Such complexity makes it difficult to model, simulate and pilot a helicopter. The present paper proposes a mathematical model of a fantail helicopter type based on Lie-group theory. The present paper first recalls the Lagrange–d'Alembert–Pontryagin principle to describe the dynamics of a multi-part object, and subsequently applies such principle to describe the motion of a helicopter in space. A good part of the paper is devoted to the numerical simulation of the motion of a helicopter, which was obtained through a dedicated numerical method. Numerical simulation was based on a series of values for the many parameters involved in the mathematical model carefully inferred from the available technical literature
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
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
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
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