3,516 research outputs found
A Generic Model for Current Collapse in Spin Blockaded Transport
A decrease in current with increasing voltage, often referred to as negative
differential resistance (NDR), has been observed in many electronic devices and
can usually be understood within a one-electron picture. However, NDR has
recently been reported in nanoscale devices with large single-electron charging
energies which require a many-electron picture in Fock space. This paper
presents a generic model in this transport regime leading to a simple criterion
for the conditions required to observe NDR and shows that this model describes
the recent observation of multiple NDR's in Spin Blockaded transport through
weakly coupled-double quantum dots quite well. This model shows clearly how a
delicate interplay of orbital energy offset, delocalization and Coulomb
interaction lead to the observed NDR under the right conditions, and also aids
in obtaining a good match with experimentally observed features. We believe the
basic model could be useful in understanding other experiments in this
transport regime as well.Comment: 10 pages, 10 figures. to appear in Phys Rev
Nonlinear feedback oscillations in resonant tunneling through double barriers
We analyze the dynamical evolution of the resonant tunneling of an ensemble
of electrons through a double barrier in the presence of the self-consistent
potential created by the charge accumulation in the well.
The intrinsic nonlinearity of the transmission process is shown to lead to
oscillations of the stored charge and of the transmitted and reflected fluxes.
The dependence on the electrostatic feedback induced by the self-consistent
potential and on the energy width of the incident distribution is discussed.Comment: 10 pages, TeX, 5 Postscript figure
Comparison of latest and innovative silica-based consolidants for volcanic stones
This research explores the new perspectives in conservation and protection of two macroporous tuff stones, widely employed in the architectural heritage of Campania region, characterized by highly heterogeneous rock fabric and texture and a variable mineralogical composition that represent crucial factors responsible for their weak durability. The consolidation treatments were performed with a recently and widely used suspension of nano-silica crystals in water and with a lithium silicate solution that has received up to now scarce attention as a consolidant agent. Physical investigations (open porosity, Hg porosimetry, water absorption), morphological observations (SEM analyses) and visual appearance test (colorimetric measurements), along with assessments of performance indicators such as ultrasonic pulse velocity, surface cohesion test (peeling test) and durability test (salt crystallization), were carried out to investigate the consolidation effectiveness. Overall, lithium silicate consolidant showed a better behavior in terms of superficial cohesion, a most successful strengthening action and a considerable enhancement of salt resistance
Quantum electrodynamical torques in the presence of Brownian motion
Quantum fluctuations of the electromagnetic field give rise to a zero-point energy that persists even in the absence of electromagnetic sources. One striking consequence of the zero-point energy is manifested in the Casimir force, which causes two electrically neutral metallic plates to attract in order to reduce the zero-point energy. A second, less well-known, effect is a torque that arises between two birefringent materials with in-plane optical anisotropy as a result of the zero-point energy. In this paper, we discuss the influence of Brownian motion on two birefringent plates undergoing quantum electrodynamical (QED) rotation as a result of the system's zero-point energy. Direct calculations for the torque are presented, and preliminary experiments are discussed. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft
Only the best for my kids: An extended TPB model to understand mothers’ use of food labels
Despite the evidence that mothers’ food purchasing behavior impacts the quality of children's diet, few studies have explored psycho-social factors influencing how mothers choose the food to buy for their children. To fill this gap, this study tested an extended Theory of Planned Behavior (TPB) model to predict mothers’ tendency to seek information on food labels before purchasing food for children. Participants included 311 Italian mothers who completed a self-report questionnaire measuring their information-seeking behavior, TPB variables, anticipated regret and healthy-eater identity. Results from a Multiple Correspondence Analysis showed that mothers’ information-seeking behavior involved a continuum of choices ranging from selecting conventional or prepackaged foods to choosing to read the food label before making a purchase. Besides, a Partial Least Squares–Structural Equation Modeling analysis showed that information-seeking behavior was positively predicted by intention (β = 0.309, p < 0.001) and healthy-eater identity (β = 0.195, p < 0.001). In turn, intention was positively affected by attitude (β = 0.208, p < 0.001), subjective norms (β = 0.155, p < 0.01), perceived behavioral control (β = 0.124, p < 0.05), anticipated regret (β = 0.193, p < 0.001), and healthy-eater identity (β = 0.191, p < 0.001). These findings emphasize that future initiatives could usefully target attitude, anticipated regret and self-identity to encourage mothers’ informed food choices for their children
Hybrid Storage System Control Strategy for All-Electric Powered Ships
Abstract In marine applications all-electric propulsion systems are employed on surface ships that are subjected to particular constraints, generally due to environmental restrictions. The technological advancement of electrochemical batteries, which are today characterized by higher capacity and efficiency, has widened their fields of application, although these storage systems require an accurate design to limit their initial and maintenance costs. In order to reduce battery charge and discharge peak currents, supercapacitor modules are generally adopted with the aim to extend batteries expected life. The proper management of energy fluxes within the hybrid architecture, and in particular among batteries, capacitors and loads requires a specific control, called EMS – Energy Management Strategy. In this paper, a novel EMS, based on constrained minimization problem, is proposed and verified with reference to a case study of a waterbus operating in restricted waterways on different routes. The procedure is based on a preliminary solution of an off-line optimization with respect to a known mission profile. Hence, a real-time control strategy is properly evaluated, in order to guarantee robustness against the unavoidable uncertainties, which occur during the operating conditions. In the last part of the paper, a numerical application is presented with the purpose to emphasize the feasibility of the proposal
Fabrication methods for a quantum cascade photonic crystal surface emitting laser
Conventional quantum cascade (QC) lasers are intrinsically edge-emitting devices with mode confinement achieved via a standard mesa stripe configuration. Surface emission in edge emitting QC lasers has therefore necessitated redirecting the waveguided laser emission using a second order grating. This paper describes the methods used to fabricate a 2D photonic crystal (PC) structure with or without a central defect superimposed on an electrically pumped QC laser structure with the goal of achieving direct surface emission. A successful systematic study of PC hole radius and spacing was performed using e-beam lithography. This PC method offers the promise of a number of interesting applications, including miniaturization and integration of QC lasers
Quantum cascade photonic crystal surface emitting injection laser
A surface emitting quantum cascade injection laser is presented. Direct surface emission is obtained by using a 2D photonic-band-gap structure that simultaneously acts as a microcavity. The approach may allow miniaturization and on-chip-integration of the devices
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