Gating of high-mobility InAs metamorphic heterostructures

We investigate the performance of gate-defined devices fabricated on high mobility InAs metamorphic heterostructures. We find that heterostructures capped with In$_{0.75}$Ga$_{0.25}$As often show signs of parallel conduction due to proximity of their surface Fermi level to the conduction band minimum. Here, we introduce a technique that can be used to estimate the density of this surface charge that involves cool-downs from room temperature under gate bias. We have been able to remove the parallel conduction under high positive bias, but achieving full depletion has proven difficult. We find that by using In$_{0.75}$Al$_{0.25}$As as the barrier without an In$_{0.75}$Ga$_{0.25}$As capping, a drastic reduction in parallel conduction can be achieved. Our studies show that this does not change the transport properties of the quantum well significantly. We achieved full depletion in InAlAs capped heterostructures with non-hysteretic gating response suitable for fabrication of gate-defined mesoscopic devices

Large deformation, damage evolution and failure of ductile structures to pulse-pressure loading

In this paper, a model is developed for an elastic perfectly-plastic structural beam system subjected to general pulse-pressure loadings - this may be either impulsive or non-impulsive - which is capable of capturing large non-linear deformation, ductile damage evolution and its consequential failure. The proposed model is an extension of Schleyer and Hsu (2000) by incorporating interactions between bending, membrane stretch and transverse shear in the fully plastic stress state, and uses damage mechanics to capture the loss of integrity at the supports and the subsequent beam detachment. Predictions by the model were validated against existing experimental data from literature and to three-dimensional finite element models developed in this paper. Parametric studies were performed to elucidate the effects of loading duration on the mode of deformation by the beam and the critical conditions governing their transition. The efficacy of Youngdahl’s (1970; 1971) technique on desensitising pulse shape effects is also investigated using different pressure pulse profiles and it will be shown that the technique is successful only for monotonically decaying pulse-pressures

The influence of deformation limits on fluid-structure interactions in underwater blasts

This paper revisits a classical fluid-structure interaction (FSI) problem on the momentum and energy transfer to a structure from an underwater blast. Hitherto, the majority of analytical models assume a rigid (non-deformable) and free-standing (unsupported) structure where resistance to its translational motion - apart from that offered by its inertial mass - comes from ‘ad-hoc’ backing spring(s) introduced to simulate compression of the fluid medium and/or the resistance to transverse deformation encountered by a real structure. These limitations/assumptions are relaxed in this paper by adopting a physically realistic fully-clamped ductile beam system that takes into account large elasto-plastic deformation, limits to material deformation, boundary compliance and boundary failure; the analytical framework was developed previously by Yuan et al. [1]. By coupling the fluid (water) domain to the analytical model of the ductile beam system, the momentum and energy transferred by the blast wave are critically re-evaluated for non-impulsive loading régime; in particular, on how the beam’s deformation mode and boundary compliance affects fluid and structure interaction, up until the point of complete beam detachment from its supports. Detailed finite-element models were also developed to simulate the interactions between the fluid and structural beam where predictions were in good agreement with those by the analytical model. Sensitivity analyses were carried out that offer new insights on the influence of the beam’s aspect ratio and inertial mass

Possible Equilibria of Interacting Dark Energy Models

Interacting dark energy and the holographic principle offer a possible way of addressing the cosmic coincidence problem as well as accounting for the size of the dark energy component. The equilibrium points of the Friedmann equations which govern the evolution behavior of dark energy, matter, and curvature components can determine the qualitative behavior of the cosmological models. These possible equilibria and their behavior are examined in a general framework, and some illustrative examples are presented.Comment: 18 pages, 5 figure

Low Speed Current Bearing Anti-force Waves

For theoretical investigation of electrical breakdown of a gas, we apply a one-dimensional, steady profile, constant velocity, three-component (electrons, ions and neutral particles) fluid model. Our fluid model consists of the equations of conservation of mass, momentum and energy, coupled with the Poison’s equation. The set of equations is referred to as the electron fluid dynamical equations (EFD). This investigation involves breakdown waves with a substantial current behind the wave front, and waves for which the electric field force on electrons is in the opposite direction of the wave propagation (anti-force waves – lightning return stroke). Therefore, the set of electron fluid dynamical equations need to be modified. For a low wave speed, we intend to find current values, and also the maximum current, for which solutions for our set of electron fluid dynamical equations become possible

Developing a model for analysis of the cooling loads of a hybrid electric vehicle by using co-simulations of verified submodels

The requirement for including the air-conditioning and the battery-cooling loads within the energy efficiency analyses of a hybrid electric vehicle is widely recognized and has promoted system-level simulations and integrated modelling, escalating the challenge of balancing the accuracy and the speed of simulations. In this paper, a hybrid electric vehicle model is created through co-simulation of the passenger cabin, the air conditioning, the battery cooling, and the powertrai. Calibration and verification of the submodels help determine their accuracy in representing the target vehicle and achieve a balance between the model fidelity and the simulation speed. The result is a model which has a higher accuracy and a higher speed than those of similar models developed previously and which provides a reliable tool for a thorough investigation of the cooling loads for different ambient conditions and different duty cycles

Carboxylated photoswitchable diarylethenes for biolabeling and super-resolution RESOLFT microscopy.

Reversibly photoswitchable 1,2-bis(2-ethyl-6-phenyl-1-benzothiophene-1,1-dioxide-3-yl)perfluorocyclopentenes (EBT) having fluorescent "closed" forms were decorated with four or eight carboxylic groups and attached to antibodies. Low aggregation, efficient photoswitching in aqueous buffers, specific staining of cellular structures, and good photophysical properties were demonstrated. Alternating light pulses of UV and blue light induce numerous reversible photochemical transformations between two stables states with distinct structures. Using relatively low light intensities, EBTs were applied in biology-related super-resolution microscopy based on the reversible saturable (switchable) optical linear fluorescence transitions (RESOLFT) and demonstrated optical resolution of 75 nm

O ensino das ciências experimentais no liceu, em Portugal, na I República (1910-1926)

O ensino das ciências experimentais (ECE) em Portugal ficou, como pretendemos demonstrar, fortemente marcado pela instauração da República, que comemorou no ano transacto o seu centenário. A República de 1910 pretendeu reformar toda a mentalidade portuguesa, através do pilar base – a educação – pela qual seria capaz de sacudir a nossa maneira de ser, lançando desta forma o país para um progresso de nível europeu. O estudo a que nos propomos, uma investigação documental no domínio da História da Ciência1, visa aprofundar os conhecimentos existentes sobre esta época e perceber o impacto da reforma do ECE, principalmente nos Liceus, caracterizando as principais figuras, políticas e docentes responsáveis pela sua conceptualização e aplicação. Através desta investigação procuraremos lançar as primeiras bases para descobrir as origens deste pensamento, querendo ainda comparar os fundamentos psicopedagógicos, epistemológicos e sociológicos da época com as principais ideias actualmente presentes no ensino da Ciência. Com este trabalho pretendemos, num primeiro momento, apresentar e divulgar o desenho da investigação e os seus objectivos, na procura de estabelecer parcerias e receber contributos da comunidade académica interessada por esta problemática

Quantized Majorana conductance

Majorana zero-modes hold great promise for topological quantum computing. Tunnelling spectroscopy in electrical transport is the primary tool to identify the presence of Majorana zero-modes, for instance as a zero-bias peak (ZBP) in differential-conductance. The Majorana ZBP-height is predicted to be quantized at the universal conductance value of 2e2/h at zero temperature. Interestingly, this quantization is a direct consequence of the famous Majorana symmetry, 'particle equals antiparticle'. The Majorana symmetry protects the quantization against disorder, interactions, and variations in the tunnel coupling. Previous experiments, however, have shown ZBPs much smaller than 2e2/h, with a recent observation of a peak-height close to 2e2/h. Here, we report a quantized conductance plateau at 2e2/h in the zero-bias conductance measured in InSb semiconductor nanowires covered with an Al superconducting shell. Our ZBP-height remains constant despite changing parameters such as the magnetic field and tunnel coupling, i.e. a quantized conductance plateau. We distinguish this quantized Majorana peak from possible non-Majorana origins, by investigating its robustness on electric and magnetic fields as well as its temperature dependence. The observation of a quantized conductance plateau strongly supports the existence of non-Abelian Majorana zero-modes in the system, consequently paving the way for future braiding experiments.Comment: 5 figure