Anisotropic Radiation in Heterostructured “Emitter in a Cavity” Nanowire

Tailorable synthesis of axially heterostructured epitaxial nanowires (NWs) with a proper choice of materials allows for the fabrication of novel photonic devices, such as a nanoemitter in the resonant cavity. An example of the structure is a GaP nanowire with ternary GaPAs insertions in the form of nano-sized discs studied in this work. With the use of the micro-photoluminescence technique and numerical calculations, we experimentally and theoretically study photoluminescence emission in individual heterostructured NWs. Due to the high refractive index and near-zero absorption through the emission band, the photoluminescence signal tends to couple into the nanowire cavity acting as a Fabry–Perot resonator, while weak radiation propagating perpendicular to the nanowire axis is registered in the vicinity of each nano-sized disc. Thus, within the heterostructured nanowire, both amplitude and spectrally anisotropic photoluminescent signals can be achieved. Numerical modeling of the nanowire with insertions emitting in infrared demonstrates a decay in the emission directivity and simultaneous rise of the emitters coupling with an increase in the wavelength. The emergence of modulated and non-modulated radiation is discussed, and possible nanophotonic applications are considered.

Collective cloaking of a cluster of electrostatically defined core-shell quantum dots in graphene

We study cloaking of a cluster of electrostatically defined core-shell quantum dots in graphene. Guided by the generalized multiparticle Mie theory, the Dirac electron scattering from a cluster of quantum dots is addressed. Indeed distant quantum dots may experience a sort of individual cloaking. But despite the multiple scattering of an incident electron from a set of adjacent quantum dots, collective cloaking may happen. Via a proper choice of the radii and bias voltages of shells, two most important scattering coefficients and hence the scattering efficiency of the cluster dramatically decrease. Energy-selective electron cloaks are realizable. More importantly, clusters simultaneously transparent to electrons of different energies, are achievable. Being quite sensitive to applied bias voltages, clusters of core-shell quantum dots may be used to develop switches with high on-off ratios.

Examining Flux Tube Interactions as a Cause of Sub-alfvénic Outflow

In accepted models, magnetic tension drives reconnected magnetic flux away from the reconnection site at the local Alfvén speed. Numerous observational signatures of these outflows have been identified in solar flares, notable among them being supra-arcade downflows (SADs), almost none move at the Alfvén speed as predicted by models. Well-studied examples of SADs or SAD loops found in the flare of 2017 September 10 (SOL2017-09-10T15:35:00) move at a quarter or less of the expected Alfvén speed. Among those reasons posited to explain such discrepancies is the possibility that reconnected flux experiences a drag force during its outflow. Drag has not been included in previous reconnection models. Here, we develop the first such model in order to test the possibility that drag can explain sub-alfveńic reconnection outflows. Our model uses thin flux tube dynamics, previously shown to match features of flare observations other than outflow speed, including for the 2017 September 10 flare. We supplement the dynamics with a drag force representing the tube’s interaction with surrounding plasma through the formation of a wake. The wake’s width appears as a parameter in the force. We perform simulations, varying the drag parameter and synthesizing EUV observations, to test whether a drag force can produce a reasonable fit to observed features of the September 10 flare. We find that that slower retraction increases the brightness of emission and lowers the temperature of the synthetic plasma sheet. With proper choice of parameters the drag enables the simulation to agree reasonably with the observations.

Renormalizable and Unitary Lorentz Invariant Model of Quantum Gravity

We analyze the R+R2 model of quantum gravity where terms quadratic in the curvature tensor are added to the General Relativity action. This model was recently proved to be a self-consistent quantum theory of gravitation, being both renormalizable and unitary. The model can be made practically indistinguishable from General Relativity at astrophysical and cosmological scales by the proper choice of parameters.

Renormalizable and Unitary Lorentz Invariant Model of Quantum Gravity

We analyze the R + R2 model of quantum gravity where terms quadratic in the curvature tensor are added to the General Relativity action. This model was recently proved to be a self-consistent quantum theory of gravitation, being both renormalizable and unitary. The model can be made practically indistinguishable from General Relativity at astrophysical and cosmological scales by the proper choice of parameters.

3D Helmholtz resonator with two close point-like windows: Regularisation for Dirichlet case

In this paper, a model of 3D Helmholtz resonator with two close point-like windows is considered. The Dirichlet condition is assumed at the boundary. The model is based on the theory of self-adjoint extensions of symmetric operators in Pontryagin space. The model is explicitly solvable and allows one to obtain the equation for resonances (quasi-eigenvalues) in an explicit form. A proper choice of the model parameter leads to the coincidence of the model solution with the main term of the asymptotics (in the window width) of the realistic solution, corresponding to small windows. A regularization is suggested to obtain a realistic limiting result for two merging windows.

Long-range Josephson effect controlled by temperature gradient and circuit topology

We demonstrate that the supercurrent can be strongly enhanced in cross-like superconducting hybrid nanostructures (X-junctions) exposed to a temperature gradient. At temperatures T exceeding the Thouless energy of our X-junction, the Josephson current decays algebraically with increasing T and can be further enhanced by a proper choice of the circuit topology. At large values of the temperature gradient, the non-equilibrium contribution to the supercurrent may become as large as the equilibrium one at low T. We also predict a variety of transitions between 0- and $$\pi $$ π -junction states controlled by the temperature gradient as well as by the system geometry. Our predictions can be directly verified in modern experiments.

Single switch Z source/quasi Z source DC-DC converters

<span>This paper analyzes a family of high step up single switch switched capacitor boost converters and Z-source/quasi Z-source dc-dc converters to provide high output dc voltage gain, a proper choice for photovoltaic applications. The operating principles, parameters design guideline of these converters are presented along with simulation results.</span>