Pramana最新文献

Tera Hertz photoconductive antennas (THz PCAs) have significantly advanced the THz research by offering room-temperature operation, broad bandwidth and relatively low cost as both emitters and detectors. However, the primary limitation has been their low power output due to inefficient conversion. This article demonstrates a substantial improvement in efficiency ((sim 200%)) by incorporating sub-micron photonic structures on the surface. These photonic structures enhance pump beam coupling, leading to increased photocarrier generation. They also facilitate efficient carrier recombination after THz emission, thereby suppressing carrier screening. Experimental and numerical studies confirm the enhanced photocarrier generation and controlled transport through defect-free paths, further reducing screening effects. The integration of photonic structures into large area emitters (LAEs) holds the potential to develop emitters and detectors suitable for real-world THz systems, overcoming the limitations of the current commercial LAEs that rely on plasmonic structures or antireflection coatings. This innovation has the potential to revolutionise THz technology, enabling the development of more powerful and efficient THz sources and detectors. This can lead to advancements in various fields, including wireless communication, imaging and sensing and spectroscopy.

Fast radio bursts (FRBs) are radio-transients of extragalactic origin lasting from fractions of a millisecond to hundreds of milliseconds. Their actual physical nature is yet to be ascertained and is still a topic of active research. In this paper, we have considered both non-CHIME and CHIME sources, and have subjected the available FRB data to various analyses. Since CHIME first catalogue provides only the lower bounds to the FRB flux density and fluence, we have devised a novel approach that utilises the ratio of the catalogued lower limits of the flux density (S_{nu _O}) to the fluence (F_{nu _O}) of individual FRB events to construct several parameters (Xi, i=1,2,ldots ,7) but ( i ne 5) to investigate the presence of underlying trends in the CHIME FRB population. These parameters are also computed for the non-CHIME FRB events using the ratio of the measured flux density (S_{nu _O}) to the fluence (F_{nu _O}). One of these defined parameters (X7) involve the actual brightness temperature as well as energy density instead of the corresponding bounds, despite one’s ignorance of thess actual size of the FRB emission region. Our first robust conclusion is that the individual non-CHIME FRB events fall under two broad categories based on their peak luminosity densities. This has been explicitly demonstrated for peak luminosity densities calculated at two distinct frequencies – 300 and 450 MHz. Our second robust result is that the parameters Xis involving the ratio of the flux density to the fluence are almost the same for both CHIME and non-CHIME FRB populations, vindicating our use of these parameters that make use of (S_{nu _O}/ F_{nu _O}) and other measured quantities. This universality is also seen in the underlying patterns exhibited by the distributions of the computed parameters Xis for both CHIME and non-CHIME FRB population, suggesting thereby the existence of two categories even for the FRB events detected by CHIME. Assuming that FRBs are caused by magnetar glitches that lead to an abrupt change in the light cylinder radius, we have considered a simple physical model to address the issue of two categories based on the FRB luminosity density.

We have investigated the gas electron multiplier (GEM) signal and time resolution using a numerical analysis method. The Garfield(++) simulation package with a known field solver, ANSYS, is used here. To examine the impacts of gas mixture and electron transport characteristics inside the detector, two other softwares, Magboltz and Heed, were utilised. By exploring the effects of detector geometry, electric fields, incoming particle energy and gas mixture characteristics, we tried improving GEM detectors for higher temporal resolution. A single GEM detector was investigated with two radiation sources, i.e., a 5.9 keV (hbox {Fe}^{55}) X-ray photon and cosmic muons with energies ranging from 1 MeV to 1 TeV. With Ar:(hbox {CO}_2) gas mixture for a particular set-up, a minimum time resolution of up to around 4 ns was recorded. This number can be reduced even more by using various detector geometries and field settings. A significant result in lowering the temporal resolution was achieved by changing the drift field and percentage of the ionisation component in the gas mixture. The admixture of (hbox {O}_2) and (hbox {N}_2) in the gas medium also improved the detector time performance. It was also observed that the initial particle energy has little effect on the timing accuracy of the detector.

Discovery of electron hydrodynamics in graphene systems has opened a new scope of theoretical research in condensed matter physics, which was traditionally well cultivated in science and engineering as a non-relativistic hydrodynamics and in high energy nuclear and astrophysics as relativistic hydrodynamics. Electrons in graphene follow neither non-relativistic nor relativistic hydrodynamics. Similar to other hydrodynamical descriptions, the energy–momentum tensor of graphene also has an ideal component and a dissipating component, but in an unconventional way, so popularly, it is sometimes called as unconventional hydrodynamics. The unconventional part of the dissipating component for the energy–momentum tensor is recently addressed in Phys. Rev. B 108, 235172 (2023) but its ideal component, which is connected with the thermodynamics of graphene, has not been zoomed in a very systematic way. This article has gone through systematic microscopic calculations of thermodynamical quantities like pressure, energy density, etc., of electron-fluid in graphene and compared with the corresponding estimations for non-relativistic and ultra-relativistic cases. We have sketched the temperature and Fermi energy dependency of electron thermodynamics for graphene and other cases where the transition from Fermi liquid to Dirac fluid domain is explored. An equivalent transition for quark matter is also discussed. Interestingly, an enhancement of specific heat within the low-temperature and Fermi energy region is found, which may be connected to the recently observed Wiedemann–Franz law violation.

We use phase-space distributions – specifically, the Wigner distribution (WD) and Husimi distribution (HD) – to investigate certain information-theoretic measures as descriptors for a given system. We extensively investigate and analyse Shannon, Wehrl and Rényi entropies, their divergences, mutual information and other correlation measures within the context of these phase-space distributions. The analysis is illustrated with an anharmonic oscillator and is studied with respect to the perturbation parameter ((lambda )) and states (n). The entropies associated with WD are observed to be lower than those of HD, which aligns with the findings regarding the marginals. Moreover, the real components of the entropies associated with WD tend to approach the entropic uncertainty bound more closely than those of the corresponding HD. Moreover, we quantify the precise amount of information lost when opting for HD over WD for characterising the specified system. Since it is not always positive definite, the entropies cannot always be defined.

This paper mainly focusses on the influence of natural frequency on a double Hopf bifurcation system with two-time scale. While the attractors may vary as the excitation amplitude expands, we try to discover all the characteristic of influence by gradually increasing the excitation amplitude. Based on the grasped mechanism of oscillators as well as comparative research concentrating at different values of natural frequency, some regular conclusions can be reached. When the excitation amplitude is small, only oscillators of single mode exist, while the natural frequency responsible for the sub-plane with no oscillation makes no difference to the one with oscillations. With the amplitude increasing, the system may switch between oscillations of different modes. The natural frequency may affect the frequency of bursting oscillation in its own sub-plane and the time that the system switches from single-mode oscillation to mixed-mode oscillations. For relatively large amplitudes, oscillations with mixed modes occupy the whole movements. The natural frequency corresponding to one sub-plane may affect the amplitude of bursting oscillation or the time that the system alternates between the spiking state and the quiescent state as well as the routes that the trajectory goes through in the other sub-plane.

Our study examines the impact of sixth-order dispersion and multiplicative white noise on the transmission of optical solitons within magneto-optic waveguides. Our findings offer valuable insights that are crucial for the advancement of optical communications. We demonstrate how these factors affect soliton behaviour by developing and analysing a stochastic version of the Sasa–Satsuma equation, which describes the dynamics of optical solitons in dispersive media. Our research introduces an enhanced analytical approach that addresses the complexities introduced by these perturbations, specifically by modifying the sub-ordinary differential equation (sub-ODE) method. The investigation reveals the substantial influence of sixth-order dispersion and multiplicative white noise on the quality and stability of soliton transmission in such waveguides. These findings emphasise the significant importance of considering these factors in designing and optimising optical communication systems, particularly those utilising the propagation of optical solitons. This research represents a substantial advancement in our understanding of and ability to mitigate the effects of higher-order dispersion and stochastic perturbations on soliton-based communication technology.

This study investigates the thermal properties of a longitudinally inclined moving porous fin with varying internal heat generation. The approach takes into account the combined influence of natural convection, radiation, and the wet condition while modelling the fin’s energy equation. Using dimensionless terms, the governing energy balance equation is converted into an ordinary differential equation (ODE), which is then solved using the Differential transform method (DTM) and Pade approximant. The machine learning (ML) algorithms is also implemented for detecting temperature fluctuations in wetted fins. The ability of stacking ensemble ML model is employed to strengthen the reliability and accuracy of forecasts, which demonstratrates the improved regression predictions with absolute error rates ranging at 10⁻⁶. The coefficient of regression of 1 indicates the best fit for the data signifying efficient ML prediction. The graphical representations demonstrate how thermal factors influence temperature dispersion. The analysis reveals that the fin’s temperature rises with increasing ambient temperature, nondimensional internal heat generation, generation number, power exponent, and Peclet number. However, under these conditions the temperature gradient reduces. Furthermore, greater values of the convective, radiative, wet porous, and inclination angle parameters result in lower fin temperatures, which aids in cooling while increasing the temperature gradient.

One of the best ways to scale down below sub-7 nm technology nodes seems to be to use vertically stacked horizontal nanosheet gates all around the transistors. To analyse transistor structure and improve the performance of the device, in this work, we compare the physical models, geometrical configuration and electrical performance of the vertically stacked horizontal nanosheet transistors. We investigate how the gate-length, gate oxide thickness, work function engineering, nanosheets – their width, height, number of stacked sheets with doping concentration, gate materials can affect the electrical performance and here we present the suitable design required for vertically stacked nanosheet field effect transistors (FETs) for improved performance using TCAD calibration. Also, the self-heating effect is analysed by varying the number of nanosheets, width of nanosheets using a thermodynamic model. The calibration set-up exhibits good efficiency towards the technology node. The significant device variability might result from the stacked nanosheet architectures becoming more complicated over the adverse device improvement.

The study focusses on analysing the intricate dynamics of heat and mass transfer in non-Newtonian fluids, emphasising the efficacy of the Williamson fluid model in characterising situations with diverse viscosities. This study investigates the mass and heat transfer of a magnetohydrodynamic Williamson fluid across a surface with stretched pores, taking into account the radiation from heat sources and chemical reactions. We reduce the extremely nonlinear governing equations to more manageable forms by applying similarity invariants and obtain the numerical solution by combining the shooting method and the BVP4C method to solve the reduced systems of ordinary differential equations MATLAB visualisations demonstrate that the non-dimensional parameters are closely related to the body of current literature. Notably, the data indicate an intensification of the temperature profile at higher radiation, Williamson and magnetic factor values, while fluid motion experiences a decrease at these elevated levels. This study’s results hold significant implications for industries such as food processing, glassmaking, oil extraction and others related to fluids, as it links higher Williamson and magnetic parameters to reduced fluid mobility, while higher Williamson, magnetic and radiation factors enhance the temperature profile. Overall, this work provides insightful information about how non-Newtonian fluids behave under various physical conditions, with useful applications for a broad range of industrial processes. The purpose of this study is to look at the dynamics of Williamson nanofluids under slip-enhanced magnetohydrodynamics, having a particular emphasis on the interaction of thermal radiation, chemical reaction and a permeable stretching sheet. This research uses the shooting technique and the BVP4C approach to examine the complicated behaviour of the system in depth.