Doklady Physics最新文献

This work presents a mixed-mode circuit analysis of a negative-capacitance heterostructure nanotube tunnel field-effect transistor (NC-HNT-TFET) using Silvaco ATLAS TCAD for analog-on-chip applications. The proposed device achieves a subthreshold swing (SS) of 20.2 mV/dec, a transconductance-to-current ratio (g_m/I_D) superior to that of a conventional Gate-All-Around (GAA) architecture, and a significantly higher intrinsic gain than MOSFET-based amplifiers, owing to enhanced drain resistance (r_o). A complementary TFET common-source (CS) amplifier demonstrates a low-frequency voltage gain of 15 dB, a 3 dB and cutoff near 310 GHz, and two-pole system behaviour consistent with the extracted transfer function. The heterostructure employs a Ge/AlGaAs heterostructure with a HfO₂ gate dielectric and a ferroelectric (FE) layer modelled using the Landau–Khalatnikov (LK) equation. Stability and non-hysteretic operation are confirmed through capacitance-matching analysis. The extracted RF figures of merit, cutoff frequency (f_T) of 7.2 THz and maximum oscillation frequency (f_max) of 11.3 THz, are obtained by extrapolation of Y-parameter-based current-gain and unilateral-power-gain roll-offs, and are physically justified by the high tunnelling-enhanced g_m and the ultra-thin ferroelectric capacitance. These results demonstrate strong potential for ultra-high-frequency analog front-end and system-on-chip integration.

An algorithm for automatic alignment of the absolute rotor position sensor of a brushless permanent-magnet synchronous motor with distributed windings is proposed and developed, which makes it possible to calculate and consider the initial positioning error angle from the values of the control action of the regulator of the direct-axis component I_d of the stator current. A deviation of the control output of the I_d regulator in a vector field-oriented control system from the known nominal value and/or a change in the rotor rotation direction makes it possible to judge the initial error in the installation angle of the absolute rotor position sensor. It is proposed to calculate the deviation of the regulator control output in order to determine and add an offset to the rotor position angle when transforming the components of the rotating reference frame into the two-phase stationary reference frame (inverse Park transformation). A model of the converter with the electric motor has been developed. The results of mathematical simulation and full-scale experiments are presented. The relationship describing the effect of the deviation of the absolute rotor position sensor on the direct-axis current component in a control system with a speed loop is derived. The results of the effect of the encoder angle error on the control output of the direct-axis current regulator are presented.

In this paper, we have identified and studied five major geomagnetic storms whose disturbance storm time Dst < –100 nT was calculated and examined during Solar Cycle 24 and the ascending phase of Solar Cycle 25. There have been five geomagnetic storms found on March 17, 2015; December 20, 2015; September 8, 2017; August 26, 2018; and November 4, 2021, with Dst magnitudes of –234, –155, –124, –174, and –105, correspondingly. Correlation analysis of hourly plasma parameters and Kp indices (April 22–26, 2023) shows a strong relationship (Cr = 0.76) between the IMF B component and the Kp index. The solar and interplanetary parameters as well as their connection with the parameters of geomagnetic storms, have been studied in this paper. In this study, we found that coronal mass ejection is the principal cause of severe storms. It has been determined that there is a positive correlation between sunspot numbers and solar flux (F10.7), with a correlation coefficient of 0.95. The investigation aims to evaluate how the results might be applied practically to enhance forecast accuracy and mitigation strategies for safeguarding critical infrastructure, such as satellite operations, power grids, and communication networks, during geomagnetic storms.

In this article a robust Guided Physics-Informed Neural Network (GPINNs) method is used for learning and predicting the nonlinear dynamic of variable-order fractional hyperchaotic mathematical model. Fractional orders are based on polynomial, trigonometric and hyperbolic function into the sigmoid function. This variable-order fractional hyperchaotic system has been solved with GPINNs scheme that integrates data-driven learning with physics-based constraints. Four distinct fractional-order scenarios are considered to capture a broad range of memory and hereditary effects, that are inherent in practical electronic circuits. These cases made comprehensive assessment of the ability of the model. Furthermore, the effectiveness of this approach is shown through detailed analyses of time-series evolution, phase-space projections, and training diagnostics for multiple control parameters. This framework also highlights the strong potential of GPINNs for modeling complex integer- and variable fractional-order hyperchaotic systems, with promising applications in electronic circuit design, secure communication, and advanced signal processing.

We present an irreversible completion of Einstein gravity as a controlled small-diamond approximation of a null-boundary ledger framework. The primitive input is protocol-level bookkeeping on a null screen patch: a context ((mathcal{A},omega )) fixing modular comparisons, a geometric capacity (mathcal{X}: = A{text{/}}(4{{G}_{{{text{ren}}}}})) in entropy units, and a nonnegative record ledger ({{N}_{{c}}}) counting logically irreversible register updates. A two-sheet carrier separates, within each update, the reference structure used to define increments from the record-bearing structure stabilized across updates, avoiding self-referential metric-increment ambiguities. Coarse-grained balance, together with the standard small-diamond modular-universality and covariant phase-space inputs, yields a local non-equilibrium screen law whose reversible sector recovers the Einstein equation. We clarify how ledger–CTP differs structurally from standard Schwinger–Keldysh, modified gravity, and stochastic gravity. We then propose two discriminator-style tests that directly target the ledger–CTP identification of record production with an irreducible imaginary influence phase: a gravitational Loschmidt-echo bound in atom interferometry and, within a stated linear/Gaussian completion class, a dissipation–noise consistency constraint linking any inferred non-GR propagation kernel to a correlated stochastic component in gravitational-wave data.

The impact of polarization-graded AlGaN back-barrier engineering on the DC and RF performance of InAlN/GaN HEMTs is systematically investigated. The study also investigates the influence of varying indium mole fraction (x) in the In_xAl_{1 – x}N barrier layer (x = 0.75–0.83). Compared to a uniform back-barrier structure, the graded back-barrier device demonstrates enhanced DC characteristics, delivering a higher drain current density of 0.73 A/mm vs. 0.66 A/mm at V_GS = –3 V and V_DS = 2 V. The graded structure also exhibits an improved peak transconductance of 0.61 S/mm, representing an 10% enhancement over the 0.56 S/mm achieved by the uniform back-barrier HEMT. Owing to reduced parasitic capacitances, the gate–source capacitance decreases from ≈1.80 × 10^–12 to ≈1.75 × 10^–12 F/mm, while the gate–drain capacitance is lowered from ≈5.35 × 10^–13 to ≈5.0 × 10^–13 F/mm. These improvements directly translate into superior RF performance, with the graded back-barrier device achieving a peak cutoff frequency of 54 GHz, compared to 50 GHz for the uniform back-barrier device. Furthermore, breakdown voltage is enhanced from ≈880 to ≈960 V, indicating improved electric-field management and carrier confinement.

Nickel oxide (NiO) nanograins were successfully synthesized through a green, eco-friendly route using jojoba oil as a natural precursor. This sustainable approach enables the formation of nanocrystalline NiO without relying on harsh chemicals or toxic solvents. XRD analysis confirmed the development of phase-pure NiO with characteristic reflections indexed to the (111), (200), (220), (311), and (222) planes of the C12/m1 space group, while a minor Ni(OH)₂ phase was also detected. The average crystallite size, calculated from the Scherrer equation, was approximately 50 nm. SEM images revealed well-defined grains and clear grain boundaries, highlighting the polycrystalline nature of the product, whereas EDX spectra verified the presence of Ni and O along with trace elements such as Na, Cl, and C originating from the natural synthesis medium. Although electrical and dielectric measurements were conducted to probe charge-transport behavior, the primary significance of this work lies in demonstrating jojoba oil as an effective, sustainable, and low-impact precursor for producing high-quality NiO nanograins. This green synthesis pathway offers a promising alternative for the environmentally responsible fabrication of functional metal oxide nanomaterials.

The mechanisms responsible for generation of Majorana zero modes in carbon nanotubes proximately represented by an s-wave superconductor and placed in a uniform axial magnetic field are theoretically and numerically analyzed. An effective 1D low-energy model is built on the basis of the Dirac description of electronic states of graphene taking into account the rolled-up structure geometry. It is shown that the quantization of transverse motion, the orbital contribution of a magnetic field (the Aharonov–Bohm effect), and the curvature-induced spin–orbit coupling jointly form a topologically nontrivial superconducting state. In the appropriate parametric mode, the effective Hamiltonian is reduced to a known 1D model with all its parameters expressed directly through the geometric characteristics of a nanotube and the value of an external magnetic field, without introducing phenomenological assumptions. The Majorana modes emerging at the nanotube edges are nonlocal quantum states protected by the superconducting gap, which makes them promising for implementing topological qubits. The analytical results are confirmed by the numerical simulation within the Bogoliubov–de Gennes Hamiltonian, which demonstrates the energy gap closing and reopening and the emergence of localized edge states.

The rivers of the North Caucasus, particularly the Terek, experience significant anthropogenic loads of heavy metals (Pb, Cd, Zn), which accumulate in bottom sediments and, during flood periods, pose a risk of secondary pollution of floodplain agricultural lands. This paper presents a comparative analysis of the hydrological and sedimentological characteristics of the Terek and Yangtze rivers (Hunan Province, China). It is shown that both rivers exhibit similarities in three key parameters: a pronounced summer flood regime, the dominant role of fine suspended solids in pollutant transport, and the presence of anthropogenic sources of heavy metals (mining activities, industrial discharges). Based on the established similarities, the feasibility of adapting hybrid architectures with bidirectional long short-term memory networks and preliminary signal decomposition, which have been successfully tested on the Yangtze River, to predict Pb, Cd, and Zn concentrations in the Terek River was substantiated. The results of the study provide a scientific and methodological basis for subsequent calibration and verification of the model using our own field data, which it is planned to collect in 2026.

The present work suggests and examines a hetero-oxide, dual-metal, negative-capacitance, double-gate tunnel field-effect transistor (HDM-NC-DGTFET) to achieve improved electrostatic control, ON-state current, and analog/RF characteristics to low-power applications. The suggested architecture combines (i) dual metal gate work-function engineering (φ₁ < φ₂), (ii) hetero-gate dielectric arrangement, and (iii) a ferroelectric covering to produce negative capacitance voltage amplification. The low-work-function gate at the source-channel interface not only sharpens the band bending and increases band-to-band tunneling (BTBT) but also the high-work-function drain-side gate prevents ambipolar conduction by reinforcing the channel-drain barrier. Extensive 2D TCAD simulations with a non-local BTBT model show a great deal of improvement over the traditional single-metal HSM-NC-DGTFET. The proposed device is able to attain a 90% increase in ON-current, 42% decrease in threshold voltage, and a 38% decrease in subthreshold swing. Work-function modulation and optimized dielectric eliminate ambipolar leakage. Also, the device demonstrates greater analog/RF figures of merit, such as increased levels of transconductance (g_m), greater transconductance generation factor (TGF), higher cut-off frequency (f_T), and gain-bandwidth product (GBP). The synergistic combination of hetero-oxide engineering, dual metal work-function modulation and negative capacitance effect makes the HDM-NC-DGTFET a good candidate in next-generation low-power, high-frequency nanoelectronic applications.