物理最新文献

In this work, a two-population neural field (TPNF) model is investigated under the influence of a more comprehensive spatiotemporal external input. The symmetric and stationary solutions (bump solutions) of the TPNF model serve as persistent activity states (working memory) in the brain. The emergence of these persistent activities in TPNF model is investigated under the influence of external inputs with an emphasis on temoral evolution. Earlier studies have used triangular and smooth alpha-type spatiotemporal external inputs, derived from experimental observations to study the emergence of bump solutions. In this work, we formulated a more comprehensive spatiotemporal external input (piecewise) that retains the characteristics of earlier inputs with some additional features that makes it more comprehensive. It is found that relative inhibition time constant (tau) is very significant in shaping the emergence of self-sustained activity states. Specific phases of the external input play crucial role for evoking these network activity states, e.g., total duration, amplitude, stimulus onset and peak time duration of the external input. It is discovered that the minimal amplitude and active duration to evoke network activity are lower than those found in earlier studies. The results in this work are computed numerically using RK-4 method.

We present a longitudinally diode-pumped Q-switched Nd:YAG/V:YAG microchip laser emitting at (1.44,upmu)m and the optimization of its output parameters in terms of pulse energy and peak power maximization. Optimization was achieved by modifying the size of the pumping beam with four compact focusing systems, each consisting of an aspheric collimator and one of four aspheric focusing lenses. The laser’s emission spectrum, average power, pulse duration, and spatial beam profile were measured for pumping repetition frequencies ranging from 10 to 715 Hz. Using different focusing systems, it was possible to increase the maximum pulse energy and peak power up to (91,upmu)J and 14.8 kW, respectively. Thermal effects due to pumping influenced both the laser operation and the parameters of the V:YAG saturable absorber, leading to a decrease in pulse duration from 9.6 to 4.9 ns.

The combination of the “2 + 1” phase-shifting algorithm with temporal phase unwrapping (TPU) not only facilitates the acquisition of phase information using fewer fringe patterns but also minimizes errors resulting from motion in the 3-step phase-shifting profilometry (PSP). By considering the influence of fringe frequency sequences on measurement accuracy, we derive the noise-induced wrapped phase error and its variance of the “2 + 1” phase-shifting algorithm and further analyze the phase unwrapping accuracy at each stage of the “2 + 1 + 2 + 2” algorithm. Consequently, a method for selecting the optimal fringe frequency sequence is introduced, ensuring that the phase unwrapping accuracy in both stages remains as consistent as possible, while the effectiveness of this method is experimentally validated. The experimental results demonstrate that the method for selecting the optimal fringe frequency is applicable to both hierarchical and heterodyne TPU and aligns well with theoretical analysis. Compared to two sets of non-optimal frequency sequences, the error rates of the optimal fringe frequency sequences are reduced by 33.41% and 72.53%, respectively.

In this work we present the power scaling of diode-pumped waveguide lasers fabricated in a Pr:LiLuF₄ crystal by direct femtosecond writing. We demonstrated a maximum output power of 360 mW at 604 nm, 420 mW at 721 nm, and 55 mW at 523 nm. Moreover, we demonstrated what we believe to be the first operation of a waveguide laser at 545 nm. In the end, we achieved stable lasing at 604 nm with an extraction of 96%, demonstrating the high gain achievable in waveguide devices.

Optical transmissions are involved in the Ge₂₅S_75−xSb_x (x = 0, 10) chalcogenides thin films within the range of wavelength 300 to 3100 nm. Swanepoel’s approach is used for evaluation of linear optical parameters (n, k, x, εʹ and εʺ) on the basis of transmission measurements. Optical band gap (2.49 and 1.89 eV) and dispersion analysis are done by using Tauc’s and WDD relations, respectively. In search of the possibility of nonlinear switching in Ge₂₅S_75−xSb_x (x = 0, 10) chalcogenides, nonlinear index of refractions (1.456 × 10⁻¹² esu and 2.153 × 10⁻¹² esu) and nonlinear susceptibility (4.55 × 10⁻¹³ and 7.01 × 10⁻¹³) are also evaluated. Based on result out comes on the basis of figure of merit, the applicability for photonics is discussed.

The increasing adoption of wearable electronic devices across various sectors has driven significant research into flexible radio frequency (RF) antennas to overcome the limitations of traditional metal-based antennas. The demand for lightweight, flexible, and low-profile designs highlights the necessity for innovative solutions in portable electronics. This work proposes a compact, broadband omnidirectional monopole antenna for wearable applications, incorporating a slotted ground plane to enhance both impedance bandwidth and omnidirectional radiation characteristics. The antenna design was developed using Computer Simulation Technology (CST) software and validated through ANSYS HFSS, demonstrating strong agreement between the results from both simulation software. The antenna was fabricated using a felt fabric substrate and e-textile conductive materials, providing excellent flexibility, lightweight properties, and seamless integration into garments. The fabricated prototype, measuring 80 mm × 57 mm × 1 mm, achieved a measured impedance bandwidth of 118% (1.78–7 GHz). The gain varies between 2.17 dBi and 8.9 dBi, while the efficiency ranges from 85 to 97% over the operational frequency range, making this antenna a promising candidate for high-data-rate and efficient communication links. Structural deformation tests confirmed the antenna’s stable performance under mechanical stress and human body loading. Additionally, the simulated specific absorption rate (SAR) values remained within FCC limits, validating the antenna’s safety for wearable applications. A potential healthcare application involves integrating the antenna into a doctor’s chest badge, which could replace manual card swiping, improve convenience, and reduce bacterial contamination risks. Overall, this antenna offers significant potential for advancing wearable communication systems and medical technology.

Nickel oxide (NiO) nanoflowers decorated with reduced graphene oxide (RGO) were synthesised via the cost-effective hydrothermal method, followed by calcination to form composites. Various analytical techniques including FE-SEM, XRD, UV-visible, and Raman were employed to characterize the morphological, structural, and optical properties of the specimens, respectively. Electrochemical properties of NiO nano flower and RGO-decorated NiO nanoflowers (NRGO) materials, were evaluated through cyclic voltammetry, galvanostatic charge-discharge testing, and electrochemical impedance analysis. Findings indicate that the addition of RGO enhances the reversibility of NiO as an electrode material by providing a continuous framework and more active sites for redox reactions due to its unique configuration. The specific capacitance of the NRGO3 composites reached 396 Fg^− 1 in a 6 M KOH electrolyte at a scan rate of 10 mV/s and has the lowest R_CT value compared to others. All the samples have shown good stability with a percentage of retention of more than 80%, suggesting that, it is a good electrode material for energy storage applications.

We develop precise formulation for the effects of vacuum polarization near a pointlike source with a zero-range ((delta)-like) potential in three spatial dimensions. There are different ways of introducing (delta)-interaction in the framework of quantum theory. We discuss the approach based on the concept of self-adjoint extensions of densely defined symmetric operators. Within this approach, we consider the real massive scalar field in three-dimensional Euclidean space with a single extracted point. Appropriate boundary conditions, imposed at this point, enable one to consider all self-adjoint extensions of (- Delta) as operators which can describe a pointlike source with a zero-range potential. In this framework, we compute the renormalized vacuum expectation value of the field square (langle phi ^{{hspace{1.0pt}}2}(x)rangle _{textrm{ren}}) and the renormalized vacuum average of the scalar-field’s energy-momentum tensor (langle T_{mu nu }(x)rangle _{textrm{ren}}). Asymptotic cases are discussed in detail.