Narrow Results

The goal of this work is to increase the beam transmission from the cyclotron to the patient location of ocular tumor treatment facility Optis 2 at the Paul Scherrer Institute and thus to reduce the patient treatment times. The examined options for such transmission increase were the installation of local degraders in the patient treatment room and modification of the energy selection collimator settings. The experiments have shown that an improvement of the beam transmission is possible to achieve, however on a cost of an increase in lateral or distal penumbra of the beam. The benefits and drawbacks of the examined options are discussed.

The Nariai black hole, whose two horizons are lying close to each other, is an extreme and important case in the research of black hole. In this paper we study the evolution of a massless scalar field scattered around in 5D Schwarzschild–de Sitter black string space. Using the method shown by Brevik and Simonsen (2001) we solve the scalar field equation as a boundary value problem, where real boundary condition is employed. Then with convenient replacement of the 5D continuous potential by square barrier, the reflection and transmission coefficients (R, T) are obtained. At last, we also compare the coefficients with the usual 4D counterpart.

Ballistic electron transport through a finite chain of quantum circular rings is studied in the presence of the Rashba coupling, of strength α, and of a perpendicular magnetic field B. The transmission and reflection coefficients for a single ring, obtained analytically, help obtain the conductance through a chain of rings as a function of the strength α, the field B, and of the wave vector k of the incident electron. Due to destructive spin interferences caused by the Rashba coupling the chain can be totally opaque for certain ranges of k the width of which depends on values of α and B. Outside these ranges the conductance oscillates with high values between e²/h and 2e²/h. The effect of a periodic modulation of α or B on the conductance gaps is investigated. A periodic, square-wave conductance pattern, pertinent to the development of the spin transistor, results within wide stripes in the parameter space spanned by k, α, and B. Finite temperatures smoothen the square-wave profile of the conductance but do not alter its periodic character.

In this paper, we study the electron transport properties in the double non-collinear δ-magnetic barriers within 2-dimensional electron gas. We find that the transmission of spin current depends on the relative orientation of each magnetic barrier. In addition to the well-known unpolarized configurations in an antiparallel magnetic barrier structure, we also find that there exists infinite unpolarized structures due to the time-reversal symmetry. These structures will be important in the designs of spin valve.

We show theoretically that the optical properties of one-dimensional metallic photonic crystals can be enhanced considerably over the corresponding constituent metal. By properly choosing the structural and material parameters, the optical properties of one-dimensional metallic-dielectric photonic crystals can be enhanced by one order of magnitude in the visible and in the THz regions.

In this paper, we investigate effects of the Dresselhaus spin-orbit coupling, inter-well coupling, and external bias on the dynamics of resonance tunneling through a semiconductor double-well structure. Based on the transfer matrix technique and the single band effective-mass approximation method, the numerical results demonstrate that the transmission peaks of the spin-up and spin-down electrons split due to the Dresselhaus spin-orbit coupling in the double-well structure. As the in-plane wave vector and external electric field increase, the split becomes farther apart. There is a prominent difference between the lifetime of the quasibound energy level for different spin-polarized electrons. The spin-dependent tunneling time is obtained using the time-dependent Schrödinger equation.

Depending on the properties of photonic band gap materials, a novel photonic crystal fiber (PCF), formed by lithium niobate and liquid crystal, has been studied numerically. Dispersion relationships and transmission spectra of the PCF are calculated by methods of the full-vector modal and the finite difference time domain, respectively. The parameter-dependent dispersion and transmission of the PCF have been found. It is shown that the design of the novel photonic crystal fiber could be supported by the theoretical analysis in the paper.

In this paper, by utilizing the variable conductivity with photo-injection in gallium arsenide (GaAs), we have designed an asymmetrical planar terahertz (THz) metamaterial, which is connected with two single-gap split ring resonator (SRR) by GaAs strip and demonstrated the resonant conversion of SRR within the THz range under appropriate optical pumping. As central trailing arm of the structure, GaAs is skillfully inserted between the two cross arms of the THz metamaterial and plays a key role in resonant conversion. Through modulation of its conductivity (σ_GaAs), the variable conductivity of GaAs can make one dual-gap SRR into two connective single-gap SRRs in physical structure, at the same time, the state conversion of two different resonances in the THz metamaterial has been achieved. The simulation results show that the resonant states of THz metamaterial can be switched from one LC and one dipole (state 1) to two LC and one new dipole (state 2) through the intermediate state with the increasing σ_GaAs. This structural design provides a new example to apply variable conductivity to achieve state conversion of resonance and can be extended to the additional application in THz devices.

We investigate transmission and reflection properties of a broadband pulse with normal incidence on silicon-metal-silicon (SMS) for the first time, to the best of our knowledge. The results show that in lower frequency range, the transmission is close to zero, and the reflection and loss are in the range 0.50–0.90, 0.10 to 0.50, respectively. In higher frequency range, the transmission spectrum has two peaks, with transmittance 0.69, 0.90, and at same frequencies as the transmission peaks, the reflection spectrum has two troughs with reflectance 0.00, 0.02 and corresponding losses are 0.10, 0.29, respectively. This simple waveguide structure may have potential applications in silicon photonics, such as filters and laser oscillation cavities.

Double barrier structures with a gradient have been studied by numerical calculations of transmission coefficient following a transfer matrix method. As the slope of the barriers becomes steep, the resonant energy is lowered. On the other hand, the full width at half maximum does not depend on the gradient.

In this paper, we study the transmission properties of light through the Family A of Generalized Thue–Morse [FAGTM(n)] aperiodic multilayers and find that for the normal incidence of light there exist three kinds of cases for propagation matrices and corresponding transmission coefficients: (1) when n is even, the former are two-circular and the latter are constant; (2) when n = 1, the former and the latter are all constant; (3) when n is odd but does not equal to 1, the former are all diagonal except the 1st-generation system. The two nonzero elements are countdowns for each other and decrease or improve rapidly with the increase of both the generation number l and the parameter n. The latter are constant when l≤2 and tend to be zero when l≥3. The analytic results are confirmed by numerical simulations.

The asymmetrical nested metamaterial, composed of two split-ring resonators (SRRs) and two embedded gallium arsenide (GaAs) islands placed in the two SRRs, has been elaborately designed on quartz substrate. Its tunable and switchable resonances at terahertz (THz) frequencies are numerically demonstrated here based on different conductivities of GaAs, which can be transformed from semiconductor to metallic state through appropriate optical excitation. Without photoexcitation, our designed metamaterial has three resonance peaks in the range of monitored frequency range, and they are located at 0.813, 1.269 and 1.722 THz, respectively. As the conductivity of the two GaAs islands increases, different new resonances appear and constantly strengthen. Finally, four new resonant points are generated, at 0.432, 0.948, 1.578 and 1.875 THz, respectively. At the same time, the metamaterial structure is changed from the original nested mode to a new integral mode. Applying reversible changing conductivity of semiconductor to push the conversion of resonance, this asymmetrical nested design provides a new instance in application and development of additional THz devices.

In this paper, a multichannel metal–insulator–metal (MIM) waveguide structure based on a disk resonator is proposed. The transmission characteristics of visible and near-infrared light in the waveguide are investigated by using the finite-difference time-domain (FDTD) method. The results show that the structure has typical band-pass filter function due to the wave resonance in the nanodisk. The energy of the second-order resonance wavelength of the disk can transmit through each output port averagely, which is realized by the energy separation function of the electromagnetic wave. Moreover, the wavelength will transmit through the output port in redshift as the radius and/or the refractive index of the disk are increased. The transmissivity is sharply reduced with the increase of the coupling thickness between the disk and the output port waveguide.

In this paper, photovoltaics (PV)- or solar cells based on two types of nanoparticles have been investigated. The suggested four-layer solar cell model consists of metallic nanoparticle (Ag–Au) layers that are Si-based and covered by SiN. The transmission and reflection of the incident light on the structure model have been computed for different physical parameters of the structure. Higher transmission and lower reflections have been obtained leading to higher efficiency of the solar cells. The matrix model is used, and the numerical results obtained by MAPLE Software Program. The obtained results confirm that the nanoparticle solar cell structure can effectively enhance the efficiency of such structure model.

We report a tunable bandpass mid-infrared filter with microstructure and graphene, and the transmission peaks can be tuned from $4.5638\mu \mathrm{\text{m}}$ to $4.5461\mu \mathrm{\text{m}}$ when the graphene’s Fermi level increases from 0.2 eV to 1.0 eV. This bandpass mid-infrared filter is originated from the guided-mode resonance (GMR) effect, and the tunable mechanism is mainly attributed to the change of the refractive index of the graphene. This tunable mid-infrared filter can be applied in non-dispersive infrared analyzer.

The optical constants and thickness of Al-doped ZnO (ZnO:Al(2.5 wt.%)) thin films prepared by high-frequency magnetron sputtering method are determined. ZnO:Al thin films are crystallized in the hexagonal structure from XRD studies. The optical constants and the bandgap of the films under study have been determined. Optical properties (refractive index $n(\lambda )$, absorption coefficient $\alpha (\lambda )$, extinction coefficient $k(\lambda )$, dielectric functions $𝜀(\lambda )$ and optical conductivity $\sigma (\lambda )$) of thin films and thickness $d$ can be determined from the transmission spectrum. The dispersion of the refractive index was explained using a single oscillator model. Single oscillator energy and dispersion energy are obtained from fitting. Optical parameters of the films were determined using the Cauchy, Sellmeier and Wemple models. The increasing value of dispersion parameter for polycrystalline thin films than for single crystals is observed. The fundamental absorption edge position (3.26 eV) in the transmittance spectrum of studied thin films corresponds to the values that are typical for ZnO:Al compound. No significant increase of the bandgap width was revealed by comparing ZnO:Al thin films with the known results of the optical studies of ZnO thin films. Possible reasons of such behavior were analyzed and the influence of bandgap increase on spectral behavior of optical functions are investigated. The material optical parameters such as normalized integrated transmission, zero and high-frequency dielectric constant, density of state effective mass ratio were also calculated.

Wireless Sensor Networks (WSNs) have come across several things which include collecting data, handling data and distribution for super visioning specific applications such as the services needed, managing anything that occurred naturally, etc. They totally rely on applications. Therefore, the WSNs are classified under major networks. This is very essential. It can be defined as a network of networks that helps in proper flow of data. The main characteristics of WSN include its continuous changes in topologies, connected nodes with several chips and tunic routing protocol. There should be the better utilization of the available resources so that its life span may exceed. There should be an effective usage of available assets to avoid the waste. In our research, we propose a hybrid approach, namely, the Power Control Tree-Based Cluster (PCTBC) to identify the Sybil attacks in WSNs. It employs several stages structured clustering of nodes based on position and identity verification. This approach is utilized for the usage of energy consumption, effectiveness of detecting Sybil attacks inside clusters. The main aspects put into consideration are the efficient routing protocol of the distance between the hops and the energy power remains, where the distance between the hops is being computed using the Received Signal Strength Indication (RSSI) and also the packet transmission can be properly tuned on the basis of the distance. Also, the proposed approach considers the energy consumption for the transmission of the defined packet.

High-Efficiency Video Coding (HEVC) has a higher coding efficiency, its encoding performance must be increased to keep up with the expanding number of multimedia applications. Therefore, this paper proposes a novel Rectified Linear Unit-Bidirectional Long Short-Term Memory-based Tree Social Relations Optimization (ReLU-BiLSTM-based TSRO) method to enhance the quality of video transmission. The significant objective of our proposed method aims in enhancing the standards of entropy encoding process in HEVC. Here, context-adaptive binary arithmetic coding (CABAC) framework which is prevalent and an improved form of entropy coding model is utilized in HEVC standards. In addition to this, the performances of the proposed method are determined by evaluating various measures such as mean square error, cumulative distribution factor, compression ratio, peak signal-to-noise ratio (PSNR) and bit error rate. Finally, the proposed method is examined with five different sequences of video from football, tennis, garden, mobile and coastguard. The performances of the proposed method are compared with various approaches, and the result analysis shows that the proposed method attained minimum mean square error (MSE) loss with maximum PSNR rate.

A simple method for determination of optical constants and thickness of semitransparent thin films deposited onto a transparent finite substrate has been developed. The method is based on the analysis of successive interference fringes of transmission spectra created by the films. It is essentially not necessary to obtain the envelope of transmission spectra in this method. The determined values of optical parameters are in good agreement with their true values used to generate transmission data. The accuracy of method in determining refractive index and thickness of the films is better than 1%.

The photoinduced birefringence effect in a type of azo-dye-doped poly (methyl methacrylate) was realized when it was pumped by a polarized argon ion laser beam. The transmission of a 632.8 nm probe beam through the pumped sample could be controlled by two kinds of methods: one employed the photoinduced thermal effect of the pump light in the azo-dye-containing sample, and the other changed the temperature of the sample directly. The tunable transmission of the probe light with different pump power and at various temperatures of the sample was investigated in detail.