Cross-layer enhanced time scheduling for multi-band OFDM UWB networks

Multi-band Orthogonal Frequency Division multiplexing based Ultra Wide-band (MB-OFDM UWB) technology is one of the strong alternatives for high data rate wireless personal area networks (WPANs) with low power consumption. The capacity of such systems is degraded by multi-path fading, shadowing, multi-user interference and noise. To improve system capacity under these adverse effects, in this paper, we devise cross-layer time scheduling methods, Proportional Time Scheduling with Modiano Algorithm (PTS-MA) and Proportional Time Scheduling with Channel State Information (PTS-CSI), in which scheduling and link adaptation are performed using instantaneous bit error probability (IBEP) estimates obtained through Modiano’s algorithm and our novel estimation technique, respectively. We evaluate the performance of the PTS schemes by using numerical experiments. Simulation results suggest PTS-CSI scheduler as the most promising candidate for practical MB-OFDM UWB WPANs with high capacity and fair throughput distribution.     

Selective removal of 17β-estradiol with molecularly imprinted particle-embedded cryogel systems

The selective removal of 17β-estradiol (E2) was investigated by using molecularly E2 imprinted (MIP) particle embedded poly(hydroxyethyl methacrylate) (PHEMA) cryogel. PHEMA/MIP composite cryogel was characterized by FTIR, SEM, swelling studies, and surface area measurements. E2 adsorption studies were performed by using aqueous solutions which contain various amounts of E2. The specificity of PHEMA/MIP cryogel to recognition of E2 was performed by using cholesterol and stigmasterol. PHEMA/MIP cryogel exhibited a high binding capacity (5.32 mg/gpolymer) and high selectivity for E2 in the presence of competitive molecules, cholesterol (k(E2/cholesterol) = 7.6) and stigmasterol (k(E2/Stigmasterol) = 85.8). There is no significant decrease in adsorption capacity after several adsorption-desorption cycles.     

Extraction of Dielectric Constant and Loss Tangent Using New Rapid Plane Solver and Analytical Debye Modeling for Printed Circuit Boards

Dielectric material properties of printed circuit boards (PCBs) are needed by designers working in various areas such as signal integrity, antennas, and embedded RF components. Among many methods to extract the material properties, the full sheet resonance technique is commonly used on PCBs due to its simplicity. The disadvantage of this method is that an analytical equation is used to extract the dielectric constant, which is accurate only for lossless dielectrics. In this paper, a new method is presented to solve the inaccuracy issue of the extraction of the dielectric constant by applying customized electromagnetic simulation based on a new rapid plane solver instead of analytical equations. For PCB dielectrics, the loss tangent tends to be flat over several decades. The dielectric constant then varies as a function of frequency based on the Kronig–Kramers relations. This paper introduces a new Debye type of a model for the complex permittivity of such dielectrics. The parameters of the Debye model can be obtained analytically without requiring any curve fitting. The resulting Debye model can then be easily integrated in SPICE or a finite-difference time-domain simulator.      

Investigation of Trap States in AlInN/AlN/GaN Heterostructures by Frequency-Dependent Admittance Analysis

We present a systematic study on the admittance characterization of surface trap states in unpassivated and SiN _x -passivated Al_0.83In_0.17N/AlN/GaN heterostructures. C–V and G/ω–V measurements were carried out in the frequency range of 1 kHz to 1 MHz, and an equivalent circuit model was used to analyze the experimental data. A detailed analysis of the frequency-dependent capacitance and conductance data was performed, assuming models in which traps are located at the metal–AlInN surface. The density (D _t) and time constant (τ _t) of the surface trap states have been determined as a function of energy separation from the conduction-band edge (E _c − E _t). The D _st and τ _st values of the surface trap states for the unpassivated samples were found to be D_st @ (4 - 13) ×10¹² D_{\rm{st}} \cong (4 - 13) \times 10^{12}  eV ^{- 1} cm ^{- 2} {\hbox{eV}}^{ - 1} {\hbox{cm}}^{ - 2} and τ _st ≈ 3 μs to 7 μs, respectively. For the passivated sample, D _st decreased to 1.5 ×10¹² 1.5 \times 10^{12}  eV ^{- 1} cm ^{- 2} {\hbox{eV}}^{ - 1} {\hbox{cm}}^{ - 2} and τ _st to 1.8 μs to 2 μs. The density of surface trap states in Al_0.83In_0.17N/AlN/GaN heterostructures decreased by approximately one order of magnitude with SiN _x passivation, indicating that the SiN _x insulator layer between the metal contact and the surface of the Al_0.83In_0.17N layer can passivate surface states.     

A microfluidic based differential plasmon resonance sensor

A new type of differential surface plasmon (SPR) sensor integrated with a microfluidic system is presented. The working principle of the microfluidic device is based on hydrodynamic modulation of two laminar streams inside a microchannel to provide periodic changes of the environment on the SPR sensor. The modulated reflectance is then demodulated using a lock-in amplifier. The presented sensor provides sensitivities of index of refraction about 4 × 10⁻⁸ RIU together with a 4 orders of magnitude dynamic range. This method demonstrates a sensitive detection scheme which could be used for label-free detection.     

The effect of different washing processes on fuel properties in camelina methyl ester

The present study was conducted to examine the effect of different washing processes on fuel properties in biodiesel produced from camelina oil through transesterification. For this purpose, dry washing with Magnesol, washing with Na₂SO₄, washing with water, and unwashing methods were compared. In dry washing with Magnesol, density, KV, CP, CFPP, PP, FP, and heating value (HV) were found to be 0.887 g/cm³, 5.090 mm²/s, 1°C, –4°C, –7°C, 165°C, and 41 MJ/kg, respectively. The effect of flash point (FP), density and kinematic viscosity (KV) on heating value (HV) was investigated and the regression among these values was determined. The r² was 0.953 and corrected r² was found to be 0.810. The effect of cloud point (CP), CFPP, and kinematic viscosity (KV) on PP (pour point) values was examined and the regression among these values was determined. The r² was found to be 0.999 and corrected r² was found to be 0.995.     

Fundamental mechanisms responsible for the temperature coefficient of resonant frequency in microwave dielectric ceramics

The temperature coefficient of resonant frequency (τ_f) of a microwave resonator is determined by three materials parameters according to the following equation: τ_f=?(½ τ_ε + ½ τ_μ + α_L), where α_L, τ_ε, and τ_μ are defined as the linear temperature coefficients of the lattice constant, dielectric constant, and magnetic permeability, respectively. We have experimentally determined each of these parameters for Ba(Zn_1/3Ta_2/3)O₃, 0.8 at.% Ni‐doped Ba(Zn_1/3Ta_2/3)O₃, and Ba(Ni_1/3Ta_2/3)O₃ ceramics. These results, in combination with density functional theory calculations, have allowed us to develop a much improved understanding of the fundamental physical mechanisms responsible for the temperature coefficient of resonant frequency, τ_f.     

Simulation of an efficient silicon heterostructure solar cell concept featuring molybdenum oxide carrier‐selective contact

Transition metal oxides/silicon heterocontact solar cells are the subject of intense research efforts owing to their simpler processing steps and reduced parasitic absorption as compared with the traditional silicon heterostructure counterparts. Recently, molybdenum oxide (MoO_x, x < 3) has emerged as an integral transition metal oxide for crystalline silicon (cSi)‐based solar cell based on carrier‐selective contacts (CSCs). In this paper, we physically modelled the CSC‐based cSi solar cell featuring MoO_x/intrinsic a‐Si:H/n‐type cSi/intrinsic a‐Si:H/n⁺‐type a‐Si:H for the first time using Silvaco technology computer‐aided design simulator. To analyse the optical and electrical properties of the proposed solar cell, several technological parameters such as work function and thickness of MoO_x contact layer, intrinsic a‐Si:H band gap, interface recombination, series resistance, and temperature coefficient have been evaluated. It has been shown that higher work function of MoO _x induces the formation of a favourable Schottky barrier height as well as an inversion at the front interface, stimulating least resistive path for holes. Utilising thinner MoO_x layer implies reduced tunnelling of minority charge carriers, thus enabling the device to numerically attain 25.33% efficiency. With an optimised interface recombination velocity and reduced parasitic absorption, the proposed device exhibited higher V_oc of 752 mV, J_sc of 38.8 mA/cm², fill‐factor of 79.0%, and an efficiency of 25.6%, which can be termed as the harbinger for industrial production of next‐generation efficient solar cell technology.     

Time-optimized hole sequence planning for 5-axis on-the-fly laser drilling

On-the-fly laser drilling requires the use of acceleration continuous trajectories, which are typically planned using time parameterized spline functions. In this operation, the choice of hole drilling sequence, and positioning timings in between the holes, play a critical role in determining the achievable cycle time. This paper presents a new algorithm for sequencing 5-axis on-the-fly laser drilling hole locations and timings. The algorithm considers machine tool and process constraints, as well as the temporal nature of the final commanded spline trajectory. The achievable productivity and motion smoothness improvement are demonstrated in the production of a gas turbine combustion chamber panel.