Adaptive Q control for tapping-mode nanoscanning using a piezoactuated bimorph probe

A new approach, called adaptive Q control, for tapping-mode atomic force microscopy (AFM) is introduced and implemented on a homemade AFM setup utilizing a laser Doppler vibrometer and a piezoactuated bimorph probe. In standard Q control, the effective Q factor of the scanning probe is adjusted prior to the scanning depending on the application. However, there is a trade-off in setting the effective Q factor of an AFM probe. The Q factor is either increased to reduce the tapping forces or decreased to increase the maximum achievable scan speed. Realizing these two benefits simultaneously using standard Q control is not possible. In adaptive Q control, the Q factor of the probe is set to an initial value as in standard Q control, but then modified on the fly during scanning when necessary to achieve this goal. In this article, we present the basic theory behind adaptive Q control, the electronics enabling the online modification of the probe's effective Q factor, and the results of the experiments comparing three different methods: scanning (a) without Q control, (b) with standard Q control, and (c) with adaptive Q control. The results show that the performance of adaptive Q control is superior to the other two methods.     

Performance of delay‐sensitive traffic in multi‐layered satellite IP networks with on‐board processing capability

In this article, performance of delay‐sensitive traffic in multi‐layered satellite Internet Protocol (IP) networks with on‐board processing (OBP) capability is investigated. With OBP, a satellite can process the received data, and according to the nature of application, it can decide on the transmission properties. First, we present a concise overview of relevant aspects of satellite networks to delay‐sensitive traffic and routing. Then, in order to improve the system performance for delay‐sensitive traffic, specifically Voice over Internet Protocol (VoIP), a novel adaptive routing mechanism in two‐layered satellite network considering the network's real‐time information is introduced and evaluated. Adaptive Routing Protocol for Quality of Service (ARPQ) utilizes OBP and avoids congestion by distributing traffic load between medium‐Earth orbit and low‐Earth orbit layers. We utilize a prioritized queueing policy to satisfy quality‐of‐service (QoS) requirements of delay‐sensitive applications while evading non‐real‐time traffic suffer low performance level. The simulation results verify that multi‐layered satellite networks with OBP capabilities and QoS mechanisms are essential for feasibility of packet‐based high‐quality delay‐sensitive services which are expected to be the vital components of next‐generation communications networks. Copyright © 2007 John Wiley & Sons, Ltd.     

Multi-machine earliness and tardiness scheduling problem: an interconnected neural network approach

This paper addresses the problem of scheduling a set of independent jobs with sequence-dependent setups and distinct due dates on non-uniform multi-machines to minimize the total weighted earliness and tardiness, and explores the use of artificial neural networks as a valid alternative to the traditional scheduling approaches. The objective is to propose a dynamical gradient neural network, which employs a penalty function approach with time varying coefficients for the solution of the problem which is known to be NP-hard. After the appropriate energy function was constructed, the dynamics are defined by steepest gradient descent on the energy function. The proposed neural network system is composed of two maximum neural networks, three piecewise linear and one log-sigmoid network all of which interact with each other. The motivation for using maximum networks is to reduce the network complexity and to obtain a simplified energy function. To overcome the tradeoff problem encountered in using the penalty function approach, a time varying penalty coefficient methodology is proposed to be used during simulation experiments. Simulation results of the proposed approach on a scheduling problem indicate that the proposed coupled network yields an optimal solution which makes it attractive for applications of larger sized problems.     

Study of CdS/Cu(In, Ga)Se2 heterojunction interface using admittance and impedance spectroscopy

The interface properties of an unusual CdS/Cu(In, Ga)Se₂ solar cell have been studied by admittance and impedance spectroscopy. The current transport in this device has previously appeared to be dominated by tunnelling enhanced recombination at junction interface. The existence of this unexpected route was attributed to the presence of Cu-rich and indium depleted thin layer which might possibly be formed on the absorber surface. We have performed temperature dependent admittance and impedance measurements in order to clarify this phenomenon. An acceptor level with ionization energy of about 50 meV seems to be strongly correlated to the appearance of the CuGaSe₂ layer. The impedance spectra obtained at 100 K and 300 K exhibited single semi-circles. This indicates the dominance of the heterojunction interface without the effect of any other capacitive components. The equivalent circuit model consisting of a parallel resistor and capacitor in series with a resistor has been found to give a good fit to the experimental data.     

Measurement and comparison of complex impedance of silicon <Emphasis Type="Italic">p-i-n</Emphasis> photodiodes at different temperatures

The dark alternating current (ac) parameters of BPW34 and BPW41 (Vishay-Telefunken) silicon p-i-n photodiodes are measured and compared at different temperatures using the impedance spectroscopy technique. The impedance plots are nearly semicircular and typically distorted on the high frequency side. For BPW41, the distortion apparently arises from one of the two interfaces as expected for a typical p-i-n device. However, for BPW34, the presence of the distortion is attributed to the variation of photodiode capacitance and resistance with measurement frequency. The text was submitted by the authors in English.     

Measurement and comparison of silicon <Emphasis Type="Italic">p-i-n</Emphasis>-photodiodes with ac impedance at different voltages

The dark alternating current (ac) parameters of commercially available silicon p-i-n-photodiodes are measured and compared at room temperature both in forward and reverse bias using the impedance spectroscopy technique. The ac behavior of the photodiodes is found to be almost the same. For bias voltages in the range from −0.8 to 0.0 V, the typical photodiode behaves like a pure capacitor. For higher voltages (V >-0.2 V) the impedance spectra are nearly semicircular and typically distorted on the high frequency side. At 0.2 V the distortion apparently arises from one of the two interfaces. However, at high bias voltages the nature of the distortion is attributed to the variation of photodiode capacitance and resistance with measurement frequency. The text was submitted by the authors in English.     

A Laser-Induced Mo2CTx MXene Hybrid Anode for High-Performance Li-Ion Batteries

MXenes, a fast-growing family of two-dimensional (2D) transition metal carbides/nitrides, are promising for electronics and energy storage applications. Mo₂CT_x MXene, in particular, has demonstrated a higher capacity than other MXenes as an anode for Li-ion batteries. Yet, such enhanced capacity is accompanied by slow kinetics and poor cycling stability. Herein, it is revealed that the unstable cycling performance of Mo₂CT_x is attributed to the partial oxidation into MoO_x with structural degradation. A laser-induced Mo₂CT_x/Mo₂C (LS-Mo₂CT_x) hybrid anode has been developed, of which the Mo₂C nanodots boost redox kinetics, and the laser-reduced oxygen content prevents the structural degradation caused by oxidation. Meanwhile, the strong connections between the laser-induced Mo₂C nanodots and Mo₂CT_x nanosheets enhance conductivity and stabilize the structure during charge–discharge cycling. The as-prepared LS-Mo₂CT_x anode exhibits an enhanced capacity of 340 mAh g⁻¹ vs 83 mAh g⁻¹ (for pristine) and an improved cycling stability (capacity retention of 106.2% vs 80.6% for pristine) over 1000 cycles. The laser-induced synthesis approach underlines the potential of MXene-based hybrid materials for high-performance energy storage applications.     

Biosorption of Cr (VI) from aqueous solutions by biomass of Agaricus bisporus

In this study, biosorption of Cr (VI) ion was investigated by using biomass of Agaricus bisporus (a species of mushroom) in a temperature and shaking speed controlled shaker. The effect of shaking speed, biomass concentration, initial metal ion concentration and initial pH on biosorption yield was determined and the fitness of biosorption data for Freundlich and Langmuir adsorption models was investigated. Optimum biosorption conditions were found to be pH 1, C0=50 mg/l, m=10 g/l, shaking speed=150 rpm, T=20 degrees C Cr (VI), respectively. It was found that biosorption of Cr (VI) ions onto biomass of A. bisporus was better suitable to Freundlich adsorption model than Langmuir adsorption model. The correlation coefficients for the second-order kinetic model obtained were found to be 0.999 for all concentrations. These indicate that the biosorption system studied belongs to the second-order kinetic model.