A Fiber Routing Problem in Designing Optical Transport Networks with Wavelength Division Multiplexed Systems

In this paper, we consider a fiber routing problem arising from the design of optical transport networks. The problem is to find an optimal routing of multiple rings and an optimal location of wavelength division multiplexed (WDM) systems for carrying demand traffic. This problem can be conceptualized as a Steiner (multiple) ring problem with link capacity constraints. We formulate the problem as a mixed-integer programming model and develop a new branch-and-cut procedure along with preprocessing routines and valid inequalities for optimally solving the problem. Exploiting the inherent special structures of the formulation, we focus on developing strong valid inequalities and devising an effective Tabu search heuristic for solving large-scale problems. Computational results indicate that preprocessing rules and valid inequalities provide a tight lower bound, and in turn reduce the effort required to solve the problem within the framework of the branch-and-cut procedure. Moreover, the proposed Tabu search heuristic works quite well for solving large-scale problems. Motivated by promising computational results, we provide insights into implementing the proposed branch-and-cut procedure for deploying fiber optic networks in practice.     

Optical and electronic properties of highly stable and textured hydrogenated ZnO:Al thin films

We have experimentally investigated the effects of hydrogen-annealing on the structural, electrical, and optical properties of Al-doped ZnO (ZnO:Al) thin films prepared by RF magnetron sputtering at room temperature. From the X-ray diffraction observations, the orientation of ZnO:Al films was found to be a c-axis in the hexagonal structure. We found that intentionally incorporated hydrogen plays an important role in n-type conduction as a donor, improving free carrier concentration and electrical stability. We simultaneously obtained improved optical transmission and enhanced absorption edge of the ZnO:Al film due to hydrogen-annealing. Our experimental data suggest the hydrogen-annealing process as an important role in the enhancement of electrical and optical properties, which is promising as a back reflector material for thin-film solar cells.     

Influence of source-drain series resistance on MOSFET field-effect mobility

A simple but general model for explaining the series resistance dependence of transconductance and field-effect mobility is developed in the letter. This model, which enables a quantitative analysis of series resistance effects on the maximum mobility and the corresponding gate voltage, has been successfully tested on short-channel MOSFETs with various channel lengths and external series resistances.     

Efficiency and deregulation of the electricity market in Singapore

This study examines production efficiency of electricity generation in the New Electricity Market of Singapore (NEMS), where deregulation is currently proceeding. Singapore is reliant on foreign direct investments and exports so competition from countries with lower costs such as China and India is exerting pressure on the government to reduce the costs of doing business here. Electricity cost is one of these. Deregulation is believed to be able to bring about lower electricity costs due to the various efficiency gains possible. This study concerns itself mainly with production efficiency and attempts to calculate possible production efficiency gains by using linear programming model. Production-efficiency gains are quantified by the base case scenario of continued regulation versus four counterfactual deregulation scenarios. The results indicate that cost gains could be about eight per cent of current production cost, and this is possibly a lower-bound estimate. However, whether the purported efficiency gains are realized is to be seen as the deregulation proceeds.     

On the performance of joint space‐frequency pre‐filtering and equalization for downlink multi‐carrier code division multiple access

We analyze the performance of joint space‐frequency pre‐filtering and equalization techniques for downlink multi‐carrier code division multiple access in terms of average bit error rate performance. Several linear power allocation strategies combined with single‐user equalization schemes are compared with a joint pre‐filtering with an equal power constraint at the base station and maximal ratio combining at the mobile terminals. Our bit error rate analysis obtained in this paper facilitates predicting the performance of various space‐frequency pre‐filtering schemes without massive simulations. Copyright © 2011 John Wiley & Sons, Ltd.     

Asymmetrical change in the pelvis and the spine during cross-legged sitting postures

People spend much time with cross-legged sitting by increasing the time spent in the chair. Prolonged cross-legged sitting postures might cause spinal disorders and trunk asymmetry problems. We investigated the biomechanical effects of cross-legged sitting postures on the pelvic and spinal regions. 3D-motion analyses were performed on 26 healthy subjects. Data were collected while the subjects sat in four different postures: the control posture (without crossed legs) of sitting upright on the chair; the knee-on-knee (KoK) posture (the right knee on the left knee), the ankle-on-knee (AoK) posture (the right ankle on the left knee) and the ankle-on-ankle (AoA) posture (the right ankle on the left ankle). EMG signals were also collected for abdominal muscles. Cross-legged sitting postures showed significantly greater kyphotic curves in the lumbar and the thoracic spines and pelvic posterior tilting, when compared with the control posture. The pressure on the right buttock area was greater in the AoK posture than in the control posture, and the pressure on the left buttock area in the KoK posture was greater than in the control posture. Cross-legged sitting postures showed significantly greater external oblique muscle activation when compared with the control posture.     

Theory of the field-assisted photomagnetoelectric effect in thin films: Experiment on n-type GaAs and applications

The field-assisted photomagnetoelectric (FAPME) effect is the generalization of the classical PME effect obtained by the application of a (strong) longitudinal electric field: photogenerated carriers are magnetoconcentrated by the Lorentz force and consequently the current-voltage (I(V)) law becomes non-linear. The theory of the FAPME effect is proposed for thin semiconductor layers, where the recombination rate at the film-substrate interface is a key parameter. The roles of other important factors (electric and magnetic fields, lifetime, dimensions) are also systematically investigated. Experimental data for the open-circuit voltage, the photomagnetoresistance and the I(V) characteristics were obtained for n-type GaAs films 1.5 μm thick in magnetic and electric fields of up to 13 T and 1.5 x 10⁴ V m^-1 respectively. A satisfactory agreement with the theory is found, in spite of some inherent limitations (film non-uniformity, influence of the semi-insulating GaAs substrate). Complementary magnetotransport measurements were performed without photoexcitation in the temperature range 77–300 K. These numerous and independent experiments are simultaneously exploited for the assessment of several basic properties of GaAs: the lifetime, the surface recombination velocities, the Hall and drift mobilities and the scattering mechanisms.     

Wedge Failure Analysis of Soil Resistance on Laterally Loaded Piles in Clay

A fundamental study of pile-soil systems subjected to lateral loads in clay soil was conducted by using experimental tests and a lateral load-transfer approach. The emphasis was on an improved wedge failure model developed by considering three-dimensional combination forces and a new hyperbolic p-y criterion. A framework for determining the p-y curve on the basis of both theoretical analysis and experimental load test results is proposed. The proposed p-y method is shown to be capable of predicting the behavior of a large-diameter pile under lateral loading. The proposed p-y curves with an improved wedge model are more appropriate and realistic for representing a pile-soil interaction for laterally loaded piles in clay than the existing p-y method.