First-order voltage-mode all-pass filter employing one active element and one grounded capacitor

A new circuit topology of first-order voltage-mode all-pass filter providing high-input and low-output impedances is described. The filter consists of only one grounded capacitor and one active element, namely VD-DIBA (Voltage Differencing-Differential Input Buffered Amplifier), with the possibility of electronically tuning the natural frequency. The filter is assembled from commercial integrated circuits, and the frequency responses measured are compared with the theoretical characteristics.     

Raman scattering at pure graphene zigzag edges

Theory has predicted rich and very distinct physics for graphene devices with boundaries that follow either the armchair or the zigzag crystallographic directions. A prerequisite to disclose this physics in experiment is to be able to produce devices with boundaries of pure chirality. Exfoliated flakes frequently exhibit corners with an odd multiple of 30°, which raised expectations that their boundaries follow pure zigzag and armchair directions. The predicted Raman behavior at such crystallographic edges however failed to confirm pure edge chirality. Here, we perform confocal Raman spectroscopy on hexagonal holes obtained after the anisotropic etching of prepatterned pits using carbothermal decomposition of SiO(2). The boundaries of the hexagonal holes are aligned along the zigzag crystallographic direction and leave hardly any signature in the Raman map indicating unprecedented purity of the edge chirality. This work offers the first opportunity to experimentally confirm the validity of the Raman theory for graphene edges.     

Experimental study on biomass gasification in a double air stage downdraft reactor

This work presents an experimental study of the gasification of a wood biomass in a moving bed downdraft reactor with two-air supply stages. This configuration is considered as primary method to improve the quality of the producer gas, regarding its tar reduction. By varying the air flow fed to the gasifier and the distribution of gasification air between stages (AR), being the controllable and measurable variables for this type of gasifiers, measuring the CO, CH₄ and H₂ gas concentrations and through a mass and energy balance, the gas yield and its power, the cold efficiency of the process and the equivalence ratio (ER), as well as other performance variables were calculated. The gasifier produces a combustible gas with a CO, CH₄ and H₂ concentrations of 19.04, 0.89 and 16.78% v respectively, at a total flow of air of 20 Nm³ h⁻¹ and an AR of 80%. For these conditions, the low heating value of the gas was 4539 kJ Nm⁻³. Results from the calculation model show a useful gas power and cold efficiency around 40 kW and 68%, respectively. The resulting ER under the referred operation condition is around 0.40. The results suggested a considerable effect of the secondary stage over the reduction of the CH₄ concentration which is associated with the decreases of the tar content in the produced gas. Under these conditions the biomass devolatilization in the pyrolysis zone gives much lighter compounds which are more easily cracked when the gas stream passes through the combustion zone.     

Proportioning with second-order information for model predictive control

We propose an algorithm for the effective solution of quadratic programming (QP) problems arising from model predictive control (MPC). MPC is a modern multivariable control method which gives the solution for a QP problem at each sample instant. Our algorithm combines the active-set strategy with the proportioning test to decide when to leave the actual active set. For the minimization in the face, we use a direct solver implemented by the Cholesky factors updates. The performance of the algorithm is illustrated by numerical experiments, and the results are compared with the state-of-the-art solvers on benchmarks from MPC.     

Anesthetic agents and visual evoked potentials in patients undergoing transphenoidal or breast reconstruction surgery

This article reports the results of a study of four hospital-based providers in varying stages of implementing case management programs. Three of the providers had most of the necessary elements in place to ensure success, such as a mix of reimbursement sources, an effective and integrated information management system, a full range of clinical services, and continuous quality improvement programs. The authors make several suggestions for key activities that must be pursued by any health care organization seeking to implement a case management program in an era of managed care, tightening reimbursement, and consumer demand for quality care. These include the need to (a) organize essential case management functions under a centralized structure; (b) set realistic, quantifiable targets, and (c) design a communications plan for the program.     

Wave propagation in fluid filled nonlinear viscoelastic tubes

Summary The present work considers one dimensional wave propagation in an infinitely long, straight and homogeneous nonlinear viscoelastic tube filled with an incompressible, inviscid fluid. In order to include the geometric dispersion in the analysis, the tube wall inertia effects are added to the pressure-area relation. Using the reductive perturbation technique, the propagation of weakly nonlinear waves in the long-wave approximation is examined. In the long-wave approximation, a general equation is obtained, and it is shown that by a proper scaling this equation reduces to the well-known nonlinear evolution equations. Intensifying the effect of nonlinearity in the perturbation process, the modified forms of these evolution equations are also obtained. In the absence of nonlinear viscoelastic effects all the equations reduce to those of the linear viscoelastic tube.     

Scalable Total BETI based algorithm for 3D coercive contact problems of linear elastostatics

A Total BETI (TBETI) based domain decomposition algorithm with the preconditioning by a natural coarse grid of the rigid body motions is adapted for the solution of contact problems of linear elastostatics and proved to be scalable for the coercive problems, i.e., the cost of the solution is asymptotically proportional to the number of variables. The analysis is based on the original results by Langer and Steinbach on the scalability of BETI for linear problems and our development of optimal quadratic programming algorithms for bound and equality constrained problems. Both theoretical results and numerical experiments indicate a high efficiency of the algorithms presented.      

Reassessment of the school location problem: A multifunctional role for the school in the urban environment

Methods for determining the optimum location site for the educational plant have traditionally classified the school as unifunctional in its production activities. Rising pressures of competition for land in urban areas suggest the need for novel approaches to planning public land use for fostering higher levels of living desirability of the urban environment. National concern about the less than optimum use of social investments in educational plants can be juxtaposed to the urban land use problem.Empirical investigations in both economic and noneconomic disciplines are drawn upon to provide a broader concept of the urban school location problem. The multifunctional production potential of the school facility can raise the expected rate of social and economic returns on a necessary social investment. Thus, the school site decision is integrated with the more general problem of urban planning.iThe author is Assistant Professor, Department of Economics, Oregon State University.