Max-min Fair Beamforming for SWIPT Systems with Non-linear EH Model

We study the beamforming design for multiuser systems with simultaneous wireless information and power transfer (SWIPT). Employing a practical non-linear energy harvesting (EH) model, the design is formulated as a non-convex optimization problem for the maximization of the minimum harvested power across several energy harvesting receivers. The proposed problem formulation takes into account imperfect channel state information (CSI) and a minimum required signal-to-interference-plus-noise ratio (SINR). The globally optimal solution of the design problem is obtained via the semidefinite programming (SDP) relaxation approach. Interestingly, we can show that at most one dedicated energy beam is needed to achieve optimality. Numerical results demonstrate that with the proposed design a significant performance gain and improved fairness can be provided to the users compared to two baseline schemes.Comment: Invited paper, IEEE VTC 2017, Fall, Toronto, Canad

Femoral Neck Stress in Older Adults During Stair Ascent and Descent

A detailed understanding of the hip loading environment is needed to help prevent hip fractures, minimize hip pain, rehabilitate hip injuries, and design osteogenic exercises for the hip. The purpose of this study was to compare femoral neck stress during stair ascent and descent and to identify the contribution of muscles and reaction forces to the stress environment in mature adult subjects (n = 17; age: 50–65 y). Motion analysis and inverse dynamics were combined with musculoskeletal modeling and optimization, then used as input to an elliptical femoral neck cross-sectional model to estimate femoral neck stress. Peak stress values at the 2 peaks of the bimodal stress curves (stress vs time plot) were compared between stair ascent and descent. Stair ascent had greater compressive stress than descent during the first peak at the anterior (ascent: −18.0 [7.9] MPa, descent: −12.9 [5.4] MPa, P \u3c .001) and posterior (ascent: −34.4 [10.9] MPa, descent: −27.8 [10.1] MPa, P \u3c .001) aspects of the femoral neck cross section. Stair descent had greater tensile stress during both peaks at the superior aspect (ascent: 1.3 [7.0] MPa, descent: 24.8 [9.7] MPa, peak 1: P \u3c .001; ascent: 15.7 [6.1] MPa, descent: 18.0 [8.4] MPa, peak 2: P = .03) and greater compressive stress during the second peak at the inferior aspect (ascent: −43.8 [9.7] MPa, descent: −51.1 [14.3] MPa, P = .004). Understanding this information can provide a more comprehensive view of bone loading at the femoral neck for older population

Oscillatory Radial Solutions of Semilinear Elliptic Equations

We study the oscillatory behavior of radial solutions of the nonlinear partial differential equation Δu + f(u) + g(|x|, u) = 0 inRn, where f and g are continuous restoring functions, uf(u) > 0 and ug(|x|, u) > 0 for u ≠ 0. We assume that for fixedq limu → 0(|f(u)|/|u|q) = B > 0, for 1 < q < n/(n − 2), and, additionally, that 2F(u) ≥ (1 − 2/n)uf(u) when n/(n − 2) ≤ q < (n + 2)/(n − 2), where F(u) = ∫u0f(s)ds. We give conditions that guarantee that the solution oscillates infinitely and tends to zero asr → ∞. Finally, we give bounds for the amplitude of the oscillations and show that the period of the oscillations increases asr → ∞

TSFPGA, a time-switched field-programmable gate array

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1996.Includes bibliographical references (p. 69-70).by Derrick Chen.M.Eng

Optimization of long range potential interaction parameters in ion mobility spectrometry

The problem of optimizing Lennard-Jones (L-J) potential parameters to perform collision cross section (CCS) calculations in ion mobility spectrometry has been undertaken. The experimental CCS of 16 small organic molecules containing carbon, hydrogen, oxygen, nitrogen, and fluoride in N2 was compared to numerical calculations using Density Functional Theory (DFT). CCS calculations were performed using the momentum transfer algorithm IMoS and a 4-6-12 potential without incorporating the ion-quadrupole potential. A ceteris paribus optimization method was used to optimize the intercept σ and potential well-depth ϵ for the given atoms. This method yields important information that otherwise would remain concealed. Results show that the optimized L-J parameters are not necessarily unique with intercept and well-depth following an exponential relation at an existing line of minimums. Similarly, the method shows that some molecules containing atoms of interest may be ill-conditioned candidates to perform optimizations of the L-J parameters. The final calculated CCSs for the chosen parameters differ 1% on average from their experimental counterparts. This result conveys the notion that DFT calculations can indeed be used as potential candidates for CCS calculations and that effects, such as the ion-quadrupole potential or diffuse scattering, can be embedded into the L-J parameters without loss of accuracy but with a large increase in computational efficiency

A Semi-Analytical Analysis of Texture Collapse

This study presents a simplified approach to studying the dynamics of global texture collapse. We derive equations of motion for a spherically symmetric field configuration using a two parameter ansatz. Then we analyse the effective potential for the resulting theory to understand possible trajectories of the field configuration in the parameter space of the ansatz. Numerical results are given for critical winding and collapse time in spatially flat non-expanding, and flat expanding universes. In addition, the open non-expanding and open-expanding cases are studied.Comment: 12 pages, figures available from author, BROWN-HET-895, uses phyzz