Computer program for transient response of structural rings subjected to fragment impact

Mathematical optimization of containment/deflection system would save time, effort, and material as well as afford designer greater opportunity to investigate new ideas and variety of materials

Regularization of Vertical-Cavity Surface-Emitting Lasers emission by periodic non-Hermitian potentials

We propose a novel physical mechanism based on periodic non-Hermitian potentials to efficiently control the complex spatial dynamics of broad-area lasers, particularly in Vertical-Cavity Surface-Emitting Lasers (VCSELs), achieving a stable emission of maximum brightness. Radially dephased periodic refractive index and gain-loss modulations accumulate the generated light from the entire active layer and concentrate it around the structure axis to emit narrow, bright beams. The effect is due to asymmetric-inward radial coupling between transverse modes, for particular phase differences of the refractive index and gain-loss modulations. Light is confined into a central beam with large intensity opening the path to design compact, bright and efficient broad-area light sources. We perform a comprehensive analysis to explore the maximum central intensity enhancement and concentration regimes. The study reveals that the optimum schemes are those holding unidirectional inward coupling but not fulfilling a perfect local PT-symmetry.Comment: 4 pages, 4 figure

Proceedings of workshops to define engineering requirements for a space vacuum research facility

The construction of a molecular wake shield for the shuttle orbiter is presented as well as a collision model with a program depicting emitted molecular density around the spacecraft giving estimates of backscattered flux and other collisional processes

New critical frontiers for the Potts and percolation models

We obtain the critical threshold for a host of Potts and percolation models on lattices having a structure which permits a duality consideration. The consideration generalizes the recently obtained thresholds of Scullard and Ziff for bond and site percolation on the martini and related lattices to the Potts model and to other lattices.Comment: 9 pages, 5 figure

Quantile Dependence between the Stock, Bond and Foreign Exchange Markets - Evidence from the UK

In the wake of Brexit, this paper aims to provide a measure for the quantile dependence amongst different financial assets – bond, stock, and currency – within the UK market and their cross–border linkages with the European equity market. We implement a nonparametric estimation method for both the tail and quantile dependence parameters on weekly data over the period 1989-2016 using copula. Our results suggest that the contagion effects between stock and currency markets are limited, even under extreme fluctuations. We also find a weak comovement between currency and bond markets, however, evidence of asymmetry is found in the dependence structure, possibly due to the ‘risk-reward’ scenario of international investors. Finally, our results indicate a weak dependence between stock returns and bond yields, possibly due to the low-yielding gilt and the thirst for income, pushing investors to diversify globally into other financial markets

The cylindrical antenna with non-reflecting resistive loading

Distribution of current along center-driven cylindrical antenna with variable internal impedance per unit lengt

Single-input and single-output (SISO) controller reduction based on the L1L_1-norm

This paper proposes a new method to solve the controller-reduction problem based on the $L_1$-norm. This method uses a reduced-order closed-loop system to deduce reduced-order controllers. The problem of obtaining the required lower-order closed-loop system was formulated as an $L_1$-norm optimization, and the conditions were provided for guaranteeing the internal stability and the existence of lower-order controllers from the obtained reduced-order closed-loop system. In addition, the particle swarm optimization and sequence linear programming were adopted to solve the resultant $L_1$-norm optimization. Two numerical examples demonstrated the effectiveness of the proposed method