On the sparse beamformer design

In designing acoustic broadband beamformers, the complexity can grow significantly when the number of microphones and the filter length increase. It is advantageous if many of the filter coefficients are zeroes so that the implementation can be executed with less computation. Moreover, the size of the array can also be pruned to reduce complexity. These problems are addressed in this paper. A suitable optimization model is proposed. Both array pruning and filter thinning can be solved together as a two-stage optimization problem to yield the final sparse designs. Numerical results show that the complexity of the designed beamformers can be reduced significantly with minimal effect on performance

Privacy-Preserving Information Gathering Using VANET

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Stationary Localized States Due to a Nonlinear Dimeric Impurity Embedded in a Perfect 1-D Chain

The formation of Stationary Localized states due to a nonlinear dimeric impurity embedded in a perfect 1-d chain is studied here using the appropriate Discrete Nonlinear Schr$\ddot{o}$dinger Equation. Furthermore, the nonlinearity has the form, $\chi |C|^\sigma$ where $C$ is the complex amplitude. A proper ansatz for the Localized state is introduced in the appropriate Hamiltonian of the system to obtain the reduced effective Hamiltonian. The Hamiltonian contains a parameter, $\beta = \phi_1/\phi_0$ which is the ratio of stationary amplitudes at impurity sites. Relevant equations for Localized states are obtained from the fixed point of the reduced dynamical system. $|\beta|$ = 1 is always a permissible solution. We also find solutions for which $|\beta| \ne 1$. Complete phase diagram in the $(\chi, \sigma)$ plane comprising of both cases is discussed. Several critical lines separating various regions are found. Maximum number of Localized states is found to be six. Furthermore, the phase diagram continuously extrapolates from one region to the other. The importance of our results in relation to solitonic solutions in a fully nonlinear system is discussed.Comment: Seven figures are available on reques

Enhancing the Financial Returns of R&D Investments through Operations Management

Although much research has been carried out to examine various contextual issues and moderating factors for successful R&D investments, very little research has been conducted to explore the role of a firm’s operational and process characteristics. In this study, we explore how firms could possibly enhance the financial returns of R&D investments through quality management, using Six Sigma implementation as an example, and efficiency improvement, using the stochastic frontier estimation of relative efficiency as a proxy. Based on data from 468 manufacturing firms in the U.S. over the period 2007-2014, we construct a dynamic panel data model to capture the effects of R&D investments on firms’ financial returns in terms of Tobin’s q. Using the system generalized method of moments estimator, our results indicate that the financial returns of R&D investments are significantly enhanced when firms adopt Six Sigma and improve efficiency in operations. Our additional analyses further suggest that such an enhancement effect through quality and efficiency improvements is more pronounced under high operational complexity as approximated by labor intensity and geographical diversity. Instead of considering innovation activities and process management as contradictory functions, we show that quality and efficiency improvements indeed support firms’ R&D investments, leading to higher financial returns

Microcapillary film reactor outperforms single-bore mesocapillary reactors in continuous flow chemical reactions

Meso- and micro-flow reactors are routinely used in continuous flow chemistry, however the role of capillary diameter, D, on conversion and reaction rates is often overlooked during scale-up. Volume, pressured drop and diffusion distances/times must be delicately balanced to fully realize the hydrodynamic capabilities of continuous chemical flow reactors. We carried out a comprehensive Computational Fluid Dynamics analysis experimentally validated with detailed fluid tracing, residence time distributions and continuous chemical reactions (neutralization and 4th Bourne reaction) to fully elucidate the role of D and molecular diffusion in reagents dispersion and chemical conversion. To our understanding, we captured and reported both numerically and experimentally for the first time the transition from convective, segregated flow to plug flow and dispersed flow, which we propose is linked to a dimensionless ratio between the time scales of diffusion to convection, tdiff/tconv. We tested three tubular systems: a small-bore (i.d. ~1100 µm) and large-bore (i.d. ~2400 µm) capillary reactor and a novel multiplexed (10-bore) Microcapillary Film Reactor (MFR) with mean i.d. 363 ± 32.2 µm. In the MFR's narrow microcapillaries we observed excellent radial diffusion linked to the small diffusion distance, with low dimensionless axial dispersion coefficient values (Dax/uL) ranging from 0.0015 ± 0.0005 to 0.0033 ± 0.0006 (for flow rates 0.5–5.0 mL/min), exhibiting all the desired features of a high-performance ‘plug’ flow system. Dax/uL remained mostly independent of the Reynolds number, whereas for the single, large bore capillary the Dax/uL values (0.032–0.057) increased linearly with the Reynolds numbers (19.4–48.5), shifting towards very dispersive flow. We propose splitting flow through multiple parallel microcapillaries as in the MFR is a superior strategy for scaling-up continuous flow reactions compared to increasing D, which neglects diffusive effects.</p

Identity Based Threshold Ring Signature

In threshold ring signature schemes, any group of $t$ entities spontaneously conscripting arbitrarily $n-t$ entities to generate a publicly verifiable $t$-out-of-$n$ signature on behalf of the whole group, yet the actual signers remain anonymous. The spontaneity of these schemes is desirable for ad-hoc groups such as mobile ad-hoc networks. In this paper, we present an identity based (ID-based) threshold ring signature scheme. The scheme is provably secure in the random oracle model and provides trusted authority compatibility. To the best of authors\u27 knowledge, our scheme is the first ID-based threshold ring signature scheme which is also the most efficient (in terms of number of pairing operations required) ID-based ring signature scheme (when $t = 1$) and threshold ring signature scheme from pairings

A Secure Modified ID-Based Undeniable Signature Scheme

Verifiable Pairing and its Applications. In Chae Hoon Lim and Moti Yung, editors, Information Security Applications: 5th International Workshop, WISA 2004, Jeju Island, Korea, August 23-25, 2004, Revised Selected Papers, volume 3325 of Lecture Notes in Computer Science, pp. 170-187. (http://www.springerlink.com/index/C4QB7C13NL0EY5VN) which contains an improved and generalized result of this paper

Engineering Microneedle Patches for Improved Penetration: Analysis, Skin Models and Factors Affecting Needle Insertion

Transdermal microneedle (MN) patches are a promising tool used to transport a wide variety of active compounds into the skin. To serve as a substitute for common hypodermic needles, MNs must pierce the human stratum corneum (~ 10 to 20&nbsp;µm), without rupturing or bending during penetration. This ensures that the cargo is released at the predetermined place and time. Therefore, the ability of MN patches to sufficiently pierce the skin is a crucial requirement. In the current review, the pain signal and its management during application of MNs and typical hypodermic needles are presented and compared. This is followed by a discussion on mechanical analysis and skin models used for insertion tests before application to clinical practice. Factors that affect insertion (e.g., geometry, material composition and cross-linking of MNs), along with recent advancements in developed strategies (e.g., insertion responsive patches and 3D printed biomimetic MNs using two-photon lithography) to improve the skin penetration are highlighted to provide a backdrop for future research.[Figure not available: see fulltext.