Highly directional emission and photon beaming from nanocrystal quantum dots embedded in metallic nanoslit arrays

We demonstrate a directional beaming of photons emitted from nanocrystal quantum dots that are embedded in a subwavelength metallic nanoslit array with a divergence angle of less than 4°. We show that the eigenmodes of the structure result in localized electromagnetic field enhancements at the Bragg cavity resonances, which could be controlled and engineered in both real and momentum space. The photon beaming is achieved using the enhanced resonant coupling of the quantum dots to these Bragg cavity modes, which dominates the emission properties of the quantum dots. We show that the emission probability of a quantum dot into the narrow angular mode is 20 times larger than the emission probability to all other modes. Engineering nanocrystal quantum dots with subwavelength metallic nanostructures is a promising way for a range of new types of active optical devices, where spatial control of the optical properties of nanoemitters is essential, on both the single and many photons level.     

Zeolite membranes for hydrogen production from natural gas: state of the art

Journal of Porous Materials - Currently, hydrogen is produced industrially by processes requiring high energy consumption, especially by cracking fossil fuels and by splitting water. In recent...     

Nonlinear filtering problems with finite-dimensional matrix estimation algebras

Matrix estimation algebras are Lie algebras that arise naturally in the nonlinear filtering problem for systems with random structure. These are systems that have finitely many modes of operation, where transitions from one mode to another are governed by a finite-state Markov process. Necessary conditions for finite dimensionality of matrix estimation algebras are given. Finite-dimensional filter realizations are constructed for some of the cases for which the matrix estimation algebra is finite dimensional.     

High-throughput automation design considerations for biotechnology processes involving RNA purification protocols using multi-centrifuge bioseparation steps

Design of an automation line is a multi-objective optimization problem involving throughput, yield, floor space and cost constraints. The paper examines the feasibility of a computer-aided automation design for biotechnology applications using Arena? software. A generic case study chosen for this study involves a sequence of steps in a preparation process of RNA from tissue-cultured cells. These steps involve repetitive usage of centrifuging operations to perform separation of biochemical substances. A sample must be loaded onto a centrifuge by a pick-and-place device (typically a robot manipulator). Consecutive centrifuging steps may involve multiple centrifuges as well as robots, or some measure of equipment sharing. The paper proposes a unified simplified cost model for all design objectives (throughput, space utilization, process capital and operational cost) and a quantitative selection criterion to allow for an optimal automation design.     

Proximity clouds — an acceleration technique for 3D grid traversal

In this paper we present a new method for the acceleration of ray traversal through a regular 3D grid. A distance transformation is precomputed and mapped onto the empty grid space. A ray traversing the empty space is assisted by the distance values which permit it to perform long skips along the ray direction. We show that the City-Block metric simplifies the preprocessing with no penalty at the traversal phase. Different schemes are discussed and the trade-off between the preprocessing time and the speed-up is analyzed.     

Modeling InAs/GaSb and InAs/InAsSb Superlattice Infrared Detectors

InAs/GaSb and InAs/InAsSb type II superlattices have been proposed as promising alternatives to HgCdTe for the photon-absorbing layer of an infrared detector. When combined with a barrier layer based on an InAs/AlSb superlattice or an AlSbAs alloy, respectively, they can be used to make diffusion-limited “barrier” detectors with very low dark currents. In this work we compare theoretical simulations with experimental bandgap and photoabsorption data for such superlattices, spanning from the mid to the long-wave infra-red (2.3–12 μm). The spectral response of detectors based on these materials is also simulated. The simulations are based on a version of the k · p model developed by one of the authors, which takes interface contributions and bandgap bowing into account. Our results provide a way of assessing the relative merits of InAs/GaSb and InAs/InAsSb superlattices as potential detector materials.     

Asymptotically optimal transmission power and rate control for CDMA channels with MF and MMSE receivers

The asymptotically combined optimal transmission power and rate control policy is derived for a DS-CDMA time varying fading channel with multiple user classes, random spreading codes and a receiver using either a conventional matched filter (MF) or a minimum mean square error (MMSE) multiuser detector. For a general objective function, the optimal policies are given by closed form functions of a single Lagrangian multiplier. The optimal policies are demonstrated by an application, where the transmission power is adapted to the channel fade variations, and the transmission rates are adapted to the tier containing the mobile. The effect of the number of tiers on the optimal transmission rate are presented for MF and MMSE receivers in an environment with Lognormal and Rayleigh fading. It is shown that with an MMSE receiver, there is a substantial increase in the total transmission rate, whereas only a negligible increase exists with a MF receiver. Zvi Rosberg received the B.Sc., M.A. and Ph.D. degrees from the Hebrew University of Jerusalem. During his graduated studies he was a senior system analyst in the Central Computing Bureau of the Israeli government, where he was one of the chief designers of a new on-line Israeli population registration system. After graduation he held a research fellowship at the Center of Operation Research and Econometric (C.O.R.E.), Belgium and a visiting assistant professorship at the department of Business Administration, University of Illinois. At 1980 he joined the Computer Science department, Technion, Israel where he was until 1990. From 1990 to 1999 he was with the Haifa Research Laboratory, Science and Technology, IBM Israel, holding a position of a Program Manager of Communication Networks. From 2000 to 2001 he was with Radware Ltd., holding the chief scientist position. During the year of 2002 he visited the ARC Special Research Centre for Ultra-Broadband Information Networks (CUBIN), University of Melbourne. Currently he is an Associate/Professor at the Department of Communication Systems Engineering, Ben Gurion University, Beer-Sheva. Since 1980 he held summer research positions and a two year visiting position in IBM Thomas J. Watson Research Center, Yorktown Heights. He also had summer research positions in the Department of Electrical and Computer Engineering, University of Massachusetts, Amherst, Department of Electrical Engineering and Computer Science, University of California, Berkeley, the Radio Communication Systems, Royal Institute of Technology (KTH) in Stockholm, the ARC Special Research Center for Ultra-Broadband Information Networks (CUBIN), University of Melbourne, and the Department of EEE, City University, Hong Kong. Presently, he is serving on the editorial board of the Wireless Networks (WINET) and the International Journal of Communication Systems. His research interest, where he has published numerous papers, include: Narrowband and spread spectrum wireless communication, Radio resource allocation and planning in cellular networks, Scheduling in wireless networks, Optical and ultra high speed networks, Control in queueing networks, Analysis of algorithms in communication and computing systems and Internet technologies     

Gradual removals in cellular PCS with constrained power control and noise

In this paper we study themobile removal problem in a cellular PCS network where transmitter powers are constrained and controlled by a Distributed Constrained Power Control (DCPC) algorithm. Receivers are subject to non-negligible noise, and the DCPC attempts to bring each receiver's CIR above a given target. To evaluate feasibility and computational complexity, we assume a paradigm where radio bandwidth is scarce and inter-base station connection is fast. We show that finding the optimal removal set is an NP-Complete problem, giving rise for heuristic algorithms. We study and compare among three classes of transmitter removal algorithms. Two classes consist of algorithms which are invoked only when reaching a stable power vector under DCPC. The third class consist of algorithms which combine transmitter removals with power control. These areOne-by-one Removals, Multiple Removals, andPower Control with Removals Combined. In the class of power control with removals combined, we also consider a distributed algorithm which uses the same local information as DCPC does. All removal algorithms are compared with respect to their outage probabilities and their time to converge to a stable state. Comparisons are made in a hexagonal macro-cellular system, and in two metropolitan micro-cellular systems. ThePower Control with Removals Combined algorithm emerges as practically the best approach with respect to both criteria.This research has been done while the 2nd author was visiting at the Royal Inst. of Tech. under a grant from ISS '90 foundation, Sweden.     

Modeling data-intensive reactive systems with relational transition systems

In this paper, the formalism of Relational Transition Systems (RTSes) is used to model data-intensive reactive systems, and four RTS models of reactive systems based on temporal logic programming, production systems, recurrence equations, and Petri nets are presented. The paper also describes different methods of comparison of the expressive powers of various RTSes in terms of the trajectories they can generate and carries out this comparison for the four RTS formalisms. It is shown that these formalisms have the same expressive power in the deterministic case. The paper also compares expressive powers of non-deterministic production systems and non-deterministic temporal logic programming systems. It is shown that, although the two formalisms are incomparable in the general case, their restricted versions are isomorphic to each other. Received December 7, 1993 / January 26, 1995