Adaptive downlink scheduling and rate selection: a cross-layer design

In this paper, we discuss a cross-layer design for joint user scheduling and adaptive rate control for downlink wireless transmission. We take a stochastic learning-based approach to achieve this. The scheduling is performed at the medium access control (MAC) layer, whereas the rate selection takes place at the physical/link (PHY/LINK) layer. These two components residing in the two layers exchange information to ensure that user defined rate requests are satisfied by the right combination of transmission schedules and rate selections. The method is highly efficient for low mobility applications with mobile speeds in the order of a few kilometers per hour. While simple to implement, this technique requires no explicit channel estimation phase. The only feedback used are the single bit ACK/NACK signal indicating the correct reception/failure of the packet. As shown in the convergence theorems, the algorithm achieves optimal performance in "stationary" channels. With slowly varying channels, the rate selection algorithm sees a "quasi-stationary" channel and adaptively converges to an optimal solution. Simulations performed using a third-generation wireless system, namely, high-speed downlink packet access (HSDPA) validate the theoretical results.     

Search for new red phosphors using genetic algorithm-assisted combinatorial chemistry

A genetic algorithm was employed in association with high-throughput synthesis and characterization in an attempt to search for red phosphors with high photoluminescent intensity. A tetravalent manganese-doped alkali earth germanium oxide system, with an emission color close to a desirable deep red, was screened with the assistance of a genetic algorithm to pinpoint the phosphor exhibiting the highest photoluminescence. As the genetic algorithm was in progress, the PL intensity increased and maximized in the fourth generation. The highest and the average PL intensity of the fourth generation improved by 23 and 120%, respectively, compared with that of the first generation.     

Forced responses of solid axially polarized piezoelectric ceramic finite cylinders with internal losses

A method is presented to determine the forced responses of piezoelectric cylinders using weighted sums of only certain exact solutions to the equations of motion and the Gauss electrostatic conditions. One infinite set of solutions is chosen such that each field variable is expressed in terms of Bessel functions that form a complete set in the radial direction. Another infinite set of solutions is chosen such that each field variable is expressed in terms of trigonometric functions that form a complete set in the axial direction. Another solution is used to account for the electric field that can exist even when there is no vibration. The weights are determined by using the orthogonal properties of the functions and are used to satisfy specified, arbitrary, axisymmetric boundary conditions on all the surfaces. Special cases including simultaneous mechanical and electrical excitation of cylinders are presented. All numerical results are in excellent agreement with those obtained using the finite element software ATILA. For example, the five lowest frequencies at which the conductance and susceptance of a stress-free cylinder, of length 10 mm and radius 5 mm, reach a local maximum or minimum differ by less than 0.01% from those computed using ATILA.     

Testing systems on a chip

Developments in fault-finding circuits built into ICs which will disclose defects in today's and tomorrow's block-based designs are examined     

Multimode power modeling and maximum-likelihood estimation

It is known that circuits exhibit multiple modes of power consumption due to various factors such as the presence of many feedback (or sequential) elements, RAM, large size, etc. Previous power-estimation techniques have largely ignored this fact. For example, Monte Carlo simulation-based power estimators tend to produce estimates for the average power consumption that corresponds only to the most probable power mode of the circuit. This can be a cause for trouble later in the design step. The aim of this paper is twofold. First, an algorithm is proposed that estimates the total number of power modes of a circuit based on simulated data. This is then followed by a maximum-likelihood estimation procedure that produces the average values of the power modes along with their probabilities of occurrence. Theoretical ideas are supported by experimental results for ISCAS '85 benchmark circuits and a large industrial circuit. The proposed method is shown to perform well by capturing the multiple power modes for both large and small circuits even when the number of simulated samples is small while the Monte Carlo estimator does not. We conclude with a note that the proposed method is also applicable to other model selection problems in VLSI.     

Selection of Voltage Thresholds for Delay Measurement

Since all physical devices have a finite non-zero responsetime, the notion of delay between the input and output logicsignals arises naturally once digital abstraction is done. Thisdelay should be positive and non-zero, since a physical devicetakes a finite amount of time to respond to the input. Defininga strictly positive delay is not a problem in the abstract domainof logic signals, since input and output events are preciselydefined. However, when the signal non-idealities are accountedfor, the notion of events is blurred and it is not obvious howto define delay such that it reflects the causal relationshipbetween the input and the output. By necessity, we define thestart and end points of these events by determining the timeinstants when the signals cross some appropriate voltage thresholds.The selection of these voltage thresholds for logic gates aswell as simple interconnect wires, is the subject of this paper.We begin by a discussion of what we mean by signal delay andhow it arises in a logic gate. With this background, startingfrom ideal inputs to ideal inverters and concluding with physicalinputs to physical inverters, we examine the problem of thresholdselection for inverters through a logical sequence of model refinement,using a combination of analytical and experimental techniques.Based on the insight gained through this analysis, we examinethe problem for multi-input (both static and dynamic) gates aswell as point-to-point interconnect wires. We show that thresholdsderived from the gates DC voltage transfer characteristic removesthe anomalies, such as negative delay and large sensitivity toinput waveshape effects, that can arise with the widely used50% and 10%–90% thresholds. Despite its fundamentalnature, however, we note that the problem of threshold selectionhas received scant attention in the literature. To the best ofour knowledge, this is the first detailed study of this problem.     

Synthesis and antimicrobial activity of 6,6′‐arylidene‐bis‐[5‐hydroxy‐9‐methyl‐2,3‐diaryl thieno[3,2‐g‐]thiocoumarins]

A variety of novel 6,6′‐arylidene‐bis‐[5‐hydroxy‐9‐methyl‐2,3‐diaryl‐thieno[3,2‐g]thiocoumarins] 3a‐d , 4a‐d , 5a‐d , and 6a‐d were obtained by a reaction between 5‐hydroxy‐9‐methyl‐2,3‐diarylthieno[3,2‐g]thiocoumarins 1a‐d with aromatic aldehydes 2a‐d in isopropyl alcohol. The synthesized compounds were tested for their antimicrobial activity.     

SYNTHESIS OF NEW 8-METHOXY-4-METHYL-3-(N-[2′-AMINO-(1′,3′,4′)THIA/OXA-DIAZOL-5′-YL]-SUBSTITUTED METHYL)-AMINO THIOCOUMARINS

8-Methoxy-4-methyl-3-(N-[2′-amino-(1′, 3′,4′)thia/oxa-diazol-5′-yl] substituted methyl)-amino thiocoumarins 6(a–f) and 7(a–f), were synthesized by using the unreported 8-methoxy-4-methyl-3-[N-(2′-oxo-2′-methoxy-1′-substituted ethan-1′-yl) amino thiocoumarins as key intermediates.     

Lithium barium silicate,Li2BaSiO4, from synchrotron powder data

The structure of lithium barium silicate, Li₂BaSiO₄, has been determined from synchrotron radiation powder data. The title compound was synthesized by high‐temperature solid‐state reaction and crystallizes in the hexagonal space group P6₃cm. It contains two Li atoms, one Ba atom (both site symmetry ..m on special position 6c), two Si atoms [on special positions 4b (site symmetry 3..) and 2a (site symmetry 3.m)] and four O atoms (one on general position 12d, and three on special positions 6c, 4b and 2a). The basic units of the structure are (Li₆SiO₁₃)⁵⁻ units, each comprising seven tetrahedra sharing edges and vertices. These basic units are connected by sharing corners parallel to [001] and through sharing (SiO₄)⁴⁻ tetrahedra in (001). The relationship between the structures and luminescence properties of Li₂SrSiO₄, Li₂CaSiO₄ and the title compound is discussed.     

Three‐Residue Turns in α/β‐Peptides and Their Application in the Design of Tertiary Structures

A new three‐residue turn was serendipitously discovered in α/β hybrid peptides derived from alternating C‐linked carbo‐β‐amino acids (β‐Caa) and L ‐Ala residues. The three‐residue β‐α‐β turn at the C termini, nucleated by a helix at the N termini, resulted in helix‐turn (HT) supersecondary structures in these peptides. The turn in the HT motif is stabilized by two H bonds—CO(i?2)–NH(i), with a seven‐membered pseudoring (γ turn) in the backward direction, and NH(i?2)–CO(i), with a 13‐membered pseudoring in the forward direction (i being the last residue)—at the C termini. The study was extended to generalize the new three‐residue turn (β‐α‐β) by using different α‐ and β‐amino acids. Furthermore, the HT motifs were efficiently converted, by an extension with helical oligomers at the C termini, into peptides with novel helix‐turn‐helix (HTH) tertiary structures. However, this resulted in the destabilization of the β‐α‐β turn with the concomitant nucleation of another three‐residue turn, α‐β‐β, which is stabilized by 11‐ and 15‐membered bifurcated H bonds. Extensive NMR spectroscopic studies were carried out to delineate the secondary and tertiary structures in these peptides, which are further supported by molecular dynamics (MD) investigations.