Solving a class of optimum multiuser detection problems withpolynomial complexity

We identify a class of optimum multiuser detection problems which can be solved with polynomial complexity in the number of users. The identification is based on transforming a quadratic 0-1 programming problem into an equivalent problem in graph theory. For a synchronous direct sequence code-division multiple access (CDMA) system, the result translates to designing a set of pseudorandom codes with the property that the cross correlation between every pair of codes in the set over one symbol period is nonpositive. We give two sets of codes with good correlation properties that fall within this class. Finally, we derive a bound on the cardinality of a signal set in an n-dimensional space, having the property that the cross correlation between every pair of signals in the set is nonpositive     

Synthesis and characterization of sodium alkoxides

Alcohol route is being adopted for cleaning sodium from sodium-wetted small components of coolant circuits of fast reactors. For better understanding of sodium-alcohol reactions and their energetics, the data on thermo-chemical properties such as heats of sodium-alcohol reactions, heats of dissolution, heat capacities, thermal decomposition behaviour, etc of their end products are essential. In order to generate such data, high purity sodium alkoxides, viz. sodium methoxide, sodium ethoxide and sodium n-propoxide, were prepared by reacting sodium metal with respective alcohol. These compounds were characterized using X-ray diffraction technique and IR spectroscopy. The elemental analysis was carried out by CHNS analyser and atomic emission spectroscopy. Normal chain sodium alkoxides were found to exhibit tetragonal crystal structure. Crystal structures of sodium ethoxide and sodium n-propoxide are reported for the first time. The IR spectrum of sodium n-propoxide is also reported for the first time.     

The employability of older workers as teleworkers: An appraisal of issues and an empirical study

The aging of the population and, concomitantly, of the workforce has a number of important implications for governments, businesses, and workers. In this article, we examine the prospects for the employability of older workers as home‐based teleworkers. This alternative work could accommodate many of the needs and preferences of older workers and at the same time benefit organizations. However, before telework can be considered a viable work option for many older workers there are a number of issues to consider, including the ability of older workers to adapt to the technological demands that are typically associated with telework jobs and managerial attitudes about older workers and about telework. Through an integrated examination of these and other issues, our goal is to provide a comprehensive understanding of the challenges associated with employing older workers as teleworkers. We also present findings from a questionnaire study that assessed managers' perceptions of worker attributes desirable for telework and how older workers compare to younger workers on these attributes. The sample included 314 managers with varying degrees of managerial experience from a large variety of companies in the United States. The results presented a mixed picture with respect to the employability of older workers as teleworkers, and strongly suggested that less experienced managers would be more resistant to hiring older people as teleworkers. We conclude with a number of recommendations for improving the prospects for employment of older workers for this type of work arrangement. © 2009 Wiley Periodicals, Inc.     

Photoresponsive Cucurbit[8]uril‐Mediated Adhesion of Bacteria on Supported Lipid Bilayers

In this work, the development of a photoresponsive platform for the presentation of bioactive ligands to study receptor–ligand interactions has been described. For this purpose, supramolecular host–guest chemistry and supported lipid bilayers (SLBs) have been combined in a microfluidic device. Quartz crystal microbalance with dissipation monitoring (QCM‐D) studies on methyl viologen (MV)‐functionalized oligo ethylene glycol‐based self‐assembled monolayers, gel and liquid‐state SLBs have been compared for their nonfouling properties in the case of ConA and bacteria. In combination with bacterial adhesion test, negligible nonspecific bacterial adhesion is observed only in the case of methyl‐viologen‐modified liquid‐state SLBs. Therefore, liquid‐state SLBs have been identified as most suitable for studying specific cell interactions when MV is incorporated as a guest on the surface. The photoswitchable supramolecular ternary complex is formed by assembling cucurbit[8]uril (CB[8]) and an azobenzene–mannose conjugate (Azo–Man) onto MV‐functionalized liquid‐state SLBs and the assembly process has been characterized using QCM‐D and fluorescence techniques. Mannose has been found to enable binding of E. coli via cell‐surface receptors on the nonfouling supramolecular SLBs. Optical switching of the azobenzene moiety allows us to “erase” the bioactive surface after bacterial binding, providing the potential to develop reusable sensors. Localized photorelease of bacterial cells has also been shown indicating the possibility of optically guiding cellular growth, migration, and intercellular interactions.     

Stochastic optimization using a sparse grid collocation scheme

In computational sciences, optimization problems are frequently encountered in solving inverse problems for computing system parameters based on data measurements at specific sensor locations, or to perform design of system parameters. This task becomes increasingly complicated in the presence of uncertainties in boundary conditions or material properties. The task of computing the optimal probability density function (PDF) of parameters based on measurements of physical fields of interest in the form of a PDF, is posed as a stochastic optimization problem. This stochastic optimization problem is solved by dividing it into two problems—an auxiliary optimization problem to construct stochastic space representations from the PDF of measurement data, and a stochastic optimization problem to compute the PDF of problem parameters. The auxiliary optimization problem is solved using a downhill simplex method, whilst a gradient based approach is employed for solving the stochastic optimization problem. The gradients required for stochastic optimization are defined, using appropriate stochastic sensitivity problems. A computationally efficient sparse grid collocation scheme is utilized to compute the solution of these stochastic sensitivity problems. The implementation discussed, requires minimum intrusion into existing deterministic solvers, and it is thus applicable to a variety of problems. Numerical examples involving stochastic inverse heat conduction problems, contamination source identification problems and large deformation robust design problems are discussed.     

Hetero-atoms as activation centers for hydrogen absorption in carbon nanotubes

Carbon materials should have specific centers for hydrogen adsorption/absorption. The role of heteroatom substitution in carbon nanotubes as an activator has been identified by Density Functional Theory. The effect of various hetero-atoms like nitrogen, phosphorus, sulphur and boron for hydrogen activation and their geometrical positions has been recognized as the one of the possible reasons for easy hydrogenation. Experimentally, nitrogen and boron containing carbon nanotubes have been synthesized by using template method. The hydrogen absorption capacity of these materials has been evaluated. It is shown that, there is a need to stabilize nitrogen in the carbon nanotube framework for reproducible hydrogen uptake. In the case of boron containing carbon nanotubes, two different chemical environment of boron facilitates hydrogen interaction. They exhibit a maximum of 2 wt.% of hydrogen storage capacity at 80 bar and 300 K. This configuration has a bearing in hydrogen sorption characteristics.     

Barrier-layer formation and its control during hydrogen permeation through Ti-24AI-11Nb alloy

Hydrogen transport through Ti-24Al-11Nb (at. pct) alloy has been measured using ultrahigh vacuum permeation techniques over the temperature range of 500 °C to 900 °C and a hydrogen pressure range of 20 to 1333 Pa. The hydrogen uptake behavior of the alloy is influenced by even very small amounts of contaminants in the hydrogen gas. It is shown that contaminants such as CO and H₂O are released from the walls of the vacuum system by the incoming hydrogen gas due to collision-induced desorption and that these species form a barrier layer. In the presence of the barrier layer, the hydrogen-permeation behavior of the alloy has two apparent temperature regimes: a high-temperature regime where the barrier layer has minimal effect, and a low-temperature regime where the barrier layer inhibits the hydrogen uptake. A physical model to explain this behavior is presented. It is further shown that the effect of the barrier layer can be minimized by maintaining dynamic flow conditions in the upstream chamber. Under these conditions, the transport process is diffusion-limited: the permeability has a weak temperature dependence, but the diffusivity has a strong temperature dependence.     

Quantifying the value of ownership of yield analysis technologies

A model based on information theory, which allows yield managers to determine an optimal portfolio of yield analysis technologies for both the R&D and volume production environments, is presented. The information extraction per experimentation cycle and information extraction per unit time serve as benchmarking metrics for yield learning. They enable yield managers to make objective comparisons of apparently unrelated technologies. Combinations of four yield analysis tools - electrical testing, automatic defect classification, spatial signature analysis and wafer position analysis - are examined in detail to determine the relative value of ownership of different yield analysis technologies.     

Spout: a transparent proxy for safe execution of Java applets

The advent of executable contents such as Java applets exposes World Wide Web (WWW) users to a new class of attacks that were not possible before. Despite an array of security checking, detection, and enforcement mechanisms built into the language model, the compiler, and the run-time system of Java, serious security breach incidents due to implementation bugs still arose repeatedly in the past several years. Without a provably correct implementation of Java's security architecture specification, it is difficult to make any conclusive statements about the security characteristic of current Java virtual machines. The Spout project takes an alternative approach to address Java's security problems. Rather than attempt a provable secure implementation, we aim to confine the damages of malicious Java applets to selective machines, thus, preventing the machines behind an organization's firewall from being attacked by malicious or buggy applets. More concretely, Spout is a distributed Java execution engine that transparently decouples the processing of an incoming applet's application logic from that of graphical user interface (GUI), such that the only part of an applet that is actually running on the requesting user's host is the harmless GUI code. A unique feature of the Spout architecture that does not exist in other similar systems, is that it is completely transparent to and does not require any modifications to WWW browsers or class libraries on the end hosts. This paper describes the detailed design, implementation, and performance measurements of the first Spout prototype, which also incorporates run-time resource monitoring mechanisms to counter denial-of-service attacks.     

Value of C-reactive protein measurements in exacerbations of chronic obstructive pulmonary disease

C-reactive protein (CRP) has been shown to be a useful and sensitive indicator of pyogenic infections in many clinical situations, including acute pneumonia and infective pulmonary exacerbations in cystic fibrosis patients. Exacerbations of COPD are often, but not always, associated with demonstrable infection. The value of CRP measurement in this situation has not been assessed. We have evaluated CRP measurement in 50 patients [age 71 +/- 8 (SD) years] who were admitted to hospital with clinical evidence of exacerbation [PaO2 = 7.3 +/- 1.3 (SD) kPa, baseline FEV1 = 0.8 +/- 0.4 (SD) l]. These patients all had serial measurement of CRP [polarizing immunofluorescence (Abbot, TDx)], peripheral white cell count (WCC), body temperature, peak expiratory flow rate, Karnofsky performance status and chest X-ray, in addition to serial sputum bacteriological analysis carried out in a specialized laboratory. CRP was elevated (> 10 mg l-1) in all patients (n = 29) with proven infection [103 +/- 98 (SD) mg l-1]. Levels were markedly elevated in patients infected with Streptococcus pneumoniae (mean 156 mg l-1); there was also a rapid fall in the CRP with therapy. WCC fell with therapy, giving a correlation with CRP level (r = 0.44, P < 0.01). Since CRP elevation was observed in patients having exacerbation with proven infections and also in those where infection was not proven, it is possible that, while it is a marker for COPD exacerbation, it is not necessarily a marker of bacterial infection per se. However, it is evident from our study that it is of value in the assessment of exacerbations of COPD, where routine bacterial culture of sputum is often unreliable, and thus the measurement of serum CRP may provide an additional objective indicator of infection.