Highly uniform and reproducible surface-enhanced Raman scattering from DNA-tailorable nanoparticles with 1-nm interior gap

An ideal surface-enhanced Raman scattering (SERS) nanostructure for sensing and imaging applications should induce a high signal enhancement, generate a reproducible and uniform response, and should be easy to synthesize. Many SERS-active nanostructures have been investigated, but they suffer from poor reproducibility of the SERS-active sites, and the wide distribution of their enhancement factor values results in an unquantifiable SERS signal. Here, we show that DNA on gold nanoparticles facilitates the formation of well-defined gold nanobridged nanogap particles (Au-NNP) that generate a highly stable and reproducible SERS signal. The uniform and hollow gap (～1 nm) between the gold core and gold shell can be precisely loaded with a quantifiable amount of Raman dyes. SERS signals generated by Au-NNPs showed a linear dependence on probe concentration (R(2) > 0.98) and were sensitive down to 10 fM concentrations. Single-particle nano-Raman mapping analysis revealed that >90% of Au-NNPs had enhancement factors greater than 1.0 × 10(8), which is sufficient for single-molecule detection, and the values were narrowly distributed between 1.0 × 10(8) and 5.0 × 10(9).     

Tubular membrane cathodes for scalable power generation in microbial fuel cells

One of the greatest challenges for using microbial fuel cells (MFCs) for wastewater treatment is creating a scalable architecture that provides large surface areas for oxygen reduction at the cathode and bacteria growth on the anode. We demonstrate here a scalable cathode concept by showing that a tubular ultrafiltration membrane with a conductive graphite coating and a nonprecious metal catalyst (CoTMPP) can be used to produce power in an MFC. Using a carbon paper anode (surface area Aan = 7 cm2, surface area per reactor volume Aan,s = 25 m2/m3), an MFC with two 3-cm tube cathodes (Acat = 27 cm2, Acat,s = 84 m2/m3) generated up to 8.8 W/m3 (403 mW/m2) using glucose [0.8 g/L in a 50 mM phosphate buffer solution (PBS)], which was only slightly less than that produced using a carbon paper cathode with a Pt catalyst (9.9 W/m3, 394 mW/m2; Acat= 7 cm2, Acat,s= 25 m2/m3). Coulombic efficiencies (CEs) with carbon paper anodes were 25-40% with tube cathodes (CoTMPP), compared to 7-19% with a carbon paper cathode. When a high-surface-area graphite brush anode was used (Aan = 2235 cm2, Aan,s = 7700 m2/m3) with two tube cathodes placed inside the reactor (Acat = 27 cm2, Acas, = 93 m2/m3), the MFC produced 17.7 W/m3 with a CE = 70-74% (200 mM PBS). Further increases in the surface area of the tube cathodes to 54 cm2 (120 m2/m3) increased the total power output (from 0.51 to 0.83 mW), but the increase in volume resulted in a constant volumetric power density (approximately 18 W/m3). These results demonstrate that an MFC design using tubular cathodes coated with nonprecious metal catalysts, and brush anodes, is a promising architecture that is intrinsically scalable for creating larger systems. Further increases in power output will be possible through the development of cathodes with lower internal resistances.     

Antimicrobial susceptibility patterns of competitive exclusion bacteria applied to newly hatched chickens

Competitive exclusion (CE) products are mixtures of obligate and facultative anaerobic bacteria applied to poultry hatchlings for prevention of Salmonella colonization. These mixtures have the potential to introduce bacteria with undesirable antimicrobial drug resistance traits into the human food supply. Antimicrobial drug susceptibilities of 27 obligate and facultative anaerobes isolated from a commercial CE product were evaluated with a microdilution minimal inhibitory concentration (MIC) assay. Bacteroides distasonis and Bacteroides fragilis isolates were resistant to tetracycline and other antimicrobial drugs. An Escherichia coli isolate was resistant to four antimicrobial drugs: erythromycin, penicillin, vancomycin, and tylosin. Erythromycin-resistant enterococci and vancomycin-resistant Lactococcus lactis isolates in the CE product were detected. These findings suggest that more work needs to be done to assess the potential effects of CE product use in poultry on the food supply.     

Conjunctive Management of Large-Scale Pressurized Water Distribution and Groundwater Systems in Semi-Arid Area with Parallel Genetic Algorithm

This study develops a production well management model for the conjunctive management of water resources in semi-arid areas. The management model integrates a large-scale pressurized water distribution system and a three-dimensional groundwater model under an optimization framework. The well pump operations optimization problem is formulated as a Boolean integer nonlinear programming (BINLP) problem to optimize the periodic 24-h pump on/off operations over a 1-week operation horizon. The management model considers multiple objectives and is solved by a parallel genetic algorithm (PGA) to overcome the difficulty of solving the BINLP problem. The PGA significantly reduces computation time for a case study in Chandler, Arizona. The Chandler water distribution model is built based on EPANET, and the Chandler three-dimension groundwater model is developed using MODFLOW. The high performance computing (HPC) of the genetic algorithm makes it possible to obtain 24-h real-time operations in the 7-day forecast model. The tank reliability, resilience, and vulnerability (R-R-V) are evaluated to infer the system reliability. The Pareto curve provides compromise solutions between the two competing objectives of energy reduction and pressure violation reduction.     

Optimization of Neural Stimuli Based Upon a Variable Threshold Potential

The commonly used assumption of a constant transmembrance potential threshold for nerve has yielded many useful threshold related results. These results include the strength-duration curve for monophasic constant current stimuli and the minimum power waveform of Offner. This paper shows that the constant threshold assumption is not adequate for ranges of pulsewidths where it has seen frequent previous application, and that it is not applicable for the case of biphasic stimulation. Based upon results from the Frankenhaeuser-Huxley model of myelinated nerve, a more accurate form of potential threshold for monophasic stimuli is developed which is shown to extend to ranges of stimulus parameters inadequately modeled by the constant threshold assumption. An extrapolation of this threshold condition to the case of biphasic stimulation is also considered, along with minimum power and damage waveforms derived with use of a nonconstant threshold potential function. A procedure for clinically determining the parameters necessary to evaluate optimal pulsewidths-is also presented.     

Implementing a graphical multi-user interface toolkit

Multi-user applications allows users in different locations to simultaneously interact with a common interface. Creating multi-user applications is complicated by issues such as process synchronization, replicated window management, and floor control. As a result, several papers describing toolkits that simplify programming of multi-user applications have appeared in the literature. This paper discusses several low-level issues that must be addressed when implementing such a toolkit. Issues relating to replicated window management, supporting heterogeneous hardware environments, and multi-user event handling are discussed.     

Demonstration of Bidirectional Services Using MPEG‐4 BIFS in Terrestrial DMB Systems

Digital broadcasting technology has developed focusing on multi‐channel/multi‐media, high‐definition quality, and mobility‐support. Recently, there has been a clear trend toward bidirectional service with the convergence between broadcasting and communication. The broadcasting viewer is no longer simply a passive receptor but has also become an information generator. Currently, the digital multimedia broadcasting (DMB) specifications are the major standard for portable digital broadcasting and have been establishing the overall guidelines for bidirectional service using the MPEG‐4 system. While detailed specifications for DMB systems are not well‐established for bidirectional service yet, they share the basic concepts underlying the European Eureka‐147 Digital Audio Broadcasting (DAB) system. This paper develops key scenarios for bidirectional service in DMB, describes the signal transaction of broadcasting and return channels, and demonstrates typical scenarios using binary format for scenes (BIFS) in the MPEG‐4 system.     

Assignment allocation and simulated annealing algorithms for cell formation

In this paper a nonlinear mathematical programming model is developed for cell formation that identifies part families and machine groups simultaneously with no manual intervention or subjective judgement. The objective of the model is minimization of the weighted sum of the voids and the exceptional elements. Changing weights for void and exceptional elements aids the designer with a systematic generation of different solutions, i.e., forming large loose cells or small tight cells. An assignment allocation algorithm (AAA) and a simulated annealing algorithm (SAA) are developed to solve the model. AAA and SAA compare favorably with many well-known procedures for the problems tested. AAA is less computer-intensive and hence large problems with 400 parts and 240 machines were solved with AAA in less than a minute on Sun Sparc station. However, AAA is sensitive to the initial machine grouping solution input to the algorithm. SAA gives consistent results but requires more computational time.     

Hidra: A Hierarchical Instrument for Distributed Real-Time Analysis of Biological Signals

This work presents a locally distributed common bus multiple-processor system intended to support a hierarchical signal processing scheme for biological signal analysis. Each peripheral unit?the so called preprocessor (PP)?executes real-time signal processsing algorithms over data multiplexed in an input bus. The result of this analysis is transferred to a host computer that integrates the received information from the PP's, saves it in disk when necessary, performs higher level data analysis, and interfaces to the user. The processing of electroencelographic (EEG) data will be used as a case study, due to the multidimensional aspects involved.     

蜂窝手机市场和技术发展趋势

从2004年末到2005年初,多数业界观察家预测今后手机业务增长率将减慢,增长速度预测不超过10%,而目前手机业务的最大潜能是为新兴市场开发极低成本手机.这种发展趋势的假设是发达国家市场已经饱和,因此销售量增长应该来自发展中国家初次使用手机的新用户.但后来市场却以15%～20%的惊人速度强势增长,从而在2005年全球手机销售量达到8亿部,而这种增长并不仅限于极低成本手机市场部分.