Spectrum sharing under the asynchronous UPCS etiquette: The performance of collocated systems under heavy load

Recently the FCC opened three 10 MHz bands for unlicensed use. In order to operate in UPCS bands, devices must comply with rules known as the UPCS etiquette (United States Code of Federal Regulations, Title 47, Part 15(d)). In this paper we study channel sharing between two or more collocated systems under the asynchronous UPCS etiquette. In particular we show that under heavy load individual systems have a tendency to hold the channel for hundreds of milliseconds, thus blocking all traffic in other, competing systems. We have calculated the distribution of the blocking time for two versions (or interpretations) of the UPCS etiquette. The impact of the average blocking time on delay sensitive traffic is discussed and possible improvements achieved through a tradeoff between system capacity and average blocking time are investigated. This revised version was published online in June 2006 with corrections to the Cover Date.     

On Prolonging the Lifetime for Wireless Video Sensor Networks

This paper investigates strategies for prolonging the system lifetime for wireless video sensor networks, by adopting a mobile sink and solar-powered video sensors. Issues of tracking moving objects in wireless video sensor networks are studied, and the effectiveness of adopting a mobile sink is evaluated. This paper applies a power-rate-distortion analysis framework, which provides a theoretical fundamental to quantify various properties of wireless video sensor networks. The performance of wireless video sensor networks is evaluated with a mobile sink versus a static sink, under different cluster sizes and number of sensors. Comparisons of network lifetime, tracking error, video distortion, are also covered in this paper. In addition, this paper also evaluates the performance of solar-powered video sensors under an unequal layered clustering topology.     

CDMA bus-based on-chip interconnect infrastructure

As technology scales toward deep submicron, the integration of complete system-on-chip (SoC) designs consisting of large number of Intellectual Property (IP) blocks (cores) on the same silicon die is becoming technically feasible. Until recently, the design-space exploration for SoCs has been mainly focused on the computational aspects of the problem. However, as the number of IP blocks on a single chip and their performance continue to increase, a shift from computation-based to communication-based designs becomes mandatory. As a result, the communication architecture plays a major role in the area, performance and energy consumption of the overall systems [Pasricha S, Dutt N. On-chip communication architectures: system on chip interconnect. Amsterdam: Elsevier Inc.; 2008, Kim J, Verbauwhede I, Chang MCF. Design of an interconnect architecture and signaling technology for parallelism in communication. IEEE Trans VLSI Syst 2007;15(8):881-94].This article presents a structure of a wrapper as a component of Code Division Multiple Access, CDMA, based shared bus architecture in a SoC. Two types of wrappers can be identified, master and slave. A master wrapper is located between the arbiter and CDMA coded physical interconnect, while a slave connects the CDMA coded bus with memory/peripheral module. In the proposal, only bus lines that carry address and data signals are CDMA coded. We implemented a pair of master-slave wrapper described in VHDL and confirmed its functionality using testbenches. Also we synthesized wrappers using a Xilinx Spartan and Virtex devices to determine resource requirements in respect to a number of equivalent gates, communication bandwidth, latency and power consumption. Specifically we involved a Design_Quality, DQ, metric for wrapper performance evaluation. A pair of master-slave wrapper seems to occupy appropriate space, in average 2000 equivalent gates, considering CPU cost of about 30,000 gates, what is less than 8% of hardware overhead per CPU. We also present experimental results which show that benefits of involving CDMA coding relates both to decreasing a number of bus lines and accomplishing simultaneous multiple master-slave connections at relatively low-power consumption and high communication bandwidth. Convenient range indices R_W and R_R to determine data transfer rate for Write and Read operations in multiprocessor bus systems that use TDMA and CDMA data transfer techniques. The obtained results show that increased data transfer latencies involved by CDMA data transfer are compensated by simultaneous master-slave transfers.     

Carbon‐Nanotube–PDMS Composite Coatings on Optical Fibers for All‐Optical Ultrasound Imaging

Polymer–carbon nanotube composite coatings have properties that are desirable for a wide range of applications. However, fabrication of these coatings onto submillimeter structures with the efficient use of nanotubes has been challenging. Polydimethylsiloxane (PDMS)–carbon nanotube composite coatings are of particular interest for optical ultrasound transmission, which shows promise for biomedical imaging and therapeutic applications. In this study, methods for fabricating composite coatings comprising PDMS and multiwalled carbon nanotubes (MWCNTs) with submicrometer thickness are developed and used to coat the distal ends of optical fibers. These methods include creating a MWCNT organogel using two solvents, dip coating of this organogel, and subsequent overcoating with PDMS. These coated fibers are used as all‐optical ultrasound transmitters that achieve high ultrasound pressures (up to 21.5 MPa peak‐to‐peak) and broad frequency bandwidths (up to 39.8 MHz). Their clinical potential is demonstrated with all‐optical pulse‐echo ultrasound imaging of an aorta. The fabrication methods in this paper allow for the creation of thin, uniform carbon nanotube composites on miniature or temperature‐sensitive surfaces, to enable a wide range of advanced sensing capabilities.     

Molecular Origin of the Charge Carrier Mobility in Small Molecule Organic Semiconductors

Small‐molecule organic semiconductors are used in a wide spectrum of applications, ranging from organic light emitting diodes to organic photovoltaics. However, the low carrier mobility severely limits their potential, e.g., for large area devices. A number of factors determine mobility, such as molecular packing, electronic structure, dipole moment, and polarizability. Presently, quantitative ab initio models to assess the influence of these molecule‐dependent properties are lacking. Here, a multiscale model is presented, which provides an accurate prediction of experimental data over ten orders of magnitude in mobility, and allows for the decomposition of the carrier mobility into molecule‐specific quantities. Molecule‐specific quantitative measures are provided how two single molecule properties, the dependence of the orbital energy on conformation, and the dipole‐induced polarization determine mobility for hole‐transport materials. The availability of first‐principles based models to compute key performance characteristics of organic semiconductors may enable in silico screening of numerous chemical compounds for the development of highly efficient optoelectronic devices.     

Transient analysis of electromagnetic systems with multiple lumped nonlinear loads

A novel method for transient analysis of electromagnetic systems with multiple lumped nonlinear loads is presented. The uniqueness of this approach is that we develop time-domain Green's functions for the multiport linear part of the electromagnetic system by suitably terminating the ports. This ensures a short duration of Green's functions. Hence the amount of frequency-domain data necessary to obtain the time-domain Green's functions is modest. The application of this technique to an arbitrary excitation is just a straightforward convolution. With this technique one can analyze responses of systems with arbitrary nonlinear loads (even with memory) as we have at any time instant Thevenin's equivalent of the linear portion of the electromagnetic system. Examples are presented to illustrate the application of this technique to multiport nonlinearly loaded antennas.     

Digraph Matrix Analysis

This paper describes a systematic procedure for constructing a Boolean reliability model from plant schematics, and a technique for determining all sets of single and double component failures which will cause system failure. This technique, called digraph matrix analysis, uses a fault graph instead of the more traditional fault tree. Digraph matrix analysis was recently applied to the system interaction analysis of a very large safety system (over ten thousand components) and is being used to determine security system vulnerabilities.     

Selective extraction,structural characterisation and antifungal activity assessment of napins from an industrial rapeseed meal

This article reports an extraction–purification of napins from an industrial rapeseed meal and the assessment of their antimicrobial activity against Fusarium langsethiae. The best extraction conditions are observed at pH 2, 12% (w/w) of rapeseed meal after 15 min of extraction in water at room temperature. Under these conditions the extraction is highly selective, allowing a simple purification process (ammonium sulfate precipitation followed by desalting size exclusion chromatography) to get purified napins. These napins possessed significant anti-Fusarium activity (IC₅₀ = 70 μM) and a compact secondary structure rich in α-helix, which may explain this bioactivity.     

Bacterial spores in spices and dried herbs: The risks for processed food

Production and world consumption of spices are constantly increasing. Although the antimicrobial properties of some spices are well documented, their use in the agri-food industry is also responsible for microbial contamination and spoilage. Bacterial spores introduced by spices can withstand different preparation processes, particularly thermal treatments, leading to food alterations during storage. This review brings together data from the literature about the prevalence and concentrations of spore-forming bacteria in all commercially available spices. The sporeformers found in spices belong mainly to the genera Bacillus and Clostridium. Such contaminations are very common and sometimes reach high levels, as in pepper and turmeric. Bacillus licheniformis and Bacillus cereus are the most frequently detected species. Studying the harvesting, processing, and storage procedures for spices provides elements to explain why high prevalence and concentrations are observed. Spices are mostly produced in developing countries on small farms using traditional production methods. Spices become contaminated by bacterial spores in two main ways: by contact with soil during harvesting or drying, as for pepper, or by cross-contamination during the water-cooking step, as for turmeric. From these observations, we propose some recommendations. Different methods that can be used to eliminate bacterial spores from spices are presented indicating their efficiency and the limitations of their use.     

Antibacterial and antifungal activities of selected microalgae and cyanobacteria

In vitro activity of nine cyanobacterial and ten microalgal newly isolated or culture collection strains against eight significant food‐borne pathogens has been evaluated and compared. Water extracts and culture liquids of Gloeocapsa sp. and Synechocystis sp. demonstrated the widest spectrum of activity with minimal inhibitory concentration (MIC) ranging from 1.56 to 12.5 mg mL^?1. Culture liquid of Anabaena sp. had the highest activity (MIC = 0.39 mg mL^?1) but only to Gram‐positive bacteria. Ethanol extracts and fatty acids from all cyanobacteria and microalgae were active against Streptococcus pyogenes and/or Staphylococcus aureus. The fatty acids of Synechocystis sp. inhibited the growth of Bacillus cereus, Escherichia coli and Candida albicans (MIC values of 2.5–1.25 mg mL^?1, respectively). Exopolysaccharides (EPS) of Gloeocapsa sp. were the sample that exhibited activity against all test pathogens with lowest MIC values (0.125–1 mg mL^?1). High activity with a narrower range of susceptible targets demonstrated the exopolysaccharides of Synechocystis sp. and Rhodella reticulata. Antimicrobial activity was proven for phycobiliproteins isolated from Synechocystis sp., Arthrospira fusiformis, Porphyridium aerugineum and Porphyridium cruentum, respectively. In conclusion Gloeocapsa sp. and Synechocystis sp. and especially their exopolysaccharides showed the most promising potential against the examined food pathogens.