Amplified chemiluminescence surface detection of DNA and telomerase activity using catalytic nucleic acid labels

A G-rich nucleic acid sequence binds hemin and yields a biocatalytic complex (DNAzyme) of peroxidase activity, namely, the biocatalyzed generation of chemiluminescence in the presence of H(2)O(2) and luminol. The DNAzyme is used as a label for the amplified detection of DNA, or for the analysis of telomerase activity in cancer cells, using chemiluminescence as an output signal. In one configuration, the analyzed DNA is hybridized with a primer nucleic acid that is associated with a Au surface, and the DNAzyme label is hybridized with the surface-confined analyte DNA. The DNA is analyzed with a detection limit of approximately 1 x 10(-)(9) M. In the second system, telomerase from HeLa cancer cells induces telomerization of a primer associated with a Au surface and the complementary DNAzyme units are hybridized with the telomere to yield the chemiluminescence. The detection limit of the system corresponds to 1000 HeLa cells in the analyzed sample.     

Analyzing the performance of a nanosatellite cluster-detector array receiver for laser communication

This work analyzes laser communication between a cluster of nanosatellites, which is a concentrated formation of small lightweight satellites and a ground station. The scenario under consideration is a cluster of nanosatellites communicating by means of a laser beam with a detector array receiver that is located on the earth's surface and equipped with a common optical system for all incoming beams. The beams are concentrated to spots over the detector plane by the receiver's optics. The detector array enables the ground station to communicate with a tight concentration of the nanosatellites, which reduces system complexity and cost. A critical parameter that determines the successful receipt and subsequent decoding of a transmitted signal for a given configuration is the angular separation between the satellites within the cluster. This separation must be retained to prevent critical overlapping of the spots on the detector's surface. The maximum allowable overlapping is calculated in terms of given bit-error rate. The spatial spreading of the beams, caused by scattering from aerosols in different layers of the atmosphere, is calculated for the case of single scattering. A stratified model of the atmosphere is used. Turbulence influences the beam width, especially for the case of short exposure, and is primarily caused by temperature changes, which result in fluctuations in the refractive index. In this research, a new approach is adopted for analyzing communication network performance through the atmosphere by applying optical-transfer function (OTF) concepts used in imaging and remote sensing. We evaluate the effectiveness of this new approach in applications where spatial spread between the users is very important.     

Stability,Sequentiality and Demand Driven Evaluation in Dataflow

We show that a given dataflow language l has the property that for any program P and any demand for outputs D (which can be satisfied) there exists a least partial computation of P which satisfies D, iff all the operators of l are stable. This minimal computation is the demand-driven evaluation of P. We also argue that in order to actually implement this mode of evaluation, the operators of l should be further restricted to be effectively sequential ones.     

Optical technique for the automatic detection and measurement of surface defects on thin metallic wires

In industrial applications of thin metallic wires it is important to characterize the surface defects of the wires. We present an optical technique for the automatic detection of surface defects on thin metallic wires (diameters, 50-2000 mum) that can be used in on-line systems for surface quality control. This technique is based on the intensity variations on the scattered cone generated when the wire is illuminated with a beam at oblique incidence. Our results are compared with those obtained by atomic-force microscopy and scanning-electron microscopy.     

Performance of expanded graphite and expanded milled‐graphite fillers in thermosetting resins

Epoxy/expanded graphite (EG) and polyester/EG composites were prepared with the aid of sonication, while epoxy/expanded‐milled graphite (epoxy/milled‐EG) and polyester/expanded‐milled graphite (polyester/milled‐EG) composites were prepared on a three‐roll paint mill. The epoxy/EG and polyester/EG composites exhibit a sharp insulator/semiconductor transition at markedly low percolation thresholds, due to the vermicular shape of EG having high aspect ratio and surface area. The morphologies of epoxy and polyester resins incorporated with EG and milled‐EG fillers were observed by scanning electron microscopy (SEM). The results of dynamic mechanical analysis of the composites reveal that both EG and milled‐EG fillers increase the T_g of the epoxy matrix. Milled‐EG increases the G′ of the epoxy matrix, while EG decreases the G′ of the epoxy matrix, due to the existence of abundant pores in EG. The milled‐EG filler has the same effect on the polyester matrix as on the epoxy matrix, but the EG filler has no significant effect on the mechanical properties of polyester matrix. POLYM. COMPOS., 26:526–533, 2005. © 2005 Society of Plastics Engineers     

Deformation behaviour of coextruded multilayer composites with polycarbonate and poly(styrene-acrylonitrile)

The tensile properties of coextruded multilayer composites comprised of predominantly 49 alternating layers of polycarbonate (PC) and polystyrene- acrylonitrile (SAN) were investigated in the bulk and microscopically. The bulk was characterized by three types of behaviour: brittle fracture at low strains, ductile yielding with fracture during neck formation, and formation of a stable neck followed by drawing to high extension. Optical microscopy was utilized to correlate deformation mechanisms within each phase to the observed modes of deformation in the bulk. Optical microscopy showed that in all cases the initial irreversible deformation event was the formation of cracks or crazes in the SAN layers. Good adhesion between the layers resulted in the subsequent initiation of shear bands in the polycarbonate layers at the craze tips. Interaction of crazes and shear bands produced an expanded damage zone ahead of the propagating crack which delocalized the stress and delayed fracture. The ultimate mode of fracture depended on the relative thickness of the SAN and PC layers, as determined by the composition, and the strain rate.     

Mechanisms of Fabric Reinforcement of Cement Matrices

The present paper discusses the mechanisms involve in fabric‐cement composites focusing on the effects of fabric geometry and the properties of the yarns. It was found that the geometry of a given fabric could enhance the bonding and enable one to obtain strain hardening behavior from low modulus yarn fabrics, due to the special shape of the yarn induced by the fabric. On the other hand, variations of the geometry in a fabric could drastically reduce the efficiency, resulting in a lower strengthening effect of the yarns in the fabric, relative to single yarns not in a fabric form. Therefore, in cement composites the fabrics can not be viewed simply as a means for holding together continuous yarns to be readily placed in the matrix, as is the case in composites with polymer matrix.     

A comparative study of wireless communication network configurations for medical applications

A comparative study of the performance characteristics of five multiple access configurations for a wireless communication network is presented and evaluated within the context of the medical field of application. A universal variable has been defined for comparison between the alternative configurations, embodying the data rate, number of channels, power consumption, and bandwidth requirements. Special medical specifications have been accommodated, while the broader applications of this approach have been addressed. CDMA is indicated as the preferred method, over ALOHA, slotted ALOHA, CSMA, and polling.     

Extinguishing class B fires with dry chemicals: Scaling studies

In a continuing study of flame extinguishment,^1,2,3,4 we report on scaling studies for dry chemicals on larger heptane diffusion flames (0.29 m² and 2.32 m² pans). We demonstrate again that small particle sizes extinguish most effectively. Extinguishment is related to heat absorption by decomposing or vaporizing particles. We show that the limiting particle size for each dry chemical—that is, the maximum size which completely decomposes or vaporizes in the flame—is independent of flame size for the systems studied. We broaden and apply the concept of latent or maximum effectiveness^2,3 to pan fires of all sizes. Finally, we describe and characterize an aerodynamic effect in the transport of powders, where large particles with their higher momentum entrain and drag smaller, more effective particles into the flame.We also show that extinction curves, involving the ratio of real-to-latent extinction weight and the proportion of small to large particles, have predictable shapes and predictable quantitative levels for most dry chemicals. We have developed the real-to-latent concept along with scaling equations for agent mixtures and for a wide spectrum of agents and particle sizes.     

Modulation of the immune response in multiple sclerosis: production of monoclonal antibodies specific to HLA/myelin basic protein

Monoclonal Abs to the complex formed between human MHC class II molecules (DR7 and DRw11) and myelin basic protein (MBP) were produced. The specificity of these Abs was established by both FACS analysis and complement-mediated cytotoxicity of MBP- or OVA-pulsed human APC of the same or of different DR restriction. These Abs bound to and lysed only MBP-pulsed human APC of the same DR restriction (DR7 or DRw11) but not to APC of different DR restriction or pulsed with a different Ag (OVA). The physiologic role of these Abs was further investigated. They blocked the in vitro proliferative response to MBP-specific T cell clones isolated from multiple sclerosis patients in an antigen-specific and DR-restricted manner. However, the Abs did not affect the response of MBP-specific T cell clones of other DR restriction nor did they interfere with the response to other Ags (purified protein derivative or copolymer 1) presented on APC with the same DR restriction. These Abs may be useful for treating multiple sclerosis in which reactivity to MBP is implicated. Moreover, this approach may be extended to other autoantigens and their counterpart autoimmune diseases.