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Signal Strength (signal + strength)
Selected AbstractsHOW BRIGHT AND HOW NASTY: EXPLAINING DIVERSITY IN WARNING SIGNAL STRENGTHEVOLUTION, Issue 3 2007Michael P. Speed The conspicuous displays that warn predators of defenses carried by potential prey have been of interest to evolutionary biologists from the time of Wallace and Darwin to the present day. Although most studies implicitly assume that these "aposematic" warning signals simply indicate the presence of some repellent defense such as a toxin, it has been speculated that the intensity of the signal might reliably indicate the strength of defense so that, for example, the nastiest prey might "shout loudest" about their unprofitability. Recent phylogenetic and empirical studies of Dendrobatid frogs provide contradictory views, in one instance showing a positive correlation between toxin levels and conspicuousness, in another showing a breakdown of this relationship. In this paper we present an optimization model, which can potentially account for these divergent results. Our model locates the optimal values of defensive traits that are influenced by a range of costs and benefits. We show that optimal aposematic conspicuousness can be positively correlated with optimal prey toxicity, especially where population sizes and season lengths vary between species. In other cases, optimal aposematic conspicuousness may be negatively correlated with toxicity; this is especially the case when the marginal costs of aposematic displays vary between members of different populations. Finally, when displays incur no allocation costs there may be no single optimum value for aposematic conspicuousness, rather a large array of alternative forms of a display may have equal fitness. [source] DS/CDMA throughput of a multi-hop sensor network in a Rayleigh fading underwater acoustic channelCONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 8 2007Choong Hock Mar Abstract Asynchronous half-duplex Direct-Sequence Code-Division Multiple-Access (DS/CDMA) is a suitable candidate for the MAC protocol design of underwater acoustic (UWA) sensor networks owing to its many attractive features. Our ad-hoc multi-hop network is infrastructureless in that it is without centralized base stations or power control. Hence, we develop an asynchronous distributed half-duplex control protocol to regulate between the transmitting and receiving phases of transmissions. Furthermore, multi-hop communications are very sensitive to the time variability of the received signal strength in the fading channel and the ambient noise dominated by snapping shrimp in harsh underwater environments, because a broken link in the multi-hop path is enough to disrupt communications and initiate new route searches. In our configuration, we use the Ad hoc On-demand Distance Vector (AODV) routing protocol optimized for UWA networks. Empirical studies show that we can model the channel as a slow-varying frequency non-selective Rayleigh fading channel. We theoretically analyze the throughput of our configuration by considering three salient features: the ability of the receiver to demodulate the data, the effect of our control protocol and the effect of disconnections on the generation of routing packets. The throughput under various operating conditions is then examined. It is observed that at optimal node separation, the throughput is improved by a factor of 10. Copyright © 2007 John Wiley & Sons, Ltd. [source] Effect of N-fertilization, plant genotype and environmental conditions on nifH gene pools in roots of riceENVIRONMENTAL MICROBIOLOGY, Issue 10 2003Zhiyuan Tan Summary Terminal restriction fragment length polymorphism (T-RFLP) analysis of PCR-amplified nitrogenase gene (nifH) fragments is a rapid technique for profiling of diazotrophic microbial communities without the necessity of cultures for study. Here, we examined the impact of N-fertilization, plant genotype and environmental conditions on diazotrophic microbial populations in association with roots of rice (Oryza species) by T-RFLP community profiling and found marked effects on the composition of the microbial community. We found a rapid change of the diazotrophic population structure within 15 days after application of nitrogen fertilizer and a strong effect of environmental conditions and plant genotype. Control experiments revealed that phylogenetically distantly related nifH genes were proportionately amplified, and that signal strength reflected the relative abundance of nifH genes in the sample within a 10-fold range of template concentrations. These results clearly demonstrated that our T-RFLP method was suitable to reflect compositional differences in the diazotrophic community in a semiquantitative manner and that the diazotrophic rhizosphere communities of rice are not static but presumably rather highly dynamic. [source] Comparison of single-nucleotide polymorphisms and microsatellite markers for linkage analysis in the COGA and simulated data sets for Genetic Analysis Workshop 14: Presentation Groups 1, 2, and 3GENETIC EPIDEMIOLOGY, Issue S1 2005Marsha A. Wilcox Abstract The papers in presentation groups 1,3 of Genetic Analysis Workshop 14 (GAW14) compared microsatellite (MS) markers and single-nucleotide polymorphism (SNP) markers for a variety of factors, using multiple methods in both data sets provided to GAW participants. Group 1 focused on data provided from the Collaborative Study on the Genetics of Alcoholism (COGA). Group 2 focused on data simulated for the workshop. Group 3 contained analyses of both data sets. Issues examined included: information content, signal strength, localization of the signal, use of haplotype blocks, population structure, power, type I error, control of type I error, the effect of linkage disequilibrium, and computational challenges. There were several broad resulting observations. 1) Information content was higher for dense SNP marker panels than for MS panels, and dense SNP markers sets appeared to provide slightly higher linkage scores and slightly higher power to detect linkage than MS markers. 2) Dense SNP panels also gave higher type I errors, suggesting that increased test thresholds may be needed to maintain the correct error rate. 3) Dense SNP panels provided better trait localization, but only in the COGA data, in which the MS markers were relatively loosely spaced. 4) The strength of linkage signals did not vary with the density of SNP panels, once the marker density was ,1 SNP/cM. 5) Analyses with SNPs were computationally challenging, and identified areas where improvements in analysis tools will be necessary to make analysis practical for widespread use. Genet. Epidemiol. 29:(Suppl. 1): S7,S28, 2005. © 2005 Wiley-Liss, Inc. [source] DFold: PCR design that minimizes secondary structure and optimizes downstream genotyping applications,HUMAN MUTATION, Issue 1 2004David Fredman Abstract Secondary structures in polymerase chain reaction (PCR) target sequences have a negative impact on amplification success rates and on downstream uses of PCR products. For example, signal strength and allele discrimination in single nucleotide polymorphism (SNP) genotyping methods can be compromised by allele-biased amplification and/or by PCR product folding that limits access of interrogating probes. To increase the fidelity and robustness of PCR, and to aid follow-on applications, we have developed DFold (http://dfold.cgb.ki.se),a generalized software solution that creates PCR oligonucleotide primer designs devoid of stable secondary structures. We demonstrate the effectiveness of the tool by applying it to a range of dynamic allele-specific hybridization (DASH) assay designs, many of which we evaluate in the laboratory. We further consider how the system throughput may be made sufficiently high for use upon millions of target sequences in order to support whole-genome analyses. Hum Mutat 24:1,8, 2004. © 2004 Wiley-Liss, Inc. [source] Timing and tuning of CD27,CD70 interactions: the impact of signal strength in setting the balance between adaptive responses and immunopathologyIMMUNOLOGICAL REVIEWS, Issue 1 2009Martijn A. Nolte Summary:, After binding its natural ligand cluster of differentiation 70 (CD70), CD27, a tumor necrosis factor receptor (TNFR)-associated factor-binding member of the TNFR family, regulates cellular activity in subsets of T, B, and natural killer cells as well as hematopoietic progenitor cells. In normal immune responses, CD27 signaling appears to be limited predominantly by the restricted expression of CD70, which is only transiently expressed by cells of the immune system upon activation. Studies performed in CD27-deficient and CD70-transgenic mice have defined a non-redundant role of this receptor,ligand pair in shaping adaptive T-cell responses. Moreover, adjuvant properties of CD70 have been exploited for the design of anti-cancer vaccines. However, continuous CD27,CD70 interactions may cause immune dysregulation and immunopathology in conditions of chronic immune activation such as during persistent virus infection and autoimmune disease. We conclude that optimal tuning of CD27,CD70 interaction is crucial for the regulation of the cellular immune response. We provide a detailed comparison of costimulation through CD27 with its closely related family members 4-1BB (CD137), CD30, herpes virus entry mediator, OX40 (CD134), and glucocorticoid-induced TNFR family-related gene, and we argue that these receptors do not have a unique function per se but that rather the timing, context, and intensity of these costimulatory signals determine the functional consequence of their activity. [source] Urban mesh and ad hoc mesh networksINTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, Issue 2 2008Anders Nilsson Plymoth Mesh networking is currently gaining much attention, within both academia and industry. Mesh networking allows cheap and fast deployment of wireless services. It is regarded as a very promising solution for urban deployment scenarios as well as for temporary emergency response situations. Another related promising field is that of ad hoc wireless networking, which consists of mobile nodes that dynamically create and maintain a network without the need for any infrastructure. We propose a solution and architecture for urban mesh ad hoc networks, a network that combines mesh networking with ad hoc networks for urban environments. We present four types of ad hoc mesh and ad hoc mesh networks. The most general one consists of mesh nodes, called mesh points (MP), that act as a type of access point for user nodes (UN). The MPs have at least two interfaces: one which is used to communicate with UNs, and one which is used to maintain the mesh access network and transport data. These two interfaces can basically use any type of technology (IEEE 802.11 a/b/g, WiMax, etc.), and for capacity reasons it is generally regarded that the best solution is to let the mesh interface operate on a separate high-capacity channel or channels. An intricate part of these types of networks are routing and location services. In our solution, UN devices operate in ad hoc mode running an ad hoc routing protocol. This allows UNs that wish to communicate to connect directly in an ad hoc manner, or through an MP. An important question is therefore whether two UNs that wish to communicate should connect through the mesh or connect directly. We show that from a capacity point of view whether a UN should route its packets to the closest available MP, or through a ad hoc network, depends on the environment the network is located, the amount traffic and the type of protocols used. Since MPs need to know where to route packets within the mesh, i.e., locating the MP closest to the destination UN, each UN run a small application that registers the UN to the mesh network. In addition to the above features we have developed a new MAC that quickly queries two candidate nodes, which picks the candidate with the currently best radio conditions. This enable nodes to cope with deep dips in signal strength due to fast fading, a well-known problem in urban environments. We show that this new protocol achieves significantly lower delays. We also show that in dense urban environments performance and battery lifetime can be improved if ad hoc technologies are used. Copyright © 2007 John Wiley & Sons, Ltd. [source] Range error detection caused by occlusion in non-coaxial LADARs for scene interpretationJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 10 2005Bingbing Liu When processing laser detection and ranging (LADAR) sensor data for scene interpretation, for example, for the purposes of feature extraction and/or data association in mobile robotics, most previous work models such devices as processing range data which follows a normal distribution. In this paper, it is demonstrated that commonly used LADARs suffer from incorrect range readings at changes in surface reflectivity and/or range discontinuities, which can have a much more detrimental effect on such algorithms than random noise. Most LADARs fall into two categories: coaxial and separated transmitter and receiver configurations. The latter offer the advantage that optical crosstalk is eliminated, since it can be guaranteed that all of the transmitted light leaves the LADAR and is not in any way partially reflected within it due to the beam-splitting techniques necessary in coaxial LADARs. However, they can introduce a significant disparity effect, as the reflected laser energy from the target can be partially occluded from the receiver. As well as demonstrating that false range values can result due to this occlusion effect from scanned LADARs, the main contribution of this paper is that the occurrence of these values can be reliably predicted by monitoring the received signal strength and a quantity we refer to as the "transceiver separation angle" of the rotating mirror. This paper will demonstrate that a correct understanding of such systematic errors is essential for the correct further processing of the data. A useful design criterion for the optical separation of the receiver and transmitter is also derived for noncoaxial LADARs, based on the minimum detectable signal amplitude of a LADAR and environmental edge constraints. By investigating the effects of various sensor and environmental parameters on occlusion, some advice is given on how to make use of noncoaxial LADARs correctly so as to avoid range errors when scanning environmental discontinuities. © 2005 Wiley Periodicals, Inc. [source] Effects of Parasite Attributes and Injected Current Parameters on Electromagnetic Detection of Parasites in Fish MuscleJOURNAL OF FOOD SCIENCE, Issue 9 2002G.S. Choudhury ABSTRACT: We examined the potential of an electromagnetic parasite detection technique to become the basis of an automated commercial system. The effects of parasite orientation and position, presence offish bone, and applied signal strength and frequency on resultant magnetic field strength were determined by scanning a conducting cell containing fish fillet and parasite below a SQUID magnetometer. The parasite orientation affected peak-to-peak voltage of the magnetic dipole. The parasite position with respect to myotome structure seemed to affect the orientation of the dipolar signal. A fish bone was readily detected. The magnetic field strength was independent of the frequency of the injected current and scaled with amplitude=. [source] The correlation between blood oxygenation level-dependent signal strength and latencyJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2005Karsten Müller PhD Abstract Purpose To investigate the relationship between signal strength and latency of the blood oxygenation level-dependent (BOLD) signal. Materials and Methods Several correlation analyses were performed on data obtained in a functional magnetic resonance imaging (fMRI) experiment, where subjects were presented with a simple visual stimulus. The BOLD signal strength was correlated with both the phase shift of the spectral density matrix and time-to-peak calculated from trial-averaged time courses. Correlation coefficients were calculated for visual stimuli of 2, 6, and 15 seconds in duration. Results Analyzing all functional runs for the same subject separately, i.e., including for each run all significantly activated voxels, we observed that correlations between phase shift and signal strength, as well as between time-to-peak and signal strength, decreased with increasing stimulus length. However, when analyses were restricted to voxels found activated in all functional runs, we observed similar correlations between BOLD signal strength and latency in all runs, independent of the length of stimulation. This result was again obtained for both latency measures: the spectral density phase shift and time-to-peak. Conclusion For both latency measures, phase shift and time-to-peak, a high correlation between BOLD signal strength and latency was observed. We have shown that this correlation is independent of the length of visual stimulation. Thus, the correlation between BOLD signal strength and latency seems to be an inherent property of the BOLD response that is independent of the length of stimulation and can be observed using different methods for determining signal latency. J. Magn. Reson. Imaging 2005;21:489,494. © 2005 Wiley-Liss, Inc. [source] Linkage Analysis of Alcohol Dependence Symptoms in the CommunityALCOHOLISM, Issue 1 2010Narelle K. Hansell Background:, We have previously identified suggestive linkage for alcohol consumption in a community-based sample of Australian adults. In this companion paper, we explore the strength of genetic linkage signals for alcohol dependence symptoms. Methods:, An alcohol dependence symptom score, based on DSM-IIIR and DSM-IV criteria, was examined. Twins and their nontwin siblings (1,654 males, 2,518 females), aged 21 to 81 years, were interviewed, with 803 individuals interviewed on 2 occasions, approximately 10 years apart. Linkage analyses were conducted on datasets compiled to maximize data collected at either the younger or the older age. In addition, linkage was compared between full samples and truncated samples that excluded the lightest drinkers (approximately 10% of the sample). Results:, Suggestive peaks on chromosome 5p (LODs >2.2) were found in a region previously identified in alcohol linkage studies using clinical populations. Linkage signal strength was found to vary between full and truncated samples and when samples differed only on the collection age for a sample subset. Conclusions:, The results support the finding that large community samples can be informative in the study of alcohol-related traits. [source] Protein secondary structure from deep-UV resonance Raman spectroscopy,JOURNAL OF RAMAN SPECTROSCOPY, Issue 1-3 2006Cheng-Yen Huang Abstract Raman spectra of proteins that are obtained with deep ultraviolet excitation contain resonance-enhanced amide bands of the polypeptide backbone, as well as aromatic side chain bands. The amide bands are sensitive to conformation, and can be used to estimate the backbone secondary structure. UV Raman spectra are reported at 206.5 and 197 nm, for a set of 12 proteins with varied secondary structure content, and are used to establish quantitative signatures of secondary structure via least-squares fitting. Amide band enhancement is greater at 197 nm, where basis spectra are established for ,-turn, as well as ,-helix, ,-sheet and unordered structures; the lower signal strength at 206.5 nm does not provide a reliable spectrum for the first of these. Application of these basis spectra is illustrated for the melting of apo-myoglobin. The amide band positions and cross sections are discussed. Copyright © 2006 John Wiley & Sons, Ltd. [source] MRI of the lungs using hyperpolarized noble gasesMAGNETIC RESONANCE IN MEDICINE, Issue 6 2002Harald E. Möller Abstract The nuclear spin polarization of the noble gas isotopes 3He and 129Xe can be increased using optical pumping methods by four to five orders of magnitude. This extraordinary gain in polarization translates directly into a gain in signal strength for MRI. The new technology of hyperpolarized (HP) gas MRI holds enormous potential for enhancing sensitivity and contrast in pulmonary imaging. This review outlines the physics underlying the optical pumping process, imaging strategies coping with the nonequilibrium polarization, and effects of the alveolar microstructure on relaxation and diffusion of the noble gases. It presents recent progress in HP gas MRI and applications ranging from MR microscopy of airspaces to imaging pulmonary function in patients and suggests potential directions for future developments. Magn Reson Med 47:1029,1051, 2002. © 2002 Wiley-Liss, Inc. [source] Physical Properties of Conventional Explosives Deduced from Radio Frequency EmissionsPROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 6 2009Jeremiah Harlin Abstract Los Alamos National Laboratory collected broadband radio frequency (RF) electric field change measurements from multiple detonations of high explosives (HE). Three types of HE were used: small cylinders of flake TNT, solid TNT, and PBX-9501. Low frequency signals (<80,MHz) were shot-to-shot repeatable and occurred within the first 100,,s at measured amplitudes of about 2,V m,1 at 35, m distance. High frequency signals (>290,MHz) occurred later, were an order of magnitude lower in signal strength, and were not repeatable. There is a positive correlation between the maximum electric field change and the shock velocity of the HE. The amount of free charge produced in the explosion estimated from the first RF pulse is between 10 and 150,,C. This implies a weakly ionized plasma with temperatures between 2600 and 2900,K. [source] Liposome-Encapsulated Hemoglobin Alleviates Brain Edema After Permanent Occlusion of the Middle Cerebral Artery in RatsARTIFICIAL ORGANS, Issue 2 2009Akira T. Kawaguchi Abstract Liposome-encapsulated hemoglobin (LEH) was proven to be protective in cerebral ischemia/reperfusion injury. The present study evaluated LEH in a rat model of permanent middle cerebral artery (MCA) occlusion to clarify its effect during ischemia and reperfusion. Five minutes after thread occlusion of the MCA, rats were infused with 10 mL/kg of LEH (LEH, n = 13), and compared with normal controls (n = 11). Additional animals received the same MCA occlusion with no treatment (CT, n = 11), saline (saline, n = 10), empty liposome solution (EL, n = 13), or washed red blood cells (RBC, n = 7). Severity of brain edema was determined 24 h later by signal strength in T2-weighted magnetic resonance imaging of the cortex, striatum, hippocampus, and pyriform lobe. The results showed that brain edema/infarction observed in any vehicle-infused control was significantly more severe than in LEH-treated rats. There was a tendency toward aggravated edema in rats receiving ELs. LEH infusion at a dose of 10 mL/kg significantly reduced edema formation as compared to other treatments in a wide area of the brain 24 h after permanent occlusion of the MCA. Low oncotic pressure of EL and LEH solution (vehicle solution) appeared to cause nonsignificant aggravation of edema and reduced protective effects of LEH. [source] The Department of External Affairs, the ABC & Reporting of the Indonesian Crisis 1965,1969AUSTRALIAN JOURNAL OF POLITICS AND HISTORY, Issue 1 2003Karim Najjarine The Department of External Affairs took a keen interest in the manner in which Radio Australia reported events in Indonesia throughout the 1950s and 1960s. Radio Australia's high signal strength gave it a massive listening audience in the region. The attempted coup in Indonesia of 1965, its immediate aftermath, and the protracted power struggle that followed, triggered a period of cooperation and conflict between the Department and the Australian Broadcasting Commission over Radio Australia's reporting of events in Indonesia. During this time the Department received and acted upon advice from the Australian ambassador to Indonesia, Keith Shann, and, via Shann, received advice from the Indonesian Army on how it wanted the situation in Indonesia reported. This period is characterised by the Department's efforts to take over Radio Australia, and by cooperation between major western powers to coordinate information policy towards Indonesia. The Department also attempted to influence reporting of events in Indonesia by the Australian press and succeeded in convincing newspaper editors to report and editorialise in a manner sensitive to the Department's concerns. [source] Characterizing perceptual learning with external noiseCOGNITIVE SCIENCE - A MULTIDISCIPLINARY JOURNAL, Issue 2 2004Jason M. Gold Abstract Performance in perceptual tasks often improves with practice. This effect is known as ,perceptual learning,' and it has been the source of a great deal of interest and debate over the course of the last century. Here, we consider the effects of perceptual learning within the context of signal detection theory. According to signal detection theory, the improvements that take place with perceptual learning can be due to increases in internal signal strength or decreases in internal noise. We used a combination of psychophysical techniques (external noise masking and double-pass response consistency) that involve corrupting stimuli with externally added noise to discriminate between the effects of changes in signal and noise as observers learned to identify sets of unfamiliar visual patterns. Although practice reduced thresholds by as much as a factor of 14, internal noise remained virtually fixed throughout training, indicating learning served to predominantly increase the strength of the internal signal. We further examined the specific nature of the changes that took place in signal strength by correlating the externally added noise with observer's decisions across trials (response classification). This technique allowed us to visualize some of the changes that took place in the linear templates used by the observers as learning occurred, as well as test the predictions of a linear template-matching model. Taken together, the results of our experiments offer important new theoretical constraints on models of perceptual learning. [source] Seal bond characterization of laminated plastic food cups by scanning electron and optic microscopesPACKAGING TECHNOLOGY AND SCIENCE, Issue 4 2004Zehra Ayhan Abstract Heat seals of laminated semi-rigid food cups were evaluated to characterize the seal bond. Laminated lidding material was sealed at temperatures of 160,180°C to thermoformed cups. Various seal regions of the cups with different ultrasonic signal strengths (%) were sectioned at the rim and examined using optical and scanning electron microscopes (SEM). Ultrasonic signals were able to pinpoint seal defects; however, the magnitude of the signals did not relate to the actual seal condition or seal quality affected by the sealing process. This was attributed to the very short seal width and non-parallel surface of the heat seal, which possibly resulted in signal loss by reflection and scattering from the seal surface. C-scan of ultrasound, SEM and optical microscopic images provided the information that the heat-sealing process was unstable, due to insufficient and non-uniform heat-seal temperature or pressure, misalignment of the sealing jaws or non-parallel sealing or cutting unit configuration. Copyright © 2004 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||