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Dispersal and coexistence of two non-native crayfish species (Pacifastacus leniusculus and Procambarus clarkii ) in NE Portugal over a 10-year period

Bernardo, J.M.; Costa, A.M.; Bruxelas, S.; Teixeira, Amílcar
Fonte: EDP Sciences Publicador: EDP Sciences
Tipo: Artigo de Revista Científica
Português
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55.63%
NE Portugal is one of the most isolated and low populated regions of Western Europe. Recently, two American crayfish species reached this area: signal crayfish Pacifastacus leniusculus coming from Spain and red swamp crayfish Procambarus clarkii in its northward expansion. The dispersion of both species was followed throughout the last decade in river Maçãs (Douro catchment). Our results support the hypothesis of faster downstream colonisation. The mean spread rate of signal crayfish was faster for the downstream expansion, 2.8 km·yr-1, while the upstream rate was 1.7 km·yr-1. Exceptionally, in one period, the rate of spread reached 6.7 km·yr-1, which was apparently caused by downstream washing in extreme conditions of flow. The mean rate of spread is higher than the observed in other studies which may also be related to the low current velocity of late spring and summer that provides favourable conditions for a fast upstream colonisation. Coexistence of signal and red swamp crayfish was detected in a large river sector. Signal crayfish strongly dominates in the upper and intermediate sectors which are the colder part of the river and in the lower sectors, species abundances are not significantly different. Winter temperature in the higher altitude reaches seems to moderate the competitive abilities of P. clarkii.

Simulação da disseminação da doença de newcastle relacionando o trânsito de veículos entre empresas integradoras e unidades de produção de frangos de corte; Simulation of spread of the newcastle disease relating the traffic of vehicles between companies and poultry farms

Giotto, Diana Bertani
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Dissertação Formato: application/pdf
Português
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Este trabalho teve como objetivo geral avaliar os fatores de risco de disseminação da Doença de Newcastle relacionados ao trânsito de veículos entre empresas integradoras e unidades de produção de frangos de corte. Uma área de grande produção avícola do estado do Rio Grande do Sul foi escolhida para ser objeto de estudo da presente pesquisa, sendo simuladas a partir de uma granja índex, as zonas de proteção e vigilância, como determina o Plano de Contingência para a Influenza Aviária e Doença de Newcastle. A metodologia foi fundamentada em análises espaciais e probabilísticas, associadas a situações reais que fazem parte do processo de logística das empresas. Foi realizada a análise espacial da região, através de técnicas de geoprocessamento, a extração da taxa reprodutiva básica, estudo exploratório da proporção de alojamento de frangos de corte e desenvolvimento do modelo epidêmico clássico de Reed-Frost, avaliando assim, as possibilidades de disseminação da doença na área de estudo. Os resultados obtidos demonstraram que somente o trânsito referente a visitas técnicas e caminhões de ração nas unidades de produção são fatores que podem desencadear um surto da doença. Quanto mais rápido for obtido o diagnóstico definitivo e tomadas medidas de contenção...

Dispersal and coexistence of two non-native crayfish species (Pacifastacus leniusculus and Procambarus clarkii ) in NE Portugal over a 10-year period

Bernardo, João Manuel; Costa, Ana Manuel; Bruxelas, Sofia; Teixeira, Amílcar
Fonte: Knowledge and Management of Aquatic Ecosystems Publicador: Knowledge and Management of Aquatic Ecosystems
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
65.63%
NE Portugal is one of the most isolated and low populated regions of Western Europe. Recently, two American crayfish species reached this area: signal crayfish Pacifastacus leniusculus coming from Spain and red swamp crayfish Procambarus clarkii in its northward expansion. The dispersion of both species was followed throughout the last decade in river Maçãs (Douro catchment). Our results support the hypothesis of faster downstream colonisation. The mean spread rate of signal crayfish was faster for the downstream expansion, 2.8 km·yr−1, while the upstream rate was 1.7 km·yr−1. Exceptionally, in one period, the rate of spread reached 6.7 km·yr−1, which was apparently caused by downstream washing in extreme conditions of flow. The mean rate of spread is higher than the observed in other studies which may also be related to the low current velocity of late spring and summer that provides favourable conditions for a fast upstream colonisation. Coexistence of signal and red swamp crayfish was detected in a large river sector. Signal crayfish strongly dominates in the upper and intermediate sectors which are the colder part of the river and in the lower sectors, species abundances are not significantly different. Winter temperature in the higher altitude reaches seems to moderate the competitive abilities of P. clarkii.

Cytoplasmically Inherited Reproductive Incompatibility in Tribolium Flour Beetles: The Rate of Spread and Effect on Population Size

Stevens, L.; Wade, M. J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/1990 Português
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65.64%
This paper reports on the effects of a cytoplasmically inherited reproductive incompatibility in different genetic strains of the flour beetle, Tribolium confusum. We measured the rate of spread and the effect of host population size using different initial frequencies of infection with a cytoplasmic factor that mediates reproductive incompatibility. There were two experiments, in one the infected and uninfected lines were from the same genetic strain, b-Yugoslavia. In the other, the infected line was from the ``high cannibalism' bIV strain and the uninfected line from the ``low cannibalism' bI strain. We estimate that the fitness ratio of infected to uninfected in b-Yugoslavia is 0.63 and the observed rate of spread for this strain corresponds to a model of cytoplasmic inheritance that takes into account the productivity differences between the infected and cured lines. In the bI-bIV experiment, because the uninfected and infected lines are from different genetic strains, we cannot partition the effects of the cytoplasmic factor from other factors. The rate of spread in the bI-bIV experiment is faster in males and slower in females than predicted from a model of cytoplasmic inheritance. In both experiments, productivity varies with initial infection frequency; however...

Early-phase transmission of Yersinia pestis by unblocked fleas as a mechanism explaining rapidly spreading plague epizootics

Eisen, Rebecca J.; Bearden, Scott W.; Wilder, Aryn P.; Montenieri, John A.; Antolin, Michael F.; Gage, Kenneth L.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
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Plague is a highly virulent disease believed to have killed millions during three historic human pandemics. Worldwide, it remains a threat to humans and is a potential agent of bioterrorism. Dissemination of Yersinia pestis, the etiological agent of plague, by blocked fleas has been the accepted paradigm for flea-borne transmission. However, this mechanism, which requires a lengthy extrinsic incubation period before a short infectious window often followed by death of the flea, cannot sufficiently explain the rapid rate of spread that typifies plague epidemics and epizootics. Inconsistencies between the expected rate of spread by blocked rat fleas and that observed during the Black Death has even caused speculation that plague was not the cause of this medieval pandemic. We used the primary vector to humans in North America, Oropsylla montana, which rarely becomes blocked, as a model for studying alternative flea-borne transmission mechanisms. Our data revealed that, in contrast to the classical blocked flea model, O. montana is immediately infectious, transmits efficiently for at least 4 d postinfection (early phase) and may remain infectious for a long time because the fleas do not suffer block-induced mortality. These factors match the criteria required to drive plague epizootics as defined by recently published mathematical models. The scenario of efficient early-phase transmission by unblocked fleas described in our study calls for a paradigm shift in concepts of how Y. pestis is transmitted during rapidly spreading epizootics and epidemics...

Unequal Evolutionary Rates in the Human Immunodeficiency Virus Type 1 (HIV-1) Pandemic: the Evolutionary Rate of HIV-1 Slows Down When the Epidemic Rate Increases▿

Berry, Irina Maljkovic; Ribeiro, Ruy; Kothari, Moulik; Athreya, Gayathri; Daniels, Marcus; Lee, Ha Youn; Bruno, William; Leitner, Thomas
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Português
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HIV-1 sequences in intravenous drug user (IDU) networks are highly homogenous even after several years, while this is not observed in most sexual epidemics. To address this disparity, we examined the human immunodeficiency virus type 1 (HIV-1) evolutionary rate on the population level for IDU and heterosexual transmissions. All available HIV-1 env V3 sequences from IDU outbreaks and heterosexual epidemics with known sampling dates were collected from the Los Alamos HIV sequence database. Evolutionary rates were calculated using phylogenetic trees with a t test root optimization of dated samples. The evolutionary rate of HIV-1 subtype A1 was found to be 8.4 times lower in fast spread among IDUs in the former Soviet Union (FSU) than in slow spread among heterosexual individuals in Africa. Mixed epidemics (IDU and heterosexual) showed intermediate evolutionary rates, indicating a combination of fast- and slow-spread patterns. Hence, if transmissions occur repeatedly during the initial stage of host infection, before selective pressures of the immune system have much impact, the rate of HIV-1 evolution on the population level will decrease. Conversely, in slow spread, where HIV-1 evolves under the pressure of the immune system before a donor infects a recipient...

On the use of contour maps in the analysis of spread of communicable disease*

Splaine, Michael; Lintott, Alan P.; Angulo, Juan J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1974 Português
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55.59%
The co-ordinates of the dwellings where cases of variola minor (alastrim) occurred during a small epidemic were used in a worked example of contour mapping of disease spread. The contoured variable was the date of onset, relative to an arbitrary base date, of the case introducing the disease into each of twenty-two households. Three contour maps prepared with slightly different computer programmes or dates exhibited similar concentric loops whose centres were close to the first infected household. The average rate of spread of the disease was estimated by regression of the number of days to onset of the first case in the household on the average distance from an arbitrary origin to the relevant contour line. The calculated average rate of spread was 1·22 metres per day. An additional map was contoured using the cumulative number of cases as the contoured variable, relative to the onset of the example epidemic.

High Rate of Recent Transposable Element–Induced Adaptation in Drosophila melanogaster

González, Josefa; Lenkov, Kapa; Lipatov, Mikhail; Macpherson, J. Michael; Petrov, Dmitri A
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Português
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Although transposable elements (TEs) are known to be potent sources of mutation, their contribution to the generation of recent adaptive changes has never been systematically assessed. In this work, we conduct a genome-wide screen for adaptive TE insertions in Drosophila melanogaster that have taken place during or after the spread of this species out of Africa. We determine population frequencies of 902 of the 1,572 TEs in Release 3 of the D. melanogaster genome and identify a set of 13 putatively adaptive TEs. These 13 TEs increased in population frequency sharply after the spread out of Africa. We argue that many of these TEs are in fact adaptive by demonstrating that the regions flanking five of these TEs display signatures of partial selective sweeps. Furthermore, we show that eight out of the 13 putatively adaptive elements show population frequency heterogeneity consistent with these elements playing a role in adaptation to temperate climates. We conclude that TEs have contributed considerably to recent adaptive evolution (one TE-induced adaptation every 200–1,250 y). The majority of these adaptive insertions are likely to be involved in regulatory changes. Our results also suggest that TE-induced adaptations arise more often from standing variants than from new mutations. Such a high rate of TE-induced adaptation is inconsistent with the number of fixed TEs in the D. melanogaster genome...

Monitoring the spread of myxoma virus in rabbit Oryctolagus cuniculus populations on the southern tablelands of New South Wales, Australia. III. Release, persistence and rate of spread of an identifiable strain of myxoma virus.

Merchant, J. C.; Kerr, P. J.; Simms, N. G.; Hood, G. M.; Pech, R. P.; Robinson, A. J.
Fonte: Cambridge University Press Publicador: Cambridge University Press
Tipo: Artigo de Revista Científica
Publicado em /02/2003 Português
Relevância na Pesquisa
55.57%
An identifiable strain of myxoma virus was introduced into four local populations of wild rabbits Oryctolagus cuniculus on the southern tablelands of New South Wales (NSW) and its spread in the presence of other field strains was monitored for 6 months. The main vector in this region was considered to be the European rabbit flea Spilopsyllis cuniculi. Each population of rabbits was of a high density and living in groups of warrens covering areas from 59 to 87 hectares. Rabbits occupying centrally located warrens were inoculated with the virus in late September or early October (spring) and the subsequent appearance of myxomatosis across the sites monitored by trapping, shooting and visual observations. Samples, taken from rabbits with myxomatosis, were examined by polymerase chain reaction (PCR) that allowed identification of the introduced strain. On all four sites the introduced virus spread from the inoculated rabbits in the centrally located warrens to rabbits in surrounding warrens. On Sites 1 and 3, this spread continued across the entire site persisting for at least 118 and 174 days respectively. On Sites 2 and 4, the virus was detected for 78 and 62 days respectively and the subsequent inability to detect the introduced virus correlated with the appearance of an unrelated field strain. Using three different methods of calculation...

Modelling the Evolution and Spread of HIV Immune Escape Mutants

Fryer, Helen R.; Frater, John; Duda, Anna; Roberts, Mick G.; ; Phillips, Rodney E.; McLean, Angela R.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Português
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55.51%
During infection with human immunodeficiency virus (HIV), immune pressure from cytotoxic T-lymphocytes (CTLs) selects for viral mutants that confer escape from CTL recognition. These escape variants can be transmitted between individuals where, depending upon their cost to viral fitness and the CTL responses made by the recipient, they may revert. The rates of within-host evolution and their concordant impact upon the rate of spread of escape mutants at the population level are uncertain. Here we present a mathematical model of within-host evolution of escape mutants, transmission of these variants between hosts and subsequent reversion in new hosts. The model is an extension of the well-known SI model of disease transmission and includes three further parameters that describe host immunogenetic heterogeneity and rates of within host viral evolution. We use the model to explain why some escape mutants appear to have stable prevalence whilst others are spreading through the population. Further, we use it to compare diverse datasets on CTL escape, highlighting where different sources agree or disagree on within-host evolutionary rates. The several dozen CTL epitopes we survey from HIV-1 gag, RT and nef reveal a relatively sedate rate of evolution with average rates of escape measured in years and reversion in decades. For many epitopes in HIV...

Linking Climate Suitability, Spread Rates and Host-Impact When Estimating the Potential Costs of Invasive Pests

Kriticos, Darren J.; Leriche, Agathe; Palmer, David J.; Cook, David C.; Brockerhoff, Eckehard G.; Stephens, Andréa E. A.; Watt, Michael S.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 06/02/2013 Português
Relevância na Pesquisa
55.53%
Biosecurity agencies need robust bioeconomic tools to help inform policy and allocate scarce management resources. They need to estimate the potential for each invasive alien species (IAS) to create negative impacts, so that relative and absolute comparisons can be made. Using pine processionary moth (Thaumetopoea pityocampa sensu lato) as an example, these needs were met by combining species niche modelling, dispersal modelling, host impact and economic modelling. Within its native range (the Mediterranean Basin and adjacent areas), T. pityocampa causes significant defoliation of pines and serious urticating injuries to humans. Such severe impacts overseas have fuelled concerns about its potential impacts, should it be introduced to New Zealand. A stochastic bioeconomic model was used to estimate the impact of PPM invasion in terms of pine production value lost due to a hypothetical invasion of New Zealand by T. pityocampa. The bioeconomic model combines a semi-mechanistic niche model to develop a climate-related damage function, a climate-related forest growth model, and a stochastic spread model to estimate the present value (PV) of an invasion. Simulated invasions indicate that Thaumetopoea pityocampa could reduce New Zealand’s merchantable and total pine stem volume production by 30%...

Spatial Assortment of Mixed Propagules Explains the Acceleration of Range Expansion

Ramanantoanina, Andriamihaja; Ouhinou, Aziz; Hui, Cang
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 08/08/2014 Português
Relevância na Pesquisa
55.7%
Range expansion of spreading organisms has been found to follow three types: (i) linear expansion with a constant rate of spread; (ii) bi-phase expansion with a faster linear expansion following a slower linear expansion; and (iii) accelerating expansion with a continuously increasing rate of spread. To date, no overarching formula exists that can be applied to all three types of range expansion. We investigated how propagule pressure, i.e., the initial number of individuals and their composition in terms of dispersal ability, affects the spread of a population. A system of integrodifference equations was then used to model the spatiotemporal dynamics of the population. We studied the dynamics of dispersal ability as well as the instantaneous and asymptotic rate of spread. We found that individuals with different dispersal abilities were spatially sorted with the stronger dispersers situated at the expanding range front, causing the velocity of expansion to accelerate. The instantaneous rate of spread was found to be fully determined by the growth and dispersal abilities of the population at the advancing edge of the invasion. We derived a formula for the asymptotic rate of spread under different scenarios of propagule pressure. The results suggest that data collected from the core of the invasion may underestimate the spreading rate of the population. Aside from better managing of invasive species...

Acceleration of evolutionary spread by long-range dispersal

Hallatschek, Oskar; Fisher, Daniel S.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
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Pathogens, invasive species, rumors, or innovations spread much more quickly around the world nowadays than in previous centuries. The speedup is caused by more frequent long-range dispersal, for example via air traffic. These jumps are crucial because they can generate satellite “outbreaks” at many distant locations, thus rapidly increasing the total rate of spread. We present a simple intuitive argument that captures the resulting spreading patterns. We show that even rare long-range jumps can transform the spread of simple epidemics from wave-like to a very fast type of “metastatic” growth. More generally, our approach can be used to describe how new evolutionary variants spread and thus improves our predictive understanding of the speed of Darwinian adaptation.

Rate of Spread of Citrus Blight Reduced When Sharpshooter Leafhoppers (Homoptera: Cicadellidae) Are Controlled

Adlerz, W. C.; Bistline, F. W.; Russo, L. W.; Hopkins, D. L.
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica Formato: text/html
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Insect traps were used to monitor populations of sharpshooter leafhopper vectors, Oncometopia nigricans (Walker) and Homalodisca coagulate (Say), of Xylella fastidiosa Wells et al., a xylem-limited bacterium, in four 11-ha plots of ‘Valencia’ oranges, Citrus sinensis (L.) Osb., and four 6-ha plots of ‘Pineapple’ oranges in a grove infected with citrus blight. When trap catches indicated that leafhopper populations were increasing, supplemental applications of insecticides were applied to half of the plots. One to three extra applications of insecticides per year were made to maintain significant differences in leafhopper populations between the routine care plots and the supplemental insecticide plots. Linear regression equations, with percentage citrus blight as a function of time in months, were fitted to the data for the supplemental insecticide and routine care plots. In the ‘Valencia’ plots, the slope of the regression line for the routine care plot was significantly greater than the slope for the supplemental insecticide plots; therefore, the rate of spread of blight was reduced significantly where supplemental insecticide applications were made. In ‘Pineapple’ plots, the trend was similar but the difference in slope was not statistically significant.

A low complexity representation of the coherent point spread function in the presence of aberrations and arbitrarily large defocus

Bagheri, Saeed, Ph. D. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 75, [1] leaves; 1980561 bytes; 1983654 bytes; application/pdf; application/pdf
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In this thesis we introduce a new method for analyzing the diffraction integral for evaluating the point spread function. The new method is based on the use of higher order Airy functions along with Zernike and Taylor expansions. Our approach is applicable when we are considering a finite, arbitrary number of aberrations and arbitrary large defocus simultaneously. We present an upper bound for the complexity and the convergence rate of this method. We also compare the cost and accuracy of this method to traditional ones and show the efficiency of our method through these comparisons. In particular, we rigorously show that this method is constructed in a way that the complexity of the analysis (i.e the number of terms needed for expressing the light disturbance) does not increase as either of defocus or resolution of interest increases. This has applications in several fields such as biological microscopy, lithography and multi-domain optimization in optical systems.; by Saeed Bagheri.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.; Includes bibliographical references (leaves 75-[76]).

Optimizing wettability of externally wetted microfabricated silicon electrospray thrusters

Garza, Tanya Cruz
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 70 leaves
Português
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55.53%
Electrospray propulsion devices with externally wetted architectures have shown favorable performance. The design of microfabricated silicon thrusters and their feed systems requires an understanding of propellant flow over a silicon surface. This research explores the parameters that affect wettability of externally wetted microfabricated silicon electrospray thruster arrays and how varied wetting surface treatments affect thruster performance. Silicon samples with various black silicon treatments were fabricated and optimal black silicon etch parameters were determined by measuring the samples wettability. Silicon wettability was analyzed by producing samples with various black silicon treatments and then measuring contact angle, measuring surface roughness, imaging surface geometry, calculating spreading rates, and performing treated thruster current output tests. Two propellants, 1-ethyl-3-methyl-imidazolium tetraflouroborate (EMI-BF4) and 1-ethyl-3-methyl-imidazolium bis(triflouromethyl-sulfonyl)amide (EMI-IM), were used in contact angle measurements and spreading rate experiments. A model describing the spread of a small drop of EMI-BF4 and EMI-IM over roughened silicon substrates is presented.; (cont.) Models which describe the spread of small...

Spread-spectrum technique in sigma-delta modulators

Moule, Eric C. (1980 - ); Ignjatovic, Zeljko
Fonte: University of Rochester Publicador: University of Rochester
Tipo: Tese de Doutorado Formato: Number of Pages:xix, 172 leaves
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Thesis (Ph. D.)--University of Rochester. Dept. of Electrical and Computer Engineering, 2008.; The application of spread-spectrum techniques to sigma-delta (ΣΔ) modulators as a method to reduce the effects of integrated circuit nonidealities is investigated in this work. The research primarily focuses on reducing the effects of DC offset, flicker noise, nonlinear amplifier DC gain, DAC and power supply noise, and substrate noise. The proposed design may prove beneficial in Power-over-Ethernet (IEEE 802.3) or other AC powered applications and vibration power-scavenging applications where the power supply and substrate noise may still exhibit strong spectral tones affecting the modulator’s performance. In addition, the insensitivity of the proposed design to process variations and circuit nonidealities such as low frequency noise and DC offset makes it suitable for high-resolution ADC applications in more advanced CMOS technologies. A step-by-step design methodology for transforming a conventional ΣΔ modulator into a spread-spectrum ΣΔ modulator is described. To illustrate this process, the design of a third-order 1-bit spread-spectrum ΣΔ modulator is shown in detail. Additionally, the requirements for a particular spread-spectrum sequence are described with respect to the expected noise performance of the ΣΔ modulator.
An experimental prototype third-order 1-bit fully-differential spread-spectrum ΣΔ modulator is implemented using the TSMC 2-poly/4-metal 0.35μm CMOS process. The spread-spectrum sequence utilized for the measurements is a second-order blue noise sequence that was synthesized on an Altera FPGA. The prototype is clocked at 200kHz and digitizes a 500Hz bandwidth signal with 94dB of dynamic range. Additionally...

A duck hepatitis B virus strain with a knockout mutation in the putative X ORF shows similar infectivity and in vivo growth characteristics to wild-type virus

Meier, P.; Scougall, C.; Will, H.; Burrell, C.; Jilbert, A.
Fonte: Academic Press Inc Publicador: Academic Press Inc
Tipo: Artigo de Revista Científica
Publicado em //2003 Português
Relevância na Pesquisa
65.51%
Hepadnaviruses including human hepatitis B virus (HBV) and duck hepatitis B virus (DHBV) express X proteins, HBx and DHBx, respectively. Both HBx and DHBx are transcriptional activators and modulate cellular signaling in in vitro assays. To test whether the DHBx protein plays a role in virus infection, we compared the in vivo infectivity and growth characteristics of a DHBV3 strain with a stop codon in the X-like ORF (DHBV3-X-K.O.) to those of the wild-type DHBV3 strain. Here we report that the two strains showed no significant difference in (i) their ability to induce infection that resulted in stable viraemia measured by serum surface antigen (DHBsAg) and DHBV DNA, and detection of viral proteins and replicative DNA intermediates in the liver; (ii) the rate of spread of infection in liver and extrahepatic sites after low-dose virus inoculation; and (iii) the ability to produce transient or persistent infection under balanced age/dose conditions designed to detect small differences between the strains. Thus, none of the infection parameters assayed were detectably affected by the X-ORF knockout mutation, raising the question whether DHBx expression plays a physiological role during in vivo infection with wild-type DHBV.; http://www.elsevier.com/wps/find/journaldescription.cws_home/622952/description#description; Copyright © 2003 Elsevier Inc

Tapering Talk : The Impact of Expectations of Reduced Federal Reserve Security Purchases on Emerging Markets

Eichengreen, Barry; Gupta, Poonam
Fonte: World Bank, Washington, DC Publicador: World Bank, Washington, DC
Tipo: Publications & Research :: Policy Research Working Paper; Publications & Research
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In May 2013, Federal Reserve officials first began to talk of the possibility of tapering their security purchases. This tapering talk had a sharp negative impact on emerging markets. Different countries, however, were affected very differently. This paper uses data on exchange rates, foreign reserves and equity prices between April and August 2013 to analyze who was hit and why. It finds that emerging markets that allowed the real exchange rate to appreciate and the current account deficit to widen during the prior period of quantitative easing saw the sharpest impact. Better fundamentals (the budget deficit, the public debt, the level of reserves, or the rate of economic growth) did not provide insulation. A more important determinant of the differential impact was the size of the country's financial market: countries with larger markets experienced more pressure on the exchange rate, foreign reserves, and equity prices. This is interpreted as showing that investors are better able to rebalance their portfolios when the target country has a relatively large and liquid financial market.

Shrubland fire behaviour modelling with microplot data

Fernandes, Paulo; Catchpole, Wendy; Rego, Francisco
Fonte: Universidade de Trás-os-Montes e Alto Douro Publicador: Universidade de Trás-os-Montes e Alto Douro
Tipo: Artigo de Revista Científica
Português
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Fire behaviour modelling has been based primarily on experiments involving the measurement of a certain number of fires, where each variable is represented by an average value per fire. The main objective of this study was to examine if data collected from a microplot sampling design could be used to derive meaningful fire behaviour models. Three burns were conducted in low shrubland of Erica umbellata Loefl. and Chamaespartium tridentatum (L.)P. Gibbs in NE Portugal. Wind speed and aerial dead fuel moisture content varied from 5 to 27 km hr-1 and 14 to 21% respectively. Rate of spread and flame length ranged from 0.3 to 14.1 m min-1 and 0.2 to 3.1 m respectively. Rate of fire spread could be described effectively in terms of an empirical model with wind speed and fuel height as independent variables. The coefficients that describe the effects of wind speed and fuel height on fire propagation were consistent with published values for similar fuel types. Flame length was strongly related to Byram's fireline intensity. Microplot sampling is not free from methodological problems - which are discussed - but can be effectively used in field studies of fire behaviour.