772 research outputs found
Baseband signal combiner for large aperture antenna array
The invention provides a means whereby the baseband output signals of all but one of the receivers associated with each of the antennas are summed and used as a correlation reference for the baseband signal not contained in the summed signal, thereby providing a plurality of correlation or alignment loops, each having an output signal related to the phase difference between its input baseband signal and the summed signal. The invention further provides a means for subtracting an output or error signal generated in one of the correlation loops whose baseband signal has a predetermined phase delay from all the other alignment loops, thereby avoiding interaction and reflection effects in the signal combiner. A variable phase delay means for each of the other baseband signals is controlled by its corresponding correlation loop
Phase-locked loop with sideband rejecting properties Patent
Phase locked loop with sideband rejecting properties in continuous wave tracking rada
Possible wave formation and martensitic transformation of iron particles in copper single crystals during argon ion bombardment
Temperature Changes in the United States
Temperature is among the most important climatic elements used in decision-making. For example, builders and insurers use temperature data for planning and risk management while energy companies and regulators use temperature data to predict demand and set utility rates. Temperature is also a key indicator of climate change: recent increases are apparent over the land, ocean, and troposphere, and substantial changes are expected for this century. This chapter summarizes the major observed and projected changes in near-surface air temperature over the United States, emphasizing new data sets and model projections since the Third National Climate Assessment (NCA3). Changes are depicted using a spectrum of observations, including surface weather stations, moored ocean buoys, polar-orbiting satellites, and temperature-sensitive proxies. Projections are based on global models and downscaled products from CMIP5 (Coupled Model Intercomparison Project Phase 5) using a suite of Representative Concentration Pathways (RCPs; see Ch. 4: Projections for more on RCPs and future scenarios)
Agricultura tropical e aquecimento global: impactos e opçÔes de mitigação
O uso intensivo da terra invariavelmente causa efeitos negativos ao ambiente e produção agrĂcola se prĂĄticas conservativas nĂŁo forem adotadas. Redução na quantidade de matĂ©ria orgĂąnica do solo significa emissĂŁo de gases (principalmente CO2, CH4, N2O) para a atmosfera e aumento do aquecimento global. A sustentabilidade do solo Ă© tambĂ©m afetada, uma vez que a qualidade da matĂ©ria orgĂąnica remanescente muda. AlteraçÔes podem ser verificadas, por exemplo, pela desagregação do solo e mudança na sua estrutura. As consequĂȘncias sĂŁo erosĂŁo, redução na disponibilidade de nutrientes para as plantas e baixa capacidade de retenção de ĂĄgua no solo. Estes e outros fatores refletem negativamente na produtivade das culturas e sustentabilidade do sistema solo-planta-atmosfera. Ao contrĂĄrio, a adoção de boas prĂĄticas de manejo, tal como o sistema plantio direto, pode parcialmente reverter o processo, uma vez que objetiva o aumento das entradas de material orgĂąnico no solo e/ou diminuição das taxas de decomposição da matĂ©ria orgĂąnica do solo.The intensive land use invariably has several negative effects on the environment and crop production if conservative practices are not adopted. Reduction in soil organic matter (SOM) quantity means gas emission (mainly CO2, CH4, N2O) to the atmosphere and increased global warming. Soil sustainability is also affected, since remaining SOM quality changes. Alterations can be verified, for example, by soil desegregation and changes in structure. The consequences are erosion, reduction in nutrient availability for the plants and lower water retention capacity. These and other factors reflect negatively on crop productivity and sustainability of the soil-plant-atmosphere system. Conversely, adoption of "best management practices", such as conservation tillage, can partly reverse the process - they are aimed at increasing the input of organic matter to the soil and/or decreasing the rates at which soil organic matter decomposes
Face-centred cubic to body-centred cubic martensitic transformation of Fe-Co particles in a copper matrix
Climatic versus biotic constraints on carbon and water fluxes in seasonally drought-affected ponderosa pine ecosystems
We investigated the relative importance of climatic versus biotic controls on gross primary production (GPP) and water vapor fluxes in seasonally drought-affected ponderosa pine forests. The study was conducted in young (YS), mature (MS), and old stands (OS) over 4 years at the AmeriFlux Metolius sites. Model simulations showed that interannual variation of GPP did not follow the same trends as precipitation, and effects of climatic variation were smallest at the OS (50%), and intermediate at the YS (<20%). In the young, developing stand, interannual variation in leaf area has larger effects on fluxes than climate, although leaf area is a function of climate in that climate can interact with age-related shifts in carbon allocation and affect whole-tree hydraulic conductance. Older forests, with well-established root systems, appear to be better buffered from effects of seasonal drought and interannual climatic variation. Interannual variation of net ecosystem exchange (NEE) was also lowest at the OS, where NEE is controlled more by interannual variation of ecosystem respiration, 70% of which is from soil, than by the variation of GPP, whereas variation in GPP is the primary reason for interannual changes in NEE at the YS and MS. Across spatially heterogeneous landscapes with high frequency of younger stands resulting from natural and anthropogenic disturbances, interannual climatic variation and change in leaf area are likely to result in large interannual variation in GPP and NEE
Local climate determines vulnerability to camouflage mismatch in snowshoe hares
AimPhenological mismatches, when lifeâevents become mistimed with optimal environmental conditions, have become increasingly common under climate change. Populationâlevel susceptibility to mismatches depends on how phenology and phenotypic plasticity vary across a speciesâ distributional range. Here, we quantify the environmental drivers of colour moult phenology, phenotypic plasticity, and the extent of phenological mismatch in seasonal camouflage to assess vulnerability to mismatch in a common North American mammal.LocationNorth America.Time period2010â2017.Major taxa studiedSnowshoe hare (Lepus americanus).MethodsWe used >Â 5,500 byâcatch photographs of snowshoe hares from 448 remote camera trap sites at three independent study areas. To quantify moult phenology and phenotypic plasticity, we used multinomial logistic regression models that incorporated geospatial and highâresolution climate data. We estimated occurrence of camouflage mismatch between haresâ coat colour and the presence and absence of snow over 7Â years of monitoring.ResultsSpatial and temporal variation in moult phenology depended on local climate conditions more so than on latitude. First, hares in colder, snowier areas moulted earlier in the fall and later in the spring. Next, hares exhibited phenotypic plasticity in moult phenology in response to annual variation in temperature and snow duration, especially in the spring. Finally, the occurrence of camouflage mismatch varied in space and time; white hares on dark, snowless background occurred primarily during lowâsnow years in regions characterized by shallow, shortâlasting snowpack.Main conclusionsLongâterm climate and annual variation in snow and temperature determine coat colour moult phenology in snowshoe hares. In most areas, climate change leads to shorter snow seasons, but the occurrence of camouflage mismatch varies across the speciesâ range. Our results underscore the populationâspecific susceptibility to climate changeâinduced stressors and the necessity to understand this variation to prioritize the populations most vulnerable under global environmental change.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154444/1/geb13049.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154444/2/geb13049_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154444/3/geb13049-sup-0001-Supinfo.pd
Dose-Additive Carcinogenicity of a Defined Mixture of âDioxin-like Compoundsâ
Use of the dioxin toxic equivalency factor (TEF) approach in human risk assessments assumes that the combined effects of dioxin-like compounds in a mixture can be predicted based on a potency-adjusted dose-additive combination of constituents of the mixture. In this study, we evaluated the TEF approach in experimental 2-year rodent cancer bioassays with female Harlan Sprague-Dawley rats receiving 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 3,3âČ,4,4âČ,5-pentachlorobiphenyl (PCB-126), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF), or a mixture of the three compounds. Statistically based doseâresponse modeling indicated that the shape of the doseâresponse curves for hepatic, lung, and oral mucosal neoplasms was the same in studies of the three individual chemicals and the mixture. In addition, the dose response for the mixture could be predicted from a combination of the potency-adjusted doses of the individual compounds. Finally, we showed that use of the current World Health Organization dioxin TEF values adequately predicted the increased incidence of liver tumors (hepatocellular adenoma and cholangiocarcinoma) induced by exposure to the mixture. These data support the use of the TEF approach for dioxin cancer risk assessments
Our Globally Changing Climate
Since the Third U.S. National Climate Assessment (NCA3) was published in May 2014, new observations along multiple lines of evidence have strengthened the conclusion that Earth's climate is changing at a pace and in a pattern not explainable by natural influences. While this report focuses especially on observed and projected future changes for the United States, it is important to understand those changes in the global context (this chapter). The world has warmed over the last 150 years, especially over the last six decades, and that warming has triggered many other changes to Earth's climate. Evidence for a changing climate abounds, from the top of the atmosphere to the depths of the oceans. Thousands of studies conducted by tens of thousands of scientists around the world have documented changes in surface, atmospheric, and oceanic temperatures; melting glaciers; disappearing snow cover; shrinking sea ice; rising sea level; and an increase in atmospheric water vapor. Rainfall patterns and storms are changing, and the occurrence of droughts is shifting
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