79717 research outputs found
Sort by
ip_base.xls
No full textThe impact of recent severe droughts throughout the United States, the potential for climate change to intensify the frequency and severity of drought, and discussion about the future of government assistance in agriculture highlight the need for a transition from drought as ‘disaster’ to drought as ‘managed risk’. However, guidance for agricultural producers about optimal drought preparedness and response is insufficient. It is particularly unclear what optimal drought preparedness and response should look like, in practice, for farm systems with uncertain water supplies and intra- and inter-year dynamics. A mathematical programming model that captures the stochastic and dynamic aspects of an irrigated row crop farm is developed and used to explore the nature of optimal drought preparedness and response. Results indicate several important characteristics. First, drought has the potential to generate heterogeneous impacts, even across a set of homogeneous farms. Second, a farm system with inter-year dynamics can continue to experience the effects of drought after the drought itself subsides; additionally, the effects of drought in one year can intensify the impact of drought in subsequent years. Third, in the presence of discount and interest rates, crop diversification does not maximize expected profit, even though it is often considered a drought management tool. Fourth, the primary effect of water supply uncertainty is the abandonment of more fall-prepared fields. Hence, the multi-peril crop insurance program’s prevented planting provision is identified as an optimal drought preparedness tool, even if unsubsidized. Finally, the predicted effects of climate change for snowmelt-dependent farm systems require distinctly different forms of adaptation, and cause profit losses of different magnitudes. Because the model captures both intra- and inter-year dynamics, it provides 1) a more thorough understanding of the complex tradeoffs that producers face when preparing for and responding to drought, 2) a more complete picture of the dynamic impacts of drought, and 3) important insights about the administration of drought assistance programs. Lastly, it elucidates the meaning of optimal drought preparedness; a notion that has received increased attention in the policy arena, but whose practical form has been only vaguely alluded to
Jakes_Mary_Clare_1979_Plate17.jpg
No full textSurface and subsurface data are combined to determine the structure of the western half of the Simi fault system in the Las Posas and Camarillo Hills area. Cretaceous to Eocene sedimentary rocks, present only in the subsurface, are overlain by late Eocene to early Miocene nonmarine stata (Sespe Formation) and middle Miocene volcanics and sedimentary rocks (Conejo Volcanics and Topanga Formation undifferentiated), in part exposed in the Las Posas Hills. Late Miocene marine beds (Modelo Formation) are present in the subsurface in the Camarillo Hills and may crop out in the eastern Santa Rosa Valley. These rocks are overlain unconformably by marine Pliocene-Pleistocene beds (Saugus Formation), older and younger Quaternary alluvium, and alluvial fan deposits. Normal faults cause the Sespe to subside towards a thick volcanic pile, built up in the Conejo Hills in the middle Miocene. Volcanic rocks buttressed against and later overtopped these Sespe subsidence structures. Reverse faults in the Oxnard plain and the left-lateral Somis fault are truncated by the unconformity at the base of the Saugus. Miocene and older strata were broadly folded in the Las Posas anti-cline and Santa Rosa syncline prior to deposition of the Saugus Formation and displacement on the Simi fault zone. The Bailey fault, a northwest-trending range-front fault, shows reverse separation, commonly follows Sespe subsidence structures and north-dipping normal faults which cut the Sespe. The Camarillo Hills anticline, Springville dome and post-Saugus Las Posas anticline appear to be pressure ridges adjacent to the Simi fault system on the north. Older alluvium deposits are uplifted and warped. The Camarillo fault cut and warped older alluvium.Surface and subsurface data are combined to determine the structure of the western half of the Simi fault system in the Las Posas and Camarillo Hills area. Cretaceous to Eocene sedimentary rock
Western Cooperative Spray Project : 1965
Get PDFThis report includes information concerning experimental use of unregistered pesticides or unregistered uses of pesticides. Experimental results should not be interpreted as recommendations for use. Use of unregistered materials or use of any registered pesticides inconsistent with its label is against both Federal Law and State Law
Annual Report Projects : 1969
No full textThis report includes information concerning experimental use of unregistered pesticides or unregistered uses of pesticides. Experimental results should not be interpreted as recommendations for use. Use of unregistered materials or use of any registered pesticides inconsistent with its label is against both Federal Law and State Law
Effects of Silviculture and Genetics on Branch/Knot Attributes of Coastal Pacific Northwest Douglas-Fir and Implications for Wood Quality—A Synthesis
Get PDFDouglas-fir is the most commercially important timber species in the US Pacific Northwest due to its ecological prevalence and its superior wood attributes, especially strength and stiffness properties that make it highly prized for structural applications. Its economic significance has led to extensive establishment and management of plantations over the last few decades. Cultural treatments and genetic improvement designed to increase production of utilizable wood volume also impact tree morphology and wood properties. Many of these impacts are mediated by crown development, particularly the amount and distribution of foliage and size and geometry of branches. Natural selection for branch architecture that optimizes reproductive fitness may not necessarily be optimal for stem volume growth rate or for wood properties controlling the quality of manufactured solid wood products. Furthermore, Douglas-fir does not self-prune within the rotation lengths currently practiced. This paper synthesizes extensive Douglas-fir research in the Pacific Northwest addressing: (1) the effects of silviculture and genetics on branch structure and associated consequences for wood quality and the product value chain; and (2) methods to measure, monitor, modify, and model branch attributes to assist managers in selecting appropriate silvicultural techniques to achieve wood quality objectives and improve the value of their Douglas-fir resource.Keywords: Genetics, Wood quality, Branch, Douglas-fir, Silvicultur
Holocene slip rate along the Gyaring Co Fault, central Tibet
Get PDFAlthough geodetic measurements of interseismic deformation in interior Tibet suggest slow strain accumulation, active slip along the right-lateral Gyaring Co Fault is suggested to be between 8 and 21 mm/yr. Reliable geologic constraints on the slip rate along this fault are sparse. Here we document 12 ± 2 m of right-lateral displacement of lacustrine shorelines across the Gyaring Co Fault. Optically stimulated luminescence ages of the shorelines are tightly clustered between 4.1 and 4.4 ka. These data require an average slip rate of 2.2–3.2 mm/yr along the central Gyaring Co Fault during the latter half of the Holocene. Consideration of seismic cycle effects allows the possibility of slightly higher average slip rates, up to 2.2–4.5 mm/yr. Overall, our results suggest that the slip rate along the Gyaring Co Fault is similar to other strike-slip faults in interior Tibet, supporting the notion that active deformation in this region is distributed among numerous, slowly moving faults.Keywords: Active faulting, Slip rate, Gyaring Co, Lacustrine shoreline
The Relationships among Wind, Horizontal Pressure Gradient, and Turbulent Momentum Transport during CASES-99
Get PDFRelationships among the horizontal pressure gradient, the Coriolis force, and the vertical momentum transport by turbulent fluxes are investigated using data collected from the 1999 Cooperative Atmosphere-Surface Exchange Study (CASES-99). Wind toward higher pressure (WTHP) adjacent to the ground occurred about 50% of the time. For wind speed at 5 m above the ground stronger than 5 m s(-1), WTHP occurred about 20% of the time. Focusing on these moderate to strong wind cases only, relationships among horizontal pressure gradients, Coriolis force, and vertical turbulent transport in the momentum balance are investigated. The magnitude of the downward turbulent momentum flux consistently increases with height under moderate to strong winds, which results in the vertical convergence of the momentum flux and thus provides a momentum source and allows WTHP.In the along-wind direction, the horizontal pressure gradient is observed to be well correlated with the quadratic wind speed, which is demonstrated to be an approximate balance between the horizontal pressure gradient and the vertical convergence of the turbulent momentum flux. That is, antitriptic balance occurs in the along-wind direction when the wind is toward higher pressure. In the crosswind direction, the pressure gradient varies approximately linearly with wind speed and opposes the Coriolis force, suggesting the importance of the Coriolis force and approximate geotriptic balance of the airflow. A simple one-dimensional planetary boundary layer eddy diffusivity model demonstrates the possibility of wind directed toward higher pressure for a baroclinic boundary layer and the contribution of the vertical turbulent momentum flux to this phenomenon.Keywords: Baroclinic flows, Turbulence, Pressure, Ekman pumping, Boundary layer, transport, Barotropic flow
Escaping the Surface: The Effect of Capture Depth on Submergence Success of Surface-Released Pacific Rockfish
Get PDFWe evaluated the effect of capture depth and fish size on the ability of several Pacific rockfishes Sebastes spp. to resubmerge after hook-and-line capture and surface release. We observed fish as they were released into a bottomless floating enclosure, and we recorded submergence success within a 5-min time limit. Submergence success was greater than 80% for all rockfish captured in depths less than 30 m. Yellowtail rockfish S. flavidus (N = 51) were 100% successful at submerging in less than 49 s at all depths sampled (10–51 m). At capture depths of 40–51 m, submergence success was 89% for quillback rockfish S. maliger (N = 9), 65% for black rockfish S. melanops (N = 46), and 30% for canary rockfish S. pinniger (N = 40). At depths of 30–51 m, submergence success was 32% for blue rockfish S. mystinus (N = 31). The external signs of barotrauma (e.g., exopthalmia, eversion of the esophagus) increased with depth of capture and were least prevalent in yellowtail rockfish and quillback rockfish. The presence of severe esophageal eversion (beyond the buccal cavity) was strongly negatively associated with submergence success for several species (P < 0.01). At 40–51-m capture depths, the frequency of severe esophageal eversion by species was correlated with the
frequency of submergence failure (P < 0.05). Logistic regression showed a negative relationship between depth of capture and submergence success for black rockfish (P < 0.001), blue rockfish (P < 0.001), and canary rockfish (P < 0.05). Larger body length negatively influenced submergence success only in blue rockfish (P < 0.05).Keywords: barotrauma, submergence, capture dept
Modeling the detection range of fish by echolocating bottlenose dolphins and harbor porpoises
Get PDFThe target strength as a function of aspect angle were measured for four species of fish using dolphin-like and porpoise-like echolocation signals. The polar diagram of target strength values measured from an energy flux density perspective showed considerably less fluctuation with azimuth than would a pure tone pulse. Using detection range data obtained from dolphin and porpoise echolocation experiments, the detection ranges for the Atlantic cod by echolocating dolphins and porpoises were calculated for three aspect angles of the cod. Maximum detection ranges occurred when the fish was broadside to the odontocete and minimum detection ranges occurred when the cod was in the tail aspect. Maximum and minimum detection ranges for the bottlenose dolphin in a noise-limited environment was calculated to be 93 and 70 m, respectively. In a quiet environment, maximum and minimum detection ranges for the bottlenose dolphin were calculated to be 173 and 107 m, respectively. The detection ranges for the harbor porpoise in a quiet environment were calculated to be between 15 and 27 m. The primary reason for the large differences in detection ranges between both species was attributed to the 36 dB higher source level of the bottlenose dolphin echolocation signals.Keywords: bioacoustics, mechanoception, acoustic signal detection, biocommunication
Multidecadal variability of atmospheric methane, 1000–1800 C.E.
Get PDFWe present a new high-precision, high-resolution record of atmospheric methane from the West Antarctic Ice Sheet (WAIS) Divide ice core covering 1000–1800 C.E., a time period known as the late preindustrial Holocene (LPIH). The results are consistent with previous measurements from the Law Dome ice core, the only other high-resolution record of methane for this time period, and confirm most of the observed variability. Multidecadal variability in methane concentrations throughout the LPIH is weakly correlated or uncorrelated with reconstructions of temperature and precipitation from a variety of geographic regions. Correlations with temperature are dominated by changes in Northern Hemisphere high latitude temperatures between 1400 and 1600 C.E. during the onset of the Little Ice Age. Times of war and plague when large population losses could have reduced anthropogenic emissions are coincident with short periods of decreasing global methane concentrations.Keywords: biogeochemistry, ice core, methane, trace ga