417 research outputs found
Measuring the Impact of the Environmental Quality Incentives Program (EQIP) on Irrigation Efficiency and Water Conservation
Since the passage of the 1996 Farm Act, the Environmental Quality Incentives Program (EQIP) has provided over $10 billion in technology adoption subsidies. One of the national conservation priorities in EQIP is water conservation, but it is not known how participation in EQIP by irrigators affects water application rates and decisions to expand or reduce a farmâs irrigated acreage. Using a farm-level panel data set drawn from three national samples of irrigators taken in 1998, 2003, and 2008, this study provides the first national scale econometric estimates of the changes in water application rates and irrigated acreage that result when a farm receives EQIP payments. Due to a five-fold increase in EQIP funding following the 2002 farm bill, the change in EQIP participation between 2008 and earlier years is largely the result of an exogenous policy shock. A difference-in-differences estimator that exploits this change in EQIP funding and also controls for unobserved farm-specific variables, suggests that for the average farm participating in EQIP between 2004 and 2008, the EQIP payments may have reduced water application rates but also may have increased total water use and led to an expansion in irrigated acreage. However, since EQIP participation is voluntary, there may still be a need to correct for bias due to sample selection. A nearest neighbor matching estimator finds no evidence of any statistically significant effect of EQIP participation on technology adoption rates, water use, water application rates or acreages, which suggests that there is a high degree of self-selection into the program.EQIP, irrigation efficiency, water conservation, difference-in-differences, matching estimator, Environmental Economics and Policy,
Q-based design equations for resonant metamaterials and experimental validation
Practical design parameters of resonant metamaterials, such as loss tangent,
are derived in terms of the quality factor of the resonant effective medium
permeability or permittivity. Through electromagnetic simulations of loop-based
resonant particles, it is also shown that the of the effective medium
response is essentially equal to the of an individual resonant particle.
Thus, by measuring the of a single fabricated metamaterial particle, the
effective permeability or permittivity of a metamaterial can be calculated
simply and accurately without requiring complex simulations, fabrication, or
measurements. Experimental validation shows that the complex permeability
analytically estimated from the measured of a single fabricated
self-resonant loop agrees with the complex permeability extracted from
parameter measurements of a metamaterial slab to better than 20%. This
equivalence reduces the design of a metamaterial to meet a given loss
constraint to the simpler problem of the design of a resonant particle to meet
a specific constraint. This analysis also yields simple analytical
expressions for estimating the loss tangent of a planar loop magnetic
metamaterial due to ohmic losses. It is shown that
is a strong lower bound for magnetic loss tangents for frequencies not too far
from 1 GHz. The ohmic loss of the metamaterial varies inversely with the
electrical size of the metamaterial particle, indicating that there is a loss
penalty for reducing the particle size at a fixed frequency
Measurement Invariance, Entropy, and Probability
We show that the natural scaling of measurement for a particular problem
defines the most likely probability distribution of observations taken from
that measurement scale. Our approach extends the method of maximum entropy to
use measurement scale as a type of information constraint. We argue that a very
common measurement scale is linear at small magnitudes grading into logarithmic
at large magnitudes, leading to observations that often follow Student's
probability distribution which has a Gaussian shape for small fluctuations from
the mean and a power law shape for large fluctuations from the mean. An inverse
scaling often arises in which measures naturally grade from logarithmic to
linear as one moves from small to large magnitudes, leading to observations
that often follow a gamma probability distribution. A gamma distribution has a
power law shape for small magnitudes and an exponential shape for large
magnitudes. The two measurement scales are natural inverses connected by the
Laplace integral transform. This inversion connects the two major scaling
patterns commonly found in nature. We also show that superstatistics is a
special case of an integral transform, and thus can be understood as a
particular way in which to change the scale of measurement. Incorporating
information about measurement scale into maximum entropy provides a general
approach to the relations between measurement, information and probability
V-ATPase expression during development of Artemia franciscana embryos: Potential role for proton gradients in anoxia signaling
Under anoxia, Artemia franciscana embryos downregulate metabolic processes and approach an ametabolic state. Entrance into this quiescent state is accompanied by a profound acidification of the intracellular space, and more than two decades of research now clearly demonstrates that this acidification is critical to metabolic downregulation in anoxic embryos. However, the proximal mechanisms responsible for the pH shift remain largely unidentified. Here, we report evidence demonstrating expression of the V-ATPase in encysted embryos and present an argument for its involvement in the intracellular acidification induced by anoxia. We identified a single B-subunit cDNA sharing the greatest degree of sequence similarity with \u27generalist-type\u27 homologues from mammals (brain-type) and invertebrates. Quantitative analysis of B-subunit mRNA demonstrates differential expression throughout early development, and western blot analyses confirm the expression of at least six V-ATPase subunits in both heavy membranes and microsomal vesicles. The critical need for proton pumping during the anoxia-tolerant stage of development is demonstrated by incubation with the V-ATPase inhibitor bafilomycin A1, which halts embryonic development. Importantly, net proton flux from V-ATPase-acidified compartments to the surrounding cytoplasm is likely under anoxia and may significantly contribute to the enigmatic acidification critical to quiescence
Cryopreservation of lipid bilayers by LEA proteins from Artemia franciscana and trehalose
© 2016 Elsevier Inc. The capacity of Late Embryogenesis Abundant (LEA) proteins and trehalose to protect liposomes against freezing-induced damage was examined by measuring the leakage of 5(6)-carboxyfluorescein (CF). Liposomes were prepared to simulate the lipid compositions of the inner leaflet of the plasma membrane, outer mitochondrial membrane (OMM), and inner mitochondrial membrane (IMM). Two recombinant LEA proteins belonging to Group 3 (AfrLEA2 and AfrLEA3m) were expressed and purified from embryos of Artemia franciscana. Only OMM-like liposomes were significantly protected by AfrLEA2 and AfrLEA3m against freeze-thaw damage; at the highest protein:lipid mass ratio tested, leakage of CF was 56.3% of control with AfrLEA3m and 29.3% with AfrLEA2. By comparison, trehalose provided protection to all compositional types. The greatest stabilization during freezing occurred when trehalose was present on both sides of the bilayer. When mitochondria isolated from rat liver were freeze-thawed in trehalose solution, the OMM remained intact based on the absence of increased oxygen consumption when cytochrome c was added during oxidative phosphorylation (OXPHOS). Respiratory control ratios (OXPHOS/LEAK) were depressed by only 30% after freeze-thawing in trehalose compared to non-frozen controls, which indicated some retention of OXPHOS capacity by the IMM. Trehalose then was loaded into the matrix (0.24 Όmol/mg mitochondrial protein) by transient opening of the permeability transition pore, a procedure optimized for retention of OMM integrity. Surprisingly, respiratory control ratios were not improved after freeze-thawing with external plus matrix trehalose, when compared to external trehalose alone. This result could perhaps be explained by insufficient accumulation of matrix trehalose
Dessication Stress
The threat of desiccation for organisms inhabiting the intertidal zone occurs during emersion at low tides or when organisms are positioned in the high intertidal zone, where wetting occurs primarily by spring tides, storm waves, and spray. Drying due to evaporative water loss is the most common mechanism for dehydration, although during winter in northern temperate regions freezing can also occur, which reduces the liquid water in extracellular fluids and can lead to intracellular dehydration in multicellular organisms. Freezing tolerance has been reported and characterized for a number of intertidal invertebrates, including gastropods such as an air-breathing snail and a periwinkle, and bivalve genera including the common and ribbed mussels
Energizing an invertebrate embryo: Bafilomycin-dependent respiration and the metabolic cost of proton pumping by the V-ATPase
We examine herein the contribution of V-ATPase activity to the energy budget of aerobically developing embryos of Artemia franciscana and discuss the results in the context of quiescence under anoxia. 31P-NMR analysis indicates that intracellular pH and NTP levels are unaffected by acute incubation of dechorionated embryos with the V-ATPase inhibitor, bafilomycin A1. Bafilomycin A1 also has no significant effect on oxygen consumption by isolated mitochondria. Taken together, these data indicate that bafilomycin does not affect energy-producing pathways in the developing embryo. However, the V-ATPase inhibitor exhibits a concentration-dependent inhibition of oxygen consumption in aerobic embryos. A conservative analysis of respirometric data indicates that proton pumping by the V-ATPase, and processes immediately dependent on this activity, constitutes approximately 31% of the aerobic energy budget of the preemergent embryo. Given the complete absence of detectable Na+K+-ATPase activity during the first hours of aerobic development, it is plausible that the V-ATPase is performing a role in both the acidification of intracellular compartments and the energization of plasma membranes. Importantly, the high metabolic cost associated with maintaining these diverse proton gradients requires that V-ATPase activity be downregulated under anoxia in order to attain the almost complete metabolic depression observed in the quiescent embryo. © 2007 by The University of Chicago. All rights reserved
Mitochondrial mRNA stability and polyadenylation during anoxia-induced quiescence in the brine shrimp Artemia franciscana
Polyadenylation of messenger RNA is known to be an important mechanism for regulating mRNA stability in a variety of systems, including bacteria, chloroplasts and plant mitochondria. By comparison, little is known about the role played by polyadenylation in animal mitochondrial gene expression. We have used embryos of the brine shrimp Artemia franciscana to test hypotheses regarding message stability and polyadenylation under conditions simulating anoxia-induced quiescence. In response to anoxia, these embryos undergo a profound and acute metabolic downregulation, characterized by a steep drop in intracellular pH (pHi) and ATP levels. Using dot blots of total mitochondrial RNA, we show that during in organello incubations both O 2 deprivation and acidic pH (pH 6.4) elicit increases in half-lives of selected mitochondrial transcripts on the order of five- to tenfold or more, relative to normoxic controls at pH 7.8. Polyadenylation of these transcripts was measured under the same incubation conditions using a reverse transcriptase-polymerase chain reaction (RT-PCR)-based assay. The results demonstrate that low pH and anoxia promote significant deadenylation of the stabilized transcripts in several cases, measured either as change over time in the amount of polyadenylation within a given size class of poly(A)+ tail, or as the total amount of polyadenylation at the endpoint of the incubation. This study is the first direct demonstration that for a metazoan mitochondrion, polyadenylation is associated with destabilized mRNA. This pattern has also been demonstrated in bacteria, chloroplasts and plant mitochondria and may indicate a conserved mechanism for regulating message half-life that differs from the paradigm for eukaryotic cytoplasm, where increased mRNA stability is associated with polyadenylation
Acute depression of mitochondrial protein synthesis during anoxia: Contributions of oxygen sensing, matrix acidification, and redox state
Mitochondrial protein synthesis is acutely depressed during anoxia-induced quiescence in embryos of Artemia franciscana. Oxygen deprivation is accompanied in vivo by a dramatic drop in extramitochondrial pH, and both of these alterations strongly inhibit protein synthesis in isolated mitochondria. Here we show that the oxygen dependence is not explained simply by blockage of the electron transport chain or by the increased redox state. Whereas oxygen deprivation substantially depressed protein synthesis within 5 min and resulted in a 77% reduction after 1 h, aerobic incubations with saturating concentrations of cyanide or antimycin A had little effect during the first 20 min and only a modest effect after 1 h (36 and 20% reductions, respectively). Yet the mitochondrial NAD(P)H pools were fully reduced after 2-3 min with all three treatments. This cyanide- and antimycin-insensitive but hypoxia-sensitive pattern of protein synthesis depression suggests the presence of a molecular oxygen sensor within the mitochondrion. Second, we show for the first time that acidification of extramitochondrial pH exerts inhibition on protein synthesis specifically through changes in matrix pH. Matrix pH was 8.2 during protein synthesis assays performed at the extramitochondrial pH optimum of 7.5. When this proton gradient was abolished with nigericin, the extramitochondrial pH optimum for protein synthesis displayed an alkaline shift of âŒ0.7 pH unit. These data suggest the presence of proton-sensitive translational components within the mitochondrion
Metabolic depression is delayed and mitochondrial impairment averted during prolonged anoxia in the ghost shrimp, Lepidophthalmus louisianensis (Schmitt, 1935)
Lepidophthalmus louisianensis burrows deeply into oxygen-limited estuarine sediments and is subjected to extended anoxia at low tides. Large specimens (\u3e 2 g) have a lethal time for 50% mortality (LT50) of 64 h under anoxia at 25 °C. Small specimens (\u3c 1 g) have a significantly higher LT50 of 113 h, which is the longest ever reported for a crustacean. Whole body lactate levels rise dramatically under anoxia and exceed 120 Όmol g.f.w.- 1 by 72 h. ATP, ADP, and AMP do not change during 48 h of anoxia, but arginine phosphate declines by over 50%. Thus arginine phosphate may help stabilize the ATP pool. Surprisingly, when compared to the aerobic resting rate, ATP production under anoxia declines only moderately during the first 12 h, and drops to only about 30% between 12 and 48 h. Finally, after 48 h of anoxia, a major metabolic depression to less than 5% occurs. Downregulation of metabolism is delayed in L. louisianensis compared to many invertebrates that exhibit facultative anaerobiosis. Bioenergetic constraints as a result of eventual metabolic depression lead to ionic disturbances like calcium overload and compromised membrane potential of mitochondria. Because these phenomena trigger apoptosis in mammalian species, we evaluated the susceptibility of ghost shrimp mitochondria to opening of the mitochondrial permeability transition pore (MPTP) and associated damage. Energized mitochondria isolated from hepatopancreas possess a pronounced capacity for calcium uptake. Exogenous calcium does not stimulate opening of the MPTP, which potentially could reduce cell death during prolonged anoxia. © 2009 Elsevier B.V. All rights reserved
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