Economic Analysis of Supplemental Deductible Coverage as Recommended in the USDA's 2007 Farm Bill Proposal

A primary change to crop insurance contained in the USDA's Farm Bill Proposal is Supplemental Deductible Coverage (SDC). SDC would allow farmers who purchase individual crop insurance coverage to purchase GRP in the amount of the individual policy deductible. GRP indemnities would be accelerated compared with the current GRP policy. Analysis indicates that SDC provides substantial benefits in terms of certainty equivalent gains. The largest benefits are realized by low risk farmers, compared to others in the county, and farmers whose yields are highly correlated with the county yield. Optimal individual policy coverage levels generally decrease when SDC is taken.

Thermodynamic properties of Mg_2SiO_4 liquid at ultra-high pressures from shock measurements to 200 GPa on forsterite and wadsleyite

Polycrystalline samples of Mg_2SiO_4 forsterite and wadsleyite were synthesized and then dynamically loaded to pressures of 39–200 GPa. Differences in initial density and internal energy between these two phases lead to distinct Hugoniots, each characterized by multiple phase regimes. Transformation to the high-pressure phase assemblage MgO + MgSiO_3 perovksite is complete by 100 GPa for forsterite starting material but incomplete for wadsleyite. The datum for wadsleyite shocked to 136 GPa, however, is consistent with the assemblage MgO + MgSiO_3 post-perovksite. Marked increases in density along the Hugoniots of both phases between ∼130 and 150 GPa are inconsistent with any known solid-solid phase transformation in the Mg_2SiO_4 system but can be explained by melting. Density increases upon melting are consistent with a similar density increase observed in the MgSiO_3 system. This implies that melts with compositions over the entire Mg/Si range likely for the mantle would be negatively or neutrally buoyant at conditions close to the core-mantle boundary, supporting the partial melt hypothesis to explain the occurrence of ultra-low velocity zones at the base of the mantle. From the energetic difference between the high-pressure segments of the two Hugoniots, we estimate a Grüneisen parameter (γ) of 2.6 ± 0.35 for Mg_2SiO_4-liquid between 150 and 200 GPa. Comparison to low-pressure data and fitting of the absolute pressures along the melt Hugoniots both require that γ for the melt increases with increasing density. Similar behavior was recently predicted in MgSiO_3 liquid via molecular dynamics simulations. This result changes estimates of the temperature profile, and hence the dynamics, of a deep terrestrial magma ocean

Polymorphism, superheating, and amorphization of silica upon shock wave loading and release

We present a detailed and quantitative examination of the thermodynamics and phase change mechanisms (including amorphization) that occur upon shock wave loading and unloading of silica. We apply Debye-Grüneisen theory to calculate both the Hugoniot of quartz and isentropic release paths. Quartz converts to stishovite (or a stishovite-like phase) between 15 and 46 GPa, and persistence of the solid phase above its liquidus (i.e., superheating) is confirmed between 77 and 110 GPa. Calculations compare favorably to measurements of shock and post-shock temperatures. For silica, the method of measuring post-shock temperature is insensitive to predicting whether phase transitions actually occur during release. Measurements of release states in pressure-particle velocity space are compared to computed frozen-phase release paths. This comparison suggests transformation of a stishovite-like phase to lower density phases including quartz, liquid, or dense amorphous glass. Transformations to liquid or glass occur upon release from peak pressure of 26 GPa and above. The isentropic release assumption appears to be approximately valid. A shock pressure-temperature scale relating metamorphism of silica in shock-loaded quartz is proposed. Neither recovery of coesite nor substantial quantities of crystalline stishovite-like phases upon shock loading of quartz is predicted. Trace amounts of crystalline stishovite-like phases from shock loading between 15 and 26 GPa are expected

Shock-compressed MgSiO_3 glass, enstatite, olivine, and quartz: Optical emission, temperatures, and melting

Optical emission of MgSiO_3 glass, enstatite, olivine, and quartz under shock wave compression was investigated with optical pyrometry at discrete wavelengths ranging from visible to near infrared. We develop a new analysis of optical emission that does not require a gray body assumption. Instead, at each wavelength, the optical linear absorption coefficients (α) and blackbody spectral radiances (L_(λb)) of shocked and unshocked materials were obtained by nonlinear fitting to the time-resolved radiance from the target assembly. The absorption spectra of unshocked samples corresponding to the measured values of α reproduce those from independent static optical spectroscopic measurements. The measured values of α (ranging from 7 to 56 mm^(−1)) for shocked samples indicate that shock-induced high-pressure phases (including melt) can be regarded essentially as black bodies in the optical range investigated, although starting phases such as enstatite and olivine have band-like spectra at ambient conditions. The effect of emission from the air gap at the driver sample interface on the recorded radiance can be resolved, but α and L_(λb) cannot be separated for this component of the signal. The shock velocity-particle velocity relationships of these silicates derived from radiance history are in accord with previous investigations using independent techniques. Given the limited amount of shock wave data, possible high-pressure melting curves of Mg-perovskite and its assemblage with periclase are deduced; their melting temperatures near the core-mantle boundary (CMB) being 6000 ± 500 K and 4000 ± 300 K, respectively. It is proposed that Mg-perovskite melts with density increase at the CMB pressure

Shock-induced melting of MgSiO_3 perovskite and implications for melts in Earth's lowermost mantle

New shock wave equation of state (EOS) data for enstatite and MgSiO_3 glass constrain the density change upon melting of Mg-silicate perovskite up to 200 GPa. The melt becomes denser than perovskite near the base of Earth's lower mantle. This inference is confirmed by shock temperature data suggesting a negative pressure-temperature slope along the melting curve at high pressure. Although melting of Earth's mantle involves multiple phases and chemical components, this implies that the partial melts invoked to explain anomalous seismic velocities in the lowermost mantle may be dynamically stable

Primordial Black Holes, Hawking Radiation and the Early Universe

The 511 keV gamma emission from the galactic core may originate from a high concentration ($\sim 10^{22}$) of primordial black holes (PBHs) in the core each of whose Hawking radiation includes $\sim 10^{21}$ positrons per second. The PBHs we consider are taken as near the lightest with longevity greater than the age of the universe (mass $\sim 10^{12}$ kg; Schwarzschild radius $\sim 1$ fm). These PBHs contribute only a small fraction of cold dark matter, $\Omega_{PBH} \sim 10^{-8}$. This speculative hypothesis, if confirmed implies the simultaneous discovery of Hawking radiation and an early universe phase transition.Comment: 4 Page

Direct shock wave loading of Stishovite to 235 GPa: Implications for perovskite stability relative to an oxide assemblage at lower mantle conditions

Pure stishovite and coesite samples with zero porosity and dimensions appropriate for planar shock wave experiments have been synthesized with multi-anvil high-pressure techniques. The equation of state of stishovite is obtained by direct shock wave loading up to 235 GPa: K_(0T) = 306 ± 5 GPa and K'_(0T) = 5.0 ± 0.2 where K_(0T) and K'_(0T) are ambient bulk modulus and its pressure derivative, respectively. The Hugoniots (shock equations of state) for stishovite, coesite and quartz achieve widely differing internal energy states at equal volume and therefore allow us to determine the Gruneisen parameter of stishovite. On the basis of the resulting P-V-T equation of state for stishovite and previous studies on other phases on the MgO-SiO_2 binary, the breakdown reaction of MgSiO_3-perovskite to MgO and SiO_2 was calculated. Our calculations show that perovskite is thermodynamically stable relative to the stishovite and periclase assemblage at lower mantle conditions. We obtain similar results for a range of models, despite the appreciable differences among these experiment-based thermodynamic parameters

Cardio-Protection Afforded by Β-Blockade Is Maintained During Resistance Exercise

Objectives Whether or not the cardio-protective effect of β-adrenergic blockade is retained during resistance exercise has not been systematically evaluated. Therefore the purpose of this study was to measure selected cardiorespiratory responses to isometric exercise involving hand-gripping, single-leg extension, or double-leg dead-lift, under placebo (control), β1-selective (atenolol), and non-selective (propranolol) adrenergic blockade conditions. Design Eleven young male adults were evaluated in a randomized, double-blinded, repeated measures study design and performed all three exercise modalities at 30% of maximal voluntary contraction under placebo, atenolol and propranolol conditions. Methods Heart rate, systolic and diastolic blood pressure, rate-pressure product, oxygen uptake, cardiac output, stroke volume and total peripheral resistance were directly measured or calculated at rest and during the third minute of each of the three exercise modes. Results Irrespective of drug condition, a graded pressor response was observed going from rest to exercise so that rest \u3c handgrip \u3c leg extension \u3c dead-lift for heart rate, systolic and diastolic blood pressures, rate-pressure product and oxygen uptake (p \u3c 0.05 for all). Cardiac output only increased with the dead-lift mode of exercise (p \u3c 0.01). Importantly β-adrenergic blockade with either atenolol or propranolol similarly attenuated the rise in heart rate, and systolic blood pressure; thus rate-pressure product demonstrated a mode-of-exercise by drug interaction effect (p \u3c 0.001) with the greatest reductions seen with the dead-lift procedure. Conclusions The findings indicate that cardio-protection afforded by selective or non-selective β-blockade at rest is preserved during isometric exercise and even enhanced once heart rate increases above 100 beats min−1