Fruit storage at subatmospheric pressures

The storage life of bananas and other fruits is prolonged by ventilating them with air at less than atmospheric pressure. This procedure accelerates the escape of the ripening hormone ethylene from the tissue; by reducing the oxygen tension it also lowers the fruit's sensitivity to the hormone.     

Microbial activity at gigapascal pressures

We observed physiological and metabolic activity of Shewanella oneidensis strain MR1 and Escherichia coli strain MG1655 at pressures of 68 to 1680 megapascals (MPa) in diamond anvil cells. We measured biological formate oxidation at high pressures (68 to 1060 MPa). At pressures of 1200 to 1600 MPa, living bacteria resided in fluid inclusions in ice-VI crystals and continued to be viable upon subsequent release to ambient pressures (0.1 MPa). Evidence of microbial viability and activity at these extreme pressures expands by an order of magnitude the range of conditions representing the habitable zone in the solar system.     

Melting of tin teliuride at high pressures

The melting curve of tintelluride (Sn(0.496)Te(0.504) was determined by differential thermal analysis at pressures between 5 and 40 kilobars. Near 844 degrees +/-4 degrees C and 12.0+/-1.0 kb, the liquid and two solid polymorphscoexist.     

Densities of liquid silicates at high pressures

Densities of molten silicates at high pressures (up to approximately 230 kilobars) have been measured for the first time with shock-wave techniques. For a model basaltic composition (36 mole percent anorthite and 64 mole percent diopside), a bulk modulus K(s), of approximately 230 kilobars and a pressure derivative (dK(s)/dP) of approximately 4 were derived. Some implications of these results are as follows: (i) basic to ultrabasic melts become denser than olivine-and pyroxene-rich host mantle at pressures of 60 to 100 kilobars; (ii) there is a maximum depth from which basaltic melt can rise within terrestrial planetary interiors; (iii) the slopes of silicate solidi [(dT(m)/dP), where T(m) is the temperature] may become less steep at high pressures; and (iv) enriched mantle reservoirs may have developed by downward segregation of melt early in Earth history.     

Paradoxical sleep: effect of low partial pressures of atmospheric oxygen

When cats are subjected to an atmosphere of 100 percent oxygen at a sufficiently low pressure, their sleeping patterns are changed: paradoxical sleep disappears and drowsiness increases. This change appears when the pressure decreases to a level close to that at which the hemoglobin begins to dissociate. Return of a cat to a normal atmosphere produces a rebound: the cat spends more time in paradoxical sleep than it did during the base-line period. This finding suggests that a mechanism, closely related to the metabolism of oxygen in the brain, must play an important role in the production of paradoxical sleep. Yet the increase in paradoxical sleep after decompression indicates that still other mechanisms must merge to produce paradoxical sleep.     

Sound velocities in olivine at Earth mantle pressures

The independent elastic constants of an upper mantle mineral, San Carlos olivine [(Mg(1.8)Fe(0.2))SiO(4)], were measured from 0 to 12.5 gigapascals. Evidence is offered in support of the proposition that the explicit temperature dependence of the bulk modulus is small over the range of temperatures and pressures thought to prevail above the 400-kilometer discontinuity, and thus the data can be extrapolated to estimate the properties of olivine under mantle conditions at a depth of 400 kilometers. In the absence of high-temperature data at high pressures, estimates are made of the properties of olivine under mantle conditions to a depth of 400 kilometers. In contrast with low-pressure laboratory data, the predicted covariance of shear and compressional velocities as a function of temperature nearly matches the seismically estimated value for the lower mantle.     

Stress gradient in solid methane at high pressures

The magnitude of the axial pressure gradient at 77 degrees K (11 percent per centimeter) in solid methane compressed along one axis for applied pressures up to 10 kilobars was determined by comparing the electrical resistance of a pair of doped tellurium pressure gages with that of a set of single-crystal gages made of high-purity bismuth. The existence of the pressure gradient revealed the causes of deformation in metal tensile specimens embedded in solid methane and cycled to high pressure.     

Metallic CsI at pressures of up to 220 gigapascals

Direct electrical transport measurements in a diamond anvil cell provide evidence for the metallization of cesium iodide (CsI) at a pressure of 115 gigapascals. A drop in the temperature dependence of the resistance was found at pressures above 180 gigapascals, indicating that the CsI was superconductive. The superconductivity changed under the influence of a magnetic field to a lower critical temperature and disappeared above 0.3 tesla. The highest critical temperature at which superconductivity was observed was 2 kelvin, and the critical temperature decreased with increasing pressure.     

Animals at very high pressures of helium and neon

At pressures up to 125 atmospheres, helium failed to anesthetize mice; at slightly higher pressures (135 to 145 atmospheres) it proved lethal. With Italian newts (Triturus italicus), whose sensitivity to anesthesia by nitrogen is similar to that of mice, responsiveness was lost at pressures between 165 and 245 atmospheres, whether the pressure was achieved with helium or neon, or hydrostatically. It was concluded that the anesthetic pressures of helium and neon, for mice and newts, are higher than the tolerable mechanical pressures.     

竹粉/低密度聚乙烯复合材料的动态流变特性

为了解木塑复合材料的动态流变特性,从而更好地提高产品的生产效率,以及揭示界面复合机理,以竹粉/低密度聚乙烯(LDPE)复合材料为研究对象,分别考察了MAPP偶联剂、EBS润滑剂、1010抗氧剂对复合材料流变行为的影响.利用密炼机对LDPE与竹粉进行密炼混合,在此过程中根据情况添加适量的偶联剂或润滑剂或抗氧剂,得到的复合...     

聚乙二醇/蒙脱石插层复合物的制备及结构表征

通过X射线衍射、傅里叶变换红外光谱和差热分析表征聚乙二醇(PEG)／蒙脱石复合物的结构结果表明,PEG以单层或双层平卧于蒙脱石层间;PEG通过转换部分层间水进入蒙脱石层间通道内;大分子量的PEG与蒙脱石层间表面有更强的相互作用．     

Liquids at large negative pressures: water at the homogeneous nucleation limit

An isochoric cooling method for obtaining unprecedented tensions on liquids was used to determine the homogeneous nucleation limit for stretching of water at a variety of water densities. At densities in the range 0.55 to 0.68 gram per milliliter (g/ml), the data agree with the homogeneous nucleation temperatures measured by Skripov for superheated water at positive pressures. At densities between 0.68 and 0.93 g/ml, cavitation occurred only at negative pressures (that is, under tension). The cavitation tensions measured were in excellent agreement with those predicted by Fisher's 1948 vapor nucleation theory. A maximum tension of 140 megapascals (=1400 bars) was reached at 42 degrees C, which lies on an extrapolation of the line of isobaric density maxima. At higher densities, cavitation of droplets that survived heterogeneous nucleation failed to occur at all unless provoked, at much lower temperatures, by freezing. This observation confirms the existence of a density maximum at 42 degrees C and -140 megapascals and hence greatly strengthens the basis for Speedy's conjecture of a reentrant spinodal for water.     

Plastic deformation of MgGeO3 post-perovskite at lower mantle pressures

Polycrystalline MgGeO3 post-perovskite was plastically deformed in the diamond anvil cell between 104 and 130 gigapascals confining pressure and ambient temperature. In contrast with phenomenological considerations suggesting (010) as a slip plane, lattice planes near (100) became aligned perpendicular to the compression direction, suggesting that slip on (100) or (110) dominated plastic deformation. With the assumption that silicate post-perovskite behaves similarly at lower mantle conditions, a numerical model of seismic anisotropy in the D' region implies a maximum contribution of post-perovskite to shear wave splitting of 3.7% with an oblique polarization.     

Phase transformations in carbon fullerenes at high shock pressures

C(60) powders were shock-compressed quasi-isentropically and quenched from pressures in the range 10 to 110 GPa (0.1 to 1.1 Mbar). Recovered specimens were analyzed by Raman spectroscopy and optical microscopy. C(60) fullerenes are stable into the 13- to 17-GPa pressure range. The onset of a fast ( approximately 0.5 micros) reconstructive transformation to graphite occurs near 17 GPa. The graphite recovered from 27 GPa and about 600 degrees C is relatively well ordered with crystal planar domain size of about 100 A. Above 50 GPa a continuous transformation to an amorphous state is observed in recovered specimens. The fast transformation to graphite is proposed to occur by pi-electron rehybridization which initiates breakup of the ball structure and formation of the graphite structure at high density.     

Structural and bonding changes in cesium iodide at high pressures

Cesium iodide, a simple ionic salt at low pressures, undergoes a second-order transformation at 40 gigapascals (400 kilobars) from the cubic B2 (cesium chloride-type) structure to the body-centered tetragonal structure. Also, the energy gap between valence and conduction bands decreases from 6.4 electron volts at zero pressure to about 1.7 electron volts at 60 gigapascals, transforming cesium iodide from a highly ionic compound to a semiconductor. The structural transition increases the rate at which the band gap closes, and an extrapolation suggests that cesium iodide becomes metallic near (or somewhat above) 100 gigapascals. Similar changes in bonding character are likely to occur in other alkali halides at pressures above 100 gigapascals.     

The formation of chondrules at high gas pressures in the solar nebula

High-precision magnesium isotope measurements of whole chondrules from the Allende carbonaceous chondrite meteorite show that some aluminum-rich Allende chondrules formed at or near the time of formation of calcium-aluminum-rich inclusions and that some others formed later and incorporated precursors previously enriched in magnesium-26. Chondrule magnesium-25/magnesium-24 correlates with [magnesium]/[aluminum] and size, the aluminum-rich, smaller chondrules being the most enriched in the heavy isotopes of magnesium. These relations imply that high gas pressures prevailed during chondrule formation in the solar nebula.     

Hydrogen-helium mixtures at megabar pressures: implications for jupiter and saturn

Models of Jupiter and Saturn postulate a central rock core surrounded by a fluid mixture of hydrogen and helium. These models suggest that the mixture is undergoing phase separation in Saturn but not Jupiter. State-of-the-art total energy calculations of the enthalpy of mixing for ordered alloys of hydrogen and helium confirm that at least partial phase separation has occurred in Saturn and predict that this process has also begun in Jupiter.     

Radiation carcinogenesis at low doses

An analysis of experimental findings indicates that the induction of a manmmary neoplasm in the Sprague-Dawley rat is dependent on the action of radiation on more than one cell. Although a linear relation between incidence and x-ray dose might be consistent with available data, such a relation would be fortuitous and linear extrapolation to lower doses is unjustified.     

Elastic wave velocities of lunar samples at high pressures and their geophysical implications

Ultrasonic measurement of P and S velocities of Apollo 11 lunar samples 10020, 10057, and 10065 to 5 kilobars pressure at room temperature shows a pronounced increase of velocity (as much as twofold) for the first 2 kilobars. The travel times predicted from the velocity-depth curve of sample 10057 are consistent with the results of the Apollo 12 seismic experiments. At pressures below 200 bars, the samples are highly attenuating; for both P and S waves, the value of Q is about 10.     

Crystal structures at megabar pressures determined by use of the cornell synchrotron source

X-ray diffraction studies have been carried out on alkali halide samples 10 micrometers in diameter (volume 10(-9) cubic centimeter) subjected to megabar pressures in the diamond anvil cell. Energy-dispersive techniques and a synchrotron source were used. These measurements can be used to detect crystallographic phase transitions. Cesium iodide was subjected to pressures of 95 gigapascals (fractional volume of 46 percent) and rubidium iodide to pressures of 89 gigapascals (fractional volume of 39 percent). Cesium iodide showed a transformation from the cubic B2 phase (cesium chloride structure) to a tetragonal phase and then to an orthorhombic phase, which was stable to 95 gigapascals. Rubidium iodide showed only a transition from the low-pressure cubic B1 phase (sodium chloride structure) to the B2 phase, which was stable up to 89 gigapascals.