Visual Observations of the Amorphous-Amorphous Transition in H2O Under Pressure

The vapor-deposited low-density amorphous phase of H(2)O was directly compressed at 77 kelvin with a diamond-anvil cell, and the boundary between the low-density amorphous phase and the high-density amorphous phase was observed while the sample was warmed under compression. The transition from the low-density amorphous phase to the high-density amorphous phase was distinct and reversible in an apparently narrow pressure range at approximately 130 to approximately 150 kelvin, which provided experimental evidence for polymorphism in amorphous H(2)O.     

A room-temperature molecular/organic-based magnet

The reaction of bis(benzene)vanadium with tetracyanoethylene, TCNE, affords an insoluble amorphous black solid that exhibits field-dependent magnetization and hysteresis at room temperature. The critical temperature could not be estimated as it exceeds 350 kelvin, the thermal decomposition temperature of the sample. The empirical composition of the reported material is V(TCNE)x.Y(CH(2)Cl(2)) with x approximately 2 and Y approximately 1/2. On the basis of the available magnetic and infrared data, threedimensional antiferromagnetic exchange of the donor and acceptor spins resulting in ferrimagnetic behavior appears to be the mode of magnetic coupling.     

Cassini encounters Enceladus: background and the discovery of a south polar hot spot

The Cassini spacecraft completed three close flybys of Saturn's enigmatic moon Enceladus between February and July 2005. On the third and closest flyby, on 14 July 2005, multiple Cassini instruments detected evidence for ongoing endogenic activity in a region centered on Enceladus' south pole. The polar region is the source of a plume of gas and dust, which probably emanates from prominent warm troughs seen on the surface. Cassini's Composite Infrared Spectrometer (CIRS) detected 3 to 7 gigawatts of thermal emission from the south polar troughs at temperatures up to 145 kelvin or higher, making Enceladus only the third known solid planetary body-after Earth and Io-that is sufficiently geologically active for its internal heat to be detected by remote sensing. If the plume is generated by the sublimation of water ice and if the sublimation source is visible to CIRS, then sublimation temperatures of at least 180 kelvin are required.     

Importance of surface morphology in interstellar H2 formation

Detailed laboratory experiments on the formation of HD from atom recombination on amorphous solid water films show that this process is extremely efficient in a temperature range of 8 to 20 kelvin, temperatures relevant for H2 formation on dust grain surfaces in the interstellar medium (ISM). The fate of the 4.5 electron volt recombination energy is highly dependent on film morphology. These results suggest that grain morphology, rather than the detailed chemical nature of the grain surface, is most important in determining the energy content of the H2 as it is released from the grain into the ISM.     

Temperatures in Earth's Core Based on Melting and Phase Transformation Experiments on Iron

Experiments on melting and phase transformations on iron in a laser-heated, diamond-anvil cell to a pressure of 150 gigapascals (approximately 1.5 million atmospheres) show that iron melts at the central core pressure of 363.85 gigapascals at 6350 +/- 350 kelvin. The central core temperature corresponding to the upper temperature of iron melting is 6150 kelvin. The pressure dependence of iron melting temperature is such that a simple model can be used to explain the inner solid core and the outer liquid core. The inner core is nearly isothermal (6150 kelvin at the center to 6130 kelvin at the inner core-outer core boundary), is made of hexagonal closest-packed iron, and is about 1 percent solid (MgSiO(3) + MgO). By the inclusion of less than 2 percent of solid impurities with iron, the outer core densities along a thermal gradient (6130 kelvin at the base of the outer core and 4000 kelvin at the top) can be matched with the average seismic densities of the core.     

Atomic-scale dynamics of a two-dimensional gas-solid interface

The interface between a two-dimensional (2D) molecular gas and a 2D molecular solid has been imaged with a low-temperature, ultrahigh-vacuum scanning tunneling microscope. The solid consists of benzene molecules strongly bound to step edges on a Cu{111} surface. Benzene molecules on the Cu{111} terraces move freely as a 2D gas at 77 kelvin. Benzene molecules transiently occupy well-defined adsorption sites at the 1D edge of the 2D solid. Diffusion of molecules between these sites and exchange between the two phases at the interface are observed. On raised terraces of the copper surface, the 2D gas is held in a cage of the solid as in a 2D nanometer-scale gas bulb.     

A low-operating-temperature solid oxide fuel cell in hydrocarbon-Air mixtures

The performance of a single-chamber solid oxide fuel cell was studied using a ceria-based solid electrolyte at temperatures below 773 kelvin. Electromotive forces of approximately 900 millivolts were generated from the cell in a flowing mixture of ethane or propane and air, where the solid electrolyte functioned as a purely ionic conductor. The electrode-reaction resistance was negligibly small in the total internal resistances of the cell. The resulting peak power density reached 403 and 101 milliwatts per square centimeter at 773 and 623 kelvin, respectively.     

Quartzlike carbon dioxide: An optically nonlinear extended solid at high pressures and temperatures

An extended-solid phase, carbon dioxide phase V (CO2-V), was synthesized in a diamond anvil cell by laser heating the molecular orthorhombic phase, carbon dioxide phase III, above 40 gigapascals and 1800 kelvin. This new material can be quenched to ambient temperature above 1 gigapascal. The vibration spectrum of CO2-V is similar to that of the quartz polymorph of silicon dioxide, indicating that it is an extended covalent solid with carbon-oxygen single bonds. This material is also optically nonlinear, generating the second harmonic of a neodymium-yttrium-lithium-fluoride laser at a wavelength of 527 nanometers with a conversion efficiency that is near 0.1 percent.     

The role of the tropical super greenhouse effect in heating the ocean surface

Measurements made by a Fourier transform infrared (FTIR) spectroradiometer operating in the middle infrared (5 to 20 micrometers, with a spectral resolution of one inverse centimeter) imply that there is an anomalously large greenhouse effect over equatorial oceans that is caused by water vapor. As sea-surface temperature increased from 297 to 303 degrees kelvin, the net infrared cooling at the surface decreased by 30 to 50 watts per square meter. Thus, according to the FTIR data, the super greenhouse effect that had been inferred from satellite measurements contributes directly to radiative heating of the sea surface. The data demonstrate that most of this heating occurs in the middle infrared by means of the continuum emission window of water vapor and that tropical deep convection contributes substantially to this super greenhouse effect.     

Nitric acid trihydrate (NAT) in polar stratospheric clouds

A comprehensive investigation of polar stratospheric clouds was performed on 25 January 2000 with instruments onboard a balloon gondola flown from Kiruna, Sweden. Cloud layers were repeatedly encountered at altitudes between 20 and 24 kilometers over a wide range of atmospheric temperatures (185 to 197 kelvin). Particle composition analysis showed that a large fraction of the cloud layers was composed of nitric acid trihydrate (NAT) particles, containing water and nitric acid at a molar ratio of 3:1; this confirmed that these long-sought solid crystals exist well above ice formation temperatures. The presence of NAT particles enhances the potential for chlorine activation with subsequent ozone destruction in polar regions, particularly in early and late winter.     

How much more rain will global warming bring?

Climate models and satellite observations both indicate that the total amount of water in the atmosphere will increase at a rate of 7% per kelvin of surface warming. However, the climate models predict that global precipitation will increase at a much slower rate of 1 to 3% per kelvin. A recent analysis of satellite observations does not support this prediction of a muted response of precipitation to global warming. Rather, the observations suggest that precipitation and total atmospheric water have increased at about the same rate over the past two decades.     

Solidus of Earth's deep mantle

The solidus of a pyrolite-like composition, approximating that of the lower mantle, was measured up to 59 gigapascals by using CO2 laser heating in a diamond anvil cell. The solidus temperatures are at least 700 kelvin below the melting temperatures of magnesiowustite, which in the deep mantle has the lowest melting temperatures of the three major components-magnesiowustite, Mg-Si-perovskite, and Ca-Si-perovskite. The solidus in the deep mantle is more than 1500 kelvin above the average present-day geotherm, but at the core-mantle boundary it is near the core temperature. Thus, partial melting of the mantle is possible at the core-mantle boundary.     

Thermal Structure of Jupiter's Upper Atmosphere Derived from the Galileo Probe

Temperatures in Jupiter's atmosphere derived from Galileo Probe deceleration data increase from 109 kelvin at the 175-millibar level to 900 ± 40 kelvin at 1 nanobar, consistent with Voyager remote sensing data. Wavelike oscillations are present at all levels. Vertical wavelengths are 10 to 25 kilometers in the deep isothermal layer, which extends from 12 to 0.003 millibars. Above the 0.003-millibar level, only 90- to 270- kilometer vertical wavelengths survive, suggesting dissipation of wave energy as the probable source of upper atmosphere heating.     

Compressibility, Phase Transitions, and Oxygen Migration in Zirconium Tungstate, ZrW2O8

In situ neutron diffraction experiments show that at pressures above 2 kilobars, cubic zirconium tungstate (ZrW2O8) undergoes a quenchable phase transition to an orthorhombic phase, the structure of which has been solved from powder diffraction data. This phase transition can be reversed by heating at 393 kelvin and 1 atmosphere and involves the migration of oxygen atoms in the lattice. The high-pressure phase shows negative thermal expansion from 20 to 300 kelvin. The relative thermal expansion and compressibilities of the cubic and orthorhombic forms can be explained in terms of the "cross-bracing" between polyhedra that occurs as a result of the phase transition.     

Large-scale thermal events in the solar nebula: evidence from Fe,Ni metal grains in primitive meteorites

Chemical zoning patterns in some iron, nickel metal grains from CH carbonaceous chondrites imply formation at temperatures from 1370 to 1270 kelvin by condensation from a solar nebular gas cooling at a rate of approximately 0.2 kelvin per hour. This cooling rate requires a large-scale thermal event in the nebula, in contrast to the localized, transient heating events inferred for chondrule formation. In our model, mass accretion through the protoplanetary disk caused large-scale evaporation of precursor dust near its midplane inside of a few astronomical units. Gas convectively moved from the midplane to cooler regions above it, and the metal grains condensed in these parcels of rising gas.     

Water-mediated proton hopping on an iron oxide surface

The diffusion of hydrogen atoms across solid oxide surfaces is often assumed to be accelerated by the presence of water molecules. Here we present a high-resolution, high-speed scanning tunneling microscopy (STM) study of the diffusion of H atoms on an FeO thin film. STM movies directly reveal a water-mediated hydrogen diffusion mechanism on the oxide surface at temperatures between 100 and 300 kelvin. Density functional theory calculations and isotope-exchange experiments confirm the STM observations, and a proton-transfer mechanism that proceeds via an H(3)O(+)-like transition state is revealed. This mechanism differs from that observed previously for rutile TiO(2)(110), where water dissociation is a key step in proton diffusion.     

Coronal transverse magnetohydrodynamic waves in a solar prominence

Solar prominences are cool 10(4) kelvin plasma clouds supported in the surrounding 10(6) kelvin coronal plasma by as-yet-undetermined mechanisms. Observations from Hinode show fine-scale threadlike structures oscillating in the plane of the sky with periods of several minutes. We suggest that these represent Alfvén waves propagating on coronal magnetic field lines and that these may play a role in heating the corona.     

Composition and physical properties of Enceladus' surface

Observations of Saturn's satellite Enceladus using Cassini's Visual and Infrared Mapping Spectrometer instrument were obtained during three flybys of Enceladus in 2005. Enceladus' surface is composed mostly of nearly pure water ice except near its south pole, where there are light organics, CO2, and amorphous and crystalline water ice, particularly in the region dubbed the "tiger stripes." An upper limit of 5 precipitable nanometers is derived for CO in the atmospheric column above Enceladus, and 2% for NH3 in global surface deposits. Upper limits of 140 kelvin (for a filled pixel) are derived for the temperatures in the tiger stripes.     

Synchrotron X-ray Study of Iron at High Pressure and Temperature

X-ray synchrotron experiments with in situ laser heating of iron in a diamond-anvil cell show that the high-pressure epsilon phase, a hexagonal close-packed (hcp) structure, transforms to another phase (possibly a polytype double-layer hcp) at a pressure of about 38 gigapascals and at temperatures between 1200 and 1500 kelvin. This information has implications for the phase relations of iron in Earth's core.     

Mercury-Based Cuprate High-Transition Temperature Grain-Boundary Junctions and SQUIDs Operating Above 110 Kelvin

The superconducting transport characteristics of HgBa(2) CaCu(2)O(6+delta) (Hg-1212) films and grain-boundary junctions grown on (100)-oriented SrTiO(3) bicrystal substrates have been investigated. The films exhibit a zero-resistance temperature of approximately 120 kelvin and sustain large critical current densities, with values as high as 10(6) amperes per square centimeter at around 100 kelvin. On the other hand, the grain boundaries behave as weak links, with substantially lower critical currents, as is observed for other cuprate superconductors. A reduction of three orders of magnitude in critical current was observed for transport across a 36.8 degrees grain boundary. The current-voltage characteristics of bridges across such a grain boundary show weak-link behavior qualitatively resembling that of a resistively shunted junction. Single-level direct-current superconducting quantum interference devices (SQUIDs) have been fabricated with such bicrystal junctions. These SQUIDs show clear periodic voltage modulations when subjected to applied magnetic fields. The SQUIDs operate at temperatures as high as 111.8 kelvin, which makes them attractive for operation in portable sensors and devices that utilize nonconventional cooling methods.