Pleistocene collapse of the west antarctic ice sheet

Some glacial sediment samples recovered from beneath the West Antarctic ice sheet at ice stream B contain Quaternary diatoms and up to 10(8) atoms of beryllium-10 per gram. Other samples contain no Quaternary diatoms and only background levels of beryllium-10 (less than 10(6) atoms per gram). The occurrence of young diatoms and high concentrations of beryllium-10 beneath grounded ice indicates that the Ross Embayment was an open marine environment after a late Pleistocene collapse of the marine ice sheet.

Satellite radar interferometry for monitoring ice sheet motion: application to an antarctic ice stream.

Satellite radar interferometry (SRI) provides a sensitive means of monitoring the flow velocities and grounding-line positions of ice streams, which are indicators of response of the ice sheets to climatic change or internal instability. The detection limit is about 1.5 millimeters for vertical motions and about 4 millimeters for horizontal motions in the radar beam direction. The grounding line, detected by tidal motions where the ice goes afloat, can be mapped at a resolution of approximately 0.5 kilometer. The SRI velocities and grounding line of the Rutford Ice Stream, Antarctica, agree fairly well with earlier ground-based data. The combined use of SRI and other satellite methods is expected to provide data that will enhance the understanding of ice stream mechanics and help make possible the prediction of ice sheet behavior.

Analysis of the ground-state band and a closely related intercalated band of 235(92)U143 by the two-revolving-cluster model with consideration of symmetric and antisymmetric resonance of the two dissimilar clusters.

The reported ground-state band of 235(92)U143 extending from J = 7/2- to 51/2- is found to be two intercalated bands, one beginning with 7/2- and the other with 9/2-, each with DeltaJ = 2. Analysis by the two-resonating-cluster model leads to 3875 Da.fm2 for the moment of inertia for the first few levels, then increasing by centrifugal stretching. This value is interpreted by the structure p70n112 for the central sphere with clusters p11n16 and p11n15 with radius of revolution R = 8.55 fm. The major principal axis of the Poinsot ellipsoid is taken to be determined by an unquantized number K, with vector intermediate in orientation between L and J. The values of K are found by empirical analysis to equal L + 0.28, with the theory of rotation of the ellipsoid giving L + 0.28 for 7/2-, slowly decreasing to L + 0.251 for 51/2-. The 7/2- band is based on odd values of L (negative parity) and the 9/2- band on even values (positive parity). Negative parity for both bands is achieved by symmetric resonance of the two dissimilar clusters in the 7/2- band and antisymmetric resonance in the 9/2- band.

Physical conditions at the base of a fast moving antarctic ice stream.

Boreholes drilled to the bottom of ice stream B in the West Antarctic Ice Sheet reveal that the base of the ice stream is at the melting point and the basal water pressure is within about 1.6 bars of the ice overburden pressure. These conditions allow the rapid ice streaming motion to occur by basal sliding or by shear deformation of unconsolidated sediments that underlie the ice in a layer at least 2 meters thick. The mechanics of ice streaming plays a role in the response of the ice sheet to climatic change.

A revised set of values of single-bond radii derived from the observed interatomic distances in metals by correction for bond number and resonance energy.

An earlier discussion [Pauling, L. (1947) J. Am. Chem. Soc. 69, 542] of observed bond lengths in elemental metals with correction for bond number and resonance energy led to a set of single-bond metallic radii with values usually somewhat less than the corresponding values obtained from molecules and complex ions. A theory of resonating covalent bonds has now been developed that permits calculation of the number of resonance structures per atom and of the effective resonance energy per bond. With this refined method of correcting the observed bond lengths for the effect of resonance energy, a new set of single-bond covalent radii, in better agreement with values from molecules and complex ions, has been constructed.

Activation of mouse T-helper cells induces abundant preproenkephalin mRNA synthesis.

Antigenic or mitogenic stimulation of T cells induces the secretion of an array of protein hormones that regulate immune responses. Molecular cloning has contributed strongly to our present understanding of the nature of this regulation. A complementary DNA (cDNA) library prepared from a cloned concanavalin A-activated mouse T-helper cell line was screened for abundant and induction-specific cDNA's. One such randomly chosen cDNA was found to encode mouse preproenkephalin messenger RNA (mRNA). Preproenkephalin mRNA represented about 0.4 percent of the mRNA in the activated cell line but was absent in resting cells of this line. Other induced T-helper cell lines have 0.1 to 0.5 percent of their mRNA as preproenkephalin mRNA. Induced T-helper cell culture supernatants have [Met]enkephalin-immunoreactive material. The production by activated T cells of a peptide neurotransmitter identifies a signal that can potentially permit T cells to modulate the nervous system.

Extension of the statistical theory of resonating valence bonds to hyperelectronic metals.

The statistical treatment of resonating covalent bonds in metals, previously applied to hypoelectronic metals, is extended to hyperelectronic metals and to metals with two kinds of bonds. The theory leads to half-integral values of the valence for hyperelectronic metallic elements.

Comparison of theoretical and experimental values of the number of metallic orbitals per atom in hypoelectronic and hyperelectronic metals.

The statistical resonating-valence-bond theory of metals is applied in the purely theoretical calculation of the composition of the Ni-Cu alloy at the foot of the curve of saturation ferromagnetic moment, which marks the boundary between hypoelectronic and hyperelectronic metals and determines the value of the number of metallic orbitals per atom. The results, Ni(44)Cu(56) and 0.722 metallic orbitals, agree with the observed values. This agreement provides strong support of the theory.

Glacier surge mechanism: 1982-1983 surge of variegated glacier, alaska.

The hundredfold speedup in glacier motion in a surge of the kind the kind that took place in Variegated Glacier in 1982-1983 is caused by the buildup of high water pressure in the basal passageway system, which is made possible by a fundamental and pervasive change in the geometry and water-transport characteristics of this system. The behavior of the glacier in surge has many remarkable features, which can provide clues to a detailed theory of the surging process. The surge mechanism is akin to a proposed mechanism of overthrust faulting.

Reliability of the pair-defect-sum approximation for the strength of valence-bond orbitals.

The pair-defect-sum approximation to the bond strength of a hybrid orbital (angular wave functions only) is compared to the rigorous value as a function of bond angle for seven types of bonding situations, with between three and eight bond directions equivalent by geometrical symmetry operations and with only one independent bond angle. The approximation is seen to be an excellent one in all cases, and the results provide a rationale for the application of this approximation to a variety of problems.