An electrical microheater technique for high-pressure and high-temperature diamond anvil cell experiments.

Small electrical heating elements have been lithographically fabricated onto the culets of "designer" diamond anvils for the purpose of performing high-pressure and high-temperature experiments on metals. The thin-film geometry of the heating elements makes them very resistant to plastic deformation during high-pressure loading, and their small cross-sectional area enables them to be electrically heated to very high temperatures with relatively modest currents (approximately = 1 A). The technique also offers excellent control and temporal stability of the sample temperature. Test experiments on gold samples have been performed for pressures up to 21 GPa and temperatures of nearly 2000 K.

Emergent magnetic moments produced by self-damage in plutonium.

Plutonium possesses the most complicated phase diagram in the periodic table, driven by the complexities of overlapping 5f electron orbitals. Despite the importance of the 5f electrons in defining the structure and physical properties, there is no experimental evidence that these electrons localize to form magnetic moments in pure Pu. Instead, a large temperature-independent Pauli susceptibility indicates that they form narrow conduction bands. Radiation damage from the alpha-particle decay of Pu creates numerous defects in the crystal structure, which produce a significant temperature-dependent magnetic susceptibility, chi(T), in both alpha-Pu and delta-Pu (stabilized by 4.3 atomic percent Ga). This effect can be removed by thermal annealing above room temperature. By contrast, below 35 K the radiation damage is frozen in place, permitting the evolution in chi(T) with increasing damage to be studied systematically. This result leads to a two-component model consisting of a Curie-Weiss term and a short-ranged interaction term consistent with disorder-induced local moment models. Thus, it is shown that self-damage creates localized magnetic moments in previously nonmagnetic plutonium.

Unconventional metallic magnetism in LaCrSb3.

Neutron-diffraction measurements in LaCrSb3 show a coexistence of ferromagnetic and antiferromagnetic sublattices below T(C)=126 K, with ordered moments of 1.65(4) and 0.49(4)mu(B)/formula unit, respectively (T=10 K), and a spin-reorientation transition at approximately 95 K. No clear peak or step was observed in the specific heat at T(C). Coexisting localized and itinerant spins are suggested.

Not traditional, not assimilated: elderly American Indians and the notion of 'cohort'.

In this article, a Native Americanist anthropologist whose research focuses on elders, and a gerontologist who specializes in American Indians, draw on their respective studies--the former primarily quantitative and the latter primarily qualitative--to illuminate the nature of ethnic identity among American Indian elderly. The regional focus is the Upper Great Lakes (primarily Michigan) and the tribal/cultural group under consideration is the Anishinaabeg (Chippewa, Ottawa, Potawatomi). The analysis is centered on a key concept--cohort--considered by the authors to be crucial to the understanding of American Indian elderly. In addition to integrating quantitative and qualitative findings, an historical framework is utilized to assist in interpreting the results. It is suggested that Anishinaabe elders, despite some superficial appearances to the contrary, are by no means fully assimilated into mainstream American culture; their ethnic identity is not necessarily stereotypically 'traditional,' but it is nonetheless quintessentially American Indian. Researchers will be better able to appreciate such subtleties by taking into consideration the ways in which various stages in the life course intersect with specific historical periods (cohort), as well as by drawing on both qualitative and quantitative studies in pursuing their investigations.

VMA12 encodes a yeast endoplasmic reticulum protein required for vacuolar H+-ATPase assembly.

The Saccharomyces cerevisiae vacuolar membrane proton-translocating ATPase (V-ATPase) can be divided into a peripheral membrane complex (V1) containing at least eight polypeptides of 69, 60, 54, 42, 32, 27, 14, and 13 kDa, and an integral membrane complex (V0) containing at least five polypeptides of 100, 36, 23, 17, and 16 kDa. Other yeast genes have been identified that are required for V-ATPase assembly but whose protein products do not co-purify with the enzyme complex. One such gene, VMA12, encodes a 25-kDa protein (Vma12p) that is predicted to contain two membrane-spanning domains. Biochemical analysis has revealed that Vma12p behaves as an integral membrane protein with both the N and C termini oriented toward the cytosol, and this protein immunolocalizes to the endoplasmic reticulum (ER). In cells lacking Vma12p (vma12Delta), the 100-kDa subunit of the V0 complex (which contains six to eight putative membrane-spanning domains) was rapidly degraded (t1/2 approximately 30 min). Protease protection assays revealed that the 100-kDa subunit was inserted/translocated correctly into the ER membrane of vma12Delta cells. These data indicate that Vma12p functions in the ER after the insertion of V0 subunits into the ER membrane. We propose that Vma12p functions directly in the assembly of the V0 subunits into a complex in the ER, and that assembly is required for the stability of the V0 subunits and their transport as a complex out of this compartment.

Hypothesis testing and earthquake prediction.

Requirements for testing include advance specification of the conditional rate density (probability per unit time, area, and magnitude) or, alternatively, probabilities for specified intervals of time, space, and magnitude. Here I consider testing fully specified hypotheses, with no parameter adjustments or arbitrary decisions allowed during the test period. Because it may take decades to validate prediction methods, it is worthwhile to formulate testable hypotheses carefully in advance. Earthquake prediction generally implies that the probability will be temporarily higher than normal. Such a statement requires knowledge of "normal behavior"--that is, it requires a null hypothesis. Hypotheses can be tested in three ways: (i) by comparing the number of actual earth-quakes to the number predicted, (ii) by comparing the likelihood score of actual earthquakes to the predicted distribution, and (iii) by comparing the likelihood ratio to that of a null hypothesis. The first two tests are purely self-consistency tests, while the third is a direct comparison of two hypotheses. Predictions made without a statement of probability are very difficult to test, and any test must be based on the ratio of earthquakes in and out of the forecast regions.

Geometric incompatibility in a fault system.

Interdependence between geometry of a fault system, its kinematics, and seismicity is investigated. Quantitative measure is introduced for inconsistency between a fixed configuration of faults and the slip rates on each fault. This measure, named geometric incompatibility (G), depicts summarily the instability near the fault junctions: their divergence or convergence ("unlocking" or "locking up") and accumulation of stress and deformations. Accordingly, the changes in G are connected with dynamics of seismicity. Apart from geometric incompatibility, we consider deviation K from well-known Saint Venant condition of kinematic compatibility. This deviation depicts summarily unaccounted stress and strain accumulation in the region and/or internal inconsistencies in a reconstruction of block- and fault system (its geometry and movements). The estimates of G and K provide a useful tool for bringing together the data on different types of movement in a fault system. An analog of Stokes formula is found that allows determination of the total values of G and K in a region from the data on its boundary. The phenomenon of geometric incompatibility implies that nucleation of strong earthquakes is to large extent controlled by processes near fault junctions. The junctions that have been locked up may act as transient asperities, and unlocked junctions may act as transient weakest links. Tentative estimates of K and G are made for each end of the Big Bend of the San Andreas fault system in Southern California. Recent strong earthquakes Landers (1992, M = 7.3) and Northridge (1994, M = 6.7) both reduced K but had opposite impact on G: Landers unlocked the area, whereas Northridge locked it up again.

Comparing tiltmeters for crustal deformation measurement--a preliminary report.

A collection of high-precision tiltmeters is being operated at Pinon Flat Observatory, southern California, both to compare instruments and to measure tectonic deformation. We report on 1.2 years of data from four of these: two Michelson-Gale long fluid tiltmeters, one long center-pressure tiltmeter, and a shallow borehole tiltmeter. The three long-base instruments are all located on the same baseline, with a precise leveling line running between their end-monuments. At nontidal frequencies, only the two Michelson-Gale instruments show some coherence (gamma 2 = .3 for periods of 2 to 4 days), while the center-pressure instrument is correlated with air temperature at periods from a few days to a few weeks. The most stable tilt record shows a secular rate of 0.28 mu rad/a, which may be real. Over much longer times, leveling to specially stabilized bench-marks should confirm this. Comparing instruments has identified more and less successful measurement techniques; it appears that low-noise data will most probably be produced only by relatively complex and expensive instruments, though even for these, the operating costs over any reasonable lifetime will exceed the capital cost. Even the best existing sensors must be improved to measure continuous tectonic motions.

An automatic method for localizing radioactive seeds in implant dosimetry.

A method for locating radioactive seeds in interstitial implants has been developed that requires three radiographic views. Spatial coordinates for the seeds are computed from the randomly digitized seed images on each of three radiographs, and information about the tube and film placement for each of the radiographs. Further, the ability to accurately (greater than 98% of the seeds within +/- 2.5 mm) locate the seeds does not require the use of a specialized radiographic technique; the radiographs need only represent three different views of the implant. Also discussed is the seed image matching technique that enables ambiguous seed matches to be resolved.

Aseismic uplift in southern california: an alternative interpretation.

The previously reported uplift in southern California may have resulted from systematic errors in leveling rather than tectonic activity. Errors are inferred from correlation between changes in elevation and topography at short and long wavelengths. Corrected data show no significant vertical motion except at the time of the San Fernando earthquake. Possible sources of error include inadequate rod calibration and refraction.

Earthquake prediction: modeling the anomalous vp/vs source region.

Soviet observations of anomalously low values of the ratio of the compressional wave velocity to the shear wave velocity (V(p)/ V(s)) in a restricted volume around the locus of a future earthquake are duplicated by models based on the dilatancy hypothesis. In nature the cracks that cause the dilation may be oriented, leading to anisotropic seismic wave propagation in the anomalous region. The models show that vertical cracks are most effective in producing the observed effects, but that a slightly higher density of randomly oriented cracks will yield similar effects. The premonitory observations at Blue Mountain Lake, New York, are also duplicated by the models. These models demonstrate that V(p)/V(s) measured at the surface is not that of the anomalous zone, but is related to it by a transfer function, involving the shape and velocity gradient of the zone boundary.

Attenuation of seismic waves by grain boundary relaxation.

Experimental observations of the attenuation of elastic waves in polycrystalline ceramics and rocks reveal an attenuation mechanism, called grain boundary relaxation, which is likely to be predominant cause of seismic attenuation in the earth's mantle. For this mechanism, the internal friction (the reciprocal of the "intrinsic Q" of the material) depends strongly upon frequency and is in good agreement with Walsh's theory of attenuation (J. Geophys. Res., 74, 4333, 1969) in partially melted rock. When Walsh's theory is extended to provide a model of the anelasticity of the earth, using the experimental values of physical parameters reported here, the results are in excellent agreement with seismic observations.