A new ultrasonic interferometer for the determination of equation of state parameters of sub-millimeter single crystals     

Hartmut A. Spetzler  Ganglin Chen  Scott Whitehead  Ivan C. Getting 《Pure and Applied Geophysics》1993,141(2-4):341-377

A new giga-Hertz ultrasonic interferometer has been developed, based on ultrasonic microscopy technology. The interferometer operates from 0.3 GHz to 1.5 GHz. The high frequency and associated small wavelengths together with the large bandwidth make it possible to measure travel times in samples with thicknesses of several microns and allow for unprecedented accuracy in bond corrections. An absolute accuracy of 1 part in 10⁵ in travel time measurements is achievable in single crystals (thickness of 200 microns) or glasses of interest to the earth sciences. The high precision travel time data, combining with sample length measurements using a laser interferometer built in our laboratory, yield very high precision ultrasonic velocities.The interferometer is intended for use in conjunction with a newly developed 4 GPa gas piston cylinder apparatus (Getting andSpetzler, 1993) for equation of state measurements under simultaneous pressure and temperature. A separate correction for the bond will be made for each datum at every point in temperature pressure space.  相似文献   

Statistical Evaluation of Compositional Differences Between Upper Eocene Impact Ejecta Layers     

Eric Marchand  James Whitehead 《Mathematical Geology》2002,34(5):555-572

Melt droplets formed by the impact of a large meteorite impact event(s) have been found in upper Eocene marine sediments from the Atlantic, Pacific, and Indian oceans. The number of discreet impacts that occurred to form these melt droplets can be gleaned by compositionally analysing the droplets and establishing the number of distinct groups. Previous studies have inferred two, three, or more source impact events, although we believe the statistical techniques used to distinguish the groupings are open to criticism. Multivariate and univariate analysis (including discriminant analysis) of the major-element composition of an increased data set of impact melt ejecta droplets have been performed. The results demonstrate that the uppermost ejecta layer is geochemically distinct from other late Eocene melt ejecta. Our statistical analysis suggests two underlying, purportedly stratigraphically separate ejecta layers, possess minimal differences that cannot be distinguished clearly from one another by discriminant analysis, which adds to the plausibility that they have a common source. Finally, our results reveal apparent disparities between the new major-element data from this study and data compiled from existing sources.  相似文献   

Creating and sustaining Islamic financial centers: Bahrain in the wake of financial and political crises     

Michael C. Ewers  Ryan Dicce  Jesse P.H. Poon  Jeffery Chow  Justin Gengler 《Urban geography》2018,39(1):3-25

Although primarily concentrated in countries with Muslim majorities, Islamic finance has become a global industry representing both a decentering of the global financial architecture and the emergence of an urban network that resides beyond the confines of traditional world city literature. While geographers have identified the “Mecca’s” of the Islamic finance industry – one of which is Bahrain – there remains a need to identify the factors necessary to create and sustain centers of Islamic finance. This paper examines these factors through a firm-level survey of foreign and local Islamic financial institutions in Bahrain, in conjunction with key informant interviews with representatives of these firms. We find that while Bahrain’s entrenched institutional advantages have preserved its role as a center in the Islamic financial landscape, ongoing political instability and the increasing attractiveness of new and emerging centers are threatening this role. As the country navigates the current social and political unrest, questions are raised as to what it takes to be an Islamic financial center.  相似文献   

Convection driven by temperature and composition flux with the same diffusivity     

J. A. Whitehead 《地球物理与天体物理流体动力学》2017,111(4):229-248

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X‐ray fluorescence measurements of the surface elemental composition of asteroid 433 Eros     

Larry R. Nittler  Richard D. Starr  Lucy Lim  Timothy J. Mccoy  Thomas H. Burbine  Robert C. Reedy  Jacob I. Trombka  Paul Gorenstein  Steven W. Squyres  William V. Boynton  Timothy P. Mcclanahan  Jesse S. Bhangoo  Pamela E. Clark  Mary Ellen Murphy  Rosemary Killen 《Meteoritics & planetary science》2001,36(12):1673-1695

Abstract— We report major element ratios determined for the S‐class asteroid 433 Eros using remote‐sensing x‐ray fluorescence spectroscopy with the near‐Earth asteroid rendezvous Shoemaker x‐ray spectrometer (XRS). Data analysis techniques and systematic errors are described in detail. Data acquired during five solar flares and during two extended “quiet Sun” periods are presented; these results sample a representative portion of the asteroid's surface. Although systematic uncertainties are potentially large, the most internally consistent and plausible interpretation of the data is that Eros has primitive Mg/Si, Al/Si, Ca/Si and Fe/Si ratios, closely similar to H or R chondrites. Global differentiation of the asteroid is ruled out. The S/Si ratio is much lower than that of chondrites, probably reflecting impact‐induced volatilization and/or photo‐ or ion‐induced sputtering of sulfur at the surface of the asteroid. An alternative explanation for the low S/Si ratio is that it reflects a limited degree of melting with loss of an FeS‐rich partial melt. Size‐sorting processes could lead to segregation of Fe‐Ni metal from silicates within the regolith of Eros; this could indicate that the Fe/Si ratios determined by the x‐ray spectrometer are not representative of the bulk Eros composition.  相似文献   

Experimental test of wind-shear theory: Do rocket-borne magnetometers measure B?     

J.D. Whitehead 《Planetary and Space Science》1973,21(10):1815-1816

Recent measurements of electron density, magnetic field and wind do not seem to be self-consistent and are unacceptable as an experimental test of the wind-shear theory.  相似文献   

Axisymmetric critical withdrawal of a rotating fluid     

John A. Whitehead  David L. Porter 《Dynamics of Atmospheres and Oceans》1977,2(1):1-18

The problem of inertial critical flow out of a rotating cylindrical container is addressed theoretically and experimentally. The inviscid steady-state Navier—Stokes equations with the approximation of no vertical shear and the hydrostatic approximation are solved by closing the problem with a critical condition which is applied at the radius of the exit sink. Although the results are presented in general, attention is focused upon the problem when the exit radius is less than the source radius, in which case rotation can be important even when the apparatus size is much less than the Rossby radius of deformation. The results of the analysis are compared to experiments to see if the assumptions were justified. The experiment leads to results that agree closely with predictions of the theory. However, one result is gleaned from the experiment which the theoretical results did not predict. It is that an instability in the flow occurs and is manifested as an azimuthally travelling wave. The role of axisymmetry in producing intense rotational effects is discussed in conext with the experimental findings, and possible implications to withdrawal of oceanic waters by ocean thermal difference power plants are discussed.  相似文献   

Re‐evaluation of late Holocene fire histories of three boreal bogs suggest a link between bog fire and climate          下载免费PDF全文

Jesse L. Morris  Minna Väliranta  Ülle Sillasoo  Eeva‐Stiina Tuittila  Atte Korhola 《Boreas: An International Journal of Quaternary Research》2015,44(1):60-67

We re‐evaluated mid‐ and late Holocene fire records at three bog sites in southern Finland and Estonia through quantitative and qualitative analysis of sedimentary charcoal records. Our analysis suggests synchrony amongst the Kontolanrahka, Männikjärve and Lakkasuo bog records. Over the last 5000 years, three episodes of elevated fire occurrence were evident in these bog records, taking place from 4500 to 4000, 3500 to 2000 and 1000 to 500 cal. a BP. These episodes were probably influenced primarily by climate, but also possibly by expansion/retreat of (pre)historic human populations. Although previous studies have proposed that during the late Holocene only weak fire?climate linkages exist, the presented analysis suggests millennial‐ and centennial‐scale synchronous burning episodes.  相似文献   

Erratum to: Impacts of rising air temperatures and emissions mitigation on electricity demand and supply in the United States: a multi-model comparison     

James McFarland  Yuyu Zhou  Leon Clarke  Patrick Sullivan  Jesse Colman  Wendy S. Jaglom  Michelle Colley  Pralit Patel  Jiyon Eom  Son H. Kim  G. Page Kyle  Peter Schultz  Boddu Venkatesh  Juanita Haydel  Charlotte Mack  Jared Creason 《Climatic change》2015,132(4):739-739

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Hydrodynamics and sediment-transport in the nearshore of Poverty Bay, New Zealand: Observations of nearshore sediment segregation and oceanic storms     

Aaron J. Bever  Jesse E. McNinch 《Continental Shelf Research》2011,31(6):507-526

Nearshore regions act as an interface between the terrestrial environment and deeper waters. As such, they play important roles in the dispersal of fluvial sediment and the transport of sand to and from the shoreline. This study focused on the nearshore of Poverty Bay, New Zealand, and the processes controlling the dispersal of sediment from the main source, the Waipaoa River. Hydrodynamics and sediment-transport in water shallower than 15 m were observed from April through mid-September 2006. This deployment afforded observations during 3-4 periods of elevated river discharge and 5 dry storms.Similar wind, river discharge, wave, current, and turbidity patterns were characterized during three of the wet storms. At the beginning of each event, winds blew shoreward, increasing wave heights to 2-3 m within Poverty Bay. As the cyclonic storms moved through the system the winds reversed direction and became seaward, reducing the local wave height and orbital velocity while river discharge remained elevated. At these times, high river discharge and relatively small waves enabled fluvially derived suspended sediment to deposit in shallow water. Altimetry measurements indicated that at least 7 cm was deposited at a 15 m deep site during a single discharge event. Turbidity and seabed observations showed this deposition to be removed, however, as large swell waves from the Southern Ocean triggered resuspension of the material within three weeks of deposition. Consequently, two periods of dispersal were associated with each discharge pulse, one coinciding with fluvial delivery, and a second driven by wave resuspension a few weeks later. These observations of nearfield sediment deposition contradict current hypotheses of very limited sediment deposition in shallow water offshore of small mountainous rivers when floods and high-energy, large wave and fast current, oceanic conditions coincide.Consistently shoreward near-bed currents, observed along the 10 m isobath of Poverty Bay, were attributed to a combination of estuarine circulation, Stokes drift, and wind driven upwelling. Velocities measured at the 15 m isobath, however, were directed more alongshore and diverged from those at the 10 m isobath. The divergence in the currents observed at the 10 and 15 m locations seemed to facilitate segregation of coarse and fine sediment, with sand transported near-bed toward the beach, while suspended silts and clays were exported to deeper water.  相似文献