A deep-sea coral record of North Atlantic radiocarbon through the Younger Dryas: Evidence for intermediate water/deepwater reorganization

Our record of Younger Dryas intermediate-depth seawater Δ^(14)C from North Atlantic deep-sea corals supports a link between abrupt climate change and intermediate ocean variability. Our data show that northern source intermediate water (∼1700 m) was partially replaced by (14)^C-depleted southern source water at the onset of the event, consistent with a reduction in the rate of North Atlantic Deep Water formation. This transition requires the existence of large, mobile gradients of Δ^(14)C in the ocean during the Younger Dryas. The Δ^(14)C water column profile from Keigwin (2004) provides direct evidence for the presence of one such gradient at the beginning of the Younger Dryas (∼12.9 ka), with a 100‰ offset between shallow (<∼2400 m) and deep water. Our early Younger Dryas data are consistent with this profile and also show a Δ^(14)C inversion, with 35‰ more enriched water at ∼2400 m than at ∼1700 m. This feature is probably the result of mixing between relatively well ^(14)C ventilated northern source water and more poorly ^(14)C ventilated southern source intermediate water, which is slightly shallower. Over the rest of the Younger Dryas our intermediate water/deepwater coral Δ^(14)C data gradually increase, while the atmosphere Δ^(14)C drops. For a very brief interval at ∼12.0 ka and at the end of the Younger Dryas (11.5 ka), intermediate water Δ^(14)C (∼1200 m) approached atmospheric Δ14C. These enriched Δ^(14)C results suggest an enhanced initial Δ^(14)C content of the water and demonstrate the presence of large lateral Δ^(14)C gradients in the intermediate/deep ocean in addition to the sharp vertical shift at ∼2500 m. The transient Δ^(14)C enrichment at ∼12.0 ka occurred in the middle of the Younger Dryas and demonstrates that there is at least one time when the intermediate/deep ocean underwent dramatic change but with much smaller effects in other paleoclimatic records

Natural Variation in \u3cem\u3eAbies\u3c/em\u3e of the Southern Appalachians

Determinations were made of several foliage, seed, and cone characteristics from material collected throughout the ranges of Abies fraseri in high elevations of Tennessee, North Carolina, and southern Virginia; Abies balsamea var phanerolepis in West Virginia and northern Virginia; and Abies balsamea from its southernmost distribution in Pennsylvania and southern New York. Natural variation was investigated to determine relationships among these taxa, especially with reference to possible hybridity of A. balsamea var phanerolepis in West Virginia and northern Virginia. Much variation was found among species groups among stands within groups. Variation patterns suggested sampling from a north-south cline. Stand values of many characteristics overlapped, in many cases obscuring taxonomic boundaries. High correlation with north-south geographic location was shown for many characteristics. Variation was no greater within the intermediate fir stands (A. balsamea var phanerolepis) than within Fraser fir stands for 12 of the 13 characteristics analyzed, and distribution of hybrid index values of the intermediate fir was normal. The theory of hybrid origin of intermediate fir in West Virginia and Virginia was not generally upheld. Only one characteristic, leaf scar width showed wider variation within the intermediate stands than within Fraser or balsam fir. Total hypodermal cells discriminated well between Fraser fir and the other firs, but not between balsam fir and intermediate fir. The traditional cone bract length-scale length ratio was the only characteristic which distinguished absolutely among the three taxa with no overlapping of values. The ratio is calculated from bract length and scale length which very more or less inversely to each other from north to south. The ratio exaggerated differences due to variation of either characteristic. Differences among Abies fraseri, A. balsamea, and A. balsamea var phanerolepis may be less distinct than heretofore believed

A viscoplastic constitutive theory for metal matrix composites at high temperature

A viscoplastic constitutive theory is presented for representing the high temperature deformation behavior of metal matrix composites. The point of view taken is a continuum one where the composite is considered a material in its own right, with its own properties that can be determined for the composite as a whole. It is assumed that a single preferential (fiber) direction is identifiable at each material point (continuum element) admitting the idealization of local transverse isotropy. A key ingredient is the specification of an experimental program for the complete determination of the material functions and parameters for characterizing a particular metal matrix composite. The parameters relating to the strength of anisotropy can be determined through tension/torsion tests on longitudinally and circumferentially reinforced thin walled tubes. Fundamental aspects of the theory are explored through a geometric interpretation of some basic features analogous to those of the classical theory of plasticity

Prognostic significance of short-term blood pressure variability in acute stroke

Background and Purpose— Blood pressure variability (BPV) may be an important prognostic factor acutely after stroke. This review investigated the existing evidence for the effect of BPV on outcome after stroke, also considering BPV measurement techniques and definitions. Methods— A literature search was performed according to a prespecified study protocol. Two reviewers independently assessed study eligibility and quality. Where appropriate, meta-analyses were performed to assess the effect of BPV on poor functional outcome. Results— Eighteen studies from 1359 identified citations were included. Seven studies were included in a meta-analysis for the effect of BPV on functional outcome (death or disability). Systolic BPV was significantly associated with poor functional outcome: pooled odds ratio per 10-mm Hg increment, 1.2; confidence interval (1.1–1.3). A descriptive review of included studies also supports these findings, and in addition, it suggests that systolic BPV may be associated with increased risk of intracranial hemorrhage in those treated with thrombolytic therapy. Conclusions— This systematic review and meta-analysis suggest that greater systolic BPV, measured early from ischemic stroke or intracerebral hemorrhage onset, is associated with poor longer-term functional outcome. Future prospective studies should investigate how best to measure and define BPV in acute stroke, as well as to determine its prognostic significance. </jats:sec

Raman spectrometer

An improved Raman spectrometer is provided, having, in a preferred embodiment, a light source comprising an injection-locked laser diode array, a multipass cell to multiply the intensity of the light source, a dynamic gas sample focusing system, and an atomic vapor filter to remove the Rayleigh scattered light. The laser diode arrays are tuned to match an absorption band of the atomic vapor filter. The Raman scattered light passes virtually unattenuated through the filter to be recorded by a Fourier transform spectrometer or other spectrometer. This invention permits higher sensitivity and resolution than prior art Raman spectrometers, in particular permitting identification and measurement of Raman emissions that occur at low wave numbers. The light source of this invention can also be used in conjunction with optical notch filters and photodetectors to permit detection and measurement of preselected species in a sample.Board of Regents, University of Texas Syste

The Metamorphosis of Mass Tort Class Actions: A Fifth Circuit Perspective

Symposium - Perspectives on Procedural Issues in the United States Court of Appeals for the Fifth Circui

Inverse Fourier transform technique of measuring averaged absorption cross section in the reverberation chamber and Monte Carlo study of its uncertainty

The averaged absorption cross section (ACS) of a lossy object characterises its ability to capture power from diffused electromagnetic waves. The averaged ACS is very important in many EMC research areas such as indoor wireless channel modelling and human safety exposure study. The measurement of averaged ACS in a reverberation chamber can be achieved by measuring the rate of power loss in the time domain, however this technique requires dense frequency sampling for taking the inverse Fourier transform, which is very time consuming. A new scenario which accelerates the measurement speed is presented in this paper. It combines the technique of non-linear curve fitting to the power delay profile, segmented frequency sweeping and continuous mode stirring. The scenario was validated by measuring the averaged ACS of a hollow plastic sphere filled with deionized water in an EMC reverberation chamber. Measurement results showed a good accordance with the simulations and the measurement uncertainty was studied numerically with the Monte Carlo method

Efficient Determination of Reverberation Chamber Time Constant

Determination of the rate of energy loss in a reverberation chamber is fundamental to many different measurements such as absorption cross-section, antenna efficiency, radiated power, and shielding effectiveness. Determination of the energy decay time-constant in the time-domain by linear fitting the power delay profile, rather than using the frequency-domain quality factor, has the advantage of being independent of the radiation efficiency of antennas used in the measurement. However, determination of chamber time constant by linear regression suffers from several practical problems, including a requirement for long measurement times. Here we present a new nonlinear curve fitting technique that can extract the time-constant with typically 60% fewer samples of the chamber transfer function for the same measurement uncertainty, which enables faster measurement of chamber time constant by sampling fewer chamber transfer function, and allows for more robust automated data post-processing. Nonlinear curve fitting could have economic benefits for test-houses, and also enables accurate broadband measurements on humans in about ten minutes for microwave exposure and medical applications. The accuracy of the nonlinear method is demonstrated by measuring the absorption cross-section of several test objects of known properties. The measurement uncertainty of the method is verified using Monte Carlo methods