The seawater neodymium and lead isotope record of the final stages of Central American Seaway closure

Key Points: Seawater Nd and Pb isotope records for the Pliocene Caribbean and EEP Caribbean Nd isotope composition became more UNADW-like during the Pliocene Short term changes support link between CAS closure and strength of AMOC The shoaling and final closure of the Central American Seaway (CAS) resulted in a major change of the global ocean circulation and has been suggested as an essential driver for strengthening of Atlantic Meridional Overturning Circulation (AMOC). The exact timing of CAS closure is key to interpreting its importance. Here we present a reconstruction of deep and intermediate water Nd and Pb isotope compositions obtained from fossil fish teeth and the authigenic coatings of planktonic foraminifera in the eastern equatorial Pacific (ODP Site 1241) and the Caribbean (ODP Sites 998, 999 and 1000) covering the final stages of CAS closure between 5.6 and 2.2 Ma. The data for the Pacific site indicate no significant Atlantic/Caribbean influence over this entire period. The Caribbean sites show a continuous trend to less radiogenic Nd isotope compositions during the Pliocene, consistent with an enhancement of Upper North Atlantic Deep Water (UNADW) inflow and a strengthening of the AMOC. Superimposed onto this long-term trend, shorter-term changes of intermediate Caribbean Nd isotope signatures approached more UNADW-like values during intervals when published reconstructions of seawater salinity suggested complete closure of the CAS. The data imply that significant deep water exchange with the Pacific essentially stopped by 7 Ma and that shallow exchange, which still occurred at least periodically until approximately 2.5 Ma, may have been linked to the strength of the AMOC but did not have any direct effect on the intermediate and deep Caribbean Nd isotope signatures through mixing with Pacific waters

Mechanical Properties Evaluation of Ti-6Al-4V Thin-Wall Structure Produced by a Hybrid Manufacturing Process

The hybrid manufacturing (HM) process combines the precision of computer numerical control (CNC) and the freeform capability of additive manufacturing to expand the versatility of advanced manufacturing. The intent of this paper is to explore the relationship between HM processing parameters and mechanical properties of the final parts manufactured by one type of HM process that combines laser metal deposition (LMD) and CNC milling. The design of experiment (DOE) is implemented to explore the Ti-6Al-4V thin-wall structure fabrication process with different HM build strategies. Vickers hardness, tensile test, and microstructure analyses are conducted to evaluate the mechanical property variance within the final parts fabricated according to the DOE matrix. Finally, a prediction model of yield strength at 0.2% offset for Ti-6Al-4V parts built through the aforementioned HM process was obtained by an analysis of variance (ANOVA) test, which revealed the significant factors are build height within each LMD process, laser energy input, and the interaction of build height within each LMD process to the preheating condition

Near-Limb Zeeman and Hanle Diagnostics

"Weak" magnetic-field diagnostics in faint objects near the bright solar disk are discussed in terms of the level of non-object signatures, in particular, of the stray light in telescopes. Calculated dependencies of the stray light caused by diffraction at the 0.5-, 1.6-, and 4-meter entrance aperture are presented. The requirements for micro-roughness of refractive and reflective primary optics are compared. Several methods for reducing the stray light (the Lyot coronagraphic technique, multiple stages of apodizing in the focal and exit pupil planes, apodizing in the entrance aperture plane with a special mask), and reducing the random and systematic errors are noted. An acceptable level of stray light in telescopes is estimated for the V-profile recording with a signal-to-noise ratio greater than three. Prospects for the limb chromosphere magnetic measurements are indicated.Comment: 11 pages, 3 figure

Preparation of fiber reinforced titanium diboride and boron carbide composite bodies

A process is described for uniformly infiltrating woven carbon cloth with either titanium diboride or boron carbide at reduced pressure (15 to 25 torr). The effects of deposition temperature on the uniformity of penetration and on coating rate are described for temperatures from 750 to 1000/sup 0/C and deposit loadings from 20 to 43 vol. %. For the boron carbides, boron composition is discussed and evidence is presented suggesting that propene is the dominant rate controlling reactant

Recent Advances in Understanding Particle Acceleration Processes in Solar Flares

We review basic theoretical concepts in particle acceleration, with particular emphasis on processes likely to occur in regions of magnetic reconnection. Several new developments are discussed, including detailed studies of reconnection in three-dimensional magnetic field configurations (e.g., current sheets, collapsing traps, separatrix regions) and stochastic acceleration in a turbulent environment. Fluid, test-particle, and particle-in-cell approaches are used and results compared. While these studies show considerable promise in accounting for the various observational manifestations of solar flares, they are limited by a number of factors, mostly relating to available computational power. Not the least of these issues is the need to explicitly incorporate the electrodynamic feedback of the accelerated particles themselves on the environment in which they are accelerated. A brief prognosis for future advancement is offered.Comment: This is a chapter in a monograph on the physics of solar flares, inspired by RHESSI observations. The individual articles are to appear in Space Science Reviews (2011

Phenomenology As Philosophy and Method

Phenomenology is a philosophical movement that approaches the study of human beings and their culture differently from the logical positivist model used in the natural sciences and in special education. phenomenologists view the application of the logical positivist model to the study of human beings as inappropriate because the model does not address the uniqueness of human life. in this article, the theroetical assumptions and methodological orientations of phenomenology are discussed, followed by their applications to ways of doing research in special education.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68638/2/10.1177_074193259501600305.pd