410 research outputs found
The synthesis of a water-soluble molecule containing a hydrophobic cavity.
Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Chemistry.Vita.Includes bibliographical references.Ph.D
Sulfur isotope fractionation between fluid and andesitic melt : an experimental study
Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 142 (2014): 501-521, doi:10.1016/j.gca.2014.07.015.Glasses produced from decompression experiments conducted by Fiege et al. (2014a) were used to
investigate the fractionation of sulfur isotopes between fluid and andesitic melt upon magma
degassing. Starting materials were synthetic glasses with a composition close to a Krakatau dacitic
andesite. The glasses contained 4.55 to 7.95 wt% H2O, ~140 to 2700 ppm sulfur (S), and 0 to 1000
ppm chlorine (Cl). The experiments were carried out in internally heated pressure vessels (IHPV) at
1030°C and oxygen fugacities (fO2) ranging from QFM+0.8 log units up to QFM+4.2 log units (QFM:
quartz-fayalite-magnetite buffer). The decompression experiments were conducted by releasing
pressure (P) continuously from ~400 MPa to final P of 150, 100, 70 and 30 MPa. The decompression
rate (r) ranged from 0.01 to 0.17 MPa/s. The samples were annealed for 0 to 72 h (annealing time, tA)
at the final P and quenched rapidly from 1030°C to room temperature (T).
The decompression led to the formation of a S-bearing aqueous fluid phase due to the relatively large
fluid-melt partitioning coefficients of S. Secondary ion mass spectrometry (SIMS) was used to
determine the isotopic composition of the glasses before and after decompression. Mass balance
calculations were applied to estimate the gas-melt S isotope fractionation factor αg-m.
No detectable effect of r and tA on αg-m was observed. However, SIMS data revealed a remarkable
increase of αg-m from ~0.9985 ± 0.0007 at >QFM+3 to ~1.0042 ± 0.0042 at ~QFM+1. Noteworthy, the
isotopic fractionation at reducing conditions was about an order of magnitude larger than predicted by previous works. Based on our experimental results and on previous findings for S speciation in fluid
and silicate melt a new model predicting the effect of fO2 on αg-m (or Î34S g-m) in andesitic systems at
1030°C is proposed. Our experimental results as well as our modeling are of high importance for the
interpretation of S isotope signatures in natural samples (e.g., melt inclusions or volcanic gases).This project was supported by the German Science Foundation (BE1720/25-1 to H. Behrens), by the
German National Academic Foundation, and by Collaborative Research Grants from the U.S. National
Science Foundation (EAR-0838482 to C. W. Mandeville, EAR-0838436 to N. Shimizu, and EAR-
0838328 to K. A. Kelley)
A Measurement of the Interference Structure Function, R_LT, for the 12C(e,e'p) reaction in the Quasielastic Region
The coincidence cross-section and the interference structure function, R_LT,
were measured for the 12C(e,e'p) 11B reaction at quasielastic kinematics and
central momentum transfer of q=400 MeV/c. The measurement was at an opening
angle of theta_pq=11 degrees, covering a range in missing energy of E_m = 0 to
65 MeV. The R_LT structure function is found to be consistent with zero for E_m
> 50 MeV, confirming an earlier study which indicated that R_L vanishes in this
region. The integrated strengths of the p- and s-shell are compared with a
Distorted Wave Impulse Approximation calculation. The s-shell strength and
shape are compared with a Hartree Fock-Random Phase Approximation calculation.
The DWIA calculation overestimates the cross sections for p- and s-shell proton
knockout as expected, but surprisingly agrees with the extracted R_LT value for
both shells. The HF-RPA calculation describes the data more consistently, which
may be due to the inclusion of 2-body currents in this calculation.Comment: 8 Pages LaTex, 5 postscript figures. Submitted to Phys. Rev.
Relativistic effects and two-body currents in using out-of-plane detection
Measurements of the reaction were performed
using an 800-MeV polarized electron beam at the MIT-Bates Linear Accelerator
and with the out-of-plane magnetic spectrometers (OOPS). The
longitudinal-transverse, and , and the
transverse-transverse, , interference responses at a missing momentum
of 210 MeV/c were simultaneously extracted in the dip region at Q=0.15
(GeV/c). On comparison to models of deuteron electrodisintegration, the
data clearly reveal strong effects of relativity and final-state interactions,
and the importance of the two-body meson-exchange currents and isobar
configurations. We demonstrate that these effects can be disentangled and
studied by extracting the interference response functions using the novel
out-of-plane technique.Comment: 4 pages, 4 figures, and submitted to PRL for publicatio
The fables of pity: Rousseau, Mandeville and the animal-fable
Copyright @ 2012 Edinburgh University PressPrompted by Derridaâs work on the animal-fable in eighteenth-century debates about political power, this article examines the role played by the fiction of the animal in thinking of pity as either a natural virtue (in Rousseauâs Second Discourse) or as a natural passion (in Mandevilleâs The Fable of the Bees). The war of fables between Rousseau and Mandeville â and their hostile reception by Samuel Johnson and Adam Smith â reinforce that the animal-fable illustrates not so much the proper of man as the possibilities and limitations of a moral philosophy that is unable to address the political realities of the state
Measurement of the Transverse-Longitudinal Cross Sections in the p (e,e'p)pi0 Reaction in the Delta Region
Accurate measurements of the p(e,e?p)pi0 reaction were performed at
Q^2=0.127(GeV/c)^2 in the Delta resonance energy region. The experiments at the
MIT-Bates Linear Accelerator used an 820 MeV polarized electron beam with the
out of plane magnetic spectrometer system (OOPS). In this paper we report the
first simultaneous determination of both the TL and TL? (``fifth" or polarized)
cross sections at low Q^{2} where the pion cloud contribution dominates the
quadrupole amplitudes (E2 and C2). The real and imaginary parts of the
transverse-longitudinal cross section provide both a sensitive determination of
the Coulomb quadrupole amplitude and a test of reaction calculations.
Comparisons with model calculations are presented. The empirical MAID
calculation gives the best overall agreement with this accurate data. The
parameters of this model for the values of the resonant multipoles are
|M_{1+}(I=3/2)|= (40.9 \pm 0.3)10^{-3}/m_pi, CMR= C2/M1= -6.5 \pm 0.3%,
EMR=E2/M1=-2.2 \pm 0.9%, where the errors are due to the experimental
uncertainties.Comment: 10 pages, 3 figures, minor corrections and addition
Locating the Binding Sites of Pb(II) Ion with Human and Bovine Serum Albumins
Lead is a potent environmental toxin that has accumulated above its natural level as a result of human activity. Pb cation shows major affinity towards protein complexation and it has been used as modulator of protein-membrane interactions. We located the binding sites of Pb(II) with human serum (HSA) and bovine serum albumins (BSA) at physiological conditions, using constant protein concentration and various Pb contents. FTIR, UV-visible, CD, fluorescence and X-ray photoelectron spectroscopic (XPS) methods were used to analyse Pb binding sites, the binding constant and the effect of metal ion complexation on HSA and BSA stability and conformations. Structural analysis showed that Pb binds strongly to HSA and BSA via hydrophilic contacts with overall binding constants of KPb-HSAâ=â8.2 (±0.8)Ă104 Mâ1 and KPb-BSAâ=â7.5 (±0.7)Ă104 Mâ1. The number of bound Pb cation per protein is 0.7 per HSA and BSA complexes. XPS located the binding sites of Pb cation with protein N and O atoms. Pb complexation alters protein conformation by a major reduction of α-helix from 57% (free HSA) to 48% (metal-complex) and 63% (free BSA) to 52% (metal-complex) inducing a partial protein destabilization
Heat treatment significantly increases the sharpness of silcrete stone tools
Humans were regularly heat-treating stone tool raw materials as early as 130,000 years ago. The late Middle Stone Age (MSA) and Late Stone Age (LSA) of South Africa's Western Cape region provides some of the earliest and most pervasive archaeological evidence for this behaviour. While archaeologists are beginning to understand the flaking implications of raw material heat treatment, its potential functional benefits remain unanswered. Using silcrete from the Western Cape region, we investigate the impact of heat treatment on stone tool cutting performance. We quantify the sharpness of silcrete in its natural, unheated form, before comparing it with silcrete heated in three different conditions. Results show that heat-treated silcrete can be significantly sharper than unheated alternatives, with cutting forces halving and energy requirements reducing by approximately two-thirds. The data suggest that silcrete may have been heat treated during the South African MSA and LSA to increase the sharpness and performance of stone cutting edges. This early example of material engineering has implications for understanding Stone Age populationsâ technological capabilities, inventiveness and raw material choices. We predict that heat-treatment behaviours in other prehistoric and ethnographic contexts may also be linked to increases in edge sharpness and concerns about functional performance
A blood pool contrast aided T1 functional MRI in patients with brain tumorsâa preliminary study
Distribution of Hyperpolarized Xenon in the Brain Following Sensory Stimulation: Preliminary MRI Findings
In hyperpolarized xenon magnetic resonance imaging (HP 129Xe MRI), the inhaled spin-1/2 isotope of xenon gas is used to generate the MR signal. Because hyperpolarized xenon is an MR signal source with properties very different from those generated from water-protons, HP 129Xe MRI may yield structural and functional information not detectable by conventional proton-based MRI methods. Here we demonstrate the differential distribution of HP 129Xe in the cerebral cortex of the rat following a pain stimulus evoked in the animal's forepaw. Areas of higher HP 129Xe signal corresponded to those areas previously demonstrated by conventional functional MRI (fMRI) methods as being activated by a forepaw pain stimulus. The percent increase in HP 129Xe signal over baseline was 13â28%, and was detectable with a single set of pre and post stimulus images. Recent innovations in the production of highly polarized 129Xe should make feasible the emergence of HP 129Xe MRI as a viable adjunct method to conventional MRI for the study of brain function and disease
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