426 research outputs found
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Time-resolved infrared studies of the dynamics of ligand binding to cytochrome c oxidase
Time-resolved infrared spectroscopy (TRIRS) has been employed to study the reactions of small molecules with the cytochrome a{sub 3}-Cu{sub B} site of cytochrome c oxidase (CcO). All phases of these reactions have been investigated, from ultrafast phenomena (hundreds of femtoseconds) to relatively slow processes (milliseconds). The ligation dynamics immediately following photodissociation have been studied using a TRIR technique with time resolution of less than 1 ps. The rate of photoinitiated transfer of CO from Fe{sub a3}{sup 2+} to Cu{sub B}{sup +} was measured directly by monitoring the development of the transient Cu{sub B}{sup +}-CO absorption. The development of a stationary Cu{sub B}{sup +}-CO spectrum which is constant until the CO dissociates from Cu{sub B}{sup +} occurs in less than 1 ps, indicating that the photoinitiated transfer of CO is remarkably fast. This unprecedented ligand transfer rate has profound implications with regard to the structure and dynamics of the cytochrome a{sub 3}-Cu{sub B} site, the functional architecture of the protein and coordination dynamics in general. The photodissociation and recombination of Cn{sup {minus}} has also been studied using a real-time TRIR technique. The CN{sup {minus}} recombination rate of 430 s{sup {minus}1} is consistent with a recombination pathway similar to the one they have previously proposed for CO. The authors suggest the rate determining step for CN{sup {minus}} recombination is the thermal dissociation of the Fe{sub a3}{sup 2+}-L bond. 25 refs., 7 figs
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Alpha decay self-damage in cubic and monoclinic zirconolite
Samples of primarily-monoclinic /sup 238/Pu-doped zirconolite were stored at ambient temperature to allow accumulation of alpha decay self-damage to a dose of 1 x 10/sup 24/ ..cap alpha../m/sup 3/ (equivalent to a SYNROC age of approx. 10/sup 3/y). Bulk swelling reached 2.3 vol% with no tendency toward saturation, a damage response similar to that observed for cubic Pu-doped zirconolite. X-ray volumetric swelling at 4 x 10/sup 24/ ..cap alpha../m/sup 3/ was 1 vol%, considerably less than that for the cubic material. Changes in cell dimensions differed significantly from those reported by others for a monoclinic natural mineral. Extensive microcracking was observed, and is attributed at least partially to swelling differences between the matrix and minor phases
Implementing evidenceâbased science to improve womenâs health globally
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135335/1/ijgo91.pd
Threshold Electrodisintegration of ^3He
Cross sections were measured for the near-threshold electrodisintegration of
^3He at momentum transfer values of q=2.4, 4.4, and 4.7 fm^{-1}. From these and
prior measurements the transverse and longitudinal response functions R_T and
R_L were deduced. Comparisons are made against previously published and new
non-relativistic A=3 calculations using the best available NN potentials. In
general, for q<2 fm^{-1} these calculations accurately predict the threshold
electrodisintegration of ^3He. Agreement at increasing q demands consideration
of two-body terms, but discrepancies still appear at the highest momentum
transfers probed, perhaps due to the neglect of relativistic dynamics, or to
the underestimation of high-momentum wave-function components.Comment: 9 pages, 7 figures, 1 table, REVTEX4, submitted to Physical Review
A Conformally Invariant Holographic Two-Point Function on the Berger Sphere
We apply our previous work on Green's functions for the four-dimensional
quaternionic Taub-NUT manifold to obtain a scalar two-point function on the
homogeneously squashed three-sphere (otherwise known as the Berger sphere),
which lies at its conformal infinity. Using basic notions from conformal
geometry and the theory of boundary value problems, in particular the
Dirichlet-to-Robin operator, we establish that our two-point correlation
function is conformally invariant and corresponds to a boundary operator of
conformal dimension one. It is plausible that the methods we use could have
more general applications in an AdS/CFT context.Comment: 1+49 pages, no figures. v2: Several typos correcte
The chemical enrichment of the ICM from hydrodynamical simulations
The study of the metal enrichment of the intra-cluster and inter-galactic
media (ICM and IGM) represents a direct means to reconstruct the past history
of star formation, the role of feedback processes and the gas-dynamical
processes which determine the evolution of the cosmic baryons. In this paper we
review the approaches that have been followed so far to model the enrichment of
the ICM in a cosmological context. While our presentation will be focused on
the role played by hydrodynamical simulations, we will also discuss other
approaches based on semi-analytical models of galaxy formation, also critically
discussing pros and cons of the different methods. We will first review the
concept of the model of chemical evolution to be implemented in any
chemo-dynamical description. We will emphasise how the predictions of this
model critically depend on the choice of the stellar initial mass function, on
the stellar life-times and on the stellar yields. We will then overview the
comparisons presented so far between X-ray observations of the ICM enrichment
and model predictions. We will show how the most recent chemo-dynamical models
are able to capture the basic features of the observed metal content of the ICM
and its evolution. We will conclude by highlighting the open questions in this
study and the direction of improvements for cosmological chemo-dynamical models
of the next generation.Comment: 25 pages, 11 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 18; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke
The rate of nitrite reduction in leaves as indicated by O2 and CO2 exchange during photosynthesis
Light response (at 300 ppm CO2 and 10â50 ppm O2 in N2) and CO2 response curves [at absorbed photon fluence rate (PAD) of 550 ÎŒmol mâ2 sâ1] of O2 evolution and CO2 uptake were measured in tobacco (Nicotiana tabacum L.) leaves grown on either NO3â or NH4+ as N source and in potato (Solanum tuberosum L.), sorghum (Sorghum bicolor L. Moench), and amaranth (Amaranthus cruentus L.) leaves grown on NH4NO3. Photosynthetic O2 evolution in excess of CO2 uptake was measured with a stabilized zirconia O2 electrode and an infrared CO2 analyser, respectively, and the difference assumed to represent the rate of electron flow to acceptors alternative to CO2, mainly NO2â, SO42â, and oxaloacetate. In NO3â-grown tobacco, as well as in sorghum, amaranth, and young potato, the photosynthetic O2âCO2 flux difference rapidly increased to about 1 ÎŒmol mâ2 sâ1 at very low PADs and the process was saturated at 50 ÎŒmol quanta mâ2 sâ1. At higher PADs the O2âCO2 flux difference continued to increase proportionally with the photosynthetic rate to a maximum of about 2 ÎŒmol mâ2 sâ1. In NH4+-grown tobacco, as well as in potato during tuber filling, the low-PAD component of surplus O2 evolution was virtually absent. The low-PAD phase was ascribed to photoreduction of NO2â which successfully competes with CO2 reduction and saturates at a rate of about 1 ÎŒmol O2 mâ2 sâ1 (9% of the maximum O2 evolution rate). The high-PAD component of about 1 ÎŒmol O2 mâ2 sâ1, superimposed on NO2â reduction, may represent oxaloacetate reduction. The roles of NO2â, oxaloacetate, and O2 reduction in the regulation of ATP/NADPH balance are discussed
Turnover of passerine birds on islands in the Aegean Sea (Greece)
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73442/1/j.1365-2699.2007.01695.x.pd
Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
We review HB stars in a broad astrophysical context, including both variable
and non-variable stars. A reassessment of the Oosterhoff dichotomy is
presented, which provides unprecedented detail regarding its origin and
systematics. We show that the Oosterhoff dichotomy and the distribution of
globular clusters (GCs) in the HB morphology-metallicity plane both exclude,
with high statistical significance, the possibility that the Galactic halo may
have formed from the accretion of dwarf galaxies resembling present-day Milky
Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the
second-parameter problem is presented. A technique is proposed to estimate the
HB types of extragalactic GCs on the basis of integrated far-UV photometry. The
relationship between the absolute V magnitude of the HB at the RR Lyrae level
and metallicity, as obtained on the basis of trigonometric parallax
measurements for the star RR Lyrae, is also revisited, giving a distance
modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are
studied. Finally, the conductive opacities used in evolutionary calculations of
low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and
Space Scienc
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