347 research outputs found
The structures of Micrococcus lysodeikticus catalase, its ferryl intermediate (compound II) and NADPH complex
The crystal structure of the bacterial catalase from Micrococcus lysodeikticus has been refined using the gene-derived sequence both at 0.88 Angstrom resolution using data recorded at 110 K and at 1.5 Angstrom resolution with room-temperature data. The atomic resolution structure has been refined with individual anisotropic atomic thermal parameters. This has revealed the geometry of the haem and surrounding protein, including many of the H atoms, with unprecedented accuracy and has characterized functionally important hydrogen-bond interactions in the active site. The positions of the H atoms are consistent with the enzymatic mechanism previously suggested for beef liver catalase. The structure reveals that a 25 Angstrom long channel leading to the haem is filled by partially occupied water molecules, suggesting an inherent facile access to the active site. In addition, the structures of the ferryl intermediate of the catalase, the so-called compound II, at 1.96 Angstrom resolution and the catalase complex with NADPH at 1.83 Angstrom resolution have been determined. Comparison of compound II and the resting state of the enzyme shows that the binding of the O atom to the iron (bond length 1.87 Angstrom) is associated with increased haem bending and is accompanied by a distal movement of the iron and the side chain of the proximal tyrosine. Finally, the structure of the NADPH complex shows that the cofactor is bound to the molecule in an equivalent position to that found in beef liver catalase, but that only the adenine part of NADPH is visible in the present structure
Skyrmion Physics Beyond the Lowest Landau Level Approximation
The effects of Landau level mixing and finite thickness of the
two-dimensional electron gas on the relative stability of skyrmion and single
spin-flip excitations at Landau level filling factor have been
investigated. Landau level mixing is studied by fixed-phase diffusion Monte
Carlo and finite thickness is included by modifying the effective Coulomb
interaction. Both Landau level mixing and finite thickness lower skyrmion
excitation energies and favor skyrmions with fewer spin flips. However, the two
effects do not work `coherently'. When finite thickness is included the effect
of Landau level mixing is strongly suppressed.Comment: 4 pages, 4 figure
Local energy-density functional approach to many-body nuclear systems with s-wave pairing
The ground-state properties of superfluid nuclear systems with ^1S_0 pairing
are studied within a local energy-density functional (LEDF) approach. A new
form of the LEDF is proposed with a volume part which fits the Friedman-
Pandharipande and Wiringa-Fiks-Fabrocini equation of state at low and moderate
densities and allows an extrapolation to higher densities preserving causality.
For inhomogeneous systems, a surface term with two free parameters is added. In
addition to the Coulomb direct and exchange interaction energy, an effective
density-dependent Coulomb-nuclear correlation term is included with one more
free parameter, giving a contribution of the same order of magnitude as the
Nolen-Schiffer anomaly in Coulomb displacement energy. The root-mean-square
deviations from experimental masses and radii with the proposed LEDF come out
about a factor of two smaller than those obtained with the conventional
functionals based on the Skyrme or finite-range Gogny force, or on the
relativistic mean-field theory. The generalized variational principle is
formulated leading to the self-consistent Gor'kov equations which are solved
exactly, with physical boundary conditions both for the bound and scattering
states. With a zero-range density-dependent cutoff pairing interaction
incorporating a density-gradient term, the evolution of differential
observables such as odd-even mass differences and staggering in charge radii,
is reproduced reasonably well, including kinks at magic neutron numbers. An
extrapolation to infinite nuclear matter is discussed. We study also the dilute
limit in both the weak and strong coupling regime.Comment: 19 pages, 8 figures. LaTeX, with modified cls file supplied. To be
published in vol. 3 of the series "Advances in Quantum Many-Body Theory",
World Scientific (Proceedings of the MBX Conference, Seattle, September
10-15, 1999
Plasmonic Nanoparticle-based Protein Detection by Optical Shift of a Resonant Microcavity
We demonstrated a biosensing approach which, for the first time, combines the
high-sensitivity of whispering gallery modes (WGM) with a metallic nanoparticle
based assay. We provided a computational model based on generalized Mie theory
to explain the higher sensitivity of protein detection through Plasmonic
enhancement. We quantitatively analyzed the binding of a model protein (i.e.,
BSA) to gold nanoparticles from high-Q WGM resonance frequency shifts, and fit
the results to an adsorption isotherm, which agrees with the theoretical
predictions of a two-component adsorption model.Comment: 12 pages, three figures first submitted to APL March 4 201
Management of complex economic security of enterprises: empirical test in Russia
There is a new meaningful interpretation of the concept of "integrated economic security of industrial enterprise"; the problems of analyzing complex economic security are substantiated. Based on the study of the regulatory and legal and methodological support of the process of managing economic security in modern economic and political conditions, generalizations and analysis of existing practice in Russia and abroad, the main shortcomings in approaches to assessing the integrated economic security of industrial enterprises have been identified. The article examines the methods for assessing economic security: matrix, product, operational, dynamic one and methods of assessment based on the market value of the company. The parameters of the integrated economic security of industrial enterprise are classified: financial and economic security, information, technological, material and technical, personnel, epidemiological security, conceptual model for assessing financial and economic and integrated security of enterprise has been developed. The practical implementation of the proposed developments has been carried out. It is recommended to use the developed model of economic security management as enterprise resource planning (ERP) module of the enterprise system
Bag Formation in Quantum Hall Ferromagnets
Charged skyrmions or spin-textures in the quantum Hall ferromagnet at filling
factor nu=1 are reinvestigated using the Hartree-Fock method in the lowest
Landau level approximation. It is shown that the single Slater determinant with
the minimum energy in the unit charge sector is always of the hedgehog form. It
is observed that the magnetization vector's length deviates locally from unity,
i.e. a bag is formed which accommodates the excess charge. In terms of a
gradient expansion for extended spin-textures a novel O(3) type of effective
action is presented, which takes bag formation into account.Comment: 13 pages, 3 figure
Enhanced Behavioral Recovery from Sensorimotor Cortex Lesions After Pyramidotomy in Adult Rats
Unilateral transection of the bulbar
pyramid, performed before the ablation of the
ipsilateral sensorimotor cortex, has been shown
to facilitate the recovery of operantly conditioned
reflexes and compensatory processes in rats.
Such enhanced behaviorai recovery was absent
when only the sensorimotor cortex was ablated.
This phenomenon is explained by the switching
of motor activity under the control of the
cortico-rubrospinal system. Switching of the
descending influences is accomplished through
the following loop: cortico-rubrai projectionred
nucleus-inferior olive-cerebellum-thalamuscerebral
cortex. This suggests that a preliminary
lesion of the peripheral part of the
system, represented by a descending spinal
projection, facilitates the recovery processes to
develop during the subsequent destruction of its
central part
Heat Capacity Evidence for the Suppression of Skyrmions at Large Zeeman Energy
Measurements on a multilayer two-dimensional electron system (2DES) near
Landau level filling =1 reveal the disappearance of the nuclear spin
contribution to the heat capacity as the ratio between the Zeeman
and Coulomb energies exceeds a critical value 0.04. This
disappearance suggests the vanishing of the Skyrmion-mediated coupling between
the lattice and the nuclear spins as the spin excitations of the 2DES make a
transition from Skyrmions to single spin-flips above . Our
experimental is smaller than the calculated =0.054
for an ideal 2DES; we discuss possible origins of this discrepancy.Comment: Experimental paper, 6 figure
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