656 research outputs found
Differential dehydration effects on globular proteins and intrinsically disordered proteins during film formation
Globular proteins composed of different secondary structures and fold types were examined by synchrotron radiation circular dichroism spectroscopy to determine the effects of dehydration on their secondary structures. They exhibited only minor changes upon removal of bulk water during film formation, contrary to previously reported studies of proteins dehydrated by lyophilization (where substantial loss of helical structure and gain in sheet structure was detected). This near lack of conformational change observed for globular proteins contrasts with intrinsically disordered proteins (IDPs) dried in the same manner: the IDPs, which have almost completely unordered structures in solution, exhibited increased amounts of regular (mostly helical) secondary structures when dehydrated, suggesting formation of new intra-protein hydrogen bonds replacing solvent-protein hydrogen bonds, in a process which may mimic interactions that occur when IDPs bind to partner molecules. This study has thus shown that the secondary structures of globular and intrinsically disordered proteins behave very differently upon dehydration, and that films are a potentially useful format for examining dehydrated soluble proteins and assessing IDPs structures
Real World Interpretations of Quantum Theory
I propose a new class of interpretations, {\it real world interpretations},
of the quantum theory of closed systems. These interpretations postulate a
preferred factorization of Hilbert space and preferred projective measurements
on one factor. They give a mathematical characterisation of the different
possible worlds arising in an evolving closed quantum system, in which each
possible world corresponds to a (generally mixed) evolving quantum state. In a
realistic model, the states corresponding to different worlds should be
expected to tend towards orthogonality as different possible quasiclassical
structures emerge or as measurement-like interactions produce different
classical outcomes. However, as the worlds have a precise mathematical
definition, real world interpretations need no definition of quasiclassicality,
measurement, or other concepts whose imprecision is problematic in other
interpretational approaches. It is natural to postulate that precisely one
world is chosen randomly, using the natural probability distribution, as the
world realised in Nature, and that this world's mathematical characterisation
is a complete description of reality.Comment: Minor revisions. To appear in Foundations of Physic
Entropy creation inside black holes points to observer complementarity
Heating processes inside large black holes can produce tremendous amounts of
entropy. Locality requires that this entropy adds on space-like surfaces, but
the resulting entropy (10^10 times the Bekenstein-Hawking entropy in an example
presented in the companion paper) exceeds the maximum entropy that can be
accommodated by the black hole's degrees of freedom. Observer complementarity,
which proposes a proliferation of non-local identifications inside the black
hole, allows the entropy to be accommodated as long as individual observers
inside the black hole see less than the Bekenstein-Hawking entropy. In the
specific model considered with huge entropy production, we show that individual
observers do see less than the Bekenstein-Hawking entropy, offering strong
support for observer complementarity.Comment: 13 pages. This is a companion paper to arXiv:0801.4415; Added
reference
An evolutionarily-unique heterodimeric voltage-gated cation channel found in aphids
We describe the identification in aphids of a unique heterodimeric voltage-gated sodium channel which has an atypical ion selectivity filter and, unusually for insect channels, is highly insensitive to tetrodotoxin. We demonstrate that this channel has most likely arisen by adaptation (gene fission or duplication) of an invertebrate ancestral mono(hetero)meric channel. This is the only identifiable voltage-gated sodium channel homologue in the aphid genome(s), and the channelâs novel selectivity filter motif (DENS instead of the usual DEKA found in other eukaryotes) may result in a loss of sodium selectivity, as indicated experimentally in mutagenised Drosophila channels
HAPEX-Sahel : a large-scale study of land-atmosphere interactions in the semi-arid tropics
The Hydrologic Atmospheric Pilot EXperiment
in the Sahel (HAPEX-Sahel) was carried out in Niger, West Africa, during 1991 -
1992, with an intensive observation period (IOP) in August - October 1992. It
aims at improving the parameterization of land surface atmosphere interactions
at the Global Circulation Model (GCM) gridbox scale. The experiment combines
remote sensing and ground based measurements with hydrological and
meteorological modelling to develop aggregation techniques for use in large
scale estimates of the hydrological and meteorological behaviour of large areas
in the Sahel. The experimental strategy consisted of a period of intensive
measurements during the transition period of the rainy to the dry season, backed
up by a series of long term measurements in a 1° by 1° square in Niger. Three
"supersites" were instrumented with a variety of hydrological and
(micro) meteorological equipment to provide detailed information on the surface
energy exchange at the local scale. Boundary layer measurements and aircraft
measurements were used to provide information at scales of 100 - 500 km2.
All relevant remote sensing images were obtained for this period. This programme
of measurements is now being analyzed and an extensive modelling programme is
under way to aggregate the information at all scales up to the GCM grid box
scale. The experimental strategy and some preliminary results of the IOP are
described
One-neutron removal reactions on neutron-rich psd-shell nuclei
A systematic study of high energy, one-neutron removal reactions on 23
neutron-rich, psd--shell nuclei (Z=5-9, A=12-25) has been carried out. The
longitudinal momentum distributions of the core fragments and corresponding
single-neutron removal cross sections are reported for reactions on a carbon
target. Extended Glauber model calculations, weighted by the spectroscopic
factors obtained from shell model calculations, are compared to the
experimental results. Conclusions are drawn regarding the use of such reactions
as a spectroscopic tool and spin-parity assignments are proposed for 15B, 17C,
19-21N, 21,23O, 23-25F. The nature of the weakly bound systems 14B and 15,17C
is discussed.Comment: 11 pages + 2 figure
Elastic electron deuteron scattering with consistent meson exchange and relativistic contributions of leading order
The influence of relativistic contributions to elastic electron deuteron
scattering is studied systematically at low and intermediate momentum transfers
( fm). In a -expansion, all leading order
relativistic -exchange contributions consistent with the Bonn OBEPQ models
are included. In addition, static heavy meson exchange currents including boost
terms and lowest order -currents are considered. Sizeable
effects from the various relativistic two-body contributions, mainly from
-exchange, have been found in form factors, structure functions and the
tensor polarization . Furthermore, static properties, viz. magnetic
dipole and charge quadrupole moments and the mean square charge radius are
evaluated.Comment: 15 pages Latex including 5 figures, final version accepted for
publication in Phys.Rev.C Details of changes: (i) The notation of the curves
in Figs. 1 and 2 have been clarified with respect to left and right panels.
(ii) In Figs. 3 and 4 an experimental point for T_20 has been added and a
corresponding reference [48] (iii) At the end of the text we have added a
paragraph concerning the quality of the Bonn OBEPQ potential
Modeling the actinides with disordered local moments
A first-principles disordered local moment (DLM) picture within the
local-spin-density and coherent potential approximations (LSDA+CPA) of the
actinides is presented. The parameter free theory gives an accurate description
of bond lengths and bulk modulus. The case of -Pu is studied in
particular and the calculated density of states is compared to data from
photo-electron spectroscopy. The relation between the DLM description, the
dynamical mean field approach and spin-polarized magnetically ordered modeling
is discussed.Comment: 6 pages, 4 figure
- âŠ