577 research outputs found
Novel Precursors for Boron Nanotubes: The Competition of Two-Center and Three-Center Bonding in Boron Sheets
We present a new class of boron sheets, composed of triangular and hexagonal
motifs, that are more stable than structures considered to date and thus are
likely to be the precursors of boron nanotubes. We describe a simple and clear
picture of electronic bonding in boron sheets and highlight the importance of
three-center bonding and its competition with two-center bonding, which can
also explain the stability of recently discovered boron fullerenes. Our
findings call for reconsideration of the literature on boron sheets, nanotubes,
and clusters.Comment: 4 pages, 4 figures, 1 tabl
Structure-based stabilization of insulin as a therapeutic protein assembly via enhanced aromatic-aromatic interactions
Key contributions to protein structure and stability are provided by weakly polar interactions, which arise from asymmetric electronic distributions within amino acids and peptide bonds. Of particular interest are aromatic side chains whose directional π-systems commonly stabilize protein interiors and interfaces. Here, we consider aromatic-aromatic interactions within a model protein assembly: the dimer interface of insulin. Semi-classical simulations of aromatic-aromatic interactions at this interface suggested that substitution of residue TyrB26 by Trp would preserve native structure while enhancing dimerization (and hence hexamer stability). The crystal structure of a [TrpB26]insulin analog (determined as a T3Rf3 zinc hexamer at a resolution of 2.25 Å) was observed to be essentially identical to that of WT insulin. Remarkably and yet in general accordance with theoretical expectations, spectroscopic studies demonstrated a 150-fold increase in the in vitro lifetime of the variant hexamer, a critical pharmacokinetic parameter influencing design of long-acting formulations. Functional studies in diabetic rats indeed revealed prolonged action following subcutaneous injection. The potency of the TrpB26-modified analog was equal to or greater than an unmodified control. Thus, exploiting a general quantum-chemical feature of protein structure and stability, our results exemplify a mechanism-based approach to the optimization of a therapeutic protein assembly
Clifford Gates by Code Deformation
Topological subsystem color codes add to the advantages of topological codes
an important feature: error tracking only involves measuring 2-local operators
in a two dimensional setting. Unfortunately, known methods to compute with them
were highly unpractical. We give a mechanism to implement all Clifford gates by
code deformation in a planar setting. In particular, we use twist braiding and
express its effects in terms of certain colored Majorana operators.Comment: Extended version with more detail
Intravenous Pamidronate for Refractory Lymphedema
Background: Based on beneficial reports of pamidronate use for reflex sympathetic dystrophy in reduction of pain and swelling, this drug can be studied as a novel treatment for refractory lymphedema. This study aims to determine the effectiveness of pamidronate on lymphedema and its possible side effects. Methods: Twelve cases of lower limb refractory lymphedema were enrolled. They received intravenous pamidronate monthly for 3 consecutive months and were followed by measuring any discomfort with visual analog scale (VAS) and physician global assessment, based on objective signs of limb volume and circumference. Results: The limb volume, circumference, and satisfaction of the patients improved significantly. Conclusion: Pamidronate when is added to conservative treatments may reduce lymphedema and improve the patient's comfort. © Iranian Red Crescent Medical Journal
Vibrational properties of amorphous silicon from tight-binding O(N) calculation
We present an O(N) algorithm to study the vibrational properties of amorphous
silicon within the framework of tight-binding approach. The dynamical matrix
elements have been evaluated numerically in the harmonic approximation
exploiting the short-range nature of the density matrix to calculate the
vibrational density of states which is then compared with the same obtained
from a standard O() algorithm. For the purpose of illustration, an
1000-atom model is studied to calculate the localization properties of the
vibrational eigenstates using the participation numbers calculation.Comment: 5 pages including 5 ps figures; added a figure and a few references;
accepted in Phys. Rev.
Minimum Degree up to Local Complementation: Bounds, Parameterized Complexity, and Exact Algorithms
The local minimum degree of a graph is the minimum degree that can be reached
by means of local complementation. For any n, there exist graphs of order n
which have a local minimum degree at least 0.189n, or at least 0.110n when
restricted to bipartite graphs. Regarding the upper bound, we show that for any
graph of order n, its local minimum degree is at most 3n/8+o(n) and n/4+o(n)
for bipartite graphs, improving the known n/2 upper bound. We also prove that
the local minimum degree is smaller than half of the vertex cover number (up to
a logarithmic term). The local minimum degree problem is NP-Complete and hard
to approximate. We show that this problem, even when restricted to bipartite
graphs, is in W[2] and FPT-equivalent to the EvenSet problem, which
W[1]-hardness is a long standing open question. Finally, we show that the local
minimum degree is computed by a O*(1.938^n)-algorithm, and a
O*(1.466^n)-algorithm for the bipartite graphs
Exponential decay properties of Wannier functions and related quantities
The spatial decay properties of Wannier functions and related quantities have
been investigated using analytical and numerical methods. We find that the form
of the decay is a power law times an exponential, with a particular power-law
exponent that is universal for each kind of quantity. In one dimension we find
an exponent of -3/4 for Wannier functions, -1/2 for the density matrix and for
energy matrix elements, and -1/2 or -3/2 for different constructions of
non-orthonormal Wannier-like functions.Comment: 4 pages, with 3 postscript figures embedded. Uses REVTEX and epsf
macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/lh_wann/index.htm
Ab Initio Study of Screw Dislocations in Mo and Ta: A new picture of plasticity in bcc transition metals
We report the first ab initio density-functional study of screw
dislocations cores in the bcc transition metals Mo and Ta. Our results suggest
a new picture of bcc plasticity with symmetric and compact dislocation cores,
contrary to the presently accepted picture based on continuum and interatomic
potentials. Core energy scales in this new picture are in much better agreement
with the Peierls energy barriers to dislocation motion suggested by
experiments.Comment: 3 figures, 3 table
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