12,082 research outputs found
The Partial Visibility Representation Extension Problem
For a graph , a function is called a \emph{bar visibility
representation} of when for each vertex , is a
horizontal line segment (\emph{bar}) and iff there is an
unobstructed, vertical, -wide line of sight between and
. Graphs admitting such representations are well understood (via
simple characterizations) and recognizable in linear time. For a directed graph
, a bar visibility representation of , additionally, puts the bar
strictly below the bar for each directed edge of
. We study a generalization of the recognition problem where a function
defined on a subset of is given and the question is whether
there is a bar visibility representation of with for every . We show that for undirected graphs this problem
together with closely related problems are \NP-complete, but for certain cases
involving directed graphs it is solvable in polynomial time.Comment: Appears in the Proceedings of the 24th International Symposium on
Graph Drawing and Network Visualization (GD 2016
Knuthian Drawings of Series-Parallel Flowcharts
Inspired by a classic paper by Knuth, we revisit the problem of drawing
flowcharts of loop-free algorithms, that is, degree-three series-parallel
digraphs. Our drawing algorithms show that it is possible to produce Knuthian
drawings of degree-three series-parallel digraphs with good aspect ratios and
small numbers of edge bends.Comment: Full versio
Planar Embeddings with Small and Uniform Faces
Motivated by finding planar embeddings that lead to drawings with favorable
aesthetics, we study the problems MINMAXFACE and UNIFORMFACES of embedding a
given biconnected multi-graph such that the largest face is as small as
possible and such that all faces have the same size, respectively.
We prove a complexity dichotomy for MINMAXFACE and show that deciding whether
the maximum is at most is polynomial-time solvable for and
NP-complete for . Further, we give a 6-approximation for minimizing
the maximum face in a planar embedding. For UNIFORMFACES, we show that the
problem is NP-complete for odd and even . Moreover, we
characterize the biconnected planar multi-graphs admitting 3- and 4-uniform
embeddings (in a -uniform embedding all faces have size ) and give an
efficient algorithm for testing the existence of a 6-uniform embedding.Comment: 23 pages, 5 figures, extended version of 'Planar Embeddings with
Small and Uniform Faces' (The 25th International Symposium on Algorithms and
Computation, 2014
Decoherence in Ion Trap Quantum Computers
The {\it intrinsic} decoherence from vibrational coupling of the ions in the
Cirac-Zoller quantum computer [Phys. Rev. Lett. {\bf 74}, 4091 (1995)] is
considered. Starting from a state in which the vibrational modes are at a
temperature , and each ion is in a superposition of an excited and a ground
state, an adiabatic approximation is used to find the inclusive probability
for the ions to evolve as they would without the vibrations, and for the
vibrational modes to evolve into any final state. An analytic form is found for
at , and the decoherence time is found for all . The decoherence
is found to be quite small, even for 1000 ions.Comment: 11 pages, no figures, uses revte
Oxypred: prediction and classification of oxygen-binding proteins
This study describes a method for predicting and classifying oxygen-binding proteins. Firstly, support vector machine (SVM) modules were developed using amino acid composition and dipeptide composition for predicting oxygen-binding proteins, and achieved maximum accuracy of 85.5% and 87.8%, respectively. Secondly, an SVM module was developed based on amino acid composition, classifying the predicted oxygen-binding proteins into six classes with accuracy of 95.8%, 97.5%, 97.5%, 96.9%, 99.4%, and 96.0% for erythrocruorin, hemerythrin, hemocyanin, hemoglobin, leghemoglobin, and myoglobin proteins, respectively. Finally, an SVM module was developed using dipeptide composition for classifying the oxygen-binding proteins, and achieved maximum accuracy of 96.1%, 98.7%, 98.7%, 85.6%, 99.6%, and 93.3% for the above six classes, respectively. All modules were trained and tested by five-fold cross validation. Based on the above approach, a web server Oxypred was developed for predicting and classifying oxygen-binding proteins (available from http://www.imtech.res.in/raghava/oxypred/)
Abstract Learning Frameworks for Synthesis
We develop abstract learning frameworks (ALFs) for synthesis that embody the
principles of CEGIS (counter-example based inductive synthesis) strategies that
have become widely applicable in recent years. Our framework defines a general
abstract framework of iterative learning, based on a hypothesis space that
captures the synthesized objects, a sample space that forms the space on which
induction is performed, and a concept space that abstractly defines the
semantics of the learning process. We show that a variety of synthesis
algorithms in current literature can be embedded in this general framework.
While studying these embeddings, we also generalize some of the synthesis
problems these instances are of, resulting in new ways of looking at synthesis
problems using learning. We also investigate convergence issues for the general
framework, and exhibit three recipes for convergence in finite time. The first
two recipes generalize current techniques for convergence used by existing
synthesis engines. The third technique is a more involved technique of which we
know of no existing instantiation, and we instantiate it to concrete synthesis
problems
Pressure-induced amorphization, crystal-crystal transformations and the memory glass effect in interacting particles in two dimensions
We study a model of interacting particles in two dimensions to address the
relation between crystal-crystal transformations and pressure-induced
amorphization. On increasing pressure at very low temperature, our model
undergoes a martensitic crystal-crystal transformation. The characteristics of
the resulting polycrystalline structure depend on defect density, compression
rate, and nucleation and growth barriers. We find two different limiting cases.
In one of them the martensite crystals, once nucleated, grow easily
perpendicularly to the invariant interface, and the final structure contains
large crystals of the different martensite variants. Upon decompression almost
every atom returns to its original position, and the original crystal is fully
recovered. In the second limiting case, after nucleation the growth of
martensite crystals is inhibited by energetic barriers. The final morphology in
this case is that of a polycrystal with a very small crystal size. This may be
taken to be amorphous if we have only access (as experimentally may be the
case) to the angularly averaged structure factor. However, this `X-ray
amorphous' material is anisotropic, and this shows up upon decompression, when
it recovers the original crystalline structure with an orientation correlated
with the one it had prior to compression. The memory effect of this X-ray
amorphous material is a natural consequence of the memory effect associated to
the underlying martensitic transformation. We suggest that this kind of
mechanism is present in many of the experimental observations of the memory
glass effect, in which a crystal with the original orientation is recovered
from an apparently amorphous sample when pressure is released.Comment: 13 pages, 13 figures, to be published in Phys. Rev.
Quantum Relaxation of Magnetisation in Magnetic Particles
At temperatures below the magnetic anisotropy energy, monodomain magnetic
systems (small particles, nanomagnetic devices, etc.) must relax quantum
mechanically. This quantum relaxation must be mediated by the coupling to both
nuclear spins and phonons (and electrons if either particle or substrate is
conducting. We analyze the effect of each of these couplings, and then combine
them. Conducting systems can be modelled by a "giant Kondo" Hamiltonian, with
nuclear spins added in as well. At low temperatures, even microscopic particles
on a conducting substrate (containing only spins) will have their
magnetisation frozen over millenia by a combination of electronic dissipation
and the "degeneracy blocking" caused by nuclear spins. Raising the temperature
leads to a sudden unblocking of the spin dynamics at a well defined
temperature. Insulating systems are quite different. The relaxation is strongly
enhanced by the coupling to nuclear spins. At short times the magnetisation of
an ensemble of particles relaxes logarithmically in time, after an initial very
fast decay; this relaxation proceeds entirely via the nuclear spins. At longer
times phonons take over, but the decay rate is still governed by the
temperature-dependent nuclear bias field acting on the particles - decay may be
exponential or power-law depending on the temperature. The most surprising
feature of the results is the pivotal role played by the nuclear spins. The
results are relevant to any experiments on magnetic particles in which
interparticle dipolar interactions are unimportant. They are also relevant to
future magnetic device technology.Comment: 30 pages, RevTex, e:mail , Submitted to J.Low
Temp.Phys. on 1 Nov. 199
Planar L-Drawings of Directed Graphs
We study planar drawings of directed graphs in the L-drawing standard. We
provide necessary conditions for the existence of these drawings and show that
testing for the existence of a planar L-drawing is an NP-complete problem.
Motivated by this result, we focus on upward-planar L-drawings. We show that
directed st-graphs admitting an upward- (resp. upward-rightward-) planar
L-drawing are exactly those admitting a bitonic (resp. monotonically
increasing) st-ordering. We give a linear-time algorithm that computes a
bitonic (resp. monotonically increasing) st-ordering of a planar st-graph or
reports that there exists none.Comment: Appears in the Proceedings of the 25th International Symposium on
Graph Drawing and Network Visualization (GD 2017
Spectrum of lactobacillus species present in healthy vagina of Indian women
Background & objectives: Lactobacilli are depleted in vagina of women suffering from recurring episodes of bacterial vaginosis with vaginal pH≥5. With the objective of making available probiotic lactobacilli for replenishment in such women, a study was undertaken to isolate and characterize the Lactobacilli present in women with eco-healthy vagina in Delhi. No information is so far available on the species of Lactobacilli resident in vagina of women in India. Methods: Vaginal swabs were taken from 80 women with informed consent after ethical approval and grown in MRS broth. Gram-positive, catalase-negative bacilli generating about 200 bp amplicon by PCR with Lactobacillus genus specifi c primers were further characterized by employing species specifi c primers followed by sequencing of 16S rDNA. Isolates of the same species were differentiated by random amplifi ed polymorphic DNA (RAPD) profi les. Results: The predominant species isolated were L. reuteri present in 26 (32.5%) women, L. fermentum in 20 (25%), and L. salivarius in 13 (16.25%) women. Sequencing of 16S rDNA of 20 isolates showed that except for two isolates of L. plantarum, sequences of the remaining agreed well with PCR identification. None of the isolates had similar RAPD profile. Interpretation & conclusions: Our fi ndings showed lactobacilli species present in healthy vagina of women in India differ from those reported from other countries. This information would be useful to development of probiotic tablets seeking to replenish the missing lactobacilli for reproductive health of women in India
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