2,772 research outputs found
Geometric Inference on Kernel Density Estimates
We show that geometric inference of a point cloud can be calculated by
examining its kernel density estimate with a Gaussian kernel. This allows one
to consider kernel density estimates, which are robust to spatial noise,
subsampling, and approximate computation in comparison to raw point sets. This
is achieved by examining the sublevel sets of the kernel distance, which
isomorphically map to superlevel sets of the kernel density estimate. We prove
new properties about the kernel distance, demonstrating stability results and
allowing it to inherit reconstruction results from recent advances in
distance-based topological reconstruction. Moreover, we provide an algorithm to
estimate its topology using weighted Vietoris-Rips complexes.Comment: To appear in SoCG 2015. 36 pages, 5 figure
Visualizing Sensor Network Coverage with Location Uncertainty
We present an interactive visualization system for exploring the coverage in
sensor networks with uncertain sensor locations. We consider a simple case of
uncertainty where the location of each sensor is confined to a discrete number
of points sampled uniformly at random from a region with a fixed radius.
Employing techniques from topological data analysis, we model and visualize
network coverage by quantifying the uncertainty defined on its simplicial
complex representations. We demonstrate the capabilities and effectiveness of
our tool via the exploration of randomly distributed sensor networks
Testing wind as an explanation for the spin problem in the continuum-fitting method
The continuum-fitting method is one of the two most advanced methods of
determining the black hole spin in accreting X-ray binary systems. There are,
however, still some unresolved issues with the underlying disk models. One of
them manifests as an apparent decrease in spin for increasing source
luminosity. Here, we perform a few simple tests to establish whether outflows
from the disk close to the inner radius can address this problem. We employ
four different parametric models to describe the wind and compare these to the
apparent decrease in spin with luminosity measured in the sources LMC~X-3 and
GRS~1915+105. Wind models in which parameters do not explicitly depend on the
accretion rate cannot reproduce the spin measurements. Models with mass
accretion rate dependent outflows, however, have spectra that emulate the
observed ones. The assumption of a wind thus effectively removes the artifact
of spin decrease. This solution is not unique; the same conclusion can be
obtained with a truncated inner disk model. To distinguish among valid models,
high resolution X-ray data and a realistic description of the Comptonization in
the wind will be needed.Comment: 14 pages, 11 figures, accepted by Ap
Graph Concatenation for Quantum Codes
Graphs are closely related to quantum error-correcting codes: every
stabilizer code is locally equivalent to a graph code, and every codeword
stabilized code can be described by a graph and a classical code. For the
construction of good quantum codes of relatively large block length,
concatenated quantum codes and their generalizations play an important role. We
develop a systematic method for constructing concatenated quantum codes based
on "graph concatenation", where graphs representing the inner and outer codes
are concatenated via a simple graph operation called "generalized local
complementation." Our method applies to both binary and non-binary concatenated
quantum codes as well as their generalizations.Comment: 26 pages, 12 figures. Figures of concatenated [[5,1,3]] and [[7,1,3]]
are added. Submitted to JM
Codeword stabilized quantum codes: algorithm and structure
The codeword stabilized ("CWS") quantum codes formalism presents a unifying
approach to both additive and nonadditive quantum error-correcting codes
(arXiv:0708.1021). This formalism reduces the problem of constructing such
quantum codes to finding a binary classical code correcting an error pattern
induced by a graph state. Finding such a classical code can be very difficult.
Here, we consider an algorithm which maps the search for CWS codes to a problem
of identifying maximum cliques in a graph. While solving this problem is in
general very hard, we prove three structure theorems which reduce the search
space, specifying certain admissible and optimal ((n,K,d)) additive codes. In
particular, we find there does not exist any ((7,3,3)) CWS code though the
linear programming bound does not rule it out. The complexity of the CWS search
algorithm is compared with the contrasting method introduced by Aggarwal and
Calderbank (arXiv:cs/0610159).Comment: 11 pages, 1 figur
Chloroquine supplementation increases the cytotoxic effect of curcumin against Her2/neu overexpressing breast cancer cells in vitro and in vivo in nude mice while counteracts it in immune competent mice
Autophagy is usually a pro-survival mechanism in cancer cells, especially in the course of chemotherapy, thus autophagy inhibition may enhance the chemotherapy-mediated anti-cancer effect. However, since autophagy is strongly involved in the immunogenicity of cell death by promoting ATP release, its inhibition may reduce the immune response against tumors, negatively influencing the overall outcome of chemotherapy. In this study, we evaluated the in vitro and in vivo anti-cancer effect of curcumin (CUR) against Her2/neu overexpressing breast cancer cells (TUBO) in the presence or in the absence of the autophagy inhibitor chloroquine (CQ). We found that TUBO cell death induced by CUR was increased in vitro by CQ and slightly in vivo in nude mice. Conversely, CQ counteracted the Cur cytotoxic effect in immune competent mice, as demonstrated by the lack of in vivo tumor regression and the reduction of overall mice survival as compared with CUR-treated mice. Immunohistochemistry analysis revealed the presence of a remarkable FoxP3 T cell infiltrate within the tumors in CUR/CQ treated mice and a reduction of T cytotoxic cells, as compared with single CUR treatment. These findings suggest that autophagy is important to elicit anti-tumor immune response and that autophagy inhibition by CQ reduces such response also by recruiting T regulatory (Treg) cells in the tumor microenvironment that may be pro-tumorigenic and might counteract CUR-mediated anti-cancer effects
Correlations in excited states of local Hamiltonians
Physical properties of the ground and excited states of a -local
Hamiltonian are largely determined by the -particle reduced density matrices
(-RDMs), or simply the -matrix for fermionic systems---they are at least
enough for the calculation of the ground state and excited state energies.
Moreover, for a non-degenerate ground state of a -local Hamiltonian, even
the state itself is completely determined by its -RDMs, and therefore
contains no genuine -particle correlations, as they can be inferred from
-particle correlation functions. It is natural to ask whether a similar
result holds for non-degenerate excited states. In fact, for fermionic systems,
it has been conjectured that any non-degenerate excited state of a 2-local
Hamiltonian is simultaneously a unique ground state of another 2-local
Hamiltonian, hence is uniquely determined by its 2-matrix. And a weaker version
of this conjecture states that any non-degenerate excited state of a 2-local
Hamiltonian is uniquely determined by its 2-matrix among all the pure
-particle states. We construct explicit counterexamples to show that both
conjectures are false. It means that correlations in excited states of local
Hamiltonians could be dramatically different from those in ground states. We
further show that any non-degenerate excited state of a -local Hamiltonian
is a unique ground state of another -local Hamiltonian, hence is uniquely
determined by its -RDMs (or -matrix)
Experimental Implementation of a Codeword Stabilized Quantum Code
A five-qubit codeword stabilized quantum code is implemented in a seven-qubit
system using nuclear magnetic resonance (NMR). Our experiment implements a good
nonadditive quantum code which encodes a larger Hilbert space than any
stabilizer code with the same length and capable of correcting the same kind of
errors. The experimentally measured quantum coherence is shown to be robust
against artificially introduced errors, benchmarking the success in
implementing the quantum error correction code. Given the typical decoherence
time of the system, our experiment illustrates the ability of coherent control
to implement complex quantum circuits for demonstrating interesting results in
spin qubits for quantum computing
Local unitary versus local Clifford equivalence of stabilizer and graph states
The equivalence of stabilizer states under local transformations is of
fundamental interest in understanding properties and uses of entanglement. Two
stabilizer states are equivalent under the usual stochastic local operations
and classical communication criterion if and only if they are equivalent under
local unitary (LU) operations. More surprisingly, under certain conditions, two
LU equivalent stabilizer states are also equivalent under local Clifford (LC)
operations, as was shown by Van den Nest et al. [Phys. Rev. \textbf{A71},
062323]. Here, we broaden the class of stabilizer states for which LU
equivalence implies LC equivalence () to include all
stabilizer states represented by graphs with neither cycles of length 3 nor 4.
To compare our result with Van den Nest et al.'s, we show that any stabilizer
state of distance is beyond their criterion. We then further prove
that holds for a more general class of stabilizer states
of . We also explicitly construct graphs representing
stabilizer states which are beyond their criterion: we identify all 58 graphs
with up to 11 vertices and construct graphs with () vertices
using quantum error correcting codes which have non-Clifford transversal gates.Comment: Revised version according to referee's comments. To appear in
Physical Review
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