3,821 research outputs found
Analytical technique for simplification of the encoder-decoder circuit for a perfect five-qubit error correction
Simpler encoding and decoding networks are necessary for more reliable
quantum error correcting codes (QECCs). The simplification of the
encoder-decoder circuit for a perfect five-qubit QECC can be derived
analytically if the QECC is converted from its equivalent one-way entanglement
purification protocol (1-EPP). In this work, the analytical method to simplify
the encoder-decoder circuit is introduced and a circuit that is as simple as
the existent simplest circuits is presented as an example. The encoder-decoder
circuit presented here involves nine single- and two-qubit unitary operations,
only six of which are controlled-NOT (CNOT) gates
Geometric and Statistical Properties of the Mean-Field HP Model, the LS Model and Real Protein Sequences
Lattice models, for their coarse-grained nature, are best suited for the
study of the ``designability problem'', the phenomenon in which most of the
about 16,000 proteins of known structure have their native conformations
concentrated in a relatively small number of about 500 topological classes of
conformations. Here it is shown that on a lattice the most highly designable
simulated protein structures are those that have the largest number of
surface-core switchbacks. A combination of physical, mathematical and
biological reasons that causes the phenomenon is given. By comparing the most
foldable model peptides with protein sequences in the Protein Data Bank, it is
shown that whereas different models may yield similar designabilities,
predicted foldable peptides will simulate natural proteins only when the model
incorporates the correct physics and biology, in this case if the main folding
force arises from the differing hydrophobicity of the residues, but does not
originate, say, from the steric hindrance effect caused by the differing sizes
of the residues.Comment: 12 pages, 10 figure
Majorana Zero-modes and Topological Phases of Multi-flavored Jackiw-Rebbi model
Motivated by the recent Kitaev's K-theory analysis of topological insulators
and superconductors, we adopt the same framework to study the topological phase
structure of Jackiw-Rebbi model in 3+1 dimensions. According to the K-theory
analysis based on the properties of the charge conjugation and time reversal
symmetries, we classify the topological phases of the model. In particular, we
find that there exist Majorana zero-modes hosted by the
hedgehogs/t'Hooft-Polyakov monopoles, if the model has a time reversal
symmetry. Guided by the K-theory results, we then explicitly show that a single
Majorana zero mode solution exists for the SU(2) doublet fermions in some
co-dimensional one planes of the mass parameter space. It turns out we can see
the existence of none or a single zero mode when the fermion doublet is only
two. We then take a step further to consider four-fermion case and find there
can be zero, one or two normalizable zero mode in some particular choices of
mass matrices. Our results also indicate that a single normalizable Majorana
zero mode can be compatible with the cancellation of SU(2) Witten anomaly.Comment: 29 pages, 3 figures; v2, typos correcte
Two novel approaches for photometric redshift estimation based on SDSS and 2MASS databases
We investigate two training-set methods: support vector machines (SVMs) and
Kernel Regression (KR) for photometric redshift estimation with the data from
the Sloan Digital Sky Survey Data Release 5 and Two Micron All Sky Survey
databases. We probe the performances of SVMs and KR for different input
patterns. Our experiments show that the more parameters considered, the
accuracy doesn't always increase, and only when appropriate parameters chosen,
the accuracy can improve. Moreover for different approaches, the best input
pattern is different. With different parameters as input, the optimal bandwidth
is dissimilar for KR. The rms errors of photometric redshifts based on SVM and
KR methods are less than 0.03 and 0.02, respectively. Finally the strengths and
weaknesses of the two approaches are summarized. Compared to other methods of
estimating photometric redshifts, they show their superiorities, especially KR,
in terms of accuracy.Comment: accepted for publication in ChJA
Prediction of Anisotropic Single-Dirac-Cones in BiSb Thin Films
The electronic band structures of BiSb thin films can be
varied as a function of temperature, pressure, stoichiometry, film thickness
and growth orientation. We here show how different anisotropic
single-Dirac-cones can be constructed in a BiSb thin film for
different applications or research purposes. For predicting anisotropic
single-Dirac-cones, we have developed an iterative-two-dimensional-two-band
model to get a consistent inverse-effective-mass-tensor and band-gap, which can
be used in a general two-dimensional system that has a non-parabolic dispersion
relation as in a BiSb thin film system
A cross-layer architecture to improve mobile host rate performance and to solve unfairness problem in WLANs
The evolution of the Internet has been mainly promoted in recent years by the emergence and pro- liferation of wireless access networks towards a global ambient and pervasive network accessed from mobile devices. These new access networks have introduced new MAC layers independently of the legacy "wire- oriented" protocols that are still at the heart of the pro- tocol stacks of the end systems. This principle of isola- tion and independence between layers advocated by the OSI model has its drawbacks of maladjustment between new access methods and higher-level protocols built on the assumption of a wired Internet. In this paper, we introduce and deliver solutions for several pathologi- cal communication behaviors resulting from the malad- justment between WLAN MAC and higher layer stan- dard protocols such as TCP/IP and UDP/IP. Specially, based on an efficient analytical model for WLANs band- width estimation, we address in this paper the two fol- lowing issues: 1) Performance degradation due to the lack of flow control between the MAC and upper layer resulting in potential MAC buffer overflow; 2) Unfair bandwidth share issues between various type of flows. We show how these syndromes can be efficiently solved from neutral "cross layer" interactions which entail no changes in the considered protocols and standards
Ambipolar Field Effect in Topological Insulator Nanoplates of (BixSb1-x)2Te3
Topological insulators represent a new state of quantum matter attractive to
both fundamental physics and technological applications such as spintronics and
quantum information processing. In a topological insulator, the bulk energy gap
is traversed by spin-momentum locked surface states forming an odd number of
surface bands that possesses unique electronic properties. However, transport
measurements have often been dominated by residual bulk carriers from crystal
defects or environmental doping which mask the topological surface
contribution. Here we demonstrate (BixSb1-x)2Te3 as a tunable topological
insulator system to manipulate bulk conductivity by varying the Bi/Sb
composition ratio. (BixSb1-x)2Te3 ternary compounds are confirmed as
topological insulators for the entire composition range by angle resolved
photoemission spectroscopy (ARPES) measurements and ab initio calculations.
Additionally, we observe a clear ambipolar gating effect similar to that
observed in graphene using nanoplates of (BixSb1-x)2Te3 in
field-effect-transistor (FET) devices. The manipulation of carrier type and
concentration in topological insulator nanostructures demonstrated in this
study paves the way for implementation of topological insulators in
nanoelectronics and spintronics.Comment: 7 pages, 4 figure
Mean-Field HP Model, Designability and Alpha-Helices in Protein Structures
Analysis of the geometric properties of a mean-field HP model on a square
lattice for protein structure shows that structures with large number of switch
backs between surface and core sites are chosen favorably by peptides as unique
ground states. Global comparison of model (binary) peptide sequences with
concatenated (binary) protein sequences listed in the Protein Data Bank and the
Dali Domain Dictionary indicates that the highest correlation occurs between
model peptides choosing the favored structures and those portions of protein
sequences containing alpha-helices.Comment: 4 pages, 2 figure
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