2,934 research outputs found
Influence of geometries on the assembly of snowman-shaped Janus nanoparticles
The self-assembly of micro/nanoparticles into suprastructures is a promising way to develop reconfigurable materials and to gain insights into the fundamental question of how matter organizes itself. The geometry of particles, especially those deviating from perfectly spherical shapes, is of significant importance in colloidal assembly because it influences the particle "recognition", determines the particle packing, and ultimately dictates the formation of assembled suprastructures. In order to organize particles into desired structures, it is of vital importance to understand the relationship between the shape of the colloidal building blocks and the assembled suprastructures. This fundamental issue is an enduring topic in the assembly of molecular surfactants, but it remained elusive in colloidal assembly. To address this issue, we use snowman-shaped Janus nanoparticles (JNPs) as a model to systematically study the effect of colloidal geometries on their assembled suprastructures. Ten types of JNPs with identical chemical compositions but with different geometries were synthesized. Specifically, the synthesized JNPs differ in their lobe size ratios, phase separation degrees, and overall sizes. We show that by altering these parameters, both finite suprastructures, such as capsules with different curvatures, and nonfinite suprastructures, including free-standing single-layered or double-layered JNPs sheets, can be obtained via self-assembly. All these different types of suprastructures are constituted by highly oriented and hexagonally packed JNPs. These findings demonstrate the significance of geometries in colloidal assembly, such that slightly changing the building block geometries could result in a large variety of very different assembled structures, without altering the chemistry of the particles
Upper bounds for the bondage number of graphs on topological surfaces
The bondage number b(G) of a graph G is the smallest number of edges of G
whose removal from G results in a graph having the domination number larger
than that of G. We show that, for a graph G having the maximum vertex degree
and embeddable on an orientable surface of genus h and a
non-orientable surface of genus k, . This generalizes known upper bounds for planar and toroidal
graphs.Comment: 10 pages; Updated version (April 2011); Presented at the 7th ECCC,
Wolfville (Nova Scotia, Canada), May 4-6, 2011, and the 23rd BCC, Exeter
(England, UK), July 3-8, 201
The bondage number of graphs on topological surfaces and Teschner's conjecture
The bondage number of a graph is the smallest number of its edges whose
removal results in a graph having a larger domination number. We provide
constant upper bounds for the bondage number of graphs on topological surfaces,
improve upper bounds for the bondage number in terms of the maximum vertex
degree and the orientable and non-orientable genera of the graph, and show
tight lower bounds for the number of vertices of graphs 2-cell embeddable on
topological surfaces of a given genus. Also, we provide stronger upper bounds
for graphs with no triangles and graphs with the number of vertices larger than
a certain threshold in terms of the graph genera. This settles Teschner's
Conjecture in positive for almost all graphs.Comment: 21 pages; Original version from January 201
Cell Stimulation and Calcium Mobilization by Picosecond Electric Pulses
We tested if picosecond electric pulses (psEP; 190 kV/cm, 500 ps at 50% height), which are much shorter than channel activation time, can activate voltage-gated (VG) channels. Cytosolic Ca2+ was monitored by Fura-2 ratiometric imaging in GH3 and NG108 cells (which express multiple types of VG calcium channels, VGCC), and in CHO cells (which express no VGCC). Trains of up to 100 psEP at 1 kHz elicited no response in CHO cells. However, even a single psEP significantly increased Ca2+ in both GH3 (by 114 +/- 48 nM) and NG108 cells (by 6 +/- 1.1 nM). Trains of 100 psEP amplified the response to 379 +/- 33 nM and 719 +/- 315 nM, respectively. Ca2+ responses peaked within 2-15 s and recovered for over 100 s; they were 80-100% inhibited by verapamil and omega-conotoxin, but not by the substitution of Na+ with N-methyl-D-glucamine. There was no response to psEP in Ca2+-free medium, but adding external Ca2+ even 10 s later evoked Ca2+ response. We conclude that electrical stimuli as short as 500 ps can cause long-lasting opening of VGCC by a mechanism which does not involve conventional electroporation, heating (which was under 0.06 K per psEP), or membrane depolarization by opening of VG Na+ channels
Fusion of the -Vertex Operators and its Application to Solvable Vertex Models
We diagonalize the transfer matrix of the inhomogeneous vertex models of the
6-vertex type in the anti-ferroelectric regime intoducing new types of q-vertex
operators. The special cases of those models were used to diagonalize the s-d
exchange model\cite{W,A,FW1}. New vertex operators are constructed from the
level one vertex operators by the fusion procedure and have the description by
bosons. In order to clarify the particle structure we estabish new isomorphisms
of crystals. The results are very simple and figure out representation
theoretically the ground state degenerations.Comment: 35 page
Parity effect and spontaneous currents in superconducting nanorings
New physical effects emerge from an interplay between the electron parity
number and persistent currents in superconducting nanorings. An odd electron,
being added to the ring, produces a countercurrent which may substantially
modify the ground state properties of the system. In superconducting nanorings
with an embedded normal metal layer a novel ``-junction'' state can
occur for the odd number of electrons. Changing this number from even to odd
yields spontaneous supercurrent in the ground state of such rings without any
externally applied magnetic flux. Further peculiar features of the parity
effect are expected in structures with resonant electron transport across the
weak link.Comment: 9 pages, 5 figures. Invited talk at the International Conference
"Frontiers of Quantum and Mesoscopic Thermodynamics", Prague, July 200
Consensus clustering and supervised classification for profiling phishing emails in internet commerce security
This article investigates internet commerce security applications of a novel combined method, which uses unsupervised consensus clustering algorithms in combination with supervised classification methods. First, a variety of independent clustering algorithms are applied to a randomized sample of data. Second, several consensus functions and sophisticated algorithms are used to combine these independent clusterings into one final consensus clustering. Third, the consensus clustering of the randomized sample is used as a training set to train several fast supervised classification algorithms. Finally, these fast classification algorithms are used to classify the whole large data set. One of the advantages of this approach is in its ability to facilitate the inclusion of contributions from domain experts in order to adjust the training set created by consensus clustering. We apply this approach to profiling phishing emails selected from a very large data set supplied by the industry partners of the Centre for Informatics and Applied Optimization. Our experiments compare the performance of several classification algorithms incorporated in this scheme. © 2010 Springer-Verlag Berlin Heidelberg
Low Loss and Magnetic Field-tuned Superconducting THz Metamaterial
Superconducting terahertz (THz) metamaterial (MM) made from superconducting
Nb film has been investigated using a continuous-wave THz spectroscopy with a
superconducting split-coil magnet. The obtained quality factors of the resonant
modes at 132 GHz and 450 GHz are about three times as large as those calculated
for a metal THz MM operating at 1 K, which indicates that superconducting THz
MM is a very nice candidate to achieve low loss performance. In addition, the
magnetic field-tuning on superconducting THz MM is also demonstrated, which
offer an alternative tuning method apart from the existed electric, optical and
thermal tuning on THz MM
Charge Density Wave-Assisted Tunneling Between Hall Edge States
We study the intra-planar tunneling between quantum Hall samples separated by
a quasi one-dimensional barrier, induced through the interaction of edge
degrees of freedom with the charge density waves of a Hall crystal defined in a
parallel layer. A field theory formulation is set up in terms of bosonic
(2+1)-dimensional excitations coupled to (1+1)-dimensional fermions. Parity
symmetry is broken at the quantum level by the confinement of
soliton-antisoliton pairs near the tunneling region. The usual Peierls argument
allows to estimate the critical temperature , so that for mass
corrections due to longitudinal density fluctuations disappear from the edge
spectrum. We compute the gap dependence upon the random global phase of the
pinned charge density wave, as well as the effects of a voltage bias applied
across the tunneling junction.Comment: Additional references + 1 figure + more detailed discussions. To be
published in Phys. Rev.
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