2,739 research outputs found
Direct current arc-plasma synthesis of B-C powder product
Measurement of blood oxygen saturation in biological tissue is of great interest for medical applications as it allows the detection of pathological alterations. Fibre based re-emission spectroscopy enables this parameter to be determined minimally-invasively in organ tissue inside the human body. In this report a measurement system for the contactless determination of blood oxygenation, as well as simulations regarding light diffusion in tissue are presented
Boundary quantum critical phenomena with entanglement renormalization
We extend the formalism of entanglement renormalization to the study of
boundary critical phenomena. The multi-scale entanglement renormalization
ansatz (MERA), in its scale invariant version, offers a very compact
approximation to quantum critical ground states. Here we show that, by adding a
boundary to the scale invariant MERA, an accurate approximation to the critical
ground state of an infinite chain with a boundary is obtained, from which one
can extract boundary scaling operators and their scaling dimensions. Our
construction, valid for arbitrary critical systems, produces an effective chain
with explicit separation of energy scales that relates to Wilson's RG
formulation of the Kondo problem. We test the approach by studying the quantum
critical Ising model with free and fixed boundary conditions.Comment: 8 pages, 12 figures, for a related work see arXiv:0912.289
Π Π²ΠΎΠΏΡΠΎΡΡ ΠΎΠΏΡΠ΅Π΄Π΅Π»Π΅Π½ΠΈΡ ΠΎΠΊΡΠ°Π½ΠΎΠ²ΡΡ ΠΈ ΡΠ΅ΡΠ°Π½ΠΎΠ²ΡΡ ΡΠΈΡΠ΅Π» ΡΠ°ΡΡΠ΅ΡΠ½ΡΠΌ ΠΌΠ΅ΡΠΎΠ΄ΠΎΠΌ
Π£ΡΡΠ°Π½ΠΎΠ²Π»Π΅Π½Π° ΡΠ²ΡΠ·Ρ ΠΎΠΊΡΠ°Π½ΠΎΠ²ΠΎΠ³ΠΎ ΡΠΈΡΠ»Π° ΠΌΠΎΡΠΎΡΠ½ΡΡ
ΡΠΎΠΏΠ»ΠΈΠ² Ρ ΠΈΡ
ΠΎΡΠ½ΠΎΡΠΈΡΠ΅Π»ΡΠ½ΠΎΠΉ ΠΏΠ»ΠΎΡΠ½ΠΎΡΡΡΡ ΠΈ Π³ΡΡΠΏΠΏΠΎΠ²ΡΠΌ ΡΠ³Π»Π΅Π²ΠΎΠ΄ΠΎΡΠΎΠ΄Π½ΡΠΌ ΡΠΎΡΡΠ°Π²ΠΎΠΌ, Π° ΡΠ΅ΡΠ°Π½ΠΎΠ²ΠΎΠ³ΠΎ ΡΠΈΡΠ»Π° - Ρ ΠΎΡΠ½ΠΎΡΠΈΡΠ΅Π»ΡΠ½ΠΎΠΉ ΠΏΠ»ΠΎΡΠ½ΠΎΡΡΡΡ, Π²ΡΠ·ΠΊΠΎΡΡΡΡ, ΡΠ΅ΠΌΠΏΠ΅ΡΠ°ΡΡΡΠ°ΠΌΠΈ Π·Π°ΡΡΡΠ²Π°Π½ΠΈΡ ΠΈ Π²ΡΠΏΡΡΠΊΠΈ, ΡΠΎΠ΄Π΅ΡΠΆΠ°Π½ΠΈΠ΅ΠΌ ΡΠ΅ΡΡ. ΠΠ½Π°Π»ΠΈΠ·ΠΎΠΌ ΠΌΠ°ΡΡΠΈΡ ΠΊΠΎΡΡΡΠΈΡΠΈΠ΅Π½ΡΠΎΠ² ΠΊΠΎΡΡΠ΅Π»ΡΡΠΈΠΈ Π²ΡΠ±ΡΠ°Π½Ρ Π°ΡΠ³ΡΠΌΠ΅Π½ΡΡ ΡΡΠ°Π²Π½Π΅Π½ΠΈΠΉ ΡΠ΅Π³ΡΠ΅ΡΡΠΈΠΈ. ΠΡΠΎΠ²Π΅ΡΠΊΠ° ΠΏΠΎΠ»ΡΡΠ΅Π½Π½ΡΡ
ΡΡΠ°Π²Π½Π΅Π½ΠΈΠΉ Π΄Π°Π»Π° ΡΠ΄ΠΎΠ²Π»Π΅ΡΠ²ΠΎΡΠΈΡΠ΅Π»ΡΠ½ΡΠ΅ ΡΠ΅Π·ΡΠ»ΡΡΠ°ΡΡ
The scattering from generalized Cantor fractals
We consider a fractal with a variable fractal dimension, which is a
generalization of the well known triadic Cantor set. In contrast with the usual
Cantor set, the fractal dimension is controlled using a scaling factor, and can
vary from zero to one in one dimension and from zero to three in three
dimensions. The intensity profile of small-angle scattering from the
generalized Cantor fractal in three dimensions is calculated. The system is
generated by a set of iterative rules, each iteration corresponding to a
certain fractal generation. Small-angle scattering is considered from
monodispersive sets, which are randomly oriented and placed. The scattering
intensities represent minima and maxima superimposed on a power law decay, with
the exponent equal to the fractal dimension of the scatterer, but the minima
and maxima are damped with increasing polydispersity of the fractal sets. It is
shown that for a finite generation of the fractal, the exponent changes at
sufficiently large wave vectors from the fractal dimension to four, the value
given by the usual Porod law. It is shown that the number of particles of which
the fractal is composed can be estimated from the value of the boundary between
the fractal and Porod regions. The radius of gyration of the fractal is
calculated analytically.Comment: 8 pages, 4 figures, accepted for publication in J. Appl. Crys
ΠΠ»ΠΈΡΠ½ΠΈΠ΅ Π³Π°Π·ΠΎΠ²ΠΎΠΉ ΡΠ°Π·Ρ Π½Π° Π²Π΅Π»ΠΈΡΠΈΠ½Ρ ΡΠΎΠΊΠ° Π² ΡΡΠ΅ΠΉΠΊΠ΅ Π±Π΅ΡΠΊΠΎΠ½ΡΠ°ΠΊΡΠ½ΠΎΠ³ΠΎ Π²ΠΎΡΡΡΠ°Π½ΠΎΠ²Π»Π΅Π½ΠΈΡ
ΠΠ»Ρ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΡ ΠΏΡΠΎΡΠ΅ΡΡΠ° Π²ΠΎΡΡΡΠ°Π½ΠΎΠ²Π»Π΅Π½ΠΈΡ ΠΎΠΊΠΈΡΠΈ ΠΆΠ΅Π»Π΅Π·Π° ΡΠ³Π»Π΅ΡΠΎΠ΄ΠΎΠΌ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½Π° ΠΌΠ΅ΡΠΎΠ΄ΠΈΠΊΠ°, ΠΎΡΠ½ΠΎΠ²Π°Π½Π½Π°Ρ Π½Π° ΠΈΠ·ΠΌΠ΅ΡΠ΅Π½ΠΈΠΈ ΡΠΎΠΊΠ°, Π²ΠΎΠ·Π½ΠΈΠΊΠ°ΡΡΠ΅Π³ΠΎ ΠΌΠ΅ΠΆΠ΄Ρ Π½Π°Π³ΡΠ΅ΡΡΠΌΠΈ ΡΠ΅Π»Π°ΠΌΠΈ. Π‘ ΡΡΠΎΠΉ ΡΠ΅Π»ΡΡ ΡΠΊΠΎΠ½ΡΡΡΡΠΈΡΠΎΠ²Π°Π½Π° ΠΊΠ²Π°ΡΡΠ΅Π²Π°Ρ ΡΡΠ΅ΠΉΠΊΠ°, ΠΏΠΎΠ·Π²ΠΎΠ»ΡΡΡΠ°Ρ ΠΆΠ΅ΡΡΠΊΠΎ ΡΡΡΠ°Π½Π°Π²Π»ΠΈΠ²Π°ΡΡ ΠΎΠ±ΡΠ°Π·ΡΡ Π³ΡΠ°ΡΠΈΡΠ° ΠΈ ΠΎΠΊΠΈΡΠΈ ΠΆΠ΅Π»Π΅Π·Π° Π½Π° ΠΎΠΏΡΠ΅Π΄Π΅Π»Π΅Π½Π½ΠΎΠΌ ΡΠ°ΡΡΡΠΎΡΠ½ΠΈΠΈ Π΄ΡΡΠ³ ΠΎΡ Π΄ΡΡΠ³Π°. ΠΠ·ΡΡΠ΅Π½ΠΎ Π²Π»ΠΈΡΠ½ΠΈΠ΅ ΠΎΡΠ΄Π΅Π»ΡΠ½ΡΡ
ΡΠ΅Π°ΠΊΡΠΈΠΉ Π½Π° ΠΊΠ°ΠΆΠ΄ΠΎΠΌ ΡΠ»Π΅ΠΊΡΡΠΎΠ΄Π΅ Π½Π° ΡΡΠΌΠΌΠ°ΡΠ½ΡΠΉ ΡΠΎΠΊ. ΠΠ»Ρ ΡΡΠΎΠ³ΠΎ ΠΏΡΠΎΠ²Π΅Π΄Π΅Π½Π° ΡΠ΅ΡΠΈΡ ΠΎΠΏΡΡΠΎΠ² Π² Π½Π΅ΠΉΡΡΠ°Π»ΡΠ½ΠΎΠΉ, ΠΎΠΊΠΈΡΠ»Π΅Π½Π½ΠΎΠΉ ΠΈ Π²ΠΎΡΡΡΠ°Π½ΠΎΠ²ΠΈΡΠ΅Π»ΡΠ½ΠΎΠΉ Π°ΡΠΌΠΎΡΡΠ΅ΡΠ°Ρ
. Π£ΡΡΠ°Π½ΠΎΠ²Π»Π΅Π½ΠΎ, ΡΡΠΎ ΠΎΠΊΠΈΡΠ»Π΅Π½ΠΈΠ΅ Π³ΡΠ°ΡΠΈΡΠ° Π² ΡΡΠ΅Π΄Π΅ Π²ΠΎΠ·Π΄ΡΡ
Π° ΡΠΎΠΏΡΠΎΠ²ΠΎΠΆΠ΄Π°Π΅ΡΡΡ Π²ΠΎΠ·ΡΠ°ΡΡΠ°Π½ΠΈΠ΅ΠΌ ΡΠΎΠΊΠ° ΠΏΠΎΠ»ΠΎΠΆΠΈΡΠ΅Π»ΡΠ½ΠΎΠΉ ΠΏΠΎΠ»ΡΡΠ½ΠΎΡΡΠΈ. Π ΡΡΠ΅Π΄Π΅ Π²ΠΎΠ΄ΠΎΡΠΎΠ΄Π° Π·Π½Π°ΡΠ΅Π½ΠΈΡ ΡΠΎΠΊΠ° Π½Π΅Π²Π΅Π»ΠΈΠΊΠΈ. Π Π½Π΅ΠΉΡΡΠ°Π»ΡΠ½ΠΎΠΉ ΡΡΠ΅Π΄Π΅ Π³Π΅Π»ΠΈΡ ΡΠΎΠΊ ΠΈΠΌΠ΅Π΅Ρ ΠΏΠΎΠ»ΠΎΠΆΠΈΡΠ΅Π»ΡΠ½ΡΡ ΠΏΠΎΠ»ΡΡΠ½ΠΎΡΡΡ, Π° Π²Π΅Π»ΠΈΡΠΈΠ½Π° Π΅Π³ΠΎ Π½Π΅ Π·Π°Π²ΠΈΡΠΈΡ ΠΎΡ ΠΏΡΠΈΡΡΡΡΡΠ²ΠΈΡ ΡΠΎΠ³ΠΎ ΠΈΠ»ΠΈ ΠΈΠ½ΠΎΠ³ΠΎ ΡΠ΅Π°Π³Π΅Π½ΡΠ°. ΠΠ΅ΠΎΠ±Ρ
ΠΎΠ΄ΠΈΠΌΠ° Π΄Π°Π»ΡΠ½Π΅ΠΉΡΠ°Ρ ΡΠ°Π±ΠΎΡΠ° ΠΏΠΎ ΠΏΠΎΠ²ΡΡΠ΅Π½ΠΈΡ Π²Π΅Π»ΠΈΡΠΈΠ½Ρ ΠΏΠΎΠ»Π΅Π·Π½ΠΎΠ³ΠΎ ΡΠΈΠ³Π½Π°Π»Π° Π² ΡΠ΅ΒΠ³ΠΈΡΡΡΠΈΡΡΠ΅ΠΌΠΎΠΌ ΡΠΎΠΊΠ΅
He Scattering from Random Adsorbates, Disordered Compact Islands and Fractal Submonolayers: Intensity Manifestations of Surface Disorder
A theoretical study is made on He scattering from three fundamental classes
of disordered ad-layers: (a) Translationally random adsorbates, (b) disordered
compact islands and (c) fractal submonolayers. The implications of the results
to experimental studies of He scattering from disordered surfaces are
discussed, and a combined experimental-theoretical study is made for Ag
submonolayers on Pt(111). Some of the main theoretical findings are: (1)
Structural aspects of the calculated intensities from translationally random
clusters were found to be strongly correlated with those of individual
clusters. (2) Low intensity Bragg interference peaks appear even for scattering
from very small ad-islands, and contain information on the ad-island local
electron structure. (3) For fractal islands, just as for islands with a
different structure, the off-specular intensity depends on the parameters of
the He/Ag interaction, and does not follow a universal power law as previously
proposed in the literature. In the experimental-theoretical study of Ag on
Pt(111), we use first experimental He scattering data from low-coverage (single
adsorbate) systems to determine an empirical He/Ag-Pt potential of good
quality. Then, we carry out He scattering calculations for high coverage and
compare with experiments. The conclusions are that the actual experimental
phase corresponds to small compact Ag clusters of narrow size distribution,
translationally disordered on the surface.Comment: 36 double-spaced pages, 10 figures; accepted by J. Chem. Phys.,
scheduled to appear March 8. More info available at
http://www.fh.huji.ac.il/~dani
Matrix product decomposition and classical simulation of quantum dynamics in the presence of a symmetry
We propose a refined matrix product state representation for many-body
quantum states that are invariant under SU(2) transformations, and indicate how
to extend the time-evolving block decimation (TEBD) algorithm in order to
simulate time evolution in an SU(2) invariant system. The resulting algorithm
is tested in a critical quantum spin chain and shown to be significantly more
efficient than the standard TEBD.Comment: 5 pages, 4 figure
A system of relational syllogistic incorporating full Boolean reasoning
We present a system of relational syllogistic, based on classical
propositional logic, having primitives of the following form:
Some A are R-related to some B;
Some A are R-related to all B;
All A are R-related to some B;
All A are R-related to all B.
Such primitives formalize sentences from natural language like `All students
read some textbooks'. Here A and B denote arbitrary sets (of objects), and R
denotes an arbitrary binary relation between objects. The language of the logic
contains only variables denoting sets, determining the class of set terms, and
variables denoting binary relations between objects, determining the class of
relational terms. Both classes of terms are closed under the standard Boolean
operations. The set of relational terms is also closed under taking the
converse of a relation. The results of the paper are the completeness theorem
with respect to the intended semantics and the computational complexity of the
satisfiability problem.Comment: Available at
http://link.springer.com/article/10.1007/s10849-012-9165-
Open-Ended Evolutionary Robotics: an Information Theoretic Approach
This paper is concerned with designing self-driven fitness functions for
Embedded Evolutionary Robotics. The proposed approach considers the entropy of
the sensori-motor stream generated by the robot controller. This entropy is
computed using unsupervised learning; its maximization, achieved by an on-board
evolutionary algorithm, implements a "curiosity instinct", favouring
controllers visiting many diverse sensori-motor states (sms). Further, the set
of sms discovered by an individual can be transmitted to its offspring, making
a cultural evolution mode possible. Cumulative entropy (computed from ancestors
and current individual visits to the sms) defines another self-driven fitness;
its optimization implements a "discovery instinct", as it favours controllers
visiting new or rare sensori-motor states. Empirical results on the benchmark
problems proposed by Lehman and Stanley (2008) comparatively demonstrate the
merits of the approach
Dynamic Scaling of an Adsorption-Diffusion Process on Fractals
A dynamic scaling of a diffusion process involving the Langmuir type
adsorption is studied. We find dynamic scaling functions in one and two
dimensions and compare them with direct numerical simulations, and we further
study the dynamic scaling law on fractal surfaces. The adsorption-diffusion
process obeys the fracton dynamics on the fractal surfaces.Comment: 9 pages, 7 figure
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