7,185 research outputs found
Ground-State Properties of a Heisenberg Spin Glass Model with a Hybrid Genetic Algorithm
We developed a genetic algorithm (GA) in the Heisenberg model that combines a
triadic crossover and a parameter-free genetic algorithm. Using the algorithm,
we examined the ground-state stiffness of the Heisenberg model in three
dimensions up to a moderate size range. Results showed the stiffness constant
of in the periodic-antiperiodic boundary condition method and that
of in the open-boundary-twist method. We considered the
origin of the difference in between the two methods and suggested that
both results show the same thing: the ground state of the open system is stable
against a weak perturbation.Comment: 11 pages, 5 figure
NMR evidence for the persistence of spin-superlattice above the 1/8 magnetization plateau in SrCu2(BO3)2
We present 11B NMR studies of the 2D frustrated dimer spin system SrCu2(BO3)2
in the field range 27-31 T covering the upper phase boundary of the 1/8
magnetization plateau, identified at 28.4 T. Our data provide a clear evidence
that above 28.4 T the spin-superlattice of the 1/8 plateau is modified but does
not melt even though the magnetization increases. Although this is precisely
what is expected for a supersolid phase, the microscopic nature of this new
phase is much more complex. We discuss the field-temperature phase diagram on
the basis of our NMR data.Comment: 5 pages, 4 figures, published versio
A simulation of high energy cosmic ray propagation 1
High energy cosmic ray propagation of the energy region 10 to the 14.5 power - 10 to the 18th power eV is simulated in the inter steller circumstances. In conclusion, the diffusion process by turbulent magnetic fields is classified into several regions by ratio of the gyro-radius and the scale of turbulence. When the ratio becomes larger then 10 to the minus 0.5 power, the analysis with the assumption of point scattering can be applied with the mean free path E sup 2. However, when the ratio is smaller than 10 to the minus 0.5 power, we need a more complicated analysis or simulation. Assuming the turbulence scale of magnetic fields of the Galaxy is 10-30pc and the mean magnetic field strength is 3 micro gauss, the energy of cosmic ray with that gyro-radius is about 10 to the 16.5 power eV
Revisit Behavior in Social Media: The Phoenix-R Model and Discoveries
How many listens will an artist receive on a online radio? How about plays on
a YouTube video? How many of these visits are new or returning users? Modeling
and mining popularity dynamics of social activity has important implications
for researchers, content creators and providers. We here investigate the effect
of revisits (successive visits from a single user) on content popularity. Using
four datasets of social activity, with up to tens of millions media objects
(e.g., YouTube videos, Twitter hashtags or LastFM artists), we show the effect
of revisits in the popularity evolution of such objects. Secondly, we propose
the Phoenix-R model which captures the popularity dynamics of individual
objects. Phoenix-R has the desired properties of being: (1) parsimonious, being
based on the minimum description length principle, and achieving lower root
mean squared error than state-of-the-art baselines; (2) applicable, the model
is effective for predicting future popularity values of objects.Comment: To appear on European Conference on Machine Learning and Principles
and Practice of Knowledge Discovery in Databases 201
Attracting shallow donors: Hydrogen passivation in (Al,Ga,In)-doped ZnO
The hydrogen interstitial and the substitutional Al_Zn, Ga_Zn and In_Zn are
all shallow donors in ZnO and lead to n-type conductivity. Although shallow
donors are expected to repel each other, we show by first principles
calculations that in ZnO these shallow donor impurities attract and form a
complex, leading to a donor level deep in the band gap. This puts a limit on
the n-type conductivity of (Al,Ga,In)-doped ZnO in the presence of hydrogen.Comment: 4 pages, 5 figure
Square Peg Problem in 2-Dimensional Lattice
The Square Peg Problem, also known as the inscribed square problem poses a question: Does every simple closed curve contain all four points of a square? This project introduces a new approach in proving the square peg problem in 2-dimensional lattice.
To accomplish the result, this research first defines the simple closed curve on 2-dimensional lattice. Then we identify the existence of inscribed half-squares, which are the set of three points of a square, in a lattice simple closed curve. Then we finally add a last point to form a half-square into a square to examine whether all four points of a square exist in a lattice simple closed curve. A sage program was used to find all missing corners of all inscribed half-squares. This has enabled us to look at the pattern of sets of all missing corners in specific shapes like rectangles.
By the end, we were able to conjecture that there exist missing corners in the interior and the exterior of the lattice simple closed curve unless the shape is a square. It is obvious that the square has an inscribed square. Hence if we could prove that the set of all missing corners is connected, we could give a new proof of the square peg problem in 2-dimensional lattice
An improved method for determining the DC magnetization curve using a ring specimen
When the DC magnetization curve (B-H) of nonoriented material is measured in a ring specimen, there is an intrinsic error due to the assumption that the mean magnetic path length is equal to the mean geometric path length. A novel method for determining the B-H curve accurately is proposed. The validity of the method is verified by experiments</p
A fresh look on the flux tube in Abelian-projected SU(2) gluodynamics
We reconsider the properties of the flux tube within
Abelian-projected SU(2) lattice gauge theory in terms of electric field and
monopole current. In the maximal Abelian gauge we assess the influence of the
Gribov copies on the apparent flux-tube profile. For the optimal gauge fixing
we study the independence of the profile on the lattice spacing for
2.3, 2.4, and 2.5115 on a lattice. We decompose the Abelian Wilson loop
into monopole and photon parts and compare the electric and monopole profile
emerging from different sources with the field strength and monopole current
within the dual Ginzburg-Landau theory.Comment: 3 pages, 6 figures, Lattice2002(topology
Compact Claude cycle refrigerator for laboratory use
A Claude cycle refrigerator with a three stage reciprocating expansion engine is described. Instead of a cam mechanism, valves are driven directly by magnetic solenoids operated by means of a micro processor control system. A swash plate mechanism is used to convert reciprocating motion of the expander pistons to rotary motion. A refrigeration capacity of 8 watts was achieved at 4.5 K with the operating pressure of 1.1 MPa and flow rate of 2.4 g/sec.. An effect of overintake operation was studied. Experimental results show that the efficiency of the expander has a peak point in the region of overintake operation with constant cycle speed, which agrees with theoretical results. The electrically controlled valve system is useful to vary the valve timing to achieve an optimum condition of operation
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