444 research outputs found
ΠΠ½Π°Π»ΠΈΠ· ΡΡΡΠ΅ΠΊΡΠΈΠ²Π½ΠΎΡΡΠΈ ΠΏΡΠΎΡΠ΅ΡΡΠΎΠ² ΠΏΠ»Π°Π½ΠΈΡΠΎΠ²Π°Π½ΠΈΡ ΡΠ»Π΅ΠΊΡΡΠΎΡΠ½Π°Π±ΠΆΠ΅Π½ΠΈΡ Π² Π₯Π°ΡΡΠΊΠΎΠ²ΡΠΊΠΎΠΌ ΡΠ΅Π³ΠΈΠΎΠ½Π΅
ΠΡΠ΅ΠΊΡΠΈΠ²Π½ΡΡΡΡ ΠΏΡΠΎΡΠ΅ΡΡΠ² Π΅Π»Π΅ΠΊΡΡΠΎΠΏΠΎΡΡΠ°ΡΠ°Π½Π½Ρ Π·Π°ΠΏΡΠΎΠΏΠΎΠ½ΠΎΠ²Π°Π½ΠΎ ΠΎΡΡΠ½ΡΠ²Π°ΡΠΈ Π½Π΅ ΡΡΠ»ΡΠΊΠΈ Π²Π΅Π»ΠΈΡΠΈΠ½ΠΎΡ ΠΏΠΎΠΌΠΈΠ»ΠΊΠΈ ΠΏΡΠΎΠ³Π½ΠΎΠ·ΡΠ²Π°Π½Π½Ρ, Π° ΠΉ ΠΊΡΠ»ΡΠΊΡΡΡΡ Π½Π΅Π³Π°ΡΠΈΠ²Π½ΠΈΡ
Ρ ΠΏΠΎΠ·ΠΈΡΠΈΠ²Π½ΠΈΡ
ΠΏΠΎΠΌΠΈΠ»ΠΎΠΊ, ΡΠΎ Π²ΠΈΠΌΡΡΡΡΡΡΡΡ Π·Π° ΠΌΠ΅ΡΠΎΠ΄ΠΈΠΊΠΎΡ Π’Π΅ΠΉΠ»Π°. ΠΠΈΠΊΠΎΠ½Π°Π½ΠΎ Π°Π½Π°Π»ΡΠ· ΠΏΠ»Π°Π½ΠΎΠ²Π°Π½ΠΈΡ
Ρ ΡΠ°ΠΊΡΠΈΡΠ½ΠΈΡ
Π΄ΠΎΠ±ΠΎΠ²ΠΈΡ
ΠΎΠ±ΡΡΠ³ΡΠ² Π΅Π»Π΅ΠΊΡΡΠΎΡΠΏΠΎΠΆΠΈΠ²Π°Π½Π½Ρ Π² Π₯Π°ΡΠΊΡΠ²ΡΡΠΊΠΎΠΌΡ ΡΠ΅Π³ΡΠΎΠ½Ρ Π² 2008 Ρ 2009 ΡΠΎΠΊΠ°Ρ
. ΠΡΡΠ½Π΅Π½ΠΎ ΠΏΠΎΠΌΠΈΠ»ΠΊΠΈ ΠΏΠ΅ΡΠ΅ΠΎΡΡΠ½ΠΊΠΈ Ρ Π½Π΅Π΄ΠΎΠΎΡΡΠ½ΠΊΠΈ ΡΠ°ΠΊΡΠΈΡΠ½ΠΈΡ
ΠΎΠ±ΡΡΠ³ΡΠ², ΠΎΠ±ΡΠΈΡΠ»Π΅Π½Ρ ΡΠΊΠ»Π°Π΄ΠΎΠ²Ρ Π·Π°Π³Π°Π»ΡΠ½ΠΎΡ ΠΏΠΎΠΌΠΈΠ»ΠΊΠΈ Ρ ΠΏΠΎΠΊΠ°Π·Π°Π½ΠΎ, ΡΠΎ ΠΏΠ΅ΡΠ΅Π²Π°ΠΆΠ°Ρ ΠΏΠΎΠΌΠΈΠ»ΠΊΠ° Π½Π΅ΠΏΠΎΠ²Π½ΠΎΡ ΠΊΠΎΠ²Π°ΡΡΠ°ΡΡΡ ΠΏΡΠΎΠ³Π½ΠΎΠ·ΠΎΠ²Π°Π½ΠΈΡ
Ρ ΡΠ°ΠΊΡΠΈΡΠ½ΠΈΡ
Π·Π½Π°ΡΠ΅Π½Ρ Π΄ΠΎΠ±ΠΎΠ²ΠΈΡ
ΠΎΠ±ΡΡΠ³ΡΠ² ΡΠΈΠ½ΠΊΡ ΡΠΏΠΎΠΆΠΈΠ²Π°ΡΡΠ² ΠΠ "Π₯Π°ΡΠΊΡΠ²ΠΎΠ±Π»Π΅Π½Π΅ΡΠ³ΠΎ".The effectiveness of the processes of electricity supply was offered to assess not only with the magnitude of forecasting error, but with the number of negative and positive errors, measured by the method of Theil. The analysis of planned and actual daily volume of electricity in Kharkov region in 2008 and 2009 is realized. Errors of revaluation and underestimation of actual volumes are estimated, components of the general error are calculated and shown that the error of incomplete covariance for predicted and actual values of daily volumes of the market of consumers ΠΠ of "Kharkovo-blenergo" prevails
Elevation, moisture and shade drive the functional and phylogenetic meadow communitiesβ assembly in the northeastern Tibetan Plateau
Despite a long history of alpine meadows studies, uncertainty remains about the importance of environmental factors in structuring their assembly. We examined the functional and phylogenetic structure of 170 alpine Tibetan meadow communities in relation to elevation, soil moisture and shade. Functional community structure was estimated with both communityweighted mean (CWM) trait values for specific leaf area (SLA), plant height and seed mass and functional diversity (Raoβs quadratic index) for their traits individually and in combination (multivariate functional diversity). We found that shade induced by woody plants significantly increased the phylogenetic diversity and functional diversity of SLA of co-occurring species, suggesting that woody plants behave as βecosystem engineersβ creating a different environment that allows the existence of shade tolerant species and thereby facilitates the coexistence of plant species with different light resource acquisition strategies. We also found evidence for a clear decrease in phylogenetic diversity, CWM and functional diversity related to plant height in the two extreme, both the dry and wet, soil moisture conditions. This indicates that both drought and excess moisture may act as environmental filters selecting species with close phylogenetic relationships and similar height. Moreover, we detected significant decreases in both CWM and functional diversity for seed mass along elevational gradients, suggesting that low net primary productivity (NPP) limits seed size. Finally, because of different individual trait responses to environmental factors, the multivariate functional diversity did not change across environmental gradients. This lack of multivariate response supports the hypothesis that multiple processes, such as environmental filtering, competition and facilitation, may operate simultaneously and exert opposing effects on community assembly along different niche (e.g., water use, light acquisition) axes, resulting in no overall functional community structure change. This contrast between individual and multivariate trait patterns highlights the importance of examining individual traits linked with different ecological processes to better understand the mechanisms of community assembly
Evidence for Complex Subleading Exponents from the High-Temperature Expansion of the Hierarchical Ising Model
Using a renormalization group method, we calculate 800 high-temperature
coefficients of the magnetic susceptibility of the hierarchical Ising model.
The conventional quantities obtained from differences of ratios of coefficients
show unexpected smooth oscillations with a period growing logarithmically and
can be fitted assuming corrections to the scaling laws with complex exponents.Comment: 10 pages, Latex , uses revtex. 2 figures not included (hard copies
available on request
Roughening Induced Deconstruction in (100) Facets of CsCl Type Crystals
The staggered 6-vertex model describes the competition between surface
roughening and reconstruction in (100) facets of CsCl type crystals. Its phase
diagram does not have the expected generic structure, due to the presence of a
fully-packed loop-gas line. We prove that the reconstruction and roughening
transitions cannot cross nor merge with this loop-gas line if these degrees of
freedom interact weakly. However, our numerical finite size scaling analysis
shows that the two critical lines merge along the loop-gas line, with strong
coupling scaling properties. The central charge is much larger than 1.5 and
roughening takes place at a surface roughness much larger than the conventional
universal value. It seems that additional fluctuations become critical
simultaneously.Comment: 31 pages, 9 figure
Monte Carlo simulation of ice models
We propose a number of Monte Carlo algorithms for the simulation of ice
models and compare their efficiency. One of them, a cluster algorithm for the
equivalent three colour model, appears to have a dynamic exponent close to
zero, making it particularly useful for simulations of critical ice models. We
have performed extensive simulations using our algorithms to determine a number
of critical exponents for the square ice and F models.Comment: 32 pages including 15 postscript figures, typeset in LaTeX2e using
the Elsevier macro package elsart.cl
Equilibrium shapes and faceting for ionic crystals of body-centered-cubic type
A mean field theory is developed for the calculation of the surface free
energy of the staggered BCSOS, (or six vertex) model as function of the surface
orientation and of temperature. The model approximately describes surfaces of
crystals with nearest neighbor attractions and next nearest neighbor
repulsions. The mean field free energy is calculated by expressing the model in
terms of interacting directed walks on a lattice. The resulting equilibrium
shape is very rich with facet boundaries and boundaries between reconstructed
and unreconstructed regions which can be either sharp (first order) or smooth
(continuous). In addition there are tricritical points where a smooth boundary
changes into a sharp one and triple points where three sharp boundaries meet.
Finally our numerical results strongly suggest the existence of conical points,
at which tangent planes of a finite range of orientations all intersect each
other. The thermal evolution of the equilibrium shape in this model shows
strong similarity to that seen experimentally for ionic crystals.Comment: 14 Pages, Revtex and 10 PostScript figures include
Phase transitions in a frustrated XY model with zig-zag couplings
We study a new generalized version of the square-lattice frustrated XY model
where unequal ferromagnetic and antiferromagnetic couplings are arranged in a
zig-zag pattern. The ratio between the couplings can be used to tune the
system, continuously, from the isotropic square-lattice to the
triangular-lattice frustrated XY model. The model can be physically realized as
a Josephson-junction array with two different couplings, in a magnetic field
corresponding to half-flux quanta per plaquette. Mean-field approximation,
Ginzburg-Landau expansion and finite-size scaling of Monte Carlo simulations
are used to study the phase diagram and critical behavior. Depending on the
value of , two separate transitions or a transition line in the
universality class of the XY-Ising model, with combined and U(1)
symmetries, takes place. In particular, the phase transitions of the standard
square-lattice and triangular-lattice frustrated XY models correspond to two
different cuts through the same transition line. Estimates of the chiral
() critical exponents on this transition line deviate significantly from
the pure Ising values, consistent with that along the critical line of the
XY-Ising model. This suggests that a frustrated XY model or Josephson-junction
array with a zig-zag coupling modulation can provide a physical realization of
the XY-Ising model critical line.Comment: 11 pages, 9 figures, RevTex, to appear in Phys. Rev.
Berry phase and adiabaticity of a spin diffusing in a non-uniform magnetic field
An electron spin moving adiabatically in a strong, spatially non-uniform
magnetic field accumulates a geometric phase or Berry phase, which might be
observable as a conductance oscillation in a mesoscopic ring. Two contradicting
theories exist for how strong the magnetic field should be to ensure
adiabaticity if the motion is diffusive. To resolve this controversy, we study
the effect of a non-uniform magnetic field on the spin polarization and on the
weak-localization effect. The diffusion equation for the Cooperon is solved
exactly. Adiabaticity requires that the spin-precession time is short compared
to the elastic scattering time - it is not sufficient that it is short compared
to the diffusion time around the ring. This strong condition severely
complicates the experimental observation.Comment: 16 pages REVTEX, including 3 figure
Two phase transitions in the fully frustrated model
The fully frustrated model on a square lattice is studied by means of
Monte Carlo simulations. A Kosterlitz-Thouless transition is found at , followed by an ordinary Ising transition at a slightly
higher temperature, . The non-Ising exponents reported by
others, are explained as a failure of finite size scaling due to the screening
length associated with the nearby Kosterlitz-Thouless transition.Comment: REVTEX file, 8 pages, 5 figures in uuencoded postscrip
Bloch-Wall Phase Transition in the Spherical Model
The temperature-induced second-order phase transition from Bloch to linear
(Ising-like) domain walls in uniaxial ferromagnets is investigated for the
model of D-component classical spin vectors in the limit D \to \infty. This
exactly soluble model is equivalent to the standard spherical model in the
homogeneous case, but deviates from it and is free from unphysical behavior in
a general inhomogeneous situation. It is shown that the thermal fluctuations of
the transverse magnetization in the wall (the Bloch-wall order parameter)
result in the diminishing of the wall transition temperature T_B in comparison
to its mean-field value, thus favouring the existence of linear walls. For
finite values of T_B an additional anisotropy in the basis plane x,y is
required; in purely uniaxial ferromagnets a domain wall behaves like a
2-dimensional system with a continuous spin symmetry and does not order into
the Bloch one.Comment: 16 pages, 2 figure
- β¦