2,925 research outputs found
Intrinsic peculiarities of real material realizations of a spin-1/2 kagome lattice
Spin-1/2 magnets with kagome geometry, being for years a generic object of
theoretical investigations, have few real material realizations. Recently, a
DFT-based microscopic model for two such materials, kapellasite Cu3Zn(OH)6Cl2
and haydeeite Cu3Mg(OH)6Cl2, was presented [O. Janson, J. Richter and H.
Rosner, arXiv:0806.1592]. Here, we focus on the intrinsic properties of real
spin-1/2 kagome materials having influence on the magnetic ground state and the
low-temperature excitations. We find that the values of exchange integrals are
strongly dependent on O--H distance inside the hydroxyl groups, present in most
spin-1/2 kagome compounds up to date. Besides the original kagome model,
considering only the nearest neighbour exchange, we emphasize the crucial role
of the exchange along the diagonals of the kagome lattice.Comment: 4 pages, 4 figures. A paper for the proceedings of the HFM 2008
conferenc
Maximum relative height of one-dimensional interfaces : from Rayleigh to Airy distribution
We introduce an alternative definition of the relative height h^\kappa(x) of
a one-dimensional fluctuating interface indexed by a continuously varying real
paramater 0 \leq \kappa \leq 1. It interpolates between the height relative to
the initial value (i.e. in x=0) when \kappa = 0 and the height relative to the
spatially averaged height for \kappa = 1. We compute exactly the distribution
P^\kappa(h_m,L) of the maximum h_m of these relative heights for systems of
finite size L and periodic boundary conditions. One finds that it takes the
scaling form P^\kappa(h_m,L) = L^{-1/2} f^\kappa (h_m L^{-1/2}) where the
scaling function f^\kappa(x) interpolates between the Rayleigh distribution for
\kappa=0 and the Airy distribution for \kappa=1, the latter being the
probability distribution of the area under a Brownian excursion over the unit
interval. For arbitrary \kappa, one finds that it is related to, albeit
different from, the distribution of the area restricted to the interval [0,
\kappa] under a Brownian excursion over the unit interval.Comment: 25 pages, 4 figure
Consequences of critical interchain couplings and anisotropy on a Haldane chain
Effects of interchain couplings and anisotropy on a Haldane chain have been
investigated by single crystal inelastic neutron scattering and density
functional theory (DFT) calculations on the model compound SrNiVO.
Significant effects on low energy excitation spectra are found where the
Haldane gap (; where is the intrachain exchange
interaction) is replaced by three energy minima at different antiferromagnetic
zone centers due to the complex interchain couplings. Further, the triplet
states are split into two branches by single-ion anisotropy. Quantitative
information on the intrachain and interchain interactions as well as on the
single-ion anisotropy are obtained from the analyses of the neutron scattering
spectra by the random phase approximation (RPA) method. The presence of
multiple competing interchain interactions is found from the analysis of the
experimental spectra and is also confirmed by the DFT calculations. The
interchain interactions are two orders of magnitude weaker than the
nearest-neighbour intrachain interaction = 8.7~meV. The DFT calculations
reveal that the dominant intrachain nearest-neighbor interaction occurs via
nontrivial extended superexchange pathways Ni--O--V--O--Ni involving the empty
orbital of V ions. The present single crystal study also allows us to
correctly position SrNiVO in the theoretical - phase
diagram [T. Sakai and M. Takahashi, Phys. Rev. B 42, 4537 (1990)] showing where
it lies within the spin-liquid phase.Comment: 12 pages, 12 figures, 3 tables PRB (accepted). in Phys. Rev. B (2015
Structure and magnetism of Cr2BP3O12: Towards the quantum-classical crossover in a spin-3/2 alternating chain
Magnetic properties of the spin-3/2 Heisenberg system Cr2BP3O12 are
investigated by magnetic susceptibility chi(T) measurements, electron spin
resonance, neutron diffraction, and density functional theory (DFT)
calculations, as well as classical and quantum Monte Carlo (MC) simulations.
The broad maximum of chi(T) at 85K and the antiferromagnetic Weiss temperature
of 139 K indicate low-dimensional magnetic behavior. Below TN = 28 K, Cr2BP3O12
is antiferromagnetically ordered with the k = 0 propagation vector and an
ordered moment of 2.5 muB/Cr. DFT calculations, including DFT+U and hybrid
functionals, yield a microscopic model of spin chains with alternating
nearest-neighbor couplings J1 and J1' . The chains are coupled by two
inequivalent interchain exchanges of similar strength (~1-2 K), but different
sign (antiferromagnetic and ferromagnetic). The resulting spin lattice is
quasi-one-dimensional and not frustrated. Quantum MC simulations show excellent
agreement with the experimental data for the parameters J1 ~= 50 K and J1'/J1
~= 0.5. Therefore, Cr2BP3O12 is close to the gapless critical point (J1'/J1 =
0.41) of the spin-3/2 bond-alternating Heisenberg chain. The applicability
limits of the classical approximation are addressed by quantum and classical MC
simulations. Implications for a wide range of low-dimensional S = 3/2 materials
are discussed.Comment: Published version: 13 pages, 7 figures, 5 tables + Supplementary
informatio
Unicyclic Components in Random Graphs
The distribution of unicyclic components in a random graph is obtained
analytically. The number of unicyclic components of a given size approaches a
self-similar form in the vicinity of the gelation transition. At the gelation
point, this distribution decays algebraically, U_k ~ 1/(4k) for k>>1. As a
result, the total number of unicyclic components grows logarithmically with the
system size.Comment: 4 pages, 2 figure
Pengembangan Sistem Agregator Berita Bahasa Indonesia Menggunakan Content Extraction Dan Hierarchical Agglomerative Clustering
The main focus of this study is to develop system to aggregate Indonesian online newspaper and cluster it according to its topic automatically. The system use content extraction to get the main content of articles and Hierarchical Agglomerative Clustering to group articles by its topic with Dice Similarity Coefficient for similarity measure. To determine the cutting point, we cut dendrogram where the gap between two successive combination similarities is largest. Additionally, we add threshold to limit cutting area to improve cluster result. We use Standard Boolean Model for searching feature and Silhouette to evaluate cluster results. Test results using 998 articles shows that limiting cutting area with 0.1 and 0.5 can produce highest average silhouette value 0.264
Data driven optimal filtering for phase and frequency of noisy oscillations: application to vortex flowmetering
A new method for extracting the phase of oscillations from noisy time series
is proposed. To obtain the phase, the signal is filtered in such a way that the
filter output has minimal relative variation in the amplitude (MIRVA) over all
filters with complex-valued impulse response. The argument of the filter output
yields the phase. Implementation of the algorithm and interpretation of the
result are discussed. We argue that the phase obtained by the proposed method
has a low susceptibility to measurement noise and a low rate of artificial
phase slips. The method is applied for the detection and classification of mode
locking in vortex flowmeters. A novel measure for the strength of mode locking
is proposed.Comment: 12 pages, 10 figure
Zoonotic Endocarditis: Is the feather mightier than the sword?
The common causes of infective endocarditis (IE) in South Africa are Staphylococcus aureus, the viridans streptococci and Bartonella species. Infection with Erysipelothrix rhusiopathiae is a rare cause of IE that is usually associated with occupational exposure and can be acquired from humans and animals. It was fi rst reported in 1912 by Gunthar, and thereafter fewer than 60 cases have been reported. We describe a case of Erysipelothrix rhusiopathiae induced endocarditis in Cape Town, South Africa. S
SAHeart 2022;19:24-2
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