Monte Carlo Calculation of the Spin-Stiffness of the Two-Dimensional Heisenberg Model

Using a collective-mode Monte Carlo method (the Wolff-Swendsen-Wang algorithm), we compute the spin-stiffness of the two-dimensional classical Heisenberg model. We show that it is the relevant physical quantity to investigate the behaviour of the model in the very low temperature range inaccessible to previous studies based on correlation length and susceptibility calculations.Comment: 6 pages, latex, 3 postscript figures appended, DIM preprint 93-3

Comment on "Critical properties of highly frustrated pyrochlore antiferromagnets"

We argue that the analysis of Reimers {\it et al.} [ Phys. Rev. B {\bf 45}, 7295 (1992)] of their Monte Carlo data on the Heisenberg pyrochlore antiferromagnet, which suggests a new universality class, is not conclusive. By re-analysis of their data, we demonstrate asymptotic volume dependence in some thermodynamic quantities, which suggests the possibility that the transition may be first order.Comment: 5 pages (RevTex 3.0), 3 figures available upon request, CRPS-93-0

Composite Pairings in Chirally Stabilized Critical Fluids

We study a one-dimensional electron gas in a special antiferromagnetic environment made by two spin-1/2 Heisenberg chains and the one-dimensional two-channel Kondo-Heisenberg lattice away from half-filling. These models flow to an intermediate fixed point which belongs to the universality class of chirally stabilized liquids. Using a Toulouse point approach, the universal properties of the models are determined as well as the identification of the leading instabilities. It is shown that these models exhibit a non-Fermi liquid behavior with strong enhanced composite pairing correlations.Comment: 4 page

Phase transitions in the one-dimensional spin-S J1−J2J_1-J_2 XY model

The one-dimensional spin-S $J_1-J_2$ XY model is studied within the bosonization approach. Around the two limits ($J_2/J_1 \ll 1,J_2/J_1 \gg 1$) where a field theoretical analysis can be derived, we discuss the phases as well as the different phase transitions that occur in the model. In particular, it is found that the chiral critical spin nematic phase, first discovered by Nersesyan et al. (Phys. Rev. Lett. {\bf 81}, 910 (1998)) for $S=1/2$, exists in the general spin-S case. The nature of the effective field theory that describes the transition between this chiral critical phase and a chiral gapped phase is also determined.Comment: 19 pages, final versio

The massive CPN−1CP^{N-1} model for frustrated spin systems

We study the classical ${SU(N)\otimes U(1)/SU(N-1)\otimes U(1)}$ Non Linear Sigma model which is the continuous low energy effective field theory for $N$ component frustrated spin systems. The $\beta$ functions for the two coupling constants of this model are calculated around two dimensions at two loop order in a low temperature expansion. Our study is completed by a large $N$ analysis of the model. The $\beta$ functions for the coupling constants and the mass gap are calculated in all dimensions between 2 and 4 at order ${1/N}$. As a main result we show that the standard procedure at the basis of the $1/N$ expansion leads to results that partially contradict those of the weak coupling analysis. We finally present the procedure that reconciles the weak coupling and large $N$ analysis, giving a consistent picture of the expected scaling of frustrated magnets.Comment: 55 pages, Late

A Comparative Study Between Two Hybrid Medical Image Compression Methods

In the medical community, it is still discussion whether to apply lossy or lossless compression methods since each has its own advantages and weaknesses. Then the idea of combining both methods arises to achieve higher compression rate for transmission and storage effciency without discarding important medical information. This combination is called hybrid method. This research aimed to compare two hybrid medical image compression methods by applying them into the same data set. The hybrid medical image compression methods were vector quantization with variable block sizes in wavelet domain (VQ- wavelet) and DCT-based subband decomposition and modied SPIHT data organization (DCT-SPIHT). Seven metrics were used to objectively evaluate the compressed images; entropy, computation time, mean square error (MSE), peak signal to noise ratio (PSNR), structural similarity (MSSIM), normalized cross correlation (NCC), and image quality index. Simulation results showed that DCT-SPIHT is the best method which is supported by fast computation time, lower MSE, higher PSNR, and almost perfect value of MSSIM, NCC, and image quality index

Pengaruh Internet Marketing Terhadap Pembentukan Word of Mouth Dan Efektivitas Iklan Dalam Meningkatkan Brand Awareness (Studi Pada Follower Akun Twitter Pocari Sweat Di Jejaring Sosial Twitter)

Several factors can be used asa determinerof the success increating brand awareness. In this research, the factors that can affect Brand AwarenessareWord of Mouth and Advertising Effectiveness which are formed of Internet Marketing. This research includes an explanatory research. This research is a survey research which uses an online questionnaire to followers of Pocari Sweat's account on Twitter (@PocariID) with a sample of 110 respondents.Using path analysis as analytical method, the results of this research indicatethat The Internet Marketing influential positive and significantly toward The Word of Mouth; The Internet Marketing influential positive and significantly toward the Effectiveness of Advertising; The Internet Marketing negative effect and insignificant if tested directly against Brand Awareness; and also theWord of Mouth that has negative effects and not significantly toward Brand Awareness. Furthermore, the Effectiveness of Advertising influential positive and significantly toward Brand Awareness

Confinement and Superfluidity in one-dimensional Degenerate Fermionic Cold Atoms

The physical properties of arbitrary half-integer spins $F = N - 1/2$ fermionic cold atoms trapped in a one-dimensional optical lattice are investigated by means of a low-energy approach. Two different superfluid phases are found for $F \ge 3/2$ depending on whether a discrete symmetry is spontaneously broken or not: an unconfined BCS pairing phase and a confined molecular superfluid instability made of $2N$ fermions. We propose an experimental distinction between these phases for a gas trapped in an annular geometry. The confined-unconfined transition is shown to belong to the $Z_N$ generalized Ising universality class. We discuss on the possible Mott phases at $1/2N$ filling.Comment: 4 pages, revised versio

Monte Carlo Simulation of the Heisenberg Antiferromagnet on a Triangular Lattice: Topological Excitations

We have simulated the classical Heisenberg antiferromagnet on a triangular lattice using a local Monte Carlo algorithm. The behavior of the correlation length $\xi$, the susceptibility at the ordering wavevector $\chi(\bf Q)$, and the spin stiffness $\rho$ clearly reflects the existence of two temperature regimes -- a high temperature regime $T > T_{th}$, in which the disordering effect of vortices is dominant, and a low temperature regime $T < T_{th}$, where correlations are controlled by small amplitude spin fluctuations. As has previously been shown, in the last regime, the behavior of the above quantities agrees well with the predictions of a renormalization group treatment of the appropriate nonlinear sigma model. For $T > T_{th}$, a satisfactory fit of the data is achieved, if the temperature dependence of $\xi$ and $\chi(\bf Q)$ is assumed to be of the form predicted by the Kosterlitz--Thouless theory. Surprisingly, the crossover between the two regimes appears to happen in a very narrow temperature interval around $T_{th} \simeq 0.28$.Comment: 13 pages, 8 Postscript figure