Critical behavior of 2 and 3 dimensional ferro- and antiferromagnetic spin ice systems in the framework of the Effective Field Renormalization Group technique

In this work we generalize and subsequently apply the Effective Field Renormalization Group technique to the problem of ferro- and antiferromagnetically coupled Ising spins with local anisotropy axes in geometrically frustrated geometries (kagome and pyrochlore lattices). In this framework, we calculate the various ground states of these systems and the corresponding critical points. Excellent agreement is found with exact and Monte Carlo results. The effects of frustration are discussed. As pointed out by other authors, it turns out that the spin ice model can be exactly mapped to the standard Ising model but with effective interactions of the opposite sign to those in the original Hamiltonian. Therefore, the ferromagnetic spin ice is frustrated, and does not order. Antiferromagnetic spin ice (in both 2 and 3 dimensions), is found to undergo a transition to a long range ordered state. The thermal and magnetic critical exponents for this transition are calculated. It is found that the thermal exponent is that of the Ising universality class, whereas the magnetic critical exponent is different, as expected from the fact that the Zeeman term has a different symmetry in these systems. In addition, the recently introduced Generalized Constant Coupling method is also applied to the calculation of the critical points and ground state configurations. Again, a very good agreement is found with both exact, Monte Carlo, and renormalization group calculations for the critical points. Incidentally, we show that the generalized constant coupling approach can be regarded as the lowest order limit of the EFRG technique, in which correlations outside a frustrated unit are neglected, and scaling is substituted by strict equality of the thermodynamic quantities.Comment: 28 pages, 9 figures, RevTeX 4 Some minor changes in the conclussions. One reference adde

Curie Temperatures for Three-Dimensional Binary Ising Ferromagnets

Using the Swendsen and Wang algorithm, high accuracy Monte Carlo simulations were performed to study the concentration dependence of the Curie temperature in binary, ferromagnetic Ising systems on the simple-cubic lattice. Our results are in good agreement with known mean-field like approaches. Based on former theoretical formulas we propose a new way of estimating the Curie temperature of these systems.Comment: nr. of pages:13, LATEX. Version 2.09, Scientific Report :02/1994 (Univ. of Bergen, Norway), 7 figures upon reques

Stationary State Solutions of a Bond Diluted Kinetic Ising Model: An Effective-Field Theory Analysis

We have examined the stationary state solutions of a bond diluted kinetic Ising model under a time dependent oscillating magnetic field within the effective-field theory (EFT) for a honeycomb lattice $(q=3)$. Time evolution of the system has been modeled with a formalism of master equation. The effects of the bond dilution, as well as the frequency $(\omega)$ and amplitude $(h/J)$ of the external field on the dynamic phase diagrams have been discussed in detail. We have found that the system exhibits the first order phase transition with a dynamic tricritical point (DTCP) at low temperature and high amplitude regions, in contrast to the previously published results for the pure case \cite{Ling}. Bond dilution process on the kinetic Ising model gives rise to a number of interesting and unusual phenomena such as reentrant phenomena and has a tendency to destruct the first-order transitions and the DTCP. Moreover, we have investigated the variation of the bond percolation threshold as functions of the amplitude and frequency of the oscillating field.Comment: 8 pages, 4 figure

Magnetic properties of exactly solvable doubly decorated Ising-Heisenberg planar models

Applying the decoration-iteration procedure, we introduce a class of exactly solvable doubly decorated planar models consisting both of the Ising- and Heisenberg-type atoms. Exact solutions for the ground state, phase diagrams and basic physical quantities are derived and discussed. The detailed analysis of the relevant quantities suggests the existence of an interesting quantum antiferromagnetic phase in the system.Comment: 9 pages, 9 figures, submitted to Physical Review

An investigation into the depth of penetration of low level laser therapy through the equine tendon in vivo

Low level laser therapy (LLLT) is frequently used in the treatment of wounds, soft tissue injury and in pain management. The exact penetration depth of LLLT in human tissue remains unspecified. Similar uncertainty regarding penetration depth arises in treating animals. This study was designed to test the hypothesis that transmission of LLLT in horses is increased by clipping the hair and/or by cleaning the area to be treated with alcohol, but is unaffected by coat colour. A LLLT probe (810 nm, 500 mW) was applied to the medial aspect of the superficial flexor tendon of seventeen equine forelimbs in vivo. A light sensor was applied to the lateral aspect, directly opposite the laser probe to measure the amount of light transmitted. Light transmission was not affected by individual horse, coat colour or leg. However, it was associated with leg condition (F = 4.42, p = 0.0032). Tendons clipped dry and clipped and cleaned with alcohol, were both associated with greater transmission of light than the unprepared state. Use of alcohol without clipping was not associated with an increase in light transmission. These results suggest that, when applying laser to a subcutaneous structure in the horse, the area should be clipped and cleaned beforehand

The effect of low-level laser irradiation (In-Ga-Al-AsP - 660 nm) on melanoma in vitro and in vivo

<p>Abstract</p> <p>Background</p> <p>It has been speculated that the biostimulatory effect of Low Level Laser Therapy could cause undesirable enhancement of tumor growth in neoplastic diseases. The aim of the present study is to analyze the behavior of melanoma cells (B16F10) <it>in vitro </it>and the <it>in vivo </it>development of melanoma in mice after laser irradiation.</p> <p>Methods</p> <p>We performed a controlled <it>in vitro </it>study on B16F10 melanoma cells to investigate cell viability and cell cycle changes by the Tripan Blue, MTT and cell quest histogram tests at 24, 48 and 72 h post irradiation. The <it>in vivo </it>mouse model (male Balb C, n = 21) of melanoma was used to analyze tumor volume and histological characteristics. Laser irradiation was performed three times (once a day for three consecutive days) with a 660 nm 50 mW CW laser, beam spot size 2 mm², irradiance 2.5 W/cm²and irradiation times of 60s (dose 150 J/cm²) and 420s (dose 1050 J/cm²) respectively.</p> <p>Results</p> <p>There were no statistically significant differences between the <it>in vitro </it>groups, except for an increase in the hypodiploid melanoma cells (8.48 ± 1.40% and 4.26 ± 0.60%) at 72 h post-irradiation. This cancer-protective effect was not reproduced in the <it>in vivo </it>experiment where outcome measures for the 150 J/cm²dose group were not significantly different from controls. For the 1050 J/cm²dose group, there were significant increases in tumor volume, blood vessels and cell abnormalities compared to the other groups.</p> <p>Conclusion</p> <p>LLLT Irradiation should be avoided over melanomas as the combination of high irradiance (2.5 W/cm²) and high dose (1050 J/cm²) significantly increases melanoma tumor growth <it>in vivo</it>.</p