Bound states of skyrmions and merons near the Lifshitz point

We study topological defects in anisotropic ferromagnets with competing interactions near the Lifshitz point. We show that skyrmions and bi-merons are stable in a large part of the phase diagram. We calculate skyrmion-skyrmion and meron-meron interactions and show that skyrmions attract each other and form ring-shaped bound states in a zero magnetic field. At the Lifshitz point merons carrying a fractional topological charge become deconfined. These results imply that unusual topological excitations may exist in weakly frustrated magnets with conventional crystal lattices.Comment: 5 pages, 4 figure

Width of the longitudinal magnon in the vicinity of the O(3) quantum critical point

We consider a three-dimensional quantum antiferromagnet in the vicinity of a quantum critical point separating the magnetically ordered and the magnetically disordered phases. A specific example is TlCuCl$_3$ where the quantum phase transition can be driven by hydrostatic pressure and/or by external magnetic field. As expected two transverse and one longitudinal magnetic excitation have been observed in the pressure driven magnetically ordered phase. According to the experimental data, the longitudinal magnon has a substantial width, which has not been understood and has remained a puzzle. In the present work, we explain the mechanism for the width, calculate the width and relate value of the width with parameters of the Bose condensate of magnons observed in the same compound. The method of an effective quantum field theory is employed in the work.Comment: 6 pages, 3 figure

Universal Finite Temperature Properties of a Three Dimensional Quantum Antiferromagnet in the Vicinity of a Quantum Critical Point

We consider a 3-dimensional quantum antiferromagnet which can be driven through a quantum critical point (QCP) by varying a tuning parameter g. Starting from the magnetically ordered phase, the N{\'e}el temperature will decrease to zero as the QCP is approached. From a generic quantum field theory, together with numerical results from a specific microscopic Heisenberg spin model, we demonstrate the existence of universal behaviour near the QCP. We compare our results with available data for TlCuCl_

A multi-criteria optimization and decision-making approach for improvement of food engineering processes

The objective of this study was to propose a multi-criteria optimization and decision-making technique to solve food engineering problems. This technique was demonstrated using experimental data obtained on osmotic dehydration of carrot cubes in a sodium chloride solution. The Aggregating Functions Approach, the Adaptive Random Search Algorithm, and the Penalty Functions Approach were used in this study to compute the initial set of non-dominated or Pareto-optimal solutions. Multiple non-linear regression analysis was performed on a set of experimental data in order to obtain particular multi-objective functions (responses), namely water loss, solute gain, rehydration ratio, three different colour criteria of rehydrated product, and sensory evaluation (organoleptic quality). Two multi-criteria decision-making approaches, the Analytic Hierarchy Process (AHP) and the Tabular Method (TM), were used simultaneously to choose the best alternative among the set of non-dominated solutions. The multi-criteria optimization and decision-making technique proposed in this study can facilitate the assessment of criteria weights, giving rise to a fairer, more consistent, and adequate final compromised solution or food process. This technique can be useful to food scientists in research and education, as well as to engineers involved in the improvement of a variety of food engineering processes.Facultad de IngenieríaCentro de Investigación y Desarrollo en Criotecnología de Alimento

Local spin spirals in the Neel phase of La_{2-x}Sr_xCuO_4

Experimental observations of lightly doped La_{2-x}Sr_xCuO_4, x < 0.02, revealed remarkable magnetic properties such as the incommensurate noncollinear ordering (additional to the Neel ordering) and a tremendous doping dependence of the uniform longitudinal susceptibility. We show that the spiral solution of the t-t'-t''-J model obtained by taking into account the Coulomb trapping of holes by Sr ions describes these puzzling data perfectly well. Our solution firstly explains why the incommensurate structure is directed along the orthorhombic b-axis, and secondly allows a numerical calculation of the positions and shapes of the incommensurate neutron scattering peaks. Thirdly, we calculate the doping dependence of the spin-wave gap, and lastly, we study the longitudinal magnetic susceptibility and show that its doping dependence is due to the noncollinearity of the spin spiral.Comment: 13 pages, 8 figure

A multi-criteria optimization and decision-making approach for improvement of food engineering processes

The objective of this study was to propose a multi-criteria optimization and decision-making technique to solve food engineering problems. This technique was demonstrated using experimental data obtained on osmotic dehydration of carrot cubes in a sodium chloride solution. The Aggregating Functions Approach, the Adaptive Random Search Algorithm, and the Penalty Functions Approach were used in this study to compute the initial set of non-dominated or Pareto-optimal solutions. Multiple non-linear regression analysis was performed on a set of experimental data in order to obtain particular multi-objective functions (responses), namely water loss, solute gain, rehydration ratio, three different colour criteria of rehydrated product, and sensory evaluation (organoleptic quality). Two multi-criteria decision-making approaches, the Analytic Hierarchy Process (AHP) and the Tabular Method (TM), were used simultaneously to choose the best alternative among the set of non-dominated solutions. The multi-criteria optimization and decision-making technique proposed in this study can facilitate the assessment of criteria weights, giving rise to a fairer, more consistent, and adequate final compromised solution or food process. This technique can be useful to food scientists in research and education, as well as to engineers involved in the improvement of a variety of food engineering processes.Facultad de IngenieríaCentro de Investigación y Desarrollo en Criotecnología de Alimento