Classical Heisenberg antiferromagnet on a garnet lattice: a Monte Carlo simulation

We have studied a classical antiferromagnet on a garnet lattice by means of Monte Carlo simulations in an attempt to examine the role of geometrical frustration in Gadolinium Gallium Garnet, Gd3Ga5O12 (GGG). Low-temperature specific heat, magnetisation, susceptibility, the autocorrelation function A(t) and the neutron scattering function S(Q) have been calculated for several models including different types of magnetic interactions and with the presence of an external magnetic field applied along the principal symmetry axes. A model, which includes only nearest-neighbour exchange, J1, neither orders down to the lowest temperature nor does it show any tendency towards forming a short-range coplanar spin structure. This model, however, does demonstrate a magnetic field induced ordering below T ~ 0.01 J1. In order to reproduce the experimentally observed properties of GGG, the simulated model must include nearest neighbour exchange interactions and also dipolar forces. The presence of weak next-to-nearest exchange interactions is found to be insignificant. In zero field S(Q) exhibits diffuse magnetic scattering around positions in reciprocal space where antiferromagnetic Bragg peaks appear in an applied magnetic field.Comment: 8 pages, 8 figures, to appear in PRB (JAN 2001

Evolution of spin correlations in SrDy2O4 in an applied magnetic field

The development of short- and long-range magnetic order induced in a frustrated zig-zag ladder compound SrDy2O4 by an applied field is studied using neutron diffraction techniques. In zero field, SrDy2O4 lacks long-range magnetic order down to temperatures as low as 60 mK, and the observed powder neutron diffraction (PND) patterns are dominated by very broad diffuse scattering peaks. Single crystal neutron diffraction reveals that the zero-field magnetic structure consists of a collection of antiferromagnetic chains running along the c axis and that there is very little correlation between the chains in the ab plane. In an applied magnetic field, the broad diffuse scattering features in PND are gradually replaced by much sharper peaks, however, the pattern remains rather complex, reflecting the highly anisotropic nature of SrDy2O4. Single crystal neutron diffraction shows that a moderate field applied along the b axis induces an up-up-down magnetic order associated with a 1/3-magnetisation plateau, in which magnetic correlation length in the ab plane is significantly increased, but it nevertheless remains finite. The resolution limited k = 0 peaks associated with a ferromagnetic arrangement appear in powder and single crystal neutron diffraction patterns in fields of 2.5 T and above.Comment: 10 pages, 11 figure

Hypothermic organ perfusion in the 2020s: mixing the benefits of low temperatures and dynamic flow outside the body

The cold chain supply of donor organs for transplantation has been an integral part of the delivery of transplant clinical services over the past five decades. Within the technologies used for this, hypothermic machine perfusion (HMP) was a concept, which was attractive to maintain organs under optimal conditions outside the body, and many early research studies on HMP were reported. However, it took the arrival of important new concepts to ensure that HMP was logistically feasible and valuable from an organ physiology perspective within the clinical pathways. This review provides details of the current status of HMP across the range of organs transplanted in the clinic, and discusses what new areas might benefit from applying HMP in coming years. In conclusion, HMP is now being used more frequently for clinical organ preservation in a variety of settings. As new therapies such as cell or gene therapy become more common, HMP will continue to play an important facilitator role for optimising organs in the donor pathway

Magnetic phase diagram of the antiferromagnetic pyrochlore Gd2Ti2O7

Gd2Ti2O7 is a highly frustrated antiferromagnet on a pyrochlore lattice, where apart from the Heisenberg exchange the spins also interact via dipole-dipole forces. We report on low-temperature specific heat measurements performed on single crystals of Gd2Ti2O7 for three different directions of an applied magnetic field. The measurements reveal the strongly anisotropic behaviour of Gd2Ti2O7 in a magnetic field despite the apparent absence of a significant single-ion anisotropy for Gd3+. The H-T phase diagrams are constructed for H//111], H//[110] and H//[112]. The results indicate that further theoretical work beyond a simple mean-field model is required.Comment: 4 figure

GRAPHO-ANALYTICAL MODELING OF PROCESSES OF INTERACTION OF ELEMENTARY COMPONENTS OF A MANAGEMENT PAIR

In order to analyze and justify the choice of the recommended modes of interaction of people in organizational entities, the article covers the main possibilities of increasing the effectiveness of human interaction on the basis of interpreting a typical management pair in the form of two elementary components that can interact in the "subject-object", "subject-subject”, “object-subject” and “object-object” modes, taking into account the fact that each component is characterized by a certain level of subjectivity. At the same time, the authors take into account the fact that during the life of a person and its life cycle in an organizational formation the level of subjectivity of any person varies within the boundary of the linear continuum object - subject, and its subjectity in organizational formation is defined by no means other, as the current state of the ratio of the number of formal and informal influences of the individual as a subject to other members of the organization to the number of the same effects on it as an object from other members of the organization. Due to the fact that the life cycles of the elementary components are characterized by the presence of each of the periods of increase in subjectivity with the achievement of each peak value and the subsequent gradual loss after release or retirement, it is demonstrated that the joint and equally effective activity of the components is possible only provided that they maintain the subject-subject mode of interaction, which corresponds to the dialogue of the two parties, rather than management of or management by one side of the other. Using the superposition of graph- analytic dependencies of Dunig-Kruger and changes in subjectivity throughout life, it is proved that the basic condition for the implementation of such a managerial dialogue is the awareness of both components of the managerial pair of the fact that the concept of the subject loses meaning without the existence of the object, and therefore maintaining the process of dialogue-cooperation is possible only under the condition of equality and freedom of the participants and the inter-orientation of each of the partners as the subject, the tool for establishing partnerships is management on the basis of the dialogue communication process with the mutual recognition of each of the participants in their freedom, equality and value - subjectivity. It has been established that the priority factors determining the results of the operation of a typical management pair are not the structure and the relationship between its constituent elements, but the intellectual, moral and psychological characteristics of these elements and the awareness of the latter as partners that jointly solve the problem with the achievement of mutually established and harmonized goals.In order to analyze and justify the choice of the recommended modes of interaction of people in organizational entities, the article covers the main possibilities of increasing the effectiveness of human interaction on the basis of interpreting a typical management pair in the form of two elementary components that can interact in the "subject-object", "subject-subject”, “object-subject” and “object-object” modes, taking into account the fact that each component is characterized by a certain level of subjectivity. At the same time, the authors take into account the fact that during the life of a person and its life cycle in an organizational formation the level of subjectivity of any person varies within the boundary of the linear continuum object - subject, and its subjectity in organizational formation is defined by no means other, as the current state of the ratio of the number of formal and informal influences of the individual as a subject to other members of the organization to the number of the same effects on it as an object from other members of the organization. Due to the fact that the life cycles of the elementary components are characterized by the presence of each of the periods of increase in subjectivity with the achievement of each peak value and the subsequent gradual loss after release or retirement, it is demonstrated that the joint and equally effective activity of the components is possible only provided that they maintain the subject-subject mode of interaction, which corresponds to the dialogue of the two parties, rather than management of or management by one side of the other. Using the superposition of graph- analytic dependencies of Dunig-Kruger and changes in subjectivity throughout life, it is proved that the basic condition for the implementation of such a managerial dialogue is the awareness of both components of the managerial pair of the fact that the concept of the subject loses meaning without the existence of the object, and therefore maintaining the process of dialogue-cooperation is possible only under the condition of equality and freedom of the participants and the inter-orientation of each of the partners as the subject, the tool for establishing partnerships is management on the basis of the dialogue communication process with the mutual recognition of each of the participants in their freedom, equality and value - subjectivity. It has been established that the priority factors determining the results of the operation of a typical management pair are not the structure and the relationship between its constituent elements, but the intellectual, moral and psychological characteristics of these elements and the awareness of the latter as partners that jointly solve the problem with the achievement of mutually established and harmonized goals

Structural and Magnetic Investigations of Single-Crystals of the Neodymium Zirconate Pyrochlore, Nd2Zr2O7

We report structural and magnetic properties studies of large high quality single-crystals of the frustrated magnet, Nd$_2$Zr$_2$O$_7$. Powder x-ray diffraction analysis confirms that Nd$_2$Zr$_2$O$_7$ adopts the pyrochlore structure. Room-temperature x-ray diffraction and time-of-flight neutron scattering experiments show that the crystals are stoichiometric in composition with no measurable site disorder. The temperature dependence of the magnetic susceptibility shows no magnetic ordering at temperatures down to 0.5 K. Fits to the magnetic susceptibility data using a Curie-Weiss law reveal a ferromagnetic coupling between the Nd moments. Magnetization versus field measurements show a local Ising anisotropy along the axes of the Nd$^{3+}$ ions in the ground state. Specific heat versus temperature measurements in zero applied magnetic field indicate the presence of a thermal anomaly below $T\sim7$ K, but no evidence of magnetic ordering is observed down to 0.5 K. The experimental temperature dependence of the single-crystal bulk dc susceptibility and isothermal magnetization are analyzed using crystal field theory and the crystal field parameters and exchange coupling constants determined.Comment: 10 pages, 6 figures, 4 tables. Accepted for publication in Physical Review