A novel method for evaluating the critical nucleus and the surface tension in systems with first order phase transition

We introduce a novel method for calculating the size of the critical nucleus and the value of the surface tension in systems with first order phase transition. The method is based on classical nucleation theory, and it consists in studying the thermodynamics of a sphere of given radius embedded in a frozen metastable surrounding. The frozen configuration creates a pinning field on the surface of the free sphere. The pinning field forces the sphere to stay in the metastable phase as long as its size is smaller than the critical nucleus. We test our method in two first-order systems, both on a two-dimensional lattice: a system where the parameter tuning the transition is the magnetic field, and a second system where the tuning parameter is the temperature. In both cases the results are satisfying. Unlike previous techniques, our method does not require an infinite volume limit to compute the surface tension, and it therefore gives reliable estimates even by using relatively small systems. However, our method cannot be used at, or close to, the critical point, i.e. at coexistence, where the critical nucleus becomes infinitely large.Comment: 12 pages, 15 figure

Differential expression and biochemical activity of the immune receptor Tim-3 in healthy and malignant human myeloid cells

The T cell immunoglobulin and mucin domain 3 (Tim-3) is a plasma membrane-associated receptor which is involved in a variety of biological responses in human immune cells. It is highly expressed in most acute myeloid leukaemia (AML) cells and therefore may serve as a possible target for AML therapy. However, its biochemical activities in primary human AML cells remain unclear. We therefore analysed the total expression and surface presence of the Tim-3 receptor in primary human AML blasts and healthy primary human leukocytes isolated from human blood. We found that Tim-3 expression was significantly higher in primary AML cells compared to primary healthy leukocytes. Tim-3 receptor molecules were distributed largely on the surface of primary AML cells, whereas in healthy leukocytes Tim-3 protein was mainly expressed intracellularly. In primary human AML blasts, both Tim-3 agonistic antibody and galectin-9 (a Tim-3 natural ligand) significantly upregulated mTOR pathway activity. This was in line with increased accumulation of hypoxia-inducible factor 1 alpha (HIF-1α) and secretion of VEGF and TNF-α. Similar results were obtained in primary human healthy leukocytes. Importantly, in both types of primary cells, Tim-3-mediated effects were compared with those induced by lipopolysaccharide (LPS) and stem cell factor (SCF). Tim-3 induced comparatively moderate responses in both AML cells and healthy leukocytes. However, Tim-3, like LPS, mediated the release of both TNF-α and VEGF, while SCF induced mostly VEGF secretion and did not upregulate TNF-α release

Grand potential in thermodynamics of solid bodies and surfaces

Using the chemical potential of a solid in a dissolved state or the corresponding component of the chemical potential tensor at equilibrium with the solution, a new concept of grand thermodynamic potential for solids has been suggested. This allows generalizing the definition of Gibbs' quantity $\sigma$ (surface work often called the solid-fluid interfacial free energy) at a planar surface as an excess grand thermodynamic potential per unit surface area that (1) does not depend on the dividing surface location and (2) is common for fluids and solids.Comment: 6 page

A flexible electronic controller for a manipulator-type robot

Manipulator arm construction has changed little over the decades and is unlikely to change radically in the near future. The mechanical design necessary to achieve dexterity results in a system with complex dynamic properties. However, many manipulator manufacturers choose to ignore this complexity, concentrating on the mechanical design aspects rather than the design of the dynamic controller. In most cases, simple fixed-parameter single-loop PID compensators are utilised. In spite of the fact that the compensators are implemented on programmable devices, there is simply not enough processing power available to implement an improved dynamic control strategy. A multiprocessor controller has been developed which allows all the hierarchical levels of a manipulator controller to be implemented. The major advantage of the new controller is its ability to handle complex and time consuming dynamic algorithms for positioning of the robot end effector. This has been accomplished by adopting a master/slave multiprocessor configuration comprising a 20 MHz IBM PC/AT (80386) with a number of DSP cards based around the NEC 77230 floating-point DSP chip. Analog and digital input/output interfaces are provided for reading position signals and providing command signals. Tile motivation for the provision of such a controller was the desire to implement linear and nonlinear self-tuning control strategies. Both centralised (multivariable) and decentralized (single-loop) control strategies are considered and the new controller caters for both schemes by virtue of (a) the master/slave configuration with individual DSP boards for each joint, and (b) inter-board communications, allowing joint interactions to be catered for. In the paper, some of the identification algorithms required to support the nonlinear self-tuning strategies are described and real-time results presented. These results demonstrate the operation of the new controller and indicate some of its capabilities