Local Virtual Times Analysis in PCS Model

Efficient scalability and process synchronization are critical for achieving high performance in distributed computing environments. Analysis of the scalability is usually done using intensive case studies, which give an answer only for the particular set of model parameters. We found an efficient way to analyze the time evolution in models simulated with the Parallel Discrete Event Simulations (PDES) approach. The essential feature of PDES is the concept of local virtual time (LVT) associated with the evolution of each process of the model. The LVT of processes evaluates in simulations and forms a complicated profile.These profiles remind the profiles of the surface growth in the physical devices. In physics, researchers use the concept of universality, which helps to divide the different regimes of the class's surface growth—each class is described by some universal laws and does not depend on the details of the model. We demonstrate the applicability of this concept and present a model of LVT profile evolution in Personal Communication Service (PCS) model. The PCS network consists of a square grid of radio ports that serve users in their zone (cell). We build the LVT-PCS model, which describes the evolution of the LVT profile associated with the PCS model. We simulate the PCS model using the ROSS simulator (optimistic PDES) and compare results with those simulated by our LVT-PCS model. We found the profile demonstrates property, which is known in physics as roughening transition. We estimate the values of ``critical’’ exponents for two models, which seem to belong to the same universality class. We believe that the similarity we found can be helpful for the preliminary analysis of the model scalability, process desynchronization, and possible deadlocks.

Local Virtual Times Analysis in PCS Model

Efficient scalability and process synchronization are critical for achieving high performance in distributed computing environments. Analysis of the scalability is usually done using intensive case studies, which give an answer only for the particular set of model parameters. We found an efficient way to analyze the time evolution in models simulated with the Parallel Discrete Event Simulations (PDES) approach. The essential feature of PDES is the concept of local virtual time (LVT) associated with the evolution of each process of the model. The LVT of processes evaluates in simulations and forms a complicated profile.These profiles remind the profiles of the surface growth in the physical devices. In physics, researchers use the concept of universality, which helps to divide the different regimes of the class's surface growth—each class is described by some universal laws and does not depend on the details of the model. We demonstrate the applicability of this concept and present a model of LVT profile evolution in Personal Communication Service (PCS) model. The PCS network consists of a square grid of radio ports that serve users in their zone (cell). We build the LVT-PCS model, which describes the evolution of the LVT profile associated with the PCS model. We simulate the PCS model using the ROSS simulator (optimistic PDES) and compare results with those simulated by our LVT-PCS model. We found the profile demonstrates property, which is known in physics as roughening transition. We estimate the values of ``critical’’ exponents for two models, which seem to belong to the same universality class. We believe that the similarity we found can be helpful for the preliminary analysis of the model scalability, process desynchronization, and possible deadlocks.

Acto-myosin network geometry defines centrosome position

The centrosome is the main organizer of microtubules and as such, its position is a key determinant of polarized cell functions. As the name says, the default position of the centrosome is considered to be the cell geometrical center. However, the mechanism regulating centrosome positioning is still unclear and often confused with the mechanism regulating the position of the nucleus to which it is linked. Here we used enucleated cells plated on adhesive micropatterns to impose regular and precise geometrical conditions to centrosome-microtubule networks. Although frequently observed there, the equilibrium position of the centrosome is not systematically at the cell geometrical center and can be close to cell edge. Centrosome positioning appears to respond accurately to the architecture and anisotropy of the actin network, which constitutes, rather than cell shape, the actual spatial boundary conditions the microtubule network is sensitive to. We found that the contraction of the actin network defines a peripheral margin, in which microtubules appeared bent by compressive forces. The disassembly of the actin network away from the cell edges defines an inner zone where actin bundles were absent and microtubules were more radially organized. The production of dynein-based forces on microtubules places the centrosome at the center of this inner zone. Cell adhesion pattern and contractile forces define the shape and position of the inner zone in which the centrosome-microtubule network is centered.

Ultrastructural analysis of initial stages of dedifferentiation of root explants of Gentiana cruciata seedlings

The studies were carried out on isolated roots of 10-day old seedlings of <em>Gentiana cruciata</em>, which were placed and cultured on induction medium of Murashige and Skoog (1962) supplemented with 1.0 mg/dm³ dicamba + 0.l mg/dm³ NAA + 2.00 mg/dm³ BAP + 80.0 mg/dm³ adenine sulphate. Changes in explants from the 3rd to the l lth day of culture with the help of light and electron microscope were observed. Observations showed gradual dedifferentiation of root tissues, which was seen earliest in cortex at the proximal end of the explant and shifted gradually inwards the root and towards distal parts of its elongation zone. The most intensive callus formation appeared at cut surface of explant, where proliferation of cells in both cortex and axial cylinder was recognised. In the distal part of the elongation zone, cell divisions occurred only in endoderm and in axial cylinder. The meristematic part of the root was inactive. Finally, the following areas were distinguished in the explant: (I) an area of intensive cell divisions, i.e., the elongation zone; (II) an area of cell dispersion; and (III) the inactive meristem. The ultrastructure brought evidences of cell reorganisation as the meaning of cell readiness to the division. Observations showed an increased activity of mitochondria and Golgi structures, thickening of walls and disappearance of plasmodesmal connections. Amyloplasts and lipid bodies in tissues in which they had been scarce or had not appeared before founding. Intensively dividing cells showed features of meristematic cells. They had dense cytoplasm with numerous organelles, large centrally located nuclei, and "nucleolar vacuoles" inside nucleoli. Cortex-derived callus formed aggregates. Both pericycle and endoderm produced callus of characteristic dense structure and regular type of divisions.