New Computational Algorithms for Analyzing the Stability of the Differential Equations System

In this paper we show how to improve the approximate solution of the large Lyapunov equation obtained by an arbitrary method. Moreover, we propose a new method based on refinement process and Weighted Arnoldi algorithm for solving large Lyapunov matrix equation. Finally, some numerical results will be reported to illustrate the efficiency of the proposed method

In regard to Cuccia et al.: impact of hydrogel peri-rectal spacer insertion on prostate gland intra-fraction motion during 1.5�T MR-guided stereotactic body radiotherapy

We read the article entitled "Impact of hydrogel peri-rectal spacer insertion on prostate gland intra-fraction motion during 1.5 T MR-guided stereotactic body radiotherapy" with great interest. In that study, the author reported that there is a statistically significant difference in the rotational antero-posterior shifts between the spacer and the non-spacer groups. Also, there was no statistically significant difference between the groups in terms of translational shifts. However, there are some points about the study. In this letter, we aimed to clarify these points

Phyllotactic regularity requires the Paf1 complex in Arabidopsis

In plants, aerial organs are initiated at stereotyped intervals, both spatially (every 137° in a pattern called phyllotaxis) and temporally (at prescribed time intervals called plastochrons). To investigate the molecular basis of such regularity, mutants with altered architecture have been isolated. However, most of them only exhibit plastochron defects and/or produce a new, albeit equally reproducible, phyllotactic pattern. This leaves open the question of a molecular control of phyllotaxis regularity. Here, we show that phyllotaxis regularity depends on the function of VIP proteins, components of the RNA polymerase II-associated factor 1 complex (Paf1c). Divergence angles between successive organs along the stem exhibited increased variance in vip3-1 and vip3-2 compared with the wild type, in two different growth conditions. Similar results were obtained with the weak vip3-6 allele and in vip6, a mutant for another Paf1c subunit. Mathematical analysis confirmed that these defects could not be explained solely by plastochron defects. Instead, increased variance in phyllotaxis in vip3 was observed at the meristem and related to defects in spatial patterns of auxin activity. Thus, the regularity of spatial, auxin-dependent, patterning at the meristem requires Paf1c

Histopathological evaluation of the effectiveness of glycyrrhizic acid as a radioprotector against the development of radiation-induced lung fibrosis

Background: Radiotherapy of the thorax often causes lung inflammation leading to fibrosis. Objectives: The aim of this study was to investigate whether the use of glycyrrhizic acid (GLA) could improve the development of lung fibrosis in irradiated animals. Materials and Methods: Wistar rats were divided into four groups. Group A rats received thoracic irradiation. Rats in group B received GLA and irradiation. Group C received GLA and no irradiation. Group D received no GLA and irradiation. GLA was administered at a dose of 4 mg/kg body weight using an intraperitoneal injection one hour before thoracic irradiation. Radiation therapy was delivered on a Cobalt-60 unit using a single fraction of 16 Gy. The animals were sacrificed at 32 weeks following thoracic irradiation. The lungs were dissected and blind histopathological evaluation was performed. Results: Histopathologically, a decrease (statistically not significant) in the thickening of alveolar or bronchial wall, formation of fibrous bands, and superimposed collagen were noted in the animals in group B as compared to the animals in group A. Conclusion: In this experimental study, administration of GLA one hour before thoracic irradiation may be a protective agent against radiation-induced fibrosis in animals and this model could be used in future studies. © 2016, Tehran University of Medical Sciences and Iranian Society of Radiology

Vector-based model of elastic bonds for DEM simulation of solids

A new model for computer simulation of solids, composed of bonded rigid body particles, is proposed. Vectors rigidly connected with particles are used for description of deformation of a single bond. The expression for potential energy of the bond and corresponding expressions for forces and moments are proposed. Formulas, connecting parameters of the model with longitudinal, shear, bending and torsional stiffnesses of the bond, are derived. It is shown that the model allows to describe any values of the bond stiffnesses exactly. Two different calibration procedures depending on bond length/thickness ratio are proposed. It is shown that parameters of model can be chosen so that under small deformations the bond is equivalent to either Bernoulli-Euler rod or Timoshenko rod or short cylinder connecting particles. Simple expressions, connecting parameters of V-model with geometrical and mechanical characteristics of the bond, are derived. Computer simulation of dynamical buckling of the straight discrete rod and half-spherical shell is carried out.Comment: 11 pages, 6 figure

Interlaminar Fracture Toughness Evaluation in Glass/Epoxy Composites Using Acoustic Emission and Finite Element Methods

© 2014, ASM International. Delamination is one of the most common modes of failure in laminated composites and it leads to the loss of structural strength and stiffness. In this paper, mode I, mode II, and mixed of these pure modes were investigated using mechanical data, Finite Element Method (FEM) and Acoustic Emission (AE) signals. Experimental data were obtained from insitu monitoring of glass/epoxy laminated composites with different lay-ups when subjected to different modes of failure. The main objective was to investigate the behavior of delamination propagation and to evaluate the critical value of the strain energy which is required for onset of the delamination (GC). For the identification of interlaminar fracture toughness of the specimens, four methods were used: (a) ASTM standard methods, (b) FEM analysis, (c) AE method, and (d) sentry function method which is a function of mechanical and AE behaviors of the specimens. The results showed that the GC values obtained by the sentry function method and FEM analysis were in a close agreement with the results of nonlinearity methods which is recommended in the ASTM standards. It was also found that the specimens under different loading conditions and various lay-up have different GC values. These differences are related to different stress components distribution in the specimens which induce various damage mechanisms. Accordingly, stress components distribution obtained from FEM analyses were in agreement with SEM observations of the damaged surfaces of the specimens

Noise and Robustness in Phyllotaxis

A striking feature of vascular plants is the regular arrangement of lateral organs on the stem, known as phyllotaxis. The most common phyllotactic patterns can be described using spirals, numbers from the Fibonacci sequence and the golden angle. This rich mathematical structure, along with the experimental reproduction of phyllotactic spirals in physical systems, has led to a view of phyllotaxis focusing on regularity. However all organisms are affected by natural stochastic variability, raising questions about the effect of this variability on phyllotaxis and the achievement of such regular patterns. Here we address these questions theoretically using a dynamical system of interacting sources of inhibitory field. Previous work has shown that phyllotaxis can emerge deterministically from the self-organization of such sources and that inhibition is primarily mediated by the depletion of the plant hormone auxin through polarized transport. We incorporated stochasticity in the model and found three main classes of defects in spiral phyllotaxis – the reversal of the handedness of spirals, the concomitant initiation of organs and the occurrence of distichous angles – and we investigated whether a secondary inhibitory field filters out defects. Our results are consistent with available experimental data and yield a prediction of the main source of stochasticity during organogenesis. Our model can be related to cellular parameters and thus provides a framework for the analysis of phyllotactic mutants at both cellular and tissular levels. We propose that secondary fields associated with organogenesis, such as other biochemical signals or mechanical forces, are important for the robustness of phyllotaxis. More generally, our work sheds light on how a target pattern can be achieved within a noisy background

Block Krylov subspace methods for large-scale matrix computations in control

AbstractIn this paper we show how to improve the approximate solution of the large Sylvester equation obtained by an arbitrary method. Such problems appear in many areas of control theory such as the computation of Hankel singular values, model reduction algorithms and others. Moreover, we propose a new method based on refinement process and weighted block Arnoldi algorithm for solving large Sylvester matrix equation. The numerical tests report the effectiveness of these methods