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Search Results: 1 - 10 of 189854 matches for " G. Sreekala "
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Acoustic Emission and Shape Memory Effect in the Martensitic Transformation
S. Sreekala,G. Ananthakrishna
Physics , 2003, DOI: 10.1103/PhysRevLett.90.135501
Abstract: Acoustic emission signals are known to exhibit a high degree of reproducibility in time and show correlations with the growth and shrinkage of martensite domains when athermal martensites are subjected to repeated thermal cycling in a restricted temperature range. We show that a recently introduced two dimensional model for the martensitic transformation mimics these features. We also show that these features are related to the shape-memory effect where near full reversal of morphological features are seen under these thermal cycling conditions.
A two dimensional model for ferromagnetic martensites
S. Sreekala,G. Ananthakrishna
Physics , 2005, DOI: 10.1103/PhysRevB.72.134403
Abstract: We consider a recently introduced 2-D square-to-rectangle martensite model that explains several unusual features of martensites to study ferromagnetic martensites. The strain order parameter is coupled to the magnetic order parameter through a 4-state clock model. Studies are carried out for several combinations of the ordering of the Curie temperatures of the austenite and martensite phases and, the martensite transformation temperature. We find that the orientation of the magnetic order which generally points along the short axis of the rectangular variant, changes as one crosses the twin or the martensite-austenite interface. The model shows the possibility of a subtle interplay between the growth of strain and magnetic order parameters as the temperature is decreased. In some cases, this leads to qualitatively different magnetization curves from those predicted by earlier mean field models. Further, we find that strain morphology can be substantially altered by the magnetic order. We have also studied the dynamic hysteresis behavior. The corresponding dissipation during the forward and reverse cycles has features similar to the Barkhausen's noise.
A simple model for some unusual properties of martensitic transformation
S. Sreekala,Rajeev Ahluwalia,G. Ananthakrishna
Physics , 2004,
Abstract: We report a detailed numerical investigation of a recently introduced two dimensional model for square-to-rectangle martensitic transformation that explains several unusual features of the martensitic transformation. This model includes inertial effects, dissipation, long-range interaction between the transformed domains and an inhomogeneous stress field to describe the effect of lattice defects which serves as nucleation centers. Both single-site nucleation and multi-site nucleation has been studied for single quench situation and thermal cycling. The final stage morphologies of single-site nucleation and multi-site nucleation bear considerable similarity suggesting that the initial distribution of the defects is not important. Thermal cycling using continuous cooling and heating simulations show the existence of hysteresis in the transformation. More importantly, the rate of energy dissipated occurs in the forms of bursts with power law statistics for their amplitudes and durations which explains the results of acoustic emission signals observed in experiments. When the system is cycled repeatedly in a restricted domain of temperatures, the dissipated bursts of energy are repetitive, a feature observed in experiments. The associated morphology shows a complete reversal of the martensite domains thus throwing light on the mechanism underlying the shape memory effect. The model also exhibits tweed like patterns.
Ion-Acoustic Instabilities in a Multi-Ion Plasma
Noble P. Abraham,Sijo Sebastian,G. Sreekala,R. Jayapal,C. P. Anilkumar,Venugopal Chandu
Journal of Astrophysics , 2013, DOI: 10.1155/2013/838534
Abstract: We have, in this paper, studied the stability of the ion-acoustic wave in a plasma composed of hydrogen, positively and negatively charged oxygen ions, and electrons, which approximates very well the plasma environment around a comet. Modelling each cometary component ( , , and ) by a ring distribution, we find that ion-acoustic waves can be generated at frequencies comparable to the hydrogen ion plasma frequency. The dispersion relation has been solved both analytically and numerically. We find that the ratio of the ring speed ( ) to the thermal spread ( ts) modifies the dispersion characteristics of the ion-acoustic wave. The contrasting behaviour of the phase velocity of the ion-acoustic wave in the presence of ions for ts (and vice versa) can be used to detect the presence of negatively charged oxygen ions and also their thermalization. 1. Introduction Low-frequency electrostatic or longitudinal ion density waves are one of the most fundamental of oscillations in a plasma [1, 2]. In the long-wavelength limit, the ions provide the inertia with the electrons as the source of the restoring force [1]. Ion-acoustic waves also exhibit strong nonlinear properties and are highly Landau damped unless , where and are, respectively, the ion and electron temperatures [3–5]. These waves have been observed in both space and laboratory plasmas; they have thus been extensively studied in many types of high-temperature laboratory plasmas [4, 6]. The waves have been invoked to explain wave characteristics observed in Earth’s ionosphere [7] and transport in the solar wind, corona, chromosphere [8], and comets [9]. In general a cometary environment contains new born hydrogen and heavier ions, with relative densities depending on the distance from the nucleus. Previous studies have concentrated on positively charged oxygen as the heavier ion species [10]. However, Giotto’s observations of the inner coma of comet Halley showed that a new component, namely, negatively charged cometary ions was present, in addition to the usual thermal electrons and ions, fast cometary pickup ions, and so forth, [11]. These negative ions were observed in three broad mass peaks at 7–19, 22–65, and 85–110 amu with being identified unambiguously [11]. A popular model of a cometary environment is the solar wind plasma environment permeated by dilute, drifting ring distribution of electrons and ions with finite thermal spreads [10]. Instabilities driven by an electron velocity ring distributions have been studied by many authors [12–14]. However, ion ring distributions are more important
Studies on Properties of Bio-Composites from Ecoflex/Ramie Fabric-Mechanical and Barrier Properties  [PDF]
K. A. Ajith Kumar, M. S. Sreekala, S. Arun
Journal of Biomaterials and Nanobiotechnology (JBNB) , 2012, DOI: 10.4236/jbnb.2012.33039
Abstract: Nowadays, utilization of biodegradable materials has become necessary in order to maintain global environmental and ecological balance. ‘Green’ composites offered the possible solution to waste disposal problems associated with traditional petroleum derived plastics. The use of plastics based on removable resources is enormous now a day for the development of true bio-composites. Fully biodegradable ‘Green’ textile composites have been prepared from Ecoflex and ramie fabric. Textile composites were fabricated from the Ecoflex polymer and the ramie fabric by hot compression molding technique. Interactions at the fiber–matrix interface and the compatibility between ramie fabric and Ecoflex polymer will affect the properties of the system. The mechanical property and barrier property of the composites were investigated. Static mechanical properties such as tensile strength, tensile modulus, and elongation at break of the textile bio-composites were analyzed. Sorption characteristics of water, oil and diesel in the textile composites were analyzed in order to determine its outdoor applications and the influence of macro fibers on the transport phenomena was investigated. The kinetics of sorption-diffusion process were investigated. Kinetic parameters such as n, k, diffusion coefficient, permeability, solubility parameter, % swelling index, etc., were analyzed. The water sorption mechanism in the textile composites was found to exhibit slight deviation from Fickian mode.
Lymphoepithelioma-Like Carcinoma of Parapharyngeal Space—A Case Report with Review of Literature  [PDF]
Produl Hazarika, Seema Elina Punnoose, John Victor,Sreekala, Nirmali Dutta
International Journal of Otolaryngology and Head & Neck Surgery (IJOHNS) , 2015, DOI: 10.4236/ijohns.2015.42028
Abstract: Extra-nasopharyngeal lymphoepithelioma-like carcinomas (LELC) are uncommon epithelial tumors. A few isolated case reports and series are available in literature involving the larynx, pharynx, salivary gland, lung etc., but involvement in the parapharyngeal space has not yet been reported. We aim to highlight one such case that has a clinical and radiological characteristic of a benign lesion whilst the histopathology reveals an infiltrating neoplasm. The typical clinical aggressiveness of a classical LELC of extra-nasopharyngeal lesion as described in literature is not present in our case. Also seen is an uncommon finding of abnormal branching of left external carotid artery. There is no standard treatment protocol for such a tumor; however, wide excision of this tumor in the parapharyngeal space via trans-cervical, trans-mandibular, trans-palatal approach has shown good and satisfactory tumor control of the primary site so far.
Osteopetrosis: A rare cause of anemia
Sreekala Sreehari,Divya Rani Naik,Malini Eapen
Hematology Reports , 2011, DOI: 10.4081/hr.2011.e1
Abstract: Normocytic anaemia is caused either by hypoproliferation of haemopoietic tissue or increased destruction of red cells. Osteope-trosis is a rare cause of anaemia. Infantile osteopetrosis (also called malignant osteopetrosis) is diagnosed early in life. But it is the adult osteopetrosis (also called benign osteopetrosis) which is diagnosed in late adolescence or adulthood that present as anaemia which is difficult to diagnose and treat. Approximately one half of patients are asymptomatic, and the diagnosis is made incidentally, often in late adolescence because radiologic abnormalities start appearing only in childhood. In other patients, the diagnosis is based on family history. Still other patients might present with osteomyelitis or fractures. We are presenting here an unusual case of osteopetrosis which was referred to us for the evaluation of anaemia.
Neuromyelitis Optica
Goyal V,Rooru S,Gafoor AS,Sreekala VK
Indian Journal of Physical Medicine and Rehabilitation , 2009,
Abstract: Neuromyelitis optica (NMO) is a rare, idiopathic,inflammatory disease affecting the spine andcharacteristically sparing the brain. It mimics multiplesclerosis (MS) in many aspects. A case report of 55 yearold house-maker, with recurrent attacks of flaccidweakness with visual and bladder disturbances who wasadmitted in the Physical Medicine and Rehabilitation(PMR) ward for neuro-rehabilitation is presented. Herserological studies and magnetic resonance imaging ofthe spine and brain revealed a diagnosis of idiopathicdemyelinating disease affecting the spine – Devic’sdisease.
Kadomstev-Petviashvilli-Burgers (KPB) Equation in a Five Component Cometary Plasma with Kappa Described Electrons and Ions  [PDF]
Manesh Michael, Sreekala Gopinathan, Sijo Sebastian, Neethu T. Willington, Anu Varghese, Renuka Gangadharan, Chandu Venugopal
Journal of Applied Mathematics and Physics (JAMP) , 2015, DOI: 10.4236/jamp.2015.311171
Abstract: We investigate the existence of Ion-Acoustic solitary/shock waves in a five component cometary plasma consisting of positively and negatively charged oxygen ions, kappa described hydrogen ions, hot electrons and cold electrons. The KPB equation is derived for the system; its solution is plotted for different kappa values, as well as for the temperature ratios of ions. It is found that the amplitude of solitary structure increases with increasing kappa values and negatively charged oxygen ion densities. As the temperature of the positively charged oxygen ions increases, the amplitude of solitary wave also increases. We have also studied the dependence of coefficients of the KPB equation on physical parameters relevant to comet Halley.
Zeylanidium as Pollution Indicators: Live Sensors to Water Parameters  [PDF]
Thara K. Simon, Veena Mathew, S. L. Sreekala
Open Access Library Journal (OALib Journal) , 2018, DOI: 10.4236/oalib.1104518
Podostemaceae family is well known as a group of aquatic angiosperms with enigmatic characters. The present work was performed to trace ecological aspects, phenology, water analysis and phylogenetic analysis of the genus Zeylanidium, in order to establish the uniqueness of the species in the fresh water habitats S-1 (9.9559°N, 76.8339°E) and S-2 (10.0538°N, 76.8294°E). Through water analysis it is revealed that the species of plants could be used as an indicator of pollution as they are present in very sensitive area of running fresh water. The phenology of the taxa understudy paved light to the co-existence of Zeylanidium maheshwari and Zeylanidium lichenoides. The data on comparison of molecular and phylogenic tree reveal that the species are highly related genetically for a sustainable coexistence.
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