Rohit Trivedi - Academia.edu (original) (raw)

Papers by Rohit Trivedi

Metallurgical and Materials Transactions A, 2002

Acta Materialia, 2009

Rapid advances in atomistic and phase-field modeling techniques as well as new experiments have l... more Rapid advances in atomistic and phase-field modeling techniques as well as new experiments have led to major progress in solidification science during the first years of this century. Here we review the most important findings in this technologically important area that impact our quantitative understanding of: (i) key anisotropic properties of the solid-liquid interface that govern solidification pattern evolution, including the solid-liquid interface free energy and the kinetic coefficient; (ii) dendritic solidification at small and large growth rates, with particular emphasis on orientation selection; (iii) regular and irregular eutectic and peritectic microstructures; (iv) effects of convection on microstructure formation; (v) solidification at a high volume fraction of solid and the related formation of pores and hot cracks; and (vi) solid-state transformations as far as they relate to solidification models and techniques. In light of this progress, critical issues that point to directions for future research in both solidification and solid-state transformations are identified.

Acta Materialia, 2015

To characterize the dynamical formation of three-dimensional (3D) arrays of cells and dendrites u... more To characterize the dynamical formation of three-dimensional (3D) arrays of cells and dendrites under diffusive growth conditions, in situ monitoring of a series of experiments on a transparent succinonitrile-0.24 wt% camphor model alloy was carried out under low gravity in the DECLIC Directional Solidification Insert onboard the International Space Station (ISS). The present article focuses on the study of the transient solid-liquid interface recoil. Numerical thermal modeling led us to identify two thermal contributions to the interface recoil that increase with the pulling rate and add to the classical recoil associated with the solute boundary layer formation. As a consequence of those additional contributions, the characteristic front recoil is characterized by a fast initial transient followed by stabilization to a plateau whose location depends on pulling rate. The analysis of comparative experiments carried out on ground shows the absence of stabilization of the interface position, attributed to longitudinal macrosegregation of solute induced by convection. This behavior is surprisingly also observed in space experiments for low pulling rates. An order of magnitude analysis of the mode of solute transport reveals that for these conditions, the effective level of reduced gravity onboard the ISS is not sufficiently low to suppress convection so that the interface recoils with longitudinal macrosegregation in a similar way as in ground experiments.

Materials Science Forum, 2005

Indian journal of experimental biology, 2000

Nitrosoamines such as N-nitrosodiethylamine (NDEA) produce oxidative stress due to generation of ... more Nitrosoamines such as N-nitrosodiethylamine (NDEA) produce oxidative stress due to generation of reactive oxygen species and may alter antioxidant defence system in the tissues. NDEA was administered ip as a single dose to rats in LD50 or in lower amounts and the animals were sacrificed after 0-48 hr of treatment. The results showed that lipid peroxidation in liver increased, however no significant increase in kidney LPO was observed after NDEA administration. Superoxide dismutase (SOD) and glutathione reductase (GSH-R) activity increased in liver, however, catalase (CAT) activity in liver was inhibited in NDEA treated rats. Kidney showed an increase in SOD activity after an initial decrease along with increase in GSH-R activity in NDEA treated rats. However, kidney CAT activity was not significantly altered in NDEA intoxicated rats. Serum transaminases, serum alkaline phosphatase blood urea nitrogen, serum creatinine and scrum proteins were elevated in NDEA treated rats. The result...

Microgravity - Science and Technology, 2005

The topic of pattern formation is important in several fields of sciences, and the process of pat... more The topic of pattern formation is important in several fields of sciences, and the process of pattern selection is quite complex since it occurs in a highly nonlinear growth regime [1]. During the directional solidification of alloys the interface between the solid and the liquid exhibits complex ...

PLoS ONE, 2013

Purpose: To evaluate the effects of pirfenidone nanoparticles on corneal re-epithelialization and... more Purpose: To evaluate the effects of pirfenidone nanoparticles on corneal re-epithelialization and scarring, major clinical challenges after alkali burn. Methods: Effect of pirfenidone on collagen I and a-smooth muscle actin (a-SMA) synthesis by TGFb induced primary corneal fibroblast cells was evaluated by immunoblotting and immunocytochemistry. Pirfenidone loaded poly (lactide-co-glycolide) (PLGA) nanoparticles were prepared, characterized and their cellular entry was examined in primary corneal fibroblast cells by fluorescence microscopy. Alkali burn was induced in one eye of Sprague Dawley rats followed by daily topical treatment with free pirfenidone, pirfenidone nanoparticles or vehicle. Corneal re-epithelialization was assessed daily by flourescein dye test; absence of stained area indicated complete re-epithelialization and the time for complete re-epithelialization was determined. Corneal haze was assessed daily for 7 days under slit lamp microscope and graded using a standard method. After 7 days, collagen I deposition in the superficial layer of cornea was examined by immunohistochemistry. Results: Pirfenidone prevented (P,0.05) increase in TGF b induced collagen I and a-SMA synthesis by corneal fibroblasts in a dose dependent manner. Pirfenidone could be loaded successfully within PLGA nanoparticles, which entered the corneal fibroblasts within 5 minutes. Pirfenidone nanoparticles but not free pirfenidone significantly (P,0.05) reduced collagen I level, corneal haze and the time for corneal re-epithelialization following alkali burn. Conclusion: Pirfenidone decreases collagen synthesis and prevents myofibroblast formation. Pirfenidone nanoparticles improve corneal wound healing and prevent fibrosis. Pirfenidone nanoparticles are of potential value in treating corneal chemical burns and other corneal fibrotic diseases.

Metallurgical and Materials Transactions B, 2004

The value of the diffusion coefficient in the liquid (D l) is generally obtained from the measure... more The value of the diffusion coefficient in the liquid (D l) is generally obtained from the measurement of composition profiles ahead of a quenched planar interface. The experimental results show significant scatter. The main reason for this scatter will be shown to be due to the presence of fluid flow in the liquid. Directional-solidification studies in the Al-Cu system have been carried out to first establish the experimental conditions required for diffusive growth. The composition profiles are then measured to obtain the values of D l for alloy compositions ranging from 4.0 to 24.0 wt pct Cu. The value of was obtained along the liquidus line, and this result is significantly smaller than the values reported in the literature, which vary from 3.0 to 5.5 ϫ 10 Ϫ3 mm 2 /s. It is shown that the scatter in the reported values can be correlated with the diameter of the sample used and, thus, with the fluid flow present in their experiments. Detailed experimental procedures to obtain and verify diffusivegrowth conditions are outlined, and appropriate analyses of the data are discussed.

Metallurgical and Materials Transactions A, 2000

In the two-phase region of a peritectic system, experimental studies have shown that the primary ... more In the two-phase region of a peritectic system, experimental studies have shown that the primary phase (␣) often forms a large treelike structure that is surrounded by the peritectic phase (␤). The formation of this novel structure has been attributed to the presence of convection in the liquid. Here, specific physical mechanisms of convection-induced treelike structure formation are proposed. A mathematical model based on advection-diffusion of solute, with prototype flows for advection, is presented and solved numerically to show that an oscillating fluid motion can give rise to a complex oscillatory, treelike structure. Three different regimes are established: diffusive, steady convective, and unsteady convective regimes. In the diffusive regime, a banded structure is predicted within a narrow composition range, and the spacing of the bands is dictated by the nucleation undercoolings of the two phases. Under steady convection, the primary phase transforms into the peritectic phase with a curved ␣:␤ interface. Finally, in the presence of oscillating convection, a treelike shape of the primary phase is predicted, as observed experimentally. P. MAZUMDER, formerly Graduate Student with the Department of response to unsteadiness in the fluid flow is often sufficient Mechanical Engineering, Iowa State University, is with Corning Inc., Cornto generate complex oscillatory structures. As we shall see,

Metallurgical and Materials Transactions A, 1998

The formation of banded microstructure in peritectic systems is examined theoretically in both di... more The formation of banded microstructure in peritectic systems is examined theoretically in both diffusive and convective regimes. A rigorous model is developed in the diffusive regime that describes the non-steady-state growth of alternate solid ␣ and ␤ phase bands with a planar solid-liquid interface. The model is extended to incorporate the effect of convection by assuming that solute diffusion takes place within a boundary layer of constant thickness, with a uniform composition in the mixed liquid zone outside this layer. The model predicts that convection effects in a semi-infinite sample narrow the composition range over which extended banding can occur, and the spacing of bands is reduced compared to the diffusive growth model. In a finite length sample, convection is shown to lead only to the transient formation of bands. In this transient banding regime, only a few bands with a variable width are formed, and this transient banding process can occur over a wide range of compositions inside the two-phase peritectic region. Directional solidification studies in the Pb-Bi system show transient bands and agree qualitatively with these predictions. However, the basic mechanism of band formation observed in this system is found to be significantly different from the one assumed in the model. A new mechanism of banding is proposed in which continuous growth of both phases is present instead of nucleation at the boundary of the pre-existing phase. This mechanism yields an oscillatory structure with a shorter spatial periodicity than the band spacing predicted by the purely diffusive or boundary layer convective models.

MRS Bulletin, 2004

Materials phenomena ranging from the melting or freezing of ice to biomineralization in living or... more Materials phenomena ranging from the melting or freezing of ice to biomineralization in living organisms, to lubrication and the commercial casting of superalloys, are known to be critically influenced by molecular-scale structure and processes occurring at the interfaces between the crystalline solid and liquid phases. The properties of solid–liquid interfaces have long been a topic of intense interest in materials science, primarily because of their role in governing nucleation, growth, and morphological evolution in crystal growth from the melt or solutions.This issue of the MRS Bulletin provides an overview, highlighting new developments in experiment, theory, and modeling techniques that have led to substantial recent progress in the characterization of the molecular-level structural and thermodynamic properties of solid–liquid interfaces and their consequences for a variety of crystallization phenomena.

IOP Conference Series: Materials Science and Engineering, 2012

Dynamical microstructure formation and selection during solidification processing, which has a ma... more Dynamical microstructure formation and selection during solidification processing, which has a major influence on the properties in the use of elaborated materials, occur during the growth process. In situ observation of the solid-liquid interface morphology evolution is thus necessary. On earth, convection effects dominate in bulk samples and may strongly interact with microstructure dynamics and alter pattern characterization. Series of solidification experiments with 3D cylindrical sample geometry were conducted in succinonitrile (SCN)-0.24 wt%camphor (model transparent system), in microgravity environment in the Directional Solidification Insert of the DECLIC facility of CNES (French space agency) on the International Space Station (ISS). Microgravity enabled homogeneous values of control parameters over the whole interface allowing the obtaining of homogeneous patterns suitable to get quantitative benchmark data. First analyses of the characteristics of the pattern (spacing, order, etc.) and of its dynamics in microgravity will be presented.