Sara Bagheri - Profile on Academia.edu (original) (raw)

Papers by Sara Bagheri

A stable fluid–structure-interaction solver for low-density rigid bodies using the immersed boundary projection method

Journal of Computational Physics, 2016

IUTAM Bookseries, 2009

This paper addresses recent developments in model-reduction techniques applicable to fluid flows.... more This paper addresses recent developments in model-reduction techniques applicable to fluid flows. The main goal is to obtain low-order models tractable enough to be used for analysis and design of feedback laws for flow control, while retaining the essential physics. We first give a brief overview of several model reduction techniques, including Proper Orthogonal Decomposition [3], balanced truncation , and the related Eigensystem Realization Algorithm , and discuss strengths and weaknesses of each approach. We then describe a new method for analyzing nonlinear flows based on spectral analysis of the Koopman operator, a linear operator defined for any nonlinear dynamical system. We show that, for an example of a jet in crossflow, the resulting Koopman modes decouple the dynamics at different timescales more effectively than POD modes, and capture the relevant frequencies more accurately than linear stability analysis.

Nature Communications, 2014

Plants and animals use plumes, barbs, tails, feathers, hairs and fins to aid locomotion. Many of ... more Plants and animals use plumes, barbs, tails, feathers, hairs and fins to aid locomotion. Many of these appendages are not actively controlled, instead they have to interact passively with the surrounding fluid to generate motion. Here, we use theory, experiments and numerical simulations to show that an object with a protrusion in a separated flow drifts sideways by exploiting a symmetry-breaking instability similar to the instability of an inverted pendulum. Our model explains why the straight position of an appendage in a fluid flow is unstable and how it stabilizes either to the left or right of the incoming flow direction. It is plausible that organisms with appendages in a separated flow use this newly discovered mechanism for locomotion; examples include the drift of plumed seeds without wind and the passive reorientation of motile animals. length ratioL ¼ L=D. (a) Vorticity contour levels (solid lines) show the von Kárman vortex street developing in the wake of the falling body (Re ¼ 156, r ¼ 1.01,L ¼ 1:0). As a result of the IPL instability, the body turns by y ¼ 19 degrees and drifts by a ¼ 8 degrees with respect to gravity (Supplementary Movie 3). The turn and drift angles as functions of the splitter-plate length are shown, respectively, in b and c for Re ¼ 45 and r ¼ 1.001. Predictions of the analytical model (B max ¼ 1.26D, k ¼ 0.90) are shown with solid blue lines in b and c. NATURE COMMUNICATIONS |

Various Antioxidative Activities of Iranian Walnut ( Juglans regia L.) Green Husks Hydroalcoholic Extract and its Effects on LDL Oxidation

Journal of Biologically Active Products from Nature, 2012

ABSTRACT Walnuts contain several antioxidant compounds which are thought to contribute to their b... more ABSTRACT Walnuts contain several antioxidant compounds which are thought to contribute to their biological properties. The present work investigated the various antioxidative activities of walnut (Juglans regia L.) green husks hydroalcoholic extract (W) and its effect on oxidation of LDL induced by CuSO 4 in vitro by monitoring the formation of conjugated dienes and thiobarbituric acid reactive substances (TBARS). It was demonstrated that total antioxidant capacity of W was 307±30 nmol of ascorbic acid equivalents/g W. The W showed remarkable scavenging activity on 2,2-diphenyl-picrylhydrazyl (DPPH) (IC 50 1819 μg/ml). Total

An agarose-Schiff's base chelating adsorbent for preconcentration and flame atomic absorption spectrophotometric determination of Cu (II) in water samples

Journal of Biologically Active Products from Nature ISSN Print: 2231-1866 Online: 2231-1874 www. jbappn. com

emisa persica Art ( ‫اﺣﻤﺪوﻧﺪ‬ ‫ﺣﺴﻦ‬ 1 ، ‫اﻣﻴﺮ‬ ‫ﺣﻤﺰه‬ ‫ي‬ 2 ، ‫داﻟﻮﻧﺪ‬ ‫ﺣﻤﻴﺪ‬ 3 ‫ﭘﺰ‬ ‫ﻋﻠﻮم‬ ‫داﻧﺸ... more emisa persica Art ( ‫اﺣﻤﺪوﻧﺪ‬ ‫ﺣﺴﻦ‬ 1 ، ‫اﻣﻴﺮ‬ ‫ﺣﻤﺰه‬ ‫ي‬ 2 ، ‫داﻟﻮﻧﺪ‬ ‫ﺣﻤﻴﺪ‬ 3 ‫ﭘﺰ‬ ‫ﻋﻠﻮم‬ ‫داﻧﺸﮕﺎه‬ ‫ﻋﻠﻤﻲ‬ ‫ﻣﺠﻠﻪ‬ ‫ﺑﻴﺮﺟﻨﺪ‬ ‫ﺷﻜﻲ‬ ‫دوره‬ 20 ‫ﺷﻤﺎره‬ ، 2 ، ‫زﻣﺴﺘﺎن‬ 1392

Model-based and adaptive laminar-flow control via dielectric-barrier-discharge plasma actuators: an experimental comparison

Synthesis and Characterization of Graphene Thin Films by Chemical Reduction of Exfoliated and Intercalated Graphite Oxide

Journal of Chemistry, 2013

ABSTRACT Commercial flakes of graphite were prepared into functionalized graphene oxide (GO) by c... more ABSTRACT Commercial flakes of graphite were prepared into functionalized graphene oxide (GO) by chemical treatment. After the exfoliation and intercalation of graphene into functionalized graphene oxide that formed stable colloidal dispersion in polar aprotic solvent, the reduction process was undertaken by continuous stirring with hydrazine hydrate. The reduced material was characterized by X-ray diffraction (XRD), attenuated total reflectance (ATR) FT-IR, ultraviolet visible (UV-vis), atomic force microscopy (AFM) and Raman spectroscopy which confirm the oxidation of graphite and reduction of graphene oxide into graphene sheet.

Journal of Magnetism and Magnetic Materials, 2015

In this contribution, we prepared water-based magnetic fluids of iron oxide nanoparticles using a... more In this contribution, we prepared water-based magnetic fluids of iron oxide nanoparticles using an insitu precipitation method. The effect of dodecanoic acid addition as a surfactant on the physico-chemical and magnetic properties of iron oxide nanoparticles was investigated as well. The quantity of the surfactant was varied between 3 and 5 g. Raman spectroscopy and X-ray diffraction (XRD) were utilized to confirm the presence of spinel phase magnetites (Fe 3 O 4 ). Dynamic light scattering (DLS) and transmission electron microscopy (TEM) were used to characterize the resulting magnetic nanoparticles' size and morphology. The results showed polydispersed hexagonal nanoparticles (average diameter of ca. 70 nm) as a result of the protocol. Moreover, the pH-dependent stability of the samples confirms that magnetite nanofluids were highly stable in the wide range of pH, from 4-12. The optimal amount of dodecanoic acid to produce ultra-stable nano-magnetite slurry with the highest saturation magnetization of 8.6 emu g À 1 was determined to be 4.5 g.

Linear control of 3D disturbances on a flat-plate

Adaptive and model-based control theory applied to convectively unstable flows

Applied Mechanics Reviews, 2014

ABSTRACT Research on active control for the delay of laminar-turbulent transition in boundary lay... more ABSTRACT Research on active control for the delay of laminar-turbulent transition in boundary layers has made a significant progress in the last two decades, but the employed strategies have been many and dispersed. Using one framework, we review model-based techniques, such as linear-quadratic regulators, and model-free adaptive methods, such as least-mean square filters. The former are supported by a elegant and powerful theoretical basis, whereas the latter may provide a more practical approach in the presence of complex disturbance environments, that are difficult to model. We compare the methods with a particular focus on efficiency, practicability and robustness to uncertainties. Each step is exemplified on the one-dimensional linearized Kuramoto-Sivashinsky equation, that shows many similarities with the initial linear stages of the transition process of the flow over a flat plate. Also, the source code for the examples are provided.

BioMed Research International, 2014

Among the wide range of renewable energy sources, the ever-increasing demand for electricity stor... more Among the wide range of renewable energy sources, the ever-increasing demand for electricity storage represents an emerging challenge. Utilizing carbon nanotubes (CNTs) for energy storage is closely being scrutinized due to the promising performance on top of their extraordinary features. In this work, well-aligned multilayer carbon nanotubes were successfully synthesized on a porous silicon (PSi) substrate in a fast process using renewable natural essential oil via chemical vapor deposition (CVD). Considering the influx of vaporized multilayer vertical carbon nanotubes (MVCNTs) to the PSi, the diameter distribution increased as the flow rate decreased in the reactor. Raman spectroscopy results indicated that the crystalline quality of the carbon nanotubes structure exhibits no major variation despite changes in the flow rate. Fourier transform infrared (FT-IR) spectra confirmed the hexagonal structure of the carbon nanotubes because of the presence of a peak corresponding to the carbon double bond. Field emission scanning electron microscopy (FESEM) images showed multilayer nanotubes, each with different diameters with long and straight multiwall tubes. Moreover, the temperature programmed desorption (TPD) method has been used to analyze the hydrogen storage properties of MVCNTs, which indicates that hydrogen adsorption sites exist on the synthesized multilayer CNTs.

Talanta, 2005

An agarose-based anion exchanger (Q-Sepharose) was loaded with chromotropic acid (CTA) and used f... more An agarose-based anion exchanger (Q-Sepharose) was loaded with chromotropic acid (CTA) and used for column preconcentration and determination of copper by flame AAS. Preliminary experiments indicated that a sample pH of 5.7-6.5 is best suited for accumulation of copper and a 2.5 ml portion of a 0.02 mol l −1 HCl solution can efficiently desorb the analyte from the column. An incomplete factorial design was used for optimization of five different variables that affect recovery of copper. The results indicated that ionic strength, pH and sample volume variables are the most important effects, respectively. Hence, these variables and their possible interactions were studied more carefully. In optimized conditions, the column could tolerate up to 0.18 mol l −1 sodium nitrate in the matrix. A 5 ml portion of a 0.02 mol l −1 CTA was sufficient for loading of a 0.5 ml column prior to preconcentration of copper from a 150 ml sample solution. Matrix ions of Ca 2+ , Mg 2+ , Na + and K + and potentially interfering ions of Pb 2+ , Ni 2+ , Cd 2+ , Co 2+ , Zn 2+ and Mn 2+ with relatively high concentrations did not have any significant effect on the recovery of the analyte. A preconcentration factor of 60 and a detection limit of 1.0 g l −1 was obtained for the determination of copper by the flame AAS method. A precision better than 2.5%, expressed as R.S.D., was also achieved. Application of the method to tap water and two different river water samples resulted in values well confirmed by direct determinations with ET-AAS.

SIAM Journal on Applied Dynamical Systems, 2010

Reduced-order models of the nonlinear complex Ginzburg-Landau (CGL) equation are computed using a... more Reduced-order models of the nonlinear complex Ginzburg-Landau (CGL) equation are computed using a nonlinear generalization of balanced truncation. The method involves Galerkin projection of the nonlinear dynamics onto modes determined by balanced truncation of a linearized system and is compared to a standard method using projection onto proper orthogonal decomposition (POD) modes computed from snapshots of nonlinear simulations. It is found that the nonlinear reducedorder models obtained using modes from linear balanced truncation capture very well the transient dynamics of the CGL equation and outperform POD models; i.e., a higher number of POD modes than linear balancing modes is typically necessary in order to capture the dynamics of the original system correctly. In addition, we find that the performance of POD models compares well to that of balanced truncation models when the degree of nonnormality in the system, in this case determined by the streamwise extent of a disturbance amplification region, is lower. Our findings therefore indicate that the superior performance of balanced truncation compared to POD/Galerkin models in capturing the input/output dynamics of linear systems extends to the case of a nonlinear system, both for the case of significant transient growth, which represents a basic model of boundary layer instabilities, and for a limit cycle case that represents a basic model of vortex shedding past a cylinder.

Proceedings of the National Academy of Sciences, 2006

Recent studies have demonstrated a role for telomerase in driving tumor progression, but its mech... more Recent studies have demonstrated a role for telomerase in driving tumor progression, but its mechanism of action remains unclear. Here we show that stable, ribozyme-mediated suppression of mouse telomerase RNA reduced telomerase RNA expression, telomerase activity, and telomere length, which significantly reduced tumor invasion and metastatic potential. Our studies reveal that previously unidentified effects of telomerase may mediate its tumor-promoting effects. First, reducing telomerase activity induced a more dendritic morphology, accompanied by increased melanin content and increased expression of tyrosinase, a key enzyme in melanin biosynthesis. Second, gene expression profiling revealed that telomerase targeting down-regulated expression of several glycolytic pathway genes, with a corresponding decrease in glucose consumption and lactate production. Thus, telomerase activity controls the glycolytic pathway, potentially altering the energy state of tumor cells and thereby modulating tyrosinase activity and melanin production. These studies have important implications for understanding the mechanisms by which telomerase promotes tumor invasion and metastasis.

Physics of Fluids, 2011

The nonlinear stability of laminar sinuously bent streaks is studied for the plane Couette flow a... more The nonlinear stability of laminar sinuously bent streaks is studied for the plane Couette flow at Re ¼ 500 in a nearly minimal box and for the Blasius boundary layer at Re d Ã ¼ 700. The initial perturbations are nonlinearly saturated streamwise streaks of amplitude A U perturbed with sinuous perturbations of amplitude A W . The local boundary of the basin of attraction of the linearly stable laminar flow is computed by bisection and projected in the A U -A W plane providing a well defined critical curve. Different streak transition scenarios are seen to correspond to different regions of the critical curve. The modal instability of the streaks is responsible for transition for A U ¼ 25%-27% for the considered flows, where sinuous perturbations of amplitude below A W % 1%-2% are sufficient to counteract the streak viscous dissipation and induce breakdown. The critical amplitude of the sinuous perturbations increases when the streamwise streak amplitude is decreased. With secondary perturbations amplitude A W % 4%, breakdown is induced on stable streamwise streaks with A U % 13%, following the secondary transient growth scenario first examined by Schoppa and Hussain [J. Fluid Mech. 453, 57 (2002)]. A cross-over, where the critical amplitude of the sinuous perturbation becomes larger than the amplitude of streamwise streaks, is observed for streaks of small amplitude A U < 5%-6%. In this case, the transition is induced by an initial transient amplification of streamwise vortices, forced by the decaying sinuous mode. This is followed by the growth of the streaks and final breakdown. The shape of the critical A U -A W curve is very similar for Couette and boundary layer flows and seems to be relatively insensitive to the nature of the edge states on the basin boundary. The shape of this critical curve indicates that the stability of streamwise streaks should always be assessed in terms of both the streak amplitude and the amplitude of spanwise velocity perturbations.

Transition delay using control theory

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2011

This review gives an account of recent research efforts to use feedback control for the delay of ... more This review gives an account of recent research efforts to use feedback control for the delay of laminar-turbulent transition in wall-bounded shear flows. The emphasis is on reducing the growth of small-amplitude disturbances in the boundary layer using numerical simulations and a linear control approach. Starting with the application of classical control theory to two-dimensional perturbations developing in spatially invariant flows, flow control based on control theory has progressed towards more realistic three-dimensional, spatially inhomogeneous flow configurations with localized sensing/actuation. The development of low-dimensional models of the Navier-Stokes equations has played a key role in this progress. Moreover, shortcomings and future challenges, as well as recent experimental advances in this multi-disciplinary field, are discussed.

The persistent risk of genital tumors among men treated with psoralen plus ultraviolet A (PUVA) for psoriasis

Journal of the American Academy of Dermatology, 2002

In the general population, squamous cell carcinomas (SCCs) of the male genitalia are rare. Ten ye... more In the general population, squamous cell carcinomas (SCCs) of the male genitalia are rare. Ten years ago, we documented a significant dose-dependent increase in the risk of malignant genital neoplasms among men treated with psoralen plus ultraviolet A (PUVA). Since that time, fewer cohort patients have used PUVA, and genital protection among PUVA users is likely to be frequent. Our aim was to determine the incidence and risk factors for genital neoplasms since 1989 and risk factors for these neoplasms among patients treated with PUVA. We conducted a prospective cohort study of 892 men first treated with PUVA in 1975-1976. Twenty-four men (2.7%) had 51 genital neoplasms, including 10 patients with a first tumor after May 1, 1989 (the ending date for our 1990 report). Since May 1, 1989, the incidence of invasive penile and scrotal SCCs was elevated 52.6-fold (95% confidence interval, 19.3-114.6) compared with that expected for the general white population. Multivariate models revealed the highest genital tumor risk among men with high-dose exposure to both PUVA and topical tar/ultraviolet B, with an incidence rate ratio of 4.5 (95% confidence interval, 1.3-16.1) compared with the low-dose exposure group. Although use of PUVA has decreased and genital shielding in our cohort has increased, the dose-dependent increase in the risk of genital tumors in men treated with PUVA has persisted. Particularly high risks occur among those with high-dose exposures to both PUVA and topical tar/ultraviolet B.

We used photonic crystal (PC) and nanoporous structure together in Si to decrease the reflection ... more We used photonic crystal (PC) and nanoporous structure together in Si to decrease the reflection and of Si.