behrouz abedian | Tufts University (original) (raw)

Papers by behrouz abedian

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Bulletin of the American …, 2005

The aqueous solution behavior of silk fibroin is of interest due to the assembly and processing o... more The aqueous solution behavior of silk fibroin is of interest due to the assembly and processing of this protein related to the spinning of protein fibers that exhibit remarkable mechanical properties. To gain insight into the origins of this functional feature, it is desired to ...

Journal of the Massachusetts Dental Society, 2002

Oscillating droplets are of interest in a number of disciplines. A practical application is the o... more Oscillating droplets are of interest in a number of disciplines. A practical application is the oscillating drop method, which is a technique for measuring surface tension and viscosity of liquid metals. It is especially suited to undercooled and highly reactive metals, because it is performed by electromagnetic levitation. The natural oscillation frequency of the droplets is related to the surface tension of the material, and the decay of oscillations is related to its viscosity. The fluid flow inside the droplet must be laminar in order for this technique to yield good results. Because no experimental method has yet been developed to visualize flow in electromagnetically-levitated oscillating metal droplets, mathematical modeling is required to determine whether or not turbulence occurs. Three mathematical models of the flow: (1) assuming laminar conditions, (2) using the k-epsilon turbulence model, and (3) using the RNG turbulence model, respectively, are compared and contrasted ...

We discuss experimental results on steady axisymmetric flow of a Newtonian incompressible fluid t... more We discuss experimental results on steady axisymmetric flow of a Newtonian incompressible fluid through circular pipes with side inlets. Circular tubes with a set of holes along their sidewalls are used in a number of medical procedures as straight catheters to transfer fluid into or out of the human body. For example, because of the small size of the incision required, they are commonly used in peritoneal dialysis. The internal diameter and the diameter of the side holes are often 1 mm and less, and as a result, the fluid flow is laminar in a typical medical procedure. An understanding of the flow inside the catheter tube in terms of its geometric parameters will be key in designing new catheters with optimal clinical performance for specific applications. In the experiments, water is withdrawn from a smooth tube with side holes and the local axial pressure and flow rates through the side holes are measured for different flow conditions. A nondimensionalization of the data shows a ...

Operative Dentistry, 2006

SUMMARY Cavity lining with flowable composites has been suggested for better marginal adaptation ... more SUMMARY Cavity lining with flowable composites has been suggested for better marginal adaptation and a reduction in interfacial stress and post-operative sensitivity. The following in vitro study compares the spreading of flowable composite that lines the inner wall of a test cavity using an explorer and a specially designed smooth, oscillating, off-center rotating bur spun at 300 to 600 rpm. Two commercial flowable materials were used in this study. Results: With use of the rotating bur, a more consistent, uniform cavity lining was achieved. This was not possible using the dental explorer. Conclusion: The specially designed rotating bur provides an effective way for clinicians to form a uniform cavity lining.

We address dynamic interactions between high-energy, reactive surfaces of polymer-matrix composit... more We address dynamic interactions between high-energy, reactive surfaces of polymer-matrix composites and solid surfaces. A common characteristic of these interfaces is that bonding occurs readily upon contact. In many industrial and biomedical applications, it is desirable to suppress this bonding phenomenon. This interfacial effect is discussed in light of the development of our new method of handling polymer-matrix composites in dental applications. This method involves vibration of the solid-polymer interface at different frequencies. For each material, there is a phcritical frequency at which the sum of the viscoelastic and inertial energies of the fluid at the surface exceeds the energy available for bonding. When the polymer is vibrated at or beyond this frequency, it does not adhere to solid surfaces. An important aspect of the developed process is that it can be used to characterize surface and interfacial properties of polymers under dynamic conditions, whereas existing tech...

Journal of Polymer Science Part B: Polymer Physics, 1998

The purpose of this article is to develop a mathematical model that describes photocure and photo... more The purpose of this article is to develop a mathematical model that describes photocure and photopolymerization kinetics. This model is neither wholly phenomenological nor mechanistic, but contains elements of both. We draw an analogy between the classical Avrami approach for first-order phase transformations and the kinetic phenomena that occur during photocuring, and take into account cure inhibition due to a decrease in mobility of the constituents. The result is an explicit algebraic two-parameter expression for the extent of cure versus time. More importantly, the two parameters have physical significance, and to some extent can be predicted a priori. The model is compared to three sets of unrelated data, and excellent agreement is obtained, except for part of the data at the onset of the reactions. Physical insight obtained by comparing our theory with experiments supports the existence of preferred sites for initiating the reaction, and indicates that irradiation is the rate-limiting step in the overall cure process in the limit of small irradiation intensities.

Journal of Colloid and Interface Science, 2006

This paper investigates the nonideal electrowetting behavior of thin fluoroploymer films. Results... more This paper investigates the nonideal electrowetting behavior of thin fluoroploymer films. Results are presented for a three phase system consisting of: (1) an aqueous water droplet containing sodium dodecyl sulfate (SDS), (2) phosphorous-doped silicon topped with SiO2 and an amorphous fluoroploymer (aFP) insulating top layer on which the droplet is situated, and (3) a dodecane oil that surrounds the droplet. The presented measurements indicate that the electrowetting equation is valid down to a 6 nm thick aFP film on a 11 nm thick SiO2. At this dielectric thickness, a remarkable contact angle change of over 100 degrees can be achieved with an applied voltage less than 3 V across the system. The data also shows that for this water/surfactant/oil system, contact angle saturation is independent of the electric field, and is reached when the surface energy of the solid-water interface approaches zero.

Journal of Applied Physics, 2013

The problem of modeling contact angle saturation in electrowetting has resisted a number of conce... more The problem of modeling contact angle saturation in electrowetting has resisted a number of concentrated efforts by leading researchers. Several models have been proposed, from charge trapping, to droplet ejection, to thermodynamic instability, but no consensus has been reached as to which model better describes the effect. In this paper, we validate the charge trapping based model of contact angle saturation in electrowetting on lipid bilayers, through careful analysis of charge movement between the liquid charge states and trapped charge states at the solid dielectric interface. We also describe a powerful new methodology for studying electrowetting systems by modeling them with an equivalent circuit and simulating the circuit using the SPICE circuit simulator. V

International Journal of Heat and Mass Transfer, 1985

Thespreadinganddecayingofachargedffuidthatisissuedintoastagnantfluidasanunconstraintsubmerged tur... more Thespreadinganddecayingofachargedffuidthatisissuedintoastagnantfluidasanunconstraintsubmerged turbulentjet isinvestigated.Thedynamicconservationequationofchargeissoived analytically for the mean charge density field in the flow by assuming a simple velocity field and numerically by using a more accurate velocity field. It is shown that the characteristics of a charged jet can be described by a dimensionless length ratio defined as avJ/uuj with E and (r being the fluid electrical permittivity and the fluid electrical condu~ti~ty, respectively. Based on the electrostatic properties of a charged jet, three conductivity ranges were identified. In the high-conductivity range, when u > 0.2 .sV,/aj, the charged region is confined only to the near field. In the other extreme, for IJ < 0.002 &I(/aj, there is a low-conductivity range in which the charge density field in the flow behaves analogously to other conservative scalar field properties in a turbulent jet with similar ratesofdecay and spread. The intermediate conductivity range falls between these two limits and here charge dispersion is controlled by migration and diffusion.

International Journal of Engineering Science, 2010

This work discusses the classical problem of effective viscosity of a Newtonian fluid with rigid ... more This work discusses the classical problem of effective viscosity of a Newtonian fluid with rigid spherical particles. It argues that the simple non-interaction approximation when formulated correctly yields an effective viscosity ratio for the suspension in the form l/ l 0 = (1 À 2.5/) À1 that remains accurate at much higher volume fractions of particles / than the usual first-order approximation l/l 0 = 1 + 2.5/.

IEEE Transactions on Dielectrics and Electrical Insulation, 2008

The effect of temperature on electrical conductivity of low-conductivity liquid solutions is disc... more The effect of temperature on electrical conductivity of low-conductivity liquid solutions is discussed theoretically and experimentally. A well-known expression for liquid viscosity is used to derive an empirical correlation for temperature dependency of electrical conductivity of insulating liquids. Five different solutions all composed of polyol (hindered) esters were tested over a wide temperature range. Viscosity measurements were used to extract the constants in the viscosity correlation. The measured electrical conductivity of the tested fluids varied over 1000-fold for the temperature range. It is shown that the suggested correlation could predict reasonably well the temperature dependency of electrical conductivity for single-phased solutions.

Journal of Microelectromechanical Systems, 2009

This paper reports on the design, fabrication, and performance of micro-sized fluidic devices tha... more This paper reports on the design, fabrication, and performance of micro-sized fluidic devices that use electrowetting to control and transport liquids. Using standard microfabrication techniques, new pumping systems are developed with significantly more capability than open digital microfluidic systems that are often associated with electrowetting. This paper demonstrates that, by integrating closed microchannels with different channel heights and using electrowetting actuation, liquid interfaces can be controlled, and pressure work can be done, resulting in fluid pumping. The operation of two different on-chip pumps and devices that can form water drops is described. In addition, a theory is presented to explain the details of single-electrode actuation in a closed channel.

Chemical Engineering Science, 1988

Metallurgical and Materials Transactions B, 2000

This article details an effort to improve the understanding and prediction of turbulent flow insi... more This article details an effort to improve the understanding and prediction of turbulent flow inside a droplet of molten metal levitated in an electromagnetic field. It is shown that the flow field in a test case, a nickel droplet levitated under microgravity conditions, is in the transitional regime between laminar and turbulent flow. Past research efforts have used laminar, enhanced viscosity, and kϪ turbulence models to describe the flow. The method highlighted in our study is the renormalization group (RNG) algorithm. We show that an accurate description of the turbulent eddy viscosity T is critical in order to obtain realistic velocity fields, and that T cannot be uniform in levitated droplets. The RNG method does not impose isotropic length or time scales on the flow field, thus allowing such nonuniform features to be captured. A number of other materials processing applications exhibit similarly complex flow characteristics, such as highly recirculating, transitional, and free surface flows, for which this modeling approach may prove useful.