The following is a synopsis of published papers by Eshel Faraggi.

Dynamics of Ferromagnetism:

Ferromagnetism, Hysteresis and Chaos:

1. Daniel T. Robb, Linda E. Reichl, and Eshel Faraggi, "Simulation of hysteresis in magnetic nanoparticles with Nose thermostatting". Physical Review E 67(5), 056130 (2003).

Much of the dynamics of ferromagnetism has to do with the temperature it is at. One method of modeling temperature is essentially assuming that the system is coupled to a thermostat. In this paper this highly analytical method was utilized while showing the emergence of chaos in the local magnetization of a growing ferromagnet. This study has significant impact on the proper use of a major model of ferromagnetism. The use of this method allowed the modeling of nanoscale hysteresis curves.

The Dilute Ferromagnet:

2. Eshel Faraggi, Linda E. Reichl, and Daniel T. Robb, "Magnetic behavior of partially filled finite Ising surfaces". Physical Review B 74(1) 014407 (2006).

A major question facing any use of magnetic materials is the minimum usable ferromagnetic density. A calculation based on the methods of statistical mechanics, and first performed in reference 2 above demonstrated that local ferromagnetic order exists bellow the previously accepted minimum value, known as the percolation threshold. This local phase of magnetization, known as superparamagnetism, will determine the ultimate storage capacity of magnetic storage devices such as hard-drives and holds one of the keys to spintronic applications.

Hysteresis:

2. Eshel Faraggi, Linda E. Reichl, and Daniel T. Robb, "Magnetic behavior of partially filled finite Ising surfaces". Physical Review B 74(1) 014407 (2006).

3. Corneliu Nistor, Eshel Faraggi, J. L. Erskine, "Magnetic Energy Loss in Permalloy Thin Films and Microstructures". Physical Review B 72, 014404 (2005).

4. Eshel Faraggi, "Explicit solutions to phenomenological models of magnetization reversal of thin ferromagnetic films in the presence of a sawtooth magnetic field". Journal of Magnetism and Magnetic Materials 303(1), 49 (2006).

Hysteresis is the fundamental building block behind magnetic memory. The processes of storing and retrieving information requires energy that is converted into heat (dissipation). A very important question regarding hysteresis is the dependence (or scaling) of this dissipation of the system parameters. Most notably on the frequency of the sweeping field since this will determine the speeds at which writing is possible. In reference 2 above it was shown that the dependence on frequency changes as the temperature of the ferromagnet is changed. In references 3 and 4 a phenomenological model was developed and solved for the hysteresis phenomenon. This model was able to analytically predict hysteresis losses for over nine decades of frequency (nine orders of magnitude), a feat not possible before. With the aid of the phenomenological model it was also possible to illuminate more on the breakdown of the so called adiabatic scaling.

Locally Converging Algorithms:

5. Eshel Faraggi and Daniel T. Robb, "Locally converging algorithms in Ising models". Submitted to Physical Review B (2003).

An offshoot from the investigation into the dilute ferromagnet is the development of the locally converging algorithm for the critical temperature. This algorithm is a continuation of the ideas of the invaded cluster algorithm which was developed in the 1990's. These models contain feedback loops that drive the system towards their critical points automatically. The full impact of these models is not well understood at this time, but their impact will range from a better understanding of the critical point of ferromagnetism to adapting algorithms for complex systems.

Spherical Absorber:

A ball immersed in fluid and illuminated by a laser pulse allows fundamental observations throughout the realm on condensed matter. My research focuses on these absorbers as models for melanosome that are present in our skin, and most notably in our eyes where they serve, among other functions, to shield the bloodstream from radiation. The sizes of the absorbers I model range from tens of nanometers to several microns, while melanosomes are approximately one micrometer in diameter.

Shockwaves:

6. Eshel Faraggi, Bernard S. Gerstman, and Jinming Sun, "Biophysical Effects of Pulsed Lasers in the Retina and Other Tissues with Strongly Absorbing Particles: Shockwaves and Explosive Bubble Generation". Journal of Biomedical Optics 10, 64029—1-12 (2005).

-- Bernard S. Gerstman, Shijun Wang, and Eshel Faraggi, "Ab-Initio Calculations for Shock Wave and Bubble Production with Gaussian Temporal Laser Pulses". Proceedings of the SPIE, Progress in Biomedical Optics and Imaging, Vol. 5319, pp. 217-223 (2004)

-- Eshel Faraggi, Shijun Wang, and Bernard Gerstman, "Stress confinement, shock wave formation, and laser-induced damage". Proceedings of the SPIE Vol. 5695, pp. 209-215 (2005).

-- Eshel Faraggi, Bernard S. Gerstman, and Shijun Wang, " Linear approximation for shock wave production by the spherical absorber". (2006).

One of the multitude of phenomena occurring in the illuminated spherical absorber is a shockwave. This wave, emitted for ultrashort pulses (sub nanosecond), are important for a variety of applications, e.g., underwater explosive detonation. In the context of melanosomes these shockwaves can be most damaging to the surrounding biological tissue. In a first of a kind calculation, the shockwaves produced by the melanosome were studied as a function of the laser/medium characteristics, as well as their decay in the media. Linear approximations were carried out to produce robust, simple, analytical expressions for the magnitude of the shockwaves as a function of the system parameters.

Bubbles:

Another very important aspect of the illuminated spherical absorber is the production of explosive vaporization around the melanosomes. These bubbles can be damaging to tissue, but they can also be used to stimulate repair in cells. One known mechanism for this is shock-protein generation. With the use of a custom designed simulation, the bubble production around melanosomes was studied. Besides giving researchers analytical predictions for the size of bubbles produced for a given laser, these results indicate the theoretical possibility of determining minimal bubble production in vivo. This is of vital importance for several laser surgery applications that require minimum bubble production. Such studies may eventually offer a cure for some forms of blindness.

Resonant Absorption:

8. Eshel Faraggi, Bernard S. Gerstman, "Resonant absorption of pulsed laser radiation by a spherical absorber". Submitted to the Journal of Applied Physics (2006).

-- Eshel Faraggi, Bernard S. Gerstman, and Shijun Wang, "Response to pulsed radiation by a spherical solid absorber immersed in a transparent fluid". Proceedings of the SPIE Vol. 5696, pp. 101-109 (2005).

-- Eshel Faraggi, Bernard S. Gerstman, "Resonant absorption in nanometer gold spherical particles". Proceedings of the SPIE, Vol. 6084, (2006).

A spherical absorber acted upon by consecutive laser pulses will behave differently depending on the duration between the pulses. For specific, resonant durations, the response has a highly acoustic component for example as shockwaves. For other durations the acoustic response is suppressed. Yet simple, this profound discovery presented in reference 8 implies that the interaction between lasers and matter can be manipulated by designing specific pulse sequences. Such considerations can greatly increase the potential of many laser applications. Most notably, in photo-dynamic therapy application for cancer.

Chaos:

9. Eshel Faraggi, Bernard S. Gerstman, and Jinming Sun, "The emergence of nonlinear behavior and chaos in laser irradiated spherical absorber". Accepted by the Journal Chaos (To be published March 2007).

-- Bernard S. Gerstman, Eshel Faraggi, and Jinming Sun, "Chaos in the pressure generated by laser absorption by microparticles". Proceedings of the SPIE, Vol. 6084, (2006).

The existence of chaos in medical applications is intriguing. It presents both beneficial and hazardous prospects depending on the circumstances. In this set of publications the existence of chaos and its location in the parameter space of the spherical absorber system was established. These chaotic signals have a spiky nature and these unpredictable spikes tend to have large gradients which can cause damage. Of course anything that can cause damage can be made beneficial in various treatments, e.g., for killing cancer.

Superposition:

10. Eshel Faraggi and Bernard Gerstman," A superposition test for the emergence of nonlinearities in a laser irradiated spherical absorber". Submitted to Physical Review Letters (2007).

The principal of superposition lays at the foundation of linear physics. In this forthcoming paper, the validity of superposition is tested and linked to the existence of nonlinear phenomena. Analytical expressions are proposed for the dividing line between the linear and nonlinear regimes of the system in parameter space.

Pulse Shape Dependence:

11. Eshel Faraggi, Bernard S. Gerstman, and Shijun Wang, "Effect of temporal pulse shape in laser absorption by a spherical absorber". (2006). Submitted to the Journal of Lasers in Surgery and Medicine (2007).

The dependence of the thermomechanical response of a spherical particle on the temporal shape of the laser pulse is of interest to researchers wishing to utilize this system in various applications. In the above mentioned paper this dependence was studied. It was found that the most critical dependence of the response is for time scales that are longer than the critical acoustic time of the absorber.

Biological Cell Division:

12. Eshel Faraggi, "An electrostatic model for biological cell division". Submitted to Physica A (2006).

A fundamental process associated with cellular biology is the division of a parent cell into two (or more) daughter cells. This process is common to almost all biological system and a better understanding of it will have profound implications for biology in general and medicine in particular. In this, first paper on this subject, a theoretical framework is developed for cell division where the mechanics of separation are carried out by electromagnetic interactions. If indeed cell division is governed by electromagnetism, this knowledge will help guide applications interacting with biological materials via electromagnetic interactions and will benefit medicine immensely.