Spring 2006

Feburary 15, 2006
Dr. Deqing Ren
Center for Solar-Terrestrial Research
Department of Physics, New Jersey Institute of technology

Title: Solar Adaptive Optics for High-Resolution Imaging

The fundamental observational success of a solar telescope depends on its spatial resolution and collected light flux that transfer to its instrumental focal plane. Recently, there have been increasing applications of adaptive optics for solar observations. Adaptive optics is enabling diffraction-limited imaging to resolve the fundamental scales of the solar fine structure that is critical for solar observation. Studies designed to verify theoretical model predictions depend on the ability to clearly resolve solar astrophysical processes on their intrinsic scales, which occur on scales smaller than 100 km.

In a joint effort, New Jersey Institute of Technology (NJIT) and National Solar Observatory (NSO) have successfully developed high- order Adaptive Optics systems, which can, in real time, correct the wavefront error induced by the atmospheric turbulence. The systems are being operated at NSO Dunn Solar telescope and Big Bear Solar Observatory (BBSO). I will introduce the general principle of solar adaptive optics, and present the systems that are being operated at NSO and BBSO. The adaptive optics is providing new applications for both instrument development and solar astrophysics, which I will address. Future development of solar adaptive optics will also be discussed.



Feburary 22, 2006
Dr. Vasyl Yurchyshyn
Big Bear Solar Observatory
30486 North Shore Lane, Big Bear City, CA 92314

Title: Solar Eruptions and Space Weather

We are currently elaborating an approach to routinely forecast the intensity of the magnetic field in interplanetary ejecta and the magnitude of geomagnetic storms, associated with them. At the beginning I will briefly introduce solar white light, H-alpha and magnetic data, major terms and demonstrate observed solar phenomena relevant to eruption of coronal magnetic fields. Also I will present the latest observations and results on solar magnetic fields, coronal mass ejections and associated and interplanetary ejecta.



Feburary 24, 2006
Dr. Yohannes Shiferaw
Department of Cardiology
David Geffen School of Medicine
UC Los Angeles

Title: Pattern formation of voltage and calcium in cardiac cells

The contraction of a cardiac cell is mediated by the release of calcium from intracellular stores. At the subcellular level calcium release is spatially distributed over the extent of the cell and non trivial spatial patterns can emerge. When an isolated cardiac cell is paced rapidly it can exhibit an alternating pattern (alternans) of calcium release from one beat to the next. In this talk I will describe numerical and analytic studies of the spatiotemporal dynamics of subcellular calcium when a cell is paced rapidly. The main result of this study is the existence of a pattern forming instability that is analogous to the classic Turing instability. This instability is mediated by the diffusion of membrane voltage and intracellular calcium, and is found to rely on the bi-directional coupling between these species. We describe the conditions for this instability to occur in terms of basic cell electrophysiology, and present a simplified mathematical description of the pattern formation process. We also discuss the potential relevance of our findings to heart rhythm disorders.



March 1, 2006
K. N. Tu
Department of Materials Science and Engineering
UC Los Angeles

Title: Trend in semiconductor technology and nano-materials research

Abstract: Approaching the end of Moore's law, the trend in semiconductor technology is moving towards nanoscale integration.

The advance in nano-technology depends on the development of nano materials. The NSF/NIRT project at CSUN/UCLA on "Nano-structured materials for interconnect and packaging technology" is to explore unique materials properties at nano-scale for near-future nano devices. We have selected nano-twinned copper thin films as conductors, hollow nano silicon dioxide particles as dielectrics, and nano-wires of silicide as source/drain contacts on nano silicon wires. In this talk, the research on these topics will be presented.



March 2, 2006
Dr. Guo Yang
New Jersey Institute of Technology

Title: High Resolution Solar Observations

Abstract: The Sun is the nearest star to the Earth. The Sun exerts a lot of influences on the Earth. It affects various aspects of activities of human beings and other life forms on the Earth. So studying the Sun, monitoring and even predicting the Sun's activity has become essential tasks for scientists. In this talk, a general introduction to the Sun is given. The physical processes occur inside the Sun are introduced. Different forms of solar activity are introduced. The concept of space weather and its connection with the solar activity.

Resolution of ground-based solar telescope is limited by seeing effect. Speckle masking imaging is one of several methods that can mitigate seeing effect and improve resolution of solar images. A system that uses the full power of speckle masking imaging by parallel processing to obtain high-spatial resolution images of the solar surface in near real-time is introduced.

A solar active region has been studied using high resolution data obtained by speckle masking imaging. Evolution of a pore in an active region is presented. Formation of a rudimentary penumbra is studied. The effects of the change of the magnetic fields on the upper level atmosphere is discussed.

High resolution observation of solar active region NOAA 10486 is presented. The flow maps of this region was derived using the high resolution observations. The possible connection of the flow pattern with an X10 flare was discussed.



March 8, 2006
Efthimios Kaxiras
Department of Physics and Division of Engineering and Applied Sciences
Harvard University

Title: Simulations of Complex Systems Across Multiple Length Scales

Abstract: A variety of physical phenomena involve multiple length and time scales in their manifestation. Some interesting examples of practical importance are: (a) the mechanical behavior of crystals and in particular the interplay of chemistry and mechanical stress in determining the macroscopic brittle or ductile response of solids; (b) the molecular-scale forces at interfaces and their effect in macroscopic phenomena like wetting and friction; (c) the alteration of the structure and electronic properties of macromolecular systems due to external forces, as in stretched DNA nanowires or carbon nanotubes. In these complex physical systems, the changes in bonding and atomic configurations at the microscopic level have profound effects on the macroscopic properties, be they of mechanical or electrical nature. Linking the processes at the two extremes of the length scale spectrum is the only means of achieving a deeper understanding of these phenomena and, ultimately, of being able to control them. In this presentation I will discuss the development of methodologies for simulations across disparate length scales with the aim of obtaining a detailed description of complex phenomena of the type described above. The methodologies are based on quantum mechanical approaches at the microscopic scale, on classical atomistic simulations at the mesoscopic scale and on continuum (computational or phenomenological) approaches at the macroscopic scale.



March 15, 2006
Prof. Mark Moldwin
UC Los Angeles

Title: The Emerging Science of Space Weather

Abstract: Space Weather is an emerging field of space science interested in understanding how solar variability impacts the space environment. In particular, space weather is interested in how radiation and electromagnetic fields affect human technology and society. This talk will give an historical overview of the field and describe the speaker's current research efforts to understand how geomagnetic activity influences the near-Earth space environment.



March 17, 2006
Dr. Henk Postma
California Institute of Technology

Title: Nanotube and nanowire mechanical and electronic devices

Abstract: I show how the fascinating properties of nanotubes and nanowires can be used to realize molecular electronic devices that work at room temperature, while also allowing us to study the elementary interaction between the electrical and mechanical degree of freedom in these nanoscale devices.

Strong power-law conductance is observed in transport measurements across junctions within individual single-wall carbon nanotubes, consistent with tunneling between two Luttinger Liquids, deriving from the one-dimensional confinement of electrons to the nanotube. We use this tunneling behavior to create single-electron transistors that operate at room temperature.

High aspect ratio nanomechanical resonators are of considerable interest due to their high force sensitivity. We show that with increasing aspect ratio, the thermomechanical noise increases, while the onset of nonlinearity decreases. We therefore study the influence of noise on the stability, and show that noise leads to transitions between the two states available, revealing the Yin-Yang shaped basins of attraction.

Using the phenomenon of electrical breakdown as thermometry, we observe ballistic phonon transport, revealing the thermal conductance quantum. We show that afterwards, this geometry can also be used to create nanotube linear bearing memory elements, with repeated cycling between on and off states.

Finally, I present an experimental strategy that we are currently working on to arrange nanotubes into hierarchical structures using the self assembling properties of DNA.



March 22, 2006
Dr Anthony Daniell
B.S. Physics: CSUN 1991
M.S. Physics: CSUN 1995 - Electron Paramagnetic Resonance Spectroscopy
Ph.D. Biomedical Physics: UCLA 2001 - Real-Time MRI Instrumentation
Current Affiliation: Technical Group Lead, Northrop-Grumman XonTech Special Programs

Title: Brief CV of Anthony L. Daniel

Abstract: The imaging of coronary calcium by X-ray computed tomography (CT) is of present day clinical relevance. A study was conducted at Cedars-Sinai Medical Center by the author to determine the agreement in the quantification of coronary calcium by a new scanner type, the Siemens Multi-Detector row CT (MDCT), and the "gold-standard" GE-Imatron Electron Beam CT (EBCT). The results of this recently published study will be presented.



March 28, 2006
Dr. Bin Chen
UC Berkeley

Title: Structural Properties of Negative Thermal Expansion Materials and Nano-ZnS

Abstract: Would the greatly desired negative thermal expansion property of materials be lost or degraded in potential application conditions? How do mixed cubic and hexagonal stacking structures behave differently from the constituent stacking structures? Are smaller particles really harder?

The pressure induced structural changes of negative thermal expansion materials including HfW2O8 are investigated with a high-pressure optical absorption study and Raman/infrared spectroscopy study. The novel pressure dependence of the band gap is observed. Based on the pressure-dependent changes of the vibrational modes, the thermal expansion coefficient is calculated, and is found to be in good agreement with the measured value.

Also presented in this talk is the study on the structural stability of mixed-stacking nano-ZnS. High pressure XRD studies were carried out in National Synchrotron Light Source, Brookhaven National Laboratory. The mixed-stacking structure of AB-ABC is lost when pressure is up to ~15 GPa. A yet unknown structure begins to form above ~16 GPa. The new phase is quenchable to room pressure. This is different from the published report that both sphalerite and wurtzite ZnS nanoparticles transform to the rocksalt phase under compression and return to sphalerite phase upon decompression. The high-pressure phase observed in this study is not rocksalt structure. High pressure induced structural changes are confirmed in IR and Raman studies. The determination of the new structure is in process. TEM and EXAFS measurements are planned. Further studies on this topic focus on why the high-pressure behavior of the mixed cubic and hexagonal stacking structure of n-ZnS is so different from that of the pure cubic and hexagonal structures. Research plans on the size-dependent mechanical properties of nanoparticles are also discussed.



March 29, 2006
Dr. Hu
UC Riverside

Title: Characterization of Interplanetary Coronal Mass Ejections and Their Connections to Solar Sources

Abstract: The Corona Mass Ejections (CMEs) are probably the most important solar drivers of geomagnetic storms. They are commonly modeled as magnetic flux ropes. The interplanetary counterparts of CMEs, the ICMEs, detected in-situ by spacecraft ACE and Wind, etc, have been examined by various means. In particular, we present the Grad- Shafranov (GS) reconstruction technique, which represents an objective means of deriving 2 1/2 dimensional cross section of a non- axisymmetric cylindrical flux rope from single-spacecraft measurements. In addition, physical quantities, including but not limited to the electric current, magnetic flux, and the relative magnetic helicity, can be obtained. Recently attempts have been made to seek connections between observables of the solar source surface regions and the CMEs in low corona from multi-wavelength remote imaging, and the corresponding ICMEs from in-situ spacecraft measurements. We will compare the axis orientation of flux-rope CMEs with their corresponding ICMEs. For about a dozen CME/ICME events, the magnetic flux content in an ICME will be compared with that due to magnetic reconnection in its corresponding solar source region. The implications of the results on CME eruption models and the applications of our approach to space weather research will be discussed.



April 5, 2006
Dr. Vasily V. Bulatov
Lawrence Livermore National Lab
University of California

Title: Deviant topology of dislocation tangles

Abstract: Stepping on a bridge or into an airplane, one may not be aware that the strong materials used for building them grow still stronger under stress. Although important in practical applications and counted on in the engineering design, it remains unclear exactly how this hardening takes place. On one hand, physicists have long known that crystals (and most strong materials are crystals) yield under applied forces by way of propagating topological wrinkles - dislocations - along crystallographic planes. On the other hand, this knowledge has never been practically used to predict how much force the material could sustain or how much it would harden under straining. Here we report on direct calculations of crystal strength and accompanying experiments that reveal one of the underlying causes of hardening, namely the tendency of dislocations to bundle together and tie themselves into knots, multi-junctions. At variance with the common paradigm of pair-wise dislocation interactions, we find that many- body dislocation interactions are key in understanding the nature of plastic strength in a crystal. The initial observation leading to this discovery came in a rather unusual way - from simulation. Subsequent theoretical analyses resulted in identification of precise conditions in which experimental observations of the newly discovered topology should become possible. The following experiments validated the theory and re-enforced our belief that the multi-junctions are strong and must contribute to strain hardening. Finally, very large scale Dislocation Dynamics simulations produced direct evidence of the key role of the multi-junctions in defining the anomalously large orientation dependence of strain hardening in BCC metals - a behavior long observed and yet puzzling.



April 12, 2006
Spring break



April 19, 2006
Prof. Vidvuds Ozolins



April 26, 2006
Prof. Gary Horowitz
UC Santa Barbara
World Year of Physics Speaker Program

Title: Black Holes

Abstract: Black holes are one of the most remarkable predictions of Einstein's general theory of relativity. I will summarize our current understanding of black holes. This includes their classical and quantum properties, and their remarkable connections with thermodynamics. Toward the end, I will describe some recent work on black holes in higher dimensions.



May 3, 2006
Prof. Ilya Krivorotov
UC Irvine

Title: Dynamics of Nanomagnets Driven by Spin-Polarized Current

Abstract: Spin-polarized electrons traversing a ferromagnet can transfer spin angular momentum to the local magnetization, thereby inducing magnetization reversal or exciting persistent spin waves. To understand the mechanism of this recently discovered effect, we make time and frequency-resolved measurements of spin-transfer-driven excitations in nanoscale ferromagnetic dots. We find that spin-polarized current can generate coherent spin waves with dephasing times significantly exceeding those of the field-driven modes observed in ferromagnetic resonance experiments. In the switching regime, magnetization reversal induced by spin-polarized current is accomplished via a process of precession, and the switching time is determined by competition between transfer of angular momentum and magnetic energy dissipation. Measurements of magnetic relaxation in the presence of spin-polarized current show that the relaxation is strongly current-dependent. Our observations provide tests of spin transfer theories and demonstrate feasibility of technological applications of spin transfer in the areas of high frequency communications and non-volatile electronics.



May 10, 2006
Prof. Kumar Chitre
Department of Physics, University of Mumbai,India

Title: The Inconstant Sun

Abstract: With the accumulation of helioseismic data from GONG & MDI projects over the past one decade,it has now become possible to study changes taking place inside the Sun as the solar cycle progresses. The temporal variations in the p- and f-mode oscillation frequencies,rotational kinetic energy and magnetic energy in the solar interior can be investigated for understanding the mechanism responsible for driving the solar dynamo and for causing the total solar irradiance.



May 17, 2006
Dr. Gerrit E.W. Bauer
Kavli Institute of NanoScience Delft in Netherlands and Kavli Institute of Theoretical Physics at UC Santa Barbara

Title: Dynamics of magnetoelectronic nanostructures

Abstract: Magnetoelectronics is the science and technology of using ferromagnets in electronic circuits and devices. It affects our daily lives most immediately in the form of hard disk drives in desk and laptop computers, video recorders and MP3 players, while new applications are being found in areas such as automobile electronics, (bio)sensors, etc.. The technology of magnetoelectronics systems develops as fast as the semiconductor integrated circuits. The exponential growth rate of the storage capacity and data access rate has been possible only by new discoveries such as the giant magnetoresistance in magnetic multilayers. Physics research is essential to sustain this development. Minimization of the power and maximization of the speed to switch a single magnetic memory element on the nanometer scale are the most important issues.

In this talk I will review the concepts and phenomena that are being investigated now and which are expected to form the basis of magnetic storage devices in the future.