Dr. Alex Small Assistant Professor, Department of Physics, Cal Poly Pomona
"Theoretical Limits to Fluorescence Microscopy
Beyond the Diffraction limit"
Techniques such as PALM (PhotoActivation Localization Microscopy) and STORM (STOchastic Reconstruction Microscopy) enable fluorescence microscopy with subwavelength resolution, using molecules that can be activated from a dark state to a fluorescent state. Only a small fraction of the molecules are activated at any given time; giving a very low probability of nearby molecules being simultaneously activated and forming overlapping blurs in the image. The fluorescent molecules are imaged individually, their positions are determined from the images, and then a new set of molecules is activated to the fluorescent state. However, there is a tradeoff between image quality (improved by minimizing the activation probability per molecule, for fewer overlapping blurs) and speed (improved by increasing the activation probability per molecule, to reduce the risk of image cycles with zero activated molecules). One method of dealing with this tradeoff is to increase the activation probability and use algorithms (called rejection algorithms) that identify and remove spots formed by overlapping blurs from more than 1 molecule.
We have performed a theoretical analysis to relate rejection algorithm performance with achievable resolution and image acquisition speed. We predict the existence of a minimum acquisition time independent of algorithm performance, and an algorithm-dependent maximum error rate. We have characterized the performance of commonly-used procedures for identifying multi-molecule spots via their shape (including linear and non-linear curve fitting), and show that procedures of widely varying complexity and speed have comparable performance, pointing to ways of reducing acquisition and post-processing time with optimized rejection algorithms. Additionally, we have analyzed errors when molecules produce overlapping blurs and are then bleached. With proper control of activation probability and the photobleaching rate, bleaching can actually be used to enable faster acquisition of an image with subwavelength resolution, with implications for the design of photoswitchable fluorescent proteins.
4/15/10 5-6 p.m.
Assistant Professor, Department of Physics, Tulsa Community College
“Non-local Effect in Superconductors as a Mean to Measure Microscopic Intrinsic Parameters”
Note Different Time: 5:00 - 6:00 p.m. (only today)
In 1953, proposing the nonlocal theory of superconductivity, B. Pippard made a remarkable prediction that magnetic field B penetrated into superconductors in the Meissner state decays nonmonotonically and, moreover, changes sign at a certain depth. According to the Pippard theory, magnetic field profile B(z) , z being the distance form a sample surface, in nonlocal superconductors at low temperature is a function of the London penetration depth l L (0) and a characteristic length x 0 (the Pippard coherence length). This nonlocal effect also follows from the BCS theory where x 0 represents the size of the Cooper pairs. Thus, measuring B(z) one can determine both “the most wanted' microscopic intrinsic parameters of superconductors. Since that time the magnetic field profile is one of the hardest challenges of experimental superconductivity. Perhaps it is worth noting that as of today neither l L (0) nor x 0 have been reliably measured in any superconductor; available tables of these quantities for conventional superconductors are based on the strong-coupling calculations.
The nonlocal effect is most pronounced in extreme low- k or Pippard superconductors, such as Al ( k = 0.01), In (0.06), and Sn (0.15). According to Kosztin and Legget, it can also take place in d-wave superconductors. In this talk I will review contemporarily approaches of measuring B(z) , which are PNR (polarized neutron reflectometry) and LE- m SR (low-energy muon spin rotation) spectrometry, and discuss results of our recent PNR and LE- m SR measurements of the field profile in In.
Dr. Edward Price
Assistant Professor, Department of Physics, CSU San Marcos
"Tablet PCs in the Physics Classroom:
The Interplay Between Tools and Practices"
Tablet PCs are laptops with a stylus and digital ink that allows quick and easy creation of graphics, drawings, and equations. With wireless networking, these electronic materials can be rapidly shared and easily archived. In this talk, I will describe how these features – combined with appropriate software – can be used in lecture courses, discussion-based courses, and introductory laboratory courses. For instance, using the Ubiquitous Presenter software*, an instructor with a Tablet can ink prepared digital material (such as exported PowerPoint slides) in real time in class. Ink is automatically archived stroke by stroke and can be reviewed, along with the original slides, through a web browser. The system also supports in-class interaction through a web interface - students with web-enabled devices (Tablet PCs, regular laptops, PDAs, and cell phones) can make text- or ink-based submissions on the instructor's slides, or upload screenshots. The instructor can review and then project submitted slides to the class and add additional ink. In addition to describing how we use Tablets, I will present data on student access of archived material, describe the impact on the classroom environment, and provide examples of how these tools shape our classroom practices.
Dr. William Y. Song
Assistant Professor, Department of Radiation Oncology, UC San Diego
“The Current State of the Art in Cancer Radiation Therapy”
Currently, two-thirds of all cancer patients receive radiation therapy, either alone or in combination with other therapeutic modalities. Once a patient is deemed radiation therapy candidate, the goal of this modality is to deliver a prescribed radiation dose to targets containing tumor and cancerous regions while sparing surrounding healthy structures. To do this accurately and consistently, the radiation oncology field employs dynamic and highly computationally efficient technologies for treatment. There are four major stages in the radiation therapy treatment process 1) diagnosis and treatment decision making, 2) CT simulation and fabrication of setup devices, 3) virtual treatment planning and optimization, and 3) treatment delivery using mega-voltage photon and electron beams. Each process requires varying degrees of advanced physics and engineering applications and each of these can be improved with the help of medical physicists. My talk will focus on the introduction and presentation of various state of the art technologies that are being deployed and developed for radiation therapy, with special emphasis on imaging and treatment of lung and liver cancers.
Dr. Adrian Hightower
Assistant Professor, Department of
Physics, Occidental College
"Nanoelectrochemistry by Atomic Force Microscopy Applied to
the Design of Fuel Cell and Rechargeable Battery Electrodes"
Fuel cells and batteries are likely to have a dominant role in the development of a sustainable global energy infrastructure. Electrochemical nanotechnology promises to be a leading contributor to the development of efficient fuel cells and batteries by providing materials tailored to particular electrochemical conversion processes. Conducting atomic force microscopy (AFM), combined with AC impedance spectroscopy (ACIS), offers many advantages for measuring electrode kinetics in fuel cell and rechargeable battery systems. This technique, also known as nanoscale impedance microscopy (NIM), permits studies of the spatial dependence of mechanistic phenomena while providing controllable electrode-electrolyte contact areas. The feasibility of using a nanoscale probe as a fuel cell electrode has been previously examined for the polymer electrolyte membrane system at room temperature and solid acid electrolyte at T = 180°C.
Our work to quantitatively characterized oxygen reduction kinetics relevant to solid acid fuel cells using NIM and cyclic voltammetry has lead to measurements at the nanoscale of the Pt | CsHSO 4 interface. Two kinetic processes are observed at ~150 ºC, one displaying a weak dependence on overpotential and the other exponentially overpotential-activated. The complete current-voltage characteristics of the Pt | CsHSO 4 interface were measured at various points across the electrolyte surface and employed to study the nanoscale heterogeneity of oxygen reduction reaction kinetics. Analysis of six different sets of Pt | CsHSO4 experiments, within the Butler-Volmer framework, yielded exchange coefficients for charge transfer ranging from 0.1 to 0.7 and exchange currents spanning five orders of magnitude. An observed correlation between the exchange current and exchange coefficient suggests that the kinetic facility of the charge transfer step is strongly affected by the symmetry of the activation barrier.
Dr. Fred Goldberg Professor, Department of Physics, and
Center for Research in Math and Science Education,
San Diego State University
“How Students Come to Understand Conceptually
Why Objects of Different Mass Fall Together”
I will first briefly describe the Physics and Everyday Thinking curriculum** and the five major design principles that guided its development. These principles are: (1) Learning builds on prior knowledge; (2) Learning is a complex process, requiring scaffolding; (3) Learning is facilitated through interaction with tools; (4) Learning is facilitated through interaction with others; and (5) Learning is facilitated through establishment of specific behavioral practices and expectations. Then I will focus on an interesting case study of three students working through one of the activities in the PET curriculum, trying to understand why (in the absence of drag forces) all objects fall together. Finally, I'll return to the five design principles and connect them with the case study.
*This work was supported by NSF grant 0096856
**Published by It's About Time, Herff Jones Education Division
Dr. Walter Gekelman
Professor, Department of Physics and Astronomy, UCLA
"Experimental Measurement of Whistler Waves
at the LAPTAG High School Plasma
Dr. William A. Taylor
Professor Emeritus, Department of Physics and Astronomy, CSU Los Angeles
"University Preparatory Program"
In 1989 Drs. Martin Epstein and William Taylor established a partnership with Lincoln High School called the University Preparatory Program (UPP). The purpose was to prepare Lincoln High School students for success at the University with an emphasis on science and mathematics. Because of the successes of UPP, the program was expanded to include Garfield High School in 1996. Both partnerships continue today and have approximately 500 students at each high school. The evolution of the programs will be described.