Last Updated : 1/18/2005 Chris Anderson
| Graduate Student Seminar Series, 2004-2005 |
The highest energies of the electromagnetic spectrum are covered in the x-ray and gamma-ray energy bands. These photons can be produced in a number of ways. I will show how these photons are detected, both X-rays and gamma-rays, and I will finish up by covering the merging galaxy cluster Abell 115 and the Blazar 1ES 1959+650. I am bringing a 1/2 gallon of tequila and we will be having many other Mexican treats. Join the fiesta before WILD!!Las energas ms altas del espectro electromgnetico se cubren en las vendas de la energa de la radiografa y del rayo gama. Estos fotones se pueden producir de un nmero de maneras. Demostrar cmo se detectan estos fotones, las radiografas y los rayos gama, y acabar para arriba cubriendo el racimo de combinacin Abell 115 de la galaxia y el Blazar 1ES 1959+650. Estoy trayendo un galn del 1/2 de tequila y comeremos muchos otros convites mexicanos. Ensamble la fiesta antes de WILD!!
Following the demonstration of extraordinary magnetoresistance (EMR) in semiconductor-metal hybrids it has been realized that EMR is but one example of a general class of EXX phenomena that can be geometrically enhance by the judicious choice of sample geometry. The second EXX phenomenon to be demonstrated was extraordinary piezoconductance, EPC. Here we report a third EXX phenomenon, extraordinary optoconductivity, EOC. The OC of a macroscopic van der Pauw plate structure consisting of Si-doped GaAs (n ~ 10^ 18 cm^¡Ý3) with an Indium shunt was compared to that of a shuntless sample. The conductance of each sample was measured as a function of temperature and of the position and wavelength of a focused Ar ion laser beam (spatial resolution of 10¦Ìm). At 300K the short carrier mean free path (¦Ë) resulted in a voltaic response that was diminished by the shunt. In contrast, at low temperature the longer ¦Ë results in EOC that, at 15K, is more than 480% in the shunted sample relative to the the unshunted sample.
Gravitational radiation was predicted by Einstein back to the first year following the publication of general relativity. However, how to detect the gravitational wave directly has been an unsolved problem since then. In recent years, ground based interferometer GW detectors such as LIGO, VIRGO, GEO and TAMA have been built, and space based detector LISA is planned to be launched in 2013. It seems that the direct detecting of gravitational waves has finally become possible. During my talk, I will give a brief introduction to the gravitational radiation detection, and I will discuss how to use the method of DIRE(Direct Integration of the Relaxed Einstein Equations) to calculate the theoretical templates of the gravitational wave form.
In this talk a brief introduction to NMR will be given with a view toward classical mechanics. Demonstrations will be used to draw analogies between a quantum spin and a classical spinning top. I will also give a brief introduction to MR imaging. At the end I will discuss the possibility of using NMR to study magnetic force on a system of spins, which remains still open to me.
Ultrasound has been used extensively over the past few decades in everything from industrial materials analysis to medical imaging. Most notably for denizens of the Laboratory for Ultrasonics, ultrasonic investigation of the heart has produced numerous advances, even without anyone losing blood or having to touch anything squishy. If you'd like to find out how ultrasound works, or how cardiac research can be conducted in a water tank, or are interested in some of the latest pursuits around the LFU, then come hear about the rudiments of ultrasound, a decidedly UN-in-depth talk chock full of words and graphics and pretty blue slides. Be there or be square.
Many research results in science education have shown that the conceptual change of learners is hard to accomplish. Employing different types of evidence including pre- and post-test, formative assessments, videotape, interviews, and observations, we in this study identified some key factors that explain why many k-8 science teachers hold alternative conceptions and why many of these conceptions are resistant to change. Detailed analysis of teachers’ understandings, confusions and rethinking processes on buoyant forces of air and water in a professional development course in Science Outreach at Washington University in fall, 2004 is presented. Also discussed are the teaching strategies used by the course instructors that facilitated, in many cases, and hindered, in some other cases, teachers’ conceptual change.
Previous studies of the liquid structure of supercooled Si by x-ray diffraction using electromagnetic and aerodynamic levitation have produced conflicting results. We describe a BESL technique that obtains complete diffraction patterns in 0.1 s using high-energy synchrotron x-rays, allowing the evolving structures of supercooled liquids to be measured continuously. Contrary to some molecular dynamic simulation studies, no first order liquid-liquid phase transition was observed in supercooled liquid Si over the measured temperature range (1100 C to 1600 C). The coordination number remained constant, in conflict with earlier measurements. Modeling suggests that the A5 structure of liquid Si distorts continuously toward cubic diamond structure with decreasing temperature.
Motion repulsion is the perceived enlargement of the angle between the directions of motion of two transparently moving patterns. An explanation of this illusion has long been sought for in the neural circuitry of the brain. We show that motion repulsion already arises from the statistical properties of the motion transparency problem when analyzed with a clustering algorithm.
Medicine and Physiology have been driven by correlative analysis (or the desire to get that cure-all drug), not by trying to quantitatively derive a relation. Few researchers are able to use physical rules to explain a physical mechanism that dominates their correlation. For instance, recently we found correlations from a consecutive iso-volumic pressure decay rate to a subsequent pressure gradient and flow decay rate. I'll show you this set of correlations we found recently and try to develop CAUSAL explanations for it. In order to do so, I'll explain how the heart works and how it is modeled.
Actin filaments in cells extend themselves by polymerizing free actin monomers onto their growing ends. The growing filaments can push obstacles and thus do mechanical work. It is known that if the filaments are not attached to the obstacle, new monomers can be added when the obstacle fluctuates away from the growing filament ends. However, experiments show that the growing ends of actin filaments are firmly attached to the obstacle. Based on the idea of the Brownian ratchet model, we develop an energy-based model to investigate the growth of attached actin filaments. In this model, the force field describing the interaction between the actin filament and surface proteins (such as ActA) on the obstacles surface is given a simplified but plausible analytic form. We use both Brownian-dynamics simulations and analytical approaches to calculate the attachment time and the growth rate. Our results show that a high binding energy (~28kT) is required for the binding of an actin filament to the obstacle, and the actin filament can remain attached to a 25 nm bead for about 30 s, while still growing at about 50% of the free-filament growth velocity.
We have carried out numerical simulations of binary neutron star system based on the Einstein equations coupled to the relativistic hydrodynamic equations using adaptive mesh refinement (AMR) techniques. AMR coalescences of neutron stars can now be simulated with sufficient resolution covering the neutron stars while having the computational domain extend to the local wave zone. An AMR simulation carried out with a workstation having an accuracy equivalent to that of a 1025^3 regular unigrid simulation, which is, to the best of our knowledge, larger than all previous simulations of similar NS systems on supercomputers. We believe the capability opens new possibilities in general relativistic simulations.
Contextual influences shape our perception of local visual stimuli. Relative-Motion stimuli represent an important contextual influence, yet the mechanism subserving relative-motion computation remains largely unknown. In the present work, we investigated the responses of an established model for simple and complex cells to relative-motion stimuli. A straightforward mathematical analysis showed that relative-motion computation is inherent in the nonlinear transformation of the complex-cell model. Tuning to relative velocity is achieved by applying a temporal filter to the complex-cell response. The mathematical inference is supported by simulations that quantitatively reproduce measured complex-cell responses in both cat and monkey to a variety of relative-motion stimuli. Importantly, the posited mechanism for cortical computation of relative motion does not require an intermediate neural representation of local velocities and does not require lateral or feedback interactions within a network.
"Ghost Busting : is a term that is associated with getting rid of unwanted ghosts or entities from places where they are not desirable." - www.paranormality.comIn this talk, I, the Ghost Terminator, will terminate the ghost state which haunted the Lee model for 50 years.
Clusters are large gravitationally bound astrophysical objects mostly made up of galaxies, stars, dust and gas. These objects are huge, usually 10^25 cm in extent and containing the mass of 10^14 suns. As well as being large and massive, the majority of clusters are far away, up to and beyond redshifts of 1 but they can also be near by as in the Virgo cluster, which is only 18 Mpc away. Our own galaxy is in fact a member a the "local group" of galaxies, a cluster in its own right. The high redshift clusters are important in cosmological terms because they are a window on the early universe while the nearby clusters allow us to view them at different wavelengths. In this talk, I will give an overview of the physics of galaxy clusters and present the details of our study of two galaxy clusters, 3C 129 and the Perseus cluster. I might mention CZT but probably not.
The weak interactions of quarks are obscured by the strong interactions of quarks, rendering experimental tests of the Standard Model description of weak quark interactions (in the lingo, the "hadronic electroweak sector") quantitatively difficult. Following a qualitative overview of the Standard Model, we review the present status of tests of the hadronic electroweak sector and discover the role that non-perturbative strong interaction calculations are playing in the search for physics beyond the Standard Model. The effective field theoretic attack on the challenges presented by computer simulations of quantum chromodynamics will be described and currently progressing calculations of hadronic quantities, summarized.
Tectal SGC-I type neurons process the retinal representation of dynamic visual stimuli. Our electrophysiological in vitro experiments have shown that synaptic properties at single SGC-I dendritic endings mediate sensitivity to dynamic spatiotemporal stimuli independent of stimulus details. But the number of stimulated SGC-I dendritic endings depends on stimulus size. This raises the question to what extent the stimulus size changes the dynamics of retino-tectal signal transfer. Our experiments with multi-site stimulation indicate that single dendritic ending responses depend on retinal activity at other sites. Specifically, the response probability of one dendritic ending decreases with the number of active stimulation site. We are testing what mechanisms contribute to this stimulus-size-dependent change in the dynamics of retino-tectal signal transfer.
There are 1,000,000 Americans that have been diagnosed with heart failure (CHF). Among these patients, more than 50% have normal systolic function (ejection fraction (EF) > 50%). This is especially evident in elderly individuals. These Patients are categorized as diastolic heart failure (DHF). Research has shown that DHF will ultimately lead to systolic heart failure. However, there is continued controversy surrounding the definition of diastolic dysfunction and the diagnostic criteria for DHF. The indexes cardiologist used to diagnose diastolic dysfunction are based on observation. As a result, clinical therapeutic trials have been slow to develop and difficult to design. Our lab is one of a few labs which make math model for diastole. I will briefly review the cardiac physiology. Then I will discuss my project on applying impedance analysis to diastole and the question which I raise from the finding.
I will talk about a statistical approach to nuclear systematics. Special emphasis is placed on modeling and prediction of nuclear ground state masses, decay halflives, and separation energies. One goal of such studies is to determine how well the existing data determines the mapping from the proton and neutron numbers to the nuclear properties. Another is to provide reliable models that can be used to forecast values from the valley of stability. The results suggest that with further development this approach may provide a valuable alternative to traditional methods based on quantum mechanics. I will also give an introduction to statistical learning theory and the coding schemes.
Don't be scared by the title. It's simple. Let me explain. Q: What is parity? A: Your left hand looks just like your right hand in the mirror. That's parity. Q: Is parity a scalar or a component of a vector or something else? A: "I have discovered a truly remarkable proof which this margin is too small to contain." Please go to the talk, I'll show you. In the talk, I'll briefly review the general representation theory of Lorentz group. I'll use a few simple examples to demonstrate this theory. I'll show how to work out the Lorentz representation of parity and what the answer is.