Penn Arts & Sciences

The University of Pennsylvania School of Arts and Sciences forms the foundation of the scholarly excellence that has established Penn as one of the world's leading research universities. We teach students across all 12 Penn schools, and our academic departments span the reach from anthropology and biology to sociology and South Asian studies.

Members of the Penn Arts & Sciences faculty are leaders in creating new knowledge in their disciplines and are engaged in nearly every area of interdisciplinary innovation. They are regularly recognized with academia's highest honors, including membership in prestigious societies like the National Academy of Sciences, the American Association for the Advancement of Science, the American Academy of Arts and Sciences, and the American Philosophical Society, as well as significant prizes such as MacArthur and Guggenheim Fellowships.

The educational experience offered by Penn Arts & Sciences is likewise recognized for its excellence. The School's three educational divisions fulfill different missions, united by a broader commitment to providing our students with an unrivaled education in the liberal arts. The College of Arts and Sciences is the academic home of the majority of Penn undergraduates and provides 60 percent of the courses taken by students in Penn's undergraduate professional schools. The Graduate Division offers doctoral training to over 1,300 candidates in more than 30 graduate programs. And the College of Liberal and Professional Studies provides a range of educational opportunities for lifelong learners and working professionals.

 

 

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Author: Nelson, Philip C ×

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  • Publication
    Beyond Conformal Field Theory
    (1990-06-01) Nelson, Philip C
    This is an account of some recent work done with H. S. La [1] [2], based ultimately on the work of Fischler and Susskind [3] and Polchinski [4].
  • Publication
    Introduction to Sigma Model Anomalies, in Symposium on Anomalies, Geometry, and Topology
    (1985-03-01) Nelson, Philip C
    Talk presented at the Symposium on Anomalies, Topology, and Geometry, Argonne National Laboratory, March, 1985.
  • Publication
    Analytic Structure of Two Dimensional Quantum Field Theory
    (1986-08-01) Nelson, Philip C
    Talk presented at the Conference on Mathematical Aspects of String Theory at La Jolla, California in August 1986.
  • Publication
    From Photon to Neuron Chapter 16: Tunneling of Photons and Electrons
    (2018-08-25) Nelson, Philip C
    This chapter extends Part III of the book From Photon to Neuron (Princeton Univ Press 2017). This preliminary version is made freely available as-is in the hope that it will be useful.
  • Publication
    Coding and Data Visualization in the Science Classroom
    (2016-09-01) Nelson, Philip C
  • Publication
    Twirling of Actin by Myosins II and V Observed via Polarized TIRF in a Modified Gliding Assay
    (2008-12-01) Beausang, John F; Schroeder, Harry W; Nelson, Philip C; Goldman, Yale E
    The force generated between actin and myosin acts predominantly along the direction of the actin filament, resulting in relative sliding of the thick and thin filaments in muscle or transport of myosin cargos along actin tracks. Previous studies have also detected lateral forces or torques that are generated between actin and myosin, but the origin and biological role of these sideways forces is not known. Here we adapt an actin gliding filament assay in order to measure the rotation of an actin filament about its axis (“twirling”) as it is translocated by myosin. We quantify the rotation by determining the orientation of sparsely incorporated rhodamine-labeledactin monomers, using polarized total internal reflection (polTIRF) microscopy. In order to determine the handedness of the filament rotation, linear incident polarizations in between the standard s- and p-polarizations were generated, decreasing the ambiguity of our probe orientation measurement four-fold. We found that whole myosin II and myosin V both twirl actin with a relatively long (~ µm), left-handed pitch that is insensitive to myosin concentration, filament length and filament velocity.
  • Publication
    From Photon to Neuron: Contents and Preface
    (2017-01-01) Nelson, Philip C
    Contents; To the Student; To the Instructor
  • Publication
    Unambiguous Fermionic String Amplitudes
    (1989-07-01) La, HoSeong; Nelson, Philip C
    We show how to treat boundary divergences in heterotic string theory covariantly and unambiguously. The method applies even to theories with nonvanishing tadpoles; in this case the Fischler-Susskind mechanism sufficies to ensure well defined answers. Also n-point functions are well defined with no special string-tension renormalizations. As an example we find the loop corrections to the linearized background equations of motion for the O(16)×O(16) string needed to give unambiguous, finite scattering amplitudes. No splitting or projection of supermoduli space is needed.
  • Publication
    First-Principles Calculation of DNA Looping in Tethered Particle Experiments
    (2009-07-01) Towles, Kevin; Beausang, John; Garcia, Hernan; Phillips, Rob; Nelson, Philip C
    We calculate the probability of DNA loop formation mediated by regulatory proteins such as Lac repressor (LacI), using a mathematical model of DNA elasticity. Our model is adapted to calculating quantities directly observable in tethered particle motion (TPM) experiments, and it accounts for all the entropic forces present in such experiments. Our model has no free parameters; it characterizes DNA elasticity using information obtained in other kinds of experiments. It assumes a harmonic elastic energy function (or wormlike chain type elasticity), but our Monte Carlo calculation scheme is flexible enough to accommodate arbitrary elastic energy functions. We show how to compute both the 'looping J factor' (or equivalently, the looping free energy) for various DNA construct geometries and LacI concentrations, as well as the detailed probability density function of bead excursions. We also show how to extract the same quantities from recent experimental data on TPM, and then compare to our model's predictions. In particular, we present a new method to correct observed data for finite camera shutter time and other experimental effects. Although the currently available experimental data give large uncertainties, our first-principles predictions for the looping free energy change are confirmed to within about 1 k(B)T, for loops of length around 300 basepairs. More significantly, our model successfully reproduces the detailed distributions of bead excursion, including their surprising three-peak structure, without any fit parameters and without invoking any alternative conformation of the LacI tetramer. Indeed, the model qualitatively reproduces the observed dependence of these distributions on tether length (e.g., phasing) and on LacI concentration (titration). However, for short DNA loops (around 95 basepairs) the experiments show more looping than is predicted by the harmonic-elasticity model, echoing other recent experimental results. Because the experiments we study are done in vitro, this anomalously high looping cannot be rationalized as resulting from the presence of DNA-bending proteins or other cellular machinery. We also show that it is unlikely to be the result of a hypothetical 'open' conformation of the LacI tetramer.
  • Publication
    Spontaneous Expulsion of Giant Lipid Vesicles Induced by Laser Tweezers
    (1997) Moroz, J David; Nelson, Philip C; Bar-Ziv, Roy; Moses, Elisha
    Irradiation of a giant unilamellar lipid bilayer vesicle with a focused laser spot leads to a tense pressurized state which persists indefinitely after laser shutoff. If the vesicle contains another object it can then be gently and continuously expelled from the tense outer vesicle. Remarkably, the inner object can be almost as large as the parent vesicle; its volume is replaced during the exit process. We offer a qualitative theoretical model to explain these and related phenomena. The main hypothesis is that the laser trap pulls in lipid and ejects it in the form of submicron objects, whose osmotic activity then drives the expulsion.