Nelson, Philip
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Publication Beyond Conformal Field Theory(1990-06-01) Nelson, Philip CThis 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 Electrostatic Repulsion of Positively Charged Vesicles and Negatively Charged Objects(1999-03-01) Aranda-Espinoza, Helim; Chen, Yi; Lubesnky, T C; Dan, Nily; Nelson, Philip C; Ramos, Lauren; Weitz, D. AA positively charged, mixed bilayer vesicle in the presence of negatively charged surfaces (for example, colloidal particles) can spontaneously partition into an adhesion zone of definite area, and another zone that repels additional negative objects. Although the membrane itself has nonnegative charge in the repulsive zone, negative counterions on the interior of the vesicle spontaneously aggregate there, and present a net negative charge to the exterior. Beyond the fundamental result that oppositely charged objects can repel, our mechanism helps explain recent experiments on surfactant vesicles.Publication Introduction to Sigma Model Anomalies, in Symposium on Anomalies, Geometry, and Topology(1985-03-01) Nelson, Philip CTalk 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 CTalk presented at the Conference on Mathematical Aspects of String Theory at La Jolla, California in August 1986.Publication Spontaneous Expulsion of Giant Lipid Vesicles Induced by Laser Tweezers(1997) Moroz, J David; Nelson, Philip C; Bar-Ziv, Roy; Moses, ElishaIrradiation 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.Publication Hidden Symmetry in Topological Gravity(1991) Distler, Jacques; Nelson, Philip CTalk presented by P.N. at “Mathematics and Physics of Strings,” Berkeley and “Topology and Geometry in Theoretical Physics,” Turku (Finland), 1991.Publication Biological Consequences of Tightly Bent DNA: The Other Life of a Macromolecular Celebrity(2006-10-01) Garcia, Hernan G; Grayson, Paul; Han, Lin; Inamdar, Mandar; Kondev, Jané; Nelson, Philip C; Phillips, Rob; Widom, Jonathan; Wiggins, Paul AThe mechanical properties of DNA play a critical role in many biological functions. For example, DNA packing in viruses involves confining the viral genome in a volume (the viral capsid) with dimensions that are comparable to the DNA persistence length. Similarly, eukaryotic DNA is packed in DNA-protein complexes (nucleosomes) in which DNA is tightly bent around protein spools. DNA is also tightly bent by many proteins that regulate transcription, resulting in a variation in gene expression that is amenable to quantitative analysis. In these cases, DNA loops are formed with lengths that are comparable to or smaller than the DNA persistence length. The aim of this review is to describe the physical forces associated with tightly bent DNA in all of these settings and to explore the biological consequences of such bending, as increasingly accessible by single-molecule techniques.Publication Physical Models of Living Systems new chapter: Single Particle Reconstruction in Cryo-electron Microscopy(2021-06-05) Nelson, Philip CThis chapter extends Part III of the book Physical Models of Living Systems (WH Freeman 2015). This preliminary version is made freely available as-is in the hope that it will be useful.Publication The Dilaton Equation in Semirigid String Theory(1991-12-01) Distler, Jacques; Nelson, Philip CWe show how to obtain explicit integration measures on ordinary moduli space corresponding to the correlation functions of pure 2-dimensional topological gravity. In particular our prescription tells how to remove the zero modes of the βγ system. We then use our formula to derive the “dilaton equation” introduced by E. Verlinde and H. Verlinde,a relation between the N-point and (N − 1)-point correlations of this theory. Just as incritical string theory we use the fact that certain brst-exact states fail to decouple. Instead they build up ˇ Cech classes, in this instance the Euler class of an N-times punctured surface. Throughout we use the “semirigid” formulation of topological gravity. Thus theLiouville sector of other approaches never enters.Publication From Photon to Neuron Chapter 16: Tunneling of Photons and Electrons(2018-08-25) Nelson, Philip CThis 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.