Is Quantum Field Theory ontologically interpretable? On localization, particles and fields in relativistic Quantum Theory

In this paper, I provide a formal set of assumptions and give a natural criterion for a quantum field theory to admit particles. I construct a na\"ive approach to localization for a free bosonic quantum field theory and show how this localization scheme, as a consequence of the Reeh-Schlieder theorem, fails to satisfy this criterion. I then examine the Newton-Wigner concept of localization and show that it fails to obey strong microcausality and thus is subject to a more general version of the Reeh-Schlieder theorem. I review approaches to quantum field theoretic explanations of particle detection events and explain how particles can be regarded as emergent phenomena of a relativistic field theory. In particular, I show that effective localization of Hilbert space vectors is equivalent to an approximate locality of observable algebras.Comment: 33 page

A Quantum Electrodynamical Foundation for Molecular Photonics

In this review the authors describe some of the advances in the quantum electrodynamical formulation of theory for molecular photonics. Earlier work has been extended and reformulated for application to real dispersive media—as reflected in the new treatment of refractive, dissipative, and resonance properties. Applications of the new theory have revealed new quantum optical features in two quite different aspects of the familiar process of second harmonic generation, one operating through local coherence within small particles and the other, a coherence between the quantum amplitudes for fundamental and harmonic excitation. Where the salient experiments have been performed, they exactly match the theoretical predictions

Dynamically-Stabilized Pores in Bilayer Membranes

Zhelev and Needham have recently created large, quasi-stable pores in artificial lipid bilayer vesicles [Biochim. Biophys. Acta 1147 (1993) 89]. Initially created by electroporation, the pores remain open for up to several seconds before quickly snapping shut. This result is surprising in light of the large line tension for holes in bilayer membranes and the rapid time scale for closure of large pores. We show how pores can be dynamically stabilized via a new feedback mechanism. We also explain quantitatively the observed sudden pore closure as a tangent bifurcation. Finally we show how Zhelev and Needham's experiment can be used to measure accurately the pore line tension, an important material parameter. For their SOPC/CHOL mixture we obtain a line tension of 2.6 10^{-6} erg/cm.Comment: 7 pages RevTeX, 3 included eps figures (published version). Postscript also available at http://dept.physics.upenn.edu/~moro

How does Internet usage influence young travellers' choices?

New technologies have significant effects on travel behavior, attitudes, habits and potentially future travel demand. Effects may be more prominent for Millennials. Little empirical research has investigated these relationships, mainly due to data limitations. This study focuses on the potential influence of using the Internet while traveling on Millennials’ plans for car ownership. We examine two questions: Does using the Internet while traveling influence trip frequencies? and Does it affect Millennials’ intention to purchase a car? Results suggest that Internet use while traveling is positively associated with travel demand and the intention to purchase a car in the near future

Linking Smartphone GPS Data with Transport Planning: A Framework of Data Aggregation and Anonymization for a Journey Planning App

With the proliferation of GPS tracking data provided by smartphone apps, it is desirable to develop a data processing and anonymizing framework to transform raw GPS data into a suitable format for transport planning models. The paper aims to describe the effort to address such issues by map matching and aggregating the GPS information derived from a journey planning app. The effectiveness and flexibility of such a framework is demonstrated by an analysis of speeding and waiting time patterns in England and Wales by tracking 120 users for a year

Entropic Elasticity of Twist-Storing Polymers

We investigate the statistical mechanics of a torsionally constrained polymer. The polymer is modeled as a fluctuating rod with bend stiffness A kT and twist stiffness C kT. In such a model, thermal bend fluctuations couple geometrically to an applied torque through the relation Lk = Tw + Wr. We explore this coupling and find agreement between the predictions of our model and recent experimental results on single lambda-DNA molecules. This analysis affords an experimental determination of the microscopic twist stiffness (averaged over a helix repeat). Quantitative agreement between theory and experiment is obtained using C=109 nm. The theory further predicts a thermal reduction of the effective twist rigidity induced by bend fluctuations. Finally, we find a small reflection of molecular chirality in the experimental data and interpret it in terms of a twist-stretch coupling of the DNA duplex.Comment: 37 pages RevTeX, 2 postscript figures. Revisions include the analysis of new data and an investigation of non-perturbative effects. Postscript also available at http://www.physics.upenn.edu/~moro

Star Formation in a Turbulent Framework: From Giant Molecular Clouds to Protostars

Turbulence is thought to be a primary driving force behind the early stages of star formation. In this framework large, self gravitating, turbulent clouds fragment into smaller clouds which in turn fragment into even smaller ones. At the end of this cascade we find the clouds which collapse into protostars. Following this process is extremely challenging numerically due to the large dynamical range so in this paper we propose a semi analytic framework which is able to follow star formation from the largest, giant molecular cloud (GMC) scale, to the final protostellar size scale. Due to the simplicity of the framework it is ideal for theoretical experimentation to explore the principal processes behind different aspects of star formation, at the cost of strong assumptions. The basic version of the model discussed in this paper only contains turbulence, gravity and crude assumptions about feedback, nevertheless it can reproduce the observed core mass function (CMF) and provide the protostellar system mass function (PSMF), which shows a striking resemblance to the observed IMF. Furthermore we find that to produce a universal IMF protostellar feedback must be taken into account otherwise the PSMF peak shows a strong dependence on the background temperature.Comment: 13 pages, 13 figure