Field theory models for tachyon and gauge field string dynamics

In hep-th/0008227, the unstable lump solution of \phi^3 theory was shown to have a spectrum governed by the solvable Schroedinger equation with the \ell=3 reflectionless potential and was used as a model for tachyon condensation in string theory. In this paper we study in detail an \ell\to \infty scalar field theory model whose lump solution mimics remarkably the string theory setup: the original field theory tachyon and the lump tachyon have the same mass, the spectrum of the lump consists of equally spaced infinite levels, there is no continuous spectrum, and nothing survives after tachyon condensation. We also find exact solutions for lumps with codimension \ge 2, and show that that their tensions satisfy (1/(2\pi)) (T_p/ T_{p+1})=e/(\sqrt{2\pi}) \approx 1.08. We incorporate gauge fixed couplings to a U(1) gauge field which preserve solvability and result in massless gauge fields on the lump.Comment: latex, 21 pages, 3 figures. Added references to reflectionless potentials, minor typos corrected, uniform use of (-, +, +, ..., +) signatur

Mechanisms for DNA Charge Transport

DNA charge transport (CT) chemistry has received considerable attention by scientific researchers over the past 15 years since our first provocative publication on long range CT in a DNA assembly.1,2 This interest, shared by physicists, chemists and biologists, reflects the potential of DNA CT to provide a sensitive route for signaling, whether in the construction of nanoscale biosensors or as an enzymatic tool to detect damage in the genome. Research into DNA CT chemistry began as a quest to determine whether the DNA double helix, a macromolecular assembly in solution with π-stacked base pairs, might share conductive characteristics with π-stacked solids. Physicists carried out sophisticated experiments to measure the conductivity of DNA samples, but the means to connect discrete DNA assemblies into the devices to gauge conductivity varied, as did the conditions under which conductivities were determined. Chemists constructed DNA assemblies to measure hole and electron transport in solution using a variety of hole and electron donors. Here, too, DNA CT was seen to depend upon the connections, or coupling, between donors and the DNA base pair stack. Importantly, these experiments have resolved the debate over whether DNA CT is possible. Moreover these studies have shown that DNA CT, irrespective of the oxidant or reductant used to initiate the chemistry, can occur over long molecular distances but can be exquisitely sensitive to perturbations in the base pair stack. Here we review some of the critical characteristics of DNA charge transport chemistry, taking examples from a range of systems, and consider these characteristics in the context of their mechanistic implications. This review is not intended to be exhaustive but instead to be illustrative. For instance, we describe studies involving measurements in solution using pendant photooxidants to inject holes, conductivity studies with covalently modified assemblies, and electrochemical studies on DNA-modified electrodes. We do not focus in detail on the differences amongst these constructs but instead on their similarities. It is the similarity among these various systems that allows us to consider different mechanisms to describe DNA CT. Thus we review also the various mechanisms for DNA CT that have been put forth and attempt to reconcile these mechanistic proposals with the many disparate measurements of DNA CT. Certainly the debate among researchers has shifted from "is DNA CT possible?" to "how does it work?". This review intends to explore this latter question in detail

Learning Development and Education for Sustainability: what are the links?

Learning Development (LD) is an emerging discipline developing a unique disciplinary identity. In common with many other new fields, it considers its position and relevance to other disciplines and bodies of thought, and in particular, educational development, applied linguistics and the sociology and philosophy of education. This paper considers one such area of debate: the link between Learning Development and Education for Sustainability (EfS). EfS is an area of pedagogic practice and a field of enquiry of considerable and growing importance in Higher Education (HE) and universities. Its underpinning systemic and epistemic philosophies suggest the need for integration across all facets of university activity, including LD. In this paper, we argue that there are identifiable links between LD and EfS that extend these philosophies, practices and fields of enquiry, characterised by the following: 1) commonalities surrounding the foci of their pedagogic practices, 2) shared methodologies for undertaking their practices, and 3) ways in which these methodologies are helping to situate both professions and disciplines within organisational contexts. The commonalities and possible distinctions between LD and EfS form a starting point for discussion, and raise the possibility that explicit identification of the links may encourage increased collaboration between the respective communities of practice, and the development of new ideas and innovative practice

Code Blue: methodology for a qualitative study of teamwork during simulated cardiac arrest.

IntroductionIn-hospital cardiac arrest (IHCA) is a particularly vexing entity from the perspective of preparedness, as it is neither common nor truly rare. Survival from IHCA requires the coordinated efforts of multiple providers with different skill sets who may have little prior experience working together. Survival rates have remained low despite advances in therapy, suggesting that human factors may be at play.Methods and analysisThis qualitative study uses a quasiethnographic data collection approach combining focus group interviews with providers involved in IHCA resuscitation as well as analysis of video recordings from in situ-simulated cardiac arrest events. Using grounded theory-based analysis, we intend to understand the organisational, interpersonal, cognitive and behavioural dimensions of IHCA resuscitation, and to build a descriptive model of code team functioning.Ethics and disseminationThis ongoing study has been approved by the IRB at UC Davis Medical Center.ResultsThe results will be disseminated in a subsequent manuscript

Single-Step Charge Transport through DNA over Long Distances

Quantum yields for charge transport across adenine tracts of increasing length have been measured by monitoring hole transport in synthetic oligonucleotides between photoexcited 2-aminopurine, a fluorescent analogue of adenine, and N_2-cyclopropyl guanine. Using fluorescence quenching, a measure of hole injection, and hole trapping by the cyclopropyl guanine derivative, we separate the individual contributions of single- and multistep channels to DNA charge transport and find that with 7 or 8 intervening adenines the charge transport is a coherent, single-step process. Moreover, a transition occurs from multistep to single-step charge transport with increasing donor/acceptor separation, opposite to that generally observed in molecular wires. These results establish that coherent transport through DNA occurs preferentially across 10 base pairs, favored by delocalization over a full turn of the helix

Utilizing Statistics and Bellwether Trials in Mass Torts: What do the Constitution and Federal Rules of Civil Procedure Permit?

Traditional judicial mechanisms that preserve litigants\u27 rights to due process and a jury trial challenge courts to provide litigants their day in court in an efficient and timely manner. This challenge is made exponentially harder where the litigation concerns tortious conduct affecting a large number of persons and giving rise to latent injury. In response to the recent increase in mass tort filings, courts have sought an alternative means of adjudication-the extrapolation of a statistically average, representative plaintiff to other plaintiffs. This Note examines the problems associated with mass tort actions and how two circuit courts of appeals have implemented the use of statistically representative bellwether plaintiffs in resolving mass tort issues. After comparing the use of bellwether plaintiffs to traditional mass tort mechanisms in questioning whether statistical representation violates due process and the right to a jury trial, the Note concludes with a proposition for the proper role that the use of extrapolating statistics to non-bellwether plaintiffs should take in mass tort litigation

Mining, concentration and refining of American flake graphite by the Griesemer Graphite Company

The Griesemer Graphite Company was incorporated June 3, 1916, under the laws of Alabama, for the purpose of mining, milling and refining of flake graphite...Owing to strong competition in the graphite game, it will be impossible to give many interesting facts and figures in this thesis. The screen analysis worked for after each operation is carefully watched and the preparing of the ore, as well as the sizing of the flake, is one of the most important features in the production of flake graphite, especially that grade required by the crucible makers and the lubricating manufacturers. The carbon content is also equally important. then, on the whole, the milling and refining of flake graphite is a very delicate operation and requires close supervision through the whole flow sheet --Introduction, page 6-7

Optimal Capital Structure in Centralized Agricultural Cooperatives

Agribusiness,

Neutron Dose Equivalent and Spectra Determination for a Medical Linear Accelerator Using Dosimetric and Monte Carlo Methods.

Medical linear accelerators (linacs) operated above 8 MV photon energy have their output contaminated with neutrons resulting from the photon interactions with the materials of the linac head components. Photoneutron contamination in the photon output was investigated on the Varian Clinac 2100C linear accelerator operating at 15 MV photon beam energy and a dose rate of 4 Gy/min using experimental and Monte Carlo (MCNP) simulations. In order to ensure that the output of the MCNP code was valid, an 241Am-Be isotopic irradiation facility was simulated to study the scattered and transmitted neutron fluxes emanating from a rectangular phantom placed in 'short' and 'long' width orientations. The results of the scattered and transmitted neutron fluxes were compared with those obtained by measurements using the Microspect-2 Neutron Probe (N-Probe) and a new neutron detector, the LGB detector, based on a scintillator containing Li, Gd, and B. Results show a reasonable agreement between measurements and MCNP calculations for both transmitted and scattered neutron flux. Good and accurate knowledge of all the relevant nuclear parameters involved and reliable as well as reproducible experimental conditions are required in neutron flux measurements using foils. A Monte Carlo based Fortran 90 program, COLDET, was developed to calculate the solid angle subtended by both 'bare' and collimated y-ray detector to point, disc and cylindrical sources. Results show good agreement with theory and those obtained by others, however, some differences arise when the finite dimensions of the source and detector are taken into account. Superheated drop detectors (SDDs) were employed in the photoneutron dose measurements due to their insensitivity to high energy and intensity photons in contrast to activation foils. The high and low neutron sensitivity SDDs (Apfel Enterprises Inc., U.S.A), recommended for out of beam and in-beam measurements were used, respectively. Measurements were carried out for both in air and in a water phantom in the patient plane at 100 cm source-to-surface (detector) distance (SSD) in order to investigate the variation of neutron dose equivalent with field size in and outside the irradiation beam and also in the maze of the linac bunker and the control room. The neutron dose equivalent on the beam axis increased gradually as field size was varied from 5x5 cm to 40x40 cm for in-air measurements and was independent of field size outside the irradiated field at distances greater than 20 cm. The neutron dose equivalent for 10x10 cm2 and 40x40 cm2 field sizes was found to be 1.57+/-0.10 mSvGy-1 and 1.74 +/- 0.09 mSvGy-1, respectively. The neutron dose equivalent in the maze for all the field sizes was much higher at gantry angles 0 and 180. The neutron dose equivalent on the beam axis for the 10x10 cm2 field size at a depth of 1 cm in water was 1.42 +/- 0.09 mSvGy-1 for the in-phantom measurements and 1.81+/-0.08 mSvGy-1 for the 5x5 cm2 field size for the same depth but was independent of field size at depth >5 cm in water. MCNP simulation of the 15 MV photon energy Varian Clinac 2100C head was carried out to investigate the photoneutron contamination in its output for the purpose of comparison with experiment. Though the precise linac information about the treatment head was not made available to us due to manufacturer's proprietary rights and commercial secrecy, there was good agreement between simulation and experiment for both in-air and in-phantom to within 15% and 20%, respectively. The fractional neutron dose equivalent to radiosensitive organs of the patient during high-energy photon treatment was determined using the tissue equivalent phantom BOMAB compatible with MCNP. In a design study, MCNP simulation of a linac bunker was undertaken to determine the effect on the total neutron flux and dose at the exit of the maze in terms of treatment room modification and in cladding the maze with neutron absorbing materials. The neutron spectrum of an isotropic 252Cf source was used for the purposes of simulation to represent the unfiltered neutron component of the linear accelerator beam and was placed at the SSD. The modification of the treatment room reduced the total neutron flux and dose by approximately 40 and 45%, respectively, whereas the addition of neutron absorbing materials resulted in further reduction of approximately 90%

Gauge Fields and Fermions in Tachyon Effective Field Theories

In this paper we incorporate gauge fields into the tachyon field theory models for unstable D-branes in bosonic and in Type II string theories. The chosen couplings yield massless gauge fields and an infinite set of equally spaced massive gauge fields on codimension one branes. A lack of a continuum spectrum is taken as evidence that the stable tachyon vacuum does not support conventional gauge excitations. For the bosonic string model we find two possible solvable couplings, one closely related to Born-Infeld forms and the other allowing a detailed comparison to the open string modes on bosonic D-branes. We also show how to include fermions in the type II model. They localize correctly on stable codimension one branes resulting in bose-fermi degeneracy at the massless level. Finally, we establish the solvability of a large class of models that include kinetic terms with more than two derivatives.Comment: 32 pages, LaTe