658 research outputs found
Closed String Amplitudes from Gauge Fixed String Field Theory
Closed string diagrams are derived from cubic open string field theory using
a gauge fixed kinetic operator. The basic idea is to use a string propagator
that does not generate a boundary to the world sheet. Using this propagator and
the closed string vertex, the moduli space of closed string surfaces is
covered, so closed string scattering amplitudes should be reproduced. This
kinetic operator could be a gauge fixed form of the string field theory action
around the closed string vacuum.Comment: 10 pages, revtex, 3 figures. Discussion on the covering of moduli
expanded, version to appear in PR
Peripheral and central inputs shape network dynamics in the developing visual cortex in vivo
Spontaneous network activity constitutes a central theme during the development of neuronal circuitry [1, 2]. Before the onset of vision, retinal neurons generate waves of spontaneous activity that are relayed along the ascending visual pathway [3, 4] and shape activity patterns in these regions [5, 6]. The spatiotemporal nature of retinal waves is required to establish precise functional maps in higher visual areas, and their disruption results in enlarged axonal projection areas (e.g., [7-10]). However, how retinal inputs shape network dynamics in the visual cortex on the cellular level is unknown. Using in vivo two-photon calcium imaging, we identified two independently occurring patterns of network activity in the mouse primary visual cortex (V1) before and at the onset of vision. Acute manipulations of spontaneous retinal activity revealed that one type of network activity largely originated in the retina and was characterized by low synchronicity (L-) events. In addition, we identified a type of high synchronicity (H-) events that required gap junction signaling but were independent of retinal input. Moreover, the patterns differed in wave progression and developmental profile. Our data suggest that different activity patterns have complementary functions during the formation of synaptic circuits in the developing visual cortex
Dynamics with Infinitely Many Time Derivatives and Rolling Tachyons
Both in string field theory and in p-adic string theory the equations of
motion involve infinite number of time derivatives. We argue that the initial
value problem is qualitatively different from that obtained in the limit of
many time derivatives in that the space of initial conditions becomes strongly
constrained. We calculate the energy-momentum tensor and study in detail time
dependent solutions representing tachyons rolling on the p-adic string theory
potentials. For even potentials we find surprising small oscillations at the
tachyon vacuum. These are not conventional physical states but rather
anharmonic oscillations with a nontrivial frequency--amplitude relation. When
the potentials are not even, small oscillatory solutions around the bottom must
grow in amplitude without a bound. Open string field theory resembles this
latter case, the tachyon rolls to the bottom and ever growing oscillations
ensue. We discuss the significance of these results for the issues of emerging
closed strings and tachyon matter.Comment: 46 pages, 14 figures, LaTeX. Replaced version: Minor typos corrected,
some figures edited for clarit
A twistor-like D=10 superparticle action with manifest N=8 world-line supersymmetry
We propose a new formulation of the Brink-Schwarz superparticle which
is manifestly invariant under both the target-space super-Poincar\'e group and
the world-line local superconformal group. This twistor-like construction
naturally involves the sphere as a coset space of the Lorentz
group. The action contains only a finite set of auxiliary fields, but they
appear in unusual trilinear combinations. The origin of the on-shell
fermionic symmetry of the standard Brink-Schwarz formulation is
explained. The coupling to a super-Maxwell background requires a new
mechanism, in which the electric charge appears only on shell as an integration
constant.Comment: 22pages, standard LATEX fil
A framework for the systematic implementation of Green-Lean and sustainability in SMEs
Evidence suggests that smaller organisations find the implementation of combined operations- and environmental Sustainability improvement initiatives such as Green-Lean and Sustainability (GLS) challenging. This paper, therefore, develops a framework for the systematic implementation of Green-Lean and Sustainability in small and medium-sized enterprises (SMEs) to achieve long-term improvement of environmental, social and economic processes and performance. A literature assessment of theories, frameworks, and concepts was employed in the study to better comprehend the difficulties confronting the modern business world. In addition, the research employed expert perspectives from the lean, green-lean, and sustainability fields to propose, develop, test, and validate a framework for addressing business concerns. The research uncovers considerable implementation problems, such as employee motivation and integration, responsibilities, and measurements. It also underlines the success factors for the implementation process, such as management, firm- goals and strategy, reviews and audits, vision, and guidance by lean, green and sustainability frameworks. The novelty in this research lies in the approach where Green-Lean and Sustainability are combined and applied in an SME context. The presented framework offers the potential to be implemented in SMEs that operate in different sectors and contexts and are affected by different environmental and social considerations
A Twistor Formulation of the Non-Heterotic Superstring with Manifest Worldsheet Supersymmetry
We propose a new formulation of the type II superstring which is
manifestly invariant under both target-space supersymmetry and worldsheet
super reparametrizations. This gives rise to a set of twistor
(commuting spinor) variables, which provide a solution to the two Virasoro
constraints. The worldsheet supergravity fields are shown to play the r\^ole of
auxiliary fields.Comment: 21p., LaTe
Thermal conditions affecting heat transfer in FDM/FFE: a contribution towards the numerical modelling of the process
The performance of parts produced by Free Form Extrusion (FFE), an increasingly popular additive manufacturing technique, depends mainly on their dimensional accuracy, surface quality and mechanical performance. These attributes are strongly influenced by the evolution of the filament temperature and deformation during deposition and solidification. Consequently, the availability of adequate process modelling software would offer a powerful tool to support efficient process set-up and optimisation. This work examines the contribution to the overall heat transfer of various thermal phenomena developing during the manufacturing sequence, including convection and radiation with the environment, conduction with support and between adjacent filaments, radiation between adjacent filaments and convection with entrapped air. The magnitude of the mechanical deformation is also studied. Once this exercise is completed, it is possible to select the material properties, process variables and thermal phenomena that should be taken in for effective numerical modelling of FFE.This work was supported by Strategic Project - LA 25 - 2013–2014 [PEst-C/CTM/LA0025/2013]
Supergravity interacting with bosonic p-branes and local supersymmetry
We study the coupling of supergravity with a purely bosonic brane source
(bosonic p-brane). The interaction, described by the sum of their respective
actions, is self-consistent if the bosonic p-brane is the pure bosonic limit of
a super-p-brane. In that case the dynamical system preserves 1/2 of the local
supersymmetry characteristic of the `free' supergravity.Comment: 11 pages, RevTe
Huyghens Principle, Planck Law: Peculiarities in the Behavior of Planar Photons
Huyghens principle and Planck law are studied in Maxwell and
Maxwell-Chern-Simons frameworks in (2+1) dimensions. Contrary to (3+1)
dimensions, massless photons are shown to violate Huyghens principle in planar
world. In addition, we obtain that Planck law is no longer proportional to
, but to the squared frequency, , of the planar photons. We also
briefly discuss possible physical consequences of these results.Comment: 10 pages, no figures. Latex forma
Baryon polarization in low-energy unpolarized meson-baryon scattering
We compute the polarization of the final-state baryon, in its rest frame, in
low-energy meson--baryon scattering with unpolarized initial state, in
Unitarized BChPT. Free parameters are determined by fitting total and
differential cross-section data (and spin-asymmetry or polarization data if
available) for , and scattering. We also compare our
results with those of leading-order BChPT
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