9,850 research outputs found
PP-Wave Holography for Dp-Brane Backgrounds
As an extension of the so-called BMN conjecture, we investigate the
plane-wave limit for possible holographic connection between bulk string
theories in non-conformal backgrounds of D-branes and the corresponding
supersymmetric gauge theories for . Our work is based on the tunneling
picture for dominant null trajectories of strings in the limit of large angular
momentum. The tunneling null trajectories start from the near-horizon boundary
and return to the boundary, and the resulting backgrounds are time-dependent
for general D-branes except for . We develop a general method for
extracting diagonalized two-point functions for boundary theories as Euclidean
(bulk) S-matrix in the time-dependent backgrounds. For the case of D0-brane,
two-point functions of supergravity modes are shown to agree with the results
derived previously by the perturbative analysis of supergravity. We then
discuss the implications of the holography for general cases of D-branes
including the stringy excitations. All the cases () exhibit
interesting infra-red behaviors, which are different from free-field theories,
suggesting the existence of quite nontrivial fixed-points in dual gauge
theories.Comment: 43 pages, corrected typos, version to be published in Nucl. Phys.
Between social control and conflict: an analytical framework for social movements
The main goal of this article is to attempt to determine the analytical framework of social movements that would constitute an essential element of this form of collective activity. In order to identify this element (or elements) I will review the four main approaches to the study of social movements, which allows me to settle the issue in sociological conflict tradition. From the point of view of the outlined objective, Alain Touraine’s approach will be a key perspective
The role of socio-technical experiments in introducing sustainable Product-Service System innovations
This is the pre-print version of the chapter published in 2015 by Springer in the book “The Handbook of Service Innovation” (edited by Renu Agarwal, Willem Selen, Göran Roos and Roy Green).
The final publication is available at Springer via http://dx.doi.org/10.1007/978-1-4471-6590-3_18Product-Service System (PSS) innovations represent a promising approach to sustainability, but their implementation and diffusion are hindered by several cultural, corporate, and regulative barriers. Hence, an important challenge is not only to conceive sustainable PSS concepts, but also to understand how to manage, support, and orient the introduction and diffusion of these concepts. Building upon insights from transition studies (in particular, the concepts of Strategic Niche Management and Transition Management), and through an action research project, the chapter investigates the role of design in introducing sustainable radical service innovations. A key role is given to the implementation of socio-technical experiments, partially protected spaces where innovations can be incubated and tested, become more mature, and potentially favor the implementation and scaling up process
Dynamics of self-interacting strings and energy-momentum conservation
Classical strings coupled to a metric, a dilaton and an axion, as
conceived by superstring theory, suffer from ultraviolet divergences
due to self-interactions. Consequently, as in the case of
radiating charged particles, the corresponding effective string dynamics
cannot be derived from an action principle. We propose a
fundamental principle to build this dynamics, based on local energymomentum
conservation in terms of a well-defined
distribution-valued energy-momentum tensor. Its continuity
equation implies a finite equation of motion for self-interacting
strings. The construction is carried out explicitly for strings in
uniform motion in arbitrary space\u2013time dimensions, where we
establish cancelations of ultraviolet divergences which parallel
superstring non-renormalization theorems. The uniqueness properties
of the resulting dynamics are analyzed
Strong-coupling phases of 3D Dirac and Weyl semimetals. A renormalization group approach
We investigate the strong-coupling phases that may arise in 3D Dirac and Weyl
semimetals under the effect of the long-range Coulomb interaction, considering
the many-body theory of these electron systems as a variant of the conventional
fully relativistic Quantum Electrodynamics (QED). For this purpose, we apply
two different nonperturbative approaches, consisting in the sum of ladder
diagrams and taking the limit of a large number N of fermion flavors. We
benefit from the renormalizability that the theory shows in both cases to
compute the anomalous scaling dimensions of different operators exclusively in
terms of the renormalized coupling constant, allowing us to determine the
precise location of the singularities signaling the onset of the
strong-coupling phases. We show then that the QED of 3D Dirac semimetals has
two competing effects at strong coupling. One of them is the tendency to chiral
symmetry breaking and dynamical mass generation, which are analogous to the
same phenomena arising in the conventional QED at strong coupling. This trend
is however outweighed by the strong suppression of electron quasiparticles that
takes place at large N, leading to a different type of critical point at
sufficiently large interaction strength, shared also by the 3D Weyl semimetals.
Overall, the phase diagram of the 3D Dirac semimetals turns out to be richer
than that of their 2D counterparts, displaying a transition to a phase with
non-Fermi liquid behavior which may be observed in materials hosting a
sufficiently large number of Dirac or Weyl points.Comment: 29 pages, 11 figure
Gold and Greater Britain: Jevons, Trollope, and Settler Colonialism
The Australian gold rushes of the 1850s provide an exemplary test case for exploring the impact of Greater Britain—the settler colonial empire—on the Victorian novel and political economy. British gold diggers’ nomadism operated in seeming antithesis to the colonies’ explosive growth, which posed a conceptual challenge both to political economy’s stadial model of societal development and to liberal narratives of labor and land—narratives that underpinned concepts of individual character and civil society. Informed by colonial writing and the experience of gold fields, W. S. Jevons’s Theory of Political Economy (1871) and Anthony Trollope’s John Caldigate (1879) reimagine metropolitan space and subjectivity in settler-colonial terms, helping lay the ground for a deterritorialized, global British identity
Cable Robot Performance Evaluation by Wrench Exertion Capability
Although cable driven robots are a type of parallel manipulators, the evaluation of their performances cannot be carried out using the performance indices already developed for parallel robots with rigid links. This is an obvious consequence of the peculiar features of flexible cables-a cable can only exert a tensile and limited force in the direction of the cable itself. A comprehensive performance evaluation can certainly be attained by computing the maximum force (or torque) that can be exerted by the cables on the moving platform along a specific (or any) direction within the whole workspace. This is the idea behind the index-called the Wrench Exertion Capability (WEC)-which can be employed to evaluate the performance of any cable robot topology and is characterized by an efficient and simple formulation based on linear programming. By significantly improving a preliminary computation method for the WEC, this paper proposes an ultimate formulation suitable for any cable robot topology. Several numerical investigations on planar and spatial cable robots are presented to give evidence of the WEC usefulness, comparisons with popular performance indices are also provided
Identifying and Encouraging Leadership Potential: Assessment Technology and the Library Profession
published or submitted for publicatio
- …