741 research outputs found
Classical Noncommutative Electrodynamics with External Source
In a -noncommutative (NC) gauge field theory we extend the
Seiberg-Witten (SW) map to include the (gauge-invariance-violating) external
current and formulate - to the first order in the NC parameter -
gauge-covariant classical field equations. We find solutions to these equations
in the vacuum and in an external magnetic field, when the 4-current is a static
electric charge of a finite size , restricted from below by the elementary
length. We impose extra boundary conditions, which we use to rule out all
singularities, included, from the solutions. The static charge proves to
be a magnetic dipole, with its magnetic moment being inversely proportional to
its size . The external magnetic field modifies the long-range Coulomb field
and some electromagnetic form-factors. We also analyze the ambiguity in the SW
map and show that at least to the order studied here it is equivalent to the
ambiguity of adding a homogeneous solution to the current-conservation
equation
Noise influence on electron dynamics in semiconductors driven by a periodic electric field
Studies about the constructive aspects of noise and fluctuations in different
non-linear systems have shown that the addition of external noise to systems
with an intrinsic noise may result in a less noisy response. Recently, the
possibility to reduce the diffusion noise in semiconductor bulk materials by
adding a random fluctuating contribution to the driving static electric field
has been tested. The present work extends the previous theories by considering
the noise-induced effects on the electron transport dynamics in low-doped
n-type GaAs samples driven by a high-frequency periodic electric field
(cyclostationary conditions). By means of Monte Carlo simulations, we calculate
the changes in the spectral density of the electron velocity fluctuations
caused by the addition of an external correlated noise source. The results
reported in this paper confirm that, under specific conditions, the presence of
a fluctuating component added to an oscillating electric field can reduce the
total noise power. Furthermore, we find a nonlinear behaviour of the spectral
density with the noise intensity. Our study reveals that, critically depending
on the external noise correlation time, the dynamical response of electrons
driven by a periodic electric field receives a benefit by the constructive
interplay between the fluctuating field and the intrinsic noise of the system.Comment: 9 pages, 4 figures, to appear in J. Stat. Mechanics: Theory and
Experim., 200
Negotiating the inhuman: Bakhtin, materiality and the instrumentalization of climate change
The article argues that the work of literary theorist Mikhail M. Bakhtin presents a starting point for thinking about the instrumentalization of climate change. Bakhtinâs conceptualization of humanâworld relationships, encapsulated in the concept of âcosmic terrorâ, places a strong focus on our perception of the âinhumanâ. Suggesting a link between the perceived alienness and instability of the world and in the exploitation of the resulting fear of change by political and religious forces, Bakhtin asserts that the latter can only be resisted if our desire for a false stability in the world is overcome. The key to this overcoming of fear, for him, lies in recognizing and confronting the worldly relations of the human body. This consciousness represents the beginning of oneâs âdeautomatizationâ from following established patterns of reactions to predicted or real changes. In the vein of several theorists and artists of his time who explored similar âdeautomatizationâ strategies â examples include Shklovskyâs âostranenieâ, Brechtâs âVerfremdungâ, Artaudâs emotional âcrueltyâ and Batailleâs âbase materialismâ â Bakhtin proposes a more playful and widely accessible experimentation to deconstruct our âhabitual picture of the worldâ. Experimentation is envisioned to take place across the material and the textual to increase possibilities for action. Through engaging with Bakhtinâs ideas, this article seeks to draw attention to relations between the imagination of the world and political agency, and the need to include these relations in our own experiments with creating climate change awareness
âFalling into the skyâ: gravity and levity in Pynchonâs Mason & Dixon
My argument follows geographer Gunnar Olsson when he asks âWhat is geography if it is not the drawing and interpreting of a line? And what is the drawing of a line if it is not also the creation of new objects?â Using Thomas Pynchonâs 1997 novel Mason & Dixon about the drawing of the Mason-Dixon line, I explore how the mapmakerâs productive power is never merely reflective but generative too, constructing a world as much as representing one. I question the consequent relation between âabove and below,â drawing on Farinelliâs insight that critique of such constructions must recognise an antagonistic humour in the production of maps and territories. Pynchonâs novel, I argue, is exemplary in the wit with which it pits the anomalous, strange and contingent phenomena of the below against the homogenising, categorising power of above. His approach helps us understand the dark heart of Enlightenment cartography and society
Relaxation of Electron Spin during High-Field Transport in GaAs Bulk
A semiclassical Monte Carlo approach is adopted to study the multivalley spin
depolarization of drifting electrons in a doped n-type GaAs bulk semiconductor,
in a wide range of lattice temperature ( K) and doping density
(cm). The decay of the initial non-equilibrium spin
polarization of the conduction electrons is investigated as a function of the
amplitude of the driving static electric field, ranging between 0.1 and 6
kV/cm, by considering the spin dynamics of electrons in both the and
the upper valleys of the semiconductor. Doping density considerably affects
spin relaxation at low temperature and weak intensity of the driving electric
field. At high values of the electric field, the strong spin-orbit coupling of
electrons in the -valleys significantly reduces the average spin
polarization lifetime, but, unexpectedly, for field amplitudes greater than 2.5
kV/cm, the spin lifetime increases with the lattice temperature. Our numerical
findings are validated by a good agreement with the available experimental
results and with calculations recently obtained by a different theoretical
approach.Comment: 14 pages, 6 figure
Towards a framework for critical citizenship education
Increasingly countries around the world are promoting forms of "critical" citizenship in the planned curricula of schools. However, the intended meaning behind this term varies markedly and can range from a set of creative and technical skills under the label "critical thinking" to a desire to encourage engagement, action and political emancipation, often labelled "critical pedagogy". This paper distinguishes these manifestations of the "critical" and, based on an analysis of the prevailing models of critical pedagogy and citizenship education, develops a conceptual framework for analysing and comparing the nature of critical citizenship
Theorizing media production: the poverty of political economy
This article argues that the Political Economy of Communication (PEC) has generally failed to develop theories of media production. Such theory as exists has been heavily influenced by accounts of mass production and flexible specialization in Hollywood. Hollywood film production has been viewed as paradigmatic of media production in general, in the same way as Ford was for manufacturing, and these theories continue to influence accounts of production across media and cultural industries. The article tests the mass production/flexible specialization paradigm against both the evidence of the Hollywood case and Fordâs mass production system. An alternative paradigm, the theory of craft media production, is also examined. The article then attempts to show how applying organization theory and media economics can provide a more convincing explanation of media production and of the Hollywood case. Finally, the article briefly attempts to show how we might develop rich theoretical explanations of media production by exploring the relationships between economic, organizational and media-specific cultural elements
Putting into Question the Imaginary of Recovery: A Dialectical Reading of the Global Financial Crisis and its Aftermath
In this article we put into question the discourses that emerged during the Global Financial Crisis (GFC) and that coalesced around a particular socio-economic imaginary of ?recovery? over the period 2009-2012. Our reading of these discourses is very much guided by the notion of the dialectic as developed by Fredric Jameson, and as such this paper can be read as attempt to put his theoretical ideas to work. Through our dialectical reading we aim to create a certain estrangement effect that makes the imaginary of recovery seem very odd and unnatural. In order to achieve such an effect we postulate four theses which are deliberately antagonistic: first, that there has been no ?crisis of capitalism?; second, that we must change the valence of the GFC from negative to positive; third, that the relationship between finance capitalism and ?free markets? is deeply contradictory; and fourth, that we must resist the regulation discourse
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