13,093 research outputs found
Quantum anti-quenching of radiation from laser-driven structured plasma channels
We demonstrate that in the interaction of a high-power laser pulse with a
structured solid-density plasma-channel, clear quantum signatures of stochastic
radiation emission manifest, disclosing a novel avenue to studying the
quantized nature of photon emission. In contrast to earlier findings we observe
that the total radiated energy for very short interaction times, achieved by
studying thin plasma channel targets, is significantly larger in a quantum
radiation model as compared to a calculation including classical radiation
reaction, i.e., we observe quantum anti-quenching. By means of a detailed
analytical analysis and a refined test particle model, corroborated by a full
kinetic plasma simulation, we demonstrate that this counter-intuitive behavior
is due to the constant supply of energy to the setup through the driving laser.
We comment on an experimental realization of the proposed setup, feasible at
upcoming high-intensity laser facilities, since the required thin targets can
be manufactured and the driving laser pulses provided with existing technology.Comment: 6 pages, 3 figure
Strong energy enhancement in a laser-driven plasma-based accelerator through stochastic friction
Conventionally, friction is understood as an efficient dissipation mechanism
depleting a physical system of energy as an unavoidable feature of any
realistic device involving moving parts, e.g., in mechanical brakes. In this
work, we demonstrate that this intuitive picture loses validity in nonlinear
quantum electrodynamics, exemplified in a scenario where spatially random
friction counter-intuitively results in a highly directional energy flow. This
peculiar behavior is caused by radiation friction, i.e., the energy loss of an
accelerated charge due to the emission of radiation. We demonstrate
analytically and numerically how radiation friction can enhance the performance
of a specific class of laser-driven particle accelerators. We find the
unexpected directional energy boost to be due to the particles' energy being
reduced through friction whence the driving laser can accelerate them more
efficiently. In a quantitative case we find the energy of the laser-accelerated
particles to be enhanced by orders of magnitude.Comment: 14 pages, 3 figure
Challenging the eco-city: residents’ perceptions of social sustainability in Tianjin Eco-City, China
In this chapter, we make the case for ‘humanizing’ new-build urban mega-projects such as eco-cities by focusing on urban social sustainability, and on the experiences of new residents in newly-built cities such as Tianjin eco-city. We base our conceptual framework in the context of debates over social sustainability (Dempsey et al. 2011; Vallance et al. 2011; Woodcraft 2015), and argue that there is a need to also focus on the way(s) in which socially sustainable urban environments are constructed, in new urban spaces, through relational networks comprised by interactions between residents, buildings, facilities and specifc (e.g. domestic) spaces. In focusing on the spaces of urban social sustainability we draw on Jane Jacobs’ seminal work on, and critique of, the modern city (Jacobs 1961). Jacobs’ work is useful here because of its focus on moving past the plans, blueprints and rational urban visions proposed by master planners, engineers and architects, and towards valuing the role of the rather messier relationality found in the everyday city. [...
Social sustainability and residents' experiences in a new Chinese eco-city
This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.The article argues for a “humanizing” research agenda on newly-built forms of eco-urbanism,
such as eco-cities. Taking the example of the Sino-Singapore Tianjin Eco-City, China, the
article focuses on urban social sustainability with a specific focus on the lived experiences of
new residents of the newly-built eco-city. Drawing on Jane Jacobs' work on the spaces of the
city, the article's focus on residents' experiences underlines the key importance of social
sustainability when analysing new flagship urban projects, and highlights the need to
consider the relational networks of lived experiences of the city as well as the visions and
techno-social designs of planners, policymakers and corporate actors in the development of
eco-city projects
The Sorting Index and Permutation Codes
In the combinatorial study of the coefficients of a bivariate polynomial that
generalizes both the length and the reflection length generating functions for
finite Coxeter groups, Petersen introduced a new Mahonian statistic ,
called the sorting index. Petersen proved that the pairs of statistics
and have the same joint distribution over
the symmetric group, and asked for a combinatorial proof of this fact. In
answer to the question of Petersen, we observe a connection between the sorting
index and the B-code of a permutation defined by Foata and Han, and we show
that the bijection of Foata and Han serves the purpose of mapping
to . We also give a type analogue of the
Foata-Han bijection, and we derive the quidistribution of and over signed
permutations. So we get a combinatorial interpretation of Petersen's
equidistribution of and . Moreover, we show that
the six pairs of set-valued statistics ,
, , ,
and are equidistributed over signed
permutations. For Coxeter groups of type , Petersen showed that the two
statistics and are equidistributed. We introduce two statistics
and for elements of and we prove that the two
pairs of statistics and are
equidistributed.Comment: 25 page
Direct laser acceleration of electrons assisted by strong laser-driven azimuthal plasma magnetic fields.
A high-intensity laser beam propagating through a dense plasma drives a strong current that robustly sustains a strong quasistatic azimuthal magnetic field. The laser field efficiently accelerates electrons in such a field that confines the transverse motion and deflects the electrons in the forward direction. Its advantage is a threshold rather than resonant behavior, accelerating electrons to high energies for sufficiently strong laser-driven currents. We study the electron dynamics via a test-electron model, specifically deriving the corresponding critical current density. We confirm the model's predictions by numerical simulations, indicating energy gains two orders of magnitude higher than achievable without the magnetic field
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