894 research outputs found
Dynamic modulation of photonic crystal nanocavities using gigahertz acoustic phonons
Photonic crystal membranes (PCM) provide a versatile planar platform for
on-chip implementations of photonic quantum circuits. One prominent quantum
element is a coupled system consisting of a nanocavity and a single quantum dot
(QD) which forms a fundamental building block for elaborate quantum information
networks and a cavity quantum electrodynamic (cQED) system controlled by single
photons. So far no fast tuning mechanism is available to achieve control within
the system coherence time. Here we demonstrate dynamic tuning by monochromatic
coherent acoustic phonons formed by a surface acoustic wave (SAW) with
frequencies exceeding 1.7 gigahertz, one order of magnitude faster than
alternative approaches. We resolve a periodic modulation of the optical mode
exceeding eight times its linewidth, preserving both the spatial mode profile
and a high quality factor. Since PCMs confine photonic and phononic
excitations, coupling optical to acoustic frequencies, our technique opens ways
towards coherent acoustic control of optomechanical crystals.Comment: 11 pages 4 figure
Playing stories?
Drawing on Janet Murray (1997), Katie Salen and Eric Zimmerman (2004), and other previous proposals, this article conceptualizes player agency as the possibility space for “meaningful” choice expressed via player action that translates into avatar action, afforded and constrained by a videogame’s design. It further distinguishes between four core dimensions of agency thus conceptualized: First, spatial-explorative agency is afforded by those elements of a videogame’s design that determine the player’s ability to navigate and traverse the game spaces via their avatar. Second, temporal-ergodic agency is afforded by those elements of a videogame’s design that determine the player’s options for interacting with the videogame as a temporal system. Third, configurative-constructive agency is afforded by those elements of a videogame’s design that allow the player to configure their avatar and/or (re)construct the game spaces. Fourth, narrative-dramatic agency is afforded by those elements of a videogame’s design that determine the player’s “meaningful” impact on the unfolding story. The article then moves on to analyze two case studies of independently developed videogames: ZA/UM’s role-playing game Disco Elysium (2019), whose complex nonlinear narrative structure primarily affords configurative and narrative agency, and System Era Softworks’s sandbox adventure game Astroneer (2019), whose procedurally generated game spaces and “open” game mechanics primarily afford explorative, constructive, and dramatic agency
The European CCS Demonstration Project Network — A forum for first movers
AbstractThe European CCS Demonstration Project Network was initiated by the European Commission in 2009. The main objective of the network is to accelerate development of CCS technologies by creating a forum for exchange and dissemination of new knowledge generated by the first large scale CCS plants in Europe. This paper provides an overview and understanding of the activities of the network and the political and theoretical context of their development. The paper focuses on how the Network has been structured to add value to demonstration projects and create vital new channels of information for enabling CCS demonstration and deployment to be advanced worldwide
Photochemistry of glycolaldehyde in cryogenic matrices
International audienceThe photochemistry of glycolaldehyde (GA) upon irradiation at 266 nm is investigated in argon, nitrogen, neon, and para-hydrogen matrices by IR spectroscopy. Isomerization and fragmentation processes are found to compete. The hydrogen-bonded Cis-Cis form of GA is transformed mainly to the open Trans-Trans conformer and to CO and CH3OH fragments and their mixed complexes. Different photo-induced behaviours appear depending on the matrix. In nitrogen, small amounts of Trans-Gauche and Trans-Trans conformers are detected after deposition and grow together upon irradiation. The Trans-Gauche conformer is characterized for the first time. In para-hydrogen due to a weaker cage effect additional H2CO and HCO fragments are seen. Calculations of the potential energy surfaces of S0, S1, and T1 states – to analyse the torsional deformations which are involved in the isomerization process – and a kinetic analysis are presented to investigate the different relaxation pathways of GA. Fragmentation of GA under UV irradiation through the CO+CH3OH molecular channel is a minor process, as in the gas phase
The Slowly Formed Guiselin Brush
We study polymer layers formed by irreversible adsorption from a polymer
melt. Our theory describes an experiment which is a ``slow'' version of that
proposed by Guiselin [Europhys. Lett., v. 17 (1992) p. 225] who considered
instantaneously irreversibly adsorbing chains and predicted a universal density
profile of the layer after swelling with solvent to produce the ``Guiselin
brush.'' Here we ask what happens when adsorption is not instantaneous. The
classic example is chemisorption. In this case the brush is formed slowly and
the final structure depends on the experiment's duration, . We find
the swollen layer consists of an inner region of thickness with approximately constant density and an outer region
extending up to height which has the same density decay as for the Guiselin case.Comment: 7 pages, submitted to Europhysics Letter
Nucleation and spreading of a heterochromatic domain in fission yeast
Outstanding questions in the chromatin field bear on how large heterochromatin domains are formed in space and time. Positive feedback, where histone-modifying enzymes are attracted to chromosomal regions displaying the modification they catalyse, is believed to drive the formation of these domains; however, few quantitative studies are available to assess this hypothesis. Here we quantified the de novo establishment of a naturally occurring ∼20-kb heterochromatin domain in fission yeast through single-cell analyses, measuring the kinetics of heterochromatin nucleation in a region targeted by RNAi and its subsequent expansion. We found that nucleation of heterochromatin is stochastic and can take from one to ten cell generations. Further silencing of the full region takes another one to ten generations. Quantitative modelling of the observed kinetics emphasizes the importance of local feedback, where a nucleosome-bound enzyme modifies adjacent nucleosomes, combined with a feedback where recruited enzymes can act at a distance
Deterministic nano-assembly of a coupled quantum emitter - photonic crystal cavity system
The interaction of a single quantum emitter with its environment is a central
theme in quantum optics. When placed in highly confined optical fields, such as
those created in optical cavities or plasmonic structures, the optical
properties of the emitter can change drastically. In particular, photonic
crystal (PC) cavities show high quality factors combined with an extremely
small mode volume. Efficiently coupling a single quantum emitter to a PC cavity
is challenging because of the required positioning accuracy. Here, we
demonstrate deterministic coupling of single Nitrogen-Vacancy (NV) centers to
high-quality gallium phosphide PC cavities, by deterministically positioning
their 50 nm-sized host nanocrystals into the cavity mode maximum with
few-nanometer accuracy. The coupling results in a 25-fold enhancement of NV
center emission at the cavity wavelength. With this technique, the NV center
photoluminescence spectrum can be reshaped allowing for efficient generation of
coherent photons, providing new opportunities for quantum science.Comment: 13 pages, 4 figure
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