357 research outputs found
Chicken and Egg? Hentagon, Icosa-Coop, and Two Types of Experience
In an essay with the title Experience and Poverty,1 Walter Benjamin writes about the lack of traditional experience (Erfahrung)—a kind of acquired knowledge—that could be handed down to younger generations through story-telling and hands-on instruction. Benjamin reads this experience as a cipher for modern architecture where one material—steel—stands in for a cultural perspective toward traditions, while glass represents a new virtual existence expressed in a short-term event-based experience—in German the word is Erlebnis—both of which, we think, can be transmitted through contemporary pedagogy. In our paper we argue that effective teaching of beginning- design students requires a hybridization of a material focus and an emphasis on immaterial modes of production
Attosecond Precision Multi-km Laser-Microwave Network
Synchronous laser-microwave networks delivering attosecond timing precision
are highly desirable in many advanced applications, such as geodesy,
very-long-baseline interferometry, high-precision navigation and
multi-telescope arrays. In particular, rapidly expanding photon science
facilities like X-ray free-electron lasers and intense laser beamlines require
system-wide attosecond-level synchronization of dozens of optical and microwave
signals up to kilometer distances. Once equipped with such precision, these
facilities will initiate radically new science by shedding light on molecular
and atomic processes happening on the attosecond timescale, such as
intramolecular charge transfer, Auger processes and their impact on X-ray
imaging. Here, we present for the first time a complete synchronous
laser-microwave network with attosecond precision, which is achieved through
new metrological devices and careful balancing of fiber nonlinearities and
fundamental noise contributions. We demonstrate timing stabilization of a
4.7-km fiber network and remote optical-optical synchronization across a 3.5-km
fiber link with an overall timing jitter of 580 and 680 attoseconds RMS,
respectively, for over 40 hours. Ultimately we realize a complete
laser-microwave network with 950-attosecond timing jitter for 18 hours. This
work can enable next-generation attosecond photon-science facilities to
revolutionize many research fields from structural biology to material science
and chemistry to fundamental physics.Comment: 42 pages, 13 figure
Gradient-free quantum optimization on NISQ devices
Variational Quantum Eigensolvers (VQEs) have recently attracted considerable
attention. Yet, in practice, they still suffer from the efforts for estimating
cost function gradients for large parameter sets or resource-demanding
reinforcement strategies. Here, we therefore consider recent advances in
weight-agnostic learning and propose a strategy that addresses the trade-off
between finding appropriate circuit architectures and parameter tuning. We
investigate the use of NEAT-inspired algorithms which evaluate circuits via
genetic competition and thus circumvent issues due to exceeding numbers of
parameters. Our methods are tested both via simulation and on real quantum
hardware and are used to solve the transverse Ising Hamiltonian and the
Sherrington-Kirkpatrick spin model.Comment: 13 pages, 6 figures, comments welcome
Flavor Ratios of Astrophysical Neutrinos: Implications for Precision Measurements
We discuss flavor-mixing probabilities and flavor ratios of high energy
astrophysical neutrinos. In the first part of this paper, we expand the
neutrino flavor-fluxes in terms of the small parameters U_{e3} and pi/4 -
theta_{23}, and show that there are universal first and second order
corrections. The second order term can exceed the first order term, and so
should be included in any analytic study. We also investigate the probabilities
and ratios after a further expansion around the tribimaximal value of sin^2
theta_{12} = 1/3. In the second part of the paper, we discuss implications of
deviations of initial flavor ratios from the usually assumed, idealized flavor
compositions for pion, muon-damped, and neutron beam sources, viz., (1 : 2 :
0), (0 : 1 : 0), and (1 : 0 : 0), respectively. We show that even small
deviations have significant consequences for the observed flavor ratios at
Earth. If initial flavor deviations are not taken into account in analyses,
then false inferences for the values in the PMNS matrix elements (angles and
phase) may result.Comment: 32 pages, 15 figures. Minor changes, matches version in JHE
Fast Excitation and Photon Emission of a Single-Atom-Cavity System
We report on the fast excitation of a single atom coupled to an optical
cavity using laser pulses that are much shorter than all other relevant
processes. The cavity frequency constitutes a control parameter that allows the
creation of single photons in a superposition of two tunable frequencies. Each
photon emitted from the cavity thus exhibits a pronounced amplitude modulation
determined by the oscillatory energy exchange between the atom and the cavity.
Our technique constitutes a versatile tool for future quantum networking
experiments.Comment: 4 pages, 5 figure
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Right care, right time, right place: improving outcomes for people with spinal cord injury through early access to intervention and improved access to specialised care: study protocol
Background: Traumatic spinal cord injury is a devastating condition impacting adversely on the health and wellbeing, functioning and independence, social participation and quality of life of the injured person. In Australia, there are approximately 15 new cases per million population per year; economic burden estimates suggest 2 billion dollars annually. For optimal patient outcomes expert consensus recommends expeditious transfer (“24 hours) in a Spinal Cord Injury Unit. Examining current health service and clinical intervention pathways in this Australian population-based sample, in relation to their outcomes, will provide an understanding of factors associated with patient flow, resource utilisation and cost, and patient and family quality of life. Barriers to streamlined effective early-care pathways and facilitators of optimal treatment for these patients will be identified
Implications of Cosmological Gamma-Ray Absorption II. Modification of gamma-ray spectra
Bearing on the model for the time-dependent metagalactic radiation field
developed in the first paper of this series, we compute the gamma-ray
attenuation due to pair production in photon-photon scattering. Emphasis is on
the effects of varying the star formation rate and the fraction of UV radiation
assumed to escape from the star forming regions, the latter being important
mainly for high-redshift sources. Conversely, we investigate how the
metagalactic radiation field can be measured from the gamma-ray pair creation
cutoff as a function of redshift, the Fazio-Stecker relation. For three
observed TeV-blazars (Mkn501, Mkn421, H1426+428) we study the effects of
gamma-ray attenuation on their spectra in detail.Comment: 10 pages, 6 figures, accepted by A&
Optimal acceleration voltage for near-atomic resolution imaging of layer-stacked 2D polymer thin films
Despite superb instrumental resolution in modern transmission electron microscopes (TEM), high-resolution imaging of organic two-dimensional (2D) materials is a formidable task. Here, we present that the appropriate selection of the incident electron energy plays a crucial role in reducing the gap between achievable resolution in the image and the instrumental limit. Among a broad range of electron acceleration voltages (300 kV, 200 kV, 120 kV, and 80 kV) tested, we found that the highest resolution in the HRTEM image is achieved at 120 kV, which is 1.9 Å. In two imine-based 2D polymer thin films, unexpected molecular interstitial defects were unraveled. Their structural nature is identified with the aid of quantum mechanical calculations. Furthermore, the increased image resolution and enhanced image contrast at 120 kV enabled the detection of functional groups at the pore interfaces. The experimental setup has also been employed for an amorphous organic 2D material
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