1,148 research outputs found
The non-Abelian state-dependent gauge field in optics
The covariant formulation of the quantum dynamics in CP(1) should lead to the
observable geometrodynamical effects for the local dynamical variable of the
light polarization states.Comment: 8 pages, 3 figures, LaTe
Electric propulsion using C.sub.60 molecules
Fullerene propellants, which are stable carbon cage structures composed of even numbers of carbon atoms in the range of about 32 to 200 atoms, particularly a combination of conveniently obtainable C.sub.60 and C.sub.70, may be carried in solid form in a spacecraft, sublimated to produce the appropriate molecular propellant such as C.sub.60 or C.sub.70, which may then be ionized by DC discharge or RF radiation to efficiently produce specific impulses in the range above 1000 lbf -s/lbm
Fibration symmetries uncover the building blocks of biological networks
A major ambition of systems science is to uncover the building blocks of any
biological network to decipher how cellular function emerges from their
interactions. Here, we introduce a graph representation of the information flow
in these networks as a set of input trees, one for each node, which contains
all pathways along which information can be transmitted in the network. In this
representation, we find remarkable symmetries in the input trees that
deconstruct the network into functional building blocks called fibers. Nodes in
a fiber have isomorphic input trees and thus process equivalent dynamics and
synchronize their activity. Each fiber can then be collapsed into a single
representative base node through an information-preserving transformation
called 'symmetry fibration', introduced by Grothendieck in the context of
algebraic geometry. We exemplify the symmetry fibrations in gene regulatory
networks and then show that they universally apply across species and domains
from biology to social and infrastructure networks. The building blocks are
classified into topological classes of input trees characterized by integer
branching ratios and fractal golden ratios of Fibonacci sequences representing
cycles of information. Thus, symmetry fibrations describe how complex networks
are built from the bottom up to process information through the synchronization
of their constitutive building blocks
Pre- and Post-selection paradoxes and contextuality in quantum mechanics
Many seemingly paradoxical effects are known in the predictions for outcomes
of intermediate measurements made on pre- and post-selected quantum systems.
Despite appearances, these effects do not demonstrate the impossibility of a
noncontextual hidden variable theory, since an explanation in terms of
measurement-disturbance is possible. Nonetheless, we show that for every
paradoxical effect wherein all the pre- and post- selected probabilities are 0
or 1 and the pre- and post-selected states are nonorthogonal, there is an
associated proof of contextuality. This proof is obtained by considering all
the measurements involved in the paradoxical effect -- the pre-selection, the
post-selection, and the alternative possible intermediate measurements -- as
alternative possible measurements at a single time.Comment: 5 pages, 1 figure. Submitted to Phys. Rev. Lett. v2.0 revised in the
light of referee comments, results unchange
Measuring Polynomial Invariants of Multi-Party Quantum States
We present networks for directly estimating the polynomial invariants of
multi-party quantum states under local transformations. The structure of these
networks is closely related to the structure of the invariants themselves and
this lends a physical interpretation to these otherwise abstract mathematical
quantities. Specifically, our networks estimate the invariants under local
unitary (LU) transformations and under stochastic local operations and
classical communication (SLOCC). Our networks can estimate the LU invariants
for multi-party states, where each party can have a Hilbert space of arbitrary
dimension and the SLOCC invariants for multi-qubit states. We analyze the
statistical efficiency of our networks compared to methods based on estimating
the state coefficients and calculating the invariants.Comment: 8 pages, 4 figures, RevTex4, v2 references update
Long-term acoustic monitoring at North Sea well site 22/4b
Highlights
• First study using long-term passive acoustic monitoring of methane seeps at well blowout site 22/4b.
• Seep acoustic temporal variations correlated with ocean tides.
• Major acoustic transient event recorded on 8 December 2011 with high temporal resolution.
Abstract
Marine seeps produce underwater sounds as a result of bubble formation and fragmentation upon emission from the seabed. The frequency content and sound levels of these emissions are related to bubble size distribution and emission flux, providing important information on methane release from the seafloor. Long-term passive acoustic monitoring was used to continuously record seep sounds over a 7-month period within the blowout crater at the abandoned well site, 22/4b, in the central North Sea. Also recorded were water column fluid velocities and near-seafloor water conductivity, temperature, and pressure. Acoustic signatures were primarily from ∼1 to 10 kHz. Key features were relatively broad spectral peaks at about 1.0, 1.5, 2.2, 3.1, 3.6 and 5.1 kHz. Temporal variations in spectral levels were apparently associated with tides.
The recordings also documented a series of major episodic events including a large and persistent increase (∼10 dB) in overall sound levels and spectral broadening on 8 December 2011. The acoustic temporal pattern of this event was consistent with other recorded large transient events in the literature, and the major event was correlated with dramatic changes in other measurements, including increased water column fluid velocities, increased pressure and decreased salinity, indicating real changes in emission flux. Observed seabed morphology changes reported elsewhere in this special issue, also likely were related to this event. These data demonstrate the dynamic nature of marine seepage systems, show the value of monitoring systems, and provide direct supporting evidence for a violent formation mechanism of many widespread seep-associated seabed features like pockmarks
The Incredible Shrinking Dewlap: Signal Size, Skin Elasticity, and Mechanical Design in the Green Anole Lizard (Anolis Carolinensis)
The expression of male secondary sexual traits can be dynamic, changing size, shape, color, or structure over the course of different seasons. However, the factors underlying such changes are poorly understood. In male Anolis carolinensis lizards, a morphological secondary sexual signal called the dewlap changes size seasonally within individuals. Here, we test the hypothesis that seasonal changes in male dewlap size are driven by increased use and extension of the dewlap in spring and summer, when males are breeding, relative to the winter and fall. We captured male green anole lizards prior to the onset of breeding and constrained the dewlap in half of them such that it could not be extended. We then measured dewlap area in the spring, summer, and winter, and dewlap skin and belly skin elasticity in summer and winter. Dewlaps in unconstrained males increase in area from spring to summer and then shrink in the winter, whereas the dewlaps of constrained males consistently shrink from spring to winter. Dewlap skin is significantly more elastic than belly skin, and skin overall is more elastic in the summer relative to winter. These results show that seasonal changes in dewlap size are a function of skin elasticity and display frequency, and suggest that the mechanical properties of signaling structures can have important implications for signal evolution and design
Detectability, Invasiveness and the Quantum Three Box Paradox
Quantum pre- and post-selection (PPS) paradoxes occur when counterfactual
inferences are made about different measurements that might have been
performed, between two measurements that are actually performed. The 3 box
paradox is the paradigm example of such a paradox, where a ball is placed in
one of three boxes and it is inferred that it would have been found, with
certainty, both in box 1 and in box 2 had either box been opened on their own.
Precisely what is at stake in PPS paradoxes has been unclear, and classical
models have been suggested which are supposed to mimic the essential features
of the problem. We show that the essential difference between the classical and
quantum pre- and post-selection effects lies in the fact that for a quantum PPS
paradox to occur the intervening measurement, had it been performed, would need
to be invasive but non-detectable. This invasiveness is required even for null
result measurements. While some quasi-classical features (such as
non-contextuality and macrorealism) are compatible with PPS paradoxes, it seems
no fully classical model of the 3 box paradox is possible.Comment: 16 pages, no figure
An Algebra of Hierarchical Graphs
We define an algebraic theory of hierarchical graphs, whose axioms characterise graph isomorphism: two terms are equated exactly when they represent the same graph. Our algebra can be understood as a high-level language for describing graphs with a node-sharing, embedding structure, and it is then well suited for defining graphical representations of software models where nesting and linking are key aspects
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