81,958 research outputs found
Stabilizing Entangled States with Quasi-Local Quantum Dynamical Semigroups
We provide a solution to the problem of determining whether a target pure
state can be asymptotically prepared using dissipative Markovian dynamics under
fixed locality constraints. Beside recovering existing results for a large
class of physically relevant entangled states, our approach has the advantage
of providing an explicit stabilization test solely based on the input state and
constraints of the problem. Connections with the formalism of frustration-free
parent Hamiltonians are discussed, as well as control implementations in terms
of a switching output-feedback law.Comment: 11 pages, no figure
Through a Lattice Darkly -- Shedding Light on Electron-Phonon Coupling in the High T Cuprates
With its central role in conventional BCS superconductivity, electron-phonon
coupling has appeared to play a more subtle role in the phase diagram of the
high temperature superconducting cuprates. The added complexity of the cuprates
with potentially numerous competing phases including charge, spin, orbital, and
lattice ordering, makes teasing out any unique phenomena challenging. In this
review, we present our work using angle resolved photoemission spectroscopy
(ARPES) to explore the role of the lattice and its effect on the valence band
electronic structure in the cuprates. We provide an introduction to the ARPES
technique and its unique ability to the probe the effect of bosonic
renormalization (or "kink") on the near-E band structure. Our survey begins
with the establishment of the ubiquitous nodal cuprate kink leading to the way
isotope substitution has shed a critical new perspective on the role and
strength of electron-phonon coupling. We continue with recently published work
on the connection between the phonon dispersion as seen with inelastic x-ray
scattering (IXS) and the location of the kink as observed by ARPES near the
nodal point. Finally, we present very recent and ongoing ARPES work examining
how induced strain through chemical pressure provides a potentially promising
avenue for understanding the broader role of the lattice to the superconducting
phase and larger cuprate phase diagram.Comment: 17 pages, 20 figures, Review Articl
Radiative cooler
A method and radiative cooling device for use in passively cooling spaces is described. It is applicable to any level of thermal radiation in vacuum and to high-intensity thermal radiation in non-vacuum environments. The device includes an enclosure nested in a multiplicity of thin, low-emittance, highly-reflective shields. The shields are suspended in a casing in mutual angular relation and having V-shaped spaces defined therebetween for redirecting, by reflection, toward the large openings of the V-shaped spaces, thermal radiation entering the sides of the shields, and emitted to the spaces, whereby successively reduced quantities of thermal radiation are reflected by the surfaces along substantially parallel paths extended through the V-shaped spaces to a common heat sink such as the cold thermal background of space
Service quality measurements for IPv6 inter-networks
Measurement-based performance evaluation of
network traffic is becoming very important, especially for
networks trying to provide differentiated levels of service quality to the different application flows. The non-identical response of flows to the different types of network-imposed performance degradation raises the need for ubiquitous measurement mechanisms, able to measure numerous performance properties, and being equally applicable to different applications and transports. This paper presents a new measurement mechanism, facilitated by the steady introduction of IPv6 in network nodes and hosts, which exploits native features of the protocol to provide support for performance measurements at the network (IP) layer. IPv6 Extension Headers have been used to carry the
triggers involving the measurement activity and the
measurement data in-line with the payload data itself, providing a high level of probability that the behaviour of the real user traffic flows is observed. End-to-end one-way delay, jitter, loss, and throughput have been measured for applications operating on top of both reliable and unreliable transports, over different-capacity
IPv6 network configurations. We conclude that this
technique could form the basis for future Internet measurements that can be dynamically deployed where and when required in a multi-service IP environment
Seismic sensitivity to sub-surface solar activity from 18 years of GOLF/SoHO observations
Solar activity has significantly changed over the last two Schwabe cycles.
After a long and deep minimum at the end of Cycle 23, the weaker activity of
Cycle 24 contrasts with the previous cycles. In this work, the response of the
solar acoustic oscillations to solar activity is used in order to provide
insights on the structural and magnetic changes in the sub-surface layers of
the Sun during this on-going unusual period of low activity. We analyze 18
years of continuous observations of the solar acoustic oscillations collected
by the Sun-as-a-star GOLF instrument onboard the SoHO spacecraft. From the
fitted mode frequencies, the temporal variability of the frequency shifts of
the radial, dipolar, and quadrupolar modes are studied for different frequency
ranges which are sensitive to different layers in the solar sub-surface
interior. The low-frequency modes show nearly unchanged frequency shifts
between Cycles 23 and 24, with a time evolving signature of the quasi-biennial
oscillation, which is particularly visible for the quadrupole component
revealing the presence of a complex magnetic structure. The modes at higher
frequencies show frequency shifts 30% smaller during Cycle~24, which is in
agreement with the decrease observed in the surface activity between Cycles 23
and 24. The analysis of 18 years of GOLF oscillations indicates that the
structural and magnetic changes responsible for the frequency shifts remained
comparable between Cycle 23 and Cycle 24 in the deeper sub-surface layers below
1400 km as revealed by the low-frequency modes. The frequency shifts of the
higher-frequency modes, sensitive to shallower regions, show that Cycle 24 is
magnetically weaker in the upper layers of Sun.Comment: Accepted for publication in A&
Photoproduction of jets and the virtual structure of the photon
We compute the ratio between the direct and the resolved photon components of
single jet and dijet production in collisions for the kinematical range
covered by the most recent ZEUS data. We analyse the phenomenological
consequences of different models for the structure of virtual photons in these
observables and compare them with the available data. We also comment on the
correlation between the so called and the `true'
, that can be inferred from the data.Comment: epsfig, 5 figure
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