1,076 research outputs found
An experimental proposal to study collapse of the wave function in travelling-wave parametric amplifiers
The read-out of a microwave qubit state occurs using an amplification chain
that enlarges the quantum state to a signal detectable with a classical
measurement apparatus. However, at what point in this process did we really
`measure' the quantum state? In order to investigate whether the `measurement'
takes place in the amplification chain, we propose to construct a microwave
interferometer that has a parametric amplifier added to each of its arms.
Feeding the interferometer with single photons, the visibility depends on the
gain of the amplifiers and whether a measurement collapse has taken place
during the amplification process. We calculate the interference visibility as
given by standard quantum mechanics as a function of gain, insertion loss and
temperature and find a magnitude of in the limit of large gain without
taking into account losses. This number reduces to in case the insertion
loss of the amplifiers is dB at a temperature of mK. We show that if
the wave function collapses within the interferometer, we will measure a
reduced visibility compared to the prediction from standard quantum mechanics
once this collapse process sets in.Comment: 21 pages and 23 figures (including appendices and subfigures). v4:
Abstract and introduction rewritten and note on stochasticity of quantum
state collapse added to section 6. v5: no content changes w.r.t. v
Boson-boson scattering and Higgs production at the LHC from a six fermion point of view: four jets + l processes at \O(\alpha_{em}^6)
Boson-boson scattering and Higgs production in boson-boson fusion hold the
key to electroweak symmetry breaking. In order to analyze these essential
features of the Standard Model we have performed a partonic level study of all
processes at the LHC using the exact matrix
elements at \O(\alpha_{em}^6) provided by \Phase, a new MC generator. These
processes include also three boson production and the purely electroweak
contribution to \toptop production as well as all irreducible backgrounds.
Kinematical cuts have been studied in order to enhance the VV scattering signal
over background. \Phase has been compared with different Monte Carlo's showing
that a complete calculation is necessary for a correct description of the
process.Comment: 26 pages, 19 figure
Simulations of a Line W-based observing system for the Atlantic meridional overturning circulation
In a series of observing system simulations, we test whether the Atlantic meridional overturning circulation (AMOC) can be observed based on the existing Line W deep western boundary array. We simulate a Line W array, which is extended to the surface and to the east to cover the basin to the Bermuda Rise. In the analyzed ocean circulation model ORCA025, such an extended Line W array captures the main characteristics of the western boundary current. Potential trans-basin observing systems for the AMOC are tested by combining the extended Line W array with a mid-ocean transport estimate obtained from thermal wind "measurements" and Ekman transport to the total AMOC (similarly to Hirschi et al., Geophys Res Lett 30(7):1413, 2003). First, we close Line W zonally supplementing the western boundary array with several "moorings" in the basin (Line W-32A degrees N). Second, we supplement the western boundary array with a combination of observations at Bermuda and the eastern part of the RAPID array at 26A degrees N (Line W-B-RAPID). Both, a small number of density profiles across the basin and also only sampling the eastern and western boundary, capture the variability of the AMOC at Line W-32A degrees N and Line W-B-RAPID. In the analyzed model, the AMOC variability at both Line W-32A degrees N and Line W-B-RAPID is dominated by the western boundary current variability. Away from the western boundary, the mid-ocean transport (east of Bermuda) shows no significant relation between the two Line W-based sections and 26A degrees N. Hence, a Line W-based AMOC estimate could yield an estimate of the meridional transport that is independent of the 26A degrees N RAPID estimate. The model-based observing system simulations presented here provide support for the use of Line W as a cornerstone for a trans-basin AMOC observing system
D-Instantons and asymptotic geometries
The large N limit of D3-branes is expected to correspond to a superconformal
field theory living on the boundary of the anti-de Sitter space appearing in
the near-horizon geometry. Dualizing the D3-brane to a D-instanton, we show
that this limit is equivalent to a type IIB S-duality. In both cases one
effectively reaches the near-horizon geometry. This provides an alternative
approach to an earlier derivation of the same result that makes use of the
properties of a gravitational wave instead of the D-instanton.Comment: 17 pages, LaTeX, 1 figure, minor corrections and refs adde
Causes and consequences of tipping points in river delta social-ecological systems
The sustainability of social-ecological systems within river deltas globally is in question as rapid development and environmental change trigger "negative” or “positive” tipping points depending on actors’ perspectives, e.g., regime shift from abundant sediment deposition to sediment shortage, agricultural sustainability to agricultural collapse or shift from rural to urban land. Using a systematic review of the literature, we show how cascading effects across anthropogenic, ecological, and geophysical processes have triggered numerous tipping points in the governance, hydrological and land use management of the world’s river deltas. Crossing tipping points had both positive and negative effects that generally enhanced economic development to the detriment of the environment. Assessment of deltas that featured prominently in the review revealed how outcomes of tipping points can inform the long-term trajectory of deltas towards sustainability or collapse. Management of key drivers at the delta scale can trigger positive tipping points to place social-ecological systems on a pathway towards sustainable development
Radio Frequency Spectra of 388 Bright 74 MHz Sources
As a service to the community, we have compiled radio frequency spectra from
the literature for all sources within the VLA Low Frequency Sky Survey (VLSS)
that are brighter than 15 Jy at 74 MHz. Over 160 references were used to
maximize the amount of spectral data used in the compilation of the spectra,
while also taking care to determine the corrections needed to put the flux
densities from all reference on the same absolute flux density scale. With the
new VLSS data, we are able to vastly improve upon previous efforts to compile
spectra of bright radio sources to frequencies below 100 MHz because (1) the
VLSS flux densities are more reliable than those from some previous low
frequency surveys and (2) the VLSS covers a much larger area of the sky
(declination >-30 deg.) than many other low frequency surveys (e.g., the 8C
survey). In this paper, we discuss how the spectra were constructed and how
parameters quantifying the shapes of the spectra were derived. Both the spectra
and the shape parameters are made available here to assist in the calibration
of observations made with current and future low frequency radio facilities.Comment: Accepted to ApJ
Charged jet cross section and fragmentation in proton-proton collisions at root S=7 TeV
We report the differential charged jet cross section and jet fragmentation distributions measured with the ALICE detector in proton-proton collisions at a center-of-mass energy root S = 7 TeV. Jets with pseudorapidity vertical bar eta vertical bar <0.5 are reconstructed from charged particles using the anti-k(T) jet-finding algorithm with a resolution parameter R = 0.4. The jet cross section is measured in the transverse momentum interval 5 40 GeV/c, the PYTHIA calculations also agree with the measured charged jet cross section. PYTHIA6 simulations describe the fragmentation distributions to 15%. Larger discrepancies are observed for PYTHIA8.Peer reviewe
- …