46,246 research outputs found
Non-commutative holonomies in 2+1 LQG and Kauffman's brackets
We investigate the canonical quantization of 2+1 gravity with {\Lambda} > 0
in the canonical framework of LQG. A natural regularization of the constraints
of 2+1 gravity can be defined in terms of the holonomies of A\pm = A \PM
\surd{\Lambda}e, where the SU(2) connection A and the triad field e are the
conjugated variables of the theory. As a first step towards the quantization of
these constraints we study the canonical quantization of the holonomy of the
connection A_{\lambda} = A + {\lambda}e acting on spin network links of the
kinematical Hilbert space of LQG. We provide an explicit construction of the
quantum holonomy operator, exhibiting a close relationship between the action
of the quantum holonomy at a crossing and Kauffman's q-deformed crossing
identity. The crucial difference is that the result is completely described in
terms of standard SU(2) spin network states.Comment: 4 pages; Proceedings of Loops'11, Madrid, to appear in Journal of
Physics: Conference Series (JPCS
Ex Ante Impact Assessment of Policies Affecting Land Use, Part B: Application of the Analytical Framework
The use of science-based tools for impact assessment has increasingly gained focus in addressing the complexity of interactions between environment, society, and economy. For integrated assessment of policies affecting land use, an analytical framework was developed. The aim of our work was to apply the analytical framework for specific scenario cases and in combination with quantitative and qualitative application methods. The analytical framework was tested for two cases involving the ex ante impact assessment of: (1) a European Common Agricultural Policy (CAP) financial reform scenario employing a modeling approach and combined with a comprehensive indicator analysis and valuation; and (2) a regional bioenergy policy scenario, employing a fully participatory approach. The results showed that European land use in general is less sensitive to changes in the Common Agricultural Policy, but in the context of regions there can be significant impacts on the functions of land use. In general, the implementation of the analytical framework for impact assessment proved to be doable with both methods, i.e., with the quantitative modeling and with the qualitative participatory approach. A key advantage of using the system of linked quantitative models is that it makes possible the simultaneous consideration of all relevant sectors of the economy without abstaining from a great level of detail for sectors of particular interest. Other advantages lie in the incontestable character of the results. Based on neutral, existing data with a fixed set of settings and regions, an absolute comparability and reproducibility throughout Europe can be maintained. Analyzing the pros and cons of both approaches showed that they could be used complementarily rather than be seen as competing alternatives
Explosive Events and the Evolution of the Photospheric Magnetic Field
Transition region explosive events have long been suggested as direct
signatures of magnetic reconnection in the solar atmosphere. In seeking further
observational evidence to support this interpretation, we study the relation
between explosive events and the evolution of the solar magnetic field as seen
in line-of-sight photospheric magnetograms. We find that about 38% of events
show changes of the magnetic structure in the photosphere at the location of an
explosive event over a time period of 1 h. We also discuss potential
ambiguities in the analysis of high sensitivity magnetograms
Early environmental field research career exploration: An analysis of impacts on precollege apprentices
Research apprenticeships offer opportunities for deep understanding of scientific practice, transparency about research careers, and possible transformational effects on precollege youth. We examined two consecutive field-based environmental biology apprenticeship programs designed to deliver realistic career exploration and connections to research scientists. The Shaw Institute for Field Training (SIFT) program combines introductory field-skills training with research assistance opportunities, and the subsequent Tyson Environmental Research Fellowships (TERF) program provides immersive internships on university field stationâbased research teams. In a longitudinal mixed-methods study grounded in social cognitive career theory, changes in youth perspectives were measured during program progression from 10th grade through college, evaluating the efficacy of encouraging career path entry. Results indicate SIFT provided self-knowledge and career perspectives more aligned with reality. During SIFT, differences were found between SIFT-only participants compared with those who progressed to TERF. Transition from educational activities to fieldwork with scientists was a pivotal moment at which data showed decreased or increased interest and confidence. Continuation to TERF provided deeper relationships with role models who gave essential early-career support. Our study indicates the two-stage apprenticeship structure influenced persistence in pursuit of an environmental research career pathway. Recommendations for other precollege environmental careerâexploration programs are presented
Limitations of quantum computing with Gaussian cluster states
We discuss the potential and limitations of Gaussian cluster states for
measurement-based quantum computing. Using a framework of Gaussian projected
entangled pair states (GPEPS), we show that no matter what Gaussian local
measurements are performed on systems distributed on a general graph, transport
and processing of quantum information is not possible beyond a certain
influence region, except for exponentially suppressed corrections. We also
demonstrate that even under arbitrary non-Gaussian local measurements, slabs of
Gaussian cluster states of a finite width cannot carry logical quantum
information, even if sophisticated encodings of qubits in continuous-variable
(CV) systems are allowed for. This is proven by suitably contracting tensor
networks representing infinite-dimensional quantum systems. The result can be
seen as sharpening the requirements for quantum error correction and fault
tolerance for Gaussian cluster states, and points towards the necessity of
non-Gaussian resource states for measurement-based quantum computing. The
results can equally be viewed as referring to Gaussian quantum repeater
networks.Comment: 13 pages, 7 figures, details of main argument extende
Search for the Standard Model Higgs Boson in the Diphoton Decay Channel with 4.9 fb^(-1) of pp Collision Data at âs = 7 TeV with ATLAS
A search for the standard model Higgs boson is performed in the diphoton decay channel. The data used correspond to an integrated luminosity of 4.9ââfb^(-1) collected with the ATLAS detector at the Large Hadron Collider in proton-proton collisions at a center-of-mass energy of âs = 7ââTeV. In the diphoton mass range 110â150 GeV, the largest excess with respect to the background-only hypothesis is observed at 126.5 GeV, with a local significance of 2.8 standard deviations. Taking the look-elsewhere effect into account in the range 110â150 GeV, this significance becomes 1.5 standard deviations. The standard model Higgs boson is excluded at 95% confidence level in the mass ranges of 113â115 GeV and 134.5â136 GeV
Measurement of the W âÏÎœ_Ï cross section in pp collisions at âs = 7 TeV with the ATLAS experiment
The cross section for the production of W bosons with subsequent decay WâÏÎœ_Ï is measured with the ATLAS detector at the LHC. The analysis is based on a data sample that was recorded in 2010 at a protonâproton center-of-mass energy of âs = 7TeV and corresponds to an integrated luminosity of 34 pb^(â1). The cross section is measured in a region of high detector acceptance and then extrapolated to the full phase space. The product of the total W production cross section and the WâÏÎœ_Ï branching ratio is measured to be Ï^(tot)
_(WâÏÎœÏ) = 11.1±0.3 (stat)±1.7 (syst)±0.4 (lumi) nb
Measurement of the W^±Z production cross section and limits on anomalous triple gauge couplings in protonâproton collisions at âs = 7 TeV with the ATLAS detector
This Letter presents a measurement of W^± Z production in 1.02 fb^(â1) of pp collision data at âs = 7 TeV collected by the ATLAS experiment in 2011. Doubly leptonic decay events are selected with electrons, muons and missing transverse momentum in the final state. In total 71 candidates are observed, with a background expectation of 12.1 ± 1.4(stat.)^(+4.1)_(â2.0)(syst.) events. The total cross section for W^± Z production for Z/Îł^â masses within the range 66 GeV to 116 GeV is determined to be Ï^(tot)_(WZ) = 20.5^(+3.1)_(â2.8)(stat.)^(+1.4)_(â1.3)(syst.)^(+0.9)_(â0.8)(lumi.) pb, which is consistent with the Standard Model expectation of 17.3^(+1.3) _(0.8) pb. Limits on anomalous triple gauge boson couplings are extracted
Search for a Light Higgs Boson Decaying to Long-Lived Weakly Interacting Particles in Proton-Proton Collisions at âs = 7 TeV with the ATLAS Detector
A search for the decay of a light Higgs boson (120â140 GeV) to a pair of weakly interacting, long-lived particles in 1.94ââfb^(-1) of proton-proton collisions at âs=7ââTeV recorded in 2011 by the ATLAS detector is presented. The search strategy requires that both long-lived particles decay inside the muon spectrometer. No excess of events is observed above the expected background and limits on the Higgs boson production times branching ratio to weakly interacting, long-lived particles are derived as a function of the particle proper decay length
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