544 research outputs found
Experimental Realization of the Quantum Box Problem
The three-box problem is a gedankenexperiment designed to elucidate some
interesting features of quantum measurement and locality. A particle is
prepared in a particular superposition of three boxes, and later found in a
different (but nonorthogonal) superposition. It was predicted that appropriate
"weak" measurements of particle position in the interval between preparation
and post-selection would find the particle in two different places, each with
certainty. We verify these predictions in an optical experiment and address the
issues of locality and of negative probability.Comment: 5 pages, 4 figure
Entanglement and four wave mixing effects in the dissipation free nonlinear interaction of two photons at a single atom
We investigate the nonlinear interaction between two photons in a single
input pulse at an atomic two level nonlinearity. A one dimensional model for
the propagation of light to and from the atom is used to describe the precise
spatiotemporal coherence of the two photon state. It is shown that the
interaction generates spatiotemporal entanglement in the output state similar
to the entanglement observed in parametric downconversion. A method of
generating photon pairs from coherent pump light using this quantum mechanical
four wave mixing process is proposed.Comment: 10 pages, including 3 figures, correction in eq.(7), updated
references, final version for publication in PR
Practical measurement of joint weak values and their connection to the annihilation operator
Weak measurements are a new tool for characterizing post-selected quantum
systems during their evolution. Weak measurement was originally formulated in
terms of von Neumann interactions which are practically available for only the
simplest single-particle observables. In the present work, we extend and
greatly simplify a recent, experimentally feasible, reformulation of weak
measurement for multiparticle observables [Resch and Steinberg (2004, Phys.
Rev. Lett., 92, 130402)]. We also show that the resulting ``joint weak values''
take on a particularly elegant form when expressed in terms of annihilation
operators.Comment: 13 pages, accepted to Physics Letters A (Dec. 2004
The Global Gridded Crop Model Intercomparison: Data and modeling protocols for Phase 1 (v1.0)
We present protocols and input data for Phase 1 of the Global Gridded Crop Model Intercomparison, a project of the Agricultural Model Intercomparison and Improvement Project (AgMIP). The project includes global simulations of yields, phenologies, and many land-surface fluxes using 12–15 modeling groups for many crops, climate forcing data sets, and scenarios over the historical period from 1948 to 2012. The primary outcomes of the project include (1) a detailed comparison of the major differences and similarities among global models commonly used for large-scale climate impact assessment, (2) an evaluation of model and ensemble hindcasting skill, (3) quantification of key uncertainties from climate input data, model choice, and other sources, and (4) a multi-model analysis of the agricultural impacts of large-scale climate extremes from the historical record
Pulsar timing arrays and the challenge of massive black hole binary astrophysics
Pulsar timing arrays (PTAs) are designed to detect gravitational waves (GWs)
at nHz frequencies. The expected dominant signal is given by the superposition
of all waves emitted by the cosmological population of supermassive black hole
(SMBH) binaries. Such superposition creates an incoherent stochastic
background, on top of which particularly bright or nearby sources might be
individually resolved. In this contribution I describe the properties of the
expected GW signal, highlighting its dependence on the overall binary
population, the relation between SMBHs and their hosts, and their coupling with
the stellar and gaseous environment. I describe the status of current PTA
efforts, and prospect of future detection and SMBH binary astrophysics.Comment: 18 pages, 4 figures. To appear in the Proceedings of the 2014 Sant
Cugat Forum on Astrophysics. Astrophysics and Space Science Proceedings, ed.
C.Sopuerta (Berlin: Springer-Verlag
Hegemonic masculine conceptualisation in gang culture
This research sought to investigate the relationship between gang processes and differing forms of masculine expression. Three hundred and sixteen male participants, drawn from secondary schools within Cape Town, were included in the study. These schools were in areas differentially characterised by gang activity. The questionnaire included the newly devised Male Attitude Norm Inventory designed to explore hegemonic conceptualisations of masculinity. Factor analytic procedures rendered a three-factor model stressing the importance of male toughness, success and control. Through a series of t-tests for independent samples, as well as supporting qualitative data, participants from areas characterised by high gang activity were found to support these hegemonic elements to a significantly greater extent
Measurement of (anti)deuteron and (anti)proton production in DIS at HERA
The first observation of (anti)deuterons in deep inelastic scattering at HERA
has been made with the ZEUS detector at a centre-of-mass energy of 300--318 GeV
using an integrated luminosity of 120 pb-1. The measurement was performed in
the central rapidity region for transverse momentum per unit of mass in the
range 0.3<p_T/M<0.7. The particle rates have been extracted and interpreted in
terms of the coalescence model. The (anti)deuteron production yield is smaller
than the (anti)proton yield by approximately three orders of magnitude,
consistent with the world measurements.Comment: 26 pages, 9 figures, 5 tables, submitted to Nucl. Phys.
Observation of isolated high-E_T photons in deep inelastic scattering
First measurements of cross sections for isolated prompt photon production in
deep inelastic ep scattering have been made using the ZEUS detector at the HERA
electron-proton collider using an integrated luminosity of 121 pb^-1. A signal
for isolated photons in the transverse energy and rapidity ranges 5 < E_T^gamma
< 10 GeV and -0.7 < eta^gamma < 0.9 was observed for virtualities of the
exchanged photon of Q^2 > 35 GeV^2. Cross sections are presented for inclusive
prompt photons and for those accompanied by a single jet in the range E_T^jet
\geq 6 GeV and -1.5 \leq eta^jet < 1.8. Calculations at order alpha^3alpha_s
describe the data reasonably well.Comment: 16 pages, 5 figure
Measurement of beauty production in deep inelastic scattering at HERA
The beauty production cross section for deep inelastic scattering events with
at least one hard jet in the Breit frame together with a muon has been
measured, for photon virtualities Q^2 > 2 GeV^2, with the ZEUS detector at HERA
using integrated luminosity of 72 pb^-1. The total visible cross section is
sigma_b-bbar (ep -> e jet mu X) = 40.9 +- 5.7 (stat.) +6.0 -4.4 (syst.) pb. The
next-to-leading order QCD prediction lies about 2.5 standard deviations below
the data. The differential cross sections are in general consistent with the
NLO QCD predictions; however at low values of Q^2, Bjorken x, and muon
transverse momentum, and high values of jet transverse energy and muon
pseudorapidity, the prediction is about two standard deviations below the data.Comment: 18 pages, 4 figure
Forward jet production in deep inelastic ep scattering and low-x parton dynamics at HERA
Differential inclusive jet cross sections in neutral current deep inelastic
ep scattering have been measured with the ZEUS detector. Three phase-space
regions have been selected in order to study parton dynamics where the effects
of BFKL evolution might be present. The measurements have been compared to the
predictions of leading-logarithm parton shower Monte Carlo models and
fixed-order perturbative QCD calculations. In the forward region, QCD
calculations at order alpha_s^1 underestimate the data up to an order of
magnitude at low x. An improved description of the data in this region is
obtained by including QCD corrections at order alpha_s^2, which account for the
lowest-order t-channel gluon-exchange diagrams, highlighting the importance of
such terms in parton dynamics at low x.Comment: 25 pages, 4 figure
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