757 research outputs found
An observation of a transverse to longitudinal emittance exchange at the Fermilab A0 photoinjector:
No full textAn experimental program to perform a proof of principle of transverse to longitudinal emittance exchange has been developed at the Fermilab A0 Photoinjector. A new beamline, including two magnetic dogleg channels and a TM110 deflecting mode radio frequency cavity, were constructed for the emittance exchange experiment.
The first priority was a measurement of the Emittance Exchange beamline transport matrix. The method of difference orbits was used to measure the transport matrix. Through varying individual beam input vector elements, such as input x, x', y, y', z, or momentum and measuring the changes in all of the beam output vector's elements, output x, x', y, y', z, and momentum the full 6X6 transport matrix was measured. The measured emittance exchange transport matrix was in overall good agreement with our calculated transport matrix.
A direct observation of an emittance exchange was performed by measuring the electron beam's characteristics before and after the emittance exchange beamline. Operating with a 14.3 MeV, 250 pC electron bunch, longitudinal input emittance of 21.1+/-1.5 mm.mrad was observed to be exchanged with output horizontal emittance of 20.8+/-2.00 mm.mrad. Diagnostic limitations in the longitudinal output emittance measurement did not account for an energy-time correlation, thus potentially returning values larger than the actual longitudinal emittance. The horizontal input emittance of 4.67+/-0.22 mm.mrad was observed to be exchanged with the longitudinal output emittance of 7.06+/-0.43 mm.mrad. The apparent longitudinal output emittance growth is consistent with calculated values in which the correlation term is neglected.Ph.D.Includes bibliographical references (p. 160-164)by Timothy W. Koet
Modeling of colossal magnetoresistance in La0.67Ca0.33MnO3/Pr0.67Ca0.33MnO3 superlattices: Comparison with individual (La1−yPry)0.67Ca0.33MnO3 films
No full textColossal magnetoresistance (CMR) and nm-scale electronic inhomogeneity close to the first order phase transition in perovskite manganites, e.g., (La1-yPry)(0.67)Ca0.33MnO3 still remain a puzzling phenomenon. We experimentally model a metal-insulator phase coexistence by growing a short period (LCMOn/PCMOn)(m) superlattices (SLs) with the same thickness for both components. CMR effect was studied as a function of the individual layer thickness n = 2-8 and then compared with chemically homogeneous (La1-yPry)(0.67)Ca0.33MnO3 LPCMO films. We show that SLs can be superimposed in the phase diagram of LPCMO. The results also point out the importance of the nm-scale electronic rather than chemical separation for realization of the CMR effect as well as limits the lowest boundary for the thickness of an individual manganite material to n similar to 4u.c. (C) 2013 American Institute of Physics
Mix and Switch Effects in Bilingual Language Processing
No full textThis study utilized a novel task design in an effort to identify the source of the second language processing advantage commonly reported in mixed language conditions, investigate switch cost asymmetry in non-balanced bilinguals, and identify task-related variables that potentially contribute to inconsistent results across studies with similar participant populations. Seventy highly-proficient Korean-English bilinguals completed modified picture naming, semantic categorization, and lexical decision tasks, as well as a cognitive control task designed to examine the potential relationship between lexical control and general cognitive control. While no significant relationship was found between lexical control and general cognitive control, several key task-related variables emerged with respect to mix and switch effects. Specifically, verbal production requirements and increased second language repetition effects significantly influenced results. Furthermore, this study revealed potential effects of semantic load as well as script differences in receptive tasks. Results from this study highlight several key variables that contribute to bilingual mix and switch effects, as well as task design-related considerations for future bilingual mix and switch studies
ExoMol line lists-IV. The rotation-vibration spectrum of methane up to 1500 K
No full textA new hot line list is calculated for CH in its ground electronic state. This line list, called 10to10, contains 9.8 billion transitions and should be complete for temperatures up to 1500 K. It covers the wavelengths longer than 1 μm and includes all transitions to upper states with energies below hc · 18 000 cm and rotational excitation up to J = 39. The line list is computed using the eigenvalues and eigenfunctions of CH obtained by variational solution of the Schrödinger equation for the rotation-vibration motion of nuclei employing program TROVE and a new 'spectroscopic' potential energy surface (PES) obtained by refining an ab initio PES (CCSD(T)-F12c/aug-cc-pVQZ) through least-squares fitting to the experimentally derived energies with J = 0-4 and a previously reported ab initio dipole moment surface (CCSD(T)-F12c/aug-cc-pVTZ). Detailed comparisons with other available sources of methane transitions including HITRAN, experimental compilations and other theoretical line lists show that these sources lack transitions both higher temperatures and near-infrared wavelengths. The 10to10 line list is suitable for modelling atmospheres of cool stars and exoplanets. It is available from the CDS data base as well as at www.exomol.com
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Emittance Exchange Results
No full textThe promise of next-generation light sources depends on the availability of ultra-low emittance electron sources. One method of producing low transverse emittance beams is to generate a low longitudinal emittance beam and exchange it with a large transverse emittance. Experiments are underway at Fermilab's A0 Photoinjector and ANL's Argonne Wakefield Accelerator using the exchange scheme of Kim and Sessler. The experiment at the A0 Photoinjector exchanges a large longitudinal emittance with a small transverse emittance. AWA expects to exchange a large transverse emittance with a small longitudinal emittance. In this paper we discuss recent results at A0 and AWA and future plans for these experiments
Ultra-low current beams in UMER to model space-charge effects in high-energy proton and ion machines
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Measurement of the t t ¯ H and tH production rates in the H → b b ¯ decay channel using proton-proton collision data at s = 13 TeV
No full textAbstract An analysis of the production of a Higgs boson (H) in association with a top quark-antiquark pair ( t t ¯ H ) or a single top quark (tH) is presented. The Higgs boson decay into a bottom quark-antiquark pair (H → b b ¯ ) is targeted, and three different final states of the top quark decays are considered, defined by the number of leptons (electrons or muons) in the event. The analysis utilises proton-proton collision data collected at the CERN LHC with the CMS experiment at s = 13 TeV in 2016–2018, which correspond to an integrated luminosity of 138 fb −1. The observed t t ¯ H production rate relative to the standard model expectation is 0.33 ± 0.26 = 0.33 ± 0.17(stat) ± 0.21(syst). Additionally, the t t ¯ H production rate is determined in intervals of Higgs boson transverse momentum. An upper limit at 95% confidence level is set on the tH production rate of 14.6 times the standard model prediction, with an expectation of 19.3 − 6.0 + 9.2 . Finally, constraints are derived on the strength and structure of the coupling between the Higgs boson and the top quark from simultaneous extraction of the t t ¯ H and tH production rates, and the results are combined with those obtained in other Higgs boson decay channels
Submonolayer uniformity of type II InAs/GaInSb W-shaped quantum wells probed by full-wafer photoluminescence mapping in the mid-infrared spectral range
No full textThe work has been supported by Project Widelase (No. 318798) of the 7-th Framework Program of the European Commission. Date of Acceptance: 06/10/2015The spatial uniformity of GaSb- and InAs substrate-based structures containing type II quantum wells was probed by means of large-scale photoluminescence (PL) mapping realized utilizing a Fourier transform infrared spectrometer. The active region was designed and grown in a form of a W-shaped structure with InAs and GaInSb layers for confinement of electrons and holes, respectively. The PL spectra were recorded over the entire 2-in. wafers, and the parameters extracted from each spectrum, such as PL peak energy position, its linewidth and integrated intensity, were collected in a form of two-dimensional spatial maps. Throughout the analysis of these maps, the wafers' homogeneity and precision of the growth procedure were investigated. A very small variation of PL peak energy over the wafer indicates InAs quantum well width fluctuation of only a fraction of a monolayer and hence extraordinary thickness accuracy, a conclusion further supported by high uniformity of both the emission intensity and PL linewidth.Peer reviewe
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