443 research outputs found
Nucleon scalar matrix elements with twisted mass fermions
The XXIX International Symposium on Lattice Field Theory, Lattice 2011We investigate scalar matrix elements of the nucleon using flavors of maximally twisted mass fermions at a fixed value of the lattice spacing of . We compute disconnected contributions to the relevant three-point functions using an efficient noise reduction technique. Using these methods together with an only multiplicative renormalization applicable for twisted mass fermions, allows us to obtain accurate results in the light and strange sector
Phase ordering and shape deformation of two-phase membranes
Within a coupled-field Ginzburg-Landau model we study analytically phase
separation and accompanying shape deformation on a two-phase elastic membrane
in simple geometries such as cylinders, spheres and tori. Using an exact
periodic domain wall solution we solve for the shape and phase ordering field,
and estimate the degree of deformation of the membrane. The results are
pertinent to a preferential phase separation in regions of differing curvature
on a variety of vesicles.Comment: 4 pages, submitted to PR
Characterization of relativistic electron bunch duration and travelling wave structure phase velocity based on momentum spectra measurements on the ARES linac at DESY
The ARES linac at DESY aims to generate and characterize ultrashort electron
bunches (fs to sub-fs duration) with high momentum and arrival time stability
for the purpose of applications related to accelerator R&D, e.g. development of
advanced and compact diagnostics and accelerating structures, test of new
accelerator components, medical applications studies, machine learning, etc.
During its commissioning phase, the bunch duration characterization of the
electron bunches generated at ARES has been performed with an RF-phasing
technique relying on momentum spectra measurements, using only common
accelerator elements (RF accelerating structures and magnetic spectrometers).
The sensitivity of the method allowed highlighting different response times for
Mo and Cs2Te cathodes. The measured electron bunch duration in a wide range of
machine parameters shows excellent agreement overall with the simulation
predictions, thus demonstrating a very good understanding of the ARES operation
on the bunch duration aspect. The importance of a precise in-situ experimental
determination of the phase velocity of the first travelling wave accelerating
structure after the electron source, for which we propose a simple new
beam-based method precise down to sub-permille variation respective to the
speed of light in vacuum, is emphasized for this purpose. A minimum bunch
duration of 20 fs rms, resolution-limited by the space charge forces, is
reported. This is, to the best of our knowledge, around 4 times shorter than
what has been previously experimentally demonstrated based on RF-phasing
techniques with a single RF structure. The present study constitutes a strong
basis for future time characterization down to the sub-fs level at ARES, using
dedicated X-band transverse deflecting structures.Comment: 17 pages, 11 figures. To be submitted to Physical Review Accelerators
and Beam
Nucleon Structure from Lattice QCD Using a Nearly Physical Pion Mass
We report the first Lattice QCD calculation using the almost physical pion
mass mpi=149 MeV that agrees with experiment for four fundamental isovector
observables characterizing the gross structure of the nucleon: the Dirac and
Pauli radii, the magnetic moment, and the quark momentum fraction. The key to
this success is the combination of using a nearly physical pion mass and
excluding the contributions of excited states. An analogous calculation of the
nucleon axial charge governing beta decay has inconsistencies indicating a
source of bias at low pion masses not present for the other observables and
yields a result that disagrees with experiment.Comment: journal version; 15 pages, 6 figure
Urban Green Parks for Long-term Subjective Well-being: Empirical Relationships between Personal Characteristics, Park Characteristics, Park Use, Sense of Place, and Satisfaction with Life in the Netherlands
As our living environment is becoming increasingly urbanized, this puts the livability, health, and quality of life in cities under pressure. Due to the urbanization process, urban green spaces are under threat of becoming scarce, while it is recognized that these green spaces can positively contribute to the subjective well-being of citizens. It is thus important to maximize the use and benefits derived from green spaces by designing them as positively experienced places. The aim of this research is to gain more empirical insights on the relationships between personal and park characteristics, park use behavior, sense of place, and park visitorsâ long-term subjective well-being (i.e., life satisfaction). An online questionnaire was administered to participants in two medium-sized cities in The Netherlands, namely Eindhoven and âs-Hertogenbosch. Data were analyzed using a structural equation model. The results of this study show that the appreciation of facilities and the absence of disturbances positively influence the use and sense of place of a park. Furthermore, the findings show that sense of place has a positive influence on life satisfaction. The findings can be used by designers and policy-makers as guidelines to improve existing parks or to design new parks that support the subjective well-being of individuals in The Netherlands
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Spectral surface albedo over Morocco and its impact on radiative forcing of Saharan dust
In May-June 2006, airborne and ground-based solar (0.3-2.2 Όm) and thermal infrared (4-42 Όm) radiation measurements have been performed in Morocco within the Saharan Mineral Dust Experiment (SAMUM). Upwelling and downwelling solar irradiances have been measured using the Spectral Modular Airborne Radiation Measurement System (SMART)-Albedometer. With these data, the areal spectral surface albedo for typical surface types in southeastern Morocco was derived from airborne measurements for the first time. The results are compared to the surface albedo retrieved from collocated satellite measurements, and partly considerable deviations are observed. Using measured surface and atmospheric properties, the spectral and broad-band dust radiative forcing at top-of-atmosphere (TOA) and at the surface has been estimated. The impact of the surface albedo on the solar radiative forcing of Saharan dust is quantified. In the SAMUM case of 19 May 2006, TOA solar radiative forcing varies by 12 W m-2 per 0.1 surface-albedo change. For the thermal infrared component, values of up to +22 W m-2 were derived. The net (solar plus thermal infrared) TOA radiative forcing varies between -19 and +24 W m-2 for a broad-band solar surface albedo of 0.0 and 0.32, respectively. Over the bright surface of southeastern Morocco, the Saharan dust always has a net warming effect. © 2008 The Author Journal compilation © 2008 Blackwell Munksgaard
Nucleon form factors and moments of generalized parton distributions using twisted mass fermions
Version accepted for publication in Phys. Rev. D. 23 pages, 27 figuresWe present results on the axial and the electromagnetic form factors of the nucleon, as well as, on the first moments of the nucleon generalized parton distributions using maximally twisted mass fermions. We analyze two N_f=2+1+1 ensembles having pion masses of 210 MeV and 354 MeV at two values of the lattice spacing. The lattice scale is determined using the nucleon mass computed on a total of 18 N_f=2+1+1 ensembles generated at three values of the lattice spacing, . The renormalization constants are evaluated non-perturbatively with a perturbative subtraction of -terms. The moments of the generalized parton distributions are given in the scheme at a scale of GeV. We compare with recent results obtained using different discretization schemes. The implications on the spin content of the nucleon are also discussed
Tunable and precise two-bunch generation at FLASHForward
Beam-driven plasma-wakefield acceleration based on external injection has the
potential to significantly reduce the size of future accelerators. Stability
and quality of the acceleration process substantially depends on the incoming
bunch parameters. Precise control of the current profile is essential for
optimising energy-transfer efficiency and preserving energy spread. At the
FLASHForward facility, driver--witness bunch pairs of adjustable bunch length
and separation are generated by a set of collimators in a dispersive section,
which enables fs-level control of the longitudinal bunch profile. The design of
the collimator apparatus and its commissioning is presented.Comment: 7 pages, 5 figures, to be published in the proceedings of the 4th
European Advanced Accelerator Concepts Workshop, 15-21 September 2019, La
Biodola Bay, Isola d'Elba, Ital
Nucleon mass and sigma term from lattice QCD with two light fermion flavors
We analyze Nf=2 nucleon mass data with respect to their dependence on the
pion mass down to mpi = 157 MeV and compare it with predictions from covariant
baryon chiral perturbation theory (BChPT). A novel feature of our approach is
that we fit the nucleon mass data simultaneously with the directly obtained
pion-nucleon sigma-term. Our lattice data below mpi = 435 MeV is well described
by O(p^4) BChPT and we find sigma=37(8)(6) MeV for the sigma-term at the
physical point. Using the nucleon mass to set the scale we obtain a Sommer
parameter of r_0=0.501(10)(11) fm.Comment: 26 pages, 11 figures, 5 tables. Version to appear in NPB with a few
more details on the fit parameter
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Erratum to: 36th International Symposium on Intensive Care and Emergency Medicine: Brussels, Belgium. 15-18 March 2016.
[This corrects the article DOI: 10.1186/s13054-016-1208-6.]
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