This article reports world averages of measurements of
b
-hadron,
c
-hadron, and
τ
-lepton properties obtained by the Heavy Flavor Averaging Group using results available through summer 2016. For the ...averaging, common input parameters used in the various analyses are adjusted (rescaled) to common values, and known correlations are taken into account. The averages include branching fractions, lifetimes, neutral meson mixing parameters,
C
P
violation parameters, parameters of semileptonic decays, and Cabbibo–Kobayashi–Maskawa matrix elements.
Ball screws are robust and economical linear positioning systems widely employed in high-speed and high-precision machines. Due to precision and stability requirements, the preload force is ...considered one of the main parameters defining the axial stiffness and the maximum axial load of the ball screw feed drives. In high-speed motions, thermal effects are also considerably relevant regarding positioning precision and dynamic stability of the machine. The temperature increase and the thermal gradient between the screw, the balls and the nuts result in geometrical variations and, consequently, variations in the preload force. This paper presents a numerical modelling strategy to predict the preload variation due to temperature increase using a thermo-mechanical 3D finite element method (FEM)-based model for double nut-ball screw drives. Two different thermo-mechanical coupling strategies are compared, and the obtained results are validated with experimental measurements for different initial preload and linear speeds. In the mechanical analysis, the nut-screw ball contact interface, the offset-based preloading and the restrictions of the ball bearings are included in the model, while the thermal analysis considers heat generation and heat diffusion. The causes of the thermal preload variation are discussed considering the ball load distribution and the axial and radial thermal displacements of the contacting points.
Permanent electric dipole moments (EDMs) of fundamental particles provide powerful probes for physics beyond the Standard Model. We propose to search for the EDM of strange and charm baryons at LHC, ...extending the ongoing experimental program on the neutron, muon, atoms, molecules and light nuclei. The EDM of strange
Λ
baryons, selected from weak decays of charm baryons produced in
p
p
collisions at LHC, can be determined by studying the spin precession in the magnetic field of the detector tracking system. A test of
C
P
T
symmetry can be performed by measuring the magnetic dipole moment of
Λ
and
Λ
¯
baryons. For short-lived
Λ
c
+
and
Ξ
c
+
baryons, to be produced in a fixed-target experiment using the 7
TeV
LHC beam and channeled in a bent crystal, the spin precession is induced by the intense electromagnetic field between crystal atomic planes. The experimental layout based on the LHCb detector and the expected sensitivities in the coming years are discussed.
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•The incorporation of azobenzene moieties into a bridged silsesquioxane led a material with light-induced healing ability.•The photoisomerization of the azobenzene increases the ...mobility and allows the material to flow in the damaged area.•A complete recovery of the damage was observed after only 30 s of UV irradiation.
Intrinsic healable polymers are materials capable of repairing itself through its chemical nature, in order to improve stability and durability and to restore the lost functionalities or properties.
In this study, azobenzene (AZO) moieties were incorporated into a previously reported bridged silsesquioxane based on the reaction of isocyanatepropyltriethoxysilane (IPTS) with bisphenol A (BPA), by replacing a small fraction of BPA by a bisazophenol (4,4′-dihydroxyazobenzene, AZOH). The incorporation of these AZO moieties led to a material with UV light-induced healing abilities. The underlying healing mechanism is attributed to the intra-molecular conformational changes of the azo-chromophores that are induced by the trans to cis photoisomerization of the azobenzene. These changes temporary increased its mobility and allowed the material to flow in the damaged area, followed by a process of restoring the physical hydrogen bonds. This process was monitored following the viscoelastic properties during successive cycles of turning ON and OFF the UV irradiation. Remarkably, the resultant healed material has not significant observed mechanical differences with the original one.
El presente estudio tiene como objetivo analizar la asociación que existe entre estrés académico y bienestar psicológico, y el rol que ejerce la procrastinación académica en esta relación, en una ...muestra de estudiantes universitarios de pregrado. Participaron 391 estudiantes universitarios de pregrado de diversas universidades de Lima Metropolitana - Perú. Los constructos fueron medidos a partir de la adaptación española de las Escalas de Bienestar Psicológico de Ryff (SPWB), el Inventario Sistémico Cognoscitivista (SISCO SV-21) y la Escala de Procrastinación Académica (EPA). Los resultados indican que la procrastinación y el estrés académico presentan una relación negativa con respecto al bienestar psicológico. Además, la presencia de estresores y síntomas asociados al estrés académico, y la procrastinación resultan ser predictores relevantes del bienestar psicológico; sin embargo, la interacción entre ambas variables no implica un efecto significativo. Por lo tanto, se concluye que no existe un efecto moderador de la procrastinación académica en la relación entre estrés académico y bienestar psicológico. En su lugar, se halló que la procrastinación ejerce un rol moderador en la relación entre la presencia de estresores y el desarrollo de síntomas asociados al estrés académico.
A comparative study of the influence of the competitive reactions that can take place in epoxy–isocyanate based azo systems over optical behavior was developed.
Diverse disperse red 19 (DR 19) azo ...urethane oligomers (PUs) were synthesized and characterized using size exclusion chromatography (SEC), Fourier transform infrared (FTIR), and UV–visible spectroscopy. Based on these urethane oligomers, epoxy-PU networks having isocyanurate and oxazolidone rings in their structures were prepared in different isocyanate/epoxy stoichiometric ratios, r=eq. NCO/eq. epoxy (0.5, 1, and 2).
Photoinduced anisotropy (Δn), remnant birefringence (RB) and dichroism were measured for the resulting polymers and evaluated as function of their Tgs and chemical structures. Final materials exhibited very high values of Δn and RB being promised materials for using in optical storage information devices.
Functionalization of epoxy-based networks by the preferential surface enrichment of perfluorinated tails to achieve hydrophobic surface is described. Two series of crosslinked fluorinated epoxy-based ...materials containing variable fluorine contents (from 0 to 5 wt % F) were prepared using formulations based on partially fluorinated diamine, epoxy monomer and a curing agent. The epoxy monomer was based on diglycidyl ether of bisphenol A (DGEBA) while the curing agents were either propyleneoxide diamine (JEFFAMINE) or 4,4′-methylenebis(3-chloro 2,6-diethylaniline) (MCDEA). The selected fluorinated epoxies (FE) were: 2,2,3,3,4,4,5,5,6,6,7,7,8,9,9,9-hexadecafluoro-8-trifluoromethyl nonyloxirane (FED3) and 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,9-heptadecafluoro nonyloxirane (FES3). The influence on surface properties of the architecture of FE, and the molecular structure of the unit building blocks was analyzed and discussed. It was found that both series showed high hydrophobicity and oleophobicity, independently of the crosslink density, bulk composition, and curing conditions. XPS measurements showed a surface composition much richer in fluorinated segments than expected from bulk composition. Fluorine enrichment was also manifested at the polymer/aluminium interface for JEFFAMINE-based networks. This observation is discussed in terms of the molecular weight dependence of surface tension and configurational entropy of the thermosetting matrix. At least for the range of this study, while increasing the amount of fluorine incorporated in both network series, dynamic friction is reduced due to surface migration of fluorine species during polymerization
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Ball screws are robust and economic linear positioning systems that are widely employed in high speed and high precision machines. Due to precision and stability requirements, the preload force has ...been considered one of the main parameters in order to define the axial rigidity and the maximum axial load capacity of ball screw feed drives. In high speed motions, thermal effects are also considerably relevant regarding positioning precision and dynamic stability of the machine. The temperature increase and the thermal gradient between the screw, the balls and the nuts led to a variation in the contact geometry and consequently in the preload force. This paper presents an experimental analysis of the preload variation due to the temperature increase. The study has been performed for several initial preload forces and linear speeds in a preloaded double nut ball screw. The heating of the system results in a decrease of the preload force, where a maximum decrease of 60 % has been observed for a temperature increase of 28 K in the test bed of the study. Regarding the consequences of the loss of rigidity, the first eigenvalue decreased by only 5 % for a preload drop of 33 %.
B semileptonic decays @ DELPHI Oyanguren, A.
The European physical journal. C, Particles and fields,
07/2004, Letnik:
33, Številka:
S1
Journal Article
Recenzirano
Odprti dostop
AbstractUpdated results on B semileptonic decays at the DELPHI experiment are presented. Measurements of b-hadron lifetimes, exclusive \(\overline{{\rm B}^0_d} \to {\rm D}^{*+} \ell^- \overline ...\nu_\ell\) decays and inclusive moments of the hadronic mass distribution are encompassed here. They focus on a precise determination of the CKM matrix element Vcb.
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