14,413 research outputs found
Controlling the ellipticity of attosecond pulses produced by laser irradiation of overdense plasmas
The interaction of high-intensity laser pulses and solid targets provides a
promising way to create compact, tunable and bright XUV attosecond sources that
can become a unique tool for a variety of applications. However, it is
important to control the polarization state of this XUV radiation, and to do so
in the most efficient regime of generation. Using the relativistic electronic
spring (RES) model and particle-in-cell (PIC) simulations, we show that the
polarization state of the generated attosecond pulses can be tuned in a wide
range of parameters by adjusting the polarization and angle of incidence of the
laser radiation. In particular, we demonstrate the possibility of producing
circularly polarized attosecond pulses in a wide variety of setups.Comment: 6 pages, 3 figure
The Near-Infrared Photometric Properties of Bright Giants in the Central Regions of the Galactic Bulge
Images recorded through broad (J, H, K), and narrow (CO, and 2.2micron
continuum) band filters are used to investigate the photometric properties of
bright (K < 13.5) stars in a 6 x 6 arcmin field centered on the SgrA complex.
The giant branch ridgelines in the (K, J-K) and (K, H-K) color-magnitude
diagrams are well matched by the Baade's Window (BW) M giant sequence if the
mean extinction is A_K ~ 2.8 mag. Extinction measurements for individual stars
are estimated using the M_K versus infrared color relations defined by M giants
in BW, and the majority of stars have A_K between 2.0 and 3.5 mag. The
extinction is locally high in the SgrA complex, where A_K ~ 3.1 mag.
Reddening-corrected CO indices, CO_o, are derived for over 1300 stars with J,
H, and K brightnesses, and over 5300 stars with H and K brightnesses. The
distribution of CO_o values for stars with K_o between 11.25 and 7.25 can be
reproduced using the M_K versus CO_o relation defined by M giants in BW. The
data thus suggest that the most metal-rich giants in the central regions of the
bulge and in BW have similar photometric properties and 2.3micron CO strengths.
Hence, it appears that the central region of the bulge does not contain a
population of stars that are significantly more metal-rich than what is seen in
BW.Comment: 29 pages, including 14 figure
Reactividad y aptitud a la cocción de crudos de cemento con elevados contenidos en manganeso
It has been verified that high manganese content in raw mixes causes alters the mineralogical composition of clinkers. New phases like 2 CaO.Mn02 and Ca2AIMnO5 are developed and C3A formation can be inhibited.
Manganese is a flux similar to iron in the traditional raw mixes. The presence of manganese will modify the expressions of the lime saturation factor (LSF), silica modulus (Ms) and aluminum modulus (Mf). This has as consequence an increase of the proportion of interstitial phase in the obtained clinkers.Se ha comprobado que contenidos elevados de manganeso en el crudo provoca una modificación significativa en la composición mineralógica del clinker. Se desarrollan las fases no tradicionales 2 CaO.Mn02 y Ca2AIMnO5 , y se puede llegar, incluso, a inhibir la formación de alumínate tricálcico.
El manganeso tiene un comportamiento fundente muy similar al jugado por el hierro en los crudos tradicionales, por lo que la incorporación de óxidos de manganeso al crudo produce una alteración significativa en los módulos tradicionales (LSF, Ms y Mf). Esto tiene como consecuencia inmediata un gran incremento en la proporción de fase intersticial en los clínkeres producidos
Encouraging the return to museums through the through enriching of the experience and the feeling of pride
The aim of the current study is to investigate the effect of museum experiences on visitors' willingness to recommend a museum and desire to return, based on the influence of the perception of coolness and the feeling of authentic pride. A sample of 308 usable questionnaires retrieved from four Lisbon (Portugal) museums provide a good understanding of the drivers of revisit and recommend intentions.
Museum Atmospheric Cues contribute to the perception of Museum Coolness and the feeling of Authentic Pride, which, in turn, have an effect on the intentions to Recommend and Revisit a museum. The perception of Museum Coolness has a stronger influence on both intentions to Revisit and Recommend.info:eu-repo/semantics/acceptedVersio
Antioxidant effects of Rosemary extract on the accelerated degradation of ethylene-propylene-diene monomer
Abstract
The goal of this paper is the qualification of natural antioxidants (rosemary extract, capsaicin,
quercetin or oleanolic acid) playing as antioxidant. The stabilization activities were investigated in
several formulations based on ethylene-propylene-diene-terpolymer (EPDM) in pristine state or after
-irradiation, when the accelerated degradation scission of polymer macromolecules followed by the
mitigation of oxidation. Three evaluation procedures: chemiluminescence, FTIR spectroscopy and
thermal analysis were applied for the characterization of the stability contribution. The durability of
studied EPDM formulations is discussed for the assessment of material life. The improved behavior
of structured hybrids useful for the optimization application regimes is essentially based on the
antioxidant properties of polyphenolic components in the cases of natural antioxidant
Kinetics of the Non-isothermal Degradation of POSS/EPDM Hybrids Composites
Polyhedral Oligomeric Silsesquioxane (POSS)/Ethylene-propylene-diene monomer (EPDM) composite, at 3% wt of POSS, is prepared by the evaporation of solvent (CHCl3) from polymer/filler system at room temperature and is investigated, by the means of thermogravimetric analysis (TGA), and the obtained TGA data are treated by the Kissinger method to get the apparent activation energy (Ea) of degradation. The results obtained for the composites, at different levels of irradiation, are discussed and compared with each other and with those obtained for pristine EPDM. A good improvement of the thermal stability, with respect to the neat polymer, is found showing the effect of the POSS molecules on the degradation rate. A classification among the samples at different levels of radiations is also drawn up, showing also in this case, the beneficial effect of the POSSs presence
Comparison of charge modulations in LaBaCuO and YBaCuO
A charge modulation has recently been reported in (Y,Nd)BaCuO
[Ghiringhelli {\em et al.} Science 337, 821 (2013)]. Here we report Cu
edge soft x-ray scattering studies comparing the lattice modulation associated
with the charge modulation in YBaCuO with that associated with
the well known charge and spin stripe order in LaBaCuO.
We find that the correlation length in the CuO plane is isotropic in both
cases, and is \AA for LaBaCuO and \AA for YBaCuO. Assuming weak inter-planar correlations of
the charge ordering in both compounds, we conclude that the order parameters of
the lattice modulations in LaBaCuO and
YBaCuO are of the same order of magnitude.Comment: 3 pages, 2 figure
Fases termodinámicamente estables en el sistema cerrado CaO-SiO2-Al2O3-CaSO4-H2O a 25 ºC. Aplicación a sistemas cementantes
One of the chief causes of cement and concrete deterioration is the loss of durability prompted by sulphate attack. The existing standards call for long test periods (2- 12 months). Thermodynamic modelling is a particularly appropriate technique for studying systems that only reach equilibrium in the long term. Used in the present study to establish the fields of thermodynamic stability for the phases in the CaO-SiO2-Al2O3-CaSO4-H2O system at 25 ºC. According to the model, gypsum is stable at sulphate ion concentrations of 1.23e-2 mol/kg and over, while ettringite exhibits stability at concentrations ranging from 7.64e-6 to 1.54e-2 mol/kg. Ettringite is compatible with all system phases except SH and gypsum only with ettringite, the C-S-H gels, AH3 and SH. None of the calcium aluminates or silicoaluminates in the system is compatible with gypsum: in its presence, they all decompose to cement deteriorating ettringite. Finally, the model revealed that the maximum sulphate concentration at which C-S-H gel is stable is slightly higher in systems with than without Al2O3.Uno de los principales problemas asociados al deterioro de cementos y hormigones es la pérdida de durabilidad por ataque de sulfatos. La normativa existente requiere largos tiempos de ensayo (2-12 meses). La modelización termodinámica es una técnica particularmente adecuada para el estudio de sistemas que alcanzan el equilibrio en tiempos largos. Aplicando esta metodología se han establecido los campos de estabilidad termodinámica de las fases del sistema CaO-SiO2-Al2O3-CaSO4-H2O a 25 ºC. El yeso es estable a partir de la [SO42-] = 1,23e-2 mol/kg, y la ettringita es estable en un rango de [SO42-] = 7,64e-6 -1,54e-2 mol/kg. La ettringita es compatible con todas las fases del sistema excepto con SH y el yeso sólo con la ettringita, los geles C-S-H, el AH3 y el SH. Ninguno de los aluminatos o silicoaluminatos cálcicos son compatibles con el yeso, en su presencia se descomponen dando etringita. Finalmente, la máxima [SO42-] en la que es estable el gel C-S-H es ligeramente superior en sistemas que contienen Al2O3 con respecto a los que no lo poseen
Lattice dynamical signature of charge density wave formation in underdoped YBa2Cu3O6+x
We report a detailed Raman scattering study of the lattice dynamics in
detwinned single crystals of the underdoped high temperature superconductor
YBa2Cu3O6+x (x=0.75, 0.6, 0.55 and 0.45). Whereas at room temperature the
phonon spectra of these compounds are similar to that of optimally doped
YBa2Cu3O6.99, additional Raman-active modes appear upon cooling below ~170-200
K in underdoped crystals. The temperature dependence of these new features
indicates that they are associated with the incommensurate charge density wave
state recently discovered using synchrotron x-ray scattering techniques on the
same single crystals. Raman scattering has thus the potential to explore the
evolution of this state under extreme conditions.Comment: 12 pages, 11 figure
- …