2,695 research outputs found
Utilização de radiação Ultravioleta (UV-C) como tecnologia alternativa aos sulfitos para a estabilização microbiológica de vinho tinto:resultados prévios
Neste trabalho avaliou -se o efeito da radiação UV -C sobre a estabilidade microbiológica do vinho tinto e, também, a sua
influência sobre alguns parâmetros fÃsico -quÃmicos e sobre o perfil sensorial. Assim, o vinho sem sulfitos foi submetido
a radiação UV -C com duas doses diferentes, 778 J.L-1 e 1415 J.L-1, e procedeu -se ainda à preparação de um controlo a que
foi adicionado 40 mg.L-1 de dióxido de enxofre. Os vinhos (C, dose 1 e dose 2) foram analisados ao longo do tempo (0,
1, 2, 3, 6 e 9 meses). Os resultados obtidos demonstram que a tecnologia UV -C é eficaz no controlo microbiológico do
vinho, não se diferenciando do tratamento tradicional para os parâmetros considerados. No que respeita à s caracterÃsticas
fÃsico -quÃmicas, não se verificou diferenças entre os vários tratamentos para a maioria dos parâmetros analisados.
Verifica -se que esta tecnologia tem um efeito muito positivo sobre a estabilidade da cor (intensidade e tonalidade) ao
longo do tempo, comparativamente com o vinho com dióxido de enxofre. A análise sensorial revelou que os vinhos
submetidos ao tratamento com radiação UV -C apresentaram uma melhor estabilização da cor, contudo verificou -se
alguma depreciação no aroma e no sabor dos vinhos, que se atenuou ao longo do tempo.This work consisted in the evaluation of the effect of UV -C radiation on the microbiological stability of red wine as well
as its and also its influence on some physical and chemical parameters and on the sensory profile. Thus, wine without
sulfites was subjected to UV -C radiation in two different doses, 778 J.L-1 and 1415 J.L-1, and a control sample was also
prepared to which 40 mg.L-1 of sulfur dioxide was added. The wines (C dose 1 and dose 2) were analyzed over time (0, 1,
2, 3, 6 and 9 months). The results show that UV -C technology is effective in the microbiological control of wine, without
any differences to the standard method for the considered parameters. As for the physical -chemical characteristics,
there were no differences between the various treatments for the majority of parameters which were analyzed. It has
been verified that this technology has a very positive effect on the stability of the colour (intensity and hue) over time,
compared with the wine with sulfur dioxide. The sensory analysis of the wines showed that the wine subjected to treatment
with UV -C radiation had better stabilization of colour, but there was some depreciation in the aroma and flavour
of the wine, which attenuated over time.info:eu-repo/semantics/publishedVersio
Ultrasonic evidence of an uncorrelated cluster formation temperature in manganites with first-order magnetic transition at T_C
Ultrasonic attenuation and phase velocity measurements have been carried out
in the ferromagnetic perovskites La_{2/3}Ca_{1/3}MnO_3 and
La_{2/3}Sr_{1/3}MnO_3. Data show that the transition at the Curie temperature,
T_C, changes from first- to second-order as Sr replaces Ca in the perovskite.
The compound with first-order transition shows also another transition at a
temperature T* > T_C. We interpret the temperature window T_C < T < T* as a
region of coexistence of a phase separated regime of metallic and insulating
regions, in the line of recent theoretical proposals.Comment: 4 pages, 2 figure
Field-induced magnetic anisotropy in La0.7Sr0.3CoO3
Magnetic anisotropy has been measured for the ferromagnetic La0.7Sr0.3CoO3
perovskite from an analysis of the high-field part of the magnetization vs.
field curves, i.e., the magnetic saturation regime. These measurements give a
magnetic anistropy one order of magnitude higher than that of reference
manganites. Surprisingly, the values of the magnetic anisotropy calculated in
this way do not coincide with those estimated from measurements of coercive
fields which are one order of magnitude smaller. It is proposed that the reason
of this anomalous behaviour is a transition of the trivalent Co ions under the
external magnetic field from a low-spin to an intermediate-spin state. Such a
transition converts the Co3+ ions into Jahn-Teller ions having an only
partially quenched orbital angular momentum, which enhances the intra-atomic
spin-orbit coupling and magnetic anisotropy.Comment: Accepted of publication in Europhysics Letters, 11 pages, 5 figure
Bifurcation Phenomena in Two-Dimensional Piecewise Smooth Discontinuous Maps
In recent years the theory of border collision bifurcations has been
developed for piecewise smooth maps that are continuous across the border, and
has been successfully applied to explain nonsmooth bifurcation phenomena in
physical systems. However, many switching dynamical systems have been found to
yield two-dimensional piecewise smooth maps that are discontinuous across the
border. The theory for understanding the bifurcation phenomena in such systems
is not available yet. In this paper we present the first approach to the
problem of analysing and classifying the bifurcation phenomena in
two-dimensional discontinuous maps, based on a piecewise linear approximation
in the neighborhood of the border. We explain the bifurcations occurring in the
static VAR compensator used in electrical power systems, using the theory
developed in this paper. This theory may be applied similarly to other systems
that yield two-dimensional discontinuous maps
First order transition and phase separation in pyrochlores with colossal-magnetoresistance
TlMnO pyrochlores present colossal magnetoresistance (CMR)
around the long range ferromagnetic ordering temperature (T). The
character of this magnetic phase transition has been determined to be first
order, by purely magnetic methods, in contrast to the second order character
previously reported by Zhao et al. (Phys. Rev. Lett. 83, 219 (1999)). The
highest CMR effect, as in TlCdMnO, corresponds to a
stronger first order character. This character implies a second type of
magnetic interaction, besides the direct superexchange between the Mn
ions, as well as a phase coexistence. A model is proposed, with a complete
Hamiltonian (including superexchange and an indirect interaction), which
reproduce the observed phenomenology.Comment: 6 pages. Figures include
Multiferroic behavior in the new double-perovskite LuMnCoO
We present a new member of the multiferroic oxides, LuMnCoO, which we
have investigated using X-ray diffraction, neutron diffraction, specific heat,
magnetization, electric polarization, and dielectric constant measurements.
This material possesses an electric polarization strongly coupled to a net
magnetization below 35 K, despite the antiferromagnetic ordering of the Mn and Co spins in an configuration along the c-direction. We discuss the magnetic order
in terms of a condensation of domain boundaries between and
ferromagnetic domains, with each domain boundary
producing a net electric polarization due to spatial inversion symmetry
breaking. In an applied magnetic field the domain boundaries slide, controlling
the size of the net magnetization, electric polarization, and magnetoelectric
coupling
Confección de claves de identificación para los parques urbanos de Melilla. Un recurso didáctico
En el marco de un proyecto de innovación docente, desarrollado en la Facultad de Educación de Melilla, se están confeccionando materiales didácticos para el ciclo superior de Educación Primaria, entre ellos claves botánicas cientifico-didácticas para los parques de la ciudad de Melilla. En este trabajo se describe el proceso de diseño y elaboración, asà como su implementación en varios colegios, tanto en salidas de campo como en la versión virtual, poniéndose de manifiesto el alto valor didáctico de estos documentos que favorecen el acercamiento del niño al trabajo del cientÃfico. La botánica, en este caso, se convierte en un recurso valioso para abordar objetivos y competencias preconizados en la legislación para diferentes áreas, especialmente Conocimiento del Medio y las instrumentales de Lengua y Matemáticas
No evidence of an 11.16 MeV 2+ state in 12C
An experiment using the 11B(3He,d)12C reaction was performed at iThemba LABS
at an incident energy of 44 MeV and analyzed with a high energy-resolution
magnetic spectrometer, to re-investigate states in 12C published in 1971. The
original investigation reported the existence of an 11.16 MeV state in 12C that
displays a 2+ nature. In the present experiment data were acquired at
laboratory angles of 25-, 30- and 35- degrees, to be as close to the c.m.
angles of the original measurements where the clearest signature of such a
state was observed. These new low background measurements revealed no evidence
of the previously reported state at 11.16 MeV in 12C
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