3,853 research outputs found
Second-order quantum nonlinear optical processes in single graphene nanostructures and arrays
Intense efforts have been made in recent years to realize nonlinear optical
interactions at the single-photon level. Much of this work has focused on
achieving strong third-order nonlinearities, such as by using single atoms or
other quantum emitters while the possibility of achieving strong second-order
nonlinearities remains unexplored. Here, we describe a novel technique to
realize such nonlinearities using graphene, exploiting the strong per-photon
fields associated with tightly confined graphene plasmons in combination with
spatially nonlocal nonlinear optical interactions. We show that in properly
designed graphene nanostructures, these conditions enable extremely strong
internal down-conversion between a single quantized plasmon and an entangled
plasmon pair, or the reverse process of second harmonic generation. A separate
issue is how such strong internal nonlinearities can be observed, given the
nominally weak coupling between these plasmon resonances and free-space
radiative fields. On one hand, by using the collective coupling to radiation of
nanostructure arrays, we show that the internal nonlinearities can manifest
themselves as efficient frequency conversion of radiative fields at extremely
low input powers. On the other hand, the development of techniques to
efficiently couple to single nanostructures would allow these nonlinear
processes to occur at the level of single input photons.Comment: 25 pages, 6 figure
Actividad eléctrica muscular en la marcha a distintas velocidades y en la carrera
En este estudio se analiza la actividad electromiográfica de los principales músculos de la extremidad inferior derecha: Glúteos Mayor y Medio, Recto Anterior y Vasto Interno del Cuádriceps, Isquiotibioperoneos, Gemelos y Tibial Anterior, al caminar en un tapiz rodante a distintas velocidades y en una carrera suave. Para dividir el ciclo de la marcha y la carrera en fases se utilizó un sistema de análisis tridimensional con dos cámaras de vídeo. La señal electromiográfica de cada una de estas fases se integró y se expresó en porcentaje de la actividad máxima isométrica de su músculo correspondiente.
Los resultados obtenidos muestran que la participación muscular en la marcha lenta y normal es muy similar, sin embargo, en la marcha rápida aparecen aumentos importantes conservando el mismo patrón de actuación. En la carrera, no sólo existen actividades del triple de las halladas en la marcha a velocidad cómoda, sino que se modifica el patrón de actuación, presentando todos los músculos sus picos de actividad durante la fase de apoyo, momento en el que el centro de gravedad se lleva hacia delante sobre el miembro inferior
Actividad eléctrica muscular en la marcha a distintas velocidades y en la carrera
En este estudio se analiza la actividad electromiográfica de los principales músculos de la extremidad
inferior derecha: Glúteos Mayor y Medio, Recto Anterior y Vasto Interno del Cuádriceps,
Isquiotibioperoneos, Gemelos y Tibial Anterior, al caminar en un tapiz rodante a distintas velocidades
y en una carrera suave. Para dividir el ciclo de la marcha y la carrera en fases se utilizó un
sistema de análisis tridimensional con dos cámaras de vídeo. La señal electromiográfica de cada
una de estas fases se integró y se expresó en porcentaje de la actividad máxima isométrica de su
músculo correspondiente.
Los resultados obtenidos muestran que la participación muscular en la marcha lenta y normal es
muy similar, sin embargo, en la marcha rápida aparecen aumentos importantes conservando el mismo
patrón de actuación. En la carrera, no sólo existen actividades del triple de las halladas en la
marcha a velocidad cómoda, sino que se modifica el patrón de actuación, presentando todos los
músculos sus picos de actividad durante la fase de apoyo, momento en el que el centro de gravedad
se lleva hacia delante sobre el miembro inferior
Biocrusts Modulate Climate Change Effects on Soil Organic Carbon Pools: Insights From a 9-Year Experiment
Accumulating evidence suggests that warming associated with climate change is decreasing the total amount of soil organic carbon (SOC) in drylands, although scientific research has not given enough emphasis to particulate (POC) and mineral-associated organic carbon (MAOC) pools. Biocrusts are a major biotic feature of drylands and have large impacts on the C cycle, yet it is largely unknown whether they modulate the responses of POC and MAOC to climate change. Here, we assessed the effects of simulated climate change (control, reduced rainfall (RE), warming (WA), and RE + WA) and initial biocrust cover (low ( 50%)) on the mineral protection of soil C and soil organic matter quality in a dryland ecosystem in central Spain for 9 years. At low initial biocrust cover levels, both WA and RE + WA increased SOC, especially POC but also MAOC, and promoted a higher contribution of carbohydrates, relative to aromatic compounds, to the POC fraction. These results suggest that the accumulation of soil C under warming treatments may be transitory in soils with low initial biocrust cover. In soils with high initial biocrust cover, climate change treatments did not affect SOC, neither POC nor MAOC fraction. Overall, our results indicate that biocrust communities modulate the negative effect of climate change on SOC, because no losses of soil C were observed with the climate manipulations under biocrusts. Future work should focus on determining the long-term persistence of the observed buffering effect by biocrust-forming lichens, as they are known to be negatively affected by warming.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. This research has received funding from the European Research Council (ERC Grant agreement 647038 [BIODESERT]), the European Union’s Horizon 2020 research and innovation programme (Marie Skłodowska-Curie Grant Agreement No 654132 [VULCAN]), the Spanish Ministerio de Ciencia e Innovación (PID2020-116578RB-I00 [VULCOCLIM]) and Generalitat Valenciana (CIDEGENT/2018/041). P.D.-M. was supported by Spanish Ministerio de Ciencia, Innovación y Universidades (FPU17/02949), M. Panettieri acknowledge the financial support by the Comunidad de Madrid and the Spanish National Council of Scientific Researches research grant Atracción de Talento (grant number 2019T1/AMB14503)
Situational analysis of the subjective well-being of university software developers in Puebla
Integral well-being is vital for the optimal functioning of people. The requirements for a software developer in the performance of their professional activity are varied and complex. These requirements range from working in multidisciplinary and multilingual teams, going through the challenge of technological advances of the discipline to commit to quality and innovation. To face these demands, it is essential that the developers have an optimal functioning, where the experience emotional and satisfaction with life play an important role. The objective of this article is to analyze the subjective well-being of university software developers in Puebla. The research is a quantitative cross-correlation study to identify statistically significant relationships between the different welfare variables. The study involved 47 university software developers from the city of Puebla. We use Pearson's multivariate correlation to validate the instruments and find relationships between variables, and Chi-squared statistics to calculate the dependency between them. The results reveal that the university software developers experience with higher incidence and intensity, the positive affections over the negatives. The affective balance (Net Affect), calculated as the difference of the weighted averages by duration between positive affective states and negative, was positive (mean = 1.31). "Concentrated" is the positive affective state with the highest incidence and with the highest reported intensity. "Tired" is the most experienced negative affect and highest in intensity. Developers spend 40% of their time experiencing negative affective states (U-index) and are moderately satisfied with their lives in general
Abell 41: shaping of a planetary nebula by a binary central star?
We present the first detailed spatio-kinematical analysis and modelling of
the planetary nebula Abell 41, which is known to contain the well-studied
close-binary system MT Ser. This object represents an important test case in
the study of the evolution of planetary nebulae with binary central stars as
current evolutionary theories predict that the binary plane should be aligned
perpendicular to the symmetry axis of the nebula.
Deep narrowband imaging in the light of [NII], [OIII] and [SII], obtained
using ACAM on the William Herschel Telescope, has been used to investigate the
ionisation structure of Abell 41. Longslit observations of the H-alpha and
[NII] emission were obtained using the Manchester Echelle Spectrometer on the
2.1-m San Pedro M\'artir Telescope. These spectra, combined with the narrowband
imagery, were used to develop a spatio-kinematical model of [NII] emission from
Abell 41. The best fitting model reveals Abell 41 to have a waisted, bipolar
structure with an expansion velocity of ~40km\s at the waist. The symmetry axis
of the model nebula is within 5\degr of perpendicular to the orbital plane of
the central binary system. This provides strong evidence that the close-binary
system, MT Ser, has directly affected the shaping of its nebula, Abell 41.
Although the theoretical link between bipolar planetary nebulae and binary
central stars is long established, this nebula is only the second to have this
link, between nebular symmetry axis and binary plane, proved observationally.Comment: 7 pages, 6 figures, Accepted for publication in MNRA
A Fast bipolar H2 outflow from IRAS 16342-3814: an old star reliving its youth
Some evolved stars in the pre-planetary nebula phase produce
highly-collimated molecular outflows that resemble the accretion-driven jets
and outflows from pre-main sequence stars. We show that IRAS 16342-3814 (the
Water Fountain Nebula) is such an object and present K-band integral field
spectroscopy revealing a fast (> 150 km/s) bipolar H2 outflow. The H2 emission
is shock excited and may arise in fast-moving clumps, accelerated by the
previously observed precessing jet. The total luminosity in H2 is 0.37
L which is comparable with that of accretion-powered outflows from
Class 0 protostars. We also detect CO overtone bandhead emission in the
scattered continuum, indicating hot molecular gas close to the centre, a
feature also observed in a number of protostars with active jets. It seems
likely that the jet and outflow in IRAS 16342-3814 are powered by accretion
onto a binary companion.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Societ
The Cosmic Microwave Background in an Inhomogeneous Universe - why void models of dark energy are only weakly constrained by the CMB
The dimming of Type Ia supernovae could be the result of Hubble-scale
inhomogeneity in the matter and spatial curvature, rather than signaling the
presence of a dark energy component. A key challenge for such models is to fit
the detailed spectrum of the cosmic microwave background (CMB). We present a
detailed discussion of the small-scale CMB in an inhomogeneous universe,
focusing on spherically symmetric `void' models. We allow for the dynamical
effects of radiation while analyzing the problem, in contrast to other work
which inadvertently fine tunes its spatial profile. This is a surprisingly
important effect and we reach substantially different conclusions. Models which
are open at CMB distances fit the CMB power spectrum without fine tuning; these
models also fit the supernovae and local Hubble rate data which favours a high
expansion rate. Asymptotically flat models may fit the CMB, but require some
extra assumptions. We argue that a full treatment of the radiation in these
models is necessary if we are to understand the correct constraints from the
CMB, as well as other observations which rely on it, such as spectral
distortions of the black body spectrum, the kinematic Sunyaev-Zeldovich effect
or the Baryon Acoustic Oscillations.Comment: 23 pages with 14 figures. v2 has considerably extended discussion and
analysis, but the basic results are unchanged. v3 is the final versio
Mössbauer and Magnetic Properties of Coherently Mixed Magnetite-Cobalt Ferrite Grown by Infrared Pulsed-Laser Deposition
We have studied the magnetic properties and the composition of cobalt ferrite single crystal films on SrTiO3 : Nb grown by infrared pulsed-laser deposition. Mössbauer spectra have been recorded from both the target used to grow the films and the films themselves. The Mössbauer spectra of the target taken at low temperatures show a strong dependence of the recoil free fraction of the octahedral sites with temperature. The films composition, with a coexistence of Co-enriched cobalt ferrite and magnetite, has been estimated assuming a similar ratio of the recoil free fractions of the films. X-ray absorption and x-ray magnetic circular dichroism measurements confirm the valence composition of the film and show ferromagnetic Fe-Co coupling in the films with a coercive field around 0.5 T at room temperature. The combination of these characterization techniques allows establishing the coherent structural and magnetic properties of this biphase system.(MINECO) through Projects No. MAT2012 - 38045 - C04 - 01, CTQ2013 - 43086 - P, and MAT2013 - 48009 - C4 - 1 - P and by the EU - FP7 NANOPYME Project (No. 310516).Peer Reviewe
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