1,985 research outputs found
Thermalization from gauge/gravity duality: Evolution of singularities in unequal time correlators
We consider a gauge/gravity dual model of thermalization which consists of a
collapsing thin matter shell in asymptotically Anti-de Sitter space. A central
aspect of our model is to consider a shell moving at finite velocity as
determined by its equation of motion, rather than a quasi-static approximation
as considered previously in the literature. By applying a divergence matching
method, we obtain the evolution of singularities in the retarded unequal time
correlator , which probes different stages of the thermalization. We
find that the number of singularities decreases from a finite number to zero as
the gauge theory thermalizes. This may be interpreted as a sign of decoherence.
Moreover, in a second part of the paper, we show explicitly that the thermal
correlator is characterized by the existence of singularities in the complex
time plane. By studying a quasi-static state, we show the singularities at real
times originate from contributions of normal modes. We also investigate the
possibility of obtaining complex singularities from contributions of
quasi-normal modes.Comment: 35 pages, 4 figure
GERVALOR: valorization of food waste in a hospital food service unit
info:eu-repo/semantics/publishedVersio
Sequelas da COVID-19 EvidĂȘncia Atual
A epidemia de Coronavirus Disease 2019 disseminou-se pelo mundo em poucos meses,
levando Ă sua designação de pandemia. MĂșltiplas medidas de saĂșde pĂșblica foram
implementadas nos paĂses afetados para conter e mitigar a disseminação da doença. A
necessidade de distanciamento fĂsico leva a que esta pandemia tenha um impacto importante na sociedade e particularmente no desporto, provocando cancelamento e adiamento
de treinos, competiçÔes e eventos. No entanto, o inĂcio da pandemia data jĂĄ de 2019,
com preocupaçÔes globais, nĂŁo sĂł na fase aguda da doença com as suas consequĂȘncias
imediatas, mas também com as eventuais sequelas a médio e a longo prazo e o risco de
cronicidade de alguns sintomas, em particular na população jovem. Neste artigo revemos
a limitada evidĂȘncia cientĂfica atual acerca da relevĂąncia clĂnica das sequelas da COVID-19,
em particular do foro respiratĂłrio e cardĂaco, e finalizamos com recomendaçÔes de avaliação das sequelas em atletas e com indicaçÔes para regresso seguro Ă prĂĄtica desportiva.info:eu-repo/semantics/publishedVersio
Extraction and Fractionation of Pigments from Saccharina latissima (Linnaeus, 2006) Using an Ionic Liquid plus Oil plus Water System
There is a strong industrial interest in the development of greener and more sustainable processes based on the use of renewable resources, and a biorefinery based on marine resources, such as macroalgae, stands as a major opportunity toward that end. In this work, Saccharina latissima (Linnaeus), a brown macroalga, was used as a source of pigments to develop an integrated platform that is able to promote the extraction and separation of chlorophyll and fucoxanthin in one single step. The process was studied, and its operational conditions were optimized with yields of extraction of chlorophyll and fucoxanthin of 4.93 ± 0.22 mgchl·gdry biomassâ1 and 1956 ± 84 ÎŒgfuco·gdry biomassâ1, respectively. These results were achieved with extraction systems composed of 84% of an aqueous solution of a tensioactive phosphonium-based ionic liquid (IL) at 350 mM + 16% of sunflower oil, during 40 min, using a solidâliquid ratio of 0.017 gdry biomass·mLsolventâ1. After the separation of both aqueous IL-rich and oil-rich phases, the IL content in both phases was investigated, the oil phase being free of IL. Envisioning the industrial potential of the process developed in this work, the recovery of the IL from the aqueous IL-rich phase of the initial system was attempted by a back-extraction using organic solvents immiscible in water, being shown that 82% of the IL can be recovered and reused in new cycles of extraction. The environmental and economic impacts of the final process proposed for the extraction and fractionation of chlorophyll and fucoxanthin were evaluated. Different scenarios were considered, but summing up the main results, the solventsâ recycling allowed better results, proving the economic and environmental viability of the overall process
Bird collisions in a railway crossing a wetland of international importance (Sado estuary, Portugal)
L. Borda-de-Ăgua et al. (eds.), Railway Ecology, chapter 7, p. 103-115Many studies have evaluated bird mortality in relation to roads and other
human structures, but little is known about the potential impacts of railways. In
particular, it is uncertain whether railways are an important mortality source when
crossing wetlands heavily used by aquatic birds. Here we analyze bird collisions in
a railway that crosses the Nature Reserve of the Sado Estuary (Portugal) over an
annual cycle, documenting bird mortality and the flight behaviour of aquatic birds
in relation to a bowstring bridge. During monthly surveys conducted on 16.3 km of
railway, we found 5.8 dead birds/km/10 survey days in the section crossing wetland
habitats (6.3 km), while <0.5 dead birds/km/10 survey days were found in two
sections crossing only forested habitats. Most birds recorded were small songbirds
(Passeriformes), while there was only a small number of aquatic birds (common
moorhen, mallard, flamingo, great cormorant, gulls) and other non-passerines
associated with wetlands (white stork). During nearly 400 h of observations, we recorded 27,000 movements of aquatic birds across the Sado bridge, particularly in
autumn and winter. However, only <1% of movements were within the area of
collision risk with trains, while about 91% were above the collision risk area, and
8% were below the bridge. Overall, our case study suggests that bird collisions may
be far more numerous in railways crossing wetland habitats than elsewhere,
although the risk to aquatic birds may be relatively low. Information from additional
study systems would be required to evaluate whether our conclusions apply
to other wetlands and railway linesinfo:eu-repo/semantics/publishedVersio
Single-shot compressed ultrafast photography at one hundred billion frames per second
The capture of transient scenes at high imaging speed has been long sought by photographers, with early examples being the well known recording in 1878 of a horse in motion and the 1887 photograph of a supersonic bullet. However, not until the late twentieth century were breakthroughs achieved in demonstrating ultrahigh-speed imaging (more than 10^5 frames per second). In particular, the introduction of electronic imaging sensors based on the charge-coupled device (CCD) or complementary metalâoxideâsemiconductor (CMOS) technology revolutionized high-speed photography, enabling acquisition rates of up to 10^7 frames per second. Despite these sensorsâ widespread impact, further increasing frame rates using CCD or CMOS technology is fundamentally limited by their on-chip storage and electronic readout speed. Here we demonstrate a two-dimensional dynamic imaging technique, compressed ultrafast photography (CUP), which can capture non-repetitive time-evolving events at up to 10^(11) frames per second. Compared with existing ultrafast imaging techniques, CUP has the prominent advantage of measuring an xâyât (x, y, spatial coordinates; t, time) scene with a single camera snapshot, thereby allowing observation of transient events with temporal resolution as tens of picoseconds. Furthermore, akin to traditional photography, CUP is receive-only, and so does not need the specialized active illumination required by other single-shot ultrafast imagers. As a result, CUP can image a variety of luminescentâsuch as fluorescent or bioluminescentâobjects. Using CUP, we visualize four fundamental physical phenomena with single laser shots only: laser pulse reflection and refraction, photon racing in two media, and faster-than-light propagation of non-information (that is, motion that appears faster than the speed of light but cannot convey information). Given CUPâs capability, we expect it to find widespread applications in both fundamental and applied sciences, including biomedical research
Learning auditory space: generalization and long-term effects
Background: Previous findings have shown that humans can learn to localize with altered auditory space cues. Here
we analyze such learning processes and their effects up to one month on both localization accuracy and sound
externalization. Subjects were trained and retested, focusing on the effects of stimulus type in learning, stimulus type
in localization, stimulus position, previous experience, externalization levels, and time.
Method: We trained listeners in azimuth and elevation discrimination in two experiments. Half participated in the
azimuth experiment first and half in the elevation first. In each experiment, half were trained in speech sounds and
half in white noise. Retests were performed at several time intervals: just after training and one hour, one day, one
week and one month later. In a control condition, we tested the effect of systematic retesting over time with post-tests
only after training and either one day, one week, or one month later.
Results: With training all participants lowered their localization errors. This benefit was still present one month after
training. Participants were more accurate in the second training phase, revealing an effect of previous experience on
a different task. Training with white noise led to better results than training with speech sounds. Moreover, the
training benefit generalized to untrained stimulus-position pairs. Throughout the post-tests externalization levels
increased. In the control condition the long-term localization improvement was not lower without additional contact
with the trained sounds, but externalization levels were lower.
Conclusion: Our findings suggest that humans adapt easily to altered auditory space cues and that such adaptation
spreads to untrained positions and sound types. We propose that such learning depends on all available cues, but
each cue type might be learned and retrieved differently. The process of localization learning is global, not limited to
stimulus-position pairs, and it differs from externalization processes.Foundation for Science and TechnologyFEDE
Phase Transitions, Inhomogeneous Horizons and Second-Order Hydrodynamics
We use holography to study the spinodal instability of a four-dimensional, strongly-coupled gauge theory with a first-order thermal phase transition. We place the theory on a cylinder in a set of homogeneous, unstable initial states. The dual gravity configurations are black branes afflicted by a Gregory-Laflamme instability. We numerically evolve Einstein's equations to follow the instability until the system settles down to a stationary, inhomogeneous black brane. The dual gauge theory states have constant temperature but non-constant energy density. We show that the time evolution of the instability and the final states are accurately described by second-order hydrodynamics. In the static limit, the latter reduces to a single, second-order, non-linear differential equation from which the inhomogeneous final states can be derived
Gravitational collapse and thermalization in the hard wall model
We study a simple example of holographic thermalization in a confining field
theory: the homogeneous injection of energy in the hard wall model. Working in
an amplitude expansion, we find black brane formation for sufficiently fast
energy injection and a scattering wave solution for sufficiently slow
injection. We comment on our expectations for more sophisticated holographic
QCD models.Comment: 33 pages, 5 figure
- âŠ