7,512 research outputs found
Biofuel scenarios in a water perspective: the global blue and green water footprint of road transport in 2030
The trend towards substitution of conventional transport fuels by biofuels requires additional water. The EU aims In the last two centuries, fossil fuels have been our major source of energy. However, issues concerning energy security and the quality of the environment have given an impulse to the development of alternative, renewable fuels. Particularly the transport sector is expected to steadily switch from fossil fuels to a larger fraction of biofuels - liquid transport fuels derived from biomass. Many governments believe that biofuels can replace substantial volumes of crude oil and that they will play a key role in diversifying the sources of energy supply in the coming decades. The growth of biomass requires water, a scarce resource. The link between water resources and (future) biofuel consumption, however, has not been analyzed in great detail yet. Existing scenarios on the use of water resources usually only consider the changes in food and livestock production, industry and domestic activity. The aim of this research is to assess the change in water use related to the expected increase in the use of biofuels for road transport in 2030, and subsequently evaluate the contribution to potential water scarcity. The study builds on earlier research on the relation between energy and water and uses the water footprint (WF) methodology to investigate the change in water demand related to a transition to biofuels in road transport. Information about this transition in each country is based on a compilation of different energy scenarios. The study distinguishes between two different bio-energy carriers, bio-ethanol and biodiesel, and assesses the ratio of fuel produced from selected first-generation energy crops per country. For ethanol these crops are sugar cane, sugar beet, sweet sorghum, wheat and maize. For biodiesel they are soybean, rapeseed, jatropha, and oil palm
Temporal dynamics of travelling theta wave activity in infants responding to visual looming
A fundamental property of most animals is the ability to see whether an object is approaching on a direct collision course and, if so, when it will collide. Using high-density electroencephalography in 5- to 11-month-old infants and a looming stimulus approaching under three different accelerations, we investigated how the young human nervous system extracts and processes information for impending collision. Here we show that infants' looming related brain activity is characterized by theta oscillations. Source analyses reveal clear localised activity in the visual cortex. Analysing the temporal dynamics of the source waveform, we provide evidence that the temporal structure of different looming stimuli is sustained during processing in the more mature infant brain, providing infants with increasingly veridical time-to-collision information about looming danger as they grow older and become mobile
Splash wave and crown breakup after disc impact on a liquid surface
In this paper we analyze the impact of a circular disc on a free surface
using experiments, potential flow numerical simulations and theory. We focus
our attention both on the study of the generation and possible breakup of the
splash wave created after the impact and on the calculation of the force on the
disc. We have experimentally found that drops are only ejected from the rim
located at the top part of the splash --giving rise to what is known as the
crown splash-- if the impact Weber number exceeds a threshold value
\Weber_{crit}\simeq 140. We explain this threshold by defining a local Bond
number based on the rim deceleration and its radius of curvature,
with which we show using both numerical simulations and experiments that a
crown splash only occurs when , revealing that the rim
disrupts due to a Rayleigh-Taylor instability. Neglecting the effect of air, we
show that the flow in the region close to the disc edge possesses a
Weber-number-dependent self-similar structure for every Weber number. From this
we demonstrate that \Bond_{tip}\propto\Weber, explaining both why the
transition to crown splash can be characterized in terms of the impact Weber
number and why this transition occurs for .
Next, including the effect of air, we have developed a theory which predicts
the time-varying thickness of the very thin air cushion that is entrapped
between the impacting solid and the liquid. Our analysis reveals that gas
critically affect the velocity of propagation of the splash wave as well as the
time-varying force on the disc, . The existence of the air layer also
limits the range of times in which the self-similar solution is valid and,
accordingly, the maximum deceleration experienced by the liquid rim, what sets
the length scale of the splash drops ejected when We>\Weber_{crit}
Exploring droplet impact near a millimetre-sized hole: comparing a closed pit with an open-ended pore
We investigate drop impact dynamics near both closed pits and open- ended
pores experimentally. The resulting impact phenomena differ greatly for a pit
or a pore. For the first, we observe three phenomena: a splash, a jet and an
air bubble, whose appearance depends on the distance between impact location
and pit. Furthermore, we found that splash velocities can reach up to seven
times the impact velocity. Drop impact near a pore, however, results solely in
splashing. Surprisingly, two distinct and disconnected splashing regimes occur,
with a region of plain spreading in-between. For pores, splashes are less
pronounced than in the pit case. We state that, for the pit case, the presence
of air inside the pit plays a crucial role: it promotes splashing and allows
for air bubbles to appear.Comment: 17 pages, 11 figures, 1 supplementary movie, submitted to JF
Physical Meaning of Orbitals in Adiabatic Linear Response Time-Dependent Orbital Functional Theories
Single-order lamellar multilayer gratings
A major challenge in the soft x-ray (SXR) and eXtreme UltraViolet (XUV) spectral ranges is the ability to manipulate the incident radiation using optical elements. By patterning conventional multilayer mirrors with nanoscale structures, novel optical elements with a variety of optical properties can be obtained. In this work, the design, fabrication and characterization of Lamellar Multilayer Gratings (LMG) was investigated. Such LMGs are a particular form of the general class of Bragg-Fresnel optics which combine Fresnel optics with Bragg reflection to provide unique dispersive and focusing optics. In particular, LMGs can be used to improve the spectral resolution of x-ray fluorescence techniques.\ud
A Coupled Waves Approach (CWA) was derived to simulate the optical performance,\ud
in terms of resolution and reflectivity, of LMGs. This CWA allowed to study the physical principles behind LMGs and resulted in the identification of an optimal LMG operating regime. In this regime, the incident beam is reflected in a single diffraction order and is hence referred to as the singleorder regime. Such single-order LMGs were fabricated using UV-NanoImprint Lithography and Bosch Deep Reactive Ion Etching, a process chosen to enable rapid practical development. Single-order operation was experimentally demonstrated and showed an improvement in spectral resolution of a factor of 3.8 with regard to convenventional multilayer mirrors. Singe-order excitation of higher diffraction orders was also measured and analyzed.\ud
Single-order operation often requires multilayer stacks and grating structures\ud
that cannot be fabricated with sufficient accuracy using current technologies.\ud
As this invalidates the semi-infinite multilayer approximation, we investigated the optical performance of LMGs with finite multilayer stacks. We determined the ratio between the absorber thickness and bi-layer period of the multilayer stack can be used to further tailor LMG optical performance to maximize bandwidth reduction or minimize peak reflectivity loss. We also investigated various degradation processes that could limit the lifetime of LMGs, which is important for the applicability of such elements. Oxidation of tungsten and silicon as well as changes to the sidewall composition were clearly seen.\ud
However, SXR reflectivity remained stable to within measurement accuracy for\ud
an extended storage period of 18 months in a 1 atm air environment. The possibility of applying a capping layer on LMG structures to reduce degradation\ud
was also studied
Spatially encoded light for Large-alphabet Quantum Key Distribution
Most Quantum Key Distribution protocols use a two-dimensional basis such as
HV polarization as first proposed by Bennett and Brassard in 1984. These
protocols are consequently limited to a key generation density of 1 bit per
photon. We increase this key density by encoding information in the transverse
spatial displacement of the used photons. Employing this higher-dimensional
Hilbert space together with modern single-photon-detecting cameras, we
demonstrate a proof-of-principle large-alphabet Quantum Key Distribution
experiment with 1024 symbols and a shared information between sender and
receiver of 7 bit per photon.Comment: 9 pages, 6 figures, Added references, Updated Fig. 1 in the main
text, Updated Fig.1 in supplementary material, Added section Trojan-horse
attacks in supplementary material, title changed, Added paragraphs about
final key rate and overfilling the detector to result sectio
A Study of the Coronal Plasma in RS CVn binary systems
XMM-Newton has been performing comprehensive studies of X-ray bright RS CVn
binaries in its Calibration and Guaranteed Time programs. We present results
from ongoing investigations in the context of a systematic study of coronal
emission from RS CVns. We concentrate in this paper on coronal abundances and
investigate the abundance pattern in RS CVn binaries as a function of activity
and average temperature. A transition from an Inverse First Ionization
Potential (FIP) effect towards an absence of a clear trend is found in
intermediately active RS CVn systems. This scheme corresponds well into the
long-term evolution from an IFIP to a FIP effect found in solar analogs. We
further study variations in the elemental abundances during a large flare.Comment: to appear in The Twelfth Cool Stars, Stellar Systems and the Sun,
eds. A. Brown, T.R. Ayres, G.M. Harper, (Boulder: Univ. of Colorado), in
pres
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