6,608 research outputs found
Transverse galloping of two-dimensional bodies having a rhombic cross-section
Transverse galloping is a type of aeroelastic instability characterized by oscillations perpendicular to wind direction, large amplitude and low frequency, which appears in some elastic two-dimensional bluff bodies when they are subjected to an incident flow, provided that the flow velocity exceeds a threshold critical value. Understanding the galloping phenomenon of different cross-sectional geometries is important in a number of engineering applications: for energy harvesting applications the interest relies on strongly unstable configurations but in other cases the purpose is to avoid this type of aeroelastic phenomenon. In this paper the aim is to analyze the transverse galloping behavior of rhombic bodies to understand, on the one hand, the dependence of the instability with a geometrical parameter such as the relative thickness and, on the other hand, why this cross-section shape, that is generally unstable, shows a small range of relative thickness values where it is stable. Particularly, the non-galloping rhombus-shaped prism?s behavior is revised through wind tunnel experiments. The bodies are allowed to freely move perpendicularly to the incoming flow and the amplitude of movement and pressure distributions on the surfaces is measured
The Gamma Ray Burst section of the White Paper on the Status and Future of Very High Energy Gamma Ray Astronomy: A Brief Preliminary Report
Original paper can be found at: http://proceedings.aip.org/proceedings/ Copyright American Institute of Physics DOI: 10.1063/1.2943545otherPeer reviewe
Politische Dimensionen von MilitĂ€rĂŒbungen und Manövern â ein Projektbericht
Die virtuellen Kriege und Operationen, die in MilitĂ€rĂŒbungen gespielt und geprobt werden, können entweder der Abschreckung dienen oder aber Angriffe vorbereiten bzw. zur Maskierung tatsĂ€chlicher Angriffe dienen. FĂŒr Beobachter ist es vielfach nicht offensichtlich, um welche Art von MilitĂ€rĂŒbung es sich handelt. Die Ergebnisse eines vierjĂ€hrigen internationalen Projektes zu politischen Dimensionen von MilitĂ€rĂŒbungen richten das Schlaglicht insbesondere auf MissverstĂ€ndnisse und deren ungewollte politische Auswirkungen, die im Extremfall unbeabsichtigt zum Krieg fĂŒhren können
Regionalized Strategies for Food Loss and Waste Management in Spain under a Life Cycle Thinking Approach
Food loss and waste (FLW) has become a central concern in the social and political debate. Simultaneously, using FLW as a bioenergy source could significantly contribute to closing the carbon cycle by reintroducing energy into the food supply chain. This study aims to identify best strategies for FLW management in each of the 17 regions in Spain, through the application of a Life Cycle Assessment. To this end, an evaluation of the environmental performance over time between 2015 and 2040 of five different FLW management scenarios implemented in a framework of (i) compliance and (ii) non-compliance with the targets of the Paris Agreement was performed. Results revealed savings in the consumption of abiotic resources in those regions in which thermal treatment has a strong presence, although their greenhouse gas (GHG) emissions in a scenario of compliance with climate change targets are higher. In contrast, scenarios that include anaerobic digestion and, to a lesser extent those applying aerobic composting, present lower impacts, including climate change, suggesting improvements of 20â60% in non-compliance and 20â80% in compliance with Paris Agreement targets, compared to the current scenarios
DADA: data assimilation for the detection and attribution of weather and climate-related events
A new nudging method for data assimilation, delayâcoordinate nudging, is presented. Delayâcoordinate nudging makes explicit use of present and past observations in the formulation of the forcing driving the model evolution at each time step. Numerical experiments with a lowâorder chaotic system show that the new method systematically outperforms standard nudging in different model and observational scenarios, also when using an unoptimized formulation of the delayânudging coefficients. A connection between the optimal delay and the dominant Lyapunov exponent of the dynamics is found based on heuristic arguments and is confirmed by the numerical results, providing a guideline for the practical implementation of the algorithm. Delayâcoordinate nudging preserves the easiness of implementation, the intuitive functioning and the reduced computational cost of the standard nudging, making it a potential alternative especially in the field of seasonalâtoâdecadal predictions with large Earth system models that limit the use of more sophisticated data assimilation procedures
A contemporaneous infrared flash from a long gamma-ray burst: an echo from the central engine
The explosion that results in a cosmic gamma-ray burst (GRB) is thought to
produce emission from two physical processes -- the activity of the central
engine gives rise to the high-energy emission of the burst through internal
shocking and the subsequent interaction of the flow with the external
environment produces long-wavelength afterglow. While afterglow observations
continue to refine our understanding of GRB progenitors and relativistic
shocks, gamma-ray observations alone have not yielded a clear picture of the
origin of the prompt emission nor details of the central engine. Only one
concurrent visible-light transient has been found and was associated with
emission from an external shock. Here we report the discovery of infrared (IR)
emission contemporaneous with a GRB, beginning 7.2 minutes after the onset of
GRB 041219a. Our robotic telescope acquired 21 images during the active phase
of the burst, yielding the earliest multi-colour observations of any
long-wavelength emission associated with a GRB. Analysis of an initial IR pulse
suggests an origin consistent with internal shocks. This opens a new
possibility to study the central engine of GRBs with ground-based observations
at long wavelengths.Comment: Accepted to Nature on March 1, 2005. 9 pages, 4 figures, nature12.cls
and nature1.cls files included. This paper is under press embargo until print
publicatio
Sirolimus-eluting stent fracture with thrombus, visualization by optical coherence tomography
FLRTs are broadly expressed proteins with the unique property of acting as homophilic cell adhesion molecules and as heterophilic repulsive ligands of Unc5/Netrin receptors. How these functions direct cell behavior and the molecular mechanisms involved remain largely unclear. Here we use X-ray crystallography to reveal the distinct structural bases for FLRT-mediated cell adhesion and repulsion in neurons. We apply this knowledge to elucidate FLRT functions during cortical development. We show that FLRTs regulate both the radial migration of pyramidal neurons, as well as their tangential spread. Mechanistically, radial migration is controlled by repulsive FLRT2-Unc5D interactions, while spatial organization in the tangential axis involves adhesive FLRT-FLRT interactions. Further, we show that the fundamental mechanisms of FLRT adhesion and repulsion are conserved between neurons and vascular endothelial cells. Our results reveal FLRTs as powerful guidance factors with structurally encoded repulsive and adhesive surfaces
Gamma-Ray Observations of a Giant Flare from The Magnetar SGR 1806-20
Magnetars comprise two classes of rotating neutron stars (Soft Gamma
Repeaters (SGRs) and Anomalous X-ray Pulsars), whose X-ray emission is powered
by an ultrastrong magnetic field, B ~ 10^15 G. Occasionally SGRs enter into
active episodes producing many short X-ray bursts; extremely rarely (about once
per 50 years per source), SGRs emit a giant flare, an event with total energy
at least 1000 times higher than their typical bursts. Here we report that, on
2004 December 27, SGR 1806-20 emitted the brightest extra-solar transient event
ever recorded, even surpassing the full moon brightness for 0.2 seconds. The
total (isotropic) flare energy is 2x10^46 erg, 100 times higher than the only
two previous events, making this flare a once in a century event. This colossal
energy release likely occurred during a catastrophic reconfiguration of the
magnetar's magnetic field. Such an event would have resembled a short, hard
Gamma Ray Burst (GRB) if it had occurred within 40 Mpc, suggesting that
extragalactic SGR flares may indeed form a subclass of GRBs.Comment: Submitted to Nature 2005-02-02, revised 2005-03-01. 21 pp, incl. 6
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Search for New Physics with Jets and Missing Transverse Momentum in pp collisions at sqrt(s) = 7 TeV
A search for new physics is presented based on an event signature of at least
three jets accompanied by large missing transverse momentum, using a data
sample corresponding to an integrated luminosity of 36 inverse picobarns
collected in proton--proton collisions at sqrt(s)=7 TeV with the CMS detector
at the LHC. No excess of events is observed above the expected standard model
backgrounds, which are all estimated from the data. Exclusion limits are
presented for the constrained minimal supersymmetric extension of the standard
model. Cross section limits are also presented using simplified models with new
particles decaying to an undetected particle and one or two jets
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