6,380 research outputs found
The Dynamics of Crowd Disasters: An Empirical Study
Many observations in the dynamics of pedestrian crowds, including various self-organization phenomena, have been successfully described by simple many-particle models. For ethical reasons, however, there is a serious lack of experimental data regarding crowd panic. Therefore, we have analyzed video recordings of the crowd disaster in Mina/Makkah during the Hajj in 1426H on January 12, 2006. They reveal two subsequent, sudden transitions from laminar to stop-and-go and ``turbulent'' flows, which question many previous simulation models. While the transition from laminar to stop-and-go flows supports a recent model of bottleneck flows [D. Helbing et al., Phys. Rev. Lett. 97, 168001 (2006)], the subsequent transition to turbulent flow is not yet well understood. It is responsible for sudden eruptions of pressure release comparable to earthquakes, which cause sudden displacements and the falling and trampling of people. The insights of this study into the reasons for critical crowd conditions are important for the organization of safer mass events. In particularly, they allow one to understand where and when crowd accidents tend to occur. They have also led to organizational changes, which have ensured a safe Hajj in 1427H
Innovative flexural strengthening of RC beams using self-anchored prestressed CFRP plates: Experimental and numerical investigations
This paper presents an innovative method of prestressing carbon fibre reinforced polymer (CFRP) plates used as externally bonded reinforcement for flexural strengthening of reinforced concrete (RC) beams. The proposed method aims to achieve self-anchorage of the prestressed CFRP plate and thus eliminate the need for conventional mechanical anchorage at its ends. Experimental tests of RC beams in four-point bending were conducted to investigate the strengthening efficiency of the self-anchored prestressed CFRP plate. The experimental results showed that using the self-anchored prestressed CFRP significantly improved the flexural performance of the strengthened beam in terms of bending stiffness, crack widths, and load-carrying capacity. The utilisation ratio of the prestressed CFRP plate reached 81% at its debonding. Numerical analyses using nonlinear finite element (FE) method were conducted to model the tested specimens. Based on the reliable simulation of flexural cracks and crack-induced CFRP debonding, parametric studies were conducted using FE analyses, in order to investigate the effect of prestressing levels and the CFRP plate\u27s stiffness on the flexural behaviour. Recommendations were then made for selecting a proper prestressing level and the mechanical properties of CFRP plates
Generating Multimode Entangled Microwaves with a Superconducting Parametric Cavity
In this Letter, we demonstrate the generation of multimode entangled states
of propagating microwaves. The entangled states are generated by parametrically
pumping a multimode superconducting cavity. By combining different pump
frequencies, applied simultaneously to the device, we can produce different
entanglement structures in a programable fashion. The Gaussian output states
are fully characterized by measuring the full covariance matrices of the modes.
The covariance matrices are absolutely calibrated using an in situ microwave
calibration source, a shot noise tunnel junction. Applying a variety of
entanglement measures, we demonstrate both full inseparability and genuine
tripartite entanglement of the states. Our method is easily extensible to more
modes.Comment: 5 pages, 1 figures, 1 tabl
Kondo effect in oscillating molecules
We consider electronic transport through break-junctions bridged by a single
molecule in the Kondo regime. We describe the system by a two-channel Anderson
model. We take the tunneling matrix elements to depend on the position of the
molecule. It is shown, that if the modulation of the tunneling by displacement
is large, the potential confining the molecule to the central position between
the leads is softened and the position of the molecule is increasingly
susceptible to external perturbations that break the inversion symmetry. In
this regime, the molecule is attracted to one of the leads and as a consequence
the conductance is small. We argue on semi-classical grounds why the softening
occurs and corroborate our findings by numerical examples obtained by Wilson's
numerical renormalization group and Schoenhammer-Gunnarsson's variational
method.Comment: 5 p., Ustron'08 conference contributio
Hur har motstÄndet mot REVA organiserats? Aktivism, sociala rörelser och internet som politiskt verktyg
MotstÄndet mot REVA kan anses ha tagit form av en social rörelse dÄ det bestÄr av kollektivt organiserat beteende i syfte att utlösa en social förÀndring. Internet och sociala medier har fungerat som infrastruktur för organiseringen av protesterna, dÀr exempelvis Facebook-grupper samt Twitter-hashtags har utgjort viktiga redskap. Dessa kanaler har anvÀnts bÄde för att koordinera motstÄndet online med hjÀlp av inofficiella ledare kallade temporala eliter, och för att organisera protester offline som exempelvis demonstrationer. AnvÀndningen av sociala medier har inneburit stor uppslutning kring frÄgan till följd av lÀttillgÀnglighet och snabb och enkel spridning av information. Traditionellt vilar sociala rörelser pÄ en gemensam vÀrdegrund men med mÄnga engagerade blir en sÄdan svÄr att hÄlla ihop. Vi har sett att anvÀndningen av sociala medier har lett till ökad samhörighet och fokus pÄ mÄlet att fÄ REVA nedlagt, vilket skapat en kollektiv identitet som kanske gottgör för avsaknaden av gemensam vÀrdegrund
Further evidence to justify reassignment of Mycoplasma mycoides subspecies mycoides Large Colony type to Mycoplasma mycoides subspecies capri
Analysis, using the polymerase chain reaction (PCR), restriction enzyme endonuclease analysis (REA), protein profile patterns, random amplification of polymorphic DNA (RAPD) fingerprinting, 16S rRNA gene sequencing and antisera growth inhibition tests, of 22 strains of Mycoplasma mycoides subsp. mycoides Large Colony type (MmmLC) and eight strains of M. mycoides subsp. capri (Mmc) are presented, along with a summary of comparative data from the literature for over 100 strains, all of which supports the reclassification of the MmmLC and Mmc strains into the single subspecies, M. mycoides subspecies capri
Alloy Steel: Properties and Use First-Principles Quantum Mechanical Approach to Stainless Steel Alloys
Accurate description of materials requires the most advanced atomic-scale techniques from both experimental and theoretical areas. In spite of the vast number of available techniques, however, the experimental study of the atomic-scale properties and phenomena even in simple solids is rather difficult. In steels the challenges become more complex due to the interplay between the structural, chemical and magnetic effects. On the other hand, advanced computational methods based on density functional theory ensure a proper platform for studying the fundamental properties of steel materials from first-principles. In 1980âs the first-principles description of the thermodynamic properties of elemental iron was still on the borderline of atomistic simulations. Today the numerous application- oriented activities at the industrial and academic sectors are paired by a rapidly increasing scientific interest. This is reflected by the number of publications on ab initio steel research, which has increased from null to about one thousand within the last two decades. Our research group has a well established position in developing and applying computational codes for steel related applications. Using our ab initio tools, we have presented an insight to the electronic and magnetic structure, and micromechanical properties of austenite and ferrite stainless steel alloys. In the present contribution, we review the most important developments within the ab initio quantum mechanics aided steel design with special emphasis on the role of magnetism on the fundamental properties of alloy steels
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