34,441 research outputs found
Recommended from our members
Experimental and Numerical Investigation on Progressive Collapse Resistance of Post-tensioned Precast Concrete Beam-Column Sub-assemblages
In this paper, four 1/2 scaled precast concrete (PC) beam-column sub-assemblages with high performance connection were tested under push-down loading procedure to study the load resisting mechanism of PC frames subjected to different column removal scenarios. The parameters investigated include the location of column removal and effective prestress in tendons. The test results indicated that the failure modes of unbonded post-tensioned precast concrete (PTPC) frames were different from that of reinforced concrete (RC) frames: no cracks formed in the beams and wide opening formed near the beam to column interfaces. For specimens without overhanging beams, the failure of side column was eccentric compression failure. Moreover, the load resisting mechanisms in PC frames were significantly different from that of RC frames: the compressive arch action (CAA) developed in concrete during column removal was mainly due to actively applied pre-compressive stress in the concrete; CAA will not vanish when severe crush in concrete occurred. Thus, it may provide negative contribution for load resistance when the displacement exceeds one-beam depth; the tensile force developed in the tendons could provide catenary action from the beginning of the test. Moreover, to deeper understand the behavior of tested specimens, numerical analyses were carried out. The effects of concrete strength, axial compression ratio at side columns, and loading approaches on the behavior of the sub-assemblages were also investigated based on validated numerical analysis
A Generalized Preferential Attachment Model for Business Firms Growth Rates: II. Mathematical Treatment
We present a preferential attachment growth model to obtain the distribution
of number of units in the classes which may represent business firms
or other socio-economic entities. We found that is described in its
central part by a power law with an exponent which depends on
the probability of entry of new classes, . In a particular problem of city
population this distribution is equivalent to the well known Zipf law. In the
absence of the new classes entry, the distribution is exponential. Using
analytical form of and assuming proportional growth for units, we derive
, the distribution of business firm growth rates. The model predicts that
has a Laplacian cusp in the central part and asymptotic power-law tails
with an exponent . We test the analytical expressions derived using
heuristic arguments by simulations. The model might also explain the
size-variance relationship of the firm growth rates.Comment: 19 pages 6 figures Applications of Physics in Financial Analysis,
APFA
On the use of colour reflectivity plots to monitor the structure of the troposphere and stratosphere
The radar reflectivity, defined as the range squared corrected power of VHF radar echoes, can be used to monitor and study the temporal development of inversion layer, frontal boundaries and convective turbulence. From typical featurs of upward or downward motion of reflectivity structures, the advection/convection of cold and warm air can be predicted. High resolution color plots appear to be useful to trace and to study the life history of these structures, particularly their persistency, descent and ascent. These displays allow an immediate determination of the tropopause height as well as the determination of the tropopause structure. The life history of warm fronts, cold fronts, and occlusions can be traced, and these reflectivity plots allow detection of even very weak events which cannot be seen in the traditional meteorological data sets. The life history of convective turbulence, particular evolving from the planetary boundary layer, can be tracked quite easily. Its development into strong convection reaching the middle troposphere can be followed and predicted
Recommended from our members
Effects of High Strength Concrete on Progressive Collapse Resistance of Reinforced Concrete Frame
Increasing terrorist activities in the past decade brought requirements in design buildings, especially government or commercial buildings, under extreme loading conditions. One of the devastating consequences due to extreme loading is the possibility of progressive collapse. Although extensive studies had been carried out in the past decade on load resistance mechanism of reinforced concrete (RC) frames in preventing progressive collapse, the effects of high-strength-concrete (HSC) on progressive collapse resistance capacity is still unclear. Therefore, in this paper six tests of reinforced concrete frames with different span-to-depth ratio and concrete strength were conducted in the present study. Among them, three are HSC frames and the remaining are normal strength concrete frames. It was found that the use of HSC could further enhance the compressive arch action (CAA) capacity, especially for those with low span-to-depth ratio. On the other hand, HSC can reduce the tensile catenary action (TCA) capacity at large deformation stage, primarily because of higher bond stress between concrete and rebar,leading to earlier fracture of the rebar.The analytical results from the model were compared with the test results. It is found that the existing CAA model could accurately predict the CAA capacity of HSC frames as well as NSC frames.However, existing model is hard to predict the CAA capacity of the frames with relatively small span-to-depth ratio (less than 7) accurately
Vortex-to-Polarization Phase Transformation Path in Pb(ZrTi)O Nanoparticles
Phase transformation in finite-size ferroelectrics is of fundamental
relevance for understanding collective behaviors and balance of competing
interactions in low-dimensional systems. We report a first-principles effective
Hamiltonian study of vortex-to-polarization transformation in
Pb(ZrTi)O nanoparticles, caused by homogeneous electric
fields normal to the vortex plane. The transformation is shown to (1) follow an
unusual {\it macroscopic} path that is symmetry non-conforming and
characterized by the occurrence of a previously unknown structure as the
bridging phase; (2) lead to the discovery of a striking collective phenomenon,
revealing how ferroelectric vortex is annihilated {\it microscopically}.
Interactions underlying these behaviors are discussed
Entanglement and Quantum Phases in the Anisotropic Ferromagnetic Heisenberg Chain in the Presence of Domain Walls
We discuss entanglement in the spin-1/2 anisotropic ferromagnetic Heisenberg
chain in the presence of a boundary magnetic field generating domain walls. By
increasing the magnetic field, the model undergoes a first-order quantum phase
transition from a ferromagnetic to a kink-type phase, which is associated to a
jump in the content of entanglement available in the system. Above the critical
point, pairwise entanglement is shown to be non-vanishing and independent of
the boundary magnetic field for large chains. Based on this result, we provide
an analytical expression for the entanglement between arbitrary spins. Moreover
the effects of the quantum domains on the gapless region and for
antiferromagnetic anisotropy are numerically analysed. Finally multiparticle
entanglement properties are considered, from which we establish a
characterization of the critical anisotropy separating the gapless regime from
the kink-type phase.Comment: v3: 7 pages, including 4 figures and 1 table. Published version. v2:
One section (V) added and references update
Recommended from our members
Experimental Study on Seismic Behaviour of RC Frames with Different Infilled Masonry
Six 1/2 scaled, single-storey, one-bay frame specimens were tested in this study to investigate the seismic behavior of masonry infilled reinforced concrete (RC) frames subjected to lateral loading. The variables investigated include types of masonry and types of openings. The crack patterns, failure modes, load-displacement hysteretic loops, stiffness degradation, and energy dissipation capacity are presented and discussed. It is found that the infilled wall (with or without openings) could improve the behavior of RC frames significantly. Moreover, as expected, the infilled frame with higher strength masonry performed better than those with relatively low strength masonry. Furthermore, the openings may detriment the stability of the infilled walls. The concentric widow opening has worse effects than the eccentric door opening. The proposed analytical model could determine the load resisting capacity of bare frame and infilled frame with reasonable accuracy
The first operation and results of the Chung-Li VHF radar
The Chung-Li Very High Frequency (VHF) radar is used in the dual-mode operations, applying Doppler beam-swinging as well as the spaced-antenna-drift method. The design of the VHF radar is examined. Results of performance tests are discussed
Decoupling of Layers in the Three-dimensional Abelian Higgs Model
The Abelian Higgs model with anisotropic couplings in 2+1 dimensions is
studied in both the compact and non-compact formulations. Decoupling of the
space-like planes takes place in the extreme anisotropic limit, so charged
particles and gauge fields are presumably localized within these planes. The
behaviour of the model under the influence of an external magnetic field is
examined in the compact case and yields further characterization of the phases.Comment: 23 pages, 12 figures, plain late
Design and Fabrication of Three-Dimensional Scaffolds for Tissue Engineering of Human Heart Valves
We developed a new fabrication technique for 3-dimensional scaffolds for tissue engineering of human heart valve tissue. A human aortic homograft was scanned with an X-ray computer tomograph. The data derived from the X-ray computed tomogram were processed by a computer-aided design program to reconstruct a human heart valve 3-dimensionally. Based on this stereolithographic model, a silicone valve model resembling a human aortic valve was generated. By taking advantage of the thermoplastic properties of polyglycolic acid as scaffold material, we molded a 3-dimensional scaffold for tissue engineering of human heart valves. The valve scaffold showed a deviation of only +/- 3-4% in height, length and inner diameter compared with the homograft. The newly developed technique allows fabricating custom-made, patient-specific polymeric cardiovascular scaffolds for tissue engineering without requiring any suture materials. Copyright (c) 2008 S. Karger AG, Base
- …