652 research outputs found
Evaluation of minimum shear reinforcement in reinforced concrete beams
Failures in reinforced concrete (RC) structures under shear loads are proved to be brittle with the presence of web reinforcement.
The minimum web reinforcement specified by many codes of practice is intended to maintain adequate reserve strength and ductility after the diagonal cracking and to control widening of diagonal cracking. However, the expressions for estimating the minimum shear reinforcement in codes of practice are based on the experimental data base observed on small beam depth made of normal strength concrete (NSC). Hence, these provisions need to be reassessed and altered for large size members made of high strength concrete (HSC). Further, there has been no consensus on the amount of shear reinforcement to be provided by different codes of practice, as they differ significantly in respect of HSC members. In this paper, many factors influencing the minimum shear reinforcement in RC beams has been incorporated. An expression has been proposed incorporating a wide range of concrete strengths. A comparison of the minimum shear reinforcement predicted by the proposed expression has been made with the codes of practice
Strength of bonded anchors in concrete in direct tension
Bonded anchors are being used in several civil engineering applications, whose performance needs to be investigated. This paper discusses the experimental investigations made on the strength and failure modes of bonded anchors in concrete. The effect of strength of concrete, embedment length and diameter of anchors has been studied. The important parameters influencing the strength of anchorage system are compressive strength of concrete and the embedment depth of anchors. Three strengths of concretes namely 45 MPa, 52MPa and 52MPa were used along with three embedment lengths of 50mm, 100mm and 150mm. It has been observed that concrete cone failure was predominant in all the specimens. The anchorage strength increases as the compressive strength of concrete increases. As the embedment length of anchor increases, the anchorage strength also increases. The diameter of the anchor does show much influence on the strength of anchorage. The strength of bonded anchors was observed to coincide with the strength estimated as per both CCD design method and ACI 349 method. Bonded anchor load carrying capacity has been observed to closely match with that of the post-installed anchors
Photoconductance Quantization in a Single-Photon Detector
We have made a single-photon detector that relies on photoconductive gain in
a narrow electron channel in an AlGaAs/GaAs 2-dimensional electron gas. Given
that the electron channel is 1-dimensional, the photo-induced conductance has
plateaus at multiples of the quantum conductance 2e/h. Super-imposed on
these broad conductance plateaus are many sharp, small, conductance steps
associated with single-photon absorption events that produce individual
photo-carriers. This type of photoconductive detector could measure a single
photon, while safely storing and protecting the spin degree of freedom of its
photo-carrier. This function is valuable for a quantum repeater that would
allow very long distance teleportation of quantum information.Comment: 4 pages, 4 figure
Reversible Pressure-Induced Amorphization in Solid C70 : Raman and Photoluminescence Study
We have studied single crystals of by Raman scattering and
photoluminescence in the pressure range from 0 to 31.1 GPa. The Raman spectrum
at 31.1 GPa shows only a broad band similar to that of the amorphous carbon
without any trace of the Raman lines of . After releasing the pressure
from 31.1 GPa, the Raman and the photoluminescence spectra of the recovered
sample are that of the starting crystal. These results indicate that
the molecules are stable upto 31.1 GPa and the amorphous carbon high
pressure phase is reversible, in sharp contrast to the results on solid
. A qualitative explaination is suggested in terms of inter- versus
intra-molecular interactions.Comment: To appear in Phys. Rev. Lett., 12 pages, RevTeX (preprint format), 3
figures available upon reques
Critical exponents and equation of state of the three-dimensional Heisenberg universality class
We improve the theoretical estimates of the critical exponents for the
three-dimensional Heisenberg universality class. We find gamma=1.3960(9),
nu=0.7112(5), eta=0.0375(5), alpha=-0.1336(15), beta=0.3689(3), and
delta=4.783(3). We consider an improved lattice phi^4 Hamiltonian with
suppressed leading scaling corrections. Our results are obtained by combining
Monte Carlo simulations based on finite-size scaling methods and
high-temperature expansions. The critical exponents are computed from
high-temperature expansions specialized to the phi^4 improved model. By the
same technique we determine the coefficients of the small-magnetization
expansion of the equation of state. This expansion is extended analytically by
means of approximate parametric representations, obtaining the equation of
state in the whole critical region. We also determine a number of universal
amplitude ratios.Comment: 40 pages, final version. In publication in Phys. Rev.
Photoinjector design for the LCLS
The design of the Linac Coherent Light Source assumes that a low-emittance,
1-nC, 10-ps beam will be available for injection into the 15-GeV linac. The
proposed rf photocathode injector that will provide a 150-MeV beam with rms
normalized emittances of 1 mm in both the transverse and longitudinal
dimensions is based on a 1.6-cell S-band rf gun that is equipped with an
emittance compensating solenoid. The booster accelerator is positioned at the
beam waist coinciding with the first emittance maximum and is provided with an
accelerating gradient of ~25 MeV/m, i.e., the "new working point." The uv
pulses required for cathode excitation will be generated by tripling the output
of a Ti:sapphire laser system consisting of a highly stable cw mode-locked
oscillator and two bow-tie amplifiers pumped by a pair of Q-switched Nd:YAG
lasers. The large bandwidth of the Ti:sapphire system accommodates the desired
temporal pulse shaping. Details of the design and the supporting simulations
are presented.Comment: 13 pages (double spaced), 4 figures, contributed to The 23rd
International Free Electron Laser Conference, Darmstadt, Germany, 20-24
August 200
Boundary work: becoming middle class in suburban Dar es Salaam
Suburban space provides a useful window onto contemporary class practices in Africa, where it is difficult to identify social classes on the basis of income or occupation. In this article I argue that the middle classes and the suburbs are mutually constitutive in the Tanzanian city of Dar es Salaam. Using interviews with residents and local government officials in the city's northern suburbs, I discuss the material and representational practices of middle-class boundary work in relation to land and landscape. If the middle classes do not presently constitute a coherent political-economic force, they are nevertheless transforming the city's former northern peri-urban zones into desirable suburban residential neighbourhoods
Accelerating Bianchi Type-V Cosmology with Perfect Fluid and Heat Flow in Saez-Ballester Theory
In this paper we discuss the law of variation of scale factor which yields a time-dependent deceleration
parameter (DP) representing a new class of models that generate a transition of
universe from the early decelerated phase to the recent accelerating phase.
Exact solutions of Einstein's modified field equations with perfect fluid and
heat conduction are obtained within the framework of Saez-Ballester
scalar-tensor theory of gravitation and the model is found to be in good
agreement with recent observations. We find, for n = 3, k = 1, the present
value of DP in derived model as q_0 = -0.67 which is very near to the observed
value of DP at present epoch. We find that the time-dependent DP is sensible
for the present day Universe and give an earmark description of evolution of
universe. Some physical and geometric properties of the models are also
discussed.Comment: 12 pages, 5 figure
- âŠ