Flexural Cracks in Fiber-Reinforced Concrete Beams with Fiber-Reinforced Polymer Reinforcing Bars

Fiber-reinforced polymer (FRP) reinforcing bars have attracted considerable attention for applications where corrosion of steel reinforcement is problematic. Due to the generally low elastic modulus and poor bond characteristics of FRP as compared to steel reinforcing bars, the use of FRP results in larger crack widths under service loads. Fiber-reinforced concrete (FRC) is proposed for use with FRP to reduce crack widths. The work presented herein includes the results from 16 beams tested under four-point bending with either Grade 420 (Grade 60) steel or FRP reinforcing bars, and either plain concrete or FRC. A modified Gergely-Lutz model was applied to the measured crack widths to calculate bond coefficients that were used to quantify the effectiveness of FRC in reducing crack widths. In the beams with steel reinforcing bars, the FRC was found to have little influence on crack widths. In the beams with FRP reinforcing bars, the FRC was found to significantly reduce maximum crack widths

Microtubule dynamics and glutathione metabolism in phagocytizing human polymorphonuclear leukocytes

Glutathione oxidants such as tertiary butyl hydroperoxide were shown previously to prevent microtubule assembly and cause breakdown of preassembled cytoplasmic microtubules in human polymorphonuclear leukocytes. The objectives of the present study were to determine the temporal relationship between the attachment and ingestion of phagocytic particles and the assembly of microtubules, and simultaneously to quantify the levels of reduced glutathione and products of its oxidation as potential physiological regulators of assembly. Polymorphonuclear leukocytes from human peripheral blood were induced to phagocytize opsonized zymosan at 30 degrees C. Microtubule assembly was assessed in the electron microscope by direct counts of microtubules in thin sections through centrioles. Acid extracts were assayed for reduced glutathione (GSH) and oxidized glutathione (GSSG), by the sensitive enzymatic procedure of Tietze. Washed protein pellets were assayed for free sulfhydryl groups and for mixed protein disulfides with glutathione (protein-SSG) after borohydride splitting of the disulfide bond. Resting cells have few assembled microtubules. Phagocytosis induces a cycle of rapid assembly followed by disassembly. Assembly is initiated by particle contact and is maximal by 3 min of phagocytosis. Disassembly after 5-9 min of phagocytosis is preceded by a slow rise in GSSG and coincides with a rapid rise in protein-SSG. Protein-SSG also increases under conditions in which butyl hydroperoxide inhibits the assembly of microtubules that normally follows binding of concanavalin A to leukocyte cell surface receptors. No evidence for direct involvement of GSH in the induction of assembly was obtained. The formation of protein-SSG, however, emerges as a possible regulatory mechanism for the inhibition of microtubule assembly and induction of their disassembly

The 'Parekh Report' - national identities with nations and nationalism

‘Multiculturalists’ often advocate national identities. Yet few study the ways in which ‘multiculturalists’ do so and in this article I will help to fill this gap. I will show that the Commission for Multi-Ethnic Britain’s report reflects a previously unnoticed way of thinking about the nature and worth of national identities that the Commission’s chair, and prominent political theorist, Bhikhu Parekh, had been developing since the 1970s. This way of thinking will be shown to avoid the questionable ways in which conservative and liberal nationalists discuss the nature and worth of national identities while offering an alternative way to do so. I will thus show that a report that was once criticised for the way it discussed national identities reflects how ‘multiculturalists’ think about national identities in a distinct and valuable way that has gone unrecognised

Too much or too little step width variability is associated with a fall history in older persons who walk at or near normal gait speed

BACKGROUND: Decreased gait speed and increased stride time, stride length, double support time, and stance time variability have consistently been associated with falling whereas step width variability has not been strongly related to falls. The purpose was to examine the linear and nonlinear associations between gait variability and fall history in older persons and to examine the influence of gait speed. METHODS: Gait characteristics and fall history were obtained in 503 older adults (mean age = 79; 61% female) participating in the Cardiovascular Health Study who could ambulate independently. Gait characteristics were recorded from two trials on a 4 meter computerized walkway at the subject's self-selected walking speed. Gait variability was calculated as the coefficient of variation. The presence of a fall in the past 12 months was determined by interview. The nonlinear association between gait variability and fall history was examined using a simple three level classification derived from the distribution of the data and from literature based cut-points. Multivariate logistic regression was used to examine the association between step width variability (extreme or moderate) and fall history stratifying by gait speed (1.0 m/s) and controlling for age and gender. RESULTS: Step length, stance time, and step time variability did not differ with respect to fall history (p > .33). Individuals with extreme step width variability (either low or high step width variability) were more likely to report a fall in the past year than individuals with moderate step width variability. In individuals who walked ≥ 1.0 m/s (n = 281), after controlling for age, gender, and gait speed, compared to individuals with moderate step width variability individuals with either low or high step width variability were more likely to have fallen in the past year (OR and 95% CI 4.38 [1.79–10.72]). The association between step width variability and fall history was not significant in individuals who walked < 1.0 m/s (n = 224). CONCLUSION: Extreme (either too little or too much) step width variability is associated with falls in the past year in older persons who walk at or near normal gait speed and not in older persons who walk slowly (<1.0 m/s)

A generalized spherical version of the Blume-Emery-Griffits model with ferromagnetic and antiferromagnetic interactions

We have investigated analitycally the phase diagram of a generalized spherical version of the Blume-Emery-Griffiths model that includes ferromagnetic or antiferromagnetic spin interactions as well as quadrupole interactions in zero and nonzero magnetic field. We show that in three dimensions and zero magnetic field a regular paramagnetic-ferromagnetic (PM-FM) or a paramagnetic-antiferromagnetic (PM-AFM) phase transition occurs whenever the magnetic spin interactions dominate over the quadrupole interactions. However, when spin and quadrupole interactions are important, there appears a reentrant FM-PM or AFM-PM phase transition at low temperatures, in addition to the regular PM-FM or PM-AFM phase transitions. On the other hand, in a nonzero homogeneous external magnetic field $H$, we find no evidence of a transition to the state with spontaneous magnetization for FM interactions in three dimensions. Nonethelesss, for AFM interactions we do get a scenario similar to that described above for zero external magnetic field, except that the critical temperatures are now functions of $H$. We also find two critical field values, $H_{c1}$, at which the reentrance phenomenon dissapears and $H_{c2}$ ($H_{c1}\approx 0.5H_{c2}$), above which the PM-AFM transition temperature vanishes.Comment: 21 pages, 6 figs. Title changed, abstract and introduction as well as section IV were rewritten relaxing the emphasis on spin S=1 and Figs. 5 an 6 were improved in presentation. However, all the results remain valid. Accepted for publication in Phys. Rev.

Vibrational Enhancement of the Effective Donor - Acceptor Coupling

The paper deals with a simple three sites model for charge transfer phenomena in an one-dimensional donor (D) - bridge (B) - acceptor (A) system coupled with vibrational dynamics of the B site. It is found that in a certain range of parameters the vibrational coupling leads to an enhancement of the effective donor - acceptor electronic coupling as a result of the formation of the polaron on the B site. This enhancement of the charge transfer efficiency is maximum at the resonance, where the effective energy of the fluctuating B site coincides with the donor (acceptor) energy.Comment: 5 pages, 3 figure

The MIDAS experiment: A prototype for the microwave emission of Ultra-High Energy Cosmic Rays

Recent measurements suggest that extensive air showers initiated by ultra-high energy cosmic rays (UHECR) emit signals in the microwave band of the electromagnetic spectrum caused by the collisions of the free-electrons with the atmospheric neutral molecules in the plasma produced by the passage of the shower. Such emission is isotropic and could allow the detection of air showers with 100% duty cycle and a calorimetric-like energy measurement, a significant improvement over current detection techniques. We have built MIDAS (MIcrowave Detection of Air Showers), a prototype of microwave detector, which consists of a 4.5 m diameter antenna with a cluster of 53 feed-horns in the 4 GHz range. The details of the prototype and first results will be presented.Comment: To appear in the proceedings of 12th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD10), Siena, Italy, 7 - 10 June 201

Glauber Critical Dynamics: Exact Solution of the Kinetic Gaussian Model

In this paper, we have exactly solved Glauber critical dynamics of the Gaussian model on three dimensions. Of course, it is much easy to apply to low dimensional case. The key steps are that we generalize the spin change mechanism from Glauber's single-spin flipping to single-spin transition and give a normalized version of the transition probability . We have also investigated the dynamical critical exponent and found surprisingly that the dynamical critical exponent is highly universal which refer to that for one- two- and three-dimensions they have same value independent of spatial dimensionality in contrast to static (equilibrium) critical exponents.Comment: 9 page

Solvable Kinetic Gaussian Model in External Field

In this paper, the single-spin transition dynamics is used to investigate the kinetic Gaussian model in a periodic external field. We first derive the fundamental dynamic equations, and then treat an isotropic d-dimensional hypercubic lattice Gaussian spin system with Fourier's transformation method. We obtain exactly the local magnetization and the equal-time pair correlation function. The critical characteristics of the dynamical, the complex susceptibility, and the dynamical response are discussed. The results show that the time evolution of the dynamical quantities and the dynamical responses of the system strongly depend on the frequency and the wave vector of the external field.Comment: 11 page

Avoided Critical Behavior in O(n) Systems

Long-range frustrating interactions, even if their strength is infinitesimal, can give rise to a dramatic proliferations of ground or near-ground states. As a consequence, the ordering temperature can exhibit a discontinuous drop as a function of the frustration. A simple model of the doped Mott insulator, where the short-range tendency of the holes to phase separate competes with long-range Coulomb effects, exhibits this "avoided critical" behavior. This model may serve as a paradigm for many other systems.Comment: 4 pages, 2 figure