Precast bridges are often constructed as single span for dead load, but continuous for live load. A diaphragm connection is provided for negative moment continuity. However, the connection may also be subjected to positive moments due to time-dependent effects. Because these moments may be large enough to damage the diaphragm or even the girders, a positive moment connection is often provided. This paper reports on a study to determine the types of positive moment connections used across the country and to identify potential problems with these types of connections. A questionnaire survey was conducted to assess the state of practice for precast prestressed concrete bridges made continuous. The survey provides valuable information on this type of bridge and updates a previous survey on this subject. 相似文献
Two hundred and fifteen children aged 4 months 6 years with acute otitis media (AOM) were randomized to be treated either by a single i.m. injection of ceftriaxone, 50 mg/kg, with a second dose in the event of unsatisfactory response after 48 h or a history of recurrent AOM (109 patients) or amoxicillin clavulanate 12.5 mg tid (106 patients). The failure rate was similar in children treated by ceftriaxone and amoxicillin clavulanate, 4.6% and 4.7%, respectively (standard error for intergroup difference -2.87%, 95% confidence interval -5.62% to 5.87%). No significant differences between the groups were found in the dynamics of the resolution of the acute symptomatology, otoscopy findings, relapse rate at 30 days or tympanographic evidence of middle ear effusion at the scheduled visits on days 30, 60 and 90. Recurrence of AOM between days 31 and 90 was observed significantly in more children treated with amoxicillin clavulanate than with ceftriaxone--25 out of 84 (29.4%) versus 11 out of 81 (13.6%) (P = 0.012). Conclusion: Ceftriaxone injection(s) is as efficient at least as 10-day oral amoxicillin clavulanate for treatment of acute otitis media in children. Although not recommended as routine, ceftriaxone can be considered in the management of acute otitis media under special circumstances, particularly in cases when the ability to tolerate or absorb oral drugs is compromised, in children refusing or unable to take oral therapy or when the compliance is questionable. 相似文献
NADPH diaphorase histochemistry is commonly used to identify cells containing nitric oxide synthase (NOS), the enzyme catalyzing the production of nitric oxide from L-arginine. NADPH diaphorase activity and NOS immunostaining was demonstrated in different cells of the vertebrate retina; photoreceptors, horizontal cells, amacrine cells, ganglion cells, and Müller cells. However, the physiological role of nitric oxide (NO) in the retina has yet to be elucidated. In this study, we tested the assumption that NADPH diaphorase activity in the retinas of rabbits and rats depended on the state of visual adaptation. In the rabbit, light adaptation enhanced NADPH diaphorase activity in amacrine cells and practically eliminated it in horizontal cells. Dark adaptation induced the opposite effects; the NADPH diaphorase activity was reduced in amacrine cells and enhanced in horizontal cells. Retinas from eyes that were injected intravitreally with L-glutamate exhibited a pattern of NADPH diaphorase activity that was similar to that seen in dark-adapted retinas. In rats, the NADPH diaphorase activity of amacrine and horizontal cells exhibited adaptation dependency similar to that of the rabbit retina. But, the most pronounced effect of dark adaptation in the rat's retina was an enhancement of NADPH diaphorase activity in Müller cells, especially of the endfoot region. Assuming that NADPH diaphorase activity is a marker for NOS, these findings suggest that NO production in the mammalian retina is modulated by the level of ambient illumination and support the notion that NO plays a physiological role in the retina. 相似文献
An exact algorithm for the multi-period facility location problem is proposed that efficiently integrates mixed-integer and dynamic programming methods. Two simplification procedures are introduced to reduce the size of the general multi-period facility location problem substantially. Because the proposed algorithm utilizes dynamic programming to obtain the optimal sequence over the entire planning horizon, many near-optimal solutions also become available that are extremely useful for postoptimality analysis. The solution method is tested and compared with a well-known procedure on several problems with varying conditions. The comparisons appear very promising, and the required CPU times by the proposed method are substantially reduced. 相似文献
In this paper fast parallel Preconditioned Conjugate Gradient (PCG) algorithms for robot manipulator forward dynamics, or dynamic simulation, problem are presented. By exploiting the inherent structure of the forward dynamics problem, suitable preconditioners are devised to accelerate the iterations. Also, based on the choice of preconditioners, a modified dynamic formulation is used to speedup both serial and parallel computation of each iteration. The implementation of the parallel algorithms on two interconnected processor arrays is discussed and their computation and communication complexities are analyzed. The simulation results for a Puma Arm are presented to illustrate the effectiveness of the proposed preconditioners. With a faster convergence due to preconditioning and a faster computation of iterations due to parallelization, the developed parallel PCG algorithms represent the fastest alternative for parallel computation of the problem withO(n) processors. 相似文献
The limitation of freshwater resources and the growing demand for water, make the issue of water resource development planning and water allocation among stakeholders even more important. Ideally, water allocation should be economically efficient and socially equitable. In this study, a water allocation model is presented in an integrated framework that considers the interaction of water supply and demand according to economic and social factors. To achieve this, a reliability-based multi-objective optimization - simulation approach has been employed. The objective functions of the problem are: 1) maximizing GDP from agricultural sectors and 2) maximizing social equality in different provinces of the basin (measured using the Williamson coefficient). The fair development and allocation among the shared provinces in the basin can reduce conflicts in the region. Karkheh basin has been considered as a case study and decision variables of the problem are area under cultivation of agricultural development sectors in different provinces. The results show that, without harming the income of the agricultural sector, the spatial distribution of development projects can be done in such a way that equality (according to income level and the number of people working in each province) is achieved. One of the solutions of Pareto front compared to previous studies shows that, in addition to an increase of about 12% of the objective function 1 (GDP), the value of the objective function 2 (Williamson coefficient) decreased from 1.19 to 0.98. This indicates a decrease in income inequality among the provinces of the basin.
In in-vivo microsystems, one of the components is a biocompatible micropump in order to produce the necessary force to deliver
the fluid from the inlet to the outlet. In this contribution, a flexible micropump is fabricated which is aimed to be suitable
in drug delivery applications. It provides high degree of biocompatibility, since the only employed materials are implantation
grade polydimethylsiloxane elastomer and gold for the electrical interconnects. The working principle of the micropump is
based on transverse DC electroosmosis which is a new variant of conventionally applied high voltage DC electroosmosis. This
new technique is based on topography irregularities introduced in the channel resulting in a non-uniform charge distribution.
The advantage is to drive the micropump using a relatively low DC voltage of 10 V while getting an effective flow speed of
60 μm/s. In order to characterize the flow speed, dyed 3 μm beads are dispersed in the working fluid and their speed is measured
by the line scanning technique using a confocal microscope. It is also observed that the flow has a helical profile which
is an attractive feature for an efficient micro-mixer in active microfluidics and μ-TAS applications. 相似文献