Stress and displacement discontinuity element method for undrained analysis

Stress (SD) and displacement (DD) discontinuity methods have been developed for problems where seepage and deformation are not coupled. This is an important limitation in geomechanics where the ground is usually saturated. Of particular importance are problems that fall within the “short term analysis” concept, where a phenomenon occurs over a period of time that is very short compared to the permeability of the medium. In this paper we present an analytical formulation to solve undrained conditions and deformation problems in a poroelastic saturated medium in plane strain conditions, with the assumption of short term analysis (i.e. no change in volume of the medium). Explicit functions for SD and DD elements are obtained and are incorporated into the code FROCK. The new code is verified by a number of comparisons with theoretical solutions, also presented in the paper, and with solutions from the Finite Element Method. In undrained compression, the compression field around the tip of an open flaw decreases and the tension field increases compared to drained compression loading, while the shear stresses remain unchanged. For a closed frictional flaw undrained compression decreases the compression and tension fields around the tip. The shear stresses however have the same distribution as in drained loading but are larger. This is caused by the decrease of the effective normal stresses due to the excess pore pressures which in turn decrease the shear resistance of the flaw.     

Phase Engineering of 2D Tin Sulfides

Tin sulfides can exist in a variety of phases and polytypes due to the different oxidation states of Sn. A subset of these phases and polytypes take the form of layered 2D structures that give rise to a wide host of electronic and optical properties. Hence, achieving control over the phase, polytype, and thickness of tin sulfides is necessary to utilize this wide range of properties exhibited by the compound. This study reports on phase‐selective growth of both hexagonal tin (IV) sulfide SnS₂ and orthorhombic tin (II) sulfide SnS crystals with diameters of over tens of microns on SiO₂ substrates through atmospheric pressure vapor‐phase method in a conventional horizontal quartz tube furnace with SnO₂ and S powders as the source materials. Detailed characterization of each phase of tin sulfide crystals is performed using various microscopy and spectroscopy methods, and the results are corroborated by ab initio density functional theory calculations.     

Optimizing coalition formation for tasks with dynamically evolving rewards and nondeterministic action effects

We consider a problem domain where coalitions of agents are formed in order to execute tasks. Each task is assigned at most one coalition of agents, and the coalition can be reorganized during execution. Executing a task means bringing it to one of the desired terminal states, which might take several time steps. The state of the task evolves even if no coalition is assigned to its execution and depends nondeterministically on the cumulative actions of the agents in the coalition. Furthermore, we assume that the reward obtained for executing a task evolves in time: the more the execution of the task is delayed, the lesser the reward. A representative example of this class of problems is the allocation of firefighters to fires in a disaster rescue environment. We describe a practical methodology through which a problem of this class can be encoded as a Markov Decision Process. Due to the three levels of factoring in the resulting MDP (the states, actions and rewards are composites of the original features of the problem) the resulting MDP can be directly solved only for small problem instances. We describe two methods for parallel decomposition of the MDP: the MDP RSUA approach for random sampling and uniform allocation and the MDP REUSE method which reuses the lower level MDP to allocate resources to the parallel subproblems. Through an experimental study which models the problem domain using the fire simulation components of the Robocup Rescue simulator, we show that both methods significantly outperform heuristic approaches and MDP REUSE provides an overall higher performance than MDP RSUA.     

Modelling 3D spatial enclosure of urban open spaces

Existing urban open space typologies within dense urban fabrics cannot meet society’s open space requirements in developing countries’ metropolitan cities, such as Istanbul. Because of high building densities, it is a challenging task to create new open spaces within urban cores. Developing new tools that work with the existing built environment is crucial to reveal ‘opportunity spaces’ that can act as breathing points within dense urban fabrics. In this research, a new model is developed to evaluate the 3D spatial enclosure of open spaces using basic geometrical properties and geographic information system (GIS) tools. As a case study, Istanbul’s changing spatial organization is analyzed using this model.     

Flow control valves for analytical microfluidic chips without mechanical parts based on thermally responsive monolithic polymers

Monolithic plugs of poly(N-isopropylacrylamide) cross-linked with 5% methylenebisacrylamide have been prepared by photoinitiated polymerization within the channel of a microfluidic device. The volume change associated with the polymer phase transition at its lower critical solution temperature of 32 degrees C allows both the rapid swelling and the deswelling of the monoliths enabling the polymer to close or open the channel as it functions as a nonmechanical valve. Thermoelectric elements capable of changing the temperature of the system between 17 and 57 degrees C were used to actuate the valve. Flow through the device was monitored by fluorescence measurements via the laser-triggered photobleaching of a dye contained in the liquid phase. Photobleaching occurs quickly once the flow is stopped, and the time required to open and close the valve was 3.5 and 5.0 s, respectively. No changes in function were observed even after 120 open-close cycles. Although the 2-mm-long valve was prepared from a polymerization mixture consisting of only a 5% aqueous solution of monomers, it resists pressures of up to 1.38 MPa (200 psi) without observable structural damage.     

Comparative tear concentrations of topically applied ciprofloxacin, ofloxacin, and norfloxacin in human eyes

The tear pharmacokinetic profiles of 0.3% ciprofloxacin, 0.3% ofloxacin, and 0.3% norfloxacin ophthalmic solutions after a single drop topically administrations in the eyes of 30 healthy volunteers were evaluated. Tear samples collected at 30, 120, 180, and 240 minutes, were analyzed for drug concentrations by high performance liquid chromatography (HPLC) with fluorometric detection. Topically applied ciprofloxacin, ofloxacin, and norfloxacin achieved the mean tear concentrations (mean +/- SD) of 11.28 +/- 6.98, 6.52 +/- 4.06, and 13.28 +/- 8.78 micrograms/g at 30 min, and then fell to 3.52 +/- 1.30, 4.82 +/- 1.80, and 5.79 +/- 4.80 micrograms/g at 240 min, respectively. Topical norfloxacin achieved mean tear level significantly higher than ofloxacin at 30 min (p = 0.031). There were no statistically significant differences in the mean tear levels of ciprofloxacin versus ofloxacin (at 30, 120, 180, and 240 min), ciprofloxacin versus norfloxacin (at 30, 120, 180, and 240 min) and ofloxacin versus norfloxacin (at 120, 180, and 240 min). However, the mean tear levels, 240 min after dosing ciprofloxacin and norfloxacin, fell to the statistically significant concentrations (p = 0.02 and p = 0.01, respectively). But, it is concluded that concentrations of ciprofloxacin, ofloxacin, and norfloxacin in tears were still significantly greater than the minimum inhibitory concentrations for the most sensitive organisms, 240 min after a single drop application.     

Development of germ tubes in various strains of Candida

57 different Candida strains are studied and it is observed that most of them developed germ tubes.     

Hierarchical modeling of availability in distributed systems

Distributed computing systems are attractive due to the potential improvement in availability, fault-tolerance, performance, and resource sharing. Modeling and evaluation of such computing systems is an important step in the design process of distributed systems. We present a two-level hierarchical model to analyze the availability of distributed systems. At the higher level (user level), the availability of the tasks (processes) is analyzed using a graph-based approach. At the lower level (component level), detailed Markov models are developed to analyze the component availabilities. These models take into account the hardware/software failures, congestion and collisions in communication links, allocation of resources, and the redundancy level. A systematic approach is developed to apply the two-level hierarchical model to evaluate the availability of the processes and the services provided by a distributed computing environment. This approach is then applied to analyze some of the distributed processes of a real distributed system, Unified Workstation Environment (UWE), that is currently being implemented at AT&T Bell Laboratories     

Synchronous optical network and broadband ISDN protocols

High-level technical information on Sonet (synchronous optical network) B-ISDN (broadband integrated services digital network) protocols, and interface structures is provided. Since the B-ISDN protocol standards to be used in the Broadband Reference Model are currently being discussed in the CCITT, most of the standards are not yet available. Therefore, some of the protocols described here are not based on agreements reached in national and international standards bodies. The discussion covers B-ISDN architecture and the ISO model. Sonet protocols and architecture, B-ISDN configuration, and the ATM (asynchronous transfer model) architecture     

Annealing and light effect on optical and electrical properties of ZnS thin films grown with the SILAR method

Zinc sulphide (ZnS) thin films were grown on glass substrates by the Successive Ionic Layer Adsorption and Reaction (SILAR) technique at room temperature and ambient pressure. Surface morphologies of grown films were characterized using scanning electron microscopy (SEM). The crystal structure and crystal size of the thin films were characterized by the X-ray diffraction (XRD) method and found that the films exhibit polycrystalline characterization. The optical absorption measurements were done as a function of the temperature at 10–320 K temperature range. Using absorption measurements, the band gap energies were calculated at 10 and 320 K, as 3.83 and 3.72 eV, respectively. The annealing temperature effect on optical band gap and the light effect on the electrical properties of ZnS thin films were investigated and it was found that the current increased with increasing light intensity. The annealed films were found have more resistance than the as-grown film.