Three-dimensional (3D) hydrogels incorporating a compendium of bioactive molecules can allow efficient proliferation and differentiation of cells and can thus act as successful tissue engineering scaffolds. Self-assembled peptide-based hydrogels can be worthy candidates for such applications as peptides are biocompatible, biodegradable and can be easily functionalized with desired moieties. Here, we report 3D growth and proliferation of mammalian cells (HeLa and L929) on a dipeptide hydrogel chemically functionalized with a pentapeptide containing Arg-Gly-Asp (RGD) motif. The method of functionalization is simple, direct and can be adapted to other functional moieties as well. The functionalized gel was noncytotoxic, exhibited enhanced cell growth promoting properties, and promoted 3D growth and proliferation of cells for almost 2 weeks, with simultaneous preservation of their metabolic activities. The presence of effective cell growth supporting properties in a simple and easy to functionalize dipeptide hydrogel is unique and makes it a promising candidate for tissue engineering and cell biological applications. 相似文献
Air cooled steam condensers (ACSC) consist of finned-tube arrays bundled in an A-frame structure. Inefficient performance under extreme temperature operating conditions is a common problem in ACSCs. The purpose of this study was to improve the heat transfer characteristics of an annular finned-tube system for better performance in extreme climatic conditions. Perforations were created on the surface of the annular fins to increase heat transfer coefficient (h). Mesh generation and finite volume analyses were performed using Gambit 2.4.6 and Fluent 6.3 with an RNG k–? turbulent model to calculate pressure drop (ΔP), heat flux (q), and heat transfer coefficient (h). Solid (no perforations) finned-tubes were simulated with free stream velocity ranging between 1 m/s–5 m/s and validated with the published data. Computations were performed for perforations at 30° interval starting at ±60°, ±90°, ±120°, ±150°, and ±180° from the stagnation point. Five cases with single perforation and three cases with multiple perforations were evaluated for determining the maximum q and h, as well as minimum ΔP. For the perforated case (perforations starting from 60° at interval of 30°), the fin q and h performance ratios increased by 5.96% and 7.07%, respectively. Consequently, the fin ΔP performance ratio increased by 11.87%. Thus, increased q and h is accompanied with a penalty of higher ΔP. In contrast, a single perforation location at 120° provided favorable results with a 1.70% and 2.23% increase in q and h performance ratios, respectively, while there was a relatively smaller increase (only 1.39%) of ΔP performance ratio. Perforations in the downstream region at ±120°, ±150°, and ±180° also resulted in a similar favorable outcome. Furthermore, the spacing of the fins along the arms of an A-frame ACSC was altered to decrease ΔP across the finned-tube array. Fin spacing in the A-frame structure with sparsely spaced fins in the center resulted in a 1.80% reduction in ΔP. Thus, penalty in ΔP for a perforated fin can possibly be offset by changing the fin spacing along the arms of an A-frame structure. 相似文献
Transient behavior of PEM fuel cells can be categorized into electrochemical, thermal and two-phase flows. Overshoot/undershoot behavior has been observed in electrochemical cell voltage during transients, and are attributed to the transition time required for saturation conditions to reestablish. Similar behavior has been reported in two-phase flow pressure drop overshoot/undershoot in a previous work by the authors. In this work, three different temperatures, five ramp rates and four amplitudes of load change were used to investigate the transient two-phase pressure drop behavior. The overshoot/undershoot behavior is observed predominantly at the lower temperature of 40 °C, and is found to decrease at higher cell temperatures. There is a linear increase in the overshoot/undershoot behavior with increase in amplitude of load change. The overshoot/undershoot behavior was found to be independent of the ramp rates used to change the load current. The magnitude of overshoot in pressure drop was always larger than the magnitude of undershoot. The pressure drop required a longer time to return to steady state after an undershoot compared to the time required to return from an overshoot incident. 相似文献
Water splitting for H2 production by absorbing sunlight is broadly used as a common technique to counter existing energy crisis and environmental problems, caused by extreme use of fossil fuels. We report a versatile and facile method to fabricate ordered Silicon nanohorns (SiNHs) by employing prefabricated metal nano-gap template on Si. The close-packed monolayer is used to develop the nanohole template, which enables the generation of SiNHs via metal-assisted controlled chemical etching. By varying monolayer parameters and etching sequences, SiNHs with desired dimensions were obtained. Growth along the crystalline plane of the base substrate ?100?, with a consistent bent at the tip of the SiNH, has been observed. The resulting SiNHs exhibited enhanced photoelectrochemical properties, with short-circuit photocurrent density more than four times higher than that of the planer Si along with enhanced trapping of photogenerated carriers. A photocurrent density of ~4.8 mA/cm2 was observed at a potential of -1 V vs. RHE. Further, the electrochemical impedance study (EIS) was carried out to understand the photoelectrochemical activity and charge transfer kinetics of the SiNHs system. These nanostructures enhance light absorption and may be one of the low-cost alternatives for optical devices, sensors, and hydrogen evolution. 相似文献
We report on the complete characterization of a hydride- and hydrogen-free chemical beam epitaxy (CBE) process for the realization
of GaAs/GaInP heterojunction bipolar transistors. Alternative group V sources tertiarybutylarsine, tertiarybutylphosphine,
and trisdimethylaminoarsenic are used instead of traditionally employed AsH3 and PH3. A very high degree of reproducibility of growth parameters (fluxes, substrate temperature, doping levels) is demonstrated.
Total defect densities lower than 10 def/cm2 are routinely obtained. Large-area GaInP/GaAs heterojunction bipolar transistors (HBTs) show a high current gain of 225 for
base sheet resistance of 400 ohm/sq. The devices also exhibit excellent high-frequency characteristics. A cut-off frequency
of 48 GHz and a maximum oscillation frequency of 60 GHz have been obtained. These results demonstrate the high potential capability
of CBE for high-throughput GaInP/GaAs HBT production. 相似文献
#SMT, or model counting for logical theories, is a well-known hard problem that generalizes such tasks as counting the number of satisfying assignments to a Boolean formula and computing the volume of a polytope. In the realm of satisfiability modulo theories (SMT) there is a growing need for model counting solvers, coming from several application domains (quantitative information flow, static analysis of probabilistic programs). In this paper, we show a reduction from an approximate version of #SMT to SMT. We focus on the theories of integer arithmetic and linear real arithmetic. We propose model counting algorithms that provide approximate solutions with formal bounds on the approximation error. They run in polynomial time and make a polynomial number of queries to the SMT solver for the underlying theory, exploiting “for free” the sophisticated heuristics implemented within modern SMT solvers. We have implemented the algorithms and used them to solve the value problem for a model of loop-free probabilistic programs with nondeterminism.
Due to advance technology, rapidly emergent complexity of networks and perseverance on network quality, reliability, and maintainability are progressively significant issues, and hence, the job of reliability analysts is becoming more challenging. A network’s optimum design is required for maintaining the reliability of a sophisticated network at a high level. Reliability of tree topology plays a key role in the measurement of quality of a network and in the performance of a network. Large-scale distributed networks are subject to frequent interruptions due to resource contention and failure. Failure of any component or subsystem affects the performance of the network. This research work has two significant goals: to design a mathematical model of a tree network using the Markov process and supplementary variable technique, and to determine the reliability characteristics such as availability, reliability, and mean time to failure (MTTF). The authors also seek the sensitivity analysis for reliability measures along with the precise values of the input parameters which is very helpful and necessary for attaining a highly reliable network. 相似文献
Due to high velocity of the vehicles, data dissemination and mobile data offloading are most difficult tasks to be performed in vehicular ad hoc networks (VANETs). In recent years, due to an exponential increase in the data generated from various sources such as smart devices, gadgets, and actuators, there arises a need of usage of an efficient communication infrastructure to handle the aforementioned issues. Most of the earlier solutions reported in the literature for data offloading problem have used the cellular communication, which may be congested in handing a large number of requests from community of users. This may result a performance bottleneck in terms of call drops and data dissemination to the other vehicles in the VANET environment. Also, these schemes lack a comprehensive approach of data dissemination to meet the quality of service (QoS) in real time. Hence, to overcome this problem, some of the mobile data can be disseminated using the existing vehicular infrastructure and Wi-Fi access points (APs). In this paper, we propose a new schedule based on game theoretic approach where the APs and vehicles act as players in a game and compete for offloading the cellular data. The proposed scheme is based on the selection of the best vehicle or AP based on the utility of the players (vehicles and APs) in the game. The utility of vehicle and AP is decided based on the parameters such as distance, velocity, connectivity to destination, bandwidth, and area of the network. A novel algorithm has been designed using the proposed game theoretic approach for handling mobile data offloading and data dissemination. The proposed solution not only successfully offloads the data but also maintains QoS with respect to the parameters such as end-to-end delay, message progress, and message dissemination speed. Results obtained confirm the superiority of the proposal in comparison with the other existing schemes. Specifically, the proposed scheme achieves improvement of 4.16 and 20.5 % in message progress, 18.91 and 4.75 % in extra messages generated, 11.26 and 54.94 % in message dissemination speed, and 78.71 and 87.94 % in end-to-end delay in sparse network as compared to GyTAR and GPCR, respectively. 相似文献