We are interested in the modeling and control of a salt gradient solar pond (SGSP) in the south of Tunisia. We developed a model of a closed cycle salt gradient solar pond (CCSGSP) that ensures successful year round operation. This model was used to study the response of the solar pond (SP) to various control techniques. It takes into account heat and salt diffusion within the pond and simulates the transient behavior of a SGSP. Furthermore, we investigated the dynamic process, which involves internal gradient stability, boundary behavior between the gradient zone and the convective zones. We thus incorporated the double diffusive processes into the SP model by using the one dimensional stability criterion produced by linear theory. The governing differential equations are solved numerically by using a control-volume scheme.The results show that successful operation of a SP requires three things: the maintenance of the storage zone temperature through heat extraction and brine injection, the use of surface washing to control the deepening of the upper mixed layer and a well designed initial salt stratification to prevent the formation of instability within the gradient. Using linear salinity profile as an initial condition, three round year simulations were run using average meteorological data with the result that adequate stability (Rρ2 throughout the gradient and Rρ10 at the interfaces) was maintained. Numerical results show also that 10–30% efficiency could have been reached if heat extraction is performed routinely especially when one considers that the storage temperature is within 40–80 °C. The model is validated against data taken from the operation of the UTEP SP. Close correlation between computed and measured data was obtained. 相似文献
Organic wastes were successfully used as soil amendment to improve agrosystems productivity. Yet, the effectiveness of this practice to enhance plant antioxidant capacities has received little attention. Here, we assess the effect of municipal solid waste (MSW) compost (at 40 t ha(-1)) on growth, polyphenol contents and antioxidant activities of Mesembryanthemum edule. MSW compost application significantly increased the soil contents of carbon, nitrogen, calcium, phosphorus and potassium. This was associated with higher nutrient (N, P, and K) uptake, which likely led to the significant improvement of the plant biomass and relative growth rate (RGR) (+93% on average) as compared to the control. In the same way, the fertilizing effect of the added organic matter significantly enhanced the antioxidant potential M. edule, assessed by radical scavenging activity, iron reducing power and β-carotene bleaching capacity. This was associated with significantly higher antioxidant contents, mainly total phenols and flavonoids. Heavy metal (Pb, Cd, Cu, and Zn) concentrations were slightly increased upon compost application, but remained lower than phytotoxic values. Overall, our results point out that short-term MSW compost application at 40 t ha(-1) is efficient in enhancing the productivity together with the antioxidant potentiality of M. edule without any adverse environmental impact. 相似文献
This paper presents a performance study for two well known quantized based watermarking schemes Scalar Costa Scheme (SCS), and Trellis Coded Quantization scheme (TCQ) in an independent domain. For our study, the independent domain is obtained by the combination of the cited schemes with Independent Component Analysis (ICA). The Independent Component Analysis is used while inserting and extracting the message. Thus a performance compromise improvement of the original SCS and TCQ schemes in terms of robustness, capacity, and security is shown. Then the obtained schemes performances are compared to the Spread Transform (ST) based scheme well known for its proven good robustness properties. Our results show that, using watermarking with side information in independent domain permits to improve the global SCS and TCQ schemes performances. For example, in the case of SCS, by studying the Bit Error Rate (BER) in function of the watermark to noise ratio (WNR), the robustness has been improved by 20 dB (1 decade) when WNR is equal to 0 dB. Moreover, the capacity study shows for the same WNR=0 dB, the amount of information to be transmitted without error for a given noise level of the proposed SCS combined with ICA scheme (SCS-ICA) is much higher than that of the existing schemes. Finally, the study of the probability density functions (PDF) of the original and marked signals has shown that the Cachin-security level of the TCQ in an independent domain scheme (TCQ-ICA) is the best one compared to the other known schemes. 相似文献
In ultrasonic testing of welds, detection of small flaws is often difficult by the superimposed noise due to the grain structure of the material. The scattering of ultrasonic waves from grain boundaries can interfere and introduce disturbance in the received signal that can sometimes mask indications due to a small but potentially dangerous defect. However, to enhance the flaw characterization, methods based on ‘thresholding’ have given good results only when the signal to noise ratio is high, and since bandwidth of the reflected signal as well as its principal frequency is subject to wide variation, it is impossible to create an appropriate band pass filter. So linear filtering does not provide good results, because both, the structure noise and flaw signal concentrate energy in the same frequency band. Non-linear filtering can be used to reduce or suppress the noise from ultrasonic signals. One way out is to use the time frequency transforms, the method is based on the wavelet packet decomposition. The Debauchee function of order 8 [Daubauchee I. Orthogonal bases of capacity wavelets. Commun Pure Appl Math 1998;41] has been chosen as the analyzing function, and each measured ultrasonic signal is analyzed by a filter bank through only three levels of decomposition. This work demonstrates that the following analysis is very efficient with respect to signal recovery from noisy data. The experimental results have shown that the proposed method has excellent performances on SNR enhancements. 相似文献
Despite the multiple benefits offered today by connected mobile objects networks (CMONs), some constraints continue to limit their development and to degrade their applications and services’ performance. Given their limited energy, some or many objects may stop functioning which leads to the deterioration of network functionalities such as monitoring, detection and transfer of data. It is in this context that our work is situated, namely the improvement of applications performance and the quality of service (QoS) within CMONs, by exploiting some communication environment parameters and geometry techniques. We propose a new technique called self-organization area coverage (SOAC) for CMONs which aims to ensure maximum coverage in the network while optimizing the exploited resources. SOAC has been evaluated and compared not only to the network without improvement but to two other solutions proposed in the literature. The obtained results show a clear improvement in terms of network coverage and several QoS parameters. 相似文献
Digital watermarking is the art of hiding information in a digital document in order to protect it. The inserted mark and the marked document can be an image, an audio or a video. In this article, we will present a comparative study between two variants of a digital audio watermarking technique operating in the frequency domain. In the first variant, the time-frequency mapping is performed by Modified Discrete Cosine Transform (MDCT). For the second variant, the time-frequency mapping is performed by the Discrete Cosine Transform (DCT). We will study the contribution of each transformation, point of view robustness against different types of attacks delivered by Stirmark audio, imperceptibility by using a statistical approach by calculating the SNR and an objective approach by calculating the ODG notes given by PEAQ and capacity of insertion. Finally, to highlight our results, we will compare the two variants of the proposed technique with some other existing techniques.
The concept of city or urban resilience has emerged as one of the key challenges for the next decades. As a consequence, institutions like the United Nations or Rockefeller Foundation have embraced initiatives that increase or improve it. These efforts translate into funded programs both for action “on the ground” and to develop quantification of resilience, under the for of an index. Ironically, on the academic side there is no clear consensus regarding how resilience should be quantified, or what it exactly refers to in the urban context. Here we attempt to link both extremes providing an example of how to exploit large, publicly available, worldwide urban datasets, to produce objective insight into one of the possible dimensions of urban resilience. We do so via well-established methods in complexity science, such as percolation theory—which has a long tradition at providing valuable information on the vulnerability in complex systems. Our findings uncover large differences among studied cities, both regarding their infrastructural fragility and the imbalances in the distribution of critical services. 相似文献
This paper introduces a novel diagnosis approach, using game theory, to solve the comparison-based system-level fault identification problem in distributed and parallel systems based on the asymmetric comparison model. Under this diagnosis model tasks are assigned to pairs of nodes and the results of executing these tasks are compared. Using the agreements and disagreements among the nodes’ outputs, i.e. the input syndrome, the fault diagnosis algorithm identifies the fault status of the system’s nodes, under the assumption that at most t of these nodes can permanently fail simultaneously. Since the introduction of the comparison model, significant progress has been made in both theory and practice associated with the original model and its offshoots. Nevertheless, the problem of efficiently identifying the set of faulty nodes when not all the comparison outcomes are available to the fault identification algorithm prior to initiating the diagnosis phase, i.e. partial syndromes, remains an outstanding research issue. In this paper, we first show how game theory can be adapted to solve the fault diagnosis problem by maximising the payoffs of all players (nodes). We then demonstrate, using results from a thorough simulation, the effectiveness of this approach in solving the fault identification problem using partial syndromes from randomly generated diagnosable systems of different sizes and under various fault scenarios. We have considered large diagnosable systems, and we have experimented extreme faulty situations by simulating all possible fault sets even those that are less likely to occur in practice. Over all the extensive simulations we have conducted, the new game-theory-based diagnosis algorithm performed very well and provided good diagnosis results, in terms of correctness, latency, and scalability, making it a viable addition or alternative to existing diagnosis algorithms. 相似文献
The collision prevention system is one of most important research issues on vehicle safety technology. Sending worming messages within the right time and reliable transmission will get prevention of a possible vehicle accident. The communication standards of vehicular networks (VANET) are unable to guarantee the delivery of critical messages within tight deadlines. Indeed, the transmission collisions are handled with probabilistic manner that can reduce the transmission latency; however, it is inept to predict an upper bound value of this delay to verify the deadline. In this paper, we propose a medium access protocol that ensures the delivery of critical messages within a deadline. It is a hard real-time system with delay constant guarantee. We are focusing on improving the EDCA medium access protocol to prioritize critical messages and to get access to the transmission channel within a predictable communication delay. We create a new enhanced access protocol that is compatible with the IEEE 802.11p VANET standards and adapted to real-time communication requirements related to the vehicle collision avoidance problem. 相似文献
Drilling and fastening of hybrid materials in one-shot operation reduces cycle time of assembly of aerospace structures. One of the most common problems encountered in automatic drilling and riveting of multimaterial is that the continuous chips curl up on the body of the tool. Drilling of carbon fiber reinforced plastic (CFRP) is manageable, but when the minute drill hits the aluminium (Al) or titanium (Ti), the hot and continuous chips produced during machining considerably damage the CFRP hole. This study aims to solve this problem by employing nano-coated drills on multimaterial made of CFRP and aluminium alloy. The influence of cutting parameters on the quality of the holes, chip formation and tool wear were also analyzed. Two types of tungsten carbide drills were used for the present study, one with nano-coating and the other, without nano coating. The experimental results indicated that the shape and the size of the chips are strongly influenced by feed rate. The thrust force generated during drilling of the composite plate with coated drills was 10–15% lesser when compared to that generated during drilling with uncoated drills; similarly, the thrust force in the aluminium alloy was 50% lesser with coated drills when compared to thrust force generated without coated drills. Thus, the use of nano-coated drills significantly reduced the surface roughness and thrust force when compared with uncoated tools. 相似文献