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71.
Multiple input multiple output (MIMO) systems showed good utilization of channel characteristics. In MIMO systems multiple
signals are transmitted using multiple antenna system. This provides each receiver the combined signals and hence, array processing
techniques helps in reducing the effects of interference among them. In this paper we devise the use of pre-coded MIMO system
to reduce the effects of frequency selectivity and hence, enhance the systems capacity and/or reduce the bit error rate. In
this technique we introduce a temporal pre-coder on each antenna signal; this creates a deterministic multi-path signals similar
to signals received when the channel is multi-path fading channel. The same antenna signal will arrive at each receiver forming
orthogonal sub-space and the receiver will be simple add and delay of the received signals. Ant colony optimization is used
in this paper to select the best pre-code. Results showed that we can diagonalize the channel matrix and practically eliminate
the interference for frequency selective fading channel. Simulation of two transmitting two receiving antennas pre-coded MIMO
system showed that the capacity can be doubled. 相似文献
72.
Abolfazl Shoja Mohamad Ali Adabi Masoud Ahmadnia Jamal Zamani 《Propellants, Explosives, Pyrotechnics》2014,39(4):574-579
In most blast loading structure analyses, it is assumed that the load acts uniformly on a target area. For the rationable design, it is useful to have a quantitative criterion to determine at which maximum distance the standoff can be placed to assume a uniform pressure distribution. Surprisingly, no standard criterion was found in the literature and the effect of blast wave clearing was not considered as well. In this paper, pressure histories applied on structures are calculated considering the non‐uniform loading characteristic as well as pressure relief from the edges. Additionally, the effects of various parameters on uniformity of impulse distribution are investigated. The results have shown that the effect of pressure relief on impulse uniformity is very important, especially when the blast wave is attenuated. This phenomenon leads an optimum distance at which impulse distribution is the most uniform. 相似文献
73.
Mohammad Amin Adibi Jamal Shahrabi 《The International Journal of Advanced Manufacturing Technology》2014,70(9-12):1955-1961
The dynamic job shop scheduling (DJSS) problem occurs when some real-time events are taken into account in the ordinary job shop scheduling problem. Most researches about the DJSS problem have focused on methods in which the problem’s input data structure and their probable relationship are not considered in the optimization process while some useful information can be extracted from such data. In this paper, the variable neighborhood search (VNS) combined with the k-means algorithm as a modified VNS (MVNS) algorithm is proposed to address the DJSS problem. The k-means algorithm as a cluster analysis algorithm is used to place similar jobs according to their processing time into the same clusters. Jobs from different clusters are considered to have greater probability to be selected when an adjacent for a solution is made in an optimization process using the MVNS algorithm. To deal with the dynamic nature of the problem, an event-driven policy is also selected. Computational results obtained using the proposed method in comparison with VNS and other common algorithms illustrate better performance in a variety of shop floor conditions. 相似文献
74.
Current performance of food safety management systems of dairy processing companies in Tanzania
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Jamal B Kussaga Pieternel A Luning Bendantunguka P M Tiisekwa Liesbeth Jacxsens 《International Journal of Dairy Technology》2015,68(2):227-252
A food safety management system (FSMS)‐diagnostic instrument was applied in 22 dairy processing companies to analyse the set‐up and operation of core control and assurance activities in view of the risk characteristics of the systems' context. Three clusters of companies were identified differing in levels of set‐up and operation of this FSMS and system outputs, but all operated in a similar moderate‐risk context. Microbiological assessment of products, environmental and hand samples indicated a poor to moderate food safety level. A two stage intervention approach has been proposed to enable commitment and sustainable improvement for the longer term. 相似文献
75.
Yousof Gheisari Hamed Pashazadeh Jamal Teimournezhad Abolfazl Masoumi 《Journal of Materials Engineering and Performance》2014,23(6):2000-2006
This work was undertaken to explore the formation of weld defects in FSWed copper metals via both numerical and experimental approaches. The 4 mm-thick copper sheets were friction stir welded at a tool rotational speed of 710 rpm and tool translational speed of 40 mm/min. Microstructural evaluations were performed on the welded specimens. Also a 3D arbitrary Lagrangian Eulerian numerical model was developed to obtain temperature and material velocity profiles. To this aim, DEFORM-3D was implemented for developing the numerical simulation. Numerical results for temperature values showed good agreement with the recorded experimental data. They also suggest that on the advancing side (AS) of the trailing side, the pin velocity has the minimum amount (zero), and this is the main reason for the formation of tunneling cavity. Experimental results show that a force is created between the reminder of material at the joint and the rim of AS. This force causes a prong of surface material from the AS rim to penetrate into lower parts of weld. It seems that the inadequate pressure (low values of the plunge depth), inadequate surface materials, and the trapped air are the main causes for the formation of the weld defects. 相似文献
76.
Polyaniline-supported acid salts such as polyaniline-hydrochloride, polyaniline-sulfate and polyaniline-nitrate were prepared by oxidation of aniline using ammonium persulfate as oxidizing agents. Polyaniline salts were used as catalyst for the preparation of β-acetamido ketones. Polyaniline-sulfate salt was found to be the best catalyst for the preparation of β-acetamido ketones. Present methodology offers several advantages, such as cheaper process, easy synthesis of stable catalyst, simple work-up procedure, and excellent activity with less amount of catalyst and in addition, the catalyst can be easily recovered after completion of the reaction and reusable without affecting its activity. 相似文献
77.
Natalia Candu Simona Coman Vasile I. Parvulescu Jamal El Haskouri Pedro Amoros Daniel Beltran 《Topics in Catalysis》2009,52(6-7):571-578
Strong Lewis acid SnTf-MCM-41 and SnTf-UVM-7 catalysts with unimodal and bimodal pore systems were prepared in a two-step synthesis in which the triflic acid (Tf) was incorporated into previously synthesized mesoporous tin-containing silicas. The Sn incorporation inside the pore walls was carried out through the Atrane method. The SnTf-UVM-7 catalysts were prepared by aggregating nanometric mesoporous particles defining a hierarchic textural-type additional pore system. Catalysts with different Si/Sn ratios in the range 21.8–50.8 for SnTf-MCM-41 and 18.4 for SnTf-UVM-7 were found to be efficient catalysts for the acylation of aromatics and heteroaromatics. Under microwave irradiation the reaction was possible even with acetic acid. The selectivity to the desired product (o-hydroxyacetophenone for phenol) or the unfavored three-substituted five ring heterocycles was dramatically increased under these conditions. The process is green, environmentally safe, and heterogeneous. 相似文献
78.
Compensation of the liquid crystal layer within twisted nematic displays operating in normally white and normally black modes was examined. Studies of commercially available compensation films allowed us to develop the optimum compensating configuration for normally white displays including negative C-plates, discotic splay layers and A-plates. The optimum compensation of the normally black display mode was achieved using a stack of A-plates. The compensation provides a wide viewing cone and no gray-scale inversion in the most important viewing directions for both optimized display types. The compensated devices exhibit an achromatic dark state. 相似文献
79.
Mohsen Gavahian Asgar Farahnaky Mahsa Majzoobi Katayoun Javidnia Mohammad Jamal Saharkhiz Gholamreza Mesbahi 《International Journal of Food Science & Technology》2011,46(12):2619-2627
Ohmic‐assisted hydrodistillation (OAHD) is a combination of ohmic heating and distillation, and could be considered as a novel method for the extraction of essential oils. Major problems with traditional methods are long extraction time and lower purity of the extract. In this study, OAHD was applied as an economic and green technology for the extraction of essential oils from Zataria multiflora Boiss. (Shirazi thyme) aerial parts and the results were compared to those obtained from hydrodistillation (HD) as a conventional method. The results showed that OAHD method had the extraction time of 32.21 ± 2.59 min while this value was about 57.21 ± 2.33 min for hydrodistillation (HD). Scanning electron micrographs of thyme leaves showed a sudden eruption of essential oil glands and their surrounding area for OAHD samples. GC–MS analysis indicated that both methods of OAHD and HD can extract the same compounds. 相似文献
80.