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排序方式: 共有245条查询结果,搜索用时 609 毫秒
91.
Niamat Ullah M. Sanaullah Chowdhury Pervez Khan Sana Ullah Kyung Sup Kwak 《International Journal of Communication Systems》2012,25(1):1-15
The IEEE 802.15.4 standard is designed to provide a low‐power, low data rate protocol offering a high reliability. As an amendment to this standard, IEEE 802.15.4a introduces new options for physical layer to enable precision ranging. In this work, we analyzed the theoretical throughput and delay bounds of the unslotted version of chirp spread spectrum PHY‐based 802.15.4a. The formulae for transmission between one sender and one receiver for an ideal channel with no transmission errors are given. The throughput and delay bounds are derived for different frequency bands and data rates. Additionally, to measure spectral utilization, we measured the bandwidth efficiency for both the standards. We also compared our results with IEEE 802.15.4. The comparative analysis concludes that the performance of 802.15.4a exceeds 802.15.4 in terms of throughput and delay. The analytical results of throughput are verified by computer simulations. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
92.
We analyze a wideband spectrum in a cognitive radio (CR) network by employing the optimal adaptive multiband sensing‐time joint detection framework. This framework detects a wideband M‐ary quadrature amplitude modulation (M‐QAM) primary signal over multiple nonoverlapping narrowband Gaussian channels, using the energy detection technique so as to maximize the throughput in CR networks while limiting interference with the primary network. The signal detection problem is formulated as an optimization problem to maximize the aggregate achievable secondary throughput capacity by jointly optimizing the sensing duration and individual detection thresholds under the overall interference imposed on the primary network. It is shown that the detection problems can be solved as convex optimization problems if certain practical constraints are applied. Simulation results show that the framework under consideration achieves much better performance for M‐QAM than for binary phase‐shift keying or any real modulation scheme. 相似文献
93.
Shumaila Azam Javaid Akhtar Sana Mushtaq Naseer Sheikh 《Energy Sources, Part A: Recovery, Utilization, and Environmental Effects》2016,38(16):2462-2470
This study was carried out for the beneficiation of Dukki (Pakistani) coal using agglomeration technique. The effect of six parameters, particle size, solid to liquid ratio, xylene concentration, agitation speed, agitation time, and pH, was investigated to improve the quality of coal in terms of reduced ash and sulfur content. The clean coal obtained at optimum parameters was found to have 69.25 and 26.6% reduction in ash and sulfur, respectively. The gross calorific value (GCV) increased to 6,377 kcal/kg compared with 5,300 kcal/kg in the original sample. A maximum reduction in ash and sulfur contents was achieved by the following input parameters: particle size, 100 mesh (150 µm); solid to liquid ratio, 20:80 (w/v); xylene dose, 6.8 mL; agitation time, 10 min; pH 7; and stirring speed, 2,520 rpm. Significant reduction in ash (%) and sulfur (%) showed the effectiveness for agglomeration of Dukki coal using xylene as agglomerant. The final product thus obtained may be used efficiently in various energy recovery schemes. 相似文献
94.
B. Satheesh Kumar Balakondareddy Sana G. Unnikrishnan Tushar Jana K. S. Santhosh Kumar 《应用聚合物科学杂志》2019,136(43):48151
In this work, pyridine-based low-molecular-weight polybenzimidazole (LMP) was synthesized (inherent viscosity: 0.52 dL g−1) by controlling the reaction time. The synthesized LMP was incorporated into polydimethylsiloxane (PDMS) matrix to impart proton conductivity. The composite membrane containing 30 wt % of LMP exhibited proton conductivity of 16 mS cm−1 at 100–120 °C. The LMP chains were bundled and formed clusters (aggregates) in the PDMS matrix as observed in field emission scanning electron microscopy. This is attributed to nonpolar (siloxane)–polar (polybenzimidazole) repulsion. An impressive weight loss of 8.6% was observed after 120 h Fenton's test that indicates the high oxidative stability of composite membranes. However, elongation of composite membranes was decreased compared to that of pristine PDMS, which is attributed to the incorporation of rigid LMP chains. The resultant composite membranes exhibited moderate proton conductivity, low moisture absorption, and good thermal stability. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48151. 相似文献
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食品安全风险评估中的不确定性 总被引:1,自引:0,他引:1
食品安全风险评估的整个过程始终伴随着不确定性,其来源大致可分为两类,即结果外推和数据局限性。不确定系数是处理这些不确定性的常用方法,相关组织或机构均推荐了用于制定健康指导值的默认不确定系数,但基准剂量法和化学物特异性调整系数法等方法可更好地处理风险评估中的不确定性。 相似文献
97.
Sana Kouba Frdric Hague Ahmed Ahidouch Halima Ouadid-Ahidouch 《International journal of molecular sciences》2022,23(18)
In the fight against cancer, therapeutic strategies using cisplatin are severely limited by the appearance of a resistant phenotype. While cisplatin is usually efficient at the beginning of the treatment, several patients endure resistance to this agent and face relapse. One of the reasons for this resistant phenotype is the emergence of a cell subpopulation known as cancer stem cells (CSCs). Due to their quiescent phenotype and self-renewal abilities, these cells have recently been recognized as a crucial field of investigation in cancer and treatment resistance. Changes in intracellular calcium (Ca2+) through Ca2+ channel activity are essential for many cellular processes such as proliferation, migration, differentiation, and survival in various cell types. It is now proved that altered Ca2+ signaling is a hallmark of cancer, and several Ca2+ channels have been linked to CSC functions and therapy resistance. Moreover, cisplatin was shown to interfere with Ca2+ homeostasis; thus, it is considered likely that cisplatin-induced aberrant Ca2+ signaling is linked to CSCs biology and, therefore, therapy failure. The molecular signature defining the resistant phenotype varies between tumors, and the number of resistance mechanisms activated in response to a range of pressures dictates the global degree of cisplatin resistance. However, if we can understand the molecular mechanisms linking Ca2+ to cisplatin-induced resistance and CSC behaviors, alternative and novel therapeutic strategies could be considered. In this review, we examine how cisplatin interferes with Ca2+ homeostasis in tumor cells. We also summarize how cisplatin induces CSC markers in cancer. Finally, we highlight the role of Ca2+ in cancer stemness and focus on how they are involved in cisplatin-induced resistance through the increase of cancer stem cell populations and via specific pathways. 相似文献
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This research investigates the impacts of proactiveness, openness to experience, and extraversion on innovative performance among engineers. The work also examines the mediating role of knowledge sharing. Using a person–situation interaction perspective, the study further explores the moderating role of perceived organizational support (POS) in personality–knowledge sharing relationships. Data collected from engineers (N = 183) across various public and private engineering firms in Pakistan reveal that knowledge sharing mediated the relationship of proactiveness and extraversion with innovative performance. In addition, highly proactive and extraverted engineers are more likely to share knowledge when the POS is high. Contrary to the expectations, engineers who highly exhibit openness to experience are less likely to share knowledge under high POS. These findings provide significant contributions to the theory and practice of engineering management by highlighting the essential link of personality traits with knowledge sharing and innovation among engineers. 相似文献