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排序方式: 共有432条查询结果,搜索用时 15 毫秒
21.
Sajid Bashir Muhammad Naeem Adnan Ahmed Khan Syed Ismail Shah 《International Journal of Communication Systems》2010,23(1):109-124
The paper discusses a sequence detector based on univariate marginal distribution algorithm (UMDA) that jointly estimates the symbols transmitted in a multiple input multiple output (MIMO) communication system. While an optimal maximum likelihood detection using an exhaustive search method is prohibitively complex, it has been shown that sphere decoder (SD) achieves the optimal bit error rate (BER) performance with polynomial time complexity for smaller array sizes. However, the worst‐case complexity of SD is exponential in the problem dimensions, this brings in question its practical implementation for larger number of spatial layers and for higher‐order signal constellation. The proposed detector shows promising results for this overly difficult and complicated operating environment, confirmed through simulation results. A performance comparison of the UMDA detector with SD is presented for higher‐order complex MIMO architectures with limited average transmit power. The proposed detector achieves substantial performance gain for higher‐order systems attaining a near optimal BER performance with reduced computational complexity as compared with SD. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
22.
A new standard mercury manometer has been developed to calibrate low vacuum gauges in the range from atmospheric pressure to 1 mbar. It consists of a cistern that is a small stainless steel container used as mercury reservoir and also as the first Hg column connected to a long glass tube used as the second Hg column. Manometer scale covers the difference in Hg heights in two columns up to the length equivalent to 1000 mbars. This is a novel low cost manometer with simple design, compact fabrication, better accuracy, easy operation, low vibration, and thermal stability. In order to evaluate the performance of the equipment, its generated pressures are compared with those of secondary standard, i.e., calibrated capacitance diaphragm gauge, giving the average correction factor 0.998. Different uncertainties of the generated pressures are discussed in detail along with the evaluation of correction factors. The relative uncertainty in the higher pressure side is found to be in the range of 10(-4) which is within the limit (approximately 10(-4)). 相似文献
23.
24.
Ho2Si2O7 material exists in four polymorphs, a triclinic low temperature phase (type-B), a monoclinic modification (type-C), high temperature monoclinic (type-D), and high temperature orthorhombic modification (type-E). The structural properties are measured by XRD and the morphology is noted through scanning electron microscopy (SEM). The dc electrical resistivity (ρ) as a function of temperature and dielectric properties of C-type Ho2Si2O7 in the microwave region is measured. The activation energy is calculated from ln ρ versus 1/kBT plot. The activation energy is 0.119 ± 0.001 eV. Both the real (?′) and imaginary parts of permittivity (?″) decrease slightly as the frequency increases up to 1.5 GHz, after that ?′ increases while ?″ decreases as the frequency increases. At around 2.45 GHz, resonance is observed. 相似文献
25.
M. Mumtaz Liaqat Ali M. Nasir Khan M. Usman Sajid 《Journal of Superconductivity and Novel Magnetism》2016,29(5):1181-1186
Nickel ferrite (NiFe2O4) nanoparticles and Cu0.5Tl0.5Ba2Ca2Cu3O10?δ (CuTl-1223) superconductor were prepared separately and then mixed in an appropriate ratios at the final stage to obtain (NiFe2O4) x /CuTl-1223 (x = 0, 0.5, and 1.0 wt%) nano-superconductor composites. There was no significant change observed in crystal structure of the host CuTl-1223 superconducting matrix after the addition of NiFe2O4 nanoparticles. The value of zero-resistivity critical temperature { T c(R = 0) (K)} was decreased with increasing content of these nanoparticles in these composites. Maximum values of dielectric loss tangent (tanδ) at lowest possible frequency of 40 Hz were increased with the increase of operating temperature, while its values were decreased and become almost zero at higher frequencies for all these samples at all operating temperatures. A peak in dielectric loss tangent was shifted towards lower frequency values with the addition of these nanoparticles in CuTl-1223 superconducting matrix. The dielectric loss tangent peak was also shifted towards lower frequency values in all these samples with increasing operating temperature, which shows the relaxator-like behavior in these samples. The dielectric parameters of these composites can be tuned by frequency, operating temperatures, and nature and content of these nanoparticles. 相似文献
26.
Liping Teng Maria Maqsood Min Zhu Yuting Zhou Mingzhu Kang Juan Zhou Jinghua Chen 《International journal of molecular sciences》2022,23(18)
Some scholars have suggested that the clinical application of exosomes derived from human umbilical cord mesenchymal stem cells (hucMSCs-exo) might represent a novel strategy to improve diabetic wound healing. However, the mechanisms underlying the effects of hucMSCs-exo on wound healing remain poorly understood. This study aimed to identify the mechanism of hucMSCs-exo in treating diabetic wounds. HucMSCs-exo were isolated from human umbilical cord mesenchymal stem cells (hucMSCs) and subcutaneously injected into full-thickness wounds in diabetic rats. Wound healing closure rates and histological analysis were performed. The levels of tumor necrosis factor-α (TNF-α), macrophage mannose receptor (MMR/CD206), platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31), and vascular endothelial growth factor (VEGF) were detected by immunohistochemistry. The degree of collagen deposition was examined using Masson’s trichrome staining. Gross evaluation of wound healing was carried out from day 0 to 14 post-surgery, and the wound site was harvested for histology on days 3, 7, and 14 post-wounding. HucMSCs-exo transplantation increased diabetic wound healing. In vitro, hucMSCs-exo promoted the proliferation of human umbilical vein endothelial cells (HUVECs) and NIH-3T3 cells. In vivo, hucMSCs-exo reduced wound area and inflammatory infiltration and increased collagen fibers. In addition, wound tissues in the hucMSCs-exo group had higher CD206, CD31, and VEGF expressions and lower TNF-α levels than those in the control group on day 14. Our results demonstrated that hucMSCs-exo facilitated diabetic wound repair by inducing anti-inflammatory macrophages and promoting angiogenesis and collagen deposition. 相似文献
27.
Bulk superconductors of the (Bi1–x
Pb
x
)2Sr2Ca2Cu3O
y
system have been synthesized by changing the Bi/Pb ratio. The effect of Pb substitution onT
c has been studied by standard d.c. resistivity measurements. An appropriate thermal procedure and time for the preparation of the 110 K phase has also been studied at length. The experiments indicate that the best results are obtained forx=0.2 and that a slow cooling process is necessary for a better control of the thermal process. Indexed X-ray diffraction patterns indicate the lattice parameters of low- and high-T
c phases asa
L=0.54004 nm,b
L=0.5445 nm,c
L=3.084 nm anda
H=0.5483 nm,b
H=0.5339 nm,c
H=3.772 nm, respectively. The observed superconducting behaviour is stable on thermal cycling between 77 and 300 K. 相似文献
28.
Muhammad Issa Khan Muhammad Sajid Arshad Faqir Muhammad Anjum Ayesha Sameen Aneeq-ur-Rehman Waqas Tariq Gill 《Food research international (Ottawa, Ont.)》2011,44(10):3125-3133
Consumers believe that foods are associated directly to their health. Today foods are not only used to satisfy our hunger but also to provide indispensible nutrients for humans and these nutrients having the health benefits regarding in controlling the diseases. The market for functional foods has seen a sharp rise in demand in the recent years. This has driven researchers to multiply their efforts in producing functional meat products also. Feed manipulation and post-mortem modification of meat coupled with enrichment of bioactive compounds are gaining importance. This review discusses the candidate ingredients and strategies, utilized in crafting such functional meat products, and the notable developments and commercial successes in functional meat industry. Dry fermented sausages meet the conditions required to carry viable probiotic microbes. This article enlists various microorganisms that are being commercially used in functional food products and potential bacteria for probiotic sausage production. 相似文献
29.
30.
Sajid Husain M. Kifayatullah G. S. R. Sastry N. Prasada Raju 《Journal of the American Oil Chemists' Society》1993,70(12):1251-1254
Application of13C nuclear magnetic resonance (NMR) spectroscopy for detection of castor oil (CO) in various edible oils, such as coconut oil,
palm oil, groundnut oil and mustard oil, is described. Characteristic signals observed at δ 132.4, δ 125.6, δ 71.3, δ 36.8
and δ 35.4 ppm, due to C10, C9, C12, C13 and C11 carbons of ricinoleic acid (RA) in CO, were selected for distinguishing it
from edible oils. Quantitative13C NMR spectra of oils were recorded in CDCl3 with a gated decoupling technique. The minimum detection limits for qualitative and quantitative analyses were 2.0 and 3.0%,
respectively. The proposed method is simple, nondestructive and requires no sample pretreatment. Its application to heat-abused
oils has also been demonstrated successfully without any of the interferences observed in most other methods. 相似文献