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1.
设G是p≥2阶几乎无桥的简单连通K3—free图,且若对任何相距为1的两条边e0及e1,有d(e0)+d(e1)≥p+3,则G有一个D—闭迹,从而G的线图L(C)是哈密顿的.  相似文献   

2.
炭/炭复合材料MoSi2/SiC抗氧化涂层的研究   总被引:1,自引:0,他引:1  
采用包埋法制备C/C复合材料抗氧化MoSi2/SiC梯度涂层,同时对抗氧化涂层的形成、组织结构以及抗氧化性能与渗料的关系和抗氧化机理进行了研究。结果表明:采用包埋法制备的C/C复合材料抗氧化MoSi2/SiC梯度涂层致密,但有少量裂纹,涂层有良好的抗氧化效果。当硅与SiC保持一定的比例,渗料中MoSi2的含量为50%时,涂层具有最好的抗氧化效果;当MoSi2与SiC保持一定的比例,渗料中硅的含量为20%时,涂层具有最好的抗氧化效果。  相似文献   

3.
本文通过逆向矩阵计算和对比模拟实验确定了诺兰达过程的合理冰铜品位和合理渣型,指出合理冰铜品位和合理渣型相当大程度是围绕渣含铜引出的,探讨了影响诺兰达过程渣含铜的主要因素与降低渣含铜的主要措施.本文还证明:用渣带走铜分率=1-铜分配系数/(铜分配系数+炉渣重量/冰铜重量)这一表达式分析渣含铜的影响是合理的.  相似文献   

4.
试样经盐硝混合酸溶解,以过氧化氢将亚磷酸氧化成正磷酸,在酸性介质中,加入钒酸铵和钼酸铵与磷酸形成黄色的磷钒钼三元杂多酸,从而进行磷的测定。磷钒钼三元缔合物形成的适宜酸度为C(H^+):0.2~1.6mol/L。酸度过高则显色过慢,甚至抑制显色反应的完成,酸度太低则硅干扰,所以,含硅铜合金试样酸度不应低于C(H^+)=0.5mol/L。  相似文献   

5.
反应熔渗法制备C/C-SiC复合材料及其影响因素的研究进展   总被引:8,自引:0,他引:8  
本文比较了C/C-SiC复合材料的三种主要制备方法,主要介绍了反应熔渗法制备工艺,以及液Si渗入C/C多孔体,液Si与固体C反应和C/C-SiC复合材料性能的主要影响因素,提出了尚待解决的关键问题。  相似文献   

6.
对浸渍前后C/C复合材料抗弯强度、剪切强度和耐压强度进行了对比,分析了浸渍工艺过程对C/C复合材料力学性能的影响。结果表明,浸渍工艺对C/C复合材料力学性能有明显提高,抗弯强度由浸渍前的101MPa提高到浸渍后的159MPa,剪切强度由浸渍前的8.6MPa提高到浸渍后的12.1MPa,耐压强度由浸渍前的82MPa提高到浸渍后的136MPa。分析浸渍前后C/C复合材料断口的扫描电镜照片,得出浸渍工艺与CVD工艺的生长层具有类似的微观结构。  相似文献   

7.
研究了含有乙二胺和羧基的聚丙烯腈纤维的离子交换性能。该纤维对Cu2+,Cd2+,Cr3+,Co2+,Mn2+,Ni2+,Pb2+,Hg2+和Zn2+等重金属离子的最大交换容量分别为1.19,0.96,0.80,0.92,0.96,0.96,0.66,0.65和0.99mmol/g(干)。按其分配系数大小和对各离子的选择性的次序各离子分别为Co2+>Zn2+>Cu2+>Ni2+>Mn2+>Pb2+>Cd2+>Cr3+>Hg2+。该离子交换纤维可用于废水中的重金属离子的去除。  相似文献   

8.
应用热压技术制备了添加不同含量Cr3C2和(W,Ti)C的Al2O3/Cr3C2/(W,Ti)C复合陶瓷材料。利用光学显微镜、环境扫描电镜、透射电镜和能谱分析仪等对~203/30%Cr3C2、Al2O3/30%(W,Ti)C、Al2O3/20%Cr3C2/10%(W,Ti)C三种复合陶瓷材料的显微组织结构进行了观察分析。研究表明:同其它两种材料相比,Al2O3/20%Cr3C2/10%(W,Ti)C陶瓷复合材料组织细化均匀,有连续骨架结构生成。Cr3G和(W,Ti)C颗粒的共同加入有利于晶粒生长的制约,裂纹分枝与偏转、晶粒拔出、以及纳米相等等,有效提高了氧化铝陶瓷材料的力学性能。  相似文献   

9.
C/C复合材料是一种良好的抗烧蚀和耐高温结构材料,广泛地应用于航天航空各领域。在此,作者综述了C/C复合材料烧蚀性能的测试方法、烧蚀机理、烧蚀模型以及抗烧蚀的研究状况。  相似文献   

10.
A new resource-saving duplex stainless steel with composition of 19Cr-6Mn-1.0Mo-0.5Ni-0.5W-0.5Cu-0.2N has been developed,and the microstructure,mechanical properties and corrosion properties have been investigated.The results show that the alloy has a balanced ferrite-austenite relation,and the ferrite content rises with the solution treatment temperature.The designed alloy is free of precipitation of sigma phase when aged at 650,750 and 850 ℃ for 3 h,respectively,whereas a few Cr23C6 precipitates are found...  相似文献   

11.
12.
Material-specific memory refers to the ability to learn and recall new episodic information on the basis of the nature of the stimulus material (e.g., verbal vs. nonverbal-visuospatial). Structural equation modeling was used to analyze data from a sample of patients with traumatic brain injury to compare 3 models of memory functioning: material-specific, material-specific plus general, and general (non-material-specific). The models were examined separately for acquisition, delayed free recall, and retention aspects of memory. Results suggest that, at least in a population with traumatic brain injury, the acquisition of new information takes place in a material-specific memory fashion, delayed free recall involves both material-specific and general (non-material-specific) memory components, but retention relies primarily on general (non-material-specific) memory processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   

13.
The residual fluctuations that naturally arise in experimental inquiry are analyzed in terms of their time histories. Although these fluctuations are generally relegated to a statistical purgatory known as unexplained variance, this article shows that they may harbor a long-term memory process known as 1/f noise. This type of noise has been encountered in a number of biological and physical systems and is theorized to be a signature of dynamic complexity. Its presence in psychological data appears to be associated with the most elementary aspect of cognitive process, the formation of representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   

14.
An individual-differences approach was used to examine the component processes that predict episodic long-term memory performance. A total of 301 participants ages 20-90 received a 7-hr cognitive battery across 3 days. Key constructs hypothesized to affect long-term memory function were assessed, including multiple measures of working memory and perceptual speed. Latent-construct, structural equation modeling was used to examine the relationship of these measures and age to different types of long-term memory tasks. Speed was a key construct for all 3 types of memory tasks, mediating substantial age-related variance; working memory was a fundamental construct for free and cued recall but not spatial memory. The data suggest that both speed and working memory are fundamental to explaining age-related changes in cognitive aging but that the relative contributions of these constructs vary as a function of the type of memory task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   

15.
Twenty-four students from a diving school undertook a hyperbaric chamber dive to a pressure equal to 36 m of seawater. Tests of cognitive function and manual dexterity, performed in the chamber during the 35-min bottom time and before, or after, the dive included immediate and delayed free recall of words presented as 7 lists of 15 each, recognition of previously presented words, number identification, and a forceps pickup of ball bearings. Delayed free recall and immediate free recall (primacy region) were significantly impaired, whereas manual dexterity and recognition memory were not. These are in keeping with previously reported findings but indicate that significant impairment of memory may occur in experienced divers at operational depths for air diving. Lack of effect on recognition memory suggests that cueing strategies might be useful for debriefing divers. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   

16.
The serial position function, with its characteristic primacy and recency effects, is one of the most ubiquitous findings in episodic memory tasks. In contrast, there are only two demonstrations of such functions in tasks thought to tap semantic memory. Here, we provide a third demonstration, showing that free recall of the prime ministers of Canada also results in a serial position function. Scale Independent Memory, Perception, and Learning (SIMPLE), a local distinctiveness model of memory that was designed to account for serial position effects in episodic memory, fit the data. According to SIMPLE, serial position functions observed in episodic and semantic memory all reflect the relative distinctiveness principle: items will be well remembered to the extent that they are more distinct than competing items at the time of retrieval. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   

17.
We examined the relationship between low levels of serum vitamin B?? (N?=?250) were selected from a group of nondemented, community dwelling persons ages 75–96. Episodic memory was tested by means of free recall and recognition of slowly and rapidly presented words. Results indicated a deterioration in both free recall and recognition as a function of serum vitamin status. However, no linear effects of vitamin levels on memory were observed, indicating that vitamin B?? and folic acid status may affect memory only among individuals at the low end of the distribution. We speculate that the vitamin-related memory deficit may reflect encoding problems, possibly due to alterations in brain metabolism. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   

18.
It has been proposed that DBA/2 and C57BL/6 mice perform differently on some learning and memory tasks because of functional differences in the hippocampal formation. To evaluate this hypothesis, DBA/2 and C57BL/6 male mice were tested on 2 forms of conditioned fear: contextual fear conditioning, which depends on the integrity of the hippocampal formation, and auditory cue conditioning, which does not. Both mouse strains displayed equivalent conditioning when the auditory cue was paired with shock, but DBA/2 mice showed significantly less conditioning to the context in which shock was experienced. These results are consistent with the hypothesis that the pattern of spared and impaired performance, which DBA/2 mice display on a variety of learning and memory tasks, is related to impaired hippocampal formation function. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   

19.
Examined effortful and automatic memory task performances in 36 schizophrenic patients and 18 normal controls. Tasks included free recall, recognition, and frequency estimation. Patients demonstrated impairment in recall, in recognition, in semantic encoding, and in frequency estimation. Deficits were observed across tasks despite differences in attentional demands. Results suggest a basic compromise of memory function, which is consistent with recent neuroimaging evidence of structural or physiological abnormalities in frontal and temporal lobe structure in schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   

20.
The present study tested the dual-component model of working memory capacity (WMC) by examining estimates of primary memory and secondary memory from an immediate free recall task. Participants completed multiple measures of WMC and general intellectual ability as well as multiple trials of an immediate free recall task. It was demonstrated that there are 2 sources of variance (primary memory and secondary memory) in immediate free recall and that, further, these 2 sources of variance accounted for independent variation in WMC. Together, these results are consistent with a dual-component model of WMC reflecting individual differences in maintenance in primary memory and in retrieval from secondary memory. Theoretical implications for working memory and dual-component models of free recall are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   

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