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1.
利用化学共沉淀法制备了磁性Fe3O4纳米微粒,用硅烷偶联剂MPS对所制备的磁性微粒进行表面有机改性,并用FTIR、XRD、TEM、XPS等表征方法对样品进行了表征,结果表明:MPS已经很好地键连到了磁性Fe3O4纳米微粒的表面。改性的磁性Fe3O4纳米微粒具有亲水和亲油两种性质,采用改性后的磁性微粒可以显著改善磁性微球的性能指标。 相似文献
2.
Mark Stanton 《Learning & behavior》1983,11(4):415-423
Sprague-Dawley rat pups aged 14 or 18 days were trained on a patterned (single) alternation schedule with either an 8- or a 105-sec intertriai interval (ITI). At the 8-sec ITI, alternation learning was obtained at both ages, but the older age group learned more rapidly. There was no evidence of response alternation at the 105-sec ITI at either age. Continuously reinforced (CRF) and partially reinforced (PRF) groups trained and extinguished along with the patterned alternation (PA) group at the 105-sec ITI showed a robust partial reinforcement extinction effect (PREE) at both ages. Moreover, there was no difference in the rate of extinction of the PRF and PA groups at either age (i.e., no effect of N-length). A PREE can therefore be obtained in infant rats under conditions that apparently preclude the formation of sequential associations. The implications of this finding for the ontogeny of instrumental learning and extinction are discussed. 相似文献
3.
利用化学共沉淀法制备了磁性Fe3O4纳米微粒,用硅烷偶联剂MPS对所制备的磁性微粒进行表面有机改性,并用FTIR、XRD、TEM、XPS等表征方法对样品进行了表征,结果表明:MPS已经很好地键连到了磁性Fe3O4纳米微粒的表面。改性的磁性Fe3O4纳米微粒具有亲水和亲油两种性质,采用改性后的磁性微粒可以显著改善磁性微球的性能指标。 相似文献
4.
A 3D multi-time scale discrete element method-computational fluid dynamic (DEM-CFD) coupling approach was applied to investigate the filtration of micron-sized particles by different types of fiber arrays. Both the pressure drop and the filtration efficiency were examined to indicate the filtration performance of the fiber arrays. Fibers that were uniformly arrayed in a parallel or staggered manner were compared. Results showed that the staggered array showed a better performance than the parallel array in terms of both pressure drop and filtration efficiency. Further, we compared the performance of different staggered arrays, i.e. a regular case, one densified in the front layers and another densified in the back layers. The front densified array was found to enter the clogging and cake filtration stage in the shortest time, leading to the highest filtration efficiency, but the highest pressure drop. The back densified array still achieved a much higher filtration efficiency, despite a much lower pressure drop comparable to that of the regular array. The results suggest that the two kinds of densified arrays may be suited for different purposes, e.g. baghouse filters or breathing masks. 相似文献
5.
The reaction of ZnO nanoparticles grafted with KH570 silane coupling agent was carried out in water-alcohol mixed solvent. Several characterization methods were applied to analyzing the results of surface modification such as Soxhlet extraction, Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), thermogravimetry (TG), differential scanning calorimetry (DSC) and zeta potential (ζ). The results of FT-IR and TG-DSC show that the desired reaction chains have been covalently bonded on the surface of ZnO nanoparticles. Zetasizer results reveal that themaximal absolute value of ζ of the modified ZnO particles in acetone medium was 67.0 mV, which was much higher than that of the unmodified ZnO particles. So the surface of nanosized ZnO changed from hydrophilicity to hydrophobicity and the dispersity of ZnO nanoparticles were improved simultaneously. Finally, the mechanism of graft modification was discussed. 相似文献
6.
The consequences in adulthood of bullying, teasing, and other peer victimization experiences in childhood rarely have been considered in prospective studies. Studies of peer victimization are mixed regarding whether negative outcomes are explained by pre-existing child vulnerabilities. Furthermore, replication of prior studies with broader definitions and other methods and demographic groups is needed. Based on mother, father, and teacher reports at ages 10–12 years, we classified American boys (n = 206) from higher delinquency neighborhoods as perpetrators of teasing, victims, perpetrator–victims, or uninvolved (n = 26, 35, 29, and 116, respectively). Family income, parent and child depressive symptoms, and child antisocial behavior served as controls. Boys were assessed to age 34 years for suicide-attempt history (including death) and adult (ages 20–32 years) suicidal ideation, depressive symptoms, alcohol use, patterned tobacco and illicit drug use, and arrest. Relative to uninvolved boys, means or odds were higher for: suicide attempt among perpetrator–victims; all three groups for depressive symptoms and clinically significant symptoms; arrest for perpetrators and perpetrator–victims; number of arrests and violent arrest among perpetrator–victims; and patterned tobacco use among perpetrators and perpetrator–victims. With childhood vulnerabilities controlled, however, odds remained higher only for suicide attempt among perpetrator–victims, and criminal arrest and patterned tobacco use among perpetrators. Overall, childhood involvement in teasing predicted serious adverse outcomes in adulthood, in some cases beyond childhood risks. Programs that prevent peer victimization and identify already involved individuals for additional services may have positive impacts on the diverse public health problems of suicide, crime, depression, and tobacco use. 相似文献
7.
Pigeons were trained to discriminate between arrays containing equal numbers of two different elements as S+, and arrays which contained more elements of one kind than the other as S?. They were then tested with the full range of the proportions of the two elements. This resulted in behavioral contrast and peak shift, as the pigeons responded more to arrays containing more positive than negative elements than they did to the positive training arrays. These findings were obtained with elements that differed in color (blue vs. red dots) and with elements that differed in orientation (horizontal vs. vertical rectangles). The results indicate that the stimulus control exerted by the derived dimension of relative numerosity involves the same processes as the fundamental dimensions that characterize simple stimulus elements. 相似文献
8.
In a random sample of 500 admissions to a residential treatment center for chemically dependent adolescents. 150 cases of physical and sexual abuse had been identified. These adolescents were matched for age, race, and socioeconomic status, with two comparison groups: a group of nonabused chemically dependent adolescents and a group of nonabused, nonchemically dependent adolescents. Self-esteem was measured, utilizing the Tennessee Self-Concept Scale (TSCS), which was administered to all subjects. The abused, chemically dependent adolescents were found to demonstrate significantly lower self-esteem on all subscales when analyzed against these two comparison groups. There were negligible differences within the abused group when the TSCS scores were analyzed according to type of abuse. Aggressive/physically abused adolescents scored higher on the Physical Self subscale and the incest group scored significantly lower on the Identity subscales. These results suggest that abuse is equally devastating, regardless of the type of abuse, e.g., physical, sexual, incest, and has a long-lasting impact on self-esteem. 相似文献
9.
应用FDTD方法分析TEM喇叭天线阵列的瞬态辐射特性，分析了阵列单元之间的互耦对天线阵列远场辐射的影响。TEM喇叭天线阵列单元沿E面叠状排列可以改善阵列的低频辐射。原理上阵元越多，天线阵列的增益越高。而线性阵列只压缩一个面的方向图。改变阵列单元间馈入信号的时延，可以实现阵列方向图主辩方向的偏移。用半TEM喇叭天线组成槽状排列二元线阵和四元线阵，进行了相应的原理性实验，实验结果与理论数值模拟基本一致。 相似文献
10.
Several recent studies suggest concrete learners make greater gains in student achievement and in cognitive development when receiving concrete instruction than when receiving formal instruction. This study examined the effect of concrete and formal instruction upon reasoning and science achievement of sixth grade students. Four intact classes of sixth grade students were randomly selected into two treatment groups; concrete and formal. The treatments were patterned after the operational definitions published by Schneider and Renner (1980). Pretest and posttest measures were taken on the two dependent variables; reasoning, measured with Lawson's Classroom Test of Formal Reasoning, and science achievement, measured with seven teacher made tests covering the following units in a sixth grade general science curriculum: Chemistry, Physics, Earth Science, Cells, Plants, Animals, and Ecology. Analysis of covariance indicated significantly higher levels (better than 0.05 and in some cases 0.01) of performance in science achievement and cognitive development favoring the concrete instruction group and a significant gender effect favoring males. 相似文献
11.
1 Ｉｎｔｒｏｄｕｃｔｉｏｎ Ｂｅｃａｕｓｅｏｆｔｈｅｃｏｍｂｉｎａｔｉｏｎｏｆａｎｕｍｂｅｒｏｆｆａｖｏｒａｂｌｅｐｒｏｐｅｒｔｉｅｓ,ｓｕｃｈａｓｈｉｇｈｈａｒｄｎｅｓｓ,ｈｉｇｈｃａｒｒｉｅｒｍｏｂｉｌｉｔｙａｎｄｂｒｅａｋｄｏｗｎｖｏｌｔａｇｅ,ｌａｒｇｅｂａｎｄｇａｐ ,ｌｏｗｄｉｅｌｅｃｔｒｉｃｃｏｎｓｔａｎｔ,ａｎｄｔｒａｎｓｐａｒｅｎｃｙｔｏｖｉｓｉｂｌｅｌｉｇｈｔ,ＩＲｌｉｇｈｔａｎｄｍｉｃｒｏｗａｖｅｓ,ｅｔｃ.[1] ,ｄｉａｍｏｎｄｆｉｌｍｈａｓｂｅｅｎｃｏｎｓｉｄｅｒ ａｂｌｙｐｒｏｍ… 相似文献
12.
We taught 8 pigeons to discriminate 16-icon arrays that differed in their visual variability or “entropy” to see whether the relationship between entropy and discriminative behavior is linear (in which equivalent differences in entropy should produce equivalent changes in behavior) or logarithmic (in which higher entropy values should be less discriminable from one another than lower entropy values). Pigeons received a go/no-go task in which the lower entropy arrays were reinforced for one group and the higher entropy arrays were reinforced for a second group. The superior discrimination of the second group was predicted by a theoretical analysis in which excitatory and inhibitory stimulus generalization gradients fall along a logarithmic, but not a linear scale. Reanalysis of previously published data also yielded results consistent with a logarithmic relationship between entropy and discriminative behavior. 相似文献
13.
Craig L. Engstrom 《Communication quarterly》2013,61(3):403-423
In residence halls on college campuses, one may hear a (male) student say, “Yes I did vandalize the wall, but I was drunk,” or “I ‘had a few’ before I kissed that ‘butter face’.” Researchers and university administrators could point to these as examples consistent with the problems of student drinking. They could also read these utterances as problematic performances of masculinity. Both groups would be correct. Ethnographers would seek to understand the underlying patterns of these statements, and ethnomethodologists the usefulness of these statements for actors in situ. This ethnography reports the findings of a study of student ways of speaking on a residential college campus. Data show that students’ patterned ways of speaking, especially when making references to drinking, mitigate problematic student behaviors, such as urinating in a corridor of a residence hall. Although such mitigating statements are, at times, by themselves problematic, they (re)produce a much more troubling masculinity. 相似文献
14.
已经制备出一种新颖.的肝素结合剂,这是一种可以被生物降解的多乳酸(PLA) 肝素聚合体.作为生物活性制剂的生物组织,如牛的心外膜,由细胞组成的或者无细胞组成的(BP/ABP)间质,是在谷氨醛(GA)交叉连接后用直接复制L 精氨酸(Arg)或肝素(Hep)而进行化学修改而成.PLA 肝素表面显示出亲水性的改善,降低了血浆蛋白质吸收性,减少了血小板的粘连性,提高了和血液的相容性以及与细胞的相容性.由此可建议,PLA 肝素聚合体对于与血液相接触的材料是有用的,特别是可以用于心血管组织的支架材料中.在由化学修改的细胞组成的间质中,经过Arg或Hep处理过的间质,它们的热力学性质和力学性质都要比原始的和经过GA处理的细胞组成间质的性能好.钙化实验中显示:在Arg和Hep处理过的间质上的钙沉积作用要少,细胞增殖的范围要比经过GA处理的材料高.本文结果证明用化学修改的无细胞间质或由细胞组成的间质作为新型生物材料在心血管及其组织的工程应用有效. 相似文献
15.
Zhi-xue Xu Ran Zhang You-xiang Wang Qiao-ling Hu 《Journal of Zhejiang University. Science. B》2010,11(4):292-297
The calcium phosphate (CaP) particles have attracted much attention in gene therapy. How to construct stable gene particles was the determining factor. In this study,hybrid multi-shell CaP gene particles were successfully constructed. First,CaP nanoparticles served as a core and were coated with DNA for colloidal stabilization. The ξ-potential of DNA-coated CaP nanoparticles was -15 mV. Then polyethylenimine (PEI) was added and adsorbed outside of the DNA layer due to the electrostatic attraction. The ξ-pot... 相似文献
16.
Discriminating same from different multiitem arrays can be represented as a discrimination between arrays involving low variability and arrays involving high variability. In the present investigation, we first trained pigeons with the extreme values along the variability continuum (arrays containing 16 identical items vs. 16 nonidentical items), and we later tested the birds with arrays involving intermediate levels of variability; we created these testing arrays either by manipulating the combination of same and different items (mixture testing) or by changing the number of items in the same and different arrays (number testing). According to an entropy account (Young & Wasserman, Journal of Experimental Psychology: Animal Behavior Processes 23:157?C170, 1997), the particular means of changing variability should have no effect on same?Cdifferent discrimination performance: Equivalent variability should yield equivalent performance. In this critical test of an entropy account, we found that entropy could explain a large portion of our data, but not the entire collection of results. 相似文献
17.
Heparin was grafted onto polycarbonate urethane (PCU) surface via a three-step procedure utilizing α, ωdiamino-poly(ethylene glycol) (APEG, M n =2 000) as a spacer. In the first step, isocyanate functional groups were introduced onto PCU surface by the treatment of hexamethylene diisocyanate (HDI) in the presence of di-n-butyltin dilaurate (DBTDL) as a catalyst. In the second step, APEG was linked to the PCU surface to obtain the APEG conjugated PCU surface (PCU-APEG). In the third step, heparin was covalently coupled with PCU-APEG in the presence of N-hydroxysuccinimide (NHS) and 1-ethyl-3-(3-dimethylamidopropyl) carbodiimide (EDAC). The amount of heparin (1.639 μg/cm 2 ) covalently immobilized on the PCU-APEG surface was determined by the toluidine blue method. The modified surface was characterized by water contact angle, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The hemocompatibility was preliminarily studied by platelet adhesion test. The results indicated that heparin was successfully grafted onto the PCU surface, and meanwhile the hydrophilicity and hemocompatibility of the modified PCU surface were improved significantly compared with the blank PCU surface. 相似文献
18.
Siliconcarbide (SiC)ceramicmaterialsareusefulad vancedmaterialsinmanyfields,suchasmedicalbiomateri als ,hightemperaturesemiconductors ,synchrotronopticalel ementsandhighstrength /lightweightstructuralmaterials[1] .However,theactualapplicationisstilllimitedduetoitslowreliability ,highmachiningcosts[2 ] .Gelcastingprovidesane conomicalandfeasiblenet shape forminghomogeneousandflawlessgreenbodieswithcomplexgreenshapes. Gelcastingconsistsofin situpolymerizationthroughwhichamacromolecularnetwor… 相似文献
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Mechanical and physical properties, such as tensile strength, elongation at break, modulus of elasticity, Shore D hardness,
melt flow rate (MFR), and electrical and thermal conductivities of composites with high density polyethylene matrix reinforced
with Al powders were investigated experimentally. Measurements of the mechanical and physical properties were performed up
to a reinforcing component concentration of 30% volume Al powder and compared with mathematical models from the literature.
The obtained results have shown that experimental data were in good agreement with theoretical data. The ultimate tensile
strength (UTS) and elongation at break decreased with increasing Al powder content, which was attributed to the introduction
of discontinuities in the polymer structure, and modulus of elasticity increased with increasing Al content. The composite
preparation conditions allowed the formation of a random distribution of metallic particles in the polymer matrix volume for
system high density polyethylene-Al (HDPE-Al). There was a cluster formation of Al particles at higher Al contents in the
polymer matrix. Electrical and thermal conductivity values of HDPE-Al composites were higher than pure HDPE values. 相似文献