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排序方式: 共有637条查询结果,搜索用时 640 毫秒
1.
One hypothesis for the transcontinental and intra-Great Lakes basin transfer of round gobies (Neogobius melanostomus) has been that round gobies were pumped into the ballast water of ships. During June 2005 in Lake Erie, we obtained evidence of a vertical migration of round goby larvae, when we collected 167 round goby larvae in surface ichthyoplankton net tows at night and zero during day. These results complemented similar findings from the Muskegon River estuary of Lake Michigan during 2003 and 2004, documenting diel vertical migration for the first time in larval round gobies. We suggest vertical migration behavior may have allowed larval round gobies to be transported to and within the Great Lakes via ballast water and dispersed in the Great Lakes via advection of 6.5–8.5-mm long larvae at the surface. Based on our results, if ballast water was only taken on near the surface during daylight hours from May through September when larval round gobies were present, it would have mitigated the spread of round gobies throughout the Great Lakes.  相似文献   
2.
Data from 296 sibling pairs (mean ages 10 and 13 years), their primary caregivers, and census records were used to test the hypothesis that African American children's likelihood of developing conduct problems associated with harsh parenting, a lack of nurturant-involved parenting, and exposure to an older sibling's deviance-prone attitudes and behavior would be amplified among families residing in disadvantaged neighborhoods. A latent construct representing harsh-inconsistent parenting and low levels of nurturant-involved parenting was positively associated with younger siblings' conduct disorder symptoms, as were older siblings' problematic attitudes and behavior. These associations were strongest among families residing in the most disadvantaged neighborhoods. Future research and prevention programs should focus on the specific neighborhood processes associated with increased vulnerability for behavior problems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
3.
Simons  R.N. Taub  S.R. 《Electronics letters》1993,29(17):1584-1586
Coplanar waveguide (CPW) and grounded coplanar waveguide (GCPW) radial line double stub resonators are experimentally characterised with respect to stub radius and sector angle. A simple closed-form design equation, which predicts the resonance radius of the stub, is presented. Use of a double stub resonator as a lowpass filter or as a harmonic suppression filter is demonstrated and design rules are given.<>  相似文献   
4.
People can recognize the meaning or gist of a scene from a single glance, and a few recent studies have begun to examine the sorts of information that contribute to scene gist recognition. The authors of the present study used visual masking coupled with image manipulations (randomizing phase while maintaining the Fourier amplitude spectrum; random image structure evolution [RISE]; J. Sadr & P. Sinha, 2004) to explore whether and when unlocalized Fourier amplitude information contributes to gist perception. In 4 experiments, the authors found that differences between scene categories in the Fourier amplitude spectrum are insufficient for gist recognition or gist masking. Whereas the global 1/f spatial frequency amplitude spectra of scenes plays a role in gist masking, local phase information is necessary for gist recognition and for the strongest gist masking. Moreover, the ability to recognize the gist of a target image was influenced by mask recognizability, suggesting that conceptual masking occurs even at the earliest stages of scene processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
5.
Human immediate hypersensitivity diseases represent the most common example of chronic excessive Th2-like activation in developed nations. While IL-13 shares many functional properties with IL-4, the intensity and regulation of environmental Ag-stimulated IL-13 synthesis by allergic vs nonallergic individuals remain ill defined. Here, we examine the intensity of polyclonally and Ag-stimulated IL-13 production by PBMC of 20 subjects with seasonal allergic rhinitis and 20 healthy controls. Polyclonally driven IL-13 responses did not differ significantly (Mann-Whitney U test, p = 0.68). In contrast, the median CD4-dependent IL-13 response among atopics was markedly stronger than nonatopics in Ag-stimulated primary culture (p = 0.0031) and exhibited a strong correlation with IL-5 (r = 0.76, p = 0.0009), but not IL-4 (r = 0.14, p > 0.05), responses. IL-13 production was unaffected by blocking endogenous IL-4 or IL-5 activity or by addition of rIL-4 or rIL-5. In contrast, it was inhibited by low levels of rIFN-gamma and strongly enhanced upon addition of neutralizing anti-IFN-gamma mAb. Collectively, the data are consistent with a negative regulatory role for endogenous IFN-gamma synthesis in controlling the intensity of systemic IL-13 responses evoked in both atopic and nonatopic populations following exposure to common Ags. They also suggest that the elevated levels of IL-4 and IL-5 characteristic of type 2-dominated responses in vivo are without detectable impact on the maintenance of recall Ag-stimulated IL-13 production.  相似文献   
6.
A number of urethane acrylate nano- and micro-composites have been developed using both ion exchange and silane grafting chemistry. The organically modified clays which were used contained either methacrylate or acrylate functionalities which were capable of reacting with the acrylate groups in the urethane acrylate matrix. [2-(Acryloyloxy)ethyl]trimethyl-ammonium ion (AOETMA) or [2-(methacryloyloxy)ethyl]trimethylammonium ion (MAOTMA) were exchanged onto montmorillonite (MMT) as shown by an increase in the inter-gallery spacing of the MMT. Silane grafting was undertaken using [3-(acryloxy)propyl]dimethylmethoxysilane (APDMMS) or [3-(methacryloxy)propyl]dimethylmethoxysilane (MAPDMMS) and also showed an increase in inter-gallery spacing. The structures of the resulting urethane acrylate composites were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM) and showed predominantly intercalated structures with some exfoliation (more evident in the silane-grafted systems). Dynamical mechanical thermal analysis (DMTA) showed a more significant increase in effective crosslink density (as measured from the plateau of the rubbery modulus) in the composites containing the reactive clays as compared to the unmodified clay, supporting the concept that the acrylate and methacrylate functionalities of the modified clays had reacted with the matrix. Other thermal and mechanical properties were also evaluated.  相似文献   
7.
知识黑市     
Jude 《微型计算机》2010,(20):14-14
在这个以市场经济为主导的世界里,经常会有各种让人跌破眼镜的交易,知识交易便是其中一种。这里所讲的知识交易可不包括传统的教育手段,而是一个全新的概念,全称是“知识和非知识黑市交易”(Blackmarket for useful knowledge and non-konwledge)。  相似文献   
8.
Jude 《微型计算机》2010,(20):52-53
有童鞋知道SpaceWarp这个玩具吗?不知道不要紧,反正放狗一搜便知。自从这玩意儿上市的那一天起就火得不得了,而且一烧就整整二十多年。现在咱们在淘X上花100多个现大洋就能买到一套——当然是山寨的(只有原版卖价五分之一)。与其买个山寨货自叹不值,不如让《Geek》来教教大家DIY一个货真价实的钢珠过山车出来!  相似文献   
9.
Mosaic organization of DNA nucleotides   总被引:23,自引:0,他引:23  
Long-range power-law correlations have been reported recently for DNA sequences containing noncoding regions. We address the question of whether such correlations may be a trivial consequence of the known mosaic structure ("patchiness") of DNA. We analyze two classes of controls consisting of patchy nucleotide sequences generated by different algorithms--one without and one with long-range power-law correlations. Although both types of sequences are highly heterogenous, they are quantitatively distinguishable by an alternative fluctuation analysis method that differentiates local patchiness from long-range correlations. Application of this analysis to selected DNA sequences demonstrates that patchiness is not sufficient to account for long-range correlation properties.  相似文献   
10.
An open question in computational molecular biology is whether long-range correlations are present in both coding and noncoding DNA or only in the latter. To answer this question, we consider all 33301 coding and all 29453 noncoding eukaryotic sequences--each of length larger than 512 base pairs (bp)--in the present release of the GenBank to dtermine whether there is any statistically significant distinction in their long-range correlation properties. Standard fast Fourier transform (FFT) analysis indicates that coding sequences have practically no correlations in the range from 10 bp to 100 bp (spectral exponent beta=0.00 +/- 0.04, where the uncertainty is two standard deviations). In contrast, for noncoding sequences, the average value of the spectral exponent beta is positive (0.16 +/- 0.05) which unambiguously shows the presence of long-range correlations. We also separately analyze the 874 coding and the 1157 noncoding sequences that have more than 4096 bp and find a larger region of power-law behavior. We calculate the probability that these two data sets (coding and noncoding) were drawn from the same distribution and we find that it is less than 10(-10). We obtain independent confirmation of these findings using the method of detrended fluctuation analysis (DFA), which is designed to treat sequences with statistical heterogeneity, such as DNA's known mosaic structure ("patchiness") arising from the nonstationarity of nucleotide concentration. The near-perfect agreement between the two independent analysis methods, FFT and DFA, increases the confidence in the reliability of our conclusion.  相似文献   
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