排序方式: 共有23条查询结果,搜索用时 15 毫秒
1.
Simultaneous multi-point hotwire measurements are used to investigate the three-dimensional wake topology of a square cylinder at high Reynolds numbers. Wavelet techniques are applied to detect the flow structures and to inquire on the validity or extension of previously proposed low Reynolds number topological models to turbulent wakes. Our results suggest that a flow topological model similar to the horizontal perturbation model proposed by Meiburg and Lasheras (J Fluid Mech 190:1–37, 1988) but with alternate rib cuts in the horizontal plane is plausible for the intermediate wake topology.
相似文献
H. HanganEmail: Phone: +1-519-6613338Fax: +1-519-6613339 |
2.
Loredana-Mihaela Dobre Anicuţa Stoica-Guzun Marta Stroescu Iuliana Mihaela Jipa Tǎnase Dobre Mariana Ferdeş Ştefana Ciumpiliac 《Chemical Papers》2012,66(2):144-151
Antimicrobial packaging protects the product from the external environment and microbial contamination, conferring numerous
advantages on human health. Interest in biopolymers as packaging materials has considerably increased recently. Bacterial
cellulose is an interesting biomaterial produced as nanofibrils by Acetobacter xylinium and is a promising candidate due to its remarkable properties. New composite materials with antimicrobial properties were
developed in this work, containing poly(vinyl alcohol) (PVA) as polymer matrix and ground bacterial cellulose (BC) as reinforcing
fibres. Sorbic acid was used as an antimicrobial agent because it is a preservative recognised in the food industry. The materials
obtained were studied using Fourier-transformed infrared spectroscopy (FTIR). The swelling rate of the composites was also
measured. Release experiments of sorbic acid from the composite films into water were performed and the mass transfer phenomena
were investigated using Fick’s law of diffusion. The antimicrobial effect was tested against Escherichia coli K12-MG1655. The results obtained indicated that the new biocomposite films could be promising antimicrobial food packaging
materials. 相似文献
3.
We have developed a dual-channel optical coherence tomography-Indocyanine Green dye (OCT-ICG) fluorescence system based on a previously reported ophthalmic OCT confocal imaging system. The confocal channel is tuned to the fluorescence wavelength range of the ICG, and light from the same optical source is used to generate the OCT image and to excite the ICG fluorescence. The system enables the clinician to visualize simultaneously en face OCT slices and corresponding ICG angiograms of the ocular fundus, displayed side by side. C-scan (constant depth) and B-scan (cross section) images are collected by a fast en face scan (T scan). The pixel-to-pixel correspondence between the OCT and angiography images allows the user to capture OCT B scans precisely at selected points on the ICG confocal images. 相似文献
4.
We report a system capable of sequentially acquiring two en-face images of different depth resolutions. The two images are generated by use of different principles, optical coherence tomography (OCT) and confocal microscopy, and have depth resolutions, at present, of better than 20 microm and over 0.12 mm, respectively. The lower-depth-resolution image is ideal for target positioning before collection of stacks of en-face OCT images. Switching between the two types of image by flipping an opaque screen in the reference arm, coupled with self-adjusting gain operation of avalanche photodiodes in the receiver. We illustrate the usefulness of the system by imaging a leaf and an optic nerve in vivo. 相似文献
5.
When the matrix of distances between cities is symmetric and circulant, the traveling salesman problem (TSP) reduces to the so-called symmetric circulant traveling salesman problem (SCTSP), that has applications in the design of reconfigurable networks, and in minimizing wallpaper waste. The complexity of the SCTSP is open, but conjectured to be NP-hard, and we compare different lower bounds on the optimal value that may be computed in polynomial time. We derive a new linear programming (LP) relaxation of the SCTSP from the semidefinite programming (SDP) relaxation in [E. de Klerk, D.V. Pasechnik, R. Sotirov, On semidefinite programming relaxation of the traveling salesman problem, SIAM Journal of Optimization 19 (4) (2008) 1559-1573]. Further, we discuss theoretical and empirical comparisons between this new bound and three well-known bounds from the literature, namely the Held-Karp bound [M. Held, R.M. Karp, The traveling salesman problem and minimum spanning trees, Operations Research 18 (1970) 1138-1162], the 1-tree bound, and the closed-form bound for SCTSP proposed in [J.A.A. van der Veen, Solvable cases of TSP with various objective functions, Ph.D. Thesis, Groningen University, The Netherlands, 1992]. 相似文献
6.
Anicuta Stoica-Guzun Marta Stroescu Iuliana Jipa Loredana Dobre Sorin Jinga Traian Zaharescu 《Macromolecular Symposia》2012,315(1):198-204
The development of biodegradable packaging materials, especially from renewable resources is a constant preoccupation of nowadays, because of the environmental problems caused by synthetic polymers. The combination of cellulose with other polymeric materials could be an ecologic alternative and a way to use renewable resources for food packaging. Bacterial cellulose which is produced by microbial fermentation is also a promising material which can be used not only in biomedical application, but also as food packaging material. In this research different composite films between poly(vinyl alcohol)-bacterial cellulose (PVA-BC) were obtained by casting method. The obtained films were UV irradiated for different periods of times from 1 to 10 hours, using a mercury lamp, Philips TUV-30, emitting light mainly at 254 nm. Changes in FT-IR spectra before and after UV irradiation and the modification of transparency and of the swelling characteristics of the films were observed. As it was expected the composites materials are sensitive at UV exposure. 相似文献
7.
8.
9.
Iuliana Mihaela Jipa Anicuta Stoica Marta Stroescu Loredana-Mihaela Dobre Tanase Dobre Sorin Jinga Christu Tardei 《Chemical Papers》2012,66(2):138-143
Active packaging materials are the subject of research because their performance exceeds that of traditional packaging. From
this class, antimicrobial materials extend the shelf-life of products and reduce the risk of contamination by pathogens. In
this paper, new composite materials with antimicrobial properties are obtained by using polyvinyl alcohol and bacterial cellulose
powder. Potassium (2E,4E)-hexa-2,4-dienoate was used as the antimicrobial agent. The films thus obtained were characterised using Fourier-transform
infrared spectroscopy and scanning electron microscopy. Mass transfer phenomena concerning the release of potassium (2E,4E)-hexa-2,4-dienoate were investigated. The results indicated that the new biocomposite films could be used as antimicrobial
packaging materials. 相似文献
10.
Ctlina Dobre Lavinia Grosu Monica Costea Mihaela Constantin 《Entropy (Basel, Switzerland)》2020,22(11)
The paper presents experimental tests and theoretical studies of a Stirling engine cycle applied to a β-type machine. The finite physical dimension thermodynamics (FPDT) method and 0D modeling by the imperfectly regenerated Schmidt model are used to develop analytical models for the Stirling engine cycle. The purpose of this study is to show that two simple models that take into account only the irreversibility due to temperature difference in the heat exchangers and imperfect regeneration are able to indicate engine behavior. The share of energy loss for each is determined using these two models as well as the experimental results of a particular engine. The energies exchanged by the working gas are expressed according to the practical parameters, which are necessary for the engineer during the entire project, namely the maximum pressure, the maximum volume, the compression ratio, the temperature of the heat sources, etc. The numerical model allows for evaluation of the energy processes according to the angle of the crankshaft (kinematic–thermodynamic coupling). The theoretical results are compared with the experimental research. The effect of the engine rotation speed on the power and efficiency of the actual operating machine is highlighted. The two methods show a similar variation in performance, although heat loss due to imperfect regeneration is evaluated differently. 相似文献