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排序方式: 共有818条查询结果,搜索用时 968 毫秒
101.
Mehmet F. Orhan Ibrahim Dincer Marc A. Rosen 《Chemical engineering journal (Lausanne, Switzerland : 1996)》2009,155(1-2):132-137
The role of the Cu–Cl cycle for thermochemical water decomposition, potentially driven by heat from a nuclear power generation station, in producing hydrogen in a sustainable way is investigated by examining efficiencies. The energy efficiency of the cycle is found to be 45% and the exergy efficiency 10%. The energy and exergy efficiencies of the cycle are observed to vary with temperatures of the reactions and reference-environment, and cycle heat losses. A parametric study is carried out considering several heat losses, reaction and reference-environment temperatures, and component-efficiency scenarios. 相似文献
102.
Different subtypes of myofibroblasts have been described according to their cytoskeletal protein patterns. It is quite likely that these different subtypes represent distinct steps of differentiation. We propose the human placental stem villi as a particularly suitable model to study this differentiation process. During the course of pregnancy, different types of placental villi develop by differentiation of the mesenchymal stroma surrounding the fetal blood vessels. In order to characterise the differentiation of placental stromal cells in the human placenta, the expression patterns of the cytoskeletal proteins vimentin, desmin, alpha- and gamma-smooth muscle actin, pan-actin, smooth muscle myosin, and the monoclonal antibody GB 42, a marker of myofibroblasts, were investigated on placental tissue of different gestational age (7th-40th week of gestation). Proliferation patterns were assessed with the proliferation markers MIB 1 and PCNA. Additionally, dipeptidyl peptidase IV distribution was studied in term placenta and the ultrastructure of placental stromal cells was assessed by electron microscopy. Different subpopulations of extravascular stromal cells were distinguished according to typical co-expression patterns of cytoskeletal proteins. Around the fetal stem vessels in term placental villi they were arranged as concentric layers with increasing stage of differentiation. A variable layer of extravascular stromal cells lying beneath the trophoblast expressed vimentin (V) or vimentin and desmin (VD). They were mitotically active. The next layer co-expressed vimentin, desmin, and alpha-smooth muscle actin (VDA). More centrally towards the fetal vessels, extravascular stromal cells co-expressed vimentin, desmin, alpha- and gamma-smooth muscle actin, and GB 42 (VDAG). Cells close to the fetal vessels additionally co-expressed smooth muscle myosin (VDAGM). Ultrastructurally, V cells resembled typical mesenchymal cells. VD cells corresponded to fibroblasts, while VDA and VDAG cells developed features of myofibroblasts. Cells of the VDAGM-type revealed a smooth muscle cell-related ultrastructure. In earlier stages of pregnancy, stromal cell types with less complex expression patterns prevailed. The media smooth muscle cells of the fetal vessels showed a mixture of different co-expression patterns. These cells were separated from extravascular stromal cells by a layer of collagen fibres. The results obtained indicate a clearly defined spatial differentiation gradient with increasing cytoskeletal complexity in human placental stromal cells from the superficial trophoblast towards the blood vessels in the centre of the stem villi. The spatial distribution of the various stages of differentiation suggests that human placental villi could be a useful model for the study of the differentiation of myofibroblasts. 相似文献
103.
B Huppertz S Kertschanska AY Demir HG Frank P Kaufmann 《Canadian Metallurgical Quarterly》1998,291(1):133-148
The invasion of extravillous trophoblast cells into the maternal endometrium is one of the key events in human placentation. The ability of these cells to infiltrate the uterine wall and to anchor the placenta to it as well as their ability to infiltrate and to adjust utero-placental vessels to pregnancy depends, among other things, on their ability to secrete enzymes that degrade the extracellular matrix. Most of the latter enzymes belong to the family of matrix metalloproteinases. Their activity is regulated by the tissue inhibitors of matrix metalloproteinases. We have studied the distribution patterns of matrix metalloproteinases-1, -2, -3, and -9 and their inhibitors TIMP-1 and TIMP-2 as compared to the distribution of their substrates along the invasive pathway of extravillous trophoblast of 1st, 2nd, and 3rd trimester placentas by means of light microscopy on paraffin and cryostat sections as well as at the ultrastructural level (only 3rd trimester placenta). The comparison of different methods proved to be necessary, since the immunohistochemical distribution patterns of these soluble enzymes are considerably influenced by the pretreatment of tissues. All three methods revealed immunoreactivities of both, proteinases and their inhibitors, not only intracellularly in the extravillous trophoblast but also extracellularly in its surrounding matrix, the distribution patterns depending on the stage of pregnancy and on the degree of differentiation of trophoblast cells along their invasive pathway. Within the extracellular matrix, immunolocalization of matrix metalloproteinases as well as their inhibitors showed a specific relation to certain extracellular matrix molecules. 相似文献
104.
The kinetics and the mechanism of the reduction of chromite in Fe-Cr-C-Si alloys were studied in the temperature range of
1534 °C to 1702 °C under an inert argon atmosphere. The rotating cylinder technique was used. The melt consisted of 10 and
20 wt Pct chromium, the carbon content varied from 2.8 wt Pct to saturation, and the silicon content varied from 0 to 2 wt
Pct. The rotational speed of the chromite cylinder ranged from 100 to 1000 rpm. The initial chromium to iron ratios of the
melts varied between 0.11 and 0.26. In Fe-C melts, the effect of rotational speed on the reduction of chromite was very limited.
Carbon saturation (5.4 wt Pct) of the alloy caused the reduction to increase 1.5 times over the reduction observed in the
unsaturated (4.87 wt Pct) alloy at a given rotational speed. The addition of chromium to the carbon-saturated Fe-C alloy increased
the reduction rate. The addition of silicon to the liquid phase increased the reduction rate drastically. The reduction of
chromite in Fe-Cr-C melts is hindered because of the formation of, approximately, a 1.5-mm-thick M7C3-type carbide layer around the chromite cylinders. This carbide layer did not form when silicon was present in the melt. It
was found that the reduction rate is controlled by the liquid-state mass transfer of oxygen. The calculated apparent activation
energies for diffusion were 102.9 and 92.9 kJ/mol of oxygen in the Si-O and C-O systems, respectively. 相似文献
105.
In this study, total contents of phenolic, flavanol and flavonol, antioxidant activities and antimicrobial activities of the Turkish endemic Salvia pisidica Boiss. & Heldr. ex Bentham (Lamiaceae) extract and essential oil were assessed in vitro. Total phenolic, flavanol and flavonol contents in the extract were 54.57 mg gallic acid equivalents (GAE)/g, 16.70 mg catechine equivalents (CE)/g and 18.19 mg rutin equivalents (RE)/g, respectively. Antioxidant activities (IC50 value) of the extract and essential oil were determined as 4.88 and 6.41 mg/mL by DPPH assay, respectively. 31 compounds were determined in the essential oil using GC-MS and the major compounds (%) were camphor (23.76), sabinol (19.2), α-thujone (14.2) and eucalyptol (1.8-cineole) (5.8).The antimicrobial activity of the methanolic extract and the essential oil against 13 bacterial and two yeast strains was determined. The extract (concentration 5 g/100 ml or 10 g/100 ml) was effective against most of the strains tested, yet not against Bacillus cereus, Staphylococcus aureus, Aeromonas hydrophila and the two yeast strains tested. The essential oil (2 g/100 ml) showed an antimicrobial effect against all the gram (+) bacteria tested, against Saccharomyces cerevisiae, but was not effective against all gram (−) bacteria and Candida albicans. These results show that S.piscidica essential oil and extract could be considered as a natural alternative to traditional food preservatives and be used to enhance food safety and shelf life. 相似文献
106.
Bekir Sami Yilbas S. Khan K. Raza Omer Keles Mustafa Ubeyli Teyfik Demir M. Serdar Karakas 《The International Journal of Advanced Manufacturing Technology》2010,50(1-4):185-193
In the present study, laser cutting of 7050 aluminum alloy sheets reinforced with Al2O3 and B4C particles are carried out. The cut geometry is examined using scanning electron microscope and the optical microscope. The lump parameter analysis technique is used to formulate and determine the kerf width size. The predictions for kerf width are compared with experimental data. The percentage kerf width size variation along the cut edges is determined and the influence of the laser power level and duty cycle of the laser pulses on the percentage kerf width size variation is examined. It is found that 7050 aluminum alloy reinforced with 20% Al2O3 composite results in relatively large kerf width size as compared to its counter parts that corresponding to 7050 aluminum alloy reinforced with 20% B4C composite. The kerf width size predicted agreed with the experimental data for both composites. 相似文献
107.
Güneş Süheyla Kürkçüoğlu Okan Zafer Yeşilel İlkan Kavlak Sema Kurtaran Orhan Büyükgüngör 《Journal of Inorganic and Organometallic Polymers and Materials》2009,19(3):314-321
The heteronuclear complex, {[Cu(4(5)-Meim)4][Ni(CN)4] · H2O}n (1), (4(5)-Meim = 4(5)-methylimidazole) was synthesized and characterized by FT-IR spectroscopy, single crystal X-ray diffraction, thermal analysis
and elemental analysis. The Cu(II) ion has a distorted square planar geometry, extended to (4 + 2) weak coordination by two
nitrogen atoms of the cyano group. The coordination sphere around the Ni(II) ion should be described as a 4 + 2 geometry with
the four cyano groups and the axial coordination site is located at the imidazole ring though a weak Ni···π interaction. The
coordination bond is much stronger than the Ni···π interactions and it is expected that the formation of the coordination
bond will affect more significantly the position of the absorption bands associated with the vibrations of the ligand. In
addition, the out-of-plane modes of 4(5)-Meim are shifted to higher frequencies relative to free ligand. We propose that these shifts are indicative of the weak CH∙∙∙π
and Ni∙∙∙π interactions, according to the crystallographic and spectroscopic data. 相似文献
108.
This paper presents a novel electronically scanning phased-array antenna with 128 switches monolithically implemented using RF microelectromechanical systems (MEMS) technology. The structure, which is designed at 15 GHz, consists of four linearly placed microstrip patch antennas, 3-bit distributed RF MEMS low-loss phase shifters, and a corporate feed network. MEMS switches and high-Q metal-air-metal capacitors are employed as loading elements in the phase shifter. The system is fabricated monolithically using an in-house surface micromachining process on a glass substrate and occupies an area of 6 cm times 5 cm. The measurement results show that the phase shifter can provide nearly 20deg/50deg/95deg phase shifts and their combinations at the expense of 1.5-dB average insertion loss at 15 GHz for eight combinations. It is also shown by measurements that the main beam can be steered to required directions by suitable settings of the RF MEMS phase shifters. 相似文献
109.
Gurinovich L. I. Trotsiuk L. L. Kulakovich O. S. Sushko N. I. Demir H. V. Gaponenko S. V. 《Semiconductors》2018,52(16):2054-2056
Semiconductors - Anisotropic polymer films containing aligned Au nanorods and semiconductor nanoparticles of various shape were fabricated. The photoluminescence of semiconductor nanoparticles in... 相似文献
110.