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121.
The macroscopically brittle fracture of five high-density polyethylenes subjected to different constant uniaxial tensile loads was studied by s.e.m. fractography on both untreated and solvent-etched samples. The low molecular weight systems showed three types of fracture propagation: interspherulitic propagation with and without reorientation and trans-spherulitic interlamellar propagation. There is evidence that the development of fracture is associated with a strength distribution in the structure caused by molecular weight segregation occurring during solidification of the samples. 相似文献
122.
Nyman A. Jaaskelainen K. Vaitomaa M. Jansson B. Danielsson K.-G. 《Power Delivery, IEEE Transactions on》1994,9(1):1-9
The commissioning of the Fenno-Skan HVDC link between Finland and Sweden, with the longest submarine DC cable in the world, is described. The main pre-commissioning activities, important for an efficient commissioning, are discussed together with time schedules and suitable organisation forms. The procedures to test special control features, such as subsynchronous oscillation (SSO) damping control are presented. The full scale network interaction tests which are an important part of the commissioning are also discussed. These tests succeeded very well and provided a lot of information about the system behaviour for future operation and planning purposes 相似文献
123.
JA Jackson NG Ducharme RP Hackett RS Rehder DM Ainsworth KJ Shannon BK Erickson HN Erb N Jansson LV Soderholm LM Thorson 《Canadian Metallurgical Quarterly》1997,58(8):897-903
OBJECTIVE: To determine whether laryngeal hemiplegia would increase transmural pulmonary artery pressure (TPAP). ANIMALS: 6 horses. DESIGN: Horses were studied under 5 conditions: control conditions, after induction of left laryngeal hemiplegia, during obstruction of the left nostril, after placement of an instrumented tracheostomy, and after placement of an open tracheostomy. Horses were evaluated after being given saline solution and after being given furosemide. PROCEDURES: Horses were exercised on a high speed treadmill, using a maximum speed of 13 m/s. During each exercise, airway pressures, airflow, esophageal and pulmonary artery pressures, and blood gas partial pressures were measured. RESULTS: When adjusted for horse, speed, and obstruction condition, mean TPAP (pulmonary artery pressure-esophageal pressure) and minimum TPAP were significantly lower after administration of furosemide than after administration of saline solution. In horses given saline solution, respiratory obstruction that increased intrapleural pressure significantly increased mean TPAP, and respiratory obstruction that decreased intrapleural pressure significantly decreased minimum TPAP. CONCLUSIONS: Changes in intrapleural pressure appear to play an important role in pulmonary artery pressure and TPAP. CLINICAL RELEVANCE: Because induction of laryngeal hemiplegia did not increase TPAP, laryngeal hemiplegia is unlikely to contribute to development of exercise-induced pulmonary hemorrhage. 相似文献
124.
Elina Mäntylä Sven Kleier Carita Lindstedt Silke Kipper Monika Hilker 《Journal of chemical ecology》2018,44(12):1127-1138
Insectivorous birds feed upon all developmental stages of herbivorous insects, including insect eggs if larvae and adults are unavailable. Insect egg deposition on plants can induce plant traits that are subsequently exploited by egg parasitoids searching for hosts. However, it is unknown whether avian predators can also use egg-induced plant changes for prey localization. Here, we studied whether great tits (Parus major) and blue tits (Cyanistes caeruleus) are attracted by traits of the Scots pine (Pinus sylvestris) induced by pine sawfly (Diprion pini) egg deposition. We chose this plant – insect system because sawfly egg deposition on pine needles is known to locally and systemically induce a change in pine volatile organic compounds (VOCs), and tits are known to prey upon sawfly eggs. In dual choice laboratory experiments, we simultaneously offered the birds an egg-free control branch and a systemically egg-induced branch. Significantly more birds visited the egg-induced branch first. We confirmed by GC-MS analyses that systemically egg-induced branches released more (E)-β-farnesene compared to control branches. Spectrophotometric analyses showed that control branches reflected more light than egg-induced branches throughout the avian visual range. Although a discrimination threshold model for blue tits suggests that the birds are poor at discriminating this visual difference, the role of visual stimuli in attracting the birds to egg-induced pines cannot be discounted. Our study shows, for the first time, that egg-induced odorous and/or visual plant traits can help birds to locate insect eggs without smelling or seeing those eggs. 相似文献
125.
Elina Eskelä 《住房,理论和社会》2018,35(4):474-494
AbstractAlthough relatively understudied, the role of affordable and acceptable housing in the accelerating global competition for talent is of utmost importance, especially if highly skilled migrants are to be absorbed into the permanent labour force. This paper concerns the housing of skilled Indian migrants in the Helsinki metropolitan area in Finland, and contributes to the literature on international migration and the housing of ethnic minorities. It presents a case study on how to analyse migrants’ housing pathways, examining the meaning of housing in the transnational lives of this relatively affluent migrant group. The results show that homeownership is a not a simple indicator of commitment to the host society, and that those responsible for national housing policy need to ensure the supply, quality and reasonable price of accommodation in order to fulfil the housing needs of skilled migrants. 相似文献
126.
127.
In this work, the influence of the preparation method of ZSM-5/TiO2 hybrids on the photocatalytic performance for removal of formaldehyde (HCHO) or trichloroethylene (C2HCl3) in gas phase was analyzed. For this purpose, two methods for the synthesis of the hybrids, the incipient wetness impregnation (I) and the mechanical mixing method (M), were selected. The photocatalysts were characterized by N2 adsorption–desorption, TEM, UV–Vis spectroscopy, XRD and electrophoretic migration. Also, the adsorption ability of the individual materials and hybrids was analyzed. ZSM-5/TiO2 hybrids showed higher photocatalytic activity than bare TiO2, independently of the preparation method selected. Mechanical mixing is a simple and easily scalable method to prepare highly active photocatalyst with high amounts of titania. The internal diffusion processes of the reactants to the active sites could be improved due to the micro–mesoporous structure developed on these hybrids. Incipient wetness impregnation method leads to photocatalysts with higher photodegradation rates per active site. The hybrids synthetized by this method show TiO2 nanoparticles homogeneously dispersed on the ZSM-5 phase. The fraction of TiO2 exposed on the surface ca. 75 mol% was similar for materials prepared by both methods, explaining the similar adsorption and photocatalytic properties, independently of the TiO2 content. The nature of the pollutant has an important role in the adsorption and photocatalytic properties of the composites. Finally, the effect of the incorporation of the zeolite in the photocatalytic system was analyzed. For this purpose, the influence of the zeolite and titania arrangement in the sample holder on the photodegradation rate was analyzed. Although the incorporation of the zeolite induces a positive effect on the photocatalytic performance, independently of the position on the sample holder, a clear synergistic effect when both phases were in intimate contact such as in the ZSM-5/TiO2 hybrid was observed. 相似文献
128.
It is shown that the annealing of a high molecular weight, high density polyethylene at different temperatures ranging from 393.2 to 405.2 K influences the density of the material, the lamellar structure as studied by differential scanning calorimetry and transmission electron microscopy, and the necking and fracture behavior at constant uniaxial tensile loading in air at 313 K. In previous reports, a marked transition in the necking and fracture behavior of high density, high molecular weight polyethylene under constant uniaxial tensile loading has been reported. The nominal stress and the maximum strain rate of this transition show minima for polyethylenes annealed at temperatures of about 401 K. By combining these data with data for the lamellar structure a hypothesis that explains the necking/fracture behavior is set up. The heat treatment at temperatures from 393.2 to 403.2 K of the original non-equilibrium lamellar structure causes a molecular fractionation preferentially of low molecular weight and branched material. These segregated parts may then act as fracture initiators and thus lower the resistance towards fracture. Other structural effects such as those proposed by McCready and co-workers may also be of importance. The fracture curves at nominal stresses below transition of the materials annealed at 396.7 and 401.2 K for 24 h are shifted to shorter times in comparison with that of the non-annealed material and this can also be explained by molecular fractionation. The time to necking at 14 MPa nominal stress seems to be related to the lamellar thickness of the samples. 相似文献
129.
The direct and indirect oxidation of cyanide at concentrations typical of those found in plating wash water have been investigated in a bipolar trickle-tower reactor. It has been found that the oxidation by hypochlorite generatedin situ was faster than direct oxidation or oxidation in the presence of base, but that the CN? concentration was easily reduced by any of these methods. Scaling-up experiments were performed by using different numbers of layers of bipoles, different electrolyte flow rates and different applied voltages. It is shown that the overall rate is determined by the mass-transport-limited generation of oxidant. 相似文献
130.
The destruction of CN– and co-deposition of copper, cadmium, nickel, zinc and lead, both as simple solutions and as mixtures, have been investigated in a number of trickle towers with from 8 to 49 layers of cells. Specific chemical effects due to the formation of cyano-complexes of some of the metals are evident, and it has been found that copper, nickel and cadmium accelerate the destruction of CN–, at least initially. For simple solutions a previously proposed scaling law is adequate.Nomenclature
a
length of bipolar element (cm)
-
c
concentration (ppm)
-
c
0
initial concentration (ppm)
-
K
mass transfer coefficient (cm s–1)
-
K=K
L
effective mass transfer coefficient (cm s–1)
-
L
wetted perimeter per layer of packing (cm)
-
p
number of layers of cells
-
t
time (s)
-
v
o
volumetric flow rate (cm3 s–1)
-
V
inventory of solution (cm3)
-
L
fractional active length
-
s
reversible potential with respect to main counter reaction (V)
-
s
T
potential applied across an element with respect to main counter reaction (V) 相似文献