共查询到20条相似文献,搜索用时 343 毫秒
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婴幼儿低发锌、铜、铁、钙与疾病的关系探讨 总被引:7,自引:1,他引:6
对846例低发锌、456例低发铜、488例低发铁以及595例低发钙婴幼儿与疾病的关系进行了探讨。结果显示,低发锌婴幼儿中反复呼吸道感染、食欲不振和异食癖的患病率分别为71.16%、57.57%和11.47%;低发铜和低发铁婴儿的贫血率分别为15.79%和73.16%,呼吸道感染的患病率分别为9.43%和35.66%:低发钙者中佝楼病的发病率为81.51%。 相似文献
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This paper reports the low energy, low temperature mass spectra of the 27 alcohols and ethers containing up to five carbon atoms. The observed fragmentation pathways are discussed in energetic terms. Except in one instance, pentan-1-ol and 3-methylbutan-1-ol, the spectra are diagnostic of the structure of the compounds; even in this case, subtle differences can be used to determine structure. The advantage of the low energy, low temperature mass spectra in identifying low energy fragmentation routes is emphasized. 相似文献
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Plasma Assisted Low Temperature Combustion 总被引:2,自引:0,他引:2
Yiguang Ju Joseph K. Lefkowitz Christopher B. Reuter Sang Hee Won Xueliang Yang Suo Yang Wenting Sun Zonglin Jiang Qi Chen 《Plasma Chemistry and Plasma Processing》2016,36(1):85-105
This paper presents recent kinetic and flame studies in plasma assisted low temperature combustion. First, the kinetic pathways of plasma chemistry to enhance low temperature fuel oxidation are discussed. The impacts of plasma chemistry on fuel oxidation pathways at low temperature conditions, substantially enhancing ignition and flame stabilization, are analyzed base on the ignition and extinction S-curve. Secondly, plasma assisted low temperature ignition, direct ignition to flame transition, diffusion cool flames, and premixed cool flames are demonstrated experimentally by using dimethyl ether and n-heptane as fuels. The results show that non-equilibrium plasma is an effective way to accelerate low temperature ignition and fuel oxidation, thus enabling the establishment of stable cool flames at atmospheric pressure. Finally, the experiments from both a non-equilibrium plasma reactor and a photolysis reactor are discussed, in which the direct measurements of intermediate species during the low temperature oxidations of methane/methanol and ethylene are performed, allowing the investigation of modified kinetic pathways by plasma-combustion chemistry interactions. Finally, the validity of kinetic mechanisms for plasma assisted low temperature combustion is investigated. Technical challenges for future research in plasma assisted low temperature combustion are then summarized. 相似文献
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《Radiation Physics and Chemistry》2004,69(3):229-238
Radiation-thermal cracking (RTC) in the high-paraffinic oil from the Kumkol field (Western Kazakhstan) is experimentally studied. It is shown that the high polymerization rate and low olefin contents in products of radiation processing together with relatively low yields of light fractions at low irradiation dose rates and the low level of their isomerization are characteristic for RTC in oil with high contents of heavy paraffins. These observations are attributed to the behavior of heavy alkyl radicals that initiate polymerization and isomerization in heavy paraffin fractions. 相似文献
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With the widespread use of rechargeable batteries, they are further expected to be used at low temperature. However, low temperature significantly slows charge transfer process and mass transport within electrolyte and electrode. Due to the inherent distinction on physical and chemical properties, low temperature imposes different limitations on non-aqueous and aqueous batteries. In this review, we provide a brief overview of the challenges in developing non-aqueous and aqueous batteries for low-temperature use. And their different design concerns at low temperature are summarized and discussed. 相似文献
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《Radiation Physics and Chemistry》2002,63(3-6):813-815
The measurements presented were undertaken to provide quantitative information on the low temperature irradiation of thermoluminiscence phosphors. The crystals used were (a) LiF co-doped with Mg, Cu and P, and (b) CaSO4 doped with Dy. The absorbed dose values in the interval studied showed a linear behavior at low doses and low temperature. The aim of this work is to test if these crystals can be used to measure the dose absorbed by solids at low temperature. 相似文献
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Kristina Elg Christoffersson Michael Sjöström Ulf Edlund Åsa Lindgren Matti Dolk 《Cellulose (London, England)》2002,9(2):159-170
The reactivity of dissolving pulp was experimentally determined in termsof residual cellulose in viscose. The correlations between 11 chemicalproperties of pulp and filter values and residual cellulose contents of viscosewere then investigated by multivariate data analysis. Both the viscose filtervalue and the residual cellulose were well modelled from the 11 propertiesby partial least squares regression. The results show that pulps with highacetone extractable fractions, high magnesium contents, low alkali resistanceand low viscosity, gave low viscose filter values and low residual cellulosecontents. Pulps with low residual cellulose contents also had low carboxylgroupcontents and low polydispersity. The results are interpreted as that in pulpwith high reactivity, the hemicellulose content is low and that the cellulosechains are shorter and more soluble in alkali. An explanation of the positiveeffect from the high extractive content is that the extractives facilitate thediffusion of carbon disulfide. A principal component analysis of CP/MAS13C-NMR spectral data of six pulp samples showed that differences inreactivity between the pulps could be explained by variations in the hydrogenbonds in the cellulose and/or changes in the glucosidic bonds. In a separatestudy electron beam processing enhanced the reactivity, i.e. lowered theresidual cellulose content, of the investigated pulps. The magnitude of theelectron dose, within the tested range (5.4–23.7 kGy), didnotseem to be important, but the reactivity within pulp sheets tended to be ratherinhomogeneous. 相似文献
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Summary: Cavitation in low molecular weight liquids under tension and in crystalline polymers during tensile drawing was recapitulated. The review indicated that the amorphous phase of crystalline polymers at temperature above its glass transition temperature differs markedly from low molecular weight liquids. Cavitation in polymers seemingly is not of a heterogeneous character, unlike in unpurified low molecular weight liquids. The most probable reasons are: confinements of amorphous layers between crystalline lamellae and macromolecular chain entanglements, the factors that are absent in low molecular weight liquids. 相似文献
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Information from blue (400–500 nm) and red (660–730 nm) wavelengths is used by plants to determine proximity of neighbors or actual shading. Plants undergo trait changes in order to out-compete neighbors or accommodate shading. Heteroblasty, the dramatic shift from one leaf type to another during juvenility, can be influenced by the light environment although it is unknown whether cues from blue or red (or both) are driving the developmental process. Seedlings of three populations of Acacia implexa (Mimosaceae) collected from low, medium and high rainfall habitats were grown in a factorial design of high/low blue and red light to determine how light signals affect heteroblasty and patterns of biomass allocation. Low blue light significantly delayed heteroblasty in the low rainfall population and low red light significantly delayed in the low and high rainfall populations. Low blue light increased stem elongation and decreased root biomass whereas low red light induced a strong shade-avoidance response. These results were consistent across populations although the low rainfall population showed greater trait variability in response to red light signals. We conclude that red light conveys a greater information signal than blue light that affects heteroblasty and seedling development in A. implexa . 相似文献
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Bhuiyan LB Outhwaite CW Henderson D 《Langmuir : the ACS journal of surfaces and colloids》2006,22(25):10630-10634
Monte Carlo simulation and the modified Poisson-Boltzmann theory are used to investigate the planar electric double layer for a restricted primitive model electrolyte at low temperatures. Capacitance as a function of temperature at low surface charge is determined for 1:1, 2:2, 2:1, and 3:1 electrolytes. Negative adsorption can occur for 1:1 electrolytes at low surface charge with low electrolyte concentration. The 1:1 electrolyte diffuse layer potential as a function of surface charge displays a maximum at low densities. At high densities, the diffuse layer potential is negative with a negative slope. The Gouy-Chapman-Stern theory fails in this low-temperature regime, whereas the modified Poisson-Boltzmann theory is fairly successful in this regard. 相似文献
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采用乙二胺四乙酸-柠檬酸联合溶胶凝胶法合成了B位掺镁的简单钙钛矿纯相样品LaMn1-xMgxO3(x=0~0.50). Mg在钙钛矿B位的掺杂和调节Mn3+/Mn4+的摩尔比强烈地影响样品的磁性行为. x≤0.08时, 样品低温下表现弱的铁磁性; x≥0.18时, 随着Mg掺杂引入的Mn4+离子间的反铁磁性超交换作用与Mn3+-Mn4+离子间的铁磁性双交换作用使样品在低温下呈现自旋玻璃态. 随着Mg2+掺杂量的增加, 样品的磁有序温度与自旋凝固温度单调降低. 相似文献
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The γ-ray initiated polymerization of 4-methyl-1-pentene, 2-methyl-1-butene, and 2,3-dimethyl-1-butene has been studied under conditions of extreme dryness. Only low yields of oily low molecular weight polymers were obtained. It is suggested that the low propagation rate constants are responsible for the results obtained. 相似文献
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N. Thornton Lipscomb Yassin Tarshiani 《Journal of polymer science. Part A, Polymer chemistry》1988,26(2):529-540
The kinetics of the photopolymerization of styrene in bulk and in dilute systems in the presence of benzoin isobutyl ether as photoinitiator have been examined. The values of the intensity exponent, calculated at different temperatures or at different styrene concentrations, and the monomer exponent, calculated at various intensities, showed significant departure from those predicted by the ideal kinetic scheme, particularly at high intensity, at low temperature, or at low styrene concentrations. Low molecular weight polymer was the dominant product when high light intensity or low polymerization temperature was used. As the temperature was raised, however, or as the intensity was reduced, a high molecular weight polymer became progressively more important. Kinetic and molecular weight data suggest that at low temperature, high intensity, and/or at low monomer concentration, the benzoyl radical is the dominant initiating species; and the benzyl ether radical was consumed mainly in the termination step. At low intensity, high temperature and/or high monomer concentration, however, it appears that both benzoyl and benzyl ether radicals initiated polymerization. 相似文献
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Page JS Tolmachev AV Tang K Smith RD 《Journal of the American Society for Mass Spectrometry》2006,17(4):586-592
The transmission of ions at low m/z can often be either necessary for an application or problematic (e.g., when large numbers of low m/z ions consume a large fraction of an ion trap's capacity). The low m/z ion transmission limit of an electrodynamic ion funnel has been characterized using both experimental and theoretical approaches. A theoretical model is developed based on a series of infinite wire conductors that represent the ring electrodes of the ion funnel. Mathematical relationships for both low and high m/z cutoffs of the idealized two-dimensional system are derived. The low m/z cutoff is also evaluated through a series of experiments that show it is influenced by both the RF frequency and the DC electric field gradient. However, unlike multipole ion guides, there is no marked dependence of the low m/z cutoff on the RF amplitude, in agreement with theoretical results. With this new understanding, ion funnels can be designed and configured to better match the m/z range requirements for various applications. 相似文献
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Jiang H Jantan MK Manolache S Denes FS Lagally MG 《Langmuir : the ACS journal of surfaces and colloids》2008,24(16):8672-8677
Radio-frequency (RF) plasma enhanced chemical vapor deposition (PECVD) provides a promising way to deposit extremely hydrophobic, highly adherent nanometer- to micrometer-thick films with thermal stability, a low coefficient of friction, a low dielectric constant, and a low value of surface energy. We describe the synthesis of these fluorinated thin films using hexafluoropropene as starting material and discuss their properties. These coatings, applied to stainless steel, provide ideal substrates for Raman spectroscopy, when extremely low backgrounds are required. Raman spectroscopy measurements of a low-concentration protein film are used to demonstrate sensitivity and level of detectability. 相似文献
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Dielectric measurements on two mixtures of a low and high molecular liquid crystal and the pure components have been carried out in the frequency range from 1 Hz to 100 kHz. In the SA and supercooled SA phase two absorption ranges were observed. The low frequency absorption belongs to the low molecular weight liquid crystal. The shift in the relaxation frequency of both compounds indicates complete miscibility. The strong difference of the absorption intensity of the polymer on heating and cooling can be associated with the formation of mixed crystals at smaller concentrations of the low molecular weight compound. 相似文献
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Robert P. Grasso Jerome B. Lando 《Journal of polymer science. Part A, Polymer chemistry》1989,27(10):3327-3341
A family of nitrile-terminated diacetylene materials were synthesized. Samples were prepared in various forms and polymerization was performed photochemically and thermally. The resulting materials exhibited low molecular weights and were obtained in low yields. Although the diacetylene group had oligomerized, no evidence was found in support of ? C?N? chain formation. Thermochromism was exhibited by the irradiated 8-nitrile sample and a molecular interpretation of this chromic transition was discussed. Diffraction data implied that strong intermolecular interactions were present between adjacent nitrile groups in the low temperature phase. It is suggested that stresses are built up during polymerization which cause the low degree of polymerization and yield. 相似文献