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981.
Saziye Ugur Ayse Alemdar Önder Pekcan 《Journal of Coatings Technology and Research》2005,2(7):565-575
This study reports a steady-state fluorescence (SSF) technique for studying film formation from surfactant-free polystyrene
(PS) latex and Na-montmorillonite (SNaM) composites. The composite films were prepared from pyrene (P)-labeled PS particles
and SNaM clay at room temperature and annealed at elevated temperatures in 10-min intervals above glass transition temperature
(t3) of polystyrene. During the annealing processes, the transparency of the film improved considerably. Scattered light (Is) and fluorescence intensity (Ip) from P were measured after each annealing step to monitor the stages of film formation. Evolution of transparency of composite
films was monitored by using photon transmission intensity, Itr. Scanning electron microscopy (SEM) was used to detect the variation in physical structure of annealed composite films. Minimum
film formation temperature, Tq, and healing temperatures, Th, were determined. Void closure and interdiffusion stages were modeled and related activation energies were determined. It
was observed that both activation energies increased as the percent of SNaM was increased in composite films. 相似文献
982.
Ming Li Zbigniew Twardowski Felix Mok Norbert Tam 《Journal of Applied Electrochemistry》2007,37(4):499-504
Sodium dichromate is commonly used in sodium chlorate production to maintain high current efficiency; however, it is also
a well documented carcinogen. To reduce the environmental impact, identification of a suitable alternative with similar buffering
characteristics to dichromate and without adverse effect on the electrolytic performance of sodium chlorate production is
important; sodium molybdate is a good candidate. Molybdate ion and its conjugated acid work as a buffer pair at pH 5–6, a
lower and slightly narrower pH window than the typical buffer region of dichromate. Nonetheless, the molybdate buffer works
effectively during the electrolytic process by maintaining pH at 5.9. Although the use of molybdate buffer will lower the
overpotential of hydrogen evolution reaction (HER) by 100 mV, the average off-gas oxygen content is noticeably compromised
at 3.6–4.6%, measured using a pilot cell operated at 3 kA m−2and 80 °C during a 3-day trial. The resulting current efficiency of 91 92% is significantly lower than when dichromate is
employed as the process additive (> 96%). Mixtures of different dichromate and molybdate ratio were also investigated in terms
of the resulting cathode surface potential. 相似文献
983.
Background
Leptin and its soluble receptor (sOB-R) are important to regulation of body composition but there are no data on the developmental variations in these plasma variables and their relationship with body composition measurements, 相似文献984.
Thomas W. Coyle William S. Coblenz Barry A. Bender 《Journal of the American Ceramic Society》1988,71(2):88-C-
The fracture and transformation behavior of tetragonal polycrystalline ZrO2 alloys containing 18 mol% CeO2 (Ce-TZP) was investigated. In the absence of applied stress the tetragonal phase was found to be stable in large-grained (>30 μm) samples at room temperature. The monoclinic phase was detected in regions of high residual stress near hardness indentations although no evidence of a wake of monoclinic phase along the fracture surface was observed. The fracture toughness increased from 4 to 7 MPa · m1/2 as density and/or grain size increased. It is proposed that the relatively high toughness of these materials is due to the occurrence of stress-driven tetragonal-to-monoclinic transformation near the crack tip, which reverses when the crack has passed. 相似文献
985.
Darwish Kamel; Li Huiying; Poulos Thomas 《Protein engineering, design & selection : PEDS》1991,4(6):701-708
A very efficient system for subcloning and studying proteinsequences, combining previously established elements for hyperexpression,replication and screening, was used to hyperproduce and characterizeseven different products. It expedited the cloning of genes,in a multipurpose recombinant DNA construct, for all the requirementsto study and engineer proteins with a strain of Escherichiacoli. Genes encoding six heme proteins and a flavoprotein havebeen subcloned and expressed to 1330% of the total cellprotein, greatly facilitating purification and analyses. Threeof the heme proteins and the flavoprotein incorporated prostheticgroups in E.coli, and exhibited the expected activities. Fourof the enzymes have been purified to homogeneity and two ofthese crystallized for X-ray diffraction analysis. A rapid muta-genesisprotocol, based on polymerase chain reactions, was successfullyapplied to clone derivatives of one of these enzymes, cytochromec peroxidase. Thus, this system fulfills all criteria for engineeringproteins in an efficient and concerted manner. 相似文献
986.
Thomas M. Odell Chong-Hua Xu Paul W. Schaefer Barbara A. Leonhardt De-Fu Yao Xiang-De Wu 《Journal of chemical ecology》1992,18(12):2153-2159
Pheromone traps baited with (+)-disparlure,cis-7,8-epoxy-2methyocta-decane, captured males ofLymantria dispar, L. monacha, andL. mathura in northeastern People's Republic of China.L. dispar responded to the addition of olefin to (+)-disparlure-baited traps in a negative doseresponse manner. Observations on site and seasonal capture ofL. dispar andL. mathura are discussed.Lepidoptera: Lymantriidae. 相似文献
987.
Fouling of membranes by colloidal organic and inorganic particles continues to be documented as the most common and challenging obstacle in attaining stable continuous operation of reverse osmosis (RO) and ultrafiltration (UF) systems. Much current research is being conducted on physical parameters to mitigate such fouling. The focus has been on membrane synthesis and element design; microfiltration and ultrafiltration pretreatment; electromagnetic devices; correlation with physical factors such as Silt Density Index, zeta potential and critical flux; technique of direct observation of fouling process through a membrane; and classification of macromolecular organics for correlation with fouling characteristics. We report initial successes with chemical control of colloidal fouling. Through screening with a large number of observable coagulations of natural colloids, we have developed a group of proprietary anticoagulants and dispersants that would, at less than 10 ppm dosage to the RO feedwater, control various classes of colloidal foulants. Case studies of the control of humic matter, elemental sulfur and colloidal silicate in problematic RO systems that became stabilized are briefly presented. We conclude that a great need and potential exists in economically controlling the myriads of fouling interactions of colloidal particles during concentration within the brine channels of RO membrane elements. Low dosages of antifoulants can in many cases obviate the need for installation and maintenance of pretreatment unit or operations designed to remove such colloidal foulants from the process stream. 相似文献
988.
Chao AC Ziadeh BI Diau GY Wijendran V Sarkadi-Nagy E Hsieh AT Nathanielsz PW Brenna JT 《Lipids》2003,38(4):425-429
One of the major survival challenges of premature birth is production of lung surfactant. The lipid component of surfactant,
dipalmitoyl PC (DPPC), increases in concentration in the period before normal term birth via a net shift in FA composition away from unsaturates. We investigated the influence of dietary DHA and arachidonic acid (AA)
on lung FA composition and DPPC concentration in term and preterm baboons. Pregnant animals/neonates were randomized to one
of four groups: breast-fed (B), term formula-fed (T−), preterm formulafed (P−), and preterm fed formula supplemented with DHA-AA (P+). Breast milk contained 0.68%wt DHA and the P+ group formula contained 0.61%wt DHA. In the preterm groups (P− and P+), pregnant females received a course of antenatal corticosteroids. At the adjusted age of 4 wk, neonate lung tissue was harvested,
and FA composition and DPPC were analyzed. Palmitate was ∼28%wt of lung total FA and no significant differences were found
among the four treatment groups. In contrast, DPPC in the B group lung tissue was significantly greater than DPPC in the unsupplemented
groups, but not compared with the P+ group. The B and P+ groups were not significantly different in DHA and AA, but were different compared with the unsupplemented (T, P−) groups. These results indicate that LCP supplementation increases lung DHA and AA, without compromising overall lung 16∶0
or DPPC. The shift in FA composition toward greater unsaturation in the groups consuming LCP supported improved surfactant
lipid concentration in preterm neonate lungs. 相似文献
989.
A series of new polyamides 3a–d containing aryl-azo, ether and sulfone groups in the main chain were synthesized from bis[4-(4-aminophenoxy)phenyl sulfone]
1 and several azo aromatic diacyl chlorides 2a–d by the low temperature solution polycondensation technique. FTIR spectroscopy, nuclear magnetic resonance (NMR) and elemental
analyses confirmed the structure of these polymers. Owing to the aryl and amide groups in the main chain, these polymers exhibit
photochromic properties as well as excellent thermal stabilities. The transition temperatures (T
g) are between 242 and 265 °C, and the char yields at 800 °C in nitrogen atmosphere were above 39%. Based on incorporation
of flexible ether linkages and polar sulfone groups, the polyamides show desirable solubility in organic solvents such as
DMAc, N,N-dimethylformamide (DMF), N-methyl-2-pyrroidinone (NMP) and dimethylsulfoxide (DMSO). And it is exemplified that
polyamide containing 2 and 2′ substitutes performed better solubility.
Funded by the National Natural Science Foundation of China (No. 50572081) 相似文献
990.
The tribological properties of perfluoro and non-perfluoro alkylsilane molecular films were investigated and compared detailedly.
Their surface properties were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and contact
angle (CA) measurement. A ball-on-disk tribometer was used to study the frictional properties of these alkylsilane monolayers.
The experimental results reveal that the alkylsilane molecular films are good candidates to decrease friction and they have
good capability to endure rigorous shear forces. Perfluoro alkylsilane molecular films are bonded better with the Si substrate
than the simple hydrocarbon ones. The effects of sliding velocity and normal load on friction coefficient are evident and
the friction coefficient increases with the increase of the sliding velocity. However, friction coefficient decreases with
the increase of normal load initially and then increases, indicating there exists a critical normal load for the load effect.
Funded by the National Natural Science Foundation of China (No.50730007 and 50805086), the Foundation of Tsighua Basic Research,
and the National Key Basic Research Program of China(No. 2007CB607604) 相似文献