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排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
González RJ Torres R De Greef D Bonaldo A Robutti J Borrás F 《Archivos latinoamericanos de nutrición》2005,55(4):354-360
Knowledge of the association between cooking properties and endosperm hardness may help nutritionist and processors to select raw materials for preparing maize based food products, particularly those eaten as cooked dispersions. Seven commercial maize cultivars differing in hardness were selected to evaluate endosperm hardness on the kernels and some characteristics such as composition and hydration and cooking properties on the grits obtained from those maizes. Results show that the differences in endosperm hardness (directly related to grits protein content) can explain the differences in swelling and amylographic consistencies values. Cultivars with the hardest endosperm show the lowest values at high temperature. They also show the lowest amylographic consistencies. On the other hand softer endosperms present the highest swelling power and the highest amylographic consistencies. These differences are attributed to the restriction for starch swelling caused by the protein matrix. Endosperm hardness measurements and swelling power at 95 degrees C, can be useful to select cultivars that are going to be used to prepare maize based foods like atoles, polenta, etc. 相似文献
992.
Tao Jian Wei‐De Shyu Yue‐Tang Lin Kan‐Nan Chen Jen‐Taut Yeh 《Polymer Engineering and Science》2003,43(11):1765-1777
The concentrations and temperatures of ultrahigh‐molecular‐weight polyethylene (UHMWPE) gel solutions exhibited a significant influence on their rheological and spinning properties. The shear viscosities of UHMWPE solutions increased consistently with increasing concentrations at a constant temperature above 80°C. Tremendously high shear viscosities of UHMWPE gel solutions were found as the temperatures reached 120–140°C, at which their shear viscosity values approached the maximum. The spinnable solutions are those gel solutions with optimum shear viscosities and relatively good homogeneity in nature. Moreover, the gel solution concentrations and spinning temperatures exhibited a significant influence on the drawability and microstructure of the as‐spun fibers. At each spinning temperature, the achievable draw ratios obtained for as‐spun fibers prepared near the optimum concentration are significantly higher than those of as‐spun fibers prepared at other concentrations. The critical draw ratio of the as‐spun fiber prepared at the optimum concentration approached a maximum value, as the spinning temperature reached the optimum value of 150°C. Further investigations indicated that the best orientation of the precursors of shish‐kebab‐like entities, birefringence, crystallinity, thermal and tensile properties were always accompanied with the as‐spun fiber prepared at the optimum concentration and temperature. Similar to those found for the as‐spun fibers, the birefringence and tensile properties of the draw fibers prepared at the optimum condition were always higher than those of drawn fibers prepared at other conditions but stretched to the same draw ratio. Possible mechanisms accounting for these interesting phenomena are proposed. 相似文献
993.
High-temperature molding of Brabender-mixed blend of polyacrylic acid (PAA) and epoxidized natural rubber (ENR) causes thermally induced crosslinking between PAA and ENR. Studies on Monsanto rheometry of the blend and physical properties, solvent swelling, and dynamic mechanical properties of the molded blend show that both mixer rotor speed and carbon black filler influence the crosslinking between the component polymers. For example, the extent of crosslinking for the 50–50 PAA–ENR blend was found maximum when the component polymers were mixed at 40 rpm, but the same blend filled with 30 phr HAF carbon black filler showed maximum crosslinking when mixing was carried out at 120 rpm. The results have been explained on the basis of formation of network on the filler surface, which in turn depends on two competing factors: increase in bound rubber formation with increase in filler loading at a fixed rotor speed and enhanced degradation of ENR at higher mixer rotor speed at a fixed filler loading. © 1994 John Wiley & Sons, Inc. 相似文献
994.
Measurement of O2-N2 binary sorption on 5A zeolite by isotope tracer and perturbation chromatography
Isotope tracer chromatography allows to extract simply and quickly multi component adsorption data and is demonstrated for single component and binary adsorption equilibria for O2 and N2 on 5A zeolite as an example. In this modification of conventional tracer chromatography, a small pulse of an isotope tracer is injected in an adsorbable carrier gas (pure or multicomponent mixture) flowing through a column filled with adsorbent and is designed to operate at almost uniform pressure. Isotherm parameters are readily extracted by fitting measurements of residence times at various pressures and carrier composition. The isotherms were in excellent agreement with volumetric measurements. Isotope tracer chromatography is shown to be superior to perturbation chromatography since the influence of the injection volume on the carrier gas composition is substantially smaller for tracer experiments. Unfortunately, this new improved gas chromatographic technique requires rather expensive isotopes. The strength of this new approach lies in the advantage of working with small adsorbent samples (1 g) making a rapid screening of newly developed materials possible.Nomenclature
K
exp,tr,i
experimental tracer adsorption constant (mol/kg pure adsorbent/Pa)
-
K
i
Henry adsorption equilibrium constant (mol/kg pure adsorbent/Pa)
-
K
i,part
partition coefficient
-
K
pert
composite Henry constant (mol/kg pure adsorbent/Pa)
-
L
column length (m)
-
L
i
Langmuir adsorption constant (1/Pa)
-
n
i
amount adsorbed on the solid (mol/kg adsorbent)
-
N
i
adsorbent loading (Pa)
-
p
total pressure (Pa)
-
p
i
partial pressure of component i (Pa)
-
p
in
column inlet pressure (Pa)
-
p
out
column outlet pressure (Pa)
-
q
i
amount of component i in the micropores (Pa)
-
R
gas constant (J/mol/K)
-
t
time (s)
-
T
temperature (K)
-
v
f
superficial velocity in adsorbent column (m/s)
-
v
out
velocity at the outlet of the column (m/s)
-
V
inlet
volumetric flow rate at inlet conditions (ml/s)
-
x
molar fraction of tracer
-
y
molar fraction of component i in the carrier gas
-
z
axial coordinate (m)
Greek letters ext
bed voidage, external porosity
- macr
macropore porosity [macr=
p
(1–ext)]
- micr
micropore porosity
- tot
total porosity
-
p
pellet porosity
-
volume fraction of binder material
-
d
dead time (s)
- tracer
tracer residence time (s)
- pert
perturbation residence time (s)
- crys
crystal density (kg/m3) 相似文献
995.
Arun Ghosh R. S. Rajeev A. K. Bhattacharya A. K. Bhowmick S. K. De 《Polymer Engineering and Science》2003,43(2):279-296
The silicone rubber vulcanizate powder (SVP) obtained from silicone rubber by mechanical grinding exists in a highly aggregated state. The particle size distribution of SVP is broad, ranging from 2 µm to 110 µm with an average particle size of 33 µm. X‐ray Photoelectron Spectroscopy (XPS) and Infrared (IR) Spectroscopy studies show that there is no chemical change on the rubber surface following mechanical grinding of the heat‐aged (200°C/10 days) silicone rubber vulcanizate. Addition of SVP in silicone rubber increases the Mooney viscosity, Mooney scorch time, shear viscosity and activation energy for viscous flow. Measurement of curing characteristics reveals that incorporation of SVP into the virgin silicone rubber causes an increase in minimum torque, but marginal decrease in maximum torque and rate constant of curing. However, the activation energy of curing shows an increasing trend with increasing loading of SVP. Expectedly, incorporation of SVP does not alter the glass‐rubber transition and cold crystallization temperatures of silicone rubber, as observed in the dynamic mechanical spectra. It is further observed that on incorporation of even a high loading of SVP (i.e., 60 phr), the tensile and tear strength of the silicone rubber are decreased by only about 20%, and modulus dropped by 15%, while the hardness, tension set and hysteresis loss undergo marginal changes and compression stress‐relaxation is not significantly changed. Atomic Force Microscopy studies reveal that incorporation of SVP into silicone rubber does not cause significant changes in the surface morphology. 相似文献
996.
产共轭亚油酸乳酸菌的选育和鉴定 总被引:1,自引:0,他引:1
采用紫外分光光度法测定共轭亚油酸的含量,从13株实验室保存的乳酸菌中筛选出8株具有转化亚油酸生成共轭亚油酸能力的菌株.其中As1.2686产量最高,发酵液中共轭亚油酸含量达到13.63 mg/L;其次是菌株B11693,共轭亚油酸产量为11.55 mg/L.选择B11693做进一步的菌种鉴定,将传统的形态学、生理生化鉴定方法和细菌16SrDNA分子生物学鉴定方法相结合,鉴定菌株B11693为短乳杆菌. 相似文献
997.
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
998.
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
999.
A micro-envioment for nerve cells and tissue growth were designed and constructed via surface modification of poly(L-lactide-co-glycolide)(PLGA)
with chitosan and hydroxyapatite(HA). The poly(L-lactide-co-glycolide)/chitosan/hydroxyapatite (PLGA/chitosan/HA) conduits
were manufactured by a combined solvent casting and particulate leaching technique. The conduits were highly porous with an
interconnected pore structure and 76.5% porosity. Micropores with 50–100 micrometer diameter were formed in the conduits.
In vivo application of PLGA/chitosan/HA conduits for reconstruction of 10 mm sciatic nerve defect was assessed by the walking
track analysis, the quantifying of the wet weight of tibialis anterior muscle and the histological assessment. The conduits
in host rats in vivo can not only be an effective in promoting regenerating of nerves but can also lead to favorable nerve
functional recovery.
Funded by the National Natural Science Foundation of China(No.50774096) 相似文献
1000.
郑立霞 《武汉理工大学学报(材料科学英文版)》2009,24(3):415-417
The deformation resistance effect of polyacrylonitrile (PAN)-based carbon fibers was investigated, and the variatipn law of
electrical resistivity under tensile stress was analyzed. The results show that the gauge factor (fractional change in resistance
per unit strain) of PAN-based carbon fibers is 1.38, which is lower than that of the commonly-used resistance strain gauge.
These may due to that the electrical resistivity of carbon fibers decreases under tensile stress. In addition when the carbon
fibers are stretched, the change of its resistance is caused by fiber physical dimension and the change of electric resistivity,
and mainly caused by the change of physical dimension. The mechanical properties of carbon fiber monofilament were also measured.
Funded by the National Natural Science Foundation of China (No. 10672128 and 50878170) 相似文献