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21.
Jin Sun Yihu Song Qiang Zheng Hong Tan Jie Yu Hong Li 《Journal of Polymer Science.Polymer Physics》2007,45(18):2594-2602
The reinforcement and nonlinear viscoelastic behavior have been investigated for silica (SiO2) filled solution‐polymerized styrene butadiene rubber (SSBR). Experimental results reveal that the nonlinear viscoelastic behavior of the filled rubber is similar to that of unfilled SSBR, which is inconsistent with the general concept that this characteristic comes from the breakdown and reformation of the filler network. It is interesting that the curves of either dynamic storage modulus (G′) or loss tangent (tan δ) versus strain amplitude (γ) for the filled rubber can be superposed, respectively, on those for the unfilled one, suggesting that the primary mechanism for the Payne effect is mainly involved in the nature of the entanglement network in rubbery matrix. It is believed there exists a cooperation between the breakdown and reformation of the filler network and the molecular disentanglement, resulting in enhancing the Payne effect and improving the mechanical hysteresis at high strain amplitudes. Moreover, the vertical and the horizontal shift factors for constructing the master curves could be well understood on the basis of the reinforcement factor f(φ) and the strain amplification factor A(φ), respectively. The surface modification of SiO2 causes a decrease in f(φ), which is ascribed to weakeness of the filler–filler interaction and improvement of the filler dispersion. However, the surface nature of SiO2 hardly affects A(φ). © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2594‐2602, 2007 相似文献
22.
本文用数字散斑相关方法测量了五种不同幂硬化指数韧性金属材料(铝和铜),双边裂纹尖端细观区域内应变场.对所得结果用韧性损伤模型进行了分析.在此法中以金属自然表面结构为散斑场,不同加载状态的散斑场进行比较,得到相对变形与应变.图象之间相关性 C 是变形参数或是位移及其导数的泛函.使其相关性 C 取最大值的试凑变形即为其真实变形场.这一方法在细观测量中应用得到满意的结果. 相似文献
23.
Claudio Albanese 《Journal of statistical physics》1994,77(1-2):77-87
The hydrodynamic regime of superfluids is dominated by a Goldstone mode corresponding to a spontaneously brokenU(1) symmetry. In this article we map the Kawasaki-Ising model for a classical lattice gas into a quantum model for a superfluid and establish a connection between the normal density fluctuations of the first and the Goldstone mode of the second. The fact that the quantum model we obtain describes a superfluid derives from an inequality by Penrose and Onsager which gives a lower bound to the Bose-Einstein condensate density. Mathematically, the Goldstone mode can be described by means of a quantum extension of the local algebra of the Ising model. The classification of its irreducible representations requires an additionalU(1) phase factor and the correspondingU(1) gauge symmetry is spontaneously broken for all finite values of the temperature and of the density. 相似文献
24.
An estimation of the mass difference of
system with heavy quark symmetry formalism is presented. The effective Hamiltonian describing the transition
(whereh=b forB
d
0
-system) is considered in a manifest left right symmetric (MLRS) model along with contribution from neutral Higgs boson. We
use the spin and flavor symmetry for heavy quarks to obtain the transition matrix element 〈B
d
0
|ℋeff(x)|
d
0
〉 in terms of Isgur-Wise function. Assuming thatB
d
0
and
states are at rest, we find that Isgur-Wise function turns out to be unity. However using the experimental values of ΔM
K and
as input, we find thatM
R=835 GeV andM
H⩾2·9 TeV. 相似文献
25.
The synthesis of norvancomycin (NVan)-capped silver nanoparticles (Ag@NVan) and their notable in vitro antibacterial activities against E. coli, a Gram-negative bacterial strain (GNB), are reported here. Mercaptoacetic acid-stabilized spherical silver nanoparticles
with a diameter of 16±4 nm are prepared by a simple chemical reaction. The formation process of the silver nanoparticles is
investigated by UV-visible (UV-vis) spectroscopy and transmission electron microscopy (TEM). NVan is then grafted to the terminal
carboxyl of the mercaptoacetic acid in the presence of N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDAC). The TEM images of single bacteria treated with Ag@NVan show that plenty of Ag@NVan
aggregate in the cell wall of E. coli. A possible antibacterial mechanism is proposed that silver nanoparticles may help destroy the stability of the outer membrane
of E. coli, which makes NVan easier to bind to the nether part of the peptidoglycan structure. The antibacterial activities of silver
nanoparticles on their own, together with the rigid polyvalent interaction between Ag@NVan and cell wall, enables Ag@NVan
to be an effective inhibitor of GNB. This kind of bionanocomposites might be used as novel bactericidal materials and we also
provide an effective synthesis method for preparing functional bioconjugated nanoparticles here.
Supported by the National Natural Science Foundation of China (Grant No. 50373036) and Fok Ying Tung Education Foundation
(Grant No. J20040212) 相似文献
26.
研究了简单剪切与纯剪切的关系,得出了:(1)简单剪切可看成纯剪切加转动,转动角θ有;(2)若简单剪切椭圆的长轴与坐标轴X的夹角为φ,相应的纯剪椭圆长袖与坐标轴y的夹角为β0,则φ=β0;(3)橡胶在双向拉伸时剪应变γ的一般表达式为,对简单剪切而言即为 相似文献
27.
Synthesis,Structure, and Fluxionality of Strained Hypercoordinate Silicon‐Bridged [1]Ferrocenophanes
《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(13):3042-3054
The first hypercoordinate sila[1]ferrocenophanes [fcSiMe(2‐C6H4CH2NMe2)] ( 5 a ) and [fcSi(CH2Cl)(2‐C6H4CH2NMe2)] ( 5 b ) (fc=(η5‐C5H4)Fe(η5‐C5H4)) were synthesized by low‐temperature (?78 °C) reactions of Li[2‐C6H4CH2NMe2] with the appropriate chlorinated sila[1]ferrocenophanes ([fcSiMeCl] ( 1 a ) and [fcSi(CH2Cl)Cl] ( 1 d ), respectively). Single‐crystal Xray diffraction studies revealed pseudo‐trigonal bipyramidal structures for both 5 a and 5 b , with one of the shortest reported Si???N distances for an sp3‐hybridized nitrogen atom interacting with a tetraorganosilane detected for 5 a (2.776(2) Å). Elongated Si? Cipso bonds trans to the donating NMe2 arms (1.919(2) and 1.909(2) Å for 5 a and 5 b , respectively) were observed relative to both the non‐trans bonds ( 5 a : 1.891(2); 5 b : 1.879(2) Å) and the Si? Cipso bonds of the non‐hypercoordinate analogues ([fcSiMePh] ( 1 b ): 1.879(4), 1.880(4) Å; [fcSi(CH2Cl)Ph] ( 1 e ): 1.881(2), 1.884(2)). Solution‐state fluxionality of 5 a and 5 b , suggestive of reversible coordination of the NMe2 group to silicon, was demonstrated by means of variable‐temperature NMR studies. The ΔG≠ of the fluxional processes for 5 a and 5 b in CD2Cl2 were estimated to be 35.0 and 37.6 kJ mol?1, respectively (35.8 and 38.3 kJ mol?1 in [D8]toluene). The quaternization of 5 a and 5 b by MeOTf, to give [fcSiMe(2‐C6H4CH2NMe3)][OTf] ( 7 a‐ OTf) and [fcSi(CH2Cl)(2‐C6H4CH2NMe3)][OTf] ( 7 b‐ OTf), respectively, supported the reversibility of NMe2 coordination at the silicon center as the source of fluxionality for 5 a and 5 b . Surprisingly, low room‐temperature stability was detected for 5 b due to its tendency to intramolecularly cyclize and form the spirocyclic [fcSi(cyclo‐CH2NMe2CH2C6H4)]Cl ( 9 ‐Cl). This process was observed in both solution and the solid state, and isolation and Xray characterization of 9 ‐Cl was achieved. The model compound, [Fc2Si(2‐C6H4CH2NMe2)2] ( 8 ), synthesized through reaction of [Fc2SiCl2] with two equivalents of Li[2‐C6H4CH2NMe2] at ?78 °C, showed a lack of hypercoordination in both the solid state and in solution (down to ?80 °C). This suggests that either the reduced steric hindrance around Si or the unique electronics of the strained sila[1]ferrocenophanes is necessary for hypercoordination to occur. 相似文献
28.
Robert M. Smith Ping Yuan David P. Weiner Caryn R. Dutton David E. Hansen 《Applied biochemistry and biotechnology》1994,47(2-3):329-343
We describe here a novel strategy for the isolation of antibodies with sequence-specific protease activity: the synthesis
of dipeptide haptens in which the targeted peptide bond has been replaced by a ring-strained or torsionally strained hydroxyethylene
transition-state analog. Thus, the analogs mimic both a peptide bond in a distorted, reactive conformation and the transition
state for peptide bond hydrolysis. In order to obtain sequence-specific antibody proteases, these analogs have been flanked
with additional amino acid residues in preparation for immunization. In particular, we have synthesized peptides containing
analogs such as 2-cis-amino-3-cis-hydroxycyclobutane carboxylic acid andendo-(3-amino-2-hydroxy)bicyclo[2.2.1]heptane-7-anti-carboxylic acid. We have also prepared a series of peptide derivatives containing
analogs, such as 2-[3-amino-2-oxo-1-azetidinyl]-3-methylbutanoic acid, in which the targeted peptide bond has been incorporated
into a β-lactam ring. Since the “peptide bond” has been left intact, these species mimic only a distorted ground state. At
present, antibodies are being elicited against a number of the above peptide derivatives. 相似文献
29.
Tarek M. Madkour Rasha A. Azzam 《Journal of polymer science. Part A, Polymer chemistry》2002,40(14):2526-2536
Polyurethane elastomers of a controlled molecular architecture were synthesized using a two‐step polymerization technique. The building blocks of the elastomeric materials included urea–urethane prepolymers end‐capped with diisocyanate groups and had an exact number of urea groups at both ends. Two‐dimensional bifurcated hydrogen‐bonding networks incorporating the urea groups were, with differential scanning calorimetric and dynamic mechanical thermal analyzer techniques, responsible for the increase in the glass‐transition temperature (Tg) of the hard block and sharp interface morphology between the pure “hard” domains and pure “soft” domains. The higher extent of the phase separation between the two phases contributed to higher elastic moduli for the hard blocks and higher tensile strength for the elastomeric samples. Higher elongation values were attributed to the liberation of the elastomeric chain ends that otherwise would have been constrained in the interface region. The higher Tg values of the hard blocks corresponded to an increase in the hardness values and a decrease in the tear‐strength values. The increase in the amount of urea groups within the hard segments, as a result of the increased amount of water and blowing catalyst, resulted in elastomeric foams with higher open‐cell content. This resulted in lower resilience values as measured using the pendulum rebound test and was attributed to the ability of the open cells to absorb and dissipate energy. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2526–2536, 2002 相似文献
30.
Glucose utilization by lysine-producing fluoroacetate-sensitive mutants ofCorynebacterium glutamicum
A fluoroacetate-sensitive mutant was isolated fromCorynebacterium glutamicum, ATCC 21513, following mutagenesis with NTG. Batch fermentations show that in terms of growth kinetics, glucose utilization,
and lysine formation, there are significant differences between the mutant and the parent. The mutant’s specific growth rate
(0.22/h) is lower than that for the parent (0.34/h). Also, the yield expressed as lysine/glucose consumed does not alter as
a function of the glucose concentration for the mutant, and is about 0.22, whereas for the parent, this coefficient decreases
with increasing glucose concentration. The maximum specific rate of lysine production for the mutant is 1.3 g/L/h that is
about two-fold higher than that for the parent. 相似文献