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991.
Somma E Chi C Loppinet B Grinshtein J Graf R Fytas G Spiess HW Wegner G 《The Journal of chemical physics》2006,124(20):204910
Orientation molecular dynamics were investigated in a series of "defect-free" oligofluorenes by depolarized dynamic light scattering and dynamic NMR spectroscopy. Typical liquid crystalline pretransitional dynamics were observed upon cooling the isotropic phase to the liquid crystalline phase with strong increase of the scattered intensity and slowing down of the characteristic time of the probed collective relaxation. This is well accounted for by the Landau-de Gennes theory, however, with a strong temperature dependence of the viscosity coefficient, reflecting the proximity of the glass transition. For the trimer the two transitions almost overlap and the molecular orientation coincide with the alpha-relaxation associated with the glass transition. The NMR measurements confirm that the time scale of the dynamics is completely governed by the glass process, yet the geometry of the motion is anisotropic, yielding order parameters ranging from 0.15 to 0.25 for the long axis in the liquid crystalline phase. The glass transition is therefore geometrically restricted with poorly ordered mesophase which is consistent with the weak transverse phonons in the light scattering experiment down to Tg+20 K. 相似文献
992.
The tert-butanethiol self-assembled monolayers (SAMs) on Au(111) surfaces were prepared from various solvents and investigated by a combination of scanning tunneling microscopy (STM) and electrochemistry in aqueous environments. High-resolution STM images reveal a (radical(7) x radical(7))R19 degrees surface lattice structure, in contrast with the conventional lattice (radical(3) x radical(3))R30 degrees structure for straight-chain alkanethiol SAMs. Interestingly, such a branched monolayer shows electrochemical rectification toward redox probes. We suggest that electrochemical rectification could be a general characteristic of short-chain branched alkanthiol SAMs, and originate in localized electronic effects. 相似文献
993.
We have synthesized a series of novel coplanar chromophores in which heteroarenes, namely, thiophene, benzothiophene, and carbazole, were fused to neighboring phenylene ring(s) through intramolecular annulation via sp(3)-hybridized carbon atoms bearing two p-tolyl groups as peripheral substituents. The molecular configurations of the pi-conjugated backbones were determined by X-ray crystallographic analysis; the heteroarene-fused molecular frameworks of these novel molecules exhibit nearly coplanar conformations. [structure: see text] 相似文献
994.
Ablikim M Bai JZ Ban Y Bian JG Cai X Chen HF Chen HS Chen HX Chen JC Chen J Chen YB Chi SP Chu YP Cui XZ Dai YS Diao LY Deng ZY Dong QF Du SX Fang J Fang SS Fu CD Gao CS Gao YN Gu SD Gu YT Guo YN Guo YQ Guo ZJ Harris FA He KL He M Heng YK Hu HM Hu T Huang GS Huang XT Ji XB Jiang XS Jiang XY Jiao JB Jin DP Jin S Jin Y Lai YF Li G Li HB Li HH Li J Li RY Li SM Li WD Li WG Li XL Li XN Li XQ Li YL Liang YF Liao HB Liu BJ Liu CX Liu F Liu F Liu HH Liu HM Liu J Liu JB Liu JP Liu Q Liu RG Liu ZA Lou YC 《Physical review letters》2006,97(20):202002
Using a data sample of 58 x 10(6) J/psi decays collected with the Beijing Spectrometer II detector at the Beijing Electron Positron Collider, searches for invisible decays of eta and eta' in J/psi to phi eta and phi eta' are performed. The phi signals, which are reconstructed in K+K- final states, are used to tag the eta and eta' decays. No signals are found for the invisible decays of either eta or eta', and upper limits at the 90% confidence level are determined to be 1.65 x 10(-3) for the ratio B(eta-->invisible)/B(eta --> gamma gamma) and 6.69 x 10(-2) for B(eta' --> invisible)/B(eta' --> gammagamma). These are the first searches for eta and eta' decays into invisible final states. 相似文献
995.
Using a narrowly distributed poly(N-isoporpylacrylamide) (PNIPAM) chain with a degree of polymerization (N) of 3100, randomly labeled with pyrene, we have, for the first time, observed the two-stage kinetics of the coil-to-globule transition. Two characteristic relaxation times, tau(fast) for the crumpling of a random coil (approximately 12 ms) and tau(slow) for the collapsing of the crumpled chain to a compact globule (approximately 270 ms), were measured. To our knowledge, this is the first experimental evidence supporting the two-stage collapsing kinetics of single synthetic polymer chain previously proposed by de Gennes, Dawson, and Grosberg. 相似文献
996.
Ablikim M Bai JZ Ban Y Cai X Chen HF Chen HS Chen HX Chen JC Chen J Chen YB Chi SP Chu YP Cui XZ Dai YS Deng ZY Dong LY Dong QF Du SX Du ZZ Fang J Fang SS Fu CD Gao CS Gao YN Gu SD Gu YT Guo YN Guo YQ Guo ZJ Harris FA He KL He M Heng YK Hu HM Hu T Huang GS Huang XP Huang XT Ji XB Jiang XS Jiao JB Jin DP Jin S Jin Y Lai YF Li G Li HB Li HH Li J Li RY Li SM Li WD Li WG Li XL Li XQ Li YL Liang YF Liao HB Liu CX Liu F Liu F Liu HH Liu HM Liu J Liu JB Liu JP Liu RG Liu ZA Lu F Lu GR Lu HJ Lu JG 《Physical review letters》2006,97(14):142002
A broad peak is observed at low K+K- invariant mass in J/psi-->K+K-pi(0) decays found in a sample of 5.8x10(7) J/psi events collected with the BESII detector. The statistical significance of the broad resonance is much larger than 5sigma. A partial wave analysis shows that the J;{PC} of this structure is 1--. Its pole position is determined to be [1576(-55)(+49)(stat)-91+98(syst)] MeV/c(2)-i/2[818(-23)(+22)(stat)-133+64(syst)] MeV/c(2). These parameters are not compatible with any known meson resonances. 相似文献
997.
In this article, we consider a model check test for linear processes with infinite variance. As a test statistic, we employ the portmanteau test with trimmed residuals. It is shown that the limiting null distribution of the test is a chi-square distribution. Simulation results are provided for illustration. 相似文献
998.
The large time behavior of strong solutions to a P1-approximation arising in radiating hydrodynamics
This paper is concerned with the study of the Cauchy problem to a multi-dimensional P1-approximation model. Based on a known global well-posedness (Danchin and Ducomet in J Evol Equ 14:155–195, 2014), in $$L^{2}$$-critical regularity framework the time decay rates of the constructed global strong solutions are obtained if the low frequencies of the data under a suitable additional condition. The proof mainly relies on an application of Fourier analysis to a mixed parabolic-hyperbolic system, and on a refined time-weighted energy functional. As a by-product, those time-decay rates of $$L^{q}$$–$$L^{r}$$ type are also captured in the critical framework. 相似文献
999.
Expedited shipments are often seen in practice. When the inventory level of an item gets dangerously low after an order has been placed, material managers are often willing to expedite the order at extra fixed and/or variable costs. This paper proposes a single-item continuous-review order expediting inventory policy, which can be considered as an extension of ordinary (s,Q) models. Besides the two usual operational parameters: reorder point s and order quantity Q, it consists of a third parameter called the expedite-up-to level R. If inventory falls below R at the end of the manufacturing lead-time, the buyer can request the upstream supplier to deliver part of an outstanding order via a fast transportation mode. The amount expedited will raise inventory to R, while the remaining order is delivered via a slow (regular) supply mode. Simple procedures are developed to obtain optimal operational parameters. Computational results show that the proposed policy can save large costs for a firm if service level is high, demand variability is large, the extra cost for expediting is small, or the manufacturing lead-time is long. 相似文献
1000.