排序方式: 共有58条查询结果,搜索用时 15 毫秒
41.
Huang DJ Lin HJ Okamoto J Chao KS Jeng HT Guo GY Hsu CH Huang CM Ling DC Wu WB Yang CS Chen CT 《Physical review letters》2006,96(9):096401
We report experimental evidence for the charge-orbital ordering in magnetite below the Verwey transition temperature T(V). Measurements of O K-edge resonant x-ray scattering on magnetite reveal that the O 2p states in the vicinity of the Fermi level exhibit a charge-orbital ordering along the c axis with a spatial periodicity of the doubled lattice parameter of the undistorted cubic phase. Such a charge-orbital ordering vanishes abruptly above T(V) and exhibits a thermal hysteresis, correlating closely with the Verwey transition in magnetite. 相似文献
42.
It has been shown that synchronizability of a network is determined by the local structure rather than the global properties. With the same global properties, networks may have very different synchronizability. In this paper, we numerically studied, through the spectral properties, the synchronizability of ensembles of networks with prescribed statistical properties. Given a degree sequence, it is found that the eigenvalues and eigenratios characterizing network synchronizability have well-defined distributions, and statistically, the networks with extremely poor synchronizability are rare. Moreover, we compared the synchronizability of three network ensembles that have the same nodes and average degree. Our work reveals that the synchronizability of a network can be significantly affected by the local pattern of connections, and the homogeneity of degree can greatly enhance network synchronizability for networks of a random nature. 相似文献
43.
Study of J/psi-->pp[over],LambdaLambda[over] and observation of eta(c)-->LambdaLambda[over] at Belle
Wu CH Wang MZ Abe K Adachi I Aihara H Aulchenko V Aushev T Bahinipati S Bakich AM Balagura V Bay A Belous K Bitenc U Bizjak I Blyth S Bondar A Bozek A Browder TE Chao Y Chen A Chen WT Cheon BG Choi Y Choi YK Chuvikov A Cole S Dalseno J Danilov M Dash M Eidelman S Gabyshev N Gershon T Go A Gokhroo G Gorisek A Ha H Haba J Hayasaka K Hayashii H Hazumi M Heffernan D Hokuue T Hou S Hou WS Hsiung YB Iijima T Inami K Ishikawa A Itoh R Iwasaki M Iwasaki Y Kang JH Kataoka SU Katayama N Kawai H 《Physical review letters》2006,97(16):162003
We study the baryonic charmonium decays of B mesons B+-->etacK+ and B+-->J/psiK+, where the etac and J/psi subsequently decay into a pp[over] or LambdaLambda[over] pair. We measure the J/psi-->pp[over] and LambdaLambda[over] anisotropy parameters alphaB=-0.60+/-0.13+/-0.14 (pp[over]), -0.44+/-0.51+/-0.31 (LambdaLambda[over ]) and compare to results from e;{+}e;{-}-->J/psi formation experiments. We also report the first observation of etac-->LambdaLambda[over]. The measured branching fraction is B(etac-->LambdaLambda[over ])=(0.87(+0.24)/(-0.21)(stat)(+0.09/-0.14) (syst)+/-0.27(PDG))x10-3. This study is based on a 357 fb-1 data sample recorded on the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+ e- collider. 相似文献
44.
Padilla-Rodal E Galindo-Uribarri A Baktash C Batchelder JC Beene JR Bijker R Brown BA Castaños O Fuentes B del Campo JG Hausladen PA Larochelle Y Lisetskiy AF Mueller PE Radford DC Stracener DW Urrego JP Varner RL Yu CH 《Physical review letters》2005,94(12):122501
The B(E2;0(+)(1)-->2(+)(1)) values for the radioactive neutron-rich germanium isotopes (78,80)Ge and the closed neutron shell nucleus 82Ge were measured at the HRIBF using Coulomb excitation in inverse kinematics. These data allow a study of the systematic trend between the subshell closures at N=40 and 50. The B(E2) behavior approaching N=50 is similar to the trend observed for heavier isotopic chains. A comparison of the experimental results with a shell model calculation demonstrates persistence of the N=50 shell gap and a strong sensitivity of the B(E2) values to the effective interaction. 相似文献
45.
We recently reported the enantioselective syntheses of quaternary 1,4-benzodiazepin-2-ones via memory of chirality. The success of this method depends on formation of conformationally chiral enolates that racemize very slowly under the reaction conditions. As a prelude to undertaking experimental and computational studies on the racemization of these enolates, we have studied the ring-inversion process of the parent 1,4-benzodiazepin-2-ones. In this paper, we use dynamic and 2D-EXSY NMR to characterize inversion barriers. Using DFT calculations, we reproduce the experimental results with high accuracy (within 1-2 kcal/mol). Structural parameters obtained from DFT calculations provide valuable insights into the important effect of the N1 substituent on the ring-inversion barrier and shed light on the mechanism of the memory of chirality method. These measurements and calculations provide a foundation for future studies of benzodiazepine enolates and will be valuable in the design of new memory of chirality reactions. 相似文献
46.
Ji S Song C Koo J Park J Park YJ Lee KB Lee S Park JG Kim JY Cho BK Hong KP Lee CH Iga F 《Physical review letters》2007,99(7):076401
X-ray and neutron scattering studies were performed on DyB4 which exhibits both a quadrupolar ordering and a macroscopic lattice distortion. A forbidden reflection at 7.792 keV near the Dy L3 absorption edge is identified as a quadrupolar ordering peak, and the quadrupolar order and a monoclinic structural distortion develop concomitantly below 12.3 K as second-order-type phase transitions. Coupling between the quadrupolar order and the strain in DyB4 is directly demonstrated by observing that both order parameters are proportional to each other. 相似文献
47.
48.
Seidel J Maksymovych P Batra Y Katan A Yang SY He Q Baddorf AP Kalinin SV Yang CH Yang JC Chu YH Salje EK Wormeester H Salmeron M Ramesh R 《Physical review letters》2010,105(19):197603
The transport physics of domain wall conductivity in La-doped bismuth ferrite (BiFeO3) has been probed using variable temperature conducting atomic force microscopy and piezoresponse force microscopy in samples with arrays of domain walls in the as-grown state. Nanoscale current measurements are investigated as a function of bias and temperature and are shown to be consistent with distinct electronic properties at the domain walls leading to changes in the observed local conductivity. Our observation is well described within a band picture of the observed electronic conduction. Finally, we demonstrate an additional degree of control of the wall conductivity through chemical doping with oxygen vacancies, thus influencing the local conductive state. 相似文献
49.
Yield stress: A time-dependent property and how to measure it 总被引:8,自引:0,他引:8
D. C-H. Cheng 《Rheologica Acta》1986,25(5):542-554
This paper reviews the different aspects of the yield stress phenomenon and attempts a synthesis of knowledge. Yield stress can be probed using constant shear stress or shear rate. The magnitude of the result depends on the time allowed to determine whether the sample has developed continuous flow or has ceased flowing. It is closely associated with creep, stress growth and thixotropic breakdown and recovery, and the characteristic times of these transient responses play a part in yield stress measurement. In thixotropic fluids, yield stress is a function of structure and hence of time. In simple thixotropy, the yield stress derived from the equilibrium flow curve is the same as that for the fully built-up structure. But in many materials, the static yield stress obtained after prolonged rest is much higher than the dynamic yield stress from the equilibrium flow curve. This is associated with the phenomenon in which the equilibrium flow curve bends upwards as the shear rate is reduced to very low values. The paper also reviews the many methods that can be used to measure yield stress. It is pointed out that the choice of observation time or shear rate to use should be related to the characteristic time of the flow process to which the result is to be applied. Examples discussed are solids suspension capability of fluids, levelling and sagging, pipeline flow and start-up power requirement of mixers.
CS
constant structure
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D
diameter of Gun Rheometer tube
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EFC
equilibrium flow curve
-
G
measured torque
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L
length of Gun Rheometer tube
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P
min
minimum pressure to cause flow
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t
time
-
form factor for shear stress
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-
y
-
shear rate
-
a particular value of shear rate
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reference shear rate
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test shear rate
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shear stress
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y
yield stress
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yd
dynamic yield stress
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ys
static yield stress
- 0
initial value after speed change
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e
equilibrium
Paper presented at the British Society of Rheology Conference on New Techniques in Experimental Rheology, University of Reading, 9–11 September 1985. 相似文献
50.
We consider the problem of scheduling jobs on two parallel machines that are not continuously available for processing. The machine is not available after processing a fixed number of jobs in order to make precision adjustment of machines such as in wafer manufacturing, to reload the feeder in printed circuit board production, or to undertake any other maintenance works such as cleaning and safety inspections. The objective of the problem is to minimize the makespan. Two different scheduling horizons are investigated for this problem. For the short-term scheduling horizon, we consider only the time period before the unavailability interval, while for the long-term horizon, machines are allowed to restart processing after the unavailability interval. For both cases, which are strongly NP-hard, exact optimization algorithms based on the branch and bound method are proposed. Although the algorithms have exponential time complexities, computational results show that they can solve optimally the various-sized problems in reasonable computation time. 相似文献