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11.
We investigate the effect of drag force on the enstrophy cascade of two-dimensional Navier-Stokes turbulence. We find a power law decrease of the energy wave number (k) spectrum that is faster than the classical (no-drag) prediction of k(-3). It is shown that the enstrophy cascade with drag can be analyzed by making use of a previous theory for finite lifetime passive scalars advected by a Lagrangian chaotic fluid flow. Using this we relate the power law exponent of the energy wave number spectrum to the distribution of finite time Lyapunov exponents and the drag coefficient. 相似文献
12.
K.S. Kim Myung Ki Cheoun Yeungun Chung Hyung Joo Nam 《The European Physical Journal A - Hadrons and Nuclei》2001,11(2):147-154
New results for the double beta decay of 76
Ge are presented. They are extracted from data obtained with the HEIDELBERG-MOSCOW experiment, which operates five enriched
76
Ge detectors in an extreme low-level environment in the Gran Sasso underground laboratory. The two-neutrino-accompanied double
beta decay is evaluated for the first time for all five detectors with a statistical significance of 47.7 kg y resulting in
a half-life of T
1/2
2ν = [1.55±0.01(stat)+0.19
-0.15(syst)]×1021 y. The lower limit on the half-life of the 0νββ decay obtained with pulse shape analysis is T
1/2
0ν > 1.9×1025(3.1×1025) y with 90% C.L. (68% C.L.) (with 35.5 kg y). This results in an upper limit of the effective Majorana-neutrino mass of 0.35
eV (0.27 eV) using the matrix elements of A. Staudt et al.'s work (Europhys. Lett. 13, 31 (1990)). This is the most stringent limit at present from double beta decay. No evidence for a majoron-emitting decay
mode is observed.
Received: 22 August 2001 / Accepted: 18 October 2001 相似文献
13.
Jaehyun Park Seonghan Kim Sangsoo Kim Ki Hyun Nam 《Journal of synchrotron radiation》2018,25(2):323-328
The multifarious injection chamber for molecular structure study (MICOSS) experimental system has been developed at the Pohang Accelerator Laboratory X‐ray Free‐Electron Laser for conducting serial femtosecond crystallography. This system comprises several instruments such as a dedicated sample chamber, sample injectors, sample environment diagnostic system and detector stage for convenient distance manipulation. Serial femtosecond crystallography experiments of lysozyme crystals have been conducted successfully. The diffraction peaks have reached to ~1.8 Å resolution at the photon energy of 9.785 keV. 相似文献
14.
15.
The geometry of carotid artery bifurcation is of high clinical interest because it determines the characteristics of blood flow that is closely related to the formation and development of atherosclerotic plaque. However, information on the dynamic changes in the vessel wall of carotid artery bifurcation during a pulsatile cycle is limited. This pilot study investigated the cyclic changes in carotid artery geometry caused by blood flow pulsation in rats. A high-resolution ultrasound imaging system with a broadband scanhead centered at 40 MHz was used to obtain longitudinal images of the rat carotid artery. A high frame rate retrospective B-scan imaging technique based on the use of electrocardiogram to trigger signal acquisition was used to examine precisely the fast arterial wall motion. Two-dimensional geometry data obtained from nine rats showed that the rat carotid artery asymmetrically contracts and dilates during each cardiac cycle. Systolic/diastolic vessel diameters near the upstream and downstream regions from the bifurcation were 0.976 ± 0.011/0.825 ± 0.015 mm and 0.766 ± 0.015/0.650 ± 0.016 mm, respectively. Their posterior/anterior wall displacement ratios in the radial direction were 41.0 ± 14.9% and 2.9 ± 1.6%, respectively. These results indicate that in the vicinity of bifurcation, the carotid artery favorably expands to the anterior side during the systolic phase. This phenomenon was observed to be more prominent in the downstream region near the bifurcation. The cyclic variation pattern in wall movement varies depending on the measurement site, which shows different patterns at far upstream and downstream of the bifurcation. The asymmetric radial expansion and contraction of the rat carotid artery observed in this study may be useful in studying the hemodynamic etiology of cardiovascular diseases because the pulsatile changes in vessel geometry may affect the local hemodynamics that determines the spatial distribution of wall shear stress, one of important cardiovascular risk factors. Further systematic study is needed to clarify the effects of wall elasticity, branch angle and vessel diameter ratio on the asymmetric wall motion of carotid artery bifurcation. 相似文献
16.
Total potential energy of non-symmetric thin-walled beam-columns in the general form is presented by introducing the displacement field based on semitangential rotations and deriving transformation equations between displacement and force parameters defined at the arbitrary axis and the centroid-shear center axis, respectively. Next, governing equations and force-deformation relations are derived from the total potential energy for a shear-deformable, uniform beam element and a system of linear eigenproblem with non-symmetric matrices is constructed based on 14 displacement parameters. And then explicit expressions for displacement parameters are derived and exact dynamic stiffness matrices are determined using force-deformatin relationships. In addition, the modified numerical method to eliminate multiple zero eigenvalues and to evaluate the exact static stiffness matrix is developed for spatial stability analysis. Finally, in order to demonstrate the validity and the accuracy of this study, the spatially coupled natural frequencies and buckling loads are evaluated and compared with analytical solutions or results analyzed by thin-walled beam elements and ABAQUS's shell elements. 相似文献
17.
Hye Jin Lee Eun Ji Nam Jung-Je Woo Seung-Hyeon Moon Jaeyoung Lee 《Current Applied Physics》2012,12(5):1235-1238
The modification of perfluorinated proton exchange membranes (e.g. Nafion) utilizing a layer by layer (LbL) electrostatic assembly of oppositely charged biophilic polymers such as poly-l-lysine as positive layer and dsDNA as a negative layer is developed to protect the interface between the catalyst layer and the membrane in a low temperature fuel cell. Various physicochemical measurements including water uptake, proton conductivity and surface tension were investigated for both the as-received Nafion and the biopolymeric LbL modified Nafion. The smaller water contact angle and the less swelling characteristics of the biopolymer modified Nafion membrane was founded compared to that of as-received Nafion. This clearly indicates that the more hydrophilic surface of biopolymeric layers on Nafion plays an important role in the enhanced dimensional stability. In addition, a potential hypothesis explaining the higher proton conductivity from the LbL biopolymeric film coated Nafion is suggested. 相似文献
18.
We provide a general procedure for characterizing radical-like functions of skew polynomial and skew Laurent polynomial rings under grading hypotheses. In particular, we are able to completely characterize the Wedderburn and Levitzki radicals of skew polynomial and skew Laurent polynomial rings in terms of ideals in the coefficient ring. We also introduce the T-nilpotent radideals, and perform similar characterizations. 相似文献
19.
Abstract In this paper we introduce generalized ideal-stable regular rings. It is shown that if a regular ring R is a generalized I-stable ring, then every square matrix over I is the product of an idempotent matrix and an generalized invertible matrix and admits a diagonal reduction by some generalized invertible matrices. 相似文献
20.
We investigated electronically excited states of caffeine and its 1:1 complex with water by using resonant two-photon ionization (R2PI) and UV-UV hole-burning techniques. Strong vibronic coupling between a pair of close-lying pi-pi* and n-pi* transitions is proposed to be responsible for the broad spectral feature observed. By comparing the experimental results with those of theoretical calculations, both the O-bonded and N-bonded forms were suggested to be initially produced for the 1:1 complex. The electronic transitions of the O-bonded complex were blueshifted in the R2PI spectrum. For the N-bonded complex, the excited state undergoes an ultrafast decay process, followed by dissociation on a repulsive potential energy surface, which gives rise to a characteristically anomalous cluster distribution in nanosecond experiments. 相似文献