A kinematic subgrid scale model for large-eddy simulation of turbulence generated sound

In the hybrid approach of large-eddy simulation (LES) and Lighthill’s acoustic analogy for turbulence-generated sound, the turbulence source fields are obtained using an LES and the turbulence-generated sound at far fields is calculated from Lighthill’s acoustic analogy. As only the velocity fields at resolved scales are available from the LES, the Lighthill stress tensor, serving as a source term in Lighthill’s acoustic equation, has to be evaluated from the resolved velocity fields. As a result, the contribution from the unresolved velocity fields is missing in the conventional LES. The sound of missing scales is shown to be important and hence needs to be modeled. The present study proposes a kinematic subgrid-scale (SGS) model which recasts the unresolved velocity fields into Lighthill’s stress tensors. A kinematic simulation is used to construct the unresolved velocity fields with the imposed temporal statistics, which is consistent with the random sweeping hypothesis. The kinematic SGS model is used to calculate sound power spectra from isotropic turbulence and yields an improved result: the missing portion of the sound power spectra is approximately recovered in the LES.

Controllable atom localization via double-dark resonances in a tripod system

We propose an atom localization scheme for a tripod-type atom making use of the sharp absorption peak resulting from interacting double-dark resonances. It is demonstrated that the probability of finding the atom at a particular position, as well as the localization precision, can be dramatically enhanced. The probability can be doubled by adjusting the Rabi frequency of the control field to the maximum Rabi frequency of the standing-wave field. Moreover, much better spatial resolution can be achieved for smaller detunings of the control and the standing-wave fields. (c) 2006 Optical Society of America.

Constitutive plasma membrane targeting and microdomain localization of Dok5 studied by single-molecule microscopy

In the present study, single-molecule fluorescence microscopy was used to examine the characteristics of plasma membrane targeting and microdomain localization of enhanced yellow fluorescent protein (eYFP)-tagged wild-type Dok5 and its variants in living Chinese hamster ovary (CHO) cells. We found that Dok5 can target constitutively to the plasma membrane, and the PH domain is essential for this process. Furthermore, single-molecule trajectories analysis revealed that Dok5 can constitutively partition into microdomain on the plasma membrane. Finally, the potential mechanism of microdomain localization of Dok5 was discussed. This study provided insights into the characteristics of plasma membrane targeting and microdomain localization of Dok5 in living CHO cells. (C) 2008 Elsevier B.V. All rights reserved.

Sub-half-wavelength atom localization via two standing-wave fields

We propose a scheme for sub-half-wavelength atom localization in a four-level ladder-type atomic system, which is coupled by two classical standing-wave fields. We find that one of the standing-wave fields can help in enhancing the localization precision, and the other is of crucial importance in increasing the detecting probability and leading sub-half-wavelength localization.

Atom localization in a four-level alkaline earth atomic system

We propose an atom localization scheme for a four-level alkaline earth atom via a classical standing-wave field, and give the analytical expressions of the localization peak positions as well as the widths versus the parameters of the optical fields. We show that the probability of finding the atom at a particular position can be increased from 1/4 to 1/3 or 1/2 by adjusting the detuning of the probe field and the Rabi frequencies of the optical fields. Furthermore, the localization precision can be dramatically enhanced by increasing the intensity of the standing-wave field or decreasing the detuning of the probe field. The analytical results are quite accordant to the numerical solutions.

Phase-sensitive atom localization in a loop Lambda-system

The behaviour of the Lambda-system has been studied theoretically in the context of atom localization. In addition to the probe field and the standing wave driving field, a microwave field is introduced to couple the two lower states, and as a result our Lambda-system forms a closed loop. Therefore phase-sensitive atom localization is expected. Indeed by appropriate choice of the relative phase between three fields, an improvement by a factor of 2 has been found in the detection probability of atoms within the sub-wavelength domain of the standing wave. The effect of other parameters is also investigated.

Atom localization via interference of dark resonances

A scheme of atom localization based on the interference of resonance of double-dark states is proposed, in which the atom interacts with a classical standing-wave field. It is found that the localization property is significantly improved due to the interaction of double-dark resonances. It is realized that the atom is localized just at the nodes of the standing-wave field with higher precision. Moreover, an improvement by a factor of 2 in the detecting probability of a single atom within the subwavelength domain can be achieved by adjusting the probe-field detuning. This scheme shows more advantages than other schemes of atom localization.