Spectral Line Width Broadening from Pair Fluctuation in a Frozen Rydberg Gas

Spectral line width broadening in Rydberg gases, a phenomenon previously attributed to the many-body effect, was observed experimentally almost a decade ago. The observed line width was typically 80-100 times larger than the average interaction strength predicted from a binary interaction. The interpretation of such a phenomenon is usually based on the so-called diffusion model, where the line width broadening mostly originates from the diffusion of excitations. In this paper, we present a model calculation to show that diffusion is not the main mechanism to the line width broadening. We find that the rare pair fluctuation at small separation is the dominant factor contributing to this broadening. Our results give a width of about 20-30 times larger than the average interaction strength. More importantly, by turning off the diffusion process, we do not observe order of magnitude change in the spectral line width

Spacetime as a topological insulator: Mechanism for the origin of the fermion generations

We suggest a mechanism whereby the three generations of quarks and leptons correspond to surface modes in a five-dimensional theory. These modes arise from a nonlinear fermion dispersion relation in the extra dimension, much in the same manner as fermion surface modes in a topological insulator or lattice implementation of domain wall fermions. We also show that the topological properties can persist in a deconstructed version of the model in four dimensions.Comment: Substantially revised version, to appear in Phys. Rev. Let

Challenge on the Astrophysical R-process Calculation with Nuclear Mass Models

Our understanding of the rapid neutron capture nucleosynthesis process in universe depends on the reliability of nuclear mass predictions. Initiated by the newly developed mass table in the relativistic mean field theory (RMF), in this paper the influence of mass models on the $r$-process calculations is investigated assuming the same astrophysical conditions. The different model predictions on the so far unreachable nuclei lead to significant deviations in the calculated r-process abundances.Comment: 3 pages, 3 figure

UV-Photolithography Fabrication of Poly-Ethylene Glycol Hydrogels Encapsulated with Hepatocytes

The development of biomanufacturing technologies particularly, layered manufacturing has advanced cell encapsulation processes in an effort to mimic the cellular microenvironment for invitro studies. This paper illustrates an inexpensive UV-photolithographic method for encapsulation of human hepatocytes in three dimensional structures using poly-ethylene diacrylate (PEGDA) hydrogels as candidate substrates. In order to further develop this technology for layered fabrication, we have quantified the long-term effects of the photo-initiator concentration and UV light exposure on the metabolic rates of encapsulated human hepatocytes under a 21 day study. The photoinitator toxicity was observed immediately after polymerization with no significant cytotoxicity on a long term basis. A cellular viability is examined and reported for the UV photopolymerization process. Cell phenotype maintenance was observed by measuring the amount of urea produced over a 1 week time period. This photo encapsulation process may find use in the fabrication of spatially complex 3D scaffolds for tissue engineering applications, elucidation of the 3D structure-pharmacokinetic response relationship and the fabrication of complex multi-compartment liver tissue analog devices for drug screening applications.Mechanical Engineerin

Modelling and control of the flame temperature distribution using probability density function shaping

This paper presents three control algorithms for the output probability density function (PDF) control of the 2D and 3D flame distribution systems. For the 2D flame distribution systems, control methods for both static and dynamic flame systems are presented, where at first the temperature distribution of the gas jet flames along the cross-section is approximated. Then the flame energy distribution (FED) is obtained as the output to be controlled by using a B-spline expansion technique. The general static output PDF control algorithm is used in the 2D static flame system, where the dynamic system consists of a static temperature model of gas jet flames and a second-order actuator. This leads to a second-order closed-loop system, where a singular state space model is used to describe the dynamics with the weights of the B-spline functions as the state variables. Finally, a predictive control algorithm is designed for such an output PDF system. For the 3D flame distribution systems, all the temperature values of the flames are firstly mapped into one temperature plane, and the shape of the temperature distribution on this plane can then be controlled by the 3D flame control method proposed in this paper. Three cases are studied for the proposed control methods and desired simulation results have been obtained

Transition of a vortex ring measured by 3D scanning Tomo-PIV

A vortex ring with piston-based Reynolds number Rep=4650 is studied experimentally by means of time-resolved scanning tomographic PIV. The present measurement technique provides the so-called 4D flow field, thus enables revealing the vortex ring’s transition from laminar to turbulent. The evolution of the ring torus as well as the generation of secondary vortex filaments in transition are first observed through 3D visualization. Analysis on the quantities of the vortex ring, such as circulation and vorticity components, defines the three evolution phases, namely laminar, transition and turbulent. The ring median plane is also examined to provide further insights on flow structure exhibited in transition. The axial vorticity component and radial velocity component are studied respectively and they are found to be organized in a multi-layer concentric-ring pattern. Spectrum analysis on the radial velocity component along the ring core and inner ring where secondary vortical activity happens reveals the dominate wavenumber in transition and broad band of wavenumbers in turbulent phase