The effect of a particle travelling through a laminar boundary layer on transition

This study investigates how a particle travelling through an initially laminar boundary layer can lead to its breakdown to turbulence With increasing kerosene costs and an awareness of limited available oil reserves, laminar flow technologies are again being considered to realize the necessary efficiency increases of aircraft, and more detailed information on the operational issues is required. The adverse impact of flying through cirrus clouds has been simplified to the effect of a single particle on a laminar boundary layer over a zero-pressure gradient flat plate. First results indicate that the critical values could be substantially smaller than initially assumed

A Lattice-Boltzmann model for suspensions of self-propelling colloidal particles

We present a Lattice-Boltzmann method for simulating self-propelling (active) colloidal particles in two-dimensions. Active particles with symmetric and asymmetric force distribution on its surface are considered. The velocity field generated by a single active particle, changing its orientation randomly, and the different time scales involved are characterized in detail. The steady state speed distribution in the fluid, resulting from the activity, is shown to deviate considerably from the equilibrium distribution.Comment: 8 pages, 13 figure

A new model for simulating colloidal dynamics

We present a new hybrid lattice-Boltzmann and Langevin molecular dynamics scheme for simulating the dynamics of suspensions of spherical colloidal particles. The solvent is modeled on the level of the lattice-Boltzmann method while the molecular dynamics is done for the solute. The coupling between the two is implemented through a frictional force acting both on the solvent and on the solute, which depends on the relative velocity. A spherical colloidal particle is represented by interaction sites at its surface. We demonstrate that this scheme quantitatively reproduces the translational and rotational diffusion of a neutral spherical particle in a liquid and show preliminary results for a charged spherical particle. We argue that this method is especially advantageous in the case of charged colloids.Comment: For a movie click on the link below Fig

Screening of Hydrodynamic Interactions in Semidilute Polymer Solutions: A Computer Simulation Study

We study single-chain motion in semidilute solutions of polymers of length N = 1000 with excluded-volume and hydrodynamic interactions by a novel algorithm. The crossover length of the transition from Zimm (short lengths and times) to Rouse dynamics (larger scales) is proportional to the static screening length. The crossover time is the corresponding Zimm time. Our data indicate Zimm behavior at large lengths but short times. There is no hydrodynamic screening until the chains feel constraints, after which they resist the flow: "Incomplete screening" occurs in the time domain.Comment: 3 figure

Colloidal electrophoresis: Scaling analysis, Green-Kubo relation, and numerical results

We consider electrophoresis of a single charged colloidal particle in a finite box with periodic boundary conditions, where added counterions and salt ions ensure charge neutrality. A systematic rescaling of the electrokinetic equations allows us to identify a minimum set of suitable dimensionless parameters, which, within this theoretical framework, determine the reduced electrophoretic mobility. It turns out that the salt-free case can, on the Mean Field level, be described in terms of just three parameters. A fourth parameter, which had previously been identified on the basis of straightforward dimensional analysis, can only be important beyond Mean Field. More complicated behavior is expected to arise when further ionic species are added. However, for a certain parameter regime, we can demonstrate that the salt-free case can be mapped onto a corresponding system containing additional salt. The Green-Kubo formula for the electrophoretic mobility is derived, and its usefulness demonstrated by simulation data. Finally, we report on finite-element solutions of the electrokinetic equations, using the commercial software package COMSOL.Comment: To appear in Journal of Physics: Condensed Matter - special issue on occasion of the CODEF 2008 conferenc

CO abundances in a protostellar cloud: freeze-out and desorption in the envelope and outflow of L483

CO isotopes are able to probe the different components in protostellar clouds. These components, core, envelope and outflow have distinct physical conditions and sometimes more than one component contributes to the observed line profile. In this study we determine how CO isotope abundances are altered by the physical conditions in the different components. We use a 3D molecular line transport code to simulate the emission of four CO isotopomers, 12CO J=2-1, 13CO J=2-1, C18O J=2-1 and C17O J=2-1 from the Class 0/1 object L483, which contains a cold quiescent core, an infalling envelope and a clear outflow. Our models replicate JCMT (James Clerk Maxwell Telescope) line observations with the inclusion of freeze-out, a density profile and infall. Our model profiles of 12CO and 13CO have a large linewidth due to a high velocity jet. These profiles replicate the process of more abundant material being susceptible to a jet. C18O and C17O do not display such a large linewidth as they trace denser quiescent material deep in the cloud.Comment: 9 figures, 13 pages, 2 table

Studying DNA methylation changes of CpG islands in different stages of prostate cancer by pyrosequencing

Abstract only availableProstate cancer is one of the most common forms of cancer in men. Our lab is currently investigating changes in DNA methylation that occur during cancer progression, and in response to the soy phytoestrogen genistein treatment. We analyze genome-wide methylation differences by using the mouse DMH (mouse-Differential Methylation Hybridization) assay, a form of microarray. We are specifically looking at broad sets of CpG islands, areas rich in cytosine-guanine dinucleotides, that are subject to epigenetic modifications. The hypermethylation of CpG islands is correlated with the silencing of a gene while hypomethylation is correlated with a gene being actively transcribed. We were looking for potential new oncogenes or tumor suppressors. To study these genes we have a mouse model called TRAMP (TRansgenic Adenocarcinoma of the Mouse Prostate), which is a good model to study the progression of prostate cancer and metastasis because it is similar to human prostate cancer. We are using double transgenic mice that are WT or KO for the transcription factor estrogen receptor alpha, on a TRAMP background. The removal of ERα has been correlated with DNA methylation changes. These methylation changes showed up in our microarray screen that led us to find a set of genes that were differentially methylated across cancer progression. We selected one gene: Kinesin superfamily protein 9 (K3_E17) which has been shown on our microarrays to be methylated in well differentiated carcinoma and unmethylated in hyperplasia and poorly differentiated carcinoma. To confirm the methylation status we performed pyrosequencing, a new method to specifically study short sequences of DNA for methylation at specific CG sites. Our hypothesis is that in well differentiated carcinoma Kinesin 9 is hypermethylated, which will correlate with this gene being turned off. This would mean that Kinesin 9 might be acting as a tumor suppressor.Life Sciences Undergraduate Research Opportunity Progra

Optical Detection of a Single Nuclear Spin

We propose a method to optically detect the spin state of a 31-P nucleus embedded in a 28-Si matrix. The nuclear-electron hyperfine splitting of the 31-P neutral-donor ground state can be resolved via a direct frequency discrimination measurement of the 31-P bound exciton photoluminescence using single photon detectors. The measurement time is expected to be shorter than the lifetime of the nuclear spin at 4 K and 10 T.Comment: 4 pages, 3 figure

Uplink Non-Orthogonal Multiple Access with Finite-Alphabet Inputs

This paper focuses on the non-orthogonal multiple access (NOMA) design for a classical two-user multiple access channel (MAC) with finite-alphabet inputs. We consider practical quadrature amplitude modulation (QAM) constellations at both transmitters, the sizes of which are assumed to be not necessarily identical. We propose to maximize the minimum Euclidean distance of the received sum-constellation with a maximum likelihood (ML) detector by adjusting the scaling factors (i.e., instantaneous transmitted powers and phases) of both users. The formulated problem is a mixed continuous-discrete optimization problem, which is nontrivial to resolve in general. By carefully observing the structure of the objective function, we discover that Farey sequence can be applied to tackle the formulated problem. However, the existing Farey sequence is not applicable when the constellation sizes of the two users are not the same. Motivated by this, we define a new type of Farey sequence, termed punched Farey sequence. Based on this, we manage to achieve a closed-form optimal solution to the original problem by first dividing the entire feasible region into a finite number of Farey intervals and then taking the maximum over all the possible intervals. The resulting sum-constellation is proved to be a regular QAM constellation of a larger size. Moreover, the superiority of NOMA over time-division multiple access (TDMA) in terms of minimum Euclidean distance is rigorously proved. Furthermore, the optimal rate allocation among the two users is obtained in closed-form to further maximize the obtained minimum Euclidean distance of the received signal subject to a total rate constraint. Finally, simulation results are provided to verify our theoretical analysis and demonstrate the merits of the proposed NOMA over existing orthogonal and non-orthogonal designs.Comment: Submitted for possible journal publicatio