Numerical Analyses of Weakly Nonlinear Velocity-Density Coupling

We study evolution of various statistical quantities of smoothed cosmic density and velocity fields using N-body simulations. The parameter $C\equiv /( )$ characterizes nonlinear coupling of these two fields and determines behavior of bulk velocity dispersion as a function of local density contrast. It is found that this parameter depends strongly on the smoothing scale even in quasi-linear regimes where the skewness parameter $S_3$ is nearly constant and close to the predicted value by the second-order perturbation theory. We also analyze weakly nonlinear effects caused by an adaptive smoothing known as the gather approach.Comment: 22 pages, 4 figures, to appear in ApJ (558, Sep 10

Revisiting the Quantum Group Symmetry of Diatomic Molecules

We propose a q-deformed model of the anharmonic vibrations in diatomic molecules. We analyse the applicability of the model to the phenomenological Dunham's expansion by comparing with experimental data. Our methodology involves a global consistency analysis of the parameters that determine the q-deformed system, when compared with fitted vibrational parameters to 161 electronic states in diatomic molecules. We show how to include both the positive and the negative anharmonicities in a simple and systematic fashion.Comment: 15 pages, 3 Table

Enhancing the transdermal delivery of rigid nanoparticles using the simultaneous application of ultrasound and sodium lauryl sulfate

The potential of rigid nanoparticles to serve as transdermal drug carriers can be greatly enhanced by improving their skin penetration. Therefore, the simultaneous application of ultrasound and sodium lauryl sulfate (referred to as US/SLS) was evaluated as a skin pre-treatment method for enhancing the passive transdermal delivery of nanoparticles. We utilized inductively coupled plasma mass spectrometry and an improved application of confocal microscopy to compare the delivery of 10- and 20-nm cationic, neutral, and anionic quantum dots (QDs) into US/SLS-treated and untreated pig split-thickness skin. Our findings include: (a) ~0.01% of the QDs penetrate the dermis of untreated skin (which we quantify for the first time), (b) the QDs fully permeate US/SLS-treated skin, (c) the two cationic QDs studied exhibit different extents of skin penetration and dermal clearance, and (d) the QD skin penetration is heterogeneous. We discuss routes of nanoparticle skin penetration and the application of the methods described herein to address conflicting literature reports on nanoparticle skin penetration. We conclude that US/SLS treatment significantly enhances QD transdermal penetration by 500–1300%. Our findings suggest that an optimum surface charge exists for nanoparticle skin penetration, and motivate the application of nanoparticle carriers to US/SLS-treated skin for enhanced transdermal drug delivery.National Institutes of Health (U.S.) (Grant EB-00351)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Grant DAAD-19-02-D-002)Conselho Nacional de Pesquisas (Brazil)Fundacao de Amparo a Pesquisa do Estado de Sao PauloNational Science Foundation (U.S.). Graduate Research Fellowshi

Fluorescent penetration enhancers for transdermal applications

Chemical penetration enhancers are often used to enhance transdermal drug delivery. However, the fundamental mechanisms that govern the interactions between penetration enhancers and skin are not fully understood. Therefore, the goal of this work was to identify naturally fluorescent penetration enhancers (FPEs) in order to utilize well-established fluorescence techniques to directly study the behavior of FPEs within skin. In this study, 12 fluorescent molecules with amphiphilic characteristics were evaluated as skin penetration enhancers. Eight of the molecules exhibited significant activity as skin penetration enhancers, determined using skin current enhancement ratios. In addition, to illustrate the novel, direct, and non-invasive visualization of the behavior of FPEs within skin, three case studies involving the use of two-photon fluorescence microscopy (TPM) are presented, including visualizing glycerol-mitigated and ultrasound-enhanced FPE skin penetration. Previous TPM studies have indirectly visualized the effect of penetration enhancers on the skin by using a fluorescent dye to probe the transdermal pathways of the enhancer. These effects can now be directly visualized and investigated using FPEs. Finally, future studies are proposed for generating FPE design principles. The combination of FPEs with fluorescence techniques represents a useful novel approach for obtaining physical insights on the behavior of penetration enhancers within the skin.National Institutes of Health (U.S.) (Grant EB-00351)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Grant DAAD-19-02-D-002)National Science Foundation (U.S.). Graduate Research FellowshipConselho Nacional de Pesquisas (Brazil)Fundacao de Amparo a Pesquisa do Estado de Sao Paul

Restructuring of colloidal aggregates in shear flow: Coupling interparticle contact models with Stokesian dynamics

A method to couple interparticle contact models with Stokesian dynamics (SD) is introduced to simulate colloidal aggregates under flow conditions. The contact model mimics both the elastic and plastic behavior of the cohesive connections between particles within clusters. Owing to this, clusters can maintain their structures under low stress while restructuring or even breakage may occur under sufficiently high stress conditions. SD is an efficient method to deal with the long-ranged and many-body nature of hydrodynamic interactions for low Reynolds number flows. By using such a coupled model, the restructuring of colloidal aggregates under stepwise increasing shear flows was studied. Irreversible compaction occurs due to the increase of hydrodynamic stress on clusters. Results show that the greater part of the fractal clusters are compacted to rod-shaped packed structures, while the others show isotropic compaction.Comment: A simulation movie be found at http://www-levich.engr.ccny.cuny.edu/~seto/sites/colloidal_aggregates_shearflow.htm

Weakly coupled states on branching graphs

We consider a Schr\"odinger particle on a graph consisting of $\,N\,$ links joined at a single point. Each link supports a real locally integrable potential $\,V_j\,$; the self--adjointness is ensured by the $\,\delta\,$ type boundary condition at the vertex. If all the links are semiinfinite and ideally coupled, the potential decays as $\,x^{-1-\epsilon}$ along each of them, is non--repulsive in the mean and weak enough, the corresponding Schr\"odinger operator has a single negative eigenvalue; we find its asymptotic behavior. We also derive a bound on the number of bound states and explain how the $\,\delta\,$ coupling constant may be interpreted in terms of a family of squeezed potentials.Comment: LaTeX file, 7 pages, no figure

Effects of ultrasound and sodium lauryl sulfate on the transdermal delivery of hydrophilic permeants: Comparative in vitro studies with full-thickness and split-thickness pig and human skin

The simultaneous application of ultrasound and the surfactant sodium lauryl sulfate (referred to as US/SLS) to skin enhances transdermal drug delivery (TDD) in a synergistic mechanical and chemical manner. Since full-thickness skin (FTS) and split-thickness skin (STS) differ in mechanical strength, US/SLS treatment may have different effects on their transdermal transport pathways. Therefore, we evaluated STS as an alternative to the well-established US/SLS-treated FTS model for TDD studies of hydrophilic permeants. We utilized the aqueous porous pathway model to compare the effects of US/SLS treatment on the skin permeability and the pore radius of pig and human FTS and STS over a range of skin electrical resistivity values. Our findings indicate that the US/SLS-treated pig skin models exhibit similar permeabilities and pore radii, but the human skin models do not. Furthermore, the US/SLS-enhanced delivery of gold nanoparticles and quantum dots (two model hydrophilic macromolecules) is greater through pig STS than through pig FTS, due to the presence of less dermis that acts as an artificial barrier to macromolecules. In spite of greater variability in correlations between STS permeability and resistivity, our findings strongly suggest the use of 700 μm-thick pig STS to investigate the in vitro US/SLS-enhanced delivery of hydrophilic macromolecules.National Institutes of Health (U.S.) (Grant EB-00351)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Grant DAAD-19-02-D-002)National Science Foundation (U.S.). Graduate Research FellowshipConselho Nacional de Pesquisas (Brazil)Fundacao de Amparo a Pesquisa do Estado de Sao Paul

Enhancement of the formation of ultracold 85^{85}Rb2_2 molecules due to resonant coupling

We have studied the effect of resonant electronic state coupling on the formation of ultracold ground-state $^{85}$Rb$_2$. Ultracold Rb$_2$ molecules are formed by photoassociation (PA) to a coupled pair of $0_u^+$ states, $0_u^+(P_{1/2})$ and $0_u^+(P_{3/2})$, in the region below the $5S+5P_{1/2}$ limit. Subsequent radiative decay produces high vibrational levels of the ground state, $X ^1\Sigma_g^+$. The population distribution of these $X$ state vibrational levels is monitored by resonance-enhanced two-photon ionization through the $2 ^1\Sigma_u^+$ state. We find that the populations of vibrational levels $v''$=112$-$116 are far larger than can be accounted for by the Franck-Condon factors for $0_u^+(P_{1/2}) \to X ^1\Sigma_g^+$ transitions with the $0_u^+(P_{1/2})$ state treated as a single channel. Further, the ground-state molecule population exhibits oscillatory behavior as the PA laser is tuned through a succession of $0_u^+$ state vibrational levels. Both of these effects are explained by a new calculation of transition amplitudes that includes the resonant character of the spin-orbit coupling of the two $0_u^+$ states. The resulting enhancement of more deeply bound ground-state molecule formation will be useful for future experiments on ultracold molecules.Comment: 6 pages, 5 figures; corrected author lis