Finding Transition Pathways on Manifolds

We consider noise-induced transition paths in randomly perturbed dynami- cal systems on a smooth manifold. The classical Freidlin-Wentzell large devia- tion theory in Euclidean spaces is generalized and new forms of action functionals are derived in the spaces of functions and the space of curves to accommodate the intrinsic constraints associated with the manifold. Numerical meth- ods are proposed to compute the minimum action paths for the systems with constraints. The examples of conformational transition paths for a single and double rod molecules arising in polymer science are numerically investigated

Meson Emission Model of Psi to N Nbar m Charmonium Strong Decays

In this paper we consider a sequential "meson emission" mechanism for charmonium decays of the type Psi -> N Nbar m, where Psi is a generic charmonium state, N is a nucleon and m is a light meson. This decay mechanism, which may not be dominant in general, assumes that an NNbar pair is created during charmonium annihilation, and the light meson m is emitted from the outgoing nucleon or antinucleon line. A straightforward generalization of this model can incorporate intermediate N* resonances. We derive Dalitz plot event densities for the cases Psi = eta_c, J/psi, chi_c0, chi_c1} and psi' and m = pi0, f0 and omega (and implicitly, any 0^{-+}, 0^{++} or 1^{--} final light meson). It may be possible to separate the contribution of this decay mechanism to the full decay amplitude through characteristic event densities. For the decay subset Psi -> p pbar pi0 the two model parameters are known, so we are able to predict absolute numerical partial widths for Gamma(Psi -> p pbar pi0). In the specific case J/psi -> p pbar pi0 the predicted partial width and M_{p pi0} event distribution are intriguingly close to experiment. We also consider the possibility of scalar meson and glueball searches in Psi -> p pbar f0. If the meson emission contributions to Psi -> N Nbar m decays can be isolated and quantified, they can be used to estimate meson-nucleon strong couplings {g_NNm}, which are typically poorly known, and are a crucial input in meson exchange models of the NN interaction. The determination of g_NNpi from J\psi -> p pbar pi0 and the (poorly known) g_NNomega and the anomalous "strong magnetic" coupling kappa_{NNomega} from J/psi -> p pbar omega are considered as examples.Comment: 10 pages, 5 figure

Transport and Optical Properties of Quantized Low-Dimensional Systems

In this thesis, we present a systematic investigation of the static and dynamic response properties of low-dimensional systems, using a variety of theoretical techniques ranging from time dependent density functional theory to the recursive Green\u27s function method. As typical low-dimensional systems, metal nanostructures can strongly interact with an electric field to support surface plasmons, making their optical properties extremely attractive in both fundamental and applied aspects. We have investigated the energy broadening of surface plasmons in metal structures of reduced dimensionality, where Landau damping is the dominant dissipation channel and presents an intrinsic limitation to plasmonics technology. We show that for every prototype class of systems considered, including nanoshells, coaxial nanotubes, and ultrathin films, Landau damping can be drastically tuned due to energy quantization of the individual electron levels and e-h pairs. Both the generic trend and oscillatory nature of the tunability are in stark contrast with the expectations of the semiclassical surface scattering picture. For a more realistic environment of low-dimensional systems, the effect of a dielectric substrate is considered to mimic the experimental setup. We have studied the dispersion of various plasmon excitations in metal thin films with growth substrates. Our results qualitatively reproduce the experimentally observed plasmon spectra of the Mg/Si systems. The underlying physics for the formation of various absorption peaks can be understood with a simple hybridization concept. Based on this concept, the coexistence of surface and bulk plasmons in experimental observation turns out to be a clear evidence for the existence of multiple-multipole surface plasmons due to the quantum confinement in thin films. To step into more confined worlds, we choose the real two-dimensional material graphene as our representive system, which is a semi-metal with zero band-gap. As the first step, the static electric response of graphene is investigated by exploring its transport properties. We have studied the pseudospin valve effect in bilayer graphene nanoribbons. The pseudospin degree of freedom is associated with the electron density in two layers and can be controlled by external gate electrodes. We find that the conductance of nanoribbons shows different behaviors compared with infinite systems due to the appearance of edge states and quantum confinement. Remarkably, a large on-off ratio can be achieved in nanoribbons with zigzag edges, even when the Fermi energy lies in the bulk energy gap. The influence of possible edge vacancies and interface conditions is also discussed. Finally, we discuss the possibility of using plasmon excitations to detach the graphene from its growth substrate, where the dynamic electric response of the graphene-metal system is expected to play a central role

On the Cultural Difference and Performance in the Modernization Process of Chinese and Japanese Painting for the Twentieth Century

China and Japan have a long history in the communication of the two countries’ culture and arts. Chinese drawing and Japanese drawing, belonging to the eastern Asian art circle, share common aesthetic tendency and cultural identity and affect, enrich each other during the process of mutual exchange and absorption, and stand in the worldwide national arts in parallel. The modern Japanese drawing, based on the absorption of Chinese traditional drawing and western drawings, forms its own distinct national characteristics, diffuses along with the culture and arts communication and brings enlightenment and influences on the modern development, transition and research

Minimal siRNA set cover heuristic for gene family knockdown

RNA interference (RNAi) is a highly evolutionally conserved process of post-transcriptional gene silencing (PTGS) by which double stranded RNA (dsRNA), when introduced into a cell, causes sequence-specific degradation of homologous mRNA sequences, siRNA (small interfering RNA are a class of 20-25 nucleotide-long double-stranded RNA molecules) is involved in the RNA interference (RNAi) pathway where the siRNA interferes with the expression of a specific gene. We focus on the problem of gene family knockdown by using the minimal number of siRNAs. The problem is to determine the minimal number of siRNAs required to knockdown a family of genes targeted by these siRNAs. This is a minimal set covering problem, and hence it is NP-hard. In this thesis, we explore a number of heuristic optimization methods for the minimal siRNA covering problem. Such methods include evolutionary heuristics, as well as novel greedy methods, applied for the first time to the minimal siRNA cover problem. Preliminary experiments with genetic algorithms show significant reduction in the siRNA cover size, when compared with branch & bound and probabilistic greedy. We are currently implementing novel greedy methods which are variants of well-known feature subset selection algorithms. In such methods, we define criterion functions over a collection of siRNA subsets to help us decide which subset is best to be included in a candidate solution. We use three gene families: the FREP genes from Biomphalaria glabrata and the olfactory genes from Caenorhabditis elegans. We also conducted experiments on one artificial data set