Date :

 28-29, 31 March 2008

Place :

 28-29 March: Room 312 (After 15:30: Room 916), Department of Physics, National Taiwan University, Taipei

 31 March: The auditorium on 1st floor, Institute of Physics of Academia Sinica, Taipei

 National Center for Theoretical Sciences (Critical Phenomena and Complex Systems Focus Group)

 Institute of Physics of Academia Sinica (Taipei)

 Department of Physics, National Taiwan university (Taipei)

  Miss Chia-Chi Liu (Secretary, Physics Division, NCTS)
 Tel:(886)-2-33665566; Fax:(886)-2-33665565; E-mail: ccliu@phys.ntu.edu.tw

 Miss Shu-Min Yang (Assistant of LSCP, Institute of Physics, Academia Sinica)

 Tel: (886)-2-2782-2467, or (886)-2-27880058 ext. 6012; FAX: (886)-2-2782-2467; E-mail: shumin@phys.sinica.edu.tw

Speakers :

Prof. Shu-Chiuan Chang

Department of Physics, National Cheng-Kung University, TAIWAN

E-mail: scchang@mail.ncku.edu.tw

Dimer Coverings on the Sierpinski Gasket

    We present the number of dimer coverings on the Sierpinski gasket SG_d(n) at stage n with dimension d equal to two, three, four or five. When the number of vertices of the Sierpinski gasket is an even number, close-packed configurations are possible. When the number of vertices is an odd number, we allow one of the outmost vertices uncovered. The entropy of absorption of diatomic molecules per site is calculated to be ln(2)/3 exactly for the ordinary two-dimensional Sierpinski gasket. The numbers of dimers on the generalized two-dimensional Sierpinski gasket SG_2,b(n) with b=3,4,5 are also obtained exactly with entropies equal to ln(6)/7, ln(28)/12, ln(200)/18, respectively. The number of dimer coverings for the three-dimensional Sierpinski gasket is given by an exact product expression, such that its entropy is expressed by an exact summation expression. The upper and lower bounds for the entropy are derived in terms of the results at a certain stage for SG_d(n) with d=3,4,5, and the numerical value of the entropy is evaluated with more than a hundred significant figures accurate.

* This project is financially sponsored by National Science Council (grand no. NSC-96-2112-M-006-001 and NSC-96-2119-M-002-001.

Prof. Hsuan-Yi Chen

Department of Physics, National Central University, TAIWAN

E-mail: hschen@mail.phy.ncu.edu.tw

Dynamics of Membranes with Anchored Active Proteins

    In the presence of energy supply, lipid bilayers with anchored active proteins are no longer in thermal equilibrium.  The power spectrum of membrane fluctuation is dominated by non-equilibrium activities of the proteins.  The spatial distribution of the proteins strongly depend on the transition rates of protein conformation and the elastic coupling between the proteins and the lipids.  I will discuss our recent study on a general theoretical framework for these systems, and introduce some interesting predictions that can be verified by experiemnts on artificial membranes.
　

Prof. Chi-Ho Cheng

Physics Department, National Changhua University of Education, TAIWAN

E-mail: phcch@cc.ncue.edu.tw

Some Issue on Polyelectrolyte Adsorption

Dr. Zh.S. Gevorkian

Institute of Physics, Academia Sinica, TAIWAN

E-mail: gevorkia@phys.sinica.edu.tw

Scaling Behavior in DNA Bubble Dynamics

Dr. Yao-Chen Hung

Institute of Physics, Academia Sinica, TAIWAN

E-mail: ychung@phys.sinica.edu.tw

Chaotic Communication by Means of Temporal Causality

    We propose a new concept for secure communication using chaos. A binary message is encoded into the temporally causal relations between two coupled chaotic systems. Applying the analysis of temporal transfer entropy (TTE), the masked information can be recovered from transmitted signals at the receiver. The communication scheme has been demonstrated to be robust against external noise.

Prof. Chai-Yu Lin

Physics Department, National Chung Cheng University, TAIWAN

E-mail: lincy@phys.sinica.edu.tw

Renormalization Group Scheme for a Stochastic Sandpile

    Based on the stochastic features and the similarity of topplings at different scales, this study proposes a renormalization group (RG) scheme for the Manna model. The full enumeration of RG events inside a 2*2 RG cell for the m-state Manna model is calculated, where m=2, 3, and 4. Fixed point analysis shows that the resulting height probabilities are very close to numerical simulations.

Prof. Yin-Chang Liu

Department of Life Science, Tsing-Hua University, TAIWAN

E-mail: ycliu@life.nthu.edu.tw

Evidence for the Direct Involvement of Tumor Suppressor p53 in Nucleotide Excision Repair

Tumor suppressor p53 functions primarily as transcription regulator of many genes involving apoptosis, cell cycle arrest and DNA repair. Previous studies have indicated that p53 may enhance the capacity of nucleotide excision repair (NER) via transcription-independent manner. Our study provides evidence that p53 may participate in NER by facilitating the recruitment of repair proteins to the UV-induced DNA damage site.

Dr. Bih-Show Lou

Chemistry division, Chang Gung University, TAIWAN
E-mail: blou@mail.cgu.edu.tw

Probing the Interaction of Na+ Channel Inactivation Gate Peptides and Local Anesthetics by NMR and ESI-MS

Dr. Karen Petrosyan

Institute of Physics, Academia Sinica, TAIWAN

E-mail: pkaren@phys.sinica.edu.tw

Long DNA Molecule as a Pseudoscalar Liquid Crystal

Prof. Rudolf A. Roemer

Centre for Scientific Computing, University of Warwick, UK
E-mail: csc-director@warwick.ac.uk

1. Anderson Localization and the Disorder-Induced Metal-Insulator Transition

    Nearly forty years have passed since Anderson's first suggestion of a disorder-induced metal-insulator transition (MIT), and yet the localization problem remains at the centre of much interest.

    For non-interacting electrons, a highly successful approach was put forward in 1979 by Abrahams et al.. This scaling hypothesis of localization suggests that an MIT exists for non-interacting electrons in three dimensions (3D) at zero magnetic field B and in the absence of spin-orbit coupling. Much further work has subsequently supported these scaling arguments both analytically and numerically. In 1D and 2D, the same hypothesis shows that there are no extended states and thus no MIT. However, since 2 is the lower critical dimension of the localization problem, the 2D case is in a sense close to 3D: states are only marginally localized for weak disorder and a small magnetic field or spin-orbit coupling can lead to the existence of extended states and thus an MIT. Consequently, the localization lengths of a 2D system with potential disorder can be quite large so that in numerical approaches one can always find a localization-delocalization transition when decreasing either system size for fixed disorder or disorder for fixed system size.

    Most numerical approaches to the localization problem use the standard tight-binding Anderson Hamiltonian with onsite potential disorder. Characteristics of the electronic eigenstates are then investigated by studies of participation numbers obtained by exact diagonalization, multifractal properties, level statistics and many others. Especially fruitful is the transfer-matrix method (TMM) which allows a direct computation of the localization lengths and further validates the scaling hypothesis by a numerical proof of the existence of a one-parameter scaling function. In my talk, I shall review the physics of the Anderson MIT, paying particular attention to its relation to critical phenomena. Also, in recent years the interest has focused on the validity of the scaling hypothesis in a variety of non-standard models and I hope to introduce these and explain the results which have been obtained. Last, I shall also introduce some of the algorithms used to study the transition in detail.

2. Multifractal Analysis, Random-Matrix Theory and All That at the Metal-Insulator Transition

    In this talk, I would like to introduce indirect measures of localization which do not directly use the experimentally accessible transport quantities such as conductivity, thermopower, etc. Rather, we will use the eigenvalues and eigenvectors of the Anderson Hamiltonian directly in order to characterize the Anderson transition. These measures have been shown in many studies to allow for very good qualitative as well as quantitative characterization of the MIT.

    For matrices with random entries, distributed according to a Gaussian probability measure, it has been shown many years ago that the statistical properties of the eigenvalues can be characterized very well by universal formulae which only depend on certain global symmetries of the matrix. If these random matrices are real and symmetric and hence the ensemble is invariant under orthogonal transformations, we find the Gaussian orthogonal ensemble (GOE) distribution P_GOE(s)for the nearest-neighbour energy differences s=(E_n+1-E_n) /Δ with Δ the so-called mean level spacing. A very good approximation for P_GOE(s) is P_W(s) = πs exp(-πs²/4)/2. For unitary, i.e. time-reversal symmetry breaking systems, one finds the P_GUE(s) distribution and, finally, P_GSE(s) corresponds the Gaussian symplectic ensemble. Similarly, formulas for correlation of eigenenergies exists and these as well as P(s) can be compared to results obtained by exact diagonalization to test how close a given system is to these universal predictions. Right at the MIT, P(s) is expected to be given by a system-size independent, new distribution not described by any of the above formulae.

    Similarly, the all three universality classes GOE, GUE and GSE, one can find predictions on the distribution of eigenfunction amplitudes – the so-called Porter-Thomas distributions. Particularly important is the study of the spatial distribution of wave function amplitudes known as multifractal analysis (MFA). A symmetry relation for the MF spectrum f(α) directly at the MIT has been found and tested by comparison to numerical data. I will show recent results for the largest ever wave-functions computed for an Anderson system of 43 million sites.

3. Electronic Transport in DNA and Its Ramifications

    Long range charge transfer experiments in DNA oligomers and the subsequently measured - and very diverse - transport response of DNA wires in solid state experiments exemplify the need for a thorough theoretical understanding of charge migration in DNA-based natural and artificial materials. Here I present a review of tight-binding models for DNA conduction which have the intrinsic merit of containing more structural information than plain rate-equation models while still retaining sufficient detail of the electronic properties. This allows for simulations of transport properties to be more manageable with respect to density functional theory methods or correlated first principle algorithms.

    At first, we shall study the electronic properties of DNA by way of a tight-binding model applied to four particular DNA sequences. The charge transfer properties are presented in terms of localisation lengths, crudely speaking the length over which electrons travel. Various types of disorder, including random potentials, are employed to account for different real environments. We have performed calculations on poly(dG)-poly(dC), telomeric-DNA, random-ATGC DNA and λ-DNA. We find that random and λ-DNA have localisation lengths allowing for electron motion among a few dozen base pairs only. A novel enhancement of localisation lengths is observed at particular energies for an increasing binary backbone disorder. We comment on the possible biological relevance of sequence dependent charge transfer in DNA.

    Next, we use these results for a theoretical study of point mutations effects on charge transfer properties in the DNA sequence of the tumor-suppressor p53 gene. On the basis of effective single-strand or double-strand tight-binding models which simulate hole propagation along the DNA, a statistical analysis of charge transmission modulations associated with all possible point mutations is performed. We find that in contrast to non-cancerous mutations, mutation hotspots tend to result in significantly weaker changes of transmission properties. This suggests that charge transport could play a significant role for DNA-repairing deficiency yielding carcinogenesis.

Prof. Ten-Ming Wu

Institute of Physics, National Chiao-Tung University, TAIWAN

E-mail: tmw@faculty.nctu.edu.tw

Anomalies in Structure and Dynamics of Liquid Ga

    The well-known shoulder in static structure factor and the recently observed anomaly in the linewidth of dynamic structure factor of liquid Ga are studied by MD simulation, with an interatomic pair potential generated by a first-principles pseudopotential theory. In our simulation, the two anomalies are confirmed to occur at the same location. The variations of the liquid structure and the linewidth of dynamic structure factor with the range of the interatomic pair potential are examined. The interaction ranges for producing the two anomalies are estimated in a nanometer scale.

Prof. Zicong Zhou

Department of Physics, Tamkang University, TAIWAN

E-mail: zzhou@mail.tku.edu.tw

Sequence-Dependent Effects on the Properties of Semiflexible Biopolymers

    Using path integral technique, we show exactly that for a semiflexible biopolymer in constant extension ensemble, no matter how long the polymer and how large the external force may be, the effects of short range correlations in the sequence-dependent spontaneous curvatures and torsions can be incorporated into a model with well-defined mean spontaneous curvature and torsion as well as a renormalized persistence length. In contrast, the effects of sequence-dependent persistence lengths are complex. For a long biopolymer with large mean persistence length, the sequence-dependent persistence lengths can be replaced by its mean. However, for a short biopolymer or for a biopolymer with small persistence lengths, inhomogeneity in persistence lengths tends to make physical observables very sensitive to details and therefore less predictable.