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The photoconversion mechanism of a green/red sensory cyanobacteriochrome AnPixJ was studied. The phycocyanobilin-binding second GAF domain of AnPixJ of Anabaena sp. PCC 7120 was expressed in Escherichia coli cells. The His-tagged AnPixJ-GAF2 domain exhibited photoconversion between the green- and red-absorbing forms, APg(543) and APr(648), respectively. We detected four intermediate states in the photocycle between them, as follows: APr(648) → red light → APr(648)* → (with a rise time constant τ(r) of <100 ns) R1(650-80) (with a decay time constant τ(d) of <1 μs) → R2(610) (τ(d) = 920 μs) → APg(543) → green light → APg(543)* → (τ(r) < 50 ns) G1(570) (τ(d) = 190 μs) → G2(630) (τ(d) = 1.01 ms) → APr(648). These intermediates were named for their absorption peak wavelengths, which were estimated on the basis of the time-resolved difference spectra and global analysis of the time courses. The absorption spectrum of APr(648) resembles that of the Pr form of the phytochrome, while all the other states showed peaks at 530-650 nm and had wider bandwidths with smaller peak amplitudes. The fastest decay phases of fluorescence from APr(648)* and APg(543)* gave lifetimes of 200 and 42 ps, respectively, suggesting fast primary reactions. The APg(543)-minus-APr(648) difference FTIR spectrum in an H(2)O medium was significantly different from those reported for the Pfr/Pr difference spectra in phytochromes. Most of the peaks in the difference spectrum were shifted in the D(2)O medium, suggesting the high accessibility to the aqueous phase. The interactions of the phycocyanobilin chromophore with the surrounding amino acid residues, which are fairly different from those in the GAF domain of phytochromes, realize the unique green/red photocycle of AnPixJ.

We extend the newly proposed probability-changing cluster (PCC) Monte Carlo algorithm to the study of systems with the vector order parameter. Wolff's idea of the embedded cluster formalism is used for assigning clusters. The Kosterlitz-Thouless (KT) transitions for the two-dimensional (2D) XY and q-state clock models are studied by using the PCC algorithm. Combined with the finite-size scaling analysis based on the KT form of the correlation length, ξ ∝ exp(c/ T /TKT − 1), we determine the KT transition temperature and the decay exponent η as TKT = 0.8933(6) and η = 0.243(5) for the 2D XY model. We investigate two transitions of the KT type for the 2D q-state clock models with q = 6, 8, 12, and for the first time confirm the prediction of η = 4/q 2 at T1, the low-temperature critical point between the ordered and XY-like phases, systematically.

Nonvolatile solvent swollen 1D periodic films were fabricated from lamellae-forming block copolymers with medium molecular weight by infiltrating an ionic liquid. A mixture of imidazole and imidazolium bis(trifluoromethanesulfonyl)imide as a room temperature ionic liquid was added after spin-coating of thin films of polystyrene-b-poly(2-vinylpyridine) (PS−P2VP) block copolymers having an approximately 50/50 composition to create photonic films reflecting in the visible regime. Under normal conditions of temperature and humidity, the films maintained their photonic properties for more than 100 days without perceptible change, stemming from the nonvolatility of the ionic liquid. Transmission electron microscopy revealed the selective swelling of the P2VP nanodomains by the IL and ultrasmall angle X-ray scattering measurements provided quantitative nanostructure information on the periodicities of the films. The wavelength of reflected light from photonic films was tunable by using different molecular weight block copolymers as well as by employing blends of two block copolymers. The experimental wavelength of the reflected light, detected by a fiber-optic spectrophotometer, agreed with values estimated from the Bragg condition and was able to be controlled from about 380 to 620 nm.

We propose a new effective cluster algorithm of tuning the critical point automatically, which is an extended version of Swendsen-Wang algorithm. We change the probability of connecting spins of the same type, p = 1 − e −J/k B T , in the process of the Monte Carlo spin update. Since we approach the canonical ensemble asymptotically, we can use the finite-size scaling analysis for physical quantities near the critical point. Simulating the two-dimensional Potts models to demonstrate the validity of the algorithm, we have obtained the critical temperatures and critical exponents which are consistent with the exact values; the comparison has been made with the invaded cluster algorithm. [3] representation to identify clusters of spins. The problem of the thermal phase transition is mapped onto the geometric percolation problem in the cluster formalism [3][4][5]. Quite recently, based on the cluster formalism, the multiple-percolating clusters of the Ising system with large aspect ratio have been studied [6].Machta et al. [7] proposed another type of cluster algorithm, which is called the invaded cluster (IC) algorithm; this algorithm samples the critical point of a spin system without a priori knowledge of the critical temperature. It is in contrast with the usual procedure that one makes simulations for various parameters to determine the critical point. The IC algorithm has been shown to be efficient in studying various physical quantities in the critical region, but the ensemble is not necessarily clear. Moreover, it has a problem of "bottlenecks", which causes the broad tail in the distribution of the fraction of the accepted satisfied bonds [7].In this Letter, extending the SW algorithm [1], we propose a new algorithm of tuning the critical point automatically. The basic idea of our algorithm is that we change the probability of connecting spins of the same type, p = 1 − e −J/kB T , in the process of the Monte Carlo spin update, where J is the exchange coupling. We decrease or increase p depending on the observation whether the KF clusters are percolating or not percolating. This simple negative feed-back mechanism together with the finite-size scaling (FSS) property of the existence probability (also called the crossing probability) E p , the probability that the system percolates, leads to the determination of the critical point. Since our ensemble is asymptotically canonical as ∆p, the amount of the change of p, becomes 0, the distribution functions of physical quantities obey the FSS; as a result, we can determine critical exponents using the FSS analysis.Let us explain the procedure for our probabilitychanging cluster (PCC) algorithm in detail. As an example, we consider the ferromagnetic q-state Potts model [8] and for q = 2 this corresponds to an Ising model. The procedure of Monte Carlo spin update is as follows:1. Start from some spin configuration and some value of p.

We study the finite-size scaling (FSS) property of the correlation ratio, the ratio of the correlation functions with different distances. It is shown that the correlation ratio is a good estimator to determine the critical point of the second-order transition using the FSS analysis. The correlation ratio is especially useful for the analysis of the Kosterlitz-Thouless (KT) transition. We also present a generalized scheme of the probability-changing cluster algorithm, which has been recently developed by the present authors, based on the FSS property of the correlation ratio. We investigate the twodimensional quantum XY model of spin 1/2 with this generalized scheme, obtaining the precise estimate of the KT transition temperature with less numerical effort. The development of efficient Monte Carlo algorithms is important for studying many-body problems in physics. We recently developed a cluster algorithm, which is called the probability-changing cluster (PCC) algorithm, of locating the critical point automatically [1]. It is an extension of the Swendsen-Wang (SW) algorithm [2], but we change the probability of cluster update (essentially, the temperature) during the Monte Carlo process. Since we do not have to make simulations for several parameters, we can extract information on critical phenomena with much less numerical effort. We applied the PCC algorithm to the 2D diluted Ising model [3], investigating the crossover and self-averaging properties. We also extended the PCC algorithm to the problem of the vector order parameter [4] with the use of Wolff's embedded cluster formalism [5]; studying the 2D classical XY and clock models, we showed that the PCC algorithm is also useful for the Kosterlitz-Thouless (KT) transition [6].In the original formulation of the PCC algorithm [1], we used the cluster representation of the Ising model (generally, the Potts model) due to Kasteleyn and Fortuin [7] in two ways. First, we make a cluster flip as in the SW algorithm [2]. Second, we change the probability of connecting spins of the same type, p, depending on the observation whether clusters are percolating or not. We use the finite-size scaling (FSS) relation for the probability that the system percolates, E p ,to determine the critical point. Here, L is the system size, p c is the critical value of p for the infinite system, and ν is the correlation-length critical exponent. We may alternatively consider that t = (T − T c )/T c , where T is the temperature. With a negative feedback mechanism, we locate the size-dependent temperature, E p of which is * Electronic address: ytomita@phys.metro-u.ac.jp † Electronic address: okabe@phys.metro-u.ac.jp 1/2. The point is that E p has the FSS property with a single scaling variable. We may use quantities other than E p which have a similar FSS relation. Then, we could generalize the PCC algorithm for a problem where the mapping to the cluster formalism does not exist.In the FSS analysis of the simulation, we often use the Binder ratio [8], which is essentially the ratio of the...

Motivated by puzzling characteristics of spin-glass transitions widely observed in pyrochlore-based frustrated materials, we investigate the effects of coupling to local lattice distortions in a bond-disordered antiferromagnet on the pyrochlore lattice by extensive Monte Carlo simulations. We show that the spin-glass transition temperature T(f) is largely enhanced by the spin-lattice coupling and, furthermore, becomes almost independent of Δ in a wide range of the disorder strength Δ. The critical property of the spin-glass transition is indistinguishable from that of the canonical Heisenberg spin glass in the entire range of Δ. These peculiar behaviors are ascribed to a modification of the degenerate manifold from a continuous to semidiscrete one by spin-lattice coupling.