To cooperate or to defect? Altruism and reputation

The basic difficulty in cooperation theory is to justify the cooperation. Here we propose a new approach, where players are driven by their altruism to cooperate or not. The probability of cooperation depends also on the co-player’s reputation. We find that players with positive altruism cooperate and meet cooperation. In this approach, payoffs are not relevant.     

Novel Nanostructures from Self‐Assembly of Chiral Block Copolymers

A diblock copolymer system constituting both achiral and chiral blocks, polystyrene‐block‐poly(L ‐lactide) (PS‐PLLA), was designed for the examination of chiral effects on the self‐assembly of block copolymers (BCPs). A unique phase with three‐dimensional hexagonally packed PLLA helices in PS matrix, a helical phase (H*), can be obtained from the self‐assembly of PS‐rich PS‐PLLA with volume fraction of PLLA f = 0.34, whereas no such phase was found in racemic polystyrene‐block‐poly(D .L ‐lactide) (PS‐PLA) BCPs. Moreover, various interesting crystalline PS‐PLLA nanostructures can be obtained by controlling the crystallization temperature of PLLA (T_c,PLLA), leading to the formation of crystalline helices (PLLA crystallization directed by helical confined microdomain) and crystalline cylinders (phase transformation of helical nanostructure dictated by crystallization) when T_c,PLLA < T_g,PS (the glass transition temperature of PS) and T_c,PLLA ≧ T_g,PS, respectively. As a result, a spring‐like behavior of the helical nanostructure can be driven by crystallization so as to dictate the transformation (i.e., stretching) of helices and to result in crystalline cylinders. For PS‐PLLA with PLLA‐rich fraction (f = 0.65), another unique phase, a hexagonally packed core‐shell cylinder phase with helical sense (CS*), in which the PS microdomains appear as shells and PLLA microdomains appear as matrix and cores, can be found in the self‐assembly of PLLA‐rich PS‐PLLA BCPs. The formation of those novel phases: helix and core‐shell cylinder is attributed to the chiral effect on the self‐assembly of BCPs, so we named this PS‐PLLA BCP as chiral BCP (BCP*). For potential applications of those materials, the spring‐like behavior with thermal reversibility might provide a method for the design of switchable nanodevices, such as nanoscale actuators. In addition, the PLLA blocks can be hydrolyzed. After hydrolysis, helical nanoporous PS bulk and PS tubular texture can be obtained and used as templates for the formation of nanocomposites.

     

Comparison of pattern recognition methods in classifying high-resolution BOLD signals obtained at high magnetic field in monkeys

Pattern recognition methods have shown that functional magnetic resonance imaging (fMRI) data can reveal significant information about brain activity. For example, in the debate of how object categories are represented in the brain, multivariate analysis has been used to provide evidence of a distributed encoding scheme [Science 293:5539 (2001) 2425–2430]. Many follow-up studies have employed different methods to analyze human fMRI data with varying degrees of success [Nature reviews 7:7 (2006) 523–534]. In this study, we compare four popular pattern recognition methods: correlation analysis, support-vector machines (SVM), linear discriminant analysis (LDA) and Gaussian naïve Bayes (GNB), using data collected at high field (7 Tesla) with higher resolution than usual fMRI studies. We investigate prediction performance on single trials and for averages across varying numbers of stimulus presentations. The performance of the various algorithms depends on the nature of the brain activity being categorized: for several tasks, many of the methods work well, whereas for others, no method performs above chance level. An important factor in overall classification performance is careful preprocessing of the data, including dimensionality reduction, voxel selection and outlier elimination.     

High Conductivity PEDOT Using Humidity Facilitated Vacuum Vapour Phase Polymerisation

The synthesis of high conductivity poly(3,4‐ethylenedioxythiophene) (PEDOT) films using vacuum vapour phase polymerisation is reported. Water vapour is introduced into the chamber and results suggest that it acts as a proton scavenger during polymerisation. Process optimisation leads to PEDOT films that have high conductivity and a blue‐black appearance. Poor quality films have lower conductivity and a characteristic greenish colour. UV‐vis‐NIR spectra show that poor PEDOT films are characterised by higher absorption in the UV‐vis region and an absorption plateau in the NIR region, which suggests an increased level of disrupted conjugation along the polymer backbone or higher oligomer content. Conversely, high quality PEDOT is characterised by an extended NIR absorption tail and lower absorption in the UV‐vis region.

     

Dynamic stiffness matrix of thin-walled composite I-beam with symmetric and arbitrary laminations

For the spatially coupled free vibration analysis of thin-walled composite I-beam with symmetric and arbitrary laminations, the exact dynamic stiffness matrix based on the solution of the simultaneous ordinary differential equations is presented. For this, a general theory for the vibration analysis of composite beam with arbitrary lamination including the restrained warping torsion is developed by introducing Vlasov's assumption. Next, the equations of motion and force–displacement relationships are derived from the energy principle and the first order of transformed simultaneous differential equations are constructed by using the displacement state vector consisting of 14 displacement parameters. Then explicit expressions for displacement parameters are derived and the exact dynamic stiffness matrix is determined using force–displacement relationships. In addition, the finite-element (FE) procedure based on Hermitian interpolation polynomials is developed. To verify the validity and the accuracy of this study, the numerical solutions are presented and compared with analytical solutions, the results from available references and the FE analysis using the thin-walled Hermitian beam elements. Particular emphasis is given in showing the phenomenon of vibrational mode change, the effects of increase of the modulus and the bending–twisting coupling stiffness for beams with various boundary conditions.     

Improved PEDOT Conductivity via Suppression of Crystallite Formation in Fe(III) Tosylate During Vapor Phase Polymerization

Vapor phase polymerization was used to synthesize high conductivity poly(3,4‐ethylenedioxyphenylene) (PEDOT). The monomer is presented to an oxidant‐rich substrate in vapor form and even for short polymerization times, 10–30 min, Fe(III) tosylate has a propensity for water absorption leading to crystal formation. Poor oxidant treatment before polymerization or high humidity during polymerization can create holes in the PEDOT film decreasing its conductivity. The addition of an amphiphilic copolymer poly(ethylene glycol)‐ran‐poly(propylene glycol) suppresses crystal growth allowing better film formation. The humidity level during synthesis was optimized at 35% relative humidity (RH), producing a conductivity of 761 S · cm⁻¹. Additionally, the copolymer extends the RH range that is tolerable for polymer synthesis.

     

Emerging biomedical and advanced applications of time-resolved fluorescence spectroscopy

Time-resolved fluorescence spectroscopy is presently regarded as a research tool in biochemistry, biophysics, and chemical physics. Advances in laser technology, the development of long-wavelength probes, and the use of lifetime-based methods, are resulting in the rapid migration of timeresolved fluorescence to the clinical chemistry lab, the patient's bedside, and even to the doctor's office and home health care. Additionally, time-resolved imaging is now a reality in fluorescence microscopy and will provide chemical imaging of a variety of intracellular analytes and/or cellular phenomena. Future horizons of state-of-the-art spectroscopy are also described. Two photon-induced fluorescence provides an increased information content to time-resolved data. Two photoninduced fluorescence, combined with fluorescence microscopy and time-resolved imaging, promises to provide detailed three-dimensional chemical imaging of cells. Additionally, it has recently been demonstrated that the pulses from modern picosecond lasers can be used to quench and/or modify the excited-state population by stimulated emission since the stimulated photons are directed along the quenching beam and are not observed. The phenomenon of light quenching should allow a new class of multipulse time-resolved fluorescence experiments, in which the excited-state population is modified by additional pulses to provide highly oriented systems.     

Determination of some scattering factors for the case of mixed scattering of charge carriers

The method of determining the Fermi energy and some scattering factors in the case of mixed scattering of charge carriers is described under the presumption that the relaxation time is given by the following equation: = Cx ^s.     

Crystal and molecular structure of guanidinium hexatungsto-bis(p-aminophenylarsonate) tetrahydrate,[C(NH2)3]4[p-NH3C6H4As)2W6O25]·4H2O

The crystal structure of a new type arylarsonic polytungstate [C(NH₂)₃]₄[p-NH₃C₆H₄As)₂W₆O₂₅]·4H₂O was determined by single-crystal X-ray diffraction analysis. It belongs to triclinic, space group \[ P\bar 1 \], with cell dimensions a = 12.863(3), b = 18.912(3), c = 21.383(4) Å α = 91.14(2)°, β = 93.65(3)°, γ = 92.25(3)°, V = 5185.9 ų, Z = 4, D_c = 2.753 g/cm³. The intensity data were collected on an Enraf-Nonius CAD4 diffractometer with Mo K_α radiation. The positions of all tungsten and arsenic atoms were determined by direct method. The other non-hydrogen atoms were revealed by difference Fourier synthesis. The structure was refined by fullmatrix least-squares procedure to a final R value of 0.070. The crystal structure contains two similar but nonidentical molecules. Two similar anions consist of a ring of six WO₆ octahedra, which are connected with one face-sharing, two corner-sharings and three edge-sharings, and two p-aminophenylarsonic tetrahedra capped above and below the ring. In each WO₆ ring, four tungsten atoms, which are joined with edge-sharing oxygen atoms, are almost coplanar, while the two others, which are joined with face-sharing oxygen atoms, protrude out of the ring towards the same side. The two arsenic atoms in each anion are not equivalent in their bonding manner. In each anion, all non-hydrogen atoms of each organic group are in the same plane. Each molecule contains one anion, four C(NH₂)₃+ cations and four water molecules. There are many hydrogen bonds between cations and anions throughout the whole crystal. The amino groups can accept protons, so that the charge of the resulting anion decreases and [(RAs)₂W₆O₂₅]^4- type complexes are formed.     

The superconductivity and structure of equiatomic ternary transition metal pnictides

Recent superconductivity and crystallographic data for the MM′X ternary compounds with M = Ti, Zr, or Hf, M′ = Ru or Os, and X = P or As are presented. Moderate to high superconducting transition temperatures (T _c 's)are exhibited by the ZrRuSi-type hexagonal phase which is found to be metastable at low temperatures. The low-temperature phase of ZrRuP has the TiNiSi-type orthorhombic structure and exhibits superconductivity at 3.9K. The low-temperature phase of HfRuAs has the TiFeSi-type orthorhombic superstructure and remains normal at 1.0K. TiRuAs exists only with the superstructure and remains normal at 0.35K. The details of these various structural modifications point to the importance of undistorted zig-zag chains of metal atoms for the occurrence of superconductivity in these compounds. The lowT _c for TiRuP and the absence of superconductivity for TiOsP above 0.35K are not accounted for by these structural modifications.