Characteristics of biogenic calcite in the prismatic layer of a pearl oyster,Pinctada fucata

The fine structure of the calcite prism in the outer layer of a pearl oyster, Pinctada fucata, has been investigated using various electron beam techniques, in order to understand its characteristics and growth mechanism including the role of intracrystalline organic substances. As the calcite prismatic layer grows thicker, sinuous boundaries develop to divide the prism into a number of domains. The crystal misorientation between the adjacent domains is several to more than ten degrees. The component of the misorientation is mainly the rotation about the c-axis. There is no continuous organic membrane at the boundaries. Furthermore, the crystal orientation inside the domains changes gradually, as indicated by the electron back-scattered diffraction (EBSD) in a scanning electron microscope (SEM). Transmission electron microscopy (TEM) examination revealed that the domain consists of sub-grains of a few hundred nanometers divided by small-angle grain boundaries, which are probably the origin of the gradual change of the crystal orientation inside the domains. Spherular Fresnel contrasts were often observed at the small-angle grain boundaries, in defocused TEM images. Electron energy-loss spectroscopy (EELS) indicated the spherules are organic macromolecules, suggesting that incorporation of organic macromolecules during the crystal growth forms the sub-grain structure of the calcite prism.     

The correlation between organic matrices and biominerals (myostracal prism and folia) of the adult oyster shell, Crassostrea gigas

The organic membrane at the interface between the myostracum (aragonite) and folia (calcite) was obtained and identified as a chitin-like macromolecule after chemical treatment. It was confirmed that the organic membrane was faced to the crystal (001) plane of the myostracum and folia. The secondary structures in soluble protein of the myostracum and the folia of oyster shell were identified as a great quantity of beta-structure. The acidic amino acids, Asp and Glu, to play a role as templates on shell formation were confirmed in the myostracum and the folia.     

Phase-field study of free growth in a channel: from thermal to chemical solidification

The thermal and the chemical phase-field models for free growth in a two-dimensional channel are both studied in their one-sided version for which diffusion only occurs in the liquid. We compare the steady state fingers obtained in our phase-field simulations with the results of boundary integral techniques available in the literature. The excellent agreement found between both methods provides a valuable benchmark of the one-sided thin-interface phase model which makes use of an antitrapping current. Coexistence of several steady states predicted by the Green’s function calculations is also recovered. The dynamical stability of two competing modes (symmetric and asymmetric finger) is studied and the extension of their respective basins of attraction is evaluated. General implications of our results for a large class of isotropic systems are discussed.     

Entanglement and irreversibility in the approach to thermal equilibrium

A grazing incidence vacuumspectrograph is converted to a spectrometer to use photo-electric detection. The detector used is a CCD-camera with special enhanced sensitivity for the soft x-ray region. The camera can be moved along a special designed rail which allows very accurate repositioning after initial calibration. We designed a procedure for alignment, which allows us to align and focus the spectrometer using only visible light. This simplifies and improves setting up the instrument.     

Searching for quarks: a quantum chemical assisted approach

The evidence for quarks as the basic blocks of matter come only from very expensive experiments, performed in very large particle accelerators. An alternative method of detection is to look for changes in spectroscopic properties that could be influenced by fractionally charged nuclei formed with the ‘wrong’ number of quarks. Although this proposal has already been made by many authors, they were not able to provide feasible and easily interpretable experiments to detect quarks in matter. In this paper, we present the results of configuration interaction (CI) calculations for the transition energies and optical oscillator strengths associated with inner shell electronic spectra of molecular nitrogen made of fractionally charged nuclei. It is shown that these bands can be used as fingerprints characterizing the presence of quarks in matter.     

Minimum electrical and thermal conductivity of graphene: a quasiclassical approach

We investigate the minimum conductivity of graphene within a quasiclassical approach taking into account electron-hole coherence effects which stem from the chiral nature of low energy excitations. Relying on an analytical solution of the kinetic equation in the electron-hole coherent and incoherent cases, we study both the electrical and the thermal conductivity whose relation satisfies the Wiedemann-Franz law. We find that most of the previous findings based on the Boltzmann equation are restricted to only high mobility samples where electron-hole coherence effects are not sufficient.     

Dimensional crossover of thermal conductance in graphene nanoribbons: a first-principles approach

First-principles density-functional calculations are performed to investigate the thermal transport properties in graphene nanoribbons (GNRs). The dimensional crossover of thermal conductance from one to two dimensions (2D) is clearly demonstrated with increasing ribbon width. The thermal conductance of GNRs of a few nanometers width already exhibits an approximate low-temperature dependence of T(1.5), like that of 2D graphene sheets which is attributed to the quadratic nature of the dispersion relation for the out-of-plane acoustic phonon modes. Using a zone-folding method, we heuristically derive the dimensional crossover of thermal conductance with the increase of ribbon width. Combining our calculations with the experimental phonon mean-free path, some typical values of thermal conductivity at room temperature are estimated for GNRs and for 2D graphene sheet. Our findings clarify the issue of the low-temperature dependence of thermal transport in GNRs and suggest a calibration range of thermal conductivity for experimental measurements in graphene-based materials.     

Magnetic and thermal Mössbauer effect scans: a new approach

Mössbauer transmission recorded at fixed photon energies as a function of a given physical parameter such as temperature, external field, etc. (Mössbauer scan), is being developed as a useful quantitative tool, complementary of Mössbauer spectroscopy. Scans are performed at selected energies, suitable for the observation of a given physical property or process. It is shown that one of main advantages of this approach is the higher speed at which the external physical parameter can be swept, which allows the recording of quasi-continuous experimental response functions as well as the study of processes which occur too fast to be followed by Mössbauer spectroscopy. The applications presented here are the determination of the temperature dependence of the ⁵⁷Fe hyperfine field in FeSn₂, the thermal evolution and nanocrystallization kinetics of amorphous Fe_73.5Si_13.5Cu₁Nb₃B₉ and the measurement of the dynamic response of Fe magnetic moments in nanocrystalline Fe₉₀Zr₇B₃ to an external ac field.     

Mechanical characteristics and morphological effect of complex crossed structure in biomaterials: fracture mechanics and microstructure of chalky layer in oyster shell

The complex crossed structures with a polymorph of calcite, termed a chalky layer, which make up much of the shell of an oyster, are composed of flames and leaflets. Two layers, folia and the chalky layer in the giant Pacific oyster (Crassostrea gigas) were examined using SEM (scanning electron microscope), micro-area-XRD (X-ray diffraction) and FT-IR (Fourier transform infrared spectrometer) to determine their morphologies and component characteristics. The chalky layer was also tested using microindentation to assess its mechanical properties, and a microcrack was generated to study the fracture mechanism of the chalky layer. From an analysis of the secondary protein structure, it was shown that the ordered structures of the two layers, α-helix and β-structure, are similar but that the unordered structures are different. Moreover, the foliated rods at the interface of the chalky layer play a key role in the crystal growth of the chalky layers. Comparing the morphology and the preferred orientation of foliated laths, the advantages of the relatively high density and low hardness of the chalky layer have interesting implications regarding the development of sophisticated complex composites.     

Oxide semiconductors for solar to chemical energy conversion: nanotechnology approach

The present work considers the application of oxide semiconductors in the conversion of solar energy into the chemical energy required for water purification (removal of microbial cells and toxic organic compounds from water) and the generation of solar hydrogen fuel by photoelectrochemical water splitting. The first part of this work considers the concept of solar energy conversion by oxide semiconductors and the key performance-related properties, including electronic structure, charge transport, flat band potential and surface properties, which are responsible to the reactivity and photoreactivity of oxides with water. The performance of oxide systems for solar energy conversion is briefly considered in terms of an electronic factor. The progress of research in the formation of systems with high performance is considered in terms of specific aspects of nanotechnology, leading to the formation of systems with high performance. The nanotechnology approach in the development of high-performance photocatalysts is considered in terms of the effect of surface energy associated with the formation of nanostructured system on the formation of surface structures that exhibit outstanding properties. The unresolved problems that should be tackled in better understanding of the effect of nanostructures on properties and performance of oxide semiconductors in solar energy conversion are discussed. This part is summarised by a list of unresolved problems of crucial importance in the formation of systems with enhanced performance. This work also formulates the questions that must be addressed in order to overcome the hurdles in the formation of oxide semiconductors with high performance in water purification and the generation of solar fuel. The research strategy in the development of oxide systems with high performance, including photocatalysts for solar water purification and photoelectrodes for photoelectrochemical water splitting, is considered. The considerations are focused on the systems based on titanium dioxide of different defect disorder as well as its solid solutions and composites.     

A versatile approach to the study of the transient response of a submerged thin shell

The transient response of submerged two-dimensional thin shell subjected to weak acoustical or mechanical excitations is addressed in this paper. The proposed approach is first exposed in a detailed manner: it is based on Laplace transform in time, in vacuo eigenvector expansion with time-dependent coefficients for the structural dynamics and boundary-integral formulation for the fluid. The projection of the fluid pressure on the in vacuo eigenvectors leads to a fully coupled system involving the modal time-dependent displacement coefficients, which are the problem unknowns. They are simply determined by matrix inversion in the Laplace domain. Application of the method to the response of a two-dimensional immersed shell to a weak acoustical excitation is then exposed: the proposed test-case corresponds to the design of immersed structures subjected to underwater explosions, which is of paramount importance in naval shipbuilding. Comparison of a numerical calculation based on the proposed approach with an analytical solution is exposed; versatility of the method is also highlighted by referring to “classical” FEM/FEM or FEM/BEM simulations. As a conspicuous feature of the method, calculation of the fluid response functions corresponding to a given geometry has to be performed once, allowing various simulations for different material properties of the structure, as well as for various excitations on the structure. This versatile approach can therefore be efficiently and extensively used for design purposes.     

Discrete and continuum spectra in the unified shell model approach

A new version of the nuclear shell model unifies the consideration of the discrete spectrum, where the results reproduce the standard shell model, and continuum. The ingredients of the method are the non-Hermitian effective Hamiltonian, energy-dependent one-body and two-body decay amplitudes, and self-consistent treatment of thresholds. The results for helium and oxygen isotope chains reproduce the data well.     

Compositional arrangement of rod/shell nanoparticles: an approach to provide efficient plasmon waveguides

In this work, we investigated the optical properties of a novel compositional configuration of gold nanorod and silver nanoshell which is embedded in a SiO₂ substance. The proper geometrical sizes for compositional rod/shell arrangement have been obtained based on the position and peak of plasmon resonance at λ ～1550 nm. Adjusting the plasmon resonance position at declared spectrum helps us to provide an arrangement which shows high efficiency and minimum losses. The influence of destructive components such as internal damping and scattering on the rod/shell combination is demonstrated by corresponding diagrams. Moreover, we proposed a nano-array based on examined configuration and the quality of light transmission along the array is studied. We figured out and depicted optical properties of the array such as transmission loss factors, group velocities, transmitted power, transmission quality, and two-dimensional snapshots of surface plasmons (SPs) coupling between nanoparticles arrangements under transverse and longitudinal modes excitations. Ultimately, it is shown that the suggested nanostructure based on studied nanoparticles configuration has a potential to utilize in designing nanophotonic devices such as splitters, couplers, and routers. Finite-difference time-domain method (FDTD) as a major simulation model has been employed to study the features of the waveguide.     

Decreasing vacuum temperature: A thermal approach to the cosmological constant problem

A natural thermal interpretation of the cosmological scenario is suggested in which the energy of the vacuum background is a variable function of the cosmic time; it is also shown that in this context one can easily formulate a simple phenomenological model which helps understanding, without fine-tuning, the extreme smallness of the present value of the cosmological constant.     

A pedestrian approach to transitions and fluctuations in simple nonequilibrium chemical systems

A method is presented for identifying the quasi-stable states of a simple class of spatially homogeneous, nonlinear, nonequilibrium chemical systems, and for numerically calculating the associated mean transition times, mean fluctuation periods and effective fluctuation ranges. The method of analysis is based on a “stochastic simulation” approach instead of a “master equation” approach, and it therefore focuses on the behavior of a typical individual system instead of on the collective behavior of a statistical ensemble of systems. Results of explicit calculations are presented for a model set of reactions proposed by Schlögl, and some clarification is achieved regarding hysteresis effects and the effects of an absorbing null state.     

A graphic approach to include dissipative-like effects in reversible thermal cycles

Since the decade of 1980’s, a connection between a family of maximum-work reversible thermal cycles and maximum-power finite-time endoreversible cycles has been established. The endoreversible cycles produce entropy at their couplings with the external heat baths. Thus, this kind of cycles can be optimized under criteria of merit that involve entropy production terms. Meanwhile the relation between the concept of work and power is quite direct, apparently, the finite-time objective functions involving entropy production have not reversible counterparts. In the present paper we show that it is also possible to establish a connection between irreversible cycle models and reversible ones by means of the concept of “geometric dissipation”, which has to do with the equivalent role of a deficit of areas between some reversible cycles and the Carnot cycle and actual dissipative terms in a Curzon-Ahlborn engine.     

Analytic approach to the thermal Casimir force between metal and dielectric

The analytic asymptotic expressions for the Casimir free energy, pressure and entropy at low temperature in the configuration of one metal and one dielectric plate are obtained. For this purpose we develop the perturbation theory in a small parameter proportional to the product of the separation between the plates and the temperature. This is done using both the simplified model of an ideal metal and of a dielectric with constant dielectric permittivity and for the realistic case of the metal and dielectric with frequency-dependent dielectric permittivities. The analytic expressions for all related physical quantities at high temperature are also provided. The obtained analytic results are compared with numerical computations and good agreement is found. We demonstrate for the first time that the Lifshitz theory, when applied to the configuration of metal-dielectric, satisfies the requirements of thermodynamics if the static dielectric permittivity of a dielectric plate is finite. If it is infinitely large, the Lifshitz formula is shown to violate the Nernst heat theorem. The implications of these results for the thermal quantum field theory in Matsubara formulation and for the recent measurements of the Casimir force between metal and semiconductor surfaces are discussed.