Collision of one-dimensional fermion clusters

We study cluster-cluster collisions in one-dimensional Fermi systems with particular emphasis on the non-trivial quantum effects of the collision dynamics. We adopt the Fermi-Hubbard model and the time-dependent density matrix renormalization group method to simulate collision dynamics between two fermion clusters of different spin states with contact interaction. It is elucidated that the quantum effects become extremely strong with the interaction strength, leading to the transmittance much more enhanced than expected from semiclassical approximation. We propose a concise model based on one-to-one collisions, which unveils the origin of the quantum effects and also explains the overall properties of the simulation results clearly. Our concise model can quite widely describe the one-dimensional collision dynamics with contact interaction. Some potential applications, such as repeated collisions, are addressed.Comment: 5 pages, 5 figure

Quantum walks and orbital states of a Weyl particle

The time-evolution equation of a one-dimensional quantum walker is exactly mapped to the three-dimensional Weyl equation for a zero-mass particle with spin 1/2, in which each wave number k of walker's wave function is mapped to a point \vec{q}(k) in the three-dimensional momentum space and \vec{q}(k) makes a planar orbit as k changes its value in [-\pi, \pi). The integration over k providing the real-space wave function for a quantum walker corresponds to considering an orbital state of a Weyl particle, which is defined as a superposition (curvilinear integration) of the energy-momentum eigenstates of a free Weyl equation along the orbit. Konno's novel distribution function of quantum-walker's pseudo-velocities in the long-time limit is fully controlled by the shape of the orbit and how the orbit is embedded in the three-dimensional momentum space. The family of orbital states can be regarded as a geometrical representation of the unitary group U(2) and the present study will propose a new group-theoretical point of view for quantum-walk problems.Comment: REVTeX4, 9 pages, 1 figure, v2: Minor corrections made for publication in Phys.Rev.

The effect of morphological changes from pulp fiber towards nano-scale fibrillated cellulose on the mechanical properties of high-strength plant fiber based composites

Fibrillated kraft pulp impregnated with phenolic resin was compressed under an extremely high pressure of 100MPa to produce high strength cellulose nanocomposites. To evaluate how the degree of fibrillation of pulp fiber affects the mechanical properties of the final composites, kraft pulp subjected to various levels of refining and high pressure homogenization treatments was used as raw material with different phenolic resin contents. It was found that fibrillation solely of the surface of the fibers is not effective in improving composite strength, though there is a distinct point in the fibrillation stage at which an abrupt increase in the mechanical properties of composites occurs. In the range between 16 and 30 passes through refiner treatments, pulp fibers underwent a degree of fibrillation that resulted in a stepwise increment of mechanical properties, most strikingly in bending strength, which increase was attributed to the complete fibrillation of the bulk of the fibers. For additional high pressure homogenization-treated pulps, composite strength increased linearly against water retention values, which characterize the cellulose’s exposed surface area, and reached maximum value at 14 passes through the homogenizer

Analysis of scale-free networks based on a threshold graph with intrinsic vertex weights

Many real networks are complex and have power-law vertex degree distribution, short diameter, and high clustering. We analyze the network model based on thresholding of the summed vertex weights, which belongs to the class of networks proposed by Caldarelli et al. (2002). Power-law degree distributions, particularly with the dynamically stable scaling exponent 2, realistic clustering, and short path lengths are produced for many types of weight distributions. Thresholding mechanisms can underlie a family of real complex networks that is characterized by cooperativeness and the baseline scaling exponent 2. It contrasts with the class of growth models with preferential attachment, which is marked by competitiveness and baseline scaling exponent 3.Comment: 5 figure

Measurements of Stellar Inclinations for Kepler Planet Candidates II: Candidate Spin-Orbit Misalignments in Single and Multiple-Transiting Systems

We present a test for spin-orbit alignment for the host stars of 25 candidate planetary systems detected by the {\it Kepler} spacecraft. The inclination angle of each star's rotation axis was estimated from its rotation period, rotational line broadening, and radius. The rotation periods were determined using the {\it Kepler} photometric time series. The rotational line broadening was determined from high-resolution optical spectra with Subaru/HDS. Those same spectra were used to determine the star's photospheric parameters (effective temperature, surface gravity, metallicity) which were then interpreted with stellar-evolutionary models to determine stellar radii. We combine the new sample with the 7 stars from our previous work on this subject, finding that the stars show a statistical tendency to have inclinations near 90$^\circ$, in alignment with the planetary orbits. Possible spin-orbit misalignments are seen in several systems, including three multiple-planet systems (KOI-304, 988, 2261). Ideally these systems should be scrutinized with complementary techniques---such as the Rossiter-McLaughlin effect, starspot-crossing anomalies or asteroseismology---but the measurements will be difficult owing to the relatively faint apparent magnitudes and small transit signals in these systems.Comment: 11 pages, 9 figures, accepted for publication in Ap

Cellulose nanofiber aerogel production and applications

Aerogels are highly porous solids formed by replacing the liquid in a gel by air, without changing the original structure. The present cellulose aerogels are made by sublimating the water from a colloidal suspension of cellulose nanofibers. The nanofibers form three-dimensional networks, crosslinked by hydrogen bonds bridging the surface hydroxyl groups and also by mechanical entanglements between nanofibers. Although the studies on aerogels from cellulose nanofiber hydrogels by freeze drying reported so far had produced small samples, improved cooling techniques that produces larger samples were attempted and the obtained cellulose nanofiber aerogels were impregnated with epoxy resin to fabricate composites. The highly porous structure allowed complete impregnation of resin and translucent composites were produced. The modulus of composites was increased in relation to neat epoxy, but due to high brittleness the ultimate strength was decreased. This is likely caused by nanofiber agglomerations of uneven pore sizes acting as stress concentrators. The evaluation of the mechanical properties of composites serves as an indirect way to assess the quality of the aerogels produced

Interference Effects on Kondo-Assisted Transport through Double Quantum Dots

We systematically investigate electron transport through double quantum dots with particular emphasis on interference induced via multiple paths of electron propagation. By means of the slave-boson mean-field approximation, we calculate the conductance, the local density of states, the transmission probability in the Kondo regime at zero temperature. It is clarified how the Kondo-assisted transport changes its properties when the system is continuously changed among the serial, parallel and T-shaped double dots. The obtained results for the conductance are explained in terms of the Kondo resonances influenced by interference effects. We also discuss the impacts due to the spin-polarization of ferromagnetic leads.Comment: 9 pages, 11 figures ; minor corrections and references adde

Finite-temperature Mott transitions in multi-orbital Hubbard model

We investigate the Mott transitions in the multi-orbital Hubbard model at half-filling by means of the self-energy functional approach. The phase diagrams are obtained at finite temperatures for the Hubbard model with up to four-fold degenerate bands. We discuss how the first-order Mott transition points $U_{c1}$ and $U_{c2}$ as well as the critical temperature $T_c$ depend on the orbital degeneracy. It is elucidated that enhanced orbital fluctuations play a key role to control the Mott transitions in the multi-orbital Hubbard model.Comment: 8 pages, 7 figure

Fabrication of Chitin Nanofiber-Reinforced PLA Nanocomposites by an Environmentally Friendly Process

Polylactic acid (PLA) reinforced with chitin nanofibers was produced from a mixture of a colloidal suspension of PLA particles with chitin nanofiber suspension. The dispersion medium was solely water, which was removed by filtration and drying. Nanocomposites were obtained by compression molding of the filtrates. Static tensile test and dynamic mechanical analysis were performed to evaluate the reinforcement as a function of nanofiber content. Chitin nanofibers delivered reinforcement similar to cellulose nanofibers, being especially effective at up to 70 wt% fiber load. The ultimate tensile modulus and strength reached 7.7 GPa and 110 MPa, respectively, at a nanofiber content of 70 wt%