Chitosan microfiber fabrication using microfluidic chips of different sheath channel angles and its application on cell culture

AbstractIn this study, we successfully produced the chitosan microfibers using the proposed various angles of microfluidic chip, which was also been simulated. By controlling the core and sheath flow rates, we were able to generate laminar flow of different diameters from 15 μm to 40 μm. And the diameter of chitosan microfiber was measured from 20 μm to 50 μm. The microchannel of angle 30° could produce chitosan laminar flow of a smaller diameter than the angle 60° and angle 45° at the fixed flow rates. Finally, the chitosan microfiber was chosen as scaffold and the schwann cell and fibroblast cell with chitosan microfibers were used for cell culture to test effect in tissue engineering application

Josephson Plasma in RuSr2GdCu2O8

Josephson plasma in RuSr$_{2}$GdCu$_{2}$O$_{8}$, Ru$_{1-x}$Sr$_{2}$GdCu$_{2+x}$O$_{8}$ (x = 0.3), and RuSr$_{2}$Eu$_{2-x}$Ce$_{x}$Cu$_{2}$O$_{10}$ (x = 0.5) compounds is investigated by the sphere resonance method. The Josephson plasma is observed in a low-frequency region (around 8.5 cm$^{-1}$ at T $\ll$ $T_{c}$) for ferromagnetic RuSr$_{2}$GdCu$_{2}$O$_{8}$, while it increases to 35 cm$^{-1}$ for non-ferromagnetic Ru$_{1-x}$Sr$_{2}$GdCu$_{2+x}$O$_{8}$ (x = 0.3), which represents a large reduction in the Josephson coupling at ferromagnetic RuO$_{2}$ block layers. The temperature dependence of the plasma does not shift to zero frequency ({\it i.e.} $j_{c}$ = 0) at low temperatures, indicating that there is no transition from the 0-phase to the $\pi$-phase in these compounds. The temperature dependence and the oscillator strength of the peak are different from those of other non-magnetic cuprates, and the origins of these anomalies are discussed.Comment: to appear in Phys. Rev.B Rapid Com

Suppression of the structural phase transition and lattice softening in slightly underdoped Ba(1-x)K(x)Fe2As2 with electronic phase separation

We present x-ray powder diffraction (XRPD) and neutron diffraction measurements on the slightly underdoped iron pnictide superconductor Ba(1-x)K(x)Fe2As2, Tc = 32K. Below the magnetic transition temperature Tm = 70K, both techniques show an additional broadening of the nuclear Bragg peaks, suggesting a weak structural phase transition. However, macroscopically the system does not break its tetragonal symmetry down to 15 K. Instead, XRPD patterns at low temperature reveal an increase of the anisotropic microstrain proportionally in all directions. We associate this effect with the electronic phase separation, previously observed in the same material, and with the effect of lattice softening below the magnetic phase transition. We employ density functional theory to evaluate the distribution of atomic positions in the presence of dopant atoms both in the normal and magnetic states, and to quantify the lattice softening, showing that it can account for a major part of the observed increase of the microstrain.Comment: 7 pages, 4 figure

Higgs algebraic symmetry of screened system in a spherical geometry

The orbits and the dynamical symmetries for the screened Coulomb potentials and isotropic harmonic oscillators have been studied by Wu and Zeng [Z. B. Wu and J. Y. Zeng, Phys. Rev. A 62,032509 (2000)]. We find the similar properties in the responding systems in a spherical space, whose dynamical symmetries are described by Higgs Algebra. There exists a conserved aphelion and perihelion vector, which, together with angular momentum, constitute the generators of the geometrical symmetry group at the aphelia and perihelia points $(\dot{r}=0)$.Comment: 8 pages, 1 fi

Micron-sized atom traps made from magneto-optical thin films

We have produced magnetic patterns suitable for trapping and manipulating neutral atoms on a $1 \mu$m length scale. The required patterns are made in Co/Pt thin films on a silicon substrate, using the heat from a focussed laser beam to induce controlled domain reversal. In this way we draw lines and "paint" shaped areas of reversed magnetization with sub-micron resolution. These structures produce magnetic microtraps above the surface that are suitable for holding rubidium atoms with trap frequencies as high as ~1 MHz.Comment: 6 pages, 7 figure

Real space renormalization group approach to the 2d antiferromagnetic Heisenberg model

The low energy behaviour of the 2d antiferromagnetic Heisenberg model is studied in the sector with total spins $S=0,1,2$ by means of a renormalization group procedure, which generates a recursion formula for the interaction matrix $\Delta_S^{(n+1)}$ of 4 neighbouring "$n$ clusters" of size $2^n\times 2^n$, $n=1,2,3,...$ from the corresponding quantities $\Delta_S^{(n)}$. Conservation of total spin $S$ is implemented explicitly and plays an important role. It is shown, how the ground state energies $E_S^{(n+1)}$, $S=0,1,2$ approach each other for increasing $n$, i.e. system size. The most relevant couplings in the interaction matrices are generated by the transitions $$ between the ground states $|S,m;n+1>$ ($m=-S,...,S$) on an $(n+1)$-cluster of size $2^{n+1}\times 2^{n+1}$, mediated by the staggered spin operator $S_q^*$Comment: 18 pages, 8 figures, RevTe

Enhanced Bound State Formation in Two Dimensions via Stripe-Like Hopping Anisotropies

We have investigated two-electron bound state formation in a square two-dimensional t-J-U model with hopping anisotropies for zero electron density; these anisotropies are introduced to mimic the hopping energies similar to those expected in stripe-like arrangements of holes and spins found in various transition metal oxides. In this report we provide analytical solutions to this problem, and thus demonstrate that bound-state formation occurs at a critical exchange coupling, J_c, that decreases to zero in the limit of extreme hopping anisotropy t_y/t_x -> 0. This result should be contrasted with J_c/t = 2 for either a one-dimensional chain, or a two-dimensional plane with isotropic hopping. Most importantly, this behaviour is found to be qualitatively similar to that of two electrons on the two-leg ladder problem in the limit of t_interchain/t_intrachain -> 0. Using the latter result as guidance, we have evaluated the pair correlation function, thus determining that the bound state corresponds to one electron moving along one chain, with the second electron moving along the opposite chain, similar to two electrons confined to move along parallel, neighbouring, metallic stripes. We emphasize that the above results are not restricted to the zero density limit - we have completed an exact diagonalization study of two holes in a 12 X 2 two-leg ladder described by the t-J model and have found that the above-mentioned lowering of the binding energy with hopping anisotropy persists near half filling.Comment: 6 pages, 3 eps figure

Inhomogeneously doped two-leg ladder systems

A chemical potential difference between the legs of a two-leg ladder is found to be harmful for Cooper pairing. The instability of superconductivity in such systems is analyzed by compairing results of various analytical and numerical methods. Within a strong coupling approach for the t-J model, supplemented by exact numerical diagonalization, hole binding is found unstable beyond a finite, critical chemical potential difference. The spinon-holon mean field theory for the t-J model shows a clear reduction of the the BCS gaps upon increasing the chemical potential difference leading to a breakdown of superconductivity. Based on a renormalization group approach and Abelian bosonization, the doping dependent phase diagram for the weakly interacting Hubbard model with different chemical potentials was determined.Comment: Revtex4, 11 pages, 7 figure

Topological effects at short antiferromagnetic Heisenberg chains

The manifestations of topological effects in finite antiferromagnetic Heisenberg chains is examined by density matrix renormalization group technique in this paper. We find that difference between integer and half-integer spin chains shows up in ground state energy per site when length of spin chain is longer than $\sim\xi$, where $\xi\sim\exp(\pi S)$ is a spin-spin correlation length, for spin magnitude S up to 5/2. For open chains with spin magnitudes $S=5/2$ to S=5, we verify that end states with fractional spin quantum numbers $S'$ exist and are visible even when the chain length is much smaller than the correlation length $\xi$. The end states manifest themselves in the structure of the low energy excitation spectrum.Comment: 4 pages, 6 figure

A glassy contribution to the heat capacity of hcp 4^4He solids

We model the low-temperature specific heat of solid $^4$He in the hexagonal closed packed structure by invoking two-level tunneling states in addition to the usual phonon contribution of a Debye crystal for temperatures far below the Debye temperature, $T < \Theta_D/50$. By introducing a cutoff energy in the two-level tunneling density of states, we can describe the excess specific heat observed in solid hcp $^4$He, as well as the low-temperature linear term in the specific heat. Agreement is found with recent measurements of the temperature behavior of both specific heat and pressure. These results suggest the presence of a very small fraction, at the parts-per-million (ppm) level, of two-level tunneling systems in solid $^4$He, irrespective of the existence of supersolidity.Comment: 11 pages, 4 figure