Spin Tube Research Articles

Heat Capacity Reveals the Physics of a Frustrated Spin Tube

We report on theoretical and experimental results concerning the low-temperature specific heat of the frustrated spin-tube material [(CuCl(2)tachH(3)Cl]Cl(2) (tach denotes 1,3,5-triaminocyclohexane). This substance turns out to be an unusually perfect spin-tube system which allows to study the physics of quasi-one-dimensional antiferromagnetic structures in rather general terms. An analysis of the specific-heat data demonstrates that at low enough temperatures the system exhibits a Tomonaga-Luttinger liquid behavior corresponding to an effective spin-3/2 antiferromagnetic Heisenberg chain with short-range exchange interactions. On the other hand, around 2 K the composite spin structure of the chain is revealed through a Schottky-type peak in the specific heat. We argue that the dominating contribution to the peak originates from gapped magnon-type excitations related to the internal degrees of freedom of the rung spins.

Optimization of cultivation conditions in spin tubes for Chinese hamster ovary cells producing erythropoietin and the comparison of glycosylation patterns in different cultivation vessels

This article describes the optimization of cultivation factor settings, that is the shaking rate and working volume in 50 mL spin tubes for a Chinese hamster ovary cell line expressing recombinant human alpha-erythropoietin, using a response D-optimal surface method. The main objectives of the research were, firstly, to determine a setting in which the product titer and product quality attributes in spin tubes are equivalent to those in 250 mL shake flasks in a seven day batch and, secondly, to find a setting in which the product titer is maximal. The model for product titer prediction as a function of shaking rate and working volume in the defined design space was successfully applied to the optimization of cultivation conditions in spin tubes for the tested cell line. Subsequently, validation experiments were carried out simultaneously in spin tubes, shake flasks and bench scale bioreactors to compare cell culture performance parameters such as growth, productivity and product quality attributes in the form of isoform profiles and glycan antennarity structures. The results of the experiments showed that similar cell culture performance and product quality could be achieved in spin tubes when compared to shake flasks. Additionally, bioreactor titers could be reproduced in spin tubes at high shaking rates and low working volumes, but with differing product quality. Cultivation at lower shaking rates in spin tubes and shake flasks produced a glycoprotein with a product quality slightly comparable to that from bioreactors, but with titers being only two thirds.

Weak D prevalence among Indian blood donors

Weak D prevalence among Indian blood donors

Field Induced Exotic Phenomena of the S=1/2 Three-Leg Quantum Spin Nanotube

The magnetization process of the S=1/2 three-leg spin tube with an asymmetric exchange interaction in each triangle unit is investigated by the numerical exact diagonalization and the density matrix renormalization group calculation. It is found that the 1/3 magnetization plateau appears due to two different mechanisms depending on the asymmetry. The phase diagrams of the 1/3 plateau is presented. In addition some cusp-like anomalies are found in the magnetization curve.

Application of ductile fracture criteria in spin-forming and tube-bending processes

Abstract As one of the principal failures that occur in metal spin-forming and tube-bending processes, ductile fracturing restricts the process of metal forming. It is difficult to predict the rupture and forming limit for the complex processes of spin forming and tube bending. Thus, in this paper we aim to choose reasonable ductile fracture criteria to accurately predict the time, position and distribution of the damage that occurs in these processes. By embedding the Lemaitre and Cockcroft–Latham (C&L) criteria into VUMAT (user material subroutine of the ABAQUS/explicit finite element method (FEM) code), finite element models are built and validated for predicting rupture failure and forming limit in the shear spin-forming, splitting spin-forming and tube-bending processes. The results show that the Lemaitre criterion is better than the C&L criterion at accurately predicting the position at which damage will occur and its distribution for both spin forming and tube bending. The maximum feed ratio varies within a small range with the splitting angle of the roller. There is an obvious difference between the distribution, variation and level of the damage that can occur for a normal bending radius without rupturing, and that for a very small bending radius, where there is a greater risk of rupturing. For tube bending using a very small bending radius and without a mandrel in the tube, the pressure die velocity increases, so the flattening of the bending area increases to some extent, which makes it opposite of normal tube bending.

Spin-Liquid State Study of Equilateral Triangle S=3/2 Spin Tubes Formed in CsCrF4

Topological effects on spin frustration in equilateral triangle S =3/2 spin tubes formed in CsCrF 4 were studied by magnetic susceptibility, heat capacity [ C ( T )], and electron spin resonance experiments. The experimental data show that there is no magnetic long-range order down to T =1.3 K, and that no spin gap due to a chiral spin structure appears. Furthermore, since the C ( T ) curve has a T -linear component, a gapless spin-liquid ground state in one-dimensional antiferromagnets, the so-called Tomonaga–Luttinger liquid, is realized. This is characteristic of equilateral triangle spin tubes with S = half-integer.

QUANTUM PHASE TRANSITION OF A TRIANGULAR LATTICE SPIN TUBE AND EDGE SPIN EFFECTS

We study the low-energy excitation of the quantum spin tube with the triangular lattice structure, using density matrix renormalization group. Taking account of the edge spin effect, we particularly investigate the spin gap behavior and the low-field magnetization curve near the quantum phase transition point in contrast with the usual free boundary condition. We then find that the bulk behavior of the spin tube can be extracted easier for the single spin termination.

NMR studies of a twisted quantum spin tube [(CuCl2tachH)3Cl]Cl2

Static properties of Cu2+(3d9; S=1/2) spins in a new class of quantum spin system, a twisted Heisenberg triangular spin tube, [(CuCl2tachH)3Cl]Cl2, have been investigated by using nuclear magnetic resonance (NMR) in a temperature region of T=0.05–300 K. An observation of magnetic broadenings of 1H-NMR spectrum at low temperatures directly revealed a gapless ground state of the system.

Structural and magnetic aspects of the nanotube systemNa2−xV3O7

We present experimental results of low-temperature x-ray synchrotron diffraction, neutron-scattering, and very low-temperature (mK range) bulk measurements on the nanotube system ${\text{Na}}_{2}{\text{V}}_{3}{\text{O}}_{7}$. The crystal structure determined from our data is similar to the previously proposed model [P. Millet et al., J. Solid State Chem. 147, 676 (1999)], but also deviates from it in significant details. The structure comprises of nanotubes along the $c$ axis formed by stacking units of two V rings buckled in the $ab$ plane. The space group is $P\overline{3}$ and the composition is nonstoichiometric, ${\text{Na}}_{2\ensuremath{-}x}{\text{V}}_{3}{\text{O}}_{7}$, $x=0.17$. The thermal evolution of the lattice parameters reveals anisotropic lattice compression on cooling. Neutron-scattering experiments monitor a very weak magnetic signal at energies from $\ensuremath{-}20$ to 9 meV. Magnetic susceptibility, specific-heat measurements, and decay of remanent magnetization in the 30--300 mK range reveal that the previously observed transition at $\ensuremath{\approx}76\text{ }\text{mK}$ is spin-glass like with no long-range order. Presented experimental observations do not support models of isolated clusters but are compatible with a model of odd-legged $S=1/2$ spin tubes possibly segmented into fragments with different lengths.

Quantum phase transitions of the asymmetric three-leg spin tube

We investigate quantum phase transitions of the $S=\frac{1}{2}$ three-leg antiferromagnetic spin tube with asymmetric interchain (rung) exchange interactions. On the basis of the electron tube system, we propose a useful effective theory to give the global phase diagram of the asymmetric spin tube. In addition, using other effective theories we raise the reliability of the phase diagram. The density-matrix renormalization-group and the numerical diagonalization analyses show that the finite spin gap appears in a narrow region around the rung-symmetric line, in contrast to a recent paper by Nishimoto and Arikawa, [Phys. Rev. B 78, 054421 (2008)]. The numerical calculations indicate that this global phase diagram obtained by use of the effective theories is qualitatively correct. In the gapless phase on the phase diagram, the numerical data are fitted by a finite-size scaling in the $c=1$ conformal field theory. We argue that all the phase transitions between the gapful and gapless phases belong to the Berezinskii-Kosterlitz-Thouless universality class.

Gel spinning of silk tubes for tissue engineering

Tubular vessels for tissue engineering are typically fabricated using a molding, dipping, or electrospinning technique. While these techniques provide some control over inner and outer diameters of the tube, they lack the ability to align the polymers or fibers of interest throughout the tube. This is an important aspect of biomaterial composite structure and function for mechanical and biological impact of tissue outcomes. We present a novel aqueous process system to spin tubes from biopolymers and proteins such as silk fibroin. Using silk as an example, this method of winding an aqueous solution around a reciprocating rotating mandrel offers substantial improvement in the control of the tube properties, specifically with regard to winding pattern, tube porosity, and composite features. Silk tube properties are further controlled via different post-spinning processing mechanisms such as methanol treatment, air-drying, and lyophilization. This approach to tubular scaffold manufacture offers numerous tissue engineering applications such as complex composite biomaterial matrices, blood vessel grafts and nerve guides, among others.

Low-lying excitations of the three-leg spin tube: A density-matrix renormalization group study

Using the (dynamical) density-matrix renormalization group method, we study the low-energy physics of three-leg antiferromagnetic Heisenberg model where the periodic boundary conditions are applied in the rung direction. We confirm that the spin excitations are always gapped as long as the intraring couplings form a regular triangle. From precise finite-size-scaling analyses of the spin gap and dimerization order parameter, we also find that the spin gap is collapsed by very small asymmetric modulation of the intraring couplings. Moreover, the dynamical spin structure factors on the intraleg and interleg correlations are calculated. It is demonstrated that the low-lying structure of the interleg spectra is particularly affected by the asymmetric modulation.

Comparative study of blood cross matching using conventional tube and gel method

Background: Conventionally tube method is used for compatibility and cross matching in transfusion medicine. Methods: A comparative study was carried out to evaluate the efficacy of conventional tube and gel technique. Result: Compatibility testing was performed on 1000 blood samples by conventional test tube method and DiaMed gel method. The results were analysed. Conclusion: The gel method was found to be a rapid and reliable procedure without controls. There was no requirement of wash phase in indirect antiglobulin test and sensitivity and specificity was comparable to spin tube method. We conclude that this technique is a better substitute for spin tube method.

Coexistence of vector chiral order and Tomonaga-Luttinger liquid in the frustrated three-leg spin tube in a magnetic field

The frustrated three-leg antiferromagnetic spin-$\frac{1}{2}$ tube with a weak interchain coupling in a magnetic field is investigated by means of Abelian bosonization techniques. It is clearly shown that a vector chiral long-range order and a one-component Tomonaga-Luttinger liquid coexist in a wide magnetic-field region from a state with a small magnetization to a nearly saturated one. The chiral order is predicted to still survive in the intermediate plateau state. We further predict that (even) when the strength of one bond in the three rung couplings is decreased (increased), an Ising-type quantum phase transition takes place and the chirality vanishes (no singular phenomena occur and the chiral order is maintained). Even without magnetic fields, the chiral order would also be present if the spin tube possesses easy-plane anisotropy.

Specific Cation Effects at the Hydroxide-Charged Air/Water Interface

The zeta potentials of individual gas bubbles in water have been measured with a spinning tube zetameter as a function of added electrolyte concentrations. The bubbles have a negative charge at pH >3 due to the preferential adsorption of hydroxide ions. Addition of alkali halide electrolytes from 10-5 to 10-2 M reduces the zeta potential due to double layer compression. The effect is independent of the anion among the sodium chloride, bromide and iodide salts, indicating that these do not compete with hydroxide ion at the surface. Lithium chloride is more effective than cesium chloride at reducing the zeta potential, indicating that electrostatic effects are more important than dispersion forces at these low ionic strengths.

Vector chirality and inhomogeneous magnetization in frustrated spin tubes in high magnetic fields

The low-energy physics of three-leg frustrated antiferromagnetic spin-S tubes in the vicinity of the upper critical field are studied. Utilizing the effective field theory based on the spin-wave approximation, we argue that in the intermediate-interchain-coupling regime, the ground state exhibits a vector chiral order or an inhomogeneous magnetization for the interchain (rung) direction and the low-energy excitations are described by a one-component Tomonaga-Luttinger liquid (TLL). In both chiral and inhomogeneous phases, the Z_2 parity symmetry along the rung direction is spontaneously broken. It is also predicted that a two-component TLL appears and all the symmetries are restored in the strong-rung-coupling case.

Streptococcus pneumoniae Sheds Syndecan-1 Ectodomains through ZmpC, a Metalloproteinase Virulence Factor

Several microbial pathogens stimulate the ectodomain shedding of host cell surface proteins to promote their pathogenesis. We reported previously that Pseudomonas aeruginosa and Staphylococcus aureus activate the ectodomain shedding of syndecan-1 and that syndecan-1 shedding promotes P. aeruginosa pathogenesis in mouse models of lung and burned skin infections. However, it remains to be determined whether activation of syndecan-1 shedding is a virulence mechanism broadly used by pathogens. Here we show that Streptococcus pneumoniae stimulates syndecan-1 shedding in cell culture-based assays. S. pneumoniae-induced syndecan-1 shedding was repressed by peptide hydroxamate inhibitors of metalloproteinases but not by inhibitors of intracellular signaling pathways previously found to be essential for syndecan-1 shedding caused by P. aeruginosa, S. aureus, or other shedding agonists. A 170-kDa protein fraction with a peptide hydroxamate-sensitive shedding activity was purified by ammonium sulfate precipitation, DEAE chromatography, and size exclusion chromatography. Mass spectrometry analyses revealed that the 170-kDa fraction is composed of ZmpB and ZmpC, two metalloproteinase virulence factors of S. pneumoniae. Both the purified 170-kDa ZmpB/ZmpC fraction and unfractionated S. pneumoniae culture supernatant generated syndecan-1 ectodomains that are smaller than those released by endogenous shedding. Further, a mutant S. pneumoniae strain deficient in zmpC, but not zmpB, lost its capacity to stimulate syndecan-1 shedding. These data demonstrate that S. pneumoniae directly sheds syndecan-1 ectodomains through the action of ZmpC.

Frustration-induced exotic properties of magnetic molecules

Geometric frustration of interacting spin systems is the driving force of a variety of fascinating phenomena in low-dimensional magnetism. In this contribution, I will review recent results on frustration-induced effects in magnetic molecules, i.e. zero-dimensional magnetic systems, as well as in a recently synthesized frustrated molecule-based spin tube, i.e. a one-dimensional spin system.

Consecutive solvent evaporation and co-rolling techniques for polymer multilayer hollow fiber preform fabrication

All-polymer multilayer hollow core photonic fiber preforms were fabricated using consecutive deposition from a solvent phase of two polymers with high and low refractive indices (RI). Processing techniques for two polymer pairs—polystyrene (PS)/poly(methyl methylacrylate) (PMMA) and polycarbonate (PC)/poly(vinylene difloride) (PVDF)—were established. The fabrication process involved consecutive film deposition by solvent evaporation of polymer solutions on the inside of a rotating PMMA or PC tube, used as a cladding material. By injecting right volumes of the polymer solutions into a spinning tube the thickness of each layer could be reliably controlled from 20 to 100 μm. Proper selection of solvents and processing conditions was crucial for ensuring high optical and mechanical quality of a resultant preform, as well as compatibility of different polymer films during co-deposition. Preforms of 10 layers for PMMA/PS material combination and 15 layers for PVDF/PC were demonstrated. Fabrication of preforms with higher number of layers is readily possible and is only a question of preform fabrication time. An alternative method of preform fabrication by co-rolling of polymer bilayers is also presented in this paper, drawing of PMMA/PS, PVDF/PC fibers with up to 32 layers is demonstrated.

Accelerated on‐column lysine derivatization and cysteine methylation by imidazole reaction in a deuterated environment for enhanced product ion analysis

The combination of separation techniques and mass spectrometry (MS) for peptide investigation allows superior sensitivity of detection and richer fragmentation data than available by direct MS analysis of a complex mixture. In this regard, liquid chromatography (LC) coupled to electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) MS have evolved as versatile analytical tools in proteomics. Very often, however, the product ion mass spectrum is either incomplete or overfilled with ions, thus making sequence analysis difficult. Here we report overall ion intensity improvement of C-terminal lysine-containing peptides from Lys-C digest by on-column derivatization of lysines with 2-methoxy-4,5-dihydro-1H-imidazole. The method is simple, fast and exhibits 100% efficiency of the reaction. Additionally, post-source decay carried out on derivatized peptides gave rise almost exclusively to y-series ion formation, at 100% sequence coverage and high intensity. The novelty of the method resides in the side reaction of this derivatization process, namely the methylation of cysteines. This facilitates the estimation of the disulfide bridge position in a protein and the fragmentation of cysteine-containing peptide fragments. Additionally, by using this derivatization procedure, the loss of peptides, their degradation and/or oxidation, usually occurring in digest alkylation procedures, is greatly minimized. The new on-column derivatization protocol is designed to be carried out on C18 Spin Tubes or Cleanup C18 Pipette Tips. We observed that use of buffered D2O solvent prevented unwanted oxidation and degradation reactions with respect to the stationary phase. This may be due to the fact that a deuteron is less polar than a proton, and thus the bonded silica stationary phase saturated with deuterons does not affect the reaction between epsilon-amino or cysteine thiol groups and 2-methoxy-4,5-dihydro-1H-imidazole. Complete tagging of the peptides by on-column reaction could be obtained when using D2O, as compared to water-based reaction. Methylation of cysteine residues was enhanced when beta-mercaptoethanol was added in the reactant solution.