Andreev reflection in graphene nanoribbons induced byd-wave superconductors.

Honeycomb and square lattices are combined as a tight-binding model to examine the Andreev reflection in graphene nanoribbons induced by a superconductor. The superconducting symmetry is assumed to be thed-wave. The zero-bias tunneling conductance peak, which is generally produced by thed-wave superconductor, is absent for the nanoribbons under conditions similar to those when a quantum wire is the normal conductor. For the anisotropic superconductivity, propagating modes appear in the superconductor even for biases below the top of the superconducting energy gap. Features appear in the conductance at the subgap population thresholds of these propagating modes as a finite-size effect of the lattice system. The surface Andreev bound states responsible for the zero-bias anomaly also cause transport resonances in the vicinity of the zero bias despite the aforementioned destruction of the anomaly. The conductance spectra revealing these excitation behaviors are fairly unchanged regardless of the presence of a hopping barrier at the interface with the superconductor. The insensitivity to the interface scattering highlights the fact that barrier-less situation cannot be realized for the model due to the heterogeneous lattice. Concerning specular Andreev reflection, the wavefunction parity gives rise to its blocking for single-mode zigzag-edged nanoribbons. The blocking is suppressed when the anisotropic superconductivity is asymmetric for the nanoribbons.

Role of symmetry in quantum blocking of Andreev reflection in graphene nanoribbons side-terminated by superconductors.

Andreev reflection can be forbidden by means of quantum interference when superconductors are attached at the side edges of graphene nanoribbons (GNRs). The blocking is restricted to single-mode nanoribbons having symmetric zigzag edges and is destroyed by the application of a magnetic field. These characteristics are shown to be the effects of the wavefunction parity on the Andreev retro and specular reflections. Not only the mirror symmetry of the GNRs but also symmetric coupling of the superconductors is required for the quantum blocking. The quasi-flat-band states around the Dirac point energy induced for armchair nanoribbons by adding carbon atoms at the nanoribbon edges do not cause the quantum blocking due to the lack of the mirror symmetry. Furthermore, the phase modulation by the superconductors is shown to be able to convert the quasi-flat dispersion for the edge states of zigzag nanoribbons to a quasi-vertical dispersion.

Magnetotransport in graphene nanoribbons sandwiched by superconductors at side edges.

Magnetotransport properties of the graphene nanoribbons (GNR) that are in contact with superconductors at side edges are investigated numerically with respect to oscillations caused by the cyclotron motion. In terms of the modelling, the superconductors are incorporated as superconducting GNRs to make the Andreev reflection at the graphene-superconductor interface almost perfect. The classical commensurability oscillation appears at low magnetic fields where the cyclotron radius is larger than the width of the nanoribbons. A transition to the circumstance dominated by the quantum interference between Andreev- and normal-reflected components takes place when the Andreev reflection probability is reduced by introducing a barrier at the interface. The near perfection of the Andreev reflection enlarges the period of the oscillation associated with skipping orbits a few orders of magnitude in the quantum limit. Chaotic fluctuations emerge furthermore in the regime of Hofstadter's butterfly. The periodicity of a transmission modulation at the onset of the chaos is revealed to change continuously over eight orders of magnitude of the magnetic-field variation. The commensurability and edge-state oscillations are examined additionally for the situations with specular Andreev reflection.

Quantum magnetotransport oscillations in graphene nanoribbons coupled to superconductors.

Magnetotransport properties of zigzag and armchair graphene nanoribbons that are in contact with superconductors are investigated using a tight-binding model. The cyclotron orbital motion together with the quantum interference under the coexistence of Andreev and normal reflections gives rise to a number of oscillations in characteristic magnetic-field regimes when the superconducting coupling is weak. The oscillations become irregular and/or suppressed as the coupling is made strong. The period of the oscillations differs from that when a nonrelativistic two-dimensional electron gas is employed rather than the graphene sheet. The modifications of the oscillations are attributed to the phase shift associated with the reflection from the graphene-superconductor interface. The presence of a magnetic field suppresses the quantum blocking of Andreev transmission, which occurs for the edge mode of zigzag nanoribbons, in the same way regardless of it being induced by the Andreev retro- or specular reflection.

Commensurability and quantum interference magnetotransport oscillations in a two-dimensional electron gas sandwiched by superconductors.

Magnetic-field dependence of the transport properties of ballistic two-dimensional electrons in a planar superconductor-normal-conductor-superconductor structure is numerically investigated. In the circumstance where the Andreev reflection from the normal-conductor-superconductor interfaces is almost perfect, two oscillatory behaviors occur for magnetic fields higher and lower than that for the coincidence of the cyclotron diameter with the separation between the superconductors. The oscillation period for the former and latter cases is proportional to the magnetic field and inverse of the magnetic field, respectively. The low-field oscillation originates from commensurability-driven guiding of Andreev-reflected trajectories along the interfaces between the normal conductor and the superconductors. If the Andreev reflection probability is considerably less than unity, the commensurability oscillation is suppressed in amplitude and is dwarfed by additionally emerged oscillations originating from the quantum interference between the Andreev- and normal-reflected components.

Klein tunneling of helical edge states in narrow strips of a two-dimensional topological insulator.

The quantum transmission of helical edge states across a square potential barrier is numerically investigated in narrow channels of a two-dimensional topological insulator. Although the transmission probability in general decreases when a potential offset is introduced in the middle of the channels, the transmission remains almost perfect regardless of the amplitude and length of the potential offset when the hybridization energy gap is closed by tuning the off-diagonal spin-orbit terms in the effective four-band Hamiltonian. The approximate absence of scattering resembling the Klein tunneling, where the transmission is unimpeded as an electron propagates relativistically as a hole in the barrier without decay, improves further when an interference condition is satisfied within the barrier. The dependence of the residual reflection on the Fermi level reveals anomalous characteristics in the Klein tunneling regime.

Alendronate does not prevent long bone fragility in an inactive rat model.

The lack of estrogen and inactivity are both important in the pathogenesis of osteoporosis in elderly women, and there have been no appropriate rodent studies to examine the effects of common bisphosphonates on these two components separately. We compared the efficacy of alendronate (ALN) on the long bones of aged female rats, which were sedentary, estrogen deficient, or both. The rats were either forced to remain in a sitting position or allowed to walk in standard cages with or without ALN administration. The 8-week experimental period began 5 weeks after ovariectomy or sham surgery. Parameters of the hindlimb bones were determined by a three-point bending test, peripheral quantitative computed tomography, microfocus computed tomography, confocal laser Raman microspectroscopy, and dynamic histomorphometry. Regardless of ovariectomy, ALN was ineffective against the deterioration of breaking stress caused by sitting even though the trabecular bone mineral density was significantly higher in the sitting-ALN groups. Toughness was significantly deficient in the ovariectomy sitting-ALN group. This was in agreement with the bone geometry with a greater marrow space. Sitting also increased the mineral-to-matrix ratio and the carbonate-to-phosphate ratio, both indicative of aged bone. A greater loss of proteinaceous amide intensity compared with mineral intensity resulted in an increased mineral-to-matrix ratio in the presence of ALN. Sitting resulted in deficits in the quality and the geometry of cortical bone, resulting in fragility. The use of bisphosphonates, such as ALN, may provide a therapy best suited for osteoporotic individuals whose daily activity is not limited.

Multiple state transport deduced by weak antilocalization and electron-electron interaction effects in Sb(x)Te(1-x) layers.

Quantum corrections to the conductivity due to the weak antilocalization (WAL) and electron-electron interaction (EEI) effects are investigated in Sb-Te layers to evaluate the number of independent conduction channels in the topological insulator system. We separate the two contributions in the logarithmic temperature dependence of conductivity relying on their distinct response to a magnetic field. For the WAL effect, the amplitude parameter α being -1 observed in magnetoconductivity is confirmed. The magnitude of the EEI contribution is too large to be produced by one transport channel. The mixing between the surface and bulk states is thus indicated to be weak in the Sb-Te system. In addition, the disorder scattering appears to be less influential for the EEI effect than for the WAL effect.

Transport properties in a Sb-Te binary topological-insulator system.

Sb-Te layers having various compositions between Sb2Te3 and Sb2Te are grown using molecular beam epitaxy. The structural and electrical properties of the layers change gradually with composition but exhibit a discontinuity involving a bistability. The holes in the layers are generated by Sb bilayers intercalated between Sb2Te3 quintuple layers and their mobility is governed by the scattering from the parent acceptors. Magnetoresistance for compositions around SbTe is linear, for which the reduction of the parabolic component due to low mobility is crucial. Density functional calculations predict Sb2Te3 and SbTe to be topological insulators (TIs) resembling Bi2Se3 and Bi2Te3, respectively. The prefactor of the weak antilocalization effect is α =- 1 regardless of the composition. The Sb-Te system is thus a family of TIs possessing undisturbed surface states for which the location of the Dirac point with respect to the bulk band gap is adjustable.

Backscattering from width variations in quasi-one-dimensional strips of topological insulators.

Conductance modulations in wide-narrow-wide electron waveguides constructed from a two-dimensional topological insulator are investigated numerically. The conductance exhibits the Fabry-Perot oscillation at the opening of the helical edge states in the narrow segment when the potential offset imposed in the segment is varied. The quantum multiple reflections between the two ends of the narrow segment manifested by the oscillation demonstrate that the topological states are not protected from the scattering caused by an abrupt change in the channel width. The bulk states do not affect the vulnerability against the geometry scattering but they give rise to resonant transmission in an unconventional fashion.

Mechanotransduction activates α5ß1 integrin and PI3K/Akt signaling pathways in mandibular osteoblasts.

It is unclear how bone cells at different sites detect mechanical loading and how site-specific mechanotransduction affects bone homeostasis. To differentiate the anabolic mechanical responses of mandibular cells from those of calvarial and long bone cells, we isolated osteoblasts from C57B6J mouse bones, cultured them for 1week, and subjected them to therapeutic low intensity pulsed ultrasound (LIPUS). While the expression of the marker proteins of osteoblasts and osteocytes such as alkaline phosphatase and FGF23, as well as Wnt1 and ß-catenin, was equally upregulated, the expression of mandibular osteoblast messages related to bone remodeling and apoptosis differed from that of messages of other osteoblasts, in that the messages encoding the pro-remodeling protein RANKL and the anti-apoptotic protein Bcl-2 were markedly upregulated from the very low baseline levels. Blockage of the PI3K and α(5)ß(1) integrin pathways showed that the mandibular osteoblast required mechanotransduction downstream of α(5)ß(1) integrin to upregulate expression of the proteins ß-catenin, p-Akt, Bcl-2, and RANKL. Mandibular osteoblasts thus must be mechanically loaded to preserve their capability to promote remodeling and to insure osteoblast survival, both of which maintain intact mandibular bone tissue. In contrast, calvarial Bcl-2 is fully expressed, together with ILK and phosphorylated mTOR, in the absence of LIPUS. The antibody blocking α(5)ß(1) integrin suppressed both the baseline expression of all calvarial proteins examined and the LIPUS-induced expression of all mandibular proteins examined. These findings indicate that the cellular environment, in addition to the tridermic origin, determines site-specific bone homeostasis through the remodeling and survival of osteoblastic cells. Differentiated cells of the osteoblastic lineage at different sites transmit signals through transmembrane integrins such as α(5)ß(1) integrin in mandibular osteoblasts, whose signaling may play a major role in controlling bone homeostasis.

Swingback in magnetization reversal in MnAs-GaAs coaxial nanowire heterostructures.

The reversal processes of magnetization in epitaxial MnAs nanotubes prepared by an overgrowth on the sidewall of GaAs nanowires having a diameter of 26 nm are investigated. While the magnetic hard axis is aligned in the direction of the nanowire axis, we apply an external magnetic field perpendicular to the axis to examine the flipping characteristics of magnetic moments. We determine the contributions from the substrate by a direct measurement in order to extract the magnetization of the core-shell heterostructures. The abrupt change in the thus-obtained magnetization due to a flip when the field is varied exhibits an overshoot at about 0.4 kOe for samples with a thickness of the ferromagnetic shell (40-50 nm) larger than the diameter of the core. Moreover, the peak value exceeds the value when the field is swept in the opposite direction. The magnetic hysteresis loop consequently involves line crossings. We speculate that the spin textures of domain walls in such thick hollow cylinders and their movement at the magnetization flip are affected by the geometry and magnetostatic interactions of various origins, giving rise to the anomalous behaviour.

Prior treatment with vitamin K(2) significantly improves the efficacy of risedronate.

UNLABELLED: Prior 8-week treatment with menatetrenone, MK-4, followed by 8-week risedronate prevented the shortcomings of individual drugs and significantly increased the strength of ovariectomized ICR mouse femur compared to the ovariectomized (OVX) controls. Neither MK-4 following risedronate nor the concomitant administration may be recommended because they brought the least beneficial effect. INTRODUCTION: The objective of this study was to determine the best combinatory administration of risedronate at 0.25 mg/kg/day (R) with vitamin K(2) at approximately 100 microg MK-4/kg/day (K) to improve strength of osteoporotic mouse bone. METHODS: Thirteen-week-old ICR mice, ovariectomized at 9-week, were treated for 8 weeks with R, K, or R plus K (R/K), and then, either the treatment was withdrawn (WO) or switched to K or R in the case of R and K. After another 8 weeks, the mice were killed, and mechanical tests and analyses of femur properties by peripheral quantitative computed tomography, microfocus X-ray tube computed tomography, and confocal laser Raman microspectroscopy were carried out. RESULTS: The K to R femur turned out superior in parameters tested such as material properties, bone mineral density, BMC, trabecular structure, and geometry of the cortex. The increased cross-sectional moment of inertia, which occurred after K withdrawal, was prevented by risedronate in K to R. In addition to K to R, some properties of R to WO diaphysis and K to WO epiphysis were significantly better than OVX controls. CONCLUSION: Prior treatment with MK-4 followed by risedronate significantly increased femur strength in comparison to the OVX controls.

Low-intensity pulsed ultrasound accelerates periodontal wound healing after flap surgery.

BACKGROUND AND OBJECTIVE: A study was conducted to evaluate the effects of low-intensity pulsed ultrasound on wound healing in periodontal tissues after mucoperiosteal flap surgery. MATERIAL AND METHODS: Bony defects were surgically produced bilaterally at the mesial roots of the mandibular fourth premolars in four beagle dogs. The flaps were repositioned to cover the defects and sutured after scaling and planing of the root surface to remove cementum. The affected area in the experimental group was exposed to low-intensity pulsed ultrasound, daily for 20 min, for a period of 4 wk from postoperative day 1 using a probe, 13 mm in diameter. On the control side, no ultrasound was emitted from the probe placed contralaterally. After the experiment, tissue samples were dissected out and fixed in 10% formalin for histological and immunohistochemical analyses. RESULTS: The experimental group showed that the processes in regeneration of both cementum and mandibular bone were accelerated by low-intensity pulsed ultrasound compared with the control group. In addition, the expression level of heat shock protein 70 was higher in the gingival epithelial cells of the low-intensity pulsed ultrasound-treated tooth. CONCLUSION: Our results suggest that osteoblasts, as well as cells in periodontal ligament and gingival epithelium, respond to mechanical stress loaded by low-intensity pulsed ultrasound, and that ultrasound accelerates periodontal wound healing and bone repair.

Characterization of new monoclonal antibodies against porcine lymphocytes: molecular characterization of clone 7G3, an antibody reactive with the constant region of the T-cell receptor delta-chains.

A battery of mouse monoclonal antibodies (mAbs) reactive with porcine peripheral blood (PB) leukocytes was generated. Among the mAbs, 6F10 was found to react probably with cluster of differentiation (CD)8 alpha-chain, while 7G3 and 3E12 were found to recognize gammadelta T-cells, as revealed by two-color flow cytometric and immunoprecipitation studies. 7G3 was shown to react with the constant (C) region of the T-cell receptor (TCR) delta-chain by the following facts: (1) 7G3 immunoprecipitated full-length TCR delta-chain protein fused with glutathione S-transferase (GST) produced by Esherichia coli and (2) 7G3 reacted with TCR delta-chain expressing Cos-7 cells transfected with either full-length or N-terminal deleted mutant cDNA, but did not react with Cos-7 cells transfected with C-terminal deleted mutant TCR delta-chain cDNA. All three mAbs produced high-quality immunostaining results on frozen sections, revealing a distinct distribution of gammadelta T-cells and CD8(+) cells. This report precisely characterizes mAbs against porcine TCR for the first time, facilitating molecular biological investigations of the porcine immune system.

The role of calcium channels in osteocyte function.

Osteocytic response to stretching, which is potentiated by PTH, is distinct from that of osteoblast to high frequency strain. A MAPK dependent signaling pathway is suggested in the osteoblast response. At least two different types of mechanotransduction pathways are present in bone cells of osteoblastic lineage.

Matrix metalloproteinase-2 in dentin matrix mineralization.

In the serum-free culture medium of bovine odontoblasts we detected active gelatinolytic metalloproteinases, matrix metalloproteinase (MMP)-2 and MMP-9 (gelatinases A and B). The activity of MMP-2, in particular, appeared suddenly around day 21 in the culture, coinciding with the development of odontoblastic cell processes and the loss of alkaline phosphatase. Reverse transcriptase-polymerase chain reaction analysis of these odontoblasts demonstrated that messages of MMP-2 but not MMP-9 increased significantly between day 15 and day 21. The in vitro observation indicates that medium conditioned by these odontoblasts and containing significant amounts of MMP-2 degrades not only the collagenous substrates but also purified dentin phosphophoryn as well. We have also observed that dephosphorylated dentin phosphoprotein becomes a better substrate for casein kinase II after limited proteolysis with MMP-2. These results support our working hypothesis that MMP-2-mediated proteolytic processing is an important step in accelerating the process of dentin matrix maturation, which includes phosphorylation and subsequent mineralization. As has been suggested previously, extracellular phosphorylation of matrix proteins is an important step in biomineralization both in bone and in dentin (Mikuni-Takagaki et al., J Bone Miner Res 1995;10:231-42; Zhu et al., Biochem J 1997; 323:637-43). Our present histochemical analysis in MMP-2 knockout mice confirms the concept with the delayed formation of mineralized tissues, dentin, and bone.

Assignment of T cell receptor (TCR) alpha-chain gene (A), beta-chain gene (B), gamma-chain gene (G), and delta-chain gene (D) loci on swine chromosomes by in situ hybridization and radiation hybrid mapping.

Using the cDNA sequence of porcine T-cell receptor (TCR) alpha-, beta-, gamma-, and delta-chain genes, we screened a porcine BAC library to isolate clones containing these genes. The isolated BAC clones were confirmed to carry these TCR genes by partial nucleotide sequencing. Among the clones obtained in the present screening, two clones carried both the TCR alpha-chain gene (TRA) and the TCR delta-chain gene (TRD) while one clone each carried only the sequence of either TRA or TRD. This observation demonstrated that TRA and TRD are localized in close proximity on a swine chromosome. Also two clones contained the sequence of the TCR beta-chain gene (TRB), and two clones contained the sequence of TCR gamma-chain gene (TRG). Fluorescence in situ hybridization using the above BAC clones as probes revealed that TRA and TRD, TRB, and TRG loci reside on swine chromosomes 7q15.3-->q21, 18q11.3-->q12, and 9q21-->q22, respectively. The chromosome positions of TRA and TRB are consistent with those determined by somatic cell hybrid analysis (Rettenberger et al., 1996). In addition, RH mapping of these genes was performed using the INRA-University of Minnesota RH panel DNA. The result confirmed the position of TRA and TRB reported earlier (http://imprh.toulouse.inra.fr/), and further demonstrated that TRG was located 11 cR away from genetic marker SW989 toward the marker S0019.

A peptide fragment of beta cardiac myosin heavy chain (beta-CMHC) can provoke autoimmune myocarditis as well as the corresponding alpha cardiac myosin heavy chain (alpha-CMHC) fragment.

The validity of the general belief that alpha cardiac myosin heavy chain (alpha-CMHC) is primarily responsible for causing experimental autoimmune myocarditis because of the more profound tolerance induction to beta-CMHC due to its expression during the embryonic stage has been examined. In order to completely avoid cross-contamination among components of the two myosin heavy chains, recombinant myosin fragments were synthesized in Escherichia coli using cDNA fragments of rat alpha- and beta-CMHC cloned by reverse transcription polymerase chain reaction (RT-PCR). Two fragments corresponding to amino acid residues 1107-1164 derived from alpha- and beta-heavy chains were equally capable of provoking severe myocarditis in Lewis rats when immunized in complete Freund's adjuvant. No significant differences in the severity, as judged from histological scoring, were observed between the diseases induced by the two different peptide fragments, indicating conclusively that beta-CMHC is as pathogenic as alpha-CMHC.