Quantum Coherence at Low Temperatures in Mesoscopic Systems: Effect of Disorder

We study the disorder dependence of the phase coherence time of quasi one-dimensional wires and two-dimensional (2D) Hall bars fabricated from a high mobility GaAs/AlGaAs heterostructure. Using an original ion implantation technique, we can tune the intrinsic disorder felt by the 2D electron gas and continuously vary the system from the semi-ballistic regime to the localized one. In the diffusive regime, the phase coherence time follows a power law as a function of diffusion coefficient as expected in the Fermi liquid theory, without any sign of low temperature saturation. Surprisingly, in the semi-ballistic regime, it becomes independent of the diffusion coefficient. In the strongly localized regime we find a diverging phase coherence time with decreasing temperature, however, with a smaller exponent compared to the weakly localized regime.Comment: 21 pages, 30 figure

Low temperature dephasing in irradiated metallic wires

We present phase coherence time measurements in quasi-one-dimensional Ag wires implanted with Ag$^{+}$ ions with an energy of $100 keV$. The measurements have been carried out in the temperature range from $100 mK$ up to $10 K$; this has to be compared with the Kondo temperature of iron in silver, i.e. $T_{K}^{Ag/Fe} \approx 4 K$, used in recent experiments on dephasing in Kondo systems\cite{mallet_prl_06,birge_prl_06}. We show that the phase coherence time is not affected by the implantation procedure, clearly proving that ion implantation process by itself \emph{does not lead to any extra dephasing} at low temperature.Comment: 4 pages, 4figure

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe

Magnetotransport in cleaved-edge-overgrown Fe/GaAs-based and rare-earth-doped GaN-based heterostructures

Diese Arbeit beschäftigt sich mit Halbleiterspintronik. Spaltflächen von GaAs-Heterrostrukturen werden per Molekularstrahlepitaxie (MBE) mit Eisen überwachsen und darin werden Spinventilstrukturen mittels FIB-Sputtern hergestellt. An diesen Strukturen wird die elektrische Spininjektion vom Metall in den Halbleiter untersucht. Die Magnetowiderstände (MRs) der Spinventilbei 4,2 K sind nicht konsistent. Elemente der selten Erden werden in GaN implantiert um verdünnt magnetische Halbleiter (DMSs) herzustellen und dann wird der Magnetotransport in Gd-implantierten GaN-Heterostrukturen untersucht. Die Messung bei 4,2 K zeigen anormale Halleffekt und anisotropen Magnetowiderstand (AMR).The aim of this work is to study semiconductor spintronics. Cleaved-edge-overgrowth (CEO) of iron on GaAs-heterostructures are carried out with molecular beam epitaxy (MBE), and the spin-valve structures are fabricated by focused ion beam (FIB) milling. These structures are employed to study the electrical spin injection from metal into semiconductors. The magnetoresistances (MRs) measured at 4.2 K from the spin valves are not consistent. Implantations of rare-earth (RE) elements into GaN are used to fabricate diluted magnetic semiconductors (DMSs) and then, the magnetotransport is studied on Gd-implanted GaN-heterostructures. The measurements at T = 4.2 K reveal anomalous Hall effect and anisotropic magnetoresistances (AMR)

Spin-dependent optical transitions in yttrium iron garnet

This study reviewed the electronic structure using density functional theory (DFT) and demostrated the transmission of optical magnetic circular spectrum in probing spin-dependent optical transitions in yttrium iron garnet (YIG). DFT + U results suggested that the t _2 orbital of tetrahedral irons are polarized by exchange-splitting O(2 p ) bands. Such polarization was found to be essential for the kinetic exchange and magnetism in YIG. DFT + U results also identified the spin-polarized energy gaps in YIG. On the basis of the distinctions of Fe _3 O _4 [J. Chen et al , Phys. Rev. B , 98 , 085 141 (2018)] and YIG in electronic band features along with their manifestations in an optical magnetic circular diachroism (OMCD) spectrum, a map of spin-dependent optical transitions in YIG is presented. Based on the analysis of OMCD spectra at room temperature, the majority-spin and minority-spin gap in YIG are determined to be 2.45 and 2.25 eV, respectively

Evidence for Inhibitory Effects of Flupirtine, a Centrally Acting Analgesic, on Delayed Rectifier K+ Currents in Motor Neuron-Like Cells

Flupirtine (Flu), a triaminopyridine derivative, is a centrally acting, non-opiate analgesic agent. In this study, effects of Flu on K+ currents were explored in two types of motor neuron-like cells. Cell exposure to Flu decreased the amplitude of delayed rectifier K+ current (IK(DR)) with a concomitant raise in current inactivation in NSC-34 neuronal cells. The dissociation constant for Flu-mediated increase of IK(DR) inactivation rate was about 9.8 μM. Neither linopirdine (10 μM), NMDA (30 μM), nor gabazine (10 μM) reversed Flu-induced changes in IK(DR) inactivation. Addition of Flu shifted the inactivation curve of IK(DR) to a hyperpolarized potential. Cumulative inactivation for IK(DR) was elevated in the presence of this compound. Flu increased the amplitude of M-type K+ current (IK(M)) and produced a leftward shift in the activation curve of IK(M). In another neuronal cells (NG108-15), Flu reduced IK(DR) amplitude and enhanced the inactivation rate of IK(DR). The results suggest that Flu acts as an open-channel blocker of delayed-rectifier K+ channels in motor neurons. Flu-induced block of IK(DR) is unlinked to binding to NMDA or GABA receptors and the effects of this agent on K+ channels are not limited to its action on M-type K+ channels

Hydrogenation Effect on Interlayer Coupling and Magneto-Transport Properties of Pd/Co/Mg/Fe Multilayers

Hydrogenation-induced modification of magnetic properties has been widely studied. A Mg spacer layer with high hydrogen storage stability was clamped in a Pd/Co/Mg/Fe multilayer structure to enhance its hydrogen storage stability and explore the structure’s magneto-transport properties. After 1 bar hydrogen exposure, the formation of a stable MgH2 phase was demonstrated in an ambient environment at room temperature through X-ray diffraction. Lower magnetic coupling and enhanced magnetoresistance, compared to those of the as-grown sample, were observed using the longitudinal magneto-optical Kerr effect and a four-probe measurement. In this study, the hydrogenation stability of ferromagnetic multilayers was improved, and the concept of a hydrogenation-based spintronic device was developed.補正完畢US

Induction of dental pulp-derived induced pluripotent stem cells in the absence of c-Myc for differentiation into neuron-like cells

Background: A recent research breakthrough has demonstrated that the ectopic expression of four genes is sufficient to reprogram human fibroblasts into inducible pluripotent stem cells (iPSCs). However, whether human dental pulp cells (DPCs) could be reprogrammed into iPSCs remains an open question. In this study, we demonstrated that DPCs from deciduous and permanent teeth can be reprogrammed into iPSCs without c-Myc and had the capacity to differentiate into neuron-like cells. Methods: DPCs were obtained from donors and reprogrammed into iPSCs using retroviral transduction with SOX2, OCT4, and KLF4. Then, these iPSCs were differentiated into neuron-like cells. Microarray and bioinformatics were used to compare the gene expression profile among these iPSCs and iPSC-derived neuron-like cells. Results: The DPCs displayed a high vitality and capability to quickly restart proliferation and expressed elevated pluripotency similar to mesenchymal stem cells. According to our results, DPC-derived iPSC colonies that could be subcultured and propagated were established as early as 10 days after transduction, in comparison with the skin fibroblast (DPC-derived iPSCs) without c-Myc presented embryonic stem cell-like properties and the pluripotent potential to differentiate into neuron-like cells, which resemble neurons both morphologically and functionally. Conclusion: The human DPCs from deciduous and permanent teeth can undergo reprogramming to establish pluripotent stem cell lines without c-Myc. These surgical residues, usually regarded as medical waste, can be used as an alternative source of pluripotent stem cells for personalized medicine

Influence of structural disorder on the elastic, frictional, and electrical properties in functionalized polyaniline thin films at the nanoscale investigated by atomic force microscopy

We investigated the influence of structural order on the elastic, frictional, and electrical properties of butylthio-functionalized PANI (PANI-SBu) films by atomic force microscopy (AFM)-based techniques, including PeakForce quantitative nanomechanical mapping, friction force microscopy, and conductive AFM. The PANI-SBu films were prepared by the drop-cast method from the solution of PANI-SBu in N-methyl-2-pyrrolidone that was continuously stirred. The PANI-SBu films were fabricated after different solution stirring times. The shear force during the mechanical stir will disentangle the highly-coiled PANI-SBu polymer chains in the solution. Therefore, the polymer chains in solution cast on the substrates will progressively self-assemble into a more organized structure when solvents evaporate, leading to PANI-SBu films with improved structural order. Our AFM studies discovered that more structurally-ordered PANI-SBu films have substantially larger out-of-plane elastic moduli and charge mobility but smaller kinetic friction coefficients. The denser packing of polymer molecules increases film elasticities and promotes chain-to-chain charge transport. In addition, stiffer PANI-SBu film surfaces are more difficult to deform when sheared by the sliding AFM probe, resulting in less energy dissipation during AFM friction measurements. Thus, smaller kinetic friction coefficients were found. Conversely, more structurally-disordered PANI-SBu films have smaller elasticity and charge mobility but larger kinetic friction coefficients. Our results demonstrate that it is possible to manipulate the elastic, frictional, and electrical properties of PANI-SBu films by controlling their structural order, which can be essential for developing polymer-based composite materials and flexible electronic devices.</p

Influence of Oxygen Vacancies on the Frictional Properties of Nanocrystalline Zinc Oxide Thin Films in Ambient Conditions

Oxygen vacancy is the most studied point defect and has been found to significantly influence the physical properties of zinc oxide (ZnO). By using atomic force microscopy (AFM), we show that the frictional properties on the ZnO surface at the nanoscale greatly depend on the amount of oxygen vacancies present in the surface layer and the ambient humidity. The photocatalytic effect (PCE) is used to qualitatively control the amount of oxygen vacancies in the surface layer of ZnO and reversibly switch the surface wettability between hydrophobic and superhydrophilic states. Because oxygen vacancies in the ZnO surface can attract ambient water molecules, during the AFM friction measurement, water meniscus can form between the asperities at the AFM tip–ZnO contact due to the capillary condensation, leading to negative dependence of friction on the logarithm of tip sliding velocity. Such dependence is found to be a strong function of relative humidity and can be reversibly manipulated by the PCE. Our results indicate that it is possible to control the frictional properties of ZnO surface at the nanoscale using optical approaches