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Local council members have become an important research issue in many countries. However, the research on the social backgrounds of local council members has not enough progressed. This study analyzed the social backgrounds of local council members in Korea elected from 1991 to 2014. For the analysis, this study used gender, age, education, occupation, and political party affiliation and also used the index of qualitative variation to understand the social backgrounds of Korean local councilors. The results showed that social backgrounds of Korean local council members are centered on male, 50s, highly educated, people with political experience, and affiliated to two major parties. The gender diversity of local council members is lowest in comparison with other social background factors. To increase the gender diversity of local council members, the election system should be reformed, and social perception towards female politicians should be improved.

The wave-particle duality for light has been well established by various experiments, such as Young’s double slit experiment and the photoelectric effect. This led de Broglie to propose that a particle also has wave characteristics. Schrodinger further established the wave equation for a moving particle. Many times, quantum mechanics textbooks do not show how Schrodinger’s equation was developed in an intuitive manner that is appropriate at the undergraduate level. This article presents a new approach for introducing Schrodinger’s equation. This new approach starts with Maxwell’s equations and then applies the quantized energy of a light wave and special relativity. This more intuitive approach should help undergraduate students understand the origin of Schrodinger’s equation in a more natural way.

2005년 출산율이 1.08명이라는 사상 초유의 최저 수준을 떨어지게 되자 저출산 문제의 해결이 국가 및 사회적 차원에서 논의되기 시작했다. 저출산 문제는 인구감소, 노령인구의 증가, 생산인구의 감소 등과 같은 문제를 안고 있다. 정부는 이러한 문제를 해결하기 위해 2006년과 2010년 두 차례에 걸쳐 저출산 및 고령화대책을 수립하였다. 그러나 이러한 노력에도 불구하고 출산율은 증가하지 않았으며, 실질적 효과를 가지기 어렵다는 비판을 받게 되었다. 이에 2016년 제3차 저출산⋅고령사회 기본계획을 마련하여 저출산 문제의 해결을 위한 패러다임의 변화를 시도 하였으나 이 역시 기존 정책과 차별화된 내용이 없다는 비판에 직면하고 있다. 이 연구에서는 우리보다 먼저, 그리고 오랫동안 저출산의 장기화에 따른 문제를 경험하고, 이를 해결하기 위해 다양한 정책적 노력을 기울여 온 일본의 경험을 통해서 저출산 문제에 대한 올바른 인식과 정책적 대응을 위한 시사점을 찾아보고자 하였다.

(ProQuest: ... denotes formulae omitted.)I. INTRODUCTIONMyanmar is a typical agriculture country, and possesses moderately natural resources which have underpinned the agricultural production. According to the published data in 2012, agricultural sector contributed 13.7% of total export earnings, shared GDP accounted for 37.8%, and employed 61.2% of the labor force in Myanmar (Department of Agricultural Planning, 2012). Due to the various agro-ecological conditions and large land area of Myanmar, several agricultural products have been produced abundantly. Among them, rice is the major crop for both economy and food security of the country. Therefore, efficient rice production would give more income and export revenue for the country because paddy production alone accounted about 35% of the total crop area in Myanmar. It would in turn allow Myanmar to make an essential step for construction of a developed country through reducing poverty, improving food security for all farms, fostering a more dynamic rural sector and making agriculture as a dynamic contributor to the national economy. Surely, all of these outcomes will be achieved only after framing and executing more effective policies at the sectorial and national levels.Dapice et al.(2011) pointed out that the long-term trend in per capita rice production was reduced, which needs to reform and revitalization of agriculture required significant changes in policy through the stimulation of non-farm sectors so that they could absorb labor leaving agriculture. When looking back the history, Myanmar stood as major rice exporter in the world, but this role became dull due to various reasons in the recent days. Still, rice is the most important crop for Myanmar agriculture which dominates the largest and most productive part of the country economy. Myanmar still has great potential to increase rice production in various aspects such as land reclamations, effective mechanization and inputs, and good infrastructure development for both rural and urban areas.There were several recent studies that focused on the estimation and explanation of agricultural efficiency in most of the Asian developing countries, e.g. in India (Battese and Coelli, 1992, Battese and Coelli, 1995), Thailand (Krasachat, 2004; Kiatpathomchai, 2008), Indonesia (Souires and Tabor, 1991: Brazdik, 2006), Pakistan (Shafiq and Rehman, 2000; Javed et al., 2008), Bangladesh (Rahman, 2003; Rahman, 2011), the Philippines (Villano and Fleming, 2004), and Vietnam (Tran et al., 1993; Huy, 2009; Khai and Yabe, 2011). All of these studies pointed out substantial inefficiency and the possible potentials to improve the agricultural productivity. However, there has been limited empirical attention on identifying the factors affecting improvement of rice production efficiency of Myanmar. There are many economic questions related to production efficiency of Myanmar rice farms which are still needed to be answered.Myanmar is still lag behind in modern agricultural production, especially in the application of farm mechanization. The use of modern agricultural mechanical tools in rice production will raise productivity, reduce the processing time, and bring about the economy of scale. Mechanization not only increases land and labor productivity, but reduce the need for human and animal labor. At present, agricultural production is more or less traditional in Myanmar. Modernization and development of agricultural sector require the efficient use of farm mechanization tools. Thus, this study also investigates the role of farm mechanization in efficient rice production in Myanmar.Myanmar has been exploring the use of farm machinery for crop cultivation instead of traditional cattle and manpower. However, the effort has not been entirely successful due to the lack of skills and experience. Continuous increases in the productivity and cropping intensity need the efficient utilization of machinery in farming from land preparation to harvesting and post harvesting activities. …

This paper estimates household demand for electricity using a micro-level household expenditure data set. A two-stage estimation method where the endogenous block price estimates are obtained from a discrete block choice model is used. This method successfully identifies a downward sloping conditional demand function with the data, while both the usual two-stage method with instrumental variable estimation and the Hewitt-Hanemann discrete-continuous model fail to do that. The paper simulates the impacts of two hypothetical pricing reforms that reduce the number of blocks and make the price gap smaller. It is shown that the reform may increase the overall consumer benefit, but is regressive.

Objective: The purpose of this systematic review is to quantitatively estimate (or invest) the impacts of sports-related concussions (SRCs) on cognitive performance among retired athletes more than 10 years after retirement. Methods: Six databases including (MEDLINE, Scopus, Web of Science, SPORTDiscus, CINAHL, and PsycArtilces) were employed to retrieve the related studies. Studies that evaluate the association between cognitive function and the SRC of retired athletes sustaining more than 10 years were included. Results: A total of 11 studies that included 792 participants (534 retired athletes with SRC) were identified. The results indicated that the retired athletes with SRCs, compared to the non-concussion group, had significant cognitive deficits in verbal memory (SMD = −0.29, 95% CI −0.59 to −0.02, I2 = 52.8%), delayed recall (SMD = −0.30, 95% CI −0.46 to 0.07, I2 = 27.9%), and attention (SMD = −0.33, 95% CI −0.59 to −0.06, I2 = 0%). Additionally, meta-regression demonstrated that the period of time between testing and the last concussion is significantly associated with reduced verbal memory (β = −0.03681, p = 0.03), and increasing age is significantly associated with the verbal memory (β = −0.03767, p = 0.01), immediate recall (β = −0.08684, p = 0.02), and delay recall (β = −0.07432, p = 0.02). Conclusion: The retired athletes who suffered from SRCs during their playing career had declined cognitive performance in partial domains (immediate recall, visuospatial ability, and reaction time) later in life.

High-temperature (high-Tc) superconductivity in the copper oxides arises from electron or hole doping of their antiferromagnetic (AF) insulating parent compounds. The evolution of the AF phase with doping and its spatial coexistence with superconductivity are governed by the nature of charge and spin correlations and provide clues to the mechanism of high-Tc superconductivity. Here we use a combined neutron scattering and scanning tunneling spectroscopy (STS) to study the Tc evolution of electron-doped superconducting Pr0.88LaCe0.12CuO4-delta obtained through the oxygen annealing process. We find that spin excitations detected by neutron scattering have two distinct modes that evolve with Tc in a remarkably similar fashion to the electron tunneling modes in STS. These results demonstrate that antiferromagnetism and superconductivity compete locally and coexist spatially on nanometer length scales, and the dominant electron-boson coupling at low energies originates from the electron-spin excitations., Comment: 30 pages, 12 figures, supplementary information included

Herein, we report the synthesis of multiscale nanostructured p-type (Bi,Sb)(2)Te(3) bulk materials by melt-spinning single elements of Bi, Sb, and Te followed by a spark plasma sintering process. The samples that were most optimized with the resulting composition (Bi(0.48)Sb(1.52)Te(3)) and specific nanostructures showed an increase of approximately 50% or more in the figure of merit, ZT, over that of the commercial bulk material between 280 and 475 K, making it suitable for commercial applications related to both power generation and refrigeration. The results of high-resolution electron microscopy and small angle and inelastic neutron scattering along with corresponding thermoelectric property measurements corroborate that the 10-20 nm nanocrystalline domains with coherent boundaries are the key constituent that accounts for the resulting exceptionally low lattice thermal conductivity and significant improvement of ZT.

We use inelastic neutron scattering to study the low-energy spin excitations of polycrystalline samples of nonsuperconducting CeFeAsO and superconducting CeFeAsO0.84F0.16. Two sharp dispersionless modes are found at 0.85 and 1.16 meV in CeFeAsO below the Ce antiferromagnetic (AF) ordering temperature of TNCe ˜ 4 K. On warming to above TNCe ˜ 4 K, these two modes become one broad dispersionless mode that disappears just above the Fe ordering temperature TNFe ˜ 140 K. For superconducting CeFeAsO0.84F0.16, where Fe static AF order is suppressed, we find a weakly dispersive mode center at 0.4 meV that may arise from short-range Ce-Ce exchange interactions. Using a Heisenberg model, we simulate powder-averaged Ce spin wave excitations. Our results show that we need both Ce spin wave and crystal electric field excitations to account for the whole spectra of low-energy spin excitations.

Efforts have been made to develop a chemoprevention strategy that selectively triggers apoptosis in malignant cancer cells. Previous studies showed that capsaicin, the major pungent ingredient of red pepper, had differential effect between normal and transformed cells. As an approach to unveil the molecular mechanism by which capsaicin selectively induces apoptosis in transformed cells, we investigated the effect of capsaicin in nontransformed and ras-transformed cells of a common origin: parental (MCF10A) and H-ras-transformed (H-ras MCF10A) human breast epithelial cells. Here, we show that capsaicin selectively induces apoptosis in H-ras-transformed cells but not in their normal cell counterparts. The capsaicin-induced apoptosis, which is dependent on ras transformation, involves the activity of DEVDase (caspase-3 like). In H-ras MCF10A cells, capsaicin treatment markedly activated c-Jun N-terminal protein kinase (JNK)-1 and p38 matigen-activated protein kinase (MAPK) while it deactivated extracellular signal-regulated protein kinases (ERKs). The use of kinase inhibitors and overexpression of dominant-negative forms of MAPKs demonstrated a role of JNK-1 and p38, but not that of ERKs, in apoptosis induced by capsaicin in H-ras-transformed MCF10A cells. Based on the present study, we propose that capsaicin selectively induces apoptosis through modulation of ras-downstream signaling molecules in ras-activated MCF10A cells. Taken in conjunction with the fact that uncontrolled ras activation is probably the most common genetic defect in human cancer cells, our finding may be critical to the chemopreventive potential of capsaicin and for developing a strategy to induce tumor cell-specific apoptosis.

Curcumin, a dietary pigment in turmeric, posseses anti-carcinogenic and anti-metastatic properties. The present study was conducted to study in vitro chemopreventive effects of curcumin in transformed breast cells. Here, we show that curcumin inhibits H-ras-induced invasive phenotype in MCF10A human breast epithelial cells (H-ras MCF10A) and downregulates matrix metalloproteinase (MMP)-2 dose-dependently. Curcumin exerted cytotoxic effect on H-ras MCF10A cells in a concentration-dependent manner. Curcumin-induced cell death was mainly due to apoptosis in which a prominent downregulation of Bcl-2 and upregulation of Bax were involved. We also suggest a possible involvement of caspase-3 in curcumin-induced apoptosis. Curcumin treatment resulted in the production of reactive oxygen species (ROS) in H-ras MCF10A cells. Apoptotic event by curcumin was significantly inhibited by pretreatment of an antioxidant N-acetyl-L-cysteine (NAC), suggesting redox signaling as a mechanism responsible for curcumin-induced apoptosis in H-ras MCF10A cells. Taken together, our results demonstrate that curcumin inhibits invasion and induces apoptosis, proving the chemopreventive potential of curcumin.

Characterization of poly(butylene adipate-co-succinate) (PBAS)/poly(butylene terephthalate) (PBT) copolyesters resulting from the intermolecular ester-exchange reaction between molten PBAS and PBT have been analyzed using 1H-NMR spectroscopy, differential scanning calorimetry, wide-angle X-ray diffraction, and total organic carbon lab analyzer. Using the assignment of proton resonance due to homogeneous and heterogeneous dyads, the average block lengths were investigated over the entire range of copolymer composition. A decrease in melting temperature was observed with the increase of a terephthalate unit in the composition. The result of X-ray diffraction curve matches well with that of average block length and thermal property. When a rich component is crystallized, the poor component is excluded completely in a crystal formation. The biodegradability in copolyesters also depended on the terephthalate unit in the composition and average block length of the aromatic unit. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 593–608, 1999

PB(GAS)/PBT block copolyesters of poly(butylene glutarate-co-adipate-co-succinate), PB(GAS), and poly(butylene terephthalate), PBT, were prepared by molten-state processing for different times. The degree of randomness, melting temperature, and crystallization behavior for these copolyesters were studied by means of 1H NMR spectroscopy, DSC, and wide angles X-ray diffraction. Average block length, LnĀl and LnĀr, of aliphatic and aromatic sequences obviously decreased with mixing time. Melting points also moved to lower temperature with mixing time. PB(GAS) sequences in copolyesters were completely excluded from the crystal formation of block copolyesters.

In this paper we deal with the q-deformed alternating tensor and prove the associativity of the q-deformed wedge product. Moreover, we construct the theory of q-deformed homology in order to prove the q-deformed Stokes theorem. Lastly we prove the q-deformed Poincare lemma.

We introduce the concept ofq-deformed probability and discuss theq-deformed binomial distribution.

In this paper we investigate aq=0 plane which cannot be obtained by puttingq=0 in the Wess-Zumino formalism and has no classical analog.

Neutron scattering in strong magnetic fields is used to show the spin-resonance in superconducting CeCoIn5 (Tc=2.3 K) is a doublet. The underdamped resonance (\hbar \Gamma=0.069 \pm 0.019 meV) Zeeman splits into two modes at E_{\pm}=\hbar \Omega_{0}\pm g\mu_{B} \mu_{0}H with g=0.96 \pm 0.05. A linear extrapolation of the lower peak reaches zero energy at 11.2 \pm 0.5 T, near the critical field for the incommensurate "Q-phase" indicating that the Q-phase is a bose condensate of spin excitons., Comment: 5 pages, 4 figures

Spin fluctuations are reported near the magnetic field driven quantum critical point in YbRh2Si2. On cooling, ferromagnetic fluctuations evolve into incommensurate correlations located at q0=+/- (delta,delta) with delta=0.14 +/- 0.04 r.l.u. At low temperatures, an in plane magnetic field induces a sharp intra doublet resonant excitation at an energy E0=g muB mu0 H with g=3.8 +/- 0.2. The intensity is localized at the zone center indicating precession of spin density extending xi=6 +/- 2 A beyond the 4f site., Comment: (main text - 4 pages, 4 figures; supplementary information - 3 pages, 3 figures; to be published in Physical Review Letters)

In this paper a newq-derivative is proposed and its properties are discussed. We defineq-addition and study its axiomatic properties. Theq-exponents andq-logarithmic function are introduced and their algebraic structure discussed.

In this article the q‐deformed gamma function and q‐deformed beta function are discussed in detail. Three definitions for the q‐gamma function are obtained and the q‐deformed duplication and multiplication formulas are proven. The q‐beta function is defined and its useful properties are derived.

In this paper we create a new combinatorics which we call q-combinatorics and investigate the meaning of q-permutations and q-combinations.

In this paper we use a special choice of the GLX,qij(2N) quantum plane and its differential calculus for a q-deformed phase space to define a modified Poisson bracket and construct the contraction rule for the q-deformed Levi-Civita symbol. We find the q-deformed phase-space variable realization of the soq(3) and q-deformed Poincare algebras.

The correlations between stripe order, superconductivity, and crystal structure in La{sub 2-x}Ba{sub x}CuO{sub 4} single crystals have been studied by means of x-ray and neutron diffraction as well as static magnetization measurements. The derived phase diagram shows that charge stripe order (CO) coexists with bulk superconductivity in a broad range of doping around x=1/8, although the CO order parameter and correlation length fall off quickly for x {ne} 1/8. Except for x=0.155, the onset of CO always coincides with the transition between the orthorhombic and the tetragonal or less orthorhombic low-temperature structures. The CO transition evolves from a sharp drop at low x to a more gradual transition at higher x, eventually falling below the structural phase boundary for optimum doping. With respect to the interlayer CO correlations, we find no qualitative change of the stripe stacking order as a function of doping, and in-plane and out-of-plane correlations disappear simultaneously at the transition. Similarly to the CO, the spin stripe order (SO) is also most pronounced at x=1/8. Truly static SO sets in below the CO and coincides with the first appearance of in-plane superconducting correlations at temperatures significantly above the bulk transition to superconductivity (SC). Indications that bulk SCmore » causes a reduction of the spin or charge stripe order could not be identified. We argue that CO is the dominant order that is compatible with SC pairing but competes with SC phase coherence. Comparing our results with data from the literature, we find good agreement if all results are plotted as a function of x' instead of the nominal x, where x' represents an estimate of the actual Ba content, extracted from the doping dependence of the structural transition between the orthorhombic phase and the tetragonal high-temperature phase.« less

We study the magnetic-field-induced quantum phase transition from a gapped quantum phase that has no magnetic long-range order into a gapless phase in the spin-1/2 ladder compound bis(2,3-dimethylpyridinium) tetrabromocuprate (DIMPY). At temperatures below about 1 K, the specific heat in the gapless phase attains an asymptotic linear temperature dependence, characteristic of a Tomonaga-Luttinger liquid. Inelastic neutron scattering and the specific heat measurements in both phases are in good agreement with theoretical calculations, demonstrating that DIMPY is the first model material for an S=1/2 two-leg spin ladder in the strong-leg regime., 4.1 pages, 4 figures (Fig. 4 updated), to appear in Physical Review Letters

We have observed a softening of phonons and a structural phase transition in a superconducting Ba0.59K0.41BiO3 (Tc = 31 K) single crystal using elastic and inelastic neutron scattering measurements. The soft phonon occurs for the [111] transverse acoustic mode at the zone boundary. The phonon energies in this vicinity are found to continuously decrease with decreasing temperature from above room temperature to 200 K, where a structural phase transition from cubic to tetragonal symmetry occurs. The overall results are consistent with previous data that reported phonon softening and a (0.5, 0.5, 0.5) type superstructure in several Ba1-xKxBiO3 systems. However, we also find weak (0.5, 0.5, 0) type superstructure peaks that reveal an additional component to the modulation. No significant change related to the superconductivity was observed for the soft phonon energies or linewidths., 15 pages

Low-energy spin excitations were investigated in the static stripe phase of La2-xSrxCuO4 using elastic and inelastic neutron scattering on single crystals. For x=1/8 in which long-range static stripe order exists, an energy gap of E(g)=4 meV exists in the excitation spectrum in addition to strong quasielastic, incommensurate spin fluctuations associated with the static stripes. When x increases, the spectral weight of the spin fluctuations shifts from the quasielastic continuum to the excitation spectrum above E(g). The dynamic correlation length as a function of energy and the temperature evolution of the energy spectrum suggest a phase separation of two distinct magnetic phases in real space.

The hydrolysis of alkoxysilane coupling agents has been followed using proton NMR. The disappearance of the silane ester and the appearance of the alkoxy group were observed to follow pseudo-first-order kinetics. The apparent rate constant was found to be dependent on the concentration of the silane coupling agent and the pH. The adsorption of the coupling agents onto Cab-O-Sil silica was quantified using FT-IR spectroscopy. It was found that monolayer coverage was obtained with about 0.65 mmol/100 m2. Solid-state deuterium NMR was used to probe the behavior of the coupling agent on the silica. The coupling agents adsorbed on the surface from deuterated aminopropyltriethoxysilane (DAPES) and deuterated aminobutyltriethoxysilane (DABES) showed similar motional characteristics. In contrast, the mobility of condensed polymers from DABES was much less restricted than that from DAPES. The amount of hydrolysis in acetone-water mixtures increased the amount of surface-adsorbed material and lessened surface mobil...

We report on neutron-scattering results on the impact of a magnetic field on stripe order in the cuprate La$_{1.875}$Ba$_{0.125}$CuO$_4$. It is found that a 7 T magnetic field applied along the {\it c} axis causes a small but finite enhancement of the spin-order peak intensity and has no observable effect on the peak width. Inelastic neutron-scattering measurements indicate that the low-energy magnetic excitations are not affected by the field, within experimental error. In particular, the small energy gap that was recently reported is still present at low temperature in the applied field. In addition, we find that the spin-correlation length along the antiferromagnetic stripes is greater than that perpendicular to them.

We present new x-ray and neutron-scattering measurements of stripe order in ${\text{La}}_{1.875}{\text{Ba}}_{0.125}{\text{CuO}}_{4}$, along with low-field susceptibility, thermal conductivity, and specific-heat data. We compare these with previously reported results for resistivity and thermopower. Temperature-dependent features indicating transitions (or crossovers) are correlated among the various experimental quantities. Taking into account recent spectroscopic studies, we argue that the most likely interpretation of the complete collection of results is that an unusual form of two-dimensional superconducting correlations appears together with the onset of spin-stripe order. Recent theoretical proposals for a sinusoidally modulated superconducting state compatible with stripe order provide an intriguing explanation of our results and motivate further experimental tests. We also discuss evidence for one-dimensional pairing correlations that appear together with the charge order. With regard to the overall phenomenology, we consider the degree to which similar behavior may have been observed in other cuprates and describe possible connections to various puzzling phenomena in cuprate superconductors.

We use neutron scattering to study the Pr(3+) crystalline electric field (CEF) excitations in the filled skutterudite PrOs(4)As(12). By comparing the observed levels and their strengths under neutron excitation with the theoretical spectrum and neutron excitation intensities, we identify the Pr(3+) CEF levels and show that the ground state is a magnetic Gamma((2))(4) triplet, and the excited states Gamma(1), Gamma((1))(4), and Gamma(23) are at 0.4, 13, and 23 meV, respectively. A comparison of the observed CEF levels in PrOs(4)As(12) with the heavy fermion superconductor PrOs(4)Sb(12) reveals the microscopic origin of the differences in the ground states of these two filled skutterudites.

Neutron scattering is used to probe antiferromagnetic spin fluctuations in the d-wave heavy fermion superconductor CeCoIn5 (T_(c)=2.3 K). Superconductivity develops from a state with slow (variant Planck's over 2piGamma=0.3+/-0.15 meV) commensurate [Q_(0)=(1/2,1/2,1/2)] antiferromagnetic spin fluctuations and nearly isotropic spin correlations. The characteristic wave vector in CeCoIn5 is the same as CeIn3 but differs from the incommensurate wave vector measured in antiferromagnetically ordered CeRhIn5. A sharp spin resonance (variant Planck's over 2piGamma

We use inelastic neutron scattering to study the temperature dependence of the spin excitations of a detwinned superconducting YBa{sub 2}Cu{sub 3}O{sub 6.45} (T{sub c} = 48 K). In contrast to earlier work on YBa{sub 2}Cu{sub 3}O{sub 6.5} (T{sub c} = 58 K), where the prominent features in the magnetic spectra consist of a sharp collective magnetic excitation termed 'resonance' and a large ({h_bar} {omega} {approx} 15 meV) superconducting spin gap, we find that the spin excitations in YBa{sub 2}Cu{sub 3}O{sub 6.45} are gapless and have a much broader resonance. Our detailed mapping of magnetic scattering along the a*/b*-axis directions at different energies reveals that spin excitations are unisotropic and consistent with the 'hourglasslike' dispersion along the a*-axis direction near the resonance, but they are isotropic at lower energies. Since a fundamental change in the low-temperature normal state of YBa{sub 2}Cu{sub 3}O{sub 6+y} when superconductivity is suppressed takes place at y {approx} 0.5 with a metal-to-insulator crossover (MIC), where the ground state transforms from a metallic to an insulating like phase, our results suggest a clear connection between the large change in spin excitations and the MIC. The resonance therefore is a fundamental feature of metallic ground state superconductors and amore » consequence of high-T{sub c} superconductivity.« less

The hydrolysis and dynamics of silane coupling agents have been probed using nuclear magnetic resonance (NMR) spectroscopy. The hydrolysis of γ-aminopropyltrimethoxysilane and γ-aminopropyltriethoxysilane were studied using proton NMR spectroscopy. The rates of hydrolysis were dependent on the water and silane coupling agent concentration as well as their chemical nature. The methoxy-substituted silane hydrolyzed much faster than the ethoxy-substituted one. The molecular motion of γ - aminopropylsilane - d 2 immobilized on a silica surface and as the bulk polymerized siloxane were characterized by 2 H solid-echo NMR techniques. It was found that the motion of the silane coupling agent on silica was more restricted than in the condensed polymer. Deuterium oxide exchange experiments also showed that the motion of deuterons on the amino group is much faster than those of the deuterons on the methylene group in silane coupling agents.

High-transition-temperature superconductivity arises in copper oxides when holes or electrons are doped into the CuO2 planes of their insulating parent compounds. While hole-doping quickly induces metallic behavior and superconductivity in many cuprates, electron-doping alone is insufficient in materials such as R2CuO4 (R is Nd, Pr, La, Ce, etc.), where it is necessary to anneal an as-grown sample in a low-oxygen environment to remove a tiny amount of oxygen in order to induce superconductivity. Here we show that the microscopic process of oxygen reduction repairs Cu deficiencies in the as-grown materials and creates oxygen vacancies in the stoichiometric CuO2 planes, effectively reducing disorder and providing itinerant carriers for superconductivity. The resolution of this long-standing materials issue suggests that the fundamental mechanism for superconductivity is the same for electron- and hole-doped copper oxides., Comment: 23 pages, 3 figures, accepted for publication in Nature Materials