Intermediate Plateau Research Articles

Quasi-Particle Tunneling in Anti-Pfaffian Quantum Hall State

We study tunneling phenomena at the edge of the anti-Pfaffian quantum Hall state at the filling factor $\nu=5/2$. The edge current in a single point-contact is considered. We focus on nonlinear behavior of two-terminal conductance with the increase in negative split-gate voltage. Expecting the appearance of the intermediate conductance plateau we calculate the value of its conductance by using the renormalization group (RG) analysis. Further, we show that non-perturbative quasi-particle tunneling is effectively described as perturbative electron tunneling by the instanton method. The two-terminals conductance is written as a function of the gate voltage. The obtained results enable us to distinguish the anti-Pfaffian state from the Pfaffian state experimentally.

Thermal decomposition of Ln(C2H5CO2)3·H2O (Ln = Ho, Er, Tm and Yb)

The thermal decomposition of Ho(III), Er(III), Tm(III) and Yb(III) propionate monohydrates in argon was studied by means of thermogravimetry (TG), differential thermal analysis (DTA), IR-spectroscopy and X-ray diffraction (XRD). Dehydration takes place around 90 °C. It is followed by the decomposition of the anhydrous propionates to Ln2O2CO3 (Ln = Ho, Er, Tm or Yb) with the evolution of CO2 and 3-pentanone (C2H5COC2H5) between 300 and 400 °C. The further decomposition of Ln2O2CO3 to the respective sesquioxides Ln2O3 is characterized by an intermediate plateau extending from approximately 500–700 °C in the TG traces. This stage corresponds to an overall composition of Ln2O2.5(CO3)0.5 but is more probably a mixture of Ln2O2CO3 and Ln2O3. The stability of this intermediate state decreases for the lighter rare-earth (RE) compounds studied. Full conversion to Ln2O3 is achieved at about 1,100 °C. The overall thermal decomposition behaviour of the title compounds is similar to that previously reported for Lu(C2H5CO2)3·H2O.

Complete Two‐Step Spin‐Transition in a 1D Chain Iron(II) Complex with a 110‐K Wide Intermediate Plateau

AbstractThree new spin crossover compounds [FeL1(azpy)] (1), [FeL1(azpy)]·toluene [1(tol)] and [FeL2(azpy)] (2), where L1 and L2 are the tetradentate N2O22– coordinating Schiff base like ligands {diethyl (E,E)‐2,2′‐[1,2‐phenyl‐bis(iminomethylidyne)]bis[3‐oxobutanoate]‐(2‐)‐N,N′,O3,O3′} and {dimethyl(E,E)‐2,2′‐[1,2‐phenyl‐bis(iminomethylidyne)]bis[3‐oxobutanoate]‐(2‐)‐N,N′,O3,O3′}, respectively, and azpy = 4,4′‐azopyridine are presented. All compounds have been investigated by using T‐dependent susceptibility measurements, and different types of spin transitions are observed. In the case of 1 and 2, intermediate plateaus (γHS ≈ 0.5) with widths of 110 and 75 K, respectively, were observed, while for 1(tol) a gradual spin transition is obtained. Upon heating of 1(tol) above 390 K, a loss of the included solvent molecule toluene is observed, which results in a two‐step spin transition of the tempered sample similar to that of 1. Mössbauer spectra of 1, 1(tol) and the tempered sample 1(temp) reveal two different iron(II) sites in the low‐spin (LS) state for all three samples. T‐dependent Mössbauer spectra indicate that the inequivalent iron centres are one but not the only reason for the wide plateau of 1. Results from X‐ray structure analysis of 1 in the region of the plateau show the presence of two inequivalent iron centres, of which one is in the high‐spin (HS) state and one in the low‐spin state. The 1D chains of alternating HS and LS iron centres are arranged in a parallel manner within one layer; between the different layers, the direction of the chains rotates by 90° relative to the previous one. This cross‐linked arrangement with an interlocking of the layers is most likely the reason for the appearance of the wide plateau.

Dielectric and Viscoelastic Investigation of Segmental Dynamics of Polystyrene above Glass Transition Temperature: Cooperative Sequence Length and Relaxation Mode Distribution

Atactic polystyrene (PS) has the type-B dipole perpendicular to the chain backbone so that its local, segmental motion activates the dielectric relaxation. For monodisperse oligostyrene (OS) and PS samples of various molecular weights M, details of this motion were examined at temperatures T well above Tg through comparison of the complex modulus, G* = G′ + iG′′, and the complex dielectric permittivity, e* =e′ – ie′′, measured as functions of the angular frequency ω. For the OS samples, G*(ω) and e*(ω) fully relaxed through the segmental dynamics thereby exhibiting respective terminal relaxation tails (low-frequency tails), G′(ω) ∝ ω2, G′′(ω) ∝ ω, Δe′(ω) ≡ e′(0) – e′(ω)∝ ω2, and e′′(ω) ∝ ω, at ω below the segmental relaxation frequency ωs. For the PS samples, G*(ω) relaxed partly through the segmental dynamics and then exhibited the polymeric full relaxation characterized by the Rouse-like behavior followed by the terminal flow behavior (with/without intermediate entanglement plateau depending on M). In c...

Unusual field-induced transitions in exactly solved mixed spin-(1/2, 1) Ising chain with axial and rhombic zero-field splitting parameters

The mixed spin-(1/2, 1) Ising chain with axial and rhombic zero-field splitting parameters in the presence of the longitudinal magnetic field is exactly solved within the framework of decoration-iteration transformation and transfer-matrix method. Our particular emphasis is laid on an investigation of the influence of the rhombic term, which is responsible for an onset of quantum entanglement between two magnetic states S k z =±1 of the spin-1 atoms. It is shown that the rhombic term gradually destroys a classical ferrimagnetic order in the ground state and simultaneously causes diversity in magnetization curves including intermediate plateau regions, regions with a continuous change in the magnetization as well as several unusual field-induced transitions accompanied with magnetization jumps. Another interesting findings concern with an appearance of the round minimum in the temperature dependence of susceptibility times temperature data, the double-peak zero-field specific heat curves and the enhanced magnetocaloric effect. The temperature dependence of the specific heat with three separate maxima may also be detected when driving the system through the axial and rhombic zero-field splitting parameters close enough to a phase boundary between the ferrimagnetic and disordered states and applying sufficiently small longitudinal magnetic field.

Two‐Step versus One‐Step Spin Transitions in Iron(II) 1D Chain Compounds

AbstractEleven iron(II) 1D coordination polymers with the general formula [FeLeq(Lax)]·solvent were synthesised and characterised, where Leq = (E,E)‐{diethyl 2,2′‐[1,2‐phenylenebis(iminomethylidyne)]bis(3‐oxobutanato) (2‐)‐N,N′,O3,O3′} (L1) and {[3,3′]‐[1,2‐phenylenebis(iminomethylidyne)]bis(2,4‐pentane‐dionato)(2‐)‐N,N′,O2,O2′} (L2); Lax = 4,4′‐bipyridine (bipy), 1,2‐bis(4‐pyridyl)ethane (bpea) and 1,3‐bis(4‐pyridyl)propane (bppa) and solvent = MeOH, EtOH and toluene (Tol). [FeL1(bpea)]·MeOH (3·MeOH) shows an abrupt one‐step spin crossover with thermal hysteresis(27 K) and [FeL2(bppa)]·MeOH (2·MeOH), [FeL2(bpea)] (4), [FeL2(bpea)]·0.25MeOH (4·0.25MeOH) and [FeL1(bipy)]·MeOH (5·MeOH) show a two‐step spin transition with an IP at γHS ≈ 0.5 (IP is intermediate plateau and γHS is high‐spin mol fraction) and up to 50 K wide hysteresis loops (5·MeOH). [FeL1(bppa)] (1), [FeL2(bppa)]·EtOH (2·EtOH) and [FeL1(bpea)]·1.5Tol (3·1.5Tol) show an abrupt incomplete spin transition that stops at γHS ≈ 0.5; for [FeL1(bppa)]·0.25MeOH (1·0.25MeOH) and [FeL1(bpea)] (3), the spin transition is gradual and incomplete. The X‐ray crystal structures of six complexes were determined (1, 2·MeOH, 3·MeOH, 3·1.5Tol, 4·0.25MeOH and 5·MeOH). In the case of 4·0.25MeOH, the crystal structures for the HS and LS states were dertermined; for compounds 1, 2·MeOH and 3·1.5Tol, the crystal structure of the HS and the IP state was investigated. For all complexes, the iron(II) centre is located in a distorted octahedral coordination sphere. Each axially coordinated ligand “connects” two iron(II) centres, which results in the formation of extended 1D chains with varying structures from linear (bipy) over steplike (bpea) to zigzag (bppa). Analysis of the intermolecular interactions reveals that the hysteresis width depends on both the stiffness of the axial ligand and the number of intermolecular contacts, while zigzag chains support stepwise spin transitions.

Magnetic properties of model non-carbon nanotubes with macroscopic value of ground state spin

The spin model of “ferrimagnetic” nanotube is proposed and some theoretical predictions concerning the ground state and low energy excitations of the model are given. In particular, the spin–wave structure of the exact ground state of bipartite magnets is proven. For tubes formed by weakly interacted cyclic fragments we show: first, the existence of gapless excitations with decreasing total spin; and second, gapped excitations. This leads to an intermediate plateau in field dependence of tube magnetization. Numerical calculations show the strong effect of frustrations on the magnetization of anisotropic spin tubes at low temperatures which may lead to the creation of an additional fractional magnetization plateau.

Dynamic Surface Tension of Aqueous Solutions of Ionic Surfactants: Role of Electrostatics

The adsorption kinetics of the cationic surfactant dodecyltrimethylammonium bromide at the air-water interface has been studied by the maximum bubble pressure method at concentrations below the critical micellar concentration. At short times, the adsorption is diffusion-limited. At longer times, the surface tension shows an intermediate plateau and can no longer be accounted for by a diffusion-limited process. Instead, adsorption appears kinetically controlled and slowed down by an adsorption barrier. A Poisson-Boltzmann theory for the electrostatic repulsion from the surface does not fully account for the observed potential barrier. The possibility of a surface phase transition is expected from the fitted isotherms but has not been observed by Brewster angle microscopy.

Organic–inorganic nanocomposite bilayers with triple shape memory effect

Various amounts of silica nanoparticles were chemically incorporated into amorphous polyurethanes (PU) of two different molecular weights by sol–gel reactions, and the effects were studied in terms of mechanical, dynamic mechanical, dual, and triple shape memory effects (DSME and TSME) of the nanocomposite films. It was found that the silica particles act as multifunctional cross-links as well as reinforcing fillers and significantly augmented the glassy and rubbery state moduli, yield strength, break strength, glass transition temperature, and dual shape memory properties. A cohesive bilayer of the two films fabricated from an interpenetrating polymer network (IPN) exhibited synergistic mechanical properties in the glassy and rubbery states along with two undisturbed glass transitions by which an intermediate plateau region and TSME were demonstrated.

Brownian motion in a Maxwell fluid

The equilibrium dynamics of a spherical particle immersed in a complex Maxwell fluid is analyzed in terms of velocity autocorrelation function (VACF), mean-square displacement (MSD), and power spectral density (PSD). We elucidate the role of hydrodynamic memory and its interplay with medium viscoelasticity for a free and a harmonically confined particle. The elastic response at high frequencies introduces oscillations in the VACF, which are found to be strongly damped by the coupling to the fluid. We show that in all Maxwell fluids hydrodynamic memory eventually leads to a power-law decay in the VACF as is already known for Newtonian fluids. The MSD displays asymptotically an intermediate plateau reflecting the elastic restoring forces of the medium. In the frequency domain, the PSD exhibits at high frequencies a step due to the trapping, whereas the low-frequency decay reflects the viscoelastic relaxation. Our results suggest that high-frequency microrheology is well-suited to infer the elastic modulus, which is sensitive over a wide range of Maxwell times.

Thermal decomposition of lutetium propionate

The thermal decomposition of lutetium(III) propionate monohydrate (Lu(C 2H 5CO 2) 3·H 2O) in argon was studied by means of thermogravimetry, differential thermal analysis, IR-spectroscopy and X-ray diffraction. Dehydration takes place around 90 °C. It is followed by the decomposition of the anhydrous propionate to Lu 2O 2CO 3 with evolution of CO 2 and 3-pentanone (C 2H 5COC 2H 5) between 300 °C and 400 °C. The further decomposition of Lu 2O 2CO 3 to Lu 2O 3 is characterized by an intermediate constant mass plateau corresponding to a Lu 2O 2.5(CO 3) 0.5 overall composition and extending from approximately 550 °C to 720 °C. Full conversion to Lu 2O 3 is achieved at about 1000 °C. Whereas the temperatures and solid reaction products of the first two decomposition steps are similar to those previously reported for the thermal decomposition of lanthanum(III) propionate monohydrate, the final decomposition of the oxycarbonate to the rare-earth oxide proceeds in a different way, which is here reminiscent of the thermal decomposition path of Lu(C 3H 5O 2)·2CO(NH 2) 2·2H 2O.

Over-volted breakdown and recovery of short nitrogen spark gaps

AbstractThe characteristic of the over-volted breakdown and the gaseous recovery in short nitrogen gaps was experimentally studied. It was found that the breakdown voltage of the gap changes from shot to shot even with the same experimental conditions and obeys Gaussian distribution. The over-volted factor is reduced with an increasing pressure. With a 2.7-mm gap the over-volted factors are 4.53 for 0.1 MPa pressure and 1.74 for 0.4 MPa. The over-volted breakdown voltage depends individually on the gap spacing d and the gas pressure p, rather than on the product of pd. An empirical formula of the breakdown voltage as a function of p and d was derived. The time-dependent recovery of the breakdown voltage, RVb, was obtained using a two-pulse technique. The second breakdown voltage also obeys Gaussian distribution, but it is normally with a smaller standard deviation especially when the interpulse spacing of Δt is relatively short. As a whole, RVb rises with the increase of Δt. However, an intermediate plateau is always observed and it starts when the second breakdown voltage is a little bit higher than the static breakdown voltage of the gap. The first rising edge of the RVb curve corresponds to the recovery of the electro-neutrality and the density. The intermediate plateau and the following rising edge take the spark gap much longer time to recover. The processes governing these two latter phases are as yet not fully clear. It is attributed to the delayed recombination of the residual nitrogen atoms on the cathode to produce the initial electrons for the second breakdown. An increase in pressure has resulted in an upward shift of the intermediate plateau and a shortening in the recovery time of the gaps. The second spark generally does not follow the path of the first spark.

Feed-forward inhibition as a buffer of the neuronal input-output relation

Neuronal processing depends on the input-output (I/O) relation between the frequency of synaptic stimulation and the resultant axonal firing rate. The all-or-none properties of spike generation and active membrane mechanisms can make the neuronal I/O relation very steep. The ensuing nearly bimodal behavior may severely limit information coding, as minimal input fluctuations within the expected natural variability could cause neuronal output to jump between quiescence and maximum firing rate. Here, using biophysically and anatomically realistic computational models of individual neurons, we demonstrate that feed-forward inhibition, a ubiquitous mechanism in which inhibitory interneurons and their target cells are activated by the same excitatory input, can change a steeply sigmoid I/O curve into a double-sigmoid typical of buffer systems. The addition of an intermediate plateau stabilizes the spiking response over a broad dynamic range of input frequency, ensuring robust integration of noisy synaptic signals. Both the buffered firing rate and its input firing range can be independently and extensively modulated by biologically plausible changes in the weight and number of excitatory synapses on the feed-forward interneuron. By providing a soft switch between essentially digital and analog rate-code, this continuous control of the circuit I/O could dramatically increase the computational power of neuronal integration.

Intersegment interactions and helix-coil transition within the generalized model of polypeptide chains approach

The generalized model of polypeptide chains is extended to describe the helix-coil transition in a system comprised of two chains interacting side-by-side. The Hamiltonian of the model takes into account four possible types of interactions between repeated units of the two chains, i.e., helix-helix, helix-coil, coil-helix, and coil-coil. Analysis reveals when the energy I(hh)+I(cc) of (h-h, c-c) interactions overwhelms the energy I(hc)+I(ch) of mixed (h-c, c-h) interactions, the correlation length rises substantially, resulting in narrowing of the transition interval. In the opposite case, when I(hh)+I(cc)<I(hc)+I(ch), nontrivial behavior of the system is predicted where an intermediate plateau appears on the denaturation curve. For the latter case, calculations of the number of junctions and the average length of helical segments indicate rearrangement of helical segments at the transition point. Conceptual links are established with experimentally oriented theories of Ghosh and Dill [J. Am. Chem. Soc. 131, 2306 (2009)] and Skolnick and Holtzer [Biochemistry 25, 6192 (1986)], providing a potential explanation for both favorable helix formation and disfavored intersegment interactions from the same theoretical perspective.

Methacrylate/acrylate ABA triblock copolymers by atom transfer radical polymerization; their properties and application as a mediator for organically dispersible gold nanoparticles

This investigation reports the preparation of a series of well-defined Poly(methyl methacrylate)-b-poly(hexyl acrylate)-b-poly (methyl methacrylate) (PMMA-b-PHA-b-PMMA) triblock copolymers by Atom Transfer Radical Polymerization (ATRP). Their morphology, dynamic mechanical and tensile properties are thoroughly investigated. Phase separation is observed for all the above-mentioned triblock copolymers, which contain PMMA outer blocks in the molecular weight (Mn) range of 10,000–80,000 and PHA inner blocks with Mn in the range 20,000–40,000. The dynamic mechanical measurements essentially reveal two glass transitions and an intermediate flat rubbery plateau in between. Tensile studies indicate that as the PMMA content increases, there is an increase in tensile strength and decrease in elongation at break, which is the case for most of the thermoplastic elastomers (TPE). Eventually, the as prepared block copolymers (with PMMA content 50–80%) offer to be an effective stabilizer for preparing gold nanoparticle aggregates, the shape and size of which can be modulated by tuning the block copolymer composition. The formation of nanoparticle aggregates and their possible non-covalent interaction with the base polymer has been substantiated by UV–vis analysis, transmission electron microscopy, energy-dispersive X-ray spectroscopy, dynamic light scattering and Fourier transform infrared spectroscopy.

Difference in Steady Shear Flow Viscosity between Polar and Nonpolar Nematic Liquid Crystals in Aromatic Polyesters Derived from VECTRA

Steady shear flow viscosities was measured for nematic liquid crystals (LCs) in the aromatic copolyesters composed of 4-hydroxybenzoic acid (HBA), 6-hydroxy-2-naphthoic acid (HNA), telephthalic acid, and biphenol whose molar contents are 0.73 − x, 0.27 − x, x, and x, respectively. Second harmonic generation (SHG) measurements showed that a SHG-active polar nematic LC formed by poly(HBA/HNA) with x = 0 is altered to a conventional nonpolar nematic LC with an increase in x more than 0.07. The shear-rate dependence of melt viscosity measured for nematic LCs of all the copolymers showed four characteristic regions; a Newtonian plateau in lowest shear-rate region 0 in addition to the well-known three regions, low-shear-rate shear-thinning region I, intermediate Newtonian plateau region II and high-shear-rate shear-thinning region III. The SHG-activity in nematic LCs reflected on the Newtonian plateau region 0. The viscosity of the SHG-active nematic LCs in this region 0 was 10 times higher than that of the non-SHG-active nematic ones. The higher viscosity of the SHG-active nematic LC was connected to the smaller domain size (or larger number of disclinations) estimated by small-angle light scattering. In the nonpolar nematic LC, many disclinations initially formed were easily annihilated because of a coalescence of two disclinations with opposite signs, whereas in the polar nematic LC, such an annihilation hardly occurred because of the polar packing symmetry.

Moving beyond the Intermediate EFL Learning Plateau

Plateau phase is an unavoidable stage which may happen constantly during the process of English language learning. This paper points out the plateau manifestations and causes, it also provides ways of overcoming and shortening the intermediate EFL learning plateau from the learner’s perspective.

Understanding the Two‐Step Spin‐Transition Phenomenon in Iron(II) 1D Chain Materials

Three analogous one dimensional (1D) polymeric iron(II) spin crossover (SCO) materials containing the new ligand 4,6-bis(2',2''-pyridyl)pyrazine (bdpp) have been comprehensively characterised magnetically (thermal and light-induced) and structurally. Within this series are two polymorphs of the formula [Fe(NCS)(2)(bdpp)], 1 and 2 a, which differ magnetically in that phase 1 undergoes a full two-step SCO (T(1/2(1))=135 K and T(1/2(2))=90 K) whereas phase 2 a remains high spin (HS) over all temperatures. The central distinction between these two materials lies in the presence of intermolecular pi-pi interactions generated by the crystal packing in 1, which are absent in 2 a. The isostructural selenocyanate analogue of 2 a, [Fe(NCSe)(2)(bdpp)], 2 b, undergoes a full two-step SCO (T(1/2(1))=200 K and T(1/2(2))=125 K). Structural analyses of 1 and 2 b at a range of temperatures provide deep insight into their two-step SCO nature. Structural analysis of 1 at 25 K (1(LS-LS)), 123 K (1(LS-HS)) and 250 K (1(HS-HS)) reveals two distinct iron(II) centres at each temperature, with ordered, alternating HS and LS (low spin) sites at the intermediate plateau (IP) temperatures. In contrast, structural analysis of 2 b at 90 K (2 b(LS)), 150 K (2 b(LS/HS)) and 250 K (2 b(HS)) reveals one unique iron(II) centre at each temperature with an "averaged" LS/HS character at the IP temperature. Weak planes of diffuse scattering in the single-crystal X-ray diffraction patterns were observed for this phase at 90 and 150 K, indicating that 1D long range ordering of alternating HS/LS iron(II) centres occurs along the 1D coordination chains, but that there is no correlation between chains. The lack of observable diffuse scattering at 250 K suggests that the onset of the 1D structural ordering in the chain direction corresponds to the first step of the SCO and that this structural transition is electronically driven. The photomagnetic properties of both 1 and 2 b have been investigated and show approximately 62 and 53 % photo-excitation of a HS metastable state at low temperatures and T(LIESST) values of 55 and 49 K, respectively. Relaxation studies on the HS fraction in 2 b fitted well to a stretched exponential model with kinetic parameters indicative of weak cooperativity.

Influence of environmental conditions on the interfacial organisation of fengycin, a bioactive lipopeptide produced by Bacillus subtilis

The effect of the environmental conditions both on the behaviour of fengycin at the air-aqueous interface and on its interaction with DPPC was studied using surface pressure–area isotherms and AFM. The ionisation state of fengycin is at the origin of its monolayer interfacial properties. The most organised interfacial arrangement is obtained when fengycin behaves as if having zero net charge (pH 2). In a fully ionised state (pH 7.4), the organisation and the stability of fengycin monolayers depend on the ionic strength in the subphase. This can modulate the surface potential of fengycin and consequently the electrostatic repulsions inside the interfacial monolayer, as well as the lipopeptide interaction with the layer of water molecules forming the air–water interface. Intermolecular interactions of fengycin with DPPC are also strongly affected by the ionisation state of lipopeptide and the surface pressure ( Π) of the monolayer. A better miscibility between both interfacial components is observed at pH 2, while negatively charged lipopeptide molecules are segregated from the DPPC phase. A progressive desorption of fengycin from the interface is observed at pH 7.4 when Π increases while at pH 2, fengycin desorption brutally occurs when Π rises above Π value of the intermediate plateau.

Magnetic and thermal properties of a one-dimensional spin-1 model

We study the one-dimensional S = 1 Blume-Emery-Grifths model. Upon transforming the spin model into an equivalent fermionic model, we provide the exact solution within the Green’s function and equations of motion formalism. We show that the relevant response functions as well as thermodynamic quantities can be determined, in the whole parameters space, in terms of a nite set of local correlators. Furthermore, considering the case of an antiferromagnetic chain with single-ion anisotropy in the presence of an external magnetic eld, we nd three plateaus in the magnetization curve. In the neighborhood of the endpoints of the intermediate plateau, the specic heat shows a double peak structure.