A simple modification of the Hodgkin and Huxley equations explains type 3 excitability in squid giant axons

The Hodgkin and Huxley (HH) model predicts sustained repetitive firing of nerve action potentials for a suprathreshold depolarizing current pulse for as long as the pulse is applied (type 2 excitability). Squid giant axons, the preparation for which the model was intended, fire only once at the beginning of the pulse (type 3 behaviour). This discrepancy between the theory and experiments can be removed by modifying a single parameter in the HH equations for the K⁺ current as determined from the analysis in this paper. K⁺ currents in general have been described by I_K=g_K(V−E_K), where g_K is the membrane''s K⁺ current conductance and E_K is the K⁺ Nernst potential. However, I_K has a nonlinear dependence on (V−E_K) well described by the Goldman–Hodgkin–Katz equation that determines the voltage dependence of g_K. This experimental finding is the basis for the modification in the HH equations describing type 3 behaviour. Our analysis may have broad significance given the use of I_K=g_K(V−E_K) to describe K⁺ currents in a wide variety of biological preparations.     

Ordre cationique 13 dans les pyrochlores AI(M0,5IAl1,5)F6 (M = Li,Na, K,Rb)

2B^II→M^I + M^III cationic substitution in AB₂X₆ fluopyrochlores leads to A^IM_0.5^IM_1.5^IIIF₆ compounds. Cubic RbNiCrF₆ - type phases with a statistical distribution of M^I and M^III cations are obtained with A  Rb, Cs; M^I  Li; M^III  Fe, Cr, V. Cationic order between M^I and M^III cations along the [111] row leads to rhomboedral phases (M^I  Li, Na, K; M^III  Al; A  Cs), however the CsRb_0.5Al_1.5F₆ compound is hexagonal; these ordered structures may be described as a succession of identical [AlF₄^?] layers and are closely related to the hexagonal tungsten bronze structure.     

Crystal structure and ferroelectric properties of Ca(Cu3−xMx)Ti4O12 (M = Fe and Ni) ceramics

M-substituted Ca(Cu_3−xM_x)Ti₄O₁₂ (CCMTO) ceramics, where M = Fe and Ni, were synthesized and the influence of M substitutions for Cu on the crystal structure and ferroelectric properties of CCMTO ceramics were investigated in this study. From the variations in the lattice parameters of CCMTO ceramics, the solubility limit of Ni substitution for Cu in CaCu_3−xNi_xTi₄O₁₂ (CCNTO) ceramics was x = 0.2, whereas that of CaCu_3−xFe_xTi₄O₁₂ (CCFTO) ceramics was x = 0.05. The crystal structural analysis of CCMTO ceramics revealed that the single phase of CCMTO ceramics belongs to the I23 non-centrosymmetric space group of I23; as a result, the P_r and E_c values of CCFTO ceramics at x = 0.05 were 1.8 μC/cm² and 40 kV/cm, respectively. The ferroelectric behavior of CCMTO ceramics by the M substitutions for Cu may be related to the displacement of a Ti⁴⁺ cation in the TiO₆ octahedra and tilting of the Ti–O–Ti angle because of the non-centrosymmetric space group.     

Inhomogeneous magnetic structure in clean magnetic superconductors

Clean magnetic superconductors are considered in which the phase transition into the ferromagnetic state takes place at a temperature ? in the absence of superconductivity, with ??T _c1, whereT _c1 is the superconducting critical temperature. The exchange and electromagnetic interactions of electrons and localized magnetic moments are taken into account, as well as magnetic anisotropy. We show that below the temperatureT _M≈? in the superconducting state the inhomogeneous magnetic structure of transverse one-dimensional domain type (DS phase) should occur at real values of the exchange interaction and anisotropy. In the DS phase gapless superconductivity is realized at temperatures sufficiently far fromT _M. Here the equilibrium direction of the magnetic structure wave vectorQ can be changed by applying a supercurrent across the sample. The behavior of this DS phase in an external magnetic field is also considered.     

Phase relations in M 2 I O-P2O5-Fe2O3-CaO(CaF2) (MI = Na, K) high-temperature solutions and the structure of Na2.5CaFe1.5(PO4)3

Phase relations in high-temperature solutions of the M ₂ ^I O-P₂O₅-Fe₂O₃-CaO(CaF₂) (M^I = Na, K) systems (M ₂ ^I O/P₂O₅ = 0.7, 1.0, 1.3; Ca/P = 0.3; Ca/Fe = 1.0; Δt = 1000–680°C) have been studied. The nature of the calcium precursor has been shown to influence the phase relations in the multicomponent alkali metal phosphate high-temperature solutions. The synthesized compounds have been characterized by X-ray powder diffraction and IR spectroscopy, and the crystal structure of the new phosphate Na_2.5CaFe_1.5(PO₄)₃ has been determined by single-crystal X-ray structure analysis.     

Experimental investigation of dimension effect on electrical oscillation in planar device based on VO2 thin film

In this paper, we report on an experimental analysis of dimension effect on a room-temperature electrical oscillation in a planar device using vanadium dioxide (VO₂) thin film. We investigate the variation of the oscillation current (I_O) and frequency (f_O) due to the variation of the dimension of the VO₂ devices, i.e., the length and width of the current channel of the device. For five different VO₂ devices with different dimensions, I_O and f_O are observed at room temperature in a simple circuit composed of a dc voltage source and a standard resistor including one of the VO₂ devices. From the experimental investigation, it is concluded that the peak-to-peak amplitude of I_O and f_O decrease with the increase of the length and width of the current channel. This indicates that f_O depends on not only the external source voltage but also the device dimension.     

Nouvelles familles de phases MIMII2Nb3O10 a feuillets “perovskites”

A new series of phases M^ICa₂Nb₃O₁₀ (M^I = Li, Na, K, Rb, Cs, NH₄, Tl) has been prepared and characterized. Their unit cells are tetragonal. The structures consist of treble perovskite sheets interleaved with M^I sheets. According to the M^I nature, the relative displacement of adjacent treble perovskite sheets, parallel to (001) is O, $\text{b}\text{4}$ or $\text{(}\text{a}\text{+}\text{b}\text{)}\text{4}$     

On the role of compression overloads in influencing crack closure and the threshold condition for fatigue crack growth in 7150 aluminum alloy

A study has been made of the effect of single compression cycles on near-threshold fatigue crack propagation in an I/M 7150 aluminum alloy. Based on experiments at a load ratio of R= 0.10 on cracks arrested at the fatigue threshold (δk_th) in under-, peak and overaged microstructures, large compression overload cycles, of magnitude five times the peak tensile load, were found to cause immediate reinitiation of crack growth, even though the applied stress intensity range did not exceed ΔK_th. Following an initial acceleration, subsequent crack advance was observed to take place at progressively decreasing growth rates until rearrest occurred. Such behavior is attributed to measured changes in crack closure which vary the effective near-tip driving force for crack extension (ΔK_eff). Specifically, roughness-induced closure primarily is reduced by the application of compressive cycles via a mechanism involving crack surface abrasion which causes flattening and cracking of fracture surface asperities. Closure, however, is regenerated on subsequent propagation resulting in the rearrest. Such observations provide further confirmation that the existence of a fatigue threshold is controlled principally by the development of crack closure and are discussed in terms of the mechanisms of closure in precipitation hardened alloys.     

Electric-field-induced phase transitions in <001>-oriented PZN-9PT and PMN-35PT single crystals

Effects of a constant electric field (0 < E < 5 kV/cm) on the optical transmission of 91PbZn_1/3Nb_2/3O₃-9PbTiO₃ (PZN-9PT) and 65PbMg_1/3Nb_2/3O₃-35PbTiO₃ (PMN-35PT) single crystals belonging to the morphotropic regions of these solid solution systems have been studied. At temperatures close that of the morphotropic phase transition, the applied electric field induces two new intermediate monoclinic phases (M_a and M_c) in PZN-9PT and a single intermediate monoclinic phase in PMN-35PT crystals. In PMN-35PT, the new phase is inhomogeneous; in PZN-9PT, the transition from M_a to M_c has a continuous character. The E-T phase diagrams for both crystals are constructed. The results are interpreted within the framework of the Devonshire theory of strongly anharmonic crystals.     

Improved DC performance of AlGaN/GaN high electron mobility transistors using hafnium oxide for surface passivation

Improved DC performance of AlGaN/GaN high electron mobility transistors (HEMTs) have been demonstrated using reactive-sputtered hafnium oxide (HfO₂) thin film as the surface passivation layer. Hall data indicate a significant increase in the product of sheet carrier concentration (n_s) and electron mobility (μ_n) in the HfO₂-passivated HEMTs, compared to the unpassivated HEMTs. This improvement in electron carrier characteristics gives rise to a 22% higher I_Dmax and an 18% higher g_mmax in HEMTs with HfO₂ passivation relative to the unpassivated devices. On the other hand, I_gleak of the HEMTs decreases by nearly one order of magnitude when HfO₂ passivation is applied. In addition, drain current is measured in the subthreshold regime. Compared to the unpassivated HEMTs, HfO₂-passivated HEMTs exhibit a much smaller off-state I_D, indicating better turn-off characteristics.     

State of uranophosphates MIPUO6·nH2O (MI = H+, Li+, Na+, K+, Rb+, Cs+, NH 4 + ) in saturated aqueous solutions

The state of uranophosphates M^IPUO₆·nH₂O (M^I = H⁺, Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, NH₄⁺) in aqueous solutions at 25°C was studied. The composition and structure of bottom phases vary depending on the acidity of the equilibrium solutions, which leads to the formation of compounds of different compositions and structures. A physicochemical model of the heterogeneous system M^IPUO₆·nH₂O-aqueous solution was suggested, allowing calculations of the phase diagrams of the bottom phases and equilibrium solutions over them, and also calculations of the equilibrium constants of the heterogeneous reactions occurring in the process.     

Fabrication of n-type Schottky barrier thin-film transistor with channel length and width of 0.1 μm and erbium silicide source/drain

In this paper, a Schottky barrier polycrystalline silicon thin-film transistor (SB TFT) with erbium silicide source/drain is demonstrated using low temperature processes. A low temperature oxide is used for a gate dielectric and the transistor channel is crystallized by a metal-induced lateral crystallization process. An n-type SB TFT shows a normal electrical performance with subthreshold slope of 239 mV/dec, I_ON/I_OFF ratio of 5.8 × 10⁴ and I_ON of 2 μA/µm at V_G = 3 V, V_D = 2.5 V for 0.1 μm device. A process temperature is maintained at less than 600 °C throughout the whole processes. The SB TFT is expected to be a promising candidate for a next system-on-glass technology and an alternative 3D integration technology.     

Quasi‐Hodgkin–Huxley Neurons with Leaky Integrate‐and‐Fire Functions Physically Realized with Memristive Devices

Artificial neurons with functions such as leaky integrate‐and‐fire (LIF) and spike output are essential for brain‐inspired computation with high efficiency. However, previously implemented artificial neurons, e.g., Hodgkin–Huxley (HH) neurons, integrate‐and‐fire (IF) neurons, and LIF neurons, only achieve partial functionality of a biological neuron. In this work, quasi‐HH neurons with leaky integrate‐and‐fire functions are physically demonstrated with a volatile memristive device, W/WO₃/poly(3,4‐ethylenedioxythiophene): polystyrene sulfonate/Pt. The resistive switching behavior of the device can be attributed to the migration of protons, unlike the migration of oxygen ions normally involved in oxide‐based memristors. With multifunctions similar to their biological counterparts, quasi‐HH neurons are advantageous over the reported HH and LIF neurons, demonstrating their potential for neuromorphic computing applications.     

Improvement of Current Density of Different Atmosphere-Sintered Y358 Superconductors

Y₃Ba₅Cu₈O₁₈ (Y358) which is the last family member of YBCO superconducting material was produced by a solid-state reaction technique. During the production process, superconducting samples were sintered in different atmosphere conditions. XRD measurements of the samples were performed. As a result of the measurements, it was seen that the superconducting phase peaks were formed. Hysteresis loops were calculated and analyzed in the framework of a critical state model including the Meissner current. Meissner currents (I _M) were calculated as 0.0062, 0.0037, and 0.0119 for S100, S50, and S0, respectively. It was observed that S50 has the highest critical current density among the other calculated values.     

High-temperature studies of MI(UO2BO3) (MI = Li, Na)

The phase transitions in uranyl borates M^I(UO₂BO₃) (M^I = Li, Na) were studied by high-temperature X-ray diffraction and differential thermal analysis. The thermal expansion coefficients of these compounds were determined. A reversible polymorphous transition, not accompanied by changes in the unit cell symmetry, was revealed in the Li derivative. The thermal expansion coefficients of β-Li(UO₂BO₃) are 3–10 times higher than those of the α-modification, and α_β changes sign and becomes positive. The anisotropy of the thermal expansion of the phases studied is determined by the structure of the layers.     

Quadrature frequency resolved spectroscopy of upconversion photoluminescence in GeGaS:Er<Superscript>3+</Superscript>: I. Determination of energy transfer upconversion parameter

The article presents the formulas of quadrature frequency resolved spectroscopy (QFRS) on the upconversion photoluminescence (UCPL) of rare-earth (RE) doped materials on the general M-level model. The formulas are derived in matrix-equation form with the first-order perturbation on the rate equations at the M energy-levels of RE ion. The QFRS spectra for three different UCPL processes, i.e., the excited state absorption (ESA), energy transfer upconversion (ETU) and photon avalanche (PA) via cross relaxation process (CRP) in a particular case of M?=?3 are demonstrated with the respective salient features of the excitation power dependence. We have measured the QFRS on the UCPL (⁴ S _3/2 → ⁴ I _15/2) by systematically varying Er-doping in Ge_28.1Ga_6.3S_65.6 chalcogenide glass from 0.01 to 0.5 at.% as well as 975 nm excitation power. Thereby the relaxation rates k ₁ at the intermediate level ⁴ I _11/2, k ₂ at the top level ⁴ S _3/2 and ETU parameter w are determined as a function of Er concentration. The UCPL dynamics on the basis of the formulas for the 3-level model is interpreted in terms of the determined parameters.     

Structure and properties of the ordered double perovskites Sr2MWO6 (M = Co,Ni) by sol-gel route

The single-phase double perovskites Sr₂MWO₆ (M = Co, Ni) were prepared by sol-gel method. Crystal Structure, magnetic properties and the morphology of Sr₂CoWO₆ and Sr₂NiWO₆ were investigated. X-ray powder diffraction (XRD) analysis shows single phase structure for Sr₂MWO₆ (M = Co, Ni) without any traces of impurities and the crystal structure of all the samples belongs to the tetragonal I4/m space group. SEM image for Sr₂MWO₆ (M = Co, Ni) indicate that the grains are homogeneous and connect each other very well. The Neel temperature for Sr₂CoWO₆ and Sr₂NiWO₆ are 23 K and 59 K, respectively. Magnetic measurements showed that the magnetic moment in these double perovskites originates mainly from the interactions between Ni ions and Co ions.     

Memory switching of ZnGa2Te4 thin films

Electrical and switching property of amorphous defect chalcopyrite ZnGa₂Te₄ thin films prepared by thermal evaporation technique has been studied. The elemental chemical compositions of the prepared bulk as well as the as-deposited film were determined by means of energy dispersive X-ray spectrometry. X-ray diffraction pattern revealed that the powder compound is polycrystalline and the as-deposited and the annealed films at t _a ≤ 548 K have the amorphous phase, while that the annealed at t ≥ 573 K are polycrystalline with a single phase of a defect chalcopyrite structure similar to that of the synthesized material. The great advantage of this material is the capability to appear in two different phases, the amorphous and the crystalline phases, with rather different electrical properties. Both dynamic and static I–V characteristics and the switching phenomenon at 601 nm are investigated. The threshold switching mechanism was explained by a thermal model of switching, i.e., joule heating with an electrically conducting channel. ZnGa₂Te₄ is good candidate in phase change memory device.     

Anisotropic Magnetocaloric Effect in Single-crystalline Pr0.52Sr0.48MnO3

We report the magnetocaloric effect (MCE) in a Pr_0.52Sr_0.48MnO₃ single crystal estimated from the isothermal magnetization curve using the Maxwell relation. Isothermal magnetization curves are measured over the range 20 K to 320 K where the field was applied parallel (??) and perpendicular (??) to the [110] direction of the perovskite structure with Pbnm space group. A peak in the temperature (T) dependence of magnetic entropy change (??S _M) with a fairly large negative value (???3.3 J/kg?K) is observed at 275 K close to the Curie temperature (T _C) for a change in field of ??H=40 kOe. The ?? and ?? components of ??S _M deviate from each other below ??260 K and an inverse MCE is observed below ??150 K. We note that the Landau theory of phase transitions satisfactorily explains the ??S _M vs T plot around the second-order transition at T _C.     

Methods for calculating stress intensity factors in anisotropic materials: Part I—z = 0 is a symmetric plane

The problem of a crack in general anisotropic material under LEFM conditions is presented. In Part I, three methods are presented for calculating stress intensity factors for various anisotropic materials in which z = 0 is a plane of symmetry. All of the methods employ the displacement field obtained by means of the finite element method. The first one is known as displacement extrapolation and requires the values of the crack face displacements. The other two are conservative integrals based upon the J-integral. One employs symmetric and asymmetric fields to separate the mode I and II stress intensity factors. The second is the M-integral which also allows for calculation of K_I and K_II separately.All of these methods were originally presented for isotopic materials. Displacement extrapolation and the M-integral are extended for orthotropic and monoclinic materials, whereas the J_I- and J_II-integrals are only extended for orthotropic material in which the crack and material directions coincide. Results are obtained by these methods for several problems appearing in the literature. Good to excellent agreement is found in comparison to published values. New results are obtained for several problems.In Part II, the M-integral is extended for more general anisotropies. In these cases, three-dimensional problems must be solved, requiring a three-dimensional M-integral.