Determination of the oxidizing ability of HTSC materials containing two elements with a variable degree of oxidation

The presence of mixed valence states of elements is supposed to be a common characteristic feature of the high-T _c superconductors, based on copper oxides. Methods have been suggested for the determination of Cu(III) in the Y-Ba-Cu-O ceramics and separate determination of two oxidants: Bi(V) and Cu(III), Tl(III) and Cu(III) in the corresponding materials. Compounds of Bi(V) oxidize in the ions of Mn(II) to MnO ₄ ⁻ in the acidic medium. Active oxygen, bound to Cu(III) is isolated, not oxidizing Mn(II). MnO ₄ ⁻ is titrated then with a solution of Fe(II) sulphate. For the determination of Tl(III) the sample is dissolved in the acid, Cu(III) is reduced to Cu(II) and Tl(III) is titrated with the hydroquinone solution. The compounds of Bi(V), Tl(III) and Cu(III), having high oxidation-reduction potentials can oxidize the complex Co(II)-EDTA to Co(III)-EDTA. The colour intensity of the latter is proportional to the content of Cu(III) or to the sum of Bi(V) and Cu(III) or Tl(III) and Cu(III). The content of Cu(III) in Bi- and Tl-containing materials is determined by the difference.     

Photochemical Reactions of Neptunium Ions in Aqueous Carbonate Solutions

Photochemical reactions of Np(VI), Np(V), and Np(IV) in aqueous solutions containing HCO₃ ^- and CO₃ ^2- anions were studied spectrophotometrically. Two parallel photoreactions, oxidation of Np(V) to Np(VI) and reduction of Np(VI) to Np(V), were revealed. The quantum efficiency of Np(VI) photoreduction in 1.95 M Na₂CO₃ is 0.003. As the pH of the solution decreases, Np(VI) photoreduction is decelerated and Np(V) photooxidation is accelerated. The photoconversion of Np(V) into Np(VI) in 1 M NaHCO₃ is 94-95%. The presence of oxygen has no effect on the oxidation. Neptunium(IV) is oxidized to Np(V) and Np(VI).     

Congestion, ramp metering and tolls

The cell transmission model of a freeway is used to compare four congestion-reducing schemes: (R) ramp control only; (T) one lane is tolled and ramps are uncontrolled; (B) bottlenecks are tolled and ramps are uncontrolled; and (RB) ramps are controlled and bottlenecks are tolled. In the base case, ramps are uncontrolled and there are no tolls. It is found that (T) is inefficient and may leave all travellers worse off; (R), (B) and (RB) can achieve efficient freeway use; (B) can eliminate queues, but has adverse spatial and equity side effects; (RB) minimizes these side effects. (RB) is likely to be least costly to implement and maintain.     

Extraction of U(VI) and Th(IV) from nitric acid solutions with tetraaryl-substituted (<Emphasis Type="Italic">o</Emphasis>-phenyleneoxymethylene)diphosphine dioxides

Extraction of U(VI) and Th(IV) from HNO₃ solutions in the form of complexes with tetraarylsubstituted (o-phenyleneoxymethylene)diphosphine dioxides is studied. The effect of substituents at the P atoms in the extractant molecule on its extraction ability and selectivity is considered. The stoichiometry of the extractable complexes is determined. The possibility of U(VI) and Th(IV) preconcentration with a complexing sorbent prepared by noncovalent immobilization of tetra-p-tolyl-substituted (o-phenyleneoxymethylene)-diphosphine dioxide on a polymeric matrix is demonstrated.     

Morphology of thermal etch-pits formed on GaP surfaces

The morphology of thermal etch-pits in GaP single crystal surface induced by heating in a low vacuum is investigated. On heating at 950° C, tetrahedral etch-pits with four (1 1 0) facets are formed on the (1 1 0) plane. Etch-pits with (1 0 0), (1 1 0), and (1 1 1) facets are formed at 1000° C, and tetrahedral pits with radiating groove-like pits develop above 1050° C. Trigonal pits with (1 1 0) walls and (1 1 1) bottom are formed on the (1 1 1)_B plane, and hexagonal pits with (1 1 1) and (1 2 1) walls and (0 1 1) bottom are formed on the (1 1 0) cleavage surface. The etch-pit density is about 10⁶ cm^–2 and is independent of heating temperature. The apparent activation energy for etch-pit growth is about 2.2 eV. It is established that dislocation is one of the primary sources of etch-pit formation.     

Electrosynthesis and characterization of a multielectrochromic copolymer of 1,4-bis(2-thienyl)-naphthalene with 2,2′-bithiophene

Electrochemical copolymerization of 1,4-bis(2-thienyl)-naphthalene (BTN) and 2,2′-bithiophene (BT) is carried out in acetonitrile (ACN) containing sodium perchlorate (NaClO₄) as a supporting electrolyte. Cyclic voltammetry (CV), UV-vis and FT-IR analyzes confirm that the resulting polymer is a copolymer rather than a blend or a composite of the respective homopolymers. The obtained P(BTN-co-BT) film exhibits five different colors (orange yellow, yellowish green, green, greenish blue and blue) under various potentials, revealing distinct electrochromic properties from that of the BTN homopolymer film. Maximum contrast (ΔT%) and response time of the copolymer film are measured as 32.7% and 0.59 s at 750 nm. Electrochromic device (ECD) based on P(BTN-co-BT) and poly(3,4-ethylenedioxythiophene) (PEDOT) is also constructed and characterized. This ECD shows a maximum optical contrast (ΔT%) of 24.2% in visible region with a response time of 0.32 s at 780 nm. The coloration efficiency (CE) of the device is calculated to be 308 cm² C⁻¹ at 780 nm.     

Solving optimization problems by searching along a curve

Abstract

This paper proposes a curve for the one‐dimensional search method in optimization problems. The search is along a curve instead of a line. This curve is determined by a parameter [u] from the following three points: (1) the initial point X_o, (2) the Cauchy point X_c, (3) the Newton point X_N, and has the following four characteristics: (1) tangents to the steepest descent direction at X_o, (2) passes through X_N, (3) decreases monotonically from X_o to X_N for a quadratic function, (4) no complex computation on the parameter u. Therefore, the proposed method has the following advantages: (1) it is globally convergent, (2) it is locally q‐quadratically (or q‐superlinearly for quasi‐Newton point) convergent, (3) the search procedure is as simple as the line search method.     

A Novel Zr‐MOF as Fluorescence Turn‐On Probe for Real‐Time Detecting H2S Gas and Fingerprint Identification

The development of fluorescence turn‐on probes for selectively sensing toxic gases and visualization identification of fingerprints is significantly important for society security and human health. Here, Zr is used as the metal center and 1,3,6,8‐tetra (4‐carboxylphenyl) pyrene (TBAPy) and tetrakis(4‐carboxyphenyl)porphyrin (TCPP) as double linkers to synthesize a novel Zr(TBAPy)₅(TCPP) material. Results indicate that Zr(TBAPy)₅(TCPP) can be used as a fluorescence turn‐on probe for highly selective and sensitive detection of H₂S gas and its derivatives S^2? in aqueous solutions with an extremely low concentration (≈1 ppb) and fast response time (<10 s). Moreover, by tailoring the particle size of samples, it is found that Zr(TBAPy)₅(TCPP) can efficiently achieve the visualization identification of fingerprints due to the fluorescence turn‐on effect. All the results indicate that the Zr(TBAPy)₅(TCPP) is a promising multifunctional fluorescence turn‐on probe.     

Carrier Co-doping Method with Size Compensation to Enhance TC of Mn-doped Nitrides

Based on ab initio electronic structure calculations of Mn-doped III–V nitrides (AlN, GaN, InN), a co-doping method with size compensation to enhance the Curie temperature (T_C) of Nitride-based DMS is proposed. Three cases are considered: (1) Single doping: cations are substituted randomly by Mn. (2) One-site co-doping: Cations or anions are substituted by co-dopants. (3) Two-site co-doping: co-dopants are introduced into both cation and anion sites. Be is chosen as co-dopant for (Al, Mn)N and (Ga, Mn)N, and Cd (or C) for (In, Mn)N. Concentrations of co-dopants are chosen as a function of Mn concentration so that the volume distortion caused by Mn doping is reduced. It is found that, by hole co-doping, the ferromagnetism is more stabilized than that in the single doping case. The anti-ferromagnetic super-exchange interaction, which remains dominant for high Mn concentrations in (Al, Mn)N and (Ga, Mn)N due to the small lattice constant, is reduced by co-doping Be into both kinds of sites, resulting in a strong enhancement of T_C in the regime of high Mn-concentrations. Furthermore, as the 3d-partial density of states at the Fermi level gains its maxima, one can expect that T_C reaches its highest value.     

Study on the reduction behavior of CoOOH during the storage of nickel/metal-hydride battery

The storage of nickel/metal-hydride (Ni-MH) battery with co-precipitated cobalt hydroxide and post-added cobalt compound as the additives for pasted Ni(OH)₂ electrode is studied in this paper by using galvanostatic charge–discharge, cyclic voltammetry and X-ray diffraction (XRD). It is shown that (I) capacity loss occurs only on the battery with post-added cobalt compound during the storage; (II) CoOOH derived from co-precipitated cobalt hydroxide has a better stability than the one from post-added cobalt compound and an irreversible reduction of the latter is observed; and (III) an inactive Co + 3O(OH) is obtained from Ni(OH)₂ electrode with post-added cobalt compound after the storage and should be responsible for the property deterioration of Ni-MH battery. Thus, it is important to increase the stability of CoOOH derived from post-added cobalt compound when Ni-MH battery suffers a long-term storage.     

Reduction of Pu(IV) and Np(VI) with carbohydrazide in nitric acid solution

The reduction of Pu(IV) and Np(VI) with carbohydrazide (NH₂NH)₂CO in 1–6 M HNO₃ solutions was studied. The Pu(IV) reduction is described by a first-order rate equation with respect to Pu(IV). At [HNO₃] ≥ 3 M, the reaction becomes reversible. The rate constants of the forward and reverse reactions were determined, and their activation energies were estimated. Neptunium(VI) is reduced to Np(V) at a high rate, whereas the subsequent reduction of Np(V) to Np(IV) is considerably slower and is catalyzed by Fe and Tc ions. The possibility of using carbohydrazide for stabilizing desired combinations of Pu and Np valence states was examined.     

Orientation and growth behavior of CaHfO3 thin films on non-oxide substrates

The growth behavior of CaHfO₃ on (001) Ni and Ge substrates was examined. CaHfO₃ is a perovskite insulator that is suitable for applications as a buffer layer or gate dielectric. The tendency for CaHfO₃ growth on both (001) Ni and (001) Ge substrates is to orient with the CaHfO₃ (200) + (121) planes parallel to the surface, which corresponds to the (110) orientation in the pseudo-cubic geometry. This differs from that of CaHfO₃ on perovskites, such as (001) LaAlO₃, where a pseudo-cube-on-cube orientation is observed.     

Origin of diameter-dependent growth direction of silicon nanowires

A nucleation thermodynamic model was developed to clarify the diameter-dependent crystallographic orientation of silicon nanowires (SiNWs) grown via the vapor-liquid-solid (VLS) mechanism with an Au catalyst. The calculated critical energies (E(r*)) and corresponding critical radii (r*) of the SiNWs with <111> and <110> orientations as a function of Au-catalyst size (D(Au)) revealed that the 110-oriented SiNW with r is preferred below D(Au) = approximately 25 nm, but the preferred direction changes to <111> above D(Au) = approximately 25 nm. The model indicated that the nucleated SiNW with a radius (r) above r is stable and continues to grow until the diameter becomes equal to D(Au) but that the crystallographic orientation is maintained. Thus, the predicted growth direction of the final SiNW with a size of D(Au) is <110> for D(Au) < approximately 25 nm and <111> for D(Au) > approximately 25 nm, which is in excellent agreement with reported experimental results.     

Nuclear Chemical Effects in the Paragenetic Mineral Association Based on Polycrase

A natural polymineral compound in which the major uranium-containing mineral is polycrase (Ti- Ta-niobate) described by the formula АВ₂О₆ was chosen as a model for studying the behavior of recoil atoms produced by α-decay of actinides. Polycrase, despite its metamict structure, is characterized by the following features distinguishing it from Ti-Ta-niobates of the formula А₂В₂О₇ (pyrochlore and betafite): (1) 1/3 of uranium atoms preserve the initial valence state, U(IV); (2) the U(IV) fraction is characterized by the isotope activity ratio AR(²³⁴U/²³⁸U) close to that at secular equilibrium; (3) the uranium atoms that underwent oxidation “memorize” their radiogenic origin; as a result, the AR(²³⁴U/²³⁸U) ratio in the U(VI) fraction is 0.90, and in the most altered part of the mineral it decreases to 0.77; (4) the parent uranium is relatively stable in the metamict structure of polycrase: The half-leaching time for ²³⁸U atoms is 2 times longer than that in betafite, zircon, or sphene.     

New Results for Superconductivity in κ-(BEDT-TTF)2Cu(NCS)2 When an Applied Magnetic Field is Aligned Parallel to the Conducting Planes

Using a Tunnel Diode Oscillator technique, we have measured the effect of a parallel magnetic field on the in-plane rf penetration depths in organic [α- (BEDT-TTF)₂NH₄Hg(SCN)₄ and κ-(BEDT-TTF)₂Cu(NCS)₂] and heavy fermion (CeCoIn₅) superconductors. We show that in this particular ge- ometry, the effects due to vortex activity are minimized. The penetration depth is then governed by the density of superconducting carriers. It is shown in many experiments including rf penetration depth measurement that α-(BEDT-TTF)₂NH₄Hg(SCN)₄ and CeCoIn₅ have s-wave and d-wave pairing symmetries, respectively. The pairing symmetry of κ-(BEDT-TTF)₂-Cu(NCS)₂, however, is still an unsolved matter, showing inconsistent results. In this paper, the penetration depth of κ-(BEDT-TTF)₂Cu(NCS)₂ is shown to be more similar to α-(BEDT-TTF)₂NH₄Hg(SCN)₄ than to CeCoIn₅, suggesting the pairing is nodeless.     

Impregnated activated carbon for the adsorption of Gd(III) radionuclides from aqueous solutions

Activated carbons (ACs) impregnated by FeCl₃, SnCl₄ and ZnCl₂ are used as adsorbents for the removal of Gd(III) radionuclides from aqueous solutions. Adsorption of Gd(III) is investigated as a function of pH, concentration of adsorbate, contact time, ionic strength and temperature. Gadolinium is efficiently removed (R%?>?95%) at pH values ≥4.8 (for FeAC and SnAC) and 2.9 (for ZnAC). The pseudo-first-order, the pseudo-second-order and Elovich kinetic models are used to analyze the kinetic data of Gd(III), at the studied concentrations (30, 100 and 200?mg/L) onto the employed materials. Of these models, Elovich is the only one that well-fitted the experimental kinetics onto the applied materials at all of the studied Gd(III) concentrations. Equilibrium data of Gd(III) are analyzed by the Freundlich, Temkin, Dubnin–Radushkevich (D-R) and Redlich–Petrson isotherm models. The adsorption efficiency of Gd(III) onto FeAC and SnAC is deleteriously affected by increasing the ionic strength, while adsorption onto ZnAC is unaffected. The thermodynamic parameters are calculated and it is revealed that the adsorption of Gd(III) onto the employed materials is an endothermic process. Desorption studies of Gd(III)-loaded ACs are performed using different desorbing agents (HCl, ZnCl₂, FeCl₃ and SnCl₄) at various concentrations (0.0005, 0.0025, 0.01 and 0.025?M).     

Synthesis of SAPO-11 and AIP04-11 molecular sieves in the presence of Cu(ll)

The possible incorporation of Cu(II) into SAPO-11 (CuSAPO-11) and AIPO₄-11 (CuAPO-11) by adding Cu(II) compounds during synthesis in the presence of di-n-propylamine or diisopropylamine templates has been assessed. The location of Cu(ll) is identified by electron spin resonance and electron spin echo modulation spectroscopies. Cu(ll) ions do not incorporate into framework positions of SAPO-11 and AIPO₄-11, i.e., Cu(II) in CuSAPO-11 is located in the same position as Cu(ll) introduced byaqueous ion-exchange and Cu(ll) in CuAPO-11 is located in an extraframework position of AlPO₄-11. It is of ancillary interest that in the presence of Cu(ll) the SAPO-5 phase can be obtained as a major product by varying the temperature and time of crystallization.     

The energy spectra of the secondary ion emission for transition metals of the fourth period

The energy spectra of the secondary ion emission (SIE) for transition metals of the fourth period are calculated under the assumption that SIE is caused by the joint action of electron-exchange and kinetic ion emission (KIE) mechanisms. Some improvement of the KIE theory is carried out for the cases of high (of the order of tens of keV) and low (less than 2 keV) energies E_O of bombarding ions. It is found that the KIE plays an essential role in SIE, starting from the E_O value of the order of tens of keV. It is shown that the KIE energy spectra (1) are broader than the sputtering energy spectra by an order of magnitude, (2) differ essentially in both cases indicated, (3) show a peak (at high E_O in accordance with an experiment) or a break (at low E_O) near to the secondary ion energy corresponding to the KIE threshold.     

Flow boiling of non-azeotropic mixture R32/R1234ze(E) in horizontal microfin tubes

Flow boiling of a potential refrigerant R32/R1234ze(E) in a horizontal microfin tube of 5.21 mm inner diameter is experimentally investigated. The heat transfer coefficient (HTC) and pressure drop are measured at a saturation temperature of 10 °C, heat fluxes of 10 and 15 kW m^?2, and mass velocities from 150 to 400 kg m^?2 s^?1. The HTC of R1234ze(E) is lower than that of R32. Degradation in the HTC of the R32/R1234ze(E) mixture is significant; the HTC is even lower than that of R1234ze(E). The HTC is minimized at the composition 0.2/0.8 by mass, where the temperature glide and the mass fraction distribution are maximized. A predicting correlation based on Momoki et al. (1995) associated with the correction methods of Thome (1981) to consider the mass transfer resistance and Stephan (1992) to consider the additionally required sensible heat is proposed and validated with the experimental results.     

Epitaxial and polycrystalline CuInS2 thin films: A comparison of opto-electronic properties

Epitaxial and polycrystalline thin CuInS₂ (CIS) layers were grown by means of molecular beam epitaxy (MBE) on single crystalline silicon substrates of 4 inch diameter. Photoluminescence (PL) studies were performed to investigate the opto-electronic properties of these layers. For the epitaxial CIS, low-energy-hydrogen implantation leads to the passivation of deep defects and several donor-acceptor (DA) pair recombinations (from 1.034 eV to 1.439 eV) and two free-to-bound (FB) transitions (at 1.436 eV and 1.485 eV) become observable at low temperatures (5 to 100 K). Excitonic luminescence is completely absent for all investigated epitaxial CIS layers. This contrasts sharply with the PL of the polycrystalline films which is dominated by excitonic luminescence (1.527 eV). Also a donor-to-valence band transition at 1.465 eV (BF-1) and one donor-acceptor recombination at 1.435 eV (DA-1) were observed, while luminescence from deep levels is not present at all. Based on these data, a refined defect model for CuInS₂ with two donor and two acceptor states is presented. Under comparable growth conditions, the electronic quality of polycrystalline CIS is superior to epitaxially grown material.