High-resolution Fourier-transform emission spectroscopy of the A(1)II-X(1)Σ(+) system of AIH

The emission spectrum of the A(1)II-X(1)Σ(+) system of AIH, excited in a hollow-cathode discharge lamp, has been observed at high resolution with a Fourier-transform spectrometer. The rotational lines in the 0-0 and the 1-1 bands have been measured with a precision of ±0.001 cm(-1). The present measurements provide a considerable improvement overthe previous data of Zeeman and Ritter [Can. J. Phys. 32, 555 (1954)]. The present data, combined with the previous high-resolution measurements of the 1-0 vibration-rotation band by White et al. [J. Chem. Phys. 99, 8371 (1993)] and the J = 1-0 pure rotational line of Goto and Saito [Astrophys. J. 452, L147 (1995)] have been used to determine improved molecular constants for the A(1)!! state.     

TEM investigation of crystallization phenomena in the metallic glass Vitrovac® 0040 (Fe40Ni40B20)

The crystallization behaviour of the amorphous alloy Fe₄₀Ni₄₀B₂₀ was investigated by transmission electron microscopy (TEM) and light microscopy. The three different types of crystals, which occur simultaneously in the temperature range between 355 and 385 C, were formed by time-dependent or athermal nucleation, respectively. The number of such athermally formed nuclei increases with decreasing quench speed, whereas the time-dependent nucleation is not influenced. The linear growth of all three crystal types is likewise independent of the quenching rate. Although the activation energies for growth, E _g, are the same for all three types, there are great differences in growth rates, and therefore the thermal stability against crystallization is controlled by the fastest-growing type of crystal. Furthermore, a mechanical treatment or plastic deformation may produce surface crystallization.     

Isothermal crystallization kinetics of poly(vinylidene fluoride) in the α-phase in the scope of the Avrami equation

Isothermal melt crystallization of poly(vinylidene fluoride) (PVDF) at different crystallization temperatures was studied by differential scanning calorimetry. Analysis by the two different approaches of the Avrami equation was performed: first the classical double logarithmic approximation was used, but a non-linear least squares search showed to clearly improve the fit of the model to the experimental isotherms. The differences found by both methods in the Avrami parameters are discussed. The limitation of the Avrami equation in this polymer has to do not only with the fitting procedure to determine the parameters but also with the lack of a consistent physical interpretation of their temperature evolution. The melting behavior of the samples was analyzed and an equilibrium melting temperature of 190.9 °C was obtained by the Hoffmann–Weeks extrapolation. The samples crystallize in a spherulitic structure, as observed by optical microscopy with polarized light (OMPL). Lauritzen–Hoffmann theory was applied to analyze the crystallization kinetics and the Regime III was found for the crystallization of α-PVDF.     

Structure-property relationships in the case of the degradation of massive poly(α-hydroxy acids) in aqueous media

In order to assess the effects of morphology on the degradation characteristics of high-molecular weight poly(l-lactic acid) (PLA100), specimens of similar sizes were processed by compression moulding and made either amorphous by quenching (PLA100A) or semicrystalline by annealing (PLA100C). PLA100A specimens were allowed to age in iso-osmolar saline and pH 7.4 phosphate buffer at 37° C for periods up to 2 years, whereas PLA100C specimens were studied in the buffer only. Various techniques were used to monitor comparatively the effects of morphology on the mechanism of hydrolytic degradation for these two types of PLA100 specimens: weighing, enzymatic assay, potentiometry, viscoelasticimetry, size-exclusive chromatography, (SEC), X-ray scattering and differential scanning calorimetry. As in the case of non-crystallizable members of the poly(-hydroxy acid) family, degradation was found to proceed more rapidly in the centre than at the surface for both PLA100A and PLA100C specimens. However, the observed multimodal SEC chromatograms have been assigned primarily to differences of degradation rates in amorphous and crystalline domains, regardless of the initial morphology. Indeed, it was found that initially amorphous PLA100A crystallized as degradation proceeded. Furthermore, PLA100A specimens retained mechanical properties for longer than semicrystalline PLA100C specimens, probably because of the sensitivity of the latter to stress and solvent microcracking. When the integrity of the polymer mass was lost, the residual crystalline matter, initially present or formed during degradation, appeared to be very resistant and was still present in a powdered form after 2 years. It is concluded that the morphology is a critical factor for the degradation of PLA100 and that the degradation of bioresorbable devices derived from this polymer should depend very strongly on both the thermal history and the initial crystallinity. The effects of the morphology do not depend significantly on the nature of the ageing medium, provided that the ionic strength is the same.     

Structure-property relationships in the case of the degradation of massive aliphatic poly-(α-hydroxy acids) in aqueous media

A standard protocol is proposed which has been used to study comparatively the degradation mechanism of bioresorbable poly(-hydroxy acids) with respect to macromolecular structural characteristics and solid-state morphologies. As a first approach, the hydrolytic degradation of poly(dl-lactic acid) (PLA50) parallelepipedic specimens (15 mm×10 mm×2 mm), processed by compression moulding and machining, was investigated in two aqueous media: iso-osmolar saline and pH 7.4 phosphate buffer. Various techniques (namely weighing, size-exclusion chromatography (SEC), potentiometry, cryometry and enzymatic assay) have been applied to these specimens in order to monitor the degradation. Data show conclusively that the degradation of massive PLA50 specimens proceeds more rapidly in the centre than at the surface. This feature has been related to the formation of an outer layer of slowly degrading polymer, which is caused by surface phenomena and entraps degrading macromolecules. Only oligomers can diffuse and dissolve in the surrounding media. Accordingly, the number of carboxylic groups present in the inner part of the degrading specimens becomes larger than at the surface and accelerates ester bond cleavage. The resultant autocatalytic mechanism explains well the fact that partially degraded PLA50 exhibits bimodal SEC chromatograms although this polymer is amorphous.     

Evaluation of the potential of the Np(VII)/(VI) couple in acid solutions using the reaction Ag(I) + Np(VII) ⇄ Ag(II) + Np(VI)

The reaction of Np(VII) with Ag(I) was studied by spectrophotometry with the aim to evaluate the potential of the Np(VII)/(VI) couple in acid solutions. In perchloric acid solutions with pH 1.5 and 3.05, the potential E is 1.93 and 1.85 V, respectively. Extrapolation to a solution with pH 0 gives 2.20 ± 0.01 V. A close value (E = 2.22 V) is obtained by extrapolating the potential from a 1 M NaOH solution (pH 13.83, E = 0.582 or 0.587 V) to acid solutions (pH 0).     

Microstructure of the Ductile Phase in Intermetallic Compound Ni_(50)Al_(20)Fe_(30)

The microstructure of the single hot extruded and annealed Ni50Al20Fe30Y0.003 intermetallic compound alloys has been examined by means of high resolution electron microscopy (HREM). In these extruded and annealed alloys. the ductile phase is of a mixture of the disordered fcc γ matrix and or dered γ' precipitates. This fact well interprets the reason why the degree of annealing treatment can influence the strength and ductility of these alloys. The HREM observation revealed directly that there was some strain concentration at γ'-γ interfaces, due to the presence of more iron atoms in these two phases. The fixed orientation relationship between the γ phase and γ' precipitates was identified to be {001}γ{00 }γ' and <100 >γ < 100 > γ'     

The role of silicon in the formation of the (Al5Cu6Mg2) σ phase in Al-Cu-Mg alloys

The role of silicon in the precipitation of the phase (Al₅Cu₆Mg₂) has been investigated through comparative studies on Al-3.63Cu-1.67Mg (wt%) and Al-3.63Cu-1.67Mg-0.5Si alloys. Both alloys were extensively examined after solution treating at 525°C for 2.5 h followed by ageing at 265°C for times up to 650 h. Limited studies were also undertaken on both alloys after ageing at 200 and 305°C. Precipitation of was observed in Al-3.62%Cu-1.66%Mg-0.5%Si for all ageing conditions studied but was absent in Si-free Al-3.62%Cu-1.66%Mg. In addition, S and phases were observed in both alloys. The volume fraction of phase in the Si containing alloy was substantially reduced by a pre-age stretch followed by ageing for 24 h at 265°C with S being the dominant precipitate type. The volume fraction of phase in the Si containing alloy was lower after ageing 24 h at 200°C than after 24 h at 265 and 305°C. Peak hardness was higher for the Si free alloy on ageing at 200 and 265°C, but the Si free alloy softened more rapidly, reflecting the more rapid coarsening kinetics of S compared with .     

Optical properties of tin in the 2.5 to 40μm region

The optical constantsn andk of evaporated tin deposited on different substrates (potassium bromide and mica-sheet discs) were determined in the 2.5 to 40m region by measuring its transmittance. From these values a second step vveacarried out to determine other physical parameters of tin films. These were the density of conduction electrons,N, the effective collision frequency of the electrons ₀ the plasma frequency, ₀, the velocity on the Fermi surface,V ₀ the effective area of the Fermi surface,A _eff, and the absorption coefficient,A. The energy-loss functions for surface and volume plasmons show sharp peak at 7.69m. These values are compared with those found in earlier work.     

Microwave response of Josephson plasma in the mixed state of κ-(BEDT-TTF)2Cu(NCS)2

A cavity perturbation technique is used to measure the magnetic-field dependence of surface impedance at 24 and 41 GHz in superconducting -(BEDT-TTF)₂Cu(NCS)₂ single crystals. A peak structure in the surface resistance R_s(H) is observed (1) below T_c, (2) when microwave electric field is perpendicular to the superconducting layer, and (3) at higher magnetic field for the lower measurement frequency (anticyclotronic behavior). These observations are identified as the Josephson plasma mode. The peak field increases as the temperature is lowered even below the irreversibility line in contrast to the case of Bi₂Sr₂CaCu₂O_8+y.     

Magnetoresistivity in the vortex liquid phase ofκ-(BEDT-TTF)2Cu(NCS)2

We report single crystal magnetoresistivity measurements of the organic superconductor -(BEDT-TTF)₂Cu(NCS)₂ in magnetic fields applied perpendicularly to the superconducting planes. We present an analysis of the behavior of the resistivity in the vortex liquid phase. It turns out, that at high temperatures and sufficiently low fields the vortex liquid phase can be described as a very viscous vortex liquid of 3D vortices with activation energies arising from generations of vortex-doublekinks. Quantitatively a value of the superconducting anisotropy parameter = _ab/_c 80 can be derived from the measurements presented here.     

Anomalous hall conductivity in the vortex state of the organic superconductor κ-(BEDT-TTF)2Cu(NCS)2

Hall effect measurements in the vortex state of the quasi two-dimensional (Q2D) organic superconductor -(BEDT-TTF)₂Cu(NCS)₂ are reported. The sign of the Hall conductivity changes with field and temperature in the vortex state. The Hall conductivity is described as the sum of the two terms resulting from the quasiparticle ( H) and the vortex motion ( 1/H). The sign of the latter term depends on the current direction in Q2D plane. The behavior can be explained by the anisotropic motion of the charged vortex in the anisotropic Q2D plane.The authors would like to thank Professor K. Takanaka and Professor H. Ebisawa for stimulating discussions. This work was carried out at HFLSM, IMR, Tohoku University and partially supported by Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan.     

Extinction efficiency in the infrared (2-18 µm) of laboratory ice clouds: observations of scattering minima in the Christiansen bands of ice

Extinction measurements with a laser diode (0.685 μm) and a Fourier transform infrared spectrometer (2-18 μm) were performed on laboratory ice clouds (5 μm ≤ D ≤ 70 μm) grown at a variety of temperatures, and thus at a variety of crystal habits and average projected crystal area. Ice clouds were grown by nucleation of a supercooled water droplet cloud with a rod cooled with liquid nitrogen. The ice crystals observed were mainly plates and dendrites at the coldest temperatures (≈-15 °C) and were mainly columns and needles at warmer temperatures (≈-5 °C). The crystals were imaged with both a novel microscope equipped with a video camera and a heated glass slide and a continuously running Formvar replicator. The IR spectral optical-depth measurements reveal a narrow (0.5-μm-width) extinction minimum at 2.84 μm and a wider (3-μm-width) minimum at 10.5 μm. These partial windows are associated with wavelengths where the real part of the index of refraction for bulk ice has a relative minimum so that extinction is primarily due to absorption rather than scattering (i.e., the Christiansen effect). Bulk ice has absorption maxima near the window wavelengths. IR extinction efficiency has a noticeable wavelength dependence on the average projected crystal area and therefore on the temperaturedependent crystal properties. The average-size parameters in the visible for different temperatures ranged from 64 to 128, and in the IR they ranged from 2.5 to 44. The extinction efficiency and the single-scatter albedo for ice spheres as computed from Mie scattering also show evidence of the Christiansen effect.     

Formation of Omega-like Nanocrystalline in the Melt-Spun Nd_(85)Al_(15) Alloy by Phase Transformation

Microstructure and subsequent phase transformations on heating of the melt-spun Nd85Al15 alloy have been studied by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. The melt-spun Nd85Al15 alloy shows two-stage transformation processes as follows: amorphous+72 nm supersaturated bcc-Nd(AI) solid solution-7 nm omega-like phase-AlNd3+hexagonal Nd. The activation energies for the first and second transformation were found to be 100 kJ/mol and 188 kJ/mol, respectively. The formation mechanism of nanoscale omega-like phase is discussed.     

Remembrance of Petre T. Frangopol (1933–2020) the promoter of scientometrics in Romania

Scientometrics - The article is an obituary aimed to pay tribute to Petre T. Frangopol, a brilliant Romanian scientist (chemist and biophysicist). He had many fields of interest: Chemistry,...     

Realization of the Temperature Scale in the Range from 234.3 K (Hg Triple Point) to 1084.62°C (Cu Freezing Point) in Croatia

This article describes the realization of the International Temperature Scale in the range from 234.3 K (mercury triple point) to 1084.62°C (copper freezing point) at the Laboratory for Process Measurement (LPM), Faculty of Mechanical Engineering and Naval Architecture (FSB), University of Zagreb. The system for the realization of the ITS-90 consists of the sealed fixed-point cells (mercury triple point, water triple point and gallium melting point) and the apparatus designed for the optimal realization of open fixed-point cells which include the gallium melting point, tin freezing point, zinc freezing point, aluminum freezing point, and copper freezing point. The maintenance of the open fixed-point cells is described, including the system for filling the cells with pure argon and for maintaining the pressure during the realization.     

Effect of (n, γ) and (n, α) reactions of framework atoms on the (n, γ) recoils in Ba and Cs cations in high-silica zeolites

The effects of (n, γ) and (n, α) reactions of framework atoms on the fate of (n, γ) recoil species ¹³¹Ba²⁺ and ¹³⁴Cs⁺ from Ba²⁺ and Cs⁺ loaded in high-silica aluminosilicate and borosilicate zeolites (boron-zeotypes) have been studied. Studies were made of the recoil from “open to locked-in” and “locked-in to open” sites. In open to locked-in recoil, target ions were eluted with efficiencies of 90% where only (n, γ) processes were in operation, but in the presence of (n, γ) and (n, α) reactions, the efficiency fell to 80%. For locked-in to open site recoil, the corresponding efficiencies were in the ranges 50–60% and 40–50%. The effect of calcination temperature on the exchange of cations present was also ascertained. The high-silica zeolites used were synthesized according to published methods and were characterized by XRD, i.r., SEM, and t.g.-d.t.g./d.s.c. techniques, and all were found to be crystalline. In boron-zeotype materials, the magnitude of (n, α) damage was increased by the use of ¹⁰B isotope.     

Evidence for the existence of faulting in a splat-cooled δ-Pu (Ti) alloy

Examination of X-ray diffraction profiles of a splat-cooled 15 Ti-85 Pu alloy has revealed that the material contains a large amount of twinning coupled with a reasonably small crystallite size and high strain. The localized strain is estimated to be 0.6%, the crystallite size 250 Å, and the twinning fault probability is large at 0.043.     

Effect of Gamma Irradiation on the Dielectric Properties of (CH3)2NH2Ga(SO4)2 · 6H2O Crystals in the Vicinity of the Ferroelectric Transition

The effect of gamma irradiation on the dielectric permittivity and loss tangent of (CH₃)₂NH₂Ga(SO₄)₂ · 6H₂O crystals was studied near the ferroelectric transition at different frequencies. Irradiation was found to sharply reduce and tan at gamma doses below 5 × 10⁷ R. At higher doses, and tan level off. With increasing gamma dose, the ferroelectric transition shifts to lower temperatures, irrespective of frequency.