Persistent internal polarizations in poly(ethylene terephthalate) films. III. Cold crystallization

A polarization process, which may be induced in commercial poly(ethylene terephthalate) films by annealing, has been found to exhibit a current peak under zero bias near 120[ddot]C. This process is identified as the “cold crystallization” phenomenon, and involves the simultaneous gauche-to-trans isomerization and paracrystalline ordering of the glycol linkages.     

Thermostimulated creep in amorphous polyolefins. II

The thermostimulated creep of three amorphous polyolefins having the repeating unit ─(CH₂)_mC(CH₃)(C₂ H₅)─, where m = 1, 2, and 3, was investigated from 77° K to 350° K. A broad relaxation process is observed around the glass transition temperature in each polyolefin. The corresponding TSC peaks have been resolved into elementary components with a relaxation time τ obeying a compensation law τ = τ_c exp {(ΔH/k)[1/T) —(1/T_c)], where T_c and T_c are characteristic of the polyolefin. From the TSC data, we have calculated, the mechanical loss peaks associated with the glass transition and we have compared them with the dielectric loss peaks.     

Comparison of two dosage regimens of the substrate for the [13C]methacetin breath test

The [¹³C]methacetin breath test ([¹³C]MBT) – a valuable non-invasive tool dedicated to the assessment of the liver metabolic capacity – still needs standardisation. The aim of this study was to check whether currently used dosage regimens of [¹³C]methacetin provide concordant [¹³C]MBT results in subjects with an atypical body constitution. Healthy volunteers: low body mass<55 kg (eight women), and high body mass>95 kg (eight large body frame men) were recruited. They underwent [¹³C]MBT on separate days, taking in random order [¹³C]methacetin: a fixed 75 mg dose (FX75), or a 1 mg kg^?1 body mass-adjusted dose (BMAD). Samples of expiratory air for ¹³CO₂ measurement were collected over 3 h. The maximum momentary ¹³C elimination in breath air occurred earlier and was higher following BMAD than with FX75 in the low body mass females (T _max 14.6±1.0 min vs. 22.1±2.4 min, p=0.019; D _max 41.9±2.9 % dose h^?1 vs. 36.6±3.6 % dose h^?1, p=0.071). In the high body mass men, T _max remained unchanged, whereas D _max was slightly higher with BMAD compared to FX75 (21.5±3.2 min vs. 23.0±3.0 min; 38.5±2.9 % dose h^?1 vs. 32.3±2.5 % dose h^?1). It is concluded that in subjects with a body constitution outside the general population average, the dosage of the substrate may affect some results of the [¹³C]MBT. The dosage-related differences appear, however, to be insignificant if the result of the [¹³C]MBT is reported as a cumulative ¹³C recovery in breath air.     

Thermally stimulated current and creep of solid amylose

Dielectric and viscoelastic properties of solid amylose were investigated by thermally stimulated current and creep techniques in order to clarify the relation between its structure and properties, and also the different binding modes of water molecules. Several current peaks were observed, and these were decomposed into elementary processes by the fractional polarization technique. A peak at about —110[ddot]C was attributed to the rotational motion around the C5-C6 axis of methylol groups attached to the C5 atom in the glucose residue. A peak at about — 50dGC was attributed to bound water: This peak was eliminated by drying the specimen. A peak at about —230[ddot]C was attributed to another kind of bound water. A peak at about 30[ddot]C was attributed to dehydration during the experiment. Thus, three different relaxation modes of bound water were separated by the present work.     

Beta-decay of even-A neutron-deficient Pr isotopes

Even-A praseodymium activities have been produced and identified in the⁴⁰Ca +^92–96Mo reactions at 5.8 MeV/u:¹²⁶Pr[T_1/2=(3.0 ±0.4)s]¹²⁸Pr[T_1/2=(3.1 ±0.3)s],¹³⁰Pr[T_1/2 =(40.0 ±0.4)s]¹³²Pr[T_1/2=1.6 min]. Several new low-energy levels have been populated in even-even cerium nuclei.     

Comparison of dynamic mechanical relaxation processes at cryogenic temperatures in polyesters

The relaxation behavior of poly (1,4-cyclohexylenedimethylene terephthalate) over the temperature range 4.2[ddot]-300[ddot]K is reported. The trans polymer shows a strong γ relaxation at 175[ddot]K (1 Hz) and a Δ relaxation at 45[ddot]K, whereas the γ and Δ peaks of the cis polymer are at 200[ddot] and 48[ddot]K, respectively. A copolymer of the two isomers shows a composite γ peak which is resolved into two components associated with the trans and cis glycols. A mechanism for the γ peak involving motions of short chain segments is proposed and discussed with reference to the analogous relaxation process in polyethylene terephthalate. The effects of crystallinity and orientation on the γ and Δ relaxations are also considered.     

Elastic constants of solid krypton at T = 77 K determined by inelastic neutron scattering

Long-wavelength acoustic phonons have been studied for each of the [ζ00]T, [ζ00]L, [ζζ0]L and [ζζ0]T₁ branches in solid Kr at T = 77 K by means of inelastic neutron scattering utilizing ‘cold neutrons’ as they are available in the long-wave length tail of the pile spectrum. The raw data have been corrected for resolution effects taking into account the curvature of the dispersion surface and variation of mode eigenvectors. It has turned out, that this yields appreciable shifts of the raw data. The results of our experiment give c₁₁ = 4·25 ± 0·10, c₄₄ = 2·04 ± 0·03, c₁₂ = 2·82 ± 0·12 and a value for B = (c₁₁ + 2c₁₂)/3 = 3·30 ± 0·09 × 10¹⁰ dyne/cm². Available thermodynamic data for Kr gives a derived value for B^ad = 2·58 ± 0·06 × 10¹⁰ dyne/cm² indicating a large difference between zero sound and first sound in solid Kr at high temperatures.     

Deformation behavior of PZN–6%PT single crystal during nanoindentation

The deformation behavior of [001]^T- and [011]^T-cut single crystal solid solution of Pb(Zn_1/3Nb_2/3)O₃–6% PbTiO₃ (PZN–6%PT) in both unpoled and poled states has been investigated by nanoindentation. Nanoindentation experiments reveal that material pile-up and local damage around the indentation impressions are observed at ultra-low loads. These pile-ups and local damage cause a pop-in event (i.e. a sudden increase in displacement at an approximately constant load) in the nanoindentation load–displacement curve (P–h curve). Detailed studies of the relationships between indentation load (P), displacement (h) and harmonic contact stiffness (S) suggest that there is a surface layer, possibly due to crystal fabrication processes, which possesses different mechanical properties from the interior. The thickness of this surface layer is estimated to be approximately 300 nm. Furthermore, it is found that [011]^T-cut crystal is stiffer than [001]^T-cut crystal. On the other hand, both [001]^T- and [011]^T-cut crystals in unpoled state possess lower contact stiffness than poled crystals. This finding suggests that poling improved the mechanical property of the crystal. In summary, poled [001]^T-cut crystals have an elastic modulus of (107 ± 6) GPa and a hardness of (5.1 ± 0.4) GPa. In contrast, the modulus for [011]^T-cut crystals is not constant but increases with indentation depth.     

Amorphous germanium III. Optical properties

The optical properties of thick sputtered films (～30μ) of amorphous Ge, grown with different substrate temperatures (0ˇ-T _sˇ-350°C), were obtained between 0·05 and 4·5 eV by a combination of reflectance, transmittance and ellipsometric measurements. The refractive index at 0·15 eV decreases monotonically with increasing T _s, or equivalently, with increasing density, and is 4·13±0·05 eV in the highest density films. The absorption edge is approximately exponential (10²?α?10⁴ cm^?1) but shifts monotonically to higher energy and increases in slope with increasing T _s. Similarly, the peak in ε₂ grows by about 10% and shifts by about 0·15 eV to higher energies, reaching a maximum of about 23 at 2·90±0·05 eV in the high density films. The peak in the transition strength ω²ε₂ occurs at 4·2±0·2 eV in all films, but increases in magnitude with increasing T _s. The sum rules for n _eff(ω) and ε_0,eff(ω) are evaluated for ▄ω?5 eV and vary monotonically with T _s. These trends are neither compatible with Galeener's void resonance theory nor with changes in the oxygen content of the films, determined by the examination of absorption peaks at 0·053 eV and 0·09 eV. An explanation, suggested here and expanded in I, is based on the observed changes in the structure of the network and voids.     

Neutron diffraction study of magnetic ordering in PrCu2Si2, PrCu2Ge2, PrFe2Ge2 and NdFe2Ge2

A neutron diffraction study of polycrystalline PrCu₂Si₂ [1], PrCu₂Ge₂ [2], PrFe₂Ge₂ [3] and NdFe₂Ge₂ [4] intermetallics carried out at liquid helium temperature shows the presence of a collinear antiferromagnetic order below T_N = 19 ± 1 K [1], T_N = 16 ± 1 K [2], T_N = 9 ± 1 K [3] and 13 ± 1 K [4]. Magnetic moment, parallel to the c-axis is localized on RE ions only. The magnetic structure of these compounds consists of ferromagnetic layers perpendicular to the c-axis coupled antiferromagnetically with sequence +-+- for PrCu₂Si₂ and PrCu₂Ge₂ and +--+ for PrFe₂Ge₂ and NdFe₂Ge₂. The RE moments amount close to the free ion values for Fe containing compounds but are smaller in those containing Cu suggesting a fairly strong influence of crystal field.     

Die isomeren Atomkerne: Yb169m,Yb175m,Yb177m

Short lived isomers of Yb were produced by neutron irradiation of enriched isotopes and have been investigated with the aid of scintillation spectrometers. Yb^169m decays with a half-life ofT _1/2=(46±2) sec emitting only L-radiation. This decay is assumed to be the same as the E 3-transition of 24 keV following the electron capture of Lu¹⁶⁹. Yb^175m [T _1/2=(0,072±0,005) sec] emitsγ-rays of (495±15) keV. The measured K-conversion coefficientα _{K 495}=0,24±0,04 and the total conversion coefficientα _{4 5}=0,6±0,3 indicate the transition to be M3. Yb^177m [T _1/2=(6,4±0,1) sec] decays by a cascade of twoγ-rays. The isomeric (228±3) keV-transition is followed by a (104±1,5) keV-radiation. The measured conversion coefficients areα _{K 228}=4,1±0,4 andα _{K 228}=6,5±0,5 for the first transition andα _{K 104}=0,39±0,05 andα ₁₀₄=0,51±0,05 for the second, indicating a M3-E1-cascade. For the M 3-transition the measured coefficients agree well with those calculated for a nucleus of finite size, but they differ by a factor of 1,5 for the E1-transition.     

Mechanical relaxation in radiation-polymerized vinyl stearate

Mechanical relaxation studies, over the temperature range from about 100[ddot] K to or above the melting point, were performed on unannealed and annealed samples of vinyl stearate, on as-received and purified samples of poly(vinyl stearate), and on a series of radiation-polymerized samples having different monomer-polymer ratios. These latter samples were polymerized in the solid state by exposure of the crystalline monomer to a ⁶⁰Co source and were characterized by density measurements, X-ray diffraction, and differential thermal analysis (DTA). The modulus-temperature and loss-temperature curves of the monomer showed a mechanical relaxation centered at 210[ddot]K (959 Hz) which appeared to decrease toward a limiting value with increase of annealing time. This behavior is similar to that observed in dielectric studies of vinyl stearate. With increase of radiation time and greater conversion to polymer, the magnitude of the 210[ddot] K loss peak increased while the peak position shifted to lower temperatures. The loss-peak is located at 172[ddot] K (864 Hz) in the polymer and is analogous to the γ -relaxation peak in polyethylene in height, breadth, and temperature location. It is attributed to local reorientational motions of (side-chain) —CH₂— segments in disordered or defect regions. X-Ray and DTA data indicate that solid solutions of the monomer and polymer are present in many of the radiation-polymerized samples. The effects of large radiation exposures on the relaxation behavior of the polymer were examined and compared with similar data on polyethylene. The implications of the current data concerning molecular interpretations of the polyethylene relaxations are discussed.     

A.C. electrical conductivity of potassium perchlorate

A.C. electrical conductivity of pottasium perchlorate (KP) has been measured in the temperature range 25–325°C at frequencies ranging from 50–500 Hz using an automated technique. Three regions with activation energies. 1.08 ± 0.02, 0.66 ± 0.01 and 0.39 ± 0.04eV are observed in ln(σT) vs 1/T plots at frequencies < - 50 Hz. Dielectric loss measurements on KP samples doped with CrO₄^2? and SO₄^2? ions show the presence of impurity-vacancy complexes with reorientation energies of 0.99 ±0.02 and 1.07 ± 0.01 eV respectively. The results are interpreted in terms of a defect model which highlights the role of various conduction and relaxation mechanisms in the a.c. electrical properties of the material.     

X and K band ESR study of the Pb Interface centres in thermally oxidized p-type (001)Si wafers at low temperatures and influence of medium-dose As+ ion implantation

Electron spin resonance (ESR) experiments have been carried out at cryogenic temperatures (4.2 ? T ? 35 K) and room temperatures at 9.0 and 20.9 GHz on the P_b0 and P_b1 (commonly referred to as P_b) spin-active defects residing at the Si/SiO₂ interface. The ESR lineshapes were shown to display gaussian characteristics with inhomogeneous line broadenings amounting to 0.7 ± 0.1 and 0.2 ± 0.1 mT at K band for P_b0, and P_b1 respectively, whereas the oscillator strength of both signals followed the paramagnetic law (~ T^?1) down to 4.2 K within experimental error. In general the observed P_b spectrum appeared to have fewer peaks than in other observations, at most displaying two distinguishable lines. Mostly however, only one somewhat broad signal (of measured peak-to-peak linewidth >B_ptp ? 1.5 ± 0.15 mT and g = 2.0058 ± 0.0002 for $\text{\$}\text{?}$B 6 [001] was observed. By fully incorporating ΔB_ptp data for the first time in these observations and using computer simulations, it has been shown that the pervailing experimental spectrum always contains the signals from both kind of centers although mostly these are not separately discernable. Further, it emerged that the actual appearance of the experimental spectra is dirigated by the presence of a distribution of the SiIII unsaturated bond orientations around the ones normally prescribed by the Si crystallinity at the interface. It is found that for both centers this “angle” distribution predominantly occurs vertically with respect to the (001) interface plane. Ion implantation of 10¹⁴ As⁺ cm^?2 at 60 or 80 keV into the oxide layer of the Si/SiO₂ structure is shown to randomize the P_b dangling bond (DB) orientations (resulting in an isotropic g value behavior) but the effect of this is totally eliminated by subsequent annealing at 1000°C in N₂ ambient. It is argued that ESR has become a very sensitive means to study the “purity” of interfacial DB positions with respect to the Si single-crystal prescribed positions and to enable the display of collective fingerprints of the interface defects.     

Structural and magnetic properties of thin epitaxial Fe films on (1 1 0) GaAs prepared by metalorganic chemical vapor deposition

Iron films have been grown on (1 1 0) GaAs substrates by atmospheric pressure metalorganic chemical vapor deposition at substrate temperatures (T_s) between 135°C and 400°C. X-ray diffraction (XRD) analysis showed that the Fe films grown at T_s between 200°C and 330°C were single crystals. Amorphous films were observed at T_s below 200°C and it was not possible to deposit films at T_s above 330°C. The full-width at half-maximum of the rocking curves showed that crystalline qualities were improved at T_s above 270°C. Single crystalline Fe films grown at different substrate temperature showed different structural behaviors in XRD measurements. Iron films grown at T_s between 200°C and 300°C showed bulk α-Fe like behavior regardless of film thickness (100–6400 Å). Meanwhile, Fe films grown at 330°C (144 and 300 Å) showed a biaxially compressed strain between substrate and epilayer, resulting in an expanded inter-planar spacing along the growth direction. Magnetization measurements showed that Fe films (>200 Å) grown at 280°C and 330°C were ferromagnetic with the in-plane easy axis along the [1 1 0] direction. For the thinner Fe films (⩽200 Å) regardless of growth temperature, square loops along the [1 0 0] easy axis were very weak and broad.     

Electron scattering studies of magnetic isovector transitions in 12C at high momentum transfer

The inelastic electron scattering cross sections for the M1 transition to the 15.11 MeV (1⁺, T = 1) level and for the M2 transition to the 16.58 MeV (2^?, T = 1) level in ¹²C have been measured in the momentum transfer region q = 0.4–3.0 fm^?1, with emphasis on precise data at high momentum transfers. Additionally, a broad state near 15.4 MeV excitation has been observed and its excitation energy and natural width have been established as 15.44 ± 0.04 MeV and 1.5 ± 0.2 MeV, respectively. The Fourier-Bessel technique for determining the Mλ transition current density has been applied to the M1 and M2 transitions. Particular attention has been paid to the Coulomb corrections required to deduce the PWBA form factors. The M1 radiative width is Γ_γ0 = 38.5 ± 0.8 eV.     

Kinetic study of the thermoluminescence glow curve of natural dolerite

T _m–T _stop and glow curve deconvolution methods have been used to determine the number of glow peaks and kinetic parameters (activation energy E and frequency factor s) associated with the glow peaks in a natural dolerite. The T _m–T _stop method indicated that the glow curve of the mineral is the superposition of at least seven first-order components, whereas deconvolution analysis indicated the presence of at least eight peaks. A possible reason for this discrepancy is given. The kinetic parameters of the eight peaks are presented and used to estimate the lifetimes of the glow peaks. The lifetimes of the peaks at 120.8 and 143 °C are few days. For application in dosimetry and dating, we suggest the use of a preheat temperature around 170 °C to ensure the complete removal of these peaks with small lifetimes.     

Setting bounds on critical exponents with event-by-event analysis of nuclear fragmentation data

And analysis of recent ISiS data [1] is performed and a comparison with percolation-based theories is conducted. We pay particular attention to detector acceptance corrections as well as the role of sequential decays of excited pre-fragments. The corrected data are subjected to a scaling analysis. We find evidence for a continuous phase transition in these nuclear multi-fragmentation events and extract the value for the critical exponents: σ=0.5±0.1 and τ=2.35±0.05. In addition, we find T _c=8.3±0.2 MeV.     

Dependence of Tg and T ll on tacticity of PMMA by differential scanning calorimetry

A differential scanning calorimeter (DSC) investigation (heating rate 10 K/min) is presented on the multiple transition (relaxation) spectra of PMMA: T_β < T_g; T_g, T_ll > T_g; and T_lρ > T_ll, as a function of tacticity. Specimens are characterized by fractional triad content: isotactic (it-), Xii; syndiotactic (st-), Xss; and atactic (at-), Xis. Values for the seven specimens are it-, 1.0;, at-, 0.495 to 0.750; st-, 0.958. Results on T_β were inconclusive. Our T_g results clarify some discrepancies in the prior literature.

Linear least squares regression analyses give: T_g (°C) = 56.6 + 76.6 Xss (our data) T_g (°C) = 49.1 + 87.3 Xss (our data plus selected literature data)

Extrapolated T_g 's for Xss = 1 are 133.2°C and 136.1°C, respectively, in contrast to Thompson's extrapolated value of 160°C. Similarly T_g(°C) = 99.5 + 71.6 (1?Xii) for our DSC data. The extrapolated T_ll for Xss = 1 is 171.1°C. The intensity of T_ll is high for st-and it-, with a broad minimum over the at-region. A second liquid state process, T_lρ > T_ll, occurs at 149°C for it-, but is above the measured range for at-and st-. T_ll (at-) from DSC compares favorably with reported literature values by a variety of techniques. T_ll and T_lρ at all tacticities agree well with those from a companion study by the thermally stimulated current (TSC) technique on the same group of specimens, as reported elsewhere. This includes the influence of tacticity on intensity. These cross-comparisons by a variety of methods indicate that neither T_ll nor T_lρ is an artifact of our DSC technique. The Frenkel segment-segment contact hypothesis is favored to explain the molecular origin of T_ll Sequences longer than triads may be needed for improved correlations of T_g and T_lρ with tacticity.     

Effect of alcohol consumption on the liver detoxication capacity as measured by [13C]methacetin- and [methyl-13C]methionine-breath tests

The aim of this study was to investigate the hepatic microsomal and mitochondrial functions by using the ¹³CO₂-breath test in healthy subjects either before or after the consumption of red wine. Fourteen adults received [¹³C]methacetin and [methyl-¹³C]methionine together with a standardised dinner. Expired air samples were taken over 6 h. After a wash-out period, the subjects consumed 0.4 ml ethanol/kg/day together with dinner over a 10-day period. Thereafter, ¹³C-tracer administration was repeated under identical conditions. The ¹³CO₂-enrichments were measured by isotope ratio mass spectrometry. The mean cumulative percentage ¹³C-dose recovery (CPDR) after administration of [¹³C]methacetin and [methyl-¹³C]methionine either without or with red wine consumption amounted to 38.2±6.3 vs. 36.3±6.7% (p=0.363) and 9.5±3.3 vs. 8.8±2.5% (p=0.47), respectively. Moderate alcohol consumption does not induce significant short-term changes of the microsomal and the mitochondrial functions of the human liver in healthy subjects.