Earlier interpretations of P,, travel-times from the extensive quarry-blast observation scheme in western Germanynow supplemented by explosion data from the 1972 Rhinegraben experimenthave been checked and enhanced using the new MOZAIC time-term method. The large data set (762 travel times) continues to require a considerable anisotropy of upper-mantle P velocity. The resulting estimates of the overall velocity variationprobably 0.50-0.60 km/s about a mean value of 8.05 km/s, that is, 6 to 7 per cent anisotropyand of the direction of the maximum velocity (close to 20" E of north) are reasonably reliable. However, the detailed form of the anisotropy is obscured by various limitations of the data.These results allow a realistic assessment of the resolving power of refraction-based studies of velocity anisotropy in the lithosphere. It is concluded that though such studies are probably adequate if the measurement of in situ anisotropy is required within the context of a generalized discussion of lithospheric dynamics they are not appropriate if a detailed specification of the anisotropy is desired.L

High-quality positron lifetime measurements (70 million total counts) are reported for polyethylenes (PEs) of different crystallinities (X c ϭ 3-82%). The specific volumes of the crystalline and amorphous phases (V c and V a , respectively) were estimated from density and wide-angle X-ray scattering (WAXS) experiments. Some samples (those with low values of X c ) were branched PEs, and those with high values of X c were linear PEs for which X c was varied with changes in the crystallization temperature. Both V c and V a increase with decreasing X c in the range 0% Յ X c Յ 56% (the branched PEs) but are constant for X c Ն 56% (the linear PEs). The lifetime spectra were analyzed with the MELT and LIFSPECFIT routines. Artifacts that can appear in the spectrum analysis were checked via an analysis of computer-generated spectra. Four lifetime components appeared in all of the PEs; the two long-lived ones are attributed to pick-off annihilation of ortho-positronium (o-Ps) in crystalline regions ( 3 ) and in holes of the amorphous phase ( 4 ). With increasing X c , 3 decreases from about 1.2 to 1 ns, 4 decreases from 3.0 to 2.5 ns, and the intensity I 4 decreases from 29 to 0%. An increase in I 3 from 6 to 12% was observed. A comparison with simulations shows that the true I 3 value approaches 0 for X c 3 0%. The decrease in I 4 is weaker than the increase in X c ; this leads to the conclusion that the apparent specific o-Ps yield in the amorphous phase I 4 Xc increases with X c . Possible reasons for this surprising results are discussed. The fractional free hole volume [h ϭ (V a Ϫ V occ )/V a , where V occ is the crystalline occupied volume] was estimated from density and WAXS results. Between X c ϭ 0 and 56%, h decreases from 0.151 to 0.090, but it does not change further above X c ϭ 56%. The mean size (v) of the local free volumes (holes) estimated from 4 decreases from 200 to 150 Å 3 . The number density of holes (N h ) calculated from these values (N h ϭ h/v) also decreases from 0.8 to 0.6 nm Ϫ3 in the range 0% Յ X c Յ 56%. The values of V a , V c , h, and N h increase with an increasing degree of branching but do not vary for linear PEs. The possible influence of a crystalline-amorphous interfacial phase (three-phase model) on the observed lifetime parameters is also discussed.

This paper presents those results from the 1974 Lithospheric Seismic Profde in Britain (LISPB) which relate to the compressional velocity structure of the crust and uppermost mantle beneath Northern Britain. A combination of interpretation techniques suitable for modelling laterally inhomogeneous media, including twodimensional ray-tracing and timeterm analysis, has resulted in a detailed seismic cross-section across the Caledonian orogenic belt. The main features of this section are a possible horizontal discontinuity in the Pre-Caledonian' basement, a change in the relationship between the lower crust and the uppermost mantle from north to south and a considerable thickening of the crust beneath the Caledonian fold belt. These results place considerable constraints upon tectonic models for the evolution of the Caledonides in particular in their implication of differing crustal structures north and south of the Southern Uplands and their indication of the primary significance of the Southern Uplands Fault. 44 mantle beneath Northern Britain. D. Barn ford et al .This paper presents LISPB results for the Pvelocity structure of the crust and uppermost 2 The LISPB experiment: data and travel-time correlationsThe LISPB experiment has been fully described in Bamford e l al. (1976) and Kaminski et al. (1976); that part of the experiment relevant to studies of the crust and uppermost mantle beneath Northern Britain in shown in Fig. I(a).In brief, during 1974 July and August, 60 German and British seismic stations (recording three components of ground motion on magnetic tape) occupied at different times the three segments ALPHA, BETA and GAMMA. Shots were fired at the various shotpoints to build up a series of reversed and overlapping crustal profiles (Fig. I@)) with observations out to at least 180 km distance, that is, sufficient for penetration to the Moho. In addition, a local earthquake (at KEQ - Fig. l(a)) was well recorded whilst the stations were occupying segments ALPHA and BETA and a single test profile had been completed in 1973 August using land shotpoint 2 and recording slightly to the east of GAMMA (Fig. l(a)).

No abstract

The size of free-volume holes in neat poly[(ethylene glycol)23dimethacrylate] [poly((EG)23DMA)] and in the same polymer doped with 0.6 mol/kg LiCF3SO3 have been studied as a function of temperature in the range between 100 and 370 K using positron annihilation lifetime spectroscopy. The results are compared with differential scanning calorimetry and ionic conductivity measurements. In both systems, the hole volume νh shows a typical glass-transition behavior, i.e., a small linear increase with temperature below the glass transition temperature Tg and a steeper increase above Tg. From these measurements Tg was estimated to be 233 K (neat polymer) and 240 K (polymer with salt) and the coefficients of the thermal expansion of the hole volume were determined. The fractional free volume (f=0.080) and the number density of holes (Nh=0.6 nm−3) were also estimated. Below Tg the average hole volume of the polymer electrolyte is larger than in the neat polymer. This is consistent with the bulky character of the CF3SO3− anion. Above Tg the salt-doped system shows the lower hole volume of the two systems, probably caused by a reduced segmental mobility as a consequence of the interactions of the Li+ ions with the ethylene oxide units of the polymer. Based on the free-volume theory of Cohen–Turnbull the ionic conductivity σ is correlated with the mean hole volume νh. A linear relation between log(σT 0.5) and 1/νh was observed to be valid for variations of the conductivity over several orders of magnitudes. From these plots critical hole sizes of γν*=0.65 nm3 (neat polymer) and 0.87 nm3 (polymer-salt system) were estimated. The parameters B and T0 of the Vogel–Tamman–Fulcher equation were also determined, as well as the apparent activation volume ΔVapp by pressure-dependent conductivity measurements. The cationic transference number in the polymer-salt system was determined by pulsed field gradient-nuclear magnetic resonance to be t+≈0.3.

Ethylene oxide based polymer electrolytes which exhibit single-ion (cation Li+ or anion ClO4−) and mixed ion (from the dissociation of LiClO4 salt) conduction were studied by employing positron lifetime annihilation spectroscopy (PALS) and conductivity (σ) measurements in the temperature range between 170 and 370 K. We present experimental evidence for the validity of (i) the linear expansion of local free volume from PALS, (ii) the Vogel–Tammann–Fulcher (VTF) law for σ, and (iii) the Cohen–Turnbull equation that relates σ to the local free volume. These were found to be valid in the temperature range above the end (or freezing) temperature of the glass transition, Tge≈1.06TgPALS≈1.18TgDSC [TgPALS and TgDSC are the Tg’s from PALS and differential scanning calorimetry (DSC), respectively]. From VTF fits to σ we obtained a Vogel temperature of T0≈TgDSC and pseudoactivations energies of B=3.7–5.7 kJ/mol. These parameters disagree with many data published in the literature but are in perfect agreement with the free volume experiments. Moreover, we found T0=TgPALS−(20–28) K and TgDSC=TgPALS−(25–27) K. Indications for the existence of two relaxation processes near Tg were observed in the free volume expansion curves, which were attributed to the motion of free polymer segments and those interacting with ions. The discrepancy between TgDSC and TgPALS can be attributed to the two-phase microseparation of the polymer electrolytes; DSC responds mainly to the polymer segments in the ion-depleted regions while PALS responds to the polymer segments in the ion-rich regions. From the Cohen–Turnbull plots the critical hole volume required for an elementary jump of an ion was estimated to be γν*≈1 nm3 and was found to be independent of the type of ion. This shows that each type of ionic conductivity is associated with the same segmental mobility. Below TgePALS the conductivity is larger than expected from the (extrapolated) VTF law, but smaller than displayed in the frozen-in free volume.

Positron annihilation lifetime spectroscopy (PALS), density, and differential scanning calorimetric (DSC) measurements were used to study systematically the variation of the glass‐transition temperature (Tg) and the size v and number density Nh of local free volumes in n‐alkyl‐branched polypropylenes. The samples were metallocene‐catalyzed propylene copolymers with different α‐olefins (from C4 to C16) and a different α‐olefin content (between 0 and 20 mol %). From the total specific volume and crystallinity the specific volume of the amorphous phase Va was estimated and used to calculate the fractional free (hole) volume h and value of Nh. The variations of Tg, v, Va, h, and Nh were related to the degree (number and length) of branching. Tg decreases and v increases linearly with the number and length of n‐alkyl branches. This behavior was attributed to an increased segmental mobility caused by branching. Both values, Tg and v, follow linear master curves as a function of the degree of branching (DB) if this is defined as the number of all side‐chain carbons with respect to a total of 1000 (main‐chain and side‐chain) carbons. Only propylene/1‐butene copolymers deviated from these relations. A linear relation between v and Tg was also found. The number density of holes was estimated to be Nh = 0.49(±0.07) nm−3 and Nh′ = 0.58(±0.11) × 1021 g−1, respectively. It shows a slight variation with the DB, which is also seen in the behavior of the specific volume Va. This variation was explained by the appearance of sterical hindrances resulting from short‐chain branches that may prevent an efficient packing of the chains. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 434–453, 2002; DOI 10.1002/polb.10108

No abstract