No abstract

Blood velocity in the umbilical artery, fetal descending aorta and fetal middle cerebral artery was recorded by means of 3.5 MHz pulsed Doppler ultrasound in 22 normal pregnancies. The measurements were performed longitudinally between 25 and 42 weeks of gestation. The maximum blood velocity curves were analysed for pulsatility index (PI), systolic/diastolic velocity ratio (S/D ratio) and in the middle cerebral artery also for the resistance index according to Pourcelot (RI). In the umbilical artery, all variables decreased significantly with increasing gestational age as an expression of the decreasing placental vascular resistance. PI in the descending aorta remained fairly constant during the examined period of gestation. In the middle cerebral artery, all three variables (PI, S/D ratio, RI) decreased significantly as gestation advanced. With the exception of the umbilical artery at 28-32 weeks, PI and S/D ratio were not influenced by the heart rate in any of the vessels examined. Diagrams of the gestational age-related reference values (means +/- 2 SD) for the variables of the blood velocity waveforms were established. Additionally, a ratio of the PI and S/D was calculated for the umbilical artery and middle cerebral artery.

The EUGENO‐S seismic profile IV in southern Sweden crossed Lake Mien, a confirmed heavily eroded 121 Ma impact structure. The Lake Mien structure has a pre‐erosion rim diameter of about 9 km. It is located within the Transscandinavian Granite Porphyry Belt (TGPB) near the border between Blekinge and Småland. The compressional‐ and shear‐velocity structure of the upper kilometre of crust in the Lake Mien area was determined using short‐period fundamental‐mode Rayleigh‐wave dispersion and independent P‐ and S‐wave data in a simultaneous inversion. A notable result was the low shear velocities of about 2.65 km s−1 in the upper 0.5 km of crust of the disruption zone (DZ) surrounding the former, now completely eroded crater rim. The disruption diameter was found to be about 17 km along the profile. The normal value of the S‐wave velocity in the TGPB and the upper 0.5 km is 3.2 ± 0.1 km s−1. Inside the crater rim, the shear velocity was about normal, 3.3 ± 0.1 km s−1. However, the ratio of P velocity to S velocity, α/β ≈ 1.66 ± 0.04, was significantly lower than normal.  In the 0.5–2 km layers, the shear velocity was, as expected, lower than normal and α/β was about normal. Known geophysical results were compiled and included in this study (Henkel 1992). The above normal shear velocity and low ratio of α/β were found in the presence of a magnetic anomaly characterized by a central strongly variable field with about normal average, surrounded by a magnetic low. The Bouguer anomaly was characterized by a distinct gravity low of −5 mGal. The source of the gravity low was concentrated close to the centre of the impact within a diameter of about 2 km. It had little influence (less than one standard error) on the average shear velocity across the crater.  An explanation of the observed normal S velocity and the low value of α/β within the crater rim and the upper 0.5 km required consideration of the thermal effects of the impact. The results of the geophysical data and interpretations were discussed in the light of a hot blanket model. It was found that the energy release in the blanket was capable of sustaining hydrothermal flow for a few thousand years, which could be sufficient to explain the above observed normal S velocity and low value of α/β. The heat from the blanket was sufficient to produce temperatures above the Curie temperature over a large enough volume to produce a central magnetic anomaly. Knowledge of the depth to the base of this anomaly could be used as a constraint on the impact energy that is independent of the scaling relations.

S U M M A R YUsing short-period Rayleigh-wave dispersion data recorded along refraction lines, the shear-velocity background structure of the uppermost part of the crystalline in the southern Baltic Shield was found. On a regional scale the dispersion was grouped into dispersion regions and inverted to shear-velocity models down to about 2-3 km depth. The inferred P-velocity models are given. The models separated naturally into categories in close agreement with the large-scale geology of the area investigated. The regional shear-velocity structure varied strongly over the area and the uppermost few hundred metres of the crust. At deeper levels the structure showed a normal variation. The variation in these uppermost layers could be explained by the variation of seismic velocities with pressure in pre-stressed rock, due to partial closure of crack porosity. As there was no significant sedimentary cover in the area, this superficial layer could be attributed to the weathering layer of crystalline rocks. On a local characteristic horizontal scale of about 6 km, the lateral heterogeneities were studied using the dispersion in the 1.5-2.5 Hz band. With a perturbation method the local variations were mapped into the background shear-velocity structure along the EUGENO-S profile IV array. The local shearvelocity models were constrained to be increasing functions of depth and to satisfy the values and slopes of the known regional dispersion. Most of the 48 models could be mapped using a reference model constructed from the profile IV average model. The models defined a strongly heterogeneous weathering layer with a thickness of 0.4-0.5 km. The uppermost crustal shear background velocities correlated in detail with the local surface geology. The velocities formed two distinct populations composed essentially of granites (population I) and granitic gneisses (population 11) with PI = 3.19 f 0.08 and P,, = 2.84 i 0.15 km s-', respectively. These velocities correspond to an in situ crack-porosity density of 0.1-0.5%.

Successive generations in the nucleon-meson cascade are calculated by means of generating functions. Expected muon spectra at different zenith angles and levels are in excellent agreement with measurements in the 0.2-50 GeV/c momentum range. A functional relation between the absolute value and slope of the primary spectrum and the inelasticity is established. On the average 1.6 intranuclear collisions in an air nucleus are taken into account. The calculated electron and positron content in an unshielded inclined muon telescope is 30%, with 100% detector efficiency. Coupling functions taking into account up to seven generations in the cascade, allowing for the primary composition are calculated. Expected time variations from anisotropies of different angular distributions in inclined meson telescopes at a high latitude station are given. Time characteristics such as expected times of maxima, phase differences and amplitude ratios for the north and south directed telescopes at Kiruna are computed for a variational spectrum of the form Pβ cos Λ, where Λ is the angle between the asymptotic direction and the axis of the anisotropy. The reduction in amplitude due to three dimensional cascading is only 0.4-0.4+2.0%. A peculiar and persistent phase shift in the Kiruna north directed telescope is interpreted as being due to Forbush decreases and temperature effects. The yearly difference vector of the two telescopes over nearly one solar cycle has been analysed. Based on a variational spectrum with β = 0.0 and selected values of the free space amplitude, the phase and upper cut-off Pu of the anisotropy are derived. The variation of Pu with time shows a pronounced solar cycle dependence.