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Notes: Objectives 1. To compare the ultrasound biparietal diameter and crown-rump length of fetuses with and without Down's syndrome in the first half of pregnancy; 2. To investigate the effect of estimation of gestational age using either measure on the detection rate of serum screening for Down's syndrome.Design Matched case-control study. Cases were singleton Down's syndrome pregnancies with a biparietal diameter or a crown-rump length recorded. Five controls were matched to each case on: medical centre; the date of the ultrasound scan examination (within two years); gestational age measured as the number of days since the first day of the last menstrual period; and the ultrasound measure used (ie the biparietal diameter (the measure of choice), or the crown-rump length otherwise). If a woman had a serum screening test for Down's syndrome, the biparietal diameter or crown-rump length measurement had to be taken prior to the screening test so that the result of the test could not influence whether a scan was performed.Setting Ten antenatal screening centres in seven countries in Europe and North America.Subjects Two hundred and one women with singleton Down's syndrome pregnancies and 1005 women with unaffected singleton pregnancies.Results The median biparietal diameter of fetuses with Down's syndrome was identical to that among the controls (median difference 0.0mm, 95% confidence intervals (CI)–0.5 to 0.5mm). The estimates of gestational age based on biparietal diameter yielded a median gestational age less than that based on the women's last menstrual period: three days less for cases and two days less for controls; small but statistically significant differences probably reflected a minor systematic difference in the conversion of a biparietal diameter to a gestational age estimate. The median crown-rump length of fetuses with Down's syndrome was also identical to that among controls (median difference 0.0mm, 95% CI–1.5 to 2.0 mm). There was no significant difference between the median gestational age estimate based on crown-rump length and that based on the women's last menstrual period.Conclusion In antenatal screening for Down's syndrome the routine use of an ultrasound biparietal diameter or crown-rump length measurement to estimate gestational age will not adversely affect the detection rate. To avoid differences in gestational age estimates using the last menstrual period and the biparietal diameter influencing screening performance, separate medians should be derived for each serum marker using the two methods of estimating gestational age. The appropriate set of medians can then be used to calculate the multiple of the median value for each woman screened depending on the method used to estimate her gestational age.

Notes: An extract of the whole brain of the frog Rana ridibunda contained high concentrations of substance P-like immunoreactivity, measured with an antiserum directed against the COOH-terminal region of mammalian substance p and neurokinin b-like immurtoreactivity, measured with an antiserum directed against the NH2-terminus of neurokinin B. The primary structure of the substance p-related peptide (ranakinin) was established as: Lys-Pro-Asn-Pro-Glu-Arg-Phe-Tyr-Gly-Leu-Met-NH2. Mammalian substance P was not present in the extract. The primary structure of the neurokinin b-related peptide was established as: Asp-Met-His-Asp-Phe-Phe-Val-Gly-Leu-Met-NH2. This amino acid sequence is the same as that of mammalian neurokinin B.Ranakinin was equipotent with substance p and [Sar9,-Met(O2)11]substance p in inhibiting the binding of 125I-Bolton-Hunter-[Sar9, Met(O2)11]substance p, a selective radio-ligand for the NK1 receptor, to binding sites in rat subman-dibular gland membranes (IC50 1.6 ± 0.3 nM; n = 5). It is concluded that ranakinin is a preferred agonist for the mammalian NK1 tachykinin receptor subtype.

Notes: In this paper we discuss a novel material which has nearly ideal properties at optical frequencies. It combines the low dissipation of a dielectric with the reflectivity of a metal. This material employs a two-dimensional photonic band gap structure to achieve in-plane confinement of light and uses index contrast to achieve vertical confinement. We discuss how this material can be used to create microcavities for the production of low threshold lasers and waveguides capable of low-loss bends.

Notes: Rate coefficients for the dissociation of Kr+2, N2Ar+, (CO)+2, CH+5, and C2H+5 ions in collisions with He have been obtained in a drift tube experiment as dependent on the mean relative kinetic energy in the center-of-mass frame Ec in the range from 0.1 to 0.5 eV. The Arrhenius activation energies obtained for dissociation are 1.15, 0.91, 1.1–1.3, 1.1–1.4, and 1.3–1.7 eV for Kr+2, N2Ar+, (CO)+2, CH+5, and C2H+5 ions, respectively. For the thermal energy region, the rate coefficients for the same processes have been calculated from three-body association rate coefficients reported in the literature, equilibrium constants, and known thermodynamic quantities. The values of the dissociation rate coefficients obtained cover a range of 15 to 50 orders of magnitude. The present data indicate that the internal temperature Ti of the drifting ions is in close equilibrium with Ec, i.e., Ec=3/2.kBTi.

Notes: Threshold photoelectron–photoion coincidence (TPEPICO), photoion–fluorescence coincidence (PIFCO), and threshold photoelectron–fluorescence coincidence (TPEFCO) spectroscopies have been used to measure, state selectively, the decay pathways of all the valence states of four gas-phase tetrahedral ion CF+4, SiF+4, SiCl+4, and GeCl+4 in the range 11–26 eV. Vacuum UV radiation from a synchrotron source dispersed by a 5 m normal-incidence McPherson monochromator ionizes the parent molecule, and electrons and ions are detected by threshold electron analysis and time-of-flight mass spectrometry, respectively. Undispersed fluorescence from the interaction region can also be detected, allowing the three different types of coincidence experiment to be performed. The optimum resolution of the monochromator is matched to that of the threshold analyzer, and this work improves on preliminary results using a 1 m Seya monochromator [Chem. Phys. 174, 441 and 453 (1993)] where the resolution of the spectra was limited by that of the optical source. TPEPICO spectra are recorded continuously as a function of photon energy, allowing both threshold photoelectron spectra and yields of all the fragment ions to be obtained. Kinetic energy releases can also be measured at fixed photon energies with good time resolution. PIFCO and TPEFCO spectra are recorded at fixed photon energies. The former experiment can yield the fate of the lower electronic state of the parent ion to which fluorescence occurs.The latter experiment yields the lifetime of the fluorescing state; with sufficient resolution of the photoionizing radiation, the lifetime is specific to one vibrational level of the emitting electronic state. For CF+4 and SiF+4 work has concentrated on the third and fourth excited states, C˜ 2T2 and D˜ 2A1, of which only the C˜ state of SiF+4 does not decay radiatively. Vibrationally state-selected fluorescence quantum yields and lifetimes have been measured for four levels of the C˜ state of CF+4, and absolute values of radiative and nonradiative decay rates have been evaluated for these levels. Jahn–Teller distortion of the C˜ state of SiF+4 from Td to C3v geometry assists internal conversion of the C˜ 2T2 state into high vibrational levels of the B˜ 2E state, and is an efficient route for nonradiative decay. A non-Franck–Condon distribution of intensities is observed in the threshold photoelectron spectrum of the D˜ 2A1 state of CF+4, due to autoionization from a high-lying Rydberg state of neutral CF4. For the two chloride molecules, SiCl4 and GeCl4, fragmentation of the ground (X˜) and the first four excited states (A˜–D˜) of the parent ion have been studied at slightly lower resolution. For SiCl+4 an important result is confirmation of the stability of its electronic ground state with respect to dissociation to SiCl+3+Cl. By contrast, a substantial part of the Franck–Condon zone of the ground state of GeCl+4 is energetically unstable with respect to GeCl+3+Cl. Radiative decay from the C˜ 2T2 state of both ions is an important process. The decay dynamics of all the valence states of this family of tetrahedral ions are reviewed. Dynamical, rather than statistical, processes generally dominate, and reasons for these surprising phenomena are discussed. © 1994 American Institute of Physics.

Notes: Objective To investigate the effect of using a routine ultrasound estimate of gestational age and maternal weight adjustment on maternal serum alpha-fetoprotein (AFP), unconjugated oestriol (uE3) and human chorionic gonadotrophin (hCG) levels in antenatal screening for Down's syndrome.Design Women with a singleton pregnancy without Down's syndrome were screened using the three serum markers and an estimate of gestational age based on ‘dates’ (time since first day of the last menstrual period) and one based on an ultrasound scan examination was recorded together with maternal weight.Setting Women attending the Homerton Hospital, Hackney, for their antenatal care between February 1989 and January 1990.Subjects 2113 women with a singleton pregnancy without Down's syndrome.Results The use of ultrasound to estimate gestational age (usually based on the biparietal diameter of the fetal skull) led to a significant reduction in the variance of each marker at a given week of pregnancy. The level of each marker was negatively associated with maternal weight, so that adjustment for weight also led to a reduction in variance. These data on gestational age and maternal weight, taken together with published data on pregnancies associated with Down's syndrome, indicate that the routine use of ultrasound to estimate gestational age will increase the detection rate from 58% to 67% while maintaining the false-positive rate at 5%, or reduce the false-positive rate from 5.7% to 3.1% while maintaining the detection rate at 60%. Routine maternal weight adjustment for the serum marker levels was much less useful, increasing the detection rate by about 0.5% for a given false-positive rate, or reducing the false-positive rate about 0.1% for a given detection rate.Conclusion An ultrasound gestational age estimate available at the time of Down's syndrome screening confers a substantial advantage to screening performance with a further small benefit resulting from maternal weight adjustment, which is worth adopting if it can be done without difficulty or extra cost.