Flight-test nacelles

Design modifications for acoustically absorbing flight test nacelles of DC-8 turbofan engin

Constraining the variation of fundamental constants using 18cm OH lines

We describe a new technique to estimate variations in the fundamental constants using 18cm OH absorption lines. This has the advantage that all lines arise in the same species, allowing a clean comparison between the measured redshifts. In conjunction with one additional transition (for example, an HCO$^+$ line), it is possible to simultaneously measure changes in $\alpha$, $g_p$ and $y \equiv m_e/m_p$. At present, only the 1665 MHz and 1667 MHz lines have been detected at cosmological distances; we use these line redshifts in conjunction with those of HI 21cm and mm-wave molecular absorption in a gravitational lens at $z\sim 0.68$ to constrain changes in the above three parameters over the redshift range $0 < z \lesssim 0.68$. While the constraints are relatively weak ($\lesssim$ 1 part in $10^3$), this is the first simultaneous constraint on the variation of all three parameters. We also demonstrate that either one (or more) of $\alpha$, $g_p$ and $y$ must vary with cosmological time or there must be systematic velocity offsets between the OH, HCO$^+$ and HI absorbing clouds.Comment: 5 pages, no figures. Accepted for publication in Phys. Rev. Let

Rotational Feshbach Resonances in Ultracold Molecular Collisions

In collisions at ultralow temperatures, molecules will possess Feshbach resonances, foreign to ultracold atoms, whose virtual excited states consist of rotations of the molecules. We estimate the mean spacing and mean widths of these resonant states, exploiting the fact the molecular collisions at low energy display chaotic motion. As examples, we consider the experimentally relevant molecules O_2, OH, and PbO. The density of s-wave resonant states for these species is quite high, implying that a large number of narrow resonant states will exist.Comment: 4 pages, 2 figure

Cold collisions of OH and Rb. I: the free collision

We have calculated elastic and state-resolved inelastic cross sections for cold and ultracold collisions in the Rb($^1 S$) + OH($^2 \Pi_{3/2}$) system, including fine-structure and hyperfine effects. We have developed a new set of five potential energy surfaces for Rb-OH($^2 \Pi$) from high-level {\em ab initio} electronic structure calculations, which exhibit conical intersections between covalent and ion-pair states. The surfaces are transformed to a quasidiabatic representation. The collision problem is expanded in a set of channels suitable for handling the system in the presence of electric and/or magnetic fields, although we consider the zero-field limit in this work. Because of the large number of scattering channels involved, we propose and make use of suitable approximations. To account for the hyperfine structure of both collision partners in the short-range region we develop a frame-transformation procedure which includes most of the hyperfine Hamiltonian. Scattering cross sections on the order of $10^{-13}$ cm$^2$ are predicted for temperatures typical of Stark decelerators. We also conclude that spin orientation of the partners is completely disrupted during the collision. Implications for both sympathetic cooling of OH molecules in an environment of ultracold Rb atoms and experimental observability of the collisions are discussed.Comment: 20 pages, 16 figure

What effect do substorms have on the content of the radiation belts?

Substorms are fundamental and dynamic processes in the magnetosphere, converting captured solar wind magnetic energy into plasma energy. These substorms have been suggested to be a key driver of energetic electron enhancements in the outer radiation belts. Substorms inject a keV “seed” population into the inner magnetosphere which is subsequently energized through wave-particle interactions up to relativistic energies; however, the extent to which substorms enhance the radiation belts, either directly or indirectly, has never before been quantified. In this study, we examine increases and decreases in the total radiation belt electron content (TRBEC) following substorms and geomagnetically quiet intervals. Our results show that the radiation belts are inherently lossy, shown by a negative median change in TRBEC at all intervals following substorms and quiet intervals. However, there are up to 3 times as many increases in TRBEC following substorm intervals. There is a lag of 1–3 days between the substorm or quiet intervals and their greatest effect on radiation belt content, shown in the difference between the occurrence of increases and losses in TRBEC following substorms and quiet intervals, the mean change in TRBEC following substorms or quiet intervals, and the cross correlation between SuperMAG AL (SML) and TRBEC. However, there is a statistically significant effect on the occurrence of increases and decreases in TRBEC up to a lag of 6 days. Increases in radiation belt content show a significant correlation with SML and SYM-H, but decreases in the radiation belt show no apparent link with magnetospheric activity levels

What effect do substorms have on the content of the radiation belts?

Substorms are fundamental and dynamic processes in the magnetosphere, converting captured solar wind magnetic energy into plasma energy. These substorms have been suggested to be a key driver of energetic electron enhancements in the outer radiation belts. Substorms inject a keV “seed” population into the inner magnetosphere which is subsequently energized through wave-particle interactions up to relativistic energies; however, the extent to which substorms enhance the radiation belts, either directly or indirectly, has never before been quantified. In this study, we examine increases and decreases in the total radiation belt electron content (TRBEC) following substorms and geomagnetically quiet intervals. Our results show that the radiation belts are inherently lossy, shown by a negative median change in TRBEC at all intervals following substorms and quiet intervals. However, there are up to 3 times as many increases in TRBEC following substorm intervals. There is a lag of 1–3 days between the substorm or quiet intervals and their greatest effect on radiation belt content, shown in the difference between the occurrence of increases and losses in TRBEC following substorms and quiet intervals, the mean change in TRBEC following substorms or quiet intervals, and the cross correlation between SuperMAG AL (SML) and TRBEC. However, there is a statistically significant effect on the occurrence of increases and decreases in TRBEC up to a lag of 6 days. Increases in radiation belt content show a significant correlation with SML and SYM-H, but decreases in the radiation belt show no apparent link with magnetospheric activity levels

CAMELS-GB : a large sample, open-source, hydro-meteorological dataset for Great Britain

Data underpins our knowledge and understanding of the hydrological system; they are used to drive, test and evaluate hydrological models and advance our understanding of hydrological processes and dynamics. With the increasing availability of observational datasets, the integration of information from many catchments for data and modelling analyses is becoming increasingly common. The production of new, open source, datasets for large samples of catchments is vital to advance knowledge on hydrological processes and to ensure hydrological research is reusable and reproducible through the use of common datasets and code. However, the availability of open source, large-sample catchment datasets is notably sparse. In this study, we present CAMELS-GB, the first large sample, open-source, hydro-meteorological catchment dataset for Great Britain (GB). CAMELS-GB integrates a wealth of different datasets derived from national, continental and global products based on observational, satellite and modelled data. The dataset consists of hydro-meteorological timeseries, catchment attributes and catchment boundaries for >800 catchments that cover a wide range of climatic, hydrological, landscape and human management characteristics across GB. Long daily timeseries is provided for a range of hydro-meteorological data (including rainfall, potential-evapotranspiration, temperature, radiation, humidity and flow) from 1970-2015 covering several major hydrological events. A comprehensive set of catchment attributes are provided describing a range of catchment characteristics including topography, climate, hydrology, land cover, soils and (hydro)-geology. Importantly, we also derive human impact attributes (including abstraction returns, percentage urban and gauge distance from reservoir), as well as attributes describing the quality of the flow data (including discharge uncertainty estimates and out of bank flow). The dataset and code used to derive the data will be made open source and provided with comprehensive metadata to allow its use in a wide range of hydro-meteorological data and environmental modelling analyses

Experiences of maternity care among women at increased risk of preterm birth receiving midwifery continuity of care compared to women receiving standard care: Results from the POPPIE pilot trial.

BACKGROUND: Midwifery continuity of care models for women at low and mixed risk of complications have been shown to improve women's experiences of care. However, there is limited research on care experiences among women at increased risk of preterm birth. We aimed to explore the experiences of care among women with risk factors for preterm birth participating in a pilot trial (POPPIE) of a midwifery continuity of care model which included a specialist obstetric clinic. METHODS: A total of 334 pregnant women identified at increased risk of preterm birth were randomly allocated to either midwifery continuity of care (POPPIE group) or standard maternity care. Women in both groups were followed up at six-to-eight weeks postpartum and were invited to complete a postnatal survey either online or by post. An equal status exploratory sequential mixed method design was chosen to collect and analyse the quantitative postnatal survey data and qualitative interviews data. The postnatal survey included measures of social support, trust, perceptions of safety, quality of care, control during childbirth, bonding and quality of life. Categorical data were analysed with chi-squared tests and continuous data were analysed with t-tests and/or Mann-Whitney U test to measure differences in measures scores among groups. The qualitative interview data were subjected to a thematic framework analysis. Data triangulation brought quantitative and qualitative data together at the interpretation stage. FINDINGS: A total of 166 women completed the survey and 30 women were interviewed (90 and 16 in POPPIE group; 76 and 14 in standard group). We found survey respondents in the POPPIE group, compared to respondents in the standard group, were significantly more likely to report greater trust in midwives (Mann-Whitney U, p<0.0001), greater perceptions of safety during the antenatal care (t-test, p = 0.0138), have a particular midwife to contact when they needed during their pregnancy (t-test, p<0.0001) and the postnatal period (chi-squared, p<0.0001). They reported increased involvement in decisions regarding antenatal, intrapartum and postnatal care (t-test, p = 0.002; p = 0.008; p = 0.006 respectively); and greater postnatal support and advice about: feeding the baby (chi-squared, p<0.0001), handling, settling and looking after the baby (chi-squared, p<0.0001), baby's health and progress (chi-squared, p = 0.039), their own health and recovery (chi-squared, p = 0.006) and who to contact about any emotional changes (chi-squared, p = 0.005). There were no significant differences between groups in the reporting of perceptions of safety during birth and the postnatal period, concerns raised during labour and birth taken seriously, being left alone during childbirth at a time of worries, control during labour, bonding, social support, and physical and mental health related quality of life after birth. Results from qualitative interviews provided insight and depth into many of these findings, with women in the POPPIE group reporting more positive experiences of bonding towards their babies and more positive physical health postnatally. CONCLUSIONS: Compared with standard maternity care, women at increased risk of PTB who received midwifery continuity of care were more likely to report increased perceptions of trust, safety and quality of care. TRIAL REGISTRATION: ISRCTN (Number: 37733900); UK CRN (ID: 31951)

Exploiting Carbonyl Groups to Control Intermolecular Rhodium-Catalyzed Alkene and Alkyne Hydroacylation

Readily available β-carbonyl-substituted aldehydes are shown to be exceptional substrates for Rh-catalyzed intermolecular alkene and alkyne hydroacylation reactions. By using cationic rhodium catalysts incorporating bisphosphine ligands, efficient and selective reactions are achieved for β-amido, β-ester, and β-keto aldehyde substrates, providing a range of synthetically useful 1,3-dicarbonyl products in excellent yields. A correspondingly broad selection of alkenes and alkynes can be employed. For alkyne substrates, the use of a catalyst incorporating the Ampaphos ligand triggers a regioselectivity switch, allowing both linear and branched isomers to be prepared with high selectivity in an efficient manner. Structural data, confirming aldehyde chelation, and a proposed mechanism are provided

Near-Infrared Classification Spectroscopy: H-band Spectra of Fundamental MK Standards

We present a catalogue of H-band spectra for 85 stars of approximately solar abundance observed at a resolving power of 3000 with the KPNO Mayall 4m FTS. The atlas covers spectral types O7-M5 and luminosity classes I-V as defined on the MK system. We identify both atomic and molecular indices and line-ratios which are temperature and luminosity sensitive allowing spectral classification to be carried out in the H-band. The line ratios permit spectral classification in the presence of continuum excess emission, which is commonly found in pre-main sequence and evolved stars. We demonstrate that with spectra of R = 1000 obtained at SNR > 50 it is possible to derive spectral types within +- 2 subclasses for late-type stars. These data are available electronically through the Astronomical Data Center in addition to being served on the World-Wide-Web.Comment: To appear in the November 20, 1998 issue of ApJ (Volume 508, #1