The regularity of pulsar emissions becomes apparent once we reference the pulses' times of arrivals to the inertial rest frame of the solar system. It follows that errors in the determination of ...Earth's position with respect to the solar system barycenter can appear as a time-correlated bias in pulsar-timing residual time series, affecting the searches for low-frequency gravitational waves performed with pulsar-timing arrays. Indeed, recent array data sets yield different gravitational-wave background upper limits and detection statistics when analyzed with different solar system ephemerides. Crucially, the ephemerides do not generally provide usable error representations. In this article, we describe the motivation, construction, and application of a physical model of solar system ephemeris uncertainties, which focuses on the degrees of freedom (Jupiter's orbital elements) most relevant to gravitational-wave searches with pulsar-timing arrays. This model, BayesEphem, was used to derive ephemeris-robust results in NANOGrav's 11 yr stochastic-background search, and it provides a foundation for future searches by NANOGrav and other consortia. The analysis and simulations reported here suggest that ephemeris modeling reduces the gravitational-wave sensitivity of the 11 yr data set and that this degeneracy will vanish with improved ephemerides and with pulsar-timing data sets that extend well beyond a single Jovian orbital period.
We present a mass spectrometry-based method for the identification of cis and trans double-bond isomers within intact complex lipid mixtures using electron impact excitation of ions from organics ...(EIEIO) mass spectrometry. EIEIO involves irradiating singly charged lipid ions with electrons having kinetic energies of 5–16 eV. The resulting EIEIO spectra can be used to discern cis and trans double-bond isomers by virtue of the differences in the fragmentation patterns at the carbon–carbon single bonds neighboring the double bonds. For trans double bonds, these characteristic fragments include unique closed-shell and open-shell (radical) products. To explain this fragmentation pattern in trans double bonds, we have proposed a reaction mechanism involving excitation of the double bond’s π electrons followed by hydrogen atom rearrangement. Several lipid standards were analyzed using the EIEIO method, including mixtures of these standards. Prior to EIEIO, some of the lipid species in these mixtures were separated from their isomeric forms by using differential mobility spectrometry (DMS). For example, mixed cis and trans forms of triacylglycerols and phosphatidylcholines were identified by this DMS–EIEIO workflow. With this combined gas-phase separation and subsequent fragmentation, we could eliminate the need for authentic standards for identification. When DMS could not separate cis and trans isomers completely, as was the case with sphingomyelins, we relied upon the aforementioned diagnostic EIEIO fragment peaks to determine the relative contribution of the trans double-bond isomer in the mixed samples. We also applied the DMS–EIEIO methodology to natural samples extracted from a ruminant (bovine), which serve as common origins of trans fatty acids in a typical Western diet that includes dairy products.
We search for an isotropic stochastic gravitational-wave background (GWB) in the newly released 11 year data set from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). ...While we find no evidence for a GWB, we place constraints on a population of inspiraling supermassive black hole (SMBH) binaries, a network of decaying cosmic strings, and a primordial GWB. For the first time, we find that the GWB constraints are sensitive to the solar system ephemeris (SSE) model used and that SSE errors can mimic a GWB signal. We developed an approach that bridges systematic SSE differences, producing the first pulsar-timing array (PTA) constraints that are robust against SSE errors. We thus place a 95% upper limit on the GW-strain amplitude of AGWB < 1.45 × 10−15 at a frequency of f = 1 yr−1 for a fiducial f−2/3 power-law spectrum and with interpulsar correlations modeled. This is a factor of ∼2 improvement over the NANOGrav nine-year limit calculated using the same procedure. Previous PTA upper limits on the GWB (as well as their astrophysical and cosmological interpretations) will need revision in light of SSE systematic errors. We use our constraints to characterize the combined influence on the GWB of the stellar mass density in galactic cores, the eccentricity of SMBH binaries, and SMBH-galactic-bulge scaling relationships. We constrain the cosmic-string tension using recent simulations, yielding an SSE-marginalized 95% upper limit of G < 5.3 × 10−11-a factor of ∼2 better than the published NANOGrav nine-year constraints. Our SSE-marginalized 95% upper limit on the energy density of a primordial GWB (for a radiation-dominated post-inflation universe) is GWB(f) h2 < 3.4 × 10−10.
To reach the pressures and densities required for ignition, it may be necessary to develop an approach to design that makes it easier for simulations to guide experiments. Here, we report on a new ...short-pulse inertial confinement fusion platform that is specifically designed to be more predictable. The platform has demonstrated 99%+0.5% laser coupling into the hohlraum, high implosion velocity (411 km/s), high hotspot pressure (220+60 Gbar), and high cold fuel areal density compression ratio (>400), while maintaining controlled implosion symmetry, providing a promising new physics platform to study ignition physics.
Few studies have examined, comprehensively and prospectively, determinants of oral-health-related quality of life. The aim of this study was to examine the relationships between psychosocial factors ...and oral health status, health perceptions, and quality of life. Measures of symptom and functional status, health perceptions, quality of life, oral health beliefs, and psychological (sense of coherence, self-esteem, health locus of control) and social factors (parents’ income and education) were collected from 439 12- and 13-year-olds at baseline and six-month follow-up, together with a clinical examination at baseline. Structural equation modeling indicated that increased levels of caries and more symptoms predicted more functional limitations, and, cross-sectionally, greater functional impact was associated with worse health perceptions, which were linked to lower quality of life. Sense of coherence was the most important psychosocial predictor. These factors are important in understanding how oral health affects young people’s daily lives.
The analysis of lipids by mass spectrometry (MS) can provide in-depth characterization for many forms of biological samples. However, such workflows can also be hampered by challenges like low ...chromatographic resolution for lipid separations and the convolution of mass spectra from isomeric and isobaric species. To address these issues, we describe the use of differential mobility spectrometry (DMS) as a rapid and predictable separation technique within a shotgun lipidomics workflow, with a special focus on phospholipids (PLs). These analytes, ionized by electrospray ionization (ESI), are filtered using DMS prior to MS analysis. The observed separation (measured in terms of DMS compensation voltage) is affected by several factors, including the m/z of the lipid ion, the structure of an individual ion, and the presence of chemical modifiers in the DMS cell. Such DMS separations can simplify the analysis of complex extracts in a robust and reproducible manner, independent of utilized MS instrumentation. The predictable separation achieved with DMS can facilitate correct lipid assignments among many isobaric and isomeric species independent of the resolution settings of the MS analysis. This leads to highly comprehensive and quantitative lipidomic outputs through rapid profiling analyses, such as Q1 and MRM scans. The ultimate benefit of the DMS separation in this unique shotgun lipidomics workflow is its ability to separate many isobaric and isomeric lipids that by standard shotgun lipidomics workflows are difficult to assess precisely, for example, ether and diacyl species and phosphatidylcholine (PC) and sphingomyelin (SM) lipids.
Particle acceleration and loss in the million electron Volt (MeV) energy range (and above) is the least understood aspect of radiation belt science. In order to measure cleanly and separately both ...the energetic electron and energetic proton components, there is a need for a carefully designed detector system. The Relativistic Electron-Proton Telescope (REPT) on board the Radiation Belt Storm Probe (RBSP) pair of spacecraft consists of a stack of high-performance silicon solid-state detectors in a telescope configuration, a collimation aperture, and a thick case surrounding the detector stack to shield the sensors from penetrating radiation and bremsstrahlung. The instrument points perpendicular to the spin axis of the spacecraft and measures high-energy electrons (up to ∼20 MeV) with excellent sensitivity and also measures magnetospheric and solar protons to energies well above
E
=100 MeV. The instrument has a large geometric factor (
g
=0.2 cm
2
sr) to get reasonable count rates (above background) at the higher energies and yet will not saturate at the lower energy ranges. There must be fast enough electronics to avert undue dead-time limitations and chance coincidence effects. The key goal for the REPT design is to measure the directional electron intensities (in the range 10
−2
–10
6
particles/cm
2
s sr MeV) and energy spectra (Δ
E
/
E
∼25 %) throughout the slot and outer radiation belt region. Present simulations and detailed laboratory calibrations show that an excellent design has been attained for the RBSP needs. We describe the engineering design, operational approaches, science objectives, and planned data products for REPT.
Lipidomic analyses aim for absolute quantification of lipid species profiles in biological samples. In past years, mass spectrometry (MS) methods based on high resolution accurate masses (HRAM) have ...increasingly been applied to identify and quantify lipid species on the MS level. This strategy requires consideration of isobaric overlaps which may also result from various adduct ions. Generally applied solvent additives favor the formation of protonated and ammoniated ions in positive ion mode, yet sodiated ions are also frequently observed. These sodiated ions interfere with protonated ions of the species of the same lipid class with two additional CH2 and three double bonds (Δm/z = 0.0025) and the first isotopic peak overlaps with ammoniated ions of a species with one additional CH2 and four double bonds (Δm/z = 0.0057). In this work, we present an algorithm based on the sodiated to protonated/ammoniated adduct ion ratios of applied internal standards to correct for these interferences. We could demonstrate that these ratios differ significantly between lipid classes but are affected by neither chain length nor number of double bonds within a lipid class. Finally, the algorithm is demonstrated for correcting human serum samples analyzed by Fourier-transform mass spectrometry (FTMS). Here, the application of sodium correction significantly reduced overestimations and misidentifications.
Since their discovery more than 50 years ago, Earth's Van Allen radiation belts have been considered to consist of two distinct zones of trapped, highly energetic charged particles. The outer zone is ...composed predominantly of megaelectron volt (MeV) electrons that wax and wane in intensity on time scales ranging from hours to days, depending primarily on external forcing by the solar wind. The spatially separated inner zone is composed of commingled high-energy electrons and very energetic positive ions (mostly protons), the latter being stable in intensity levels over years to decades. In situ energy-specific and temporally resolved spacecraft observations reveal an isolated third ring, or torus, of high-energy (>2 MeV) electrons that formed on 2 September 2012 and persisted largely unchanged in the geocentric radial range of 3.0 to ~3.5 Earth radii for more than 4 weeks before being disrupted (and virtually annihilated) by a powerful interplanetary shock wave passage.
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