Characterization of acyl chain position in unsaturated phosphatidylcholines using differential mobility-mass spectrometry

Glycerophospholipids (GPs) that differ in the relative position of the two fatty acyl chains on the glycerol backbone (i.e., sn-positional isomers) can have distinct physicochemical properties. The unambiguous assignment of acyl chain position to an individual GP represents a significant analytical challenge. Here we describe a workflow where phosphatidylcholines (PCs) are subjected to ESI for characterization by a combination of differential mobility spectrometry and MS (DMS-MS). When infused as a mixture, ions formed from silver adduction of each phospholipid isomer {e.g., [PC (16:0/18:1) + Ag]+ and [PC (18:1/16:0) + Ag]+} are transmitted through the DMS device at discrete compensation voltages. Varying their relative amounts allows facile and unambiguous assignment of the sn-positions of the fatty acyl chains for each isomer. Integration of the well-resolved ion populations provides a rapid method (\u3c 3 min) for relative quantification of these lipid isomers. The DMS-MS results show excellent agreement with established, but time-consuming, enzymatic approaches and also provide superior accuracy to methods that rely on MS alone. The advantages of this DMS-MS method in identification and quantification of GP isomer populations is demonstrated by direct analysis of complex biological extracts without any prior fractionation

Evidence for Dust Related X-ray Emission from Comet C/1995 O1 (Hale-Bopp)

We report the discovery of X-ray emission from comet C/1995 O1 (Hale-Bopp) by the LECS instrument on-board BeppoSAX on 1996 September 10--11. The 0.1--2.0 keV luminosity decayed by a factor of 2 on a timescale of ~10 hr with a mean value of 5.10E16 erg s-1. The spectrum is well fit by a thermal bremsstrahlung model with a temperature of 0.29 +/- 0.06 keV, or a power-law with a photon index of 3.1 +{0.6} -{0.2}. The lack of detected C and O line emission places severe constraints on many models for cometary X-ray emission, especially those which involve X-ray production in cometary gas. The luminosity is a factor of at least 3.4 greater than measured by Extreme Ultraviolet Explorer (EUVE) 4 days later. This difference may be related to the emergence from the nucleus on 1996 September 9 of a dust-rich cloud. Over the next few days the cloud continued to expand becoming increasingly tenuous, until it had reached an extent of ~3.10E5 km (or ~2 arcmin) by the start of EUVE observation. We speculate that the observed reduction in X-ray intensity is evidence for dust fragmentation. These results support the view that cometary X-ray emission arises from the interaction between solar X-rays and cometary dust.Comment: 17 pages. 4 postscript figs (2 in color). Accepted for publication in ApJ (Letters

GX 339-4: the distance, state transitions, hysteresis and spectral correlations

We study X-ray and variability and distance of GX 339-4. We derive d>7 kpc, based on recent determination of the binary parameters. We study data from the Ginga/ASM, the CGRO/BATSE, and the RXTE/ASM, PCA and HEXTE. From 1987 to 2004, GX 339-4 underwent 15 outbursts and went through all known states of black-hole binaries. We also present the PCA data from the initial stage of the 2004 outburst. We then study colour-colour and colour-flux correlations. In the hard state, there is a strong anticorrelation between the 1.5-5 and 3-12 keV spectral slopes, which we explain by thermal Comptonization of disc photons. There is also a softening of the spectrum above 3 keV with the increasing flux that becomes stronger with increasing energy up to 200 keV. This indicates an anticorrelation between the electron temperature and luminosity, explained by hot accretion models. In addition, we see a variable broad-band slope with a pivot at 200 keV. We confirm the presence of pronounced hysteresis, with the hard-to-soft state transitions occurring at much higher (and variable) luminosities than the soft-to-hard transitions. We fit the ASM data with a model consisting of an outer accretion disc and a hot inner flow. State transitions are associated then with variations in the disc truncation radius, which we fit as 6GM/c^2 in the soft state and several times that in the hard state. The disappearence of the inner disc takes place at a lower accretion rate than its initial appearance due to the dependence of the transitions on the source history. We provide further evidence against the X-ray emission in the hard state being nonthermal synchrotron, and explain the observed radio-X-ray correlation by the jet power being correlated with the accretion power.Comment: MNRAS, in press (a substantially revised version, including new data from the Feb. 2004 outburst of GX 339-4

The X-ray Polarization Probe mission concept

The X-ray Polarization Probe (XPP) is a second generation X-ray polarimeter following up on the Imaging X-ray Polarimetry Explorer (IXPE). The XPP will offer true broadband polarimetery over the wide 0.2-60 keV bandpass in addition to imaging polarimetry from 2-8 keV. The extended energy bandpass and improvements in sensitivity will enable the simultaneous measurement of the polarization of several emission components. These measurements will give qualitatively new information about how compact objects work, and will probe fundamental physics, i.e. strong-field quantum electrodynamics and strong gravity.Comment: submitted to Astrophysics Decadal Survey as a State of the Profession white pape

Diurnal timing of nonmigratory movement by birds: the importance of foraging spatial scales

Timing of activity can reveal an organism's efforts to optimize foraging either by minimizing energy loss through passive movement or by maximizing energetic gain through foraging. Here, we assess whether signals of either of these strategies are detectable in the timing of activity of daily, local movements by birds. We compare the similarities of timing of movement activity among species using six temporal variables: start of activity relative to sunrise, end of activity relative to sunset, relative speed at midday, number of movement bouts, bout duration and proportion of active daytime hours. We test for the influence of flight mode and foraging habitat on the timing of movement activity across avian guilds. We used 64 570 days of GPS movement data collected between 2002 and 2019 for local (non‐migratory) movements of 991 birds from 49 species, representing 14 orders. Dissimilarity among daily activity patterns was best explained by flight mode. Terrestrial soaring birds began activity later and stopped activity earlier than pelagic soaring or flapping birds. Broad‐scale foraging habitat explained less of the clustering patterns because of divergent timing of active periods of pelagic surface and diving foragers. Among pelagic birds, surface foragers were active throughout all 24 hrs of the day while diving foragers matched their active hours more closely to daylight hours. Pelagic surface foragers also had the greatest daily foraging distances, which was consistent with their daytime activity patterns. This study demonstrates that flight mode and foraging habitat influence temporal patterns of daily movement activity of birds.We thank the Nature Conservancy, the Bailey Wildlife Foundation, the Bluestone Foundation, the Ocean View Foundation, Biodiversity Research Institute, the Maine Outdoor Heritage Fund, the Davis Conservation Foundation and The U.S. Department of Energy (DE‐EE0005362), and the Darwin Initiative (19-026), EDP S.A. ‘Fundação para a Biodiversidade’ and the Portuguese Foundation for Science and Technology (FCT) (DL57/2019/CP 1440/CT 0021), Enterprise St Helena (ESH), Friends of National Zoo Conservation Research Grant Program and Conservation Nation, ConocoPhillips Global Signature Program, Maryland Department of Natural Resources, Cellular Tracking Technologies and Hawk Mountain Sanctuary for providing funding and in-kind support for the GPS data used in our analyses

Using X-Ray Polarimetry to Probe the Physics of Black Holes and Neutron Stars

This white paper highlights compact object and fundamental physics science opportunities afforded by high-throughput broadband (0.1-60 keV) X-ray polarization observations. The polarimetric observations can reveal the inner workings of high-energy sources, and allow us to test physical laws in the extreme conditions close to compact objects

Some aspects of feeding and foraging behaviour of three corvids in Newfoundland

Research began with a study of nest predation by a pair of Common Ravens in a colony of cliff-nesting kittiwakes during summer, 1979. Patrols by single ravens were twice as successful as when both birds hunted together. Kittiwake anti-predator defense was important in reducing predation. Results of a cost/benefit analysis suggest that the ravens obtained sufficient prey to meet daily energy requirements. -- A series of feeding and foraging experiments, designed to test several basic assumptions of Optimal Foraging Theory, was carried out between September 1979 and June 1980, using freeliving Gray Jays and Common Crows and artificial prey populations. Both species became more discriminating in bait selection when relative and absolute abundances of profitable baits were increased. When populations of artificial baits consisted of two and three different types, jays differentially selected bait types on the basis of net energy value. Individuals differed in food preference and foraging efficiency. The possible influences of social status and prior experience are discussed. -- Three experiments were designed to induce switching of prey preferences among the jays by decreasing the profitability of a preferred food. Manipulations that produced increases in handling, search, and recognition times caused the jays to switch to an alternate bait, but they were reluctant to take a second alternate that was low in net energy value. Many of these data support current models of Optimal Foraging Theory. -- In a final experiment, a Great Horned Owl decoy was used to disrupt the feeding behaviour of a family of Gray Jays. Differences were found between juveniles and adults in anti-predator behaviour and food preference, juveniles being less cautious in the presence of the decoy and less discriminating in bait preference. Possible reasons for these differences are discussed

Selecting and identifying gas-phase protonation isomers of nicotineH+ using combined laser, ion mobility and mass spectrometry techniques

The detection and assignment of protonation isomers, termed protomers, of gas-phase ions remains a challenge in mass spectrometry. With the emergence of ion-mobility techniques combined with tuneable-laser photodissociation spectroscopy, new experimental combinations are possible to now meet this challenge. In this paper, the differences in fragmentation and electronic spectroscopy of singly protonated (S)-nicotine (nicH+) ions are analysed using action spectroscopy in the ultraviolet region and field asymmetric ion mobility spectrometry (FAIMS). Experiments are supported by quantum chemical calculations (DFT, TD-DFT and CC2) of both spectroscopic and thermochemical properties. Electrospray ionisation (ESI) of (S)-nicotine from different solvents leads to different populations of two nicH+ protomers corresponding to protonation on the pyridine nitrogen and pyrrolidine nitrogen, respectively. FAIMS gives partial resolution of these protomers and enables characteristic product ions to be identified for each isomer as verified directly by analysis of product-ion specific action spectroscopy. It is shown that while characteristic, these product ions are not exclusive to each protomer. Calculations of vertical electronic transitions assist in rationalising the photodissociation action spectra. The integration of photodissociation action spectroscopy with FAIMS-mass spectrometry is anticipated to be a useful approach for separating and assigning protonation isomers of many other small molecular ions