69 research outputs found
Defining a clade by morphological, molecular, and toxinological criteria: distinctive forms related to Conus praecellens A. Adams, 1854 (Gastropoda: Conidae)
Journal ArticleWe carried out a definition of the Conus praecellens A. Adams, 1854, species group using a combination of comparative morphological data, molecular phylogeny based on standard genetic markers, and toxinological markers. Prior to this work, Conus praecellens was generally postulated to belong to a clade of similarly high-spired, smaller species such as Conus pagodus Kiener, 1845, Conus memiae (Habe and Kosuge, 1970) and Conus arcuatus Broderip and Sowerby, 1829. The molecular phylogeny and toxinological data demonstrate that these earlier hypotheses are incorrect, and that instead, Conus praecellens is in a branch of Conus that includes Conus stupa (Kuroda, 1956), Conus stupella (Kuroda, 1956), Conus acutanguhis Lamarck, 1810, and surprisingly, some species that are morphologically strikingly different, Conus mitratus Sowerby, 1870, and Conus cilindraceus Broderip and Sowerby, 1830. A more careful analysis of the morphologically diverse forms assigned to Conus praecellens suggests that from the Philippine material alone, there are at least three additional species new to science, Conus andremenezi, Conus miniexcclsus, and Conus rizali
Using Wave-Packet Interferometry to Monitor the External Vibrational Control of Electronic Excitation Transfer
We investigate the control of electronic energy transfer in molecular dimers
through the preparation of specific vibrational coherences prior to electronic
excitation, and its observation by nonlinear wave-packet interferometry.
Laser-driven coherent nuclear motion can affect the instantaneous resonance
between site-excited electronic states and thereby influence short-time
electronic excitation transfer (EET). We first illustrate this control
mechanism with calculations on a dimer whose constituent monomers undergo
harmonic vibrations. We then consider the use of nonlinear wave-packet
interferometry (nl-WPI) experiments to monitor the nuclear dynamics
accompanying EET in general dimer complexes following impulsive vibrational
excitation by a sub-resonant control pulse (or control pulse sequence). In
measurements of this kind, two pairs of polarized phase-related femtosecond
pulses following the control pulse generate superpositions of coherent nuclear
wave packets in optically accessible electronic states. Interference
contributions to the time- and frequency-integrated fluorescence signal due to
overlaps among the superposed wave packets provide amplitude-level information
on the nuclear and electronic dynamics. We derive the basic expression for a
control-pulse-dependent nl-WPI signal. The electronic transition moments of the
constituent monomers are assumed to have a fixed relative orientation, while
the overall orientation of the complex is distributed isotropically. We include
the limiting case of coincident arrival by pulses within each phase-related
pair in which control-influenced nl-WPI reduces to a fluorescence-detected
pump-probe difference experiment. Numerical calculations of pump-probe signals
based on these theoretical expressions are presented in the following paper
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Multi-Omic Profiling of Melophlus Sponges Reveals Diverse Metabolomic and Microbiome Architectures that Are Non-overlapping with Ecological Neighbors.
Marine sponge holobionts, defined as filter-feeding sponge hosts together with their associated microbiomes, are prolific sources of natural products. The inventory of natural products that have been isolated from marine sponges is extensive. Here, using untargeted mass spectrometry, we demonstrate that sponges harbor a far greater diversity of low-abundance natural products that have evaded discovery. While these low-abundance natural products may not be feasible to isolate, insights into their chemical structures can be gleaned by careful curation of mass fragmentation spectra. Sponges are also some of the most complex, multi-organismal holobiont communities in the oceans. We overlay sponge metabolomes with their microbiome structures and detailed metagenomic characterization to discover candidate gene clusters that encode production of sponge-derived natural products. The multi-omic profiling strategy for sponges that we describe here enables quantitative comparison of sponge metabolomes and microbiomes to address, among other questions, the ecological relevance of sponge natural products and for the phylochemical assignment of previously undescribed sponge identities
GBT Discovery of Two Binary Millisecond Pulsars in the Globular Cluster M30
We report the discovery of two binary millisecond pulsars in the
core-collapsed globular cluster M30 using the Green Bank Telescope (GBT) at 20
cm. PSR J2140-2310A (M30A) is an eclipsing 11-ms pulsar in a 4-hr circular
orbit and PSR J2140-23B (M30B) is a 13-ms pulsar in an as yet undetermined but
most likely highly eccentric (e>0.5) and relativistic orbit. Timing
observations of M30A with a 20-month baseline have provided precise
determinations of the pulsar's position (within 4" of the optical centroid of
the cluster), and spin and orbital parameters, which constrain the mass of the
companion star to be m_2 >~ 0.1Msun. The position of M30A is coincident with a
possible thermal X-ray point source found in archival Chandra data which is
most likely due to emission from hot polar caps on the neutron star. In
addition, there is a faint (V_555 ~ 23.8) star visible in archival HST F555W
data that may be the companion to the pulsar. Eclipses of the pulsed radio
emission from M30A by the ionized wind from the compact companion star show a
frequency dependent duration (\propto\nu^{-\alpha} with \alpha ~ 0.4-0.5) and
delay the pulse arrival times near eclipse ingress and egress by up to 2-3 ms.
Future observations of M30 may allow both the measurement of post-Keplerian
orbital parameters from M30B and the detection of new pulsars due to the
effects of strong diffractive scintillation.Comment: 10 pages, 6 figures, Submitted to ApJ. This version includes many
recommended modifications, an improved structure, a new author, and a
completely redone optical analysi
Two-Dimensional Stimulated Resonance Raman Spectroscopy of Molecules with Broadband X-ray Pulses
Expressions for the two-dimensional Stimulated x-ray Raman Spectroscopy
(2D-SXRS) signal obtained using attosecond x-ray pulses are derived. The 1D-
and 2D-SXRS signals are calculated for trans-N-methyl acetamide (NMA) with
broad bandwidth (FWHM ~14.2eV, 181 as) pulses tuned to the oxygen and nitrogen
K-edges. Crosspeaks in 2D signals reveal electronic Franck-Condon overlaps
between valence orbitals and relaxed orbitals in the presence of the core hole
Understanding excitation energy transfer in metalloporphyrin heterodimers with different linkers, bonding structures, and geometries through stimulated X-ray Raman spectroscopy
We present simulations of stimulated X-ray Raman (SXRS) signals from covalent porphyrin heterodimers with different linkers, chemical bonding structures and geometries. The signals are interpreted in terms of valence electron wavepacket motion. One- and two-color SXRS signals can jointly indicate excitation energy transfer (EET) between the porphyrin monomers. It is shown that the SXRS signals provide a novel window into EET dynamics in multiporphyrin systems, and can be used as a powerful tool to monitor the subtle chemical environment which affects EET
A Population of Non-Recycled Pulsars Orginating in Globular Clusters
We explore the enigmatic population of long-period, apparently non-recycled
pulsars in globular clusters, building on recent work by Boyles et al (2011).
This population is difficult to explain if it formed through typical core
collapse supernovae, leading many authors to invoke electron capture
supernovae. Where Boyles et al. dealt only with non-recycled pulsars in
clusters, we focus on the pulsars that originated in clusters but then escaped
into the field of the Galaxy due to the kicks they receive at birth. The
magnitude of the kick induced by electron capture supernovae is not well known,
so we explore various models for the kick velocity distribution and size of the
population. The most realistic models are those where the kick velocity is <~
10 km/s and where the number of pulsars scales with the luminosity of the
cluster (as a proxy for cluster mass). This is in good agreement with other
estimates of the electron capture supernovae kick velocity. We simulate a
number of large-area pulsar surveys to determine if a population of pulsars
originating in clusters could be identified as being separate from normal disk
pulsars. We find that the spatial and kinematical properties of the population
could be used, but only if large numbers of pulsars are detected. In fact, even
the most optimistic surveys carried out with the future Square Kilometer Array
are likely to detect < 10% of the total population, so the prospects for
identifying these as a separate group of pulsars are presently poor.Comment: Accepted for publication in ApJ, 23 pages, 3 figures, 6 tables,
corrected typo in affiliation
Eight New Millisecond Pulsars in NGC 6440 and NGC 6441
Motivated by the recent discovery of 30 new millisecond pulsars in Terzan 5,
made using the Green Bank Telescope's S-band receiver and the Pulsar Spigot
spectrometer, we have set out to use the same observing system in a systematic
search for pulsars in other globular clusters. Here we report on the discovery
of five new pulsars in NGC 6440 and three in NGC 6441; each cluster previously
had one known pulsar. Using the most recent distance estimates to these
clusters, we conclude that there are as many potentially observable pulsars in
NGC 6440 and NGC 6441 as in Terzan 5. We present timing solutions for all of
the pulsars in these globular clusters. Four of the new discoveries are in
binary systems; one of them, PSR J1748-2021B (NGC 6440B), has a wide (P_b =
20.5 d) and eccentric (e = 0.57) orbit. This allowed a measurement of its rate
of advance of periastron: 0.00391(18) degrees per year. If due to the effects
of general relativity, the total mass of this binary system is 2.92 +/- 0.20
solar masses (1 sigma), implying a median pulsar mass of 2.74 +/- 0.21 solar
masses. There is a 1 % probability that the inclination is low enough that
pulsar mass is below 2 solar masses, and 0.10 % probability that it is between
1.20 and 1.44 solar masses. If confirmed, this anomalously large mass would
strongly constrain the equation of state for dense matter. The other highly
eccentric binary, PSR J1750-37A, has e = 0.71, and periastron advance of
0.0055(3) degrees per year, implying a total system mass of 1.97 +/-0.15 solar
masses and, along with the mass function, maximum and median pulsar masses of
1.65 and 1.26 solar masses respectively.Comment: Accepted for publication by the Astrophysical Journal. 14 pages in
emulate format, 6 tables, 7 figure
Multiple Core and Vibronic Coupling Effects in Attosecond Stimulated X-Ray Raman Spectroscopy
Attosecond Stimulated X-ray Raman Spectroscopy (SXRS) is a promising technique for investigating molecular electronic structure and photochemical processes with high spatial and temporal resolution. We present a theoretical study of SXRS from multiple core excitation sites of the same element. Two issues are addressed: interference between pathways contributing the signals from different sites; and how nuclear vibrations influence the signals. Taking furan as a model system, which contains two types of carbons Cα and Cβ, we performed time-dependent density functional theory calculations and computed the SXRS signals with two pulses tuned at the carbon K-edge. Our simulations demonstrate that the SXRS signal from the Cα and Cβ sites are non-additive, owing to the significant mixed contributions (Cα 1s excitations by the pump pulse followed by Cβ 1s excitations by the probe, or vice verse). Harmonic vibrations linearly coupled to the electronic transitions are incorporated using the cumulant expansion. The nuclei act as a bath for electronic transitions which accelerate the decay of time-domain signal. The frequency-domain spectrum is modified by a small red shift and high-resolution fine-structure features are introduced
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