130 research outputs found
Effect of Circadian Rhythmicity on Sensory Reception in Weakly Electric Fish
From the Washington University Office of Undergraduate Research Digest (WUURD), Vol. 12, 05-01-2017. Published by the Office of Undergraduate Research. Joy Zalis Kiefer, Director of Undergraduate Research and Associate Dean in the College of Arts & Sciences; Lindsey Paunovich, Editor; Helen Human, Programs Manager and Assistant Dean in the College of Arts and Sciences Mentor: Bruce Carlso
New Black Hole Spin Values for Sagittarius A* Obtained with the Outflow Method
Six archival Chandra observations are matched with eight sets of radio data
and studied in the context of the outflow method to measure and study the spin
properties of . Three radio and X-ray data sets obtained
simultaneously, or partially simultaneously, are identified as preferred for
the purpose of measuring the spin properties of . Similar
results are obtained with other data sets. Results obtained with the preferred
data sets are combined and indicate a weighted mean value of the spin function
of and dimensionless spin angular momentum of
. The spin function translates into measurements of
the black hole rotational mass, , irreducible mass,
, and spin mass-energy available for extraction, ,
relative to the total black hole dynamical mass, . Weighted mean
values of , , ,
, , and are obtained; of course since . Values obtained for are compared with those obtained for M87 based on the published spin
function which indicate that M87 carries substantially more rotational energy
and spin mass-energy relative to the total (i.e., dynamical) black hole mass,
the irreducible black hole mass, and in absolute terms.Comment: Accepted for publication in MNRAS on October 16, 202
Internal dynamics in the molecular complex of CF3CN and H2O
The rotational spectrum of trifluoroacetonitrile–water complex has been studied by pulsed-nozzle, Fourier transform microwave spectroscopy. Both a-type and b-type transitions have been observed. The rotational constants, centrifugal distortion constants, and the 14N nuclear quadrupole coupling constants have been determined. The complex is T-shaped, with the oxygen atom from the water located 3.135 Å from the carbon atom of CF3 of the trifluoroacetonitrile molecule
Grain boundary and texture evolution of TiB/Ti–2Al–6Sn titanium matrix composite under electroshocking treatment
This work used electroshocking treatment (EST) plus external loading to regulate the microstructure of titanium matrix composites (TMCs). The external loading was 0.3 MPa. After EST plus external loading with 0.3 MPa, the was reduced to 2.53 m in size. The percentage of high angle grain boundaries (HAGBs) in increased first and then decreased. The percent of HAGBs in TiB decreased, mainly due to the introduction of abundant dislocations in the TiB/matrix interface after EST. After EST, the maximum texture strength of TiB decreased from 13.09 to 12.97, and that of decreased from 3.11 to 1.58. After EST under external loading with 0.3 MPa, the maximum texture strength of TiB decreased to 8.10. The orientation of TiB experienced significant variation. TEM results showed that TiB and formed a distorted interface after EST under external loading with 0.3 MPa. The interplanar spacing of TiB and was varied. All results show that the texture of TMCs can be relieved by EST plus external loading with 0.3 MPa. It is mainly attributed to the thermal and athermal effects and the imposed external loads with EST. EST plus external loading provides a new method for manipulating the microstructure of TMCs
Chemoselectivity in Gold(I)-Catalyzed Propargyl Ester Reactions: Insights From DFT Calculations.
Au-catalyzed propargyl ester reactions have been investigated by a comprehensive density functional theory (DFT) study. Our calculations explain the experimental observed chemoselectivity of Au-catalyzed propargyl ester reactions very well by considering all possible pathways both in the absence and presence of 1,2,3-triazole (TA). The "X-factor" of TA is disclosed to have triple effects on this reaction. First of all, it can stabilize and prevent rapid decomposition of the Au catalyst. Secondly, the existence of TA promotes the nucleophilic attack and alters the chemoselectivity of this reaction. Moreover, TA acts as a "relay" to promote the proton transfer
WISDOM Project -- XV. Giant Molecular Clouds in the Central Region of the Barred Spiral Galaxy NGC 5806
We present high spatial resolution ( pc) Atacama Large
Millimeter/sub-millimeter Array CO(2-1) observations of the central
region of the nearby barred spiral galaxy NGC 5806. NGC 5806 has a highly
structured molecular gas distribution with a clear nucleus, a nuclear ring and
offset dust lanes. We identify spatially- and spectrally-resolved giant
molecular clouds (GMCs). These clouds have comparable sizes ()
and larger gas masses, observed linewidths () and
gas mass surface densities than those of clouds in the Milky Way disc. The size
-- linewidth relation of the clouds is one of the steepest reported so far
(), the clouds are on
average only marginally bound (with a mean virial parameter
), and high velocity dispersions
are observed in the nuclear ring. These behaviours are likely due to bar-driven
gas shocks and inflows along the offset dust lanes, and we infer an inflow
velocity of kms and a total molecular gas mass inflow rate
of M yr into the nuclear ring. The observed internal
velocity gradients of the clouds are consistent with internal turbulence. The
number of clouds in the nuclear ring decreases with azimuthal angle downstream
from the dust lanes without clear variation of cloud properties. This is likely
due to the estimated short lifetime of the clouds ( Myr), which
appears to be mainly regulated by cloud-cloud collision and/or shear processes.
Overall, it thus seems that the presence of the large-scale bar and gas inflows
to the centre of NGC 5806 affect cloud properties.Comment: Accepted for publication in MNRAS, 20 pages, 16 figure
WISDOM project -- XVI. SMBH mass in the early-type galaxies NGC0612, NGC1574, and NGC4261 from CO dynamical modelling
We present a CO dynamical estimate of the mass of the super-massive black
hole (SMBH) in three nearby early-type galaxies: NGC0612, NGC1574 and NGC4261.
Our analysis is based on Atacama Large Millimeter/submillimeter Array (ALMA)
Cycle 3-6 observations of the CO(2-1) emission line with spatial
resolutions of pc (). We detect disc-like CO
distributions on scales from pc (NGC1574 and NGC4261) to
kpc (NGC0612). In NGC0612 and NGC1574 the bulk of the gas is
regularly rotating. The data also provide evidence for the presence of a
massive dark object at the centre of NGC1574, allowing us to obtain the first
measure of its mass, M
(1 uncertainty). In NGC4261, the CO kinematics is clearly dominated by
the SMBH gravitational influence, allowing us to determine an accurate black
hole mass of M (
uncertainty). This is fully consistent with a previous CO dynamical estimate
obtained using a different modelling technique. Signs of non-circular gas
motions (likely outflow) are also identified in the inner regions of NGC4261.
In NGC0612, we are only able to obtain a (conservative) upper limit of M. This has likely to be ascribed to the
presence of a central CO hole (with a radius much larger than that of the SMBH
sphere of influence), combined with the inability of obtaining a robust
prediction for the CO velocity curve. The three SMBH mass estimates are overall
in agreement with predictions from the relation.Comment: Main text: 20 pages, 14 Figures; Appendix: 7 pages, 6 Figures.
Accepted for publication in MNRAS on 2023 March 2
WISDOM Project - XXI. Giant molecular clouds in the central region of the barred spiral galaxy NGC 613: a steep size - linewidth relation
NGC 613 is a nearby barred spiral galaxy with a nuclear ring. Exploiting high spatial resolution (≈20 pc) Atacama Large Millimetre/submillimetre Array 12CO(1–0) observations, we study the giant molecular clouds (GMCs) in the nuclear ring and its vicinity, identifying 158 spatially and spectrally resolved GMCs. The GMC sizes (Rc) are comparable to those of the clouds in the Milky Way (MW) disc, but their gas masses, observed linewidths (σobs,los), and gas mass surface densities are larger. The GMC size–linewidth relation (
) is steeper than that of the clouds of the MW disc and centre, and the GMCs are on average only marginally gravitationally bound (with a mean virial parameter 〈αobs,vir〉 ≈ 1.7). We discuss the possible origins of the steep size–linewidth relation and enhanced observed linewidths of the clouds and suggest that a combination of mechanisms such as stellar feedback, gas accretion, and cloud–cloud collisions, as well as the gas inflows driven by the large-scale bar, may play a role
Metadata harvesting for content-based distributed information retrieval
We propose an approach to content-based Distributed Information Retrieval based on the periodic and incremental centralisation of full content indices of widely dispersed and autonomously managed document sources. Inspired by the success of the Open Archive Initiative’s protocol for metadata harvesting, the approach occupies middle ground between content crawling and distributed retrieval. As in crawling, some data moves towards the retrieval process, but it is statistics about the content rather than content itself; this grants more efficient use of network resources and wider scope of application. As in distributed retrieval, some processing is distributed along with the data, but it is indexing rather than retrieval; this reduces the costs of content provision whilst promoting the simplicity, effectiveness, and responsiveness of retrieval. Overall, we argue that the approach retains the good properties of centralised retrieval without renouncing to cost-effective, large-scale resource pooling. We discuss the requirements associated with the approach and identify two strategies to deploy it on top of the OAI infrastructure. In particular, we define a minimal extension of the OAI protocol which supports the coordinated harvesting of full-content indices and descriptive metadata for content resources. Finally, we report on the implementation of a proof-of-concept prototype service for multi-model content-based retrieval of distributed file collections
WISDOM project - XVIII. Molecular gas distributions and kinematics of three megamaser galaxies
The co-evolution of galaxies and supermassive black holes (SMBHs) underpins our understanding of galaxy evolution, but different methods to measure SMBH masses have only infrequently been cross-checked. We attempt to identify targets to cross-check two of the most accurate methods, megamaser, and cold molecular gas dynamics. Three promising galaxies are selected from all those with existing megamaser SMBH mass measurements. We present Atacama Large Millimeter/sub-millimeter Array (ALMA) 12CO (2–1) and 230-GHz continuum observations with angular resolutions of ≈0
5. Every galaxy has an extended rotating molecular gas disc and 230-GHz continuum source(s), but all also have irregularities and/or non-axisymmetric features: NGC 1194 is highly inclined and has disturbed and lopsided central 12CO (2–1) emission; NGC 3393 has a nuclear disc with fairly regular but patchy 12CO (2–1) emission with little gas near the kinematic major axis, faint emission in the very centre, and two brighter structures reminiscent of a nuclear ring and/or spiral; NGC 5765B has a strong bar and very bright 12CO (2–1) emission concentrated along two bisymmetric offset dust lanes and two bisymmetric nuclear spiral arms. 12CO (2–1) and 12CO (3–2) observations with the James Clerk Maxwell Telescope are compared with the ALMA observations. Because of the disturbed gas kinematics and the impractically long integration times required for higher angular resolution observations, none of the three galaxies is suitable for a future SMBH mass measurement. None the less, increasing the number of molecular gas observations of megamaser galaxies is valuable, and the ubiquitous disturbances suggest a link between large-scale gas properties and the existence of megamasers
- …