2,127 research outputs found
Metallicity gradients in local field star-forming galaxies: Insights on inflows, outflows, and the coevolution of gas, stars and metals
We present metallicity gradients in 49 local field star-forming galaxies. We
derive gas-phase oxygen abundances using two widely adopted metallicity
calibrations based on the [OIII]/Hbeta, [NII]/Halpha and [NII]/[OII] line
ratios. The two derived metallicity gradients are usually in good agreement
within +/-0.14 dex/R25 (R25 is the B-band iso-photoal radius), but the
metallicity gradients can differ significantly when the ionisation parameters
change systematically with radius. We investigate the metallicity gradients as
a function of stellar mass (8<log(M*/Msun)<11) and absolute B-band luminosity
(-16 > MB > -22). When the metallicity gradients are expressed in dex/kpc, we
show that galaxies with lower mass and luminosity, on average, have steeper
metallicity gradients. When the metallicity gradients are expressed in dex/R25,
we find no correlation between the metallicity gradients, and stellar mass and
luminosity. We provide a local benchmark metallicity gradient of field
star-forming galaxies useful for comparison with studies at high redshifts. We
investigate the origin of the local benchmark gradient using simple chemical
evolution models and observed gas and stellar surface density profiles in
nearby field spiral galaxies. Our models suggest that the local benchmark
gradient is a direct result of the coevolution of gas and stellar disk under
virtually closed-box chemical evolution when the stellar-to-gas mass ratio
becomes high (>>0.3). These models imply low current mass accretion rates
(<0.3xSFR), and low mass outflow rates (<3xSFR) in local field star-forming
galaxies.Comment: 25 pages, 21 figures, accepted to MNRA
DEVELOPMENT OF NEW PYRAZOLE HYBRIDS AS ANTITUBERCULAR AGENTS: SYNTHESIS, BIOLOGICAL EVALUATION AND MOLECULAR DOCKING STUDY
Objective: synthesis of new 1, 3-diphenyl pyrazole derivatives 9(a-f) and 10(a-f) using molecular hybridization approach for antitubercular and cytotoxic studies.Methods: The structures of synthesized compounds were confirmed by 1H-NMR, 13C-NMR and mass spectra's. The antitubercular activity of compounds and standard drugs were assessed against Mycobacterium tuberculosis using microplate Alamar Blue assay (MABA).  The cytotoxic activities were performed by Sulforhodamine B (SRB) assay. The molecular docking and in silico ADME prediction were studied by using Schrodinger.Results: The results reveals that the compounds 9c, 9d, 10c and 10d exhibited substantial antitubercular potential with MIC < 20 μM. The cytotoxic studies revealed that the active compounds (9d, 10a, and 10d) are non-toxic to HeLa cancer cell lines with selectivity index >10. The molecular docking study was performed to study the binding orientation and affinity of synthesized compounds for InhA enzyme.Conclusion: The study explored that the 1, 3-diphenyl pyrazole hybrids coupled with well known antitubercular drugs could be a potential lead for antitubercular agents. In-silico molecular docking study helps to identify their corresponding intermolecular ligand-protein interactions with target enzyme. Also ADME prediction studies revealed that the compounds were in acceptable range to have pharmacokinetic parameters
A Rare Case of HIV-Induced Inflammatory Demyelinating Polyneuropathy.
Background:Acute inflammatory demyelinating polyneuropathy (AIDP) is an uncommon form of neuropathy in HIV-infected patients that can cause pain, sensory disturbance, and motor weakness. Case presentation:A 23-year-old African American male with past medical history of Guillain-Barre Syndrome (GBS), Lyme disease, and sexually transmitted infections including syphilis and chlamydia presented with acute back pain radiating to bilateral lower extremities with worsening right foot weakness for four days. Cerebrospinal fluid (CSF) studies including meningoencephalitis panel were negative as well as blood tests for Lyme disease and HIV antibody testing. Patient was initially treated with penicillin for positive treponemal serology but without improvement in lower extremity weakness. Electromyogram showed evidence of early demyelinating motor polyneuropathy. Four days after presentation, repeat HIV antibody testing returned positive. Recurrent AIDP in this case was suspected to be secondary to acute HIV infection, and highly active antiretroviral therapy (HAART) was administered along with intravenous immunoglobulin (IVIG). Muscle strength improved with therapy and patient was expected to have continued improvement with intensive rehabilitation after discharge. Conclusion:Acute inflammatory demyelinating polyneuropathy (AIDP) tends to present early in course of HIV infection. Therefore, HIV testing should be obtained in individuals presenting with new neurological deficits. Our patient received HAART therapy, in addition to the traditional modalities to manage AIDP, which led to a substantial recovery of his sensorimotor function
Topological phase diagram and saddle point singularity in a tunable topological crystalline insulator
We report the evolution of the surface electronic structure and surface
material properties of a topological crystalline insulator (TCI) Pb1-xSnxSe as
a function of various material parameters including composition x, temperature
T and crystal structure. Our spectroscopic data demonstrate the electronic
groundstate condition for the saddle point singularity, the tunability of
surface chemical potential, and the surface states' response to circularly
polarized light. Our results show that each material parameter can tune the
system between trivial and topological phase in a distinct way unlike as seen
in Bi2Se3 and related compounds, leading to a rich and unique topological phase
diagram. Our systematic studies of the TCI Pb1-xSnxSe are valuable materials
guide to realize new topological phenomena.Comment: 10 pages, 7 figures. Expanded version of arXiv:1403.156
The FMOS-COSMOS survey of star-forming galaxies at z~1.6 III. Survey design, performance, and sample characteristics
We present a spectroscopic survey of galaxies in the COSMOS field using the
Fiber Multi-Object Spectrograph (FMOS), a near-infrared instrument on the
Subaru Telescope. Our survey is specifically designed to detect the Halpha
emission line that falls within the H-band (1.6-1.8 um) spectroscopic window
from star-forming galaxies with 1.4 ~10^10 Msolar. With
the high multiplex capability of FMOS, it is now feasible to construct samples
of over one thousand galaxies having spectroscopic redshifts at epochs that
were previously challenging. The high-resolution mode (R~2600) effectively
separates Halpha and [NII]6585 thus enabling studies of the gas-phase
metallicity and photoionization state of the interstellar medium. The primary
aim of our program is to establish how star formation depends on stellar mass
and environment, both recognized as drivers of galaxy evolution at lower
redshifts. In addition to the main galaxy sample, our target selection places
priority on those detected in the far-infrared by Herschel/PACS to assess the
level of obscured star formation and investigate, in detail, outliers from the
star formation rate - stellar mass relation. Galaxies with Halpha detections
are followed up with FMOS observations at shorter wavelengths using the J-long
(1.11-1.35 um) grating to detect Hbeta and [OIII]5008 that provides an
assessment of extinction required to measure star formation rates not hampered
by dust, and an indication of embedded Active Galactic Nuclei. With 460
redshifts measured from 1153 spectra, we assess the performance of the
instrument with respect to achieving our goals, discuss inherent biases in the
sample, and detail the emission-line properties. Our higher-level data
products, including catalogs and spectra, are available to the community.Comment: 26 pages, Updated version resubmitted to ApJSS; Data products and
catalogs are now available at http://member.ipmu.jp/fmos-cosmos
Lifshitz transition and van Hove singularity in a Topological Dirac Semimetal
A topological Dirac semimetal is a novel state of quantum matter which has
recently attracted much attention as an apparent 3D version of graphene. In
this paper, we report critically important results on the electronic structure
of the 3D Dirac semimetal Na3Bi at a surface that reveals its nontrivial
groundstate. Our studies, for the first time, reveal that the two 3D Dirac
cones go through a topological change in the constant energy contour as a
function of the binding energy, featuring a Lifshitz point, which is missing in
a strict 3D analog of graphene (in other words Na3Bi is not a true 3D analog of
graphene). Our results identify the first example of a band saddle point
singularity in 3D Dirac materials. This is in contrast to its 2D analogs such
as graphene and the helical Dirac surface states of a topological insulator.
The observation of multiple Dirac nodes in Na3Bi connecting via a Lifshitz
point along its crystalline rotational axis away from the Kramers point serves
as a decisive signature for the symmetry-protected nature of the Dirac
semimetal's topological groundstate.Comment: 5 pages, 4 Figures, Related papers on topological Fermi arcs and Weyl
Semimetals (WSMs) are at
http://physics.princeton.edu/zahidhasangroup/index.htm
Friction and wear phenomena of vegetable oil based lubricants with additives at severe sliding wear conditions
The tribological responses of palm oil and soybean oil, combined with two commercial antiwear
additives (zinc dialkyl dithiophosphate and boron compound), were investigated at a lubricant
temperature of 100 °C and under severe contact conditions in a reciprocating sliding contact. The
friction coefficient of palm oil with zinc dialkyl dithiophosphate was closest to the commercial
mineral engine oil, with a 2% difference. The soybean oil with zinc dialkyl dithiophosphate
produced a 57% improvement in wear resistance compared to its pure oil state. The existence of
boron nitride in vegetable oils was only responsive in reduction of wear rather than friction. The
response of commercial antiwear additives with vegetable oils showed a potential for the future
improvement in the performance of vegetable oils
Tunnel progression effects to the ground surface and the adjacent pile
Tunnelling close to existing structure in urban area has become unavoidable. The progression tunneling activities induced ground movement and might affect the integrity of existing structure especially the one lies within the tunneling influence zone. It may cause catastrophic failures of structures and can cause losses of human lives. Therefore, considering its risk, this study focuses on the tunnel-soil-pile interaction by performing a physical model testing. By conducting a series of laboratory tests, the ground subsidence and pile behavior is presented herein. For a twice diameter distance of tunnel and pile, the pile axial settlement is 0.04% of the tunnel diameter respectively, while the maximum pile bending moment is 4928. 93kN.m. Maximum ground settlement is 0.56% respectively to tunnel diameter. To sum up, the axial displacement of pile decreases when the pile located further away from the tunneling zone. Similarly, the ground surface subsidence decreases when the pile location is more in distance during the tunneling advancement
The Chemical Evolution Carousel of Spiral Galaxies : Azimuthal Variations of Oxygen Abundance in NGC1365
19 pages, 13 figures. Accepted to ApJThe spatial distribution of oxygen in the interstellar medium of galaxies is the key to understanding how efficiently metals that are synthesized in massive stars can be redistributed across a galaxy. We present here a case study in the nearby spiral galaxy NGC1365 using 3D optical data obtained in the TYPHOON Program. We find systematic azimuthal variations of the HII region oxygen abundance imprinted on a negative radial gradient. The 0.2 dex azimuthal variations occur over a wide radial range of 0.3 to 0.7 R25 and peak at the two spiral arms in NGC1365. We show that the azimuthal variations can be explained by two physical processes: gas undergoes localized, sub-kpc scale self-enrichment when orbiting in the inter-arm region, and experiences efficient, kpc scale mixing-induced dilution when spiral density waves pass through. We construct a simple chemical evolution model to quantitatively test this picture and find that our toy model can reproduce the observations. This result suggests that the observed abundance variations in NGC1365 are a snapshot of the dynamical local enrichment of oxygen modulated by spiral-driven, periodic mixing and dilution.Peer reviewedFinal Published versio
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