234 research outputs found
Synthetic retinal analogues modify the spectral and kinetic characteristics of microbial rhodopsin optogenetic tools
Optogenetic tools have become indispensable in neuroscience to stimulate or inhibit excitable cells by light. Channelrhodopsin-2 (ChR2) variants have been established by mutating the opsin backbone or by mining related algal genomes. As an alternative strategy, we surveyed synthetic retinal analogues combined with microbial rhodopsins for functional and spectral properties, capitalizing on assays in C. elegans, HEK cells and larval Drosophila. Compared with all-trans retinal (ATR), Dimethylamino-retinal (DMAR) shifts the action spectra maxima of ChR2 variants H134R and H134R/T159C from 480 to 520 nm. Moreover, DMAR decelerates the photocycle of ChR2(H134R) and (H134R/T159C), thereby reducing the light intensity required for persistent channel activation. In hyperpolarizing archaerhodopsin-3 and Mac, naphthyl-retinal and thiophene-retinal support activity alike ATR, yet at altered peak wavelengths. Our experiments enable applications of retinal analogues in colour tuning and altering photocycle characteristics of optogenetic tools, thereby increasing the operational light sensitivity of existing cell lines or transgenic animals
Synthetic retinal analogues modify the spectral and kinetic characteristics of microbial rhodopsin optogenetic tools
Optogenetic tools have become indispensable in neuroscience to stimulate or inhibit excitable cells by light. Channelrhodopsin-2 (ChR2) variants have been established by mutating the opsin backbone or by mining related algal genomes. As an alternative strategy, we surveyed synthetic retinal analogues combined with microbial rhodopsins for functional and spectral properties, capitalizing on assays in C. elegans, HEK cells and larval Drosophila. Compared with all-trans retinal (ATR), Dimethylamino-retinal (DMAR) shifts the action spectra maxima of ChR2 variants H134R and H134R/T159C from 480 to 520 nm. Moreover, DMAR decelerates the photocycle of ChR2(H134R) and (H134R/T159C), thereby reducing the light intensity required for persistent channel activation. In hyperpolarizing archaerhodopsin-3 and Mac, naphthyl-retinal and thiophene-retinal support activity alike ATR, yet at altered peak wavelengths. Our experiments enable applications of retinal analogues in colour tuning and altering photocycle characteristics of optogenetic tools, thereby increasing the operational light sensitivity of existing cell lines or transgenic animals
The Influence of the effect of solute on the thermodynamic driving force on grain refinement of Al alloys
Grain refinement is known to be strongly affected by the solute in cast alloys. Addition of some solute can reduce grain size considerably while others have a limited effect. This is usually attributed to the constitutional supercooling which is quantified by the growth restriction factor, Q. However, one factor that has not been considered is whether different solutes have differing effects on the thermodynamic driving force for solidification. This paper reveals that addition of solute reduces the driving force for solidification for a given undercooling, and that for a particular Q value, it is reduced more substantially when adding eutectic-forming solutes than peritectic-forming elements. Therefore, compared with the eutectic-forming solutes, addition of peritectic-forming solutes into Al alloys not only possesses a higher initial nucleation rate resulted from the larger thermodynamic driving force for solidification, but also promotes nucleation within the constitutionally supercooled zone during growth. As subsequent nucleation can occur at smaller constitutional supercoolings for peritectic-forming elements, a smaller grain size is thus produced. The very small constitutional supercooling required to trigger subsequent nucleation in alloys containing Ti is considered as a major contributor to its extraordinary grain refining efficiency in cast Al alloys even without the deliberate addition of inoculants.The Australian Research Council (ARC DP10955737)
The Distance to NGC 1316 (Fornax A) From Observations of Four Type Ia Supernovae
The giant elliptical galaxy NGC 1316 (Fornax A) is a well-studied member of
the Fornax Cluster and a prolific producer of Type Ia supernovae, having hosted
four observed events since 1980. Here we present detailed optical and
near-infrared light curves of the spectroscopically normal SN 2006dd. These
data are used, along with previously published photometry of the normal SN
1980N and SN 1981D, and the fast-declining, low-luminosity SN 2006mr, to
compute independent estimates of the host reddening for each supernova, and the
distance to NGC 1316. From the three normal supernovae, we find a distance of
17.8 +/- 0.3 (random) +/- 0.3 (systematic) Mpc for Ho = 72. Distance moduli
derived from the "EBV" and Tripp methods give values that are mutually
consistent to 4 -- 8%. Moreover, the weighted means of the distance moduli for
these three SNe for three methods agree to within 3%. This consistency is
encouraging and supports the premise that Type Ia supernovae are reliable
distance indicators at the 5% precision level or better. On the other hand, the
two methods used to estimate the distance of the fast-declining SN 2006mr both
yield a distance to NGC 1316 which is 25-30% larger. This disparity casts doubt
on the suitability of fast-declining events for estimating extragalactic
distances. Modest-to-negligible host galaxy reddening values are derived for
all four supernovae. Nevertheless, two of them (SN 2006dd and SN 2006mr) show
strong NaID interstellar lines in the host galaxy system. The strength of this
absorption is completely inconsistent with the small reddening values derived
from the supernova light curves if the gas in NGC 1316 is typical of that found
in the interstellar medium of the Milky Way. In addition, the equivalent width
of the NaID lines in SN 2006dd appear to have weakened significantly some
100-150 days after explosion.Comment: 50 pages, 13 figures, 10 tables; constructive comments welcome.
Accepted for publication in A
THE CARNEGIE SUPERNOVA PROJECT: LIGHT-CURVE FITTING WITH SNooPy
In providing an independent measure of the expansion history of the Universe,
the Carnegie Supernova Project (CSP) has observed 71 high-z Type Ia supernovae
(SNe Ia) in the near-infrared bands Y and J. These can be used to construct
rest-frame i-band light curves which, when compared to a low-z sample, yield
distance moduli that are less sensitive to extinction and/or decline-rate
corrections than in the optical. However, working with NIR observed and i-band
rest frame photometry presents unique challenges and has necessitated the
development of a new set of observational tools in order to reduce and analyze
both the low-z and high-z CSP sample. We present in this paper the methods used
to generate uBVgriYJH light-curve templates based on a sample of 24
high-quality low-z CSP SNe. We also present two methods for determining the
distances to the hosts of SN Ia events. A larger sample of 30 low-z SNe Ia in
the Hubble Flow are used to calibrate these methods. We then apply the method
and derive distances to seven galaxies that are so nearby that their motions
are not dominated by the Hubble flow.Comment: 58 pages, 19 figures. Accepted for publication in the Astronomical
Journa
The Al-Rich Part of the Fe-Al Phase Diagram
The Al-rich part of the Fe-Al phase diagram between 50 and 80 at.% Al including the complex intermetallic phases FeAl (ε), FeAl, FeAl, and Fe4Al was re-investigated in detail. A series of 19 alloys was produced and heat-treated at temperatures in the range from 600 to 1100 °C for up to 5000 h. The obtained data were further complemented by results from a number of diffusion couples, which helped to determine the homogeneity ranges of the phases FeAl, FeAl, and FeAl. All microstructures were inspected by scanning electron microscopy (SEM), and chemical compositions of the equilibrium phases as well as of the alloys were obtained by electron probe microanalysis (EPMA). Crystal structures and the variation of the lattice parameters were studied by x-ray diffraction (XRD) and differential thermal analysis (DTA) was applied to measure all types of transition temperatures. From these results, a revised version of the Al-rich part of the phase diagram was constructed
Microscopic View on Short-Range Wetting at the Free Surface of the Binary Metallic Liquid Gallium-Bismuth: An X-ray Reflectivity and Square Gradient Theory Study
We present an x-ray reflectivity study of wetting at the free surface of the
binary liquid metal gallium-bismuth (Ga-Bi) in the region where the bulk phase
separates into Bi-rich and Ga-rich liquid phases. The measurements reveal the
evolution of the microscopic structure of wetting films of the Bi-rich,
low-surface-tension phase along different paths in the bulk phase diagram. A
balance between the surface potential preferring the Bi-rich phase and the
gravitational potential which favors the Ga-rich phase at the surface pins the
interface of the two demixed liquid metallic phases close to the free surface.
This enables us to resolve it on an Angstrom level and to apply a mean-field,
square gradient model extended by thermally activated capillary waves as
dominant thermal fluctuations. The sole free parameter of the gradient model,
i.e. the so-called influence parameter, , is determined from our
measurements. Relying on a calculation of the liquid/liquid interfacial tension
that makes it possible to distinguish between intrinsic and capillary wave
contributions to the interfacial structure we estimate that fluctuations affect
the observed short-range, complete wetting phenomena only marginally. A
critical wetting transition that should be sensitive to thermal fluctuations
seems to be absent in this binary metallic alloy.Comment: RevTex4, twocolumn, 15 pages, 10 figure
PEARLS: Near Infrared Photometry in the JWST North Ecliptic Pole Time Domain Field
We present Near-Infrared (NIR) ground-based Y, J, H, and K imaging obtained
in the James Webb Space Telescope North Ecliptic Pole Time Domain Field (TDF)
using the MMT-Magellan Infrared Imager and Spectrometer (MMIRS) on the
MMT.These new observations cover a field of approximately 230 arcmin^2 in Y, H,
and K and 313 arcmin^2 in J. Using Monte Carlo simulations we estimate a 1
sigma depth relative to the background sky of (Y, J, H, K}) = (23.80, 23.53,
23.13, 23.28) in AB magnitudes for point sources at a 95% completeness level.
These observations are part of the ground-based effort to characterize this
region of the sky, supplementing space-based data obtained with Chandra,
NuSTAR, XMM, AstroSat, HST, and JWST. This paper describes the observations and
reduction of the NIR imaging and combines these NIR data with archival imaging
in the visible, obtained with the Subaru Hyper-Suprime-Cam, to produce a merged
catalog of 57,501 sources. The new observations reported here, plus the
corresponding multi-wavelength catalog, will provide a baseline for time-domain
studies of bright sources in the TDF.Comment: 23 pages, 10 figures. Accepted for publication in ApJS. Images and
catalogs available at https://doi.org/10.5281/zenodo.7934393. Data
description available under ancillary files and at the Zenodo site. Added a
reference, fixed typos in metadat
PEARLS: Near-infrared Photometry in the JWST North Ecliptic Pole Time Domain Field * * Partly based on observations taken with the MMT, a joint facility operated by the University of Arizona and the Smithsonian Institution.
We present near-infrared (NIR) ground-based Y, J, H, and K imaging obtained in the James Webb Space Telescope (JWST) North Ecliptic Pole Time Domain Field (NEP TDF) using the MMT-Magellan Infrared Imager and Spectrometer on the MMT. These new observations cover a field of approximately 230 arcmin2 in Y, H, and K, and 313 arcmin2 in J. Using Monte Carlo simulations, we estimate a 1σ depth relative to the background sky of (Y, J, H, K) = (23.80, 23.53, 23.13, 23.28) in AB magnitudes for point sources at a 95% completeness level. These observations are part of the ground-based effort to characterize this region of the sky, supplementing space-based data obtained with Chandra, NuSTAR, XMM, AstroSat, Hubble Space Telescope, and JWST. This paper describes the observations and reduction of the NIR imaging and combines these NIR data with archival imaging in the visible, obtained with the Subaru Hyper-Suprime-Cam, to produce a merged catalog of 57,501 sources. The new observations reported here, plus the corresponding multiwavelength catalog, will provide a baseline for time-domain studies of bright sources in the NEP TDF
Ocean acidification reduces demersal zooplankton that reside in tropical coral reefs
The in situ effects of ocean acidification on zooplankton communities remain largely unexplored. Using natural volcanic CO2
seep sites around tropical coral communities, we show a threefold reduction in the biomass of demersal zooplankton in
high-CO2 sites compared with sites with ambient CO2. Differences were consistent across two reefs and three expeditions.
Abundances were reduced in most taxonomic groups. There were no regime shifts in zooplankton community composition and
no differences in fatty acid composition between CO2 levels, suggesting that ocean acidification affects the food quantity but
not the quality for nocturnal plankton feeders. Emergence trap data show that the observed reduction in demersal plankton
may be partly attributable to altered habitat. Ocean acidification changes coral community composition from branching to
massive bouldering coral species, and our data suggest that bouldering corals represent inferior daytime shelter for demersal
zooplankton. Since zooplankton represent a major source of nutrients for corals, fish and other planktivores, this ecological
feedback may represent an additional mechanism of how coral reefs will be affected by ocean acidification
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