5,426 research outputs found
The Rising Light Curves of Type Ia Supernovae
We present an analysis of the early, rising light curves of 18 Type Ia
supernovae (SNe Ia) discovered by the Palomar Transient Factory (PTF) and the
La Silla-QUEST variability survey (LSQ). We fit these early data flux using a
simple power-law to determine the time of first
light , and hence the rise-time from first light to
peak luminosity, and the exponent of the power-law rise (). We find a mean
uncorrected rise time of days, with individual SN rise-times
ranging from to days. The exponent n shows significant
departures from the simple 'fireball model' of (or ) usually assumed in the literature. With a mean value of , our data also show significant diversity from event to event. This
deviation has implications for the distribution of 56Ni throughout the SN
ejecta, with a higher index suggesting a lesser degree of 56Ni mixing. The
range of n found also confirms that the 56Ni distribution is not standard
throughout the population of SNe Ia, in agreement with earlier work measuring
such abundances through spectral modelling. We also show that the duration of
the very early light curve, before the luminosity has reached half of its
maximal value, does not correlate with the light curve shape or stretch used to
standardise SNe Ia in cosmological applications. This has implications for the
cosmological fitting of SN Ia light curves.Comment: 19 pages, 19 figures, accepted for publication in MNRA
Unmanned Aerial System-Based Data Ferrying over a Sensor Node Station Network in Maize
© 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/)
A comparative study of Type II-P and II-L supernova rise times as exemplified by the case of LSQ13cuw
We report on our findings based on the analysis of observations of the Type
II-L supernova LSQ13cuw within the framework of currently accepted physical
predictions of core-collapse supernova explosions. LSQ13cuw was discovered
within a day of explosion, hitherto unprecedented for Type II-L supernovae.
This motivated a comparative study of Type II-P and II-L supernovae with
relatively well-constrained explosion epochs and rise times to maximum
(optical) light. From our sample of twenty such events, we find evidence of a
positive correlation between the duration of the rise and the peak brightness.
On average, SNe II-L tend to have brighter peak magnitudes and longer rise
times than SNe II-P. However, this difference is clearest only at the extreme
ends of the rise time versus peak brightness relation. Using two different
analytical models, we performed a parameter study to investigate the physical
parameters that control the rise time behaviour. In general, the models
qualitatively reproduce aspects of the observed trends. We find that the
brightness of the optical peak increases for larger progenitor radii and
explosion energies, and decreases for larger masses. The dependence of the rise
time on mass and explosion energy is smaller than the dependence on the
progenitor radius. We find no evidence that the progenitors of SNe II-L have
significantly smaller radii than those of SNe II-P.Comment: 19 pages, 10 figures, accepted by A&
Comparison of stationary and mobile canopy sensing systems for irrigation management of maize and soybean in Nebraska
Accurate knowledge of plant and field characteristics is crucial for irrigation management. Irrigation can potentially be better managed by utilizing data collected from various sensors installed on different platforms. The accuracy and repeatability of each data source are important considerations when selecting a sensing system suitable for irrigation management. The objective of this study was to compare data from multispectral (red and near-infrared bands) and thermal (long wave thermal infrared band) sensors mounted on different platforms to investigate their comparative usability and accuracy. The different sensor platforms included stationary posts fixed on the ground, the lateral of a center pivot irrigation system, unmanned aircraft systems (UAS), and Planet (PlanetScope multispectral imager, Planet Labs, Inc., San Francisco, Calif.) satellites. The surface reflectance data from multispectral (MS) sensors were used to compute the Normalized Difference Vegetation Index (NDVI) and Soil Adjusted Vegetation Index (SAVI). The experimental plots were managed with rainfed and irrigated treatments. Irrigation was applied according to a spatial evapotranspiration model informed with Planet satellite imagery. The NDVI and SAVI curves computed from the different sensing systems exhibited similar patterns and were able to capture differences between the rainfed and irrigated treatments when the crops were approaching senescence. Strong correlations were observed for canopy temperature measurements between the stationary and pivot-mounted infrared thermometer (IRT) sensors (p-value of less than 0.01 for the correlations) when canopy were scanned with no irrigation application (dry scans). The best correlation was obtained for the irrigated maize, which yielded r2 of 0.99, RMSE of 0.4°C, and MAE of 0.3°C. The correlation for the canopy temperature data collected during dry scan between UAS and pivot-mounted thermal sensors was weak with r2 = 0.26 to 0.28, larger RMSE values of 3.7°C and MAE values of 3.4°C. Secondary analysis between thermal data from stationary and pivot-mounted IRTs collected during wet scans (during an irrigation event) demonstrated reduced canopy temperature from pivot-mounted IRTs by approximately 2°C for irrigated soybean due to wetting of the canopy by the irrigation. Understanding the performance of these sensor systems is valuable in configuring practical design and operational considerations when using sensor feedback for irrigation management
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Forty years of temporal analysis of products
A detailed understanding of reaction mechanisms and kinetics is required in order to develop and optimize catalysts and catalytic processes. While steady-state investigations are known to give a global view of the catalytic system, transient studies are invaluable since they can provide more comprehensive insight into elementary steps. For almost forty years temporal analysis of products (TAP) has been successfully utilized for transient studies of gas phase heterogeneous reactions, and there have been a number of advances in instrumentation and numerical modeling methods in that time. Since TAP is a complex methodology it is often viewed as a niche specialty. With the purpose to make TAP more relevant and approachable to a wider segment of the catalytic research community, part of the intention of this work is to highlight the significant contributions TAP has made to elucidating mechanistic and kinetic aspects of complex, multi-step heterogeneous reactions. With this in mind, an outlook is also disclosed for the technique in terms of what is needed to revitalize the field and make it more applicable to the recent advances in catalyst characterization (e.g. operando modes)
Early ultraviolet emission in the Type Ia supernova LSQ12gdj: No evidence for ongoing shock interaction
We present photospheric-phase observations of LSQ12gdj, a slowly-declining,
UV-bright Type Ia supernova. Classified well before maximum light, LSQ12gdj has
extinction-corrected absolute magnitude , and pre-maximum
spectroscopic evolution similar to SN 1991T and the super-Chandrasekhar-mass SN
2007if. We use ultraviolet photometry from Swift, ground-based optical
photometry, and corrections from a near-infrared photometric template to
construct the bolometric (1600-23800 \AA) light curve out to 45 days past
-band maximum light. We estimate that LSQ12gdj produced
of Ni, with an ejected mass near or slightly above the
Chandrasekhar mass. As much as 27% of the flux at the earliest observed phases,
and 17% at maximum light, is emitted bluewards of 3300 \AA. The absence of
excess luminosity at late times, the cutoff of the spectral energy distribution
bluewards of 3000 \AA, and the absence of narrow line emission and strong Na I
D absorption all argue against a significant contribution from ongoing shock
interaction. However, up to 10% of LSQ12gdj's luminosity near maximum light
could be produced by the release of trapped radiation, including kinetic energy
thermalized during a brief interaction with a compact, hydrogen-poor envelope
(radius cm) shortly after explosion; such an envelope arises
generically in double-degenerate merger scenarios.Comment: 18 pages, 10 figures, accepted to MNRAS; v2 accepted version. Spectra
available on WISEReP (http://www.weizmann.ac.il/astrophysics/wiserep/).
Natural-system photometry and bolometric light curve available as online
tables in MNRAS versio
Type Ia supernovae with and without blueshifted narrow Na I D lines - how different is their structure?
In studies on intermediate- and high-resolution spectra of Type Ia supernovae (SNe Ia), some objects exhibit narrow Na I D absorptions often blueshifted with respect to the rest wavelength within the host galaxy. The absence of these in other SNe Ia may reflect that the explosions have different progenitors: blueshifted Na I D features might be explained by the outflows of ‘single-degenerate’ systems (binaries of a white dwarf with a non-degenerate companion). In this work, we search for systematic differences among SNe Ia for which the Na I D characteristics have been clearly established in previous studies. We perform an analysis of the chemical abundances in the outer ejecta of 13 ‘spectroscopically normal’ SNe Ia (five of which show blueshifted Na lines), modelling time series of photospheric spectra with a radiative-transfer code. We find only moderate differences between ‘blueshifted-Na’, ‘redshifted-Na’ and ‘no-Na’ SNe Ia, so that we can neither conclusively confirm a ‘one-scenario’ nor a ‘two-scenario’ theory for normal SNe Ia. Yet, some of the trends we see should be further studied using larger observed samples: models for blueshifted-Na SNe tend to show higher photospheric velocities than no-Na SNe, corresponding to a higher opacity of the envelope. Consistently, blueshifted-Na SNe show hints of a somewhat larger iron-group content in the outer layers with respect to the no-Na subsample (and also to the redshifted-Na subsample). This agrees with earlier work where it was found that the light curves of no-Na SNe – often appearing in elliptical galaxies – are narrower, that is, decline more rapidly
Automated analysis of digital fundus autofluorescence images of geographic atrophy in advanced age-related macular degeneration using confocal scanning laser ophthalmoscopy (cSLO)
BACKGROUND: Fundus autofluorescence (AF) imaging using confocal scanning laser ophthalmoscopy (cSLO) provides an accurate delineation of areas of geographic atrophy (GA). Automated computer-assisted methods for detecting and removing interfering vessels are needed to support the GA quantification process in longitudinal studies and in reading centres. METHODS: A test tool was implemented that uses region-growing techniques to segment GA areas. An algorithm for illuminating shadows can be used to process low-quality images. Agreement between observers and between three different methods was evaluated by two independent readers in a pilot study. Agreement and objectivity were assessed using the Bland-Altman approach. RESULTS: The new method (C) identifies vascular structures that interfere with the delineation of GA. Results are comparable to those of two commonly used procedures (A, B), with a mean difference between C and A of -0.67 mm(2 )(95% CI [-0.99, -0.36]), between B and A of -0.81 mm(2), (95% CI [-1.08, -0.53]), and between C and B of 0.15 mm(2 )(95% CI [-0.12, 0.41]). Objectivity of a method is quantified by the mean difference between observers: A 0.30 mm(2 )(95% CI [0.02, 0.57]), B -0.11 mm(2 )(95% CI [-0.28, 0.10]), and C 0.12 mm(2 )(95% CI [0.02, 0.22]). CONCLUSION: The novel procedure is comparable with regard to objectivity and inter-reader agreement to established methods of quantifying GA. It considerably speeds up the lengthy measurement process in AF with well defined GA zones
On the Functional Relationship Between Fluorescence and Photochemical Yields in Complex Evergreen Needleleaf Canopies
Recent advancements in understanding remotely sensed solar‐induced chlorophyll fluorescence often suggest a linear relationship with gross primary productivity at large spatial scales. However, the quantum yields of fluorescence and photochemistry are not linearly related, and this relationship is largely driven by irradiance. This raises questions about the mechanistic basis of observed linearity from complex canopies that experience heterogeneous irradiance regimes at subcanopy scales. We present empirical data from two evergreen forest sites that demonstrate a nonlinear relationship between needle‐scale observations of steady‐state fluorescence yield and photochemical yield under ambient irradiance. We show that accounting for subcanopy and diurnal patterns of irradiance can help identify the physiological constraints on needle‐scale fluorescence at 70–80% accuracy. Our findings are placed in the context of how solar‐induced chlorophyll fluorescence observations from spaceborne sensors relate to diurnal variation in canopy‐scale physiology
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