10 research outputs found
Thermally Induced Nano-Structural and Optical Changes of nc-Si:H Deposited by Hot-Wire CVD
We report on the thermally induced changes of the nano-structural and optical properties of hydrogenated nanocrystalline silicon in the temperature range 200–700 °C. The as-deposited sample has a high crystalline volume fraction of 53% with an average crystallite size of ~3.9 nm, where 66% of the total hydrogen is bonded as ≡Si–H monohydrides on the nano-crystallite surface. A growth in the native crystallite size and crystalline volume fraction occurs at annealing temperatures ≥400 °C, where hydrogen is initially removed from the crystallite grain boundaries followed by its removal from the amorphous network. The nucleation of smaller nano-crystallites at higher temperatures accounts for the enhanced porous structure and the increase in the optical band gap and average gap
Cosmology intertwined: A review of the particle physics, astrophysics, and cosmology associated with the cosmological tensions and anomalies
The standard Cold Dark Matter (CDM) cosmological model provides a good description of a wide range of astrophysical and cosmological data. However, there are a few big open questions that make the standard model look like an approximation to a more realistic scenario yet to be found. In this paper, we list a few important goals that need to be addressed in the next decade, taking into account the current discordances between the different cosmological probes, such as the disagreement in the value of the Hubble constant H0, the σ8–S8 tension, and other less statistically significant anomalies. While these discordances can still be in part the result of systematic errors, their persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the necessity for new physics or generalisations beyond the standard model. In this paper, we focus on the 5.0 σ tension between the Planck CMB estimate of the Hubble constant H0 and the SH0ES collaboration measurements. After showing the H0 evaluations made from different teams using different methods and geometric calibrations, we list a few interesting new physics models that could alleviate this tension and discuss how the next decade’s experiments will be crucial. Moreover, we focus on the tension of the Planck CMB data with weak lensing measurements and redshift surveys, about the value of the matter energy density m, and the amplitude or rate of the growth of structure (σ8, f σ8). We list a few interesting models proposed for alleviating this tension, and we discuss the importance of trying to fit a full array of data with a single model and not just one parameter at a time. Additionally, we present a wide range of other less discussed anomalies at a statistical significance level lower than the H0–S8 tensions which may also constitute hints towards new physics, and we discuss possible generic theoretical approaches that can collectively explain the non-standard nature of these signals. Finally, we give an overview of upgraded experiments and next-generation space missions and facilities on Earth that will be of crucial importance to address all these open questions
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Differential sampling in the assessment of conservation and biodiversity merit: a comparison of the seagrass macrofauna in three nearby South African estuaries
AbstractTo what extent is the relative biodiversity of some flagship conservation sites a result of differential attention? Knysna estuarine bay is the topmost ranked South African estuary for conservation importance and biodiversity. It is also one of the most intensively studied, and hence differential sampling effort could partly be responsible for its apparent relative richness. To assess the extent to which this might be true, identical sampling area, effort and methodology were employed to compare the benthic macrofauna of one specific major Knysna habitat (Zostera capensis seagrass beds) with equivalent ones in two nearby lesser-studied estuaries, the Keurbooms/Bitou and Swartvlei. Investigation showed all three localities to share a common species pool, but different elements of it dominated the shared habitat type in each. The seagrass and adjacent sandflat macrobenthos proved just as biodiverse in unprotected Keurbooms/Bitou as in the Protected Area of Knysna, but that in Swartvlei (also a Protected Area) was impoverished in comparison, presumably consequent on mouth closure and the prevailing lower salinity. Despite marked geomorphological and hydrological differences, all three estuaries share a suite of unusual faunal elements and such particularly close faunal similarity suggests the importance of historical biogeographic processes. The analysis emphasises the need for caution when assessing the relative conservation importance or other merits of different individual systems in a data-limited environment.non
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JWST Photometric Time-delay and Magnification Measurements for the Triply Imaged Type Ia “SN H0pe” at z = 1.78
Abstract
Supernova (SN) SN H0pe is a gravitationally lensed, triply imaged, Type Ia SN (SN Ia) discovered in James Webb Space Telescope imaging of the PLCK G165.7+67.0 cluster of galaxies. Well-observed multiply imaged SNe provide a rare opportunity to constrain the Hubble constant (H
0), by measuring the relative time delay between the images and modeling the foreground mass distribution. SN H0pe is located at z = 1.783 and is the first SN Ia with sufficient light-curve sampling and long enough time delays for an H
0 inference. Here we present photometric time-delay measurements and SN properties of SN H0pe. Using JWST/NIRCam photometry, we measure time delays of Δt
ab =
−
116.6
−
9.3
+
10.8
observer-frame days and Δt
cb =
−
48.6
−
4.0
+
3.6
observer-frame days relative to the last image to arrive (image 2b; all uncertainties are 1σ), which corresponds to a ∼5.6% uncertainty contribution for H
0 assuming 70 km s−1 Mpc−1. We also constrain the absolute magnification of each image to μ
a
=
4.3
−
1.8
+
1.6
, μ
b
=
7.6
−
2.6
+
3.6
, μ
c
=
6.4
−
1.5
+
1.6
by comparing the observed peak near-IR magnitude of SN H0pe to the nonlensed population of SNe Ia.</jats:p