scholarly journals A demographic and evolutionary analysis of maternal effect senescence

2020 ◽  
Vol 117 (28) ◽  
pp. 16431-16437 ◽  
Author(s):  
Christina M. Hernández ◽  
Silke F. van Daalen ◽  
Hal Caswell ◽  
Michael G. Neubert ◽  
Kristin E. Gribble
Keyword(s):  
Growth Rate ◽  
Maternal Effect ◽  
Maternal Age ◽  
High Growth ◽  
High Growth Rate ◽  
Fertility Schedule ◽  
Evolutionary Analysis ◽  
Matrix Population Models ◽  
Selection Gradients ◽  
Age Related

Maternal effect senescence—a decline in offspring survival or fertility with maternal age—has been demonstrated in many taxa, including humans. Despite decades of phenotypic studies, questions remain about how maternal effect senescence impacts evolutionary fitness. To understand the influence of maternal effect senescence on population dynamics, fitness, and selection, we developed matrix population models in which individuals are jointly classified by age and maternal age. We fit these models to data from individual-based culture experiments on the aquatic invertebrate,Brachionus manjavacas(Rotifera). By comparing models with and without maternal effects, we found that maternal effect senescence significantly reduces fitness forB. manjavacasand that this decrease arises primarily through reduced fertility, particularly at maternal ages corresponding to peak reproductive output. We also used the models to estimate selection gradients, which measure the strength of selection, in both high growth rate (laboratory) and two simulated low growth rate environments. In all environments, selection gradients on survival and fertility decrease with increasing age. They also decrease with increasing maternal age for late maternal ages, implying that maternal effect senescence can evolve through the same process as in Hamilton’s theory of the evolution of age-related senescence. The models we developed are widely applicable to evaluate the fitness consequences of maternal effect senescence across species with diverse aging and fertility schedule phenotypes.

scholarly journals Maternal Effect Senescence and Fitness: A Demographic Analysis of a Novel Model Organism

2019 ◽  
Author(s):  
Christina M. Hernández ◽  
Silke F. van Daalen ◽  
Hal Caswell ◽  
Michael G. Neubert ◽  
Kristin E. Gribble
Keyword(s):  
Population Structure ◽  
Maternal Effect ◽  
Maternal Age ◽  
Model Organism ◽  
Maternal Investment ◽  
Fertility Schedule ◽  
Matrix Population Models ◽  
Selection Gradients ◽  
Fitness Consequences ◽  
The Impact

AbstractMaternal effect senescence—a decline in offspring fitness with maternal age—has been demonstrated in a range of taxa, including humans. Despite decades of phenotypic studies, it remains unclear how maternal effect senescence impacts population structure or evolutionary fitness. To understand the impact of maternal effect senescence on population dynamics, fitness, and selection, we used data from individual-based culture experiments on the microscopic aquatic invertebrate, Brachionus manjavacas (Rotifera), to develop a series of matrix population models in which individuals are classified jointly by age and maternal age. By comparing the results derived from models with and without maternal effects, we found that the fitness difference due to maternal effect senescence arises primarily through decreased fertility, particularly at maternal ages corresponding to the peak reproductive output. In all models, selection gradients decrease with increasing age. They also decrease with maternal age for large maternal ages, implying that maternal effect senescence can evolve through the same process as in Hamilton’s theory of the evolution of demographic senescence. We find that maternal effect senescence significantly alters population structure and fitness for B. manjavacas, a species with high maternal investment and maximum reproduction in early-to mid-life. The models developed here were built with data from an emerging model organism, and are widely applicable to evaluate the fitness consequences of maternal effect senescence across species with diverse aging and fertility schedule phenotypes.

Exploring SiC Growth Limitation of Vapor-Liquid-Solid Mechanism when Using Two Different Carbon Precursors

2013 ◽  
Vol 740-742 ◽  
pp. 323-326
Author(s):  
Kassem Alassaad ◽  
François Cauwet ◽  
Davy Carole ◽  
Véronique Soulière ◽  
Gabriel Ferro
Keyword(s):  
Growth Rate ◽  
High Growth ◽  
High Growth Rate ◽  
Carbon Precursor ◽  
Growth Limitation ◽  
Vapor Liquid Solid ◽  
Partial Pressures ◽  
Vapor Liquid Solid Mechanism ◽  
Vls Growth ◽  
Vapor Liquid

Abstract. In this paper, conditions for obtaining high growth rate during epitaxial growth of SiC by vapor-liquid-solid mechanism are investigated. The alloys studied were Ge-Si, Al-Si and Al-Ge-Si with various compositions. Temperature was varied between 1100 and 1300°C and the carbon precursor was either propane or methane. The variation of layers thickness was studied at low and high precursor partial pressure. It was found that growth rates obtained with both methane and propane are rather similar at low precursor partial pressures. However, when using Ge based melts, the use of high propane flux leads to the formation of a SiC crust on top of the liquid, which limits the growth by VLS. But when methane is used, even at extremely high flux (up to 100 sccm), no crust could be detected on top of the liquid while the deposit thickness was still rather small (between 1.12 μm and 1.30 μm). When using Al-Si alloys, no crust was also observed under 100 sccm methane but the thickness was as high as 11.5 µm after 30 min growth. It is proposed that the upper limitation of VLS growth rate depends mainly on C solubility of the liquid phase.

Very High Growth Rate of 4H-SiC Using MTS as Chloride-Based Precursor

2008 ◽  
Vol 600-603 ◽  
pp. 115-118 ◽  
Author(s):  
Henrik Pedersen ◽  
Stefano Leone ◽  
Anne Henry ◽  
Franziska Christine Beyer ◽  
Vanya Darakchieva ◽  
...  
Keyword(s):  
Growth Rate ◽  
Linear Dependence ◽  
Growth Rates ◽  
Molar Fraction ◽  
High Growth ◽  
High Growth Rate ◽  
Epitaxial Layers ◽  
Single Precursor ◽  
Very High

The chlorinated precursor methyltrichlorosilane (MTS), CH3SiCl3, has been used to grow epitaxial layers of 4H-SiC in a hot wall CVD reactor, with growth rates as high as 170 µm/h at 1600°C. Since MTS contains both silicon and carbon, with the C/Si ratio 1, MTS was used both as single precursor and mixed with silane or ethylene to study the effect of the C/Si and Cl/Si ratios on growth rate and doping of the epitaxial layers. When using only MTS as precursor, the growth rate showed a linear dependence on the MTS molar fraction in the reactor up to about 100 µm/h. The growth rate dropped for C/Si < 1 but was constant for C/Si > 1. Further, the growth rate decreased with lower Cl/Si ratio.

Emission characteristics of GaInN/GaN multiple quantum shell nanowire-based LEDs with different p-GaN growth conditions

Nanophotonics ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Sae Katsuro ◽  
Weifang Lu ◽  
Kazuma Ito ◽  
Nanami Nakayama ◽  
Naoki Sone ◽  
...  
Keyword(s):  
Growth Rate ◽  
Shell Growth ◽  
Light Output ◽  
High Growth ◽  
Growth Conditions ◽  
High Growth Rate ◽  
Current Injection ◽  
Emission Characteristics ◽  
Multiple Quantum ◽  
Plane Region

Abstract Improving current injection into r- and m-planes of nanowires (NWs) is essential to realizing efficient GaInN/GaN multiple quantum shell (MQS) NW-based light-emitting diodes (LEDs). Here, we present the effects of different p-GaN shell growth conditions on the emission characteristics of MQS NW-LEDs. Firstly, a comparison between cathodoluminescence (CL) and electroluminescence (EL) spectra indicates that the emission in NW-LEDs originates from the top region of the NWs. By growing thick p-GaN shells, the variable emission peak at around 600 nm and degradation of the light output of the NW-LEDs are elaborated, which is attributable to the localization of current in the c-plane region with various In-rich clusters and deep-level defects. Utilizing a high growth rate of p-GaN shell, an increased r-plane and a reduced c-plane region promote the deposition of indium tin oxide layer over the entire NW. Therefore, the current is effectively injected into both the r- and m-planes of the NW structures. Consequently, the light output and EL peak intensity of the NW-LEDs are enhanced by factors of 4.3 and 13.8, respectively, under an injection current of 100 mA. Furthermore, scanning transmission electron microscope images demonstrate the suppression of dislocations, triangular defects, and stacking faults at the apex of the p-GaN shell with a high growth rate. Therefore, localization of current injection in nonradiative recombination centers near the c-plane was also inhibited. Our results emphasize the possibility of realizing high efficacy in NW-LEDs via optimal p-GaN shell growth conditions, which is quite promising for application in the long-wavelength region.

High growth-rate atomic layer deposition process of cerium oxide thin film for solid oxide fuel cell

2019 ◽  
Vol 45 (3) ◽  
pp. 3811-3815 ◽  
Author(s):  
Jin-Geun Yu ◽  
Byung Chan Yang ◽  
Jeong Woo Shin ◽  
Sungje Lee ◽  
Seongkook Oh ◽  
...  
Keyword(s):  
Thin Film ◽  
Growth Rate ◽  
High Growth ◽  
Atomic Layer ◽  
Deposition Process ◽  
High Growth Rate ◽  
Solid Oxide ◽  
Oxide Thin Film ◽  
Oxide Fuel ◽  
Layer Deposition
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