471 research outputs found
Experimentally increased brood size accelerates actuarial senescence and increases subsequent reproductive effort in a wild bird population
The assumption that reproductive effort decreases somatic state, accelerating ageing, is central to our understanding of life-history variation. Maximal reproductive effort early in life is predicted to be maladaptive by accelerating ageing disproportionally, decreasing fitness. Optimality theory predicts that reproductive effort is restrained early in life to balance the fitness contribution of reproduction against the survival cost induced by the reproductive effort. When adaptive, the level of reproductive restraint is predicted to be inversely linked to the remaining life expectancy, potentially resulting in a terminal effort in the last period of reproduction. Experimental tests of the reproductive restraint hypothesis require manipulation of somatic state and subsequent investigation of reproductive effort and residual life span. To our knowledge the available evidence remains inconclusive, and hence reproductive restraint remains to be demonstrated. We modulated somatic state through a lifelong brood size manipulation in wild jackdaws and measured its consequences for age-dependent mortality and reproductive success. The assumption that lifelong increased brood size reduced somatic state was supported: Birds rearing enlarged broods showed subsequent increased rate of actuarial senescence, resulting in reduced residual life span. The treatment induced a reproductive response in later seasons: Egg volume and nestling survival were higher in subsequent seasons in the increased versus reduced broods' treatment group. We detected these increases in egg volume and nestling survival despite the expectation that in the absence of a change in reproductive effort, the reduced somatic state indicated by the increased mortality rate would result in lower reproductive output. This leads us to conclude that the higher reproductive success we observed was the result of higher reproductive effort. Our findings show that reproductive effort negatively covaries with remaining life expectancy, supporting optimality theory and confirming reproductive restraint as a key factor underpinning life-history variation
Electric-field-induced coherent coupling of the exciton states in a single quantum dot
The signature of coherent coupling between two quantum states is an
anticrossing in their energies as one is swept through the other. In single
semiconductor quantum dots containing an electron-hole pair the eigenstates
form a two-level system that can be used to demonstrate quantum effects in the
solid state, but in all previous work these states were independent. Here we
describe a technique to control the energetic splitting of these states using a
vertical electric field, facilitating the observation of coherent coupling
between them. Near the minimum splitting the eigenstates rotate in the plane of
the sample, being orientated at 45{\deg} when the splitting is smallest. Using
this system we show direct control over the exciton states in one quantum dot,
leading to the generation of entangled photon pairs
Quantum Memories. A Review based on the European Integrated Project "Qubit Applications (QAP)"
We perform a review of various approaches to the implementation of quantum
memories, with an emphasis on activities within the quantum memory sub-project
of the EU Integrated Project "Qubit Applications". We begin with a brief
overview over different applications for quantum memories and different types
of quantum memories. We discuss the most important criteria for assessing
quantum memory performance and the most important physical requirements. Then
we review the different approaches represented in "Qubit Applications" in some
detail. They include solid-state atomic ensembles, NV centers, quantum dots,
single atoms, atomic gases and optical phonons in diamond. We compare the
different approaches using the discussed criteria.Comment: 22 pages, 12 figure
40-Gbaud 16-QAM transmitter using tandem IQ modulators with binary driving electronic signals
We propose a novel 16-quadrature amplitude modulation (QAM) transmitter based on two cascaded IQ modulators driven by four separate binary electrical signals. The proposed 16-QAM transmitter features scalable configuration and stable performance with simple bias-control. Generation of 16-QAM signals at 40 Gbaud is experimentally demonstrated for the first time and visualized with a high speed constellation analyzer. The proposed modulator is also compared to two other schemes. We investigate the modulator bandwidth requirements and tolerance to accumulated chromatic dispersion through numerical simulations, and the minimum theoretical insertion attenuation is calculated analytically
Multi-criteria assessment of household preferences for reducing greenhouse gas emissions: an analysis of household survey data from four European cities
In a study of households living in mid-size cities in France, Germany, Norway and Sweden we assessed preferences (among 65 possible actions) for reducing greenhouse gas (GHG) emissions. Each GHG reduction action was compared in terms of three objective criteria â CO2e emissions, health impact and cost â using scores which gave alternative priority weightings to each. The multi-criteria scores were then compared with the proportion of respondents declaring their willingness to implement each action. Actions that respondents were often willing to implement and scored highly on the three assessment criteria included measures with likely ancillary benefits for health such as eating 30% more vegetarian food, walking and cycling instead of using public transport, and improvements of roof and window insulation. Although most householders appeared willing to make appreciable changes to their lifestyle and home in order to help achieve GHG emissions reductions, relatively few signaled their willingness to adopt major changes, such as becoming entirely vegetarian or giving up use of the car, even if there were appreciable health benefits. The evidence of these analyses provides insights into household preferences for actions that may help achieve important mitigation and health benefits
Temporal deconvolution of vascular plant-derived fatty acids exported from terrestrial watersheds
Relatively little is known about the amount of time that lapses between the photosynthetic fixation of carbon by vascular land plants and its incorporation into the marine sedimentary record, yet the dynamics of terrestrial carbon sequestration have important implications for the carbon cycle. Vascular plant carbon may encounter multiple potential intermediate storage pools and transport trajectories, and the age of vascular plant carbon accumulating in marine sediments will reflect these different pre-depositional histories. Here, we examine down-core 14C profiles of higher plant leaf wax-derived fatty acids isolated from high fidelity sedimentary sequences spanning the so-called âbomb-spikeâ, and encompassing a ca. 60-degree latitudinal gradient from tropical (Cariaco Basin), temperate (Saanich Inlet), and polar (Mackenzie Delta) watersheds to constrain integrated vascular plant carbon storage/transport times (âresidence timesâ).
Using a modeling framework, we find that, in addition to a "young" (conditionally defined as < 50 y) carbon pool, an old pool of compounds comprises 49 to 78 % of the fractional contribution of organic carbon (OC) and exhibits variable ages reflective of the environmental setting. For the Mackenzie Delta sediments, we find a mean age of the old pool of 28 ky (±9.4, standard deviation), indicating extensive pre-aging in permafrost soils, whereas the old pools in Saanich Inlet and Cariaco Basin sediments are younger, 7.9 (±5.0) and 2.4 (±0.50) to 3.2 (±0.54) ky, respectively, indicating less protracted storage in terrestrial reservoirs. The "young" pool showed clear annual contributions for Saanich Inlet and Mackenzie Delta sediments (comprising 24% and 16% of this pool, respectively), likely reflecting episodic transport of OC from steep hillside slopes surrounding Saanich Inlet and annual spring flood deposition in the Mackenzie Delta, respectively. Contributions of 5-10 year old OC to the Cariaco Basin show a short delay of OC inflow, potentially related to transport time to the offshore basin. Modeling results also indicate that the Mackenzie Delta has an influx of young but decadal material (20-30 years of age), pointing to the presence of an intermediate reservoir.
Overall, these results show that a significant fraction of vascular plant C undergoes pre-aging in terrestrial reservoirs prior to accumulation in deltaic and marine sediments. The age distribution, reflecting both storage and transport times, likely depends on landscape-specific factors such as local topography, hydrographic characteristics, and mean annual temperature of the catchment, all of which affect the degree of soil buildup and preservation. We show that catchment-specific carbon residence times across landscapes can vary by an order of magnitude, with important implications both for carbon cycle studies and for the interpretation of molecular terrestrial paleoclimate records preserved in sedimentary sequences
Temporal deconvolution of vascular plant-derived fatty acids exported from terrestrial watersheds
Author Posting. © The Author(s), 2018. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 244 (2019): 502-521, doi:10.1016/j.gca.2018.09.034.Relatively little is known about the amount of time that lapses between the
photosynthetic fixation of carbon by vascular land plants and its incorporation into the
marine sedimentary record, yet the dynamics of terrestrial carbon sequestration have
important implications for the carbon cycle. Vascular plant carbon may encounter
multiple potential intermediate storage pools and transport trajectories, and the age of
vascular plant carbon accumulating in marine sediments will reflect these different predepositional
histories. Here, we examine down-core 14C profiles of higher plant leaf waxderived
fatty acids isolated from high fidelity sedimentary sequences spanning the socalled
âbomb-spikeâ, and encompassing a ca. 60-degree latitudinal gradient from tropical
(Cariaco Basin), temperate (Saanich Inlet), and polar (Mackenzie Delta) watersheds to
constrain integrated vascular plant carbon storage/transport times (âresidence timesâ).
Using a modeling framework, we find that, in addition to a "young" (conditionally
defined as < 50 y) carbon pool, an old pool of compounds comprises 49 to 78 % of the
fractional contribution of organic carbon (OC) and exhibits variable ages reflective of the
environmental setting. For the Mackenzie Delta sediments, we find a mean age of the old
pool of 28 ky (±9.4, standard deviation), indicating extensive pre-aging in permafrost
soils, whereas the old pools in Saanich Inlet and Cariaco Basin sediments are younger,
7.9 (±5.0) and 2.4 (±0.50) to 3.2 (±0.54) ky, respectively, indicating less protracted
storage in terrestrial reservoirs. The "young" pool showed clear annual contributions for
Saanich Inlet and Mackenzie Delta sediments (comprising 24% and 16% of this pool,
respectively), likely reflecting episodic transport of OC from steep hillside slopes
surrounding Saanich Inlet and annual spring flood deposition in the Mackenzie Delta,
respectively. Contributions of 5-10 year old OC to the Cariaco Basin show a short delay
of OC inflow, potentially related to transport time to the offshore basin. Modeling results
also indicate that the Mackenzie Delta has an influx of young but decadal material (20-30
years of age), pointing to the presence of an intermediate reservoir.
Overall, these results show that a significant fraction of vascular plant C
undergoes pre-aging in terrestrial reservoirs prior to accumulation in deltaic and marine
sediments. The age distribution, reflecting both storage and transport times, likely
depends on landscape-specific factors such as local topography, hydrographic characteristics, and mean annual temperature of the catchment, all of which affect the
degree of soil buildup and preservation. We show that catchment-specific carbon
residence times across landscapes can vary by an order of magnitude, with important
implications both for carbon cycle studies and for the interpretation of molecular
terrestrial paleoclimate records preserved in sedimentary sequences.Financial support was provided by a Schlanger Ocean
Drilling Graduate Fellowship (NJD), an EPA STAR Graduate Fellowship (NJD), a Dutch
NWO Veni grant #825.10.022 (JEV), US NSF grants #OCE-0137005 (TIE and KAH),
#OCE-052626800 (TIE), #OCE-0961980 (ERMD), and #EAR-0447323 (ERMD and
JRS), a Swiss SNF grant #200021_140850 (TIE), a Swedish Research Council grant
#2013-05204 (MS), as well as the Stanley Watson Chair for Excellence in Oceanography
at WHOI (TIE) and the WHOI Arctic Research Initiative (TIE and LG)
Effect of the GaAsP shell on optical properties of self-catalyzed GaAs nanowires grown on silicon
We realize growth of self-catalyzed core-shell GaAs/GaAsP nanowires (NWs) on
Si substrates using molecular-beam epitaxy. Transmission electron microscopy
(TEM) of single GaAs/GaAsP NWs confirms their high crystal quality and shows
domination of the zinc-blende phase. This is further confirmed in optics of
single NWs, studied using cw and time-resolved photoluminescence (PL). A
detailed comparison with uncapped GaAs NWs emphasizes the effect of the GaAsP
capping in suppressing the non-radiative surface states: significant PL
enhancement in the core-shell structures exceeding 2000 times at 10K is
observed; in uncapped NWs PL is quenched at 60K whereas single core-shell
GaAs/GaAsP NWs exhibit bright emission even at room temperature. From analysis
of the PL temperature dependence in both types of NW we are able to determine
the main carrier escape mechanisms leading to the PL quench
Long telomeres are associated with clonality in wild populations of the fissiparous starfish Coscinasterias tenuispina
7 pĂĄginas, 4 figuras, 3 tablasTelomeres usually shorten during an organismâs lifespan and have thus been used as an aging and health marker. When
telomeres become sufficiently short, senescence is induced. The most common method of restoring telomere length is via
telomerase reverse transcriptase activity, highly expressed during embryogenesis. However, although asexual reproduction from
adult tissues has an important role in the life cycles of certain species, its effect on the aging and fitness of wild populations,
as well as its implications for the long-term survival of populations with limited genetic variation, is largely unknown. Here we
compare relative telomere length of 58 individuals from four populations of the asexually reproducing starfish Coscinasterias
tenuispina. Additionally, 12 individuals were used to compare telomere lengths in regenerating and non-regenerating arms, in
two different tissues (tube feet and pyloric cecum). The level of clonality was assessed by genotyping the populations based on
12 specific microsatellite loci and relative telomere length was measured via quantitative PCR. The results revealed significantly
longer telomeres in Mediterranean populations than Atlantic ones as demonstrated by the KruskalâWallis test (K=24.17,
significant value: P-valueo0.001), with the former also characterized by higher levels of clonality derived from asexual
reproduction. Telomeres were furthermore significantly longer in regenerating arms than in non-regenerating arms within
individuals (pyloric cecum tissue: MannâWhitney test, V=299, P-valueo10â 6; and tube feet tissue Student's t= 2.28,
P-value =0.029). Our study suggests that one of the mechanisms responsible for the long-term somatic maintenance and
persistence of clonal populations is telomere elongation.This research was financially supported by a
PhD fellowship FPI-MICINN (BES-2011-044154) (ACG), the European
ASSEMBLY project (227799), the Swedish Royal Academy of Sciences (ACG)
and the Spanish Government project CTM2010-22218-C02. The research was
also supported by a âJuan de la Ciervaâ contract from the Spanish Government
(RPP) and by the Adlerbertska Research Foundation (HNS).Peer reviewe
Mapping and Evaluating Marine Protected Areas and Ecosystem Services: A Transdisciplinary Delphi Forecasting Process Framework
Marine Protected Areas (MPAs) are an important tool for management and conservation and play an increasingly recognised role in societal and human well-being. However, the assessment of MPAs often lacks a simultaneous consideration of ecological and socio-economic outcomes, and this can lead to misconceptions on the effectiveness of MPAs. In this perspective, we present a transdisciplinary approach based on the Delphi method for mapping and evaluating Marine Protected Areas for their ability to protect biodiversity while providing Ecosystem Services (ES) and related human well-being benefits - i.e., the ecosystem outputs from which people benefit. We highlight the need to include the human dimensions of marine protection in such assessments, given that the effectiveness of MPAs over time is conditional on the social, cultural and institutional contexts in which MPAs evolve. Our approach supports Ecosystem-Based Management and highlights the importance of MPAs in achieving restoration, conservation, and sustainable development objectives in relation to EU Directives such as the Marine Strategy Framework Directive (MSFD), the Maritime Spatial Planning Directive (MSPD), and the Common Fisheries Policy (CFP)
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