12,556 research outputs found
Trust, morality and altruism in the donation of biological material : the case of Portugal
This paper examines a number of social, ethical and cultural issues related to the
application of biotechnology. The focus of the paper relies on two different cases
of governing biotechnology in Portugal, referring to donation of biological
material: the act of donation of eggs and sperm; and volunteers for donation of
DNA material for the forensic national DNA database. We analyze the
discourses on donation of biological material framing them in rhetorical
devices of gift, altruism, informed consent and social responsibility. This comes
blended with still unclear and emergent regulation and policies of access,
retention, preservation and governing of biological material and of donors’
identification. The risks are mitigated by narratives of science and technology
as social progress and providers of public good and health benefits, as well as
by underlining the individual responsibility in this domain and by reinforcing
the rhetoric of gene quality, based on socio-cultural and bio-genetic criteria
Beyond the required LISA free-fall performance: new LISA pathfinder results down to 20  μHz
In the months since the publication of the first results, the noise performance of LISA Pathfinder has improved because of reduced Brownian noise due to the continued decrease in pressure around the test masses, from a better correction of noninertial effects, and from a better calibration of the electrostatic force actuation. In addition, the availability of numerous long noise measurement runs, during which no perturbation is purposely applied to the test masses, has allowed the measurement of noise with good statistics down to 20  μHz. The Letter presents the measured differential acceleration noise figure, which is at (1.74±0.05)  fm s^{-2}/sqrt[Hz] above 2 mHz and (6±1)×10  fm s^{-2}/sqrt[Hz] at 20  μHz, and discusses the physical sources for the measured noise. This performance provides an experimental benchmark demonstrating the ability to realize the low-frequency science potential of the LISA mission, recently selected by the European Space Agency
Late Holocene climatic oscillations traced by clay mineral assemblages and other palaeoceanographic proxies in Ria de Vigo (NW Spain)
This work aims to study recent climatic oscillations and their influence on sedimentation in the Ria de Vigo, a
coastal embayment in Galicia, NW Spain. It is based on the study of clay mineral assemblages, in conjunction with other
proxies (granulometric, geochemical, geochronological and microfaunal), in the core KSGX 24. A Benthic Foraminifera
High Productivity (BFHP) proxy was used to determine changes in the flux of organic matter (OM) at the bottom of
the study area. Total organic carbon (TOC) content is not a suitable proxy to estimate changes in the past supply of OM
due to diagenetic processes.The sedimentation was finest in 3 sections: ~ 230–214 cm, ~ 185–73 cm and ~ 20–0 cm. These muddy sections are
characterised, in general, by higher proportions of detrital minerals, concentrations of several chemical elements related
to lithogenic sources and BFHP values. In addition, these sections are impoverished in carbonates, Ca, Sr and La when
compared with the layers with the highest sand content.The clay mineral assemblage of the studied site, characterised by the dominance of illite, intermediate concentrations
of kaolinite and minor amounts of smectite and chlorite, reveals the prevalence of a typical temperate humid climate in
the last 3 ka BP, the estimated age for the core base. However, the quantities of illite and chlorite increase in the muddy
layers. The characteristics of these muddy layers were interpreted as representing relatively cold climatic oscillations
associated with the strengthening of northerly winds and the prevalence of an upwelling regime corresponding to wellknown
periods, such as the first cold period of the Upper Holocene (~ 2.9 ka cal BP), the Dark Ages (between ~ 2.2 - 1.2
ka cal BP) and the Little Ice Age (~ 0.6 ka cal BP)
Comparing the performance of FA, DFA and DMA using different synthetic long-range correlated time series
Notwithstanding the significant efforts to develop estimators of long-range
correlations (LRC) and to compare their performance, no clear consensus exists
on what is the best method and under which conditions. In addition, synthetic
tests suggest that the performance of LRC estimators varies when using
different generators of LRC time series. Here, we compare the performances of
four estimators [Fluctuation Analysis (FA), Detrended Fluctuation Analysis
(DFA), Backward Detrending Moving Average (BDMA), and centred Detrending Moving
Average (CDMA)]. We use three different generators [Fractional Gaussian Noises,
and two ways of generating Fractional Brownian Motions]. We find that CDMA has
the best performance and DFA is only slightly worse in some situations, while
FA performs the worst. In addition, CDMA and DFA are less sensitive to the
scaling range than FA. Hence, CDMA and DFA remain "The Methods of Choice" in
determining the Hurst index of time series.Comment: 6 pages (including 3 figures) + 3 supplementary figure
Molecular motors robustly drive active gels to a critically connected state
Living systems often exhibit internal driving: active, molecular processes
drive nonequilibrium phenomena such as metabolism or migration. Active gels
constitute a fascinating class of internally driven matter, where molecular
motors exert localized stresses inside polymer networks. There is evidence that
network crosslinking is required to allow motors to induce macroscopic
contraction. Yet a quantitative understanding of how network connectivity
enables contraction is lacking. Here we show experimentally that myosin motors
contract crosslinked actin polymer networks to clusters with a scale-free size
distribution. This critical behavior occurs over an unexpectedly broad range of
crosslink concentrations. To understand this robustness, we develop a
quantitative model of contractile networks that takes into account network
restructuring: motors reduce connectivity by forcing crosslinks to unbind.
Paradoxically, to coordinate global contractions, motor activity should be low.
Otherwise, motors drive initially well-connected networks to a critical state
where ruptures form across the entire network.Comment: Main text: 21 pages, 5 figures. Supplementary Information: 13 pages,
8 figure
Sub-femto-g free fall for space-based gravitational wave observatories: LISA pathfinder results
We report the first results of the LISA Pathfinder in-flight experiment. The results demonstrate that two free-falling reference test masses, such as those needed for a space-based gravitational wave observatory like LISA, can be put in free fall with a relative acceleration noise with a square root of the power spectral density of 5.2 ± 0.1 fm s−2/√Hz or (0.54 ± 0.01) × 10−15 g/√Hz, with g the standard gravity, for frequencies between 0.7 and 20 mHz. This value is lower than the LISA Pathfinder requirement by more than a factor 5 and within a factor 1.25 of the requirement for the LISA mission, and is compatible with Brownian noise from viscous damping due to the residual gas surrounding the test masses. Above 60 mHz the acceleration noise is dominated by interferometer displacement readout noise at a level of (34.8 ± 0.3) fm/√Hz, about 2 orders of magnitude better than requirements. At f ≤ 0.5 mHz we observe a low-frequency tail that stays below 12 fm s−2/√Hz down to 0.1 mHz. This performance would allow for a space-based gravitational wave
observatory with a sensitivity close to what was originally foreseen for LISA
Micrometeoroid Events in LISA Pathfinder
The zodiacal dust complex, a population of dust and small particles that
pervades the Solar System, provides important insight into the formation and
dynamics of planets, comets, asteroids, and other bodies. Here we present a new
set of data obtained using a novel technique: direct measurements of momentum
transfer to a spacecraft from individual particle impacts. This technique is
made possible by the extreme precision of the instruments flown on the LISA
Pathfinder spacecraft, a technology demonstrator for a future space-based
gravitational wave observatory that operated near the first Sun-Earth Lagrange
point from early 2016 through Summer of 2017. Using a simple model of the
impacts and knowledge of the control system, we show that it is possible to
detect impacts and measure properties such as the transferred momentum (related
to the particle's mass and velocity), direction of travel, and location of
impact on the spacecraft. In this paper, we present the results of a systematic
search for impacts during 4348 hours of Pathfinder data. We report a total of
54 candidates with momenta ranging from 0.2 to
230. We furthermore make a comparison of these candidates
with models of micrometeoroid populations in the inner solar system including
those resulting from Jupiter-family comets, Oort-cloud comets, Hailey-type
comets, and Asteroids. We find that our measured population is consistent with
a population dominated by Jupiter-family comets with some evidence for a
smaller contribution from Hailey-type comets. This is in agreement with
consensus models of the zodiacal dust complex in the momentum range sampled by
LISA Pathfinder.Comment: 22 pages, 14 figures, accepted in Ap
- …