53 research outputs found
A Gaudier Future that Almost Blinds the Eye: A Review of The Future of Ideas by Lawrence Lessig
Spectropolarimetry of life: airborne measurements from a hot air balloon
Does life exist outside our Solar System? A first step towards searching for
life outside our Solar System is detecting life on Earth by using remote
sensing applications. One powerful and unambiguous biosignature is the circular
polarization resulting from the homochirality of biotic molecules and systems.
We aim to investigate the possibility of identifying and characterizing life on
Earth by using airborne spectropolarimetric observations from a hot air balloon
during our field campaign in Switzerland, May 2022.
In this work we present the optical-setup and the data obtained from aerial
circular spectropolarimetric measurements of farmland, forests, lakes and urban
sites. We make use of the well-calibrated FlyPol instrument that measures the
fractionally induced circular polarization () of (reflected) light with a
sensitivity of . The instrument operates in the visible spectrum,
ranging from 400 to 900 nm. We demonstrate the possibility to distinguish
biotic from abiotic features using circular polarization spectra and additional
broadband linear polarization information. We review the performance of our
optical-setup and discuss potential improvements. This sets the requirements on
how to perform future airborne spectropolarimetric measurements of the Earth's
surface features from several elevations.Comment: 13 pages, 10 figures, to be submitted in SPIE Proceedings 12214-
A snapshot full-Stokes spectropolarimeter for detecting life on Earth
We present the design of a point-and-shoot non-imaging full-Stokes
spectropolarimeter dedicated to detecting life on Earth from an orbiting
platform like the ISS. We specifically aim to map circular polarization in the
spectral features of chlorophyll and other biopigments for our planet as a
whole. These non-zero circular polarization signatures are caused by
homochirality of the molecular and supramolecular configurations of organic
matter, and are considered the most unambiguous biomarker. To achieve a fully
solid-state snapshot design, we implement a novel spatial modulation that
completely separates the circular and linear polarization channels. The
polarization modulator consists of a patterned liquid-crystal quarter-wave
plate inside the spectrograph slit, which also constitutes the first optical
element of the instrument. This configuration eliminates cross-talk between
linear and circular polarization, which is crucial because linear polarization
signals are generally much stronger than the circular polarization signals.
This leads to a quite unorthodox optical concept for the spectrograph, in which
the object and the pupil are switched. We discuss the general design
requirements and trade-offs of LSDpol (Life Signature Detection polarimeter), a
prototype instrument that is currently under development
Biosignatures of the Earth
ontext. Homochirality is a generic and unique property of life on Earth and is considered a universal and agnostic biosignature. Homochirality induces fractional circular polarization in the incident light that it reflects. Because this circularly polarized light can be sensed remotely, it can be one of the most compelling candidate biosignatures in life detection missions. While there are also other sources of circular polarization, these result in spectrally flat signals with lower magnitude. Additionally, circular polarization can be a valuable tool in Earth remote sensing because the circular polarization signal directly relates to vegetation physiology.
Aims. While high-quality circular polarization measurements can be obtained in the laboratory and under semi-static conditions in the field, there has been a significant gap to more realistic remote sensing conditions.
Methods. In this study, we present sensitive circular spectropolarimetric measurements of various landscape elements taken from a fast-moving helicopter.
Results. We demonstrate that during flight, within mere seconds of measurements, we can differentiate (S∕N > 5) between grass fields, forests, and abiotic urban areas. Importantly, we show that with only nonzero circular polarization as a discriminant, photosynthetic organisms can even be measured in lakes.
Conclusions. Circular spectropolarimetry can be a powerful technique to detect life beyond Earth, and we emphasize the potential of utilizing circular spectropolarimetry as a remote sensing tool to characterize and monitor in detail the vegetation physiology and terrain features of Earth itself
Design of the Life Signature Detection Polarimeter LSDpol
Many biologically produced chiral molecules such as amino acids and sugars
show a preference for left or right handedness (homochirality). Light reflected
by biological materials such as algae and leaves therefore exhibits a small
amount of circular polarization that strongly depends on wavelength. Our Life
Signature Detection polarimeter (LSDpol) is optimized to measure these
signatures of life. LSDpol is a compact spectropolarimeter concept with no
moving parts that instantaneously measures linear and circular polarization
averaged over the field of view with a sensitivity of better than 1e-4. We
expect to launch the instrument into orbit after validating its performance on
the ground and from aircraft.
LSDpol is based on a spatially varying quarter-wave retarder that is
implemented with a patterned liquid-crystal. It is the first optical element to
maximize the polarimetric sensitivity. Since this pattern as well as the
entrance slit of the spectrograph have to be imaged onto the detector, the slit
serves as the aperture, and an internal field stop limits the field of view.
The retarder's fast axis angle varies linearly along one spatial dimension. A
fixed quarter-wave retarder combined with a polarization grating act as the
disperser and the polarizing beam-splitter. Circular and linear polarization
are thereby encoded at incompatible modulation frequencies across the spectrum,
which minimizes the potential cross-talk from linear into circular
polarization.Comment: 10 pages, 10 figures, SPIE Proceedings 11443-16
Molecular Characterization of the Gastrula in the Turtle Emys orbicularis: An Evolutionary Perspective on Gastrulation
Due to the presence of a blastopore as in amphibians, the turtle has been suggested to exemplify a transition form from an amphibian- to an avian-type gastrulation pattern. In order to test this hypothesis and gain insight into the emergence of the unique characteristics of amniotes during gastrulation, we have performed the first molecular characterization of the gastrula in a reptile, the turtle Emys orbicularis. The study of Brachyury, Lim1, Otx2 and Otx5 expression patterns points to a highly conserved dynamic of expression with amniote model organisms and makes it possible to identify the site of mesoderm internalization, which is a long-standing issue in reptiles. Analysis of Brachyury expression also highlights the presence of two distinct phases, less easily recognizable in model organisms and respectively characterized by an early ring-shaped and a later bilateral symmetrical territory. Systematic comparisons with tetrapod model organisms lead to new insights into the relationships of the blastopore/blastoporal plate system shared by all reptiles, with the blastopore of amphibians and the primitive streak of birds and mammals. The biphasic Brachyury expression pattern is also consistent with recent models of emergence of bilateral symmetry, which raises the question of its evolutionary significance
SPICES: Spectro-Polarimetric Imaging and Characterization of Exoplanetary Systems
SPICES (Spectro-Polarimetric Imaging and Characterization of Exoplanetary
Systems) is a five-year M-class mission proposed to ESA Cosmic Vision. Its
purpose is to image and characterize long-period extrasolar planets and
circumstellar disks in the visible (450 - 900 nm) at a spectral resolution of
about 40 using both spectroscopy and polarimetry. By 2020/22, present and
near-term instruments will have found several tens of planets that SPICES will
be able to observe and study in detail. Equipped with a 1.5 m telescope, SPICES
can preferentially access exoplanets located at several AUs (0.5-10 AU) from
nearby stars (25 pc) with masses ranging from a few Jupiter masses to Super
Earths (2 Earth radii, 10 M) as well as circumstellar
disks as faint as a few times the zodiacal light in the Solar System
Recommended from our members
ESA Voyage 2050 White Paper: Detecting life outside our solar system with a large high-contrast-imaging mission
In this white paper, we recommend the European Space Agency plays a proactive role in developing a global collaborative effort to construct a large high-contrast imaging space telescope, e.g. as currently under study by NASA. Such a mission will be needed to characterize a sizable sample of temperate Earth-like planets in the habitable zones of nearby Sun-like stars and to search for extraterrestrial biological activity. We provide an overview of relevant European expertise, and advocate ESA to start a technology development program towards detecting life outside the Solar system
The Impact of Brand Quality on Shareholder Wealth
This study examines the impact of brand quality on three components of shareholder wealth: stock returns, systematic risk, and idiosyncratic risk. The study finds that brand quality enhances shareholder wealth insofar as unanticipated changes in brand quality are positively associated with stock returns and negatively related to changes in idiosyncratic risk. However, unanticipated changes in brand quality can also erode shareholder wealth because they have a positive association with changes in systematic risk. The study introduces a contingency theory view to the marketing-finance interface by analyzing the moderating role of two factors that are widely followed by investors. The results show an unanticipated increase (decrease) in current-period earnings enhances (depletes) the positive impact of unanticipated changes in brand quality on stock returns and mitigates (enhances) their deleterious effects on changes in systematic risk. Similarly, brand quality is more valuable for firms facing increasing competition (i.e., unanticipated decreases in industry concentration). The results are robust to endogeneity concerns and across alternative models. The authors conclude by discussing the nuanced implications of their findings for shareholder wealth, reporting brand quality to investors, and its use in employee evaluation
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