179 research outputs found
A geometrical origin for the covariant entropy bound
Causal diamond-shaped subsets of space-time are naturally associated with
operator algebras in quantum field theory, and they are also related to the
Bousso covariant entropy bound. In this work we argue that the net of these
causal sets to which are assigned the local operator algebras of quantum
theories should be taken to be non orthomodular if there is some lowest scale
for the description of space-time as a manifold. This geometry can be related
to a reduction in the degrees of freedom of the holographic type under certain
natural conditions for the local algebras. A non orthomodular net of causal
sets that implements the cutoff in a covariant manner is constructed. It gives
an explanation, in a simple example, of the non positive expansion condition
for light-sheet selection in the covariant entropy bound. It also suggests a
different covariant formulation of entropy bound.Comment: 20 pages, 8 figures, final versio
Geometric entropy, area, and strong subadditivity
The trace over the degrees of freedom located in a subset of the space
transforms the vacuum state into a density matrix with non zero entropy. This
geometric entropy is believed to be deeply related to the entropy of black
holes. Indeed, previous calculations in the context of quantum field theory,
where the result is actually ultraviolet divergent, have shown that the
geometric entropy is proportional to the area for a very special type of
subsets. In this work we show that the area law follows in general from simple
considerations based on quantum mechanics and relativity. An essential
ingredient of our approach is the strong subadditive property of the quantum
mechanical entropy.Comment: Published versio
Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS) I. Detection of hot neutral sodium at high altitudes on WASP-49b
High-resolution optical spectroscopy during the transit of HD 189733b, a
prototypical hot Jupiter, allowed the resolution of the Na I D sodium lines in
the planet, giving access to the extreme conditions of the planet upper
atmosphere. We have undertaken HEARTS, a spectroscopic survey of exoplanet
upper atmospheres, to perform a comparative study of hot gas giants and
determine how stellar irradiation affect them. Here, we report on the first
HEARTS observations of the hot Saturn-mass planet WASP-49b. We observed the
planet with the HARPS high-resolution spectrograph at ESO 3.6m telescope. We
collected 126 spectra of WASP-49, covering three transits of WASP-49b. We
analyzed and modeled the planet transit spectrum, while paying particular
attention to the treatment of potentially spurious signals of stellar origin.
We spectrally resolve the Na I D lines in the planet atmosphere and show that
these signatures are unlikely to arise from stellar contamination. The large
contrasts of (D) and (D) require the
presence of hot neutral sodium ( K) at high altitudes
(1.5 planet radius or 45,000 km). From estimating the cloudiness
index of WASP-49b, we determine its atmosphere to be cloud free at the
altitudes probed by the sodium lines. WASP-49b is close to the border of the
evaporation desert and exhibits an enhanced thermospheric signature with
respect to a farther-away planet such as HD 189733b.Comment: Accepted for publication in A&A. 14 page
Orbital misalignment of the super-Earth Men c with the spin of its star
Planet-planet scattering events can leave an observable trace of a planet's
migration history in the form of orbital misalignment with respect to the the
stellar spin axis, which is measurable from spectroscopic timeseries taken
during transit. We present high-resolution spectroscopic transits observed with
ESPRESSO of the close-in super-Earth Men c. The system also contains an
outer giant planet on a wide, eccentric orbit, recently found to be inclined
with respect to the inner planetary orbit. These characteristics are
reminiscent of past dynamical interactions. We successfully retrieve the
planet-occulted light during transit and find evidence that the orbit of
Men c is moderately misaligned with the stellar spin axis with ().
This is consistent with the super-Earth Men c having followed a
high-eccentricity migration followed by tidal circularisation, and hints that
super-Earths can form at large distances from their star. We also detect clear
signatures of solar-like oscillations within our ESPRESSO radial velocity
timeseries, where we reach a radial velocity precision of cm/s. We
model the oscillations using Gaussian processes and retrieve a frequency of
maximum oscillation, Hz. These
oscillations makes it challenging to detect the Rossiter-McLaughlin effect
using traditional methods. We are, however, successful using the reloaded
Rossiter-McLaughlin approach. Finally, in an appendix we also present updated
physical parameters and ephemerides for Men c from a Gaussian process
transit analysis of the full TESS Cycle 1 data.Comment: 20 pages, 11 figures. Published in MNRA
The Hot Neptune WASP-166 b with ESPRESSO II: Confirmation of atmospheric sodium
The hot Neptune desert, a distinct lack of highly irradiated planets in the
size range of Neptune, remains one of the most intriguing results of exoplanet
population studies. A deeper understanding of the atmosphere of exoplanets
sitting at the edge or even within the Neptune desert will allow us to better
understand if planetary formation or evolution processes are at the origin of
the desert. A detection of sodium in WASP-166b was presented previously with
tentative line broadening at the 3.4 sigma with the HARPS spectrograph. We
update this result with two transits observed with the ESPRESSO spectrograph,
confirming the detection in each night and the broadened character of the line.
This result marks the first confirmed resolved sodium detection within the
Neptune desert. In this work, we additionally highlight the importance of
treating low-SNR spectral regions, particularly where absorption lines of
stellar sodium and planetary sodium overlap at mid-transit - an important
caveat for future observations of the system.Comment: Letter, re-submitted to MNRAS after minor referee report; comments
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Protein-Polymer Conjugates Synthesized Using Water-Soluble Azlactone-Functionalized Polymers Enable Receptor-Specific Cellular Uptake Toward Targeted Drug Delivery
Conjugation of proteins to drug-loaded polymeric structures is an attractive strategy for facilitating target-specific drug delivery for a variety of clinical needs. Polymers currently available for conjugation to proteins generally have limited chemical versatility for subsequent drug loading. Many polymers that do have chemical functionality useful for drug loading are often insoluble in water, making it difficult to synthesize functional protein–polymer conjugates for targeted drug delivery. In this work, we demonstrate that reactive, azlactone-functionalized polymers can be grafted to proteins, conjugated to a small-molecule fluorophore, and subsequently internalized into cells in a receptor-specific manner. Poly(2-vinyl-4,4-dimethylazlactone), synthesized using reversible addition–fragmentation chain transfer polymerization, was modified post-polymerization with substoichiometric equivalents of triethylene glycol monomethyl ether to yield reactive water-soluble, azlactone-functionalized copolymers. These reactive polymers were then conjugated to proteins holo-transferrin and ovotransferrin. Protein gel analysis verified successful conjugation of proteins to polymer, and protein–polymer conjugates were subsequently purified from unreacted proteins and polymers using size exclusion chromatography. Internalization experiments using a breast cancer cell line that overexpresses the transferrin receptor on its surface showed that the holo-transferrin–polymer conjugate was successfully internalized by cells in a mechanism consistent with receptor-mediated endocytosis. Internalization of protein–polymer conjugate demonstrated that the protein ligand maintained its overall structure and function following conjugation to polymer. Our approach to protein–polymer conjugate synthesis offers a simple, tailorable strategy for preparing bioconjugates of interest for a broad range of biomedical applications
Stellar surface magneto-convection as a source of astrophysical noise II. Center-to-limb parameterisation of absorption line profiles and comparison to observations
Manifestations of stellar activity (such as star-spots, plage/faculae, and
convective flows) are well known to induce spectroscopic signals often referred
to as astrophysical noise by exoplanet hunters. For example, setting an
ultimate goal of detecting true Earth-analogs demands reaching radial velocity
(RV) precisions of ~9 cm/s. While this is becoming technically feasible with
the latest generation of highly stabilised spectrographs, it is astrophysical
noise that sets the true fundamental barrier on attainable RV precisions. In
this paper we parameterise the impact of solar surface magneto-convection on
absorption line profiles, and extend the analysis from the solar disc centre
(Paper I) to the solar limb. Off disc-centre, the plasma flows orthogonal to
the granule tops begin to lie along the line-of-sight and those parallel to the
granule tops are no longer completely aligned with the observer. Moreover, the
granulation is corrugated and the granules can block other granules, as well as
the intergranular lane components. Overall, the visible plasma flows and
geometry of the corrugated surface significantly impact the resultant line
profiles and induce centre-to-limb variations in shape and net position. We
detail these herein, and compare to various solar observations. We find our
granulation parameterisation can recreate realistic line profiles and induced
radial velocity shifts, across the stellar disc, indicative of both those found
in computationally heavy radiative 3D magnetohydrodynamical simulations and
empirical solar observations.Comment: 17 pages, 14 figures, accepted to Ap
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