8,789 research outputs found
Exoplanet Characterization by Multi-Observatory Transit Photometry with TESS and CHEOPS
Space-based photometric surveys have discovered large numbers of planets
transiting other stars, but these observe in a single band-pass and yield only
the planet radius, orbital period, and transit duration. Information on the
masses, compositions, and any atmospheres of these planets requires additional
observations from the ground or space. The Transiting Exoplanet Survey
Satellite (TESS) will yield thousands of planets around bright stars suitable
for such follow-up. In the absence of spectroscopy or spectrophotometry from
space, observations through the different pass-bands of multiple space
telescopes provide some spectral information useful for identifying false
positive signals, distinguishing between reflected light and thermal emission
from hot Jupiters, and detecting Rayleigh scattering by planetary atmospheres.
We calculated the expected difference in transit depths measured by the TESS
and Characterizing Exoplanets Satellites (CHEOPS) missions, which will be more
sensitive to redder and bluer optical wavelengths, respectively. The difference
due to companion or background stars is small (<3% for main sequence
companions) and likely to be negligible and undetectable. For only a few "hot"
Jupiters, can combined photometry disambiguate between the reflected and
thermal signals from planets. However, Rayleigh scattering by hazy atmospheres
with particles sizes near 0.04 m and at pressure altitudes above ~1 mbar
can be detected for ~100 transiting planets, assuming every planet has such an
atmosphere. Hazes with this characteristic particle size do not obscure
observations at longer (near-infrared) wavelengths; CHEOPS follow-up of
TESS-detected planets could thus identify candidates suitable for further study
with the James Webb Space Telescope.Comment: MNRAS, in pres
EVOLUTION OF DOLLAR/EURO EXCHANGE RATE BEFORE AND AFTER THE BIRTH OF EURO AND POLICY IMPLICATIONS
One possible consequence of the establishment of the Euro is a challenge to the hegemony of the US dollar as the predominant international currency. No other currency has been able to rival the international role of the national currency of the US since World War II. The fact that the unipolar international monetary system can be unstable in the presence of large shocks opens a window of opportunity for the Euro to promote systemic stability. The present study pursues this conjecture by, first, exploring with cointegration and ECM techniques the interdependence between the dynamics of the Dollar/Euro exchange rate and economic fundamentals in the context of a monetary exchange rate model. Identification of the key determinants of the value of the Euro informs our analysis of the policy stance of the European Central Bank regarding the long-run global role of the Euro. Secondly, we explore whether the opportunity for a prominent systemic role of the Euro has been realized by examining the impact of the Euro on the global financial market.Euro, Exchange rate, Monetary model, Cointegration
pH-triggered phase inversion and separation of hydrophobised bacterial cellulose stabilised Pickering emulsions
The pH-triggered transitional phase behaviour of Pickering emulsions stabilised by hydrophobised bacterial cellulose (BC) is reported in this work. Neat BC was esterified with acetic (C2–), hexanoic (C6–) and dodecanoic (C12–) acids, respectively. We observed that C6– and C12–BC stabilised emulsions exhibited a pH-triggered reversible transitional phase separation. Water-in-toluene emulsions containing of 60 vol.% dispersed phase stabilised by C6– and C12–BC were produced at pH 5. Lowering the pH of the aqueous phase to 1 did not affect the emulsion type. Increasing the pH to 14, however, caused the emulsions to phase separate. This phase separation was caused by electrostatic repulsion between modified BC due to dissociable acidic surface groups at high pH, which lowered the surface coverage of the water droplets by modified BC. When the pH was re-adjusted to 1 again, w/o emulsions re-formed for C6– and C12–BC stabilised emulsions. C2–BC stabilised emulsions, on the other hand, underwent an irreversible pH-triggered transitional phase separation and inversion. This difference in phase behaviour between C2–BC and C6–/C12–BC was attributed to the hydrolysis of the ester bonds of C2–BC at high pH. This hypothesis is in good agreement with the measured degree of surface substitution (DSS) of modified BC after the pH-triggered experiments. The DSS of C2–BC decreased by 20% whilst the DSS remained constant for C6– and C12–BC
Bulk matter fields on two-field thick branes
In this paper we obtain a new solution of a brane made up of a scalar field
coupled to a dilaton. There is a unique parameter in the solution, which
decides the distribution of the energy density and will effect the localization
of bulk matter fields. For free vector fields, we find that the zero mode can
be localized on the brane. And for vector fields coupled with the dilaton via
, the condition for localizing the zero mode is
with with , which
includes the case . While the zero mode for free Kalb-Ramond fields can
not be localized on the brane, if only we introduce a coupling between the
Kalb-Ramond fields and the dilaton via .
When the coupling constant satisfies with or
with , the zero mode for the KR fields can
be localized on the brane. For spin half fermion fields, we consider the
coupling between the fermions
and the background scalars with positive Yukawa coupling . The effective
potentials for both chiral fermions have three types of shapes decided by the
relation between the dilaton-fermion coupling constant and the
parameter . For , the zero mode of left-chiral
fermion can be localized on the brane. While for with
or with , the zero mode for
left-chiral fermion also can be localized.Comment: 22 pages, 8 figures, improved version, accepted by Physical Review
A Naturally Minute Quantum Correction to the Cosmological Constant Descended from the Hierarchy
We demonstrate that an extremely small but positive quantum correction, or
the Casimir energy, to the cosmological constant can arise from a massive bulk
fermion field in the Randall-Sundrum model. Specifically, a cosmological
constant doubly descended from the Planck-electroweak hierarchy and as minute
as the observed dark energy scale can be naturally achieved without fine-tuning
of the bulk fermion mass. To ensure the stabilization of the system, we discuss
two stabilization mechanisms under this setup. It is found that the
Goldberger-Wise mechanism can be successfully introduced in the presence of a
massive bulk fermion, without spoiling the smallness of the quantum correction.Comment: 5 page
Study of and decays
We study the charmless two-body
and three-body decays. We obtain to agree with the
recent LHCb measurement. However, we find that is unable to explain the
LHCb observation of , which implies the possibility for other
contributions, such as that from the resonant decay with as a higher-wave baryon state. For
, we show that ,
which are consistent with the current data of , respectively. Our results also support the relation of ,
given by the previous study.Comment: 8 pages, 1 figure, revised version accepted by EPJ
Non-leptonic two-body weak decays of
We study the non-leptonic two-body weak decays of with () representing as the baryon (meson) states. Based
on the flavor symmetry, we can describe most of the data reexamined by
the BESIII Collaboration with higher precisions. However, our result of is larger than the
current experimental limit of (90\% C.L.) by BESIII. In
addition, we find that , , and , which are accessible
to the BESIII experiments.Comment: 12 pages, 1 figure, revised version accepted by PL
A Non-isothermal Theory for Interpreting Sodium Lines in Transmission Spectra of Exoplanets
We present a theory for interpreting the sodium lines detected in
transmission spectra of exoplanetary atmospheres. Previous analyses employed
the isothermal approximation and dealt only with the transit radius. By
recognising the absorption depth and the transit radius as being independent
observables, we develop a theory for jointly interpreting both quantities,
which allows us to infer the temperatures and number densities associated with
the sodium lines. We are able to treat a non-isothermal situation with a
constant temperature gradient. Our novel diagnostics take the form of
simple-to-use algebraic formulae and require measurements of the transit radii
(and their corresponding absorption depths) at line center and in the line wing
for both sodium lines. We apply our diagnostics to the HARPS data of HD
189733b, confirm the upper atmospheric heating reported by Huitson et al.
(2012), derive a temperature gradient of K km and
find densities to cm.Comment: Accepted by ApJ Letters. 6 pages, 3 figure
- …