2,077 research outputs found
Theoretical models of planetary system formation: mass vs semi-major axis
Planet formation models have been developed during the last years in order to
try to reproduce the observations of both the solar system, and the extrasolar
planets. Some of these models have partially succeeded, focussing however on
massive planets, and for the sake of simplicity excluding planets belonging to
planetary systems. However, more and more planets are now found in planetary
systems. This tendency, which is a result of both radial velocity, transit and
direct imaging surveys, seems to be even more pronounced for low mass planets.
These new observations require the improvement of planet formation models,
including new physics, and considering the formation of systems. In a recent
series of papers, we have presented some improvements in the physics of our
models, focussing in particular on the internal structure of forming planets,
and on the computation of the excitation state of planetesimals, and their
resulting accretion rate. In this paper, we focus on the concurrent effect of
the formation of more than one planet in the same protoplanetary disc, and show
the effect, in terms of global architecture and composition of this
multiplicity. We use a N-body calculation including collision detection to
compute the orbital evolution of a planetary system. Moreover, we describe the
effect of competition for accretion of gas and solids, as well as the effect of
gravitational interactions between planets. We show that the masses and
semi-major axis of planets are modified by both the effect of competition and
gravitational interactions. We also present the effect of the assumed number of
forming planets in the same system (a free parameter of the model), as well as
the effect of the inclination and eccentricity damping.Comment: accepted in Astronomy and Astrophysic
Astronomical spectrograph calibration with broad-spectrum frequency combs
Broadband femtosecond-laser frequency combs are filtered to
spectrographically resolvable frequency-mode spacing, and the limitations of
using cavities for spectral filtering are considered. Data and theory are used
to show implications to spectrographic calibration of high-resolution,
astronomical spectrometers
The impact of geographic expansion in banking: some axioms to grind
Interstate banking ; Banking structure ; Banking market
Kilohertz-resolution spectroscopy of cold atoms with an optical frequency comb
We have performed sub-Doppler spectroscopy on the narrow intercombination
line of cold calcium atoms using the amplified output of a femtosecond laser
frequency comb. Injection locking of a 657-nm diode laser with a femtosecond
comb allows for two regimes of amplification, one in which many lines of the
comb are amplified, and one where a single line is predominantly amplified. The
output of the laser in both regimes was used to perform kilohertz-level
spectroscopy. This experiment demonstrates the potential for high-resolution
absolute-frequency spectroscopy over the entire spectrum of the frequency comb
output using a single high-finesse optical reference cavity.Comment: 4 pages, 4 Figure
Ultralow phase noise microwave generation with an Er:fiber-based optical frequency divider
We present an optical frequency divider based on a 200 MHz repetition rate
Er:fiber mode-locked laser that, when locked to a stable optical frequency
reference, generates microwave signals with absolute phase noise that is equal
to or better than cryogenic microwave oscillators. At 1 Hz offset from a 10 GHz
carrier, the phase noise is below -100 dBc/Hz, limited by the optical
reference. For offset frequencies > 10 kHz, the phase noise is shot noise
limited at -145 dBc/Hz. An analysis of the contribution of the residual noise
from the Er:fiber optical frequency divider is also presented.Comment: 4 pages, 3 figure
Fermionic Symmetries: Extension of the two to one Relationship Between the Spectra of Even-Even and Neighbouring Odd mass Nuclei
In the single j shell there is a two to one relationship between the spectra
of certain even-even and neighbouring odd mass nuclei e.g. the calculated
energy levels of J=0^+ states in ^{44}Ti are at twice the energies of
corresponding levels in ^{43}Ti(^{43}Sc) with J=j=7/2. Here an approximate
extension of the relationship is made by adopting a truncated seniority scheme
i.e. for ^{46}Ti and ^{45}Sc we get the relationship if we do not allow the
seniority v=4 states to mix with the v=0 and v=2 states. Better than that, we
get very close to the two to one relationship if seniority v=4 states are
admixed perturbatively. In addition, it is shown that the higher isospin states
do not contain seniority 4 admixtures.Comment: 11 pages, RevTex file and no figures, typos added, references changed
and changed content
A New Bound on Excess Frequency Noise in Second Harmonic Generation in PPKTP at the 10^-19 Level
We report a bound on the relative frequency fluctuations in nonlinear second
harmonic generation. A 1064nm Nd:YAG laser is used to read out the phase of a
Mach-Zehnder interferometer while PPKTP, a nonlinear crystal, is placed in each
arm to generate second harmonic light. By comparing the arm length difference
of the Mach Zehnder as read out by the fundamental 1064 nm light, and its
second harmonic at 532 nm, we can bound the excess frequency noise introduced
in the harmonic generation process. We report an amplitude spectral density of
frequency noise with total RMS frequency deviation of 3mHz and a minimum value
of 20 {\mu}Hz/rtHz over 250 seconds with a measurement bandwidth of 128 Hz,
corresponding to an Allan deviation of 10^-19 at 20 seconds.Comment: Submitted to Optics Express June 201
Observation of the 1S0 - 3P0 clock transition in 27Al+
We report for the first time, laser spectroscopy of the 1S0 - 3P0 clock
transition in 27Al+. A single aluminum ion and a single beryllium ion are
simultaneously confined in a linear Paul trap, coupled by their mutual Coulomb
repulsion. This coupling allows the beryllium ion to sympathetically cool the
aluminum ion, and also enables transfer of the aluminum's electronic state to
the beryllium's hyperfine state, which can be measured with high fidelity.
These techniques are applied to a measurement of the clock transition
frequency, \nu = 1 121 015 393 207 851(8) Hz. They are also used to measure the
lifetime of the metastable clock state, \tau = 20.6 +/- 1.4 s, the ground state
1S0 g-factor, g_S = -0.00079248(14), and the excited state 3P0 g-factor, g_P =
-0.00197686(21), in units of the Bohr magneton.Comment: 4 pages, 2 figures; updated author lis
Origin, burial and preservation of late Pleistocene-age glacier ice in Arctic permafrost (Bylot Island, NU, Canada)
Over the past decades, observations of buried glacier ice exposed in coastal
bluffs and headwalls of retrogressive thaw slumps of the Arctic have
indicated that considerable amounts of late Pleistocene glacier ice survived
the deglaciation and are still preserved in permafrost. In exposures, relict
glacier ice and intrasedimental ice often coexist and look alike but their
genesis is strikingly different. This paper aims to present a detailed
description and infer the origin of a massive ice body preserved in the
permafrost of Bylot Island (Nunavut). The massive ice exposure and core
samples were described according to the cryostratigraphic approach, combining
the analysis of permafrost cryofacies and cryostructures, ice
crystallography, stable O-H isotopes and cation contents. The ice was clear
to whitish in appearance with large crystals (cm) and small gas inclusions
(mm) at crystal intersections, similar to observations of englacial ice
facies commonly found on contemporary glaciers and ice sheets. However, the
δ18O composition (-34.0±0.4 ‰) of
the massive ice was markedly lower than contemporary glacier ice and was
consistent with the late Pleistocene age ice in the Barnes Ice Cap. This ice
predates the aggradation of the surrounding permafrost and can be used as an
archive to infer palaeo-environmental conditions at the study site. As most
of the glaciated Arctic landscapes are still strongly determined by their
glacial legacy, the melting of these large ice bodies could lead to extensive
slope failures and settlement of the ground surface, with significant impact
on permafrost geosystem landscape dynamics, terrestrial and aquatic
ecosystems and infrastructure.</p
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