4,469 research outputs found
Copepod life strategy and population viability in response to prey timing and temperature : testing a new model across latitude, time, and the size spectrum
A new model ("Coltrane": Copepod Life-history Traits and Adaptation to Novel Environments) describes environmental controls on copepod populations via (1) phenology and life history and (2) temperature and energy budgets in a unified framework. The model tracks a cohort of copepods spawned on a given date using a set of coupled equations for structural and reserve biomass, developmental stage, and survivorship, similar to many other individual-based models. It then analyzes a family of cases varying spawning date over the year to produce population-level results, and families of cases varying one or more traits to produce community-level results. In an idealized global-scale testbed, the model correctly predicts life strategies in large Calanus spp. ranging from multiple generations per year to multiple years per generation. In a Bering Sea testbed, the model replicates the dramatic variability in the abundance of Calanus glacialis/marshallae observed between warm and cold years of the 2000s, and indicates that prey phenology linked to sea ice is a more important driver than temperature per se. In a Disko Bay, West Greenland testbed, the model predicts the viability of a spectrum of large-copepod strategies from income breeders with a adult size ~100 μgC reproducing once per year through capital breeders with an adult size > 1000 μgC with a multiple-year life cycle. This spectrum corresponds closely to the observed life histories and physiology of local populations of Calanus finmarchicus, C. glacialis, and Calanus hyperboreus. Together, these complementary initial experiments demonstrate that many patterns in copepod community composition and productivity can be predicted from only a few key constraints on the individual energy budget: the total energy available in a given environment per year; the energy and time required to build an adult body; the metabolic and predation penalties for taking too long to reproduce; and the size and temperature dependence of the vital rates involved
Nonlinear acoustic waves in channels with variable cross sections
The point symmetry group is studied for the generalized Webster-type equation
describing non-linear acoustic waves in lossy channels with variable cross
sections. It is shown that, for certain types of cross section profiles, the
admitted symmetry group is extended and the invariant solutions corresponding
to these profiles are obtained. Approximate analytic solutions to the
generalized Webster equation are derived for channels with smoothly varying
cross sections and arbitrary initial conditions.Comment: Revtex4, 10 pages, 2 figure. This is an enlarged contribution to
Acoustical Physics, 2012, v.58, No.3, p.269-276 with modest stylistic
corrections introduced mainly in the Introduction and References. Several
typos were also correcte
The structure of the protoplanetary disk surrounding three young intermediate mass stars. II. Spatially resolved dust and gas distribution
[Abridged] We present the first direct comparison of the distribution of the
gas, as traced by the [OI] 6300 AA emission, and the dust, as traced by the 10
micron emission, in the protoplanetary disk around three intermediate-mass
stars: HD 101412, HD 135344 B and HD 179218. N-band visibilities were obtained
with VLTI/MIDI. Simple geometrical models are used to compare the dust emission
to high-resolution optical spectra in the 6300 AA [OI] line of the same
targets. The disks around HD 101412 and HD 135344 B appear strongly flared in
the gas, but self-shadowed in the dust beyond ~ 2 AU. In both systems, the 10
micron emission is rather compact (< 2 AU) while the [OI] brightness profile
shows a double peaked structure. The inner peak is strongest and is consistent
with the location of the dust, the outer peak is fainter and is located at 5-10
AU. Spatially extended PAH emission is found in both disks. The disk around HD
179218 is flared in the dust. The 10 micron emission emerges from a double
ring-like structure with the first ring peaking at ~ 1 AU and the second at ~
20 AU. No dust emission is detected between ~ 3 -- 15 AU. The oxygen emission
seems also to come from a flared structure, however, the bulk of this emission
is produced between ~ 1 -- 10 AU. This could indicate a lack of gas in the
outer disk or could be due to chemical effects which reduce the abundance of OH
-- the parent molecule of the observed [OI] emission -- further away from the
star. The three systems, HD 179218, HD 135344 B and HD 101412, may form an
evolutionary sequence: the disk initially flared becomes flat under the
combined action of gas-dust decoupling, grain growth and dust settling.Comment: Accepted for publication in A&
High resolution spectroscopy of Ne II emission from young stellar objects
Constraining the spatial and thermal structure of the gaseous component of
circumstellar disks is crucial to understand star and planet formation. Models
predict that the [Ne II] line at 12.81 {\mu}m detected in young stellar objects
with Spitzer traces disk gas and its response to high energy radiation, but
such [Ne II] emission may also originate in shocks within powerful outflows. To
distinguish between these potential origins for mid-infrared [Ne II] emission
and to constrain disk models, we observed 32 young stellar objects using the
high resolution (R~30000) mid-infrared spectrograph VISIR at the VLT. We
detected the 12.81 {\mu}m [Ne II] line in 12 objects, tripling the number of
detections of this line in young stellar objects with high spatial and spectral
resolution spectrographs. We obtain the following main results: a) In Class I
objects the [Ne II] emission observed from Spitzer is mainly due to gas at a
distance of more than 20-40 AU from the star, where neon is, most likely,
ionized by shocks due to protostellar outflows. b) In transition and
pre-transition disks, most of the emission is confined to the inner disk,
within 20-40 AU from the central star. c) Detailed analysis of line profiles
indicates that, in transition and pre-transition disks, the line is slightly
blue-shifted (2-12 km s{^-1}) with respect to the stellar velocity, and the
line width is directly correlated with the disk inclination, as expected if the
emission is due to a disk wind. d) Models of EUV/X-ray irradiated disks
reproduce well the observed relation between the line width and the disk
inclination, but underestimate the blue-shift of the line.Comment: 35 pages, 7 figures, accepted for publication on Ap
Imaging protoplanets: observing transition disks with non-redundant masking
Transition disks, protoplanetary disks with inner clearings, are promising
objects in which to directly image forming planets. The high contrast imaging
technique of non-redundant masking is well posed to detect planetary mass
companions at several to tens of AU in nearby transition disks. We present
non-redundant masking observations of the T Cha and LkCa 15 transition disks,
both of which host posited sub-stellar mass companions. However, due to a loss
of information intrinsic to the technique, observations of extended sources
(e.g. scattered light from disks) can be misinterpreted as moving companions.
We discuss tests to distinguish between these two scenarios, with applications
to the T Cha and LkCa 15 observations. We argue that a static,
forward-scattering disk can explain the T Cha data, while LkCa 15 is best
explained by multiple orbiting companions.Comment: SPIE conference proceedin
Accreting Protoplanets in the LkCa 15 Transition Disk
Exoplanet detections have revolutionized astronomy, offering new insights
into solar system architecture and planet demographics. While nearly 1900
exoplanets have now been discovered and confirmed, none are still in the
process of formation. Transition discs, protoplanetary disks with inner
clearings best explained by the influence of accreting planets, are natural
laboratories for the study of planet formation. Some transition discs show
evidence for the presence of young planets in the form of disc asymmetries or
infrared sources detected within their clearings, as in the case of LkCa 15.
Attempts to observe directly signatures of accretion onto protoplanets have
hitherto proven unsuccessful. Here we report adaptive optics observations of
LkCa 15 that probe within the disc clearing. With accurate source positions
over multiple epochs spanning 2009 - 2015, we infer the presence of multiple
companions on Keplerian orbits. We directly detect H{\alpha} emission from the
innermost companion, LkCa 15 b, evincing hot (~10,000 K) gas falling deep into
the potential well of an accreting protoplanet.Comment: 35 pages, 3 figures, 1 table, 9 extended data item
Water Futures and Solution - Fast Track Initiative (Final Report)
The Water Futures and Solutions Initiative (WFaS) is a cross-sector, collaborative global water project. Its objective is to apply systems analysis, develop scientific evidence and identify water-related policies and management practices, working together consistently across scales and sectors to improve human well-being through water security. The approach is a stakeholder-informed, scenario-based assessment of water resources and water demand that employs ensembles of state-of-the-art socio-economic and hydrological models, examines possible futures and tests the feasibility, sustainability and robustness of options that can be implemented today and can be sustainable and robust across a range of possible futures and associated uncertainties. This report aims at assessing the global current and future water situation
Evidence for Neutrino Oscillations from Muon Decay at Rest
A search for nu_bar_mu to nu_bar_e oscillations has been conducted at the Los
Alamos Meson Physics Facility using nu_bar_mu from mu+ decay at rest. The
nu_bar_e are detected via the reaction (nu_bar_e,p) -> (e+,n), correlated with
the 2.2 MeV gamma from (n,p) -> (d,gamma). The use of tight cuts to identify e+
events with correlated gamma rays yields 22 events with e+ energy between 36
and 60 MeV and only 4.6 (+/- 0.6) background events. The probability that this
excess is due entirely to a statistical fluctuation is 4.1E-08. A chi^2 fit to
the entire e+ sample results in a total excess of 51.8 (+18.7) (-16.9) (+/-
8.0) events with e+ energy between 20 and 60 MeV. If attributed to nu_bar_mu ->
nu_bar_e oscillations, this corresponds to an oscillation probability (averaged
over the experimental energy and spatial acceptance) of 0.0031 (+0.0011)
(-0.0010) (+/- 0.0005).Comment: 57 pages, 34 figures, revtex, additional information available at
http://nu1.lampf.lanl.gov/~lsnd
A system of ODEs for a Perturbation of a Minimal Mass Soliton
We study soliton solutions to a nonlinear Schrodinger equation with a
saturated nonlinearity. Such nonlinearities are known to possess minimal mass
soliton solutions. We consider a small perturbation of a minimal mass soliton,
and identify a system of ODEs similar to those from Comech and Pelinovsky
(2003), which model the behavior of the perturbation for short times. We then
provide numerical evidence that under this system of ODEs there are two
possible dynamical outcomes, which is in accord with the conclusions of
Pelinovsky, Afanasjev, and Kivshar (1996). For initial data which supports a
soliton structure, a generic initial perturbation oscillates around the stable
family of solitons. For initial data which is expected to disperse, the finite
dimensional dynamics follow the unstable portion of the soliton curve.Comment: Minor edit
Photometric variability of the Herbig Ae star HD 37806
The more massive counterparts of T Tauri stars, Herbig Ae/Be stars, are known
to vary in a complex way with no variability mechanism clearly identified. We
attempt to characterize the optical variability of HD~37806 (MWC 120) on time
scales ranging between minutes and several years. A continuous, one-minute
resolution, 21 day-long sequence of MOST (Microvariability & Oscillations of
STars) satellite observations has been analyzed using wavelet, scalegram and
dispersion analysis tools. The MOST data have been augmented by sparse
observations over 9 seasons from ASAS (All Sky Automated Survey), by previously
non-analyzed ESO (European Southern Observatory) data partly covering 3 seasons
and by archival measurements dating back half a century ago. Mutually
superimposed flares or accretion instabilities grow in size from about 0.0003
of the mean flux on a time scale of minutes to a peak-to-peak range of <~0.05
on a time scale of a few years. The resulting variability has properties of
stochastic "red" noise, whose self-similar characteristics are very similar to
those observed in cataclysmic binary stars, but with much longer characteristic
time scales of hours to days (rather than minutes) and with amplitudes which
appear to cease growing in size on time scales of tens of years. In addition to
chaotic brightness variations combined with stochastic noise, the MOST data
show a weakly defined cyclic signal with a period of about 1.5 days, which may
correspond to the rotation of the star.Comment: Accepted for publication by Astron. & Astroph. 8 pages, 9 figures.
For some reason Fig.5 incorrectly shows in arXiv: Contours OK, gray scale no
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