3,717 research outputs found
Sub-cycle time resolution of multi-photon momentum transfer in strong-field ionization
During multi-photon ionization of an atom it is well understood how the
involved photons transfer their energy to the ion and the photoelectron.
However, the transfer of the photon linear momentum is still not fully
understood. Here, we present a time-resolved measurement of linear momentum
transfer along the laser pulse propagation direction. Beyond the limit of the
electric dipole approximation we observe a time-dependent momentum transfer. We
can show that the time-averaged photon radiation pressure picture is not
generally applicable and the linear momentum transfer to the photoelectron
depends on the ionization time within the electromagnetic wave cycle using the
attoclock technique. We can mostly explain the measured linear momentum
transfer within a classical model for a free electron in a laser field.
However, corrections are required due to the interaction of the outgoing
photoelectron with the parent ion and due to the initial momentum when the
electron appears in the continuum. The parent ion interaction induces a
measurable negative attosecond time delay between the appearance in the
continuum of the electron with minimal linear momentum transfer and the point
in time with maximum ionization rate
Anticoagulant rodenticides on our public and community lands: spatial distribution of exposure and poisoning of a rare forest carnivore.
Anticoagulant rodenticide (AR) poisoning has emerged as a significant concern for conservation and management of non-target wildlife. The purpose for these toxicants is to suppress pest populations in agricultural or urban settings. The potential of direct and indirect exposures and illicit use of ARs on public and community forest lands have recently raised concern for fishers (Martes pennanti), a candidate for listing under the federal Endangered Species Act in the Pacific states. In an investigation of threats to fisher population persistence in the two isolated California populations, we investigate the magnitude of this previously undocumented threat to fishers, we tested 58 carcasses for the presence and quantification of ARs, conducted spatial analysis of exposed fishers in an effort to identify potential point sources of AR, and identified fishers that died directly due to AR poisoning. We found 46 of 58 (79%) fishers exposed to an AR with 96% of those individuals having been exposed to one or more second-generation AR compounds. No spatial clustering of AR exposure was detected and the spatial distribution of exposure suggests that AR contamination is widespread within the fisher's range in California, which encompasses mostly public forest and park lands Additionally, we diagnosed four fisher deaths, including a lactating female, that were directly attributed to AR toxicosis and documented the first neonatal or milk transfer of an AR to an altricial fisher kit. These ARs, which some are acutely toxic, pose both a direct mortality or fitness risk to fishers, and a significant indirect risk to these isolated populations. Future research should be directed towards investigating risks to prey populations fishers are dependent on, exposure in other rare forest carnivores, and potential AR point sources such as illegal marijuana cultivation in the range of fishers on California public lands
Faint dwarfs as a test of DM models: WDM vs. CDM
We use high resolution HydroN-Body cosmological simulations to compare the
assembly and evolution of a small field dwarf (stellar mass ~ 10
M, total mass 10 M in dominated CDM and 2keV WDM
cosmologies. We find that star formation (SF) in the WDM model is reduced and
delayed by 1-2 Gyr relative to the CDM model, independently of the details of
SF and feedback. Independent of the DM model, but proportionally to the SF
efficiency, gas outflows lower the central mass density through `dynamical
heating', such that all realizations have circular velocities 20kms at
500pc, in agreement with local kinematic constraints. As a result of
dynamical heating, older stars are less centrally concentrated than younger
stars, similar to stellar population gradients observed in nearby dwarf
galaxies. Introducing an important diagnostic of SF and feedback models, we
translate our simulations into artificial color-magnitude diagrams and star
formation histories in order to directly compare to available observations. The
simulated galaxies formed most of their stars in many 10 Myr long bursts.
The CDM galaxy has a global SFH, HI abundance and Fe/H and alpha-elements
distribution well matched to current observations of dwarf galaxies. These
results highlight the importance of directly including `baryon physics' in
simulations when 1) comparing predictions of galaxy formation models with the
kinematics and number density of local dwarf galaxies and 2) differentiating
between CDM and non-standard models with different DM or power spectra.Comment: 13 pages including Appendix on Color Magnitude Diagrams. Accepted by
MNRAS. Added one plot and details on ChaNGa implementation. Reduced number of
citations after editorial reques
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