6,550 research outputs found
Multiphoton inner-shell ionization of the carbon atom
We apply time-dependent R-matrix theory to study inner-shell ionization of C
atoms in ultra-short high-frequency light fields with a photon energy between
170 and 245 eV. At an intensity of 10 W/cm, ionization is dominated
by single-photon emission of a electron, with two-photon emission of a
1s electron accounting for about 2-3\% of all emission processes, and
two-photon emission of contributing about 0.5-1\%. Three-photon
emission of a 1s electron is estimated to contribute about 0.01-0.03\%. Around
a photon energy of 225 eV, two-photon emission of a 1s electron, leaving C
in either 1s2s2p or 1s2p is resonantly enhanced by intermediate
1s2s2p states. The results demonstrate the capability of time-dependent
R-matrix theory to describe inner-shell ionization processes including
rearrangement of the outer electrons.Comment: 7 pages, 2 figures, 2 table
Angular distributions in two-colour two-photon ionization of He
We present R-Matrix with time dependence (RMT) calculations for the
photoionization of helium irradiated by an EUV laser pulse and an overlapping
IR pulse with an emphasis on the anisotropy parameters of the sidebands
generated by the dressing laser field. We investigate how these parameters
depend on the amount of atomic structure included in the theoretical model for
two-photon ionization. To verify the accuracy of the RMT approach, our
theoretical results are compared with experiment.Comment: 8 pages, 4 figures, 1 tabl
Electron dynamics in the carbon atom induced by spin-orbit interaction
We use R-Matrix theory with Time dependence (RMT) to investigate multiphoton
ionization of ground-state atomic carbon with initial orbital magnetic quantum
number =0 and =1 at a laser wavelength of 390 nm and peak intensity
of 10 W cm. Significant differences in ionization yield and
ejected-electron momentum distribution are observed between the two values for
. We use our theoretical results to model how the spin-orbit interaction
affects electron emission along the laser polarization axis. Under the
assumption that an initial C atom is prepared at zero time delay with ,
the dynamics with respect to time delay of an ionizing probe pulse modelled
using RMT theory is found to be in good agreement with available experimental
data.Comment: 8 pages, 5 figure
Developing drought resilience in irrigated agriculture in the face of increasing water scarcity
In many countries, drought is the natural hazard that causes the greatest agronomic impacts. After recurrent droughts, farmers typically learn from experience and implement changes in management to reduce their future drought risks and impacts. This paper aims to understand how irrigated agriculture in a humid climate has been affected by past droughts and how different actors have adapted their activities and strategies over time to increase their resilience. After examining recent drought episodes from an agroclimatic perspective, information from an online survey was combined with evidence from semi-structured interviews with farmers to assess: drought risk perceptions, impacts of past drought events, management strategies at different scales (regional to farm level) and responses to future risks. Interviews with the water regulatory agency were also conducted to explore their attitudes and decision-making processes during drought events. The results highlight how agricultural drought management strategies evolve over time, including how specific aspects have helped to reduce future drought risks. The importance of adopting a vertically integrated drought management approach in the farming sector coupled with a better understanding of past drought impacts and management options is shown to be crucial for improving decision-making during future drought events
Phase transitions, entanglement and quantum noise interferometry in cold atoms
We show that entanglement monotones can characterize the pronounced
enhancement of entanglement at a quantum phase transition if they are sensitive
to long-range high order correlations. These monotones are found to develop a
sharp peak at the critical point and to exhibit universal scaling. We
demonstrate that similar features are shared by noise correlations and verify
that these experimentally accessible quantities indeed encode entanglement
information and probe separability.Comment: 4 pages 4 figure
Diffusion Variational Autoencoders
A standard Variational Autoencoder, with a Euclidean latent space, is
structurally incapable of capturing topological properties of certain datasets.
To remove topological obstructions, we introduce Diffusion Variational
Autoencoders with arbitrary manifolds as a latent space. A Diffusion
Variational Autoencoder uses transition kernels of Brownian motion on the
manifold. In particular, it uses properties of the Brownian motion to implement
the reparametrization trick and fast approximations to the KL divergence. We
show that the Diffusion Variational Autoencoder is capable of capturing
topological properties of synthetic datasets. Additionally, we train MNIST on
spheres, tori, projective spaces, SO(3), and a torus embedded in R3. Although a
natural dataset like MNIST does not have latent variables with a clear-cut
topological structure, training it on a manifold can still highlight
topological and geometrical properties.Comment: 10 pages, 8 figures Added an appendix with derivation of asymptotic
expansion of KL divergence for heat kernel on arbitrary Riemannian manifolds,
and an appendix with new experiments on binarized MNIST. Added a previously
missing factor in the asymptotic expansion of the heat kernel and corrected a
coefficient in asymptotic expansion KL divergence; further minor edit
Hanbury Brown-Twiss Interferometry for Fractional and Integer Mott Phases
Hanbury-Brown-Twiss interferometry (HBTI) is used to study integer and
fractionally filled Mott Insulator (MI) phases in period-2 optical
superlattices. In contrast to the quasimomentum distribution, this second order
interferometry pattern exhibits high contrast fringes in the it insulating
phases. Our detailed study of HBTI suggests that this interference pattern
signals the various superfluid-insulator transitions and therefore can be used
as a practical method to determine the phase diagram of the system. We find
that in the presence of a confining potential the insulating phases become
robust as they exist for a finite range of atom numbers. Furthermore, we show
that in the trapped case the HBTI interferogram signals the formation of the MI
domains and probes the shell structure of the system.Comment: 13 pages, 15 figure
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