8,262 research outputs found
meV resolution in laser-assisted energy-filtered transmission electron microscopy
The electronic, optical, and magnetic properties of quantum solids are
determined by their low-energy (< 100 meV) many-body excitations. Dynamical
characterization and manipulation of such excitations relies on tools that
combine nm-spatial, fs-temporal, and meV-spectral resolution. Currently,
phonons and collective plasmon resonances can be imaged in nanostructures with
sub-nm and 10s meV space/energy resolution using state-of-the-art
energy-filtered transmission electron microscopy (TEM), but only under static
conditions, while fs-resolved measurements are common but lack spatial or
energy resolution. Here, we demonstrate a new method of spectrally resolved
photon-induced near-field electron microscopy (SRPINEM) that allows us to
obtain nm-fs-resolved maps of nanoparticle plasmons with an energy resolution
determined by the laser linewidth (20 meV in this work), and not limited by
electron beam and spectrometer energy spreading. This technique can be extended
to any optically-accessible low-energy mode, thus pushing TEM to a previously
inaccessible spectral domain with an unprecedented combination of space, energy
and temporal resolution.Comment: 19 pages, 7 figure
Understanding the bulk electronic structure of Ca1-xSrxVO3
We investigate the electronic structure of Ca1-xSrxVO3 using careful
state-of-the-art experiments and calculations. Photoemission spectra using
synchrotron radiation reveal a hitherto unnoticed polarization dependence of
the photoemission matrix elements for the surface component leading to a
substantial suppression of its intensity. Bulk spectra extracted with the help
of experimentally determined electron escape depth and estimated suppression of
surface contributions resolve outstanding puzzles concerning the electronic
structure in Ca1-xSrxVO3.Comment: 4 pages including 3 figure
From attosecond to zeptosecond coherent control of free-electron wave functions using semi-infinite light fields
Light-electron interaction in empty space is the seminal ingredient for
free-electron lasers and also for controlling electron beams to dynamically
investigate materials and molecules. Pushing the coherent control of free
electrons by light to unexplored timescales, below the attosecond, would enable
unprecedented applications in light-assisted electron quantum circuits and
diagnostics at extremely small timescales, such as those governing
intramolecular electronic motion and nuclear phenomena. We experimentally
demonstrate attosecond coherent manipulation of the electron wave function in a
transmission electron microscope, and show that it can be pushed down to the
zeptosecond regime with existing technology. We make a relativistic pulsed
electron beam interact in free space with an appropriately synthesized
semi-infinite light field generated by two femtosecond laser pulses reflected
at the surface of a mirror and delayed by fractions of the optical cycle. The
amplitude and phase of the resulting coherent oscillations of the electron
states in energymomentum space are mapped via momentum-resolved ultrafast
electron energy-loss spectroscopy. The experimental results are in full
agreement with our theoretical framework for light-electron interaction, which
predicts access to the zeptosecond timescale by combining semi-infinite X-ray
fields with free electrons.Comment: 22 pages, 6 figure
Plastic potential: how the phenotypes and adaptations of pathogens are influenced by microbial interactions within plants
Predicting the effects of plant-associated microbes on emergence, spread, and evolution of plant pathogens demands an understanding of how pathogens respond to these microbes at two levels of biological organization: that of an individual pathogen and that of a pathogen population across multiple individual plants. We first examine the plastic responses of individual plant pathogens to microbes within a shared host, as seen through changes in pathogen growth and multiplication. We then explore the limited understanding of how within-plant microbial interactions affect pathogen populations and discuss the need to incorporate population-level observations with population genomic techniques. Finally, we suggest that integrating across levels will further our understanding of the ecological and evolutionary impacts of within-plant microbial interactions on pathogens
Analysis of cancellation in two-dimensional magnetohydrodynamic turbulence
A signed measure analysis of two-dimensional intermittent magnetohydrodynamic
turbulence is presented. This kind of analysis is performed to characterize the
scaling behavior of the sign-oscillating flow structures, and their geometrical
properties. In particular, it is observed that cancellations between positive
and negative contributions of the field inside structures, are inhibited for
scales smaller than the Taylor microscale, and stop near the dissipative scale.
Moreover, from a simple geometrical argument, the relationship between the
cancellation exponent and the typical fractal dimension of the structures in
the flow is obtained.Comment: 21 pages, 5 figures (3 .jpg not included in the latex file
Tensor force effects and high-momentum components in the nuclear symmetry energy
We analyze microscopic many-body calculations of the nuclear symmetry energy and its density dependence. The calculations are performed in the framework of the Brueckner-Hartree-Fock and the self-consistent Green’s functions methods. Within Brueckner-Hartree-Fock, the Hellmann-Feynman theorem gives access to the kinetic energy contribution as well as the contributions of the different components of the nucleon-nucleon interaction. The tensor component gives the largest contribution to the symmetry energy. The decomposition of the symmetry energy in a kinetic part and a potential energy part provides physical insight on the correlated nature of the system, indicating that neutron matter is less correlated than symmetric nuclear matter. Within the self-consistent Green’s function approach, we compute the momentum distributions and we identify the effects of the high momentum components in the symmetry energy. The results are obtained for the realistic interaction Argonne V18 potential, supplemented by the Urbana IX three-body force in the Brueckner-Hartree-Fock calculations
AIOCJ: A Choreographic Framework for Safe Adaptive Distributed Applications
We present AIOCJ, a framework for programming distributed adaptive
applications. Applications are programmed using AIOC, a choreographic language
suited for expressing patterns of interaction from a global point of view. AIOC
allows the programmer to specify which parts of the application can be adapted.
Adaptation takes place at runtime by means of rules, which can change during
the execution to tackle possibly unforeseen adaptation needs. AIOCJ relies on a
solid theory that ensures applications to be deadlock-free by construction also
after adaptation. We describe the architecture of AIOCJ, the design of the AIOC
language, and an empirical validation of the framework.Comment: Technical Repor
Precise and ultrafast molecular sieving through graphene oxide membranes
There has been intense interest in filtration and separation properties of
graphene-based materials that can have well-defined nanometer pores and exhibit
low frictional water flow inside them. Here we investigate molecular permeation
through graphene oxide laminates. They are vacuum-tight in the dry state but,
if immersed in water, act as molecular sieves blocking all solutes with
hydrated radii larger than 4.5A. Smaller ions permeate through the membranes
with little impedance, many orders of magnitude faster than the diffusion
mechanism can account for. We explain this behavior by a network of
nanocapillaries that open up in the hydrated state and accept only species that
fit in. The ultrafast separation of small salts is attributed to an 'ion
sponge' effect that results in highly concentrated salt solutions inside
graphene capillaries
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