7,704 research outputs found
Gamma-rays from massive protostars
Massive protostars have associated bipolar outflows with velocities of
hundreds of km/s. Such outflows produce strong shocks when interact with the
ambient medium leading to regions of non-thermal radio emission. Under certain
conditions, the population of relativistic particles accelerated at the
terminal shocks of the protostellar jets can produce significant gamma-ray
emission. We estimate the conditions necessary for high-energy emission in the
non-thermal hot spots of jets associated with massive protostars embedded in
dense molecular clouds. Our results show that particle-matter interactions can
lead to the detection of molecular clouds hosting massive young stellar objects
by the Fermi satellite at MeV-GeV energies and even by Cherenkov telescope
arrays in the GeV-TeV range. Astronomy at gamma-rays can be used to probe the
physical conditions in star forming regions and particle acceleration processes
in the complex environment of massive molecular clouds.Comment: Proceeding of the conference "High Energy Phenomena in Massive
Stars". Jaen (Spain), 2-5 February 200
Pairing, crystallization and string correlations of mass-imbalanced atomic mixtures in one-dimensional optical lattices
We numerically determine the very rich phase diagram of mass-imbalanced
binary mixtures of hardcore bosons (or equivalently -- fermions, or
hardcore-Bose/Fermi mixtures) loaded in one-dimensional optical lattices.
Focusing on commensurate fillings away from half filling, we find a strong
asymmetry between attractive and repulsive interactions. Attraction is found to
always lead to pairing, associated with a spin gap, and to pair crystallization
for very strong mass imbalance. In the repulsive case the two atomic components
remain instead fully gapless over a large parameter range; only a very strong
mass imbalance leads to the opening of a spin gap. The spin-gap phase is the
precursor of a crystalline phase occurring for an even stronger mass imbalance.
The fundamental asymmetry of the phase diagram is at odds with recent
theoretical predictions, and can be tested directly via time-of-flight
experiments on trapped cold atoms.Comment: 4 pages, 4 figures + Supplementary Materia
Pfaffian-like ground state for 3-body-hard-core bosons in 1D lattices
We propose a Pfaffian-like Ansatz for the ground state of bosons subject to
3-body infinite repulsive interactions in a 1D lattice. Our Ansatz consists of
the symmetrization over all possible ways of distributing the particles in two
identical Tonks-Girardeau gases. We support the quality of our Ansatz with
numerical calculations and propose an experimental scheme based on mixtures of
bosonic atoms and molecules in 1D optical lattices in which this Pfaffian-like
state could be realized. Our findings may open the way for the creation of
non-abelian anyons in 1D systems
Observation of the Meissner effect with ultracold atoms in bosonic ladders
We report on the observation of the Meissner effect in bosonic flux ladders
of ultracold atoms. Using artificial gauge fields induced by laser-assisted
tunneling, we realize arrays of decoupled ladder systems that are exposed to a
uniform magnetic field. By suddenly decoupling the ladders and projecting into
isolated double wells, we are able to measure the currents on each side of the
ladder. For large coupling strengths along the rungs of the ladder, we find a
saturated maximum chiral current corresponding to a full screening of the
artificial magnetic field. For lower coupling strengths, the chiral current
decreases in good agreement with expectations of a vortex lattice phase. Our
work marks the first realization of a low-dimensional Meissner effect and,
furthermore, it opens the path to exploring interacting particles in low
dimensions exposed to a uniform magnetic field
The economics of multisystemic resilience
The concept of resilience in the economic literature is centered around the capacity to overcome adverse circumstances and to mitigate the impacts of shocks through the development of human capital starting in early childhood. In this chapter, the authors review the existing evidence on multisystemic resilience in economics, from both a micro- and a macroperspective. To do so, they first introduce the theory of human capital development and the large body of empirical evidence about early interventions that seek to boost resilience in children. They then discuss two more recent strands of literature: one that examines whether subsequent investments can offset the effects of early-life shocks and another that uses micro-founded macroeconomic models to understand the indirect (multisystemic) effects of early interventions
Predicting Future Instance Segmentation by Forecasting Convolutional Features
Anticipating future events is an important prerequisite towards intelligent
behavior. Video forecasting has been studied as a proxy task towards this goal.
Recent work has shown that to predict semantic segmentation of future frames,
forecasting at the semantic level is more effective than forecasting RGB frames
and then segmenting these. In this paper we consider the more challenging
problem of future instance segmentation, which additionally segments out
individual objects. To deal with a varying number of output labels per image,
we develop a predictive model in the space of fixed-sized convolutional
features of the Mask R-CNN instance segmentation model. We apply the "detection
head'" of Mask R-CNN on the predicted features to produce the instance
segmentation of future frames. Experiments show that this approach
significantly improves over strong baselines based on optical flow and
repurposed instance segmentation architectures
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