2,208 research outputs found
Kondo effect in graphene with Rashba spin-orbit coupling
We study the Kondo screening of a magnetic impurity adsorbed in graphene in
the presence of Rashba spin-orbit interaction. The system is described by an
effective single-channel Anderson impurity model, which we analyze using the
numerical renormalization group. The nontrivial energy dependence of the host
density of states gives rise to interesting behaviors under variation of the
chemical potential or the spin-orbit coupling. Varying the Rashba coupling
produces strong changes in the Kondo temperature characterizing the many-body
screening of the impurity spin, and at half filling allows approach to a
quantum phase transition separating the strong-coupling Kondo phase from a
free-moment phase. Tuning the chemical potential close to sharp features of the
hybridization function results in striking features in the temperature
dependences of thermodynamic quantities and in the frequency dependence of the
impurity spectral function.Comment: 11 pages, 9 figures. Minor changes. Accepted in PR
Direct laser acceleration of electrons in free-space
Compact laser-driven accelerators are versatile and powerful tools of
unarguable relevance on societal grounds for the diverse purposes of science,
health, security, and technology because they bring enormous practicality to
state-of-the-art achievements of conventional radio-frequency accelerators.
Current benchmarking laser-based technologies rely on a medium to assist the
light-matter interaction, which impose material limitations or strongly
inhomogeneous fields. The advent of few cycle ultra-intense radially polarized
lasers has materialized an extensively studied novel accelerator that adopts
the simplest form of laser acceleration and is unique in requiring no medium to
achieve strong longitudinal energy transfer directly from laser to particle.
Here we present the first observation of direct longitudinal laser acceleration
of non-relativistic electrons that undergo highly-directional multi-GeV/m
accelerating gradients. This demonstration opens a new frontier for direct
laser-driven particle acceleration capable of creating well collimated and
relativistic attosecond electron bunches and x-ray pulses
Signatures of quantum phase transitions in parallel quantum dots: Crossover from local-moment to underscreened spin-1 Kondo physics
We study a strongly interacting "quantum dot 1" and a weakly interacting "dot
2" connected in parallel to metallic leads. Gate voltages can drive the system
between Kondo-quenched and non-Kondo free-moment phases separated by
Kosterlitz-Thouless quantum phase transitions. Away from the immediate vicinity
of the quantum phase transitions, the physical properties retain signatures of
first-order transitions found previously to arise when dot 2 is strictly
noninteracting. As interactions in dot 2 become stronger relative to the
dot-lead coupling, the free moment in the non-Kondo phase evolves smoothly from
an isolated spin-one-half in dot 1 to a many-body doublet arising from the
incomplete Kondo compensation by the leads of a combined dot spin-one. These
limits, which feature very different spin correlations between dot and lead
electrons, can be distinguished by weak-bias conductance measurements performed
at finite temperatures.Comment: 7 pages, 7 figures. Accepted for publication in Phys. Rev.
Laser-Induced Linear Electron Acceleration in Free Space
Linear acceleration in free space is a topic that has been studied for over
20 years, and its ability to eventually produce high-quality, high energy
multi-particle bunches has remained a subject of great interest. Arguments can
certainly be made that such an ability is very doubtful. Nevertheless, we chose
to develop an accurate and truly predictive theoretical formalism to explore
this remote possibility in a computational experiment. The formalism includes
exact treatment of Maxwell's equations, exact relativistic treatment of the
interaction among the multiple individual particles, and exact treatment of the
interaction at near and far field. Several surprising results emerged. For
example, we find that 30 keV electrons (2.5% energy spread) can be accelerated
to 7.7 MeV (2.5% spread) and to 205 MeV (0.25% spread) using 25 mJ and 2.5 J
lasers respectively. These findings should hopefully guide and help develop
compact, high-quality, ultra-relativistic electron sources, avoiding
conventional limits imposed by material breakdown or structural constraints.Comment: Supplementary Information starts on pg 1
GoRela: Go Relative for Viewpoint-Invariant Motion Forecasting
The task of motion forecasting is critical for self-driving vehicles (SDVs)
to be able to plan a safe maneuver. Towards this goal, modern approaches reason
about the map, the agents' past trajectories and their interactions in order to
produce accurate forecasts. The predominant approach has been to encode the map
and other agents in the reference frame of each target agent. However, this
approach is computationally expensive for multi-agent prediction as inference
needs to be run for each agent. To tackle the scaling challenge, the solution
thus far has been to encode all agents and the map in a shared coordinate frame
(e.g., the SDV frame). However, this is sample inefficient and vulnerable to
domain shift (e.g., when the SDV visits uncommon states). In contrast, in this
paper, we propose an efficient shared encoding for all agents and the map
without sacrificing accuracy or generalization. Towards this goal, we leverage
pair-wise relative positional encodings to represent geometric relationships
between the agents and the map elements in a heterogeneous spatial graph. This
parameterization allows us to be invariant to scene viewpoint, and save online
computation by re-using map embeddings computed offline. Our decoder is also
viewpoint agnostic, predicting agent goals on the lane graph to enable diverse
and context-aware multimodal prediction. We demonstrate the effectiveness of
our approach on the urban Argoverse 2 benchmark as well as a novel highway
dataset
La comunicación en los programas sociales de lucha contra la pobreza : el caso del Programa Juntos en la Región de Junín
La presente investigación nace motivada por aproximaciones teóricas del investigador a
los procesos históricos a los que se ha enfrentado el Perú, un país que ha atravesado
diversos sistemas políticos, fenómenos migratorios y una búsqueda constante por
pensarnos como una nación con identidad propia, estos factores entre algunos otros más,
nos podrían dar, en principio, luces para una comprensión integral de esta sociedad.Tesi
Hyperpolarization-activated cyclic nucleotide-gated 2 (HCN2) ion channels drive pain in mouse models of diabetic neuropathy
Blocking HCN2 ion channel activity in peripheral nociceptive neurons alleviates the pain hypersensitivity associated with diabetic neuropathy.</jats:p
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