57,915 research outputs found
Bose-enhanced chemistry: Amplification of selectivity in the dissociation of molecular Bose-Einstein condensates
We study the photodissociation chemistry of a quantum degenerate gas of
bosonic triatomic molecules, assuming two open rearrangement channels
( or ). The equations of motion are equivalent to those of a
parametric multimode laser, resulting in an exponential buildup of macroscopic
mode populations. By exponentially amplifying a small differential in the
single-particle rate-coefficients, Bose stimulation leads to a nearly complete
selectivity of the collective -body process, indicating a novel type of
ultra-selective quantum degenerate chemistry.Comment: 5 pages, 3 figure
Magneto-optical absorption properties of a Weyl semimetal thin film
In this study, we investigate the magneto-optical absorption properties of a Weyl semimetal thin film by calculating the magneto-optical absorption coefficients (MOACs) for both intra-band and inter-band transitions. The wave function and energy spectrum were determined using the Hamiltonian minimal model in the presence of magnetic and electric fields. The expressions for the MOACs in both x- and z-directions are obtained using the compact density matrix approach. The numerical results demonstrate that the MOACs are significantly influenced by temperature, carrier concentration, and magnetic and electric fields
A mid-IR study of Hickson Compact Groups II. Multi-wavelength analysis of the complete GALEX-Spitzer Sample
We present a comprehensive study on the impact of the environment of compact
galaxy groups on the evolution of their members using a multi-wavelength
analysis, from the UV to the infrared, for a sample of 32 Hickson compact
groups (HCGs) containing 135 galaxies. Fitting the SEDs of all galaxies with
the state-of-the-art model of da Cunha (2008) we can accurately calculate their
mass, SFR, and extinction, as well as estimate their infrared luminosity and
dust content. We compare our findings with samples of field galaxies,
early-stage interacting pairs, and cluster galaxies with similar data. We find
that classifying the groups as dynamically "old" or "young", depending on
whether or not at least one quarter of their members are early-type systems, is
physical and consistent with past classifications of HCGs based on their atomic
gas content. [...ABRIDGED...] We also examine their SF properties, UV-optical
and mid-IR colors, and we conclude that all the evidence point to an
evolutionary scenario in which the effects of the group environment and the
properties of the galaxy members are not instantaneous. Early on, the influence
of close companions to group galaxies is similar to the one of galaxy pairs in
the field. However, as the time progresses, the effects of tidal torques and
minor merging, shape the morphology and star formation history of the group
galaxies, leading to an increase of the fraction of early-type members and a
rapid built up of the stellar mass in the remaining late-type galaxies.Comment: Accepted for publication in A&A. Figure resolution degraded for arXiv
limits, full resolution paper available at
http://www.physics.uoc.gr/~bitsakis/paperII_bitsakis.pd
Exploring L2 learners' Task-related Identities in a Reading Circle Task Through Conversation Analysis
Using conversation analysis as the research approach, this study explores how L2 learners utilize their task-related identities during task interactions and how those identities are used as resources for task management. Eight students in an ESL academic reading class formed two groups while they did their reading circle task for six rounds. In each round, the students took turns to be in charge of a specific role in the discussion session (i.e., discussion leader, notetaker, vocabulary definer, and contextualizer). Data was collected from all rounds and analyzed for emerging patterns. Results showed that (a) the participants used each other’s assigned identities skillfully to orient the group to the institutional goal, and (b) the participants used their own existing obligations to problematize the task interactions. By providing insights on those dynamic task-related identities, this study broadens our understanding of interactions happening at the task implementation stage and suggests pedagogical implications.S’inscrivant dans le courant de l’analyse de la conversation, cette étude explore comment les apprenants d'anglais utilisent leurs identités liées aux tâches lors des interactions entre les tâches et comment ces identités sont utilisées comme ressources pour la gestion des tâches. Huit étudiants dans une classe de lecture universitaire en anglais ont formé deux groupes pendant qu'ils effectuaient leur tâche de cercle de lecture pendant six tours. À chaque tour, les étudiants se sont relayés pour être responsables d'un rôle spécifique dans la session de discussion. Les données ont été collectées à tous les cycles et analysées afin de dégager les éléments les plus saillants. Les résultats ont montré que (a) les participants utilisaient habilement les identités qui leur avaient été attribuées pour orienter le groupe vers l’objectif identifié en amont; et que (b) les participants ont utilisé leurs propres obligations existantes pour problématiser les interactions entre les tâches
Weak local rules for planar octagonal tilings
We provide an effective characterization of the planar octagonal tilings
which admit weak local rules. As a corollary, we show that they are all based
on quadratic irrationalities, as conjectured by Thang Le in the 90s.Comment: 23 pages, 6 figure
Robust probabilistic-constrained optimization for IRS-aided MISO communication systems
Taking into account imperfect channel state information, this letter formulates and solves a joint active/passive beamforming optimization problem in multiple-input single-output systems with the support of an intelligent reflecting surface. In particular, we introduce an optimization problem to minimize the total transmit power subject to maintaining the users' signal-to-interference-plus-noise-ratio coverage probability above a predefined target. Due to the presence of probabilistic constraints, the proposed optimization problem is non-convex. To circumvent this issue, we first recast the proposed problem in a convex form by adopting the Bernstein-type inequality, and we then introduce a converging alternating optimization approach to iteratively find the active/passive beamforming vectors. In particular, the transformed robust optimization problem can be effectively solved by using standard interior-point methods. Numerical results demonstrate the effectiveness of jointly optimizing the active/passive beamforming vectors
Correlation between electric-field-induced phase transition and piezoelectricity in lead zirconate titanate films
We observed that electric field induces phase transition from tetragonal to
rhombohedral in polycrystalline morphotropic lead zirconate titanate (PZT)
films, as reported in 2011 for bulk PZT. Moreover, we evidenced that this
field-induced phase transition is strongly correlated with PZT film
piezoelectric properties, that is to say the larger the phase transition, the
larger the longitudinal piezoelectric coefficient d 33,eff . Although d 33,eff
is already comprised between as 150 to 170 pm/V, our observation suggests that
one could obtain larger d 33,eff values, namely 250 pm/V, by optimizing the
field-induced phase transition thanks to composition fine tuning
Revival of Silenced Echo and Quantum Memory for Light
We propose an original quantum memory protocol. It belongs to the class of
rephasing processes and is closely related to two-pulse photon echo. It is
known that the strong population inversion produced by the rephasing pulse
prevents the plain two-pulse photon echo from serving as a quantum memory
scheme. Indeed gain and spontaneous emission generate prohibitive noise. A
second -pulse can be used to simultaneously reverse the atomic phase and
bring the atoms back into the ground state. Then a secondary echo is radiated
from a non-inverted medium, avoiding contamination by gain and spontaneous
emission noise. However, one must kill the primary echo, in order to preserve
all the information for the secondary signal. In the present work, spatial
phase mismatching is used to silence the standard two-pulse echo. An
experimental demonstration is presented.Comment: 13 pages, 6 figure
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