372 research outputs found
The rotational shear layer inside the early red-giant star KIC 4448777
We present the asteroseismic study of the early red-giant star KIC 4448777,
complementing and integrating a previous work (Di Mauro et al. 2016), aimed at
characterizing the dynamics of its interior by analyzing the overall set of
data collected by the {\it Kepler} satellite during the four years of its first
nominal mission. We adopted the Bayesian inference code DIAMOND (Corsaro \& De
Ridder 2014) for the peak bagging analysis and asteroseismic splitting
inversion methods to derive the internal rotational profile of the star. The
detection of new splittings of mixed modes, more concentrated in the very inner
part of the helium core, allowed us to reconstruct the angular velocity profile
deeper into the interior of the star and to disentangle the details better than
in Paper I: the helium core rotates almost rigidly about 6 times faster than
the convective envelope, while part of the hydrogen shell seems to rotate at a
constant velocity about 1.15 times lower than the He core. In particular, we
studied the internal shear layer between the fast-rotating radiative interior
and the slow convective zone and we found that it lies partially inside the
hydrogen shell above and extends across the core-envelope
boundary. Finally, we theoretically explored the possibility for the future to
sound the convective envelope in the red-giant stars and we concluded that the
inversion of a set of splittings with only low-harmonic degree , even
supposing a very large number of modes, will not allow to resolve the
rotational profile of this region in detail.Comment: accepted for publication on Ap
Simulation of Dissipative Dynamics Without Interferometers
The development of techniques that reduce experimental complexity and
minimize errors is an utmost importance for modeling quantum channels. In
general, quantum simulators are focused on universal algorithms, whose
practical implementation requires extra qubits necessary to control the quantum
operations. In contrast, our technique is based on finding a way to optimally
sum Kraus operators. These operators provide us with an experimentally
simplified setup where only a degree of freedom is needed to implement any
one-qubit quantum channel. Therefore, using entanglement polarized photon pairs
and post-processing techniques, we experimentally built the Kraus maps,
carrying out unitary and projection operations
A General Organocatalytic System for Enantioselective Radical Conjugate Additions to Enals
Herein, we report a general iminium ion-based catalytic method for the enantioselective conjugate addition of carbon-centered radicals to aliphatic and aromatic enals. The process uses an organic photoredox catalyst, which absorbs blue light to generate radicals from stable precursors, in combination with a chiral amine catalyst, which secures a consistently high level of stereoselectivity. The generality of this catalytic platform is demonstrated by the stereoselective interception of a wide variety of radicals, including non-stabilized primary ones which are generally difficult to engage in asymmetric processes. The system also served to develop organocatalytic cascade reactions that combine an iminium-ion-based radical trap with an enamine-mediated step, affording stereochemically dense chiral products in one-step
Analogue of atomic collapse for adatoms on rhombohedral multilayer graphene
We propose that a multi-graphene of ABC-type stacking yields virtual bound
states lying within the Coulomb insulating gap of an Anderson-like adatom.
Wondrously, a virtual state constitutes the counterpart of the atomic collapse
phenomenon proposed in relativistic atomic Physics, while the second emerges as
its particle-hole symmetric, analogous to a positron state. Thus, we introduce
the effect as the adatomic collapse, which occurs due to a flat band with a
dispersionless state and a divergent density of states
near the Fermi energy
for where is the Berry phase. We conclude
this scenario based on the Kramers-Kronig transformation of the quasiparticle
broadening, from where we observe that the aforementioned van Hove singularity
induces virtual bound states. Counterintuitively, near the singularity, we find
these states above and below the Fermi energy correlated to the existence of
the bottom and top edges of the Coulomb insulating region, respectively. As
such a behavior rises without a twist, the system is known as Moir\'eless and
the phenomenon emerges also assisted by the adatom Coulomb correlations.
Similarly to Science 340, 734 (2013) we find the effective critical atomic
number in contrast to an ultra-heavy nucleus. Thus,
we point out that multi-graphene is a proper playground for testing a predicted
phenomenon of the relativistic atomic Physics in the domain of the condensed
matter Physics
Fractionalization of Majorana-Ising-type quasiparticles
We theoretically investigate the spectral properties of a quantum impurity
(QI) hosting the here proposed {Majorana-Ising-type quasiparticle (MIQ)
excitation}. It arises from the coupling between a finite topological
superconductor (TSC) based on a chain of magnetic adatoms-superconducting
hybrid system and an integer large spin flanking the QI. Noteworthy, the
spin couples to the QI via the Ising-type exchange interaction. As the
Majorana zero-modes (MZMs) at the edges of the TSC chain are overlapped, we
counterintuitively find a regime wherein the Ising term modulates the
localization of a fractionalized and resonant MZM at the QI site. Interestingly
enough, the fermionic nature of this state is revealed as purely of electron
tunneling-type and most astonishingly, it has the Andreev conductance
completely null in its birth. Therefore, we find that a resonant edge state
appears as a zero-mode and discuss it in terms of a poor man's Majorana[Nature
614, 445 (2023)]
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