Publications by authors named "Sergio Ulloa"

Article Synopsis
  • The study examines the effects of anisotropy on a system of three qubits using the antiferromagnetic Heisenberg XXX model in a magnetic field, focusing on Stirling and Otto cycles.
  • Results show that easy-axis anisotropy boosts engine efficiency, with the ring topology outperforming the chain at low temperatures in the Stirling cycle.
  • The Stirling cycle achieves Carnot efficiency with useful work at quantum critical points, while the quasistatic Otto cycle reaches Carnot efficiency but doesn't produce useful work, and the Stirling cycle operates across various thermal regimes compared to the Otto cycle.
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Rare-earth complexes are vital for separation chemistry and useful in many advanced applications including emission and energy upconversion. Here, 2D rare-earth clusters having net charges are formed on a metal surface, enabling investigations of their structural and electronic properties on a one-cluster-at-a-time basis using scanning tunneling microscopy. While these ionic complexes are highly mobile on the surface at ≈100 K, their mobility is greatly reduced at 5 K and reveals stable and self-limiting clusters.

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Superconductivity in graphene-based systems has recently attracted much attention, as either intrinsic behavior or induced by proximity to a superconductor may lead to interesting topological phases and symmetries of the pairing function. A prominent system considers the pairing to have chiral symmetry. The question arises as to the effect of possible spin-orbit coupling on the resulting superconducting quasiparticle (QP) spectrum.

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Background: Despite surgical reconstruction and extensive rehabilitation, persistent quadriceps inhibition, gait asymmetry, and functional impairment remain prevalent in patients after anterior cruciate ligament (ACL) injury. A combination of reports have suggested underlying central nervous system adaptations in those after injury govern long-term neuromuscular impairments. The classic assumption has been to attribute neurophysiologic deficits to components of injury, but other factors across the continuum of care (e.

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Objectives: Determine the effect of visual-based motor and cognitive dual tasking on postural stability in those with anterior cruciate ligament reconstruction relative to matched controls.

Design: Cohort study.

Methods: Fourteen volunteers with history of anterior crucaite ligament reconstruction were matched with fourteen healthy controls.

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Article Synopsis
  • Charge density waves (CDWs) and negative differential resistance (NDR) are distinct physical phenomena, with CDWs being an ordered state of electrons associated with superconductivity and NDR gaining interest for its electronics applications.
  • Recent findings demonstrate that CDWs and NDR can coexist in the transition metal dichalcogenide 1T-TaS2, with the localized electronic states of the CDW playing a crucial role in inducing NDR.
  • Using scanning tunneling microscopy, the study reveals that the interaction of tunneling between different layers and localized states at the CDW peaks and troughs explains the observed NDR, highlighting how lattice defects influence this coupling.
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  • Researchers have created a synthetic molecular propeller that can rotate in one direction when energized on material surfaces, potentially useful for solid state devices.
  • The propeller consists of three molecular blades attached to a ratchet-shaped gear, with the rotation direction determined by the gear's design and the influence of the surface.
  • The study successfully visualizes the propeller's step-wise rotations using scanning tunneling microscopy, showing that the propellers can rotate clockwise or anticlockwise depending on their handedness.
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We undertake a theoretical study of the role of spin orbit interactions in a silicon double quantum dot. We propose that an accurate estimate of the strength of this interaction can be obtained through the study of the return probability of the double occupation singlet state in a magnetic field, as the system is gated dynamically across the relevant states in the low energy two-electron manifold. Landau-Zener type of processes involving appropriate control of voltage pulses across neighboring avoided crossings in the energy spectrum of the system are utilized to explore the system dynamics.

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Kondo resonances in heterostructures formed by magnetic molecules on a metal require free host electrons to interact with the molecular spin and create delicate many-body states. Unlike graphene, semiconducting graphene nanoribbons do not have free electrons due to their large bandgaps, and thus they should electronically decouple molecules from the metal substrate. Here, we observe unusually well-defined Kondo resonances in magnetic molecules separated from a gold surface by graphene nanoribbons in vertically stacked heterostructures.

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The transport properties of nanostructured systems are deeply affected by the geometry of the effective connections to metallic leads. In this work we derive a conductance expression for a class of interacting systems whose connectivity geometries do not meet the Meir-Wingreen proportional coupling condition. As an interesting application, we consider a quantum dot connected coherently to tunable electronic cavity modes.

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Osteoarthritis is the most common cause of arthritis and one of the main causes of chronic pain. Although opioids are frequently employed for chronic pain treatment, their usage for osteoarthritis pain remains controversial due to the associated adverse effects. Most guidelines reserve their use for refractory pain in patients with hip and knee osteoarthritis.

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Article Synopsis
  • - The study explores how charge carriers in graphene can pass through barriers perfectly due to a phenomenon called Klein tunneling, which is based on the Dirac equation.
  • - Researchers observed resonance states in a type of hybrid material made from photoswitchable self-assembled molecules and graphene, allowing current resonances to be toggled on and off with light.
  • - Conductive AFM measurements show the resonances’ voltage separation aligns with the predictions of the Dirac equation, indicating a potential radius of about 7 nm and suggesting new methods for controlling charge transport in graphene materials.
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Background: Shoulder instability can cause both soft tissue injury and bone defects, requiring both computed tomography (CT) and magnetic resonance imaging (MRI) for a thorough workup, which results in high patient costs and radiation exposure. Prior studies in cadaveric and nonclinical models have shown promise in assessing preoperative bone loss utilizing MRI.

Purpose: To evaluate the utility of MRI in detecting and evaluating glenoid bone defects in a clinical setting.

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Broken symmetries in graphene affect the massless nature of its charge carriers. We present an analysis of scattering by defects in graphene in the presence of spin-orbit interactions (SOIs). A characteristic constant ratio (≃2) of the transport to elastic times for massless electrons signals the anisotropy of the scattering.

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We study a one-orbital Anderson impurity in a two-dimensional electron bath with Rashba spin-orbit interactions in the Kondo regime. The spin SU(2) symmetry-breaking term couples the impurity to a two-band electron gas. A Schrieffer-Wolff transformation shows the existence of the Dzyaloshinsky-Moriya interaction away from the particle-hole symmetric impurity state.

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Magnetoelectric effects at the atomic scale are demonstrated to afford unique functionality. This is shown explicitly for a quantum corral defined by a wall of magnetic atoms on a metal surface where spin-orbit coupling is observable. We show these magnetoelectric effects allow one to control the properties of systems placed inside the corral as well as their electronic signatures; they provide powerful alternative tools for probing electronic properties at the atomic scale.

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Article Synopsis
  • Charge transport in DNA is significant for biological processes and potential applications in nanoscale devices, with a focus on its quasi-one-dimensional structure made of base pairs and sugar phosphate backbones.
  • Recent research highlights the crucial role of the integrity of the DNA backbone in facilitating charge transport through disordered base stacks.
  • Analytical and numerical analyses show that coupling between the backbone and base pairs greatly enhances charge transport and localization length, offering explanations for various experimental findings.
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We study two quantum dots embedded in the arms of an Aharonov-Bohm ring threaded by a magnetic flux. This system can be described by an effective one-impurity Anderson model with an energy- and flux-dependent density of states. For specific values of the flux, this density of states vanishes at the Fermi energy, yielding a controlled realization of the pseudogap Kondo effect.

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Article Synopsis
  • Double quantum dots allow for the exploration of complex many-body interactions in quantum systems.
  • In the studied system, a Kondo dot interacts with a noninteracting dot, which behaves like a single-impurity Anderson model with a varying density of states.
  • Numerical simulations indicate that although the Kondo resonance is affected by band filtering, the overall singlet ground state remains stable, and the system can be adjusted to reach a critical point between Kondo and non-Kondo phases.
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We develop a realistic model of Rabi oscillations in a quantum-dot photodiode. Based in a multiexciton density matrix formulation we show that for short pulses the two-level model fails and higher levels should be taken into account. This affects some of the experimental conclusions, such as the inferred efficiency of the state rotation (population inversion) and the deduced value of the dipole interaction.

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