Deep Potential Well Research Articles

Signatures of Mass Segregation from Competitive Accretion and Monolithic Collapse

The two main competing theories proposed to explain the formation of massive (>10 M ⊙) stars—competitive accretion and monolithic core collapse—make different observable predictions for the environment of the massive stars during, and immediately after, their formation. Proponents of competitive accretion have long predicted that the most massive stars should have a different spatial distribution to lower-mass stars, through the stars being either mass segregated or being in areas of higher relative densities or sitting deeper in gravitational potential wells. We test these predictions by analyzing a suite of smoothed-particle hydrodynamics simulations where star clusters form massive stars via competitive accretion with and without feedback. We find that the most massive stars have higher relative densities, and sit in deeper potential wells, only in simulations in which feedback is not present. When feedback is included, only half of the simulations have the massive stars residing in deeper potential wells, and there are no other distinguishing signals in their spatial distributions. Intriguingly, in our simple models for monolithic core collapse, the massive stars may also end up in deeper potential wells because if massive cores fragment then the stars that form are also massive, and dominate their local environs. We find no robust diagnostic test in the spatial distributions of massive stars that can distinguish their formation mechanisms, and so other predictions for distinguishing between competitive accretion and monolithic collapse are required.

A tight N/O–potential relation in star-forming galaxies

ABSTRACT We report a significantly tighter trend between gaseous N/O and $M_*/R_\mathrm{ e}$ (a proxy for gravitational potential) than has previously been reported between gaseous metallicity and $M_*/R_\mathrm{ e}$, for star-forming galaxies in the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. We argue this result to be a consequence of deeper potential wells conferring greater resistance to metal outflows while also being associated with earlier star-formation histories, combined with N/O being comparatively unaffected by metal-poor inflows. The potential–N/O relation thus appears to be both more resistant to short time-scale baryonic processes and also more reflective of a galaxy’s chemical evolution state, when compared to previously considered relations.

From Seeds to Supermassive Black Holes: Capture, Growth, Migration, and Pairing in Dense Protobulge Environments

The origins and mergers of supermassive black holes (SMBHs) remain a mystery. We describe a scenario from a novel multiphysics simulation featuring rapid (≲1 Myr) hyper-Eddington gas capture by a ∼1000 M ⊙ “seed” black hole (BH) up to supermassive (≳106 M ⊙) masses in a massive, dense molecular cloud complex typical of high-redshift starbursts. Due to the high cloud density, stellar feedback is inefficient, and most of the gas turns into stars in star clusters that rapidly merge hierarchically, creating deep potential wells. Relatively low-mass BH seeds at random positions can be “captured” by merging subclusters and migrate to the center in ∼1 freefall time (vastly faster than dynamical friction). This also efficiently produces a paired BH binary with ∼0.1 pc separation. The centrally concentrated stellar density profile (akin to a “protobulge”) allows the cluster as a whole to capture and retain gas and build up a large (parsec-scale) circumbinary accretion disk with gas coherently funneled to the central BH (even when the BH radius of influence is small). The disk is “hypermagnetized” and “flux-frozen”: dominated by a toroidal magnetic field with plasma β ∼ 10−3, with the fields amplified by flux-freezing. This drives hyper-Eddington inflow rates ≳1 M ⊙ yr−1, which also drive the two BHs to nearly equal masses. The late-stage system appears remarkably similar to recently observed high-redshift “little red dots.” This scenario can provide an explanation for rapid SMBH formation, growth, and mergers in high-redshift galaxies.

Quantum tunneling in deep potential wells and strong magnetic field revisited

Quantum tunneling in deep potential wells and strong magnetic field revisited

Computational study of the mechanism of binding of antifungal icofungipen in the active site of eukaryotic isoleucyl tRNA synthetase from Candida albicans

The eukaryotic fungal species Candida albicans is a critical infective pathogenic agent. The β-amino acid, Icofungipen, is an effective inhibitor of Candida albicans. Icofungipen binds at the active site of the isoleucyl tRNA synthetase (IleRS) from Candida albicans ( Ca IleRS) and halts protein translation in fungus. In the present work, we have investigated the mechanism of binding of Icogungipen (abbreviated as IFP). Molecular dynamics (MD) simulations show that the carboxylic acid group of IFP in the CaIleRS: IFP complex is more oriented towards the Connective Polypeptide (CP) core loop compared to the carboxylic acid group of Ile in the CaIleRS: Ile complex. The Arg 410 of the CP core loop near the substrate is extended towards the IFP. Due to the difference in the conformation of residues of the CP core loop, the KMSKR loop is more proximal to the CP core loop in Ca IleRS: IFP. The editing domain which is covalently linked with the CP core loop in the Ca IleRS: IFP complex is also oriented in such a way that the active site cavity is narrow and longer. The metadynamics calculation shows that the IFP is trapped in a deeper potential well compared to Ile which is due to the effective closure of the gateway of the active site by KMSKR and CP core loop. The thin, long shape of the active site and the closed gate of the active site in Ca IleRS: IFP complex is responsible for the effective capture of IFP relative to Ile in the active site. Communicated by Ramaswamy H. Sarma

Attractor neural networks with double well synapses.

It is widely believed that memory storage depends on activity-dependent synaptic modifications. Classical studies of learning and memory in neural networks describe synaptic efficacy either as continuous or discrete. However, recent results suggest an intermediate scenario in which synaptic efficacy can be described by a continuous variable, but whose distribution is peaked around a small set of discrete values. Motivated by these results, we explored a model in which each synapse is described by a continuous variable that evolves in a potential with multiple minima. External inputs to the network can switch synapses from one potential well to another. Our analytical and numerical results show that this model can interpolate between models with discrete synapses which correspond to the deep potential limit, and models in which synapses evolve in a single quadratic potential. We find that the storage capacity of the network with double well synapses exhibits a power law dependence on the network size, rather than the logarithmic dependence observed in models with single well synapses. In addition, synapses with deeper potential wells lead to more robust information storage in the presence of noise. When memories are sparsely encoded, the scaling of the capacity with network size is similar to previously studied network models in the sparse coding limit.

Galaxy Quenching at the High Redshift Frontier: A Fundamental Test of Cosmological Models in the Early Universe with JWST-CEERS

We present an analysis of the quenching of star formation in massive galaxies (M * > 109.5 M ⊙) within the first 0.5–3 Gyr of the Universe’s history utilizing JWST-CEERS data. We utilize a combination of advanced statistical methods to accurately constrain the intrinsic dependence of quenching in a multidimensional and intercorrelated parameter space. Specifically, we apply random forest classification, area statistics, and a partial correlation analysis to the JWST-CEERS data. First, we identify the key testable predictions from two state-of-the-art cosmological simulations (IllustrisTNG and EAGLE). Both simulations predict that quenching should be regulated by supermassive black hole mass in the early Universe. Furthermore, both simulations identify the stellar potential (ϕ *) as the optimal proxy for black hole mass in photometric data. In photometric observations, where we have no direct constraints on black hole masses, we find that the stellar potential is the most predictive parameter of massive galaxy quenching at all epochs from z = 0–8, exactly as predicted by simulations for this sample. The stellar potential outperforms stellar mass, galaxy size, galaxy density, and Sérsic index as a predictor of quiescence at all epochs probed in JWST-CEERS. Collectively, these results strongly imply a stable quenching mechanism operating throughout cosmic history, which is closely connected to the central gravitational potential in galaxies. This connection is explained in cosmological models via massive black holes forming and growing in deep potential wells, and subsequently quenching galaxies through a mix of ejective and preventative active galactic nucleus feedback.

Dependence between glass transition and plasticity in amorphous aluminum oxide: A molecular dynamics study

Aluminum oxide (Al2O3) is known to form amorphous structures that exhibit a unique plastic deforming ability at room temperature. However, alumina is considered a poor glass former, and it has been unclear whether alumina undergoes a glass transition during solidification from melt, and what effects such a transition would have on the plastic deform ability of the material. Here, we show using molecular dynamics simulations that a melt-quenched alumina indeed exhibits a glass transition, and that the glass transition greatly affects the observed material ductility. The glass transition temperature is found to positively correlate with the used cooling rate and we observe that maximum stress correlates with varying quench cooling rates in tensile test simulations, indicating that profound structural differences are formed during the glass transition. Significantly, we show that inducing plastic deformation allows erasing the structural memory of the material, and at 50% strain, all samples quenched at different rates shift again to exhibit similar flow stress. Characterizing methods that include medium-range structural information show a better ability to capture the structural differences formed during the glass transition. Our analysis results indicate that lower glass transition temperature imposes deeper potential wells of atoms and, therefore, a ’colder’ structure. The mechanical work input plays a similar role as input thermal energy to the structure. A ’colder’ structure needs more mechanical energy to get activated, thus showing a higher maximum stress. At a steady state flow, all samples show similar flow stress, indicating a similar structure.

Unveiling Quantum Interference in the D+ + H2 Nonadiabatic Reaction Dynamics at Low Collision Energies.

Fully converged nonadiabatic dynamics calculations of the D+ + H2 → H+ + HD reaction are performed at low temperatures using the time-dependent wave packet approach based on a set of precise 3 × 3 diabatic potential energy surfaces (PESs) ( Phys. Chem. Chem. Phys., 2021, 23, 7735-7747, DOI: 10.1039/D0CP04100A). The D+ + H2 reaction is mediated by a dense manifold of resonances associated with the deep potential well on the ground-state PES. The calculated results show that the nonadiabatic coupling can affect the resonance positions, deviating from the expectation based solely on adiabatic considerations. Furthermore, significant forward-backward asymmetry in total differential cross sections (DCSs) is revealed, which is markedly influenced by nonadiabatic effects. The nonadiabatic effects not only affect the contribution of partial waves in the reaction but also make the interference patterns in the DCSs change significantly.

Improvement of DC and RF characteristics for a novel AlGaAs/InGaAs HEMT with decreased single event effect

In order to promotion the RF performance, a grade In1-xGaxAs channel (G-HEMT) introduced to the AlGaAs/InGaAs HEMT. The G-HEMT with the grade In1-xGaxAs channel forms a deeper potential well and confines more electrons in the channel, results in improving the DC and RF characteristics. Moreover, because of the grade In1-xGaxAs is effectively reduced the peak electric field, and leads to a significant increase in breakdown voltage (BV). Moreover, the G-HEMT also increases resistance to single event effects (SEE). The simulation results indicate that the fmax is significantly increased to 889 GHz of G-HEMT from 616 GHz of conventional AlGaAs/InGaAs HEMT (C-HEMT). The the fT is significantly increased to 521 GHz of G-HEMT from 326 GHz of C-HEMT, as well as the IDsat is increased by 64.8% and the BV increases by 37%. In addition, the SEE peak drain current of G-HEMT is dramatically reduced 51%.

Lowest electronic states of neutral and ionic LiN

AbstractWe have investigated the potential energy curves (PECs) of the LiN heteronuclear diatomic molecule, including its ionic species LiN+ and LiN−, using explicitly correlated multi‐reference configuration interaction (MRCI‐F12) calculations in conjunction with the correlation consistent quintuple‐𝜁 basis set. The effect of core–valence correlation, scalar relativistic effects, and the size of the basis sets has been investigated. A comprehensive set of spectroscopic constants determined based on the above‐mentioned calculations are also reported for the lowest electronic states and all systems, including dissociation energies, harmonic and anharmonic vibrational frequencies, and rotational constants. Additional parameters, such as the dipole moments, equilibrium spin‐orbit constants, excitation energies, and rovibrational energy levels, are also documented. We found that the three triplet states of LiN, namely, X 3∑−, A 3Π, and 2 3∑−, exhibit substantial potential wells in the PEC diagrams, while the quintet states are repulsive in nature. The ground state of the anion also shows a deep potential well in the vicinity of its equilibrium geometry. In contrast, the ground and excited states of the cation are very loosely bound. Charge transfer properties of each of these states are also analyzed to obtain an in‐depth understanding of the interatomic interactions. We found that the core–valence correlation has a substantial effect on the calculated spectroscopic constants.

Study of spontaneous radiation during axial channeling of relativistic positrons in hexagonal crystals

In the study, using the Moliere, Firsov and Barrett approximations, the interaction potentials of positively charged particles channeled along the c-axes in hexagonal crystals such as Be, Mg, Sc, Ti, Co, Zn, Se, Y, Zr, Tc, Ru, Cd, Te, La are calculated at T = 300K. For the Co crystal, the Doyle – Turner approximation was additionally used. It is demonstrated that in these directions, sufficiently deep potential wells are formed. Using optimal approximation functions, energy levels and their corresponding wave functions are determined for channeled positrons with Lorentz-factors of 25, 50, 75. Using these data for positron beams with various angular dispersions, spontaneous radiation spectra are calculated for all the investigated hexagonal crystals.

High-performance normally off AlGaN/GaN high electron mobility transistor with p-type h-BN cap layer

Normally off AlGaN/GaN high electron mobility transistors (HEMTs) with p-type gates are attracting increasing attention due to their high safety and low power loss in the field of power switching. In this work, to solve the Mg difficult activating problem of the conventional p-GaN gate AlGaN/GaN HEMTs, we propose an advanced design for the normally off AlGaN/GaN HEMT with a p-type hexagonal boron nitride (h-BN) gate cap layer to effectively manipulate the channel transport of the device. The simulation results demonstrate that the p-hBN gate cap HEMTs yield superior performance over conventional p-GaN gate HEMTs in terms of output current and breakdown voltage, which can be attributed to the deeper potential well formation at the AlGaN/GaN interface and more accumulation of holes located at the p-hBN/AlGaN interface. Moreover, we investigate the effect of bandgap variation on device performance, taking into account that the exact bandgap of h-BN remains under debate. Herein, valuable insights into h-BN cap-gate E-mode AlGaN/GaN HEMT devices are provided, which could serve as a useful reference for the future development of robust III-nitride material power electronic devices.

Particle dynamics in dusty plasma: Classical tunneling

A Hamiltonian formalism for studying the dynamics of a dust particle with variable electric charge in dusty plasma is proposed. The Hamiltonian and the equations of motion are presented, and the dynamics is shown to be conservative. The problem is cast in terms of the motion of a particle with a constant fictitious charge QA moving in a suitably defined potential, while the actual particle charge is spatially distributed. With this formalism, the problem of trapping of dust particles in potential wells and barriers is studied. The results show that because of the spatial “delocalization”/distribution of the particle charge, a particle with insufficient energy to cross the potential barrier can penetrate it to tunnel out, i.e., “classical tunneling,” similar to a high jumper clearing the bar by the Fosbury flop technique or the usual quantum tunneling. For energies greater than a critical value, the charged particle is shown to tunnel out of even an infinitely deep potential well. A modified criterion for trapping in potential wells is given.

Unidirectional flow of flat-top solitons

We numerically demonstrate the unidirectional flow of flat-top solitons when interacting with two reflectionless potential wells with slightly different depths. The system is described by a nonlinear Schrödinger equation with dual nonlinearity. The results show that for shallow potential wells, the velocity window for unidirectional flow is larger than for deeper potential wells. A wider flat-top solitons also have a narrow velocity window for unidirectional flow than those for thinner flat-top solitons.

A hybrid mechanism of 3D optical trapping of particles immersed in a cold buffer gas

A novel mechanism of the formation of a deep optical superlattice (OSL) for three-dimensional (3D) trapping of resonant impurity atoms immersed in a transparent cold buffer gas is proposed and investigated theoretically. This mechanism is associated with the joint action of two factors of different physical nature: rectification effect of the gradient force of light pressure and effect of the light induced drift (LID) of atoms (a consequence of the difference in gas-kinetic cross sections of excited and unexcited atoms). Such a situation can be realised when a gas mixture is irradiated by a bichromatic combined light beam which is a special coaxial superposition of cosine-Gaussian optical beams. Here, the RcGF creates a periodic 1D array of deep potential wells (OSL) along the beam axes, and an effective force, causing LID, pulls resonant particles into the combined light beam and provides their transverse (with respect to the beam axes) confinement in OSL. As a result, there can occur a giant accumulation of impurity particles in the OSL cells, accompanied by a strong spatial particle localization far away from the walls of the reservoir, in which the gas mixture is located.

Quantum size effects and transport properties of Bi2(Te1-xSex)3 3D-topological insulator thin films

In this work, it was established that the room-temperature thickness (d = 16–207 nm) dependences of the Seebeck coefficient, Hall coefficient, and electrical conductivity in n-Bi2(Te0.9Se0.1)3 topological insulator thin films grown on glass substrates, in the thickness range of d = 16–85 nm exhibit an undamped oscillatory behavior with a large amplitude and are well approximated by a harmonic function with a period Δd=(8.0 ± 0.5)nm. The anionic substitution leads to some changes in the quantum size effects manifestation. The experimental results are consistent with theoretical calculations of Δd based on the infinitely deep potential well model. A sustained character of the oscillations is attributed to topologically protected surface states.

Rotational (de-)excitation of protonated tricarbon monosulfide HC3S+ by collision with helium atoms

A new two-dimensional potential energy surface of the interaction between HC3S+ molecule and helium atom is mapped using an explicitly correlated coupled cluster approach with a single, double and perturbative triple excitation-F12a approach with an augmented-correlation-consistent polarized valence triple-zeta Gaussian basis set. The deepest potential well is identified at θ = 95∘ and R = 6.0 bohr with a depth of 100.67 cm−1. Cross-sections are determined for total energy up to 300 cm−1 using a coupled states method. Thermal rate coefficients are derived from the determined cross-sections for temperatures ranging between 3 K and 50 K. A clear predominance of = 2 processes is observed.

Emergence of damped-localized excitations of the Mott state due to disorder

A key aspect of ultracold bosonic quantum gases in deep optical lattice potential wells is the realization of the strongly interacting Mott insulating phase. Many characteristics of this phase are well understood, however little is known about the effects of a random external potential on its gapped quasiparticle and quasihole low-energy excitations. In the present study we investigate the effect of disorder upon the excitations of the Mott insulating state at zero temperature described by the Bose–Hubbard model. Using a field-theoretical approach we obtain a resummed expression for the disorder ensemble average of the spectral function. Its analysis shows that disorder leads to an increase of the effective mass of both quasiparticle and quasihole excitations. Furthermore, it yields the emergence of damped states, which exponentially decay during propagation in space and dominate the whole band when disorder becomes comparable to interactions. We argue that such damped-localized states correspond to single-particle excitations of the Bose-glass phase.

Room Temperature Light Emission from Superatom-like Ge-Core/Si-Shell Quantum Dots.

We have demonstrated the high-density formation of super-atom-like Si quantum dots with Ge-core on ultrathin SiO2 with control of high-selective chemical-vapor deposition and applied them to an active layer of light-emitting diodes (LEDs). Through luminescence measurements, we have reported characteristics carrier confinement and recombination properties in the Ge-core, reflecting the type II energy band discontinuity between the Si-clad and Ge-core. Additionally, under forward bias conditions over a threshold bias for LEDs, electroluminescence becomes observable at room temperature in the near-infrared region and is attributed to radiative recombination between quantized states in the Ge-core with a deep potential well for holes caused by electron/hole simultaneous injection from the gate and substrate, respectively. The results will lead to the development of Si-based light-emitting devices that are highly compatible with Si-ultra-large-scale integration processing, which has been believed to have extreme difficulty in realizing silicon photonics.