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The <i>Gaia</i> DR2 view of the Gamma Velorum cluster: resolving the 6D structure
摘要： Gaia-ESO Survey observations of the young Gamma Velorum cluster led to the discovery of two kinematically distinct populations, Gamma Vel A and B, respectively, with population B extended over several square degrees in the Vela OB2 association. Using the Gaia DR2 data for a sample of high-probability cluster members, we find that the two populations differ not only kinematically, but are also located at different distances along the line of sight, with the main cluster Gamma Vel A being closer. A combined fit of the two populations yields (cid:36)A = 2.895 0.011 mas 11.5 pc and 383.4+2.5+15.3 and 0.091 14.2 pc, respectively, showing that Gamma Vel A is closer than Gamma Vel B by 38 pc. We find that the two clusters are nearly coeval, and that Gamma Vel B is expanding. We suggest that Gamma Vel A and B are two independent clusters located along the same line of sight.
关键词： open clusters and associations: individual: Gamma Velorum,stars: late-type,stars: pre-main sequence,stars: distances,stars: kinematics and dynamics
更新于2025-09-23 15:21:21
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Effects of vacancy defects location on thermal conductivity of silicon nanowire: a molecular dynamics study
摘要： The improvement of thermoelectric ?gure of merit of silicon nanowire (SiNW) can be achieved by lowering its thermal conductivity. In this work, non-equilibrium molecular dynamics method was used to demonstrate that the thermal conductivity of bulk silicon crystal is drastically reduced when it is crafted as SiNW and that it can be reduced remarkably by including vacancy defects. It has been found that ‘centre vacancy defect’ contributes much more in reducing the thermal conductance than ‘surface vacancy defect’. The lowest thermal conductivity that occurs is about 52.1% of that of pristine SiNW, when 2% vacancy defect is introduced in the nanowire. The vibrational density of states analysis was performed to understand the nature of this reduction and it has been found that the various boundary scatterings of phonon signi?cantly reduce the thermal conductivity. Also, larger mass difference due to voids induces smaller thermal conductivity values. These results indicate that the inclusion of vacancy defects can enhance the thermoelectric performance of SiNWs.
关键词： molecular dynamics,silicon nanowire,thermoelectric performance,thermal conductivity,vacancy defects
更新于2025-09-23 15:21:21
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State transition identification in multivariate time series (STIMTS) applied to rotational jump trajectories from single molecules
摘要： Time resolved data from single molecule experiments often suffer from contamination with noise due to a low signal level. Identifying a proper model to describe the data thus requires an approach with sufficient model parameters without misinterpreting the noise as relevant data. Here, we report on a generalized data evaluation process to extract states with piecewise constant signal level from simultaneously recorded multivariate data, typical for multichannel single molecule experiments. The method employs the minimum description length principle to avoid overfitting the data by using an objective function, which is based on a tradeoff between fitting accuracy and model complexity. We validate our method with synthetic data from Monte Carlo simulations modeling fluorescence resonance energy transfer and rotational jumps, respectively. The method is applied to quantify rotational jump dynamics of single terrylene diimide (TDI) molecules deposited on a solid substrate. Depending on the substitution pattern of the TDI molecules and the chosen substrate materials, we find significant differences in time scale and geometry of molecular reorientation. From an additional application of our state transition identification in multivariate time series approach, a significant correlation between shifts of emission spectra and the occurrence of rotational jumps was found.
关键词： minimum description length,rotational jump dynamics,state transition identification,multivariate time series,single molecule
更新于2025-09-23 15:21:21
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Sub-50 picosecond to microsecond carrier transport dynamics in pentacene thin films
摘要： Carrier transport dynamics from sub-50 ps to (cid:2)ls over five temporal decades in pentacene films was studied by transient photoconductivity. The behavior of the temperature independent photocurrent peak suggests that the photogenerated carriers exhibit pre-trapping transport in extended states upon pulsed laser excitation. From 300 ps to (cid:2)30 ns, the carriers thermalize and fall into shallow band tail states, and multiple-trapping and release transport dominates. From (cid:2)30 ns to (cid:2)ls, the weak temperature dependence of power-law photocurrent decay and the linear relation of logarithmic photocurrent with T(cid:3)1/4 suggest a variable range hopping transport in deep trap states.
关键词： transient photoconductivity,carrier transport dynamics,pentacene thin films,multiple-trapping and release transport,variable range hopping transport
更新于2025-09-23 15:21:21
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Live-cell super-resolution microscopy reveals a primary role for diffusion in polyglutamine-driven aggresome assembly
摘要： The mechanisms leading to self-assembly of misfolded proteins into amyloid aggregates have been studied extensively in the test tube under well-controlled conditions. However, to what extent these processes are representative of those in the cellular environment remains unclear. Using super-resolution imaging of live cells, we show here that an amyloidogenic polyglutamine-containing protein first forms small, amorphous aggregate clusters in the cytosol, chiefly by diffusion. Dynamic interactions among these clusters limited their elongation and led to structures with a branched morphology, differing from the predominantly linear fibrils observed in vitro. Some of these clusters then assembled via active transport at the microtubule-organizing center and thereby initiated the formation of perinuclear aggresomes. Although it is widely believed that aggresome formation is entirely governed by active transport along microtubules, here we demonstrate, using a combined approach of advanced imaging and mathematical modeling, that diffusion is the principal mechanism driving aggresome expansion. We found that increasing surface area of the expanding aggresome increases the rate of accretion due to diffusion of cytosolic aggregates and that this pathway soon dominates aggresome assembly. Our findings lead to a different view of aggresome formation than that proposed previously. We also show that aggresomes mature over time, becoming more compacted as the structure grows. The presence of large perinuclear aggregates profoundly affects the behavior and health of the cell, and our super-resolution imaging results indicate that aggresome formation and development are governed by highly dynamic processes that could be important for the design of potential therapeutic strategies.
关键词： molecular modelling,protein aggregation,molecular imaging,passive transport,amyloid protein,aggresome formation,transport,live cell SIM,protein misfolding,molecular dynamics
更新于2025-09-23 15:21:21
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Explosion induced rogue waves and chaotic multi-pulsing in a passively mode-locked all-normal dispersion fiber laser
摘要： In this work, an experimental study of non-stationary pulse dynamics consisting of explosion events and chaotic multi-pulsing from an all-normal dispersion Yb-fiber laser operating in noise-like pulse (NLP) state have been reported. During explosion in NLP state, which resembled soliton explosion, dispersive Fourier transform measurements revealed large, intermittent amplitude fluctuations in the real-time spectrum indicative of rogue waves. The fluctuations either appeared randomly at the lasing wavelength within the Yb-gain spectra or at the frequency downshifted Raman Stokes wavelength. It was also observed that such fluctuation at the Raman wavelength could even exceed the amplitude of the spectral components at the main lasing wavelength. With suitable adjustments, the laser operation could be switched to chaotic multi-pulsing state where the acquisition of a large number of consecutive roundtrips revealed inter-pulse motion with unique trajectories occurring over millisecond time scales.
关键词： optical rogue waves,multi-pulsing,non-stationary pulse dynamics,noise-like pulse,fiber lasers,mode-locked fiber lasers,non-linear dynamics
更新于2025-09-23 15:21:01
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Quench dynamics of finite bosonic ensembles in optical lattices with spatially modulated interactions
摘要： The nonequilibrium quantum dynamics of few boson ensembles which experience a spatially modulated interaction strength and are confined in finite optical lattices is investigated. We utilize a cosinusoidal spatially modulated effective interaction strength which is characterized by its wavevector, inhomogeneity amplitude, interaction offset and a phase. Performing quenches either on the wavevector or the phase of the interaction profile an enhanced imbalance of the interatomic repulsion between distinct spatial regions of the lattice is induced. Following both quench protocols triggers various tunneling channels and a rich excitation dynamics consisting of a breathing and a cradle mode. All modes are shown to be amplified for increasing inhomogeneity amplitude of the interaction strength. Especially the phase quench induces a directional transport enabling us to discern energetically, otherwise, degenerate tunneling pathways. Moreover, a periodic population transfer between distinct momenta for quenches of increasing wavevector is observed, while a directed occupation of higher momenta can be achieved following a phase quench. Finally, during the evolution regions of partial coherence are revealed between the predominantly occupied wells.
关键词： nonequilibrium dynamics,spatially dependent interactions,excited states,few-body systems,quench dynamics,optical lattices
更新于2025-09-23 15:21:01
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Reducing Anomalous Hysteresis in Perovskite Solar Cells by Suppressing Interfacial Ferroelectric Order
摘要： Despite booming researches in organometal halide perovskite solar cells (PSCs) of recent years, considerable roadblocks remain for their large-scale deployment, ranging from undesirable current-voltage hysteresis to inferior device stability. Among various plausible origins of the hysteresis, interfacial ferroelectricity is particularly intriguing and warrants a close scrutiny. Here, we examine interfacial ferroelectricity in MAPbI3 (FAPbI3)/TiO2 and MAPbI3/PCBM heterostructures, and explore the correlations between the interfacial ferroelectricity and the hysteresis from the perspective of nonadiabatic electronic dynamics. It is found that ferroelectric order develops at the MAPbI3/TiO2 interface owing to the interaction between the polar MA ions and TiO2. The polarization switching of the MA ions under an applied gate field would result in drastically different rates in interfacial photoelectron injection and electron-hole recombination, contributing to the undesirable hysteresis. In a sharp contrast, ferroelectricity is suppressed at the FAPbI3/TiO2 and MAPbI3/PCBM interfaces, thanks to elimination of the interfacial electric field between perovskite and TiO2 via substitution of strong polar MA (dipole moment: 2.29 Debye) by weak polar FA ions (dipole moment: 0.29 Debye) and interface passivation, leading to consistent interfacial electronic dynamics and the absence of the hysteresis. The present work sheds light to the physical cause for hysteresis and points to the direction to which the hysteresis could be mitigated in PSCs.
关键词： Ferroelectricity,Hysteresis,Perovskite Solar Cells,Excited-state Electronic Dynamics,Electron-Hole Recombination,Orientation Selectivity
更新于2025-09-23 15:21:01
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Endosome motility defects revealed at super-resolution in live cells using HIDE probes
摘要： We report new lipid-based, high-density, environmentally sensitive (HIDE) probes that accurately and selectively image endo-lysosomes and their dynamics at super-resolution for extended times. Treatment of live cells with the small molecules DiIC16TCO or DiIC16’TCO followed by in situ tetrazine ligation reaction with the silicon-rhodamine dye SiR-Tz generates the HIDE probes DiIC16-SiR and DiIC16’-SiR in the endo-lysosomal membrane. These new probes support the acquisition of super-resolution videos of organelle dynamics in primary cells for more than 7 min with no detectable change in endosome structure or function. Using DiIC16-SiR and DiIC16’-SiR, we describe direct evidence of endosome motility defects in cells from patients with Niemann–Pick Type-C disease. In wild-type fibroblasts, the probes reveal distinct but rare inter-endosome kiss-and-run events that cannot be observed using confocal methods. Our results shed new light on the role of NPC1 in organelle motility and cholesterol trafficking.
关键词： HIDE probes,endo-lysosomes,super-resolution,organelle dynamics,Niemann–Pick Type-C disease
更新于2025-09-23 15:21:01
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Numerical stability of time-dependent coupled-cluster methods for many-electron dynamics in intense laser pulses
摘要： We investigate the numerical stability of time-dependent coupled-cluster theory for many-electron dynamics in intense laser pulses, comparing two coupled-cluster formulations with full configuration interaction theory. Our numerical experiments show that orbital-adaptive time-dependent coupled-cluster doubles (OATDCCD) theory offers significantly improved stability compared with the conventional Hartree-Fock-based time-dependent coupled-cluster singles-and-doubles (TDCCSD) formulation. The improved stability stems from greatly reduced oscillations in the doubles amplitudes, which, in turn, can be traced to the dynamic biorthonormal reference determinants of OATDCCD theory. As long as these are good approximations to the Brueckner determinant, OATDCCD theory is numerically stable. We propose the reference weight as a diagnostic quantity to identify situations where the TDCCSD and OATDCCD theories become unstable.
关键词： time-dependent coupled-cluster theory,OATDCCD,Brueckner determinant,TDCCSD,intense laser pulses,numerical stability,many-electron dynamics
更新于2025-09-23 15:21:01