Browse Articles

Tracking and controlling dissociative ionization of formic acid molecules by femtosecond laser fields

We present an experimental investigation aimed at tracking and controlling the dissociative ionization of formic acid molecules using intense femtosecond laser pulses. The resulting ionic products, formyl and hydroxyl radicals, are measured in coincidence. By analyzing the kinetic energy release spectra of these ionic radicals as a function of the time delay between the pump and probe laser pulses, we identify two distinct formation pathways. Furthermore, we show the manipulation of the spatial emission characteristics of these ionic radicals by adjusting the relative phase of spatiotemporally shaped two-color femtosecond laser fields. These findings offer valuable insights into the fragmentation dynamics of formic acid molecules in femtosecond laser pulses.

Daidzin improves the cisplatin chemosensitivity for osteosarcoma via binding to β-catenin protein and suppressing the wnt pathway

Daily briefing: Scientists use AI to design life-like enzymes from scratch

Freezing, melting, and the onset of glassiness in binary mixtures

We clarify the relationship between freezing, melting, and the onset of glassy dynamics in a prototypical glass-forming mixture model. Our starting point is a precise operational definition of the onset of glassiness, as expressed by the emergence of inflections in time-dependent correlation functions. By scanning the temperature–composition phase diagram of the mixture, we find a disconnect between the onset of glassiness and freezing. Surprisingly, however, the onset temperature closely tracks the melting line, along which the excess entropy is approximately constant. At fixed composition, all characteristic temperatures display nonetheless similar pressure dependencies, which are very well predicted by the isomorph theory. While our results rule out a general connection between thermodynamic metastability and glassiness, they call for a reassessment of the role of crystalline precursors in glass-forming liquids.

Synthesis of divanillic acid-based aromatic polyamides with linear and branched side-chains and the effect of side-chain structure on thermal and mechanical properties

Why I retracted part of my PhD dissertation

Non-ideal mixing of lipids: A molecular dynamics perspective

Lipid membranes have complex compositions, and modeling the thermodynamic properties of multi-component lipid systems remains a remote goal. In this work, we attempt to describe the thermodynamics of binary lipid mixtures by mapping coarse-grained molecular dynamics systems to two-dimensional simple fluid mixtures. By computing and analyzing the density fluctuations of this model lipid bilayer, we determine the numerical value of the quadratic coupling term appearing in a model of regular solutions for the dipalmitoylphosphatidylcholine–dilinoleoylphosphatidylcholine pair of lipids at three different compositions. Our methodology is general and discussed in detail.

The media morphosis of science communication during crises

Abstract Effective science communication is crucial in informing citizens in times of crisis. The ICT-driven metamorphosis of the media industry (media-morphosis) has facilitated the shift from a rather one-directional information deficit model in science communication to a more bidirectional communication corresponding to a dialogue model. Little is known about the preferences for social media communication from the supply side of institutional and scholarly communication. Analyzing survey data from nearly 8,700 scientists, we compared their preferences for press media and social media, proxies of traditional centralized communication channels and modern decentralized channels, respectively. Our empirical results show that trust in governments and prioritizing access to all perspectives on the crisis are important factors that influence scientists’ preferences regarding forms of communication. Trust favors centralized systems, while social media serves as an alternative in contexts lacking trust in politics. Prioritizing the diffusion of different perspectives drives a shift to stated preferences for decentralized communication systems. We also show that scientists’ stated preferences for communication systems depend on the socio-political context.

NASA embraced diversity. Trump’s DEI purge is hitting space scientists hard

Insights into the impact of small anionic additives on Mg-silicate hydrate nucleation

Magnesium silicate (MS) cement, which uses magnesium silicate hydrate (M-S-H) as its primary binding phase, is a promising low-carbon alternative to Portland cement. However, the slow dissolution of MgO limits the release of Mg ions, which is critical for the formation of M-S-H. To address this issue, solubilizers that complex Mg2+ and promote MgO dissolution have been proposed, provided that they do not significantly hinder M-S-H formation. This study systematically examined the effects of four anionic additives—acetate, citrate, orthophosphate, and carbonate—on M-S-H nucleation and early growth, developing a highly reproducible crystallization scenario. The observed reduction in supersaturation at the nucleation point for specific additive concentrations suggests that Mg-anion complexes may play an active role in M-S-H nucleation, potentially allowing M-S-H to form at lower supersaturation levels, which could be beneficial for MS cement applications. However, as shown here, additives such as citrate, while not inhibiting nucleation, can significantly slow the growth of M-S-H, potentially compromising the strength development of MS cement. Among the additives studied, moderate concentrations of phosphate and carbonate show the most promise, as they have minimal effects on the formation process while potentially reducing the supersaturation for M-S-H nucleation. Although further research is necessary to fully understand the effects of these anions, this study provides valuable insights into their impact on M-S-H nucleation and early growth.

Security verification framework for NDN access control

Exact factorization method for bound vibrational states: An analytical tool for accurate approximations

The Exact Factorization (XF) method represents an interesting formulation of the Schrödinger equation where subsystem wavefunctions are exactly coupled. Here, I show that the XF method can be employed as an analytical tool to study the quantum vibrational problem of bound systems. In particular, after elaborating suitable XF-based wavefunction Ansätze, the ground-state energy approximated expression for bilinearly and quartically coupled harmonic oscillators is estimated. The XF-based analytical solution is compared with adiabatic and perturbative ones, and it is usually found to be an order of magnitude more accurate than these for estimating the anharmonic and coupling correction part of the ground-state energy. This procedure will possibly increase the numerical stability and accuracy of perturbative or Hartree-product based methods when applied to bound state calculations.

In vitro and in vivo assessment of a new acellular human amnion/chorion membrane device for guided bone regeneration

Highly efficient path-integral molecular dynamics simulations with GPUMD using neuroevolution potentials: Case studies on thermal properties of materials

Path-integral molecular dynamics (PIMD) simulations are crucial for accurately capturing nuclear quantum effects in materials. However, their computational intensity often makes it challenging to address potential finite-size effects. Here, we present a specialized graphics processing units (GPUs) implementation of PIMD methods, including ring-polymer molecular dynamics (RPMD) and thermostatted ring-polymer molecular dynamics (TRPMD), into the open-source Graphics Processing Units Molecular Dynamics (GPUMD) package, combined with highly accurate and efficient machine-learned neuroevolution potential (NEP) models. This approach achieves almost the accuracy of first-principles calculations with the computational efficiency of empirical potentials, enabling large-scale atomistic simulations that incorporate nuclear quantum effects, effectively overcoming finite-size limitations at a relatively affordable computational cost. We validate and demonstrate the efficacy of the combined NEP-PIMD approach by examining various thermal properties of diverse materials, including lithium hydride (LiH), three porous metal–organic frameworks (MOFs), liquid water, and elemental aluminum. For LiH, our NEP-PIMD simulations successfully capture the isotope effect, reproducing the experimentally observed dependence of the lattice parameter on the reduced mass. For MOFs, our results reveal that achieving good agreement with experimental data requires consideration of both nuclear quantum effects and dispersive interactions. For water, our PIMD simulations capture the significant impact of nuclear quantum effects on its microscopic structure. For aluminum, the TRPMD method effectively captures thermal expansion and phonon properties, aligning well with quantum mechanical predictions. This efficient GPU-accelerated NEP-PIMD implementation in the GPUMD package provides an alternative, accessible, accurate, and scalable tool for exploring complex material properties influenced by nuclear quantum effects, with potential applications across a broad range of materials.

Biometry-based verification system with symmetric key generation method for internet of things environments

Simulating phase inversion processes by coupled map lattice: Toward the theoretical design of food texture and quality in dairy processing from fresh cream to butter via whipped cream

We present a theoretical model and simulation for the formation dynamics of diverse texture patterns that emerge spontaneously or self-organize during phase inversion processes of fresh cream by mechanical whipping. The results suggest that the model should be applied for theoretically designing the texture and quality of whipped cream and butter products. The modeling complexity in phase inversion processes, from fresh cream via whipped cream to butter, was overcome by using a well-established complex systems approach, the coupled map lattice (CML). The proposed CML consists of a minimal set of procedures (i.e., parameterized nonlinear maps), such as whipping, coalescence, and flocculation, acting on the appropriately coarse-grained field variables, surface energy, cohesive energy, and velocity (flow) of the emulsion defined on a two-dimensional square lattice. In the CML simulations, two well-known and different phase inversion processes are reproduced at high and low whipping temperatures. The overrun and viscosity changes simulated in these processes are at least qualitatively consistent with those observed in experiments. We characterize these processes exhibiting different texture patterns as the viscosity dominance at high whipping temperatures and as the overrun dominance at low whipping temperatures on the viscosity–overrun plane, which is one of the state diagrams.

Gait impairment associated with neuroimaging biomarkers in Alzheimer’s disease

Isolating non-adiabatically enhanced ground state quantum beats through two-dimensional electronic spectroscopy

Resonant vibrational–electronic (vibronic) couplings in donor–acceptor systems may play a crucial role in driving non-adiabatic internal conversion reported in natural photosynthesis, organic photovoltaic polymers, and singlet exciton fission. Quantum beats arising from impulsive excitation are often employed as spectroscopic reporters of the specific vibrational modes driving this process. However, distinguishing these promoter modes from spectator modes, which do not participate in vibronic mixing and simply accompany ultrafast internal conversion, remains a challenge. This is so because vibrational quantum beats arising from uncoupled monomers can modulate pump–probe transients by themselves. In this paper, we show that vibronic mixing induces quantum beats whose amplitude is anisotropic with respect to the polarization of the light. We propose a readily implementable polarization-controlled two-dimensional electronic spectroscopy experiment to uniquely identify signatures of excited state vibronic resonance using ground state quantum beats by discriminating against vibrational motions (and corresponding quantum beats) that are simply spectators. Through analytical expressions and simulation of two-dimensional electronic spectra, we show that the resulting 2D spectra are expected to exhibit distinct spectral lineshapes with a strong temperature dependence that arises solely due to the excited state vibronic mixing. Our findings suggest an interesting experiment to decipher the presence of excited state vibronic resonances.

Allosteric modulation and direct activation of glycine receptors by a tricyclic sulfonamide

Ionic association and Wien effect in 2D confined electrolytes

Recent experimental advances in nanofluidics have allowed to explore ion transport across molecular-scale pores, in particular, for iontronic applications. Two-dimensional nanochannels—in which a single molecular layer of electrolyte is confined between solid walls—constitute a unique platform to investigate fluid and ion transport in extreme confinement, highlighting unconventional transport properties. In this work, we study ionic association in 2D nanochannels, and its consequences on non-linear ionic transport, using both molecular dynamics simulations and analytical theory. We show that under sufficient confinement, ions assemble into pairs or larger clusters in a process analogous to a Kosterlitz–Thouless transition, here modified by the dielectric confinement. We further show that the breaking of pairs results in an electric-field dependent conduction, a mechanism usually known as the second Wien effect. However the 2D nature of the system results in non-universal, temperature-dependent, scaling of the conductivity with electric field, leading to ionic coulomb blockade in some regimes. A 2D generalization of the Onsager theory fully accounts for the non-linear transport. These results suggest ways to exploit electrostatic interactions between ions to build new nanofluidic devices.