Browse Articles

Research on metabolic characteristics of multiple sclerosis

Improved Debye–Callaway model for calculating the lattice thermal conductivity of anisotropic two-dimensional crystals

Thermal management in two-dimensional (2D) materials is pivotal, given their extensive technological utility in miniaturized devices. However, an expedient yet precise method for predicting the thermal transport properties of 2D materials remains to be established. In this study, we derive analytical formulas for calculating the scattering rate of three-phonon Umklapp processes, specifically tailored to 2D materials, based on the continuous elasticity assumption, quasi-harmonic approximation, and central force approximation. These formulas enable the construction of a refined Debye–Callaway model that incorporates the effects of both three-phonon Umklapp scattering and boundary scattering, eliminating the need for any fitting parameters. Notably, we explicitly disentangle the contributions of optical phonons, treating them within a framework analogous to the Einstein model. This improved model facilitates efficient and accurate predictions of the anisotropic lattice thermal conductivities in 2D materials. The results generated by our model for 12 2D crystals show excellent agreement with those from fully first-principles calculations reported in the literature. In particular, this study clarifies how the relaxation time fitting parameter adopted in previous work depends on the crystal structure and dimensional characteristics of the materials. It also provides an understanding of the logarithmic divergence of lattice thermal conductivity with respect to the size of 2D crystals within a framework involving only three-phonon scattering processes and Debye approximation. Owing to its low computational cost and high prediction precision, this model can serve as a valuable tool for high-throughput screening and machine learning applications in the identification of 2D materials with tailored thermal conductivity.

The association between systemic inflammation markers and breast cancer

Squeezing new information out of small systems

Confinement alters many aspects of the structure and dynamics of polymers, macromolecules, and other related molecular systems, impacting the properties of nanocomposites (including surface attached polymers), microphase separated polymers, and ultrathin films. Alterations include large changes in glass transition temperatures, crystallization behavior, and rheological response, among other properties. A wide range of relevant length scales (local relaxation processes up to entire chain motion) makes this a multifaceted and rich arena. This Special Topic Collection includes 35 articles by experts in the field of “Polymer Nanoconfinement.”

Magnetic flux imaging in a 3D superconductor integrated circuit

Abstract We report on imaging magnetic flux distributions in a multilayered superconductor integrated circuit which emerge during magnetization and after field cooling of the circuit in the DC magnetic field. The obtained complicated field maps expose the flux propagation across the patterned superconducting ground planes sandwiching layers with Josephson junction-based logic cells, fine wire grid around the functional units, and multiple superconducting fill structures located in different inner layers. The observed intricate flux distributions are explained by specific patterns of Meissner screening currents and superconducting critical currents in different mutually interacting parts of the integrated circuit. Our results provide important insights into possible ways of improving the protection of superconductor integrated circuits from magnetic fields and their resilience against flux trapping.

Modeling high-order harmonic generation in quantum dots using a real-space tight-binding approach

Recently, the size-dependence of high-order harmonic generation (HHG) in quantum dots (QDs) has been investigated experimentally. In particular, for longer driving wavelengths and quantum dots smaller than 3 nm, HHG was strongly suppressed; however, there is no computational model capable of describing the strong-field response of such systems. In this work, we introduce a computationally efficient three-dimensional real-space tight-binding model specifically designed for the simulation of HHG in confined systems. The model parameters are meticulously derived from density functional theory calculations for the semiconductor bulk, followed by a process of Wannierization. Our findings demonstrate that the proposed model accurately captures the observed dependency of the HHG yield on the quantum dot size. In addition, we simulate the HHG yield for elliptically polarized pulses for different QD-sizes and driving wavelengths up to 5 μm. The proposed model fills the theoretical void in simulating HHG within medium-sized nanostructures, which cannot be described by methods applied for periodic solids, or small molecules or atoms.

Study on establishment of cardiovascular interventional disease database and prediction of postoperative mortality risk

Atom-centered electric multipole moments dynamically generated from QM/MM MD simulations

Atom-centered electric multipole moments can be extremely useful in chemistry, as they enable the systematic mapping of a complex electrostatic problem to a simpler model. However, since they do not correspond to physical observables, there is no unique way to define them. In this study, we present an extension of the dynamically generated RESP charges (D-RESP) method, referred to as xDRESP, where atom-centered multipoles are computed from mixed quantum mechanics/molecular mechanics molecular dynamics simulations. We compare the ability of xDRESP charges to reproduce the electrostatic potential, as well as molecular multipoles, against the performance of fixed point-charge models commonly used in force fields. Moreover, we highlight cases where xDRESP atomic multipoles can provide valuable information about chemical systems, such as indicating when polarization plays a significant role, and chemical reactions in which xDRESP atomic multipoles can be used as an on-the-fly analysis tool to track changes in electron density.

Social encapsulation of parasite eggs by honeybee colonies

Abstract Eusocial insect colonies can choose different behaviours to combat the same parasites. While honeybee (HB), Apis mellifera , colonies remove eggs and larvae of parasitic small hive beetles (SHB), Aethina tumida , they encapsulate adults in propolis. It is currently unknown whether there is flexibility in this system. Here, we show encapsulation of eggs by colonies as an alternative to removal. Oviposition sites with or without SHB eggs were introduced into HB field colonies of mixed European origin. After 24 h, sites were removed to measure the propolised area and to quantify the remaining eggs. Further, SHB egg laying depth, and HB worker proboscis length and thickness, were measured. Even though the proboscises were long enough to reach most eggs, the number of eggs before and after introduction did not differ. Instead, HB used more propolis on sites with eggs compared to controls. This suggests decision making by colonies for either egg removal or encapsulation and demonstrates considerable flexibility in social immunity. Such flexibility probably contributes to eusocial insect resilience and calls for efforts to understand colony decision making.

Precision ultranarrow-linewidth resonance excitation (PURE) preparation of a molecular beam of nitric oxide molecules for inelastic scattering with argon

We recently reported a novel technique that utilizes narrow-linewidth lasers to selectively excite molecules into a pure quantum state with a well-resolved, tunable distribution of velocities [O. A. Krohn and D. W. Chandler, J. Phys. Chem. Lett. 15(50), 12455–12463 (2024)]. We refer to the preparation of molecules by this technique as precision ultranarrow-linewidth resonant excitation (PURE) preparation. Here, we pair this PURE preparation methodology with active frequency stabilization of the quantum cascade laser that drives the excitation. In doing so, highly velocity-resolved packets of molecules are possible, with the limitations of this velocity resolution set by the stability of the laser locking and the spectral linewidth of the transition. We show that side-of-fringe locking to a Doppler-broadened absorption spectrum of our target molecule is sufficiently stable for PURE preparation of molecules for long timescales (several hours) with highly resolved velocity spreads (σ < 3 m/s). To demonstrate the scientific utility of this new capability, we present differential cross sections from scattering between a neat molecular beam of argon and a velocity-selected beam of nitric oxide (NO) in a pure quantum state. We observe well-resolved quantum diffraction oscillations in the forward-scattered collisions as well as general trends consistent with prior characterized collisions of NO + Ar.

Functional near-infrared spectroscopy identifies neural biomarkers of burnout in active-duty Police officers

Seeding and controlling colloidal self-assembly through focused ion beam deposition

To obtain high yields of a desired structure from self-assembly, one often needs a seed: a template that favors formation of the structure. The physical mechanisms of seeding have been studied in detail in micrometer-scale colloidal systems, but much of this prior work has focused on quasi-planar substrates. Our overarching aim is to seed colloidal self-assembly on curved surfaces, for which the orientation of a two-dimensional (2D) crystal nucleus—typically unimportant for assembly on a flat surface—determines whether defects form. Because existing methods lack the spatial control to seed colloidal crystals on curved surfaces, we develop a new method that can be applied to both flat and curved surfaces. Our method leverages the spatial precision of focused ion beam (FIB) deposition. We deposit perhaps the simplest nanostructures that can seed the growth of 2D crystals: triangular configurations of three wells. We then use confocal microscopy to monitor the dynamics of depletion-mediated colloidal self-assembly in the presence and absence of the FIB nanostructures. On flat surfaces, we find that nucleation can be either directly or indirectly controlled by the seeding nanostructure, depending on the supersaturation and the interaction strength, and we observe growth occurring by both particle attachment and oriented attachment. Based on these results, we extend our seeding method to control the crystal orientation on a highly curved 5 μm glass fiber. Our FIB-deposition approach to seeding might be useful not only for controlling assembly on geometrically frustrated systems but also for modifying functional devices such as optical fibers and neural probes.

Study on the impact of urban underground public space expansion on near-ground carbon monoxide concentrations

Photodissociation dynamics of the OCS + <i>hv</i> → CO(1Σ+) + S(3P <i>J</i> =2, 1, 0) in the first UV absorption band

The OCS photodissociation dynamics of the minor triplet S(3PJ=2, 1, 0) channels across the first UV absorption band (202–248 nm) have been studied using the time-sliced velocity-mapped ion imaging technique. Wavelength-dependent dynamical features are directly revealed from the sliced images of the S(3PJ=2, 1, 0) photofragments. The internal energy distributions of the counter CO fragments exhibit a vibrational progression, superimposed by a dominant high-energy feature characterized by low vibrational but high rotational excitation. In addition, a minor fraction of extremely high rotationally excited CO(v = 0, 1) is observed near the limitation of available energy. The relative populations of these components show pronounced dependences on both photolysis wavelength and spin–orbit state. The internal-energy-dependent anisotropy parameters β(Eint), combined with insights from potential energy surfaces, indicate distinct dissociation mechanisms. The large positive β(Eint) values for both the dominant highly rotationally excited CO and a substantial population of vibrationally excited CO support a dissociation mechanism dominated by intersystem crossing from the initially excited 21A′ (and minor 11A″) state to the dissociative triplet 23A″ state. In contrast, the minor component of extremely high rotationally excited CO is generated via a two-step nonadiabatic pathway involving internal conversion from the 21A′ state to the ground state followed by intersystem crossing to the triplet 13A′ or 13A″ state, which yields near-zero or small negative β(Eint) values due to the nonaxial recoil effect. Furthermore, an abrupt drop in β(Eint) for low vibrationally excited CO fragments near 223 nm suggests an additional contribution from direct excitation to the triplet 23A″ state and its subsequent nonadiabatic dissociation.

Extraction method shapes soil water-soluble organic matter composition as revealed by absorbance, fluorescence, and parallel factor analysis (PARAFAC)

Abstract Organic matter (OM) is central to biogeochemical processes in both soils and aquatic systems. Water-soluble organic matter (WSOM), leached from soil, is widely analyzed as a proxy for the mobile OM fraction, yet the chemical composition of extracts depends strongly on the extraction method used. We compared two WSOM extraction protocols—distilled water and 0.5 M K 2 SO 4 —across 217 soil samples from 83 depth profiles spanning four central European regions. Absorbance and fluorescence spectroscopy with PARAFAC modeling were used to characterize dissolved organic carbon (DOC) concentration and composition—approaches increasingly applied in soil science to trace soil organic matter dynamics. DOC generally declined with profile depth. K 2 SO 4 extracts consistently yielded higher DOC concentrations, dominated by humic-like fluorescence. Water extracts were more variable, with stronger protein-like signals—showing clearer depth-related trends, with deeper layers enriched in microbially-derived DOM. This higher variability likely reflects the dynamic nature of labile WSOM fractions. We highlight the importance of extraction chemistry: water-based methods capture reactive, microbially-produced WSOM—likely indicators of immediate inputs to aquatic systems, whereas salt-based methods emphasize more stable pools—acting as indicators of less bio-available, long-term terrestrial reservoirs. Extraction methodology selection should consider the study objectives and specific biological and physicochemical processes investigated.

Numerically exact quantum dynamics with tensor networks: Predicting the decoherence of interacting spin systems

Predicting the quantum dynamics of promising solid-state and molecular quantum technology candidates remains a formidable challenge. Yet, accessing these dynamics is key to understanding and controlling decoherence mechanisms—a prerequisite for designing better qubits, sensors, and memories. We leverage a matrix product state representation to introduce a numerically exact and scalable method to achieve this goal. We demonstrate that our method accurately predicts coherence and population dynamics of spin networks across a wide range of parameter regimes, encompassing nuclear spin sensors and qubits in solid-state semiconductors and molecular magnets. Our method further predicts spin dynamics under the influence of repeated light pulses, which are commonly used to mitigate decoherence and perform quantum sensing experiments. Our method thus provides reliable results for moderately sized spin platforms spanning molecular magnets and solid-state spins that can guide the development of approximate but efficient quantum dynamics methods and enable principled inquiry into decoherence mechanisms.

Primary dysmenorrhea and associated factors among female adolescents in Jinka town, Southern Ethiopia, 2024

Non-equivalent local excitations and conformation dependent charge transfer in N,N-dimethylethylenediamine

The discrimination of local excitation sites in multi-charge-center molecular systems remains a long-standing challenge and is rarely explored. Herein, non-equivalent local excitations of two distinct 3s Rydberg states (3s1 and 3s2, as excited from the N1 and N4 atoms, respectively) in two-charge-center N,N-dimethylethylenediamine and their ensuing conformation-dependent charge transfer dynamics have been observed by femtosecond time-resolved photoelectron spectra. In particular, following local excitation at N4, the 3s2 state structurally evolves away from the Franck–Condon region driven by charge redistribution from N1 to the hole of N4 via through-bond interaction, leading to the 3s1 and 3s2 states being energetically indistinguishable after 300 fs. The preferential charge stabilization at N4 is observed, exhibiting a new paradigm of charge localization. Concurrently, the 3p state undergoes internal conversion to 3s_h and 3s_l states and approaches a dynamic conformation equilibrium (3s_h/3s_l = 61%:39%) within about 1.1 ps. This work provides new insight into the understanding of charge localization and transfer phenomena in biologically relevant molecular systems with multiple charge centers.

Highly sensitive hierarchically structured Si-based UV sensor–photodetectors via optimized ZnO–Al2O3 nanocomposite architectures

Abstract The rapid and reliable detection of ultraviolet (UV) radiation is critical for applications ranging from environmental monitoring to optoelectronic security systems. This study presents an integrated theoretical and experimental investigation into highly sensitive, hierarchically structured Si-based UV sensor–photodetectors optimized via ZnO–Al 2 O 3 nanocomposite architectures. A combination of density functional theory (B3LYP/6-31G(d,p)) calculations and comprehensive materials characterization was employed to elucidate the interplay between electronic structure, surface morphology, and optical performance. Theoretical modeling provided detailed insights into band alignment, total and partial density of states, frontier molecular orbitals, and electrostatic potential distributions for pure and hybrid oxide systems, revealing that ZnO–Al 2 O 3 exhibits superior electronic coupling and enhanced carrier mobility pathways. Experimentally, ZnO and Al 2 O 3 nanoparticles were synthesized via hydrothermal routes, integrated into hybrid thin-film architectures on Si substrates, and structurally verified by XRD, FE-SEM, and EDX analyses. Surface roughness and apparent porosity measurements indicated that Al 2 O 3 incorporation increased roughness from 6.7 to 8.2 µm and porosity from 26 to 36%, fostering enhanced light scattering and active site density. Optical absorption spectroscopy (250–650 nm) revealed strong UV selectivity with calculated band gaps of 3.18 eV (ZnO), 3.11 eV (Al 2 O 3 ), and 3.26 eV (ZnO–Al 2 O 3 ), while electrochemical impedance spectroscopy confirmed reduced charge transfer resistance in the hybrid architecture. Electrical conductivity improved from 27.7 × 10 −2  S/m (ZnO) to 44.5 × 10 −2  S/m (ZnO–Al 2 O 3 ), correlating with faster response and recovery dynamics under UV illumination. These synergistic structural, optical, and electronic enhancements establish ZnO–Al 2 O 3 as a promising candidate for next-generation, high-performance UV photodetectors with superior sensitivity, stability, and spectral selectivity.

The second Gibbs paradox

Gibbs’s monumental article on the equilibrium of heterogeneous substances contains a paradoxical sentence stating that, for a crystallite in equilibrium with a fluid, the chemical potential of the solid will not be equal to that of the fluid if the surface free-energy density differs from the mechanical surface-tension. How can this be? After all, in chemical equilibrium, the chemical potential of any species should be the same throughout the system. This “second Gibbs paradox” has intrigued many authors. In the present paper, I sketch my interpretation of the approach of Gibbs and that of Mullins [J. Chem. Phys. 81, 1436–1442 (1984)], which accounts for the possibility of vacancies and interstitials. I argue that a consistent treatment of point defects in a critical nucleus is essential for clarifying the meaning of the chemical potential of the nucleus. My paper lacks the rigor of Gibbs or Mullins but will hopefully be more accessible for scientists who think primarily in terms of atoms and molecules. In my attempt, I am motivated by a quote that is sometimes attributed to Paul Valéry: “The glass must be absolutely transparent for one to perceive the mud at the bottom.”