Geometry Dependence Research Articles

Climate and ice sheet dynamics in Patagonia throughout marine isotope stages 2 and 3

Abstract. During the Last Glacial Maximum (LGM, ∼ 23 000 to 19 000 years ago), the Patagonian Ice Sheet (PIS) covered the central chain of the Andes between ∼ 38 to 55° S. Existing paleoclimate evidence – mostly derived from glacial landforms – suggests that maximum ice sheet expansions in the Southern Hemisphere and Northern Hemisphere were not synchronized. However, large uncertainties still exist in the timing of the onset of regional deglaciation and its major drivers. Here we present an ensemble of numerical simulations of the PIS during the LGM. We assess the skill of paleoclimate model products in reproducing the range of atmospheric conditions needed to enable an ice sheet growth in concordance with geomorphological and geochronological evidence. The resulting best-fit climate product is then combined with records from southern South America offshore sediment cores and Antarctic ice cores to drive transient simulations throughout the last 70 ka using a glacial index approach. Our analysis suggests a strong dependence of the PIS geometry on near-surface air temperature forcing. Most ensemble members underestimate the ice cover in the northern part of Patagonia, while tending to expand beyond its constrained eastern boundaries. We largely attribute these discrepancies between the model-based ice geometries and geological evidence to the low resolution of paleoclimate models and their prescribed ice mask. In the southernmost sector, evidence suggests full glacial conditions during marine isotope stage 3 (MIS3, ∼ 59 400 to 27 800 years ago), followed by a warming trend towards MIS2 (∼ 27 800 to 14 700 years ago). However, in northern Patagonia, this deglacial trend is absent, indicating a relatively consistent signal throughout MIS3 and MIS2. Notably, Antarctic cores do not reflect a glacial history consistent with the geochronological observations. Therefore, investigations of the glacial history of the PIS should take into account southern midlatitude records to capture effectively its past climatic variability.

Enhancing Precision in SQUID Sensors: Analyzing Washer Geometry Dependence at the Microscale

In the field of high-precision physical field detection, measurements based on magnetic signals are crucial due to their exceptional accuracy, sensitivity, and stability. Superconducting Quantum Interference Devices (SQUIDs), with their ultra-high sensitivity, have become key in detecting minute changes in magnetic flux. However, with increasing demands for higher precision, further enhancing device performance under quantum constraints remains a significant challenge. This study improved the precision of SQUID sensors by optimizing the geometry of microscale washers using the physical response of superconducting films under micromachining technologies and quantum constraints. Our research extensively examined the effects of square, octagonal, and circular washers on the magnetic field response, shielding currents, and inductance. Experimental results showed that, compared to traditional square washers, octagonal washers significantly enhanced sensor sensitivity and efficiency by minimizing edge magnetic flux and optimizing current distribution. Notably, all observed inductance values exceeded predictions based on traditional empirical formulas, with square washers showing the highest average relative error of 80.8%, while circular and octagonal washers had errors of 65.31% and 66.43%, respectively. This breakthrough not only lays a new theoretical foundation for the design of SQUID sensors but also provides robust evidence for enhancing magnetic field detection through microscale technological innovation.

Chiral and directional optical emission from a dipole source coupled to a helical plasmonic antenna

Plasmonic antennas with helical geometry can convert linearly polarized dipole radiation into purely circularly polarized far-fields, and vice versa. Besides large Purcell enhancements, they possess a wide tunability due to the geometry dependence of their resonant modes. Here, the coupling of a dipole emitter embedded in a thin film to plasmonic single and double helices is numerically studied. Using a higher-order finite element method (FEM), the wavelength dependent Purcell enhancement of a dipole with different positions and orientations is calculated and the far-fields with respect to their chirality and radiation patterns are analyzed. Both single and double helices demonstrate highly directional and circularly polarized far-fields for resonant excitation but with significantly improved directional radiation for the case of double helices.

Neutron emission characterization of IPR 14 MeV neutron generator

Accelerator-based neutron sources are being developed worldwide due to their wide applications. Institute for Plasma Research in India has developed an accelerator-based high-yield 14 MeV neutron generator based on deuterium-tritium (D-T) reaction to perform fusion-related benchmark experiments. This neutron generator is designed to produce 1012 neutrons per second in both mode continuous and pulse. The emission of neutrons from an accelerator-based neutron generator is not isotropic due to target geometry and angular dependency of reaction cross-section. A detailed and accurate description of neutron source emission and distribution is required to use such a neutron generator for various experiments. The neutron generator is characterized using experiments and simulations to accomplish the request. Energy and angular distributions of emitted neutrons are measured using a calibrated single crystal diamond (SCD) detector. Experimental data of neutron distributions are used to validate source neutron definition for Monte Carlo N Particle (MCNP) simulation. An accurate model of the Titanium Tritide (TiT) target and its holder geometry is prepared for the simulation. Finally, to validate the simulation model, simulated neutron fluxes are compared with measured ones by the SCD detector. This paper discusses the methodology adopted to characterize emitted neutrons and its results.

Virtual photon exchange vs electron transfer in interparticle Coulombic electron capture.

We have investigated Interparticle Coulombic Electron Capture (ICEC) using an abinitio approach for two systems, H+ + H2O and H + H2O+. In this work, we have determined the contribution of virtual photon exchange and electron transfer to the total ICEC cross section as a function of the distance between the charged and neutral particles. Furthermore, we have shown that the relative orientation of the electron acceptor and neighbor systems affects the magnitude of the ICEC cross sections by at least two orders at relatively small distances. This geometry dependence, present even for distances as large as 10 a0, is due to the electron transfer contribution. The relative magnitude of each contribution to ICEC seems to depend on the system studied. By replacing the projectile electron with a positron, we have confirmed that electron transfer also takes place in positron collisions and that the charge of the projectile has a noticeable effect on the process, particularly at low scattering energies.

On the geometry dependence of the nuclear magnetic resonance chemical shift of mercury in thiolate complexes: A relativistic density functional theory study.

Thiolate containing mercury(II) complexes of the general formula [Hg(SR) ] have been of great interest since the toxicity of mercury was recognized. 199Hg nuclear magnetic resonance spectroscopy (NMR) is a powerful tool for characterization of mercury complexes. In this work, the Hg shielding constants in a series of [Hg(SR) ] complexes are therefore investigated computationally with particular emphasis on their geometry dependence. Geometry optimizations and NMR chemical shift calculations are performed at the density functional theory (DFT) level with both the zeroth-order regular approximation (ZORA) and four-component relativistic methods. The four exchange-correlation (XC) functionals PBE0, PBE, B3LYP, and BLYP are used in combination with either Dyall's Gaussian-type (GTO) or Slater-type orbitals (STOs) basis sets. Comparing ZORA and four-component calculations, one observes that the calculated shielding constants for a given molecular geometry have a constant difference of 1070 ppm. This confirms that ZORA is an acceptable relativistic method to compute NMR chemical shifts. The combinations of four-component/PBE0/v3z and ZORA/PBE0/QZ4P are applied to explore the geometry dependence of the isotropic shielding. For a given coordination number, the distance between mercury and sulfur is the key factor affecting the shielding constant, while changes in bond and dihedral angles and even different side groups have relatively little impact.

New Pyridine Dicarbene Pincer Ligands with Ring Expanded NHCs and their Nickel and Chromium Complexes.

The pincer complexes [NiIIBr(CNC)]Br (4), [CrIIIBr3(CNC)] (5 a) and [CrIIIBr2.3Cl0.7(CNC)] (5 b), where CNC=3,3'-(pyridine-2,6-diyl)bis(1-mesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene), were obtained from the novel ligand CNC, generated in situ from the precursor (CHNCH)Br2 and [NiIIBr2(PPh3)2] or from [CrII{N(SiMe3)2}2(THF)2] and (CHNCH)Br2 by aminolysis, respectively. The tetrahedrally distorted square planar (τ4≅0.30) geometry and the singlet ground state of Ni in 4 were attributed to steric constraints of the CNC backbone. Computational methods highlighted the dependence of the coordination geometry and the singlet-triplet energy difference on the size of the N-substituent of the tetrahydropyrimidine wingtips and contrasted it to the situation in 5-membered imidazolin-2-ylidene pincer analogues. The octahedral CrIII metal center in 5 a and 5 b is presumably formed after one electron oxidation from CH2Cl2. 4/MAO and 5 a/MAO were catalysts of moderate activity for the oligomerization and polymerization of ethylene, respectively. The analogous (CH^N^CH)Br2 precursor, where (CH^N^CH)=3,3'-(pyridine-2,6-diylbis(methylene))bis(1-mesityl-3,4,5,6-tetrahydropyrimidin-1-ium), was also prepared, however its coordination chemistry was not studied due to the inherent instability of the resulting free C^N^C ligand.

Modeling of Casting Deformation Prediction During Investment Casting Based on Geometry Dependence

Modeling of Casting Deformation Prediction During Investment Casting Based on Geometry Dependence

Dynamic Tunable Liquid-Core Photonic Crystal Fiber Sensor Based on Graphene Plasmon

AbstractThe combination of photonic crystal fiber (PCF) and graphene-supporting surface plasmon polaritons (SPP) presents a new approach to achieving a plasmonic sensor with adjustable properties in the terahertz (THz) frequency range. In this study, we investigate a liquid-core PCF-based graphene plasmonic sensor, where the analyte to be detected is located on both the sensing layer surface and the fiber core. As a result, the dispersion relations of both graphene plasmon (GP) and core-guide mode can be influenced by the analyte, leading to a negative refractive index (RI) wavelength sensitivity. This unique performance is attributed to the higher modulation degree of the core mode on the analyte RI (Δneff.core) compared to that of the GP mode (Δneff.GP). By reducing the graphene Fermi energy, a positive sensibility is achieved with the modulation relationship of Δneff.core < Δneff.GP. Subsequently, the geometry dependence is explored to optimize the sensing capabilities. Furthermore, we demonstrate the sensor’s tunability by dynamically varying the graphene Fermi energy (Ef). By adjusting the Ef from 0.6 to 0.9 eV, the detection range can be artificially shifted from 0.554–0.574 THz to 0.686–0.724 THz, obtaining a tunability of 0.44 THz/eV and a higher sensitivity of 1.2667 THz/RIU. This design facilitates the efficient utilization of the limited bandwidth to detect various RIs and provides a flexible approach to constructing multiple sensing channels. To the best of our knowledge, this is the first report of graphene plasmonic sensing based on core-filled PCF in the THz frequency range. The novel analysis method of modulation degree and dispersion matching has the potential to be widely applied in THz plasmonic sensing and could lead to various nanoscience applications.

Experimental tests of the lipid dependence of single heptameric alpha-hemolysin channel ionic conductance and pore geometry

Experimental tests of the lipid dependence of single heptameric alpha-hemolysin channel ionic conductance and pore geometry

Frequency shifts of free water signals from compact bone: Simulations and measurements using a UTE-FID sequence.

Free water in cortical bone is either contained in nearly cylindrical structures (mainly Haversian canals oriented parallel to the bone axis) or in more spherically shaped pores (lacunae). Those cavities have been reported to crucially influence bone quality and mechanical stability. Susceptibility differences between bone and water can lead to water frequency shifts dependent on the geometric characteristics. The purpose of this study is to calculate and measure the frequency distribution of the water signal in MRI in dependence of the microscopic bone geometry. Finite element modeling and analytical approaches were performed to characterize the free water components of bone. The previously introduced UTE-FID technique providing spatially resolved FID-spectra was used to measure the frequency distribution pixel-wise for different orientations of the bone axis. The frequency difference between free water in spherical pores and in canals parallel to B0 amounts up to approximately 100 Hz at 3T. Simulated resonance frequencies showed good agreement with the findings in UTE-FID spectra. The intensity ratio of the two signal components (parallel canals and spherical pores) was found to vary between periosteal and endosteal regions. Spatially resolved UTE-FID examinations allow the determination of the frequency distribution of signals from free water in cortical bone. This frequency distribution indicates the composition of the signal contributions from nearly spherical cavities and cylindrical canals which allows for further characterization of bone structure and status.

Spin Coupling Effect on Geometry-Dependent X-Ray Absorption of Diradicals.

We theoretically investigate the influence of diradical electron spin coupling on the time-resolved X-ray absorption spectra of the photochemical ring opening of furanone. We predict geometry-dependent carbon K-edge signals involving transitions from core orbitals to both singly and unoccupied molecular orbitals. The most obvious features of the ring opening come from the carbon atom directly involved in the bond breaking through its transition to both the newly formed singly occupied and the available lowest unoccupied molecular orbitals (SOMO and LUMO, respectively). In addition to this primary feature, the singlet spin coupling of four unpaired electrons that arises in the core-to-LUMO states creates additional geometry dependence in some spectral features with both oscillator strengths and relative excitation energies varying observably as a function of the ring opening. We attribute this behavior to a spin-occupancy-induced selection rule, which occurs when singlet spin coupling is enforced in the diradical state. Notably, one of these geometry-sensitive core-to-LUMO transitions excites core electrons from a backbone carbon not involved in the bond breaking, providing a novel nonlocal X-ray probe of chemical dynamics arising from electron spin coupling.

Small-x structure of oxygen and neon isotopes as seen by the Large Hadron Collider

Results on collisions of 16O nuclei performed at the Relativistic Heavy Ion Collider (RHIC) have been presented for the first time at Quark Matter 2023 by the STAR collaboration. 16O+16O collisions are also expected to take place in the near future at the Large Hadron Collider (LHC) at much higher beam energies. We explore the potential of beam-energy-dependent studies for this system to probe small-x dynamics and QCD evolution. We perform 3 + 1D IP-Glasma simulations to predict the rapidity dependence of the initial geometry of light-ion collisions, focusing on 16O+16O and 20Ne+20Ne collisions at √SNN = 70 GeV and 7 TeV. The choice of 20Ne is motivated by its strongly elongated geometry, which may respond differently to the effect of the highenergy evolution compared to the more spherical 16O. We find that smearing induced by soft gluon production at high energy causes mild variations in the initial-state eccentricities as a function of the collision energy. These effects could be resolved in future experiments and deserve further investigation.

Hydrogen-iodine scattering. I. Development of an accurate spin-orbit coupled diabatic potential energy model.

The scattering of H by I is a prototypical model system for light-heavy scattering in which relativistic coupling effects must be taken into account. Scattering calculations depend strongly on the accuracy of the potential energy surface (PES) model. The methodology to obtain such an accurate PES model suitable for scattering calculations is presented, which includes spin-orbit (SO) coupling within the Effective Relativistic Coupling by Asymptotic Representation (ERCAR) approach. In this approach, the SO coupling is determined only for the atomic states of the heavy atom, and the geometry dependence of the SO effect is accounted for by a diabatization with respect to asymptotic states. The accuracy of the full model, composed of a Coulomb part and the SO model, is achieved in the following ways. For the SO model, the extended ERCAR approach is applied, which accounts for both intra-state and inter-state SO coupling, and an extended number of diabatic states are included. The corresponding coupling constants for the SO operator are obtained from experiments, which are more accurate than computed values. In the Coulomb Hamiltonian model, special attention is paid to the long range behavior and accurate c6 dispersion coefficients. The flexibility and accuracy of this Coulomb model are achieved by combining partial models for three different regions. These are merged via artificial neural networks, which also refine the model further. In this way, an extremely accurate PES model for hydrogen iodide is obtained, suitable for accurate scattering calculations.

Growth, Distribution, and Photosynthesis of Chlamydomonas Reinhardtii in 3D Hydrogels.

Engineered living materials (ELMs) are a novel class of functional materials that typically feature spatial confinement of living components within an inert polymer matrix to recreate biological functions. Understanding the growth and spatial configuration of cellular populations within a matrix is crucial to predicting and improving their responsive potential and functionality. Here, this work investigates the growth, spatial distribution, and photosynthetic productivity of eukaryotic microalga Chlamydomonas reinhardtii (C. reinhardtii) in three-dimensionally shaped hydrogels in dependence of geometry and size. The embedded C. reinhardtii cells photosynthesize and form confined cell clusters, which grow faster when located close to the ELM periphery due to favorable gas exchange and light conditions. Taking advantage of location-specific growth patterns, this work successfully designs and prints photosynthetic ELMs with increased CO2 capturing rate, featuring high surface to volume ratio. This strategy to control cell growth for higher productivity of ELMs resembles the already established adaptations found in multicellular plant leaves.

Campo del Cielo modeling and comparison with observations: II. Funnels and craters

AbstractThe Campo del Cielo impact structure exhibits several penetration funnels and impact craters. Here, we model the formation of these funnels with pre‐impact conditions consistent with the results of meteoroid entry models. We study vertical impacts to find the dependence of funnel geometry (depth, diameter) on impact velocity and target porosity. At velocities above 1 km s−1, we observe strong deformation of the projectile and transformation of funnels into regular impact craters. We also use 3‐D impact models to study oblique impacts and find that in the case of impact angles <25° to the horizon, the projectile bounces off the target. Instead of a funnel, an elongated groove forms, while the fragmented projectile escapes and moves farther downrange. At steeper impact angles, funnels form with the projectile at its tip. Early interpretations of the Campo del Cielo impact angle at 9–10° were based on (i) an oversimplified atmospheric model allowing “correct” strewn field elongation and (ii) the results of excavation in which the sloping boundary between breccia‐like materials and infilling loess was interpreted as a true crater floor and its slope was equated to the impact angle. As our models show, the projectile trajectory within the target is not a straight line, and the angle to horizon changes from a steep one at the impact point to zero and then to a negative value (the projectile is moving upward). We also model two impact craters (Hoyo de la Cañada and Laguna Negra) created by high‐velocity fragments to demonstrate the projectile remnants ricochet in the downrange direction.

Scaling up picosecond laser ablation of a LATGP-type glass-ceramic solid electrolyte for all-solid-state battery production

All-solid-state batteries are an intensively studied technology expected to complement conventional lithium-ion batteries in the near future. Research into fundamental production processes is crucial for enabling economic, industrial-scale all-solid-state battery production. Laser radiation is a production tool suited for contour cutting and surface structuring of inorganic solid electrolyte separators. In the scope of this work, the laser ablation of the commercial glass-ceramic solid electrolyte lithium aluminum germanium titanium phosphate (LAGTP) using ultrashort-pulsed laser radiation at different wavelengths, fluences, and pulse repetition rates is studied. Ablation thresholds, efficiencies, and rates were determined by manufacturing percussion drillings, trenches, and cavities. Geometry dependencies, such as the ablation rate decay with advancing depth during laser cutting, necessitated an application-oriented determination of ablation metrics. The surface qualities of the solid electrolyte layers were evaluated after laser ablation by scanning electron microscopy and surface roughness measurements. A wavelength of 532 nm was found to be beneficial compared to shorter and longer wavelengths in terms of productivity and ablation quality, reaching volume ablation efficiencies up to 36 μm3∙μJ−1 and surface roughnesses Sa below 500 nm. The determined metrics are discussed for ablation cutting and structuring of solid electrolyte layers in all-solid-state battery production, considering throughput and surface quality. The results provide insight into the ablation behavior of glass-ceramic materials and support the application of ultrashort-pulsed laser ablation in next-generation battery production.

Prediction of railroad track geometry change using a hybrid CNN-LSTM spatial-temporal model

Track geometry is highly important for ensuring railroad safety. Predicting track geometry degradation can support preventive maintenance by identifying and prioritizing track segments that are more prone to potential track geometry defects. This paper develops a novel machine learning approach that can simultaneously geospatially align track geometry data from multiple inspections accounting for positional errors, and also predict foot-by-foot track geometry change over time. The proposed position correction method considers multiple geometry parameters to provide highly accurate positional information for geometry measurements, which is a prerequisite for foot-by-foot track geometry prediction. A hybrid CNN (convolutional neural network)-LSTM (long short-term memory neural network) machine learning model is developed to account for spatial–temporal dependence with respect to foot-by-foot track geometry change. Specifically, CNN is used to incorporate spatial dependence of track geometry on adjacent segments. LSTM is applied to learn dynamic changes in track geometry data over time to consider the temporal dependence. The hybrid CNN-LSTM model is validated using track inspection data provided by one major freight railroad in the United States. The results show that our positional error correction method can reduce the relative positional error to less than 1 foot with a 99% confidence interval. Our proposed CNN-LSTM model outperforms four other models, including a naïve model (using the last observation), multi-layer perceptron (MLP), plain CNN, and plain LSTM, for both short-term and long-term prediction periods. The proposed hybrid machine learning methodology can be adapted to various other freight and passenger rail lines. The predictive track geometry change information can be used by the industry to plan and prioritize resources for preventative maintenance, yielding benefits in safety and operational efficiency.

The isolation feature geometry dependence of reverse gate-leakage current of AlGaN/GaN HFETs

Reverse gate-leakage current of AlGaN/GaN heterojunction field-effect transistors (HFETs) realized on array of submicron sized fins and conventional mesa isolation feature geometries is investigated at room temperature and zero drain-source bias. For each of the abovementioned device categories, the significance of leakage from the top surface gate as well as gated etched GaN surfaces, especially sidewalls, is studied for a wide range of gate-source voltages (VGS) (i.e. below and above the threshold voltage). It is proven that in the explored fin-type HFETs, for all values of VGS leakage through the gated GaN surfaces, especially the sidewalls, is more significant than the leakage from the top surface gate. This is while in the mesa category, the sidewall leakage is of importance only at less negative values of VGS, and leakage from the top surface gate substantially takes over at more negative VGS values. The discrepancy in the dominance of the aforementioned leakage paths at more negative VGS values among the explored fin and mesa-type HFETs is demonstrated to be due to the stronger electric field across the barrier in the gated region of the mesa-type HFET for this range of VGS. While in the explored fin-type HFETs Ion/Ioff ratio is as high as 2 × 107, the total amount of reverse gate-leakage at all values of VGS is substantially larger compared to the mesa category sharing an equal value of the overall gate width, which substantiates the significance of leakage through etched GaN surfaces in devices composed of larger number of sidewalls, incorporating larger area of gate-overlapping etched GaN surface.

Total-Ionizing-Dose Effects in IGZO Thin-Film Transistors

Total-ionizing-dose (TID) effects are evaluated in back-gated IGZO thin-film transistors irradiated under different gate biases. Negative-bias irradiation leads to worst-case degradation of TID response in these devices, primarily as a result of enhanced charge trapping in the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> overlayer. The relatively small peak transconductance decrease after irradiation illustrates that IGZO transistors are much less sensitive to interface-trap buildup and other instabilities due to hydrogen release and transport than amorphous Si thin film transistors examined previously. The TID response of devices with different gate sizes is also investigated. No significant geometry dependence is observed, which is promising for future scaling down of the technology.