Low Electron Density Research Articles

An atomic surface site interaction point description of non-covalent interactions.

Molecular electrostatic potential surfaces (MEPS) calculated using density functional theory have been used to develop a simplified description of the non-covalent interaction properties of organic molecules. The Atomic Interaction Point (AIP) model introduced here represents an evolution of the Surface Site Interaction Point (SSIP) model described previously, in which a molecule is represented by a discrete set of interaction points that define sites of interaction with other molecules. The interaction sites are described by interaction parameters that are equivalent to the experimentally determined H-bond donor and acceptor parameters α and β. By using high electron density MEPS that lie inside the van der Waals surface, it is possible to obtain accurate interaction parameters and locations for polar sites (s-holes, H-bond donors and acceptors), which are identified as local maxima and minima on the MEPS. For non-polar sites that represent π-systems and halogens, an approach based on molecular orbitals was used to assign the locations of the AIPs, and the interaction parameters were obtained using a lower electron density MEPS that lies close to the van der Waals surface. The AIP descriptions can be implemented directly in the Surface Site Interaction Point Model for Liquids at Equilibrium (SSIMPLE) to calculate solvation free energies, and the free energy of transfer of 1504 compounds from n-hexadecane to water was predicted with a root mean square error of 5 kJ mol-1. AIPs also provide a useful tool for mapping non-covalent interactions in intermolecular complexes, and examples are provided showing how X-ray crystal structures can be converted into AIP interaction maps that allow quantification of the free energy contributions of both polar and non-polar interactions to the stabilities of complexes in solution.

Unveiling the Dynamics of Solid Electrolyte Interphase Evolution in Li-Ion Batteries Via Operando X-Ray Reflectivity: Experimental Insights for Advanced Energy Storage

The Solid-Electrolyte-Interphase (SEI) is a crucial component of Li-ion batteries (LIBs), as it passivates the highly reactive electrode from the electrolyte and helps to stabilize the electrode/electrolyte interface. However, the SEI formation and evolution can also limit the cycling performance and the capacity retention of the battery. Accurate electrochemical models must therefore account for the SEI and properly simulate it. In order to investigate experimentally the SEI, various techniques have been deployed, including electron microscopy1, X-ray photoelectron spectroscopy (XPS)2,3 and Nuclear magnetic resonance (NMR)4.Providing reliable information on the SEI evolution during cycling, and thus benchmarking models, is challenging with these ex-situ or destructive techniques, as they hardly allow in situ observation. On the other hand, synchrotron X-ray reflectivity (XRR) can be used for the operando investigation of interfacial phenomena. It provides information on the thickness, density, and roughness of the SEI, as well as their changes upon (de)lithiation or in out-of-equilibrium conditions. Moreover, operando XRR can be performed under controlled battery operating conditions, providing relevant information on the SEI. Recently, several works reported that operando XRR experiment can provide in situ structural information of the formation and the growth of SEI with sub-nanometer resolution during the cycling5–7.Herein, we report the results of operando XRR experiments performed at the beamline BM32 of the European Synchrotron Radiation Facility (ESRF) to investigate the SEI on Si anode using novel, sustainable fluorine-free electrolytes. Indeed, in the quest for environmentally friendly and safe LIBs, removing the fluorinated electrolytes that are toxic and release corrosive compounds is a necessary step. One way to enhance the safety and sustainability of LIBs is to replace the conventional fluorinated electrolytes by fluorine-free alternatives. A F-free composition based on the lithium bis(oxalato) borate (LiBOB) salt recently showed promising performance in commercially relevant cell configurations8. As with conventional electrolytes, the F-free electrolyte reacts at the surface of the electrodes during the first charge, thus forming the SEI. Characterizing the F-free SEI growth and stability is thus key to understand its behavior and to improve the cell performance for this promising green electrolyte.In this work, operando XRR experiments were performed in electrochemical cells with different electrolyte compositions: 1 M LiPF6 in ethylene carbonate (EC):ethyl methyl carbonate (EMC) = 3:7 vol % (LP57), 0.7 M LiBOB in EC:EMC = 3:7 vol % (LiBOB), and 0.7 M LiBOB in EC:EMC = 3:7 vol % with 2 wt% vinylene carbonate (LiBOB-VC) during at least three cycles. XRR data show that the formations of SEI layers and their evolutions during the cycling for these two types of electrolytes are different. Furthermore, a layer with low electron density (ED) is still present after total delithiation in the LiBOB-cells, while the ED evolutions are generally reversible for LP57 cell. This suggests that the F-free SEI has different properties during cycling than the SEI formed with conventional salt LiPF6.In summary, operando XRR is a powerful technique for investigating the impact of new electrolyte chemistry and formulation on the SEI properties, which significally influence batteries performances. Moreover, the in situ and in real-time experimental insights with sub-nanometer resolution from this technique provides valuable information for the development of more accurate and predictive models for the SEI evolution. Its unique capabilities make it an essential tool for advancing the understanding of SEI behavior and designing more efficient and stable energy storage systems.Figure 1: (a) Principle of operando X-ray reflectometry. (b) XRR data and fit-derived EDP of LiBOB cell upon lithiation. Figure 1

Investigating the Effect of Plasma Parameters on the Dielectric Constant of Sicoh Thin Films Grown by PECVD Using Dimethyldimethoxysilane

The demand for high-performance, low-power, and high-density semiconductor devices has led to the reduction in size of semiconductor chips, resulting in resistance-capacitance (RC) delay. To mitigate the RC delay, low dielectric constant (low-k) insulators have been developed, with the focus on developing new materials with lower dielectric constant. In this report, we present our investigation into the effect of electron density and temperature on the reduction of dielectric constant in SiCOH thin films, utilizing dimethyldimethoxysilane (DMDMS) as a variable with respect to pressure. Our results reveal that both electron density and temperature decline with increasing pressure due to localized electron kinetics and increased inelastic collisions between electrons and neutral species in the chamber, respectively. Our findings also show that the dielectric constant and refractive index of SiCOH thin films decrease at low electron density and temperature. Quadrupole mass spectroscopy reveals that CH3 radicals dissociate less at higher pressures, while Fourier transform infrared spectroscopy confirms an increase in Si-CH3 bonds in SiCOH thin films with increasing pressure. Our findings provide insights into the relationship between electron density and temperature and the dielectric constant of SiCOH thin films, which can contribute to the development of low-k insulators for high-performance semiconductor devices for applications such as big data, mobility, and the Internet of Things (IoT).

Revealing quasi-excitations in the low-density homogeneous electron gas with model exchange–correlation kernels

Time-dependent density functional theory within the linear response regime provides a solid mathematical framework to capture excitations. The accuracy of the theory, however, largely depends on the approximations for the exchange–correlation (xc) kernels. Away from the long-wavelength (or q = 0 short wave-vector) and zero-frequency (ω = 0) limit, the correlation contribution to the kernel becomes more relevant and dominant over exchange. The dielectric function, in principle, can encompass xc effects relevant to describe low-density physics. Furthermore, besides collective plasmon excitations, the dielectric function can reveal collective electron–hole excitations, often dubbed “ghost excitons.” Besides collective excitons, the physics of the low-density regime is rich, as exemplified by a static charge-density wave that was recently found for rs > 69, and was shown to be associated with softening of the plasmon mode. These excitations are seen to be present in much higher density 2D homogeneous electron gases of rs ≳ 4. In this work, we perform a thorough analysis with xc model kernels for excitations of various nature. The uniform electron gas, as a useful model of real metallic systems, is used as a platform for our analysis. We highlight the relevance of exact constraints as we display and explain screening and excitations in the low-density region.

PECULIARITIES OF RESPIRATORY CELLULAR IMPLICATIONS IN STREPTOZOTOCIN-INDUCED DIABETES: A FOCUS ON TYPE I ALVEOLOCYTES

Introduction. The escalating global prevalence of diabetes mellitus has ignited concerns, given its multifaceted repercussions that extend beyond conventional metabolic considerations. Recent scientific inquiries have firmly established a profound association between diabetes mellitus and abnormalities within the respiratory system, unveiling a nuanced interplay that transcends mere glycemic control. This study delves into the intricate and far-reaching influence of diabetes on the respiratory system, recognizing it as a vulnerable target organ susceptible to systemic repercussions. Compelling epidemiological evidence underscores a heightened prevalence of respiratory complications among individuals grappling with diabetes. This observation prompts a meticulous exploration of the pathophysiological underpinnings of this intricate relationship, spanning from molecular intricacies to clinical manifestations.
 The aim was to deepen our understanding of the impact of diabetes mellitus on the respiratory system by investigating the pathological alterations in type I alveolocytes within an experimental model of diabetes mellitus.
 Methods. In this experimental model we used 88 male Wistar rats (170-210 g). The rats were divided into three groups: Group 1 (n=10) consisted of intact rats; Group 2 (n=40) served as the control group, and Group 3 (n=38) constituted the experimental group where diabetes was induced by intraperitoneal administration of streptozotocin (Sigma, USA) diluted in 0.1 M citrate buffer with pH 4.5 at a dosage of 60 mg/kg of body weight. The control group received an equivalent volume of 0.1 M citrate buffer solution with a pH of 4.5 via intraperitoneal injection. All procedures were performed under sodium thiopental anesthesia at a dose of 60 mg/kg of body weight. Tissue samples were collected at intervals of 14, 28, 42, and 70 days post streptozotocin injection.
 For electron microscopy analysis, fragments of lung tissue were immersed in a 2.5% glutaraldehyde solution for fixation, followed by fixation in a 1% osmium tetroxide solution. After dehydration, the specimens were embedded in Epon Araldite. Sections, obtained through a "Tesla VS-490" ultramicrotome, underwent examination using a "PEM-125K" electron microscope.
 Results. Throughout the experiment, discernible changes in type I alveolocytes were observed. At 14 days, nuclei exhibited rounding or oval shape with uniform chromatin distribution. Mitochondria displayed small size, and the Golgi apparatus (GA) and granulated endoplasmic reticulum (GER) showed no significant alterations. By 28 days, nuclei adopted an oval shape, chromatin localized peripherally, and mitochondria exhibited diverse morphologies. Increased micropinocytotic vesicles indicated heightened cellular activity. At 42 days, hyperhydration became pronounced, nuclei displayed lower electron density, and cellular components showed advanced changes. By 70 days, dystrophic-destructive changes included low electron density nuclei, disorganized mitochondria, and fragmented GA and GER.
 Conclusion. This comprehensive ultrastructural analysis unveils the progressive impact of diabetes on type I alveolocytes, elucidating unique facets of pulmonary alterations over time. This study contributes to a growing body of knowledge, shedding light on the dynamic nature of pulmonary changes in diabetes mellitus, ultimately urging further exploration for a holistic understanding of its implications on respiratory health.

Infant glycogen storage disease type Ⅳ: a clinicopathological and genetic characteristics analysis of five cases

Objective: To investigate the clinical pathology and gene mutation characteristics of patients with glycogen storage disease type Ⅳ (GSD Ⅳ). Methods: The clinical data, liver histopathology and ultrastructural morphology, and gene sequencing results of 5 GSD Ⅳ cases diagnosed in the Children's Hospital Affiliated to Shanghai Jiaotong University School of Medicine and the Children's Hospital of Fudan University from January 2015 to February 2022 were collected and analyzed retrospectively. Results: Among the 5 cases, 3 were male and 2 were female, ranging in age from 4 months to 1 year and 9 months. The clinical manifestations included fever, hepatosplenomegaly, liver insufficiency, growth retardation and hypotonia. Four cases had liver biopsy showing ground-glass-like changes in hepatocytes with intracytoplasmic inclusion bodies and varying degrees of fibrosis. Liver electron microscopy in 2 cases showed that the level of glycogen increased to varying degrees, and the cytoplasm was filled with low electron density substances. Genetic testing revealed that 3 cases had compound heterozygous variants in GBE1 gene; 1 case had a single pathogenic variant in GBE1 gene; and 1 case was deceased with no genetic testing, but each parent was tested for a heterozygous variant in the GBE1 gene. A total of 9 GBE1 gene mutations were detected, 3 of which were reported mutations and 6 novel mutations. One case died of liver cirrhosis, and 1 case underwent autologous liver transplantation. After transplantation, the liver function basically returned to normal, and the growth and development improved; the other 3 cases were managed through diet control and symptomatic treatment. Conclusions: CSD Ⅳ is an extremely rare inherited metabolic disease caused by GBE1 gene mutation, often presenting with hepatic and neuromuscular disorders, with heterogeneous clinical manifestations. The diagnosis mainly depends on histopathology and a pedigree gene analysis.

Dwarf Galaxies Show Little ISM Evolution from z ∼ 1 to z ∼ 0: A Spectroscopic Study of Metallicity, Star Formation, and Electron Density

We present gas-phase metallicity measurements for 583 emission line galaxies at 0.3 < z < 0.85, including 388 dwarf galaxies with , and explore the dependence of the metallicity on the stellar mass and star formation (SF) properties of the galaxies. Metallicities are determined through the measurement of emission lines in very deep (∼7 hr exposure) Keck/DEIMOS spectra taken primarily from the HALO7D survey. We measure metallicity with three strong-line calibrations (O3Hβ, R23, and O3O2) for the overall sample, as well as with the faint [Ne iii]λ3869 and [O iii]λ4363 emission lines for 112 and 17 galaxies where robust detections were possible. We construct mass–metallicity relations (MZR) for each calibration method, finding MZRs consistent with other strong-line results at comparable redshift, as well as with z ∼ 0 galaxies. We quantify the intrinsic scatter in the MZR as a function of mass, finding it increases with lower stellar mass. We also measure a weak but significant correlation between increased MZR scatter and higher specific star formation rate (SFR). We find a weak influence of SFR in the fundamental metallicity relation as well, with an SFR coefficient of α = 0.21. Finally, we use the flux ratios of the [O ii]λ λ 3727,3729 doublet to calculate gas electron density in ∼1000 galaxies with as a function of redshift. We measure low electron densities (n e ∼ 25 cm−3) for z < 1 galaxies, again consistent with z ≈ 0 conditions, but measure higher densities (n e ∼ 100 cm−3) at z > 1. These results all suggest that there is little evolution in star-forming interstellar medium conditions from z ∼ 1 to z = 0, confirmed with a more complete sample of low-mass galaxies than has previously been available in this redshift range.

Optimized plasma waveguides for single-stage bubble acceleration of monoenergetic electron beams with enhanced quality

The laser wakefield acceleration in bubble regime is now a promising method for producing high-quality electron beams, which is crucial to the development of the next-generation compact and low-cost particle accelerators. In this paper, we demonstrate the possibility of controlling particle injection and electron beam quality in sub-petawatt laser pulse interaction with simple plasma waveguides with a radially step-like density profile. Fully relativistic particle-in-cell calculations for different laser intensities indicate that by considering a sufficiently low electron density for a central plasma channel to ensure both increased acceleration length and formation of a well-structured bubble, one can optimize the surrounding plasma density and central channel diameter to reach the best injection conditions and produce a high-quality monoenergetic electron beam with improved peak energy and reduced energy spread. Calculations are performed for 33 fs, 140–315 TW laser pulses interacting with a ∼2 cm long plasma waveguide. It is demonstrated that by using the proposed scheme in optimized conditions, monoenergetic electron beams with peak energies 3–4 GeV and energy spreads less than 1.5% can be obtained in a single acceleration length of 1.85 cm. The beam charge and conversion efficiency of laser energy into the beam energy were also enhanced to values around 195 pC and 14.7%, respectively.

Luminescence and photocatalytic properties of bifunctional materials CaTi2O4(OH)2:Eu3+ and [CaTi2O4(OH)2–CaTiO3]:Eu3+

CaTi2O4(OH)2:Eu3+, CaTiO3:Eu3+ and [CaTi2O4(OH)2–CaTiO3]:Eu3+ were synthesized by a solvothermal method without the help of templates or surfactants. And their structures, luminescence properties, and photocatalytic properties were systematically studied. The RIR (reference intensity ratio) data of CaTi2O4(OH)2 were first investigated via X-ray diffraction (XRD), thus the ratios of each phase in the (m%CaTi2O4(OH)2-n%CaTiO3):3%Eu3+ biphasic mixture was determined. The bandgap value of CaTi2O4(OH)2:3%Eu3+ is 0.28 eV less than that of CaTiO3:3%Eu3+. The specific surface area of CaTi2O4(OH)2 is 8.2 times larger than that of CaTiO3. Compared with CaTiO3:Eu3+, the CaTi2O4(OH)2:Eu3+ showed stronger luminescence intensity. The Judd-Ofelt theory analysis show that the Eu3+ ions in CaTi2O4(OH)2:Eu3+ have low local symmetry, high Eu–O bonds covalence and low ligands electron density. The photocatalytic properties of CaTi2O4(OH)2:y%Eu3+, CaTiO3:x%Eu3+ and [62.2%CaTi2O4(OH)2-37.8%CaTiO3]:3% Eu3+ were comparatively studied in detail. The band-gap value of [62.2 % CaTi2O4(OH)2–37.8%CaTiO3]:3%Eu3+ is significantly reduced due to the presence of heterojunctions compared to CaTi2O4(OH)2:y%Eu3+ and CaTiO3: x%Eu3+. The built-in electric potential at heterojunction interface will guide electrons and holes to move in opposite directions, therefore [CaTi2O4(OH)2–CaTiO3]:Eu3+ has excellent photocatalytic activity.

Optoelectronic tuning of plasmon resonances via optically modulated hot electrons.

Fast optical modulation of nanoplasmonics is fundamental for on-chip integration of all-optical devices. Although various strategies have been proposed for dynamic modulation of surface plasmons, critical issues of device compatibility and extremely low efficiency in the visible spectrum hamper the application of optoplasmonic nanochips. Here we establish an optoplasmonic system based on Au@Cu2-xS hybrid core-shell nanoparticles. The optical excitation of hot electrons and their charge transfer to the semiconductor coating (Cu2-xS) lead to lowered electron density of Au, which results in the red shift of the localized surface plasmon resonance. The hot electrons can also transport through the Cu2-xS layer to the metal substrate, which increases the conductance of the nanogap. As such, the coupled gap plasmon blue-shifts with a magnitude of up to ∼15nm, depending on the excitation power and the thickness of the coatings, which agrees with numerical simulations. All of this optoelectronic tuning process is highly reversible, controllable and fast with a modulated laser beam, which is highly compatible and sufficiently useful for on-chip integration of nanophotonic devices.

Feasibility of determining electron energy distribution function using optical emission lines in low-pressure Ar/Kr discharge

The electron energy distribution function (EEDF) were reconstructed from both collected emission line intensities and a collisional radiative model. The obtained EEDFs from this method were compared with those obtained from Langmuir probe diagnostics over a wide range of discharge conditions ( ∼1010–1012 cm − 3, ∼ 1–3 eV, ≲ 67 Pa) for low-pressure Ar/Kr discharges. In particular, we investigated the factors that affect the accuracy and uncertainty of the EEDF via sensitivity analysis. The following conclusions were obtained: (1) using a sufficiently large number (≳20–30) of Ar/Kr2p-1s emission lines can increase the accuracy of the determined EEDF; (2) for discharges with low electron densities, using emission line sets for both Ar and Kr [instead of only one (Ar or Kr) line set] can significantly reduce the uncertainty in the determined EEDF.

Unifying VLF Transmitter and Sferic Modeling Efforts Via Tomography

AbstractWe demonstrate a methodology for utilizing measurements from very low frequency (VLF, 3−30 kHz) transmitters and lightning emissions to produce 3D lower electron density maps, and apply it to multiple geophysical disturbances. The D‐region lower ionosphere (60−90 km) forms the upper boundary of the Earth‐ionosphere waveguide which allows VLF radio waves to propagate to global distances. Measurements of these signals have, in many prior studies, been used to infer path‐average electron density profiles within the D region. Historically, researchers have focused on either measurements of VLF transmitters or radio atmospherics (sferics) from lightning. In this work, we build on recently published methods for each and present a method to unify the two approaches via tomography. The output of the tomographic inversion produces maps of electron density over a large portion of the United States and Gulf of Mexico. To illustrate the benefits of this unified approach, daytime and nighttime maps are compared between a sferic‐only model and the new approach suggested here. We apply the model to characterize two geophysical disturbances: solar flares and lower ionospheric changes associated with thunderstorms.

Spin independence of the strongly enhanced effective mass in ultra-clean SiGe/Si/SiGe two-dimensional electron system

The effective mass at the Fermi level is measured in the strongly interacting two-dimensional (2D) electron system in ultra-clean SiGe/Si/SiGe quantum wells in the low-temperature limit in tilted magnetic fields. At low electron densities, the effective mass is found to be strongly enhanced and independent of the degree of spin polarization, which indicates that the mass enhancement is not related to the electrons’ spins. The observed effect turns out to be universal for silicon-based 2D electron systems, regardless of random potential, and cannot be explained by existing theories.

Automated Image Analysis of Transmission Electron Micrographs: Nanoscale Evaluation of Radiation-Induced DNA Damage in the Context of Chromatin.

Heavy ion irradiation (IR) with high-linear energy transfer (LET) is characterized by a unique depth dose distribution and increased biological effectiveness. Following high-LET IR, localized energy deposition along the particle trajectories induces clustered DNA lesions, leading to low electron density domains (LEDDs). To investigate the spatiotemporal dynamics of DNA repair and chromatin remodeling, we established the automated image analysis of transmission electron micrographs. Human fibroblasts were irradiated with high-LET carbon ions or low-LET photons. At 0.1 h, 0.5 h, 5 h, and 24 h post-IR, nanoparticle-labeled repair factors (53BP1, pKu70, pKu80, DNA-PKcs) were visualized using transmission electron microscopy in interphase nuclei to monitor the formation and repair of DNA damage in the chromatin ultrastructure. Using AI-based software tools, advanced image analysis techniques were established to assess the DNA damage pattern following low-LET versus high-LET IR. Low-LET IR induced single DNA lesions throughout the nucleus, and most DNA double-strand breaks (DSBs) were efficiently rejoined with no visible chromatin decondensation. High-LET IR induced clustered DNA damage concentrated along the particle trajectories, resulting in circumscribed LEDDs. Automated image analysis was used to determine the exact number of differently sized nanoparticles, their distance from one another, and their precise location within the micrographs (based on size, shape, and density). Chromatin densities were determined from grayscale features, and nanoparticles were automatically assigned to euchromatin or heterochromatin. High-LET IR-induced LEDDs were delineated using automated segmentation, and the spatial distribution of nanoparticles in relation to segmented LEDDs was determined. The results of our image analysis suggest that high-LET IR induces chromatin relaxation along particle trajectories, enabling the critical repair of successive DNA damage. Following exposure to different radiation qualities, automated image analysis of nanoparticle-labeled DNA repair proteins in the chromatin ultrastructure enables precise characterization of specific DNA damage patterns.

Transition from a filamentary mode to a diffuse one with varying distance from needle to stream of an argon plasma jet

Plasma jet has extensive application potentials in various fields, which normally operates in a diffuse mode when helium is used as the working gas. However, when less expensive argon is used, the plasma jet often operates in a filamentary mode. Compared to the filamentary mode, the diffuse mode is more desirable for applications. Hence, many efforts have been exerted to accomplish the diffuse mode of the argon plasma jet. In this paper, a novel single-needle argon plasma jet is developed to obtain the diffuse mode. It is found that the plasma jet operates in the filamentary mode when the distance from the needle tip to the central line of the argon stream (d) is short. It transits to the diffuse mode with increasing d. For the diffuse mode, there is always one discharge pulse per voltage cycle, which initiates at the rising edge of the positive voltage. For comparison, the number of discharge pulse increases with an increase in the peak voltage for the filamentary mode. Fast photography reveals that the plasma plume in the filamentary mode results from a guided positive streamer, which propagates in the argon stream. However, the plume in the diffuse mode originates from a branched streamer, which propagates in the interfacial layer between the argon stream and the surrounding air. By optical emission spectroscopy, plasma parameters are investigated for the two discharge modes, which show a similar trend with increasing d. The diffuse mode has lower electron temperature, electron density, vibrational temperature, and gas temperature compared to the filamentary mode.

Insights into the mechanism of [3+2] cycloaddition reactions between N-benzyl fluoro nitrone and maleimides, its selectivity and solvent effects.

We present a theoretical study of the [3+2] cycloaddition (32CA) reactions of N-benzyl fluoro nitrone with a series of maleimides producing isoxazolidines. We use the Molecular Electron Density Theory at the MPWB1K/6-311G(d) level. We focus on the reaction mechanism, selectivity, solvent, and temperature effects. In addition, we perform topological analyses at the minimal and transition states to identify the intermolecular interactions. Electron Localization Function approach classifies the N-benzyl fluoro nitrone as zwitterionic (zw-) three-atom components (TACs), associated with a high energy barrier. The low polar character of the reaction is evaluated using the Conceptual Density Functional Theory analysis of the reactants, confirmed by the low global electron density transfer computed at the transition states. Computations show that these 32CA reactions follow a one-step mechanism under kinetic control, with highly asynchronous bond formation and no new covalent bond is formed at the TS. Besides, the potential energy surfaces along the reaction pathways in gas phase and in solvent are mapped. The corresponding Gibbs free energy profiles reveal that the exo-cycloadducts are kinetically and thermodynamically more favored than endo-cycloadducts, in agreement with the exo-selectivity observed experimentally. In particular, we found that solvent and temperature did not affect this selectivity and mainly influence the activation energies and the exothermic character of these 32CA reactions.

Ground-based noontime D-region electron density climatology over northern Norway

Abstract. The bottom part of the Earth's ionosphere is the so-called D region, which is typically less dense than the upper regions. Despite the comparably lower electron density, the ionization state of the D region has a significant influence on signal absorption for propagating lower to medium radio frequencies. We present local noon climatologies of electron densities in the upper middle atmosphere (50–90 km) at high latitudes as observed by an active radar experiment. The radar measurements cover 9 years (2014–2022) from the solar maximum of cycle 24 to the beginning of cycle 25. Reliable electron densities are derived by employing signal processing, applying interferometry methods, and applying the Faraday-International Reference Ionosphere (FIRI) model. For all years a consistent spring–fall asymmetry of the electron density pattern with a gradual increase during summer as well as a sharp decrease at the beginning of October was found. These findings are consistent with very low frequency (VLF) studies showing equivalent signatures for nearby propagation paths. It is suggested that the meridional circulation associated with downwelling in winter could cause enhanced electron densities through NO transport. However, this mechanism can not explain the reduction in electron density in early October.

Bias-dependent degradation of single quantum well on InGaN-based light emitting diode

This paper investigates the factors that influence the efficiency and the reliability of InGaN-based light emitting diodes. The devices under test have a single InGaN quantum well, with a nominal emission wavelength of 495 nm. From the preliminary characterization, the L-I curve shows an anomalous slope mainly due to: i) high Shockley Read Hall recombination rate, and ii) low electron densities in the explored range of injection, as also confirmed by simulation. The reliability of the devices was investigated by performing a constant current stress test at J = 80 A/cm2 at room temperature. Optical degradation occurs with different trends, depending on the injection regime. For low injection levels, the optical power decay is monotonic. In the high injection range, for I > 10 mA, we can recognize different degradation phases. The optical degradation can be ascribed to the generation and relocation of defects in the active region, as also confirmed by DLOS measurement. The origin of degradation was also investigated by a stress test with photoluminescence measurement. The results suggest that the variation of the optical characteristics can be related to the variation of the intrinsic characteristics of the material.

Accuracy of Electron Density Mapping of a Novel kVCBCT System Designed for Planning

A recently developed advanced kVCBCT system, designed for simulation and planning, includes improvements to the imaging panel and reconstruction technique, enabling more accurate electron density mapping than a typical CBCT. This study investigates the accuracy, limitations, and dosimetric impact of this new system. CBCT images were taken of both large (pelvis) and small (head) electron density phantoms with inserts ranging from lung (0.29) to cortical bone (1.69). Images were taken with several pre-set protocols with energies of 125 kVp and 140 kVp. The effects of longitudinal buildup (for scatter due to the cone-beam geometry) and blade position were also investigated. The HU values of each insert were measured over a small region of interest. Several electron density curves were generated - pelvis protocol on the large phantom, head protocol on the small phantom, and average - and imported into a treatment planning system. Dose calculation was performed using each curve and differences were observed. HU to electron density mapping was sensitive to the use of longitudinal buildup and blade position, with differences in the curves observed at both low and high electron densities, due to imager saturation effects not found in typical clinical scenarios. Subsequent studies used both longitudinal buildup and fully opened blades. Under these conditions, mapping was not sensitive to technique or phantom size at low electron densities. At higher values, the curves diverged, with the head protocol showing higher HU values and the pelvis protocol showing lower. The average curve matched very closely with the curve from our standard CT simulator. Dose calculation showed little dependence on the curve chosen, with max point dose differences of 1.2% between the pelvis and average scans, though most of the plan was <0.5% different. Results for the head protocol were similar. The system provides reliable HU values comparable to a CT simulator, though it is important to consider the effects of imager saturation by choosing appropriate scatter and collimation. The calibration is slightly sensitive to the choice of phantom size and beam energy, though these differences led to negligible (<0.5%) differences in dose calculation accuracy.

Insight into (Z)-ethyl-2-(2-((E)-2,4-dinitro benzylidene amino)-4-oxo-3-phenylthiazolidin-5-ylidene) acetate in-silico anti-SARS-CoV-2 performance: Synthesis, structural-spectral characterizations and DFT computations

This study reports on the synthesis of a 4-thiazolidinone derivative (EN2Th), namely, (Z)-Ethyl-2-(2-((E)-2,4-dinitro benzylidene amino)-4-oxo-3-phenylthiazolidin-5-ylidene) acetate. Its crystal structure has been determined by single crystal X-ray diffraction and the spectral characterizations were carried out by means of 1H and 13C NMR, and FT-IR techniques. The molecule of EN2Th crystallizes in the monoclinic P21/c symmetry and its crystal structure consists of a herringbone packing along [100]. The density functional theory (DFT) at the B3LYP/6-311G (d,p) level has been employed for structure optimization, the results confirm a good consistency between the theoretical and the experimental geometrical data. Hirshfeld surface and 2D fingerprints indicate C−H···O (29.7%) and H···H (24.5%) as the most relevant intermolecular interactions in the crystal packing of EN2Th. According to the reduced density gradient (RDG) analysis, EN2Th exhibits vdW to weak repulsive regions with low electron densities. The theoretical electronic circular dichroism (ECD) spectrum displays an exciton coupled transitions associated with the Z-configuration of the thiazolidin-4-one moiety reflecting the steric effect of the ester group. Charge transfer inside the 4-thiazolidinone derivative EN2Th was considered via the frontier molecular orbitals (FMOs) and natural bond orbital (NBO) investigations along with molecular electrostatic potential (MEP) distribution maps. The HOMO and LUMO energies allowed the estimation of the chemical reactivity descriptors. In accordance with the NBO results, the predicted hyperpolarizabilities indicate a strong donor to acceptor π-electrons delocalization in EN2Th. The anti-viral performance of EN2Th was evaluated in silico against SARS-CoV-2 main protease (MPro) via molecular docking simulations. Finally, ADMET (absorption, distribution, metabolism, excretion and toxicity) online software tools were utilized to uncover the title compound's potential cytotoxicity.