Line Shape Research Articles

Impact of penetrating collisions of plasma ions on spectral line shapes

Impact of penetrating collisions of plasma ions on spectral line shapes

Characterization testing of the Northrop Grumman MiniCoolerPlus (MCP)

Northrop Grumman Space Park (NGSP) introduced the Mini Cooler Plus (MCP) to their family of pulse tube cryocoolers in 2019 [1] and presented the details of its TRL6 qualification testing in 2022 [2]. The thermal mechanical unit (TMU) of the MCP is an extension of space-qualified pulse tube coolers, all of which are designed to provide a long life (ten-plus years) of delivering low-mass, high-cooling capacity for hyperspectral and infrared imaging payloads in tactical airborne and space applications. The cooler is of modular split configuration allowing flexibility in the compressor (wave generator) and cold head placements to meet the available envelope of packaging constraints. The cold head assembly can be oriented at any position relative to the compressor assembly, and the transfer line (length and shape) can be customized to individual applications. The TMU (thermo-mechanical unit) weighs less than 3kg and can lift 1.5 W at 45 K or 11 W at 110K with 150 W electrical input at 300 K reject. The thermal performance has been characterized as a function of input voltage and as a function of cold tip load and temperature at variety of heat sink temperatures of -20C, 0C, +20C and +40C. Functional testing of the MCP was performed to higher input powers and MCP performance data versus operating conditions were collected. An analytical expression for cold tip load (Qc), impedance (Z) and power factor (PF) as a function of reject temperature (Trej), cold tip temperature (Tc), frequency (f), and input power (Pac) were generated. These tests were repeated with third party control electronics. All results will be presented here.

Perturbation of Fermi Resonance on Hydrogen-Bonded > C═O: 2D IR Studies of Small Ester Probes.

We utilized linear and 2D infrared spectroscopy to analyze the carbonyl stretching modes of small esters in different solvents. Particularly noteworthy were the distinct carbonyl spectral line shapes in aqueous solutions, prompting our investigation of the underlying factors responsible for these differences. Through our experimental and theoretical calculations, we identified the presence of the hydrogen-bond-induced Fermi resonance as the primary contributor to the varied line shapes of small esters in aqueous solutions. Furthermore, our findings revealed that the skeletal deformation mode plays a crucial role in the Fermi resonance for all small esters. Specifically, the first overtone band of the skeletal deformation mode intensifies when hydrogen bonds form with the carbonyl group of esters, whereas such coupling is rare in aprotic organic solvents. These spectral insights carry significant implications for the utilization of esters as infrared probes in both biological and chemical systems.

Circumnuclear Multiphase Gas in the Circinus Galaxy. VI. Detectability of Molecular Inflow and Atomic Outflow

Recent submillimeter observations have revealed signs of parsec-scale molecular inflow and atomic outflow in the nearest Seyfert 2 galaxy, the Circinus galaxy. To verify the gas kinematics suggested by these observations, we performed molecular and atomic line transfer calculations based on a physics-based 3D radiation-hydrodynamic model, which has been compared with multiwavelength observations in this paper series. The major-axis position–velocity diagram (PVD) of CO(3–2) reproduces the observed faint emission at the systemic velocity, and our calculations confirm that this component originates from failed winds falling back to the disk plane. The minor-axis PVD of [C i](3 P 1–3 P 0), when created using only the gas with positive radial velocities, presents a sign of blueshifted and redshifted offset peaks similar to those in the observation, suggesting that the observed peaks indeed originate from the outflow, but that the model may lack outflows as strong as those in the Circinus galaxy. Similar to the observed HCN(3–2), the similar dense-gas tracer HCO+(3–2) can exhibit nuclear spectra with inverse P-Cygni profiles with ∼0.5 pc beams, but the line shape is azimuthally dependent. The corresponding continuum absorbers are inflowing clumps at 5–10 pc from the center. To detect significant absorption with a high probability, the inclination must be fairly edge-on (≳85°), and the beam size must be small (≲1 pc). These results suggest that HCN or HCO+ and [C i] lines are effective for observing parsec-scale inflows and outflows, respectively.

VT‐NMR Analysis of Rotation‐Inversion of N‐(4‐hydroxybutyl)‐N‐(2,2,2‐trifluoroethyl) tert‐butyl Carbamate: Utilizing the −CH2CF3 Appendage as a Reporter on E/Z‐Isomerization

AbstractThe rotational barrier about the CN carbamate bond of N‐(4‐hydroxybutyl)‐N‐(2,2,2‐trifluoroethyl) tert‐butyl carbamate 1 was determined by variable temperature (VT) 13C and 19F NMR spectroscopy. The −CH2CF3 appendage reports on rotational isomerism and allows for the observation of separate signals for the E‐ and Z‐ensembles at low temperature. The activation barrier for E/Z‐isomerization was quantified using Eyring‐Polanyi theory which requires the measurements of the maximum difference in Larmor frequency Δνmax and the convergence temperature Tc. Both Δνmax and Tc were interpolated by analyzing sigmoidal functions fitted to data describing signal separation and the quality of the superposition of the E‐ and Z‐signals, respectively. Methods for generating the quality‐of‐fit parameters for Lorentzian line shape analysis are discussed. Our best experimental value for the rotational barrier ΔGc≠(1)=15.65±0.13 kcal/mol is compared to results of a higher level ab initio study of the model N‐ethyl‐N‐(2,2,2‐trifluoroethyl) methyl carbamate.

Tip-enhanced Raman scattering and near-field optical imaging of semiconducting monolayer and few-layer MoTe2

Transition metal dichalcogenides (TMDs) offer exceptional platforms to study unique phenomena in two-dimensional (2D) materials. The understanding of phonon interactions in atomically thin TMDs is crucial for the development of novel applications. However, advancing our knowledge on phonon dynamics in TMDs under optical, thermal, electric, and strain perturbations requires comprehensive and minimally invasive chemical imaging techniques with nanoscale spatial resolution. Tip-enhanced Raman scattering (TERS) provides new promising avenues towards this goal while also enabling a detailed analysis of structural heterogeneity. Here, we demonstrate gap-mode TERS imaging of mechanically exfoliated monolayer and few-layer 2H–MoTe2. At 633 nm, 671 nm, and 785 nm laser excitations, we report an overwhelmingly selective TERS enhancement of the out-of-plane A1g phonon mode relative to in-plane E12g phonon mode for mono-to few-layer MoTe2. The pure near-field spectral line shapes are clearly distinct from the well-characterized far-field counterparts. We demonstrate that near-field interactions of selective phonon modes are extremely sensitive to the excitation wavelength, sample thickness, and structural defects. Our results therefore provide fundamental information for the nanoscale characterization of semiconducting MoTe2-based devices.

X-Ray Magnetic Circular Dichroism in Altermagnetic α-MnTe.

Altermagnetism is a recently identified magnetic symmetry class combining characteristics of conventional collinear ferromagnets and antiferromagnets, that were regarded as mutually exclusive, and enabling phenomena and functionalities unparalleled in either of the two traditional elementary magnetic classes. In this work we use symmetry, abinitio theory, and experiments to explore x-ray magnetic circular dichroism (XMCD) in the altermagnetic class. As a representative material for our XMCD study we choose α-MnTe with compensated antiparallel magnetic order in which an anomalous Hall effect has been already demonstrated. We predict and experimentally confirm a characteristic XMCD line shape for compensated moments lying in a plane perpendicular to the light propagation vector. Our results highlight the distinct phenomenology in altermagnets of this time-reversal symmetry breaking response, and its potential utility for element-specific spectroscopy and microscopy.

Computational Protocol for the Spectral Assignment of NMR Resonances in Covalent Organic Frameworks.

Solid-state nuclear magnetic resonance spectroscopy is routinely used in the field of covalent organic frameworks to elucidate or confirm the structure of the synthesized samples and to understand dynamic phenomena. Typically this involves the interpretation and simulation of the spectra through the assumption of symmetry elements of the building units, hinging on the correct assignment of each line shape. To avoid misinterpretation resulting from library-based assignment without a theoretical basis incorporating the impact of the framework, this work proposes a first-principles computational protocol for the assignment of experimental spectra, which exploits the symmetry of the underlying building blocks for computational feasibility. In this way, this protocol accommodates the validation of previous experimental assignments and can serve to complement new NMR measurements.

Observation of Structures in the Processes e^{+}e^{-}→ωχ_{c1} and ωχ_{c2}.

We present measurements of the Born cross sections for the processes e^{+}e^{-}→ωχ_{c1} and ωχ_{c2} at center-of-mass energies sqrt[s] from 4.308 to 4.951GeV. The measurements are performed with data samples corresponding to an integrated luminosity of 11.0 fb^{-1} collected with the BESIII detector operating at the Beijing Electron Positron Collider storage ring. Assuming the e^{+}e^{-}→ωχ_{c2} signals come from a single resonance, the mass and width are determined to be M=(4413.6±9.0±0.8) MeV/c^{2} and Γ=(110.5±15.0±2.9) MeV, respectively, which is consistent with the parameters of the well-established resonance ψ(4415). In addition, we also use one single resonance to describe the e^{+}e^{-}→ωχ_{c1} line shape and determine the mass and width to be M=(4544.2±18.7±1.7) MeV/c^{2} and Γ=(116.1±33.5±1.7) MeV, respectively. The structure of this line shape, observed for the first time, requires further understanding.

PigmentHunter: A point-and-click application for automated chlorophyll-protein simulations.

Chlorophyll proteins (CPs) are the workhorses of biological photosynthesis, working together to absorb solar energy, transfer it to chemically active reaction centers, and control the charge-separation process that drives its storage as chemical energy. Yet predicting CP optical and electronic properties remains a serious challenge, driven by the computational difficulty of treating large, electronically coupled molecular pigments embedded in a dynamically structured protein environment. To address this challenge, we introduce here an analysis tool called PigmentHunter, which automates the process of preparing CP structures for molecular dynamics (MD), running short MD simulations on the nanoHUB.org science gateway, and then using electrostatic and steric analysis routines to predict optical absorption, fluorescence, and circular dichroism spectra within a Frenkel exciton model. Inter-pigment couplings are evaluated using point-dipole or transition-charge coupling models, while site energies can be estimated using both electrostatic and ring-deformation approaches. The package is built in a Jupyter Notebook environment, with a point-and-click interface that can be used either to manually prepare individual structures or to batch-process many structures at once. We illustrate PigmentHunter's capabilities with example simulations on spectral line shapes in the light harvesting 2 complex, site energies in the Fenna-Matthews-Olson protein, and ring deformation in photosystems I and II.

Tunable zero-field magnetoresistance responses in Si transistors: Origins and applications

The near-zero-field magnetoresistance (NZFMR) response has proven to be a useful tool for studying atomic-scale, paramagnetic defects that are relevant to the reliability of semiconductor devices. The measurement is simple to make and, in some cases, simple to interpret. In other cases, more sophisticated modeling based on the stochastic Liouville equation (SLE) is needed to access valuable information from NZFMR results. It has been shown that hyperfine and dipolar coupling interactions at atomic-scale defects affect the NZFMR line shape, but experimental parameters related to the detection method of NZFMR can also affect the nature of the response. Here, we demonstrate four distinct NZFMR detection methods in Si MOSFETs, which all access identical Si/SiO2 interface defects. In all four cases, we show that the line shape of the response is tunable based on experimental parameters alone. Using SLE-based modeling, we verify that time constants connected to physical carrier capture rates at the defect sites lead to these NZFMR line shape changes. The results demonstrate a method to extract some atomic-scale information for the purpose of defect identification. They also have broader applications to the continued development of ultra-sensitive magnetometers based on NZFMR in semiconductors. Additionally, the NZFMR effect in common Si-based devices may provide an inexpensive and accessible platform that mimics similar radical pair mechanisms that have become increasingly important in various biology fields.

Understanding and Controlling the Photoluminescence Line Shapes of 2D Perovskites with Chiral Methylbenzylammonium-Based Cations

Understanding and Controlling the Photoluminescence Line Shapes of 2D Perovskites with Chiral Methylbenzylammonium-Based Cations

Experimental and model study of swirling fluid flow in a converging channel as a simulation of blood flow in the heart and aorta

The study of swirling flows in channels corresponding to the static approximation of flow channels of the heart and major vessels with a longitudinal-radial profile zR2 = const and a concave streamlined surface at the beginning of the longitudinal coordinate has been carried out. A comparative analysis of the flow structure in channel configurations zRN = const, where N = –1; 1; 2; 3, in the absence and presence of a concave surface was carried out. The numerical modelling was compared with the results of hydrodynamic experiments on the flow characteristics and the shape of the flow lines. The numerical model was used to determine the velocity structure, viscous friction losses and shear stresses. Numerical modelling of steady-state flows for channels without a concave surface showed that in the channel zR2 = const there is a stable vortex flow structure with the lowest viscous friction losses. The presence of a concave surface of sufficient size significantly reduces viscous friction losses and shear stresses in both steady state and pulsed modes.

Exploring Crystal-Phase Molecular Dynamics of the Low-Viscous Mesogen 6CHBT: A Combined FFC and High-Field NMR Relaxometry Investigation.

The molecular dynamics study of thermotropic mesogens exhibiting the crystal phases is valuable in unraveling the complex global (collective) and local (noncollective) motions executed by liquid crystal molecules, which would further advance the existing knowledge on orientationally disordered crystalline (ODIC) phases. Toward the fulfillment of such a task, a combined nuclear magnetic resonance (NMR) relaxometry approach employing the fast field cycling (FFC) NMR (10 kHz-30 MHz) and high-field pulsed NMR (400 MHz) techniques is utilized to sample the broad frequency range offered by molecular motions in the crystal phase of 4-(trans-4'-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT). The validity of the observed relaxation data is tested and interpreted by the Bloembergen-Purcell-Pound (BPP) model involving the superposition of four mutually independent Lorentzian spectral densities, reflecting molecular dynamical processes on different time scales. The salient feature of the detailed analysis reveals that the lengthening of temporal dynamics in the crystal phase due to molecular rotations by jumps, which are of intermolecular origin, is evident and further supports the presence of collective-like local dynamics. The analysis does permit decoupling of the molecular reorientations about their short axes (∼100 ns) as well as long axes (∼50 ns) and methyl group rotations (∼0.5 ns) on distinct time scales. The activation energies for reorientations about the short axes and methyl group rotations are found to be 27.3 ± 2.7 and 15.8 ± 1.1 kJ/mol, respectively. The fast methyl rotations in the crystal phase of 6CHBT obtained from FFC NMR are further well complemented by high-field NMR, where 1H NMR line shapes are relatively narrow when compared to those of the nematic phase.

Coupled-Channel Analysis of the χ_{c1}(3872) Line Shape with BESIII Data.

We perform a study of the χ_{c1}(3872) line shape using the data samples of e^{+}e^{-}→γχ_{c1}(3872), χ_{c1}(3872)→D^{0}D[over ¯]^{0}π^{0}, and π^{+}π^{-}J/ψ collected with the BESIII detector. The effects of the coupled channels and the off-shell D^{*0} are included in the parametrization of the line shape. The line shape mass parameter is obtained to be M_{X}=(3871.63±0.13_{-0.05}^{+0.06}) MeV. Two poles are found on the first and second Riemann sheets corresponding to the D^{*0}D[over ¯]^{0} branch cut. The pole location on the first sheet is much closer to the D^{*0}D[over ¯]^{0} threshold than the other, and is determined to be 7.04±0.15_{-0.08}^{+0.07} MeV above the D^{0}D[over ¯]^{0}π^{0} threshold with an imaginary part -0.19±0.08_{-0.19}^{+0.14} MeV.

A form-grinding wheel optimization method for helical gears based on a PSO-SVM model

A gear form-grinding optimization method is proposed to obtain an optimal profile of a form-grinding wheel by solving a transcendental equation of the contact line between a form-grinding wheel and a helical gear workpiece. Since the equation of the contact line is transcendental, the relationship between the installation angle of the form-grinding wheel and the shape of the contact line cannot be represented by explicit functions, which makes it difficult to obtain the optimal profile of the form-grinding wheel. An optimization method of the contact line between the form-grinding wheel and the gear is proposed using three evaluation parameters that are the overrun, the shift, and the offset. Some gear form-grinding performances, such as machining stroke, tooth deviation, and grinding chatter, can be quantitatively described using those evaluation parameters. Further, a method for optimizing evaluation parameters is proposed, which uses a particle swarm optimization-support vector machine (PSO-SVM) model with the advantage of small-sample robustness to solve evaluation parameters. The PSO-SVM model is trained under the condition of different installation angles of the form-grinding wheel as the input and the evaluation function as the output. The R-squared value of the overrun is 0.986 that vilidate the high accuracy of the PSO-SVM model. Gear form-grinding test results show the proposed method can effectively improve grinding accuracy.

A new synergistic hydrocolloid with superior rheology: Locust bean /xanthan gum binary solution powdered by different drying methods

In the current study, a novel gum powder containing locust bean and xanthan gums was prepared by three different drying methods of their synergistic aqueous solutions: direct cabinet drying (CD), drying after alcohol precipitation (PD), and direct freeze drying (FD). The purpose of this process is to develop ready-to-use synergistic gum powders with improved rheological properties by modifying intermolecular interactions. Significant improvements in viscosity, consistency efficiency and pseudoplastic character were observed for PD, followed by CD and FD, as well as the higher values of G′ and G″ values of PD, indicating a stronger entanglement network development between the macromolecules for PD. PD exhibited better elasticity and shear resistance compared to FD and CD in the strain sweep test. In Lissajous curves, straight line shapes were found for synergistic solutions at low strain, which continued for increasing strain values for PD and CD. However, the pronounced viscous behavior was found for FD at 500% strain. Compared to CD and FD, PD exhibited a more desirable thixotropic character. A lower zeta potential was observed in the production of synergistic gums using the PD process. Gel strength was found to be higher for PD. Therefore, PD was a more effective method to produce a ready-to-use synergistic powder with better viscoelastic properties and a more stable solution.

Determining effects of doping lithium nickel oxide with tungsten using Compton scattering

X-ray Compton scattering experiments along with parallel first-principles computations were carried out on LiNiO2 to understand the effects of W doping on this cathode material for Li-ion batteries. By employing high-energy x rays exceeding 100 keV, an insight is gained into the fate of the W valence electrons, which are adduced to undergo transfer to empty O 2p energy bands within the active oxide matrix of the cathode. The substitution of W for Ni is shown to increase the electronic conductivity and to enhance the total magnetization per Ni atom. Our study demonstrates that an analysis of line shapes of Compton scattered x rays in combination with theoretical modeling can provide a precise method for an atomic level understanding of the nature of the doping process.

Observation of the Anomalous Shape of X(1840) in J/ψ→γ3(π^{+}π^{-}) Indicating a Second Resonance Near pp[over ¯] Threshold.

Using a sample of (10087±44)×10^{6} J/ψ events, which is about 45 times larger than that was previously analyzed, a further investigation on the J/ψ→γ3(π^{+}π^{-}) decay is performed. A significant distortion at 1.84 GeV/c^{2} in the line shape of the 3(π^{+}π^{-}) invariant mass spectrum is observed for the first time, which could be resolved by two overlapping resonant structures, X(1840) and X(1880). The new state X(1880) is observed with a statistical significance larger than 10σ. The mass and width of X(1880) are determined to be 1882.1±1.7±0.7 MeV/c^{2} and 30.7±5.5±2.4 MeV, respectively, which indicates the existence of a pp[over ¯] bound state.

Endoscopic sleeve gastroplasty: the identification of the key procedural steps through a modified Delphi method

BackgroundEndoscopic sleeve gastroplasty (ESG) is an innovative, minimally invasive bariatric procedure with an excellent safety and efficacy profile in adults with obesity. The purpose of the procedure is to shorten and tubularize the stomach along its greater curvature. Nevertheless, there are some heterogeneities in the approach to ESG, which will be important to address as the procedure sees increasingly widespread clinical adoption. Here, an expert consensus on standardized ESG techniques is presented. MethodsThe modified Delphi method was used to establish the key procedural steps of an ESG. A panel of 8 experts was selected, of which 6 participated. The panel was selected based on their experience with performing the procedure and consisted of 1 bariatric surgeon and 5 interventional gastroenterologists. A neutral facilitator was designated and produced a skeletonized initial version of the key steps that was sent to each expert. Each survey began with the experts rating the given steps on a Likert scale of 1 to 5, with 1 being the most inaccurate and 5 being the most accurate. Furthermore, the final product was rated. The survey continued with open-ended questions designed to revise and polish the key steps. Areas of discrepancy were addressed using binary questions and a majority vote. The respondents were given 10 days to complete each survey. At the end of each round, the survey was redistributed with updated key steps and questions. This process was continued for a predesignated 3 rounds. ResultsOf the 8 experts who were queried, 6/8, 5/8, and 5/8 replied to each round. The given ratings for the accuracy of the steps in each round were 4.2, 4.6, and 4.4. The final rating was 4.8. Although expert opinion varied around smaller portions of the procedure, such as the placement of an overtube and the shape of each suture line, there was consensus on the need for full-thickness bites and appropriate swirling of the tissue with the helix device. Whether or not to include the fundus in the gastroplasty was an additional area of discrepancy. Of note, 4 of 5 experts agreed that the fundus should remain intact. The final protocol consisted of 21 steps curated from the summarized responses of the experts. ConclusionUsing the modified Delphi method, 21 key steps have been described for a safe and effective ESG. This rubric will be standardized across institutions and practitioners. Furthermore, these findings allow for the generation of educational assessment tools to facilitate training and increase the adoption of ESG by endoscopists.