Lineshape Effects Research Articles

Experimental investigation of flow-induced sound of kite lines

In times of increasing importance of renewable energies, airborne wind energy (AWE) systems represent an emerging extension to conventional wind turbines. Many AWE systems use powerful kites to provide tether traction to mechanically unwind the tether, generating electricity on the ground. In addition to the traction tether, a large number of kite lines spanning the kite are moved through the air at high speed. This can produce a loud unpleasant whistling noise on the ground, which is due to a superposition of the aeolian tones of the many different lines. In the present work, differently structured kite lines were investigated in the aeroacoustic wind tunnel with respect to their sound radiation when they were exposed to a flow at up to 34 ms−1 resulting in Re ≦ 7300 and angles of attack (AOA) in the range of 90° ≧ AOA ≧ 45°. It was found that greater surface roughness increases sound radiation while line tension has negligible influence. By weaving a single-helix-shaped protrusion into the sheath of the kite line, the total radiated sound pressure level can be reduced by up to 9 dB. If the line itself has a helical contour, even a reduction of up to 11.5 dB is reachable. For decreasing AOA the noise suppression effect of helical surface protrusions and helical line shape is significantly reduced. The results provide initial guidelines on how to effectively reduce sound radiation from aircraft kites. Further investigations should consider the individual contributions of fluid and structural sounds to the total radiated sound of a flying kite.

The effects of advanced spectral line shapes on atmospheric carbon dioxide retrievals

Line shape effects such as speed-dependence and collisional (Dicke) narrowing are manifest in high signal-to-noise ratio laboratory spectra for a wide range of molecular species and sample conditions. However, these effects are usually neglected in spectroscopic models used in remote sensing of atmospheric greenhouse gases. Here we examine the effects of line profile choice on laboratory spectra and XCO2 values retrieved from Total Carbon Column Observing Network (TCCON) spectra. To this end, we utilize limiting cases of the Hartmann-Tran profile (HTP) with shape parameters recently measured by cavity ring-down spectroscopy. Significant differences highlighting the importance of including speed-dependence effects in forward models were observed both in scaling retrievals as well as profile retrievals. However, because of uncertainties associated with the atmospheric temperature gradient, it was not possible to extract accurate carbon column profiles even with inclusion of these new line shape parameters and advanced line profiles.

Compressive nano-FTIR chemical mapping

Nano-Fourier-transform infrared spectroscopy (nano-FTIR) combines infrared spectroscopy with scanning probe microscopy (SPM) techniques and enables spectroscopic imaging of molecular and electronic properties of matter at nanometer spatial resolution. The spectroscopic imaging can be used to derive chemical mappings, i.e. the spatial distribution of concentrations of the species contained in a given sample. However, due to the sequential scanning principle underlying SPM, recording the complete spectrum over a large spatial area leads to long measurement times. Furthermore, the acquired spectrum often contains additional signals from species and lineshape effects that are not explicitly accounted for. A compressive chemical mapping approach is proposed for undersampled nano-FTIR data that utilizes sparsity of these additional signals in the spectral domain. The approach combines a projection technique with standard compressed sensing, followed by a spatially regularized regression. Using real nano-FTIR measurements superimposed by simulated interferograms representing the chemical mapping of the contained species, it is demonstrated that the proposed procedure performs well even in cases in which the simulated interferograms and the sparse additional signals exhibit a strong spectral overlap.

Vibrational line shape effects in plasmon-enhanced stimulated Raman spectroscopies.

A density matrix treatment of plasmon-enhanced (PE) stimulated Raman spectroscopies is developed. Specifically, PE stimulated Raman Gain/Loss (PE-SRG/L) and coherent anti-Stokes Raman scattering (PE-CARS) due to monochromatic excitation and PE femtosecond stimulated Raman spectroscopy (PE-FSRS) are considered. A Lorentz oscillator model is used to explicitly describe the time dependence of plasmon-enhanced optical fields. These temporal characteristics are required for a density matrix based description of all plasmon-enhanced nonlinear molecular spectroscopies. Dispersive vibrational line shapes in PE-SRG/L and PE-FSRS spectra are shown to result primarily from terms proportional to the square of the complex optical field enhancement factor. The dependence on the plasmon resonance, picosecond and femtosecond pulse characteristics, and molecular vibrational properties are evident in the density matrix derived PE-FSRS intensity expression. The difference in signal detection mechanisms accounts for the lack of dispersive line shapes in PE spontaneous Raman spectroscopy. This density matrix treatment of PE-FSRS line shapes is compared with prior coupled wave results.

Collisional line-shape effects in accurate He-perturbed H[formula omitted] spectra

We investigate collisional line-shape effects that are present in highly accurate experimental spectra of the 3-0 S(1) and 2-0 Q(1) molecular hydrogen absorption lines perturbed by helium. We clearly distinguish the influence of six different collisional effects (i.e.: collisional broadening and shift, their speed dependencies and the complex Dicke effect) on the shapes of H2 lines. We demonstrate that only a very specific combination of these six contributions, determined from our ab initio calculations, gives unprecedentedly good agreement with experimental spectra. If any of the six contributions is neglected, then the experiment-theory comparison deteriorates at least several times. We also analyze the influence of the centrifugal distortion on our ab initio calculations and we demonstrate that the inclusion of this effect slightly improves the agreement with the experimental spectra.

Application of a pulsed OPO seeded by a CW OPO to investigation of linewidth effects on TALIF excitation efficiency

In this article we present a widely tunable laser architecture for high-resolution nonlinear spectroscopy which incorporates a continuous wave optical parametric oscillator (OPO) for injection-seeding of a singly resonant actively-locked β-Ba(BO2)2 nanosecond OPO. Such an instrumental configuration is designed to provide near-transform-limited pulses over 450–650 nm signal, and 225–325 nm after signal doubling. Novel features that enable frequency agility and ramp-lock injection-seeding over a wide frequency range are described. System performance was demonstrated through investigations of two-photon laser induced fluorescence (TALIF) and the influence of excitation linewidth on the signal strength of the 5p6S0 - 6p[3/2]2 transition of atomic xenon at 252.49 nm. Measurements conducted at xenon partial pressures of 1×10-1-4×10-4 Torr, with and without active cavity locking and injection seeding, resulted in a 17× increased TALIF fluorescence yield during injection-seeded operation. The results are found to be consistent with modeling, taking into account the effects of lineshape, energy, and beam spatial cross-section. Modeling was informed by direct single-shot measurements of the signal beam lineshape in seeded and free-running operation using a virtually imaged phased array (VIPA) spectrometer.

η2-Alkene Complexes of [Rh(PONOP-iPr)(L)]+ Cations (L = COD, NBD, Ethene). Intramolecular Alkene-Assisted Hydrogenation and Dihydrogen Complex [Rh(PONOP-iPr)(η-H2)]+

Rhodium-alkene complexes of the pincer ligand κ3-C5H3N-2,6-(OPiPr2)2 (PONOP-iPr) have been prepared and structurally characterized: [Rh(PONOP-iPr)(η2-alkene)][BArF4] [alkene = cyclooctadiene (COD), norbornadiene (NBD), ethene; ArF = 3,5-(CF3)2C6H3]. Only one of these, alkene = COD, undergoes a reaction with H2 (1 bar), to form [Rh(PONOP-iPr)(η2-COE)][BArF4] (COE = cyclooctene), while the others show no significant reactivity. This COE complex does not undergo further hydrogenation. This difference in reactivity between COD and the other alkenes is proposed to be due to intramolecular alkene-assisted reductive elimination in the COD complex, in which the η2-bound diene can engage in bonding with its additional alkene unit. H/D exchange experiments on the ethene complex show that reductive elimination from a reversibly formed alkyl hydride intermediate is likely rate-limiting and with a high barrier. The proposed final product of alkene hydrogenation would be the dihydrogen complex [Rh(PONOP-iPr)(η2-H2)][BArF4], which has been independently synthesized and undergoes exchange with free H2 on the NMR time scale, as well as with D2 to form free HD. When the H2 addition to [Rh(PONOP-iPr)(η2-ethene)][BArF4] is interrogated using pH2 at higher pressure (3 bar), this produces the dihydrogen complex as a transient product, for which enhancements in the 1H NMR signal for the bound H2 ligand, as well as that for free H2, are observed. This is a unique example of the partially negative line-shape effect, with the enhanced signals that are observed for the dihydrogen complex being explained by the exchange processes already noted.

Effect of Contact Line Shape on Horizontal Shear Force of Water Droplet on Silicone Sheet

Effect of Contact Line Shape on Horizontal Shear Force of Water Droplet on Silicone Sheet

In situ investigating the size-dependent scattering signatures and sensing sensitivity of single silver nanocube through a multi-model approach

Insightful understanding of size-dependent optical signatures and precise regularity of nanosensors is critical for developing applications of plasmonic sensing. This work presents a systematic study on localized surface plasmon resonance (LSPR)-based nanosensors of plasmonic silver nanocubes (AgNCs) with the edge lengths of 59.84 ± 7.97 nm (no. 1 AgNCs), 75.70 ± 9.05 nm (no. 2 AgNCs) and 110.32 ± 14.63 nm (no. 3 AgNCs), respectively. The effects of different sizes on the scattering signatures and refractive index (RI) sensitivities of AgNCs were in situ determined using the multi-model co-localization approach of single AgNC by dark-field microscope (DFM), LSPR spectroscopy and scanning electron microscopy (SEM). The scattering light colour of single AgNC took place bathochromic shift from monocolour to multicolour with the growth of edge length of single AgNC. The LSPR scattering spectra of no. 1 and 2 AgNCs exhibited singlet and singlet with the shoulder peak from quadrupolar resonance mode, respectively. Compared with the scattering signatures of no. 1 and 2 AgNCs, the interesting LSPR effect of plasmon line shape with two distinct peaks was observed on single no. 3 AgNC. In situ studies on the scattering spectral response of single AgNC to the ambient solvents and probing the small-molecule adsorbates on the surface of single silver nanocube reveal that no. 2 AgNC is more suitable as nanosensor due to strong regularity and higher sensitivity. The mechanism involved in optical signatures was elaborated clearly by combining with the experiments and theoretical simulation.

On the microscopic origins of relaxation processes in aqueous peptide solutions undergoing a glass transition.

We combine broadband dielectric spectroscopy (BDS) with 1H and 2H nuclear magnetic resonance (NMR) to study molecular dynamics in mixtures of ε-polylysine with H2O or D2O. In BDS, four relaxation processes can be attributed to molecular dynamics. While the fastest process P1 obeys the Arrhenius law, the slowest process P4 shows prominent non-Arrhenius behavior typical of structural α relaxation. For the intermediate processes P2 and P3, the temperature dependence changes at the glass transition temperature Tg. The 1H and 2H NMR results yield insights into the molecular origins of these relaxation phenomena. In these NMR analyses, we exploit, in addition to the isotope selectivity of the method, the possibility to distinguish between various types of motion based on their respective line-shape effects and the capability to single out specific molecular moieties based on different spin-lattice relaxation behaviors. In this way, we reveal that process P1 results from the rotation of side and end groups of the peptide, while process P2 is caused by a reorientation of essentially all water molecules, which are quasi-isotropic and survive well below Tg. As for the peptide backbone dynamics, we find evidence that rotational motion of polar groups is involved in process P3 and that nonpolar regions show a dynamical process, which is located between P3 and P4. Thus, the NMR analyses do not yield evidence for coexisting fast peptide-decoupled and slow peptide-coupled water species, which contribute to BDS processes P2 and P3, respectively, but minor bimodality of water motion may remain undetected. Finally, it is demonstrated that the proton/deuteron exchange needs to be considered when interpreting experimental results for molecular dynamics in aqueous peptide solutions.

Reorientational dynamics of trimethoxyboroxine: A molecular glass former studied by dielectric spectroscopy and 11B nuclear magnetic resonance.

In this work, trimethoxyboroxine (TMB) is identified as a small-molecule glass former. In its viscous liquid as well as glassy states, static and dynamic properties of TMB are explored using various techniques. It is found that, on average, the structure of the condensed TMB molecules deviates from threefold symmetry so that TMB's electric dipole moment is nonzero, thus rendering broadband dielectric spectroscopy applicable. This method reveals the super-Arrhenius dynamics that characterizes TMB above its glass transition, which occurs at about 204 K. To extend the temperature range in which the molecular dynamics can be studied, 11B nuclear magnetic resonance experiments are additionally carried out on rotating and stationary samples: Exploiting dynamic second-order shifts, spin-relaxation times, line shape effects, as well as stimulated-echo and two-dimensional exchange spectroscopy, a coherent picture regarding the dynamics of this glass former is gained.

Effect of weld line shape on laser welded joint strength of automotive high strength steel sheets

Effect of weld line shape on laser welded joint strength of automotive high strength steel sheets

Effect of weld line shape on laser welded joint strength of automotive high-strength steel sheets

ABSTRACT The optimum weld line shape for the remote laser welding was investigated to improve shear strength and peel strength of the lap joints of 980 and 1180 MPa grade automotive high-tensile strength steel sheets. Lap joints were prepared with two kinds of weld line shapes that were straight line and circle. These lap joints were exposed to three different tensile tests of tensile shear test, cross tension test and L-form tension test. In tensile shear test, weld line shapes did not affect on tensile shear strength (TSS), and TSS was proportional to weld line length. In cross tension test, weld line shapes much affected on cross tension strength (CTS). CTS of the circle weld line shape joints was much higher than that of the straight weld line shape joints. In L-form tension test, the weld line shapes also much affected on L-form tension strength (LTS). LTS of continuous straight line weld joints was much higher than that of circle shape weld joints. The factors which controlled TSS, CTS and LTS were discussed by conducting FEA of the tensile tests from a viewpoint of local stress concentration considering the loading types of shear stress and tensile stress.

FMR line shape effect on spin pumping in bilayer structures

FMR line shape effect on spin pumping in bilayer structures

Modeling the absorption lineshape of embedded systems from molecular dynamics: A tutorial review

AbstractIn this tutorial review, we focus on a multiscale method to compute the electronic absorption line shape of molecular dyes embedded in a biological environment. To treat the coupling of the electronic excitations with the nuclear degrees of freedom of the system, we use the spectral density (SD) of the exciton–phonon coupling computed from a Born–Oppenheimer molecular dynamics, which takes into account the effect of the biological environment on the dye's nuclear and electronic degrees of freedom. The theoretical basis of the approach is given, as well as a comprehensive description of the computational protocol for the extraction of the energy gap autocorrelation function evaluating the electronic excitation along the classical trajectory. Furthermore a benchmark application from a recently published study is presented as an example of how the derived SD can be used in computational spectroscopy to accurately simulate the absorption lineshape, including both vibronic and temperature effects.

Accurate deuterium spectroscopy for fundamental studies

We present an accurate measurement of the weak quadrupole S(2) 2-0 line in self-perturbed D2 and theoretical ab initio calculations of both collisional line-shape effects and energy of this rovibrational transition. The spectra were collected at the 247–984 Torr pressure range with a frequency-stabilized cavity ring-down spectrometer linked to an optical frequency comb (OFC) referenced to a primary time standard. Our line-shape modeling employed quantum calculations of molecular scattering (the pressure broadening and shift and their speed dependencies were calculated, while the complex frequency of optical velocity-changing collisions was fitted to experimental spectra). The velocity-changing collisions are handled with the hard-sphere collisional kernel. The experimental and theoretical pressure broadening and shift are consistent within 5% and 27%, respectively (the discrepancy for shift is 8% when referred not to the speed averaged value, which is close to zero, but to the range of variability of the speed-dependent shift). We use our high pressure measurement to determine the energy, ν0, of the S(2) 2-0 transition. The ab initio line-shape calculations allowed us to mitigate the expected collisional systematics reaching the 410 kHz accuracy of ν0. We report theoretical determination of ν0 taking into account relativistic and QED corrections up to α5. Our estimation of the accuracy of the theoretical ν0 is 1.3 MHz. We observe 3.4σ discrepancy between experimental and theoretical ν0.

Curved convex slot: an effective needleless electrospinning spinneret

Slot electrospinning that uses narrow slot as a spinneret combines the advantages of both needle and needleless electrospinning with precisely controlled solution condition. Most of the existing slot electrospinning techniques, however, use a straight linear slot as spinneret. The effects of slot geometry on electrospinning process and fiber morphology have not been reported in the research literature. In this study, four convex slots with different line shapes, i.e., curved, straight, rectangle and triangle, have been used as spinnerets to examine the effects of slot line shape on electrospinning process, fiber morphology and productivity. The electric field intensity distribution of these slot spinnerets was analyzed by finite element method. Our experimental results have indicated that the slot line shape played an important role in affecting fiber diameter, productivity and uniformity of the fibrous membranes. Compared to the other slots studied, the curved slot can produce nanofibers with larger productivity and the resulting fibrous membranes were more uniform as well; the curved slot had higher electric field with more uniform distribution of electric field intensity along the slot length direction. These understandings may be helpful for designing new slot electrospinning systems.

Radiation Transfer Calculations and Assessment of Global Warming by CO2

We present detailed line-by-line radiation transfer calculations, which were performed under different atmospheric conditions for the most important greenhouse gases water vapor, carbon dioxide, methane, and ozone. Particularly cloud effects, surface temperature variations, and humidity changes as well as molecular lineshape effects are investigated to examine their specific influence on some basic climatologic parameters like the radiative forcing, the long wave absorptivity, and back-radiation as a function of an increasing CO2 concentration in the atmosphere. These calculations are used to assess the CO2 global warming by means of an advanced two-layer climate model and to disclose some larger discrepancies in calculating the climate sensitivity. Including solar and cloud effects as well as all relevant feedback processes our simulations give an equilibrium climate sensitivity of CS = 0.7°C (temperature increase at doubled CO2) and a solar sensitivity of SS = 0.17°C (at 0.1% increase of the total solar irradiance). Then CO2 contributes 40% and the Sun 60% to global warming over the last century.

Nonclassical dynamics of the methyl group in 1,1,1-triphenylethane. Evidence from powder 1H NMR spectra.

According to the damped quantum rotation (DQR) theory, hindered rotation of methyl groups, evidenced in nuclear magnetic resonance (NMR) line shapes, is a nonclassical process. It comprises a number of quantum-rate processes measured by two different quantum-rate constants. The classical jump model employing only one rate constant is reproduced if these quantum constants happen to be equal. The values of their ratio, or the nonclassicallity coefficient, determined hitherto from NMR spectra of single crystals and solutions range from about 1.20 to 1.30 in the latter case to above 5.0 in the former, with the value of 1 corresponding to the jump model. Presently, first systematic investigations of the DQR effects in wide-line NMR spectra of a powder sample are reported. For 1,1,1-triphenylethane deuterated in the aromatic positions, the relevant line-shape effects were monitored in the range 99-121 K. The values of the nonclassicality coefficient dropping from 2.7 to 1.7 were evaluated in line shape fits to the experimental powder spectra from the range 99-108 K. At these temperatures, the fits with the conventional line-shape model are visibly inferior to the DQR fits. Using a theoretical model reported earlier, a semiquantitative interpretation of the DQR parameters evaluated from the spectra is given. It is shown that the DQR effects as such can be detected in wide-line NMR spectra of powdered samples, which are relatively facile to measure. However, a fully quantitative picture of these effects can only be obtained from the much more demanding experiments on single crystals.

Multi-spectrum fitting software for advanced spectral line shapes analysis

We present a multi-spectrum fitting software that enables advanced analysis of high-resolution atomic and molecular spectra in a large range of pressures. Individual lines are modeled with theoretical profiles that take into account the non-Voigt line shape effects, such as the speed-dependence of collisional broadening and shift, velocity-changing collisions and their correlations with phase/state changing collisions, first order line mixing and collision-time asymmetry.