Dipole Strength Research Articles

Annealing effect on the morphology, linear and non-linear optical properties of squaraine derivative thin films for optoelectronics applications

Squaraine is a class of organic compounds that possess unique optical properties, including strong absorption of light, high fluorescence quantum yields, etc. Here, we explore the structural and spectroscopic investigations of 2,4-Bis[4-(N,N-dibenzylamino)-2,6 dihydroxyphenyl] squaraine dye (SQ) under different conditions of thermal effects. The molar absorptivity (εmolar) spectra were used to describe the electric dipole strength (q2) and the oscillator strengths (f) of SQ dye. The Surface morphology of SQ dye was investigated by AFM and the average roughness shows dependence on the annealing effect. A slight change in the optical energy gap (⁓ 0.3 eV) after annealing up to 473 K reflects the optical stability of our investigated thin films. The optical band transitions and photoluminescence (PL) emission spectra were described before and after annealing at 423 & 473 K. As the temperature annealing film increased to 473 K, the nonlinear parameters such as χ(3) and n2 decreased by about 44% and 36%, respectively. The good thermal stability, suitable optical band gap, and refractive index offer potential applications as active photonic materials in photonic/optoelectronic applications.

Number of virtual photons in the Coulomb dipole excitation

In this study, the number of virtual photons obtained through general, relativistic, nonrelativistic, and intermediate methods was investigated, which is an important factor in obtaining the Coulomb dipole strength distribution. The number of virtual photons was studied according to the incident energy ${E}_{\text{lab}}$ using five methods. The general method, which has two different forms (integral and differential), is valid for all energy regions, whereas the relativistic method is effective for regions with high $\ensuremath{\beta}$ values. In addition, the validity of the nonrelativistic approximation was tested by comparing it with the general method in the low-incident-energy region, and the intermediate method was shown to be not effective in the high-excitation-energy region. Further, an investigation was conducted on the dependence of the number of virtual photons on the charges of the projectile and target nuclei. Using the same $R$ value, target nuclei, and incident energy, it was found that the number of virtual photons does not depend on the charge number of the projectile in the relativistic method. With the same $R$ value, projectile, and incident energy, in contrast it can be seen that the number of virtual photon depends on the square of the charge number of target nuclei.

Global Geomagnetic Field Evolution From 900 to 700 ka Including the Matuyama‐Brunhes Reversal

AbstractPolarity reversals and excursions are the most significant geomagnetic field changes generated in the liquid outer core of the Earth, therefore studying them helps understand geodynamo processes. This study examines the Matuyama‐Brunhes (MB) reversal using a new reconstruction of the global geomagnetic field based on paleomagnetic data, termed Global Geomagnetic Field Model for the MB reversal (GGFMB). GGFMB covers 900–700 ka, including late Matuyama and early Brunhes. This allows us to also investigate the Kamikatsura excursion (ca. 888 ka). The model is based on 38 high‐quality paleomagnetic sediment records with age control mostly independent of the magnetic signal. GGFMB suggests that the MB reversal began about ∼799 ka, when non‐dipole field components increased and the axial dipole component decreased. The transitional fields first appeared on Earth's surface in the high‐latitude southern hemisphere and equatorial regions. The minimum dipole strength was reached around 780 ka and the axial dipole changed sign. After ∼10 Kyr, the field stabilized in the normal polarity of the early Brunhes. The MB reversal lasted ∼29 Kyr (from 799 to 770 ka) and had slower rate of dipole decay than recovery as well as lower dipole moment for several millennia before than after the reversal. According to GGFMB, the dipole moment during the Kamikatsura excursion was approximately half that of the current field and it was a regional excursion observed only over eastern Asia and North America. Our sediment data collection is heavily biased toward the northern hemisphere, thus more southern hemisphere records are needed to demonstrate GGFMB's robustness in this region.

Timing analysis of Swift J0243.6+6124 with NICER and Fermi/GBM during the decay phase of the 2017–2018 outburst

ABSTRACT We present a timing and noise analysis of the Be/X-ray binary system Swift J0243.6+6124 during its 2017–2018 super-Eddington outburst using NICER/XTI observations. We apply a synthetic pulse timing analysis to enrich the Fermi/GBM spin frequency history of the source with the new measurements from NICER/XTI. We show that the pulse profiles switch from double-peaked to single-peaked when the X-ray luminosity drops below ∼7 × 1036 erg s−1. We suggest that this transitional luminosity is associated with the transition from a pencil beam pattern to a hybrid beam pattern when the Coulomb interactions become ineffective to decelerate the accretion flow, which implies a dipolar magnetic field strength of ∼5 × 1012 G. We also obtained the power density spectra (PDS) of the spin frequency derivative fluctuations. The red noise component of the PDS is found to be steeper (ω−3.36) than the other transient accreting sources. We find significantly high noise strength estimates above the super-Eddington luminosity levels, which may arise from the torque fluctuations due to interactions with the quadrupole fields at such levels.

Distance and size dependence of the interactions within highly ordered magnetic nanoparticle mesocrystals

Arranging magnetic nanoparticles (MNPs) into highly ordered structures, so-called superlattices or mesocrystals, is of great interest from a fundamental point of view, as the employment of the corresponding coupled nanoentities introduces additional degrees of freedom to manipulate the overall magnetic characteristics of such hierarchical materials. Characterizing the associated magnetic interactions on the mesoscopic scale is indispensable for obtaining a profound understanding of the relative strengths of the types of interactions involved, such as dipole-dipole interactions, which affect the collective response of a corresponding mesocrystal. In this paper, nanoparticles are deposited onto silicon substrates by spin coating, leading to two-dimensional monolayered structures showing a close-packed hexagonal arrangement. The MNPs consist of iron oxide (magnetite ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$) and are coated with a nonmagnetic polymer (polystyrene). The MNPs are synthesized such that their diameters ${d}_{\text{MNP}}$ are tuned in a range between 9 and 18 nm. A precise manipulation of the shell thickness ${d}_{\text{shell}}$ is achieved by coating the MNPs with polystyrene of different molecular weights. In this fashion, the spacing between the MNPs, ${d}_{\text{spacer}}=2{d}_{\text{shell}}$, is varied in a range between 6 and 14 nm. Within the investigated ${d}_{\text{spacer}}$ range, dipolar interactions govern the collective properties showing distinct distance-dependent characteristics. As ${d}_{\text{spacer}}$ increases, the dipolar coupling strength between the MNPs decreases, as deduced from the spectral features of ferromagnetic resonance experiments. These observations are further corroborated by numerical simulations of the dynamic properties of appropriate model systems. A comparison of the experimental and theoretical findings shows that material parameters, such as the magnetization ${M}_{\text{MNP}}$ and the magnetocrystalline anisotropy ${C}_{\text{MNP}}$ of the MNPs, are reduced compared to their bulk values.

Fine structure calculations, polarizability and oscillator strengths for C VI ion embedded in Debye plasma applying accurate Numerov method

The dipole polarizabilities, dipole and quadruple oscillator strengths and relativistic energy corrections are calculated for plasma embedded C VI ion which is of relevance in astrophysics and plasma physics. Numerical simulation of Numerov method is used to find the energy eigenvalues and eigenfunctions by solving the time-independent Schrodinger equation. The dependence of dipole and quadruple polarizabilities, oscillator strengths and relativistic energy corrections on Debye length is shown.

Effects of Temporal Light Modulation on Cognitive Performance,Eye Movements, and Brain Function

ABSTRACT Temporal light modulation (TLM) describes variations in light output from a light source or lighting system and can be a characteristic of their normal operation. TLM at 100 or 120 Hz can disrupt eye movements and reduce visual performance compared to 40 kHz, but little is known of the effects between those frequencies. Such evidence could provide the basis for lighting product and application standards to support the development of energy-efficient lighting systems. This repeated-measures experiment compared the effects of three stimuli (no TLM [DC], 100 Hz, and 500 Hz [both rectangular-wave, 100% modulation depth, 50% duty cycle]) on state anxiety, eye movements (blinks, saccades, fixations, and pupil size), cognitive performance (Stroop task and sentence reading speed), and visual event-related potentials (ERPs). Post-processing of EEG data included dipole source analysis and estimates of source dipole strength. TLM at 100 Hz was associated with larger pupil sizes and greater ERP dipole strength during 100 Hz exposure than no TLM, particularly in the right hemisphere. Cognitive interference was lower for 500 Hz TLM than 100 Hz. State anxiety was unaffected. The addition of TLM to the light source signal increased arousal and altered brain activity; at the highest frequency tested here this reduced cognitive interference. Arousal theory and stochastic facilitation can provide possible explanations.

Structure of amorphous materials in the NASICON system NaTi2Si x PO12

The structure of glasses in the sodium (Na) super-ionic conductor (NASICON) system NaTi2Si x PO12 with x = 0.8 and x = 1.0 was explored by combining neutron and high-energy x-ray diffraction with 29Si, 31P and 23Na solid-state nuclear magnetic resonance (NMR) spectroscopy. The 29Si magic angle spinning (MAS) NMR spectra reveal that the silica component remains fully polymerized in the form of Si4 units, i.e. the silicon atoms are bound to four bridging oxygen atoms. The 31P{23Na} rotational echo adiabatic passage double resonance (REAPDOR) NMR data suggest that the 31P MAS NMR line shape originates from four-coordinated P n units, where n = 1, 2 or 3 is the number of bridging oxygen atoms per phosphorus atom. These sites differ in their 31P-23Na dipolar coupling strengths. The results support an intermediate range order scenario of a phosphosilicate mixed network-former glass in which the phosphate groups selectively attract the Na+ modifier ions. Titanium takes a sub-octahedral coordination environment with a mean Ti–O coordination number of 5.17(4) for x = 0.8 and 4.86(4) for x = 1.0. A mismatch between the P–O and Si–O bond lengths of 8% is likely to inhibit the incorporation of silicon into the phosphorus sites of the NASICON crystal structure.

Investigation of giant dipole resonance in Mo isotopes within TDHF theory

The isovector giant dipole resonance (IVGDR) in the chain of even-even Mo isotopes is investigated within the time-dependent Hartree-Fock (TDHF) using the Skyrme force Sly6. The GDR calculated in Mo92−108 are presented, and compared with the available experimental data. An overall agreement between them is obtained. Moreover, the dipole strength in Mo102−108 is predicted. Shape phase transition from spherical to oblate as well as shape coexistence (A ∼ 100) in Mo isotopes are also investigated in this work. In addition, the correlation between the deformation splitting ΔE and the quadrupole deformation parameter β2 is studied. The results confirm that ΔE is proportional to the deformation of nucleus. We also discuss the dependence of GDR strength on some nuclear properties of Skyrme forces, such as the asymmetry energy as. We find that as=32 MeV, corresponding to SLy6, is quite consistent with experimental data.

Role of interaction-induced tunneling in the dynamics of polar lattice bosons

Intersite dipolar interactions induce, even in absence of disorder, an intriguing nonergodic dynamics for dipolar bosons in an optical lattice. We show that the inherent dipole-induced density-dependent tunneling, typically neglected, plays a crucial role in this dynamics. For shallow-enough lattices, the delocalization stemming from the interaction-induced hopping overcomes the localization induced by intersite interactions. As a result, in stark contrast to the more studied case of hard-core bosons, delocalization is counterintuitively strengthened when the dipolar strength increases. Furthermore, the quasicancellation between bare and interaction-induced tunneling may lead, near a lattice-depth-dependent value of the dipole strength, to an exact decoupling of the Hilbert space between ergodic hard-core states and strongly nonergodic soft-core ones. Our results show that interaction-induced hopping should play a crucial role in future experiments on the dynamics of polar lattice gases.

1H multiple quantum NMR in alternating quasi-one-dimensional spin chains of hambergite

Multiple quantum (MQ) dynamics was investigated in quasi-one-dimensional 1H zigzag spin chains in hambergite (Be2BO3OH) single crystals. Due to the non-linear arrangement of the spins, dipolar coupling strengths alternate along the chain. To solve the problem of MQ NMR experiments taking too much time due to extremely long 1H spin–lattice relaxation times, the samples were exposed to gamma irradiation to produce the defects accelerating the relaxation. The influence of the radiation dose was investigated. The experimental dependencies of MQ coherence intensities on the MQ excitation time in alternating spin chains were obtained and compared with the theory for inhomogeneous spin chains with nearest neighbor interactions developed earlier. The correspondence of the observed MQ dynamics to the alternating spin chain was demonstrated.

Surface structure of 45 Hercules: an otherwise unremarkable Ap star with a surprisingly weak magnetic field

ABSTRACTThe origin of magnetic fields and their role in chemical spot formation on magnetic Ap stars is currently not understood. Here, we contribute to solving this problem with a detailed observational characterization of the surface structure of 45 Her, a weak-field Ap star. We find this object to be a long-period, single-lined spectroscopic binary and determine the binary orbit as well as fundamental and atmospheric parameters of the primary. We study magnetic field topology and chemical spot distribution of 45 Her with the help of the Zeeman Doppler imaging technique. Magnetic mapping reveals the stellar surface field to have a distorted dipolar topology with a surface-averaged field strength of 77 G and a dipolar component strength of 119 G – confirming it as one of the weakest well-characterized Ap-star fields known. Despite its feeble magnetic field, 45 Her shows surface chemical inhomogeneities with abundance contrasts of up to 6 dex. Of the four chemical elements studied, O concentrates at the magnetic equator, whereas Ti, Cr, and Fe avoid this region. Apart from this trend, the positions of Fe-peak element spots show no apparent correlation with the magnetic field geometry. No signs of surface differential rotation or temporal evolution of chemical spots on the time-scale of several years were detected. Our findings demonstrate that chemical spot formation does not require strong magnetic fields to proceed and that both the stellar structure and the global field itself remain stable for sub-100 G field strengths contrary to theoretical predictions.

Multiple scattering model for collections of bianisotropic acoustic scatterers

The magnitude of an acoustic point source is traditionally described as monopole, dipole, or higher-order multipole source strengths. The polarizability tensor, commonly used in electromagnetics, can be used to describe the scattering from an acoustically small heterogeneity in a background medium as monopole, dipole, and higher order multipoles due to the pressure and particle velocity at the scattering site. Recent research on bianisotropic acoustic (or Willis) metamaterials has employed the acoustic polarizability tensor as a convenient descriptor of the scattered fields from scatterers with asymmetries since non-zero off-diagonal terms indicate the existence and relative strength of Willis coupling. In the present work, we employ the polarizability tensor in a multiple scattering formulation for N arbitrary, point scatterers. The polarizability tensor for an example scatterer is extracted from finite element simulations by generalizing the approach of Su and Norris [Phys. Rev. B 98, 174305, (2018)]. We then provide a metasurface example to demonstrate the ability of the multiple scattering approach to consider variability in scatterer position and orientation in the calculation of the total scattered field.

Determining the impact of gold nanoparticles on amyloid aggregation with 2D IR spectroscopy.

As nanomaterials become more prevalent in both industry and medicine, it is crucial to fully understand their health risks. One area of concern is the interaction of nanoparticles with proteins, including their ability to modulate the uncontrolled aggregation of amyloid proteins associated with diseases, such as Alzheimer's disease and type II diabetes, and potentially extend the lifetime of cytotoxic soluble oligomers. This work demonstrates that two-dimensional infrared spectroscopy and 13C18O isotope labeling can be used to follow the aggregation of human islet amyloid polypeptide (hIAPP) in the presence of gold nanoparticles (AuNPs) with single-residue structural resolution. 60nm AuNPs were found to inhibit hIAPP, tripling the aggregation time. Furthermore, calculating the actual transition dipole strength of the backbone amide I' mode reveals that hIAPP forms a more ordered aggregate structure in the presence of AuNPs. Ultimately, such studies can provide insight into how mechanisms of amyloid aggregation are altered in the presence of nanoparticles, furthering our understanding of protein-nanoparticle interactions.

Catalyzation of supersolidity in binary dipolar condensates

In this work, the authors show realistic conditions for which doping an unmodulated scalar condensate with a second component catalyzes droplet nucleation and supersolidity. In miscible mixtures, droplet nucleation may be induced even by a surprisingly small impurity doping due to the effective modification of the relative dipolar strength. As a result, binary dipolar condensates present different ground-state phases, most intriguingly the possibility of realizing an interacting two-fluid supersolid.

Voltage-Dependent FTIR and 2D Infrared Spectroscopies within the Electric Double Layer Using a Plasmonic and Conductive Electrode.

Strong electric fields exist between the electric double layer and charged surfaces. These fields impact molecular structures and chemistry at interfaces. We have developed a transparent electrode with infrared plasmonic enhancement sufficient to measure FTIR and two-dimensional infrared spectra at submonolayer coverages on the surface to which a voltage can be applied. Our device consists of an infrared transparent substrate, a 10-20 nm layer of conductive indium tin oxide (ITO), an electrically resistive layer of 3-5 nm Al2O3, and a 3 nm layer of nonconductive plasmonic gold. The materials and thicknesses are set to maximize the surface number density of the monolayer molecules, electrical conductivity, and plasmonic enhancement while minimizing background signals and avoiding Fano line shape distortions. The design was optimized by iteratively characterizing the material roughness and thickness with atomic force microscopy and electron microscopy and by monitoring the plasmon resonance enhancement with spectroscopy. The design is robust to repeated fabrication. This new electrode is tested on nitrile functional groups using a monolayer of 4-mercaptobenzonitrile as well as on CO and CC stretching modes using 4-mercaptobenzoic acid methyl ester. A voltage-dependent Stark shift is observed on both monolayers. We also observe that the transition dipole strength of the CN mode scales linearly with the applied voltage, providing a second way of measuring the surface electric field strength. We anticipate that this cell will enable many new voltage-dependent infrared experiments under applied voltages.

Role of magnetic field in three-component antiferromagnetic dipolar Bose gases

In this paper, we study the dynamics properties of three-component antiferromagnetic dipolar Bose–Einstein condensates with external magnetic field. Our results are obtained by numerical simulations of the spinor Gross–Pitaevskii equation. We find that the population of the spin components is seriously influenced by magnetic field. The dynamical evolution process is accelerated in the presence of magnetic field. As a result, the periodic oscillation of spin exchange dynamics emerges and the components [Formula: see text] have the same amplitude. In addition, the density profile displays that the influences of dipolar interaction are masked by magnetic field. Moreover, we introduce an order parameter to characterize the disorder-order crossover, where it is seen that the system develops toward the disordered state with strong dipole strength when magnetic field is included.

Förster Blockade and Excitation Transfer Behaviors of Two-Photon Rabi Oscillations of Exciton–Biexciton Levels in Coupled Quantum Dots

We provide a theoretical study for the dynamical behavior of two-photon Rabi oscillations in two coupled quantum dots. Each dot is a three-level quantum system (ground, one-exciton, and biexciton states). We describe the optical dynamics within the density matrix formalism framework. The two-photon Rabi oscillations are found to be significantly affected by the strength of the interdot dipolar interaction. Using a detuned laser pulse with an exciton state of the driven quantum dot in our numerical simulations, a direct coherent excitation between the biexciton states can be established, but whether Rabi oscillations can be observed depend mainly on the strength of the dipolar interaction and bandwidth of the excitation laser. When the strength of the dipolar coupling is less than the excitation laser bandwidth, the time-dependent populations of the various two biexciton states of the system exhibit coherent oscillations with several frequencies. However, as we increase the dipolar coupling strength, the population transfer between the quantum dots levels amazingly becomes forbidden, and the excitation gets trapped at the initial state. The reduction of the influence of the dipolar interaction leads to a manipulation of two-photon Rabi oscillation in an ultrashort timescale (∼ps), opening possibilities to achieve ultrafast quantum state control and quantum logic gate generation.

Phthalocyanine photosensitizers with bathochromic shift, of suitable brightness, capable of producing singlet oxygen with effective efficiency

• New phthalocyanine derivatives as photosensitizers were designed and synthesized. • The phthalocyanines dissolve well in common solvents without aggregation. • The phthalocyanines have improved fluorescence and optical absorption properties. • The phthalocyanines have improved photochemical properties and photostability. • The phthalocyanines can be used as photosensitizers in photocatalytic applications. In this study, novel 3-(2,3-dimethoxyphenoxy)phthalonitrile 2 and its non-peripheral tetra-2,3-dimethoxyphenoxy substituted metal-free phthalocyanine 3 compounds were synthesized. Then, the magnesium(II), zinc(II), and indium(III) acetate phthalocyanine complex derivatives ( 4-6 ) of compound 3 were synthesized using the corresponding metal salts by the template effect. The structures of novel phthalonitrile derivative 2 and its metal-free phthalocyanine compounds 3 as well as different metal-containing phthalocyanine complexes ( 4-6 ) were characterized by elemental analysis, FTIR, UV-vis, 1 H NMR, and MALDI-TOF mass spectroscopic techniques. The phthalocyanines ( 3-6 ) can dissolve well in different polar protic, polar aprotic, and non-polar solvent types without aggregation, with maximum absorption intensity and bathochromic effect. Photophysicochemical properties of the phthalocyanines ( 3-6 ) in dimethyl sulfoxide and important spectral parameter values such as molar extinction coefficient, oscillator strength, and electrical dipole strength were determined, and they were also compared with each other and with their unsubstituted counterparts. It was determined that the phthalocyanines ( 3-6 ) have suitable and sufficient fluorescence quantum yields, fluorescence lifetimes, fluorescence brightness, and other photophysical properties, as well as singlet oxygen generation, phototoxic power, and photostability properties. The phthalocyanines ( 3-6 ), particularly zinc(II) and indium(III) acetate phthalocyanines have remarkable potential for use as Type II photosensitizers for cancer therapy in photodynamic therapy. The phthalocyanines ( 3-6 ) may be promising candidates for various applications as photosensitizers for photodynamic therapy, especially in combination with fluorescent imaging.

Towards a mesoscale physical modeling framework for stereotactic-EEG recordings

Objective. Stereotactic-electroencephalography (SEEG) and scalp EEG recordings can be modeled using mesoscale neural mass population models (NMMs). However, the relationship between those mathematical models and the physics of the measurements is unclear. In addition, it is challenging to represent SEEG data by combining NMMs and volume conductor models due to the intermediate spatial scale represented by these measurements. Approach. We provide a framework combining the multi-compartmental modeling formalism and a detailed geometrical model to simulate the transmembrane currents that appear in layer 3, 5 and 6 pyramidal cells due to a synaptic input. With this approach, it is possible to realistically simulate the current source density (CSD) depth profile inside a cortical patch due to inputs localized into a single cortical layer and the induced voltage measured by two SEEG contacts using a volume conductor model. Based on this approach, we built a framework to connect the activity of a NMM with a volume conductor model and we simulated an example of SEEG signal as a proof of concept. Main results. CSD depends strongly on the distribution of the synaptic inputs onto the different cortical layers and the equivalent current dipole strengths display substantial differences (of up to a factor of four in magnitude in our example). Thus, the inputs coming from different neural populations do not contribute equally to the electrophysiological recordings. A direct consequence of this is that the raw output of NMMs is not a good proxy for electrical recordings. We also show that the simplest CSD model that can accurately reproduce SEEG measurements can be constructed from discrete monopolar sources (one per cortical layer). Significance. Our results highlight the importance of including a physical model in NMMs to represent measurements. We provide a framework connecting microscale neuron models with the neural mass formalism and with physical models of the measurement process that can improve the accuracy of predicted electrophysiological recordings.