Atomic Resonance Research Articles

Analytical Techniques for the Assessment of Drug-Lipid Interactions and the Active Substance Distribution in Liquid Dispersions of Solid Lipid Microparticles (SLM) Produced de novo and Reconstituted from Spray-Dried Powders.

Solid lipid microparticles (SLM) can be presented as liquid suspension or spray-dried powder. The main challenge in SLM technology is to precisely determine the location of the active substance (API) in the different compartments of the formulation and its changes during SLM processing. Therefore, the purpose of the research was to assess the distribution of the API and to investigate the nature of the API-lipid interaction when the formulation was subjected to spray drying, with an indication of the most suitable techniques for this purpose. SLM were prepared with two various lipids (Compritol or stearic acid) and two model APIs: cyclosporine (0.1% and 1% w/w) and spironolactone (0.1% and 0.5% w/w). Physicochemical characterizations of the formulations, before and after spray drying, were performed by differential scanning calorimetry (DSC), atomic force microscopy (AFM), Raman spectroscopy and nuclear magnetic resonance (NMR). The API distribution between the SLM matrix, SLM surface and the aqueous phase was determined, and the release study was performed. It was demonstrated that, in general, the spray drying did not affect the drug release and drug distribution; however, some changes were observed in the SLM with Compritol and when the API concentration was lower. Only in the SLM with stearic acid was a change in the DSC curves noted. Measurements with the AFM technique proved to be a useful method for detecting differences in the surface properties between the placebo and API-loaded SLM, while the Raman spectroscopy did not show such evident differences.

Bichromatic dark trap immersed in a buffer gas with an admixture of resonant atoms

The quasiclassical kinetic theory of optical forces has been applied to describe the kinetics of accumulation, deep trapping and cooling of particles in a bichromatic dark trap (BDT), which is placed into a reservoir with a thermal gas at room temperature containing an admixture of resonant atoms. BDT (proposed in our previous works, Krasnov 2016 Laser Phys. 26 105 501, 2017 27 085 501) is a multiple-optical-beam dark trap, in which rectified gradient forces in a bichromatic light field are used to manipulate the particles. The purpose of the present study is to investigate the possibility of direct BDT loading from the equilibrium gas mixture which will result in trapping and cooling of a sufficiently great amount of atoms by BDT. We derived a reduced Fokker-Planck equation in the energy space (for the Wigner particle distribution function) including the collision term. This equation takes into account the optical trapping force, its quantum fluctuations, particle loss from the trap and weakly-dissipative nature of BDT. Its asymptotic solution allows one to describe the particle kinetics and obtain explicit formulas for the main characteristics of BDT (particle capture rate into BDT, temperature and number of the trapped particles). Ultimately, we demonstrate the high efficiency of the particle accumulation in BDT. In particular, the concentration of the trapped particles (with the temperature at least by four orders of magnitude lower than the room temperature) has been shown to be able to exceed the concentration of the ‘hot’ untrapped particles by several dozens of times, and it has been demonstrated that the accumulation efficiency can reach the values of the order of 103.

Origin of the multiphoton-regime harmonic-generation plateau structure

A physical interpretation is provided for the formation of the multiphoton-regime plateau feature in the spectra of nonlinear and correlated process of high-order harmonic generation (HHG) of two-active-electron atoms interacting with an intense linearly polarized laser field [Phys. Rev. A 88, 053412 (2013) for beryllium]. While in the strong-field tunneling regime the plateau feature is well known to be due to rescattering effects of the freed electron, its counterpart in the multiphoton regime is due to atomic resonance effects involving both singly excited states and doubly excited states. Here, we propose a strategy to uncover which kind of these states are responsible for this phenomenon. By studying the sensitivity of HHG to the initial state in helium, we show that this multiphoton-regime plateau structure mostly originates from singly excited states.

Phenanthroline Covalent Organic Framework Electrodes for High-Performance Zinc-Ion Supercapattery

Aqueous zinc-ion batteries and capacitors are potentially competitive grid-scale energy storage devices because of their great features such as safety, environmental friendliness, and low cost. Herein, a completely new phenanthroline covalent organic framework (PA-COF) was synthesized and introduced in zinc-ion supercapatteries (ZISs) for the first time. Our as-synthesized PA-COF shows a high capacity of 247 mAh g–1 at a current density of 0.1 A g–1, with only 0.38% capacity decay per cycle during 10 000 cycles at a current density of 1.0 A g–1. Although covalent organic frameworks (COFs) are attracting great attention in many fields, our PA-COF has been synthesized using a new strategy involving the condensation reaction of hexaketocyclohexanone and 2,3,7,8-phenazinetetramine. Detailed mechanistic investigations, through experimental and theoretical methods, reveal that the phenanthroline functional groups in PA-COF are the active zinc ion storage sites. Furthermore, we provide evidence for the cointercalation of Zn2+ (60%) and H+ (40%) into PA-COF using inductively coupled plasma atomic emission spectroscopy and deuterium solid-state nuclear magnetic resonance (NMR). We believe that this study opens a new avenue for COF material design for zinc-ion storage in aqueous ZISs.

Experimental study of high temperature oxidation of dimethyl ether, n-butanol and methane

An experimental study of the kinetics of oxidation of dimethyl ether, n-butanol, and methane was carried out using emission and atomic resonance absorption spectroscopy. All experiments were performed in a shock tube behind reflected shock wave in a wide temperature range from 1890 to 3250 K at a pressure of 2.4 ± 0.4 bar. In all investigated conditions, the peaks of nonequilibrium UV radiation of electronically excited carbon monoxide CO(a3Πr) were observed. Besides, the resonant absorption profiles of atomic oxygen in the ground electronic state O(3P) converted to O-atom concentration profiles were for the first time measured at this temperature range. For simulating the CO(a3Πr) radiation experimental profiles a kinetic mechanism of its formation and consumption was developed. This mechanism was implemented into existing comprehensive detailed kinetic models (such as Ranzi et al. (2014), Vasu and Sarathy (2013), NUIG Mech 56.54 (2013), GRI-Mech 3.0 (1999) and Alviso et al. (2018)), which were then tested on the obtained experimental profiles of atomic oxygen and electronically excited carbon monoxide. It was shown that the proposed CO(a3Πr) sub-mechanism nearly correct describes the ongoing reaction processes, however, complete compliance was not achieved. To elucidate reactions responsible for the differences observed, a sensitivity analysis was performed. As a result, the most important elementary reactions were determined.

Instability threshold in a large balanced magneto-optical trap

Large clouds of cold atoms prepared in a magneto-optical trap can develop spatiotemporal instabilities when the frequency of the trapping lasers is brought close to the atomic resonance. This system bears close similarities with trapped plasmas, whereby effective Coulomb interactions are induced by the exchange of scattered photons and lead to collective nonlinear dynamics of the trapped atoms. We report in this paper a detailed experimental study of the instability threshold, and comparisons with three-dimensional simulations of the interacting, laser-driven cloud.

Atom Assisted Photochemistry in Optical Cavities.

Strong light–matter coupling can modify the photochemistry of molecular systems. The collective dynamics of an ensemble of molecules coupled to the light field plays a crucial role in experimental observations. However, the theory of polaritonic chemistry is primarily understood in terms of single molecules, since even in small molecular ensembles the collective dynamics becomes difficult to disentangle. Understanding of the underlying ensemble mechanisms is key to a conceptual understanding and interpretation of experiments. We present a model system that simplifies the problem by mixing two-level Mg atoms with a single MgH+ molecule and investigate its collective dynamics. Our focus is on the modified chemical properties of a single diatomic molecule in the presence of an ensemble of resonant atoms as well as the structure of the major and intermediate polariton states. We present quantum dynamics simulations of the coupled vibronic–photonic system for a variable size of the atomic ensemble. Special attention is given to dissociative the dynamics of the MgH+ molecule.

Graphene Oxide Nanosheets Tailored With Aromatic Dipeptide Nanoassemblies for a Tuneable Interaction With Cell Membranes.

Engineered graphene-based derivatives are attractive and promising candidates for nanomedicine applications because of their versatility as 2D nanomaterials. However, the safe application of these materials needs to solve the still unanswered issue of graphene nanotoxicity. In this work, we investigated the self-assembly of dityrosine peptides driven by graphene oxide (GO) and/or copper ions in the comparison with the more hydrophobic diphenylalanine dipeptide. To scrutinize the peptide aggregation process, in the absence or presence of GO and/or Cu2+, we used atomic force microscopy, circular dichroism, UV–visible, fluorescence and electron paramagnetic resonance spectroscopies. The perturbative effect by the hybrid nanomaterials made of peptide-decorated GO nanosheets on model cell membranes of supported lipid bilayers was investigated. In particular, quartz crystal microbalance with dissipation monitoring and fluorescence recovery after photobleaching techniques were used to track the changes in the viscoelastic properties and fluidity of the cell membrane, respectively. Also, cellular experiments with two model tumour cell lines at a short time of incubation, evidenced the high potential of this approach to set up versatile nanoplatforms for nanomedicine and theranostic applications.

Far Off-Resonance Laser Frequency Stabilization Technology

In atomic physics experiments, a frequency-stabilized or ‘locked’ laser source is commonly required. Many established techniques are available for locking close to an atomic resonance. However, in many instances, such as atomic magnetometer and magic wavelength optical lattices in ultra-cold atoms, it is desirable to lock the frequency of the laser far away from the resonance. This review presents several far off-resonance laser frequency stabilization methods, by which the frequency of the probe beam can be locked on the detuning as far as several tens of gigahertz (GHz) away from atomic resonance line, and discusses existing challenges and possible future directions in this field.

Saturation effect of atomic magnetic resonance

In this paper, we experimentally study the saturation effect of rubidium atomic magnetic resonance. A pump beam is applied to create atomic spin polarization, a radio frequency (RF) magnetic field is used to drive the spin precession about a static magnetic field, and an off-resonant linearly polarized probe beam is applied to detect the spin dynamics based on the Faraday-rotation effect. When the RF magnetic field intensity becomes strong, a saturation effect is observed. We measure the resonant peak under strong RF magnetic field driving and obtain a saturation dip as an indication of the saturation effect. Furthermore, we show that the line-width of the saturation dip is much smaller than that of magnetic resonance. Accordingly, the sensitivity of the precision measurement based on the saturation dip can be significantly improved. The relations between the saturation dip in the resonant peak and the driving RF magnetic field intensity, as well as pumping intensity, are also studied in our experiment.

Monomolecular decomposition of C3F7I and CF3I: Theory meets experiment

For the first time, the rate constant of the thermal monomolecular decomposition of n-C3F7I in Ar was measured directly using the technique of atomic resonance absorption spectroscopy on a resonant line of iodine atom. Experiments were conducted behind the incident and reflected shock waves in a broad range of thermodynamic parameters (T = 800–1200 K and P = 0.6–8.3 bar). Experimental data were found to conform reasonably to the results of the Rice–Ramsperger–Kassel–Marcus theory master equation modeling based on the results of quantum chemical calculations. The obtained low- and high-pressure limiting rate constants for n-C3F7I and CF3I dissociation in Ar were reported. Third body efficiencies for Kr were also evaluated.

Insert magnet and shim coils design for a 27 T nuclear magnetic resonance spectrometer with hybrid high and low temperature superconductors

An extremely-high field nuclear magnetic resonance (NMR) spectrometer has the potential to significantly augment the resolution and sensitivity of the atomic resonance spectrum, which will significantly boost the development of a range of scientific areas. The success of an extremely-high field NMR spectrometer depends to a great extent on the development of a superconducting magnet system. A high-temperature superconducting (HTS) insert magnet and low-temperature superconducting (LTS) shim coils design scheme for a 27 T NMR spectrometer is proposed in this work. A LTS background magnet was used to generate a 15 T magnetic field in the central area and the designed HTS insert magnet contributed the remaining 12 T magnetic field. The HTS insert magnet adopted notch double-pancake (DP) optimization to improve the rough magnetic field distribution in the central area to a highly-homogeneous level, and shim compensation schemes were proposed for the hybrid magnet to eliminate the inhomogeneous magnetic field components in the practical fabrication. The HTS insert magnet design had a current margin of 45.64% in terms of the perpendicular magnetic field intensity and the maximum hoop stress was reduced to 260 MPa with binding. There were in total eight shim coils, including two Nb3Sn zonal coils located between the insert magnet and the background magnet and six NbTi tesseral coils placed outside the background magnet. The magnet system will be fabricated in the near future.

Laser-induced breakdown self-reversal isotopic spectrometry for isotopic analysis of lithium

Online monitoring or in-situ isotopic analysis techniques in extreme environments are strategic tools in nuclear industry. A new optical method for performing isotopic analysis in solid samples at ambient pressure has been developed: Laser-Induced Breakdown self-Reversal Isotopic Spectrometry (LIBRIS). This method uses self-absorption of atomic or ionic resonance lines that are emitted from a non-uniform laser-induced plasma. It takes advantage of the fact that the spectral width of the absorption dip is much smaller than the spectral width of the emission line profile. Isotopic measurements were carried out on lithium samples by measuring the spectral position of the absorption dip that is shown to have a linear dependence on the 6Li isotopic abundance. Stand-off and real-time analysis can be performed without any sample preparation or pre-treatment. The effect of the laser wavelength, of the ambient gas and of the gate delay is investigated. Optimum conditions lead to a relative uncertainty of about 6% on the isotopic abundance measurement of 6Li. The influence of the spectral shifts due to Stark and Doppler effects on the performance of LIBRIS are discussed.

On the performance of wavelength meters: Part 1—consequences for medium-to-high-resolution laser spectroscopy

Present-day laser-spectroscopy experiments increasingly rely on modern commercial devices to monitor, stabilize, and scan the wavelength of their probe laser. Recently, new techniques are capable of achieving unprecedented levels of precision on atomic and nuclear observables, pushing these devices to their performance limits. Considering the fact that these observables themselves are deduced from the frequency difference between specific atomic resonances, in the order of MHz–GHz, the uncertainty on the output of the device measuring the wavelength is often directly related to the final systematic uncertainty on the experimental results. Owing to its importance, the performance of several commercial wavelength meters was compared against different reference sources, including a Scanning Fabry–Perot Interferometer (SFPI) and a frequency comb. Reproducible, wavelength- and device-dependent disagreements are observed, potentially skewing the experimental output at high precision. In this paper, a practical and relatively inexpensive wavelength meter characterization procedure is presented and validated. This method is capable of improving the precision on wavelength differences considerably depending on the device, while together with a second investigation that is published separately, (Konig et al., in Appl Phys B, 2020), it offers a full description of the expected wavelength meter performance for users.

Atomic line versus lens cavity filters: a comparison of their merits

We present a comparison between lens cavity filters and atomic line filters, discussing their relative merits for applications in quantum optics. We describe the design, characterization, and stabilization procedure of a lens cavity filter, which consists of a high-reflection coated commercially available plano-convex lens, and compare it to an ultra-narrow atomic band-pass filter utilizing the D2 absorption line in atomic rubidium vapor. We find that the cavity filter peak transmission frequency and bandwidth can be chosen arbitrarily but the transmission frequency is subject to thermal drift and the cavity needs stabilization to better than a few mK, while the atomic filter is intrinsically stable and tied to an atomic resonance frequency such that it can be used in a non-laboratory environment.

Evidence of Nonrigidity Effects in the Description of Low-Energy Anisotropic Molecular Collisions of Hydrogen Molecules with Excited Metastable Helium Atoms.

Cold collisions serve as a sensitive probe of the interaction potential. In the recent study of Klein et al. (Nature Phys.2017, 13, 35–38), the one-parameter scaling of the interaction potential was necessary to obtain agreement between theoretical and observed patterns of the orbiting resonances for excited metastable helium atoms colliding with hydrogen molecules. Here, we show that the effect of nonrigidity of the H2 molecule on the resonant structure, absent in the previous study, is critical to predict the correct positions of the resonances in that case. We have complemented the theoretical description of the interaction potential and revised reaction rate coefficients by proper inclusion of the flexibility of the molecule. The calculated reaction rate coefficients are in remarkable agreement with the experimental data without empirical adjustment of the interaction potential. We have shown that even state-of-the-art calculations of the interaction energy cannot ensure agreement with the experiment if such an important physical effect as flexibility of the interacting molecule is neglected. Our findings about the significance of the nonrigidity effects can be especially crucial in cold chemistry, where the quantum nature of molecules is pronounced.

Atom interferometry with ultracold Mg atoms: frequency standard and quantum sensors

The results of theoretical and experimental studies aimed at the creation of matter wave interferometers with Mg atoms are presented. Atom-optical interferometers based on the Ramsey-Bordé scheme are of great interest for the development of optical frequency standards. Ultracold Mg atoms are promising for the development of an optical frequency standard with relative uncertainty and long-term frequency instability at a level of 10−17 − 10−18. A long-term frequency stability of 3·10−15 is obtained at an averaging time τ = 103 s while stabilizing the frequency of a ‘clock’ laser at 457 nm (1 S 0 → 3 P 1 transition) to narrow Ramsey-Bordé resonances of Mg atoms cooled and localized in a magneto-optical trap. The measured frequency stability is determined by the stability of the measurement system based on an optical frequency comb stabilized to the optical frequency of a Yb:YAG/I2 standard. We also present the results of theoretical studies aimed at the use of Mg atom interferometers based on Bragg diffraction for quantum sensing.

A New Chlorinated Phenolic Compound From the Antarctic Lichen, Pertusaria dactylina

A new chlorinated phenolic compound, methyl-3-chloro-2-hydroxy-4-methoxy-6-pentylbenzoate (1) and 4 known compounds (2-5) were isolated from the Antarctic lichen, Pertusaria dactylina ( Pertusariaceae). The structure of the new compound was determined by means of One-dimensional and two dimensional nuclear magnetic resonance (1D and 2D NMR) and high-resolution fast atom bombardment mass spectrometry (HRFABMS) experiments. The antimicrobial activities of compounds 1 to 5 against Staphylococcus aureus and Candida albicans were evaluated. The results showed that compound 1 exhibited a weak inhibitory effect against C. albicans with an IC50 value of 67 ± 7 μg/mL.

Near-Resonant Light Scattering by a Subwavelength Ensemble of Identical Atoms.

We study theoretically the scattering of light by an ensemble of N resonant atoms in a subwavelength volume. We consider the low intensity regime so that each atom responds linearly to the field. While N noninteracting atoms would scatter N^{2} more than a single atom, we find that N interacting atoms scatter less than a single atom near resonance. In addition, the scattered power presents strong fluctuations, either from one realization to another or when varying the excitation frequency. We analyze this counterintuitive behavior in terms of collective modes resulting from the light-induced dipole-dipole interactions. We find that for small samples and sufficiently large atom number, their properties are governed only by their volume.

Frustrated orbital Feshbach resonances in a Fermi gas

The orbital Feshbach resonance (OFR) is a novel scheme for magnetically tuning the interactions in closed-shell fermionic atoms. Remarkably, unlike the Feshbach resonances in alkali atoms, the open and closed channels of the OFR are only very weakly detuned in energy. This leads to a unique effect whereby a medium in the closed channel can Pauli block, or frustrate, the two-body scattering processes. Here, we theoretically investigate the impact of frustration in the few- and many-body limits of the experimentally accessible three-dimensional $^{173}$Yb system. We find that by adding a closed-channel atom to the two-body problem, the binding energy of the ground state is significantly suppressed, and by introducing a closed-channel Fermi sea to the many-body problem, we can drive the system towards weaker fermion pairing. These results are potentially relevant to superconductivity in solid-state multiband materials, as well as to the current and continuing exploration of unconventional Fermi-gas superfluids near the OFR.