Comprehensive Quantum Framework for Describing Retarded and Non-Retarded Molecular Interactions in External Electric Fields

We employ various quantum-mechanical approaches for studying the impact of electric fields on both nonretarded and retarded noncovalent interactions between atoms or molecules. To this end, we apply perturbative and non-perturbative methods within the frameworks of quantum mechanics (QM) as well as quantum electrodynamics (QED). In addition, to provide a transparent physical picture of the different types of resulting interactions, we employ a stochastic electrodynamic approach based on the zero-point fluctuating field. Atomic response properties are described via harmonic Drude oscillators - an efficient model system that permits an analytical solution and has been convincingly shown to yield accurate results when modeling non-retarded intermolecular interactions. The obtained intermolecular energy contributions are classified as field-induced (FI) electrostatics, FI polarization, and dispersion interactions. The interplay between these three types of interactions enables the manipulation of molecular dimer conformations by applying transversal or longitudinal electric fields along the intermolecular axis. Our framework combining four complementary theoretical approaches paves the way toward a systematic description and improved understanding of molecular interactions when molecules are subject to both external and vacuum fields.Comment: 23 pages, 10 figures; some slight improvement in comparison to the preceding versio

An Investigation into Different Power Consumption Parameters of Rushton Turbines: A Computational Survey

In the present work, the mixing process of shear thinning liquids in a six-blade Rushton turbine is studied. A finite volume based computational fluid dynamics (CFD) simulation has been carried out and the three-dimensional turbulent flow is numerically analyzed by using the Shear Stress Transport k-ω (k-ω SST) model. Shear thinning liquids were investigated and shear thinning behaviour was modelled by the Ostwald-de Waele law. The used stirred vessel has a cylindrical shape with a flat bottom and the liquid height was kept equal to the vessel diameter. Effects of the power law index and the angle of attack of the blade on power consumption have been investigated. The results show that decreasing the angle of attack from 90° to 45° not only results in an increase in the flow rate down to the bottom of the vessel, resulting in a better mixture qualification, but also reduces the power consumption of the stirring process. To verify the simulation, axial, radial and tangential velocity components were compared with other experimental data and satisfactory agreement was found

Molecular Interactions Induced by a Static Electric Field in Quantum Mechanics and Quantum Electrodynamics

By means of quantum mechanics and quantum electrodynamics applied to coupled harmonic Drude oscillators, we study the interaction between two neutral atoms or molecules subject to a uniform static electric field. Our focus is to understand the interplay between leading contributions to field-induced electrostatics/polarization and dispersion interactions, as considered within the employed Drude model for both non-retarded and retarded regimes. For the first case, we present an exact solution for two coupled oscillators obtained by diagonalizing the corresponding quantum-mechanical Hamiltonian and demonstrate that the external field can control the strength of different intermolecular interactions and relative orientations of the molecules. In the retarded regime described by quantum electrodynamics, our analysis shows that field-induced electrostatic and polarization energies remain unchanged (in isotropic and homogeneous vacuum) compared to the nonretarded case. For interacting species modeled by quantum Drude oscillators, the developed framework based on quantum mechanics and quantum electrodynamics yields the leading contributions to molecular interactions under the combined action of external and vacuum fields.Comment: 23 pages, 3 figure

Dexmedetomidine versus Fentanyl in Children Undergoing Central Venous Catheter Placement at the Pediatric Intensive Care Unit: A Randomized Double-Blind Clinical Trial

Background: The amount of sedation required for children in the pediatric intensive care unit (PICU) is a usually challenging issue. Fentanyl is a commonly used sedative in PICU, but respiratory depression limits its use. Dexmedetomidine (DEX) is an effective sedative and anesthetic agent with negligible respiratory depression and hemodynamic stability.This study was aimed to assess the effects of using DEX as a sedative in comparison to fentanyl. Methods: We conducted a randomized double-blind clinical trial on children aging 1 month to 18 years who were required central venous catheter at PICU. The patients were randomized into the DEX and fentanyl (loading dose 1 mcg/kg and 1 mcg/kg/h for continuous infusion) groups. The primary outcome was defined as the time to achieve Ramsay Sedation Scale (RSS) ≥3, along with the safety outcome. Results: A total of 55 patients were recruited for the analysis between July 7 and December 30, 2020. The two groups were comparable at baseline. There was no statistical difference in the number of patients (63% in DEX and 50% in fentanyl group p=0.39) and the time of reaching RSS≥3 (10 min for DEX and 15 min for fentanyl group p=0.098). Furthermore, the catheterization time between the two groups was not different when the agents were administered individually or with propofol (15 min for DEX and 17.5 min for fentanyl, p=0.225, and 22.5 for DEX and 30 min for fentanyl group, p=0.075 respectively); neither was the safety profile significantly different in the two groups. Conclusions: This study found that DEX as a primary sedative is non-inferior to fentanyl, and it could facilitate sedation alone or in combination with propofol

Cytotoxic Activity of Juniperus excelsa M. Bieb. Leaves Essential Oil in Breast Cancer Cell Lines

Background and objectives: Juniperus excelsa is a flowering plant that has been applied as traditional medicine for treatment of various disorders such as dysmenorrhea, bronchitis and colds, jaundice and tuberculosis. The aims of the present study were analyzing J. excelsa essential oil and investigation of its cytotoxic activity on three breast cancer cell lines.  Methods:  Juniperus excelsa leaves were collected from Dena mountains, located in the south-west of Iran. The composition of the essential oil was analyzed by gas chromatography-mass spectrometry (GC/MS). Cytotoxic activity was evaluated using MTT assay.   Results: Forty-one components, related to 99.83% of the total oil, were identified. Monoterpene hydrocarbons represented the major components of the volatile oil while α-pinene (73.27%) was the major component. The essential oil showed significant cytotoxic activity against breast cancer cell lines MCF-7 (IC50=0.084 µg/mL), MDA-MB-231 (IC50=0.090 µg/mL) and T-47D (IC50=0.124 µg/mL).  Conclusion: The analysis of J. excelsa oil revealed α-pinene and cedrol as the main compounds of the volatile oil that could justifiy its remarkable cytotoxic effect against the tested cell lines

Four-Dimensional Scaling of Dipole Polarizability in Quantum Systems

Polarizability is a key response property of physical and chemical systems, which has an impact on intermolecular interactions, spectroscopic observables, and vacuum polarization. The calculation of polarizability for quantum systems involves an infinite sum over all excited (bound and continuum) states, concealing the physical interpretation of polarization mechanisms and complicating the derivation of efficient response models. Approximate expressions for the dipole polarizability, $\alpha$, rely on different scaling laws $\alpha \propto$ $R^3$, $R^4$, or $R^7$, for various definitions of the system radius $R$. Here, we consider a range of single-particle quantum systems of varying spatial dimensionality and having qualitatively different spectra, demonstrating that their polarizability follows a universal four-dimensional scaling law $\alpha = C (4 \mu q^2/\hbar^2)L^4$, where $\mu$ and $q$ are the (effective) particle mass and charge, $C$ is a dimensionless excitation-energy ratio, and the characteristic length $L$ is defined via the $\mathcal{L}^2$-norm of the position operator. %The applicability of this unified formula is demonstrated by accurately predicting the dipole polarizability of 36 atoms and 1641 small organic~molecules. This unified formula is also applicable to many-particle systems, as shown by} accurately predicting the dipole polarizability of 36 atoms, 1641 small organic \rrr{molecules, and Bloch electrons in periodic systems.Comment: 3 figures are include

Intermolecular Interactions in Static Electric Fields Studied with Quantum Mechanics and Quantum Electrodynamics

In the present work, the interactions between neutral molecular systems subject to external static electric fields are studied. To comprehensively explore the effects of external fields on intermolecular interactions, the two most reliable frameworks in the subject, namely molecular quantum mechanics and quantum electrodynamics are employed while atomic and molecular responses are modeled using quantum Drude oscillators (QDO). In the first part of the work, the focus is to understand the interplay between dispersion and field-induced forces in two-body systems for both nonretarded and retarded ranges of inter-species distances. To identify the origin and the mechanism responsible for different field-induced interactions, a complementary approach based on classical electrodynamics with a zero-point radiation field, namely stochastic electrodynamics, is employed. The results show that neglecting higher-order contributions coming from field-induced hyperpolarizabilities of atoms, the dispersion interaction remains unchanged by the external uniform static field, for both regimes. However, using an external static field one can control the magnitude and characteristics of intermolecular interactions. The second part of the work is devoted to the extension of the study to many-body interacting systems. There, the total interaction energy in systems with many interacting atoms or molecules is obtained by extending the well-established theory of many-body dispersion (MBD) interactions to the presence of external static electric fields. Diagonalization of the Hamiltonian of the system in the nonretarded regime and in the framework of quantum mechanics yields the total energy of the interacting system in terms of the corresponding normal mode frequencies. Subtraction of the energy of the non-interacting QDOs-in-fields from the total energy of the interacting system results in the many-body interaction energy. The impact of the field-induced many-body contributions is investigated for a benzene dimer as well as for two carbyne chains. Varying the number of carbon atoms per chain demonstrates the significance of the field-induced many-body terms in the interplay between dispersion and field-induced interactions. Such contributions can be of great importance for controlling delamination and self-assembly of materials in static electric fields