The dynamic crossover in dielectric relaxation behavior of ice Ih

© the Owner Societies 2015. The main mechanism of the dielectric relaxation process of ordinary hexagonal ice (ice Ih) and its temperature dependence remains unclear. The most interesting and as yet unexplained feature of ice is the presence of the dynamical crossover in relaxation time behavior around Tc = 230 ± 3 K. Since there are no phase transitions in the ice at this temperature (first or second order), we cannot correlate the origin of this crossover with any structural change. Here we present a model according to which the temperature of the crossover is defined by the polarization mechanism. The dielectric relaxation driven by the diffusion of L-D orientational Bjerrum defects (at high temperature, T > Tc) is transformed into a dielectric relaxation dominated by the diffusion of intrinsic ionic H3O+/OH- defects (at low temperature, T < Tc). In the framework of the model, we propose an analytical equation for the complex dielectric permittivity that takes into account the contribution of both types of defects

State of water in confinement near hydrophilic surfaces below the freezing temperature

The main goal of the research is to find a relationship between the dynamic and the structural properties of water in hydrated heterogeneous systems. The results of dielectric spectroscopy studies of hydrated matrixes of porous glasses, clays and hydrated powder of Lysozyme are presented in wide frequency and temperature intervals. It is shown that for all systems studied the low temperature relaxation process demonstrates Arrhenius kinetics and exhibits a Cole-Cole (CC) behavior. A new phenomenological approach has been recently presented (see Puzenko A, Ben Ishai P, Feldman Yu, Phys Rev Lett 105:037601, 2010) that clarifies the physical mechanism of the dipole-matrix interaction in complex systems (CS) underlying the CC behaviour. A comparison porous glass with clays helps one to understand the specific adsorbed water dynamics due to the variety in the distribution of hydration centers. © 2013 Springer Science+Business Media Dordrecht

The variety of states of adsorbed water in heterogeneous materials and their dielectric response

Whenever water interacts with another dipolar or charged entity, there exists a broadening of its dielectric relaxation peak. Often this broadening can be described by the phenomenological Cole-Cole (CC) spectral function. A new approach has been recently presented (A. Puzenko, P. Ben Ishai, and Y. Feldman, Phys. Rev. Letters 105, 037601-4 (2010)), which is based on the fractal nature of the time set of the interaction of the relaxing water dipoles with their encompassing matrix. It demonstrates a fundamental connection between the relaxation time, τ, the broadening parameter, α, and the Kirkwood-Froehlich correlation function B. The parameters B, τ and α were chosen as the coordinates of the new 3D space, wherein the evolution of the relaxation process, as a result of the variation of external macroscopic parameters (temperature, pressure etc.), will depict a trajectory. This trajectory is a result of the connection between the kinetic and the structural properties of water in the complex system. © 2013 American Institute of Physics

Dielectric relaxation of water in clay minerals

The study of confined water dynamics in clay minerals is a very important topic in aluminosilicate-surface chemistry. Aluminosilicates are among the most technologically versatile materials in industry today. Dielectric spectroscopy is a very useful method for investigating the structure and dynamics of water adsorbed on solid matrix surfaces and water in the vicinity of ions in solutions. Use of this method for the study of clay minerals has been underutilized to date, however. The main goal of the present research was to understand the relaxation mechanisms of water molecules interacting with different hydration centers in clay minerals, with a view to eventually control this interaction. Two types of natural layered aluminosilicates (clay minerals) montmorillonite with exchangeable K+, Co2+, and Ni2+ cations and kaolinite with exchangeable K+ and Ba2+ cations were examined by means of dielectric spectroscopy over wide ranges of temperature (from -121°C to +300°C) and frequency (1 Hz-1 MHz). An analysis of the experimental data is provided in terms of four distributed relaxation processes. The low-temperature relaxation was observed only in montmorillonites and could be subdivided into two processes, each related to a specific hydration center. The cooperative behavior of water at the interface was observed in the intermediate temperature region, together with a proton percolation. The dielectric properties of ice-like and confined water structures in the layered clay minerals were compared with the dielectric response observed in porous glasses. The spatial fractal dimensions of the porous aluminosilicates were calculated by two separate methods - from an analysis of the fractality found in photomicrographs and from the dielectric response

Effect of penetration enhancers on the dynamic behavior of phosphatidylcholine headgroups in liposomes

The results of a time-domain dielectric spectroscopy (TDDS) study of the effect of two skin penetration modulators on phosphatidylcholine (PC) bilayer vesicles are presented. The complex dielectric permittivity spectra of PC vesicle suspensions were described as the sum of two processes: the interfacial polarization of the bilayer and the reorientation of the zwitterionic PC headgroups in a plane approximately tangential to the bilayer surface. The influence of two additives (Azone and Transcutol) on the structure and dynamic behavior of PC headgroups of the bilayer vesicles was analyzed in terms of the interconnection of the dielectric spectra Cole-Davidson parameter, β, and the correlation factor, g, of the dielectric relaxation Kirkwood cell model. Analytically, these parameters are connected in the proposed model via the spatial distribution of headgroup dipole nonhomogeneities. In terms of the physical modulation of the polar surface phase, it appears that these additives can behave either as enhancers or as retarders. Their activity in this respect depends on the concentration of additive and temperature. © 2000 American Chemical Society

Электрон-избыточные металлoфенантроцианины – новый класс тетраазахромофорных комплексов d-элементов

Data of experimental and theoretical study (DFT method) of electron-rich metal phenanthrocyanines – new class of tetraazachromophore complexes of delements Pt2+, Pd2+, Rh3+, Cr3+, Co2+, Ni2+, Zn2+ and Cd2+ was presented. On basis of experimental data on electron absorption spectra (EAS) and quantum chemical calculations of EAS of model anion-radical 1,10-phenanthroline and electron-rich 1,10-phenanthroline complexes suggest of long-wave bands in EAS of metal phenanthrocyanines was made. Some general regularities of new metal phenanthrocyanines formation in C(sp2 )H-C(sp2 )H-coupling reactions of coordinated 1,10-phenanthrolines concerned with metal promotion and elementary electron and proton transfer processes in initialization stage of C(sp2 )H-C(sp2 )H-coupling was analysedредставлены результаты экспериментального и теоретического (методом DFT) исследования электрон-избыточных металлофенантроцианинов – нового класса тетраазахромофорных комплексов d-элементов Pt2+, Pd2+, Rh3+, Cr3+, Co2+, Ni2+, Zn2+ и Cd2+. Сделаны отнесения длинноволновых полос в ЭСП металлофенантроцианинов. Проанализированы некоторые общие закономерности образования новых металлофенантроцианинов в реакциях C(sp2 )H-C(sp2 )H-сочетания координированных 1,10-фенантролинов, связанные с металл-промотированием, а также с элементарными процессами электронного и протонного переноса на стадии инициирования C(sp2 )H-C(sp2 )H-сочетания

Burnout among surgeons before and during the SARS-CoV-2 pandemic: an international survey

Background: SARS-CoV-2 pandemic has had many significant impacts within the surgical realm, and surgeons have been obligated to reconsider almost every aspect of daily clinical practice. Methods: This is a cross-sectional study reported in compliance with the CHERRIES guidelines and conducted through an online platform from June 14th to July 15th, 2020. The primary outcome was the burden of burnout during the pandemic indicated by the validated Shirom-Melamed Burnout Measure. Results: Nine hundred fifty-four surgeons completed the survey. The median length of practice was 10&nbsp;years; 78.2% included were male with a median age of 37&nbsp;years old, 39.5% were consultants, 68.9% were general surgeons, and 55.7% were affiliated with an academic institution. Overall, there was a significant increase in the mean burnout score during the pandemic; longer years of practice and older age were significantly associated with less burnout. There were significant reductions in the median number of outpatient visits, operated cases, on-call hours, emergency visits, and research work, so, 48.2% of respondents felt that the training resources were insufficient. The majority (81.3%) of respondents reported that their hospitals were included in the management of COVID-19, 66.5% felt their roles had been minimized; 41% were asked to assist in non-surgical medical practices, and 37.6% of respondents were included in COVID-19 management. Conclusions: There was a significant burnout among trainees. Almost all aspects of clinical and research activities were affected with a significant reduction in the volume of research, outpatient clinic visits, surgical procedures, on-call hours, and emergency cases hindering the training. Trial registration: The study was registered on clicaltrials.gov "NCT04433286" on 16/06/2020

State of water in confinement near hydrophilic surfaces below the freezing temperature

The main goal of the research is to find a relationship between the dynamic and the structural properties of water in hydrated heterogeneous systems. The results of dielectric spectroscopy studies of hydrated matrixes of porous glasses, clays and hydrated powder of Lysozyme are presented in wide frequency and temperature intervals. It is shown that for all systems studied the low temperature relaxation process demonstrates Arrhenius kinetics and exhibits a Cole-Cole (CC) behavior. A new phenomenological approach has been recently presented (see Puzenko A, Ben Ishai P, Feldman Yu, Phys Rev Lett 105:037601, 2010) that clarifies the physical mechanism of the dipole-matrix interaction in complex systems (CS) underlying the CC behaviour. A comparison porous glass with clays helps one to understand the specific adsorbed water dynamics due to the variety in the distribution of hydration centers. © 2013 Springer Science+Business Media Dordrecht

State of water in confinement near hydrophilic surfaces below the freezing temperature

The main goal of the research is to find a relationship between the dynamic and the structural properties of water in hydrated heterogeneous systems. The results of dielectric spectroscopy studies of hydrated matrixes of porous glasses, clays and hydrated powder of Lysozyme are presented in wide frequency and temperature intervals. It is shown that for all systems studied the low temperature relaxation process demonstrates Arrhenius kinetics and exhibits a Cole-Cole (CC) behavior. A new phenomenological approach has been recently presented (see Puzenko A, Ben Ishai P, Feldman Yu, Phys Rev Lett 105:037601, 2010) that clarifies the physical mechanism of the dipole-matrix interaction in complex systems (CS) underlying the CC behaviour. A comparison porous glass with clays helps one to understand the specific adsorbed water dynamics due to the variety in the distribution of hydration centers. © 2013 Springer Science+Business Media Dordrecht

The dynamic crossover in dielectric relaxation behavior of ice Ih

© the Owner Societies 2015. The main mechanism of the dielectric relaxation process of ordinary hexagonal ice (ice Ih) and its temperature dependence remains unclear. The most interesting and as yet unexplained feature of ice is the presence of the dynamical crossover in relaxation time behavior around Tc = 230 ± 3 K. Since there are no phase transitions in the ice at this temperature (first or second order), we cannot correlate the origin of this crossover with any structural change. Here we present a model according to which the temperature of the crossover is defined by the polarization mechanism. The dielectric relaxation driven by the diffusion of L-D orientational Bjerrum defects (at high temperature, T > Tc) is transformed into a dielectric relaxation dominated by the diffusion of intrinsic ionic H3O+/OH- defects (at low temperature, T < Tc). In the framework of the model, we propose an analytical equation for the complex dielectric permittivity that takes into account the contribution of both types of defects