Carbon supported Pt nanoparticles with diameters ranging from 2 to 28 nm have been studied using X-ray diffraction. The unit cell parameter of synthesized Pt/C nanoparticles is always lower than that ...of bulk Pt. By decreasing the average particle size D to approximately 2 nm, the unit cell parameter a nonlinearly decreases by about 0.03 Å which corresponds to a variation of 0.7% in comparison to bulk Pt, and the size effect is predominant for sizes ranging from 2 to 10 nm. The dependence a (1/ D ) is approximated well using a straight line with a slope of −0.0555 ± 0.0067 nm −1 and an intercept of −3.9230 ± 0.0017 Å. For interpreting the obtained experimental dependence of the unit cell parameter of Pt/C nanoparticles, four different theoretical approaches such as the thermal vacancy mechanism, continuous-medium model, Laplace pressure, and bond order–length–strength correlation mechanism, were used. Comparison of the calculated dependencies, based on the above models, with the experimental ones, shows that the continuous-medium model agrees best with the experimentally found unit cell parameter dependence of our carbon supported Pt nanoparticles.
This paper presents the results of X-ray diffraction studies on a single crystal of lead zirconate titanate PbZr
0.993
Ti
0.007
O
3
in the region of existence of an intermediate ferroelectric phase. ...In addition to the known superstructure reflections of the M type
q
M
=
and the first-order satellite reflections
q
M
+ {δ, δ, δ}, unknown second-order satellites have been observed near
q
M
and near the Bragg reflections. Structural model of regular system of antiphase domains is used for diffraction calculation. The model is shown to describe the first- and second-orders satellite reflections in the vicinity of
q
M
, but it cannot explain the appearance of satellites around the main Bragg peaks. A possible origin of the system of the superstructures observed in the intermediate phase is discussed.
Electronic polarizability is an important factor in molecular interactions. In the conventional force fields such as AMBER or CHARMM, however, there is inconsistency in how the effect of electronic ...dielectric screening of Coulombic interactions, inherent for the condensed phase media, is treated. Namely, the screening appears to be accounted for via effective charges only for neutral moieties, whereas the charged residues are treated as if they were in a vacuum. As a result, the electrostatic interactions between ionized groups are exaggerated in molecular simulations by a factor of about 2. The model discussed here, MDEC (Molecular Dynamics in Electronic Continuum) provides a theoretical framework for modification of the standard nonpolarizable force fields to make them consistent with the idea of uniform electronic screening of partial atomic charges. The present theory states that the charges of ionized groups and ions should be scaled, i.e., reduced by a factor of about 0.7. In several examples, including the interaction between Na+ ions, which is of interest for ion-channel simulations, and the dynamics of an important salt bridge in cytochrome c oxidase, we compared the standard nonpolarizable MD simulations with MDEC simulations and demonstrated that the MDEC charge scaling procedure results in more accurate interactions. The inclusion of electronic screening for charged moieties is shown to result in significant changes in protein dynamics and can give rise to new qualitative results compared with the traditional nonpolarizable force fields simulations.
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•We have highlighted a simple, one-step, cost-effective route for manufacturing of the nanostructural NiO/C composite.•This method based on dispergation of Ni electrodes under pulsed ...alternating current.•The mass capacitance value of the prepared NiO/C composite as high as 1012Fg−1.
NiO/C nanocomposite was prepared directly by means a one-step electrochemical technique based on electrochemical dispergation of nickel by the alternating current. The prepared material was well characterized using different analytical techniques such as X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and N2 adsorption/desorption. The X-ray diffraction and Raman scattering investigations of the freshly prepared sample confirmed the formation of β-NiO. The morphology of synthesized NiO/C can be described as dispersed on carbon support nano-leaves consisting of tightly packed array of nanoparticles (around 10nm in diam) with length of 500–2000nm and ∼20nm thick. NiO/C composite possesses high specific surface area of 137m2g−1 and a micro–meso–macroporous structure with a distribution of the pore size from 1 to 200nm. The electrochemical properties of the nanostructured NiO/C were investigated using cyclic voltammetry (CV) and galvanostatic charge-discharge tests. The synthesized NiO/C composite exhibited pseudo-capacitive behavior with the mass capacitance value as high as 1012Fg−1 and 750Fg−1 measured from CV and discharge curves, respectively. Compared with the theoretical specific capacitance of NiO 2573Fg−1, the degree of electrochemical utilization is 97% for NiO in the synthesized NiO/C composite. The superior electrochemical performance is attributed to the hierarchically porous structure of the synthesized NiO/C, its with a high specific surface area as well as a wide pore size distribution. Considering the excellent performance and facile preparation, this NiO/C composite should have great potential for application in energy storage and conversion devices.
A technology for producing a new homogeneous Ti–20Nb–13Ta–5Zr alloy has been developed. It is shown that the alloy is single-phase with a β-Ti type crystal lattice. The alloy has the required ...mechanical properties (tensile strength of about 745 MPa). On the surface of plates and wire made of alloy, a relief of micro- and nanoscale is observed. In terms of the ability to generate reactive oxygen species and long-lived reactive protein species, the Ti–20Nb–13Ta–5Zr alloy is more preferable than nitinol. It was established that cell cultures growing on plates or wire made of Ti–20Nb–13Ta–5Zr alloy had a significant mitotic index (2%). The number of viable cells was at least 95–96% of the overall cell count. According to the results of implantation of the alloy in the form of plates or wire ring to animals, it can be concluded that the alloy is biocompatible. The morphology of the surface of the samples did not change after biological experiments. It can be assumed that the alloy Ti–20Nb–13Ta–5Zr is a material potentially suitable for medical applications.
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•Developed manufacturing technology of a new homogeneous alloy Ti–25Nb–10Ta–5Zr.•Wire and plates from the alloy have excellent physicochemical and mechanical properties.•The alloy reacts with biological fluids much worse than nitinol.•Using cell and animal models, it was shown that alloy is biocompatible.
Treatment of patients with a burn injury is a complex process involving multicomponent multidirectional intensive therapy of the majority of organs and systems damaged by thermal effects on the skin, ...alternating with repeated surgical interventions aimed at removing nonviable tissues with subsequent plastic closure of wound defects. After the recovery from the burn shock, local infectious complications are considered to be the leading problem that decelerates the process of recovery and is the main cause of lethal outcomes. Since the skin integrity is broken, microorganisms penetrate readily into the internal environment of the human organism resulting in a septic state with multiple organ failure. A widespread and often uncontrollable use of antibacterial drugs in medical practice has led to the emergence of multiple drug resistance (MDR) in microorganisms. Introduction of drugs made on the basis of bacteriophages into practice is presently becoming increasingly important. This is confirmed by the growing interest in this field of pharmacology, the development of special programs aimed at studying the processes of phage and bacterial cell interaction. This review presents the main types of bacteria pertaining to MDR pathogens, principles of their classification, and the risk factors for infecting patients. The mechanisms of the selective action of phage particles on a bacterial cell and the possibility of using phage therapy in the treatment of burn injury (experimental and clinical data) based on the analysis of foreign literature are demonstrated as well as new positive properties of phages related to the changes in the macroorganism immune status caused by the interaction with bacteriophage particles.
Earlier, using phenomenological approach, we showed that in some cases polarizable models of condensed phase systems can be reduced to nonpolarizable equivalent models with scaled charges. Examples ...of such systems include ionic liquids, TIPnP-type models of water, protein force fields, and others, where interactions and dynamics of inherently polarizable species can be accurately described by nonpolarizable models. To describe electrostatic interactions, the effective charges of simple ionic liquids are obtained by scaling the actual charges of ions by a factor of 1/√(ε(el)), which is due to electronic polarization screening effect; the scaling factor of neutral species is more complicated. Here, using several theoretical models, we examine how exactly the scaling factors appear in theory, and how, and under what conditions, polarizable Hamiltonians are reduced to nonpolarizable ones. These models allow one to trace the origin of the scaling factors, determine their values, and obtain important insights on the nature of polarizable interactions in condensed matter systems.
We studied the dynamics of photoinduced charge carriers in core/shell CdSe/CdS quantum dots (QDs) of two sizes, 2.0 and 2.9 nm, in a toluene colloid by femtosecond up-conversion spectroscopy. We ...observed the luminescence kinetics of QDs excited by 50 fs laser pulses at a wavelength of 385 nm. The modeling of experimental data showed that a 0.5 ps rise of the luminescence intensity corresponds to the process of electron thermalization. The two-exponential luminescence decay with characteristic times in the picosecond range corresponds to populating of two types of traps, which we associate with core and shell defects. Electron-hole recombination process does not affect the shape of the luminescence kinetics in the picosecond range. A comparative analysis indicates that the concentration of defects in 2.0 nm QDs is greater than that in 2.9 nm QDs, while potential wells, which charge carriers eventually escape due to thermal activation, are deeper for 2.9 nm QDs.
Employing the continuum dielectric model for electronic polarizability, we have developed a new consistent procedure for parametrization of the effective nonpolarizable potential of liquid water. The ...model explains the striking difference between the value of water dipole moment μ ≈ 3D reported in recent ab initio and experimental studies with the value μeff ≈ 2.3D typically used in the empirical potentials, such as TIP3P or SPC/E. It is shown that the consistency of the parametrization scheme can be achieved if the magnitude of the effective dipole of water is understood as a scaled value μeff = μ/√εel, where εel = 1.78 is the electronic (high-frequency) dielectric constant of water, and a new electronic polarization energy term, missing in the previous theories, is included. The new term is evaluated by using Kirkwood−Onsager theory. The new scheme is fully consistent with experimental data on enthalpy of vaporization, density, diffusion coefficient, and static dielectric constant. The new theoretical framework provides important insights into the nature of the effective parameters, which is crucial when the computational models of liquid water are used for simulations in different environments, such as proteins, or for interaction with solutes.
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