Theories of Gravitation

This paper presents a systematic study of the theories of gravitation that have been proposed. We restrict ourselves to an investigation of the linear approximation since new connections with experiment can be expected in this order in χ only. It turns out that all theories that differ from general relativity contain a scalar field and describe gravitation by a mixture of scalar and tensor interactions. The scalar has negative energy in theories with light deflection larger than the Einstein value. As a consequence instabilities of cosmic systems and continuous creation result in this case. Furthermore, the emission of gravitational radiation with negative energy could be the energy source of the quasars. The question of the mass renormalization of the scalar is investigated. No unique answer is possible at present. Finally a new class of gravitational theories is given.     

The Kinetics of Formation of Microporous Polytriazine in Diphenyl Sulfone

This study highlights the value of nonisothermal kinetic methods in selecting temperature conditions for the isothermal preparation of microporous polymeric materials. A dicyanate ester is synthesized and the kinetics of its polymerization in diphenyl sulfone are studied by calorimetry under nonisothermal conditions. The kinetics are analyzed by a model-based approach, using the Kamal model, as well as by a model-free approach, using an advanced isoconversional method. Both approaches correctly predict the time to completion of polymerization at a given temperature. The material prepared independently at the predicted temperature is characterized by electron microscopy and CO₂ adsorption measurements and is confirmed to possess a microporous structure with a multimodal distribution of micropores with two major maxima at ~0.5 and 0.8 nm.     

New Cysteine-Containing PEG-Glycerolipid Increases the Bloodstream Circulation Time of Upconverting Nanoparticles

Upconverting nanoparticles have unique spectral and photophysical properties that make them suitable for development of theranostics for imaging and treating large and deep-seated tumors. Nanoparticles based on NaYF₄ crystals doped with lanthanides Yb³⁺ and Er³⁺ were obtained by the high-temperature decomposition of trifluoroacetates in oleic acid and 1-octadecene. Such particles have pronounced hydrophobic properties. Therefore, to obtain stable dispersions in aqueous media for the study of their properties in vivo and in vitro, the polyethylene glycol (PEG)-glycerolipids of various structures were obtained. To increase the circulation time of PEG-lipid coated nanoparticles in the bloodstream, long-chain substituents are needed to be attached to the glycerol backbone using ether bonds. To prevent nanoparticle aggregation, an L-cysteine-derived negatively charged carboxy group should be included in the lipid molecule.     

Preparation of nano-hydroxyapatite/poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactide) biocomposite microspheres

Nano-hydroxyapatite (HA)/poly(l-lactide) (PLLA) composite microspheres with relatively uniform size distribution were prepared by a solid-in-oil-in-water (s/o/w) emusion solvent evaporation method. The encapsulation of the HA nanopaticles in microshperes was significantly improved by grafting PLLA on the surface of the HA nanoparticles (p-HA) during emulsion process. This procedure gave a possibility to obtain p-HA/PLLA composite microspheres with uniform morphology and the encapsulated p-HA nanoparticle loading reached up to 40 wt% (33 wt% of pure HA) in the p-HA/PLLA composite microspheres. The microstructure of composite microspheres from core-shell to single phase changed with the variation of p-HA to PLLA ratios. p-HA/PLLA composite microspheres with the diameter range of 2–3 μm were obtained. The entrapment efficiency of p-HA in microspheres could high up to 90 wt% and that of HA was only 13 wt%. Surface and bulk characterizations of the composite microspheres were performed by measurements such as wide angle X-ray diffraction (WAXD), thermal gravimetric analysis (TGA), environmental scanning electron microscope (ESEM) and transmission electron microscopy (TEM).     

Features of the surface morphology of brass and bronze upon irradiation with a high power ion beam

The change in the morphology and surface composition of copper alloys (brass LS 59-1, bronzes BrOS 10-10 and BrAJ 9-4) upon irradiation with a high power ion beam of nanosecond duration is studied. It is shown that craters are mainly formed at the location of lead or sulfur inclusions. The reverse deposition of zinc onto the surface of brass is found. Possible mechanisms of these phenomena are considered.     

Spin-injection radiation of terahertz waves in ferromagnetic structures

We propose and discuss the mechanisms of terahertz sd exchange radiation during transmission of the spin-polarized current in a structure from a thin steel rod pressured to an ultrathin ferromagnetic film. The two mechanisms considered are quantum transitions between the quasi-Fermi levels in the film near the rod and precession of injected spins around the film magnetization.     

Polaronic origin of the isotope effect on the London penetration depth in high-temperature superconducting oxides

Direct measurements of the in-plane London penetration depth λ _L have recently been performed on high-temperature superconducting copper oxides by a new low-energy muon spin rotation technique. The results show that λ _L is isotope dependent, evidencing unconventional electron–phonon interactions as its source. The data are interpreted here in terms of polaronic effects on the single-particle energies, which leads to level shifts and exponential band narrowing. Good agreement with the experimental data is obtained.