Torsion-free covers

This paper studies the existence and properties of a torsion-free cover with respect to a faithful hereditary torsion theory (T, F) of modules over a ring with unity. A direct sum of a finite number of torsion-free covers of modules is the torsion-free cover of the direct sum of the modules. The concept of aT-near homomorphism, which generalizes Enochs’ definition of a neat submodule, is introduced and studied. This allows the generalization of a result of Enochs on liftings of homomorphisms. Hereditary torsion theories for which every module has a torsion-free cover are called universally covering. If the inclusion map ofR into the appropriate quotient ringQ is a left localization in the sense of Silver, the problem of the existence of universally-covering torsion theories can be reduced to the caseR=Q. As a consequence, many sufficient conditions for a hereditary torsion theory to be universally covering are obtained. For a universally-covering hereditary torsion theory (T, F), the following conditions are equivalent: (1) the product ofF-neat homomorphisms is alwaysT-neat; (2) the product of torsion-free covers is alwaysT-neat; (3) every nonzero module inT has a nonzero socle.     

Submerged Arc Breakdown of Sulfadimethoxine (SDM) in Aqueous Solutions

Low voltage, low energy submerged pulsed arcs were used to break-down Sulfadimethoxine (SDM) contamination in aqueous solutions. The SDM concentration decreased exponentially with rate constants of 0.13–1.9 min⁻¹ during processing by pulsed arcs with a pulse repetition rate of 100 Hz, energies of 2.6–192 mJ and durations of 20, 50 and 100 μs. The electrical energy consumption was minimized with short duration pulses––1.5 kW-hr/m³ with 7.5 mJ, 20 μs pulses for 90% SDM removal.     

Synthesis, assembly, and optical properties of shape- and phase-controlled ZnSe nanostructures

Shape-, size-, and phase-controlled ZnSe nanostructures were synthesized by thermolysis of zinc acetate and selenourea using liganding solvents of octadecylamine (ODA) and trioctylphosphineoxide (TOPO) at different molar ratios. Materials synthesized in pure ODA resulted in uniform ultranarrow nanorods and nanowires of 1.3 nm in diameter. Morphological change from nanowire to spherical particle of larger diameter occurs with increasing TOPO/ODA ratio. Variation of the TOPO content in the mixed solvent also allows control of the crystallographic phase of ZnSe (wurtzite or zinc blende). The conditions and mechanisms of shape and phase control are discussed. Ultra-high-density networks of the ordered wires are achieved using the Langmuir-Blodgett technique in a single step as an essential stage on the route to ultra-high-density semiconductor nanocircuit fabrication.     

Sexual dimorphism in the human brain: evidence from neuroimaging

In recent years, more and more emphasis has been placed on the investigation of sex differences in the human brain. Noninvasive neuroimaging techniques represent an essential tool in the effort to better understand the effects of sex on both brain structure and function. In this review, we provide a comprehensive summary of the findings that were collected in human neuroimaging studies in vivo thus far: we explore sexual dimorphism in the human brain at the level of (1) brain structure, in both gray and white matter, observed by voxel-based morphometry (VBM) and diffusion tensor imaging (DTI), respectively; (2) baseline neural activity, studied using resting-state functional magnetic resonance imaging (rs-fMRI) and positron emission tomography (PET); (3) neurochemistry, visualized by means of neuroreceptor ligand PET; and (4) task-related neural activation, investigated using fMRI. Functional MRI findings from the literature are complemented by our own meta-analysis of fMRI studies on sex-specific differences in human emotional processing. Specifically, we used activation likelihood estimation (ALE) to provide a quantitative approach to mapping the consistency of neural networks involved in emotional processing across studies. The presented evidence for sex-specific differences in neural structure and function highlights the importance of modeling sex as a contributing factor in the analysis of brain-related data.     

Luminescence and structure of nanosized inclusions formed in SiO2 layers under double implantation of silicon and carbon ions

Luminescent and structural characteristics of SiO₂ layers exposed to double implantation by Si⁺ and C⁺ ions in order to synthesize nanosized silicon carbide inclusions have been investigated by the photoluminescence, electron spin resonance, transmission electron microscopy, and electron spectroscopy methods. It is shown that the irradiation of SiO₂ layers containing preliminary synthesized silicon nanocrystals by carbon ions is accompanied by quenching the nanocrystal-related photoluminescence at 700–750 nm and by the enhancement of light emission from oxygen-deficient centers in oxide in the range of 350–700 nm. Subsequent annealing at 1000 or 1100°C results in the healing of defects and, correspondingly, in the weakening of the related photoluminescence peaks and also recovers in part the photoluminescence of silicon nanocrystals if the carbon dose is less than the silicon dose and results in the intensive white luminescence if the carbon and silicon doses are equal. This luminescence is characterized by three bands at ～400, ～500, and ～625 nm, which are related to the SiC, C, and Si phase inclusions, respectively. The presence of these phases has been confirmed by electron spectroscopy, the carbon precipitates have the sp ³ bond hybridization. The nanosized amorphous inclusions in the Si⁺ + C⁺ implanted and annealed SiO₂ layer have been revealed by high-resolution transmission electron microscopy.     

Rings over which all torsion theories cogenerated by simple modules are jansian

Summary It is given a caracterization of (associative) rings (with unit element) over which all torsion theories cogenerated by simple modules are jansian. In the commutative case it is shown that such rings are finite products of local rings.

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Riassunto Vengono caratterizzati gli anelli (associativi con unità) per i quali tutte le teorie di torsione cogenerate da moduli semplici sono Jansiane. Nel caso commutativo si prova che tali anelli sono prodotti finiti di anelli locali.

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This work was written while the second author was visiting Università dell'Aquila, supported by a grant from the Consiglio Nazionale delle Ricerche.     

Frictional properties of surfactant-coated rod-shaped nanoparticles in dry and humid dodecane

We have investigated the effects of humidity (water content or activity from 0 to approximately 0.98) on the frictional properties of surfactant-coated ZnS nanoparticles of various shapes, specifically, nanorods and nanowires, dispersed in an organic solvent (dodecane). The friction coefficients were found to be sensitive to even trace amounts of water, increasing logarithmically with time after the systems were exposed to humid air, doubling after 2-4 h of exposure time to air of relative humidity approximately 98%. We also show that increasing the humidity caused noticeable effects on the interactions of the nanoparticles, increasing their adhesion and aggregation through capillary forces. These effects should be considered in the design of organic solvents containing nanoparticles with physisorbed surfactants, for example, lube oils with nanoparticles additives, particularly those exposed to atmospheric conditions.     

Adhesion and stable low friction provided by a subnanometer-thick monolayer of a natural polysaccharide

Using a surface forces apparatus, we have investigated the adhesive and lubrication forces of mica surfaces separated by a molecularly thin, subnanometer film of a high-molecular-weight (2.3 MDa) anionic polysaccharide from the algae Porphyridium sp. adsorbed from aqueous solution. The adhesion and friction forces of the confined biopolymer were monitored as a function of time, shearing distance, and driving velocity under a large range of compressive loads (pressures). Although the thickness of the dilute polysaccharide was <1 nm, the friction was low (coefficient of friction = 0.015), and no wear was ever observed even at a pressure of 110 atm over 3 decades of velocity, so long as the shearing distances were less than twice the contact diameter. Atomic force microscopy in solution shows that the biopolymer is able to adsorb to the mica surface but remains mobile and easily dragged upon shearing. The adhesion (adsorption) of this polysaccharide even to negatively charged surfaces, its stable low friction, its robustness (high-load carrying capacity and good wear protection), and the weak (logarithmic) dependence of the friction force on the sliding velocity make this class of polyelectrolytes excellent candidates for use in water-based lubricant fluids and as potential additives to synovial fluid in joints and other biolubricating fluids. The physical reasons for the remarkable tribological properties of the ultrathin polysaccharide monolayer are discussed and appear to be quite different from those of other polyelectrolytes and proteins that act as thick "polymer brush" layers.     

Interfacial characterization of chemical solution‐deposited thin films of PbSe on GaAs(100)

The microstructure and composition of the interfacial layer between chemically deposited PbSe and GaAs substrates were studied using high‐resolution transmission electron microscopy (HRTEM), Auger electron spectroscopy (AES), x‐ray photoelectron spectroscopy (XPS) and energy‐filtered TEM. The thickness of the interfacial layer varied significantly from direct contact of the film with the substrate to 5 nm in the thickest regions. The results established the presence of a discontinuous, amorphous intermediate layer of Ga₂O₃ at the PbSe/GaAs interface. Copyright © 2008 John Wiley & Sons, Ltd.