Grain shape and size and structural and phase conditions modified by aluminum ion implantation in UFG titanium

The paper presents the transmission electron microscopy investigations of the granular state and the structural and phase conditions of commercially pure ultra-fine grain (UFG) titanium VT1-0 alloyed with aluminum ions. The UFG-titanium is obtained by the multiple uniaxial compaction with intermediate annealing. The ion implantation is carried out on Mevva-V.Ru ion source at ion-implantation dosages of 1·10{17}, 5·10{17} and 1·10{18} ion/cm{2}. The functions are constructed for the grain size distribution in longitudinal and cross sections; the average grain size and the grain anisotropy factor are determined in this paper. It is shown that the grain shape and size of titanium specimens are modified due to the ion implantation. With the increase of the ion-implantation dosage the anisotropy factor decreases three times. At 1·10{18} ion/cm{2} ion-implantation dosage the longitudinal grain size comes to 0.7 [mu]m. The phase composition of the alloy is detected after the ion implantation and its modification induced by the implantation dosage. The quantitative characteristics and locations of secondary [beta]-Ti, TiAl[3], Ti[3] Al, TiC and TiO[2] phases are ascertained during the investigations. It is shown that TiAl[3] and Ti[3] Al are ordered phases formed during the ion implantation on [alpha]-Ti grain boundaries. The volume ratios of these phases are detected and determined by the ion-implantation dosage. The volume ratios of [alpha]-Ti and secondary TiC and TiO[2] phases do not depend on the implantation dosage and range between 0.3-0.9 vol.%

Central nervous system functions of PAK protein family: From spine morphogenesis to mental retardation

Several of the genes currently known to be associated, when mutated, with mental retardation, code for molecules directly involved in Rho guanosine triphosphatase (GTPase) signaling. These include PAK3, a member of the PAK protein kinase family, which are important effectors of small GTPases. In many systems, PAK kinases play crucial roles regulating complex mechanisms such as cell migration, differentiation, or survival. Their precise functions in the central nervous system remain, however, unclear. Although their activity does not seem to be required for normal brain development, several recent studies point to a possible involvement in more subtle mechanisms such as neurite outgrowth, spine morphogenesis or synapse formation, and plasticity. This article reviews this information in the light of the current knowledge available on the molecular characteristics of the different members of this family and discuss the mechanisms through which they might contribute to cognitive function

Hardening by ion implantation of VT1-0 alloy having different grain size

The paper presents a transmission electron microscopy (TEM) study of the structural and phase state of commercially pure titanium implanted by aluminum ions. TEM study has been carried out for two types of grains, namely coarse (0.4 µm) and small (0.5 µm). This paper presents details of the yield stress calculations and the analysis of strength components for the both grain types in two areas of the modified layer: at a distance of 0-150 nm (surface area I) and ∼300 nm (central area II) from the irradiated surface. It is shown that the ion implantation results in a considerable hardening of the entire thickness of the implanted layer in the both grain types. The grain size has, however, a different effect on the yield stress in areas I and II. Thus, near the ion-alloyed layer, the yield stress decreases with the increase of the grain size, whilst area II demonstrates its increase. Moreover, the contribution to the general hardening of the alloy made by certain hardening mechanisms differs from contributions made by each of these mechanisms in each certain case

The effect of aluminum ion implantation on the grain size and structure of UFG titanium

Using the transmission electron microscopy technique, we have studied the structural-phase state of UFG titanium with an average grain size ~0.2 μm implanted with aluminum ions. An MEVVA-V.RU source has been used to implant the specimen at room temperature, implantation time 5.25 hours, and irradiation dose 1⋅1018 ion/cm2. To produce the UFG titanium samples, we have employed the combined multiple uniaxial pressing technique (abc-pressing) followed by grooved rolling and subsequent annealing at 573 K for one hour. The samples have been studied in two states: 1) before implantation (initial state) and 2) after implantation at a distance 70-100 nm from the sample surface. We have obtained the aluminum concentration profile of implanted α-Ti. It has been established that the maximum concentration of aluminum is 70 at.% and the thickness of the implanted layer is 200 nm. We have determined the grain distribution functions over the grain size, calculated the grain anisotropy coefficient before and after implantation. It has been established that implantation decreases the average longitudinal and transversal sizes of α-Ti grains, and reduces the anisotropy coefficient by three times. It has been established that aluminum implantation into titanium brings about formation of a whole set of phases with different crystal lattices, namely, β-Ti, TiAl3, Ti3Al, TiC, and TiO2

Modification of structural phase state and mechanical properties of poly-grained titanium alloy implanted by aluminum ions

The paper presents TEM analysis of microstructure, phase composition, and mechanical properties of commercially pure titanium. These properties of two types of grains are compared before and after modification of titanium by aluminum ions, namely: large grains (1.4 μm) and small (0.5μm) grains. The analysis shows that ion implantation results in a considerable improvement of mechanical properties of both large and small grains throughout their implantation depth. However, with increase of the grain size, the stress in the ion-modified surface layer decreases while in the subsurface layer it increases

Influence of the grain size on the dispersion strengthening of VT1-0 alloy implanted with aluminum ions

The method of translucent diffraction electronic microscopy conducted researches of a microstructure and phase structure of a titanic alloy of VT1-0 implanted by ions of aluminum. There are two types of grains; 1) large grains (LG) with an average size of 1.4 microns and 2) the small grains (FG) with an average size of 0.5 μm. It is established that as a result of radiation the ion-alloyed layer, on the basis of α-Ti grains is formed. The sizes, form and places of localization of secondary phases (Ti3Al, Al3Ti and TiO2) depend on the size of grain of a titanic matrix. The size of dispersive hardening of σor for different type of grains on depth of the ion-alloyed layer is calculated. It is shown that in MZ the size σor is provided only with TiO2 particles, in LG – generally TiO2 particles.</jats:p

PSD-95 promotes synaptogenesis and multiinnervated spine formation through nitric oxide signaling

Postsynaptic density 95 (PSD-95) is an important regulator of synaptic structure and plasticity. However, its contribution to synapse formation and organization remains unclear. Using a combined electron microscopic, genetic, and pharmacological approach, we uncover a new mechanism through which PSD-95 regulates synaptogenesis. We find that PSD-95 overexpression affected spine morphology but also promoted the formation of multiinnervated spines (MISs) contacted by up to seven presynaptic terminals. The formation of multiple contacts was specifically prevented by deletion of the PDZ2 domain of PSD-95, which interacts with nitric oxide (NO) synthase (NOS). Similarly, PSD-95 overexpression combined with small interfering RNA–mediated down-regulation or the pharmacological blockade of NOS prevented axon differentiation into varicosities and multisynapse formation. Conversely, treatment of hippocampal slices with an NO donor or cyclic guanosine monophosphate analogue induced MISs. NOS blockade also reduced spine and synapse density in developing hippocampal cultures. These results indicate that the postsynaptic site, through an NOS–PSD-95 interaction and NO signaling, promotes synapse formation with nearby axons

Grain size effect on yield strength of titanium alloy implanted with aluminum ions

The paper presents a transmission electron microscopy (TEM) study of the microstructure and phase state of commercially pure titanium VT1-0 implanted by aluminum ions. This study has been carried out before and after the ion implantation for different grain size, i.e. 0.3 µm (ultra-fine grain condition), 1.5 µm (fine grain condition), and 17 µm (polycrystalline condition). This paper presents details of calculations and analysis of strength components of the yield stress. It is shown that the ion implantation results in a considerable hardening of the entire thickness of the implanted layer in the both grain types. The grain size has, however, a different effect on the yield stress. So, both before and after the ion implantation, the increase of the grain size leads to the decrease of the alloy hardening. Thus, hardening in ultra-fine and fine grain alloys increased by four times, while in polycrystalline alloy it increased by over six times

Anesthetics Rapidly Promote Synaptogenesis during a Critical Period of Brain Development

Experience-driven activity plays an essential role in the development of brain circuitry during critical periods of early postnatal life, a process that depends upon a dynamic balance between excitatory and inhibitory signals. Since general anesthetics are powerful pharmacological modulators of neuronal activity, an important question is whether and how these drugs can affect the development of synaptic networks. To address this issue, we examined here the impact of anesthetics on synapse growth and dynamics. We show that exposure of young rodents to anesthetics that either enhance GABAergic inhibition or block NMDA receptors rapidly induce a significant increase in dendritic spine density in the somatosensory cortex and hippocampus. This effect is developmentally regulated; it is transient but lasts for several days and is also reproduced by selective antagonists of excitatory receptors. Analyses of spine dynamics in hippocampal slice cultures reveals that this effect is mediated through an increased rate of protrusions formation, a better stabilization of newly formed spines, and leads to the formation of functional synapses. Altogether, these findings point to anesthesia as an important modulator of spine dynamics in the developing brain and suggest the existence of a homeostatic process regulating spine formation as a function of neural activity. Importantly, they also raise concern about the potential impact of these drugs on human practice, when applied during critical periods of development in infants