An optimized sol-gel protocol was carried out to produce an yttrium aluminum garnet (YAG) xerogel from aluminum alkoxide and an yttrium salt on a semi-pilot scale. This xerogel was successfully used ...without prior pyrolysis as a solid load with the aid of additives in the preparation of pastes. Thermal treatment of the green bodies, obtained by robocasting of the paste, led to cohesive single-phase YAG ceramics. Manufacturing ceramic pieces by additive methods will allow shaping complex forms, while the single step conversion/consolidation would simplify the technological process, reducing global energy costs. Since YAG possesses high strength and good creep behavior at high temperatures, these refractory pieces could replace the metal alloys used in turbine blades for deep space exploration. Structural, thermal and chemical characterizations were performed on xerogel powders, pastes, and YAG ceramics.
Abstract
Purpose
Bardet-Biedl syndrome (BBS) is a ciliopathy with a wide spectrum of symptoms due to primary cilia dysfunction, including genitourinary developmental anomalies as well as impaired ...reproduction, particularly in males. Primary cilia are known to be required at the following steps of reproduction function: (i) genitourinary organogenesis, (ii) in fetal firing of hypothalamo-pituitary axe, (iii) sperm flagellum structure, and (iv) first zygotic mitosis conducted by proximal sperm centriole. BBS phenotype is not fully understood.
Methods
This study explored all steps of reproduction in 11 French male patients with identified BBS mutations.
Results
BBS patients frequently presented with genitourinary malformations, such as cryptorchidism (5/11), short scrotum (5/8), and micropenis (5/8), but unexpectedly, with normal testis size (7/8). Ultrasonography highlighted epididymal cysts or agenesis of one seminal vesicle in some cases. Sexual hormones levels were normal in all patients except one. Sperm numeration was normal in 8 out of the 10 obtained samples. Five to 45% of sperm presented a progressive motility. Electron microscopy analysis of spermatozoa did not reveal any homogeneous abnormality. Moreover, a psychological approach pointed to a decreased self-confidence linked to blindness and obesity explaining why so few BBS patients express a child wish.
Conclusions
Primary cilia dysfunction in BBS impacts the embryology of the male genital tract, especially epididymis, penis, and scrotum through an insufficient fetal androgen production. However, in adults, sperm structure does not seem to be impacted. These results should be confirmed in a greater BBS patient cohort, focusing on fertility.
The aim of this study is to assess the effects of the addition of aluminum (NaAlO2) into the activating solution on the geopolymerization reactions and the characteristics of the porous network. It ...was established by liquid state NMR that the speciation of the aluminosilicate oligomers and then the mean degree of polymerization were modified by the addition of sodium aluminate in the activating solution. Time-resolved SAXS and rheology results on geopolymer pastes showed that the molar ratios Si/Al and (Si+Al)/Na2O in the activating solution play a major role in the geopolymer properties at liquid and solid state. Indeed, the geopolymer percolating network appeared sooner and the properties of the porous network were dramatically changed with the addition of the NaAlO2. On the other hand, two geopolymers having identical final chemical composition but a different activating solution composition, showed to the same setting time and the same porous network characteristics.
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Nitrogen sorption and small‐ and wide‐angle X‐ray and neutron scattering techniques were used to study the porous structure of geopolymers, inorganic polymers synthesized by reaction of a strongly ...alkaline solution and an aluminosilicate source (metakaolin). The effects of aging and the use of alkali activators (Na+, K+) of different sizes were investigated at room temperature. The influence of aging time on the microstructure of both geopolymer matrixes was verified in terms of pore volume and specific surface area. The results suggested a refinement of the porosity and therefore a reduction in the pore volume over time. Regardless of the age considered, some characteristics of the porous network such as pore size, shape and distribution depend on the alkali activator used. Whatever the technique considered, the potassium geopolymer has a greater specific surface area than the sodium geopolymer. According to the scattering results, the refinement of the porosity can be associated with, first, a densification of the solid network and, secondly, a partial closure of the porosity at the nanometre scale. The kinetics are much slower for the sodium geopolymer than for the potassium geopolymer in the six months of observation.
The objective of this work is to study the effect of the nature (potassium or a mixture of potassium and sodium) and concentration of alkali cations on the behavior of geopolymers at a high ...temperature (1150 °C). First, the physico-chemical characteristics of the different geopolymers, such as the initial viscosity, the density of the mixture and structural data (Raman spectroscopy), are presented. Then, thermal analysis, dilatometry and mercury porosity are conducted, as well as the mechanical behavior and X-ray diffraction after 1150 °C. The different formulations display different trends depending on the concentration and the nature of the alkaline cations. In comparison to the use of a potassium cation, the addition of sodium leads to an increase of the viscosity and a decrease of the onset temperature of the viscous flow. The potassium-based formulations show better behavior after treatment at high temperature (1150 °C). The improvement in the mechanical properties after thermal treatment is controlled by the different crystalline phases formed, such as leucite and anorthite.
A microstructural approach to the prediction of heat flux transport in porous geopolymers is used experimentally to understand the effects of the pore size distribution and pores connectivity to the ...transfer of the thermal flux across the porous network of geopolymers. Controlling the mix design and the concentration of porogen agent, capillary pores can be introduced into the system for a final homogeneous microstructure. The roundness of pores, their geometrical distribution, and their connectivity allow the possibility to extend the length of the pathway of the tortuous route for potential heat flux. The nonlinear relationship between tortuosity–porosity and tortuosity–thermal conductivity confirms that the volume of pores is not the only parameter affecting the heat flux transport. The results achieved in terms of homogeneous microstructure with geometric description of pore, their level of isolation, and the spatial distribution allow the prediction of the heat flux transport in environmentally friendly and sustainable porous geopolymer materials.
Dimension reduction, cost efficiency, and environmental sustainability are important factors in absorbent designs. Geopolymers represent an eco-friendly and cost-efficient solution for such ...applications, and the objective of this study is to develop new geopolymer-based composites with tailored dielectric properties. To develop such composites, different formulations based on three types of carbon and various surfactants are tested. The nonionic surfactant is preferred over the anionic surfactant. Dielectric investigations between 2 and 3.3 GHz are performed. The results reveal that the carbon content and its type (origin) have significant effects on the dielectric characteristics and less on the magnetic characteristics. Indeed, an increase in permittivity from 2 to 24 and an increase from 0.09 to 0.6 for loss tangent are shown with changes in the carbon content and type. A permittivity (ε) of 2.27 and loss (tan δ) of 0.19 are obtained for a pore size of 1.6 mm, for the carbon type with the lowest purity, and with a nonionic surfactant. Finally, it is shown that the addition of magnetite has little impact on the overall magnetic properties of the geopolymer.
Silver-Russell syndrome (SRS, OMIM 180860) is a congenital disorder characterized by severe intrauterine and postnatal growth retardation, dysmorphic facial features and body asymmetry. SRS is ...genetically heterogenous with maternal uniparental disomy with respect to chromosome 7 occurring in ∼10% of affected individuals. Given the crucial role of the 11p15 imprinted region in the control of fetal growth, we hypothesized that dysregulation of genes at 11p15 might be involved in syndromic intrauterine growth retardation. We identified an epimutation (demethylation) in the telomeric imprinting center region ICR1 of the 11p15 region in several individuals with clinically typical SRS. This epigenetic defect is associated with, and probably responsible for, relaxation of imprinting and biallelic expression of H19 and downregulation of IGF2. These findings provide new insight into the pathogenesis of SRS and strongly suggest that the 11p15 imprinted region, in addition to those of 7p11.2-p13 and 7q31-qter, is involved in SRS.
A series of N, S-substituted Titanium (IV) (diisopropoxide) bis (2,4-pentadionate) precursor were synthesized by the sol-gel method. The obtained solids were calcined at 550 deg C for two hours to ...obtain photoactive phases. A thermogravimetric analysis of the solid precipitates shows that crystallization has been almost completed at this value of calcination temperature. The samples were characterized by X-Ray diffraction (XRD), determination of the BET specific surface area and UV-Vis diffuse reflectance spectroscopy. The photocatalytic activity of the obtained catalyst was estimated on a basis of decolouration of Congo red dye under near visible light.
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