34 research outputs found
Synthesis and physical properties of pyrochlore cobalt oxides Bi1.56-xCaxSb1.48Co0.96O7-δ
Abstract A new solid solution Bi1.56-xCaxSb1.48Co0.96O7-δ (0≤x≤0.3) with a pyrochlore-like structure (A2B2O7) was synthesized in air by chemical solid-state reaction. The solution crystallized in the cubic system with the Fd-3m space group. A regular decrease of the lattice parameter was observed when calcium replaced bismuth in the A site. The electric measurements showed that the electrical conductivity increased with the temperature and that high values of relative permittivity and dielectric loss were put in evidence. Measurements of magnetic susceptibility indicated a paramagnetic behavior of the samples with an effective moment included between 4.81 and 5.12 μB and at a low temperature para-ferromagnetic transition was observed for fractions x= 0.2 and 0.3
Biomolecular Filters for Improved Separation of Output Signals in Enzyme Logic Systems Applied to Biomedical Analysis
Biomolecular logic systems processing biochemical input signals and producing
"digital" outputs in the form of YES/NO were developed for analysis of
physiological conditions characteristic of liver injury, soft tissue injury and
abdominal trauma. Injury biomarkers were used as input signals for activating
the logic systems. Their normal physiological concentrations were defined as
logic-0 level, while their pathologically elevated concentrations were defined
as logic-1 values. Since the input concentrations applied as logic 0 and 1
values were not sufficiently different, the output signals being at low and
high values (0, 1 outputs) were separated with a short gap making their
discrimination difficult. Coupled enzymatic reactions functioning as a
biomolecular signal processing system with a built-in filter property were
developed. The filter process involves a partial back-conversion of the
optical-output-signal-yielding product, but only at its low concentrations,
thus allowing the proper discrimination between 0 and 1 output values
Calorimetric study of geopolymer binders based on natural pozzolan
This paper investigates the kinetics of geopolymerisation in an inorganic polymeric binder based on a natural pozzolan. The heat released by the exothermic geopolymerisation reaction process is monitored under isothermal temperature conditions, maintained in a differential scanning calorimeter using a water circulation cell. Calorimetric data are obtained isothermally at 65, 75, and 85 °C with various Na2O/Al2O3 and SiO2/Na2O molar ratios and in the presence and absence of small amounts of calcium aluminate cement (used as an efflorescence control admixture in these binder systems). The first stage of reaction, which is rapid and strongly exothermic, is shortened as the temperature increases. The total heat of reaction increases in the mixes containing calcium aluminate cement, but the apparent activation energy calculated using a pseudo-first-order reaction model is lower than without added calcium aluminate cement. At a constant overall SiO2/Na2O molar ratio, the apparent activation energy is decreased as the Na2O/Al2O3 molar ratio increases. Calcium aluminate cement, therefore, reduces the minimum energy required to initiate geopolymerisation reactions of this natural pozzolan and facilitates the progress of the reactions which lead to formation of a cementitious product
Optimization of Enzymatic Biochemical Logic for Noise Reduction and Scalability: How Many Biocomputing Gates Can Be Interconnected in a Circuit?
We report an experimental evaluation of the "input-output surface" for a
biochemical AND gate. The obtained data are modeled within the rate-equation
approach, with the aim to map out the gate function and cast it in the language
of logic variables appropriate for analysis of Boolean logic for scalability.
In order to minimize "analog" noise, we consider a theoretical approach for
determining an optimal set for the process parameters to minimize "analog"
noise amplification for gate concatenation. We establish that under optimized
conditions, presently studied biochemical gates can be concatenated for up to
order 10 processing steps. Beyond that, new paradigms for avoiding noise
build-up will have to be developed. We offer a general discussion of the ideas
and possible future challenges for both experimental and theoretical research
for advancing scalable biochemical computing
Combined effect of chemical nature of fineness of mineral powders on Portland cement hydration
This paper focuses on the influence of the chemical nature and the fineness of the fillers on the hydration process and on the compressive strength development. Four different types of fillers are considered in combination with Portland cement: quartzite filler, alumina filler, limestone filler, and silica fume. The study deals with blended mortars having a 0.45 water to powder (cement and filler) ratio with a 10% substitution of cement by filler. Quartzite fillers do not seem to accelerate the hydration process in a significant way. No positive effect is noticed on the strength development either. The presence of a fine inert alumina powder increases the rate of early hydration of Portland cement. The greater the fineness, the faster the rate of hydration heat development. This reactivity leads to an increase in the compressive strength at early age for mortar containing the finest alumina powders. In case of coarse alumina powder, no acceleration effect is obtained. Finely ground limestone (calcite) fillers promote heterogeneous nucleation of hydrates which significantly accelerates hydration. At early age, this also results in an increased mortar compressive strength in comparison with the control mortar. From the obtained results, it is clear that both chemical natures as well as fineness are important with regard to the accelerating effect of the hydration process. With increasing fineness, the accelerating effect increases. For powders with comparable fineness, it is clear that limestone powder has a more significant accelerating effect than silica fume and alumina filler. Quartzite filler seems to have no significant effect