To maintain a constant growth rate in the absence of convection it is necessary to program down the temperature. Trial and error numerical computations were performed to find the first approximation for the required isothermal dissolution period, linear ramp; and polynomial temperature variation period. The linear ramp rate was limited by the specified maximum temperature gradient. The isothermal dissolution turned out to be unnecessary. The linear ramp had to be stopped before the polynomial period was begun to avoid overshooting the specified maximum growth rate. After a few hours the temperature profile approached steady state behavior.

The Vickers hardness number Hv of a typical glassy inorganic polymer, a-Se, is studied as a function of temperature with the heating rate varied as a parameter from 0.032 to 3 °C/min, over two decades. It is shown that Hv(T), as a function of temperature, goes through a sharp drop in the glass transformation region following the similar drop for the shear modulus G(T) reported previously. By defining an empirical glass transition temperature TG at the inflection point of Hv vs T behavior, the heating rate dependence of TG is examined and interpreted via the kinetic structural relaxation model of glass transformation. It is shown that over the temperature range 36–50 °C the rate of structural relaxation processes controlling the mechanical properties obeys an Arrhenius type of temperature dependence with an activation energy ∼2.75 cV/atom. Furthermore, over the temperature range accessed, the structural relaxation rate seems to follow the viscosity-temperature behavior.

Monte Carlo simulations of some typical order-disorder ferroelectrics such as TGS, NaNO2 and DKDP nanocrystals were studied using a Transverse Ising Model Hamiltonian with four-spins interactions. The microscopic parameters corresponding to this Hamiltonian were adjusted to fit the experimental polarization-temperature curves for each one of the materials in the bulk phase. Then the dependences of the ferroelectric-paraelectric phase transition temperatures, Tc, on the sizes of those crystals were studied with Monte Carlo simulations of the order-disorder system. We report a weak dependence of Tc on the size of the crystal (d) for these materials above d∼6nm. The addition of surface effects showed that the expected lowtemperature shift of Tc due to size effects, can be reverted.

The growth of crystals from solution is greatly influenced by buoyancy driven convection. In a low-g environment, convection is greatly suppressed and diffusion becomes the predominant mechanism for thermal and mass transport. An experiment to grow TGS crystals by solution technique during the orbital Spacelab III mission has been designed. Crystals are grown by a new and unique technique of extracting heat from the crystal through a sting. The cooling at the sting tip is responsible for the desired supersaturation near the growing crystal. Calculations indicate that the cooled sting technique for solution crystal growth is necessary in low-g to maintain a maximum growth rate of 1 mm/day. Results of groundbased work in support of the flight experiment are discussed.

A uranopilite from The South Alligator River, Northern Territory, Australia, has been studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) with EDAX attachment, and thermogravimetry in conjunction with evolved gas mass spectrometry. The XRD shows that the mineral is a pure uranopilite with few if any impurities. The SEM images show that the uranopilite consists of elongated crystals, up to 50μm long and 5 μm wide. Thermogravimetry combined with mass spectrometry shows that dehydration occurs at ∼31°C resulting in the formation of metauranopilite. The first dehydration step over 20–71°C corresponds to a decrease of 5.4 wt.%, equivalent to 6.076 H2O. The second dehydration step, over the temperature range 71 –162.4°C corresponds to a decrease of 4.7 wt.%, equivalent to 5.288 H2O, making a total of 11.364 moles of H2O, close to 12 H2O for uranopilite.

Dehydroxylation takes place over the temperature range 80–160°C. The loss of sulphate occurs at higher temperatures in two steps at 622 and 636°C. A mass loss also occurs at 755°C, accounted for by evolved oxygen.

Licencing procedures for the disposal of vitrified HLW require that there should be no unforeseen changes in the product properties prior to and after emplacement of the waste. Such changes could occur upon deliberate or accidental self-heating of the glass up to or even beyond the glass transformation temperature, Tg, over extended periods of time. Hence, an evaluation of the consequences of excessively high temperatures in the waste form is necessary.

Since 1996, the incidence of rickettsiosis has been increasing in Yucatán, Mexico, but recent prevalence data are lacking. This study aimed to determine exposure to the Spotted Fever Group (SFG) and Typhus Group (TG) in human serum samples suspected of tick-borne diseases (TBD) between 2015 and 2022. A total of 620 samples were analysed using indirect immunofluorescence assay (IFA) to detect IgG antibodies against SFG (Rickettsia rickettsii) and TG (Rickettsia typhi), considering a titer of ≥64 as positive. Results showed that 103 samples (17%) were positive for R. rickettsii and 145 (24%) for R. typhi, while 256 (41%) and 229 (37%) were negative, respectively. There was a cross-reaction in 244 samples (39%). Individuals with contact with vectors, such as ticks, showed significant exposure to fleas (p = 0.0010). The study suggests a high prevalence of rickettsiosis and recommends prospective studies to assess the disease burden and strengthen surveillance and prevention in Yucatán, considering factors like temperature and ecological changes.

Boulos et al. [1], derived a mathematical expression predicting the minimum time needed for a glassy system to experience fractional crystallization, not exceeding a few volume percent at temperatures lower than the glass transition temperature, T. The range of applicability of this expression is extended to include crystallization processes governed by either homogeneous or heterogeneous nucleation and by diffusion controlled one-, two-, and three-dimensional crystal growth. This study demonstrates that the Boulos et al. expression is fairly independent of the nucleation, growth habit and dimensionality of the crystallization process. Moreover, the inherent theoretical as well as experimental limitations of the technique are reviewed and discussed.

The calculation for evaluating this minimum time limit has been applied for an alkali ferrisilicate alpha-waste reference glass. It is found that, for this system, a barely observable crystallized volume fraction (less than 5 % vol) will be reached at 25°C only after storage for more than 10 years. This time period is certainly beyond the times to be considered for evaluations of geological disposal. In addition some preliminary calculations of the minimum time limit for two types of borosilicate high level waste glass forms (HLW) are presented. These indicate safe time limits of the order of 10–100 years at 450°C, suggesting that crystallization effects cannot be ignored if the assumptions made in the calculations are valid.

Intercalation of a wide variety of alkylammonium cations into the interlayer spaces of swelling clay minerals leads to many different applications, ranging from surface-charge measurements to rendering the clay compatible for the preparation of clay nanocomposites, but knowledge of the exact conformation of the intercalated organic species is still incomplete, thus preventing a full understanding of this process. The purpose of this study was to investigate the interlayer conformation of dodecyltrimethylammonium (DDTMA) bromide in rectorite as affected by the amounts of DDTMA intercalated, using a battery of physical and spectroscopic methods. The capacity of rectorite to intercalate DDTMA was equivalent to 1.67 times the cation exchange capacity (1.67 CEC) of the mineral even though the initial input was as much as 5.00 CEC. When the DDTMA intercalated was <0.50 CEC of the mineral, minimal counterion sorption was associated with DDTMA intercalation. Derivative thermogravimetric (DTG) analyses revealed a single-peak decomposition temperature (Tpeak) at 430°C. X-ray diffraction (XRD) analyses indicated a flat-lying monolayer of the intercalated molecules, while shifts in Fourier Transform infrared (FTIR) bands confirmed gauche conformation. These results suggested that cation exchange was the dominant mechanism. At the maximum intercalation, the DDTMA adopted a horizontal trilayer arrangement with mainly gauche conformation as determined by FTIR and XRD. Meanwhile a second Tpeak appeared at 255°C, similar to the Tpeak of solid DDTMA. Counterion bromide sorption accompanying DDTMA intercalation reached a capacity of 310 mmol/kg. The results indicated that van der Waals interaction was responsible for the DDTMA uptake at the amount beyond 0.50 CEC. When the amount of DDTMA intercalated was between 0.5 and 1.67 CEC, the XRD patterns showed non-integrality, i.e. the 002 reflection was split into two non-integral peaks with 2 × d002 < d001 and 3 × d003 > d001. They became integral at 1.67 CEC. The results suggest that the mineral might be composed of mixed layers of a monolayer intercalated rectorite and a trilayer intercalated rectorite, without a bilayer as intermediate, when the amount of DDTMA intercalated was between 0.5 and 1.67 CEC.

We show that every μ-constant family of isolated hypersurface singularities of type F(x, t) =f(x)+tg(x), where t is a parameter, is topologically trivial. The proof uses only the curve selection lemma, and hence, for an appropriately translated statement, also works over the reals and for some families of non-isolated singularities. Some applications to study the singularities at infinity of complex polynomials are given.

Ferroelectric triglycine sulphate crystals have been grown under the influence of an intense electric field of 6×104 V/m. Relative to crystals grown under ambient conditions (TGS) the crystals grown under the electric field (TGS-E) display a dielectric permittivity a factor of two lower. Significant differences are observed in the Curie-Weiss behavior of the ferroelectric phase, in the x-ray diffraction patterns and in the differential calorimetry measurements.

Three approaches to the construction of high-Tg polyimides and polyureas as second-order NLO materials are discussed. In the first approach, copolymerization of bismaleimides with o,o‚-diallylbisphenol-A followed by functionalization with high-β NLO chromophores using a Mitsunobu procedure yields, after poling and curing, a series of heavily crosslinked chromophoric polyimides with Tg values as high as 320°C and partially resonant χ(2) responses as high as 1.0×10-7 esu (42 pm/V at 1064 nm, 1.17 eV). In the second two approaches, copolymerization of the chromophore 4,5-bis(4‚-aminophenyl)-2-(4„- nitrophenyl)imidazole with bismaleimides or diisocyanates yields polyimides and polyureas with Tg values as high as 292°C and partially resonant χ(2)values as high as 0.62× 10-7 esu(25 pm/V at 1064 nm). It is found that careful attention to the details of curing and crosslinking during poling results in NLO- active matrices exhibiting negligible decay in ( on aging in air at 100°C for periods of 1,000-4,000 h. The imidazole based materials exhibit only about 10% χ(2) decay on aging for 100 h at 200°C under N2.

In recent years, nuclear waste management has become a fundamental issue in the nuclear energy production cycle. Tomographic Gamma Scanner (TGS) is an essential tool for nuclear waste characterization. It is crucial to rely on local support and cost effective solutions; for this reasons, we are designing our TGS system based on local technology. In this work, we present a study of different geometries and instrumentation chain parameters to design a TGS.

A set of Monte Carlo simulations were performed to evaluate energy and spatial resolution limitations of scintillator, CZT (Cadmium Zinc Telluride), and HPGe (high purity germanium) detectors. Collimator and detector geometries were studied to maximize the characteristics of the system. In this study, a phantom of 137Cs and 60Co was utilized to evaluate the overall performance of the proposed TGS system. In addition, the impact of electronic instrumentation chain and image reconstruction algorithms was taken into account.

A new material for second-order nonlinear optics was synthesized, which was a copolymer of N-phenylmaleimide, 4-isopropenylphenol and 4'-[N-ethyl-N-(4-isopropenylphenoxyethyl) amino]-4”-nitroazobenzene (PMPD). PMPD films were poled by corona-poling technique. The optical nonlinearity of poled PMPD was measured by second harmonic generation (SHG) and electro-optic (EO) effect, and it was demonstrated that this polymer had large optical nonlinearity and a very long-time stability, as was expected. These properties were thought to be sufficient enough for practical EO devices. On the other hand, from the viewpoint of the sample preparation technique, poling conditions were investigated in order to achieve the highest possible dipolar orientation. As a result, it was found that the relationship between the electric resistance of polymer film and substrate was a critical factor for corona-poling efficiency. From a simple model, it was suggested that the poled PMPD film prepared onto the glass substrate with a resistance of ˜0.8 GΩ (at 160 °C) exhibits large SHG and EO coefficients, more than ˜500 × 10−9 e.s.u (d33 at λ = 1.064 μm) and ˜70 pm/V(r33 at λ = 632.8 nm), respectively. It should be noted that this expected values are approximately twice as much as obtained under conventional corona-poling conditions.

Pyroelectric properties of triglycine sulfate (TGS) thick films, separately doped with L and D alanine were investigated. Internal bias field of about 1 kV/cm, induced by the two dopants, stabilize the polarization in the opposite direction on the ferroelectric axis. Pyroelectric current (under constant stress) was recorded with a computer controlled Keithley 6517 electrometer, crossing up and down the Curie point. A reverse external electric field was applied on doped materials during heating, crossing up the Curie point. It is shown that the pyroelectric coefficient can be increased about four times at room temperature under un optimized DC electric field applied on the pyroelectric wafer.

A maximum Al3+-substitution has been demonstrated to be 45 mole% of (M + Al) in the brucite layer of hydrotalcites. The chemical composition of the highly substituted hydrotalcites can be typically represented by [M0.55Al0.45(OH)2] [(CO3)0.225 · 0.50H2O] where M = Mg, Ni, Zn, and Co. It showed the small lattice parameters of a0 3.05–2.98 A in the hexagonal lattice, which corroborates Al3+-substitution in the brucite layer. The simultaneous thermal analyses (TG and DTA) and mass spectrometry (MS) study have been performed. The highly Al3+-substituted hydrotalcites also showed quite different isotherms for the CO2 adsorption. These materials adsorbed CO2 gas by removing water within the interlayer and showed the selectivity for CO2 adsorption: Cu–Al ∼Zn—Al < Co—Al < Mg—Al < Ni—Al. The Mg—Al and Co—Al hydrotalcite-like compounds showed a doubled amount of CO2 by removing carbonate ions within the interlayer.

The complementarity between 57Fe Mössbauer spectrometry and classical methods of powder characterizations is pointed out for determining the formula of metal-ferrite composites(Fe $_p^0$ Co $_{1-p}^0$ )a (Cox Fe $_{3-x-t}$ $\square_t$ O4). It is shown that X-ray diffraction is essential to determine the composition of the metal, while TG measurements in air give an approximate value for the metal ratio. In-fieldspectrometry is expected as the most suitable tool to determine the Fe sites occupancy, although the complex hyperfine structure might originate some misfits. The composites formulae were therefore determined by selecting the set of refined Mössbauer parameters that were in best agreement with the TG measurements. Magnetic measurements prove the validity of such an approach.

Next generation microelectronic packaging requirements are driving the need to produce increasingly lower dielectric constant materials while maintaining high thermal stability and ease of processing. Polymer candidates with exceptionally low dielectric constant (2.0-2.4), high thermal stability (degradation temperature higher than 400°C), high glass transition temperature (greater than 350°C), low water uptake (less than one percent), solubility in selected organic solvents, and low thermal expansion are all required. We have successfully synthesized and characterized several candidate polymers in an effort to address these needs.