Δε Values Research Articles

Thermochromic VO2-based smart radiator devices with ultralow refractive index cavities for increased performance

VO2 thermochromic coatings show great potential as the main component in smart radiator devices (SRD) for spacecraft, most notably for micro- and nano-satellites. Indeed, the inherent metal to insulator transition (MIT) of VO2 allows such a coating to act as a lightweight thermal regulator, eliminating the need for heavy and failure-prone mechanical louvers. However, spacecraft industry standards require an emissivity variation Δε of at least 60%, a value which, to our knowledge, has yet to be demonstrated. To reach and surpass this value, we first apply a modeling approach to optimize the optical properties and thicknesses of the individual constituent films of a typical SRD with the following architecture: mirror | dielectric resonant cavity | VO2. This study then highlights various possible avenues to enhance the performance of the devices, one of these being the use of an infrared transparent ultralow refractive index dielectric material for the resonant cavity. This theoretical prediction is then confirmed by the deposition of various prototype devices implementing a CaF2 cavity layer with n @ 10 μm = 1.17 and with measured values of Δε in excess of 60% for the full 3 to 25 μm wavelength range. In fact, we demonstrate a prototype device with a maximum Δε value of 66%, thus bringing this technology one step closer to implementation.

Domain contribution to the aging characteristics in BaTiO3 ceramics

The domain contribution to the aging characteristics of BaTiO3 (BTO) ceramics in a DC electric field was quantitatively investigated using microwave dielectric spectroscopy. The BTO aging effect was related to its domain size (DS): the reduction in the apparent permittivity by the DC electric field, Δε, increased with decreasing BTO DS. Inspection of the microwave dielectric spectra revealed that dipole polarization governed the overall aging effect regardless of the BTO DS, and that the ionic and electronic polarizations contributions were small. Substitutional loading of acceptor Mg2+ into the Ti4+ site decreased the BTO’s DS because defect pairs consisting of and its counterpart acted as nucleation sites for new domain walls. Magnesium-loaded BTO (Mg-BTO) had smaller Δε values (attributed to dipole polarization) than BTO for similar DS. The – defect complex effectively clamped the domain walls, thereby suppressing domain wall migration in the presence of an electric field. The measured permittivity decrease under a DC field was 423 for BTO but 246 for Mg-BTO with a similar DS, corresponding to a 41.8% improvement.

Dynamic compression-induced twins and martensite and their combined effects on the adiabatic shear behavior in a Ti-8.5Cr-1.5Sn alloy

The samples cut from the Ti-8.5Cr-1.5Sn titanium alloy were prepared to explore the combined effects of dynamic compression-induce twins and martensite on the adiabatic shear behavior. The morphologies of the deformed microstructures were examined by means of optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) observations, which revealed a high density of twins and martensite. The volume fraction of these features increased when the strain rate increased from 1000/s to 1500/s, owing to the relatively large driving force associated with twinning induced plasticity (TWIP) and transformation induced plasticity (TRIP) effects. Such phenomena resulted in an increase in the unit strain increment (induced by the unit stress increment Δε / Δσ) and the energy absorbed. At strain rates of 2000/s or higher, adiabatic shear failure occurred and the values of Δε / Δσ and the absorbed energy were far greater than that at 1500/s. The twins and martensite around the adiabatic shear bands (ASBs) were broken due to severe local deformation and subsequent dynamic recrystallization. Furthermore, the presence of twins and martensite induced (in general) bifurcation of the ASBs, which played a crucial role in the plasticity of the alloy.

Deformation of a sandstone–mudstone particle mixture induced by periodic saturation

ABSTRACTThis study focuses on the evaluation on deformation induced by periodic saturation of a sandstone–mudstone particle mixture. Two types of triaxial tests, without and with periodic saturation, were performed. The strain–stress relationships from the two types of tests indicate that the periodic saturation may induce an increment of axial strain (Δε), and the Δε values are related to the ratio of confining to atmospheric pressure (σ3/pa), stress level for periodic saturation (L), and number of periodic saturation or cycles (N). The values of Δε are increasing along logarithmic curves with increment of N value from 1 to 20, and increase along straight lines with increasing L value from 0.18 to 0.82 or σ3/pa value from 1 to 4. Based on the analyses of experimental data, a logarithmic fitting equation, which is a function of N, L, and σ3/pa, is suggested to predict the Δε value. And based on the fitting equation and simple analyses on stress state, another equation, which may be used to estimate the settlement induced by periodic saturation of a large-area foundation filled using the sandstone–mudstone particle mixture, is also suggested.

Evaluation of color stability of preshaded and liquid-shaded monolithic zirconia

Statement of problemThe effect of thermal aging on the color stability of monolithic zirconia has not been thoroughly investigated. PurposeThe purpose of this in vitro study was to evaluate the color stability before and after thermocycling of monolithic zirconia specimens, which were either preshaded or characterized in the laboratory through the assessment of color parameters L*, a*, and b*. Material and methodsA total of 80 specimens (10×10×15 mm) were prepared from zirconia disks (BruxZir) and divided into 2 groups. The first group consisted of preshaded specimens from disks 100, 200, 300, and 400, and the second group consisted of white specimens characterized before the sintering stage with coloring liquids in shades A2, B2, C2, and D2. Ten specimens of each shade were used. A double-beam ultraviolet-visible light recording spectrophotometer was used to assess the color parameters L*, a*, and b* before and after thermocycling. The color difference ΔE was calculated based on ΔΕ=[(ΔL*)2+(Δa*)2+(Δb*)2]½. The reliability of the examiner was investigated by MedCalc v12.5 software, and the tests of normality, homogeneity of variances, and 1-way ANOVA statistical analysis of variance were performed by IBM Statistics SPSS v20.0 software (α=.05). ResultsNo statistically significant ΔΕ (P>.05) was observed among the different groups after thermocycling. All ΔΕ values were below the limit of the 3.7 that an untrained observer can perceive. Only for the specimens in shades 200 and 400 was ΔΕ above 1, revealing a visible color difference, which, however, was still clinically acceptable. The L*, a*, and b* values for both liquid-shaded and preshaded zirconia specimens were not significantly affected by thermocycling. A higher color stability for laboratory-characterized compared with preshaded monolithic zirconia was observed irrespective of the color shade. ConclusionsWithin the limitations of this in vitro study, monolithic zirconia specimens of any shade, either preshaded or characterized in the laboratory, can be considered as color-stable materials after thermocycling.

In vitro combination therapy with isavuconazole against Candida spp.

Combination therapy may be an alternative therapeutic approach for difficult-to-treat Candida infections with the aim of increasing efficacy of antifungal therapy. Whether isavuconazole, an extended-spectrum triazole, possesses synergistic activity in combination therapy with echinocandins or polyenes for the treatment of invasive candidiasis has not been studied. We used Bliss independence drug interaction analysis and time-kill assays to examine the in vitro interactions of isavuconazole with amphotericin B or micafungin, an echinocandin, against strains of Candida albicans, Candida parapsilosis, Candida glabrata, Candida tropicalis, and Candida krusei. The Bliss independence-based drug interactions modeling showed that the combination of isavuconazole and micafungin resulted in synergistic interactions against C. albicans, C. parapsilosis, and C. krusei. The degree of synergy ranged from 1.8% to 16.7% (mean %ΔΕ value) with the highest synergy occurring against C. albicans (⊙SYN% = 8.8%-110%). Time-kill assays showed that the isavuconazole-micafungin combination demonstrated concentration-depended synergy against C. albicans and C. parapsilosis. The combined interaction by Bliss analysis between isavuconazole and amphotericin B was indifferent for C. albicans, C. parapsilosis, and C. tropicalis while for C. glabrata was antagonistic (-2% to -6%) and C. krusei synergistic (3.4% to 7%). The combination of isavuconazole-amphotericin B by time-kill assay was antagonistic against C. krusei and C. glabrata. Collectively, our findings demonstrate that combinations of isavuconazole and micafungin are synergistic against Candida spp., while those of isavuconazole and amphotericin B are indifferent in vitro.

RESEARCH OF THE STRESS STATE OF A MODIFIED IN-SITU CONCRETE

Purpose. The article focuses on investigation of the stress state of a modified in-situ concrete of natural hardening. Methodology. To achieve the aim, the research of the microstructure of the modified cement matrix of concrete, as well as the mechanism of structure formation of modified concrete with natural hardening was conducted; the methods for reliable evaluation of concrete strength were defined. Findings. The development of internal stresses affects the properties of concretedifferently. With an increase in temperature-shrinkage deformations in time and, thus, with increasing structural stresses in the cement sheath around the grains of the filler two opposite processes may develop: zone of plastic flow or cracking. Originality. It was established that the structural features complex of the modified concrete when the load transfer leads to the formation of extensive zones of prefracture which is able to absorb a significant amount of elastic strain energy that provides the design deformation properties of the concrete for special purposes. Ideas about the definition of the criteria of cracking modified concrete, hardening under natural conditions had further development. Practical value. The resulting equations allow to solve the problem about the minimum level of structural stress in monolithic concrete in a saturated large placeholder, as well as to assess the influence of structural stresses on the properties of concrete. In normal concrete with a relatively thin cement sheath at temperature-shrinkage deformations, high tangential and low radial tension occur. In vivo, this stress is higher as a result of higher values of Δε(τ), which is not observed in the modified concrete. In the modified concretes only tangential stresses are the greatest danger to structures. The change of shrinkage stress with time is straightforward. The total temperature-shrinkage deformations have a sawtooth graph. For modified concrete the amplitude is 48…53% less. This will allow solving a number of technological challenges in the construction of monolithic buildings.

Electrically induced anchoring transition in nematics with small or zero dielectric anisotropy

ABSTRACTThe orientational transitions induced by electrically controlled ionic modification of surface anchoring in liquid crystal cells based on the nematics with small or zero dielectric anisotropy Δε are considered. The type of director reorientation is shown to be independent of the sign of dielectric anisotropy and can be the same for the nematics with both negative and positive Δε. Besides, the orientational transition and corresponding switchable optical states do not depend on the Δε value and can be effectively realised even for the nematics with zero dielectric anisotropy.

Anticancer activities of proanthocyanidins from the plant Urceola huaitingii and their synergistic effects in combination with chemotherapeutics

Phytochemical investigation of the stem of Urceola huaitingii resulted in the isolation of nine proanthocyanidins (1–9), including a new compound (9). Their chemical structures were determined by UV, (HR) ESI-MS, 1D-, 2D-NMR, and CD spectra in combination with chemical derivatization. Determination of the absolute configuration of proanthocyanidins were discussed, which suggested that positive Δε values at 245nm can be applied to determine the absolute configuration of them. In addition, anticancer activities of proanthocyanidins (1–9) and their synergistic anticancer effects in combination with chemotherapeutics were evaluated. The results showed that some proanthocyanidins, especially compound 7 possessing two doubly interflavonoid linkages, exhibited significant synergistic anticancer effects with some chemotherapeutics in multiple cancer cell lines.

A Study on the Mechanism of Crystal Cracking in GTA Welding of Copper Plates

Crystal cracking is one of the major defects when large copper structures are joined by gas tungsten arc welding (GTA welding). In order to research the mechanism of crystal cracking, the criterion for crystal cracking formation has been optimized based on Prokhorov's theory, which shows that the interior deformation rate (Δϵ) is the main factor that leads to crystal cracking. A finite element model of thick copper plates in GTA welding based on the rigid constraint experiments has been established, and the Δϵ variation of the welds is obtained. The physical model of the tendency of crystal cracking has been established, and then the mechanism of crystal cracking has been discussed systematically by comparing the variations between Δϵ obtained from numerical simulations and the weld ductility (Pmin) obtained from hot-tension experiments within the brittle temperature range (BTR). Results show that during GTA welding, the values of Δϵ and Pmin are varied, respectively, with the temperature descending, and the tendency of crystal cracking and expansion velocity can be controlled by the value of (Δϵ − Pmin). Then experiments with the preheated temperatures of 300°C and 500°C, verified the validity of the optimized criterion of cracking.

Color match of resin composites to intact tooth structure.

The optical properties of dental restorative materials have a dramatic effect on patient esthetics, which may be compromised by the poor blending effect of composites resins at the composite-tooth interface. The objective of this study was to evaluate the color-matching ability and the blending effects of 3 different composite resins when restoring natural teeth. Three commercially available composites and 60 central incisors were used for this experiment. Each tooth was sectioned horizontally at the level of the cementum-enamel junction, and the crown was then bisected along the long axis of the tooth. One half of each tooth was restored individually with composite resin, after matching with the corresponding tooth shade. The tooth color was evaluated preoperatively and postoperatively using an intraoral spectrophotometer and a scientific spectrophotometer. Color differences were then evaluated by the CIEDE2000 color difference formula. The results showed the existence of color differences between the intact and the restored sections of the teeth. However, these differences were considered acceptable, since the ΔΕ value ranged below 3.3. The ΔE, Δa and Δb parameters showed no statistically significant differences between the groups (p>0.05). The 3 composites tested were able to mimic natural teeth and produce acceptable restorations. However, the color of the resin composites needs to be evaluated over the long term, because it is subject to alterations in the oral environment over time.

The effect of lateral fluorination on the properties of phenyl-tolane liquid crystals

Multifluorinated phenyl-tolane liquid crystals were synthesised by two steps cross-coupling reactions, and their structures were confirmed by nuclear magnetic resonance (NMR), mass spectra (MS) and infrared spectrometry (IR). All of these compounds show only nematic phase, and their melting points decrease dramatically with the introduction of lateral fluorine atom. The physical properties of the compounds were also evaluated. The extrapolated birefringence of the compounds are at the range of 0.32–0.37 at 589 nm, and the dielectric anisotropies exist between 3.1 and 20.6, and the rotational viscosities are as low as 63.7–130.7 mPa·s. With the increase of lateral fluorine substituents in the benzene ring, the Δε value increases tremendously while the clearing points, birefringence and rotational viscosity decrease. These compounds show good solubilities and are favourable to form eutectic mixtures. The effect of lateral fluorine atoms at different region of the core on the dielectric anisotropy and mesophase is also discussed.

Stereoselective synthesis and physicochemical properties of liquid-crystal compounds possessing a trans-2,5-disubstituted tetrahydropyran ring with negative dielectric anisotropy.

Three stereoselective syntheses and the physicochemical properties of trans,trans-5-(4-ethoxy-2,3-difluorophenyl)-2-(4-propylcyclohexyl)tetrahydropyran, which is an important liquid-crystal compound with a large negative dielectric anisotropy (Δε=-7.3), are described. The key step in the construction of the trans-2,5-disubstituted tetrahydropyran ring in the first approach involved a benzylic cation mediated intramolecular olefin cyclization of a 2-allyloxy-1-arylethanol derivative. The second method included the Et2 Zn-induced 1,2-aryl shift of a bromohydrin obtained from a hetero-Diels-Alder reaction, followed by stereoselective bromination. The third approach utilized the hetero-Diels-Alder reaction of trans-4-propylcyclohexanecarboxaldehyde and a 2-aryl-3-(trimethylsilyl)oxy-1,3-butadiene, followed by stereoselective protonation. From results obtained by using a quantum chemical calculation method, the reason why the target compound shows a large negative Δε value is discussed.

Variable‐emittance infrared electrochromic skins combining unique conducting polymers, ionic liquid electrolytes, microporous polymer membranes, and semiconductor/polymer coatings, for spacecraft thermal control

ABSTRACTVariable emittance (ε) is a property vital for the increasing needs in thermal control of future microspacecraft. This article describes fabrication, function, and performance of thin‐film, flexible, variable‐emittance (V‐E) electrochromic skins that use a conducting polymer/‐Au/‐microporous membrane (CP/Au/µP) base, and a new, unique ionic liquid electrolyte (IonEl). Poly(aniline‐co‐diphenyl amine) with a long‐chain polymeric dopant is used as the CP. A unique, patented device design yields no barrier between the active, electrochromic CP surface and the external environment, except for a thin, infrared‐transparent semiconductor/polymer film that lowers solar absorptance [α(s)] and protects from atomic‐O/far‐UV. Use of the IonEl requires special activation methods. Data presented show tailorable ε variations from 0.19 to 0.90, Δε values of >0.50 (which is the highest reported thus far for any functional V‐E material, to our knowledge), α(s) < 0.35, and nearly indefinite cyclability. Extended space durability testing, including calorimetric thermal vacuum and continuous light/dark cycling over >7 months under space conditions (<10−5Pa vacuum, far‐UV), show excellent durability. Other data show resistance to solar wind, atomic‐O, electrostatic discharge, and micrometeoroids. These lightweight, inexpensive, advanced polymeric materials represent the only technology that can work with micro‐ (<20 kg) and nano‐ (<2 kg) spacecraft, thus eventually allowing for much greater flexibility in their design and potentially “democratizing” the entire space industry, for example, allowing small firms to launch their own, dedicated satellites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2014,131, 40850.

<i>In Vitro</i> Evaluation of the Staining Effects of Two Intracanal Medicaments over a 3-Month Period

Aim: The aim of this study was to evaluate in vitro the tooth color alterations associated with two intracanal medicaments, calcium hydroxide and calcium hydroxide combined with aquatic solution of chlorexidine, for up to three months post-treatment. Materials & Methods: Thirty-one intact human anterior mature teeth were used. Black adhesive tape with a 4-mm diameter window was used to standardize the enamel surface intended for color analysis. After access cavity preparation, cleaning and shaping were completed with rotary nickel-titanium files. The teeth were randomly divided into two groups (n = 15), each according to the intracanal medicament used: (A) calcium hydroxide paste (UltraCalTM XSTM Ultradent Products, Inc., USA); (B) 2% chlorhexidine aquatic solution combined with pure calcium hydroxide powder. In one tooth, no medicament was placed (pilot). The enamel surfaces were colormetrically evaluated at the following time intervals: before placing the medicaments, immediately after placement, after 1 week as well as after 1, 2 and 3 months post-treatment. The CIE color parameters (L*, a*, b*) were recorded for each material and the corresponding color differences (ΔΕ) were calculated and statistically analyzed. Results: The most significant factor in tooth discoloration was the time intervals. The most important changes of the ΔΕ values were recorded after the 1st week and after the 3rd month. L* presented an overall increase in both groups, resulting in a higher lightness of the crown color. Only L* did show significant alterations during specific time intervals. Conclusions: There is no statistically significant relationship between the type of intracanal medicament and tooth color alteration. Time is statistically the most important factor affecting the discoloration ability of Ca(OH)2, either combined with chlorexidine or not. Consequently, the clinician should always take this into account before using such medicaments for a long-term treatment.

Dielectric anisotropy properties of nanostructure metal oxide semiconductor and 4-4′-n-pentylcyanobiphenyl based on nano-nematic composite systems

Dielectric anisotropy properties of SnO2, ZnO and Fe2O3 nanoparticles doped into 4-4′-n-pentylcyanobiphenyl (5CB) composite liquid crystals have been investigated. The dielectric anisotropy parameters and splay rotation coefficient of the 5CB nematic liquid crystal were improved by doping of SnO2, ZnO and Fe2O3 nanoparticles. The prepared nano-nematic composites exhibited p-type Δε at room temperature. The highest Δε value was found to be for Fe2O3 nanoparticles. The prepared nano-nematic composite systems exhibited an increase in the critical dielectric anisotropy transition frequency from 800kHz to 1MHz. The increase in Δε of the 5CB is due to the dipolar interaction between nanoparticles and liquid crystal molecules. The obtained results indicate that the new liquid crystals having high dielectric anisotropy can be prepared with the nanoparticles doping for the liquid crystal displays.

Evaluation of the effectiveness of an in-office bleaching system and the effect of potassium nitrate as a desensitizing agent

The aims of the study were to evaluate by spectrophotometer the in vivo colour changes resulting from the application of an in-office tooth bleaching system containing 28% H2O2 by light-emitting diode (LED) activation and to determine whether the application of 5% potassium nitrate 30 min before bleaching decreased tooth sensitivity. Thirty-two individuals were assigned randomly to two groups (n = 16). Group A received 5% potassium nitrate as a desensitizing agent 30 min before bleaching with 28% hydrogen peroxide activated by LED. Group B received glycerin as a placebo and the same bleaching protocol was applied. The colour of the right central incisor of each patient was measured visually and by spectrophotometer before bleaching, immediately thereafter, 15 days and 3 months later. Differences in L* a* b* values were tested with a repeated measures analysis of variance (ANOVA). Differences in ΔΕ values were tested with ANOVA statistical analysis at a 0.05 level of significance. Significant (p < 0.05) differences were detected in L*, as well as in b* values, between initial (I) and post bleaching (PB) and between initial (I) and 3 months post-op. In contrast, there was no significant difference between PB and 3 months post-op. The a* values showed no statistically significant differences among the different time points. Tooth sensitivity decreased significantly when potassium nitrate was applied. In-office bleaching system gave quantitatively stable results over a 3-month period. Tooth sensitivity was reduced significantly, when a desensitizing agent was applied 30 min before treatment, but the efficacy of bleaching decreased.

A comparative study of the mesomorphic properties of fluoro-isothiocyanated and fluorinated terphenyl liquid crystals from birefringence, static dielectric permittivity, splay elastic constant and rotational viscosity measurements

A few recently synthesized fluoro-substituted alkyl terphenyl isothiocyanates as well as three analogous fluoro-substituted terphenyl fluorides were investigated by birefringence, static dielectric permittivity, splay elastic constant and rotational viscosity measurements. The influence of the position of fluoro substituent on the physical properties was investigated. In 3,3′ and 3,5-difluoro substitution, although the fluorine atoms point in the same direction, 3,5 substitution leads to higher values of Δε, ε∥, ε⊥, Δn, no and ne than 3,3′-difluoro substitution. The figure of merit values, however, indicate that the 3,5-difluoro substituted isothiocyanated compound is a better component for mixture formulation in comparison with both the 3,3'-difluoro substituted or the 3',3,5-trifluoro substituted compound. Terphenyl isothiocyanated compounds are found to exhibit high birefringence and low rotational viscosity, which are suitable candidates for infrared applications while the fluorinated analogues are for visible applications.

Spectrophotometric analysis of coronal discolouration induced by grey and white MTA

To evaluate the specific alterations in tooth colour with white and grey MTA when used to fill pulp chambers. Forty-five fully developed, intact, mandibular third molars were sectioned 1 mm below their cemento-enamel junction (CEJ). Their pulp chambers were chemo-mechanically debrided, and the specimens were randomly assigned into three groups: Group 1-white MTA (Angelus(™)), Group 2-grey MTA (Angelus(™)) and Group 3-negative control (unfilled). During the experimental period, specimens were immersed in vials containing distilled water up to the CEJ (37±1 °C). Spectral reflectance lines were recorded by utilizing a UV-vis spectrophotometer equipped with an integration sphere in the visual spectrum, at baseline, 1 week and 1, 2 and 3 months after placement of the materials. Data were transformed into values of the CIE L*a*b* colour system, and the corresponding ΔΕ values were calculated. The results were analysed using two-way mixed anova models, whilst pairwise comparisons were conducted with Bonferroni's method at P < 0.05 level of significance. Both types of MTA induced significant decreases in L*, a* and b* values. The colour change was greater with grey MTA. Grey MTA led to clinically perceptible crown discolouration after 1 month, whilst the total colour change caused by white MTA exceeded the perceptible threshold for the human eye after 3 months. The application of both grey and white MTA formulations induced a decrease in lightness and reduction in redness and yellowness in teeth. The present findings suggest that application of grey MTA in the aesthetic zone should be avoided, whilst white MTA should be used with caution when filling pulp chambers with the materials.

Protonated Amino Acid-Induced One-Handed Helicity of Polynorbornene Having Monoaza-18-crown-6 Pendants

Upon complexation with protonated amino acids, one-handed helical polynorbornenes appended with monoaza-18-crown-6 (7a) are obtained. The cooperativity is observed as revealed by the sergeant−soldier effect and the majority rule. When sterically hindered amino acids such as phenylalanine, isovaline or proline, esters of amino acids, and aminoalcohols are used, the Δε values in CD spectra are significantly reduced. The protonated ammonium ion may form complex with a crown ether moiety whereas the carboxylic acid may form hydrogen bonding with the adjacent crown ether pendant resulting in unidirectional orientation of the pendants leading to a helical scaffold. The corresponding dimer 10 with the same isotactic stereochemistry as that of polynorbornene 7a behaves similarly to exhibit bisignate CD curve upon treatment with protonated alanine. On the other hand, polynorbornene with monoaza-15-crown-5 (7b) does not exhibit any CD response under the same conditions.