Σe Values Research Articles

How Consistent are Publicly Reported Cytotoxicity Data? Large-Scale Statistical Analysis of the Concordance of Public Independent Cytotoxicity Measurements.

While increased attention is being paid to the impact of data quality in cell-line sensitivity and toxicology modeling, to date, no systematic study has evaluated the comparability of independent cytotoxicity measurements on a large-scale. Here, we estimate the experimental uncertainty of public cytotoxicity data from ChEMBL version 19. We applied stringent filtering criteria to assemble a curated data set comprised of pIC50 data for compound-cell line systems measured in independent laboratories. The estimated experimental uncertainty calculated was a mean unsigned error (MUE) value of 0.61-0.76, a median unsigned error (MedUE) value of 0.51-0.58, and a standard deviation of 0.76-1.00 pIC50 units. The experimental uncertainty (σE) estimated from all pairs of cytotoxicity measurements with a ΔpIC50 value lower than 2.5 was found to be 0.59-0.77 pIC50 units, and thus 21-60% and 21-26% higher than that of pKi and pIC50 data for ligand-protein data (σE =0.47-0.48 pKi units and σE =0.57-0.61 pIC50 units, respectively). The estimated σE value from the pairs of pIC50 values measured with metabolic assays was 0.98, whereas the σE value was found to be 0.69 when using the 1388 pIC50 pairs measured using exactly the same experimental setup. The maximum achievable Pearson correlation coefficient (RPearsonmax.2) of in silico models trained on cytotoxicity data from different laboratories was estimated to be 0.51-0.85, which is considerably different from the value of 1 corresponding to perfect predictions, hinting at the maximum performance one can expect also from computational cytotoxicity predictions. The lowest concordance between pairs of measurements was found for the drugs paclitaxel, methotrexate, zidovudine, and docetaxel, and for the cell lines HepG2, NCI-H460, L1210, and CCRF-CEM, hinting at particular sensitivity of those systems to experimental setups. The highest concordance was estimated for the compound-cell line system HL-60-etoposide (σE =0.70), whereas the lowest for L1210-methotrexate (σE =1.68). We found that annotation errors are responsible for the high discordance observed for some pairs of measurements, pointing out the importance of data curation when automatically extracting cytotoxicity data from public databases. Likewise, these results highlight the importance of estimating compound cytotoxicity with assays providing complementary biological information (i.e., metabolic, clonogenic and assays based on cell membrane integrity), especially when the mechanism of action of test compounds is unknown. From this analysis, guidelines can be created on the reliability of cytotoxicity data from public databases, which could ultimately prove valuable for modeling purposes, and to guide reporting of data in the literature.

(Invited) Rate-Determining Step for Oxygen Reduction Reaction on Oxide Cathode in SOFC and Its Interpretation Based on Band Energy Diagram

It is well known that the rate-determining step (RDS) of highly reactive oxide cathodes like La1-xSrxCoO3 (LSC), La1-xSrxCo1-yFeyO3 (LSCF), and Ba1-xSrxCo1-yFeyO3 (BSCF), for solid oxide fuel cells (SOFCs) is the surface reaction of oxygen reduction reaction (ORR), shown as 1/2O2(g) + Vö -> Oo + 2h, while its elementary step is still under discussion to date. The authors focus on the surface reactivity, defined as interfacial conductivity, σe, which is inverse of area-specific resistance, using dense thin film cathode. In the present study, σe was estimated using conventional triple-electrode cells composed of thin dense cathodes with additional thin surface modified layer, either polycrystalline pellet of Gd-doped CeO2 (GDC) or single crystalline yttria-stabilized zirconia (YSZ) with GDC barrier layer, and porous platinum anode. Various type of cathodes of LaCoO3 (LC) and LSC with variable (La+Sr)/Co ratios as well as pure and BaPrO3 coated PrOx, which shows stoichiometric composition of Pr6O11 at low temperatures below ≈480˚C in high oxygen pressure regime. The compact cathode films of LC/LSC with typically 500 nm thick coated with surface modification layer of 0, 10, 20 and 40nm are sputtered at RT, followed by a post heat-treatment at 600 ˚C. PrOx is selected to examine the influence of electronic band structure by comparison with LC and LSC systems, since PrOx is known as a mixed Vö and electron conductor in contrast to Vö and electron hole dominance in nonstoichiometric LC and LSCs. The measurements were made from 400 to 600˚C in pure O2 gas flow and the oxygen partial pressure (Po2) dependence of σe was examined at 600˚C from 10-2 to 1 atm. All the impedance data show three distinct semicircles in the impedance spectra, and specific types of resistance, corresponding to the electrolyte impedance, REl, middle frequency impedance, RMF, and low frequency impedance, RLF were extracted for further analyses. Although the origin of RMF is not well understood, it is reasonable to assume as the impedance that occurs out of cathode region; presumably an interfacial impedance between cathode and electrolyte. Although RMF of all the samples does not show the Po2 dependence, RLF clearly exhibits 1/2 power dependence for all the cathode materials from LC/LSC to PrOx system. The σe values of PrOx were 3-5 and 1-2 orders of magnitude lower than LSC and LC, respectively, which were greatly improved by adding merely 1nm thick surface layer of BaPrO3, presumably due to increased surface basicity. The rate equation with square root dependence of Po2 can be interpreted that the RDS is the reaction between the peroxide ion (O2 2-) adsorbed on the oxide cathode surface and Vö diffusing from cathode/electrolyte interface. Therefore, σe is proportional to the probability for bi-dentate immobile O2 2- to meet with Vö, expressed by the concentration product of [O2 2-][Vö]. Poor performance of PrOx can be attributed to a low [O2 2-] due to low basicity. The ab initio molecular dynamics were employed to observe the surface reaction of oxygen molecules on NiO with and without Vö at the surface. NiO was selected as a model system and GGA functional without spin correlation were employed. O2 molecules are adsorbed on NiO surface in step-by-step manner from mono-dentate O2 - to bi-dentate O2 2-. The increase of coordination number of O2 immediately increase the number of donated electron, maintaining one electron per coordination as average, and no further electron donation occurs without a help of Vö. Upon meeting of O2 2- and Vö, O2 2- splits and the third electron is donated to decompose O2 2- into OoX and O- ad. The observation above justify our conclusion from the experiments that the reaction between O2 2- and Vö is the RDS for ORR. A combination of O1s XAS and XPS measurements were made to estimate the electronic structure of oxide cathode materials to understand the energy level alignment between adsorbed O2 2- and cathode oxide surface. A higher EF of cathode material contributes to easy transfer of electrons, which is assumed to be represented, as a zeroth approximation, by the energy separation between EF and the maximum occupied partial DOS of O2p orbital in the valence band, ΔE, which corresponds to the basicity of the oxides. The σe for ORR observed shows excellent proportionality with ΔE, suggesting an important role of O2 2- in the cathodic ORR.

Different thermal analysis technique application in determination of fold surface-free energy

In this work, the crystallization rates and spherulitic growth rate of miscible blends of poly(vinylidene fluoride) (PVDF) and acrylic rubber (ACM) were determined using differential scanning calorimetry (DSC), real-time FTIR, and optical microscopy. FTIR results suggest that blending does not induce the creation of polymorphic crystalline forms of PVDF. SAXS data demonstrate the formation of interlamellar structure after blending. The fold surface-free energy (σe) was analyzed and compared using different thermal analysis techniques. The isothermal crystallization curves obtained using real-time FTIR and DSC explored in two different methods: t1/2 or Avrami equation. While the Avrami equation is more widespread and precise, both analytical methods gave similar free energy of folding values. However, it was found that the direct optical method of measuring spherulitic growth rate yields σe values 30–50 % lower than those obtained from the overall crystallization rate data. Conversely, the σe values were found to increase with increasing amorphous ACM phase content regardless of the analytical methods.

Crystallization of poly(ethylene oxide) with acetaminophen – A study on solubility, spherulitic growth, and morphology

A simple, sensitive, efficient, and novel method analyzing the number of spherulitic nuclei was proposed to estimate the solubility of a model drug acetaminophen (APAP) in poly(ethylene oxide) (PEO). At high crystallization temperature (323K), 10% APAP–PEO had the same low number of spherulitic nuclei as pure PEO, indicating that APAP and PEO were fully miscible. At low crystallization temperature (303K), the number of nuclei for 10% APAP–PEO was significantly higher, suggesting that APAP was oversaturated and therefore recrystallized and acted as a nucleating agent. Based on the results obtained, the solubility of APAP in PEO is possibly between the concentration of 0.1% and 1% at 303K. The spherulitic growth rate G of PEO was found to decrease with increasing APAP concentration, suggesting that APAP is most likely functioning as a chemical defect and is either rejected from or included in the PEO crystals during chain folding. APAP could possibly locate in the inter-spherulitic, inter-fibrillar, inter-lamellar, or intra-lamellar regions of PEO. At 323K, the morphology of 10% APAP–PEO is more dendritic than spherulitic with large unfilled space in between dendrites and spherulites, which is a sign of one or the combination of the four modes of segregation. An extensive spherulitic nucleation and growth kinetics study using the classical theoretical relationships, for example, the Hoffman–Lauritzen (HL) and Avrami theories, was conducted. Both microscopic and differential scanning calorimetric (DSC) analysis yielded similar values for the nucleation constant Kg as well as the fold surface free energy σe and work of chain folding q. The values of σe and q increased with APAP concentration, indicating that the chain folding of PEO was hindered by APAP.

Toward highly fluorescence and ultralow-threshold amplified spontaneous emission in ordered solid state from twin-tapered bi-1,3,4-oxadiazole derivatives

We report several influential factors for achieving high fluorescent quantum yield and low ASE threshold from twin-tapered bi-1,3,4-oxadiazole derivatives by theoretical and experimental investigations. High fluorescence of BOXD-T3 in either apolar solvents or in the aggregating states were due to increased conjugation and a co-planar structure in the excited state, a four-level photophysical cycle between ground state and excited state, and co-planar formation of a rigid backbone with the tendency for slipped stacking. High fluorescence efficiency, high kr value, high σe value, polarized and self-waveguided emissions in BOXD-T3 solution processed aligned film contributed to the ultralow ASE threshold. Extremely strong fluorescence of the microbelt-like organogel BOXD-T3 with fluorescence quantum yield of near unity was achieved. This work paves the way toward obtaining highly fluorescent and ultralow-threshold ASE in an ordered solid state from bi-1,3,4-oxadiazole derivatives.

Optical evaluation of multichannel radiative transitions originating from G45/2 level of Sm3+ in heavy-metal-gallate glasses

Conventional visible and novel infrared (IR) emissions of Sm3+ in heavy-metal-gallate glasses (Li2O–K2O–BaO–PbO–Bi2O3–Ga2O3, LKBPBG for short) with low phonon energy have been observed. Judd–Ofelt parameters Ω2 (3.00×10−20 cm2), Ω4 (5.19×10−20 cm2), and Ω6 (1.69×10−20 cm2) indicate a higher asymmetry and stronger covalent environment in the optical glasses. For the visible fluorescence bands peaked at 564, 601, 648, and 710 nm, the maximum stimulated emission cross-sections (σe) were derived to be 1.35×10−22, 9.21×10−22, 9.58×10−22, and 3.91×10−22 cm2, respectively, the values are larger than those in phosphate, oxyfluoroborate, tellurite, and calibo glasses obviously. The observed 1185 nm IR emission lies in the low-loss window of telecommunication system, and the maximum value of σe for this band was obtained to be 6.09×10−23 cm2. The characterization of multichannel radiative transitions of Sm3+ in LKBPBG glasses is beneficial in exposing its potential applications in visible and IR optoelectronic devices.

Excess conductivities of isobutyric acid + water binary mixtures near and far away from the critical temperature

The excess conductivities, σ E and excess energy of activation (ΔEσ )E of electrical conductivity have been investigated by using electrical conductivities measurements for isobutyric acid + water (IBAW) mixtures over the entire range of mole fractions at six different temperatures, both near and close to the critical temperature (0.055 < (T–T c)/K < 13.055). The results were also fitted with the Redlich–Kister equation. This system exhibited very large negative values of σE and very large positive values of (ΔEσ )E due to increased hydrogen bonding interactions and correlation length between unlike molecules in the critical region, and to very large differences between the molar volumes of the pure components at low temperatures. The activation parameters ΔHσ and ΔSσ have also been calculated, and show that the critical region has an important effect on the electrical conductivity properties.

Isothermal crystallization kinetics of modified bamboo cellulose/PCL composites

Abstract For the purpose of utilizing bamboo cellulose and providing a theoretical basis, the isothermal crystallization kinetics of modified bamboo cellulose/poly(e-caprolactone) (MBC/PCL) composites has been investigated by differential scanning calorimetry (DSC) at different crystallization temperature (Tc). The Avrami model was applied to describe the process of isothermal crystallization. According to Hoffman–Weeks theory, the values of the equilibrium melting point ( T m 0 ) increased with an increase in the content of MBC in the composites. The spherulite growth rate, the overall crystallization rate, the activation energy and folding-surface free energy (σe) of PCL/MBC composites are markedly affected by the presence of MBC. According to Avrami theory, MBC accelerates the crystallization of PCL in the composites. However, as compared to neat PCL, all the composites of PCL/MBC had the higher σe value. This indicates that there exist constraints on the mobility of the PCL chains in the interspherulitic regions due to the presence of MBC.

Thermodynamic Characterization of Polymorphs in Bulk-Crystallized Syndiotactic Polystyrene via Small/Wide-Angle X-ray Scattering and Differential Scanning Calorimetry

By means of in situ small/wide-angle X-ray scattering (SAXS/WAXS) and differential scanning calorimetry (DSC), we examined evolutions of lamellar crystal thickness for R and β crystals, respectively, in bulk-crystallized syndiotactic polystyrene (sPS) during the partial melting-reorganization process upon progressive heating up to 290 � C. For the SAXS data analysis, the Kratky-Porod approxima- tionprovestobeparticularlyhelpfulinextractingthecrystalthicknesswhenapproachingfinalmeltingwhere crystalline lamellae (near equilibration with the melt) exist in low concentrations as dispersed entities instead of in arrays. On the basis of the crystal thicknesses at elevated temperatures under solid-melt equilibration, weconstructedmeltinglinesofthetwoseparateformsintheGibbs-Thomsonphaseplane.Theextrapolated (to infinite lamellar thickness) equilibrium melting temperature Tm,R* ≈ 294 � C of the R form is moderately lower than Tm,β* ≈ 306 � C of the β form. The two melting lines intercept at a crossover temperature TQ ≈ 284 � C and crystal thickness lQ ≈ 9.6 nm, where the relative thermal stability of the two phases inverses. For crystals thicker than lQ (practically hard to reach for bulk crystallization under ambient pressure), the β form is the stable phase; for crystals thinner than lQ (the commonly accessible case), the R form is circumstantially more stable. With crystallinity-corrected values of the heat of fusion ΔHf,R ≈ 82 MJ m -3 and ΔHf,β ≈ 146 MJ m -3 obtained from a combination of DSC and WAXS results, we determined from the slope (= 2σe/ΔHf) of the melting line that basal surface energy σe,R ≈ 8.2 mJ m -2 and σe,β ≈ 26.8 mJ m -2 , which are considerably lower than those expected for tight folds, indicative of nonadjacently re-entered or loosely looped folds. The combination of lower Tm*, ΔHf, ΔSf, and σe values renders the R phase highly competitive in the rate of nucleation at low temperatures but much less so at high temperatures as compared tothe βphase.Thehigher σe,βvalueisalsoconsistentwiththeobservationthatthe βphaseismoreresponsive to externally added heterogeneous nucleation agents.

Crystallization Behavior of the Blends of Isotactic Polypropylene and Ethylene-Propylene Blocky Copolymers

Two ethylene-propylene copolymer fractions (EP90 and EP120) were separated from a polypropylene in-reactor alloy by extraction with n-octane at different temperatures. 13C-NMR shows that these two fractions have a blocky structure and WAXD reveals that both ethylene and propylene sequences in these two fractions are crystallizable. However, EP90 has higher propylene content and the average length of propylene sequences is longer. These two fractions were blended with isotactic polypropylene (PP) at various proportions, respectively, and crystallization behavior and morphology of the blends were investigated. It is found that both EP90 and EP120 are partially compatible with PP. The phase-separated domains have a nucleation effect on crystallization of PP, leading to increase in crystallization temperature and crystallinity of PP in the blends. EP90 and EP120 also affect the relative content of β crystals in an irregular way. The number of EP90-rich domains in PP/EP90 blends is larger than that of EP120-rich domains in PP/EP120 blends, but the size of EP90-rich domains is smaller, indicating that EP90 has better compatibility with PP than EP120. Spherulites are formed in all the blends. The data were analyzed with Hoffman-Lauritzen theory of crystallization regime and the free energy of the folding surface (σe) was derived. Addition of EP90 and EP120 has little effect on the transition temperature from regime II to regime III. The value of σe for the PP/EP90 blends is similar to that of neat PP, but σe of the PP/EP120 blends is a little higher than that of neat PP.

Thermodynamic investigation of the surface tension of liquid mixtures of cis-decaline with either methyl–acetate or n-pentyl–acetate in the temperature range from 283.15 to 303.15 K

Surface tensions (σ) and densities (ρ) of binary liquid mixtures of cis-decaline with either methyl–acetate (MAC) or n-pentyl–acetate (PAC) were measured over the entire composition range at the temperatures 283.15, 288.15, 298.15 and 303.15 K. The excess surface tensions (σE ) and the excess molar volumes (VE ) were calculated. The σE and VE values were fitted by the Redlich–Kister polynomial equation and the Ak coeffients as well as the standard deviations (d) between the calculated and the experimental excess parameters were derived. The σ values were further used for the calculation of the surface entropy (SS ) and the surface enthalpy (HS ) per unit surface area. The lyophobicity (β) and the surface mole fraction () of the surfactant component (either MAC or PAC) were also derived using the extended Langmuir model. The results were used for the characterisation of the molecular interactions at the surface and the bulk-phase region.

Estimation of changes in energy consumption for heat supply due to interannual temperature variability in the south of the Ukraine

The influence of low-frequency variability of average over the heating season air temperature on population demands in heat supply is considered. Based on monthly mean temperature values for the period from 1882 to 1999, standard deviations σe in distributions of energy consumption probability for heating in relative units were estimated; frequency of realization of different values of energy consumption for standard intervals was calculated. It is shown that values of σe = 9.5% are characteristic of the Ukrainian south. In the last ten-year periods, the required energy consumption for energy supply more than once exceeded the mean values by more than 2σe. A conclusion is made that designed power-generating units of the HPP (heat and power plant) and required fuel reserves for the region should be calculated based on the possible load that is 20% above average demands in fuel.

Isothermal Crystallization Behaviors of Isotactic Polypropylene Nucleated with the Third Generation Sorbitol Derivative Nucleating Agents

Differential scanning calorimetry (DSC) was used to study the isothermal crystallization kinetics of isotactic polypropylene (iPP) nucleated with a third generation sorbitol derivative l,3:2,4-bis(3,4-dimethylbenzylidene) sorbitol (DMDBS). The results show that the incorporation of DMDBS can greatly shorten crystallization half time (t1/2) and increase the crystallization rate of iPP. The Avrami exponents of both virgin iPP and iPP nucleated with DMDBS are close to 3, which indicates that the addition of the nucleating agent DMDBS doesn't change the crystallization growth patterns of iPP under isothermal conditions. The Hoffman theory is adopted to calculate the σe—interfacial free energy per unit area perpendicular to PP chains of virgin iPP and iPP nucleated with DMDBS. The result shows that the addition of DMDBS can decrease the σe value of iPP so that the nucleation rate of iPP is increased greatly.

Substrate orientation effect on potential fluctuations in multiquantum wells of GaAs∕AlGaAs

The photoluminescence (PL) technique as a function of temperature and excitation intensity was used to study the optical properties of multiquantum wells (MQWs) of GaAs∕AlxGa1−xAs grown by molecular beam epitaxy on GaAs substrates oriented in the [100], [311]A, and [311]B directions. The asymmetry presented by the PL spectra of the MQWs with an apparent exponential tail in the lower-energy side and the unusual behavior of the PL peak energy versus temperature (blueshift) at low temperatures are explained by the exciton localization in the confinement potential fluctuations of the heterostructures. The PL peak energy dependence with temperature was fitted by the expression proposed by Pässler [Phys. Status Solidi B 200, 155 (1997)] by subtracting the term σE2∕kBT, which considers the presence of potential fluctuations. It can be verified from the PL line shape, the full width at half maximum of PL spectra, the σE values obtained from the adjustment of experimental points, and the blueshift maximum values that the samples grown in the [311]A∕B directions have higher potential fluctuation amplitude than the sample grown in the [100] direction. This indicates a higher degree of the superficial corrugations for the MQWs grown in the [311] direction.

Effect of molecular weight on spherulitic growth rate of poly(ϵ‐caprolactone) and poly(ϵ‐caprolactone)‐b‐poly(ethylene glycol)

AbstractThe spherulitic growth rates of a series poly (ϵ‐caprolactone) homopolymers and poly(ϵ‐caprolactone)‐b‐ poly(ethylene glycol) (PCL‐b‐PEG) block copolymers with different molecular weights but narrow polydispersity were studied. The results show that for both PCL homopolymers and PCL‐b‐PEG block copolymers, the spherulitic growth rate first increases with molecular weight and reaches a maximum, then decreases as molecular weight increases. Crystallization temperature has greater influence on the spherulitic growth rate of polymers with higher molecular weight. Hoffman–Lauritzen theory was used to analyze spherulitic growth kinetics and the free energy of the folding surface (σe) was derived. It is found that the values of σe decrease with molecular weight at low molecular weight level and become constant for high molecular weight polymers. The chemically linked PEG block does not change the values of σe significantly. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Effect of nucleating agents on crystallization kinetics of PET

Effects of three nucleating agents concluding talc, sodium benzoate (SB) and an ionomer (Ion., Na+) on crystal- lization of poly(ethylene terephthalate) (PET) were studied by differential scanning calorimetry (DSC) and polarized opti- cal microscope (POM), the parameters of crystallization kinetics were obtained through Avrami and Ozawa equations. The fold surface free energy σe of pure PET and PET/nucleating agent blends was calculated by Hoffman-Lauritzen theory. The results indicate that the three kinds of nucleating agents increase the crystallization rate constant through promoting their nucleating effect for PET crystallization, among which SB is the best one with the same content. The crystallization mode of PET might shift from three-dimensional growth to two-dimensional growth by the addition of the nucleating agents. The values of σe of PET/nucleating agent blends are much less than that of pure PET, and PET/SB (99:1) blend has the least value of σe (18.2 mJ/m2). The conclusion based on Hoffman theory is similar to the analysis by Avrami and Ozawa equa- tions.

2.0 μm emission properties and energy transfer of Tm3+/Ho3+-codoped tellurite glass

This paper reports on spectroscopic properties and energy transfer of Tm3+/Ho3+-codoped ZnO-WO3-TeO2 glass upon excitation of 808nm diode laser. The J-O strength parameters， spontaneous emission probability and radiative lifetime of Ho3+ were calculated using Judd-Ofelt theory. The absorption cross-section and stimulated emission cross-section were also investigated. Our result indicates that the highest gain of 2.0 μm emission, which comes from 5I7 to 5I8 transition of Ho3+, might be achieved from the glass at the rare-earth ion concentration of 0.5 mol% of Tm2O3 and 0.15 mol% of Ho2O3. It is found that coefficients of the forward Tm3+→Ho3+ energy transfer is about 18 times that for the backward Tm3+←Ho3+ energy transfer. The calculated fluorescence lifetime of the 5I7 level of Ho3+ is 3.9 ms and the emission cross section of the 5I7→5I8 transition of Ho3+ exhibits a maximum of 9.15×10-21 cm2 at 2027 nm. We also found that Tm3+/Ho3+-codoped tellurite glass is a promising host material for potential 2.0 μm laser by comparing the quantum efficiencies, the values of σe×τm and gain coefficients of fluoride and heavy metal oxide glasses respectively.

Gibbs–Thomson analysis of crystalline poly(9,9-di-n-octyl-2,7-fluorene)

Based on results of small-angle X-ray scattering and differential scanning calorimetric measurements, the equilibrium melting temperature and basal surface energy (σe) of crystalline poly(9,9-di-n-octyl-2,7-fluorene) (PFO) were preliminarily estimated as ca 451.6 K and 0.084 J m−2, respectively, via Gibbs–Thomson analysis. This σe value leads to a value of 76 kJ mol−1 for the work of fold that greatly exceeds the values for typical polymers, reflecting the semi-rigid nature of the PFO backbone and consistent with the large-loop folds proposed earlier for this particular conjugated-backbone polymer. This is in strong contrast to the commonly held belief that conjugated polymers are generally too rigid to form folded-chain lamellar crystals.

An investigation of the optical properties of Nd3+ ions in alkali tellurofluorophosphate glasses

Absorption and fluorescence spectra of Nd3+-doped alkali tellurofluorophosphate glasses with molar compositions of 50(NaPO3)6+10TeO2+20AlF3+19RF+1Nd2O3 (R=Li, Na and K) have been recorded and analyzed. Judd–Ofelt analysis has been accomplished for the measured oscillator strengths to calculate different optical parameters such as Judd–Ofelt intensity parameters Ωλ (λ=2, 4 and 6), radiative transition probabilities (AR), branching ratios (βR) and radiative lifetimes (τR). In order to ascertain the efficiency of these glasses for device applications, the values of quantum efficiencies (η) and non-radiative relaxation rates (WNR) of the 4F3/2 emission level due to multiphonon relaxation is obtained from the measured and calculated lifetimes. Branching ratio calculations also indicate that the 4F3/2→4I11/2 transition has the potential for laser applications. From the measured near infrared luminescence spectra, the peak stimulated emission cross-section (σe) values were evaluated for selected laser transitions. The relatively high values of σe obtained for Nd3+ in alkali tellurofluorophosphate glasses suggest that these materials can be considered as candidates for optical device applications.

Isothermal and nonisothermal crystallization kinetics of isotactic polypropylene nucleated with substituted aromatic heterocyclic phosphate salts

AbstractThe crystallization kinetics of isotactic polypropylene (iPP) and nucleated iPP with substituted aromatic heterocyclic phosphate salts were investigated by means of a differential scanning calorimeter under isothermal and nonisothermal conditions. During isothermal crystallization, Avrami equation was used to describe the crystallization kinetics. Moreover, kinetics parameters such as the Avrami exponent n, crystallization rate constant Zt, and crystallization half‐time t1/2 were compared. The results showed that a remarkable decrease in t1/2 as well as a significant increase in overall crystallization rate was observed in the presence of monovalent salts of substituted aromatic heterocyclic phosphate, while bivalent and trivalent salts have little effect on crystallization rate of iPP. The addition of monovalent metal salts could decrease the interfacial free energy per unit area perpendicular to PP chains σe value of iPP so that the nucleation rate of iPP was increased. During nonisothermal crystallization, Caze method was used to analyze the crystallization kinetics. It also showed that monovalent metal salts had better nucleation effects than bivalent and trivalent metal salts. From the obtained Avrami exponents of iPP and nucleated iPP it could be concluded that the addition of different nucleating agents changed the crystal growth pattern of iPP. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3307–3316, 2006