X‐ray diffraction and differential scanning calorimetry studies of a BaTiO3/polyvinylidene fluoride composites

Barium titanate/polyvinylidene fluoride (BaTiO₃)_x (PVDF)_100–x composite samples were prepared and characterized using X‐ray diffraction (XRD) and differential scanning calorimetry (DSC) techniques. In this work, the ratio of the constituents of this composite was altered, and the structural and thermal changes were studied. Also, the variation of tetragonality of BaTiO₃ (BT) in the composite samples as a function of BT content was studied for the first time. The results show that all the samples are in the α‐phase, and the hindrance to the PVDF crystallization increases with the increase of BaTiO₃ (BT) ratio in the composite. Tetragonal distortion of BT nanoparticles in the composite increases with the increase in BT ratio up to 30%, where it gets a saturation value. Also, it seems that stretching the samples enhances the BT tetragonality. Both melting and crystallization behaviors of the composite samples show double‐melting endotherms (reorganization) and crystallization exotherms. The inclusion of BT in the composite samples results in a decrease in the melting temperature of the samples. POLYM. ENG. SCI., 52:1945–1950, 2012. © 2012 Society of Plastics Engineers     

Crystallization kinetics of poly (L‐lactic acid)/montmorillonite nanocomposites under isothermal crystallization condition

Poly(L ‐lactic acid)/o‐MMT nanocomposites, incorporating various amounts of organically modified montmorillonite (o‐MMT; 0–10 wt %), were prepared by solution intercalation. The montmorillonite (MMT) was organically modified with dilauryl dimethyl ammonium bromide (DDAB) by ion exchange. Transmission electron microscopy (TEM) and X‐ray diffraction (XRD) reveal that the o‐MMT was exfoliated in a poly(L ‐lactic acid), (PLLA) matrix. A series of the test specimens were prepared and subjected to isothermal crystallization at various temperatures (T₁–T₅). The DSC plots revealed that the PLLA/o‐MMT nanocomposites that were prepared under nonisothermal conditions exhibited an obvious crystallization peak and recrystallization, but neat PLLA exhibited neither. The PLLA/o‐MMT nanocomposites (2–10 wt %) yielded two endothermic peaks only under isothermal conditions at low temperature (T₁), and the intensity of Tm₂ (the higher melting point) was proportional to the o‐MMT content (at around 171°C). The melting point of the test samples increased with the isothermal crystallization temperature. In the Avrami equation, the constant of the crystallization rate (k) was inversely proportional to the isothermal crystallization temperature and increased with the o‐MMT content, especially at low temperature (T₁). The Avrami exponent (n) of the PLLA/o‐MMT nanocomposites (4–10 wt %) was 2.61–3.56 higher than that of neat PLLA, 2.10–2.56, revealing that crystallization occurred in three dimensions. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Differential scanning calorimetric analysis of edible oils: Comparison of thermal properties and chemical composition

The thermal profiles of 17 edible oil samples from different plant origins were examined by differential scanning calorimetry (DSC). Two other confirmatory analytical techniques, namely gas-liquid chromatography (GLC) and high-performance liquid chromatography (HPLC), were used to determine fatty acid (FA) and triacylglycerol (TAG) compositions. The FA and TAG compositions were used to complement the DSC data. Iodine value (IV) analysis was carried out to measure the degree of unsaturation in these oil samples. The DSC melting and crystallization curves of the oil samples are reported. The contrasting DSC thermal curves provide a way of distinguishing among these oil samples. Generally, the oil samples with a high degree of saturation (IV<65) showed DSC melting and crystallization profiles at higher temperature regions than the oil samples with high degree of unsaturation (IV>65). Each thermal curve was used to determine three DSC parameters, namely, onset temperature (T _o ), offset temperature (T _f ) and temperature range (difference between T _o and T _f ). Reproducibility of DSC curves was evaluated based on these parameters. Satisfactory reproducibility was achieved for quantitation of these DSC parameters. The results show that T _o of the crystallization curve and T _f of the melting curve differed significantly (P<0.01) in all oil samples. Our observations strengthen the premise that DSC is an efficient and accurate method for characterizing edible oils.     

Synthesis and characterization of poly(ethylene‐co‐trimethylene terephthalate)s

Taking advantage of a melt polycondensation process, a series of copolyesters composed of pure terephthalate acid (PTA), ethylene glycol (EG), and 1,3‐propanediol (1,3‐PDO) were synthesized. The component, molecular weight, molecular weight distribution, and thermal properties of the copolymers were characterized. The results show that the contents of trimethylene terephthalate (TT) units in the resulting copolyesters are higher than PDO compositions in original diol. Oligomer content in the copolyesters varies with the compositions and attains a minimum value when the TT ingredient is 49.52 mol %. The glass transition temperature (T_g) of the copolyesters varies from 78.5°C for PET (polyethylene terephthalate) to 43.5°C for PTT (polytrimethylene terephthalate) and decreases monotonically with the components. The copolyesters are amorphous copolymers when TT content is in the range of 32.4–40.8 mol %, as calculated from the melting enthalpy (ΔH_m) measured via differential scanning calorimetry. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1511–1521 2006     

Temperature changes in poly(methyl methacrylate) and high-density polyethylene during rapid compressive deformation

The adiabatic temperature changes for poly(methyl methacrylate) (PMMA) and high-density polyethylene are reported as the result of rapid compressive stress applications at different temperatures. A specially-modified Instron capillary rheometer was used in the experiments. Results were examined by determining the experimental thermoelastic coefficients (δT/δ). These were compared with the predicted coefficients from the equation (δT/δ) = ∝_LT_o/ρC_p. Good agreement was found for ambient temperature, and deviations were found for higher temperatures. High-density polyethylene showed higher temperature changes than PMMA, the causes for which are also discussed.     

The glass transition,crystallization, and melting characteristics of a class of polyester ionomers

The glass transition temperature (T_g), crystallization, and melting character of a class of random polyester ionomers (polymer containing < 10 mol % ionic groups) were investigated. The nonlinear change of the T_g and crystallization and melting behavior were characterized using differential scanning colorimetry (DSC). The ionomers are derived from polyethylene terephathalate (PET) modified through copolycondensation with a fully neutralized sulfonate moiety (sodiosulfo) isophthalate (Na‐SIP). Significant and systematic changes in the glass transition temperature and thermal characteristics upon addition of Na‐SIP on the PET backbone were observed, indicating strong association and interaction on the ionic species. At Na‐SIP levels ≥ 4 mol %, the turn of the the glass transition temperature was found, and the same results were obtained for the samples treated either by quenching or dissolution, suggesting the presence of reversible crosslink and aggregation of the ionic species within the organic matrix. When crystallized from the healing or cooling the samples during the DSC nonisothermal crystallization run at a 10°C/min, the enthalpy of the cold crystallization and melting showed an obvious decrease with the increase of Na‐SIP content, and changes of the crystal temperature had an analogy to those of the T_g. A tune of the crystal temperature was found at Na‐SIP levels ≥ 3 mol % (see Figs. 4 , 5 , and 7 ). The experimental data were discussed in the context of the restricted mobility model of the aggregation in the ionomers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3660–3666, 2002     

Thermally treated low density polyethylene biodegradation by Penicillium pinophilum and Aspergillus niger

Differential scanning calorimetry (DSC), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to determine morphological, structural and surface changes (biodegradation) on thermo‐oxidized (80°C, 15 days) low‐density polyethylene (TO‐LDPE) incubated with Aspergillus niger and Penicillium pinophilum fungi, with and without ethanol as cosubstrate for 31 months. TO‐LDPE mineralization by fungi was also evaluated. Significantly morphological and structural final changes on biologically treated TO‐LDPE samples were observed. Decreases to three units on crystallinity and crystalline lamellar thickness (0.4–1.8 Å), and increases in small‐crystals content (up to 3.2%) and mean crystallite size (8.4–14 Å) were registered. An oxidation decrease (almost twice) on samples without ethanol with respect to the control was observed, while in those with ethanol it was increased (up to 2.5 times). Double bond index increased more than twice from 21 to 31 months. The higher TO‐LDPE changes and fungi‐LDPE interaction was observed in samples with ethanol, suggesting that ethanol favors the TO‐LDPE biodegradation, at least in case of P. pinophilum, probably by means of a cometabolic process. Mineralization of 0.50 % and 0.57 % for A. niger, and of 0.64 % and 0.37 % for P. pinophilum were obtained, for samples with and without ethanol, respectively. A model to explain morphological and structural changes on biologically treated TO‐LDPE is also proposed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 305–314, 2002     

Thermal properties and morphology of noncrosslinking linear low‐density polyethylene‐grafted acrylic acid

Noncrosslinking linear low‐density polyethylene‐grafted acrylic acid (LLDPE‐g‐AA) was prepared by melt‐reactive extrusion in our laboratory. The thermal behavior of LLDPE‐g‐AA was investigated by using differential scanning calorimetry (DSC). Compared with neat linear low‐density polyethylene (LLDPE), melting temperature (T_m) of LLDPE‐g‐AA increased a little, the crystallization temperature (T_c) increased about 4°C, and the melting enthalpy (ΔH_m) decreased with an increase in acrylic acid content. Isothermal crystallization kinetics of LLDPE and LLDPE‐g‐AA samples were carried out by using DSC. The overall crystallization rate of LLDPE was smaller than that of grafted samples. It showed that the grafted acrylic acid monomer onto LLDPE acted as a nucleating agent. Crystal morphologies of LLDPE‐g‐AA and LLDPE were examined by using SEM. Spherulite sizes of LLDPE‐g‐AA samples were lower than that of LLDPE. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2626–2630, 2002     

The influence of acrylic acid groups on the microstructure of HDPE/BT system studied by positron annihilation

Two types of composites, high‐density polyethylene (HDPE)/Bentonite (BT) and high‐density polyethylene grafted with acrylic acid (HDPE‐g‐AA)/(BT), are prepared by melt compounding. The microstructure of the composite has been studied by the means of positron annihilation lifetime spectroscopy (PALS). It has been found that the mean free volume size is nearly the same in composites and HDPE matrices with different BT concentration. While the ortho‐positronium (o‐Ps) intensity decreased for HDPE‐g‐AA and its lifetime distribution is narrower than that for pure HDPE. With the increasing of BT content, the o‐Ps intensity increases for HDPE‐g‐AA/BT composites and the o‐Ps intensity decreases for HDPE/BT composites. It is found that the carboxyl group of Acrylic acid plays a significant chemical inhibition on positronium formation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Gel,thermal, and X‐ray diffraction characterization of virgin,scrapped polyethylene and its blends

The characterizations of virgin and scrapped polyethylene samples (VPE and SPE) and VPE/SPE blends were studied using different analytical techniques. The obtained data regarding crosslink density demonstrated that the radiation‐induced crosslinking of VPE, SPE, and VPE/SPE samples increased as a result of increasing irradiation dose, blending VPE with SPE, and loading the VPE/SPE blend with trimethylol propane triacrylate (TMPTA). The use of differential scanning calorimetry technique was aimed at revealing the effect of sample composition (VPE, SPE, and VPE/SPE) and also the effect and type of irradiation on the melting temperature (T_m) and the heat of transformation (ΔH_f). The melting temperature and heat of transformation increased with increasing either irradiation dose or loading the polymeric samples with TMPTA. In addition, the application of thermogravimetric analysis (TGA) was used to study the degradation characteristics of the polymeric samples in terms of onset temperature (T_i), temperature at maximum weight loss (T_s), and activation energy (E_a). The TGA results showed that the irradiation (EB and γ‐rays) and loading of polymeric samples with TMPTA led to a thermally stable polymeric matrix with higher T_i, T_s, and E_a values. The blank SPE sample or those blend rich in SPE matrix were highly thermally stable than that blank VPE one. The X‐ray diffraction investigation illustrated that VPE samples undergoes phase transformation between orthorhombic, monomclinic, and/or hexagonal as a result of irradiation. POLYM. COMPOS. 27:709–717, 2006. © 2006 Society of Plastics Engineers     

Hydrostatic extrusion under back pressure of high-density polyethylene

The possibility of hydrostatic extrusion of solid polymer under back pressure has been studied. Operation of equipment is described that permits hydrostatic extrusion under back pressure at elevated temperatures. To understand how the pressure influences hydrostatic extrusion, extrusions of polyethylene under back pressure up to 392 MPa were conducted at temperatures below the melting point of polyethylene at atmospheric pressure (T_m¹). Furthermore, hydrostatic extrusion in the solid phase could be conducted at temperatures beyond T_m¹, since the melting point of polyethylene increased markedly with increasing back pressure.     

Thermal analyses of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)

Thermal analyses of poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(HB–HV)], and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(HB–HHx)] were made with thermogravimetry and differential scanning calorimetry (DSC). In the thermal degradation of PHB, the onset of weight loss occurred at the temperature (°C) given by T_o = 0.75B + 311, where B represents the heating rate (°C/min). The temperature at which the weight-loss rate was at a maximum was T_p = 0.91B + 320, and the temperature at which degradation was completed was T_f = 1.00B + 325. In the thermal degradation of P(HB–HV) (70:30), T_o = 0.96B + 308, T_p = 0.99B + 320, and T_f = 1.09B + 325. In the thermal degradation of P(HB–HHx) (85:15), T_o = 1.11B + 305, T_p = 1.10B + 319, and T_f = 1.16B + 325. The derivative thermogravimetry curves of PHB, P(HB–HV), and P(HB–HHx) confirmed only one weight-loss step change. The incorporation of 30 mol % 3-hydroxyvalerate (HV) and 15 mol % 3-hydroxyhexanoate (HHx) components into the polyester increased the various thermal temperatures T_o, T_p, and T_f relative to those of PHB by 3–12°C (measured at B = 40°C/min). DSC measurements showed that the incorporation of HV and HHx decreased the melting temperature relative to that of PHB by 70°C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 90–98, 2001     

Effects of crystalline and orientational memory phenomena on the isothermal bulk crystallization and subsequent melting behavior of poly(trimethylene terephthalate)

The effects of crystalline and orientational memory phenomena on the subsequent isothermal crystallization and subsequent melting behavior of poly(trimethylene terephthalate) (PTT) were investigated by studying the effect of prior melt‐annealing temperature, T_f, on the subsequent isothermal crystallization kinetics, crystalline structure and subsequent melting behavior of neat and sheared PTT samples. On partial melting, choices of the T_f used to melt the samples played an important role in determining their bulk crystallization rates, in which the bulk crystallization rate parameters studied were all found to decrease monotonically with increasing T_f. The decrease in the values of these rate parameters with T_f continued up to a critical T_f value (ie ca 275 °C for neat PTT samples and ca 280 °C for PTT samples which were sheared at shear rates of 92.1 and 245.6 s^?1). Choices of the T_f used to melt neat PTT samples had no effect on the crystal structure formed. The subsequent melting behavior suggested that the T_f used to melt both neat and sheared samples had no effect on the peak positions of the melting endotherms observed and that the observed peak values of these endotherms for all sample types studied were almost identical. Copyright © 2004 Society of Chemical Industry     

Composition-dependent properties of polyethylene/kaolin composites. i. degree of crystallinity and melting behavior of polyethylene

Injection-molding and blow-molding grades of high-density polyethylene composites containing up to 30 vol. % of calcinated Kaolin were characterized by measurements of melting temperatures (T_m), heats of fusion (ΔH_m) and room-temperature densities. Both T_m and the degree of crystallinity of a polymer matrix proved essentially unchanged regardless of filler content and/or presence of a custom coupling agent. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1267–1271, 1999     

Surface functionalization of polypropylene‐bearing isocyanate groups in solid state and their cyclotrimerization with diisocyanates

Solid‐state graft polymerization of 3‐isopropenyl‐α,α′‐dimethylbenzene isocyanate (TMI) onto the surface of polypropylene beads was carried out in a triethylborane/oxygen redox system. Chemical structures were characterized using attenuated total reflectance–Fourier transform infrared spectroscopy. Results showed that TMI was successfully grafted because of the appearance of an ? NCO absorption peak at 2255 cm^?1. The emergence of oxygen and nitrogen elements detected by EDS and XPS also demonstrated the existence of isocyanate group on PP‐grafted. The grafting ratio of TMI to polypropylene was examined using 9‐(methylamino‐methyl)anthracene (MAMA) as an intermediate substance. The fluorescent property of MAMA before and after reaction was characterized to guarantee interaction between MAMA and isocyanate. Thermal properties were examined using differential scanning calorimetry–thermogravimetric analysis. Results indicated that melting temperature (T_m) of pure PP was 168^oC, while the PP‐grafted decreased to 164^oC. Meanwhile, decomposition temperature (T_d) decreased with increased grafting ratio for about 8 to 15^oC; however, when styrene was introduced, T_m increased probably because of the stabilizing effect on macromolecular radicals and the suppression effect on chain degradation. Besides, the cyclotrimerization of isocyanates on the grafted polymer chain was further conducted to prepare thermally stable isocyanurate composite materials, remedying the T_d loss of PP‐g‐TMI by improving for 10^oC appropriately. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42186.     

Protection of high‐density polyethylene–silicon composites from ultraviolet–visible photodegradation

The extent of the ultraviolet–visible (UV–vis) photoirradiation effect on high‐density polyethylene (HDPE) and HDPE–silicon (Si) composites is reported in terms of the addition of Si microparticles at contents of 0.1, 1, and 5 wt %. A standard accelerated UV–vis exposure was applied over 2750 h, corresponding to 22 months in Florida. Thermogravimetry, differential scanning calorimetry, and Fourier transform infrared spectroscopy were used as reliable techniques for monitoring the quality of the HDPE–Si composites. The increasing addition of Si microparticles delayed the photodegradation of the HDPE–Si composites. Because of their strong light‐scattering effects, Si microparticles blocked the degradation of tertiary carbons of the HDPE backbone and reduced the apparition of vinyl groups; this prevented the structural impoverishment of HDPE–Si composites. Consequently, variations in the crystallization temperature (T_c) and melting temperature (T_m), which were indicators of photodegradation, were not modified. In general, the HDPE–Si composite formulation with 5 wt % Si microparticles was useful for protecting the material from photodegradation and, thus, should be an environmentally friendly, reliable alternative UV–vis blocker. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45439.     

Differential scanning calorimetry of copolymer of isotactic polypropylene backbone with grafted poly(ethylene‐co‐propylene) branches

A series of graft polymers having polypropylene (PP) backbone and poly(ethylene‐co‐propylene) (EPR) side chains was prepared. PP backbone molecular weight (M_n) was 28–98 kg/mol, EPR side chain M_n was 2.6–17 kg/mol, and EPR content was 0–16 wt %. In this work, thermal analysis of the copolymers was performed using differential scanning calorimetry (DSC). Nonisothermal crystallization was performed at different cooling rates. The DSC thermograms revealed multiple melting peaks for slowly cooled samples, most likely the result of the melting of thinner tangential lamellae followed by the melting of thicker radial lamellae. Equilibrium melting temperature (T_m⁰) was determined using the linear Hoffman–Weeks method. Another approach was also used for determining T_m⁰: melting temperature (T_m) and crystallization temperature (T_c) were plotted as functions of logarithmic cooling rate. Linear relationships were observed for all samples with the cross points as T_m⁰'s. As cooling rate decreased, T_c, T_m, and enthalpy of fusion (ΔH_f) increased. T_m and T_m⁰ increased with increasing PP M_n. T_c and T_m were unaffected by the grafting of EPR onto the PP backbone. T_m⁰ and ΔH_f decreased as EPR content increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3380–3388, 2006     

Remarkable piezoelectricity and stable high‐temperature dielectric properties of quenched BiFeO3–BaTiO3 ceramics

Effects of quenching process on dielectric, ferroelectric, and piezoelectric properties of 0.71BiFeO₃?0.29BaTiO₃ ceramics with Mn modification (BF–BT?xmol%Mn) were investigated. The dielectric, ferroelectric, and piezoelectric properties of BF–BT?xmol%Mn were improved by quenching, especially to the BF–BT?0.3 mol%Mn ceramics. The dielectric loss tanδ of quenched BF–BT?0.3 mol%Mn ceramics was only 0.28 at 500°C, which was half of the slow cooling one. Meanwhile, the remnant polarization P_r of quenched BF–BT?0.3 mol%Mn ceramics increased to 21 μC/cm². It was notable that the piezoelectric constant d₃₃ of quenched BF–BT?0.3 mol%Mn ceramics reached up to 191 pC/N, while the T_C was 530°C, showing excellent compatible properties. The BF–BT?xmol%Mn system ceramics showed to obey the Rayleigh law within suitable field regions. The Rayleigh law results indicated that the extrinsic contributions to the dielectric and piezoelectric responses of quenched BF–BT?xmol%Mn ceramics were larger than the unquenched ceramics. These results presented that the quenched BF–BT?xmol%Mn ceramics were promising candidates for high‐temperature piezoelectric devices.     

Isothermal cold crystallization and melting behaviors of poly(L‐lactic acid)s prepared by melt polycondensation

The isothermal cold crystallization and melting behaviors of poly(L ‐lactic acid)s (PLLAs, weight average molecular weight, M_w, 6000–80,000) prepared via melt polycondensation were studied with differential scanning calorimeter in this work. It is found that the crystallization rate increased with decreasing M_w, reached a maximum at M_w of ca. 21,000 and then decreased again. The crystallinity of PLLA can be controlled in the range 30–50% by crystallization temperature (T_c) and time to fulfill the requirement of subsequent solid state polycondensation. The melting behavior strongly depends on T_c. The samples crystallized at high T_c melted with a single peak but those crystallized at low T_c melted with double peaks. The higher melting point (T_mH) kept almost constant and the lower melting point (T_mL) increased clearly with T_c. But the T_mL changed in jumps and a triple melting peak appeared at the vicinity of a characteristic crystallization temperature T_b, possibly because of a change of crystal structure. The equilibrium melting temperature of PLLA with M_w of 21,300 was extrapolated to be 222°C with nonlinear Hoffman‐Weeks method. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Investigation of crystallization of PVCH‐PE‐PVCH triblock copolymer in supercritical carbon dioxide

Crystallization of glassy‐crystalline‐glassy poly(vinylcyclohexane)‐b‐polyethylene‐b‐poly(vinylcyclo hexane) (PVCH‐PE‐PVCH) triblock copolymer treated in supercritical Carbon Dioxide (scCO₂) was investigated by using differential scanning calorimetry (DSC) and atomic force microscope (AFM). It was found that the melting temperatures (T_m) and the crystallinity (X_c) of the PVCH‐PE‐PVCH samples treated in scCO₂ at different annealing temperatures (T) were all much higher than those of the untreated PVCH‐PE‐PVCH, indicating that the scCO₂ could effectively induce the samples to further crystallize. With increasing the T, the T_m of the samples linearly increased, even up to 108°C, close to the T_m (～ 110°C) of the PE homopolymer hydrogenated from polybutadiene which is equal to the PE block in the triblock copolymer. The results could be ascribed to the released PE chain ends linked to the PVCH block due to the lowered T_g of the PVCH block swollen by scCO₂. It suggested that the origin of the confined crystallization in PVCH‐PE‐PVCH was the fixed PE chain ends by the glassy PVCH. AFM images of the samples treated in scCO₂ showed that the PVCH lamella phase tended to connect each other and led to the aggregated structures. The result indicated that the PVCH block could be availably swollen by scCO₂. It supported the DSC experiment results of the samples treated in scCO₂. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 102: 2584–2589, 2006