bluuebunny/crossref_metadata_2025_split huggingface dataset:
Differential scanning calorimetric studies on bound water in 1,4‐dioxane acidolysis lignin
Authors: Hatakeyama Tatsuko , Hirose Shigeo , Hatakeyama Hyoe 
Published: April 2003

AbstractThe amounts of three different types of water adsorbed on hydrolyzed lignin, which was obtained by acid hydrolysis of softwood meal in 1,4‐dioxane containing trace amounts of hydrochloric acid (in the following called DL), and on its derivatives, i.e., methylated and acetylated lignins, were determined by differential scanning calorimetry (DSC). The first type of water is non‐freezing water, the glass transition of which was detected by DSC. The second type of water corresponds to a kind of bound water which was detected from a crystallization peak in the vicinity of 225 K (peak II). This peak appeared when the water content exceeded a critical amount of non‐freezing water. The third type of water is free water, the crystallization peak (peak I) of which was found at the same temperature as that of pure water. From the enthalpies of crystallization of the above two types of water and the known weight of sorbed water, the amount of bound water in DL was determined to be 0,10 (weight of bound water/weight of dry sample). Furthermore, it was found that bound water breaks hydrogen bonds in DL and decreases its glass transition temperature (Tg) from 425 K to 330 K. The amount of hydroxyl groups, which varies with the degree of methylation or acetylation, was also found to affect the bound water content and inevitaby to decrease T g.
Copolymerization of unsaturated carboxylic acids with styrene and an unsaturated tertiary amine in dimethyl sulfoxide
Authors: Bezděk Milan , Hynková Vlasta , Hrabák František 
Published: April 2003

AbstractThe copolymerization parameters of N‐methyl‐N‐phenyl‐2‐aminoethyl methacrylate (MPAM) and 2‐acryloyloxybenzoic (AOB), 2‐methacryloyloxybenzoic (MOB), and methacrylic acid (MAA) with styrene in DMSO solution at 50°C were determined and used in the calculation of the Alfrey‐Price copolymerization constants e and Q for MPAM, AOB, MOB, and MAA. From the e and Q constants of the monomers thus determined, the copolymerization parameters of the pairs MPAM‐AOB, MPAM‐MOB, MPAM‐MAA were calculated and compared with those determined by the copolymerization of the corresponding pairs in DMSO.
Comparison of methods for determination of the number of active centers in Ziegler‐Natta polymerizations
Authors: Mejzlík Jiří , Lesná Marie , Majer Josef 
Published: April 2003

AbstractFour intrinsically different methods for the determination of the number of active centers were employed in propylene polymerization catalyzed by the typical heterogeneous system TiCl3/AlEt2Cl: (i) determination of M̄n (GPC method) and calculation of number of macromolecules therefrom; (ii) quenching with BuOT and determination of tritium in the polymer; (iii) quenching with CO or CO2 and determination of carbonyl groups in the polymer (IR spectroscopy); (iv) quenching with SO2 and determination of sulfur in the polymer. The first two methods exhibited a reasonable agreement for the number of active centers. Method (iii) gave much lower values, whereas method (iv) was found to be virtually unsuitable due to a high extent of side reactions of SO2 with the polymer. A similar comparison of the methods was made in ethylene polymerization catalyzed by the typical homogeneous systems Cp2TiEtCl/AlEtCl2 and Cp2TiEtCl/alumoxane. Method (ii) gave a much lower number of active centers than method (i), due perhaps to a low extent of alcoholysis of the TiC bond or to a high kinetic isotope effect. CO2 appeared to be entirely inert as a quenching agent and CO had been reported to show side reactions. It follows that none of the above quenching methods have universal application and thus literature data should be considered with caution.
Correlation of data on intrinsic viscosities in mixed solvents by means of the modified flory‐huggins equation
Authors: Pouchlý Julius , Živný Antonín 
Published: April 2003

AbstractAn equation for the total sorption potential Y derived from the modified Flory‐Huggins equation and containing concentration‐dependent interaction parameters, including the ternary parameter χT, was used to correlate reported data on intrinsic viscosities in mixed solvents. Similarly to the evaluation of data on preferential sorption, the assumption of proportionality between the ternary parameter and the interaction parameter of components of the mixed solvent, g12, was successfully applied to the case of total sorption. The assumption proved to be useful in the treatment of 12 ternary systems, if the single‐liquid approximation was employed. The calculated proportionality constant between the ternary parameter and g12 has properties similar to that evaluated from the data on preferential sorption. The conditions of occurrence of a maximum or minimum in the dependence of total sorption on composition are discussed.
Study of conformational transitions of graft copolymers by UV spectrophotometry, 2. The behaviour of poly(vinyl acetate) grafted hydroxyethyl‐cellulose in selective solvents
Authors: Goşa Kristiana , Carp Nicoleta , Donescu Dan 
Published: April 2003

AbstractThe behaviour of poly(vinyl acetate) grafted hydroxyethylcellulose (PVAc/HEC) in the binary solvent mixture ethanol‐water (90:10 by vol.) was studied by absorption spectrophotometry. The macromolecules of PVAc/HEC graft copolymer exhibit a conformational transition at ca. 55°C where they pass from a monomicelle conformation to a segregated conformation. This intramolecular transition occurs both below and above the critical micellar concentration (c.m.c). In dilute solutions a critical concentration was evidenced, which is one order of magnitude higher than the c.m.c.
Hydrodynamic crossover in two‐polymer mixtures from viscosity measurements
Authors: Dondos Anastasios , Skondras Panayotis , Pierri Evgenia , Benoît Henri 
Published: April 2003

AbstractA very sharp crossover is observed in the variation of the reduced viscosity ηsp/c as a function of the concentration c for mixtures of 1:1 by weight mixtures of polystyrene and poly(methylmethacrylate) in benzene at 20°C and a 1:1 by weight mixture of poly(ethylene glycol) and polystyrene in benzene at 20°C. The crossover is attributed to the critical to the concentration of the two respective polymers in the solution and its sharpness is due to the incompatibility between the two different polymers.
Study on the molecular weight dependence of dilute solution properties of narrowly distributed polystyrene in toluene and in the unperturbed state
Authors: Kniewske Reinhard , Kulicke Werner‐Michael 
Published: April 2003

AbstractIntrinsic viscosities [η], second and third virial coefficients A2 and A3, respectively, and mean square radius of gyration 〈RG2〉 of a polymer homologous series of narrow‐molecular‐weight‐distribution polystyrene samples in a molecular weight range of 2000 up to 24 · 106 were determined in toluene at 25°C by light scattering and viscometry measurements. The results are (3 · 104 < Mw < 24 · 106, Mw/Mn ≤ 1,3):

These results were obtained by consideration of the limit of the dilute solution regime, the determination of zero‐shear rate intrinsic viscosities, and the molecular weight dependence of the refractive index increment dn/dc. It was found that dn/dc increases slightly up to Mw = 1,8 · 106. A comparison of the [η]−Mw‐relationship with literature data is given. In addition the unperturbed (theta) dimension parameters K0, 〈h2〉0/M, the characteristic ratio C∞, the steric factor σ, and the thermodynamic interaction parameter B were calculated from the modified Burchard‐Stockmayer‐Fixman procedure using polymolecularity correction and the results compared with experimental data from the literature.
Small angle neutron scattering studies of poly(ethylene oxide) in the melt
Authors: Kugler Joachim , Fischer Erhard W. , Peuscher Manfred , Eisenbach Claus D. 
Published: April 2003

AbstractThe neutron scattering from mixtures of deuterated and undeuterated poly(ethylene oxide), (D‐PEO, H‐PEO), in the small angle and intermediate angle region has been measured in the melt. We found no indications of a molecular segregation. The value of molecular weight evaluated agreed with that obtained by other methods. For a sample with a molar mass of 120000 g/mol the radius of gyration 〈rw2〉1/2 was found to be 13,6 nm, which corresponds to a characteristic ratio of C = 6,9. The form factor of a single chain can be described by the Debye equation for a random coil with the same unperturbed dimensions. Our results are compared with rotational isomeric state calculations and measurements in solvents.
A chain of intramolecular hydrogen bonds, an important factor for the acidity of oligo[(2‐hydroxy‐1,3‐phenylene)methylene]s
Authors: Böhmer Volker , Schade Eckart , Antes Claus , Pachta Jiri , Vogt Walter , Kämmerer Hermann 
Published: April 2003

AbstractThe first dissociation constant of oligonuclear phenolic compounds consisting of one nitrophenol unit besides further alkyl phenol units (10 dinuclear, 15 trinuclear, 6 tetranuclear compounds, and 4 nitrophenols as model) was determined spectroscopically in water/methanol (50/50 by vol.) at 25°C. For the ortho‐linked title compounds with the nitrophenol unit at the end of the molecule a decrease of pK1 is observed which becomes stronger with increasing chain length. The introduction of bulky groups in ortho‐position of the dissociating phenolic unit, as well as at the opposite end of the molecule causes a further decrease of pK1. The lowest value is found for a p‐nitrophenol unit in the middle of the molecule. The results do not only prove the stabilization of the monoanion by intramolecular hydrogen bonds, but they give also strong evidence for a chain of intramolecular hydrogen bonds in the undissociated molecule. The UV‐spectra of the monoanions directly show the existence of intramolecular hydrogen bonds. Especially the p‐nitrophenol system makes it possible, to differentiate according to their strength.
Decay of the spin echo in a pulsed magnetic field gradient NMR
Authors: Peterlin A. 
Published: April 2003

AbstractThe additional attenuation of the spin echo of a pulsed magnetic field gradient NMR caused by the diffusion of the spins carrying molecules is calculated for a time dependent diffusion coefficient. The cases of a Constant D0, of an exponential decay with time, and an abrupt drop from D0 to zero at time t0 are considered. In all cases the time dependence of the experimentally observed attenuation is less steep than that of D. The time scale, however, Changes very little. The calculation was based on the consideration that the diffusion transports the precessing spins to a location with a different Larmor frequency so that a complete reversal after the 180° pulse is not possible any more. Hence, any deviation from a straight line in a plot of the excess attenuation versus δ2(1 − δ/3Δ) may by interpreted in terms of a time dependence of the diffusion coefficient.
Free‐radical polymerization kinetics of methyl methacrylate at very high conversions
Authors: Stickler Manfred 
Published: April 2003

AbstractThe free‐radical polymerization of methyl methacrylate (MMA) at very high conversions (x > 0,8) was studied in the temperature range 60C° to 160C°. 2,2′‐Azodiisobutyronitrile (AIBN) and benzoyl peroxide (BPO) were used as initiators. In the case of the latter, decomposition kinetics at very high monomer conversions was investigated, too. For temperatures T ⩽ 120C° where depropagation can be neglected a simple kinetic model based on “reaction diffusion” and free volume theory was developed. The model contains only a single adjustable parameter, the critical free volume fraction V*. Good agreement between model predictions and experiments was obtained. V* is independent of initial initiator concentration and reaction temperature, and there is some evidence that V* is also independent of the chemical nature of the initiator.
Properties of liquid crystalline polymers in solution, 2. Viscosimetric investigations of polymethacrylates with mesogenic sidegroups
Authors: Springer J. , Weigelt F. W. 
Published: April 2003

AbstractDilute solutions of poly(methacrylic acid) derivatives with mesogenic side groups of the benzoic acid phenyl ester type are structurally viscous. This property due to aggregation appears during storage and is attributed to the geometric shape of the dissolved particles. While solutions of freshly polymerized samples show no, or only a slight temperature dependence of the intrinsic viscosity between 298 and 368 K, the intrinsic viscosity of the stored samples decreases suddenly at temperatures above 348 K.
Relation between structure and thermal transitions in comb‐like polymers, 1. Poly(N‐n‐alkylmaleimide)s
Authors: Barrales‐Rienda José M. , Fernandez‐Martín Fernando , Galicia Carmen Romero , Chaves Manuel Sánchez 
Published: April 2003

AbstractA series of nine poly(N‐n‐alkylmaleimide)s (PMIs) with the n‐alkyl side chain ranging in length from ethyl to octadecyl and including only the even members of the series was studied by differential scanning calorimetry (DSC) from 100 K to above the glass transition temperature. The nine members of the PMI series generally were found to exhibit a glass transition temperature (Tg), a sub‐glass transition temperature (sub‐Tg = Tγ), and, but only the four higher homologs a melting point (Tm) with the respective melting enthalpy (ΔHf). The glass transition of the amorphous members is directly related to the number of methylene groups (including terminal methyl) of the n‐alkyl side chain of the repeating unit. The values of Tg estimated according to a semi‐empirical equation are in good agreement with the experimental data. The melting points of the members of the series presenting crystallinity in the n‐alkyl side chain were analyzed. A good fit of a Garner plot by a least‐mean‐squares procedure is obtained with T = 408,0K, a = −6,26 and b = −2,03. The contribution to the heat of melting per methylene unit clearly demonstrates that the hexagonal paraffin crystal structure is present in the crystalline members, in agreement with X‐ray data. The data when analyzed by Jordan′s procedure show that only part of the n‐alkyl side chain is forming a crystal lattice.
Sliding mode control design for uncertain time‐delay systems subjected to a class of nonlinear inputs
Authors: Yan Jun‐Juh 
Published: April 2003

AbstractA sliding mode controller is developed for uncertain time‐delay systems with a class of nonlinear inputs. Two main results are derived in this paper. The first result is the presentation of a new delay‐dependent stability condition of uncertain time‐delay systems. In a comparison example, this stability condition is shown to be less conservative than the ones reported recently. The second result is to present a new sliding mode control for uncertain time‐delay systems subjected to a class of nonlinear inputs. The stability of time‐delay systems with unmatching condition in the sliding mode is also discussed. Two illustrative examples are included to demonstrate the superiority of the obtained results. Copyright © 2003 John Wiley & Sons, Ltd.
Venous pulsation in the fetal left portal branch: the effect of pulse and flow direction
Authors: Kiserud T. , Kilavuz Ö. , Hellevik L. R. 
Published: April 2003

AbstractObjectiveTo determine whether the waveform in the left portal branch is reciprocal to the waveform found in the ductus venosus and umbilical vein due to difference in pulse direction compared to flow.MethodsTen fetuses (gestational age, 18–33 weeks), six with intrauterine growth restriction, three with non‐immune hydrops and one with sacrococcygeal teratoma, were examined using ultrasound imaging and pulsed Doppler. Techniques were adjusted to record simultaneously the waveform from neighboring sections of the veins, relate wave components to each other and determine degree of pulsatility. The corresponding vessel diameters were determined. ANOVA with t‐test or Wilcoxon signed rank test was used to compare paired measurements.ResultsPulsation in the left portal branch was noted in all fetuses. The pulsatility index was higher than in the umbilical vein (P = 0.005) and the diameter smaller (P = 0.001). In the left portal branch the atrial contraction wave appeared as a velocity peak while there was a nadir during ventricular systole. Simultaneous recordings showed that the waveform was reciprocal to that found in the ductus venosus and umbilical vein. In three cases an augmented pulsatility represented a pendulation of blood in the left portal branch with time‐averaged velocity near zero.ConclusionsThe velocity waveform recorded in the left portal vein is an inverse image of that in the ductus venosus, proving that pulse wave and blood flow run in the same direction in the left portal vein. Low compliance (i.e. small diameter) is probably a main reason for the high incidence of pulsation in this vein. Time‐averaged velocity near zero recorded in three fetuses indicates that this area acts also as a watershed. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Intraobserver and interobserver agreement in the diagnosis of anal sphincter tears by postpartum endosonography
Authors: Faltin D. L. , Boulvain M. , Stan C. , Epiney M. , Weil A. , Irion O. 
Published: April 2003

AbstractObjectiveTo evaluate intraobserver and interobserver agreement in the diagnosis of anal sphincter tears by endosonography when performed immediately postpartum by resident obstetricians.MethodsFifty‐four primiparous women who delivered vaginally and had no anal sphincter tears (third‐ or fourth‐degree perineal tears) diagnosed clinically were recruited. Four observers assessed photographic prints and video recordings of anal endosonography performed before the suture of the perineum. We calculated the intra‐ and interobserver agreement and the kappa coefficient to quantify the reliability of the diagnosis of clinically occult sphincter tears.ResultsThe observers described sphincter tears in 13–28% of the prints, and in 7–32% of the video recordings. Intraobserver agreement was rated as substantial for prints (kappa, 0.63), and moderate for video recordings (kappa, 0.48). The interobserver agreement was fair for prints (kappa, 0.34) and moderate for video recordings (kappa, 0.42).ConclusionEndosonography performed immediately postpartum to diagnose anal sphincter tears is of moderate reliability. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Relationship of isolated fetal intracardiac echogenic focus to trisomy 21 at the mid‐trimester sonogram in women younger than 35 years
Authors: Anderson N. , Jyoti R. 
Published: April 2003

AbstractObjectiveTo determine whether an isolated echogenic intracardiac focus in the fetal heart in the mid‐trimester (16–24 weeks) in women aged 18–34 years of age is associated with trisomy 21.MethodThis was a prospective population‐based observational study. A search of all obstetric sonograms performed in our region from January 1997 to December 1999 was carried out. From 12 373 pregnancies we identified 267 cases of echogenic foci in the fetal heart. Trisomy 21 was detected in 38 deliveries (0.31%). An echogenic focus was seen in 193 of the 9167 women < 35 years of age who had an obstetric sonogram at 16–24 weeks' gestation, and an echogenic focus was seen in 67 of the 1968 women > 35 years. The study group comprised the 149 women aged 18–34 years who had an echogenic focus in the fetal heart as the only abnormality at an obstetric sonogram performed at 16–24 weeks' gestation.ResultsThere were no abnormal outcomes or cases of trisomy 21 among the 149 pregnancies with an echogenic focus as an isolated finding in women aged 18–34 years (0% (95% confidence interval, 0.00–2.43)). The prevalence of isolated echogenic focus was 1.6% for women < 35 and 1.8% for women ≥ 35 years old. Of the 25 fetuses with trisomy 21 undergoing an obstetric sonogram at any gestational age, five (20%) had an echogenic focus. An isolated echogenic focus was present in one fetus with trisomy 21 seen at 26 weeks' gestation in a 17‐year‐old mother. Echogenic foci were single and in the left ventricle in 84.7% of cases.ConclusionAn isolated echogenic focus in the fetal heart at mid‐trimester ultrasound in women aged 18–34 years is not associated with increased risk for trisomy 21. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Abdominal wall defects and congenital heart disease
Authors: Gibbin C. , Touch S. , Broth R. E. , Berghella V. 
Published: April 2003

AbstractObjectivesTo determine the incidence of cardiac disease associated with abdominal wall defects of fetuses and associated parameters including maternal age, sex, gestational age at delivery, outcome, karyotypes, Apgar scores and associated congenital anomalies.MethodsThis was a retrospective study of fetuses with a prenatal diagnosis of gastroschisis or omphalocele. The Maternal–Fetal Medicine Fetal Therapy (MFM) database was reviewed for all fetuses with abdominal wall defects identified prenatally. All available MFM records, fetal echocardiograms, neonatal echocardiograms and neonatal charts were reviewed for the types of abdominal wall defects and associated cardiac disease identified by ultrasound. Other parameters reviewed included: maternal age, sex, gestational age at delivery, outcome, karyotypes (when available), Apgar scores and associated congenital abnormalities.ResultsForty‐eight fetuses with an abdominal wall defect and cardiac disease findings were identified. Of these fetuses 26 had gastroschisis and 22 had omphalocele. The mean maternal age was 24.0 ± 5.40 years in the gastroschisis and 29.2 ± 7.23 years in the omphalocele group (P < 0.01). Differences in mean gestational age at delivery, mean birth weight and median Apgar scores at 1 and 5 min were not statistically significant. Abnormal cardiac findings were seen in 4/26 (15%) cases of gastroschisis and included one case of peripheral pulmonary stenosis, two cases of supraventricular tachycardia and one case of persistent pulmonary hypertension (PPHN) of the newborn. Abnormal cardiac findings were seen in 10/22 (45%) cases of omphalocele and included one muscular ventricular septal defect, two atrial septal defects of the secundum variety, one ectopia cordis, one coarctation of the aorta, one dysplasia of the tricuspid valve, one large pericardial effusion and four cases of PPHN.ConclusionsFetuses with omphalocele appear to have an increased risk not only of congenital heart disease (CHD) but also of perinatal cardiac abnormalities, especially PPHN. A prenatal maternal hyperoxia test may be of predictive value in determining which patients may develop PPHN. The fact that both CHD and PPHN are increased in fetuses with abdominal wall defects may be of value in counseling parents prenatally, and stresses the importance of performing echocardiography both prenatally and postnatally in these cases. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.