EFFECT OF TEMPERATURE ON THE RHEOLOGY OF POLYMERIC LIQUID CRYSTALS

As part of a more general effort to elucidate the flow of polymeric liquid crystals, the effect of temperature on the rheological properties has been investigated. A lyotropic sample of poly(γ-benzyl-L-glutamate) in m-cresol has been used throughout the measurements. Under steady state shear flow the viscosity and the first normal stress difference have been measured. Oscillatory flow after cessation of steady shear flow reveals a time effect which led to the determination of initial and final moduli; both have been measured as a function of temperature. Finally some transients have been considered as well.

The limiting zero frequency value of the dynamic viscosity and the zero shear value of the steady state viscosity have different activation energies. The dynamic moduli can be scaled for temperature effects by means of the zero frequency viscosity. Because of the difference in activation energies this scaling does not hold for the steady state properties. An alternative scaling procedure is suggested. The time scale of the transients is nearly independent of temperature. None of the available theoretical models describes the measured phenomena.     

ON THE DYNAMIC PROPERTIES OF THE EXTENSIVE VARIABLE CONTROL STRUCTURES

The purpose of this paper is to investigate the dynamic properties of controller structures synthesized using extensive thermodynamic variables of a process. Several state-space and frequency domain multivariable techniques, including INA, and Modal Interaction Analysis, are used in order to evaluate the dynamic properties of these control structures. These structures show zero steady state interaction and minimal dynamic interaction for all processes examined. Dynamic simulation of several application examples, including distillation columns and a network of two stirred tank heaters in series, shows that the loops in these structures can also be tuned with minimum effort. Comparison of the proposed structures, with the conventional parallel single-input single-output control structures, shows the advantages of the proposed method.     

LAG WINDOW ESTIMATION OF THE DEGREE OF DIFFERENCING IN FRACTIONALLY INTEGRATED TIME SERIES MODELS

Abstract. In this paper we consider the estimation of the degree of differencing d in the fractionally integrated autoregressive moving-average time series model ARFIMA ( p, d, q ). Using lag window spectral density estimators we develop a regression type estimator of d which is easy to calculate and does not require prior knowledge of p and q. Some large sample properties of the estimator are studied and the performance of the estimator for small samples is investigated using the simulation method for a range of commonly used lag windows. Some practical recommendations on the choice of lag windows and the choice of the window parameters are provided.     

ESTIMATION OF THE FRACTIONAL DIFFERENCE PARAMETER IN THE ARIMA(p, d, q) MODEL USING THE SMOOTHED PERIODOGRAM

Abstract. In recent work on time series analysis considerable interest has been focused on series having the property of long memory. Long memory is a characteristic of time series in which the dependence between distant observations is not negligible. The model that has been most frequently studied, which in some situations shows properties of long memory, is based on the autoregressive integrated moving-average ARIMA( p, d, q ) process. Hosking (Fractional differencing, Biometrika 68 (1) (1981), 165–76) generalized this model by permitting the degree of differencing d to take fractional values. He then demonstrated that for d in the range 0 < d < 0.5 the process is stationary and possesses the long memory property. Our study is based on the ARIMA( p, d, q ) model when d takes any real non-integer value in the interval (-0.5, 0.5). The main aim of our study is to examine methods for estimating the parameters of this model. For estimating d we suggest an estimator based on the smoothed periodogram. Using an empirical approach we compare this estimator with other which are well known in the literature of long memory models, e.g. the raw periodogram regression method and the Hurst coefficient method.     

SOLVENT EFFECTS ON THE RHEOLOGY OF AQUEOUS POLYACRYLAMIDE SOLUTIONS†

The influence of solvent chemistry on steady shear viscosity and first normal stress difference for aqueous polyacrylamide solutions (Separan AP-273) was investigated in the Weissenberg rheogoniometer and capillary tube viscometer. It was found that these rheological properties are particularly sensitive to the chemistry of the solvent. For example, the zero shear rate viscosity of a 1000 wppm Separan solution with distilled water as the solvent was greater than that with Chicago tap water as the solvent by a factor of 25, while the first normal force difference varied by a factor of two. The addition of an acid or a base to the Chicago tap water-Separan solution also influenced the zero shear rate viscosity and first normal force difference. It was found that there is an optimum pH of approximately 10 which yields a maximum value of the zero shear rate viscosity for the Separan-tap water solution.

Limited data on the influence of solvent chemistry were obtained for 5000 wppm aqueous solutions of polyethylene oxide (WSR-301) and reveal the same quantitative trends found for the polyacrylamide solutions although the magnitude of the observed changes are smaller.     

高效催化剂对聚丙烯树脂分子量、分子量分布及纺丝性能的影响

燕山石化公司化纤地毯厂在采用高效催化剂前、后生产的新、老3702聚丙烯树脂(熔体流动指数MFI均为12—15)纺丝时,纺丝温度和纤维性能发生了显著变化。研究结果表明,这种差别主要是由于它们的分子量分布不同所引起的。新3702由于分子量分布较窄,与老3702聚丙烯树脂相比,即使在相同的MFI条件下,粘均分子量和零切变粘度也是较低的,因而纺丝温度也低。在工业生产中表明,除测定MFI外还应测定聚丙烯熔体在230℃下的零切变速率粘度,这对指导生产,能提供可靠依据。采用高效催化剂生产MFI为7—11的新3602牌号聚丙烯在燕山石化公司化纤地毯厂试纺中,废丝率下降了7%以上,成丝质量得到了提高。     

SOME SIMPLE TESTS OF THE MOVING-AVERAGE UNIT ROOT HYPOTHESIS

Abstract. This paper deals with three test statistics for a moving-average (MA) unit root. The spectral test is based on the estimate of the spectral density at frequency zero. The variance difference statistic compares the sample variance of the integrated series with the estimated variance imposing the MA unit root constraint. Furthermore, Tanaka's score type test statistic is modified to improve the power in higher order models. The asymptotic power of the tests is considered and Monte Carlo experiments are performed to investigate the small sample properties of the tests. Finally, the tests are applied to a number of economic time series to determine the degree of integration.     

Pd deposited on Cu(110): a highly performant catalyst for the 1,3-butadiene hydrogenation reaction

The catalytic properties, with respect to the 1,3-butadiene hydrogenation reaction, of strained Pd films on Cu(110) (lattice mismatch 8%) has been probed as a function of the film thickness. The characterization of the adlayer has been made by the combined use of STM with LEED and AES. For deposits below 10¹⁵ Pd/cm² (i.e., about 1 ML) the catalytic activity is near zero. This is the consequence of the formation of a Pd–Cu surface alloy with tendency for Cu to migrate/segregate to the surface. The catalytic activity suddenly increases to reach a maximum value for about 3 ML; the activity is then one order of magnitude higher than that of the pure Pd(110) surface. This is the consequence of the presence of a strained Pd overlayer, with Pd surface atoms having very unusual geometry, and hence very peculiar electronic and chemical properties. The catalytic activity then decreases as the Pd coverage is increased, and tends to values near that of the pure Pd(110). Gradual relaxation of the film geometry towards that of the normal fcc Pd structure probably exists.     

Rheological properties of poly(ε-caprolactone) and poly(styrene-co-acrylonitrile) blends

Summary Rheological properties of poly(-caprolactone) (PCL) and Poly (styrene-co-acrylonitrile) (SAN) blends were examined as a function of the acrylonitrile (AN) content in SAN, to systematically understand the correlation between the interaction parameter and the theological properties of miscible polymer blends. When the plateau modulus (G _N ⁰) and zero shear viscosity ( ₀) of the PCL/SAN blends are plotted against the AN content in SAN, a minimum is observed. Qualitatively, the results obtained parallel the variation of the interchain interaction with the AN content. The negative deviation ofG _N ⁰ and ₀ from linearity seems to be attributed to the increase in the entanglement molecular weight between dissimilar chains which results from the chain extension caused by interchain interaction.     

TEMPORAL AGGREGATION IN THE ARIMA PROCESS

Abstract. The effect of temporal aggregation on ARIMA models is investigated. The paper discusses the change of model form resulting from aggregation. For the IMA model it is noted that reduction of model order may occur, due to aggregation, which takes an arbitrarily high order IMA ( d , q) process to an IMA ( d , 0) process for the aggregates. For the AR process, we derive the exact order for the aggregate model and show that aggregation of an AR (p) series does not necessarily produce an ARMA (p, q) aggregate series as has been suggested in the literature. In particular, the AR order of AR (p) and ARIMA (p, d, q) can be reduced upon aggregation. The paper gives the general conditions under which this reduction of order may occur.     

IDENTIFYING MULTIVARIATE TIME SERIES MODELS

Abstract. This paper is concerned with how canonical variate analysis can be used to identify the structure of a linear multivariate time series model. The procedure used is based on that of Akaike and Cooper and Wood. A correction and a refinement are made, however. The correction is on the testing statistic and the refinement on the allowed order ( p, q ). Appropriate asymptotic distributions for testing zero canonical correlations are also given.     

SOME ASYMPTOTIC PROPERTIES OF THE SAMPLE COVARIANCES OF GAUSSIAN AUTOREGRESSIVE MOVING-AVERAGE PROCESSES

Abstract. The paper deals with the asymptotic variances of the sample covariances of autoregressive moving average processes. Using state-space representations and some matrix Lyapunov equation theory, closed-form expressions are derived for the asymptotic variances of the sample covariances and for the Cramer-Rao bounds on the process covariances. The main results obtained from these expressions are as follows: For ARMA ( p, q ) processes with p ≥ q , the sample covariance of order n is asymptotically efficient if and only if 0 ≤ n ≤ p – q .
For ARMA ( p, q ) processes with p < q , none of the sample covariances is asymptotically efficient.     

国产第一炉Kellogg型竖琴管排的制造及应用

总结国产第一炉Ｋｅｌｌｏｇｇ型竖琴管排的制造、组焊情况。首次提出上仍国际先进水平的严密合理的订货技术条件,加强制造过程中的质量监检,采购到一炉高质量的国产炉管。首创在现场采用垂直固定焊组焊竖琴管排,并应用无间隙地单面焊双面形成的焊接技术。     

Porosity‐dependent properties of Nb‐doped Pb(Zr,Ti)O3 ceramics

In the present work, it is shown how the controlled porosity can be exploited to obtain a compromise between a reduced permittivity down to a few hundreds and maintaining a high tunability level as in the dense material, to fulfill requirements for tunable applications. Nb‐doped Pb(Zr,Ti)O₃ ceramics with porosity in the range 5%‐30% have been prepared by direct sintering method. X‐ray diffraction analysis and Rietveld refinement indicated a co‐existence of tetragonal and monoclinic phases in the porous ceramics. Dielectric properties revealed a gradual reduction in permittivity when increasing the porosity level, while maintaining low dielectric losses below 3%. The ferroelectric switching behavior is also influenced by the porosity level: a continuous reduction in the saturation and remnant polarization is observed with increasing porosity. The nonlinear dielectric properties of all the investigated ceramics preserve a high level of tunability in comparison with one of the dense material, irrespective of the porosity level, while zero field permittivity was decreased below 1000. An optimum behavior is found for the ceramic sample with 25% porosity, which shows a high tunability, smaller losses, and moderate dielectric constant (ε ~600).     

ON THE COVARIANCE OF THE PERIODOGRAM

Abstract. The paper discusses the covariance of the periodogram from a zero mean fourth order stationary stochastic process. The fourth order cumulant term appearing in the covariance is shown to be a convolution between the fourth order cumulant spectrum and a bounded approximate identity, and this gives precise results about its asymptotic behaviour. The covariance is also studied both pointwise and as a measure of two variables. This leads to necessary and sufficient conditions for mean square consistency of estimates of the spectral moments and related parameters.     

RATE OPTIMAL SEMIPARAMETRIC ESTIMATION OF THE MEMORY PARAMETER OF THE GAUSSIAN TIME SERIES WITH LONG-RANGE DEPENDENCE

There exist several estimators of the memory parameter in long- memory time series models with the spectrum specified only locally near zero frequency. In this paper we give an asymptotic lower bound for the minimax risk of any estimator of the memory parameter as a function of the degree of local smoothness of the spectral density at zero. The lower bound allows one to evaluate and compare different estimators by their asymptotic behaviour, and to claim the rate optimality for any estimator attaining the bound. A log-periodogram regression estimator, analysed by Robinson (Log-periodogram regression of time series with long range dependence. Ann. Stat. 23 (1995), 1048--72), is then shown to attain the lower bound, and is thus rate optimal.     

成核剂对尼龙结构与性能影响的研究进展

从成核剂的作用机理和尼龙加工条件出发，将尼龙用成核剂分为无机、有机和高分子三类，并分别介绍了其最佳用量、应用情况及对尼龙结构与性能的影响。尼龙用成核剂用量一般要低于5％。成核剂的添加可加快尼龙结晶速率，缩短注塑周期；使球晶颗粒更细微化；改变制品收缩；拉伸强度和弯曲弹性模量增加，耐热性提高，断裂伸长率和冲击强度降低。     

Avoidance of bird repellents by mice (Mus musculus)

It is believed that mammalian chemosensory irritants are not aversive to birds and vice versa. Nevertheless, few avian repellents have been tested against mammals. For that reason, we evaluated the efficacy of 1.0% w/v methyl anthranilate, orthoaminoacetophenone, 2-amino-4,5-methoxyacetophenone, 2-methoxyacetophenone, and veratryl amine as mouse repellents in 3-hr no-choice drinking tests. Relative to ingestion of plain water, all test substances significantly reduced (P < 0.05) intake. Orthoaminoaceto-phenone was the most effective repellent, with intake reduced to levels statistically indistinguishable from zero.     

ASSESSMENT OF THE SUITABILITY OF USING THE COMPOSITE G2, G3, AND CBS-RAD METHODS FOR PREDICTING ACTIVATION ENERGIES

In this work, the accuracy of the G2, G3, and CBS-RAD methods for predicting activation barriers of ligand transfer reactions is investigated. We find that the zero point corrected G2 method has an RMS error of 3.82 kcal/mol for activation barriers. The G3 method has an RMS error of 4.16 kcal/mol. After adding thermal corrections to the G2 and zero point corrected results, the RMS error for the G2 method is 4.92 kcal/mol, while the error for the G3 method is 4.55 kcal/mol. In contrast, the CBS-RAD method has errors of 3.80 kcal/mol for zero point energy corrected activation energies, and 2.82 kcal/mol for thermally corrected results. The G3 method was found to require only 40% of the computational time required for the G2 method, making it an attractive alternative for predicting activation energies yielding errors of about 4 kcal/mol. The CBS-RAD method has a computational cost four times greater than that of the G2 method and gives an improvement of only about 1 kcal/mol.