Drag reduction and mechanical degradation in polymer solutions in flow

A list of conclusions from experimental studies of drag reduction (DR) and mechanucal degradation in flow (MDF) is made. A statistical-mechanical model of chain conformations developed by the author⁹ is used, and its consequences for DR and MDF established. Experimental findings are explained in terms of the model, including those considered to be puzzling and contrary to expectations. A relation between the extent of mechanical degradation and flow time is derived. The equation obtained for relative drag reduction in function of time reproduces perfectly the experimental data for polystyrene+toluene solutions reported by Hunston and Zakin¹². Some predictions from the present model have yet to be tested experimentally.     

Calculation of impact transition temperature of low density polyethylene from shift factor via a free volume approach

A relationship between the impact transition temperatureT _i and the stress concentration factorK _s is derived. The relationship involves the temperature shift factora _T; in turn,a _T depends on the free volume. In earlier work in this problem Zewi and Corneliussen [6] utilized the W-L-F equation. Here a more direct relationship betweena _T and the free volume is applied. Satisfactory values ofK _s corresponding to givenT _i are obtained for a wide temperature range; the range also includes temperatures below the glass transition pointT _g. The opinion that a free volume exists between 0 K andT _g is upheld.     

Wheat endosperm hardness. Part I. Relationships to colour of kernel cross-section

The aim of this study was to determine to what extent the measurement of wheat endosperm colour can be used to predict its hardness. The results indicate that there is no general (for all varieties) relationship between the colour of wheat endosperm and its hardness. Nevertheless, endosperm hardness tends to increase along with increasing values of b*, H and S attributes and decreasing values of a*. More promising results were obtained when the colour–hardness relationship was examined within a variety. In all cases, the results were statistically significant, but the endosperm hardnesses of Zyta, Rysa, Banti, Sakwa, and Mewa varieties were found to be more closely linked with the colour of the central part of the endosperm (r ranging from 0.53 to 0.76), whereas that of durum and Elena wheats were found to be more closely linked with the colour of the whole endosperm (r=0.70 and 0.57 respectively). It was observed that the varieties examined can be divided into three groups differing in the range of changes in hardness as a function of the b* attribute of endosperm colour. For group I (durum and Zyta), the rate of hardness increase was higher than that of group II (Rysa, Banti and Sakwa). The third group (Elena and Mewa) was characterised by the highest slope of hardness versus b*; however, it was well differentiated from group I by its low values for yellow.     

Spectral density matrix description of polarization mode dispersion

We introduce a power spectral density matrix formalism that incorporates both the pulse shape and the field polarization and can therefore easily describe averages over random fluctuations of the local birefringence vector. We demonstrate that quantities such as the differential time delay, power diffusion, and decoherence effects can be obtained directly from the equations of motion for the power density matrix. This approach can be applied to pulses with arbitrary frequency-dependent polarization and intensity distributions and in particular makes possible the minimization of the eye-opening penalty through the proper choice of the initial pulse profile.     

Free volume in condensed phases: Separation of contributions

Free volume present in condensed phases is either divided among the atoms present, or treated as independent holes. If a distribution of hole sizes is assumed, both approaches can be reconciled: smaller holes (interstitials) can be considered as being attached to atoms, while holes larger than a critical size (e.g. atomic) can be treated as independent. The distribution obtained depends on the choice of a free volume model. The model of Landau and Lifshits is studied in detail as an example. Numerical calculations are reported for liquid toluene in the 220–370K range. Temperature increase produces an increase in the number of independant holes which continually coalesce. Initially, interstitial holes grow slightly with a temperature increase, but then their size tends asymptotically to a limit.     

Synthesis of passive networks containing periodically operated thyristors

This paper gives a new approach to the designing of power electronic networks. A method for the determination of passive time-varying networks is given when time functions of the excitation and response are given. These time functions are periodic. the period is divided into intervals. the network is linear and time-invariant in each interval. A sequence of the linear time-invariant networks is realized using switches. Switched windings of a multiport transformer are defined. Such elements enable one to realize the sequence of the linear time-invariant networks. Conditions for the substitution switches for thyristors are formulated. A structure of a thyristor converter is presented as an example.     

Effect of some operating variables on cobalt(II) transport across a bulk liquid membrane

An experimental study is presented on facilitated transport of cobalt(II) cations through a bulk liquid membrane containing di(2-ethylhexyl)phosphoric acid (D2EHPA). The effects on the kinetics of cobalt(II) transport of stirring rate of the receiving phase and its acidity, mobile carrier (D2EHPA) concentration, emulsifier (Span 80) concentration, initial cobalt concentration, interfacial area, and membrane thickness have been investigated. It has been found that cobalt transport increased with both stirring of the receiving phase and its acidity, while the presence of emulsifier reduced this transport, particularly at the membrane/receiving phase interface. Moreover, the mean cobalt transport rate was practically independent of membrane/feed solution interfacial area (under experimental conditions), while this rate substantially increased with the initial cobalt concentration in aqueous feed solution.     

A kinetic study of precipitate flotation of Zinc(II), Cobalt(II) and Copper(II) hydroxides

An experimental kinetic study has been completed on precipitate flotation of Zn(II), Co(II) and Cu(II) hydroxides (initial metal concentration 1 × 10^?-2M) with the anionic surfactant, sodium dodecyl benzenesulphonate (1 × 10^?-4M), at varying equilibrium pH. An original radioactive isotope procedure was applied and proved to be sufficiently accurate. Kinetic equations of Rubin and co-workers were found to be relevant for precipitate flotation of hydroxides. From the flotation rate constant (k_p) determined at varying equilibrium pH of floated suspensions it appeared that the selective flotation of individual compounds from mixed precipitate was possible as a result of the ‘kinetic effect’.     

Studies on the usefulness of Cucurbita maxima for the production of ready-to-eat dried vegetable snacks with a high carotenoid content

Recent research indicates a beneficial influence of a diet rich in β-carotene on human health. For that reason, experiments were undertaken to process winter squash with a high carotenoid content into ready-to-eat dried snacks. Sensory quality and dietary value of chips and crispy cubes made from different cultivars were investigated.The suitability of winter squash for drying purposes depended mainly on the dry matter content in the raw material. Although all the investigated cultivars can be used for producing chips, obtaining high quality porous cubes requires at least 15% of dry matter. ‘Justynka F1’ emerged as the most suitable cultivar for processing; both chips and cubes produced from its fruits were characterized by a high sensory quality and contained significant amounts of beta-carotene (225- 253 μg g-1). Also, the cultivar ‘Amazonka’ could be considered for the production of chips as it allowed us to obtain a product with a high beta-carotene content (200 μg g-1) and good sensory properties. The dried ready-to-eat crispy vegetable snacks made from the new cultivars of winter squash could be exploited as a novel attractive product with the attractive taste and colour to serve as a valuable source of carotenoids in human diet.     

Microvaristors in thick-film and LTCC circuits

ZnO-based varistors protect electronic circuits against overvoltage. High temperature from the range of 1150-1300 °C is required for proper sintering of such material. Varistor inks with lower firing temperature are needed for application in thick-film and LTCC technology. ZnO-based thick-film composition was prepared and varistors were fabricated on alumina and LTCC substrate. Different topologies (capacitor-like or planar), electrode metallurgies (PdAg, Au or Pt-based) and firing profiles (850 °C or 950 °C) were used. Samples microstructure was investigated. Varistor I-V characteristics, long-term stability and durability to high voltage pulses were examined. Satisfactory results were achieved, because nonlinearity coefficient α up to 23 was obtained for capacitor-like varistors with Pt terminations on LTCC substrates, long-term thermally aged (150 h at 250 °C) varistors had slightly smaller nonlinearity coefficient and characteristic voltage, V_1 mA and components subjected to series of high voltage pulse (1000 pulses with 10 mA amplitude and 5 ms duration each) exhibited almost the same electrical parameters.