Shear softening and thixotropic properties of wheat flour doughs in dynamic testing at high shear strain

Shear softening and thixotropic properties of wheat flour doughs are demonstrated in dynamic testing with a constant stress rheometer. This behaviour appears beyond the strictly linear domain (strain amplitude ₀ 0.2%),G,G and |^*| decreasing with ₀, the strain response to a sine stress wave yet retaining a sinusoidal shape. It is also shown thatG recovers progressively in function of rest time. In this domain, as well as in the strictly linear domain, the Cox-Merz rule did not apply but() and | ^*())| may be superimposed by using a shift factor, its value decreasing in the former domain when ₀ increases. Beyond a strain amplitude of about 10–20%, the strain response is progressively distorted and the shear softening effects become irreversible following rest.     

The study of the mechanical impedance of foods and biomaterials to characterize their linear viscoelastic behavior at high frequencies

A new instrumental setup, which is based on the oscillatory squeezing flow model, was developed to characterize the viscoelastic properties of foods and biopolymers. Analysis of the data was performed by two different approaches. The first approach employed principles of vibration to determine viscous damping and elasticity of the sample harmonically compressed between two plates. The second approach involved the use of additional calculations based on the squeezing flow model which were linked to concepts of vibration analysis, such as mechanical impedance, to determine fundamental rheological parameters like complex viscosity and related (elastic and viscous) moduli. The experimental setup for the method is simple to use and could be attached to existing commercial instruments such as texture analyzers and universal testing machines. The use of the proposed method with this type of instruments would provide them with the additional capability of performing dynamic rheological testing. The dynamic mass of the instrument was significantly low when compared to that of other instruments that use similar principles. This low dynamic mass enabled the use of relatively higher frequencies for the testing of the samples. Comparison of the viscous and elastic moduli obtained with the proposed method and from conventional rheometers for a variety of foods and biopolymers showed good agreements.     

Experimental and conceptual problems in the rheological characterization of wheat flour doughs

Wheat flour dough is an industrially important material and a better understanding of its rheological behavior could have long ranging impact on the agricultural and the food processing industries. However, rheological characterization of dough is proving to be difficult due to a range of testing issues and anomalies in flow behavior. In a cone-and-plate rheometer wheat flour doughs “roll-out” of the gap before steady state viscosities can be established, as discussed by Bloksma and Nieman (1975). However, the mirror image of the transient viscosity-time plot obtained using a cone-and-plate viscometer has been used to obtain an estimate of steady shear viscosity behavior (Gleissle, 1975). To check this transient methodology for doughs, a second method, in addition to cone-and-plate transient flow, for determination of the shear viscosity, was needed. For this, capillary extrusion was chosen. Both a piston-driven and pressure driven capillary rheometer were employed. End corrections were determined to provide information on both the shear viscosity and, following Binding (1988), the extensional viscosity of the doughs. There are few data available on end corrections for doughs, though published data by Kieffer indicate that the corrections are unexpectedly very high. In this present work it was found that the end correction experiments were very difficult and imprecise in part due to the time-dependent nature of the doughs and difficulties in preparing replicate batches required to compare dies of differing L/R values. Further it was unexpectedly found that the samples, though prepared by normal mixing procedures to the “optimum” level, were so heterogeneous that large fluctuations in the pressure at constant output rate (in the piston-driven rheometer) and in output rate at constant pressure (in the pressure-driven instrument) were observed. These fluctuations could be eliminated by overmixing of the doughs, but overmixed doughs are of little practical interest. Although the problems encountered in this work were significant, it was encouraging that even these preliminary studies indicate that rheological measurements are effective in differentiating between spring and winter wheats. Defining a constitutive model for dough rheology still remains a major challenge, as results from one type of testing do not corroborate the findings from a different type of testing. Received: 19 May 1998 Accepted: 27 July 1998     

Lubricated squeezing flow of thin slabs of wheat flour dough: comparison of results at constant plate speed and constant extension rates

Lubricated squeezing flow experiments on wheat flour dough have, until now, mostly been performed in constant plate speed mode (CPS), i.e. at a permanently increasing extension rate. We have compared the results obtained under the CPS and constant extension rate (CER) modes using one of the very few commercial rheometers that allow operation in the CER mode. In both cases, and at any constant biaxial strain, a power law could be fitted to the stress versus extension rate data, the “consistency index” (K) increasing continuously with the strain and the “flow behaviour index” (n) being constant only up to a low strain value (≈0.25) and then decreasing. When compared to the CER mode, the CPS mode produced higher K and n values. For wheat flour doughs, an increase in K with extension may be associated to a strain-hardening phenomenon but the roles of viscoelasticity and lubricant thinning are discussed.     

Psychological distress and breast self-examination frequency in women at increased risk for hereditary or familial breast cancer

BACKGROUND: The Magnetic Resonance Imaging Screening study evaluates the efficacy and psychological impact of a surveillance program for women at increased risk for hereditary or familial breast cancer in the Netherlands. Surveillance consists of biannual physical examination, annual mammography, annual MRI and monthly breast self-examination (BSE). OBJECTIVE: To examine the association between psychological distress and reported BSE frequency. METHODS: Two months prior to surveillance demographics, BSE frequency, general distress (Hospital Anxiety and Depression Scale and the somatic scale of the Symptom Checklist-90) and breast cancer-specific distress (Impact of Event Scale) were assessed in 316 women (mean age 40.5 years, range 21-63 years). RESULTS: The majority (57%) reported performing monthly BSE. Ten percent reported never performing BSE, 20% less frequently than once a month and 13% at least once a week. Women below the age of 40 who examined their breasts more frequently than recommended (i.e. at least once a week) were shown to be significantly more distressed than the other women in the sample (p = 0.03). These women represented 15% of all the women below the age of 40 years in our study sample. CONCLUSION: Higher breast cancer-specific distress scores were observed among younger women who examined their breasts at least once a week. It is important for physicians to be aware of this hypervigilant behaviour, especially since it is correlated with breast cancer-specific distress.     

Genetic services and research in the state of Minas Gerais, Brazil

The state of Minas Gerais in Brazil has a surface of 586,528 km(2), and 18 million inhabitants. Infant mortality rate is 20/1,000, and congenital anomalies are its second cause. There are 11 medical schools where basic genetics, but not clinical genetics, is taught. Genetic services in the state include: newborn screening for hypothyroidism, phenylketonuria, sickle cell disease and cystic fibrosis; clinical-genetic diagnostic evaluation and counseling; prenatal diagnosis, fetal medicine and paternity testing. Medical genetic services and research are underdeveloped because of limitations such as lack of health policies in genetics, small number of trained specialists, little knowledge about genetics among health professionals and low reimbursement rates.     

A short account of some women in mathematics,engineering and astronomy

Editor's Note: This paper may serve as a greeting to the United Nations Fourth World Conference on Women to be held in Beijing in September, 1995. It is also the first paper contributed to the newcolumn “The History of Mechanics” in our journal, which was set up also at the suggestion of Dr. Johnson. We will welcome further contributions on that line.     

The role of tsunami buoy played in tsunami warning and its application in South China Sea

The tsunami was a sudden marine disasters. Tsunami waves can quickly spread to near-shore and cause the disaster after the tsunami. So it is very important of timely monitoring and early warning of the tsunami. After several unsuccessful tsunami forecasting, the United States developed tsunami buoy specifically for the early detection of tsunami waves. Tsunami buoy can not only be able to display occurrence of the tsunami, it is real time data but also be assimilated into the tsunami warning system, to improve the accuracy of the tsunami forecasting. Several tsunami events in the recent few years have proven the important role of the tsunami buoys. Subsequently, the tsunami warning system based on tsunami buoys was into regular operation. The system accurately predicted the results on March 11, 2011 Japan tsunami event. State Oceanic Administration (SOA), China also deployed 2 tsunami buoys in the South China Sea (SCS), which also played an important role in the warning process of Japan tsunami on March 11, 2011. National Marine Environmental Forecasting Center/State Oceanic Administration (NMEFC/SOA) will collaborate with Pacific Marine Environmental Laboratory/National Oceanic and Atmospheric Administration (PMEL/NOAA) to develop assimilation method making use of real time data of tsunami buoy and build a forecasting system in SCS in the future.     

Relationship between bearing capacity and depth of soft layer of paddy fields in South China

The bearing capacity of paddy field in South China was measured with a kind of penetrometer. A straight line relationship is valuable in summarizing the dependence of bearing capacity on depth of soft soil layer.     

Viscosity of concentrated solutions of ethylene-vinylacetate copolymers in paraffin at three molecular weights and at three temperatures

Summary Measurements of the viscosity of concentrated solutions of the ethylene-vinyl-acetate copolymer (EVA) in paraffin were carried out at a temperature 80°C; 120.5°C; 150°C, at molecular weights of the EVA,M ₂ = 150 000; 200 000; 250 000, and at concentrationsc ₂ up to 11 g/100 cm³ solution.The equation ofBueche andKelley and its extension to the lower concentrations (both related to the free-volume theory) and the semiempirical equations ofOnogi et al. and ofWeissberg et al., were considered with the aim of correlating the values of vs.c ₂ in the most general way possible. The numerical elaboration of the data made it possible to calculate the value of (root-mean-square deviation between calculated and experimental ln) in the various cases, and it emerged that when curves ln vs.c ₂ are considered atT andM ₂ constant, the best interpolation is obtained withBueche's equation with three parameters (,f ₁,f₂), while if all the experimental points are considered withT andM ₂ variableWeissberg's equation gives the best interpolation. The behaviour ofOnogi's equation is intermediate, however the master curves atT = constant make it possible to assemble the data with limited dispersion.The comparison of our viscosity data with the ones calculated by means of the free-volume theoretical expressions leads to the conclusion that the paraffin-EVA system has been studied in a concentration region below the critical value of the polymer concentration above which the chain entanglements prevail.

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Zusammenfassung Viskositätsmessungen an konzentrierten Lösungen von Äthylen-Vinylacetat-Copolymer (EVA) mit MolekulargewichtenM ₂ von 150 000; 200 000 und 250 000 in Paraffin wurden bei Temperaturen von 80; 120,5 und 150°C für Konzentrationenc ₂ bis zu 11 g/100 cm³ durchgeführt.Die aus der Theorie des Freien Volumens abgeleitete Gleichung vonBueche undKelley und ihre Modifikation für niedrige Konzentrationen sowie die halbempirischen Gleichungen vonOnogi et al. und vonWeissberg et al. werden in möglichst allgemeiner Weise mit den experimentellen Kurven(c ₂) korreliert. Die numerische Auswertung mit der Methode der kleinsten Quadrate ergibt, daß für konstant gehaltenesT undM ₂ die beste Interpolation von ln gegenc ₂ durch die drei-parametrige Bueche-Gleichung gegeben wird, wohingegen für die Gesamtheit der experimentellen Werte mit variabler TemperaturT und KonzentrationM ₂ die Weissberg-Gleichung die beste Korrelation liefert. Die Onogi-Gleichung liegt in ihrem Verhalten zwischen den beiden genannten Gleichungen, doch ermöglichen es die Master-Kurven fürT = const, alle Daten mit begrenzter Streuung zusammenzufassen.Ein Vergleich der hier gemessenen Viskositätswerte mit den aus der Theorie des Freien Volumens berechneten führt zu dem Schluß, daß das Paraffin-EVA-System in einem Konzentrationsbereich untersucht worden ist, der unterhalb der kritischen Polymerkonzentration liegt, bei dem der Einfluß der Kettenverhängungen die Oberhand gewinnt.

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With 5 figures and 5 tables     

Combined effects of topography and bottom friction on shoaling internal solitary waves in the South China Sea

A numerical study to a generalized Korteweg-de Vries (KdV) equation is adopted to model the propagation and disintegration of large-amplitude internal solitary waves (ISWs) in the South China Sea (SCS). Based on theoretical analysis and in situ measurements, the drag coefficient of the Chezy friction is regarded as inversely proportional to the initial amplitude of an ISW, rather than a constant as assumed in the previous studies. Numerical simulations of ISWs propagating from a deep basin to a continental shelf are performed with the generalized KdV model. It is found that the depression waves are disintegrated into several solitons on the continental shelf due to the variable topography. It turns out that the amplitude of the leading ISW reaches a maximum at the shelf break, which is consistent with the field observation in the SCS.Moreover, a dimensionless parameter defining the relative importance of the variable topography and friction is presented.     

国内外大学工科专业力学课程设置情况对比

调查了国内外若干大学机械、土木与航空宇航专业力学基础课程的设置情况,通过对统计数据的对比、分析,揭示了力学作为基础和专业基础在航空、机械、土木等专业培养计划中的重要性,指出了国际工程教育中“大力学”的趋势以及相应的在教学内容上所出现的整合与优化. 同时,文中还对国内有关专业力学基础课程的设置与教学提出了建议.     

Instability and localization of plastic flow in shear at high strain rates

Shear band formation in a thermal viscoplastic heat conducting material is described in a simple shear test at high strain rate with inertia effects. The classical perturbation method is discussed, and a new relative perturbation method accounting for non-steadiness of plastic flow is presented. They respectively provide instability and localization criteria which are compared. Furthermore both are compared to available nonlinear exact results and to experimental data. The influence of material parameters, initial imperfections, and boundary conditions is described.     

Frequency and development of slugs in a horizontal pipe at large liquid flows

The generation of slugs was studied for air–water flow in horizontal 0.0763 m and 0.095 m pipes. The emphasis was on high liquid rates (u_LS ? 0.5 m/s) for which slugs are formed close to the entry and the time intervals between slugs are stochastic. A “fully developed” slug flow is defined as consisting of slugs with different sizes interspersed in a stratified flow with a height slightly larger than the height, h₀, needed for a slug to be stable. Properties of this “fully developed” pattern are discussed. A correlation for the frequency of slugging is suggested, which describes our data as well as the data from other laboratories for a wide range of conditions. The possibility is explored that there is a further increase of slug length beyond the “fully developed” condition because slugs slowly overtake one another.     

The expression of stress and strain at the tip of notch in reissner plate

In this paper, the eigenequation of notch in Reissner plate is derived by the eigenfunction method. Eigenvalues of different notches with different angles are calculated by Muller iteration method.The expression of stress and strain at the tip of notch in Reissner plate is obtained.