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We provide an overview of transient extensional rheometry techniques for wheat flour doughs in which the deformation and material response is well defined. The behavior of a range of model doughs was explored with a Filament Stretching Extensional Rheometer (FISER). The measurements were also compared to data obtained with a new wind-up extensional rheometer; the SER universal testing platform. A simple empirical constitutive equation, which allows characterization of the experimental results with a small number of parameters, is presented to describe the resulting measurements. To characterize the relaxation modulus of the doughs, small amplitude oscillatory tests were performed on samples that have been shear-mixed in a mixograph for varying lengths of time. The linear viscoelastic properties were found to exhibit a broad power-law dependence on the imposed oscillatory frequency that is very reminiscent of that exhibited by a critical gel. The critical gel model of Winter-Chambon [1, 2] was used as the basis for constructing a non-linear constitutive equation for the material stress by combining the relaxation modulus for the critical gel with a Lodge rubber-like liquid form for the kinematics. Transient uniaxial extensional data recorded from the FISER and SER instruments were then compared to the predictions of the constitutive equation. The model captures the initial power-law response and subsequent strain-hardening; however additional physics is required to describe the rheological phenomena at very large Hencky strains, including finite extensibility effects and filament rupture in extensional flows. Zusammenfassung: Wir geben eine Ubersicht uber Techniken der transienten Dehnrheometrie fur Weizenmehlteig, bei denen die Deformation und die Antwort des Materials wohl definiert sind. Das Verhalten einer Serie von Weizenmehlteigmodellsubstanzen wurde mit dem sog. Filament Stretching Extensional Rheometer (FISER) untersucht. Die Messungen wurden auch mit Daten verglichen, die mit einem sog. Wind-Up-Rheometer erhalten wurden, der SER Universal Testing Platform. Eine einfache empirische Konstitutivgleichung wurde entwickelt, um die Messresultate zu beschreiben, die die Charakterisierung der experimentellen Resultate mit Hilfe von wenigen Parametern erlaubt. Um den Relaxationsmodul von Weizenmehlteig zu charakterisieren, wurden Oszillationsmessungen bei kleiner Amplitude mit Weizenmehlteig durchgefuhrt, der bei unterschiedlicher Dauer in einem Mixograph durch Scherung gemischt worden war. Die linear-viskoelastischen Eigenschaften zeigten eine breite Potenzgesetzabhangigkeit als Funktion der Frequenz, die ahnlich dem Verhalten eines kritischen Gels ist. Das Modell des kritischen Gels von Winter-Chambon [1, 2] wurde als Grundlage genutzt, um eine nichtlineare Konstitutivgleichung fur die Materialspannung zu erhalten durch die Kombination des Relaxationsmoduls des kritischen Gels mit einer Lodge-Gummi-Flussigkeit-Gleichung fur die Kinematik. Transiente uniaxiale Dehndaten des FISER und des SER wurden dann mit den Vorhersagen der Konstitutivgleichung verglichen. Das Modell beschreibt die anfangliche Potenzgesetz-Antwort und die nachfolgende Dehnverfestigung. Jedoch ist zusatzliche Physik notwendig, um die Phanomene bei grossen Dehnungen zu beschreiben einschliesslich der Effekte basierend auf der endlichen Verstreckbarkeit und des Reissens des Filaments in der Dehnstromung. Resume

Objective To determine the prevalence of diabetes-related complications in subjects with fibrocalculous pancreatic diabetes (FCPD) and compare them with subjects with type 2 diabetes mellitus matched for age, sex, and duration of diabetes. Methods The study group comprised of 277 FCPD patients and 277 age, sex, and duration of diabetes-matched type 2 diabetic patients. All the study subjects underwent a detailed clinical examination, and fasting blood samples were obtained for biochemical studies. Peripheral Doppler was used for diagnosis of peripheral vascular disease (PVD). Vibratory perception threshold (VPT) was determined using biothesiometry for diagnosis of neuropathy. Diagnosis of coronary artery disease (CAD) was based on medical history and 12-lead resting ECG. Retinal photographs were used for diagnosis of retinopathy using a modified version of Early Treatment Diabetic Retinopathy Study (ETDRS) grading system. Results FCPD patients had lower body mass index (BMI) ( P P P P P P P P P =.028), duration of diabetes ( P P =.026); nephropathy: diastolic blood pressure ( P =.016) and glycosylated hemoglobin ( P =.040); neuropathy: age ( P P =.003), and glycosylated hemoglobin ( P =.001). Among subjects with FCPD, systolic blood pressure ( P =.013), glycosylated hemoglobin ( P =.021), and duration of diabetes ( P P =.057), glycosylated hemoglobin ( P =.010), and duration of diabetes ( P =.024) with nephropathy and age ( P =.011) and BMI ( P =.010) with neuropathy. Conclusion: The prevalence of retinopathy, nephropathy, neuropathy, and PVD was similar among FCPD patients and type 2 diabetic patients, but the prevalence of CAD was lower among FCPD patients.

Extensional rheological properties are important in characterization and processing of polymeric liquids. The use of entrance pressure drop to obtain extensional viscosity is particularly attractive because it can be applied to both low and high viscosity liquids using the Bagley correction obtained from a conventional capillary rheometer. Low density polyethylene of three different melt index values, including IUPAC-X (a different batch of IUPAC-A), and a high density polyethylene were tested using a commercial capillary rheometer. The entrance pressure drop (ΛP en ) was obtained with a “zero-length” orifice die with an abrupt contraction. The contraction ratio was 12:1. Predictions from several approximate analyses to calculate the uniaxial extensional viscosity ηu (using an axisymmetric contraction) from ΔP en were compared. These comparisons are summarized in the appendices. Due to the transient nature of contraction flows, η u is also a function of the strain (ɛ). This was examined by comparing η u from ΔP en (Cogswell's analysis was chosen for convenience) with transient extensional viscosity (η u +) at different magnitudes of ɛ from fiber-windup technique (Padmanabhan et al., 1996). η + at ɛ≈ 3 was found to be close to η u from ΔP en (using Cogswell's analysis) for two LDPE samples that had fiber-windup data available. The magnitude of the strain in the contraction did not vary with strain rate.

The fiber‐windup technique, developed by Macosko and Lorntson [SPE Tech. Papers 19, 461–467 (1973)] for rotational shear rheometers, was re‐examined to obtain transient uniaxial extensional viscosity data. Macosko and Lorntson used a special force transducer to measure the tension in the filament being pulled. In contrast, in this study commercial rotational shear rheometers (Rheometrics Mechanical Spectrometer‐800 and Rheometrics Fluids Spectrometer‐II) with torque transducers were used to obtain the extensional viscosity. One end of the sample is clamped, while the other end is wound around a drum at a constant rotational speed, to achieve a given extension rate. Tests were conducted with a polyisobutylene sample at room temperature to verify reproducibility and were compared with published studies. Results for polyisobutylene and IUPAC‐X low density polyethylene were found to be in good agreement with published results. Hencky strains of up to 6 could be achieved. The technique can provide valuable ext...

Extensional rheology of foods can be important and helpful in various stages of food manufacture, starting from the initial stage of formulation to the final stage of sensory perception of the product by the consumer. Several new techniques have been developed over the last two decades to measure the extensional flow properties of polymeric liquids. Some of these techniques can be employed to measure the extensional viscosity of foods. Three such techniques are reviewed in this paper: the fiber wind-up and the entrance pressure drop technique for high viscosity liquids, and the opposed jets device for low viscosity liquids. The fiber wind-up technique requires a special set of fixtures which is attached to a conventional rotational rheometer. The entrance pressure drop technique requires a capillary rheometer. A large-diameter barrel capillary rheometer is useful to obtain data for wheat doughs. A commercial rheometer is available with the opposed jets configuration for low viscosity liquids (RFX). Extensional viscosity data from all these techniques are examined and their application to foods discussed. The transient extensional viscosity of a high viscosity polyisobutylene (a polymer melt at room temperature) obtained using the fiber wind-up technique over extension rates of 0.5–10 s−1, and up to strains of three is examined. The extensional viscosity of two different wheat flour-water mixtures estimated using the entrance pressure drop technique is presented. Both doughs showed extension-thinning behavior over the range of extension rates examined. The use of the opposed jets device to characterize polysaccharide solutions is discussed based on a study conducted by R. C. Clark in 1991 (Extensional viscosity of some food hydrocolloids. Paper presented at the Sixth International Conference on Gums and Stabilizers in the food industry, Wrexham, Wales, 15–19 July 1991).

A new class of inelastic constitutive equations is presented and discussed. In addition to the rate-of-strain tensor, the stress is assumed to depend also on the relative-rate-of-rotation tensor, a frame-indifferent quantity that brings information about the nature of the flow. The material functions predicted by these constitutive equations are given for simple shear and uniaxial extension. A special case of these equations takes the Newtonian form, except that the viscosity is a function of the invariants of both kinematic tensors on which the stress depends. This simple constitutive equation has potential applications in liquid flow process simulations, since it combines simplicity with the capability of responding independently to shear and extension, as real liquids seem to do. Finally, possible forms for the new viscosity function are discussed.

Rheological properties of food dough melt, such as steady shear viscosity (η) and first normal stress difference (N1), were measured using an in-line slit die rheometer attached to a laboratory model single-screw extruder. The flow rate through the rheometer was varied by altering the screw speed. Alternatively, a sidestream valve, to vary the flow rate through the rheometer at fixed screw speed, was also used to obtain rheological data. The slit die rheometer was tested with corn meal at three different experimental conditions: 25% and 35% moisture contents at 180C barrel temperature and 35% moisture content at 150C barrel temperature. N1 was measured using the hole-pressure and exit-pressure method. Exit pressure measurements were found to be erratic and unreliable. Hole pressure increased monotonically with increasing flow rate and was found to be affected by the processing history. The magnitude of the hole pressure ranged between 2% and 21% of pressure of the flush mounted transducer. For the experimental conditions used in this study, N1 ranged from 3 × 104 to 6 × 105 Pa for shear rates between 30 to 400 s−1. Possible sources of errors in the hole pressure measurements are discussed.

The entrance pressure drop during extrusion cooking of corn grits was measured using a cylindrical die viscometer attached to a single screw extruder and compared with results obtained using low-density polyethylene (LDPE). The cylindrical die viscometer had a length to diameter ratio of 40 with half-entry angles of 30, 37.5, 45 and 90° with the horizontal. The entrance pressure drop at the die was measured as a function of extrusion temperature, product moisture content and the die entry angle. Results indicate that the flow behavior of corn grits and the entrance pressure drop were affected by product moisture content, process temperature and the shear history in the extruder. Entrance pressure drop also increased with wall shear stress for plastic melt, but for food biopolymer, the increase was observed provided shear history effects were minimized. Entrance correction increased with apparent shear rate for LDPE, but the reverse was true for corn meal. Using Cogswell's analysis, corn grits exhibit severe extension thinning behavior in entry flow.

Shear viscosity (η), first normal stress difference (N1), and extensional viscosity (ηE) of polymer melts measured under processing conditions are important in process modeling, quality control, and process control. A slit rheometer that could simultaneously measure η, N1, and the planar extensional viscosity (ηp) was designed and tested by attaching it in-line to a laboratory model single-screw extruder. A tube (circular cross-section) rheometer to measure η and the uniaxial extensional viscosity (ηu) simultaneously was also designed and tested. Two commercial grades of LDPE (low density polyethylene) with melt index values of 6 and 12 were used as test materials for the study. Exit and hole pressure methods were used to estimate N1, and the entrance pressure drop method using the analyses of Cogswell, Binding, and Gibson (the last analysis used with the axisymmetric case only) was used to estimate ηE.

Uniaxial extensional viscosity of cornmeal at moisture contents of 30 and 35% (dry weight basis) and temperature of 160 and 180 o C was estimated from entrance pressure drop measurements during extrusion cooking. The value of the sheat component of the entrance pressure drop was an order of magnitude below that of the extensional component. Food doughs exhibited sheat thinning and extension thinning behavior during processing conditions used. Increasing moisture and temperature decreased extensional viscosity at highet extension rates. The Trouton ratio ranged from 25 to 50 and was affected by product moisture content, barrel temperature, and deformation rate

Slit and capillary dies attached in-line to an extruder are a popular configuration for obtaining the flow curves of food doughs during extrusion-cooking. However, it is demonstrated in this paper that the use of screw speed, especially for a single-screw extruder, to vary the shear rate through the die can result in erroneous flow curves for single-screw extruders. Furthermore, the use of a sidestream valve to vary the flow rate for a given screw speed is shown to result in flow curves that are different and better behaved. Such a procedure will be helpful in single-screw extruder systems, not only in obtaining the true flow curves of the food dough, but also in rheological measurements with in-line rheometers. Data for hole pressure (a measure of the first normal stress difference) are also presented to demonstrate the validity of using the sidestream valve and the error in using the screw speed to obtain rheological measurements during extrusion of starchy foods.

The application of the entrance pressure drop method to evaluate the extensional viscosity of corn meal during extrusion-cooking was investigated. An approximate planar extensional flow was generated by forcing the dough from a circular channel barrel into a slit die. The pressure drop along the contraction was calculated to obtain the entrance pressure drop Δ P en . Both Cogswell's and Binding's analyses were applied to estimate the apparent planar extensional viscosity η pa from Δ P en . The magnitude of η pa from Cogswell's analysis was found to be much larger than that predicted by Binding's analysis. In addition, the severe extension-thinning behavior exhibited by the fluid introduced problems in the calculations of Binding's analysis for some cases. Calculation and interpretation of the Trouton ratios have to be done carefully when extrapolation of the viscosities is required. Moderate to large entrance corrections were obtained, with lower values obtained for the lower moisture contents and temperatures of extrusion. In all cases the entrance correction decreased with increasing flow rate.

Mrs. M.S. is a 67-year-old African American woman with a history of rheumatoid arthritis and psoriatic arthritis who presented to the emergency room with complaint of new-onset rash, chills, and fatigue after she started taking ramipril (5 mg orally every day) for her hypertension. The rash involved entire upper chest, both arms, palms, and soles and was characterized as exfoliating with scattered small pustules of 1-2 mm in size. Patient was admitted with a differential diagnosis of exfoliative dermatitis versus adverse drug reaction for which her ramipril was stopped. After admission, the patient spiked a temperature of 102 degrees F with chills, the entire workup for which was negative, including blood cultures, chest x-ray, and urine analysis. She underwent skin biopsy to find the cause of her rash. With her given clinical characteristics, she was presumed to have generalized pustular psoriasis (GPP), which was later confirmed by biopsy results. She was treated with methylprednisolone to which she responded dramatically with much improvement in her rash and her fever subsided. The flare of GPP was considered to be secondary to ramipril. After reviewing the published literature, there are no published cases of ramipril-induced GPP. Captopril, a different angiotensin converting enzyme (ACE) inhibitor, is known to cause flare of GPP. We presented this case as apart from being the first reported case of ramipril-induced GPP; clinicians and dermatologist should also be aware of this potentially serious complication of psoriasis when they start ramipril in patients with psoriasis.

Corn meal and commercial low density polyethylene (LDPE) were extruded through a slit die using a laboratory model single‐screw extruder at various extrusion conditions. Flow curves for the corn meal showed severe shear thinning behavior (n≲0) at lower moisture contents; molecular degradation, pressure dependence of viscosity, viscous dissipation, slip, and yield stress were identified as the possible factors. Survey of the available literature and the behavior observed in this study indicates that molecular degradation is the major factor responsible for n≲0. A modified viscosity model that includes the die entrance pressure (barrel pressure) for molecular degradation effects was developed; such a model also accounts for the pressure dependence of viscosity. Negative exit pressures for LDPE and both positive and negative exit pressures for corn meal were obtained. Statistical analysis indicated large errors in the exit pressures predicted by the linear extrapolation. These errors originate from several s...

To determine the prevalence of diabetes-related complications in subjects with fibrocalculous pancreatic diabetes (FCPD) and compare them with subjects with type 2 diabetes mellitus matched for age, sex, and duration of diabetes.The study group comprised of 277 FCPD patients and 277 age, sex, and duration of diabetes-matched type 2 diabetic patients. All the study subjects underwent a detailed clinical examination, and fasting blood samples were obtained for biochemical studies. Peripheral Doppler was used for diagnosis of peripheral vascular disease (PVD). Vibratory perception threshold (VPT) was determined using biothesiometry for diagnosis of neuropathy. Diagnosis of coronary artery disease (CAD) was based on medical history and 12-lead resting ECG. Retinal photographs were used for diagnosis of retinopathy using a modified version of Early Treatment Diabetic Retinopathy Study (ETDRS) grading system.FCPD patients had lower body mass index (BMI) (P.001), systolic blood pressure (P.0001), diastolic blood pressure (P.001), serum cholesterol (P.001), serum triglyceride (P.001), and serum creatinine (P.01) but higher glycosylated hemoglobin (P.001) levels compared to patients with type 2 diabetes. Prevalence of CAD was significantly higher among type 2 diabetic patients (11.9%) compared to FCPD patients (5.1%), P.003. There was no significant difference in the prevalence of other diabetic complications between the two study groups (type 2 diabetes vs. FCPD: retinopathy-37.2% vs. 30.1%, PVD-4.3% vs. 4.7%, Neuropathy-25.3% vs. 20.9%, Nephropathy-15.0% vs. 10.1%). Multiple logistic regression analysis revealed the following risk factors for diabetes complications among type 2 diabetic subjects-retinopathy: BMI (P=.028), duration of diabetes (P.001), and glycosylated hemoglobin (P=.026); nephropathy: diastolic blood pressure (P=.016) and glycosylated hemoglobin (P=.040); neuropathy: age (P.001), duration of diabetes (P=.003), and glycosylated hemoglobin (P=.001). Among subjects with FCPD, systolic blood pressure (P=.013), glycosylated hemoglobin (P=.021), and duration of diabetes (P.001) were associated with retinopathy; BMI (P=.057), glycosylated hemoglobin (P=.010), and duration of diabetes (P=.024) with nephropathy and age (P=.011) and BMI (P=.010) with neuropathy.The prevalence of retinopathy, nephropathy, neuropathy, and PVD was similar among FCPD patients and type 2 diabetic patients, but the prevalence of CAD was lower among FCPD patients.

The use of slit rheometers for on-line viscosity measurements of fluid foodstuffs has been gaining increasing popularity in recent years. However, the viscoelastic nature of fluid foodstuffs necessitates the measurement of their elastic properties, which will provide a better overall understanding of the behavior of the foodstuffs during processing. This review discusses the exit-pressure and hole-pressure methods for the on-line measurement of fluid elasticity, and the application of these methods to the control of the extrusion-cooking process. The potential application of the methods to the rheological characterization of viscoelastic fluid foodstuffs in general is also discussed.

Volumetric flowrate was studied in the die of a single screw extruder. Variables included the ratio of die length to die diameter, barrel to die diameter, barrel and die temperature, screw speed and product moisture. Die conductance was determined graphically and analytically. Results indicated that for a constant pressure drop across the die, increasing temperature, die diameter or moisture increased flowrate. Dimensional analysis was used to study the effect of each parameter on the flow through the extruder die. An expression for temperature rise due to viscous dissipation for isothermal flow in the die was developed and nomographs are presented.

Entrance pressure drop of extruder dies increased with a decrease in the ratio of barrel-to-die diameter during the extrusion of corn. For the low Reynolds number flow studied (1.77 x 10−3≤ Re ≤ 9 x 10−5) the viscous component, obtained from Weissberg's analysis, contributed 2% to 40% of the entrance pressure drop and increased as the barrel-to-die diameter ratio decreased. The friction factor for laminar fully developed flow through the die followed the expression f = 16/Re'. Fully developed flow within the die was achieved at a die length-to-diameter ratio of 9.