Edelen’s dissipation potentials and the visco-plasticity of particulate media

Following is an elaboration on D. G. B. Edelen’s (1972–1973) nonlinear generalization of the classical Rayleigh-Onsager dissipation potentials and the implications for the models of viscoplasticity. A brief derivation is given via standard vector calculus of Edelen’s potentials and the associated non-dissipative or “gyroscopic” forces and fluxes. It is also shown that certain extensions of Edelen’s formulae can be obtained by means of a recently proposed source-flux relation or “inverse divergence,” a generalization of the classical Gauss-Maxwell construct. The Legendre–Fenchel duality of Edelen’s potentials is explored, with important consequences for rate-independent friction or plasticity. The use of dissipation potentials serves to facilitate the development of viscoplastic constitutive equations, a point illustrated here by the special cases of Stokesian fluid-particle suspensions and granular media. In particular, we consider inhomogeneous systems with particle migration coupled to gradients in particle concentration, strain rate, and fabric. Employing a mixture-theoretic treatment of Stokesian suspensions, one is able to identify particle stress as the work conjugate of the global deformation of the particle phase. However, in contrast to past treatments, this stress is not assumed to be a privileged driving force for particle migration. A comparison is made with models based on extremal dissipation or entropy production. It is shown that such models yield the correct dissipative components of force or flux but generally fail to capture certain non-dissipative, but mechanically relevant components. The significance of Edelen’s gyroscopic forces and their relation to reactive constraints or other reversible couplings is touched upon. When gyroscopic terms are absent, one obtains a class of strongly dissipative or hyperdissipative materials whose quasi-static mechanics are governed by variational principles based on dissipation potential. This provides an interesting analog to elastostatic variational principles based on strain energy for hyperelastic materials and to the associated material instabilities arising from loss of convexity.     

Electrical impedance spectroscopy and electrical response in metal/non-metal systems

A new analysis of the electrical response of a macroscopic solid state system to an arbitrary electrical voltage input is presented. The results indicate that with a small, sinusoidal voltage input within the classical frequency range (ω < 10¹⁰Hz), the electrical response in spatially homogeneous systems mirrors first of all the static, spatial distribution of the mobile charge carrier density through the local electrical conductivity relaxation time. This enables any system, inclusive interface and electrical contact regions to be modelled by a simple, passive R, C electrical network, where each of the network elements has a very direct physical meaning. Ultra pure, single crystal silicon, pure polycrystalline silicon and Al-Al₂O₃-Au metal-insulator-metal (MIM) structure are used as illustrative examples.     

Layer by Layer Assembly of a Biocatalytic Packaging Film: Lactase covalently Bound to Low‐Density Polyethylene

Active packaging is utilized to overcome limitations of traditional processing to enhance the health, safety, economics, and shelf life of foods. Active packaging employs active components to interact with food constituents to give a desired effect. Herein we describe the development of an active package in which lactase is covalently attached to low‐density polyethylene (LDPE) for in‐package production of lactose‐free dairy products. The specific goal of this work is to increase the total protein content loading onto LDPE using layer by layer (LbL) deposition, alternating polyethylenimine, glutaraldehyde (GL), and lactase, to enhance the overall activity of covalently attached lactase. The films were successfully oxidized via ultraviolet light, functionalized with polyethylenimine and glutaraldehyde, and layered with immobilized purified lactase. The total protein content increased with each additional layer of conjugated lactase, the 5‐layer sample reaching up to 1.3 μg/cm². However, the increase in total protein did not lend to an increase in overall lactase activity. Calculated apparent K_m indicated the affinity of immobilized lactase to substrate remains unchanged when compared to free lactase. Calculated apparent turnover numbers (k_cat) showed with each layer of attached lactase, a decrease in substrate turnover was experienced when compared to free lactase; with a decrease from 128.43 to 4.76 s^?1 for a 5‐layer conjugation. Our results indicate that while LbL attachment of lactase to LDPE successfully increases total protein mass of the bulk material, the adverse impact in enzyme efficiency may limit the application of LbL immobilization chemistry for bioactive packaging use.     

Inactivation of Listeria monocytogenes on a polyethylene surface modified by layer-by-layer deposition of the antimicrobial N-halamine

Modification of food contact surfaces to be antimicrobial represents an approach to address the problem of cross-contamination in the food industry. The effect of increasing levels of surface modification on low density polyethylene (LDPE) through application of N-halamines on the inactivation kinetics of Listeria monocytogenes Scott A was evaluated. Increasing levels of modification were applied through layer by layer deposition on LDPE surface (1–5 double layers of polyethyleneimine and poly(acrylic acid)). Surface modification was achieved and confirmed through Fourier Transform Infrared Spectroscopy (FTIR). From 1 to 5 double layers, the N-halamine content ranged from 3.42 ± 1.2 to 27.30 ± 3.5 nmol cm⁻². More than four logarithmic cycles (>99.99%) reduction was reached against L. monocytogenes Scott A after different contact times depending on the level of modification, that varied from 50 to 110 min (from 5 to 2 double layers). Inactivation kinetics followed a sigmoidal behavior.     

Frictionless conveying of frictional materials

Following a brief review of the technology and previous analyses of vibratory conveying of granular materials, a general solution is derived for a well-known rigid-slab model of slide-conveying in open and closed conduits, with Coulomb friction at the walls. The solution is applied to periodic rectangular-wave and sinusoidal forcing, and it is shown that the rectangular-wave forcing admits ideal cycles in which the kinematically optimal transport is also thermodynamically optimal, in the sense that no energy is dissipated by sliding friction.     

Rats with area postrema lesions have lengthy eating and drinking bouts when fed ad libitum: implications for feedback inhibition of ingestive behavior

Ad libitum ingestive behavior of rats with area postrema lesions (APX) was monitored electronically every 6 s for 23 hr. Whereas control rats ate on average 32.2 g of food each day in 16.3 distinct bouts, rats with APX ate comparable amounts of food (28.6 g) in much fewer daily bouts (5.8) that were very large. Controls drank 38.4 ml of water daily in 17.8 bouts, whereas rats with APX consumed more than twice as much water (101.5 ml) in a similar number of bouts (18.5). Controls drank 5.3 ml of 0.5 M NaCl daily in 7.0 bouts, whereas rats with APX consumed 9 times as much saline (45.5 ml) in more bouts (18.2) that were relatively large. These and other results suggest that the area postrema plays an important role in detecting inhibitory signals generated by food or fluid intake and that feeding and drinking bouts may increase in size after APX, because the feedback inhibition provided by those signals is diminished.     

In vitro susceptibility of Malassezia furfur to the essential oil of Melaleuca alternifolia

The susceptibility of 64 Malassezia furfur isolates to Melaleuca alternifolia oil was determined. The minimum inhibitory concentration for 90% of isolates was 0.25% by agar dilution and 0.12% by broth dilution. These data indicate that tea tree oil may be useful in the treatment of skin conditions involving M. furfur.     

Ethanol inhibits human osteoblastic cell proliferation

Increasingly, patients undergoing coronary artery bypass grafting (CABG) are elders, have had previous CABG, and have poor left ventricular function. To evaluate determinants of perioperative myocardial infarction (PMI) after isolated CABG, 499 consecutive patients were reviewed. Definite PMI (total peak creatine kinase [CK] > 700 U/L, creatine kinase MB [CK-MB] > 30 ng/ml, and new pathologic electrocardiographic Q waves) occurred in 25 patients (5.0%) and probable PMI (total peak CK > 700 U/L, CK-MB > 30 ng/ml, and a new wall-motion abnormality) occurred in 10 (2.0%) patients. According to multivariate logistic regression analysis, independent risk factors for definite or probable PMI (adds ratios; 95% confidence intervals) were emergency surgery (3.1; 1.1 to 8.4; p = 0.003), aortic cross-clamp time > 100 minutes (4.2; 1.6 to 11.2; p = 0.004), myocardial infarction in the preceding week (2.6; 1.0 to 6.4; p = 0.04), and previous revascularization (2.4; 1.1 to 5.2; p = 0.02). In conclusion, both preoperative and intraoperative factors influence the risk of PMI after CABG. Despite changes in the profile of patients undergoing CABG, the incidence of PMI in this tertiary center is comparable with that found in earlier series, probably because of improvements in surgical techniques and postoperative care.