Chemical and biochemical changes of hybrid catfish fillet stored at 4 °C and its gel properties

Chemical and biochemical changes of aquacultured hybrid catfish fillet (Clarias macrocephalus × Clarias gariepinus) and its gel-forming ability as affected by age and sex of fish along with storage time were investigated. Fillets were stored at 4 °C for 0, 3, 6, 9, 12 and 15 days. There was no significant effect of sex and age of fish as well as storage time on fat, moisture and ash contents (P > 0.05). The total protein, water soluble protein, and salt soluble protein contents of the fillets significantly decreased with storage time (P < 0.05). On the other hand, pH, total volatile base nitrogen (TVB-N) and autolytic degradation products (ADP) increased as storage time continued (P < 0.05). Decreases in Ca²⁺-ATPase activity and gel properties were observed as storage time increased. However, there was no significant effect of either sex or age of fish on textural properties of gel (P > 0.05). Hybrid catfish fillet stored at 4 °C should be processed within 6 days.     

Rapid detection of hairline cracks on the surface of piezoelectric ceramics

Lead zirconate titanate, also known as PZT, is a type of piezoelectric ceramics commonly used for actuators in modern hard disk drives (HDDs). These PZT actuators are prone to hairline surface cracks, prompting detection and removal during the HDD production. Machine vision is then utilized for automatic detection of these cracks. The developed image processing approach comprises three steps: extraction of the region of interest, enhancement of crack regions, and elimination of irrelevant features. The key step, crack region enhancement, employs image filtering with a specifically designed filter kernel, capable of extracting thin crack regions from the rough surface of PZT actuators. The experiments show that the algorithm reveals cracks with high accuracy and high sensitivity, whereas the overall processing time satisfies the industrial environment.     

Transient dynamics of a rotating spherical liquid drop

The transient rotation of a liquid drop in an infinite gaseous medium is analyzed for two cases: viscous retardation from constant-speed rotation, and steady-torque start-up with development to the steady state. This situation arises when a levitated liquid drop is rotated with an acoustically applied torque. Subsequent changes in the torque cause transient effects. To understand such a system, the two basic problems of start-up and retardation are studied. The rotational Reynolds number is considered to be low enough so that nonlinear inertial effects may be neglected. The Laplace-transform method is used to deal with the time dependence. Since the fluid velocity has only the azimuthal direction (and the profile is independent of it), and the other angular dependence is factorable as sin θ, the solution turns out to be effectively a two-variable problem in r and t. Nevertheless, the finite mass of the spherical drop and its finite viscosity make it a mathematically challenging problem. Besides the full analytical solution, results are obtained in the limits of a solid sphere, and small time for the liquid drop. In all liquid-drop cases, the results are limited to the drop viscosity being higher than the surrounding region. For several common liquids in a gas, the flow field indicates nearly a solid-sphere like behavior, except at small times in the region near the interface. The deviations from the asymptotic center-point velocity are amplified for illustration.     

High‐field electrical properties of new LDPE films prepared using metallocene catalyst

Now low‐density polyethylene (M‐LDPE) prepared using metallocene catalyst has narrower composition distribution and molecular weight distributions than linear low‐density polyethylene (LLDPE) using Ziegler catalyst. The authors compared the electrical insulating properties of M‐LDPE films and conventional LLDPE films. The high‐field current of M‐LDPE was found to be lower than that of LLDPE. The difference in current increased with the decrease of temperature. The high‐field current was much reduced in M‐LDPE with a low melting point. The impulse breakdown strength of M‐LDPE increased with the decrease of temperature. The insulating properties of M‐LDPE with a low melting point were improved at 30 °C. These results were explained by the fact that M‐LDPE with a low melting point includes more low‐molecular‐weight components. We also discuss the effects of antioxidant on the electrical properties of M‐LDPE. We compared the electrical conduction and breakdown strength of undoped M‐LDPE and antioxidant‐doped M‐LDPE. Differences in their electrical properties were minor. It was found that the excellent properties of M‐LDPE do not depend on the effects of antioxidant. © 1999 Scripta Technica, Electr Eng Jpn, 130(2): 1–9, 2000