Mono-aryloxy or mono-alkoxy zirconium complexes/methylaluminoxane catalyst system in ethylene polymerization

Summary Mono-aryloxy zirconium complexes 1–6 or mono-alkoxy zirconium complexes 7–10 were prepared and the ethylene polymerization was carried out in the presence of these complexes/methylaluminoxane. Steric factor of the aryloxy and alkoxy ligands in the complexes remarkably influenced on activity of ethylene polymerization.     

Application of catastrophe theory to power systems

In recent publications dealing with nonlinear systems, nonlinearities existing in the systems under study have drawn much attention. Studies on the effects of nonlinearities in power systems are becoming an increasingly important part of the research on system stability. It is probable that heretofore undiscovered phenomena caused by the nonlinearities involved in load flow equations, generator swing equations and characteristics of control equipments and loads, etc., may be found. This paper presents a new Catastrophe Theory application to nonlinear power systems. Making use of the concept of Duffing's equation, it is shown that a Catastrophe Theory analogy can be used to interpret unstable phenomena caused by system nonlinearities from the viewpoint of oscillations. When considering system nonlinearities due to poor combinations of system parameters and periodic disturbances, there may exist the characteristic “jumps” in system ates that correspond to slow (quasi-dynamic) changes of the frequencies of periodic disturbances. With this Catastrophe Theory approach, a system bifurcation set can be identified to assess the unstable phenomena of power systems.     

Evaluation of Polyvinyl Alcohol Hydrogel as Sustained-Release Vehicle for Transdermal Sytem of Bunitrolol-HCL

In order to evaluate a bunitrolol (β-blocker preparation using poly(vinyl alchol) (PVA) hydrogel for hypertension as a transdermal delivery system, in vitro release characteristics and the permeation of bunitrolol through rat sking from hydrogel and the bunitrolol plasma profile after application onto abdominal skin in rats were examined. The PVA hydrogel containing bunitrolol-HCl was prepared by a low temperature crystallization method. The release of bunitrolol from PVA hydrogel followed with Ficklan diffusion (Higuchi model); the drug relaase, profile versus square root of relase. The release rate and premeation through rat skins of bunitrolol from hydrogels affected with preparation at various physical and chemical states. Longer freezing times, higher polymerization and higher concentration of PVA resulted in lower permeation. These results had relations with the results of release tests. Higher pH of preparation resulted in a higher permeation of bunitrolol, which did not have a relaion with the results of release tests. The plasma concentration of bunitrolol after application of hydrogel preparation onto the abdominal skins were relatively high at early times and sustained a plateau level during 48 h in rates. In conclusion, transdermal delivery system using PVA hydrogel is favorable with prolonged action for low available drugs such as bunitrolol-HCl.     

Incommensurate phase transition of cholesteryl 2,2,3,3-tetrafluoropropionate (CTFP)

This paper describes a paraelectric-incommensurate phase transition of cholesteryl 2,2,3,3-tetrafluoropropionate(CTFP) found at about -94°C by means of X-ray diffraction and dielectric constant studies performed with the single crystal.     

The Glue-Nail deductive database system: Design,implementation, and evaluation

We describe the design and implementation of the Glue-Nail deductive database system. Nail is a purely declarative query language; Glue is a procedural language used for non-query activities. The two languages combined are sufficient to write a complete application. Nail and Glue code are both compiled into the target language IGlue. The Nail compiler uses variants of the magic sets algorithm and supports well-founded models. The Glue compiler's static optimizer uses peephole techniques and data flow analysis to improve code. The IGlue interpreter features a run-time adaptive optimizer that reoptimizes queries and automatically selects indexes. We also describe the Glue-Nail benchmark suite, a set of applications developed to evaluate the Glue-Nail language and to measure the performance of the system.Part of this article was presented at the ACM SIGMOD International Conference on Management of Data, Washington, DC, 1993.Much of this research was done while the authors were at Stanford University, Stanford, California, USA.     

Visualization of progressive breakdown evolution in gate dielectric by conductive atomic force microscopy

To understand the breakdown (BD) mechanism in gate oxide of MOSFET, BD evolution is investigated by a conductive atomic force microscope. High electric fields of both polarities are applied to induce a pre-BD degradation and a BD transient. Structural hillocks and negative charges are simultaneously observed at both pre- and post-BD stages. The hillocks show stress-polarity dependence, and the height increases with BD evolution. A flat-band shift caused by negative charges does not depend on stress polarity. Lateral size of the hillocks and the electrical degradation remains similar throughout the BD evolution. Progressive structural evolution of dielectric BD is confirmed, where polarity-dependent Si deformation plays an important role.     

Digital tracking control of space robots using a transpose of the generalized Jacobian matrix

We have proposed discrete time-control methods using the transpose of the generalized Jacobian matrix (GJM) for free-floating space robots having manipulators. The control methods are robust for singular configurations of robots. Since the methods belong to a class of constant-value control, in this article we propose a digital trajectory tracking control method using the transpose of the GJM. Computer simulations show the effectiveness of the proposed method. This work was presented in part at the 11th International Symposium on Artificial Life and Robotics, Oita, Japan, January 23–25, 2006     

A Review on Current Nanofiber Technologies: Electrospinning,Centrifugal Spinning,and Electro-Centrifugal Spinning

Nanofiber-based products are widely used in the fields of public health, air/water filtration, energy storage, etc. The demand for nonwoven products is rapidly increasing especially after COVID-19 pandemic. Electrospinning is the most popular technology to produce nanofiber-based products from various kinds of materials in bench and commercial scales. While centrifugal spinning and electro-centrifugal spinning are considered to be the other two well-known technologies to fabricate nanofibers. However, their developments are restricted mainly due to the unnormalized spinning devices and spinning principles. High solution concentration and high production efficiency are the two main strengths of centrifugal spinning, but beaded fibers can be formed easily due to air perturbation or device vibration. Electro-centrifugal spinning is formed by introducing a high voltage electrostatic field into the centrifugal spinning system, which suppresses the formation of beaded fibers and results in producing elegant nanofibers. It is believed that electrospinning can be replaced by electro-centrifugal spinning in some specific application areas. This article gives an overview on the existing devices and the crucial processing parameters of these nanofiber technologies, also constructive suggestions are proposed to facilitate the development of centrifugal and electro-centrifugal spinning.     

Radioactivity measurement of Sr/Y-90 mixed with Cs-134 and Cs-137 using large solid angle detectors without chemical separation

We proposed a method to measure the radioactivity of Sr/Y-90 in the mixture of Cs-134 and Cs-137 without chemical pretreatment. It was realized by subtracting the electrons produced in Cs-134 and Cs-137 from entire electron emission rate that can be determined by the efficiency tracer technique in the 4πβ–γ coincidence counting method. The radioactivity of Cs-134 and Cs-137 can be determined by gamma ray spectrometry. The measurements were conducted using plastic and NaI(Tl) scintillation detector with a large solid angle. The validity of the measurement method was shown by agreement of the results with the known radioactivities.     

HRTEM observations on composites of tin and tin dioxide nanoparticles dispersed on carbon nanotubes by single-atoms-to-clusters method

Nano-composites of tin and tin dioxide particles were synthesized on carbon nanotubes by the single-atoms-to-clusters (SAC) method, and their structures were investigated by high-resolution transmission electron microscopy. By changing the heat-treatment temperature during the SAC process, two different types of samples were obtained. The samples prepared around 450 K were aggregates of 2–4 nm-sized tin dioxide nanoparticles, and their size distributions on carbon nanotubes are in the range 20–40 nm. The other samples formed above 600 K had a core–shell structure of diameter 20–40 nm. The core and shell were made of tin single crystal and disordered oxidized tin, respectively. The thickness of the oxidized layers was ca. 4 nm.