PALS Methods Research Articles

Radiation‐induced defects in chalcogenide glasses characterized by combined optical spectroscopy, XPS and PALS methods

AbstractTemperature‐dependent optical absorption spectroscopy, high‐resolution X‐ray photoelectron spectroscopy and positron annihilation lifetimes spectroscopy are utilized to understand radiation‐induced changes in Ge–Sb–S chalcogenide glasses. Theoretically predicted topological scheme of γ‐induced coordination defect formation in stoichiometric Ge23.5Sb11.8S64.7 glass composition is supported by these measurements. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Tracking the physical aging of poly(ethylene oxide): A technical note

Physical aging of 2 types of PEO could be tracked by the combination of PALS, DSC, and SEM methods. After storing the samples at 40°C±2°C and 75%±5% RH, a decrease in the o-Ps lifetime values and an increase in the melting enthalpies as a function of storage time indicated a reorientation of the polymer chains. The limitations of monitoring enthalpy relaxation confirm the importance of methods that track volume relaxation, such as PALS. Structural changes could be observed even after a short storage time (4 weeks), which highlights the effect of further investigations of the influence of physical aging on the properties of PEO-containing dosage forms.

Dynamics study of free volume properties of SMA/SMMA blends by PAL method

Miscibility of poly(styrene- co-maleic anhydride) (containing 7 wt% maleic anhydride)/poly(styrene- co-methyl methacrylate) (containing 40 wt% styrene) blends were previously studied. It was obtained that SMA70 (containing 70 wt% of SMA in SMA/SMMA blends) is miscible in molecular level but SMA20 is not. In this paper, the two blends selected were used to investigate the temperature dependence of free volume parameters. It showed there are different deviations of free volume parameters in SMA20 and SMA70, and it was interesting that temperature dependence of ortho-positronium lifetime τ 3 of the SMA20 mixture exhibits two breaks in the range temperature from 90 °C to 120 °C, which revealed that the mixture has two glass transition ranges. Also, ortho-positronium lifetime τ 3 of the SMA20 mixture is nearly constant in the temperature range from 130 °C to 160 °C. These indicated that SMA20 blend is phase-separated in room temperature and become miscible above 130 °C, which may be due to steric hindrance effect of phenyl rings of SMMA and SMA. From the deviation of o-Ps lifetimes of SMA70, the single glass transition temperature of SMA70 blend was shown. Combining the previous study, it was further concluded that PAL method seems to be a powerful method to detect in situ phase behavior of immiscible polymer blends and glass transition of miscible polymer blends.

ON ARITHMETIC OPERATIONS OF INTERVAL NUMBERS

In this paper, by using Sengupta and Pal's method of comparison of interval numbers and a new set of arithmetic operations for interval numbers, we propose a theory for the study of arithmetic operations on interval numbers.

Pore Formation in Vycor Glasses Studied by PAL Method

Pore Formation in Vycor Glasses Studied by PAL Method

A Peer-Assisted Learning System ('PALS') approach to teaching basic sciences. A model developed in basic medical pharmacology instruction

This paper describes the development of an activelearning approach to basic science instruction. In this model, students learn facts and concepts with minimal input from subject matter experts. Analysis of examination performance reveals a favorable outcome for this teaching-learning paradigm. During this era of promoting active learning methodologies in higher education, the PALS method offers an alternative to the passive-learning, through lecture-listening and note-recording, approach traditionally used to teach basic sciences.The author invites readership comments and is willing to share teaching materials, exam questions and evaluation instruments upon request.

PAL study of graft polymerization of MMA on polyethylene

PAL measurements were used to study the process of graft polymerization of methyl methacrylate (MMA) to low density polyethylene (LDPE). When the monomer was just sorbed to LDPE, both I 3 and τ 3 were increased. Then MMA was grafted to LDPE, on the other hand, they were decreased. These contrasting results suggests usefulness of the PAL method to study the micro-structures of polymers

THE WEIGERT-PAL METHOD FOR PARAFFIN-EMBEDDED MATERIAL: II. DECALCIFICATION OF MATERIAL CONTAINING BONE

Several methods were tried of decalcifying material to be stained by the Weigert-Pal method for myelin sheaths. Pieces of the tail of a teleost, Porichthys notatus, and peroneal and tibial nerves of the white rat were used. The following procedure was found to give good staining of myelin sheaths after treatment with acid. Fix tissue in 10% neutral formol. Transfer to 5% trichloroacetic acid for five days. Wash one hour, and mordant in potassium bichromate followed by gliabeze, Prepare paraffin sections, stain with Kulschitzky's hematoxylin, and differentiate by Pal's method.

THE WEIGERT-PAL METHOD FOR PARAFFIN-EMBEDDED MATERIAL: I. BULK STAINING AND STAINING OF PARAFFIN SECTIONS

Three methods of staining myelin sheaths by the Weigert-Pal method in paraffin sections are compared. Hyomandibular nerves and spinal cord of the ratfish (Hydrolagus colliei) and tibial and peroneal nerves of the white rat were used. Fixation and mordanting comprised: 10% neutral formol, 48 hr.; 2.5% potassium bichromate at 37 °C., 12 days; gliabeze, 2 days. The tissue was washed for 24 hr., and stained for 24 hr. either in bulk, or while in paraffin sections, or on the slide after coating with celloidin. Kulschitzky's haematoxylin, freshly prepared and artificially ripened, was used for staining. Differentiation was carried out by Pal's method. Bulk staining gave most satisfactory results, with the other methods as second and third alternatives, respectively. Treating the sections with safranin and dehydrating in dioxan was found to give a satisfactory counterstain.