Phase changes in polyethylene single crystals. The effects of thermal stress and electron irradiation

Single crystals of polyethylene have been reported to undergo a crystallographic phase change from an orthorhombic unit cell to monoclinic when heated to temperatures near their original crystallization temperatures. This change is shown to be due purely to thermal stresses set up between the crystals and substrate on which they lie, arising from a difference in expansion coefficients of crystals and substrate. The orientation of the monoclinic lattice with respect to the orthorhombic lattice is consistent with an effective deformation parallel to the orthorhombic b-axis. At temperatures above 110°C the monoclinic phase relaxes almost completely back to orthorhombic primarily through the greatly increased mobility of the chains in their folded portions. The effects of an electron beam on the polyethylene crystal lattice have been studied by electron diffraction during irradiation at temperatures from −161 to + 110°C. The changes in dimensions of the unit (sub)-cell were determined as functions of the time of irradiation. Above about 30°C a stable hexagonal phase is formed before the crystalline diffraction pattern degrades to a diffuse halo. This change is ascribed to (i) a depression of a transition temperature (due to defects) analogous to that found in n-paraffins when the orthorhombic unit cell becomes hexagonal, and (ii) elastic distortions around the lattice defects. It is also noted that the transformation proceeds readily at 110°C in the absence of radiation if a small dose is given initially: the number of defects under these conditions are few and consequently on cooling to room temperature the hexagonal and orthorhombic phase co-exist. Although no definitive conclusions as to the nature of the reaction can be determined, the evidence is that the defects are primarily scissions and cross-links in the crystal lattice.     

The optimization of pencil beam widths for use in an electron pencil beam algorithm

Pencil beam algorithms for the calculation of electron beam dose distributions have come into widespread use. These algorithms, however, have generally exhibited difficulties in reproducing dose distributions for small field dimensions or, more specifically, for those conditions in which lateral scatter equilibrium does not exist. The work described here has determined that this difficulty can arise from the manner in which the width of the pencil beam is calculated. A unique approach for determining the pencil beam widths required to accurately reproduce small field dose distributions in a homogeneous phantom is described and compared with measurements and the results of other calculations. This method has also been extended to calculate electron beam dose distributions in heterogeneous media and the results of this work are presented. Suggestions for further improvements are discussed.     

A microcomputer based system for quantifying the spatial distribution of inhaled particles in histological lung sections

A system is described for quantifying the spatial distribution of inhaled particles in complete lobar histological sections of rodent lung. It is based on a semi-automatic image analyser, linked to a readily available microcomputer. Application of the system to quantify the aggregation of particles, and their distances from airways and lung periphery is described. The observed distributions are compared with the expected distributions from a random set of particles, and the significance of the difference is calculated. Each statistical test is illustrated by an example.     

Characterization of the water-equivalent material WTe for use in electron beam dosimetry

This paper describes the characterization of the water-equivalent material WTe (produced by St Bartholomew's Hospital, London). The use of epoxy resin phantoms offers a number of advantages over water for radiotherapy dosimetry in terms of robustness and ease of use, but the published uncertainties in the fluence corrections for such phantoms significantly increase the overall uncertainty in the measurement of absorbed dose to water at the reference point. Depth-ionization data were obtained in water and WTe for electron beams in the range 4 MeV to 16 MeV and it was found that the measured fluence in the WTe phantom was approximately 0.4% higher than in a water phantom at the same depth. For measurements only at the reference depth this difference was less, with the fluence in the WTe phantom being 0.2% higher. The standard uncertainty on this value is estimated to be +/- 0.12%, which represents a significant improvement over previous measurements. It was also found that the range scaling factor is not equal to unity, as previously recommended for this material, but that the data was best fitted by the relation 1 mm WTe = 1.01 mm water (with an uncertainty of +/- 0.2%). The results obtained confirm previous investigations of WTe as to its suitability for reference ion chamber dosimetry in the radiotherapy clinic. However, the recommendation is still to use a water phantom wherever possible.     

Activity of antibodies against Salmonella dublin, Toxoplasma gondii, or Actinobacillus pleuropneumoniae in sera after treatment with electron beam irradiation or binary ethylenimine.

Viral contamination of biological material may constitute a risk when samples are exchanged between countries, and it may be necessary to subject the material to an inactivation treatment. The present study investigated possible adverse effects on antibody activity subsequent to either electron beam irradiation or binary ethylenimine (BEI) treatment. The treatments were performed with sera obtained from pigs or cattle. For each treatment level, the posttreatment activity was plotted against the pretreatment activity, and regression analyses were carried out. The slope of the regression line was used as an estimate for the relative posttreatment activity. For a Toxoplasma gondii indirect enzyme-linked immunosorbent assay (ELISA) and agglutination assay as well as for a Salmonella dublin indirect ELISA, the posttreatment activity was more than 89% of the pretreatment activity when the samples were irradiated in the frozen state (on dry ice) with up to 46. kGy or when they were treated with 5 or 10 mM BEI for up to 48 h. The samples were more sensitive to irradiation in the liquid state. Thus, samples irradiated with 22.6 kGy retained 98% of their activity in the indirect ELISA when they were irradiated in the frozen state on dry ice but only 35% of their activity when they were irradiated in the liquid state at 0 degrees C. The patterns seen in an S. dublin blocking ELISA and an Actinobacillus pleuropneumoniae complement fixation assay differed in that samples with a low level of pretreatment activity were subject to a relatively greater decrease in activity than samples with a high level of pretreatment activity. The complement fixation assay was particularly sensitive to irradiation of serum. It is concluded that serum samples retain sufficient activity by both methods of virus inactivation, especially when used in indirect ELISA or in the T. gondii agglutination assay.     

Dose distributions produced by shielded applicators using 241Am for intracavitary irradiation of tumors in the vagina.

Dosimetric characteristics of shielded vaginal applicators containing encapsulated 241Am sources are investigated in this work. Encapsulated 241Am sources emit primarily 60-keV photons which are more effectively shielded by thin layers of high atomic number materials than the 662-keV photons from 137Cs sources. With 241Am, it is possible to achieve almost unidirectional irradiation of localized vaginal tumors. The drastic decrease in irradiation volume on the contralateral side (uninvolved with tumor) is observed to decrease dose by up to 20%, even in the forward direction (unshielded side toward the tumor) of the applicator. A possible explanation for the observed effects of shields in both the forward and backward directions is the reduction of scattered photon fluence due to absorption of photons in the lead shield via photoelectric effect. Current theoretical models do not include this perturbation effect caused by shields on brachytherapy applicators.     

The use of electron beam lithographic graft-polymerization on thermoresponsive polymers for regulating the directionality of cell attachment and detachment

A simple process for nano-patterned cell culture substrates by direct graft-polymerization has been developed using an electron beam (EB) lithography system requiring no photo-masks or EB-sensitive resists. The compound N-isopropylacrylamide (IPAAm) was locally polymerized and grafted directly by EB lithographic exposure onto hydrophilic polyacrylamide (PAAm)-grafted glass surfaces. The size of the surface grafted polymers was controlled by varying the area of EB dose, and a minimal stripe pattern with a 200 nm line-width could be fabricated onto the surface. On the stripe-patterned surfaces, above the lower critical solution temperature (LCST), the cells initially adhered and spread with an orientation along the pattern direction. The magnitude of the spreading angle and elongation of adhered cells depended on the pattern intervals of the grafted PIPAAm. When culture temperature was lower than the LCST, cultured cells detached from the surfaces with strong shrinkage along the pattern direction, and sometimes folded and became parallel with the stripe pattern. This patterned cell recovery technique may be useful for the construction of muscle cell sheets with efficient shrinkage/relaxation in a specific direction and spheroidal 3D cell structures, with application to tissue engineering and microfluidic cellular devices.     

Centrosomes, microtubules, and microfilaments in the reendothelialization and remodeling of double-sided in vitro wounds.

The maintenance of endothelial monolayer integrity is an important function of aortic endothelial cells. Our study was designed to test two hypotheses related to the repair of the wounded endothelial monolayer. First, that the reappearance of the highly ordered cobblestone monolayer after wound closure is associated with specific sequential changes in the cytoskeletal system. Second, that there are different patterns of reendothelialization depending on whether microfilaments or microtubules are disrupted. One and a half millimeter wide wounds were created down the middle of confluent endothelial monolayers so that there were two wound edges facing each other. During the initiation of repair, the centrosomes of the cells on both sides of the wound reorientated to the front of the cell. The dense peripheral band of actin microfilaments disappeared, the cells elongated and migrated as a uniform sheet with wound closure occurring within 60 hours. The rate of closure remained constant until the migrating fronts met. The cytoskeletal changes observed and the rate of closure were similar to those we reported in a single edge wound. At closure, however, there was a transient piling up of cells which disappeared after 24 to 36 hours. Within 36 to 48 hours after closure, the centrosomes became randomly distributed around the nucleus. By 40 to 48 hours, the dense peripheral band started to reappear and the cells returned to a cobblestone appearance 72 to 96 hours after closure. Thus, the remodeling of the confluent monolayer after wound closure occurs in association with a specific series of cytoskeletal changes. When the microfilaments were disrupted with cytochalasin B, cell migration still occurred but it took up to four times longer for closure. These cells were initially flatter than normal and contained only a few microfilament fibers; however, the microtubule system was intact and centrosome reorientation occurred, but at a slower rate. However, when the microtubules were disrupted with colchicine, either at the onset of wounding or during repair, neither centrosome reorientation nor cell migration occurred. Thus wound closure of small-sized wounds require the presence of intact microtubules, whereas the additional presence of microfilaments results in a more rapid and efficient system of reendothelialzation.     

Effect of electron beam irradiation on the structure and properties of electrospun PLLA and PLLA/PDLA blend nanofibers

Poly(l-lactide) (PLLA) and a PLLA/poly(d-lactide) (PDLA) blend (50/50 wt.%) were electrospun into nanofibers. Electron beam (e-beam) irradiation of the electrospun PLLA and blend nanofibers was used as a method to alter their structures and surface properties. The crystalline structures of the nanofibers before and after irradiation were investigated by differential scanning calorimetry. Tensile tests of the aligned nanofibers were also performed to determine the effects of irradiation on the mechanical properties of the nanofibers. The hydrophilicity of the nanofibers was determined by water contact angle measurements, while any degradation of the fibers caused by irradiation could be detected by intrinsic viscosity measurements. The e-beam irradiation method was able to improve the surface hydrophilicity of the PLLA and blend nanofibers, although bulk degradation was inevitable.     

Infrared spectroscopic studies on polyethylene, 7. The use of the methyl deformation band for branch characterisation

The factors relating to measuring the position of the methyl deformation mode at about 1378 cm^?1 with sufficient precision to permit its use for the identification of the different branches present in the various types of “linear” low density polyethylene(as manufactured by the copolymerization of ethylene and a 1-alkene) have been examined systematically. With a data density of eight points per wavenumber, and the well established subtraction procedure with polymethylene or with a near-linear polyethylene to remove the overlapping methylene deformation band, it is possible to achieve a precision of ±0,15 cm^?1. This is ample to distinguish between methyl, ethyl, and butyl or hexyl branches, but not to characterise uniquely these last two. The use of Fourier self-deconvolution to separate the methyl band has also proved very effective. The precision obtainable when these methods are applied to spectra measured with one data point per wavenumber is somewhat lower, but is still adequate for characterisational purposes. The results for a series of polymers containing ethyl branches at various concentrations suggest a small difference for the peak position for branches present in crystalline and amorphous regions.     

Temporal and spatial distribution of Toxoplasma gondii differentiation into Bradyzoites and tissue cyst formation in vivo

During Toxoplasma gondii infection, a fraction of the multiplying parasites, the tachyzoites, converts into bradyzoites, a dormant stage, which form tissue cysts localized mainly in brain, heart, and skeletal muscles that persist for several years after infection. At this stage the parasite is protected from the immune system, and it is believed to be inaccessible to drugs. While the long persistence of tissue cysts does not represent a medical problem for healthy individuals, this condition represents a major risk for patients with a compromised immune system, who can develop recrudescent life-threatening T. gondii infections. We have investigated for the first time the dynamics and the kinetics of tachyzoite-to-bradyzoite interconversion and cyst formation in vivo by using stage-specific bioluminescent parasites in a mouse model. Our findings provide a new framework for understanding the process of bradyzoite differentiation in vivo. We have also demonstrated that complex molecules such as d-luciferin have access to tissue cysts and are metabolically processed, thus providing a rationale for developing drugs that attack the parasite at this developmental stage.     

Geography of surnames in the Azores: specificity and spatial distribution analysis.

In order to obtain a better understanding of the genetic structure of the Azorean population, a specificity and spatial distribution analysis was performed, based on 2,454 different surnames present in the Azorean telephone directory (2002). We considered as specific surnames those with an absolute frequency ratio equal to or higher than 50%. The results revealed 51 specific surnames in the whole archipelago. The smallest island presents the only surname with 100% specificity (Pedras). In addition, São Miguel island, which contains 54% of the Azorean population, has the highest number of specific surnames (25 specific surnames). The spatial distribution analysis was used to detect genetic similarity between municipalities through the calculation of spatial autocorrelation (Moran's I coefficient). Of 240 surnames included in the analysis, 113 showed statistically significant patterns. Five different patterns were obtained, of which the most relevant was isolation by distance and depression (41.6%). However, 43.4% had no defined pattern. The overall correlogram shows a majority of positive values for distances lower than 49 km and between 269–309 km, indicating high similarity between closer municipalities and between distant municipalities whose populations show historic and sociocultural affinities. In conclusion, our data are in agreement with the historical background of the Azorean population. Am. J. Hum. Biol. 17:634–645, 2005. © 2005 Wiley‐Liss, Inc.     

The use of low-intensity laser irradiation of the blood in myocardial infarction

A total of 119 patients with myocardial infarction hospitalized within 24 hrs from the disease onset were examined. He-Ne laser irradiation of the blood (daily 40 min sessions for 3-5 days) was carried out in 45 patients (Group 1). The rest 74 patients (Group 2) were administered common therapy. A number of biologically active substances were radioimmunoassayed in the blood of 12 Group 1 and 11 Group 2 patients on days 1, 3, and 7 of the disease. The pain syndrome was alleviated in Group 1 patients, in contrast to Group 2 patients, and the frequencies of ventricular arrhythmias, of heart failures, and of the condition recurrences were reduced, as was the mortality rate. Laser therapy resulted in reduction of the activities of the hypophyseoadrenocortical and aldosteron-renin-angiotensin systems. Besides blood levels of dilatants and proaggregants (PGF2 alpha, vasopressin, angiotensin II) reduced in these patients, whereas vasodilating and antiaggregation hormones (PGE, PGI2) levels increased and the PGI2/TxB2 ratio improved.     

The spatial distribution of electrical activity in the cerebral cortex of man and animals

Summary Using the electroencephaloscopic method of Livanov and Anan'ev, the author studied the spatial distribution of cortical electrical activity in man and animals. He note that in certain physiological and pathological conditions of the central nervous system a special form of dynamic distribution of synchronous electrical activity (cortical mosaic) is recorded, called an overflow, or spreading wave of activity, representing a movement of the peak of negativity (or positivity) from certain areas of the cortex into others, with a generalized rhythm of bioelectric activity all over the cortex. Recorded with monopolar leads, spreading waves appear as movement of the point of maximum amplitude of corresponding potential variations. With bipolar leads, it is manifested mainly as a phase shift in space.Certain conditions for these spreading waves are described, and an attempt is made to analyze their mechanism.(Presented by Active Member AMN SSSR V. V. Parin) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 50. No. 10, pp. 23–28, October, 1960