Zone Melting of Uranium

ABSTRACT A study was made of the possible application of the zone melting technique to the separation of u r a n i u m from fission products and other impurities. Bar specimens of U having various aRoying elements were zone purified in thoriacoated alumina boats. U r a n i u m bars previously irradiated in the Brookhaven pile were also zone melted. Zone melting has potential application in the removal of such impurities as B, Fe, Si, Ni, and Co from ordinary U. In the reprocessing of irradiated U, zone melting offers a method for removing such fission products as Zr, Nb, Ru. However, as employed here, it shows little promise as a method for complete decontamination of irradiated U from fission products, primarily because of concurrent slagging effects. Zone m e l t i n g is a purification t e c h n i q u e which has b e e n used to p r e p a r e v e r y p u r e Ge m e t a l in w h i c h the q u a n t i t y of i m p u r i t i e s p r e s e n t is of the order of parts per billion. The :;uccess of this t e c h n i q u e w i t h Ge suggested an i n v e s t i g a t i o n of its possible application to the purification of U f r o m fission products a n d other impurities. This r e p o r t p r e s e n t s the results of such a n investigation. In the zone m e l t i n g process a n a r r o w m o l t e n zone, p r o d u c e d b y i n d u c t i o n or resistance heating, is m a d e to t r a v e r s e t h e solid m e t a l by m o v e m e n t either of the heater or of the metal, as s h o w n in t i m a t e d i s t r i b u t i o n " is r e a c h e d after w h i c h a d d itional passes h a v e no effect. A m e a s u r e of the t e n d e n c y of the i m p u r i t y to m i g r a t e is given by the d i s t r i b u t i o n coefficient k, which is defined as the ratio of the solute c o n c e nt r a t i o n in the solid to that in the liquid at e q u il i b r i u m . The g r e a t e r the factor b y w h i c h k differs from unity, the m o r e r e a d i l y i m p u r i t i e s migrate. A simple t h e o r y of zone m e l t i n g has b e e n developed by P f a n n (1), in w h i c h it is a s s u m e d that solute diffusion in the liquid is sufficiently r a p i d that the i m p u r i t y c o n c e n t r a t i o n is u n i f o r m in the m o l t e n zone while diffusion in the solid phase is negligible. F r o m this theory it is possible to calculate the effect of repeated zone passes if the d i s t r i b u t i o n coefficient is k n o w n . In practice, one expects less m i g r a t i o n t h a n that calculated, because the a s s u m p t i o n s of complete e q u i l i b r i u m on which the c a l c u l a t i o n is based are not strictly true. In a n y case, the p u r ification a t t a i n e d depends on the n u m b e r of passes, the ratio of m o l t e n zone l e n g t h to b a r length, the e q u i l i b r i u m d i s t r i b u t i o n coefficient k, a n d the rate of zone travel. I n T a b l e I are given k v a l u e s for some metals in U, e s t i m a t e d f r o m the p a r t i c u l a r u r a n i u m -m e t a l phase d i a g r a m s (2). It should be n o t e d t h a t these k values are at best a p p r o x i m a t e since g e n e r a l l y the phase d i a g r a m s h a v e not b e e n a c c u r a t e l y d e t e r m i n e d in the region of low i m p u r i t y c o n c e n t r a t i o n . The theoretical ratio of i m p u r i t y c o n c e n t r a t i o n at the low c o n c e n t r a t i o n end of the b a r before a n d afte

A person-centered perspective on working with people who have experienced psychological trauma and helping them move forward to posttraumatic growth

Over the past decade posttraumatic growth (PTG) has become a major topic for theory, research and practice in mainstream trauma psychology. The aim of this paper is to discuss the implications of PTG for the person-centered approach. It is argued that PTG provides a new non-medical language for understanding psychological trauma that is consistent with the person-centered approach. Person-centered personality theory provides an explanation for how PTG arises and leads to new testable predictions for research into how person-centered therapy may be able to facilitate PTG

Magnetostimulated Chandges of Microhardness in Potassium Acid Phthalate Crystals

A decrease in microhardness along the (010) cleavage in potassium acid phthalate single crystals by 15--18% after the application of a permanent magnetic field was revealed for the first time. It is shown that the effect revealed is of the volume character. The role of interlayer water in the processes stimulated by a magnetic field is studied., Interlayer water plays does not cause the observed changes it only plays the part of an indicator of these changes in potassium acid phthalate crystals in a magnetic field. It is established that microhardness in the (100) plane of the crystal in an applied a magnetic field first increases by 12--15% and then remains constant in time within the accuracy of the experiment. The possibility of varying the crystal structure of potassium acid phthalate crystals by applying magnetic fields inducing rearrangement in the system of hydrogen bonds or in the defect structure is discussed.Comment: 6 pages, 7 figure

The Current State of Performance Appraisal Research and Practice: Concerns, Directions, and Implications

On the surface, it is not readily apparent how some performance appraisal research issues inform performance appraisal practice. Because performance appraisal is an applied topic, it is useful to periodically consider the current state of performance research and its relation to performance appraisal practice. This review examines the performance appraisal literature published in both academic and practitioner outlets between 1985 and 1990, briefly discusses the current state of performance appraisal practice, highlights the juxtaposition of research and practice, and suggests directions for further research

Use of a fluorescence-based approach to assess short-term responses of the alga Pseudokirchneriella subcapitata to metal stress

This work explores the use of fluorescent probes to evaluate the responses of the green alga Pseudokirchneriella subcapitata to the action of three nominal concentrations of Cd(II), Cr(VI), Cu(II) and Zn(II) for a short time (6 h). The toxic effect of the metals on algal cells was monitored using the fluorochromes SYTOX Green (SG, membrane integrity), fluorescein diacetate (FDA, esterase activity) and rhodamine 123 (Rh123, mitochondrial membrane potential). The impact of metals on chlorophyll a (Chl a) autofluorescence was also evaluated. Esterase activity was the most sensitive parameter. At the concentrations studied, all metals induced the loss of esterase activity. SG could be used to effectively detect the loss of membrane integrity in algal cells exposed to 0.32 or 1.3 mol L1 Cu(II). Rh123 revealed a decrease in the mitochondrial membrane potential of algal cells exposed to 0.32 and 1.3 mol L1 Cu(II), indicating that mitochondrial activity was compromised. Chl a autofluorescence was also affected by the presence of Cr(VI) and Cu(II), suggesting perturbation of photosynthesis. In conclusion, the fluorescence-based approach was useful for detecting the disturbance of specific cellular characteristics. Fluorescent probes are a useful diagnostic tool for the assessment of the impact of toxicants on specific targets of P. subcapitata algal cells.The authors thank the FCT Strategic Project PEst-OE/EQB/LA0023/2013. Manuela D. Machado gratefully acknowledges the post-doctoral grant from FCT (SFRH/BPD/72816/2010)

Activation of adherent vascular neutrophils in the lung during acute endotoxemia

BACKGROUND: Neutrophils constitute the first line of defense against invading microorganisms. Whereas these cells readily undergo apoptosis under homeostatic conditions, their survival is prolonged during inflammatory reactions and they become biochemically and functionally activated. In the present study, we analyzed the effects of acute endotoxemia on the response of a unique subpopulation of neutrophils tightly adhered to the lung vasculature. METHODS: Rats were treated with 5 mg/kg lipopolysaccharide (i.v.) to induce acute endotoxemia. Adherent neutrophils were isolated from the lung vasculature by collagenase digestion and sequential filtering. Agarose gel electrophoresis, RT-PCR, western blotting and electrophoretic mobility shift assays were used to evaluate neutrophil activity. RESULTS: Adherent vascular neutrophils isolated from endotoxemic animals exhibited decreased apoptosis when compared to cells from control animals. This was associated with a marked increase in expression of the anti-apoptotic protein, Mcl-1. Cells isolated 0.5–2 hours after endotoxin administration were more chemotactic than cells from control animals and expressed increased tumor necrosis factor-alpha and cyclooxygenase-2 mRNA and protein, demonstrating that they are functionally activated. Endotoxin treatment of the animals also induced p38 and p44/42 mitogen activated protein kinases in the adherent lung neutrophils, as well as nuclear binding activity of the transcription factors, NF-κB and cAMP response element binding protein. CONCLUSION: These data demonstrate that adherent vascular lung neutrophils are highly responsive to endotoxin and that pathways regulating apoptosis and cellular activation are upregulated in these cells

Protist-Type Lysozymes of the Nematode Caenorhabditis elegans Contribute to Resistance against Pathogenic Bacillus thuringiensis

Pathogens represent a universal threat to other living organisms. Most organisms express antimicrobial proteins and peptides, such as lysozymes, as a protection against these challenges. The nematode Caenorhabditis elegans harbours 15 phylogenetically diverse lysozyme genes, belonging to two distinct types, the protist- or Entamoeba-type (lys genes) and the invertebrate-type (ilys genes) lysozymes. In the present study we characterized the role of several protist-type lysozyme genes in defence against a nematocidal strain of the Gram-positive bacterium Bacillus thuringiensis. Based on microarray and subsequent qRT-PCR gene expression analysis, we identified protist-type lysozyme genes as one of the differentially transcribed gene classes after infection. A functional genetic analysis was performed for three of these genes, each belonging to a distinct evolutionary lineage within the protist-type lysozymes (lys-2, lys-5, and lys-7). Their knock-out led to decreased pathogen resistance in all three cases, while an increase in resistance was observed when two out of three tested genes were overexpressed in transgenic lines (lys-5, lys-7, but not lys-2). We conclude that the lysozyme genes lys-5, lys-7, and possibly lys-2 contribute to resistance against B. thuringiensis, thus highlighting the particular role of lysozymes in the nematode's defence against pathogens

Time-temperature dependent fracture toughness of PMMA

A toughness-biased Ree-Eyring relationship gives a good description of fracture toughness data of PMMA over a range of temperatures (283 to 353 K) and crack velocities (10 −5 to 1 m sec −1 ). Fracture toughness was measured by Gurney's sector method. The activation energy associated with the equation supports earlier work which suggests that, in the same temperature and velocity range, cracking in PMMA is controlled by craze growth, which is governed by secondary ( β ) molecular processes. Unstable cracking at moderate velocities (10 −2 to 1 m sec −1 ) seems to be produced by an isothermal/adiabatic transformation; an analysis for the onset of instability is given. At temperatures below 283 K, changes in toughness behaviour are seen, and below 243 K no stable cracking at all was obtained. A discussion is given of various methods of characterizing resistance to cracking, and methods of transforming R (à, T ) and K (à, T ) data are compared.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44668/1/10853_2004_Article_BF00540829.pd