In this paper, both the magneto-electronic properties and the magnetic domain structure of a magnetic tunnel junction (MJT) have been characterized simultaneously.

We have investigated the Antarctic sponge Isodictya erinacea as part of our ongoing study of Antarctic chemical ecology. I. erinacea was found to produce a tryptophan catabolite as its yellow pigment. The pigment, erebusinone, causes significantly reduced molting and proportionally increased mortality at ecologically relevant concentrations when fed to sympatric predatory amphipods. This appears to be the first example of molt inhibition as a mechanism of chemical defense.

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The thiirane complexes W(CO)(5)(SCH2CH2), 1, W(CO)(5)(cis-SCHMeCHMe), 2, and W(CO)(5)(trans-SCHMeCHMe), 3, have been prepared and characterized. The molecular structure of compound 2 was also determined crystallographically. It was found to contain an S-coordinated cis-dimethylthiirane ligand with a pyramidal sulfur atom coordinated to a W(CO)(5) group. Compounds 1-3 decompose slowly to yield sulfur and the corresponding olefin. Compound 1 and W(CO)(5)(NCMe) were both found to transform free thiirane into a mixture of cyclic polydisulfides (SCH2CH2S)(n), 4-7, n = 2, 3, 4, and 5, and ethylene, catalytically. The turnover frequency for the formation of 4 by 1 at 25 degrees C is 6.8 h(-1). When the catalytic reaction was performed in the presence of dimethyl acetylene dicarboxylate, DMAD, compounds 4 and 5 and the six-membered heterocycle SCH2CH2SC(CO(2)Me)C(CO(2)Me), 8 were formed, the last by the trapping of a suspected SCH2CH2S intermediate. Small amounts of polythioether macrocycles (CH2CH2S)(n), 12S4, n = 4, and 15S5, n = 5, were also formed. (2R,3S)-dimethylthiirane (cis-DMT) and (2R,3R(2S,3S))-dimethylthiirane (trans-DMT) undergo a combination of isomerization and desulfurization to yield a mixture of cis- and trans-butene by 2 and 3, respectively. In the presence of DMAD, the isomerization of the substituted thiiranes is suppressed and small amounts of the cyclic disulfides [C(H)CH3C(H)CH3SS](3), 9, and [C(H)CH3C(H)SS](2), 10, and the cyclic trisulfide (4S,5S(4R,5R))-[S3C(H)CH3C(H)CH3], 12, were formed. The molecular structure of 9 was determined crystallographically and established a pattern of identical R,R/S,S stereochemistries at adjacent stereogenic carbon atoms about the ring. A similar stereochemical result was indicated for the stereogenic carbon centers in 12 by preparing the osmium complex Os-2(Co)(6)[mu-(R,R(S,S))-SC(H)CH3C(H)CH3S], 13, from it and determining the configurations at the stereogenic carbon atoms in the SC(H)CH3C(H)CH3S ligand by an X-ray crystallographic analysis. All of the catalytic transformations can be explained by a back-side addition of a sulfur atom from an uncoordinated molecule of thiirane to a carbon atom of a thiirane ligand. This leads to an opening of the thiirane ligand and formation of a zwitterionic thiiranium/thiolato intermediate having the thiolato sulfur atom coordinated to the tungsten atom. Release of the added thiirane from a conformer for the zwitterion would result in isomerization of the thiirane ligand. Alternatively, loss of olefin from the thietanium ion group would yield a (SCH2CH2S)W(CO)(5) intermediate that could decompose by loss of SCH2CH2S groups, which could then combine to form the cyclic disulfides, 4-7. In the presence of DMAD, the SCH2CH2S group is trapped to yield 8. A series of similar ring-opening additions followed by a cyclization could lead to the formation of the polythioether macrocycles 12S4 and 15S5, but these compounds are minor products even under the best conditions. It was also found that compound 4 has moderate antimicrobial activity toward Escherichia coli.

Hexane, chloroform, and methanol extracts of 18 species of antarctic sponges were tested for their ability to induce sustained tube-foot retraction in the antarctic spongivorous sea star Perknaster fuscus. Extracts were imbedded in silicone and used to coat the tip of a glass rod, which was allowed to contact an extended tube-foot. Retraction times were measured and compared with three controls: contact with a glass rod coated with a hexane extract of fish (feeding stimulant), contact with the glass rod alone (mechanical control), and contact with the glass rod coated with silicone alone (silicone control). Only extracts of the sponge Mycale acerata did not elicit significantly longer tube-foot retraction times than controls for at least one of the three organic extracts. Hexane sponge extracts elicited the lowest levels of significant tube-foot responses, with only 39% of the sponge species tested showing activity in this fraction. In contrast, chloroform and methanol extracts elicited a significant tube-foot retraction response in 73% and 78% of the species tested, respectively. This indicates that in this assay repellent metabolites are generally more polar substances. It remains to be determined that secondary metabolites are responsible for all of the tube-foot retraction responses detected in sea stars exposed to sponge extracts; bioactive secondary metabolites have been isolated from a number of these antarctic sponges. It may be of ecological significance that the two rapidly growing sponges, Homaxinella balfourensis and Mycale acerata, were either not repellent or had low repellency, and that M. acerata is the primary dietary item of Perknaster fuscus.

The common bright yellow antarctic lamellarian gastropodMarseniopsis mollis was examined for the presence of defensive chemistry. Proton nuclear magnetic resonance (NMR) spectroscopy indicated that a major component of ethanolic extracts purified by reversed-phase column chromatography was homarine. Further high-performance liquid chromatography (HPLC) analysis of the mantle, foot, and viscera verified the presence of homarine in all body tissues at concentrations ranging from 6 to 24 mg/g dry tissue. A conspicuous macroinvertebrate predator of the shallow antarctic benthos, the sea starOdontaster validus, always rejected live individuals ofM. mollis, while readily feeding on pieces of fish tail muscle. Filter paper disks treated with shrimp elicited a broad range of feeding behaviors in the sea starO. validus (movement of disc to mouth, extrusion of cardiac stomach, humped feeding posture). Shrimp disks treated with homarine (0.4 and 4 mg/disk) were rejected byO. validus significantly more frequently than control disks treated with solvent carrier and shrimp or shrimp alone. The highest concentration of homarine tested not only caused feeding deterrence, but in several sea stars a flight response was noted. Homarine was not detected in the tunic of the antarctic ascidianCnemidocarpa verrucosa, a presumed primary prey ofM. mollis. Nonetheless, crude extracts of the epizooites that foul the tunic (primarily the bryozoans and hydroids) contain homarine, suggestingM. mollis may ingest and derive its chemistry from these organisms. This appears to be only the third example of chemical defense in a member of the Order Mesogastropoda. As the vestigial internalized shell ofM. mollis is considered a primitive condition, the findings of this study lend support to the hypothesis that chemical defense evolved prior to shell loss in shell-less gastropods.

Extracts of the dorid nudibranchTritoniella belli and stoloniferan coralClavularia frankliniana were chromatographed and analyzed by(1)H NMR and thin-layer chromatography. Three glycerol ethers were detected inT. belli, primarily 1-O-hexadecyl glycerol (chimyl alcohol). Chimyl alcohol was also detected after gradient flash chromatography and reverse-phase HPLC purification in the tissues ofC. frankliniana. The common omnivorous predatory Antarctic sea starOdontaster validus, a likely predator of benthic invertebrates, showed feeding deterrence to small cubes ofT. belli mantle tissue placed on the tube feet along the ambulacral feeding groove, while always extruding the cardiac stomach when presented with cubes of shrimp tissue of similar size. Filter-paper disks soaked in an aqueous shrimp solution and then dried were found to elicit a broad range of feeding behaviors inO. validus, including movement of the shrimp disk to the mouth, extrusion of the cardiac stomach, and the assumption of a humped feeding posture. Chimyl alcohol-treated shrimp disks caused significant feeding deterrence in sea stars when compared with control disks (solvent plus shrimp treated disks alone).T. belli andC. frankliniana appear to employ a defensive compound that has been found in a variety of temperate and tropical mollusks, where it has been demonstrated to deter fish predators. We provide evidence for further deterrent capabilities of chimyl alcohol and of its trophic relationship in the polar ecosystem of McMurdo Sound, Antarctica.

Extracts of the dorid nudibranch and stoloniferan coral were chromatographed and analyzed byH NMR and thin-layer chromatography. Three glycerol ethers were detected in, primarily 1--hexadecyl glycerol (chimyl alcohol). Chimyl alcohol was also detected after gradient flash chromatography and reverse-phase HPLC purification in the tissues of. The common omnivorous predatory Antarctic sea star, a likely predator of benthic invertebrates, showed feeding deterrence to small cubes of mantle tissue placed on the tube feet along the ambulacral feeding groove, while always extruding the cardiac stomach when presented with cubes of shrimp tissue of similar size. Filter-paper disks soaked in an aqueous shrimp solution and then dried were found to elicit a broad range of feeding behaviors in, including movement of the shrimp disk to the mouth, extrusion of the cardiac stomach, and the assumption of a humped feeding posture. Chimyl alcohol-treated shrimp disks caused significant feeding deterrence in sea stars when compared with control disks (solvent plus shrimp treated disks alone). and appear to employ a defensive compound that has been found in a variety of temperate and tropical mollusks, where it has been demonstrated to deter fish predators. We provide evidence for further deterrent capabilities of chimyl alcohol and of its trophic relationship in the polar ecosystem of McMurdo Sound, Antarctica.

R. G. Kerr and B. J. Baker, Nat. Prod. Rep., 1991, 8, 465 DOI: 10.1039/NP9910800465

A method for measuring paid staff support for volunteer involvement is described. The method is based on an econometric model that compares an organization's investment (the cost of paid staff support) to the value of the volunteer contribution. This method makes it possible to design strategies for more efficient volunteer involvement, and to quantify the effectiveness of these strategies in a non-profit organization.

Journal of the London Mathematical SocietyVolume s1-42, Issue 1 p. 385-388 Notes and papers Concerning Separation of Variables B. J. Baker, B. J. Baker University of Texas Austin, Texas, U.S.A.Search for more papers by this author B. J. Baker, B. J. Baker University of Texas Austin, Texas, U.S.A.Search for more papers by this author First published: 1967 https://doi.org/10.1112/jlms/s1-42.1.385Citations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volumes1-42, Issue11967Pages 385-388 RelatedInformation