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2.
This paper addresses two problems in the skein theory of homotopy spheres first posed by P. Traczyk. Solutions to both problems are obtained for a large class of manifolds and, since one of the basic techniques used requires the first homology group of the ambient manifold to be torsion free, the extent to which this hypothesis is actually necessary is further explored.  相似文献   
3.
Some New Results on Key Distribution Patterns and Broadcast Encryption   总被引:1,自引:0,他引:1  
This paper concerns methods by which a trusted authority can distribute keys and/or broadcast a message over a network, so that each member of a privileged subset of users can compute a specified key or decrypt the broadcast message. Moreover, this is done in such a way that no coalition is able to recover any information on a key or broadcast message they are not supposed to know. The problems are studied using the tools of information theory, so the security provided is unconditional (i.e., not based on any computational assumption).In a recent paper st95a, Stinson described a method of constructing key predistribution schemes by combining Mitchell-Piper key distribution patterns with resilient functions; and also presented a construction method for broadcast encryption schemes that combines Fiat-Naor key predistribution schemes with ideal secret sharing schemes. In this paper, we further pursue these two themes, providing several nice applications of these techniques by using combinatorial structures such as orthogonal arrays, perpendicular arrays, Steiner systems and universal hash families.  相似文献   
4.
Applied Biochemistry and Biotechnology - Soil column studies were used to evaluate petroleum hydrocarbon (PHC) remediation in soils from Kwajalein Atoll. Treatments included controls, and...  相似文献   
5.
The isolation and structure determination of cryptomisrine, a novel indolo[3,2-b]quinoline dimeric alkaloid obtained from extracts of the roots of the Ghanaian medicinal plant Cryptolepis sanguinolenta is reported. The structure determination was made via a consideration of the spectral data, including uv, ir, nmr, and mass spectra. In particular, one-dimensional proton/carbon nmr, one-dimensional nOe difference nmr, and a series of homonuclear (COSY) and inverse-detected heteronuclear two-dimensional (HMQC, HMBC) experiments were utilized, as well as high resolution FABMS. Cryptomisrine is most unusual in that its two monomeric parts apparently exist in such a C2 symmetric environment that only one set of proton and carbon nmr resonances are observed. Cryptomisrine is the first example of a dimeric indolo-[3,2-b]quinoline alkaloid to have been isolated from nature.  相似文献   
6.
It is apparent that, in electro-chromatographic separations, the change of area undergone by the initial spot of test solution plays a part in the final interpretation of results almost as important as the actual movement of the centre of the spot.Several interesting facts have emerged from this research concerning the role of the carrier electrolyte on tlie movement, the spot size, and the stability of complex salts.  相似文献   
7.
The Role of Oxygen in the Antiviral Activity of Hypericin and Hypocrellin   总被引:7,自引:0,他引:7  
The light-induced antiviral activity of hypericin and hypocrellin in the presence and absence of oxygen was examined under experimental conditions where the effect of oxygen depletion could be quantified. There was a significant reduction of light-induced antiviral activity of hypericin and hypocrellin under hypoxic conditions. Interestingly, antiviral activity of hypocrellin was not observed at low oxygen levels at which hypericin retained measurable virucidal activity. This suggests that additional pathways, such as the generation of protons from excited states of hypericin, may enhance the biological activity of activated oxygen species.  相似文献   
8.
The dithiocarbene complex W(CO)5[C(SCH3)2 reacts with tertiary phosphines, PPh2CH3, PPh(CH3)2, P(C2H5)3 and P(OCH3)3 to form the phosphorane complexes W(CO)5[CH3S)2C-PR3] and with HPPh2 to form the phosphine complex W(CO)5[PPh2[CH(SCH3)2]. Kinetic studies of both types of reactions show that their rates are first order each in W(CO)5[C(SCH3)2] and in the phosphorus ligand. A mechanism involving rate determining phosphorus attack at the carbene carbon followed by rapid rearrangement to the product is consistent with this rate law. Rate constants for the reactions increase with increasing nucleophilicities of the phosphines: P(OCH3)3 < PPh2H < PPh2CH3 ? PPh(CH3)2 < P(C2H5)3. The ΔH values decrease (P(OCH3)3 > PPh2H > PPh2(CH3) > PPh(CH3)2 > P(C2H5)3) as the nucleophilicities of the phosphines increase. The ΔS values (≈-30 e.u.) remain essentially constant for all the reactions. The cyclic dithiorcarbenes W(CO)5[CS(CH2)nS], wheren- 3 or 4, react with PPh2(CH3) to form the cyclic phosphorane complexes, W(CO)5[S(CH2)nSC-PPh2(CH3)]. The 6- and 7- membered cyclic dithiocarbenes also react with PPh2H to form the phosphine complexes, W(CO)5 {PPh2- [CS(CH2)nS(H)]}.  相似文献   
9.
A one-pot synthesis of substituted imidazoles is described. The cornerstone of this methodology involves the thiazolium-catalyzed addition of an aldehyde to an acyl imine to generate the corresponding alpha-ketoamide in situ followed by ring closure to the imidazole in a one-pot sequence. The extension of this methodology to the one-pot synthesis of substituted oxazoles and thiazoles is also described. [reaction: see text]  相似文献   
10.
Molecular growth processes utilizing a beta-octamolybdate synthon and {Ag2} dimers are described and the directing influence of "encapsulating" cations and coordinating solvent is also demonstrated. The growth of two 1D chains, (nBu4N)2n[Ag2Mo8O26]n (1) and (nBu4N)2n[Ag2Mo8O26(CH3CN)2]n (2), is achieved when nBu4N+ ions are used, and the diameter of the chains can be expanded by the coordination of CH3CN solvent (2). The formation of a type of gridlike structure in which 1D chains are crossed-over each other in alternatively packed layers is achieved in DMSO as the solvent; DMSO acts as a linking group to give (nBu4N)2n[Ag2Mo8O26(dmso)2]n (3), which, similar to 1 and 2, still incorporates the Bu4N+ ions that exert an "encapsulating" influence. However, in (HDMF)n[Ag3(Mo8O26)(dmf)4]n (4) the relatively bulky Bu4N+ ions are exchanged for protonated DMF cations, thereby allowing the chains to condense to a 2D array. The building block concept is further enforced by the isolation of a "monomeric" unit (Ph4P)2[Ag2Mo8O26(dmso)4] (5), which is isolated when the Ph4P+ ions are so "encapsulating" as to prevent aggregation of the {Ag-Mo8-Ag} building blocks. The nature of the AgAg dimers in each of the compounds 1-4 is examined by DFT calculations and the interplay between these Ag-Ag interactions and the structure types is described.  相似文献   
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