First stability eigenvalue characterization of Clifford hypersurfaces

The stability operator of a compact oriented minimal hypersurface is given by , where is the norm of the second fundamental form. Let be the first eigenvalue of and define . In 1968 Simons proved that for any non-equatorial minimal hypersurface . In this paper we will show that only for Clifford hypersurfaces. For minimal surfaces in , let denote the area of and let denote the genus of . We will prove that . Moreover, if is embedded, then we will prove that . If in addition to the embeddeness condition we have that , then we will prove that .

     

Transient reduction in the tRNA 4-thiouridine content induced by ultraviolet A during post-irradiation growth in Enterobacter cloacae

The influence of previous exposure to ultraviolet-A radiation (UVA) was studied on the susceptibility of Enterobacter cloacae to undergo the growth delay effect. Comparison of growth curves corresponding to irradiated and control cells showed that a previous treatment with UVA almost abolished the growth delay effect. UV absorption spectra of tRNA, and reverse phase HPLC analysis of hydrolysed tRNA, demonstrated a low content of 4-thiouridine in E. cloacae cells grown after UVA exposure at low doses. Since 4-thiouridine is the UVA target responsible for initiation of growth delay, this observation explained the influence of previous exposure to UVA on the susceptibility of this organism to undergo growth delay. A similar but weaker alteration was found when Escherichia coli was assayed. The results suggest that, in addition to cross-linking with cytidine residues, the content of 4-thiouridine in tRNA may be modified by UVA by an unknown mechanism.     

Bypass high-performance liquid chromatography for purification of trace analytes

Stability constants of binary Fe(III)-methylcysteine, Cr(III)-methylcysteine and mixed Fe(III)-methylcysteine-cysteine, Cr(III)-methylcysteine-cysteine complexes have been determined by paper electrophoresis at 0.1 M ionic strength and a temperature of 35 degrees C. The stability constants of Fe(III)-methylcysteine-cysteine and Cr(III)-methylcysteine-cysteine mixed complexes were found to be 6.00 +/- 0.07 and 5.05 +/- 0.15 (logarithm of stability constant values), respectively.     

Low-molecular-weight organoiodine and organobromine compounds released by polar macroalgae--the influence of abiotic factors

The influence of temperature, light, salinity and nutrient availability on the release of volatile halogenated hydrocarbons was investigated in the Antarctic red macroalgal species Gymnogongrus antarcticus Skottsberg. Compared to standard culture condition, an increase in the release rates of iodocompounds was generally found for the exposure of the alga to altered environmental conditions. Macroalgae exhibited higher release rates after adaptation for two months to the changed factors, than after short-term exposure. Monitoring the release rates during a 24 h incubation period (8.25 h light, 15.75 h darkness) showed that changes between light and dark periods had no influence on the release of volatile halocarbons. Compounds like bromoform and 1-iodobutane exhibited constant release rates during the 24 h period. The formation mechanisms and biological role of volatile organohalogens are discussed. Although marine macroalgae are not considered to be the major source of biogenically-produced volatile organohalogens, they contribute significantly to the bromine and iodine cycles in the environment. Under possible environmental changes like global warming and uncontrolled entrophication of the oceans their significance may be increase.     

Complete rotation hypersurfaces with Hk constant in space forms

In this paper we classify all complete rotation hypersurfaces withH _k constant in ⁿ⁺¹ andH ⁿ⁺¹, is the normalizedk-th symmetric function of the principal curvatures. Partial results are also given forH ⁿ⁺¹.Partially supported by DGAPA-UNAM, México, CONACYT, México, under Project 1068P, and CNPp, Brazil.     

Synthesis of 1,6-heterosubstituted products via radicals

Ketones and electron deficient alkenes are combined with each other via a methylene group to yield 1,6-heterosubstituted products in a radical chain reaction.