Menopausal transition of Korean immigrant women: a literature review

The menopausal transition needs to be understood in terms of the multiple mediating factors within the context in which women experience it. For immigrant women especially, the menopausal experience is complicated by multiple transitions and social marginality, so it cannot be adequately explained without considering this complexity. In this paper we review the literature on the menopausal transition of a group of vulnerable immigrant women in two ways: describing the transitions themselves (menopause, immigration, and housewife to employee), and describing factors that mediate the menopausal transition experience (family norms, meaning of menopause and women's work, and health practices). We emphasize the context and suggest areas of needed research.     

Charged nucleobases and their potential for RNA catalysis

Catalysis in living cells is carried out by both proteins and RNA. Protein enzymes have been known for over 200 years, but RNA enzymes, or "ribozymes", were discovered only 30 years ago. Developing insight into RNA enzyme mechanisms is invaluable for better understanding both extant biological catalysis as well as the primitive catalysis envisioned in an early RNA-catalyzed life. Natural ribozymes include large RNAs such as the group I and II introns; small RNAs such as the hepatitis delta virus and the hairpin, hammerhead, VS, and glmS ribozymes; and the RNA portion of the ribosome and spliceosome. RNA enzymes use many of the same catalytic strategies as protein enzymes, but do so with much simpler side chains. Among these strategies are metal ion, general acid-base, and electrostatic catalysis. In this Account, we examine evidence for participation of charged nucleobases in RNA catalysis. Our overall approach is to integrate direct measurements on catalytic RNAs with thermodynamic studies on oligonucleotide model systems. The charged amino acids make critical contributions to the mechanisms of nearly all protein enzymes. Ionized nucleobases should be critical for RNA catalysis as well. Indeed, charged nucleobases have been implicated in RNA catalysis as general acid-bases and oxyanion holes. We provide an overview of ribozyme studies involving nucleobase catalysis and the complications involved in developing these mechanisms. We also consider driving forces for perturbation of the pK(a) values of the bases. Mechanisms for pK(a) values shifting toward neutrality involve electrostatic stabilization and the addition of hydrogen bonding. Both mechanisms couple protonation with RNA folding, which we treat with a thermodynamic formalism and conceptual models. Furthermore, ribozyme reaction mechanisms can be multichannel, which demonstrates the versatility of ribozymes but makes analysis of experimental data challenging. We examine advances in measuring and analyzing perturbed pK(a) values in RNA. Raman crystallography and fluorescence spectroscopy have been especially important for pK(a) measurement. These methods reveal pK(a) values for the nucleobases A or C equal to or greater than neutrality, conferring potential histidine- and lysine/arginine-like behavior on them. Structural support for ionization of the nucleobases also exists: an analysis of RNA structures in the databases conducted herein suggests that charging of the bases is neither especially uncommon nor difficult to achieve under cellular conditions. Our major conclusions are that cationic and anionic charge states of the nucleobases occur in RNA enzymes and that these states make important catalytic contributions to ribozyme activity. We conclude by considering outstanding questions and possible experimental and theoretical approaches for further advances.     

Effect of alleles governing 16:0 concentration on glycerolipid composition in developing soybeans

Soybean [Glycine max (L.) Merr.] oil typically contains 11% palmitic acid, but germplasm with recessive alleles at Fap gene loci exhibit from less than 4% to about 35% 16:0, Although these alleles are used to develop new cultivars, little is known about how they influence palmitic acid concentration. One theory suggests that fap alleles may mediate differences in triacylglycerol composition through genetic effects on the activity or substrate specificity of acyltransferases, such as diacylglycerol acyltransferase (EC 2.3.1.20). Based on logistic function analysis of developing seed, differences in fag allele expression are evident in the rate of palmitic acid accumulation in triacylglycerol, with peak deposition near mid-seed fill. Acetate saturation kinetics also reveal a strong positive relation between the relative amount of de novo palmitic acid synthesis and the indigenous palmitic acid concentration in triacylglycerol among fap genotypes. However, no differences appear in the kinetics of palmitoyl-CoA metabolism in developing seed of these genotypes. Therefore, the fap alleles apparently do not encode or regulate the activities of glycerolipid acyltransferase enzymes. Rather, major genetic effects on triacylglycerol composition accrue through regulation of palmitic acid production in the plastids of developing soybean cotyledons.     

Devitrification Kinetics and Mechanism of K2O–CaO–SrO–BaO–B2O3–SiO2 Glass-Ceramic

The devitrification kinetics and mechanism of a low-dielectric, low-temperature, cofirable K₂O–CaO–SrO–BaO–B₂O₃–SiO₂ glass-ceramic have been investigated. Crystalline phases including cristobalite (SiO₂) and pseudowollastonite ((Ca,Ba,Sr) SiO₃) are formed during firing. Activation energy analysis shows that the nucleation of the crystalline phases is controlled by phase separation of the glass. The crystallization kinetics of both cristobalite and pseudowollastonite obey Avrami-like behavior, and the results show an apparent activation energy close to that of the diffusion of alkaline and alkali ions in the glass, suggesting that diffusion is rate limiting. The above conclusion is further supported by analysis of measured growth rates.     

Chemical Ecology of the host searching behavior in an Egg Parasitoid: are Common Chemical Cues exploited to locate hosts in Taxonomically Distant Plant Species?

Parasitoids are known to exploit volatile cues emitted by plants after herbivore attack to locate their hosts. Feeding and oviposition of a polyphagous herbivore can induce the emission of odor blends that differ among distant plant species, and parasitoids have evolved an incredible ability to discriminate them and locate their hosts relying on olfactive cues. We evaluated the host searching behavior of the egg parasitoid Cosmocomoidea annulicornis (Ogloblin) (Hymenoptera: Mymaridae) in response to odors emitted by two taxonomically distant host plants, citrus and Johnson grass, after infestation by the sharpshooter Tapajosa rubromarginata (Signoret) (Hemiptera: Cicadellidae), vector of Citrus Variegated Chlorosis. Olfactory response of female parasitoids toward plants with no herbivore damage and plants with feeding damage, oviposition damage, and parasitized eggs was tested in a Y-tube olfactometer. In addition, volatiles released by the two host plant species constitutively and under herbivore attack were characterized. Females of C. annulicornis were able to detect and significantly preferred plants with host eggs, irrespectively of plant species. However, wasps were unable to discriminate between plants with healthy eggs and those with eggs previously parasitized by conspecifics. Analysis of plant volatiles induced after sharpshooter attack showed only two common volatiles between the two plant species, indole and β-caryophyllene. Our results suggest that this parasitoid wasp uses common chemical cues released by many different plants after herbivory at long range and, once on the plant, other more specific chemical cues could trigger the final decision to oviposit.

     

Advances on methane steam reforming to produce hydrogen through membrane reactors technology: A review

Methane steam reforming is the most common industrial process used for almost the 50% of the world’s hydrogen production. Commonly, this reaction is performed in fixed bed reactors and several stages are needed for separating hydrogen with the desired purity. The membrane reactors represent a valid alternative to the fixed bed reactors, by combining the reforming reaction for producing hydrogen and its separation in only one stage. This article deals with the recent progress on methane steam reforming reaction, giving a short overview on catalysts utilization as well as on the fundamentals of membrane reactors, also summarizing the relevant advancements in this field.     

Further Observation on Tin Whisker from Electroplated Sn-Mn Alloy

Tin whiskers from Sn-(0-49 wt%)Mn alloy electroplating on polished mild steel were examined with FEG-SEM with EDX.The raw materials were Hull Cell samples kept in an office ambient with different storage time,up to 240 h.It is found that,depending on Mn content and plating microstructure,Sn-Mn alloy shows various types of whiskering.Except for the whisker forest found previously in Sn-20Mn,there exists another in Sn-(1%-5%)Mn.The latter also has a very short incubation time,less than 4 h.Another interesting finding is that one type of whiskering with surface cap supports an established model.     

An Electrochemical Evaluation of Possible Non-Chromate Conversion Coating Treatments for Electrodeposited Zinc-Nickel Alloys

A number of possible non-chromate conversion coating formulations have been studied to examine their efficacy as replacements for chromate-based coating treatments on electrodeposited zinc-nickel alloys. Data have been collected from both electrochemical and conventional salt fog corrosion tests. In the latter tests all the alternative non-chromate systems studied delayed the onset of the corrosion of the zinc-nickel coating itself but only the simple molybdate and the permanganatelmolybdate dual treatment brought about improvements in times to red rusting of the steel substrate. The electrochemical evaluations suggested that simple molybdate-treated surfaces act as only moderate barriers to the chloride environments. Of the two dual treatments, permanganatel molybdate behaved similarly to the simple molybdate treated surfaces in the electrochemical tests, but the molybdatel permanganate was more protective, although this was not exhibited in the salt fog corrosion tests.     

Tin whisker mitigation by means of a post-electroplating electrochemical oxidation treatment

There are very few studies that have investigated directly the effect of an oxide film on tin whisker growth, since the ‘cracked oxide theory’ was proposed by Tu in 1994 [K.-N. Tu: Phys. Rev., 1994, 49, (3), 2030–2034]. The current study has investigated the effect of an electrochemically produced oxide on tin whisker growth, for both Sn–Cu electrodeposits on Cu and pure Sn electrodeposits on brass. X-ray photoelectron spectroscopy (XPS) has been used to investigate the effect of the applied electrochemical oxidation potential on the oxide film thickness. Focused ion beam has been used to prepare cross sections from electrodeposited samples to investigate the influence of the electrochemically formed oxide film on deposit microstructure during long-term room temperature storage. The XPS studies show that the thickness of electrochemically formed oxide film is directly influenced by the applied potential and the total charge passed. Whisker growth studies show that the electrochemical oxidation treatment mitigates whisker growth for both Sn–Cu electrodeposits on Cu and pure Sn electrodeposits on brass. For Sn electrodeposits on brass, the electrochemically formed oxide greatly reduces both the formation of zinc oxide at the surface and the formation of intermetallic compounds, which results in the mitigation of tin whisker growth. For Sn–Cu electrodeposits on Cu, the electrochemically formed oxide has no apparent effect on intermetallic compound formation and acts simply as a physical barrier to hinder tin whisker growth.     

Long term assessment of a hybrid electrochemical treatment

Monitoring the performance of systems installed to protect against/halt the corrosion of reinforcing steel in concrete is essential in ensuring that the reinforcing bar (rebar) is adequately protected and remains in a non‐corroding state. A chloride contaminated concrete test block containing a hybrid anode system has been periodically monitored over the past 4.5 years to assess the anode current output and thus, the protection offered to the steel. De‐polarisation and impedance analysis data have been acquired to calculate steel corrosion rates. Both tests indicated that the steel was passive in the concrete environment and that the anode was able to protect all of the embedded steel despite the difficult geometry of the sample. It was also found that after 2 years it was still possible to drive a high current from the installed anode.