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Moiré band model and band gaps of graphene on hexagonal boron nitride
Jung, Jeil,Laksono, Evan,DaSilva, Ashley M.,MacDonald, Allan H.,Mucha-Kruczyń,ski, Marcin,Adam, Shaffique American Physical Society 2017 Physical Review B Vol.96 No.8
<P>Nearly aligned graphene on hexagonal boron nitride (G/BN) can be accurately modeled by a Dirac Hamiltonian perturbed by smoothly varying moire pattern pseudospin fields. Here, we present the moire-band model of G/BN for arbitrary small twist angles under a framework that combines symmetry considerations with input from ab initio calculations. Our analysis of the band gaps at the primary and secondary Dirac points highlights the role of inversion symmetry breaking contributions of the moire patterns, leading to primary Dirac point gaps when the moire strains give rise to a finite average mass, and to secondary gaps when the moire pseudospin components are mixed appropriately. The pseudomagnetic strain fields, which can reach values of up to similar to 40 T near symmetry points in the moire cell stem almost entirely from virtual hopping and dominate over the contributions arising from bond length distortions due to the moire strains.</P>
Saccharomyces cerevisiae M3G3를 이용한 1,2-Propanediol의 생산 최적화
구자룡(Ja-Ryong Koo),Nancy A. DaSilva,윤현식(Hyun Shik Yun) 한국생물공학회 2011 KSBB Journal Vol.26 No.5
1,2-propanediol (1,2-PD) is a commodity chemical that is currently produced from petrochemical derivatives. Saccharomyces cerevisiae is well characterized and a successful industrial microorganism to enable the improvement of the 1,2-propanediol production by metabolic engineering. A recombinant S. cerevisiae M3G3 was used to produce 1,2-propanediol. S. cerevisiae M3G3 is the diploid strain that contains 3 copies of mgs (methylglyoxal synthase) and gldA (glycerol dehydrogenase). S. cerevisiae M3G3 was cultivated at various culture conditions by changing culture temperature, glucose concentration, and inducer concentration. Also the effect of induction time was studied to optimize the production of 1,2-propanediol. Batch and fed-batch cultivation of S. cerevisiae M3G3 was performed by using a 5 L jar fermenter. The highest concentration of 1,2-propanediol in batch cultivation was 0.86 g/L and it was further improved to 1.33 g/L in fed-batch cultivation.
Effects of Expression of lcb1/lcb2 and lac1/lag1 Genes on the Biosynthesis of Ceramides
김세경,Yong Ho Noh,Ja-Ryong Koo,윤현식,Nancy A. DaSilva 한국생물공학회 2011 Biotechnology and Bioprocess Engineering Vol.16 No.1
Ceramides are important signal messenger molecules due to their role in regulating diverse responses such as cell cycle arrest, apoptosis, and senescence. Yeasts are more suitable for ceramides production than any other microorganisms since they grow fast and are non-pathogenic. However, regulations of the expression of genes involved in sphingolipid synthesis pathway are required to enhance ceramides production. In this study, we investigated the effects of co-expression of two pairs of genes that encode for serine palmitoyltransferase and ceramide synthase,respectively. Effect of other genes of the enzymes associated with the sphingolipid synthesis pathway, 3-ketosphinganine reductase and sphinganine C-4 hydroxylase were also studied and compared. The genes were cloned in to pESC-URA vector. Saccharomyces cerevisiae was cultivated aerobically in YPDG medium at 30oC. Ceramides were seperated from cell extracts by solvent extraction and quantified by HPLC with ELSD. The highest ceramides production (10.52 mg ceramides/g cell) was obtained when 3-ketosphinganine reductase, which is encoded by tsc10gene, was overexpressed. Also, S. cerevisiae SCEL2,1 overexpressing serine palmitoyltransferase encoded by lcb2 and lcb1 genes, and S. cerevisiae SCEG1C1 overexpressing ceramide synthase encode by lag1 and lac1 genes, showed a high level of ceramides production (10.08 mg ceramides/g cell and 9.88 mg ceramides/g cell, respectively).
Carabali, Mabel,Lim, Jacqueline Kyungah,Velez, Diana Carolina,Trujillo, Andrea,Egurrola, Jorge,Lee, Kang Sung,Kaufman, Jay S.,DaSilva, Luiz Jacinto,Velez, Ivan Dario,Osorio, Jorge E. Elsevier 2017 INTERNATIONAL JOURNAL OF INFECTIOUS DISEASES Vol.58 No.-
<▼1><P><B>Highlights</B></P><P>•<P>A total of 3684 individuals between 1 and 65 years old participated in the survey.</P>•<P>The overall seroprevalence by IgG Indirect ELISA was 61%.</P>•<P>The overall seroconversion rate was 8.7% per 1000 person-months over 2.5 years.</P>•<P>The highest rate of infection was observed during the fifth visit (February 2014).</P></P></▼1><▼2><P><B>Summary</B></P><P><B>Background</B></P><P>Dengue is an important public health problem worldwide. A vaccine has recently been licensed in some countries of Latin America and Asia. Recommendations for dengue vaccine introduction include endemicity and a high serological prevalence of dengue in the territories considering its introduction.</P><P><B>Methods</B></P><P>A community-based survey was conducted to estimate dengue seroprevalence and age-specific seroconversion rates in a community in Medellin, Colombia, using a dengue serological test (IgG indirect ELISA). Residents were selected at random and were first screened for dengue infection; they were then followed over 2.5 years.</P><P><B>Results</B></P><P>A total of 3684 individuals aged between 1 and 65 years participated in at least one survey. The overall dengue seroprevalence was 61%, and only 3.3% of seropositive subjects self-reported a past history of dengue. Among dengue virus (DENV)-naïve subjects with more than two visits (<I>n</I> = 1002), the overall seroconversion rate was 8.7% (95% confidence interval 7.3–10.4) per 1000 person-months, over the study period. Overall, the mean age of DENV prevalent subjects was significantly higher than the mean age of seroconverted subjects. Specifically, DENV seropositivity over 70% was observed in participants over 21 years old. Serotype-specific plaque-reduction neutralization tests (PRNT) revealed that all four dengue serotypes were circulating, with DENV4 being most prevalent.</P><P><B>Conclusions</B></P><P>These laboratory-based findings could inform dengue vaccine decisions, as they provide age-specific seroprevalence and seroconversion data, evidencing permanent and ongoing dengue transmission in the study area. This study provides evidence for the existing rates of secondary and heterotypic responses, presenting a challenge that must be addressed adequately by the new vaccine candidates.</P></▼2>