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Search Results: 1 - 10 of 463374 matches for " Sonja A. Rasmussen "
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Hypomethylation of Serum Blood Clot DNA, but Not Plasma EDTA-Blood Cell Pellet DNA, from Vitamin B12-Deficient Subjects
Eoin P. Quinlivan, Krista S. Crider, Jiang-Hui Zhu, David R. Maneval, Ling Hao, Zhu Li, Sonja A. Rasmussen, R. J. Berry, Lynn B. Bailey
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0065241
Abstract: Vitamin B12, a co-factor in methyl-group transfer, is important in maintaining DNA (deoxycytidine) methylation. Using two independent assays we examined the effect of vitamin B12-deficiency (plasma vitamin B12<148 pmol/L) on DNA methylation in women of childbearing age. Coagulated blood clot DNA from vitamin B12-deficient women had significantly (p<0.001) lower percentage deoxycytidine methylation (3.23±0.66%; n = 248) and greater [3 H]methyl-acceptance (42,859±9,699 cpm; n = 17) than DNA from B12-replete women (4.44±0.18%; n = 128 and 26,049±2,814 cpm; n = 11) [correlation between assays: r = –0.8538; p<0.001; n = 28]. In contrast, uncoagulated EDTA-blood cell pellet DNA from vitamin B12-deficient and B12-replete women exhibited similar percentage methylation (4.45±0.15%; n = 77 vs. 4.47±0.15%; n = 47) and [3 H]methyl-acceptance (27,378±4,094 cpm; n = 17 vs. 26,610±2,292 cpm; n = 11). Therefore, in simultaneously collected paired blood samples, vitamin B12-deficiency was associated with decreased DNA methylation only in coagulated samples. These findings highlight the importance of sample collection methods in epigenetic studies, and the potential impact biological processes can have on DNA methylation during collection.
Genomic DNA Methylation Changes in Response to Folic Acid Supplementation in a Population-Based Intervention Study among Women of Reproductive Age
Krista S. Crider, Eoin P. Quinlivan, Robert J. Berry, Ling Hao, Zhu Li, David Maneval, Thomas P. Yang, Sonja A. Rasmussen, Quanhe Yang, Jiang-Hui Zhu, Dale J. Hu, Lynn B. Bailey
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0028144
Abstract: Folate is a source of one-carbons necessary for DNA methylation, a critical epigenetic modification necessary for genomic structure and function. The use of supplemental folic acid is widespread however; the potential influence on DNA methylation is unclear. We measured global DNA methylation using DNA extracted from samples from a population-based, double-blind randomized trial of folic acid supplementation (100, 400, 4000 μg per day) taken for 6 months; including a 3 month post-supplementation sample. We observed no changes in global DNA methylation in response to up to 4,000 μg/day for 6 months supplementation in DNA extracted from uncoagulated blood (approximates circulating blood). However, when DNA methylation was determined in coagulated samples from the same individuals at the same time, significant time, dose, and MTHFR genotype-dependent changes were observed. The baseline level of DNA methylation was the same for uncoagulated and coagulated samples; marked differences between sample types were observed only after intervention. In DNA from coagulated blood, DNA methylation decreased (?14%; P<0.001) after 1 month of supplementation and 3 months after supplement withdrawal, methylation decreased an additional 23% (P<0.001) with significant variation among individuals (max+17%; min-94%). Decreases in methylation of ≥25% (vs. <25%) after discontinuation of supplementation were strongly associated with genotype: MTHFR CC vs. TT (adjusted odds ratio [aOR] 12.9, 95%CI 6.4, 26.0). The unexpected difference in DNA methylation between DNA extracted from coagulated and uncoagulated samples in response to folic acid supplementation is an important finding for evaluating use of folic acid and investigating the potential effects of folic acid supplementation on coagulation.
The Benefits of Supplementary Fat in Feed Rations for Ruminants with Particular Focus on Reducing Levels of Methane Production
J. Rasmussen,A. Harrison
ISRN Veterinary Science , 2011, DOI: 10.5402/2011/613172
Abstract: Methane (CH4), a highly potent greenhouse gas, has repeatedly been identified as a significant contributor to global warming. In this connection, ruminants, animals that produce large quantities of methane, have been singled out as an area for reduction with regard to their emissions to the atmosphere. In an analysis of recently published data, we identify the underlying mechanisms of methane production in ruminants and focus on the efficacy of different fat sources in terms of their ability to reduce methane production. Specific attention has been placed on in vivo studies involving cattle and sheep, as well as studies based on a large number of animals (>10), recorded over a longer period (>21 days), and employing reliable techniques for the quantification of methane production. Data clearly indicate that supplementary fat, given to ruminants inhibits methane production, with medium-chain fatty acids (laurin, myristic acid) as well as poly-unsaturated fatty acids (linoleic and especially linolenic acid) having a significant effect. It is also apparent that conflicting findings between individual published trials can largely be resolved when one takes into consideration differences in experimental design, the composition of the basic feeds, the fat sources used, and the number of animals involved. 1. Implications The addition of supplementary fat to the diet of ruminants has been reported to effectively reduce methane production. Primarily it is the medium chain (laurin and myristic acids) and polyunsaturated (linoleic and especially linolenic) fatty acids that appear to be most efficacious. In terms of the future, and alternate cost-effective sources of such fatty acids, researchers and ruminant nutritionists might consider using the n-3 alpha-linolenic acid typically found at high levels in and readily extractable from AFA aphanizomenon flos-aquae, a type of blue green algae that grows worldwide. 2. Introduction There has been considerable interest in recent years in those factors that appear to contribute to global warming, as determined by an observed increase in atmospheric temperature. Moreover, global warming has thus far been linked to an increased concentration of greenhouse gases in the atmosphere, among them carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) [1]. Methane is a very important greenhouse gas since it has been reported to have an effect that is 21-times greater than that of carbon dioxide in terms of global warming [2]. Furthermore, a rise in emission of methane is positively correlated with an increase in population
Khovanov homology and the slice genus
Jacob A. Rasmussen
Mathematics , 2004,
Abstract: We use Lee's work on the Khovanov homology to define a knot invariant s. We show that s(K) is a concordance invariant and that it provides a lower bound for the slice genus of K. As a corollary, we give a purely combinatorial proof of the Milnor conjecture.
Moncada Rasmussen,Dora María;
Colombia Forestal , 2010,
Abstract: this research was conducted at aguabuena, ráquira–boyacá, and the main objective was to iden tify the changes in the settlement patterns and oak - forest cover, due to the development of new tech nologies and destinies for ceramics production. the study was carried out using aerial photographs from 1985 and 1993 processed in arcgis v. 9.0, as well as the application of participatory methods and spatial statistics. the spatio-temporal analysis of the forests allowed the measurement of perime ter and area changes and the number of fragments, where the loss of forest cover was 43.43% for the evaluated years. for analytical purposes related to the ceramics production organization, two different types of workshops can be pointed out: domestic and family - industry. in the domestic workshops spatial aggregation is due to the forest presence, its relative and different antiquity. the family - indus try- workshops are located along roads, for their relatives and population increment. each ceramic production system represents different forms of relations with nature; the domestic ones are locat ed in the oaks forests, using high quality fuel in the heating ceramics, while the industrial-family looks for the roads with the purpose of centralizing the production and favoring the intermediate rela tions. these two modes of production reflect the human role in the change and creation of new land scapes from the pottery.
Fusion Algebras of Logarithmic Minimal Models
Jorgen Rasmussen,Paul A. Pearce
Physics , 2007, DOI: 10.1088/1751-8113/40/45/013
Abstract: We present explicit conjectures for the chiral fusion algebras of the logarithmic minimal models LM(p,p') considering Virasoro representations with no enlarged or extended symmetry algebra. The generators of fusion are countably infinite in number but the ensuing fusion rules are quasi-rational in the sense that the fusion of a finite number of representations decomposes into a finite direct sum of representations. The fusion rules are commutative, associative and exhibit an sl(2) structure but require so-called Kac representations which are reducible yet indecomposable representations of rank 1. In particular, the identity of the fundamental fusion algebra is in general a reducible yet indecomposable Kac representation of rank 1. We make detailed comparisons of our fusion rules with the results of Gaberdiel and Kausch for p=1 and with Eberle and Flohr for (p,p')=(2,5) corresponding to the logarithmic Yang-Lee model. In the latter case, we confirm the appearance of indecomposable representations of rank 3. We also find that closure of a fundamental fusion algebra is achieved without the introduction of indecomposable representations of rank higher than 3. The conjectured fusion rules are supported, within our lattice approach, by extensive numerical studies of the associated integrable lattice models. Details of our lattice findings and numerical results will be presented elsewhere. The agreement of our fusion rules with the previous fusion rules lends considerable support for the identification of the logarithmic minimal models LM(p,p') with the augmented c_{p,p'} (minimal) models defined algebraically.
Coset construction of logarithmic minimal models: branching rules and branching functions
Paul A. Pearce,Jorgen Rasmussen
Physics , 2013, DOI: 10.1088/1751-8113/46/35/355402
Abstract: Working in the Virasoro picture, it is argued that the logarithmic minimal models LM(p,p')=LM(p,p';1) can be extended to an infinite hierarchy of logarithmic conformal field theories LM(p,p';n) at higher fusion levels n=1,2,3,.... From the lattice, these theories are constructed by fusing together n x n elementary faces of the appropriate LM(p,p') models. It is further argued that all of these logarithmic theories are realized as diagonal cosets (A_1^{(1)})_k \oplus (A_1^{(1)})_n / (A_1^{(1)})_{k+n} where n is the integer fusion level and k=np/(p'-p)-2 is a fractional level. These cosets mirror the cosets of the higher fusion level minimal models of the form M(m,m';n), but are associated with certain reducible representations. We present explicit branching rules for characters in the form of multiplication formulas arising in the logarithmic limit of the usual Goddard-Kent-Olive coset construction of the non-unitary minimal models M(m,m';n). The limiting branching functions play the role of Kac characters for the LM(p,p';n) theories.
Affine su(3) and su(4) fusion multiplicities as polytope volumes
Jorgen Rasmussen,Mark A. Walton
Physics , 2001, DOI: 10.1088/0305-4470/35/32/313
Abstract: Affine su(3) and su(4) fusion multiplicities are characterised as discretised volumes of certain convex polytopes. The volumes are measured explicitly, resulting in multiple sum formulas. These are the first polytope-volume formulas for higher-rank fusion multiplicities. The associated threshold levels are also discussed. For any simple Lie algebra we derive an upper bound on the threshold levels using a refined version of the Gepner-Witten depth rule.
su(N) tensor product multiplicities and virtual Berenstein-Zelevinsky triangles
Jorgen Rasmussen,Mark A. Walton
Physics , 2000, DOI: 10.1088/0305-4470/34/49/324
Abstract: Information on su(N) tensor product multiplicities is neatly encoded in Berenstein-Zelevinsky triangles. Here we study a generalisation of these triangles by allowing negative as well as non-negative integer entries. For a fixed triple product of weights, these generalised Berenstein-Zelevinsky triangles span a lattice in which one may move by adding integer linear combinations of so-called virtual triangles. Inequalities satisfied by the coefficients of the virtual triangles describe a polytope. The tensor product multiplicities may be computed as the number of integer points in this convex polytope. As our main result, we present an explicit formula for this discretised volume as a multiple sum. As an application, we also address the problem of determining when a tensor product multiplicity is non-vanishing. The solution is represented by a set of inequalities in the Dynkin labels. We also allude to the question of when a tensor product multiplicity is greater than a given non-negative integer.
Polynomial Fusion Rings of Logarithmic Minimal Models
Jorgen Rasmussen,Paul A. Pearce
Physics , 2007, DOI: 10.1088/1751-8113/41/17/175210
Abstract: We identify quotient polynomial rings isomorphic to the recently found fundamental fusion algebras of logarithmic minimal models.
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