2,018 research outputs found
Line Bundles and Curves on a del Pezzo Order
Orders on surfaces provide a rich source of examples of noncommutative
surfaces. Other than some existence results, very little is known about the
various moduli spaces that can be associated to them. Even fewer examples have
been explicitly computed. In this paper we compute the Picard and Hilbert
schemes of an order on the projective plane ramified on a union of two conics.
Our main result is that, upon carefully selecting the right Chern classes, the
Hilbert scheme is a ruled surface over a genus two curve. Furthermore, this
genus two curve is, in itself, the Picard scheme of the order
Quasiclassical theory of electronic transport in mesoscopic systems: Luttinger liquids revisited
The method of the quasiclassical Green's function is used to determine the
equilibrium properties of one-dimensional (1D) interacting Fermi systems, in
particular, the bulk and the local (near a hard wall) density of states. While
this is a novel approach to 1D systems, our findings do agree with standard
results for Luttinger liquids obtained with the bosonization method. Analogies
to the so-called theory of tunneling through ultrasmall junctions are
pointed out and are exploited. Further applications of the Green's function
method for 1D systems are discussed.Comment: 7 pages, Proceedings of ECNM06, Ustron, Poland (references added
Estimation of methane emissions from local and crossbreed beef cattle in Daklak province of Vietnam
Objective: This study was aimed at evaluating effects of cattle breed resources and alternative mixed-feeding practices on meat productivity and emission intensities from household farming systems (HFS) in Daklak Province, Vietnam.
Methods: Records from Local Yellow×Red Sindhi (Bos indicus; Lai Sind) and 1/2 Limousin, 1/2 Drought Master, and 1/2 Red Angus cattle during the growth (0 to 21 months) and fattening (22 to 25 months) periods were used to better understand variations on meat productivity and enteric methane emissions. Parameters were determined by the ruminant model. Four scenarios were developed: (HFS1) grazing from birth to slaughter on native grasses for approximately 10 h plus 1.5 kg dry matter/d (0.8% live weight [LW]) of a mixture of Guinea grass (19%), cassava (43%) powder, cotton (23%) seed, and rice (15%) straw; (HFS2) growth period fed with elephant grass (1% of LW) plus supplementation (1.5% of LW) of rice bran (36%), maize (33%), and cassava (31%) meals; and HFS3 and HFS4 computed elephant grass, but concentrate supplementation reaching 2% and 1% of LW, respectively.
Results: Results show that compared to HFS1, emissions (72.3±0.96 kg CH 4 /animal/life; least squares means± standard error of the mean) were 15%, 6%, and 23% lower (p < 0.01) for the HFS2, HFS3, and HFS4, respectively. The predicted methane efficiencies (CO 2 eq) per kg of LW at slaughter (4.3±0.15), carcass weight (8.8±0.25 kg) and kg of edible protein (44.1±1.29) were also lower (p < 0.05) in the HFS4. In particular, irrespective of the HSF, feed supply and ratio changes had a more positive impact on emission intensities when crossbred 1/2 Red Angus cattle were fed than in their crossbred counterparts.
Conclusion: Modest improvements on feeding practices and integrated modelling frameworks may offer potential trade-offs to respond to climate change in Vietnam
Inflation with Non-minimal Gravitational Couplings and Supergravity
We explore in the supergravity context the possibility that a Higgs scalar
may drive inflation via a non-minimal coupling to gravity characterised by a
large dimensionless coupling constant. We find that this scenario is not
compatible with the MSSM, but that adding a singlet field (NMSSM, or a variant
thereof) can very naturally give rise to slow-roll inflation. The inflaton is
necessarily contained in the doublet Higgs sector and occurs in the D-flat
direction of the two Higgs doublets.Comment: 13 pages, 1 figur
Total Cellular ATP Production Changes With Primary Substrate in MCF7 Breast Cancer Cells.
Cancer growth is predicted to require substantial rates of substrate catabolism and ATP turnover to drive unrestricted biosynthesis and cell growth. While substrate limitation can dramatically alter cell behavior, the effects of substrate limitation on total cellular ATP production rate is poorly understood. Here, we show that MCF7 breast cancer cells, given different combinations of the common cell culture substrates glucose, glutamine, and pyruvate, display ATP production rates 1.6-fold higher than when cells are limited to each individual substrate. This increase occurred mainly through faster oxidative ATP production, with little to no increase in glycolytic ATP production. In comparison, non-transformed C2C12 myoblast cells show no change in ATP production rate when substrates are limited. In MCF7 cells, glutamine allows unexpected access to oxidative capacity that pyruvate, also a strictly oxidized substrate, does not. Pyruvate, when added with other exogenous substrates, increases substrate-driven oxidative ATP production, by increasing both ATP supply and demand. Overall, we find that MCF7 cells are highly flexible with respect to maintaining total cellular ATP production under different substrate-limited conditions, over an acute (within minutes) timeframe that is unlikely to result from more protracted (hours or more) transcription-driven changes to metabolic enzyme expression. The near-identical ATP production rates maintained by MCF7 and C2C12 cells given single substrates reveal a potential difficulty in using substrate limitation to selectively starve cancer cells of ATP. In contrast, the higher ATP production rate conferred by mixed substrates in MCF7 cells remains a potentially exploitable difference
Field theory of self-avoiding walks in random media
Based on the analogy with the quantum mechanics of a particle propagating in
a {\em complex} potential, we develop a field-theoretical description of the
statistical properties of a self-avoiding polymer chain in a random
environment. We show that the account of the non-Hermiticity of the quantum
Hamiltonian results in a qualitatively different structure of the effective
action, compared to previous studies. Applying the renormalisation group
analysis, we find a transition between the weak-disorder regime, where the
quenched randomness is irrelevant, and the strong-disorder regime, where the
polymer chain collapses. However, the fact that the renormalised interaction
constants and the chiral symmetry breaking regularisation parameter flow
towards strong coupling raises questions about the applicability of the
perturbative analysis.Comment: RevTeX, 9 pages; accepted for publication in J. Phys.
Polarization of coalitions in an agent-based model of political discourse
Political discourse is the verbal interaction between political actors in a policy domain. This article explains the formation of polarized advocacy or discourse coalitions in this complex phenomenon by presenting a dynamic, stochastic, and discrete agent-based model based on graph theory and local optimization. In a series of thought experiments, actors compute their utility of contributing a specific statement to the discourse by following ideological criteria, preferential attachment, agenda-setting strategies, governmental coherence, or other mechanisms. The evolving macro-level discourse is represented as a dynamic network and evaluated against arguments from the literature on the policy process. A simple combination of four theoretical mechanisms is already able to produce artificial policy debates with theoretically plausible properties. Any sufficiently realistic configuration must entail innovative and path-dependent elements as well as a blend of exogenous preferences and endogenous opinion formation mechanisms
High-gradient operators in perturbed Wess-Zumino-Witten field theories in two dimensions
Many classes of non-linear sigma models (NLSMs) are known to contain
composite operators with an arbitrary number 2s of derivatives ("high-gradient
operators") which appear to become strongly relevant within RG calculations at
one (or fixed higher) loop order, when the number 2s of derivatives becomes
large. This occurs at many conventional fixed points of NLSMs which are
perturbatively accessible within the usual epsilon-expansion in d=2+\epsilon
dimensions. Since such operators are not prohibited from occurring in the
action, they appear to threaten the very existence of such fixed points. At the
same time, for NLSMs describing metal-insulator transitions of Anderson
localization in electronic conductors, the strong RG-relevance of these
operators has been previously related to statistical properties of the
conductance of samples of large finite size ("conductance fluctuations"). In
this paper, we analyze this question, not for perturbative RG treatments of
NLSMs, but for 2d Wess-Zumino-Witten (WZW) models at level k, perturbatively in
the current-current interaction of the Noether current. WZW models are special
("Principal Chiral") NLSMs on a Lie Group G with a WZW term at level k. In
these models the role of high-gradient operators is played by homogeneous
polynomials of order 2s in the Noether currents, whose scaling dimensions we
analyze. For the Lie Supergroup G=GL(2N|2N) and k=1, this corresponds to
time-reversal invariant problems of Anderson localization in the so-called
chiral symmetry classes, and the strength of the current-current interaction, a
measure of the strength of disorder, is known to be completely marginal (for
any k). We find that all high-gradient (polynomial) operators are, to one loop
order, irrelevant or relevant depending on the sign of that interaction.Comment: 22 page
Sequence-Specific Binding of Recombinant Zbed4 to DNA: Insights into Zbed4 Participation in Gene Transcription and Its Association with Other Proteins
Zbed4, a member of the BED subclass of Zinc-finger proteins, is expressed in cone photoreceptors and glial Müller cells of human retina whereas it is only present in Müller cells of mouse retina. To characterize structural and functional properties of Zbed4, enough amounts of purified protein were needed. Thus, recombinant Zbed4 was expressed in E. coli and its refolding conditions optimized for the production of homogenous and functionally active protein. Zbed4’s secondary structure, determined by circular dichroism spectroscopy, showed that this protein contains 32% α-helices, 18% β-sheets, 20% turns and 30% unordered structures. CASTing was used to identify the target sites of Zbed4 in DNA. The majority of the DNA fragments obtained contained poly-Gs and some of them had, in addition, the core signature of GC boxes; a few clones had only GC-boxes. With electrophoretic mobility shift assays we demonstrated that Zbed4 binds both not only to DNA and but also to RNA oligonucleotides with very high affinity, interacting with poly-G tracts that have a minimum of 5 Gs; its binding to and GC-box consensus sequences. However, the latter binding depends on the GC-box flanking nucleotides. We also found that Zbed4 interacts in Y79 retinoblastoma cells with nuclear and cytoplasmic proteins Scaffold Attachment Factor B1 (SAFB1), estrogen receptor alpha (ERα), and cellular myosin 9 (MYH9), as shown with immunoprecipitation and mass spectrometry studies as well as gel overlay assays. In addition, immunostaining corroborated the co-localization of Zbed4 with these proteins. Most importantly, in vitro experiments using constructs containing promoters of genes directing expression of the luciferase gene, showed that Zbed4 transactivates the transcription of those promoters with poly-G tracts
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