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941.
942.
We investigate by molecular dynamics simulation how thin film confinement modifies the fragility of a model glass-forming liquid characterized previously in the bulk. Film confinement is found to reduce the relative fragility of the polymer fluid, leading to effects similar to simulations of the addition of an antiplasticizer additive. A reduction of fragility is not observed for the antiplasticized polymer film. These effects are interpreted in terms of variation in the string (cooperatively moving segments) concentration with film confinement and the addition of antiplasticizing additives. 相似文献
943.
The sonic midshipman fish, Porichthys notatus, is a bottom-dwelling species whose swim bladder has evolved into a highly specialized, sound-producing organ. The males of this species exist in two distinct morphs with different physical characteristics and sexual strategies. The Type I males have a much larger sound organ and are capable of generating a loud approximately 100 Hz tone continuously for over an hour to attract females. This sound is produced by sonic muscle and represents one of the most superfast and super-enduring striated muscles found in nature. Each fiber contains a hollow, tubular contractile apparatus composed of radially arranged myofibrils with extremely broad Z-bands that are supported by a desmin-rich cytoskeleton. We have used micro computed tomography (CT) imaging and magnetic resonance (MR) imaging to visualize the location of the sonic organ in an intact male fish. We have also obtained high-resolution MR images of the excised swim bladders from both male types. The images of the Type I sonic organ are strikingly detailed and high-contrast, revealing both the internal organization of the bladder and the crisscrossing muscle fibers and their mode of attachment to the underlying bladder. The high-contrast variation in these images is due to different T(2) values for fiber bundles and the spaces between the bundles. Direct MR imaging of intact Type I sonic organ in Type I midshipman fish is a powerful approach to understanding the contraction of this superfast muscle and the oscillation of its bladder to produce mating calls, and how placement of the sonic organ in the body of the fish sheds light on its prodigious ability to produce and transmit its loud mating call. 相似文献
944.
945.
We present two classes of polynomially separable valid inequalities for the Maximum Flow Network Interdiction Problem. We prove that the integrality gap of the standard integer program is not bounded by a constant, even when strengthened by our valid inequalities. Finally, we provide an approximation-factor-preserving reduction from a simpler interdiction problem. 相似文献
946.
The slow-coloring game is played by Lister and Painter on a graph . On each round, Lister marks a nonempty subset of the uncolored vertices, scoring points. Painter then gives a color to a subset of that is independent in . The game ends when all vertices are colored. Painter and Lister want to minimize and maximize the total score, respectively. The best score that each player can guarantee is the sum-color cost of , written . The game is an online variant of online sum list coloring.We prove , where is the independence number, and we study when equality holds in the bounds. We compute for graphs with . Among -vertex trees, we prove that is minimized by the star and maximized by the path. We also study . 相似文献
947.
A balloon in a graph G is a maximal 2‐edge‐connected subgraph incident to exactly one cut‐edge of G. Let b(G) be the number of balloons, let c(G) be the number of cut‐edges, and let α′(G) be the maximum size of a matching. Let ${\mathcal{F}}_{{{n}},{{r}}}A balloon in a graph G is a maximal 2‐edge‐connected subgraph incident to exactly one cut‐edge of G. Let b(G) be the number of balloons, let c(G) be the number of cut‐edges, and let α′(G) be the maximum size of a matching. Let ${\mathcal{F}}_{{{n}},{{r}}}$ be the family of connected (2r+1)‐regular graphs with n vertices, and let ${{b}}={{max}}\{{{b}}({{G}}): {{G}}\in {\mathcal{F}}_{{{n}},{{r}}}\}$. For ${{G}}\in{\mathcal{F}}_{{{n}},{{r}}}$, we prove the sharp inequalities c(G)?[r(n?2)?2]/(2r2+2r?1)?1 and α′(G)?n/2?rb/(2r+1). Using b?[(2r?1)n+2]/(4r2+4r?2), we obtain a simple proof of the bound proved by Henning and Yeo. For each of these bounds and each r, the approach using balloons allows us to determine the infinite family where equality holds. For the total domination number γt(G) of a cubic graph, we prove γt(G)?n/2?b(G)/2 (except that γt(G) may be n/2?1 when b(G)=3 and the balloons cover all but one vertex). With α′(G)?n/2?b(G)/3 for cubic graphs, this improves the known inequality γt(G)?α′(G). © 2009 Wiley Periodicals, Inc. J Graph Theory 64: 116–131, 2010 相似文献
948.
Yulin Ren Esperanza J. Carcache de Blanco Leonardus B.S. Kardono Heebyung Chai Norman R. Farnsworth Steven M. Swanson Yuanqing Ding Jannie P.J. Marais A. Douglas Kinghorn 《Tetrahedron》2010,66(29):5311-5320
A new biflavonoid (1), a new xanthone enantiomer (2), five new caged xanthones (3-7), and several known compounds were isolated from the stem bark of Garcinia lateriflora, collected in Indonesia. The structures of the new compounds were determined by analysis of spectroscopic data, and the absolute configuration of the caged xanthones was shown for the first time at carbons 5, 7, 8, 8a, 10a, and 27, by analysis of COSY and NOESY NMR and ECD spectra. The biflavonoids exhibited proteasome-inhibitory activity, and the known compound, morelloflavone (8) was found to have the greatest potency (IC50=1.3 μM). The caged xanthones were cytotoxic toward HT-29 cells, with the known compound, morellic acid (10) being the most active (ED50=0.36 μM). However, when tested in an in vivo hollow fiber assay, it was inactive at the highest dose tested (20 mg/kg). 相似文献
949.
Godlewski G Alapafuja SO Bátkai S Nikas SP Cinar R Offertáler L Osei-Hyiaman D Liu J Mukhopadhyay B Harvey-White J Tam J Pacak K Blankman JL Cravatt BF Makriyannis A Kunos G 《Chemistry & biology》2010,17(11):1256-1266
The enzyme fatty acid amide hydrolase (FAAH) catalyzes the in vivo degradation of the endocannabinoid anandamide, thus controlling its action at receptors. A novel FAAH inhibitor, AM3506, normalizes the elevated blood pressure and cardiac contractility of spontaneously hypertensive rats (SHR) without affecting these parameters in normotensive rats. These effects are due to blockade of FAAH and a corresponding rise in brain anandamide levels, resulting in CB? receptor-mediated decrease in sympathetic tone. The supersensitivity of SHR to CB? receptor-mediated cardiovascular depression is related to increased G protein coupling of CB? receptors. Importantly, AM3506 does not elicit hyperglycemia and insulin resistance seen with other FAAH inhibitors or in FAAH?/? mice, which is related to its inability to inhibit FAAH in the liver due to rapid hepatic uptake and metabolism. This unique activity profile offers improved therapeutic value in hypertension. 相似文献
950.
The reaction kinetics of ammonium bisulfate clusters with dimethylamine (DMA) gas were investigated using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Clusters ranged in size from 1 to 10 bisulfate ions. Although displacement of the first several ammonium ions by DMA occurred with near unit efficiency, displacement of the final ammonium ion was cluster size dependent. For small clusters, all ammonium ions are exposed to incoming DMA molecules, allowing for facile exchange ("surface" exchange). However, with increasing cluster size, an ammonium ion can be trapped in an inaccessible region of the cluster ("core" exchange), thereby rendering exchange difficult. DMA was also observed to add onto existing dimethylaminium bisulfate clusters above a critical size, whereas ammonia did not add onto ammonium bisulfate clusters. The results suggest that as the cluster size increases, di-dimethylaminium sulfate formation becomes more favorable. The results of this study give further evidence to suggest that ambient sub-3 nm diameter particles are likely to contain aminium salts rather than ammonium salts. 相似文献