1,934 research outputs found
Hybrid LTA vehicle controllability as affected by buoyancy ratio
The zero and low speed controllability of heavy lift airships under various wind conditions as affected by the buoyancy ratio are investigated. A series of three hybrid LTA vehicls were examined, each having a dynamic thrust system comprised of four H-34 helicopters, but with buoyant envelopes of different volumes (and hence buoyancies), and with varying percentage of helium inflation and varying useful loads (hence gross weights). Buoyancy ratio, B, was thus examined varying from approximately 0.44 to 1.39. For values of B greater than 1.0, the dynamic thrusters must supply negative thrust (i.e. downward)
Comment on "Drip Paintings and Fractal Analysis", arXiv:0710.4917v2, by K. Jones-Smith, H. Mathur and L.M. Krauss
In a recent manuscript (arXiv:0710.4917v2), Jones-Smith et al. attempt to use
the well-established box-counting technique for fractal analysis to
"demonstrate conclusively that fractal criteria are not useful for
authentication". Here, in response to what we view to be an extremely
simplistic misrepresentation of our earlier work by Jones-Smith et al., we
reiterate our position regarding the potential of fractal analysis for artwork
authentication. We also point out some of the flaws in the analysis presented
in by Jones-Smith et al.Comment: Comment on arXiv:0710.4917v2 [cond-mat.stat-mech
Trends in fire patterns in a southern African savanna under alternative land use practices
Climate, topography, vegetation and land use interact to influence fire regimes. Variable fire regimes may promote landscape heterogeneity, diversification in vegetation pattern and biotic diversity. The objective was to compare effects of alternative land use practices on landscape heterogeneity. Patch characteristics of fire scars were measured from 21 annual burn maps produced from 1972 to 2001 Landsat imagery. Trends in fire patterns under alternative land use practices were compared across a 250,000 ha savanna in southern Africa partitioned into three land use zones. Zone 1, Madikwe Game Reserve (MGR), has had mostly prescribed fires since 1993. Zone 2, cattle farms near MGR in South Africa (SAF), has experienced occasional fires. Zone 3, communal grazing lands in neighboring Botswana (BOT), has had the fewest fires. Cattle ranching was the predominant land use throughout the study area until 1992, when land use switched to conservation and eco-tourism in MGR. Sixteen landscape metrics were applied to this data set to uncover trends in the patch characteristics of the fire scars. A principal components analysis (PCA) reduced the dimensionality of the results so trends in the 10 most important size, shape, and proximity metrics could be better interpreted. The PCA results showed that more burning over time in MGR, and to a lesser extent in SAF, increased patch size, size variability, shape complexity and proximity, while fire exclusion in BOT produced no change or decreasing trends. We tested for significant differences in these metrics between the three land use zones and between two periods, 1972ā1992 and 1993ā2001. Most patch characteristics in MGR and SAF differed significantly from those in BOT, especially during the latter period, while between MGR and SAF they did not. Patch area, shape complexity and core area increased significantly between periods in MGR, while patch size, size variability and core area increased significantly between periods in SAF. In BOT, no patch characteristics changed significantly between periods. Within the time span analyzed for the study area, we conclude that increased fire occurrence promoted landscape heterogeneity while fire exclusion did not
A compositional account of motifs, mechanisms, and dynamics in biochemical regulatory networks
Regulatory networks depict promoting or inhibiting interactions between
molecules in a biochemical system. We introduce a category-theoretic formalism
for regulatory networks, using signed graphs to model the networks and signed
functors to describe occurrences of one network in another, especially
occurrences of network motifs. With this foundation, we establish functorial
mappings between regulatory networks and other mathematical models in
biochemistry. We construct a functor from reaction networks, modeled as Petri
nets with signed links, to regulatory networks, enabling us to precisely define
when a reaction network could be a physical mechanism underlying a regulatory
network. Turning to quantitative models, we associate a regulatory network with
a Lotka-Volterra system of differential equations, defining a functor from the
category of signed graphs to a category of parameterized dynamical systems. We
extend this result from closed to open systems, demonstrating that
Lotka-Volterra dynamics respects not only inclusions and collapsings of
regulatory networks, but also the process of building up complex regulatory
networks by gluing together simpler pieces. Formally, we use the theory of
structured cospans to produce a lax double functor from the double category of
open signed graphs to that of open parameterized dynamical systems. Throughout
the paper, we ground the categorical formalism in examples inspired by systems
biology.Comment: 33 pages. Added several examples, plus minor revision
Lincoln, the Friendly Neighbor
The sculpture depicts a full-length Abraham Lincoln dressed in a suit. He stands with two children - male and female - and a dog. This particular sculpture is number one in a limited release of thirty.https://scholarsjunction.msstate.edu/fvw-statuettes-and-figurines/1031/thumbnail.jp
Lincoln, the Friendly Neighbor
The sculpture depicts a full-length Abraham Lincoln dressed in a suit. He stands with two children - male and female - and a dog. This particular sculpture is number one in a limited release of thirty.https://scholarsjunction.msstate.edu/fvw-artifacts/2377/thumbnail.jp
Electrospinning of 2-hydroxypropyl-Ī²-cyclodextrin aqueous solutions with added salts
It has been proposed that hydrogen bonding plays a role in promoting the electrospinnability of some materials. In this study, the role of non-covalent interactions in the electrospinnability of 2-hydroxypropyl-Ī²-cyclodextrin (2HP-Ī²-CD) was investigated by varying the physical-chemical properties the solvents. The rheological behaviour of a peroxide-aqueous/acetone-ethanol/NaHCO3 solution and an aqueous urea solution, as a function of aqueous 2HP-Ī²-CD concentration, was compared. The rheological behaviour of 2HP-Ī²-CD solutions was characterized by a frequency-independent stress relaxation plateau such as that observed in cross-linked polymer networks and reversible polymer gels with non-linear viscoelasticity. We conclude that the electrospinnability of 2HP-Ī²-CD is, as evidenced by the changes in the morphology of the electrospun 2HP-Ī²-CD materials, in agreement with other related studies on the electrospinning of Cyclodextrins. Also, the electrospinnability of 2HP-Ī²-CD does appear to be related to the physical-chemical properties of the solvent systems
Tissue engineering for total meniscal substitution : Animal study in sheep model
Objective: The aim of the study was to investigate the use of a novel hyaluronic acid/polycaprolactone material for meniscal tissue engineering and to evaluate the tissue regeneration after the augmentation of the implant with expanded autologous chondrocytes. Two different surgical implantation techniques in a sheep model were evaluated. Methods: Twenty-four skeletally mature sheep were treated with total medial meniscus replacements, while two meniscectomies served as empty controls. The animals were divided into two groups: cell-free scaffold and scaffold seeded with autologous chondrocytes. Two different surgical techniques were compared: in 12 animals, the implant was sutured to the capsule and to the meniscal ligament; in the other 12 animals, also a transtibial fixation of the horns was used. The animals were euthanized after 4 months. The specimens were assessed by gross inspection and histology. Results: All implants showed excellent capsular ingrowth at the periphery. Macroscopically, no difference was observed between cell-seeded and cell-free groups. Better implant appearance and integrity was observed in the group without transosseous horns fixation. Using the latter implantation technique, lower joint degeneration was observed in the cell-seeded group with respect to cell-free implants. The histological analysis indicated cellular infiltration and vascularization throughout the implanted constructs. Cartilaginous tissue formation was significantly more frequent in the cell-seeded constructs. Conclusion: The current study supports the potential of a novel HYAFF/polycaprolactone scaffold for total meniscal substitution. Seeding of the scaffolds with autologous chondrocytes provides some benefit in the extent of fibrocartilaginous tissue repair
Metabolite and thymocyte development defects in ADA-SCID mice receiving enzyme replacement therapy
Deficiency of adenosine deaminase (ADA, EC3.5.4.4), a housekeeping enzyme intrinsic to the purine salvage pathway, leads to severe combined immunodeficiency (SCID) both in humans and mice. Lack of ADA results in the intracellular accumulation of toxic metabolites which have effects on T cell development and function. While untreated ADA-SCID is a fatal disorder, there are different therapeutic options available to restore ADA activity and reconstitute a functioning immune system, including enzyme replacement therapy (ERT). Administration of ERT in the form of pegylated bovine ADA (PEG-ADA) has proved a life-saving though non-curative treatment for ADA-SCID patients. However, in many patients treated with PEG-ADA, there is suboptimal immune recovery with low T and B cell numbers. Here, we show reduced thymus cellularity in ADA-SCID mice despite weekly PEG-ADA treatment. This was associated with lack of effective adenosine (Ado) detoxification in the thymus. We also show that thymocyte development in ADA-deficient thymi is arrested at the DN3-to-DN4 stage transition with thymocytes undergoing dATP-induced apoptosis rather than defective TCRĪ² rearrangement or Ī²-selection. Our studies demonstrate at a detailed level that exogenous once-a-week enzyme replacement does not fully correct intra-thymic metabolic or immunological abnormalities associated with ADA deficiency
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