SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Abstract algebra

35

A new bioprinting method is reported for fabricating 3D tissue constructs replete with vasculature, multiple types of cells, and extracellular matrix. These intricate, heterogeneous structures are created by precisely co-printing multiple materials, known as bioinks, in three dimensions. These 3D micro-engineered environments open new -avenues for drug screening and fundamental studies of wound healing, angiogenesis, and stem-cell niches.

Concepts: Healing, Method, Dimension, Abstract algebra, Angiogenesis, Euclidean space, Wound healing, Extracellular matrix

27

The literature is replete with rich connections between the structure of a graph G = (V, E) and the spectral properties of its Laplacian matrix L. This paper establishes similar connections between the structure of G and the Laplacian L* of a second graph G*. Our interest lies in L* that can be obtained from L by Schur complementation, in which case we say that G* is partially-supplied with respect to G. In particular, we specialize to where G is a tree with points of articulation r ∈ R and consider the partially-supplied graph G* derived from G by taking the Schur complement with respect to R in L. Our results characterize how the eigenvectors of the Laplacian of G* relate to each other and to the structure of the tree.

Concepts: Eigenvalue, eigenvector and eigenspace, Matrices, Laplacian matrix, Abstract algebra, Linear algebra, Graph theory

26

Objective: To establish an experimental rabbit model of urethral stricture using holmium laser under direct urethroscopic visualization. Methods: Sixteen adult male New Zealand rabbits were divided into equally-sized control and experimental groups. All rabbits underwent retrograde urethrography and transurethral endoscopy with a 7.5 F urethroscope after intramuscular anesthetic injection. We used a holmium:YAG laser to injure the distal urethra in all rabbits in the experimental group under direct visualization. Thirty days after surgery, all animals were evaluated with retrograde urethrography and urethroscopy. The flow rate of the isolated urethras was measured to evaluate urethral stricture formation. Results: One rabbit in the experimental group (12.5%) died of infection 4 days after surgery. Thirty days after surgery, retrograde urethrography and urethroscopy revealed strictures in all seven surviving rabbits (87.5%) in the experimental group. The mean flow rate of the isolated urethras was significantly lower in the experimental group than in the control group. Conclusion: A rabbit model of urethral stricture can be successfully established using holmium laser under direct urethroscopic visualization, providing an ideal object for research concerning the pathogenesis and molecular biology of urethral strictures. © 2014 S. Karger AG, Basel.

Concepts: Urethrotomy, New Zealand white rabbit, Surgery, Abstract algebra, Biology, Chemistry, Urethra, Urethral stricture

25

Biomimic electrospun matrix derived from silk fibroin nanofiber solution was recently prepared in our group. The feasibility of the matrix as mucosa repair scaffold was evaluated in a rat model in the present study.

Concepts: Abstract algebra

24

The bacterial flagellar type III export apparatus, which is required for flagellar assembly beyond the cell membranes, consists of a transmembrane export gate complex and a cytoplasmic ATPase complex. FlhA, FlhB, FliP, FliQ, and FliR form the gate complex inside the basal body MS ring, although FliO is required for efficient export gate formation in Salmonella enterica. However, it remains unknown how they form the gate complex. Here we report that FliP forms a homohexameric ring with a diameter of 10 nm. Alanine substitutions of conserved Phe-137, Phe-150, and Glu-178 residues in the periplasmic domain of FliP (FliPP) inhibited FliP6 ring formation, suppressing flagellar protein export. FliO formed a 5-nm ring structure with 3 clamp-like structures that bind to the FliP6 ring. The crystal structure of FliPP derived from Thermotoga maritia, and structure-based photo-crosslinking experiments revealed that Phe-150 and Ser-156 of FliPP are involved in the FliP-FliP interactions and that Phe-150, Arg-152, Ser-156, and Pro-158 are responsible for the FliP-FliO interactions. Overexpression of FliP restored motility of a ∆fliO mutant to the wild-type level, suggesting that the FliP6 ring is a functional unit in the export gate complex and that FliO is not part of the final gate structure. Copurification assays revealed that FlhA, FlhB, FliQ, and FliR are associated with the FliO/FliP complex. We propose that the assembly of the export gate complex begins with FliP6 ring formation with the help of the FliO scaffold, followed by FliQ, FliR, and FlhB and finally FlhA during MS ring formation.

Concepts: Abstract algebra, Unit, Gene, Protein, Salmonella enterica, Flagellum, Cell, Cell membrane

24

In this study, we constructed a novel vector (BioPf-M-loaded Alg-microparticles [Alg-BioPf-M]) with nano-in-micro structure to improve the oral absorption of docetaxel (DTX) by sequentially dual-targeting functions toward intestine and sodium-dependent multivitamin transporter based on entrapping biotin-modified micelles into alginate microparticles.

Concepts: Better, Small intestine, Abstract algebra, Ring, In vivo, Improve, Group

24

In this paper, Model Predictive Control and Dead-beat predictive control strategies are proposed for the control of a PMSG based wind energy system. The proposed MPC considers the model of the converter-based system to forecast the possible future behavior of the controlled variables. It allows selecting the voltage vector to be applied that leads to a minimum error by minimizing a predefined cost function. The main features of the MPC are low current THD and robustness against parameters variations. The Dead-beat predictive control is based on the system model to compute the optimum voltage vector that ensures zero-steady state error. The optimum voltage vector is then applied through Space Vector Modulation (SVM) technique. The main advantages of the Dead-beat predictive control are low current THD and constant switching frequency. The proposed control techniques are presented and detailed for the control of back-to-back converter in a wind turbine system based on PMSG. Simulation results (under Matlab-Simulink software environment tool) and experimental results (under developed prototyping platform) are presented in order to show the performances of the considered control strategies.

Concepts: Group, Derivative, Windmill, Wind power, Abstract algebra, Vector space, Wind turbine, Electrical generator

15

One of the most mysterious phenomena in science is the nature of conscious experience. Due to its subjective nature, a reductionist approach is having a hard time in addressing some fundamental questions about consciousness. These questions are squarely and quantitatively tackled by a recently developed theoretical framework, called integrated information theory (IIT) of consciousness. In particular, IIT proposes that a maximally irreducible conceptual structure (MICS) is identical to conscious experience. However, there has been no principled way to assess the claimed identity. Here, we propose to apply a mathematical formalism, category theory, to assess the proposed identity and suggest that it is important to consider if there exists a proper translation between the domain of conscious experience and that of the MICS. If such translation exists, we postulate that questions in one domain can be answered in the other domain; very difficult questions in the domain of consciousness can be resolved in the domain of mathematics. We claim that it is possible to empirically test if such a functor exists, by using a combination of neuroscientific and computational approaches. Our general, principled and empirical framework allows us to assess the relationship between the domain of consciousness and the domain of mathematical structures, including those suggested by IIT.

Concepts: Abstract algebra, Empiricism, Physics, Category theory, Scientific method, Science, Mathematics, Group

12

The ability to fabricate nanoscale domains of uniform size in two-dimensional materials could potentially enable new applications in nanoelectronics and the development of innovative metamaterials. However, achieving even minimal control over the growth of two-dimensional lateral heterostructures at such extreme dimensions has proven exceptionally challenging. Here we show the spontaneous formation of ordered arrays of graphene nano-domains (dots), epitaxially embedded in a two-dimensional boron-carbon-nitrogen alloy. These dots exhibit a strikingly uniform size of 1.6 ± 0.2 nm and strong ordering, and the array periodicity can be tuned by adjusting the growth conditions. We explain this behaviour with a model incorporating dot-boundary energy, a moiré-modulated substrate interaction and a long-range repulsion between dots. This new two-dimensional material, which theory predicts to be an ordered composite of uniform-size semiconducting graphene quantum dots laterally integrated within a larger-bandgap matrix, holds promise for novel electronic and optoelectronic properties, with a variety of potential device applications.The nanoscale patterning of two-dimensional materials offers the possibility of novel optoelectronic properties; however, it remains challenging. Here, Camilli et al. show the self-assembly of large arrays of highly-uniform graphene dots imbedded in a BCN matrix, enabling novel devices.

Concepts: Model theory, Array, Dimension, Abstract algebra, Nanomaterials, Physics, Manifold, Nanotechnology

7

Biological networks entail important topological features and patterns critical to understanding interactions within complicated biological systems. Despite a great progress in understanding their structure, much more can be done to improve our inference and network analysis. Spectral methods play a key role in many network-based applications. Fundamental to spectral methods is the Laplacian, a matrix that captures the global structure of the network. Unfortunately, the Laplacian does not take into account intricacies of the network’s local structure and is sensitive to noise in the network. These two properties are fundamental to biological networks and cannot be ignored. We propose an alternative matrix Vicus. The Vicus matrix captures the local neighborhood structure of the network and thus is more effective at modeling biological interactions. We demonstrate the advantages of Vicus in the context of spectral methods by extensive empirical benchmarking on tasks such as single cell dimensionality reduction, protein module discovery and ranking genes for cancer subtyping. Our experiments show that using Vicus, spectral methods result in more accurate and robust performance in all of these tasks.

Concepts: Evolution, Manifold, Biology, Fourier analysis, DNA, Gene, Ring, Abstract algebra