Flat Topology Research Articles

A functorial formalism for quasi-coherent sheaves on a geometric stack

A geometric stack is a quasi-compact and semi-separated algebraic stack. We prove that the quasi-coherent sheaves on the small flat topology, Cartesian presheaves on the underlying category, and comodules over a Hopf algebroid associated to a presentation of a geometric stack are equivalent categories. As a consequence, we show that the category of quasi-coherent sheaves on a geometric stack is a Grothendieck category.We also associate, in a 2-functorial way, to a 1-morphism of geometric stacks f:X→Y, an adjunction f∗⊣f∗ for the corresponding categories of quasi-coherent sheaves that agrees with the classical one defined for schemes. This construction is described both geometrically in terms of the small flat site and algebraically in terms of comodules over the Hopf algebroid.

Nanotopology potentiates growth hormone signalling and osteogenesis of mesenchymal stem cells

Custom engineered materials can influence the differentiation of human mesenchymal stem cells (MSCs) towards osteoblasts, chondrocytes and adipocytes, through the control of chemistry, stiffness and nanoscale topography. Here we demonstrate that polycaprolactone growth surfaces engineered with disordered (but controlled) 120nm diameter dots (NSQ50), but not flat surfaces, promote osteogenic conversion of MSCs in the absence of other osteogenic stimuli. Differentiating MSCs on NSQ50 were found to express growth hormone receptors (GH) and stimulation with recombinant human GH (rhGH) further enhanced NSQ50-driven osteogenic conversion of MSCs. This increased osteogenesis coincided with an enhanced ability of GH to activate ERK MAP kinase on NSQ50, but not on flat topology. The importance of ERK for MSC differentiation was demonstrated by using the inhibitor of ERK activation, U0126, which completely suppressed osteogenesis of GH-stimulated MSCs on NSQ50. The ability of GH to activate ERK in MSCs may therefore be a central control mechanism underlying bone development and growth.

Tunable mixed amorphous–crystalline cellulose substrates (MACS) for dynamic degradation studies by atomic force microscopy in liquid environments

Atomic force microscopy in liquid environments (L-AFM) became a state of the art technique in the field of enzymatic cellulose degradation due to its capability of in situ investigations on enzymatic relevant scales. Current investigations are however limited to few substrates like valonia cellulose, cotton linters and processed amorphous cellulose as only these show required flatness and purity. Structurally monophasic, these substrates confine conclusions regarding enzymatic degradation of mixed amorphous–crystalline substrates as commonly found in nature. To exploit the full potential of the technique, cellulose substrates with multiphase properties, flat topology and purity are therefore absolutely required. In this study we introduce a special preparation route based on highly crystalline Avicel PH101® cellulose and the ionic liquid 1-butyl-3-methylimmidazolium chloride as dissolution reagent. As comprehensively shown by atomic force microscopy, wide angle X-ray scattering, Raman spectroscopy and electron microscopy, the developed material allows precise control of its polymorphic composition by means of cellulose types I and II embedded in an amorphous matrix. Together with the tunable composition and flat topology over large areas (>10 × 10 µm2) the material is highly suited for L-AFM studies.

Comparison of Energy Efficient Data Transmission Approaches for Flat Wireless Sensor Networks

In this paper we have analyzed energy efficient neighbour selection algorithms for routing in wireless sensor networks. Since energy saving or consumption is an important aspect of wireless sensor networks, its precise usage is highly desirable both for the faithful performance of network and to increase the network life time. For this work, we have considered a flat network topology where every node has the same responsibility and capability. We have compared two energy efficient algorithms and analyzed their performances when all sensor nodes in a network have either homogeneous or heterogeneous energy with increase in number of nodes, time rounds and node failures. Wireless sensor networks consist of number of small nodes deployed in an area under supervision. Each node has limited storage, computational and sensing capability and limited energy resource, as nodes are battery operated. Since energy is the main concern in wireless sensor networks (WSN) to maximize the performance and to increase the lifetime of a network, various approaches are implemented to reduce energy consumption in a network. Most of the energy is consumed during idle period and during transmission of data from one node to another i.e. routing. An efficient media access control (MAC) and routing protocol should be designed to save energy. While MAC protocol targets at reduction of energy in scanning and accessing the channel, routing protocol helps to reduce the energy requirement for end-to-end transmission. In WSN, there are number of routing protocols that have been proposed for different network criteria. Based on the network topology WSN protocols have been categorized as - flat network protocols and hierarchical protocols as shown in Figure 1. Protocols that fall under hierarchical class select one head amongst all and form a hierarchy (1). This hierarchy may be a cluster, a chain or a grid. Cluster head or a leader collects the information from all the other nodes in its region and sends it to the sink node or gateway node. Some examples are low energy adaptive clustering hierarchy (LEACH), power efficient gathering in sensor information systems (PEGASIS), virtual grid architecture (VGA), etc. The work presented in this paper considers flat protocols and thus we are not including descriptions of hierarchical protocols and will only be

Stability of black holes and solitons in Anti-de Sitter space-time

The stability of black holes and solitons in d-dimensional Anti-de Sitter (AdSd) space-time against scalar field condensation is discussed. The resulting solutions are “hairy” black holes and solitons, respectively. In particular, we will discuss static black hole solutions with hyperbolic, flat and spherical horizon topology and emphasize that two different type of instabilities exist depending on whether the scalar field is charged or uncharged, respectively. We will also discuss the influence of Gauss-Bonnet curvature terms. The results have applications within the AdS/CFT correspondence and describe e.g. holographic insulator/conductor/superconductor phase transitions.

Investigation of ISFET device parameters to optimize for impedimetric sensing of cellular adhesion

In this study we describe how we were able to use an equivalent‐electrical circuit for the cell–transistor contact to optimize a future chip design for better performance in cell–substrate adhesion experiments. From our simulations we found that higher capacitances of the source and drain contact lines are able to shift the cell adhesion effects to more moderate frequencies in the range of up to 200 kHz. For larger cell–substrate adhesion effects, the transconductance value of the FET devices needs to be increased as well. We used these simulation results to design a new generation of FET devices. These devices were successfully fabricated in our clean room facilities. In electronic cell–substrate adhesion experiments this new generation of devices showed superior performance compared to an earlier version. Most importantly, our new devices have now an almost flat topology enabling future single‐cell migration experiments. HEK293 cells adhered with a flat morphology to a newly fabricated FET sensor device (scale bar 50 µm)

High-speed Image compression based on the Combination of Modified Self organizing Maps and Back-Propagation Neural Networks

This paper presents a high speed image compression based on the combination of modified self- organizing maps and Back-Propagation neural networks. In the self-organizing model number of the neurons are in a flat topology. These neurons in interaction formed self- organizing neural network. The task this neural network is estimated a distribute function. Finally network disperses cells in the input space until estimated probability density of inputs. Distribute of neurons in input space probability is an information compression. So in the proposed method first by Modified Self- Organizing Feature Maps (MSOFM) we achieved distributed function of the input image by a weight vector then in the next stage these information compressed are applied to back-propagation algorithm until image again compressed. The performance of the proposed method has been evaluated using some standard images. The results demonstrate that the proposed method has High- speed over other existing works.

CluLoR: Clustered Localized Routing for FiWi Networks

The integration of passive optical networks (PONs) and wireless mesh networks (WMNs) into Fiber- Wireless (FiWi) networks can lead to effective access networks. Existing routing schemes for FiWi networks consider mainly hop-count and delay metrics over a flat WMN node topology and do not specifically prioritize the local network structure, i.e., the local wireless-optical network gateway. In this study, we explore a simple, yet effective routing algorithm for FiWi networks with a WMN organized into zones operating on different radio channels. We examine the effects of routing the traffic into and out of a zone through one or more cluster heads. We investigate the effectiveness of localized routing that prioritizes transmissions over the local gateway to the optical network and avoids wireless packet transmissions in zones that do not contain the packet source or destination. We find that this combination of clustered and localized routing (CluLoR) gives good throughput-delay performance compared to routing schemes that transmit packets wirelessly through “transit zones” (that do not contain the packet source or destination) following minimum hop-count routing.

Comparisons of adaptive TIN modelling filtering method and threshold segmentation filtering method of LiDAR point cloud

Point cloud filtering is the basic and key step in LiDAR data processing. Adaptive Triangle Irregular Network Modelling (ATINM) algorithm and Threshold Segmentation on Elevation Statistics (TSES) algorithm are among the mature algorithms. However, few researches concentrate on the parameter selections of ATINM and the iteration condition of TSES, which can greatly affect the filtering results. First the paper presents these two key problems under two different terrain environments. For a flat area, small height parameter and angle parameter perform well and for areas with complex feature changes, large height parameter and angle parameter perform well. One-time segmentation is enough for flat areas, and repeated segmentations are essential for complex areas. Then the paper makes comparisons and analyses of the results by these two methods. ATINM has a larger I error in both two data sets as it sometimes removes excessive points. TSES has a larger II error in both two data sets as it ignores topological relations between points. ATINM performs well even with a large region and a dramatic topology while TSES is more suitable for small region with flat topology. Different parameters and iterations can cause relative large filtering differences.

Two-Minute Assembly of Pristine Large-Area Graphene Based Films

We report a remarkably rapid method for assembling pristine graphene platelets into a large area transparent film at a liquid surface. Some 2-3 layer pristine graphene platelets temporally solvated with N-methyl-2-pyrrolidone (NMP) are assembled at the surface of a dilute aqueous suspension using an evaporation-driven Rayleigh-Taylor instability and then are driven together by Marangoni forces. The platelets are fixed through physical binding of their edges. Typically, 8-cm-diameter circular graphene films are generated within two minutes. Once formed, the films can be transferred onto various substrates with flat or textured topologies. This interfacial assembly protocol is generally applicable to other nanomaterials, including 0D fullerene and 1D carbon nanotubes, which commonly suffer from limited solution compatibility.

The design of dynamic access control for hierarchical sensor networks with key-lock-pair mechanism

In recent years, Wireless Sensor Networks (WSNs) have been applied extensively. Since low-power and mobile sensor networks with flat topology demand high efficiency, good scalability and security, a new structural dynamic access control scheme is needed. In this paper, we explore the task of providing access privileges in hierarchical sensor networks with directed graph and partially ordered set tools. In some traditional schemes, there will be a huge overhead of calculations on the large-scale network when the new class of sensors joins or an old one leaves. We present a novel, efficient and dynamic access control scheme that makes it unnecessary to change all the keys for the Central Authority (CA) and requires only a small amount of computation for each sensor. Specifically, we make use of a key-lock-pair mechanism based on Newton's interpolating polynomial for key management. Extensive analysis showed that our proposed scheme is secure under security models and efficient for both the CA and users.

Operator Calculus of Differential Chains and Differential Forms

We describe a subspace of de Rham currents called “differential chains,” given as an inductive limit of Banach spaces. We make use of the viewpoint introduced by Mackey and developed by Whitney in which currents are treated as chains instead of cochains. This approach gives our space and its topology an intrinsic geometric definition. Moreover, our sequence of norms gives fine control over convergence and compactness, providing viable alternatives to the weak and flat topologies on currents. Boundary is a continuous operator, as are operators that dualize to Hodge star, Lie derivative, pullback and interior product. Partitions of unity exist in this setting, and we are also able to define a Cartesian wedge product. We conclude with an application of this framework, generalizing the Reynolds’ Transport Theorem to nonsmooth domains.

A Survey of Cluster-based Routing Schemes for Wireless Sensor Networks

In recent times, wireless sensor networks (WSNs) have become progressively more attractive and have found their way into a wide variety of applications and systems because of their low cost, self-organizing behavior, and sensing ability in harsh environments. A WSN is a collection of nodes organized into a network. Routing is a vital technology in WSNs and can be roughly divided into two categories: flat routing and hierarchical routing. In a flat routing topology, all nodes have identical functionality and carry out the same task in the network. Nodes in a hierarchical topology do different tasks in WSNs and are usually arranged into clusters. In this paper, a survey on cluster-based routing schemes for WSNs has been done and comparisons made on the basis of performance factors such as latency, scalability, and energy awareness. Strengths and limitations of each scheme are presented, and open issues that must be addressed in the design of cluster-based routing algorithms are discussed.

The topology and size of the universe from CMB temperature and polarization data

We analyze seven year and nine year WMAP temperature maps for signatures of three finite flat topologies ℳ0 = \U0001d54b3, ℳ1 = \U0001d54b2 × ℝ1, and ℳ2 = S1 × ℝ2. We use Monte-Carlo simulations with the Feldman-Cousins method to obtain confidence intervals for the size of the topologies considered. We analyze the V, W, and Q frequency bands along with the ILC map and find no significant difference in the results. The 95.5% confidence level lower bound on the size of the topology is 1.5L0 for ℳ0, 1.4L0 for ℳ1, and 1.1L0 for ℳ2, where L0 is the radius of the last scattering surface. Our results agree very well with the recently released results from the Planck temperature data. We show that the likelihood function is not Gaussian in the size, and therefore simulations are important for obtaining accurate bounds on the size. We then introduce the formalism for including polarization data in the analysis. The improvement that we find from WMAP polarization maps is small because of the high level of instrumental noise, but our forecast for Planck maps shows a much better improvement on the lower bound for L. For the ℳ0 topology we expect an improvement on the lower bound of L from 1.7L0 to 1.9L0 at 95.5% confidence level. Using both polarization and temperature data is important because it tests the hypothesis that deviations in the TT spectrum at small l originate in the primordial perturbation spectrum.

Piezoelectric nanogenerator with a nanoforest structure

Piezoelectric nanogenerators have been intensively developed in terms of their materials and applications; however, only modest structural progress has been made due to limitations in the growth mechanisms of nano-materials. In this work, a piezoelectric nanogenerator based on a nanoforest structure is introduced. Through a metal-assisted chemical etching (mac-etch) process, densely packed vertical nanowires and nanovoids are fabricated. The nanoforest structure serves as a bottom electrode, which increases the interfacial area with a subsequently deposited piezoelectric material, in this case barium titanate (BaTiO3). In the proposed fabrication method, more various piezoelectric materials can be used for a piezoelectric device compared to previously reported methods because the process relies not on the growth mechanism but on the deposition technique. The proposed nanoforest structured nanogenerator produces a 4.2 times enhanced power density compared to the control generator, which uses the same material but has a flat topology. The strong relationship between the enhancement ratio and the nanoforest height is found. Both the experiment and the simulation data present a consistent trend of a gradual increase with a short height and saturation at a tall height.

Edge-functionalization of graphene by polyglycerol; A way to change its flat topology

This work presents a procedure for functionalization of graphene sheets from edges by polyglycerol. Hyperbranched polyglycerol with a bi-dentate aromatic segment in its focal point was synthesized and used to sandwich graphene sheets from the cut-edges. Due to the hydrophobicity of the flat surface of the edge-functionalized graphenes and hydrophilicity of their edges, they changed their conformation from the extended- to the closed-state and formed nanocapsules in aqueous solutions. Spectroscopy and microscopy evaluations showed that the average size for nanocapsules is 300 nm. They were able to encapsulate hydrophobic molecules such as doxorubicin in aqueous solutions with a high loading capacity. Aqueous solutions of nanocapsules and those with encapsulated doxorubicin were stable at room temperature for several weeks. Due to their unique properties including suitable size and shape, stability in aqueous solutions, and high loading capacity for hydrophobic anticancer drugs, graphene-based nanocapsules are promising systems in order to use in nanomedicine, especially for future cancer therapy.

Importance of C–H···O Intramolecular Hydrogen Bonding Across a Nonproteinogenic γ-Aminobenzoic Acid Residue: Stabilization of a Flat β-Strand-like Template

This paper describes the conformational characteristics of a nonproteinogenic γ-aminobenzoic acid (γ-Abz), investigated experimentally as well as theoretically. The single crystal X-ray diffraction analysis of the model system Boc-γ-Abz-NHMe (1) revealed the existence of an unusual β-strand-like molecular structure. The two weak unconventional C–H···O intramolecular hydrogen-bonds, i.e., main-chain to main-chain: Cβi+1–H···O═Ci+1 and main-chain to side-chain Cδi+1–H···O═Ci interactions, evidently stabilize the flat molecular topology. The favorable antiparallel β-strand mimics are held together by a network of cross-strand N–H···O intermolecular hydrogen bonds. Interestingly, the noncovalent β-sheet-like duplexes facilitate the fabrication of offset face-to-face aromatic–aromatic interactions, whereas the dimers of dimers are aligned edge-to-edge. The two-dimensional 1H NMR ROESY experiment ascertained the extraordinary stability of the rigid β-strand template and molecular self-assembly in a nonpolar env...

Universality and symmetry breaking in conformally reduced quantum gravity

The scaling properties of quantum gravity are discussed by employing a class of proper-time regulators in the functional flow equation for the conformal factor within the formalism of the background field method. Renormalization group trajectories obtained by projecting the flow on a flat topology are more stable than those obtained from a projection on a spherical topology. In the latter case the ultraviolet flow can be characterized by a Hopf bifurcation with an ultraviolet attractive limiting cycle. Although the possibility of determining the infrared flow for an extended theory space can be severely hampered due to the conformal factor instability, we present a robust numerical approach to study the flow structure around the non-gaussian fixed point as an inverse-problem strategy. In particular it is shown the possibility of having a spontaneous breaking of the diffeomorphism invariance can be realized with non-local functionals of the volume operator.

Uniqueness of the Fock quantization of scalar fields in spatially flat cosmological spacetimes

We study the Fock quantization of scalar fields in (generically) time dependent scenarios, focusing on the case in which the field propagation occurs in –either a background or effective– spacetime with spatial sections of flat compact topology. The discussion finds important applications in cosmology, like e.g. in the description of test Klein-Gordon fields and scalar perturbations in Friedmann-Robertson-Walker spacetime in the observationally favored flat case. Two types of ambiguities in the quantization are analyzed. First, the infinite ambiguity existing in the choice of a Fock representation for the canonical commutation relations, understandable as the freedom in the choice of inequivalent vacua for a given field. Besides, in cosmological situations, it is customary to scale the fields by time dependent functions, which absorb part of the evolution arising from the spacetime, which is treated classically. This leads to an additional ambiguity, this time in the choice of a canonical pair of field variables. We show that both types of ambiguities are removed by the requirements of (a) invariance of the vacuum under the symmetries of the three-torus, and (b) unitary implementation of the dynamics in the quantum theory. In this way, one arrives at a unique class of unitarily equivalent Fock quantizations for the system. This result provides considerable robustness to the quantum predictions and renders meaningful the confrontation with observation.

Scaling Low-Latency Optical Packet Switches to a Thousand Ports

Optical packet switches that scale to thousands of input/output ports might find their application in next-generation datacenters (DCs). They will allow interconnecting the servers of a DC in a flat topology, providing higher bandwidth and lower latency in comparison with currently applied electronic switches. Using a simple analytic model that allows computing end-to-end latency and throughput, we show that optical interconnects that employ a centralized (electronic) controller cannot scale to thousands of ports while providing end-to-end latencies below 1 μs and high throughput. We therefore investigate architectures with highly distributed control. We present astrictly non-blocking wavelength division multiplexing architecture with contention resolution based on wavelength conversion. We study the packet loss probability of such architecture for different implementations of the contention resolution functionality. Furthermore, we show that the proposed architecture, applied in a short link with flow control, provides submicrosecond end-to-end latencies and allows high load operation, while scaling over a thousand ports.