Virtual Coordinates Research Articles

Zero-Axis Virtual Synchronous Coordinate Based Current Control Strategy for Grid-Connected Inverter

Unbalanced power has a great influence on the safe and stable operation of the distribution network system. The static power compensator, which is essentially a grid-connected inverter, is an effective solution to the three-phase power imbalance problem. In order to solve the tracking error problem of zero-sequence AC current signals, a novel control strategy based on zero-axis virtual synchronous coordinates is proposed in this paper. By configuring the operation of filter transmission matrices, a specific orthogonal signal is obtained for zero-axis reconstruction. In addition, a controller design scheme based on this method is proposed. Compared with the traditional zero-axis direct control, this control strategy is equivalent to adding a frequency tuning module by the orthogonal signal generator. The control gain of an open loop system can be equivalently promoted through linear transformation. With its clear mathematical meaning, zero- sequence current control can be controlled with only a first-order linear controller. Through reasonable parameter design, zero steady-state error, fast response and strong stability can be achieved. Finally, the performance of the proposed control strategy is verified by both simulations and experiments.

RRDVCR: Real-Time Reliable Data Delivery Based on Virtual Coordinating Routing for Wireless Sensor Networks

Real-time industrial application requires a routing protocol that guarantees data delivery with reliable, efficient and low end-to-end delay. Existing Two-Hop Velocity based Routing (THVR) protocol relates two-hop velocity to end-to-end delay to select the next forwarding node, that has the overhead of exchanging control packets and depleting the available energy in nodes. We propose a Real-Time Reliable Data delivery based on Virtual Coordinates Routing (RRDVCR) algorithm, based on the number of hops to the destination rather than geographic distance. Selection of forwarding node is based on packet progress offered by two-hops, link quality and available energy at the forwarding nodes. All these metric are co-related by dynamic co-relation factor. The proposed protocol uses a selective acknowledgment scheme that results in lower overhead and energy consumption. Simulation results show that there is about 22 and 9.5% decrease in energy consumption compared to SPEED respectively, 16 and 38% increase in packet delivery compared to THVR and SPEED respectively and overhead is reduced by 50%.

A circular feature-based pose measurement method for metal part grasping

The grasping of circular metal parts such as bearings and flanges is a common task in industry. Limited by low texture and repeated features, the point-feature-based method is not applicable in pose measurement of these parts. In this paper, we propose a novel pose measurement method for grasping circular metal parts. This method is based on cone degradation and involves a monocular camera. To achieve higher measurement accuracy, a position-based visual servoing method is presented to continuously control an eye-in-hand, six-degrees-of-freedom robot arm to grasp the part. The uncertainty of the part’s coordinate frame during the control process is solved by defining a fixed virtual coordinate frame. Experimental results are provided to illustrate the effectiveness of the proposed method and the factors that affect measurement accuracy are analyzed.

Multi-dimensional virtual system introduced to enhance canonical sampling.

When an important process of a molecular system occurs via a combination of two or more rare events, which occur almost independently to one another, computational sampling for the important process is difficult. Here, to sample such a process effectively, we developed a new method, named the "multi-dimensional Virtual-system coupled Monte Carlo (multi-dimensional-VcMC)" method, where the system interacts with a virtual system expressed by two or more virtual coordinates. Each virtual coordinate controls sampling along a reaction coordinate. By setting multiple reaction coordinates to be related to the corresponding rare events, sampling of the important process can be enhanced. An advantage of multi-dimensional-VcMC is its simplicity: Namely, the conformation moves widely in the multi-dimensional reaction coordinate space without knowledge of canonical distribution functions of the system. To examine the effectiveness of the algorithm, we introduced a toy model where two molecules (receptor and its ligand) bind and unbind to each other. The receptor has a deep binding pocket, to which the ligand enters for binding. Furthermore, a gate is set at the entrance of the pocket, and the gate is usually closed. Thus, the molecular binding takes place via the two events: ligand approach to the pocket and gate opening. In two-dimensional (2D)-VcMC, the two molecules exhibited repeated binding and unbinding, and an equilibrated distribution was obtained as expected. A conventional canonical simulation, which was 200 times longer than 2D-VcMC, failed in sampling the binding/unbinding effectively. The current method is applicable to various biological systems.

Approximating nonlinear forces with phase-space decoupling

Beam tracking software for accelerators typically falls into two categories: fast envelope simulations limited to linear beam optics, and slower multiparticle simulations that can model nonlinear effects. To find a middle ground between these approaches, we introduce virtual coordinates in position and momentum which have a cross-dependency (i.e. p* = f (x0) where x0 is an initial position and p* is a virtual projection of momentum onto the position axis). This technique approximates multiparticle simulations with a significant reduction in calculation cost.

Ultrasound-Guided Biopsies of Bone Lesions Without Cortical Disruption Using Fusion Imaging and Needle Tracking: Proof of Concept.

To assess the technical feasibility and safety of combined fusion imaging and needle tracking under ultrasound guidance to target bone lesions without cortical disruption. Between January 2016 and March 2016, seven patients underwent US-guided biopsy of bone lesions without cortical disruption. Targeted bone lesions were measuring more than 1.5cm with a thin cortex, a trans-osseous pathway not exceeding 2cm and without any adjacent vulnerable structures. First three procedures were performed in the CT suite to aid the needle tracking where necessary (group 1), the remaining four procedures were performed in the US suite (group 2). In group 1, deviation from the real position of the bone trocar (estimated on CT) was compared to the virtual position (estimated on the fusion CT-US images). In both group, procedure data and histopathological results were collected, and compared to the suspected diagnosis and follow-up. Mean procedure duration was 44min. Total number of synchronisation points for combined fusion imaging were 3.3 on average. In group 1, mean deviation between the virtual and real CT coordinates was 5.3mm on average. All biopsies yielded adequate quality analysable bone sample. Histopathological analysis revealed malignancy in three cases, non-specific inflammation in two cases, and normal bone in two cases. The four benign results were confirmed as true negative results. There were no immediate or post-procedural complications. The use of combined fusion imaging and needle tracking ultrasound guidance to target bone lesions without cortical disruption seems technically feasible, provided the patient and lesion selection is appropriate.

Virtual coordinate system using dominating set for GPS-free adhoc networks

Reported work on virtual coordinate assignment (VCA) schemes are iterative-based techniques which rely upon geometric projection (i.e., projecting on circle) or embedding of network topology to low-dimensional Euclidean space (like graph embedding, multidimensional scaling). The performance of existing VCA techniques is constrained by topological situations such as low density or having voids/holes, where greedy forwarding suffers due to local minima when no neighbor is found closer to the destination or low-quality routes comprised of long distance hops. Another drawback of existing VCA techniques is the requirement of thousand iterations for usable coordinate convergence. In order to overcome these drawbacks, we propose a novel virtual coordinate construction technique using graph-theoretic dominating sets. Dominating set (DS) of G is a subset of vertices such that each vertex in G is either in DS or has a neighbor in DS. We found that our virtual coordinate assignment using dominating set algorithm has an approximation ratio \(((4.8+\ln 5)opt +1.2)\), where opt is the minimum size dominating set which has the same approximation ratio as minimum dominating set problem. Our algorithm has time complexity \(\mathcal {O}(n)\) times and \(\mathcal {O}(D)\) rounds and message complexity is \(\mathcal {O}(n\log n)\), where D is the radius and n is the number of nodes in networks.

Packet routing in 3D nanonetworks: A lightweight, linear-path scheme

Packet routing in nanonetworks requires novel approaches, which can cope with the extreme limitations posed by the nano-scale. Highly lossy wireless channels, extremely limited hardware capabilities and non-unique node identifiers are among the restrictions. The present work offers an addressing and routing solution for static 3D nanonetworks that find applications in material monitoring and programmatic property tuning. The addressing process relies on virtual coordinates from multiple, alternative anchor point sets that act as viewports. Each viewport offers different address granularity within the network space, and its selection is optimized by a packet sending node using a novel heuristic. Regarding routing, each node can deduce whether it is located on the linear segment connecting the sender to the recipient node. This deduction is made using integer calculations, node-local information and in a stateless manner, minimizing the computational and storage overhead of the proposed scheme. Most importantly, the nodes can regulate the width of the linear path, thus trading energy efficiency (redundant transmissions) for increased path diversity. This trait can enable future adaptive routing schemes. Extensive evaluation via simulations highlights the advantages of the novel scheme over related approaches.

A reversible watermarking for authenticating 2D CAD engineering graphics based on iterative embedding and virtual coordinates

Aim to authenticate the integrity of 2D CAD engineering graphics, a reversible watermarking method based on iterative embedding and virtual coordinates is proposed. For each vertex in 2D CAD engineering graphics, two neighboring virtual coordinates are generated to form an embedding data unit, which is good for the improvement of the correlation of them. Meanwhile, iterative embedding policy is implemented to enhance the capacity. Experimental results and analysis show that it is strictly reversible, and the capacity is positive proportion to the embedding times. Meanwhile, the distortion can be well controlled in a small range, and it is robust against translation and scaling. It has potential application in the integrity protection of 2D CAD engineering graphics with low correlation and high data precision requirements.

Effect of touch coordinate display as a form of augmented, concurrent visual feedback on the accuracy of single-handed typing via smartphone virtual keyboards

This study assessed the effect of an easily perceived real-time visual feedback method on touchscreen typing accuracy. Thirty subjects were asked to hold a smartphone with a capacitive touchscreen in one hand and enter a text using the thumb of the same hand via a custom designed virtual keyboard. There were two types of text entry sessions: with or without visual feedback. The visual feedback consisted of a full-screen crosshair, representing the accurate coordinate of touch in real time. In each session, touch-down time on the virtual keyboard and touch coordinates were recorded for every touch action. Two types of typing errors were defined: 1) centering error (CE), which was calculated as the mm distance between the coordinate of the touch and the center of the key, and 2) incorrect entry (IE), which was the number of missed keys. Student t-tests and Wilcoxon tests were used for mean and mean-rank comparisons of CE and IE, respectively. The results showed that visual feedback decreased CE (mean $\pm $ SD) significantly from 1.34 $\pm $ 0.38 mm to 0.85 $\pm $ 0.24 mm (P < 0.0005), and decreased IE (median and range, # of incorrect entries) significantly from 5.50 and 32.00 to 1.00 and 7.00 (P < 0.005). In conclusion, the accurate, easily perceived, and 2D real-time feedback decreases touch-typing error rates markedly and therefore can be of practical importance for increasing the productivity of smartphone users.

Billiardo: A Novel Virtual Coordinates Routing Protocol Based on Multiple Sinks for Wireless Sensor Network

Geographic routing protocols based on virtual coordinate system are used in wireless sensor networks without GPS assistance or any localization technique. They rely completely on virtual coordinates derived from relative distances or hop counting to a set of anchor nodes in the sensor network. Despite the fact that the recently proposed virtual coordinate protocols have gained advantages as they are GPS free, they suffer from crucial inevitable problems. The reason for such a case lies, in fact, on these protocols which depend widely on the characteristic of "fixed reference points" (called anchors). The worst of these engendered problems is that of the unique reference framework where it is quite difficult to assign the existing nodes a unique identity. This lack of uniqueness cannot guarantee delivery and fails most of the time to forward the packet successfully. Moreover, a question rises here on how to select the anchors in order to use them in the field of work. Therefore; this paper comes to find out another way to solve the above-mentioned problems. The proposed routing protocol "Billiardo" is of greedy type based on virtual coordinates system. Its key idea is to use more than one sink, and all these sinks are used as anchors to allow each sensor to get its virtual coordinates. This protocol depends on hops' count to find the shortest path towards just one selected sink among the other sinks without any complicated formula. Through tested simulation Billiardo proves to be far better and more efficient than the others to avoid all the thwarting problems in forwarding the packet.

Compact Conformal Map for Greedy Routing in Wireless Mobile Sensor Networks

Motivated by mobile sensor networks as in participatory sensing applications, we are interested in developing a practical, lightweight solution for routing in a mobile network. While greedy routing is robust to mobility, it may get stuck in a local minimum, which then requires non-trivial recovery methods. We find an embedding of the network such that greedy routing using the virtual coordinates guarantees delivery, thus eliminating the necessity of any recovery methods. Our contribution is to replace the in-network computation of the embedding by a preprocessing of the domain before network deployment and encode the map of network domain to virtual coordinate space by using a small number of parameters which can be preloaded to all sensor nodes. As a result, the map is only dependent on the network domain and is independent of the network connectivity. Each node can directly compute or update its virtual coordinates by applying the locally stored map on its geographical coordinates. This represents the first practical solution for using virtual coordinates for greedy routing in a sensor network and could be easily extended to the case of a mobile network. The paper describes algorithmic innovations as well as implementations on a real testbed.

SECURING THE LOCATIONS OF SENSORS USING VIRTUAL CO-ORDINATES

A network topology is the design of connections which includes nodes and links. When the nodes change their positions, the topology either increases or decreases and hence methods for obtaining the maps that preserves the topology from the virtual coordinates is presented. Firstly Received Signal Strength(RSS) technique which relies on frequency parameter for distance calculation between the nodes is presented. Next another approach known as Location Aware Routing Technique (LART) which relies on latitudinal and longitudinal values for the distance estimation is presented. Lastly the proposed approach of DALD (Distance based Attack Localization and Detection) which is a counter measure to restore/ preserve the network region and a methodology to overcome the disadvantages of the existing frequency based approaches is implemented. The proposed T&S mapping (Track and Sector) based user check maintains a record of the communicating nodes which tracks the sector in which the node lays. It improves the communication by avoiding hidden node problem which distorts the mapping co-ordinates and other malicious access in the network path. Besides, the AOD (Angle Of Deviation) improves the accuracy of detection and localization based on angular presence verification on each and every transmission, allowing secure nodes to communicate, minimizing the anonymous distortions in the network mapping.

A New Multi-Dimensional Hyperbolic Structure for Cloud Service Indexing

Nowadays, the structure of cloud uses the data processing of simple key value, which cannot adapted in search of closeness effectively because of the lack of structures of effective indexes, and with the increase of dimension, the structures of indexes similar to the tree existing could lead to the problem of the curse of dimension”. In this paper, we define a new cloud computing architecture in such global index, storage nodes is based on a Distributed Hash Table (DHT). In order to reduce the cost of calculation, store different services on the hyperbolic tree by using virtual coordinates thus that greedy routing based on hyperbolic space properties in order to improve query storage and retrieving performance effectively. Next, we perform and evaluate our cloud computing indexing structure based on a hyperbolic tree using virtual coordinates taken in the hyperbolic plane. We show through our experimental results that we compare with others clouds systems to show our solution ensures consistence and scalability for Cloud platform.

Efficient Geometric Routing in Large-Scale Complex Networks with Low-Cost Node Design

The growth of the size of the routing tables limits the scalability of the conventional IP routing. As scalable routing schemes for large-scale networks are highly demanded, this paper proposes and evaluates an efficient geometric routing scheme and related low-cost node design applicable to large-scale networks. The approach guarantees that greedy forwarding on derived coordinates will result in successful packet delivery to every destination in the network by relying on coordinates deduced from a spanning tree of the network. The efficiency of the proposed scheme is measured in terms of routing quality (stretch) and size of the coordinates. The cost of the proposed router is quantified in terms of area complexity of the hardware design and all the evaluations involve comparison with a state-of-the-art approach with virtual coordinates in the hyperbolic plane. Extensive simulations assess the proposal in large topologies consisting of up to 100K nodes. Experiments show that the scheme has stretch properties comparable to geometric routing in the hyperbolic plane, while enabling a more efficient hardware design, and scaling considerably better in terms of storage requirements for coordinate representation. These attractive properties make the scheme promising for routing in large networks.

Geographic routing on Virtual Raw Anchor Coordinate systems

In this manuscript, we present geographic routing algorithms with delivery guarantees on a virtual coordinate system, namely Virtual Raw Anchor Coordinates (VRAC). Proposed algorithms can be seen as a variant of GFG (Greedy Face Greedy of Bose et al.) algorithm and based on combinatorial and geometric properties derived in the Virtual Raw Anchor Coordinate system. We utilize a local planarization algorithm of a geometric graph, which is based on the Schnyder's characterization of planar graphs. The new approach is combinatorial in the sense that the nodes are ordered with respect to three distinct order relations satisfying suitable properties. The coordinate system that motivated the development of this routing algorithm is VRAC, which localizes the nodes with the raw distances from three fixed anchors. Since the positions of the anchors are not known, the VRAC coordinate system does not correspond to the Euclidean location of nodes, yet leaving sufficient information to define necessary combinatorial and geometric constructs for routing with guaranteed delivery. In particular, the routing algorithm avoids the references to geographical arguments and makes use only of the order relations on the nodes. We expect that our approach will foster further research on building efficient order relations, that will prove to be useful in practical implementation of geographic routing algorithms. In particular, we expect that further work will prove that the geographic routing based on a raw anchor based positioning system is more robust in the presence of distance measurement errors.

On k-greedy routing algorithms

Let G=(V,E) and G′=(V′,E′) be two graphs. A k-inverse-adjacency-preserving mapping ρ from G to G′ is a one-to-many and onto mapping from V to V′ satisfying the following: (1) Each vertex v∈V in G is mapped to a non-empty subset ρ(v)⊂V′ in G′, the cardinality of ρ(v) is at most k; (2) if u≠v, then ρ(u)∩ρ(v)=∅; and (3) for any u′∈ρ(u) and v′∈ρ(v), if (u′,v′)∈E′, then (u,v)∈E. A vertex u′ in ρ(u) is called a virtual location for u.Let ρ be a k-inverse-adjacency-preserving-mapping (k-IAPM for short) from G to G′. Let δ be a greedy drawing of G′ into a metric space M. Consider a message from u to be delivered to v in G. Using the k-IAPM ρ from G to G′, intuitively, one can treat the message to be routed as if it were from one virtual location u′ for u to one virtual location v′ for v, except that all the virtual locations of a vertex u were identified with each other (which can be thought as instantaneously synchronized mirror sites for a particular website, for example). Then a routing path P′ can be computed from u′ to v′ while identifying all virtual locations for any vertex in G. Since ρ inversely preserves adjacency from G′ to G, such a routing path P′ corresponds to exactly one routing path P in G, which connects u to v.In this paper, we formalize the above intuition into a concept which we call k-greedy routing algorithm for a graph G with n vertices, where k refers to the maximum number of virtual locations any vertex of G can have. Using this concept, the result presented in [18] can be rephrased as a 3-greedy routing algorithm for 3-connected plane graphs, where the virtual coordinates used are from 1 to 2n−2. In this paper, we present a 2-greedy routing algorithm for 3-connected plane graphs, where each vertex uses at least one but at most two virtual locations numbered from 1 to 2n−1. For the special case of plane triangulations (in a plane triangulation, every face is a triangle, including the exterior face), the numbers used are further reduced to from 1 to ⌊5n+13⌋. Hence, there are at least ⌈n−13⌉ vertices that use only one virtual location.

Dynamic greedy routing in overlay networks using virtual coordinates from the hyperbolic plane

AbstractGreedy routing algorithms based on virtual coordinates have attracted considerable interest in recent years. Those based on coordinates taken from the hyperbolic plane have interesting theoretical scalability properties. However, their scalability and reliability are yet to be ensured when applied to large‐scale dynamic networks. In this paper, we propose a scalable and reliable solution for creating and managing dynamic overlay networks where nodes have hyperbolic coordinates. In this context, our solution provides a greedy routing algorithm based on the hyperbolic distance. To cope with network dynamics, we have defined two methods for avoiding temporary local minima and one method for maintaining the greedy embedding over time. Through analysis, we evaluate the complexity costs of our solution. Through simulations, we assess the scalability of our solution on static networks and its reliability on dynamic networks. Results show that using our solution based on hyperbolic geometry provides scalability and reliability to both addressing and routing tasks in dynamic overlay networks. Copyright © 2015 John Wiley &amp; Sons, Ltd.

An effective phase shift diffusion equation method for analysis of PFG normal and fractional diffusions

Pulsed field gradient (PFG) diffusion measurement has a lot of applications in NMR and MRI. Its analysis relies on the ability to obtain the signal attenuation expressions, which can be obtained by averaging over the accumulating phase shift distribution (APSD). However, current theoretical models are not robust or require approximations to get the APSD. Here, a new formalism, an effective phase shift diffusion (EPSD) equation method is presented to calculate the APSD directly. This is based on the idea that the gradient pulse effect on the change of the APSD can be viewed as a diffusion process in the virtual phase space (VPS). The EPSD has a diffusion coefficient, Kβ(t)D radβ/sα, where α is time derivative order and β is a space derivative order, respectively. The EPSD equations of VPS are built based on the diffusion equations of real space by replacing the diffusion coefficients and the coordinate system (from real space coordinate to virtual phase coordinate). Two different models, the fractal derivative model and the fractional derivative model from the literature were used to build the EPSD fractional diffusion equations. The APSD obtained from solving these EPSD equations were used to calculate the PFG signal attenuation. From the fractal derivative model the attenuation is exp(−γβgβδβDf1tα), a stretched exponential function (SEF) attenuation, while from the fractional derivative model the attenuation is Eα,1(−γβgβδβDf2tα), a Mittag–Leffler function (MLF) attenuation. The MLF attenuation can be reduced to SEF attenuation when α=1, and can be approximated as a SEF attenuation when the attenuation is small. Additionally, the effect of finite gradient pulse widths (FGPW) is calculated. From the fractal derivative model, the signal attenuation including FGPW effect is exp-Df1∫0τKβ(t)dtα. The results obtained in this study are in good agreement with the results in literature. Several expressions that describe signal attenuation have not been reported and that can be of great importance for the PFG experiments. This EPSD equation method provides a new, simple path to calculate signal attenuation of PFG NMR experiments.

Transformation Media in Acoustics with Constant Bulk Modulus or Constant Density Tensor

AbstractThis work is to present a formulation of cloaking or concentrating device in acoustics in which the transformed material could be either having uniform bulk modulus or having homogeneous density tensor. The transformed material parameters, depending on the mapping of physical and virtual coordinates, are often position-varying and anisotropic. This often adds substantial complexity in practical implementation. Here we present a theoretical algorithm that allows us to design a transformation field that could have either uniform bulk modulus or constant density tensor. For cloaking devices with constant bulk modulus, analytical and numerical results are presented for circular as well as for non-circular cloaking devices. Specifically, elliptical and twin-cloak devices are exemplified. To achieve the effect of constant density tensor, we consider only circular geometry. Devices with cloaking or concentrating effects can be exactly formulated. We note, however, that it seems unlikely at this moment to have a transformation device that has constant bulk modulus and constant density tensor at the same time. Nevertheless, we remark the present results are of still sufficient merit in that the uniform material parameters, in either set of material parameters, indeed greatly simplify the practice in real implementations.