Space Shift Research Articles

A unified Hamiltonian solution to Maxwell–Schrödinger equations for modeling electromagnetic field–particle interaction

A novel unified Hamiltonian approach is proposed to solve Maxwell–Schrödinger equation for modeling the interaction between classical electromagnetic (EM) fields and particles. Based on the Hamiltonian of electromagnetics and quantum mechanics, a unified Maxwell–Schrödinger system is derived by the variational principle. The coupled system is well-posed and symplectic, which ensures energy conserving property during the time evolution. However, due to the disparity of wavelengths of EM waves and that of electron waves, a numerical implementation of the finite-difference time-domain (FDTD) method to the multiscale coupled system is extremely challenging. To overcome this difficulty, a reduced eigenmode expansion technique is first applied to represent the wave function of the particle. Then, a set of ordinary differential equations (ODEs) governing the time evolution of the slowly-varying expansion coefficients are derived to replace the original Schrödinger equation. Finally, Maxwell’s equations represented by the vector potential with a Coulomb gauge, together with the ODEs, are solved self-consistently. For numerical examples, the interaction between EM fields and a particle is investigated for both the closed, open and inhomogeneous electromagnetic systems. The proposed approach not only captures the Rabi oscillation phenomenon in the closed cavity but also captures the effects of radiative decay and shift in the open free space. After comparing with the existing theoretical approximate models, it is found that the approximate models break down in certain cases where a rigorous self-consistent approach is needed. This work is helpful for the EM simulation of emerging nanodevices or next-generation quantum electrodynamic systems.

Tensor DoA Estimation With Directional Elements

Directivity gain patterns are treated as a physical diversity for tensor array processing, replacing space diversity, in addition to time and space shift diversities. We show that the tensor formulation allows to estimate directions of arrival under the assumption of unknown gain patterns, improving the performance of the omnidirectional case. We propose a trilinear model where one dimension of the multiway data array is fully provided by gain patterns, allowing tensor approaches even when space diversity is missing due to sensor overlap.

Fast Resampling of Three-Dimensional Point Clouds via Graphs

To reduce cost in storing, processing and visualizing a large-scale point cloud, we consider a randomized resampling strategy to select a representative subset of points while preserving application-dependent features. The proposed strategy is based on graphs, which can represent underlying surfaces and lend themselves well to efficient computation. We use a general feature-extraction operator to represent application-dependent features and propose a general reconstruction error to evaluate the quality of resampling. We obtain a general form of optimal resampling distribution by minimizing the reconstruction error. The proposed optimal resampling distribution is guaranteed to be shift, rotation and scale-invariant in the 3D space. We next specify the feature-extraction operator to be a graph filter and study specific resampling strategies based on all-pass, low-pass, high-pass graph filtering and graph filter banks. We finally apply the proposed methods to three applications: large-scale visualization, accurate registration and robust shape modeling. The empirical performance validates the effectiveness and efficiency of the proposed resampling methods.

Performance Evaluation of Space Shift Keying in Free-Space Optical Communication

In this paper, we study the performance of a space shift keying (SSK) scheme in a free-space optical (FSO) communication system under indoor and outdoor conditions. For the outdoor N t χ 1 FSO-SSK system, where N t is the number of transmitters (Txs), a novel closed-form mathematical expression for the probability density function (pdf) of the difference between two weighted gamma-gamma random variables is derived. Using this pdf, a new analytical expression is obtained for the tight upper bound of the average bit error rate (ABER) of this system. We also study the analytical bit error rate (BER) of an indoor N t χ 1 FSO-SSK system experiencing a deterministic channel. For this system, optimized values of transmit power weights are obtained by minimizing the analytical BER; it is observed that the optimized nonuniform power distribution is better than the uniform power distribution. However, for the outdoor FSO-SSK system, the best error performance can be achieved by employing uniform transmit power. An asymptotic BER analysis of uniformly weighted general outdoor FSO-SSK with an arbitrary number of Tx and receiver (Rx) apertures is also performed. Furthermore, the analytical coding gain and diversity order of the considered system are found based on the derived analytical BER expression. An interesting result observed from the coding gain analysis is that the performance of the outdoor FSO-SSK system remains unaltered from a moderate to a strong atmospheric turbulence regime, which makes the considered system nearly independent of turbulence. In addition, it is found by simulation and analysis that the considered system performs more poorly under the weak turbulence regime as compared to the other (strong and moderate) turbulence regimes. Our analysis also shows that the diversity order of the outdoor FSO-SSK system is N r /2, where N r is the number of Rx apertures, irrespective of the number of optical sources and turbulence conditions. In addition, it is observed that the performance of the FSO-SSK system degrades with an increasing number of optical sources under both indoor and outdoor conditions. Therefore, a trade-off between spectral efficiency and ABER is observed.

A reliable relay selection scheme for SSK modulation in cooperative communication systems

Space shift keying (SSK) modulation is a scheme in which the indices of active transmit antennas play an essential role in carrying information bits. In SSK modulation, the communication channel acts as modulating unit. Therefore, using the conventional relay selection schemes based on channel coefficients are impossible in cooperative systems using SSK modulation. In this paper, we propose a novel relay selection scheme that is applicable in cooperative systems using SSK modulation. The proposed scheme is based on calculating and measuring the Euclidean distances between received signal and all active or inactive channel coefficients. The proposed relay selection scheme is applied for a cooperative communication system with multiple relay nodes and a direct link between source and destination. The analytical expressions are derived to calculate the average bit error rate over Rayleigh fading channels. The analytical and simulation results show that this relay selection scheme can provide a full cooperative diversity order, for SSK modulation. In addition, we show that this scheme can be used at destination as a signal selection method, to select the best received signal from different paths. The analytical results are validated using Monte Carlo simulation studies.

3D Space Shift from CityGML LoD3-Based Multiple Building Elements to a 3D Volumetric Object

In contrast with photorealistic visualizations, urban landscape applications, and building information system (BIM), 3D volumetric presentations highlight specific calculations and applications of 3D building elements for 3D city planning and 3D cadastres. Knowing the precise volumetric quantities and the 3D boundary locations of 3D building spaces is a vital index which must remain constant during data processing because the values are related to space occupation, tenure, taxes, and valuation. To meet these requirements, this paper presents a five-step algorithm for performing a 3D building space shift. This algorithm is used to convert multiple building elements into a single 3D volumetric building object while maintaining the precise volume of the 3D space and without changing the 3D locations or displacing the building boundaries. As examples, this study used input data and building elements based on City Geography Markup Language (CityGML) LoD3 models. This paper presents a method for 3D urban space and 3D property management with the goal of constructing a 3D volumetric object for an integral building using CityGML objects, by fusing the geometries of various building elements. The resulting objects possess true 3D geometry that can be represented by solid geometry and saved to a CityGML file for effective use in 3D urban planning and 3D cadastres.

Achievable Error Rate Performance Analysis of Space Shift Keying Systems with Imperfect CSI

Achievable Error Rate Performance Analysis of Space Shift Keying Systems with Imperfect CSI

Complex Hadamard Matrix-Aided Generalized Space Shift Keying Modulation

In this paper, we present a complex Hadamard matrix-aided generalized space shift keying (HSSK) modulation scheme, which introduces complex-Hadamard-based signal vectors at the transmitter to provide higher spectrum efficiency than generalized space shift keying (GSSK). It also has lower maximum-likelihood detection complexity than the multiple active spatial modulation (MA-SM) and generalized spatial modulation (GSM) systems due to the corresponding fast complex Hadamard transform at the receiver. Based on the Lee distance of our signal vectors, we provide an optimized mapping between our data bits and signal vectors. We also analyze the upper bound on the average bit error rate of our HSSK system, which agrees well with the simulation results. Finally, the performance of HSSK is compared with MA-SM, GSM, and GSSK systems through Monte Carlo simulations. It is shown that for the same transmission rate the HSSK system performs better than the GSM, MA-SM, and GSSK systems.

Performance Improvement of Space Shift Keying MIMO Systems with Orthogonal Codebook-Based Phase-Rotation Precoding

This paper considers codebook-based precoding for Space Shift Keying (SSK) modulation MIMO system. Codebook-based precoding avoids the necessity for full knowledge of Channel State Information (CSI) at the transmitter and alleviates the complexity of generating a CSI-optimized precoder. The receiver selects the codeword that maximizes the Minimum Euclidean Distance (MED) of the received constellation and feeds back its index to the transmitter. In this paper, we first develop a new accurate closed-form Bit Error Rate (BER) for SSK without precoding. Then, we investigate several phase-rotation codebooks with quantized set of phases and systematic structure. Namely, we investigate the Full-Combination, Walsh-Hadamard, Quasi-Orthogonal Sequences, and Orthogonal Array Testing codebooks. In addition, since the size of the Full-Combination codebook may be large, we develop an iterative search method for fast selection of its best codeword. The proposed codebooks significantly improve the BER performance in Rayleigh and Nakagami fading channels, even at high spatial correlation among transmit antennas and CSI estimation error. Moreover, we show that only four phases {+1,+j,-1,-j} are sufficient and further phase granularity does yield significant gain. This avoids hardware multiplication during searching the codebook and applying the codeword.

Space Shift Keying Transmission for Intervehicular Communications

In this paper, we investigate the performance of space shift keying (SSK) transmission over a generalized multiple scattering channel. This channel model provides a realistic statistical description of an intervehicular communication environment and includes as special cases the Rician, Rayleigh, and double-Rayleigh channels. We derive an accurate closed-form expression for the pairwise error probability of SSK, which is used to obtain the uncoded and coded error rate performances of SSK over various propagation scenarios. An asymptotic analysis for high values of the signal-to-noise ratio is carried out to determine the diversity and coding gains of the proposed system. The performance analysis reveals the impact of the number of receive antennas and the use of soft and hard decision decoding on the error rate performance of the SSK transmission over multiple scattering channels. Various numerically evaluated results accompanied by Monte Carlo simulations are presented to demonstrate the correctness of the proposed analysis.

Analyzing signal attenuation in PFG anomalous diffusion via a non-Gaussian phase distribution approximation approach by fractional derivatives.

Anomalous diffusion exists widely in polymer and biological systems. Pulsed-field gradient (PFG) techniques have been increasingly used to study anomalous diffusion in nuclear magnetic resonance and magnetic resonance imaging. However, the interpretation of PFG anomalous diffusion is complicated. Moreover, the exact signal attenuation expression including the finite gradient pulse width effect has not been obtained based on fractional derivatives for PFG anomalous diffusion. In this paper, a new method, a Mainardi-Luchko-Pagnini (MLP) phase distribution approximation, is proposed to describe PFG fractional diffusion. MLP phase distribution is a non-Gaussian phase distribution. From the fractional derivative model, both the probability density function (PDF) of a spin in real space and the PDF of the spin's accumulating phase shift in virtual phase space are MLP distributions. The MLP phase distribution leads to a Mittag-Leffler function based PFG signal attenuation, which differs significantly from the exponential attenuation for normal diffusion and from the stretched exponential attenuation for fractional diffusion based on the fractal derivative model. A complete signal attenuation expression Eα(-Dfbα,β*) including the finite gradient pulse width effect was obtained and it can handle all three types of PFG fractional diffusions. The result was also extended in a straightforward way to give a signal attenuation expression of fractional diffusion in PFG intramolecular multiple quantum coherence experiments, which has an nβ dependence upon the order of coherence which is different from the familiar n2 dependence in normal diffusion. The results obtained in this study are in agreement with the results from the literature. The results in this paper provide a set of new, convenient approximation formalisms to interpret complex PFG fractional diffusion experiments.

Guest Editorial: Incentivizing Energy and Climate Innovation

Guest editorial In a quiet industrial park in suburban Toronto, there is a machine that eats carbon dioxide (CO2) and spits out fuel. This place, typically associated with its strip malls, ethnic and cultural diversity, and peaceful middle class life, might also soon be known as a hotbed of energy innovation. The project’s code name is “Pond.” A world away, at a world-class research institute in Bangalore, India, engineers have developed a completely different technology to convert CO2 into industrial chemicals. They are motivated by the desire to begin tackling rising global CO2 emissions. Their project code name is “Breathe.” Aside from a healthy obsession with carbon, what these two efforts have in common might surprise you. Rather than collaborating on an international science project or with a company’s industrial research and development, both are competing to win a global competition to transform CO2 from a liability into an asset and, in so doing, create a paradigm shift in the energy space. Both are competitors in the NRG COSIA Carbon XPRIZE. And the competition is just getting started. The XPRIZE Foundation relies on the growing power of exponential technologies and revolutionary science to catalyze radical breakthroughs. This means developments in science and technology such as robotics, artificial intelligence, nanotechnology, big data, and other disruptive forces have the potential to show exponential impact on grand challenges such as sustainable energy and climate change. By offering a suite of incentives in a prize competition, XPRIZE seeks to inspire the world’s scientists, technologists, and innovators to tackle seemingly intractable challenges. Transforming our energy systems may be the 21st century’s greatest challenge. Articulating a grand challenge does not solve any problems, but a clear and deep articulation of the problem demands an understanding of the complexity and nuance involved in the problem itself and in a vision for defining characteristics of a solution. In our approach to energy innovation, XPRIZE recognizes that the technological, sociopolitical, and economic changes occurring globally present innovators with a rare opportunity to apply truly groundbreaking research to challenges of worldwide importance. We operate at the intersection of audacious and achievable. The Carbon XPRIZE is a USD 20 million global competition to incentivize technologies that convert CO2 emissions into valuable products. The winning teams will convert the largest quantity of CO2 from actual flue gas from coal or natural gas power plants into one or more products with the highest net value. The 10 teams that survive the first two elimination rounds (proposal evaluation was in summer of 2016, and lab-scale demonstration from late 2016 through 2017) will use two brand new test centers adjacent to operating power plants in western Canada and the US state of Wyoming to demonstrate their solutions at industrial scale.

The Last Night of Freedom: Consumerism, Deviance and the “Stag Party”

ABSTRACTThis article offers an ethnographic examination of the stag party phenomenon in the United Kingdom. Stag parties have become socially expected as a rite of passage, pre-marriage celebration for men that usually involves excessive alcohol consumption and engagement in deviant, potentially harmful, behavior. These events produce a shift in time and space, and together with group expectations for celebration, increase the impetus for excessive consumption. Our contention is that excessive consumption of alcohol and deviant behavior that often takes place are partially rooted in commercial ideology, which has become firmly embedded in the attitudes of young British men.

Characterization of IDF and SDF Relaying Protocols in SSK Modulation Systems

In this paper, the performance of space shift keying (SSK) modulation is investigated in a cooperative communication system, using incremental decode-and-forward (IDF) and selective decode-and-forward (SDF) relays. The IDF and SDF relays use instantaneous signal-to-noise ratio (SNR) to verify the quality of received signal, which is not applicable to SSK modulation. In addition to instantaneous SNR, channel coefficients play the main role in the performance of SSK modulation. Moreover, in this modulation scheme, the active channel coefficient is unknown. In this paper, instead of instantaneous SNR, a new reliable criterion is introduced to be used in the IDF or SDF protocols for SSK modulation. This criterion is based on the Euclidean distances between active channel coefficient and other inactive channel coefficients. The analytical expressions are derived to calculate the average bit error rate (ABER) and the power consumptions in a cooperative system, over Rayleigh fading channels, for both IDF and SDF relaying protocols. There is good agreement between the Monte Carlo simulated and analytical results. These results show that this Euclidean distance-based criterion, in IDF or SDF relaying protocols, improves cooperative diversity gain and the ABER performance significantly.

Predicting shifts in the climate space of freshwater fishes in Great Britain due to climate change

The implications of climate change for terrestrial and aquatic taxa are for their dispersal pole-wards and/ or to higher altitudes as they track their climate niches. Here, bioclimatic models are developed to predict how projected climate change scenarios for a northern temperate region (Great Britain) shift the climate spaces (i.e. areas of suitable thermal habitat) for 12 freshwater fishes of the Salmonidae, Percidae, Esocidae and Cyprinidae families. Climate envelope models developed in Biomod2 used the current species' distributions and their relationships with current climatic variables, and projected these onto the BCC-CSM1-1 and HadGEM2-AO climate change scenarios (low and high emissions, 2050 and 2070) in full and no dispersal scenarios. Substantial contractions in climate spaces were predicted for native salmonid fishes, with decreases of up to 78% for Atlantic salmon Salmo salar, with these largely unchanged between the dispersal scenarios. Conversely, for the majority of cyprinid fishes, expansions were predicted, including into northern regions where they are current not present biogeographically. Only under the no dispersal scenarios did their predicted distributions remain the same as their current distributions. For all non-salmonid species, the most important climate variables in the model predictions related to temperature; for salmonids, they were a combination of temperature and shifts in annual mean precipitation. As these predictions suggest that there is potential for considerable alterations to the climate spaces of freshwater fishes in Great Britain during this century then regulatory and mitigation conservation actions should be undertaken to minimise these.

Transmission Optimized Generalized Spatial Modulation Over Correlated Fading Channels

Generalized spatial modulation (GSM) has shown its promising performance as an alternative to large-scale multiple-input multiple-output technology for future wireless communications. A novel transmission optimized GSM (TOGSM) is proposed based on minimizing the average bit error probability (ABEP) over spatial correlated fading environments. First, a union upper bound and a high signal-to-noise ratio (SNR) approximation of ABEP for traditional GSM with multi-stream transmission is derived when assuming maximum likelihood detection at the receiver side. In contrast, the new analytical result relaxes basic constraints on the channel model and the symbol modulation type in use when measuring the ABEP of SM. Then, TOGSM is presented through seeking the solution of an optimization problem for particular channel realizations, where the best combination of spatial modulation set and symbol modulation set can be obtained at a given spectral efficiency. Finally, the accuracy of the ABEP upper bound and its high SNR approximation is verified by Monte Carlo simulations. In addition, the performance advantages of TOGSM over the other schemes, such as fixed-GSM, V-BLAST and generalized space shift keying, are comparatively illustrated via some numerical examples.

Complex solitons with real energies

Using Hirota’s direct method and Bäcklund transformations we construct explicit complex one and two-soliton solutions to the complex Korteweg–de Vries (KdV) equation, the complex modified KdV (mKdV) equation and the complex sine-Gordon equation. The one-soliton solutions of trigonometric and elliptic type turn out to be -symmetric when a constant of integration is chosen to be purely imaginary with one special choice corresponding to solutions recently found by Khare and Saxena. We show that alternatively complex -symmetric solutions to the KdV equation may also be constructed alternatively from real solutions to the mKdV by means of Miura transformations. The multi-soliton solutions obtained from Hirota’s method break the -symmetric, whereas those obtained from Bäcklund transformations are -invariant under certain conditions. Despite the fact that some of the Hamiltonian densities are non-Hermitian, the total energy is found to be positive in all cases, that is irrespective of whether they are -symmetric or not. The reason is that the symmetry can be restored by suitable shifts in space–time and the fact that any of our N-soliton solutions may be decomposed into N separate -symmetrizable one-soliton solutions.

Driver-system state interaction in regime shifts: A model study of desertification in drylands

An ecosystem may abruptly switch into a contrasting stable state at a critical threshold under the effect of external drivers, a phenomenon called regime shifts. However, drivers are generally assumed to be independent of system states, and thus associated driver-system state interaction is largely ignored when studying regime shifts. With dryland ecosystems as study objective, this study used a mean field model with drift potential as driver to investigate the influences of driver-system state interaction on dynamics of regime shifts. Our results showed following three aspects of influences of the interaction. (1) The interaction pushed the equilibria of regime shifts as a whole into higher drift potential, especially for the forward path. Under annual rainfall of 150mm, 300mm and 500mm, tipping points of the upper branches moved forward 140VU, 151VU and 152VU with strength of the interaction of 200VU relative to these with strength of the interaction of 0VU, respectively. (2) The interaction could expand the bi-stability region of regime shifts in driver space, e.g., from 125VU (annual rainfall of 150mm), 181VU (annual rainfall of 300mm) and 209VU (annual rainfall of 500mm) under the interaction of 0VU up to 145VU, 257VU and 290VU under the interaction of 200VU, respectively. (3) The interaction might repel ecosystems away from the middle range of system states. These results suggest that the driver-system state interaction should be considered in the studies of regime shifts, and thus to better understand, predict and combat desertification in practice.

Early Weight Bearing on a Fixed Syndesmosis. Does it Matter?

Category: Trauma Introduction/Purpose: Introduction: There is no consensus about when to allow weight bearing in ankle fractures in which a screw was used to maintain reduction of the syndesmosis. There has been no evaluation, of the radiographic fate of the syndesmosis when syndesmotic screws are retained and early weight bearing is encouraged. The aim of this study was to evaluate the radiographic parameters of the syndesmosis over time in patients who had a screw fixation of the syndesmosis and early weight bearing was allowed. Methods: We analyzed 42 patients with ankle fractures treated in our institution, with at least one syndesmotic screw in which early weight bearing was allowed (3 weeks postoperatively). Weight bearing radiographs were obtained at 2 weeks, 2 months and at final follow up (41.2 months). We measure medial clear space (MCS), tibiofibular overlap (OL), tibiofibular clear space (CS) and talar shift (TS). Results: At final follow up, 66,6% of the screws were broken, 30,9% showed significant loosening and only 1 patient (4,7%) had a screw that remained solid with no signs of osteolysis. MCS at 2 weeks, 2 months and at final follow up was 2,94 mm; 3,03 mm; 3,02, respectively. OL was 6,76 mm; 6,78 mm; 6,83 and CS was 4,26 mm; 4,66 mm; 4,6 mm. No TS was detected. There was no difference in measurements along time (p>0,05). Also no difference was found in measurements within patients with intact versus broken screws (p>0,05). Conclusion: Early weight bearing on a fixed syndesmosis appears to be safe, with no measurable consequences on plain X rays regarding ankle joint parameters. Despite screw breakage or loosening on x-rays, loss of reduction is seldom observed. We believe aggressive functional rehabilitation after ankle fractures including early weight bearing is beneficial for our patients and may lead to improved functional results.

Performance Analysis of Spatial Modulation in Overlay Cognitive Radio Communications

We study the application of spatial modulation (SM) in overlay cognitive radio (CR) networks, in which the primary and secondary networks work concurrently over the same spectrum band. We assume that the direct link between the primary transmitter and receiver is not available, i.e. broken, and that the CR transmitter assists the primary network as a relay to amplify-and-forward the transmitted symbols of the primary. SM is used in the secondary to split the transmission space into two amplitude-phase modulation (APM) and spatial domains. In the proposed scheme, the secondary transmitter retransmits the primary symbols in APM domain, while its own information is transmitted by the index of transmitting antenna, similar to space shift keying, without causing any interference to the primary receiver. We analyze the performance of the optimal detectors at both the primary and secondary receivers for the case of phase shift keying modulation in terms of the average symbol error rate (ASER). We also study the asymptotic behavior of the ASER at both the primary and secondary at high signal-to-noise ratios. Simulation results show that the SM can be effectively used in overlay CR systems.