Guard Region Research Articles

The influence of the structure of guard rings on the dark currents of silicon p-i-n photodiodes

The article examines the influence of the guard rings (GR) system structure on the dark currents of responsive elements (RE) and the actual guard rings of silicon 4-element p-i-n photodiodes (PD). The samples were made on the basis of p-silicon by planar technology. Samples with one, two, and three GR were produced. It was found that increasing the amount of n+-GRs does not reduce the dark current of the REs. But with an increase in the number of n+-GRs, the probability of an edge breakdown of the n+-p-junction in the regions of the exit of the hetero-junction of the GR to the surface increases. It is possible to reduce the levels of dark current of REs and GR by combining n+- and p+- guard regions, where p+-GR is a region of restriction of dark current leakage channels, isotypic with the substrate material. PD was made with p+-GR on the periphery of the crystal in the form of a concentric ring, as well as with a p+- region on the entire periphery of the crystal. This makes it possible to reduce the level of of dark current of n+- GR due to the reduction of the area of collection of charge carriers from the surface. But a significant decrease in the dark current of REs was not observed in such cases. We proposed to carry out boron diffusion in the gaps between REs and between REs and n+-GR.

Modeling of a chain of three plasma accelerator stages with the WarpX electromagnetic PIC code on GPUs

The fully electromagnetic particle-in-cell code WarpX is being developed by a team of the U.S. DOE Exascale Computing Project (with additional non-U.S. collaborators on part of the code) to enable the modeling of chains of tens to hundreds of plasma accelerator stages on exascale supercomputers, for future collider designs. The code is combining the latest algorithmic advances (e.g., Lorentz boosted frame and pseudo-spectral Maxwell solvers) with mesh refinement and runs on the latest computer processing unit and graphical processing unit (GPU) architectures. In this paper, we summarize the strategy that was adopted to port WarpX to GPUs, report on the weak parallel scaling of the pseudo-spectral electromagnetic solver, and then present solutions for decreasing the time spent in data exchanges from guard regions between subdomains. In Sec. IV, we demonstrate the simulations of a chain of three consecutive multi-GeV laser-driven plasma accelerator stages.

Peak-to-Average Power Ratio Reduction in Pilot-Embedded OTFS Modulation Through Iterative Clipping and Filtering

In this letter, the method to reduce peak-to-average power ratio (PAPR) is studied in the pilot-embedded orthogonal time frequency space modulation where guard symbols with zero padding are introduced to avoid the interference between data and pilot symbols. By permitting the guard symbols to be padded with signals of small magnitudes, an efficient PAPR reduction method based on the iterative clipping and filtering (ICF) framework is proposed. In the proposed method, first, the clipping noise other than the clipped signal is filtered; second, the filtering coefficients for the clipping noises in the data-plus-pilot region and guard region are set to be different values to achieve good tradeoff between PAPR and bit error rate (BER) performance. Simulation results show that the proposed method can reduce the PAPR efficiently with mild BER performance loss.

Light and transmission electron microscopy of the haptoral sclerites of the monogenean gill parasite Macrogyrodactylus clarii.

The present study represents the first detailed description of the haptoral sclerites of Macrogyrodactylus clarii Gussev 1961. Light microscopy reveals outgrowths of the hamuli roots; two lateral spine-like extensions of the hood-like accessory sclerites; a ridged, fan-shaped distal end of an accessory sclerite; and two thread-like accessory sclerites with biforked ends associated with the pointed hooked region of each hamulus. Transmission electron microscopy (TEM) reveals the presence of parallel tubules in the root of the hamuli and structural differences along the length of the hamulus including the root, shaft, and pointed hooked region. The root consists of two layers, the shaft four layers and pointed hooked region only one layer with dense outer serrations. Characteristic features of the hamulus root are the presence of longitudinally orientated parallel tubules in its central core and parallel electron-dense ridges in the outer layer of its middle region; features not observed in either the shaft or the pointed hooked region. Each hamulus blade of M. clarii is associated with haptoral gland cells producing electron-dense secretory bodies. The 16 marginal hooklets each consist of a blade (sickle) articulating with a handle at the guard region and a domus. TEM revealed structural differences between the handle, the blade at the articulation region, and the distal hooked region. The domus, a filamentous thread-like sclerite at the light microscope level, consists of two electron-dense, fibrous thickenings connected to each other by a cytoplasmic process. Each marginal hooklet is associated with a small cavity and a large reservoir of homogeneous particles and secretory bodies. The possible functions of these structures are discussed in relation to equivalent features in other monogeneans.

A generalized massively parallel ultra-high order FFT-based Maxwell solver

Dispersion-free ultra-high order FFT-based Maxwell solvers have recently proven to be paramount to a large range of applications, including the high-fidelity modeling of high-intensity laser–matter interactions with Particle-In-Cell (PIC) codes. To enable a massively parallel scaling of these solvers, a novel parallelization technique was recently proposed, which consists in splitting the simulation domain into several processor sub-domains, with guard regions appended at each sub-domain boundary. Maxwell’s equations are advanced independently on each sub-domain using local shared-memory FFTs (instead of a single distributed global FFT). This implies small truncation errors at sub-domain boundaries, the amplitude of which depends on guard regions sizes and order of the Maxwell solver. For moderate guard region sizes, this ’local’ technique proved to be highly scalable on up to a million cores and notably enabled the 3D modelingof so-called plasma mirrors, for which 8 guard cells only were enough to prevent truncation error growth. Yet, for other applications, the required number of guard cells might be much higher, which would severely limit the parallel efficiency of this technique due to the large volume of guard cells to be exchanged between sub-domains. In this context, we propose a novel parallelization technique that ensures very good scaling of FFT-based solvers with an arbitrarily high number of guard cells. Our ’hybrid’ technique consists in performing distributed FFTs on local groups of processors with guard regions now appended to boundaries of each group of processors. It uses a dual domain decomposition method for the Maxwell solver and other parts of the PIC cycle to keep the simulation load-balanced. This ’hybrid’ technique was implemented in the open source exascale library PICSAR. Benchmarks show that for a large number of guard cells (>16), the ’hybrid’ technique offers up to ×3 speed-up and ×8 memory savings compared to the ’local’ one.

Cross-Mode Interference Characterization in Cellular Networks With Voronoi Guard Regions

Advances in cellular networks such as device-to-device communications and full-duplex radios, as well as the inherent elimination of intra-cell interference achieved by network-controlled multiple access schemes, motivate the investigation of the cross-mode interference properties under a guard region corresponding to the Voronoi cell of an access point (AP). By modeling the positions of interfering APs and user equipments (UEs) as Poisson distributed, analytical expressions for the statistics of the cross-mode interference generated by either APs or UEs are obtained based on appropriately defined density functions. The considered system model and analysis are general enough to capture many operational scenarios of practical interest, including conventional downlink/uplink transmissions with nearest AP association, as well as direct communication between UEs that do not necessarily lie in the same cell. Analysis provides insights on the level of protection offered by a Voronoi guard region and its dependence on type of interference and receiver position. Numerical examples demonstrate the validity/accuracy of the analysis in obtaining the system coverage probability for operational scenarios of practical interest.

Euclidean Matchings in Ultra-Dense Networks

In order to study the fundamental limits of network densification, we look at the spatial spectral efficiency gain achieved when densely deployed communication devices embedded in the $d$-dimensional Euclidean space are optimally `matched' in near-neighbour pairs. In light of recent success in probabilisitc modelling, we study devices distributed uniformly at random in the unit cube which enter into one-on-one contracts with each another. This is known in statistical physics as an Euclidean `matching'. Communication channels each have their own maximal data capacity given by Shannon's theorem. The length of the shortest matching then corresponds to the maximum one-hop capacity on those points. Interference is then added as a further constraint, which is modelled using shapes as guard regions, such as a disk, diametral disk, or equilateral triangle, matched to points, in a similar light to computational geometry. The disk, for example, produces the Delaunay triangulation, while the diametral disk produces a beta-skeleton. We also discuss deriving the scaling limit of both models using the replica method from the physics of disordered systems.

Full-Duplex Small-Cell Networks: A Physical-Layer Security Perspective

We provide a theoretical study of physical (PHY)-layer security performance in full-duplex (FD) small-cell networks. Here, the multi-antenna base stations (BSs) and user equipments (UEs) follow from the homogeneous Poisson point process-based abstraction model. To facilitate FD communications, we take into account: 1) successive interference cancellation capability at the UE side via guard regions of arbitrary radii and 2) residual self-interference at the BS side using Rician fading distribution with arbitrary statistics. We investigate the small-cell network PHY-layer security performance in the presence of a Poisson field of eavesdroppers, under the different scenarios of passive and colluding eavesdropping. Considering linear zero-forcing beamforming, we characterize the downlink and the uplink ergodic secrecy rates and derive closed-form expressions for the different useful and interference signals statistics. In certain special cases of interest, we apply non-linear curve-fitting techniques to large sets of (exact) theoretical data in order to obtain closed-form approximations for the different ergodic rates and ergodic secrecy rates under consideration. Our findings indicate that the FD functionality, in addition to enhancing the spectral efficiency, can significantly improve the PHY-layer security performance, especially with the aid of multi-antenna communications and interference cancellation schemes.

A Topology Controlling Scheme Based on Guard Region in Wireless Sensor Network

In dense wireless sensor network, we usually remove the unnecessary communication links by topology control in order to get an energy efficient routing. The channel environment becomes more complex, which results in difficulty to control topology under a mass node distribution according to the accurate interference model. This paper introduces the concept of a guard region, defined as the region around each receiver where interfering transmissions are inhibited to make the topology control. Based on the hard-core process in stochastic geometry, the scheduling of interfering node in guard region and the density of active sensors are achieved theoretically. Then we do the analysis of coverage of receiver; the interference around receiver is computed as main interference in guard region and secondary interference outside guard region. Finally, through Monte-Carlo simulation, the topology model based on guard region is proved to be correct and the influences on coverage under different parameters are analyzed.

Dynamic frequency reuse based on guard regions in two‐layer heterogeneous networks

The guard region for a randomly select user is introduced based on the stochastic geometry model. The guard region, through which a frequency reuse criterion is proposed, is calculated based on parameters such as user position, path loss exponents and transmission power. A dynamic frequency reuse scheme based on the guard regions of macrocell users is proposed to mitigate inter-layer interference. A frequency reuse criterion, which changes along with user position adaptively and is derived through stochastic geometry theory, is believed to be the first effort that can be found in the literature.

Modeling Heterogeneous Network Interference Using Poisson Point Processes

Cellular systems are becoming more heterogeneous with the introduction of low power nodes including femtocells, relays, and distributed antennas. Unfortunately, the resulting interference environment is also becoming more complicated, making evaluation of different communication strategies challenging in both analysis and simulation. Leveraging recent applications of stochastic geometry to analyze cellular systems, this paper proposes to analyze downlink performance in a fixed-size cell, which is inscribed within a weighted Voronoi cell in a Poisson field of interferers. A nearest out-of-cell interferer, out-of-cell interferers outside a guard region, and cross-tier interferers are included in the interference calculations. Bounding the interference power as a function of distance from the cell center, the total interference is characterized through its Laplace transform. An equivalent marked process is proposed for the out-of-cell interference under additional assumptions. To facilitate simplified calculations, the interference distribution is approximated using the Gamma distribution with second order moment matching. The Gamma approximation simplifies calculation of the success probability and average rate, incorporates small-scale and large-scale fading, and works with co-tier and cross-tier interference. Simulations show that the proposed model provides a flexible way to characterize outage probability and rate as a function of the distance to the cell edge.

A Miniatured WLAN/Wi-MAX Chip Antenna for Mobile Phone Applications

A compact WLAN/Wi-MAX chip antenna for mobile phone applications is pre- sented in this paper. Two chip antenna designs are proposed. One is for WLAN (2.4»2.48, 5.15»5.35, 5.725»5.85GHz) and Wi-MAX (3.4»3.7GHz). Its dimensions are 3mm £ 9mm £ 1.6mm. The other is for WLAN (2.4»2.48, 5.15»5.35, 5.725»5.85GHz)/Wi-MAX (2.5 » 2.7GHz). The dimensions are 3mm £ 11mm £ 1.6mm. The antenna conflguration of the two designs comprises two resonant branches. Not only the fundamental mode but also the second order resonance are utilized. Furthermore, the meander line structure is used to create two adja- cent resonant frequencies to achieve a tri-band operation. Measurements of the return loss and antenna patterns were performed. The measured result shows good agreement with simulated ones. The main advantage of the proposed chip antenna is that it doesn't require a guard region from other circuit components and is therefore attractive to mobile devices.

Blind estimation of symbol timing and carrier frequency offset in wireless OFDM systems

Orthogonal frequency-division multiplexing (OFDM) systems are highly sensitive to synchronization errors. We introduce an algorithm for the blind estimation of symbol timing and carrier frequency offset in wireless OFDM systems. The proposed estimator is an extension of the Gini-Giannakis (see IEEE Trans. Commun., vol.46, p.400-411, 1998) estimator for single-carrier systems. It exploits the cyclostationarity of OFDM signals and relies on second-order statistics only. Our method can be applied to pulse shaping OFDM systems with arbitrary time-frequency guard regions, OFDM based on offset quadrature amplitude modulation, and biorthogonal frequency-division multiplexing systems. We furthermore propose the use of different subcarrier transmit powers (subcarrier weighting) and periodic transmitter precoding to achieve a carrier frequency acquisition range of the entire bandwidth of the OFDM signal, and a symbol timing acquisition range of arbitrary length. Finally, we provide simulation results demonstrating the performance of the new estimator.

ENHANCING CANADA'S SPILL RESPONSE CAPABILITY: OIL SPILL EQUIPMENT REQUIREMENTS FOR A 10,000 TON RESPONSE CAPABILITY

ABSTRACT Oil spills in the past several years have focused considerable attention and public concern on marine environmental issues. The Public Review Panel on Tanker Safety and Marine Spills Response Capability and a Government of Canada internal review, coupled with independent studies, highlighted the fact that Canada's existing spill response capability requires improvement. Among its conclusions, the panel report recommended that a figure of 10,000 tonnes (metric tons, t) be used for planning the establishment of a response capability in each Coast Guard region. The study identified in detail the equipment needed to respond to a 10,000 t oil spill by examining four areas: the operating environment, containment and recovery equipment, the temporary storage of recovered oil and water, and the support equipment needed to provide an efficient operation.

Recent Developments with the Thin-Heater Thermal Conductivity Apparatus

A thin-foil heating element is employed in a thermal conductivity apparatus that operates in accordance with the basic concept of the guarded hot plate. The metal foil is sufficiently thin that lateral heat flow along the plane of the heater is insignificant, at least in the central region, so there is no need for isola tion and separate temperature control of a guard region. This makes the appa ratus simple and inexpensive to construct and operate. The resultant low-mass configuration minimizes drift error and usually reaches steady state in less than 30 min with 0.5-cm-thick specimens of nonmetallic solids. Thermal conductivity values are calculated on an absolute basis with an estimated accuracy of ±3%. Speed and simplicity make the apparatus well suited for product-development and quality control applications. Because temperature differences within the sample do not exceed a few degrees, uncertainty in mean sample temperature is sharply limited, water-vapor-migration problems are minimized, and thermal conductivity can be measured close to melting points or other critical tempera tures. New data obtained with dry calcium silicate give preliminary experi mental verification of the validity of the apparatus in the temperature range extending between ambient and 550°K.

Ion chamber response and Awall correction factors in a 60Co beam by Monte Carlo simulation

The responses and wall correction factors for ion chambers in broad parallel 60Co beams have been calculated using Monte Carlo techniques. The calculated responses are in good agreement with Bragg-Gray cavity theory. In particular, the response divided by the wall correction factor Awall is found to be independent of the detector's shape but dependent on the material used for the chamber wall in a manner predicted by Bragg-Gray cavity theory. A simple theory is given which predicts the increase in response of a Farmer ion chamber due to an electrode of an arbitrary material and radius. The change in chamber response as a function of build-up cap composition is in good agreement with analytic expressions. The effect of guard regions in pancake chambers is found to be negligible. Embedding a pancake chamber in a flat phantom during calibration is shown to increase the response by 1.0+or-0.2%. Calculated values of Awall are in good agreement with most experimental results and with those given in the AAPM protocol but with a considerably lower uncertainty of +or-0.2%. When using these values with the AAPM protocol, the beta cep factor should not be used since it is included in these calculated values.

28. Vacuum developments for fusion plasma experiments

Summary The vacuum design of a proposed large toroidal pinch experiment and some of the development work undertaken is described. The system comprises four main parts. A thin inconel bellows liner (surface area 160 m 2 ) contains the plasma and is bakeable to achieve uhv. This liner is protected by a guard vacuum to relieve it of atmospheric pressure load and the consequences of pinhole formation. The guard region also gives thermal and electrical insulation. A gas admittance system is used to pulse fill the liner with 0.1 to 10 mtorr of H 2 , D 2 or He with tracer gases. Criteria for choosing the pumping speed (7000 l s −1 at the liner) and other vacuum parameters (e.g. maximum permitted leakage) have been developed to minimize impurities in the plasma. Contamination by low mass number elements Data obtained from tests of several materials (including perflouroelastomer) likely to be used in vacuum and plasma diagnostic components will be given.