bluuebunny/crossref_metadata_2025 huggingface dataset:
Scattering by a partially exposed nearly rigid cylinder: Experiments and analysis
Authors: Baik Kyungmin , Marston Philip L.
Published: May 2008

The backscattering from a partially exposed circular cylinder was measured for broad side illumination under conditions where the contributions associated with the elastic response of the cylinder were expected to be weak. Grazing illumination was used. Since the objective was to investigate the transition in the number of reflected rays with increasing exposure, it was convenient to partially submerge the cylinder through the free surface of a tank of water. The magnitude of the scattering was measured for ka between 9.6 and 16 where k is the acoustic wave number and a is the radius of the cylinder. The scattering varied smoothly as a function of the cylinder's exposure in agreement with analytical results based on a Kirchhoff approximation [K. Baik and P. L. Marston, IEEE J. Oceanic Eng. (accepted)]. The analysis is easily modified for the case a cylinder breaking through a flat hard interface. For the different types of rays, path length calculations (as a function of the exposure) that are part of that analysis are also relevant to identifying echoes in SAS images of partially exposed cylinders and spheres. [Research supported by ONR.]
Elastic and interfacial contributions to SAS images of tilted metal cylinders: Laboratory experiments
Authors: La Follett Jon , Baik Kyungmin , Marston Philip L.
Published: May 2008

Laboratory experiments were carried out to explore interfacial and elastic contributions to synthetic aperture sonar (SAS) images of a solid aluminum circular cylinder having flat ends. Some of the elastic responses for free field backscattering as a function of tilt angle could be interpreted using prior ray-based theory of generalized Rayleigh wave contributions [K. Gipson and P.L. Marston, J. Acoust. Soc. Am. 106, 1673-1680 (1999); 107, 112-117 (2000)]. Simplified acoustic holography was also used to interpret aspects of the free field bistatic response. To study the effects of proximity to a flat reflecting surface, the cylinder was hung through the free surface of a water tank and monostatic SAS images were acquired by scanning the transducer location along a horizontal line. This arrangement partially simulates SAS images of cylinders on the ocean bottom at grazing incidence. There were bright contributions to the SAS images of tilted cylinders associated with direct elastic rays as well as with indirect elastic rays due to acoustic reflections from the free surface of the water tank. [Research supported by ONR.]
Forward looking techniques for environment modeling, obstacle detection and characterization
Authors: Quidu Isabelle , Dupas Yann
Published: May 2008

Military underwater robots are designed to perform complex underwater missions in both known and unknown environments. To achieve these tasks, an Autonomous Underwater Vehicle (AUV) must be supplied with appropriate sensors to deal with unpredictable events that can put it in danger, and with a high degree of decisional autonomy. In this paper, we have studied the architecture of forward looking sensors to allow the creation of a 3D model of the environment presenting the seabed and the obstacles that are on the path of the AUV. Our approach is based on experimental trials using different and complementary ways (sonars with several configurations) to gather an information as complete as possible. This information will be processed by the vehicle during a survey mission. Practically, we create a reference model of a static environment using a multibeam system which produces bathymetric images at different grazing angles. In the same environment we then use a Forward Looking Sonar intended for the recognition of detected echoes in comparison with the reference model. If an echo cannot be related to a known object on the reference map, it is considered as an obstacle, and the map is updated.
Automated change detection with area matching
Authors: Dubberley John , Gendron Marlin , Lohrenz Maura
Published: May 2008

When resurveying a geographic area of the seafloor during sidescan change detection operations, an automated method to match bottom objects imaged previously with objects imaged in the resurvey can increase efficiency and accuracy. The geographic position of a new object relative to a historical object is a good indicator of a match. However, due to position error within either survey, there may be more than one spatially-close object in the new imagery. To complicate matters further, the reflected energy from the new object may be significantly different given a different incidence angle in the resurvey or the partial burial of the object. In addition, the resurveyed object image may be below the threshold set for automatic recognition and falsely eliminated. This presentation will address these problems and suggest possible methods for matching “constellations” of bottom objects by Dijkstra's minimum cost - maximum flow algorithm, control point matching, and the data-association procedure.
An acoustic barrier based on amplitude variations of the ray paths and double beamforming
Authors: Nicolas Barbara , Roux Philippe , Iturbe Ion , Mars Jérôme I.
Published: May 2008

The objective of this work is to build an acoustic barrier to detect and localize a target between two vertical arrays of sensors. To perform this detection/localisation, we record the signal between each source (of the source array) and each reveiver (of the receiver array). Using these data, we extract the different ray paths between sources and receivers thanks to a new signal processing method: double beamforming. Then, we show that ray paths and their arrival times are not affected by a target in the medium but that ray amplitudes change. As a result, it is possible to use amplitude variation of the rays to find the target localisation. To validate these methods we perform ultrasonic experiments in a tank. These experiments are often used in underwater acoustics as they emulate shallow water waveguides: indeed, by multiplying the frequency by a factor x, distances are divided by the same factor. As acoustic and elastic propagation properties are not affected by this scaling down, it is possible to achieve “oceanic experiments” in a simple tank. Results of double beamforming and target detection are shown.
Advanced ATR techniques based on High-Resolution SAS Sensors
Authors: Coiras Enrique , Groen Johannes , Evans Benjamin , Pinto Marc
Published: May 2008

Automatic Target Recognition (ATR) is a key element of expeditionary Mine Countermeasures (MCM) and port protection operations. Most existing approaches to ATR are currently based on high resolution sonar sensors, which provide enough information to obtain satisfactory detection and classification performance for the large World War 2 mine types (e.g., 2 m long cylinder). False alarm rates, however, are still unacceptably high for modern mines, which constrains the way operations are undertaken and often requires either confirmation or re-evaluation by a human operator. The introduction of new AUV-mounted Synthetic Aperture Sonars (SAS) increases the resolution, quality and range of acquired sonar images, which broadens the set of machine vision and computer image analysis techniques that can be used for underwater ATR operations. In this paper we study the impact that the increased quality and resolution have on performance gains and false alarm reduction. A number of classification algorithms are selected to represent the pool of existing approaches to target detection and classification, and their performances are estimated using both simulated and real image data in order to quantify the benefits associated to the new SAS technology. Evolution and near-future plans are discussed, introducing emerging bio-sonar sensors, anomaly detectors and autonomous AUV systems.
Rapid distinction of dumpsite objects using Multiple-Aspect Scattering - Results from scaled tank experiments
Authors: Blondel Philippe
Published: May 2008

Toxic dumpsites on the seafloor are causing increasing environmental concern, but traditional sonar imaging strains to distinguish objects in unconsolidated sediments, in particular in cluttered terrains. Scaled tank experiments were conducted with four different cylinders (fluid-filled and solid aluminium, air-filled and solid stainless steel, respectively) and two seabed types (silt and gravel), using the facilities at the University of Bath. The setup was a 10:1 scaled version of the EC-SITAR sea trials site in the Stockholm Archipelago (Sweden). The main aim of these experiments was to design efficient surveying strategies, later used at sea. Our studies showed large variations depending on the aspect of these targets and their bistatic imaging configuration. These variations can be directly related to the shapes of the targets (e.g., dimensions, presence of ribs), their content (hollow or solid) and the material of the shells (e.g., stainless steel or aluminium). They are quantified using the combined L4 norm of the time-domain signals at each aspect. Using appropriate ranges of multistatic configurations and imaging each target at three distinct aspects (45° apart), it is possible to successfully distinguish between similar targets with distinct contents and/or material, even in cluttered terrains.
Sonar target-phase measurement and effects of transducer-matching
Authors: Atkins Philip , Islas Alan , Foote Kenneth G.
Published: May 2008

Active sonar systems normally detect and classify a target based on the amplitude of the received echo or the induced Doppler shift. However, additional classification information may be available from the phase shift introduced by some targets as a result of the boundary conditions. For example, reverberation from the sea surface and scattering from fish swimbladders introduce an additional phase shift that may not be present in returns from an acoustically stiffer seabed or synthetic target. Algorithms based on the use of subband correlators are presented for measuring the phase shifts introduced by the boundary conditions on stationary and moving targets when insonified by broadband transmissions. These techniques are used to remove the phase shifts introduced by the unknown target. However, the unknown phase characteristics of the transducer, matching circuit, and electronic circuitry of a sonar system imply that target-phase measurements are very difficult to make in any practical system. The effects of adding a Butterworth-derived matching circuit to a Reson TC2130 transducer are presented for the case of sinusoidal frequency-modulated excitation of solid elastic and thin elastic-shelled hollow spheres. It is concluded that target-phase measurements can enhance the classification performance of a suitably calibrated sonar system.
Features for propagation-invariant classification of underwater targets
Authors: Loughlin Patrick , Okopal Greg
Published: May 2008

As sound propagates in shallow water, it is subject to frequency-dependent spreading and attenuation (dispersion and damping). In active sonar, these propagation-induced changes can be detrimental to automatic classification because the observed backscatter depends on the propagation environment and how far the wave has traveled. One way to address this problem is to develop propagation-invariant features of the wave that can be used in automatic classification. In this talk, we present temporal, spectral, and cepstral moment-like features of a wave that are invariant per mode to dispersion and damping. Classification results on numerical simulations of the backscatter from different steel shells propagating in a Pekeris waveguide with damping and random variations will be presented. [Supported by ONR grants N00014-06-1-0009 and N00014-07-10355]
Multisegmentation of sonar images using belief function theory
Authors: Dhibi Mounir , Courtis Romain , Martin Arnaud , Quidu Isabelle
Published: May 2008

Today side scan sonar is one of the most efficient sensors for Rapid Environment Assessment missions. Unfortunately, features extracted from a given area are strongly dependent on the relative position of the sensor (e.g., due to the shadow or the gain variation). That could conduct to a bad segmentation of the seabed. However, due to the fact that operational systems give very often multiple views of the same area we use the redundancy. In this work, we propose to fuse multiview segmentations in order to outperform the seabed classification. First we present a way to characterize the seabed using as a start point, a texture analysis in order to extract parameters on images. Then, a classification method allows allocating a class according to the type of sediment for the different standpoints. The proposed classifier fusion is based on the belief function theory. We present results from a set of experiments conducted to evaluate the proposed approach with real sonar images and we discuss them.
“Venus's-noisetrap” high-gain adaptive processor
Authors: Wagstaff Ronald A. , Rice Heath E.
Published: May 2008

The Venus's-noisetrap is a high gain adaptive signal processor inspired by Venus's-flytrap, an insect eating plant. The Venus's-noisetrap utilizes single sensor or beamformed spectral data. It “traps” the data samples by modifying the governing equations in a manner that each spectral sample is adaptively “trapped” before averaging. The trapping process is a fluctuation-based temporal coherence determination of whether the time history in each spatial or spectral bin is signal or noise. Signals are set “free”, while the noise remains trapped, blocking it from participating in the averaging process. For ocean acoustic data, the processor automatically identifies signals from submerged sources. In addition, the Venus's-noisetrap achieves large signal-to-noise ratio (SNR), high spectral and spatial resolution, and auto-identification of signals. The techniques that cause this processor to mimic the Venus's-flytrap will be discussed, and the method of continuously adapting the governing equations to the unpredictable signal and noise environment will be illustrated. Results will be presented to show the processor's large SNRs and corresponding enhancements in spectral and spatial resolution.
Coherent effects of flow- and pressure-hull of a generic submarine on target scattering in an active sonar performance model
Authors: Schippers Pieter
Published: May 2008

Since the late eighties the sonar performance model ALMOST for active and passive sonar is under development at TNO. For active detection performance, first a point target was used, with a single target strength value dependent on parameters like aspect angle, based on measurements or other sources. However by now there is a demand for TS of ships and wakes with realistic dimensions and characteristics. A generic sub was modeled with additional software routines, as a pixel file. A newly developed time domain model for hull reflection was implemented, also using scattering pixels, assuming multiple scattering with damping in the metal hull layer. This extension of the pixel modelling is evaluated versus literature data. Some modeling results of target strength computations are shown, for a generic submarine with pressure hull, with aspect angle, frequency and bandwidth as parameters.
A numerical method for array sensor noise field calculation in detection performance optimization
Authors: Sun Chao , Yang Bo , Yang Yixin
Published: May 2008

Different from the generally adopted criteria of minimizing the sidelobe level and maximizing the array gain in the weighting design of a sonar array, an approach was proposed recently to optimize the shading weights with the aim of maximizing the deflection coefficient in the square-law detector, which in essence suppresses the self-noise by including the noise information at array sensors in the optimization procedure. When several noise sources are present and/or an analytical expression of the noise transfer function is not available, the sensor noise needs to be measured in forming the sensor noise response cross correlation matrix required in the optimization which is very demanding when an array with large number of sensors is considered. To avoid the tedious work of noise measurement, a numerical method is developed in this paper. In this method, the main self-noise sources are assigned with different positions and strengths and the noise field at the array sensors is calculated via either the finite element method or the boundary element method. Tank experiment validated the effectiveness of this method. By using this method, the detection performance of a sensor array can be predicted before it is physically built and tested in under practical conditions.
Adaptive removal of a known interference and its scattered energy
Authors: Lee Yung P. , Lee William
Published: May 2008

In underwater passive processing, the nearby fast moving loud surface ships produce nonstationary interference field and limit most sonar performance. After 9/11, AIS (automatic identify system) is required for ships larger than 60's, providing ground truth of positions, speeds, and other ancillary information for the nearby surface ships. This study investigates adaptive removal of a known loud signal using the ground truth information and acoustic propagation modeling. In addition, scattered energy away from the loud signal is identified through a delay correlation processing and is also removed. In a segment of MAPEX2k experiment conducted by SACLANT Centre off the west coast of Italy on November 28, 2000, the research vessel ALLIANCE towed an array at 2 m/s passing by a moored controlled source. The controlled source transmitted a loud 1-s 150-500 Hz LFM sequence every 15 s. In this setting, the fixed controlled source generated a nonstationary interference field received on the towed array. With the knowledge of the array tow track and source position the performance of removing the known interference and its scattered energy in a real shallow water environment is examined.
Neural classification of ships hydroacoustic signatures
Authors: Zak Andrzej
Published: May 2008

The paper presents method of classification of hydroacoustic signatures generated by moving ship. Classification is a procedure in which individual items are placed into groups based on quantitative information on one or more characteristics inherent in the items. In this paper the hydroacoustics signals classification is understood as the process of automatically recognition what kind of object is generating acoustics signals on the basis of individual information included in generated sounds. Hydroacoustics signal classification is a difficult task and it is still an active research area. Automatic signal classification works based on the premise that sounds emitted by object to the environment are unique for that object. However this task has been challenged by the highly variant of input signals. The paper includes discussion about unique of sound generated by moving ships. To solve problem of hydroacoustic signatures classification the Kohonen networks which belongs to group of self organizing networks where chosen. Hydroacoustic signals were acquired on the Polish Navy Range during the complex ship measurement. At the end the results of classification of underwater noises made by ship were presented.
Underwater acoustic generation with narrow and broadband lasers
Authors: Jones Theodore G. , Hornstein Melissa K. , Ting Antonio C. , Wilkes Zachary W. , Lindwall Dennis A.
Published: May 2008

Underwater laser acoustic sources, generated by intense pulsed lasers on above-water and underwater platforms, are under investigation. In a novel configuration, a tailored intense broadband laser pulse can be designed to propagate many meters underwater and compress at a predetermined remote location. Controlled compression of these optical pulses is governed by a combination of optical group velocity dispersion (GVD) and nonlinear Kerr self-focusing, resulting in photoionization, localized heating, and shock generation. Recent and ongoing experiments include near-field acoustic source characterization using lens-focused pulses of a broadband 400 nm Ti:sapphire laser, as well as 1064 nm and 532 nm narrowband YAG laser pulses. Also, the nonlinear optical Kerr index of water at 400 nm was precisely measured. Acoustic source characterization includes measurements of photoacoustic energy conversion efficiency, acoustic power spectrum, and directivity. Experimental results will be presented, and laser sources and techniques for underwater acoustic generation will be compared. [This work is supported by the U.S. Office of Naval Research.]
Recent progress on the theoretical modeling of underwater acoustics induced by sonic booms
Authors: Wang Johnson C. , Griffice Charles P. , Fincham Adam M. , Edwards John R. , Hashad Adel A.
Published: May 2008

This paper, review and status in nature, consists of three parts: (1) The salient nature and results of the published papers from an ocean sonic boom (OSB) project will be reviewed including theoretical and experimental studies of the wavy surface effect on the underwater acoustics, a three-dimensional theory of underwater acoustics and the underwater acoustics induced by a sonic boom traveling at hyper-velocity speeds. (2) New unpublished results will be reported including studies of sonic boom underwater overpressures affected by ocean finite depth and ocean stratification (variable sound speed). These studies are possible due to the derivation of a semi-similar transformation for the underwater acoustics governing equations and the application of high performance computers. (3) The preliminary results of the work-in-progress will also be discussed including three-dimensional extensions of former professor H. K. Cheng's two-dimensional wavy surface theory and laboratory verification.
Influence of a resonance changer on the sound radiation of a submarine
Authors: Merz Sascha , Kinns Roger , Kessissoglou Nicole J.
Published: May 2008

In order to reduce the excitation of the submarine hull through the shaft, a vibration attenuation system, called a resonance changer, can be implemented in the propeller/propulsion system. The effectiveness of such a system in reducing the low frequency sound radiation characteristics of a submarine is investigated. Only sound radiation due to fluctuating propeller forces, which are generated by the operation of the propeller in a nonuniform wake, is considered. These fluctuating forces are transmitted to the submarine hull through the fluid, as well as through the propeller shaft. Both types of excitation cause hull vibration and sound radiation. The accordion modes of the pressure hull, are particularly efficient sound radiators. Parameters for the resonance changer system have been optimised previously by considering only excitation of the hull through the shaft. It is shown that the effectiveness of the resonance changer at different frequencies is modified significantly in a typical full-scale implementation, due to the sound radiation from the propeller. The effect on performance is increased further when the vibration of the propeller itself is taken into account. Therefore overall optimisation of any resonance changer system requires a comprehensive model. Some of the principal effects are explored in this paper.
Stand structure and growing space efficiency following thinning in an even-aged Douglas-fir stand
Authors: O'Hara K. L.
Published: May 2008

The growth of individual trees from four thinning treatments in a 64-year-old Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) stand was analyzed to determine desirable residual stand structures after thinning. Dominant and codominant trees had the highest individual tree stem volume growth rates over the previous 5 years, and accounted for most stand volume growth in thinned and unthinned stands. Two measures of growing space, crown projection area and sapwood basal area (a surrogate for leaf area), were used to measure how efficiently individual trees used their growing space. Crown classes were useful in characterizing growing space efficiency (volume growth per unit of growing space) only in the unthinned treatment. In thinned treatments, tall trees with medium-sized crowns were most efficient, while in the unthinned treatment, tall trees with relatively large crowns were most efficient. A large crown in an unthinned stand was comparable in size to a medium-sized crown in a thinned stand. Results suggest growing space is not limiting individual tree growth in thinned stands and that thinning to a particular stand structure is more appropriate than thinning to a particular level of stand density.
Growth and ectomycorrhiza formation of containerized black spruce seedlings as affected by nitrogen fertilization, Inoculum type, and symbiont
Authors: Gagnon J. , Langlois C. G. , Fortin J. A.
Published: May 2008

Piceamariana (Mill.)B.S.P. seedlings were grown in containers under three levels of nitrogen fertilization (6, 8.5, and 15 mg/seedling per season). Seedlings were inoculated at sowing with Laccariabicolor and Hebelomacylindrosporum, using two methods: mycelial suspension liquid inoculum and peat–vermiculite solid inoculum. Results show that liquid inoculum was as effective as solid inoculum for development of Laccariabicolor ectomycorrhizae on black spruce seedlings. After 20 weeks in the greenhouse, seedlings fertilized with 8.5 mg N and inoculated with L. bicolor had the highest percentage of ectomycorrhizal short roots for both inoculum types, with 59 and 53% for liquid and solid inocula, respectively. These L. bicolor seedlings had significantly more ectomycorrhizae with 8.5 mg N than with 15 mg N. Very few ectomycorrhizae were obtained with Hebelomacylindrosporum for any of the nitrogen levels or either of the inoculum types. There were no significant differences for any growth parameters except shoot/root ratio between L. bicolor seedlings and the controls, regardless of the N level and inoculum type. For both inoculum types, only shoot height of seedlings differed significantly among the three N levels. Seedlings fertilized with 8.5 mg N had root-collar diameter and dry weights that were not significantly less than those that received 15 mg N for both inoculum types. It is only at the lower level of 6 mg N that seedlings inoculated with liquid L. bicolor inoculum absorbed significantly more N than the controls. Analysis of percent N and P concentration in seedlings with the greatest ectomycorrhizal development and analysis of available N and P in their substrate indicated that tissue concentrations of 1.9% N and 0.2% P and substrate fertility of 40 ppm N and 50 ppm P would be appropriate to maintain the ectomycorrhizal association Piceamariana–Laccariabicolor. Salinity in the substrate of control seedlings was generally significantly different between the three N levels during the growing period.
Cycle annuel des éléments nutritifs dans un bassin-versant forestier: contribution de la litière fraîche
Authors: Courchesne F. , Hendershot W. H.
Published: May 2008

The contribution of fresh litter to the input of dissolved substances at the soil surface during the dormant period of vegetation (October–April) was studied in a Laurentian watershed dominated by sugar maple (Acersaccharum), American beech (Fagusgrandifolia), and yellow birch (Betulaalleghaniensis). Net cycling (total litter input minus throughfall or snowmelt total input) of Ca, Mg, and K in the litter solution was 256.3, 195.7, and 203.4 equiv. ha−1, respectively, for the whole period. These values are much larger than the annual basic cation input due to incident precipitation. Even though net SO4 cycling in the litter solution is high during dormancy (244.2 equiv. ha−1), the atmospheric contribution probably remains the dominant source of SO4 reaching the soil surface on an annual basis. H+ ions were neutralized in the litter during winter and spring while H+ production occurred in the fall. NO3 flux decreased as water flowed through the litter, possibly because of denitrification or consumption of NO3 by living organisms present in the litter. Maximum net transport of dissolved substances occurred in the fall, even though the water flux is smaller than in the spring. During the fall, Ca, Mg, and K movement in the litter solution is strongly associated with SO4 and organic anions.
Effect of root injury and auxin treatments on adventitious root development in second-growth Douglas-fir
Authors: Bloomberg W. J. , Brix H.
Published: May 2008

Major roots of five 40-year-old Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) were subjected insitu to one of five treatments: (1) a 2.5-cm disk was excised from the root and the exposed surface was left untreated or (2) the exposed surface was smeared with lanolin paste or (3) with lanolin paste containing indolebutyric acid; (4) the root was girdled by excising a 2.5 cm wide ring of bark; or (5) a patch of bark 7.5 × 2.5 cm was removed from the upper root surface. One to two additional roots in each tree were left untreated. Roots were re-covered with soil. Seven years later the roots were hydraulically excavated and examined for callus formation and adventitious root development. All treatments resulted in callus development and all but the excised bark patch showed adventitious root development. There were no significant differences among the other treatments with respect to number of roots, total length, diameter, and number of root tips. Individual trees varied in their responses to different treatments. Two trees had prolific root production, averaged over all treatments, one had very meager production, and two were intermediate. No untreated roots developed adventitious roots. Percent stem basal area increment of trees since treatment was ranked in the same order as their adventitious root length and number.
Initial size hierarchy development within second-growth black spruce stands
Authors: Newton Peter F.
Published: May 2008

Size hierarchy development is a commonly observed structural feature within naturally regenerating forest tree populations. The objective of this study was to describe initial size hierarchy development within second-growth black spruce (Piceamariana (Mill.) B.S.P.) stands. Three dense black spruce stands that developed naturally following conventional cut and skid harvesting, conducted in 1970, were selected for analysis within insular Newfoundland. Employing historical stand reconstruction techniques within 13 temporary sample plots of variable size, temporal and spatial establishment patterns, structural development patterns, and competitive relationships were described. Size inequality peaked during the period in which 87.5% of the population became established (degree of inequality within the height and volume frequency distributions as measured by the Gini coefficient). Subsequently, size inequality and asymmetry decreased (degree of asymmetry within the volume frequency distribution as measured by the skewness coefficient and Shapiro–Wilk's W statistic). The rate of decline in size inequality and asymmetry was inversely proportional to stand density. Temporal declines in individual-tree vigour across size classes were approximately proportional (vigour as measured by relative volume production rate). These patterns suggested competition was symmetric (individuals share the finite environmental resources equally or in direct proportion to their relative sizes). However, variation in individual-tree vigour, possibly due to temporal and spatial establishment pattern heterogeneity, negated the conclusive acceptance of the resource depletion hypothesis. Based on these observations, a size hierarchy developmental pattern is proposed for second-growth black spruce stands.
Nursery and field fertilization of 2 + 0 ponderosa pine seedlings: the effect on morphology, physiology, and field performance
Authors: Gleason J. F. , Duryea M. , Rose R. , Atkinson M.
Published: May 2008

Ponderosa pine (Pinusponderosa Laws.) from two seed zones in central Oregon were grown at two nurseries where they were subjected to fall applications of N, N + K, or no fertilizer. For one seed zone, foliar N concentration increased from 1.47 to 1.53% for the N application and to 1.57% for N + K application. For the other seed zone, seedlings did not show any differences in foliar N after nursery fertilization. Seedlings that received the N application appeared to be less susceptible to frost damage, but nursery fertilization had little or no effect on seedling morphology or bud break. One month after outplanting 2 + 0 seedlings back to their respective seed-zone sites, slow-release fertilizer pellets were placed 10–13 cm from half the trees. Soils at the outplanting sites differed in mineral content, percent organic matter, and pH. The nursery-fertilized seedlings with increased N concentration grew more than control seedlings during the first season. Field-fertilized seedlings at the less fertile field site grew more in the second and third growing seasons, indicating that field fertilization after outplanting is more effective on nutrient-poor sites. Soil fertility had a greater impact on seedling performance than did nursery- and field-fertilizer treatments. At the less fertile site, N concentration decreased by 14% during the first growing season and increased by 22% during the second season, whereas at the more fertile site it increased during both the first season (12%) and the second season (6%). Seedlings at the more fertile site almost doubled in height in the 3rd year and were more than 20 cm taller than those at the other site.
Relationships among jack pine budworm damage, selected tree characteristics, and Armillaria root rot in jack pine
Authors: Mallett K. I. , Volney W. J. A.
Published: May 2008

Trees in a 94-year-old jack pine (Pinusbanksiana Lamb.) stand defoliated by the jack pine budworm (Choristoneurapinus Freeman) were examined to see if there was an association of root condition and stem growth with tree condition. Healthy trees had heavier root systems, larger root volumes, and larger annual volume increments than top-killed or dead trees in the years prior to elevated tree mortality within the stand. Roots of all the dead trees contained Armillariaostoyae (Romag.) Herink (North American Biological Species I). Three of five top-killed trees and one of five healthy trees were infected by A. ostoyae. There was no clear indication whether infection by root pathogens determines the extent to which trees are damaged following jack pine budworm defoliation, or conversely, whether repeated defoliation predisposes trees to root pathogen attack. Numbers of live branches in the crown, radial increment over the past 10 years, and prevalence of Armillaria root rot within a stand may be used to hazard rate stands prior to budworm outbreaks. The management implications of the results are discussed.
Variation in field response of Pinussylvestris to nursery inoculation with four different ectomycorrhizal fungi
Authors: Stenström Elna , Ek Mats , Unestam Torgny
Published: May 2008

Pinussylvestris L. seedlings were inoculated in nursery containers with the assertive mycorrhizal formers Laccarialaccata (Scop, ex Fr.) Bk. & Br., Hebelomacrustuliniforme (Bull, ex Fr.) Quélet, and Cenococcumgeophilum Fr. After outplanting, seedling size and the frequency of mycorrhizal root tips were monitored over 6 years. Between 25 and 90% of the root tips of inoculated seedlings were mycorrhizal with the target fungi at outplanting, whereas the noninoculated control seedlings were spontaneously colonized by other fungi at rates between 25 and 50%. After 1.5 years the inoculated fungi were still present on the roots; however, they were slowly being replaced by indigenous forest species. In the nursery, most of the inoculations resulted in reduced seedling growth. This inhibition of growth rate was pronounced up to 1.5 years in the field, except for seedlings inoculated with C. geophilum. By this time, L. laccata and H. crustuliniforme inoculated seedlings were about 40 to 50% smaller in volume than the control seedlings, and the relative difference in size was maintained or slightly decreased during the following 4 years. The noninoculated nursery production seedlings were about 50% larger in volume than the corresponding control seedlings at outplanting. In the field, however, they grew relatively slower and consequently, were soon similar in volume to the control seedlings.
Impacts of technical assistance on private nonindustrial reforestation
Authors: Skinner Michael D. , Klemperer W. David , Moulton Robert J.
Published: May 2008

This study explores the relationship between the number of foresters providing assistance to nonindustrial private forest (NIPF) owners in the southern United States and the NIPF acres planted with pine. For the year 1985, for 29 substate zones in 12 southern states, data were gathered on numbers of NIPF assistance foresters by four types, NIPF acres planted with pine, and several other variables thought to influence levels of pine planting. Using this data, a cross-sectional regression analysis was unable to demonstrate a significant south-wide effect of technical assistance on NIPF tree planting when all significant variables were included in the equations. Within the range of data gathered, equations showed that additional cost sharing and the accompanying forestry assistance should increase reforestation, but added forestry assistance alone is less likely to influence reforestation. Some previous studies support our results, others do not. In the future, if better data on the relevant variables are gathered, more definitive conclusions might be reached about the effects of technical assistance on NIPF reforestation.
Clinical Utility of Contemporary Molecular Cytogenetics
Authors: Bejjani Bassem A. , Shaffer Lisa G.
Published: May 2008

The development of microarray-based comparative genomic hybridization (array CGH) methods represents a critical new advance in molecular cytogenetics. This new technology has driven a technical convergence between molecular diagnostics and clinical cytogenetics, questioned our naïve understanding of the complexity of the human genome, revolutionized the practice of medical genetics, challenged conventional wisdom related to the genetic bases of multifactorial and sporadic conditions, and is poised to impact all areas of medicine. The use of contemporary molecular cytogenetic techniques in research and diagnostics has resulted in the identification of many new syndromes, expanded our knowledge about the phenotypic spectrum of recognizable syndromes, elucidated the genomic bases of well-established clinical conditions, and refined our view about the molecular mechanisms of some chromosomal aberrations. Newer methodologies are being developed, which will likely lead to a new understanding of the genome and its relationship to health and disease.
Chlamydiaeas Symbionts in Eukaryotes
Authors: Horn Matthias
Published: May 2008

Members of the phylum Chlamydiae are obligate intracellular bacteria that were discovered about a century ago. Although Chlamydiae are major pathogens of humans and animals, they were long recognized only as a phylogenetically well-separated, small group of closely related microorganisms. The diversity of chlamydiae, their host range, and their occurrence in the environment had been largely underestimated. Today, several chlamydia-like bacteria have been described as symbionts of free-living amoebae and other eukaryotic hosts. Some of these environmental chlamydiae might also be of medical relevance for humans. Their analysis has contributed to a broader understanding of chlamydial biology and to novel insights into the evolution of these unique microorganisms.
Replacing SiO2 - Material and Processing Aspects of New Dielectrics
Authors: De Gendt Stefan , Adelmann Christoph , Delabie Annelies , Nyns Laura , Pourtois Geoffrey , Van Elshocht Sven
Published: May 2008

The paper aims at presenting a concise overview of the process development and material issues often encountered during the development of dielectric deposition processes, and make you reminiscence of the past when 'good old' silicondioxide dominated the dielectric landscape.
The Impact of the Dielectric/Semiconductor Interface on Microstructure and Charge Carrier Transport in High-Performance Polythiophene Transistors
Authors: Jung Youngsuk , Kline R. Joseph , Lin Eric K. , Fischer Daniel A. , Toney Michael F. , Heeney Martin , McCulloch Iain , DeLongchamp Dean
Published: May 2008

The performance of organic field-effect transistors (OFETs) significantly depends on the properties of the interface between the semiconductor and gate dielectric. Here, we study the impact of chemically modified and morphologically controlled dielectrics on the performance of poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (pBTTT) semiconductors. We find that the molecular packing, domain size, and carrier mobility of pBTTT are highly sensitive to dielectric chemistry and dielectric roughness. The large and well-oriented terraced domains that are the origin of pBTTT's high performance can develop well on certain dielectrics, but can be disrupted on others.
a-Si:H Metal-Semiconductor-Metal (MSM) Photoconductor Detector for Biomolecular Imaging Applications
Authors: Karim Karim S. , Khodami Ida , Taghibakhsh Farhad
Published: May 2008

The design, fabrication and operation of a hydrogenated amorphous silicon (a-Si:H) metal-semiconductor-metal (MSM) photoconductor for short wavelength imaging applications is presented. The design of the photoconductor sensor is simpler than that of pin photodiode sensors used in conventional active-matrix arrays owing to the similarity of the photoconductor and thin film transistor fabrication processes and by eliminating the need for a p+ contact layer commonly used in p-i-n diode fabrication. The reported devices exhibit three times better responsivity for ultraviolet wavelengths as compared to state-of-the-art pin photodiodes. Experimental results for different a-Si film thicknesses, bias voltages, and electrode gaps are presented and the integration of these devices with TFT fabrication processes is discussed.
Inorganic and Organic Ferroelectric Thin Films for Memory Applications
Authors: Ishiwara Hiroshi
Published: May 2008

Electrical properties of inorganic and organic ferroelectric thin films are discussed from viewpoints of ferroelectric random access memory (FeRAM) applications. It has been found in BiFeO3 films formed by chemical solution deposition that the leakage current at high electric field decreases significantly by substituting Mn atoms for Fe atoms. In these films, well saturated hysteresis loops in P-E (polarization vs. electric field) characteristics have been observed. It has also been found that co-substitution of La and Ni atoms to BiFeO3 films is effective to decrease the leakage current. Next, properties of organic ferroelectric thin films suitable for fabricating ferroelectric-gate FETs (field effect transistors) are discussed. It has been found in capacitors with a 60nm-thick P(VDF+TrFE) (polyvinyliden fluoride-trifluoroethylene) film that the remanent polarization is as large as 11.9 μC/cm2 and the coercive voltage is as low as 2 V.
Exciton Lifetime in Sio2 Layers with Embedded Silicon Nanocrystals as a Function of the "Dark" Fraction Of Nanocrystals in the System
Authors: Stuchinsky Victor A.
Published: May 2008

Previously reported data on photoluminescence quenching in ion-beam irradiated silicon dioxide layers with embedded silicon nanocrystals were used to analyze the exciton lifetime in such systems versus the quenched fraction of nanocrystals. Estimates of the characteristic time of exciton hopping between adjacent nanocrystal grains, the length of excitonic wavefunction decay into the dielectric, and the cross-section of exciton recombination at deep-level centers introduced by the irradiation into the SiO2 matrix are given.
Impact of Millisecond Laser Anneal on the Thermal Stress- Induced Defect Creation in Si1-xGex Source /Drain Junctions
Authors: Bargallo Gonzalez Mireia , Simoen Eddy , Rosseel Erik , Verheyen Peter , Souriau Laurent , Geypen Jef , Bender Hugo , Yves Hoffmann Thomas , Loo Roger , Absil Philippe , Claeys Cor
Published: May 2008

The purpose of this paper is to evaluate the impact of the laser anneal on the thermal stress induced defect creation in Si1-xGex S/D junctions. It is shown that several factors play a key role in the motion of the glide dislocations during the laser anneal process, when huge thermal stress gradients are present in both lateral and vertical directions: firstly, the stress levels prior to a post-epi implantation; secondly, the ion implantation conditions and finally, the laser energy beam conditions. Nomarski inspections of preferentially etched Si1-xGex/Si hetero-epitaxial junctions have been performed in order to analyze the laser-induced morphology changes. Additionally, I-V measurements were employed to further investigate the leakage current enhancement due to the thermal stress induced defect creation in the embedded Si1-xGex S/D junctions. Both analysis methods resulted in fully consistent results, revealing an increase in motion of dislocations and dislocation density only for the splits that already showed some relaxation induced-extended defects before the laser annealing process. Moreover, the only conditions where the extended defects prior to the laser anneal were observed were when a post-epi ion implantation was processed in the epilayers with 25%Ge (the highest Ge content studied).
Enabling Effective Work Function Tuning by RF-PVD Metal Oxide on High-k Gate Dielectric
Authors: Yoshida Naomi , Tang Xianmin , Ahmed Khaled , Conti Giuseppina , Liu Dave , Agustin Melody , Hung Steven , Ku Victor , Chan Osbert , Liang Robert , Chen Hao , Wang Rongjun , Zheng Bo , Lazik Christopher , Jin Miao , Lavu Kishore , Chang Chorng-Ping , Mandrekar Tushar , Gandikota Srinivas
Published: May 2008

RF-PVD was investigated as a metal oxide cap deposition process to tune the effective work function in a gate first flow for high-k metal gate stacks. Samples with an aluminum oxide cap layer showed a large flat band voltage shift at minimal equivalent oxide thickness increase by about 0.1 nm. It was confirmed that RF-PVD induced no additional charge damage. Extended RF-PVD process runs also promised a robust process for high-k metal gate device manufacturing.
Quantum (5 5 12)Si Nanowire 300K MOSFET
Authors: Kendall Don L. , De la Hidalga-W Francisco J. , Rodríguez-M Ramiro , Castro-L Miguel , Torres-J Alfonso , Calleja-A Wilfrido , Meza Prieto Elizabeth , Landa-V Mauro , Zúñiga-I Carlos , Murphy-A Roberto , Carlos-R Netzahualcoyotl , Juárez-R Ignacio , Kendall Michael
Published: May 2008

A nanowire (NW) device in parallel with a normal nMOSFET is fabricated with a poly-Si planar CMOS process on (5 5 12)Si. With a unit cell of 5.35 nm, this plane has the largest stable atomically flat Si surface. When output current Isd flows from source S to drain D along <110>, the device has 15 positive spikes at integer multiples of 154 mV, all at 300K and zero magnetic field. Ids has only 9 positive and 2 negative spikes. The positive spikes in Isd and Ids are due to parabolic confinement of elongated q-dots in the NWs near D. Both Isd and Ids show missing spikes and one-dimensional artificial atom behavior. The negative spikes appear to be Kronig-Penney effects on the NWs. The NWs and q-dots have estimated widths near 2 nm and Line Edge Roughness (LER) less than 0.1 nm due to the crystal-lattice precision of the surface.