Naval Air Warfare Center Aircraft Division

We present a new formulation of Maker fringes in parallel-surface films, using self-consistent boundary conditions for reflections and allowing for any degree of refractive-index dispersion. This treatment of the second-harmonic reflections and dispersion, unlike a number of previous derivations, leads correctly to the expected form for the effective second-harmonic d coefficients. Complete expressions with physically meaningful factors are given for the generated second-harmonic power for either absorbing or birefringent films including reflections for the case of no pump depletion. A comparison with the isotropic approximation is given, and practical considerations in the use of these expressions for the fitting of experimental data are discussed.

A quantitative measure of determinism in a recurrent time series is developed. Specifically, scalar time series data are used to form a vector series in reconstructed phase space. A statistic is then developed to measure the observed ``continuity'' of the vector series. The statistic is used as a measure of determinism. Several examples are included to demonstrate the effectiveness of the method.

Abstract An experimental study of hidden corrosion detection by using ultrasonic guided waves is presented combined with a BEM numerical simulation. Both corrosion simulation specimens by machine cutting and real corrosion specimens by electrochemical processing were used in the investigation, with a range of corrosion depths from 0.02 to 0.4 mm (1.5 to 20% of the original plate thickness). Various wave modes were subsequently generated on these specimens to examine the implications of thinning on mode cutoff, group velocity, and transmission and reflection amplitudes. The transmission and reflection of guided waves upon entering the corrosion zone were simulated by a hybrid BEM calculation that combines a normal mode expansion technique of Lamb waves for far fields with the boundary element representation for the scattered near fields. A quantitative technique for hidden corrosion depth with guided waves is developed based on a frequency compensation concept. The estimated depth of the real corrosion by this method shows good agreement with that by an optical microscope.

Abstract Corrosion detection and monitoring are essential diagnostic and prognostic means for preserving material “health” and reducing life-cycle cost of industrial infrastructures, weapon systems, ships, aircraft, ground vehicles, pipelines etc. This paper provides a literature review of technologies currently under use or in the development stage, and promises a non-destructive approach to corrosion measurement, detection and monitoring. A major portion of the lifecycle cost for all platforms and infrastructures is due to labor hours spent in finding the problem and then fixing them with either a major overhaul or extensive part replacement. Knowing where the problem is early on could save up to 30% total ownership cost. It is estimated that U.S. spends over $300 billion in corrosion costs annually. This review is by no means exhaustive, but is comprehensive enough in describing major technology areas such as visual, fiber-optic, ultrasonic, acoustic, radiographic, thermal imaging, electrochemical, chemical, fluorescence and miscellaneous other techniques. It provides numerous references, which would be very helpful in finding the details of each technique described.

In Brief Study Design. Determination of lateral mass screw lengths with Roy-Camille and Magerl techniques of screw insertion using computerized tomography in 98 young, asymptomatic North American volunteers. Objective. To provide reliable and normative data on safe screw lengths using the Roy-Camille and Magerl techniques of lateral mass fixation in the subaxial cervical spine. Summary of Background Data. Lateral mass screw lengths have been studied in the past using differing subject and measurement characteristics and small sample sizes. Results demonstrated considerable variation in screw length and influencing factors. Inappropriate screw lengths can result in neurovascular injury during screw insertion, facet joint damage, or inadequate fixation. Methods. Bicortical screw lengths were bilaterally measured at each spinal level from C3–C7 in 98 young volunteers using computed tomography reconstructions through the lateral masses obtained in the plane of the screw in Roy-Camille and Magerl techniques. Results. With both techniques, trajectories were longest at C4–C6, shorter at C3, and shortest at C7. Screw lengths were greater in males when compared with females at all levels. Average Magerl screw lengths were approximately 2.6 mm longer at C3–C6 levels, and approximately 1.3 mm longer at the C7 level when compared with Roy-Camille technique. There was minimal correlation between screw lengths and anthropometric measurements including stature, body weight, and neck length. Conclusion. Significant variations exist at each subaxial level with either technique. We recommend the surgeon determine screw lengths for fixation at each level using preoperative sagittal oblique computed tomography scans, which provide the most accurate technique of preoperative templating for screw length. Inappropriate screw length selection during lateral mass screw insertion can result in neurovascular injury or facet joint damage. Mean lateral mass screw lengths with Roy-Camille and Magerl techniques of screw insertion were determined at all subaxial cervical levels using computed tomography scans of an asymptomatic, young North American population.

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTThermally Stable Nonlinear Optical Films by Alternating Polyelectrolyte Deposition on Hydrophobic SubstratesM. Joseph Roberts, Geoffrey A. Lindsay, Warren N. Herman, and Kenneth J. WynneView Author Information Naval Air Warfare Center Weapons Division Chemistry and Materials Branch Code 4B2200D, 1 Administration Circle China Lake, California 93555 Naval Air Warfare Center Aircraft Division Electrooptic Sensors Branch 48110 Shaw Road Unit 5 Patuxent River, Maryland 20657 Office of Naval Research 800 North Quincy Street Arlington, Virginia 22217 Cite this: J. Am. Chem. Soc. 1998, 120, 43, 11202–11203Publication Date (Web):October 16, 1998Publication History Received29 June 1998Published online16 October 1998Published inissue 1 November 1998https://pubs.acs.org/doi/10.1021/ja9822613https://doi.org/10.1021/ja9822613rapid-communicationACS PublicationsCopyright © Not subject to U.S. Copyright. Published 1998 American Chemical SocietyRequest reuse permissionsArticle Views247Altmetric-Citations56LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Deposition,Hydrophobicity,Nonlinear optics,Solution chemistry,Vesicles Get e-Alerts

BACKGROUND: Although cervical spine pedicle screws have been shown to provide excellent fixation, widespread acceptance of their use is limited because of the risk of injury to the spinal cord, nerve roots, and vertebral arteries. The risks of pedicle screw insertion in the cervical spine can be mitigated by a three-dimensional appreciation of pedicle anatomy. Normative data on three-dimensional subaxial pedicle geometry from a large, young, and asymptomatic North American population are lacking. The purpose of the present study was to determine three-dimensional subaxial pedicle geometry in a large group of young volunteers and to determine level and sex-specific morphologic differences. METHODS: Helical computerized tomography scans were made from the third cervical to the seventh cervical vertebra in ninety-eight volunteers (sixty-three men and thirty-five women) with an average age of twenty-five years. Pedicle width, height, length, and transverse and sagittal angulations were measured bilaterally. Pedicle screw insertion positions were quantified in terms of mediolateral and superoinferior offsets relative to readily identifiable landmarks. RESULTS: The mean pedicle width and height at all subaxial levels were sufficient to accommodate 3.5-mm screws in 98% of the volunteers. Pedicle width and height dimensions of <4.0 mm were rare (observed in association with only 1.7% of the pedicles), with 82% occurring in women and 72% occurring unilaterally. Screw insertion positions generally moved medially and superiorly at caudal levels. Transverse angulation was approximately 45 degrees at the third to fifth cervical levels and was less at more caudal levels. Sagittal angulation changed from a cranial orientation at superior levels to a caudal orientation at inferior levels. Mediolateral and superoinferior insertion positions and sagittal angulations were significantly dependent (p < 0.05) on sex and spinal level. Transverse angulation was significantly dependent (p < 0.05) on spinal level. CONCLUSIONS: Pedicle screw insertion points and orientation are significantly different (p < 0.05) at most subaxial cervical levels and between men and women. Preoperative imaging studies should be carefully templated for pedicle size in all patients on a level-specific basis. Although the prevalence was low, women were more likely to have pedicle width and height dimensions of <4.0 mm.

Polarized Ni K-edge x-ray-absorption spectroscopy (XAS) results on ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{NiO}}_{4}$ (x=0.2--1.3) are presented and interpreted with the aid of polarized Cu K-edge results on the high-${\mathit{T}}_{\mathit{c}}$ analog material ${\mathrm{La}}_{1.85}$${\mathrm{Sr}}_{0.15}$${\mathrm{CuO}}_{4}$. The Sr-substitution-induced reduction in the disparity between the Ni-O apical and in-plane distances is seen to result in the collapse of the energy splitting 4${\mathit{p}}_{\mathrm{\ensuremath{\pi}}}$ and 4${\mathit{p}}_{\mathrm{\ensuremath{\sigma}}}$ spectral features in the polarized Ni K-edge XAS (mainly by shifting the 4${\mathit{p}}_{\mathrm{\ensuremath{\pi}}}$ feature to higher energies). The 4p feature identifications used in previous Cu and Ni compound studies are clarified and the chemical shift estimates of the d hole count variation in the ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{NiO}}_{4}$ system are revised in the light of this observed continuous 4${\mathit{p}}_{\mathrm{\ensuremath{\pi}}\mathrm{\ensuremath{-}}}$4${\mathit{p}}_{\mathrm{\ensuremath{\sigma}}}$ splitting collapse. The area increase in the 1s\ensuremath{\rightarrow}3d quadrupole transition is quantitatively correlated with the Sr content of the compound. The magnitude of the area increase of this feature suggests that in addition to an increase in Ni d hole count there is also an increase in Ni-p/Ni-d hybridization which opens a dipole-allowed transition channel. Finally the dramatic appearance and growth of a prominent high-energy feature and its correlation with the increase in Ni d hole count is described and discussed.

An effort was conducted to study and characterize the effects of nanodiamond particles as an additive to lubricating mineral oil. The tests were run for varying concentrations ranging from pure mineral oil to 0.01% weight-concentration of nanodiamonds. The friction was measured throughout the tests, and the resulting wear was measured with optical profilometry. It was observed that both the average friction coefficient and the wear would decrease proportionally to the concentration of nanodiamond particles, and the 0.01% nanodiamond weight concentration was observed to improve the tribological performance of lubricating mineral oil. Chemical analysis of contacting surfaces showed no significant distinction from the nanodiamond mixture versus the pure mineral oil, while particle size analysis demonstrated that the nanoparticles themselves remained intact (i.e., no breakup) in the contact interface. This helps to conclude that a mechanical and not a chemical effect of the nanodiamond particles helped to protect the metallic surface from wear and improve the lubricating ability of the mineral oil.

The attenuation and temporal dispersion of beams with and without orbital angular momentum (OAM) underwater are investigated in a controlled laboratory water tank environment. Both spherical polystyrene beads and a commercial antacid are used to determine the effect of scattering particle size and shape on the results. Varying concentrations of the scattering agents were used to study the propagation of light in both minimally scattered and multiply scattered regimes (over 20 attenuation lengths). To study temporal dispersion, a custom diode seeded fiber amplified laser source is used to modulate beams up to 1 GHz, and diffractive spiral phase plates are used to compare performance over different spatial modes. We observe an increase in received signal with increasing OAM order (|m|=0, 8, and 16) under multiple scattering conditions. Initial experimental results suggest that this variation is dependent on particle shape and size. We do not observe any dependency of OAM order on temporal dispersion.

Persistent spectral hole-burning has been reported for singly, Eu-doped, and doubly, Eu- and Sm-doped, CaS phosphors. Efficient photon gated holeburning in the 4f7 (8S7/2)−4f65d1 transition of Eu2+ is a result of photoionization of Eu2+ to Eu3+. These holes have a width of &amp;lt;5 GHz (2 K), survive thermal cycling of the phosphor up to the room temperature, 300 K, and have no detectable deterioration over more than a day of storage time at low temperature (2 K). Although self-gated holeburning is observed with the reading laser at higher powers, the photon budget for reading these holes is so small that in excess of 1000 reading cycles can be performed without destroying the optical signal. The nature of holes burned by photon-gating is found to be very different from the self-gated holes. The characteristics for the holeburning are the same in singly and doubly doped phosphors, suggesting that under the conditions of our experiments, Sm traps do not play any significant role in spectral holeburning. Possibilities of high density optical memory storage using photon-gated holeburning in this THz broad transition are discussed.

Ejection from military aircraft exerts substantial loads on the lumbar spine. Fractures remain common, although the overall survivability of the event has considerably increased over recent decades. The present study was performed to develop and validate a biomechanically accurate experimental model for the high vertical acceleration loading to the lumbar spine that occurs during the catapult phase of aircraft ejection. The model consisted of a vertical drop tower with two horizontal platforms attached to a monorail using low friction linear bearings. A total of four human cadaveric spine specimens (T12-L5) were tested. Each lumbar column was attached to the lower platform through a load cell. Weights were added to the upper platform to match the thorax, head-neck, and upper extremity mass of a 50th percentile male. Both platforms were raised to the drop height and released in unison. Deceleration characteristics of the lower platform were modulated by foam at the bottom of the drop tower. The upper platform applied compressive inertial loads to the top of the specimen during deceleration. All specimens demonstrated complex bending during ejection simulations, with the pattern dependent upon the anterior-posterior location of load application. The model demonstrated adequate inter-specimen kinematic repeatability on a spinal level-by-level basis under different subfailure loading scenarios. One specimen was then exposed to additional tests of increasing acceleration to induce identifiable injury and validate the model as an injury-producing system. Multiple noncontiguous vertebral fractures were obtained at an acceleration of 21 g with 488 g/s rate of onset. This clinically relevant trauma consisted of burst fracture at L1 and wedge fracture at L4. Compression of the vertebral body approached 60% during the failure test, with -6,106 N axial force and 168 Nm flexion moment. Future applications of this model include developing a better understanding of the vertebral injury mechanism during pilot ejection and developing tolerance limits for injuries sustained under a variety of different vertical acceleration scenarios.

Steady-state performance models can be used to evaluate a new engine’s baseline performance. As a gas turbine accumulates operating time in the field, its performance deteriorates due to fouling, erosion, and wear. This paper presents the development of a model for predicting the performance deterioration of aircraft gas turbines. The model accounts for rotating component deterioration based on the aircraft mission profiles and environmental conditions and the engine’s physical and design characteristics. The methodology uses data correlations combined with a stage stacking technique for the compressor and a tip rub model, along with data correlations for the turbine to determine the amount of performance deterioration. The performance deterioration model interfaces with the manufacturer’s baseline engine simulation model in order to create a deteriorated performance model for that engine.

Recent advances in nonlinear dynamics have led to more informative characterizations of complex signals making it possible to probe correlations in data to which traditional linear statistical and spectral analyses were not sensitive. Many of these new tools require detailed knowledge of small scale structures of the attractor; knowledge that can be acquired only from relatively large amounts of precise data that are not contaminated by noise---not the kind of data one usually obtains from experiments. There is a need for tools that can take advantage of ``coarse-grained'' information, but which nevertheless remain sensitive to higher-order correlations in the data. We propose that the correlation integral, now much used as an intermediate step in the calculation of dimensions and entropies, can be used as such a tool and that the Kolmogorov-Smirnov test is a convenient and reliable way of comparing correlation integrals quantitatively. This procedure makes it possible to distinguish between attractors with similar dimensions. For example, it can unambiguously distinguish (p${10}^{\mathrm{\ensuremath{-}}8}$) the Lorenz, R\"ossler, and Mackey-Glass (delay=17) attractors whose correlation dimensions are within 1% of each other. We also show that the Kolmogorov-Smirnov test is a convenient way of comparing a data set with its surrogates.

December 01 1999 Spatial Orientation and Wayfinding in Large-Scale Virtual Spaces II: Guest Editors' Introduction Rudolph P. Darken, Rudolph P. Darken Department of Computer Science, Naval Postgraduate School Monterey, CA 93943-5118, darken@nps.navy.mil Search for other works by this author on: This Site Google Scholar Terry Allard, Terry Allard Cognitive and Neural Science and Technology Division, Office of Naval Research Search for other works by this author on: This Site Google Scholar Lisa B. Achille Lisa B. Achille Crewstation Technology Laboratory, Naval Air Warfare Center, Aircraft Division Search for other works by this author on: This Site Google Scholar Author and Article Information Rudolph P. Darken Department of Computer Science, Naval Postgraduate School Monterey, CA 93943-5118, darken@nps.navy.mil Terry Allard Cognitive and Neural Science and Technology Division, Office of Naval Research Lisa B. Achille Crewstation Technology Laboratory, Naval Air Warfare Center, Aircraft Division © 1999 Massachusetts Institute of Technology1999 Presence: Teleoperators and Virtual Environments (1999) 8 (6): iii–vi. https://doi.org/10.1162/pres.1999.8.6.iii Cite Icon Cite Permissions Share Icon Share Facebook Twitter LinkedIn MailTo Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Search Site Citation Rudolph P. Darken, Terry Allard, Lisa B. Achille; Spatial Orientation and Wayfinding in Large-Scale Virtual Spaces II: Guest Editors' Introduction. Presence: Teleoperators and Virtual Environments 1999; 8 (6): iii–vi. doi: https://doi.org/10.1162/pres.1999.8.6.iii Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsPRESENCE: Virtual and Augmented Reality Search Advanced Search This content is only available as a PDF. © 1999 Massachusetts Institute of Technology1999 Article PDF first page preview Close Modal You do not currently have access to this content.

Ni K-edge x-ray-absorption spectroscopy (XAS) measurements on a series of perovskite-layer-based nickelate compounds, with varying formal Ni valence, are presented. Spectral features that vary systematically with the Ni configuration are identified for these Ruddlesden-Popper phase and Sr substituted ${\mathrm{Ln}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{NiO}}_{4}$ (Ln=La and Nd) materials. Selected polarized XAS results on the ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{NiO}}_{4}$ system emphasize that a collapse of the Ni 4${\mathit{p}}_{\mathrm{\ensuremath{\sigma}}}$-4${\mathit{p}}_{\mathrm{\ensuremath{\pi}}}$ energy separation accompanies the substantial contraction of the apical Ni-O bond length in this series. In view of this, it is suggested that a displacement of the apical oxygen (${\mathrm{O}}_{\mathrm{ab}}$) could play an important role in the small polarons previously proposed to form in this system. The polarized XAS results also provide evidence for in-plane character for the Ni-site component of the doped holes in this system. The XAS evidence supporting an increasing Ni ${\mathit{d}}^{7}$ ground-state admixture in these materials, with increasing formal Ni valence, is discussed. This discussion is couched in terms of simplified Ni d configuration modeling, which emphasizes the close energetic proximity of the Ni ${\mathit{d}}^{8}$ state to O p states in these systems. \textcopyright{} 1996 The American Physical Society.

A cinematic particle image velocimeter (PIV) for measurement of time varying fields in two-phase flow is described. This system has the capability to track detailed characteristics of individual bubbles moving through a turbulent flow field, e.g., size, shape, velocity, and acceleration, and simultaneously to measure the instantaneous fluid velocity field on a two-dimensional plane. The system employs an argon-ion laser, a rotating polygonal mirror and a single 35 mm movie camera. Two features of this technique are the ability to capture bubble trajectories for long periods of time and the use of bubble images which appear as two fine point images for each instant, from which centroid and diameter can be deduced. The instrument is evaluated in an experiment on the dispersion of nominally 3.5 mm diameter bubbles from a point source in a two stream, turbulent, planar free-shear layer. Characteristics of the fluid field and the bubble motion are described.

An effort was made to study and characterize the evolution of transient tribological wear in the presence of sliding contact. Sliding contact is often characterized experimentally via the standard ASTM D4172 four-ball test, and these tests were conducted for varying times ranging from 10 seconds to 1 hour, as well as at varying temperatures and loads. A numerical model was developed to simulate the evolution of wear in the elastohydrodynamic regime. This model uses the results of a Monte Carlo study to develop novel empirical equations for wear rate as a function of asperity height and lubricant thickness; these equations closely represented the experimental data and successfully modeled the sliding contact.

Lumbar endplate fractures were investigated in different experimental scenarios, however the biomechanical effect of segmental alignment was not outlined. The objectives of this study were to quantify effects of spinal orientation on lumbar spine injuries during single-cycle compressive loads and understand lumbar spine endplate injury tolerance. Twenty lumbar motion segments were compressed to failure. Two methods were used in the preparation of the lumbar motion segments. Group 1 (n = 7) preparation maintained pre-test sagittal lordosis, whereas Group 2 (n = 13) specimens had a free-rotational end condition for the cranial vertebra, allowing sagittal rotation of the cranial vertebra to create parallel endplates. Five Group 1 specimens experienced posterior vertebral body fracture prior to endplate fracture, whereas two sustained endplate fracture only. Group 2 specimens sustained isolated endplate fractures. Group 2 fractures occurred at approximately 41% of the axial force required for Group 1 fracture (p < 0.05). Imaging and specimen dissection indicate endplate injury consistently took place within the confines of the endplate boundaries, away from the vertebral periphery. These findings indicate that spinal alignment during compressive loading influences the resulting injury pattern. This investigation identified the specific mechanical conditions under which an endplate breach will take place. Development of endplate injuries has significant clinical implication as previous research identified internal disc disruption (IDD) and degenerative disc disease (DDD) as long-term consequences of the axial load-shift that occurs following a breach of the endplate. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1084-1091, 2016.

BACKGROUND: Lumbar back pain and radiculopathy are common diagnoses. Unfortunately, conventional magnetic resonance imaging (MRI) findings and clinical symptoms do not necessarily correlate in the lumbar spine. With upright imaging, disc pathologies or foraminal stenosis may become more salient, leading to improvements in diagnosis. MATERIALS AND METHODS: Seventeen adults (10 asymptomatic and 7 symptomatic volunteers) provided their informed consent and participated in the study. A 0.6T upright MRI scan was performed on each adult in the seated position. Parameters were obtained from the L2/3 level to the L5/S1 level including those pertaining to the foramen [cross-sectional area (CSA), height, mid-disc width, width, thickness of ligamentum flavum], disc (bulge, height, width), vertebral body (height and width), and alignment (lordosis angle, wedge angle, lumbosacral angle). Each parameter was compared based on the spinal level and volunteer group using two-factor analysis of variance (ANOVA). Bonferroni post hoc analysis was used to assess the differences between individual spinal levels. RESULTS: Mid-disc width accounted for 56% of maximum foramen width in symptomatic volunteers and over 63% in asymptomatic volunteers. Disc bulge was 48% greater in symptomatic volunteers compared to asymptomatic volunteers. CSA was generally smaller in symptomatic volunteers compared to asymptomatic volunteers, particularly at the L4-L5 and L5-S1 spinal levels. Thickness of ligamentum flavum (TLF) generally increased from the cranial to caudal spinal levels where the L4-L5 and L5-S1 spinal levels were significantly thicker than the L1-L2 spinal level. CONCLUSIONS: The data implied that upright MRI could be a useful diagnostic option, as it can delineate pertinent differences between symptomatic volunteers and asymptomatic volunteers, especially with respect to foraminal geometry.