Testing and modeling of PBX-9591 shock initiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lam, Kim; Foley, Timothy; Novak, Alan

2010-01-01

This paper describes an ongoing effort to develop a detonation sensitivity test for PBX-9501 that is suitable for studying pristine and damaged HE. The approach involves testing and comparing the sensitivities of HE pressed to various densities and those of pre-damaged samples with similar porosities. The ultimate objectives are to understand the response of pre-damaged HE to shock impacts and to develop practical computational models for use in system analysis codes for HE safety studies. Computer simulation with the CTH shock physics code is used to aid the experimental design and analyze the test results. In the calculations, initiation andmore » growth or failure of detonation are modeled with the empirical HVRB model. The historical LANL SSGT and LSGT were reviewed and it was determined that a new, modified gap test be developed to satisfy the current requirements. In the new test, the donor/spacer/acceptor assembly is placed in a holder that is designed to work with fixtures for pre-damaging the acceptor sample. CTH simulations were made of the gap test with PBX-9501 samples pressed to three different densities. The calculated sensitivities were validated by test observations. The agreement between the computed and experimental critical gap thicknesses, ranging from 9 to 21 mm under various test conditions, is well within 1 mm. These results show that the numerical modeling is a valuable complement to the experimental efforts in studying and understanding shock initiation of PBX-9501.« less

Simulation Study on Jet Formability and Damage Characteristics of a Low-Density Material Liner

PubMed Central

Tang, Wenhui; Ran, Xianwen

2018-01-01

The shaped charge tandem warhead is an effective weapon against the ERA (explosive reactive armor). Whether the pre-warhead can reliably initiate the ERA directly determines the entire performance of the tandem warhead. The existing shaped charge pre-warhead mostly adopts a metal shaped jet, which effectively initiates the ERA, but interferes the main shaped jet. This article, on the other hand, explores the possibility of producing a pre-warhead using a low-density material as the liner. The nonlinear dynamic analysis software Autodyn-2D is used to simulate and compare three kinds of low-density shaped jets, including floatglass, Lucite, and Plexiglas, to the copper shaped jet in the effectiveness of impacting ERA. Based on the integrative criteria (including u-d initiation criterion, explosive reactive degree, explosive pressure, and particle velocity of the panels), it can be determined whether the low-density shaped jet can reliably initiate the sandwich charge. The results show that the three kinds of low-density shaped jets can not only initiate the reaction armor, but are also superior to the existing copper shaped jet in ductility, jet tip velocity, jet tip diameter, and the mass; namely, it is feasible to use the low-density material shaped jet to destroy the ERA. PMID:29300351

Detecting Cracks in Ceramic Matrix Composites by Electrical Resistance

NASA Technical Reports Server (NTRS)

Smith, Craig; Gyekenyesi, Andrew

2011-01-01

The majority of damage in SiC/SiC ceramic matrix composites subjected to monotonic tensile loads is in the form of distributed matrix cracks. These cracks initiate near stress concentrations, such as 90o fiber tows or large matrix pores and continue to accumulate with additional stress until matrix crack saturation is achieved. Such damage is difficult to detect with conventional nondestructive evaluation techniques (immersion ultrasonics, x-ray, etc.). Monitoring a specimen.s electrical resistance change provides an indirect approach for monitoring matrix crack density. Sylramic-iBN fiber- reinforced SiC composites with a melt infiltrated (MI) matrix were tensile tested at room temperature. Results showed an increase in resistance of more than 500% prior to fracture, which can be detected either in situ or post-damage. A relationship between resistance change and matrix crack density was also determined.

Correlation between He-Ne scatter and 2.7-microm pulsed laser damage at coating defects.

PubMed

Porteus, J O; Spiker, C J; Franck, J B

1986-11-01

A reported correlation between defect-initiated pulsed laser damage and local predamage scatter in multilayer infrared mirror coatings has been analyzed in detail. Examination of a much larger data base confirms the previous result on dielectric-enhanced reflectors with polished substrates over a wide range of energy densities above the damage onset. Scatter signals from individual undamaged defects were detected using a He-Ne scatter probe with a focal spot that nearly coincides with the 150-microm-diam (D1/e(2)) focal spot of the damage-probe beam. Subsequent damage frequency measurements (1-on-1) were made near normal or at 45 degrees incidence with 100-ns pulses at 2.7-microm wavelength. The correlation is characterized by an increase in damage frequency with increasing predamage scatter signal and by equivalence of the defect densities indicated by the two probes. Characteristics of the correlation are compared with a simple model based on focal spot intensity profiles. Conditions that limit correlation are discussed, including variable scatter from defects and background scatter from diamond-turned substrates. Results have implication for nondestructive defect detection and coating quality control.

Fundamental mechanisms of laser damage of dielectric crystals by ultrashort pulse: ionization dynamics for the Keldysh model

NASA Astrophysics Data System (ADS)

Gruzdev, Vitaly

2014-12-01

Laser-induced ionization is a major process that initiates and drives the initial stages of laser-induced damage (LID) of high-quality transparent solids. The ionization and its contribution to LID are characterized in terms of the time-dependent ionization rate and conduction-band electron density. Considering femtosecond pulses of various durations (from 35 to 706 fs) and variable peak irradiances (from 0.01 to 60 TW/cm2), we use a single-rate equation to simulate time variations of conduction-band electron density and rates of the photoionization and impact ionization. The photoionization rate is evaluated with the Keldysh equation. At low irradiance, the electron density and total ionization rate demonstrate power scaling characteristic of multiphoton ionization. With the increase of irradiance, there is observed a saturation of the photoionization rate due to photoionization suppression by the Keldysh-type singularity during the increase in the number of simultaneously absorbed photons by 1. A striking result is that the saturation is followed by a stepwise transition from the ionization regime which is completely dominated by the photoionization to a regime totally dominated by the impact ionization. The transition results in the increase of the electron density by a few orders of magnitude induced by a variation of peak laser irradiance by about 15% to 20%. The physical effects that are involved are discussed.

Mechanisms of Pulsed Laser Induced Damage to Optical Coatings

DTIC Science & Technology

1986-07-01

photoionization of absorption centers . . . . . . . . . . . . . . . . . . . . 82 5 Electron densities achieved at 12.xiO" cm from color center initiation due...lends validity to this =~ del . It also provides an order of magnitide estimate of thýe range of the otherwise unknor optical absorption coefficient and...very high temperaturas can be reacheS in the center of the film while the boundaries remain nearly at their initial temperataure. In this case a

Electron Radiation Damage of (alga) As-gaas Solar Cells

NASA Technical Reports Server (NTRS)

Loo, R.; Kamath, G. S.; Knechtli, R.

1979-01-01

Solar cells (2 cm by 2 cm (AlGa) As-GaAs cells) were fabricated and then subjected to irradiation at normal incidence by electrons. The influence of junction depth and n-type buffer layer doping level on the cell's resistance to radiation damage was investigated. The study shows that (1) a 0.3 micrometer deep junction results in lower damage to the cells than does a 0.5 micrometer junction, and (2) lowering the n buffer layer doping density does not improve the radiation resistance of the cell. Rather, lowering the doping density decreases the solar cell's open circuit voltage. Some preliminary thermal annealing experiments in vacuum were performed on the (AlGa)As-GaAs solar cells damaged by 1-MeV electron irradiation. The results show that cell performance can be expected to partially recover at 200 C with more rapid and complete recovery occurring at higher temperature. For a 0.5hr anneal at 400 C, 90% of the initial power is recovered. The characteristics of the (AlGa)As-GaAs cells both before and after irradiation are described.

Experimental Verification of a Progressive Damage Model for IM7/5260 Laminates Subjected to Tension-Tension Fatigue

NASA Technical Reports Server (NTRS)

Coats, Timothy W.; Harris, Charles E.

1995-01-01

The durability and damage tolerance of laminated composites are critical design considerations for airframe composite structures. Therefore, the ability to model damage initiation and growth and predict the life of laminated composites is necessary to achieve structurally efficient and economical designs. The purpose of this research is to experimentally verify the application of a continuum damage model to predict progressive damage development in a toughened material system. Damage due to monotonic and tension-tension fatigue was documented for IM7/5260 graphite/bismaleimide laminates. Crack density and delamination surface area were used to calculate matrix cracking and delamination internal state variables to predict stiffness loss in unnotched laminates. A damage dependent finite element code predicted the stiffness loss for notched laminates with good agreement to experimental data. It was concluded that the continuum damage model can adequately predict matrix damage progression in notched and unnotched laminates as a function of loading history and laminate stacking sequence.

Characterization of the influence of polarization orientation on bulk damage in KDP crystals at different wavelengths

NASA Astrophysics Data System (ADS)

Zheng, YinBo; Ding, Lei; Zhou, XinDa; Ba, RongSheng; Yuan, Jing; Xu, HongLei; Na, Jin; Li, YaJun; Yang, XiaoYu; Chai, Liqun; Chen, Bo; Zheng, WanGuo

2016-08-01

The investigation of polarization orientation on damage performance of type I doubler KDP crystals under different wavelengths pulses irradiation is presented in this work. Pinpoints densities (PPD) and the size distribution of pinpoints are extracted through light scattering pictures captured by microscope. The obtained results indicate that the measured PPD as a function of the fluence is both wavelength and polarization dependent, although neither fluence nor polarization have impact on the size distribution of pinpoints. We also find that the damage performances can separate into three groups depending on the wavelength, which suggests the existence of different categories of precursors and different mechanisms responsible for bulk damage initiation in SHG KDP crystals.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bury, Charles S.; Carmichael, Ian; Garman, Elspeth F.

During macromolecular X-ray crystallography experiments, protein crystals held at 100 K have been widely reported to exhibit reproducible bond scission events at doses on the order of several MGy. With the objective to mitigate the impact of radiation damage events on valid structure determination, it is essential to correctly understand the radiation chemistry mechanisms at play. OH-cleavage from tyrosine residues is regularly cited as amongst the most available damage pathways in protein crystals at 100 K, despite a lack of widespread reports of this phenomenon in protein crystal radiation damage studies. Furthermore, no clear mechanism for phenolic C—O bond cleavagemore » in tyrosine has been reported, with the tyrosyl radical known to be relatively robust and long-lived in both aqueous solutions and the solid state. Here, the initial findings of Tyr –OH group damage in a myrosinase protein crystal have been reviewed. Consistent with that study, at increasing doses, clear electron density loss was detectable local to Tyr –OH groups. A systematic investigation performed on a range of protein crystal damage series deposited in the Protein Data Bank has established that Tyr –OH electron density loss is not generally a dominant damage pathway in protein crystals at 100 K. Full Tyr aromatic ring displacement is here proposed to account for instances of observable Tyr –OH electron density loss, with the original myrosinase data shown to be consistent with such a damage model. Also presented are systematic analysis of the effects of other environmental factors, including solvent accessibility and proximity to disulfide bonds or hydrogen bond interactions. Residues in known active sites showed enhanced sensitivity to radiation-induced disordering, as has previously been reported.« less

OH cleavage from tyrosine: debunking a myth

DOE PAGES

Bury, Charles S.; Carmichael, Ian; Garman, Elspeth F.

2017-01-01

During macromolecular X-ray crystallography experiments, protein crystals held at 100 K have been widely reported to exhibit reproducible bond scission events at doses on the order of several MGy. With the objective to mitigate the impact of radiation damage events on valid structure determination, it is essential to correctly understand the radiation chemistry mechanisms at play. OH-cleavage from tyrosine residues is regularly cited as amongst the most available damage pathways in protein crystals at 100 K, despite a lack of widespread reports of this phenomenon in protein crystal radiation damage studies. Furthermore, no clear mechanism for phenolic C—O bond cleavagemore » in tyrosine has been reported, with the tyrosyl radical known to be relatively robust and long-lived in both aqueous solutions and the solid state. Here, the initial findings of Tyr –OH group damage in a myrosinase protein crystal have been reviewed. Consistent with that study, at increasing doses, clear electron density loss was detectable local to Tyr –OH groups. A systematic investigation performed on a range of protein crystal damage series deposited in the Protein Data Bank has established that Tyr –OH electron density loss is not generally a dominant damage pathway in protein crystals at 100 K. Full Tyr aromatic ring displacement is here proposed to account for instances of observable Tyr –OH electron density loss, with the original myrosinase data shown to be consistent with such a damage model. Also presented are systematic analysis of the effects of other environmental factors, including solvent accessibility and proximity to disulfide bonds or hydrogen bond interactions. Residues in known active sites showed enhanced sensitivity to radiation-induced disordering, as has previously been reported.« less

An experimental study to investigate biomechanical aspects of the initial stability of press-fit implants.

PubMed

Berahmani, Sanaz; Janssen, Dennis; van Kessel, Sal; Wolfson, David; de Waal Malefijt, Maarten; Buma, Pieter; Verdonschot, Nico

2015-02-01

Initial fixation of press-fit implants depends on interference fit, surface morphology, and bone material properties. To understand the biomechanical effect of each factor and their interactions, the pull-out strength of seven types of CoCrMo tapered implants, with four different interference fits, three different surface morphologies (low, medium and high roughness), and at two time points (0 and 30 min) were tested in trabecular bone with varying density. The effect of interference fit on pull-out strength depended on the surface morphology and time. In contrast with our expectations, samples with a higher roughness had a lower pull-out strength. We found a similar magnitude of bone damage for the different surface morphologies, but the type of damage was different, with bone compaction versus bone abrasion for low and high frictional surfaces, respectively. This explains a reduced sensitivity of fixation strength to bone mineral density in the latter group. In addition, a reduction in fixation strength after a waiting period only occurred for the low frictional specimens. Our study demonstrates that it is essential to evaluate the interplay between different factors and emphasizes the importance of testing in natural bone in order to optimize the initial stability of press-fit implants. Copyright © 2014 Elsevier Ltd. All rights reserved.

Cracking evolution behaviors of lightweight materials based on in situ synchrotron X-ray tomography: A review

NASA Astrophysics Data System (ADS)

Luo, Y.; Wu, S. C.; Hu, Y. N.; Fu, Y. N.

2018-03-01

Damage accumulation and failure behaviors are crucial concerns during the design and service of a critical component, leading researchers and engineers to thoroughly identifying the crack evolution. Third-generation synchrotron radiation X-ray computed microtomography can be used to detect the inner damage evolution of a large-density material or component. This paper provides a brief review of studying the crack initiation and propagation inside lightweight materials with advanced synchrotron three-dimensional (3D) X-ray imaging, such as aluminum materials. Various damage modes under both static and dynamic loading are elucidated for pure aluminum, aluminum alloy matrix, aluminum alloy metal matrix composite, and aluminum alloy welded joint. For aluminum alloy matrix, metallurgical defects (porosity, void, inclusion, precipitate, etc.) or artificial defects (notch, scratch, pit, etc.) strongly affect the crack initiation and propagation. For aluminum alloy metal matrix composites, the fracture occurs either from the particle debonding or voids at the particle/matrix interface, and the void evolution is closely related with fatigued cycles. For the hybrid laser welded aluminum alloy, fatigue cracks usually initiate from gas pores located at the surface or sub-surface and gradually propagate to a quarter ellipse or a typical semi-ellipse profile.

Thin-Film Module Reverse-Bias Breakdown Sites Identified by Thermal Imaging: Preprint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnston, Steven; Sulas, Dana; Guthrey, Harvey L

Thin-film module sections are stressed under reverse bias to simulate partial shading conditions. Such stresses can cause permanent damage in the form of 'wormlike' defects due to thermal runaway. When large reverse biases with limited current are applied to the cells, dark lock-in thermography (DLIT) can detect where spatially-localized breakdown initiates before thermal runaway leads to permanent damage. Predicted breakdown defect sites have been identified in both CIGS and CdTe modules using DLIT. These defects include small pinholes, craters, or voids in the absorber layer of the film that lead to built-in areas of weakness where high current densities maymore » cause thermal damage in a partial-shading event.« less

Thin-Film Module Reverse-Bias Breakdown Sites Identified by Thermal Imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnston, Steven; Sulas, Dana; Guthrey, Harvey L

Thin-film module sections are stressed under reverse bias to simulate partial shading conditions. Such stresses can cause permanent damage in the form of 'wormlike' defects due to thermal runaway. When large reverse biases with limited current are applied to the cells, dark lock-in thermography (DLIT) can detect where spatially-localized breakdown initiates before thermal runaway leads to permanent damage. Predicted breakdown defect sites have been identified in both CIGS and CdTe modules using DLIT. These defects include small pinholes, craters, or voids in the absorber layer of the film that lead to built-in areas of weakness where high current densities maymore » cause thermal damage in a partial-shading event.« less

Evaluation of quality indicators and disease damage in childhood-onset systemic lupus erythematosus patients.

PubMed

Harris, Julia G; Maletta, Kristyn I; Kuhn, Evelyn M; Olson, Judyann C

2017-02-01

The aim of this study was to describe compliance with select quality indicators and assess organ-specific dysfunction in a childhood-onset systemic lupus erythematosus population by using a validated damage index and to evaluate associations between compliance with quality indicators and disease damage. A retrospective chart review was performed on patients diagnosed with systemic lupus erythematosus prior to age 18 followed at a single center in the USA from 1999 to 2012 (n = 75). Data regarding quality indicators and outcome variables, including the Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index, were collected. The median disease duration was 3.8 years. The proportion of patients or patient-years in which care complied with the proposed quality measures was 94.4% for hydroxychloroquine use, 84.3% for vitamin D recommendation,75.8% for influenza vaccination (patient-years), 67.2% for meningococcal vaccination, 49.0% for ophthalmologic examination (patient-years), 31.7% for pneumococcal vaccination, and 28.6% for bone mineral density evaluation. Disease damage was present in 41.3% of patients at last follow-up, with an average damage index score of 0.81. Disease damage at last follow-up was associated with minority race/ethnicity (p = 0.008), bone mineral density evaluation (p = 0.035), and vitamin D recommendation (p = 0.018). Adherence to quality indicators in a childhood-onset systemic lupus erythematosus population is varied, and disease damage is prevalent. This study highlights the importance of quality improvement initiatives aimed at optimizing care delivery to reduce disease damage in pediatric lupus patients.

Fire effects on tree overstories in the oak savannas of the Southwestern Borderlands Region

Treesearch

Peter F. Ffolliott; Gerald J. Gottfried; Cody L. Stropki; Hui Chen; Daniel G. Neary

2011-01-01

Effects of cool-season and warm-season prescribed burning treatments and a wildfire on tree overstories in oak savannas on the Cascabel Watersheds of the Southwestern Borderlands Region are reported in this paper. Information on the initial survival, levels of crown damage, species compositions and densities, annual growth rates, and basal sprouting following these...

Understanding self ion damage in FCC Ni-Cr-Fe based alloy using X-ray diffraction techniques

NASA Astrophysics Data System (ADS)

Halder Banerjee, R.; Sengupta, P.; Chatterjee, A.; Mishra, S. C.; Bhukta, A.; Satyam, P. V.; Samajdar, I.; Dey, G. K.

2018-04-01

Using X-ray diffraction line profile analysis (XRDLPA) approach the radiation response of FCC Ni-Cr-Fe based alloy 690 to 1.5 and 3 MeV Ni2+ ion damage was quantified in terms of its microstructural parameters. These microstructural parameters viz. average domain size, microstrain and dislocation density were found to vary anisotropically with fluence. The anisotropic behaviour is mainly attributable to presence of twins in pre-irradiated microstructure. After irradiation, surface roughness increases as a function of fluence attributable to change in surface and sub-surface morphology caused by displacement cascade, defects and sputtered atoms created by incident energetic ion. The radiation hardening in case of 1.5 MeV Ni2+ irradiated specimens too is a consequence of the increase in dislocation density formed by interaction of radiation induced defects with pre-existing dislocations. At highest fluence there is an initiation of saturation.

Study of the radiation damage effect on Titanium metastable beta alloy by high intensity proton beam

DOE PAGES

Ishida, Taku; Wakai, E.; Hagiwara, M.; ...

2018-04-26

Here, a foil of a metastable β Titanium alloy Ti-15V-3Cr-3Sn-3Al was irradiated at the J-PARC neutrino experimental facility with 1.4 × 10 20 30 GeV protons at low temperature (100–130°C at most), and microstructural characterization and hardness testing were conducted as an initial study on the radiation damage effects of Titanium alloy by the high energy proton beam exposure. Expected radiation damage at the beam center is about 0.06–0.12 displacement per atom. A high density (> 10 23 m –3) of a nanometer-sized precipitate was observed by TEM studies, which would be identified as martensite α-phase and athermal ω-phase formedmore » during the solution-treatment process to fabricate metastable β alloy. They did not appear to change substantially after irradiation with protons. In the irradiated specimen, we could not identify an obvious signature of radiation damage distributed along the proton beam profile. Very small, nanometer-scale black dots were present at a low density in the most highly irradiated region, and may be small dislocation loops formed during irradiation. The micro-indentation test indicated that the radiation exposure led to tiny increase in Vickers micro-hardness of ΔH V= 20 at beam center. Atom probe tomography reveals compositional fluctuations that reach a maximum amplitude of 10 at% Ti within a space of < 5 nm both before and after irradiation, which may also indicate presence of rich precipitates. These experimental results suggest this specific β alloy may exhibit radiation damage resistance due to the existence of a high density of nano-scale precipitates, but further studies with higher exposure are required to explore this possibility.« less

Study of the radiation damage effect on Titanium metastable beta alloy by high intensity proton beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ishida, Taku; Wakai, E.; Hagiwara, M.

Here, a foil of a metastable β Titanium alloy Ti-15V-3Cr-3Sn-3Al was irradiated at the J-PARC neutrino experimental facility with 1.4 × 10 20 30 GeV protons at low temperature (100–130°C at most), and microstructural characterization and hardness testing were conducted as an initial study on the radiation damage effects of Titanium alloy by the high energy proton beam exposure. Expected radiation damage at the beam center is about 0.06–0.12 displacement per atom. A high density (> 10 23 m –3) of a nanometer-sized precipitate was observed by TEM studies, which would be identified as martensite α-phase and athermal ω-phase formedmore » during the solution-treatment process to fabricate metastable β alloy. They did not appear to change substantially after irradiation with protons. In the irradiated specimen, we could not identify an obvious signature of radiation damage distributed along the proton beam profile. Very small, nanometer-scale black dots were present at a low density in the most highly irradiated region, and may be small dislocation loops formed during irradiation. The micro-indentation test indicated that the radiation exposure led to tiny increase in Vickers micro-hardness of ΔH V= 20 at beam center. Atom probe tomography reveals compositional fluctuations that reach a maximum amplitude of 10 at% Ti within a space of < 5 nm both before and after irradiation, which may also indicate presence of rich precipitates. These experimental results suggest this specific β alloy may exhibit radiation damage resistance due to the existence of a high density of nano-scale precipitates, but further studies with higher exposure are required to explore this possibility.« less

Damage Evaluation for Ti Alloys in Creep based on Incompatibility Field Measurement via EBSD Technique and Micro-Pillar Experiments Toward Identification of Roles of Dislocation Substructures on Fatigue Crack Initiation

DTIC Science & Technology

2011-02-07

Reproduction of a slip band with a PSB -ladder-like internal structure is attempted assuming initial conditions with and without corresponding strain...into heat at the PSB region, the present study extensively examined possible transition mechanisms toward the growth of grooves thereabout and that...arrangements even with the same dislocation density. (2)A slip band-like region having a substructure mimicking PSB ladder is demonstrated to be

Reduction of the 355-nm laser-induced damage initiators by removing the subsurface cracks in fused silica

NASA Astrophysics Data System (ADS)

Yang, Minghong; Qi, Hongji; Zhao, Yuanan; Yi, Kui

2012-01-01

The 355 nm laser-induced damage thresholds (LIDTs) of polished fused silica with and without the residual subsurface cracks were explored. HF based wet etching and magnetorheological finishing was used to remove the subsurface cracks. To isolate the effect of subsurface cracks, chemical leaching was used to eliminate the photoactive impurities in the polishing layer. Results show that the crack number density decreased from~103 to <1cm-2, and the LIDT was improved as high as 2.8-fold with both the subsurface cracks and the polishing layer being removed. Subsurface cracks play a significant role in laser damage at fluencies between 15~31 J/cm2 (355nm, 8ns). HF Etching of the cracks was shown to increase the damage performance as nearly high as that of the samples in which subsurface cracks are well controlled.

Local strain and damage mapping in single trabeculae during three-point bending tests

PubMed Central

Jungmann, R.; Szabo, M.E.; Schitter, G.; Tang, Raymond Yue-Sing; Vashishth, D.; Hansma, P.K.; Thurner, P.J.

2012-01-01

The use of bone mineral density as a surrogate to diagnose bone fracture risk in individuals is of limited value. However, there is growing evidence that information on trabecular microarchitecture can improve the assessment of fracture risk. One current strategy is to exploit finite element analysis (FEA) applied to 3D image data of several mm-sized trabecular bone structures obtained from non-invasive imaging modalities for the prediction of apparent mechanical properties. However, there is a lack of FE damage models, based on solid experimental facts, which are needed to validate such approaches and to provide criteria marking elastic–plastic deformation transitions as well as microdamage initiation and accumulation. In this communication, we present a strategy that could elegantly lead to future damage models for FEA: direct measurements of local strains involved in microdamage initiation and plastic deformation in single trabeculae. We use digital image correlation to link stress whitening in bone, reported to be correlated to microdamage, to quantitative local strain values. Our results show that the whitening zones, i.e. damage formation, in the presented loading case of a three-point bending test correlate best with areas of elevated tensile strains oriented parallel to the long axis of the samples. The average local strains along this axis were determined to be (1.6 ± 0.9)% at whitening onset and (12 ± 4)% just prior to failure. Overall, our data suggest that damage initiation in trabecular bone is asymmetric in tension and compression, with failure originating and propagating over a large range of tensile strains. PMID:21396601

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Dependence of the photoluminescence density on surface preparation and properties of n-type InP

NASA Astrophysics Data System (ADS)

Knauer, A.; Gramlich, S.; Staske, R.

1988-11-01

Comprehensive studies were made of the relationship between the photoluminescence intensity and the effective carrier lifetime, on the one hand, and the quality of the surface treatment of wafers (damage, oxide layer thickness) and the initial properties of a material (surface and bulk defects, inhomogeneity of the dopant concentration), on the other.

On the phenomenon of curved microcracks in /(S)/90n/s laminates - Their shapes, initiation angles and locations

NASA Technical Reports Server (NTRS)

Hu, Shoufeng; Bark, Jong S.; Nairn, John A.

1993-01-01

A variational analysis of the stress state in microcracked cross-ply laminates has been used to investigate the phenomenon of curved microcracking in /(S)/90n/s laminates. Previous investigators proposed that the initiation and orientation of curved microcracks are controlled by local maxima and stress trajectories of the principal stresses. We have implemented a principal stress model using a variational mechanics stress analysis and we were able to make predictions about curved microcracks. The predictions agree well with experimental observations and therefore support the assertion that the variational analysis gives an accurate stress state that is useful for modeling the microcracking properties of cross-ply laminates. An important prediction about curved microcracks is that they are a late stage of microcracking damage. They occur only when the crack density of straight microcracks exceeds the critical crack density for curved microcracking. The predicted critical crack density for curved microcracking agrees well with experimental observations.

Public support for river restoration funding in relation to local river ecomorphology, population density, and mean income

NASA Astrophysics Data System (ADS)

SchläPfer, Felix; Witzig, Pieter-Jan

2006-12-01

In 1997, about 140,000 citizens in 388 voting districts in the Swiss canton of Bern passed a ballot initiative to allocate about 3 million Swiss Francs annually to a canton-wide river restoration program. Using the municipal voting returns and a detailed georeferenced data set on the ecomorphological status of the rivers, we estimate models of voter support in relation to local river ecomorphology, population density, mean income, cultural background, and recent flood damage. Support of the initiative increased with increasing population density and tended to increase with increasing mean income, in spite of progressive taxation. Furthermore, we found evidence that public support increased with decreasing "naturalness" of local rivers. The model estimates may be cautiously used to predict the public acceptance of similar restoration programs in comparable regions. Moreover, the voting-based insights into the distribution of river restoration benefits provide a useful starting point for debates about appropriate financing schemes.

Dispersal Behavior of Tetranychus evansi and T. urticae on Tomato at Several Spatial Scales and Densities: Implications for Integrated Pest Management

PubMed Central

Azandémè-Hounmalon, Ginette Y.; Fellous, Simon; Kreiter, Serge; Fiaboe, Komi K. M.; Subramanian, Sevgan; Kungu, Miriam; Martin, Thibaud

2014-01-01

Studying distribution is necessary to understand and manage the dynamics of species with spatially structured populations. Here we studied the distribution in Tetranychus evansi and T. urticae, two mite pests of tomato, in the scope of evaluating factors that can influence the effectiveness of Integrated Pest Management strategies. We found greater positive density-dependent distribution with T. evansi than T. urticae when assayed on single, detached tomato leaves. Indeed, T. evansi distribution among leaflets increased with initial population density while it was high even at low T. urticae densities. Intensity and rate of damage to whole plants was higher with T. evansi than T. urticae. We further studied the circadian migration of T. evansi within plant. When T. evansi density was high the distribution behavior peaked between 8 am and 3 pm and between 8 pm and 3 am local time of Kenya. Over 24 h the total number of mites ascending and descending was always similar and close to the total population size. The gregarious behavior of T. evansi combined with its rapid population growth rate, may explain why few tomato plants can be severely damaged by T. evansi and how suddenly all the crop can be highly infested. However the localisation and elimination of the first infested plants damaged by T. evansi could reduce the risk of outbreaks in the entire crop. These findings suggest also that an acaricide treated net placed on the first infested plants could be very effective to control T. evansi. Moreover circadian migration would therefore accentuate the efficiency of an acaricide treated net covering the infested plants. PMID:24743580

New Concept Study for Repair of Bomb-Damaged Runways. Volume I. Concept Identification.

DTIC Science & Technology

1979-09-01

Expanded polystyrene beads would be pneumatically mixed with the cement to form a low density material. Initially, the ratio of foam to cement would...the combinations are presented with this concept. PRIMARY MATERIALS 0 Expanded polystyrene foam beads * Graded aggregate * Quick setting cement 61 E-4...probability of success - high ALTERNATE MATERIALS * Expanded polystyrene foam beads * Organic binders Furan Methyl Methacrylate Epoxy Aminos * Graded

Crack Damage Parameters and Dilatancy of Artificially Jointed Granite Samples Under Triaxial Compression

NASA Astrophysics Data System (ADS)

Walton, G.; Alejano, L. R.; Arzua, J.; Markley, T.

2018-06-01

A database of post-peak triaxial test results was created for artificially jointed planes introduced in cylindrical compression samples of a Blanco Mera granite. Aside from examining the artificial jointing effect on major rock and rock mass parameters such as stiffness, peak strength and residual strength, other strength parameters related to brittle cracking and post-yield dilatancy were analyzed. Crack initiation and crack damage values for both the intact and artificially jointed samples were determined, and these damage envelopes were found to be notably impacted by the presence of jointing. The data suggest that with increased density of jointing, the samples transition from a combined matrix damage and joint slip yielding mechanism to yield dominated by joint slip. Additionally, post-yield dilation data were analyzed in the context of a mobilized dilation angle model, and the peak dilation angle was found to decrease significantly when there were joints in the samples. These dilatancy results are consistent with hypotheses in the literature on rock mass dilatancy.

Expanded Polystyrene Re-Expansion Analysis Following Impact Compression

DTIC Science & Technology

2015-03-04

on the higher density (0.08 g/cm3) EAL used in the Sound Protective Helmet No. 4 ( SPH -4) showed a linear relationship between initial EPS...temperature on the cushioning properties of some foamed plastic materials. Packaging Technology Science. 16: 69-76. Palmer, R.P. 1991. SPH -4 aircrew...Slobodnik, B.A. 1979. SPH -4 helmet damage and head injury correlation. Aviation, Space, and Environmental Medicine. 50: 139-146. Slobodnik, B.A

Method for producing damage resistant optics

DOEpatents

Hackel, Lloyd A.; Burnham, Alan K.; Penetrante, Bernardino M.; Brusasco, Raymond M.; Wegner, Paul J.; Hrubesh, Lawrence W.; Kozlowski, Mark R.; Feit, Michael D.

2003-01-01

The present invention provides a system that mitigates the growth of surface damage in an optic. Damage to the optic is minimally initiated. In an embodiment of the invention, damage sites in the optic are initiated, located, and then treated to stop the growth of the damage sites. The step of initiating damage sites in the optic includes a scan of the optic using a laser to initiate defects. The exact positions of the initiated sites are identified. A mitigation process is performed that locally or globally removes the cause of subsequent growth of the damaged sites.

Fracture and damage localization in volcanic edifice rocks from El Hierro, Stromboli and Tenerife.

PubMed

Harnett, Claire E; Benson, Philip M; Rowley, Pete; Fazio, Marco

2018-01-31

We present elastic wave velocity and strength data from a suite of three volcanic rocks taken from the volcanic edifices of El Hierro and Tenerife (Canary Islands, Spain), and Stromboli (Aeolian Islands, Italy). These rocks span a range of porosity and are taken from volcanoes that suffer from edifice instability. We measure elastic wave velocities at known incident angles to the generated through-going fault as a function of imposed strain, and examine the effect of the damage zone on P-wave velocity. Such data are important as field measurements of elastic wave tomography are key tools for understanding volcanic regions, yet hidden fractures are likely to have a significant effect on elastic wave velocity. We then use elastic wave velocity evolution to calculate concomitant crack density evolution which ranges from 0 to 0.17: highest values were correlated to the damage zone in rocks with the highest initial porosity.

Relationship Between Crop Losses and Initial Population Densities of Meloidogyne arenaria in Winter-Grown Oriental Melon in Korea

PubMed Central

Kim, D.G.; Ferris, H.

2002-01-01

To determine the economic threshold level, oriental melon (Cucumis melo L. cv. Geumssaragi-euncheon) grafted on Shintozoa (Cucurbita maxima × Cu. moschata) was planted in plots (2 × 3 m) under a plastic film in February with a range of initial population densities (Pi) of Meloidogyne arenaria. The relationships of early, late, and total yield to Pi measured in September and January were adequately described by both linear regression and the Seinhorst damage model. Initial nematode densities in September in excess of 14 second-stage juveniles (J2)/100 cm³ soil caused losses in total yields that exceeded the economic threshold and indicate the need for fosthiazate nematicide treatment at current costs. Differences in yield-loss relationships to Pi between early- and late-season harvests enhance the resolution of the management decision and suggest approaches for optimizing returns. Determination of population levels for advisory purposes can be based on assay samples taken several months before planting, which allows time for implementation of management procedures. We introduce (i) an amendment of the economic threshold definition to reflect efficacy of the nematode management procedure under consideration, and (ii) the concept of profit limit as the nematode population at which net returns from the system will become negative. PMID:19265907

Applications of ASFCM(Assessment System of Flood Control Measurement) in Typhoon Committee Members

NASA Astrophysics Data System (ADS)

Kim, C.

2013-12-01

Due to extreme weather environment such as global warming and greenhouse effect, the risks of having flood damage has been increased with larger scale of flood damages. Therefore, it became necessary to consider modifying climate change, flood damage and its scale to the previous dimension measurement evaluation system. In this regard, it is needed to establish a comprehensive and integrated system to evaluate the most optimized measures for flood control through eliminating uncertainties of socio-economic impacts. Assessment System of Structural Flood Control Measures (ASFCM) was developed for determining investment priorities of the flood control measures and establishing the social infrastructure projects. ASFCM consists of three modules: 1) the initial setup and inputs module, 2) the flood and damage estimation module, and 3) the socio-economic analysis module. First, we have to construct the D/B for flood damage estimation, which is the initial and input data about the estimation unit, property, historical flood damages, and applied area's topographic & hydrological data. After that, it is important to classify local characteristic for constructing flood damage data. Five local characteristics (big city, medium size city, small city, farming area, and mountain area) are classified by criterion of application (population density). Next step is the floodplain simulation with HEC-RAS which is selected to simulate inundation. Through inputting the D/B and damage estimation, it is able to estimate the total damage (only direct damage) that is the amount of cost to recover the socio-economic activities back to the safe level before flood did occur. The last module suggests the economic analysis index (B/C ratio) with Multidimensional Flood Damage Analysis. Consequently, ASFCM suggests the reference index in constructing flood control measures and planning non-structural systems to reduce water-related damage. It is possible to encourage flood control planners and managers to consider and apply the socio-economic analysis results. ASFCM was applied in Republic of Korea, Thailand and Philippines to review efficiency and applicability. Figure 1. ASFCM Application(An-yang Stream, Republic of Korea)

Does variable-density thinning increase wind damage in conifer stands on the Olympic Peninsula?

Treesearch

S.D. Roberts; C.A. Harrington; K.R. Buermeyer

2007-01-01

Silvicultural treatments designed to enhance stand structural diversity may result in increased wind damage. The ability to avoid conditions that might lead to excessive wind damage would benefit forest managers. We analyzed wind damage following implementation of a variable-density thinning at four sites on the Olympic National Forest in northwest Washington. The...

Assessment of fragment projection hazard: probability distributions for the initial direction of fragments.

PubMed

Tugnoli, Alessandro; Gubinelli, Gianfilippo; Landucci, Gabriele; Cozzani, Valerio

2014-08-30

The evaluation of the initial direction and velocity of the fragments generated in the fragmentation of a vessel due to internal pressure is an important information in the assessment of damage caused by fragments, in particular within the quantitative risk assessment (QRA) of chemical and process plants. In the present study an approach is proposed to the identification and validation of probability density functions (pdfs) for the initial direction of the fragments. A detailed review of a large number of past accidents provided the background information for the validation procedure. A specific method was developed for the validation of the proposed pdfs. Validated pdfs were obtained for both the vertical and horizontal angles of projection and for the initial velocity of the fragments. Copyright © 2014 Elsevier B.V. All rights reserved.

Nanosecond laser-induced damage at different initial temperatures of Ta{sub 2}O{sub 5} films prepared by dual ion beam sputtering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Cheng, E-mail: xucheng@cumt.edu.cn; Jia, Jiaojiao; Fan, Heliang

2014-08-07

Ta{sub 2}O{sub 5} films were deposited by dual ion beam sputtering method. The nanosecond laser-induced damage threshold (LIDT) at different initial temperatures and time of the films was investigated by an in situ high temperature laser-induced damage testing platform. It was shown that, when the initial temperature increased from 298 K to 383 K, the LIDT at 1064 nm and 12 ns significantly decreased by nearly 14%. Then the LIDT at 1064 nm and 12 ns decreased slower with the same temperature increment. Different damage morphologies were found at different initial temperatures. At low initial temperatures, it was the defects-isolated damage while at high initial temperaturesmore » it was the defects-combined damage. The theoretical calculations based on the defect-induced damage model revealed that both the significant increase of the highest temperature and the duration contributed to the different damage morphologies. With the initial temperature being increased, the thermal-stress coupling damage mechanism transformed gradually to the thermal dominant damage mechanism.« less

High-Resolution Characterizations of Grain Boundary Damage and Stress Corrosion Cracks in Cold-Rolled Alloy 690

NASA Astrophysics Data System (ADS)

Bruemmer, S. M.; Olszta, M. J.; Toloczko, M. B.; Thomas, L. E.

Unidirectional cold rolling has been shown to promote intergranular stress corrosion cracking (IGSCC) in alloy 690 tested in PWR primary water. High-resolution scanning (SEM) and transmission electron microscopy (TEM) have been employed to investigate the microstructural reasons for this enhanced susceptibility in two stages, first examining grain boundary damage produced by cold rolling and second by characterization of stress corrosion crack tips. The degree of permanent grain boundary damage from cold rolling was found to depend directly on the initial IG precipitate distribution. Cold rolling to high levels of reduction was discovered to produce small IG voids and cracked carbides in alloys with a high density of grain boundary carbides. For the same degree of cold rolling, alloys with few IG carbides exhibited much less permanent damage. Although this difference in grain boundary damage appears to correlate with measured SCC growth rates, crack tip examinations reveal no interaction between the preexisting voids and cracked carbides with the propagation. In many cases, these features appeared to blunt propagation of IGSCC cracks. High-resolution characterizations are described for cold-rolled alloy 690 CRDM tubing and plate materials to gain insights into IGSCC mechanisms.

Composite Structural Materials

NASA Technical Reports Server (NTRS)

Ansell, G. S.; Loewy, R. G.; Wiberly, S. E.

1984-01-01

The development and application of filamentary composite materials, is considered. Such interest is based on the possibility of using relatively brittle materials with high modulus, high strength, but low density in composites with good durability and high tolerance to damage. Fiber reinforced composite materials of this kind offer substantially improved performance and potentially lower costs for aerospace hardware. Much progress has been made since the initial developments in the mid 1960's. There were only limited applied to the primary structure of operational vehicles, mainly as aircrafts.

Effects of Peanut-Tobacco Rotations on Population Dynamics of Meloidogyne arenaria in Mixed Race Populations.

PubMed

Hirunsalee, A; Barker, K R; Beute, M K

1995-06-01

A 3-year microplot study was initiated to characterize the population dynamics, reproduction potential, and survivorship of single or mixed populations of Meloidogyne arenaria race 1 (Ma1) and race 2 (Ma2), as affected by crop rotations of peanut 'Florigiant' and M. incognita races 1 and 3-resistant 'McNair 373' and susceptible 'Coker 371-Gold' tobacco. Infection, reproduction, and root damage by Ma2 on peanut and by Ma1 on resistant tobacco were limited in the first year. Infection, reproduction, and root-damage potentials on susceptible tobacco were similar for Ma1 and Ma2. In the mixed (1:1) population, Ma1 was dominant on peanut and Ma2 was dominant on both tobacco cultivars. Crop rotation affected the population dynamics of different nematode races. For years 2 and 3, the low numbers of Ma1 and Ma2 from a previous-year poor host increased rapidly on suitable hosts. Ma1 had greater reproduction factors ([RF] = population density at harvest/population density at preplandng) than did Ma2 and Ma1 + Ma2 in second-year peanut plots following first-year resistant tobacco, and in third-year peanut plots following second-year tobacco. In mixed infestations, Ma1 predominated over Ma2 in previous-year peanut plots, whereas Ma2 predominated over Ma1 in previous-year tobacco plots. Moderate damage on resistant tobacco was induced by Ma1 in the second year. In the third year, moderate damage on peanut was associated with 'Ma2' from previous-year peanut plots. The resistant tobacco supported sufficient reproduction of Ma1 over 2 years to effect moderate damage and yield suppression to peanut in year 3.

Effects of Peanut-Tobacco Rotations on Population Dynamics of Meloidogyne arenaria in Mixed Race Populations

PubMed Central

Hirunsalee, Anan; Barker, K. R.; Beute, M. K.

1995-01-01

A 3-year microplot study was initiated to characterize the population dynamics, reproduction potential, and survivorship of single or mixed populations of Meloidogyne arenaria race 1 (Ma1) and race 2 (Ma2), as affected by crop rotations of peanut 'Florigiant' and M. incognita races 1 and 3-resistant 'McNair 373' and susceptible 'Coker 371-Gold' tobacco. Infection, reproduction, and root damage by Ma2 on peanut and by Ma1 on resistant tobacco were limited in the first year. Infection, reproduction, and root-damage potentials on susceptible tobacco were similar for Ma1 and Ma2. In the mixed (1:1) population, Ma1 was dominant on peanut and Ma2 was dominant on both tobacco cultivars. Crop rotation affected the population dynamics of different nematode races. For years 2 and 3, the low numbers of Ma1 and Ma2 from a previous-year poor host increased rapidly on suitable hosts. Ma1 had greater reproduction factors ([RF] = population density at harvest/population density at preplandng) than did Ma2 and Ma1 + Ma2 in second-year peanut plots following first-year resistant tobacco, and in third-year peanut plots following second-year tobacco. In mixed infestations, Ma1 predominated over Ma2 in previous-year peanut plots, whereas Ma2 predominated over Ma1 in previous-year tobacco plots. Moderate damage on resistant tobacco was induced by Ma1 in the second year. In the third year, moderate damage on peanut was associated with 'Ma2' from previous-year peanut plots. The resistant tobacco supported sufficient reproduction of Ma1 over 2 years to effect moderate damage and yield suppression to peanut in year 3. PMID:19277278

Relationships of Initial Population Densities of Meloidogyne incognita and M. hapla to Yield of Tomato

PubMed Central

Barker, K. R.; Shoemaker, P. B.; Nelson, L. A.

1976-01-01

Microplots 80 × 100 cm, infested with varying initial population densities (Pi) of Meloidogyne incognita or M. hapla, were planted to tomato at two locations. Experiments were conducted in a sandy loam soil at Fletcher, N. C. (mountains) where the mean temperature for May to September is ca 20.7 C, and in a loamy saml at Clayton, N. C. (coastal plain) where the mean temperature for May to Septemher is ca 24.8 C. In these experimentally infested plots, M. incognita and M. hapla caused maximunt yield losses of 20-30%, at lhe mountain site with Pi of 0-12,500 eggs and larvae/500 cm³ of soil. In the coaslal plain, M. incognita suppressed yields up to 85%, and M. hapla suppressed yields up to 50% in comparison with the noninfested control. A part of the high losses at this site apparently was due to M. incognita predisposing tomato to the early blight fungus. In a second experintent, in which a nematicide was used to obtain a range of Pis (with Pi as high as 25,000/50 cm³ of soil) at Fletcher, losses due to M. incognita were as great as 50%, but similar densities of M. hapla suppressed yields by only 10-25%. Approximate threshold densities for both species ranged from 500 to 1,000 larvae and eggs (higher for surviving larvae) for the mountain site, whereas nutnbers as low as 20 larvae/500 cm³ of soil of either species caused signiticant damage in the coastal plain. Chemical soil treatments proved useful in obtaining various initial population densities; however, problems were encountered in measuring effective inoculum after such treatments, especially in the heavier soil. PMID:19308228

Forest Health Monitoring in New Hampshire, 1996-1999

Treesearch

Northeastern Research Station

2002-01-01

New Hampshire has mature forests dominated by hardwood species but with significant softwood resources. The majority of the trees are healthy with full crowns (low transparency, high density), little dieback and little damage. Red maple had higher dieback and more damage than other species. Eastern white pine had lower crown densities and little damage.

Lamb wave propagation in Z-pin reinforced co-cured composite pi-joints

NASA Astrophysics Data System (ADS)

Swenson, Eric D.; Soni, Som R.; Kapoor, Hitesh

2010-04-01

This paper presents an initial study on Lamb wave propagation characteristics in z-pin reinforced, co-cured composite pi-joints for the purposes of structural health monitoring (SHM). Pi-joint test articles were designed and created to replicate a co-cured, all composite skin-spar joint found within a typical aircraft wing structure. Because pi-joints exhibit various complex damage modes, formal studies are required if SHM systems are to be developed to monitor these types of joints for potential damage. Experiments were conducted on a undamaged (healthy) and damaged test articles where Lamb waves were excited using one lead zirconate titanate (PZT) transducer. A three-dimensional (3D) scanning laser Doppler vibrometer (LDV) was used to collect high-density scans of both the in-plane and out-of-plane velocity measurements. In the damaged test article, where delamination, matrix cracking, and fiber breakage can clearly be seen, changes in both the fundamental antisymmetric A0 and symmetric S0 Lamb wave modes are apparent. In both test articles, the effects of narrow geometry, discontinuity due to the attachment of the web, and thickness has detectable effects on Lamb wave propagation. From the comparisons between Lamb waves propagating through the undamaged and damaged test articles, it is clear that damage can be detected using Lamb waves in z-pin reinforced, co-cured composite pi-joints for this case of extensive damage.

Creep rupture analysis of a beam resting on high temperature foundation

NASA Technical Reports Server (NTRS)

Gu, Randy J.; Cozzarelli, Francis A.

1988-01-01

A simplified uniaxial strain controlled creep damage law is deduced with the use of experimental observation from a more complex strain dependent law. This creep damage law correlates the creep damage, which is interpreted as the density variation in the material, directly with the accumulated creep strain. Based on the deduced uniaxial strain controlled creep damage law, a continuum mechanical creep rupture analysis is carried out for a beam resting on a high temperature elastic (Winkler) foundation. The analysis includes the determination of the nondimensional time for initial rupture, the propagation of the rupture front with the associated thinning of the beam, and the influence of creep damage on the deflection of the beam. Creep damage starts accumulating in the beam as soon as the load is applied, and a creep rupture front develops at and propagates from the point at which the creep damage first reaches its critical value. By introducing a series of fundamental assumptions within the framework of technical Euler-Bernoulli type beam theory, a governing set of integro-differential equations is derived in terms of the nondimensional bending moment and the deflection. These governing equations are subjected to a set of interface conditions at the propagating rupture front. A numerical technique is developed to solve the governing equations together with the interface equations, and the computed results are presented and discussed in detail.

Role of tool marks inside spherical mitigation pit fabricated by micro-milling on repairing quality of damaged KH2PO4 crystal

PubMed Central

Chen, Ming-Jun; Cheng, Jian; Yuan, Xiao-Dong; Liao, Wei; Wang, Hai-Jun; Wang, Jing-He; Xiao, Yong; Li, Ming-Quan

2015-01-01

Repairing initial slight damage site into stable structures by engineering techniques is the leading strategy to mitigate the damage growth on large-size components used in laser-driven fusion facilities. For KH2PO4 crystals, serving as frequency converter and optoelectronic switch-Pockels cell, micro-milling has been proven the most promising method to fabricate these stable structures. However, tool marks inside repairing pit would be unavoidably introduced due to the wearing of milling cutter in actual repairing process. Here we quantitatively investigate the effect of tool marks on repairing quality of damaged crystal components by simulating its induced light intensification and testing the laser-induced damage threshold. We found that due to the formation of focusing hot spots and interference ripples, the light intensity is strongly enhanced with the presence of tool marks, especially for those on rear surfaces. Besides, the negative effect of tool marks is mark density dependent and multiple tool marks would aggravate the light intensification. Laser damage tests verified the role of tool marks as weak points, reducing the repairing quality. This work offers new criterion to comprehensively evaluate the quality of repaired optical surfaces to alleviate the bottleneck issue of low laser damage threshold for optical components in laser-driven fusion facilities. PMID:26399624

Electrical effects of plasma damage in p-GaN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cao, X.A.; Pearton, S.J.; Zhang, A.P.

1999-10-01

The reverse breakdown voltage of p-GaN Schottky diodes was used to measure the electrical effects of high density Ar or H{sub 2} plasma exposure. The near surface of the p-GaN became more compensated through introduction of shallow donor states whose concentration depended on ion flux, ion energy, and ion mass. At high fluxes or energies, the donor concentration exceeded 10{sup 19}&hthinsp;cm{sup {minus}3} and produced {ital p}-to-{ital n} surface conversion. The damage depth was established as {approximately}400 {Angstrom} based on electrical and wet etch rate measurements. Rapid thermal annealing at 900&hthinsp;{degree}C under a N{sub 2} ambient restored the initial electrical propertiesmore » of the p-GaN. {copyright} {ital 1999 American Institute of Physics.}« less

Safety parameter considerations of anodal transcranial Direct Current Stimulation in rats.

PubMed

Jackson, Mark P; Truong, Dennis; Brownlow, Milene L; Wagner, Jessica A; McKinley, R Andy; Bikson, Marom; Jankord, Ryan

2017-08-01

A commonly referenced transcranial Direct Current Stimulation (tDCS) safety threshold derives from tDCS lesion studies in the rat and relies on electrode current density (and related electrode charge density) to support clinical guidelines. Concerns about the role of polarity (e.g. anodal tDCS), sub-lesion threshold injury (e.g. neuroinflammatory processes), and role of electrode montage across rodent and human studies support further investigation into animal models of tDCS safety. Thirty-two anesthetized rats received anodal tDCS between 0 and 5mA for 60min through one of three epicranial electrode montages. Tissue damage was evaluated using hemotoxylin and eosin (H&E) staining, Iba-1 immunohistochemistry, and computational brain current density modeling. Brain lesion occurred after anodal tDCS at and above 0.5mA using a 25.0mm 2 electrode (electrode current density: 20.0A/m 2 ). Lesion initially occurred using smaller 10.6mm 2 or 5.3mm 2 electrodes at 0.25mA (23.5A/m 2 ) and 0.5mA (94.2A/m 2 ), respectively. Histological damage was correlated with computational brain current density predictions. Changes in microglial phenotype occurred in higher stimulation groups. Lesions were observed using anodal tDCS at an electrode current density of 20.0A/m 2 , which is below the previously reported safety threshold of 142.9A/m 2 using cathodal tDCS. The lesion area is not simply predicted by electrode current density (and so not by charge density as duration was fixed); rather computational modeling suggests average brain current density as a better predictor for anodal tDCS. Nonetheless, under the assumption that rodent epicranial stimulation is a hypersensitive model, an electrode current density of 20.0A/m 2 represents a conservative threshold for clinical tDCS, which typically uses an electrode current density of 2A/m 2 when electrodes are placed on the skin (resulting in a lower brain current density). Copyright © 2017 Elsevier Inc. All rights reserved.

On the threshold conditions for electron beam damage of asbestos amosite fibers in the transmission electron microscope (TEM).

PubMed

Martin, Joannie; Beauparlant, Martin; Sauvé, Sébastien; L'Espérance, Gilles

2016-12-01

Asbestos amosite fibers were investigated to evaluate the damage caused by a transmission electron microscope (TEM) electron beam. Since elemental x-ray intensity ratios obtained by energy dispersive x-ray spectroscopy (EDS) are commonly used for asbestos identification, the impact of beam damage on these ratios was evaluated. It was determined that the magnesium/silicon ratio best represented the damage caused to the fiber. Various tests showed that most fibers have a current density threshold above which the chemical composition of the fiber is modified. The value of this threshold current density varied depending on the fiber, regardless of fiber diameter, and in some cases could not be determined. The existence of a threshold electron dose was also demonstrated. This value was dependent on the current density used and can be increased by providing a recovery period between exposures to the electron beam. This study also established that the electron beam current is directly related to the damage rate above a current density of 165 A/cm 2 . The large number of different results obtained suggest, that in order to ensure that the amosite fibers are not damaged, analysis should be conducted below a current density of 100 A/cm 2 .

Impact strength of small icy bodies that experienced multiple collisions

NASA Astrophysics Data System (ADS)

Yasui, Minami; Hayama, Ryo; Arakawa, Masahiko

2014-05-01

Frequent collisions are common for small bodies in the Solar System, and the cumulative damage to these bodies is thought to significantly affect their evolution. It is important to study the effects of multiple impacts such as the number of impacts on the impact strength and the ejection velocity of impact fragments. Here we conducted multiple-impact experiments using a polycrystalline water ice target, varying the number of impacts from 1 to 10 times. An ice cylindrical projectile was impacted at 84-502 m s-1 by using a single-stage gas gun in a cold room between -10 and -15 °C. The impact strength of the ice target that experienced a single impact and multiple impacts is expressed by the total energy density applied to the same target, ΣQ, and this value was observed to be 77.6 J kg-1. The number of fine impact fragments at a fragment mass normalized by an initial target mass, m/Mt0 ∼ 10-6, nm, had a good correlation with the single energy density at each shot, Qj, and the relationship was shown to be nm=10·Qj1.31±0.12. We also estimated the cumulative damage of icy bodies as a total energy density accumulated by past impacts, according to the crater scaling laws proposed by Housen et al. (Housen, K.R., Schmidt, R.M., Holsapple, K.A. [1983]. J. Geophys. Res. 88, 2485-2499) of ice and the crater size distributions observed on Phoebe, a saturnian icy satellite. We found that the cumulative damage of Phoebe depended significantly on the impact speed of the impactor that formed the craters on Phoebe; and the cumulative damage was about one-third of the impact strength ΣQ* at 500 m s-1 whereas it was almost zero at 3.2 km s-1.

Compression of thick laminated composite beams with initial impact-like damage

NASA Technical Reports Server (NTRS)

Breivik, N. L.; Guerdal, Z.; Griffin, O. H., Jr.

1992-01-01

While the study of compression after impact of laminated composites has been under consideration for many years, the complexity of the damage initiated by low velocity impact has not lent itself to simple predictive models for compression strength. The damage modes due to non-penetrating, low velocity impact by large diameter objects can be simulated using quasi-static three-point bending. The resulting damage modes are less coupled and more easily characterized than actual impact damage modes. This study includes the compression testing of specimens with well documented initial damage states obtained from three-point bend testing. Compression strengths and failure modes were obtained for quasi-isotropic stacking sequences from 0.24 to 1.1 inches thick with both grouped and interspersed ply stacking. Initial damage prior to compression testing was divided into four classifications based on the type, extent, and location of the damage. These classifications are multiple through-thickness delaminations, isolated delamination, damage near the surface, and matrix cracks. Specimens from each classification were compared to specimens tested without initial damage in order to determine the effects of the initial damage on the final compression strength and failure modes. A finite element analysis was used to aid in the understanding and explanation of the experimental results.

A polycrystal plasticity model of strain localization in irradiated iron

NASA Astrophysics Data System (ADS)

Barton, Nathan R.; Arsenlis, Athanasios; Marian, Jaime

2013-02-01

At low to intermediate homologous temperatures, the degradation of structural materials performance in nuclear environments is associated with high number densities of nanometric defects produced in irradiation cascades. In polycrystalline ferritic materials, self-interstitial dislocations loops are a principal signature of irradiation damage, leading to a mechanical response characterized by increased yield strengths, decreased total strain to failure, and decreased work hardening as compared to the unirradiated behavior. Above a critical defect concentration, the material deforms by plastic flow localization, giving rise to strain softening in terms of the engineering stress-strain response. Flow localization manifests itself in the form of defect-depleted crystallographic channels, through which all dislocation activity is concentrated. In this paper, we describe the formulation of a crystal plasticity model for pure Fe embedded in a finite element polycrystal simulator and present results of uniaxial tensile deformation tests up to 10% strain. We use a tensorial damage descriptor variable to capture the evolution of the irradiation damage loop subpopulation during deformation. The model is parameterized with detailed dislocation dynamics simulations of tensile tests up to 1.5% deformation of systems containing various initial densities of irradiation defects. The coarse-grained simulations are shown to capture the essential details of the experimental stress response observed in ferritic alloys and steels. Our methodology provides an effective linkage between the defect scale, of the order of one nanometer, and the continuum scale involving multiple grain orientations.

Heterogeneous dislocation loop formation near grain boundaries in a neutron-irradiated commercial FeCrAl alloy

NASA Astrophysics Data System (ADS)

Field, Kevin G.; Briggs, Samuel A.; Hu, Xunxiang; Yamamoto, Yukinori; Howard, Richard H.; Sridharan, Kumar

2017-01-01

FeCrAl alloys are an attractive class of materials for nuclear power applications because of their increased environmental compatibility compared with more traditional nuclear materials. Preliminary studies into the radiation tolerance of FeCrAl alloys under accelerated neutron testing between 300 and 400 °C have shown post-irradiation microstructures containing dislocation loops and a Cr-rich α‧ phase. Although these initial studies established the post-irradiation microstructures, there was little to no focus on understanding the influence of pre-irradiation microstructures on this response. In this study, a well-annealed commercial FeCrAl alloy, Alkrothal 720, was neutron irradiated to 1.8 displacements per atom (dpa) at 382 °C and then the effect of random high-angle grain boundaries on the spatial distribution and size of a〈100〉 dislocation loops, a/2〈111〉 dislocation loops, and black dot damage was analyzed using on-zone scanning transmission electron microscopy. Results showed a clear heterogeneous dislocation loop formation with a/2〈111〉 dislocation loops showing an increased number density and size, black dot damage showing a significant number density decrease, and a〈100〉 dislocation loops exhibiting an increased size in the vicinity of the grain boundary. These results suggest the importance of the pre-irradiation microstructure and, specifically, defect sink density spacing to the radiation tolerance of FeCrAl alloys.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jung, Woo-Young; Seol, Jae-Bok, E-mail: jb-seol@postech.ac.kr; Kwak, Chan-Min

The compositional distribution of In atoms in InGaN/GaN multiple quantum wells is considered as one of the candidates for carrier localization center, which enhances the efficiency of the light-emitting diodes. However, two challenging issues exist in this research area. First, an inhomogeneous In distribution is initially formed by spinodal decomposition during device fabrication as revealed by transmission electron microscopy. Second, electron-beam irradiation during microscopy causes the compositional inhomogeneity of In to appear as a damage contrast. Here, a systematic approach was proposed in this study: Electron-beam with current density ranging from 0 to 20.9 A/cm{sup 2} was initially exposed to themore » surface regions during microscopy. Then, the electron-beam irradiated regions at the tip surface were further removed, and finally, atom probe tomography was performed to run the samples without beam-induced damage and to evaluate the existence of local inhomegenity of In atoms. We proved that after eliminating the electron-beam induced damage regions, no evidence of In clustering was observed in the blue-emitting InGaN/GaN devices. In addition, it is concluded that the electron-beam induced localization of In atoms is a surface-related phenomenon, and hence spinodal decomposition, which is typically responsible for such In clustering, is negligible for biaxially strained blue-emitting InGaN/GaN devices.« less

Impact Cratering Physics al Large Planetary Scales

NASA Astrophysics Data System (ADS)

Ahrens, Thomas J.

2007-06-01

Present understanding of the physics controlling formation of ˜10^3 km diameter, multi-ringed impact structures on planets were derived from the ideas of Scripps oceanographer, W. Van Dorn, University of London's, W, Murray, and, Caltech's, D. O'Keefe who modeled the vertical oscillations (gravity and elasticity restoring forces) of shock-induced melt and damaged rock within the transient crater immediately after the downward propagating hemispheric shock has processed rock (both lining, and substantially below, the transient cavity crater). The resulting very large surface wave displacements produce the characteristic concentric, multi-ringed basins, as stored energy is radiated away and also dissipated upon inducing further cracking. Initial calculational description, of the above oscillation scenario, has focused upon on properly predicting the resulting density of cracks, and, their orientations. A new numerical version of the Ashby--Sammis crack damage model is coupled to an existing shock hydrodynamics code to predict impact induced damage distributions in a series of 15--70 cm rock targets from high speed impact experiments for a range of impactor type and velocity. These are compared to results of crack damage distributions induced in crustal rocks with small arms impactors and mapped ultrasonically in recent Caltech experiments (Ai and Ahrens, 2006).

MaRIE first experiments summaries version: May 9, 2010

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sarrao, John L

2010-01-01

A predictive understanding of microstructure-based heterogeneity and its consequences for materials damage & failure and phase transformation initiation is presently lacking. Most metallic materials used in applications are polycrystalline aggregates - individual single crystals separated by grain boundaries. Most of these materials are either metallic alloys or contain impurities. In either case, there is spatial variability in their chemical composition. These materials also contain dislocations which will be distributed in some way throughout the individual grains and increase in density with deformation and typically form dislocation sub-cell arrangements - producing spatial distribution in dislocation density. Many materials also produce twinmore » or slip band structures with deformation which produce further heterogeneity within individual crystals. The objective of this first experiment is to probe the physics of dynamic solid-solid phase transformation and damage at length scales approaching those at which they nucleate in order to gain a detailed understanding of this process and the influence real material microstructure has on these events. These experiments would simultaneously be simulated by the appropriate modeling tools to further develop these predictive tools and to assist in our interpretation of experimental results.« less

Thermal shock behaviour of H and H/He-exposed tungsten at high temperature

NASA Astrophysics Data System (ADS)

Lemahieu, N.; Greuner, H.; Linke, J.; Maier, H.; Pintsuk, G.; Wirtz, M.; Van Oost, G.; Noterdaeme, J.-M.

2016-02-01

Polycrystalline tungsten samples were characterized and exposed to a pure H beam or mixed H/He beam containing 6% He in GLADIS at a surface temperature of 600 °C, 1000 °C, or 1500 °C. After 5400 s of exposure time with a heat flux of 10.5 MW m-2, the total accumulated fluence of 2 × 1025 m-2 was reached. Thereafter, edge localized mode (ELM)-like thermal shocks with a duration of 1 ms and an absorbed power density of 190 MW m-2 and 380 MW m-2 were applied on the samples in JUDITH 1. During the thermal shocks, the base temperature was kept at 1000 °C. The ELM-experiments with the lowest transient power density did not result in any detected damage. The other tests showed the beginning of crack formation for every sample, except the sample pre-exposed with the pure H-beam at 1500 °C in GLADIS. This sample was roughened, but did not show any crack initiation. With exception to the roughened sample, the category of ELM-induced damage for the pre-exposed samples is identical to the reference tests without pre-exposure to a particle flux.

Laser-induced Hertzian fractures in silica initiated by metal micro-particles on the exit surface

DOE PAGES

Feigenbaum, Eyal; Raman, Rajesh N.; Cross, David; ...

2016-05-16

Laser-induced Hertzian fractures on the exit surface of silica glass are found to result from metal surface-bound micro particles. Two types of metal micro-spheres are studied (stainless-steel and Al) using ultraviolet laser light. The fracture initiation probability curve as a function of fluence is obtained, resulting in an initiation threshold fluence of 11.1 ± 4.7 J/cm 2 and 16.5 ± 4.5 J/cm 2 for the SS and Al particles, accordingly. The modified damage density curve is calculated based on the fracture probability. Here, the calculated momentum coupling coefficient linking incident laser fluence to the resulting plasma pressure is found tomore » be similar for both particles: 32.6 ± 15.4 KN/J and 28.1 ± 10.4 KN/J for the SS and Al cases accordingly.« less

Micromechanics of soil responses in cyclic simple shear tests

NASA Astrophysics Data System (ADS)

Cui, Liang; Bhattacharya, Subhamoy; Nikitas, George

2017-06-01

Offshore wind turbine (OWT) foundations are subjected to a combination of cyclic and dynamic loading arising from wind, wave, rotor and blade shadowing. Under cyclic loading, most soils change their characteristics including stiffness, which may cause the system natural frequency to approach the loading frequency and lead to unplanned resonance and system damage or even collapse. To investigate such changes and the underlying micromechanics, a series of cyclic simple shear tests were performed on the RedHill 110 sand with different shear strain amplitudes, vertical stresses and initial relative densities of soil. The test results showed that: (a) Vertical accumulated strain is proportional to the shear strain amplitude but inversely proportional to relative density of soil; (b) Shear modulus increases rapidly in the initial loading cycles and then the rate of increase diminishes and the shear modulus remains below an asymptote; (c) Shear modulus increases with increasing vertical stress and relative density, but decreasing with increasing strain amplitude. Coupled DEM simulations were performed using PFC2D to analyse the micromechanics underlying the cyclic behaviour of soils. Micromechanical parameters (e.g. fabric tensor, coordination number) were examined to explore the reasons for the various cyclic responses to different shear strain amplitudes or vertical stresses. Both coordination number and magnitude of fabric anisotropy contribute to the increasing shear modulus.

Models for integrated pest control and their biological implications.

PubMed

Tang, Sanyi; Cheke, Robert A

2008-09-01

Successful integrated pest management (IPM) control programmes depend on many factors which include host-parasitoid ratios, starting densities, timings of parasitoid releases, dosages and timings of insecticide applications and levels of host-feeding and parasitism. Mathematical models can help us to clarify and predict the effects of such factors on the stability of host-parasitoid systems, which we illustrate here by extending the classical continuous and discrete host-parasitoid models to include an IPM control programme. The results indicate that one of three control methods can maintain the host level below the economic threshold (ET) in relation to different ET levels, initial densities of host and parasitoid populations and host-parasitoid ratios. The effects of host intrinsic growth rate and parasitoid searching efficiency on host mean outbreak period can be calculated numerically from the models presented. The instantaneous pest killing rate of an insecticide application is also estimated from the models. The results imply that the modelling methods described can help in the design of appropriate control strategies and assist management decision-making. The results also indicate that a high initial density of parasitoids (such as in inundative releases) and high parasitoid inter-generational survival rates will lead to more frequent host outbreaks and, therefore, greater economic damage. The biological implications of this counter intuitive result are discussed.

Damage instability and Earthquake nucleation

NASA Astrophysics Data System (ADS)

Ionescu, I. R.; Gomez, Q.; Campillo, M.; Jia, X.

2017-12-01

Earthquake nucleation (initiation) is usually associated to the loss of the stability of the geological structure under a slip-weakening friction acting on the fault. The key parameters involved in the stability of the fault are the stress drop, the critical slip distance but also the elastic stiffness of the surrounding materials (rocks). We want to explore here how the nucleation phenomena are correlated to the material softening during damage accumulation by dynamic and/or quasi-static processes. Since damage models are describing micro-cracks growth, which is generally an unstable phenomenon, it is natural to expect some loss of stability on the associated micro-mechanics based models. If the model accurately captures the material behavior, then this can be due to the unstable nature of the brittle material itself. We obtained stability criteria at the microscopic scale, which are related to a large class of damage models. We show that for a given continuous strain history the quasi-static or dynamic problems are instable or ill-posed (multiplicity of material responses) and whatever the selection rule is adopted, shocks (time discontinuities) will occur. We show that the quasi-static equilibria chosen by the "perfect delay convention" is always stable. These stability criteria are used to analyze how NIC (Non Interacting Crack) effective elasticity associated to "self similar growth" model work in some special configurations (one family of micro-cracks in mode I, II and III and in plane strain or plain stress). In each case we determine a critical crack density parameter and critical micro-crack radius (length) which distinguish between stable and unstable behaviors. This critical crack density depends only on the chosen configuration and on the Poisson ratio.

Personal characteristics relating to radium loss over a decade or more in radium dial workers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stebbings, J.H.; Jansen, A.; Kotek, T.J.

1986-01-01

Personal habits and biological characteristics of 42 female Illinois radium workers first employed during the 1920s were analyzed in relationship to radium loss in late adult life. The 42 women met the criteria that they first were examined between 1957 and 1969 and are no longer employed, have had two or more radium body-burden measurements by gamma spectroscopy, 10-year minimum interval exists between initial and final measurements, and exhibit a RaC body burden in 1970 or later of greater than or equal to.137 kBQ. High radium body burdens are associated with decreased rates of radium elimination, as previously described. However,more » the most powerful predictor was coffee/tea consumption, increased consumption being associated with increased rates of radium elimination and explaining approx.35% of the variance. The effect persisted after deletion of smokers and subjects with x-ray evidence of bone damage. Weight/height ratios were positively associated with radium excretion. Individuals smoking cigarettes throughout the study period had significantly low rates of elimination of radium, similar to subjects with x-ray evidence of significant radiation-induced bone damage. Both smokers and subjects with x-ray evidence of radiation damage to bone had low weight/height ratios, suggesting that biological promoters of radiation damage to bone may exist. Rates of radium elimination were significantly associated with (linear) bone density, demonstrating that rates of loss of radium cannot be assumed to be independent of adult or postmenopausal bone density losses. Number of children and age of menopause did not have demonstrable effects on radium elimination. 9 refs., 2 figs., 7 tabs.« less

Computational micromechanics of dynamic compressive loading of a brittle polycrystalline material using a distribution of grain boundary properties

NASA Astrophysics Data System (ADS)

Kraft, R. H.; Molinari, J. F.; Ramesh, K. T.; Warner, D. H.

A two-dimensional finite element model is used to investigate compressive loading of a brittle ceramic. Intergranular cracking in the microstructure is captured explicitly by using a distribution of cohesive interfaces. The addition of confining stress increases the maximum strength and if high enough, can allow the effective material response to reach large strains before failure. Increasing the friction at the grain boundaries also increases the maximum strength until saturation of the strength is approached. Above a transitional strain rate, increasing the rate-of-deformation also increases the strength and as the strain rate increases, fragment sizes of the damaged specimen decrease. The effects of flaws within the specimen were investigated using a random distribution at various initial flaw densities. The model is able to capture an effective modulus change and degradation of strength as the initial flaw density increases. Effects of confinement, friction, and spatial distribution of flaws seem to depend on the crack coalescence and dilatation of the specimen, while strain-rate effects are result of inertial resistance to motion.

The initiation and growth of delaminations induced by matrix microcracks in laminated composites

NASA Technical Reports Server (NTRS)

Nairn, J. A.; Hu, S.

1992-01-01

A recent variational mechanics analysis of microcracking damage in cross-ply laminates of the form /(S)/90n/s, where (S) is any orthotropic sublaminate much stiffer than /90n/, has been extended to account for the presence of delaminations emanating from the tips of microcracks in the /90 2n/T sublaminate. The new two-dimensional stress analysis is used to calculate the total strain energy, effective modulus, and longitudinal thermal expansion coefficient for a laminate having microcracks and delaminations. These results are used to calculate the energy release rate for the initiation and growth of a delamination induced by a matrix microcrack. At low crack densities, /(S)/90n/s laminates are expected to fail by microcracking and to show little or no delamination. At some critical crack density, which is a function of laminate structure and material properties, the energy release rate for delamination exceeds that for microcracking and delamination is predicted to dominate over microcracking. A quasi-three-dimensional model is used to predict the propagation of arbitrarily shaped delamination fronts. All predictions agree with experimental observations.

Stability Study on Steel Structural Columns with Initial Blast Damage under High Temperatures

NASA Astrophysics Data System (ADS)

Baoxin, Qi; Yan, Shi; Li, Peng

2018-03-01

Blast may bring light-weight steel columns with initial damages, resulting in lowering its critical fire-resistance temperature whose reduced amplitude is relevant to the form and degree of the damages. Finite element analysis software ANSYS was used in the paper to analyze the issue of the fire-resistance temperature of the column with the blast damages, and the coupling method for heat and structure was applied during the simulation. The emphasis was laid on parametric factors of axial compression ratio, the form and the degree of the initial damages, as well as the confined condition at the ends of the columns. The numerical results showed that the fire-resistance temperature will lower as increasing of the axial compression ratio, the form and the degree of the initial damages and it will be also affected by the restraint conditions at the ends of the columns. The critical stress formula with initial bending damage under elevated temperature was set up under flexural small deformation condition, then the stability coefficient was determined and the method for evaluating the limit temperature of the column was put forward. The theoretical result was also compared with that of the finite element method (FEM). The results both showed that the stability capacity for the damaged columns was dramatically reduced as increasing the temperature and the initial damage level.

Why do some intervertebral discs degenerate, when others (in the same spine) do not?

PubMed

Adams, Michael A; Lama, Polly; Zehra, Uruj; Dolan, Patricia

2015-03-01

This review suggests why some discs degenerate rather than age normally. Intervertebral discs are avascular pads of fibrocartilage that allow movement between vertebral bodies. Human discs have a low cell density and a limited ability to adapt to mechanical demands. With increasing age, the matrix becomes yellowed, fibrous, and brittle, but if disc structure remains intact, there is little impairment in function, and minimal ingrowth of blood vessels or nerves. Approximately half of old lumbar discs degenerate in the sense of becoming physically disrupted. The posterior annulus and lower lumbar discs are most affected, presumably because they are most heavily loaded. Age and genetic inheritance can weaken discs to such an extent that they are physically disrupted during everyday activities. Damage to the endplate or annulus typically decompresses the nucleus, concentrates stress within the annulus, and allows ingrowth of nerves and blood vessels. Matrix disruption progresses by mechanical and biological means. The site of initial damage leads to two disc degeneration "phenotypes": endplate-driven degeneration is common in the upper lumbar and thoracic spine, and annulus-driven degeneration is common at L4-S1. Discogenic back pain can be initiated by tissue disruption, and amplified by inflammation and infection. Healing is possible in the outer annulus only, where cell density is highest. We conclude that some discs degenerate because they are disrupted by excessive mechanical loading. This can occur without trauma if tissues are weakened by age and genetic inheritance. Moderate mechanical loading, in contrast, strengthens all spinal tissues, including discs. © 2014 Wiley Periodicals, Inc.

Intraspecific competition facilitates the evolution of tolerance to insect damage in the perennial plant Solanum carolinense.

PubMed

McNutt, David W; Halpern, Stacey L; Barrows, Kahaili; Underwood, Nora

2012-12-01

Tolerance to herbivory (the degree to which plants maintain fitness after damage) is a key component of plant defense, so understanding how natural selection and evolutionary constraints act on tolerance traits is important to general theories of plant-herbivore interactions. These factors may be affected by plant competition, which often interacts with damage to influence trait expression and fitness. However, few studies have manipulated competitor density to examine the evolutionary effects of competition on tolerance. In this study, we tested whether intraspecific competition affects four aspects of the evolution of tolerance to herbivory in the perennial plant Solanum carolinense: phenotypic expression, expression of genetic variation, the adaptive value of tolerance, and costs of tolerance. We manipulated insect damage and intraspecific competition for clonal lines of S. carolinense in a greenhouse experiment, and measured tolerance in terms of sexual and asexual fitness components. Compared to plants growing at low density, plants growing at high density had greater expression of and genetic variation in tolerance, and experienced greater fitness benefits from tolerance when damaged. Tolerance was not costly for plants growing at either density, and only plants growing at low density benefited from tolerance when undamaged, perhaps due to greater intrinsic growth rates of more tolerant genotypes. These results suggest that competition is likely to facilitate the evolution of tolerance in S. carolinense, and perhaps in other plants that regularly experience competition, while spatio-temporal variation in density may maintain genetic variation in tolerance.

PHARMACOLOGIC SUPPRESSION OF OXIDATIVE DAMAGE AND DENDRITIC DEGENERATION FOLLOWING KAINIC ACID-INDUCED EXCITOTOXICITY IN MOUSE CEREBRUM

PubMed Central

Zaja-Milatovic, Snjezana; Gupta, Ramesh C.; Aschner, Michael; Montine, Thomas J.; Milatovic, Dejan

2008-01-01

Intense seizure activity associated with status epilepticus and excitatory amino acid (EAA) imbalance initiates oxidative damage and neuronal injury in CA1 of the ventral hippocampus. We tested the hypothesis that dendritic degeneration of pyramidal neurons in the CA1 hippocampal area resulting from seizure-induced neurotoxicity is modulated by cerebral oxidative damage. Kainic acid (KA, 1 nmol/5 μl) was injected intracerebroventricularly to C57Bl/6 mice. F2-isoprostanes (F2-IsoPs) and F4-neuroprostanes (F4-NeuroPs) were used as surrogate measures of in vivo oxidative stress and biomarkers of lipid peroxidation. Nitric oxide synthase (NOS) activity was quantified by evaluating citrulline level and pyramidal neuron dendrites and spines were evaluated using rapid Golgi stains and a Neurolucida system. KA produced severe seizures in mice immediately after its administration and a significant (p<0.001) increase in F2-IsoPs, F4-NeuroPs and citrulline levels were seen 30 min following treatment. At the same time, hippocampal pyramidal neurons showed significant (p<0.001) reduction in dendritic length and spine density. In contrast, no significant change in neuronal dendrite and spine density or F2-IsoP, F4-NeuroPs and citrulline levels were found in mice pretreated with Vitamin E (α-tocopherol, 100 mg/kg, ip) for 3 days, or with N-tert-butyl-α-phenylnitrone (PBN, 200 mg/kg, ip) or ibuprofen (inhibitors of cyclooxygenase, COX, 14 μg/ml of drinking water) for 2 weeks prior to KA treatment. These findings indicate novel interactions among free radical-induced generation of F2-IsoPs and F4-NeuroPs, nitric oxide and dendritic degeneration, closely associate oxidative damage to neuronal membranes with degeneration of the dendritic system, and point to possible interventions to limit severe damage in acute neurological disorders. PMID:18556069

Effects of the herbicide glyphosate on avian community structure in the Oregon coast range

USGS Publications Warehouse

Morrison, M.L.; Meslow, E.C.

1984-01-01

A study was conducted on vegetative changes induced by the herbicide glyphosate, and the resultant habitat use of birds nesting on two clearcuts in western Oregon. About 23 percent of total plant cover was initially damaged by aerial application of glyphosate. Most measures of vegetation on the treated site decreased relative to the untreated site 1 year after glyphosate application. By 2 years post-spray, vegetation on the treated site had recovered to near pre-spray status. No difference in density of the bird community was evident between treated and untreated sites during all years of study although individual species densities were modified. Several bird species decreased their use of shrub cover, and increased their use of deciduous trees 1 year after treatment. By 2 years post-spray, many species had returned to pre-spray use of most measured habitat components. Results indicated that application of glyphosate can modify the density and habitat use of birds.

Crustal Rock: Recorder of Oblique Impactor Meteoroid Trajectories

NASA Astrophysics Data System (ADS)

Ahrens, Thomas J.

2005-07-01

Oblique impact experiments in which 2g lead bullets strike samples of San Marcos granite and Bedford limestone at 1.2 km/s induce zones of increased crack density (termed shocked damage) which result in local decreases in bulk and shear moduli that results in maximum decreases of 30-40% in compressional and shear wave velocity (Budianski and O'Connell). Initial computer simulation of oblique impacts of meteorites (Pierazzo and Melosh) demonstrate the congruence of peak shock stress trajectory with the pre-impact meteoroid trajectory. We measure (Ai and Ahrens) via multi-beam (˜ 300) tomographic inversion, the sub-impact surface distribution of damage from the decreases in compressional wave velocity in the 20 x 20 x 15 cm rock target. The damage profiles for oblique impacts are markedly asymmetric (in plane of pre-impact meteoroid pre-impact trajectory) beneath the nearly round excavated craters. Thus, meteorite trajectory information can be recorded in planetary surfaces. Asymmetric sub-surface seismic velocity profiles beneath the Manson (Iowa) and Ries (Germany) impact craters demonstrate that pre-impact meteoroid trajectories records remain accessible for at least ˜ 10 ^ 8 years.

Data-Science Analysis of the Macro-scale Features Governing the Corrosion to Crack Transition in AA7050-T7451

NASA Astrophysics Data System (ADS)

Co, Noelle Easter C.; Brown, Donald E.; Burns, James T.

2018-05-01

This study applies data science approaches (random forest and logistic regression) to determine the extent to which macro-scale corrosion damage features govern the crack formation behavior in AA7050-T7451. Each corrosion morphology has a set of corresponding predictor variables (pit depth, volume, area, diameter, pit density, total fissure length, surface roughness metrics, etc.) describing the shape of the corrosion damage. The values of the predictor variables are obtained from white light interferometry, x-ray tomography, and scanning electron microscope imaging of the corrosion damage. A permutation test is employed to assess the significance of the logistic and random forest model predictions. Results indicate minimal relationship between the macro-scale corrosion feature predictor variables and fatigue crack initiation. These findings suggest that the macro-scale corrosion features and their interactions do not solely govern the crack formation behavior. While these results do not imply that the macro-features have no impact, they do suggest that additional parameters must be considered to rigorously inform the crack formation location.

Linking Grain Boundary Microstructure to Stress Corrosion Cracking of Cold Rolled Alloy 690 in PWR Primary Water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bruemmer, Stephen M.; Olszta, Matthew J.; Toloczko, Mychailo B.

2012-10-01

Grain boundary microstructures and microchemistries are examined in cold-rolled alloy 690 tubing and plate materials and comparisons are made to intergranular stress corrosion cracking (IGSCC) behavior in PWR primary water. Chromium carbide precipitation is found to be a key aspect for materials in both the mill annealed and thermally treated conditions. Cold rolling to high levels of reduction was discovered to produce small IG voids and cracked carbides in alloys with a high density of grain boundary carbides. The degree of permanent grain boundary damage from cold rolling was found to depend directly on the initial IG carbide distribution. Formore » the same degree of cold rolling, alloys with few IG precipitates exhibited much less permanent damage. Although this difference in grain boundary damage appears to correlate with measured SCC growth rates, crack tip examinations reveal that cracked carbides appeared to blunt propagation of IGSCC cracks in many cases. Preliminary results suggest that the localized grain boundary strains and stresses produced during cold rolling promote IGSCC susceptibility and not the cracked carbides and voids.« less

Delayed Exercise Promotes Remodeling in Sub-Rupture Fatigue Damaged Tendons

PubMed Central

Bell, R.; Boniello, M.R.; Gendron, N.R.; Flatow, E.L.; Andarawis-Puri, N.

2015-01-01

Tendinopathy is a common musculoskeletal injury whose treatment is limited by ineffective therapeutic interventions. Previously we have shown that tendons ineffectively repair early sub-rupture fatigue damage. In contrast, physiological exercise has been shown to promote remodeling of healthy tendons but its utility as a therapeutic to promote repair of fatigue damaged tendons remains unknown. Therefore, the objective of this study was to assess the utility of exercise initiated 1 and 14 days after onset of fatigue damage to promote structural repair in fatigue damaged tendons. We hypothesized that exercise initiated 14 days after fatigue loading would promote remodeling as indicated by a decrease in area of collagen matrix damage, increased procollagen I and decorin, while decreasing proteins indicative of tendinopathy. Rats engaged in 6-week exercise for 30 min/day or 60 min/day starting 1 or 14 days after fatigue loading. Initiating exercise 1-day after onset of fatigue injury led to exacerbation of matrix damage, particularly at the tendon insertion. Initiating exercise 14 days after onset of fatigue injury led to remodeling of damaged regions in the midsubstance and collagen synthesis at the insertion. Physiological exercise applied after the initial biological response to injury has dampened can potentially promote remodeling of damaged tendons. PMID:25732052

Development of binomial sequential sampling plans for forecasting Listronotus maculicollis (Coleoptera: Curculionidae) larvae based on the relationship to adult counts and turfgrass damage.

PubMed

McGraw, Benjamin A; Koppenhöfer, Albrecht M

2009-06-01

Binomial sequential sampling plans were developed to forecast weevil Listronotus maculicollis Kirby (Coleoptera: Curculionidae), larval damage to golf course turfgrass and aid in the development of integrated pest management programs for the weevil. Populations of emerging overwintered adults were sampled over a 2-yr period to determine the relationship between adult counts, larval density, and turfgrass damage. Larval density and composition of preferred host plants (Poa annua L.) significantly affected the expression of turfgrass damage. Multiple regression indicates that damage may occur in moderately mixed P. annua stands with as few as 10 larvae per 0.09 m2. However, > 150 larvae were required before damage became apparent in pure Agrostis stolonifera L. plots. Adult counts during peaks in emergence as well as cumulative counts across the emergence period were significantly correlated to future densities of larvae. Eight binomial sequential sampling plans based on two tally thresholds for classifying infestation (T = 1 and two adults) and four adult density thresholds (0.5, 0.85, 1.15, and 1.35 per 3.34 m2) were developed to forecast the likelihood of turfgrass damage by using adult counts during peak emergence. Resampling for validation of sample plans software was used to validate sampling plans with field-collected data sets. All sampling plans were found to deliver accurate classifications (correct decisions were made between 84.4 and 96.8%) in a practical timeframe (average sampling cost < 22.7 min).

Impact behaviour of auxetic Kevlar®/ epoxy composites

NASA Astrophysics Data System (ADS)

Yang, S.; Chalivendra, V. B.; Kim, Y. K.

2017-10-01

Experimental study was performed to investigate fracture and impact properties of novel Auxetic Kevlar® laminated composites. For comparison, standard Kevlar® woven composites with and without polyurethane surface treatment were also considered in this study. For these three composites, short nylon fibers of two different fiber lengths and three different fiber densities were flocked between laminates. Vacuum infusion process along with optimized compaction was employed to fabricate composites. The double cantilever beam configuration was used to investigate the fracture properties. The Auxetic Kevlar® composites showed a significant improvement of 225% in fracture toughness compared to regular woven Kevlar® composites. Furthermore, the initiation toughness was increased by 577% with the application of flocking in Auxetic Kevlar®. During impact testing, the Auxetic Kevlar® reinforced composites showed a significant reduction in damaged area compared to woven counterpart. On the other hand, the reduction in damaged area influenced the reduction in impact energy absorption.

Increased consumer density reduces the strength of neighborhood effects in a model system.

PubMed

Merwin, Andrew C; Underwood, Nora; Inouye, Brian D

2017-11-01

An individual's susceptibility to attack can be influenced by conspecific and heterospecifics neighbors. Predicting how these neighborhood effects contribute to population-level processes such as competition and evolution requires an understanding of how the strength of neighborhood effects is modified by changes in the abundances of both consumers and neighboring resource species. We show for the first time that consumer density can interact with the density and frequency of neighboring organisms to determine the magnitude of neighborhood effects. We used the bean beetle, Callosobruchus maculatus, and two of its host beans, Vigna unguiculata and V. radiata, to perform a response-surface experiment with a range of resource densities and three consumer densities. At low beetle density, damage to beans was reduced with increasing conspecific density (i.e., resource dilution) and damage to the less preferred host, V. unguiculata, was reduced with increasing V. radiata frequency (i.e., frequency-dependent associational resistance). As beetle density increased, however, neighborhood effects were reduced; at the highest beetle densities neither focal nor neighboring resource density nor frequency influenced damage. These findings illustrate the importance of consumer density in mediating indirect effects among resources, and suggest that accounting for consumer density may improve our ability to predict population-level outcomes of neighborhood effects and our use of them in applications such as mixed-crop pest management. © 2017 by the Ecological Society of America.

Laser Induced Damage of Potassium Dihydrogen Phosphate (KDP) Optical Crystal Machined by Water Dissolution Ultra-Precision Polishing Method

PubMed Central

Gao, Hang; Wang, Xu; Guo, Dongming; Liu, Ziyuan

2018-01-01

Laser induced damage threshold (LIDT) is an important optical indicator for nonlinear Potassium Dihydrogen Phosphate (KDP) crystal used in high power laser systems. In this study, KDP optical crystals are initially machined with single point diamond turning (SPDT), followed by water dissolution ultra-precision polishing (WDUP) and then tested with 355 nm nanosecond pulsed-lasers. Power spectral density (PSD) analysis shows that WDUP process eliminates the laser-detrimental spatial frequencies band of micro-waviness on SPDT machined surface and consequently decreases its modulation effect on the laser beams. The laser test results show that LIDT of WDUP machined crystal improves and its stability has a significant increase by 72.1% compared with that of SPDT. Moreover, a subsequent ultrasonic assisted solvent cleaning process is suggested to have a positive effect on the laser performance of machined KDP crystal. Damage crater investigation indicates that the damage morphologies exhibit highly thermal explosion features of melted cores and brittle fractures of periphery material, which can be described with the classic thermal explosion model. The comparison result demonstrates that damage mechanisms for SPDT and WDUP machined crystal are the same and WDUP process reveals the real bulk laser resistance of KDP optical crystal by removing the micro-waviness and subsurface damage on SPDT machined surface. This improvement of WDUP method makes the LIDT more accurate and will be beneficial to the laser performance of KDP crystal. PMID:29534032

Object Kinetic Monte Carlo Simulations of Radiation Damage In Bulk Tungsten

NASA Astrophysics Data System (ADS)

Nandipati, Giridhar; Setyawan, Wahyu; Heinisch, Howard; Roche, Kenneth; Kurtz, Richard; Wirth, Brian

2015-11-01

Results are presented for the evolution of radiation damage in bulk tungsten investigated using the object KMC simulation tool, KSOME, as a function of dose, dose rate and primary knock-on atom (PKA) energies in the range of 10 to 100 keV, at temperatures of 300, 1025 and 2050 K. At 300 K, the number density of vacancies changes minimally with dose rate while the number density of vacancy clusters slightly decreases with dose rate indicating that larger clusters are formed at higher dose rates. Although the average vacancy cluster size increases slightly, the vast majority exists as mono-vacancies. At 1025 K void lattice formation was observed at all dose rates for cascades below 60 keV and at lower dose rates for higher PKA energies. After the appearance of initial features of the void lattice, vacancy cluster density increased minimally while the average vacancy cluster size increases rapidly with dose. At 2050 K, no accumulation of defects was observed over a broad range of dose rates for all PKA energies studied in this work. Further comparisons of results of irradiation simulations at various dose rates and PKA spectra, representative of the High Flux Isotope Reactor and future fusion relevant irradiation facilities will be discussed. The U.S. Department of Energy, Office of Fusion Energy Sciences (FES) and Office of Advanced Scientific Computing Research (ASCR) has supported this study through the SciDAC-3 program.

Pyroclastic Density Current Hazards in the Auckland Volcanic Field, New Zealand

NASA Astrophysics Data System (ADS)

Brand, B. D.; Gravley, D.; Clarke, A. B.; Bloomberg, S. H.

2012-12-01

The most dangerous phenomena associated with phreatomagmatic eruptions are dilute pyroclastic density currents (PDCs). These are turbulent, ground-hugging sediment gravity currents that travel radially away from the explosive center at up to 100 m/s. The Auckland Volcanic Field (AVF), New Zealand, consists of approximately 50 eruptive centers, at least 39 of which have had explosive phreatomagmatic behaviour. A primary concern for future AVF eruptions is the impact of dilute PDCs in and around the Auckland area. We combine field observations from the Maungataketake tuff ring, which has one of the best exposures of dilute PDC deposits in the AVF, with a quantitative model for flow of and sedimentation from a radially-spreading, steady-state, depth-averaged dilute PDC (modified from Bursik and Woods, 1996 Bull Volcanol 58:175-193). The model allows us to explore the depositional mechanisms, macroscale current dynamics, and potential impact on societal infrastructure of dilute PDCs from a future AVF eruption. The lower portion of the Maungataketake tuff ring pyroclastic deposits contains trunks, limbs and fragments of Podocarp trees (<1 m in diameter) that were blown down by dilute PDCs up to 0.7-0.9 km from the vent. Beyond this trees were encapsulated and buried in growth position up to the total runout distance of 1.6-1.8 km. This observation suggests that the dynamic pressure of the current quickly dropped as it travelled away from source. Using the tree diameter and yield strength of the wood, we calculate that dynamic pressures (Pdyn) of 10-75 kPa are necessary to topple trees of this size and composition. Thus the two main criteria for model success based on the field evidence include (a) Pdyn must be >10 kPa nearer than 0.9 km to the vent, and <10 kPa beyond 0.9 km, and (b) the total run-out distance must be between 1.6 and 1.8 km. Model results suggest the two main forces controlling the runout distance and Pdyn over the extent of the current are sedimentation rate and entrainment of ambient atmosphere, which are a function of the grain size and initial bulk density, thickness and velocity of a given current. Initial velocities of 60 m s-1, initial bulk densities of 35 kg m-3 and initial current thickness of 70 m are the input parameters that reproduce the best fit to our field data. This preliminary validation of the model allows us to estimate the impact of dilute PDCs from future larger phreatomagmatic eruptions. In the case of a dilute PDC traveling 5-7 km from source: Pdyn >35 kPa can be expected within 3 km from source, ensuring complete destruction of the area; Pdyn > 15 kPa up to 5 km from source, resulting in heavy structural damage to most buildings and near destruction of weaker buildings; and Pdyn <10 kPa at ~6 km from source, resulting in severe damage to weaker structures at least up to this distance. This exercise illustrates our ability to combine field measurements with numerical techniques to explore controlling parameters of dilute PDC dynamics. These tools can be used to understand and estimate the damage potential and extent of past and future eruptions in the AVF or other similar volcanically active regions.

Southern pine beetle in loblolly pine: simulating within stand interactions using the process model SPBLOBTHIN

Treesearch

Brian Strom; J. R. Meeker; J. Bishir; James Roberds; X. Wan

2016-01-01

Pine stand density is a key determinant of damage resulting from attacks by the southern pine beetle (SPB, Dendroctonus frontalis Zimm.). High-density stands of maturing loblolly pine (Pinus taeda L.) are at high risk for losses to SPB, and reducing stand density is the primary tool available to forest managers for preventing and mitigating damage. Field studies are...

Numerical and Experimental Validation of a New Damage Initiation Criterion

NASA Astrophysics Data System (ADS)

Sadhinoch, M.; Atzema, E. H.; Perdahcioglu, E. S.; van den Boogaard, A. H.

2017-09-01

Most commercial finite element software packages, like Abaqus, have a built-in coupled damage model where a damage evolution needs to be defined in terms of a single fracture energy value for all stress states. The Johnson-Cook criterion has been modified to be Lode parameter dependent and this Modified Johnson-Cook (MJC) criterion is used as a Damage Initiation Surface (DIS) in combination with the built-in Abaqus ductile damage model. An exponential damage evolution law has been used with a single fracture energy value. Ultimately, the simulated force-displacement curves are compared with experiments to validate the MJC criterion. 7 out of 9 fracture experiments were predicted accurately. The limitations and accuracy of the failure predictions of the newly developed damage initiation criterion will be discussed shortly.

How Predictable Are the Behavioral Responses of Insects to Herbivore Induced Changes in Plants? Responses of Two Congeneric Thrips to Induced Cotton Plants

PubMed Central

Silva, Rehan; Furlong, Michael J.; Wilson, Lewis J.; Walter, Gimme H.

2013-01-01

Changes in plants following insect attack are referred to as induced responses. These responses are widely viewed as a form of defence against further insect attack. In the current study we explore whether it is possible to make generalizations about induced plant responses given the unpredictability and variability observed in insect-plant interactions. Experiments were conducted to test for consistency in the responses of two congeneric thrips, Frankliniella schultzei Trybom and Frankliniella occidentalis Pergrande (Thysanoptera: Thripidae) to cotton seedlings (Gossypium hirsutum Linneaus (Malvales: Malvaceae)) damaged by various insect herbivores. In dual-choice experiments that compared intact and damaged cotton seedlings, F. schultzei was attracted to seedlings damaged by Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), Tetranychus urticae (Koch) (Trombidiforms: Tetranychidae), Tenebrio molitor Linnaeus (Coleoptera: Tenebrionidae), F. schultzei and F. occidentalis but not to mechanically damaged seedlings. In similar tests, F. occidentalis was attracted to undamaged cotton seedlings when simultaneously exposed to seedlings damaged by H. armigera, T. molitor or F. occidentalis. However, when exposed to F. schultzei or T. urticae damaged plants, F. occidentalis was more attracted towards damaged plants. A quantitative relationship was also apparent, F. schultzei showed increased attraction to damaged seedlings as the density of T. urticae or F. schultzei increased. In contrast, although F. occidentalis demonstrated increased attraction to plants damaged by higher densities of T. urticae, there was a negative relationship between attraction and the density of damaging conspecifics. Both species showed greater attraction to T. urticae damaged seedlings than to seedlings damaged by conspecifics. Results demonstrate that the responses of both species of thrips were context dependent, making generalizations difficult to formulate. PMID:23691075

Heterogeneous dislocation loop formation near grain boundaries in a neutron-irradiated commercial FeCrAl alloy

DOE PAGES

Field, Kevin G.; Briggs, Samuel A.; Hu, Xunxiang; ...

2016-11-01

FeCrAl alloys are an attractive materials class for nuclear power applications due to their increased environmental compatibility over more traditional nuclear materials. Preliminary studies into the radiation tolerance of FeCrAl alloys under accelerated neutron testing between 300-400 °C have shown post-irradiation microstructures containing dislocation loops and Cr-rich ' phase. Although these initial works established the post-irradiation microstructures, little to no focus was applied towards the influence of pre-irradiation microstructures on this response. Here, a well annealed commercial FeCrAl alloy, Alkrothal 720, was neutron irradiated to 1.8 dpa at 382 °C and then the role of random high angle grain boundariesmore » on the spatial distribution and size of dislocation loops, dislocation loops, and black dot damage was analyzed using on-zone scanning transmission electron microscopy. Results showed a clear heterogeneous dislocation loop formation with dislocation loops showing an increased number density and size, black dot damage showing a significant number density decrease, and an increased size of dislocation loops in the vicinity directly adjacent to the grain boundary. Lastly, these results suggest the importance of the pre-irradiation microstructure on the radiation tolerance of FeCrAl alloys.« less

Ultrasonic survey and monitoring of the excavation damaged zone in callovo-oxfordian argillaceous rock

NASA Astrophysics Data System (ADS)

Balland, C.; Morel, J.

2010-12-01

The mining of galleries in geological claystones formation induces a stress redistribution that can cause a microfissuration of the rock around the works which, by coalescence, may generate macro field fractures. In this area called EDZ (Excavation Damaged Zone), permeability is expected to increase drastically. Those induced cracking along with increased permeability, shall be taken into account in safety assessment of deep geological disposal. Ultrasonic survey and monitoring experiments have been performed in the Underground Research Laboratory of Meuse/Haute-Marne to contribute to the understanding of the extension and evolution of this damage. Ultrasonic devices have been deployed around shaft, gallery, slot and borehole to characterize the initiation, the extension and the level of the EDZ, P-wave velocity being very sensitive to the mechanical rock perturbations. The analysis of spatial and temporal velocity field changes gave reliable information on the cracks characteristics of the especially about their opening or their preferential orientation. The results provided by an ultrasonic device around shaft mine by test highlighted the initialization and extension of the damage as the shaft front proceeded. They also showed a polarisation of the velocity field and an oscillation of the transversal isotropy with a preferential orientation of the stress release and the microcracking. Otherwise, with a new automatic and ultrasonic probe, we have found around a borehole that the damage zone extends up to 0.175 diameter of depth with an anisotropic damage pattern oriented according to the regional stress field (Figure 1). Nevertheless, the evolution of this damaged zone is still not well known at longer term, particularly under the influence of parameters such as the reconfining rock in contact with a rigid concrete surface. Is it possible that cracks close up significantly toward their seal? Induced mechanical perturbations are in this case much weaker than those generated by the excavation itself. A new ultrasonic experiment has been designed to be more sensitive to the frequency modulation of the P and S-wave sources. The purpose is to determine on site the dynamic elastic stiffness and the corresponding crack density tensors change before and during the resaturation and reconfining of the damaged and undamaged excavation vicinity. P-wave velocity field around a vertical borehole

Validity of reciprocity rule on mouse skin thermal damage due to CO2 laser irradiation

NASA Astrophysics Data System (ADS)

Parvin, P.; Dehghanpour, H. R.; Moghadam, M. S.; Daneshafrooz, V.

2013-07-01

CO2 laser (10.6 μm) is a well-known infrared coherent light source as a tool in surgery. At this wavelength there is a high absorbance coefficient (860 cm-1), because of vibration mode resonance of H2O molecules. Therefore, the majority of the irradiation energy is absorbed in the tissue and the temperature of the tissue rises as a function of power density and laser exposure duration. In this work, the tissue damage caused by CO2 laser (1-10 W, ˜40-400 W cm-2, 0.1-6 s) was measured using 30 mouse skin samples. Skin damage assessment was based on measurements of the depth of cut, mean diameter of the crater and the carbonized layer. The results show that tissue damage as assessed above parameters increased with laser fluence and saturated at 1000 J cm-2. Moreover, the damage effect due to high power density at short duration was not equivalent to that with low power density at longer irradiation time even though the energy delivered was identical. These results indicate the lack of validity of reciprocity (Bunsen-Roscoe) rule for the thermal damage.

Compression of laminated composite beams with initial damage

NASA Technical Reports Server (NTRS)

Breivik, Nicole L.; Gurdal, Zafer; Griffin, O. H., Jr.

1993-01-01

The effect of isolated damage modes on the compressive strength and failure characteristics of laminated composite test specimens were evaluated experimentally and numerically. In addition to specimens without initial damage, specimens with three types of initial damage were considered: (1) specimens with short delaminations distributed evenly through the specimen thickness, (2) specimens with few long delaminations, and (3) specimens with local fiber damage in the surface plies under the three-point bend contact point. It was found that specimens with short multiple delamination experienced the greatest reduction in compression strength compared to the undamaged specimens. Single delaminations far from the specimen surface had little effect on the final compression strength, and moderate strength reduction was observed for specimens with localized surface ply damage.

Progressive Fracture of Fiber Composite Build-Up Structures

NASA Technical Reports Server (NTRS)

Gotsis, Pascal K.; Chamis, C. C.; Minnetyan, Levon

1997-01-01

Damage progression and fracture of built-up composite structures is evaluated by using computational simulation. The objective is to examine the behavior and response of a stiffened composite (0/ +/- 45/90)(sub s6) laminate panel by simulating the damage initiation, growth, accumulation, progression and propagation to structural collapse. An integrated computer code, CODSTRAN, was augmented for the simulation of the progressive damage and fracture of built-up composite structures under mechanical loading. Results show that damage initiation and progression have significant effect on the structural response. Influence of the type of loading is investigated on the damage initiation, propagation and final fracture of the build-up composite panel.

Progressive Fracture of Fiber Composite Build-Up Structures

NASA Technical Reports Server (NTRS)

Minnetyan, Levon; Gotsis, Pascal K.; Chamis, C. C.

1997-01-01

Damage progression and fracture of built-up composite structures is evaluated by using computational simulation. The objective is to examine the behavior and response of a stiffened composite (0 +/-45/90)(sub s6) laminate panel by simulating the damage initiation, growth, accumulation, progression and propagation to structural collapse. An integrated computer code CODSTRAN was augmented for the simulation of the progressive damage and fracture of built-up composite structures under mechanical loading. Results show that damage initiation and progression to have significant effect on the structural response. Influence of the type of loading is investigated on the damage initiation, propagation and final fracture of the build-up composite panel.

Characterization of hypervelocity metal fragments for explosive initiation

DOE PAGES

Yeager, John D.; Bowden, Patrick R.; Guildenbecher, Daniel R.; ...

2017-07-17

The fragment impact response of two plastic-bonded explosive (PBX) formulations was studied using explosively driven aluminum fragments. A generic aluminum-capped detonator generated sub-mm aluminum particles moving at hypersonic velocities. The ability of these fragments to initiate reaction or otherwise damage two PBX materials was assessed using go/no-go experiments at standoff distances of up to 160 mm. Lower density PBX 9407 (RDX-based) was initiable at up to 115 mm, while higher density PBX 9501 (HMX-based) was only initiable at up to 6 mm. Several techniques were used to characterize the size, distribution, and velocity of the particles. Witness plate materials, includingmore » copper and polycarbonate, and backlit high speed video were used to characterize the distribution of particles, finding that the aluminum cap did not fragment homogeneously but rather with larger particles in a ring surrounding finer particles. Finally, precise digital holography experiments were conducted to measure the three-dimensional shape and size of the fastest-moving fragments, which ranged between 100 and 700 μm and traveled between 2.2 and 3.2 km/s. Crucially, these experiments showed variability in the fragmentation in terms of the number of fragments at the leading edge of the fragment field, indicating that both single and multiple shock impacts could be imparted to the target material. As a result, these types of data are critical for safety experiments and hydrocode simulations to quantify shock-to-detonation transition mechanisms and the associated risk-margins for these materials.« less

Characterization of hypervelocity metal fragments for explosive initiation

NASA Astrophysics Data System (ADS)

Yeager, John D.; Bowden, Patrick R.; Guildenbecher, Daniel R.; Olles, Joseph D.

2017-07-01

The fragment impact response of two plastic-bonded explosive (PBX) formulations was studied using explosively driven aluminum fragments. A generic aluminum-capped detonator generated sub-mm aluminum particles moving at hypersonic velocities. The ability of these fragments to initiate reaction or otherwise damage two PBX materials was assessed using go/no-go experiments at standoff distances of up to 160 mm. Lower density PBX 9407 (RDX-based) was initiable at up to 115 mm, while higher density PBX 9501 (HMX-based) was only initiable at up to 6 mm. Several techniques were used to characterize the size, distribution, and velocity of the particles. Witness plate materials, including copper and polycarbonate, and backlit high speed video were used to characterize the distribution of particles, finding that the aluminum cap did not fragment homogeneously but rather with larger particles in a ring surrounding finer particles. Finally, precise digital holography experiments were conducted to measure the three-dimensional shape and size of the fastest-moving fragments, which ranged between 100 and 700 μm and traveled between 2.2 and 3.2 km/s. Crucially, these experiments showed variability in the fragmentation in terms of the number of fragments at the leading edge of the fragment field, indicating that both single and multiple shock impacts could be imparted to the target material. These types of data are critical for safety experiments and hydrocode simulations to quantify shock-to-detonation transition mechanisms and the associated risk-margins for these materials.

A Computational Efficient Physics Based Methodology for Modeling Ceramic Matrix Composites (Preprint)

DTIC Science & Technology

2011-11-01

elastic range, and with some simple forms of progressing damage . However, a general physics-based methodology to assess the initial and lifetime... damage evolution in the RVE for all possible load histories. Microstructural data on initial configuration and damage progression in CMCs were...the damaged elements will have changed, hence, a progressive damage model. The crack opening for each crack type in each element is stored as a

Subsurface defects of fused silica optics and laser induced damage at 351 nm.

PubMed

Hongjie, Liu; Jin, Huang; Fengrui, Wang; Xinda, Zhou; Xin, Ye; Xiaoyan, Zhou; Laixi, Sun; Xiaodong, Jiang; Zhan, Sui; Wanguo, Zheng

2013-05-20

Many kinds of subsurface defects are always present together in the subsurface of fused silica optics. It is imperfect that only one kind of defects is isolated to investigate its impact on laser damage. Therefore it is necessary to investigate the impact of subsurface defects on laser induced damage of fused silica optics with a comprehensive vision. In this work, we choose the fused silica samples manufactured by different vendors to characterize subsurface defects and measure laser induced damage. Contamination defects, subsurface damage (SSD), optical-thermal absorption and hardness of fused silica surface are characterized with time-of-flight secondary ion mass spectrometry (TOF-SIMS), fluorescence microscopy, photo-thermal common-path interferometer and fully automatic micro-hardness tester respectively. Laser induced damage threshold and damage density are measured by 351 nm nanosecond pulse laser. The correlations existing between defects and laser induced damage are analyzed. The results show that Cerium element and SSD both have a good correlation with laser-induced damage thresholds and damage density. Research results evaluate process technology of fused silica optics in China at present. Furthermore, the results can provide technique support for improving laser induced damage performance of fused silica.

SU-G-TeP3-14: Three-Dimensional Cluster Model in Inhomogeneous Dose Distribution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wei, J; Penagaricano, J; Narayanasamy, G

2016-06-15

Purpose: We aim to investigate 3D cluster formation in inhomogeneous dose distribution to search for new models predicting radiation tissue damage and further leading to new optimization paradigm for radiotherapy planning. Methods: The aggregation of higher dose in the organ at risk (OAR) than a preset threshold was chosen as the cluster whose connectivity dictates the cluster structure. Upon the selection of the dose threshold, the fractional density defined as the fraction of voxels in the organ eligible to be part of the cluster was determined according to the dose volume histogram (DVH). A Monte Carlo method was implemented tomore » establish a case pertinent to the corresponding DVH. Ones and zeros were randomly assigned to each OAR voxel with the sampling probability equal to the fractional density. Ten thousand samples were randomly generated to ensure a sufficient number of cluster sets. A recursive cluster searching algorithm was developed to analyze the cluster with various connectivity choices like 1-, 2-, and 3-connectivity. The mean size of the largest cluster (MSLC) from the Monte Carlo samples was taken to be a function of the fractional density. Various OARs from clinical plans were included in the study. Results: Intensive Monte Carlo study demonstrates the inverse relationship between the MSLC and the cluster connectivity as anticipated and the cluster size does not change with fractional density linearly regardless of the connectivity types. An initially-slow-increase to exponential growth transition of the MSLC from low to high density was observed. The cluster sizes were found to vary within a large range and are relatively independent of the OARs. Conclusion: The Monte Carlo study revealed that the cluster size could serve as a suitable index of the tissue damage (percolation cluster) and the clinical outcome of the same DVH might be potentially different.« less

Forest Health Monitoring in Maine, 1996-1999.

Treesearch

Northeastern Research Station

2002-01-01

Maine has mixed-age forests dominated by softwood species. Most of the trees are healthy, with full crowns (low transparency, high density), little dieback and little damage. Red maple had higher amounts of dieback but seemed to maintain crown fullness. Eastern white pine and northern white cedar had lower densities as well as higher rates of damage.

Simulation of 90{degrees} ply fatigue crack growth along the width of cross-ply carbon-epoxy coupons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Henaff-Gardin, C.; Urwald, E.; Lafarie-Frenot, M.C.

1994-07-01

We study the mechanism of fatigue cracking of the matrix of cross-ply carbon-epoxy laminates. Primary attention is given to the study of the influence of the specimen width on the evolution of damage. On the basis of shear lag analysis, we determine the strain energy release rate in the processes of initiation and growth of transverse fatigue cracks. We also present results of experimental research on the evolution of the edge crack density per ply, the average length of the cracks, and the crack propagation rate under transverse fatigue cracking. It is shown that these characteristics are independent of themore » specimen width. At the same time, as soon as the edge crack density reaches its saturation value, the average crack growth rate becomes constant. All the experimental results are in good agreement with results obtained by using the theoretical model.« less

Numerical investigation of contact stresses for fretting fatigue damage initiation

NASA Astrophysics Data System (ADS)

Bhatti, N. A.; Abdel Wahab, M.

2017-05-01

Fretting fatigue phenomena occurs due to interaction between contacting bodies under application of cyclic and normal loads. In addition to environmental conditions and material properties, the response at the contact interface highly depends on the combination of applied loads. High stress concentration is present at the contact interface, which can start the damage nucleation process. At the culmination of nucleation process several micro cracks are initiated, ultimately leading to the structural failure. In this study, effect of ratio of tangential to normal load on contact stresses, slip amplitude and damage initiation is studied using finite element analysis. The results are evaluated for Ruiz parameter as it involves the slip amplitude which in an important factor in fretting fatigue conditions. It is observed that tangential to normal load ratio influences the stick zone size and damage initiation life. Furthermore, it is observed that tensile stress is the most important factor that drives the damage initiation to failure for the cases where failure occurs predominantly in mode I manner.

A Hybrid Approach to Composite Damage and Failure Analysis Combining Synergistic Damage Mechanics and Peridynamics

DTIC Science & Technology

2016-03-31

fiber distributions. Task 2.1 is concerned with damage evolution in a peridynamic model of poroelastic materials. Initial results for both tasks are...distributions. Task 2.1 is concerned with damage evolution in a peridynamic model of poroelastic materials. Initial results for both tasks are reported and...Task 2.1: Damage evolution in a peridynamic model of poroelastic materials. Background and Motivation In order to model the presence of pores and

Microvascular disease precedes the decline in renal function in the streptozotocin-induced diabetic rat

PubMed Central

Maric-Bilkan, Christine; Flynn, Elizabeth R.

2012-01-01

Diabetic nephropathy is a progressive and generalized vasculopathic condition associated with abnormal angiogenesis. We aim to determine whether changes in renal microvascular (MV) density correlate with and play a role in the progressive deterioration of renal function in diabetes. We hypothesize that MV changes represent the early steps of renal injury that worsen as diabetes progresses, initiating a vicious circle that leads to irreversible renal injury. Male nondiabetic (ND) or streptozotocin-induced diabetic (D) Sprague-Dawley rats were followed for 4 or 12 wk. Renal blood flow and glomerular filtration rate (GFR) were measured by PAH and 125I-[iothalamate], respectively. Renal MV density was quantified ex vivo using three-dimensional micro computed tomography and JG-12 immunoreactivity. Vascular endothelial growth factor (VEGF) levels (ELISA) and expression of VEGF receptors and factors involved in MV remodeling were quantified in renal tissue by Western blotting. Finally, renal morphology was investigated by histology. Four weeks of diabetes was associated with increased GFR, accompanied by a 34% reduction in renal MV density and augmented renal VEGF levels. However, at 12 wk, while GFR remained similarly elevated, reduction of MV density was more pronounced (75%) and associated with increased MV remodeling, renal fibrosis, but unchanged renal VEGF compared with ND at 12 wk. The damage, loss, and subsequent remodeling of the renal MV architecture in the diabetic kidney may represent the initiating events of progressive renal injury. This study suggests a novel concept of MV disease as an early instigator of diabetic kidney disease that may precede and likely promote the decline in renal function. PMID:22031855

Progressive Fracture of Fiber Composite Builtup Structures

NASA Technical Reports Server (NTRS)

Gotsis, Pascal K.; Chamis, Christos C.; Minnetyan, Levon

1996-01-01

The damage progression and fracture of builtup composite structures was evaluated by using computational simulation to examine the behavior and response of a stiffened composite (0 +/- 45/90)(sub s6) laminate panel subjected to a bending load. The damage initiation, growth, accumulation, progression, and propagation to structural collapse were simulated. An integrated computer code (CODSTRAN) was augmented for the simulation of the progressive damage and fracture of builtup composite structures under mechanical loading. Results showed that damage initiation and progression have a significant effect on the structural response. Also investigated was the influence of different types of bending load on the damage initiation, propagation, and final fracture of the builtup composite panel.

Damage Assessment of Heat Resistant Steels through Electron BackScatter Diffraction Strain Analysis under Creep and Creep-Fatigue Conditions

NASA Astrophysics Data System (ADS)

Fujiyama, Kazunari; Kimachi, Hirohisa; Tsuboi, Toshiki; Hagiwara, Hiroyuki; Ogino, Shotaro; Mizutani, Yoshiki

EBSD(Electron BackScatter Diffraction) analyses were conducted for studying the quantitative microstructural metrics of creep and creep-fatigue damage for austenitic SUS304HTB boiler tube steel and ferritic Mod.9Cr piping steel. KAM(Kernel Average Misorientation) maps and GOS(Grain Orientation Spread) maps were obtained for these samples and the area averaged values KAMave and GOSave were obtained. While the increasing trends of these misorientation metrics were observed for SUS304HTB steel, the decreasing trends were observed for damaged Mod.9Cr steel with extensive recovery of subgrain structure. To establish more universal parameter representing the accumulation of damage to compensate these opposite trends, the EBSD strain parameters were introduced for converting the misorientation changes into the quantities representing accumulated permanent strains during creep and creep-fatigue damage process. As KAM values were dependent on the pixel size (inversely proportional to the observation magnification) and the permanent strain could be expressed as the shear strain which was the product of dislocation density, Burgers vector and dislocation movement distance, two KAM strain parameters MεKAMnet and MεδKAMave were introduced as the sum of product of the noise subtracted KAMnet and the absolute change from initial value δKAMave with dislocation movement distance divided by pixel size. MεδKAMave parameter showed better relationship both with creep strain in creep tests and accumulated creep strain range in creep-fatigue tests. This parameter can be used as the strain-based damage evaluation and detector of final failure.

Rapid Multi-Damage Identification for Health Monitoring of Laminated Composites Using Piezoelectric Wafer Sensor Arrays

PubMed Central

Si, Liang; Wang, Qian

2016-01-01

Through the use of the wave reflection from any damage in a structure, a Hilbert spectral analysis-based rapid multi-damage identification (HSA-RMDI) technique with piezoelectric wafer sensor arrays (PWSA) is developed to monitor and identify the presence, location and severity of damage in carbon fiber composite structures. The capability of the rapid multi-damage identification technique to extract and estimate hidden significant information from the collected data and to provide a high-resolution energy-time spectrum can be employed to successfully interpret the Lamb waves interactions with single/multiple damage. Nevertheless, to accomplish the precise positioning and effective quantification of multiple damage in a composite structure, two functional metrics from the RMDI technique are proposed and used in damage identification, which are the energy density metric and the energy time-phase shift metric. In the designed damage experimental tests, invisible damage to the naked eyes, especially delaminations, were detected in the leftward propagating waves as well as in the selected sensor responses, where the time-phase shift spectra could locate the multiple damage whereas the energy density spectra were used to quantify the multiple damage. The increasing damage was shown to follow a linear trend calculated by the RMDI technique. All damage cases considered showed completely the developed RMDI technique potential as an effective online damage inspection and assessment tool. PMID:27153070

Induction and repair of DNA strand breaks in bovine lens epithelial cells after high LET irradiation

NASA Astrophysics Data System (ADS)

Baumstark-Khan, C.; Heilmann, J.; Rink, H.

The lens epithelium is the initiation site for the development of radiation induced cataracts. Radiation in the cortex and nucleus interacts with proteins, while in the epithelium, experimental results reveal mutagenic and cytotoxic effects. It is suggested that incorrectly repaired DNA damage may be lethal in terms of cellular reproduction and also may initiate the development of mutations or transformations in surviving cells. The occurrence of such genetically modified cells may lead to lens opacification. For a quantitative risk estimation for astronauts and space travelers it is necessary to know the relative biological effectiveness (RBE), because the spacial and temporal distribution of initial physical damage induced by cosmic radiation differ significantly from that of X-rays. RBEs for the induction of DNA strand breaks and the efficiency of repair of these breaks were measured in cultured diploid bovine lens epithelial cells exposed to different LET irradiation to either 300 kV X-rays or to heavy ions at the UNILAC accelerator at GSI. Accelerated ions from Z=8 (O) to Z=92 (U) were used. Strand breaks were measured by hydroxyapatite chromatography of alkaline unwound DNA (overall strand breaks). Results showed that DNA damage occurs as a function of dose, of kinetic energy and of LET. For particles having the same LET the severity of the DNA damage increases with dose. For a given particle dose, as the LET rises, the numbers of DNA strand breaks increase to a maximum and then reach a plateau or decrease. Repair kinetics depend on the fluence (irradiation dose). At any LET value, repair is much slower after heavy ion exposure than after X-irradiation. For ions with an LET of less than 10,000 keV μ -1 more than 90 percent of the strand breaks induced are repaired within 24 hours. At higher particle fluences, especially for low energetic particles with a very high local density of energy deposition within the particle track, a higher proportion of non-rejoined breaks is found, even after prolonged periods of incubation. At the highest LET value (16,300 keV μ -1 no significant repair is observed. These LET-dependencies are consistent with the current mechanistic model for radiation induced cataractogenesis which postulates that genomic damage to the surviving fraction of epithelial cells is responsible for lens opacification.

Herbivory modifies conifer phenology: induced amelioration by a specialist folivore.

PubMed

Carroll, Allan L; Quiring, Dan T

2003-06-01

Herbivory by Zeiraphera canadensis Mut. & Free. (Lepidoptera: Tortricidae), an early season folivore of white spruce [ Picea glauca(Moench) Voss], has been associated with a shift in the timing of bud burst by its host during the subsequent year. We tested the hypothesis that a herbivory-induced shift in the phenology of bud development improves the window for colonisation of white spruce buds by Z. canadensis. Feeding on cortical tissue of elongating shoots caused the destruction of apical buds and an interruption of apical dominance in the year following herbivory. White spruce compensated for damage with the activation of dormant buds; mainly at proximal positions along shoots. As a result, half of all active buds on previously damaged branches were located immediately adjacent egg sites (i.e. previous year's bud scales), whereas <10% of active buds on intact shoots were situated there. More than 40% of newly emerged larvae colonised the basal buds of damaged shoots versus just 10% for intact shoots. Previous herbivory also influenced the initiation of bud burst. All buds flushed 2 days earlier on damaged shoots and date of bud burst was inversely correlated to bud density, indicating that short damaged shoots with large numbers of buds were stronger sinks for nutrients required for bud development. Egg hatch was best synchronized with early bursting buds on damaged branches. As a consequence, 89% of first-instar larvae successfully colonised buds on damaged branches while only 55% were successful on undamaged branches. Improved survival of larvae in the year following herbivory was a direct result of the evolved response by white spruce to the interruption of apical dominance. The pattern of herbivory by Z. canadensis may have evolved as a strategy to enhance the quality of white spruce for their offspring.

3-ω damage threshold evaluation of final optics components using Beamlet Mule and off-line testing

NASA Astrophysics Data System (ADS)

Kozlowski, Mark R.; Maricle, Stephen M.; Mouser, Ron P.; Schwartz, Sheldon; Wegner, Paul J.; Weiland, Timothy L.

1999-07-01

A statistics-based model is being develop to predict the laser-damage-limited lifetime of UV optical components on the NIF laser. In order to provide data for the mode, laser damage experiments were performed on the Beamlet laser system at LLNL. An early protoype NIF focus lens was exposed to twenty 351 nm pulses at an average fluence of 5 J/cm2, 3ns. Using a high resolution optic inspection inspection system a total of 353 damage sites was detected within the 1160 cm2 beam aperture. Through inspections of the lens before, after and, in some cases, during the campaign, pulse to pulse damage growth rates were measured for damage initiating both on the surface and at bulk inclusions. Growth rates as high as 79 micrometers /pulse were observed for damage initiating at pre-existing scratches in the surface. For most damage sites on the optic, both on the surface and at bulk inclusions. Growth rates as high as 79 micrometers /pulse were observed for damage initiating at per- existing scratches in the surface. For most damage sites on the optic, both surface and bulk, the damage growth rate was approximately 10(Mu) m/pulse.

Laser damage initiation and growth of antireflection coated S-FAP crystal surfaces prepared by pitch lap and magnetorheological finishing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stolz, C J; Menapace, J A; Schaffers, K I

Antireflection (AR) coatings typically damage at the interface between the substrate and coating. Therefore the substrate finishing technology can have an impact on the laser resistance of the coating. For this study, AR coatings were deposited on Yb:S-FAP [Yb{sup 3+}:Sr{sub 5}(PO{sub 4}){sub 3}F] crystals that received a final polish by both conventional pitch lap finishing as well as magnetorheological finishing (MRF). SEM images of the damage morphology reveals laser damage originates at scratches and at substrate coating interfacial absorbing defects. Previous damage stability tests on multilayer mirror coatings and bare surfaces revealed damage growth can occur at fluences below themore » initiation fluence. The results from this study suggest the opposite trend for AR coatings. Investigation of unstable HR and uncoated surface damage morphologies reveals significant radial cracking that is not apparent with AR damage due to AR delamination from the coated surface with few apparent cracks at the damage boundary. Damage stability tests show that coated Yb:S-FAP crystals can operate at 1057 nm at fluences around 20 J/cm{sup 2} at 10 ns; almost twice the initiation damage threshold.« less

Acute SSRI-induced anxiogenic and brain metabolic effects are attenuated 6 months after initial MDMA-induced depletion.

PubMed

Andó, Rómeó D; Adori, Csaba; Kirilly, Eszter; Molnár, Eszter; Kovács, Gábor G; Ferrington, Linda; Kelly, Paul A T; Bagdy, György

2010-03-05

To assess the functional state of the serotonergic system, the acute behavioural and brain metabolic effect of SSRI antidepressants were studied during the recovery period after MDMA-induced neuronal damage. The effects of the SSRI fluoxetine and the serotonin receptor agonist meta-chloro-phenylpiperazine (m-CPP) were investigated in the social interaction test in Dark Agouti rats, 6 months after treatment with a single dose of MDMA (15 or 30 mg kg(-1), i.p.). At earlier time points these doses of MDMA have been shown to cause 30-60% loss in axonal densities in several brain regions. Densities of the serotonergic axons were assessed using serotonin-transporter and tryptophan-hydroxylase immunohistochemistry. In a parallel group of animals, brain function was examined following an acute challenge with either fluoxetine or citalopram, using 2-deoxyglucose autoradiographic imaging. Six months after MDMA treatment the densities of serotonergic axons were decreased in only a few brain areas including hippocampus and thalamus. Basal anxiety was unaltered in MDMA-treated animals. However, the acute anxiogenic effects of fluoxetine, but not m-CPP, were attenuated in animals pretreated with MDMA. The metabolic response to both citalopram and fluoxetine was normal in most of the brain areas examined with the exception of ventromedial thalamus and hippocampal sub-fields where the response was attenuated. These data provide evidence that 6 months after MDMA-induced damage serotonergic axons show recovery in most brain areas, but serotonergic functions to challenges with SSRIs including anxiety and aggression remain altered. Copyright 2009 Elsevier B.V. All rights reserved.

Evaluation of Dicyphus hersperus (Heteroptera: Miridae) for biological control of Frankliniella occidentalis (Thysanoptera: Thripidae) on greenhouse tomato.

PubMed

Shipp, J L; Wang, K

2006-04-01

The effectiveness of inoculative releases of the mirid predator Dicyphus hesperus Knight for control of Frankliniella occidentalis (Pergande) on greenhouse tomatoes was evaluated in terms of suppression of the population densities of F. occidentalis and associated fruit damage in the presence of the predator over two seasonal trials. An inoculative release of one D. hesperus per plant (approximately 0.1:10 predator:prey ratio) at a high F. occidentalis population density (140 thrips per plant) suppressed the thrips population density to a significantly lower level, compared with the nonrelease greenhouse, but not below a thrips level that caused economic fruit damage. As the predator:prey ratio increased to approximately 0.5:10 D. hesperus:F. occidentalis, the mean percentage of the thrips-damaged fruit in the D. hesperus release greenhouse decreased to 1.6%. However, the amount of fruit feeding by D. hesperus was highly correlated to the availability of prey (or predator:prey ratio) under greenhouse conditions. D. hesperus-induced fruit damage occurred when the predator:prey ratio was >1:10 D. hesperus:F. occidentalis. Considering the potential risk of fruit damage by D. hesperus and the need for effective control of F. occidentalis, a 0.5-1:10 D. hesperus:F. occidentalis ratio is recommended when the thrips population density is in the range of 60-150 thrips per plant.

Response of Soybean to Heterodera glycines Races 1 and 2 in Different Soil Types.

PubMed

Schmitt, D P; Ferris, H; Barker, K R

1987-04-01

Experiments were conducted for 3 years at four locations and 1 year with six soil types at a common location in North Carolina to determine damage and control-cost functions for Heterodera glycines races 1 and 2 on soybean. In the experiments on native loamy sand and sandy soils, tolerance limits for initial population densities were 0 or very low, whereas in a muck, the tolerance limit was 315 eggs/500 cm(3) soil. The aggressive race 2 was more damaging than race 1 in Lakeland sand and Norfolk loamy sand. The crop response was not different between races in the Appling sandy clay loam and Belhaven muck. Soybean yield responses to H. glycines were linear in six soil types in microplots at a common site. The amount of damage varied among these soil types, with lowest yields in the muck because of severe drought stress in this soil. An exponential function adequately described soybean yield response relative to nematode control with increasing rates of aldicarb in Norfolk loamy sand. Treatment with aldicarb in the Lakeland sand decreased the effective egg population of H. glycines but had only a minor effect in the muck.

In silico nanodosimetry: new insights into nontargeted biological responses to radiation.

PubMed

Kuncic, Zdenka; Byrne, Hilary L; McNamara, Aimee L; Guatelli, Susanna; Domanova, Westa; Incerti, Sébastien

2012-01-01

The long-held view that radiation-induced biological damage must be initiated in the cell nucleus, either on or near DNA itself, is being confronted by mounting evidence to suggest otherwise. While the efficacy of cell death may be determined by radiation damage to nuclear DNA, a plethora of less deterministic biological responses has been observed when DNA is not targeted. These so-called nontargeted responses cannot be understood in the framework of DNA-centric radiobiological models; what is needed are new physically motivated models that address the damage-sensing signalling pathways triggered by the production of reactive free radicals. To this end, we have conducted a series of in silico experiments aimed at elucidating the underlying physical processes responsible for nontargeted biological responses to radiation. Our simulation studies implement new results on very low-energy electromagnetic interactions in liquid water (applicable down to nanoscales) and we also consider a realistic simulation of extranuclear microbeam irradiation of a cell. Our results support the idea that organelles with important functional roles, such as mitochondria and lysosomes, as well as membranes, are viable targets for ionizations and excitations, and their chemical composition and density are critical to determining the free radical yield and ensuing biological responses.

Damage morphology study of high cycle fatigued as-cast Mg–3.0Nd–0.2Zn–Zr (wt.%) alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yue, Haiyan; Fu, Penghuai, E-mail: fph112sjtu@sjtu.edu.cn; Peng, Liming

Laser scanning confocal microscopy (LSCM) and Electron back-scattered diffraction (EBSD) were applied to the study of surface morphology variation of as-cast Mg–3.0Nd–0.2Zn–Zr (NZ30K) (wt.%) alloy under tension-compression fatigue test at room temperature. Two kinds of typical damage morphologies were observed in fatigued NZ30K alloy: One was parallel lines on basal planes led by the cumulation of basal slips, called persistent slip markings (PSMs), and the other was lens shaped, thicker and in less density, led by the formation of twinning. The surface fatigue damage morphology evolution was analyzed in a statistical way. The influences of stress amplitude and grain orientationmore » on fatigue deformation mechanisms were discussed and the non-uniform deformation among grains and the PSMs, within twinning were described quantitatively. - Highlights: • Fatigue morphology evolution was studied by Laser Scanning Confocal Microscopy. • 3D morphology of persistent slip markings and twins was characterized. • Non-uniform deformation among grains, the PSMs and twins were quantified. • Initiations of fatigue crack were clearly investigated.« less

Predicting infestation levels of the nantucket pine tip moth (Lepidoptera: Tortricidae) using pheromone traps

Treesearch

Christopher Asaro; C. Wayne Berisford

2001-01-01

There is considerable interest in using pheromone trap catches of the Nantucket pine tip moth, Rhyacionia frustrana (Conistock), to estimate or predict population density and damage. At six sites in the Georgia Piedmont, adult tip moths were monitored through one or more years using pheromone traps while population density and damage for each tip...

Snow breakage in a pole-sized ponderosa pine plantation ... more damage at high stand-densities

Treesearch

Robert F. Powers; William W. Oliver

1970-01-01

Damage by snow breakage to pole-sized ponderosa pine (Pinus pondvosa Laws.) increased as stand density increased. In a plantation on the west slope of California's Sierra Nevada, the tallest trees were most often broken. Thinning in the sapling stage is recommended as a preventative measure in dense plantations subject to heavy snowfall.

Removal of nutrient limitations in forest gaps enhances growth rate and resistance to cavitation in subtropical canopy tree species differing in shade tolerance.

PubMed

Villagra, Mariana; Campanello, Paula I; Montti, Lia; Goldstein, Guillermo

2013-03-01

A 4-year fertilization experiment with nitrogen (N) and phosphorus (P) was carried out in natural gaps of a subtropical forest in northeastern Argentina. Saplings of six dominant canopy species differing in shade tolerance were grown in five control and five N + P fertilized gaps. Hydraulic architectural traits such as wood density, the leaf area to sapwood area ratio (LA : SA), vulnerability to cavitation (P50) and specific and leaf-specific hydraulic conductivity were measured, as well as the relative growth rate, specific leaf area (SLA) and percentage of leaf damage by insect herbivores. Plant growth rates and resistance to drought-induced embolisms increased when nutrient limitations were removed. On average, the P50 of control plants was -1.1 MPa, while the P50 of fertilized plants was -1.6 MPa. Wood density and LA : SA decreased with N + P additions. A trade-off between vulnerability to cavitation and efficiency of water transport was not observed. The relative growth rate was positively related to the total leaf surface area per plant and negatively related to LA : SA, while P50 was positively related to SLA across species and treatments. Plants with higher growth rates and higher total leaf area in fertilized plots were able to avoid hydraulic dysfunction by becoming less vulnerable to cavitation (more negative P50). Two high-light-requiring species exhibited relatively low growth rates due to heavy herbivore damage. Contrary to expectations, shade-tolerant plants with relatively high resistance to hydraulic dysfunction and reduced herbivory damage were able to grow faster. These results suggest that during the initial phase of sapling establishment in gaps, species that were less vulnerable to cavitation and exhibited reduced herbivory damage had faster realized growth rates than less shade-tolerant species with higher potential growth rates. Finally, functional relationships between hydraulic traits and growth rate across species and treatments were maintained regardless of soil nutrient status.

Measuring the consequences of wildfires in a Bayesian network with vulnerability and exposure indicators

NASA Astrophysics Data System (ADS)

Papakosta, Panagiota; Botzler, Sebastian; Krug, Kai; Straub, Daniel

2013-04-01

Mediterranean climate type areas have always been experiencing fire events. However, population growth and expansion of urban centers into wildland areas during the 20th century (expansion of wildland-urban interface) has increased the threat to humans and their activities. Life and property losses, damage on infrastructure and crops, and forest degradation are some of the damages caused by wildfires. Although fires repeatedly occur along the Mediterranean basin, not all areas have experienced severe consequences. The extent of damage by wildfires is influenced by several factors, such as population density, vegetation type, topography, weather conditions and social preparedness [1]. Wildfire consequence estimation by means of vulnerability and exposure indicators is an essential part of wildfire risk analysis. Vulnerability indicators express the conditions that increase the susceptibility of a site to the impact of wildfires and exposure indicators describe the elements at risk [2],[3]. Appropriate indicators to measure wildfire vulnerability and exposure can vary with scale and site. The consequences can be classified into economic, social, environmental and safety, and they can be tangible (human life losses, buildings damaged) or intangible (damage of cultural heritage site). As a consequence, a variety of approaches exist and there is a lack of generalized unified easy-to-implement methodologies. In this study we present a methodology for measuring consequences of wildfires in a Mediterranean area in the mesoscale (1 km² spatial resolution). Vulnerability and exposure indicators covering all consequence levels are identified and their interrelations are stressed. Variables such as building materials, roofing type, and average building values are included in the economic vulnerability level. Safety exposure is expressed by population density, demographic structure, street density and distance to closest fire station. Environmental vulnerability of protected areas and rare species is also included. Presence of cultural heritage sites, power stations and power line network influence social exposure. The conceptual framework is demonstrated with a Bayesian Network (BN). The BN model incorporates empirical observation, physical models and expert knowledge; it can also explicitly account for uncertainty in the indicators. The proposed model is applied to the island of Cyprus. Maps support the demonstration of results. [1] Keeley, J.E.; Bond, W.J.; Bradstock, R.A.; Pausas, J.G.; Rundel, P.W. (2012): Fire in Mediterranean ecosystems: ecology, evolution and management. Cambridge University Press, New York, USA. [2] UN/ISDR (International Strategy for Disaster Reduction (2004): Living with Risk: A Global Review of Disaster Reduction Initiatives, Geneva, UN Publications. [3] Birkmann, J. (2006): Measuring vulnerability to natural hazards: towards disaster resilient societies. United Nations University Press, Tokyo, Japan.

Indicators of replicative damage in equine tendon fibroblast monolayers

PubMed Central

2013-01-01

Background Superficial digital flexor tendon (SDFT) injuries of horses usually follow cumulative matrix microdamage; it is not known why the reparative abilities of tendon fibroblasts are overwhelmed or subverted. Relevant in vitro studies of this process require fibroblasts not already responding to stresses caused by the cell culture protocols. We investigated indicators of replicative damage in SDFT fibroblast monolayers, effects of this on their reparative ability, and measures that can be taken to reduce it. Results We found significant evidence of replicative stress, initially observing consistently large numbers of binucleate (BN) cells. A more variable but prominent feature was the presence of numerous gammaH2AX (γH2AX) puncta in nuclei, this being a histone protein that is phosphorylated in response to DNA double-stranded breaks (DSBs). Enrichment for injury detection and cell cycle arrest factors (p53 (ser15) and p21) occurred most frequently in BN cells; however, their numbers did not correlate with DNA damage levels and it is likely that the two processes have different causative mechanisms. Such remarkable levels of injury and binucleation are usually associated with irradiation, or treatment with cytoskeletal-disrupting agents. Both DSBs and BN cells were greatest in subconfluent (replicating) monolayers. The DNA-damaged cells co-expressed the replication markers TPX2/repp86 and centromere protein F. Once damaged in the early stages of culture establishment, fibroblasts continued to express DNA breaks with each replicative cycle. However, significant levels of cell death were not measured, suggesting that DNA repair was occurring. Comet assays showed that DNA repair was delayed in proportion to levels of genotoxic stress. Conclusions Researchers using tendon fibroblast monolayers should assess their “health” using γH2AX labelling. Continued use of early passage cultures expressing initially high levels of γH2AX puncta should be avoided for mechanistic studies and ex-vivo therapeutic applications, as this will not be resolved with further replicative cycling. Low density cell culture should be avoided as it enriches for both DNA damage and mitotic defects (polyploidy). As monolayers differing only slightly in baseline DNA damage levels showed markedly variable responses to a further injury, studies of effects of various stressors on tendon cells must be very carefully controlled. PMID:24025445

A Fundamental Investigation of Crack and Surrounding Damage in Stiff Clays

DTIC Science & Technology

1988-09-01

equation of state is written in terms of entropy production. A generalized flux is identified as the centroidal movement of the damage zone, and the...on the following governing equation. I I a14 ( 1.1] Ti = z ’_Xc + "_.wXrOt + a.’X ef = 0 where Si is the global entropy production, 1, , and a are...convenient to express the internal energy density u in terms of i Gibb’s potential density and the entropy density s [6.3] u = g + Ts +’ijciji Here

Optimization of the Hot Forging Processing Parameters for Powder Metallurgy Fe-Cu-C Connecting Rods Based on Finite Element Simulation

NASA Astrophysics Data System (ADS)

Li, Fengxian; Yi, Jianhong; Eckert, Jürgen

2017-12-01

Powder forged connecting rods have the problem of non-uniform density distributions because of their complex geometric shape. The densification behaviors of powder metallurgy (PM) connecting rod preforms during hot forging processes play a significant role in optimizing the connecting rod quality. The deformation behaviors of a connecting rod preform, a Fe-3Cu-0.5C (wt pct) alloy compacted and sintered by the powder metallurgy route (PM Fe-Cu-C), were investigated using the finite element method, while damage and friction behaviors of the material were considered in the complicated forging process. The calculated results agree well with the experimental results. The relationship between the processing parameters of hot forging and the relative density of the connecting rod was revealed. The results showed that the relative density of the hot forged connecting rod at the central shank changed significantly compared with the relative density at the big end and at the small end. Moreover, the relative density of the connecting rod was sensitive to the processing parameters such as the forging velocity and the initial density of the preform. The optimum forging processing parameters were determined and presented by using an orthogonal design method. This work suggests that the processing parameters can be optimized to prepare a connecting rod with uniform density distribution and can help to better meet the requirements of the connecting rod industry.

Effect of Ar{sup +} ion irradiation on the microstructure of pyrolytic carbon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, Shanglei; Zhang, Dongsheng; Yang, Xinmei

2015-03-21

Pyrolytic carbon (PyC) coatings prepared by chemical vapor deposition were irradiated by 300 keV Ar{sup +} ions. Then, atomic force microscopy, synchrotron-based grazing incidence X-ray diffraction, Raman spectroscopy, X-ray photoemission spectroscopy, and transmission electron microscopy were employed to study how Ar{sup +} irradiation affects the microstructure of PyC, including the microstructural damage mechanisms and physics driving these phenomena. The 300 keV Ar{sup +} ion irradiation deteriorated the structure along the c-axis, which increased the interlayer spacing between graphene layers. With increasing irradiation dose, the density of defect states on the surface of PyC coating increases, and the basal planes gradually loses theirmore » initial ordering resulting in breaks in the lattice and turbulence at the peak damage dose reaches 1.58 displacement per atom (dpa). Surprisingly, the PyC becomes more textured as it becomes richer in structural defects with increasing irradiation dose.« less

Application of positron annihilation lineshape analysis to fatigue damage and thermal embrittlement for nuclear plant materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Uchida, M.; Ohta, Y.; Nakamura, N.

1995-08-01

Positron annihilation (PA) lineshape analysis is sensitive to detect microstructural defects such as vacancies and dislocations. The authors are developing a portable system and applying this technique to nuclear power plant material evaluations; fatigue damage in type 316 stainless steel and SA508 low alloy steel, and thermal embrittlement in duplex stainless steel. The PA technique was found to be sensitive in the early fatigue life (up to 10%), but showed a little sensitivity for later stages of the fatigue life in both type 316 stainless steel and SA508 ferritic steel. Type 316 steel showed a higher PA sensitivity than SA508more » since the initial SA508 microstructure already contained a high dislocation density in the as-received state. The PA parameter increased as a fraction of aging time in CF8M samples aged at 350 C and 400 C, but didn`t change much in CF8 samples.« less

Cell signaling by reactive nitrogen and oxygen species in atherosclerosis

NASA Technical Reports Server (NTRS)

Patel, R. P.; Moellering, D.; Murphy-Ullrich, J.; Jo, H.; Beckman, J. S.; Darley-Usmar, V. M.

2000-01-01

The production of reactive oxygen and nitrogen species has been implicated in atherosclerosis principally as means of damaging low-density lipoprotein that in turn initiates the accumulation of cholesterol in macrophages. The diversity of novel oxidative modifications to lipids and proteins recently identified in atherosclerotic lesions has revealed surprising complexity in the mechanisms of oxidative damage and their potential role in atherosclerosis. Oxidative or nitrosative stress does not completely consume intracellular antioxidants leading to cell death as previously thought. Rather, oxidative and nitrosative stress have a more subtle impact on the atherogenic process by modulating intracellular signaling pathways in vascular tissues to affect inflammatory cell adhesion, migration, proliferation, and differentiation. Furthermore, cellular responses can affect the production of nitric oxide, which in turn can strongly influence the nature of oxidative modifications occurring in atherosclerosis. The dynamic interactions between endogenous low concentrations of oxidants or reactive nitrogen species with intracellular signaling pathways may have a general role in processes affecting wound healing to apoptosis, which can provide novel insights into the pathogenesis of atherosclerosis.

Strain rate sensitivity of the tensile strength of two silicon carbides: experimental evidence and micromechanical modelling

NASA Astrophysics Data System (ADS)

Zinszner, Jean-Luc; Erzar, Benjamin; Forquin, Pascal

2017-01-01

Ceramic materials are commonly used to design multi-layer armour systems thanks to their favourable physical and mechanical properties. However, during an impact event, fragmentation of the ceramic plate inevitably occurs due to its inherent brittleness under tensile loading. Consequently, an accurate model of the fragmentation process is necessary in order to achieve an optimum design for a desired armour configuration. In this work, shockless spalling tests have been performed on two silicon carbide grades at strain rates ranging from 103 to 104 s-1 using a high-pulsed power generator. These spalling tests characterize the tensile strength strain rate sensitivity of each ceramic grade. The microstructural properties of the ceramics appear to play an important role on the strain rate sensitivity and on the dynamic tensile strength. Moreover, this experimental configuration allows for recovering damaged, but unbroken specimens, giving unique insight on the fragmentation process initiated in the ceramics. All the collected data have been compared with corresponding results of numerical simulations performed using the Denoual-Forquin-Hild anisotropic damage model. Good agreement is observed between numerical simulations and experimental data in terms of free surface velocity, size and location of the damaged zones along with crack density in these damaged zones. This article is part of the themed issue 'Experimental testing and modelling of brittle materials at high strain rates'.

Crop Damage: The Hail Size Factor.

NASA Astrophysics Data System (ADS)

Sánchez, J. L.; Fraile, R.; de La Madrid, J. L.; de La Fuente, M. T.; Rodríguez, P.; Castro, A.

1996-09-01

Between 1986 and 1992 a research project was developed and carried out on hail climatology and the economic repercussions of hail on agriculture in León (northwestern Spain). A target area with an extent of 6825 km2 was defined, within which a network of meteorological observers was established at an average density of 1 per 17 km2. A network of 250 hailpads installed in a grid formation was also laid out over an area of 1000 km2 inside the target area. The frequent occurrence of hailfalls—122 hail days over seven consecutive summers—provided a detailed database and allowed several climatological studies to be made. Crop damage was also closely monitored and quantified. Barley and wheat were selected as crops on which to base an analysis of the relationship between hailfall characteristics and crop damage. As the resistance of plants to hailstones is held to vary according to their physiological state, four different stages of plant growth were defined, beginning with the formation of grain heads.An important conclusion was drawn: the dispersion of percentages of damage always covers the possible variations in resistance caused by the physiological state of the plants. As a result, using only minimal information about hailfall characteristics—namely, the initial reports of observers regarding hailstone size—a working statistical model has successfully been constructed to predict losses to barley and wheat, using data provided by the León hail project.

Strain rate sensitivity of the tensile strength of two silicon carbides: experimental evidence and micromechanical modelling.

PubMed

Zinszner, Jean-Luc; Erzar, Benjamin; Forquin, Pascal

2017-01-28

Ceramic materials are commonly used to design multi-layer armour systems thanks to their favourable physical and mechanical properties. However, during an impact event, fragmentation of the ceramic plate inevitably occurs due to its inherent brittleness under tensile loading. Consequently, an accurate model of the fragmentation process is necessary in order to achieve an optimum design for a desired armour configuration. In this work, shockless spalling tests have been performed on two silicon carbide grades at strain rates ranging from 10 3 to 10 4  s -1 using a high-pulsed power generator. These spalling tests characterize the tensile strength strain rate sensitivity of each ceramic grade. The microstructural properties of the ceramics appear to play an important role on the strain rate sensitivity and on the dynamic tensile strength. Moreover, this experimental configuration allows for recovering damaged, but unbroken specimens, giving unique insight on the fragmentation process initiated in the ceramics. All the collected data have been compared with corresponding results of numerical simulations performed using the Denoual-Forquin-Hild anisotropic damage model. Good agreement is observed between numerical simulations and experimental data in terms of free surface velocity, size and location of the damaged zones along with crack density in these damaged zones.This article is part of the themed issue 'Experimental testing and modelling of brittle materials at high strain rates'. © 2016 The Author(s).

Strain rate sensitivity of the tensile strength of two silicon carbides: experimental evidence and micromechanical modelling

PubMed Central

Erzar, Benjamin

2017-01-01

Ceramic materials are commonly used to design multi-layer armour systems thanks to their favourable physical and mechanical properties. However, during an impact event, fragmentation of the ceramic plate inevitably occurs due to its inherent brittleness under tensile loading. Consequently, an accurate model of the fragmentation process is necessary in order to achieve an optimum design for a desired armour configuration. In this work, shockless spalling tests have been performed on two silicon carbide grades at strain rates ranging from 103 to 104 s−1 using a high-pulsed power generator. These spalling tests characterize the tensile strength strain rate sensitivity of each ceramic grade. The microstructural properties of the ceramics appear to play an important role on the strain rate sensitivity and on the dynamic tensile strength. Moreover, this experimental configuration allows for recovering damaged, but unbroken specimens, giving unique insight on the fragmentation process initiated in the ceramics. All the collected data have been compared with corresponding results of numerical simulations performed using the Denoual–Forquin–Hild anisotropic damage model. Good agreement is observed between numerical simulations and experimental data in terms of free surface velocity, size and location of the damaged zones along with crack density in these damaged zones. This article is part of the themed issue ‘Experimental testing and modelling of brittle materials at high strain rates’. PMID:27956504

Impact of storage induced outgassing organic contamination on laser induced damage of silica optics at 351 nm.

PubMed

Bien-Aimé, K; Belin, C; Gallais, L; Grua, P; Fargin, E; Néauport, J; Tovena-Pecault, I

2009-10-12

The impact of storage conditions on laser induced damage density at 351 nm on bare fused polished silica samples has been studied. Intentionally outgassing of polypropylene pieces on silica samples was done. We evidenced an important increase of laser induced damage density on contaminated samples demonstrating that storage could limit optics lifetime performances. Atomic Force Microscopy (AFM) and Gas Chromatography -Mass Spectrometry (GC-MS) have been used to identify the potential causes of this effect. It shows that a small quantity of organic contamination deposited on silica surface is responsible for this degradation. Various hypotheses are proposed to explain the damage mechanism. The more likely hypothesis is a coupling between surface defects of optics and organic contaminants.

Damage development under compression-compression fatigue loading in a stitched uniwoven graphite/epoxy composite material

NASA Technical Reports Server (NTRS)

Vandermey, Nancy E.; Morris, Don H.; Masters, John E.

1991-01-01

Damage initiation and growth under compression-compression fatigue loading were investigated for a stitched uniweave material system with an underlying AS4/3501-6 quasi-isotropic layup. Performance of unnotched specimens having stitch rows at either 0 degree or 90 degrees to the loading direction was compared. Special attention was given to the effects of stitching related manufacturing defects. Damage evaluation techniques included edge replication, stiffness monitoring, x-ray radiography, residual compressive strength, and laminate sectioning. It was found that the manufacturing defect of inclined stitches had the greatest adverse effect on material performance. Zero degree and 90 degree specimen performances were generally the same. While the stitches were the source of damage initiation, they also slowed damage propagation both along the length and across the width and affected through-the-thickness damage growth. A pinched layer zone formed by the stitches particularly affected damage initiation and growth. The compressive failure mode was transverse shear for all specimens, both in static compression and fatigue cycling effects.

Postbuckling Investigations of Piezoelectric Microdevices Considering Damage Effects

PubMed Central

Sun, Zhigang; Wang, Xianqiao

2014-01-01

Piezoelectric material has been emerging as a popular building block in MEMS devices owing to its unique mechanical and electrical material properties. However, the reliability of MEMS devices under buckling deformation environments remains elusive and needs to be further explored. Based on the Talreja's tensor valued internal state damage variables as well as the Helmhotlz free energy of piezoelectric material, a constitutive model of piezoelectric materials with damage is presented. The Kachanvo damage evolution law under in-plane compressive loads is employed. The model is applied to the specific case of the postbuckling analysis of the piezoelectric plate with damage. Then, adopting von Karman's plate theory, the nonlinear governing equations of the piezoelectric plates with initial geometric deflection including damage effects under in-plane compressive loads are established. By using the finite difference method and the Newmark scheme, the damage evolution for damage accumulation is developed and the finite difference procedure for postbuckling equilibrium path is simultaneously employed. Numerical results show the postbuckling behaviors of initial flat and deflected piezoelectric plates with damage or no damage under different sets of electrical loading conditions. The effects of applied voltage, aspect ratio of plate, thick-span ratio of plate, damage as well as initial geometric deflections on the postbuckling behaviors of the piezoelectric plate are discussed. PMID:24618774

Acutely damaged axons are remyelinated in multiple sclerosis and experimental models of demyelination.

PubMed

Schultz, Verena; van der Meer, Franziska; Wrzos, Claudia; Scheidt, Uta; Bahn, Erik; Stadelmann, Christine; Brück, Wolfgang; Junker, Andreas

2017-08-01

Remyelination is in the center of new therapies for the treatment of multiple sclerosis to resolve and improve disease symptoms and protect axons from further damage. Although remyelination is considered beneficial in the long term, it is not known, whether this is also the case early in lesion formation. Additionally, the precise timing of acute axonal damage and remyelination has not been assessed so far. To shed light onto the interrelation between axons and the myelin sheath during de- and remyelination, we employed cuprizone- and focal lysolecithin-induced demyelination and performed time course experiments assessing the evolution of early and late stage remyelination and axonal damage. We observed damaged axons with signs of remyelination after cuprizone diet cessation and lysolecithin injection. Similar observations were made in early multiple sclerosis lesions. To assess the correlation of remyelination and axonal damage in multiple sclerosis lesions, we took advantage of a cohort of patients with early and late stage remyelinated lesions and assessed the number of APP- and SMI32- positive damaged axons and the density of SMI31-positive and silver impregnated preserved axons. Early de- and remyelinating lesions did not differ with respect to axonal density and axonal damage, but we observed a lower axonal density in late stage demyelinated multiple sclerosis lesions than in remyelinated multiple sclerosis lesions. Our findings suggest that remyelination may not only be protective over a long period of time, but may play an important role in the immediate axonal recuperation after a demyelinating insult. © 2017 The Authors GLIA Published by Wiley Periodicals, Inc.

Variability in Damage Caused by the Mite Tetranychus urticae (Trombidiformes: Tetranychidae) Koch on Three Varieties of Strawberry.

PubMed

González-Domínguez, S G; Santillán-Galicia, M T; González-Hernández, V; Suárez Espinosa, J; González-Hernández, H

2015-06-01

The strawberry, Fragaria×ananassa Duchesne (Rosales: Rosaceae), is an important crop in Mexico. We evaluated the tolerance of three newly developed Mexican strawberry varieties (CP0615, CPLE-7, and CPJacona) to Tetranychus urticae Koch (Trombidiformes: Tetranychidae), the most important pest of strawberry. We evaluated the effect of three different initial mite densities on population growth, duration of each developmental stage and survival of T. urticae on the three strawberry varieties. We also compared the photosynthetic activity (Pn), sub-stomatal CO2 concentration (Ci), stomatal conductance (gs) and the area of leaf damaged in the three varieties. The largest final density of mites occurred on the variety CP0615, followed by the varieties CPLE-7 and CPJacona. There were no significant differences in the duration of T. urticae developmental stages amongst the varieties, except for larvae where the shortest duration was on variety CPLE-7. The proportion of eggs reaching the adult stage (survival) was significantly lower on the variety CPLE-7. The number and morphology of the trichomes did not play an important role in the outcomes, as they were similar in the three varieties. There were no significant differences in Pn, Ci, and gs values amongst the three varieties in the presence and absence of T. urticae. The area of leaf damaged in variety CPLE-7 was significantly smaller than for the other varieties. Based on these results, and with regard to spider mite tolerance, we believe that the variety CPLE-7 has the greatest potential for further development, and eventually, for use on a commercial scale in Mexico. © The Authors 2015. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Influence of fruit age of the Brazilian Green Dwarf coconut on the relationship between Aceria guerreronis population density and percentage of fruit damage.

PubMed

Sousa, André Silva Guimarães; Argolo, Poliane Sá; Gondim, Manoel Guedes Correa; de Moraes, Gilberto José; Oliveira, Anibal Ramadan

2017-08-01

The coconut mite, Aceria guerreronis Keifer (Acari: Eriophyidae), is one of the main coconut pests in the American, African and parts of the Asian continents, reaching densities of several thousand mites per fruit. Diagrammatic scales have been developed to standardize the estimation of the population densities of A. guerreronis according to the estimated percentage of damage, but these have not taken into account the possible effect of fruit age, although previous studies have already reported the variation in mite numbers with fruit age. The objective of this study was to re-construct the relation between damage and mite density at different fruit ages collected in an urban coconut plantation containing the green dwarf variety ranging from the beginning to nearly the end of the infestation, as regularly seen under field conditions in northeast Brazil, in order to improve future estimates with diagrammatic scales. The percentage of damage was estimated with two diagrammatic scales on a total of 470 fruits from 1 to 5 months old, from a field at Ilhéus, Bahia, Brazil, determining the respective number of mites on each fruit. The results suggested that in estimates with diagrammatic scales: (1) fruit age has a major effect on the estimation of A. guerreronis densities, (2) fruits of different ages should be analyzed separately, and (3) regular evaluation of infestation levels should be done preferably on fruits of about 3-4 months old, which show the highest densities.

Relative binding affinity of carboxylate-, phosphonate-, and bisphosphonate-functionalized gold nanoparticles targeted to damaged bone tissue

NASA Astrophysics Data System (ADS)

Ross, Ryan D.; Cole, Lisa E.; Roeder, Ryan K.

2012-10-01

Functionalized Au NPs have received considerable recent interest for targeting and labeling cells and tissues. Damaged bone tissue can be targeted by functionalizing Au NPs with molecules exhibiting affinity for calcium. Therefore, the relative binding affinity of Au NPs surface functionalized with either carboxylate ( l-glutamic acid), phosphonate (2-aminoethylphosphonic acid), or bisphosphonate (alendronate) was investigated for targeted labeling of damaged bone tissue in vitro. Targeted labeling of damaged bone tissue was qualitatively verified by visual observation and backscattered electron microscopy, and quantitatively measured by the surface density of Au NPs using field-emission scanning electron microscopy. The surface density of functionalized Au NPs was significantly greater within damaged tissue compared to undamaged tissue for each functional group. Bisphosphonate-functionalized Au NPs exhibited a greater surface density labeling damaged tissue compared to glutamic acid- and phosphonic acid-functionalized Au NPs, which was consistent with the results of previous work comparing the binding affinity of the same functionalized Au NPs to synthetic hydroxyapatite crystals. Targeted labeling was enabled not only by the functional groups but also by the colloidal stability in solution. Functionalized Au NPs were stabilized by the presence of the functional groups, and were shown to remain well dispersed in ionic (phosphate buffered saline) and serum (fetal bovine serum) solutions for up to 1 week. Therefore, the results of this study suggest that bisphosphonate-functionalized Au NPs have potential for targeted delivery to damaged bone tissue in vitro and provide motivation for in vivo investigation.

Generation of Scratches and Their Effects on Laser Damage Performance of Silica Glass

PubMed Central

Li, Yaguo; Ye, Hui; Yuan, Zhigang; Liu, Zhichao; Zheng, Yi; Zhang, Zhe; Zhao, Shijie; Wang, Jian; Xu, Qiao

2016-01-01

Scratches are deleterious to precision optics because they can obscure and modulate incident laser light, which will increase the probability of damage to optical components. We here imitated the generation of brittle and ductile scratches during polishing process and endeavored to find out the possible influence of scratches on laser induced damage. Brittle scratches can be induced by spiking large sized abrasives and small abrasives may only generate ductile scratches. Both surface roughness and transmittivity are degraded due to the appearance of brittle scratches while ductile scratches make little difference to surface roughness and transmittance. However, ductile and brittle scratches greatly increase the density of damage about one order of magnitude relative to unscratched surface. In particular, ductile scratches also play an unignorable role in laser induced damage, which is different from previous knowledge. Furthermore, ZrO2 and Al2O3 polished surfaces appear to perform best in terms of damage density. PMID:27703218

Neutral beam and ICP etching of HKMG MOS capacitors: Observations and a plasma-induced damage model

NASA Astrophysics Data System (ADS)

Kuo, Tai-Chen; Shih, Tzu-Lang; Su, Yin-Hsien; Lee, Wen-Hsi; Current, Michael Ira; Samukawa, Seiji

2018-04-01

In this study, TiN/HfO2/Si metal-oxide-semiconductor (MOS) capacitors were etched by a neutral beam etching technique under two contrasting conditions. The configurations of neutral beam etching technique were specially designed to demonstrate a "damage-free" condition or to approximate "reactive-ion-etching-like" conditions to verify the effect of plasma-induced damage on electrical characteristics of MOS capacitors. The results show that by neutral beam etching (NBE), the interface state density (Dit) and the oxide trapped charge (Qot) were lower than routine plasma etching. Furthermore, the decrease in capacitor size does not lead to an increase in leakage current density, indicating less plasma induced side-wall damage. We present a plasma-induced gate stack damage model which we demonstrate by using these two different etching configurations. These results show that NBE is effective in preventing plasma-induced damage at the high-k/Si interface and on the high-k oxide sidewall and thus improve the electrical performance of the gate structure.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kozlowski, M.F.; Maricle, S.; Mouser, R.

A statistics-based model is being developed to predict the laser-damage-limited lifetime of UV optical components on the NIF laser. In order to provide data for the model, laser damage experiments were performed on the Beamlet laser system at LLNL. An early prototype NIF focus lens was exposed to twenty 35 1 nm pulses at an average fluence of 5 J/cm{sup 2}, 3ns. Using a high resolution optic inspection system a total of 353 damage sites was detected within the 1160 cm{sup 2} beam aperture. Through inspections of the lens before, after and, in some cases, during the campaign, pulse tomore » pulse damage growth rates were measured for damage initiating both on the surface and at bulk inclusions. Growth rates as high as 79 {micro}m/pulse (surface diameter) were observed for damage initiating at pre-existing scratches in the surface. For most damage sites on the optic, both surface and bulk, the damage growth rate was approximately l0{micro}m/pulse. The lens was also used in Beamlet for a subsequent 1053 {micro}m/526 {micro}m campaign. The 352 {micro}m-initiated damage continued to grow during that campaign although at generally lower growth rate.« less

Ballistic Impact of Braided Composites With a Soft Projectile

NASA Technical Reports Server (NTRS)

Roberts, Gary D.; Pereira, J. Michael; Revilock, Duane M., Jr.; Binienda, Wieslaw; Xie, Ming; Braley, Mike

2004-01-01

Impact tests using a soft gelatin projectile were performed to identify failure modes that occur at high strain energy density during impact loading. Use of a soft projectile allows a large amount of kinetic energy to be transferred into strain energy in the target before penetration occurs. Failure modes were identified for flat aluminum plates and for flat composite plates made from a triaxial braid having a quasi-isotropic fiber architecture with fibers in the 0 and +/- 60 deg. directions. For the aluminum plates, a large hole formed as a result of crack propagation from the initiation site at the center of the plate to the fixed boundaries. For the composite plates, fiber tensile failure occurred in the back ply at the center of the plate. Cracks then propagated from this site along the +/- 60 deg. fiber directions until triangular flaps opened to allow the projectile to pass through the plate. The damage size was only slightly larger than the initial impact area. It was difficult to avoid slipping of the fixed edges of the plates during impact, and slipping was shown to have a large effect on the penetration threshold. Failure modes were also identified for composite half-rings fabricated with the 0 deg. fibers aligned circumferentially. Slipping of the edges was not a problem in the half-ring tests. For the composite half-rings, fiber tensile failure also occurred in the back ply. However, cracks initially propagated from this site in a direction transverse to the 0 deg. fibers. The cracks then turned to follow the +/- 60 deg. fibers for a short distance before turning again to follow 0 deg. fibers until two approximately rectangular flaps opened to allow the projectile to pass through the plate. The damage size in the composite half-rings was also only slightly larger than the initial impact area. Cracks did not propagate to the boundaries, and no delamination was observed. The damage tolerance demonstrated by the quasi-isotropic triaxial braid composites indicate that composites of this type can reasonably be considered as a lightweight alternative to metals for fan cases in commercial jet engines.

Ocular Effects of Exposure to 40, 75, and 95 GHz Millimeter Waves

NASA Astrophysics Data System (ADS)

Kojima, Masami; Suzuki, Yukihisa; Sasaki, Kensuke; Taki, Masao; Wake, Kanako; Watanabe, Soichi; Mizuno, Maya; Tasaki, Takafumi; Sasaki, Hiroshi

2018-05-01

The objective of this study was to develop a model of ocular damage induced by 40, 75, and 95 GHz continuous millimeter waves (MMW), thereby allowing assessment of the clinical course of ocular damage resulting from exposure to thermal damage-inducing MMW. This study also examined the dependence of ocular damage on incident power density. Pigmented rabbit eyes were exposed to 40, 75, and 95 GHz MMW from a spot-focus-type lens antenna. Slight ocular damage was observed 10 min after MMW exposure, including reduced cornea thickness and reduced transparency. Diffuse fluorescein staining around the pupillary area indicated corneal epithelial injury. Slit-lamp examination 1 day after MMW exposure revealed a round area of opacity, accompanied by fluorescence staining, in the central pupillary zone. Corneal edema, indicative of corneal stromal damage, peaked 1 day after MMW exposure, with thickness gradually subsiding to normal. Three days after exposure, ocular conditions had almost normalized, though corneal thickness was slightly greater than that before exposure. The 50% probability of ocular damage (DD50) was in the order 40 > 95 ≈ 75 GHz at the same incident power densities.

Black bear (Ursus americanus Pallas) feeding damage across timber harvest edges in northern California coast redwood (Sequoia sempervirens[D. Don] Endl.) forests, USA

USGS Publications Warehouse

Russell, W.H.; Carnell, K.; McBride, J.R.

2001-01-01

Feeding damage to trees by black bears (Ursus americanus Pallas) was recorded in proximity to timber harvest edges in harvested and old-growth stands of coast redwood (Sequoia sempervirens [D. Don] Endl.) in northern California, USA. Bears exhibited distinct preference in their feeding patterns related to stand structure and composition and to distance from the timber-harvest edge. Most damage was recorded within regenerating stands. Regression analysis indicated that density of damaged trees was negatively correlated with distance from timber harvest edges within old-growth stands. A significant negative correlation was also found between the density of trees damaged by bears and habitat diversity (H') as measured by the Shannon diversity index. In addition, bears exhibited preference for pole-size trees (dbh = 10-50 cm) over all other size classes, and coast redwood over other species. In general, damage by bears appeared to act as a natural thinning agent in even-aged stands. No damage was recorded in old-growth stands except in close proximity to the timber-harvest edge where subcanopy recruitment was high.

Relevance of impacter shape to nonvisible damage and residual tensile strength of a thick graphite/epoxy laminate

NASA Technical Reports Server (NTRS)

Poe, Clarence C., Jr.

1991-01-01

A study was made to determine the relevance of impacter shape to nonvisible damage and tensile residual strength of a 36 mm thick graphite/epoxy motor case. The shapes of the impacters were as follows: 12.7 mm and 25.4 mm diameter hemispheres, a sharp corner, and a 6.3 mm diameter bolt-like rod. The investigation revealed that damage initiated when the contact pressure exceeded a critical level. However, the damage was not visible on the surface until an even higher pressure was exceeded. The impact energy to initiate damage or cause visible damage on the surface increased approximately with impacter diameter to the third power. The reduction in strength for nonvisible damage increased with increasing diameter, 9 and 30 percent for the 12.7 mm and 25.4 mm diameter hemispheres, respectively. The corner impacter made visible damage on the surface for even the smallest impact energy. The rod impacter acted like a punch and sliced through the composite. Even so, the critical level of pressure to initiate damage was the same for the rod and hemispherical impacters. Factors of safety for nonvisible damage increased with increasing kinetic energy of impact. The effects of impacter shape on impact force, damage size, damage visibility, and residual tensile strength were predicted quite well assuming Hertzian contact and using maximum stress criteria and a surface crack analysis.

Challenges in devising economic spray thresholds for a major pest of Australian canola, the redlegged earth mite (Halotydeus destructor).

PubMed

Arthur, Aston L; Hoffmann, Ary A; Umina, Paul A

2015-10-01

A key component for spray decision-making in IPM programmes is the establishment of economic injury levels (EILs) and economic thresholds (ETs). We aimed to establish an EIL for the redlegged earth mite (Halotydeus destructor Tucker) on canola. Complex interactions between mite numbers, feeding damage and plant recovery were found, highlighting the challenges in linking H. destructor numbers to yield. A guide of 10 mites plant(-1) was established at the first-true-leaf stage; however, simple relationships were not evident at other crop development stages, making it difficult to establish reliable EILs based on mite number. Yield was, however, strongly associated with plant damage and plant densities, reflecting the impact of mite feeding damage and indicating a plant-based alternative for establishing thresholds for H. destructor. Drawing on data from multiple field trials, we show that plant densities below 30-40 plants m(-2) could be used as a proxy for mite damage when reliable estimates of mite densities are not possible. This plant-based threshold provides a practical tool that avoids the difficulties of accurately estimating mite densities. The approach may be applicable to other situations where production conditions are unpredictable and interactions between pests and plant hosts are complex. © 2015 Society of Chemical Industry.

Mesh Convergence Requirements for Composite Damage Models

NASA Technical Reports Server (NTRS)

Davila, Carlos G.

2016-01-01

The ability of the finite element method to accurately represent the response of objects with intricate geometry and loading renders the finite element method as an extremely versatile analysis technique for structural analysis. Finite element analysis is routinely used in industry to calculate deflections, stress concentrations, natural frequencies, buckling loads, and much more. The method works by discretizing complex problems into smaller, simpler approximations that are valid over small uniform domains. For common analyses, the maximum size of the elements that can be used is often be determined by experience. However, to verify the quality of a solution, analyses with several levels of mesh refinement should be performed to ensure that the solution has converged. In recent years, the finite element method has been used to calculate the resistance of structures, and in particular that of composite structures. A number of techniques such as cohesive zone modeling, the virtual crack closure technique, and continuum damage modeling have emerged that can be used to predict cracking, delaminations, fiber failure, and other composite damage modes that lead to structural collapse. However, damage models present mesh refinement requirements that are not well understood. In this presentation, we examine different mesh refinement issues related to the representation of damage in composite materials. Damage process zone sizes and their corresponding mesh requirements will be discussed. The difficulties of modeling discontinuities and the associated need for regularization techniques will be illustrated, and some unexpected element size constraints will be presented. Finally, some of the difficulties in constructing models of composite structures capable of predicting transverse matrix cracking will be discussed. It will be shown that to predict the initiation and propagation of transverse matrix cracks, their density, and their saturation may require models that are significantly more refined than those that have been contemplated in the past.

Effect of annealing on the laser induced damage of polished and CO2 laser-processed fused silica surfaces

NASA Astrophysics Data System (ADS)

Doualle, T.; Gallais, L.; Cormont, P.; Donval, T.; Lamaignère, L.; Rullier, J. L.

2016-06-01

We investigate the effect of different heat treatments on the laser-induced damage probabilities of fused silica samples. Isothermal annealing in a furnace is applied, with different temperatures in the range 700-1100 °C and 12 h annealing time, to super-polished fused silica samples. The surface flatness and laser damage probabilities at 3 ns, 351 nm are measured before and after the different annealing procedures. We have found a significant improvement of the initial laser damage probabilities of the silica surface after annealing at 1050 °C for 12 h. A similar study has been conducted on CO2 laser-processed sites on the surface of the samples. Before and after annealing, we have studied the morphology of the sites, the evolution of residual stress, and the laser-induced damage threshold measured at 351 nm, 3 ns. In this case, we observe that the laser damage resistance of the laser created craters can reach the damage level of the bare fused silica surface after the annealing process, with a complete stress relieve. The obtained results are then compared to the case of local annealing process by CO2 laser irradiation during 1 s, and we found similar improvements in both cases. The different results obtained in the study are compared to numerical simulations made with a thermo-mechanical model based on finite-element method that allows the simulation of the isothermal or the local annealing process, the evolution of stress and fictive temperature. The simulation results were found to be very consistent with experimental observations for the stresses evolution after annealing and estimation of the heat affected area during laser-processing based on the density dependence with fictive temperature. Following this work, the temperature for local annealing should reach 1330-1470 °C for an optimized reduction of damage probability and be below the threshold for material removal, whereas furnace annealing should be kept below the annealing point to avoid sample deformation.

Adjacent Habitat Influence on Stink Bug (Hemiptera: Pentatomidae) Densities and the Associated Damage at Field Corn and Soybean Edges

PubMed Central

Venugopal, P. Dilip; Coffey, Peter L.; Dively, Galen P.; Lamp, William O.

2014-01-01

The local dispersal of polyphagous, mobile insects within agricultural systems impacts pest management. In the mid-Atlantic region of the United States, stink bugs, especially the invasive Halyomorpha halys (Stål 1855), contribute to economic losses across a range of cropping systems. Here, we characterized the density of stink bugs along the field edges of field corn and soybean at different study sites. Specifically, we examined the influence of adjacent managed and natural habitats on the density of stink bugs in corn and soybean fields at different distances along transects from the field edge. We also quantified damage to corn grain, and to soybean pods and seeds, and measured yield in relation to the observed stink bug densities at different distances from field edge. Highest density of stink bugs was limited to the edge of both corn and soybean fields. Fields adjacent to wooded, crop and building habitats harbored higher densities of stink bugs than those adjacent to open habitats. Damage to corn kernels and to soybean pods and seeds increased with stink bug density in plots and was highest at the field edges. Stink bug density was also negatively associated with yield per plant in soybean. The spatial pattern of stink bugs in both corn and soybeans, with significant edge effects, suggests the use of pest management strategies for crop placement in the landscape, as well as spatially targeted pest suppression within fields. PMID:25295593

Adjacent habitat influence on stink bug (Hemiptera: Pentatomidae) densities and the associated damage at field corn and soybean edges.

PubMed

Venugopal, P Dilip; Coffey, Peter L; Dively, Galen P; Lamp, William O

2014-01-01

The local dispersal of polyphagous, mobile insects within agricultural systems impacts pest management. In the mid-Atlantic region of the United States, stink bugs, especially the invasive Halyomorpha halys (Stål 1855), contribute to economic losses across a range of cropping systems. Here, we characterized the density of stink bugs along the field edges of field corn and soybean at different study sites. Specifically, we examined the influence of adjacent managed and natural habitats on the density of stink bugs in corn and soybean fields at different distances along transects from the field edge. We also quantified damage to corn grain, and to soybean pods and seeds, and measured yield in relation to the observed stink bug densities at different distances from field edge. Highest density of stink bugs was limited to the edge of both corn and soybean fields. Fields adjacent to wooded, crop and building habitats harbored higher densities of stink bugs than those adjacent to open habitats. Damage to corn kernels and to soybean pods and seeds increased with stink bug density in plots and was highest at the field edges. Stink bug density was also negatively associated with yield per plant in soybean. The spatial pattern of stink bugs in both corn and soybeans, with significant edge effects, suggests the use of pest management strategies for crop placement in the landscape, as well as spatially targeted pest suppression within fields.

Radiation-damage-induced transitions in zircon: Percolation theory applied to hardness and elastic moduli as a function of density

NASA Astrophysics Data System (ADS)

Beirau, Tobias; Nix, William D.; Ewing, Rodney C.; Pöllmann, Herbert; Salje, Ekhard K. H.

2018-05-01

Two in literature predicted percolation transitions in radiation-damaged zircon (ZrSiO4) were observed experimentally by measurement of the indentation hardness as a function of density and their correlation with the elastic moduli. Percolations occur near 30% and 70% amorphous fractions, where hardness deviates from its linear correlation with the elastic modulus (E), the shear modulus (G) and the bulk modulus (K). The first percolation point pc1 generates a cusp in the hardness versus density evolution, while the second percolation point is seen as a change of slope.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yeager, John D.; Bowden, Patrick R.; Guildenbecher, Daniel R.

The fragment impact response of two plastic-bonded explosive (PBX) formulations was studied using explosively driven aluminum fragments. A generic aluminum-capped detonator generated sub-mm aluminum particles moving at hypersonic velocities. The ability of these fragments to initiate reaction or otherwise damage two PBX materials was assessed using go/no-go experiments at standoff distances of up to 160 mm. Lower density PBX 9407 (RDX-based) was initiable at up to 115 mm, while higher density PBX 9501 (HMX-based) was only initiable at up to 6 mm. Several techniques were used to characterize the size, distribution, and velocity of the particles. Witness plate materials, includingmore » copper and polycarbonate, and backlit high speed video were used to characterize the distribution of particles, finding that the aluminum cap did not fragment homogeneously but rather with larger particles in a ring surrounding finer particles. Finally, precise digital holography experiments were conducted to measure the three-dimensional shape and size of the fastest-moving fragments, which ranged between 100 and 700 μm and traveled between 2.2 and 3.2 km/s. Crucially, these experiments showed variability in the fragmentation in terms of the number of fragments at the leading edge of the fragment field, indicating that both single and multiple shock impacts could be imparted to the target material. As a result, these types of data are critical for safety experiments and hydrocode simulations to quantify shock-to-detonation transition mechanisms and the associated risk-margins for these materials.« less

Natural thermal convection in fractured porous media

NASA Astrophysics Data System (ADS)

Adler, P. M.; Mezon, C.; Mourzenko, V.; Thovert, J. F.; Antoine, R.; Finizola, A.

2015-12-01

In the crust, fractures/faults can provide preferential pathways for fluid flow or act as barriers preventing the flow across these structures. In hydrothermal systems (usually found in fractured rock masses), these discontinuities may play a critical role at various scales, controlling fluid flows and heat transfer. The thermal convection is numerically computed in 3D fluid satured fractured porous media. Fractures are inserted as discrete objects, randomly distributed over a damaged volume, which is a fraction of the total volume. The fluid is assumed to satisfy Darcy's law in the fractures and in the porous medium with exchanges between them. All simulations were made for Rayleigh numbers (Ra) < 150 (hence, the fluid is in thermal equilibrium with the medium), cubic boxes and closed-top conditions. Checks were performed on an unfractured porous medium and the convection cells do start for the theoretical value of Ra, namely 4p². 2D convection was verified up to Ra=800. The influence of parameters such as fracture aperture (or fracture transmissivity), fracture density and fracture length is studied. Moreover, these models are compared to porous media with the same macroscopic permeability. Preliminary results show that the non-uniqueness associated with initial conditions which makes possible either 2D or 3D convection in porous media (Schubert & Straus 1979) is no longer true for fractured porous media (at least for 50

The atomic nature of polymer-metal interactions in adhesion, friction and wear

NASA Technical Reports Server (NTRS)

Buckley, D. H.; Brainard, W. A.

1973-01-01

Adhesion experiments with polytetra-fluoroethylene (PTFE) and polyimide contacting tungsten indicate that the polymers bond chemically to the clean metal surface. Polymer chain fragments which transfer to the surface of tungsten in field ion microscopy adhesion studies are highly oriented. Auger emission spectroscopy of PTFE transfer films to various metal surfaces indicates that the PTFE is bonded to the metal surface via the carbon atom. With PTFE in sliding contact with different orientations of aluminum, metal orientation is found to influence surfaces in sliding. The lowest friction and least amount of surface damage is detected on the highest atomic density (111) plane. The friction process itself can initiate polymer film formation from simple organic molecules.

Emulsions Containing Perfluorocarbon Support Cell Cultures

NASA Technical Reports Server (NTRS)

Ju, Lu-Kwang; Lee, Jaw Fang; Armiger, William B.

1990-01-01

Addition of emulsion containing perfluorocarbon liquid to aqueous cell-culture medium increases capacity of medium to support mammalian cells. FC-40 Fluorinert (or equivalent) - increases average density of medium so approximately equal to that of cells. Cells stay suspended in medium without mechanical stirring, which damages them. Increases density enough to prevent cells from setting, and increases viscosity of medium so oxygen bubbled through it and nutrients stirred in with less damage to delicate cells.

Fatigue Damage Mechanisms in Advanced Hybrid Titanium Composite Laminates

NASA Technical Reports Server (NTRS)

Johnson, W. Steven; Rhymer, Donald W.; St.Clair, Terry L. (Technical Monitor)

2000-01-01

Hybrid Titanium Composite Laminates (HTCL) are a type of hybrid composite laminate with promise for high-speed aerospace applications, specifically designed for improved damage tolerance and strength at high-temperature (350 F, 177 C). However, in previous testing, HTCL demonstrated a propensity to excessive delamination at the titanium/PMC interface following titanium cracking. An advanced HTCL has been constructed with an emphasis on strengthening this interface, combining a PETI-5/IM7 PMC with Ti-15-3 foils prepared with an alkaline-perborate surface treatment. This paper discusses how the fatigue capabilities of the "advanced" HTCL compare to the first generation HTCL which was not modified for interface optimization, in both tension-tension (R = 0.1) and tension-compression (R=-0.2). The advanced HTCL under did not demonstrate a significant improvement in fatigue life, in either tension-tension or tension-compression loading. However, the advanced HTCL proved much more damage tolerant. The R = 0.1 tests revealed the advanced HTCL to increase the fatigue life following initial titanium ply damage up to 10X that of the initial HTCL at certain stress levels. The damage progression following the initial ply damage demonstrated the effect of the strengthened PMC/titanium interface. Acetate film replication of the advanced HTCL edges showed a propensity for some fibers in the adjacent PMC layers to fail at the point of titanium crack formation, suppressing delamination at the Ti/PMC interface. The inspection of failure surfaces validated these findings, revealing PMC fibers bonded to the majority of the titanium surfaces. Tension compression fatigue (R = -0.2) demonstrated the same trends in cycles between initial damage and failure, damage progression, and failure surfaces. Moreover, in possessing a higher resistance to delamination, the advanced HTCL did not exhibit buckling following initial titanium ply cracking under compression unlike the initial HTCL.

A macrophage response to Mycobacterium leprae phenolic glycolipid initiates nerve damage in leprosy

PubMed Central

Madigan, Cressida A.; Cambier, C.J.; Kelly-Scumpia, Kindra M.; Scumpia, Philip O.; Cheng, Tan-Yun; Zailaa, Joseph; Bloom, Barry R.; Moody, D. Branch; Smale, Stephen T.; Sagasti, Alvaro; Modlin, Robert L.; Ramakrishnan, Lalita

2018-01-01

SUMMARY Mycobacterium leprae causes leprosy, and is unique among mycobacterial diseases in producing peripheral neuropathy. This debilitating morbidity is attributed to axon demyelination resulting from direct interactions of the M. leprae-specific phenolic glycolipid 1 (PGL-1) with myelinating glia, and their subsequent infection. Here, we use transparent zebrafish larvae to visualize the earliest events of M. leprae-induced nerve damage. We find that demyelination and axonal damage are not directly initiated by M. leprae but by infected macrophages that patrol axons; demyelination occurs in areas of intimate contact. PGL-1 confers this neurotoxic response on macrophages: macrophages infected with M. marinum expressing PGL-1 also damage axons. PGL-1 induces nitric oxide synthase in infected macrophages, and the resultant increase in reactive nitrogen species damages axons by injuring their mitochondria and inducing demyelination. Our findings implicate the response of innate macrophages to M. leprae PGL-1 in initiating nerve damage in leprosy. PMID:28841420

A Macrophage Response to Mycobacterium leprae Phenolic Glycolipid Initiates Nerve Damage in Leprosy.

PubMed

Madigan, Cressida A; Cambier, C J; Kelly-Scumpia, Kindra M; Scumpia, Philip O; Cheng, Tan-Yun; Zailaa, Joseph; Bloom, Barry R; Moody, D Branch; Smale, Stephen T; Sagasti, Alvaro; Modlin, Robert L; Ramakrishnan, Lalita

2017-08-24

Mycobacterium leprae causes leprosy and is unique among mycobacterial diseases in producing peripheral neuropathy. This debilitating morbidity is attributed to axon demyelination resulting from direct interaction of the M. leprae-specific phenolic glycolipid 1 (PGL-1) with myelinating glia and their subsequent infection. Here, we use transparent zebrafish larvae to visualize the earliest events of M. leprae-induced nerve damage. We find that demyelination and axonal damage are not directly initiated by M. leprae but by infected macrophages that patrol axons; demyelination occurs in areas of intimate contact. PGL-1 confers this neurotoxic response on macrophages: macrophages infected with M. marinum-expressing PGL-1 also damage axons. PGL-1 induces nitric oxide synthase in infected macrophages, and the resultant increase in reactive nitrogen species damages axons by injuring their mitochondria and inducing demyelination. Our findings implicate the response of innate macrophages to M. leprae PGL-1 in initiating nerve damage in leprosy. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

Difference in transient ischemia-induced neuronal damage and glucose transporter-1 immunoreactivity in the hippocampus between adult and young gerbils

PubMed Central

Park, Seung Min; Lee, Jae-Chul; Chen, Bai Hui; Shin, Bich-Na; Cho, Jeong Hwi; Kim, In Hye; Park, Joon Ha; Won, Moo-Ho; Ahn, Ji Hyeon; Tae, Hyun-Jin; Shin, Myoung Cheol; Park, Chan Woo; Cho, Jun Hwi; Lee, Hui Young

2016-01-01

Objective(s): The alteration of glucose transporters is closely related with the pathogenesis of brain edema. We compared neuronal damage/death in the hippocampus between adult and young gerbils following transient cerebral ischemia/reperfusion and changes of glucose transporter-1(GLUT-1)-immunoreactive microvessels in their ischemic hippocampal CA1 region. Materials and Methods: Transient cerebral ischemia was developed by 5-min occlusion of both common carotid arteries. Neuronal damage was examined by cresyl violet staining, NeuN immunohistochemistry and Fluoro-Jade B histofluorescence staining and changes in GLUT-1 expression was carried out by immunohistochemistry. Results: About 90% of pyramidal neurons only in the adult CA1 region were damaged after ischemia/reperfusion; in the young, about 53 % of pyramidal neurons were damaged from 7 days after ischemia/reperfusion. The density of GLUT-1-immunoreactive microvessels was significantly higher in the young sham-group than that in the adult sham-group. In the ischemia-operated-groups, the density of GLUT-1-immunoreactive microvessels was significantly decreased in the adult and young at 1 and 4 days post-ischemia, respectively, thereafter, the density of GLUT-1-immunoreactive microvessels was gradually increased in both groups after ischemia/reperfusion. Conclusion: CA1 pyramidal neurons of the young gerbil were damaged much later than that in the adult and that GLUT-1-immunoreactive microvessels were significantly decreased later in the young. These data indicate that GLUT-1 might differently contribute to neuronal damage according to age after ischemic insults. PMID:27403259

Thermomechanical fatigue life prediction for several solders

NASA Astrophysics Data System (ADS)

Wen, Shengmin

Since solder connections operate at high homologous temperature, solders are high temperature materials. This feature makes their mechanical behavior and fatigue phenomena unique. Based on experimental findings, a physical damage mechanism is introduced for solders. The mechanism views the damage process as a series of independent local damage events characterized by the failure of individual grains, while the structural damage is the eventual percolation result of such local events. Fine's dislocation energy density concept and Mura's microcrack initiation theory are adopted to derive the fatigue formula for an individual grain. A physical damage metric is introduced to describe the material with damage. A unified creep and plasticity constitutive model is adopted to simulate the mechanical behavior of solders. The model is cast into a continuum damage mechanics framework to simulate material with damage. The model gives good agreement with the experimental results of 96.5Pb-3.5Sn and 96.5Sn-3.5Ag solders under uniaxial strain-controlled cyclic loading. The model is convenient for implementation into commercial computational packages. Also presented is a fatigue theory with its failure criterion for solders based on physical damage mechanism. By introducing grain orientation into the fatigue formula, an m-N curve (m is Schmid factor) at constant loading condition is suggested for fatigue of grains with different orientations. A solder structure is defined as fatigued when the damage metric reaches a critical threshold, since at this threshold the failed grains may form a cluster and percolate through the structure according to percolation theory. Fatigue data of 96.5Pb-3.5Sn solder bulk specimens under various uniaxial tension tests were analyzed. Results show that the theory gives consistent predictions under broad conditions, while inelastic strain theory does not. The theory is anisotropic with no size limitation to its application, which could be suitable for anisotropic small-scale (micron or nano scale) solder joints. More importantly, the theory is materials science based so that the parameters of the fatigue formula can be worked out by testing of bulk specimens while the formula can be applicable to small-scale structures. The theory suggests metallurgical control in the manufacturing process to optimize the fatigue life of solder structures.

Healing of damaged metal by a pulsed high-energy electromagnetic field

NASA Astrophysics Data System (ADS)

Kukudzhanov, K. V.; Levitin, A. L.

2018-04-01

The processes of defect (intergranular micro-cracks) transformation are investigated for metal samples in a high-energy short-pulsed electromagnetic field. This investigation is based on a numerical coupled model of the impact of high-energy electromagnetic field on the pre-damaged thermal elastic-plastic material with defects. The model takes into account the melting and evaporation of the metal and the dependence of its physical and mechanical properties on the temperature. The system of equations is solved numerically by finite element method with an adaptive mesh using the arbitrary Euler–Lagrange method. The calculations show that the welding of the crack and the healing of micro-defects under treatment by short pulses of the current takes place. For the macroscopic description of the healing process, the healing and damage parameters of the material are introduced. The healing of micro-cracks improves the material healing parameter and reduces its damage. The micro-crack shapes practically do not affect the time-dependence of the healing and damage under the treatment by the current pulses. These changes are affected only by the value of the initial damage of the material and the initial length of the micro-crack. The time-dependence of the healing and the damage is practically the same for all different shapes of micro-defects, provided that the initial lengths of micro-cracks and the initial damages are the same for these different shapes of defects.

Radiation Tolerant Interfaces: Influence of Local Stoichiometry at the Misfit Dislocation on Radiation Damage Resistance of Metal/Oxide Interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shutthanandan, Vaithiyalingam; Choudhury, Samrat; Manandhar, Sandeep

To understand how variations in interface properties such as misfit-dislocation density and local chemistry affect radiation-induced defect absorption and recombination, we have explored a model system of CrxV1-x alloy epitaxial films deposited on MgO single crystals. By controlling film composition, the lattice mismatch with MgO was adjusted so that the misfit-dislocation density varies at the interface. These interfaces were exposed to irradiation and in situ results show that the film with a semi-coherent interface (Cr) withstands irradiation while V film, which has similar semi-coherent interface like Cr, showed the largest damage. Theoretical calculations indicate that, unlike at metal/metal interfaces, themore » misfit dislocation density does not dominate radiation damage tolerance at metal/oxide interfaces. Rather, the stoichiometry, and the precise location of the misfit-dislocation density relative to the interface, drives defect behavior. Together, these results demonstrate the sensitivity of defect recombination to interfacial chemistry and provide new avenues for engineering radiation-tolerant nanomaterials.« less

Bilateral cerebellar and brain stem infarction resulting from vertebral artery injury following cervical trauma without radiographic damage of the spinal column: a case report.

PubMed

Mimata, Yoshikuni; Murakami, Hideki; Sato, Kotaro; Suzuki, Yoshiaki

2014-01-01

Vertebral artery injury can be a complication of cervical spine injury. Although most cases are asymptomatic, the rare case progresses to severe neurological impairment and fatal outcomes. We experienced a case of bilateral cerebellar and brain stem infarction with fatal outcome resulting from vertebral artery injury associated with cervical spine trauma. A 69-year-old male was admitted to our hospital because of tetraplegia after falling down the stairs and hitting his head on the floor. Marked bony damage of the cervical spine was not apparent on radiographs and CT scans, so the injury was initially considered to be a cervical cord injury without bony damage. However, an intensity change in the intervertebral disc at C5/C6, and a ventral epidural hematoma were observed on MRI. A CT angiogram of the neck showed the right vertebral artery was completely occluded at the C4 level of the spine. Forty-eight hours after injury, the patient lapsed into drowsy consciousness. The cranial CT scan showed a massive low-density area in the bilateral cerebellar hemispheres and brain stem. Anticoagulation was initiated after a diagnosis of the right vertebral artery injury, but the patient developed bilateral cerebellar and brain stem infarction. The patient's brain herniation progressed and the patient died 52 h after injury. We considered that not only anticoagulation but also treatment for thrombosis would have been needed to prevent cranial embolism. We fully realize that early and appropriate treatment are essential to improve the treatment results, and constructing a medical system with a team of orthopedists, radiologists, and neurosurgeons is also very important.

Effects of plant density on the photosynthetic and chloroplast characteristics of maize under high-yielding conditions

NASA Astrophysics Data System (ADS)

Ren, Baizhao; Liu, Wei; Zhang, Jiwang; Dong, Shuting; Liu, Peng; Zhao, Bin

2017-04-01

Plant density has been recognized as a major factor determining the grain yield. The photosynthetic performance changes as the density increases. The main objective of this research was to evaluate responses of photosynthetic performance and chloroplast ultrastructure to planting densities in two summer maize ( Zea mays L.) hybrids Denghai661 (DH661) and Nongda108 (ND108). DH661 was planted at densities of 30,000, 45,000, 60,000, 75,000, 90,000, 105,000, 120,000, or 135,000 plants ha-1. ND108 was planted at densities of 30,000, 45,000, 60,000, 75,000, or 90,000 plants ha-1. Research variables included leaf area, grain yield, chlorophyll content, leaf gas exchange parameters, number of chloroplasts, and chloroplast ultrastructure. As plant density increased, chlorophyll a and b content significantly decreased; carotenoids initially decreased and then increased; the net photosynthetic rate during each growth period significantly decreased; the membrane structure of mesophyll cells was gradually damaged; the number of chloroplasts significantly decreased; the external form of chloroplasts shifted from long and oval to elliptical or circular; the number of grana significantly decreased, while the number of grana lamellae increased; grana gradually became hypogenetic and eventually dissolved; plot yield increased; and yield per plant significantly decreased. The yield per plant of DH661 at 135,000 plants ha-1 and that of ND108 at 90,000 plants ha-1 decreased by 65.8 and 42.5%, respectively, compared with those at 30,000 plants ha-1.

Induction and repair of DNA strand breaks in bovine lens epithelial cells after high LET irradiation.

PubMed

Baumstark-Khan, C; Heilmann, J; Rink, H

2003-01-01

The lens epithelium is the initiation site for the development of radiation induced cataracts. Radiation in the cortex and nucleus interacts with proteins, while in the epithelium, experimental results reveal mutagenic and cytotoxic effects. It is suggested that incorrectly repaired DNA damage may be lethal in terms of cellular reproduction and also may initiate the development of mutations or transformations in surviving cells. The occurrence of such genetically modified cells may lead to lens opacification. For a quantitative risk estimation for astronauts and space travelers it is necessary to know the relative biological effectiveness (RBE), because the spacial and temporal distribution of initial physical damage induced by cosmic radiation differ significantly from that of X-rays. RBEs for the induction of DNA strand breaks and the efficiency of repair of these breaks were measured in cultured diploid bovine lens epithelial cells exposed to different LET irradiation to either 300 kV X-rays or to heavy ions at the UNILAC accelerator at GSI. Accelerated ions from Z=8 (O) to Z=92 (U) were used. Strand breaks were measured by hydroxyapatite chromatography of alkaline unwound DNA (overall strand breaks). Results showed that DNA damage occurs as a function of dose, of kinetic energy and of LET. For particles having the same LET the severity of the DNA damage increases with dose. For a given particle dose, as the LET rises, the numbers of DNA strand breaks increase to a maximum and then reach a plateau or decrease. Repair kinetics depend on the fluence (irradiation dose). At any LET value, repair is much slower after heavy ion exposure than after X-irradiation. For ions with an LET of less than 10,000 keV micrometers-1 more than 90 percent of the strand breaks induced are repaired within 24 hours. At higher particle fluences, especially for low energetic particles with a very high local density of energy deposition within the particle track, a higher proportion of non-rejoined breaks is found, even after prolonged periods of incubation. At the highest LET value (16,300 keV micrometers-1) no significant repair is observed. These LET-dependencies are consistent with the current mechanistic model for radiation induced cataractogenesis which postulates that genomic damage to the surviving fraction of epithelial cells is responsible for lens opacification. c2003 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

Progressive Fracture of [0/90/ + or - Theta]s Composite Structure Under Uniform Pressure Load

NASA Technical Reports Server (NTRS)

Gotsis, Pascalis K.; Chamis, Christos C.; Gotsis, Christos K.; Mouratidis, Ericos

2007-01-01

S-Glass/epoxy [0/90/plus or minus theta]s for theta =45 deg., 60 deg., and 75 deg. laminated fiber-reinforced composite stiffened plate was simulated to investigated for damage and fracture progression under uniform pressure. An integrated computer code was augmented for the simulation of the damage initiation, growth, accumulation, and propagation to fracture and to structural collapse. Results show in detail the damage progression sequence and structural fracture resistance during different degradation stages. Damage through the thickness of the laminate initiated first at [0/90/plus or minus 45]s at 15.168 MPa (2200 psi), followed by [0/90/plus or minus 60]s at 16.96 MPa (2460 psi) and finally by [0/90/plus or minus 75]s at 19.3 MPa (2800 psi). After damage initiation happened the cracks propagate rapidly to structural fracture.

A two-population sporadic meteoroid bulk density distribution and its implications for environment models

NASA Astrophysics Data System (ADS)

Moorhead, Althea V.; Blaauw, Rhiannon C.; Moser, Danielle E.; Campbell-Brown, Margaret D.; Brown, Peter G.; Cooke, William J.

2017-12-01

The bulk density of a meteoroid affects its dynamics in space, its ablation in the atmosphere, and the damage it does to spacecraft and lunar or planetary surfaces. Meteoroid bulk densities are also notoriously difficult to measure, and we are typically forced to assume a density or attempt to measure it via a proxy. In this paper, we construct a density distribution for sporadic meteoroids based on existing density measurements. We considered two possible proxies for density: the KB parameter introduced by Ceplecha and Tisserand parameter, TJ. Although KB is frequently cited as a proxy for meteoroid material properties, we find that it is poorly correlated with ablation-model-derived densities. We therefore follow the example of Kikwaya et al. in associating density with the Tisserand parameter. We fit two density distributions to meteoroids originating from Halley-type comets (TJ < 2) and those originating from all other parent bodies (TJ > 2); the resulting two-population density distribution is the most detailed sporadic meteoroid density distribution justified by the available data. Finally, we discuss the implications for meteoroid environment models and spacecraft risk assessments. We find that correcting for density increases the fraction of meteoroid-induced spacecraft damage produced by the helion/antihelion source.

The role of defects in laser-induced modifications of silica coatings and fused silica using picosecond pulses at 1053 nm: I Damage morphology

DOE PAGES

Laurence, T. A.; Ly, S.; Shen, N.; ...

2017-06-22

Laser-induced damage with ps pulse widths straddles the transition from intrinsic, multi-photon ionization and avalanche ionization-based ablation with fs pulses to defect-dominated, thermal-based damage with ns pulses. We investigated the morphology of damage for fused silica and silica coatings between 1 ps and 60 ps at 1053 nm. Using calibrated laser-induced damage experiments, in situ imaging, and high-resolution optical microscopy, atomic force microscopy, and scanning electron microscopy, we show that defects play an important role in laser-induced damage down to 1 ps. Three types of damage are observed: ablation craters, ultra-high density pits, and smooth, circular depressions with central pits.more » For 10 ps and longer, the smooth, circular depressions limit the damage performance of fused silica and silica coatings. The observed high-density pits and material removal down to 3 ps indicate that variations in surface properties limit the laser-induced damage onset to a greater extent than expected below 60 ps. Below 3 ps, damage craters are smoother although there is still evidence as seen by AFM of inhomogeneous laser-induced damage response very near the damage onset. These results show that modeling the damage onset only as a function of pulse width does not capture the convoluted processes leading to laser induced damage with ps pulses. It is necessary to account for the effects of defects on the processes leading to laser-induced damage. In conclusion, the effects of isolated defects or inhomogeneities are most pronounced above 3 ps but are still discernible and possibly important down to the shortest pulse width investigated here.« less

The role of defects in laser-induced modifications of silica coatings and fused silica using picosecond pulses at 1053 nm: I Damage morphology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laurence, T. A.; Ly, S.; Shen, N.

Laser-induced damage with ps pulse widths straddles the transition from intrinsic, multi-photon ionization and avalanche ionization-based ablation with fs pulses to defect-dominated, thermal-based damage with ns pulses. We investigated the morphology of damage for fused silica and silica coatings between 1 ps and 60 ps at 1053 nm. Using calibrated laser-induced damage experiments, in situ imaging, and high-resolution optical microscopy, atomic force microscopy, and scanning electron microscopy, we show that defects play an important role in laser-induced damage down to 1 ps. Three types of damage are observed: ablation craters, ultra-high density pits, and smooth, circular depressions with central pits.more » For 10 ps and longer, the smooth, circular depressions limit the damage performance of fused silica and silica coatings. The observed high-density pits and material removal down to 3 ps indicate that variations in surface properties limit the laser-induced damage onset to a greater extent than expected below 60 ps. Below 3 ps, damage craters are smoother although there is still evidence as seen by AFM of inhomogeneous laser-induced damage response very near the damage onset. These results show that modeling the damage onset only as a function of pulse width does not capture the convoluted processes leading to laser induced damage with ps pulses. It is necessary to account for the effects of defects on the processes leading to laser-induced damage. In conclusion, the effects of isolated defects or inhomogeneities are most pronounced above 3 ps but are still discernible and possibly important down to the shortest pulse width investigated here.« less

Carbon nanotube-embedded advanced aerospace composites for early-stage damage sensing

NASA Astrophysics Data System (ADS)

Nataraj, Latha; Coatney, Michael; Cain, Jason; Hall, Asha

2018-03-01

Fiber reinforced polymer (FRP) composites featuring outstanding fatigue performance, high specific stiffness and strength, and low density have evolved as critical structural materials in aerospace applications. Microscale damage such as fiber breakage, matrix cracking, and delamination could occur in layered composites compromising structural integrity, emphasizing the critical need to monitor structural health. Early damage detection would lead to enhanced reliability, lifetime, and performance while minimizing maintenance time, leading to enormous scientific and technical interest in realizing physically stable, quick responding, and cost effective strain sensing materials, devices, and techniques with high sensitivity over a broad range of the practical strain spectrum. Today's most commonly used strain sensing techniques are metal foil strain gauges and optical fiber sensors. Metal foil gauges offer high stability and cost-effectiveness but can only be surface-mounted and have a low gauge factor. Optical fibers require expensive instrumentation, are mostly insensitive to cracks parallel to the fiber orientation and may lead to crack initiation as the diameter is larger than that of the reinforcement fibers. Carbon nanotubes (CNTs) have attracted much attention due to high aspect ratio and superior electrical, thermal, and mechanical properties. CNTs embedded in layered composites have improved performance. A variety of CNT architectures and configurations have shown improved piezoresistive behavior and stability for sensing applications. However, scaling up and commercialization remain serious challenges. The current study investigates a simple, cost effective and repeatable technique for highly sensitive, stable, linear and repeatable strain sensing for damage detection by integrating CNT laminates into composites.

A two-stage model of fracture of rocks

USGS Publications Warehouse

Kuksenko, V.; Tomilin, N.; Damaskinskaya, E.; Lockner, D.

1996-01-01

In this paper we propose a two-stage model of rock fracture. In the first stage, cracks or local regions of failure are uncorrelated occur randomly throughout the rock in response to loading of pre-existing flaws. As damage accumulates in the rock, there is a gradual increase in the probability that large clusters of closely spaced cracks or local failure sites will develop. Based on statistical arguments, a critical density of damage will occur where clusters of flaws become large enough to lead to larger-scale failure of the rock (stage two). While crack interaction and cooperative failure is expected to occur within clusters of closely spaced cracks, the initial development of clusters is predicted based on the random variation in pre-existing Saw populations. Thus the onset of the unstable second stage in the model can be computed from the generation of random, uncorrelated damage. The proposed model incorporates notions of the kinetic (and therefore time-dependent) nature of the strength of solids as well as the discrete hierarchic structure of rocks and the flaw populations that lead to damage accumulation. The advantage offered by this model is that its salient features are valid for fracture processes occurring over a wide range of scales including earthquake processes. A notion of the rank of fracture (fracture size) is introduced, and criteria are presented for both fracture nucleation and the transition of the failure process from one scale to another.

Characteristics and mechanism of laser-induced surface damage initiated by metal contaminants

NASA Astrophysics Data System (ADS)

Shi, Shuang; Sun, Mingying; Shi, Shuaixu; Li, Zhaoyan; Zhang, Ya-nan; Liu, Zhigang

2015-08-01

In high power laser facility, contaminants on optics surfaces reduce damage resistance of optical elements and then decrease their lifetime. By damage test experiments, laser damage induced by typical metal particles such as stainless steel 304 is studied. Optics samples with metal particles of different sizes on surfaces are prepared artificially based on the file and sieve. Damage test is implemented in air using a 1-on-1 mode. Results show that damage morphology and mechanism caused by particulate contamination on the incident and exit surfaces are quite different. Contaminants on the incident surface absorb laser energy and generate high temperature plasma during laser irradiation which can ablate optical surface. Metal particles melt and then the molten nano-particles redeposit around the initial particles. Central region of the damaged area bears the same outline as the initial particle because of the shielding effect. However, particles on the exit surface absorb a mass of energy, generate plasma and splash lots of smaller particles, only a few of them redeposit at the particle coverage area on the exit surface. Most of the laser energy is deposited at the interface of the metal particle and the sample surface, and thus damage size on the exit surface is larger than that on the incident surface. The areas covered by the metal particle are strongly damaged. And the damage sites are more serious than that on the incident surface. Besides damage phenomenon also depends on coating and substrate materials.

Initial stages of cavitation damage and erosion on copper and brass tested in a rotating disk device

NASA Technical Reports Server (NTRS)

Rao, P. V.; Rao, B. C. S.; Rao, N. S. L.

1982-01-01

In view of the differences in flow and experimental conditions, there has been a continuing debate as to whether or not the ultrasonic method of producing cavitation damage is similar to the damage occurring in cavitating flow systems, namely, venturi and rotating disk devices. In this paper, the progress of cavitation damage during incubation periods on polycrystalline copper and brass tested in a rotating disk device is presented. The results indicate several similarities and differences in the damage mechanism encountered in a rotating disk device (which simulates field rotary devices) and a magnetostriction apparatus. The macroscopic erosion appears similar to that in the vibratory device except for nonuniform erosion and apparent plastic flow during the initial damage phase.

Relevance of impacter shape to nonvisible damage and residual tensile strength of a thick graphite/epoxy laminate

NASA Technical Reports Server (NTRS)

Poe, C. C., Jr.

1990-01-01

A study was made to determine the relevance of impacter shape to nonvisible damage and tensile residual strength of a 36 mm (1.4 in.) thick graphite/epoxy motor case. The shapes of the impacters were as follows: 12.7 mm (0.5 in.) and 25.4 mm (1.0 in.) diameter hemispheres, a sharp corner, and a 6.3 mm (0.25 in.) diameter bolt-like rod. The investigation revealed that damage initiated when the contact pressure exceeded a critical level. However, the damage was not visible on the surface until an even higher pressure was exceeded. The damage on the surface consisted of a crater shaped like the impacter, and the damage below the surface consisted of broken fibers. The impact energy to initiate damage or cause visible damage on the surface increased approximately with impacter diameter to the third power. The reduction in strength for nonvisible damage increased with increasing diameter, 9 and 30 percent for the 12.7 mm (0.5 in.) and 25.4 mm (1.0 in.) diameter hemispheres, respectively. The corner impacter made visible damage on the surface for even the smallest impact energy. The rod impacter acted like a punch and sliced through the composite. Even so, the critical level of pressure to initiate damage was the same for the rod and hemispherical impacters. Factors of safety for nonvisible damage increased with increasing kinetic energy of impact. The effects of impacter shape on impact force, damage size, damage visibility, and residual tensile strength were predicted quite well assuming Hertzian contact and using maximum stress criteria and a surface crack analysis.

Excessive centrifugal fields damage high density lipoprotein[S

PubMed Central

Munroe, William H.; Phillips, Martin L.; Schumaker, Verne N.

2015-01-01

HDL is typically isolated ultracentrifugally at 40,000 rpm or greater, however, such high centrifugal forces are responsible for altering the recovered HDL particle. We demonstrate that this damage to HDL begins at approximately 30,000 rpm and the magnitude of loss increases in a rotor speed-dependent manner. The HDL is affected by elevated ultracentrifugal fields resulting in a lower particle density due to the shedding of associated proteins. To circumvent the alteration of the recovered HDL, we utilize a KBr-containing density gradient and a lowered rotor speed of 15,000 rpm to separate the lipoproteins using a single 96 h centrifugation step. This recovers the HDL at two density ranges; the bulk of the material has a density of about 1.115 g/ml, while lessor amounts of material are recovered at >1.2 g/ml. Thus, demonstrating the isolation of intact HDL is possible utilizing lower centrifuge rotor speeds. PMID:25910941

Hydrogen Permeability of Polymer Matrix Composites at Cryogenic Temperatures

NASA Technical Reports Server (NTRS)

Grenoble, Ray W.; Gates, Thomas S

2005-01-01

This paper presents experimental methods and results of an ongoing study of the correlation between damage state and hydrogen gas permeability of laminated composite materials under mechanical strains and thermal loads. A specimen made from IM-7/977-2 composite material has been mechanically cycled at room temperature to induce microcrack damage. Crack density and tensile modulus were observed as functions of number of cycles. Damage development was found to occur most quickly in the off-axis plies near the outside of the laminate. Permeability measurements were made after 170,000 cycles and 430,000 cycles. Leak rate was found to depend on applied mechanical strain, crack density, and test temperature.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Doualle, T.; Gallais, L., E-mail: laurent.gallais@fresnel.fr; Cormont, P.

We investigate the effect of different heat treatments on the laser-induced damage probabilities of fused silica samples. Isothermal annealing in a furnace is applied, with different temperatures in the range 700–1100 °C and 12 h annealing time, to super-polished fused silica samples. The surface flatness and laser damage probabilities at 3 ns, 351 nm are measured before and after the different annealing procedures. We have found a significant improvement of the initial laser damage probabilities of the silica surface after annealing at 1050 °C for 12 h. A similar study has been conducted on CO{sub 2} laser-processed sites on the surface of the samples. Before andmore » after annealing, we have studied the morphology of the sites, the evolution of residual stress, and the laser-induced damage threshold measured at 351 nm, 3 ns. In this case, we observe that the laser damage resistance of the laser created craters can reach the damage level of the bare fused silica surface after the annealing process, with a complete stress relieve. The obtained results are then compared to the case of local annealing process by CO{sub 2} laser irradiation during 1 s, and we found similar improvements in both cases. The different results obtained in the study are compared to numerical simulations made with a thermo-mechanical model based on finite-element method that allows the simulation of the isothermal or the local annealing process, the evolution of stress and fictive temperature. The simulation results were found to be very consistent with experimental observations for the stresses evolution after annealing and estimation of the heat affected area during laser-processing based on the density dependence with fictive temperature. Following this work, the temperature for local annealing should reach 1330–1470 °C for an optimized reduction of damage probability and be below the threshold for material removal, whereas furnace annealing should be kept below the annealing point to avoid sample deformation.« less

Influence of interface ply orientation on fatigue damage of adhesively bonded composite joints

NASA Technical Reports Server (NTRS)

Johnson, W. S.; Mall, S.

1985-01-01

An experimental study of cracked-lap-shear specimens was conducted to determine the influence of adherend stacking sequence on debond initiation and damage growth in a composite-to-composite bonded joint. Specimens consisted of quasi-isotropic graphite/epoxy adherends bonded together with either FM-300 or EC 3445 adhesives. The stacking sequence of the adherends was varied such that 0 deg, 45 deg, or 90 deg plies were present at the adherend-adhesive interfaces. Fatigue damage initiated in the adhesive layer in those specimens with 0 deg nd 45 deg interface plies. Damage initiated in the form of ply cracking in the strap adherend for the specimens with 90 deg interface plies. The fatigue-damage growth was in the form of delamination within the composite adherends for specimens with the 90 deg and 45 deg plies next to the adhesive, while debonding in the adhesive resulted for the specimens with 0 deg plies next to the adhesive. Those joints with the 0 deg and 45 deg plies next to either adhesive has essentially the same fatigue-damage-initiation stress levels. These stress levels were 13 and 71 percent higher, respectively, than those for specimens with 90 deg plies next to the EC 3445 and FM-300 adhesives.

Weak trophic interactions among birds, insects and white oak saplings (Quercus alba)

USGS Publications Warehouse

Lichtenberg, J.S.; Lichtenberg, D.A.

2002-01-01

We examined the interactions among insectivorous birds, arthropods and white oak saplings (Quercus alba L.) in a temperate deciduous forest under 'open' and 'closed' canopy environments. For 2 y, we compared arthropod densities, leaf damage and sapling growth. Saplings from each canopy environment were assigned to one of four treatments: (1) reference, (2) bird exclosure, (3) insecticide and (4) exclosure + insecticide. Sap-feeding insects were the most abundant arthropod feeding guild encountered and birds reduced sap-feeder densities in 1997, but not in 1998. Although there was no detectable influence of birds on leaf-chewer densities in either year, leaf damage to saplings was greater within bird exclosures than outside of bird exclosures in 1997. Insecticide significantly reduced arthropod densities and leaf damage to saplings, but there was no corresponding increase in sapling growth. Growth and biomass were greater for saplings in more open canopy environments for both years. Sap-feeder densities were higher on closed canopy than open canopy saplings in 1997, but canopy environment did not influence the effects of birds on lower trophic levels. Although previous studies have found birds to indirectly influence plant growth and biomass, birds did not significantly influence the growth or biomass of white oak saplings during our study.

Tree Species Composition and Harvest Intensity Affect Herbivore Density and Leaf Damage on Beech, Fagus sylvatica, in Different Landscape Contexts

PubMed Central

Mangels, Jule; Blüthgen, Nico; Frank, Kevin; Grassein, Fabrice; Hilpert, Andrea; Mody, Karsten

2015-01-01

Most forests are exposed to anthropogenic management activities that affect tree species composition and natural ecosystem processes. Changes in ecosystem processes such as herbivory depend on management intensity, and on regional environmental conditions and species pools. Whereas influences of specific forest management measures have already been addressed for different herbivore taxa on a local scale, studies considering effects of different aspects of forest management across different regions are rare. We assessed the influence of tree species composition and intensity of harvesting activities on arthropod herbivores and herbivore-related damage to beech trees, Fagus sylvatica, in 48 forest plots in three regions of Germany. We found that herbivore abundance and damage to beech trees differed between regions and that – despite the regional differences - density of tree-associated arthropod taxa and herbivore damage were consistently affected by tree species composition and harvest intensity. Specifically, overall herbivore damage to beech trees increased with increasing dominance of beech trees – suggesting the action of associational resistance processes – and decreased with harvest intensity. The density of leaf chewers and mines was positively related to leaf damage, and several arthropod groups responded to beech dominance and harvest intensity. The distribution of damage patterns was consistent with a vertical shift of herbivores to higher crown layers during the season and with higher beech dominance. By linking quantitative data on arthropod herbivore abundance and herbivory with tree species composition and harvesting activity in a wide variety of beech forests, our study helps to better understand the influence of forest management on interactions between a naturally dominant deciduous forest tree and arthropod herbivores. PMID:25938417

Effects of the nematicide imicyafos on soil nematode community structure and damage to radish caused by Pratylenchus penetrans

PubMed Central

Toyota, Koki; Takada, Atsushi

2011-01-01

The effects of the non-fumigant nematicide imicyafos on soil nematode community structure and damage to radish caused by Pratylenchus penetrans were evaluated in two field experiments in consecutive years (2007 and 2008). Nematode densities in soil at 0 - 10 cm (the depth of nematicide incorporation) and 10 - 30 cm were measured. The application of imicyafos had a significant impact on the density of P. penetrans at 0 - 10 cm but had no effect on free-living nematode density. PCR-DGGE analysis conducted using extracted nematodes showed that the nematode community structure 12 d after application in 2007 was altered by the application of imicyafos at the 0 - 10 cm depth, but not at 10 - 30 cm. No significant differences were observed in the diversity of the nematode community at harvest (89 and 91 d after application) between the control and imicyafos treatments in both depths and both years. In both years, the damage to radish caused by P. penetrans was markedly suppressed by the nematicide. Overall, the nematicide imicyafos decreased populations of P. penetrans in soil and thereby decreased damage to radish, while having little impact on the soil nematode community. PMID:22791909

Experimental study of ELM-like heat loading on beryllium under ITER operational conditions

NASA Astrophysics Data System (ADS)

Spilker, B.; Linke, J.; Pintsuk, G.; Wirtz, M.

2016-02-01

The experimental fusion reactor ITER, currently under construction in Cadarache, France, is transferring the nuclear fusion research to the power plant scale. ITER’s first wall (FW), armoured by beryllium, is subjected to high steady state and transient power loads. Transient events like edge localized modes not only deposit power densities of up to 1.0 GW m-2 for 0.2-0.5 ms in the divertor of the machine, but also affect the FW to a considerable extent. Therefore, a detailed study was performed, in which transient power loads with absorbed power densities of up to 1.0 GW m-2 were applied by the electron beam facility JUDITH 1 on beryllium specimens at base temperatures of up to 300 °C. The induced damage was evaluated by means of scanning electron microscopy and laser profilometry. As a result, the observed damage was highly dependent on the base temperatures and absorbed power densities. In addition, five different classes of damage, ranging from ‘no damage’ to ‘crack network plus melting’, were defined and used to locate the damage, cracking, and melting thresholds within the tested parameter space.

Diagnosis of retrofit fatigue crack re-initiation and growth in steel-girder bridges for proactive repair and emergency planning.

DOT National Transportation Integrated Search

2014-07-01

This report presents a vibration : - : based damage : - : detection methodology that is capable of effectively capturing crack growth : near connections and crack re : - : initiation of retrofitted connections. The proposed damage detection algorithm...

A review on plasma-etch-process induced damage of HgCdTe

NASA Astrophysics Data System (ADS)

Liu, Lingfeng; Chen, Yiyu; Ye, Zhenhua; Ding, Ruijun

2018-05-01

Dry etching techniques with minimal etch induced damage are required to develop highly anisotropic etch for pixel delineation of HgCdTe infrared focal plane arrays (IRFPAs). High density plasma process has become the main etching technique for HgCdTe in the past twenty years, In this paper, high density plasma electron cyclotron resonance (ECR) and inductively coupled plasma (ICP) etching of HgCdTe are summarized. Common plasma-etch-process induced type conversion and related mechanisms are reviewed particularly.

Micromechanics Based Failure Analysis of Heterogeneous Materials

NASA Astrophysics Data System (ADS)

Sertse, Hamsasew M.

In recent decades, heterogeneous materials are extensively used in various industries such as aerospace, defense, automotive and others due to their desirable specific properties and excellent capability of accumulating damage. Despite their wide use, there are numerous challenges associated with the application of these materials. One of the main challenges is lack of accurate tools to predict the initiation, progression and final failure of these materials under various thermomechanical loading conditions. Although failure is usually treated at the macro and meso-scale level, the initiation and growth of failure is a complex phenomena across multiple scales. The objective of this work is to enable the mechanics of structure genome (MSG) and its companion code SwiftComp to analyze the initial failure (also called static failure), progressive failure, and fatigue failure of heterogeneous materials using micromechanics approach. The initial failure is evaluated at each numerical integration point using pointwise and nonlocal approach for each constituent of the heterogeneous materials. The effects of imperfect interfaces among constituents of heterogeneous materials are also investigated using a linear traction-displacement model. Moreover, the progressive and fatigue damage analyses are conducted using continuum damage mechanics (CDM) approach. The various failure criteria are also applied at a material point to analyze progressive damage in each constituent. The constitutive equation of a damaged material is formulated based on a consistent irreversible thermodynamics approach. The overall tangent modulus of uncoupled elastoplastic damage for negligible back stress effect is derived. The initiation of plasticity and damage in each constituent is evaluated at each numerical integration point using a nonlocal approach. The accumulated plastic strain and anisotropic damage evolution variables are iteratively solved using an incremental algorithm. The damage analyses are performed for both brittle failure/high cycle fatigue (HCF) for negligible plastic strain and ductile failure/low cycle fatigue (LCF) for large plastic strain. The proposed approach is incorporated in SwiftComp and used to predict the initial failure envelope, stress-strain curve for various loading conditions, and fatigue life of heterogeneous materials. The combined effects of strain hardening and progressive fatigue damage on the effective properties of heterogeneous materials are also studied. The capability of the current approach is validated using several representative examples of heterogeneous materials including binary composites, continuous fiber-reinforced composites, particle-reinforced composites, discontinuous fiber-reinforced composites, and woven composites. The predictions of MSG are also compared with the predictions obtained using various micromechanics approaches such as Generalized Methods of Cells (GMC), Mori-Tanaka (MT), and Double Inclusions (DI) and Representative Volume Element (RVE) Analysis (called as 3-dimensional finite element analysis (3D FEA) in this document). This study demonstrates that a micromechanics based failure analysis has a great potential to rigorously and more accurately analyze initiation and progression of damage in heterogeneous materials. However, this approach requires material properties specific to damage analysis, which are needed to be independently calibrated for each constituent.

Fatigue damage behavior of a surface-mount electronic package under different cyclic applied loads

NASA Astrophysics Data System (ADS)

Ren, Huai-Hui; Wang, Xi-Shu

2014-04-01

This paper studies and compares the effects of pull-pull and 3-point bending cyclic loadings on the mechanical fatigue damage behaviors of a solder joint in a surface-mount electronic package. The comparisons are based on experimental investigations using scanning electron microscopy (SEM) in-situ technology and nonlinear finite element modeling, respectively. The compared results indicate that there are different threshold levels of plastic strain for the initial damage of solder joints under two cyclic applied loads; meanwhile, fatigue crack initiation occurs at different locations, and the accumulation of equivalent plastic strain determines the trend and direction of fatigue crack propagation. In addition, simulation results of the fatigue damage process of solder joints considering a constitutive model of damage initiation criteria for ductile materials and damage evolution based on accumulating inelastic hysteresis energy are identical to the experimental results. The actual fatigue life of the solder joint is almost the same and demonstrates that the FE modeling used in this study can provide an accurate prediction of solder joint fatigue failure.

DNA Damage Levels Determine Cyclobutyl Pyrimidine Dimer Repair Mechanisms in Alfalfa Seedlings.

PubMed Central

Quaite, F. E.; Takayanagi, S.; Ruffini, J.; Sutherland, J. C.; Sutherland, B. M.

1994-01-01

Ultraviolet radiation in sunlight damages DNA in plants, but little is understood about the types, lesion capacity, and coordination of repair pathways. We challenged intact alfalfa seedlings with UV doses that induced different initial levels of cyclobutyl pyrimidine dimers and measured repair by excision and photoreactivation. By using alkaline gel electrophoresis of nonradioactive DNAs treated with a cyclobutyl pyrimidine dimer-specific UV endonuclease, we quantitated ethidium-stained DNA by electronic imaging and calculated lesion frequencies from the number average molecular lengths. At low initial dimer frequencies (less than ~30 dimers per million bases), the seedlings used only photoreactivation to repair dimers; excision repair was not significant. At higher damage levels, both excision and photorepair contributed significantly. This strategy would allow plants with low damage levels to use error-free repair requiring only an external light energy source, whereas seedlings subjected to higher damage frequencies could call on additional repair processes requiring cellular energy. Characterization of repair in plants thus requires an investigation of a range of conditions, including the level of initial damage. PMID:12244228

Thermal shock tests to qualify different tungsten grades as plasma facing material

NASA Astrophysics Data System (ADS)

Wirtz, M.; Linke, J.; Loewenhoff, Th; Pintsuk, G.; Uytdenhouwen, I.

2016-02-01

The electron beam device JUDITH 1 was used to establish a testing procedure for the qualification of tungsten as plasma facing material. Absorbed power densities of 0.19 and 0.38 GW m-2 for an edge localized mode-like pulse duration of 1 ms were chosen. Furthermore, base temperatures of room temperature, 400 °C and 1000 °C allow investigating the thermal shock performance in the brittle, ductile and high temperature regime. Finally, applying 100 pulses under all mentioned conditions helps qualifying the general damage behaviour while with 1000 pulses for the higher power density the influence of thermal fatigue is addressed. The investigated reference material is a tungsten product produced according to the ITER material specifications. The obtained results provide a general overview of the damage behaviour with quantified damage characteristics and thresholds. In particular, it is shown that the damage strongly depends on the microstructure and related thermo-mechanical properties.

Kinetics of UV laser radiation defects in high performance glasses

NASA Astrophysics Data System (ADS)

Natura, U.; Feurer, T.; Ehrt, D.

2000-05-01

High purity fluoride phosphate glasses are attractive candidates as UV transmitting materials. The calculated values for the ultraviolet resonance wavelength are comparable with those of pure silica glass or fluoride single crystal CaF2. The formation of radiation-induced defect centers leads to additional absorption bands in the VUV-UV-vis range. The damage and the healing behavior by lamps and lasers are investigated in dependence on phosphate content and the content of impurities, mainly transition metals. Experiments were carried out using pulsed lasers with a duration of femto- and nanoseconds at a wavelength of 248 nm. The initial slope of the induced absorption shows a nonlinear dependence on the pulse energy density. Resonant and non-resonant two-photon mechanisms were observed. Two-photon-absorption coefficients at 248 nm for samples with different phosphate contents were measured. Models of the kinetics of the radiation-induced defects were developed. The inclusion of energy transfer was necessary to explain the difference in the damage behavior for nanosecond (248 nm, 193 nm) and femtosecond (248 nm) laser pulses.

The effects of treading by two breeds of dairy cow with different live weights on soil physical properties, poaching damage and herbage production on a poorly drained clay-loam soil.

PubMed

Tuohy, P; Fenton, O; Holden, N M; Humphreys, J

2015-11-01

There is little empirical evidence to indicate that dairy cow live weight affects the extent of soil damage at the hoof-soil interface during grazing on poorly drained permanent grassland. In the present study the impact of Holstein-Friesian (HF) dairy cows with a mean (±standard deviation) live weight of 570 (±61) kg were compared with Jersey × Holstein-Friesian (JX) with a mean live weight of 499 (±52) kg each at two stocking densities: mean 2·42 ± (0·062) and 2·66 (±0·079) cows/ha. Soil physical properties (bulk density, macroporosity, gravimetric water content, air-filled porosity, penetration resistance and shear strength), poaching damage (post-grazing soil surface deformation and hoof-print depth), herbage yield and milk production were measured throughout 2011 and 2012. Soil physical properties, post-grazing soil surface deformation and herbage production were not affected by dairy cow breed or by interactions between breed and stocking density. Hoof-print depth was higher in the HF treatments (39 v. 37 mm, s.e. 0·5 mm). Loading pressure imposed at the soil surface was the same for both breeds due to a direct correlation between live weight and hoof size. Poaching damage was greater at higher stocking density. Using the lighter JX cow offered little advantage in terms of lowering the negative impact of treading on soil physical properties or reducing poaching damage and no advantage in terms of herbage or milk production compared with the heavier HF cow.

Numerical Modeling of S-Wave Generation by Fracture Damage in Underground Nuclear Explosions

DTIC Science & Technology

2009-09-30

Element Package, ABAQUS. A user -defined subroutine , VUMAT, was written that incorporates the micro-mechanics based damage constitutive law described...dynamic damage evolution on the elastic and anelastic response. 2) whereas the Ashby/Sammis model was only applicable to the case where the initial cracks ...are all parallel and the same size, we can now include a specified distribution of initial crack sizes with random azimuthal orientation about the

Effective of diode laser on teeth enamel in the teeth whitening treatment

NASA Astrophysics Data System (ADS)

Klunboot, U.; Arayathanitkul, K.; Chitaree, R.; Emarat, N.

2011-12-01

This research purpose is to investigate the changing of teeth color and to study the surface of teeth after treatment by laser diode at different power densities for tooth whitening treatment. In the experiment, human-extracted teeth samples were divided into 7 groups of 6 teeth each. After that laser diode was irradiated to teeth, which were coated by 38% concentration of hydrogen peroxide, during for 20, 30 and 60 seconds at power densities of 10.9 and 52.1 W/cm2. The results of teeth color change were described by the CIEL*a*b* systems and the damage of teeth surface were investigated by scanning electron microscopy (SEM). The results showed that the power density of the laser diode could affect the whiteness of teeth. The high power density caused more luminous teeth than the low power density did, but on the other hand the high power density also caused damage to the teeth surface. Therefore, the laser diode at the low power densities has high efficiency for tooth whitening treatment and it has a potential for other clinical applications.

Comparative toxicological effects of two antifouling biocides on the marine diatom Chaetoceros lorenzianus: Damage and post-exposure recovery.

PubMed

Chavan, Pooja; Kumar, Rajesh; Kirubagaran, Ramalingam; Venugopalan, Vayalam P

2017-10-01

Antifouling biocides are commonly used in coastal electric power stations to prevent biofouling in their condenser cooling systems. However, the environmental impact of the chemical biocides is less understood than the thermal stress effects caused by the condenser effluents. In this study, Chaetoceros lorenzianus, a representative marine diatom, was used to analyse the toxicity of two antifouling biocides, chlorine and chlorine dioxide. The diatom cells were subjected to a range of concentrations of the biocides (from 0.05 to 2mg/L, as total residual oxidants, TRO) for contact time of 30min. They were analysed for viability, genotoxicity, chlorophyll a and cell density endpoints. The cells were affected at all concentrations of the biocides (0.05-2mg/L), showing dose-dependent decrease in viability and increase in DNA damage. The treated cells were later incubated in filtered seawater devoid of biocide to check for recovery. The cells were able to recover in terms of overall viability and DNA damage, when they had been initially treated with low concentrations of the biocides (0.5mg/L of Cl 2 or 0.2mg/L of ClO 2 ). Chlorophyll a analysis showed irreparable damage at all concentrations, while cell density showed increasing trend of reduction, if treated above 0.5mg/L of Cl 2 and 0.2mg/L of ClO 2 . The data indicated that in C. lorenzianus, cumulative toxic effects and recovery potential of ClO 2 up to 0.2mg/L were comparable with those of Cl 2 , up to 0.5mg/L concentration in terms of the studied endpoints. The results indicate that at the biocide levels currently being used at power stations, recovery of the organism is feasible upon return to ambient environment. Similar studies should be carried out on other planktonic and benthic organisms, which will be helpful in the formulation of future guidelines for discharge of upcoming antifouling biocides such as chlorine dioxide. Copyright © 2017 Elsevier Inc. All rights reserved.

Approach to failure in porous granular materials under compression

NASA Astrophysics Data System (ADS)

Kun, Ferenc; Varga, Imre; Lennartz-Sassinek, Sabine; Main, Ian G.

2013-12-01

We investigate the approach to catastrophic failure in a model porous granular material undergoing uniaxial compression. A discrete element computational model is used to simulate both the microstructure of the material and the complex dynamics and feedbacks involved in local fracturing and the production of crackling noise. Under strain-controlled loading, microcracks initially nucleate in an uncorrelated way all over the sample. As loading proceeds the damage localizes into a narrow damage band inclined at 30∘-45∘ to the load direction. Inside the damage band the material is crushed into a poorly sorted mixture of mainly fine powder hosting some larger fragments. The mass probability density distribution of particles in the damage zone is a power law of exponent 2.1, similar to a value of 1.87 inferred from observations of the length distribution of wear products (gouge) in natural and laboratory faults. Dynamic bursts of radiated energy, analogous to acoustic emissions observed in laboratory experiments on porous sedimentary rocks, are identified as correlated trails or cascades of local ruptures that emerge from the stress redistribution process. As the system approaches macroscopic failure consecutive bursts become progressively more correlated. Their size distribution is also a power law, with an equivalent Gutenberg-Richter b value of 1.22 averaged over the whole test, ranging from 3 to 0.5 at the time of failure, all similar to those observed in laboratory tests on granular sandstone samples. The formation of the damage band itself is marked by a decrease in the average distance between consecutive bursts and an emergent power-law correlation integral of event locations with a correlation dimension of 2.55, also similar to those observed in the laboratory (between 2.75 and 2.25).

Modeling of Damage Initiation and Progression in a SiC/SiC Woven Ceramic Matrix Composite

NASA Technical Reports Server (NTRS)

Mital, Subodh K.; Goldberg, Robert K.; Bonacuse, Peter J.

2012-01-01

The goal of an ongoing project at NASA Glenn is to investigate the effects of the complex microstructure of a woven ceramic matrix composite and its variability on the effective properties and the durability of the material. Detailed analysis of these complex microstructures may provide clues for the material scientists who `design the material? or to structural analysts and designers who `design with the material? regarding damage initiation and damage propagation. A model material system, specifically a five-harness satin weave architecture CVI SiC/SiC composite composed of Sylramic-iBN fibers and a SiC matrix, has been analyzed. Specimens of the material were serially sectioned and polished to capture the detailed images of fiber tows, matrix and porosity. Open source analysis tools were used to isolate various constituents and finite elements models were then generated from simplified models of those images. Detailed finite element analyses were performed that examine how the variability in the local microstructure affected the macroscopic behavior as well as the local damage initiation and progression. Results indicate that the locations where damage initiated and propagated is linked to specific microstructural features.

Effect of water availability on tolerance of leaf damage in tall morning glory, Ipomoea purpurea

NASA Astrophysics Data System (ADS)

Atala, Cristian; Gianoli, Ernesto

2009-03-01

Resource availability may limit plant tolerance of herbivory. To predict the effect of differential resource availability on plant tolerance, the limiting resource model (LRM) considers which resource limits plant fitness and which resource is mostly affected by herbivore damage. We tested the effect of experimental drought on tolerance of leaf damage in Ipomoea purpurea, which is naturally exposed to both leaf damage and summer drought. To seek mechanistic explanations, we also measured several morphological, allocation and gas exchange traits. In this case, LRM predicts that tolerance would be the same in both water treatments. Plants were assigned to a combination of two water treatments (control and low water) and two damage treatments (50% defoliation and undamaged). Plants showed tolerance of leaf damage, i.e., a similar number of fruits were produced by damaged and undamaged plants, only in control water. Whereas experimental drought affected all plant traits, leaf damage caused plants to show a greater leaf trichome density and reduced shoot biomass, but only in low water. It is suggested that the reduced fitness (number of fruits) of damaged plants in low water was mediated by the differential reduction of shoot biomass, because the number of fruits per shoot biomass was similar in damaged and undamaged plants. Alternative but less likely explanations include the opposing direction of functional responses to drought and defoliation, and resource costs of the damage-induced leaf trichome density. Our results somewhat challenge the LRM predictions, but further research including field experiments is needed to validate some of the preliminary conclusions drawn.

In Situ Imaging during Compression of Plastic Bonded Explosives for Damage Modeling

NASA Astrophysics Data System (ADS)

Yeager, John; Manner, Virginia; Patterson, Brian; Walters, David; Cordes, Nikolaus; Henderson, Kevin; Tappan, Bryce; Luscher, Darby

2017-06-01

The microstructure of plastic bonded explosives (PBXs) is known to influence behavior during insults such as deformation, heating or initiation to detonation. Obtaining three-dimensional microstructural data can be difficult due in part to fragility of the material and small feature size. X-ray computed tomography (CT) is an ideal characterization technique but the explosive crystals and binder in formulations such as PBX 9501 do not have sufficient x-ray contrast to differentiate between the components. Here, we have formulated several PBXs using octahydro-1,3,5,7-tetranitro-1,3,5,7- tetrazocine (HMX) crystals and low-density binder systems. The full three-dimensional microstructure of these samples has been characterized using microscale CT during uniaxial mechanical compression in an interrupted in situ modality. The rigidity of the binder was observed to significantly influence fracture, crystal-binder delamination, and material flow. Additionally, the segmented, 3D images were meshed for finite element simulation. Initial results of the mesoscale modeling exhibit qualitatively similar delamination. Los Alamos National Laboratory - LDRD.

Reactive pathways of hydrogen and carbon removal from organosilicate glass low- κ films by F atoms

NASA Astrophysics Data System (ADS)

Voronina, Ekaterina N.; Mankelevich, Yuri A.; Rakhimova, Tatyana V.

2017-07-01

Direct molecular dynamic simulation on the base of the density functional theory (DFT) method is used to study some critical reactions of F atoms with organosilicate glass (OSG) low-κ films. Here static and dynamic DFT-based approaches are applied for a variety of reactive pathways of hydrogen and carbon removal in the form of volatile products (HF, CF2 and CF3 molecules) from initial SiCH3 surface groups. These reactions constitute an important part of the proposed multi-step mechanism of OSG films damage and etching by thermal F atoms. Two models (POSS and TMCTS macromolecules and their modifications) are used to illustrate the peculiarities and dynamics of the successive reactions of F atoms with the initial SiCH3 and appeared SiCHxFy (x + y ≤ 3) surface groups. Contribution to the Topical Issue "Dynamics of Molecular Systems (MOLEC 2016)", edited by Alberto Garcia-Vela, Luis Banares and Maria Luisa Senent.

Self-Healing Characteristics of Damaged Rock Salt under Different Healing Conditions

PubMed Central

Chen, Jie; Ren, Song; Yang, Chunhe; Jiang, Deyi; Li, Lin

2013-01-01

Salt deposits are commonly regarded as ideal hosts for geologic energy reservoirs. Underground cavern construction-induced damage in salt is reduced by self-healing. Thus, studying the influencing factors on such healing processes is important. This research uses ultrasonic technology to monitor the longitudinal wave velocity variations of stress-damaged rock salts during self-recovery experiments under different recovery conditions. The influences of stress-induced initial damage, temperature, humidity, and oil on the self-recovery of damaged rock salts are analyzed. The wave velocity values of the damaged rock salts increase rapidly during the first 200 h of recovery, and the values gradually increase toward stabilization after 600 h. The recovery of damaged rock salts is subjected to higher initial damage stress. Water is important in damage recovery. The increase in temperature improves damage recovery when water is abundant, but hinders recovery when water evaporates. The presence of residual hydraulic oil blocks the inter-granular role of water and restrains the recovery under triaxial compression. The results indicate that rock salt damage recovery is related to the damage degree, pore pressure, temperature, humidity, and presence of oil due to the sealing integrity of the jacket material. PMID:28811444

Self-Healing Characteristics of Damaged Rock Salt under Different Healing Conditions.

PubMed

Chen, Jie; Ren, Song; Yang, Chunhe; Jiang, Deyi; Li, Lin

2013-08-12

Salt deposits are commonly regarded as ideal hosts for geologic energy reservoirs. Underground cavern construction-induced damage in salt is reduced by self-healing. Thus, studying the influencing factors on such healing processes is important. This research uses ultrasonic technology to monitor the longitudinal wave velocity variations of stress-damaged rock salts during self-recovery experiments under different recovery conditions. The influences of stress-induced initial damage, temperature, humidity, and oil on the self-recovery of damaged rock salts are analyzed. The wave velocity values of the damaged rock salts increase rapidly during the first 200 h of recovery, and the values gradually increase toward stabilization after 600 h. The recovery of damaged rock salts is subjected to higher initial damage stress. Water is important in damage recovery. The increase in temperature improves damage recovery when water is abundant, but hinders recovery when water evaporates. The presence of residual hydraulic oil blocks the inter-granular role of water and restrains the recovery under triaxial compression. The results indicate that rock salt damage recovery is related to the damage degree, pore pressure, temperature, humidity, and presence of oil due to the sealing integrity of the jacket material.

Plasma sterilization of Geobacillus Stearothermophilus by O{mathsf2}:N{mathsf2} RF inductively coupled plasma

NASA Astrophysics Data System (ADS)

Kylián, O.; Sasaki, T.; Rossi, F.

2006-05-01

The aim of this work is to identify the main process responsible for sterilization of Geobacillus Stearothermophilus spores in O{2}:N{2} RF inductively coupled plasma. In order to meet this objective the sterilization efficiencies of discharges in mixtures differing in the initial O{2}/N{2} ratios are compared with plasma properties and with scanning electron microscopy images of treated spores. According to the obtained results it can be concluded that under our experimental conditions the time needed to reach complete sterilization is more related to O atom density than UV radiation intensity, i.e. complete sterilization is not related only to DNA damage as in UV sterilization but more likely to the etching of the spore.

Effects of collision cascade density on radiation defect dynamics in 3C-SiC

PubMed Central

Bayu Aji, L. B.; Wallace, J. B.; Kucheyev, S. O.

2017-01-01

Effects of the collision cascade density on radiation damage in SiC remain poorly understood. Here, we study damage buildup and defect interaction dynamics in 3C-SiC bombarded at 100 °C with either continuous or pulsed beams of 500 keV Ne, Ar, Kr, or Xe ions. We find that bombardment with heavier ions, which create denser collision cascades, results in a decrease in the dynamic annealing efficiency and an increase in both the amorphization cross-section constant and the time constant of dynamic annealing. The cascade density behavior of these parameters is non-linear and appears to be uncorrelated. These results demonstrate clearly (and quantitatively) an important role of the collision cascade density in dynamic radiation defect processes in 3C-SiC. PMID:28304397

Effects of collision cascade density on radiation defect dynamics in 3C-SiC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bayu Aji, L. B.; Wallace, J. B.; Kucheyev, S. O.

Effects of the collision cascade density on radiation damage in SiC remain poorly understood. We study damage buildup and defect interaction dynamics in 3C-SiC bombarded at 100 °C with either continuous or pulsed beams of 500 keV Ne, Ar, Kr, or Xe ions. Here, we find that bombardment with heavier ions, which create denser collision cascades, results in a decrease in the dynamic annealing efficiency and an increase in both the amorphization cross-section constant and the time constant of dynamic annealing. The cascade density behavior of these parameters is non-linear and appears to be uncorrelated. Our results demonstrate clearly (andmore » quantitatively) an important role of the collision cascade density in dynamic radiation defect processes in 3C-SiC.« less

Effects of collision cascade density on radiation defect dynamics in 3C-SiC

DOE PAGES

Bayu Aji, L. B.; Wallace, J. B.; Kucheyev, S. O.

2017-03-17

Effects of the collision cascade density on radiation damage in SiC remain poorly understood. We study damage buildup and defect interaction dynamics in 3C-SiC bombarded at 100 °C with either continuous or pulsed beams of 500 keV Ne, Ar, Kr, or Xe ions. Here, we find that bombardment with heavier ions, which create denser collision cascades, results in a decrease in the dynamic annealing efficiency and an increase in both the amorphization cross-section constant and the time constant of dynamic annealing. The cascade density behavior of these parameters is non-linear and appears to be uncorrelated. Our results demonstrate clearly (andmore » quantitatively) an important role of the collision cascade density in dynamic radiation defect processes in 3C-SiC.« less

Analytical monitoring of soil bioengineering structures in the Tuscan Emilian Apennines of Italy

NASA Astrophysics Data System (ADS)

Selli, Lavinia; Guastini, Enrico

2014-05-01

Soil bioengineering has been an appropriate solution to deal with erosion problems and shallow landslides in the North Apennines, Italy. The objective of our research was a check about critical aspects of soil bioengineering works. We monitored the works that have been carried out in the Tuscan Emilian Apennines by testing the suitability of different plant species and analyzed in detail timber structures of wooden crib walls. Plant species were mainly Salix alba and Salix purpurea that gave good sprouting and survival rates. However, showed some issues in growing on dry and sunny Apennine lands, where other shrubs like Spanish Broom, blackthorn, cornel-tree and Eglantine would be more indicated. The localized analysis on wooden elements has been led gathering parts from the poles and obtaining samples in order to determine their density. The hypothetical initial density of the wood used in the structure has been estimated, then calculating the residual density. This analysis allows us to determine the general condition of the wood, highlighting the structures in worst condition (the one in Pianaccio show a residual density close to 70%, instead of 90% as found on other structures) and those whose degraded wood has undergone the greatest damage (Pianaccio here too, with 50%, followed by Campoferrario - 60% - and by Pian di Favale with 85%, a rather good value for the most degraded wood in the structure).

Herbivore pressure increases toward the equator

PubMed Central

Salazar, Diego; Marquis, Robert J.

2012-01-01

Increases in species diversity and density from higher to lower latitudes are well documented. Nevertheless, the consequences of these changes in diversity for structuring ecological communities and influencing biotic evolution are largely unknown. It is widely believed that this increase in species diversity is associated with increased intensity of ecological interactions closer to the equator. For plant–herbivore interactions in particular, the predictions are that, at lower latitudes, plants will be attacked by more individual herbivores, more herbivore species, and more specialized herbivores and, therefore, will suffer greater damage. We used a large-scale latitudinal transect from Mexico to Bolivia to quantify changes in leaf damage, diversity, and abundance of lepidopteran larvae on two widely distributed host species of the genus Piper (Piperaceae). We show that both density and species richness of herbivores were highest at the equator and decreased with increasing latitude, both northward and southward. Contrary to expectation, however, this increase in herbivore diversity was attributable to the addition of generalist not specialist species. Finally, and again contrary to expectation, the increase in herbivore density with decreasing latitude did not produce a corresponding damage gradient. We propose that the lack of a latitudinal concordance between increases in herbivore density and diversity with decreasing latitude, and the resulting herbivore damage, supports the hypothesis of better plant antiherbivore defenses at lower latitudes. Furthermore, the changes in the relative abundance of generalist vs. specialist species suggest that the nature of the selective pressure is intrinsically different between higher and lower latitudes. PMID:22802664

Electron microscopy observations of radiation damage in irradiated and annealed tungsten

NASA Astrophysics Data System (ADS)

Grzonka, J.; Ciupiński, Ł.; Smalc-Koziorowska, J.; Ogorodnikova, O. V.; Mayer, M.; Kurzydłowski, K. J.

2014-12-01

In the present work tungsten samples were irradiated with W6+ ions with a kinetic energy of 20 MeV in order to simulate radiation damage by fast neutrons. Two samples with cumulative damage of 2.3 and 6.36 displacements per atom were produced. The scanning transmission electron microscopy investigations were carried out in order to determine structure changes resulting from the irradiation. The evolution of the damage with post implantation annealing in the temperature range 673-1100 K was also assessed. Damage profiles were studied at cross-sections. Scanning transmission electron microscopy studies of the lamellae after annealing revealed aggregation of defects and rearrangement as well as partial healing of dislocations at higher temperatures. The results confirm the higher density of radiation-induced dislocations in the near surface area of the sample (1.8 * 1014 m-2) in comparison with a deeper damage area (1.5 * 1014 m-2). Significant decrease of dislocation density was observed after annealing with a concurrent growth of dislocation loops. Transmission electron microscopy analyses show that the dislocation loops are perfect dislocations with the Burgers vectors of b = ½[ 1 1 1].

Specialists Meeting on Impact Damage Tolerance of Structures

DTIC Science & Technology

1976-01-01

example, fatigue, timl-de tectIable initial defects and in-fliglht d amalt such aS that inflicted by miilitary weapons or by debris from ’n din tegra t...relative to many types of damaging mechanisms, lncludlig for example: I. Fat Igue 2. Non-detectable Initial defects 3. In-flight damage, such as Inflicted...undetected flaw or defect . In both cases, the benefits of successful design are Improved safety and economics. With respect to In-flight darvqe, tre

Crack initiation modeling of a directionally-solidified nickel-base superalloy

NASA Astrophysics Data System (ADS)

Gordon, Ali Page

Combustion gas turbine components designed for application in electric power generation equipment are subject to periodic replacement as a result of cracking, damage, and mechanical property degeneration that render them unsafe for continued operation. In view of the significant costs associated with inspecting, servicing, and replacing damaged components, there has been much interest in developing models that not only predict service life, but also estimate the evolved microstructural state of the material. This thesis explains manifestations of microstructural damage mechanisms that facilitate fatigue crack nucleation in a newly-developed directionally-solidified (DS) Ni-base superalloy components exposed to elevated temperatures and high stresses. In this study, models were developed and validated for damage and life prediction using DS GTD-111 as the subject material. This material, proprietary to General Electric Energy, has a chemical composition and grain structure designed to withstand creep damage occurring in the first and second stage blades of gas-powered turbines. The service conditions in these components, which generally exceed 600°C, facilitate the onset of one or more damage mechanisms related to fatigue, creep, or environment. The study was divided into an empirical phase, which consisted of experimentally simulating service conditions in fatigue specimens, and a modeling phase, which entailed numerically simulating the stress-strain response of the material. Experiments have been carried out to simulate a variety of thermal, mechanical, and environmental operating conditions endured by longitudinally (L) and transversely (T) oriented DS GTD-111. Both in-phase and out-of-phase thermo-mechanical fatigue tests were conducted. In some cases, tests in extreme environments/temperatures were needed to isolate one or at most two of the mechanisms causing damage. Microstructural examinations were carried out via SEM and optical microscopy. A continuum crystal plasticity model was used to simulate the material behavior in the L and T orientations. The constitutive model was implemented in ABAQUS and a parameter estimation scheme was developed to obtain the material constants. A physically-based model was developed for correlating crack initiation life based on the experimental life data and predictions are made using the crack initiation model. Assuming a unique relationship between the damage fraction and cycle fraction with respect to cycles to crack initiation for each damage mode, the total crack initiation life has been represented in terms of the individual damage components (fatigue, creep-fatigue, creep, and oxidation-fatigue) observed at the end state of crack initiation.

Combined effects of environmental disturbance and climate warming on insect herbivory in mountain birch in subarctic forests: Results of 26-year monitoring.

PubMed

Kozlov, M V; Zverev, V; Zvereva, E L

2017-12-01

Both pollution and climate affect insect-plant interactions, but the combined effects of these two abiotic drivers of global change on insect herbivory remain almost unexplored. From 1991 to 2016, we monitored the population densities of 25 species or species groups of insects feeding on mountain birch (Betula pubescens ssp. czerepanovii) in 29 sites and recorded leaf damage by insects in 21 sites in subarctic forests around the nickel-copper smelter at Monchegorsk, north-western Russia. The leaf-eating insects demonstrated variable, and sometimes opposite, responses to pollution-induced forest disturbance and to climate variations. Consequently, we did not discover any general trend in herbivory along the disturbance gradient. Densities of eight species/species groups correlated with environmental disturbance, but these correlations weakened from 1991 to 2016, presumably due to the fivefold decrease in emissions of sulphur dioxide and heavy metals from the smelter. The densities of externally feeding defoliators decreased from 1991 to 2016 and the densities of leafminers increased, while the leaf roller densities remained unchanged. Consequently, no overall temporal trend in the abundance of birch-feeding insects emerged despite a 2-3°C elevation in spring temperatures. Damage to birch leaves by insects decreased during the observation period in heavily disturbed forests, did not change in moderately disturbed forests and tended to increase in pristine forests. The temporal stability of insect-plant interactions, quantified by the inverse of the coefficient of among-year variations of herbivore population densities and of birch foliar damage, showed a negative correlation with forest disturbance. We conclude that climate differently affects insect herbivory in heavily stressed versus pristine forests, and that herbivorous insects demonstrate diverse responses to environmental disturbance and climate variations. This diversity of responses, in combination with the decreased stability of insect-plant interactions, increases the uncertainty in predictions on the impacts of global change on forest damage by insects. Copyright © 2017 Elsevier B.V. All rights reserved.

Self-healing cable apparatus and methods

NASA Technical Reports Server (NTRS)

Huston, Dryver (Inventor); Esser, Brian (Inventor)

2007-01-01

Self-healing cable apparatus and methods are disclosed. The cable has a central core surrounded by an adaptive cover that can extend over the entire length of the cable or just one or more portions of the cable. The adaptive cover includes a protective layer having an initial damage resistance, and a reactive layer. When the cable is subjected to a localized damaging force, the reactive layer responds by creating a corresponding localized self-healed region. The self-healed region provides the cable with enhanced damage resistance as compared to the cable's initial damage resistance. Embodiments of the invention utilize conventional epoxies or foaming materials in the reactive layer that are released to form the self-healed region when the damaging force reaches the reactive layer.

Ginger Treatment Ameliorates Alcohol-induced Myocardial Damage by Suppression of Hyperlipidemia and Cardiac Biomarkers in Rats.

PubMed

Subbaiah, Ganjikunta Venkata; Mallikarjuna, Korivi; Shanmugam, Bhasha; Ravi, Sahukari; Taj, Patan Usnan; Reddy, Kesireddy Sathyavelu

2017-01-01

Alcohol-induced hyperlipidemia is positively correlated with cardiovascular diseases. Several herbal extracts have been reported to protect the cardiac injury and suppress the hyperlipidemia. However, the effect of ginger extracts on alcohol-induced hyperlipidemia and associated myocardial damage remains unclear. This study investigated the cardio-protective properties of ginger ethanolic extract (Gt) against alcohol-induced myocardial damage, and further distinguished the association between hyperlipidemia and occurrence of myocardial damage in rats. Twenty four Wistar male albino rats (250 ± 20 g) were divided into four groups including, Normal control (NC) (0.9% NaCl), Ginger treated (Gt) (200 mg/Kg b.w.), Alcohol treated (At) (20% of 6g/kg b.w. alcohol), and Alcohol along with Ginger treatment (At+Gt). In this study, lipid profiles such as fatty acids, triglycerides, total cholesterol, phospholipids, low density lipoprotein and high density lipoproteins, and cardiac biomarkers, including LDH, AST, CK-MB, cTn-T and cTn-I were examined in rats. Furthermore, histopathological studies were also conducted. We found that alcohol-induced myocardial damage was associated with increased lipid profile except high density lipoprotein in alcohol treated (20%, 6g/kg b.w.) rats compared with control. Ginger treatment significantly reduced the alcohol-induced lipid profiles except high density lipoproteins. Furthermore, elevated cardiac biomarkers activity with alcohol intoxication was substantially suppressed by ginger treatment. In addition, ginger treatment for 7-weeks significantly minimized the alcohol-induced myocardial damage. Our results concluded that ginger could protect alcohol-induced myocardial damage by suppression of hyperlipidemia and cardiac biomarkers. Ginger extract could alleviate the myocardial injury partially due to the suppression of circulating FFAs and TG levels.Increased circulating cholesterol, LDL and phospholipids with alcohol intake were substantially suppressed by ginger treatmentAlcohol, induced an increase in cardiac damage biomarkers, CK-MB, cTn-T and cTn-I were remarkably suppressed by ginger treatmentPerformed histopathological studies by transmission electron microscopy and light microscopy shows additional convincing evidence on ginger cardio-protective effects. The drastic changes were rehabilitated in cardiac tissue by ginger treatment may be it acts as a good antioxidant and possessing hypolipidemic activity.Collectively, our findings confirm hypothesis that ginger has cardio protective potential through suppression of hyperlipidemia, preserving the tissue damage bio markers, cardiac biomarkers in plasma and preservation of histoarchitecture of myocytes. Abbreviations used: Gt: Ginger Ethanolic Extract; NC: Normal Control; At: Alcohol treated; MI: Myocardial Infarction.

Dynamic Evolution Of Off-Fault Medium During An Earthquake: A Micromechanics Based Model

NASA Astrophysics Data System (ADS)

Thomas, Marion Y.; Bhat, Harsha S.

2018-05-01

Geophysical observations show a dramatic drop of seismic wave speeds in the shallow off-fault medium following earthquake ruptures. Seismic ruptures generate, or reactivate, damage around faults that alter the constitutive response of the surrounding medium, which in turn modifies the earthquake itself, the seismic radiation, and the near-fault ground motion. We present a micromechanics based constitutive model that accounts for dynamic evolution of elastic moduli at high-strain rates. We consider 2D in-plane models, with a 1D right lateral fault featuring slip-weakening friction law. The two scenarios studied here assume uniform initial off-fault damage and an observationally motivated exponential decay of initial damage with fault normal distance. Both scenarios produce dynamic damage that is consistent with geological observations. A small difference in initial damage actively impacts the final damage pattern. The second numerical experiment, in particular, highlights the complex feedback that exists between the evolving medium and the seismic event. We show that there is a unique off-fault damage pattern associated with supershear transition of an earthquake rupture that could be potentially seen as a geological signature of this transition. These scenarios presented here underline the importance of incorporating the complex structure of fault zone systems in dynamic models of earthquakes.

Dynamic Evolution Of Off-Fault Medium During An Earthquake: A Micromechanics Based Model

NASA Astrophysics Data System (ADS)

Thomas, M. Y.; Bhat, H. S.

2017-12-01

Geophysical observations show a dramatic drop of seismic wave speeds in the shallow off-fault medium following earthquake ruptures. Seismic ruptures generate, or reactivate, damage around faults that alter the constitutive response of the surrounding medium, which in turn modifies the earthquake itself, the seismic radiation, and the near-fault ground motion. We present a micromechanics based constitutive model that accounts for dynamic evolution of elastic moduli at high-strain rates. We consider 2D in-plane models, with a 1D right lateral fault featuring slip-weakening friction law. The two scenarios studied here assume uniform initial off-fault damage and an observationally motivated exponential decay of initial damage with fault normal distance. Both scenarios produce dynamic damage that is consistent with geological observations. A small difference in initial damage actively impacts the final damage pattern. The second numerical experiment, in particular, highlights the complex feedback that exists between the evolving medium and the seismic event. We show that there is a unique off-fault damage pattern associated with supershear transition of an earthquake rupture that could be potentially seen as a geological signature of this transition. These scenarios presented here underline the importance of incorporating the complex structure of fault zone systems in dynamic models of earthquakes.

Characterization of laser damage performance of fused silica using photothermal absorption technique

NASA Astrophysics Data System (ADS)

Wan, Wen; Shi, Feng; Dai, Yifan; Peng, Xiaoqiang

2017-06-01

The subsurface damage and metal impurities have been the main laser damage precursors of fused silica while subjected to high power laser irradiation. Light field enhancement and thermal absorption were used to explain the appearance of damage pits while the laser energy is far smaller than the energy that can reach the intrinsic threshold of fused silica. For fused silica optics manufactured by magnetorheological finishing or advanced mitigation process, no scratch-related damage site occurs can be found on the surface. In this work, we implemented a photothermal absorption technique based on thermal lens method to characterize the subsurface defects of fused silica optics. The pump beam is CW 532 nm wavelength laser. The probe beam is a He-Ne laser. They are collinear and focused through the same objective. When pump beam pass through the sample, optical absorption induces the local temperature rise. The lowest absorptance that we can detect is about the order of magnitude of 0.01 ppm. When pump beam pass through the sample, optical absorption induces the local temperature rise. The photothermal absorption value of fused silica samples range from 0.5 to 10 ppm. The damage densities of the samples were plotted. The damage threshold of samples at 8J/cm2 were gived to show laser damage performance of fused silica.The results show that there is a strong correlation between the thermal absorption and laser damage density. The photothermal absorption technique can be used to predict and evaluate the laser damage performance of fused silica optics.

A methodology to predict damage initiation, damage growth and residual strength in titanium matrix composites

NASA Technical Reports Server (NTRS)

Bakuckas, J. G., Jr.; Johnson, W. S.

1994-01-01

In this research, a methodology to predict damage initiation, damage growth, fatigue life, and residual strength in titanium matrix composites (TMC) is outlined. Emphasis was placed on micromechanics-based engineering approaches. Damage initiation was predicted using a local effective strain approach. A finite element analysis verified the prevailing assumptions made in the formulation of this model. Damage growth, namely, fiber-bridged matrix crack growth, was evaluated using a fiber bridging (FB) model which accounts for thermal residual stresses. This model combines continuum fracture mechanics and micromechanics analyses yielding stress-intensity factor solutions for fiber-bridged matrix cracks. It is assumed in the FB model that fibers in the wake of the matrix crack are idealized as a closure pressure, and an unknown constant frictional shear stress is assumed to act along the debond length of the bridging fibers. This frictional shear stress was used as a curve fitting parameter to the available experimental data. Fatigue life and post-fatigue residual strength were predicted based on the axial stress in the first intact 0 degree fiber calculated using the FB model and a three-dimensional finite element analysis.

A Hybrid Approach to Composite Damage and Failure Analysis Combining Synergistic Damage Mechanics and Peridynamics

DTIC Science & Technology

2017-06-30

along the intermetallic component or at the interface between the two components of the composite. The availability of rnicroscale experimental data in...obtained with the PD model; (c) map of strain energy density; (d) the new quasi -index damage is a predictor of fai lure. As in the case of FRCs, one...which points are most likely to fail, before actual failure happens. The " quasi -damage index", shown in the formula below, is a point-wise measure

Thermally ruggedized ITO transparent electrode films for high power optoelectronics.

PubMed

Yoo, Jae-Hyuck; Matthews, Manyalibo; Ramsey, Phil; Barrios, Antonio Correa; Carter, Austin; Lange, Andrew; Bude, Jeff; Elhadj, Selim

2017-10-16

We present two strategies to minimize laser damage in transparent conductive films. The first consists of improving heat dissipation by selection of substrates with high thermal diffusivity or by addition of capping layer heatsinks. The second is reduction of bulk energy absorption by lowering free carrier density and increasing mobility, while maintaining film conductance with thicker films. Multi-pulse laser damage tests were performed on tin-doped indium oxide (ITO) films configured to improve optical lifetime damage performance. Conditions where improvements were not observed are also described. When bulk heating is not the dominant damage process, discrete defect-induced damage limits damage behavior.

How plant neighborhood composition influences herbivory: Testing four mechanisms of associational resistance and susceptibility

PubMed Central

2017-01-01

Neighboring plants can decrease or increase each other’s likelihood of damage from herbivores through associational resistance or susceptibility, respectively. Associational effects (AE) can transpire through changes in herbivore or plant traits that affect herbivore movement, densities, and feeding behaviors to ultimately affect plant damage. While much work has focused on understanding the mechanisms that underlie associational effects, we know little about how these mechanisms are influenced by neighborhood composition, i.e., plant density or relative frequency which is necessary to make predictions about when AE should occur in nature. Using a series of field and greenhouse experiments, I examined how plant density and relative frequency affected plant damage to Solanum carolinense and four mechanisms that underlie AE; (i) accumulation of insect herbivores and arthropod predators, (ii) microclimate conditions, (iii) plant resistance, and (iv) specialist herbivore preference. I found a positive relationship between S. carolinense damage and the relative frequency of a non-focal neighbor (Solidago altissima) and all four AE mechanisms were influenced by one or multiple neighborhood components. Frequency-dependence in S. carolinense damage is most likely due to greater generalist herbivore load on S. carolinense (through spillover from S. altissima) with microclimate variables, herbivore preference, predation pressures, and plant resistance having relatively weaker effects. Associational effects may have long-term consequences for these two plant species during plant succession and understanding context-dependent herbivory has insect pest management implication for other plant species in agriculture and forestry. PMID:28486538

Traditional cattle vs. introduced deer management in Chaco Serrano woodlands (Argentina): Analysis of environmental sustainability at increasing densities.

PubMed

Charro, José Luis; López-Sánchez, Aida; Perea, Ramón

2018-01-15

Wild ungulate populations have increased and expanded considerably in many regions, including austral woodlands and forests where deer (Cervus elaphus) have been introduced as an alternative management to traditional cattle grazing. In this study, we compared traditional cattle with introduced deer management at increasing deer densities in the "Chaco Serrano" woodlands of Argentina to assess their ecological sustainability. We used three ecological indicators (abundance of tree regeneration, woody plant diversity and browsing damage) as proxies for environmental sustainability in woody systems. Our results indicate that traditional cattle management, at stocking rates of ∼10 ind km -2 , was the most ecologically sustainable management since it allowed greater tree regeneration abundance, higher richness of woody species and lower browsing damage. Importantly, cattle management and deer management at low densities (10 ind km -2 ) showed no significant differences in species richness and abundance of seedlings, although deer caused greater browsing damage on saplings and juveniles. However, management regimes involving high deer densities (∼35 deer km 2 ) was highly unsustainable in comparison to low (∼10 deer km -2 ) and medium (∼20 deer km -2 ) densities, with 40% probability of unsustainable browsing as opposed to less than 5% probability at low and medium densities. In addition, high deer densities caused a strong reduction in tree regeneration, with a 19-30% reduction in the abundance of seedlings and young trees when compared to low deer densities. These results showed that the effect of increasing deer densities on woody plant conservation was not linear, with high deer densities causing a disproportional deleterious effect on tree regeneration and sustainable browsing. Our results suggest that traditional management at low densities or the use of introduced ungulates (deer breeding areas) at low-medium densities (<20 deer km -2 ) are compatible with woody vegetation conservation. However, further research is needed on plant palatability, animal habitat use (spatial heterogeneity) and species turnover and extinction (comparison to areas of low-null historical browsing) to better estimate environmental sustainability of Neotropical ungulate-dominated woodlands. Copyright © 2017 Elsevier Ltd. All rights reserved.

A Markov Chain Approach to Probabilistic Swarm Guidance

NASA Technical Reports Server (NTRS)

Acikmese, Behcet; Bayard, David S.

2012-01-01

This paper introduces a probabilistic guidance approach for the coordination of swarms of autonomous agents. The main idea is to drive the swarm to a prescribed density distribution in a prescribed region of the configuration space. In its simplest form, the probabilistic approach is completely decentralized and does not require communication or collabo- ration between agents. Agents make statistically independent probabilistic decisions based solely on their own state, that ultimately guides the swarm to the desired density distribution in the configuration space. In addition to being completely decentralized, the probabilistic guidance approach has a novel autonomous self-repair property: Once the desired swarm density distribution is attained, the agents automatically repair any damage to the distribution without collaborating and without any knowledge about the damage.

Linking JNK Activity to the DNA Damage Response

PubMed Central

Picco, Vincent

2013-01-01

The activity of c-Jun N-terminal kinase (JNK) was initially described as ultraviolet- and oncogene-induced kinase activity on c-Jun. Shortly after this initial discovery, JNK activation was reported for a wider variety of DNA-damaging agents, including γ-irradiation and chemotherapeutic compounds. As the DNA damage response mechanisms were progressively uncovered, the mechanisms governing the activation of JNK upon genotoxic stresses became better understood. In particular, a recent set of papers links the physical breakage in DNA, the activation of the transcription factor NF-κB, the secretion of TNF-α, and an autocrine activation of the JNK pathway. In this review, we will focus on the pathway that is initiated by a physical break in the DNA helix, leading to JNK activation and the resultant cellular consequences. The implications of these findings will be discussed in the context of cancer therapy with DNA-damaging agents. PMID:24349633

Accelerated hand bone mineral density loss is associated with progressive joint damage in hands and feet in recent-onset rheumatoid arthritis.

PubMed

Güler-Yüksel, Melek; Klarenbeek, Naomi B; Goekoop-Ruiterman, Yvonne P M; de Vries-Bouwstra, Jeska K; van der Kooij, Sjoerd M; Gerards, Andreas H; Ronday, H Karel; Huizinga, Tom W J; Dijkmans, Ben A C; Allaart, Cornelia F; Lems, Willem F

2010-01-01

To investigate whether accelerated hand bone mineral density (BMD) loss is associated with progressive joint damage in hands and feet in the first year of rheumatoid arthritis (RA) and whether it is an independent predictor of subsequent progressive total joint damage after 4 years. In 256 recent-onset RA patients, baseline and 1-year hand BMD was measured in metacarpals 2-4 by digital X-ray radiogrammetry. Joint damage in hands and feet were scored in random order according to the Sharp-van der Heijde method at baseline and yearly up to 4 years. 68% of the patients had accelerated hand BMD loss (>-0.003 g/cm2) in the first year of RA. Hand BMD loss was associated with progressive joint damage after 1 year both in hands and feet with odds ratios (OR) (95% confidence intervals [CI]) of 5.3 (1.3-20.9) and 3.1 (1.0-9.7). In univariate analysis, hand BMD loss in the first year was a predictor of subsequent progressive total joint damage after 4 years with an OR (95% CI) of 3.1 (1.3-7.6). Multivariate analysis showed that only progressive joint damage in the first year and anti-citrullinated protein antibody positivity were independent predictors of long-term progressive joint damage. In the first year of RA, accelerated hand BMD loss is associated with progressive joint damage in both hands and feet. Hand BMD loss in the first year of recent-onset RA predicts subsequent progressive total joint damage, however not independent of progressive joint damage in the first year.

Shock Initiation and Equation of State of Ammonium Nitrate

NASA Astrophysics Data System (ADS)

Robbins, David; Sheffield, Steve; Dattelbaum, Dana; Chellappa, Raja; Velisavljevic, Nenad

2013-06-01

Ammonium nitrate (AN) is a widely used fertilizer and mining explosive commonly found in ammonium nitrate-fuel oil. Neat AN is a non-ideal explosive with measured detonation velocities approaching 4 km/s. Previously, we reported a thermodynamically-complete equation of state for AN based on its maximum density, and showed that near-full density AN did not initiate when subjected to shock input conditions up to 22 GPa. In this work, we extend these initial results, by presenting new Hugoniot data for intermediate density neat AN obtained from gas gun-driven plate impact experiments. AN at densities from 1.8 to 1.5 g/cm3 were impacted into LiF windows using a two-stage light gas gun. Dual VISARs were used to measure the interfacial particle velocity wave profile as a function of time following impact. The new Hugoniot data, in addition to updates to thermodynamic parameters derived from structural analysis and vibrational spectroscopy measurements in high pressure diamond anvil cell experiments, are used to refine the unreacted EOS for AN. Furthermore, shock initiation of neat AN was observed as the initial porosity increased (density decreased). Insights into the relationship(s) between initial density and shock initiation sensitivity are also presented, from evidence of shock initiation in the particle velocity profiles obtained for the lower density AN samples.

Influence of interface ply orientation on fatigue damage of adhesively bonded composite joints

NASA Technical Reports Server (NTRS)

Johnson, W. S.; Mall, S.

1986-01-01

An experimental study of cracked-lap-shear specimens was conducted to determine the influence of adherend stacking sequence on debond initiation and damage growth in a composite-to-composite bonded joint. Specimens consisted of quasi-isotropic graphite/epoxy adherends bonded together with either FM-300 or EC 3445 adhesives. The stacking sequence of the adherends was varied such that 0 deg, 45 deg, or 90 deg plies were present at the adherend-adhesive interfaces. Fatigue damage initiated in the adhesive layer in those specimens with 0 deg and 45 deg interface plies. Damaage initiated in the form of ply cracking in the strap adherend for the specimens with 90 deg interface plies. The fatigue-damage growth was in the form of delamination within the composite adherends for specimens with the 90 deg and 45 deg plies next to the adhesive, while debonding in the adhesive resulted for the specimens with 0 deg plies next to the adhesive. Those joints with the 0 deg and 45 deg plies next to either adhesive has essentially the same fatigue-damage-initiation stress levels. These stress levels were 13 and 71 percent higher, respectively, than those for specimens with 90 deg plies next to the EC 3445 and FM-300 adhesives.

Development of a Remote External Repair Tool for Damaged or Defective Polyethylene Pipe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kenneth H. Green; Willie E. Rochefort; Nick Wannenmacher

2006-06-30

Current procedures for repairing polyethylene (PE) gas pipe require excavation, isolation, and removal of the damaged section of pipe followed by fusing a new section of pipe into place. These techniques are costly and very disruptive. An alternative repair method was developed at Timberline Tool with support from Oregon State University (OSU) and funding by the U. S. Department of Energy National Energy Technology Laboratory (DOE/NETL). This project was undertaken to design, develop and test a tool and method for repairing damaged PE pipe remotely and externally in situ without squeezing off the flow of gas, eliminating the need formore » large-scale excavations. Through an iterative design and development approach, a final engineered prototype was developed that utilizes a unique thermo-chemical and mechanical process to apply a permanent external patch to repair small nicks, gouges and punctures under line pressure. The project identified several technical challenges during the design and development process. The repair tool must be capable of being installed under live conditions and operate in an 18-inch keyhole. This would eliminate the need for extensive excavations thus reducing the cost of the repair. Initially, the tool must be able to control the leak by encapsulating the pipe and apply slight pressure at the site of damage. Finally, the repair method must be permanent at typical operating pressures. The overall results of the project have established a permanent external repair method for use on damaged PE gas pipe in a safe and cost-effective manner. The engineered prototype was subjected to comprehensive testing and evaluation to validate the performance. Using the new repair tool, samples of 4-inch PE pipe with simulated damage were successfully repaired under line pressure to the satisfaction of DOE/NETL and the following natural gas companies: Northwest Natural; Sempra Energy, Southwest Gas Corporation, Questar, and Nicor. However, initial results of accelerated age testing on repaired pipe samples showed that the high density polyethylene (HDPE) pipe patch material developed a small crack at the high stress areas surrounding the patched hole within the first 48 hours of hot water testing, indicating that the patch material has a 25-year lifespan. Based on these results, further research is continuing to develop a stronger repair patch for a satisfactory 50-year patch system. Additional tests were also conducted to evaluate whether any of the critical performance properties of the PE pipe were reduced or compromised by the repair technique. This testing validated a satisfactory 50-year patch system for the pipe.« less

RNF168 forms a functional complex with RAD6 during the DNA damage response

PubMed Central

Liu, Chao; Wang, Degui; Wu, Jiaxue; Keller, Jennifer; Ma, Teng; Yu, Xiaochun

2013-01-01

Summary Protein ubiquitination plays an important role in initiating the DNA damage response. Following DNA damage, E2 ubiquitin conjugating enzymes are crucial for catalyzing substrate ubiquitination that recruits downstream DNA repair factors to DNA lesions. To identify novel E2 conjugating enzymes important for initiating the DNA-damage-induced ubiquitination cascade, we screened most of the known E2 enzymes and found that RAD6A and RAD6B function together with RNF168 in the ionizing radiation (IR)-induced DNA damage response. Similarly to RNF168-deficient cells, RAD6A- or RAD6B-deficient cells exhibit a reduction in DNA-damage-induced protein ubiquitination. Correspondingly, DNA-damage-induced foci formation of DNA damage repair proteins, such as BRCA1 and 53BP1, is impaired in the absence of RAD6A or RAD6B. Moreover, the RNF168–RAD6 complex targeted histone H1.2 for ubiquitination in vitro and regulated DNA-damage-induced histone H1.2 ubiquitination in vivo. Collectively, these data demonstrate that RNF168, in complex with RAD6A or RAD6B, is activated in the DNA-damage-induced protein ubiquitination cascade. PMID:23525009

Technical Operating Procedures for Providing Funding to Natural Resource Trustees to Conduct an Initiation of Assessment of Natural Resource Damages Under the Oil Pollution Act of 1990

DOT National Transportation Integrated Search

1996-06-01

Technical Operating Procedures (TOPS) for Providing Funding to Natural Resources : Trustees To Conduct An Initiation of Assessment of Natural Resource Damages : under the Oil Pollution Act of 1990 have been developed to provide guidance on : funding ...

Statistical damage constitutive model for rocks subjected to cyclic stress and cyclic temperature

NASA Astrophysics Data System (ADS)

Zhou, Shu-Wei; Xia, Cai-Chu; Zhao, Hai-Bin; Mei, Song-Hua; Zhou, Yu

2017-10-01

A constitutive model of rocks subjected to cyclic stress-temperature was proposed. Based on statistical damage theory, the damage constitutive model with Weibull distribution was extended. Influence of model parameters on the stress-strain curve for rock reloading after stress-temperature cycling was then discussed. The proposed model was initially validated by rock tests for cyclic stress-temperature and only cyclic stress. Finally, the total damage evolution induced by stress-temperature cycling and reloading after cycling was explored and discussed. The proposed constitutive model is reasonable and applicable, describing well the stress-strain relationship during stress-temperature cycles and providing a good fit to the test results. Elastic modulus in the reference state and the damage induced by cycling affect the shape of reloading stress-strain curve. Total damage induced by cycling and reloading after cycling exhibits three stages: initial slow increase, mid-term accelerated increase, and final slow increase.

An enhancement to the NA4 gear vibration diagnostic parameter

NASA Technical Reports Server (NTRS)

Decker, Harry J.; Handschuh, Robert F.; Zakrajsek, James J.

1994-01-01

A new vibration diagnostic parameter for health monitoring of gears, NA4*, is proposed and tested. A recently developed gear vibration diagnostic parameter NA4 outperformed other fault detection methods at indicating the start and initial progression of damage. However, in some cases, as the damage progressed, the sensitivity of the NA4 and FM4 parameters tended to decrease and no longer indicated damage. A new parameter, NA4* was developed by enhancing NA4 to improve the trending of the parameter. This allows for the indication of damage both at initiation and also as the damage progresses. The NA4* parameter was verified and compared to the NA4 and FM4 parameters using experimental data from single mesh spur and spiral bevel gear fatigue rigs. The primary failure mode for the test cases was naturally occurring tooth surface pitting. The NA4* parameter is shown to be a more robust indicator of damage.

Damage and recovery characteristics of lithium-containing solar cells.

NASA Technical Reports Server (NTRS)

Faith, T. J.

1971-01-01

Damage and recovery characteristics were measured on lithium-containing solar cells irradiated by 1-MeV electrons. Empirical expressions for cell recovery time, diffusion-length damage coefficient immediately after irradiation, and diffusion-length damage coefficient after recovery were derived using results of short-circuit current, diffusion-length, and reverse-bias capacitance measurements. The damage coefficients were expressed in terms of a single lithium density parameter, the lithium gradient. A fluence dependence was also established, this dependence being the same for both the immediate-post-irradiation and post-recovery cases. Cell recovery rates were found to increase linearly with lithium gradient.

Tobacco Retail Outlet Density and Young Adult Tobacco Initiation

PubMed Central

Pearson, Jennifer L.; Anesetti-Rothermel, Andrew; Xiao, Haijun; Kirchner, Thomas R.; Vallone, Donna

2016-01-01

Background: A growing body of evidence indicates that the density of tobacco retail outlets around the home residence may influence tobacco use among youth and adults. The purpose of this study was to examine the impact of neighborhood tobacco retail outlet density on young adult initiation of different tobacco product types. Methods: Cross-sectional data from a 2013 nationally representative sample of young adults aged 18–34 was examined in relation to a 2012 geocoded listing of all outlets likely to sell tobacco in the United States. Separate multivariable logistic regression analyses examined associations between neighborhood outlet density and past 6 months first use of cigarettes, non-cigarette combustible products, and noncombustible products among adults aged 18–24 and 25–34. Results: Outlet density was significantly associated with recent initiation of cigarettes and other combustibles, but this impact varied for younger and older groups. Increased density was significantly associated with a higher likelihood of initiating cigarette use among adults aged 25–34 (OR = 3.75, 95% CI = 1.18, 11.90), and of initiating non-cigarette combustible use among 18–24 year olds (OR = 3.16, 95% CI = 1.03, 9.74). There was no impact of outlet density on recent noncombustible product initiation among either group. Conclusion: This study is the first to examine the impact of tobacco outlet density on young adult initiation of cigarettes and other tobacco products. Findings demonstrate that residential neighborhood outlet density is associated with recent initiation of combustible products and this effect varies by product type and age. The tobacco outlet environment may be a critical factor in promoting young adult tobacco use initiation. PMID:25666816

Mapping auditory nerve firing density using high-level compound action potentials and high-pass noise masking a

PubMed Central

Earl, Brian R.; Chertoff, Mark E.

2012-01-01

Future implementation of regenerative treatments for sensorineural hearing loss may be hindered by the lack of diagnostic tools that specify the target(s) within the cochlea and auditory nerve for delivery of therapeutic agents. Recent research has indicated that the amplitude of high-level compound action potentials (CAPs) is a good predictor of overall auditory nerve survival, but does not pinpoint the location of neural damage. A location-specific estimate of nerve pathology may be possible by using a masking paradigm and high-level CAPs to map auditory nerve firing density throughout the cochlea. This initial study in gerbil utilized a high-pass masking paradigm to determine normative ranges for CAP-derived neural firing density functions using broadband chirp stimuli and low-frequency tonebursts, and to determine if cochlear outer hair cell (OHC) pathology alters the distribution of neural firing in the cochlea. Neural firing distributions for moderate-intensity (60 dB pSPL) chirps were affected by OHC pathology whereas those derived with high-level (90 dB pSPL) chirps were not. These results suggest that CAP-derived neural firing distributions for high-level chirps may provide an estimate of auditory nerve survival that is independent of OHC pathology. PMID:22280596

Effects of Thermal and Pressure Histories on the Chemical Strengthening of Sodium Aluminosilicate Glass

NASA Astrophysics Data System (ADS)

Svenson, Mouritz; Thirion, Lynn; Youngman, Randall; Mauro, John; Bauchy, Mathieu; Rzoska, Sylwester; Bockowski, Michal; Smedskjaer, Morten

2016-03-01

Glasses can be chemically strengthened through the ion exchange process, wherein smaller ions in the glass (e.g., Na+) are replaced by larger ions from a salt bath (e.g., K+). This develops a compressive stress (CS) on the glass surface, which, in turn, improves the damage resistance of the glass. The magnitude and depth of the generated CS depends on the thermal and pressure histories of the glass prior to ion exchange. In this study, we investigate the ion exchange-related properties (mutual diffusivity, CS, and hardness) of a sodium aluminosilicate glass, which has been densified through annealing below the initial fictive temperature of the glass or through pressure-quenching from the glass transition temperature at 1 GPa prior to ion exchange. We show that the rate of alkali interdiffusivity depends only on the density of the glass, rather than on the applied densification method. However, we also demonstrate that for a given density, the increase in CS and increase in hardness induced by ion exchange strongly depends on the densification method. Specifically, at constant density, the CS and hardness values achieved through thermal annealing are larger than those achieved through pressure-quenching. These results are discussed in relation to the structural changes in the environment of the network-modifier and the overall network densification.

Wood properties and trunk allometry of co-occurring rainforest canopy trees in a cyclone-prone environment.

PubMed

Read, Jennifer; Evans, Robert; Sanson, Gordon D; Kerr, Stuart; Jaffré, Tanguy

2011-11-01

New Caledonia commonly experiences cyclones, so trees there are expected to have enhanced wood traits and trunk allometry that confer resistance to wind damage. We ask whether there is evidence of a trade-off between these traits and growth rate among species. Wood traits, including density, microfibril angle (MFA), and modulus of elasticity (MOE), ratio of tree height to stem diameter, and growth rate were investigated in mature trees of 15 co-occurring canopy species in a New Caledonian rainforest. In contrast to some studies, wood density did not correlate negatively with growth increment. Among angiosperms, wood density and MOE correlated positively with diameter-adjusted tree height, and MOE correlated positively with stem-diameter growth increment. Tall slender trees achieved high stiffness with high efficiency with respect to wood density, in part by low MFA, and with a higher diameter growth increment but a lower buckling safety factor. However, some tree species of a similar niche differed in whole-tree resistance to wind damage and achieved wood stiffness in different ways. There was no evidence of a growth-safety trade-off in these trees. In forests that regularly experience cyclones, there may be stronger selection for high wood density and/or stiffness in fast-growing trees of the upper canopy, with the potential growth trade-off amortized by access to the upper canopy and by other plant traits. Furthermore, decreasing wood density does not necessarily decrease resistance to wind damage, resistance being influenced by other characteristics including cell-level traits (e.g., MFA) and whole-plant architecture.

Atmospheric electromagnetic pulse propagation effects from thick targets in a terawatt laser target chamber.

PubMed

Remo, John L; Adams, Richard G; Jones, Michael C

2007-08-20

Generation and effects of atmospherically propagated electromagnetic pulses (EMPs) initiated by photoelectrons ejected by the high density and temperature target surface plasmas from multiterawatt laser pulses are analyzed. These laser radiation pulse interactions can significantly increase noise levels, thereby obscuring data (sometimes totally) and may even damage sensitive probe and detection instrumentation. Noise effects from high energy density (approximately multiterawatt) laser pulses (approximately 300-400 ps pulse widths) interacting with thick approximately 1 mm) metallic and dielectric solid targets and dielectric-metallic powder mixtures are interpreted as transient resonance radiation associated with surface charge fluctuations on the target chamber that functions as a radiating antenna. Effective solutions that minimize atmospheric EMP effects on internal and proximate electronic and electro-optical equipment external to the system based on systematic measurements using Moebius loop antennas, interpretations of signal periodicities, and dissipation indicators determining transient noise origin characteristics from target emissions are described. Analytic models for the effect of target chamber resonances and associated noise current and temperature in a probe diode laser are described.

Atmospheric electromagnetic pulse propagation effects from thick targets in a terawatt laser target chamber

NASA Astrophysics Data System (ADS)

Remo, John L.; Adams, Richard G.; Jones, Michael C.

2007-08-01

Generation and effects of atmospherically propagated electromagnetic pulses (EMPs) initiated by photoelectrons ejected by the high density and temperature target surface plasmas from multiterawatt laser pulses are analyzed. These laser radiation pulse interactions can significantly increase noise levels, thereby obscuring data (sometimes totally) and may even damage sensitive probe and detection instrumentation. Noise effects from high energy density (approximately multiterawatt) laser pulses (˜300-400 ps pulse widths) interacting with thick (˜1 mm) metallic and dielectric solid targets and dielectric-metallic powder mixtures are interpreted as transient resonance radiation associated with surface charge fluctuations on the target chamber that functions as a radiating antenna. Effective solutions that minimize atmospheric EMP effects on internal and proximate electronic and electro-optical equipment external to the system based on systematic measurements using Moebius loop antennas, interpretations of signal periodicities, and dissipation indicators determining transient noise origin characteristics from target emissions are described. Analytic models for the effect of target chamber resonances and associated noise current and temperature in a probe diode laser are described.

Atmospheric electromagnetic pulse propagation effects from thick targets in a terawatt laser target chamber

DOE PAGES

Remo, John L.; Adams, Richard G.; Jones, Michael C.

2007-08-16

Generation and effects of atmospherically propagated electromagnetic pulses (EMPs) initiated by photoelectrons ejected by the high density and temperature target surface plasmas from multiterawatt laser pulses are analyzed. These laser radiation pulse interactions can significantly increase noise levels, thereby obscuring data (sometimes totally) and may even damage sensitive probe and detection instrumentation. Noise effects from high energy density (approximately multiterawatt) laser pulses (~300–400 ps pulse widths) interacting with thick (~1 mm) metallic and dielectric solid targets and dielectric–metallic powder mixtures are interpreted as transient resonance radiation associated with surface charge fluctuations on the target chamber that functions as a radiatingmore » antenna. Effective solutions that minimize atmospheric EMP effects on internal and proximate electronic and electro-optical equipment external to the system based on systematic measurements using Moebius loop antennas, interpretations of signal periodicities, and dissipation indicators determining transient noise origin characteristics from target emissions are described. Analytic models for the effect of target chamber resonances and associated noise current and temperature in a probe diode laser are described.« less

Cotton Defense Induction Patterns Under Spatially, Temporally and Quantitatively Varying Herbivory Levels.

PubMed

Eisenring, Michael; Meissle, Michael; Hagenbucher, Steffen; Naranjo, Steven E; Wettstein, Felix; Romeis, Jörg

2017-01-01

In its defense against herbivores, cotton ( Gossypium sp.) relies in part on the production of a set of inducible, non-volatile terpenoids. Under uniform damage levels, in planta allocation of induced cotton terpenoids has been found to be highest in youngest leaves, supporting assumptions of the optimal defense theory (ODT) which predicts that plants allocate defense compounds to tissues depending on their value and the likelihood of herbivore attack. However, our knowledge is limited on how varying, and thus more realistic, damage levels might affect cotton defense organization. We hypothesized that the allocation of terpenoids and densities of terpenoid-storing glands in leaves aligns with assumptions of the ODT, even when plants are subjected to temporally, spatially and quantitatively varying caterpillar ( Heliothis virescens ) damage. As expected, cotton plants allocated most of their defenses to their youngest leaves regardless of damage location. However, defense induction in older leaves varied with damage location. For at least 14 days after damage treatments ended, plants reallocated defense resources from previously young leaves to newly developed leaves. Furthermore, we observed a positive hyperbolic relationship between leaf damage area and both terpenoid concentrations and gland densities, indicating that cotton plants can fine-tune defense allocation. Although it appears that factors like vascular constraints and chemical properties of individual defense compounds can affect defense levels, our results overall demonstrate that induced defense organization of cotton subjected to varying damage treatments is in alignment with key assumptions of the ODT.

Cotton Defense Induction Patterns Under Spatially, Temporally and Quantitatively Varying Herbivory Levels

PubMed Central

Eisenring, Michael; Meissle, Michael; Hagenbucher, Steffen; Naranjo, Steven E.; Wettstein, Felix; Romeis, Jörg

2017-01-01

In its defense against herbivores, cotton (Gossypium sp.) relies in part on the production of a set of inducible, non-volatile terpenoids. Under uniform damage levels, in planta allocation of induced cotton terpenoids has been found to be highest in youngest leaves, supporting assumptions of the optimal defense theory (ODT) which predicts that plants allocate defense compounds to tissues depending on their value and the likelihood of herbivore attack. However, our knowledge is limited on how varying, and thus more realistic, damage levels might affect cotton defense organization. We hypothesized that the allocation of terpenoids and densities of terpenoid-storing glands in leaves aligns with assumptions of the ODT, even when plants are subjected to temporally, spatially and quantitatively varying caterpillar (Heliothis virescens) damage. As expected, cotton plants allocated most of their defenses to their youngest leaves regardless of damage location. However, defense induction in older leaves varied with damage location. For at least 14 days after damage treatments ended, plants reallocated defense resources from previously young leaves to newly developed leaves. Furthermore, we observed a positive hyperbolic relationship between leaf damage area and both terpenoid concentrations and gland densities, indicating that cotton plants can fine-tune defense allocation. Although it appears that factors like vascular constraints and chemical properties of individual defense compounds can affect defense levels, our results overall demonstrate that induced defense organization of cotton subjected to varying damage treatments is in alignment with key assumptions of the ODT. PMID:28270830

Phenology and density of balsam twig aphid, Mindarus abietinus Koch (Homoptera: Aphididae) in relation to bud break, shoot damage, and value of fir Christmas trees.

PubMed

Fondren, K M; McCullough, D G

2003-12-01

The balsam twig aphid, Mindarus abietinus Koch (Homoptera: Aphididae), is a major insect pest of balsam and Fraser fir grown for Christmas trees. Our objectives in this study were to 1) monitor the phenology of A. abietinus in fir plantations; 2) assess relationships among M. abietinus density, tree phenology, and damage to tree foliage; and 3) develop an esthetic injury level for M. abietinus on Christmas trees. We monitored phenology of M. abietinus and fir trees on three commercial Christmas tree plantations in central and northern Lower Michigan for 3 yr (1999-2001). Phenology of M. abietinus fundatrices and sexuparae was strongly correlated with accumulated degree-days (DD) base 10 degrees C. Fundatrices matured by approximately 83 DD(10 degrees C) and sexuparae were first observed at approximately 83-111 DD(10 degrees C). Trees that broke bud approximately 1 wk later than other trees in the same field escaped M. abietinus damage and shoot expansion rate in spring was generally positively correlated with M. abietinus damage. Retail customers surveyed at a choose-and-cut Christmas plantation in 2 yr did not consistently differentiate between similarly sized trees with no, light, and moderate M. abietinus damage, but heavy damage (>50% damaged shoots) did affect customer perception. Similarly, when wholesale grades were assigned, the high quality Grade 1 trees had up to 40% shoot damage, whereas Grade 2 trees had 32-62% shoot damage. Two trees ranked as unsaleable had sparse canopies and distorted needles on 42% to almost 100% of the shoots.

Using Non-linear Homogenization to Improve the Performance of Macroscopic Damage Models of Trabecular Bone.

PubMed

Levrero-Florencio, Francesc; Pankaj, Pankaj

2018-01-01

Realistic macro-level finite element simulations of the mechanical behavior of trabecular bone, a cellular anisotropic material, require a suitable constitutive model; a model that incorporates the mechanical response of bone for complex loading scenarios and includes post-elastic phenomena, such as plasticity (permanent deformations) and damage (permanent stiffness reduction), which bone is likely to experience. Some such models have been developed by conducting homogenization-based multiscale finite element simulations on bone micro-structure. While homogenization has been fairly successful in the elastic regime and, to some extent, in modeling the macroscopic plastic response, it has remained a challenge with respect to modeling damage. This study uses a homogenization scheme to upscale the damage behavior from the tissue level (microscale) to the organ level (macroscale) and assesses the suitability of different damage constitutive laws. Ten cubic specimens were each subjected to 21 strain-controlled load cases for a small range of macroscopic post-elastic strains. Isotropic and anisotropic criteria were considered, density and fabric relationships were used in the formulation of the damage law, and a combined isotropic/anisotropic law with tension/compression asymmetry was formulated, based on the homogenized results, as a possible alternative to the currently used single scalar damage criterion. This computational study enhances the current knowledge on the macroscopic damage behavior of trabecular bone. By developing relationships of damage progression with bone's micro-architectural indices (density and fabric) the study also provides an aid for the creation of more precise macroscale continuum models, which are likely to improve clinical predictions.

Loop and void damage during heavy ion irradiation on nanocrystalline and coarse grained tungsten: Microstructure, effect of dpa rate, temperature, and grain size

DOE Office of Scientific and Technical Information (OSTI.GOV)

El-Atwani, O.; Esquivel, E.; Efe, M.

Displacement damage, through heavy ion irradiation was studied on two tungsten grades (coarse grained tungsten (CGW) and nanocrystalline and ultrafine grained tungsten (NCW)) using different displacement per atom rates and different irradiation temperatures (RT and 1050 K). Percentage of <111> and <100> type loops at the irradiation conditions was determined. Irradiation damage in the microstructure was quantified using average loop areas and densities (method A) and loop areal fraction in the grain matrices under 2-beam diffraction conditions (method B). Average values of <111> and <100> loops were calculated from method A. Loop coalescence was shown to occur for CGW atmore » 0.25 dpa. Using both methods of quantifying microstructural damage, no effect of dpa rate was observed and damage in CGW was shown to be the same at RT and 1050 K. Swelling from voids observed at 1050 K was quantified. The loop damage in NCW was compared to CGW at the same diffraction and imaging conditions. NCW was shown to possess enhanced irradiation resistance at RT regarding loop damage and higher swelling resistance at 1050 K compared to CGW. For irradiation at 1050 K, the NCW was shown to have a similar defect densities to the CGW which is attributed to higher surface effects in the CGW, vacancy loop growth to voids and a better sink efficiency in the CGW deduced from the vacancy distribution profiles from Kinetic Monte Carlo simulations. Loop density and swelling was shown to have similar values in grains sizes that range from 80-600 nm. No loop or void denuded zones occurred at any of the irradiation conditions. This work has a collection of experiments and conclusions that are of vital importance to materials and nuclear communities.« less

Loop and void damage during heavy ion irradiation on nanocrystalline and coarse grained tungsten: Microstructure, effect of dpa rate, temperature, and grain size

DOE PAGES

El-Atwani, O.; Esquivel, E.; Efe, M.; ...

2018-02-20

Displacement damage, through heavy ion irradiation was studied on two tungsten grades (coarse grained tungsten (CGW) and nanocrystalline and ultrafine grained tungsten (NCW)) using different displacement per atom rates and different irradiation temperatures (RT and 1050 K). Percentage of <111> and <100> type loops at the irradiation conditions was determined. Irradiation damage in the microstructure was quantified using average loop areas and densities (method A) and loop areal fraction in the grain matrices under 2-beam diffraction conditions (method B). Average values of <111> and <100> loops were calculated from method A. Loop coalescence was shown to occur for CGW atmore » 0.25 dpa. Using both methods of quantifying microstructural damage, no effect of dpa rate was observed and damage in CGW was shown to be the same at RT and 1050 K. Swelling from voids observed at 1050 K was quantified. The loop damage in NCW was compared to CGW at the same diffraction and imaging conditions. NCW was shown to possess enhanced irradiation resistance at RT regarding loop damage and higher swelling resistance at 1050 K compared to CGW. For irradiation at 1050 K, the NCW was shown to have a similar defect densities to the CGW which is attributed to higher surface effects in the CGW, vacancy loop growth to voids and a better sink efficiency in the CGW deduced from the vacancy distribution profiles from Kinetic Monte Carlo simulations. Loop density and swelling was shown to have similar values in grains sizes that range from 80-600 nm. No loop or void denuded zones occurred at any of the irradiation conditions. This work has a collection of experiments and conclusions that are of vital importance to materials and nuclear communities.« less

Logging damage to residual trees following partial cutting in a green ash-sugarberry stand in the Mississippi Delta

Treesearch

James S. Meadows

1993-01-01

Partial cutting in bottomland hardwoods to control stand density and species composition sometimes results in logging damage to the lower bole and/or roots of residual trees. If severe, logging damage may lead to a decline in tree vigor, which may subsequently stimulate the production of epicormic branches, causing a decrease in bole quality and an eventual loss in...

Logging Damage to Residual Trees Following Partial Cutting in a Green Ash-Sugarberry Stand in the Mississippi Delta

Treesearch

James S. Meadows

1993-01-01

Partial cutting in bottomland hardwoods to control stand density and species composition sometimes results in logging damage to the lower bole and/or roots of residual trees. If severe, logging damage may lead to a decline in tree vigor, which may subsequently stimulate the production of epicormic branches, causing a decrease in bole quality and an eventual loss in...

Mating Disruption of Planococcus ficus (Hemiptera: Pseudococcidae) in Vineyards Using Reservoir Pheromone Dispensers

PubMed Central

Cocco, Arturo; Lentini, Andrea; Serra, Giuseppe

2014-01-01

Abstract Mating disruption field experiments to control the vine mealybug, Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae), were carried out in 2008 and 2009 in two commercial vineyards in Sardinia (Italy). The effectiveness of mating disruption was evaluated by testing reservoir dispensers loaded with 100 mg (62.5 g/ha) and 150 mg (93.8 g/ha) of the sex pheromone in 2008 and 2009, respectively. The number of males captured in pheromone traps, the P. ficus population density and age structure, the parasitism rate, the percentage of ovipositing females, and the crop damage were compared between disrupted and untreated plots. In both field trials, the number of males captured in mating disruption plots was significantly reduced by 86% and 95%, respectively. Mating disruption at the initial dose of 62.5 g/ha of active ingredient gave inconclusive results, whereas the dose of 93.8 g/ha significantly lowered the mealybug density and modified the age structure, which showed a lower percentage of ovipositing females and a higher proportion of preovipositing females. Mating disruption did not affect negatively the parasitism rate, which was higher in the disrupted than in the control plots (>1.5-fold). Crop damage at harvest was very low in both field trials and did not differ between treatments. Mating disruption was effective in wide plots protected with dispensers loaded with 150 mg of the sex pheromone, showing its potential to be included in the overall integrated control programs in Mediterranean wine-growing regions. PMID:25347835

Temperature Prediction Model for Bone Drilling Based on Density Distribution and In Vivo Experiments for Minimally Invasive Robotic Cochlear Implantation.

PubMed

Feldmann, Arne; Anso, Juan; Bell, Brett; Williamson, Tom; Gavaghan, Kate; Gerber, Nicolas; Rohrbach, Helene; Weber, Stefan; Zysset, Philippe

2016-05-01

Surgical robots have been proposed ex vivo to drill precise holes in the temporal bone for minimally invasive cochlear implantation. The main risk of the procedure is damage of the facial nerve due to mechanical interaction or due to temperature elevation during the drilling process. To evaluate the thermal risk of the drilling process, a simplified model is proposed which aims to enable an assessment of risk posed to the facial nerve for a given set of constant process parameters for different mastoid bone densities. The model uses the bone density distribution along the drilling trajectory in the mastoid bone to calculate a time dependent heat production function at the tip of the drill bit. Using a time dependent moving point source Green's function, the heat equation can be solved at a certain point in space so that the resulting temperatures can be calculated over time. The model was calibrated and initially verified with in vivo temperature data. The data was collected in minimally invasive robotic drilling of 12 holes in four different sheep. The sheep were anesthetized and the temperature elevations were measured with a thermocouple which was inserted in a previously drilled hole next to the planned drilling trajectory. Bone density distributions were extracted from pre-operative CT data by averaging Hounsfield values over the drill bit diameter. Post-operative [Formula: see text]CT data was used to verify the drilling accuracy of the trajectories. The comparison of measured and calculated temperatures shows a very good match for both heating and cooling phases. The average prediction error of the maximum temperature was less than 0.7 °C and the average root mean square error was approximately 0.5 °C. To analyze potential thermal damage, the model was used to calculate temperature profiles and cumulative equivalent minutes at 43 °C at a minimal distance to the facial nerve. For the selected drilling parameters, temperature elevation profiles and cumulative equivalent minutes suggest that thermal elevation of this minimally invasive cochlear implantation surgery may pose a risk to the facial nerve, especially in sclerotic or high density mastoid bones. Optimized drilling parameters need to be evaluated and the model could be used for future risk evaluation.

Thermally ruggedized ITO transparent electrode films for high power optoelectronics

DOE PAGES

Yoo, Jae-Hyuck; Matthews, Manyalibo; Ramsey, Phil; ...

2017-10-06

Here, we present two strategies to minimize laser damage in transparent conductive films. The first consists of improving heat dissipation by selection of substrates with high thermal diffusivity or by addition of capping layer heatsinks. The second is reduction of bulk energy absorption by lowering free carrier density and increasing mobility, while maintaining film conductance with thicker films. Multi-pulse laser damage tests were performed on tin-doped indium oxide (ITO) films configured to improve optical lifetime damage performance. Conditions where improvements were not observed are also described. Finally, when bulk heating is not the dominant damage process, discrete defect-induced damage limitsmore » damage behavior.« less

Irradiation-enhanced α' precipitation in model FeCrAl alloys

DOE PAGES

Edmondson, Philip D.; Briggs, Samuel A.; Yamamoto, Yukinori; ...

2016-02-17

We have irradiated the model FeCrAl alloys with varying compositions (Fe(10–18)Cr(10–6)Al at.%) with a neutron at ~ 320 to damage levels of ~ 7 displacements per atom (dpa) to investigate the compositional influence on the formation of irradiation-induced Cr-rich α' precipitates using atom probe tomography. In all alloys, significant number densities of these precipitates were observed. Cluster compositions were investigated and it was found that the average cluster Cr content ranged between 51.1 and 62.5 at.% dependent on initial compositions. Furthermore, this is significantly lower than the Cr-content of α' in binary FeCr alloys. As a result, significant partitioning ofmore » the Al from the α' precipitates was also observed.« less

Shock wave induced damage of a protein by void collapse

DOE PAGES

Lau, Edmond Y.; Berkowitz, Max L.; Schwegler, Eric R.

2016-01-05

In this study, we report on a series of molecular dynamics simulations that were used to examine the effects of shockwaves on a membrane bound ion channel. A planar shockwave was found to compress the ion channel upon impact but the protein geometry resembles the initial structure as soon as the solvent density begins to dissipate. When a void was placed in close proximity to the membrane, the shockwave proved to be much more destructive to the protein due to formation of a nanojet that results from the asymmetric collapse of the void. The nanojet was able to cause significantmore » structural changes to the protein even at low particle velocities that are not able to directly cause poration of the membrane.« less

Double Linear Damage Rule for Fatigue Analysis

NASA Technical Reports Server (NTRS)

Halford, G.; Manson, S.

1985-01-01

Double Linear Damage Rule (DLDR) method for use by structural designers to determine fatigue-crack-initiation life when structure subjected to unsteady, variable-amplitude cyclic loadings. Method calculates in advance of service how many loading cycles imposed on structural component before macroscopic crack initiates. Approach eventually used in design of high performance systems and incorporated into design handbooks and codes.

Processing and mechanical characterization of alumina laminates

NASA Astrophysics Data System (ADS)

Montgomery, John K.

2002-08-01

Single-phase ceramics that combine property gradients or steps in monolithic bodies are sought as alternatives to ceramic composites made of dissimilar materials. This work describes novel processing methods to produce stepped-density (or laminated) alumina single-phase bodies that maintain their mechanical integrity. One arrangement consists of a stiff, dense bulk material with a thin, flaw tolerant, porous exterior layer. Another configuration consists of a lightweight, low-density bulk material with a thin, hard, wear resistant exterior layer. Alumina laminates with strong interfaces have been successfully produced in this work using two different direct-casting processes. Gelcasting is a useful near-net shape processing technique that has been combined with several techniques, such as reaction bonding of aluminum oxide and the use of starch as a fugative filler, to successfully produced stepped-density alumina laminates. The other direct casting process that has been developed in this work is thermoreversible gelcasting (TRG). This is a reversible gelation process that has been used to produce near-net shape dense ceramic bodies. Also, individual layers can be stacked together and heated to produce laminates. Bilayer laminate samples were produced with varied thickness of porous and dense layers. It was shown that due to the difference in modulus and hardness, transverse cracking is found upon Hertzian contact when the dense layer is on the exterior. In the opposite arrangement, compacted damage zones formed in the porous material and no damage occurred in the underlying dense layer. Flaw tolerant behavior of the porous exterior/dense underlayer was examined by measuring biaxial strength as a function of Vickers indentation load. It was found that the thinnest layer of porous material results in the greatest flaw tolerance. Also, higher strength was exhibited at large indentation loads when compared to dense monoliths. The calculated stresses on the surfaces and interface afforded an explanation of the behavior that failure initiates at the interface between the layers for the thinnest configuration, rather than the sample surface.

Succession after stand replacing disturbances by fire, wind throw, and insects in the dark Taiga of Central Siberia.

PubMed

Schulze, E-D; Wirth, C; Mollicone, D; Ziegler, W

2005-11-01

The dark taiga of Siberia is a boreal vegetation dominated by Picea obovata, Abies sibirica, and Pinus sibirica during the late succession. This paper investigates the population and age structure of 18 stands representing different stages after fire, wind throw, and insect damage. To our knowledge, this is the first time that the forest dynamics of the Siberian dark taiga is described quantitatively in terms of succession, and age after disturbance, stand density, and basal area. The basis for the curve-linear age/diameter relation of trees is being analyzed. (1) After a stand-replacing fire Betula dominates (4,000 trees) for about 70 years. Although tree density of Betula decreases rapidly, basal area (BA) reached >30 m2/ha after 40 years. (2) After fire, Abies, Picea, and Pinus establish at the same time as Betula, but grow slower, continue to gain height and eventually replace Betula. Abies has the highest seedling number (about 1,000 trees/ha) and the highest mortality. Picea establishes with 100-400 trees/ha, it has less mortality, but reached the highest age (>350 years, DBH 51 cm). Picea is the most important indicator for successional age after disturbance. Pinus sibirica is an accompanying species. The widely distributed "mixed boreal forest" is a stage about 120 years after fire reaching a BA of >40 m2/ha. (3) Wind throw and insect damage occur in old conifer stands. Betula does not establish. Abies initially dominates (2,000-6,000 trees/ha), but Picea becomes dominant after 150-200 years since Abies is shorter lived. (4) Without disturbance the forest develops into a pure coniferous canopy (BA 40-50 m2/ha) with a self-regenerating density of 1,000 coniferous canopy trees/ha. There is no collapse of old-growth stands. The dark taiga may serve as an example in which a limited set to tree species may gain dominance under certain disturbance conditions without ever getting monotypic.

Tear geometry at active STEPs: an analogue model approach

NASA Astrophysics Data System (ADS)

Broerse, Taco; Sokoutis, Dimitrios; Willingshofer, Ernst; Govers, Rob

2017-04-01

At the lateral end of a subduction zone, tearing of lithosphere is the result of subduction of oceanic lithosphere while adjacent buoyant continental lithosphere stays at the surface. The location of lithospheric tearing is called a Subduction-Transform-Edge-Propagator (STEP), which continuously extends the plate boundary between overriding plate and continental lithosphere. One of our areas of interest is the southern Caribbean where Atlantic lithosphere subducts below the Caribbean plate. Mantle tomography suggests a clear southern edge of the Lesser Antilles slab, which makes the boundary between the Caribbean and South America a clear STEP candidate. At the surface, the San Sebastián/El Pilar fault zone forms the plate boundary between the Caribbean and South America and the active STEP is located near Trinidad. For the deeper part of the damage/shear zone, some information is available from a recent 3D gravity study: significant lateral variability in densities of the lithospheric mantle to the south of the STEP fault zone. The low-density zone may result from higher sub-crustal temperatures, such as would arise from an asthenospheric window resulting from detachment. Interpreted in this way, the mantle part of the damage zone may be 200-250 km wide. So, while the location of the plate boundary at the surface is relatively well resolved, little is known about the deeper continuation of the active STEP in the mantle lithosphere. We study the evolution of the tearing process at a STEP using analogue models. In our models we use silicone putty (lithosphere) and glucose (asthenosphere). Solely gravitational forces resulting from density differences between oceanic lithosphere and asthenosphere drive our model. Lithospheric tearing commences after subduction has initiated. The geometry of the tear varies with the rheology of the lithosphere and asthenosphere, particularly Newtonian versus power-law. We investigate the dependence on model parameters of the width of the tearing zone and the depth at which tearing occurs.

Flexural testing on carbon fibre laminates taking into account their different behaviour under tension and compression

NASA Astrophysics Data System (ADS)

Serna Moreno, M. C.; Romero Gutierrez, A.; Martínez Vicente, J. L.

2016-07-01

An analytical model has been derived for describing the results of three-point-bending tests in materials with different behaviour under tension and compression. The shift of the neutral plane and the damage initiation mode and its location have been defined. The validity of the equations has been reviewed by testing carbon fibre-reinforced polymers (CFRP), typically employed in different weight-critical applications. Both unidirectional and cross-ply laminates have been studied. The initial failure mode produced depends directly on the beam span- thickness relation. Therefore, specimens with different thicknesses have been analysed for examining the damage initiation due to either the bending moment or the out-of-plane shear load. The experimental description of the damage initiation and evolution has been shown by means of optical microscopy. The good agreement between the analytical estimations and the experimental results shows the validity of the analytical model exposed.

The study of past damaging hydrogeological events for damage susceptibility zonation

NASA Astrophysics Data System (ADS)

Petrucci, O.; Pasqua, A. A.

2008-08-01

Damaging Hydrogeological Events are defined as periods during which phenomena, such as landslides, floods and secondary floods, cause damage to people and the environment. A Damaging Hydrogeological Event which heavily damaged Calabria (Southern Italy) between December 1972, and January 1973, has been used to test a procedure to be utilised in the zonation of a province according to damage susceptibility during DHEs. In particular, we analyzed the province of Catanzaro (2391 km2), an administrative district composed of 80 municipalities, with about 370 000 inhabitants. Damage, defined in relation to the reimbursement requests sent to the Department of Public Works, has been quantified using a procedure based on a Local Damage Index. The latter, representing classified losses, has been obtained by multiplying the value of the damaged element and the percentage of damage affecting it. Rainfall has been described by the Maximum Return Period of cumulative rainfall, for both short (1, 3, 5, 7, 10 consecutive days) and long duration (30, 60, 90, 180 consecutive days), recorded during the event. Damage index and population density, presumed to represent the location of vulnerable elements, have been referred to Thiessen polygons associated to rain gauges working at the time of the event. The procedure allowed us to carry out a preliminary classification of the polygons composing the province according to their susceptibility to damage during DHEs. In high susceptibility polygons, severe damage occurs during rainfall characterised by low return periods; in medium susceptibility polygons maximum return period rainfall and induced damage show equal levels of exceptionality; in low susceptibility polygons, high return period rainfall induces a low level of damage. The east and west sectors of the province show the highest susceptibility, while polygons of the N-NE sector show the lowest susceptibility levels, on account of both the low population density and high average rainfall characterizing these mountainous areas. The future analysis of further DHEs, using the tested procedure, can strengthen the obtained zonation. Afterwards, the results can prove useful in establishing civil defence plans, emergency management, and prioritizing hazard mitigation measures.

TEM Analyses of Itokawa Regolith Grains and Lunar Soil Grains to Directly Determine Space Weathering Rates on Airless Bodies

NASA Technical Reports Server (NTRS)

Berger, Eve L.; Keller, Lindsay P.; Christoffersen, Roy

2016-01-01

Samples returned from the moon and Asteroid Itokawa by NASA's Apollo Missions and JAXA's Hayabusa Mission, respectively, provide a unique record of their interaction with the space environment. Space weathering effects result from micrometeorite impact activity and interactions with the solar wind. While the effects of solar wind interactions, ion implantation and solar flare particle track accumulation, have been studied extensively, the rate at which these effects accumulate in samples on airless bodies has not been conclusively determined. Results of numerical modeling and experimental simulations do not converge with observations from natural samples. We measured track densities and rim thicknesses of three olivine grains from Itokawa and multiple olivine and anorthite grains from lunar soils of varying exposure ages. Samples were prepared for analysis using a Leica EM UC6 ultramicrotome and an FEI Quanta 3D dual beam focused ion beam scanning electron microscope (FIB-SEM). Transmission electron microscope (TEM) analyses were performed on the JEOL 2500SE 200kV field emission STEM. The solar wind damaged rims on lunar anorthite grains are amorphous, lack inclusions, and are compositionally similar to the host grain. The rim width increases as a smooth function of exposure age until it levels off at approximately 180 nm after approximately 20 My (Fig. 1). While solar wind ion damage can only accumulate while the grain is in a direct line of sight to the Sun, solar flare particles can penetrate to mm-depths. To assess whether the track density accurately predicts surface exposure, we measured the rim width and track density in olivine and anorthite from the surface of rock 64455, which was never buried and has a surface exposure age of 2 My based on isotopic measurements. The rim width from 64455 (60-70nm) plots within error of the well-defined trend for solar wind amorphized rims in Fig. 1. Measured solar flare track densities are accurately reflecting the surface exposure of the grains. Track densities correlate with the amorphous rim thicknesses. While the space-weathered rims of anorthite grains are amorphous, the space-weathered rims on both Itokawa and lunar olivine grains show solar wind damaged rims that are not amorphous. Instead, the rims are nanocrystalline with high dislocation densities and sparse inclusions of nanophase Fe metal. The rim thicknesses on the olivine grains also correlate with track density. The Itokawa olivine grains have track densities that indicate surface exposures of approximately 10(exp 5) years. Longer exposures (up to approximately 10(exp 7) years) do not amorphize the rims, as evidenced by lunar soil olivines with high track densities (approximately 10(exp 11) cm(exp -2)). From the combined data, shown in Fig. 1, it is clear that olivine is damaged (but not amorphized) more rapidly by the solar wind compared to anorthite. The olivine damaged rim forms quickly (in approximately 10(exp 6) y) and saturates at approximately 120nm with longer exposure time. The anorthite damaged rims form more slowly, amorphize, and grow thicker than the olivine rims. This is in agreement with numerical modeling data which predicts that solar wind damaged rims on anorthite will be thicker than olivine. However, the models predict that both olivine and anorthite rims will amorphize and reach equilibrium widths in less than 10(exp 3) y, in contrast to what is observed for natural samples. Laboratory irradiation experiments, which show rapid formation of fully amorphous and blistered surfaces from simulated solar wind exposures are also in contrast to observations of natural samples. These results suggest that there is a flux dependence on the type and extent of irradiation damage that develops in olivine. This flux dependence suggests that great caution be used in extrapolating between high-flux laboratory experiments and the natural case, as demonstrated by. We constrain the space weathering rate through analysis of returned samples. Provided that the track densities and the solar wind damaged rim widths exhibited by the Itokawa grains are typical of the fine-grained regions of Itokawa, then the space weathering rate is on the order of 10(exp 5) y. Space weathering effects in lunar soils saturate within a few My of exposure while those in Itokawa regolith grains formed in approximately 10(exp 5) y. Olivine and anorthite respond differently to solar wind irradiation. The space weathering effects in olivine are particularly difficult to reconcile with laboratory irradiation studies and numerical models. Additional measurements, experiments, and modeling are required to resolve the discrepancies among the observations and calculations involving solar wind amorphization of different minerals on airless bodies.

Damage Progression in Buckle-Resistant Notched Composite Plates Loaded in Uniaxial Compression

NASA Technical Reports Server (NTRS)

McGowan, David M.; Davila, Carlos G.; Ambur, Damodar R.

2001-01-01

Results of an experimental and analytical evaluation of damage progression in three stitched composite plates containing an angled central notch and subjected to compression loading are presented. Parametric studies were conducted systematically to identify the relative effects of the material strength parameters on damage initiation and growth. Comparisons with experiments were conducted to determine the appropriate in situ values of strengths for progressive failure analysis. These parametric studies indicated that the in situ value of the fiber buckling strength is the most important parameter in the prediction of damage initiation and growth in these notched composite plates. Analyses of the damage progression in the notched, compression-loaded plates were conducted using in situ material strengths. Comparisons of results obtained from these analyses with experimental results for displacements and axial strains show good agreement.

Damage Recovery in Carrara Marble

NASA Astrophysics Data System (ADS)

Meyer, G.; Brantut, N.; Mitchell, T. M.; Meredith, P. G.

2017-12-01

We investigate the effect of confining pressure on the recovery of elastic wave velocities following deformation episodes in Carrara Marble. Dry Carrara Marble cores were deformed in the ductile regime (Pc = 40 MPa) up to 3% axial strain. After deformation, samples were held at constant stress conditions for extended periods of time (5-8 days) whilst continuously recording volumetric strain and seismic wave velocities. The velocity data were used to invert for microcrack densities using an effective medium approach. Finally, thin sections were produced to characterise the microstructures after recovery. During deformation, elastic wave speeds decreased with increasing strain by more than 30% of the value for the intact rock due to the formation of distributed microcracks. Under constant hydrostatic pressure, wave speeds progressively recovered 12-90% of the initial drop, depending on the applied confining pressure. In contrast, the strain recovery (deformation towards the initial shape of the sample) during holding time is negligible (of the order of 10-4). Tests performed under nonhydrostatic (triaxial) stress conditions during recovery showed some time-dependent creep deformation together with very significant recovery of wave velocities. The recovery is interpreted as a progressive reduction in crack density within the sample. The process is highly dependent on confining pressure, which favours it. We propose that the driving process for wave speed recovery is the time-dependent increase of contact area between crack surfaces due to the formation and growth of asperity contacts. We develop a micromechanical model for crack closure driven by asperity creep, which shows a good fit to the experimental data. Most of the recovery is achieved in the initial few hours, implying it is the fastest recovery or healing process, and thus occurs prior to any chemical healing or mineral precipitation. Our data corroborate field observations of post-seismic fault behavior.

Spatial variability in oviposition damage by periodical cicadas in a fragmented landscape.

PubMed

Cook, William M; Holt, Robert D; Yao, Jin

2001-03-01

Effects of the periodical cicada (Magicicada spp.) on forest dynamics are poorly documented. A 1998 emergence of M. cassini in eastern Kansas led to colonization of a fragmented experimental landscape undergoing secondary succession. We hypothesized that per-tree rates of oviposition damage by cicadas would reflect: (1) distance from the source of the emergence, (2) patch size, and (3) local tree density. Ovipositing females displayed clear preferences for host species and damage incidence showed predictable spatial patterns. Two species (smooth sumac, Rhus glabra, and eastern red cedar, Juniperus virginiana) were rarely attacked, whereas others (rough-leaved dogwood, Cornus drummondii; slippery elm, Ulmus rubra; box elder, Acer negundo, and honey locust, Gleditsia triacanthos) were strongly attacked. The dominant early successional tree, dogwood, received on average the most attacks. As predicted, attacks per stem declined strongly with distance from the emergence source, and with local stem density (a "dilution" effect). Contrary to expectations, there were more attacks per stem on larger patches. Because ovipositing cicadas cut damaging slits in host tree branches, potentially affecting tree growth rate, competitive ability, and capacity to reproduce, cicada damage could potentially influence spatial variation in secondary succession.

Radiofrequency radiation injures trees around mobile phone base stations.

PubMed

Waldmann-Selsam, Cornelia; Balmori-de la Puente, Alfonso; Breunig, Helmut; Balmori, Alfonso

2016-12-01

In the last two decades, the deployment of phone masts around the world has taken place and, for many years, there has been a discussion in the scientific community about the possible environmental impact from mobile phone base stations. Trees have several advantages over animals as experimental subjects and the aim of this study was to verify whether there is a connection between unusual (generally unilateral) tree damage and radiofrequency exposure. To achieve this, a detailed long-term (2006-2015) field monitoring study was performed in the cities of Bamberg and Hallstadt (Germany). During monitoring, observations and photographic recordings of unusual or unexplainable tree damage were taken, alongside the measurement of electromagnetic radiation. In 2015 measurements of RF-EMF (Radiofrequency Electromagnetic Fields) were carried out. A polygon spanning both cities was chosen as the study site, where 144 measurements of the radiofrequency of electromagnetic fields were taken at a height of 1.5m in streets and parks at different locations. By interpolation of the 144 measurement points, we were able to compile an electromagnetic map of the power flux density in Bamberg and Hallstadt. We selected 60 damaged trees, in addition to 30 randomly selected trees and 30 trees in low radiation areas (n=120) in this polygon. The measurements of all trees revealed significant differences between the damaged side facing a phone mast and the opposite side, as well as differences between the exposed side of damaged trees and all other groups of trees in both sides. Thus, we found that side differences in measured values of power flux density corresponded to side differences in damage. The 30 selected trees in low radiation areas (no visual contact to any phone mast and power flux density under 50μW/m 2 ) showed no damage. Statistical analysis demonstrated that electromagnetic radiation from mobile phone masts is harmful for trees. These results are consistent with the fact that damage afflicted on trees by mobile phone towers usually start on one side, extending to the whole tree over time. Copyright © 2016 Elsevier B.V. All rights reserved.

Catastrophic failure of contaminated fused silica optics at 355 nm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Genin, F. Y., LLNL

1996-12-03

For years, contamination has been known to degrade the performance of optics and to sometimes initiate laser-induced damage to initiate. This study has W to quantify these effects for fused silica windows used at 355 mm Contamination particles (Al, Cu, TiO{sub 2} and ZrO{sub 2}) were artificially deposited onto the surface and damage tests were conducted with a 3 ns NdYAG laser. The damage morphology was characterized by Nomarski optical microscopy. The results showed that the damage morphology for input and output surface contamination is different. For input surface contamination, both input and output surfaces can damage. In particular, themore » particle can induce pitting or drilling of the surface where the beam exits. Such damage usually grows catastrophically. Output surface contamination is usually ablated away on the shot but can also induce catastrophic damage. Plasmas are observed during illumination and seem to play an important role in the damage mechanism. The relationship between fluence and contamination size for which catastrophic damage occurred was plotted for different contamination materials. The results show that particles even as small as 10 {micro}m can substantially decrease the damage threshold of the window and that metallic particles on the input surface have a more negative effect than oxide particles.« less

Nematode Damage Functions: The Problems of Experimental and Sampling Error

PubMed Central

Ferris, H.

1984-01-01

The development and use of pest damage functions involves measurement and experimental errors associated with cultural, environmental, and distributional factors. Damage predictions are more valuable if considered with associated probability. Collapsing population densities into a geometric series of population classes allows a pseudo-replication removal of experimental and sampling error in damage function development. Recognition of the nature of sampling error for aggregated populations allows assessment of probability associated with the population estimate. The product of the probabilities incorporated in the damage function and in the population estimate provides a basis for risk analysis of the yield loss prediction and the ensuing management decision. PMID:19295865

Automatic Quantification of X-ray Computed Tomography Images of Cores: Method and Application to Shimokita Cores (Northeast Coast of Honshu, Japan)

NASA Astrophysics Data System (ADS)

Gaillot, P.

2007-12-01

X-ray computed tomography (CT) of rock core provides nondestructive cross-sectional or three-dimensional core representations from the attenuation of electromagnetic radiation. Attenuation depends on the density and the atomic constituents of the rock material that is scanned. Since it has the potential to non-invasively measure phase distribution and species concentration, X-ray CT offers significant advantages to characterize both heterogeneous and apparently homogeneous lithologies. In particular, once empirically calibrated into 3D density images, this scanning technique is useful in the observation of density variation. In this paper, I present a procedure from which information contained in the 3D images can be quantitatively extracted and turned into very-high resolution core logs and core image logs including (1) the radial and angular distributions of density values, (2) the histogram of distribution of the density and its related statistical parameters (average, 10- 25- 50, 75 and 90 percentiles, and width at half maximum), and (3) the volume, the average density and the mass contribution of three core fractions defined by two user-defined density thresholds (voids and vugs < 1.01 g/cc ≤ damaged core material < 1.25 g/cc < non-damaged core material). In turn, these quantitative outputs (1) allow the recognition of bedding and sedimentary features, as well as natural and coring-induced fractures, (2) provide a high-resolution bulk density core log, and (3) provide quantitative estimates of core voids and core damaged zones that can further be used to characterize core quality and core disturbance, and apply, where appropriate, volume correction on core physical properties (gamma-ray attenuation density, magnetic susceptibility, natural gamma radiation, non-contact electrical resistivity, P-wave velocity) acquired via Multi- Sensors Core loggers (MSCL). The procedure is illustrated on core data (XR-CT images, continuous MSCL physical properties and discrete Moisture and Density measurements) from the Hole C9001C drilled off-shore Shimokita (northeast coast of Honshu, Japan) during the shake-down cruise (08-11/2006) of the scientific drilling vessel, Chikyu.

Tactile stimulation partially prevents neurodevelopmental changes in visual tract caused by early iron deficiency.

PubMed

Horiquini-Barbosa, Everton; Gibb, Robbin; Kolb, Bryan; Bray, Douglas; Lachat, Joao-Jose

2017-02-15

Iron deficiency has a critical impact on maturational mechanisms of the brain and the damage related to neuroanatomical parameters is not satisfactorily reversed after iron replacement. However, emerging evidence suggest that enriched early experience may offer great therapeutic efficacy in cases of nutritional disorders postnatally, since the brain is remarkably responsive to its interaction with the environment. Given the fact that tactile stimulation (TS) treatment has been previously shown to be an effective therapeutic approach and with potential application to humans, here we ask whether exposure to TS treatment, from postnatal day (P) 1 to P32 for 3min/day, could also be employed to prevent neuroanatomical changes in the optic nerve of rats maintained on an iron-deficient diet during brain development. We found that iron deficiency changed astrocyte, oligodendrocyte, damaged fiber, and myelinated fiber density, however, TS reversed the iron-deficiency-induced alteration in oligodendrocyte, damaged fiber and myelinated fiber density, but failed to reverse astrocyte density. Our results suggest that early iron deficiency may act by disrupting the timing of key steps in visual system development thereby modifying the normal progression of optic nerve maturation. However, optic nerve development is sensitive to enriching experiences, and in the current study we show that this sensitivity can be used to prevent damage from postnatal iron deficiency during the critical period. Copyright © 2016 Elsevier B.V. All rights reserved.

Microstructural characterisation of proton irradiated niobium using X-ray diffraction technique

NASA Astrophysics Data System (ADS)

Dutta, Argha; Gayathri, N.; Neogy, S.; Mukherjee, P.

2018-04-01

The microstructural parameters in pure Nb, irradiated with 5 MeV proton beam have been evaluated as a function of dose using X-ray diffraction line profile analysis. In order to assess the microstructural changes in the homogeneous region and in the peak damage region of the damage energy deposition profile, X-ray diffraction patterns have been collected using two different geometries (Bragg-Brentano and parallel beam geometries). Different X-ray line profile analysis like Williamson-Hall (W-H) analysis, modified W-H analysis, double-Voigt analysis, modified Rietveld technique and convolutional multiple whole profile fitting have been employed to extract the microstructural parameters like coherent domain size, microstrain within the domain, dislocation density and arrangement of dislocations. The coherent domain size decreases drastically along with increase in microstrain and dislocation density in the first dose for both the geometries. With increasing dose, a decreasing trend in microstrain associated with decrease in dislocation density is observed for both the geometries. This is attributed to the formation of defect clusters due to irradiation which with increasing dose collapse to dislocation loops to minimise the strain in the matrix. This is corroborated with the observation of black dots and loops in the TEM images. No significant difference is observed in the trend of microstructural parameters between the homogeneous and peak damage region of the damage profile.

Phytoseiulus persimilis response to herbivore-induced plant volatiles as a function of mite-days.

PubMed

Nachappa, Punya; Margolies, David C; Nechols, James R; Loughin, Thomas

2006-01-01

The predatory mite, Phytoseiulus persimilis (Acari: Phytoseiidae), uses plant volatiles (i.e., airborne chemicals) triggered by feeding of their herbivorous prey, Tetranychus urticae (Acari: Tetranychidae), to help locate prey patches. The olfactory response of P. persimilis to prey-infested plants varies in direct relation to the population growth pattern of T. urticae on the plant; P. persimilis responds to plants until the spider mite population feeding on a plant collapses, after which infested plants do not attract predators. It has been suggested that this represents an early enemy-free period for T. urticae before the next generation of females is produced. We hypothesize that the mechanism behind the diminished response of predators is due to extensive leaf damage caused by T. urticae feeding, which reduces the production of volatiles irrespective of the collapse of T. urticae population on the plant. To test this hypothesis we investigated how the response of P. persimilis to prey-infested plants is affected by: 1) initial density of T. urticae, 2) duration of infestation, and 3) corresponding leaf damage due to T. urticae feeding. Specifically, we assessed the response of P. persimilis to plants infested with two T. urticae densities (20 or 40 per plant) after 2, 4, 6, 8, 10, 12 or 14 days. We also measured leaf damage on these plants. We found that predator response to T. urticae-infested plants can be quantified as a function of mite-days, which is a cumulative measure of the standing adult female mite population sampled and summed over time. That is, response to volatiles increased with increasing numbers of T. urticae per plant or with the length of time plant was infested by T. urticae, at least as long at the leaves were green. Predatory mites were significantly attracted to plants that were infested for 2 days with only 20 spider mites. This suggests that the enemy-free period might only provide a limited window of opportunity for T. urticae because relatively low numbers of T. urticae per plant can attract predators. Leaf damage also increased as a function of mite-days until the entire leaf was blanched. T. urticae populations decreased at this time, but predator response to volatiles dropped before the entire leaf was blanched and before the T. urticae population decreased. This result supports our hypothesis that predator response to plant volatiles is linked to and limited by the degree of leaf damage, and that the quantitative response to T. urticae populations occurs only within a range when plant quality has not been severely compromised.

Model for transport and reaction of defects and carriers within displacement cascades in gallium arsenide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wampler, William R., E-mail: wrwampl@sandia.gov; Myers, Samuel M.

A model is presented for recombination of charge carriers at evolving displacement damage in gallium arsenide, which includes clustering of the defects in atomic displacement cascades produced by neutron or ion irradiation. The carrier recombination model is based on an atomistic description of capture and emission of carriers by the defects with time evolution resulting from the migration and reaction of the defects. The physics and equations on which the model is based are presented, along with the details of the numerical methods used for their solution. The model uses a continuum description of diffusion, field-drift and reaction of carriers,more » and defects within a representative spherically symmetric cluster of defects. The initial radial defect profiles within the cluster were determined through pair-correlation-function analysis of the spatial distribution of defects obtained from the binary-collision code MARLOWE, using recoil energies for fission neutrons. Properties of the defects are discussed and values for their parameters are given, many of which were obtained from density functional theory. The model provides a basis for predicting the transient response of III-V heterojunction bipolar transistors to displacement damage from energetic particle irradiation.« less

Creep of trabecular bone from the human proximal tibia

PubMed Central

Novitskaya, Ekaterina; Zin, Carolyn; Chang, Neil; Cory, Esther; Chen, Peter; D'Lima, Darryl; Sah, Robert L.; McKittrick, Joanna

2014-01-01

Creep is the deformation that occurs under a prolonged, sustained load and can lead to permanent damage in bone. Creep in bone is a complex phenomenon and varies with type of loading and local mechanical properties. Human trabecular bone samples from proximal tibia were harvested from a 71-year old female cadaver with osteoporosis. The samples were initially subjected to one cycle load up to 1% strain to determine the creep load. Samples were then loaded in compression under a constant stress for two hours and immediately unloaded. All tests were conducted with the specimens soaked in phosphate buffered saline with proteinase inhibitors at 37°C. Steady state creep rate and final creep strain were estimated from mechanical testing and compared with published data. The steady state creep rate correlated well with values obtained from bovine tibial and human vertebral trabecular bone, and was higher for lower density samples. Tissue architecture was analyzed by micro-computed tomography (μCT) both before and after creep testing to assess creep deformation and damage accumulated. Quantitative morphometric analysis indicated that creep induced changes in trabecular separation and the structural model index. A main mode of deformation was bending of trabeculae. PMID:24857486

Material damage modeling and detection in a thin metallic sheet and sandwich panel using passive acoustic transmission

NASA Astrophysics Data System (ADS)

Jiang, Hao

A method is developed for modeling, detecting, and locating material damage in homogeneous thin metallic sheets and sandwich panels. Analytical and numerical models are used along with non-contact, passive acoustic transmission measurements. It is shown that global and local damage mechanisms characterized by both material and geometrical changes in structural components can be detected using passive acoustic transmission measurements. Theoretical models of a flat sheet and sandwich panel are developed to describe the effects of global material damage due to density, modulus, or thickness changes on backplane radiated sound pressure level distributions. To describe the effects of local material damage, a three-segment stepped beam model and finite element beam, plate, and sandwich panel models are developed and analyzed using the acoustic transmission approach. It is shown that increases or decreases in transmitted sound energy occur behind a damaged material component that exhibits changes in thickness or other geometric or material properties. The damage due to thickness and density changes can be detected from the acoustic transmission, but modulus changes cannot. If the damage is located at an anti-node of a certain forced vibration pattern, the damage can be more readily observed in the data. Higher excitation frequencies within the operating spectrum are preferred to lower frequencies for damage detection. With the finite element beam, plate, and sandwich panel models, local damage detection has been performed in simulations. Experiments on a baffled homogeneous sheet and sandwich panel subjected to broadband acoustic energy show that transmitted intensity measurements with non-contact probes can be used to identify and locate material defects in the sheet and sandwich panel. Material damage is most readily identified where the changes in transmitted sound intensity are largest in the resonant frequency range of the panel. The three main contributions of this research are: (1) the use of non-contact sensing to detect global and localized damage in structural components; (2) the analytical and numerical modeling of material and geometrical damage mechanisms in structural components; and, (3) the experimental verification of acoustic transmission measurements for detecting both material and geometric damage mechanisms.

A multi-damages identification method for cantilever beam based on mode shape curvatures and Kriging surrogate model

NASA Astrophysics Data System (ADS)

Xie, Fengle; Jiang, Zhansi; Jiang, Hui

2018-05-01

This paper presents a multi-damages identification method for Cantilever Beam. First, the damage location is identified by using the mode shape curvatures. Second, samples of varying damage severities at the damage location and their corresponding natural frequencies are used to construct the initial Kriging surrogate model. Then a particle swarm optimization (PSO) algorithm is employed to identify the damage severities based on Kriging surrogate model. The simulation study of a double-damaged cantilever beam demonstrated that the proposed method is effective.

Fatigue In Continuous-Fiber/Metal-Matrix Composites

NASA Technical Reports Server (NTRS)

Johnson, William S.

1992-01-01

Report describes experimental approaches to quantification of fatigue damage in metal-matrix composites (MMC's). Discusses number of examples of development of damage and failure along with associated analytical models of behavior of MMC. Objectives of report are twofold. First, present experimental procedures and techniques for conducting meaningful fatigue tests to detect and quantify fatigue damage in MMC's. Second, present examples of how fatigue damage initiated and grows in various MMC's. Report furnishes some insight into what type of fatigue damage occurs and how damage quantified.

Mathematical modeling of damage in unidirectional composites

NASA Technical Reports Server (NTRS)

Goree, J. G.; Dharani, L. R.; Jones, W. F.

1983-01-01

Extending the work of Goree and Gross (1979), solutions are given for a two-dimensional region of unidirectional fibers embedded in an elastic matrix whose initial flaw may take the form of a transverse notch, a rectangular cutout, or a circular hole. Subsequent flaw-induced damage is generated by remote stresses acting parallel to the fibers. For the case of such ductile matrix composites as boron/aluminum, present results indicate that both longitudinal matrix yielding and transverse notch extension must be included in order for the model to agree with experimental results. Little difference is found for the three types of initial damage considered. In all cases, the presence of additional damage changes the nature of stress distribution through the unbroken fibers.

Progressive Fracture of Fiber Composite Thin Shell Structures Under Internal Pressure and Axial Loads

NASA Technical Reports Server (NTRS)

Gotsis, Pascal K.; Chamis, Christos C.; Minnetyan, Levon

1996-01-01

Graphite/epoxy composite thin shell structures were simulated to investigate damage and fracture progression due to internal pressure and axial loading. Defective and defect-free structures (thin cylinders) were examined. The three different laminates examined had fiber orientations of (90/0/+/-0)(sub s), where 0 is 45, 60, and 75 deg. CODSTRAN, an integrated computer code that scales up constituent level properties to the structural level and accounts for all possible failure modes, was used to simulate composite degradation under loading. Damage initiation, growth, accumulation, and propagation to fracture were included in the simulation. Burst pressures for defective and defect-free shells were compared to evaluate damage tolerance. The results showed that damage initiation began with matrix failure whereas damage and/or fracture progression occurred as a result of additional matrix failure and fiber fracture. In both thin cylinder cases examined (defective and defect-free), the optimum layup configuration was (90/0/+/-60)(sub s) because it had the best damage tolerance with respect to the burst pressure.

Probabilistic Assessment of Fracture Progression in Composite Structures

NASA Technical Reports Server (NTRS)

Chamis, Christos C.; Minnetyan, Levon; Mauget, Bertrand; Huang, Dade; Addi, Frank

1999-01-01

This report describes methods and corresponding computer codes that are used to evaluate progressive damage and fracture and to perform probabilistic assessment in built-up composite structures. Structural response is assessed probabilistically, during progressive fracture. The effects of design variable uncertainties on structural fracture progression are quantified. The fast probability integrator (FPI) is used to assess the response scatter in the composite structure at damage initiation. The sensitivity of the damage response to design variables is computed. The methods are general purpose and are applicable to stitched and unstitched composites in all types of structures and fracture processes starting from damage initiation to unstable propagation and to global structure collapse. The methods are demonstrated for a polymer matrix composite stiffened panel subjected to pressure. The results indicated that composite constituent properties, fabrication parameters, and respective uncertainties have a significant effect on structural durability and reliability. Design implications with regard to damage progression, damage tolerance, and reliability of composite structures are examined.

Nonlinear damage analysis: Postulate and evaluation

NASA Technical Reports Server (NTRS)

Leis, B. N.; Forte, T. P.

1983-01-01

The objective of this program is to assess the viability of a damage postulate which asserts that the fatigue resistance curve of a metal is history dependent due to inelastic action. The study focusses on OFE copper because this simple model material accentuates the inelastic action central to the damage postulate. Data relevant to damage evolution and crack initiation are developed via a study of surface topography. The effects of surface layer residual stresses are explored via comparative testing as were the effects in initial prestraining. The results of the study very clearly show the deformation history dependence of the fatigue resistance of OFE copper. Furthermore the concept of deformation history dependence is shown to qualitatively explain the fatigue resistance of all histories considered. Likewise quantitative predictions for block cycle histories are found to accurately track the observed results. In this respect the assertion that damage per cycle for a given level of the damage parameter is deformation history dependent appears to be physically justified.

Effect of Curvature on the Impact Damage Characteristics and Residual Strength of Composite Plates

NASA Technical Reports Server (NTRS)

Ambur, Damodar R.; Starnes, James H., Jr.

1998-01-01

The results of a study of the response and failure characteristics of thin, cylindrically curved, composite plates subjected to low-speed impact damage are presented. The results indicate that the plate radius and the plate thickness are important structural parameters that influence the nonlinear response of a plate for a given amount of impact energy. Analytical and experimental contact-force results are compared for several plates and the results correlate well. The impact-energy levels required to cause damage initiation and barely visible impact damage are a function of the plate radius for a given plate thickness. The impact-energy levels required to initiate impact damage for plates with a certain range of radii are greater than plates with other radii. The contact-force results corresponding to these impact-energy levels follow a similar trend. Residual strength results for plates with barely visible impact damage suggest that the compression-after-impact residual strength is also a function of plate radius. The residual strength of impact-damaged flat plates appears to be lower than the residual strength of the corresponding cylindrically curved plates.

Long-term effects of bottom trawling on large sponges in the Gulf of Alaska

NASA Astrophysics Data System (ADS)

Malecha, Patrick; Heifetz, Jonathan

2017-11-01

Manipulative studies that characterize short-term effects of bottom trawls on seafloor habitats are numerous, but studies that examine long-term effects are rare. The long-term (13 years) effects of a single bottom trawl on large (>20 cm) erect sponges were investigated by revisiting the site of prior experimental trawling studies. In prior studies, large sponges were assessed immediately after trawling and 1 yr post-trawling. Thirteen years post-trawling, the average density of large sponges was 31.7% lower (range 1.5-53.0%) and the incidence of sponge damage (torn, necrotic, missing tissue, prone) was 58.8% higher within strip transects in trawled versus untrawled reference areas. For all sponge species combined, the mean density of large sponges was 3.19 individuals 100 m-2 in trawled areas and 4.67 individuals 100 m-2 in reference areas. The most abundant sponge species in both trawled and reference areas was Rhabdocalyptus dawsoni. Mean density of this species differed greatly between trawled (1.57 individuals 100 m-2) and reference areas (2.91 individuals 100 m-2). Thirteen years after trawling, the mean percentage of damaged sponges on strip transects was 15.3% in trawled areas and 6.3% in reference areas. The rate of damage in trawled areas was less than that observed both immediately after trawling and 1 year later. The persistence of damage (lower sponge densities and higher rates of injury in trawled areas) and the potential resultant changes to benthic communities where deepwater habitat-forming biota, such as large erect sponges, are present provide rationale for cautious management of the long term effects of bottom trawling.

Effects of density on growth, metamorphosis, and survivorship in tadpoles of Scaphiopus holbrooki

DOE Office of Scientific and Technical Information (OSTI.GOV)

Semlitsch, R.D.; Caldwell, J.P.

1982-08-01

Density-dependent aspects of growth, metamorphosis, and survivorship of Scaphiopus holbrooki tadpoles were examined in the laboratory under two experimental regimes. In the first density experiment, the growth index (W) of tadpoles decreased exponentially with density. Mean growth rate varied from 0.023 mL/d at the lowest density to 0.006 mL/d at the highest density. The mean number of days to metamorphic climax was positively associated with the initial density treatment: 27 d at the lowest density to 86 d at the highest density. The body size of tadpoles at metamorphosis showed a concave curvilinear relationship to initial density, indicating tadpoles atmore » the highest densities are apparently capable to growth recovery once released from density stress. The survival of tadpoles decreased exponentially with initial density, from 90% at the lowest density to 20% at the highest initial density. In the second experiment a cross-classified design was used to examine the effects of density and duration of treatment (time) on growth and metamorphosis. Density and time had significant effects on body size at metamorphosis and days to metamorphosis. There was no significant interaction between density and time. These results indicate that the inhibitory effect of density stress varies with the duration of the stress. Scaphiopus holbrooki tadpoles exhibit developmental traits (rapid growth, short larval period, small body size at metamorphosis) that should be favored by natural selection in high density habitats. Dispersability may be a mechanism whereby S. holbrooki can minimize the detrimental effects of density stress.« less

A cross-sectional case control study on genetic damage in individuals residing in the vicinity of a mobile phone base station.

PubMed

Gandhi, Gursatej; Kaur, Gurpreet; Nisar, Uzma

2015-01-01

Mobile phone base stations facilitate good communication, but the continuously emitting radiations from these stations have raised health concerns. Hence in this study, genetic damage using the single cell gel electrophoresis (comet) assay was assessed in peripheral blood leukocytes of individuals residing in the vicinity of a mobile phone base station and comparing it to that in healthy controls. The power density in the area within 300 m from the base station exceeded the permissive limits and was significantly (p = 0.000) higher compared to the area from where control samples were collected. The study participants comprised 63 persons with residences near a mobile phone tower, and 28 healthy controls matched for gender, age, alcohol drinking and occupational sub-groups. Genetic damage parameters of DNA migration length, damage frequency (DF) and damage index were significantly (p = 0.000) elevated in the sample group compared to respective values in healthy controls. The female residents (n = 25) of the sample group had significantly (p = 0.004) elevated DF than the male residents (n = 38). The linear regression analysis further revealed daily mobile phone usage, location of residence and power density as significant predictors of genetic damage. The genetic damage evident in the participants of this study needs to be addressed against future disease-risk, which in addition to neurodegenerative disorders, may lead to cancer.

The influence of vegetation cover on debris-flow density during an extreme rainfall in the northern Colorado Front Range

USGS Publications Warehouse

Rengers, Francis K.; McGuire, Luke; Coe, Jeffrey A.; Kean, Jason W.; Baum, Rex L.; Staley, Dennis M.; Godt, Jonathan W.

2016-01-01

We explored regional influences on debris-flow initiation throughout the Colorado Front Range (Colorado, USA) by exploiting a unique data set of more than 1100 debris flows that initiated during a 5 day rainstorm in 2013. Using geospatial data, we examined the influence of rain, hillslope angle, hillslope aspect, and vegetation density on debris-flow initiation. In particular we used a greenness index to differentiate areas of high tree density from grass and bare soil. The data demonstrated an overwhelming propensity for debris-flow initiation on south-facing hillslopes. However, when the debris-flow density was analyzed with respect to total rainfall and greenness we found that most debris flows occurred in areas of high rainfall and low tree density, regardless of hillslope aspect. These results indicate that present-day tree density exerts a stronger influence on debris-flow initiation locations than aspect-driven variations in soil and bedrock properties that developed over longer time scales.

High speed imaging for assessment of impact damage in natural fibre biocomposites

NASA Astrophysics Data System (ADS)

Ramakrishnan, Karthik Ram; Corn, Stephane; Le Moigne, Nicolas; Ienny, Patrick; Leger, Romain; Slangen, Pierre R.

2017-06-01

The use of Digital Image Correlation has been generally limited to the estimation of mechanical properties and fracture behaviour at low to moderate strain rates. High speed cameras dedicated to ballistic testing are often used to measure the initial and residual velocities of the projectile but rarely for damage assessment. The evaluation of impact damage is frequently achieved post-impact using visual inspection, ultrasonic C-scan or other NDI methods. Ultra-high speed cameras and developments in image processing have made possible the measurement of surface deformations and stresses in real time during dynamic cracking. In this paper, a method is presented to correlate the force- displacement data from the sensors to the slow motion tracking of the transient failure cracks using real-time high speed imaging. Natural fibre reinforced composites made of flax fibres and polypropylene matrix was chosen for the study. The creation of macro-cracks during the impact results in the loss of stiffness and a corresponding drop in the force history. However, optical instrumentation shows that the initiation of damage is not always evident and so the assessment of damage requires the use of a local approach. Digital Image Correlation is used to study the strain history of the composite and to identify the initiation and progression of damage. The effect of fly-speckled texture on strain measurement by image correlation is also studied. The developed method can be used for the evaluation of impact damage for different composite materials.

Investigation of mud density and weighting materials effect on drilling fluid filter cake properties and formation damage

NASA Astrophysics Data System (ADS)

Fattah, K. A.; Lashin, A.

2016-05-01

Drilling fluid density/type is an important factor in drilling and production operations. Most of encountered problems during rotary drilling are related to drilling mud types and weights. This paper aims to investigate the effect of mud weight on filter cake properties and formation damage through two experimental approaches. In the first approach, seven water-based drilling fluid samples with same composition are prepared with different densities (9.0-12.0 lb/gal) and examined to select the optimum mud weight that has less damage. The second approach deals with investigating the possible effect of the different weighting materials (BaSO4 and CaCO3) on filter cake properties. High pressure/high temperature loss tests and Scanning Electron Microscopy (SEM) analyses were carried out on the filter cake (two selected samples). Data analysis has revealed that mud weigh of 9.5 lb/gal has the less reduction in permeability of ceramic disk, among the seven used mud densities. Above 10.5 ppg the effect of the mud weight density on formation damage is stabilized at constant value. Fluids of CaCO3-based weighting material, has less reduction in the porosity (9.14%) and permeability (25%) of the filter disk properties than the BaSO4-based fluid. The produced filter cake porosity increases (from 0.735 to 0.859) with decreasing of fluid density in case of drilling samples of different densities. The filtration loss tests indicated that CaCO3 filter cake porosity (0.52) is less than that of the BaSO4 weighted material (0.814). The thickness of the filter cake of the BaSO4-based fluid is large and can cause some problems. The SEM analysis shows that some major elements do occur on the tested samples (Ca, Al, Si, and Ba), with dominance of Ca on the expense of Ba for the CaCO3 fluid sample and vice versa. The less effect of 9.5 lb/gal mud sample is reflected in the well-produced inter-particle pore structure and relatively crystal size. A general recommendation is given to minimize the future utilization of Barium Sulfate as a drilling fluid.

Pilot investigation of the correlation between histological and clinical effects of infrared fractional resurfacing lasers.

PubMed

Walgrave, Susan; Zelickson, Brian; Childs, James; Altshuler, Gregory; Erofeev, Andrei; Yaroslavsky, Ilya; Kist, David; Counters, Jeff

2008-11-01

Yucatan Black pig skin was treated with a 1,540-nm erbium (Er):glass laser (Lux1540, 15 and 30 mJ) and two 1,550-nm Er-doped fiber lasers (Fraxel SR750 and SR1500, 8, 10, and 12 mJ). Histologic sections were examined to determine the depth of damage and to correlate subjects' clinical response. Concurrently, six subjects with photodamaged skin received three split-face and ipsilateral dorsal hand treatments with the 1,540-nm Er:glass laser on one side and one of the 1,550-nm Er-doped lasers (Fraxel SR750) on the other. The 1,550-nm Er-doped lasers, using lower fluences and higher densities, produced shallower micro-columns than the 1,540-nm Er:glass device at higher fluences and lower densities (mean depths 250-275 microm vs 425-525 microm, respectively). Blinded assessors found greater overall improvement in pigmentation with the 1,550-nm Er-doped laser and better overall improvement in texture with the 1,540-nm Er:glass laser. Greater densities of shallower damage columns at lower energies may better improve pigmentation, whereas deeper injuries, using higher energies and moderate densities, may better improve texture. This pilot study did not compare similar fluences and histologic damage between the two systems, and newer available systems allow for greater depth of penetration.

Lateral Root Initiation in Arabidopsis: Developmental Window, Spatial Patterning, Density and Predictability

PubMed Central

DUBROVSKY, J. G.; GAMBETTA, G. A.; HERNÁNDEZ-BARRERA, A.; SHISHKOVA, S.; GONZÁLEZ, I.

2006-01-01

• Background and Aims The basic regulatory mechanisms that control lateral root (LR) initiation are still poorly understood. An attempt is made to characterize the pattern and timing of LR initiation, to define a developmental window in which LR initiation takes place and to address the question of whether LR initiation is predictable. • Methods The spatial patterning of LRs and LR primordia (LRPs) on cleared root preparations were characterized. New measures of LR and LRP densities (number of LRs and/or LRPs divided by the length of the root portions where they are present) were introduced and illustrate the shortcomings of the more customarily used measure through a comparative analysis of the mutant aux1-7. The enhancer trap line J0121 was used to monitor LR initiation in time-lapse experiments and a plasmolysis-based method was developed to determine the number of pericycle cells between successive LRPs. • Key Results LRP initiation occurred strictly acropetally and no de novo initiation events were found between already developed LRs or LRPs. However, LRPs did not become LRs in a similar pattern. The longitudinal spacing of lateral organs was variable and the distance between lateral organs was proportional to the number of cells and the time between initiations of successive LRPs. There was a strong tendency towards alternation in LR initiation between the two pericycle cell files adjacent to the protoxylem poles. LR density increased with time due to the emergence of slowly developing LRPs and appears to be unique for individual Arabidopsis accessions. • Conclusions. In Arabidopsis there is a narrow developmental window for LR initiation, and no specific cell-count or distance-measuring mechanisms have been found that determine the site of successive initiation events. Nevertheless, the branching density and lateral organ density (density of LRs and LRPs) are accession-specific, and based on the latter density the average distance between successive LRs can be predicted. PMID:16390845

Support for the existence of invertible maps between electronic densities and non-analytic 1-body external potentials in non-relativistic time-dependent quantum mechanics

NASA Astrophysics Data System (ADS)

Mosquera, Martín A.

2017-10-01

Provided the initial state, the Runge-Gross theorem establishes that the time-dependent (TD) external potential of a system of non-relativistic electrons determines uniquely their TD electronic density, and vice versa (up to a constant in the potential). This theorem requires the TD external potential and density to be Taylor-expandable around the initial time of the propagation. This paper presents an extension without this restriction. Given the initial state of the system and evolution of the density due to some TD scalar potential, we show that a perturbative (not necessarily weak) TD potential that induces a non-zero divergence of the external force-density, inside a small spatial subset and immediately after the initial propagation time, will cause a change in the density within that subset, implying that the TD potential uniquely determines the TD density. In this proof, we assume unitary evolution of wavefunctions and first-order differentiability (which does not imply analyticity) in time of the internal and external force-densities, electronic density, current density, and their spatial derivatives over the small spatial subset and short time interval.

Dependence of optimal initial density on laser parameters for multi-keV x-ray radiators generated by nanosecond laser-produced underdense plasma

NASA Astrophysics Data System (ADS)

Tu, Shao-yong; Yuan, Yong-teng; Hu, Guang-yue; Miao, Wen-yong; Zhao, Bin; Zheng, Jian; Jiang, Shao-en; Ding, Yong-kun

2016-01-01

Efficient multi-keV x-ray sources can be produced using nanosecond laser pulse-heated middle-Z underdense plasmas generated using gas or foam. Previous experimental results show that an optimal initial target density exists for efficient multi-keV x-ray emission at which the laser ionization wave is supersonic. Here we explore the influence of the laser intensity and the pulse duration on this optimal initial target density via a one-dimensional radiation hydrodynamic simulation. The simulation shows that the optimal initial density is sensitive to both the laser intensity and the pulse duration. However, the speed of the supersonic ionization wave at the end of the laser irradiation is always maintained at 1.5 to 1.7 times that of the ion acoustic wave under the optimal initial density conditions.

Forest Health Monitoring in Massachusetts, 1996-1999

Treesearch

Northeastern Research Station

2002-01-01

Massachusetts has mature forests dominated by hardwood species. Most of the trees are healthy, with full crowns (low transparency, high density), little dieback and little damage. Red maple trees made up almost one quarter of the trees and had slightly higher amounts of dieback, thinner crowns, and more damage than other common tree species.

Evaluation of external hazards to nuclear power plants in the United States

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kimura, C.Y.; Budnitz, R.J.

1987-12-01

The Lawrence Livermore National Laboratory (LLNL) has performed a study of the risk of core damage to nuclear power plants in the United States due to externally initiated events. The broad objective has been to gain an understanding of whether or not each external initiator is among the major potential accident initiators that may pose a threat of severe reactor core damage or of large radioactive release to the environment from the reactor. Four external hazards were investigated in this report. These external hazards are internal fires, high winds/tornadoes, external floods, and transportation accidents. Analysis was based on two figures-of-merit,more » one based on core damage frequency and the other based on the frequency of large radioactive releases. Using these two figures-of-merit as evaluation criteria, it has been feasible to ascertain whether the risk from externally initiated accidents is, or is not, an important contributor to overall risk for the US nuclear power plants studied. This has been accomplished for each initiator separately. 208 refs., 17 figs., 45 tabs.« less

Irradiation response of commercial, high-Tc superconducting tapes: Electromagnetic transport properties

DOE PAGES

Gapud, A. A.; Greenwood, N. T.; Alexander, J. A.; ...

2015-07-01

Effects of low dose irradiation on the electrical transport current properties of commercially available high-temperature superconducting, coated-conductor tapes were investigated, in view of potential applications in the irradiative environment of fusion reactors. Three different tapes, each with unique as-grown flux-pinning structures, were irradiated with Au and Ni ions at energies that provide a range of damage effects, with accumulated damage levels near that expected for conductors in a fusion reactor environment. Measurements using transport current determined the pre- and post-irradiation resistivity, critical current density, and pinning force density, yielding critical temperatures, irreversibility lines, and inferred vortex creep rates. Results showmore » that at the irradiation damage levels tested, any detriment to as-grown pre-irradiation properties is modest; indeed in one case already-superior pinning forces are enhanced, leading to higher critical currents.« less

Next generation control system for reflexive aerostructures

NASA Astrophysics Data System (ADS)

Maddux, Michael R.; Meents, Elizabeth P.; Barnell, Thomas J.; Cable, Kristin M.; Hemmelgarn, Christopher; Margraf, Thomas W.; Havens, Ernie

2010-04-01

Cornerstone Research Group Inc. (CRG) has developed and demonstrated a composite structural solution called reflexive composites for aerospace applications featuring CRG's healable shape memory polymer (SMP) matrix. In reflexive composites, an integrated structural health monitoring (SHM) system autonomously monitors the structural health of composite aerospace structures, while integrated intelligent controls monitor data from the SHM system to characterize damage and initiate healing when damage is detected. Development of next generation intelligent controls for reflexive composites were initiated for the purpose of integrating prognostic health monitoring capabilities into the reflexive composite structural solution. Initial efforts involved data generation through physical inspections and mechanical testing. Compression after impact (CAI) testing was conducted on composite-reinforced shape memory polymer samples to induce damage and investigate the effectiveness of matrix healing on mechanical performance. Non-destructive evaluation (NDE) techniques were employed to observe and characterize material damage. Restoration of mechanical performance was demonstrated through healing, while NDE data showed location and size of damage and verified mitigation of damage post-healing. Data generated was used in the development of next generation reflexive controls software. Data output from the intelligent controls could serve as input to Integrated Vehicle Health Management (IVHM) systems and Integrated Resilient Aircraft Controls (IRAC). Reflexive composite technology has the ability to reduce maintenance required on composite structures through healing, offering potential to significantly extend service life of aerospace vehicles and reduce operating and lifecycle costs.

DNA damage in wounded, hypoxic and acidotic human skin fibroblast cell cultures after low laser irradiation

NASA Astrophysics Data System (ADS)

Hawkins Evans, D.; Mbene, A.; Zungu, I.; Houreld, N.; Abrahamse, H.

2009-02-01

Phototherapy has become more popular and widely used in the treatment of a variety of medical conditions. To ensure sound results as evidence of its effectiveness, well designed experiments must be conducted when determining the effect of phototherapy. Cell culture models such as hypoxic, acidotic and wounded cell cultures simulating different disease conditions including ischemic heart disease, diabetes and wound healing were used to determine the effect of laser irradiation on the genetic integrity of the cell. Even though phototherapy has been found to be beneficial in a wide spectrum of conditions, it has been shown to induce DNA damage. However, this damage appears to be repairable. The risk lies in the fact that phototherapy may help the medical condition initially but damage DNA at the same time leaving undetected damage that may result in late onset, more severe, induced medical conditions including cancer. Human skin fibroblasts were cultured and used to induce a wound (by the central scratch model), hypoxic (by incubation in an anaerobic jar, 95% N2 and 5% O2) and acidotic (reducing the pH of the media to 6.7) conditions. Different models were irradiated using a Helium-Neon (632.8 nm) laser with a power density of 2.07 mW/cm2 and a fluence of 5 J/cm2 or 16 J/cm2. The effect of the irradiation was determined using the Comet assay 1 and 24 h after irradiation. In addition, the Comet assay was performed with the addition of formamidopyrimidine glycosylase (FPG) obviating strand brakes in oxidized bases at a high fluence of 16 J/cm2. A significant increase in DNA damage was seen in all three injured models at both 1 and 24 h post-irradiation when compared to the normal un-injured cells. However, when compared to non-irradiated controls the acidotic model showed a significant decrease in DNA damage 24 h after irradiation indicating the possible induction of cellular DNA repair mechanisms. When wounded cells were irradiated with higher fluences of 16 J/cm2, there was a significant increase in DNA damage in irradiated cells with and without the addition of FPG. These results are indicative of the importance of both cell injury model as well as fluence when assessing the effect of phototherapy on DNA integrity.

Structural Health Monitoring in Composite Structures by Fiber-Optic Sensors.

PubMed

Güemes, Alfredo; Fernández-López, Antonio; F Díaz-Maroto, Patricia; Lozano, Angel; Sierra-Perez, Julian

2018-04-04

Fiber-optic sensors cannot measure damage; to get information about damage from strain measurements, additional strategies are needed, and several alternatives are available in the existing literature. This paper discusses two independent procedures. The first is based on detecting new strains appearing around a damage spot. The structure does not need to be under loads, the technique is very robust, and damage detectability is high, but it requires sensors to be located very close to the damage, so it is a local technique. The second approach offers wider coverage of the structure; it is based on identifying the changes caused by damage on the strain field in the whole structure for similar external loads. Damage location does not need to be known a priori, and detectability is dependent upon the sensor's network density, the damage size, and the external loads. Examples of application to real structures are given.

Structural Health Monitoring in Composite Structures by Fiber-Optic Sensors †

PubMed Central

Güemes, Alfredo; Díaz-Maroto, Patricia F.; Lozano, Angel; Sierra-Perez, Julian

2018-01-01

Fiber-optic sensors cannot measure damage; to get information about damage from strain measurements, additional strategies are needed, and several alternatives are available in the existing literature. This paper discusses two independent procedures. The first is based on detecting new strains appearing around a damage spot. The structure does not need to be under loads, the technique is very robust, and damage detectability is high, but it requires sensors to be located very close to the damage, so it is a local technique. The second approach offers wider coverage of the structure; it is based on identifying the changes caused by damage on the strain field in the whole structure for similar external loads. Damage location does not need to be known a priori, and detectability is dependent upon the sensor’s network density, the damage size, and the external loads. Examples of application to real structures are given. PMID:29617345

Comparing simulations and test data of a radiation damaged CCD for the Euclid mission

NASA Astrophysics Data System (ADS)

Skottfelt, Jesper; Hall, David; Gow, Jason; Murray, Neil; Holland, Andrew; Prod'homme, Thibaut

2016-07-01

The radiation damage effects from the harsh radiative environment outside the Earth's atmosphere can be a cause for concern for most space missions. With the science goals becoming ever more demanding, the requirements on the precision of the instruments on board these missions also increases, and it is therefore important to investigate how the radiation induced damage affects the Charge-Coupled Devices (CCDs) that most of these instruments rely on. The primary goal of the Euclid mission is to study the nature of dark matter and dark energy using weak lensing and baryonic acoustic oscillation techniques. The weak lensing technique depends on very precise shape measurements of distant galaxies obtained by a large CCD array. It is anticipated that over the 6 year nominal lifetime of mission, the CCDs will be degraded to an extent that these measurements will not be possible unless the radiation damage effects are corrected. We have therefore created a Monte Carlo model that simulates the physical processes taking place when transferring signal through a radiation damaged CCD. The software is based on Shockley-Read-Hall theory, and is made to mimic the physical properties in the CCD as close as possible. The code runs on a single electrode level and takes charge cloud size and density, three dimensional trap position, and multi-level clocking into account. A key element of the model is that it takes device specific simulations of electron density as a direct input, thereby avoiding to make any analytical assumptions about the size and density of the charge cloud. This paper illustrates how test data and simulated data can be compared in order to further our understanding of the positions and properties of the individual radiation-induced traps.

Quantitative Characterisation of Fracturing Around the Damage Zone Surrounding New Zealand's Alpine Fault Using X-ray CT Scans of DFDP-1 Core

NASA Astrophysics Data System (ADS)

Williams, J. N.; Toy, V.; Massiot, C.; Mcnamara, D. D.; Wang, T.

2015-12-01

X-ray computer tomography (CT) scans of core recovered from the first phase of the Deep Fault Drilling Project (DFDP-1) through the Alpine Fault provide an excellent opportunity to analyse brittle deformation around the fault. In particular, assessment can be made of the heavily fractured protolith constituting the damage zone. Damage zone structures are divided into two types that result from two distinct processes: (1) "off fault damage" formed by stress changes induced by the passage of a seismic rupture and (2) "off fault deformation" that represent structures, which accommodate strain around the fault that was not localised on the principal slip zone (PSZ). The distribution of these damage zones structures within CT scans of the recovered core was measured along a scanline parallel to the core axis and assessed using a weighted moving average technique to account for orientation bias. The results of this analysis reveal that within the part of the fault rocks sampled by DFDP-1 there is no increase in density of these structures towards the PSZ. This is in agreement with independent analysis using Borehole Televiewer Data of the DFDP-1B borehole. Instead, we consider the density of these structures to be controlled to the first order by lithology, which modulates the mechanical properties of the fault rocks such as its frictional strength and cohesion. Comparisons of fracture density to p-wave velocities obtained from wireline logs indicate they are independent of each other, therefore, for the cores sampled in this study fractures impart no influence on the elastic properties of the rock. This is consistent with the observation from core that the majority of fractures are cemented. We consider how this might influence future rupture dynamics.

Healing of polymer interfaces: Interfacial dynamics, entanglements, and strength

DOE PAGES

Ge, Ting; Robbins, Mark O.; Perahia, Dvora; ...

2014-07-25

Self-healing of polymer films often takes place as the molecules diffuse across a damaged region, above their melting temperature. Using molecular dynamics simulations we probe the healing of polymer films and compare the results with those obtained for thermal welding of homopolymer slabs. These two processes differ from each other in their interfacial structure since damage leads to increased polydispersity and more short chains. A polymer sample was cut into two separate films that were then held together in the melt state. The recovery of the damaged film was followed as time elapsed and polymer molecules diffused across the interface.more » The mass uptake and formation of entanglements, as obtained from primitive path analysis, are extracted and correlated with the interfacial strength obtained from shear simulations. We find that the diffusion across the interface is signifcantly faster in the damaged film compared to welding because of the presence of short chains. Though interfacial entanglements increase more rapidly for the damaged films, a large fraction of these entanglements are near chain ends. As a result, the interfacial strength of the healing film increases more slowly than for welding. For both healing and welding, the interfacial strength saturates as the bulk entanglement density is recovered across the interface. However, the saturation strength of the damaged film is below the bulk strength for the polymer sample. At saturation, cut chains remain near the healing interface. They are less entangled and as a result they mechanically weaken the interface. When the strength of the interface saturates, the number of interfacial entanglements scales with the corresponding bulk entanglement density. Chain stiffness increases the density of entanglements, which increases the strength of the interface. Our results show that a few entanglements across the interface are sufficient to resist interfacial chain pullout and enhance the mechanical strength.« less

On the monitoring and implications of growing damages caused by manufacturing defects in composite structures

NASA Astrophysics Data System (ADS)

Schagerl, M.; Viechtbauer, C.; Hörrmann, S.

2015-07-01

Damage tolerance is a classical safety concept for the design of aircraft structures. Basically, this approach considers possible damages in the structure, predicts the damage growth under applied loading conditions and predicts the following decrease of the structural strength. As a fundamental result the damage tolerance approach yields the maximum inspection interval, which is the time a damage grows from a detectable to a critical level. The above formulation of the damage tolerance safety concept targets on metallic structures where the damage is typically a simple fatigue crack. Fiber-reinforced polymers show a much more complex damage behavior, such as delaminationsin laminated composites. Moreover, progressive damage in composites is often initiated by manufacturing defects. The complex manufacturing processes for composite structures almost certainly yield parts with defects, e.g. pores in the matrix or undulations of fibers. From such defects growing damages may start after a certain time of operation. The demand to simplify or even avoid the inspection of composite structures has therefore led to a comeback of the traditional safe-life safety concept. The aim of the so-called safe-life flaw tolerance concept is a structure that is capable of carrying the static loads during operation, despite significant damages and after a representative fatigue load spectrum. A structure with this property does not need to be inspected, respectively monitored at all during its service life. However, its load carrying capability is thereby not fully utilized. This article presents the possible refinement of the state-of-the-art safe-life flaw tolerance concept for composite structures towards a damage tolerance approach considering also the influence of manufacturing defects on damage initiation and growth. Based on fundamental physical relations and experimental observations the challenges when developing damage growth and residual strength curves are discussed.

Damage spreading and opinion dynamics on scale-free networks

NASA Astrophysics Data System (ADS)

Fortunato, Santo

2005-03-01

We study damage spreading among the opinions of a system of agents, subjected to the dynamics of the Krause-Hegselmann consensus model. The damage consists in a sharp change of the opinion of one or more agents in the initial random opinion configuration, supposedly due to some external factors and/or events. This may help to understand for instance under which conditions special shocking events or targeted propaganda are able to influence the results of elections. For agents lying on the nodes of a Barabási-Albert network, there is a damage spreading transition at a low value εd of the confidence bound parameter. Interestingly, we find as well that there is some critical value εs above which the initial perturbation manages to propagate to all other agents.

Extent of the Disturbed Rock Zone Around a WIPP Disposal Room

NASA Astrophysics Data System (ADS)

Herrick, C. G.; Park, B. Y.; Holcomb, D. J.

2008-12-01

The Waste Isolation Pilot Plant (WIPP), located in southeastern New Mexico, is operated by the U.S. Department of Energy (DOE) as the underground disposal facility for transuranic (TRU) nuclear waste. It is located in a bedded salt formation at a depth of about 650 m. Salt at this depth behaves as a viscous material having an initially lithostatic state of stress. Mining of an opening disturbs the static equilibrium to a degree where fracturing of the rock surrounding a room occurs, changing its mechanical and hydrologic properties. This disturbed rock zone (DRZ) is an important geomechanical feature included in the performance assessment process models used to predict future repository conditions as a part of certification by the EPA as meeting regulatory compliance. Based on ongoing scientific investigations and evaluation of published data since the original certification in 1998, our understanding of the DRZ has continued to progress. Three deformation processes are activated as deviatoric stresses are induced upon excavation of a room in a salt formation: (1) elastic response, (2) inelastic viscoplastic flow, and (3) inelastic- damage induced flow. Damage, the least understood of these processes, is manifested by the time- dependent initiation, growth, coalescence, and healing of microfractures with a deviatoric stress state. Since the ability to model the spatial and temporal changes in salt damage is not available at this time, various means to measure it have been attempted. At the WIPP, for this study, we used sonic velocity measurements obtained over a 12 year period as the principal field method to describe the extent of the DRZ. Predictions of the DRZ extent based on these experimental results are substantiated by permeability measurements and microfracture density analysis from other places in the repository. Extensive laboratory salt creep data demonstrate that damage can be assessed in terms of volumetric strain and principal stresses. Stress states that cause dilatant damage can be defined in terms of the ratio of stress invariants, which allow reasonable models of DRZ evolution and devolution. The change of DRZ extent with time is calculated based on a dilatant damage potential criterion: D = (C · I1) / √J2 where D is the damage potential, I1 is the first invariant of the stress tensor, and J2 is the second invariant of the deviatoric stress tensor. When D < 1, damage is predicted. The proportionality constant C in the damage criterion is determined by comparing the numerical analysis results with the sonic velocity field data obtained in the Room Q access drift of WIPP. The most extensive DRZ exists during early times, within the first ten years after a room is mined. As the creeping salt tries to fill the excavation, back stresses from the waste and gas pressure within the repository resist its deformation and damage to the salt decreases. The maximum extents of the DRZ calculated below and above a room reach approximately 2.25 m and 4.75 m, respectively. The maximum lateral DRZ extent in the side of the room is estimated to be roughly 2 m. Sandia is a multi program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000. This research is funded by WIPP programs administered by the Office of Environmental Management (EM) of the U.S. Department of Energy.

An improved initialization center k-means clustering algorithm based on distance and density

NASA Astrophysics Data System (ADS)

Duan, Yanling; Liu, Qun; Xia, Shuyin

2018-04-01

Aiming at the problem of the random initial clustering center of k means algorithm that the clustering results are influenced by outlier data sample and are unstable in multiple clustering, a method of central point initialization method based on larger distance and higher density is proposed. The reciprocal of the weighted average of distance is used to represent the sample density, and the data sample with the larger distance and the higher density are selected as the initial clustering centers to optimize the clustering results. Then, a clustering evaluation method based on distance and density is designed to verify the feasibility of the algorithm and the practicality, the experimental results on UCI data sets show that the algorithm has a certain stability and practicality.

Defect reaction network in Si-doped InAs. Numerical predictions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schultz, Peter A.

This Report characterizes the defects in the def ect reaction network in silicon - doped, n - type InAs predicted with first principles density functional theory. The reaction network is deduced by following exothermic defect reactions starting with the initially mobile interstitial defects reacting with common displacement damage defects in Si - doped InAs , until culminating in immobile reaction p roducts. The defect reactions and reaction energies are tabulated, along with the properties of all the silicon - related defects in the reaction network. This Report serves to extend the results for the properties of intrinsic defects in bulkmore » InAs as colla ted in SAND 2013 - 2477 : Simple intrinsic defects in InAs : Numerical predictions to include Si - containing simple defects likely to be present in a radiation - induced defect reaction sequence . This page intentionally left blank« less

Evaluation of potential severe accidents during low power and shutdown operations at Surry, Unit 1. Volume 5: Analysis of core damage frequency from seismic events during mid-loop operations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Budnitz, R.J.; Davis, P.R.; Ravindra, M.K.

1994-08-01

In 1989 the US Nuclear Regulatory Commission (NRC) initiated an extensive program to examine carefully the potential risks during low-power and shutdown operations. The program included two parallel projects, one at Brookhaven National Laboratory studying a pressurized water reactor (Surry Unit 1) and the other at Sandia National Laboratories studying a boiling water reactor (Grand Gulf). Both the Brookhaven and Sandia projects have examined only accidents initiated by internal plant faults--so-called ``internal initiators.`` This project, which has explored the likelihood of seismic-initiated core damage accidents during refueling shutdown conditions, is complementary to the internal-initiator analyses at Brookhaven and Sandia. Thismore » report covers the seismic analysis at Surry Unit 1. All of the many systems modeling assumptions, component non-seismic failure rates, and human error rates that were used in the internal-initiator study at Surry have been adopted here, so that the results of the two studies can be as comparable as possible. Both the Brookhaven study and this study examine only two shutdown plant operating states (POSs) during refueling outages at Surry, called POS 6 and POS 10, which represent mid-loop operation before and after refueling, respectively. This analysis has been limited to work analogous to a level-1 seismic PRA, in which estimates have been developed for the core-damage frequency from seismic events during POSs 6 and 10. The results of the analysis are that the core-damage frequency of earthquake-initiated accidents during refueling outages in POS 6 and POS 10 is found to be low in absolute terms, less than 10{sup {minus}6}/year.« less

Evaluation of potential severe accidents during low power and shutdown operations at Grand Gulf, Unit 1. Volume 5: Analysis of core damage frequency from seismic events for plant operational state 5 during a refueling outage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Budnitz, R.J.; Davis, P.R.; Ravindra, M.K.

In 1989 the US Nuclear Regulatory Commission (NRC) initiated an extensive program to examine carefully the potential risks during low-power and shutdown operations. The program included two parallel projects, one at Sandia National Laboratories studying a boiling water reactor (Grand Gulf), and the other at Brookhaven National Laboratory studying a pressurized water reactor (Surry Unit 1). Both the Sandia and Brookhaven projects have examined only accidents initiated by internal plant faults---so-called ``internal initiators.`` This project, which has explored the likelihood of seismic-initiated core damage accidents during refueling outage conditions, is complementary to the internal-initiator analyses at Brookhaven and Sandia. Thismore » report covers the seismic analysis at Grand Gulf. All of the many systems modeling assumptions, component non-seismic failure rates, and human effort rates that were used in the internal-initiator study at Grand Gulf have been adopted here, so that the results of the study can be as comparable as possible. Both the Sandia study and this study examine only one shutdown plant operating state (POS) at Grand Gulf, namely POS 5 representing cold shutdown during a refueling outage. This analysis has been limited to work analogous to a level-1 seismic PRA, in which estimates have been developed for the core-damage frequency from seismic events during POS 5. The results of the analysis are that the core-damage frequency for earthquake-initiated accidents during refueling outages in POS 5 is found to be quite low in absolute terms, less than 10{sup {minus}7}/year.« less

Estimation of Damage Costs Associated with Flood Events

NASA Astrophysics Data System (ADS)

Andrews, T. A.; Wauthier, C.; Zipp, K.

2017-12-01

This study investigates the possibility of creating a mathematical function that enables the estimation of flood-damage costs. We begin by examining the costs associated with past flood events in the United States. The data on these tropical storms and hurricanes are provided by the National Oceanic and Atmospheric Administration. With the location, extent of flooding, and damage reparation costs identified, we analyze variables such as: number of inches rained, land elevation, type of landscape, region development in regards to building density and infrastructure, and population concentration. We seek to identify the leading drivers of high flood-damage costs and understand which variables play a large role in the costliness of these weather events. Upon completion of our mathematical analysis, we turn out attention to the 2017 natural disaster of Texas. We divide the region, as we did above, by land elevation, type of landscape, region development in regards to building density and infrastructure, and population concentration. Then, we overlay the number of inches rained in those regions onto the divided landscape and apply our function. We hope to use these findings to estimate the potential flood-damage costs of Hurricane Harvey. This information is then transformed into a hazard map that could provide citizens and businesses of flood-stricken zones additional resources for their insurance selection process.

The effect of the initial microstructure in terms of sink strength on the ion-irradiation-induced hardening of ODS alloys studied by nanoindentation

NASA Astrophysics Data System (ADS)

Duan, Binghuang; Heintze, Cornelia; Bergner, Frank; Ulbricht, Andreas; Akhmadaliev, Shavkat; Oñorbe, Elvira; de Carlan, Yann; Wang, Tieshan

2017-11-01

Oxide dispersion strengthened (ODS) Fe-Cr alloys are promising candidates for structural components in nuclear energy production. The small grain size, high dislocation density and the presence of particle matrix interfaces may contribute to the improved irradiation resistance of this class of alloys by providing sinks and/or traps for irradiation-induced point defects. The extent to which these effects impede hardening is still a matter of debate. To address this problem, a set of alloys of different grain size, dislocation density and oxide particle distribution were selected. In this study, three-step Fe-ion irradiation at both 300 °C and 500 °C up to 10 dpa was used to introduce damage in five different materials including three 9Cr-ODS alloys, one 14Cr-ODS alloy and one 14Cr-non-ODS alloy. Electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), small angle neutron scattering (SANS), and nanoindentation testing were applied, the latter before and after irradiation. Significant hardening occurred for all materials and temperatures, but it is distinctly lower in the 14Cr alloys and also tends to be lower at the higher temperature. The possible contribution of Cr-rich α‧-phase particles is addressed. The impact of grain size, dislocation density and particle distribution is demonstrated in terms of an empirical trend between total sink strength and hardening.

Pressure effects on the relaxation of an excited nitromethane molecule in an argon bath

NASA Astrophysics Data System (ADS)

Rivera-Rivera, Luis A.; Wagner, Albert F.; Sewell, Thomas D.; Thompson, Donald L.

2015-01-01

Classical molecular dynamics simulations were performed to study the relaxation of nitromethane in an Ar bath (of 1000 atoms) at 300 K and pressures 10, 50, 75, 100, 125, 150, 300, and 400 atm. The molecule was instantaneously excited by statistically distributing 50 kcal/mol among the internal degrees of freedom. At each pressure, 1000 trajectories were integrated for 1000 ps, except for 10 atm, for which the integration time was 5000 ps. The computed ensemble-averaged rotational energy decay is ˜100 times faster than the vibrational energy decay. Both rotational and vibrational decay curves can be satisfactorily fit with the Lendvay-Schatz function, which involves two parameters: one for the initial rate and one for the curvature of the decay curve. The decay curves for all pressures exhibit positive curvature implying the rate slows as the molecule loses energy. The initial rotational relaxation rate is directly proportional to density over the interval of simulated densities, but the initial vibrational relaxation rate decreases with increasing density relative to the extrapolation of the limiting low-pressure proportionality to density. The initial vibrational relaxation rate and curvature are fit as functions of density. For the initial vibrational relaxation rate, the functional form of the fit arises from a combinatorial model for the frequency of nitromethane "simultaneously" colliding with multiple Ar atoms. Roll-off of the initial rate from its low-density extrapolation occurs because the cross section for collision events with L Ar atoms increases with L more slowly than L times the cross section for collision events with one Ar atom. The resulting density-dependent functions of the initial rate and curvature represent, reasonably well, all the vibrational decay curves except at the lowest density for which the functions overestimate the rate of decay. The decay over all gas phase densities is predicted by extrapolating the fits to condensed-phase densities.

Pressure effects on the relaxation of an excited nitromethane molecule in an argon bath

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rivera-Rivera, Luis A.; Wagner, Albert F.; Sewell, Thomas D.

2015-01-07

Classical molecular dynamics simulations were performed to study the relaxation of nitromethane in an Ar bath (of 1000 atoms) at 300 K and pressures 10, 50, 75, 100, 125, 150, 300, and 400 atm. The molecule was instantaneously excited by statistically distributing 50 kcal/mol among the internal degrees of freedom. At each pressure, 1000 trajectories were integrated for 1000 ps, except for 10 atm, for which the integration time was 5000 ps. The computed ensemble-averaged rotational energy decay is similar to 100 times faster than the vibrational energy decay. Both rotational and vibrational decay curves can be satisfactorily fit withmore » the Lendvay-Schatz function, which involves two parameters: one for the initial rate and one for the curvature of the decay curve. The decay curves for all pressures exhibit positive curvature implying the rate slows as the molecule loses energy. The initial rotational relaxation rate is directly proportional to density over the interval of simulated densities, but the initial vibrational relaxation rate decreases with increasing density relative to the extrapolation of the limiting low-pressure proportionality to density. The initial vibrational relaxation rate and curvature are fit as functions of density. For the initial vibrational relaxation rate, the functional form of the fit arises from a combinatorial model for the frequency of nitromethane "simultaneously" colliding with multiple Ar atoms. Roll-off of the initial rate from its low-density extrapolation occurs because the cross section for collision events with L Ar atoms increases with L more slowly than L times the cross section for collision events with one Ar atom. The resulting density-dependent functions of the initial rate and curvature represent, reasonably well, all the vibrational decay curves except at the lowest density for which the functions overestimate the rate of decay. The decay over all gas phase densities is predicted by extrapolating the fits to condensed-phase densities. (C) 2015 AIP Publishing LLC.« less

Pressure effects on the relaxation of an excited nitromethane molecule in an argon bath.

PubMed

Rivera-Rivera, Luis A; Wagner, Albert F; Sewell, Thomas D; Thompson, Donald L

2015-01-07

Classical molecular dynamics simulations were performed to study the relaxation of nitromethane in an Ar bath (of 1000 atoms) at 300 K and pressures 10, 50, 75, 100, 125, 150, 300, and 400 atm. The molecule was instantaneously excited by statistically distributing 50 kcal/mol among the internal degrees of freedom. At each pressure, 1000 trajectories were integrated for 1000 ps, except for 10 atm, for which the integration time was 5000 ps. The computed ensemble-averaged rotational energy decay is ∼100 times faster than the vibrational energy decay. Both rotational and vibrational decay curves can be satisfactorily fit with the Lendvay-Schatz function, which involves two parameters: one for the initial rate and one for the curvature of the decay curve. The decay curves for all pressures exhibit positive curvature implying the rate slows as the molecule loses energy. The initial rotational relaxation rate is directly proportional to density over the interval of simulated densities, but the initial vibrational relaxation rate decreases with increasing density relative to the extrapolation of the limiting low-pressure proportionality to density. The initial vibrational relaxation rate and curvature are fit as functions of density. For the initial vibrational relaxation rate, the functional form of the fit arises from a combinatorial model for the frequency of nitromethane "simultaneously" colliding with multiple Ar atoms. Roll-off of the initial rate from its low-density extrapolation occurs because the cross section for collision events with L Ar atoms increases with L more slowly than L times the cross section for collision events with one Ar atom. The resulting density-dependent functions of the initial rate and curvature represent, reasonably well, all the vibrational decay curves except at the lowest density for which the functions overestimate the rate of decay. The decay over all gas phase densities is predicted by extrapolating the fits to condensed-phase densities.

Pressure effects on the relaxation of an excited nitromethane molecule in an argon bath

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rivera-Rivera, Luis A.; Sewell, Thomas D.; Thompson, Donald L.

2015-01-07

Classical molecular dynamics simulations were performed to study the relaxation of nitromethane in an Ar bath (of 1000 atoms) at 300 K and pressures 10, 50, 75, 100, 125, 150, 300, and 400 atm. The molecule was instantaneously excited by statistically distributing 50 kcal/mol among the internal degrees of freedom. At each pressure, 1000 trajectories were integrated for 1000 ps, except for 10 atm, for which the integration time was 5000 ps. The computed ensemble-averaged rotational energy decay is ∼100 times faster than the vibrational energy decay. Both rotational and vibrational decay curves can be satisfactorily fit with the Lendvay-Schatzmore » function, which involves two parameters: one for the initial rate and one for the curvature of the decay curve. The decay curves for all pressures exhibit positive curvature implying the rate slows as the molecule loses energy. The initial rotational relaxation rate is directly proportional to density over the interval of simulated densities, but the initial vibrational relaxation rate decreases with increasing density relative to the extrapolation of the limiting low-pressure proportionality to density. The initial vibrational relaxation rate and curvature are fit as functions of density. For the initial vibrational relaxation rate, the functional form of the fit arises from a combinatorial model for the frequency of nitromethane “simultaneously” colliding with multiple Ar atoms. Roll-off of the initial rate from its low-density extrapolation occurs because the cross section for collision events with L Ar atoms increases with L more slowly than L times the cross section for collision events with one Ar atom. The resulting density-dependent functions of the initial rate and curvature represent, reasonably well, all the vibrational decay curves except at the lowest density for which the functions overestimate the rate of decay. The decay over all gas phase densities is predicted by extrapolating the fits to condensed-phase densities.« less

Animal Studies in the Mode of Action of Agents, That Are Antitransformers in Cell Cultures.

DTIC Science & Technology

1987-10-28

The oel- let was hydrolysed at 90 C in 6% PCA for 30 min. The DNA content (ootical density at 260 nm and 290 nm) and the radioactivitv ( liquid ...required: DNA damage, excision of the damage and DNA-strand polimerization and ligation. The misrepair or incomplete repair of DNA damage may be an ini...with non ionic deter- gents in the ?resence of high salt concentration. The secondary and tertiary structure (supercoils) of DNA remains intact under

Simulating the Initial Dynamics of the 18 May 1980 Mount St.Helens Blast

NASA Astrophysics Data System (ADS)

Esposti Ongaro, T.; Widiwijayanti, C.; Voight, B.; Clarke, A. B.; Neri, A.

2008-12-01

The initial stage of the 18 May 1980 blast at Mount St. Helens (MSH) has been simulated numerically by the 2D/3D multiphase multiparticle flow model PDAC (Neri et al., J. Geophys. Res. 108 (B4), 2003; Esposti Ongaro et al., Parallel Computing 33, 2007), to provide further insight into the fluid dynamics of this phenomenon. Initial source conditions, including the gas content, the total mass of juvenile and entrained rocks, the temperature, grain size distribution and pre-eruption pressure distribution in the lava dome have been parameterized accordingly to field evidence, available geological constraints and simple theoretical models. Simulation results suggest that the MSH blast can be characterized as an expansion phase (burst), lasting about ten seconds, followed by collapse and pyroclastic density current (PDC) phases. In the burst phase the pressure forces dominate and the flow can locally reach supersonic velocities and generate pressure waves that can be tracked by the numerical model. In the collapse and PDC phases the flow is dominantly gravity-driven and the dynamics are strongly controlled by the source geometry, vertical stratification within the flow and by the 3D topography. The simulations suggest that the severe damage observed at MSH can be explained by high dynamic pressures in gravity currents, and the rapid decrease of dynamic pressure from proximal to distal areas (and related parameters of PDC velocity and density) was largely related to rugged topography beyond the North Fork Toutle River valley. Although the source models investigated thus far represent a simplification of the actual geometry and complex sequence of initial events, we show that the explosion mechanisms are significantly robust over a wide range of initial conditions. Simulation results for MSH are also consistent with those obtained in a previous application of a similar model to the 1997 Boxing Day blast pulses at Soufriere Hills volcano (Montserrat, West Indies) (Esposti Ongaro et al., J. Geophys. Res. 113 (B03211), 2008), which were at least ten times smaller, thus suggesting that the simulated mechanisms are largely independent of eruption scale.

Damage Tolerance of Large Shell Structures

NASA Technical Reports Server (NTRS)

Minnetyan, L.; Chamis, C. C.

1999-01-01

Progressive damage and fracture of large shell structures is investigated. A computer model is used for the assessment of structural response, progressive fracture resistance, and defect/damage tolerance characteristics. Critical locations of a stiffened conical shell segment are identified. Defective and defect-free computer models are simulated to evaluate structural damage/defect tolerance. Safe pressurization levels are assessed for the retention of structural integrity at the presence of damage/ defects. Damage initiation, growth, accumulation, and propagation to fracture are included in the simulations. Damage propagation and burst pressures for defective and defect-free shells are compared to evaluate damage tolerance. Design implications with regard to defect and damage tolerance of a large steel pressure vessel are examined.

Reduced Microvascular Density in Omental Biopsies of Children with Chronic Kidney Disease

PubMed Central

Grabe, Niels; Lahrmann, Bernd; Nasser, Hamoud; Freise, Christian; Schneider, Axel; Lingnau, Anja; Degenhardt, Petra; Ranchin, Bruno; Sallay, Peter; Cerkauskiene, Rimante; Malina, Michal; Ariceta, Gema; Schmitt, Claus Peter; Querfeld, Uwe

2016-01-01

Background Endothelial dysfunction is an early manifestation of cardiovascular disease (CVD) and consistently observed in patients with chronic kidney disease (CKD). We hypothesized that CKD is associated with systemic damage to the microcirculation, preceding macrovascular pathology. To assess the degree of “uremic microangiopathy”, we have measured microvascular density in biopsies of the omentum of children with CKD. Patients and Methods Omental tissue was collected from 32 healthy children (0–18 years) undergoing elective abdominal surgery and from 23 age-matched cases with stage 5 CKD at the time of catheter insertion for initiation of peritoneal dialysis. Biopsies were analyzed by independent observers using either a manual or an automated imaging system for the assessment of microvascular density. Quantitative immunohistochemistry was performed for markers of autophagy and apoptosis, and for the abundance of the angiogenesis-regulating proteins VEGF-A, VEGF-R2, Angpt1 and Angpt2. Results Microvascular density was significantly reduced in uremic children compared to healthy controls, both by manual imaging with a digital microscope (median surface area 0.61% vs. 0.95%, p<0.0021 and by automated quantification (total microvascular surface area 0.89% vs. 1.17% p = 0.01). Density measured by manual imaging was significantly associated with age, height, weight and body surface area in CKD patients and healthy controls. In multivariate analysis, age and serum creatinine level were the only independent, significant predictors of microvascular density (r2 = 0.73). There was no immunohistochemical evidence for apoptosis or autophagy. Quantitative staining showed similar expression levels of the angiogenesis regulators VEGF-A, VEGF-receptor 2 and Angpt1 (p = 0.11), but Angpt2 was significantly lower in CKD children (p = 0.01). Conclusions Microvascular density is profoundly reduced in omental biopsies of children with stage 5 CKD and associated with diminished Angpt2 signaling. Microvascular rarefaction could be an early systemic manifestation of CKD-induced cardiovascular disease. PMID:27846250

Self-focusing and defocusing of Gaussian laser beams in collisional inhomogeneous plasmas with linear density and temperature ramps

NASA Astrophysics Data System (ADS)

Hashemzadeh, M.

2018-01-01

Self-focusing and defocusing of Gaussian laser beams in collisional inhomogeneous plasmas are investigated in the presence of various laser intensities and linear density and temperature ramps. Considering the ponderomotive force and using the momentum transfer and energy equations, the nonlinear electron density is derived. Taking into account the paraxial approximation and nonlinear electron density, a nonlinear differential equation, governing the focusing and defocusing of the laser beam, is obtained. Results show that in the absence of ramps the laser beam is focused between a minimum and a maximum value of laser intensity. For a certain value of laser intensity and initial electron density, the self-focusing process occurs in a temperature range which reaches its maximum at turning point temperature. However, the laser beam is converged in a narrow range for various amounts of initial electron density. It is indicated that the σ2 parameter and its sign can affect the self-focusing process for different values of laser intensity, initial temperature, and initial density. Finally, it is found that although the electron density ramp-down diverges the laser beam, electron density ramp-up improves the self-focusing process.

Estimation of Confined Peak Strength of Crack-Damaged Rocks

NASA Astrophysics Data System (ADS)

Bahrani, Navid; Kaiser, Peter K.

2017-02-01

It is known that the unconfined compressive strength of rock decreases with increasing density of geological features such as micro-cracks, fractures, and veins both at the laboratory specimen and rock block scales. This article deals with the confined peak strength of laboratory-scale rock specimens containing grain-scale strength dominating features such as micro-cracks. A grain-based distinct element model, whereby the rock is simulated with grains that are allowed to deform and break, is used to investigate the influence of the density of cracks on the rock strength under unconfined and confined conditions. A grain-based specimen calibrated to the unconfined and confined strengths of intact and heat-treated Wombeyan marble is used to simulate rock specimens with varying crack densities. It is demonstrated how such cracks affect the peak strength, stress-strain curve and failure mode with increasing confinement. The results of numerical simulations in terms of unconfined and confined peak strengths are used to develop semi-empirical relations that relate the difference in strength between the intact and crack-damaged rocks to the confining pressure. It is shown how these relations can be used to estimate the confined peak strength of a rock with micro-cracks when the unconfined and confined strengths of the intact rock and the unconfined strength of the crack-damaged rock are known. This approach for estimating the confined strength of crack-damaged rock specimens, called strength degradation approach, is then verified by application to published laboratory triaxial test data.

Characterisation of radiation damage in W and W-based alloys from 2MeV self-ion near-bulk implantations

DOE PAGES

Yi, Xiaoou; Culham Science Centre, Abingdon; Jenkins, Michael L.; ...

2015-04-21

The displacement damage induced in bulk W and W-5 wt.% Re and W-5 wt.% Ta alloys by 2 MeV W + irradiation to doses 3.3×10 17 - 2.5×10 19 W +/m 2 at temperatures ranging from 300 to750°C has been characterized by transmission electron microscopy. An automated sizing and counting approach based on Image J has been proposed and performed for all irradiation data. In all cases the damage comprised dislocation loops, mostly of interstitial type, with Burgers vectors b = ½<111> (> 60%) and b = <100>. The diameters of loops did not exceed 20 nm, with the majoritymore » being ≤ 6 nm. The loop number density varied between 10 22 and 10 23 loops/m 3 . With increasing irradiation temperature, the loop size distributions shifted towards larger sizes, and there was a substantial decrease in loop number densities. The damage microstructure was less sensitive to dose than to temperature. Under the same irradiation conditions, loop number densities in the alloys were higher than in pure W but loops were smaller. In grains with normals close to z = <001>, loop strings developed in W at temperatures ≥ 500°C and doses ≥ 1.2 dpa, but such strings were not observed in the W-Re or W-Ta alloys. However, in other grain orientations complex structures appeared in all materials and dense dislocation networks formed at higher doses.« less

Low-energy BF2, BCl2, and BBr2 implants for ultrashallow P+-N junctions

NASA Astrophysics Data System (ADS)

Nandan, S. R.; Agarwal, Vikas; Banerjee, Sanjay K.

1997-08-01

We have examined low energy BCl2 and BBr2 implants as a means of fabricating ultra-shallow P+-N junctions. Five keV and 9 keV BCl2 implants and 18 keV BBr2 implants have been compared to 5 keV BF2 implants to study the benefits of using these species. BCl2 and BBr2, being heavier species, have a lower projected range and produce more damage. The greater damage restricts channeling, resulting in shallower as-implanted profiles. The increased damage amorphizes the substrate at low implant doses which results in reduced transient enhanced diffusion (TED) during the post-implant anneal. Post-anneal SIMS profiles indicate a junction depth reduction of over 10 nm (at 5 X 1017 cm-3 background doping) for 5 keV BCl2 implants as compared to 5 keV BF2 implants. Annealed junctions as shallow as 10 nm have been obtained from the 18 keV BBr2 implants. The increased damage degrades the electrical properties of these junctions by enhancing the leakage current densities. BCl2 implanted junctions have leakage current densities of approximately 1 (mu) A/cm2 as compared to 10 nA/cm2 for the BF2 implants. BBr2 implants have a lower leakage density of approximately 50 nA/cm2. Low energy BBr2 implants offer an exciting alternative for fabricating low leakage, ultra-shallow P+-N junctions.

Oral administration of vitamin C prevents alveolar bone resorption induced by high dietary cholesterol in rats.

PubMed

Sanbe, Toshihiro; Tomofuji, Takaaki; Ekuni, Daisuke; Azuma, Tetsuji; Tamaki, Naofumi; Yamamoto, Tatsuo

2007-11-01

A high-cholesterol diet stimulates alveolar bone resorption, which may be induced via tissue oxidative damage. Vitamin C reduces tissue oxidative damage by neutralizing free radicals and scavenging hydroxyl radicals, and its antioxidant effect may offer the clinical benefit of preventing alveolar bone resorption in cases of hyperlipidemia. We examined whether vitamin C could suppress alveolar bone resorption in rats fed a high-cholesterol diet. In this 12-week study, rats were divided into four groups: a control group (fed a regular diet) and three experimental groups (fed a high-cholesterol diet supplemented with 0, 1, or 2 g/l vitamin C). Vitamin C was provided by adding it to the drinking water. The bone mineral density of the alveolar bone was analyzed by microcomputerized tomography. As an index of tissue oxidative damage, the 8-hydroxydeoxyguanosine level in the periodontal tissue was determined using a competitive enzyme-linked immunosorbent assay. Hyperlipidemia, induced by a high-cholesterol diet, decreased rat alveolar bone density and increased the number of tartrate-resistant acid phosphatase-positive osteoclasts. The expression of 8-hydroxydeoxyguanosine was upregulated in the periodontal tissues. Intake of vitamin C reduced the effect of a high-cholesterol diet on alveolar bone density and osteoclast differentiation and decreased periodontal 8-hydroxydeoxyguanosine expression. In the rat model, vitamin C suppressed alveolar bone resorption, induced by high dietary cholesterol, by decreasing the oxidative damage of periodontal tissue.

RNA protects a nucleoprotein complex against radiation damage.

PubMed

Bury, Charles S; McGeehan, John E; Antson, Alfred A; Carmichael, Ian; Gerstel, Markus; Shevtsov, Mikhail B; Garman, Elspeth F

2016-05-01

Radiation damage during macromolecular X-ray crystallographic data collection is still the main impediment for many macromolecular structure determinations. Even when an eventual model results from the crystallographic pipeline, the manifestations of radiation-induced structural and conformation changes, the so-called specific damage, within crystalline macromolecules can lead to false interpretations of biological mechanisms. Although this has been well characterized within protein crystals, far less is known about specific damage effects within the larger class of nucleoprotein complexes. Here, a methodology has been developed whereby per-atom density changes could be quantified with increasing dose over a wide (1.3-25.0 MGy) range and at higher resolution (1.98 Å) than the previous systematic specific damage study on a protein-DNA complex. Specific damage manifestations were determined within the large trp RNA-binding attenuation protein (TRAP) bound to a single-stranded RNA that forms a belt around the protein. Over a large dose range, the RNA was found to be far less susceptible to radiation-induced chemical changes than the protein. The availability of two TRAP molecules in the asymmetric unit, of which only one contained bound RNA, allowed a controlled investigation into the exact role of RNA binding in protein specific damage susceptibility. The 11-fold symmetry within each TRAP ring permitted statistically significant analysis of the Glu and Asp damage patterns, with RNA binding unexpectedly being observed to protect these otherwise highly sensitive residues within the 11 RNA-binding pockets distributed around the outside of the protein molecule. Additionally, the method enabled a quantification of the reduction in radiation-induced Lys and Phe disordering upon RNA binding directly from the electron density.

Optical damage testing at the Z-Backlighter facility at Sandia National Laboratories

NASA Astrophysics Data System (ADS)

Kimmel, Mark; Rambo, Patrick; Broyles, Robin; Geissel, Matthias; Schwarz, Jens; Bellum, John; Atherton, Briggs

2009-10-01

To enable laser-based radiography of high energy density physics events on the Z-Accelerator[4,5] at Sandia National Laboratories, a facility known as the Z-Backlighter has been developed. Two Nd:Phosphate glass lasers are used to create x-rays and/or proton beams capable of this radiographic diagnosis: Z-Beamlet (a multi-kilojoule laser operating at 527nm in a few nanoseconds) and Z-Petawatt (a several hundred joule laser operating at 1054nm in the subpicosecond regime) [1,2]. At the energy densities used in these systems, it is necessary to use high damage threshold optical materials, some of which are poorly characterized (especially for the sub-picosecond pulse). For example, Sandia has developed a meter-class dielectric coating capability for system optics. Damage testing can be performed by external facilities for nanosecond 532nm pulses, measuring high reflector coating damage thresholds >80J/cm2 and antireflection coating damage thresholds >20J/cm2 [3]. However, available external testing capabilities do not use femtosecond/picosecond scale laser pulses. To this end, we have constructed a sub-picoseond-laser-based optical damage test system. The damage tester system also allows for testing in a vacuum vessel, which is relevant since many optics in the Z-Backlighter system are used in vacuum. This paper will present the results of laser induced damage testing performed in both atmosphere and in vacuum, with 1054nm sub-picosecond laser pulses. Optical materials/coatings discussed are: bare fused silica and protected gold used for benchmarking; BK7; Zerodur; protected silver; and dielectric optical coatings (halfnia/silica layer pairs) produced by Sandia's in-house meter-class coating capability.

RNA protects a nucleoprotein complex against radiation damage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bury, Charles S.; McGeehan, John E.; Antson, Alfred A.

Radiation damage during macromolecular X-ray crystallographic data collection is still the main impediment for many macromolecular structure determinations. Even when an eventual model results from the crystallographic pipeline, the manifestations of radiation-induced structural and conformation changes, the so-called specific damage, within crystalline macromolecules can lead to false interpretations of biological mechanisms. Although this has been well characterized within protein crystals, far less is known about specific damage effects within the larger class of nucleoprotein complexes. We developed a methodology whereby per-atom density changes could be quantified with increasing dose over a wide (1.3–25.0 MGy) range and at higher resolution (1.98more » Å) than the previous systematic specific damage study on a protein–DNA complex. Specific damage manifestations were determined within the largetrpRNA-binding attenuation protein (TRAP) bound to a single-stranded RNA that forms a belt around the protein. Over a large dose range, the RNA was found to be far less susceptible to radiation-induced chemical changes than the protein. The availability of two TRAP molecules in the asymmetric unit, of which only one contained bound RNA, allowed a controlled investigation into the exact role of RNA binding in protein specific damage susceptibility. The 11-fold symmetry within each TRAP ring permitted statistically significant analysis of the Glu and Asp damage patterns, with RNA binding unexpectedly being observed to protect these otherwise highly sensitive residues within the 11 RNA-binding pockets distributed around the outside of the protein molecule. In addition, the method enabled a quantification of the reduction in radiation-induced Lys and Phe disordering upon RNA binding directly from the electron density.« less

The damage is done: Low fault friction recorded in the damage zone of the shallow Japan Trench décollement

NASA Astrophysics Data System (ADS)

Keren, Tucker T.; Kirkpatrick, James D.

2016-05-01

Fault damage zones record the integrated deformation caused by repeated slip on faults and reflect the conditions that control slip behavior. To investigate the Japan Trench décollement, we characterized the damage zone close to the fault from drill core recovered during Integrated Ocean Drilling Program Expedition 343 (Japan Trench Fast Drilling Project (JFAST)). Core-scale and microscale structures include phyllosilicate bands, shear fractures, and joints. They are most abundant near the décollement and decrease in density sharply above and below the fault. Power law fits describing the change in structure density with distance from the fault result in decay exponents (n) of 1.57 in the footwall and 0.73 in the hanging wall. Microstructure decay exponents are 1.09 in the footwall and 0.50 in the hanging wall. Observed damage zone thickness is on the order of a few tens of meters. Core-scale structures dip between ~10° and ~70° and are mutually crosscutting. Compared to similar offset faults, the décollement has large decay exponents and a relatively narrow damage zone. Motivated by independent constraints demonstrating that the plate boundary is weak, we tested if the observed damage zone characteristics could be consistent with low-friction fault. Quasi-static models of off-fault stresses and deformation due to slip on a wavy, frictional fault under conditions similar to the JFAST site predict that low-friction fault produces narrow damage zones with no preferred orientations of structures. These results are consistent with long-term frictional weakness on the décollement at the JFAST site.

RNA protects a nucleoprotein complex against radiation damage

DOE PAGES

Bury, Charles S.; McGeehan, John E.; Antson, Alfred A.; ...

2016-04-26

Radiation damage during macromolecular X-ray crystallographic data collection is still the main impediment for many macromolecular structure determinations. Even when an eventual model results from the crystallographic pipeline, the manifestations of radiation-induced structural and conformation changes, the so-called specific damage, within crystalline macromolecules can lead to false interpretations of biological mechanisms. Although this has been well characterized within protein crystals, far less is known about specific damage effects within the larger class of nucleoprotein complexes. We developed a methodology whereby per-atom density changes could be quantified with increasing dose over a wide (1.3–25.0 MGy) range and at higher resolution (1.98more » Å) than the previous systematic specific damage study on a protein–DNA complex. Specific damage manifestations were determined within the largetrpRNA-binding attenuation protein (TRAP) bound to a single-stranded RNA that forms a belt around the protein. Over a large dose range, the RNA was found to be far less susceptible to radiation-induced chemical changes than the protein. The availability of two TRAP molecules in the asymmetric unit, of which only one contained bound RNA, allowed a controlled investigation into the exact role of RNA binding in protein specific damage susceptibility. The 11-fold symmetry within each TRAP ring permitted statistically significant analysis of the Glu and Asp damage patterns, with RNA binding unexpectedly being observed to protect these otherwise highly sensitive residues within the 11 RNA-binding pockets distributed around the outside of the protein molecule. In addition, the method enabled a quantification of the reduction in radiation-induced Lys and Phe disordering upon RNA binding directly from the electron density.« less

Modern Initial Management of Severe Limbs Trauma in War Surgery: Orthopaedic Damage Control

DTIC Science & Technology

2010-04-01

avoid fat embolism , allow an optimal nursing and medical evacuation without any secondary functional consequences [3]. 2.2.1 Indications: The...decrease the risk of fat embolism . Modern Initial Management of Severe Limbs Trauma in War Surgery: “Orthopaedic Damage Control” RTO-MP-HFM-182 17...injuries. Orthopaedic Imperious: Multiple open shaft fractures with blood loss, complex epiphysal fractures requiring a long difficult surgical bloody

Hot-Spot Fatigue and Impact Damage Detection on a Helicopter Tailboom

DTIC Science & Technology

2011-09-01

other 14 PZT disks were used as sensors. Among the 28 PZT disks, 16 PZT disks were placed in the two fatigue hot-spot areas to detect cracks initiated...more efficient and effective airframe maintenance, fatigue cracking and impact damage detection technologies were developed and demonstrated on a...SHM system in successfully monitoring fatigue cracks initiated from cyclical loading conditions; detecting, locating and quantifying ballistic

Particle Size Effects on CL-20 Initiation and Detonation

NASA Astrophysics Data System (ADS)

Valancius, Cole; Bainbridge, Joe; Love, Cody; Richardson, Duane

2017-06-01

Particle size or specific surface area effects on explosives has been of interest to the explosives community for both application and modeling of initiation and detonation. Different particles sizes of CL-20 were used in detonator experiments to determine the effects of particle size on initiation, run-up to steady state detonation, and steady state detonation. Historical tests have demonstrated a direct relationship between particle size and initiation. However, historical tests inadvertently employed density gradients, making it difficult to discern the effects of particle size from the effects of density. Density gradients were removed from these tests using a larger diameter, shorter charge column, allowing for similar loading across different particle sizes. Without the density gradient, the effects of particle size on initiation and detonation are easier to determine. The results of which contrast with historical results, showing particle size does not directly affect initiation threshold.

Damage threshold dependence of optical coatings on substrate materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhouling, W.; Zhenxiu, F.

1996-04-01

Damage threshold dependence on substrate materials was investigated for TiO2, ZrO2, SiO2, MgF2, ZnS, and single and TiO2/SiO2 multilayers. The results show that the damage threshold increases with increasing substrate thermal conductivity for single layers and AR coatings and remains the same for HR coatings. With the help of localized absorption measurement and in-situ damage process analysis, these phenomena were well correlated with local absorption-initiated thermal damage mechanism.

Forest Health Monitoring in Connecticut, 1996-1999

Treesearch

Northeastern Research Station

2002-01-01

Connecticut has mature forests dominated by hardwoods. Most trees are healthy with full crowns (low transparency and high density), little dieback and little damage. The exception is eastern hemlock, which was in poor condition, with thin crowns, more dieback and more damage, especially broken tops. These conditions are likely the result of attack by the hemlock woolly...

Forest Health Monitoring in New York, 1996-1999

Treesearch

Northeastern Research Station

2002-01-01

New York has mature forests dominated by hardwood species, but with a significant and varied softwood resource. Most of the trees are healthy, with full crowns (low transparency, high density), little dieback and little damage. American beech tends to be in poorer condition, with thin crowns, higher dieback, and more damage, especially broken and dead branches.

Mice cause severe damage to Virginia pine reproduction

Treesearch

Thomas W., Jr. Church

1954-01-01

Heavy damage to a young Virginia pine stand was noticed recently on the Beltsville Experimental Forest in Maryland. The injury was confined to pine trees that had come in on an abandoned field. This reproduction ranged from 1 to 10 feet in height and had an average density of 19,000 per acre. Andropogon was the predominant ground vegetation.

Harvest operations for density management: planning requirements, production, costs, stand damage, and recommendations

Treesearch

Loren D. Kellogg; Stephen J. Pilkerton

2013-01-01

Since the early 1990s, several studies have been undertaken to determine the planning requirements, productivity, costs, and residual stand damage of harvest operations in thinning treatments designed to promote development of complex forest structure in order to enhance ecological functioning and biological diversity. Th ese studies include the Oregon State...

Irrigation and Fertilization Effects on Nantucket Pine Tip Moth (Lepidoptera: Tortricidae) Damage Levels and Pupal Weight in an Intensively-Managed Pine Plantation

Treesearch

David R. Coyle; John T. Nowak; Christopher J. Fettig

2003-01-01

The widespread application of intensive forest management practices throughout the southeastern U.S. has increased loblolly pine, pinus taeda L., yields and shortened conventional rotation lengths. Fluctuations in Nantucket pine tip moth, Rhyacionia frustrana (Comstock), population density and subsequent damage levels have been...

Essential oil yield and composition reflect browsing damage of junipers.

PubMed

Markó, Gábor; Gyuricza, Veronika; Bernáth, Jeno; Altbacker, Vilmos

2008-12-01

The impact of browsing on vegetation depends on the relative density and species composition of browsers. Herbivore density and plant damage can be either site-specific or change seasonally and spatially. For juniper (Juniperus communis) forests of a sand dune region in Hungary, it has been assumed that plant damage investigated at different temporal and spatial scales would reflect selective herbivory. The level of juniper damage was tested for a possible correlation with the concentration of plant secondary metabolites (PSMs) in plants and seasonal changes in browsing pressure. Heavily browsed and nonbrowsed junipers were also assumed to differ in their chemical composition, and the spatial distribution of browsing damage within each forest was analyzed to reveal the main browser. Long-term differences in local browsing pressure were also expected and would be reflected in site-specific age distributions of distant juniper populations. The concentrations of PSMs (essential oils) varied significantly among junipers and seasons. Heavily browsed shrubs contained the lowest oil yield; essential oils were highest in shrubs bearing no damage, indicating that PSMs might contribute to reduce browsing in undamaged shrubs. There was a seasonal fluctuation in the yield of essential oil that was lower in the summer period than in other seasons. Gas chromatography (GC) revealed differences in some essential oil components, suggesting that certain chemicals could have contributed to reduced consumption. The consequential long-term changes were reflected in differences in age distribution between distant juniper forests. These results confirm that both the concentration of PSMs and specific compounds of the essential oil may play a role in selective browsing damage by local herbivores.

Impact of reflective mulch on yield of strawberry plants and incidence of damage by tarnished plant bug (Heteroptera: Miridae).

PubMed

Rhainds, N; Kovach, J; Dosa, E L; English-Loeb, G

2001-12-01

The current study investigated the impact of reflective mulch on yield of strawberry plants and incidence of damage by tarnished plant bugs, Lygus lineolaris (Palisot de Beauvois), for three strawberry cultivars: 'Honeoye', 'Earliglow', and two sibling Dayneutrals ('Tribute' and 'Tristar', herein considered as one cultivar). Of all cultivars tested, Honeoye was the most productive and least susceptible to tarnished plant bug. For Earliglow and Honeoye, reflective mulch enhanced productivity of strawberry plants and suppressed density of nymphs per flower cluster and proportion of damaged fruits, but did not significantly impact numbers of nymphs or damaged fruits per hectare, Results with Dayneutrals were not consistently significant. Both in the presence or absence of reflective mulch, proportion of damaged fruits increased with increasing density of nymphs per flower cluster and with decreasing number of fruits harvested per row section, suggesting that planting productive strawberry cultivars or maintaining cultural practices that promote high yield may provide an effective line of defense against tarnished plant bug. These results also suggest that reflective mulch may suppress incidence of damage by tarnished plant bug both directly, by reducing number of nymphs per flower cluster, and indirectly, by enhancing productivity of strawberry plants. Economic analyses evaluating costs and benefits of using reflective mulch, as well as studies investigating mechanisms that underlie the impact of reflective mulch on yield and incidence of damage by tarnished plant bug, are still needed before reflective mulch can be implemented as a management strategy in commercial strawberry fields.

MESOSCALE MODELING OF DEFLAGRATION-INDUCED DECONSOLIDATION IN POLYMER-BONDED EXPLOSIVES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Springer, H K; Glascoe, E A; Reaugh, J E

Initially undamaged polymer-bonded explosives can transition from conductive burning to more violent convective burning via rapid deconsolidation at higher pressures. The pressure-dependent infiltration of cracks and pores, i.e., damage, by product gases at the burn-front is a key step in the transition to convective burning. However, the relative influence of pre-existing damage and the evolution of deflagration-induced damage during the transition to convective burning is not well understood. The objective of this study is to investigate the role of microstructure and initial pressurization on deconsolidation. We performed simulations using the multi-physics hydrocode, ALE3D. HMX-Viton A served as our model explosive.more » A Prout-Tompkins chemical kinetic model, Vielle's Law pressure-dependent burning, Gruneisen equation-of-state, and simplified strength model were used for the HMX. The propensity for deconsolidation increased with increasing defect size and decreasing initial pressurization, as measured by the increase in burning surface area. These studies are important because they enable the development of continuum-scale damage models and the design of inherently safer explosives.« less

Sam68 Is Required for DNA Damage Responses via Regulating Poly(ADP-ribosyl)ation

PubMed Central

Hodgson, Andrea; Wier, Eric M.; Wen, Matthew G.; Kamenyeva, Olena; Xia, Xue; Koo, Lily Y.

2016-01-01

The rapid and robust synthesis of polymers of adenosine diphosphate (ADP)-ribose (PAR) chains, primarily catalyzed by poly(ADP-ribose) polymerase 1 (PARP1), is crucial for cellular responses to DNA damage. However, the precise mechanisms through which PARP1 is activated and PAR is robustly synthesized are not fully understood. Here, we identified Src-associated substrate during mitosis of 68 kDa (Sam68) as a novel signaling molecule in DNA damage responses (DDRs). In the absence of Sam68, DNA damage-triggered PAR production and PAR-dependent DNA repair signaling were dramatically diminished. With serial cellular and biochemical assays, we demonstrated that Sam68 is recruited to and significantly overlaps with PARP1 at DNA lesions and that the interaction between Sam68 and PARP1 is crucial for DNA damage-initiated and PARP1-conferred PAR production. Utilizing cell lines and knockout mice, we illustrated that Sam68-deleted cells and animals are hypersensitive to genotoxicity caused by DNA-damaging agents. Together, our findings suggest that Sam68 plays a crucial role in DDR via regulating DNA damage-initiated PAR production. PMID:27635653

Aag DNA Glycosylase Promotes Alkylation-Induced Tissue Damage Mediated by Parp1

PubMed Central

Calvo, Jennifer A.; Moroski-Erkul, Catherine A.; Lake, Annabelle; Eichinger, Lindsey W.; Shah, Dharini; Jhun, Iny; Limsirichai, Prajit; Bronson, Roderick T.; Christiani, David C.; Meira, Lisiane B.; Samson, Leona D.

2013-01-01

Alkylating agents comprise a major class of front-line cancer chemotherapeutic compounds, and while these agents effectively kill tumor cells, they also damage healthy tissues. Although base excision repair (BER) is essential in repairing DNA alkylation damage, under certain conditions, initiation of BER can be detrimental. Here we illustrate that the alkyladenine DNA glycosylase (AAG) mediates alkylation-induced tissue damage and whole-animal lethality following exposure to alkylating agents. Aag-dependent tissue damage, as observed in cerebellar granule cells, splenocytes, thymocytes, bone marrow cells, pancreatic β-cells, and retinal photoreceptor cells, was detected in wild-type mice, exacerbated in Aag transgenic mice, and completely suppressed in Aag −/− mice. Additional genetic experiments dissected the effects of modulating both BER and Parp1 on alkylation sensitivity in mice and determined that Aag acts upstream of Parp1 in alkylation-induced tissue damage; in fact, cytotoxicity in WT and Aag transgenic mice was abrogated in the absence of Parp1. These results provide in vivo evidence that Aag-initiated BER may play a critical role in determining the side-effects of alkylating agent chemotherapies and that Parp1 plays a crucial role in Aag-mediated tissue damage. PMID:23593019

Experimental Aerothermodynamics In Support Of The Columbia Accident Investigation

NASA Technical Reports Server (NTRS)

Horvath, Thomas J.

2004-01-01

The technical foundation for the most probable damage scenario reported in the Columbia Accident Investigation Board's final report was largely derived from synergistic aerodynamic/aerothermodynamic wind tunnel measurements and inviscid predictions made at NASA Langley Research Center and later corroborated with engineering analysis, high fidelity numerical viscous simulations, and foam impact testing near the close of the investigation. This report provides an overview of the hypersonic aerothermodynamic wind tunnel program conducted at NASA Langley and illustrates how the ground-based heating measurements provided early insight that guided the direction and utilization of agency resources in support of the investigation. Global surface heat transfer mappings, surface streamline patterns, and shock shapes were measured on 0.0075 scale models of the Orbiter configuration with and without postulated damage to the thermal protection system. Test parametrics include angle of attack from 38 to 42 degs, sideslip angles of 38 to 42 degs, sideslip angles of plus or minus 1 deg, Reynolds numbers based upon model length from 0.05 x 10(exp 6) to 6.5 x 10(exp 6), and normal shock density ratios of 5 (Mach 6 Air) and 12 (Mach 6 CF4). The primary objective of the testing was to provide surface heating characteristics on scaled Orbiter models with outer mold line perturbations to simulate various forms of localized surface damage to the thermal protection system. Initial experimental testing conducted within two weeks of the accident simulated a broad spectrum of thermal protection system damage to the Orbiter windward surface and was used to refute several hypothesized forms of thermal protection system damage, which included gouges in the windward thermal protection system tiles, breaches through the wing new the main landing gear door, and protuberances along the wing leading edge that produced asymmetric boundary layer transition. As the forensic phase of the investigation developed and the condition of recovered debris was examined, increasing emphasis was placed on identifying wing leading edge damage (partially and fully missing reinforced carbon-carbon panels, and eventually holes in the wing leading edge with venting to the wing upper surface) that produced off-nominal heating trends consistent with extracted Orbiter flight recorder temperature data.

Experimental verification of a progressive damage model for composite laminates based on continuum damage mechanics. M.S. Thesis Final Report

NASA Technical Reports Server (NTRS)

Coats, Timothy William

1994-01-01

Progressive failure is a crucial concern when using laminated composites in structural design. Therefore the ability to model damage and predict the life of laminated composites is vital. The purpose of this research was to experimentally verify the application of the continuum damage model, a progressive failure theory utilizing continuum damage mechanics, to a toughened material system. Damage due to tension-tension fatigue was documented for the IM7/5260 composite laminates. Crack density and delamination surface area were used to calculate matrix cracking and delamination internal state variables, respectively, to predict stiffness loss. A damage dependent finite element code qualitatively predicted trends in transverse matrix cracking, axial splits and local stress-strain distributions for notched quasi-isotropic laminates. The predictions were similar to the experimental data and it was concluded that the continuum damage model provided a good prediction of stiffness loss while qualitatively predicting damage growth in notched laminates.

Fatty acid production in genetically modified cyanobacteria

PubMed Central

Liu, Xinyao; Sheng, Jie; Curtiss III, Roy

2011-01-01

To avoid costly biomass recovery in photosynthetic microbial biofuel production, we genetically modified cyanobacteria to produce and secrete fatty acids. Starting with introducing an acyl–acyl carrier protein thioesterase gene, we made six successive generations of genetic modifications of cyanobacterium Synechocystis sp. PCC6803 wild type (SD100). The fatty acid secretion yield was increased to 197 ± 14 mg/L of culture in one improved strain at a cell density of 1.0 × 109 cells/mL by adding codon-optimized thioesterase genes and weakening polar cell wall layers. Although these strains exhibited damaged cell membranes at low cell densities, they grew more rapidly at high cell densities in late exponential and stationary phase and exhibited less cell damage than cells in wild-type cultures. Our results suggest that fatty acid secreting cyanobacteria are a promising technology for renewable biofuel production. PMID:21482809

Continuum damage modeling and simulation of hierarchical dental enamel

NASA Astrophysics Data System (ADS)

Ma, Songyun; Scheider, Ingo; Bargmann, Swantje

2016-05-01

Dental enamel exhibits high fracture toughness and stiffness due to a complex hierarchical and graded microstructure, optimally organized from nano- to macro-scale. In this study, a 3D representative volume element (RVE) model is adopted to study the deformation and damage behavior of the fibrous microstructure. A continuum damage mechanics model coupled to hyperelasticity is developed for modeling the initiation and evolution of damage in the mineral fibers as well as protein matrix. Moreover, debonding of the interface between mineral fiber and protein is captured by employing a cohesive zone model. The dependence of the failure mechanism on the aspect ratio of the mineral fibers is investigated. In addition, the effect of the interface strength on the damage behavior is studied with respect to geometric features of enamel. Further, the effect of an initial flaw on the overall mechanical properties is analyzed to understand the superior damage tolerance of dental enamel. The simulation results are validated by comparison to experimental data from micro-cantilever beam testing at two hierarchical levels. The transition of the failure mechanism at different hierarchical levels is also well reproduced in the simulations.

Engineering long term clinical success of advanced ceramic prostheses.

PubMed

Rekow, Dianne; Thompson, Van P

2007-01-01

Biocompatability and, in some applications, esthetics make all-ceramic prostheses compelling choices but despite significant improvements in materials properties and toughening mechanisms, these still have significant failure rates. Factors that contribute to the degradation in strength and survival include material selection and prosthesis design which set the upper limit for performance. However, fabrication operations introduce damage that can be exacerbated by environmental conditions and clinical function. Using all-ceramic dental crowns as an example, experimentally derived models provide insight into the relationships between materials properties and initial critical loads to failure. Analysis of fabrication operations suggests strategies to minimize damage. Environmental conditions can create viscoplastic flow of supporting components which can contribute additional stress within the prosthesis. Fatigue is a particularly challenging problem, not only providing the energy to propagate existing damage but, when combined with the wet environment, can create new damage modes. While much is known, the influence of these new damage modes has not been completely elucidated. The role of complex prosthesis geometry and its interaction with other factors on damage initiation and propagation has yet to be well characterized.

Fatigue testing and damage development in continuous fiber reinforced metal matrix composites

NASA Technical Reports Server (NTRS)

Johnson, W. S.

1988-01-01

A general overview of the fatigue behavior of metal matrix composites (MMC) is presented. The first objective is to present experimental procedures and techniques for conducting a meaningful fatigue test to detect and quantify fatigue damage in MMC. These techniques include interpretation of stress-strain responses, acid etching of the matrix, edge replicas of the specimen under load, radiography, and micrographs of the failure surfaces. In addition, the paper will show how stiffness loss in continuous fiber reinforced metal matrix composites can be a useful parameter for detecting fatigue damage initiation and accumulation. Second, numerous examples of how fatigue damage can initiate and grow in various MMC are given. Depending on the relative fatigue behavior of the fiber and matrix, and the interface properties, the failure modes of MMC can be grouped into four categories: (1) matrix dominated, (2) fiber dominated, (3) self-similar damage growth, and (4) fiber/matrix interfacial failures. These four types of damage will be discussed and illustrated by examples with the emphasis on the fatigue of unnotched laminates.

Fatigue testing and damage development in continuous fiber reinforced metal matrix composites

NASA Technical Reports Server (NTRS)

Johnson, W. S.

1989-01-01

A general overview of the fatigue behavior of metal matrix composites (MMC) is presented. The first objective is to present experimental procedures and techniques for conducting a meaningful fatigue test to detect and quantify fatigue damage in MMC. These techniques include interpretation of stress-strain responses, acid etching of the matrix, edge replicas of the specimen under load, radiography, and micrographs of the failure surfaces. In addition, the paper will show how stiffness loss in continuous fiber reinforced metal matrix composites can be a useful parameter for detecting fatigue damage initiation and accumulation. Second, numerous examples of how fatigue damage can initiate and grow in various MMC are given. Depending on the relative fatigue behavior of the fiber and matrix, and the interface properties, the failure modes of MMC can be grouped into four categories: (1) matrix dominated, (2) fiber dominated, (3) self-similar damage growth, and (4) fiber/matrix interfacial failures. These four types of damage will be discussed and illustrated by examples with the emphasis on the fatigue of unnotched laminates.

Depletion of ribosomal protein L37 occurs in response to DNA damage and activates p53 through the L11/MDM2 pathway.

PubMed

Llanos, Susana; Serrano, Manuel

2010-10-01

Perturbation of ribosomal biogenesis has recently emerged as a relevant p53-activating pathway. This pathway can be initiated by depletion of certain ribosomal proteins, which is followed by the binding and inhibition of MDM2 by a different subset of ribosomal proteins that includes L11. Here, we report that depletion of L37 leads to cell cycle arrest in a L11- and p53-dependent manner. DNA damage can initiate ribosomal stress, although little is known about the mechanisms involved. We have found that some genotoxic insults, namely, UV light and cisplatin, lead to proteasomal degradation of L37 in the nucleoplasm and to the ensuing L11-dependent stabilization of p53. Moreover, ectopic L37 overexpression can attenuate the DNA damage response mediated by p53. These results support the concept that DNA damage-induced proteasomal degradation of L37 constitutes a mechanistic link between DNA damage and the ribosomal stress pathway, and is a relevant contributing signaling pathway for the activation of p53 in response to DNA damage.

Analysing hydro-mechanical behaviour of reinforced slopes through centrifuge modelling

NASA Astrophysics Data System (ADS)

Veenhof, Rick; Wu, Wei

2017-04-01

Every year, slope instability is causing casualties and damage to properties and the environment. The behaviour of slopes during and after these kind of events is complex and depends on meteorological conditions, slope geometry, hydro-mechanical soil properties, boundary conditions and the initial state of the soils. This study describes the effects of adding reinforcement, consisting of randomly distributed polyolefin monofilament fibres or Ryegrass (Lolium), on the behaviour of medium-fine sand in loose and medium dense conditions. Direct shear tests were performed on sand specimens with different void ratios, water content and fibre or root density, respectively. To simulate the stress state of real scale field situations, centrifuge model tests were conducted on sand specimens with different slope angles, thickness of the reinforced layer, fibre density, void ratio and water content. An increase in peak shear strength is observed in all reinforced cases. Centrifuge tests show that for slopes that are reinforced the period until failure is extended. The location of shear band formation and patch displacement behaviour indicate that the design of slope reinforcement has a significant effect on the failure behaviour. Future research will focus on the effect of plant water uptake on soil cohesion.

Unusual plastic deformation and damage features in titanium: Experimental tests and constitutive modeling

NASA Astrophysics Data System (ADS)

Revil-Baudard, Benoit; Cazacu, Oana; Flater, Philip; Chandola, Nitin; Alves, J. L.

2016-03-01

In this paper, we present an experimental study on plastic deformation and damage of polycrystalline pure HCP Ti, as well as modeling of the observed behavior. Mechanical characterization data were conducted, which indicate that the material is orthotropic and displays tension-compression asymmetry. The ex-situ and in-situ X-ray tomography measurements conducted reveal that damage distribution and evolution in this HCP Ti material is markedly different than in a typical FCC material such as copper. Stewart and Cazacu (2011) anisotropic elastic/plastic damage model is used to describe the behavior. All the parameters involved in this model have a clear physical significance, being related to plastic properties, and are determined from very few simple mechanical tests. It is shown that this model predicts correctly the anisotropy in plastic deformation, and its strong influence on damage distribution and damage accumulation. Specifically, for a smooth axisymmetric specimen subject to uniaxial tension, damage initiates at the center of the specimen, and is diffuse; the level of damage close to failure being very low. On the other hand, for a notched specimen subject to the same loading the model predicts that damage initiates at the outer surface of the specimen, and further grows from the outer surface to the center of the specimen, which corroborates with the in-situ tomography data.

Individual variations in the correlation between erythemal threshold, UV-induced DNA damage and sun-burn cell formation.

PubMed

Heenen, M; Giacomoni, P U; Golstein, P

2001-10-01

A linear correlation between erythema intensity and DNA damage upon exposure to UV has not been firmly established. Many of the deleterious effects of UV exposure do occur after exposure to suberythemal doses. After DNA damage, cells undergo DNA repair. It is commonly accepted that when the burden of damage is beyond the repair capacities, the cell undergoes programmed cell death or apoptosis. The aim of this study is to quantify the amount of UV-induced DNA damage (estimated via the measurement of DNA repair or unscheduled DNA synthesis or UDS) and cellular damage (estimated via the determination of the density of sunburn cells or SBC). If DNA damage and erythema are correlated, similar intensity of UDS and similar density of SBC should be found in volunteers irradiated with a UV dose equal to two minimal erythema doses (MED). Our results show that in 15 different individuals the same relative dose (2 MEDs) provokes UDS values, which vary within a factor of 4. An even larger variability affects SBC counts after the same relative dose. When DNA damage or SBC are plotted versus the absolute dose (i.e. the dose expressed in J/m(2)), there is a rough correlation (with several exceptions) between dose and extent of UDS and SBC counts. It seems possible to divide the volunteers into two subpopulations with different susceptibilities to UV damage. It is well known that UDS and SBC measurements are often affected by large experimental indeterminacy, yet, the analysis of our results makes it plausible to suggest that for the triggering of erythema, a common threshold value for DNA damage or for SBC count are not to be found. In conclusion, the erythema response seems to be loosely correlated with DNA damage. This suggests that the protection offered by the sunscreens against DNA damage, the molecular basis of UV-induced mutagenesis, might not be related to the sun protection factor (SPF) indicated on the label of sunscreens, which is evaluated using the erythema as an endpoint.

Impact of different cleaning processes on the laser damage threshold of antireflection coatings for Z-Backlighter optics at Sandia National Laboratories

DOE Office of Scientific and Technical Information (OSTI.GOV)

Field, Ella; Bellum, John; Kletecka, Damon

We have examined how different cleaning processes affect the laser-induced damage threshold of antireflection coatings for large dimension, Z-Backlighter laser optics at Sandia National Laboratories. Laser damage thresholds were measured after the coatings were created, and again 4 months later to determine which cleaning processes were most effective. There is a nearly twofold increase in laser-induced damage threshold between the antireflection coatings that were cleaned and those that were not cleaned. Aging of the coatings after 4 months resulted in even higher laser-induced damage thresholds. Also, the laser-induced damage threshold results revealed that every antireflection coating had a high defectmore » density, despite the cleaning process used, which indicates that improvements to either the cleaning or deposition processes should provide even higher laser-induced damage thresholds.« less

Impact of different cleaning processes on the laser damage threshold of antireflection coatings for Z-Backlighter optics at Sandia National Laboratories

DOE PAGES

Field, Ella; Bellum, John; Kletecka, Damon

2014-11-06

We have examined how different cleaning processes affect the laser-induced damage threshold of antireflection coatings for large dimension, Z-Backlighter laser optics at Sandia National Laboratories. Laser damage thresholds were measured after the coatings were created, and again 4 months later to determine which cleaning processes were most effective. There is a nearly twofold increase in laser-induced damage threshold between the antireflection coatings that were cleaned and those that were not cleaned. Aging of the coatings after 4 months resulted in even higher laser-induced damage thresholds. Also, the laser-induced damage threshold results revealed that every antireflection coating had a high defectmore » density, despite the cleaning process used, which indicates that improvements to either the cleaning or deposition processes should provide even higher laser-induced damage thresholds.« less

Induction and repair of DNA strand breaks in bovine lens epithelial cells after high LET irradiation

NASA Astrophysics Data System (ADS)

Baumstark-Khan, C.; Heilmann, J.; Rink, H.

The lens epithelium is the initiation site for the development of radiation induced cataracts. While in the cortex and nucleus radiation interacts with proteins, experimental results from cultured lenses and lens epithelial cells demonstrate mutagenic and cytotoxic effects in the epithelium. It is suggested that incorrectly repaired DNA damage may be lethal in terms of cellular reproduction and also may initiate the development of mutations or transformations in surviving cells. The occurrence of such genetically modified cells may lead to lens opacification. For a quantitative risk estimation for astronauts and space travelers it is necessary to know the radiation's relative biological effectiveness (RBE), because cosmic rays differ significantly from X-rays. RBEs for the induction of DNA strand breaks and the efficiency of repair of these breaks were measured in cultured diploid bovine lens epithelial cells exposed to different LET irradiations. Irradiations were performed either with 300 kV X-rays or at the UNILAC accelerator at GSI. Accelerated ions from Z=8 (O) to Z=92 (U) were used. For strand break measurements hydroxyapatite chromatography of alka-line unwound DNA (overall strand breaks) and non-denaturing filter elution technique (double strand breaks) were applied. Experiments showed that DNA damage occurs as a function of dose, of kinetic energy and of LET. For particles having the same LET the severity of the DNA damage increases with dose. For a given particle dose, as the LET rises, the numbers of DNA strand breaks increase to a maximum and then reach a plateau or decrease. Repair kinetics depend on the fluence (irradiation dose). At any LET value, repair is much slower after heavy ion exposure than after X-irradiation. For ions with an LET of less than 10,000 keV/μm more than 90 percent of the strand breaks induced are repaired within 24 hours. At higher particle fluences, especially for low energetic particles with a very high local density of energy deposition within the particle track, a higher proportion of non-rejoined breaks is found, even after prolonged periods of incubation. At the highest LET value (16,300 keV/μm) no significant repair is observed. These observations are consistent with the current theory of the mechanism of radiation induced cataractogenesis which posts that genomic damage to the epithelial cells surviving the exposure is responsible for lens opacification.

Sensitivity to methylmercury toxicity is enhanced in oxoguanine glycosylase 1 knockout murine embryonic fibroblasts and is dependent on cellular proliferation capacity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ondovcik, Stephanie L.; Tamblyn, Laura; McPherson, John Peter

2013-07-01

Methylmercury (MeHg) is a persistent environmental contaminant with potent neurotoxic action for which the underlying molecular mechanisms remain to be conclusively delineated. Our objectives herein were twofold: first, to corroborate our previous findings of an increased sensitivity of spontaneously-immortalized oxoguanine glycosylase 1-null (Ogg1{sup −/−}) murine embryonic fibroblasts (MEFs) to MeHg through generation of Simian virus 40 (SV40) large T antigen-immortalized wild-type and Ogg1{sup −/−} MEFs; and second, to determine whether MeHg toxicity is proliferation-dependent. As with the spontaneously-immortalized cells used previously, the SV40 large T antigen-immortalized cells exhibited similar tendencies to undergo MeHg-initiated cell cycle arrest, with increased sensitivity inmore » the Ogg1{sup −/−} MEFs as measured by clonogenic survival and DNA damage. Compared to exponentially growing cells, those seeded at a higher density exhibited compromised proliferation, which proved protective against MeHg-mediated cell cycle arrest and induction of DNA double strand breaks (DSBs), measured by phosphorylation of the core histone H2A variant (H2AX) on serine 139 (γH2AX), and by its functional confirmation by micronucleus assessment. This enhanced sensitivity of Ogg1{sup −/−} MEFs to MeHg toxicity using discrete SV40 immortalization corroborates our previous studies, and suggests a novel role for OGG1 in minimizing MeHg-initiated DNA lesions that trigger replication-associated DSBs. Furthermore, proliferative capacity may determine MeHg toxicity in vivo and in utero. Accordingly, variations in cellular proliferative capacity and interindividual variability in repair activity may modulate the risk of toxicological consequences following MeHg exposure. - Highlights: • SV40 large T antigen-immortalized Ogg1{sup −/−} cells are more sensitive to MeHg. • Sensitivity to MeHg is dependent on cellular proliferation capacity. • OGG1 maintains genomic integrity following MeHg-initiated DNA damage. • OGG1 may limit MeHg-initiated DNA lesions that trigger replication-associated DSBs. • Variations in proliferation and repair activity may modulate toxicological risk.« less

Physiological responses to acid stress by Saccharomyces cerevisiae when applying high initial cell density

PubMed Central

2016-01-01

High initial cell density is used to increase volumetric productivity and shorten production time in lignocellulosic hydrolysate fermentation. Comparison of physiological parameters in high initial cell density cultivation of Saccharomyces cerevisiae in the presence of acetic, formic, levulinic and cinnamic acids demonstrated general and acid-specific responses of cells. All the acids studied impaired growth and inhibited glycolytic flux, and caused oxidative stress and accumulation of trehalose. However, trehalose may play a role other than protecting yeast cells from acid-induced oxidative stress. Unlike the other acids, cinnamic acid did not cause depletion of cellular ATP, but abolished the growth of yeast on ethanol. Compared with low initial cell density, increasing initial cell density reduced the lag phase and improved the bioconversion yield of cinnamic acid during acid adaptation. In addition, yeast cells were able to grow at elevated concentrations of acid, probable due to the increase in phenotypic cell-to-cell heterogeneity in large inoculum size. Furthermore, the specific growth rate and the specific rates of glucose consumption and metabolite production were significantly lower than at low initial cell density, which was a result of the accumulation of a large fraction of cells that persisted in a viable but non-proliferating state. PMID:27620460

Effect of initial densities in the lattice Boltzmann model for non-ideal fluid with curved interface

NASA Astrophysics Data System (ADS)

Gong, Jiaming; Oshima, Nobuyuki

2017-06-01

The effect of initial densities in a free energy based two-phase-flow lattice Boltzmann method for non-ideal fluids with a curved interface was investigated in the present work. To investigate this effect, the initial densities in the liquid and gas phases coming from the saturation points and the equilibrium state were adopted in the simulation of a static droplet in an open and a closed system. For the purpose of simplicity and easier comparison, the closed system is fabricated by the implementation of the periodic boundary condition at the inlet and outlet of a gas channel, and the open system is fabricated by the implementation of a constant flux boundary condition at the inlet and a free-out boundary condition at the outlet of the same gas channel. By comparing the simulation results from the two types of initial densities in the open and closed systems, it is proven that the commonly used saturation initial densities setting is the reason for droplet mass and volume variation which occurred in the simulation, particularly in the open system with a constant flux boundary condition. Such problems are believed to come from the curvature effect of the surface tension and can be greatly reduced by adopting the initial densities in the two phases from equilibrium state.

Seasonal occurrence and impact of Halyomorpha halys (Hemiptera: Pentatomidae) in tree fruit.

PubMed

Nielsen, Anne L; Hamilton, George C

2009-06-01

Halyomorpha halys is an introduced stink bug species from Asia that is spreading throughout the Mid-Atlantic United States. It is native to South Korea, Japan, and eastern China, where it is an occasional pest of tree fruit, including apple and pear. Cage experiments with adults placed on apple and peach during critical plant growth stages demonstrate that it can cause damage to developing fruit during mid- and late season growth periods and that feeding occurs on all regions of the fruit. Feeding that occurred during pit hardening/mid-season and final swell periods were apparent as damage at harvest, whereas feeding at shuck split/petal fall in peaches and apples caused fruit abscission. Tree fruit at two commercial farms were sampled weekly in 2006-2007 to determine H. halys seasonality. Low densities of nymphs in apple suggest that it is an unsuitable developmental host. Both nymphs and adults were found on pear fruits with peak populations occurring in early July and mid-August, the time when pit hardening/mid-season and swell period damage occurs. At both farms, stink bug damage was greater than 25% damaged fruit per tree. We attribute this to H. halys because population densities were significantly higher than native pentatomids at both locations in both beat samples and blacklight trap captures. The data presented here documents the potential for H. halys to cause damage in orchards throughout the Mid-Atlantic United States and shows the need for development of appropriate control strategies.

Land cover as an important factor for landslide risk assessment

NASA Astrophysics Data System (ADS)

Promper, C.; Glade, T.; Puissant, A.; Malet, J.-P.

2012-04-01

Landcover change is a crucial component of hazard and vulnerability in terms of quantification of possible future landslide risk, and the importance for spatial planners but also individuals is obvious. Damage of property, losses of agricultural land, loss of production but also damaged infrastructures and fatalities may be the result of landslide hazards. To avoid these economic damages as well as possible fatalities in the future, a method of assessing spatial but also temporal patterns of landslides is necessary. This study represents results of landcover modeling as a first step to the proposition of scenario of landslide risk for the future. The method used for future land cover analysis is the CLUE modeling framework combining past and actual observed landcover conditions. The model is based on a statistical relationship between the actual land cover and driving forces. The allocation of landcover pixel is modified by possible autonomous developments and competition between land use types. (Verburg et al. 1999) The study area is located in a district in the alpine foreland of Lower Austria: Waidhofen/Ybbs, of about 130km2. The topography is characterized by narrow valleys, flat plateau and steep slopes. The landcover is characterized by region of densely populated areas in the valley bottom along the Ybbs River, and a series of separated farm houses on the top of the plateau. Population density is about 90 persons / km2 which represent the observed population density of Austria. The initial landcover includes forest, grassland, culture, built-up areas and individual farms. Most of the observed developments are controlled by the topography (along the valleys) and the actual road network. The results of the landcover model show different scenarios of changes in the landslide prone landcover types. These maps will be implemented into hazard analysis but also into vulnerability assessment regarding elements at risk. Verburg, P.H., de Koning, G.H.J., Kok, K., Veldkamp, A. & Bouma, J. 1999. A spatial explicit allocation procedure for modelling the pattern of land use change based upon actual land use. Ecological Modelling 116 (1): 45-61.

An Interface Damage Model for the Simulation of Delamination Under Variable-Mode Ratio in Composite Materials

NASA Technical Reports Server (NTRS)

Turon, Albert; Camanho, Pedro P.; Costa, Josep; Davila, Carlos G.

2004-01-01

A thermodynamically consistent damage model for the simulation of progressive delamination under variable mode ratio is presented. The model is formulated in the context of the Damage Mechanics (DM). The constitutive equations that result from the variation of the free energy with damage are used to model the initiation and propagation of delamination. A new delamination initiation criterion is developed to assure that the formulation can account for changes in the loading mode in a thermodynamically consistent way. Interfacial penetration of two adjacent layers after complete decohesion is prevented by the formulation of the free energy. The model is implemented into the commercial finite element code ABAQUS by means of a user-written decohesion element. Finally, the numerical predictions given by the model are compared with experimental results.

Dissociating basal forebrain and medial temporal amnesic syndromes: insights from classical conditioning.

PubMed

Myer, Catherine E; Bryant, Deborah; DeLuca, John; Gluck, Mark A

2002-01-01

In humans, anterograde amnesia can result from damage to the medial temporal (MT) lobes (including hippocampus), as well as to other brain areas such as basal forebrain. Results from animal classical conditioning studies suggest that there may be qualitative differences in the memory impairment following MT vs. basal forebrain damage. Specifically, delay eyeblink conditioning is spared after MT damage in animals and humans, but impaired in animals with basal forebrain damage. Recently, we have likewise shown delay eyeblink conditioning impairment in humans with amnesia following anterior communicating artery (ACoA) aneurysm rupture, which damages the basal forebrain. Another associative learning task, a computer-based concurrent visual discrimination, also appears to be spared in MT amnesia while ACoA amnesics are slower to learn the discriminations. Conversely, animal and computational models suggest that, even though MT amnesics may learn quickly, they may learn qualitatively differently from controls, and these differences may result in impaired transfer when familiar information is presented in novel combinations. Our initial data suggests such a two-phase learning and transfer task may provide a double dissociation between MT amnesics (spared initial learning but impaired transfer) and ACoA amnesics (slow initial learning but spared transfer). Together, these emerging data suggest that there are subtle but dissociable differences in the amnesic syndrome following damage to the MT lobes vs. basal forebrain, and that these differences may be most visible in non-declarative tasks such as eyeblink classical conditioning and simple associative learning.

FEM investigation of concrete silos damaged and reinforced externally with CFRP

NASA Astrophysics Data System (ADS)

Kermiche, Sihem; Boussaid, Ouzine; Redjel, Bachir; Amirat, Abdelaziz

2018-03-01

The present work investigates the reinforcement of concrete wheat-grain silos under initial damage. The reinforcement is achieved by mounting bands of carbon fiber reinforced polymer (CFRP) on the external walls of the silo. 4 modes of reinforcement are adapted according to the width of the band, the gap between two bands, the height of reinforcement and the number of layers achieved through banding. Analytical analyses were conducted using the Reimbert method and the Eurocode 1 Part 4 method, as well as numerically through the finite element software Abaqus. Results show that the normal pressure reaches a peak value when approaching the silo hopper. Initial damage in a concrete silo was first determined using a 3D geometrical model, while the damage analyses were conducted to optimize the CFRP reinforcement by mounting 2 CFRP bands close together above and below the cylinder-hopper joint. Increasing the number of banding layers could produce better performance as the damage was slightly decreased from 0.161 to 0.152 for 1 and 4 layers respectively.

Fatigue Life of Postbuckled Structures with Indentation Damage

NASA Technical Reports Server (NTRS)

Davila, Carlos G.; Bisagni, Chiara

2016-01-01

The fatigue life of composite stiffened panels with indentation damage was investigated experimentally using single stringer compression specimens. Indentation damage was induced on one of the two flanges of the stringer. The experiments were conducted using advanced instrumentation, including digital image correlation, passive thermography, and in-situ ultrasonic scanning. Specimens with initial indentation damage lengths of 37 millimeters to 56 millimeters were tested in fatigue and the effects of cyclic load amplitude and damage size were studied. A means of comparison of the damage propagation rates and collapse loads based on a stress intensity measure and the Paris law is proposed.

Changes in Mauna Kea Dry Forest Structure 2000-2014

USGS Publications Warehouse

Banko, Paul C.; Brinck, Kevin W.

2014-01-01

Changes in the structure of the subalpine vegetation of Palila Critical Habitat on the southwestern slope of Mauna Kea Volcano, Hawai‘i, were analyzed using 12 metrics of change in māmane (Sophora chrysophylla) and naio (Myoporum sandwicense) trees surveyed on plots in 2000 and 2014. These two dominant species were analyzed separately, and changes in their structure indicated changes in the forest’s health. There was a significant increase in māmane minimum crown height (indicating a higher ungulate “browse line”), canopy area, canopy volume, percentage of trees with ungulate damage, and percentage of dead trees. No significant changes were observed in māmane maximum crown height, proportion of plots with trees, sapling density, proportion of plots with saplings, or the height distribution of trees. The only significant positive change was for māmane tree density. Significantly negative changes were observed for naio minimum crown height, tree height, canopy area, canopy volume, and percentage of dead trees. No significant changes were observed in naio tree density, proportion of plots with trees, proportion of plots with saplings, or percentage of trees with ungulate damage. Significantly positive changes were observed in naio sapling density and the height distribution of trees. There was also a significant increase in the proportion of māmane vs. naio trees in the survey area. The survey methods did not allow us to distinguish among potential factors driving these changes for metrics other than the percentage of trees with ungulate damage. Continued ungulate browsing and prolonged drought are likely the factors contributing most to the observed changes in vegetation, but tree disease or insect infestation of māmane, or naio, and competition from alien grasses and other weeds could also be causing or exacerbating the impacts to the forest. Although māmane tree density has increased since 2000, this study also demonstrates that efforts by managers to remove sheep (Ovis spp.) from Palila Critical Habitat have not overcome the ability of sheep to continue to damage māmane trees and impede restoration of the vegetation.

Recent corrections to meteoroid environment models

NASA Astrophysics Data System (ADS)

Moorhead, A.; Brown, P.; Campbell-Brown, M. D.; Moser, D. E.; Blaauw, R. C.; Cooke, W.

2017-12-01

The dynamical and physical characteristics of a meteoroid affects its behavior in the atmosphere and the damage it does to spacecraft surfaces. Accurate environment models must therefore correctly describe the speed, size, density, and direction of meteoroids. However, the measurement of dynamical characteristics such as speed is subject to observational biases, and physical properties such as size and density cannot be directly measured. De-biasing techniques and proxies are needed to overcome these challenges. In this presentation, we discuss several recent improvements to the derivation of the meteoroid velocity, directionality, and bulk density distributions. We derive our speed distribution from observations made by the Canadian Meteor Orbit Radar. These observations are de-biased using modern descriptions of the ionization efficiency and sharpened to remove the effects of measurement uncertainty, and the result is a meteoroid speed distribution that is skewed slower than in previous analyses. We also adopt a higher fidelity density distribution than that used by many older models. In our distribution, meteoroids with TJ < 2 are assigned to a low-density population, while those with TJ > 2 have higher densities. This division and the distributions themselves are derived from the densities reported by Kikwaya et al. (2009, 2011). These changes have implications for the environment. For instance, helion and antihelion meteors have lower speeds and higher densities than apex and toroidal meteors. A slower speed distribution therefore corresponds to a sporadic environment that is more completely dominated by the helion and antihelion sources than in previous models. Finally, assigning these meteors high densities further increases their significance from a spacecraft damage perspective.

Recent Corrections to Meteoroid Environment Models

NASA Technical Reports Server (NTRS)

Moorhead, A. V.; Brown, P. G.; Campbell-Brown, M. D.; Moser, D. E.; Blaauw, R. C.; Cooke, W. J.

2017-01-01

The dynamical and physical characteristics of a meteoroid affects its behavior in the atmosphere and the damage it does to spacecraft surfaces. Accurate environment models must therefore correctly describe the speed, size, density, and direction of meteoroids. However, the measurement of dynamical characteristics such as speed is subject to observational biases, and physical properties such as size and density cannot be directly measured. De-biasing techniques and proxies are needed to overcome these challenges. In this presentation, we discuss several recent improvements to the derivation of the meteoroid velocity, directionality, and bulk density distributions. We derive our speed distribution from observations made by the Canadian Meteor Orbit Radar. These observations are de-biased using modern descriptions of the ionization efficiency and sharpened to remove the effects of measurement uncertainty, and the result is a meteoroid speed distribution that is skewed slower than in previous analyses. We also adopt a higher fidelity density distribution than that used by many older models. In our distribution, meteoroids with T(sub J) less than 2 are assigned to a low-density population, while those with T(sub J) greater than 2 have higher densities. This division and the distributions themselves are derived from the densities reported by Kikwaya et al. (2009, 2011). These changes have implications for the environment. For instance, helion and antihelion meteors have lower speeds and higher densities than apex and toroidal meteors. A slower speed distribution therefore corresponds to a sporadic environment that is more completely dominated by the helion and antihelion sources than in previous models. Finally, assigning these meteors high densities further increases their significance from a spacecraft damage perspective.

Forest Health Monitoring in Vermont, 1996-1999

Treesearch

Northeastern Research Station

2002-01-01

Vermont forests vary in size and age class. Trees are distributed evenly between hardwood and softwood species but hardwood dominated the seedling sample. Most of the trees are healthy, with full crowns (low transparency, high density), little dieback and little damage. White and green ash had higher transparencies and lower crown densities possibly explained by the...

A Micro-Mechanism-Based Continuum Corrosion Fatigue Damage Model for Steels

NASA Astrophysics Data System (ADS)

Sun, Bin; Li, Zhaoxia

2018-05-01

A micro-mechanism-based corrosion fatigue damage model is developed for studying the high-cycle corrosion fatigue of steel from multi-scale viewpoint. The developed physical corrosion fatigue damage model establishes micro-macro relationships between macroscopic continuum damage evolution and collective evolution behavior of microscopic pits and cracks, which can be used to describe the multi-scale corrosion fatigue process of steel. As a case study, the model is used to predict continuum damage evolution and number density of the corrosion pit and short crack of steel component in 5% NaCl water under constant stress amplitude at 20 kHz, and the numerical results are compared with experimental results. It shows that the model is effective and can be used to evaluate the continuum macroscopic corrosion fatigue damage and study microscopic corrosion fatigue mechanisms of steel.

A Micro-Mechanism-Based Continuum Corrosion Fatigue Damage Model for Steels

NASA Astrophysics Data System (ADS)

Sun, Bin; Li, Zhaoxia

2018-04-01

A micro-mechanism-based corrosion fatigue damage model is developed for studying the high-cycle corrosion fatigue of steel from multi-scale viewpoint. The developed physical corrosion fatigue damage model establishes micro-macro relationships between macroscopic continuum damage evolution and collective evolution behavior of microscopic pits and cracks, which can be used to describe the multi-scale corrosion fatigue process of steel. As a case study, the model is used to predict continuum damage evolution and number density of the corrosion pit and short crack of steel component in 5% NaCl water under constant stress amplitude at 20 kHz, and the numerical results are compared with experimental results. It shows that the model is effective and can be used to evaluate the continuum macroscopic corrosion fatigue damage and study microscopic corrosion fatigue mechanisms of steel.

Early density management of longleaf pine reduces susceptibility to ice storm damage

Treesearch

Timothy B. Harrington; Thaddeus A. Harrington

2016-01-01

The Pax winter storm of February 2014 caused widespread damage to forest stands throughout the southeastern U.S. In a long-term study of savanna plant community restoration at the Savannah River Site, Aiken, SC, precommercial thinning (PCT) of 8- to 11-year-old plantations of longleaf pine (Pinus palustris) in 1994 reduced...

Verde plant bug, Creontiades signatus (Hemiptera: Miridae) effects of insect density and bloom period of infestation on cotton damage and yield

USDA-ARS?s Scientific Manuscript database

The verde plant bug, Creontiades signatus Distant (Hemiptera: Miridae), has emerged as a threat to cotton in South Texas, causing boll damage similar to boll-feeding stink bugs (Hemiptera: Pentatomidae). Verde plant bugs were released into caged cotton for a one-week period to characterize the effec...

Effects of laser power density and initial grain size in laser shock punching of pure copper foil

NASA Astrophysics Data System (ADS)

Zheng, Chao; Zhang, Xiu; Zhang, Yiliang; Ji, Zhong; Luan, Yiguo; Song, Libin

2018-06-01

The effects of laser power density and initial grain size on forming quality of holes in laser shock punching process were investigated in the present study. Three different initial grain sizes as well as three levels of laser power densities were provided, and then laser shock punching experiments of T2 copper foil were conducted. Based upon the experimental results, the characteristics of shape accuracy, fracture surface morphology and microstructures of punched holes were examined. It is revealed that the initial grain size has a noticeable effect on forming quality of holes punched by laser shock. The shape accuracy of punched holes degrades with the increase of grain size. As the laser power density is enhanced, the shape accuracy can be improved except for the case in which the ratio of foil thickness to initial grain size is approximately equal to 1. Compared with the fracture surface morphology in the quasistatic loading conditions, the fracture surface after laser shock can be divided into three zones including rollover, shearing and burr. The distribution of the above three zones strongly relates with the initial grain size. When the laser power density is enhanced, the shearing depth is not increased, but even diminishes in some cases. There is no obvious change of microstructures with the enhancement of laser power density. However, while the initial grain size is close to the foil thickness, single-crystal shear deformation may occur, suggesting that the ratio of foil thickness to initial grain size has an important impact on deformation behavior of metal foil in laser shock punching process.

Experimental test of an eco-evolutionary dynamic feedback loop between evolution and population density in the green peach aphid.

PubMed

Turcotte, Martin M; Reznick, David N; Daniel Hare, J

2013-05-01

An eco-evolutionary feedback loop is defined as the reciprocal impacts of ecology on evolutionary dynamics and evolution on ecological dynamics on contemporary timescales. We experimentally tested for an eco-evolutionary feedback loop in the green peach aphid, Myzus persicae, by manipulating initial densities and evolution. We found strong evidence that initial aphid density alters the rate and direction of evolution, as measured by changes in genotype frequencies through time. We also found that evolution of aphids within only 16 days, or approximately three generations, alters the rate of population growth and predicts density compared to nonevolving controls. The impact of evolution on population dynamics also depended on density. In one evolution treatment, evolution accelerated population growth by up to 10.3% at high initial density or reduced it by up to 6.4% at low initial density. The impact of evolution on population growth was as strong as or stronger than that caused by a threefold change in intraspecific density. We found that, taken together, ecological condition, here intraspecific density, alters evolutionary dynamics, which in turn alter concurrent population growth rate (ecological dynamics) in an eco-evolutionary feedback loop. Our results suggest that ignoring evolution in studies predicting population dynamics might lead us to over- or underestimate population density and that we cannot predict the evolutionary outcome within aphid populations without considering population size.

Thermomechanical Fatigue Damage/Failure Mechanisms in SCS-6/Timetal 21S [0/90](Sub S) Composite

NASA Technical Reports Server (NTRS)

Castelli, Michael G.

1994-01-01

The thermomechanical fatigue (TMF) deformation, damage, and life behaviors of SCS6/Timetal 21S (0/90)s were investigated under zero-tension conditions. In-phase (IP) and out-of-phase (OP) loadings were investigated with a temperature cycle from 150 to 650 deg C. An advanced TMF test technique was used to quantify mechanically damage progression. The technique incorporated explicit measurements of the macroscopic (1) isothermal static moduli at the temperature extremes of the TMF cycle and (2) coefficient of thermal expansion (CTE) as functions of the TMF cycles. The importance of thermal property degradation and its relevance to accurate post-test data analysis and interpretation is briefly addressed. Extensive fractography and metallography were conducted on specimens from failed and interrupted tests to characterize the extent of damage at the microstructure level. Fatigue life results indicated trends analogous to those established for similar unidirectional(0) reinforced titanium matrix composite systems. High stress IP and mid to low stress OP loading conditions were life-limiting in comparison to maximum temperature isothermal conditions. Dominant damage mechanisms changed with cycle type. Damage resulting from IP TMF conditions produced measurable decreases in static moduli but only minimal changes in the CTE. Metallography on interrupted and failed specimens revealed extensive (0) fiber cracking with sparse matrix damage. No surface initiated matrix cracks were present. Comparable OP TMF conditions initiated environment enhanced surface cracking and matrix cracking initiated at (90) fiber/matrix (F/M) interfaces. Notable static moduli and CTE degradations were measured. Fractography and metallography revealed that the transverse cracks originating from the surface and (90) F/M interfaces tended to converge and coalesce at the (0) fibers.

Does Surface Topography Play a Role in Taper Damage in Head-neck Modular Junctions?

PubMed

Pourzal, Robin; Hall, Deborah J; Ha, Nguyen Q; Urban, Robert M; Levine, Brett R; Jacobs, Joshua J; Lundberg, Hannah J

2016-10-01

There are increasing reports of total hip arthroplasty failure subsequent to modular taper junction corrosion. The surfaces of tapers are machined to have circumferential machining marks, resulting in a surface topography of alternating peaks and valleys on the scale of micrometers. It is unclear if the geometry of this machined surface topography influences the degree of fretting and corrosion damage present on modular taper junctions or if there are differences between modular taper junction material couples. (1) What are the differences in damage score and surface topography between CoCr/CoCr and CoCr/Ti modular junctions? (2) How are initial surface topography, flexural rigidity, taper angle mismatch, and time in situ related to visual taper damage scores for CoCr/CoCr couples? (3) How are initial surface topography, flexural rigidity, taper angle mismatch, and time in situ related to visual taper damage scores for CoCr/Ti couples? Damage on stem and head tapers was evaluated with a modified Goldberg score. Differences in damage scores were determined between a group of 140 CoCr/CoCr couples and 129 CoCr/Ti couples using a chi-square test. For a subgroup of 70 retrievals, selected at random, we measured five variables, including initial stem taper machining mark height and spacing, initial head taper roughness, flexural rigidity, and taper angle mismatch. All retrievals were obtained at revision surgeries. None were retrieved as a result of metal-on-metal failures or were recalled implants. Components were chosen so there was a comparable number of each material couple and damage score. Machining marks around the circumference of the tapers were measured using white light interferometry to characterize the initial stem taper surface topography in terms of the height of and spacing between machining mark peaks as well as initial head taper roughness. The taper angle mismatch was assessed with a coordinate measuring machine. Flexural rigidity was determined based on measurements of gross taper dimensions and material properties. Differences of median or mean values of all variables between material couples were determined (Wilcoxon rank-sum tests and t-tests). The effect of all five variables along with time in situ on stem and head taper damage scores was tested with a multiple regression model. With 70 retrievals, a statistical power of 0.8 could be achieved for the model. Damage scores were different between CoCr/CoCr and CoCr/Ti modular taper junction material couples. CoCr/CoCr stem tapers were less likely to be mildly damaged (11%, p = 0.006) but more likely to be severely damaged (4%, p = 0.02) than CoCr/Ti stem tapers (28% and 1%, respectively). CoCr/CoCr couples were less likely to have moderately worn head tapers (7% versus 17%, p = 0.003). Stem taper machining mark height and spacing and head taper roughness were 11 (SD 3), 185 (SD 46), and 0.57 (SD 0.5) for CoCr/CoCr couples and 10 (SD 3), 170 (SD 56), and 0.64 (SD 0.4) for CoCr/Ti couples, respectively. There was no difference (p = 0.09, p = 0.1, p = 0.16, respectively) for either factor between material couples. Larger stem taper machining mark heights (p = 0.001) were associated with lower stem taper damage scores, and time in situ (p = 0.006) was associated with higher stem taper damage scores for CoCr/CoCr material couples. Stem taper machining marks that had higher peaks resulted in slower damage progression over time. For CoCr/Ti material couples, head taper roughness was associated with higher stem (p = 0.001) and head taper (p = 0.003) damage scores, and stem taper machining mark height, but not time in situ, was associated with lower stem taper damage scores (p = 0.007). Stem taper surface topography was related to damage scores on retrieved head-neck modular junctions; however, it affected CoCr/CoCr and CoCr/Ti couples differently. A taper topography of circumferential machining marks with higher peaks appears to enable slower damage progression and, subsequently, a reduction of the reported release of corrosion products. This may be of interest to implant designers and manufacturers in an effort to reduce the effects of metal release from modular femoral components.

Berberine attenuates oxidative stress and hepatocytes apoptosis via protecting mitochondria in blunt snout bream Megalobrama amblycephala fed high-fat diets.

PubMed

Lu, Kang-Le; Wang, Li-Na; Zhang, Ding-Dong; Liu, Wen-Bin; Xu, Wei-Na

2017-02-01

High-fat diets may have favorable effects on growth and cost, but high-fat diets often induce excessive fat deposition, resulting in liver damage. This study aimed to identify the hepatoprotective of a Chinese herb (berberine) for blunt snout bream (Megalobrama amblycephala). Fish were fed with a normal diet (LFD, 5 % fat), high-fat diet (HFD, 15 % fat) or berberine-supplemented diets (BSD, 15 % fat with berberine 50 or 100 mg/kg level) for 8 weeks. After the feeding, histology, oxidative status and mitochondrial function of liver were assessed. The results showed that HFD caused fat accumulation, oxidative stress and apoptosis in hepatocytes of fish. Hepatocytes in HFD group appeared to be hypertrophied, with larger liver cells diameter than these of LFD group. Berberine-supplemented diets could attenuate oxidative stress and hepatocytes apoptosis. HFD induced the decreasing mitochondrial complexes activities and bulk density and surface area density. Berberine improved function of mitochondrial respiratory chain via increasing the complex activities. Moreover, the histological results showed that berberine has the potential to repair mitochondrial ultrastructural damage and elevate the density in cells. In conclusion, our study demonstrated that berberine has attenuated liver damage induced by the high fat mainly via the protection for mitochondria.

Progressive Fracture and Damage Tolerance of Composite Pressure Vessels

NASA Technical Reports Server (NTRS)

Chamis, Christos C.; Gotsis, Pascal K.; Minnetyan, Levon

1997-01-01

Structural performance (integrity, durability and damage tolerance) of fiber reinforced composite pressure vessels, designed for pressured shelters for planetary exploration, is investigated via computational simulation. An integrated computer code is utilized for the simulation of damage initiation, growth, and propagation under pressure. Aramid fibers are considered in a rubbery polymer matrix for the composite system. Effects of fiber orientation and fabrication defect/accidental damages are investigated with regard to the safety and durability of the shelter. Results show the viability of fiber reinforced pressure vessels as damage tolerant shelters for planetary colonization.

A picture on the wall: innovative mapping reveals cold-water coral refuge in submarine canyon.

PubMed

Huvenne, Veerle A I; Tyler, Paul A; Masson, Doug G; Fisher, Elizabeth H; Hauton, Chris; Hühnerbach, Veit; Le Bas, Timothy P; Wolff, George A

2011-01-01

Cold-water corals are azooxanthellate species found throughout the ocean at water depths down to 5000 m. They occur in patches, reefs or large mound structures up to 380 m high, and as ecosystem engineers create important habitats for a diverse fauna. However, the majority of these habitats are now within reach of deep-sea bottom trawling. Many have been severely damaged or are under threat, despite recent protection initiatives. Here we present a cold-water coral habitat type that so far has been overlooked--quite literally--and that has received minimal impact from human activities. Vertical and overhanging cliffs in deep-sea canyons, revealed using an innovative approach to marine habitat mapping, are shown to provide the perfect substratum for extensive cold-water coral-based communities. Typical canyon-related processes, including locally enhanced internal tides and focussed downslope organic carbon transport, provide favourable environmental conditions (current regime, food input) to sustain the communities, even outside the optimal depth and density envelopes reported elsewhere in the NE Atlantic. Our findings show that deep-sea canyons can form natural refuges for faunal communities sensitive to anthropogenic disturbance, and have the potential to fulfil the crucial role of larval sources for the recolonisation of damaged sites elsewhere on the margin.

A Picture on the Wall: Innovative Mapping Reveals Cold-Water Coral Refuge in Submarine Canyon

PubMed Central

Huvenne, Veerle A. I.; Tyler, Paul A.; Masson, Doug G.; Fisher, Elizabeth H.; Hauton, Chris; Hühnerbach, Veit; Le Bas, Timothy P.; Wolff, George A.

2011-01-01

Cold-water corals are azooxanthellate species found throughout the ocean at water depths down to 5000 m. They occur in patches, reefs or large mound structures up to 380 m high, and as ecosystem engineers create important habitats for a diverse fauna. However, the majority of these habitats are now within reach of deep-sea bottom trawling. Many have been severely damaged or are under threat, despite recent protection initiatives. Here we present a cold-water coral habitat type that so far has been overlooked – quite literally – and that has received minimal impact from human activities. Vertical and overhanging cliffs in deep-sea canyons, revealed using an innovative approach to marine habitat mapping, are shown to provide the perfect substratum for extensive cold-water coral-based communities. Typical canyon-related processes, including locally enhanced internal tides and focussed downslope organic carbon transport, provide favourable environmental conditions (current regime, food input) to sustain the communities, even outside the optimal depth and density envelopes reported elsewhere in the NE Atlantic. Our findings show that deep-sea canyons can form natural refuges for faunal communities sensitive to anthropogenic disturbance, and have the potential to fulfil the crucial role of larval sources for the recolonisation of damaged sites elsewhere on the margin. PMID:22194903

Polymer brush covalently attached to OH-functionalized mica surface via surface-initiated ATRP: control of grafting density and polymer chain length.

PubMed

Lego, Béatrice; François, Marion; Skene, W G; Giasson, Suzanne

2009-05-05

The controlled grafting density of poly(tert-butyl acrylate) was studied on OH-activated mica substrates via surface-initiated atom-transfer radical polymerization (ATRP). By properly adjusting parameters such as the immobilization reaction time and the concentration of an ATRP initiator, a wide range of initiator surface coverages and hence polymer densities on mica were possible. The covalently immobilized initiator successfully promoted the polymerization of tert-butyl acrylate on mica surfaces. The resulting polymer layer thickness was measured by AFM using a step-height method. Linear relationships of the polymer thickness with respect to the molecular weight of the free polymer and with respect to the monomer conversion were observed, suggesting that ATRP is well controlled and relatively densely end-grafted layers were obtained. The polymer grafting density controlled by adjusting the initiator surface coverage was confirmed by the polymer layer swelling capacity and film thickness measurements.

New method for estimating clustering of DNA lesions induced by physical/chemical mutagens using fluorescence anisotropy.

PubMed

Akamatsu, Ken; Shikazono, Naoya; Saito, Takeshi

2017-11-01

We have developed a new method for estimating the localization of DNA damage such as apurinic/apyrimidinic sites (APs) on DNA using fluorescence anisotropy. This method is aimed at characterizing clustered DNA damage produced by DNA-damaging agents such as ionizing radiation and genotoxic chemicals. A fluorescent probe with an aminooxy group (AlexaFluor488) was used to label APs. We prepared a pUC19 plasmid with APs by heating under acidic conditions as a model for damaged DNA, and subsequently labeled the APs. We found that the observed fluorescence anisotropy (r obs ) decreases as averaged AP density (λ AP : number of APs per base pair) increases due to homo-FRET, and that the APs were randomly distributed. We applied this method to three DNA-damaging agents, 60 Co γ-rays, methyl methanesulfonate (MMS), and neocarzinostatin (NCS). We found that r obs -λ AP relationships differed significantly between MMS and NCS. At low AP density (λ AP  < 0.001), the APs induced by MMS seemed to not be closely distributed, whereas those induced by NCS were remarkably clustered. In contrast, the AP clustering induced by 60 Co γ-rays was similar to, but potentially more likely to occur than, random distribution. This simple method can be used to estimate mutagenicity of ionizing radiation and genotoxic chemicals. Copyright © 2017 Elsevier Inc. All rights reserved.

Zingiber officinale Mitigates Brain Damage and Improves Memory Impairment in Focal Cerebral Ischemic Rat

PubMed Central

Wattanathorn, Jintanaporn; Jittiwat, Jinatta; Tongun, Terdthai; Muchimapura, Supaporn; Ingkaninan, Kornkanok

2011-01-01

Cerebral ischemia is known to produce brain damage and related behavioral deficits including memory. Recently, accumulating lines of evidence showed that dietary enrichment with nutritional antioxidants could reduce brain damage and improve cognitive function. In this study, possible protective effect of Zingiber officinale, a medicinal plant reputed for neuroprotective effect against oxidative stress-related brain damage, on brain damage and memory deficit induced by focal cerebral ischemia was elucidated. Male adult Wistar rats were administrated an alcoholic extract of ginger rhizome orally 14 days before and 21 days after the permanent occlusion of right middle cerebral artery (MCAO). Cognitive function assessment was performed at 7, 14, and 21 days after MCAO using the Morris water maze test. The brain infarct volume and density of neurons in hippocampus were also determined. Furthermore, the level of malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) in cerebral cortex, striatum, and hippocampus was also quantified at the end of experiment. The results showed that cognitive function and neurons density in hippocampus of rats receiving ginger rhizome extract were improved while the brain infarct volume was decreased. The cognitive enhancing effect and neuroprotective effect occurred partly via the antioxidant activity of the extract. In conclusion, our study demonstrated the beneficial effect of ginger rhizome to protect against focal cerebral ischemia. PMID:21197427

Human ISWI complexes are targeted by SMARCA5 ATPase and SLIDE domains to help resolve lesion-stalled transcription

PubMed Central

Aydin, Özge Z.; Marteijn, Jurgen A.; Ribeiro-Silva, Cristina; Rodríguez López, Aida; Wijgers, Nils; Smeenk, Godelieve; van Attikum, Haico; Poot, Raymond A.; Vermeulen, Wim; Lans, Hannes

2014-01-01

Chromatin compaction of deoxyribonucleic acid (DNA) presents a major challenge to the detection and removal of DNA damage. Helix-distorting DNA lesions that block transcription are specifically repaired by transcription-coupled nucleotide excision repair, which is initiated by binding of the CSB protein to lesion-stalled RNA polymerase II. Using live cell imaging, we identify a novel function for two distinct mammalian ISWI adenosine triphosphate (ATP)-dependent chromatin remodeling complexes in resolving lesion-stalled transcription. Human ISWI isoform SMARCA5/SNF2H and its binding partners ACF1 and WSTF are rapidly recruited to UV-C induced DNA damage to specifically facilitate CSB binding and to promote transcription recovery. SMARCA5 targeting to UV-C damage depends on transcription and histone modifications and requires functional SWI2/SNF2-ATPase and SLIDE domains. After initial recruitment to UV damage, SMARCA5 re-localizes away from the center of DNA damage, requiring its HAND domain. Our studies support a model in which SMARCA5 targeting to DNA damage-stalled transcription sites is controlled by an ATP-hydrolysis-dependent scanning and proofreading mechanism, highlighting how SWI2/SNF2 chromatin remodelers identify and bind nucleosomes containing damaged DNA. PMID:24990377

Towards the damage evaluation using Gurson-Tvergaard-Needleman (GTN) model for hot forming processes

NASA Astrophysics Data System (ADS)

Imran, Muhammad; Bambach, Markus

2018-05-01

In the production of semi-finished metal products, hot forming is used to eliminate the pores and voids from the casting process under compressive stresses and to modify the microstructure for further processing. In the case of caliber and flat rolling processes, tensile stresses occur at certain roll gap ratios which promote pore formation on nonmetallic inclusion. The formation of new pores contributes to ductile damage and reduces the load carrying capacity of the material. In the literature, the damage nucleation and growth during the hot forming process are not comprehensively described. The aim of this study is to understand the damage initiation and growth mechanism during hot forming processes. Hot tensile tests are performed at different temperatures and strain rates for 16MnCrS5 steel. To investigate the influence of geometrical variations on the damage mechanism, specimens with different stress triaxiality ratios are used. Finite element simulations using the Gurson-Tvergaard-Needleman (GTN) damage model are performed to estimate the critical void fraction for the damage initiation and the evolution of the void volume fraction. The results showed that the GTN model underestimates the softening of the material due to the independence of the temperature and the strain rate.

Optical damage observed in the LHMEL II output coupler

NASA Astrophysics Data System (ADS)

Eric, John J.; Bagford, John O.; Devlin, Christie L. H.; Hull, Robert J.; Seibert, Daniel B.

2008-01-01

During the annual NIST calibration testing done at the LHMEL facility in FY06 on its high energy Carbon-Dioxide lasers, the LHMEL II device suffered severe damage to the internal surface of its ZnSe output coupler optics. The damage occurred during a high power, short duration run and it was believed to have been the result of a significant amount of surface contaminants interacting with the LHMEL cavity beam. Initial theories as to the source of the contamination led to the inspection of the vacuum grease that seals the piping that supplies the source gases to the laser cavity. Other contamination sources were considered, and analysis was conducted in an effort to identify the material found at the damage sites on the optic, but the tests were mainly inconclusive. Some procedure changes were initiated to identify possible contamination before high energy laser operation in an attempt to mitigate and possibly prevent the continued occurrence of damage to the output coupler window. This paper is to illustrate the type and extent of the damage encountered, highlight some of the theories as to the contamination source, and serve as a notice as to the severity and consequences of damage that is possible even due to small amounts of foreign material in a high energy laser environment.

SURFplus Model Calibration for PBX 9502

DOE Office of Scientific and Technical Information (OSTI.GOV)

Menikoff, Ralph

2017-12-06

The SURFplus reactive burn model is calibrated for the TATB based explosive PBX 9502 at three initial temperatures; hot (75 C), ambient (23 C) and cold (-55 C). The CJ state depends on the initial temperature due to the variation in the initial density and initial specific energy of the PBX reactants. For the reactants, a porosity model for full density TATB is used. This allows the initial PBX density to be set to its measured value even though the coeffcient of thermal expansion for the TATB and the PBX differ. The PBX products EOS is taken as independent ofmore » the initial PBX state. The initial temperature also affects the sensitivity to shock initiation. The model rate parameters are calibrated to Pop plot data, the failure diameter, the limiting detonation speed just above the failure diameters, and curvature effect data for small curvature.« less

A Three-Parameter Model for Predicting Fatigue Life of Ductile Metals Under Constant Amplitude Multiaxial Loading

NASA Astrophysics Data System (ADS)

Liu, Jia; Li, Jing; Zhang, Zhong-ping

2013-04-01

In this article, a fatigue damage parameter is proposed to assess the multiaxial fatigue lives of ductile metals based on the critical plane concept: Fatigue crack initiation is controlled by the maximum shear strain, and the other important effect in the fatigue damage process is the normal strain and stress. This fatigue damage parameter introduces a stress-correlated factor, which describes the degree of the non-proportional cyclic hardening. Besides, a three-parameter multiaxial fatigue criterion is used to correlate the fatigue lifetime of metallic materials with the proposed damage parameter. Under the uniaxial loading, this three-parameter model reduces to the recently developed Zhang's model for predicting the uniaxial fatigue crack initiation life. The accuracy and reliability of this three-parameter model are checked against the experimental data found in literature through testing six different ductile metals under various strain paths with zero/non-zero mean stress.

Investigation of Sideband Index Response to Prototype Gear Tooth Damage

NASA Technical Reports Server (NTRS)

Dempsey, Paula J.

2013-01-01

The objective of this analysis was to evaluate the ability of gear condition indicators (CI) to detect contact fatigue damage on spiral bevel gear teeth. Tests were performed in the NASA Glenn Spiral Bevel Gear Fatigue Rig on eight prototype gear sets (pinion/gear). Damage was initiated and progressed on the gear and pinion teeth. Vibration data was measured during damage progression at varying torque values while varying damage modes to the gear teeth were observed and documented with inspection photos. Sideband indexes (SI) and root mean square (RMS) CIs were calculated from the time synchronous averaged vibration data. Results found that both CIs respond differently to varying torque levels, damage levels and damage modes

Modelling low velocity impact induced damage in composite laminates

NASA Astrophysics Data System (ADS)

Shi, Yu; Soutis, Constantinos

2017-12-01

The paper presents recent progress on modelling low velocity impact induced damage in fibre reinforced composite laminates. It is important to understand the mechanisms of barely visible impact damage (BVID) and how it affects structural performance. To reduce labour intensive testing, the development of finite element (FE) techniques for simulating impact damage becomes essential and recent effort by the composites research community is reviewed in this work. The FE predicted damage initiation and propagation can be validated by Non Destructive Techniques (NDT) that gives confidence to the developed numerical damage models. A reliable damage simulation can assist the design process to optimise laminate configurations, reduce weight and improve performance of components and structures used in aircraft construction.

Development and simulation study of a new inverse-pinch high Coulomb transfer switch

NASA Technical Reports Server (NTRS)

Choi, Sang H.

1989-01-01

The inverse-pinch plasma switch was studied using a computer simulation code. The code was based on a 2-D, 2-temperature magnetohydrodynamic (MHD) model. The application of this code was limited to the disk-type inverse-pinch plasma switch. The results of the computer analysis appear to be in agreement with the experimental results when the same parameters are used. An inverse-pinch plasma switch for closing has been designed and tested for high-power switching requirements. An azimuthally uniform initiation of breakdown is a key factor in achieving an inverse-pinch current path in the switch. Thus, various types of triggers, such as trigger pins, wire-brush, ring trigger, and hypocycloidal-pinch (HCP) devices have been tested for uniform breakdown. Recently, triggering was achieved by injection of a plasma-ring (plasma puff) that is produced separately with hypocycloidal-pinch electrodes placed under the cathode of the main gap. The current paths at switch closing, initiated by the injection of a plasma-ring from the HCP trigger are azimuthally uniform, and the local current density is significantly reduced, so that damage to the electrodes and the insulator surfaces is minimized. The test results indicate that electron bombardment on the electrodes and the insulator surfaces is minimized. The test results indicate that electron bombardment on the electrodes is four orders of magnitude less than that of a spark-gap switch for the same switching power. Indeed, a few thousand shots with peak current exceeding a mega-ampere and with hold-off voltage up to 20 kV have been conducted without showing measurable damage to the electrodes and insulators.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kruska, Karen; Zhai, Ziqing; Bruemmer, Stephen M.

Due to its superior resistance to corrosion and stress corrosion cracking (SCC), high Cr, Ni-base Alloy 690 is now commonly used in pressurized water reactors (PWRs). Even though highly cold-worked (CW) Alloy 690 has been shown to be susceptible to SCC crack growth in PWR primary water environments, an open question remains whether SCC initiation was possible for these materials under constant load test conditions. Testing has been performed on a series of CW alloy 690 CRDM tubing specimens at constant load for up to 9,220 hours in 360°C simulated PWR primary water. A companion paper will discuss the overallmore » testing approach and describe results on different alloy 690 heats and cold work levels. The focus of the current paper is to illustrate the use of focused ion beam (FIB), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for the high-resolution investigation of precursor damage and intergranular (IG) crack nucleation in these specimens. Three-dimensional (3D) FIB/SEM imaging has been conducted on a series of grain boundary (GB) damage precursors, such as IG small cavities, local corrosion and even shallow cracks observed at the specimen surface. Contrast variations and EDS mapping were used to distinguish oxides, carbides and cavities from the matrix material. Nanometer-sized cavities were observed associated with GB carbides in the highly CW specimens. Shallow IG cracks were present in the 30%CW specimens and exhibited oxidized crack flanks and a higher density of cavities ahead of the oxide front in all cases. The shape and distribution of carbides and cavities in the plane of the cracked GBs was analyzed in 3D to gain a mechanistic understanding of the processes that may be leading to crack initiation in highly CW alloy 690.« less

Assessment of compressive failure process of cortical bone materials using damage-based model.

PubMed

Ng, Theng Pin; R Koloor, S S; Djuansjah, J R P; Abdul Kadir, M R

2017-02-01

The main failure factors of cortical bone are aging or osteoporosis, accident and high energy trauma or physiological activities. However, the mechanism of damage evolution coupled with yield criterion is considered as one of the unclear subjects in failure analysis of cortical bone materials. Therefore, this study attempts to assess the structural response and progressive failure process of cortical bone using a brittle damaged plasticity model. For this reason, several compressive tests are performed on cortical bone specimens made of bovine femur, in order to obtain the structural response and mechanical properties of the material. Complementary finite element (FE) model of the sample and test is prepared to simulate the elastic-to-damage behavior of the cortical bone using the brittle damaged plasticity model. The FE model is validated in a comparative method using the predicted and measured structural response as load-compressive displacement through simulation and experiment. FE results indicated that the compressive damage initiated and propagated at central region where maximum equivalent plastic strain is computed, which coincided with the degradation of structural compressive stiffness followed by a vast amount of strain energy dissipation. The parameter of compressive damage rate, which is a function dependent on damage parameter and the plastic strain is examined for different rates. Results show that considering a similar rate to the initial slope of the damage parameter in the experiment would give a better sense for prediction of compressive failure. Copyright © 2016 Elsevier Ltd. All rights reserved.

Determination on Damage Mechanism of the Planet Gear of Heavy Vehicle Final Drive

NASA Astrophysics Data System (ADS)

Ramdan, RD; Setiawan, R.; Sasmita, F.; Suratman, R.; Taufiqulloh

2018-02-01

The works focus on the investigation of damage mechanism of fractured in the form of spalling of the planet gears from the final drive assembly of 160-ton heavy vehicles. The objective of this work is to clearly understand the mechanism of damage. The work is the first stage of the on-going research on the remaining life estimation of such gears. The understanding of the damage mechanism is critical in order to provide accurate estimate of the gear’s remaining life with observed initial damage. The analysis was performed based on the metallurgy laboratory works, including visual observation, macro-micro fractography by optical stereo and optical microscope and micro-vickers hardness test. From visual observation it was observed pitting that form lining defect at common position, which is at gear flank position. From spalling sample it was observed ratchet mark at the boundary between macro pitting and the edge of fractured parts. Further observation on the cross-section of the samples by optical microscope confirm that initial micro pitting occur without spalling of the case hardened surface. Spalling occur when pitting achieve certain critical size, and occur at multiple initiation site of crack propagation. From the present research it was concluded that pitting was resulted due to repeated contact fatigue. In addition, development of micro to macro pitting as well as spalling occur at certain direction towards the top of the gear teeth.

Chemotaxis in P. Aeruginosa Biofilm Formation

NASA Astrophysics Data System (ADS)

Bienvenu, Samuel; Strain, Shinji; Thatcher, Travis; Gordon, Vernita

2010-10-01

Pseudomonas biofilms form infections in the lungs of Cystic Fibrosis (CF) patients that damage lung tissue and lead to death. Previous work shows chemotaxis is important for Pseudomonas in CF lungs. The work studied swimming bacteria at high concentrations. In contrast, medically relevant biofilms initiate from sparse populations of surface-bound bacteria. The recent development of software techniques for automated, high-throughput bacteria tracking leaves us well-poised to quantitatively study these chemotactic conditions. We will develop experimental systems for such studies, focusing on L-Arginine (an amino acid), D-Galactose (a sugar present in lungs), and succinate and glucose (carbon sources for bacteria). This suite of chemoattractants will allow us to study how chemoattractant characteristics--size and diffusion behavior--change bacterial response; the interaction of competing chemoattractants; and, differences in bacterial behaviors, like motility modes, in response to different types of chemoattractions and varying neighbor cell density.

AmeriFlux US-Wrc Wind River Crane Site

DOE Data Explorer

Bible, Ken [University of Washington; Wharton, Sonia [Lawrence Livermore National Laboratory

2016-01-01

This is the AmeriFlux version of the carbon flux data for the site US-Wrc Wind River Crane Site. Site Description - Wind River Field Station flux tower site is located in the T.T. Munger Research Area of the Wind River Ranger District in the Gifford Pinchot National Forest. Protected since 1926, the T.T. Munger Research Natural Area (RNA) is administered by the USDA Forest Service Pacific Northwest Research Station and Gifford Pinchot National Forest. The Douglas-fir/western hemlock dominant stand is approximately 500 years old and represents end points of several ecological gradients including age, biomass, structural complexity, and density of the dominant overstory species. A complete stand replacement fire, approximately 450-500 years ago, resulted in the initial establishment. No significant disturbances have occurred since the fire aside from those confined to small groups of single trees, such as overturn from high wind activity and mechanical damage from winter precipitation.

Inertial Confinement Fusion Quarterly Report: April--June 1993. Volume 3, Number 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

MacGowan, B.J.; Kotowski, M.; Schleich, D.

1993-11-01

This issue of the ICF Quarterly contains six articles describing recent advances in Lawrence Livermore National Laboratory`s inertial confinement fusion (ICF) program. The current emphasis of the ICF program is in support of DOE`s National Ignition Facility (NIF) initiative for demonstrating ignition and gain with a 1-2 MJ glass laser. The articles describe recent Nova experiments and investigations tailored towards enhancing understanding of the key physics and technological issues for the NIF. Titles of the articles are: development of large-aperture KDP crystals; inner-shell photo-ionized X-ray lasers; X-ray radiographic measurements of radiation-driven shock and interface motion in solid density materials; themore » role of nodule defects in laser-induced damage of multilayer optical coatings; techniques for Mbar to near-Gbar equation-of-state measurements with the Nova laser; parametric instabilities and laser-beam smoothing.« less

Accelerated reliability testing of highly aligned single-walled carbon nanotube networks subjected to DC electrical stressing.

PubMed

Strus, Mark C; Chiaramonti, Ann N; Kim, Young Lae; Jung, Yung Joon; Keller, Robert R

2011-07-01

We investigate the electrical reliability of nanoscale lines of highly aligned, networked, metallic/semiconducting single-walled carbon nanotubes (SWCNTs) fabricated through a template-based fluidic assembly process. We find that these SWCNT networks can withstand DC current densities larger than 10 MA cm(-2) for several hours and, in some cases, several days. We develop test methods that show that the degradation rate, failure predictability and total device lifetime can be linked to the initial resistance. Scanning electron and transmission electron microscopy suggest that fabrication variability plays a critical role in the rate of degradation, and we offer an empirical method of quickly determining the long-term performance of a network. We find that well-fabricated lines subject to constant electrical stress show a linear accumulation of damage reminiscent of electromigration in metallic interconnects, and we explore the underlying physical mechanisms that could cause such behavior.

Quantitative Analysis of Charge Injection and Discharging of Si Nanocrystals and Arrays by Electrostatic Force Microscopy

NASA Technical Reports Server (NTRS)

Bell, L. D.; Boer, E.; Ostraat, M.; Brongersma, M. L.; Flagan, R. C.; Atwater, H. A.

2000-01-01

NASA requirements for computing and memory for microspacecraft emphasize high density, low power, small size, and radiation hardness. The distributed nature of storage elements in nanocrystal floating-gate memories leads to intrinsic fault tolerance and radiation hardness. Conventional floating-gate non-volatile memories are more susceptible to radiation damage. Nanocrystal-based memories also offer the possibility of faster, lower power operation. In the pursuit of filling these requirements, the following tasks have been accomplished: (1) Si nanocrystal charging has been accomplished with conducting-tip AFM; (2) Both individual nanocrystals on an oxide surface and nanocrystals formed by implantation have been charged; (3) Discharging is consistent with tunneling through a field-lowered oxide barrier; (4) Modeling of the response of the AFM to trapped charge has allowed estimation of the quantity of trapped charge; and (5) Initial attempts to fabricate competitive nanocrystal non-volatile memories have been extremely successful.

Global existence and large time asymptotic behavior of strong solutions to the Cauchy problem of 2D density-dependent Navier–Stokes equations with vacuum

NASA Astrophysics Data System (ADS)

Lü, Boqiang; Shi, Xiaoding; Zhong, Xin

2018-06-01

We are concerned with the Cauchy problem of the two-dimensional (2D) nonhomogeneous incompressible Navier–Stokes equations with vacuum as far-field density. It is proved that if the initial density decays not too slow at infinity, the 2D Cauchy problem of the density-dependent Navier–Stokes equations on the whole space admits a unique global strong solution. Note that the initial data can be arbitrarily large and the initial density can contain vacuum states and even have compact support. Furthermore, we also obtain the large time decay rates of the spatial gradients of the velocity and the pressure, which are the same as those of the homogeneous case.

Increasing dietary vitamin D3 improves the walking ability and welfare status of broiler chickens reared at high stocking densities.

PubMed

Sun, Z W; Yan, L; G, Y Y; Zhao, J P; Lin, H; Guo, Y M

2013-12-01

A study was conducted to evaluate the effects of varying dietary vitamin D3 and stocking density on growing performance, carcass characteristics, bone biomechanical properties, and welfare responses in Ross (308) broilers. Experimental diets, containing 1, 10, or 20 times the NRC recommended level of vitamin D3 (200 IU/kg), were formulated with low, medium, or high vitamin D3 levels for 3 growing phases. Two stocking densities were 10 and 16 birds/m(2). One-day-old hatchlings (1,872 males) were randomly assigned to 6 pens in each treatment. Results showed that high stocking density decreased the feed intake, BW gain (P < 0.01), breast muscle yield (P = 0.010), and tibial development (P < 0.01), whereas increasing feed conversion ratio (P < 0.001), and the scores of gait, footpad and hock burn, and abdominal plumage damage (P < 0.01), particularly toward the age when birds attained their market size. Increasing dietary vitamin D3 improved the birds' walking ability and tibial quality (P < 0.05), and reduced the development of footpad or hock dermatitis and abdominal plumage damage (P < 0.01), some aspects of which were age-dependent and appeared to vary with stocking density. These data indicate that increasing supplemental vitamin D3 has a favorable effect on walking ability and welfare status of high stocking density birds, but not on performance.

Relationships between common forest metrics and realized impacts of Hurricane Katrina on forest resources in Mississippi

Treesearch

Sonja N. Oswalt; Christopher M. Oswalt

2008-01-01

This paper compares and contrasts hurricane-related damage recorded across the Mississippi landscape in the 2 years following Katrina with initial damage assessments based on modeled parameters by the USDA Forest Service. Logistic and multiple regressions are used to evaluate the influence of stand characteristics on tree damage probability. Specifically, this paper...

Rapid assessment of wildfire damage using Forest Inventory data: A case in Georgia

Treesearch

Richard A. Harper; John W. Coulsten; Jeffery A. Turner

2009-01-01

The rapid assessment of damage caused by natural disasters is essential for planning the appropriate amount of disaster relief funds and public communication. Annual Forest Inventory and Analysis (FIA) data provided initial estimates of damage to timberland in a timely manner to State leaders during the 2007 Georgia Bay Complex Wildfire in southeast Georgia. FIA plots...

Biaxial deformation in high purity aluminum

DOE PAGES

Livescu, V.; Bingert, J. F.; Liu, C.; ...

2015-09-25

The convergence of multiple characterization tools has been applied to investigate the relationship of microstructure on damage evolution in high purity aluminum. The extremely coarse grain size of the disc-shaped sample provided a quasi-two dimensional structure from which the location of surface-measured features could be inferred. In particular, the role of pre-existing defects on damage growth was accessible due to the presence of casting porosity in the aluminum. Micro tomography, electron backscatter diffraction, and digital image correlation were applied to interrogate the sample in three dimensions. Recently micro-bulge testing apparatus was used to deform the pre-characterized disc of aluminum inmore » biaxial tension, and related analysis techniques were applied to map local strain fields. Subsequent post-mortem characterization of the failed sample was performed to correlate structure to damaged regions. We determined that strain localization and associated damage was most strongly correlated with grain boundary intersections and plastic anisotropy gradients between grains. Pre-existing voids played less of an apparent role than was perhaps initially expected. Finally, these combined techniques provide insight to the mechanism of damage initiation, propagation, and failure, along with a test bed for predictive damage models incorporating anisotropic microstructural effects.« less

Fabrication of spherical mitigation pit on KH2PO4 crystal by micro-milling and modeling of its induced light intensification.

PubMed

Cheng, Jian; Chen, Mingjun; Liao, Wei; Wang, Haijun; Xiao, Yong; Li, Mingquan

2013-07-15

Micro-machining is the most promising method for KH(2)PO(4) crystal to mitigate the surface damage growth in high power laser system. In this work, spherical mitigation pit is fabricated by micro-milling with an efficient machining procedure. The light intensification caused by rear surface features before and after mitigation is numerically modeled based on the finite-difference time-domain method. The results indicate that the occurrence of total internal reflections should be responsible for the largest light intensification inside the crystal. For spherical pits after mitigation, the light intensification can be greatly alleviated by preventing the occurrence of total internal reflections. The light intensification caused by spherical mitigation pit is strongly dependent on the width-depth ratio and it is suggested that the width-depth ratio of spherical mitigation pit must be devised to be larger than 5.0 to achieve the minimal light intensification for the mitigation of surface damage growth. Laser damage tests for KH(2)PO(4) crystal validate that the laser damage resistance of initially damaged surface can be retrieved to near the level of ideal surface by replacing initial damage site with predesigned mitigation pit.

Detailed Post-Soft Impact Progressive Damage Assessment for Hybrid Structure Jet Engines

NASA Technical Reports Server (NTRS)

Siddens, Aaron; Bayandor, Javid; Celestina, Mark L.

2014-01-01

Currently, certification of engine designs for resistance to bird strike is reliant on physical tests. Predictive modeling of engine structural damage has mostly been limited to evaluation of individual forward section components, such as fan blades within a fixed frame of reference, to direct impact with a bird. Such models must be extended to include interactions among engine components under operating conditions to evaluate the full extent of engine damage. This paper presents the results of a study aim to develop a methodology for evaluating bird strike damage in advanced propulsion systems incorporating hybrid composite/metal structures. The initial degradation and failure of individual fan blades struck by a bird were investigated. Subsequent damage to other fan blades and engine components due to resultant violent fan assembly vibrations and fragmentation was further evaluated. Various modeling parameters for the bird and engine components were investigated to determine guidelines for accurately capturing initial damage and progressive failure of engine components. Then, a novel hybrid structure modeling approach was investigated and incorporated into the crashworthiness methodology. Such a tool is invaluable to the process of design, development, and certification of future advanced propulsion systems.

The Effects of Fracture Anisotropy on the Damage Pattern and Seismic Radiation from a Chemical Explosion in a Granite Quarry

NASA Astrophysics Data System (ADS)

Rogers-Martinez, M. A.; Sammis, C. G.; Ezzedine, S. M.

2017-12-01

As part of the New England Damage Experiment (NEDE) a 122.7 kg Heavy ANFO charge was detonated at a depth of 13 m in a granite quarry in Barre Vt. Subsequent drill cores from the source region revealed that most of the resultant fracturing was concentrated in the rift plane of the highly anisotropic Barre granite. We simulated this explosion using a dynamic damage mechanics model embedded in the ABAQUS 3D finite element code. The damage mechanics was made anisotropic by taking the critical stress intensity factor to be a function of azimuth in concert with the physics of interacting parallel fractures and laboratory studies of anisotropic granite. In order to identify the effects of anisotropy, the explosion was also simulated assuming 1) no initial damage (pure elasticity) and 2) isotropic initial damage. For the anisotropic case, the calculated fracture pattern simulated that observed in NEDE. The simulated seismic radiation looked very much like that from a tensile fracture oriented in the rift plane, and similar to the crack-like moment tensor observed in the far field of many nuclear explosions.

Depletion of ribosomal protein L37 occurs in response to DNA damage and activates p53 through the L11/MDM2 pathway

PubMed Central

Llanos, Susana; Serrano, Manuel

2013-01-01

Perturbation of ribosomal biogenesis has recently emerged as a relevant p53-activating pathway. This pathway can be initiated by depletion of certain ribosomal proteins, which is followed by the binding and inhibition of MDM2 by a different subset of ribosomal proteins that includes L11. Here, we report that depletion of L37 leads to cell cycle arrest in a L11- and p53-dependent manner. DNA damage can initiate ribosomal stress, although little is known about the mechanisms involved. We have found that some genotoxic insults, namely UV light and cisplatin, lead to proteasomal degradation of L37 in the nucleoplasm and to the ensuing L11-dependent stabilization of p53. Moreover, ectopic L37 overexpression can attenuate the DNA damage response mediated by p53. These results support the concept that DNA damage-induced proteasomal degradation of L37 constitutes a mechanistic link between DNA damage and the ribosomal stress pathway, and is a relevant contributing signaling pathway for the activation of p53 in response to DNA damage. PMID:20935493

Radiation-damage-induced phasing: a case study using UV irradiation with light-emitting diodes.

PubMed

de Sanctis, Daniele; Zubieta, Chloe; Felisaz, Franck; Caserotto, Hugo; Nanao, Max H

2016-03-01

Exposure to X-rays, high-intensity visible light or ultraviolet radiation results in alterations to protein structure such as the breakage of disulfide bonds, the loss of electron density at electron-rich centres and the movement of side chains. These specific changes can be exploited in order to obtain phase information. Here, a case study using insulin to illustrate each step of the radiation-damage-induced phasing (RIP) method is presented. Unlike a traditional X-ray-induced damage step, specific damage is introduced via ultraviolet light-emitting diodes (UV-LEDs). In contrast to UV lasers, UV-LEDs have the advantages of small size, low cost and relative ease of use.

Fatigue Life of Postbuckled Structures with Indentation Damages

NASA Technical Reports Server (NTRS)

Davila, Carlos G.; Bisagni, Chiara

2016-01-01

The fatigue life of composite stiffened panels with indentation damage was investigated experimentally using single stringer compression specimens. Indentation damage was induced on one of the two flanges of each stringer. The experiments were conducted using advanced instrumentation, including digital image correlation, passive thermography, and in-situ ultrasonic scanning. Specimens with initial indentation damage lengths of 32 millimeters to 56 millimeters were tested quasi-statically and in fatigue, and the effects of cyclic load amplitude and damage size were studied. A means of comparison of the damage propagation rates and collapse loads based on a stress intensity measure and the Paris law is proposed.

Chromosome damage evolution after low and high LET irradiation

NASA Astrophysics Data System (ADS)

Andreev, Sergey; Eidelman, Yuri

Ionizing radiation induces DNA and chromatin lesions which are converted to chromosome lesions detected in the first post-irradiation mitosis by classic cytogenetic techniques as chromosomal aberrations (CAs). These techniques allow to monitor also delayed aberrations observed after many cell generations post-irradiation - the manifestation of chromosomal instability phenotype (CIN). The problem discussed is how to predict time evolution from initial to delayed DNA/chromosome damage. To address this question, in the present work a mechanistic model of CIN is elaborated which integrates pathways of (*) DNA damage induction and its conversion to chromosome lesions (aberrations), (**) lesion transmission and generation through cell cycles. Delayed aberrations in subsequent cycles are formed in the model owing to two pathways, DNA damage generation de novo as well as CA transmission from previous cycles. DNA damage generation rate is assumed to consist of bystander and non-bystander components. Bystander signals impact all cells roughly equally, whereas non-bystander DSB generation rate differs for the descendants of unirradiated and irradiated cells. Monte Carlo simulation of processes underlying CIN allows to predict the time evolution of initial radiation-induced damage - kinetics curve for delayed unstable aberrations (dicentrics) together with dose response and RBE as a function of time after high vs low LET irradiation. The experimental data for radiation-induced CIN in TK6 lymphoblastoid cells and human lymphocytes irradiated with low (gamma) and high (Fe, C) LET radiation are analyzed on the basis of the proposed model. One of the conclusions is that without bystander signaling, just taking into account the initial DNA damage and non-bystander DSB generation, it is impossible to describe the available experimental data for high-LET-induced CIN. The exact contribution of bystander effects for high vs low LET remains unknown, but the relative contribution may be assessed at large times after initial acute irradiation. RBE for delayed aberrations depends on LET, time and cell line, which probably reflects a genetic background for bystander component. The proposed modeling approach creates a basis for integration of complex network of bystander/inflammatory signaling in systems-level platform for quantification of radiation induced CIN.

On crack initiation in notched, cross-plied polymer matrix composites

NASA Astrophysics Data System (ADS)

Yang, Q. D.; Schesser, D.; Niess, M.; Wright, P.; Mavrogordato, M. N.; Sinclair, I.; Spearing, S. M.; Cox, B. N.

2015-05-01

The physics of crack initiation in a polymer matrix composite are investigated by varying the modeling choices made in simulations and comparing the resulting predictions with high-resolution in situ images of cracks. Experimental data were acquired using synchrotron-radiation computed tomography (SRCT) at a resolution on the order of 1 μm, which provides detailed measurement of the location, shape, and size of small cracks, as well as the crack opening and shear displacements. These data prove sufficient to discriminate among competing physical descriptions of crack initiation. Simulations are executed with a high-fidelity formulation, the augmented finite element method (A-FEM), which permits consideration of coupled damage mechanisms, including both discrete cracks and fine-scale continuum damage. The discrete cracks are assumed to be nonlinear fracture events, governed by reasonably general mixed-mode cohesive laws. Crack initiation is described in terms of strength parameters within the cohesive laws, so that the cohesive law provides a unified model for crack initiation and growth. Whereas the cracks investigated are typically 1 mm or less in length, the fine-scale continuum damage refers to irreversible matrix deformation occurring over gauge lengths extending down to the fiber diameter (0.007 mm). We find that the location and far-field stress for crack initiation are predicted accurately only if the variations of local stress within plies and in the presence of stress concentrators (notches, etc.) are explicitly computed and used in initiation criteria; stress redistribution due to matrix nonlinearity that occurs prior to crack initiation is accounted for; and a mixed-mode criterion is used for crack initiation. If these factors are not all considered, which is the case for commonly used failure criteria, predictions of the location and far-field stress for initiation are not accurate.

Transcription factor Nrf2 hyperactivation in early-phase renal ischemia-reperfusion injury prevents tubular damage progression.

PubMed

Nezu, Masahiro; Souma, Tomokazu; Yu, Lei; Suzuki, Takafumi; Saigusa, Daisuke; Ito, Sadayoshi; Suzuki, Norio; Yamamoto, Masayuki

2017-02-01

Acute kidney injury is a devastating disease with high morbidity in hospitalized patients and contributes to the pathogenesis of chronic kidney disease. An underlying mechanism of acute kidney injury involves ischemia-reperfusion injury which, in turn, induces oxidative stress and provokes organ damage. Nrf2 is a master transcription factor that regulates the cellular response to oxidative stress. Here, we examined the role of Nrf2 in the progression of ischemia-reperfusion injury-induced kidney damage in mice using genetic and pharmacological approaches. Both global and tubular-specific Nrf2 activation enhanced gene expression of antioxidant and NADPH synthesis enzymes, including glucose-6-phosphate dehydrogenase, and ameliorated both the initiation of injury in the outer medulla and the progression of tubular damage in the cortex. Myeloid-specific Nrf2 activation was ineffective. Short-term administration of the Nrf2 inducer CDDO during the initial phase of injury ameliorated the late phase of tubular damage. This inducer effectively protected the human proximal tubular cell line HK-2 from oxidative stress-mediated cell death while glucose-6-phosphate dehydrogenase knockdown increased intracellular reactive oxygen species. These findings demonstrate that tubular hyperactivation of Nrf2 in the initial phase of injury prevents the progression of reactive oxygen species-mediated tubular damage by inducing antioxidant enzymes and NADPH synthesis. Thus, Nrf2 may be a promising therapeutic target for preventing acute kidney injury to chronic kidney disease transition. Copyright © 2016 International Society of Nephrology. Published by Elsevier Inc. All rights reserved.

Fatigue analysis of multiple site damage at a row of holes in a wide panel

NASA Technical Reports Server (NTRS)

Buhler, Kimberley; Grandt, Alten F., Jr.; Moukawsher, E. J.

1994-01-01

This paper is concerned with predicting the fatigue life of unstiffened panels which contain multiple site damage (MSD). The initial damage consists of through-the-thickness cracks emanating from a row of holes in the center of a finite width panel. A fracture mechanics analysis has been developed to predict the growth, interaction, and coalescence of the various cracks which propagate in the panel. A strain-life analysis incorporating Neuber's rule for notches, and Miner's rule for cumulative damage, is also employed to predict crack initiation for holes without initial cracking. This analysis is compared with the results of a series of fatigue tests on 2024-T3 aluminum panels, and is shown to do an excellent job of predicting the influence of MSD on the fatigue life of nine inch wide specimens. Having established confidence in the ability to analyze the influence of MSD on fatigue life, a parametric study is conducted to examine the influence of various MSD scenarios in an unstiffened panel. The numerical study considered 135 cases in all, with the parametric variables being the applied cyclic stress level, the lead crack geometry, and the number and location of MSD cracks. The numerical analysis provides details for the manner in which lead cracks and MSD cracks grow and coalesce leading to final failure. The results indicate that MSD located adjacent to lead cracks is the most damaging configuration, while for cases without lead cracks, MSD clusters which are not separated by uncracked holes are most damaging.

Cataract surgery in eyes with low corneal endothelial cell density.

PubMed

Hayashi, Ken; Yoshida, Motoaki; Manabe, Shin-ichi; Hirata, Akira

2011-08-01

To compare corneal endothelial damage after cataract surgery in eyes with low endothelial cell density (ECD) and eyes with normal ECD. Hayashi Eye Hospital, Fukuoka, Japan. Case-control study. Cataract surgery was performed in eyes with a low ECD (500 to 1000 cells/mm(2)) (low-density group) and control eyes with a normal ECD. The ECD and central corneal thickness (CCT) were measured preoperatively and 1 and 3 months postoperatively, and the percentage cell loss and increase in CCT were compared. The low-density group and control group each comprised 50 eyes. In the low-density group, 39 eyes had nonprogressive endothelial pathology and 11 had Fuchs dystrophy. The mean ECD was significantly less and the CCT significantly greater in the low-density group than in the control group throughout the follow-up (P ≤.0066). However, no significant difference in the percentage of cell loss was found between groups at 1 or 3 months (5.1%, low-density group; 4.2%, control group) (P ≥.1477). The percentage increase in CCT was significantly greater in the low-density group than in the control group at 1 month (P<.0001), although there was no significant difference at 3 months (0.4% and -0.4%, respectively) (P=.2172). Corneal endothelial damage after cataract surgery in eyes with low ECD was slight and comparable to that in healthy eyes, which suggests that cataract surgery alone (without corneal transplantation) should be performed first. Copyright © 2011 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.

Corneal Confocal Microscopy Detects Corneal Nerve Damage in Patients Admitted With Acute Ischemic Stroke.

PubMed

Khan, Adnan; Akhtar, Naveed; Kamran, Saadat; Ponirakis, Georgios; Petropoulos, Ioannis N; Tunio, Nahel A; Dargham, Soha R; Imam, Yahia; Sartaj, Faheem; Parray, Aijaz; Bourke, Paula; Khan, Rabia; Santos, Mark; Joseph, Sujatha; Shuaib, Ashfaq; Malik, Rayaz A

2017-11-01

Corneal confocal microscopy can identify corneal nerve damage in patients with peripheral and central neurodegeneration. However, the use of corneal confocal microscopy in patients presenting with acute ischemic stroke is unknown. One hundred thirty patients (57 without diabetes mellitus [normal glucose tolerance], 32 with impaired glucose tolerance, and 41 with type 2 diabetes mellitus) admitted with acute ischemic stroke, and 28 age-matched healthy control participants underwent corneal confocal microscopy to quantify corneal nerve fiber density, corneal nerve branch density, and corneal nerve fiber length. There was a significant reduction in corneal nerve fiber density, corneal nerve branch density, and corneal nerve fiber length in stroke patients with normal glucose tolerance ( P <0.001, P <0.001, P <0.001), impaired glucose tolerance ( P =0.004, P <0.001, P =0.002), and type 2 diabetes mellitus ( P <0.001, P <0.001, P <0.001) compared with controls. HbA1c and triglycerides correlated with corneal nerve fiber density ( r =-0.187, P =0.03; r =-0.229 P =0.01), corneal nerve fiber length ( r =-0.228, P =0.009; r =-0.285; P =0.001), and corneal nerve branch density ( r =-0.187, P =0.033; r =-0.229, P =0.01). Multiple linear regression showed no independent associations between corneal nerve fiber density, corneal nerve branch density, and corneal nerve fiber length and relevant risk factors for stroke. Corneal confocal microscopy is a rapid noninvasive ophthalmic imaging technique that identifies corneal nerve fiber loss in patients with acute ischemic stroke. © 2017 American Heart Association, Inc.

A Lattice-Misfit-Dependent Damage Model for Non-linear Damage Accumulations Under Monotonous Creep in Single Crystal Superalloys

NASA Astrophysics Data System (ADS)

le Graverend, J.-B.

2018-05-01

A lattice-misfit-dependent damage density function is developed to predict the non-linear accumulation of damage when a thermal jump from 1050 °C to 1200 °C is introduced somewhere in the creep life. Furthermore, a phenomenological model aimed at describing the evolution of the constrained lattice misfit during monotonous creep load is also formulated. The response of the lattice-misfit-dependent plasticity-coupled damage model is compared with the experimental results obtained at 140 and 160 MPa on the first generation Ni-based single crystal superalloy MC2. The comparison reveals that the damage model is well suited at 160 MPa and less at 140 MPa because the transfer of stress to the γ' phase occurs for stresses above 150 MPa which leads to larger variations and, therefore, larger effects of the constrained lattice misfit on the lifetime during thermo-mechanical loading.

Population Dynamics of Dactylella oviparasitica and Heterodera schachtii: Toward a Decision Model for Sugar Beet Planting

PubMed Central

Yang, Jiue-in; Benecke, Scott; Jeske, Daniel R.; Rocha, Fernando S.; Smith Becker, Jennifer; Timper, Patricia; Ole Becker, J.

2012-01-01

A series of experiments were performed to examine the population dynamics of the sugarbeet cyst nematode, Heterodera schachtii, and the nematophagus fungus Dactylella oviparasitica. After two nematode generations, the population densities of H. schachtii were measured in relation to various initial infestation densities of both D. oviparasitica and H. schachtii. In general, higher initial population densities of D. oviparasitica were associated with lower final population densities of H. schachtii. Regression models showed that the initial densities of D. oviparasitica were only significant when predicting the final densities of H. schachtii J2 and eggs as well as fungal egg parasitism, while the initial densities of J2 were significant for all final H. schachtii population density measurements. We also showed that the densities of H. schachtii-associated D. oviparasitica fluctuate greatly, with rRNA gene numbers going from zero in most field-soil-collected cysts to an average of 4.24 x 108 in mature females isolated directly from root surfaces. Finally, phylogenetic analysis of rRNA genes suggested that D. oviparasitica belongs to a clade of nematophagous fungi that includes Arkansas Fungus strain L (ARF-L) and that these fungi are widely distributed. We anticipate that these findings will provide foundational data facilitating the development of more effective decision models for sugar beet planting. PMID:23481664

SEMICONDUCTOR TECHNOLOGY: Influence of nitrogen dose on the charge density of nitrogen-implanted buried oxide in SOI wafers

NASA Astrophysics Data System (ADS)

Zhongshan, Zheng; Zhongli, Liu; Ning, Li; Guohua, Li; Enxia, Zhang

2010-02-01

To harden silicon-on-insulator (SOI) wafers fabricated using separation by implanted oxygen (SIMOX) to total-dose irradiation, the technique of nitrogen implantation into the buried oxide (BOX) layer of SIMOX wafers can be used. However, in this work, it has been found that all the nitrogen-implanted BOX layers reveal greater initial positive charge densities, which increased with increasing nitrogen implantation dose. Also, the results indicate that excessively large nitrogen implantation dose reduced the radiation tolerance of BOX for its high initial positive charge density. The bigger initial positive charge densities can be ascribed to the accumulation of implanted nitrogen near the Si-BOX interface after annealing. On the other hand, in our work, it has also been observed that, unlike nitrogen-implanted BOX, all the fluorine-implanted BOX layers show a negative charge density. To obtain the initial charge densities of the BOX layers, the tested samples were fabricated with a metal-BOX-silicon (MBS) structure based on SIMOX wafers for high-frequency capacitance-voltage (C-V) analysis.

Beaver lodge distributions and damage assessments in a forested wetland ecosystem in the southern United States

USGS Publications Warehouse

King, S.L.; Keeland, B.D.; Moore, J.L.

1998-01-01

Caddo Lake, USA, a Ramsar Wetland of International Importance, is a lacustrine wetland complex consisting of stands of flooded baldcypress intermixed with open water and emergent wetland habitats. Recently, concern has been expressed over a perceived increase in the beaver population and the impact of beaver on the long-term sustainability of the baldcypress ecosystem. We used intensive beaver lodge surveys to determine the distribution and relative abundance of beaver and the amount, type, and distribution of beaver damage to mature trees and seedlings at Caddo Lake. A total of 229 lodges were located with a combination of aerial and boat/ground surveys. Most lodges were located in open water and edge habitats. About 95% of the lodges were occupied by beaver or nutria. Some form of damage was exhibited by one or more trees near 85% of the lodges. Intensive damage assessments around 35 lodges indicated that most damage to trees, baldcypress in particular, was restricted to peeling or stripping of bark which is believed to have minimal effect on tree survival. Surveys of regeneration indicated that baldcypress seedlings were very abundant; however, over 99.9% were less than 30 cm tall. The lack of recruitment into the larger size classes appears to be a result of high stand densities and water management practices. At this time, the young age and density of the baldcypress forests suggest that recruitment is not a major concern and herbivore damage appears to be having a minimal effect on the forest.

Climate mitigation: sustainable preferences and cumulative carbon

NASA Astrophysics Data System (ADS)

Buckle, Simon

2010-05-01

We develop a stylized AK growth model with both climate damages to ecosystem goods and services and sustainable preferences that allow trade-offs between present discounted utility and long-run climate damages. The simplicity of the model permits analytical solutions. Concern for the long-term provides a strong driver for mitigation action. One plausible specification of sustainable preferences leads to the result that, for a range of initial parameter values, an optimizing agent would choose a level of cumulative carbon dioxide (CO2) emissions independent of initial production capital endowment and CO2 levels. There is no technological change so, for economies with sufficiently high initial capital and CO2 endowments, optimal mitigation will lead to disinvestment. For lower values of initial capital and/or CO2 levels, positive investment can be optimal, but still within the same overall level of cumulative emissions. One striking aspect of the model is the complexity of possible outcomes, in addition to these optimal solutions. We also identify a resource constrained region and several regions where climate damages exceed resources available for consumption. Other specifications of sustainable preferences are discussed, as is the case of a hard constraint on long-run damages. Scientists are currently highlighting the potential importance of the cumulative carbon emissions concept as a robust yet flexible target for climate policymakers. This paper shows that it also has an ethical interpretation: it embodies an implicit trade off in global welfare between present discounted welfare and long-term climate damages. We hope that further development of the ideas presented here might contribute to the research and policy debate on the critical areas of intra- and intergenerational welfare.

Model-Based Structural Health Monitoring of Fatigue Damage Test-Bed Specimens

DTIC Science & Technology

2011-11-15

the hull welds or notches along component edges are good initial candidates for the hypothetical damage initiation areas. The branching process adds...to it off-center. The base plate and the stiffener plate are rigidly welded by a tungsten inert gas ( TIG ) weld . Three different crack paths...shown in Figure 9(a), an 18 in long stiffener plate has been welded to each of the tested plates with 0.625 in long discrete TIG welds at 5 locations

Mutualists or parasites? Context-dependent influence of symbiotic fly larvae on carnivorous investment in the Albany pitcher plant.

PubMed

Lymbery, Samuel J; Didham, Raphael K; Hopper, Stephen D; Simmons, Leigh W

2016-11-01

Carnivorous plants allocate more resources to carnivorous structures under nutrient-limited conditions, and relative investment can also be influenced by animals (infauna) that live in association with these plants and feed on their prey. We investigated these effects within a population of the pitcher plant Cephalotus follicularis containing varying densities of larvae of the fly Badisis ambulans . For plants with a relatively high proportion of adult pitchers, increasing larval density was associated with lower relative leaf allocation to new pitcher buds. For plants with relatively few adult pitchers, however, there was greater relative leaf allocation to pitcher buds with increasing larval density. In a field experiment, there was no significant effect of experimental larval presence or absence on the change in carbon-to-nitrogen (C/N) ratio of plants. Although the direction of the correlation between B. ambulans larvae and relative investment in carnivorous and non-carnivorous structures depends on the relative number of mature structures, whether the larvae enhance or reduce nutrient stress under different conditions remains unclear. The change in C/N was, however, less variable for pitchers that contained larvae, suggesting a stabilizing effect. Eighteen of 52 experimental pitchers were damaged by an unknown species, causing the pitcher fluid to drain. These pitchers were significantly more likely to survive if they contained larvae. These results suggest that the relationship between infauna and host varies with the initial resource status and environmental context of the host plant.

Mutualists or parasites? Context-dependent influence of symbiotic fly larvae on carnivorous investment in the Albany pitcher plant

PubMed Central

Didham, Raphael K.; Hopper, Stephen D.

2016-01-01

Carnivorous plants allocate more resources to carnivorous structures under nutrient-limited conditions, and relative investment can also be influenced by animals (infauna) that live in association with these plants and feed on their prey. We investigated these effects within a population of the pitcher plant Cephalotus follicularis containing varying densities of larvae of the fly Badisis ambulans. For plants with a relatively high proportion of adult pitchers, increasing larval density was associated with lower relative leaf allocation to new pitcher buds. For plants with relatively few adult pitchers, however, there was greater relative leaf allocation to pitcher buds with increasing larval density. In a field experiment, there was no significant effect of experimental larval presence or absence on the change in carbon-to-nitrogen (C/N) ratio of plants. Although the direction of the correlation between B. ambulans larvae and relative investment in carnivorous and non-carnivorous structures depends on the relative number of mature structures, whether the larvae enhance or reduce nutrient stress under different conditions remains unclear. The change in C/N was, however, less variable for pitchers that contained larvae, suggesting a stabilizing effect. Eighteen of 52 experimental pitchers were damaged by an unknown species, causing the pitcher fluid to drain. These pitchers were significantly more likely to survive if they contained larvae. These results suggest that the relationship between infauna and host varies with the initial resource status and environmental context of the host plant. PMID:28018659

A computationally efficient ductile damage model accounting for nucleation and micro-inertia at high triaxialities

DOE PAGES

Versino, Daniele; Bronkhorst, Curt Allan

2018-01-31

The computational formulation of a micro-mechanical material model for the dynamic failure of ductile metals is presented in this paper. The statistical nature of porosity initiation is accounted for by introducing an arbitrary probability density function which describes the pores nucleation pressures. Each micropore within the representative volume element is modeled as a thick spherical shell made of plastically incompressible material. The treatment of porosity by a distribution of thick-walled spheres also allows for the inclusion of micro-inertia effects under conditions of shock and dynamic loading. The second order ordinary differential equation governing the microscopic porosity evolution is solved withmore » a robust implicit procedure. A new Chebyshev collocation method is employed to approximate the porosity distribution and remapping is used to optimize memory usage. The adaptive approximation of the porosity distribution leads to a reduction of computational time and memory usage of up to two orders of magnitude. Moreover, the proposed model affords consistent performance: changing the nucleation pressure probability density function and/or the applied strain rate does not reduce accuracy or computational efficiency of the material model. The numerical performance of the model and algorithms presented is tested against three problems for high density tantalum: single void, one-dimensional uniaxial strain, and two-dimensional plate impact. Here, the results using the integration and algorithmic advances suggest a significant improvement in computational efficiency and accuracy over previous treatments for dynamic loading conditions.« less

Lamb Wave Assessment of Fatigue and Thermal Damage in Composites

NASA Technical Reports Server (NTRS)

Seale, Michael D.; Smith, Barry T.; Prosser, W. H.

2004-01-01

Among the various techniques available, ultrasonic Lamb waves offer a convenient method of evaluating composite materials. Since the Lamb wave velocity depends on the elastic properties of a structure, an effective tool exists to monitor damage in composites by measuring the velocity of these waves. Lamb wave measurements can propagate over long distances and are sensitive to the desired in-plane elastic properties of the material. This paper describes two studies which monitor fatigue damage and two studies which monitor thermal damage in composites using Lamb waves. In the fatigue studies, the Lamb wave velocity is compared to modulus measurements obtained using strain gage measurements in the first experiment and the velocity is monitored along with the crack density in the second. In the thermal damage studies, one examines samples which were exposed to varying temperatures for a three minute duration and the second includes rapid thermal damage in composites by intense laser beams. In all studies, the Lamb wave velocity is demonstrated to be an excellent method to monitor damage in composites.

A Novel Approach to Rotorcraft Damage Tolerance

NASA Technical Reports Server (NTRS)

Forth, Scott C.; Everett, Richard A.; Newman, John A.

2002-01-01

Damage-tolerance methodology is positioned to replace safe-life methodologies for designing rotorcraft structures. The argument for implementing a damage-tolerance method comes from the fundamental fact that rotorcraft structures typically fail by fatigue cracking. Therefore, if technology permits prediction of fatigue-crack growth in structures, a damage-tolerance method should deliver the most accurate prediction of component life. Implementing damage-tolerance (DT) into high-cycle-fatigue (HCF) components will require a shift from traditional DT methods that rely on detecting an initial flaw with nondestructive inspection (NDI) methods. The rapid accumulation of cycles in a HCF component will result in a design based on a traditional DT method that is either impractical because of frequent inspections, or because the design will be too heavy to operate efficiently. Furthermore, once a HCF component develops a detectable propagating crack, the remaining fatigue life is short, sometimes less than one flight hour, which does not leave sufficient time for inspection. Therefore, designing a HCF component will require basing the life analysis on an initial flaw that is undetectable with current NDI technology.

The resistance of cortical bone tissue to failure under cyclic loading is reduced with alendronate.

PubMed

Bajaj, Devendra; Geissler, Joseph R; Allen, Matthew R; Burr, David B; Fritton, J C

2014-07-01

Bisphosphonates are the most prescribed preventative treatment for osteoporosis. However, their long-term use has recently been associated with atypical fractures of cortical bone in patients who present with low-energy induced breaks of unclear pathophysiology. The effects of bisphosphonates on the mechanical properties of cortical bone have been exclusively studied under simple, monotonic, quasi-static loading. This study examined the cyclic fatigue properties of bisphosphonate-treated cortical bone at a level in which tissue damage initiates and is accumulated prior to frank fracture in low-energy situations. Physiologically relevant, dynamic, 4-point bending applied to beams (1.5 mm × 0.5 mm × 10 mm) machined from dog rib (n=12/group) demonstrated mechanical failure and micro-architectural features that were dependent on drug dose (3 groups: 0, 0.2, 1.0mg/kg/day; alendronate [ALN] for 3 years) with cortical bone tissue elastic modulus (initial cycles of loading) reduced by 21% (p<0.001) and fatigue life (number of cycles to failure) reduced in a stress-life approach by greater than 3-fold with ALN1.0 (p<0.05). While not affecting the number of osteons, ALN treatment reduced other features associated with bone remodeling, such as the size of osteons (-14%; ALN1.0: 10.5±1.8, VEH: 12.2±1.6, ×10(3) μm2; p<0.01) and the density of osteocyte lacunae (-20%; ALN1.0: 11.4±3.3, VEH: 14.3±3.6, ×10(2) #/mm2; p<0.05). Furthermore, the osteocyte lacunar density was directly proportional to initial elastic modulus when the groups were pooled (R=0.54, p<0.01). These findings suggest that the structural components normally contributing to healthy cortical bone tissue are altered by high-dose ALN treatment and contribute to reduced mechanical properties under cyclic loading conditions. Copyright © 2014 Elsevier Inc. All rights reserved.

A Damage Model for the Simulation of Delamination in Advanced Composites under Variable-Mode Loading

NASA Technical Reports Server (NTRS)

Turon, A.; Camanho, P. P.; Costa, J.; Davila, C. G.

2006-01-01

A thermodynamically consistent damage model is proposed for the simulation of progressive delamination in composite materials under variable-mode ratio. The model is formulated in the context of Damage Mechanics. A novel constitutive equation is developed to model the initiation and propagation of delamination. A delamination initiation criterion is proposed to assure that the formulation can account for changes in the loading mode in a thermodynamically consistent way. The formulation accounts for crack closure effects to avoid interfacial penetration of two adjacent layers after complete decohesion. The model is implemented in a finite element formulation, and the numerical predictions are compared with experimental results obtained in both composite test specimens and structural components.

Shelters of leaf-tying herbivores decompose faster than leaves damaged by free-living insects: Implications for nutrient turnover in polluted habitats.

PubMed

Kozlov, Mikhail V; Zverev, Vitali; Zvereva, Elena L

2016-10-15

Leaf-eating insects can influence decomposition processes by modifying quality of leaf litter, and this impact can be especially pronounced in habitats where leaf-eating insects reach high densities, for example in heavily polluted areas. We hypothesized that the decomposition rate is faster for shelters of leaf-tying larvae than for leaves damaged by free-living insects, in particular due to the accumulation of larval frass within shelters. We exposed litter bags containing samples of three different compositions (shelters built by moth larvae, leaves damaged by free-living insects and intact leaves of mountain birch, Betula pubescens ssp. czerepanovii) for one year at two heavily polluted sites near the nickel-copper smelter at Monchegorsk in north-western Russia and at two unpolluted sites. The decomposition rate of leaves damaged by free-living insects was 91% of that of undamaged leaves, whereas the mass loss of leaves composing shelters did not differ of that of undamaged leaves. These differences between leaves damaged by different guilds of herbivorous insects were uniform across the study sites, although the decomposition rate in polluted sites was reduced to 77% of that in unpolluted sites. Addition of larval frass to undamaged leaves had no effect on the subsequent decomposition rate. Therefore we suggest that damaged leaves tied by shelter-building larvae decompose faster than untied damaged leaves due to a looser physical structure of the litter, which creates favourable conditions for detritivores and soil decomposers. Thus, while leaf damage by insects per se reduces litter quality and its decomposition rate, structuring of litter by leaf-tying insects counterbalances these negative effects. We conclude that leaf-tying larvae, in contrast to free-living defoliators, do not impose negative effects on nutrient turnover rate even at their high densities, which are frequently observed in heavily polluted sites. Copyright © 2016 Elsevier B.V. All rights reserved.

A nonlinear CDM based damage growth law for ductile materials

NASA Astrophysics Data System (ADS)

Gautam, Abhinav; Priya Ajit, K.; Sarkar, Prabir Kumar

2018-02-01

A nonlinear ductile damage growth criterion is proposed based on continuum damage mechanics (CDM) approach. The model is derived in the framework of thermodynamically consistent CDM assuming damage to be isotropic. In this study, the damage dissipation potential is also derived to be a function of varying strain hardening exponent in addition to damage strain energy release rate density. Uniaxial tensile tests and load-unload-cyclic tensile tests for AISI 1020 steel, AISI 1030 steel and Al 2024 aluminum alloy are considered for the determination of their respective damage variable D and other parameters required for the model(s). The experimental results are very closely predicted, with a deviation of 0%-3%, by the proposed model for each of the materials. The model is also tested with predictabilities of damage growth by other models in the literature. Present model detects the state of damage quantitatively at any level of plastic strain and uses simpler material tests to find the parameters of the model. So, it should be useful in metal forming industries to assess the damage growth for the desired deformation level a priori. The superiority of the new model is clarified by the deviations in the predictability of test results by other models.

Reconstructing the Initial Density Field of the Local Universe: Methods and Tests with Mock Catalogs

NASA Astrophysics Data System (ADS)

Wang, Huiyuan; Mo, H. J.; Yang, Xiaohu; van den Bosch, Frank C.

2013-07-01

Our research objective in this paper is to reconstruct an initial linear density field, which follows the multivariate Gaussian distribution with variances given by the linear power spectrum of the current cold dark matter model and evolves through gravitational instabilities to the present-day density field in the local universe. For this purpose, we develop a Hamiltonian Markov Chain Monte Carlo method to obtain the linear density field from a posterior probability function that consists of two components: a prior of a Gaussian density field with a given linear spectrum and a likelihood term that is given by the current density field. The present-day density field can be reconstructed from galaxy groups using the method developed in Wang et al. Using a realistic mock Sloan Digital Sky Survey DR7, obtained by populating dark matter halos in the Millennium simulation (MS) with galaxies, we show that our method can effectively and accurately recover both the amplitudes and phases of the initial, linear density field. To examine the accuracy of our method, we use N-body simulations to evolve these reconstructed initial conditions to the present day. The resimulated density field thus obtained accurately matches the original density field of the MS in the density range 0.3 \\lesssim \\rho /\\bar{\\rho } \\lesssim 20 without any significant bias. In particular, the Fourier phases of the resimulated density fields are tightly correlated with those of the original simulation down to a scale corresponding to a wavenumber of ~1 h Mpc-1, much smaller than the translinear scale, which corresponds to a wavenumber of ~0.15 h Mpc-1.

Ignitor with stable low-energy thermite igniting system

DOEpatents

Kelly, Michael D.; Munger, Alan C.

1991-02-05

A stable compact low-energy igniting system in an ignitor utilizes two components, an initiating charge and an output charge. The initiating charge is a thermite in ultra-fine powder form compacted to 50-70% of theoretical maximum density and disposed in a cavity of a header of the ignitor adjacent to an electrical ignition device, or bridgewire, mounted in the header cavity. The initiating charge is ignitable by operation of the ignition device in a hot-wire mode. The output charge is a thermite in high-density consoladated form compacted to 90-99% of theoretical maximum density and disposed adjacent to the initiating charge on an opposite end thereof from the electrical ignition device and ignitable by the initiating charge. A sleeve is provided for mounting the output charge to the ignitor header with the initiating charge confined therebetween in the cavity.

Laser induced damage thresholds and laser safety levels. Do the units of measurement matter?

NASA Astrophysics Data System (ADS)

Wood, R. M.

1998-04-01

The commonly used units of measurement for laser induced damage are those of peak energy or power density. However, the laser induced damage thresholds, LIDT, of all materials are well known to be absorption, wavelength, spot size and pulse length dependent. As workers using these values become divorced from the theory it becomes increasingly important to use the correct units and to understand the correct scaling factors. This paper summarizes the theory and highlights the danger of using the wrong LIDT units in the context of potentially hazardous materials, laser safety eyewear and laser safety screens.

Development and application of an empirical probability distribution for the prediction error of re-entry body maximum dynamic pressure

NASA Technical Reports Server (NTRS)

Lanzi, R. James; Vincent, Brett T.

1993-01-01

The relationship between actual and predicted re-entry maximum dynamic pressure is characterized using a probability density function and a cumulative distribution function derived from sounding rocket flight data. This paper explores the properties of this distribution and demonstrates applications of this data with observed sounding rocket re-entry body damage characteristics to assess probabilities of sustaining various levels of heating damage. The results from this paper effectively bridge the gap existing in sounding rocket reentry analysis between the known damage level/flight environment relationships and the predicted flight environment.

Ecosystem responses to variable-density thinning for forest restoration in Mill Creek

Treesearch

Lathrop P. Leonard; John-Pascal Berrill; Christa M. Dagley

2017-01-01

Variable-density thinning (VDT) has promise as a forest restoration tool that accelerates development of old-growth redwood (Sequoia sempervirens (D.Don) Endl.) forest characteristics (O’Hara et al. 2010) but can lead to bear damage in north coastal California (Hosack and Fulgham 1998, Perry et al. 2016). Three novel VDT prescriptions (O’...

Repetition rate dependency of low-density plasma effects during femtosecond-laser-based surgery of biological tissue

NASA Astrophysics Data System (ADS)

Kuetemeyer, K.; Baumgart, J.; Lubatschowski, H.; Heisterkamp, A.

2009-11-01

Femtosecond laser based nanosurgery of biological tissue is usually done in two different regimes. Depending on the application, low kHz repetition rates above the optical breakdown threshold or high MHz repetition rates in the low-density plasma regime are used. In contrast to the well understood optical breakdown, mechanisms leading to dissection below this threshold are not well known due to the complexity of chemical effects with high numbers of interacting molecules. Furthermore, the laser repetition rate may influence their efficiency. In this paper, we present our study on low-density plasma effects in biological tissue depending on repetition rate by static exposure of porcine corneal stroma to femtosecond pulses. We observed a continuous increase of the laser-induced damage with decreasing repetition rate over two orders of magnitude at constant numbers of applied laser pulses or constant laser pulse energies. Therefore, low repetition rates in the kHz regime are advantageous to minimize the total delivered energy to biological tissue during femtosecond laser irradiation. However, due to frequent excessive damage in this regime directly above the threshold, MHz repetition rates are preferable to create nanometer-sized cuts in the low-density plasma regime.

Computational Simulation of Damage Progression of Composite Thin Shells Subjected to Mechanical Loads

NASA Technical Reports Server (NTRS)

Gotsis, P. K.; Chamis, C. C.; Minnetyan, L.

1996-01-01

Defect-free and defected composite thin shells with ply orientation (90/0/+/-75) made of graphite/epoxy are simulated for damage progression and fracture due to internal pressure and axial loading. The thin shells have a cylindrical geometry with one end fixed and the other free. The applied load consists of an internal pressure in conjunction with an axial load at the free end, the cure temperature was 177 C (350 F) and the operational temperature was 21 C (70 F). The residual stresses due to the processing are taken into account. Shells with defect and without defects were examined by using CODSTRAN an integrated computer code that couples composite mechanics, finite element and account for all possible failure modes inherent in composites. CODSTRAN traces damage initiation, growth, accumulation, damage propagation and the final fracture of the structure. The results show that damage initiation started with matrix failure while damage/fracture progression occurred due to additional matrix failure and fiber fracture. The burst pressure of the (90/0/+/- 75) defected shell was 0.092% of that of the free defect. Finally the results of the damage progression of the (90/0/+/- 75), defective composite shell was compared with the (90/0/+/- theta, where theta = 45 and 60, layup configurations. It was shown that the examined laminate (90/0/+/- 75) has the least damage tolerant of the two compared defective shells with the (90/0/+/- theta), theta = 45 and 60 laminates.

Engineered Defects for Investigation of Laser-Induced Damage of Fused Silica at 355nm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hamza, A V; Siekhaus, W J; Rubenchik, A M

2001-12-18

Embedded gold and mechanical deformation in silica were used to investigate initiation of laser-induced damage at 3.55-nm (7.6 ns). The nanoparticle-covered surfaces were coated with between 0 and 500 nm of SiO{sub 2} by e-beam deposition. The threshold for observable damage and initiation site morphology for these ''engineered'' surfaces was determined. The gold nanoparticle coated surfaces with 500nm SiO{sub 2} coating exhibited pinpoint damage threshold of <0.7 J/cm{sup 2} determined by light scattering and Nomarski microscopy. The gold nanoparticle coated surfaces with the 100nm SiO{sub 2} coatings exhibited what nominally appeared to be film exfoliation damage threshold of 19 J/cm{supmore » 2} via light scattering and Nomarski microscopy. With atomic force microscopy pinholes could be detected at fluences greater than 7 J/cm{sup 2} and blisters at fluences greater than 3 J/cm{sup 2} on the 100 nm-coated surfaces. A series of mechanical indents and scratches were made in the fused silica substrates using a nano-indentor. Plastic deformation without cracking led to damage thresholds of -25 J/cm{sup 2}, whereas indents and scratches with cracking led to damage thresholds of only {approx}5 J/cm{sup 2}. Particularly illuminating was the deterministic damage of scratches at the deepest end of the scratch, as if the scratch acted as a waveguide.« less

Effects of hydromechanical loading history and antecedent soil mechanical damage on shallow landslide triggering

NASA Astrophysics Data System (ADS)

Fan, Linfeng; Lehmann, Peter; Or, Dani

2015-10-01

Evidence suggests that the sudden triggering of rainfall-induced shallow landslides is preceded by accumulation of local internal failures in the soil mantle before their abrupt coalescence into a landslide failure plane. The mechanical status of a hillslope at any given time reflects competition between local damage accumulated during antecedent rainfall events and rates of mechanical healing (e.g., rebonding of microcracks and root regrowth). This dynamic interplay between damage accumulation and healing rates determines the initial mechanical state for landslide modeling. We evaluated the roles of these dynamic processes on landslide characteristics and patterns using a hydromechanical landslide-triggering model for a sequence of rainfall scenarios. The progressive nature of soil failure was represented by the fiber bundle model formalism that considers threshold strength of mechanical bonds linking adjacent soil columns and bedrock. The antecedent damage induced by prior rainfall events was expressed by the fraction of broken fibers that gradually regain strength or mechanically heal at rates specific to soil and roots. Results indicate that antecedent damage accelerates landslide initiation relative to pristine (undamaged) hillslopes. The volumes of first triggered landslides increase with increasing antecedent damage; however, for heavily damaged hillslopes, landslide volumes tend to decrease. Elapsed time between rainfall events allows mechanical healing that reduces the effects of antecedent damage. This study proposed a quantitative framework for systematically incorporating hydromechanical loading history and information on precursor events (e.g., such as recorded by acoustic emissions) into shallow landslide hazard assessment.

The DNA damage response during mitosis.

PubMed

Heijink, Anne Margriet; Krajewska, Małgorzata; van Vugt, Marcel A T M

2013-10-01

Cells are equipped with a cell-intrinsic signaling network called the DNA damage response (DDR). This signaling network recognizes DNA lesions and initiates various downstream pathways to coordinate a cell cycle arrest with the repair of the damaged DNA. Alternatively, the DDR can mediate clearance of affected cells that are beyond repair through apoptosis or senescence. The DDR can be activated in response to DNA damage throughout the cell cycle, although the extent of DDR signaling is different in each cell cycle phase. Especially in response to DNA double strand breaks, only a very marginal response was observed during mitosis. Early on it was recognized that cells which are irradiated during mitosis continued division without repairing broken chromosomes. Although these initial observations indicated diminished DNA repair and lack of an acute DNA damage-induced cell cycle arrest, insight into the mechanistic re-wiring of DDR signaling during mitosis was only recently provided. Different mechanisms appear to be at play to inactivate specific signaling axes of the DDR network in mitosis. Importantly, mitotic cells not simply inactivate the entire DDR, but appear to mark their DNA damage for repair after mitotic exit. Since the treatment of cancer frequently involves agents that induce DNA damage as well as agents that block mitotic progression, it is clinically relevant to obtain a better understanding of how cancer cells deal with DNA damage during interphase versus mitosis. In this review, the molecular details concerning DDR signaling during mitosis as well as the consequences of encountering DNA damage during mitosis for cellular fate are discussed. Copyright © 2013 Elsevier B.V. All rights reserved.

Influence of subsurface defects on damage performance of fused silica in ultraviolet laser

NASA Astrophysics Data System (ADS)

Huang, Jin; Zhou, Xinda; Liu, Hongjie; Wang, Fengrui; Jiang, Xiaodong; Wu, Weidong; Tang, Yongjian; Zheng, Wanguo

2013-02-01

In ultraviolet pulse laser, damage performance of fused silica optics is directly dependent on the absorptive impurities and scratches in subsurface, which are induced by mechanical polishing. In the research about influence of subsurface defects on damage performance, a series of fused silica surfaces with various impurity concentrations and scratch structures were created by hydrofluoric (HF) acid solution etching. Time of Flight secondary ion mass spectrometry and scanning probe microprobe revealed that with increasing etching depth, impurity concentrations in subsurface layers are decreased, the scratch structures become smoother and the diameter:depth ratio is increased. Damage performance test with 355-nm pulse laser showed that when 600 nm subsurface thickness is removed by HF acid etching, laser-induced damage threshold of fused silica is raised by 40 percent and damage density is decreased by over one order of magnitude. Laser weak absorption was tested to explain the cause of impurity elements impacting damage performance, field enhancement caused by change of scratch structures was calculated by finite difference time domain simulation, and the calculated results are in accord with the damage test results.

Stereoscopic Analysis of Silicone Breast Implant Shells Damaged by Surgical Instruments.

PubMed

Rapp, Derek A; Neaman, Keith C; Hammond, Dennis C

2015-07-01

Iatrogenic shell injury during the implantation and explantation of silicone gel breast implants may lead to eventual device failure. Identification of the patterns of injury caused by surgical instruments is important when attempting to characterize the cause of shell rupture. Understanding the true causes of device failure may help with its prevention. The purpose of this study was to microscopically characterize patterns of shell injury induced by various surgical instruments. Textured and smooth silicone gel implants were intentionally damaged with a variety of surgical instruments. Various scalpels and surgical scissors ranging in fineness were used to create full-thickness injuries in the implant shell. Optical microscopy and scanning electron microscopy were then used to image the injured area to determine patterns of injury. Full-thickness striations across the thickness of the shell could be seen with damage caused by scissors. The density of these striations correlated directly with the fineness of scissors used. No striations were seen with injuries caused by scalpels. Striations were only observed in injuries caused by scissors and suture needles. Striation density correlated with the coarseness of the cutting edge. No such striations were seen in shells damaged by a scalpel even when the angle of approach was changed. This difference can be of assistance in distinguishing between scissors versus scalpel injury of an implant shell.

Effect of surface roughness and subsurface damage on grazing-incidence x-ray scattering and specular reflectance.

PubMed

Lodha, G S; Yamashita, K; Kunieda, H; Tawara, Y; Yu, J; Namba, Y; Bennett, J M

1998-08-01

Grazing-incidence specular reflectance and near-specular scattering were measured at Al-K(alpha) (1.486-keV, 8.34-?) radiation on uncoated dielectric substrates whose surface topography had been measured with a scanning probe microscope and a mechanical profiler. Grazing-incidence specular reflectance was also measured on selected substrates at the Cu-K(alpha) (8.047-keV, 1.54-?) wavelength. Substrates included superpolished and conventionally polished fused silica; SiO(2) wafers; superpolished and precision-ground Zerodur; conventionally polished, float-polished, and precision-ground BK-7 glass; and superpolished and precision-ground silicon carbide. Roughnesses derived from x-ray specular reflectance and scattering measurements were in good agreement with topographic roughness values measured with a scanning probe microscope (atomic force microscope) and a mechanical profiler that included similar ranges of surface spatial wavelengths. The specular reflectance was also found to be sensitive to the density of polished surface layers and subsurface damage down to the penetration depth of the x rays. Density gradients and subsurface damage were found in the superpolished fused-silica and precision-ground Zerodur samples. These results suggest that one can nondestructively evaluate subsurface damage in transparent materials using grazing-incidence x-ray specular reflectance in the 1.5-8-keV range.

Landslide Distribution, Damage and Land Use Interactions During the 2004 Chuetsu Earthquake

NASA Astrophysics Data System (ADS)

Sidle, R. C.; Trandafir, A. C.; Kamai, T.

2005-05-01

A series of earthquakes struck Niigata Prefecture, Japan, on 23 October 2004 killing about 40 people and injuring about 3000. These earthquakes were characterized by a shallow focal depth (13 km) that generated strong levels of ground motion, resulting in extensive damage and thousands of landslides throughout the region. Most landslides on natural slopes occurred in the regional geological structure consisting of sandy siltstone and thin-bedded alternations of sandstone and siltstone. Earthquakes exacerbate such potential instabilities by the ground motion induced and the enhancement of pore water pressure in wet regoliths. The three strongest earthquakes occurred within a period of less than 40 minutes, and had sequential magnitudes (JMA) of 6.8, 6.3, and 6.5. The highest density of landslides (12/km2) was mapped within a 2.9 km radius of the M6.5 epicenter near Yamakoshi village; about 4 times higher density compared to the other epicenters located to the east and west. This higher density may be a consequence of the cumulative shaking effects associated with the two earlier earthquakes of M6.8 and 6.5, in addition to the topographic and geologic factors controlling the stability of the region. Roads, residential fills, agricultural terraces on hillslopes, and other earthworks increased the susceptibility of sites to slope failure. Numerous earthquake-induced failures in terraces and adjacent hillslopes around rice paddy fields occurred near Yamakoshi village. A housing development in Nagaoka city constructed on an old earthflow suffered from severe damage to fill slopes during the earthquake. Nearly saturated conditions in these deep fills together with poor drainage systems contributed to the landslide damages. Clearly, land use activities in rural and urban areas exacerbated the extent of earthquake-triggered landslides.

Evaluation of interference fit and bone damage of an uncemented femoral knee implant.

PubMed

Berahmani, Sanaz; Hendriks, Maartje; de Jong, Joost J A; van den Bergh, Joop P W; Maal, Thomas; Janssen, Dennis; Verdonschot, Nico

2018-01-01

During implantation of an uncemented femoral knee implant, press-fit interference fit provides the primary stability. It is assumed that during implantation a combination of elastic and plastic deformation and abrasion of the bone will occur, but little is known about what happens at the bone-implant interface and how much press-fit interference fit is eventually achieved. Five cadaveric femora were prepared and implantation was performed by an experienced surgeon. Micro-CT- and conventional CT-scans were obtained pre- and post-implantation for geometrical measurements and to measure bone mineral density. Additionally, the position of the implant with respect to the bone was determined by optical scanning of the reconstructions. By measuring the differences in surface geometry, assessments were made of the cutting error, the actual interference fit, the amount of bone damage, and the effective interference fit. Our analysis showed an average cutting error of 0.67mm (SD 0.17mm), which pointed mostly towards bone under-resections. We found an average actual AP interference fit of 1.48mm (SD 0.27mm), which was close to the nominal value of 1.5mm. We observed combinations of bone damage and elastic deformation in all bone specimens, which showed a trend to be related with bone density. Higher bone density tended to lead to lower bone damage and higher elastic deformation. The results of the current study indicate different factors that interact while implanting an uncemented femoral knee component. This knowledge can be used to fine-tune design criteria of femoral components to achieve adequate primary stability for all patients. Copyright © 2017 Elsevier Ltd. All rights reserved.

Reactive oxygen species generation is not different during isometric and lengthening contractions of mouse muscle

PubMed Central

Sloboda, Darcée D.

2013-01-01

Skeletal muscles can be injured by lengthening contractions, when the muscles are stretched while activated. Lengthening contractions produce structural damage that leads to the degeneration and regeneration of damaged muscle fibers by mechanisms that have not been fully elucidated. Reactive oxygen species (ROS) generated at the time of injury may initiate degenerative or regenerative processes. In the present study we hypothesized that lengthening contractions that damage the muscle would generate more ROS than isometric contractions that do not cause damage. To test our hypothesis, we subjected muscles of mice to lengthening contractions or isometric contractions and simultaneously monitored intracellular ROS generation with the fluorescent indicator 5-(and-6)-chloromethyl-2′,7′-dichlorodihydrofluorescein (CM-DCFH), which is oxidized by ROS to form the fluorescent product CM-DCF. We found that CM-DCF fluorescence was not different during or shortly after lengthening contractions compared with isometric controls, regardless of the amount of stretch and damage that occurred during the lengthening contractions. The only exception was that after severe stretches, the increase in CM-DCF fluorescence was impaired. We conclude that lengthening contractions that damage the muscle do not generate more ROS than isometric contractions that do not cause damage. The implication is that ROS generated at the time of injury are not the initiating signals for subsequent degenerative or regenerative processes. PMID:23948772

Reactive oxygen species generation is not different during isometric and lengthening contractions of mouse muscle.

PubMed

Sloboda, Darcée D; Brooks, Susan V

2013-10-01

Skeletal muscles can be injured by lengthening contractions, when the muscles are stretched while activated. Lengthening contractions produce structural damage that leads to the degeneration and regeneration of damaged muscle fibers by mechanisms that have not been fully elucidated. Reactive oxygen species (ROS) generated at the time of injury may initiate degenerative or regenerative processes. In the present study we hypothesized that lengthening contractions that damage the muscle would generate more ROS than isometric contractions that do not cause damage. To test our hypothesis, we subjected muscles of mice to lengthening contractions or isometric contractions and simultaneously monitored intracellular ROS generation with the fluorescent indicator 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein (CM-DCFH), which is oxidized by ROS to form the fluorescent product CM-DCF. We found that CM-DCF fluorescence was not different during or shortly after lengthening contractions compared with isometric controls, regardless of the amount of stretch and damage that occurred during the lengthening contractions. The only exception was that after severe stretches, the increase in CM-DCF fluorescence was impaired. We conclude that lengthening contractions that damage the muscle do not generate more ROS than isometric contractions that do not cause damage. The implication is that ROS generated at the time of injury are not the initiating signals for subsequent degenerative or regenerative processes.

Particle-based simulations of bilayer membranes: self-assembly, structural analysis, and shock-wave damage

NASA Astrophysics Data System (ADS)

Steinhauser, Martin O.; Schindler, Tanja

2017-01-01

We report on the results of particle-based, coarse-grained molecular dynamics simulations of amphiphilic lipid molecules in aqueous environment where the membrane structures at equilibrium are subsequently exposed to strong shock waves, and their damage is analyzed. The lipid molecules self-assemble from unbiased random initial configurations to form stable bilayer membranes, including closed vesicles. During self-assembly of lipid molecules, we observe several stages of clustering, starting with many small clusters of lipids, gradually merging together to finally form one single bilayer membrane. We find that the clustering of lipids sensitively depends on the hydrophobic interaction h_c of the lipid tails in our model and on temperature T of the system. The self-assembled bilayer membranes are quantitatively analyzed at equilibrium with respect to their degree of order and their local structure. We also show that—by analyzing the membrane fluctuations and using a linearized theory— we obtain area compression moduli K_A and bending stiffnesses κ _B for our bilayer membranes which are within the experimental range of in vivo and in vitro measurements of biological membranes. We also discuss the density profile and the pair correlation function of our model membranes at equilibrium which has not been done in previous studies of particle-based membrane models. Furthermore, we present a detailed phase diagram of our lipid model that exhibits a sol-gel transition between quasi-solid and fluid domains, and domains where no self-assembly of lipids occurs. In addition, we present in the phase diagram the conditions for temperature T and hydrophobicity h_c of the lipid tails of our model to form closed vesicles. The stable bilayer membranes obtained at equilibrium are then subjected to strong shock waves in a shock tube setup, and we investigate the damage in the membranes due to their interaction with shock waves. Here, we find a transition from self-repairing membranes (reducing their damage after impact) and permanent (irreversible) damage, depending on the shock front speed. The here presented idea of using coarse-grained (CG) particle models for soft matter systems in combination with the investigation of shock-wave effects in these systems is a quite new approach.

Dose-rate effect of ultrashort electron beam radiation on DNA damage and repair in vitro.

PubMed

Babayan, Nelly; Hovhannisyan, Galina; Grigoryan, Bagrat; Grigoryan, Ruzanna; Sarkisyan, Natalia; Tsakanova, Gohar; Haroutiunian, Samvel; Aroutiounian, Rouben

2017-11-01

Laser-generated electron beams are distinguished from conventional accelerated particles by ultrashort beam pulses in the femtoseconds to picoseconds duration range, and their application may elucidate primary radiobiological effects. The aim of the present study was to determine the dose-rate effect of laser-generated ultrashort pulses of 4 MeV electron beam radiation on DNA damage and repair in human cells. The dose rate was increased via changing the pulse repetition frequency, without increasing the electron energy. The human chronic myeloid leukemia K-562 cell line was used to estimate the DNA damage and repair after irradiation, via the comet assay. A distribution analysis of the DNA damage was performed. The same mean level of initial DNA damages was observed at low (3.6 Gy/min) and high (36 Gy/min) dose-rate irradiation. In the case of low-dose-rate irradiation, the detected DNA damages were completely repairable, whereas the high-dose-rate irradiation demonstrated a lower level of reparability. The distribution analysis of initial DNA damages after high-dose-rate irradiation revealed a shift towards higher amounts of damage and a broadening in distribution. Thus, increasing the dose rate via changing the pulse frequency of ultrafast electrons leads to an increase in the complexity of DNA damages, with a consequent decrease in their reparability. Since the application of an ultrashort pulsed electron beam permits us to describe the primary radiobiological effects, it can be assumed that the observed dose-rate effect on DNA damage/repair is mainly caused by primary lesions appearing at the moment of irradiation. © The Author 2017. Published by Oxford University Press on behalf of The Japan Radiation Research Society and Japanese Society for Radiation Oncology.

Sequential projection pursuit for optimised vibration-based damage detection in an experimental wind turbine blade

NASA Astrophysics Data System (ADS)

Hoell, Simon; Omenzetter, Piotr

2018-02-01

To advance the concept of smart structures in large systems, such as wind turbines (WTs), it is desirable to be able to detect structural damage early while using minimal instrumentation. Data-driven vibration-based damage detection methods can be competitive in that respect because global vibrational responses encompass the entire structure. Multivariate damage sensitive features (DSFs) extracted from acceleration responses enable to detect changes in a structure via statistical methods. However, even though such DSFs contain information about the structural state, they may not be optimised for the damage detection task. This paper addresses the shortcoming by exploring a DSF projection technique specialised for statistical structural damage detection. High dimensional initial DSFs are projected onto a low-dimensional space for improved damage detection performance and simultaneous computational burden reduction. The technique is based on sequential projection pursuit where the projection vectors are optimised one by one using an advanced evolutionary strategy. The approach is applied to laboratory experiments with a small-scale WT blade under wind-like excitations. Autocorrelation function coefficients calculated from acceleration signals are employed as DSFs. The optimal numbers of projection vectors are identified with the help of a fast forward selection procedure. To benchmark the proposed method, selections of original DSFs as well as principal component analysis scores from these features are additionally investigated. The optimised DSFs are tested for damage detection on previously unseen data from the healthy state and a wide range of damage scenarios. It is demonstrated that using selected subsets of the initial and transformed DSFs improves damage detectability compared to the full set of features. Furthermore, superior results can be achieved by projecting autocorrelation coefficients onto just a single optimised projection vector.

Radiation Tolerant Interfaces: Influence of Local Stoichiometry at the Misfit Dislocation on Radiation Damage Resistance of Metal/Oxide Interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shutthanandan, Vaithiyalingam; Choudhury, Samrat; Manandhar, Sandeep

The interaction of radiation with materials controls the performance, reliability, and safety of many structures in nuclear power systems. Revolutionary improvements in radiation damage resistance may be attainable if methods can be found to manipulate interface properties to give optimal interface stability and point defect recombination capability. To understand how variations in interface properties such as misfit dislocation density and local chemistry affect radiation-induced defect absorption and recombination, a model system of metallic Cr xV 1-x (0 ≤ x ≤ 1) epitaxial films deposited on MgO(001) single crystal substrates has been explored in this paper. By controlling film composition, themore » lattice mismatch between the film and MgO is adjusted to vary the misfit dislocation density at the metal/oxide interface. The stability of these interfaces under various irradiation conditions is studied experimentally and theoretically. The results indicate that, unlike at metal/metal interfaces, the misfit dislocation density does not dominate radiation damage tolerance at metal/oxide interfaces. Rather, the stoichiometry and the location of the misfit dislocation extra half-plane (in the metal or the oxide) drive radiation-induced defect behavior. Finally, together, these results demonstrate the sensitivity of defect recombination to interfacial chemistry and provide new avenues for engineering radiation-tolerant nanomaterials for next-generation nuclear power plants.« less

Radiation Tolerant Interfaces: Influence of Local Stoichiometry at the Misfit Dislocation on Radiation Damage Resistance of Metal/Oxide Interfaces

DOE PAGES

Shutthanandan, Vaithiyalingam; Choudhury, Samrat; Manandhar, Sandeep; ...

2017-04-24

The interaction of radiation with materials controls the performance, reliability, and safety of many structures in nuclear power systems. Revolutionary improvements in radiation damage resistance may be attainable if methods can be found to manipulate interface properties to give optimal interface stability and point defect recombination capability. To understand how variations in interface properties such as misfit dislocation density and local chemistry affect radiation-induced defect absorption and recombination, a model system of metallic Cr xV 1-x (0 ≤ x ≤ 1) epitaxial films deposited on MgO(001) single crystal substrates has been explored in this paper. By controlling film composition, themore » lattice mismatch between the film and MgO is adjusted to vary the misfit dislocation density at the metal/oxide interface. The stability of these interfaces under various irradiation conditions is studied experimentally and theoretically. The results indicate that, unlike at metal/metal interfaces, the misfit dislocation density does not dominate radiation damage tolerance at metal/oxide interfaces. Rather, the stoichiometry and the location of the misfit dislocation extra half-plane (in the metal or the oxide) drive radiation-induced defect behavior. Finally, together, these results demonstrate the sensitivity of defect recombination to interfacial chemistry and provide new avenues for engineering radiation-tolerant nanomaterials for next-generation nuclear power plants.« less

Distribution and Feeding Behavior of Omorgus suberosus (Coleoptera: Trogidae) in Lepidochelys olivacea Turtle Nests

PubMed Central

Baena, Martha L.; Escobar, Federico; Halffter, Gonzalo; García–Chávez, Juan H.

2015-01-01

Omorgus suberosus (Fabricius, 1775) has been identified as a potential predator of the eggs of the turtle Lepidochelys olivacea (Eschscholtz, 1829) on one of the main turtle nesting beaches in the world, La Escobilla in Oaxaca, Mexico. This study presents an analysis of the spatio–temporal distribution of the beetle on this beach (in areas of high and low density of L. olivacea nests over two arrival seasons) and an evaluation, under laboratory conditions, of the probability of damage to the turtle eggs by this beetle. O. suberosus adults and larvae exhibited an aggregated pattern at both turtle nest densities; however, aggregation was greater in areas of low nest density, where we found the highest proportion of damaged eggs. Also, there were fluctuations in the temporal distribution of the adult beetles following the arrival of the turtles on the beach. Under laboratory conditions, the beetles quickly damaged both dead eggs and a mixture of live and dead eggs, but were found to consume live eggs more slowly. This suggests that O. suberosus may be recycling organic material; however, its consumption of live eggs may be sufficient in some cases to interrupt the incubation period of the turtle. We intend to apply these results when making decisions regarding the L. olivacea nests on La Escobilla Beach, one of the most important sites for the conservation of this species. PMID:26422148

46 CFR 185.304 - Navigation underway.

Code of Federal Regulations, 2013 CFR

2013-10-01

... direction of the transiting area; (2) Tidal state; (3) Prevailing and forecasted visibility and environmental conditions, including wind and waves; (4) Density of marine traffic; (5) Potential damage caused...

46 CFR 185.304 - Navigation underway.

Code of Federal Regulations, 2012 CFR

2012-10-01

... direction of the transiting area; (2) Tidal state; (3) Prevailing and forecasted visibility and environmental conditions, including wind and waves; (4) Density of marine traffic; (5) Potential damage caused...

46 CFR 185.304 - Navigation underway.

Code of Federal Regulations, 2014 CFR

2014-10-01

... direction of the transiting area; (2) Tidal state; (3) Prevailing and forecasted visibility and environmental conditions, including wind and waves; (4) Density of marine traffic; (5) Potential damage caused...

46 CFR 185.304 - Navigation underway.

Code of Federal Regulations, 2011 CFR

2011-10-01

... direction of the transiting area; (2) Tidal state; (3) Prevailing and forecasted visibility and environmental conditions, including wind and waves; (4) Density of marine traffic; (5) Potential damage caused...

Adhesion and splash dispersal of Salmonella enterica Typhimurium on tomato leaflets: effects of rdar morphotype and trichome density.

PubMed

Cevallos-Cevallos, Juan M; Gu, Ganyu; Danyluk, Michelle D; van Bruggen, Ariena H C

2012-11-01

Salmonella enterica strains with rdar (red dry and rough) and saw (smooth and white) morphotypes have previously been associated with tomato outbreaks but the dispersal mechanisms of these morphotypes are still poorly understood. In this study, Salmonella adhesion was distinguished from attachment by comparing different contact periods. Initial adhesion of rdar and saw morphotypes of Salmonella was compared in relation to tomato plants with different leaf trichome densities. Trichome densities were increased or reduced by treatment with jasmonic or salicylic acid, respectively. The overall effect of Salmonella morphotype and trichome density on splash dispersal was assessed in a rain simulator and correlated to cell hydrophobicity and initial adhesion. The presence of the rdar morphotype increased initial adhesion at high trichome densities but not at low trichome densities. Attachment of the rdar strain occurred after 30s contact time regardless of trichome density. Splash dispersal was slightly further for the saw morphotype than the rdar morphotype of S. enterica at all trichome densities. Salmonella cells of both morphotypes survived significantly better on the surface of high trichome density leaflets. Copyright © 2012 Elsevier B.V. All rights reserved.

Ipsilesional motor deficits following stroke reflect hemispheric specializations for movement control.

PubMed

Schaefer, Sydney Y; Haaland, Kathleen Y; Sainburg, Robert L

2007-08-01

Recent reports of functional impairment in the 'unaffected' limb of stroke patients have suggested that these deficits vary with the side of lesion. This not only supports the idea that the ipsilateral hemisphere contributes to arm movements, but also implies that such contributions are lateralized. We have previously suggested that the left and right hemispheres are specialized for controlling different features of movement. In reaching movements, the non-dominant arm appears better adapted for achieving accurate final positions and the dominant arm for specifying initial trajectory features, such as movement direction and peak acceleration. The purpose of this study was to determine whether different features of control could characterize ipsilesional motor deficits following stroke. Healthy control subjects and patients with either left- or right-hemisphere damage performed targeted single-joint elbow movements of different amplitudes in their ipsilateral hemispace. We predicted that left-hemisphere damage would produce deficits in specification of initial trajectory features, while right-hemisphere damage would produce deficits in final position accuracy. Consistent with our predictions, patients with left, but not right, hemisphere damage showed reduced modulation of acceleration amplitude. However, patients with right, but not left, hemisphere damage showed significantly larger errors in final position, which corresponded to reduced modulation of acceleration duration. Neither patient group differed from controls in terms of movement speed. Instead, the mechanisms by which speed was specified, through modulation of acceleration amplitude and modulation of acceleration duration, appeared to be differentially affected by left- and right-hemisphere damage. These findings support the idea that each hemisphere contributes differentially to the control of initial trajectory and final position, and that ipsilesional deficits following stroke reflect this lateralization in control.

Temperature-dependent elimination efficiency on Phaeocystis globosa by different initial population sizes of rotifer Brachionus plicatilis.

PubMed

Sun, Yunfei; Wang, Yuanyuan; Lei, Jin; Qian, Chenchen; Zhu, Xuexia; Akbar, Siddiq; Huang, Yuan; Yang, Zhou

2018-07-01

Due to sea water eutrophication and global warming, the harmful Phaeocystis blooms outbreak frequently in coastal waters, which cause a serious threat to marine ecosystem. The application of rotifer to control the harmful alga is a promising way. To investigate the influence of initial rotifer density and temperature on the ability of rotifer Brachionus plicatilis to eliminate Phaeocystis globosa population, we cultured P. globosa with different initial rotifer densities (1, 3, 5 inds mL -1 ) at 19, 22, 25, 28, and 31 °C for 9-16 d. Results showed that the population of rotifer feeding on Phaeocystis increased rapidly and higher temperatures favored the growth of P. globosa and B. plicatilis. With increased initial rotifer density and temperature, both the clearance rate of rotifer and the reduction rate of P. globosa increased, and thus P. globosa were eliminated earlier. Both temperature and initial rotifer density had significant effects on clearance rate of rotifer and the time to Phaeocystis extinction, and there was a significant interaction between the two factors on the two parameters, i.e., the effect of initial rotifer density on eliminating Phaeocystis decreased with increasing temperature. The rotifer in 5 inds mL -1 at 28 °C eliminated P. globosa in 4 d, whereas the rotifer in 1 ind mL -1 at 19 °C spent about 16 d on eliminating P. globosa. In conclusion, higher temperature and bigger initial rotifer density promote rotifer to eliminate the harmful P. globosa, and the optimal temperature for rotifer to clear P. globosa is 28 °C. Copyright © 2018 Elsevier Ltd. All rights reserved.

Engine materials characterization and damage monitoring by using x ray technologies

NASA Technical Reports Server (NTRS)

Baaklini, George Y.

1993-01-01

X ray attenuation measurement systems that are capable of characterizing density variations in monolithic ceramics and damage due to processing and/or mechanical testing in ceramic and intermetallic matrix composites are developed and applied. Noninvasive monitoring of damage accumulation and failure sequences in ceramic matrix composites is used during room-temperature tensile testing. This work resulted in the development of a point-scan digital radiography system and an in situ x ray material testing system. The former is used to characterize silicon carbide and silicon nitride specimens, and the latter is used to image the failure behavior of silicon-carbide-fiber-reinforced, reaction-bonded silicon nitride matrix composites. State-of-the-art x ray computed tomography is investigated to determine its capabilities and limitations in characterizing density variations of subscale engine components (e.g., a silicon carbide rotor, a silicon nitride blade, and a silicon-carbide-fiber-reinforced beta titanium matrix rod, rotor, and ring). Microfocus radiography, conventional radiography, scanning acoustic microscopy, and metallography are used to substantiate the x ray computed tomography findings. Point-scan digital radiography is a viable technique for characterizing density variations in monolithic ceramic specimens. But it is very limited and time consuming in characterizing ceramic matrix composites. Precise x ray attenuation measurements, reflecting minute density variations, are achieved by photon counting and by using microcollimators at the source and the detector. X ray computed tomography is found to be a unique x ray attenuation measurement technique capable of providing cross-sectional spatial density information in monolithic ceramics and metal matrix composites. X ray computed tomography is proven to accelerate generic composite component development. Radiographic evaluation before, during, and after loading shows the effect of preexisting volume flaws on the fracture behavior of composites. Results from one-, three-, five-, and eight-ply ceramic composite specimens show that x ray film radiography can monitor damage accumulation during tensile loading. Matrix cracking, fiber-matrix debonding, fiber bridging, and fiber pullout are imaged throughout the tensile loading of the specimens. In situ film radiography is found to be a practical technique for estimating interfacial shear strength between the silicon carbide fibers and the reaction-bonded silicon nitride matrix. It is concluded that pretest, in situ, and post-test x ray imaging can provide greater understanding of ceramic matrix composite mechanical behavior.

The Initial Physical Conditions of Kepler-36 b and c

NASA Astrophysics Data System (ADS)

Owen, James E.; Morton, Timothy. D.

2016-03-01

The Kepler-36 planetary system consists of two exoplanets at similar separations (0.115 and 0.128 au), which have dramatically different densities. The inner planet has a density consistent with an Earth-like composition, while the outer planet is extremely low density, such that it must contain a voluminous H/He envelope. Such a density difference would pose a problem for any formation mechanism if their current densities were representative of their composition at formation. However, both planets are at close enough separations to have undergone significant evaporation in the past. We constrain the core mass, core composition, initial envelope mass, and initial cooling time of each planet using evaporation models conditioned on their present-day masses and radii, as inferred from Kepler photometry and transit timing analysis. The inner planet is consistent with being an evaporatively stripped core, while the outer planet has retained some of its initial envelope due to its higher core mass. Therefore, both planets could have had a similar formation pathway, with the inner planet having an initial envelope-mass fraction of ≲10% and core mass of ˜4.4 M⊕, while the outer had an initial envelope-mass fraction of the order of 15%-30% and core mass ˜7.3 M⊕. Finally, our results indicate that the outer planet had a long (≳30 Myr) initial cooling time, much longer than would naively be predicted from simple timescale arguments. The long initial cooling time could be evidence for a dramatic early cooling episode such as the recently proposed “boil-off” process.

The Correlation Between Green Density and the Occurrence of Honeycomb in Kiln-Dried

Treesearch

Robert A. Harris; Philip A. Araman

1995-01-01

Fresh-cut, 5/4 red oak (Quercus sp.) boards were weighed, measured to determine volume and then kiln-dried to determine if the initial green density (green weight/green volume) was correlated to the occurrence of honeycomb. A positive relationship was found between the occurrence of honeycomb during drying and the initial green density. These results...

Using remotely sensed data and elementary analytical techniques in post-katrina mississippi to examine storm damage modeling

Treesearch

Curtis A. Collins; David L. Evans; Keith L. Belli; Patrick A. Glass

2010-01-01

Hurricane Katrina’s passage through south Mississippi on August 29, 2005, which damaged or destroyed thousands of hectares of forest land, was followed by massive salvage, cleanup, and assessment efforts. An initial assessment by the Mississippi Forestry Commission estimated that over $1 billion in raw wood material was downed by the storm, with county-level damage...

Dynamic changes to survivin subcellular localization are initiated by DNA damage

PubMed Central

Asumen, Maritess Gay; Ifeacho, Tochukwu V; Cockerham, Luke; Pfandl, Christina; Wall, Nathan R

2010-01-01

Subcellular distribution of the apoptosis inhibitor survivin and its ability to relocalize as a result of cell cycle phase or therapeutic insult has led to the hypothesis that these subcellular pools may coincide with different survivin functions. The PIK kinases (ATM, ATR and DNA-PK) phosphorylate a variety of effector substrates that propagate DNA damage signals, resulting in various biological outputs. Here we demonstrate that subcellular repartitioning of survivin in MCF-7 cells as a result of UV light-mediated DNA damage is dependent upon DNA damage-sensing proteins as treatment with the pan PIK kinase inhibitor wortmannin repartitioned survivin in the mitochondria and diminished it from the cytosol and nucleus. Mitochondrial redistribution of survivin, such as was recorded after wortmannin treatment, occurred in cells lacking any one of the three DNA damage sensing protein kinases: DNA-PK, ATM or ATR. However, failed survivin redistribution from the mitochondria in response to low-dose UV occurred only in the cells lacking ATM, implying that ATM may be the primary kinase involved in this process. Taken together, this data implicates survivian’s subcellular distribution is a dynamic physiological process that appears responsive to UV light-initiated DNA damage and that its distribution may be responsible for its multifunctionality. PMID:20856848

Continuous Quadrupole Magnetic Separation of Islets during Digestion Improves Purified Porcine Islet Viability.

PubMed

Weegman, Bradley P; Kumar Sajja, Venkata Sunil; Suszynski, Thomas M; Rizzari, Michael D; Scott Iii, William E; Kitzmann, Jennifer P; Mueller, Kate R; Hanley, Thomas R; Kennedy, David J; Todd, Paul W; Balamurugan, Appakalai N; Hering, Bernhard J; Papas, Klearchos K

2016-01-01

Islet transplantation (ITx) is an emerging and promising therapy for patients with uncontrolled type 1 diabetes. The islet isolation and purification processes require exposure to extended cold ischemia, warm-enzymatic digestion, mechanical agitation, and use of damaging chemicals for density gradient separation (DG), all of which reduce viable islet yield. In this paper, we describe initial proof-of-concept studies exploring quadrupole magnetic separation (QMS) of islets as an alternative to DG to reduce exposure to these harsh conditions. Three porcine pancreata were split into two parts, the splenic lobe (SPL) and the combined connecting/duodenal lobes (CDL), for paired digestions and purifications. Islets in the SPL were preferentially labeled using magnetic microparticles (MMPs) that lodge within the islet microvasculature when infused into the pancreas and were continuously separated from the exocrine tissue by QMS during the collection phase of the digestion process. Unlabeled islets from the CDL were purified by conventional DG. Islets purified by QMS exhibited significantly improved viability (measured by oxygen consumption rate per DNA, p < 0.03) and better morphology relative to control islets. Islet purification by QMS can reduce the detrimental effects of prolonged exposure to toxic enzymes and density gradient solutions and substantially improve islet viability after isolation.

Continuous Quadrupole Magnetic Separation of Islets during Digestion Improves Purified Porcine Islet Viability

PubMed Central

Kumar Sajja, Venkata Sunil; Rizzari, Michael D.; Scott III, William E.; Kitzmann, Jennifer P.; Kennedy, David J.; Todd, Paul W.; Balamurugan, Appakalai N.; Hering, Bernhard J.

2016-01-01

Islet transplantation (ITx) is an emerging and promising therapy for patients with uncontrolled type 1 diabetes. The islet isolation and purification processes require exposure to extended cold ischemia, warm-enzymatic digestion, mechanical agitation, and use of damaging chemicals for density gradient separation (DG), all of which reduce viable islet yield. In this paper, we describe initial proof-of-concept studies exploring quadrupole magnetic separation (QMS) of islets as an alternative to DG to reduce exposure to these harsh conditions. Three porcine pancreata were split into two parts, the splenic lobe (SPL) and the combined connecting/duodenal lobes (CDL), for paired digestions and purifications. Islets in the SPL were preferentially labeled using magnetic microparticles (MMPs) that lodge within the islet microvasculature when infused into the pancreas and were continuously separated from the exocrine tissue by QMS during the collection phase of the digestion process. Unlabeled islets from the CDL were purified by conventional DG. Islets purified by QMS exhibited significantly improved viability (measured by oxygen consumption rate per DNA, p < 0.03) and better morphology relative to control islets. Islet purification by QMS can reduce the detrimental effects of prolonged exposure to toxic enzymes and density gradient solutions and substantially improve islet viability after isolation. PMID:27843954

[Live coral predation by fish in Tayrona Nature National Park, Colombian Caribbean].

PubMed

Reyes-Nivia, María Catalina; Garzón-Ferreira, Jaime; Rodríguez-Ramírez, Alberto

2004-12-01

Live coral predation by fish was evaluated in two bays of the Tayrona National Natural Park (Colombia), as a possible biological agent causing coral mortality. Visual censuses were used to identify the most important predator. Predation incidence was determined by examining all colonies present in permanent belt transects (20 x 2 m) in two reef environments (one dominated by Colpophyllia natans and the other one by Montastraea faveolata), for two climatic seasons (rainy and dry seasons). The parrotfish Sparisoma viride was the most important predator due to its biting frequency and bite size. S. viride adults of the initial and terminal phases, removed live tissue and part of the calcareous matrix of M. faveolata, M. annularis, Porites astreoides and C. natans, of which, the last one lost a major amount of tissue per area (3.51 cm2) and volume (3.22 cm3) per bite. A negative exponential tendency (r2=0.94), between coral density and volume removed was found, indicating that the coral density determines the bite's damage. There is no clear relationship between predation incidence and climatic seasons at the sites studied. At Chengue and Gayraca bays, live coral predation is one of the factors contributing to coral tissue loss and could have important consequences on the dynamic of these reefs.

Preferential reduction of bone mineral density at the femur reflects impairment of physical activity in patients with low-activity rheumatoid arthritis.

PubMed

Sugiguchi, Shigeru; Goto, Hitoshi; Inaba, Masaaki; Nishizawa, Yoshiki

2010-02-01

Bone mineral density (BMD) and factors influencing BMD in rheumatoid arthritis (RA) under good or moderate control were examined to assess management of osteoporosis in RA. BMD of the lumbar spine, femur, and distal radius was measured in 105 female patients with well-controlled RA. Laboratory and clinical variables associated with disease activity were measured in the same subjects, and correlations between these variables and BMD were evaluated. The RA patients showed a greater decrease in BMD of the femoral neck than of the lumbar spine. Age, Health Assessment Questionnaire (HAQ) score, and Larsen damage score had negative correlations with BMD of the femoral neck. In multiple regression analysis of the parameters associated with BMD of the femoral neck in simple regression analysis, an increase in HAQ score showed a negative correlation with BMD of the femoral neck. After initiation of treatment with alendronate (ALN), BMD of the femoral neck increased and correlated with improvement in HAQ score. A decrease in BMD of the femoral neck is a characteristic of RA. This suggests that muscle tonus has more effect than weight-bearing activity on BMD in patients with RA. BMD of the femoral neck is a useful index for general evaluation of RA patients.

Ancestor of land plants acquired the DNA-3-methyladenine glycosylase (MAG) gene from bacteria through horizontal gene transfer.

PubMed

Fang, Huimin; Huangfu, Liexiang; Chen, Rujia; Li, Pengcheng; Xu, Shuhui; Zhang, Enying; Cao, Wei; Liu, Li; Yao, Youli; Liang, Guohua; Xu, Chenwu; Zhou, Yong; Yang, Zefeng

2017-08-24

The origin and evolution of land plants was an important event in the history of life and initiated the establishment of modern terrestrial ecosystems. From water to terrestrial environments, plants needed to overcome the enhanced ultraviolet (UV) radiation and many other DNA-damaging agents. Evolving new genes with the function of DNA repair is critical for the origin and radiation of land plants. In bacteria, the DNA-3-methyladenine glycosylase (MAG) recognizes of a variety of base lesions and initiates the process of the base excision repair for damaged DNA. The homologs of MAG gene are present in all major lineages of streptophytes, and both the phylogenic and sequence similarity analyses revealed that green plant MAG gene originated through an ancient horizontal gene transfer (HGT) event from bacteria. Experimental evidence demonstrated that the expression of the maize ZmMAG gene was induced by UV and zeocin, both of which are known as DNA-damaging agents. Further investigation revealed that Streptophyta MAG genes had undergone positive selection during the initial evolutionary period in the ancestor of land plants. Our findings demonstrated that the ancient HGT of MAG to the ancestor of land plants probably played an important role in preadaptation to DNA-damaging agents in terrestrial environments.

Fatigue resistance of unnotched and post impact(+/- 30 deg/0 deg) 3-D braided composites

NASA Technical Reports Server (NTRS)

Portanova, Marc A.

1994-01-01

The fatigue resistance of a multiaxial braided (3-D) graphite/expoxy composite in both unnotched and post impacted conditions has been evaluated. The material tested is a (+/- 30/0 deg) multiaxial braid constructed from AS4/12K tow graphite fibers and British Petroleum E905L epoxy resin. These materials were braided as dry preforms and the epoxy was added using a resin transfer molding process (RTM). The unnotched and post-impact specimens were tested in compression-compression fatigue at 10 Hz with a stress ratio of R=10. The unnotched tension-tension fatigue specimens were tested at S Hz with a stress ration of R=0.1. Damage initiation and growth was documented through the application of radiography and ultrasonic through transmission (C-scans). Visible inspection of surface and edge damage was also noted to describe the initiation and progression of damage in these materials. The mechanisms leading to damage initiation were established and failure modes were determined. Stiffness and strength degradation were measured as a function of applied cycles. These 3-D braided composite results were compared to strain levels currently used to design primary structure in commercial aircraft composite components made from prepreg tape and autoclave cured.

46 CFR 122.304 - Navigation underway.

Code of Federal Regulations, 2014 CFR

2014-10-01

...; (2) Tidal state; (3) Prevailing and forecasted visibility and environmental conditions, including wind and waves; (4) Density of marine traffic; (5) Potential damage caused by own wake; (6) The danger...

46 CFR 122.304 - Navigation underway.

Code of Federal Regulations, 2013 CFR

2013-10-01

...; (2) Tidal state; (3) Prevailing and forecasted visibility and environmental conditions, including wind and waves; (4) Density of marine traffic; (5) Potential damage caused by own wake; (6) The danger...

46 CFR 122.304 - Navigation underway.

Code of Federal Regulations, 2011 CFR

2011-10-01

...; (2) Tidal state; (3) Prevailing and forecasted visibility and environmental conditions, including wind and waves; (4) Density of marine traffic; (5) Potential damage caused by own wake; (6) The danger...

46 CFR 122.304 - Navigation underway.

Code of Federal Regulations, 2012 CFR

2012-10-01

...; (2) Tidal state; (3) Prevailing and forecasted visibility and environmental conditions, including wind and waves; (4) Density of marine traffic; (5) Potential damage caused by own wake; (6) The danger...

Visualization of impact damage of composite plates by means of the Moire technique

NASA Technical Reports Server (NTRS)

Knauss, W. G.; Babcock, C. D.; Chai, H.

1980-01-01

The phenomenological aspects of propagation damage due to low velocity impact on heavily loaded graphite-epoxy composite laminates were investigated using high speed photography coupled with the moire fringe technique. High speed moire motion records of the impacted specimens are presented. The results provide information on the time scale and sequence of the failure process. While the generation of the initial damage cannot always be separated temporally from the spreading of the damage, the latter takes place on the average with a speed on the order of 200 m/sec.

Constraints on rapidity-dependent initial conditions from charged-particle pseudorapidity densities and two-particle correlations

NASA Astrophysics Data System (ADS)

Ke, Weiyao; Moreland, J. Scott; Bernhard, Jonah E.; Bass, Steffen A.

2017-10-01

We study the initial three-dimensional spatial configuration of the quark-gluon plasma (QGP) produced in relativistic heavy-ion collisions using centrality and pseudorapidity-dependent measurements of the medium's charged particle density and two-particle correlations. A cumulant-generating function is first used to parametrize the rapidity dependence of local entropy deposition and extend arbitrary boost-invariant initial conditions to nonzero beam rapidities. The model is then compared to p +Pb and Pb + Pb charged-particle pseudorapidity densities and two-particle pseudorapidity correlations and systematically optimized using Bayesian parameter estimation to extract high-probability initial condition parameters. The optimized initial conditions are then compared to a number of experimental observables including the pseudorapidity-dependent anisotropic flows, event-plane decorrelations, and flow correlations. We find that the form of the initial local longitudinal entropy profile is well constrained by these experimental measurements.

Rapid detection of Colorado potato beetle damage using small unmanned aircraft

USDA-ARS?s Scientific Manuscript database

Remote sensing with small unmanned aircraft systems (sUAS) has potential applications in agriculture because low flight altitudes allow image acquisition at very high spatial resolution. Damage to potato fields by the Colorado potato beetle (Leptinotarsa decemlineata) rapidly increases from initial...

Heat damaged forages: effects on forage energy content

USDA-ARS?s Scientific Manuscript database

Traditionally, educational materials describing the effects of heat damage within baled hays have focused on reduced bioavailability of crude protein as a result of Maillard reactions. These reactions are not simple, but actually occur in complex, multi-step pathways. Typically, the initial step inv...

Fatigue Failure in Extra-Articular Proximal Tibia Fractures: Locking Intramedullary Nail Versus Double Locking Plates-A Biomechanical Study.

PubMed

Kandemir, Utku; Herfat, Safa; Herzog, Mary; Viscogliosi, Paul; Pekmezci, Murat

2017-02-01

The goal of this study is to compare the fatigue strength of a locking intramedullary nail (LN) construct with a double locking plate (DLP) construct in comminuted proximal extra-articular tibia fractures. Eight pairs of fresh frozen cadaveric tibias with low bone mineral density [age: 80 ± 7 (SD) years, T-score: -2.3 ± 1.2] were used. One tibia from each pair was fixed with LN, whereas the contralateral side was fixed with DLP for complex extra-articular multifragmentary metaphyseal fractures (simulating OTA 41-A3.3). Specimens were cyclically loaded under compression simulating single-leg stance by staircase method out to 260,000 cycles. Every 2500 cycles, localized gap displacements were measured with a 3D motion tracking system, and x-ray images of the proximal tibia were acquired. To allow for mechanical settling, initial metrics were calculated at 2500 cycles. The 2 groups were compared regarding initial construct stiffness, initial medial and lateral gap displacements, stiffness at 30,000 cycles, medial and lateral gap displacements at 30,000 cycles, failure load, number of cycles to failure, and failure mode. Failure metrics were reported for initial and catastrophic failures. DLP constructs exhibited higher initial stiffness and stiffness at 30,000 cycles compared with LN constructs (P < 0.03). There were no significant differences between groups for loads at failure or cycles to failure. For the fixation of extra-articular proximal tibia fractures, a LN provides a similar fatigue performance to double locked plates. The locked nail could be safely used for fixation of proximal tibia fractures with the advantage of limited extramedullary soft tissue damage.

Healing of polymer interfaces: Interfacial dynamics, entanglements, and strength

NASA Astrophysics Data System (ADS)

Ge, Ting; Robbins, Mark O.; Perahia, Dvora; Grest, Gary S.

2014-07-01

Self-healing of polymer films often takes place as the molecules diffuse across a damaged region, above their melting temperature. Using molecular dynamics simulations we probe the healing of polymer films and compare the results with those obtained for thermal welding of homopolymer slabs. These two processes differ from each other in their interfacial structure since damage leads to increased polydispersity and more short chains. A polymer sample was cut into two separate films that were then held together in the melt state. The recovery of the damaged film was followed as time elapsed and polymer molecules diffused across the interface. The mass uptake and formation of entanglements, as obtained from primitive path analysis, are extracted and correlated with the interfacial strength obtained from shear simulations. We find that the diffusion across the interface is significantly faster in the damaged film compared to welding because of the presence of short chains. Though interfacial entanglements increase more rapidly for the damaged films, a large fraction of these entanglements are near chain ends. As a result, the interfacial strength of the healing film increases more slowly than for welding. For both healing and welding, the interfacial strength saturates as the bulk entanglement density is recovered across the interface. However, the saturation strength of the damaged film is below the bulk strength for the polymer sample. At saturation, cut chains remain near the healing interface. They are less entangled and as a result they mechanically weaken the interface. Chain stiffness increases the density of entanglements, which increases the strength of the interface. Our results show that a few entanglements across the interface are sufficient to resist interfacial chain pullout and enhance the mechanical strength.

Development of the monitoring technique on the damage of piles using the biggest shaking table "E-defense"

NASA Astrophysics Data System (ADS)

Hayashi, Kazuhiro; Hachimori, Wataru; Kaneda, Shogo; Tamura, Shuji; Saito, Taiki

2017-10-01

In case of earthquake damage to buildings, the damage to a superstructure is visible, but the damage to a foundation structure, e.g. the underground pile, is difficult to detect. In this study, the authors aim to develop a monitoring technique for pile damage due to earthquakes. The world's biggest shaking table, E-Defense, was used to reproduce damage to RC pile models embedded in the soil inside a large scale shear box (8m in diameter and 6.5m in height). The diameter of the RC pile model was 154mm. It consisted of mortar (27.2N/mm2 in compressive strength), 6 main reinforcements (6.35mm in diameter) and shear reinforcement hard steel wire (2mm in diameter at intervals of 20mm). The natural period of the superstructure above the pile models is around 0.12sec. The soil consisted of 2 layers. The lower layer is Albany sand of 80% relative density while the upper layer is only 2m from the surface ground and is Kaketsu sand of 60% relative density. Primary four excitations were scaled from JMA Kobe waves in notification at different amplitudes. The maximum acceleration of each wave is 31gal, 67gal, 304gal, and 458gal, respectively. In the test result, reinforcing steels at the pile head of the RC model yielded when the maximum acceleration was 304gal. After that, mortar of the pile head peeled off and a bending shear failure occurred when the maximum acceleration was 458gal. The peak frequency of rotational spectrum on the foundation did not change in elastic range in the piles. However, the peak frequency fell after the plastic hinge occurred.

[Public health, damage containment and the prevention of blood-borne and sexually transmitted infections: a review of the core concepts and their implementation in Brazil].

PubMed

Elias, Lucília de Almeida; Bastos, Francisco Inacio

2011-12-01

This article assesses the historical context and the conceptual frame of setting up damage containment programs in the field of public health, with special emphasis on the Brazilian experience. The survey seeks to assess the relevance of such programs in the ongoing efforts to curb the spread of blood-borne and sexually transmitted infections, especially AIDS and hepatitis C. Findings from both the Brazilian and the international literature demonstrate that practical damage containment initiatives tend to be more effective when integrated with other public health measures based on common goals. Damage containment initiatives, aligned with the basic principles of public health do not limit themselves to a priori models or health care per se. They encompass a variety of pragmatic measures based on public policies and should be in line with the demands of the communities since the moment of their inception and implemented in the context of full partnership with such communities.

The characterization of widespread fatigue damage in fuselage structure

NASA Technical Reports Server (NTRS)

Piascik, Robert S.; Willard, Scott A.; Miller, Matthew

1994-01-01

The characteristics of widespread fatigue damage (WSFD) in fuselage riveted structure were established by detailed nondestructive and destructive examinations of fatigue damage contained in a full size fuselage test article. The objectives of this were to establish an experimental data base for validating emerging WSFD analytical prediction methodology and to identify first order effects that contribute to fatigue crack initiation and growth. Detailed examinations were performed on a test panel containing four bays of a riveted lap splice joint. The panel was removed from a full scale fuselage test article after receiving 60,000 full pressurization cycles. The results of in situ examinations document the progression of fuselage skin fatigue crack growth through crack linkup. Detailed tear down examinations and fractography of the lap splice joint region revealed fatigue crack initiation sites, crack morphology, and crack linkup geometry. From this large data base, distributions of crack size and locations are presented and discussions of operative damage mechanisms are offered.

The characterization of widespread fatigue damage in fuselage structure

NASA Technical Reports Server (NTRS)

Piascik, Robert S.; Willard, Scott A.; Miller, Matthew

1994-01-01

The characteristics of widespread fatigue damage (WSFD) in fuselage riveted structure were established by detailed nondestructive and destructive examinations of fatigue damage contained in a full size fuselage test article. The objectives of this work were to establish an experimental data base for validating emerging WSFD analytical prediction methodology and to identify first order effects that contribute to fatigue crack initiation and growth. Detailed examinations were performed on a test panel containing four bays of a riveted lap splice joint. The panel was removed from a full scale fuselage test article after receiving 60,000 full pressurization cycles. The results of in situ examinations document the progression of fuselage skin fatigue crack growth through crack linkup. Detailed tear down examinations and fractography of the lap splice joint region revealed fatigue crack initiation sites, crack morphology and crack linkup geometry. From this large data base, distributions of crack size and locations are presented and discussions of operative damage mechanisms are offered.

Factors contributing to inactivation of isolated thylakoid membranes during freezing in the presence of variable amounts of glucose and NaCl.

PubMed Central

Santarius, K A; Giersch, C

1984-01-01

During freezing of isolated spinach thylakoids in sugar/salt solutions, the two solutes affected membrane survival in opposite ways: membrane damage due to increased electrolyte concentration can be prevented by sugar. Calculation of the final concentrations of NaCl or glucose reached in the residual unfrozen portion of the system revealed that the effects of the solutes on membrane activity can be explained in part by colligative action. In addition, the fraction of the residual liquid in the frozen system contributes to membrane injury. During severe freezing in the presence of very low initial solute concentrations, membrane damage drastically increased with a decrease in the volume of the unfrozen solution. Freezing injury under these conditions is likely to be due to mechanical damage by the ice crystals that occupy a very high fraction of the frozen system. At higher starting concentrations of sugar plus salt, membrane damage increased with an increase in the amount of the residual unfrozen liquid. Thylakoid inactivation at these higher initial solute concentrations can be largely attributed to dilution of the membrane fraction, as freezing damage at a given sugar/salt ratio decreased with increasing the thylakoid concentration in the sample. Moreover, membrane survival in the absence of freezing decreased with lowering the temperature, indicating that the temperature affected membrane damage not only via alterations related to the ice formation. From the data it was evident that damage of thylakoid membranes was determined by various individual factors, such as the amount of ice formed, the final concentrations of solutes and membranes in the residual unfrozen solution, the final volume of this fraction, the temperature and the freezing time. The relative contribution of these factors depended on the experimental conditions, mainly the sugar/salt ratio, the initial solute concentrations, and the freezing temperature. PMID:6478028

Electromigration Failure Mechanism in Sn-Cu Solder Alloys with OSP Cu Surface Finish

NASA Astrophysics Data System (ADS)

Chu, Ming-Hui; Liang, S. W.; Chen, Chih; Huang, Annie T.

2012-09-01

Organic solderable preservative (OSP) has been adopted as the Cu substrate surface finish in flip-chip solder joints for many years. In this study, the electromigration behavior of lead-free Sn-Cu solder alloys with thin-film under bump metallization and OSP surface finish was investigated. The results showed that severe damage occurred on the substrate side (cathode side), whereas the damage on the chip side (cathode side) was not severe. The damage on the substrate side included void formation, copper dissolution, and formation of intermetallic compounds (IMCs). The OSP Cu interface on the substrate side became the weakest point in the solder joint even when thin-film metallization was used on the chip side. Three-dimensional simulations were employed to investigate the current density distribution in the area between the OSP Cu surface finish and the solder. The results indicated that the current density was higher along the periphery of the bonding area between the solder and the Cu pad, consistent with the area of IMC and void formation in our experimental results.

Sperm DNA damage has a negative association with live-birth rates after IVF.

PubMed

Simon, L; Proutski, I; Stevenson, M; Jennings, D; McManus, J; Lutton, D; Lewis, S E M

2013-01-01

Sperm DNA damage has a negative impact on pregnancy rates following assisted reproduction treatment (ART). The aim of the present study was to examine the relationship between sperm DNA fragmentation and live-birth rates after IVF and intracytoplasmic sperm injection (ICSI). The alkaline Comet assay was employed to measure sperm DNA fragmentation in native semen and in spermatozoa following density-gradient centrifugation in semen samples from 203 couples undergoing IVF and 136 couples undergoing ICSI. Men were divided into groups according to sperm DNA damage. Following IVF, couples with <25% sperm DNA fragmentation had a live-birth rate of 33%; in contrast, couples with >50% sperm DNA fragmentation had a much lower live-birth rate of 13%. Following ICSI, no significant differences in sperm DNA damage were found between any groups of patients. Sperm DNA damage was also associated with low live-birth rates following IVF in both men and couples with idiopathic infertility: 39% of couples and 41% of men with idiopathic infertility have high sperm DNA damage. Sperm DNA damage assessed by the Comet assay has a close inverse relationship with live-birth rates after IVF. Sperm DNA damage has a negative impact on assisted reproduction treatment outcome, in particular, on pregnancy rates. The aim of the present study was to examine the relationship between sperm DNA fragmentation and live-birth rates after IVF and intracytoplasmic sperm injection (ICSI). The alkaline Comet assay was employed to measure sperm DNA fragmentation in native semen and in spermatozoa following density-gradient centrifugation in semen samples from 203 couples undergoing IVF and 136 couples undergoing ICSI. Men were divided into groups according to sperm DNA damage and treatment outcome. Following IVF, couples with <25% sperm DNA fragmentation had a live birth rate of 33%. In contrast, couples with >50% sperm DNA fragmentation had a much lower live-birth rate of 13% following IVF. Following ICSI, there were no significant differences in levels of sperm DNA damage between any groups of patients. Sperm DNA damage was also associated with the very low live-birth rates following IVF in both men and couples with idiopathic infertility: 39% of couples and 41% of men have high level of sperm DNA damage. Sperm DNA damage assessed by the Comet assay has a close inverse relationship with live-birth rates after IVF. Copyright © 2012 Reproductive Healthcare Ltd. Published by Elsevier Ltd. All rights reserved.