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Sample records for damage threshold prediction

  1. Predicting threshold and location of laser damage on optical surfaces

    DOEpatents

    Siekhaus, Wigbert

    1987-01-01

    An apparatus useful in the prediction of the damage threshold of various optical devices, the location of weak spots on such devices and the location, identification, and elimination of optical surface impurities comprising, a focused and pulsed laser, an photo electric detector/imaging means, and a timer. The weak spots emit photoelectrons when subjected to laser intensities that are less than the intensity actually required to produce the damage. The weak spots may be eliminated by sustained exposure to the laser beam.

  2. Predicting threshold and location of laser damage on optical surfaces

    DOEpatents

    Siekhaus, W.

    1985-02-04

    Disclosed is an apparatus useful in the prediction of the damage threshold of various optical devices, the location of weak spots on such devices and the location, identification, and elimination of optical surface impurities. The apparatus comprises a focused and pulsed laser, a photo electric detector/imaging means, and a timer. The weak spots emit photoelectrons when subjected to laser intensities that are less than the intensity actually required to produce the damage. The weak spots may be eliminated by sustained exposure to the laser beam.

  3. Damage thresholds for terahertz radiation

    NASA Astrophysics Data System (ADS)

    Dalzell, Danielle R.; McQuade, Jill; Vincelette, Rebecca; Ibey, Bennet; Payne, Jason; Thomas, Robert; Roach, W. P.; Roth, Caleb L.; Wilmink, Gerald J.

    2010-02-01

    Several international organizations establish minimum safety standards to ensure that workers and the general population are protected against adverse health effects associated with electromagnetic radiation. Suitable standards are typically defined using published experimental data. To date, few experimental studies have been conducted at Terahertz (THz) frequencies, and as a result, current THz standards have been defined using extrapolated estimates from neighboring spectral regions. In this study, we used computational modeling and experimental approaches to determine tissue-damage thresholds at THz frequencies. For the computational modeling efforts, we used the Arrhenius damage integral to predict damage-thresholds. We determined thresholds experimentally for both long (minutes) and short (seconds) THz exposures. For the long exposure studies, we used an in-house molecular gas THz laser (υ= 1.89 THz, 189.92 mW/cm2, 10 minutes) and excised porcine skin. For the short exposure studies, we used the Free Electron Laser (FEL) at Jefferson Laboratory (υ= 0.1-1.0 THz, 2.0-14.0 mW/cm2, 2 seconds) and wet chamois cloths. Thresholds were determined using conventional damage score determination and probit analysis techniques, and tissue temperatures were measured using infrared thermographic techniques. We found that the FEL was ideal for tissue damage studies, while our in-house THz source was not suitable to determine tissue damage thresholds. Using experimental data, the tissue damage threshold (ED50) was determined to be 7.16 W/cm2. This value was in well agreement with that predicted using our computational models. We hope that knowledge of tissue-damage thresholds at THz frequencies helps to ensure the safe use of THz radiation.

  4. Laser damage threshold of diamond films

    NASA Technical Reports Server (NTRS)

    Albin, Sacharia; Cropper, Andre D.; Watkins, Linwood C.; Byvik, Charles E.; Buoncristiani, A. Martin

    1989-01-01

    The possibility that diamond films may inhibit laser-induced damage to optical components in laser systems films was investigated by measuring laser damage thresholds of free-standing diamond film windows, diamond films deposited on silicon substrates, and bare silicon substrate. Polycrystalline diamond films were deposited using a dc plasma-enhanced CVD process. It was found that free-standing diamond films had the highest laser damage threshold at 1064 nm. For a diamond film of 630 nm, the damage threshold was found to be 7 J/sq cm, as compared to a damage threshold of 4.5 J/sq cm for bare silicon, and a low value of 1.5 J/sq cm for the film/substrate combination. The damage mechanism is considered to involve melting or dielectric breakdown induced by laser radiation. The low value of the film/substrate combination is attributed to film stress and conditions of film deposition.

  5. Laser damage threshold of diamond films

    NASA Astrophysics Data System (ADS)

    Albin, Sacharia; Cropper, Andre D.; Watkins, Linwood C.; Byvik, Charles E.; Buoncristiani, A. Martin

    1989-03-01

    The possibility that diamond films may inhibit laser-induced damage to optical components in laser systems films was investigated by measuring laser damage thresholds of free-standing diamond film windows, diamond films deposited on silicon substrates, and bare silicon substrate. Polycrystalline diamond films were deposited using a dc plasma-enhanced CVD process. It was found that free-standing diamond films had the highest laser damage threshold at 1064 nm. For a diamond film of 630 nm, the damage threshold was found to be 7 J/sq cm, as compared to a damage threshold of 4.5 J/sq cm for bare silicon, and a low value of 1.5 J/sq cm for the film/substrate combination. The damage mechanism is considered to involve melting or dielectric breakdown induced by laser radiation. The low value of the film/substrate combination is attributed to film stress and conditions of film deposition.

  6. Tissue damage thresholds during therapeutic electrical stimulation

    NASA Astrophysics Data System (ADS)

    Cogan, Stuart F.; Ludwig, Kip A.; Welle, Cristin G.; Takmakov, Pavel

    2016-04-01

    Objective. Recent initiatives in bioelectronic modulation of the nervous system by the NIH (SPARC), DARPA (ElectRx, SUBNETS) and the GlaxoSmithKline Bioelectronic Medicines effort are ushering in a new era of therapeutic electrical stimulation. These novel therapies are prompting a re-evaluation of established electrical thresholds for stimulation-induced tissue damage. Approach. In this review, we explore what is known and unknown in published literature regarding tissue damage from electrical stimulation. Main results. For macroelectrodes, the potential for tissue damage is often assessed by comparing the intensity of stimulation, characterized by the charge density and charge per phase of a stimulus pulse, with a damage threshold identified through histological evidence from in vivo experiments as described by the Shannon equation. While the Shannon equation has proved useful in assessing the likely occurrence of tissue damage, the analysis is limited by the experimental parameters of the original studies. Tissue damage is influenced by factors not explicitly incorporated into the Shannon equation, including pulse frequency, duty cycle, current density, and electrode size. Microelectrodes in particular do not follow the charge per phase and charge density co-dependence reflected in the Shannon equation. The relevance of these factors to tissue damage is framed in the context of available reports from modeling and in vivo studies. Significance. It is apparent that emerging applications, especially with microelectrodes, will require clinical charge densities that exceed traditional damage thresholds. Experimental data show that stimulation at higher charge densities can be achieved without causing tissue damage, suggesting that safety parameters for microelectrodes might be distinct from those defined for macroelectrodes. However, these increased charge densities may need to be justified by bench, non-clinical or clinical testing to provide evidence of device

  7. Acoustic emission sensor radiation damage threshold experiment

    SciTech Connect

    Beeson, K.M.; Pepper, C.E.

    1994-09-01

    Determination of the threshold for damage to acoustic emission sensors exposed to radiation is important in their application to leak detection in radioactive waste transport and storage. Proper response to system leaks is necessary to ensure the safe operation of these systems. A radiation impaired sensor could provide ``false negative or false positive`` indication of acoustic signals from leaks within the system. Research was carried out in the Radiochemical Technology Division at Oak Ridge National Laboratory to determine the beta/gamma radiation damage threshold for acoustic emission sensor systems. The individual system consisted of an acoustic sensor mounted with a two part epoxy onto a stainless steel waveguide. The systems were placed in an irradiation fixture and exposed to a Cobalt-60 source. After each irradiation, the sensors were recalibrated by Physical Acoustics Corporation. The results were compared to the initial calibrations performed prior to irradiation and a control group, not exposed to radiation, was used to validate the results. This experiment determines the radiation damage threshold of each acoustic sensor system and verifies its life expectancy, usefulness and reliability for many applications in radioactive environments.

  8. Predictability of threshold exceedances in dynamical systems

    NASA Astrophysics Data System (ADS)

    Bódai, Tamás

    2015-12-01

    In a low-order model of the general circulation of the atmosphere we examine the predictability of threshold exceedance events of certain observables. The likelihood of such binary events-the cornerstone also for the categoric (as opposed to probabilistic) prediction of threshold exceedances-is established from long time series of one or more observables of the same system. The prediction skill is measured by a summary index of the ROC curve that relates the hit- and false alarm rates. Our results for the examined systems suggest that exceedances of higher thresholds are more predictable; or in other words: rare large magnitude, i.e., extreme, events are more predictable than frequent typical events. We find this to hold provided that the bin size for binning time series data is optimized, but not necessarily otherwise. This can be viewed as a confirmation of a counterintuitive (and seemingly contrafactual) statement that was previously formulated for more simple autoregressive stochastic processes. However, we argue that for dynamical systems in general it may be typical only, but not universally true. We argue that when there is a sufficient amount of data depending on the precision of observation, the skill of a class of data-driven categoric predictions of threshold exceedances approximates the skill of the analogous model-driven prediction, assuming strictly no model errors. Therefore, stronger extremes in terms of higher threshold levels are more predictable both in case of data- and model-driven prediction. Furthermore, we show that a quantity commonly regarded as a measure of predictability, the finite-time maximal Lyapunov exponent, does not correspond directly to the ROC-based measure of prediction skill when they are viewed as functions of the prediction lead time and the threshold level. This points to the fact that even if the Lyapunov exponent as an intrinsic property of the system, measuring the instability of trajectories, determines predictability

  9. Damage thresholds in laser irradiated optical materials

    SciTech Connect

    Guignard, F.; Autric, M.; Baudinaud, V.

    1997-12-01

    An experimental study on the damage induced by laser irradiation on different materials, borosilicate glass, fused silicate, moulded and stretched polymethylmethacrylate (PMMA), has been performed. The irradiation source is a 1KJ pulsed cold cathode electron gun preionized TEA CO{sub 2} laser. Damage mechanisms are controlled by the in-depth absorption of the 10,6 {mu}m radiation according to the Beer-Lambert law. The heating of the interaction area gives rise to thermal or thermo-mechanical damages. PMMA is damaged following a boiling process. Stretched PMMA is fractured first, releasing stresses, then boiled like moulded PMMA at higher energy. BK7 crazed after the irradiation due to thermomechanical stresses, silicate melt and vaporized. Optical damages have been characterized by measuring the contrast transfer function through the irradiated samples.

  10. Temperature thresholds to freeze damage in cranberry

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Sprinkler irrigation is required for frost protection of cranberry and is arguably the most important cultural practice used in production of the crop. A study was initiated in a commercial bed of ‘Stevens’ cranberry located in Langlois, OR. The objectives are to identify temperature thresholds to...

  11. Optical Damage Threshold of Silicon for Ultrafast Infrared Pulses

    SciTech Connect

    Cowan, B.; /SLAC

    2006-09-07

    While silicon has several properties making it an attractive material for structure-based laser-driven acceleration, its optical damage threshold, a key parameter for high-gradient acceleration, has been unknown. Here we present measurements of the optical damage threshold of crystalline silicon for ultrafast pulses in the mid-infrared. The wavelengths tested span a range from the telecommunications band at 1550 nm extending longer toward the two-photon absorption threshold at around 2200 nm. We discuss the prevailing theories of ultrafast optical breakdown, describe the experimental setup and preliminary results, and propose a relevant performance parameter for candidate accelerator structures.

  12. Evaluation of a threshold-based model of fatigue in gamma titanium aluminide following impact damage

    NASA Astrophysics Data System (ADS)

    Harding, Trevor Scott

    2000-10-01

    Recent interest in gamma titanium aluminide (gamma-TiAl) for use in gas turbine engine applications has centered on the low density and good elevated temperature strength retention of gamma-TiAl compared to current materials. However, the relatively low ductility and fracture toughness of gamma-TiAl leads to serious concerns regarding its ability to resist impact damage. Furthermore, the limited fatigue crack growth resistance of gamma-TiAl means that the potential for fatigue failures resulting from impact damage is real if a damage tolerant design approach is used. A threshold-based design approach may be required if fatigue crack growth from potential impact sites is to be avoided. The objective of the present research is to examine the feasibility of a threshold-based approach for the design of a gamma-TiAl low-pressure turbine blade subjected to both assembly-related impact damage and foreign object damage. Specimens of three different gamma-TiAl alloys were damaged in such a way as to simulate anticipated impact damage for a turbine blade. Step-loading fatigue tests were conducted at both room temperature and 600°C. In terms of the assembly-related impact damage, the results indicate that there is reasonably good agreement between the threshold-based predictions of the fatigue strength of damaged specimens and the measured data. However, some discrepancies do exist. In the case of very lightly damaged specimens, prediction of the resulting fatigue strength requires that a very conservative small-crack fatigue threshold be used. Consequently, the allowable design conditions are significantly reduced. For severely damaged specimens, an analytical approach found that the potential effects of residual stresses may be related to the discrepancies observed between the threshold-based model and measured fatigue strength data. In the case of foreign object damage, a good correlation was observed between impacts resulting in large cracks and a long-crack threshold

  13. Measurement of Laser Damage Threshold of 355-nm Antireflection Coating

    NASA Astrophysics Data System (ADS)

    Tamura, Shigeharu; Kimura, Saburo; Sato, Yoshiyuki; Otani, Minoru; Yoshida, Hidetsugu; Yoshida, Kunio

    1989-06-01

    The laser damage thresholds of various types of antireflection (AR) coatings for an UV (355-nm) laser system were measured. Among them, the coatings consisting of two low-index materials, SiO2 and MgF2, had the highest average thresholds: 2.1 J/cm2 on fused silica substrates and 2.6 J/cm2 on sapphire substrates. The SiO2/MgF2 coating is hopeful for UV laser component.

  14. Laser damage threshold: useful idea or dangerous misconception?

    NASA Astrophysics Data System (ADS)

    Arenberg, Jonathan W.

    2015-11-01

    The concept of a laser damage threshold as a safe operating level is both useful and confounding. This paper examines and analyzes the power of the concept of a laser damage threshold, identifying the good and the danger in its use. The history of the definition and concept of the laser damage threshold is traced from the earliest days of the laser through to the present day. Criteria for an accurate threshold measurement are presented and distribution of the weakest site on an optic is derived to provide a basis of analysis. Using a pedagogically selected defect distribution, the statistics of the weakest site are derived. The dependence of the weakest site on the area of the test is shown explicitly. It is argued that typical small area tests, characteristic of most main stream damage tests have insufficient area to include the true weakest site, and are therefore generally inaccurate. The paper concludes with some ideas on how to redefine the threshold measurement technique resulting in a more accurate test procedure.

  15. Influence of microstructure on laser damage threshold of IBS coatings

    SciTech Connect

    Stolz, C.J.; Genin, F.Y.; Kozlowski, M.R.; Long, D.; Lalazari, R.; Wu, Z.L.; Kuo, P.K.

    1996-01-05

    Ion-beam sputtering (IBS) coatings were developed for the laser gyro industry to meet significantly different requirements than those of fusion lasers. Laser gyro mirrors are small (< 25 mm) and require low losses (< 30 ppm typical) and high stability with long exposures to low power laser energy. In contrast, fusion laser optics are large (< 1 meter), have significantly reduced loss requirements (< 5,000 ppm) and high damage thresholds (> 26 J/cm{sup 2} at 1,064 nm with 3-ns pulses). As part of the National Ignition Facility (NIF) coating development effort, IBS coatings are being studied to explore the possible benefits of this technology to NIF optics. As an initial step to achieving the NIF size and damage threshold requirements, the coating process is being scaled to uniformly coat a 20 x 40 cm{sup 2} area with reduced spectral, reflected wavefront, and laser damage threshold requirements. Here, multilayer coatings deposited by ion-beam sputtering with amorphous layers were found to have lower damage thresholds at 1,064 nm than similar coatings with crystalline layers. Interestingly, at higher fluences the damage was less severe for the amorphous coatings. The magnitude of the difference in damage thresholds between the two different microstructures was strongly influenced by the size of the tested area. To better understand the microstructure effects, single layers of HfO{sub 2} with different microstructures were studied using transmission electron microscopy, ellipsometry, and a photothermal deflection technique. Since the laser damage initiated at defects, the influence of thermal diffusivity on thermal gradients in nodular defects is also presented.

  16. Prediction of tissue thermal damage.

    PubMed

    Li, Xin; Zhong, Yongmin; Subic, Aleksandar; Jazar, Reza; Smith, Julian; Gu, Chengfan

    2016-04-29

    This paper presents a method to characterize tissue thermal damage by taking into account the thermal-mechanical effect of soft tissues for thermal ablation. This method integrates the bio-heating conduction and non-rigid motion dynamics to describe thermal-mechanical behaviors of soft tissues and further extends the traditional tissue damage model to characterize thermal-mechanical damage of soft tissues. Simulations and comparison analysis demonstrate that the proposed method can effectively predict tissue thermal damage and it also provides reliable guidelines for control of the thermal ablation procedure. PMID:27163325

  17. An evaluation of corn earworm damage and thresholds in soybean

    NASA Astrophysics Data System (ADS)

    Adams, Brian Patrick

    Interactions between corn earworm, Helicoverpa zea (Boddie), and soybean, Glycine max L. (Merrill), were investigated in the Mid-South to evaluate thresholds and damage levels. Field studies were conducted in both indeterminate and determinate modern cultivars to evaluate damage, critical injury levels, and soybean response to simulated corn earworm injury. Field studies were also conducted to evaluate the response of indeterminate cultivars to infestations of corn earworm. Field studies were also conducted to investigate the relationship between pyrethroid insecticide application and corn earworm oviposition in soybean. Results of field studies involving simulated corn earworm damage indicated the need for a dynamic threshold that becomes more conservative as soybean phenology progressed through the reproductive growth stages. This suggested that soybean was more tolerant to fruit loss during the earlier reproductive stages and was able to compensate for fruit loss better during this time than at later growth stages. Results of field studies involving infestations of corn earworm indicated that current thresholds are likely too liberal. This resulted in economic injury level tables being constructed based upon a range of crop values and control costs, however, a general action threshold was also recommended for indeterminate soybean in the Mid-South. Field study results investigating the relationship of pyrethroid application and corn earworm oviposition indicated that even in the presence of an insecticide, corn earworm prefers to oviposit in the upper portion of the canopy, as well as on the leaves as opposed to all other plant parts, consistent with all previous literature.

  18. Effects of Accelerated Aging on Fiber Damage Thresholds

    SciTech Connect

    Setchell, R.E.

    1999-02-15

    Laser-induced damage mechanisms that can occur during high-intensity fiber transmission have been under study for a number of years. Our particular interest in laser initiation of explosives has led us to examine damage processes associated with the transmission of Q-switched, Nd:YAG pulses at 1.06 {micro}m through step-index, multimode, fused silica fiber. Laser breakdown at the fiber entrance face is often the first process to limit fiber transmission but catastrophic damage can also occur at either fiber end face, within the initial entry segment of the fiber, and at other internal sites along the fiber path. Past studies have examined how these various damage mechanisms depend upon fiber end-face preparation, fiber fixturing and routing, laser characteristics, and laser-to-fiber injection optics. In some applications of interest, however, a fiber transmission system may spend years in storage before it is used. Consequently, an important additional issue for these applications is whether or not there are aging processes that can result in lower damage thresholds over time. Fiber end-face contamination would certainly lower breakdown and damage thresholds at these surfaces, but careful design of hermetic seals in connectors and other end-face fixtures can minimize this possibility. A more subtle possibility would be a process for the slow growth of internal defects that could lead to lower thresholds for internal damage. In the current study, two approaches to stimulating the growth of internal defects were used in an attempt to produce observable changes in internal damage thresholds. In the first approach test fibers were subjected to a very high tensile stress for a time sufficient for some fraction to fail from static fatigue. In the second approach, test fibers were subjected to a combination of high tensile stress and large, cyclic temperature variations. Both of these approaches were rather arbitrary due to the lack of an established growth mechanism for

  19. Femtosecond pulse damage thresholds of dielectric coatings in vacuum

    SciTech Connect

    Michelle D. Shinn, Duy N. Nguyen, Luke A. Emmert ,Paul Schwoebel, Dinesh Patel, Carmen S. Menoni, Wolfgang Rudolph

    2011-03-01

    At 10-7 Torr, the multiple femtosecond pulse damage threshold, F(?), is about 10% of the single pulse damage fluence F(1) for hafnia and silica films compared to about 65% and 50%, respectively, at 630 Torr. In contrast, the single-pulse damage threshold is pressure independent. The decrease of F(?) with decreasing air pressure correlates with the water vapor and oxygen content of the ambient gas with the former having the greater effect. The decrease in F(?) is likely associated with an accumulation of defects derived from oxygen deficiency, for example vacancies. From atmospheric air pressure to pressures of {approx}3 x 10{sup -6} Torr, the damage 'crater' starts deterministically at the center of the beam and grows in diameter as the fluence increases. At pressure below 3x10-6 Torr, damage is initiated at random 'sites' within the exposed area in hafnia films, while the damage morphology remains deterministic in silica films. A possible explanation is that absorbing centers are created at predisposed sample sites in hafnia, for example at boundaries between crystallites, or crystalline and amorphous phases.

  20. Optical Damage Threshold of Silicon for Ultrafast Infrared Pulses

    SciTech Connect

    Cowan, Benjamin M.; /Tech-X, Boulder /SLAC

    2007-11-28

    We present measurements of the optical damage threshold of crystalline silicon in air for ultrafast pulses in the near infrared. The wavelengths tested span a range from the telecommunications band at 1550 nm, extending to 2260 nm. We discuss the motivation for the measurements and give theoretical context. We then describe the experimental setup, diagnostics, and procedure. The results show a breakdown threshold of 0.2J/cm{sup 2} at 1550 nm and 1.06 ps FWHM pulse duration, and a weak dependence on wavelength.

  1. Revision of laser-induced damage threshold evaluation from damage probability data

    SciTech Connect

    Bataviciute, Gintare; Grigas, Povilas; Smalakys, Linas; Melninkaitis, Andrius

    2013-04-15

    In this study, the applicability of commonly used Damage Frequency Method (DFM) is addressed in the context of Laser-Induced Damage Threshold (LIDT) testing with pulsed lasers. A simplified computer model representing the statistical interaction between laser irradiation and randomly distributed damage precursors is applied for Monte Carlo experiments. The reproducibility of LIDT predicted from DFM is examined under both idealized and realistic laser irradiation conditions by performing numerical 1-on-1 tests. A widely accepted linear fitting resulted in systematic errors when estimating LIDT and its error bars. For the same purpose, a Bayesian approach was proposed. A novel concept of parametric regression based on varying kernel and maximum likelihood fitting technique is introduced and studied. Such approach exhibited clear advantages over conventional linear fitting and led to more reproducible LIDT evaluation. Furthermore, LIDT error bars are obtained as a natural outcome of parametric fitting which exhibit realistic values. The proposed technique has been validated on two conventionally polished fused silica samples (355 nm, 5.7 ns).

  2. Damage threshold of lithium niobate crystal under single and multiple femtosecond laser pulses: theoretical and experimental study

    NASA Astrophysics Data System (ADS)

    Meng, Qinglong; Zhang, Bin; Zhong, Sencheng; Zhu, Liguo

    2016-06-01

    The damage threshold of lithium niobate crystal under single and multiple femtosecond laser pulses has been studied theoretically and experimentally. Firstly, the model for the damage threshold prediction of crystal materials based on the improved rate equation has been proposed. Then, the experimental measure method of the damage threshold of crystal materials has been given in detail. On the basis, the variation of the damage threshold of lithium niobate crystal with the pulse duration has also been analyzed quantitatively. Finally, the damage threshold of lithium niobate crystal under multiple laser pulses has been measured and compared to the theoretical results. The results show that the transmittance of lithium niobate crystal is almost a constant when the laser pulse fluence is relative low, whereas it decreases linearly with the increase in the laser pulse fluence below the damage threshold. The damage threshold of lithium niobate crystal increases with the increase in the duration of the femtosecond laser pulse. And the damage threshold of lithium niobate crystal under multiple laser pulses is obviously lower than that irradiated by a single laser pulse. The theoretical data fall in good agreement with the experimental results.

  3. Laser-induced retinal damage thresholds for annular retinal beam profiles

    NASA Astrophysics Data System (ADS)

    Kennedy, Paul K.; Zuclich, Joseph A.; Lund, David J.; Edsall, Peter R.; Till, Stephen; Stuck, Bruce E.; Hollins, Richard C.

    2004-07-01

    The dependence of retinal damage thresholds on laser spot size, for annular retinal beam profiles, was measured in vivo for 3 μs, 590 nm pulses from a flashlamp-pumped dye laser. Minimum Visible Lesion (MVL)ED50 thresholds in rhesus were measured for annular retinal beam profiles covering 5, 10, and 20 mrad of visual field; which correspond to outer beam diameters of roughly 70, 160, and 300 μm, respectively, on the primate retina. Annular beam profiles at the retinal plane were achieved using a telescopic imaging system, with the focal properties of the eye represented as an equivalent thin lens, and all annular beam profiles had a 37% central obscuration. As a check on experimental data, theoretical MVL-ED50 thresholds for annular beam exposures were calculated using the Thompson-Gerstman granular model of laser-induced thermal damage to the retina. Threshold calculations were performed for the three experimental beam diameters and for an intermediate case with an outer beam diameter of 230 μm. Results indicate that the threshold vs. spot size trends, for annular beams, are similar to the trends for top hat beams determined in a previous study; i.e., the threshold dose varies with the retinal image area for larger image sizes. The model correctly predicts the threshold vs. spot size trends seen in the biological data, for both annular and top hat retinal beam profiles.

  4. A damage model based on failure threshold weakening

    NASA Astrophysics Data System (ADS)

    Gran, Joseph D.; Rundle, John B.; Turcotte, Donald L.; Holliday, James R.; Klein, William

    2011-04-01

    A variety of studies have modeled the physics of material deformation and damage as examples of generalized phase transitions, involving either critical phenomena or spinodal nucleation. Here we study a model for frictional sliding with long-range interactions and recurrent damage that is parameterized by a process of damage and partial healing during sliding. We introduce a failure threshold weakening parameter into the cellular automaton slider-block model which allows blocks to fail at a reduced failure threshold for all subsequent failures during an event. We show that a critical point is reached beyond which the probability of a system-wide event scales with this weakening parameter. We provide a mapping to the percolation transition, and show that the values of the scaling exponents approach the values for mean-field percolation (spinodal nucleation) as lattice size L is increased for fixed R. We also examine the effect of the weakening parameter on the frequency-magnitude scaling relationship and the ergodic behavior of the model.

  5. Thresholds for thermal damage to normal tissues: An update

    PubMed Central

    Yarmolenko, Pavel S.; Moon, Eui Jung; Landon, Chelsea; Manzoor, Ashley; Hochman, Daryl W.; Viglianti, Benjamin L.; Dewhirst, Mark W.

    2013-01-01

    The purpose of this review is to summarise a literature survey on thermal thresholds for tissue damage. This review covers published literature for the consecutive years from 2002–2009. The first review on this subject was published in 2003. It included an extensive discussion of how to use thermal dosimetric principles to normalise all time-temperature data histories to a common format. This review utilises those same principles to address sensitivity of a variety of tissues, but with particular emphasis on brain and testis. The review includes new data on tissues that were not included in the original review. Several important observations have come from this review. First, a large proportion of the papers examined for this review were discarded because time–temperature history at the site of thermal damage assessment was not recorded. It is strongly recommended that future research on this subject include such data. Second, very little data is available examining chronic consequences of thermal exposure. On a related point, the time of assessment of damage after exposure is critically important for assessing whether damage is transient or permanent. Additionally, virtually no data are available for repeated thermal exposures which may occur in certain recreational or occupational activities. For purposes of regulatory guidelines, both acute and lasting effects of thermal damage should be considered. PMID:21591897

  6. Generic incubation law for laser damage and ablation thresholds

    NASA Astrophysics Data System (ADS)

    Sun, Zhanliang; Lenzner, Matthias; Rudolph, Wolfgang

    2015-02-01

    In multi-pulse laser damage and ablation experiments, the laser-induced damage threshold (LIDT) usually changes with the number of pulses in the train, a phenomenon known as incubation. We introduce a general incubation model based on two physical mechanisms—pulse induced change of (i) absorption and (ii) critical energy that must be deposited to cause ablation. The model is applicable to a broad class of materials and we apply it to fit data for dielectrics and metals. It also explains observed changes of the LIDT as a function of the laser repetition rate. We discuss under which conditions the crater-size method to determine LIDTs can be applied in multi-pulse experiments.

  7. Damage Threshold of Meloidogyne hapla to Lettuce in Organic Soil

    PubMed Central

    Viaene, N. M.; Abawi, G. S.

    1996-01-01

    Lettuce was seeded in pots in the greenhouse and in field microplots in 1991 and 1992. Pots and microplots were filled with untreated or fumigated organic soil infested with Meloidogyne hapla at seven initial population densities (Pi) (0 to 32 eggs/cm³ soil). Lettuce weight, severity of root galling, and number of eggs per root system (Pf) were determined after 8 weeks. At the highest Pi, M. hapla caused yield losses up to 64% in the microplots and plant death in the greenhouse tests. The Seinhorst equation was used to describe the relation between lettuce weight and Pi (r² = 0.73 - 0.98) and to calculate the damage threshold density (T). Values of T were 7 and 8 eggs/cm³ soil in the greenhouse tests of 1991 and 1992, respectively. In the microplot tests, T was 1 egg/cm³ soil in 1991 and 2 eggs/cm³ soil in 1992. The damage threshold was the same in untreated and fumigated soils. At low Pi, root galling was more severe in the pots than in the microplots. Pf increased with increasing Pi of M. hapla in both tests, but declined at Pi > T in the greenhouse tests. The reproduction rate (Pf/Pi) of M. hapla was highest at the lowest Pi. PMID:19277172

  8. Damage Threshold of Meloidogyne hapla to Lettuce in Organic Soil.

    PubMed

    Viaene, N M; Abawi, G S

    1996-12-01

    Lettuce was seeded in pots in the greenhouse and in field microplots in 1991 and 1992. Pots and microplots were filled with untreated or fumigated organic soil infested with Meloidogyne hapla at seven initial population densities (Pi) (0 to 32 eggs/cm(3) soil). Lettuce weight, severity of root galling, and number of eggs per root system (Pf) were determined after 8 weeks. At the highest Pi, M. hapla caused yield losses up to 64% in the microplots and plant death in the greenhouse tests. The Seinhorst equation was used to describe the relation between lettuce weight and Pi (r(2) = 0.73 - 0.98) and to calculate the damage threshold density (T). Values of T were 7 and 8 eggs/cm(3) soil in the greenhouse tests of 1991 and 1992, respectively. In the microplot tests, T was 1 egg/cm(3) soil in 1991 and 2 eggs/cm(3) soil in 1992. The damage threshold was the same in untreated and fumigated soils. At low Pi, root galling was more severe in the pots than in the microplots. Pf increased with increasing Pi of M. hapla in both tests, but declined at Pi > T in the greenhouse tests. The reproduction rate (Pf/Pi) of M. hapla was highest at the lowest Pi. PMID:19277172

  9. Infrared skin damage thresholds from 1319-nm continuous-wave laser exposures

    NASA Astrophysics Data System (ADS)

    Oliver, Jeffrey W.; Vincelette, Rebecca; Noojin, Gary D.; Clark, Clifton D.; Harbert, Corey A.; Schuster, Kurt J.; Shingledecker, Aurora D.; Kumru, Semih S.; Maughan, Justin; Kitzis, Naomi; Buffington, Gavin D.; Stolarski, David J.; Thomas, Robert J.

    2013-12-01

    A series of experiments were conducted in vivo using Yucatan miniature pigs (Sus scrofa domestica) to determine thermal damage thresholds to the skin from 1319-nm continuous-wave Nd:YAG laser irradiation. Experiments employed exposure durations of 0.25, 1.0, 2.5, and 10 s and beam diameters of ˜0.6 and 1 cm. Thermal imagery data provided a time-dependent surface temperature response from the laser. A damage endpoint of fifty percent probability of a minimally visible effect was used to determine threshold for damage at 1 and 24 h postexposure. Predicted thermal response and damage thresholds are compared with a numerical model of optical-thermal interaction. Resultant trends with respect to exposure duration and beam diameter are compared with current standardized exposure limits for laser safety. Mathematical modeling agreed well with experimental data, predicting that though laser safety standards are sufficient for exposures <10 s, they may become less safe for very long exposures.

  10. Laser damage threshold measurements of optical materials for direct laser accelerators

    SciTech Connect

    Soong, Ken; Byer, R. L.; Colby, E. R.; England, R. J.; Peralta, E. A.

    2012-12-21

    The laser-damage threshold is a fundamental limit for any dielectric laser-driven accelerator and is set by the material of the structure. In this paper, we present a theoretical model of the laser damage mechanism, in comparison with experimental data on the damage threshold of silicon. Additionally, we present damage threshold measurement data of various optical materials, most of which have not been previously characterized in the picosecond-regime.

  11. Damage and strength of composite materials: Trends, predictions, and challenges

    NASA Technical Reports Server (NTRS)

    Obrien, T. Kevin

    1994-01-01

    Research on damage mechanisms and ultimate strength of composite materials relevant to scaling issues will be addressed in this viewgraph presentation. The use of fracture mechanics and Weibull statistics to predict scaling effects for the onset of isolated damage mechanisms will be highlighted. The ability of simple fracture mechanics models to predict trends that are useful in parametric or preliminary designs studies will be reviewed. The limitations of these simple models for complex loading conditions will also be noted. The difficulty in developing generic criteria for the growth of these mechanisms needed in progressive damage models to predict strength will be addressed. A specific example for a problem where failure is a direct consequence of progressive delamination will be explored. A damage threshold/fail-safety concept for addressing composite damage tolerance will be discussed.

  12. Large-aperture, high-damage-threshold optics for beamlet

    SciTech Connect

    Campbell, J.H.; Atherton, L.J.; DeYoreo, J.J.

    1996-06-01

    Beamlet serves as a test bed for the proposed National Ignition Facility (NIF) laser design and components. Therefore, its optics are similar in size and quality to those proposed for the NIF. In general, the optics in the main laser cavity and transport section of Beamlet are larger and have higher damage thresholds than the optics manufactured for any of the previous laser systems. In addition, the quality of the Beamlet optical materials is higher, leading to better wavefront quality, higher optical transmission, and lower-intensity modulation of the output laser beam than, for example, that typically achieved on Nova. In this article, the authors discuss the properties and characteristics of the large-aperture optics used on Beamlet.

  13. Laser-induced damage threshold of silicon in millisecond, nanosecond, and picosecond regimes

    SciTech Connect

    Wang, X.; Shen, Z. H.; Lu, J.; Ni, X. W.

    2010-08-15

    Millisecond, nanosecond, and picosecond laser pulse induced damage thresholds on single-crystal are investigated in this study. The thresholds of laser-induced damage on silicon are calculated theoretically for three pulse widths based on the thermal damage model. An axisymmetric mathematical model is established for the transient temperature field of the silicon. Experiments are performed to test the damage thresholds of silicon at various pulse widths. The results indicate that the damage thresholds obviously increase with the increasing of laser pulse width. Additionally, the experimental results agree well with theoretical calculations and numerical simulation results.

  14. High-efficiency, dielectric multilayer gratings optimized for manufacturability and laser damage threshold

    SciTech Connect

    Britten, J.A.; Perry, M.D.; Shore, B.W.; Boyd, R.D.; Loomis, G.E.; Chow, R.

    1995-11-29

    Ultrashort pulse, high-intensity lasers offer new opportunities for the study of light-matter interaction and for inertial confinement fusion. A 100 Terawatt laser operating 400 fs and 1.053 {mu}m is operational at LLNL, and a 1000 Terawatt (Petawatt) laser will come online in early 1996. These lasers use large-aperture (40 cm and 94 cm diameter, respectively) diffraction gratings to compress the amplified laser pulse. At present, hologrphically produced, gold overcoated photoresist gratings are used: these gratings represent the fuse in the laser chain. Higher laser damage thresholds and higher diffraction efficiencies are theoretically possible with multilayer dielectric gratings (MDG`s). A number of design parameters regarding both the multilayer stack and the etched grating structure can be optimized to maximize the laser damage threshold and also improve the processing latitude for the interference lithography and reactive ion etching steps used during manufacture of these gratings. This paper presents model predictions for the behavior of hafnia/silica MDG`s both during processing and in operation, and presents experimental data on the diffraction efficiency and short- pulse laser damage threshold for optimized witness gratings.

  15. Increased damage thresholds due to laser pulse modulation

    SciTech Connect

    Feit, M.D.; Musher, S.L.; Shapiro, E.G.; Rubenchik, A.M. |

    1995-05-30

    Nonlinear self-focusing in laser glass imposes limits on the energy fluence that can be safely transmitted without risking damage. For this reason, it is desirable to strictly limit the peak to average spatial variations of fluence by smoothing schemes such as Smoothing by Spectral Dispersion (SSD). While spatial variations are problematic, the same is not necessarily true of temporal variations since normal group velocity dispersion tends to smooth out temporal peaks caused by spatial self-focusing. Earlier work indicated that increased bandwidth can delay the onset of self focusing. The present work re-examines the question of self focusing threshold increases due to high bandwidth by investigating another source of such increase in three dimensional beam breakup--the bending instability. For simplicity, the authors consider the behavior of a single space-time speckle. Normal dispersion can lead to splitting of the pulse and delay of self focusing for short enough pulses as noted above. In addition to the self focusing instability, the laser beam is also subject to the so-called bending (sausage like) instability which can spatially disperse the field maxima over time. Because the bending instability breaks an initial axial symmetry, a full three dimensional numerical simulation is required to study it accurately. Such calculations are possible, but costly. The authors have used a modified 2D nonlinear Schroedinger equation with a high power nonlinearity since this mimics the 3D behavior of the competition between self focusing and bending. This study is relevant for inertial confinement conditions.

  16. Confronting uncertainty in flood damage predictions

    NASA Astrophysics Data System (ADS)

    Schröter, Kai; Kreibich, Heidi; Vogel, Kristin; Merz, Bruno

    2015-04-01

    Reliable flood damage models are a prerequisite for the practical usefulness of the model results. Oftentimes, traditional uni-variate damage models as for instance depth-damage curves fail to reproduce the variability of observed flood damage. Innovative multi-variate probabilistic modelling approaches are promising to capture and quantify the uncertainty involved and thus to improve the basis for decision making. In this study we compare the predictive capability of two probabilistic modelling approaches, namely Bagging Decision Trees and Bayesian Networks. For model evaluation we use empirical damage data which are available from computer aided telephone interviews that were respectively compiled after the floods in 2002, 2005 and 2006, in the Elbe and Danube catchments in Germany. We carry out a split sample test by sub-setting the damage records. One sub-set is used to derive the models and the remaining records are used to evaluate the predictive performance of the model. Further we stratify the sample according to catchments which allows studying model performance in a spatial transfer context. Flood damage estimation is carried out on the scale of the individual buildings in terms of relative damage. The predictive performance of the models is assessed in terms of systematic deviations (mean bias), precision (mean absolute error) as well as in terms of reliability which is represented by the proportion of the number of observations that fall within the 95-quantile and 5-quantile predictive interval. The reliability of the probabilistic predictions within validation runs decreases only slightly and achieves a very good coverage of observations within the predictive interval. Probabilistic models provide quantitative information about prediction uncertainty which is crucial to assess the reliability of model predictions and improves the usefulness of model results.

  17. A ruggedness evaluation of procedures for damage threshold testing optical materials

    NASA Technical Reports Server (NTRS)

    Hooker, Matthew W.; Thomas, Milfred E.; Wise, Stephanie A.; Tappan, Nina D.

    1995-01-01

    A ruggedness evaluation of approaches to damage threshold testing was performed to determine the influence of three procedural variables on damage threshold data. The differences between the number of test sites evaluated at an applied fluence level (1 site versus 10 sites), the number of laser pulses at each test site (1 pulse versus 200 pulses), and the beam diameter (0.35 mm versus 0.70 mm) were all found to significantly influence the damage threshold data over a 99-percent confidence interval.

  18. Theoretical analysis for temperature dependence of laser- induced damage threshold of optical thin films

    NASA Astrophysics Data System (ADS)

    Mikami, K.; Motokoshi, S.; Somekawa, T.; Jitsuno, T.; Fujita, M.; Tanaka, KA; Azechi, H.

    2016-03-01

    The temperature dependence of the laser-induced damage threshold on optical coatings was studied in detail for laser pulses from 123 K to 473 K at different temperatures. The laser-induced damage threshold increased with decreasing temperatures when we tested long pulses (200 ps and 4 ns). The temperature dependence, however, was reversed for pulses shorter than a few picoseconds (100 fs testing). We propose a scaling model with a flowchart that includes three separate processes: free-electron generation, electron multiplication, and electron heating. Furthermore, we calculated the temperature dependence of laser-induced damage thresholds at different temperatures. Our calculation results agreed well with the experimental results.

  19. Femtosecond laser threshold: retinal damage versus induced breakdown mechanisms

    NASA Astrophysics Data System (ADS)

    Cain, Clarence P.; Toth, Cynthia A.; Stein, Cindy D.; Noojin, Gary D.; Stolarski, David J.; Rockwell, Benjamin A.; Boppart, Stephen A.; Roach, William P.

    1994-08-01

    Threshold measurements at 90 femtoseconds (fs) and 600 fs have been made for minimum visible lesions (MVLs) using Dutch Belted rabbit and Rhesus monkey eyes. Laser induced breakdown (LIB) thresholds on biological materials including vitreous, normal saline, tap water, and ultrapure water are reported along with irradiance calculations utilizing nonlinear transmission properties including self-focusing. At both pulsewidths the ED50 dose required for the Rhesus monkey eye was less than half the value determined for the Dutch Belted rabbit eye, all thresholds being 1 microjoule ((mu) J) or less. Measurements on the Rhesus eye at 600 fs found the ED50 dose (0.26 (mu) J) to be much lower than the ED50 dose at 90 fs (0.43 (mu) J). But for these two pulsewidths, almost the same energy level was determined for the Dutch Belted rabbit eye (0.94 (mu) J vs. 1.0 (mu) J). LIB threshold measurements at 100 fs and 300 fs using a simulated eye with isolated vitreous found the ED50 dosages to be 3.5 and 6.0 (mu) J respectively. We found in all cases that the ED50 dosages required to produce MVLs in 24 hours for rabbit and monkey eyes were less than the ED50 values measured for LIB in vitreous or saline or any other breakdown values reported. Also observed was the fact that many of the threshold lesions did not appear in the 1-hour postexposure check but clearly showed up at the 24-hour reading which provided for a much lower threshold dose after 24 hours. We discuss the energy levels and peak powers at which nonlinear effects can begin to occur.

  20. Predicting Damage of Meloidogyne incognita on Watermelon.

    PubMed

    Xing, Lijuan; Westphal, Andreas

    2012-06-01

    Quantitative growth response of watermelon (Citrullus lanatus) sensitive to Meloidogyne incognita is poorly understood. Determination of soil population densities of second-stage juveniles (J2) of M. incognita with Baermann funnel extraction often is inaccurate at low soil temperatures. In greenhouse experiments, three sandy soils were inoculated with dilution series of population densities of eggs or J2 of M. incognita and planted in small containers to watermelon 'Royal Sweet' or subjected to Baermann funnel extraction. After five weeks of incubation in the greenhouse bioassay plants in egg-inoculated soils, gall numbers on watermelon roots related more closely to inoculated population densities than J2 counts after Baermann funnel extraction. In April 2004, perpendicularly-inserted tubes (45-cm diameter, 55-cm deep) served as microplots where two methyl bromide-fumigated sandy soils were inoculated with egg suspensions of M. incognita at 0, 100, 1,000 or 10,000 eggs/100 cm(3) of soil in 15-cm depth. At transplanting of 4-week old watermelon seedlings, soils were sampled for the bioassay or for extraction of J2 by Baermann funnel. In the Seinhorst function of harvested biomass in relation to nematode numbers, decline of biomass with increasing population densities of M. incognita was accurately modeled by the inoculated eggs (R(2) = 0.93) and by the counts of galls on the bioassay roots (R(2) = 0.98); but poorly by J2 counts (R(2) = 0.68). Threshold levels of watermelon top dry weight to M. incognita were 122 eggs/100 cm(3) soil, 1.6 galls on bioassay roots, or 3.6 J2/100 cm(3) of soil. Using the bioassay in early spring for predicting risk of nematode damage appeared useful in integrated pest management systems of watermelon. PMID:23482631

  1. Predicting Damage of Meloidogyne incognita on Watermelon

    PubMed Central

    Xing, Lijuan; Westphal, Andreas

    2012-01-01

    Quantitative growth response of watermelon (Citrullus lanatus) sensitive to Meloidogyne incognita is poorly understood. Determination of soil population densities of second-stage juveniles (J2) of M. incognita with Baermann funnel extraction often is inaccurate at low soil temperatures. In greenhouse experiments, three sandy soils were inoculated with dilution series of population densities of eggs or J2 of M. incognita and planted in small containers to watermelon ‘Royal Sweet’ or subjected to Baermann funnel extraction. After five weeks of incubation in the greenhouse bioassay plants in egg-inoculated soils, gall numbers on watermelon roots related more closely to inoculated population densities than J2 counts after Baermann funnel extraction. In April 2004, perpendicularly-inserted tubes (45-cm diameter, 55-cm deep) served as microplots where two methyl bromide-fumigated sandy soils were inoculated with egg suspensions of M. incognita at 0, 100, 1,000 or 10,000 eggs/100 cm3 of soil in 15-cm depth. At transplanting of 4-week old watermelon seedlings, soils were sampled for the bioassay or for extraction of J2 by Baermann funnel. In the Seinhorst function of harvested biomass in relation to nematode numbers, decline of biomass with increasing population densities of M. incognita was accurately modeled by the inoculated eggs (R2 = 0.93) and by the counts of galls on the bioassay roots (R2 = 0.98); but poorly by J2 counts (R2 = 0.68). Threshold levels of watermelon top dry weight to M. incognita were 122 eggs/100 cm3 soil, 1.6 galls on bioassay roots, or 3.6 J2/100 cm3 of soil. Using the bioassay in early spring for predicting risk of nematode damage appeared useful in integrated pest management systems of watermelon. PMID:23482631

  2. Damage thresholds in laser-irradiated optical materials

    NASA Astrophysics Data System (ADS)

    Guignard, Franck; Autric, Michel L.; Baudinaud, Vincent

    1997-05-01

    An experimental study on the damage induced by laser irradiation on different materials, borosilicate glass, fused silicate, molded and stretched polymethylmethacrylate (PMMA), has been performed. The irradiation source is a 1KL pulsed cold cathode electron gun preionized TEA CO2 laser. Damage mechanisms are controlled by the in-depth absorption of the 10.6 micrometers radiation according to the Beer-Lambert law. PMMA is damaged following a boiling process. Stretched PMMA is fractured first, releasing stresses, then boiled like molded PMMA at a higher energy. BK7 crazed after the irradiation due to thermomechanical stresses, silicate melt and vaporized. Optical damages have been characterized by measuring the contrast transfer function through the irradiated samples.

  3. Increase of bulk optical damage threshold fluences of KDP crystals by laser irradiation and heat treatment

    DOEpatents

    Swain, J.E.; Stokowski, S.E.; Milam, D.; Kennedy, G.C.; Rainer, F.

    1982-07-07

    The bulk optical damage threshold fluence of potassium dihydrogen phosphate (KDP) crystals is increased by irradiating the crystals with laser pulses of duration 1 to 20 nanoseconds of increasing fluence, below the optical damage threshold fluence for untreated crystals, or by baking the crystals for times of the order of 24 hours at temperatures of 110 to 165/sup 0/C, or by a combination of laser irradiation and baking.

  4. Experimental Determination of Damage Threshold Characteristics of IR Compatible Optical Materials

    SciTech Connect

    Soong, Ken

    2011-05-20

    The accelerating gradient in a laser-driven dielectric accelerating structure is often limited by the laser damage threshold of the structure. For a given laser-driven dielectric accelerator design, we can maximize the accelerating gradient by choosing the best combination of the accelerator's constituent material and operating wavelength. We present here a model of the damage mechanism from ultrafast infrared pulses and compare that model with experimental measurements of the damage threshold of bulk silicon. Additionally, we present experimental measurements of a variety of candidate materials, thin films, and nanofabricated accelerating structures.

  5. Laser damage threshold of gelatin and a copper phthalocyanine doped gelatin optical limiter

    SciTech Connect

    Brant, M.C.; McLean, D.G.; Sutherland, R.L.

    1996-12-31

    The authors demonstrate optical limiting in a unique guest-host system which uses neither the typical liquid or solid host. Instead, they dope a gelatin gel host with a water soluble Copper (II) phthalocyaninetetrasulfonic acid, tetrasodium salt (CuPcTs). They report on the gelatin`s viscoelasticity, laser damage threshold, and self healing of this damage. The viscoelastic gelatin has mechanical properties quite different than a liquid or solid. The authors` laser measurements demonstrate that the single shot damage threshold of the undoped gelatin host increases with decreasing gelatin concentration. The gelatin also has a much higher laser damage threshold than a stiff acrylic. Unlike brittle solids, the soft gelatin self heals from laser induced damage. Optical limiting test also show the utility of a gelatin host doped with CuPcTs. The CuPcTs/gelatin matrix is not damaged at incident laser energies 5 times the single shot damage threshold of the gelatin host. However, at this high laser energy the CuPcTs is photo bleached at the beam waist. The authors repair photo bleached sites by annealing the CuPcTs/gelatin matrix.

  6. Higher-than-predicted saltation threshold wind speeds on Titan.

    PubMed

    Burr, Devon M; Bridges, Nathan T; Marshall, John R; Smith, James K; White, Bruce R; Emery, Joshua P

    2015-01-01

    Titan, the largest satellite of Saturn, exhibits extensive aeolian, that is, wind-formed, dunes, features previously identified exclusively on Earth, Mars and Venus. Wind tunnel data collected under ambient and planetary-analogue conditions inform our models of aeolian processes on the terrestrial planets. However, the accuracy of these widely used formulations in predicting the threshold wind speeds required to move sand by saltation, or by short bounces, has not been tested under conditions relevant for non-terrestrial planets. Here we derive saltation threshold wind speeds under the thick-atmosphere, low-gravity and low-sediment-density conditions on Titan, using a high-pressure wind tunnel refurbished to simulate the appropriate kinematic viscosity for the near-surface atmosphere of Titan. The experimentally derived saltation threshold wind speeds are higher than those predicted by models based on terrestrial-analogue experiments, indicating the limitations of these models for such extreme conditions. The models can be reconciled with the experimental results by inclusion of the extremely low ratio of particle density to fluid density on Titan. Whereas the density ratio term enables accurate modelling of aeolian entrainment in thick atmospheres, such as those inferred for some extrasolar planets, our results also indicate that for environments with high density ratios, such as in jets on icy satellites or in tenuous atmospheres or exospheres, the correction for low-density-ratio conditions is not required. PMID:25487154

  7. Higher-than-predicted saltation threshold wind speeds on Titan

    NASA Astrophysics Data System (ADS)

    Burr, Devon M.; Bridges, Nathan T.; Marshall, John R.; Smith, James K.; White, Bruce R.; Emery, Joshua P.

    2015-01-01

    Titan, the largest satellite of Saturn, exhibits extensive aeolian, that is, wind-formed, dunes, features previously identified exclusively on Earth, Mars and Venus. Wind tunnel data collected under ambient and planetary-analogue conditions inform our models of aeolian processes on the terrestrial planets. However, the accuracy of these widely used formulations in predicting the threshold wind speeds required to move sand by saltation, or by short bounces, has not been tested under conditions relevant for non-terrestrial planets. Here we derive saltation threshold wind speeds under the thick-atmosphere, low-gravity and low-sediment-density conditions on Titan, using a high-pressure wind tunnel refurbished to simulate the appropriate kinematic viscosity for the near-surface atmosphere of Titan. The experimentally derived saltation threshold wind speeds are higher than those predicted by models based on terrestrial-analogue experiments, indicating the limitations of these models for such extreme conditions. The models can be reconciled with the experimental results by inclusion of the extremely low ratio of particle density to fluid density on Titan. Whereas the density ratio term enables accurate modelling of aeolian entrainment in thick atmospheres, such as those inferred for some extrasolar planets, our results also indicate that for environments with high density ratios, such as in jets on icy satellites or in tenuous atmospheres or exospheres, the correction for low-density-ratio conditions is not required.

  8. Smooth-Threshold Multivariate Genetic Prediction with Unbiased Model Selection.

    PubMed

    Ueki, Masao; Tamiya, Gen

    2016-04-01

    We develop a new genetic prediction method, smooth-threshold multivariate genetic prediction, using single nucleotide polymorphisms (SNPs) data in genome-wide association studies (GWASs). Our method consists of two stages. At the first stage, unlike the usual discontinuous SNP screening as used in the gene score method, our method continuously screens SNPs based on the output from standard univariate analysis for marginal association of each SNP. At the second stage, the predictive model is built by a generalized ridge regression simultaneously using the screened SNPs with SNP weight determined by the strength of marginal association. Continuous SNP screening by the smooth thresholding not only makes prediction stable but also leads to a closed form expression of generalized degrees of freedom (GDF). The GDF leads to the Stein's unbiased risk estimation (SURE), which enables data-dependent choice of optimal SNP screening cutoff without using cross-validation. Our method is very rapid because computationally expensive genome-wide scan is required only once in contrast to the penalized regression methods including lasso and elastic net. Simulation studies that mimic real GWAS data with quantitative and binary traits demonstrate that the proposed method outperforms the gene score method and genomic best linear unbiased prediction (GBLUP), and also shows comparable or sometimes improved performance with the lasso and elastic net being known to have good predictive ability but with heavy computational cost. Application to whole-genome sequencing (WGS) data from the Alzheimer's Disease Neuroimaging Initiative (ADNI) exhibits that the proposed method shows higher predictive power than the gene score and GBLUP methods. PMID:26947266

  9. Critical storm thresholds for significant morphological changes and damage along the Emilia-Romagna coastline, Italy

    NASA Astrophysics Data System (ADS)

    Armaroli, Clara; Ciavola, Paolo; Perini, Luisa; Calabrese, Lorenzo; Lorito, Samantha; Valentini, Andrea; Masina, Marinella

    2012-03-01

    The definition of storm morphological thresholds along the coast of the Emilia-Romagna Region strictly depends on its configuration and variability. The region is located in northern Italy, facing the Adriatic Sea. The coastline is characterised by very different levels of economic development, ranging from natural zones with dunes to highly developed stretches protected by breakwaters and groynes. The Integrated Coastal Zone Management effort is mainly concentrated on preserving urban areas that generate significant income for the regional economy. Natural areas, while small in comparison to the urbanised zone, are important for environment preservation. Because of such a multiplicity of issues at stake, it was decided to produce two different thresholds: one for the morphological impact on natural sectors and another for inundation and damage to structures along urbanised zones. The "forcing" component of the threshold definition for natural areas was calculated by summing the effects of surge + tide + waves (run-up elevation) to find the Maximum Water Level (MWL) reached by the sea during one, ten and one-hundred year storm return periods. For urbanised zones, historical storm information was collected starting from the 1960s in order to identify the forcing conditions causing real damages. Each storm was classified in terms of wave height, period, direction and surge level. Morphological information were obtained from Lidar flights performed in 2003 and 2004 and from direct surveys undertaken in September 2008 and February 2009 as part of the monitoring programme for the MICORE Project. The computed MWL for each return period was then compared to beach elevations along natural areas in order to calculate the Dune Stability Factor (DSF), an index that accounts for the eroded sediment volume above the MWL during a storm. Based on analysis along 41 profile lines at a 500 m spacing, it was found that the 1-in-1 year return period wave height + 1-in-1 year return

  10. Analysis of damage threshold of K9 glass irradiated by 248-nm KrF excimer laser

    NASA Astrophysics Data System (ADS)

    Wang, Xi; Shao, Jingzhen; Li, Hua; Nie, Jinsong; Fang, Xiaodong

    2016-02-01

    The theoretical model of K9 glass irradiated by a 248-nm KrF excimer laser was established, and a numerical simulation was performed to calculate temperature and thermal stress fields in the K9 glass sample using the finite element method. The laser-induced damage thresholds were defined and calculated, and the effect of repetition frequency and the number of pulses on the damage threshold were also studied. Furthermore, the experiment research was carried out to confirm the numerical simulation. The damage threshold and damage morphology were analyzed by means of a metallurgical microscope and scanning electron microscopy. The simulation and experimental results indicated that the damage mechanism of K9 glass irradiated by a KrF excimer laser was melting damage and stress damage, and the stress damage first appeared inside the K9 glass sample. The tensile stress damage threshold, the compressive stress damage threshold, and the melting damage threshold were 0.64, 0.76, and 1.05 J/cm2, respectively. The damage threshold decreased with increasing repetition frequency and number of laser pulses. The experimental results indicated that the damage threshold of K9 glass was 2.8 J/cm2.

  11. Damage Prediction in Sheet Metal Forming

    NASA Astrophysics Data System (ADS)

    Saanouni, Khémais; Badreddine, Houssem

    2007-05-01

    to kill the fully damaged elements in order to describe the macroscopic crack propagation. Various 2D and 3D examples are given in order to show the capability of the methodology to predict the damage initiation and growth during various sheet metal forming processes.

  12. Laser damage threshold of SiO{sub 2} films by the photoacoustic mirage technique

    SciTech Connect

    Alvisi, M.; Vasanelli, L.; De Nunzio, G.; Diso, D.; Perrone, M. R.; Protopapa, L.; Rizzo, A.; Scaglione, S.

    1999-03-15

    SiO{sub 2} thin films of 240 nm thickness have been deposited by a dual-ion-beam sputtering technique using argon or xenon ions mixed with oxygen ions in the assisting ion beam and the role of the assisting ion beam and of the substrate temperature on the laser damage threshold at 308 nm (XeCl excimer laser) has been investigated by the photo acoustic mirage technique. It has been found that the laser damage threshold was quite dependent on the film deposition conditions. The sample grown at a substrate temperature of 300 deg. C and with the argon ion assisting beam was characterized by the highest damage threshold ( congruent with 10 J/cm{sup 2})

  13. A study of ps-laser-induced-damage-threshold in hybrid metal-dielectric mirrors

    NASA Astrophysics Data System (ADS)

    Škoda, Václav; Vanda, Jan

    2014-10-01

    Laser-induced-damage-threshold of two types of metal-dielectric mirrors was tested using a laser apparatus working at 800 nm wavelength with 1 ps pulse length at 1 kHz repetition rate and in 106-on-1 test mode. Four sets of mirror samples with different layer system designs using a multilayer Ta2O5/SiO2 coating on silver or gold metal layer were manufactured. Both BK7 and fused silica substrate materials were used for manufacturing of samples. The measured damage thresholds at 45 deg incidence and P-polarization were compared with computed properties of layer system and used materials.

  14. Predictions Of Fatigue Damage From Strain Histories

    NASA Technical Reports Server (NTRS)

    Sire, Robert A.; Besuner, Philip M.; Toomey, Tim

    1989-01-01

    Semiempirical mathematical model of fatigue damage in stressed objects uses experimental histories of strains in those objects to predict fatigue lives. Accounts for initiation and propagation of fatigue cracks on cycle-by-cycle basis. Measured strain history first digitized, then converted to history of turning-point strains for purposes of analysis. Data between turning points not used. When model calibrated against proper test data for each type of object characterized, its predictions of fatigue lives superior to statistical models as one based on root-mean-square strain.

  15. Development of high damage threshold optics for petawatt-class short-pulse lasers

    NASA Astrophysics Data System (ADS)

    Stuart, Brent C.; Perry, Michael D.; Boyd, Robert D.; Britten, Jerald A.; Shore, Bruce W.; Feit, Michael D.; Rubenchik, Alexander M.

    1995-04-01

    We report laser-induced damage threshold measurements on pure and multilayer dielectrics and gold-coated optics at 1053 and 526 nm for pulse durations, (tau) , ranging from 140 fs to 1 ns. Damage thresholds of gold coatings are limited to 500 mJ/cm2 in the subpicosecond range from 1053-nm pulses. In dielectrics, qualitative differences in the morphology of damage and a departure from the diffusion-dominated (tau) 1/2 scaling indicate that damage results from plasma formation and ablation for (tau) 50 ps. A theoretical model based on electron production via multiphoton ionization, Joule heating, and collisional (avalanche) ionization is in quantitative agreement with both the pulsewidth and wavelength scaling of experimental results.

  16. Development of high damage threshold optics for petawatt-class short-pulse lasers

    SciTech Connect

    Stuart, B.C.; Perry, M.D.; Boyd, R.D.

    1995-02-22

    The authors report laser-induced damage threshold measurements on pure and multilayer dielectrics and gold-coated optics at 1053 and 526 nm for pulse durations, {tau}, ranging from 140 fs to 1 ns. Damage thresholds of gold coatings are limited to 500 mJ/cm{sup 2} in the subpicosecond range for 1053-nm pulses. In dielectrics, qualitative differences in the morphology of damage and a departure from the diffusion-dominated {tau}1/2 scaling indicate that damage results from plasma formation and ablation for {tau}{le}10 ps and from conventional melting and boiling for {tau}>50 ps. A theoretical model based on electron production via multiphoton ionization, Joule heating, and collisional (avalanche) ionization is in quantitative agreement with both the pulsewidth and wavelength scaling of experimental results.

  17. Cleaning Process Versus Laser-Damage Threshold of Coated Optical Components

    SciTech Connect

    Rigatti, A.L.

    2005-03-31

    The cleaning of optical surfaces is important in the manufacture of high-laser-damage-threshold coatings, which are a key component on peak-power laser systems such as OMEGA located at the Laboratory for Laser Energetics (LLE). Since cleaning adds time, labor, and ultimately cost to the final coated component, this experiment was designed to determine the impact of different cleaning protocols on the measured laser-damage performance.

  18. Advanced Mitigation Process (AMP) for Improving Laser Damage Threshold of Fused Silica Optics.

    PubMed

    Ye, Xin; Huang, Jin; Liu, Hongjie; Geng, Feng; Sun, Laixi; Jiang, Xiaodong; Wu, Weidong; Qiao, Liang; Zu, Xiaotao; Zheng, Wanguo

    2016-01-01

    The laser damage precursors in subsurface of fused silica (e.g. photosensitive impurities, scratches and redeposited silica compounds) were mitigated by mineral acid leaching and HF etching with multi-frequency ultrasonic agitation, respectively. The comparison of scratches morphology after static etching and high-frequency ultrasonic agitation etching was devoted in our case. And comparison of laser induce damage resistance of scratched and non-scratched fused silica surfaces after HF etching with high-frequency ultrasonic agitation were also investigated in this study. The global laser induce damage resistance was increased significantly after the laser damage precursors were mitigated in this case. The redeposition of reaction produce was avoided by involving multi-frequency ultrasonic and chemical leaching process. These methods made the increase of laser damage threshold more stable. In addition, there is no scratch related damage initiations found on the samples which were treated by Advanced Mitigation Process. PMID:27484188

  19. Advanced Mitigation Process (AMP) for Improving Laser Damage Threshold of Fused Silica Optics

    PubMed Central

    Ye, Xin; Huang, Jin; Liu, Hongjie; Geng, Feng; Sun, Laixi; Jiang, Xiaodong; Wu, Weidong; Qiao, Liang; Zu, Xiaotao; Zheng, Wanguo

    2016-01-01

    The laser damage precursors in subsurface of fused silica (e.g. photosensitive impurities, scratches and redeposited silica compounds) were mitigated by mineral acid leaching and HF etching with multi-frequency ultrasonic agitation, respectively. The comparison of scratches morphology after static etching and high-frequency ultrasonic agitation etching was devoted in our case. And comparison of laser induce damage resistance of scratched and non-scratched fused silica surfaces after HF etching with high-frequency ultrasonic agitation were also investigated in this study. The global laser induce damage resistance was increased significantly after the laser damage precursors were mitigated in this case. The redeposition of reaction produce was avoided by involving multi-frequency ultrasonic and chemical leaching process. These methods made the increase of laser damage threshold more stable. In addition, there is no scratch related damage initiations found on the samples which were treated by Advanced Mitigation Process. PMID:27484188

  20. Advanced Mitigation Process (AMP) for Improving Laser Damage Threshold of Fused Silica Optics

    NASA Astrophysics Data System (ADS)

    Ye, Xin; Huang, Jin; Liu, Hongjie; Geng, Feng; Sun, Laixi; Jiang, Xiaodong; Wu, Weidong; Qiao, Liang; Zu, Xiaotao; Zheng, Wanguo

    2016-08-01

    The laser damage precursors in subsurface of fused silica (e.g. photosensitive impurities, scratches and redeposited silica compounds) were mitigated by mineral acid leaching and HF etching with multi-frequency ultrasonic agitation, respectively. The comparison of scratches morphology after static etching and high-frequency ultrasonic agitation etching was devoted in our case. And comparison of laser induce damage resistance of scratched and non-scratched fused silica surfaces after HF etching with high-frequency ultrasonic agitation were also investigated in this study. The global laser induce damage resistance was increased significantly after the laser damage precursors were mitigated in this case. The redeposition of reaction produce was avoided by involving multi-frequency ultrasonic and chemical leaching process. These methods made the increase of laser damage threshold more stable. In addition, there is no scratch related damage initiations found on the samples which were treated by Advanced Mitigation Process.

  1. Determination of ultra-short laser induced damage threshold of KH2PO4 crystal: Numerical calculation and experimental verification

    NASA Astrophysics Data System (ADS)

    Cheng, Jian; Chen, Mingjun; Kafka, Kyle; Austin, Drake; Wang, Jinghe; Xiao, Yong; Chowdhury, Enam

    2016-03-01

    Rapid growth and ultra-precision machining of large-size KDP (KH2PO4) crystals with high laser damage resistance are tough challenges in the development of large laser systems. It is of high interest and practical significance to have theoretical models for scientists and manufacturers to determine the laser-induced damage threshold (LIDT) of actually prepared KDP optics. Here, we numerically and experimentally investigate the laser-induced damage on KDP crystals in ultra-short pulse laser regime. On basis of the rate equation for free electron generation, a model dedicated to predicting the LIDT is developed by considering the synergistic effect of photoionization, impact ionization and decay of electrons. Laser damage tests are performed to measure the single-pulse LIDT with several testing protocols. The testing results combined with previously reported experimental data agree well with those calculated by the model. By taking the light intensification into consideration, the model is successfully applied to quantitatively evaluate the effect of surface flaws inevitably introduced in the preparation processes on the laser damage resistance of KDP crystals. This work can not only contribute to further understanding of the laser damage mechanisms of optical materials, but also provide available models for evaluating the laser damage resistance of exquisitely prepared optical components used in high power laser systems.

  2. Laser-Induced Damage Threshold and Certification Procedures for Optical Materials

    NASA Technical Reports Server (NTRS)

    1997-01-01

    This document provides instructions for performing laser-induced-damage-threshold tests and pass-fail certification tests on optical materials used in pulsed-laser systems. The optical materials to which these procedures apply include coated and uncoated optical substrates, laser crystals, Q-switches, polarizers, and other optical components employed in pulsed-laser systems.

  3. Quasi-Static 3-Point Reinforced Carbon-Carbon Bend Test and Analysis for Shuttle Orbiter Wing Leading Edge Impact Damage Thresholds

    NASA Technical Reports Server (NTRS)

    Fasanella, Edwin L.; Sotiris, Kellas

    2006-01-01

    Static 3-point bend tests of Reinforced Carbon-Carbon (RCC) were conducted to failure to provide data for additional validation of an LS-DYNA RCC model suitable for predicting the threshold of impact damage to shuttle orbiter wing leading edges. LS-DYNA predictions correlated well with the average RCC failure load, and were good in matching the load vs. deflection. However, correlating the detectable damage using NDE methods with the cumulative damage parameter in LS-DYNA material model 58 was not readily achievable. The difficulty of finding internal RCC damage with NDE and the high sensitivity of the mat58 damage parameter to the load near failure made the task very challenging. In addition, damage mechanisms for RCC due to dynamic impact of debris such as foam and ice and damage mechanisms due to a static loading were, as expected, not equivalent.

  4. Predicting severe winter coastal storm damage

    NASA Astrophysics Data System (ADS)

    Hondula, David M.; Dolan, Robert

    2010-07-01

    Over the past 40 years residents of, and visitors to, the North Carolina coastal barrier islands have experienced the destructive forces of several 'named' extratropical storms. These storms have caused large-scale redistributions of sand and loss of coastal structures and infrastructure. While most of the population living on the islands are familiar with the wintertime storms, the damage and scars of the 'super northeasters'—such as the Ash Wednesday storm of 7 March 1962, and the Halloween storm of 1989—are slipping away from the public's memory. In this research we compared the damage zones of the 1962 Ash Wednesday storm, as depicted on aerial photographs taken after the storm, with photos taken of the same areas in 2003. With these high-resolution aerial photos we were able to estimate the extent of new development which has taken place along the Outer Banks of North Carolina since 1962. Three damage zones were defined that extend across the islands from the ocean landward on the 1962 aerial photos: (1) the zone of almost total destruction on the seaward edge of the islands where the storm waves break; (2) the zone immediately inland where moderate structural damage occurs during severe storms; and (3) the zone of flood damage at the landward margin of the storm surge and overwash. We considered the rate of coastal erosion, the rate of development, and increases in property values as factors which may contribute to changing the financial risk for coastal communities. In comparing the values of these four factors with the 1962 damage data, we produced a predicted dollar value for storm damage should another storm of the magnitude of the 1962 Ash Wednesday storm occur in the present decade. This model also provides an opportunity to estimate the rate of increase in the potential losses through time as shoreline erosion continues to progressively reduce the buffer between the development and the edge of the sea. Our data suggest that the losses along the

  5. Review of structural influences on the laser damage thresholds of oxide coatings

    SciTech Connect

    Hacker, E.; Lauth, H.; Weibbrodt, P.

    1996-12-31

    The laser damage thresholds (LDT) of optical coatings lie, as a rule, markedly below those of the respective bulk materials. This is due to diverse specific real structure properties with regard to composition, crystallography, microstructure and the physico-chemical structure of the interfaces. These properties depend in a highly complex and sensitive way on the substrate treatment, coating techniques and deposition conditions. With evaporated and sputtered oxide coatings as example, some correlations between structural thin film properties (e.g. crystallography, microstructure, anisotropy, chemical composition, defects) and the ultraviolet (248 nm) or near infrared (1064 nm) laser damage thresholds are discussed with concern to a further increase of the damage resistance. It is evident from data that an approach to the problem requires complex investigations of the technology-structure-properties relationships.

  6. The effect of pseudo-accumulation in the measurement of fatigue laser-induced damage threshold

    NASA Astrophysics Data System (ADS)

    Melninkaitis, A.; Mirauskas, J.; Jupé, M.; Ristau, D.; Arenberg, J. W.; Sirutkaitis, V.

    2008-10-01

    Laser-induced damage threshold determination as a function of the number of incident pulses on a specific optic is a classic problem in laser damage studies. There are several models of the fundamental mechanisms explaining the fatigue laser damage behavior including temperature accumulation and changes of electronic or chemical material structure. Herewith we discuss the effects of unstable laser radiation on S-on-1 laser-induced damage probability. Numerical simulations of S-on-1 measurements for specific cases of defect densities, spot sizes and beam jitters are performed. It is demonstrated that the statistical effects of "pseudo-accumulation" reasoned by unstable laser radiation in transparent dielectrics containing nanometer sized defects leads to accumulation-like behavior. The magnitudes of the random beam walking and the energy fluctuations are directly related to the damage probability. Experimental results are also introduced to illustrate the theoretical results.

  7. Single-drop impact damage prediction for low density, coated ceramic materials. [rain erosion

    NASA Technical Reports Server (NTRS)

    Mustelier, D.

    1984-01-01

    A technique utilizing finite element analysis, liquid impact kinematics, and momentum theory is described and compared to single-drop impact test data performed on various configurations of coated ceramic material. The method correlates well with test data and is useful in predicting the single-drop impact damage velocity threshold for low-density, coated ceramic materials.

  8. Impact of contaminates on the laser damage threshold of 1w HR coatings

    SciTech Connect

    Norton, M A; Stolz, C J; Donohue, E; Hollingsworth, W G; Listiyo, K; Pryatel, J A; Hackel, R P

    2005-10-28

    In operational laser systems, it is often difficult to keep optical components completely free of foreign material. We have investigated the performance of high damage threshold 1.053 {micro}m high reflectors in the presence of surface contaminants. We have looked at the impact of stainless steel, aluminum, Azurlite{reg_sign}, dust, cotton fibers and polyester fibers on the performance of the mirrors under laser irradiation. The first four contaminants were deposited in sizes ranging from 30 microns to 150 microns. The fibers included lengths ranging to several millimeters. The testing was done at either a single fluence in the range of 6 J/cm{sup 2} to 24 J/cm{sup 2}, or a ramped sequence of shots starting at 1 J/cm{sup 2}. We will present data showing the onset of damage, the type of damage, and the propensity to damage growth in the fluence range studied.

  9. Tornado risk analysis at Savannah River Plant using windspeed damage thresholds and single building strike frequencies

    SciTech Connect

    Taylor, D.H.; McDonald, J.R.; Twisdale, L.A.

    1985-01-01

    In order to evaluate the safety of existing structures and properly design new structures, an analysis of tornado resistance was conducted on each process building at SRP and other buildings by type. Damage estimates were cataloged for each Fujita class windspeed interval and windspeeds were cataloged as a function of increased levels of damage. The probability, for any structure, of a tornado exceeding each windspeed threshold was calculated using the TORRISK computer code which was developed for calculating the probability of a tornado strike on nuclear power generating plants.

  10. A comparison of laser-induced-damage-threshold of two types of dielectric polarizing beam splitters

    NASA Astrophysics Data System (ADS)

    Å koda, Václav

    2013-11-01

    Laser-induced-damage-threshold (LIDT) of polarizing Brewster-angle beam splitters based on two different layer system designs was measured using a laser apparatus working at 1060 nm wavelength with 10 ns pulse length and 1-on-1 test mode. Two sets of samples with different design of layer system using TiO2/SiO2 coating materials were examined. Both BK7 and fused silica substrate materials were used for manufacturing of samples. The measured damage thresholds in S- and P-polarization were compared with computed values of the internal electric field inside of the layer system and with computed values of absorption as a measure of integral interaction of laser beam throughout the layer system.

  11. Higher certainty of the laser-induced damage threshold test with a redistributing data treatment

    NASA Astrophysics Data System (ADS)

    Jensen, Lars; Mrohs, Marius; Gyamfi, Mark; Mädebach, Heinrich; Ristau, Detlev

    2015-10-01

    As a consequence of its statistical nature, the measurement of the laser-induced damage threshold holds always risks to over- or underestimate the real threshold value. As one of the established measurement procedures, the results of S-on-1 (and 1-on-1) tests outlined in the corresponding ISO standard 21 254 depend on the amount of data points and their distribution over the fluence scale. With the limited space on a test sample as well as the requirements on test site separation and beam sizes, the amount of data from one test is restricted. This paper reports on a way to treat damage test data in order to reduce the statistical error and therefore measurement uncertainty. Three simple assumptions allow for the assignment of one data point to multiple data bins and therefore virtually increase the available data base.

  12. Higher certainty of the laser-induced damage threshold test with a redistributing data treatment

    SciTech Connect

    Jensen, Lars; Mrohs, Marius; Gyamfi, Mark; Mädebach, Heinrich; Ristau, Detlev

    2015-10-15

    As a consequence of its statistical nature, the measurement of the laser-induced damage threshold holds always risks to over- or underestimate the real threshold value. As one of the established measurement procedures, the results of S-on-1 (and 1-on-1) tests outlined in the corresponding ISO standard 21 254 depend on the amount of data points and their distribution over the fluence scale. With the limited space on a test sample as well as the requirements on test site separation and beam sizes, the amount of data from one test is restricted. This paper reports on a way to treat damage test data in order to reduce the statistical error and therefore measurement uncertainty. Three simple assumptions allow for the assignment of one data point to multiple data bins and therefore virtually increase the available data base.

  13. High-damage-threshold static laser beam shaping using optically patterned liquid-crystal devices.

    PubMed

    Dorrer, C; Wei, S K-H; Leung, P; Vargas, M; Wegman, K; Boulé, J; Zhao, Z; Marshall, K L; Chen, S H

    2011-10-15

    Beam shaping of coherent laser beams is demonstrated using liquid crystal (LC) cells with optically patterned pixels. The twist angle of a nematic LC is locally set to either 0 or 90° by an alignment layer prepared via exposure to polarized UV light. The two distinct pixel types induce either no polarization rotation or a 90° polarization rotation, respectively, on a linearly polarized optical field. An LC device placed between polarizers functions as a binary transmission beam shaper with a highly improved damage threshold compared to metal beam shapers. Using a coumarin-based photoalignment layer, various devices have been fabricated and tested, with a measured single-shot nanosecond damage threshold higher than 30 J/cm2. PMID:22002377

  14. Investigations of the Cavitation and Damage Thresholds of Histotripsy and Applications in Targeted Tissue Ablation

    NASA Astrophysics Data System (ADS)

    Vlaisavljevich, Eli

    Histotripsy is a noninvasive ultrasound therapy that controls acoustic cavitation to mechanically fractionate soft tissue. This dissertation investigates the physical thresholds to initiate cavitation and produce tissue damage in histotripsy and factors affecting these thresholds in order to develop novel strategies for targeted tissue ablation. In the first part of this dissertation, the effects of tissue properties on histotripsy cavitation thresholds and damage thresholds were investigated. Results demonstrated that the histotripsy shock scattering threshold using multi-cycle pulses increases in stiffer tissues, while the histotripsy intrinsic threshold using single-cycle pulses is independent of tissue stiffness. Further, the intrinsic threshold slightly decreases with lower frequencies and significantly decreases with increasing temperature. The effects of tissue properties on the susceptibility to histotripsy-induced tissue damage were also investigated, demonstrating that stiffer tissues are more resistant to histotripsy. Two strategies were investigated for increasing the effectiveness of histotripsy for the treatment of stiffer tissues, with results showing that thermal preconditioning may be used to alter tissue susceptibility to histotripsy and that lower frequency treatments may increase the efficiency of histotripsy tissue ablation due to enhanced bubble expansion. In the second part of this dissertation, the feasibility of using histotripsy for targeted liver ablation was investigated in an intact in vivo porcine model, with results demonstrating that histotripsy was capable of non-invasively creating precise lesions throughout the entire liver. Additionally, a tissue selective ablation approach was developed, where histotripsy completely fractionated the liver tissue surrounding the major hepatic vessels and gallbladder while being self-limited at the boundaries of these critical structures. Finally, the long-term effects of histotripsy liver

  15. Hydro-oleophobic silica antireflective films with high laser-damage threshold

    NASA Astrophysics Data System (ADS)

    Yan, Lianghong; Lv, Haibing; Wang, Chengcheng; Yuan, Xiaodong

    2011-02-01

    A simple method of preparing hydro-oleophobic anitreflective films with high laser-damage threshold is reported in this article. By adding fluoroalkylsilanes (FAS) into reactant mixture as a co-precursor, FAS modified SiO 2 was obtained under base catalyzed hydrolysis and condensation of tetraethoxysilane. The dip-coating films were deposited on two sides of fused silica substrates. The experimental results on the effect of adding fluoroalkylsilanes (FAS) as a co-precursor on the hydro-oleophobicity and optical properties of tetraethoxysilane (TEOS) based silica AR films, are reported. The hydro-oleophobicity of the films was tested by the contact angle measurements and the highest water contact angle of 136° and oil (peanut) contact angle of 93° were obtained. The surface chemical modification of the hydro-oleophobic films was confirmed using Fourier transform infrared spectroscopy (FTIR). For the films based on FAS and TEOS, additional absorption bands at 1100 cm -1 corresponding to C-F bond presented, clearly indicating the organic modification of the films. The highest optical transmittance of the hydro-oleophobic films was found to be 99.5%. By a Nd:YAG lasers the laser-damage threshold of as-deposited films was measured at 351 nm wavelength (1 ns). The laser-damage threshold was as high as 22.6 J/cm 2.

  16. Long-range pulselength scaling of 351nm laser damage thresholds

    NASA Astrophysics Data System (ADS)

    Foltyn, S. R.; Jolin, L. J.

    1986-12-01

    In a series of experiments incorporating 351nm pulselength of 9, 26, 54, and 625ns, it was found that laser damage thresholds increased as (pulselength)/sup x/, and that the exponent averaged 0.36 and ranged, for different samples, from 0.23 to 0.48. Similar results were obtained when only catastrophic damage was considered. Samples included Al2O3/SiO2 in both AR and HR multilayers, HR's of Sc2O3/SiO2 and HfO2/SiO2, and Al-on-pyrex mirror; 9ns thresholds were between 0.2 to 5.6 J/sq cm. When these data were compared with a wide range of other results - for wavelengths from 0.25 to 10.6 microns and pulselengths down to 4ps - a remarkably consistent picture emerged. Damage thresholds, on average, increase approximately as the cube-root of pulselength from picoseconds to nearly a microsecond, and do so regardless of wavelength or material under test.

  17. A SMALL-SCALE DAMAGE APPROACH TO PREDICT FATIGUE CRACK GROWTH IN CERAMIC MATERIALS

    SciTech Connect

    Nguyen, Ba Nghiep; Koeppel, Brian J.; Khaleel, Mohammad A.

    2006-05-19

    This paper proposes a small-scale damage modeling approach to predict fatigue crack growth in ceramic materials. A fatigue damage model is formulated that uses two variables. One variable is the scalar damage variable governing the reduction of stiffness, and the other is the number of cycles. The damage evolution law is obtained based on thermodynamics of continuous media and a damage criterion containing a damage threshold function that depends on the damage variable and the cyclic loading parameters. The model has been implemented into the ABAQUS finite element code via user-subroutines and has been used in a modified boundary layer (MBL) modeling approach to analyze fatigue crack growth in a small fracture process zone situated at an initial crack tip. The model application is illustrated through an analysis of fatigue crack growth in an yttria-stabilized tetragonal zirconia material.

  18. Prediction and measurement of radiation damage to CMOS devices on board spacecraft

    NASA Technical Reports Server (NTRS)

    Cliff, R. A.; Danchenko, V.; Stassinopoulos, E. G.; Sing, M.; Brucker, G. J.; Ohanian, R. S.

    1976-01-01

    The initial results obtained from the Complementary Metal Oxide Semiconductors Radiation Effects Measurement experiment are presented. Predictions of radiation damage to C-MOS devices are based on standard environment models and computational techniques. A comparison of the shifts in CMOS threshold potentials, that is, those measured in space to those obtained from the on the ground simulation experiment with Co 60, indicated that the measured space damage is greater than predicted by a factor of two for shields thicker than 100 mils (2.54 mm), but agrees well with predictions for the thinner shields.

  19. Wavelength dependence of femtosecond laser-induced damage threshold of optical materials

    SciTech Connect

    Gallais, L. Douti, D.-B.; Commandré, M.; Batavičiūtė, G.; Pupka, E.; Ščiuka, M.; Smalakys, L.; Sirutkaitis, V.; Melninkaitis, A.

    2015-06-14

    An experimental and numerical study of the laser-induced damage of the surface of optical material in the femtosecond regime is presented. The objective of this work is to investigate the different processes involved as a function of the ratio of photon to bandgap energies and compare the results to models based on nonlinear ionization processes. Experimentally, the laser-induced damage threshold of optical materials has been studied in a range of wavelengths from 1030 nm (1.2 eV) to 310 nm (4 eV) with pulse durations of 100 fs with the use of an optical parametric amplifier system. Semi-conductors and dielectrics materials, in bulk or thin film forms, in a range of bandgap from 1 to 10 eV have been tested in order to investigate the scaling of the femtosecond laser damage threshold with the bandgap and photon energy. A model based on the Keldysh photo-ionization theory and the description of impact ionization by a multiple-rate-equation system is used to explain the dependence of laser-breakdown with the photon energy. The calculated damage fluence threshold is found to be consistent with experimental results. From these results, the relative importance of the ionization processes can be derived depending on material properties and irradiation conditions. Moreover, the observed damage morphologies can be described within the framework of the model by taking into account the dynamics of energy deposition with one dimensional propagation simulations in the excited material and thermodynamical considerations.

  20. Improving UV laser damage threshold of fused silica optics by wet chemical etching technique

    NASA Astrophysics Data System (ADS)

    Ye, Hui; Li, Yaguo; Yuan, Zhigang; Wang, Jian; Xu, Qiao; Yang, Wei

    2015-07-01

    Fused silica is widely used in high-power laser systems because of its good optical performance and mechanical properties. However, laser damage initiation and growth induced by 355 nm laser illumination in optical elements have become a bottleneck in the development of high energy laser system. In order to improve the laser-induced damage threshold (LIDT), the fused silica optics were treated by two types of HF-based etchants: 1.7%wt. HF acid and buffer oxide etchant (BOE: the mixture of 0.4%wt. HF and 12%wt. NH4F), respectively, for varied etching time. Damage testing shows that both the etchants increase the damage threshold at a certain depth of material removal, but further removal of material lowers the LIDT markedly. The etching rates of both etchants keep steady in our processing procedure, ~58 μg/min and ~85 μg/min, respectively. The micro-surface roughness (RMS and PV) increases as etching time extends. The hardness (H) and Young's modulus (E) of the fused silica etched for diverse time, measured by nano-indenter, show no solid evidence that LIDT can be related to hardness or Young's modulus.

  1. Analysis of damage threshold on HgCdTe crystal irradiated by multi-pulsed CO2 laser

    NASA Astrophysics Data System (ADS)

    Tang, Wei; Guo, Jin; Shao, Junfeng; Wang, Tingfeng

    2014-06-01

    Damage threshold for the onset of surface melting was investigated theoretically and experimentally on HgCdTe crystal irradiated by multi-pulsed CO2 laser. The impact of repetition frequency and irradiation time on damage threshold was analyzed and damage morphology of the crystal was observed by scanning electron microscope (SEM). Thermal accumulate effect is obvious, and damage threshold gradually reduces with the increase of irradiation time and does not depend on laser repetition frequency. Damage threshold calculated by thermal model is in good agreement with the experimental data. Melting and solidification phenomenon were evident on the crystal surface, and the obvious crack which was caused by thermal stress was not found. Theoretical model gives a reasonable explanation on surface morphology changes.

  2. Superhydrophobic antireflective silica films: fractal surfaces and laser-induced damage thresholds.

    PubMed

    Xu, Yao; Wu, Dong; Sun, Yu Han; Huang, Zu Xing; Jiang, Xiao Dong; Wei, Xiao Feng; Li, Zhi Hong; Dong, Bao Zhong; Wu, Zhong Hua

    2005-02-01

    Several superhydrophobic antireflective silica films have been prepared by a solgel method that uses hexamethyl-disilizane (HMDS) as a modifier. In a high-power laser, laser-induced damage thresholds (LIDTs) of 23-30 J/cm2 were obtained at 1064-nm wavelength with 1-ns pulse duration. By atomic-force microscopy and optical microscopy, the fractal surfaces of films were studied, and multifractal spectra (MFSs) were calculated both before and after laser damage. The two-sided effect of HMDS on particle growth determined the surface fractal of a particle and the multifractal structure of a film's surface. The bigger deltaalpha was, both before and after laser damage, the lower the LIDT was. The effect of methyl groups should be included in the determination of the MFS of the LIDT. PMID:15726949

  3. Superhydrophobic antireflective silica films: fractal surfaces and laser-induced damage thresholds

    NASA Astrophysics Data System (ADS)

    Xu, Yao; Wu, Dong; Sun, Yu Han; Huang, Zu Xing; Jiang, Xiao Dong; Wei, Xiao Feng; Li, Zhi Hong; Zhong Dong, Bao; Wu, Zhong Hua

    2005-02-01

    Several superhydrophobic antireflective silica films have been prepared by a solgel method that uses hexamethyl-disilizane (HMDS) as a modifier. In a high-power laser, laser-induced damage thresholds (LIDTs) of 23-30 J/cm2 were obtained at 1064-nm wavelength with 1-ns pulse duration. By atomic-force microscopy and optical microscopy, the fractal surfaces of films were studied, and multifractal spectra (MFSs) were calculated both before and after laser damage. The two-sided effect of HMDS on particle growth determined the surface fractal of a particle and the multifractal structure of a film's surface. The bigger Deltaa was, both before and after laser damage, the lower the LIDT was. The effect of methyl groups should be included in the determination of the MFS of the LIDT.

  4. Investigation of laser induced damage threshold measurement with single-shot on thin films

    NASA Astrophysics Data System (ADS)

    Liu, Zhichao; Zheng, Yi; Pan, Feng; Lin, Qi; Ma, Ping; Wang, Jian

    2016-09-01

    A method for rapid determination of laser induced damage threshold (LIDT) of optical coatings is proposed and investigated in this paper. By use of this method, the LIDT of thin film can be rapidly obtained by only one shot. The modulation of laser beam profile, which is considered as a negative factor in conventional LIDT test, is utilized in this method. Basing on image processing technique, the damage information could be extracted from the comparison between the damage pattern and beam intensity distribution in the test region. The applicability and repeatability of this testing method has been verified on three type reflectors, HfO2/SiO2, HfO2/Al2O3 and Ta2O5/SiO2. In addition, the experimental results showed that appropriate beam size, laser energy and image compression ratio are the key factors to ensure a high accuracy of LIDT.

  5. A Closer Look at the Thresholds of Thermal Damage: Workshop Report by an ICNIRP Task Group.

    PubMed

    Sienkiewicz, Zenon; van Rongen, Eric; Croft, Rodney; Ziegelberger, Gunde; Veyret, Bernard

    2016-09-01

    The International Commission on Non-Ionizing Radiation Protection issued guidelines in 1998 for limiting public and occupational exposure to radiofrequency electromagnetic fields (100 kHz to 300 GHz). As part of the process of updating this advice, a 2-d workshop titled "A closer look at the thresholds of thermal damage" was held from 26-28 May 2015 in Istanbul to re-examine the thermal basis of the guidelines and to provide further information on heat-related effects and thresholds of thermal damage. Overall, the workshop provided much useful information relevant to revision of the guidelines. Participants indicated that the effects of heating from radiofrequency fields are consistent with those from other sources, and that the information derived from those studies can be applied to radiofrequency-induced heating. Another conclusion was that absolute temperature of tissues was more important for thermal damage than temperature change. The discussion suggested that the 6-min averaging time used in international guidelines was valid for whole-body exposures but with a large uncertainty: 30 min may be a more appropriate averaging time for localized exposures, and less than 1 min for implanted medical devices. The duration of whole-body radiofrequency exposure is a critical parameter that often determines the effect threshold, but this will be affected by other, ongoing thermoregulation, which is dependant on many factors. The thresholds for localized radiofrequency exposure were difficult to determine because of the potential range of exposure conditions and the possibility of radiofrequency-induced local hotspots. Suggestions for future dose metrics and further research were discussed and are included in this report. PMID:27472755

  6. A Closer Look at the Thresholds of Thermal Damage: Workshop Report by an ICNIRP Task Group

    PubMed Central

    Sienkiewicz, Zenon; van Rongen, Eric; Croft, Rodney; Ziegelberger, Gunde; Veyret, Bernard

    2016-01-01

    Abstract The International Commission on Non-Ionizing Radiation Protection issued guidelines in 1998 for limiting public and occupational exposure to radiofrequency electromagnetic fields (100 kHz to 300 GHz). As part of the process of updating this advice, a 2‐d workshop titled “A closer look at the thresholds of thermal damage” was held from 26–28 May 2015 in Istanbul to re-examine the thermal basis of the guidelines and to provide further information on heat-related effects and thresholds of thermal damage. Overall, the workshop provided much useful information relevant to revision of the guidelines. Participants indicated that the effects of heating from radiofrequency fields are consistent with those from other sources, and that the information derived from those studies can be applied to radiofrequency-induced heating. Another conclusion was that absolute temperature of tissues was more important for thermal damage than temperature change. The discussion suggested that the 6‐min averaging time used in international guidelines was valid for whole-body exposures but with a large uncertainty: 30 min may be a more appropriate averaging time for localized exposures, and less than 1 min for implanted medical devices. The duration of whole-body radiofrequency exposure is a critical parameter that often determines the effect threshold, but this will be affected by other, ongoing thermoregulation, which is dependant on many factors. The thresholds for localized radiofrequency exposure were difficult to determine because of the potential range of exposure conditions and the possibility of radiofrequency-induced local hotspots. Suggestions for future dose metrics and further research were discussed and are included in this report. PMID:27472755

  7. Crystalline perfection, birefringence and laser damage threshold properties of piperidinium p-hydroxybenzoate

    SciTech Connect

    Sudhahar, S.; Zahid, I. MD; Kumar, M. Krishna; Kumar, R. Mohan

    2015-06-24

    Piperidinium p-hydroxybenzoate (PPHB) crystal was grown by slow evaporation method. Single crystal X-ray diffraction studies confirm that PPHB crystallizes in monoclinic crystal system with noncentrosymmetric space group Cc. The crystalline perfection of the grown crystal was evaluated by using high resolution X-ray diffractometry. UV-Visible transmission and birefringence studies were employed on the grown PPHB crystal. The laser induced damage threshold value was estimated using Nd:YAG laser. Thermal behavior of PPHB crystal has been investigated by TG-DTA analyses. Etching studies have been performed to assess the growth pattern of PPHB crystal.

  8. Development of an efficient large-aperture high damage-threshold sol-gel diffraction grating.

    SciTech Connect

    Ashley, Carol S.; Rambo, Patrick K.; Schwarz, Jens; Dunphy, Darren Robert; Branson, Eric D.; Smith, Ian Craig; Johnson, William Arthur; Reed, Scott T.; Cook, Adam W.

    2005-03-01

    In order to develop the next generation of high peak intensity lasers, new grating technology providing higher damage thresholds and large apertures is required. The current assumption is that this technical innovation will be multilayer dielectric gratings, wherein the uppermost layer of a thin film mirror is etched to create the desired binary phase grating. A variant of this is explored with the upper grating layer being a lower density gelatin-based volume phase grating in either sol-gel or dichromated gelatin. One key benefit is the elimination of the etching step.

  9. Development of high damage threshold multilayer thin film beam combiner for laser application

    NASA Astrophysics Data System (ADS)

    Nand, Mangla; Babita, Jena, S.; Tokas, R. B.; Rajput, P.; Mukharjee, C.; Thakur, S.; Jha, S. N.; Sahoo, N. K.

    2016-05-01

    A polarized wavelength multiplexer with high laser induced damage threshold has been developed to combine two laser beam of high peak power in the visible region. The present wavelength multiplexer is a multilayer thin film device deposited by reactive electron beam evaporation. The developed device is capable of combining two p-polarized laser beams of peak power density of 1.7 GW/cm2 at an angle of incidence of 45°. High transmission (T> 90%) in high pass region and high reflection (R> 99%) in stop band region have been achieved.

  10. Multiple pulse thermal damage thresholds of materials for x-ray free electron laser optics investigated with an ultraviolet laser

    SciTech Connect

    Hau-Riege, Stefan P.; London, Richard A.; Bionta, Richard M.; Soufli, Regina; Ryutov, Dmitri; Shirk, Michael; Baker, Sherry L.; Smith, Patrick M.; Nataraj, Pradeep

    2008-11-17

    Optical elements to be used for x-ray free electron lasers (XFELs) must withstand multiple high-fluence pulses. We have used an ultraviolet laser to study the damage of two candidate materials, crystalline Si and B{sub 4}C-coated Si, emulating the temperature profile expected to occur in optics exposed to XFEL pulses. We found that the damage threshold for 10{sup 5} pulses is {approx}20% to 70% lower than the melting threshold.

  11. Experimental study on GaP surface damage threshold induced by a high repetition rate femtosecond laser

    SciTech Connect

    Li Yi; Liu Feng; Li Yanfeng; Chai Lu; Xing Qirong; Hu Minglie; Wang Chingyue

    2011-05-01

    The surface damage threshold of undoped bulk <110> GaP induced by a high repetition rate femtosecond pulse at 1040 nm with a duration of 61 fs was studied. The threshold value was obtained by a linear fit of the incident single pulse fluence and was confirmed with a breakdown test around the threshold level. The result will be useful in high intensity, high repetition rate laser applications and ultrafast processes.

  12. Predictions of cell damage rates for Lifesat missions

    NASA Technical Reports Server (NTRS)

    Cucinotta, Francis A.; Atwell, William; Hardy, Alva C.; Golightly, Michael J.; Wilson, John W.; Townsend, Lawrence W.; Shinn, Judy; Nealy, John E.; Katz, Robert

    1990-01-01

    The track model of Katz is used to make predictions of cell damage rates for possible Lifesat experiments. Contributions from trapped protons and electrons and galactic cosmic rays are considered for several orbits. Damage rates for survival and transformation of C3HT10-1/2 cells are predicted for various spacecraft shields.

  13. Cavitation damage prediction for the JSNS mercury target vessel

    NASA Astrophysics Data System (ADS)

    Naoe, Takashi; Kogawa, Hiroyuki; Wakui, Takashi; Haga, Katsuhiro; Teshigawara, Makoto; Kinoshita, Hidetaka; Takada, Hiroshi; Futakawa, Masatoshi

    2016-01-01

    The liquid mercury target system for the Japan Spallation Neutron Source (JSNS) at the Materials and Life science experimental Facility (MLF) in the Japan Proton Accelerator Research Complex (J-PARC) is designed to produce pulsed neutrons. The mercury target vessel in this system, which is made of type 316L stainless steel, is damaged by pressure wave-induced cavitation due to proton beam bombardment. Currently, cavitation damage is considered to be the dominant factor influencing the service life of the target vessel rather than radiation damage. In this study, cavitation damage to the interior surface of the target vessel was predicted on the basis of accumulated damage data from off-beam and on-beam experiments. The predicted damage was compared with the damage observed in a used target vessel. Furthermore, the effect of injecting gas microbubbles on cavitation damage was predicted through the measurement of the acoustic vibration of the target vessel. It was shown that the predicted depth of cavitation damage is reasonably coincident with the observed results. Moreover, it was confirmed that the injection of gas microbubbles had an effect on cavitation damage.

  14. The impact of degree of hearing loss on auditory brainstem response predictions of behavioral thresholds

    PubMed Central

    McCreery, Ryan W.; Kaminski, Jan; Beauchaine, Kathryn; Lenzen, Natalie; Simms, Kendell; Gorga, Michael P.

    2014-01-01

    Objectives: Diagnosis of hearing loss and prescription of amplification for infants and young children require accurate estimates of ear- and frequency-specific behavioral thresholds based on auditory brainstem response measurements. Although the overall relationship between ABR and behavioral thresholds has been demonstrated, the agreement is imperfect, and the accuracy of predictions of behavioral threshold based on ABR may depend on degree of hearing loss. Behavioral thresholds are lower than ABR thresholds, at least in part due to differences in calibration interacting with the effects of temporal integration, which are manifest in behavioral measurements but not ABR measurements and depend on behavioral threshold. Listeners with sensory hearing loss exhibit reduced or absent temporal integration, which could impact the relationship between ABR and behavioral thresholds as degree of hearing loss increases. The current study evaluated the relationship between ABR and behavioral thresholds in infants and children over a range of hearing thresholds, and tested an approach for adjusting the correction factor based on degree of hearing loss as estimated by ABR measurements. Design: A retrospective review of clinical records was completed for 309 ears of 177 children with hearing thresholds ranging from normal to profound hearing loss and for whom both ABR and behavioral thresholds were available. Children were required to have the same middle-ear status at both evaluations. The relationship between ABR and behavioral thresholds was examined. Factors that potentially could affect the relationship between ABR and behavioral thresholds were analyzed, including degree of hearing loss observed on the ABR, behavioral test method (visual reinforcement, conditioned play or conventional audiometry), the length of time between ABR and behavioral assessments, and clinician-reported reliability of the behavioral assessment. Predictive accuracy of a correction factor based on

  15. Muscle Weakness Thresholds for Prediction of Diabetes in Adults

    PubMed Central

    Peterson, Mark D.; Zhang, Peng; Choksi, Palak; Markides, Kyriakos S.; Al Snih, Soham

    2016-01-01

    Background Despite the known links between weakness and early mortality, what remains to be fully understood is the extent to which strength preservation is associated with protection from cardiometabolic diseases such as diabetes. Purpose The purposes of this study were to determine the association between muscle strength and diabetes among adults, and to identify age- and sex-specific thresholds of low strength for detection of risk. Methods A population-representative sample of 4,066 individuals, aged 20–85 years, was included from the combined 2011–2012 National Health and Nutrition Examination Survey datasets. Strength was assessed using a hand-held dynamometer, and the single largest reading from either hand was normalized to body mass. A logistic regression model was used to assess the association between normalized grip strength and risk of diabetes, as determined by hemoglobin A1c (HbA1c) levels (≥6.5% [≥48 mmol/mol]), while controlling for sociodemographic characteristics, anthropometric measures, and television viewing time. Results For every 0.05 decrement in normalized strength, there was a 1.26 times increased adjusted odds for diabetes in men and women. Women were at lower odds of having diabetes (OR: 0.49; 95% CI: 0.29–0.82), whereas age, waist circumference and lower income were inversely associated. Optimal sex- and age-specific weakness thresholds to detect diabetes were 0.56, 0.50, and 0.45 for men, and 0.42, 0.38, and 0.33 for women, for ages 20–39 years, 40–59 years, and 60–80 years. Conclusions and Clinical Relevance We present thresholds of strength that can be incorporated into a clinical setting for identifying adults that are at risk for developing diabetes, and that might benefit from lifestyle interventions to reduce risk. PMID:26744337

  16. Spike-Threshold Adaptation Predicted by Membrane Potential Dynamics In Vivo

    PubMed Central

    Fontaine, Bertrand; Peña, José Luis; Brette, Romain

    2014-01-01

    Neurons encode information in sequences of spikes, which are triggered when their membrane potential crosses a threshold. In vivo, the spiking threshold displays large variability suggesting that threshold dynamics have a profound influence on how the combined input of a neuron is encoded in the spiking. Threshold variability could be explained by adaptation to the membrane potential. However, it could also be the case that most threshold variability reflects noise and processes other than threshold adaptation. Here, we investigated threshold variation in auditory neurons responses recorded in vivo in barn owls. We found that spike threshold is quantitatively predicted by a model in which the threshold adapts, tracking the membrane potential at a short timescale. As a result, in these neurons, slow voltage fluctuations do not contribute to spiking because they are filtered by threshold adaptation. More importantly, these neurons can only respond to input spikes arriving together on a millisecond timescale. These results demonstrate that fast adaptation to the membrane potential captures spike threshold variability in vivo. PMID:24722397

  17. Comparative studies of laser-induced damage threshold measurements in highly reflecting mirrors

    NASA Astrophysics Data System (ADS)

    Melninkaitis, Andrius; Mikšys, Darius; Grigonis, Rimantas; Sirutkaitis, Valdas; Jupé, Marco; Ristau, Detlev

    2008-01-01

    S-on-1 laser-induced damage threshold (LIDT) dependence on the pulse duration at two different wavelengths was experimentally investigated in metallic and dielectric laser mirrors. LIDT's of high-reflective dielectric coatings made of alternating λ/4 layers of TiO II/SiO II and Ta IIO 5/SiO II and those of protected metallic Au and Ag coatings were tested at 800 nm and 400 nm wavelengths with Ti:Sapphire laser pulses of 46 fs, 130 fs and 1.8 ps duration. S-on-1 measurements were performed according to international ISO 11254-2 standard using 10000 pulses/per site and compared with 1-on-1 measurements.

  18. Influence of cleaning process on the laser-induced damage threshold of substrates

    SciTech Connect

    Shen Zhengxiang; Ding Tao; Ye Xiaowen; Wang Xiaodong; Ma Bin; Cheng Xinbin; Liu Huasong; Ji Yiqin; Wang Zhanshan

    2011-03-20

    The cleaning process of optical substrates plays an important role during the manufacture of high-power laser coatings. Two kinds of substrates, fused silica and BK7 glass, and two cleaning processes, called process 1 and process 2 having different surfactant solutions and different ultrasonic cleaning parameters, are adopted to compare the influence of the ultrasonic cleaning technique on the substrates. The evaluation standards of the cleaning results include contaminant-removal efficiency, weak absorption, and laser-induced damage threshold of the substrates. For both fused silica and BK7, process 2 is more efficient than process 1. Because acid and alkaline solutions can increase the roughness of BK7, process 2 is unsuitable for BK7 glass cleaning. The parameters of the cleaning protocol should be changed depending on the material of the optical components and the type of contamination.

  19. A historical perspective on fifteen years of laser damage thresholds at LLNL

    SciTech Connect

    Rainer, F.; De Marco, F.P.; Staggs, M.C.; Kozlowski, M.R.; Atherton, L.J.; Sheehan, L.M.

    1993-12-21

    We have completed a fifteen year, referenced and documented compilation of more than 15,000 measurements of laser-induced damage thresholds (LIDT) conducted at the Lawrence Livermore National Laboratory (LLNL). These measurements cover the spectrum from 248 to 1064 nm with pulse durations ranging from < 1 ns to 65 ns and at pulse-repetition frequencies (PRF) from single shots to 6.3 kHz. We emphasize the changes in LIDTs during the past two years since we last summarized our database. We relate these results to earlier data concentrating on improvements in processing methods, materials, and conditioning techniques. In particular, we highlight the current status of anti-reflective (AR) coatings, high reflectors (HR), polarizers, and frequency-conversion crystals used primarily at 355 nm and 1064 nm.

  20. Correlating optical damage threshold with intrinsic defect populations in fused silica as a function of heat treatment temperature

    SciTech Connect

    Shen, N.; Matthews, M. J.; Elhadj, S.; Miller, P. E.; Nelson, A. J.; Hamilton, J.

    2013-04-03

    Here, chemical vapor deposition (CVD) is used for the production of fused silica optics in high-power laser applications. However, relatively little is known about the ultraviolet laser damage threshold of CVD films and how they relate to intrinsic defects produced during deposition. We present here a study relating structural and electronic defects in CVD films to 355 nm pulsed-laser damage threshold as a function of post-deposition annealing temperature (THT). Plasma-enhanced CVD based on SiH4/N2O under oxygen-rich conditions was used to deposit 1.5, 3.1 and 6.4 µm thick films on etched SiO2 substrates. Rapid annealing was performed using a scanned CO2 laser beam up to THT ~ 2100 K. The films were then characterized using x-ray photoemission spectroscopy, Fourier transform infrared spectroscopy (FTIR) and photoluminescence spectroscopy. A gradual transition in the damage threshold of annealed films was observed for THT values up to 1600 K, correlating with a decrease in non-bridging silanol and oxygen deficient centres. An additional sharp transition in damage threshold also occurs at ~1850 K indicating substrate annealing. Based on our results, a mechanism for damage-related defect annealing is proposed, and the potential of using high-THT CVD SiO2 to mitigate optical damage is also discussed.

  1. Dual wavelength laser-induced damage threshold measurements of alumina/silica and hafnia/silica ultraviolet antireflective coatings.

    PubMed

    Mrohs, Marius; Jensen, Lars; Günster, Stefan; Alig, Thimotheus; Ristau, Detlev

    2016-01-01

    An approach for the measurement of the laser-induced damage threshold with two wavelengths combined was made while testing antireflective coatings for the wavelengths 266 and 532 nm. Samples were made of Al2O3/SiO2 and HfO2/SiO2 ion beam sputtered films. The results show that adding radiation of a second wavelength might lead to a significant reduction of the threshold. The damage morphology of single and dual wavelength tests is very similar and does not suggest an altered damage mechanism. Further investigations indicated that the dual wavelength threshold is a function of the temporal delay of the two pulses. PMID:26835628

  2. Differential DNA damage signalling and apoptotic threshold correlate with mouse epiblast-specific hypersensitivity to radiation.

    PubMed

    Laurent, Audrey; Blasi, Francesco

    2015-11-01

    Between implantation and gastrulation, mouse pluripotent epiblast cells expand enormously in number and exhibit a remarkable hypersensitivity to DNA damage. Upon low-dose irradiation, they undergo mitotic arrest followed by p53-dependent apoptosis, whereas the other cell types simply arrest. This protective mechanism, active exclusively after E5.5 and lost during gastrulation, ensures the elimination of every mutated cell before its clonal expansion and is therefore expected to greatly increase fitness. We show that the insurgence of apoptosis relies on the epiblast-specific convergence of both increased DNA damage signalling and stronger pro-apoptotic balance. Although upstream Atm/Atr global activity and specific γH2AX phosphorylation are similar in all cell types of the embryo, 53BP1 recruitment at DNA breaks is immediately amplified only in epiblast cells after ionizing radiation. This correlates with rapid epiblast-specific activation of p53 and its transcriptional properties. Moreover, between E5.5 and E6.5 epiblast cells lower their apoptotic threshold by enhancing the expression of pro-apoptotic Bak and Bim and repressing the anti-apoptotic Bcl-xL. Thus, even after low-dose irradiation, the cytoplasmic priming of epiblast cells allows p53 to rapidly induce apoptosis via a partially transcription-independent mechanism. PMID:26395482

  3. Complete characterization of damage threshold in titanium doped sapphire crystals with nanosecond, picosecond, and femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Canova, F.; Chambaret, J.-P.; Mourou, G.; Sentis, M.; Uteza, O.; Delaporte, P.; Itina, T.; Natoli, J.-Y.; Commandre, M.; Amra, C.

    2005-12-01

    The major bottleneck for the development of robust and cost-effective femtosecond amplification systems is the uncertainty concerning the damage threshold of Ti: Sapphire crystals. Up to now, Ti: Sapphire is the only material that supports the generation of temporally short pulses (few femtosecond) at high repetition rates, and overcoming this bottleneck will represent a major advance in laser performance for all the femtosecond community. Currently, when pumped at 532nm, the uncertainty on Ti:Sapphire damage threshold, is about a factor of ten. The empirically estimated threshold is 10J/cm2 but for safety reasons the femtosecond laser community (especially the companies producing the lasers) uses the conservative value of 1J/cm2. Such a low pumping fluency means low extraction efficiency during the amplification process and a great waste of pumping energy, the most expensive part of a Ti:Sapphire amplifier. In order to remove this bottleneck, we launch a complete analysis of all the factors that influence the damage threshold in Ti:Sapphire Crystals. Our program is to first measure the bulk threshold to define the upper threshold limit, and the influence of Ti ion concentration in the crystal garnet. Then, we will analyze all the surface effects that influence the value of the threshold. These effects depend on the polishing, on the cleaning process, as well as the type of anti-reflective coating. Only a complete understanding of all the mechanisms involved in threshold limitation will allow us to produce Ti:Sa crystals with the best performances. The study of the characteristics of the Ti:Sapphire damage threshold will not be complete and reliable without a complete characterization of the pump beams (temporal and spatial modulations), and this analysis will be done with nanosecond and picosecond pulses at 532nm. Finally, to complete the exploration of the the behavior of the titanium doped sapphire crystal, we will characterize the damage threshold with

  4. Finite element prediction of fatigue damage growth in cancellous bone.

    PubMed

    Hambli, Ridha; Frikha, Sana; Toumi, Hechmi; Tavares, João Manuel R S

    2016-01-01

    Cyclic stresses applied to bones generate fatigue damage that affects the bone stiffness and its elastic modulus. This paper proposes a finite element model for the prediction of fatigue damage accumulation and failure in cancellous bone at continuum scale. The model is based on continuum damage mechanics and incorporates crack closure effects in compression. The propagation of the cracks is completely simulated throughout the damaged area. In this case, the stiffness of the broken element is reduced by 98% to ensure no stress-carrying capacities of completely damaged elements. Once a crack is initiated, the propagation direction is simulated by the propagation of the broken elements of the mesh. The proposed model suggests that damage evolves over a real physical time variable (cycles). In order to reduce the computation time, the integration of the damage growth rate is based on the cycle blocks approach. In this approach, the real number of cycles is reduced (divided) into equivalent blocks of cycles. Damage accumulation is computed over the cycle blocks and then extrapolated over the corresponding real cycles. The results show a clear difference between local tensile and compressive stresses on damage accumulation. Incorporating stiffness reduction also produces a redistribution of the peak stresses in the damaged region, which results in a delay in damage fracture. PMID:26077722

  5. Predicting bulk damage in NIF triple harmonic generators

    SciTech Connect

    De Yoreo, J; Runkel, M; Williams, W

    1998-09-18

    Recently reported experiments have investigated the statistics of laser damage in KDP and KD*P. Automated damage tests have allowed cumulative failure and damage probability distributions to be constructed. Large area tests have investigated the feasibility of on-line laser conditioning and damage evolution for tripler harmonic generation (THG) crystals on the National Ignition Facility (NIF). These tests have shown that there is a nonzero probability of damage at NIF redline fluence (14.3 J/cm2, 351 nm, 3 ns) and that the damage pinpoint density evolves exponentially with fluence. In this paper, the results of these tests are used in conjunction with model spatial profiles of the NIP beam to predict the level of damage created in the THG crystal. A probabilistic calculation based on the overlap of the beam fluence and damage probabiity distribution shows that the overall damage probability is less than 3% for well-conditioned, high quality KDP/KD*P crystals of conventional or rapid growth. The number density of generated pinpoints has been calculated by mapping the damage evolution curves onto the NlF model profile. This shows that the number of damage pinpoints generated in high fluence portions of the NIF beam will be low for well-conditioned THG crystals. In contrast, unconditioned triplers of the same material will exhibit an increase in pinpoint density of greater than 20x. To test the validity of these calculations a 37 cm, conventionally grown KD*P tripler from the Beamlet laser was scatter mapped for bulk damage. The tripler had been exposed to NE-like fluences during its operational lifetime on Beamlet and exhibited very low levels of bulk pinpoint damage, essentially supporting the predictions based on tests and modeling.

  6. Prediction of residual strength of impact damaged aerospace composite structures

    SciTech Connect

    Garg, A.C.

    1993-12-31

    The importance of composites for aerospace structures is well known and therefore its increased use is being made for such structural components. However, these structures may be damaged as a result of various causes. One of the important causes is the impact damage either during manufacture or service. The amount of damage by impact created in the structure depends on several parameters such as impactor mass and velocity (impact energy), the structure material and support conditions. Since the magnitude of damage depends on impact energy, the residual strength may be expressed as a function of impact energy. Using a three parametric approach, a model is proposed to predict the residual strength behavior of impact damaged structure. The predicted behavior is shown to compare favorably with the available test data.

  7. Investigation of surface damage precursor evolutions and laser-induced damage threshold improvement mechanism during Ion beam etching of fused silica.

    PubMed

    Shi, Feng; Zhong, Yaoyu; Dai, Yifan; Peng, Xiaoqiang; Xu, Mingjin; Sui, Tingting

    2016-09-01

    Surface damage precursor evolution has great influence on laser-induced damage threshold improvement of fused silica surface during Ion beam etching. In this work, a series of ion sputtering experiment are carried out to obtain the evolutions of damage precursors (dot-form microstructures, Polishing-Induced Contamination, Hertz scratches, and roughness). Based on ion sputtering theory, surface damage precursor evolutions are analyzed. The results show that the dot-form microstructures will appear during ion beam etching. But as the ion beam etching depth goes up, the dot-form microstructures can be mitigated. And ion-beam etching can broaden and passivate the Hertz scratches without increasing roughness value. A super-smooth surface (0.238nm RMS) can be obtained finally. The relative content of Fe and Ce impurities both significantly reduce after ion beam etching. The laser-induced damage threshold of fused silica is improved by 34% after ion beam etching for 800nm. Research results can be a reference on using ion beam etching process technology to improve laser-induced damage threshold of fused silica optics. PMID:27607688

  8. Impact of different cleaning processes on the laser damage threshold of antireflection coatings for Z-Backlighter optics at Sandia National Laboratories

    SciTech Connect

    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 defect 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.

  9. Impact of different cleaning processes on the laser damage threshold of antireflection coatings for Z-Backlighter optics at Sandia National Laboratories

    DOE PAGESBeta

    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

  10. Prediction and measurement of radiation damage to CMOS devices on board spacecraft

    NASA Technical Reports Server (NTRS)

    Cliff, R. A.; Danchenko, V.; Stassinopoulos, E. G.; Sing, M.; Brucker, G. J.; Ohanian, R. S.

    1976-01-01

    The CMOS Radiation Effects Measurement (CREM) experiment is presently being flown on the Explorer-55. The purpose of the experiment is to evaluate device performance in the actual space radiation environment and to correlate the respective measurements to on-the-ground laboratory irradiation results. The experiment contains an assembly of C-MOS and P-MOS devices shielded in front by flat slabs of aluminum and by a practically infinite shield in the back. Predictions of radiation damage to C-MOS devices are based on standard environment models and computational techniques. A comparison of the shifts in CMOS threshold potentials, that is, those measured in space to those obtained from the on-the-ground simulation experiment with Co-60, indicates that the measured space damage is smaller than predicted by about a factor of 2-3 for thin shields, but agrees well with predictions for thicker shields.

  11. Tree mortality predicted from drought-induced vascular damage

    NASA Astrophysics Data System (ADS)

    Anderegg, William R. L.; Flint, Alan; Huang, Cho-Ying; Flint, Lorraine; Berry, Joseph A.; Davis, Frank W.; Sperry, John S.; Field, Christopher B.

    2015-05-01

    The projected responses of forest ecosystems to warming and drying associated with twenty-first-century climate change vary widely from resiliency to widespread tree mortality. Current vegetation models lack the ability to account for mortality of overstorey trees during extreme drought owing to uncertainties in mechanisms and thresholds causing mortality. Here we assess the causes of tree mortality, using field measurements of branch hydraulic conductivity during ongoing mortality in Populus tremuloides in the southwestern United States and a detailed plant hydraulics model. We identify a lethal plant water stress threshold that corresponds with a loss of vascular transport capacity from air entry into the xylem. We then use this hydraulic-based threshold to simulate forest dieback during historical drought, and compare predictions against three independent mortality data sets. The hydraulic threshold predicted with 75% accuracy regional patterns of tree mortality as found in field plots and mortality maps derived from Landsat imagery. In a high-emissions scenario, climate models project that drought stress will exceed the observed mortality threshold in the southwestern United States by the 2050s. Our approach provides a powerful and tractable way of incorporating tree mortality into vegetation models to resolve uncertainty over the fate of forest ecosystems in a changing climate.

  12. Retinal thermal damage threshold dependence on exposure duration for the transitional near-infrared laser radiation at 1319 nm.

    PubMed

    Wang, Jiarui; Jiao, Luguang; Jing, Xiaomin; Chen, Hongxia; Hu, Xiangjun; Yang, Zaifu

    2016-05-01

    The retinal damage effects induced by transitional near-infrared (NIR) lasers have been investigated for years. However, the damage threshold dependence on exposure duration has not been revealed. In this paper, the in-vivo retinal damage ED50 thresholds were determined in chinchilla grey rabbits for 1319 nm laser radiation for exposure durations from 0.1 s to 10 s. The incident corneal irradiance diameter was fixed at 5 mm. The ED50 thresholds given in terms of the total intraocular energy (TIE) for exposure durations of 0.1, 1 and 10 s were 1.36, 6.33 and 28.6 J respectively. The ED50 thresholds were correlated by a power law equation, ED50 = 6.31t (0.66) [J] where t is time [s], with correlation coefficient R = 0.9999. There exists a sufficient safety margin (factor of 28~60) between the human ED50 thresholds derived from the rabbit and the maximum permissible exposure (MPE) values in the current laser safety standards. PMID:27231639

  13. Retinal thermal damage threshold dependence on exposure duration for the transitional near-infrared laser radiation at 1319 nm

    PubMed Central

    Wang, Jiarui; Jiao, Luguang; Jing, Xiaomin; Chen, Hongxia; Hu, Xiangjun; Yang, Zaifu

    2016-01-01

    The retinal damage effects induced by transitional near-infrared (NIR) lasers have been investigated for years. However, the damage threshold dependence on exposure duration has not been revealed. In this paper, the in-vivo retinal damage ED50 thresholds were determined in chinchilla grey rabbits for 1319 nm laser radiation for exposure durations from 0.1 s to 10 s. The incident corneal irradiance diameter was fixed at 5 mm. The ED50 thresholds given in terms of the total intraocular energy (TIE) for exposure durations of 0.1, 1 and 10 s were 1.36, 6.33 and 28.6 J respectively. The ED50 thresholds were correlated by a power law equation, ED50 = 6.31t0.66 [J] where t is time [s], with correlation coefficient R = 0.9999. There exists a sufficient safety margin (factor of 28~60) between the human ED50 thresholds derived from the rabbit and the maximum permissible exposure (MPE) values in the current laser safety standards. PMID:27231639

  14. Predicting the epidemic threshold of the susceptible-infected-recovered model

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Liu, Quan-Hui; Zhong, Lin-Feng; Tang, Ming; Gao, Hui; Stanley, H. Eugene

    2016-04-01

    Researchers have developed several theoretical methods for predicting epidemic thresholds, including the mean-field like (MFL) method, the quenched mean-field (QMF) method, and the dynamical message passing (DMP) method. When these methods are applied to predict epidemic threshold they often produce differing results and their relative levels of accuracy are still unknown. We systematically analyze these two issues—relationships among differing results and levels of accuracy—by studying the susceptible-infected-recovered (SIR) model on uncorrelated configuration networks and a group of 56 real-world networks. In uncorrelated configuration networks the MFL and DMP methods yield identical predictions that are larger and more accurate than the prediction generated by the QMF method. As for the 56 real-world networks, the epidemic threshold obtained by the DMP method is more likely to reach the accurate epidemic threshold because it incorporates full network topology information and some dynamical correlations. We find that in most of the networks with positive degree-degree correlations, an eigenvector localized on the high k-core nodes, or a high level of clustering, the epidemic threshold predicted by the MFL method, which uses the degree distribution as the only input information, performs better than the other two methods.

  15. Predicting the epidemic threshold of the susceptible-infected-recovered model

    PubMed Central

    Wang, Wei; Liu, Quan-Hui; Zhong, Lin-Feng; Tang, Ming; Gao, Hui; Stanley, H. Eugene

    2016-01-01

    Researchers have developed several theoretical methods for predicting epidemic thresholds, including the mean-field like (MFL) method, the quenched mean-field (QMF) method, and the dynamical message passing (DMP) method. When these methods are applied to predict epidemic threshold they often produce differing results and their relative levels of accuracy are still unknown. We systematically analyze these two issues—relationships among differing results and levels of accuracy—by studying the susceptible-infected-recovered (SIR) model on uncorrelated configuration networks and a group of 56 real-world networks. In uncorrelated configuration networks the MFL and DMP methods yield identical predictions that are larger and more accurate than the prediction generated by the QMF method. As for the 56 real-world networks, the epidemic threshold obtained by the DMP method is more likely to reach the accurate epidemic threshold because it incorporates full network topology information and some dynamical correlations. We find that in most of the networks with positive degree-degree correlations, an eigenvector localized on the high k-core nodes, or a high level of clustering, the epidemic threshold predicted by the MFL method, which uses the degree distribution as the only input information, performs better than the other two methods. PMID:27091705

  16. Noise-induced damage to ribbon synapses without permanent threshold shifts in neonatal mice.

    PubMed

    Shi, L; Guo, X; Shen, P; Liu, L; Tao, S; Li, X; Song, Q; Yu, Z; Yin, S; Wang, J

    2015-09-24

    Recently, ribbon synapses to the hair cells (HCs) in the cochlea have become a novel site of interest in the investigation of noise-induced cochlear lesions in adult rodents (Kujawa and Liberman, 2009; Lin et al., 2011; Liu et al., 2012; Shi et al., 2013). Permanent noise-induced damage to this type of synapse can result in subsequent degeneration of spiral ganglion neurons (SGNs) in the absence of permanent changes to hearing sensitivity. To verify whether noise exposure during an early developmental period produces a similar impact on ribbon synapses, the present study examined the damaging effects of noise exposure in neonatal Kunming mice. The animals received exposure to broadband noise at 105-decibel (dB) sound pressure level (SPL) for 2h on either postnatal day 10 (P10d) or postnatal day 14 (P14d), and then hearing function (based on the auditory brainstem response (ABR)) and cochlear morphology were evaluated during either postnatal weeks 3-4 (P4w) or postnatal weeks 7-8 (P8w). There were no significant differences in the hearing threshold between noise-exposed and control animals, which suggests that noise did not cause permanent loss of hearing sensitivity. However, noise exposure did produce a significant loss of ribbon synapses, particularly in P14d mice, which continued to increase from P4w to P8w. Additionally, a corresponding reduction in the amplitude of compound action potential (CAP) was observed in the noise-exposed groups at P4w and P8w, and the CAP latency was elongated, indicating a change in synaptic function. PMID:26232715

  17. Etching, micro hardness and laser damage threshold studies of a nonlinear optical material L-valine

    NASA Astrophysics Data System (ADS)

    Anbuchezhiyan, M.; Ponnusamy, S.; Muthamizhchelvan, C.; Kanakam, C. C.; Singh, S. P.; Pal, P. K.; Datta, P. K.

    2012-04-01

    A nonlinear optical crystal of L-valine was grown from an aqueous solution containing a small amount of phosphoric acid by the slow evaporation method. The grown crystal was characterized by a single crystal X-ray diffraction to determine the unit cell parameters. The powder X-ray diffraction analysis also confirmed the lattice parameters to be a = 9.6687(7) Å, b = 5.2709(4) Å, c = 12.0371(10) Å and β = 90.805(4)°. The results of the Inductively Coupled Plasma Optical Emission Spectrometry (ICPOES) indicate the presence of a small amount of phosphorus in the grown crystal. The Vickers micro hardness test was performed to study the mechanical strength of the crystals. Chemical etching studies were carried out to analyze the dislocation structure. The laser damaged threshold of the grown crystal was measured to be 11.11 GW/cm2 for 10 ns pulse at 1064 nm, which is higher than that of the standard nonlinear optical crystals like KDP. Second harmonic generation of the grown crystals was also 1.44 times that of KDP.

  18. Durable solgel antireflective films with high laser-induced damage thresholds for inertial confinement fusion

    NASA Astrophysics Data System (ADS)

    Xu, Yao; Zhang, Lei; Wu, Dong; Sun, Yu Han; Huang, Zu Xing; Jiang, Xiao Dong; Wei, Xiao Feng; Li, Zhi Hong; Dong, Bao Zhong; Wu, Zhong Hua

    2005-04-01

    We tested the use of two hydrophobic methyl-substituted silane precursors, methyltriethoxysilane and dimethyldiethoxysilane, to synthesize methyl-modified silica sols by a two-step method and a cohydrolysis method to produce durable antireflective films with high laser-induced-damage thresholds (LIDTs). Using small-angle x-ray scattering technology, we obtained details of the microstructure of clusters in sol and found various double fractal structural characteristics in the methyl-modified silica clusters; our findings were confirmed by transmission-electron micrographs. Through a 29Si magic-angle spin nuclear magnetic resonance study of the corresponding xerogels, we determined the double-fractal microstructure, which we then related to the LIDTs of AR films. The distribution configuration of methyls in clusters determined the double-fractal microstructure of clusters and then the LIDTs of AR films. The LIDTs of films produced by the cohydrolysis method (the highest was 38 J/cm2 for 1-ns, 1064-nm laser action) were much higher than those from the two-step method because of the loose netlike clusters in the former configuration. During the 220-day aging, the transmittance of hydrophobic AR film decreased ~0.2%. So it is practicable to prepare durable AR films with higher LIDTs than those of normal AR SiO2 films only by introducing hydrophobic methyls into a Si-O-Si matrix of clusters if an appropriate hydrophobic precursor is chosen.

  19. Empirical predictions of hypervelocity impact damage to the space station

    NASA Technical Reports Server (NTRS)

    Rule, W. K.; Hayashida, K. B.

    1991-01-01

    A family of user-friendly, DOS PC based, Microsoft BASIC programs written to provide spacecraft designers with empirical predictions of space debris damage to orbiting spacecraft is described. The spacecraft wall configuration is assumed to consist of multilayer insulation (MLI) placed between a Whipple style bumper and the pressure wall. Predictions are based on data sets of experimental results obtained from simulating debris impacts on spacecraft using light gas guns on Earth. A module of the program facilitates the creation of the data base of experimental results that are used by the damage prediction modules of the code. The user has the choice of three different prediction modules to predict damage to the bumper, the MLI, and the pressure wall. One prediction module is based on fitting low order polynomials through subsets of the experimental data. Another prediction module fits functions based on nondimensional parameters through the data. The last prediction technique is a unique approach that is based on weighting the experimental data according to the distance from the design point.

  20. On the selection of thresholds for predicting species occurrence with presence-only data.

    PubMed

    Liu, Canran; Newell, Graeme; White, Matt

    2016-01-01

    Presence-only data present challenges for selecting thresholds to transform species distribution modeling results into binary outputs. In this article, we compare two recently published threshold selection methods (maxSSS and maxF pb) and examine the effectiveness of the threshold-based prevalence estimation approach. Six virtual species with varying prevalence were simulated within a real landscape in southeastern Australia. Presence-only models were built with DOMAIN, generalized linear model, Maxent, and Random Forest. Thresholds were selected with two methods maxSSS and maxF pb with four presence-only datasets with different ratios of the number of known presences to the number of random points (KP-RP ratio). Sensitivity, specificity, true skill statistic, and F measure were used to evaluate the performance of the results. Species prevalence was estimated as the ratio of the number of predicted presences to the total number of points in the evaluation dataset. Thresholds selected with maxF pb varied as the KP-RP ratio of the threshold selection datasets changed. Datasets with the KP-RP ratio around 1 generally produced better results than scores distant from 1. Results produced by We conclude that maxFpb had specificity too low for very common species using Random Forest and Maxent models. In contrast, maxSSS produced consistent results whichever dataset was used. The estimation of prevalence was almost always biased, and the bias was very large for DOMAIN and Random Forest predictions. We conclude that maxF pb is affected by the KP-RP ratio of the threshold selection datasets, but maxSSS is almost unaffected by this ratio. Unbiased estimations of prevalence are difficult to be determined using the threshold-based approach. PMID:26811797

  1. Multiphoton absorption is probably not the primary threshold damage mechanism for femtosecond laser pulse exposures in the retinal pigment epithelium

    NASA Astrophysics Data System (ADS)

    Glickman, Randolph D.; Johnson, Thomas E.

    2004-07-01

    Laser induced breakdown has the lowest energy threshold in the femtosecond domain, and is responsible for production of threshold ocular lesions. It has been proposed that multiphoton absorption may also contribute to ultrashort-pulse tissue damage, based on the observation that 33 fs, 810 nm pulse laser exposures caused more DNA breakage in cultured, primary RPE cells, compared to CW laser exposures delivering the same average power. Subsequent studies, demonstrating two-photon excitation of fluorescence in isolated RPE melanosomes, appeared to support the role of multiphoton absorption, but mainly at suprathreshold irradiance. Additional experiments have not found a consistent difference in the DNA strand breakage produced by ultrashort and CW threshold exposures. DNA damage appears to be dependent on the amount of melanin pigmentation in the cells, rather than the pulsewidth of the laser; current studies have found that, at threshold, CW and ultrashort pulse laser exposures produce almost identical amounts of DNA breakage. A theoretical analysis suggest that the number of photons delivered to the RPE melanosome during a single 33-fsec pulse at the ED50 irradiance is insufficient to produce multiphoton excitation. This result appears to exclude the melanosome as a locus for two- or three-photon excitation; however, a structure with a larger effective absorption cross-section than the melanosome may interact with the laser pulses. One possibility is that the nuclear chromatin acts as a unit absorber of photons resulting in DNA damage, but this does not explain the near equivalence of ultrashort and CW exposures in the comet assay model. This equivalence indicated that multiphoton absorption is not a major contributor to the ultrashort pulse laser damage threshold in the near infrared.

  2. Structural Damage Prediction and Analysis for Hypervelocity Impact: Consulting

    NASA Technical Reports Server (NTRS)

    1995-01-01

    A portion of the contract NAS8-38856, 'Structural Damage Prediction and Analysis for Hypervelocity Impacts,' from NASA Marshall Space Flight Center (MSFC), included consulting which was to be documented in the final report. This attachment to the final report contains memos produced as part of that consulting.

  3. A STATISTICAL MODELING METHODOLOGY FOR THE DETECTION, QUANTIFICATION, AND PREDICTION OF ECOLOGICAL THRESHOLDS

    EPA Science Inventory

    This study will provide a general methodology for integrating threshold information from multiple species ecological metrics, allow for prediction of changes of alternative stable states, and provide a risk assessment tool that can be applied to adaptive management. The integr...

  4. Pulse-width and pulse-shape dependencies of laser-induced damage threshold to transparent optical materials

    NASA Astrophysics Data System (ADS)

    Koldunov, M. F.; Manenkov, Alexander A.; Pokotilo, I. L.

    1996-05-01

    Theory of pulsewidth dependence of laser induced damage threshold (LIDT) in transparent solids is presented. The damage is supposed to be initiated by thermal explosion of absorbing inclusions. The investigation of thermal explosion is based on an analysis of the heat transfer equation and a new approach to solving this equation is developed allowing to study kinetics of thermal explosion without any modeling presentation of an absorption mechanism. It is shown that the key parameter determining a dependence of LIDT upon a laser pulsewidth, (tau) p, is the heat transfer time, (tau) , from an inclusion to a surrounding medium. At (tau) p >> (tau) a damage threshold is characterized by a laser radiation intensity, whereas at (tau) p << (tau) --by an energy density. The pulsewidth dependence of the LIDT has been investigated for rectangular and gaussian shapes of laser pulses and it has been established that the dependencies considerably differ in these two cases in a range of (tau) p approximately (tau) . An effect of damage statistics, connected with a random spatial distribution of inclusions in a material, is also investigated. For the case of one-type inclusions (single-(tau) inclusions) it is shown: the statistics does not change a functional form of the pulsewidth dependence of the LIDT and correct only the LIDT values by a spot-size factor. Theoretical results are compared with experimental data published by different research groups for the laser damage in a nanosecond-picosecond region.

  5. Force Criterion Prediction of Damage for Carbon/Epoxy Composite Panels Impacted by High Velocity Ice

    NASA Astrophysics Data System (ADS)

    Rhymer, Jennifer D.

    The use of advanced fiber-reinforced polymer matrix composites in load-bearing aircraft structures is increasing, as evident by the various composites-intensive transport aircraft presently under development. A major impact source of concern for these structures is hail ice, which affects design and skin-sizing (skin thickness determination) at various locations of the aircraft. Impacts onto composite structures often cause internal damage that is not visually detectable due to the high strength and resiliency of the composite material (unlike impacts onto metallic structures). This internal damage and its effect on the performance of the structure are of great concern to the aircraft industry. The prediction of damage in composite structures due to SHI impact has been accomplished via experimental work, explicit dynamic nonlinear finite element analysis (FEA) and the definition of design oriented relationships. Experiments established the critical threshold and corresponding analysis provided contact force results not readily measurable in high velocity SHI impact experiments. The design oriented relationships summarize the FEA results and experimental database into contact force estimation curves that can be easily applied for damage prediction. Failure thresholds were established for the experimental conditions (panel thickness ranging from 1.56 to 4.66 mm and ice diameters from 38.1 to 61.0 mm). Additionally, the observations made by high-speed video during the impact event, and ultrasonic C-scan post-impact, showed how the ice failed during impact and the overall shape and location of the panel damage. Through analysis, the critical force, the force level where damage occurs above but not below, of a SHI impact onto the panel was found to be dependent only on the target structure. However, the peak force generated during impact was dependent on both the projectile and target. Design-oriented curves were generated allowing the prediction of the allowable

  6. Increase in the optical damage threshold of a ZnSe-passivated front mirror of a laser diode

    SciTech Connect

    Davydova, Evgeniya I; Dmitriev, V V; Kozlov, Yu Yu; Kukushkin, I A; Uspenskiy, Mikhail B; Shishkin, Viktor A

    2011-05-31

    The operation of single-mode diode lasers with a front mirror passivated by ZnSe films of different thicknesses is studied in the pulsed regime (pulse duration {tau} = 0.2 - 10 {mu}s). It is found that in the case of short (0.2 {mu}s) pulses, the catastrophic optical damage threshold grows almost linearly as the film thickness on the front mirror increases from 0.1 to 0.5 {mu}m. It is shown that lasers with mirrors passivated by 'thick' (0.4 - 0.6 {mu}m) ZnSe films can operate stably in the case of 'long' (2 - 10 {mu}s) pulses. It is assumed that in this pulsed regime the ZnSe film provides an additional heat removal from the hot zone of the front mirror, and consequently increases the optical damage threshold. (lasers)

  7. Prediction of load threshold of fibre-reinforced laminated composite panels subjected to low velocity drop-weight impact using efficient data filtering techniques

    NASA Astrophysics Data System (ADS)

    Farooq, Umar; Myler, Peter

    This work is concerned with physical testing of carbon fibrous laminated composite panels with low velocity drop-weight impacts from flat and round nose impactors. Eight, sixteen, and twenty-four ply panels were considered. Non-destructive damage inspections of tested specimens were conducted to approximate impact-induced damage. Recorded data were correlated to load-time, load-deflection, and energy-time history plots to interpret impact induced damage. Data filtering techniques were also applied to the noisy data that unavoidably generate due to limitations of testing and logging systems. Built-in, statistical, and numerical filters effectively predicted load thresholds for eight and sixteen ply laminates. However, flat nose impact of twenty-four ply laminates produced clipped data that can only be de-noised involving oscillatory algorithms. Data filtering and extrapolation of such data have received rare attention in the literature that needs to be investigated. The present work demonstrated filtering and extrapolation of the clipped data using Fast Fourier Convolution algorithm to predict load thresholds. Selected results were compared to the damage zones identified with C-scan and acceptable agreements have been observed. Based on the results it is proposed that use of advanced data filtering and analysis methods to data collected by the available resources has effectively enhanced data interpretations without resorting to additional resources. The methodology could be useful for efficient and reliable data analysis and impact-induced damage prediction of similar cases' data.

  8. Damage Mechanisms In Polymers Upon NIR Femtosecond Pulse Laser Irradiation: Sub-Threshold Processes And Their Implications For Laser Safety Applications

    SciTech Connect

    Bonse, Joern; Krueger, Joerg; Solis, Javier; Spielmann, Christian; Lippert, Thomas

    2010-10-08

    This contribution investigates laser-induced damage of thin film and bulk polymer samples, with the focus on physical processes occurring close to the damage threshold. In-situ real-time reflectivity (RTR) measurements with picosecond (ps) and nanosecond (ns) temporal resolution were performed on thin polymer films on a timescale up to a few microseconds ({mu}s). A model for polymer thin film damage is presented, indicating that irreversible chemical modification processes take place already below the fluence threshold for macroscopic damage. On dye-doped bulk polymer filters (as used for laser goggles), transmission studies using fs-and ps-laser pulses reveal the optical saturation behavior of the material and its relation to the threshold of permanent damage. Implications of the sub-threshold processes for laser safety applications will be discussed for thin film and bulk polymer damage.

  9. Threshold Values for Identification of Contamination Predicted by Reduced-Order Models

    DOE PAGESBeta

    Last, George V.; Murray, Christopher J.; Bott, Yi-Ju; Brown, Christopher F.

    2014-12-31

    The U.S. Department of Energy’s (DOE’s) National Risk Assessment Partnership (NRAP) Project is developing reduced-order models to evaluate potential impacts on underground sources of drinking water (USDWs) if CO2 or brine leaks from deep CO2 storage reservoirs. Threshold values, below which there would be no predicted impacts, were determined for portions of two aquifer systems. These threshold values were calculated using an interwell approach for determining background groundwater concentrations that is an adaptation of methods described in the U.S. Environmental Protection Agency’s Unified Guidance for Statistical Analysis of Groundwater Monitoring Data at RCRA Facilities.

  10. Corneal thermal damage threshold dependence on the exposure duration for near-infrared laser radiation at 1319 nm

    NASA Astrophysics Data System (ADS)

    Wang, Jiarui; Jiao, Luguang; Chen, Hongxia; Yang, Zaifu; Hu, Xiangjun

    2016-01-01

    The corneal damage effects induced by 1319-nm transitional near-infrared laser have been investigated for years. However, the damage threshold dependence on exposure duration has not been revealed. The in vivo corneal damage thresholds (ED50s) were determined in New Zealand rabbits for 1319-nm laser radiation for exposure durations from 75 ms to 10 s. An additional corneal ED50 was determined at 1338 nm for a 5-ms exposure. The incident corneal irradiance diameter was fixed at 2 mm for all exposure conditions to avoid the influence of spot size on threshold. The ED50s given in terms of the corneal radiant exposure for exposure durations of 5 ms, 75 ms, 0.35 s, 2 s, and 10 s were 39.4, 51.5, 87.2, 156.3, and 311.1 J/cm2, respectively. The 39.4 J/cm2 was derived from the ED50 for 1338 nm (27.0 J/cm2). The ED50s for exposure durations of 75 ms to 10 s were correlated by a power law equation, ED50=128.9t0.36 in J/cm2, where t was the input in the unit of second, with correlation coefficient (R) of 0.997. Enough safe margins existed between the ED50s and the maximum permitted exposures from current laser safety standard.

  11. Wearable Lactate Threshold Predicting Device is Valid and Reliable in Runners.

    PubMed

    Borges, Nattai R; Driller, Matthew W

    2016-08-01

    Borges, NR and Driller, MW. Wearable lactate threshold predicting device is valid and reliable in runners. J Strength Cond Res 30(8): 2212-2218, 2016-A commercially available device claiming to be the world's first wearable lactate threshold predicting device (WLT), using near-infrared LED technology, has entered the market. The aim of this study was to determine the levels of agreement between the WLT-derived lactate threshold workload and traditional methods of lactate threshold (LT) calculation and the interdevice and intradevice reliability of the WLT. Fourteen (7 male, 7 female; mean ± SD; age: 18-45 years, height: 169 ± 9 cm, mass: 67 ± 13 kg, V[Combining Dot Above]O2max: 53 ± 9 ml·kg·min) subjects ranging from recreationally active to highly trained athletes completed an incremental exercise test to exhaustion on a treadmill. Blood lactate samples were taken at the end of each 3-minute stage during the test to determine lactate threshold using 5 traditional methods from blood lactate analysis which were then compared against the WLT predicted value. In a subset of the population (n = 12), repeat trials were performed to determine both inter-reliability and intrareliability of the WLT device. Intraclass correlation coefficient (ICC) found high to very high agreement between the WLT and traditional methods (ICC > 0.80), with TEMs and mean differences ranging between 3.9-10.2% and 1.3-9.4%. Both interdevice and intradevice reliability resulted in highly reproducible and comparable results (CV < 1.2%, TEM <0.2 km·h, ICC > 0.97). This study suggests that the WLT is a practical, reliable, and noninvasive tool for use in predicting LT in runners. PMID:27457915

  12. Wing Leading Edge RCC Rapid Response Damage Prediction Tool (IMPACT2)

    NASA Technical Reports Server (NTRS)

    Clark, Robert; Cottter, Paul; Michalopoulos, Constantine

    2013-01-01

    This rapid response computer program predicts Orbiter Wing Leading Edge (WLE) damage caused by ice or foam impact during a Space Shuttle launch (Program "IMPACT2"). The program was developed after the Columbia accident in order to assess quickly WLE damage due to ice, foam, or metal impact (if any) during a Shuttle launch. IMPACT2 simulates an impact event in a few minutes for foam impactors, and in seconds for ice and metal impactors. The damage criterion is derived from results obtained from one sophisticated commercial program, which requires hours to carry out simulations of the same impact events. The program was designed to run much faster than the commercial program with prediction of projectile threshold velocities within 10 to 15% of commercial-program values. The mathematical model involves coupling of Orbiter wing normal modes of vibration to nonlinear or linear springmass models. IMPACT2 solves nonlinear or linear impact problems using classical normal modes of vibration of a target, and nonlinear/ linear time-domain equations for the projectile. Impact loads and stresses developed in the target are computed as functions of time. This model is novel because of its speed of execution. A typical model of foam, or other projectile characterized by material nonlinearities, impacting an RCC panel is executed in minutes instead of hours needed by the commercial programs. Target damage due to impact can be assessed quickly, provided that target vibration modes and allowable stress are known.

  13. 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.

  14. Damage threshold of coating materials on x-ray mirror for x-ray free electron laser.

    PubMed

    Koyama, Takahisa; Yumoto, Hirokatsu; Miura, Takanori; Tono, Kensuke; Togashi, Tadashi; Inubushi, Yuichi; Katayama, Tetsuo; Kim, Jangwoo; Matsuyama, Satoshi; Yabashi, Makina; Yamauchi, Kazuto; Ohashi, Haruhiko

    2016-05-01

    We evaluated the damage threshold of coating materials such as Mo, Ru, Rh, W, and Pt on Si substrates, and that of uncoated Si substrate, for mirror optics of X-ray free electron lasers (XFELs). Focused 1 μm (full width at half maximum) XFEL pulses with the energies of 5.5 and 10 keV, generated by the SPring-8 angstrom compact free electron laser (SACLA), were irradiated under the grazing incidence condition. The damage thresholds were evaluated by in situ measurements of X-ray reflectivity degradation during irradiation by multiple pulses. The measured damage fluences below the critical angles were sufficiently high compared with the unfocused SACLA beam fluence. Rh coating was adopted for two mirror systems of SACLA. One system was a beamline transport mirror system that was partially coated with Rh for optional utilization of a pink beam in the photon energy range of more than 20 keV. The other was an improved version of the 1 μm focusing mirror system, and no damage was observed after one year of operation. PMID:27250368

  15. Fluence Thresholds for Laser-Induced Damage of Optical Components in the Injector Laser of the SSRL Gun Test Facility

    SciTech Connect

    Boton, P

    2005-01-31

    Damage threshold fluences for several optical components were measured at three wavelengths using the injector laser at SSRL's Gun Test Facility. Measurements were conducted using the fundamental ir wavelength at 1053 nanometers and harmonics at 526 nm and 263 nm with 3.4ps pulses (1/e{sup 2} full width intensity); ir measurements were also conducted with 850 ps pulses. Practical surfaces relevant to the laser system performance are emphasized. Damage onset was evidenced by an alteration of the specular reflection of a cw probe laser (650 nm) from the irradiated region of the target surface. For the case of stretched ir pulses, damage to a Nd:glass rod was observed to begin at a site within the bulk material and to progress back toward the incident surface.

  16. Residual Strength Prediction of Fuselage Structures with Multiple Site Damage

    NASA Technical Reports Server (NTRS)

    Chen, Chuin-Shan; Wawrzynek, Paul A.; Ingraffea, Anthony R.

    1999-01-01

    This paper summarizes recent results on simulating full-scale pressure tests of wide body, lap-jointed fuselage panels with multiple site damage (MSD). The crack tip opening angle (CTOA) fracture criterion and the FRANC3D/STAGS software program were used to analyze stable crack growth under conditions of general yielding. The link-up of multiple cracks and residual strength of damaged structures were predicted. Elastic-plastic finite element analysis based on the von Mises yield criterion and incremental flow theory with small strain assumption was used. A global-local modeling procedure was employed in the numerical analyses. Stress distributions from the numerical simulations are compared with strain gage measurements. Analysis results show that accurate representation of the load transfer through the rivets is crucial for the model to predict the stress distribution accurately. Predicted crack growth and residual strength are compared with test data. Observed and predicted results both indicate that the occurrence of small MSD cracks substantially reduces the residual strength. Modeling fatigue closure is essential to capture the fracture behavior during the early stable crack growth. Breakage of a tear strap can have a major influence on residual strength prediction.

  17. A prediction model for ocular damage - Experimental validation.

    PubMed

    Heussner, Nico; Vagos, Márcia; Spitzer, Martin S; Stork, Wilhelm

    2015-08-01

    With the increasing number of laser applications in medicine and technology, accidental as well as intentional exposure of the human eye to laser sources has become a major concern. Therefore, a prediction model for ocular damage (PMOD) is presented within this work and validated for long-term exposure. This model is a combination of a raytracing model with a thermodynamical model of the human and an application which determines the thermal damage by the implementation of the Arrhenius integral. The model is based on our earlier work and is here validated against temperature measurements taken with porcine eye samples. For this validation, three different powers were used: 50mW, 100mW and 200mW with a spot size of 1.9mm. Also, the measurements were taken with two different sensing systems, an infrared camera and a fibre optic probe placed within the tissue. The temperatures were measured up to 60s and then compared against simulations. The measured temperatures were found to be in good agreement with the values predicted by the PMOD-model. To our best knowledge, this is the first model which is validated for both short-term and long-term irradiations in terms of temperature and thus demonstrates that temperatures can be accurately predicted within the thermal damage regime. PMID:26267496

  18. Comparison of retinal damage thresholds of laser pulses in the macula/paramacula regions of the live eye

    NASA Astrophysics Data System (ADS)

    Noojin, Gary D.; Cain, Clarence P.; Toth, Cynthia A.; Stolarski, David J.; Rockwell, Benjamin A.

    1999-06-01

    Single pulses in the near-infrared (800 nanometers) were used to measure retinal minimum visible lesion (MVL) thresholds in rhesus monkey eyes at a pulse width of 130 femtoseconds (fs) within both the macula and paramacula regions. We report the MVL thresholds, determined at 1 hour and 24 hours post exposure, which were obtained within the macula and adjacent paramacula. This data will provide a direct comparison of the sensitivities of different retinal areas to laser injury and provide additional insight to laser damage. These new data points will be added to the databank for MVLs for single pulses. The MVL-ED50 threshold for the macula was measured to be 0.35 (mu) J at 24 hours postexposure, which compares with 0.43 (mu) J measured at 580 nm and the 0.17 (mu) J measured at 532 nm in our laboratory. Our measurements show that the retinal ED50 threshold in the paramacula was larger by a factor of 1.6 than in the macula. This factor of 1.6 is in good agreement with the factor of 1.1 to 2.5 reported in previous studies.

  19. Damage threshold of inorganic solids under free-electron-laser irradiation at 32.5 nm wavelength

    SciTech Connect

    Hau-Riege, S; London, R A; Bionta, R M; McKernan, M A; Baker, S L; Krzywinski, J; Sobierajski, R; Nietubyc, R; Pelka, J B; Jurek, M; Klinger, D; Juha, L; Chalupsky, J; Cihelka, J; Hajkova, V; Koptyaev, S; Velyhan, A; Krasa, J; Kuba, J; Tiedtke, K; Toleikis, S; Tschentscher, T; Wabnitz, H; Bergh, M; Caleman, C; Sokolowski-Tinten, K; Stojanovic, N; Zastrau, U; Tronnier, A; Meyer-ter-Vehn, J

    2007-12-03

    We exposed samples of B4C, amorphous C, chemical-vapor-deposition (CVD)-diamond C, Si, and SiC to single 25 fs-long pulses of 32.5 nm free-electron-laser radiation at fluences of up to 2.2 J/cm{sup 2}. The samples were chosen as candidate materials for x-ray free electron laser (XFEL) optics. We found that the threshold for surface-damage is on the order of the fluence required for thermal melting. For larger fluences, the crater depths correspond to temperatures on the order of the critical temperature, suggesting that the craters are formed by two-phase vaporization [1]. XFELs have the promise of producing extremely high-intensity ultrashort pulses of coherent, monochromatic radiation in the 1 to 10 keV regime. The expected high output fluence and short pulse duration pose significant challenges to the optical components, including radiation damage. It has not been possible to obtain direct experimental verification of the expected damage thresholds since appropriate x-ray sources are not yet available. FLASH has allowed us to study the interaction of high-fluence short-duration photon pulses with materials at the shortest wavelength possible to date. With these experiments, we have come closer to the extreme conditions expected in XFEL-matter interaction scenarios than previously possible.

  20. Threshold models for genome-enabled prediction of ordinal categorical traits in plant breeding.

    PubMed

    Montesinos-López, Osval A; Montesinos-López, Abelardo; Pérez-Rodríguez, Paulino; de Los Campos, Gustavo; Eskridge, Kent; Crossa, José

    2015-02-01

    Categorical scores for disease susceptibility or resistance often are recorded in plant breeding. The aim of this study was to introduce genomic models for analyzing ordinal characters and to assess the predictive ability of genomic predictions for ordered categorical phenotypes using a threshold model counterpart of the Genomic Best Linear Unbiased Predictor (i.e., TGBLUP). The threshold model was used to relate a hypothetical underlying scale to the outward categorical response. We present an empirical application where a total of nine models, five without interaction and four with genomic × environment interaction (G×E) and genomic additive × additive × environment interaction (G×G×E), were used. We assessed the proposed models using data consisting of 278 maize lines genotyped with 46,347 single-nucleotide polymorphisms and evaluated for disease resistance [with ordinal scores from 1 (no disease) to 5 (complete infection)] in three environments (Colombia, Zimbabwe, and Mexico). Models with G×E captured a sizeable proportion of the total variability, which indicates the importance of introducing interaction to improve prediction accuracy. Relative to models based on main effects only, the models that included G×E achieved 9-14% gains in prediction accuracy; adding additive × additive interactions did not increase prediction accuracy consistently across locations. PMID:25538102

  1. Threshold Models for Genome-Enabled Prediction of Ordinal Categorical Traits in Plant Breeding

    PubMed Central

    Montesinos-López, Osval A.; Montesinos-López, Abelardo; Pérez-Rodríguez, Paulino; de los Campos, Gustavo; Eskridge, Kent; Crossa, José

    2014-01-01

    Categorical scores for disease susceptibility or resistance often are recorded in plant breeding. The aim of this study was to introduce genomic models for analyzing ordinal characters and to assess the predictive ability of genomic predictions for ordered categorical phenotypes using a threshold model counterpart of the Genomic Best Linear Unbiased Predictor (i.e., TGBLUP). The threshold model was used to relate a hypothetical underlying scale to the outward categorical response. We present an empirical application where a total of nine models, five without interaction and four with genomic × environment interaction (G×E) and genomic additive × additive × environment interaction (G×G×E), were used. We assessed the proposed models using data consisting of 278 maize lines genotyped with 46,347 single-nucleotide polymorphisms and evaluated for disease resistance [with ordinal scores from 1 (no disease) to 5 (complete infection)] in three environments (Colombia, Zimbabwe, and Mexico). Models with G×E captured a sizeable proportion of the total variability, which indicates the importance of introducing interaction to improve prediction accuracy. Relative to models based on main effects only, the models that included G×E achieved 9–14% gains in prediction accuracy; adding additive × additive interactions did not increase prediction accuracy consistently across locations. PMID:25538102

  2. Evaluation of self-focusing influence on laser-induced damage threshold of anti-reflective coated windows

    NASA Astrophysics Data System (ADS)

    Rakickas, T.; Kudriašov, V.; Sirutkaitis, V.; Grigonis, R.; Gaižauskas, E.

    2005-12-01

    For high intensity lasers it is very important to choose appropriate optical elements. Since invention of high power lasers laser-induced damage of optical coatings was subject of extensive investigations. At high laser intensities the self-focusing in optical elements appears and intensity at rear optics surface can be much higher than at the front surface. Due to this damage of rear-surface can be reached much faster than damage of the front surface. We investigated the influence of self-focusing on damage threshold in fused-silica windows with anti-reflective coatings on both sides. In our experiments we used titanium-sapphire chirped pulse amplification system (130 fs, 2 mJ, 1 kHz repetition rate pulses at 800 nm). We have tested 1 mm, 3 mm and 6 mm thickness fused-silica windows with identical anti-reflective coatings. The front surface of the samples was placed in the waist of focused beam. The experiments were performed for effective spot diameters on the front 145 μm, 95 μm and 43 μm respectively. The experiments showed the self-focusing of beam inside the fused silica window and self-focusing dependence on initial beam diameter. The damage behavior was dependent on irradiation history. Also we found quite strong nonlinear absorption in fused silica.

  3. Investigations on the SR method growth, etching, birefringence, laser damage threshold and dielectric characterization of sodium acid phthalate single crystals

    NASA Astrophysics Data System (ADS)

    Senthil, A.; Ramasamy, P.; Verma, Sunil

    2011-03-01

    Optically good quality semi-organic single crystal of sodium acid phthalate (NaAP) was successfully grown by Sankaranarayanan-Ramasamy (SR) method. Transparent, colourless <0 0 1> oriented unidirectional bulk single crystals of diameters 10 and 20 mm and length maximum up to 75 mm were grown by the SR method. The grown crystals were subjected to various characterization studies such as etching, birefringence, laser damage threshold, UV-vis spectrum and dielectric measurement. The value of birefringence and quality were ascertained by birefringence studies.

  4. Efficient Phase Locking of Fiber Amplifiers Using a Low-Cost and High-Damage-Threshold Phase Control System

    NASA Astrophysics Data System (ADS)

    Zhou, Pu; Ma, Yan-Xing; Wang, Xiao-Lin; Ma, Hao-Tong; Xu, Xiao-Jun; Liu, Ze-Jin

    2010-03-01

    We propose a low-cost and high-damage-threshold phase control system that employs a piezoelectric ceramic transducer modulator controlled by a stochastic parallel gradient descent algorithm. Efficient phase locking of two fiber amplifiers is demonstrated. Experimental results show that energy encircled in the target pinhole is increased by a factor of 1.76 and the visibility of the fringe pattern is as high as 90% when the system is in close-loop. The phase control system has potential in phase locking of large-number and high-power fiber laser endeavors.

  5. Life prediction modeling based on cyclic damage accumulation

    NASA Technical Reports Server (NTRS)

    Nelson, Richard S.

    1988-01-01

    A high temperature, low cycle fatigue life prediction method was developed. This method, Cyclic Damage Accumulation (CDA), was developed for use in predicting the crack initiation lifetime of gas turbine engine materials, where initiation was defined as a 0.030 inch surface length crack. A principal engineering feature of the CDA method is the minimum data base required for implementation. Model constants can be evaluated through a few simple specimen tests such as monotonic loading and rapic cycle fatigue. The method was expanded to account for the effects on creep-fatigue life of complex loadings such as thermomechanical fatigue, hold periods, waveshapes, mean stresses, multiaxiality, cumulative damage, coatings, and environmental attack. A significant data base was generated on the behavior of the cast nickel-base superalloy B1900+Hf, including hundreds of specimen tests under such loading conditions. This information is being used to refine and extend the CDA life prediction model, which is now nearing completion. The model is also being verified using additional specimen tests on wrought INCO 718, and the final version of the model is expected to be adaptable to most any high-temperature alloy. The model is currently available in the form of equations and related constants. A proposed contract addition will make the model available in the near future in the form of a computer code to potential users.

  6. Predictability of formation damage: An assessment study and generalized models

    SciTech Connect

    Civan, F.

    1991-01-01

    The project objective is to develop improved generalized predictive models to be used for investigation of reservoir formation damage and control for various fluid and rock conditions and to account for these effects in reservoir simulation. To accomplish its objective the proposed study will first critically study and evaluate the previous modeling efforts and the experimental studies reported in the literature. Then, generalized predictive models will be formulated by combining the previous attempts and by improving and generalizing the modeling approaches to accommodate for a wide variety of conditions encountered in actual field applications. A critical review of the previous work addressing their theoretical basis, assumptions and limitations, and the generalized and improved model developed in this study will be presented in a systematic manner in terms of a standardized definition and nomenclature for direct comparison. Case studies with the generalized model will be presented to demonstrate its capacity and validity. User friendly computer programs implementing the improved modeling approaches will also be supplied. This study will form an assessment of the presently available models and methods for evaluating and predicting formation damage and present improved models. Therefore, it will be an important reference for the petroleum industry. 1 tab.

  7. Nonlinear optical effects on retinal damage thresholds in the 1200-1400 nm wavelength range

    NASA Astrophysics Data System (ADS)

    Echeverria, Francesco Jozac

    Recent changes in the maximum permissible exposure (MPE) limits for near-infrared (NIR) laser exposures are analyzed in light of nonlinear optical phenomena. We have evaluated the thresholds for supercontinuum (SC) generation for ultra-short (femtosecond) laser exposures in the NIR region and compared these values with the MPEs listed in the American National Standard for Safe Use of Lasers 2014 Edition (ANSI Z136.1-2014). Due to the strong increase in ocular absorption in the 1.2 to 1.4 micrometer (i.e. 1200-1400 nm) range, evaluation of the SC generation phenomenon is necessary because any shift in laser energy within the eye to shorter wavelengths (i.e. greater frequency) could lead to unforeseen increases in hazards to the retina. The findings of this research do in fact indicate a shift in laser energy to shorter wavelengths for femtosecond pulsed lasers. In addition, an analysis involving spectral measurements through a water cuvette leads to estimations involving the eye configuration that show radiant exposures exceeding the ANSI thresholds for visible wavelengths. The implications of these findings are such that enough NIR energy is converted to visible energy near the retina when dealing with femtosecond pulsed lasers, warranting further studies in examining what the effects caused by nonlinear optical phenomena due to ultrashort pulsed lasers have on MPE thresholds established for eye safety.

  8. Determining beam resistance of large-scale optics by measuring thresholds for surface damage caused by low-size laser beams

    NASA Astrophysics Data System (ADS)

    Dmitriev, D. I.; Ivanova, I. V.; Pasunkin, V. N.; Sirazetdinov, V. S.

    2010-07-01

    The paper describes an experimental method of determining probability density distribution for random threshold values of laser fluence, damaging surface of optical components. The method is as follows. Numerous surface sites of an optical component have been irradiated by a laser beam with a known non-uniform fluence distribution and magnitude sufficient for surface damage. Subsequently, the minimal fluence value ɛ has beens determined at the boundary of the damaged zone for each irradiation spot. It is shown that the sampling of minimal damage threshold values obtained from the above-described data assembly makes it possible to construct the probability density distribution f(ɛ). Knowledge of this distribution provides for the use of order statistics in damage threshold fluence data analysis and, thus, enhances accuracy and reliability of determination of surface strength for sizable optic components tested by small-diameter beams.

  9. Determining beam resistance of large-scale optics by measuring thresholds for surface damage caused by low-size laser beams

    NASA Astrophysics Data System (ADS)

    Dmitriev, D. I.; Ivanova, I. V.; Pasunkin, V. N.; Sirazetdinov, V. S.

    2011-03-01

    The paper describes an experimental method of determining probability density distribution for random threshold values of laser fluence, damaging surface of optical components. The method is as follows. Numerous surface sites of an optical component have been irradiated by a laser beam with a known non-uniform fluence distribution and magnitude sufficient for surface damage. Subsequently, the minimal fluence value ɛ has beens determined at the boundary of the damaged zone for each irradiation spot. It is shown that the sampling of minimal damage threshold values obtained from the above-described data assembly makes it possible to construct the probability density distribution f(ɛ). Knowledge of this distribution provides for the use of order statistics in damage threshold fluence data analysis and, thus, enhances accuracy and reliability of determination of surface strength for sizable optic components tested by small-diameter beams.

  10. Material properties of lithium fluoride for predicting XUV laser ablation rate and threshold fluence

    NASA Astrophysics Data System (ADS)

    Blejchař, Tomáś; Nevrlý, Václav; Vašinek, Michal; Dostál, Michal; Pečínka, Lukáś; Dlabka, Jakub; Stachoň, Martin; Juha, Libor; Bitala, Petr; Zelinger, Zdeněk.; Pira, Peter; Wild, Jan

    2015-05-01

    This paper deals with prediction of extreme ultraviolet (XUV) laser ablation of lithium fluoride at nanosecond timescales. Material properties of lithium fluoride were determined based on bibliographic survey. These data are necessary for theoretical estimation of surface removal rate in relevance to XUV laser desorption/ablation process. Parameters of XUV radiation pulses generated by the Prague capillary-discharge laser (CDL) desktop system were assumed in this context. Prediction of ablation curve and threshold laser fluence for lithium fluoride was performed employing XUV-ABLATOR code. Quasi-random sampling approach was used for evaluating its predictive capabilities in the means of variance and stability of model outputs in expected range of uncertainties. These results were compared to experimental data observed previously.

  11. Thickness effect on laser-induced-damage threshold of indium-tin oxide films at 1064 nm

    SciTech Connect

    Wang Haifeng; Huang Zhimeng; Zhang Dayong; Luo Fei; Huang Lixian; Li Yanglong; Luo Yongquan; Wang Weiping; Zhao Xiangjie

    2011-12-01

    Laser-induced-damage characteristics of commercial indium-tin oxide (ITO) films deposited by DC magnetron sputtering deposition on K9 glass substrates as a function of the film thickness have been studied at 1064 nm with a 10 ns laser pulse in the 1-on-1 mode, and the various mechanisms for thickness effect on laser-induced-damage threshold (LIDT) of the film have been discussed in detail. It is observed that laser-damage-resistance of ITO film shows dramatic thickness effect with the LIDT of the 50-nm ITO film 7.6 times as large as the value of 300 nm film, and the effect of depressed carrier density by decreasing the film thickness is demonstrated to be the primary reason. Our experiment findings indicate that searching transparent conductive oxide (TCO) film with low carrier density and high carrier mobility is an efficient technique to improve the laser-damage-resistance of TCO films based on maintaining their well electric conductivity.

  12. Computational prediction of the chromosome-damaging potential of chemicals.

    PubMed

    Rothfuss, Andreas; Steger-Hartmann, Thomas; Heinrich, Nikolaus; Wichard, Jörg

    2006-10-01

    We report on the generation of computer-based models for the prediction of the chromosome-damaging potential of chemicals as assessed in the in vitro chromosome aberration (CA) test. On the basis of publicly available CA-test results of more than 650 chemical substances, half of which are drug-like compounds, we generated two different computational models. The first model was realized using the (Q)SAR tool MCASE. Results obtained with this model indicate a limited performance (53%) for the assessment of a chromosome-damaging potential (sensitivity), whereas CA-test negative compounds were correctly predicted with a specificity of 75%. The low sensitivity of this model might be explained by the fact that the underlying 2D-structural descriptors only describe part of the molecular mechanism leading to the induction of chromosome aberrations, that is, direct drug-DNA interactions. The second model was constructed with a more sophisticated machine learning approach and generated a classification model based on 14 molecular descriptors, which were obtained after feature selection. The performance of this model was superior to the MCASE model, primarily because of an improved sensitivity, suggesting that the more complex molecular descriptors in combination with statistical learning approaches are better suited to model the complex nature of mechanisms leading to a positive effect in the CA-test. An analysis of misclassified pharmaceuticals by this model showed that a large part of the false-negative predicted compounds were uniquely positive in the CA-test but lacked a genotoxic potential in other mutagenicity tests of the regulatory testing battery, suggesting that biologically nonsignificant mechanisms could be responsible for the observed positive CA-test result. Since such mechanisms are not amenable to modeling approaches it is suggested that a positive prediction made by the model reflects a biologically significant genotoxic potential. An integration of the

  13. Threshold field for soft damage and electron drift velocity in InGaN two-dimensional channels

    NASA Astrophysics Data System (ADS)

    Ardaravičius, L.; Kiprijanovič, O.; Liberis, J.; Šermukšnis, E.; Matulionis, A.; Ferreyra, R. A.; Avrutin, V.; Özgür, Ü.; Morkoç, H.

    2015-10-01

    Experimental investigation of electron transport along a two-dimensional channel confined in an InGaN alloy of Al{}0.82In{}0.18N/AlN/In{}0.1Ga{}0.9N/GaN structure was performed at room temperature under near-equilibrium thermal-bath temperature. A soft damage was observed at a threshold electric field applied in the channel plane. The threshold current for soft damage and the supplied electric power were lower in the channels with a higher electron density. The results are interpreted in terms of plasmon-assisted heat dissipation. In agreement with ultra-fast decay of hot phonons in the vicinity of the resonance with plasmons, the electron drift velocity acquires a highest value of ˜2 × 107 cm s-1 at 180 kV cm-1 in channels with 1 × 1013 cm-2 and decreases as the electron density increases. No negative differential resistance is observed. The effective hot-phonon lifetime is estimated as ˜ 2 ps at 1.6 × 1013 cm-2 at low electric fields and is found to decrease as the field increases.

  14. Applying hafnia mixtures to enhance the laser-induced damage threshold of coatings for third-harmonic generation optics

    NASA Astrophysics Data System (ADS)

    Mende, Mathias; Jensen, Lars O.; Ehlers, Henrik; Bruns, Stefan; Vergöhl, Michael; Burdack, Peer; Ristau, Detlev

    2012-11-01

    The generation of third harmonic radiation (THG) is required for many pulsed solid-state laser applications in industry and science. In this contribution, the coatings for two necessary optical components, dichroic mirrors and nonlinear optical (NLO) crystals are in the focus of investigation. Because of the high bulk damage threshold lithium triborate (LBO) crystals are applied for this study. HfO2/SiO2 mixtures are employed as high refractive index material to improve the power handling capability of the multilayers. All coatings are produced by ion beam sputtering (IBS) using a zone target assembly for the deposition of material mixtures. The atomic composition and the oxidation ratio of different HfO2/SiO2 mixtures are analyzed by X-ray photoelectron spectroscopy (XPS). The influence of different deposition temperatures and post annealing on the optical properties and the amorphous micro structure of the films is investigated by UV/Vis/NIR spectroscopy and X-ray diffraction (XRD). The laser induced damage thresholds at 355 nm wavelength for nanosecond pulse durations are measured in a 10,000on1 experiment according with the standard ISO21254. Furthermore, the optical components are tested under real application conditions.

  15. Predicting aphasia type from brain damage measured with structural MRI.

    PubMed

    Yourganov, Grigori; Smith, Kimberly G; Fridriksson, Julius; Rorden, Chris

    2015-12-01

    Chronic aphasia is a common consequence of a left-hemisphere stroke. Since the early insights by Broca and Wernicke, studying the relationship between the loci of cortical damage and patterns of language impairment has been one of the concerns of aphasiology. We utilized multivariate classification in a cross-validation framework to predict the type of chronic aphasia from the spatial pattern of brain damage. Our sample consisted of 98 patients with five types of aphasia (Broca's, Wernicke's, global, conduction, and anomic), classified based on scores on the Western Aphasia Battery (WAB). Binary lesion maps were obtained from structural MRI scans (obtained at least 6 months poststroke, and within 2 days of behavioural assessment); after spatial normalization, the lesions were parcellated into a disjoint set of brain areas. The proportion of damage to the brain areas was used to classify patients' aphasia type. To create this parcellation, we relied on five brain atlases; our classifier (support vector machine - SVM) could differentiate between different kinds of aphasia using any of the five parcellations. In our sample, the best classification accuracy was obtained when using a novel parcellation that combined two previously published brain atlases, with the first atlas providing the segmentation of grey matter, and the second atlas used to segment the white matter. For each aphasia type, we computed the relative importance of different brain areas for distinguishing it from other aphasia types; our findings were consistent with previously published reports of lesion locations implicated in different types of aphasia. Overall, our results revealed that automated multivariate classification could distinguish between aphasia types based on damage to atlas-defined brain areas. PMID:26465238

  16. Using self-organizing maps to determine observation threshold limit predictions in highly variant data

    USGS Publications Warehouse

    Paganoni, C.A.; Chang, K.C.; Robblee, M.B.

    2006-01-01

    A significant data quality challenge for highly variant systems surrounds the limited ability to quantify operationally reasonable limits on the data elements being collected and provide reasonable threshold predictions. In many instances, the number of influences that drive a resulting value or operational range is too large to enable physical sampling for each influencer, or is too complicated to accurately model in an explicit simulation. An alternative method to determine reasonable observation thresholds is to employ an automation algorithm that would emulate a human analyst visually inspecting data for limits. Using the visualization technique of self-organizing maps (SOM) on data having poorly understood relationships, a methodology for determining threshold limits was developed. To illustrate this approach, analysis of environmental influences that drive the abundance of a target indicator species (the pink shrimp, Farfantepenaeus duorarum) provided a real example of applicability. The relationship between salinity and temperature and abundance of F. duorarum is well documented, but the effect of changes in water quality upstream on pink shrimp abundance is not well understood. The highly variant nature surrounding catch of a specific number of organisms in the wild, and the data available from up-stream hydrology measures for salinity and temperature, made this an ideal candidate for the approach to provide a determination about the influence of changes in hydrology on populations of organisms.

  17. The role of roughness in predicting transport thresholds on desert surfaces: temporal and spatial variability

    NASA Astrophysics Data System (ADS)

    King, James; Haustein, Karsten; Wiggs, Giles F. S.; Eckardt, Frank; Thomas, David S. G.; Washington, Richard

    2013-04-01

    Dust emission schemes in climate models are relatively simple and tuned to represent observed background aerosol concentrations. A key component of the dust emission scheme is the sediment transport threshold, which is a function of soil size distribution, soil moisture, air and soil particle density, and surface roughness. For a particular region or landform that is not vegetated the variable that controls the transport threshold is soil moisture. This is because it is assumed that the other components vary little (air and soil particle densities) or are kept constant (soil size distribution and surface roughness). This in turn puts the emphasis very heavily on soil moisture and wind stress as the key drivers of dust emission for specific landforms and dust emission schemes. This highlights the necessity for current models to tune their model parameters to observations. Observations of dust emission were undertaken in 2011 and 2012 on Sua Pan in Botswana, a large, flat, unvegetated salt pan, as part of the Dust Observation for Models (DO4 Models) campaign. The observations consisted of eleven meteorological stations placed within a 144 km2 region recording wind velocity, soil moisture, soil and air temperature, horizontal transport, vertical transport, and radiative properties. Out of the measured and calculated erodibility parameters responsible for predicting transport threshold within current schemes, surface soil moisture and aerodynamic roughness length varied the most over the duration of the project and spatially across the pan. In some cases, the aerodynamic roughness length of the bare soil increased by three orders of magnitude within a three month period. This increase in roughness would almost double the modelled threshold shear velocity required for this surface to be emissive. The temporal and spatial variability of the calculated transport threshold is explored with observed data and compared with the modelled transport threshold for this region for

  18. Effect of Imaging Parameter Thresholds on MRI Prediction of Neoadjuvant Chemotherapy Response in Breast Cancer Subtypes

    PubMed Central

    Jones, Ella F.; Newitt, David C.; Kornak, John; Wilmes, Lisa J.; Esserman, Laura J.; Hylton, Nola M.

    2016-01-01

    The purpose of this study is to evaluate the predictive performance of magnetic resonance imaging (MRI) markers in breast cancer patients by subtype. Sixty-four patients with locally advanced breast cancer undergoing neoadjuvant chemotherapy were enrolled in this study. Each patient received a dynamic contrast-enhanced (DCE-MRI) at baseline, after 1 cycle of chemotherapy and before surgery. Functional tumor volume (FTV), the imaging marker measured by DCE-MRI, was computed at various thresholds of percent enhancement (PEt) and signal-enhancement ratio (SERt). Final FTV before surgery and percent changes of FTVs at the early and final treatment time points were used to predict patients’ recurrence-free survival. The full cohort and each subtype defined by the status of hormone receptor and human epidermal growth factor receptor 2 (HR+/HER2-, HER2+, triple negative) were analyzed. Predictions were evaluated using the Cox proportional hazard model when PEt changed from 30% to 200% in steps of 10% and SERt changed from 0 to 2 in steps of 0.2. Predictions with high hazard ratios and low p-values were considered as strong. Different profiles of FTV as predictors for recurrence-free survival were observed in each breast cancer subtype and strong associations with survival were observed at different PEt/SERt combinations that resulted in different FTVs. Findings from this retrospective study suggest that the predictive performance of imaging markers based on FTV may be improved with enhancement thresholds being optimized separately for clinically-relevant subtypes defined by HR and HER2 receptor expression. PMID:26886725

  19. Effect of Imaging Parameter Thresholds on MRI Prediction of Neoadjuvant Chemotherapy Response in Breast Cancer Subtypes.

    PubMed

    Lo, Wei-Ching; Li, Wen; Jones, Ella F; Newitt, David C; Kornak, John; Wilmes, Lisa J; Esserman, Laura J; Hylton, Nola M

    2016-01-01

    The purpose of this study is to evaluate the predictive performance of magnetic resonance imaging (MRI) markers in breast cancer patients by subtype. Sixty-four patients with locally advanced breast cancer undergoing neoadjuvant chemotherapy were enrolled in this study. Each patient received a dynamic contrast-enhanced (DCE-MRI) at baseline, after 1 cycle of chemotherapy and before surgery. Functional tumor volume (FTV), the imaging marker measured by DCE-MRI, was computed at various thresholds of percent enhancement (PEt) and signal-enhancement ratio (SERt). Final FTV before surgery and percent changes of FTVs at the early and final treatment time points were used to predict patients' recurrence-free survival. The full cohort and each subtype defined by the status of hormone receptor and human epidermal growth factor receptor 2 (HR+/HER2-, HER2+, triple negative) were analyzed. Predictions were evaluated using the Cox proportional hazard model when PEt changed from 30% to 200% in steps of 10% and SERt changed from 0 to 2 in steps of 0.2. Predictions with high hazard ratios and low p-values were considered as strong. Different profiles of FTV as predictors for recurrence-free survival were observed in each breast cancer subtype and strong associations with survival were observed at different PEt/SERt combinations that resulted in different FTVs. Findings from this retrospective study suggest that the predictive performance of imaging markers based on FTV may be improved with enhancement thresholds being optimized separately for clinically-relevant subtypes defined by HR and HER2 receptor expression. PMID:26886725

  20. Energy Thresholds of DNA Damage Induced by UV Radiation: An XPS Study.

    PubMed

    Gomes, P J; Ferraria, A M; Botelho do Rego, A M; Hoffmann, S V; Ribeiro, P A; Raposo, M

    2015-04-30

    This work stresses on damage at the molecular level caused by ultraviolet radiation (UV) in the range from 3.5 to 8 eV, deoxyribonucleic acid (DNA) films observed by X-ray photoelectron spectroscopy (XPS). Detailed quantitative XPS analysis, in which all the amounts are relative to sodium-assumed not to be released from the samples, of the carbon, oxygen, and particularly, nitrogen components, reveals that irradiation leads to sugar degradation with CO-based compounds release for energies above 6.9 eV and decrease of nitrogen groups which are not involved in hydrogen bonding at energies above 4.2 eV. Also the phosphate groups are seen to decrease to energies above 4.2 eV. Analysis of XPS spectra allowed to conclude that the damage on bases peripheral nitrogen atoms are following the damage on phosphates. It suggests that very low kinetic energy photoelectrons are ejected from the DNA bases, as a result of UV light induced breaking of the phosphate ester groups which forms a transient anion with resonance formation and whereby most of the nitrogen DNA peripheral groups are removed. The degree of ionization of DNA was observed to increase with radiation energy, indicating that the ionized phosphate groups are kept unchanged. This result was interpreted by the shielding of phosphate groups caused by water molecules hydration near sodium atoms. PMID:25844940

  1. Assessment of mono-shot measurement as a fast and accurate determination of the laser-induced damage threshold in the sub-picosecond regime.

    PubMed

    Sozet, Martin; Neauport, Jérôme; Lavastre, Eric; Roquin, Nadja; Gallais, Laurent; Lamaignère, Laurent

    2016-02-15

    Standard test protocols need several laser shots to assess the laser-induced damage threshold of optics and, consequently, large areas are necessary. Taking into account the dominating intrinsic mechanisms of laser damage in the sub-picosecond regime, a simple, fast, and accurate method, based on correlating the fluence distribution with the damage morphology after only one shot in optics is therein presented. Several materials and components have been tested using this method and compared to the results obtained with the classical 1/1 method. Both lead to the same threshold value with an accuracy in the same order of magnitude. Therefore, this mono-shot testing could be a straightforward protocol to evaluate damage threshold in short pulse regime. PMID:26872193

  2. Predicting the speech reception threshold of cochlear implant listeners using an envelope-correlation based measure

    PubMed Central

    Yousefian, Nima; Loizou, Philipos C.

    2012-01-01

    A modulation-based index is proposed for predicting speech intelligibility by cochlear implant (CI) listeners. The input to the proposed index are speech envelopes extracted using the individual CI user's daily strategy, and as such, this approach incorporates information about the number of active electrodes, shape of the compression function and electrical dynamic range. High correlation (r = 0.96) was achieved with the proposed index when evaluated with speech-reception thresholds (SRTs) obtained by CI users in steady and speech-masker conditions. This outcome suggests that the information contained in electrodograms seems to be sufficient for reliably predicting CI user's performance in noise. The proposed index can be used by clinicians to optimize the selection of fitting parameters of individual CI users for better performance in noise. PMID:23145620

  3. On the experimental prediction of the stability threshold speed caused by rotating damping

    NASA Astrophysics Data System (ADS)

    Vervisch, B.; Derammelaere, S.; Stockman, K.; De Baets, P.; Loccufier, M.

    2016-08-01

    An ever increasing demand for lighter rotating machinery and higher operating speeds results in a raised probability of instabilities. Rotating damping is one of the reasons, instability occurs. Rotating damping, or rotor internal damping, is the damping related to all rotating parts while non-rotating damping appearing in the non-rotating parts. The present study describes a rotating setup, designed to investigate rotating damping experimentally. An efficient experimental procedure is presented to predict the stability threshold of a rotating machine. The setup consists of a long thin shaft with a disk in the middle and clamped boundary conditions. The goal is to extract the system poles as a function of the rotating speed. The real parts of these poles are used to construct the decay rate plot, which is an indication for the stability. The efficiency of the experimental procedure relies on the model chosen for the rotating shaft. It is shown that the shaft behavior can be approximated by a single degree of freedom model that incorporates a speed dependent damping. As such low measurement effort and only one randomly chosen measurement location are needed to construct the decay rate plot. As an excitation, an automated impact hammer is used and the response is measured by eddy current probes. The proposed method yields a reliable prediction of the stability threshold speed which is validated through measurements.

  4. Investigating the relationship between material properties and laser-induced damage threshold of dielectric optical coatings at 1064 nm

    NASA Astrophysics Data System (ADS)

    Bassiri, Riccardo; Clark, Caspar; Martin, Iain W.; Markosyan, Ashot; Murray, Peter G.; Tessmer, Joseph; Rowan, Sheila; Fejer, Martin M.

    2015-11-01

    The Laser Induced Damage Threshold (LIDT) and material properties of various multi-layer amorphous dielectric optical coatings, including Nb2O5, Ta2O5, SiO2, TiO2, ZrO2, AlN, SiN, LiF and ZnSe, have been studied. The coatings were produced by ion assisted electron beam and thermal evaporation; and RF and DC magnetron sputtering at Helia Photonics Ltd, Livingston, UK. The coatings were characterized by optical absorption measurements at 1064 nm by Photothermal Common-path Interferometry (PCI). Surface roughness and damage pits were analyzed using atomic force microscopy. LIDT measurements were carried out at 1064 nm, with a pulse duration of 9.6 ns and repetition rate of 100 Hz, in both 1000-on-1 and 1-on-1 regimes. The relationship between optical absorption, LIDT and post-deposition heat-treatment is discussed, along with analysis of the surface morphology of the LIDT damage sites showing both coating and substrate failure.

  5. Closing the loop: a spatial analysis to link observed environmental damage to predicted heavy metal emissions.

    PubMed

    Colgan, Anja; Hankard, Peter K; Spurgeon, David J; Svendsen, Claus; Wadsworth, Richard A; Weeks, Jason M

    2003-05-01

    In many cases, the link between industrial emissions and damage to the environment can only be inferred. The Environment Agency of the United Kingdom imposes emissions limits on industrial sites so that predicted concentrations and deposition rates remain below standard thresholds. Estimates of appropriate critical levels and loads are usually based on laboratory results and rarely estimate synergistic effects between pollutants or consider biological adaptation or selection in the target receptor organisms. The Avonmouth smelter has been emitting zinc and other heavy metals since 1929. It has been the subject of a number of detailed and synoptic studies, especially the impact on soil invertebrates. Damage was assessed using both physiological and ecological measurements. Two methods of spatial analysis were investigated, namely interpolation using standard geographical information system (GIS) operators and atmospheric dispersal modeling using an off-the-shelf model. Both methods can be used to compute contours (isolines) of predicted biological effect. Correlation results show that dispersal modeling is at least as good as kriging but requires much less data. This article demonstrates the usefulness of GIS and dispersal models as tools in decision making to determine the most suitable sampling sites in the assessment and monitoring of the impact of contamination around major point sources. PMID:12729205

  6. Ductile damage prediction in sheet and bulk metal forming

    NASA Astrophysics Data System (ADS)

    Badreddine, Houssem; Labergère, Carl; Saanouni, Khemais

    2016-04-01

    This paper is dedicated to the presentation of an advanced 3D numerical methodology for virtual sheet and/or bulk metal forming simulation to predict the anisotropic ductile defects occurrence. First, the detailed formulation of thermodynamically-consistent fully coupled and fully anisotropic constitutive equations is given. The proposed constitutive equations account for the main material nonlinearities as the anisotropic plastic flow, the mixed isotropic and kinematic hardening and the anisotropic ductile damage under large inelastic strains. Second, the related numerical aspects required to solve the initial and boundary value problem (IBVP) are very briefly presented in the framework of the 3D finite element method. The global resolution schemes as well as the local integration schemes of the fully coupled constitutive equations are briefly discussed. Finally, some typical examples of sheet and bulk metal forming processes are numerically simulated using the proposed numerical methodology.

  7. A multi-timescale adaptive threshold model for the SAI tactile afferent to predict response to mechanical vibration

    PubMed Central

    Jahangiri, Anila F.; Gerling, Gregory J.

    2011-01-01

    The Leaky Integrate and Fire (LIF) model of a neuron is one of the best known models for a spiking neuron. A current limitation of the LIF model is that it may not accurately reproduce the dynamics of an action potential. There have recently been some studies suggesting that a LIF coupled with a multi-timescale adaptive threshold (MAT) may increase LIF’s accuracy in predicting spikes in cortical neurons. We propose a mechanotransduction process coupled with a LIF model with multi-timescale adaptive threshold to model slowly adapting type I (SAI) mechanoreceptor in monkey’s glabrous skin. In order to test the performance of the model, the spike timings predicted by this MAT model are compared with neural data. We also test a fixed threshold variant of the model by comparing its outcome with the neural data. Initial results indicate that the MAT model predicts spike timings better than a fixed threshold LIF model only. PMID:21814636

  8. Investigation of damage threshold of ion beam deposited oxide thin film optics for high-peak-power short-pulse lasers

    NASA Astrophysics Data System (ADS)

    Fitzgerald Dummer, Ann M.; Brizuela, Fernando; Duskis, Charissa; Luther, Brad; Larotonda, Miguel; Rocca, Jorge J.; George, Jason; Kohli, Sandeep; McCurdy, Pat; Menoni, Carmen S.

    2004-09-01

    In this work we report on the damage threshold of ion beam deposited oxide films designed for high peak power short pulse laser systems. Single layers of ZrO2, SiO2, Al2O3, TiO2, and Ta2O5 and multilayers of Al2O 3/TiO2, SiO2/Ta2O5, and SiO2/ZrO2 were grown on polished borosilicate glass substrates using ion beam sputter deposition. Deposition conditions were optimized to yield fully oxidized films as determined from x-ray photoelectron spectroscopy (XPS). Damage threshold testing was performed using an amplified Ti:Sapphire laser producing a train of 120 picosecond pulses at a wavelength of 800 nm. The laser output was focused with a lens to generate fluences ranging from 0.1 to 24 J/cm2. The highest damage threshold of 15.4 J/cm2 was measured for a single layer film of SiO2. The damage threshold of high reflectance and anti-reflection multilayer coatings fabricated for 800 nm applications was evaluated using the same procedure as for the single layer films. Highest damage thresholds of 2.5 and 3.5 J/cm2 were measured for a 6-pair ZrO2/SiO2 high reflectance coating and a 5 layer anti-reflection coating of the same materials.

  9. Damage threshold study of sonic IR imaging on carbon-fiber reinforced laminated composite materials

    NASA Astrophysics Data System (ADS)

    Han, Xiaoyan; He, Qi; Zhang, Ding; Ashbaugh, Mike; Favro, Lawrence D.; Newaz, Golam; Thomas, Robert L.

    2013-01-01

    Sonic Infrared Imaging, as a young NDE technology, has drawn a lot of attentions due to it's fast, wide-area evaluation capability, and due to its broad applications in different materials such as metal/metal alloy, composites and detection of various types of defects: surface, subsurface, cracks, delaminations/disbonds. Sonic IR Imaging combines pulsed ultrasound excitation and infrared imaging to detect defects in materials. The sound pulse causes rubbing due to non-unison motion between faces of defects, and infrared sensors image the temperature map over the target to identify defects. However, concerns have also been brought up about possible damages which might occur at the contact spots between the ultrasound transducer from the external excitation source and the target materials. In this paper, we present our results from a series of systematically designed experiments on carbon-fiber reinforced laminated composite panels to address the concerns.

  10. Predicting the sparticle spectrum from GUTs via SUSY threshold corrections with SusyTC

    NASA Astrophysics Data System (ADS)

    Antusch, Stefan; Sluka, Constantin

    2016-07-01

    Grand Unified Theories (GUTs) can feature predictions for the ratios of quark and lepton Yukawa couplings at high energy, which can be tested with the increasingly precise results for the fermion masses, given at low energies. To perform such tests, the renormalization group (RG) running has to be performed with sufficient accuracy. In su-persymmetric (SUSY) theories, the one-loop threshold corrections (TC) are of particular importance and, since they affect the quark-lepton mass relations, link a given GUT flavour model to the sparticle spectrum. To accurately study such predictions, we extend and generalize various formulas in the literature which are needed for a precision analysis of SUSY flavour GUT models. We introduce the new software tool SusyTC, a major extension to the Mathematica package REAP [1], where these formulas are implemented. SusyTC extends the functionality of REAP by a full inclusion of the (complex) MSSM SUSY sector and a careful calculation of the one-loop SUSY threshold corrections for the full down-type quark, up-type quark and charged lepton Yukawa coupling matrices in the electroweak-unbroken phase. Among other useful features, SusyTC calculates the one-loop corrected pole mass of the charged (or the CP-odd) Higgs boson as well as provides output in SLHA conventions, i.e. the necessary input for external software, e.g. for performing a two-loop Higgs mass calculation. We apply SusyTC to study the predictions for the parameters of the CMSSM (mSUGRA) SUSY scenario from the set of GUT scale Yukawa relations y_e/y_d=-1/2{-}^2,y_{μ }/y_s = 6 , and y_{τ }/y_b=-3/2 , which has been proposed recently in the context of SUSY GUT flavour models.

  11. Wavelength dependence of repetitive-pulse laser-induced damage threshold in beta-BaB2O4.

    PubMed

    Kouta, H

    1999-01-20

    The dependence on wavelength of repetitive-pulse (10 Hz, 8-10 ns) laser-induced damage on beta barium metaborate (BBO) has been investigated. The thresholds of dielectric breakdown in bulk crystal have been found to be 0.3 GW/cm(2) at 266 nm, 0.9 GW/cm(2) at 355 nm, 2.3 GW/cm(2) at 532 nm, and 4.5 GW/cm(2) at 1064 nm. Results indicate two-photon absorption at 266 and 355 nm, which helps to produce an avalanche effect that causes breakdown at each of the four wavelengths tested. Neither the BBO refractive indices nor the absorption spectrum change until breakdown occurs. PMID:18305644

  12. Unidirectional growth of potassium hydrogen malate single crystals and its characterizations on optical, mechanical, dielectric, laser damage threshold studies

    NASA Astrophysics Data System (ADS)

    Boopathi, K.; Rajesh, P.; Ramasamy, P.

    2013-02-01

    Single crystals of potassium hydrogen malate (PHM) were successfully grown by Sankaranarayanan-Ramasamy (SR) method and conventional slow evaporation solution technique which have the sizes of 35 mm in length, 20 mm in diameter and 15 × 10 × 3 mm3 respectively. The grown PHM crystals have been subjected to single crystal X-ray diffractometer, UV-Vis NIR studies, dielectric measurements, Vickers microhardness analysis and Laser damage threshold. The range and percentage of optical transmission is represented by recording UV-Vis-NIR analysis. The dielectric constant and loss measurement was made as function of temperature in the range of 40-150°C. Mechanical strength and laser stability of the SR method grown crystals was higher than the conventional method grown crystal.

  13. Growth, structural, optical, thermal and laser damage threshold studies of an organic single crystal: 1,3,5 - triphenylbenzene (TPB)

    NASA Astrophysics Data System (ADS)

    Raja, R. Subramaniyan; Babu, G. Anandha; Ramasamy, P.

    2016-05-01

    Good quality single crystals of pure hydrocarbon 1,3,5-Triphenylbenzene (TPB) have been successfully grown using toluene as a solvent using controlled slow cooling solution growth technique. TPB crystallizes in orthorhombic structure with the space group Pna21. The structural perfection of the grown crystal has been analysed by high resolution X-ray diffraction measurements. The range and percentage of the optical transmission are ascertained by recording the UV-vis spectrum. Thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) were used to study its thermal properties. Powder second harmonic generation studies were carried out to explore its NLO properties. Laser damage threshold value has been determined using Nd:YAG laser operating at 1064 nm.

  14. Borate protection of softwood from Coptotermes acinaciformis (Isoptera: Rhinotermitidae) damage: variation in protection thresholds explained.

    PubMed

    Peters, Brenton C; Fitzgerald, Christopher J

    2006-10-01

    Laboratory and field data reported in the literature are confusing with regard to "adequate" protection thresholds for borate timber preservatives. The confusion is compounded by differences in termite species, timber species and test methodology. Laboratory data indicate a borate retention of 0.5% mass/mass (m/m) boric acid equivalent (BAE) would cause > 90% termite mortality and restrict mass loss in test specimens to < or = 5%. Field data generally suggest that borate retentions appreciably > 0.5% m/m BAE are required. We report two field experiments with varying amounts of untreated feeder material in which Coptotermes acinaciformis (Froggatt) (Isoptera: Rhinotermitidae) responses to borate-treated radiata (Monterey) pine, Pinus radiata D. Don, were measured. The apparently conflicting results between laboratory and field data are explained by the presence or absence of untreated feeder material in the test environment. In the absence of untreated feeder material, wood containing 0.5% BAE provided adequate protection from Coptotermes sp., whereas in the presence of untreated feeder material, increased retentions were required. Furthermore, the retentions required increased with increased amounts of susceptible material present. Some termites, Nasutitermes sp. and Mastotermes darwiniensis Froggatt, for example, are borate-tolerant and borate timber preservatives are not a viable management option with these species. The lack of uniform standards for termite test methodology and assessment criteria for efficacy across the world is recognized as a difficulty with research into the performance of timber preservatives with termites. The many variables in laboratory and field assays make "prescriptive" standards difficult to recommend. The use of "performance" standards to define efficacy criteria ("adequate" protection) is discussed. PMID:17066808

  15. Observed physical processes in mechanical tests of PBX9501 and recomendations for experiments to explore a possible plasticity/damage threshold

    SciTech Connect

    Buechler, Miles A.

    2012-05-02

    This memo discusses observations that have been made in regards to a series of monotonic and cyclic uniaxial experiments performed on PBX9501 by Darla Thompson under Enhanced Surveilance Campaign support. These observations discussed in Section Cyclic compression observations strongly suggest the presence of viscoelastic, plastic, and damage phenomena in the mechanical response of the material. In Secton Uniaxial data analysis and observations methods are discussed for separating out the viscoelastic effects. A crude application of those methods suggests the possibility of a critical stress below which plasticity and damage may be negligible. The threshold should be explored because if it exists it will be an important feature of any constitutive model. Additionally, if the threshold exists then modifications of experimental methods may be feasible which could potentially simplify future experiments or provide higher quality data from those experiments. A set of experiments to explore the threshold stress are proposed in Section Exploratory tests program for identifying threshold stress.

  16. Growth of ADP-KDP mixed crystal and its optical, mechanical, dielectric, piezoelectric and laser damage threshold studies

    NASA Astrophysics Data System (ADS)

    Rajesh, P.; Ramasamy, P.; Bhagavannarayana, G.

    2013-01-01

    Good quality ADP-KDP mixed crystal (90:10) is grown by slow cooling method. The size of the grown crystal is 80×10×10 mm3. The mounted seed size was 5×10×10 mm3 and the crystal was grown along the 'c' axis. HRXRD studies have been done in the near and far regions of the seed crystal. The FWHM of these diffraction curves are 28 and 29 arcsec, which are almost the same. The close values of FWHM of both the specimens indicate that the quality of the crystal remains nearly the same throughout the crystal. 80% of transparency is observed from the UV-vis studies in the entire visible region. Vickers hardness studies indicate that the mixed crystal is mechanically more stable compared to the ADP. Higher piezoelectric coefficient is observed in mixed crystals. Dielectric measurements are carried out. From the laser damage threshold studies, it is observed that higher energy is required to damage the mixed crystal and it indicates that the laser stability of the mixed crystal is high.

  17. On the necessity and biological significance of threshold-free regulon prediction outputs.

    PubMed

    Rigali, Sébastien; Nivelle, Renaud; Tocquin, Pierre

    2015-02-01

    The in silico prediction of cis-acting elements in a genome is an efficient way to quickly obtain an overview of the biological processes controlled by a trans-acting factor, and connections between regulatory networks. Several regulon prediction web tools are available, designed to identify DNA motifs predicted to be bound by transcription factors using position weight matrix-based algorithms. In this paper we expose and discuss the conflicting objectives of software creators (bioinformaticians) and software users (biologists), who aim for reliable and exhaustive prediction outputs, respectively. Software makers, concerned with providing tools that minimise the number of false positive hits, often impose a stringent threshold score for a sequence to be included in the list of the putative cis-acting sites. This rigidity eventually results in the identification of strongly reliable but largely straightforward sites, i.e. those associated with genes already anticipated to be targeted by the studied transcription factor. Importantly, this biased identification of strongly bound sequences contrasts with the biological reality where, in many circumstances, a weak DNA-protein interaction is required for the appropriate gene's expression. We show here a series of transcriptionally controlled systems involving weakly bound cis-acting elements that could never have been discovered because of the policy of preventing software users from modifying the screening parameters. Proposing only trustworthy prediction outputs thus prevents biologists from fully utilising their knowledge background and deciding to analyse statistically irrelevant hits that could nonetheless be potentially involved in subtle, unexpected, though essential cis-trans relationships. PMID:25387521

  18. Influence of laser conditioning on laser induced damage threshold of single layers of ZrO2 with various deposition conditions

    NASA Astrophysics Data System (ADS)

    Sahraee, M.; Reza Fallah, H.; Zabolian, H.; Moradi, B.; Haji Mahmoodzade, M.

    2015-04-01

    Single layers of ZrO2 were coated at base pressure of 10-5 mbar by electron beam evaporation (EBE) technique. The influence of oxygen partial pressure on spectral properties and laser induced damage threshold (LIDT) of the samples were investigated. Spectral transmittance of the samples was measured by spectrophotometer. Laser induced damage threshold was detected according to ISO standard 11254. Laser conditioning was conducted by scanning the surface of the samples. Results showed that laser damage resistance was enhanced by increasing the oxygen partial pressure during deposition. LIDT of the samples was changed after laser conditioning. Experimental results revealed that there is enhancement of laser damage resistance of the samples with higher oxygen partial pressure after laser conditioning.

  19. Numerical Simulation for Predicting Fatigue Damage Progress in Notched CFRP Laminates by Using Cohesive Elements

    NASA Astrophysics Data System (ADS)

    Okabe, Tomonaga; Yashiro, Shigeki

    This study proposes the cohesive zone model (CZM) for predicting fatigue damage growth in notched carbon-fiber-reinforced composite plastic (CFRP) cross-ply laminates. In this model, damage growth in the fracture process of cohesive elements due to cyclic loading is represented by the conventional damage mechanics model. We preliminarily investigated whether this model can appropriately express fatigue damage growth for a circular crack embedded in isotropic solid material. This investigation demonstrated that this model could reproduce the results with the well-established fracture mechanics model plus the Paris' law by tuning adjustable parameters. We then numerically investigated the damage process in notched CFRP cross-ply laminates under tensile cyclic loading and compared the predicted damage patterns with those in experiments reported by Spearing et al. (Compos. Sci. Technol. 1992). The predicted damage patterns agreed with the experiment results, which exhibited the extension of multiple types of damage (e.g., splits, transverse cracks and delaminations) near the notches.

  20. Porcine skin damage thresholds for 0.6 to 9.5 cm beam diameters from 1070-nm continuous-wave infrared laser radiation.

    PubMed

    Vincelette, Rebecca; Noojin, Gary D; Harbert, Corey A; Schuster, Kurt J; Shingledecker, Aurora D; Stolarski, Dave; Kumru, Semih S; Oliver, Jeffrey W

    2014-03-01

    There is an increasing use of high-power fiber lasers in manufacturing and telecommunications industries operating in the infrared spectrum between 1000 and 2000 nm, which are advertised to provide as much as 10 kW continuous output power at 1070 nm. Safety standards have traditionally been based on experimental and modeling investigations with scant data available for these wavelengths. A series of studies using 1070-nm infrared lasers to determine the minimum visible lesion damage thresholds in skin using the Yucatan miniature pig (Sus scrofa domestica) for a range of beam diameters (0.6, 1.1, 1.9, 2.4, 4.7, and 9.5 cm) and a range of exposure durations (10 ms to 10 s) is presented. Experimental peak temperatures associated with each damage threshold were measured using thermal imaging. Peak temperatures at damage threshold for the 10-s exposures were ∼10°C lower than those at shorter exposures. The lowest and highest experimental minimum visible lesion damage thresholds were found to have peak radiant exposures of 19 and 432  J/cm2 for the beam diameter-exposure duration pairs of 2.4 cm, 25 ms and 0.6 cm, 10 s, respectively. Thresholds for beam diameters >2.5  cm had a weak to no effect on threshold radiant exposure levels for exposure times ≤0.25  s, but may have a larger effect on thresholds for exposures ≥10  s. PMID:24658776

  1. Quantitative prediction of perceptual decisions during near-threshold fear detection

    NASA Astrophysics Data System (ADS)

    Pessoa, Luiz; Padmala, Srikanth

    2005-04-01

    A fundamental goal of cognitive neuroscience is to explain how mental decisions originate from basic neural mechanisms. The goal of the present study was to investigate the neural correlates of perceptual decisions in the context of emotional perception. To probe this question, we investigated how fluctuations in functional MRI (fMRI) signals were correlated with behavioral choice during a near-threshold fear detection task. fMRI signals predicted behavioral choice independently of stimulus properties and task accuracy in a network of brain regions linked to emotional processing: posterior cingulate cortex, medial prefrontal cortex, right inferior frontal gyrus, and left insula. We quantified the link between fMRI signals and behavioral choice in a whole-brain analysis by determining choice probabilities by means of signal-detection theory methods. Our results demonstrate that voxel-wise fMRI signals can reliably predict behavioral choice in a quantitative fashion (choice probabilities ranged from 0.63 to 0.78) at levels comparable to neuronal data. We suggest that the conscious decision that a fearful face has been seen is represented across a network of interconnected brain regions that prepare the organism to appropriately handle emotionally challenging stimuli and that regulate the associated emotional response. decision making | emotion | functional MRI

  2. A logistic regression based approach for the prediction of flood warning threshold exceedance

    NASA Astrophysics Data System (ADS)

    Diomede, Tommaso; Trotter, Luca; Stefania Tesini, Maria; Marsigli, Chiara

    2016-04-01

    A method based on logistic regression is proposed for the prediction of river level threshold exceedance at short (+0-18h) and medium (+18-42h) lead times. The aim of the study is to provide a valuable tool for the issue of warnings by the authority responsible of public safety in case of flood. The role of different precipitation periods as predictors for the exceedance of a fixed river level has been investigated, in order to derive significant information for flood forecasting. Based on catchment-averaged values, a separation of "antecedent" and "peak-triggering" rainfall amounts as independent variables is attempted. In particular, the following flood-related precipitation periods have been considered: (i) the period from 1 to n days before the forecast issue time, which may be relevant for the soil saturation, (ii) the last 24 hours, which may be relevant for the current water level in the river, and (iii) the period from 0 to x hours in advance with respect to the forecast issue time, when the flood-triggering precipitation generally occurs. Several combinations and values of these predictors have been tested to optimise the method implementation. In particular, the period for the precursor antecedent precipitation ranges between 5 and 45 days; the state of the river can be represented by the last 24-h precipitation or, as alternative, by the current river level. The flood-triggering precipitation has been cumulated over the next 18 hours (for the short lead time) and 36-42 hours (for the medium lead time). The proposed approach requires a specific implementation of logistic regression for each river section and warning threshold. The method performance has been evaluated over the Santerno river catchment (about 450 km2) in the Emilia-Romagna Region, northern Italy. A statistical analysis in terms of false alarms, misses and related scores was carried out by using a 8-year long database. The results are quite satisfactory, with slightly better performances

  3. On the prediction of threshold friction velocity of wind erosion using soil reflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    Li, Junran; Flagg, Cody; Okin, Gregory S.; Painter, Thomas H.; Dintwe, Kebonye; Belnap, Jayne

    2015-12-01

    Current approaches to estimate threshold friction velocity (TFV) of soil particle movement, including both experimental and empirical methods, suffer from various disadvantages, and they are particularly not effective to estimate TFVs at regional to global scales. Reflectance spectroscopy has been widely used to obtain TFV-related soil properties (e.g., moisture, texture, crust, etc.), however, no studies have attempted to directly relate soil TFV to their spectral reflectance. The objective of this study was to investigate the relationship between soil TFV and soil reflectance in the visible and near infrared (VIS-NIR, 350-2500 nm) spectral region, and to identify the best range of wavelengths or combinations of wavelengths to predict TFV. Threshold friction velocity of 31 soils, along with their reflectance spectra and texture were measured in the Mojave Desert, California and Moab, Utah. A correlation analysis between TFV and soil reflectance identified a number of isolated, narrow spectral domains that largely fell into two spectral regions, the VIS area (400-700 nm) and the short-wavelength infrared (SWIR) area (1100-2500 nm). A partial least squares regression analysis (PLSR) confirmed the significant bands that were identified by correlation analysis. The PLSR further identified the strong relationship between the first-difference transformation and TFV at several narrow regions around 1400, 1900, and 2200 nm. The use of PLSR allowed us to identify a total of 17 key wavelengths in the investigated spectrum range, which may be used as the optimal spectral settings for estimating TFV in the laboratory and field, or mapping of TFV using airborne/satellite sensors.

  4. On the prediction of threshold friction velocity of wind erosion using soil reflectance spectroscopy

    USGS Publications Warehouse

    Li, Junran; Flagg, Cody B.; Okin, Gregory S.; Painter, Thomas H.; Dintwe, Kebonye; Belnap, Jayne

    2015-01-01

    Current approaches to estimate threshold friction velocity (TFV) of soil particle movement, including both experimental and empirical methods, suffer from various disadvantages, and they are particularly not effective to estimate TFVs at regional to global scales. Reflectance spectroscopy has been widely used to obtain TFV-related soil properties (e.g., moisture, texture, crust, etc.), however, no studies have attempted to directly relate soil TFV to their spectral reflectance. The objective of this study was to investigate the relationship between soil TFV and soil reflectance in the visible and near infrared (VIS–NIR, 350–2500 nm) spectral region, and to identify the best range of wavelengths or combinations of wavelengths to predict TFV. Threshold friction velocity of 31 soils, along with their reflectance spectra and texture were measured in the Mojave Desert, California and Moab, Utah. A correlation analysis between TFV and soil reflectance identified a number of isolated, narrow spectral domains that largely fell into two spectral regions, the VIS area (400–700 nm) and the short-wavelength infrared (SWIR) area (1100–2500 nm). A partial least squares regression analysis (PLSR) confirmed the significant bands that were identified by correlation analysis. The PLSR further identified the strong relationship between the first-difference transformation and TFV at several narrow regions around 1400, 1900, and 2200 nm. The use of PLSR allowed us to identify a total of 17 key wavelengths in the investigated spectrum range, which may be used as the optimal spectral settings for estimating TFV in the laboratory and field, or mapping of TFV using airborne/satellite sensors.

  5. Structural Damage Prediction and Analysis for Hypervelocity Impacts: Handbook

    NASA Technical Reports Server (NTRS)

    Elfer, N. C.

    1996-01-01

    This handbook reviews the analysis of structural damage on spacecraft due to hypervelocity impacts by meteoroid and space debris. These impacts can potentially cause structural damage to a Space Station module wall. This damage ranges from craters, bulges, minor penetrations, and spall to critical damage associated with a large hole, or even rupture. The analysis of damage depends on a variety of assumptions and the area of most concern is at a velocity beyond well controlled laboratory capability. In the analysis of critical damage, one of the key questions is how much momentum can actually be transfered to the pressure vessel wall. When penetration occurs without maximum bulging at high velocity and obliquities (if less momentum is deposited in the rear wall), then large tears and rupture may be avoided. In analysis of rupture effects of cylindrical geometry, biaxial loading, bending of the crack, a central hole strain rate and R-curve effects are discussed.

  6. Design of high-efficiency broad-bandwidth pulse compression device based on composite transmission grating with high damage threshold

    NASA Astrophysics Data System (ADS)

    Chen, Xinrong; Li, Chaoming; Liu, Linyue; Li, Lin; Wu, Jianhong; Chang, Zenghu

    2014-11-01

    A novel pulse compression device has been developed for femto-second Ti: sapphire laser at 800nm center wavelength with 700nm~900nm bandwidth. This new kind of composite pulse compression device consists of two fused silica transmission gratings with 1250lp/mm and 3300lp/mm respectively and these two fused silica transmission gratings are located in two optical surfaces of the same fused silica plate. Owing to use anti-reflection transmission gratings with high space frequency (3300lp/mm), it can avoid the wave-front distort derived from coating antireflection film on one surface of the fused silica plate. Being made of fused silica, this new composite pulse compression device will be expected to have high laser damage threshold. The calculation results show that: the -1st order diffraction efficiency of 1250lp/mm grating is over 87% within the 700nm and 900nm broad-bandwidth for rectangular groove and TE polarization state. And the average diffraction efficiency within the 700nm and 900nm broad-bandwidth is more than 92%. At 800nm, the -1st transmitted order diffraction efficiency is great to 96% while the transmittance of 3300lp/mm grating is up to 99.9%.

  7. Influence of period and amplitude of microwaviness on KH{sub 2}PO{sub 4} crystal's laser damage threshold

    SciTech Connect

    Chen Mingjun; Li Mingquan; Jiang Wei; Xu Qiao

    2010-08-15

    The laser induced damage threshold (LIDT) has become a technical bottleneck which restricts the application and development of the inertial confinement fusion. Using single point diamond turning method to process KH{sub 2}PO{sub 4} (KDP) crystals, the periodic microwaviness will be left on the machined surface which has a significant impact on the LIDT. In this paper, after acquiring the frequency information of machined surface of KDP crystals with the power spectral density method, we analyze quantitatively the influence of microwaviness on the LIDT of KDP crystal with the Fourier modal theory. Research results indicate that: the surface morphology of KDP crystal is consisted of the subwaviness with different characteristic spatial frequencies; and the reduced amount of the LIDT of KDP crystal leaded by such subwaviness is different; the experimental results of the LIDT are consistent with the theoretical calculations basically; for the machine tool and the processing technology we used, the leading frequency of microwaviness which caused the LIDT decreasing is between (350 {mu}m){sup -1} and (30 {mu}m){sup -1}, especially between (90 {mu}m){sup -1} and (180 {mu}m){sup -1}.

  8. Abrasion-resistant solgel antireflective films with a high laser-induced damage threshold for inertial confinement fusion

    NASA Astrophysics Data System (ADS)

    Xu, Yao; Zhang, Lei; Wu, Dong; Sun, Yu Han; Huang, Zu Xing; Jiang, Xiao Dong; Wei, Xiao Feng; Li, Zhi Hong; Dong, Bao Zhong; Wu, Zhong Hua

    2005-09-01

    To prepare abrasion-resistant antireflective (AR) films for inertial confinement fusion, four solgel routes have been investigated on polysiloxane-modified and polyvinylalcohol- (PVA-) modified SiO2 sols. As confirmed with a transmissive electron microscope, different fractal structure characteristics of the modified SiO2 particles are disclosed by small-angle x-ray scattering technology. And it is these special fractal characteristics that determine the performance of AR films on the level of internal microstructure. A 29Si magic angle spinning and nuclear magnetic resonance study has been successfully applied in explaining the fractal microstructure and its relation to the laser-induced damage threshold (LIDT) of AR films. The films modified by PVA120000 or acetic acid-catalyzed polysiloxane have higher LIDTs than those films modified by PVA16000 or hydrochloride acid-catalyzed polysiloxane. The films from PVA-modified SiO2 sols have a stronger abrasion resistance but lower antireflection than those films from polysiloxane-modified SiO2 sols. In addition, the films from polysiloxane-modified SiO2 sols can possess high transmittance and high LIDT if the polysiloxane synthesis condition is appropriately chosen, but the abrasion resistance is not as good as that from PVA modification. If strong abrasion resistance is necessary, a possible resolution may be to choose a more appropriate hydrophilic polymer than PVA. If not, polysiloxane-modified silica sol can also work when polysiloxane is synthesized under acetic acid catalysis.

  9. Numerical Prediction of Fatigue Damage Progress in Holed CFRP Laminates Using Cohesive Elements

    NASA Astrophysics Data System (ADS)

    Yashiro, Shigeki; Okabe, Tomonaga

    This study presents a numerical simulation to predict damage progress in notched composite laminates under cyclic loading by using a cohesive zone model. A damage-mechanics concept was introduced directly into the fracture process in the cohesive elements in order to express crack growth by cyclic loading. This approach then conformed to the established damage mechanics and facilitated understanding the procedure and reducing computation costs. We numerically investigated the damage progress in holed CFRP cross-ply laminates under tensile cyclic loading and compared the predicted damage patterns with experiment results. The predicted damage patterns agreed with the experiment results that exhibited the extension of multiple types of damage (splits, transverse cracks, and delamination) near the hole. A numerical study indicated that the change in the distribution of in-plane shear stress due to delamination induced the extension of splits and transverse cracks near the hole.

  10. Improved laser damage threshold performance of calcium fluoride optical surfaces via Accelerated Neutral Atom Beam (ANAB) processing

    NASA Astrophysics Data System (ADS)

    Kirkpatrick, S.; Walsh, M.; Svrluga, R.; Thomas, M.

    2015-11-01

    Optics are not keeping up with the pace of laser advancements. The laser industry is rapidly increasing its power capabilities and reducing wavelengths which have exposed the optics as a weak link in lifetime failures for these advanced systems. Nanometer sized surface defects (scratches, pits, bumps and residual particles) on the surface of optics are a significant limiting factor to high end performance. Angstrom level smoothing of materials such as calcium fluoride, spinel, magnesium fluoride, zinc sulfide, LBO and others presents a unique challenge for traditional polishing techniques. Exogenesis Corporation, using its new and proprietary Accelerated Neutral Atom Beam (ANAB) technology, is able to remove nano-scale surface damage and particle contamination leaving many material surfaces with roughness typically around one Angstrom. This surface defect mitigation via ANAB processing can be shown to increase performance properties of high intensity optical materials. This paper describes the ANAB technology and summarizes smoothing results for calcium fluoride laser windows. It further correlates laser damage threshold improvements with the smoothing produced by ANAB surface treatment. All ANAB processing was performed at Exogenesis Corporation using an nAccel100TM Accelerated Particle Beam processing tool. All surface measurement data for the paper was produced via AFM analysis on a Park Model XE70 AFM, and all laser damage testing was performed at Spica Technologies, Inc. Exogenesis Corporation's ANAB processing technology is a new and unique surface modification technique that has demonstrated to be highly effective at correcting nano-scale surface defects. ANAB is a non-contact vacuum process comprised of an intense beam of accelerated, electrically neutral gas atoms with average energies of a few tens of electron volts. The ANAB process does not apply mechanical forces associated with traditional polishing techniques. ANAB efficiently removes surface

  11. Threshold Dose of Three Types of Quantum Dots (QDs) Induces Oxidative Stress Triggers DNA Damage and Apoptosis in Mouse Fibroblast L929 Cells

    PubMed Central

    Zhang, Ting; Wang, Yiqing; Kong, Lu; Xue, Yuying; Tang, Meng

    2015-01-01

    Although it has been reported that fluorescent quantum dots (QDs) have obvious acute toxic effects in vitro, their toxic effects at low doses or threshold doses are still unknown. Therefore, we evaluated the biological histocompatibility and in vitro toxicity of three types of QDs at threshold doses. Also, we compared the toxic effects of QDs with different raw chemical compositions and sizes. The results showed that low concentrations of QDs (≤7 μg/mL) had no obvious effect on cell viability and cell membrane damage, oxidative damage, cell apoptosis or DNA damage. However, QD exposure led to a significant cytotoxicity at higher doses (≥14 μg/mL) and induced abnormal cellular morphology. In addition, when comparing the three types of QDs, 2.2 nm CdTe QDs exposure showed a significantly increased proportion of apoptotic cells and significant DNA damage, suggesting that size and composition contribute to the toxic effects of QDs. Based on these discussions, it was concluded that the concentration (7 μg/mL) may serve as a threshold level for these three types of QDs only in L929 fibroblasts, whereas high concentrations (above 14 μg/mL) may be toxic, resulting in inhibition of proliferation, induction of apoptosis and DNA damage in L929 fibroblasts. PMID:26516873

  12. Predicting Bed Grain Size in Threshold Channels Using Lidar Digital Elevation Models

    NASA Astrophysics Data System (ADS)

    Snyder, N. P.; Nesheim, A. O.; Wilkins, B. C.; Edmonds, D. A.

    2011-12-01

    Over the past 20 years, researchers have developed GIS-based algorithms to extract channel networks and measure longitudinal profiles from digital elevation models (DEMs), and have used these to study stream morphology in relation to tectonics, climate and ecology. The accuracy of stream elevations from traditional DEMs (10-50 m pixels) is typically limited by the contour interval (3-20 m) of the rasterized topographic map source. This is a particularly severe limitation in low-relief watersheds, where 3 m of channel elevation change may occur over several km. Lidar DEMs (~1 m pixels) allow researchers to resolve channel elevation changes of ~0.5 m, enabling reach-scale calculations of gradient, which is the most important parameter for understanding channel processes at that scale. Lidar DEMs have the additional advantage of allowing users to make estimates of channel width. We present a process-based model that predicts median bed grain size in threshold gravel-bed channels from lidar slope and width measurements using the Shields and Manning equations. We compare these predictions to field grain size measurements in segments of three Maine rivers. Like many paraglacial rivers, these have longitudinal profiles characterized by relatively steep (gradient >0.002) and flat (gradient <0.0005) segments, with length scales of several km. This heterogeneity corresponds to strong variations in channel form, sediment supply, bed grain size, and aquatic habitat characteristics. The model correctly predicts bed sediment size within a factor of two in ~70% of the study sites. The model works best in single-thread channels with relatively low sediment supply, and poorly in depositional, multi-thread and/or fine (median grain size <20 mm) reaches. We evaluate the river morphology (using field and lidar measurements) in the context of the Parker et al. (2007) hydraulic geometry relations for single-thread gravel-bed rivers, and find correspondence in the locations where both

  13. Influence of injury risk thresholds on the performance of an algorithm to predict crashes with serious injuries.

    PubMed

    Bahouth, George; Digges, Kennerly; Schulman, Carl

    2012-01-01

    This paper presents methods to estimate crash injury risk based on crash characteristics captured by some passenger vehicles equipped with Advanced Automatic Crash Notification technology. The resulting injury risk estimates could be used within an algorithm to optimize rescue care. Regression analysis was applied to the National Automotive Sampling System / Crashworthiness Data System (NASS/CDS) to determine how variations in a specific injury risk threshold would influence the accuracy of predicting crashes with serious injuries. The recommended thresholds for classifying crashes with severe injuries are 0.10 for frontal crashes and 0.05 for side crashes. The regression analysis of NASS/CDS indicates that these thresholds will provide sensitivity above 0.67 while maintaining a positive predictive value in the range of 0.20. PMID:23169132

  14. Influence of Injury Risk Thresholds on the Performance of an Algorithm to Predict Crashes with Serious Injuries

    PubMed Central

    Bahouth, George; Digges, Kennerly; Schulman, Carl

    2012-01-01

    This paper presents methods to estimate crash injury risk based on crash characteristics captured by some passenger vehicles equipped with Advanced Automatic Crash Notification technology. The resulting injury risk estimates could be used within an algorithm to optimize rescue care. Regression analysis was applied to the National Automotive Sampling System / Crashworthiness Data System (NASS/CDS) to determine how variations in a specific injury risk threshold would influence the accuracy of predicting crashes with serious injuries. The recommended thresholds for classifying crashes with severe injuries are 0.10 for frontal crashes and 0.05 for side crashes. The regression analysis of NASS/CDS indicates that these thresholds will provide sensitivity above 0.67 while maintaining a positive predictive value in the range of 0.20. PMID:23169132

  15. A model for predicting damage induced fatigue life of laminated composite structural components

    NASA Technical Reports Server (NTRS)

    Allen, David H.; Lo, David C.; Georgiou, Ioannis T.; Harris, Charles E.

    1990-01-01

    This paper presents a model for predicting the life of laminated composite structural components subjected to fatigue induced microstructural damage. The model uses the concept of continuum damage mechanics, wherein the effects of microcracks are incorporated into a damage dependent lamination theory instead of treating each crack as an internal boundary. Internal variables are formulated to account for the effects of both matrix cracks and internal delaminations. Evolution laws for determining the damage variables as functions of ply stresses are proposed, and comparisons of predicted damage evolution are made to experiment. In addition, predicted stiffness losses, as well as ply stresses are shown as functions of damage state for a variety of stacking sequences.

  16. A robust operational model for predicting where tropical cyclone waves damage coral reefs.

    PubMed

    Puotinen, Marji; Maynard, Jeffrey A; Beeden, Roger; Radford, Ben; Williams, Gareth J

    2016-01-01

    Tropical cyclone (TC) waves can severely damage coral reefs. Models that predict where to find such damage (the 'damage zone') enable reef managers to: 1) target management responses after major TCs in near-real time to promote recovery at severely damaged sites; and 2) identify spatial patterns in historic TC exposure to explain habitat condition trajectories. For damage models to meet these needs, they must be valid for TCs of varying intensity, circulation size and duration. Here, we map damage zones for 46 TCs that crossed Australia's Great Barrier Reef from 1985-2015 using three models - including one we develop which extends the capability of the others. We ground truth model performance with field data of wave damage from seven TCs of varying characteristics. The model we develop (4MW) out-performed the other models at capturing all incidences of known damage. The next best performing model (AHF) both under-predicted and over-predicted damage for TCs of various types. 4MW and AHF produce strikingly different spatial and temporal patterns of damage potential when used to reconstruct past TCs from 1985-2015. The 4MW model greatly enhances both of the main capabilities TC damage models provide to managers, and is useful wherever TCs and coral reefs co-occur. PMID:27184607

  17. A robust operational model for predicting where tropical cyclone waves damage coral reefs

    PubMed Central

    Puotinen, Marji; Maynard, Jeffrey A.; Beeden, Roger; Radford, Ben; Williams, Gareth J.

    2016-01-01

    Tropical cyclone (TC) waves can severely damage coral reefs. Models that predict where to find such damage (the ‘damage zone’) enable reef managers to: 1) target management responses after major TCs in near-real time to promote recovery at severely damaged sites; and 2) identify spatial patterns in historic TC exposure to explain habitat condition trajectories. For damage models to meet these needs, they must be valid for TCs of varying intensity, circulation size and duration. Here, we map damage zones for 46 TCs that crossed Australia’s Great Barrier Reef from 1985–2015 using three models – including one we develop which extends the capability of the others. We ground truth model performance with field data of wave damage from seven TCs of varying characteristics. The model we develop (4MW) out-performed the other models at capturing all incidences of known damage. The next best performing model (AHF) both under-predicted and over-predicted damage for TCs of various types. 4MW and AHF produce strikingly different spatial and temporal patterns of damage potential when used to reconstruct past TCs from 1985–2015. The 4MW model greatly enhances both of the main capabilities TC damage models provide to managers, and is useful wherever TCs and coral reefs co-occur. PMID:27184607

  18. A robust operational model for predicting where tropical cyclone waves damage coral reefs

    NASA Astrophysics Data System (ADS)

    Puotinen, Marji; Maynard, Jeffrey A.; Beeden, Roger; Radford, Ben; Williams, Gareth J.

    2016-05-01

    Tropical cyclone (TC) waves can severely damage coral reefs. Models that predict where to find such damage (the ‘damage zone’) enable reef managers to: 1) target management responses after major TCs in near-real time to promote recovery at severely damaged sites; and 2) identify spatial patterns in historic TC exposure to explain habitat condition trajectories. For damage models to meet these needs, they must be valid for TCs of varying intensity, circulation size and duration. Here, we map damage zones for 46 TCs that crossed Australia’s Great Barrier Reef from 1985–2015 using three models – including one we develop which extends the capability of the others. We ground truth model performance with field data of wave damage from seven TCs of varying characteristics. The model we develop (4MW) out-performed the other models at capturing all incidences of known damage. The next best performing model (AHF) both under-predicted and over-predicted damage for TCs of various types. 4MW and AHF produce strikingly different spatial and temporal patterns of damage potential when used to reconstruct past TCs from 1985–2015. The 4MW model greatly enhances both of the main capabilities TC damage models provide to managers, and is useful wherever TCs and coral reefs co-occur.

  19. Abrasion-resistant solgel antireflective films with a high laser-induced damage threshold for inertial confinement fusion

    SciTech Connect

    Xu Yao; Zhang Lei; Wu Dong; Sun Yu Han; Huang Zuxing; Jiang Xiaodong; Wei Xiaofeng; Li Zhihong; Dong Baozhong; Wu Zhonghua

    2005-09-01

    To prepare abrasion-resistant antireflective (AR) films for inertial confinement fusion, four solgel routes have been investigated on polysiloxane-modified and polyvinylalcohol- (PVA-) modified SiO{sub 2} sols. As confirmed with a transmissive electron microscope, different fractal structure characteristics of the modified SiO{sub 2} particles are disclosed by small-angle x-ray scattering technology. And it is these special fractal characteristics that determine the performance of AR films on the level of internal microstructure. A {sup 29}Si magic angle spinning and nuclear magnetic resonance study has been successfully applied in explaining the fractal microstructure and its relation to the laser-induced damage threshold (LIDT) of AR films. The films modified by PVA120000 or acetic acid-catalyzed polysiloxane have higher LIDTs than those films modified by PVA16000 or hydrochloride acid-catalyzed polysiloxane. The films from PVA-modified SiO{sub 2} sols have a stronger abrasion resistance but lower antireflection than those films from polysiloxane-modified SiO{sub 2} sols. In addition, the films from polysiloxane-modified SiO{sub 2} sols can possess high transmittance and high LIDT if the polysiloxane synthesis condition is appropriately chosen, but the abrasion resistance is not as good as that from PVA modification. If strong abrasion resistance is necessary, a possible resolution may be to choose a more appropriate hydrophilic polymer than PVA. If not, polysiloxane-modified silica sol can also work when polysiloxane is synthesized under acetic acid catalysis.

  20. Predicting Avoidance of Skin Damage Feedback among College Students

    PubMed Central

    Dwyer, Laura A.; Shepperd, James A.; Stock, Michelle L.

    2015-01-01

    Background Showing people a personal ultraviolet (UV) photograph depicting skin damage can be an effective method for changing sun protection cognitions and behaviors. Purpose We examined whether people opt not to see their UV photograph if given a choice. We also examined predictors of avoidance of skin damage feedback. Methods College students (N = 257) completed questionnaires, viewed example UV photographs, and received the opportunity to see a UV photograph of their face. Results Over one-third of participants opted not to see their UV photograph. Greater perceived risk of sun damage and having fewer coping resources corresponded with greater avoidance, particularly among participants who reported infrequent sun protection behavior. Conclusion The health benefits of UV photography are realized only if people are willing to view the photograph. Our findings suggest the need for interventions that increase receptivity to viewing one’s UV photograph. PMID:25894276

  1. Time-dependent damage in predictions of fatigue behaviour of normal and healing ligaments

    NASA Astrophysics Data System (ADS)

    Thornton, Gail M.; Bailey, Soraya J.; Schwab, Timothy D.

    2015-08-01

    Ligaments are dense fibrous tissues that connect bones across a joint and are exposed daily to creep and fatigue loading. Ligaments are tensile load-bearing tissues; therefore, fatigue loading will have a component of time-dependent damage from the non-zero mean stress and cycle-dependent damage from the oscillating stress. If time-dependent damage is not sufficient to completely predict the fatigue response, then cycle-dependent damage could be an important contributor. Using data from normal ligaments (current study and Thornton et al., Clin. Biomech. 22:932-940, 2007a) and healing ligaments (Thornton and Bailey, J. Biomech. Eng. 135:091004-1-091004-6, 2013), creep data was used to predict the fatigue response considering time-dependent damage. Relationships between creep lifetime and test stress or initial strain were modelled using exponential or power-law regression. In order to predict fatigue lifetimes, constant rates of damage were assumed and time-varying stresses were introduced into the expressions for time-dependent damage from creep. Then, the predictions of fatigue lifetime were compared with curvefits to the fatigue data where exponential or power-law regressions were used to determine the relationship between fatigue lifetime and test stress or initial strain. The fatigue prediction based on time-dependent damage alone greatly overestimated fatigue lifetime suggesting that time-dependent damage alone cannot account for all of the damage accumulated during fatigue and that cycle-dependent damage has an important role. At lower stress and strain, time-dependent damage was a greater relative contributor for normal ligaments than healing ligaments; however, cycle-dependent damage was a greater relative contributor with incremental increases in stress or strain for normal ligaments than healing ligaments.

  2. The Effect of Delamination on Damage Path and Failure Load Prediction for Notched Composite Laminates

    NASA Technical Reports Server (NTRS)

    Satyanarayana, Arunkumar; Bogert, Philip B.; Chunchu, Prasad B.

    2007-01-01

    The influence of delamination on the progressing damage path and initial failure load in composite laminates is investigated. Results are presented from a numerical and an experimental study of center-notched tensile-loaded coupons. The numerical study includes two approaches. The first approach considers only intralaminar (fiber breakage and matrix cracking) damage modes in calculating the progression of the damage path. In the second approach, the model is extended to consider the effect of interlaminar (delamination) damage modes in addition to the intralaminar damage modes. The intralaminar damage is modeled using progressive damage analysis (PDA) methodology implemented with the VUMAT subroutine in the ABAQUS finite element code. The interlaminar damage mode has been simulated using cohesive elements in ABAQUS. In the experimental study, 2-3 specimens each of two different stacking sequences of center-notched laminates are tensile loaded. The numerical results from the two different modeling approaches are compared with each other and the experimentally observed results for both laminate types. The comparisons reveal that the second modeling approach, where the delamination damage mode is included together with the intralaminar damage modes, better simulates the experimentally observed damage modes and damage paths, which were characterized by splitting failures perpendicular to the notch tips in one or more layers. Additionally, the inclusion of the delamination mode resulted in a better prediction of the loads at which the failure took place, which were higher than those predicted by the first modeling approach which did not include delaminations.

  3. Critical Thresholds of Antioxidant and Immune Function Parameters for Se deficiency Prediction in Dairy Cows.

    PubMed

    Wu, Ling; Zhang, Hongyou; Xu, Chuang; Xia, Cheng

    2016-08-01

    The aim of this study was to determine the plasma selenium (Se) levels of lactating cows and to evaluate its association with antioxidant ability and immune function. In a descriptive study, 20 healthy Holstein cows with normal Se level (C) and 30 Holstein cows with subclinical Se deficiency (T) were randomly selected between 14 and 21 days postpartum from a dairy farm, according to a cutoff point of 70 mg/L Se in plasma. Analysis of biochemical parameters of antioxidant and immune function were performed on all the cows, and the risk prediction thresholds for subclinical Se deficiency were determined by area under receiver operating characteristic curve. Cows in the T group had significantly lower plasma Se concentrations compared with cows in the C group (52.16 ± 8.81 vs. 80.37 ± 8.46 μg/L, P = 0.02). There was a marked decrease in plasma glutathione peroxidase (GSH-Px) activity in the T group that correlated positively with the plasma Se level (R = 0.65, P = 0.00), and a significant increase of plasma methane dicarboxylic aldehyde (MDA), total nitric oxide synthase, and lipid peroxidation that correlated negatively with plasma Se levels (R = -0.47, P = 0.01; R = -0.33, P = 0.04; R = -0.40, P = 0.03). Furthermore, there were significantly lower plasma tumor necrosis factor-α and immunoglobulin G levels in the T group that correlated positively with plasma Se levels (R = 0.41, P = 0.01 and R = 0.45, P = 0.01), and a markedly lower plasma interleukin-6 level that correlated negatively with plasma Se levels (R = -0.38, P = 0.02). In addition, if plasma GSH-Px activity was less than 42.37 U/ml, the risk of Se deficiency was significantly increased in lactating cows. These results suggest that low plasma Se levels may reduce the antioxidant ability and immune function, and the risk of low plasma Se level may be predicted effectively by plasma GSH-Px activity in lactating cows. PMID:26743861

  4. Impact of different cleaning processes on the laser damage threshold of antireflection coatings for Z-Backlighter optics at Sandia National Laboratories

    NASA Astrophysics Data System (ADS)

    Field, Ella; Bellum, John; Kletecka, Damon

    2014-12-01

    We have examined how three different cleaning processes affect the laser-induced damage threshold (LIDT) 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. Coatings that received cleaning exhibited the highest LIDTs compared to coatings that were not cleaned. In some cases, there is nearly a twofold increase in the LIDT between the cleaned and uncleaned coatings (19.4 J/cm2 compared to 39.1 J/cm2). Higher LIDTs were realized after 4 months of aging. The most effective cleaning process involved washing the coated surface with mild detergent, and then soaking the optic in a mixture of ethyl alcohol and deionized water. Also, the laser damage results indicate that the presence of nonpropagating (NP) damage sites dominates the LIDTs of almost every optic, despite the cleaning process used. NP damage sites can be attributed to defects such as nodules in the coating or surface contamination, which suggests that pursuing further improvements to the deposition or cleaning processes are worthwhile to achieve even higher LIDTs.

  5. Damage Thresholds and Morphology of the Front- and Back-Irradiated SiO2 Thin Films Containing Gold Nanoparticles as Artificial Absorbing Defects

    SciTech Connect

    Papernov, S.; Schmid, A.W.; Oliver, J.B.; Rigatti, A.L.

    2008-01-30

    Previous ultraviolet-pulsed, laser-damage studies using model thin films with gold nanoparticles as artificial absorbing defects revealed damage morphology in a form of submicrometer-scaled craters. It was also demonstrated that for defects smaller than 20 nm, crater formation is preceded by plasma-ball formation around absorbing defects. In this work an attempt is made to verify symmetry of the plasma ball by conducting film irradiation from the side of the air/film or substrate/film interfaces. In each case, crater-formation thresholds are derived and crater morphology is analyzed by means of atomic force microscopy.

  6. Damage threshold and focusability of mid-infrared free-electron laser pulses gated by a plasma mirror with nanosecond switching pulses

    SciTech Connect

    Wang, Xiaolong; Nakajima, Takashi; Zen, Heishun; Kii, Toshiteru; Ohgaki, Hideaki

    2013-11-04

    The presence of a pulse train structure of an oscillator-type free-electron laser (FEL) results in the immediate damage of a solid target upon focusing. We demonstrate that the laser-induced damage threshold can be significantly improved by gating the mid-infrared FEL pulses with a plasma mirror. Although the switching pulses we employ have a nanosecond duration which does not guarantee the clean wavefront of the gated FEL pulses, the high focusability is experimentally confirmed through the observation of spectral broadening by a factor of 2.1 when we tightly focus the gated FEL pulses onto the Ge plate.

  7. Mercury Bromide (HgBr{sub 2}): A promising nonlinear optical material in IR region with a high laser damage threshold

    SciTech Connect

    Liu, T.; Zhang, G.; Zhu, T.; Niu, F.; Qin, J.; Wu, Y.; Chen, C.

    2008-09-01

    Nonlinear optical (NLO) crystals have played a key role in laser technology, and the existing materials for the IR range showed relatively low laser damage threshold in common. A NLO material HgBr{sub 2} is presented here. It shows a powder second harmonic generation about ten times as large as that of KH{sub 2}PO{sub 4}, a wide transparency in whole mid-IR region (from 2.5 to 25 {mu}m), and a good stability to the environment. Most importantly it exhibits a high laser damage threshold of about 0.3 GW/cm{sup 2}. Therefore, it is believed that HgBr{sub 2} is a promising candidate for NLO materials in the IR region.

  8. Cumulative-strain-damage model of ductile fracture: simulation and prediction of engineering fracture tests

    SciTech Connect

    Wilkins, M.L.; Streit, R.D.; Reaugh, J.E.

    1980-10-03

    A cumulative-strain-damage criterion is used to predict the initiation and propagation of fracture in ductile materials. The model is consistent with a model of ductile rupture that involves void growth and coalescence. Two- and three-dimensional finite difference computer codes, which use incremental-plasticity theory to describe large strains with rotation, are used to trace the history of damage in a material due to external forces. Fracture begins when the damage exceeds a critical value over a critical distance and proceeds as the critical-damage state is reached elsewhere. This unified approach to failure prediction can be applied to an arbitrary geometry if the material behavior has been adequately characterized. The damage function must be calibrated for a particular material using various material property tests. The fracture toughness of 6061-T651 aluminum is predicted.

  9. Damage prediction in cross-plied curved composite laminates

    NASA Technical Reports Server (NTRS)

    Martin, Roderick H.; Jackson, Wade C.

    1991-01-01

    Analytical and experimental work is detailed which is required to predict delamination onset and growth in a curved cross plied composite laminate subjected to static and fatigue loads. The composite used was AS4/3501/6, graphite/epoxy. Analytically, a closed form stress analysis and 2-D and 3-D finite element analyses were conducted to determine the stress distribution in an undamaged curved laminate. The finite element analysis was also used to determine values of strain energy release rate at a delamination emanating from a matrix crack in a 90 deg ply. Experimentally, transverse tensile strength and fatigue life were determined from flat 90 deg coupons. The interlaminar tensile strength and fatigue life were determined from double cantilevered beam specimens. Cross plied curved laminates were tested statically and in fatigue to give a comparison to the analytical predictions. A comparison of the fracture mechanics life prediction technique and the strength based prediction technique is given.

  10. An analytical prediction of the oscillation and extinction thresholds of a clarinet

    NASA Astrophysics Data System (ADS)

    Dalmont, Jean-Pierre; Gilbert, Joël; Kergomard, Jean; Ollivier, Sébastien

    2005-11-01

    This paper investigates the dynamic range of the clarinet from the oscillation threshold to the extinction at high pressure level. The use of an elementary model for the reed-mouthpiece valve effect combined with a simplified model of the pipe assuming frequency independent losses (Raman's model) allows an analytical calculation of the oscillations and their stability analysis. The different thresholds are shown to depend on parameters related to embouchure parameters and to the absorption coefficient in the pipe. Their values determine the dynamic range of the fundamental oscillations and the bifurcation scheme at the extinction.

  11. An analytical prediction of the oscillation and extinction thresholds of a clarinet.

    PubMed

    Dalmont, Jean-Pierre; Gilbert, Joël; Kergomard, Jean; Ollivier, Sébastien

    2005-11-01

    This paper investigates the dynamic range of the clarinet from the oscillation threshold to the extinction at high pressure level. The use of an elementary model for the reed-mouthpiece valve effect combined with a simplified model of the pipe assuming frequency independent losses (Raman's model) allows an analytical calculation of the oscillations and their stability analysis. The different thresholds are shown to depend on parameters related to embouchure parameters and to the absorption coefficient in the pipe. Their values determine the dynamic range of the fundamental oscillations and the bifurcation scheme at the extinction. PMID:16334700

  12. Analysis of the damage threshold of the GaAs pseudomorphic high electron mobility transistor induced by the electromagnetic pulse

    NASA Astrophysics Data System (ADS)

    Xi, Xiao-Wen; Chai, Chang-Chun; Liu, Yang; Yang, Yin-Tang; Fan, Qing-Yang; Shi, Chun-Lei

    2016-08-01

    An electromagnetic pulse (EMP)-induced damage model based on the internal damage mechanism of the GaAs pseudomorphic high electron mobility transistor (PHEMT) is established in this paper. With this model, the relationships among the damage power, damage energy, pulse width and signal amplitude are investigated. Simulation results show that the pulse width index from the damage power formula obtained here is higher than that from the empirical formula due to the hotspot transferring in the damage process of the device. It is observed that the damage energy is not a constant, which decreases with the signal amplitude increasing, and then changes little when the signal amplitude reaches up to a certain level. Project supported by the National Basic Research Program of China (Grant No. 2014CB339900) and the Open Fund of Key Laboratory of Complex Electromagnetic Environment Science and Technology, China Academy of Engineering Physics (CAEP) (Grant No. 2015-0214.XY.K).

  13. Representation of Vegetation and Other Nonerodible Elements in Aeolian Shear Stress Partitioning Models for Predicting Transport Threshold

    NASA Technical Reports Server (NTRS)

    King, James; Nickling, William G.; Gillies, John A.

    2005-01-01

    The presence of nonerodible elements is well understood to be a reducing factor for soil erosion by wind, but the limits of its protection of the surface and erosion threshold prediction are complicated by the varying geometry, spatial organization, and density of the elements. The predictive capabilities of the most recent models for estimating wind driven particle fluxes are reduced because of the poor representation of the effectiveness of vegetation to reduce wind erosion. Two approaches have been taken to account for roughness effects on sediment transport thresholds. Marticorena and Bergametti (1995) in their dust emission model parameterize the effect of roughness on threshold with the assumption that there is a relationship between roughness density and the aerodynamic roughness length of a surface. Raupach et al. (1993) offer a different approach based on physical modeling of wake development behind individual roughness elements and the partition of the surface stress and the total stress over a roughened surface. A comparison between the models shows the partitioning approach to be a good framework to explain the effect of roughness on entrainment of sediment by wind. Both models provided very good agreement for wind tunnel experiments using solid objects on a nonerodible surface. However, the Marticorena and Bergametti (1995) approach displays a scaling dependency when the difference between the roughness length of the surface and the overall roughness length is too great, while the Raupach et al. (1993) model's predictions perform better owing to the incorporation of the roughness geometry and the alterations to the flow they can cause.

  14. A physically-based continuum damage mechanics model for numerical prediction of damage growth in laminated composite plates

    NASA Astrophysics Data System (ADS)

    Williams, Kevin Vaughan

    Rapid growth in use of composite materials in structural applications drives the need for a more detailed understanding of damage tolerant and damage resistant design. Current analytical techniques provide sufficient understanding and predictive capabilities for application in preliminary design, but current numerical models applicable to composites are few and far between and their development into well tested, rigorous material models is currently one of the most challenging fields in composite materials. The present work focuses on the development, implementation, and verification of a plane-stress continuum damage mechanics based model for composite materials. A physical treatment of damage growth based on the extensive body of experimental literature on the subject is combined with the mathematical rigour of a continuum damage mechanics description to form the foundation of the model. The model has been implemented in the LS-DYNA3D commercial finite element hydrocode and the results of the application of the model are shown to be physically meaningful and accurate. Furthermore it is demonstrated that the material characterization parameters can be extracted from the results of standard test methodologies for which a large body of published data already exists for many materials. Two case studies are undertaken to verify the model by comparison with measured experimental data. The first series of analyses demonstrate the ability of the model to predict the extent and growth of damage in T800/3900-2 carbon fibre reinforced polymer (CFRP) plates subjected to normal impacts over a range of impact energy levels. The predicted force-time and force-displacement response of the panels compare well with experimental measurements. The damage growth and stiffness reduction properties of the T800/3900-2 CFRP are derived using published data from a variety of sources without the need for parametric studies. To further demonstrate the physical nature of the model, a IM6

  15. Electrical Resistance of Ceramic Matrix Composites for Damage Detection and Life-Prediction

    NASA Technical Reports Server (NTRS)

    Smith, Craig; Morscher, Gregory N.; Xia, Zhenhai

    2008-01-01

    The electric resistance of woven SiC fiber reinforced SiC matrix composites were measured under tensile loading conditions. The results show that the electrical resistance is closely related to damage and that real-time information about the damage state can be obtained through monitoring of the resistance. Such self-sensing capability provides the possibility of on-board/in-situ damage detection or inspection of a component during "down time". The correlation of damage with appropriate failure mechanism can then be applied to accurate life prediction for high-temperature ceramic matrix composites.

  16. MLIBlast: A program to empirically predict hypervelocity impact damage to the Space Station

    NASA Technical Reports Server (NTRS)

    Rule, William K.

    1991-01-01

    MLIBlast is described, which consists of a number of DOC PC based MIcrosoft BASIC program modules written to provide spacecraft designers with empirical predictions of space debris damage to orbiting spacecraft. The Spacecraft wall configuration is assumed to consist of multilayer insulation (MLI) placed between a Whipple style bumper and a pressure wall. Predictions are based on data sets of experimental results obtained from simulating debris impact on spacecraft. One module of MLIBlast facilitates creation of the data base of experimental results that is used by the damage prediction modules of the code. The user has a choice of three different prediction modules to predict damage to the bumper, the MLI, and the pressure wall.

  17. Dense and nanometric electronic excitations induced by swift heavy ions in an ionic CaF2 crystal: Evidence for two thresholds of damage creation

    NASA Astrophysics Data System (ADS)

    Toulemonde, M.; Benyagoub, A.; Trautmann, C.; Khalfaoui, N.; Boccanfuso, M.; Dufour, C.; Gourbilleau, F.; Grob, J. J.; Stoquert, J. P.; Costantini, J. M.; Haas, F.; Jacquet, E.; Voss, K.-O.; Meftah, A.

    2012-02-01

    CaF2 crystals as representatives of the class of ionic nonamorphizable insulators were irradiated with many different swift heavy ions of energy above 0.5 MeV/u providing a broad range of electronic energy losses (Se). Beam-induced modifications were characterized by Channeling Rutherford Backscattering Spectrometry (C-RBS) and x-ray diffraction (XRD), complemented by transmission electron microscopy (TEM). Results from C-RBS give evidence of significant damage appearing above a Se threshold of 5 ± 2 keV/nm. A second critical Se appears around 18 ± 3 keV/nm; below this value the damage as function of ion fluence saturates at 20%, while above this the damage saturation level increases with Se, reaching ˜60% for ions of Se = 30 keV/nm. XRD measurements also show effects indicating two threshold values. Above 5 keV/nm, the widths of the XRD reflection peaks increase due to the formation of nanograins, as seen by TEM, while a significant decrease of the peak areas only occurs above 18 keV/nm. The track radii deduced from C-RBS measurements are in agreement with those extracted from the fluence evolution of the widths of the XRD peaks. Moreover, track radii deduced from the peak area analysis are slightly smaller but in agreement with previous track observations by high resolution electron microscopy. Calculations based on the inelastic thermal spike model suggest that the lower threshold at 5 keV/nm is linked to the quenching of the molten phase, whereas the threshold at 18 keV/nm can be interpreted as quenching of the boiling phase. The results of CaF2 are compared with other nonamorphizable materials such as LiF and UO2.

  18. Prediction of Size Effects in Notched Laminates Using Continuum Damage Mechanics

    NASA Technical Reports Server (NTRS)

    Camanho, D. P.; Maimi, P.; Davila, C. G.

    2007-01-01

    This paper examines the use of a continuum damage model to predict strength and size effects in notched carbon-epoxy laminates. The effects of size and the development of a fracture process zone before final failure are identified in an experimental program. The continuum damage model is described and the resulting predictions of size effects are compared with alternative approaches: the point stress and the inherent flaw models, the Linear-Elastic Fracture Mechanics approach, and the strength of materials approach. The results indicate that the continuum damage model is the most accurate technique to predict size effects in composites. Furthermore, the continuum damage model does not require any calibration and it is applicable to general geometries and boundary conditions.

  19. Prediction Of Formability In Sheet Metal Forming Processes Using A Local Damage Model

    SciTech Connect

    Teixeira, P.; Santos, Abel; Cesar Sa, J.; Andrade Pires, F.; Barata da Rocha, A.

    2007-05-17

    The formability in sheet metal forming processes is mainly conditioned by ductile fracture resulting from geometric instabilities due to necking and strain localization. The macroscopic collapse associated with ductile failure is a result of internal degradation described throughout metallographic observations by the nucleation, growth and coalescence of voids and micro-cracks. Damage influences and is influenced by plastic deformation and therefore these two dissipative phenomena should be coupled at the constitutive level. In this contribution, Lemaitre's ductile damage model is coupled with Hill's orthotropic plasticity criterion. The coupling between damaging and material behavior is accounted for within the framework of Continuum Damage Mechanics (CDM). The resulting constitutive equations are implemented in the Abaqus/Explicit code, for the prediction of fracture onset in sheet metal forming processes. The damage evolution law takes into account the important effect of micro-crack closure, which dramatically decreases the rate of damage growth under compressive paths.

  20. Structural Damage Prediction and Analysis for Hypervelocity Impact

    NASA Technical Reports Server (NTRS)

    Elfer, Norman

    1995-01-01

    It is necessary to integrate a wide variety of technical disciplines to provide an analysis of structural damage to a spacecraft due to hypervelocity impact. There are many uncertainties, and more detailed investigation is warranted, in each technical discipline. However, a total picture of the debris and meteoroid hazard is required to support manned spaceflight in general, and the international Space Station in particular. In the performance of this contract, besides producing a handbook, research and development was conducted in several different areas. The contract was broken into six separate tasks. Each task objectives and accomplishments will be reviewed in the following sections. The Handbook and separate task reports are contained as attachments to the final report. The final section summarizes all of the recommendations coming out of this study. The analyses and comments are general design guidelines and not necessarily applicable to final Space Station designs since several configuration and detailed design changes were being made during the course of this contract. Rather, the analyses and comments may indicate either a point-in-time concept analysis, available test data, or desirable protection goals, not hindered by the design and operation constraints faced by Space Station designers.

  1. A Progressive Damage Methodology for Residual Strength Predictions of Notched Composite Panels

    NASA Technical Reports Server (NTRS)

    Coats, Timothy W.; Harris, Charles E.

    1998-01-01

    The translaminate fracture behavior of carbon/epoxy structural laminates with through-penetration notches was investigated to develop a residual strength prediction methodology for composite structures. An experimental characterization of several composite materials systems revealed a fracture resistance behavior that was very similar to the R-curve behavior exhibited by ductile metals. Fractographic examinations led to the postulate that the damage growth resistance was primarily due to fractured fibers in the principal load-carrying plies being bridged by intact fibers of the adjacent plies. The load transfer associated with this bridging mechanism suggests that a progressive damage analysis methodology will be appropriate for predicting the residual strength of laminates with through-penetration notches. A progressive damage methodology developed by the authors was used to predict the initiation and growth of matrix cracks and fiber fracture. Most of the residual strength predictions for different panel widths, notch lengths, and material systems were within about 10% of the experimental failure loads.

  2. Evaluation of damage models by finite element prediction of fracture in cylindrical tensile test.

    PubMed

    Eom, Jaegun; Kim, Mincheol; Lee, Seongwon; Ryu, Hoyeun; Joun, Mansoo

    2014-10-01

    In this research, tensile tests of cylindrical specimens of a mild steel are predicted via the finite element method, with emphasis on the fracture predictions of various damage models. An analytical model is introduced for this purpose. An iterative material identification procedure is used to obtain the flow stress, making it possible to exactly predict a tensile test up to the fracture point, in the engineering sense. A node-splitting technique is used to generate the cracks on the damaged elements. The damage models of McClintock, Rice-Tracey, Cockcroft-Latham, Freudenthal, Brozzo et al. and Oyane et al. are evaluated by comparing their predictions from the tensile test perspective. PMID:25942914

  3. Forming Prediction of Magnesium Alloy Sheets using a Continuum Damage Mechanics Multistep Inverse Approach

    SciTech Connect

    Bapanapalli, Satish K.; Nguyen, Ba Nghiep

    2008-06-30

    This paper applies multistep inverse approach using a new method to generate the intermediate configurations to analyze the press forming of magnesium alloys. The developed approach considers a final configuration to be formed from a flat blank sheet. It accounts for a series of intermediate configurations that are estimated based on the initial and final configurations as well as tooling conditions using optimization techniques. The approach is based on the concept of minimization of the surface area of the sheet metal subject to the constraints that the punch and die surfaces are not penetrated. Due to the limited formability of magnesium alloys, it is important to realistically estimate the intermediate configurations so that a damage mechanics approach can be explored to predict damage accumulations that can cause rupture of the sheet during forming. Elastic-plastic constitutive laws are used with the modified Hill’s criterion and deformation theory of plasticity to describe the behavior of AZ31 magnesium alloys. Damage is captured by a damage variable that governs the equivalent stress. A damage-plasticity coupled approach is employed for the integration of the constitutive equations. The computed strain increment from two consecutive intermediate configurations is used to predict the resulting damage accumulations during forming. The continuum damage mechanics multistep inverse approach is applied to predict forming of AZ31 magnesium alloys.

  4. Prediction of feather damage in laying hens using optical flows and Markov models

    PubMed Central

    Lee, Hyoung-joo; Roberts, Stephen J.; Drake, Kelly A.; Dawkins, Marian Stamp

    2011-01-01

    Feather pecking in laying hens is a major welfare and production problem for commercial egg producers, resulting in mortality, loss of production as well as welfare issues for the damaged birds. Damaging outbreaks of feather pecking are currently impossible to control, despite a number of proposed interventions. However, the ability to predict feather damage in advance would be a valuable research tool for identifying which management or environmental factors could be the most effective interventions at different ages. This paper proposes a framework for forecasting the damage caused by injurious pecking based on automated image processing and statistical analysis. By frame-by-frame analysis of video recordings of laying hen flocks, optical flow measures are calculated as indicators of the movement of the birds. From the optical flow datasets, measures of disturbance are extracted using hidden Markov models. Based on these disturbance measures and age-related variables, the levels of feather damage in flocks in future weeks is predicted. Applying the proposed method to real-world datasets, it is shown that the disturbance measures offer improved predictive values for feather damage thus enabling an identification of flocks with probable prevalence of damage and injury later in lay. PMID:20659929

  5. Threshold effects for resistance to optical damage and nonvolatile holographic storage properties in In:Mn:Fe:LiNbO3 crystals

    SciTech Connect

    Zhen Xihe; Li Qiang; Xu Yuheng

    2005-07-20

    The threshold concentration for In2O3 was found in In:Mn:Fe:LiNbO3 crystals by measurement of the infrared spectra of the crystals. The resistance of the In:Mn:Fe:LiNbO3 crystals to optical damage is characterized by changes in photoinduced birefringence as well as by distortion of the transmitted beam pattern. The resistance increases remarkably when the concentration of In2O3 exceeds its threshold. The resistance to optical damage of a In(3.0 mol. %):Mn:Fe:LiNbO3 crystal is 2 orders of magnitude higher that of a Mn:Fe:LiNbO3 crystal. The dependence of defects on the resistance to optical damage of the In:Mn:Fe:LiNbO3 crystals is discussed in detail. Nonvolatile holographic storage was achieved for all crystals, and the sensitivity of the In(3.0 mol. %):Mn:Fe:LiNbO3 crystal is much higher than that of the others.

  6. Observation and analysis of structural changes in fused silica by continuous irradiation with femtosecond laser light having an energy density below the laser-induced damage threshold.

    PubMed

    Nomura, Wataru; Kawazoe, Tadashi; Yatsui, Takashi; Naruse, Makoto; Ohtsu, Motoichi

    2014-01-01

    The laser-induced damage threshold (LIDT) is widely used as an index for evaluating an optical component's resistance to laser light. However, a degradation in the performance of an optical component is also caused by continuous irradiation with laser light having an energy density below the LIDT. Therefore, here we focused on the degradation in performance of an optical component caused by continuous irradiation with femtosecond laser light having a low energy density, i.e., laser-induced degradation. We performed an in situ observation and analysis of an increase in scattering light intensity in fused silica substrates. In experiments conducted using a pulsed laser with a wavelength of 800 nm, a pulse width of 160 fs and pulse repetition rate of 1 kHz, we found that the scattered light intensity increased starting from a specific accumulated fluence, namely, that the laser-induced degradation had a threshold. We evaluated the threshold fluence F t as 6.27 J/cm(2) and 9.21 J/cm(2) for the fused silica substrates with surface roughnesses of 0.20 nm and 0.13 nm in R a value, respectively, showing that the threshold decreased as the surface roughness increased. In addition, we found that the reflected light spectrum changed as degradation proceeded. We analyzed the details of the degradation by measuring instantaneous reflectance changes with a pump-probe method; we observed an increase in the generation probability of photogenerated carriers in a degraded silica substrate and a damaged silica substrate and observed a Raman signal originating from a specific molecular structure of silica. From these findings, we concluded that compositional changes in the molecular structure occurred during degradation due to femtosecond laser irradiation having an energy density below the LIDT. PMID:25247116

  7. Comparative study of the laser damage threshold and optical characteristics of Ta2O5-SiO2 multilayers deposited using various methods

    NASA Astrophysics Data System (ADS)

    Botha, Roelene; Schwyn Thöny, Silvia; Grössl, Martin; Mourad, Safer; Maissen, Clau; Venter, Jacobus I.; Südmeyer, Thomas; Hoffmann, Martin; Bulkin, Pavel V.; Linz-Dittrich, Sabine; Bischof, David; Michler, Markus; Rinner, Stefan J.; Ettemeyer, Andreas

    2015-11-01

    Manufacturing processes from the private and academic sectors were used to deposit anti-reflective and high-reflective coatings composed of Ta2O5 - SiO2 multilayers. Used deposition techniques included three Ion Assisted Deposition (IAD) systems and an Ion Beam Sputtering (IBS) system. Coatings were performed on fused silica (Corning 7980) substrates polished by two different suppliers. LIDT Measurements were performed using a Q-Switched Nd:YAG laser operating at 1064nm. The paper presents a comparison of the coatings in terms of laser damage threshold values, optical properties and surface quality.

  8. Infrared laser damage thresholds for skin at wavelengths from 0.810 to 1.54 microns for femto-to-microsecond pulse durations

    NASA Astrophysics Data System (ADS)

    Cain, Clarence P.; Roach, William P.; Stolarski, David J.; Noojin, Gary D.; Kumru, Semih S.; Stockton, Kevin L.; Zohner, Justin J.; Rockwell, Benjamin A.

    2007-02-01

    In this paper we report on our combined measurements of the visible lesion thresholds for porcine skin for wavelengths in the infrared from 810 nm at 44 fs to 1318 nm at pulse durations of 50 ns and 350μs to 1540 nm including pulse durations of 31 ns and 600 μs. We also measure thresholds for various spot sizes from less than 1 mm to 5 mm in diameter. All three wavelengths and five pulse durations are used extensively in research and the military. We compare these minimum visible lesion thresholds with ANSI standards set for maximum permissible exposures in the infrared wavelengths. We have measured non-linear effects at the laser-tissue interface for pulse durations below 1μs and determined that damage at these short pulse durations are usually not thermal effects. Damage at the skin surface may include acoustical effects, laser ablation and/or low-density plasma effects, depending on the wavelength and pulse duration. Also the damage effects may be short-lived and disappear within a few days or may last for much longer time periods including permanent discolorations. For femtosecond pulses at 810 nm, damage was almost instant and at 1 hour had an ED50 of 8.2 mJ of pulse energy. After 24 hours, most of the lesions disappeared and the ED50 increased by almost a factor of 3 to 21.3 mJ. There was a similar trend for the 1.318 μ laser for spot sizes of 2 mm and 5 mm where the ED50 was larger after 24 hours. However, for the 1.54 μ laser with a spot size of 5 mm, the ED50 actually decreased by a small amount; from 6.3 Jcm-2 to 6.1 Jcm-2 after 24 hours. Thresholds also decreased for the 1314 nm laser at 350 μs for spot sizes of 0.7 mm and 1.3 mm diameter after 24 hours. Different results were obtained for the 1540 nm laser at 600 μs pulse durations where the ED50 decreased for spot sizes 1 mm and below, but increased slightly for the 5 mm diameter spot size from 6.4 Jcm-2 to 7.4 Jcm-2

  9. Glycosylated Hemoglobin Threshold for Predicting Diabetes and Prediabetes from the Fifth Korea National Health and Nutrition Examination Survey

    PubMed Central

    Hong, Sangmo; Kim, Chul Sik; Lee, Seong Jin; Park, Cheol-Young; Lee, Chang Beom; Ihm, Sung-Hee

    2016-01-01

    We aimed to estimate the threshold level of glycosylated hemoglobin (HbA1c) for the fasting plasma glucose of 100 and 126 mg/dL in the Korean adult population, using the 2011 Korea National Health and Nutrition Examination Survey. A total of 4,481 participants over 19 years of age without diabetic medications and conditions to influence the interpretation of HbA1c levels, such as anemia, renal insufficiency, liver cirrhosis, and cancers, were analyzed. A point-wise area under the receiver operating characteristic curve was used to estimate the optimal HbA1c cutoff value. A HbA1c threshold of 6.35% was optimal for predicting diabetes with a sensitivity of 86.9% and a specificity of 99.1%. Furthermore, the threshold of HbA1c was 5.65% for prediabetes, with a sensitivity of 69.3% and a specificity of 71%. Further prospective studies are needed to evaluate the HbA1c cutoff point for diagnosing prediabetes and diabetes in the Korean population. PMID:27126887

  10. Glycosylated Hemoglobin Threshold for Predicting Diabetes and Prediabetes from the Fifth Korea National Health and Nutrition Examination Survey.

    PubMed

    Hong, Sangmo; Kang, Jun Goo; Kim, Chul Sik; Lee, Seong Jin; Park, Cheol Young; Lee, Chang Beom; Ihm, Sung Hee

    2016-04-01

    We aimed to estimate the threshold level of glycosylated hemoglobin (HbA1c) for the fasting plasma glucose of 100 and 126 mg/dL in the Korean adult population, using the 2011 Korea National Health and Nutrition Examination Survey. A total of 4,481 participants over 19 years of age without diabetic medications and conditions to influence the interpretation of HbA1c levels, such as anemia, renal insufficiency, liver cirrhosis, and cancers, were analyzed. A point-wise area under the receiver operating characteristic curve was used to estimate the optimal HbA1c cutoff value. A HbA1c threshold of 6.35% was optimal for predicting diabetes with a sensitivity of 86.9% and a specificity of 99.1%. Furthermore, the threshold of HbA1c was 5.65% for prediabetes, with a sensitivity of 69.3% and a specificity of 71%. Further prospective studies are needed to evaluate the HbA1c cutoff point for diagnosing prediabetes and diabetes in the Korean population. PMID:27126887

  11. A Modified Nonlinear Damage Accumulation Model for Fatigue Life Prediction Considering Load Interaction Effects

    PubMed Central

    Huang, Hong-Zhong; Yuan, Rong

    2014-01-01

    Many structures are subjected to variable amplitude loading in engineering practice. The foundation of fatigue life prediction under variable amplitude loading is how to deal with the fatigue damage accumulation. A nonlinear fatigue damage accumulation model to consider the effects of load sequences was proposed in earlier literature, but the model cannot consider the load interaction effects, and sometimes it makes a major error. A modified nonlinear damage accumulation model is proposed in this paper to account for the load interaction effects. Experimental data of two metallic materials are used to validate the proposed model. The agreement between the model prediction and experimental data is observed, and the predictions by proposed model are more possibly in accordance with experimental data than that by primary model and Miner's rule. Comparison between the predicted cumulative damage by the proposed model and an existing model shows that the proposed model predictions can meet the accuracy requirement of the engineering project and it can be used to predict the fatigue life of welded aluminum alloy joint of Electric Multiple Units (EMU); meanwhile, the accuracy of approximation can be obtained from the proposed model though more simple computing process and less material parameters calling for extensive testing than the existing model. PMID:24574866

  12. Noninvasive prediction of prostatic DNA damage by oxidative stress challenge of peripheral blood lymphocytes.

    PubMed

    Waters, David J; Shen, Shuren; Xu, Huiping; Kengeri, Seema S; Cooley, Dawn M; Chiang, Emily C; Chen, Yu; Schlittler, Deborah; Oteham, Carol; Combs, Gerald F; Glickman, Lawrence T; Morris, J Steven; Bostwick, David G

    2007-09-01

    To move closer to the goal of individualized risk prediction for prostate cancer, we used an in vivo canine model to evaluate whether the susceptibility of peripheral blood lymphocytes (PBLs) to oxidative stress-induced DNA damage could identify those individuals with the highest prostatic DNA damage. This hypothesis was tested in a population of 69 elderly male beagle dogs after they had completed a 7-month randomized feeding trial to achieve the broad range of dietary selenium status observed in U.S. men. The alkaline Comet assay was used to directly compare the extent of DNA damage in PBLs with prostatic DNA damage in each dog. Using stepwise logistic regression, the sensitivity of PBLs to oxidative stress challenge with hydrogen peroxide (H(2)O(2)) predicted dogs in the highest tertile of prostatic DNA damage. Dogs with PBLs highly sensitive to H(2)O(2) were 7.6 times [95% confidence interval (95% CI), 1.5-38.3] more likely to have high prostatic DNA damage than those in the H(2)O(2)-resistant group. This risk stratification was observed in multivariate analysis that considered other factors that might influence DNA damage, such as age, toenail selenium concentration, and serum testosterone concentration. Our data show that the sensitivity of PBLs to oxidative stress challenge, but not endogenous DNA damage in PBLs, provides a noninvasive surrogate marker for prostatic DNA damage. These findings lend support to the concept that oxidative stress contributes to genotoxic damage, and that oxidative stress challenge may stratify men for prostate cancer risk. PMID:17855713

  13. Multivariate Feature Selection for Predicting Scour-Related Bridge Damage using a Genetic Algorithm

    NASA Astrophysics Data System (ADS)

    Anderson, I.

    2015-12-01

    Scour and hydraulic damage are the most common cause of bridge failure, reported to be responsible for over 60% of bridge failure nationwide. Scour is a complex process, and is likely an epistatic function of both bridge and stream conditions that are both stationary and in dynamic flux. Bridge inspections, conducted regularly on bridges nationwide, rate bridge health assuming a static stream condition, and typically do not include dynamically changing geomorphological adjustments. The Vermont Agency of Natural Resources stream geomorphic assessment data could add value into the current bridge inspection and scour design. The 2011 bridge damage from Tropical Storm Irene served as a case study for feature selection to improve bridge scour damage prediction in extreme events. The bridge inspection (with over 200 features on more than 300 damaged and 2,000 non-damaged bridges), and the stream geomorphic assessment (with over 300 features on more than 5000 stream reaches) constitute "Big Data", and together have the potential to generate large numbers of combined features ("epistatic relationships") that might better predict scour-related bridge damage. The potential combined features pose significant computational challenges for traditional statistical techniques (e.g., multivariate logistic regression). This study uses a genetic algorithm to perform a search of the multivariate feature space to identify epistatic relationships that are indicative of bridge scour damage. The combined features identified could be used to improve bridge scour design, and to better monitor and rate bridge scour vulnerability.

  14. Creep crack growth predictions in INCO 718 using a continuum damage model

    NASA Technical Reports Server (NTRS)

    Walker, K. P.; Wilson, D. A.

    1985-01-01

    Creep crack growth tests have been carried out in compact type specimens of INCO 718 at 1200 F (649 C). Theoretical creep crack growth predictions have been carried out by incorporating a unified viscoplastic constitutive model and a continuum damage model into the ARAQUS nonlinear finite element program. Material constants for both the viscoplastic model and the creep continuum damage model were determined from tests carried out on uniaxial bar specimens of INCO 718 at 1200 F (649 C). A comparison of the theoretical creep crack growth rates obtained from the finite element predictions with the experimentally observed creep crack growth rates indicates that the viscoplastic/continuum damage model can be used to successfully predict creep crack growth in compact type specimens using material constants obtained from uniaxial bar specimens of INCO 718 at 1200 F (649 C).

  15. Factors predicting kidney damage in Puumala virus infected patients in Southern Denmark.

    PubMed

    Skarphedinsson, S; Thiesson, H C; Shakar, S A; Tepel, M

    2015-10-01

    In Europe, infections with Puumala hantavirus cause nephropathia epidemica. Presently the risk factors predicting severe kidney damage after Puumala virus infection are not well known. The objective of the study was to investigate environmental and individual factors predicting severe kidney damage caused by serologically established Puumala infections. In a nationwide cohort study we investigated all serologically established Puumala infections in Southern Denmark from 1996 to 2012. A total of 184 patients had serologically verified Puumala virus infection. In patients with Puumala virus infections the decrease of platelet counts preceded acute kidney failure. Multivariable logistic regression demonstrated that recent activities in the forest, platelet counts, and flu-like symptoms predicted estimated glomerular filtration rates less than 30 mL/min/1.73 m(²), but not age, gender, fever, nor abdominal pain. Severe kidney damage in Puumala infections in Southern Denmark is associated with the risk of recent activities in the forest. PMID:26205664

  16. Tools for Predicting Optical Damage on Inertial Confinement Fusion-Class Laser Systems

    SciTech Connect

    Nostrand, M C; Carr, C W; Liao, Z M; Honig, J; Spaeth, M L; Manes, K R; Johnson, M A; Adams, J J; Cross, D A; Negres, R A; Widmayer, C C; Williams, W H; Matthews, M J; Jancaitis, K S; Kegelmeyer, L M

    2010-12-20

    Operating a fusion-class laser to its full potential requires a balance of operating constraints. On the one hand, the total laser energy delivered must be high enough to give an acceptable probability for ignition success. On the other hand, the laser-induced optical damage levels must be low enough to be acceptably handled with the available infrastructure and budget for optics recycle. Our research goal was to develop the models, database structures, and algorithmic tools (which we collectively refer to as ''Loop Tools'') needed to successfully maintain this balance. Predictive models are needed to plan for and manage the impact of shot campaigns from proposal, to shot, and beyond, covering a time span of years. The cost of a proposed shot campaign must be determined from these models, and governance boards must decide, based on predictions, whether to incorporate a given campaign into the facility shot plan based upon available resources. Predictive models are often built on damage ''rules'' derived from small beam damage tests on small optics. These off-line studies vary the energy, pulse-shape and wavelength in order to understand how these variables influence the initiation of damage sites and how initiated damage sites can grow upon further exposure to UV light. It is essential to test these damage ''rules'' on full-scale optics exposed to the complex conditions of an integrated ICF-class laser system. Furthermore, monitoring damage of optics on an ICF-class laser system can help refine damage rules and aid in the development of new rules. Finally, we need to develop the algorithms and data base management tools for implementing these rules in the Loop Tools. The following highlights progress in the development of the loop tools and their implementation.

  17. Multiscale Modeling of Advanced Materials for Damage Prediction and Structural Health Monitoring

    NASA Astrophysics Data System (ADS)

    Borkowski, Luke

    Advanced aerospace materials, including fiber reinforced polymer and ceramic matrix composites, are increasingly being used in critical and demanding applications, challenging the current damage prediction, detection, and quantification methodologies. Multiscale computational models offer key advantages over traditional analysis techniques and can provide the necessary capabilities for the development of a comprehensive virtual structural health monitoring (SHM) framework. Virtual SHM has the potential to drastically improve the design and analysis of aerospace components through coupling the complementary capabilities of models able to predict the initiation and propagation of damage under a wide range of loading and environmental scenarios, simulate interrogation methods for damage detection and quantification, and assess the health of a structure. A major component of the virtual SHM framework involves having micromechanics-based multiscale composite models that can provide the elastic, inelastic, and damage behavior of composite material systems under mechanical and thermal loading conditions and in the presence of microstructural complexity and variability. Quantification of the role geometric and architectural variability in the composite microstructure plays in the local and global composite behavior is essential to the development of appropriate scale-dependent unit cells and boundary conditions for the multiscale model. Once the composite behavior is predicted and variability effects assessed, wave-based SHM simulation models serve to provide knowledge on the probability of detection and characterization accuracy of damage present in the composite. The research presented in this dissertation provides the foundation for a comprehensive SHM framework for advanced aerospace materials. The developed models enhance the prediction of damage formation as a result of ceramic matrix composite processing, improve the understanding of the effects of architectural and

  18. Measuring single-shot, picosecond optical damage threshold in Ge, Si, and sapphire with a 5.1-μm laser

    SciTech Connect

    Agustsson, R.; Pogorelsky, I.; Arab, E.; Murokh, A.; O"Shea, B.; Ovodenko, A.; Rosenzweig, J.; Solovyov, V.; Tilton, R.

    2015-11-18

    Optical photonic structures driven by picosecond, GW-class lasers are emerging as promising novel sources of electron beams and high quality X-rays. Due to quadratic dependence on wavelength of the laser ponderomotive potential, the performance of such sources scales very favorably towards longer drive laser wavelengths. However, to take full advantage of photonic structures at mid-IR spectral region, it is important to determine optical breakdown limits of common optical materials. To this end, an experimental study was carried out at a wavelength of 5 µm, using a frequency-doubled CO2 laser source, with 5 ps pulse length. Single-shot optical breakdowns were detected and characterized at different laser intensities, and damage threshold values of 0.2, 0.3, and 7.0 J/cm2, were established for Ge, Si, and sapphire, respectively. As a result, the measured damage threshold values were stable and repeatable within individual data sets, and across varying experimental conditions.

  19. Laser-induced damage threshold of ZrO{sub 2} thin films prepared at different oxygen partial pressures by electron-beam evaporation

    SciTech Connect

    Zhang Dongping; Shao Jianda; Zhao Yuanan; Fan Shuhai; Hong Ruijing; Fan Zhengxiu

    2005-01-01

    ZrO{sub 2} films were deposited by electron-beam evaporation with the oxygen partial pressure varying from 3x10{sup -3} Pa to 11x10{sup -3} Pa. The phase structure of the samples was characterized by x-ray diffraction (XRD). The thermal absorption of the films was measured by the surface thermal lensing technique. A spectrophotometer was employed to measure the refractive indices of the samples. The laser-induced damage threshold (LIDT) was assessed using a 1064 nm Nd: yttritium-aluminum-garnet pulsed laser at pulse width of 12 ns. The influence of oxygen partial pressure on the microstructure and LIDT of ZrO{sub 2} films was investigated. XRD data revealed that the films changed from polycrystalline to amorphous as the oxygen partial pressure increased. The variation of refractive index at 550 nm wavelength indicated that the packing density of the films decreased gradually with increasing oxygen partial pressure. The absorptance of the samples decreased monotonically from 125.2 to 84.5 ppm with increasing oxygen partial pressure. The damage threshold values increased from 18.5 to 26.7 J/cm{sup 2} for oxygen partial pressures varying from 3x10{sup -3} Pa to 9x10{sup -3} Pa, but decreased to 17.3 J/cm{sup 2} in the case of 11x10{sup -3} Pa.

  20. A study on crystalline perfection, optical, dielectric, mechanical, laser damage threshold and NLO properties of glycine added potassium dihydrogen phosphate single crystals

    NASA Astrophysics Data System (ADS)

    Boopathi, K.; Rajesh, P.; Ramasamy, P.

    2012-06-01

    Single crystals of glycine doped potassium dihydrogen phosphate have been grown by slow evaporation solution technique, slow cooling along with seed rotation and Sankaranaryanan-Ramasamy method. The size of the grown crystal in slow cooling method was 35×25×20 mm3 and in SR method it was 20 mm in diameter and 110 mm in length. The grown crystals were characterized by HRXRD, UV-Visible, dielectric, Vickers microhardness, laser damage threshold and SHG studies. The crystalline perfection of the grown crystals has been analyzed by high resolution X-ray diffraction. The transmittance of the grown crystals is 66%, 70%, and 77% respectively and all the crystals have good transparency in the entire visible region. The crystal grown by SR method glycine added KDP has much higher hardness value than other method grown crystals. Higher laser damage threshold was observed in SR method grown glycine added KDP crystal compared to SR method grown pure KDP crystal. The second harmonic generation efficiency of the glycine doped KDP is increased compared to pure KDP.

  1. Measuring single-shot, picosecond optical damage threshold in Ge, Si, and sapphire with a 5.1-μm laser

    DOE PAGESBeta

    Agustsson, R.; Pogorelsky, I.; Arab, E.; Murokh, A.; O"Shea, B.; Ovodenko, A.; Rosenzweig, J.; Solovyov, V.; Tilton, R.

    2015-11-18

    Optical photonic structures driven by picosecond, GW-class lasers are emerging as promising novel sources of electron beams and high quality X-rays. Due to quadratic dependence on wavelength of the laser ponderomotive potential, the performance of such sources scales very favorably towards longer drive laser wavelengths. However, to take full advantage of photonic structures at mid-IR spectral region, it is important to determine optical breakdown limits of common optical materials. To this end, an experimental study was carried out at a wavelength of 5 µm, using a frequency-doubled CO2 laser source, with 5 ps pulse length. Single-shot optical breakdowns were detectedmore » and characterized at different laser intensities, and damage threshold values of 0.2, 0.3, and 7.0 J/cm2, were established for Ge, Si, and sapphire, respectively. As a result, the measured damage threshold values were stable and repeatable within individual data sets, and across varying experimental conditions.« less

  2. Can tail damage outbreaks in the pig be predicted by behavioural change?

    PubMed

    Larsen, Mona Lilian Vestbjerg; Andersen, Heidi Mai-Lis; Pedersen, Lene Juul

    2016-03-01

    Tail biting, resulting in outbreaks of tail damage in pigs, is a multifactorial welfare and economic problem which is usually partly prevented through tail docking. According to European Union legislation, tail docking is not allowed on a routine basis; thus there is a need for alternative preventive methods. One strategy is the surveillance of the pigs' behaviour for known preceding indicators of tail damage, which makes it possible to predict a tail damage outbreak and prevent it in proper time. This review discusses the existing literature on behavioural changes observed prior to a tail damage outbreak. Behaviours found to change prior to an outbreak include increased activity level, increased performance of enrichment object manipulation, and a changed proportion of tail posture with more tails between the legs. Monitoring these types of behaviours is also discussed for the purpose of developing an automatic warning system for tail damage outbreaks, with activity level showing promising results for being monitored automatically. Encouraging results have been found so far for the development of an automatic warning system; however, there is a need for further investigation and development, starting with the description of the temporal development of the predictive behaviour in relation to tail damage outbreaks. PMID:26831153

  3. Ultrasonic Method for Prediction of Residual Life of Creep Damaged Materials

    NASA Astrophysics Data System (ADS)

    Kim, Dong-Yeol; Kim, Hak-Joon; Song, Sung-Jin; Kim, Bum-Joon; Lim, Byeong-Soo

    2009-03-01

    In the previous study, residual life time of creep damaged 9Cr-2W steel specimens were evaluated using attenuation of ultrasound and area fraction of precipitates. Since attenuation coefficients and area fraction of precipitates were increased as increasing their aging time. However, cause of increasing attenuation of ultrasound is not only increase in precipitates but also grain growth. So, in this study, we calculated attenuation coefficients for grain growth using the single scattering model in order to find effect grain growth in the creep damaged materials on attenuation. Then, we extract attenuation coefficients for precipitates from the measured ultrasonic attenuation of creep damaged specimens by subtracting attenuation coefficients for grain boundaries using the calculated attenuation. And, we predicted residual life time of the creep damaged specimens by using the attenuation for precipitates.

  4. Predictive modeling techniques for nanosecond-laser damage growth in fused silica optics.

    PubMed

    Liao, Zhi M; Abdulla, Ghaleb M; Negres, Raluca A; Cross, David A; Carr, Christopher W

    2012-07-01

    Empirical numerical descriptions of the growth of laser-induced damage have been previously developed. In this work, Monte-Carlo techniques use these descriptions to model the evolution of a population of damage sites. The accuracy of the model is compared against laser damage growth observations. In addition, a machine learning (classification) technique independently predicts site evolution from patterns extracted directly from the data. The results show that both the Monte-Carlo simulation and machine learning classification algorithm can accurately reproduce the growth of a population of damage sites for at least 10 shots, which is extremely valuable for modeling optics lifetime in operating high-energy laser systems. Furthermore, we have also found that machine learning can be used as an important tool to explore and increase our understanding of the growth process. PMID:22772252

  5. Comparison of Damage Path Predictions for Composite Laminates by Explicit and Standard Finite Element Analysis Tools

    NASA Technical Reports Server (NTRS)

    Bogert, Philip B.; Satyanarayana, Arunkumar; Chunchu, Prasad B.

    2006-01-01

    Splitting, ultimate failure load and the damage path in center notched composite specimens subjected to in-plane tension loading are predicted using progressive failure analysis methodology. A 2-D Hashin-Rotem failure criterion is used in determining intra-laminar fiber and matrix failures. This progressive failure methodology has been implemented in the Abaqus/Explicit and Abaqus/Standard finite element codes through user written subroutines "VUMAT" and "USDFLD" respectively. A 2-D finite element model is used for predicting the intra-laminar damages. Analysis results obtained from the Abaqus/Explicit and Abaqus/Standard code show good agreement with experimental results. The importance of modeling delamination in progressive failure analysis methodology is recognized for future studies. The use of an explicit integration dynamics code for simple specimen geometry and static loading establishes a foundation for future analyses where complex loading and nonlinear dynamic interactions of damage and structure will necessitate it.

  6. A simple nonlocal damage model for predicting failure of notched laminates

    NASA Technical Reports Server (NTRS)

    Kennedy, T. C.; Nahan, M. F.

    1995-01-01

    The ability to predict failure loads in notched composite laminates is a requirement in a variety of structural design circumstances. A complicating factor is the development of a zone of damaged material around the notch tip. The objective of this study was to develop a computational technique that simulates progressive damage growth around a notch in a manner that allows the prediction of failure over a wide range of notch sizes. This was accomplished through the use of a relatively simple, nonlocal damage model that incorporates strain-softening. This model was implemented in a two-dimensional finite element program. Calculations were performed for two different laminates with various notch sizes under tensile loading, and the calculations were found to correlate well with experimental results.

  7. Noninvasive prediction of prostatic DNA damage by oxidative stress challenge of peripheral blood lymphocytes

    Technology Transfer Automated Retrieval System (TEKTRAN)

    To move closer to the goal of individualized risk prediction for prostate cancer, we used an in vivo canine model to evaluate whether genetic instability, expressed as the susceptibility of peripheral blood lymphocytes (PBLs) to oxidative stress-induced DNA damage, could identify those individuals w...

  8. Dispersal of NOW and Prediction and Prevention of NOW Damage in Almonds

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The current proceedings reports the results of experiments in 2007 examining: 1) use of pheromone and egg traps for in-season prediction of navel orangeworm damage to almonds; 2) movement of navel orangeworm females in and between adjacent blocks under mating disruption and conventional control, and...

  9. Isothermal Fatigue, Damage Accumulation, and Life Prediction of a Woven PMC

    NASA Technical Reports Server (NTRS)

    Gyekenyesi, Andrew L.

    1998-01-01

    This dissertation focuses on the characterization of the fully reversed fatigue behavior exhibited by a carbon fiber/polyimide resin, woven laminate at room and elevated temperatures. Nondestructive video edge view microscopy and destructive sectioning techniques were used to study the microscopic damage mechanisms that evolved. The residual elastic stiffness was monitored and recorded throughout the fatigue life of the coupon. In addition, residual compressive strength tests were conducted on fatigue coupons with various degrees of damage as quantified by stiffness reduction. Experimental results indicated that the monotonic tensile properties were only minimally influenced by temperature, while the monotonic compressive and fully reversed fatigue properties displayed noticeable reductions due to the elevated temperature. The stiffness degradation, as a function of cycles, consisted of three stages; a short-lived high degradation period, a constant degradation rate segment composing the majority of the life, and a final stage demonstrating an increasing rate of degradation up to failure. Concerning the residual compressive strength tests at room and elevated temperatures, the elevated temperature coupons appeared much more sensitive to damage. At elevated temperatures, coupons experienced a much larger loss in compressive strength when compared to room temperature coupons with equivalent damage. The fatigue damage accumulation law proposed for the model incorporates a scalar representation for damage, but admits a multiaxial, anisotropic evolutionary law. The model predicts the current damage (as quantified by residual stiffness) and remnant life of a composite that has undergone a known load at temperature. The damage/life model is dependent on the applied multiaxial stress state as well as temperature. Comparisons between the model and data showed good predictive capabilities concerning stiffness degradation and cycles to failure.

  10. Annealing effects on microstructure and laser-induced damage threshold of HfO2/SiO2 multilayer mirrors.

    PubMed

    Jena, Shuvendu; Tokas, Raj Bahadur; Rao, K Divakar; Thakur, Sudhakar; Sahoo, Naba Kishore

    2016-08-01

    HfO2/SiO2 periodic multilayer high reflection mirrors have been prepared by a reactive electron-beam evaporation technique. The deposited mirrors were annealed in the temperature range from 300°C to 500°C. The effects of annealing on optical, microstructural, and laser-induced damage characteristics of the mirrors have been investigated. The high reflection band of the mirror shifts toward a shorter wavelength with increasing annealing temperature. As-deposited and annealed mirrors show polycrystalline structure with a monoclinic phase of HfO2. Crystalinity and grain size increase upon annealing. The laser-induced damage threshold (LIDT) has been assessed using a 532 nm pulsed laser at a pulse width of 7 ns. The LIDT value of the multilayer mirror increases from 44.1  J/cm2 to 77.6  J/cm2 with annealing up to 400°C. The improvement of LIDT with annealing is explained through oxygen vacancy defects as well as grain-size-dependent thermal conductivity. Finally, the observed laser damage morphology, such as circular scalds and ablated multilayer stacks with terrace structure, are analyzed. PMID:27505395

  11. [Prediction of histological liver damage in asymptomatic alcoholic patients by means of clinical and laboratory data].

    PubMed

    Iturriaga, H; Hirsch, S; Bunout, D; Díaz, M; Kelly, M; Silva, G; de la Maza, M P; Petermann, M; Ugarte, G

    1993-04-01

    Looking for a noninvasive method to predict liver histologic alterations in alcoholic patients without clinical signs of liver failure, we studied 187 chronic alcoholics recently abstinent, divided in 2 series. In the model series (n = 94) several clinical variables and results of common laboratory tests were confronted to the findings of liver biopsies. These were classified in 3 groups: 1. Normal liver; 2. Moderate alterations; 3. Marked alterations, including alcoholic hepatitis and cirrhosis. Multivariate methods used were logistic regression analysis and a classification and regression tree (CART). Both methods entered gamma-glutamyltransferase (GGT), aspartate-aminotransferase (AST), weight and age as significant and independent variables. Univariate analysis with GGT and AST at different cutoffs were also performed. To predict the presence of any kind of damage (Groups 2 and 3), CART and AST > 30 IU showed the higher sensitivity, specificity and correct prediction, both in the model and validation series. For prediction of marked liver damage, a score based on logistic regression and GGT > 110 IU had the higher efficiencies. It is concluded that GGT and AST are good markers of alcoholic liver damage and that, using sample cutoffs, histologic diagnosis can be correctly predicted in 80% of recently abstinent asymptomatic alcoholics. PMID:7903815

  12. Predicting the hurricane damage ratio of commercial buildings by claim payout from Hurricane Ike

    NASA Astrophysics Data System (ADS)

    Kim, J. M.; Woods, P. K.; Park, Y. J.; Kim, T. H.; Choi, J. S.; Son, K.

    2013-07-01

    The increasing occurrence of natural disaster events and related damages have led to a growing demand for models that predict financial loss. Although considerable research has studied the financial losses related to natural disaster events, and has found significant predictors, there has not yet been a comprehensive study that addresses the relationship among the vulnerabilities, natural disasters, and economic losses of the individual buildings. This study identified hurricanes and their vulnerability indicators in order to establish a metric to predict the related financial loss. We identify hurricane-prone areas by imaging the spatial distribution of the losses and vulnerabilities. This study utilized a Geographical Information System (GIS) to combine and produce spatial data, as well as a multiple linear regression method, to establish a hurricane damage prediction model. As the dependent variable, we utilized the following ratio to predict the real pecuniary loss: the value of the Texas Windstorm Insurance Association (TWIA) claim payout divided by the appraised values of the buildings. As independent variables, we selected the hurricane indicators and vulnerability indicators of the built environment and the geographical features. The developed statistical model and results can be used as important guidelines by insurance companies, government agencies, and emergency planners for predicting hurricane damage.

  13. A Progressive Damage Methodology for Residual Strength Predictions of Center-Crack Tension Composite Panels

    NASA Technical Reports Server (NTRS)

    Coats, Timothy William

    1996-01-01

    An investigation of translaminate fracture and a progressive damage methodology was conducted to evaluate and develop a residual strength prediction capability for laminated composites with through penetration notches. This is relevant to the damage tolerance of an aircraft fuselage that might suffer an in-flight accident such as an uncontained engine failure. An experimental characterization of several composite materials systems revealed an R-curve type of behavior. Fractographic examinations led to the postulate that this crack growth resistance could be due to fiber bridging, defined here as fractured fibers of one ply bridged by intact fibers of an adjacent ply. The progressive damage methodology is currently capable of predicting the initiation and growth of matrix cracks and fiber fracture. Using two difference fiber failure criteria, residual strength was predicted for different size panel widths and notch lengths. A ply discount fiber failure criterion yielded extremely conservative results while an elastic-perfectly plastic fiber failure criterion showed that the fiber bridging concept is valid for predicting residual strength for tensile dominated failure loads. Furthermore, the R-curves predicted by the model using the elastic-perfectly plastic fiber criterion compared very well with the experimental R-curves.

  14. Analysis and prediction of Multiple-Site Damage (MSD) fatigue crack growth

    NASA Technical Reports Server (NTRS)

    Dawicke, D. S.; Newman, J. C., Jr.

    1992-01-01

    A technique was developed to calculate the stress intensity factor for multiple interacting cracks. The analysis was verified through comparison with accepted methods of calculating stress intensity factors. The technique was incorporated into a fatigue crack growth prediction model and used to predict the fatigue crack growth life for multiple-site damage (MSD). The analysis was verified through comparison with experiments conducted on uniaxially loaded flat panels with multiple cracks. Configuration with nearly equal and unequal crack distribution were examined. The fatigue crack growth predictions agreed within 20 percent of the experimental lives for all crack configurations considered.

  15. Heart Rate-Based Prediction of Fixed Blood Lactate Thresholds in Professional Team-Sport Players.

    PubMed

    Garcia-Tabar, Ibai; Llodio, Iñaki; Sánchez-Medina, Luis; Ruesta, Maite; Ibañez, Javier; Gorostiaga, Esteban M

    2015-10-01

    The aim of this study was to investigate whether the speed associated with 90% of maximal heart rate (S90%HRmax) could predict speeds at fixed blood lactate concentrations of 3 mmol·L(-1) (S3mM) and 4 mmol·L(-1) (S4mM). Professional team-sport players of futsal (n = 10), handball (n = 16), and basketball (n = 10) performed a 4-stage discontinuous progressive running test followed, if exhaustion was not previously achieved, by an additional maximal continuous incremental running test to attain maximal heart rate (HRmax). The individual S3mM, S4mM, and S90%HRmax were determined by linear interpolation. S3mM (11.6 ± 1.5 km·h(-1)) and S4mM (12.5 ± 1.4 km·h(-1)) did not differ (p > 0.05) from S90%HRmax (12.0 ± 1.2 km·h(-1)). Very large significant (p < 0.001) relationships were found between S90%HRmax and S3mM (r = 0.82; standard error of the estimates [SEE] = 0.87 km·h(-1)), as well as between S90%HRmax and S4mM (r = 0.82; SEE = 0.87 km·h(-1)). S3mM and S4mM inversely correlated with %HRmax associated with running speeds of 10 and 12 km·h(-1) (r = 0.78-0.81; p < 0.001; SEE = 0.94-0.87 km·h(-1)). In conclusion, S3mM and S4mM can be accurately predicted by S90%HRmax in professional team-sport players. PMID:25844867

  16. Possible recovery or unavoidable fall? A model to predict the one step balance recovery threshold and its stepping characteristics.

    PubMed

    Vallée, Pascal; Tisserand, Romain; Robert, Thomas

    2015-11-01

    In order to prevent fall related injuries and their consequences, one needs to be able to predict the outcome of a given balance perturbation: a possible Balance Recovery (BR) or an unavoidable fall? Given that results from the existing experimental studies are difficult to compare and to generalize, we propose to address this question with a numerical tool. Built on existing concepts from the biomechanics and robotics literature, it includes the optimal use of BR reactions and particularly the possibility to perform a recovery step. It allows estimating 1) the possibility to recover a steady balance from a given initial state or perturbation using at most one recovery step; 2) the set of recovery steps leading to a BR. Using standard sets of parameters for young and elderly population, we assessed this model's predictions against experimental data from the literature in the anterior direction. Two classical representations of the human body (inverted pendulum (IP) vs. linear inverted pendulum (LIP)) were also compared. The results showed that the model correctly predicted the possibility to recover using a single protective step (1-Step BR threshold) and the characteristics (step length and time) of the protective step for both the young and the elderly. This tool has a real potential in the field of fall prevention to detect risky situation. It could also be used to get insights into the neuromuscular mechanisms involved in the BR process. PMID:26602371

  17. Coupling continuous damage and debris fragmentation for energy absorption prediction by cfrp structures during crushing

    NASA Astrophysics Data System (ADS)

    Espinosa, Christine; Lachaud, Frédéric; Limido, Jérome; Lacome, Jean-Luc; Bisson, Antoine; Charlotte, Miguel

    2015-05-01

    Energy absorption during crushing is evaluated using a thermodynamic based continuum damage model inspired from the Matzenmiller-Lubliner-Taylors model. It was found that for crash-worthiness applications, it is necessary to couple the progressive ruin of the material to a representation of the matter openings and debris generation. Element kill technique (erosion) and/or cohesive elements are efficient but not predictive. A technique switching finite elements into discrete particles at rupture is used to create debris and accumulated mater during the crushing of the structure. Switching criteria are evaluated using the contribution of the different ruin modes in the damage evolution, energy absorption, and reaction force generation.

  18. Investigations on structural, optical, dielectric, laser damage threshold and NLO properties of 2-amino-5-nitropyridinium p-tolunesulfonate (2A5NPT) single crystal

    NASA Astrophysics Data System (ADS)

    Pandian, Muthu Senthil; Sivasubramani, V.; Ramasamy, P.

    2016-05-01

    The highly efficient organic nonlinear optical (NLO) 2-amino-5-nitropyridinium p-tolunesulfonate single crystals have been grown by conventional slow evaporation technique using Millipore water as a solvent in the period of 60 days. The single crystal XRD confirms the unit cell parameters of the grown crystal. The morphology of the grown crystal was analyzed using Bruker-Kappa APEXII single crystal instrument and their planes are identified. The optical transmittance range and the cut-off wavelength are recorded using UV-Visible NIR characterization. The laser damage threshold (LDT) studies were carried out using Nd:YAG laser and LDT value was found to be 3.7 GW/cm2. The dielectric constant and dielectric loss of 2A5NPT single crystals were measured. The SHG efficiency was tested by powder Kurtz-Perry technique and the SHG efficiency is 15 times greater than that of standard KDP material.

  19. Comparison of retina damage thresholds simulating the femtosecond-laser in situ keratomileusis (fs-LASIK) process with two laser systems in the CW- and fs-regime

    NASA Astrophysics Data System (ADS)

    Sander, M.; Minet, O.; Zabarylo, U.; Müller, M.; Tetz, M. R.

    2012-04-01

    The femtosecond-laser in situ keratomileusis procedure affords the opportunity to correct ametropia by cutting transparent corneal tissue with ultra-short laser pulses. Thereby the tissue cut is generated by a laser-induced optical breakdown in the cornea with ultra-short laser pulses in the near-infrared range. Compared to standard procedures such as photorefractive keratectomy and laser in-situ keratomileusis with the excimer laser, where the risk potential for the eye is low due to the complete absorption of ultraviolet irradiation from corneal tissue, only a certain amount of the pulse energy is deposited in the cornea during the fs-LASIK process. The remaining energy propagates through the eye and interacts with the retina and the strong absorbing tissue layers behind. The objective of the presented study was to determine and compare the retina damage thresholds during the fs-LASIK process simulated with two various laser systems in the CW- and fs-regime.

  20. Ovipositional preferences, damage thresholds, and detection of the tomato-potato psyllid Bactericera cockerelli (Homoptera: Psyllidae) on selected tomato accessions.

    PubMed

    Liu, D; Trumble, J T

    2006-04-01

    The tomato-potato psyllid Bactericera [Paratrioza] cockerelli (Sulc) has recently caused losses exceeding 50% on fresh market tomatoes in California and Baja, Mexico by injecting a toxin that results in a condition known as 'psyllid yellows'. The objectives of this study were to: (i) document oviposition preferences on a range of tomato cultivars; (ii) determine threshold levels for psyllid densities that would cause psyllid yellows on tomatoes within the first three weeks following transplanting; and (iii) identify the most important 'psyllid yellows' symptoms that might be used in surveying and monitoring for this pest. Plant lines tested included the commonly-planted commercial cultivars 'Shady Lady' and 'QualiT 21', an older, previously commercial cultivar '7718 VFN', a common cultivar planted by consumers 'Yellow Pear', and a wild type plant accession, PI 134417. When given a choice, psyllids significantly preferred 'Yellow Pear' and avoided PI 134417 for oviposition. Under no-choice conditions psyllids laid significantly fewer eggs on PI 134417, but all the other plant lines were equally good substrates for laying eggs. Thus, oviposition preference is not likely to provide a functional management strategy in large plantings. On 'Shady Lady', psyllids preferred to oviposit on plants already infested with adults. On both 'Shady Lady' and '7718 VFN' oviposition was significantly greater on plants previously infested by nymphs as compared to uninfested control plants. This suggests that, at least for some cultivars, there is a physiological change in plant attractiveness following psyllid feeding. 'Yellow Pear' and 'QualiT 21' were relatively tolerant of psyllids, requiring 18 nymphs per plant to produce the disease symptoms. Only eight nymphs per plant were needed on 'Shady Lady' and '7718 VFN'. For all cultivars, the pest density showed strong correlations with measurements such as the number of yellowing leaves and leaflets and distorted leaves, which were as

  1. Physics-based damage predictions for simulating testing and evaluation (T and E) experiments

    SciTech Connect

    Addessio, F.L.; Schraad, M.W.; Lewis, M.W.

    1999-03-01

    This is the final report of a two-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). This report addresses the need to develop computational techniques and physics-based material models for simulating damage to weapons systems resulting from ballistic threats. Modern weapons systems, such as fighter aircraft, are becoming more dependent upon composite materials to reduce weight, to increase strength and stiffness, and to resist adverse conditions resulting from high temperatures and corrosion. Unfortunately, damaged components can have severe and detrimental effects, as evidenced by statistics from Desert Storm indicating that 75% of aircraft losses were attributable to fuel system vulnerability with hydrodynamic ram being the primary kill mechanism. Therefore, this project addresses damage predictions for composite systems that are subjected to ballistic threats involving hydrodynamic ram. A computational technique for simulating fluid-solid interaction phenomena and physics-based material models have been developed for this purpose.

  2. MLITemp: A computer program to predict the thermal effects associated with hypervelocity impact damage to space station MLI

    NASA Technical Reports Server (NTRS)

    Rule, W. K.; Giridharan, V.

    1991-01-01

    A family of user-friendly, DOS PC based, Microsoft BASIC programs written to provide spacecraft designers with empirical predictions of space debris damage to orbiting spacecraft are described. Spacecraft wall temperatures and condensate formation is also predicted. The spacecraft wall configuration is assumed to consist of multilayered insulation (MLI) placed between a Whipple style bumper and the pressure wall. Impact damage predictions are based on data sets of experimental results obtained from simulating debris impacts on spacecraft using light gas guns on earth. A module of the program facilitates the creation of the database of experimental results that is used by the damage prediction modules to predict damage to the bumper, the MLI, and the pressure wall. A finite difference technique is used to predict temperature distributions in the pressure wall, the MLI, and the bumper. Condensate layer thickness is predicted for the case where the pressure wall temperature drops below the dew point temperature of the spacecraft atmosphere.

  3. Visual detection following retinal damage: predictions of an inhomogeneous retino-cortical model

    NASA Astrophysics Data System (ADS)

    Arnow, Thomas L.; Geisler, Wilson S.

    1996-04-01

    A model of human visual detection performance has been developed, based on available anatomical and physiological data for the primate visual system. The inhomogeneous retino- cortical (IRC) model computes detection thresholds by comparing simulated neural responses to target patterns with responses to a uniform background of the same luminance. The model incorporates human ganglion cell sampling distributions; macaque monkey ganglion cell receptive field properties; macaque cortical cell contrast nonlinearities; and a optical decision rule based on ideal observer theory. Spatial receptive field properties of cortical neurons were not included. Two parameters were allowed to vary while minimizing the squared error between predicted and observed thresholds. One parameter was decision efficiency, the other was the relative strength of the ganglion-cell center and surround. The latter was only allowed to vary within a small range consistent with known physiology. Contrast sensitivity was measured for sinewave gratings as a function of spatial frequency, target size and eccentricity. Contrast sensitivity was also measured for an airplane target as a function of target size, with and without artificial scotomas. The results of these experiments, as well as contrast sensitivity data from the literature were compared to predictions of the IRC model. Predictions were reasonably good for grating and airplane targets.

  4. Predicted molecular signaling guiding photoreceptor cell migration following transplantation into damaged retina

    PubMed Central

    Unachukwu, Uchenna John; Warren, Alice; Li, Ze; Mishra, Shawn; Zhou, Jing; Sauane, Moira; Lim, Hyungsik; Vazquez, Maribel; Redenti, Stephen

    2016-01-01

    To replace photoreceptors lost to disease or trauma and restore vision, laboratories around the world are investigating photoreceptor replacement strategies using subretinal transplantation of photoreceptor precursor cells (PPCs) and retinal progenitor cells (RPCs). Significant obstacles to advancement of photoreceptor cell-replacement include low migration rates of transplanted cells into host retina and an absence of data describing chemotactic signaling guiding migration of transplanted cells in the damaged retinal microenvironment. To elucidate chemotactic signaling guiding transplanted cell migration, bioinformatics modeling of PPC transplantation into light-damaged retina was performed. The bioinformatics modeling analyzed whole-genome expression data and matched PPC chemotactic cell-surface receptors to cognate ligands expressed in the light-damaged retinal microenvironment. A library of significantly predicted chemotactic ligand-receptor pairs, as well as downstream signaling networks was generated. PPC and RPC migration in microfluidic ligand gradients were analyzed using a highly predicted ligand-receptor pair, SDF-1α – CXCR4, and both PPCs and RPCs exhibited significant chemotaxis. This work present a systems level model and begins to elucidate molecular mechanisms involved in PPC and RPC migration within the damaged retinal microenvironment. PMID:26935401

  5. Predicted molecular signaling guiding photoreceptor cell migration following transplantation into damaged retina

    NASA Astrophysics Data System (ADS)

    Unachukwu, Uchenna John; Warren, Alice; Li, Ze; Mishra, Shawn; Zhou, Jing; Sauane, Moira; Lim, Hyungsik; Vazquez, Maribel; Redenti, Stephen

    2016-03-01

    To replace photoreceptors lost to disease or trauma and restore vision, laboratories around the world are investigating photoreceptor replacement strategies using subretinal transplantation of photoreceptor precursor cells (PPCs) and retinal progenitor cells (RPCs). Significant obstacles to advancement of photoreceptor cell-replacement include low migration rates of transplanted cells into host retina and an absence of data describing chemotactic signaling guiding migration of transplanted cells in the damaged retinal microenvironment. To elucidate chemotactic signaling guiding transplanted cell migration, bioinformatics modeling of PPC transplantation into light-damaged retina was performed. The bioinformatics modeling analyzed whole-genome expression data and matched PPC chemotactic cell-surface receptors to cognate ligands expressed in the light-damaged retinal microenvironment. A library of significantly predicted chemotactic ligand-receptor pairs, as well as downstream signaling networks was generated. PPC and RPC migration in microfluidic ligand gradients were analyzed using a highly predicted ligand-receptor pair, SDF-1α - CXCR4, and both PPCs and RPCs exhibited significant chemotaxis. This work present a systems level model and begins to elucidate molecular mechanisms involved in PPC and RPC migration within the damaged retinal microenvironment.

  6. Predictive and Prognostic Significance of Glutathione Levels and DNA Damage in Cervix Cancer Patients Undergoing Radiotherapy

    SciTech Connect

    Vidyasagar, Mamidipudi Srinivasa; Kodali, Maheedhar; Prakash Saxena, Pu

    2010-10-01

    Purpose: To assess the predictive significance of serum glutathione (GSH) and tumor tissue DNA damage in the treatment of cervical cancer patients undergoing chemoradiotherapy. Methods and Materials: This study included subjects undergoing hysterectomy (for normal cervix tissue) and cervical cancer patients who underwent conventional concurrent chemoradiotherapy (cisplatin once per week for 5 weeks with concurrent external radiotherapy of 2 Gy per fraction for 5 weeks, followed by two applications of intracavitary brachytherapy once per week after 2 weeks' rest). Blood was collected after two fractions, whereas both blood and tissues were collected after five fractions of radiotherapy in separate groups of subjects. Serum for total GSH content and tissues were processed for single-cell gel electrophoresis (SCGE) assay for DNA damage analysis. Clinical tumor radioresponse was assessed 2 months after the completion of treatment as complete responders (CR) (100% shrinkage), partial responders (PR) (>50%), and nonresponders (NR) (<50%). Results: Serum GSH content depleted significantly after a total dose of 4 Gy and 10 Gy of radiotherapy with a single dose of cisplatin, which was significantly lesser in NR than of CR patients. Similarly, Olive Tail Moment, the index of DNA damage, indicated significantly higher values in the fifth fraction of radiotherapy (5-RT) than in pretreatment. The DNA damage after 5-RT in the NR subgroup was significantly lower than that of CR. Conclusions: Serum GSH analysis and tumor tissue SCGE assay found to be useful parameters for predicting chemoradioresponse prior to and also at an early stage of treatment of cervical cancers.

  7. Predicted molecular signaling guiding photoreceptor cell migration following transplantation into damaged retina.

    PubMed

    Unachukwu, Uchenna John; Warren, Alice; Li, Ze; Mishra, Shawn; Zhou, Jing; Sauane, Moira; Lim, Hyungsik; Vazquez, Maribel; Redenti, Stephen

    2016-01-01

    To replace photoreceptors lost to disease or trauma and restore vision, laboratories around the world are investigating photoreceptor replacement strategies using subretinal transplantation of photoreceptor precursor cells (PPCs) and retinal progenitor cells (RPCs). Significant obstacles to advancement of photoreceptor cell-replacement include low migration rates of transplanted cells into host retina and an absence of data describing chemotactic signaling guiding migration of transplanted cells in the damaged retinal microenvironment. To elucidate chemotactic signaling guiding transplanted cell migration, bioinformatics modeling of PPC transplantation into light-damaged retina was performed. The bioinformatics modeling analyzed whole-genome expression data and matched PPC chemotactic cell-surface receptors to cognate ligands expressed in the light-damaged retinal microenvironment. A library of significantly predicted chemotactic ligand-receptor pairs, as well as downstream signaling networks was generated. PPC and RPC migration in microfluidic ligand gradients were analyzed using a highly predicted ligand-receptor pair, SDF-1α - CXCR4, and both PPCs and RPCs exhibited significant chemotaxis. This work present a systems level model and begins to elucidate molecular mechanisms involved in PPC and RPC migration within the damaged retinal microenvironment. PMID:26935401

  8. Predicting and Mitigating Corrosion Related Damage in Geothermal Facilities, Phase-I

    SciTech Connect

    M. Shirmohamadi; S. Bratt; J. Ridgely

    2000-08-25

    Corrosion related damage (CRD) is probably the most important and costly damage mechanism for components operating in geothermal fields. This problem is further complicated as steam chemistry in such fields changes continuously with season, time, and load. Unfortunately, such changes are not predictable. The problem is further complicated in the area where early condensate (first moisture) forms. The chemistry of these first droplets is significantly different from that of built steam and this, again, cannot be predicted with reasonable accuracy. Therefore, a formidable challenge facing the geothermal field operators remains in knowing the chemistry of the condensate and, more importantly, how it affects specific field equipment such as rotor, piping, valves, etc. This project showed that testing in such an environment is feasible and concluded that continuous monitoring of steam conditions is needed to detect and prevent conditions leading to CRD of components. This project also developed tools and techniques for continuous monitoring of corrosion potential and detection of pitting events.

  9. Numerical prediction of rock mass damage due to accidental explosions in an underground ammunition storage chamber

    NASA Astrophysics Data System (ADS)

    Wu, Chengqing; Hao, Hong

    2006-03-01

    Accidental detonations in an underground ammunition storage chamber inside a rock mass may cause severe damage to the rock mass around the chamber, adjacent tunnels and chambers, ground surface, and in the worst case cause sympathetic detonation of explosives in adjacent storage chambers. To prevent such damage, underground ammunition storage chambers are often situated at minimum depth below the ground surface, and spaced at minimum distance from each other, so that damage, should it occur, is limited to the accidental chamber. Different codes and regulations for ammunition storage chambers specify minimum embedment depth and separation distance for underground ammunition storage chambers. They are usually given in terms of the rock mass properties and the weight of explosive stored in chambers. Some empirical formulae, usually based on the peak particle velocity of the stress wave or the maximum strain of the rock mass, are also available to estimate the damage zones in the rock mass from an explosion. All these empirical methods do not include the effects of explosion details, such as the loading density, chamber geometry and explosive distribution. In this paper, a previously calibrated numerical model is used to estimate the damage zones in a granite mass resulting from an accidental explosion in an underground ammunition storage chamber. Effects of various explosion conditions on rock mass damage are investigated. On the basis of the numerical results, some empirical formulae are derived to predict damage zones around the explosion chamber, as well as safe embedment depth of the storage chamber and safe separation distance between adjacent chambers. The numerical results are also compared with available empirical formulae and code specifications. It should be noted that the characteristics of stress wave propagation around an ammunition storage chamber has been published in a preceding paper (Int. J. Blast. Fragm. 5:57 90, 2001.

  10. Fatigue Life Prediction of Steel Bridges for Extreme Loading Using a New Damage Indicator

    NASA Astrophysics Data System (ADS)

    Karunananda, Pallaha Athawudagedara Kamal; Ohga, Mitao; Dissanayake, Punchi Bandage Ranjith; Siriwardane, Siriwardane Arachchilage Sudath Chaminda

    High cycle fatigue (HCF) damage caused by normal traffic loading is one of the major modes of failures in steel bridges. During bridge service life, there are extreme loading situations such as typhoons, earthquakes which cause higher amplitude loading than normal traffic loading. Due to this reason, critical members could undergo overstress cycles in the plastic range. Therefore, such members are subjected to low cycle fatigue (LCF) during these situations while subjecting to HCF in serviceable condition. Bridges, which are not seriously damaged, generally continue to be functioned after these extreme loading situations and fatigue life estimation is required to ensure their safety. Therefore, this paper presents a new damage indicator based fatigue model to predict life of steel bridges due to combined effect of extreme and normal traffic loadings. It consists of a modified strain life curve and a strain based damage indicator. Both the strain life curve and the damage indicator are newly proposed in the study. Modified strain life curve consists of Coffin Manson relation in the LCF regime and a new strain life curve in the HCF regime. Damage variable is based on von Mises equivalent strain and modified by factors to consider effects of loading non proportionality and loading path in multiaxial stress state. The new damage indicator can capture the loading sequence effect. The proposed model is verified with experimental test results of combined HCF and LCF of three materials; S304L stainless steel, Haynes 188 (a Cobolt superalloy) and S45C steel obtained from the literature. The verification of experimental results confirms the validity of the proposed model.

  11. Effect of deposition method and substrate surface quality on laser-induced damage threshold for repetitive 13-ns and 130-fs pulses

    NASA Astrophysics Data System (ADS)

    Melninkaitis, Andrius; Rakickas, Tomas; Miksys, Darius; Grigonis, Rimantas; Sirutkaitis, Valdas; Skrebutenas, Alfridas; Buzelis, Rytis; Drazdys, Ramutis; Abromavicius, Giedrius; Juskenas, Remigijus; Selskis, Algirdas

    2005-02-01

    A comparison of laser induced damage thresholds (LIDT) of ion assisted deposition (IAD) and standard electron beam deposition dielectric coatings on BK7 glass with different surface roughness was performed. Five types of high reflectance mirrors at 800 nm and two types of high reflectance mirrors at 1064 nm were tested. Mirror coatings were made of ZrO2 and SiO2. Automated LIDT measurements were performed according to the requirements of current ISO 11254-2 standard. Two lasers were used for the measurements: Nd:YAG (l = 1064 nm, t = 13 ns) and Ti:Sapphire (l = 800 nm, t = 130 fs ). All measurements were performed at 1-kHz pulse repetition rate (S-on-1 test). A fixed spot size was used for each laser. For 1064 nm it was ~ 70 um and for 800 nm ~ 500 um. The damage morphology and structure of coatings were characterized by an atomic force microscopy (AFM), Nomarski microscopy and X-ray diffraction (XRD).

  12. Influence of Crystallinity on the Bulk Laser-Induced Damage Threshold and Absorption of Laser Light in CsLiB6O10 Crystals

    NASA Astrophysics Data System (ADS)

    Kamimura, Tomosumi; Ono, Richi; Yap, Yoke Khin; Yoshimura, Masashi; Mori, Yusuke; Sasaki, Takatomo

    2001-02-01

    The relationships among the bulk laser-induced damage threshold (LIDT), dislocation density and absorption of laser light in CsLiB6O10 (CLBO) were investigated. A newly developed synthesis process allows the growth of CLBO crystals with a LIDT of 2.5-fold higher than that grown by the conventional top-seeded solution growth (TSSG) technique. High-quality CLBO possesses lower dislocation density (6.6× 103/cm2) than conventional CLBO (˜ 15.0× 103/cm2). The absorption of laser light in CLBO was characterized by measuring the temperature increase on the crystal output surface during the generation of fourth-harmonic (@266 nm) light of Nd:YAG lasers. At a UV power of 5 W, the maximum temperature increase was 6°C for high-quality CLBO, which was ˜ 30% lower than that generated on conventional CLBO crystal. Thus, the reduction of dislocation density can suppress the absorption of laser light, which helps to enhance the resistance of CLBO against laser-induced damage and alleviate thermal dephasing during the high-power generation of UV light.

  13. Structural, optical, thermal, photoconductivity, laser damage threshold and fluorescence analysis of an organic material: β-P-amino benzoic acid single crystal

    NASA Astrophysics Data System (ADS)

    Chandran, SenthilKumar; Paulraj, Rajesh; Ramasamy, P.

    2016-02-01

    β-P-amino benzoic acid, an organic single crystal was grown by slow evaporation technique. Single crystal X-ray diffraction studies show that the grown crystal has β-polymorph of P-amino benzoic acid [β-PABA] form and the lattice parameters are a = 6.30 Å, b = 8.61 Å, c = 12.43 Å α = γ = 90° and β = 100.20°. FTIR analysis confirms that bands at 1588 cm-1, 1415 cm-1 are assigned to ring skeletal vibrations of title compound. The molecular structure of the grown crystal has been identified by Nuclear Magnetic Resonance spectral study. The optical absorbance spectrum from 200 to 1100 nm shows that there is an edge absorbance in UV region. Optical band gap of the crystal has been assessed from the absorbance spectrum. The thermal properties of crystals were evaluated from TG-DTA analysis, it exhibits that there is no weight loss up to 187 °C. Laser damage threshold indicates that the grown crystal has no surface damage up to 35 mJ. Photoconductivity and fluorescence spectral experiments are also carried out and the results are discussed.

  14. A Micromechanics-Based Damage Model For The Strength Prediction of Composite Laminates

    NASA Technical Reports Server (NTRS)

    Camanho, Pedro P.; Mayugo, Joan A.; Maimi, Pere; Davila, Carlos G.

    2006-01-01

    A new damage model based on a micromechanical analysis of cracked [+/-0deg/90deg(sub n)]s laminates subjected to multiaxial loads is proposed. The model predicts the onset and accumulation of transverse matrix cracks in uniformly stressed laminates, the effect of matrix cracks on the stiffness of the laminate, as well as the ultimate failure of the laminate. The model also accounts for the effect of the ply thickness on the ply strength. Predictions relating the elastic properties of several laminates and multiaxial loads are presented.

  15. Application of cyclic damage accumulation life prediction model to high temperature components

    NASA Technical Reports Server (NTRS)

    Nelson, Richard S.

    1989-01-01

    A high temperature, low cycle fatigue life prediction method was developed. This method, Cyclic Damage Accumulation (CDA), was developed for use in predicting the crack initiation lifetime of gas turbine engine materials, but it can be applied to other materials as well. The method is designed to account for the effects on creep-fatigue life of complex loading such as thermomechanical fatigue, hold periods, waveshapes, mean stresses, multiaxiality, cumulative damage, coatings, and environmental attack. Several features of this model were developed to make it practical for application to actual component analysis, such as the ability to handle nonisothermal loading (including TMF), arbitrary cycle paths, and multiple damage modes. The CDA life prediction model was derived from extensive specimen tests conducted on cast nickel-base superalloy B1900 + Hf. These included both monotonic tests (tensile and creep) and strain-controlled fatigue experiments (uniaxial, biaxial, TMF, mixed creep-fatigue, and controlled mean stress). Additional specimen tests were conducted on wrought INCO 718 to verify the applicability of the final CDA model to other high-temperature alloys. The model will be available to potential users in the near future in the form of a FORTRAN-77 computer program.

  16. Tension Strength, Failure Prediction and Damage Mechanisms in 2D Triaxial Braided Composites with Notch

    NASA Technical Reports Server (NTRS)

    Norman, Timothy L.; Anglin, Colin

    1995-01-01

    The unnotched and notched (open hole) tensile strength and failure mechanisms of two-dimensional (2D) triaxial braided composites were examined. The effect of notch size and notch position were investigated. Damage initiation and propagation in notched and unnotched coupons were also examined. Theory developed to predict the normal stress distribution near an open hole and failure for tape laminated composites was evaluated for its applicability to 2D triaxial braided textile composite materials. Four different fiber architectures were considered; braid angle, yarn and braider size, percentage of longitudinal yarns and braider angle varied. Tape laminates equivalent to textile composites were also constructed for comparison. Unnotched tape equivalents were stronger than braided textiles but exhibited greater notch sensitivity. Notched textiles and tape equivalents have roughly the same strength at large notch sizes. Two common damage mechanisms were found: braider yarn cracking and near notch longitudinal yarn splitting. Cracking was found to initiate in braider yarns in unnotched and notched coupons, and propagate in the direction of the braider yarns until failure. Damage initiation stress decreased with increasing braid angle. No significant differences in prediction of near notch strain between textile and tape equivalents could be detected for small braid angle, but the correlations were weak for textiles with large braid angle. Notch strength could not be predicted using existing anisotropic theory for braided textiles due to their insensitivity to notch.

  17. Prediction of plasma-induced damage distribution during silicon nitride etching using advanced three-dimensional voxel model

    SciTech Connect

    Kuboi, Nobuyuki Tatsumi, Tetsuya; Kinoshita, Takashi; Shigetoshi, Takushi; Fukasawa, Masanaga; Komachi, Jun; Ansai, Hisahiro

    2015-11-15

    The authors modeled SiN film etching with hydrofluorocarbon (CH{sub x}F{sub y}/Ar/O{sub 2}) plasma considering physical (ion bombardment) and chemical reactions in detail, including the reactivity of radicals (C, F, O, N, and H), the area ratio of Si dangling bonds, the outflux of N and H, the dependence of the H/N ratio on the polymer layer, and generation of by-products (HCN, C{sub 2}N{sub 2}, NH, HF, OH, and CH, in addition to CO, CF{sub 2}, SiF{sub 2}, and SiF{sub 4}) as ion assistance process parameters for the first time. The model was consistent with the measured C-F polymer layer thickness, etch rate, and selectivity dependence on process variation for SiN, SiO{sub 2}, and Si film etching. To analyze the three-dimensional (3D) damage distribution affected by the etched profile, the authors developed an advanced 3D voxel model that can predict the time-evolution of the etched profile and damage distribution. The model includes some new concepts for gas transportation in the pattern using a fluid model and the property of voxels called “smart voxels,” which contain details of the history of the etching situation. Using this 3D model, the authors demonstrated metal–oxide–semiconductor field-effect transistor SiN side-wall etching that consisted of the main-etch step with CF{sub 4}/Ar/O{sub 2} plasma and an over-etch step with CH{sub 3}F/Ar/O{sub 2} plasma under the assumption of a realistic process and pattern size. A large amount of Si damage induced by irradiated hydrogen occurred in the source/drain region, a Si recess depth of 5 nm was generated, and the dislocated Si was distributed in a 10 nm deeper region than the Si recess, which was consistent with experimental data for a capacitively coupled plasma. An especially large amount of Si damage was also found at the bottom edge region of the metal–oxide–semiconductor field-effect transistors. Furthermore, our simulation results for bulk fin-type field-effect transistor side-wall etching

  18. Experimental and Theoretical Investigation of Periodic Nanostructuring of Au with Ultrashort UV Laser Pulses near the Damage Threshold

    NASA Astrophysics Data System (ADS)

    Ivanov, D. S.; Lipp, V. P.; Blumenstein, A.; Kleinwort, F.; Veiko, V. P.; Yakovlev, E.; Roddatis, V.; Garcia, M. E.; Rethfeld, B.; Ihlemann, J.; Simon, P.

    2015-12-01

    The mechanism of surface restructuring by ultrashort laser pulses involves a number of fast, nonequilibrium, and interrelated processes while the solid is in a transient state. As a result, the analysis of the experimental data cannot address all of the mechanisms of nanostructuring. In this paper, we present a direct comparison of a simulation and the experimental results of surface nanomodifications induced by a single laser pulse. The experimental results are obtained by using a mask-projection setup with a laser wavelength of 248 nm and a pulse length of 1.6 ps. Two-beam interference of this short wavelength allows for producing a large-area intensity grating of 40 μ m in diameter on a gold surface with a sinusoidal shape and a period of 500 nm. The formed structures are analyzed at the surface and in a cross section by a scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. Then a hybrid atomistic-continuum model capable of capturing the essential mechanisms responsible for the nanostructuring process is used to model the interaction of the laser pulse with a thick gold target. The good agreement between the modeling results and the experimental data justifies the proposed approach as a powerful tool revealing the physics behind the nanostructuring process at a gold surface and providing a microscopic insight into the dynamics of the structuring processes of metals in general. The presented model, therefore, is an important step towards a computational tool for predicting a materials response to an ultrashort laser pulse on the atomic scale. This detailed understanding of the dynamics of the process will pave the way towards predesigned topologies for functionalized surfaces on nanoscales and microscales.

  19. Prediction of myocardial damage depth induced by extracellular photosensitization reaction using fluorescence measurement in vivo

    NASA Astrophysics Data System (ADS)

    Takahashi, M.; Ogawa, E.; Nakamura, T.; Kawakami, H.; Machida, N.; Yajima, M.; Kurotsu, M.; Ito, A.; Kimura, T.; Arai, T.

    2014-03-01

    We experimentally studied the correlation between myocardial damage depth due to the extracellular photosensitization reaction (PR) using talaporfin sodium and fluorescence-fall amount (FA), which is calculated from the measured backscattering fluorescence intensity via a manipulatable 7 Fr. laser catheter during the PR operation in vivo to establish treatment depth predictor for a non-thermal tachyarrhythmia treatment. The PR was performed to left and/or right ventricle in the open-chest canine heart. The laser irradiation of 663+/-2 nm in wavelength via the laser catheter was operated 15 min after the intravenous administration of talaporfin sodium with concentration of 36.2+/-8.0 μg/ml in plasma. The irradiation was operated with irradiance of 5, 10, 20 W/cm2, and duration of 5, 10, 20 s. Backscattering fluorescence of 710+/-2 nm in wavelength was measured via the laser catheter during the PR. The FA was calculated multiplying the irradiation duration by the fluorescence-fall, which is subtraction of the fluorescence intensity at the kickoff and end of the irradiation. The canine heart was extracted 1 week after the PR and HE stained specimen was histologically evaluated. The correlation of the myocardial damage depth and FA was investigated. We found that FA obtained a logarithmic relation to the myocardial damage depth. We think that the FA might be available to predict the PR induced myocardial damage depth for the application of tachyarrhythmia treatment under catheterization in vivo.

  20. Neural network/acoustic emission burst pressure prediction for impact damaged composite pressure vessels

    SciTech Connect

    Walker, J.L.; Workman, G.L.; Russell, S.S.; Hill, E.V.K.

    1997-08-01

    Acoustic emission signal analysis has been used to measure the effect impact damage has on the burst pressure of 146 mm (5.75 in.) diameter graphite/epoxy and the organic polymer, Kevlar/epoxy filament wound pressure vessels. Burst pressure prediction models were developed by correlating the differential acoustic emission amplitude distribution collected during low level hydroproof tests to known burst pressures using backpropagation artificial neural networks. Impact damage conditions ranging from barely visible to obvious fiber breakage, matrix cracking, and delamination were included in this work. A simulated (inert) propellant was also cast into a series of the vessels from each material class, before impact loading, to provide boundary conditions during impact that would simulate those found on solid rocket motors. The results of this research effort demonstrate that a quantitative assessment of the effects that impact damage has on burst pressure can be made for both organic polymer/epoxy and graphite/epoxy pressure vessels. Here, an artificial neural network analysis of the acoustic emission parametric data recorded during low pressure hydroproof testing is used to relate burst pressure to the vessel`s acoustic signature. Burst pressure predictions within 6.0% of the actual failure pressure are demonstrated for a series of vessels.

  1. Damage Prediction and Estimation in Structural Mechanics Based on Data Mining

    SciTech Connect

    Sandhu, S S; Kanapady, R; Tamma, K K; Kamath, C; Kumar, V

    2001-07-23

    Damage in a material includes localized softening or cracks in a structural component due to high operational loads, or the presence of flaws in a structure due to various manufacturing processes. Methods that identify the presence, the location and the severity of damage in the structure are useful for non-destructive evaluation procedures that are typically employed in agile manufacturing and rapid prototyping systems. The current state-of-the art techniques for these inverse problems are computationally intensive or ill conditioned when insufficient data exists. Early work by a number of researchers has shown that data mining techniques can provide a potential solution to this problem. In this paper, they investigate the use of data mining techniques for predicting failure in a variety of 2D and 3D structures using artificial neural networks (ANNs) and decision trees. This work shows that if the correct features are chosen to build the model, and the model is trained on an adequate amount of data, the model can then correctly classify the failure event as well as predict location and severity of the damage in these structures.

  2. Pressure pain thresholds fluctuate with - but do not usefully predict - the clinical course of painful temporomandibular disorder

    PubMed Central

    Slade, Gary D.; Sanders, Anne E.; Ohrbach, Richard; Fillingim, Roger B.; Dubner, Ron; Gracely, Richard H.; Bair, Eric; Maixner, William; Greenspan, Joel D

    2014-01-01

    Central sensitization elicits pain hypersensitivity and is thought to be causally implicated in painful temporomandibular disorder (TMD). This causal inference is based on cross-sectional evidence that people with TMD have greater sensitivity than controls to noxious stimuli. We tested this inference in the OPPERA prospective cohort study of 3,258 adults with no lifetime history of TMD when enrolled (Visit 1). During five years of follow-up, one group labelled “persistent TMD cases” (n=72) developed first-onset TMD by Visit 2 that persisted ≥6 months until Visit 3. Another group labelled “transient TMD cases” (n=75) developed first-onset TMD at Visit 2 which resolved by Visit 3. Randomly sampled “controls” (n=126) remained TMD-free throughout all three visits. At each visit, pressure pain thresholds (PPTs) were measured by algometry at 10 cranial and bodily sites. In persistent TMD cases, mean PPTs reduced 43 kPa (P<0.0001) between Visits 1 and 2 and thereafter did not change significantly. In transient TMD cases, mean PPTs reduced 41 kPa (P<0.001) between Visits 1 and 2, and then increased 20 kPa (P<0.001) by Visit 3. These patterns were similar after excluding cranial sites symptomatic for TMD. Importantly, Visit 1 PPTs had no clinically useful prognostic value in predicting first-onset TMD (odds ratio [OR] 1.07, P=0.15). Among first-onset cases, Visit 2 PPTs were modest predictors of persistent TMD (OR=1=.36, P=0.002). In this longitudinal study, PPTs reduced when TMD developed then rebounded when TMD resolved. However, pre-morbid PPTs poorly predicted TMD incidence, countering the hypothesis that they signify mechanisms causing first-onset TMD. PMID:25130428

  3. A Finite Element Analysis for Predicting the Residual Compression Strength of Impact-Damaged Sandwich Panels

    NASA Technical Reports Server (NTRS)

    Ratcliffe, James G.; Jackson, Wade C.

    2008-01-01

    A simple analysis method has been developed for predicting the residual compression strength of impact-damaged sandwich panels. The method is tailored for honeycomb core-based sandwich specimens that exhibit an indentation growth failure mode under axial compression loading, which is driven largely by the crushing behavior of the core material. The analysis method is in the form of a finite element model, where the impact-damaged facesheet is represented using shell elements and the core material is represented using spring elements, aligned in the thickness direction of the core. The nonlinear crush response of the core material used in the analysis is based on data from flatwise compression tests. A comparison with a previous analysis method and some experimental data shows good agreement with results from this new approach.

  4. A Finite Element Analysis for Predicting the Residual Compressive Strength of Impact-Damaged Sandwich Panels

    NASA Technical Reports Server (NTRS)

    Ratcliffe, James G.; Jackson, Wade C.

    2008-01-01

    A simple analysis method has been developed for predicting the residual compressive strength of impact-damaged sandwich panels. The method is tailored for honeycomb core-based sandwich specimens that exhibit an indentation growth failure mode under axial compressive loading, which is driven largely by the crushing behavior of the core material. The analysis method is in the form of a finite element model, where the impact-damaged facesheet is represented using shell elements and the core material is represented using spring elements, aligned in the thickness direction of the core. The nonlinear crush response of the core material used in the analysis is based on data from flatwise compression tests. A comparison with a previous analysis method and some experimental data shows good agreement with results from this new approach.

  5. The Effect of General Statistical Fiber Misalignment on Predicted Damage Initiation in Composites

    NASA Technical Reports Server (NTRS)

    Bednarcyk, Brett A.; Aboudi, Jacob; Arnold, Steven M.

    2014-01-01

    A micromechanical method is employed for the prediction of unidirectional composites in which the fiber orientation can possess various statistical misalignment distributions. The method relies on the probability-weighted averaging of the appropriate concentration tensor, which is established by the micromechanical procedure. This approach provides access to the local field quantities throughout the constituents, from which initiation of damage in the composite can be predicted. In contrast, a typical macromechanical procedure can determine the effective composite elastic properties in the presence of statistical fiber misalignment, but cannot provide the local fields. Fully random fiber distribution is presented as a special case using the proposed micromechanical method. Results are given that illustrate the effects of various amounts of fiber misalignment in terms of the standard deviations of in-plane and out-of-plane misalignment angles, where normal distributions have been employed. Damage initiation envelopes, local fields, effective moduli, and strengths are predicted for polymer and ceramic matrix composites with given normal distributions of misalignment angles, as well as fully random fiber orientation.

  6. Predictive modeling of interfacial damage in substructured steels: application to martensitic microstructures

    NASA Astrophysics Data System (ADS)

    Maresca, F.; Kouznetsova, V. G.; Geers, M. G. D.

    2016-02-01

    Metallic composite phases, like martensite present in conventional steels and new generation high strength steels exhibit microscale, locally lamellar microstructures characterized by alternating layers of phases or crystallographic variants. The layers can be sub-micron down to a few nanometers thick, and they are often characterized by high contrasts in plastic properties. As a consequence, fracture in these lamellar microstructures generally occurs along the layer interfaces or within one of the layers, typically parallel to the interface. This paper presents a computational framework that addresses the lamellar nature of these microstructures, by homogenizing the plastic deformation at the mesoscale by using the microscale response of the laminates. Failure is accounted for by introducing a family of damaging planes that are parallel to the layer interface. Mode I, mode II and mixed-mode opening are incorporated. The planes along which failure occurs are captured using a smeared damage approach. Coupling of damage with isotropic or anisotropic plasticity models, like crystal plasticity, is straightforward. The damaging planes and directions do not need to correspond to crystalline slip planes, and normal opening is also included. Focus is given on rate-dependent formulations of plasticity and damage, i.e. converged results can be obtained without further regularization techniques. The validation of the model using experimental observations in martensite-austenite lamellar microstructures in steels reveals that the model correctly predicts the main features of the onset of failure, e.g. the necking point, the failure initiation region and the failure mode. Finally, based on the qualitative results obtained, some material design guidelines are provided for martensitic and multi-phase steels.

  7. Threshold doses and prediction of visually apparent liver dysfunction after stereotactic body radiation therapy in cirrhotic and normal livers using magnetic resonance imaging

    PubMed Central

    Doi, Hiroshi; Shiomi, Hiroya; Masai, Norihisa; Tatsumi, Daisaku; Igura, Takumi; Imai, Yasuharu; Oh, Ryoong-Jin

    2016-01-01

    The purpose of the present study was to investigate the threshold dose for focal liver damage after stereotactic body radiation therapy (SBRT) in cirrhotic and normal livers using magnetic resonance imaging (MRI). A total of 64 patients who underwent SBRT for liver tumors, including 54 cirrhotic patients with hepatocellular carcinoma (HCC) and 10 non-cirrhotic patients with liver metastases, were analyzed. MRI was performed 3−6 months after SBRT, using gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid-enhanced T1-weighted sequences. All MRI datasets were merged with 3D dosimetry data. All dose distributions were corrected to the biologically effective dose using the linear–quadratic model with an assumed α/β ratio of 2 Gy. The development of liver dysfunction was validly correlated with isodose distribution. The median biologically effective dose (BED2) that provoked liver dysfunction was 57.3 (30.0−227.9) and 114.0 (70.4−244.9) Gy in cirrhotic and normal livers, respectively (P = 0.0002). The BED2 associated with a >5% risk of liver dysfunction was 38.5 in cirrhotic livers and 70.4 Gy in normal livers. The threshold BED2 for liver dysfunction was not significantly different between Child−Pugh A and B patients (P = 0.0719). Moreover, the fractionation schedule was not significantly correlated with threshold BED2 for liver dysfunction in the cirrhotic liver (P = 0.1019). In the cirrhotic liver, fractionation regimen and Child−Pugh classification did not significantly influence the threshold BED2 for focal liver damage after SBRT. We suggest that the threshold BED2 for liver dysfunction after SBRT is 40 and 70 Gy in the cirrhotic and normal liver, respectively. PMID:26983986

  8. Investigation on crystalline perfection, optical transmittance, birefringence, temperature-dependent refractive index, laser damage threshold and pyroelectric characteristics of inversely soluble lithium sulfate monohydrate single crystals

    NASA Astrophysics Data System (ADS)

    Silambarasan, A.; Rajesh, P.; Bhatt, Rajeev; Bhaumik, Indranil; Karnal, A. K.; Ramasamy, P.; Gupta, P. K.

    2016-08-01

    Bulk prismatic lithium sulfate monohydrate (LSMH) single crystals were grown by seed rotation with slow heating method from aqueous solution. Small FWHM obtained from high-resolution X-ray diffraction spectrum shows that the crystals grown by this method have less defects and absence of low-angle grain boundaries. The high transmittance and low reflectance nature of the grown crystal was observed using UV-Vis-NIR spectrometer. The principal refractive indices of a LSMH crystal have been measured by a prism coupling method for the wavelengths of 0.407, 0.532, 0.828, 1.064 and 1.551 µm at room temperature, and Sellmeier equations are determined from the fitting of the data point. The refractive index data confirm that LSMH crystal is negative biaxial and the optic axis lies in YZ plane with an angle (2 V y ) of 51.74° with respect to y axis at 532 nm wavelength. The thermo-optic coefficients were determined from the temperature-dependent refractive indices measured in the range of 30-125 °C for the wavelengths of 532 and 1064 nm. The surface laser damage threshold studies reveal the higher optical radiation stability against 532-nm laser. The pyroelectric coefficients and pyroelectric figure of merit were determined from the pyroelectric current measurement by the Byer and Roundy method.

  9. Design and fabrication of thin-film polarizer at wavelength of 1540 nm and investigation of its laser-induced damage threshold

    NASA Astrophysics Data System (ADS)

    Sahraee, Masoume; Fallah, Hamid Reza; Moradi, Badri; Zabolian, Hosein; Mahmoodzade, Morteza Haji

    2014-12-01

    In this paper a thin-film polarizer at a wavelength of 1540 nm was designed and fabricated. These types of polarizer are usually used in laser systems to obtain linearly polarized light beams. Our design consists of a system of eighteen dielectric thin-film layers from repeated pairs of titanium dioxide and silicon dioxide layers that are deposited on a BK7 glass substrate. Design was carried out based on theoretical principles and computer calculations. Thin-film design software was used for designing the polarizer. The angle of incidence was supposed to be 56° that is the Browster angle for BK7 glass. Performance and laser-induced damage threshold of the polarizer were enhanced by a suitable selection of various parameters including thickness of each layer, their number and the electric field distribution of layers. After several designs, fabrications and refinement of parameters, the final polarizer was designed. Then the final sample of the polarizer was prepared using the electron beam evaporation (EBE) technique with Balzers BAK 760 coating machine. Spectral transmittance of the sample was measured by Shimadzu 3100 UV-VIS-NIR spectrophotometer. Investigation of spectral transmittance showed that at a wavelength of 1540nm, the transmission of P polarization is 87.82 and the transmission of S polarization is 0.43 which show a ratio ( T P / T S of 204. So, this ratio is an acceptable value for our desired polarizer.

  10. Improving Anti-Reflection MgF2 Thin Films by Laser Shock Peening and Investigation of its Laser Damage Threshold

    NASA Astrophysics Data System (ADS)

    Maleki, M. H.; Dizaji, H. R.; Ghorbani, A.

    2015-03-01

    This study is divided into two parts. In the first part, the influence of laser shock peening (LSP) on the surface properties of MgF2 thin films is studied. The MgF2 monolayer films with thickness of 100 nm were prepared on a BK7 glass substrate by physical vapor deposition (PVD). An ArF excimer laser with 110 mJ energy, 53 J/cm2 power density, 20 ns pulse duration and wavelength of 193 nm in TEM00 mode was used for the LSP experiments at different (20, 50, 90, and 120) number of the pulses. Transmittance of MgF2 thin films, before and after the LSP treatment, was evaluated by a spectrophotometer and the surface morphology of samples was examined by scanning electron microscope. In the second part, the effect of the LSP treatment on the laser induced damage threshold of a sample irradiated by 90 pulses of the ArF excimer laser was examined.

  11. Directional growth of organic NLO crystal by different growth methods: A comparative study by means of XRD, HRXRD and laser damage threshold

    NASA Astrophysics Data System (ADS)

    Arivanandhan, M.; Huang, Xinming; Uda, Satoshi; Bhagavannarayana, G.; Vijayan, N.; Sankaranarayanan, K.; Ramasamy, P.

    2008-10-01

    Unidirectional benzophenone single crystals grown by vertical Bridgman (VB), microtube-Czochralski (μT-CZ), uniaxially solution crystallization method of Sankaranarayanan-Ramasamy (SR) were characterized using X-ray diffraction (XRD), high-resolution XRD (HRXRD), laser damage threshold (LDT) studies and the results were compared. The XRD study exhibits the growth direction of the benzophenone crystal ingots. The HRXRD curves recorded by multicrystal X-ray diffractometer (MCD) revealed that the crystals grown by all the three methods contain internal structural grain boundaries. The SR grown sample shows relatively good crystalline nature with the full-width half-maximum (FWHM) of the main peak of 39 arcsec. While, the VB grown crystal contain multiple low-angle ( α⩾1 arcmin) grain boundaries, probably due to thermal stress during post-growth annealing caused by the difference in the lattice expansion coefficients of the crystal and the ampoule, whereas such thermal stress are absent in μT-CZ grown sample due to the free standing nature of the grown crystal. Hence, the μT-CZ grown crystals contain only one very low-angle ( α<1 arcmin) grain boundary. LDT study shows that the SR grown benzophenone crystal has higher LDT than the samples grown by other methods, probably due to relatively high-crystalline perfection of the SR grown crystals.

  12. Study on characteristic parameters influencing laser-induced damage threshold of KH2PO4 crystal surface machined by single point diamond turning

    PubMed Central

    Chen, Mingjun; Li, Mingquan; Cheng, Jian; Jiang, Wei; Wang, Jian; Xu, Qiao

    2011-01-01

    It has fundamental meaning to find the elements influencing the laser-induced damage threshold (LIDT) of KH2PO4 (KDP) crystal and to provide suitable characterization parameters for these factors in order to improve the LIDT of KDP. Using single-point diamond turning (SPDT) to process the KDP crystal, the machined surface quality has important effects on its LIDT. However, there are still not suitable characteristic parameters of surface quality of KDP to correspond with the LIDT nowadays. In this paper, guided by the Fourier model theory, we study deeply the relationship between the relevant characteristic parameters of surface topography of KDP crystal and the experimental LIDT. Research results indicate that the waviness rather than the roughness is the leading topography element on the KDP surface machined by the SPDT method when the LIDT is considered and the amplitude of micro-waviness has greater influence on the light intensity inside the KDP crystal within the scope of dangerous frequencies between (180 μm)−1 and (90 μm)−1; with suitable testing equipment, the characteristic parameters of waviness amplitude, such as the arithmetical mean deviation of three-dimensional profile Sa or root mean square deviation of three-dimensional contour Sq, are able to be considered as suitable parameters to reflect the optical quality of the machined surface in order to judge approximately the LIDT of the KDP surface and guide the machining course. PMID:22247567

  13. Studies on growth, structural, dielectric, laser damage threshold, linear and nonlinear optical properties of methylene blue admixtured L-arginine phosphate single crystal

    NASA Astrophysics Data System (ADS)

    Peramaiyan, G.; Pandi, P.; Bhagavannarayana, G.; Mohan Kumar, R.

    2012-12-01

    L-Arginine phosphate (LAP) and methylene blue dye admixtured L-arginine phosphate single crystals were grown by slow cooling technique and their cell parameters, crystalline perfection, dopant inclusion were confirmed by single crystal, powder X-ray diffraction and high resolution X-ray diffraction analyses respectively. The modes of vibrations of different functional groups present in pure and dye admixtured LAP crystals have been identified by FTIR spectral analysis. The UV-Vis-NIR spectral study was performed on the grown crystals and found that the crystals are transparent in the entire visible-NIR region. The dielectric measurement was carried out on the grown crystals as a function of frequency at room temperature. The microhardness hardness study on (1 0 0) plane of grown crystals reveals the mechanical behavior of the crystals. The laser damage threshold value significantly enhanced for dye admixtured crystal in comparison with pure LAP crystal. The relative SHG efficiency of methylane blue admixtured LAP crystal was found to be 1.3 times higher than that of pure LAP crystal.

  14. Investigations on the growth, optical, thermal, dielectric, and laser damage threshold properties of crystal violet dye-doped potassium acid phthalate single crystal

    NASA Astrophysics Data System (ADS)

    Rao, G. Babu; Rajesh, P.; Ramasamy, P.

    2016-03-01

    Influence of crystal violet dye with different concentration on potassium acid phthalate single crystal grown by conventional method has been studied. No change has been observed in the structure, whereas changes have been observed in the external morphology of the crystal when the dyes are incorporated in the crystal lattice. Thermogravimetric and differential thermal analyses show the onset decomposition temperatures to be at 302, 285, 284, and 285 °C for pure, 0.1, 0.3, and 0.5 mol% crystal violet-doped potassium acid phthalate crystals, respectively. The dielectric measurement was carried out on the grown crystals as a function of frequency at various temperatures. In addition, strong luminescent emission bands at 638, 648, and 640 nm were observed in which the relative intensity was found to be reversed as a result of doping concentration. The laser damage threshold value significantly increased for dye-doped crystal in comparison with pure crystal which may make it suitable for the solid-state dye laser applications.

  15. Finite Element Prediction of Sheet Forming Defects Using Elastic-Plastic, Damage and Localization Models

    NASA Astrophysics Data System (ADS)

    Haddag, Badis; Abed-Meraim, Farid; Balan, Tudor

    2007-05-01

    In this work, an advanced anisotropic elastic-plasticity model is combined with a damage model and a strain localization criterion in the aim to describe accurately the mechanical behavior of sheet metals. Large strain, fully three-dimensional, implicit time integration algorithms are developed for this model and implemented in the finite element code Abaqus. The resulting code is used to predict the strain localization limits as well as the springback after forming of sheet steels. The impact of strain-path dependent hardening models on the limit strains and on the amount of springback is addressed.

  16. Deformation history and load sequence effects on cumulative fatigue damage and life predictions

    NASA Astrophysics Data System (ADS)

    Colin, Julie

    Fatigue loading seldom involves constant amplitude loading. This is especially true in the cooling systems of nuclear power plants, typically made of stainless steel, where thermal fluctuations and water turbulent flow create variable amplitude loads, with presence of mean stresses and overloads. These complex loading sequences lead to the formation of networks of microcracks (crazing) that can propagate. As stainless steel is a material with strong deformation history effects and phase transformation resulting from plastic straining, such load sequence and variable amplitude loading effects are significant to its fatigue behavior and life predictions. The goal of this study was to investigate the effects of cyclic deformation on fatigue behavior of stainless steel 304L as a deformation history sensitive material and determine how to quantify and accumulate fatigue damage to enable life predictions under variable amplitude loading conditions for such materials. A comprehensive experimental program including testing under fully-reversed, as well as mean stress and/or mean strain conditions, with initial or periodic overloads, along with step testing and random loading histories was conducted on two grades of stainless steel 304L, under both strain-controlled and load-controlled conditions. To facilitate comparisons with a material without deformation history effects, similar tests were also carried out on aluminum 7075-T6. Experimental results are discussed, including peculiarities observed with stainless steel behavior, such as a phenomenon, referred to as secondary hardening characterized by a continuous increase in the stress response in a strain-controlled test and often leading to runout fatigue life. Possible mechanisms for secondary hardening observed in some tests are also discussed. The behavior of aluminum is shown not to be affected by preloading, whereas the behavior of stainless steel is greatly influenced by prior loading. Mean stress relaxation in

  17. Finite Element Creep Damage Analyses and Life Prediction of P91 Pipe Containing Local Wall Thinning Defect

    NASA Astrophysics Data System (ADS)

    Xue, Jilin; Zhou, Changyu

    2016-03-01

    Creep continuum damage finite element (FE) analyses were performed for P91 steel pipe containing local wall thinning (LWT) defect subjected to monotonic internal pressure, monotonic bending moment and combined internal pressure and bending moment by orthogonal experimental design method. The creep damage lives of pipe containing LWT defect under different load conditions were obtained. Then, the creep damage life formulas were regressed based on the creep damage life results from FE method. At the same time a skeletal point rupture stress was found and used for life prediction which was compared with creep damage lives obtained by continuum damage analyses. From the results, the failure lives of pipe containing LWT defect can be obtained accurately by using skeletal point rupture stress method. Finally, the influence of LWT defect geometry was analysed, which indicated that relative defect depth was the most significant factor for creep damage lives of pipe containing LWT defect.

  18. Predictive value of tender joints compared to synovitis for structural damage in rheumatoid arthritis

    PubMed Central

    Cheung, Peter P; Mari, Karine; Devauchelle-Pensec, Valérie; Jousse-Joulin, Sandrine; D'Agostino, Maria Antonietta; Chalès, Gérard; Gaudin, Philippe; Mariette, Xavier; Saraux, Alain; Dougados, Maxime

    2016-01-01

    Objective To evaluate the predictive value of tender joints compared to synovitis for structural damage in rheumatoid arthritis (RA). Methods A post hoc analysis was performed on a prospective 2-year study of 59 patients with active RA starting on antitumour necrosis factor (TNF). Tenderness and synovitis was assessed clinically at baseline, followed by blinded ultrasound assessment (B-mode and power Doppler ultrasound (PDUS)) on the hands and feet (2 wrists, 10 metacarpophalangeal, 10 proximal interphalangeal and 10 metatarsophalangeal (MTP) joints). Radiographs of these joints were performed at baseline and at 2 years. The risk of radiographic progression with respect to the presence of baseline tenderness or synovitis, as well as its persistence (after 4 months of anti-TNF), was estimated by OR (95% CI). Results Baseline tender joints were the least predictive for radiographic progression (OR=1.53 (95% CI 1.02 to 2.29) p<0.04), when compared to synovitis (clinical OR=2.08 (95% CI 1.39 to 3.11) p<0.001 or PDUS OR=1.80 (95% CI 1.20 to 2.71) p=0.005, respectively). Tender joints with the presence of synovitis were predictive of radiographic progression (OR=1.89 (95% CI 1.25 to 2.85) p=0.002), especially seen in the MTP joints. Non-tender joints with no synovitis were negatively predictive (OR=0.57 (95% CI 0.39 to 0.82) p=0.003). Persistence of tender joints was negatively predictive (OR=0.38 (95% CI 0.18 to 0.78) p=0.009) while persistence of synovitis was predictive (OR=2.41 (95% CI 1.24 to 4.67) p=0.01) of radiographic progression. Conclusions Synovitis is better than tenderness to predict for subsequent structural progression. However, coexistence of tenderness and synovitis at the level of an individual joint is predictive of structural damage, particularly in the MTP joints. Trial registration number NCT00444691. PMID:27042336

  19. Development of advanced structural analysis methodologies for predicting widespread fatigue damage in aircraft structures

    NASA Technical Reports Server (NTRS)

    Harris, Charles E.; Starnes, James H., Jr.; Newman, James C., Jr.

    1995-01-01

    NASA is developing a 'tool box' that includes a number of advanced structural analysis computer codes which, taken together, represent the comprehensive fracture mechanics capability required to predict the onset of widespread fatigue damage. These structural analysis tools have complementary and specialized capabilities ranging from a finite-element-based stress-analysis code for two- and three-dimensional built-up structures with cracks to a fatigue and fracture analysis code that uses stress-intensity factors and material-property data found in 'look-up' tables or from equations. NASA is conducting critical experiments necessary to verify the predictive capabilities of the codes, and these tests represent a first step in the technology-validation and industry-acceptance processes. NASA has established cooperative programs with aircraft manufacturers to facilitate the comprehensive transfer of this technology by making these advanced structural analysis codes available to industry.

  20. Cyclic fatigue damage characteristics observed for simple loadings extended to multiaxial life prediction

    NASA Technical Reports Server (NTRS)

    Jones, David J.; Kurath, Peter

    1988-01-01

    Fully reversed uniaxial strain controlled fatigue tests were performed on smooth cylindrical specimens made of 304 stainless steel. Fatigue life data and cracking observations for uniaxial tests were compared with life data and cracking behavior observed in fully reversed torsional tests. It was determined that the product of maximum principle strain amplitude and maximum principle stress provided the best correlation of fatigue lives for these two loading conditions. Implementation of this parameter is in agreement with observed physical damage and it accounts for the variation of stress-strain response, which is unique to specific loading conditions. Biaxial fatigue tests were conducted on tubular specimens employing both in-phase and out-of-phase tension torsion cyclic strain paths. Cracking observations indicated that the physical damage which occurred in the biaxial tests was similar to the damage observed in uniaxial and torsional tests. The Smith, Watson, and Topper parameter was then extended to predict the fatigue lives resulting from the more complex loading conditions.

  1. Continuum Damage Mechanics Used to Predict the Creep Life of Monolithic Ceramics

    NASA Technical Reports Server (NTRS)

    Powers, Lynn M.; Jadaan, Osama M.

    1998-01-01

    Significant improvements in propulsion and power generation for the next century will require revolutionary advances in high-temperature materials and structural design. Advanced ceramics are candidate materials for these elevated temperature applications. High-temperature and long-duration applications of monolithic ceramics can place their failure mode in the creep rupture regime. An analytical methodology in the form of the integrated design program-Ceramics Analysis and Reliability Evaluation of Structures/Creep (CARES/Creep) has been developed by the NASA Lewis Research Center to predict the life of ceramic structural components subjected to creep rupture conditions. This program utilizes commercially available finite element packages and takes into account the transient state of stress and creep strain distributions (stress relaxation as well as the asymmetric response to tension and compression). The creep life of a component is discretized into short time steps, during which the stress distribution is assumed constant. Then, the damage is calculated for each time step on the basis of a modified Monkman-Grant (MMG) creep rupture criterion. The cumulative damage is subsequently calculated as time elapses in a manner similar to Miner's rule for cyclic fatigue loading. Failure is assumed to occur when the normalized cumulative damage at any point in the component reaches unity. The corresponding time is the creep rupture life for that component.

  2. Prediction of sand particle trajectories and sand erosion damage on helicopter rotor blades

    NASA Astrophysics Data System (ADS)

    Shin, Bong Gun

    Therefore, in this dissertation, accurate and time-efficient methodologies were developed for performing sand particle tracking and predicting sand erosion damage on actual helicopter rotor blades under realistic hover and vertical lift conditions. In this dissertation, first, injection (release) conditions of solid particles with new injection parameter, sand particle mass flow rate (SPmFR), were specified to deal with the effect of non-uniform and unsteady flow conditions surrounding at each injection point from which solid particles are released. The SPmFR defines the number of solid particles released from the same injection position per unit time. Secondly, a general definition of erosion rate, "mass or volume loss from the metal surface due to the impact of a unit "mass" of solid particles" was also modified by multiplying with SPmFR in order to solve the limitation for predicting erosion damage on actual helicopter rotor blade. Next, a suitable empirical particle rebound model and an erosion damage model for spherical sand particles with diameters ranging from 10 microm to 500 microm impacting on the material Ti-6A1-4V, the material of helicopter rotor blade, were developed. Finally, C++ language based codes in the form of User Defined Functions (UDFs) were developed and implemented into the commercially available multi-dimensional viscous flow solver ANSYS-FLUENT in order to develop and integrate with the general purpose flow solver, ANSYS-FLUENT, for a specific Lagrangian particle trajectory computing algorithm and rebound and erosion quantification purposes. In the erosion simulation, a reasonably accurate fluid flow solution is necessary. In order to validate the numerical results obtained in this dissertation, computations for flow-only around 2D RAE2822 airfoil and 3D rotating rotor blade (NACA0012) without any sand particle were performed. In the comparison of these results with experimental results, it is found that the flow solutions are in good

  3. The Space Shuttle Program Pre-Flight Meteoroid and Orbital Debris Risk/Damage Predictions and Post-Flight Damage Assessments

    NASA Technical Reports Server (NTRS)

    Levin, George M.; Christiansen, Eric L.

    1997-01-01

    The pre-flight predictions and postflight assessments carried out in relation to a series of Space Shuttle missions are reviewed, and data are presented for the meteoroid and orbital debris damage observed on the Hubble Space Telescope during the 1994 Hubble repair mission. Pre-flight collision risk analyses are carried out prior to each mission, and in the case of an unacceptable risk, the mission profile is altered until the risk is considered to be acceptable. The NASA's BUMPER code is used to compute the probability of damage from debris and meteoroid particle impacts based on the Poisson statistical model for random events. The penetration probability calculation requires information concerning the geometry of the critical systems, the penetration resistance and mission profile parameters. Following each flight, the orbiter is inspected for meteoroid and space debris damage. The emphasis is on areas such as the radiator panels, the windows and the reinforced carbon-carbon structures on the leading wing edges and on the nose cap. The contents of damage craters are analyzed using a scanning electron microscope to determine the nature and origin of the impactor. Hypervelocity impact tests are often performed to simulate the observed damage and to estimate the nature of the damaging particles. The number and type of damage observed provides information concerning the orbital debris environment.

  4. Prediction of damage evolution in continuous fiber metal matrix composites subjected to fatigue loading

    SciTech Connect

    Allen, D.; Helms, K.; Lagoudas, D.

    1995-08-01

    A life prediction model is being developed by the authors for application to metal matrix composites (MMC`s). The systems under study are continuous silicon carbide fibers imbedded in titanium matrix. The model utilizes a computationally based framework based on thermodynamics and continuum mechanics, and accounts for matrix inelasticity, damage evolution, and environmental degradation due to oxidation. The computational model utilizes the finite element method, and an evolutionary analysis of a unit cell is accomplished via a time stepping algorithm. The computational scheme accounts for damage growth such as fiber-matrix debonding, surface cracking, and matrix cracking via the inclusion of cohesive zone elements in the unit cell. These elements are located based on experimental evidence also obtained by the authors. The current paper outlines the formulation utilized by the authors to solve this problem, and recent results are discussed. Specifically, results are given for a four-ply unidirectional composite subjected to cyclic fatigue loading at 650{degrees}C both in air and inert gas. The effects of oxidation on the life of the composite are predicted with the model, and the results are compared to limited experimental results.

  5. Interface modeling to predict well casing damage for big hill strategic petroleum reserve.

    SciTech Connect

    Ehgartner, Brian L.; Park, Byoung Yoon

    2012-02-01

    Oil leaks were found in well casings of Caverns 105 and 109 at the Big Hill Strategic Petroleum Reserve site. According to the field observations, two instances of casing damage occurred at the depth of the interface between the caprock and top of salt. This damage could be caused by interface movement induced by cavern volume closure due to salt creep. A three dimensional finite element model, which allows each cavern to be configured individually, was constructed to investigate shear and vertical displacements across each interface. The model contains interfaces between each lithology and a shear zone to examine the interface behavior in a realistic manner. This analysis results indicate that the casings of Caverns 105 and 109 failed by shear stress that exceeded shear strength due to the horizontal movement of the top of salt relative to the caprock, and tensile stress due to the downward movement of the top of salt from the caprock, respectively. The casings of Caverns 101, 110, 111 and 114, located at the far ends of the field, are predicted to be failed by shear stress in the near future. The casings of inmost Caverns 107 and 108 are predicted to be failed by tensile stress in the near future.

  6. Structural kinematics based damage zone prediction in gradient structures using vibration database

    NASA Astrophysics Data System (ADS)

    Talha, Mohammad; Ashokkumar, Chimpalthradi R.

    2014-05-01

    To explore the applications of functionally graded materials (FGMs) in dynamic structures, structural kinematics based health monitoring technique becomes an important problem. Depending upon the displacements in three dimensions, the health of the material to withstand dynamic loads is inferred in this paper, which is based on the net compressive and tensile displacements that each structural degree of freedom takes. These net displacements at each finite element node predicts damage zones of the FGM where the material is likely to fail due to a vibration response which is categorized according to loading condition. The damage zone prediction of a dynamically active FGMs plate have been accomplished using Reddy's higher-order theory. The constituent material properties are assumed to vary in the thickness direction according to the power-law behavior. The proposed C0 finite element model (FEM) is applied to get net tensile and compressive displacement distributions across the structures. A plate made of Aluminum/Ziconia is considered to illustrate the concept of structural kinematics-based health monitoring aspects of FGMs.

  7. [Risk predictive model for damage caused by the spittlebug Aeneolamiapostica (Walker) Fennah (Hemiptera: Cercopidae)].

    PubMed

    García-García, Carlos G; López-Collado, José; Nava-Tablada, Martha E; Villanueva-Jiménez, Juan A; Vera-Graziano, Jorge

    2006-01-01

    This paper evaluated the risk that Aenolamia postica (Walker) Fennah populations reach the economic threshold in sugar cane fields in Veracruz, México. A risk deductive model was constructed to include the sequence of events leading to damaging populations, considered the top event or critical failure in the crop. Model events were identified and quantified, and model was validated on field conditions. The model components and their state values were identified as: temperature e" 28 degrees C, precipitation e" 45% during June and July, soil clay content e" 40%, infested adjoining fields, deficient weed control, wind dominance, crop phenology and variety, deficient chemical and biological control, and irrigation. Sensitivity analysis showed that the most important events triggering high densities of A. postica were high temperatures and precipitation, previous field infestation, nymph and weed presence. Event probability estimates were combined using Boolean algebra to compute the minimum, mean and maximum probabilities for the top event, yielding values of 0.417, 0.563, y 0.734 respectively. Model was tested in field, by selecting sugar cane fields having the model properties and compared to fields without these features. Fields were sampled in both conditions during 2004 year and high-risk fields had significantly (F = 13, 4, gl = 1, 18, P = 0,0018) higher densities (2.4 adults m(-1)) than low-risk plots (0.4 adults m(-1)) thus agreeing with the model forecast. PMID:17144142

  8. Near-threshold fatigue crack growth behavior of 2195 aluminum-lithium-alloy—prediction of crack propagation direction and influence of stress ratio

    NASA Astrophysics Data System (ADS)

    Chen, D. L.; Chaturvedi, M. C.

    2000-06-01

    Tensile properties and fatigue crack propagation behavior of a 2195-T8 Al-Li alloy were investigated at different stress ratios, with particular emphasis on their dependence on specimen orientation. Specimens with orientations of 0, 15, 30, 45, and 90 deg to the rolling direction were tested. The alloy contained a strong brass-type texture and a profuse distribution of platelike precipitates of T 1 (Al2CuLi) phase on {111} matrix planes. Both tensile strength and fatigue thresholds were found to be strongly dependent on the specimen orientation, with the lowest values observed along the direction at 45 deg to the rolling direction. The effect of stress ratio on fatigue threshold could generally be explained by a modified crack closure concept. The growth of fatigue crack in this alloy was found to exhibit a significant crystallographic cracking and especially macroscopic crack deflection. The specimens oriented in the L-T + 45 deg had the smallest deflection angle, while the specimens in the L-T and T-L orientations exhibited a large deflection angle. The dependence of the fatigue threshold on the specimen orientation could be rationalized by considering an equivalent fatigue threshold calculated from both mode I and mode II values due to the crack deflection. A four-step approach on the basis of Schmid’s law combined with specific crystallographic textures is proposed to predict the fatigue crack deflection angle. Good agreement between the theoretical prediction and experimental results was observed.

  9. The impact of different cleaning processes on the laser damage threshold of antireflection coatings for Z-Backlighter optics at Sandia National Laboratories

    NASA Astrophysics Data System (ADS)

    Field, Ella; Bellum, John; Kletecka, Damon

    2014-09-01

    The Z-Backlighter lasers at Sandia National Laboratories are kilojoule class, pulsed systems operating with ns pulse lengths at 527 nm and ns and sub-ps pulse lengths at 1054 nm (www.z-beamlet.sandia.gov), and are linked to the most powerful and energetic x-ray source in the world, the Z-Accelerator (http://www.sandia.gov/z-machine/). An important Z-Backlighter optic is a flat, fused silica optic measuring 32.5 cm × 32.5 cm × 1 cm with an antireflection (AR) coating on both sides. It is used as a debris shield to protect other Z-Backlighter laser optics from high-velocity particles released by the experiments conducted in the Z-Accelerator. Each experiment conducted in the Z-Accelerator releases enough debris to cloud the surface of a debris shield, which means that a debris shield cannot be used for more than one experiment. Every year, the large optics coating facility [1] at Sandia provides AR coatings for approximately 50 debris shields, in addition to AR coatings for numerous other meter-class Z-Backlighter lenses and windows. As with all Z-Backlighter optical coatings, these AR coatings must have a high laser-induced damage threshold (LIDT) in order to withstand the powerful Z-Backlighter laser fluences. Achieving a good LIDT depends not only on the coating deposition processes but also on the polishing and cleaning processes used to prepare the coated and uncoated surfaces [2]. We spend a lot of time, both before and after the coatings have been deposited, manually cleaning the optics, including the debris shields, even though they are an expendable type of optic. Therefore, in this study we have tested new cleaning methods in addition to our current method to determine their impact on the LIDT of AR coatings, and conclude whether a shorter-duration or less labor-intensive cleaning process would suffice.

  10. Crack Growth Prediction Methodology for Multi-Site Damage: Layered Analysis and Growth During Plasticity

    NASA Technical Reports Server (NTRS)

    James, Mark Anthony

    1999-01-01

    A finite element program has been developed to perform quasi-static, elastic-plastic crack growth simulations. The model provides a general framework for mixed-mode I/II elastic-plastic fracture analysis using small strain assumptions and plane stress, plane strain, and axisymmetric finite elements. Cracks are modeled explicitly in the mesh. As the cracks propagate, automatic remeshing algorithms delete the mesh local to the crack tip, extend the crack, and build a new mesh around the new tip. State variable mapping algorithms transfer stresses and displacements from the old mesh to the new mesh. The von Mises material model is implemented in the context of a non-linear Newton solution scheme. The fracture criterion is the critical crack tip opening displacement, and crack direction is predicted by the maximum tensile stress criterion at the crack tip. The implementation can accommodate multiple curving and interacting cracks. An additional fracture algorithm based on nodal release can be used to simulate fracture along a horizontal plane of symmetry. A core of plane strain elements can be used with the nodal release algorithm to simulate the triaxial state of stress near the crack tip. Verification and validation studies compare analysis results with experimental data and published three-dimensional analysis results. Fracture predictions using nodal release for compact tension, middle-crack tension, and multi-site damage test specimens produced accurate results for residual strength and link-up loads. Curving crack predictions using remeshing/mapping were compared with experimental data for an Arcan mixed-mode specimen. Loading angles from 0 degrees to 90 degrees were analyzed. The maximum tensile stress criterion was able to predict the crack direction and path for all loading angles in which the material failed in tension. Residual strength was also accurately predicted for these cases.

  11. On predicting future economic losses from tropical cyclones: Comparing damage functions for the Eastern USA

    NASA Astrophysics Data System (ADS)

    Geiger, Tobias; Levermann, Anders; Frieler, Katja

    2015-04-01

    Recent years have seen an intense scientific debate of what to expect from future tropical cyclone activity under climate change [1,2]. Besides the projection of cyclones' genesis points and trajectories it is the cyclone's impact on future societies that needs to be quantified. In our present work, where we focus on the Eastern USA, we start out with a comprehensive comparison of a variety of presently available and novel functional relationships that are used to link cyclones' physical properties with their damage caused on the ground. These so-called damage functions make use of high quality data sets consisting of gridded population data, exposed capital at risk, and information on the cyclone's extension and its translational and locally resolved maximum wind speed. Based on a cross-validation ansatz we train a multitude of damage functions on a large variety of data sets in order to evaluate their performance on an equally sized test sample. Although different damage analyses have been conducted in the literature [3,4,5,6], the efforts have so far primarily been focused on determining fit parameters for individual data sets. As our analysis consists of a wide range of damage functions implemented on identical data sets, we can rigorously evaluate which (type of) damage function (for which set of parameters) does best in reproducing damages and should therefore be used for future loss analysis with highest certainty. We find that the benefits of using locally resolved data input tend to be outweighed by the large uncertainties that accompany the data. More coarse and generalized data input therefore captures the diversity of cyclonic features better. Furthermore, our analysis shows that a non-linear relation between wind speed and damage outperforms the linear as well as the exponential relationship discussed in the literature. In a second step, the damage function with the highest predictive quality is implemented to predict potential future cyclone losses

  12. The EST Model for Predicting Progressive Damage and Failure of Open Hole Bending Specimens

    NASA Technical Reports Server (NTRS)

    Joseph, Ashith P. K.; Waas, Anthony M.; Pineda, Evan J.

    2016-01-01

    Progressive damage and failure in open hole composite laminate coupons subjected to flexural loading is modeled using Enhanced Schapery Theory (EST). Previous studies have demonstrated that EST can accurately predict the strength of open hole coupons under remote tensile and compressive loading states. This homogenized modeling approach uses single composite shell elements to represent the entire laminate in the thickness direction and significantly reduces computational cost. Therefore, when delaminations are not of concern or are active in the post-peak regime, the version of EST presented here is a good engineering tool for predicting deformation response. Standard coupon level tests provides all the input data needed for the model and they are interpreted in conjunction with finite element (FE) based simulations. Open hole bending test results of three different IM7/8552 carbon fiber composite layups agree well with EST predictions. The model is able to accurately capture the curvature change and deformation localization in the specimen at and during the post catastrophic load drop event.

  13. MRI osteitis predicts cartilage damage at the wrist in RA: a three-year prospective 3T MRI study examining cartilage damage

    PubMed Central

    2014-01-01

    Introduction Cartilage damage impacts on patient disability in rheumatoid arthritis (RA). The aims of this magnetic resonance imaging (MRI) study were to investigate cartilage damage over three years and determine predictive factors. Methods A total of 38 RA patients and 22 controls were enrolled at t = 0 (2009). After 3 years, clinical and MRI data were available in 28 patients and 15 controls. 3T MRI scans were scored for cartilage damage, bone erosion, synovitis and osteitis. A model was developed to predict cartilage damage from baseline parameters. Results Inter-reader reliability for the Auckland MRI cartilage score (AMRICS) was high for status scores; intraclass correlation coefficient (ICC), 0.90 (0.81 to 0.95) and moderate for change scores (ICC 0.58 (0.24 to 0.77)). AMRICS scores correlated with the Outcome MEasures in Rheumatoid Arthritis Clinical Trials (OMERACT) MRI joint space narrowing (jsn) and X-Ray (XR) jsn scores (r =0.96, P < 0.0001 and 0.80, P < 0.0001, respectively). AMRICS change scores were greater for RA patients than controls (P = 0.06 and P = 0.04 for the two readers). Using linear regression, baseline MRI cartilage, synovitis and osteitis scores predicted the three-year AMRICS (R2 = 0.67, 0.37 and 0.39, respectively). A multiple linear regression model predicted the three-year AMRICS (R2 = 0.78). Baseline radial osteitis predicted increased cartilage scores at the radiolunate and radioscaphoid joints, P = 0.0001 and 0.0012, respectively and synovitis at radioulnar, radiocarpal and intercarpal-carpometacarpal joints also influenced three-year cartilage scores (P-values of 0.001, 0.04 and 0.01, respectively). Conclusions MRI cartilage damage progression is preceded by osteitis and synovitis but is most influenced by pre-existing cartilage damage suggesting primacy of the cartilage damage pathway in certain patients. PMID:24476340

  14. Prediction of Damage Factor in end Milling of Glass Fibre Reinforced Plastic Composites Using Artificial Neural Network

    NASA Astrophysics Data System (ADS)

    Erkan, Ömer; Işık, Birhan; Çiçek, Adem; Kara, Fuat

    2013-08-01

    Glass fibre reinforced plastic (GFRP) composites are an economic alternative to engineering materials because of their superior properties. Some damages on the surface occur due to their complex cutting mechanics in cutting process. Minimisation of the damages is fairly important in terms of product quality. In this study, a GFRP composite material was milled to experimentally minimise the damages on the machined surfaces, using two, three and four flute end mills at different combinations of cutting parameters. Experimental results showed that the damage factor increased with increasing cutting speed and feed rate, on the other hand, it was found that the damage factor decreased with increasing depth of cut and number of the flutes. In addition, analysis of variance (ANOVA) results clearly revealed that the feed rate was the most influential parameter affecting the damage factor in end milling of GFRP composites. Also, in present study, Artificial Neural Network (ANN) models with five learning algorithms were used in predicting the damage factor to reduce number of expensive and time-consuming experiments. The highest performance was obtained by 4-10-1 network structure with LM learning algorithm. ANN was notably successful in predicting the damage factor due to higher R2 and lower RMSE and MEP.

  15. Failure Predictions for VHTR Core Components using a Probabilistic Contiuum Damage Mechanics Model

    SciTech Connect

    Fok, Alex

    2013-10-30

    The proposed work addresses the key research need for the development of constitutive models and overall failure models for graphite and high temperature structural materials, with the long-term goal being to maximize the design life of the Next Generation Nuclear Plant (NGNP). To this end, the capability of a Continuum Damage Mechanics (CDM) model, which has been used successfully for modeling fracture of virgin graphite, will be extended as a predictive and design tool for the core components of the very high- temperature reactor (VHTR). Specifically, irradiation and environmental effects pertinent to the VHTR will be incorporated into the model to allow fracture of graphite and ceramic components under in-reactor conditions to be modeled explicitly using the finite element method. The model uses a combined stress-based and fracture mechanics-based failure criterion, so it can simulate both the initiation and propagation of cracks. Modern imaging techniques, such as x-ray computed tomography and digital image correlation, will be used during material testing to help define the baseline material damage parameters. Monte Carlo analysis will be performed to address inherent variations in material properties, the aim being to reduce the arbitrariness and uncertainties associated with the current statistical approach. The results can potentially contribute to the current development of American Society of Mechanical Engineers (ASME) codes for the design and construction of VHTR core components.

  16. Effect of Assumed Damage and Location on the Delamination Onset Predictions for Skin-Stiffener Debonding

    NASA Technical Reports Server (NTRS)

    Paris, Isabelle L.; Krueger, Ronald; OBrien, T. Kevin

    2004-01-01

    The difference in delamination onset predictions based on the type and location of the assumed initial damage are compared in a specimen consisting of a tapered flange laminate bonded to a skin laminate. From previous experimental work, the damage was identified to consist of a matrix crack in the top skin layer followed by a delamination between the top and second skin layer (+45 deg./-45 deg. interface). Two-dimensional finite elements analyses were performed for three different assumed flaws and the results show a considerable reduction in critical load if an initial delamination is assumed to be present, both under tension and bending loads. For a crack length corresponding to the peak in the strain energy release rate, the delamination onset load for an assumed initial flaw in the bondline is slightly higher than the critical load for delamination onset from an assumed skin matrix crack, both under tension and bending loads. As a result, assuming an initial flaw in the bondline is simpler while providing a critical load relatively close to the real case. For the configuration studied, a small delamination might form at a lower tension load than the critical load calculated for a 12.7 mm (0.5") delamination, but it would grow in a stable manner. For the bending case, assuming an initial flaw of 12.7 mm (0.5") is conservative, the crack would grow unstably.

  17. Models for predicting damage evolution in metal matrix composites subjected to cyclic loading

    SciTech Connect

    Allen, D.H.; Hurtado, L.D.; Helms, K.L.E.

    1995-03-01

    A thermomechanical analysis of a continuous fiber metal matrix composite (MMC) subjected to cyclic loading is performed herein. The analysis includes the effects of processing induced residual thermal stresses, matrix inelasticity, and interface cracking. Due to these complexities, the analysis is performed computationally using the finite element method. Matrix inelasticity is modelled with a rate dependent viscoplasticity model. Interface fracture is modelled by the use of a nonlinear interface constitutive model. The problem formulation is summarized, and results are given for a four-ply unidirectional SCS-6/{beta}21S titanium composite under high temperature isothermal mechanical fatigue. Results indicate rate dependent viscoplasticity can be a significant mechanism for dissipating the energy available for damage propagation, thus contributing to improved ductility of the composite. Results also indicate that the model may be useful for inclusion in life prediction methodologies for MMC`s.

  18. Meteoroid/orbital debris impact damage predictions for the Russian space station MIR

    NASA Technical Reports Server (NTRS)

    Christiansen, E. L.; Hyde, J. L.; Lear, D.

    1997-01-01

    Components of the Mir space station have been exposed to the meteoroid/orbital debris (M/OD) environment for up to 11 years. During this period, no M/OD impact perforation of the pressure shell of the manned modules were reported. The NASA standard M/OD analysis code BUMPER was used to predict the probability of M/OD impact damage to various components of Mir. The analysis indicates a 1 in 2.2 chance that a M/OD impact would have caused a penetration resulting in a pressure leak of the Mir modules since its launch up to the February 1997. For the next five years, the estimated odds become 1 in 3. On an annual basis, penetration risks are 60 percent higher, on the average, in the next five years due to the larger size of Mir and the growth in the orbital debris population.

  19. A comparison of South Asian specific and established BMI thresholds for determining obesity prevalence in pregnancy and predicting pregnancy complications: Findings from the Born in Bradford cohort

    PubMed Central

    Bryant, Maria; Santorelli, Gillian; Lawlor, Debbie A; Farrar, Diane; Tuffnell, Derek; Bhopal, Raj; Wright, John

    2013-01-01

    Objective To describe how maternal obesity prevalence varies by established international and South Asian specific BMI cut-offs in women of Pakistani origin and investigate whether different BMI thresholds can help to identify women at risk of adverse pregnancy and birth outcomes. Design Prospective bi-ethnic birth cohort study (The Born in Bradford Cohort). Setting Bradford, a deprived city in the North of the UK. Participants 8,478 South Asian and White British pregnant women participating in the Born in Bradford cohort study Main outcome measures Maternal obesity prevalence; prevalence of known obesity related adverse pregnancy outcomes: mode of birth, hypertensive disorders of pregnancy (HDP), gestational diabetes, macrosomia, pre-term births. Results Application of South Asian BMI cut-offs increased prevalence of obesity in Pakistani women from 18.8% (95% CI 17.6 to 19.9) to 30.9% (95% CI 29.5 to 32.2). With the exception of pre-term births, there was a positive linear relationship between BMI and prevalence of adverse pregnancy and birth outcomes, across almost the whole BMI distribution. Risk of gestational diabetes and HDP increased more sharply in Pakistani women after a BMI threshold of at least 30kg/m2, but there was no evidence of a sharp increase in any risk factors at the new, lower thresholds suggested for use in South Asian women. BMI was a good single predictor of outcomes (Area Under the Receiver Operating Curve: 0.596 to 0.685 for different outcomes); prediction was more discriminatory and accurate with BMI as a continuous variable than as a binary variable for any possible cut-point. Conclusion Applying the new South Asian threshold to pregnant women would markedly increase those referred for monitoring and lifestyle advice. However, our results suggest that lowering the BMI threshold in South Asian women would not improve the predictive ability for identifying those at risk of adverse pregnancy outcomes. PMID:23797188

  20. CONTAMINANT THRESHOLDS FOR PREDICTING ADVERSE IMPACTS IN BENTHIC COMMUNITIES ALONG THE U.S. ATLANTIC AND GULF OF MEXICO COASTS

    EPA Science Inventory

    EMAP 2001 Symposium, April 24-27, 2001, Pensacola, FL

    Matching data on sediment contaminants and macroinfauna from 1,349 samples collected as part of EMAP in estuaries along the U.S. Atlantic and Gulf of Mexico coasts were used to define thresholds for evaluating risks of ...

  1. A study of the possibility of predicting the threshold of plasma formation on a metal surface by the optoacoustic method

    NASA Astrophysics Data System (ADS)

    Aver'ianov, N. E.; Baloshin, Iu. A.; Martiukhina, L. I.; Pavlishin, I. V.; Sud'Enkov, Iu. V.

    1987-09-01

    The amplitudes of the acoustic signals excited in metal reflectors by laser pulses are analyzed as a function of the energy density of target irradiation. It is shown that the slope of the resulting plot is related to the threshold of plasma generation near the specimen surface. Results are presented for the emission wavelengths of Nd-glass and CO2 lasers.

  2. Modeling of plasma-induced damage during the etching of ultimately-scaled transistors in ULSI circuits--A model prediction of damage in three dimensional structures

    NASA Astrophysics Data System (ADS)

    Eriguchi, Koji

    2014-10-01

    An increasing demand for high performance field-effect transistors (FETs) leads to the aggressive critical dimension shrinkage and the currently-emerging three dimensional (3D) geometry. Plasma processing is widely used also in the scaled- and 3D-FET (e.g. FinFET) manufacturing, where precise control of the reaction on the (sidewall) surfaces is a prime issue. In this study, damage creation mechanism during plasma etching--plasma-induced physical damage (PPD)--was investigated in such structures on the basis of the PPD range theory, atomistic simulations, and experiments. Compared to PPD in planar FETs (e.g. Si recess [2,3]), a stochastic modeling and atomistic simulations predicted that, during etching of ``fins'' in a 3D-FET, the following two mechanisms are responsible for damage creation in addition to an ion impact on the sidewall at an oblique incident angle: 1) incoming ions penetrate into the Si substrate and undergo scattering by Si atoms in the lateral direction even if the incident angle is normal to the surface and 2) some of Si atoms and ions sputtered at the surface being etched impact on the sidewall with energies sufficient to break Si-Si bonds. These straggling and sputtering processes are stochastic and fundamental, thus, result in 3D structure damage (``fin-damage''). The ``fin-damage'' induced by straggling was modeled by the PPD range theory. Molecular dynamics simulations clarified the mechanisms under the various plasma conditions. Quantum mechanical calculations showed that created defect structures play the role of a carrier trap site, which was experimentally verified by an electrical measurement. Since they are intrinsic natures of etching, both straggling and sputtering noted here should be implemented to design a low-damage etching process. This work was supported in part by Grant-in-Aid for Scientific Research (B) 23360321 from JSPS and STARC project.

  3. Thermally induced damage in composite space structure: Predictive methodology and experimental correlation

    NASA Technical Reports Server (NTRS)

    Park, Cecelia; Mcmanus, Hugh L.

    1994-01-01

    A general analysis method is presented to predict matrix cracks in all plies of a composite laminate, and resulting degraded laminate properties, as functions of temperature or thermal cycles. A shear lag solution of the stresses in the vicinity of cracks and a fracture mechanics crack formation criteria are used to predict cracks. Damage is modeled incrementally, which allows the inclusion of the effects of temperature dependent material properties and softening of the laminate due to previous cracking. The analysis is incorporated into an easy-to-use computer program. The analysis is correlated with experimentally measured crack densities in a variety of laminates exposed to monotonically decreasing temperatures. Crack densities are measured at the edges of specimens by microscopic inspection, and throughout the specimen volumes by x-ray and sanding down of the edges. Correlation between the analytical results and the crack densities in the interiors of the specimens was quite good. Crack densities measured at specimen edges did not agree with internal crack densities (or analyses) in some cases. A free-edge stress analysis clarified the reasons for these discrepancies.

  4. Interbed Modeling to Predict Wellbore Damage for Big Hill Strategic Petroleum Reserve

    NASA Astrophysics Data System (ADS)

    Park, Byoung Yoon

    2014-09-01

    Oil leaks were found in wellbores of Caverns 105 and 109 at the Big Hill Strategic Petroleum Reserve site. According to the field observations, two instances of casing damage occurred at the depth of the interbed between the caprock bottom and salt top. A three-dimensional finite element model, which allows each cavern to be configured individually, was constructed to investigate horizontal and vertical displacements in each well as it crosses the various interbeds. The model contains interfaces between each lithology and a shear zone (fault) to examine the interbed behavior in a realistic manner. This analysis results indicate that the casings of Caverns 105 and 109 failed, respectively, from shear stress that exceeded the casing shear strength due to the horizontal movement of the salt top relative to the caprock and tensile stress due to the downward movement of the salt top from the caprock. The wellbores of Caverns 114 and 104, located at the far end of the field and near the fault, respectively, are predicted to fail by shear stress in the near future. The wellbores of inmost Caverns 107 and 108 are predicted to fail by tensile stress in the near future. The salt top subsides because the volumes of caverns in the salt dome decrease with time due to salt creep closure, while the caprock does not subside at the same rate as the salt top because the caprock is thick and stiff. This discrepancy yields deformation of the well.

  5. Thermally induced damage in composite space structure: Predictive methodology and experimental correlation

    SciTech Connect

    Park, C.H.; McManus, H.L.

    1994-12-31

    A general analysis method is presented to predict matrix cracks in all plies of a composite laminate, and resulting degraded laminate properties, as functions of temperature or thermal cycles. A shear lag solution of the stresses in the vicinity of cracks and a fracture mechanics crack formation criteria are used to predict cracks. Damage is modeled incrementally, which allows the inclusion of the effects of temperature dependent material properties and softening of the laminate due to previous cracking. The analysis is incorporated into an easy-to-use computer program. The analysis is correlated with experimentally measured crack densities in a variety of laminates exposed to monotonically decreasing temperatures. Crack densities are measured at the edges of specimens by microscopic inspection, and throughout the specimen volumes by X-ray and sanding down of the edges. Correlation between the analytical results and the crack densities in the interiors of the specimens was quite good. Crack densities measured at specimen edges did not agree with internal crack densities (or analyses) in some cases. A free-edge stress analysis clarified the reasons for these discrepancies.

  6. Multiscale Model Predicts Tissue-Level Failure From Collagen Fiber-Level Damage

    PubMed Central

    Hadi, Mohammad F.; Sander, Edward A.; Barocas, Victor H.

    2013-01-01

    Excessive tissue-level forces communicated to the microstructure and extracellular matrix of soft tissues can lead to damage and failure through poorly understood physical processes that are multiscale in nature. In this work, we propose a multiscale mechanical model for the failure of collagenous soft tissues that incorporates spatial heterogeneity in the microstructure and links the failure of discrete collagen fibers to the material response of the tissue. The model, which is based on experimental failure data derived from different collagen gel geometries, was able to predict the mechanical response and failure of type I collagen gels, and it demonstrated that a fiber-based rule (at the micrometer scale) for discrete failure can strongly shape the macroscale failure response of the gel (at the millimeter scale). The model may be a useful tool in predicting the macroscale failure conditions for soft tissues and engineered tissue analogs. In addition, the multiscale model provides a framework for the study of failure in complex fiber-based mechanical systems in general. PMID:22938372

  7. Adaptive Thresholds

    SciTech Connect

    Bremer, P. -T.

    2014-08-26

    ADAPT is a topological analysis code that allow to compute local threshold, in particular relevance based thresholds for features defined in scalar fields. The initial target application is vortex detection but the software is more generally applicable to all threshold based feature definitions.

  8. Prediction of spatially explicit rainfall intensity-duration thresholds for post-fire debris-flow generation in the western United States

    NASA Astrophysics Data System (ADS)

    Staley, Dennis; Negri, Jacquelyn; Kean, Jason

    2016-04-01

    burned areas. Our approach synthesizes the two methods by incorporating measured rainfall intensity into each model variable (based on measures of topographic steepness, burn severity and surface properties) within the logistic regression equation. This approach provides a more realistic representation of the relation between rainfall intensity and debris-flow likelihood, as likelihood values asymptotically approach zero when rainfall intensity approaches 0 mm/h, and increase with more intense rainfall. Model performance was evaluated by comparing predictions to several existing regional thresholds. The model, based upon training data collected in southern California, USA, has proven to accurately predict rainfall intensity-duration thresholds for other areas in the western United States not included in the original training dataset. In addition, the improved logistic regression model shows promise for emergency planning purposes and real-time, site-specific early warning. With further validation, this model may permit the prediction of spatially-explicit intensity-duration thresholds for debris-flow generation in areas where empirically derived regional thresholds do not exist. This improvement would permit the expansion of the early-warning system into other regions susceptible to post-fire debris flow.

  9. Chronic hepatitis C virus infection: Serum biomarkers in predicting liver damage

    PubMed Central

    Valva, Pamela; Ríos, Daniela A; De Matteo, Elena; Preciado, Maria V

    2016-01-01

    Currently, a major clinical challenge in the management of the increasing number of hepatitis C virus (HCV) infected patients is determining the best means for evaluating liver impairment. Prognosis and treatment of chronic hepatitis C (CHC) are partly dependent on the assessment of histological activity, namely cell necrosis and inflammation, and the degree of liver fibrosis. These parameters can be provided by liver biopsy; however, in addition to the risks related to an invasive procedure, liver biopsy has been associated with sampling error mostly due to suboptimal biopsy size. To avoid these pitfalls, several markers have been proposed as non-invasive alternatives for the diagnosis of liver damage. Distinct approaches among the currently available non-invasive methods are (1) the physical ones based on imaging techniques; and (2) the biological ones based on serum biomarkers. In this review, we discuss these approaches with special focus on currently available non-invasive serum markers. We will discuss: (1) class I serum biomarkers individually and as combined panels, particularly those that mirror the metabolism of liver extracellular matrix turnover and/or fibrogenic cell changes; (2) class II biomarkers that are indirect serum markers and are based on the evaluation of common functional alterations in the liver; and (3) biomarkers of liver cell death, since hepatocyte apoptosis plays a significant role in the pathogenesis of HCV infection. We highlight in this review the evidence behind the use of these markers and assess the diagnostic accuracy as well as advantages, limitations, and application in clinical practice of each test for predicting liver damage in CHC. PMID:26819506

  10. Modelling the influence of predicted future climate change on the risk of wind damage within New Zealand's planted forests.

    PubMed

    Moore, John R; Watt, Michael S

    2015-08-01

    Wind is the major abiotic disturbance in New Zealand's planted forests, but little is known about how the risk of wind damage may be affected by future climate change. We linked a mechanistic wind damage model (ForestGALES) to an empirical growth model for radiata pine (Pinus radiata D. Don) and a process-based growth model (cenw) to predict the risk of wind damage under different future emissions scenarios and assumptions about the future wind climate. The cenw model was used to estimate site productivity for constant CO2 concentration at 1990 values and for assumed increases in CO2 concentration from current values to those expected during 2040 and 2090 under the B1 (low), A1B (mid-range) and A2 (high) emission scenarios. Stand development was modelled for different levels of site productivity, contrasting silvicultural regimes and sites across New Zealand. The risk of wind damage was predicted for each regime and emission scenario combination using the ForestGALES model. The sensitivity to changes in the intensity of the future wind climate was also examined. Results showed that increased tree growth rates under the different emissions scenarios had the greatest impact on the risk of wind damage. The increase in risk was greatest for stands growing at high stand density under the A2 emissions scenario with increased CO2 concentration. The increased productivity under this scenario resulted in increased tree height, without a corresponding increase in diameter, leading to more slender trees that were predicted to be at greater risk from wind damage. The risk of wind damage was further increased by the modest increases in the extreme wind climate that are predicted to occur. These results have implications for the development of silvicultural regimes that are resilient to climate change and also indicate that future productivity gains may be offset by greater losses from disturbances. PMID:25703827

  11. Exposure to ultraviolet light as a means of predicting damage in oranges exposed to freezing conditions

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Current methods of evaluating whether an orange has been damaged by a period of freezing temperatures require fruit to be cut and physically examined for signs of freeze damage. This method is destructive, slow, and inaccurate and relies on visual evaluation. Visual symptoms of freeze damage may t...

  12. Finite element prediction with experimental validation of damage distribution in single trabeculae during three-point bending tests.

    PubMed

    Ridha, Hambli; Thurner, Philipp J

    2013-11-01

    There is growing evidence that information on trabecular microarchitecture can improve the assessment of fracture risk. One current strategy is to exploit finite element (FE) analysis applied to experimental data of mechanically loaded single trabecular bone tissue obtained from non-invasive imaging techniques for the investigation of the damage initiation and growth of bone tissue. FE analysis of this type of bone has mainly focused on linear and non-linear analysis to evaluate the bone's failure properties. However, there is a lack of experimentally validated FE damage models at trabecular bone tissue level allowing for the simulation of the progressive damage process (initiation and growth) till complete fracture. Such models are needed to perform enhanced prediction of the apparent failure mechanical properties needed to assess the fracture risk of bone organs. In the current study, we develop a FE model based on a continuum damage mechanics (CDM) approach to simulate the damage initiation and propagation of a single trabecula till complete facture in quasi-static regime. Three-point bending experiments were performed on single bovine trabeculae and compared to FE results. In order to validate the proposed FE mode, (i) the force displacement curve was compared to the experimental one and (ii) the damage distribution was correlated to the measured one obtained by digital image correlation based on stress whitening in bone, reported to be correlated to microdamage. A very good agreement was obtained between the FE and experimental results, indicating that the proposed damage investigation protocol based on FE analysis and testing is reliable to assess the damage behavior of bone tissue and that the current damage model is able to accurately simulate the damaging and fracturing process of single trabeculae under quasi static load. PMID:23890577

  13. Finite Element Analysis of 2.5D Woven Composites, Part II: Damage Behavior Simulation and Strength Prediction

    NASA Astrophysics Data System (ADS)

    Song, Jian; Wen, Weidong; Cui, Haitao; Zhang, Hongjian; Xu, Ying

    2016-02-01

    In the first part of the work, a new 2.5D woven composites finite element model (2.5D WCFEM) which took into consideration the impact of face structures and can accurately predict the main elastic performances has been established. In this part, the stress-strain behavior and the damage characteristic of this material under uniaxial tension are simulated using nonlinear progressive damage analysis based on damage mechanics. Meanwhile, experimental investigation and fracture analysis are conducted to evaluate the validity of the proposed method. Finally, the influence of woven parameters on the mechanical behavior is discussed. Compared with the test results, a good agreement between the computational and experimental results has been obtained. The progressive damage characteristic and main failure modes are also revealed.

  14. Comparison of Damage Models for Predicting the Non-Linear Response of Laminates Under Matrix Dominated Loading Conditions

    NASA Technical Reports Server (NTRS)

    Schuecker, Clara; Davila, Carlos G.; Rose, Cheryl A.

    2010-01-01

    Five models for matrix damage in fiber reinforced laminates are evaluated for matrix-dominated loading conditions under plane stress and are compared both qualitatively and quantitatively. The emphasis of this study is on a comparison of the response of embedded plies subjected to a homogeneous stress state. Three of the models are specifically designed for modeling the non-linear response due to distributed matrix cracking under homogeneous loading, and also account for non-linear (shear) behavior prior to the onset of cracking. The remaining two models are localized damage models intended for predicting local failure at stress concentrations. The modeling approaches of distributed vs. localized cracking as well as the different formulations of damage initiation and damage progression are compared and discussed.

  15. Speech intelligibility index predictions for young and old listeners in automobile noise: Can the index be improved by incorporating factors other than absolute threshold?

    NASA Astrophysics Data System (ADS)

    Saweikis, Meghan; Surprenant, Aimée M.; Davies, Patricia; Gallant, Don

    2003-10-01

    While young and old subjects with comparable audiograms tend to perform comparably on speech recognition tasks in quiet environments, the older subjects have more difficulty than the younger subjects with recognition tasks in degraded listening conditions. This suggests that factors other than an absolute threshold may account for some of the difficulty older listeners have on recognition tasks in noisy environments. Many metrics, including the Speech Intelligibility Index (SII), used to measure speech intelligibility, only consider an absolute threshold when accounting for age related hearing loss. Therefore these metrics tend to overestimate the performance for elderly listeners in noisy environments [Tobias et al., J. Acoust. Soc. Am. 83, 859-895 (1988)]. The present studies examine the predictive capabilities of the SII in an environment with automobile noise present. This is of interest because people's evaluation of the automobile interior sound is closely linked to their ability to carry on conversations with their fellow passengers. The four studies examine whether, for subjects with age related hearing loss, the accuracy of the SII can be improved by incorporating factors other than an absolute threshold into the model. [Work supported by Ford Motor Company.

  16. A new low threshold bi-directional wind vane and its potential impact on unplanned atmospheric release prediction

    SciTech Connect

    Parker, M.J.

    1996-12-31

    At the Savannah River Site, the Environmental Transport Group (ETG) maintains and develops a comprehensive meteorological monitoring program which employs bi-directional wind vanes (bivanes) for the measurement of horizontal and vertical wind direction and turbulence. Wind data collected near and below instrument starting thresholds under stable nighttime conditions with these bivanes can result in artificially large standard deviations of horizontal wind direction ({sigma}A). In one hypothetical case, downwind concentrations could be underestimated by a factor of 40 by using artificially high {sigma}A data in a Gaussian dispersion model. In an effort to improve low wind speed measurements of wind direction, a Cooperative Research and Development Agreement (CRADA) between Met One Instruments and the Westinghouse Savannah River Company (WSRC) has been created to improve the dynamic performance of the Met One Model 1585 Bi-Directional Wind Vane.

  17. Prediction of Damage in Randomly Oriented Short-Fibre Composites by means of A Mechanistic Approach

    SciTech Connect

    Nguyen, Ba Nghiep; Khaleel, Mohammad A.

    2004-05-01

    A micro-macro mechanistic approach to damage in short-fiber composites is developed in this paper. At the micro-scale, the damage mechanisms such as matrix cracking, fiber/matrix debonding are analyzed to define the associated damage variables. The stiffness reduction law dependent on these variables is then established using micromechanical models and average orientation distributions of fibers and microcracks. The macroscopic response is obtained by means of thermodynamics of continuous media, continuum damage mechanics and a finite element formulation.

  18. Prediction of Damage in Randomly Oriented Short-Fibre Composites by means of A Mechanistic Approach

    SciTech Connect

    Nguyen, Ba NGHIEP; Khaleel, Mohammad A.

    2004-03-01

    A micro-macro mechanistic approach to damage in short-fiber composites is developed in this paper. At the micro-scale, the damage mechanisms such as matrix cracking, fiber/matrix debonding are analyzed to define the associated damage variables. The stiffness reduction law dependent on these variables is then established using micromechanical models and average orientation distributions of fibers and microcracks. The macroscopic response is obtained by means of thermodynamics of continuous media, continuum damage mechanics and a finite element formulation.

  19. Evaluation of nonesterified fatty acids and beta-hydroxybutyrate in transition dairy cattle in the northeastern United States: Critical thresholds for prediction of clinical diseases.

    PubMed

    Ospina, P A; Nydam, D V; Stokol, T; Overton, T R

    2010-02-01

    The objectives of this study were to 1) establish cow-level critical thresholds for serum concentrations of nonesterified fatty acids (NEFA) and beta-hydroxybutyrate (BHBA) to predict periparturient diseases [displaced abomasa (DA), clinical ketosis (CK), metritis and retained placenta, or any of these three], and 2) investigate the magnitude of the metabolites' association with these diseases within 30 d in milk. In a prospective cohort study of 100 freestall, total mixed ration-fed herds in the northeastern United States, blood samples were collected from approximately 15 prepartum and 15 different postpartum transition animals in each herd, for a total of 2,758 samples. Serum NEFA concentrations were measured in the prepartum group, and both NEFA and BHBA were measured in the postpartum group. The critical thresholds for NEFA or BHBA were evaluated with receiver operator characteristic analysis for all diseases in both cohorts. The risk ratios (RR) of a disease outcome given NEFA or BHBA concentrations and other covariates were modeled with multivariable regression techniques, accounting for clustering of cows within herds. The NEFA critical threshold that predicted any of the 3 diseases in the prepartum cohort was 0.29mEq/L and in the postpartum cohort was 0.57mEq/L. The critical threshold for serum BHBA in the postpartum cohort was 10mg/dL, which predicted any of the 3 diseases. All RR with NEFA as a predictor of disease were >1.8; however, RR were greatest in animals sampled postpartum (e.g., RR for DA=9.7; 95% CI=4.2 to 22.4. All RR with BHBA as the predictor of disease were >2.3 (e.g., RR for DA=6.9; 95% CI=3.7 to 12.9). Although prepartum NEFA and postpartum BHBA were both significantly associated with development of clinical disease, postpartum serum NEFA concentration was most associated with the risk of developing DA, CK, metritis, or retained placenta during the first 30 d in milk. PMID:20105526

  20. Weighted quantification of ¹⁸F-FDG tumor metabolism activity using fuzzy-thresholding to predict post-treatment tumor recurrence.

    PubMed

    Roman-Jimenez, Geoffrey; Acosta, Oscar; Leseur, Julie; Devillers, Anne; Le Gouestre, Jonathan; Ospina, Juan-David; Simon, Antoine; Terve, Pierre; De Crevoisier, Renaud

    2015-08-01

    Cervical cancer is one of the most common cancer to affect women worldwide. Despite the efficiency of radiotherapy treatment, some patients present post-treatment tumor recurrence which increases the risk of death. Early outcome prediction could help oncologists to adapt the treatment. Several studies suggest that quantification of tumor activity using (18)FFDG PET imaging could be used to predict post-treatment tumor recurrence. In this paper we study the predictive value of weighted quantification of tumor metabolism extracted by fuzzy-thresholding for tumor recurrence of locally advanced cervical cancer. Fifty-three patients with locally advanced cervical cancer treated by chemo-radiotherapy were considered in our study. For each patient, a coregistered (18)F-FDG PET/CT scan was acquired before the treatment and was segmented using different hard and fuzzy segmentations methods. The tumor activity was extracted through the total lesion glycolysis and through a weighted analog of the total lesion glycolysis using the probability maps provided by the fuzzy segmentations. Outcomes prediction was performed using the area under the receiver operating characteristic curve (AUC) and the Harrell's C-index. Results suggest that weighted quantification of tumor activity seems to be strongly informative and could be used to predict post-treatment tumor recurrence in cervical cancer. PMID:26736737

  1. Assessing the safety of cosmetic chemicals: Consideration of a flux decision tree to predict dermally delivered systemic dose for comparison with oral TTC (Threshold of Toxicological Concern).

    PubMed

    Williams, Faith M; Rothe, Helga; Barrett, Gordon; Chiodini, Alessandro; Whyte, Jacqueline; Cronin, Mark T D; Monteiro-Riviere, Nancy A; Plautz, James; Roper, Clive; Westerhout, Joost; Yang, Chihae; Guy, Richard H

    2016-04-01

    Threshold of Toxicological Concern (TTC) aids assessment of human health risks from exposure to low levels of chemicals when toxicity data are limited. The objective here was to explore the potential refinement of exposure for applying the oral TTC to chemicals found in cosmetic products, for which there are limited dermal absorption data. A decision tree was constructed to estimate the dermally absorbed amount of chemical, based on typical skin exposure scenarios. Dermal absorption was calculated using an established predictive algorithm to derive the maximum skin flux adjusted to the actual 'dose' applied. The predicted systemic availability (assuming no local metabolism), can then be ranked against the oral TTC for the relevant structural class. The predictive approach has been evaluated by deriving the experimental/prediction ratio for systemic availability for 22 cosmetic chemical exposure scenarios. These emphasise that estimation of skin penetration may be challenging for penetration enhancing formulations, short application times with incomplete rinse-off, or significant metabolism. While there were a few exceptions, the experiment-to-prediction ratios mostly fell within a factor of 10 of the ideal value of 1. It can be concluded therefore, that the approach is fit-for-purpose when used as a screening and prioritisation tool. PMID:26825378

  2. A stochastic damage model for the rupture prediction of a multi-phase solid. I - Parametric studies. II - Statistical approach

    NASA Technical Reports Server (NTRS)

    Lua, Yuan J.; Liu, Wing K.; Belytschko, Ted

    1992-01-01

    A stochastic damage model for predicting the rupture of a brittle multiphase material is developed, based on the microcrack-macrocrack interaction. The model, which incorporates uncertainties in locations, orientations, and numbers of microcracks, characterizes damage by microcracking and fracture by macrocracking. A parametric study is carried out to investigate the change of the stress intensity at the macrocrack tip by the configuration of microcracks. The inherent statistical distribution of the fracture toughness arising from the intrinsic random nature of microcracks is explored using a statistical approach. For this purpose, a computer simulation model is introduced, which incorporates a statistical characterization of geometrical parameters of a random microcrack array.

  3. Predicting Thaumastocoris peregrinus damage using narrow band normalized indices and hyperspectral indices using field spectra resampled to the Hyperion sensor

    NASA Astrophysics Data System (ADS)

    Oumar, Z.; Mutanga, O.; Ismail, R.

    2013-04-01

    Thaumastocoris peregrinus (T. peregrinus) is a sap sucking insect that feeds on Eucalyptus leaves. It poses a threat to the forest industry by reducing the photosynthetic ability of the tree, resulting in stunted growth and even death of severely infested trees. Remote sensing techniques offer the potential to detect and map T. peregrinus infestations in plantation forests using current operational hyperspectral scanners. This study resampled field spectral data measured from a field spectrometer to the band settings of the Hyperion sensor in order to assess its potential in predicting T. peregrinus damage. Normalized indices based on NDVI ratios were calculated using the resampled visible and near-infrared bands of the Hyperion sensor to assess its utility in predicting T. peregrinus damage using Partial Least Squares (PLS) regression. The top 20 normalized indices were based on specific biochemical absorption features that predicted T. peregrinus damage with a mean bootstrapped R2 value of 0.63 on an independent test dataset. The top 20 indices were located in the near-infrared region between 803.3 nm and 894.9 nm. Twenty three previously published hyperspectral indices which have been used to assess stress in vegetation were also used to predict T. peregrinus damage and resulted in a mean bootstrapped R2 value of 0.59 on an independent test dataset. The datasets were combined to assess its collective strength in predicting T. peregrinus damage and significant indices were chosen based on variable importance scores (VIP) and were then entered into a PLS model. The indices chosen by VIP predicted T. peregrinus damage with a mean bootstrapped R2 value of 0.71 on an independent test dataset. A greedy backward variable selection model was further tested on the VIP selected indices in order to find the best subset of indices with the best predictive accuracy. The greedy backward variable selection model identified 3 indices and performed the best by predicting damage

  4. Particle Arrangement Design for Predicting the Percolation Threshold of Silver/Epoxy Composite for Electrically Conductive Adhesive Application

    NASA Astrophysics Data System (ADS)

    Zulkarnain, M.; Husaini, Muhammad; Mariatti, M.; Azid, I. A.

    2015-11-01

    The early use of electrically conductive adhesives (ECAs) provided an alternative to solder because of their several advantages, such as good electrical conductivity, low cost, extendability to fine pitch of interconnecting material and environmental friendliness. According to previous works, an optimal particle volume fraction became a major objective of many researchers in order to obtain highly conductive ECAs, realizing that the need for transitions from an insulator to a conductor is controlled by the geometric arrangement of particles. In the current study, particle arrangement models of ECAs are developed by establishing the effects of van der Waals' attraction energy and particle motion, which act as a kind of particle interaction to generate a conducting structure. The methodology is divided into three major parts: the formulation of a particle arrangement technique, and numerical and experimental studies. The formulation of particle arrangement is developed in an epoxy colloidal system. During verification, the particle arrangement model is validated by the theoretical fractal dimension and guided by a morphological study of the experimental assessments. The model was simulated through representative volume elements with the volume fraction factor, which was set in the range of 2-8 vol.%, while electrical conductivity was an observed parameter. The numerical results showed good agreement with the experiments in which the percolation threshold occurred between 4 and 6% of the volume of filler loading.

  5. Hydrological extremes in Calabria (Italy): the potential of historical data for predicting rainfall/damage scenarios

    NASA Astrophysics Data System (ADS)

    Caloiero, Tommaso; Petrucci, Olga; Pasqua, A. Aurora

    2015-04-01

    A Damaging Hydrogeological Event (DHE) is made of two components: a Rainfall Event and a subsequent Damage Event, resulting from floods and landslides triggered by rainfall. The characteristics of both events depend on climatic, geomorphological and anthropogenic factors. In fact, depending on both rivers and slopes conditions, the same rain amount either can or cannot cause damage. Moreover, damage occurrence also depends on the geographical distribution of damageable elements such as population, lifelines and urbanized sectors. In this paper, a methodology based on a chart, which considers indicators of both the Damage (Dscore) and the daily Rainfall values (Rscore) recorded in a study area, has been applied to classify the severity of DHEs. In particular, the methodology was applied to a series of 30 DHEs which occurred in Calabria (southern Italy) between 1981 and 2010. According to the chart, the events were classified into four types: ordinary events, having low Dscore and Rscore values; extraordinary events, with high Rscore values but low Dscore values; catastrophic events, characterized by non-exceptional rainfall (low Rscore) and severe damage (high Dscore); major catastrophic events, obtained by high Dscore and Rscore values. The objective of this study was the production of a chart that will enable an objective classification of the severity of the DHEs that the media accounts and first or second-hand personal accounts fail to provide.

  6. Cavitation damage prediction for spallation target vessels by assessment of acoustic vibration

    SciTech Connect

    Futakawa, Masatoshi; Kogawa, Hiroyuki; Hasegawa, Shoichi; Ikeda, Dr. Yujiro; Riemer, Bernie; Wendel, Mark W; Haines, John R; Bauer, Guenter; Naoe, Dr. Takashi; Okita, Dr. Kohei; Fujiwara, Dr. Akiko; Matsumoto, Dr. Yoichiro; Tanaka, Dr. Nobuatsu

    2008-01-01

    Liquid-mercury target systems for MW-class spallation neutron sources are being developed around the world. Proton beams are used to induce the spallation reaction. At the moment the proton beam hits the target, pressure waves are generated in the mercury because of the abrupt heat deposition. The pressure waves interact with the target vessel leading to negative pressure that may cause cavitation along the vessel wall. In order to estimate the cavitation erosion, i.e. the pitting damage formed by the collapse of cavitation bubbles, off-beam tests were performed by using an electric magnetic impact testing machine (MIMTM), which can impose equivalent pressure pulses in mercury. The damage potential was defined based on the relationship between the pitting damage and the time-integrated acoustic vibration induced by impact due to the bubble collapses. Additionally, the damage potential was measured in on-beam tests carried out by using the proton beam at WNR (Weapons Neutron Research) facility in Los Alamos Neutron Science Center (LANSCE). In this paper, the concept of the damage potential, the relationship between the pitting damage formation and the damage potential both in off-beam and on-beam tests is shown.

  7. Re-assess Vector Indices Threshold as an Early Warning Tool for Predicting Dengue Epidemic in a Dengue Non-endemic Country

    PubMed Central

    Hsu, Pi-Shan; Chen, Chaur-Dong; Lian, Ie-Bin; Chao, Day-Yu

    2015-01-01

    Background Despite dengue dynamics being driven by complex interactions between human hosts, mosquito vectors and viruses that are influenced by climate factors, an operational model that will enable health authorities to anticipate the outbreak risk in a dengue non-endemic area has not been developed. The objectives of this study were to evaluate the temporal relationship between meteorological variables, entomological surveillance indices and confirmed dengue cases; and to establish the threshold for entomological surveillance indices including three mosquito larval indices [Breteau (BI), Container (CI) and House indices (HI)] and one adult index (AI) as an early warning tool for dengue epidemic. Methodology/Principal Findings Epidemiological, entomological and meteorological data were analyzed from 2005 to 2012 in Kaohsiung City, Taiwan. The successive waves of dengue outbreaks with different magnitudes were recorded in Kaohsiung City, and involved a dominant serotype during each epidemic. The annual indigenous dengue cases usually started from May to June and reached a peak in October to November. Vector data from 2005–2012 showed that the peak of the adult mosquito population was followed by a peak in the corresponding dengue activity with a lag period of 1–2 months. Therefore, we focused the analysis on the data from May to December and the high risk district, where the inspection of the immature and mature mosquitoes was carried out on a weekly basis and about 97.9% dengue cases occurred. The two-stage model was utilized here to estimate the risk and time-lag effect of annual dengue outbreaks in Taiwan. First, Poisson regression was used to select the optimal subset of variables and time-lags for predicting the number of dengue cases, and the final results of the multivariate analysis were selected based on the smallest AIC value. Next, each vector index models with selected variables were subjected to multiple logistic regression models to examine the

  8. Autoantibodies predicting the outcome of rheumatoid arthritis: evaluation in two subsets of patients according to severity of radiographic damage

    PubMed Central

    Meyer, O; Combe, B; Elias, A; Benali, K; Clot, J; Sany, J; Eliaou, J

    1997-01-01

    OBJECTIVE—Autoantibodies such as rheumatoid factor (RF), antikeratin antibodies (AKA), antiperinuclear factor (APF), and anti-RA 33 antibodies are considered of value for the diagnosis of RA. The purpose of this study was to evaluate these autoantibodies as predictors of severe radiographic damage in rheumatoid arthritis (RA). 
PATIENTS AND METHODS—Eighty six patients with RA (70 women, 16 men) fulfilling 1987 ACR criteria were selected from a cohort of 469 patients followed up since the first year of RA onset because they could be divided in two groups according to the severity of the radiographic damage. These 86 patients had a mean (SD) disease duration of eight (four) years: 43 patients had severe radiographic damage (Larsen score ⩾2) and 43 had limited radiographic damage (Larsen score < 2). The two groups were matched by disease duration and sex. The following autoantibodies were looked for: RF, ANA, AKA, APF, and anti-RA 33 antibodies. In addition, HLA class II DR β alleles and standard inflammatory parameters (erythrocyte sedimentation rate, C reactive protein) were determined.
RESULTS—Patients with severe radiographic damage differed from those with limited radiographic damage in that they had higher RF (p=0.01), APF (p<0.02), and AKA (p=0.001) titres. Stepwise regression analysis was done to calculate the odds ratios (OR) for each clinical and laboratory variable; only presence of cutaneous nodules (OR: 14.9; 95% CI: 7, 128), HLA DRB1*04 or DRB1*01 (OR: 7.53; 95% CI: 1.32, 42.9), AKA (OR: 3.11; 95%, CI: 0.58, 16.8 ), a high erthrocyte sedimentation rate (OR: 2.66; 95% CI: 0.60, 11.9), and a high C reactive protein value (OR: 7.4; 95% CI : 1.43, 38.1) were predictive of severe radiographic damage.
CONCLUSION—These data suggest that the risk of severe radiographic damage in RA patients is higher when cutaneous nodules, HLA DRB1*04 or DRB1*01, and/or AKA are present. The other autoantibodies of diagnostic significance are

  9. A numerical model for predicting crack path and modes of damage in unidirectional metal matrix composites

    NASA Technical Reports Server (NTRS)

    Bakuckas, J. G.; Tan, T. M.; Lau, A. C. W.; Awerbuch, J.

    1993-01-01

    A finite element-based numerical technique has been developed to simulate damage growth in unidirectional composites. This technique incorporates elastic-plastic analysis, micromechanics analysis, failure criteria, and a node splitting and node force relaxation algorithm to create crack surfaces. Any combination of fiber and matrix properties can be used. One of the salient features of this technique is that damage growth can be simulated without pre-specifying a crack path. In addition, multiple damage mechanisms in the forms of matrix cracking, fiber breakage, fiber-matrix debonding and plastic deformation are capable of occurring simultaneously. The prevailing failure mechanism and the damage (crack) growth direction are dictated by the instantaneous near-tip stress and strain fields. Once the failure mechanism and crack direction are determined, the crack is advanced via the node splitting and node force relaxation algorithm. Simulations of the damage growth process in center-slit boron/aluminum and silicon carbide/titanium unidirectional specimens were performed. The simulation results agreed quite well with the experimental observations.

  10. Investigation of Bearing Fatigue Damage Life Prediction Using Oil Debris Monitoring

    NASA Technical Reports Server (NTRS)

    Dempsey, Paula J.; Bolander, Nathan; Haynes, Chris; Toms, Allison M.

    2011-01-01

    Research was performed to determine if a diagnostic tool for detecting fatigue damage of helicopter tapered roller bearings can be used to determine remaining useful life (RUL). The taper roller bearings under study were installed on the tail gearbox (TGB) output shaft of UH- 60M helicopters, removed from the helicopters and subsequently installed in a bearing spall propagation test rig. The diagnostic tool was developed and evaluated experimentally by collecting oil debris data during spall progression tests on four bearings. During each test, data from an on-line, in-line, inductance type oil debris sensor was monitored and recorded for the occurrence of pitting damage. Results from the four bearings tested indicate that measuring the debris generated when a bearing outer race begins to spall can be used to indicate bearing damage progression and remaining bearing life.

  11. Aircraft ground damage and the use of predictive models to estimate costs

    NASA Astrophysics Data System (ADS)

    Kromphardt, Benjamin D.

    Aircraft are frequently involved in ground damage incidents, and repair costs are often accepted as part of doing business. The Flight Safety Foundation (FSF) estimates ground damage to cost operators $5-10 billion annually. Incident reports, documents from manufacturers or regulatory agencies, and other resources were examined to better understand the problem of ground damage in aviation. Major contributing factors were explained, and two versions of a computer-based model were developed to project costs and show what is possible. One objective was to determine if the models could match the FSF's estimate. Another objective was to better understand cost savings that could be realized by efforts to further mitigate the occurrence of ground incidents. Model effectiveness was limited by access to official data, and assumptions were used if data was not available. However, the models were determined to sufficiently estimate the costs of ground incidents.

  12. Predicted Role of NAD Utilization in the Control of Circadian Rhythms during DNA Damage Response.

    PubMed

    Luna, Augustin; McFadden, Geoffrey B; Aladjem, Mirit I; Kohn, Kurt W

    2015-05-01

    The circadian clock is a set of regulatory steps that oscillate with a period of approximately 24 hours influencing many biological processes. These oscillations are robust to external stresses, and in the case of genotoxic stress (i.e. DNA damage), the circadian clock responds through phase shifting with primarily phase advancements. The effect of DNA damage on the circadian clock and the mechanism through which this effect operates remains to be thoroughly investigated. Here we build an in silico model to examine damage-induced circadian phase shifts by investigating a possible mechanism linking circadian rhythms to metabolism. The proposed model involves two DNA damage response proteins, SIRT1 and PARP1, that are each consumers of nicotinamide adenine dinucleotide (NAD), a metabolite involved in oxidation-reduction reactions and in ATP synthesis. This model builds on two key findings: 1) that SIRT1 (a protein deacetylase) is involved in both the positive (i.e. transcriptional activation) and negative (i.e. transcriptional repression) arms of the circadian regulation and 2) that PARP1 is a major consumer of NAD during the DNA damage response. In our simulations, we observe that increased PARP1 activity may be able to trigger SIRT1-induced circadian phase advancements by decreasing SIRT1 activity through competition for NAD supplies. We show how this competitive inhibition may operate through protein acetylation in conjunction with phosphorylation, consistent with reported observations. These findings suggest a possible mechanism through which multiple perturbations, each dominant during different points of the circadian cycle, may result in the phase advancement of the circadian clock seen during DNA damage. PMID:26020938

  13. Predicted Role of NAD Utilization in the Control of Circadian Rhythms during DNA Damage Response

    PubMed Central

    Luna, Augustin; McFadden, Geoffrey B.; Aladjem, Mirit I.; Kohn, Kurt W.

    2015-01-01

    The circadian clock is a set of regulatory steps that oscillate with a period of approximately 24 hours influencing many biological processes. These oscillations are robust to external stresses, and in the case of genotoxic stress (i.e. DNA damage), the circadian clock responds through phase shifting with primarily phase advancements. The effect of DNA damage on the circadian clock and the mechanism through which this effect operates remains to be thoroughly investigated. Here we build an in silico model to examine damage-induced circadian phase shifts by investigating a possible mechanism linking circadian rhythms to metabolism. The proposed model involves two DNA damage response proteins, SIRT1 and PARP1, that are each consumers of nicotinamide adenine dinucleotide (NAD), a metabolite involved in oxidation-reduction reactions and in ATP synthesis. This model builds on two key findings: 1) that SIRT1 (a protein deacetylase) is involved in both the positive (i.e. transcriptional activation) and negative (i.e. transcriptional repression) arms of the circadian regulation and 2) that PARP1 is a major consumer of NAD during the DNA damage response. In our simulations, we observe that increased PARP1 activity may be able to trigger SIRT1-induced circadian phase advancements by decreasing SIRT1 activity through competition for NAD supplies. We show how this competitive inhibition may operate through protein acetylation in conjunction with phosphorylation, consistent with reported observations. These findings suggest a possible mechanism through which multiple perturbations, each dominant during different points of the circadian cycle, may result in the phase advancement of the circadian clock seen during DNA damage. PMID:26020938

  14. A Functional Threshold for Long-Term Use of Hand and Arm Function Can Be Determined: Predictions From a Computational Model and Supporting Data From the Extremity Constraint-Induced Therapy Evaluation (EXCITE) Trial

    PubMed Central

    Han, Cheol E.; Wolf, Steven L.; Arbib, Michael A.; Winstein, Carolee J.

    2009-01-01

    Background Although spontaneous use of the more-affected arm and hand after stroke is an important determinant of participation and quality of life, a number of patients exhibit decreases in use following rehabilitative therapy. A previous neurocomputational model predicted that if the dose of therapy is sufficient to bring performance above a certain threshold, training can be stopped. Objective The aim of this study was to test the hypothesis that there exists a threshold for function of the paretic arm and hand after therapy. If function is above this threshold, spontaneous use will increase in the months following therapy. In contrast, if function is below this threshold, spontaneous use will decrease. Methods New computer simulations are presented showing that changes in arm use following therapy depend on a performance threshold. This prediction was tested by reanalyzing the data from the Extremity Constraint-Induced Therapy Evaluation (EXCITE) trial, a phase III randomized controlled trial in which participants received constraint-induced movement therapy for 2 weeks and were tested both 1 week and 1 year after therapy. Results The results demonstrate that arm and hand function measured immediately after therapy predicts, on average, the long-term change of arm use. Above a functional threshold, use improves. Below this threshold, use decreases. Limitations The reanalysis of the EXCITE trial data provides a “group” threshold above which a majority of patients, but not all, improve spontaneously. A goal of future research is to provide the means to assess when patients reach their individual threshold. Conclusion Understanding of the causal and nonlinear relationship between limb function and daily use is important for the future development of cost-effective interventions and prevention of “rehabilitation in vain.” PMID:19797304

  15. Prediction of Damage Extension in CFRP Quasi-Isotropic Laminated Plates under Low-Velocity Impact

    NASA Astrophysics Data System (ADS)

    Zemba, Yutaka; Hu, Ning; Hara, Eiichi; Fukunaga, Hisao

    In this paper, to understand the mechanism of delamination propagation in low-velocity impact problems, a weight-drop test is performed for quasi-isotropic composite plates of 32 plies. Due to the high computational cost, up to date, there have been almost no computational effects for simulating the damage propagations in quasi-isotropic composite laminates of 32 plies. This low-velocity impact problem is further numerically modeled and the damage propagation is simulated. A stress-based criterion is adopted for modeling various in-plane damages, such as transverse matrix cracking. A bi-linear cohesive interface model is employed for interface damages, such as delaminations. Moreover, to remove the numerical instability in simulations when using the traditional cohesive model, we propose a new technique, i.e., adaptive cohesive model. The effectiveness of this cohesive model is investigated using a DCB example. Then, it is applied to the low-velocity impact problem of quasi-isotropic composite laminates of 32 plies. The validity of the proposed numerical methodology is verified by comparing the numerical results with the experimental results.

  16. Detection and Prediction of Creep-Damage of Copper Using Nonlinear Acoustic Techniques

    NASA Astrophysics Data System (ADS)

    Narayana, V. J. S.; Balasubramaniam, K.; Prakash, R. V.

    2010-02-01

    This paper describes the use of nonlinear acoustic techniques for the characterization of material damage gradient in 99.98% pure copper due to high temperature creep. Creep damage progression was monitored by conducting continuous and interrupted modes of creep tests. In case of continuous loading, nonlinear ultrasonic (NLU) measurements were conducted, after fracture at different locations along the gage length of the sample. For interrupted tests, the NLU measurements were conducted at different creep life fractions, through periodic interruption of creep test. The third harmonic was more sensitive to creep damage compared to second and static component nonlinearity. All samples show one peak in the nonlinear response at 25-45% of creep life. Finally, we presented the results of nonlinear response working at low power levels, since the interesting effect of accumulated dislocations. Using that effect we applied to creep damage detection. In this the NLU amplitude vs. input amplitude was observed to correlate well with the micro-void concentrations caused by creep conditions.

  17. Isothermal life prediction of composite lamina using a damage mechanics approach

    NASA Technical Reports Server (NTRS)

    Abuelfoutouh, Nader Mohamed; Verrilli, M. J.; Halford, G. R.

    1989-01-01

    A method for predicting isothermal plastic fatigue life of a composite lamina is presented in which both fibers and matrix are isotropic materials. In general, the fatigue resistances of the matrix, fibers, and interfacial material must be known in order to predict composite fatigue life. Composite fatigue life is predicted using only the matrix fatigue resistance due to inelasticity micromechanisms. The effect of the fiber orientation on loading direction is accounted for while predicting composite life. The application is currently limited to isothermal cases where the internal thermal stresses that might arise from thermal strain mismatch between fibers and matrix are negligible. The theory is formulated to predict the fatigue life of a composite lamina under either load or strain control. It is applied currently to predict the life of tungsten-copper composite lamina at 260 C under tension-tension load control. The calculated life of the lamina is in good agreement with available composite low cycle fatigue data.

  18. Electrical Resistance of SiC/SiC Ceramic Matrix Composites for Damage Detection and Life-Prediction

    NASA Technical Reports Server (NTRS)

    Smith, Craig; Morscher, Gregory; Xia, Zhenhai

    2009-01-01

    Ceramic matrix composites (CMC) are suitable for high temperature structural applications such as turbine airfoils and hypersonic thermal protection systems due to their low density high thermal conductivity. The employment of these materials in such applications is limited by the ability to accurately monitor and predict damage evolution. Current nondestructive methods such as ultrasound, x-ray, and thermal imaging are limited in their ability to quantify small scale, transverse, in-plane, matrix cracks developed over long-time creep and fatigue conditions. CMC is a multifunctional material in which the damage is coupled with the material s electrical resistance, providing the possibility of real-time information about the damage state through monitoring of resistance. Here, resistance measurement of SiC/SiC composites under mechanical load at both room temperature monotonic and high temperature creep conditions, coupled with a modal acoustic emission technique, can relate the effects of temperature, strain, matrix cracks, fiber breaks, and oxidation to the change in electrical resistance. A multiscale model can in turn be developed for life prediction of in-service composites, based on electrical resistance methods. Results of tensile mechanical testing of SiC/SiC composites at room and high temperatures will be discussed. Data relating electrical resistivity to composite constituent content, fiber architecture, temperature, matrix crack formation, and oxidation will be explained, along with progress in modeling such properties.

  19. Fully Coupled Micro/Macro Deformation, Damage, and Failure Prediction for SiC/Ti-15-3 Laminates

    NASA Technical Reports Server (NTRS)

    Bednarcyk, Brett A.; Arnold, Steven M.; Lerch, Brad A.

    2001-01-01

    The deformation, failure, and low cycle fatigue life of SCS-6/Ti-15-3 composites are predicted using a coupled deformation and damage approach in the context of the analytical generalized method of cells (GMC) micromechanics model. The local effects of inelastic deformation, fiber breakage, fiber-matrix interfacial debonding, and fatigue damage are included as sub-models that operate on the micro scale for the individual composite phases. For the laminate analysis, lamination theory is employed as the global or structural scale model, while GMC is embedded to operate on the meso scale to simulate the behavior of the composite material within each laminate layer. While the analysis approach is quite complex and multifaceted, it is shown, through comparison with experimental data, to be quite accurate and realistic while remaining extremely efficient.

  20. Prediction of Corrosion Fatigue Damages for Turbine Blades Subjecting to Randomly Distributed Power System Unbalance

    NASA Astrophysics Data System (ADS)

    Lin, Chi-Hshiung

    In this paper, a fatigue damage estimation procedure is implemented by integrating the results of an EPRI and a GE testing reports as well as a shareware developed by the Oslo University, which is incorporated with a verified transient simulation program developed by the Aberdeen University to study the effects of power system unbalance on turbine blade damaging. Based on the Weibull distribution in the negative sequence current (I2) and the operational environment containing 22% NaCl, the probability level of fatigue life as well as the reliability against fatigue failure for the long blades of low-pressure (LP) turbine are evaluated. It is shown that even though the blades could withstand the most serious impact arising from three-phase-to-ground fault, still it cannot guarantee adequate long-term reliability in the normal operational condition.

  1. Predicting fault damage zones by modeling dynamic rupture propagation and comparison with field observations

    NASA Astrophysics Data System (ADS)

    Johri, Madhur; Dunham, Eric M.; Zoback, Mark D.; Fang, Zijun

    2014-02-01

    We use a two-dimensional plane strain dynamic rupture model with strongly rate-weakening friction and off-fault Drucker-Prager plasticity to model damage zones associated with buried second-order thrust faults observed in the SSC reservoir. The modeling of ruptures propagating as self-sustaining pulses is performed in the framework of continuum plasticity where the plasticity formulation includes both deviatoric and volumetric plastic strains. The material deforming inelastically due to stress perturbations generated by the propagating rupture is assumed to be the damage zone associated with the fault. Dilatant plastic strains are converted into a fracture population by assuming that the dilatant plastic strain is manifested in the form of fractures. The cumulative effect of multiple slip events is considered by superposition of the plastic strain field obtained from individual slip events. The relative number of various magnitude slip events is chosen so as to honor the Gutenberg-Richter law. Results show that the decay of fracture density (F) with distance (r) from the fault can be described by a power law F = F0r- n. The fault constant F0 represents the fracture density at unit distance from the fault. The decay rate (n) in fracture density is approximately 0.85 close to the fault and increases to ~1.4 at larger distances (>10 m). Modeled damage zones are approximately 60-100 m wide. These attributes are similar to those observed in the SSC reservoir using wellbore image logs and those reported in outcrop studies. Considering fault roughness affects local damage zone characteristics, these characteristics are similar to those modeled around planar faults at a scale (~10 m) that affects bulk fluid-flow properties.

  2. Prediction of Cardiovascular Disease Risk by Cardiac Biomarkers in 2 United Kingdom Cohort Studies: Does Utility Depend on Risk Thresholds For Treatment?

    PubMed

    Welsh, Paul; Hart, Carole; Papacosta, Olia; Preiss, David; McConnachie, Alex; Murray, Heather; Ramsay, Sheena; Upton, Mark; Watt, Graham; Whincup, Peter; Wannamethee, Goya; Sattar, Naveed

    2016-02-01

    We tested the predictive ability of cardiac biomarkers N-terminal pro B-type natriuretic peptide (NT-proBNP), high-sensitivity troponin T, and midregional pro adrenomedullin for cardiovascular disease (CVD) events using the British Regional Heart Study (BRHS) of men aged 60 to 79 years, and the MIDSPAN Family Study (MFS) of men and women aged 30 to 59 years. They included 3757 and 2226 participants, respectively, and during median 13.0 and 17.3 years follow-up the primary CVD event rates were 16.6 and 5.3 per 1000 patient-years, respectively. In Cox models adjusted for basic classical risk factors, 1 SD increases in log-transformed NT-proBNP, high-sensitivity troponin T, and midregional pro adrenomedullin were generally associated with increased primary CVD risk in both the studies (P<0.006) except midregional pro adrenomedullin in MFS (P=0.10). In BRHS, QRISK2 risk factors yielded a C-index of 0.657, which was improved by 0.017 (P=0.005) by NT-proBNP, but not by other biomarkers. Using 28% 14-year risk as a proxy for 20% 10-year risk, NT-proBNP improved risk classification for primary CVD cases (case net reclassification index, 5.9%; 95% confidence interval, 2.8%-9.2%), but only improved classification of noncases at a 14% 14-year risk threshold (4.6%; 2.9%-6.3%). In MFS, ASSIGN risk factors yielded a C-index of 0.752 for primary CVD; none of the cardiac biomarkers improved the C-index. Improvements in risk classification were only seen using NT-proBNP and high-sensitivity troponin T among cases using the 28% 14-year risk threshold (4.7%; 1.0%-9.2% and 2.6%; 0.0%-5.8%, respectively). In conclusion, the improvement in treatment allocation gained by adding cardiac biomarkers to risk scores seems to depend on the risk threshold chosen for commencing preventative treatments. PMID:26667414

  3. Population and assay thresholds for the predictive value of lipoprotein (a) for coronary artery disease: the EPIC-Norfolk Prospective Population Study.

    PubMed

    Verbeek, Rutger; Boekholdt, S Matthijs; Stoekenbroek, Robert M; Hovingh, G Kees; Witztum, Joseph L; Wareham, Nicholas J; Sandhu, Manjinder S; Khaw, Kay-Tee; Tsimikas, Sotirios

    2016-04-01

    Variable agreement exists between different lipoprotein (a) [Lp(a)] measurement methods, but their clinical relevance remains unclear. The predictive value of Lp(a) measured by two different assays [Randox and University of California, San Diego (UCSD)] was determined in 623 coronary artery disease (CAD) cases and 948 controls in a case-control study within the EPIC-Norfolk Prospective Population Study. Participants were divided into sex-specific quintiles, and by Lp(a) <50 versus ∼50 mg/dl, which represents the 80th percentile in northern European subjects. Randox and UCSD Lp(a) levels were strongly correlated; Spearman's correlation coefficients for men, women, and sexes combined were 0.905, 0.915, and 0.909, respectively (P< 0.001 for each). The >80th percentile cutoff values, however, were 36 mg/dl and 24 mg/dl for the Randox and UCSD assays, respectively. Despite this, Lp(a) levels were significantly associated with CAD risk, with odds ratios of 2.18 (1.58-3.01) and 2.35 (1.70-3.26) for people in the top versus bottom Lp(a) quintile for the Randox and UCSD assays, respectively. This study demonstrates that CAD risk is present at lower Lp(a) levels than the currently suggested optimal Lp(a) level of <50 mg/dl. Appropriate thresholds may need to be population and assay specific until Lp(a) assays are standardized and Lp(a) thresholds are evaluated broadly across all populations at risk for CVD and aortic stenosis. PMID:26828068

  4. Gear Damage Detection Using Oil Debris Analysis

    NASA Technical Reports Server (NTRS)

    Dempsey, Paula J.

    2001-01-01

    The purpose of this paper was to verify, when using an oil debris sensor, that accumulated mass predicts gear pitting damage and to identify a method to set threshold limits for damaged gears. Oil debris data was collected from 8 experiments with no damage and 8 with pitting damage in the NASA Glenn Spur Gear Fatigue Rig. Oil debris feature analysis was performed on this data. Video images of damage progression were also collected from 6 of the experiments with pitting damage. During each test, data from an oil debris sensor was monitored and recorded for the occurrence of pitting damage. The data measured from the oil debris sensor during experiments with damage and with no damage was used to identify membership functions to build a simple fuzzy logic model. Using fuzzy logic techniques and the oil debris data, threshold limits were defined that discriminate between stages of pitting wear. Results indicate accumulated mass combined with fuzzy logic analysis techniques is a good predictor of pitting damage on spur gears.

  5. Methods Developed by the Tools for Engine Diagnostics Task to Monitor and Predict Rotor Damage in Real Time

    NASA Technical Reports Server (NTRS)

    Baaklini, George Y.; Smith, Kevin; Raulerson, David; Gyekenyesi, Andrew L.; Sawicki, Jerzy T.; Brasche, Lisa

    2003-01-01

    Tools for Engine Diagnostics is a major task in the Propulsion System Health Management area of the Single Aircraft Accident Prevention project under NASA s Aviation Safety Program. The major goal of the Aviation Safety Program is to reduce fatal aircraft accidents by 80 percent within 10 years and by 90 percent within 25 years. The goal of the Propulsion System Health Management area is to eliminate propulsion system malfunctions as a primary or contributing factor to the cause of aircraft accidents. The purpose of Tools for Engine Diagnostics, a 2-yr-old task, is to establish and improve tools for engine diagnostics and prognostics that measure the deformation and damage of rotating engine components at the ground level and that perform intermittent or continuous monitoring on the engine wing. In this work, nondestructive-evaluation- (NDE-) based technology is combined with model-dependent disk spin experimental simulation systems, like finite element modeling (FEM) and modal norms, to monitor and predict rotor damage in real time. Fracture mechanics time-dependent fatigue crack growth and damage-mechanics-based life estimation are being developed, and their potential use investigated. In addition, wireless eddy current and advanced acoustics are being developed for on-wing and just-in-time NDE engine inspection to provide deeper access and higher sensitivity to extend on-wing capabilities and improve inspection readiness. In the long run, these methods could establish a base for prognostic sensing while an engine is running, without any overt actions, like inspections. This damage-detection strategy includes experimentally acquired vibration-, eddy-current- and capacitance-based displacement measurements and analytically computed FEM-, modal norms-, and conventional rotordynamics-based models of well-defined damages and critical mass imbalances in rotating disks and rotors.

  6. Aberrant DNA Damage Response Pathways May Predict the Outcome of Platinum Chemotherapy in Ovarian Cancer

    PubMed Central

    Stefanou, Dimitra T.; Bamias, Aristotelis; Episkopou, Hara; Kyrtopoulos, Soterios A.; Likka, Maria; Kalampokas, Theodore; Photiou, Stylianos; Gavalas, Nikos; Sfikakis, Petros P.; Dimopoulos, Meletios A.; Souliotis, Vassilis L.

    2015-01-01

    Ovarian carcinoma (OC) is the most lethal gynecological malignancy. Despite the advances in the treatment of OC with combinatorial regimens, including surgery and platinum-based chemotherapy, patients generally exhibit poor prognosis due to high chemotherapy resistance. Herein, we tested the hypothesis that DNA damage response (DDR) pathways are involved in resistance of OC patients to platinum chemotherapy. Selected DDR signals were evaluated in two human ovarian carcinoma cell lines, one sensitive (A2780) and one resistant (A2780/C30) to platinum treatment as well as in peripheral blood mononuclear cells (PBMCs) from OC patients, sensitive (n = 7) or resistant (n = 4) to subsequent chemotherapy. PBMCs from healthy volunteers (n = 9) were studied in parallel. DNA damage was evaluated by immunofluorescence γH2AX staining and comet assay. Higher levels of intrinsic DNA damage were found in A2780 than in A2780/C30 cells. Moreover, the intrinsic DNA damage levels were significantly higher in OC patients relative to healthy volunteers, as well as in platinum-sensitive patients relative to platinum-resistant ones (all P<0.05). Following carboplatin treatment, A2780 cells showed lower DNA repair efficiency than A2780/C30 cells. Also, following carboplatin treatment of PBMCs ex vivo, the DNA repair efficiency was significantly higher in healthy volunteers than in platinum-resistant patients and lowest in platinum-sensitive ones (t1/2 for loss of γH2AX foci: 2.7±0.5h, 8.8±1.9h and 15.4±3.2h, respectively; using comet assay, t1/2 of platinum-induced damage repair: 4.8±1.4h, 12.9±1.9h and 21.4±2.6h, respectively; all P<0.03). Additionally, the carboplatin-induced apoptosis rate was higher in A2780 than in A2780/C30 cells. In PBMCs, apoptosis rates were inversely correlated with DNA repair efficiencies of these cells, being significantly higher in platinum-sensitive than in platinum-resistant patients and lowest in healthy volunteers (all P<0.05). We conclude that

  7. PREDICTION/MITIGATION OF SUBSIDENCE DAMAGE TO HAZARDOUS WASTE LANDFILL COVERS

    EPA Science Inventory

    Characteristics of Resource Conservation and Recovery Act hazardous waste landfills and of landfilled hazardous wastes have been described to permit development of models and other analytical techniques for predicting, reducing, and preventing landfill settlement and related cove...

  8. Underground Excavation Behaviour of the Queenston Formation: Tunnel Back Analysis for Application to Shaft Damage Dimension Prediction

    NASA Astrophysics Data System (ADS)

    Perras, Matthew A.; Wannenmacher, Helmut; Diederichs, Mark S.

    2015-07-01

    The Niagara Tunnel Project (NTP) is a 10.1 km long water-diversion tunnel in Niagara Falls, Ontario, which was excavated by a 7.2 m radius tunnel boring machine. Approximately half the tunnel length was excavated through the Queenston Formation, which locally is a shale to mudstone. Typical overbreak depths ranged between 2 and 4 m with a maximum of 6 m observed. Three modelling approaches were used to back analyse the brittle failure process at the NTP: damage initiation and spalling limit, laminated anisotropy modelling, and ubiquitous joint approaches. Analyses were conducted for three tunnel chainages: 3 + 000, 3 + 250, and 3 + 500 m because the overbreak depth increased from 2 to 4 m. All approaches produced similar geometries to those measured. The laminated anisotropy modelling approach was able to produced chord closures closest to those measured, using a joint normal to shear stiffness ratio between 1 and 2. This understanding was applied to a shaft excavation model in the Queenston Formation at the proposed Deep Geological Repository (DGR) site for low and intermediate level nuclear waste storage in Canada. The maximum damage depth was 1.9 m; with an average of 1.0 m. Important differences are discussed between the tunnel and shaft orientation with respect to bedding. The models show that the observed normalized depth of failure at the NTP would over-predict the depth of damage expected in the Queenston Formation at the DGR.

  9. Finite-Element Damage Analysis for Failure Prediction of Warm Hydroforming Tubular Magnesium Alloy Sheets

    NASA Astrophysics Data System (ADS)

    Chan, L. C.

    2015-02-01

    Bursting has been recognized by many researchers as a common failure mode in the tube hydroforming (THF) process. Therefore, the prediction of the bursting that occurs during the THF process has received much attention in the manufacturing industry and research institutions. Effective prediction of failure can reduce significantly the number of practical trials required to obtain the desired products. However, the prediction of such bursting for magnesium-based (Mg-based) alloy can be a rather difficult issue due to the nonlinear nature of the model used to describe the deformation process at elevated temperatures. This article proposes the failure prediction of Mg-based alloy during the THF process at elevated temperatures by using the Marciniak and Kuczynski (M-K) model. In the study, numerical simulation was performed by the finite-element (FE) analysis commercial software ABAQUS, with the material model assumed to be elastic-plastic. The constitutive model of Mg-based alloy (AZ31B) tube at different elevated temperatures, for instance at 493 K, 523 K, and 553 K, was represented by the Fields-Backofen constitutive equation, with material parameters collected from relevant literature. Accordingly, THF experiments were conducted by a self-developed thermal hydroforming attachment coping with an existing hydraulic power press to validate the prediction of the numerical results. The geometrical parameters for the specimen tubes used in the experiment were Ø22 × 150 mm, and 1.5 mm wall thickness. The numerical and the experimental results were demonstrated to have good agreement. The results of the simulation and the THF experiments imply that the model proposed in this study can provide a reliable prediction of the failure analysis of the Mg-based alloy tube during the THF process.

  10. Neural Network Prediction of Failure of Damaged Composite Pressure Vessels from Strain Field Data Acquired by a Computer Vision Method

    NASA Technical Reports Server (NTRS)

    Russell, Samuel S.; Lansing, Matthew D.

    1997-01-01

    This effort used a new and novel method of acquiring strains called Sub-pixel Digital Video Image Correlation (SDVIC) on impact damaged Kevlar/epoxy filament wound pressure vessels during a proof test. To predict the burst pressure, the hoop strain field distribution around the impact location from three vessels was used to train a neural network. The network was then tested on additional pressure vessels. Several variations on the network were tried. The best results were obtained using a single hidden layer. SDVIC is a fill-field non-contact computer vision technique which provides in-plane deformation and strain data over a load differential. This method was used to determine hoop and axial displacements, hoop and axial linear strains, the in-plane shear strains and rotations in the regions surrounding impact sites in filament wound pressure vessels (FWPV) during proof loading by internal pressurization. The relationship between these deformation measurement values and the remaining life of the pressure vessels, however, requires a complex theoretical model or numerical simulation. Both of these techniques are time consuming and complicated. Previous results using neural network methods had been successful in predicting the burst pressure for graphite/epoxy pressure vessels based upon acoustic emission (AE) measurements in similar tests. The neural network associates the character of the AE amplitude distribution, which depends upon the extent of impact damage, with the burst pressure. Similarly, higher amounts of impact damage are theorized to cause a higher amount of strain concentration in the damage effected zone at a given pressure and result in lower burst pressures. This relationship suggests that a neural network might be able to find an empirical relationship between the SDVIC strain field data and the burst pressure, analogous to the AE method, with greater speed and simplicity than theoretical or finite element modeling. The process of testing SDVIC

  11. Z-scan theoretical and experimental studies for accurate measurements of the nonlinear refractive index and absorption of optical glasses near damage threshold

    NASA Astrophysics Data System (ADS)

    Olivier, Thomas; Billard, Franck; Akhouayri, Hassan

    2004-06-01

    Self-focusing is one of the dramatic phenomena that may occur during the propagation of a high power laser beam in a nonlinear material. This phenomenon leads to a degradation of the wave front and may also lead to a photoinduced damage of the material. Realistic simulations of the propagation of high power laser beams require an accurate knowledge of the nonlinear refractive index γ. In the particular case of fused silica and in the nanosecond regime, it seems that electronic mechanisms as well as electrostriction and thermal effects can lead to a significant refractive index variation. Compared to the different methods used to measure this parmeter, the Z-scan method is simple, offers a good sensitivity and may give absolute measurements if the incident beam is accurately studied. However, this method requires a very good knowledge of the incident beam and of its propagation inside a nonlinear sample. We used a split-step propagation algorithm to simlate Z-scan curves for arbitrary beam shape, sample thickness and nonlinear phase shift. According to our simulations and a rigorous analysis of the Z-scan measured signal, it appears that some abusive approximations lead to very important errors. Thus, by reducing possible errors on the interpretation of Z-scan experimental studies, we performed accurate measurements of the nonlinear refractive index of fused silica that show the significant contribution of nanosecond mechanisms.

  12. Prediction of the percolation threshold and electrical conductivity of self-assembled antimony-doped tin oxide nanoparticles into ordered structures in PMMA/ATO nanocomposites.

    PubMed

    Jin, Youngho; Gerhardt, Rosario A

    2014-12-24

    Electrical percolation in nanocomposites consisting of poly(methyl methacrylate) (PMMA) and antimony tin oxide (ATO) nanoparticles was investigated experimentally using monosize and polydisperse polymer particles. The nanocomposites were fabricated by compression molding at 170 °C. The matrix PMMA was transformed into space filling polyhedra while the ATO nanoparticles distributed along the sharp edges of the matrix, forming a 3D interconnected network. The measured electrical resistivity showed that percolation was achieved in these materials at a very low ATO content of 0.99 wt % ATO when monosize PMMA was used, whereas 1.48 wt % ATO was needed to achieve percolation when the PMMA was polydispersed. A parametric finite element approach was chosen to model this unique microstructure-driven self-assembling percolation behavior. COMSOL Multiphysics was used to solve the effects of phase segregation between the matrix and the filler using a 2D simplified model in the frequency domain of the AC/DC module. It was found that the percolation threshold (pc) is affected by the size ratio between the matrix and the filler in a systematic way. Furthermore, simulations indicate that small deviations from perfect interconnection result mostly in changes in the electrical resistivity while the minimum DC resistivity achievable in any given composite is governed by the electrical conductivity of the filler, which must be accurately known in order to obtain an accurate prediction. The model is quite general and is able to predict percolation behavior in a number of other similarly processed segregated network nanocomposites. PMID:25427537

  13. In situ damage monitoring in vibration mechanics: diagnostics and predictive maintenance

    NASA Astrophysics Data System (ADS)

    Basseville, M.; Benveniste, A.; Gach-Devauchelle, B.; Goursat, M.; Bonnecase, D.; Dorey, P.; Prevosto, M.; Olagnon, M.

    1993-09-01

    A system identification approach is presented for damage monitoring in vibration mechanics. Identification, detection, and diagnostics are performed using accelerometer measurements from the system at work so that the excitation is not controlled, usually not observed and may involve turbulent phenomena. Targeted applications include power engineering (rotating machines, core and pipes of nuclear power plants), civil engineering (large buildings subject to hurricanes or earthquakes, bridges, dams, offshore structures), aeronautics (wings and other structures subject to strength), automobile, rail transportation etc. The method is illustrated by a laboratory example, and the results of 3 years industrial usage. This paper is a progress report on a 10 year project involving three people almost permanently. We describe here the whole approach but omit the technical details which are available in previous papers.

  14. Spotsize effects in laser damage testing

    NASA Astrophysics Data System (ADS)

    Foltyn, S. R.

    1982-12-01

    An unconventional method was employed to plot damage data: ten sites are irradiated at each test fluence and the fraction of damaging sites is plotted as a function of peak fluence. The resulting curves slope from a fluence at which no damage was produced to a higher fluence at which all ten sites were damaged. Attempts to explain wide slope variations among a variety of tested samples have led to a simple model which correlates slope, defect density, and Gaussian spotsize of the test beam. Specifically, the model predicts steep slopes if the beam is large compared to the mean defect spacing. In contract to conventional notation, threshold is defined as the highest fluence at which the sample could not be damaged. Implicit in the model is that threshold thus defined is independent of spotsize while conventional thresholds have a calculable dependence. In the limit of large spotsize, the two thresholds are identical. Test results for various spotsizes are reported and analyses of published experimental data are presented in support of this model.

  15. Learning foraging thresholds for lizards

    SciTech Connect

    Goldberg, L.A.; Hart, W.E.; Wilson, D.B.

    1996-01-12

    This work gives a proof of convergence for a randomized learning algorithm that describes how anoles (lizards found in the Carribean) learn a foraging threshold distance. This model assumes that an anole will pursue a prey if and only if it is within this threshold of the anole`s perch. This learning algorithm was proposed by the biologist Roughgarden and his colleagues. They experimentally confirmed that this algorithm quickly converges to the foraging threshold that is predicted by optimal foraging theory our analysis provides an analytic confirmation that the learning algorithm converses to this optimal foraging threshold with high probability.

  16. Ex-plant retinal laser induced threshold studies in the millisecond time regime

    NASA Astrophysics Data System (ADS)

    Schulmeister, Karl; Husinsky, Johannes; Seiser, Bernhard; Edthofer, Florian; Tuschl, Helga; Lund, David J.

    2006-02-01

    Excised bovine retinas were used as model for threshold determination of laser induced thermal damage in the pulse regime of 1 ms to 655 ms for a range of laser spot size diameters. The thresholds as determined by fluorescence viability staining compare very well with the prediction of thermal damage models. Both models compare well with published and new Rhesus monkey threshold data. A distinctive dependence of the threshold on laser spot size diameter for different pulse duration was found which indicates that current (ICNIRP, ANSI and IEC) laser exposure limits for large spots can be increased in this pulse duration regime. A time dependent α max is proposed which only for the case of long exposure durations has the current value of 100 mrad, but decreases to smaller angles for short exposure durations, effectively increasing the permissible exposure level. An explanation based on intra-retinal scattering is offered for the unexpected spot size dependence for spot diameters less than about 80 µm. The time dependence and nature of damage is discussed for pulse durations shorter than 1 ms where bubble induced damage seems to lead to a threshold a factor of 10 lower than the thermally induced threshold, resulting in the need to lower the MPE values for this condition. Possible changes of the MPE values are offered and discussed.

  17. Next-to-Next-to-Next-to-Leading Order QCD Prediction for the Top Antitop S-Wave Pair Production Cross Section Near Threshold in e(+)e(-) Annihilation.

    PubMed

    Beneke, Martin; Kiyo, Yuichiro; Marquard, Peter; Penin, Alexander; Piclum, Jan; Steinhauser, Matthias

    2015-11-01

    We present the third-order QCD prediction for the production of top antitop quark pairs in electron-positron collisions close to the threshold in the dominant S-wave state. We observe a significant reduction of the theoretical uncertainty and discuss the sensitivity to the top quark mass and width. PMID:26588372

  18. Identification of structural damage using wavelet-based data classification

    NASA Astrophysics Data System (ADS)

    Koh, Bong-Hwan; Jeong, Min-Joong; Jung, Uk

    2008-03-01

    Predicted time-history responses from a finite-element (FE) model provide a baseline map where damage locations are clustered and classified by extracted damage-sensitive wavelet coefficients such as vertical energy threshold (VET) positions having large silhouette statistics. Likewise, the measured data from damaged structure are also decomposed and rearranged according to the most dominant positions of wavelet coefficients. Having projected the coefficients to the baseline map, the true localization of damage can be identified by investigating the level of closeness between the measurement and predictions. The statistical confidence of baseline map improves as the number of prediction cases increases. The simulation results of damage detection in a truss structure show that the approach proposed in this study can be successfully applied for locating structural damage even in the presence of a considerable amount of process and measurement noise.

  19. Prediction of Foreign Object Debris/Damage (FOD) type for elimination in the aeronautics manufacturing environment through logistic regression model

    NASA Astrophysics Data System (ADS)

    Espino, Natalia V.

    Foreign Object Debris/Damage (FOD) is a costly and high-risk problem that aeronautics industries such as Boeing, Lockheed Martin, among others are facing at their production lines every day. They spend an average of $350 thousand dollars per year fixing FOD problems. FOD can put pilots, passengers and other crews' lives into high-risk. FOD refers to any type of foreign object, particle, debris or agent in the manufacturing environment, which could contaminate/damage the product or otherwise undermine quality control standards. FOD can be in the form of any of the following categories: panstock, manufacturing debris, tools/shop aids, consumables and trash. Although aeronautics industries have put many prevention plans in place such as housekeeping and "clean as you go" philosophies, trainings, use of RFID for tooling control, etc. none of them has been able to completely eradicate the problem. This research presents a logistic regression statistical model approach to predict probability of FOD type under given specific circumstances such as workstation, month and aircraft/jet being built. FOD Quality Assurance Reports of the last three years were provided by an aeronautical industry for this study. By predicting type of FOD, custom reduction/elimination plans can be put in place and by such means being able to diminish the problem. Different aircrafts were analyzed and so different models developed through same methodology. Results of the study presented are predictions of FOD type for each aircraft and workstation throughout the year, which were obtained by applying proposed logistic regression models. This research would help aeronautic industries to address the FOD problem correctly, to be able to identify root causes and establish actual reduction/elimination plans.

  20. Structure-odor correlations in homologous series of alkanethiols and attempts to predict odor thresholds by 3D-QSAR studies.

    PubMed

    Polster, Johannes; Schieberle, Peter

    2015-02-11

    Homologous series of alkane-1-thiols, alkane-2-thiols, alkane-3-thiols, 2-methylalkane-1-thiols, 2-methylalkane-3-thiols, 2-methylalkane-2-thiols, and alkane-1,ω-dithiols were synthesized to study the influence of structural changes on odor qualities and odor thresholds. In particular, the odor thresholds were strongly influenced by steric effects: In all homologous series a minimum was observed for thiols with five to seven carbon atoms, whereas increasing the chain length led to an exponential increase in the odor threshold. Tertiary alkanethiols revealed clearly lower odor thresholds than found for primary or secondary thiols, whereas neither a second mercapto group in the molecule nor an additional methyl substitution lowered the threshold. To investigate the impact of the SH group, odor thresholds and odor qualities of thiols were compared to those of the corresponding alcohols and (methylthio)alkanes. Replacement of the SH group by an OH group as well as S-methylation of the thiols significantly increased the odor thresholds. By using comparative molecular field analysis, a 3D quantitative structure-activity relationship model was created, which was able to simulate the odor thresholds of alkanethiols in good agreement with the experimental results. NMR and mass spectrometric data for 46 sulfur-containing compounds are additionally supplied. PMID:25608797

  1. Development of an Image-based Multi-Scale Finite Element Approach to Predict Fatigue Damage in Asphalt Mixtures

    NASA Astrophysics Data System (ADS)

    Arshadi, Amir

    Image-based simulation of complex materials is a very important tool for understanding their mechanical behavior and an effective tool for successful design of composite materials. In this thesis an image-based multi-scale finite element approach is developed to predict the mechanical properties of asphalt mixtures. In this approach the "up-scaling" and homogenization of each scale to the next is critically designed to improve accuracy. In addition to this multi-scale efficiency, this study introduces an approach for consideration of particle contacts at each of the scales in which mineral particles exist. One of the most important pavement distresses which seriously affects the pavement performance is fatigue cracking. As this cracking generally takes place in the binder phase of the asphalt mixture, the binder fatigue behavior is assumed to be one of the main factors influencing the overall pavement fatigue performance. It is also known that aggregate gradation, mixture volumetric properties, and filler type and concentration can affect damage initiation and progression in the asphalt mixtures. This study was conducted to develop a tool to characterize the damage properties of the asphalt mixtures at all scales. In the present study the Viscoelastic continuum damage model is implemented into the well-known finite element software ABAQUS via the user material subroutine (UMAT) in order to simulate the state of damage in the binder phase under the repeated uniaxial sinusoidal loading. The inputs are based on the experimentally derived measurements for the binder properties. For the scales of mastic and mortar, the artificially 2-Dimensional images of mastic and mortar scales were generated and used to characterize the properties of those scales. Finally, the 2D scanned images of asphalt mixtures are used to study the asphalt mixture fatigue behavior under loading. In order to validate the proposed model, the experimental test results and the simulation results were

  2. Optimization of rainfall thresholds for a flood warning system to Taiwan urban areas during storm events

    NASA Astrophysics Data System (ADS)

    Liao, Hao-Yu; Pan, Tsung-Yi; Su, Ming-Daw; Hsieh, Ming-Chang; Tan, Yih-Chi

    2016-04-01

    Flood is one of the most damage disaster that always happen around the world. Because of the extreme weather change, the flood disaster damage becomes higher than before. In recent years, Taiwan suffered from flood damage frequently by excessive rainfall induced by extreme weather, like typhoons. Therefore, it is necessary to build an effective flood warning system to reduce the flood damage. The operational flood warning system in Taiwan is based on the rainfall thresholds. When cumulative rainfall over the rainfall thresholds, the flood warning system would alert the local government where region would happen flood disaster. According to the flood warning system alert, the governments have more time to prepare how to face the flood disaster before happens. Although Taiwanese government has a preliminary flood warning system, the system has still lack of theoretical background. For this reason, the alert accuracy of the system is limited. Thus it is important to develop the effective rainfall thresholds that could predict flood disaster successfully. The research aims to improve the accuracy of the system through statistical methods. When the accumulated rainfall reaches the alert value, the warning message would be announced early to government for dealing with flooding damage which would happen. According to extreme events, the data driven and statistical methods are adopted to calculate the optimum rainfall thresholds. The results of this study could be applied to enhance rainfall thresholds forecasting accuracy, and could reduce the risk of floods.

  3. Modeling laser damage to the retina

    NASA Astrophysics Data System (ADS)

    Clark, Clifton D.

    This dissertation presents recent progress in several areas related to modeling laser damage to the retina. In Chapter 3, we consider the consequences of using the Arrhenius damage model to predict the damage thresholds of multiple pulse, or repetitive pulse, exposures. We have identified a few fundamental trends associated with the multiple pulse damage predictions made by the Arrhenius model. These trends differ from what would be expected by non-thermal mechanisms, and could prove useful in differentiating thermal and non-thermal damage. Chapter 4 presents a new rate equation damage model hypothesized to describe photochemical damage. The model adds a temperature dependent term to the simple rate equation implied by the principle of reciprocity that is characteristic of photochemical damage thresholds. A recent damage threshold study, conducted in-vitro, has revealed a very sharp transition between thermal and photochemical damage threshold trends. For the wavelength used in the experiment (413 nm), thermal damage thresholds were observed at exposure levels that were twice the expected photochemical damage threshold, based on the traditional understanding of photochemical damage. Our model accounts for this observed trend by introducing a temperature dependent quenching, or repair, rate to the photochemical damage rate. For long exposures that give a very small temperature rise, the model reduces to the principle of reciprocity. Near the transition region between thermal and photochemical damage, the model allows the damage threshold to be set by thermal mechanisms, even at exposure above the reciprocity exposure. In Chapter 5, we describe a retina damage model that includes thermal lensing in the eye by coupling beam propagation and heat transfer models together. Thermal lensing has recently been suggested as a contributing factor to the large increase in measured retinal damage thresholds in the near infrared. The transmission of the vitreous decreases

  4. Optical damage performance measurements of multilayer dielectric gratings for high energy short pulse lasers

    NASA Astrophysics Data System (ADS)

    Alessi, D.; Carr, C. W.; Negres, R. A.; Hackel, R. P.; Stanion, K. A.; Cross, D. A.; Guss, G.; Nissen, J. D.; Luthi, R.; Fair, J. E.; Britten, J. A.; Haefner, C.

    2015-02-01

    We investigate the laser damage resistance of multilayer dielectric (MLD) diffraction gratings used in the pulse compressors for high energy, high peak power laser systems such as the Advanced Radiographic Capability (ARC) Petawatt laser on the National Ignition Facility (NIF). Our study includes measurements of damage threshold and damage density (ρ(Φ)) with picosecond laser pulses at 1053 nm under relevant operational conditions. Initial results indicate that sparse defects present on the optic surface from the manufacturing processes are responsible for damage initiation at laser fluences below the damage threshold indicated by the standard R-on-1 test methods, as is the case for laser damage with nanosecond pulse durations. As such, this study supports the development of damage density measurements for more accurate predictions on the damage performance of large area optics.

  5. Prediction of STS-107 Hypervelocity Flow Fields about the Shuttle Orbiter with Various Wing Leading Edge Damage

    NASA Technical Reports Server (NTRS)

    Pulsonetti, Maria V.; Thompson, Richard A.; Alter, Stephen J.

    2004-01-01

    Computations were performed for damaged configurations of the Shuttle Orbiter in support of the STS-107 Columbia accident investigation. Two configurations with missing wing leading-edge reinforced carbon-carbon (RCC) panels were evaluated at conditions just prior to the peak heating trajectory point. The initial configuration modeled the Orbiter with an approximate missing RCC panel 6 to determine whether this damage could result in anomalous temperatures measured during the STS-107 reentry. This missing RCC panel 6 computation was found to produce heating augmentation factors of 5 times the nominal heating rates on the side fuselage with lesser heat increases on the front of the OMS pod. This is consistent with the thermocouple and resistance temperature detector sensors from the STS-107 re-entry which observed off nominal high early in the re-entry trajectory. A second damaged configuration modeled the Orbiter with missing RCC panel 9 and included ingestion of the flow into the outboard RCC channel. This computation lowered the level (only 2 times nominal) and moved the location of the heating augmentation on the leeside fuselage relative to the missing RCC panel 6 configuration. The lesser heating augmentation for missing RCC panel 9 was confined near the wing fuselage juncture. Near nominal heating was predicted on the remainder of the side fuselage with some lower than nominal heating on the front surface of the OMS pod. These results for missing RCC panel 9 are consistent with data from the STS-107 re-entry where the heating augmentation was observed to move off the side fuselage and OMS pod sensors at later times in the trajectory. As this solution requires supersonic mass ingestion into the RCC channel, it is probably not an appropriate model prior to penetration of the flow through the spar into the wing structure. It may, however, be representative of the conditions at later times and could account for the movement of the heating signature on the side

  6. Evolution of Extra-Nigral Damage Predicts Behavioural Deficits in a Rat Proteasome Inhibitor Model of Parkinson's Disease

    PubMed Central

    Vernon, Anthony C.; Crum, William R.; Johansson, Saga M.; Modo, Michel

    2011-01-01

    Establishing the neurological basis of behavioural dysfunction is key to provide a better understanding of Parkinson's disease (PD) and facilitate development of effective novel therapies. For this, the relationships between longitudinal structural brain changes associated with motor behaviour were determined in a rat model of PD and validated by post-mortem immunohistochemistry. Rats bearing a nigrostriatal lesion induced by infusion of the proteasome inhibitor lactacystin into the left-medial forebrain bundle and saline-injected controls underwent magnetic resonance imaging (MRI) at baseline (prior to surgery) and 1, 3 and 5 weeks post-surgery with concomitant motor assessments consisting of forelimb grip strength, accelerating rotarod, and apormorphine-induced rotation. Lactacystin-injected rats developed early motor deficits alongside decreased ipsilateral cortical volumes, specifically thinning of the primary motor (M1) and somatosensory cortices and lateral ventricle hypertrophy (as determined by manual segmentation and deformation-based morphometry). Although sustained, motor dysfunction and nigrostriatal damage were maximal by 1 week post-surgery. Additional volume decreases in the ipsilateral ventral midbrain; corpus striatum and thalamus were only evident by week 3 and 5. Whilst cortical MRI volume changes best predicted the degree of motor impairment, post-mortem tyrosine hydroxylase immunoreactivity in the striatum was a better predictor of motor behaviour overall, with the notable exception of performance in the accelerating rotarod, in which, M1 cortical thickness remained the best predictor. These results highlight the importance of identifying extra-nigral regions of damage that impact on behavioural dysfunction from damage to the nigrostriatal system. PMID:21364887

  7. A predictive nature for tactile awareness? Insights from damaged and intact central-nervous-system functioning

    PubMed Central

    Pia, Lorenzo; Garbarini, Francesca; Burin, Dalila; Fossataro, Carlotta; Berti, Anna

    2015-01-01

    In the present paper, we will attempt to gain hints regarding the nature of tactile awareness in humans. At first, we will review some recent literature showing that an actual tactile experience can emerge in absence of any tactile stimulus (e.g., tactile hallucinations, tactile illusions). According to the current model of tactile awareness, we will subsequently argue that such (false) tactile perceptions are subserved by the same anatomo-functional mechanisms known to underpin actual perception. On these bases, we will discuss the hypothesis that tactile awareness is strongly linked to expected rather than actual stimuli. Indeed, this hypothesis is in line with the notion that the human brain has a strong predictive, rather than reactive, nature. PMID:26042020

  8. A predictive nature for tactile awareness? Insights from damaged and intact central-nervous-system functioning.

    PubMed

    Pia, Lorenzo; Garbarini, Francesca; Burin, Dalila; Fossataro, Carlotta; Berti, Anna

    2015-01-01

    In the present paper, we will attempt to gain hints regarding the nature of tactile awareness in humans. At first, we will review some recent literature showing that an actual tactile experience can emerge in absence of any tactile stimulus (e.g., tactile hallucinations, tactile illusions). According to the current model of tactile awareness, we will subsequently argue that such (false) tactile perceptions are subserved by the same anatomo-functional mechanisms known to underpin actual perception. On these bases, we will discuss the hypothesis that tactile awareness is strongly linked to expected rather than actual stimuli. Indeed, this hypothesis is in line with the notion that the human brain has a strong predictive, rather than reactive, nature. PMID:26042020

  9. Deterministic and Probabilistic Creep and Creep Rupture Enhancement to CARES/Creep: Multiaxial Creep Life Prediction of Ceramic Structures Using Continuum Damage Mechanics and the Finite Element Method

    NASA Technical Reports Server (NTRS)

    Jadaan, Osama M.; Powers, Lynn M.; Gyekenyesi, John P.

    1998-01-01

    High temperature and long duration applications of monolithic ceramics can place their failure mode in the creep rupture regime. A previous model advanced by the authors described a methodology by which the creep rupture life of a loaded component can be predicted. That model was based on the life fraction damage accumulation rule in association with the modified Monkman-Grant creep ripture criterion However, that model did not take into account the deteriorating state of the material due to creep damage (e.g., cavitation) as time elapsed. In addition, the material creep parameters used in that life prediction methodology, were based on uniaxial creep curves displaying primary and secondary creep behavior, with no tertiary regime. The objective of this paper is to present a creep life prediction methodology based on a modified form of the Kachanov-Rabotnov continuum damage mechanics (CDM) theory. In this theory, the uniaxial creep rate is described in terms of stress, temperature, time, and the current state of material damage. This scalar damage state parameter is basically an abstract measure of the current state of material damage due to creep deformation. The damage rate is assumed to vary with stress, temperature, time, and the current state of damage itself. Multiaxial creep and creep rupture formulations of the CDM approach are presented in this paper. Parameter estimation methodologies based on nonlinear regression analysis are also described for both, isothermal constant stress states and anisothermal variable stress conditions This creep life prediction methodology was preliminarily added to the integrated design code CARES/Creep (Ceramics Analysis and Reliability Evaluation of Structures/Creep), which is a postprocessor program to commercially available finite element analysis (FEA) packages. Two examples, showing comparisons between experimental and predicted creep lives of ceramic specimens, are used to demonstrate the viability of this methodology and

  10. The Relative Utility of Home, Ambulatory, and Office Blood Pressures in the Prediction of End-Organ Damage

    PubMed Central

    Shimbo, Daichi; Pickering, Thomas G.; Spruill, Tanya M.; Abraham, Dennis; Schwartz, Joseph E.; Gerin, William

    2007-01-01

    Background Home blood pressure (HBP) monitoring plays an increasingly important role in the diagnosis and treatment of hypertension. We evaluated the independent value of HBP compared to ambulatory blood pressure (ABP) and office blood pressure (OBP) in the prediction of cardiovascular end-organ damage in normotensive subjects and untreated patients with mild hypertension. Methods 163 subjects underwent measurements of OBP, HBP, ABP, and echocardiography. A physician using a mercury column sphygmomanometer performed three OBP measurements. ABP was recorded using a noninvasive ambulatory monitor (mean 35.4 awake readings per subject). Participants took HBP readings with an automatic, oscillometric device over a 10-week period (mean 277.9 readings per subject). Left ventricular mass index (LVMI) was calculated from measurements obtained from 2-dimensionally guided M-mode or linear tracings on echocardiography. Results For systolic and diastolic blood pressures (SBP/DBP), the correlation coefficients of LVMI with OBP, awake ABP, and HBP were .29/.27, .41/.26, and .47/.35 respectively (all ps<.01). In a multivariate regression analysis in which age, sex, body mass index, OBP, awake ABP, and HBP were included, only age, sex, and HBP were significant predictors of LVMI. When only the first 12 home readings were used, the superiority of HBP was no longer evident. Conclusions In contrast to OBP and ABP, HBP measurements, when averaged over a 10-week period, are independently related to LVMI. HBP adds prognostic information over and above OBP and ABP in the prediction of cardiovascular end-organ damage, but this relation appears to depend on the number of readings taken. PMID:17485006

  11. Can Structural Joint Damage Measured with MR Imaging Be Used to Predict Knee Replacement in the Following Year?

    PubMed Central

    Kwoh, C. Kent; Hannon, Michael J.; Hunter, David J.; Eckstein, Felix; Wang, Zhijie; Boudreau, Robert M.; John, Markus R.; Nevitt, Michael C.; Guermazi, Ali

    2015-01-01

    Purpose To assess whether magnetic resonance (MR) imaging–based cross-sectional measures of structural joint damage can be used to predict knee replacement during the following year. Materials and Methods Participants were drawn from the Osteoarthritis Initiative, a longitudinal observational study that includes 4796 participants who have knee osteoarthritis or are at risk. The HIPAA-compliant protocol was approved by the institutional review boards of all participating centers, and written informed consent was obtained from all participants. During the 5 years of follow-up, 199 knees underwent knee replacement and were matched with 199 control knees that did not undergo knee replacement. Knees were matched according to radiographic disease stage and patient sex and age. All knees that underwent knee replacement and had MR images available from the year before surgery were included. MR images were assessed for cartilage damage, bone marrow lesions, meniscal damage, meniscal extrusion, synovitis, and effusion prior to reported knee replacement. Conditional logistic regression was applied to assess the risk of knee replacement. Analyses were performed on a compartmental and knee level. Results Participants had a mean age ± standard deviation of 64.2 years ± 8.4 (range, 47–82 years) and were predominantly women (232 of 398 participants, 58.3%). Risk for knee replacement was significantly increased for knees that exhibited two or more subregions with severe cartilage loss (odds ratio [OR], 16.5; 95% confidence interval [CI]: 3.96, 68.76), more than two subregions with bone marrow lesions (OR, 4.00; 95% CI: 1.75, 9.16), medial meniscal maceration (OR, 1.84; 95% CI: 1.13, 2.99), effusion (OR, 4.75; 95% CI: 2.55, 8.85), or synovitis (OR, 2.17; 95% CI: 1.33, 3.56), but not extrusion (OR, 1.00; 95% CI: 0.60,1.67), when compared with knees that did not exhibit these features as the reference standard. Conclusion Apart from meniscal extrusion, all features of tissue

  12. Damage-based life prediction model for uniaxial low-cycle stress fatigue of super-elastic NiTi shape memory alloy microtubes

    NASA Astrophysics Data System (ADS)

    Song, Di; Kang, Guozheng; Kan, Qianhua; Yu, Chao; Zhang, Chuanzeng

    2015-08-01

    Based on the experimental observations for the uniaxial low-cycle stress fatigue failure of super-elastic NiTi shape memory alloy microtubes (Song et al 2015 Smart Mater. Struct. 24 075004) and a new definition of damage variable corresponding to the variation of accumulated dissipation energy, a phenomenological damage model is proposed to describe the damage evolution of the NiTi microtubes during cyclic loading. Then, with a failure criterion of Dc = 1, the fatigue lives of the NiTi microtubes are predicted by the damage-based model, the predicted lives are in good agreement with the experimental ones, and all of the points are located within an error band of 1.5 times.

  13. Molecular damage in Fabry disease: characterization and prediction of alpha-galactosidase A pathological mutations.

    PubMed

    Riera, Casandra; Lois, Sergio; Domínguez, Carmen; Fernandez-Cadenas, Israel; Montaner, Joan; Rodríguez-Sureda, Victor; de la Cruz, Xavier

    2015-01-01

    Loss-of-function mutations of the enzyme alpha-galactosidase A (GLA) causes Fabry disease (FD), that is a rare and potentially fatal disease. Identification of these pathological mutations by sequencing is important because it allows an early treatment of the disease. However, before taking any treatment decision, if the mutation identified is unknown, we first need to establish if it is pathological or not. General bioinformatic tools (PolyPhen-2, SIFT, Condel, etc.) can be used for this purpose, but their performance is still limited. Here we present a new tool, specifically derived for the assessment of GLA mutations. We first compared mutations of this enzyme known to cause FD with neutral sequence variants, using several structure and sequence properties. Then, we used these properties to develop a family of prediction methods adapted to different quality requirements. Trained and tested on a set of known Fabry mutations, our methods have a performance (Matthews correlation: 0.56-0.72) comparable or better than that of the more complex method, Polyphen-2 (Matthews correlation: 0.61), and better than those of SIFT (Matthews correl.: 0.54) and Condel (Matthews correl.: 0.51). This result is validated in an independent set of 65 pathological mutations, for which our method displayed the best success rate (91.0%, 87.7%, and 73.8%, for our method, PolyPhen-2 and SIFT, respectively). These data confirmed that our specific approach can effectively contribute to the identification of pathological mutations in GLA, and therefore enhance the use of sequence information in the identification of undiagnosed Fabry patients. PMID:25382311

  14. A rat retinal damage model predicts for potential clinical visual disturbances induced by Hsp90 inhibitors

    SciTech Connect

    Zhou, Dan; Liu, Yuan; Ye, Josephine; Ying, Weiwen; Ogawa, Luisa Shin; Inoue, Takayo; Tatsuta, Noriaki; Wada, Yumiko; Koya, Keizo; Huang, Qin; Bates, Richard C.; Sonderfan, Andrew J.

    2013-12-01

    In human trials certain heat shock protein 90 (Hsp90) inhibitors, including 17-DMAG and NVP-AUY922, have caused visual disorders indicative of retinal dysfunction; others such as 17-AAG and ganetespib have not. To understand these safety profile differences we evaluated histopathological changes and exposure profiles of four Hsp90 inhibitors, with or without clinical reports of adverse ocular effects, using a rat retinal model. Retinal morphology, Hsp70 expression (a surrogate marker of Hsp90 inhibition), apoptotic induction and pharmacokinetic drug exposure analysis were examined in rats treated with the ansamycins 17-DMAG and 17-AAG, or with the second-generation compounds NVP-AUY922 and ganetespib. Both 17-DMAG and NVP-AUY922 induced strong yet restricted retinal Hsp70 up-regulation and promoted marked photoreceptor cell death 24 h after the final dose. In contrast, neither 17-AAG nor ganetespib elicited photoreceptor injury. When the relationship between drug distribution and photoreceptor degeneration was examined, 17-DMAG and NVP-AUY922 showed substantial retinal accumulation, with high retina/plasma (R/P) ratios and slow elimination rates, such that 51% of 17-DMAG and 65% of NVP-AUY922 present at 30 min post-injection were retained in the retina 6 h post-dose. For 17-AAG and ganetespib, retinal elimination was rapid (90% and 70% of drugs eliminated from the retina at 6 h, respectively) which correlated with lower R/P ratios. These findings indicate that prolonged inhibition of Hsp90 activity in the eye results in photoreceptor cell death. Moreover, the results suggest that the retina/plasma exposure ratio and retinal elimination rate profiles of Hsp90 inhibitors, irrespective of their chemical class, may predict for ocular toxicity potential. - Highlights: • In human trials some Hsp90 inhibitors cause visual disorders, others do not. • Prolonged inhibition of Hsp90 in the rat eye results in photoreceptor cell death. • Retina/plasma ratio and retinal

  15. COMPARISON OF MERCURY BLOOD PRESSURE READINGS TO OSCILLOMETRIC AND CENTRAL BLOOD PRESSURE IN PREDICTING TARGET ORGAN DAMAGE IN YOUTH

    PubMed Central

    Urbina, Elaine M; Khoury, Philip R; McCoy, Connie E; Daniels, Stephen R; Dolan, Lawrence M; Kimball, Thomas R

    2015-01-01

    Objective Hypertension (HT) is an important risk factor for target organ damage (TOD). New methods for measuring BP are replacing mercury sphygmomanometry in many clinics. We examined the utility of different BP measurement techniques in predicting subclinical TOD in adolescents and young adults. Methods Subjects in a study of the CV effects of obesity and type 2 diabetes (T2DM) were evaluated (N=677, 18 ± 3.3 years, 35% male, 60% non-Caucasian, 30% T2DM). We measured adiposity, lab, left ventricular mass, carotid intima-media thickness & pulse wave. BP was measured 3 times with mercury sphygmomanometery (BPm) an oscillometric device (BPo) and central aortic BP (BPc) was derived with arterial tonometry. Subjects were stratified as normotensive (N), pre-hypertensive (P) or hypertensive (H). Results The prevalence of HT this cohort with mean BMI of 31 was highest with BPo (16%), followed by BPm (11%) and BPc (9%), p≤0.001. BPm was most consistent in differentiating left ventricular mass and pulse wave velocity among subjects in the P group as compared to the N & H groups. Mercury BP was also more sensitive and specific in predicting greater left ventricular mass, pulse wave velocity and carotid thickness than the other BP measurement techniques in logistic regression. Conclusions We conclude that mercury sphygmomanometry should remain the gold standard for evaluation of HT and the risk for TOD in adolescents and young adults. PMID:25647284

  16. DNA damage induction and/or repair as mammalian cell biomarker for the prediction of cellular radiation response

    NASA Astrophysics Data System (ADS)

    Baumstark-Khan, C.

    DNA damage and its repair processes are key factors in cancer induction and also in the treatment of malignancies. Cancer prevention during extended space missions becomes a topic of great importance for space radiobiology. The knowledge of individual responsiveness would allow the protection strategy to be tailored optimally in each case. Radiobiological analysis of cultured cells derived from tissue explants from individuals has shown that measurement of the surviving fraction after 2 Gy (SF2) may be used to predict the individual responsiveness. However, clonogenic assays are timeconsuming, thus alternative assays for the determination of radiore-sponse are being sought. For that reason CHO cell strains having different repair capacities were used for examining whether DNA strand break repair is a suitable experimental design to allow predictive statements. Cellular survival (CFA assay) and DNA strand breaks (total DNA strand breaks: FADU technique; DSBs: non-denaturing elution) were determined in parallel immediately after irradiation as well as after a 24 hour recovery period according to dose. There were no correlations between the dose-response curves of the initial level of DNA strand breaks and parameters that describe clonogenic survival curves (SF2). A good correlation exists between intrinsic cellular radioresistance and the extent of residual DNA strand breaks.

  17. Predicting Formation Damage in Aquifer Thermal Energy Storage Systems Utilizing a Coupled Hydraulic-Thermal-Chemical Reservoir Model

    NASA Astrophysics Data System (ADS)

    Müller, Daniel; Regenspurg, Simona; Milsch, Harald; Blöcher, Guido; Kranz, Stefan; Saadat, Ali

    2014-05-01

    In aquifer thermal energy storage (ATES) systems, large amounts of energy can be stored by injecting hot water into deep or intermediate aquifers. In a seasonal production-injection cycle, water is circulated through a system comprising the porous aquifer, a production well, a heat exchanger and an injection well. This process involves large temperature and pressure differences, which shift chemical equilibria and introduce or amplify mechanical processes. Rock-fluid interaction such as dissolution and precipitation or migration and deposition of fine particles will affect the hydraulic properties of the porous medium and may lead to irreversible formation damage. In consequence, these processes determine the long-term performance of the ATES system and need to be predicted to ensure the reliability of the system. However, high temperature and pressure gradients and dynamic feedback cycles pose challenges on predicting the influence of the relevant processes. Within this study, a reservoir model comprising a coupled hydraulic-thermal-chemical simulation was developed based on an ATES demonstration project located in the city of Berlin, Germany. The structural model was created with Petrel, based on data available from seismic cross-sections and wellbores. The reservoir simulation was realized by combining the capabilities of multiple simulation tools. For the reactive transport model, COMSOL Multiphysics (hydraulic-thermal) and PHREEQC (chemical) were combined using the novel interface COMSOL_PHREEQC, developed by Wissmeier & Barry (2011). It provides a MATLAB-based coupling interface between both programs. Compared to using COMSOL's built-in reactive transport simulator, PHREEQC additionally calculates adsorption and reaction kinetics and allows the selection of different activity coefficient models in the database. The presented simulation tool will be able to predict the most important aspects of hydraulic, thermal and chemical transport processes relevant to

  18. Na2ZnGe2S6: A New Infrared Nonlinear Optical Material with Good Balance between Large Second-Harmonic Generation Response and High Laser Damage Threshold.

    PubMed

    Li, Guangmao; Wu, Kui; Liu, Qiong; Yang, Zhihua; Pan, Shilie

    2016-06-15

    The development of frequency-conversion technology in the infrared region is in urgent need of new excellent infrared nonlinear optical (IR NLO) materials. How to achieve a good balance between laser damage threshold (LDT) and NLO coefficient (dij) for new IR NLO candidates is still a challenge. The combination of the highly electropositive alkali metal (Na) and Zn with d(10) electronic configuration into crystal structure affords one new IR NLO material, Na2ZnGe2S6. It exhibits excellent properties including a wide transparent region (0.38-22 μm), large band gap (3.25 eV), and especially a balance between a strong NLO coefficient (30-fold that of KDP) and a high LDT (6-fold that of AgGaS2), indicating a promising application in the IR region. Moreover, novel common-vertex-linked wavelike ∞[GeS3]n chains are interestingly discovered in Na2ZnGe2S6, which rarely exist in the reported thiogermanides containing alkali metals. In addition, calculated SHG density and dipole moment demonstrate that the large NLO response is mainly attributed to the cooperative effects of the [GeS4] and [ZnS4] units. PMID:27196357

  19. A holistic numerical model to predict strain hardening and damage of UHMWPE under multiple total knee replacement kinematics and experimental validation.

    PubMed

    Willing, Ryan; Kim, Il Yong

    2009-11-13

    Experimental wear testing is an essential step in the evaluation of total knee replacement (TKR) design. Unfortunately, experiments can be prohibitively expensive and time consuming, which has made computational wear simulation a more desirable alternative for screening designs. While previous attempts have demonstrated positive results, few models have fully incorporated the affect of strain hardening (or cross shear), or tested the model under more than one loading condition. The objective of this study was to develop and evaluate the performance of a new holistic TKR damage model, capable of predicting damage caused by wear, including the effects of strain hardening and creep. For the first time, a frictional work-based damage model was compared against multiple sets of experimental TKR wear testing data using different input kinematics. The wear model was tuned using experimental measurements and was then able to accurately predict the volumetric polyethylene wear volume during experiments with different kinematic inputs. The size and shape of the damage patch on the surface of the polyethylene inserts were also accurately predicted under multiple input kinematics. The ability of this model to predict implant damage under multiple loading profiles by accounting for strain hardening makes it ideal for screening new implant designs, since implant kinematics are largely a function of the shape of the components. PMID:19647828

  20. 1.064-μm laser damage studies of silicon oxy-nitride narrow band reflectors

    NASA Astrophysics Data System (ADS)

    Milward, Jonathan R.; Lewis, Keith L.; Sheach, K.; Heinecke, Rudolf A.

    1994-07-01

    In a paper presented at the 1992 Boulder Damage Symposium, we discussed the role of electric field effects, defect type, surface roughness, film thickness and coating absorption on the laser damage thresholds of sinusoidally modulated, plasma deposited, silicon oxy-nitride narrow band reflectors. We concluded that the damage threshold, which was essentially constant at 2 J/cm2 at the test wavelength of 0.532 micrometers , was defect dominated. A sizeable fraction of the damage events occurred at a particular type of defect--a hemispherical hillock feature typically 5 micrometers in diameter as identified by SEM and interferometric surface profiling. We postulated that this defect initiated damage because of either a microlensing effect or an enhanced electric field effect. We have since measured the laser damage thresholds of all these samples at 1.064 micrometers , and found significant variations in the damage thresholds, which were a factor of three higher on average than those at 0.532 micrometers . The microlens model presented can explain damage thresholds up to a factor of four higher at the longer wavelength, and predicts a minimum nodule height for increased damage susceptibility. The minimum nodule height is dependent on the wavelength and the coating average index. The wavelength scaling of the fluence enhancement and the minimum nodule height imply that nodule initiated damage will become an even more serious problem as the wavelength approaches the UV.

  1. Prediction of Foreign Object Debris/Damage type based in human factors for aeronautics using logistic regression model

    NASA Astrophysics Data System (ADS)

    Romo, David Ricardo

    Foreign Object Debris/Damage (FOD) has been an issue for military and commercial aircraft manufacturers since the early ages of aviation and aerospace. Currently, aerospace is growing rapidly and the chances of FOD presence are growing as well. One of the principal causes in manufacturing is the human error. The cost associated with human error in commercial and military aircrafts is approximately accountable for 4 billion dollars per year. This problem is currently addressed with prevention programs, elimination techniques, and designation of FOD areas, controlled access, restrictions of personal items entering designated areas, tool accountability, and the use of technology such as Radio Frequency Identification (RFID) tags, etc. All of the efforts mentioned before, have not show a significant occurrence reduction in terms of manufacturing processes. On the contrary, a repetitive path of occurrence is present, and the cost associated has not declined in a significant manner. In order to address the problem, this thesis proposes a new approach using statistical analysis. The effort of this thesis is to create a predictive model using historical categorical data from an aircraft manufacturer only focusing in human error causes. The use of contingency tables, natural logarithm of the odds and probability transformation is used in order to provide the predicted probabilities of each aircraft. A case of study is shown in this thesis in order to show the applied methodology. As a result, this approach is able to predict the possible outcomes of FOD by the workstation/area needed, and monthly predictions per workstation. This thesis is intended to be the starting point of statistical data analysis regarding FOD in human factors. The purpose of this thesis is to identify the areas where human error is the primary cause of FOD occurrence in order to design and implement accurate solutions. The advantages of the proposed methodology can go from the reduction of cost

  2. Growth arrest DNA damage-inducible gene 45 gamma expression as a prognostic and predictive biomarker in hepatocellular carcinoma

    PubMed Central

    Ou, Da-Liang; Shyue, Song-Kun; Lin, Liang-In; Feng, Zi-Rui; Liou, Jun-Yang; Fan, Hsiang-Hsuan; Lee, Bin-Shyun; Hsu, Chiun; Cheng, Ann-Lii

    2015-01-01

    Growth arrest DNA damage-inducible gene 45 (GADD45) family proteins play a crucial role in regulating cellular stress responses and apoptosis. The present study explored the prognostic and predictive role of GADD45γ in hepatocellular carcinoma (HCC) treatment. GADD45γ expression in HCC cells was examined using quantitative reverse transcription-PCR (qRT-PCR) and Western blotting. The control of GADD45γ transcription was examined using a luciferase reporter assay and chromatin immunoprecipitation. The in vivo induction of GADD45γ was performed using adenoviral transfer. The expression of GADD45γ in HCC tumor tissues from patients who had undergone curative resection was measured using qRT-PCR. Sorafenib induced expression of GADD45γ mRNA and protein, independent of its RAF kinase inhibitor activity. GADD45γ induction was more prominent in sorafenib-sensitive HCC cells (Huh-7 and HepG2, IC50 6–7 μM) than in sorafenib-resistant HCC cells (Hep3B, Huh-7R, and HepG2R, IC50 12–15 μM). Overexpression of GADD45γ reversed sorafenib resistance in vitro and in vivo, whereas GADD45γ expression knockdown by using siRNA partially abrogated the proapoptotic effects of sorafenib on sorafenib-sensitive cells. Overexpression of survivin in HCC cells abolished the antitumor enhancement between GADD45γ overexpression and sorafenib treatment, suggesting that survivin is a crucial mediator of antitumor effects of GADD45γ. GADD45γ expression decreased in tumors from patients with HCC who had undergone curative surgery, and low GADD45γ expression was an independent prognostic factor for poor survival, in addition to old age and vascular invasion. The preceding data indicate that GADD45γ suppression is a poor prognostic factor in patients with HCC and may help predict sorafenib efficacy in HCC. PMID:26172295

  3. Prediction of bending set, wave efficacy, and hair damage using an extensional permanent waving treatment and the 20% index value.

    PubMed

    Ueno, Yuzo; Namiki, Hideo

    2015-01-01

    To predict "wave efficacy" as evaluated by hairdressers, an extensional permanent waving treatment was performed on human hair fibers using various wave lotions manufactured in Japan. Glass columns devised for the purpose were equipped with a tensile tester in order to increase the measurement accuracy. Notably, the observed set agreed with the theoretical set. In addition, the data for the extensional set exhibited good correlation with the bending set and the wave efficacy assessed in a beauty parlor, and hair damage was estimated by the characteristic change in the 20% index. The following facts were experimentally determined. First, the Young's modulus of the hair fibers after extensional permanent waving treatment continually decreased with an increase in the reduction of the fibers and then abruptly decreased at 80% reduction. Second, the reduction of hair treated with the ammonium salt of thioglycolic acid followed pseudo first-order kinetics only during the initial stage of the reaction, independent of the pH level. Third, the 20% index of the individual virgin hairs remained constant in water at 30°C and also correlated with the Young's modulus of the hair after extensional permanent waving treatment. PMID:26152046

  4. Thalamic fractional anisotropy predicts accrual of cerebral white matter damage in older subjects with small-vessel disease

    PubMed Central

    Cavallari, Michele; Moscufo, Nicola; Meier, Dominik; Skudlarski, Pawel; Pearlson, Godfrey D; White, William B; Wolfson, Leslie; Guttmann, Charles RG

    2014-01-01

    White matter hyperintensities (WMHs) and lacunes are magnetic resonance imaging hallmarks of cerebral small-vessel disease, which increase the risk of stroke, cognitive, and mobility impairment. Although most studies of cerebral small-vessel disease have focused on white matter abnormalities, the gray matter (GM) is also affected, as evidenced by frequently observed lacunes in subcortical GM. Diffusion tensor imaging (DTI) is sensitive to subtle neurodegenerative changes in deep GM structures. We explored the relationship between baseline DTI characteristics of the thalamus, caudate, and putamen, and the volume and subsequent accrual of WMHs over a 4-year period in 56 community-dwelling older (⩾75 years) individuals. Baseline thalamic fractional anisotropy (FA) was an independent predictor of WMH accrual. WMH accrual also correlated with baseline lacune count and baseline WMH volume, the latter showing the strongest predictive power, explaining 27.3% of the variance. The addition of baseline thalamic FA in multivariate modeling increased this value by 70%, which explains 46.5% of the variance in WMH accrual rate. Thalamic FA might serve as a novel predictor of cerebral small-vessel disease progression in clinical settings and trials. Furthermore, our findings point to the possibility of a causal relationship between thalamic damage and the accrual of WMHs. PMID:24824915

  5. Polymer damage mitigation---predictive lifetime models of polymer insulation degradation and biorenewable thermosets through cationic polymerization for self-healing applications

    NASA Astrophysics Data System (ADS)

    Hondred, Peter Raymond

    Over the past 50 years, the industrial development and applications for polymers and polymer composites has become expansive. However, as with any young technology, the techniques for predicting material damage and resolving material failure are in need of continued development and refinement. This thesis work takes two approaches to polymer damage mitigation---material lifetime prediction and spontaneous damage repair through self-healing while incorporating bio-renewable feedstock. First, material lifetime prediction offers the benefit of identifying and isolating material failures before the effects of damage results in catastrophic failure. Second, self-healing provides a systematic approach to repairing damaged polymer composites, specifically in applications where a hands-on approach or removing the part from service are not feasible. With regard to lifetime prediction, we investigated three specific polymeric materials---polytetrafluoroethylene (PTFE), poly(ethylene-alt-tetrafluoroethylene) (ETFE), and Kapton. All three have been utilized extensively in the aerospace field as a wire insulation coating. Because of the vast amount of electrical wiring used in aerospace constructions and the potential for electrical and thermal failure, this work develops mathematical models for both the thermal degradation kinetics as well as a lifetime prediction model for electrothermal breakdown. Isoconversional kinetic methods, which plot activation energy as a function of the extent of degradation, present insight into the development each kinetic model. The models for PTFE, ETFE, and Kapton are one step, consecutive three-step, and competitive and consecutive five-step respectively. Statistical analysis shows that an nth order autocatalytic reaction best defined the reaction kinetics for each polymer's degradation. Self-healing polymers arrest crack propagation through the use of an imbedded adhesive that reacts when cracks form. This form of damage mitigation focuses on

  6. Laser Damage Lab

    NASA Technical Reports Server (NTRS)

    1993-01-01

    Optical Damage Threshold Testing Instrumentation at NASA Langley Research Center. This work was sanctioned and funded by Code Q, R, & AE to develop a new standard for damage testing various types of optical materials and coatings. Laser Induced Damage Threshold (LIDT) testing is a destructive test procedure to determine the minimum applied laser energy level that will result in damage and is referred to as the damage threshold. The damage threshold is often the critical limitation in the section of optical materials for use in high-energy laser systems.The test station consists of diagnostic equipment, beam conditioning optical elements, an inspection microscope and three lasers: a high energy pulsed ND: Yag, which develops 650mJ at 10 hz and outputs three wavelengths which include 1.06m, 532nm and 355 nm; a Ti:sapphire laser which produces a continuum of laser output from 790nm to 900nm; and a alignment HeNe, which looks yellow when mixed with the 2nd harmonic ND:Yag laser. Laser sources are used to perform damage threshold testing at the specific wavelength of interest.

  7. Methodologies for reproducing in-flight loads of aircraft wings on the ground and predicting their response to battle-induced damage

    NASA Astrophysics Data System (ADS)

    Bou-Mosleh, Charbel Fouad

    Survivability of an aircraft in combat is achieved by not getting hit or by withstanding the effects of some suffered hits. Combat damage is described by the removal of one or more portions of the wing or any other flight control surface. To determine whether a wing will survive a specific damage, the structural and aerodynamic response of the wing should be predicted and tested. The response of wings to battle-induced damage is currently addressed through live-fire testing on the ground. The loading methodology used in these live-fire tests does not reproduce the loads encountered during flight, and does not account for the changes in structural stiffness and mass of the wing after damage infliction. In addition, current live-fire tests fail to address the changes in the aerodynamic performance of the wing caused by the battle-induced damage. To better address the structural response of aircraft wings to combat damage, this thesis investigates a concept for an alternative loading methodology that exploits recent advances in nonlinear aeroelastic simulations and smart material actuators. The main idea behind this concept is to accurately predict the stress states of the wing before, during, and after sustaining a hit, for a given flight condition, and reproduce them on the ground by loading the spars and ribs of the wings with programmable actuators and/or a few external tethers. Mathematically, this entails solving an optimization problem to determine the locations and gains of the actuators. Two different types of actuators are investigated: 1D actuators or actuators with tension/compression capability and bimorph bender actuators. The potential of the investigated loading methodology is evaluated for "slender" wings (ARW-2 wing) and for "delta" wings (HSCT and F-16 wing) at a transonic flight condition. The obtained numerical results suggest that the investigated loading methodology can reproduce a desired stress state fairly accurately using external tethers

  8. Atomistic simulation of damage accumulation and amorphization in Ge

    SciTech Connect

    Gomez-Selles, Jose L. Martin-Bragado, Ignacio; Claverie, Alain; Benistant, Francis

    2015-02-07

    Damage accumulation and amorphization mechanisms by means of ion implantation in Ge are studied using Kinetic Monte Carlo and Binary Collision Approximation techniques. Such mechanisms are investigated through different stages of damage accumulation taking place in the implantation process: from point defect generation and cluster formation up to full amorphization of Ge layers. We propose a damage concentration amorphization threshold for Ge of ∼1.3 × 10{sup 22} cm{sup −3} which is independent on the implantation conditions. Recombination energy barriers depending on amorphous pocket sizes are provided. This leads to an explanation of the reported distinct behavior of the damage generated by different ions. We have also observed that the dissolution of clusters plays an important role for relatively high temperatures and fluences. The model is able to explain and predict different damage generation regimes, amount of generated damage, and extension of amorphous layers in Ge for different ions and implantation conditions.

  9. Synthesis, growth, structural and HOMO and LUMO, MEP analysis of a new stilbazolium derivative crystal: A enhanced third-order NLO properties with a high laser-induced damage threshold for NLO applications

    NASA Astrophysics Data System (ADS)

    Senthil, K.; Kalainathan, S.; Hamada, F.; Yamada, M.; Aravindan, P. G.

    2015-08-01

    A new organic third-order nonlinear optical crystal from stilbazolium family 2-[2-(4-methoxy-phenyl) vinyl]-1-methyl-pyridinium tetrafluoroborate (4MSTB) has been synthesized and grown by slow evaporation method for the first time. The grown crystal structure was confirmed by single crystal X-ray diffraction analysis, and it is revealed that the grown crystal crystallized in a triclinic crystal system with centrosymmetric space group P 1 bar . The HOMO and LUMO energies were calculated for the grown crystal explains charge transfer takes place within the molecule and confirms the suitability of the title crystal for NLO applications. The presence of various vibration modes of expected functional groups was identified by FT-IR analysis. The transmittance ability of the grown crystal was also analyzed by using UV-Vis-NIR spectral studies and shows that the crystal has no absorption of light in the entire Vis-NIR region. The thermal stability of the title crystal has been investigated by TGA/DTA studies and revealed that the material was thermally stable up to the melting point, 193 °C. The hardness number, Meyer index, yield strength, and elastic stiffness constant has been estimated for the grown 4MSTB crystal using Vickers microhardness tester. Photoluminescence excitation studies showed green emission radiation occurred at 517 nm. The dielectric properties of the grown crystal have been analyzed as a function of temperature over a wide range of frequency (50 Hz-5 MHz) by using LCR meter. The result of ac electrical conductivity of 4MSTB was found to be 5.25 × 10-5 (Ω m)-1. The laser damage threshold (LDT) energy for the grown crystal has been measured by using a Q-switched Nd:YAG laser as a source in single-shot mode (1064 nm, 10 Hz, 420 mJ). The result of LDT indicates that grown title crystal has excellent resistance to laser radiation than those of known some inorganic NLO materials. The chemical etching studies were carried out to assess the perfection of

  10. Nav Channels in Damaged Membranes.

    PubMed

    Morris, C E; Joos, B

    2016-01-01

    Sick excitable cells (ie, Nav channel-expressing cells injured by trauma, ischemia, inflammatory, and other conditions) typically exhibit "acquired sodium channelopathies" which, we argue, reflect bleb-damaged membranes rendering their Nav channels "leaky." The situation is excitotoxic because untreated Nav leak exacerbates bleb damage. Fast Nav inactivation (a voltage-independent process) is so tightly coupled, kinetically speaking, to the inherently voltage-dependent process of fast activation that when bleb damage accelerates and thus left-shifts macroscopic fast activation, fast inactivation accelerates to the same extent. The coupled g(V) and availability(V) processes and their window conductance regions consequently left-shift by the same number of millivolts. These damage-induced hyperpolarizing shifts, whose magnitude increases with damage intensity, are called coupled left shift (CLS). Based on past work and modeling, we discuss how to test for Nav-CLS, emphasizing the virtue of sawtooth ramp clamp. We explain that it is the inherent mechanosensitivity of Nav activation that underlies Nav-CLS. Using modeling of excitability, we show the known process of Nav-CLS is sufficient to predict a wide variety of "sick excitable cell" phenomena, from hyperexcitability through to depolarizing block. When living cells are mimicked by inclusion of pumps, mild Nav-CLS produces a wide array of burst phenomena and subthreshold oscillations. Dynamical analysis of mild damage scenarios shows how these phenomena reflect changes in spike thresholds as the pumps try to counteract the leaky Nav channels. Smart Nav inhibitors designed for sick excitable cells would target bleb-damaged membrane, buying time for cell-mediated removal or repair of Nav-bearing membrane that has become bleb-damaged (ie, detached from the cytoskeleton). PMID:27586295

  11. CARA Risk Assessment Thresholds

    NASA Technical Reports Server (NTRS)

    Hejduk, M. D.

    2016-01-01

    Warning remediation threshold (Red threshold): Pc level at which warnings are issued, and active remediation considered and usually executed. Analysis threshold (Green to Yellow threshold): Pc level at which analysis of event is indicated, including seeking additional information if warranted. Post-remediation threshold: Pc level to which remediation maneuvers are sized in order to achieve event remediation and obviate any need for immediate follow-up maneuvers. Maneuver screening threshold: Pc compliance level for routine maneuver screenings (more demanding than regular Red threshold due to additional maneuver uncertainty).

  12. A new insight into defect-induced laser damage in UV multilayer coatings

    SciTech Connect

    Reichling, M.; Bodemann, A.; Kaiser, N.

    1995-12-31

    High performance Al{sub 2}O{sub 3}SiO{sub 2} mirror coatings for 248 nm have been investigated with respect to their excimer laser damage resistivity. Global damage thresholds (in the range of 10-20 J/cm{sup 2}) averaged over large areas were determined with the pulsed photoacoustic mirage detection method. With a raster scanning technique utilizing the same detection scheme, the local damage behaviour was studied with 100 {mu}m spatial resolution. It was found that the local damage threshold at specific sites was lower than the global damage threshold and it was assumed that this phenomenon was associated with micrometer-scale defects in the multilayer coating. To test this hypothesis photothermal displacement microscopy with {mu}m lateral resolution was performed on the investigated regions prior to excimer laser light irradiation. Photothermal images revealed an extremely small background absorption and a small number of absorbing defect sites. For a number of such sites a clear correlation between the local absorption and the onset of laser damage at that specific location was found. We conclude that the crucial factor determining the damage resistivity of the high quality coating systems are defects and contaminants and that it will be possible to predict their damage thresholds by a complete microscopic photothermal inspection.

  13. Threshold models in radiation carcinogenesis

    SciTech Connect

    Hoel, D.G.; Li, P.

    1998-09-01

    Cancer incidence and mortality data from the atomic bomb survivors cohort has been analyzed to allow for the possibility of a threshold dose response. The same dose-response models as used in the original papers were fit to the data. The estimated cancer incidence from the fitted models over-predicted the observed cancer incidence in the lowest exposure group. This is consistent with a threshold or nonlinear dose-response at low-doses. Thresholds were added to the dose-response models and the range of possible thresholds is shown for both solid tumor cancers as well as the different leukemia types. This analysis suggests that the A-bomb cancer incidence data agree more with a threshold or nonlinear dose-response model than a purely linear model although the linear model is statistically equivalent. This observation is not found with the mortality data. For both the incidence data and the mortality data the addition of a threshold term significantly improves the fit to the linear or linear-quadratic dose response for both total leukemias and also for the leukemia subtypes of ALL, AML, and CML.

  14. Laser threshold magnetometry

    NASA Astrophysics Data System (ADS)

    Jeske, Jan; Cole, Jared H.; Greentree, Andrew D.

    2016-01-01

    We propose a new type of sensor, which uses diamond containing the optically active nitrogen-vacancy (NV-) centres as a laser medium. The magnetometer can be operated at room-temperature and generates light that can be readily fibre coupled, thereby permitting use in industrial applications and remote sensing. By combining laser pumping with a radio-frequency Rabi-drive field, an external magnetic field changes the fluorescence of the NV- centres. We use this change in fluorescence level to push the laser above threshold, turning it on with an intensity controlled by the external magnetic field, which provides a coherent amplification of the readout signal with very high contrast. This mechanism is qualitatively different from conventional NV--based magnetometers which use fluorescence measurements, based on incoherent photon emission. We term our approach laser threshold magnetometer (LTM). We predict that an NV--based LTM with a volume of 1 mm3 can achieve shot-noise limited dc sensitivity of 1.86 fT /\\sqrt{{{Hz}}} and ac sensitivity of 3.97 fT /\\sqrt{{{Hz}}}.

  15. Threshold quantum cryptography

    SciTech Connect

    Tokunaga, Yuuki; Okamoto, Tatsuaki; Imoto, Nobuyuki

    2005-01-01

    We present the concept of threshold collaborative unitary transformation or threshold quantum cryptography, which is a kind of quantum version of threshold cryptography. Threshold quantum cryptography states that classical shared secrets are distributed to several parties and a subset of them, whose number is greater than a threshold, collaborates to compute a quantum cryptographic function, while keeping each share secretly inside each party. The shared secrets are reusable if no cheating is detected. As a concrete example of this concept, we show a distributed protocol (with threshold) of conjugate coding.

  16. Intelligence and Creativity: Over the Threshold Together?

    ERIC Educational Resources Information Center

    Welter, Marisete Maria; Jaarsveld, Saskia; van Leeuwen, Cees; Lachmann, Thomas

    2016-01-01

    Threshold theory predicts a positive correlation between IQ and creativity scores up to an IQ level of 120 and no correlation above this threshold. Primary school children were tested at beginning (N = 98) and ending (N = 70) of the school year. Participants performed the standard progressive matrices (SPM) and the Test of Creative…

  17. Optimal thresholds for the estimation of area rain-rate moments by the threshold method

    NASA Technical Reports Server (NTRS)

    Short, David A.; Shimizu, Kunio; Kedem, Benjamin

    1993-01-01

    Optimization of the threshold method, achieved by determination of the threshold that maximizes the correlation between an area-average rain-rate moment and the area coverage of rain rates exceeding the threshold, is demonstrated empirically and theoretically. Empirical results for a sequence of GATE radar snapshots show optimal thresholds of 5 and 27 mm/h for the first and second moments, respectively. Theoretical optimization of the threshold method by the maximum-likelihood approach of Kedem and Pavlopoulos (1991) predicts optimal thresholds near 5 and 26 mm/h for lognormally distributed rain rates with GATE-like parameters. The agreement between theory and observations suggests that the optimal threshold can be understood as arising due to sampling variations, from snapshot to snapshot, of a parent rain-rate distribution. Optimal thresholds for gamma and inverse Gaussian distributions are also derived and compared.

  18. Correlation between stimulated scattering processes and laser-induced damage in crystalline quartz

    NASA Technical Reports Server (NTRS)

    Yu, C.; Haw, M. F.; Hsu, H.

    1977-01-01

    The results of a systematic series of experiments to uncover possible correlation between laser-induced stimulated-Brillouin-scattering (SBS) phonons and damage in quartz are presented. Such correlation is confirmed and the various thresholds are established. The anomalous transmission factor under phonon generation is found to decay exponentially as predicted with increasing incident laser power. The LF SBS phonon is also demonstrated to be a sensitive probe for precatastrophic damage.

  19. [Nonlinear magnetohydrodynamics]. [Threshold unstable MHD activity

    SciTech Connect

    Not Available

    1992-01-01

    Theoretical predictions were compared with available data from JET on the threshold unstable MHD activity in toroidal confinement devices. In particular, questions arising as to Hartmans number and the selection of a kinematic viscosity are discussed.

  20. Threshold Concepts in Biochemistry

    ERIC Educational Resources Information Center

    Loertscher, Jennifer

    2011-01-01

    Threshold concepts can be identified for any discipline and provide a framework for linking student learning to curricular design. Threshold concepts represent a transformed understanding of a discipline, without which the learner cannot progress and are therefore pivotal in learning in a discipline. Although threshold concepts have been…

  1. Ultrasonic impact damage assessment in 3D woven composite materials

    NASA Astrophysics Data System (ADS)

    Mannai, E.; Lamboul, B.; Roche, J. M.

    2015-03-01

    An ultrasonic nondestructive methodology is proposed for the assessment of low velocity impact damage in a 3D woven composite material. The output data is intended for material scientists and numerical scientists to validate the damage tolerance performance of the manufactured materials and the reliability of damage modeling predictions. A depth-dependent threshold based on the reflectivity of flat bottom holes is applied to the ultrasonic data to remove the structural noise and isolate echoes of interest. The methodology was applied to a 3 mm thick 3D woven composite plate impacted with different energies. An artificial 3D representation of the detected echoes is proposed to enhance the spatial perception of the generated damage by the end user. The paper finally highlights some statistics made on the detected echoes to quantitatively assess the impact damage resistance of the tested specimens.

  2. Numerical Predictions of Damage and Failure in Carbon Fiber Reinforced Laminates Using a Thermodynamically-Based Work Potential Theory

    NASA Technical Reports Server (NTRS)

    Pineda, Evan Jorge; Waas, Anthony M.

    2013-01-01

    A thermodynamically-based work potential theory for modeling progressive damage and failure in fiber-reinforced laminates is presented. The current, multiple-internal state variable (ISV) formulation, referred to as enhanced Schapery theory (EST), utilizes separate ISVs for modeling the effects of damage and failure. Consistent characteristic lengths are introduced into the formulation to govern the evolution of the failure ISVs. Using the stationarity of the total work potential with respect to each ISV, a set of thermodynamically consistent evolution equations for the ISVs are derived. The theory is implemented into a commercial finite element code. The model is verified against experimental results from two laminated, T800/3900-2 panels containing a central notch and different fiber-orientation stacking sequences. Global load versus displacement, global load versus local strain gage data, and macroscopic failure paths obtained from the models are compared against the experimental results.

  3. Whole-body vibration perception thresholds

    NASA Astrophysics Data System (ADS)

    Parsons, K. C.; Griffin, M. J.

    1988-03-01

    This paper presents the results of a series of laboratory experiments concerned with perception thresholds for whole-body vibration. The nature of absolute perception thresholds is discussed and a method of determining vibration thresholds, based upon signal detection theory, is proposed. Thresholds of subjects exposed to x-, y- and z-axis sinusoidal vibration were determined for sitting and standing subjects (from 2 to 100 Hz). Perception thresholds have also been determined for supine subjects exposed to vertical ( x-axis) sinusoidal vibration (10-63 Hz). In additional experiments the effects of complex (e.g., random) vibration and the effects of duration on the perception thresholds were investigated. The relation between perception thresholds and vibration levels, said by subjects to be unacceptable if they occurred in their own homes, was investigated as well as the effects of subjects' personality and the visual and acoustic conditions in the laboratory. For the vertical vibration of seated subjects no significant differences were found between the responses of male and female subjects. Significant differences were found between perception thresholds for sitting and standing postures. The median threshold was approximately 0·01 m/s 2 r.m.s. between 2 and 100 Hz. Perception thresholds for x-axis and y-axis vibration were not significantly different in either sitting or standing subjects but significant differences in thresholds were found between sitting and standing positions for both x-axis and y-axis vibration. Subjects tended to be more sensitive to vibration when lying than when sitting or standing. The results suggested that the perception of random vibrations can be predicted from a knowledge of the perception of its component vibrations. The number of cycles of vibration did not affect perception thresholds for vibration durations of more than about 0·25 s. Some assessments suggested that vibration at more than twice the perception threshold may not

  4. Slow Crack Growth Analysis of Advanced Structural Ceramics Under Combined Loading Conditions: Damage Assessment in Life Prediction Testing

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Gyekenyesi, John P.

    2000-01-01

    Slow crack growth analysis was performed with three different loading histories including constant stress-rate/constant stress-rate testing (Case I loading), constant stress/constant stress-rate testing (Case II loading), and cyclic stress/constant stress-rate testing (Case III loading). Strength degradation due to slow crack growth arid/or damage accumulation was determined numerically as a Function of percentage of interruption time between the two loading sequences for a given loading history. The numerical solutions were examined with the experimental data determined at elevated temperatures using four different advanced ceramic materials, two silicon nitrides, one silicon carbide and one alumina for the Case I loading history, and alumina for the Case II loading history. The numerical solutions were in reasonable agreement with the experimental data, indicating that notwithstanding some degree of creep deformation presented for some test materials slow crack growth was a governing mechanism associated with failure for all the test material&

  5. Slow Crack Growth Analysis of Advanced Structural Ceramics Under Combined Loading Conditions: Damage Assessment in Life Prediction Testing

    NASA Technical Reports Server (NTRS)

    Choi, S. R.; Gyekenyesi, J. P.

    2001-01-01

    Slow crack growth analysis was performed with three different loading histories including constant stress- rate/constant stress-rate testing (Case I loading), constant stress/constant stress-rate testing (Case II loading), and cyclic stress/constant stress-rate testing (Case III loading). Strength degradation due to slow crack growth and/or damage accumulation was determined numerically as a function of percentage of interruption time between the two loading sequences for a given loading history. The numerical solutions were examined with the experimental data determined at elevated temperatures using four different advanced ceramic materials, two silicon nitrides, one silicon carbide and one alumina for the Case I loading history, and alumina for the Case II loading history. The numerical solutions were in reasonable agreement with the experimental data, indicating that notwithstanding some degree of creep deformation presented for some test materials slow crack growth was a governing mechanism associated with failure for all the rest materials.

  6. Slow Crack Growth Analysis of Advanced Structural Ceramics Under Combined Loading Conditions: Damage Assessment in Life Prediction Testing

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Gyekenyesi, John P.

    2000-01-01

    Slow crack growth analysis was performed with three different loading histories including constant stress-rate/constant stress-rate testing (Case 1 loading), constant stress/constant stress-rate testing (Case 2 loading), and cyclic stress/constant stress-rate testing (Case 2 loading). Strength degradation due to slow crack growth and/or damage accumulation was determined numerically as a function of percentage of interruption time between the two loading sequences for a given loading history. The numerical solutions were examined with the experimental data determined at elevated temperatures using four different advanced ceramic materials, two silicon nitrides, one silicon carbide and one alumina for the Case 1 loading history, and alumina for the Case 3 loading history. The numerical solutions were in reasonable agreement with the experimental data, indicating that notwithstanding some degree of creep deformation presented for some test materials slow crack growth was a governing mechanism associated with failure for all the test materials.

  7. Anaemia may add information to standardised disease activity assessment to predict radiographic damage in rheumatoid arthritis: a prospective cohort study

    PubMed Central

    Möller, Burkhard; Scherer, Almut; Förger, Frauke; Villiger, Peter M; Finckh, Axel

    2014-01-01

    Objective Anaemia in rheumatoid arthritis (RA) is prototypical of the chronic disease type and is often neglected in clinical practice. We studied anaemia in relation to disease activity, medications and radiographic progression. Methods Data were collected between 1996 and 2007 over a mean follow-up of 2.2 years. Anaemia was defined according to WHO (♀ haemoglobin<12 g/dl, ♂: haemoglobin<13 g/dl), or alternative criteria. Anaemia prevalence was studied in relation to disease parameters and pharmacological therapy. Radiographic progression was analysed in 9731 radiograph sets from 2681 patients in crude longitudinal regression models and after adjusting for potential confounding factors, including the clinical disease activity score with the 28-joint count for tender and swollen joints and erythrocyte sedimentation rate (DAS28ESR) or the clinical disease activity index (cDAI), synthetic antirheumatic drugs and antitumour necrosis factor (TNF) therapy. Results Anaemia prevalence decreased from more than 24% in years before 2001 to 15% in 2007. Erosions progressed significantly faster in patients with anaemia (p<0.001). Adjusted models showed these effects independently of clinical disease activity and other indicators of disease severity. Radiographic damage progression rates were increasing with severity of anaemia, suggesting a ‘dose-response effect’. The effect of anaemia on damage progression was maintained in subgroups of patients treated with TNF blockade or corticosteroids, and without non-selective nonsteroidal anti-inflammatory drugs (NSAIDs). Conclusions Anaemia in RA appears to capture disease processes that remain unmeasured by established disease activity measures in patients with or without TNF blockade, and may help to identify patients with more rapid erosive disease. PMID:23505235

  8. Using wavelet analysis to compare the QCD prediction and experimental data on R_{e^+e^-} and to determine parameters of the charmonium states above the Dbar{D} threshold

    NASA Astrophysics Data System (ADS)

    Henner, V. K.; Davis, C. L.; Belozerova, T. S.

    2015-10-01

    The first part of our analysis uses the wavelet method to compare the quantum chromodynamic (QCD) prediction for the ratio of hadronic to muon cross sections in electron-positron collisions, R, with experimental data for R over a center of mass energy range up to about 7 GeV. A direct comparison of the raw experimental data and the QCD prediction is difficult because the data have a wide range of structures and large statistical errors and the QCD description contains sharp quark-antiquark thresholds. However, a meaningful comparison can be made if a type of "smearing" procedure is used to smooth out rapid variations in both the theoretical and experimental values of R. A wavelet analysis (WA) can be used to achieve this smearing effect. The second part of the analysis concentrates on the 3.0-6.0 GeV energy region which includes the relatively wide charmonium resonances ψ (1^-). We use the wavelet methodology to distinguish these resonances from experimental noise, background and from each other, allowing a reliable determination of the parameters of these states. Both analyses are examples of the usefulness of WA in extracting information in a model independent way from high energy physics data.

  9. Nd:YAG surgical laser effects in canine prostate tissue: temperature and damage distribution

    NASA Astrophysics Data System (ADS)

    van Nimwegen, S. A.; L'Eplattenier, H. F.; Rem, A. I.; van der Lugt, J. J.; Kirpensteijn, J.

    2009-01-01

    An in vitro model was used to predict short-term, laser-induced, thermal damage in canine prostate tissue. Canine prostate tissue samples were equipped with thermocouple probes to measure tissue temperature at 3, 6, 9 and 12 mm depths. The tissue surface was irradiated with a Nd:YAG laser in contact or non-contact mode for up to 20 s, using powers from 5 to 20 W. Prediction of thermal damage using Arrhenius theory was discussed and compared to the in vitro damage threshold, determined by histological evaluation. The threshold temperature for acute thermal tissue damage was 69 ± 6 °C (means ± SD), irrespective of exposure time. Contact mode laser application caused vaporization of tissue, leaving a crater underneath the fiber tip. The mean extent of tissue damage underneath the vaporization crater floor was 0.9 ± 0.6 mm after 5, 10 or 20 s of contact mode laser irradiation at 10 W, whereas 20 W non-contact exposure up to 20 s causes up to 4.7 ± 0.2 mm coagulation necrosis. It was concluded that short-term acute thermal tissue damage can be comprehensively described by a single threshold temperature.

  10. Pausing at the Threshold

    ERIC Educational Resources Information Center

    Morgan, Patrick K.

    2015-01-01

    Since about 2003, the notion of threshold concepts--the central ideas in any field that change how learners think about other ideas--have become difficult to escape at library conferences and in general information literacy discourse. Their visibility will likely only increase because threshold concepts figure prominently in the Framework for…

  11. Threshold Concepts in Economics

    ERIC Educational Resources Information Center

    Shanahan, Martin

    2016-01-01

    Purpose: The purpose of this paper is to examine threshold concepts in the context of teaching and learning first-year university economics. It outlines some of the arguments for using threshold concepts and provides examples using opportunity cost as an exemplar in economics. Design/ Methodology/Approach: The paper provides an overview of the…

  12. Bayesian Threshold Estimation

    ERIC Educational Resources Information Center

    Gustafson, S. C.; Costello, C. S.; Like, E. C.; Pierce, S. J.; Shenoy, K. N.

    2009-01-01

    Bayesian estimation of a threshold time (hereafter simply threshold) for the receipt of impulse signals is accomplished given the following: 1) data, consisting of the number of impulses received in a time interval from zero to one and the time of the largest time impulse; 2) a model, consisting of a uniform probability density of impulse time…

  13. Computational gestalts and perception thresholds.

    PubMed

    Desolneux, Agnès; Moisan, Lionel; Morel, Jean-Michel

    2003-01-01

    In 1923, Max Wertheimer proposed a research programme and method in visual perception. He conjectured the existence of a small set of geometric grouping laws governing the perceptual synthesis of phenomenal objects, or "gestalt" from the atomic retina input. In this paper, we review this set of geometric grouping laws, using the works of Metzger, Kanizsa and their schools. In continuation, we explain why the Gestalt theory research programme can be translated into a Computer Vision programme. This translation is not straightforward, since Gestalt theory never addressed two fundamental matters: image sampling and image information measurements. Using these advances, we shall show that gestalt grouping laws can be translated into quantitative laws allowing the automatic computation of gestalts in digital images. From the psychophysical viewpoint, a main issue is raised: the computer vision gestalt detection methods deliver predictable perception thresholds. Thus, we are set in a position where we can build artificial images and check whether some kind of agreement can be found between the computationally predicted thresholds and the psychophysical ones. We describe and discuss two preliminary sets of experiments, where we compared the gestalt detection performance of several subjects with the predictable detection curve. In our opinion, the results of this experimental comparison support the idea of a much more systematic interaction between computational predictions in Computer Vision and psychophysical experiments. PMID:14766147

  14. Neurolaw: Differential brain activity for black and white faces predicts damage awards in hypothetical employment discrimination cases.

    PubMed

    Korn, Harrison A; Johnson, Micah A; Chun, Marvin M

    2012-07-01

    Currently, potential jurors' racial biases are measured by explicit questioning--a poor measure because people often hide their views to adhere to social norms, and people have implicit views they are not consciously aware of. In this experiment, we investigated whether two alternative methods of measuring racial bias--a standard black/white, good/bad implicit association test (IAT) and neural activity, measured by fMRI, in response to seeing faces of black and white individuals--could predict how much money subjects would award Black victims in hypothetical employment discrimination cases. IAT scores failed to predict how much money subjects awarded victims. However, in right inferior parietal lobule (BA 40) and in right superior/middle frontal gyrus (BA 9/10)--which have both previously been implicated in measuring biases and implicit preferences--the difference in neural activity between when subjects viewed black faces paired with neutral adjectives and when subjects viewed white faces paired with neutral adjectives was positively correlated with the amount of money the subjects awarded victims. This suggests that brain activity measures racial bias with more practical validity, at least in this situation and with our sample size, than a common behavioral measure (the IAT). PMID:22059860

  15. Prediction of shear damage of plasmid DNA in pump and centrifuge operations using an ultra scale-down device.

    PubMed

    Zhang, Hu; Kong, Simyee; Booth, Andrew; Boushaba, Rihab; Levy, M Susana; Hoare, Michael

    2007-01-01

    Supercoiled circular (SC) plasmid DNA is often subjected to fluid stress in large-scale manufacturing processes. It is thus important to characterize the engineering environment within a particular unit operation as well as within the associated ancillary equipment during process design for plasmid DNA manufacture so as to avoid shear-induced degradation of the SC isoform, which would compromise product efficacy in therapeutic applications. In the past few years, ultra scale-down (USD) tools were developed within our laboratory to mimic the engineering environments experienced by biomolecules within a range of manufacturing-scale ancillary, primary recovery, and purification operations, using milliliter quantities of material. Through the use of a USD shear device, the effect of elongational strain rate on SC plasmid DNA degradation was studied in this paper, and from that, the impact of a centrifugal pump, a Mono pump, and a disk-stack centrifuge feed zone on SC plasmid DNA degradation was predicted and experimentally verified at scale. Model predictions, over the range of conditions studied, were in good agreement with experimental values, demonstrating the potential of the USD approach as a decisional tool during bioprocess design. PMID:17672520

  16. Thresholds of Etchable Track Formation and Chemical Damage Parameters in Poly(ethylene terephthalate), Bisphenol A polycarbonate, and Poly(allyl diglycol carbonate) Films at the Stopping Powers Ranging from 10 to 12,000 keV/µm

    NASA Astrophysics Data System (ADS)

    Yamauchi, Tomoya; Mori, Yutaka; Morimoto, Akira; Kanasaki, Masato; Oda, Keiji; Kodaira, Satoshi; Konishi, Teruaki; Yasuda, Nakahiro; Tojo, Sachiko; Honda, Yoshihide; Barillon, Rémi

    2012-05-01

    The damage structure of latent tracks in poly(ethylene terephthalate) (PET) has been examined by Fourier transform infrared (FT-IR) measurements. Results are compared with those from previous studies on bisphenol A polycarbonate (PC) and poly(allyl diglycol carbonate) (PADC). These polymers are exposed to protons and heavy ions (He, C, Ne, Si, Ar, Fe, Kr, and Xe) in air with energies less than 6 MeV/n, as well as gamma rays from an intense Co-60 source. Chemical damage parameters, namely, damage density, which is the number of losses of considered functional groups per unit length of tracks, radial size of the track core, in which the considered chemical groups are lost, and radiation chemical yields (G values) for each group are evaluated as a function of the stopping power. It has been confirmed that latent tracks will be etchable when the radial track core size is larger than the distance between two adjacent breaking points of polymer chains. The predominant breaking points are the C-O bonds in ether, ester, and carbonate ester bonds.

  17. Vanishing of {1}/{m} corrections at threshold

    NASA Astrophysics Data System (ADS)

    Boyd, C. Glenn; Brahm, David E.

    1991-03-01

    Heavy-quark predictions for hadronic weak-decay transition amplitudes have O( {1}/{m}) corrections, but we show these always vanish at threshold. This follows from the nonrenormalization of the threshold effective currents at O( {1}/{m}) , and an application of the Ademollo-Gatto theorem. The result, which we call Luke's theorem, holds for initial and final particles consisting of a heavy quark or scalar and light degrees of freedom in an arbitrary spin state.

  18. The reliability and predictive ability of a biomarker of oxidative DNA damage on functional outcomes after stroke rehabilitation.

    PubMed

    Hsieh, Yu-Wei; Lin, Keh-Chung; Korivi, Mallikarjuna; Lee, Tsong-Hai; Wu, Ching-Yi; Wu, Kuen-Yuh

    2014-01-01

    We evaluated the reliability of 8-hydroxy-2'-deoxyguanosine (8-OHdG), and determined its ability to predict functional outcomes in stroke survivors. The rehabilitation effect on 8-OHdG and functional outcomes were also assessed. Sixty-one stroke patients received a 4-week rehabilitation. Urinary 8-OHdG levels were determined by liquid chromatography-tandem mass spectrometry. The test-retest reliability of 8-OHdG was good (interclass correlation coefficient=0.76). Upper-limb motor function and muscle power determined by the Fugl-Meyer Assessment (FMA) and Medical Research Council (MRC) scales before rehabilitation showed significant negative correlation with 8-OHdG (r=-0.38, r=-0.30; p<0.05). After rehabilitation, we found a fair and significant correlation between 8-OHdG and FMA (r=-0.34) and 8-OHdG and pain (r=0.26, p<0.05). Baseline 8-OHdG was significantly correlated with post-treatment FMA, MRC, and pain scores (r=-0.34, -0.31, and 0.25; p<0.05), indicating its ability to predict functional outcomes. 8-OHdG levels were significantly decreased, and functional outcomes were improved after rehabilitation. The exploratory study findings conclude that 8-OHdG is a reliable and promising biomarker of oxidative stress and could be a valid predictor of functional outcomes in patients. Monitoring of behavioral indicators along with biomarkers may have crucial benefits in translational stroke research. PMID:24743892

  19. A Global/Local Finite Element Approach for Predicting Interlaminar and Intralaminar Damage Evolution in Composite Stiffened Panels Under Compressive Load

    NASA Astrophysics Data System (ADS)

    Pietropaoli, Elisa; Riccio, Aniello

    2011-04-01

    This paper addresses the prediction of intralaminar and interlaminar damage onset and evolution in composite structures through the use of a finite element based procedure. This procedure joins methodologies whose credibility has been already assessed in literature such as the Virtual Crack Closure Technique (for delamination) and the ply discount approach (for matrix/fiber failures). In order to establish the reliability of the procedure developed, comparisons with literature experimental results on a stiffened panel with an embedded delamination are illustrated. The methodology proposed, implemented in ANSYS as post-processing routines, is combined with a finite element model of the panel, built by adopting both shell and solid elements within the frame of an embedded global/local approach to connect differently modelled substructures.

  20. Large area damage testing of optics

    SciTech Connect

    Sheehan, L.; Kozlowski, M.; Stolz, C.

    1996-04-26

    The damage threshold specifications for the National Ignition Facility will include a mixture of standard small-area tests and new large-area tests. During our studies of laser damage and conditioning processes of various materials we have found that some damage morphologies are fairly small and this damage does not grow with further illumination. This type of damage might not be detrimental to the laser performance. We should therefore assume that some damage can be allowed on the optics, but decide on a maximum damage allowance of damage. A new specification of damage threshold termed {open_quotes}functional damage threshold{close_quotes} was derived. Further correlation of damage size and type to system performance must be determined in order to use this measurement, but it is clear that it will be a large factor in the optics performance specifications. Large-area tests have verified that small-area testing is not always sufficient when the optic in question has defect-initiated damage. This was evident for example on sputtered polarizer and mirror coatings where the defect density was low enough that the features could be missed by standard small- area testing. For some materials, the scale-length at which damage non-uniformities occur will effect the comparison of small-area and large-area tests. An example of this was the sub-aperture tests on KD*P crystals on the Beamlet test station. The tests verified the large-area damage threshold to be similar to that found when testing a small-area. Implying that for this KD*P material, the dominate damage mechanism is of sufficiently small scale-length that small-area testing is capable of determining the threshold. The Beamlet test station experiments also demonstrated the use of on-line laser conditioning to increase the crystals damage threshold.

  1. The Application of a New Maximum Color Contrast Sensitivity Test to the Early Prediction of Chiasma Damage in Cases of Pituitary Adenoma: The Pilot Study

    PubMed Central

    Liutkeviciene, Rasa; Glebauskiene, Brigita; Zaliuniene, Dalia; Kriauciuniene, Loresa; Bernotas, Giedrimantas; Tamasauskas, Arimantas

    2016-01-01

    Purpose Our objective was to estimate the maximum color contrast sensitivity (MCCS) thresholds in individuals with chiasma opticum damage. Methods The pilot study tested 41 people with pituitary adenoma (PA) and 100 age- and gender-matched controls. Patients were divided into two groups according to PA size, PA ≤1 cm or PA >1 cm. A new MCCS test program was used for color discrimination. Results The mean total error score (TES) of MCCS was 1.8 in the PA ≤1 cm group (standard deviation [SD], 0.38), 3.5 in the PA >1 cm group (SD, 0.96), and 1.4 in the control group (SD, 0.31; p < 0.001). There was a positive correlation between tumor size and MCCS result (r = 0.648, p < 0.01). In the group that had PA-producing hormones, the TES was 2.5 (SD, 1.09), compared to 4.2 value in the non-functioning PA group of patients that did not have clinically significant hormone excess (SD, 3.16; p < 0.01). In patients with normal visual acuity (VA) or visual field MCCS, the TES was 3.3 (SD, 1.8), while that in patients with VA <0.00 was 4.6 (SD, 2.9). Conclusions Results of the MCCS test TES were 1.9 times better in patients with PA ≤1 cm compared to patients with PA >1 cm (p < 0.01). In PA patients with normal VA, the TES was 2.35 times worse than that of healthy persons (p < 0.01). PMID:27478357

  2. Injury thresholds for topical-cream-coated skin of hairless guinea pigs (cavia porcellus) in the near-infrared region

    NASA Astrophysics Data System (ADS)

    Pocock, Ginger M.; Zohner, Justin J.; Stolarski, David J.; Buchanan, Kelvin C.; Jindra, Nichole M.; Figueroa, Manuel A.; Chavey, Lucas J.; Imholte, Michelle L.; Thomas, Robert J.; Rockwell, Benjamin A.

    2006-02-01

    The reflectance and absorption of the skin plays a vital role in determining how much radiation will be absorbed by human tissue. Any substance covering the skin would change the way radiation is reflected and absorbed and thus the extent of thermal injury. Hairless guinea pigs (cavia porcellus) in vivo were used to evaluate how the minimum visible lesion threshold for single-pulse laser exposure is changed with a topical agent applied to the skin. The ED 50 for visible lesions due to an Er: glass laser at 1540-nm with a pulse width of 50-ns was determined, and the results were compared with model predictions using a skin thermal model. The ED50 is compared with the damage threshold of skin coated with a highly absorbing topical cream at 1540 nm to determine its effect on damage pathology and threshold. The ED 50 for the guinea pig was then compared to similar studies using Yucatan minipigs and Yorkshire pigs at 1540-nm and nanosecond pulse duration. 1,2 The damage threshold at 24-hours of a Yorkshire pig for a 2.5-3.5-mm diameter beam for 100 ns was 3.2 Jcm -2; very similar to our ED 50 of 3.00 Jcm -2 for the hairless guinea pigs.

  3. Threshold Assessment of Gear Diagnostic Tools on Flight and Test Rig Data

    NASA Technical Reports Server (NTRS)

    Dempsey, Paula J.; Mosher, Marianne; Huff, Edward M.

    2003-01-01

    A method for defining thresholds for vibration-based algorithms that provides the minimum number of false alarms while maintaining sensitivity to gear damage was developed. This analysis focused on two vibration based gear damage detection algorithms, FM4 and MSA. This method was developed using vibration data collected during surface fatigue tests performed in a spur gearbox rig. The thresholds were defined based on damage progression during tests with damage. The thresholds false alarm rates were then evaluated on spur gear tests without damage. Next, the same thresholds were applied to flight data from an OH-58 helicopter transmission. Results showed that thresholds defined in test rigs can be used to define thresholds in flight to correctly classify the transmission operation as normal.

  4. A Threshold Continuum for Aeolian Sand Transport

    NASA Astrophysics Data System (ADS)

    Swann, C.; Ewing, R. C.; Sherman, D. J.

    2015-12-01

    The threshold of motion for aeolian sand transport marks the initial entrainment of sand particles by the force of the wind. This is typically defined and modeled as a singular wind speed for a given grain size and is based on field and laboratory experimental data. However, the definition of threshold varies significantly between these empirical models, largely because the definition is based on visual-observations of initial grain movement. For example, in his seminal experiments, Bagnold defined threshold of motion when he observed that 100% of the bed was in motion. Others have used 50% and lesser values. Differences in threshold models, in turn, result is large errors in predicting the fluxes associated with sand and dust transport. Here we use a wind tunnel and novel sediment trap to capture the fractions of sand in creep, reptation and saltation at Earth and Mars pressures and show that the threshold of motion for aeolian sand transport is best defined as a continuum in which grains progress through stages defined by the proportion of grains in creep and saltation. We propose the use of scale dependent thresholds modeled by distinct probability distribution functions that differentiate the threshold based on micro to macro scale applications. For example, a geologic timescale application corresponds to a threshold when 100% of the bed in motion whereas a sub-second application corresponds to a threshold when a single particle is set in motion. We provide quantitative measurements (number and mode of particle movement) corresponding to visual observations, percent of bed in motion and degrees of transport intermittency for Earth and Mars. Understanding transport as a continuum provides a basis for revaluating sand transport thresholds on Earth, Mars and Titan.

  5. Hydrodynamics of sediment threshold

    NASA Astrophysics Data System (ADS)

    Ali, Sk Zeeshan; Dey, Subhasish

    2016-07-01

    A novel hydrodynamic model for the threshold of cohesionless sediment particle motion under a steady unidirectional streamflow is presented. The hydrodynamic forces (drag and lift) acting on a solitary sediment particle resting over a closely packed bed formed by the identical sediment particles are the primary motivating forces. The drag force comprises of the form drag and form induced drag. The lift force includes the Saffman lift, Magnus lift, centrifugal lift, and turbulent lift. The points of action of the force system are appropriately obtained, for the first time, from the basics of micro-mechanics. The sediment threshold is envisioned as the rolling mode, which is the plausible mode to initiate a particle motion on the bed. The moment balance of the force system on the solitary particle about the pivoting point of rolling yields the governing equation. The conditions of sediment threshold under the hydraulically smooth, transitional, and rough flow regimes are examined. The effects of velocity fluctuations are addressed by applying the statistical theory of turbulence. This study shows that for a hindrance coefficient of 0.3, the threshold curve (threshold Shields parameter versus shear Reynolds number) has an excellent agreement with the experimental data of uniform sediments. However, most of the experimental data are bounded by the upper and lower limiting threshold curves, corresponding to the hindrance coefficients of 0.2 and 0.4, respectively. The threshold curve of this study is compared with those of previous researchers. The present model also agrees satisfactorily with the experimental data of nonuniform sediments.

  6. Predictive significance of DNA damage and repair biomarkers in triple-negative breast cancer patients treated with neoadjuvant chemotherapy: An exploratory analysis

    PubMed Central

    Ercolani, Cristiana; Pizzuti, Laura; Lauro, Luigi Di; Sergi, Domenico; Sperati, Francesca; Terrenato, Irene; Dattilo, Rosanna; Botti, Claudio; Fabi, Alessandra; Ramieri, Maria Teresa; Mentuccia, Lucia; Marinelli, Camilla; Iezzi, Laura; Gamucci, Teresa; Natoli, Clara; Vitale, Ilio; Barba, Maddalena; Mottolese, Marcella; De Maria, Ruggero; Maugeri-Saccà, Marcello

    2015-01-01

    Response of cancer cells to chemotherapy-induced DNA damage is regulated by the ATM-Chk2 and ATR-Chk1 pathways. We investigated the association between phosphorylated H2AX (γ-H2AX), a marker of DNA double-strand breaks that trigger the ATM-Chk2 cascade, and phosphorylated Chk1 (pChk1), with pathological complete response (pCR) in triple-negative breast cancer (TNBC) patients treated with neoadjuvant chemotherapy. γ-H2AX and pChk1 were retrospectively assessed by immunohistochemistry in a series of pretreatment biopsies related to 66 patients. In fifty-three tumors hormone receptor status was negative in both the diagnostic biopsies and residual cancers, whereas in 13 cases there was a slight hormone receptor expression that changed after chemotherapy. Internal validation was carried out. In the entire cohort elevated levels of γ-H2AX, but not pChk1, were associated with reduced pCR rate (p = 0.009). The association tested significant in both uni- and multivariate logistic regression models (OR 4.51, 95% CI: 1.39–14.66, p = 0.012, and OR 5.07, 95% CI: 1.28–20.09, p = 0.021, respectively). Internal validation supported the predictive value of the model. The predictive ability of γ-H2AX was further confirmed in the multivariate model after exclusion of tumors that underwent changes in hormone receptor status during chemotherapy (OR 7.07, 95% CI: 1.39–36.02, p = 0.018). Finally, in residual diseases a significant decrease of γ-H2AX levels was observed (p < 0.001). Overall, γ-H2AX showed ability to predict pCR in TNBC and deserves larger, prospective studies. PMID:26544894

  7. Navigating the Nucleotide Excision Repair Threshold

    PubMed Central

    Liu, Liren; Lee, Jennifer; Zhou, Pengbo

    2010-01-01

    Nucleotide excision repair (NER) is the primary DNA repair pathway that removes helix-distorting DNA strand damage induced by ultraviolet light (UV) irradiation or chemical carcinogens to ensure genome integrity. While the core NER proteins that carry out damage recognition, excision and repair reactions have been identified and extensively characterized, and the NER pathway has been reconstituted in vitro, the regulatory pathways that govern the threshold levels of NER have not been fully elucidated. This mini-review focuses on recently discovered transcriptional and post-translational mechanisms that specify the capacity of NER, and suggests the potential implications of modulating NER activity in cancer prevention and therapeutic intervention. PMID:20458729

  8. Combinatorial DNA Damage Pairing Model Based on X-Ray-Induced Foci Predicts the Dose and LET Dependence of Cell Death in Human Breast Cells

    SciTech Connect

    Vadhavkar, Nikhil; Pham, Christopher; Georgescu, Walter; Deschamps, Thomas; Heuskin, Anne-Catherine; Tang, Jonathan; Costes, Sylvain V.

    2014-09-01

    In contrast to the classic view of static DNA double-strand breaks (DSBs) being repaired at the site of damage, we hypothesize that DSBs move and merge with each other over large distances (m). As X-ray dose increases, the probability of having DSB clusters increases as does the probability of misrepair and cell death. Experimental work characterizing the X-ray dose dependence of radiation-induced foci (RIF) in nonmalignant human mammary epithelial cells (MCF10A) is used here to validate a DSB clustering model. We then use the principles of the local effect model (LEM) to predict the yield of DSBs at the submicron level. Two mechanisms for DSB clustering, namely random coalescence of DSBs versus active movement of DSBs into repair domains are compared and tested. Simulations that best predicted both RIF dose dependence and cell survival after X-ray irradiation favored the repair domain hypothesis, suggesting the nucleus is divided into an array of regularly spaced repair domains of ~;;1.55 m sides. Applying the same approach to high-linear energy transfer (LET) ion tracks, we are able to predict experimental RIF/m along tracks with an overall relative error of 12percent, for LET ranging between 30 350 keV/m and for three different ions. Finally, cell death was predicted by assuming an exponential dependence on the total number of DSBs and of all possible combinations of paired DSBs within each simulated RIF. Relative biological effectiveness (RBE) predictions for cell survival of MCF10A exposed to high-LET showed an LET dependence that matches previous experimental results for similar cell types. Overall, this work suggests that microdosimetric properties of ion tracks at the submicron level are sufficient to explain both RIF data and survival curves for any LET, similarly to the LEM assumption. Conversely, high-LET death mechanism does not have to infer linear-quadratic dose formalism as done in the LEM. In addition, the size of repair domains derived in our model

  9. Mitochondrial threshold effects.

    PubMed Central

    Rossignol, Rodrigue; Faustin, Benjamin; Rocher, Christophe; Malgat, Monique; Mazat, Jean-Pierre; Letellier, Thierry

    2003-01-01

    The study of mitochondrial diseases has revealed dramatic variability in the phenotypic presentation of mitochondrial genetic defects. To attempt to understand this variability, different authors have studied energy metabolism in transmitochondrial cell lines carrying different proportions of various pathogenic mutations in their mitochondrial DNA. The same kinds of experiments have been performed on isolated mitochondria and on tissue biopsies taken from patients with mitochondrial diseases. The results have shown that, in most cases, phenotypic manifestation of the genetic defect occurs only when a threshold level is exceeded, and this phenomenon has been named the 'phenotypic threshold effect'. Subsequently, several authors showed that it was possible to inhibit considerably the activity of a respiratory chain complex, up to a critical value, without affecting the rate of mitochondrial respiration or ATP synthesis. This phenomenon was called the 'biochemical threshold effect'. More recently, quantitative analysis of the effects of various mutations in mitochondrial DNA on the rate of mitochondrial protein synthesis has revealed the existence of a 'translational threshold effect'. In this review these different mitochondrial threshold effects are discussed, along with their molecular bases and the roles that they play in the presentation of mitochondrial diseases. PMID:12467494

  10. DNA damage response and anti-apoptotic proteins predict radiosensitization efficacy of HDAC inhibitors SAHA and LBH589 in patient-derived glioblastoma cells.

    PubMed

    Pont, Lotte M E Berghauser; Naipal, Kishan; Kloezeman, Jenneke J; Venkatesan, Subramanian; van den Bent, Martin; van Gent, Dik C; Dirven, Clemens M F; Kanaar, Roland; Lamfers, Martine L M; Leenstra, Sieger

    2015-01-28

    HDAC inhibitors have radiosensitizing effects in established cancer cell lines. This study was conducted to compare the efficacy of SAHA, LBH589, Valproic Acid (VPA), MS275 and Scriptaid in the patient-derived glioblastoma model. In more detail, SAHA and LBH589 were evaluated to determine predictors of response. Acetylated-histone-H3, γH2AX/53BP1, (p)Chek2/ATM, Bcl-2/Bcl-XL, p21(CIP1/WAF1) and caspase-3/7 were studied in relation to response. SAHA sensitized 50% of cultures, LBH589 45%, VPA and Scriptaid 40% and MS275 60%. Differences after treatment with SAHA/RTx or LBH589/RTx in a sensitive and resistant culture were increased acetylated-H3, caspase-3/7 and prolonged DNA damage repair γH2AX/53BP1 foci. pChek2 was found to be associated with both SAHA/RTx and LBH589/RTx response with a positive predictive value (PPV) of 90%. Bcl-XL had a PPV of 100% for LBH589/RTx response. Incubation with HDACi 24 and 48 hours pre-RTx resulted in the best efficacy of combination treatment. In conclusion a subset of patient-derived glioblastoma cultures were sensitive to HDACi/RTx. For SAHA and LBH589 responses were strongly associated with pChek2 and Bcl-XL, which warrant further clinical exploration. Additional information on responsiveness was obtained by DNA damage response markers and apoptosis related proteins. PMID:25305451

  11. Yield threshold decision framework

    SciTech Connect

    Judd, B.R.; Younker, L.W.; Hannon, W.J.

    1989-08-17

    The USA is developing a decision analysis framework for evaluating the relative value of lower yield thresholds and related verification policies. The framework facilitates systematic analysis of the major issues in the yield threshold decision. The framework can be used to evaluate options proposed either in the inter-agency process or in the negotiations. In addition, the framework can measure the importance of uncertainties and alternative judgments, and thereby determine the advantages of additional research. Since the model is explicit and quantitative, it provides a rational, defensible approach for reaching important treaty and verification decisions. 9 figs.

  12. Oxidative Damage, Platelet Activation, and Inflammation to Predict Mobility Disability and Mortality in Older Persons: Results From the Health Aging and Body Composition Study

    PubMed Central

    Kritchevsky, Stephen B.; Nicklas, Barbara; Kanaya, Alka M.; Patrignani, Paola; Tacconelli, Stefania; Tranah, Gregory J.; Tognoni, Gianni; Harris, Tamara B.; Incalzi, Raffaele Antonelli; Newman, Anne B.; Pahor, Marco

    2012-01-01

    Background. Inflammation, oxidative damage, and platelet activation are hypothesized biological mechanisms driving the disablement process. The aim of the present study is to assess whether biomarkers representing these mechanisms predicted major adverse health-related events in older persons. Methods. Data are from 2,234 community-dwelling nondisabled older persons enrolled in the Health Aging and Body Composition study. Biomarkers of lipid peroxidation (ie, urinary levels of 8-iso-prostaglandin F2α), platelet activation (ie, urinary levels of 11-dehydro-thromboxane B2), and inflammation (serum concentrations of interleukin-6) were considered as independent variables of interest and tested in Cox proportional hazard models as predictors of (severe) mobility disability and overall mortality. Results. The sample’s (women 48.0%, whites 64.3%) mean age was 74.6 (SD 2.9) years. During the follow-up (median 11.4 years), 792 (35.5%), 269 (12.0%), and 942 (42.2%) events of mobility disability, severe mobility disability, and mortality occurred, respectively. Only interleukin-6 showed significant independent associations with the onset of all the study outcomes. Higher levels of urinary 8-iso-prostaglandin F2α and 11-dehydro-thromboxane B2 independently predicted increased risk of death (hazard ratio 1.10, 95% confidence interval 1.03–1.19 and hazard ratio 1.14, 95% confidence interval 1.06–1.23, respectively). No significant interactions of gender, race, cardiovascular disease, diabetes, and antiplatelet drugs were detected on the studied relationships. Conclusions. The inflammatory marker interleukin-6 is confirmed to be a robust predictor for the onset of negative health-related events. Participants with higher urinary levels of 8-iso-prostaglandin F2α and 11-dehydro-thromboxane B2 presented a higher mortality risk. PMID:22389462

  13. Elaborating on Threshold Concepts

    ERIC Educational Resources Information Center

    Rountree, Janet; Robins, Anthony; Rountree, Nathan

    2013-01-01

    We propose an expanded definition of Threshold Concepts (TCs) that requires the successful acquisition and internalisation not only of knowledge, but also its practical elaboration in the domains of applied strategies and mental models. This richer definition allows us to clarify the relationship between TCs and Fundamental Ideas, and to account…

  14. Impact damage and fatigue behavior of gamma TiAl

    SciTech Connect

    Harding, T.S.; Jones, J.W.; Pollock, T.M.; Steif, P.S.; Rubal, M.P.

    1997-12-31

    The relationship between impact damage and the fatigue behavior of gamma titanium aluminide has been examined. Axial fatigue specimens fabricated from cast Ti-47.9Al-2Cr-2Nb alloy and Ti-47.3Al-2.2Nb-0.5Mn-0.4W-0.4Mo-0.23Si alloy were impacted under controlled conditions with various indentor shapes to simulate manufacturing related damage in low pressure turbine blades. Damage was quantified and related to impact parameters. A measure of the ambient temperature fatigue strength in the damaged specimens was obtained by standard fatigue testing employing a step-loading approach. Fractographic studies were performed to differentiate impact damage from subsequent fatigue crack growth and to elucidate the mechanisms responsible for the dependence of fatigue strength on the severity of impact damage. A threshold-based fracture mechanics analysis of crack advance from damage zones, and its use in fatigue failure strength prediction, has been developed.

  15. Damage testing of sapphire and Ti: sapphire laser materials

    NASA Technical Reports Server (NTRS)

    1999-01-01

    Diffusion bonded sapphire and Ti (Titanium). Sapphire laser materials that will be damage tested to determine if there is an increase in damage threshold. Photographed in building 1145, photographic studio.

  16. Thin film contamination effects on laser-induced damage of fused silica surfaces at 355 nm

    SciTech Connect

    Burnham, A. K.; Cordillot, C.; Fornier, A.; Genin, F. Y.; Rubenchick, A. M.; Schirmann, D.; Yoshiyama, J.

    1998-07-28

    Fused silica windows were artificially contaminated to estimate the resistance of target chamber debris shields against laser damage during NIF operation. Uniform contamination thin films (1 to 5 nm thick) were prepared by sputtering various materials (Au, Al, Cu, and B4C). The loss of transmission of the samples was first measured. They were then tested at 355 nm in air with an 8-ns Nd:YAG laser. The damage morphologies were characterized by Nomarski optical microscopy and SEM. Both theory and experiments showed that metal contamination for films as thin as 1 nm leads to a substantial loss of transmission. The laser damage resistance dropped very uniformly across the entire surface (e.g. 6 J/cm2 for 5 nm of Cu). The damage morphology characterization showed that contrary to clean silica, metal coated samples did not produce pits on the surface. B4C coated silica, on the other hand, led to a higher density of such damage pits. A model for light absorption in the thin film was coupled with a simple heat deposition and diffusion model to perform preliminary theoretical estimates of damage thresholds. The estimates of the loss due to light absorption and reflection pointed out significant .differences between metals (e.g. Al and Au). The damage threshold predictions were in qualitative agreement with experimental measurements.

  17. Thresholds of Transient Cavitation Produced by Pulsed Ultrasound in a Controlled Nuclei Environment.

    NASA Astrophysics Data System (ADS)

    Holland, Christy Katherine Smith

    The possibility of hazardous bioeffects from medical ultrasound examinations and therapy, although not demonstrated in current epidemiologic data, is still of interest to the medical community. In particular, concern persists over the potential of damage at the cellular level due to transient cavitation produced by diagnostic and high intensity therapeutic ultrasound. Transient cavitation is a discrete phenomenon which relies on the existence of stabilized nuclei, or pockets of gas within a host fluid, for its genesis. A convenient descriptor for assessing the likelihood of transient cavitation is the threshold pressure, or the minimum acoustic pressure necessary to initiate bubble growth and subsequent collapse. Experimental measurements of cavitation thresholds are presented here which elucidate the importance of ultrasound host fluid and nuclei parameters in determining these thresholds. These results are interpreted in the context of an approximate theory, included as an appendix, describing the relationship between these parameters and cavitation threshold pressures. An automated experimental apparatus has been developed to determine thresholds for cavitation produced in a fluid by short tone bursts of ultrasound at 0.76, 0.99, and 2.30 MHz. A fluid jet was used to convect potential cavitation nuclei through the focal region of the insonifying transducer. Potential nuclei tested include 1mum polystyrene spheres, microbubbles in the 1-10 μm range that are stabilized with human serum albumin, and whole blood constituents. Cavitation was detected by a passive acoustical technique which is sensitive to sound scattered from cavitation bubbles. Measurements of the transient cavitation threshold in water, in a fluid of higher viscosity, and in diluted whole blood are presented. Results from these experiments which permit the control of nuclei and host fluid properties are compared to the approximate analytical theory for the prediction of the onset of cavitation.

  18. Network problem threshold

    NASA Technical Reports Server (NTRS)

    Gejji, Raghvendra, R.

    1992-01-01

    Network transmission errors such as collisions, CRC errors, misalignment, etc. are statistical in nature. Although errors can vary randomly, a high level of errors does indicate specific network problems, e.g. equipment failure. In this project, we have studied the random nature of collisions theoretically as well as by gathering statistics, and established a numerical threshold above which a network problem is indicated with high probability.

  19. Elaborating on threshold concepts

    NASA Astrophysics Data System (ADS)

    Rountree, Janet; Robins, Anthony; Rountree, Nathan

    2013-09-01

    We propose an expanded definition of Threshold Concepts (TCs) that requires the successful acquisition and internalisation not only of knowledge, but also its practical elaboration in the domains of applied strategies and mental models. This richer definition allows us to clarify the relationship between TCs and Fundamental Ideas, and to account for both the important and the problematic characteristics of TCs in terms of the Knowledge/Strategies/Mental Models Framework defined in previous work.

  20. Towards a damage tolerance philosophy for composite materials and structures

    NASA Technical Reports Server (NTRS)

    O'Brien, T. Kevin

    1990-01-01

    A damage-threshold/fail-safe approach is proposed to ensure that composite structures are both sufficiently durable for economy of operation, as well as adequately fail-safe or damage tolerant for flight safety. Matrix cracks are assumed to exist throughout the off-axis plies. Delamination onset is predicted using a strain energy release rate characterization. Delamination growth is accounted for in one of three ways: either analytically, using delamination growth laws in conjunction with strain energy release rate analyses incorporating delamination resistance curves; experimentally, using measured stiffness loss; or conservatively, assuming delamination onset corresponds to catastrophic delamination growth. Fail-safety is assessed by accounting for the accumulation of delaminations through the thickness. A tension fatigue life prediction for composite laminates is presented as a case study to illustrate how this approach may be implemented. Suggestions are made for applying the damage-threshold/fail-safe approach to compression fatigue, tension/compression fatigue, and compression strength following low velocity impact.

  1. Towards a damage tolerance philosophy for composite materials and structures

    NASA Technical Reports Server (NTRS)

    Obrien, T. Kevin

    1988-01-01

    A damage-threshold/fail-safe approach is proposed to ensure that composite structures are both sufficiently durable for economy of operation, as well as adequately fail-safe or damage tolerant for flight safety. Matrix cracks are assumed to exist throughout the off-axis plies. Delamination onset is predicted using a strain energy release rate characterization. Delamination growth is accounted for in one of three ways: either analytically, using delamination growth laws in conjunction with strain energy release rate analyses incorporating delamination resistance curves; experimentally, using measured stiffness loss; or conservatively, assuming delamination onset corresponds to catastrophic delamination growth. Fail-safety is assessed by accounting for the accumulation of delaminations through the thickness. A tension fatigue life prediction for composite laminates is presented as a case study to illustrate how this approach may be implemented. Suggestions are made for applying the damage-threshold/fail-safe approach to compression fatigue, tension/compression fatigue, and compression strength following low velocity impact.

  2. Epidemic thresholds for bipartite networks

    NASA Astrophysics Data System (ADS)

    Hernández, D. G.; Risau-Gusman, S.

    2013-11-01

    It is well known that sexually transmitted diseases (STD) spread across a network of human sexual contacts. This network is most often bipartite, as most STD are transmitted between men and women. Even though network models in epidemiology have quite a long history now, there are few general results about bipartite networks. One of them is the simple dependence, predicted using the mean field approximation, between the epidemic threshold and the average and variance of the degree distribution of the network. Here we show that going beyond this approximation can lead to qualitatively different results that are supported by numerical simulations. One of the new features, that can be relevant for applications, is the existence of a critical value for the infectivity of each population, below which no epidemics can arise, regardless of the value of the infectivity of the other population.

  3. Erosion thresholds and land surface morphology

    NASA Astrophysics Data System (ADS)

    Dietrich, William E.; Wilson, Cathy J.; Montgomery, David R.; McKean, James; Bauer, Romy

    1992-08-01

    We propose a graphical technique to analyze the entirety of landforms in a catchment to define quantitatively the spatial variation in the dominance of different erosion processes. High-resolution digital elevation data of a 1.2 km2 hilly area where the channel network had been mapped in the field were used in the digital terrain model, TOPOG, to test threshold theories for erosion. The land surface was divided into ˜20 m2 elements whose shapes were then classified as convergent, planar, or divergent. The entire landscape plotted on a graph of area per unit contour length against surface gradient shows each planform plotting as a separate field. A simple steady-state hydrologic model was used to predict zones of saturation and areas of high pore pressure to mimic the extreme hydrologic events responsible for erosive instability of the land surface. The field observation that saturation overland flow is rare outside convergent zones provided a significant constraint on the hydrologic parameter in the model. This model was used in threshold theories to predict areas of slope instability and areas subject to erosion by saturation overland flow, both of which can contribute to channel initiation. The proportion of convergent elements predicted to exceed the threshold varies greatly with relatively small changes in surface resistance, demonstrating a high sensitivity to land use such as cattle grazing. Overall, the landscape can be divided, using erosion threshold lines, into areas prone to channel instability due to runoff and stable areas where diffusive transport predominates.

  4. Relationship between visual field loss and contrast threshold elevation in glaucoma

    PubMed Central

    Tochel, CM; Morton, JS; Jay, JL; Morrison, JD

    2005-01-01

    Background There is a considerable body of literature which indicates that contrast thresholds for the detection of sinusoidal grating patterns are abnormally high in glaucoma, though just how these elevations are related to the location of visual field loss remains unknown. Our aim, therefore, has been to determine the relationship between contrast threshold elevation and visual field loss in corresponding regions of the peripheral visual field in glaucoma patients. Methods Contrast thresholds were measured in arcuate regions of the superior, inferior, nasal and temporal visual field in response to laser interference fringes presented in the Maxwellian view. The display consisted of vertical green stationary laser interference fringes of spatial frequency 1.0 c deg-1 which appeared in a rotatable viewing area in the form of a truncated quadrant extending from 10 to 20° from fixation which was marked with a central fixation light. Results were obtained from 36 normal control subjects in order to provide a normal reference for 21 glaucoma patients and 5 OHT (ocular hypertensive) patients for whom full clinical data, including Friedmann visual fields, had been obtained. Results Abnormally high contrast thresholds were identified in 20 out of 21 glaucoma patients and in 2 out of 5 OHT patients when compared with the 95% upper prediction limit for normal values from one eye of the 36 normal age-matched control subjects. Additionally, inter-ocular differences in contrast threshold were also abnormally high in 18 out of 20 glaucoma patients who had vision in both eyes compared with the 95% upper prediction limit. Correspondence between abnormally high contrast thresholds and visual field loss in the truncated quadrants was significant in 5 patients, borderline in 4 patients and absent in 9 patients. Conclusion While the glaucoma patients tested in our study invariably had abnormally high contrast thresholds in one or more of the truncated quadrants in at least one eye

  5. Congenital ureteropelvic junction obstruction: physiopathology, decoupling of tout court pelvic dilatation-obstruction semantic connection, biomarkers to predict renal damage evolution.

    PubMed

    Alberti, C

    2012-02-01

    The widespread use of fetal ultrasonography results in a frequent antenatally observation of hydronephrosis, ureteropelvic junction obstruction (UPJO) accounting for the greatest fraction of congenital obstructive nephropathy. UPJO may be considered, in most cases, as a functional obstructive condition, depending on defective fetal smooth muscle/nerve development at this level, with lack of peristaltic wave propagation--aperistaltic segment--and, therefore, poor urine ejection from the renal pelvis into the ureter. The UPJO-related physiopathologic events are, at first, the compliant dilatation of renal pelvis that, acting as hydraulic buffer, protects the renal parenchyma from the rising intrapelvic pressure-related potential damages, and, subsequently, beyond such phase of dynamic balance, the tubular cell stretch-stress induced by increased intratubular pressure and following parenchymal inflammatory lesions: inflammatory infiltrates, fibroblast proliferation, activation of myofibroblasts, tubulo-interstitial fibrosis. Reactive oxygen species (ROS), nitric oxide (NO), several chemo- and cytokines, growth factors, prostaglandins and eicosanoids, angiotensin-II are the main pathogenetic mediators of the obstructive nephropathy. Apoptosis of tubular cells is the major cause of the tubular atrophy, together with epithelial-mesenchymal transdifferentiation. Some criticisms on tout court semantic renal pelvis dilatation-obstruction connection have been raised considering that the renal pelvis expansion isn't, in any case, linked to an ostructive condition, as it may be verified by diuretic (furosemide) renogram together with scintiscan-based evaluation of differential renal function. In this regard, rather than repetitive invasive nuclear procedures that expose the children to ionizing radiations, an intriguing noninvasive strategy, based on the evaluation of urinary biomarkers and urinary proteome, can define the UPJO-related possible progress of parenchymal lesions

  6. Temperature-Mediated Development Thresholds of Sparganothis sulfureana (Lepidoptera: Tortricidae) in Cranberries.

    PubMed

    Deutsch, Annie E; Rodriguez-Saona, Cesar R; Zalapa, Juan E; Steffan, Shawn A

    2015-04-01

    Larvae of Sparganothis sulfureana Clemens frequently attack cranberries, often resulting in economic damage to the crop. Because temperature dictates insect growth rate, development can be accurately estimated based on daily temperature measurements. To better predict S. sulfureana development across the growing season, we investigated the temperature range within which S. sulfureana larvae can feed and grow. Larvae were reared at 13 constant temperatures ranging from 6.5-38.6 °C. Larval growth rate was determined by the rate of change of larval weight across time. The respective growth rates among these temperatures were modeled using simple linear, cubic, and Lactin nonlinear development functions. These models isolated the lower temperature threshold at which growth became nonzero and the upper temperature at which growth was maximized. All three models were significantly predictive of S. sulfureana growth, but the cubic model best represented the observed growth rates, effectively isolating lower and upper thresholds of 9.97 and 29.89 °C, respectively. We propose that these thresholds be used to create a degree-day model of temperature-mediated S. sulfureana development. PMID:26313194

  7. Correlating cookoff violence with pre-ignition damage.

    SciTech Connect

    Wente, William Baker; Hobbs, Michael L.; Kaneshige, Michael Jiro

    2010-03-01

    Predicting the response of energetic materials during accidents, such as fire, is important for high consequence safety analysis. We hypothesize that responses of ener-getic materials before and after ignition depend on factors that cause thermal and chemi-cal damage. We have previously correlated violence from PETN to the extent of decom-position at ignition, determined as the time when the maximum Damkoehler number ex-ceeds a threshold value. We seek to understand if our method of violence correlation ap-plies universally to other explosive starting with RDX.

  8. Coloring geographical threshold graphs

    SciTech Connect

    Bradonjic, Milan; Percus, Allon; Muller, Tobias

    2008-01-01

    We propose a coloring algorithm for sparse random graphs generated by the geographical threshold graph (GTG) model, a generalization of random geometric graphs (RGG). In a GTG, nodes are distributed in a Euclidean space, and edges are assigned according to a threshold function involving the distance between nodes as well as randomly chosen node weights. The motivation for analyzing this model is that many real networks (e.g., wireless networks, the Internet, etc.) need to be studied by using a 'richer' stochastic model (which in this case includes both a distance between nodes and weights on the nodes). Here, we analyze the GTG coloring algorithm together with the graph's clique number, showing formally that in spite of the differences in structure between GTG and RGG, the asymptotic behavior of the chromatic number is identical: {chi}1n 1n n / 1n n (1 + {omicron}(1)). Finally, we consider the leading corrections to this expression, again using the coloring algorithm and clique number to provide bounds on the chromatic number. We show that the gap between the lower and upper bound is within C 1n n / (1n 1n n){sup 2}, and specify the constant C.

  9. Guest Editorial: Laser Damage

    SciTech Connect

    Vitaly Gruzdev, Michelle D. Shinn

    2012-12-01

    . Bublitz; B. Cho, E. Danielewicz, and J. Rudisill; W. Palm et al; and J. Lu et al.). Statistical treatment of measurements of the laser-damage threshold (J. Arenberg) and the relationship to damage mechanisms (F. Wagner et al.) represent the large subfield of laser-damage measurements. Various aspects of multilayer coating and thin-film characterization are considered in papers by B. Cho, J. Rudisill, and E. Danielewicz (spectral shift in multilayer mirrors) and R. Weber et al. (novel approach to damage studies based on third-harmonic generation microscopy). Of special interest for readers is the paper by C. Stolz that summarizes the results of four “thin-film damage competitions” organized as a part of the Laser Damage Symposium. Another paper is devoted to thermal annealing of damage precursors (N. Shen et al.). Finally, the influence of nano-size contamination on initiation of laser damage by ultrashort pulses is considered in paper of V. Komolov et al.

  10. Thresholded Power law Size Distributions of Instabilities in Astrophysics

    NASA Astrophysics Data System (ADS)

    Aschwanden, Markus J.

    2015-11-01

    Power-law-like size distributions are ubiquitous in astrophysical instabilities. There are at least four natural effects that cause deviations from ideal power law size distributions, which we model here in a generalized way: (1) a physical threshold of an instability; (2) incomplete sampling of the smallest events below a threshold x0; (3) contamination by an event-unrelated background xb; and (4) truncation effects at the largest events due to a finite system size. These effects can be modeled in the simplest terms with a “thresholded power law” distribution function (also called generalized Pareto [type II] or Lomax distribution), N(x){dx}\\propto {(x+{x}0)}-a{dx}, where x0 > 0 is positive for a threshold effect, while x0 < 0 is negative for background contamination. We analytically derive the functional shape of this thresholded power law distribution function from an exponential growth evolution model, which produces avalanches only when a disturbance exceeds a critical threshold x0. We apply the thresholded power law distribution function to terrestrial, solar (HXRBS, BATSE, RHESSI), and stellar flare (Kepler) data sets. We find that the thresholded power law model provides an adequate fit to most of the observed data. Major advantages of this model are the automated choice of the power law fitting range, diagnostics of background contamination, physical instability thresholds, instrumental detection thresholds, and finite system size limits. When testing self-organized criticality models that predict ideal power laws, we suggest including these natural truncation effects.

  11. Development and Integration of Single-Asperity Nanotribology Experiments & Nanoscale Interface Finite Element Modeling for Prediction and Control of Friction and Damage in Micro- and Nano-mechnical Systems

    SciTech Connect

    R.W. Carpick; M.E. Plesha

    2007-03-03

    This report describes the accomplishments of the DOE BES grant entitled "Development and Integration of Single-Asperity Nanotribology Experiments & Nanoscale Interface Finite Element Modeling for Prediction and Control of Friction and Damage in Micro- and Nano-mechnical Systems". Key results are: the determination of nanoscale frictional properties of MEMS surfaces, self-assembled monolayers, and novel carbon-based films, as well as the development of models to describe this behavior.

  12. Critique of Macro Flow/Damage Surface Representations for Metal Matrix Composites Using Micromechanics

    NASA Technical Reports Server (NTRS)

    Lissenden, Cliff J.; Arnold, Steven M.

    1996-01-01

    Guidance for the formulation of robust, multiaxial, constitutive models for advanced materials is provided by addressing theoretical and experimental issues using micromechanics. The multiaxial response of metal matrix composites, depicted in terms of macro flow/damage surfaces, is predicted at room and elevated temperatures using an analytical micromechanical model that includes viscoplastic matrix response as well as fiber-matrix debonding. Macro flow/damage surfaces (i.e., debonding envelopes, matrix threshold surfaces, macro 'yield' surfaces, surfaces of constant inelastic strain rate, and surfaces of constant dissipation rate) are determined for silicon carbide/titanium in three stress spaces. Residual stresses are shown to offset the centers of the flow/damage surfaces from the origin and their shape is significantly altered by debonding. The results indicate which type of flow/damage surfaces should be characterized and what loadings applied to provide the most meaningful experimental data for guiding theoretical model development and verification.

  13. Oscillatory Threshold Logic

    PubMed Central

    Borresen, Jon; Lynch, Stephen

    2012-01-01

    In the 1940s, the first generation of modern computers used vacuum tube oscillators as their principle components, however, with the development of the transistor, such oscillator based computers quickly became obsolete. As the demand for faster and lower power computers continues, transistors are themselves approaching their theoretical limit and emerging technologies must eventually supersede them. With the development of optical oscillators and Josephson junction technology, we are again presented with the possibility of using oscillators as the basic components of computers, and it is possible that the next generation of computers will be composed almost entirely of oscillatory devices. Here, we demonstrate how coupled threshold oscillators may be used to perform binary logic in a manner entirely consistent with modern computer architectures. We describe a variety of computational circuitry and demonstrate working oscillator models of both computation and memory. PMID:23173034

  14. Factors Affecting Perceptual Threshold in Argus II Retinal Prosthesis Subjects

    PubMed Central

    Ahuja, A. K.; Yeoh, J.; Dorn, J. D.; Caspi, A.; Wuyyuru, V.; McMahon, M. J.; Humayun, M. S.; Greenberg, R. J.; daCruz, L.

    2013-01-01

    Purpose The Argus II epiretinal prosthesis has been developed to provide partial restoration of vision to subjects blinded from outer retinal degenerative disease. Participants were surgically implanted with the system in the United States and Europe in a single arm, prospective, multicenter clinical trial. The purpose of this investigation was to determine which factors affect electrical thresholds in order to inform surgical placement of the device. Methods Electrode–retina and electrode–fovea distances were determined using SD-OCT and fundus photography, respectively. Perceptual threshold to electrical stimulation of electrodes was measured using custom developed software, in which current amplitude was varied until the threshold was found. Full field stimulus light threshold was measured using the Espion D-FST test. Relationships between electrical threshold and these three explanatory variables (electrode–retina distance, electrode–fovea distance, and monocular light threshold) were quantified using regression. Results Regression analysis showed a significant correlation between electrical threshold and electrode–retina distance (R2 = 0.50, P = 0.0002; n = 703 electrodes). 90.3% of electrodes in contact with the macula (n = 207) elicited percepts at charge densities less than 1 mC/cm2/phase. These threshold data also correlated well with ganglion cell density profile (P = 0.03). A weaker, but still significant, inverse correlation was found between light threshold and electrical threshold (R2 < 0.52, P = 0.01). Multivariate modeling indicated that electrode–retina distance and light threshold are highly predictive of electrode threshold (R2 = 0.87; P < 0.0005). Conclusions Taken together, these results suggest that while light threshold should be used to inform patient selection, macular contact of the array is paramount. Translational Relevance Reported Argus II clinical study results are in good agreement with prior in vitro and in vivo studies

  15. Ductile damage evolution and experimental simulation under high rates of strain in 10100 copper.

    SciTech Connect

    Thissell, W. R.; McKirgan, J. B.; Chen, S. R.; Trujillo, C. P.; Macdougall, D. A. S.

    2001-01-01

    The high strain-rate damage evolution and Eracture behavior of half-hard 10 LOO Cu was investigated by experiments and computer simulations. Testing of uniaxial stress and axisymmetric notched bars of the Hancock-Mackenzie geometries were performetl using a momentum trapped tensile split Hopkinson pressure bar. Specimens were. tested to fracture and to several stages of incipient failure prior to fracture. Recovered specimens were sectioned and metallographically examined using image analysis and optical profilornelry to quantify the resulting damage. The quantified damage is described by spatially resolved porosity distributions, spatially resolved volumetric number densiries, and spatia Ily resolved void size distributions. Concurrent to mechanical testing, explicit finite element simulations of the tensile split Hopkinson pressure bar experiments were perfornicd to quantify the local stress-state and strain-state within the material and to determine the evolution of damage within the notch region. The coinpressive plasticity behavior of the material was fit to the mechanical threshold stress constitutive model, and was used in the simulations. The quantified damage was coniprued with damage model (TEPLA) predictions and used to refine model parameters and damage nucleation criteria. The simulation results also show that the maximum stress triaxiality in the specimens quickly enlarges after the onset of plastic flow or tensile instability to almost twice that of the Bridgman predicted levels.

  16. Pulsed laser damage to optical fibers

    SciTech Connect

    Allison, S.W.; Gillies, G.T.; Magnuson, D.W.; Pagano, T.S.

    1985-10-01

    This paper describes some observations of pulsed laser damage to optical fibers with emphasis on a damage mode characterized as a linear fracture along the outer core of a fiber. Damage threshold data are presented which illustrate the effects of the focusing lens, end-surface preparation, and type of fiber. An explanation based on fiber-beam misalignment is given and is illustrated by a simple experiment and ray trace.

  17. Laser damage growth with picosecond pulses.

    PubMed

    Sozet, Martin; Neauport, Jérôme; Lavastre, Eric; Roquin, Nadja; Gallais, Laurent; Lamaignère, Laurent

    2016-05-15

    Laser-induced damage growth has been investigated in the subpicosecond regime at 1030 nm. We have herein studied the growth of damage sites initiated on a high-reflective dielectric coating under subsequent laser irradiations at a constant fluence. We show through an experimental approach that growth can be triggered for fluences as low as 50% of the intrinsic damage threshold of the mirror. Moreover, once growth starts, damage areas increase linearly with the number of laser shots. The behavior of defect-induced damage sites has been observed more extensively, and it appears that their growth probability depends on their initiation fluence. PMID:27176998

  18. Hairpin Vortex Regeneration Threshold

    NASA Astrophysics Data System (ADS)

    Sabatino, Daniel; Maharjan, Rijan

    2015-11-01

    A free surface water channel is used to study hairpin vortex formation created by fluid injection through a narrow slot into a laminar boundary layer. Particle image velocimetry is used to calculate the circulation of the primary hairpin vortex head which is found to monotonically decrease in strength with downstream distance. When a secondary hairpin vortex is formed upstream of the primary vortex, the circulation strength of the head is comparable to the strength of the primary head at the time of regeneration. However, the legs of the primary vortex strengthen up to the moment the secondary hairpin is generated. Although the peak circulation in the legs is not directly correlated to the strength of the original elongated ring vortex, when the circulation is scaled with the injection momentum ratio it is linearly related to scaled injection time. It is proposed that the injection momentum ratio and nondimensionalized injection time based on the wall normal penetration time can be used to identify threshold conditions which produce a secondary vortex. Supported by the National Science Foundation under Grant CBET- 1040236.

  19. Probabilistic Threshold Criterion

    SciTech Connect

    Gresshoff, M; Hrousis, C A

    2010-03-09

    The Probabilistic Shock Threshold Criterion (PSTC) Project at LLNL develops phenomenological criteria for estimating safety or performance margin on high explosive (HE) initiation in the shock initiation regime, creating tools for safety assessment and design of initiation systems and HE trains in general. Until recently, there has been little foundation for probabilistic assessment of HE initiation scenarios. This work attempts to use probabilistic information that is available from both historic and ongoing tests to develop a basis for such assessment. Current PSTC approaches start with the functional form of the James Initiation Criterion as a backbone, and generalize to include varying areas of initiation and provide a probabilistic response based on test data for 1.8 g/cc (Ultrafine) 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) and LX-17 (92.5% TATB, 7.5% Kel-F 800 binder). Application of the PSTC methodology is presented investigating the safety and performance of a flying plate detonator and the margin of an Ultrafine TATB booster initiating LX-17.

  20. Characterization of Mode 1 and Mode 2 delamination growth and thresholds in graphite/peek composites

    NASA Technical Reports Server (NTRS)

    Martin, Roderick H.; Murri, Gretchen B.

    1988-01-01

    Composite materials often fail by delamination. The onset and growth of delamination in AS4/PEEK, a tough thermoplastic matrix composite, was characterized for mode 1 and mode 2 loadings, using the Double Cantilever Beam (DCB) and the End Notched Flexure (ENF) test specimens. Delamination growth per fatigue cycle, da/dN, was related to strain energy release rate, G, by means of a power law. However, the exponents of these power laws were too large for them to be adequately used as a life prediction tool. A small error in the estimated applied loads could lead to large errors in the delamination growth rates. Hence strain energy release rate thresholds, G sub th, below which no delamination would occur were also measured. Mode 1 and 2 threshold G values for no delamination growth were found by monitoring the number of cycles to delamination onset in the DCB and ENF specimens. The maximum applied G for which no delamination growth had occurred until at least 1,000,000 cycles was considered the threshold strain energy release rate. Comments are given on how testing effects, facial interference or delamination front damage, may invalidate the experimental determination of the constants in the expression.

  1. Laser-induced damage initiated on the surface of particle contamination fused silica at 1064nm

    SciTech Connect

    Michlitsch, K.J.

    1998-06-01

    An experimental study was undertaken to quantify the effects of contamination particles on the damage threshold of laser-illuminated fused silica optics and set cleanliness requirements for optics on the beam line of the National Ignition Facility at Lawrence Livermore National Laboratory. Circular contamination particles were sputter-deposited onto fused silica windows which were then illuminated repetitively using a 1064nm laser. A variety of contaminants were tested including metals, oxides, and organics. Tests were conducted with particles on the input and output surfaces of the window, and the morphological features of the damage were very reproducible. A plasma often ignited at the contamination particle; its intensity was dependent upon the mass of the contaminant. Input surface damage was characteristically more severe than output surface damage. The size of the damaged area scaled with the size of the particle. On a few occasions, catastrophic damage (cracking or ablation of the substrate) initiated on the output surface due to contamination particles on either the input or output surface. From damage growth plots, predictions can be made about the severity of damage expected from contamination particles of known size and material.

  2. Prediction of residual tensile strength of transversely impacted composite laminates

    NASA Technical Reports Server (NTRS)

    Lal, K. M.

    1982-01-01

    The response to low velocity impact of graphite-epoxy T300/5208 composite laminates is discussed. Steel balls of 3/8 inch, 5/8 inch, and 1 inch diameter were the projectiles. Impact energy was limited to 1.2 joules. Impacted specimens were ultrasonically C scanned to determine the impact damaged region. The threshold value of impact energy for impact damage was found to be approximately 0.3 joules. A model was developed to predict the tensile residual strength of impact damaged specimens from fracture mechanics concepts. Impacted specimens were tested in tension to provide a fracture data base. The experimental results agreed well with the predictions from fracture mechanics. In this study, the maximum impact velocity used to simulate the low velocity transverse impact from common objects like tool drops was 10 m/s.

  3. Cumulative fatigue damage models

    NASA Technical Reports Server (NTRS)

    Mcgaw, Michael A.

    1988-01-01

    The problem of calculating expected component life under fatigue loading conditions is complicated by the fact that component loading histories contain, in many cases, cyclic loads of widely varying amplitudes. In such a case a cumulative damage model is required, in addition to a fatigue damage criterion, or life relationship, in order to compute the expected fatigue life. The traditional cumulative damage model used in design is the linear damage rule. This model, while being simple to use, can yield grossly unconservative results under certain loading conditions. Research at the NASA Lewis Research Center has led to the development of a nonlinear cumulative damage model, named the double damage curve approach (DDCA), that has greatly improved predictive capability. This model, which considers the life (or loading) level dependence of damage evolution, was applied successfully to two polycrystalline materials, 316 stainless steel and Haynes 188. The cumulative fatigue behavior of the PWA 1480 single-crystal material is currently being measured to determine the applicability of the DDCA for this material.

  4. Life below the threshold.

    PubMed

    Castro, C

    1991-01-01

    This article explains that malnutrition, poor health, and limited educational opportunities plague Philippine children -- especially female children -- from families living below the poverty threshold. Nearly 70% of households in the Philippines do not meet the required daily level of nutritional intake. Because it is often -- and incorrectly -- assumed that women's nutritional requirements are lower than men's, women suffer higher rates of malnutrition and poor health. A 1987 study revealed that 11.7% of all elementary students were underweight and 13.9% had stunted growths. Among elementary-school girls, 17% were malnourished and 40% suffered from anemia (among lactating mothers, more than 1/2 are anemic). A 1988 Program for Decentralized Educational Development study showed that grade VI students learn only about 1/2 of what they are supposed to learn. 30% of the children enrolled in grade school drop out before they reach their senior year. The Department of Education, Culture and Sports estimates that some 2.56 million students dropped out of school in l989. That same year, some 3.7 million children were counted as part of the labor force. In Manila alone, some 60,000 children work the streets, whether doing odd jobs or begging, or turning to crime or prostitution. the article tells the story of a 12 year-old girl named Ging, a 4th grader at a public school and the oldest child in a poor family of 6 children. The undernourished Ging dreams of a good future for her family and sees education as a way out of poverty; unfortunately, her time after school is spend working in the streets or looking after her family. She considers herself luckier than many of the other children working in the streets, since she at least has a family. PMID:12285009

  5. Threshold Hypothesis: Fact or Artifact?

    ERIC Educational Resources Information Center

    Karwowski, Maciej; Gralewski, Jacek

    2013-01-01

    The threshold hypothesis (TH) assumes the existence of complex relations between creative abilities and intelligence: linear associations below 120 points of IQ and weaker or lack of associations above the threshold. However, diverse results have been obtained over the last six decades--some confirmed the hypothesis and some rejected it. In this…

  6. The Nature of Psychological Thresholds

    ERIC Educational Resources Information Center

    Rouder, Jeffrey N.; Morey, Richard D.

    2009-01-01

    Following G. T. Fechner (1966), thresholds have been conceptualized as the amount of intensity needed to transition between mental states, such as between a states of unconsciousness and consciousness. With the advent of the theory of signal detection, however, discrete-state theory and the corresponding notion of threshold have been discounted.…

  7. Threshold Concepts and Information Literacy

    ERIC Educational Resources Information Center

    Townsend, Lori; Brunetti, Korey; Hofer, Amy R.

    2011-01-01

    What do we teach when we teach information literacy in higher education? This paper describes a pedagogical approach to information literacy that helps instructors focus content around transformative learning thresholds. The threshold concept framework holds promise for librarians because it grounds the instructor in the big ideas and underlying…

  8. A Thermodynamically-Based Mesh Objective Work Potential Theory for Predicting Intralaminar Progressive Damage and Failure in Fiber-Reinforced Laminates

    NASA Technical Reports Server (NTRS)

    Pineda, Evan J.; Waas, Anthony M.

    2012-01-01

    A thermodynamically-based work potential theory for modeling progressive damage and failure in fiber-reinforced laminates is presented. The current, multiple-internal state variable (ISV) formulation, enhanced Schapery theory (EST), utilizes separate ISVs for modeling the effects of damage and failure. Damage is considered to be the effect of any structural changes in a material that manifest as pre-peak non-linearity in the stress versus strain response. Conversely, failure is taken to be the effect of the evolution of any mechanisms that results in post-peak strain softening. It is assumed that matrix microdamage is the dominant damage mechanism in continuous fiber-reinforced polymer matrix laminates, and its evolution is controlled with a single ISV. Three additional ISVs are introduced to account for failure due to mode I transverse cracking, mode II transverse cracking, and mode I axial failure. Typically, failure evolution (i.e., post-peak strain softening) results in pathologically mesh dependent solutions within a finite element method (FEM) setting. Therefore, consistent character element lengths are introduced into the formulation of the evolution of the three failure ISVs. Using the stationarity of the total work potential with respect to each ISV, a set of thermodynamically consistent evolution equations for the ISVs is derived. The theory is implemented into commercial FEM software. Objectivity of total energy dissipated during the failure process, with regards to refinements in the FEM mesh, is demonstrated. The model is also verified against experimental results from two laminated, T800/3900-2 panels containing a central notch and different fiber-orientation stacking sequences. Global load versus displacement, global load versus local strain gage data, and macroscopic failure paths obtained from the models are compared to the experiments.

  9. Forecasting Corrosion of Steel in Concrete Introducing Chloride Threshold Dependence on Steel Potential

    NASA Astrophysics Data System (ADS)

    Sanchez, Andrea Nathalie

    Corrosion initiates in reinforced concrete structures exposed to marine environments when the chloride ion concentration at the surface of an embedded steel reinforcing bar exceeds the chloride corrosion threshold (CT) value. The value of CT is generally assumed to have a conservative fixed value ranging from 0.2% to - 0.5 % of chloride ions by weight of cement. However, extensive experimental investigations confirmed that C T is not a fixed value and that the value of CT depends on many variables. Among those, the potential of passive steel embedded in concrete is a key influential factor on the value of CT and has received little attention in the literature. The phenomenon of a potential-dependent threshold (PDT) permits accounting for corrosion macrocell coupling between active and passive steel assembly components in corrosion forecast models, avoiding overly conservative long-term damage projections and leading to more efficient design. The objectives of this investigation was to 1) expand by a systematic experimental assessment the knowledge and data base on how dependent the chloride threshold is on the potential of the steel embedded in concrete and 2) introduce the chloride threshold dependence on steel potential as an integral part of corrosion-related service life prediction of reinforced concrete structures. Experimental assessments on PDT were found in the literature but for a limited set of conditions. Therefore, experiments were conducted with mortar and concrete specimens and exposed to conditions more representative of the field than those previously available. The experimental results confirmed the presence of the PDT effect and provided supporting information to use a value of -550 mV per decade of Cl- for the cathodic prevention slope betaCT, a critical quantitative input for implementation in a practical model. A refinement of a previous corrosion initiation-propagation model that incorporated PDT in a partially submerged reinforced concrete

  10. Threshold selection for regional peaks-over-threshold data

    NASA Astrophysics Data System (ADS)

    Roth, Martin; Jongbloed, Geurt; Adri Buishand, T.

    2016-04-01

    A hurdle in the peaks-over-threshold approach for analyzing extreme values is the selection of the threshold. A method is developed to reduce this obstacle in the presence of multiple, similar data samples. This is for instance the case in many environmental applications. The idea is to combine threshold selection methods into a regional method. Regionalized versions of the threshold stability and the mean excess plot are presented as graphical tools for threshold selection. Moreover, quantitative approaches based on the bootstrap distribution of the spatially averaged Kolmogorov-Smirnov and Anderson-Darling test statistics are introduced. It is demonstrated that the proposed regional method leads to an increased sensitivity for too low thresholds, compared to methods that do not take into account the regional information. The approach can be used for a wide range of univariate threshold selection methods. We test the methods using simulated data and present an application to rainfall data from the Dutch water board Vallei en Veluwe.

  11. Estimating bird damage from damage incidence in wine grape vineyards

    USGS Publications Warehouse

    DeHaven, R.W.; Hothem, R.L.

    1981-01-01

    Bird damage was measured during 1977 and 1978 at 32 wine grape vineyards in the San Joaquin Valley and North Coastal Region of California. Both the percentage bird loss (PBL) and the percentage of bunches damaged (BDI = bird damage incidence) were determined during 55 total-damage assessments, and the resulting data pairs were used to develop a regression of PBL on BDI. The final prediction equation was loge (PBL + 1) = 0.0385 BDI, for which the SE = 9.6297 10-4, and it accounted for 97% of the observed variation. We conclude that by using that equation, reasonably accurate predictions of PBL can be obtained from relatively quick and inexpensive estimates of BDI. Guidelines for the use of the prediction method and the accuracy of some PBL predictions are discussed.

  12. 77 FR 71354 - Adjustment of Monetary Threshold for Reporting Rail Equipment Accidents/Incidents for Calendar...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-11-30

    ...This rule increases the rail equipment accident/incident reporting threshold from $9,500 to $9,900 for certain railroad accidents/incidents involving property damage that occur during calendar year 2013. This action is needed to ensure that FRA's reporting requirements reflect cost increases that have occurred since the reporting threshold was last published in November of...

  13. Crossing thresholds: Analysis of hazardous tipping points in alpine catchments

    NASA Astrophysics Data System (ADS)

    Lutzmann, Silke; Sass, Oliver

    2016-04-01

    Steep mountain channels or torrents in small alpine catchments are characterized by high geomorphic activity with sediment dynamics being inherently nonlinear and threshold-mediated. Localized, high intensity rainstorms can drive torrential systems past a tipping point resulting in a sudden onset of hazardous events like (flash-) flooding, heavy bedload transport or debris flows. Such responses exhibit an abrupt switch in the fluvial system's mode (e.g. transport / supply limited). Changes in functional connectivity may persist beyond the tipping point. Torrential hazards cause costly damage in the densely populated Alpine Region. Thus, there is a rising interest in potential effects of climate change on torrential sediment dynamics. Understanding critical conditions close to tipping points is important to reduce uncertainty in predicting sediment fluxes. In this study we aim at (i) establishing threshold precipitation characteristics for the Eastern Alps of Austria. Precipitation is hypothesized to be the main forcing factor of torrential events. (ii) How do thresholds vary in space and time? (iii) The effect of external triggers is strongly mediated by the internal disposition of catchments to respond. Which internal conditions are critical for susceptibility? (iv) Is there a change in magnitude or frequency in the recent past and what can be expected for the future? The 71 km2 catchment of the river Schöttlbach in the East Alpine Region of Styria (Austria) is monitored since a heavy precipitation event resulted in a catastrophic flood in July 2011. Sediment mobilization from slopes as well as within-channel storage and bedload transport are regularly measured using photogrammetric methods and sediment impact sensors. Thus, detailed knowledge exists on magnitude and spatial propagation of sediment waves through the catchment. The associated hydro-meteorological (pre-) conditions can be inferred from a dense station network. Changing bedload transport rates and

  14. Physical Thresholds as Ecological Proxies in Aquatic Ecosystems

    NASA Astrophysics Data System (ADS)

    Hausner, M. B.; Gaines, D. B.; Morrison, R. R.; Sada, D. W.; Scoppettone, G. G.; Stone, M. C.; Suarez, F. I.; Tyler, S. W.; Wilson, K. P.

    2015-12-01

    It is often difficult to directly quantify ecological thresholds and predict ecological responses to changing environmental conditions. Here, we present two case studies from Death Valley National Park - Devils Hole and Travertine Springs - in which physical parameters are used as proxies for ecological processes to assess the consequences of environmental change on aquatic ecosystems. In Devils Hole, seasonal thresholds for water temperature and food availability are defined to quantify the optimal recruitment window for the Devils Hole pupfish (Cyprinodon diabolis). At Travertine Springs, physical thresholds of water depth, velocity, and temperature are used to define the spatial extent of the preferred habitat of several threatened macroinvertebrate species. In both systems, mechanistic models are developed to predict the response of those physical thresholds to changing environmental conditions informed by climate change scenarios and potential changes in water availability. By examining the temporal and spatial response of targeted physical parameters to alternative scenarios, we can assess potential ecosystem impacts without direct measurement of ecological processes.

  15. Damage mechanisms in components for fiber lasers and amplifiers

    NASA Astrophysics Data System (ADS)

    Carter, Adrian; Samson, Bryce N.; Tankala, Kanishka; Machewirth, David P.; Khitrov, Victor; Manyam, Upendra H.; Gonthier, Francois; Seguin, Francois

    2005-02-01

    In this paper we review the damage mechanisms that need to be considered when building high power fibre lasers. More specifically we look at thermal issues, optically induced coating damage, bulk and surface damage thresholds of the host glass. We also discuss the reliability of tapered fibre bundles and Bragg gratings at these power densities.

  16. Bayesian estimation of dose thresholds

    NASA Technical Reports Server (NTRS)

    Groer, P. G.; Carnes, B. A.

    2003-01-01

    An example is described of Bayesian estimation of radiation absorbed dose thresholds (subsequently simply referred to as dose thresholds) using a specific parametric model applied to a data set on mice exposed to 60Co gamma rays and fission neutrons. A Weibull based relative risk model with a dose threshold parameter was used to analyse, as an example, lung cancer mortality and determine the posterior density for the threshold dose after single exposures to 60Co gamma rays or fission neutrons from the JANUS reactor at Argonne National Laboratory. The data consisted of survival, censoring times and cause of death information for male B6CF1 unexposed and exposed mice. The 60Co gamma whole-body doses for the two exposed groups were 0.86 and 1.37 Gy. The neutron whole-body doses were 0.19 and 0.38 Gy. Marginal posterior densities for the dose thresholds for neutron and gamma radiation were calculated with numerical integration and found to have quite different shapes. The density of the threshold for 60Co is unimodal with a mode at about 0.50 Gy. The threshold density for fission neutrons declines monotonically from a maximum value at zero with increasing doses. The posterior densities for all other parameters were similar for the two radiation types.

  17. Digital Image Sensor-Based Assessment of the Status of Oat (Avena sativa L.) Crops after Frost Damage

    PubMed Central

    Macedo-Cruz, Antonia; Pajares, Gonzalo; Santos, Matilde; Villegas-Romero, Isidro

    2011-01-01

    The aim of this paper is to classify the land covered with oat crops, and the quantification of frost damage on oats, while plants are still in the flowering stage. The images are taken by a digital colour camera CCD-based sensor. Unsupervised classification methods are applied because the plants present different spectral signatures, depending on two main factors: illumination and the affected state. The colour space used in this application is CIELab, based on the decomposition of the colour in three channels, because it is the closest to human colour perception. The histogram of each channel is successively split into regions by thresholding. The best threshold to be applied is automatically obtained as a combination of three thresholding strategies: (a) Otsu’s method, (b) Isodata algorithm, and (c) Fuzzy thresholding. The fusion of these automatic thresholding techniques and the design of the classification strategy are some of the main findings of the paper, which allows an estimation of the damages and a prediction of the oat production. PMID:22163940

  18. HF-based etching processes for improving laser damage resistance of fused silica optical surfaces

    SciTech Connect

    Suratwala, T I; Miller, P E; Bude, J D; Steele, R A; Shen, N; Monticelli, M V; Feit, M D; Laurence, T A; Norton, M A; Carr, C W; Wong, L L

    2010-02-23

    The effect of various HF-based etching processes on the laser damage resistance of scratched fused silica surfaces has been investigated. Conventionally polished and subsequently scratched fused silica plates were treated by submerging in various HF-based etchants (HF or NH{sub 4}F:HF at various ratios and concentrations) under different process conditions (e.g., agitation frequencies, etch times, rinse conditions, and environmental cleanliness). Subsequently, the laser damage resistance (at 351 or 355 nm) of the treated surface was measured. The laser damage resistance was found to be strongly process dependent and scaled inversely with scratch width. The etching process was optimized to remove or prevent the presence of identified precursors (chemical impurities, fracture surfaces, and silica-based redeposit) known to lead to laser damage initiation. The redeposit precursor was reduced (and hence the damage threshold was increased) by: (1) increasing the SiF{sub 6}{sup 2-} solubility through reduction in the NH4F concentration and impurity cation impurities, and (2) improving the mass transport of reaction product (SiF{sub 6}{sup 2-}) (using high frequency ultrasonic agitation and excessive spray rinsing) away from the etched surface. A 2D finite element crack-etching and rinsing mass transport model (incorporating diffusion and advection) was used to predict reaction product concentration. The predictions are consistent with the experimentally observed process trends. The laser damage thresholds also increased with etched amount (up to {approx}30 {micro}m), which has been attributed to: (1) etching through lateral cracks where there is poor acid penetration, and (2) increasing the crack opening resulting in increased mass transport rates. With the optimized etch process, laser damage resistance increased dramatically; the average threshold fluence for damage initiation for 30 {micro}m wide scratches increased from 7 to 41 J/cm{sup 2}, and the statistical

  19. Predictors of hearing threshold levels and distortion product otoacoustic emissions among noise exposed young adults

    PubMed Central

    Seixas, N; Kujawa, S; Norton, S; Sheppard, L; Neitzel, R; Slee, A

    2004-01-01

    Aim: To examine the relations between noise exposure and other risk factors with hearing function as measured by audiometric thresholds and distortion product otoacoustic emissions. Methods: A total of 456 subjects were studied (393 apprentices in construction trades and 63 graduate students). Hearing and peripheral auditory function were quantified using standard, automated threshold audiometry, tympanometry, and distortion product otoacoustic emissions (DPOAEs). The analysis addressed relations of noise exposure history and other risk factors with hearing threshold levels (HTLs) and DPOAEs at the baseline test for the cohort. Results: The cohort had a mean age of 27 (7) years. The construction apprentices reported more noise exposure than students in both their occupational and non-occupational exposure histories. A strong effect of age and years of work in construction was observed at 4, 6, and 8 kHz for both HTLs and DPOAEs. Each year of construction work reported prior to baseline was associated with a 0.7 dB increase in HTL or 0.2 dB decrease DPOAE amplitude. Overall, there was a very similar pattern of effects between the HTLs and DPOAEs. Conclusions: This analysis shows a relatively good correspondence between the associations of noise exposures and other risk factors with DPOAEs and the associations observed with pure-tone audiometric thresholds in a young adult working population. The results provide further evidence that DPOAEs can be used to assess damage to hearing from a variety of exposures including noise. Clarifying advantages of DPOAEs or HTLs in terms of sensitivity to early manifestations of noise insults, or their utility in predicting future loss in hearing will require longitudinal follow up. PMID:15477283

  20. Studying the effects of the heat stress on the various layers of human skin using damage function