Cumulative approaches to track formation under swift heavy ion (SHI) irradiation: Phenomenological correlation with formation energies of Frenkel pairs

NASA Astrophysics Data System (ADS)

Crespillo, M. L.; Agulló-López, F.; Zucchiatti, A.

2017-03-01

An extensive survey for the formation energies of Frenkel pairs, as representative candidates for radiation-induced point defects, is presented and discussed in relation to the cumulative mechanisms (CM) of track formation in dielectric materials under swift heavy ion (SHI) irradiation. These mechanisms rely on the generation and accumulation of point defects during irradiation followed by collapse of the lattice once a threshold defect concentration is reached. The physical basis of those approaches has been discussed by Fecht as a defect-assisted transition to an amorphous phase. Although a first quantitative analysis of the CM model was previously performed for LiNbO3 crystals, we have, here, adopted a broader phenomenological approach. It explores the correlation between track formation thresholds and the energies for Frenkel pair formation for a broad range of materials. It is concluded that the threshold stopping powers can be roughly scaled with the energies required to generate a critical Frenkel pair concentration in the order of a few percent of the total atomic content. Finally, a comparison with the predictions of the thermal spike model is discussed within the analytical Szenes approximation.

Defective Autophagy, Mitochondrial Clearance and Lipophagy in Niemann-Pick Type B Lymphocytes

PubMed Central

Salucci, Sara; Luchetti, Francesca; Falcieri, Elisabetta; Di Sario, Gianna; Palma, Fulvio; Papa, Stefano

2016-01-01

Niemann-Pick disease type A (NP-A) and type B (NP-B) are lysosomal storage diseases (LSDs) caused by sphingomyelin accumulation in lysosomes relying on reduced or absent acid sphingomyelinase. A considerable body of evidence suggests that lysosomal storage in many LSD impairs autophagy, resulting in the accumulation of poly-ubiquitinated proteins and dysfunctional mitochondria, ultimately leading to cell death. Here we test this hypothesis in a cellular model of Niemann-Pick disease type B, in which autophagy has never been studied. The basal autophagic pathway was first examined in order to evaluate its functionality using several autophagy-modulating substances such as rapamycin and nocodazole. We found that human NP-B B lymphocytes display considerable alteration in their autophagic vacuole accumulation and mitochondrial fragmentation, as well as mitophagy induction (for damaged mitochondria clearance). Furthermore, lipid traceability of intra and extra-cellular environments shows lipid accumulation in NP-B B lymphocytes and also reveals their peculiar trafficking/management, culminating in lipid microparticle extrusion (by lysosomal exocytosis mechanisms) or lipophagy. All of these features point to the presence of a deep autophagy/mitophagy alteration revealing autophagic stress and defective mitochondrial clearance. Hence, rapamycin might be used to regulate autophagy/mitophagy (at least in part) and to contribute to the clearance of lysosomal aberrant lipid storage. PMID:27798705

Molecular dynamics simulations of oxygen vacancy diffusion in SrTiO3.

PubMed

Schie, Marcel; Marchewka, Astrid; Müller, Thomas; De Souza, Roger A; Waser, Rainer

2012-12-05

A classical force-field model with partial ionic charges was applied to study the behaviour of oxygen vacancies in the perovskite oxide strontium titanate (SrTiO(3)). The dynamical behaviour of these point defects was investigated as a function of temperature and defect concentration by means of molecular dynamics (MD) simulations. The interaction between oxygen vacancies and an extended defect, here a Σ3(111) grain boundary, was also examined by means of MD simulations. Analysis of the vacancy distribution revealed considerable accumulation of vacancies in the envelope of the grain boundary. The possible clustering of oxygen vacancies in bulk SrTiO(3) was studied by means of static lattice calculations within the Mott-Littleton approach. All binary vacancy-vacancy configurations were found to be energetically unfavourable.

Effects of crystallization interfaces on irradiated ferroelectric thin films

NASA Astrophysics Data System (ADS)

Brewer, S. J.; Williams, S. C.; Cress, C. D.; Bassiri-Gharb, N.

2017-11-01

This work investigates the role of crystallization interfaces and chemical heterogeneity in the radiation tolerance of chemical solution-deposited lead zirconate titanate (PZT) thin films. Two sets of PZT thin films were fabricated with crystallization performed at (i) every deposited layer or (ii) every three layers. The films were exposed to a range of 60Co gamma radiation doses, between 0.2 and 20 Mrad, and their functional response was compared before and after irradiation. The observed trends indicate enhancements of dielectric, ferroelectric, and piezoelectric responses at low radiation doses and degradation of the same at higher doses. Response enhancements are expected to result from low-dose (≤2 Mrad), ionizing radiation-induced charging of internal interfaces—an effect that results in neutralization of pre-existing internal bias in the samples. At higher radiation doses (>2 Mrad), accumulation and self-ordering of radiation-modified, mobile, oxygen vacancy-related defects contribute to degradation of dielectric, ferroelectric, and piezoelectric properties, exacerbated in the samples with more crystallization layers, potentially due to increased defect accumulation at these internal interfaces. These results suggest that the interaction between radiation and crystallization interfaces is multifaceted—the effects of ionization, domain wall motion, point defect mobility, and microstructure are considered.

Intrinsic point-defect balance in self-ion-implanted ZnO.

PubMed

Neuvonen, Pekka T; Vines, Lasse; Svensson, Bengt G; Kuznetsov, Andrej Yu

2013-01-04

The role of excess intrinsic atoms for residual point defect balance has been discriminated by implanting Zn or O ions into Li-containing ZnO and monitoring Li redistribution and electrical resistivity after postimplant anneals. Strongly Li-depleted regions were detected in the Zn-implanted samples at depths beyond the projected range (R(p)) upon annealing ≥ 600 °C, correlating with a resistivity decrease. In contrast, similar anneals of the O-implanted samples resulted in Li accumulation at R(p) and an increased resistivity. Control samples implanted with Ar or Ne ions, yielding similar defect production as for the Zn or O implants but with no surplus of intrinsic atoms, revealed no Li depletion. Thus, the depletion of Li shows evidence of excess Zn interstitials (Zn(I)) being released during annealing of the Zn-implanted samples. These Zn(I)'s convert substitutional Li atoms (Li(Zn)) into highly mobile interstitial ones leading to the strongly Li-depleted regions. In the O-implanted samples, the high resistivity provides evidence of stable O(I)-related acceptors.

New solutions with accelerated expansion in string theory

DOE PAGES

Dodelson, Matthew; Dong, Xi; Silverstein, Eva; ...

2014-12-05

We present concrete solutions with accelerated expansion in string theory, requiring a small, tractable list of stress energy sources. We explain how this construction (and others in progress) evades previous no go theorems for simple accelerating solutions. Our solutions respect an approximate scaling symmetry and realize discrete sequences of values for the equation of state, including one with an accumulation point at w = –1 and another accumulating near w = –1/3 from below. In another class of models, a density of defects generates scaling solutions with accelerated expansion. Here, we briefly discuss potential applications to dark energy phenomenology, andmore » to holography for cosmology.« less

Assessing Urinary Tract Junction Obstruction Defects by Methylene Blue Dye Injection.

PubMed

Yun, Kangsun

2017-10-12

Urinary tract junction obstruction defects are congenital anomalies inducing hydronephrosis and hydroureter. Murine urinary tract junction obstruction defects can be assessed by tracking methylene blue dye flow within the urinary system. Methylene blue dye is injected into the renal pelvis of perinatal embryonic kidneys and dye flow is monitored from the renal pelvis of the kidney through the ureter and into the bladder lumen after applying hydrostatic pressure. Dye accumulation will be evident in the bladder lumen of the normal perinatal urinary tract, but will be constrained between the renal pelvis and the end point of an abnormal ureter, if urinary tract obstructions occur. This method facilitates the confirmation of urinary tract junction obstructions and visualization of hydronephrosis and hydroureter. This manuscript describes a protocol for methylene blue dye injection into the renal pelvis to confirm urinary tract junction obstructions.

Mechanism of Na accumulation at extended defects in Si from first-principles

NASA Astrophysics Data System (ADS)

Park, Ji-Sang; Chan, Maria K. Y.

2018-04-01

Sodium (Na) impurities in silicon solar cells are considered to play an important role in potential-induced degradation (PID), a significant cause of solar cell degradation and failure. Shorting due to Na accumulation at extended defects has been suggested as a culprit for PID. However, it is not clear how the extended defects are decorated by Na impurities. Using first-principles density functional theory calculations, we find that Na impurities segregate from the bulk into extended defects such as intrinsic stacking faults and Σ3 (111) grain boundaries. The energy barrier required for Na to escape from the extended defects is substantial and similar to the sum of the barrier energy in bulk Si (1.1-1.2 eV) and the segregation energy to the stacking fault (˜0.7 eV). Surprisingly, the migration barrier for Na diffusion within the extended defects is even higher than the energy barrier for escaping. The results suggest that the extended defects likely accumulate Na as the impurities segregate to the defects from the bulk, rather than because of migration through the extended defects.

Cadmium inhibits the protein degradation of Sml1 by inhibiting the phosphorylation of Sml1 in Saccharomyces cerevisiae

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

Baek, In-Joon; Kang, Hyun-Jun; Chang, Miwha

Highlights: Black-Right-Pointing-Pointer Cd inhibits Sml1-p formation. Black-Right-Pointing-Pointer Cd affects cell cycle. Black-Right-Pointing-Pointer Cd inhibits Sml1 ubiquitination. -- Abstract: Cadmium is a toxic metal, and the mechanism of cadmium toxicity in living organisms has been well studied. Here, we used Saccharomyces cerevisiae as a model system to examine the detailed molecular mechanism of cell growth defects caused by cadmium. Using a plate assay of a yeast deletion mutant collection, we found that deletion of SML1, which encodes an inhibitor of Rnr1, resulted in cadmium resistance. Sml1 protein levels increased when cells were treated with cadmium, even though the mRNA levels ofmore » SML1 remained unchanged. Using northern and western blot analyses, we found that cadmium inhibited Sml1 degradation by inhibiting Sml1 phosphorylation. Sml1 protein levels increased when cells were treated with cadmium due to disruption of the dependent protein degradation pathway. Furthermore, cadmium promoted cell cycle progression into the G2 phase. The same result was obtained using cells in which SML1 was overexpressed. Deletion of SML1 delayed cell cycle progression. These results are consistent with Sml1 accumulation and with growth defects caused by cadmium stress. Interestingly, although cadmium treatment led to increase Sml1 levels, intracellular dNTP levels also increased because of Rnr3 upregulation due to cadmium stress. Taken together, these results suggest that cadmium specifically affects the phosphorylation of Sml1 and that Sml1 accumulates in cells.« less

Evolution of irradiation-induced strain in an equiatomic NiFe alloy

DOE PAGES

Ullah, Mohammad W.; Zhang, Yanwen; Sellami, Neila; ...

2017-07-10

Here, we investigate the formation and accumulation of irradiation-induced atomic strain in an equiatomic NiFe concentrated solid-solution alloy using both atomistic simulations and x-ray diffraction (XRD) analysis of irradiated samples. Experimentally, the irradiations are performed using 1.5 MeV Ni ions to fluences ranging from 1 × 10 13 to 1 × 10 14 cm -2. The irradiation simulations are carried out by overlapping 5 keV Ni recoils cascades up to a total of 300 recoils. An increase of volumetric strain is observed at low dose, which is associated with production of point defects and small clusters. A relaxation of strainmore » occurs at higher doses, when large defect clusters, like dislocation loops, dominate.« less

Evolution of Radiation Induced Defects in SiC: A Multiscale Simulation Approach

NASA Astrophysics Data System (ADS)

Jiang, Hao

Because of various excellent properties, SiC has been proposed for many applications in nuclear reactors including cladding layers in fuel rod, fission products container in TRISO fuel, and first wall/blanket in magnetic controlled fusion reactors. Upon exposure to high energy radiation environments, point defects and defect clusters are generated in materials in amounts significantly exceeding their equilibrium concentrations. The accumulation of defects can lead to undesired consequences such as crystalline-to-amorphous transformation1, swelling, and embrittlement, and these phenomena can adversely affect the lifetime of SiC based components in nuclear reactors. It is of great importance to understand the accumulation process of these defects in order to estimate change in properties of this material and to design components with superior ability to withstand radiation damages. Defect clusters are widely in SiC irradiated at the operation temperatures of various reactors. These clusters are believed to cause more than half of the overall swelling of irradiated SiC and can potentially lead to lowered thermal conductivity and mechanical strength. It is critical to understand the formation and growth of these clusters. Diffusion of these clusters is one importance piece to determine the growth rate of clusters; however it is unclear so far due to the challenges in simulating rare events. Using a combination of kinetic Activation Relaxation Technique with empirical potential and ab initio based climbing image nudged elastic band method, I performed an extensive search of the migration paths of the most stable carbon tri-interstitial cluster in SiC. This research reveals paths with the lowest energy barriers to migration, rotation, and dissociation of the most stable cluster. Based on these energy barriers, I concluded defect clusters are thermally immobile at temperatures lower than 1500 K and can dissociate into smaller clusters and single interstitials at temperatures beyond that. Even though clusters cannot diffuse by thermal vibrations, we found they can migrate at room temperature under the influence of electron radiation. This is the first direct observation of radiation-induced diffusion of defect clusters in bulk materials. We show that the underlying mechanism of this athermal diffusion is elastic collision between incoming electrons and cluster atoms. Our findings suggest that defect clusters may be mobile under certain irradiation conditions, changing current understanding of cluster annealing process in irradiated SiC. With the knowledge of cluster diffusion in SiC demonstrated in this thesis, we now become able to predict cluster evolution in SiC with good agreement with experimental measurements. This ability can enable us to estimate changes in many properties of irradiated SiC relevant for its applications in reactors. Internal interfaces such as grain boundaries can behave as sinks to radiation induced defects. The ability of GBs to absorb, transport, and annihilate radiation-induced defects (sink strength) is important to understand radiation response of polycrystalline materials and to better design interfaces for improved resistance to radiation damage. Nowadays, it is established GBs' sink strength is not a static property but rather evolves with many factors, including radiation environments, grain size, and GB microstructure. In this thesis, I investigated the response of small-angle tilt and twist GBs to point defects fluxes in SiC. First of all, I found the pipe diffusion of interstitials in tilt GBs is slower than bulk diffusion. This is because the increased interatomic distance at dislocation cores raises the migration barrier of interstitial dumbbells. Furthermore, I show that both the annihilation of interstitials at jogs and jog nucleation from clusters are diffusion-controlled and can occur under off-stoichiometric interstitial fluxes. Finally, a dislocation line model is developed to predict the role of tilt GBs in annihilating radiation damage. The model predicts the role of tilt GBs in annihilating defects depends on the rate of defects segregation to and diffusion along tilt GBs. Tilt GBs mainly serve as diffusion channel for defects to reach other sinks when defect diffusivity is high at boundaries. When defect diffusivity is low, most of the defects segregated to tilt GBs are annihilated by dislocation climb. Up-to-date, the response of twist GBs under irradiation has been rarely reported in literature and is still unclear. It is important to develop atom scale insight on this question in order to predict twist GBs' sink strength for a better understanding of radiation response of polycrystalline materials. By using a combination of molecular dynamics and grand canonical Monte Carlo, here I demonstrate the defect kinetics in {001} and {111} twist GBs and the microstructural evolution of these GBs under defect fluxes in SiC. I found due to the deep potential well for interstitials at dislocation intersections within the interface, the mobility of defects on dislocation grid is retard and this leads to defect accumulation at GBs for many cases. Furthermore, I conclude both types of twist GBs have to form mixed dislocations with edge component in order to absorb accumulated interstitials at the interface. The formation of mixed dislocation is either by interstitial loop nucleation or by dislocation reactions at the interface. The continuous formation and climb of these mixed dislocations make twist GBs unsaturatable sinks to radiation induced defects.

Delayed damage accumulation by athermal suppression of defect production in concentrated solid solution alloys

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

Velişa, G.; Wendler, E.; Zhao, S.

A combined experimental and computational evaluation of damage accumulation in ion-irradiated Ni, NiFe, and NiFeCoCr is presented. Furthermore, a suppressed damage accumulation, at early stages (low-fluence irradiation), is revealed in NiFeCoCr, with a linear dependence as a function of ion fluence, in sharp contrast with Ni and NiFe. This effect, observed at 16 K, is attributed to the complex energy landscape in these alloys that limits defect mobility and therefore enhances defect interaction and recombination. Our results, together with previous room-temperature and high-temperature investigations, suggest "self-healing" as an intrinsic property of complex alloys that is not a thermally activated process.

Delayed damage accumulation by athermal suppression of defect production in concentrated solid solution alloys

DOE PAGES

Velişa, G.; Wendler, E.; Zhao, S.; ...

2017-12-17

A combined experimental and computational evaluation of damage accumulation in ion-irradiated Ni, NiFe, and NiFeCoCr is presented. Furthermore, a suppressed damage accumulation, at early stages (low-fluence irradiation), is revealed in NiFeCoCr, with a linear dependence as a function of ion fluence, in sharp contrast with Ni and NiFe. This effect, observed at 16 K, is attributed to the complex energy landscape in these alloys that limits defect mobility and therefore enhances defect interaction and recombination. Our results, together with previous room-temperature and high-temperature investigations, suggest "self-healing" as an intrinsic property of complex alloys that is not a thermally activated process.

Accumulation of cholesterol and GM2 ganglioside in cells cultured in the presence of progesterone: an implication for the basic defect in Niemann-Pick disease type C.

PubMed

Sato, M; Akaboshi, S; Katsumoto, T; Taniguchi, M; Higaki, K; Tai, T; Sakuraba, H; Ohno, K

1998-01-01

Cultured fibroblasts from patients with Niemann-Pick disease type C (NP-C) are characterized by lysosomal accumulation of unesterified cholesterol and a defect in intracellular trafficking of cholesterol. We have found the accumulation of GM2 ganglioside in NP-C fibroblasts [Yano T, Taniguchi M, Akaboshi S, Vanier MT, Tai T, Sakuraba H, et al. Proc Japan Acad 1996;72B:214-219]. In this communication we show that several inhibitors known to inhibit intracellular cholesterol transport, progesterone, imipramine and KN-62, elicit accumulation of not only unesterified cholesterol but also GM2 ganglioside. This finding suggests that intracellular transport of cholesterol may be coupled with that of GM2 ganglioside. The accumulation of free cholesterol and GM2 ganglioside may be a clue for understanding the basic defect of NP-C. Recently NPC1 gene is found by the positional cloning. The mechanism of accumulating of GM2 ganglioside should be further investigated by studying of the functions of NPC1 gene.

Holographic evaluation of the marginal fit of complete crowns loaded at central fossa

NASA Astrophysics Data System (ADS)

Chen, Terry Y.; Chang, Guan L.; Wu, Shih H.

1993-07-01

In dentistry, the defect of cementation on the margins of crowns accumulates bacterial plaque easily. This can result in recurrent caries and periodontal disease. In this paper holographic interferometry is applied to study the effect of masticatory force on various complete crowns. Four complete molar crowns made from different casting materials (Au, Pd-Ag, Ni-Cr, and PFM) were tested. The horizontal displacements of two points near the margin, measured by the method of multiple observations, could be as large as 15 micrometers under normal load (25 kgw). However, the marginal discrepancy of all four crowns estimated were quite small (< 0.2 micrometers ). This also indicates that the cementation between the crown and the tooth is quite good. Nevertheless, when the load was increased to 45 kgw, a defect of cementation was found on the Pd-Ag crown.

Dynamical stability of plutonium alloys

NASA Astrophysics Data System (ADS)

Torrent, Marc; Dorado, Boris; Bieder, Jordan

Plutonium sits at the center of the actinide series and marks the transition between localization and delocalization of the 5 f electrons. From a metallurgical standpoint, the monoclinic α phase (stable at low T) is brittle, not suitable for engineering applications, as opposed to the ductile fcc δ phase (stable at 580K). The δ - α transition can be avoided by alloying δ-Pu with ''deltagen'' elements. There is a wide unexplored area for Pu when it comes to lattice dynamics. Due to the changes in the composition, the dynamical stability of is constantly challenged. Displ. cascades are created in the material, which in turn produce numerous of point defects. Therefore, the accumulation of defects preclude a thermodynamic equilibrium. Given the importance for engineering applications, it is crucial that we understand the mechanisms that lead to stabilization with respect to the alloy composition. We use first-principles calculations to provide evidence of the effect of defects/impurities (C, O, Al, Fe, Ni, Ga, Ce, U, Am) on the dynamical stability of δ-Pu. We show that this phase is dynamically unstable at low T and that it depends on the 5 f orbital occupancies. We investigate how defects affect the stability by comparing the phonon DoS.

Atomistic simulation of damage accumulation and amorphization in Ge

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

Gomez-Selles, Jose L., E-mail: joseluis.gomezselles@imdea.org; Martin-Bragado, Ignacio; Claverie, Alain

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.more » 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.« less

Modelling of creep curves of Ni3Ge single crystals

NASA Astrophysics Data System (ADS)

Starenchenko, V. A.; Starenchenko, S. V.; Pantyukhova, O. D.; Solov'eva, Yu V.

2015-01-01

In this paper the creep model of alloys with L12 superstructure is presented. The creep model is based on the idea of the mechanisms superposition connected with the different elementary deformation processes. Some of them are incident to the ordered structure L12 (anomalous mechanisms), others are typical to pure metals with the fcc structure (normal mechanisms): the accumulation of thermal APBs by means of the intersection of moving dislocations; the formation of APB tubes; the multiplication of superdislocations; the movement of single dislocations; the accumulation of point defects, such as vacancies and interstitial atoms; the accumulation APBs at the climb of edge dislocations. This model takes into account the experimental facts of the wetting antiphase boundaries and emergence of the disordered phase within the ordered phase. The calculations of the creep curves are performed under different conditions. This model describes different kinds of the creep curves and demonstrates the important meaning of the deformation superlocalisation leading to the inverse creep. The experimental and theoretical results coincide rather well.

Precise correlation of histopathological and fluorescein angiographic morphology using retinal vascular casting.

PubMed

Bek, T; Prause, J U

1996-12-01

The histopathology of three eyes obtained post mortem from 2 patients with age-related macular degeneration was correlated with the pre mortem fluorescein angiographic morphology. A precise point-by-point correlation between histopathology and the corresponding angiographic appearance was ensured by using the cast retinal vascular system as a pattern of reference. The study showed that both the photoreceptors, the pigment epithelium, and substances accumulated between the retinal and the choroidal vascular systems, may have a blocking effect on choroidal background fluorescence as seen on fluorescein angiograms. Furthermore, it is confirmed that fluorescein angiographic hyperfluorescence may be due to a lack of blocking of the choroidal fluorescence because of a window defect in the retinal photoreceptor layer and/or the pigment epithelium.

Design and analysis of forward and reverse models for predicting defect accumulation, defect energetics, and irradiation conditions

DOE PAGES

Stewart, James A.; Kohnert, Aaron A.; Capolungo, Laurent; ...

2018-03-06

The complexity of radiation effects in a material’s microstructure makes developing predictive models a difficult task. In principle, a complete list of all possible reactions between defect species being considered can be used to elucidate damage evolution mechanisms and its associated impact on microstructure evolution. However, a central limitation is that many models use a limited and incomplete catalog of defect energetics and associated reactions. Even for a given model, estimating its input parameters remains a challenge, especially for complex material systems. Here, we present a computational analysis to identify the extent to which defect accumulation, energetics, and irradiation conditionsmore » can be determined via forward and reverse regression models constructed and trained from large data sets produced by cluster dynamics simulations. A global sensitivity analysis, via Sobol’ indices, concisely characterizes parameter sensitivity and demonstrates how this can be connected to variability in defect evolution. Based on this analysis and depending on the definition of what constitutes the input and output spaces, forward and reverse regression models are constructed and allow for the direct calculation of defect accumulation, defect energetics, and irradiation conditions. Here, this computational analysis, exercised on a simplified cluster dynamics model, demonstrates the ability to design predictive surrogate and reduced-order models, and provides guidelines for improving model predictions within the context of forward and reverse engineering of mathematical models for radiation effects in a materials’ microstructure.« less

Design and analysis of forward and reverse models for predicting defect accumulation, defect energetics, and irradiation conditions

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

Stewart, James A.; Kohnert, Aaron A.; Capolungo, Laurent

The complexity of radiation effects in a material’s microstructure makes developing predictive models a difficult task. In principle, a complete list of all possible reactions between defect species being considered can be used to elucidate damage evolution mechanisms and its associated impact on microstructure evolution. However, a central limitation is that many models use a limited and incomplete catalog of defect energetics and associated reactions. Even for a given model, estimating its input parameters remains a challenge, especially for complex material systems. Here, we present a computational analysis to identify the extent to which defect accumulation, energetics, and irradiation conditionsmore » can be determined via forward and reverse regression models constructed and trained from large data sets produced by cluster dynamics simulations. A global sensitivity analysis, via Sobol’ indices, concisely characterizes parameter sensitivity and demonstrates how this can be connected to variability in defect evolution. Based on this analysis and depending on the definition of what constitutes the input and output spaces, forward and reverse regression models are constructed and allow for the direct calculation of defect accumulation, defect energetics, and irradiation conditions. Here, this computational analysis, exercised on a simplified cluster dynamics model, demonstrates the ability to design predictive surrogate and reduced-order models, and provides guidelines for improving model predictions within the context of forward and reverse engineering of mathematical models for radiation effects in a materials’ microstructure.« less

Mertk receptor mutation reduces efferocytosis efficiency and promotes apoptotic cell accumulation and plaque necrosis in atherosclerotic lesions of apoe-/- mice.

PubMed

Thorp, Edward; Cui, Dongying; Schrijvers, Dorien M; Kuriakose, George; Tabas, Ira

2008-08-01

Atherosclerotic plaques that are prone to disruption and acute thrombotic vascular events are characterized by large necrotic cores. Necrotic cores result from the combination of macrophage apoptosis and defective phagocytic clearance (efferocytosis) of these apoptotic cells. We previously showed that macrophages with tyrosine kinase-defective Mertk receptor (Mertk(KD)) have a defect in phagocytic clearance of apoptotic macrophages in vitro. Herein we test the hypothesis that the Mertk(KD) mutation would result in increased accumulation of apoptotic cells and promote necrotic core expansion in a mouse model of advanced atherosclerosis. Mertk(KD);Apoe(-/-) mice and control Apoe(-/-) mice were fed a Western-type diet for 10 or 16 weeks, and aortic root lesions were analyzed for apoptosis and plaque necrosis. We found that the plaques of the Mertk(KD);Apoe(-/-) mice had a significant increase in terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive apoptotic cells. Most importantly, there were more non-macrophage-associated apoptotic cells in the Mertk(KD) lesions, consistent with defective efferocytosis. The more advanced (16-week) Mertk(KD);Apoe(-/-) plaques were more necrotic, consistent with a progression from apoptotic cell accumulation to plaque necrosis in the setting of a defective efferocytosis receptor. In a mouse model of advanced atherosclerosis, mutation of the phagocytic Mertk receptor promotes the accumulation of apoptotic cells and the formation of necrotic plaques. These data are consistent with the notion that a defect in an efferocytosis receptor can accelerate the progression of atherosclerosis and suggest a novel therapeutic target to prevent advanced plaque progression and its clinical consequences.

Synchronous parallel spatially resolved stochastic cluster dynamics

DOE PAGES

Dunn, Aaron; Dingreville, Rémi; Martínez, Enrique; ...

2016-04-23

In this work, a spatially resolved stochastic cluster dynamics (SRSCD) model for radiation damage accumulation in metals is implemented using a synchronous parallel kinetic Monte Carlo algorithm. The parallel algorithm is shown to significantly increase the size of representative volumes achievable in SRSCD simulations of radiation damage accumulation. Additionally, weak scaling performance of the method is tested in two cases: (1) an idealized case of Frenkel pair diffusion and annihilation, and (2) a characteristic example problem including defect cluster formation and growth in α-Fe. For the latter case, weak scaling is tested using both Frenkel pair and displacement cascade damage.more » To improve scaling of simulations with cascade damage, an explicit cascade implantation scheme is developed for cases in which fast-moving defects are created in displacement cascades. For the first time, simulation of radiation damage accumulation in nanopolycrystals can be achieved with a three dimensional rendition of the microstructure, allowing demonstration of the effect of grain size on defect accumulation in Frenkel pair-irradiated α-Fe.« less

OBJECT KINETIC MONTE CARLO SIMULATIONS OF RADIATION DAMAGE IN TUNGSTEN

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

Nandipati, Giridhar; Setyawan, Wahyu; Heinisch, Howard L.

2015-04-16

We used our recently developed lattice-based object kinetic Monte Carlo code; KSOME [1] to carryout simulations of radiation damage in bulk tungsten at temperatures of 300, and 2050 K for various dose rates. Displacement cascades generated from molecular dynamics (MD) simulations for PKA energies at 60, 75 and 100 keV provided residual point defect distributions. It was found that the number density of vacancies in the simulation box does not change with dose rate while the number density of vacancy clusters slightly decreases with dose rate indicating that bigger clusters are formed at larger dose rates. At 300 K, althoughmore » the average vacancy cluster size increases slightly, the vast majority of vacancies exist as mono-vacancies. At 2050 K no accumulation of defects was observed during irradiation over a wide range of dose rates for all PKA energies studied in this work.« less

Study on the intrinsic defects in tin oxide with first-principles method

NASA Astrophysics Data System (ADS)

Sun, Yu; Liu, Tingyu; Chang, Qiuxiang; Ma, Changmin

2018-04-01

First-principles and thermodynamic methods are used to study the contribution of vibrational entropy to defect formation energy and the stability of the intrinsic point defects in SnO2 crystal. According to thermodynamic calculation results, the contribution of vibrational entropy to defect formation energy is significant and should not be neglected, especially at high temperatures. The calculated results indicate that the oxygen vacancy is the major point defect in undoped SnO2 crystal, which has a higher concentration than that of the other point defect. The property of negative-U is put forward in SnO2 crystal. In order to determine the most stable defects much clearer under different conditions, the most stable intrinsic defect as a function of Fermi level, oxygen partial pressure and temperature are described in the three-dimensional defect formation enthalpy diagrams. The diagram visually provides the most stable point defects under different conditions.

Defect quasi Fermi level control-based CN reduction in GaN: Evidence for the role of minority carriers

NASA Astrophysics Data System (ADS)

Reddy, Pramod; Kaess, Felix; Tweedie, James; Kirste, Ronny; Mita, Seiji; Collazo, Ramon; Sitar, Zlatko

2017-10-01

Compensating point defect reduction in wide bandgap semiconductors is possible by above bandgap illumination based defect quasi Fermi level (dQFL) control. The point defect control technique employs excess minority carriers that influence the dQFL of the compensator, increase the corresponding defect formation energy, and consequently are responsible for point defect reduction. Previous studies on various defects in GaN and AlGaN have shown good agreement with the theoretical model, but no direct evidence for the role of minority carriers was provided. In this work, we provide direct evidence for the role of minority carriers in reducing point defects by studying the predicted increase in work done against defect (CN-1) formation with the decrease in the Fermi level (free carrier concentration) in Si doped GaN at a constant illumination intensity. Comparative defect photoluminescence measurements on illuminated and dark regions of GaN show an excellent quantitative agreement with the theory by exhibiting a greater reduction in yellow luminescence attributed to CN-1 at lower doping, thereby providing conclusive evidence for the role of the minority carriers in Fermi level control-based point defect reduction.

Formation Energies of Native Point Defects in Strained-Layer Superlattices (Postprint)

DTIC Science & Technology

2017-06-05

AFRL-RX-WP-JA-2017-0217 FORMATION ENERGIES OF NATIVE POINT DEFECTS IN STRAINED-LAYER SUPERLATTICES (POSTPRINT) Zhi-Gang Yu...2016 Interim 11 September 2013 – 5 November 2016 4. TITLE AND SUBTITLE FORMATION ENERGIES OF NATIVE POINT DEFECTS IN STRAINED-LAYER SUPERLATTICES...native point defect (NPD) formation energies and absence of mid-gap levels. In this Letter we use first-principles calculations to study the formation

Formation Energies of Native Point Defects in Strained layer Superlattices (Postprint)

DTIC Science & Technology

2017-06-05

AFRL-RX-WP-JA-2017-0440 FORMATION ENERGIES OF NATIVE POINT DEFECTS IN STRAINED-LAYER SUPERLATTICES (POSTPRINT) Zhi Gang Yu...2017 Interim 11 September 2013 – 31 May 2017 4. TITLE AND SUBTITLE FORMATION ENERGIES OF NATIVE POINT DEFECTS IN STRAINED-LAYER SUPERLATTICES...Hamiltonian, tight-binding Hamiltonian, and Green’s function techniques to obtain energy levels arising from native point defects (NPDs) in InAs-GaSb and

Lithium-ion drifting: Application to the study of point defects in floating-zone silicon

NASA Technical Reports Server (NTRS)

Walton, J. T.; Wong, Y. K.; Zulehner, W.

1997-01-01

The use of lithium-ion (Li(+)) drifting to study the properties of point defects in p-type Floating-Zone (FZ) silicon crystals is reported. The Li(+) drift technique is used to detect the presence of vacancy-related defects (D defects) in certain p-type FZ silicon crystals. SUPREM-IV modeling suggests that the silicon point defect diffusivities are considerably higher than those commonly accepted, but are in reasonable agreement with values recently proposed. These results demonstrate the utility of Li(+) drifting in the study of silicon point defect properties in p-type FZ crystals. Finally, a straightforward measurement of the Li(+) compensation depth is shown to yield estimates of the vacancy-related defect concentration in p-type FZ crystals.

Point defects in Cd(Zn)Te and TlBr: Theory

NASA Astrophysics Data System (ADS)

Lordi, Vincenzo

2013-09-01

The effects of various crystal defects on the performances of CdTe, CdZnxTe (CZT), and TlBr for room-temperature high-energy radiation detection are examined using first-principles theoretical methods. The predictive, parameter-free, atomistic approaches used provide fundamental understanding of defect properties that are difficult to measure and also allow rapid screening of possibilities for material engineering, such as optimal doping and annealing conditions. Several recent examples from the author's work are reviewed, including: (i) accurate calculations of the thermodynamic and electronic properties of native point defects and point defect complexes in CdTe and CZT; (ii) the effects of Zn alloying on the native point defect properties in CZT; (iii) point defect diffusion and binding leading to Te clustering in Cd(Zn)Te; (iv) the profound effect of native point defects—principally vacancies—on the intrinsic material properties of TlBr, particularly its electronic and ionic conductivity; and (v) a study on doping TlBr to independently control the electronic and ionic conductivity.

BAX channel activity mediates lysosomal disruption linked to Parkinson disease.

PubMed

Bové, Jordi; Martínez-Vicente, Marta; Dehay, Benjamin; Perier, Celine; Recasens, Ariadna; Bombrun, Agnes; Antonsson, Bruno; Vila, Miquel

2014-05-01

Lysosomal disruption is increasingly regarded as a major pathogenic event in Parkinson disease (PD). A reduced number of intraneuronal lysosomes, decreased levels of lysosomal-associated proteins and accumulation of undegraded autophagosomes (AP) are observed in PD-derived samples, including fibroblasts, induced pluripotent stem cell-derived dopaminergic neurons, and post-mortem brain tissue. Mechanistic studies in toxic and genetic rodent PD models attribute PD-related lysosomal breakdown to abnormal lysosomal membrane permeabilization (LMP). However, the molecular mechanisms underlying PD-linked LMP and subsequent lysosomal defects remain virtually unknown, thereby precluding their potential therapeutic targeting. Here we show that the pro-apoptotic protein BAX (BCL2-associated X protein), which permeabilizes mitochondrial membranes in PD models and is activated in PD patients, translocates and internalizes into lysosomal membranes early following treatment with the parkinsonian neurotoxin MPTP, both in vitro and in vivo, within a time-frame correlating with LMP, lysosomal disruption, and autophagosome accumulation and preceding mitochondrial permeabilization and dopaminergic neurodegeneration. Supporting a direct permeabilizing effect of BAX on lysosomal membranes, recombinant BAX is able to induce LMP in purified mouse brain lysosomes and the latter can be prevented by pharmacological blockade of BAX channel activity. Furthermore, pharmacological BAX channel inhibition is able to prevent LMP, restore lysosomal levels, reverse AP accumulation, and attenuate mitochondrial permeabilization and overall nigrostriatal degeneration caused by MPTP, both in vitro and in vivo. Overall, our results reveal that PD-linked lysosomal impairment relies on BAX-induced LMP, and point to small molecules able to block BAX channel activity as potentially beneficial to attenuate both lysosomal defects and neurodegeneration occurring in PD.

Displacement cascades and defects annealing in tungsten, Part I: Defect database from molecular dynamics simulations

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

Setyawan, Wahyu; Nandipati, Giridhar; Roche, Kenneth J.

Molecular dynamics simulations have been used to generate a comprehensive database of surviving defects due to displacement cascades in bulk tungsten. Twenty-one data points of primary knock-on atom (PKA) energies ranging from 100 eV (sub-threshold energy) to 100 keV (~780 × Ed, where Ed = 128 eV is the average displacement threshold energy) have been completed at 300 K, 1025 K and 2050 K. Within this range of PKA energies, two regimes of power-law energy-dependence of the defect production are observed. A distinct power-law exponent characterizes the number of Frenkel pairs produced within each regime. The two regimes intersect atmore » a transition energy which occurs at approximately 250 × Ed. The transition energy also marks the onset of the formation of large self-interstitial atom (SIA) clusters (size 14 or more). The observed defect clustering behavior is asymmetric, with SIA clustering increasing with temperature, while the vacancy clustering decreases. This asymmetry increases with temperature such that at 2050 K (~0.5 Tm) practically no large vacancy clusters are formed, meanwhile large SIA clusters appear in all simulations. The implication of such asymmetry on the long-term defect survival and damage accumulation is discussed. In addition, <100> {110} SIA loops are observed to form directly in the highest energy cascades, while vacancy <100> loops are observed to form at the lowest temperature and highest PKA energies, although the appearance of both the vacancy and SIA loops with Burgers vector of <100> type is relatively rare.« less

Lower Length Scale Model Development for Embrittlement of Reactor Presure Vessel Steel

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

Zhang, Yongfeng; Schwen, Daniel; Chakraborty, Pritam

2016-09-01

This report summarizes the lower-length-scale effort during FY 2016 in developing mesoscale capabilities for microstructure evolution, plasticity and fracture in reactor pressure vessel steels. During operation, reactor pressure vessels are subject to hardening and embrittlement caused by irradiation induced defect accumulation and irradiation enhanced solute precipitation. Both defect production and solute precipitation start from the atomic scale, and manifest their eventual effects as degradation in engineering scale properties. To predict the property degradation, multiscale modeling and simulation are needed to deal with the microstructure evolution, and to link the microstructure feature to material properties. In this report, the development ofmore » mesoscale capabilities for defect accumulation and solute precipitation are summarized. A crystal plasticity model to capture defect-dislocation interaction and a damage model for cleavage micro-crack propagation is also provided.« less

Effective scheme to determine accurate defect formation energies and charge transition levels of point defects in semiconductors

NASA Astrophysics Data System (ADS)

Yao, Cang Lang; Li, Jian Chen; Gao, Wang; Tkatchenko, Alexandre; Jiang, Qing

2017-12-01

We propose an effective method to accurately determine the defect formation energy Ef and charge transition level ɛ of the point defects using exclusively cohesive energy Ecoh and the fundamental band gap Eg of pristine host materials. We find that Ef of the point defects can be effectively separated into geometric and electronic contributions with a functional form: Ef=χ Ecoh+λ Eg , where χ and λ are dictated by the geometric and electronic factors of the point defects (χ and λ are defect dependent). Such a linear combination of Ecoh and Eg reproduces Ef with an accuracy better than 5% for electronic structure methods ranging from hybrid density-functional theory (DFT) to many-body random-phase approximation (RPA) and experiments. Accordingly, ɛ is also determined by Ecoh/Eg and the defect geometric/electronic factors. The identified correlation is rather general for monovacancies and interstitials, which holds in a wide variety of semiconductors covering Si, Ge, phosphorenes, ZnO, GaAs, and InP, and enables one to obtain reliable values of Ef and ɛ of the point defects for RPA and experiments based on semilocal DFT calculations.

Elastic dipoles of point defects from atomistic simulations

NASA Astrophysics Data System (ADS)

Varvenne, Céline; Clouet, Emmanuel

2017-12-01

The interaction of point defects with an external stress field or with other structural defects is usually well described within continuum elasticity by the elastic dipole approximation. Extraction of the elastic dipoles from atomistic simulations is therefore a fundamental step to connect an atomistic description of the defect with continuum models. This can be done either by a fitting of the point-defect displacement field, by a summation of the Kanzaki forces, or by a linking equation to the residual stress. We perform here a detailed comparison of these different available methods to extract elastic dipoles, and show that they all lead to the same values when the supercell of the atomistic simulations is large enough and when the anharmonic region around the point defect is correctly handled. But, for small simulation cells compatible with ab initio calculations, only the definition through the residual stress appears tractable. The approach is illustrated by considering various point defects (vacancy, self-interstitial, and hydrogen solute atom) in zirconium, using both empirical potentials and ab initio calculations.

Initial stages of ion beam-induced phase transformations in Gd2O3 and Lu2O3

NASA Astrophysics Data System (ADS)

Chen, Chien-Hung; Tracy, Cameron L.; Wang, Chenxu; Lang, Maik; Ewing, Rodney C.

2018-02-01

The atomic-scale evolution of lanthanide sesquioxides Gd2O3 and Lu2O3 irradiated with 1 MeV Kr ions at room temperature and 120 K, up to fluences of 1 × 1016 ions/cm2 (˜20 dpa), has been characterized by in situ transmission electron microscopy. At room temperature, both oxides exhibited high radiation tolerance. Irradiation did not cause any observable structural change in either material, likely due to the mobility of irradiation-induced point defects, causing efficient defect annihilation. For Gd2O3, having the larger cation ionic radius of the two materials, an irradiation-induced stacking fault structure appeared at low fluences in the low temperature irradiation. As compared with the cubic-to-monoclinic phase transformations known to result from higher energy (˜GeV) ion irradiation, Kr ions of lower energies (˜MeV) yield much lower rates of damage accumulation and thus less extensive structural modification. At a fluence of 2.5 × 1015 ions/cm2, only the initial stages of the cubic-to-monoclinic (C to B) phase transformation process, consisting of the formation and aggregation of defects, have been observed.

Surface effects on the radiation response of nanoporous Au foams

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

Fu, E. G.; Caro, M.; Wang, Y. Q.

2012-11-05

We report on an experimental and simulation campaign aimed at exploring the radiation response of nanoporous Au (np-Au) foams. We find different defect accumulation behavior by varying radiation dose-rate in ion-irradiated np-Au foams. Stacking fault tetrahedra are formed when np-Au foams are irradiated at high dose-rate, but they do not seem to be formed in np-Au at low dose-rate irradiation. A model is proposed to explain the dose-rate dependent defect accumulation based on these results.

Point Defect Properties of Cd(Zn)Te and TlBr for Room-Temperature Gamma Radiation Detectors

NASA Astrophysics Data System (ADS)

Lordi, Vincenzo

2013-03-01

The effects of various crystal defects in CdTe, Cd1-xZnxTe (CZT), and TlBr are critical for their performance as room-temperature gamma radiation detectors. We use predictive first principles theoretical methods to provide fundamental, atomic scale understanding of the defect properties of these materials to enable design of optimal growth and processing conditions, such as doping, annealing, and stoichiometry. Several recent cases will be reviewed, including (i) accurate calculations of the thermodynamic and electronic properties of native point defects and point defect complexes in CdTe and CZT; (ii) the effects of Zn alloying on the native point defect properties of CZT; (iii) point defect diffusion and binding related to Te clustering in Cd(Zn)Te; (iv) the profound effect of native point defects--principally vacancies--on the intrinsic material properties of TlBr, particularly electronic and ionic conductivity; (v) tailored doping of TlBr to independently control the electronic and ionic conductivity; and (vi) the effects of metal impurities on the electronic properties and device performance of TlBr detectors. Prepared by LLNL under Contract DE-AC52-07NA27344 with support from the National Nuclear Security Administration Office of Nonproliferation and Verification Research and Development NA-22.

RBS/C, HRTEM and HRXRD study of damage accumulation in irradiated SrTiO3

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

Jagielski, Jacek; Jozwik, Przemyslaw A.; Jozwik Biala, Iwona

2013-05-14

Damage accumulation in argon-irradiated SrTiO3 single crystals has been studied by using combination of Rutherford Backscattering/Channeling (RBS/C), High Resolution Transmission Electron Microscopy (HRTEM) and High Resolution X-Ray Diffraction (HRXRD) techniques. The RBS/C spectra were fitted using McChasy, a Monte Carlo simulation code allowing the quantitative analysis of amorphous-like and dislocation-like types of defects. The results were interpreted by using a Multi-Step Damage Accumulation model which assumes, that the damage accumulation occurs in a series of structural transformations, the defect transformations are triggered by a stress caused by formation of a free volume in the irradiated crystal. This assumption has beenmore » confirmed by High Resolution Transmission Electron Microscopy and High Resolution X-Ray Diffraction analysis.« less

Identifying and counting point defects in carbon nanotubes.

PubMed

Fan, Yuwei; Goldsmith, Brett R; Collins, Philip G

2005-12-01

The prevailing conception of carbon nanotubes and particularly single-walled carbon nanotubes (SWNTs) continues to be one of perfectly crystalline wires. Here, we demonstrate a selective electrochemical method that labels point defects and makes them easily visible for quantitative analysis. High-quality SWNTs are confirmed to contain one defect per 4 microm on average, with a distribution weighted towards areas of SWNT curvature. Although this defect density compares favourably to high-quality, silicon single-crystals, the presence of a single defect can have tremendous electronic effects in one-dimensional conductors such as SWNTs. We demonstrate a one-to-one correspondence between chemically active point defects and sites of local electronic sensitivity in SWNT circuits, confirming the expectation that individual defects may be critical to understanding and controlling variability, noise and chemical sensitivity in SWNT electronic devices. By varying the SWNT synthesis technique, we further show that the defect spacing can be varied over orders of magnitude. The ability to detect and analyse point defects, especially at very low concentrations, indicates the promise of this technique for quantitative process analysis, especially in nanoelectronics development.

Effect of laser pulse repetition frequency on the optical breakdown threshold of quartz glass

NASA Astrophysics Data System (ADS)

Kononenko, T. V.; Schöneseiffen, S.; Konov, V. I.; Dausinger, F.

2013-08-01

The thresholds of optical breakdown in the volume of quartz glass were measured in relation to the number of pulses under irradiation by ultrashort laser pulses with different pulse repetition frequencies (1 - 400 kHz). Increasing this frequency from 10 to 400 kHz was found to substantially lower the breakdown threshold for 500-fs long pulses (at a wavelength of 1030 nm) and to lower to a smaller degree for 5-ps long pulses (515 nm). A strong frequency dependence of the breakdown threshold is observed under the same conditions as a manifold decrease of the breakdown threshold with increase in the number of pulses in a pulse train. The dependence of the optical breakdown on the number of pulses is attributable to the accumulation of point defects under multiple subthreshold irradiation, which affects the mechanism of collisional ionisation. In this case, the frequency dependence of the breakdown threshold of quartz glass is determined by the engagement of shortlived defects in the ionisation mechanism.

New Insights into Intrinsic Point Defects in V2VI3 Thermoelectric Materials.

PubMed

Zhu, Tiejun; Hu, Lipeng; Zhao, Xinbing; He, Jian

2016-07-01

Defects and defect engineering are at the core of many regimes of material research, including the field of thermoelectric study. The 60-year history of V 2 VI 3 thermoelectric materials is a prime example of how a class of semiconductor material, considered mature several times, can be rejuvenated by better understanding and manipulation of defects. This review aims to provide a systematic account of the underexplored intrinsic point defects in V 2 VI 3 compounds, with regard to (i) their formation and control, and (ii) their interplay with other types of defects towards higher thermoelectric performance. We herein present a convincing case that intrinsic point defects can be actively controlled by extrinsic doping and also via compositional, mechanical, and thermal control at various stages of material synthesis. An up-to-date understanding of intrinsic point defects in V 2 VI 3 compounds is summarized in a (χ, r)-model and applied to elucidating the donor-like effect. These new insights not only enable more innovative defect engineering in other thermoelectric materials but also, in a broad context, contribute to rational defect design in advanced functional materials at large.

Amorphization driven by defect-induced mechanical instability.

PubMed

Jiang, Chao; Zheng, Ming-Jie; Morgan, Dane; Szlufarska, Izabela

2013-10-11

Using ab initio molecular dynamics simulations, we perform a comparative study of the defect accumulation process in silicon carbide (SiC) and zirconium carbide (ZrC). Interestingly, we find that the fcc Si sublattice in SiC spontaneously and gradually collapses following the continuous introduction of C Frenkel pairs (FPs). Above a critical amorphization dose of ~0.33 displacements per atom (dpa), the pair correlation function exhibits no long-range order. In contrast, the fcc Zr sublattice in ZrC remains structurally stable against C sublattice displacements up to the highest dose of 1.0 dpa considered. Consequently, ZrC cannot be amorphized by the accumulation of C FPs. We propose defect-induced mechanical instability as the key mechanism driving the amorphization of SiC under electron irradiation.

Damage Tolerance of Large Shell Structures

NASA Technical Reports Server (NTRS)

Minnetyan, L.; Chamis, C. C.

1999-01-01

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

Effect of point defects and disorder on structural phase transitions

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

Toulouse, J.

1997-06-01

Since the beginning in 1986, the object of this project has been Structural Phase Transitions (SPT) in real as opposed to ideal materials. The first stage of the study has been centered around the role of Point Defects in SPT`s. Our intent was to use the previous knowledge we had acquired in the study of point defects in non-transforming insulators and apply it to the study of point defects in insulators undergoing phase transitions. In non-transforming insulators, point defects, in low concentrations, marginally affect the bulk properties of the host. It is nevertheless possible by resonance or relaxation methods tomore » study the point defects themselves via their local motion. In transforming solids, however, close to a phase transition, atomic motions become correlated over very large distances; there, even point defects far removed from one another can undergo correlated motions which may strongly affect the transition behavior of the host. Near a structural transition, the elastic properties win be most strongly affected so as to either raise or decrease the transition temperature, prevent the transition from taking place altogether, or simply modify its nature and the microstructure or domain structure of the resulting phase. One of the well known practical examples is calcium-stabilized zirconia in which the high temperature cubic phase is stabilized at room temperature with greatly improved mechanical properties.« less

Identification of dopant-induced point defects and their effect on the performance of CZT detectors (Conference Presentation)

NASA Astrophysics Data System (ADS)

Gul, Rubi; Bolotnikov, Aleksey E.; Camarda, Giuseppe S.; Cui, Yonggang; Didic, Václav; Egarievwe, Stephen U.; Hossain, Anwar; Roy, Utpal N.; Yang, Ge; James, Ralph B.

2016-09-01

In our prior research we investigated room-temperature radiation detectors (CZT, CMT, CdMgTe, CTS, among other compound semiconductors) for point defects related to different dopants and impurities. In this talk we will report on our most recent research on newly grown CZT crystals doped with In, In+Al, In+Ni, and In+Sn. The main focus will be on the study of dopant-induced point defects using deep-level current transient spectroscopy (i-DLTS). In addition the performance, ? product, gamma-ray spectral response and internal electric field of the detectors were measured and correlated with the dopant-induced point defects and their concentrations. Characterization of the detectors was carried out using i-DLTS for the point defects, Pockels effect for the internal electric-field distribution, and γ-ray spectroscopy for the spectral properties.

Study of point- and cluster-defects in radiation-damaged silicon

NASA Astrophysics Data System (ADS)

Donegani, Elena M.; Fretwurst, Eckhart; Garutti, Erika; Klanner, Robert; Lindstroem, Gunnar; Pintilie, Ioana; Radu, Roxana; Schwandt, Joern

2018-08-01

Non-ionising energy loss of radiation produces point defects and defect clusters in silicon, which result in a significant degradation of sensor performance. In this contribution results from TSC (Thermally Stimulated Current) defect spectroscopy for silicon pad diodes irradiated by electrons to fluences of a few 1014 cm-2 and energies between 3.5 and 27 MeV for isochronal annealing between 80 and 280∘C, are presented. A method based on SRH (Shockley-Read-Hall) statistics is introduced, which assumes that the ionisation energy of the defects in a cluster depends on the fraction of occupied traps. The difference of ionisation energy of an isolated point defect and a fully occupied cluster, ΔEa, is extracted from the TSC data. For the VOi (vacancy-oxygen interstitial) defect ΔEa = 0 is found, which confirms that it is a point defect, and validates the method for point defects. For clusters made of deep acceptors the ΔEa values for different defects are determined after annealing at 80∘C as a function of electron energy, and for the irradiation with 15 MeV electrons as a function of annealing temperature. For the irradiation with 3.5 MeV electrons the value ΔEa = 0 is found, whereas for the electron energies of 6-27 MeV ΔEa > 0. This agrees with the expected threshold of about 5 MeV for cluster formation by electrons. The ΔEa values determined as a function of annealing temperature show that the annealing rate is different for different defects. A naive diffusion model is used to estimate the temperature dependencies of the diffusion of the defects in the clusters.

Native point defects in MoS2 and their influences on optical properties by first principles calculations

NASA Astrophysics Data System (ADS)

Saha, Ashim Kumar; Yoshiya, Masato

2018-03-01

Stability of native point defect species and optical properties are quantitatively examined through first principles calculations in order to identify possible native point defect species in MoS2 and its influences on electronic structures and resultant optical properties. Possible native point defect species are identified as functions of thermodynamic environment and location of Fermi-level in MoS2. It is found that sulphur vacancies can be introduced more easily than other point defect species which will create impurity levels both in bandgap and in valence band. Additionally, antisite Mo and/or Mo vacancies can be created depending on chemical potential of sulphur, both of which will create impurity levels in bandgap and in valence band. Those impurity levels result in pronounced photon absorption in visible light region, though each of these point defects alone has limited impact on the optical properties unless their concentration remained low. Thus, attention must be paid when intentional impurity doping is made to MoS2 to avoid unwanted modification of optical properties of MoS2. Those impurity may enable further exploitation of photovoltaic energy conversion at longer wavelength.

XRD and EBSD analysis of anisotropic microstructure development in cold rolled F138 stainless steel

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

De Vincentis, N.S., E-mail: devincentis@ifir-conic

The microstructural characteristics of deformation-processed materials highly influence their mechanical properties. For a complete characterization of a microstructure both local and global information must be gathered, which requires the combination of different analysis techniques. X-ray and Electron Backscatter Diffraction were used in the present paper to characterize the deformation induced in a cold rolled F138 austenitic stainless steel sample. The results obtained using laboratory and synchrotron X-ray sources were compared and combined with EBSD quantitative results, allowing the global and local characterization and orientation dependence of the deformation microstructure. A particular behavior was observed in the XRD data corresponding tomore » the planes with < 220 >∥ ND, likely due to a smaller amount of defects accumulated in the crystals with that particular orientation. EBSD was used to separate the scans data into partitions and to calculate misorientation variables and parameters, showing that this behavior can be attributed to a combination of larger grain sizes, lower local boundary misorientations and dislocation densities for crystals having < 220 >∥ ND. Several conclusions, of general validity for the evaluation of microstructure anisotropy, can be extracted from the results. - Highlights: •Combined XRD and EBSD for studying microstructure gave a superb insight on anisotropic accumulation of defects. •W-H and CMWP methods were applied for checking consistency of results. •XRD showed that a smaller accumulation of defects occurred in crystals with < 220 >∥ ND. •High brilliance X-ray beam allowed to study the anisotropy of defect accumulation.« less

Optical spectroscopy and microscopy of radiation-induced light-emitting point defects in lithium fluoride crystals and films

NASA Astrophysics Data System (ADS)

Montereali, R. M.; Bonfigli, F.; Menchini, F.; Vincenti, M. A.

2012-08-01

Broad-band light-emitting radiation-induced F2 and F3+ electronic point defects, which are stable and laser-active at room temperature in lithium fluoride crystals and films, are used in dosimeters, tuneable color-center lasers, broad-band miniaturized light sources and novel radiation imaging detectors. A brief review of their photoemission properties is presented, and their behavior at liquid nitrogen temperatures is discussed. Some experimental data from optical spectroscopy and fluorescence microscopy of these radiation-induced point defects in LiF crystals and thin films are used to obtain information about the coloration curves, the efficiency of point defect formation, the effects of photo-bleaching processes, etc. Control of the local formation, stabilization, and transformation of radiation-induced light-emitting defect centers is crucial for the development of optically active micro-components and nanostructures. Some of the advantages of low temperature measurements for novel confocal laser scanning fluorescence microscopy techniques, widely used for spatial mapping of these point defects through the optical reading of their visible photoluminescence, are highlighted.

Functional Accumulation of Antenna Proteins in Chlorophyll b-Less Mutants of Chlamydomonas reinhardtii.

PubMed

Bujaldon, Sandrine; Kodama, Natsumi; Rappaport, Fabrice; Subramanyam, Rajagopal; de Vitry, Catherine; Takahashi, Yuichiro; Wollman, Francis-André

2017-01-09

The green alga Chlamydomonas reinhardtii contains several light-harvesting chlorophyll a/b complexes (LHC): four major LHCIIs, two minor LHCIIs, and nine LHCIs. We characterized three chlorophyll b-less mutants to assess the effect of chlorophyll b deficiency on the function, assembly, and stability of these chlorophyll a/b binding proteins. We identified point mutations in two mutants that inactivate the CAO gene responsible for chlorophyll a to chlorophyll b conversion. All LHCIIs accumulated to wild-type levels in a CAO mutant but their light-harvesting function for photosystem II was impaired. In contrast, most LHCIs accumulated to wild-type levels in the mutant and their light-harvesting capability for photosystem I remained unaltered. Unexpectedly, LHCI accumulation and the photosystem I functional antenna size increased in the mutant compared with in the wild type when grown in dim light. When the CAO mutation was placed in a yellow-in-the-dark background (yid-BF3), in which chlorophyll a synthesis remains limited in dim light, accumulation of the major LHCIIs and of most LHCIs was markedly reduced, indicating that sustained synthesis of chlorophyll a is required to preserve the proteolytic resistance of antenna proteins. Indeed, after crossing yid-BF3 with a mutant defective for the thylakoid FtsH protease activity, yid-BF3-ftsh1 restored wild-type levels of LHCI, which defines LHCI as a new substrate for the FtsH protease. Copyright © 2017 The Author. Published by Elsevier Inc. All rights reserved.

On the validity of the amphoteric-defect model in gallium arsenide and a criterion for Fermi-level pinning by defects

NASA Astrophysics Data System (ADS)

Chen, C.-H.; Tan, T. Y.

1995-10-01

Using the theoretically calculated point-defect total-energy values of Baraff and Schlüter in GaAs, an amphoteric-defect model has been proposed by Walukiewicz to explain a large number of experimental results. The suggested amphoteric-defect system consists of two point-defect species capable of transforming into each other: the doubly negatively charged Ga vacancy V {Ga/2-} and the triply positively charged defect complex (ASGa+ V As)3+, with AsGa being the antisite defect of an As atom occupying a Ga site and V As being an As vacancy. When present in sufficiently high concentrations, the amphoteric defect system V {Ga/2-}/(AsGa+ V As)3+ is supposed to be able to pin the GaAs Fermi level at approximately the E v +0.6 eV level position, which requires that the net free energy of the V Ga/(AsGa+ V As) defect system to be minimum at the same Fermi-level position. We have carried out a quantitative study of the net energy of this defect system in accordance with the individual point-defect total-energy results of Baraff and Schlüter, and found that the minimum net defect-system-energy position is located at about the E v +1.2 eV level position instead of the needed E v +0.6 eV position. Therefore, the validity of the amphoteric-defect model is in doubt. We have proposed a simple criterion for determining the Fermi-level pinning position in the deeper part of the GaAs band gap due to two oppositely charged point-defect species, which should be useful in the future.

A 3D Laser Profiling System for Rail Surface Defect Detection

PubMed Central

Li, Qingquan; Mao, Qingzhou; Zou, Qin

2017-01-01

Rail surface defects such as the abrasion, scratch and peeling often cause damages to the train wheels and rail bearings. An efficient and accurate detection of rail defects is of vital importance for the safety of railway transportation. In the past few decades, automatic rail defect detection has been studied; however, most developed methods use optic-imaging techniques to collect the rail surface data and are still suffering from a high false recognition rate. In this paper, a novel 3D laser profiling system (3D-LPS) is proposed, which integrates a laser scanner, odometer, inertial measurement unit (IMU) and global position system (GPS) to capture the rail surface profile data. For automatic defect detection, first, the deviation between the measured profile and a standard rail model profile is computed for each laser-imaging profile, and the points with large deviations are marked as candidate defect points. Specifically, an adaptive iterative closest point (AICP) algorithm is proposed to register the point sets of the measured profile with the standard rail model profile, and the registration precision is improved to the sub-millimeter level. Second, all of the measured profiles are combined together to form the rail surface through a high-precision positioning process with the IMU, odometer and GPS data. Third, the candidate defect points are merged into candidate defect regions using the K-means clustering. At last, the candidate defect regions are classified by a decision tree classifier. Experimental results demonstrate the effectiveness of the proposed laser-profiling system in rail surface defect detection and classification. PMID:28777323

On the interplay of point defects and Cd in non-polar ZnCdO films

NASA Astrophysics Data System (ADS)

Zubiaga, A.; Reurings, F.; Tuomisto, F.; Plazaola, F.; García, J. A.; Kuznetsov, A. Yu.; Egger, W.; Zúñiga-Pérez, J.; Muñoz-Sanjosé, V.

2013-01-01

Non-polar ZnCdO films, grown over m- and r-sapphire with a Cd concentration ranging between 0.8% and 5%, have been studied by means of slow positron annihilation spectroscopy (PAS) combined with chemical depth profiling by secondary ion mass spectroscopy and Rutherford back-scattering. Vacancy clusters and Zn vacancies with concentrations up to 1017 cm-3 and 1018 cm-3, respectively, have been measured inside the films. Secondary ion mass spectroscopy results show that most Cd stays inside the ZnCdO film but the diffused atoms can penetrate up to 1.3 μm inside the ZnO buffer. PAS results give an insight to the structure of the meta-stable ZnCdO above the thermodynamical solubility limit of 2%. A correlation between the concentration of vacancy clusters and Cd has been measured. The concentration of Zn vacancies is one order of magnitude larger than in as-grown non-polar ZnO films and the vacancy cluster are, at least partly, created by the aggregation of smaller Zn vacancy related defects. The Zn vacancy related defects and the vacancy clusters accumulate around the Cd atoms as a way to release the strain induced by the substitutional CdZn in the ZnO crystal.

Enthalpy Landscape Dictates the Irradiation-Induced Disordering of Quartz

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

Krishnan, N. M. Anoop; Wang, Bu; Yu, Yingtian

Here, under irradiation, minerals tend to experience an accumulation of structural defects, ultimately leading to a disordered atomic network. Despite the critical importance of understanding and predicting irradiation-induced damage, the physical origin of the initiation and saturation of defects remains poorly understood. Here, based on molecular dynamics simulations of α-quartz, we show that the topography of the enthalpy landscape governs irradiation-induced disordering. Specifically, we show that such disordering differs from that observed upon vitrification in that, prior to saturation, irradiated quartz accesses forbidden regions of the enthalpy landscape, i.e., those that are inaccessible by simply heating and cooling. Furthermore, wemore » demonstrate that damage saturates when the system accesses a local region of the enthalpy landscape corresponding to the configuration of an allowable liquid. At this stage, a sudden decrease in the heights of the energy barriers enhances relaxation, thereby preventing any further accumulation of defects and resulting in a defect-saturated disordered state.« less

Enthalpy Landscape Dictates the Irradiation-Induced Disordering of Quartz

DOE PAGES

Krishnan, N. M. Anoop; Wang, Bu; Yu, Yingtian; ...

2017-07-28

Here, under irradiation, minerals tend to experience an accumulation of structural defects, ultimately leading to a disordered atomic network. Despite the critical importance of understanding and predicting irradiation-induced damage, the physical origin of the initiation and saturation of defects remains poorly understood. Here, based on molecular dynamics simulations of α-quartz, we show that the topography of the enthalpy landscape governs irradiation-induced disordering. Specifically, we show that such disordering differs from that observed upon vitrification in that, prior to saturation, irradiated quartz accesses forbidden regions of the enthalpy landscape, i.e., those that are inaccessible by simply heating and cooling. Furthermore, wemore » demonstrate that damage saturates when the system accesses a local region of the enthalpy landscape corresponding to the configuration of an allowable liquid. At this stage, a sudden decrease in the heights of the energy barriers enhances relaxation, thereby preventing any further accumulation of defects and resulting in a defect-saturated disordered state.« less

A Computational Framework for Automation of Point Defect Calculations

NASA Astrophysics Data System (ADS)

Goyal, Anuj; Gorai, Prashun; Peng, Haowei; Lany, Stephan; Stevanovic, Vladan; National Renewable Energy Laboratory, Golden, Colorado 80401 Collaboration

A complete and rigorously validated open-source Python framework to automate point defect calculations using density functional theory has been developed. The framework provides an effective and efficient method for defect structure generation, and creation of simple yet customizable workflows to analyze defect calculations. The package provides the capability to compute widely accepted correction schemes to overcome finite-size effects, including (1) potential alignment, (2) image-charge correction, and (3) band filling correction to shallow defects. Using Si, ZnO and In2O3as test examples, we demonstrate the package capabilities and validate the methodology. We believe that a robust automated tool like this will enable the materials by design community to assess the impact of point defects on materials performance. National Renewable Energy Laboratory, Golden, Colorado 80401.

Point defect weakened thermal contraction in monolayer graphene

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

Zha, Xian-Hu; Department of Physics, University of Science and Technology of China, Hefei; USTC-CityU Joint Advanced Research Centre, Suzhou 215123

We investigate the thermal expansion behaviors of monolayer graphene and three configurations of graphene with point defects, namely the replacement of one carbon atom with a boron or nitrogen atom, or of two neighboring carbon atoms by boron-nitrogen atoms, based on calculations using first-principles density functional theory. It is found that the thermal contraction of monolayer graphene is significantly decreased by point defects. Moreover, the corresponding temperature for negative linear thermal expansion coefficient with the maximum absolute value is reduced. The cause is determined to be point defects that enhance the mechanical strength of graphene and then reduce the amplitudemore » and phonon frequency of the out-of-plane acoustic vibration mode. Such defect weakening of graphene thermal contraction will be useful in nanotechnology to diminish the mismatching or strain between the graphene and its substrate.« less

Cyclic deformation leads to defect healing and strengthening of small-volume metal crystals

DOE PAGES

Wang, Zhang-Jie; Li, Qing-Jie; Cui, Yi-Nan; ...

2015-10-19

When microscopic and macroscopic specimens of metals are subjected to cyclic loading, the creation, interaction, and accumulation of defects lead to damage, cracking, and failure. We demonstrate that when aluminum single crystals of submicrometer dimensions are subjected to low-amplitude cyclic deformation at room temperature, the density of preexisting dislocation lines and loops can be dramatically reduced with virtually no change of the overall sample geometry and essentially no permanent plastic strain. Furthermore, this “cyclic healing” of the metal crystal leads to significant strengthening through dramatic reductions in dislocation density, in distinct contrast to conventional cyclic strain hardening mechanisms arising frommore » increases in dislocation density and interactions among defects in microcrystalline and macrocrystalline metals and alloys. Our real-time, in situ transmission electron microscopy observations of tensile tests reveal that pinned dislocation lines undergo shakedown during cyclic straining, with the extent of dislocation unpinning dependent on the amplitude, sequence, and number of strain cycles. Those unpinned mobile dislocations moving close enough to the free surface of the thin specimens as a result of such repeated straining are then further attracted to the surface by image forces that facilitate their egress from the crystal. Our results point to a versatile pathway for controlled mechanical annealing and defect engineering in submicrometer-sized metal crystals, thereby obviating the need for thermal annealing or significant plastic deformation that could cause change in shape and/or dimensions of the specimen.« less

Cyclic deformation leads to defect healing and strengthening of small-volume metal crystals

PubMed Central

Wang, Zhang-Jie; Li, Qing-Jie; Cui, Yi-Nan; Liu, Zhan-Li; Ma, Evan; Li, Ju; Sun, Jun; Zhuang, Zhuo; Dao, Ming; Shan, Zhi-Wei; Suresh, Subra

2015-01-01

When microscopic and macroscopic specimens of metals are subjected to cyclic loading, the creation, interaction, and accumulation of defects lead to damage, cracking, and failure. Here we demonstrate that when aluminum single crystals of submicrometer dimensions are subjected to low-amplitude cyclic deformation at room temperature, the density of preexisting dislocation lines and loops can be dramatically reduced with virtually no change of the overall sample geometry and essentially no permanent plastic strain. This “cyclic healing” of the metal crystal leads to significant strengthening through dramatic reductions in dislocation density, in distinct contrast to conventional cyclic strain hardening mechanisms arising from increases in dislocation density and interactions among defects in microcrystalline and macrocrystalline metals and alloys. Our real-time, in situ transmission electron microscopy observations of tensile tests reveal that pinned dislocation lines undergo shakedown during cyclic straining, with the extent of dislocation unpinning dependent on the amplitude, sequence, and number of strain cycles. Those unpinned mobile dislocations moving close enough to the free surface of the thin specimens as a result of such repeated straining are then further attracted to the surface by image forces that facilitate their egress from the crystal. These results point to a versatile pathway for controlled mechanical annealing and defect engineering in submicrometer-sized metal crystals, thereby obviating the need for thermal annealing or significant plastic deformation that could cause change in shape and/or dimensions of the specimen. PMID:26483463

Interplay of point defects, biaxial strain, and thermal conductivity in homoepitaxial SrTiO3 thin films

NASA Astrophysics Data System (ADS)

Wiedigen, S.; Kramer, T.; Feuchter, M.; Knorr, I.; Nee, N.; Hoffmann, J.; Kamlah, M.; Volkert, C. A.; Jooss, Ch.

2012-02-01

Separating out effects of point defects and lattice strain on thermal conductivity is essential for improvement of thermoelectric properties of SrTiO3. We study relations between defects generated during deposition, induced lattice strain, and their impact on thermal conductivity κ in homoepitaxial SrTiO3 films prepared by ion-beam sputtering. Lowering the deposition temperature gives rise to lattice expansion by enhancement of point defect density which increases the hardness of the films. Due to a fully coherent substrate-film interface, the lattice misfit induces a large biaxial strain. However, we can show that the temperature dependence of κ is mainly sensitive on the defect concentration.

EFFECTS OF ETHANOL AND HYDROGEN PEROXIDE ON MOUSE LIMB BUD MESENCHYME DIFFERENTIATION AND CELL DEATH

EPA Science Inventory

Many of the morphological defects associated with embryonic alcohol exposure are a result of cell death. During limb development, ethanol administration produces cell death in the limb and digital defects, including postaxial ectrodactyly. Because an accumulation of reactive oxyg...

Nanoscale interfacial defect shedding in a growing nematic droplet.

PubMed

Gurevich, Sebastian; Provatas, Nikolas; Rey, Alejandro

2017-08-01

Interfacial defect shedding is the most recent known mechanism for defect formation in a thermally driven isotropic-to-nematic phase transition. It manifests in nematic-isotropic interfaces going through an anchoring switch. Numerical computations in planar geometry established that a growing nematic droplet can undergo interfacial defect shedding, nucleating interfacial defect structures that shed into the bulk as +1/2 point defects. By extending the study of interfacial defect shedding in a growing nematic droplet to larger length and time scales, and to three dimensions, we unveil an oscillatory growth mode involving shape and anchoring transitions that results in a controllable regular distributions of point defects in planar geometry, and complex structures of disclination lines in three dimensions.

Complex Interaction Mechanisms between Dislocations and Point Defects Studied in Pure Aluminium by a Two-Wave Acoustic Coupling Technique

NASA Astrophysics Data System (ADS)

Bremnes, O.; Progin, O.; Gremaud, G.; Benoit, W.

1997-04-01

Ultrasonic experiments using a two-wave coupling technique were performed on 99.999% pure Al in order to study the interaction mechanisms occurring between dislocations and point defects. The coupling technique consists in measuring the attenuation of ultrasonic waves during low-frequency stress cycles (t). One obtains closed curves () called signatures whose shape and evolution are characteristic of the interaction mechanism controlling the low-frequency dislocation motion. The signatures observed were attributed to the interaction of the dislocations with extrinsic point defects. A new interpretation of the evolution of the signatures measured below 200 K with respect to temperature and stress frequency had to be established: they are linked to depinning of immobile point defects, whereas a thermally activated depinning mechanism does not fit the observations. The signatures measured between 200 and 370 K were interpreted as dragging and depinning of extrinsic point defects which are increasingly mobile with temperature.

Asymmetric interaction of point defects and heterophase interfaces in ZrN/TaN multilayered nanofilms.

PubMed

Lao, Yuanxia; Hu, Shuanglin; Shi, Yunlong; Deng, Yu; Wang, Fei; Du, Hao; Zhang, Haibing; Wang, Yuan

2017-01-05

Materials with a high density of heterophase interfaces, which are capable of absorbing and annihilating radiation-induced point defects, can exhibit a superior radiation tolerance. In this paper, we investigated the interaction behaviors of point defects and heterophase interfaces by implanting helium atoms into the ZrN/TaN multilayered nanofilms. It was found that the point defect-interface interaction on the two sides of the ZrN/TaN interface was asymmetric, likely due to the difference in the vacancy formation energies of ZrN and TaN. The helium bubbles could migrate from the ZrN layers into the TaN layers through the heterophase interfaces, resulting in a better crystallinity of the ZrN layers and a complete amorphization of the TaN layers. The findings provided some clues to the fundamental behaviors of point defects near the heterophase interfaces, which make us re-examine the design rules of advanced radiation-tolerant materials.

Asymmetric interaction of point defects and heterophase interfaces in ZrN/TaN multilayered nanofilms

NASA Astrophysics Data System (ADS)

Lao, Yuanxia; Hu, Shuanglin; Shi, Yunlong; Deng, Yu; Wang, Fei; Du, Hao; Zhang, Haibing; Wang, Yuan

2017-01-01

Materials with a high density of heterophase interfaces, which are capable of absorbing and annihilating radiation-induced point defects, can exhibit a superior radiation tolerance. In this paper, we investigated the interaction behaviors of point defects and heterophase interfaces by implanting helium atoms into the ZrN/TaN multilayered nanofilms. It was found that the point defect-interface interaction on the two sides of the ZrN/TaN interface was asymmetric, likely due to the difference in the vacancy formation energies of ZrN and TaN. The helium bubbles could migrate from the ZrN layers into the TaN layers through the heterophase interfaces, resulting in a better crystallinity of the ZrN layers and a complete amorphization of the TaN layers. The findings provided some clues to the fundamental behaviors of point defects near the heterophase interfaces, which make us re-examine the design rules of advanced radiation-tolerant materials.

Asymmetric interaction of point defects and heterophase interfaces in ZrN/TaN multilayered nanofilms

PubMed Central

Lao, Yuanxia; Hu, Shuanglin; Shi, Yunlong; Deng, Yu; Wang, Fei; Du, Hao; Zhang, Haibing; Wang, Yuan

2017-01-01

Materials with a high density of heterophase interfaces, which are capable of absorbing and annihilating radiation-induced point defects, can exhibit a superior radiation tolerance. In this paper, we investigated the interaction behaviors of point defects and heterophase interfaces by implanting helium atoms into the ZrN/TaN multilayered nanofilms. It was found that the point defect-interface interaction on the two sides of the ZrN/TaN interface was asymmetric, likely due to the difference in the vacancy formation energies of ZrN and TaN. The helium bubbles could migrate from the ZrN layers into the TaN layers through the heterophase interfaces, resulting in a better crystallinity of the ZrN layers and a complete amorphization of the TaN layers. The findings provided some clues to the fundamental behaviors of point defects near the heterophase interfaces, which make us re-examine the design rules of advanced radiation-tolerant materials. PMID:28053307

Change in Imaging Findings on Angiography-Assisted CT During Balloon-Occluded Transcatheter Arterial Chemoembolization for Hepatocellular Carcinoma

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

Yoshimatsu, Rika; Yamagami, Takuji, E-mail: yamagami@kochi-u.ac.jp; Ishikawa, Masaki

2016-06-15

PurposeTo evaluate changes in imaging findings on CT during hepatic arteriography (CTHA) and CT during arterial portography (CTAP) by balloon occlusion of the treated artery and their relationship with iodized oil accumulation in the tumor during balloon-occluded transcatheter arterial chemoembolization (B-TACE).MethodsBoth B-TACE and angiography-assisted CT were performed for 27 hepatocellular carcinomas. Tumor enhancement on selective CTHA with/without balloon occlusion and iodized oil accumulation after B-TACE were evaluated. Tumorous portal perfusion defect size on CTAP was compared with/without balloon occlusion. Factors influencing discrepancies between selective CTHA with/without balloon occlusion and the degree of iodized oil accumulation were investigated.ResultsAmong 27 tumors, tumormore » enhancement on selective CTHA changed after balloon occlusion in 14 (decreased, 11; increased, 3). In 18 tumors, there was a discrepancy between tumor enhancement on selective CTHA with balloon occlusion and the degree of accumulated iodized oil, which was higher than the tumor enhancement grade in all 18. The tumorous portal perfusion defect on CTAP significantly decreased after balloon occlusion in 18 of 20 tumors (mean decrease from 21.9 to 19.1 mm in diameter; p = 0.0001). No significant factors influenced discrepancies between selective CTHA with/without balloon occlusion. Central area tumor location, poor tumor enhancement on selective CTHA with balloon occlusion, and no decrease in the tumorous portal perfusion defect area on CTAP after balloon occlusion significantly influenced poor iodized oil accumulation in the tumor.ConclusionsTumor enhancement on selective CTHA frequently changed after balloon occlusion, which did not correspond to accumulated iodized oil in most cases.« less

The pmr gene, encoding a Ca2+-ATPase, is required for calcium and manganese homeostasis and normal development of hyphae and conidia in Neurospora crassa.

PubMed

Bowman, Barry J; Abreu, Stephen; Johl, Jessica K; Bowman, Emma Jean

2012-11-01

The pmr gene is predicted to encode a Ca(2+)-ATPase in the secretory pathway. We examined two strains of Neurospora crassa that lacked PMR: the Δpmr strain, in which pmr was completely deleted, and pmr(RIP), in which the gene was extensively mutated. Both strains had identical, complex phenotypes. Compared to the wild type, these strains required high concentrations of calcium or manganese for optimal growth and had highly branched, slow-growing hyphae. They conidiated poorly, and the shape and size of the conidia were abnormal. Calcium accumulated in the Δpmr strains to only 20% of the wild-type level. High concentrations of MnCl(2) (1 to 5 mM) in growth medium partially suppressed the morphological defects but did not alter the defect in calcium accumulation. The Δpmr Δnca-2 double mutant (nca-2 encodes a Ca(2+)-ATPase in the plasma membrane) accumulated 8-fold more calcium than the wild type, and the morphology of the hyphae was more similar to that of wild-type hyphae. Previous experiments failed to show a function for nca-1, which encodes a SERCA-type Ca(2+)-ATPase in the endoplasmic reticulum (B. J. Bowman, S. Abreu, E. Margolles-Clark, M. Draskovic, and E. J. Bowman, Eukaryot. Cell 10:654-661, 2011). The pmr(RIP) Δnca-1 double mutant accumulated small amounts of calcium, like the Δpmr strain, but exhibited even more extreme morphological defects. Thus, PMR can apparently replace NCA-1 in the endoplasmic reticulum, but NCA-1 cannot replace PMR. The morphological defects in the Δpmr strain are likely caused, in part, by insufficient concentrations of calcium and manganese in the Golgi compartment; however, PMR is also needed to accumulate normal levels of calcium in the whole cell.

Caenorhabditis elegans flamingo cadherin fmi-1 regulates GABAergic neuronal development.

PubMed

Najarro, Elvis Huarcaya; Wong, Lianna; Zhen, Mei; Carpio, Edgar Pinedo; Goncharov, Alexandr; Garriga, Gian; Lundquist, Erik A; Jin, Yishi; Ackley, Brian D

2012-03-21

In a genetic screen for regulators of synaptic morphology, we identified the single Caenorhabditis elegans flamingo-like cadherin fmi-1. The fmi-1 mutants exhibit defective axon pathfinding, reduced synapse number, aberrant synapse size and morphology, as well as an abnormal accumulation of synaptic vesicles at nonsynaptic regions. Although FMI-1 is primarily expressed in the nervous system, it is not expressed in the ventral D-type (VD) GABAergic motorneurons, which are defective in fmi-1 mutants. The axon and synaptic defects of VD neurons could be rescued when fmi-1 was expressed exclusively in non-VD neighboring neurons, suggesting a cell nonautonomous action of FMI-1. FMI-1 protein that lacked its intracellular domain still retained its ability to rescue the vesicle accumulation defects of GABAergic motorneurons, indicating that the extracellular domain was sufficient for this function of FMI-1 in GABAergic neuromuscular junction development. Mutations in cdh-4, a Fat-like cadherin, cause similar defects in GABAergic motorneurons. The cdh-4 is expressed by the VD neurons and seems to function in the same genetic pathway as fmi-1 to regulate GABAergic neuron development. Thus, fmi-1 and cdh-4 cadherins might act together to regulate synapse development and axon pathfinding.

The Interface Influence in TiN/SiN x Multilayer Nanocomposite Under Irradiation

NASA Astrophysics Data System (ADS)

Uglov, V. V.; Safronov, I. V.; Kvasov, N. T.; Remnev, G. E.; Shimanski, V. I.

2018-01-01

The paper focuses on studying the kinetics of radiation-induced point defects formed in TiN/SiN x multilayer nanocomposites with account of their generation, diffusion recombination, and the influence of sinks functioning as interfaces. In order to describe the kinetics in nanocrystalline TiN and amorphous SiN x phases, a finite-difference method is used to solve the system of balance kinetic equations for absolute defect concentrations depending on the spatiotemporal variables. A model of the disclination-dislocation interface structure is used to study the absorption of radiation-induced point defects on the boundaries in created stress fields. It is shown that the interface effectively absorbs point defects in these phases of TiN/SiN x multilayer nanocomposite, thereby reducing their amount within the space between phases. This behavior of point defects partially explains a mechanism of the radiation resistance in this type of nanocomposites.

Three-dimensional imaging of individual point defects using selective detection angles in annular dark field scanning transmission electron microscopy.

PubMed

Johnson, Jared M; Im, Soohyun; Windl, Wolfgang; Hwang, Jinwoo

2017-01-01

We propose a new scanning transmission electron microscopy (STEM) technique that can realize the three-dimensional (3D) characterization of vacancies, lighter and heavier dopants with high precision. Using multislice STEM imaging and diffraction simulations of β-Ga 2 O 3 and SrTiO 3 , we show that selecting a small range of low scattering angles can make the contrast of the defect-containing atomic columns substantially more depth-dependent. The origin of the depth-dependence is the de-channeling of electrons due to the existence of a point defect in the atomic column, which creates extra "ripples" at low scattering angles. The highest contrast of the point defect can be achieved when the de-channeling signal is captured using the 20-40mrad detection angle range. The effect of sample thickness, crystal orientation, local strain, probe convergence angle, and experimental uncertainty to the depth-dependent contrast of the point defect will also be discussed. The proposed technique therefore opens new possibilities for highly precise 3D structural characterization of individual point defects in functional materials. Copyright © 2016 Elsevier B.V. All rights reserved.

Defect Genome of Cubic Perovskites for Fuel Cell Applications

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

Balachandran, Janakiraman; Lin, Lianshan; Anchell, Jonathan S.

Heterogeneities such as point defects, inherent to material systems, can profoundly influence material functionalities critical for numerous energy applications. This influence in principle can be identified and quantified through development of large defect data sets which we call the defect genome, employing high-throughput ab initio calculations. However, high-throughput screening of material models with point defects dramatically increases the computational complexity and chemical search space, creating major impediments toward developing a defect genome. In this paper, we overcome these impediments by employing computationally tractable ab initio models driven by highly scalable workflows, to study formation and interaction of various point defectsmore » (e.g., O vacancies, H interstitials, and Y substitutional dopant), in over 80 cubic perovskites, for potential proton-conducting ceramic fuel cell (PCFC) applications. The resulting defect data sets identify several promising perovskite compounds that can exhibit high proton conductivity. Furthermore, the data sets also enable us to identify and explain, insightful and novel correlations among defect energies, material identities, and defect-induced local structural distortions. Finally, such defect data sets and resultant correlations are necessary to build statistical machine learning models, which are required to accelerate discovery of new materials.« less

Defect Genome of Cubic Perovskites for Fuel Cell Applications

DOE PAGES

Balachandran, Janakiraman; Lin, Lianshan; Anchell, Jonathan S.; ...

2017-10-10

Heterogeneities such as point defects, inherent to material systems, can profoundly influence material functionalities critical for numerous energy applications. This influence in principle can be identified and quantified through development of large defect data sets which we call the defect genome, employing high-throughput ab initio calculations. However, high-throughput screening of material models with point defects dramatically increases the computational complexity and chemical search space, creating major impediments toward developing a defect genome. In this paper, we overcome these impediments by employing computationally tractable ab initio models driven by highly scalable workflows, to study formation and interaction of various point defectsmore » (e.g., O vacancies, H interstitials, and Y substitutional dopant), in over 80 cubic perovskites, for potential proton-conducting ceramic fuel cell (PCFC) applications. The resulting defect data sets identify several promising perovskite compounds that can exhibit high proton conductivity. Furthermore, the data sets also enable us to identify and explain, insightful and novel correlations among defect energies, material identities, and defect-induced local structural distortions. Finally, such defect data sets and resultant correlations are necessary to build statistical machine learning models, which are required to accelerate discovery of new materials.« less

Point defects in CdTe xSe 1-x crystals grown from a Te-rich solution for applications in detecting radiation

DOE PAGES

Gul, R.; Roy, U. N.; Bolotnikov, A. E.; ...

2015-04-15

We investigated cadmium telluride selenide (CdTeSe) crystals, newly grown by the Traveling Heater Method (THM), for the presence and abundance of point defects. Deep Level Transient spectroscopy (I-DLTS) was used to determine the energies of the traps, their capture cross sections, and densities. The bias across the detectors was varied from (1–30) V. Four types of point defects were identified, ranging from 10 meV to 0.35 eV. Two dominant traps at energies of 0.18 eV and 0.14 eV were studied in depth. Cd vacancies are found at lower concentrations than other point defects present in the material.

Use of Isobestic and Isoemission Points in Absorption and Luminescence Spectra for Study of the Transformation of Radiation Defects in Lithium Fluoride

NASA Astrophysics Data System (ADS)

Voitovich, A. P.; Kalinov, V. S.; Stupak, A. P.; Runets, L. P.

2015-03-01

Isobestic and isoemission points are recorded in the combined absorption and luminescence spectra of two types of radiation defects involved in complex processes consisting of several simultaneous parallel and sequential reactions. These points are observed if a constant sum of two terms, each formed by the product of the concentration of the corresponding defect and a characteristic integral coefficient associated with it, is conserved. The complicated processes involved in the transformation of radiation defects in lithium fluoride are studied using these points. It is found that the ratio of the changes in the concentrations of one of the components and the reaction product remains constant in the course of several simultaneous reactions.

Cascades in model steels: The effect of cementite (Fe3C) and Cr23C6 particles on short-term crystal damage

NASA Astrophysics Data System (ADS)

Henriksson, K. O. E.

2015-06-01

Ferritic stainless steel can be modeled as an iron matrix containing precipitates of cementite (Fe3C) and Cr23C6. When used in nuclear power production the steels in the vicinity of the core start to accumulate damage due to neutrons. The role of the afore-mentioned carbides in this process is not well understood. In order to clarify the situation bulk cascades created by primary recoils in model steels have been carried out in the present work. Investigated configurations consisted of bulk ferrite containing spherical particles (diameter of 4 nm) of either (1) Fe3C or (2) Cr23C6. Primary recoils were initiated at different distances from the inclusions, with recoil energies varying between 100 eV and 1 keV. Results for the number of point defects such as vacancies and antisites are presented. These findings indicate that defects are also remaining when cascades are started outside the carbide inclusions. The work uses a recently developed Abell-Brenner-Tersoff potential for the Fe-Cr-C system.

Characterization of point defects in monolayer arsenene

NASA Astrophysics Data System (ADS)

Liang, Xiongyi; Ng, Siu-Pang; Ding, Ning; Wu, Chi-Man Lawrence

2018-06-01

Topological defects that are inevitably found in 2D materials can dramatically affect their properties. Using density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) method, the structural, thermodynamic, electronic and magnetic properties of six types of typical point defects in arsenene, i.e. the Stone-Wales defect, single and double vacancies and adatoms, were systemically studied. It was found that these defects were all more easily generated in arsenene with lower formation energies than those with graphene and silicene. Stone-Wales defects can be transformed from pristine arsenene by overcoming a barrier of 2.19 eV and single vacancy defects tend to coalesce into double vacancy defects by diffusion. However, a type of adatom defect does not exhibit kinetic stability at room temperature. In addition, SV defects and another type of adatom defect can remarkably affect the electronic and magnetic properties of arsenene, e.g. they can introduce localized states near the Fermi level, as well as a strongly local magnetic moment due to dangling bond and unpaired electron. Furthermore, the simulated scanning tunneling microscopy (STM) and Raman spectroscopy were computed and the types of point defects can be fully characterized by correlating the STM images and Raman spectra to the defective atomistic structures. The results provide significant insights to the effect of defects in arsenene for potential applications, as well as identifications of two helpful tools (STM and Raman spectroscopy) to distinguish the type of defects in arsenene for future experiments.

Effect of point defects on the electronic density states of SnC nanosheets: First-principles calculations

NASA Astrophysics Data System (ADS)

Majidi, Soleyman; Achour, Amine; Rai, D. P.; Nayebi, Payman; Solaymani, Shahram; Beryani Nezafat, Negin; Elahi, Seyed Mohammad

In this work, we investigated the electronic and structural properties of various defects including single Sn and C vacancies, double vacancy of the Sn and C atoms, anti-sites, position exchange and the Stone-Wales (SW) defects in SnC nanosheets by using density-functional theory (DFT). We found that various vacancy defects in the SnC monolayer can change the electronic and structural properties. Our results show that the SnC is an indirect band gap compound, with the band gap of 2.10 eV. The system turns into metal for both structure of the single Sn and C vacancies. However, for the double vacancy contained Sn and C atoms, the structure remains semiconductor with the direct band gap of 0.37 eV at the G point. We also found that for anti-site defects, the structure remains semiconductor and for the exchange defect, the structure becomes indirect semiconductor with the K-G point and the band gap of 0.74 eV. Finally, the structure of SW defect remains semiconductor with the direct band gap at K point with band gap of 0.54 eV.

A Method for Automatic Surface Inspection Using a Model-Based 3D Descriptor.

PubMed

Madrigal, Carlos A; Branch, John W; Restrepo, Alejandro; Mery, Domingo

2017-10-02

Automatic visual inspection allows for the identification of surface defects in manufactured parts. Nevertheless, when defects are on a sub-millimeter scale, detection and recognition are a challenge. This is particularly true when the defect generates topological deformations that are not shown with strong contrast in the 2D image. In this paper, we present a method for recognizing surface defects in 3D point clouds. Firstly, we propose a novel 3D local descriptor called the Model Point Feature Histogram (MPFH) for defect detection. Our descriptor is inspired from earlier descriptors such as the Point Feature Histogram (PFH). To construct the MPFH descriptor, the models that best fit the local surface and their normal vectors are estimated. For each surface model, its contribution weight to the formation of the surface region is calculated and from the relative difference between models of the same region a histogram is generated representing the underlying surface changes. Secondly, through a classification stage, the points on the surface are labeled according to five types of primitives and the defect is detected. Thirdly, the connected components of primitives are projected to a plane, forming a 2D image. Finally, 2D geometrical features are extracted and by a support vector machine, the defects are recognized. The database used is composed of 3D simulated surfaces and 3D reconstructions of defects in welding, artificial teeth, indentations in materials, ceramics and 3D models of defects. The quantitative and qualitative results showed that the proposed method of description is robust to noise and the scale factor, and it is sufficiently discriminative for detecting some surface defects. The performance evaluation of the proposed method was performed for a classification task of the 3D point cloud in primitives, reporting an accuracy of 95%, which is higher than for other state-of-art descriptors. The rate of recognition of defects was close to 94%.

A Method for Automatic Surface Inspection Using a Model-Based 3D Descriptor

PubMed Central

Branch, John W.

2017-01-01

Automatic visual inspection allows for the identification of surface defects in manufactured parts. Nevertheless, when defects are on a sub-millimeter scale, detection and recognition are a challenge. This is particularly true when the defect generates topological deformations that are not shown with strong contrast in the 2D image. In this paper, we present a method for recognizing surface defects in 3D point clouds. Firstly, we propose a novel 3D local descriptor called the Model Point Feature Histogram (MPFH) for defect detection. Our descriptor is inspired from earlier descriptors such as the Point Feature Histogram (PFH). To construct the MPFH descriptor, the models that best fit the local surface and their normal vectors are estimated. For each surface model, its contribution weight to the formation of the surface region is calculated and from the relative difference between models of the same region a histogram is generated representing the underlying surface changes. Secondly, through a classification stage, the points on the surface are labeled according to five types of primitives and the defect is detected. Thirdly, the connected components of primitives are projected to a plane, forming a 2D image. Finally, 2D geometrical features are extracted and by a support vector machine, the defects are recognized. The database used is composed of 3D simulated surfaces and 3D reconstructions of defects in welding, artificial teeth, indentations in materials, ceramics and 3D models of defects. The quantitative and qualitative results showed that the proposed method of description is robust to noise and the scale factor, and it is sufficiently discriminative for detecting some surface defects. The performance evaluation of the proposed method was performed for a classification task of the 3D point cloud in primitives, reporting an accuracy of 95%, which is higher than for other state-of-art descriptors. The rate of recognition of defects was close to 94%. PMID:28974037

Optically inactive defects in monolayer and bilayer phosphorene: A first-principles study

NASA Astrophysics Data System (ADS)

Huang, Ling-yi; Zhang, Xu; Zhang, Mingliang; Lu, Gang

2018-05-01

Many-body excitonic effect is crucial in two-dimensional (2D) materials and can significantly impact their optoelectronic properties. Because defects are inevitable in 2D materials, understanding how they influence the optical and excitonic properties of the 2D materials is of significant scientific and technological importance. Here we focus on intrinsic point defects in monolayer and bilayer phosphorene and examine whether and how their optoelectronic properties may be modified by the defects. Based on large-scale first-principles calculations, we have systematically explored the optical and excitonic properties of phosphorene in the presence and absence of the point defects. We find that the optical properties of bilayer phosphorene depend on the stacking order of the layers. More importantly, we reveal that the dominant point defects in few-layer phosphorene are optically inactive, which renders phosphorene particularly attractive in optoelectronic applications.

Characterization of Local Carrier Dynamics in AlN and AlGaN Films using High Spatial- and Time-resolution Cathodoluminescence Spectroscopy

DTIC Science & Technology

2012-10-12

21/2012 Abstract: In order to assess the impacts of structural and point defects on the local carrier (exciton) recombination dynamics in...quantitatively understood as functions of structural / point defect and impurity concentrations (crystal imperfections). However, only few papers [5...NOTES 14. ABSTRACT In order to assess the impacts of structural and point defects on the local carrier (exciton) recombination dynamics in wide bandgap

Toward understanding dynamic annealing processes in irradiated ceramics

NASA Astrophysics Data System (ADS)

Myers, Michael Thomas

High energy particle irradiation inevitably generates defects in solids in the form of collision cascades. The ballistic formation and thermalization of cascades occur rapidly and are believed to be reasonably well understood. However, knowledge of the evolution of defects after damage cascade thermalization, referred to as dynamic annealing, is quite limited. Unraveling the mechanisms associated with dynamic an- nealing is crucial since such processes play an important role in the formation of stable post-irradiation disorder in ion-beam-processed semiconductors and determines the "radiation tolerance" of many nuclear materials. The purpose of this dissertation is to further our understanding of the processes involved in dynamic annealing. In order to achieve this, two main tasks are undertaken. First, the effects of dynamic annealing are investigated in ZnO, a technologically relevant material that exhibits very high dynamic defect annealing at room temper- ature. Such high dynamic annealing leads to unusual defect accumulation in heavy ion bombarded ZnO. Through this work, the puzzling features that were observed more than a decade ago in ion-channeling spectra have finally been explained. We show that the presence of a polar surface substantially alters damage accumulation. Non-polar surface terminations of ZnO are shown to exhibit enhanced dynamic an- nealing compared to polar surface terminated ZnO. Additionally, we demonstrate one method to reduce radiation damage in polar surface terminated ZnO by means of a surface modification. These results advance our efforts in the long-sought-after goal of understanding complex radiation damage processes in ceramics. Second, a pulsed-ion-beam method is developed and demonstrated in the case of Si as a prototypical non-metallic target. Such a method is shown to be a novel experimental technique for direct extraction of dynamic annealing parameters. The relaxation times and effective diffusion lengths of mobile defects during the dynamic annealing process play a vital role in damage accumulation. We demonstrate that these parameters dominate the formation of stable post-irradiation disorder. In Si, a defect lifetime of ˜ 6 ms and a characteristic defect diffusion length of ˜ 30 nm are measured. These results should nucleate future pulsed-beam studies of dynamic defect interaction processes in technologically relevant materials. In particular, un- derstanding length- and time-scales of defect interactions are essential for extending laboratory findings to nuclear material lifetimes and to the time-scales of geological storage of nuclear waste.

Modeling a distribution of point defects as misfitting inclusions in stressed solids

NASA Astrophysics Data System (ADS)

Cai, W.; Sills, R. B.; Barnett, D. M.; Nix, W. D.

2014-05-01

The chemical equilibrium distribution of point defects modeled as non-overlapping, spherical inclusions with purely positive dilatational eigenstrain in an isotropically elastic solid is derived. The compressive self-stress inside existing inclusions must be excluded from the stress dependence of the equilibrium concentration of the point defects, because it does no work when a new inclusion is introduced. On the other hand, a tensile image stress field must be included to satisfy the boundary conditions in a finite solid. Through the image stress, existing inclusions promote the introduction of additional inclusions. This is contrary to the prevailing approach in the literature in which the equilibrium point defect concentration depends on a homogenized stress field that includes the compressive self-stress. The shear stress field generated by the equilibrium distribution of such inclusions is proved to be proportional to the pre-existing stress field in the solid, provided that the magnitude of the latter is small, so that a solid containing an equilibrium concentration of point defects can be described by a set of effective elastic constants in the small-stress limit.

Producibility improvements suggested by a validated process model of seeded CdZnTe vertical Bridgman growth

NASA Astrophysics Data System (ADS)

Larson, David J., Jr.; Casagrande, Louis G.; Di Marzio, Don; Levy, Alan; Carlson, Frederick M.; Lee, Taipao; Black, David R.; Wu, Jun; Dudley, Michael

1994-07-01

We have successfully validated theoretical models of seeded vertical Bridgman-Stockbarger CdZnTe crystal growth and post-solidification processing, using in-situ thermal monitoring and innovative material characterization techniques. The models predict the thermal gradients, interface shape, fluid flow and solute redistribution during solidification, as well as the distributions of accumulated excess stress that causes defect generation and redistribution. Data from the furnace and ampoule wall have validated predictions from the thermal model. Results are compared to predictions of the thermal and thermo-solutal models. We explain the measured initial, change-of-rate, and terminal compositional transients as well as the macrosegregation. Macro and micro-defect distributions have been imaged on CdZnTe wafers from 40 mm diameter boules. Superposition of topographic defect images and predicted excess stress patterns suggests the origin of some frequently encountered defects, particularly on a macro scale, to result from the applied and accumulated stress fields and the anisotropic nature of the CdZnTe crystal. Implications of these findings with respect to producibility are discussed.

Luminescence properties of defects in GaN

NASA Astrophysics Data System (ADS)

Reshchikov, Michael A.; Morkoç, Hadis

2005-03-01

Gallium nitride (GaN) and its allied binaries InN and AIN as well as their ternary compounds have gained an unprecedented attention due to their wide-ranging applications encompassing green, blue, violet, and ultraviolet (UV) emitters and detectors (in photon ranges inaccessible by other semiconductors) and high-power amplifiers. However, even the best of the three binaries, GaN, contains many structural and point defects caused to a large extent by lattice and stacking mismatch with substrates. These defects notably affect the electrical and optical properties of the host material and can seriously degrade the performance and reliability of devices made based on these nitride semiconductors. Even though GaN broke the long-standing paradigm that high density of dislocations precludes acceptable device performance, point defects have taken the center stage as they exacerbate efforts to increase the efficiency of emitters, increase laser operation lifetime, and lead to anomalies in electronic devices. The point defects include native isolated defects (vacancies, interstitial, and antisites), intentional or unintentional impurities, as well as complexes involving different combinations of the isolated defects. Further improvements in device performance and longevity hinge on an in-depth understanding of point defects and their reduction. In this review a comprehensive and critical analysis of point defects in GaN, particularly their manifestation in luminescence, is presented. In addition to a comprehensive analysis of native point defects, the signatures of intentionally and unintentionally introduced impurities are addressed. The review discusses in detail the characteristics and the origin of the major luminescence bands including the ultraviolet, blue, green, yellow, and red bands in undoped GaN. The effects of important group-II impurities, such as Zn and Mg on the photoluminescence of GaN, are treated in detail. Similarly, but to a lesser extent, the effects of other impurities, such as C, Si, H, O, Be, Mn, Cd, etc., on the luminescence properties of GaN are also reviewed. Further, atypical luminescence lines which are tentatively attributed to the surface and structural defects are discussed. The effect of surfaces and surface preparation, particularly wet and dry etching, exposure to UV light in vacuum or controlled gas ambient, annealing, and ion implantation on the characteristics of the defect-related emissions is described.

System-size convergence of point defect properties: The case of the silicon vacancy

NASA Astrophysics Data System (ADS)

Corsetti, Fabiano; Mostofi, Arash A.

2011-07-01

We present a comprehensive study of the vacancy in bulk silicon in all its charge states from 2+ to 2-, using a supercell approach within plane-wave density-functional theory, and systematically quantify the various contributions to the well-known finite size errors associated with calculating formation energies and stable charge state transition levels of isolated defects with periodic boundary conditions. Furthermore, we find that transition levels converge faster with respect to supercell size when only the Γ-point is sampled in the Brillouin zone, as opposed to a dense k-point sampling. This arises from the fact that defect level at the Γ-point quickly converges to a fixed value which correctly describes the bonding at the defect center. Our calculated transition levels with 1000-atom supercells and Γ-point only sampling are in good agreement with available experimental results. We also demonstrate two simple and accurate approaches for calculating the valence band offsets that are required for computing formation energies of charged defects, one based on a potential averaging scheme and the other using maximally-localized Wannier functions (MLWFs). Finally, we show that MLWFs provide a clear description of the nature of the electronic bonding at the defect center that verifies the canonical Watkins model.

PyCDT: A Python toolkit for modeling point defects in semiconductors and insulators

DOE PAGES

Broberg, Danny; Medasani, Bharat; Zimmermann, Nils E. R.; ...

2018-02-13

Point defects have a strong impact on the performance of semiconductor and insulator materials used in technological applications, spanning microelectronics to energy conversion and storage. The nature of the dominant defect types, how they vary with processing conditions, and their impact on materials properties are central aspects that determine the performance of a material in a certain application. This information is, however, difficult to access directly from experimental measurements. Consequently, computational methods, based on electronic density functional theory (DFT), have found widespread use in the calculation of point-defect properties. Here we have developed the Python Charged Defect Toolkit (PyCDT) tomore » expedite the setup and post-processing of defect calculations with widely used DFT software. PyCDT has a user-friendly command-line interface and provides a direct interface with the Materials Project database. This allows for setting up many charged defect calculations for any material of interest, as well as post-processing and applying state-of-the-art electrostatic correction terms. Our paper serves as a documentation for PyCDT, and demonstrates its use in an application to the well-studied GaAs compound semiconductor. As a result, we anticipate that the PyCDT code will be useful as a framework for undertaking readily reproducible calculations of charged point-defect properties, and that it will provide a foundation for automated, high-throughput calculations.« less

PyCDT: A Python toolkit for modeling point defects in semiconductors and insulators

NASA Astrophysics Data System (ADS)

Broberg, Danny; Medasani, Bharat; Zimmermann, Nils E. R.; Yu, Guodong; Canning, Andrew; Haranczyk, Maciej; Asta, Mark; Hautier, Geoffroy

2018-05-01

Point defects have a strong impact on the performance of semiconductor and insulator materials used in technological applications, spanning microelectronics to energy conversion and storage. The nature of the dominant defect types, how they vary with processing conditions, and their impact on materials properties are central aspects that determine the performance of a material in a certain application. This information is, however, difficult to access directly from experimental measurements. Consequently, computational methods, based on electronic density functional theory (DFT), have found widespread use in the calculation of point-defect properties. Here we have developed the Python Charged Defect Toolkit (PyCDT) to expedite the setup and post-processing of defect calculations with widely used DFT software. PyCDT has a user-friendly command-line interface and provides a direct interface with the Materials Project database. This allows for setting up many charged defect calculations for any material of interest, as well as post-processing and applying state-of-the-art electrostatic correction terms. Our paper serves as a documentation for PyCDT, and demonstrates its use in an application to the well-studied GaAs compound semiconductor. We anticipate that the PyCDT code will be useful as a framework for undertaking readily reproducible calculations of charged point-defect properties, and that it will provide a foundation for automated, high-throughput calculations.

PyCDT: A Python toolkit for modeling point defects in semiconductors and insulators

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

Broberg, Danny; Medasani, Bharat; Zimmermann, Nils E. R.

Point defects have a strong impact on the performance of semiconductor and insulator materials used in technological applications, spanning microelectronics to energy conversion and storage. The nature of the dominant defect types, how they vary with processing conditions, and their impact on materials properties are central aspects that determine the performance of a material in a certain application. This information is, however, difficult to access directly from experimental measurements. Consequently, computational methods, based on electronic density functional theory DFT), have found widespread use in the calculation of point defect properties. Here we have developed the Python Charged Defect Toolkit (PyCDT)more » to expedite the setup and post-processing of defect calculations with widely used DFT software. PyCDT has a user-friendly command-line interface and provides a direct interface with the Materials Project database. This allows for setting up many charged defect calculations for any material of interest, as well as post-processing and applying state-of-the-art electrostatic correction terms. Our paper serves as a documentation for PyCDT, and demonstrates its use in an application to the well-studied GaAs compound semiconductor. We anticipate that the PyCDT code will be useful as a framework for undertaking readily reproducible calculations of charged point-defect properties, and that it will provide a foundation for automated, high-throughput calculations.« less

PyCDT: A Python toolkit for modeling point defects in semiconductors and insulators

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

Broberg, Danny; Medasani, Bharat; Zimmermann, Nils E. R.

Point defects have a strong impact on the performance of semiconductor and insulator materials used in technological applications, spanning microelectronics to energy conversion and storage. The nature of the dominant defect types, how they vary with processing conditions, and their impact on materials properties are central aspects that determine the performance of a material in a certain application. This information is, however, difficult to access directly from experimental measurements. Consequently, computational methods, based on electronic density functional theory (DFT), have found widespread use in the calculation of point-defect properties. Here we have developed the Python Charged Defect Toolkit (PyCDT) tomore » expedite the setup and post-processing of defect calculations with widely used DFT software. PyCDT has a user-friendly command-line interface and provides a direct interface with the Materials Project database. This allows for setting up many charged defect calculations for any material of interest, as well as post-processing and applying state-of-the-art electrostatic correction terms. Our paper serves as a documentation for PyCDT, and demonstrates its use in an application to the well-studied GaAs compound semiconductor. As a result, we anticipate that the PyCDT code will be useful as a framework for undertaking readily reproducible calculations of charged point-defect properties, and that it will provide a foundation for automated, high-throughput calculations.« less

Line and point defects in nonlinear anisotropic solids

NASA Astrophysics Data System (ADS)

Golgoon, Ashkan; Yavari, Arash

2018-06-01

In this paper, we present some analytical solutions for the stress fields of nonlinear anisotropic solids with distributed line and point defects. In particular, we determine the stress fields of (i) a parallel cylindrically symmetric distribution of screw dislocations in infinite orthotropic and monoclinic media, (ii) a cylindrically symmetric distribution of parallel wedge disclinations in an infinite orthotropic medium, (iii) a distribution of edge dislocations in an orthotropic medium, and (iv) a spherically symmetric distribution of point defects in a transversely isotropic spherical ball.

A DFT study on the failure mechanism of Al2O3 film by various point defects in solution

NASA Astrophysics Data System (ADS)

Zhang, Chuan-Hui; Chen, Bao; Jin, Ying; Sun, Dong-Bai

2018-03-01

The defects on oxide film surface are very important, and they would occur when the film is peeled or scratched. The periodic DFT calculations have been performed on Al2O3 surface to model the influences of various point-defects. Three kinds of point defect surfaces (vacancy, inversion, substitution) are considered, and the molecular H2O dissociation and the transition state are calculated. The predicted formation energy of O vacancy is 8.30 eV, whereas that corresponding to the formation of Al vacancy is found to be at least a 55% larger. On the vacancy point defect surfaces, upward H2O molecule surfaces prefer to occur chemical reaction, leading the surfaces to be hydroxylated. And then the D-Cl-substitution-Al surface is corroded, which suggests a Cl adsorption induced failure mechanism of the oxide film. At last, the process of H2O dissociation on the OH-substitution-Al surfaces with four or five transition paths are discussed.

A Mitochondrial Pyruvate Carrier Required for Pyruvate Uptake in Yeast, Drosophila, and Humans

PubMed Central

Bricker, Daniel K.; Taylor, Eric B.; Schell, John C.; Orsak, Thomas; Boutron, Audrey; Chen, Yu-Chan; Cox, James E.; Cardon, Caleb M.; Van Vranken, Jonathan G.; Dephoure, Noah; Redin, Claire; Boudina, Sihem; Gygi, Steven P.; Brivet, Michèle; Thummel, Carl S.; Rutter, Jared

2013-01-01

Pyruvate constitutes a critical branch point in cellular carbon metabolism. We have identified two proteins, Mpc1 and Mpc2, as essential for mitochondrial pyruvate transport in yeast, Drosophila, and humans. Mpc1 and Mpc2 associate to form an ~150-kilodalton complex in the inner mitochondrial membrane. Yeast and Drosophila mutants lacking MPC1 display impaired pyruvate metabolism, with an accumulation of upstream metabolites and a depletion of tricarboxylic acid cycle intermediates. Loss of yeast Mpc1 results in defective mitochondrial pyruvate uptake, and silencing of MPC1 or MPC2 in mammalian cells impairs pyruvate oxidation. A point mutation in MPC1 provides resistance to a known inhibitor of the mitochondrial pyruvate carrier. Human genetic studies of three families with children suffering from lactic acidosis and hyperpyruvatemia revealed a causal locus that mapped to MPC1, changing single amino acids that are conserved throughout eukaryotes. These data demonstrate that Mpc1 and Mpc2 form an essential part of the mitochondrial pyruvate carrier. PMID:22628558

Point defect reduction in MOCVD (Al)GaN by chemical potential control and a comprehensive model of C incorporation in GaN

NASA Astrophysics Data System (ADS)

Reddy, Pramod; Washiyama, Shun; Kaess, Felix; Kirste, Ronny; Mita, Seiji; Collazo, Ramon; Sitar, Zlatko

2017-12-01

A theoretical framework that provides a quantitative relationship between point defect formation energies and growth process parameters is presented. It enables systematic point defect reduction by chemical potential control in metalorganic chemical vapor deposition (MOCVD) of III-nitrides. Experimental corroboration is provided by a case study of C incorporation in GaN. The theoretical model is shown to be successful in providing quantitative predictions of CN defect incorporation in GaN as a function of growth parameters and provides valuable insights into boundary phases and other impurity chemical reactions. The metal supersaturation is found to be the primary factor in determining the chemical potential of III/N and consequently incorporation or formation of point defects which involves exchange of III or N atoms with the reservoir. The framework is general and may be extended to other defect systems in (Al)GaN. The utility of equilibrium formalism typically employed in density functional theory in predicting defect incorporation in non-equilibrium and high temperature MOCVD growth is confirmed. Furthermore, the proposed theoretical framework may be used to determine optimal growth conditions to achieve minimum compensation within any given constraints such as growth rate, crystal quality, and other practical system limitations.

Unraveling energy conversion modeling in the intrinsic persistent upconverted luminescence of solids: a study of native point defects in antiferromagnetic Er2O3.

PubMed

Huang, Bolong

2016-05-11

We investigated the mechanism of the intrinsic persistent luminescence of Er2O3 in the A-type lattice based on first-principles calculations. We found that the native point defects were engaged in mutual subtle interactions in the form of chemical reactions between different charge states. The release of energy related to lattice distortion facilitates the conversion of energy for electrons to be transported between the valence band and the trap levels or even between the deep trap levels so as to generate persistent luminescence. The defect transitions that take place along the zero-phonon line release energy to enable optical transitions, with the exact amount of negative effective correlation energy determined by the lattice distortions. Our calculations on the thermodynamic transition levels confirm that both the visible and NIR experimentally observed intrinsic persistent luminescence (phosphor or afterglow) are related to the thermodynamic transition levels of oxygen-related defects, and the thermodynamic transition levels within different charge states for these defects are independent of the chemical potentials of the given species. Lattice distortion defects such as anion Frenkel (a-Fr) pair defects play an important role in transporting O-related defects between different lattice sites. To obtain red persistent luminescence that matches the biological therapeutic window, it is suggested to increase the electron transition levels between high-coordinated O vacancies and related metastable a-Fr defects; a close-packed core-shell structure is required to quench low-coordinated O-related defects so as to reduce the green band luminescence. We further established a conversed chain reaction (CCR) model to interpret the energy conversion process of persistent luminescence in terms of the inter-reactions of native point defects between different charge states. It is advantageous to use the study of defect levels combined with formation energies to suggest limits to doping energy and explain photostimulated luminescence in terms of native point defects.

Cystinosin, the small GTPase Rab11, and the Rab7 effector RILP regulate intracellular trafficking of the chaperone-mediated autophagy receptor LAMP2A.

PubMed

Zhang, Jinzhong; Johnson, Jennifer L; He, Jing; Napolitano, Gennaro; Ramadass, Mahalakshmi; Rocca, Celine; Kiosses, William B; Bucci, Cecilia; Xin, Qisheng; Gavathiotis, Evripidis; Cuervo, Ana María; Cherqui, Stephanie; Catz, Sergio D

2017-06-23

The lysosomal storage disease cystinosis, caused by cystinosin deficiency, is characterized by cell malfunction, tissue failure, and progressive renal injury despite cystine-depletion therapies. Cystinosis is associated with defects in chaperone-mediated autophagy (CMA), but the molecular mechanisms are incompletely understood. Here, we show CMA substrate accumulation in cystinotic kidney proximal tubule cells. We also found mislocalization of the CMA lysosomal receptor LAMP2A and impaired substrate translocation into the lysosome caused by defective CMA in cystinosis. The impaired LAMP2A trafficking and localization were rescued either by the expression of wild-type cystinosin or by the disease-associated point mutant CTNS-K280R, which has no cystine transporter activity. Defective LAMP2A trafficking in cystinosis was found to associate with decreased expression of the small GTPase Rab11 and the Rab7 effector RILP. Defective Rab11 trafficking in cystinosis was rescued by treatment with small-molecule CMA activators. RILP expression was restored by up-regulation of the transcription factor EB (TFEB), which was down-regulated in cystinosis. Although LAMP2A expression is independent of TFEB, TFEB up-regulation corrected lysosome distribution and lysosomal LAMP2A localization in Ctns -/- cells but not Rab11 defects. The up-regulation of Rab11, Rab7, or RILP, but not its truncated form RILP-C33, rescued LAMP2A-defective trafficking in cystinosis, whereas dominant-negative Rab11 or Rab7 impaired LAMP2A trafficking. Treatment of cystinotic cells with a CMA activator increased LAMP2A localization at the lysosome and increased cell survival. Altogether, we show that LAMP2A trafficking is regulated by cystinosin, Rab11, and RILP and that CMA up-regulation is a potential clinically relevant mechanism to increase cell survival in cystinosis. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

Point mutation in D8C domain of Tamm-Horsfall protein/uromodulin in transgenic mice causes progressive renal damage and hyperuricemia

PubMed Central

Landry, Nichole K.; El-Achkar, Tarek M.; Lieske, John C.

2017-01-01

Hereditary mutations in Tamm-Horsfall protein (THP/uromodulin) gene cause autosomal dominant kidney diseases characterized by juvenile-onset hyperuricemia, gout and progressive kidney failure, although the disease pathogenesis remains unclear. Here we show that targeted expression in transgenic mice of a mutation within the domain of 8 cysteines of THP in kidneys’ thick ascending limb (TAL) caused unfolded protein response in younger (1-month old) mice and apoptosis in older (12-month old) mice. While the young mice had urine concentration defects and polyuria, such defects progressively reversed in the older mice to marked oliguria, highly concentrated urine, fibrotic kidneys and reduced creatinine clearance. Both the young and the old transgenic mice had significantly higher serum uric acid and its catabolic product, allantoin, than age-matched wild-type mice. This THP mutation apparently caused primary defects in TAL by compromising the luminal translocation and reabsorptive functions of NKCC2 and ROMK and secondary responses in proximal tubules by upregulating NHE3 and URAT1. Our results strongly suggest that the progressive worsening of kidney functions reflects the accumulation of the deleterious effects of the misfolded mutant THP and the compensatory responses. Transgenic mice recapitulating human THP/uromodulin-associated kidney diseases could be used to elucidate their pathogenesis and test novel therapeutic strategies. PMID:29145399

Point mutation in D8C domain of Tamm-Horsfall protein/uromodulin in transgenic mice causes progressive renal damage and hyperuricemia.

PubMed

Ma, Lijie; Liu, Yan; Landry, Nichole K; El-Achkar, Tarek M; Lieske, John C; Wu, Xue-Ru

2017-01-01

Hereditary mutations in Tamm-Horsfall protein (THP/uromodulin) gene cause autosomal dominant kidney diseases characterized by juvenile-onset hyperuricemia, gout and progressive kidney failure, although the disease pathogenesis remains unclear. Here we show that targeted expression in transgenic mice of a mutation within the domain of 8 cysteines of THP in kidneys' thick ascending limb (TAL) caused unfolded protein response in younger (1-month old) mice and apoptosis in older (12-month old) mice. While the young mice had urine concentration defects and polyuria, such defects progressively reversed in the older mice to marked oliguria, highly concentrated urine, fibrotic kidneys and reduced creatinine clearance. Both the young and the old transgenic mice had significantly higher serum uric acid and its catabolic product, allantoin, than age-matched wild-type mice. This THP mutation apparently caused primary defects in TAL by compromising the luminal translocation and reabsorptive functions of NKCC2 and ROMK and secondary responses in proximal tubules by upregulating NHE3 and URAT1. Our results strongly suggest that the progressive worsening of kidney functions reflects the accumulation of the deleterious effects of the misfolded mutant THP and the compensatory responses. Transgenic mice recapitulating human THP/uromodulin-associated kidney diseases could be used to elucidate their pathogenesis and test novel therapeutic strategies.

A computational framework for automation of point defect calculations

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

Goyal, Anuj; Gorai, Prashun; Peng, Haowei

We have developed a complete and rigorously validated open-source Python framework to automate point defect calculations using density functional theory. Furthermore, the framework provides an effective and efficient method for defect structure generation, and creation of simple yet customizable workflows to analyze defect calculations. This package provides the capability to compute widely-accepted correction schemes to overcome finite-size effects, including (1) potential alignment, (2) image-charge correction, and (3) band filling correction to shallow defects. Using Si, ZnO and In2O3 as test examples, we demonstrate the package capabilities and validate the methodology.

A computational framework for automation of point defect calculations

DOE PAGES

Goyal, Anuj; Gorai, Prashun; Peng, Haowei; ...

2017-01-13

We have developed a complete and rigorously validated open-source Python framework to automate point defect calculations using density functional theory. Furthermore, the framework provides an effective and efficient method for defect structure generation, and creation of simple yet customizable workflows to analyze defect calculations. This package provides the capability to compute widely-accepted correction schemes to overcome finite-size effects, including (1) potential alignment, (2) image-charge correction, and (3) band filling correction to shallow defects. Using Si, ZnO and In2O3 as test examples, we demonstrate the package capabilities and validate the methodology.

Defect interactions in GaAs single crystals

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.

1984-01-01

The two-sublattice structural configuration of GaAs and deviations from stoichiometry render the generation and interaction of electrically active point defects (and point defect complexes) critically important for device applications and very complex. Of the defect-induced energy levels, those lying deep into the energy band are very effective lifetime ""killers". The level 0.82 eV below the condition band, commonly referred to as EL2, is a major deep level, particularly in melt-grown GaAs. This level is associated with an antisite defect complex (AsGa - VAS). Possible mechanisms of its formation and its annihilation were further developed.

Negative impact of surface Ti3+ defects on the photocatalytic hydrogen evolution activity of SrTiO3

NASA Astrophysics Data System (ADS)

Chen, Haidong; Zhang, Feng; Zhang, Weifeng; Du, Yingge; Li, Guoqiang

2018-01-01

Defects play an important and in many cases dominant role in the physical and chemical properties of many oxide materials. In this work, we show that the surface Ti3+ defects in SrTiO3 (STO), characterized by electron paramagnetic resonance and X-ray photoelectron spectroscopy, directly impact the photocatalytic activity of STO. O2 species are found to absorb preferentially on Ti3+ defect sites. Hydrogen evolution under ambient air diminishes with the increase in the concentration of surface Ti3+. This is explained by the over-accumulation of Pt cocatalysts on the site of surface Ti3+ defects after the removal of adsorbed O2.

Steady distribution structure of point defects near crystal-melt interface under pulling stop of CZ Si crystal

NASA Astrophysics Data System (ADS)

Abe, T.; Takahashi, T.; Shirai, K.

2017-02-01

In order to reveal a steady distribution structure of point defects of no growing Si on the solid-liquid interface, the crystals were grown at a high pulling rate, which Vs becomes predominant, and the pulling was suddenly stopped. After restoring the variations of the crystal by the pulling-stop, the crystals were then left in prolonged contact with the melt. Finally, the crystals were detached and rapidly cooled to freeze point defects and then a distribution of the point defects of the as-grown crystals was observed. As a result, a dislocation loop (DL) region, which is formed by the aggregation of interstitials (Is), was formed over the solid-liquid interface and was surrounded with a Vs-and-Is-free recombination region (Rc-region), although the entire crystals had been Vs rich in the beginning. It was also revealed that the crystal on the solid-liquid interface after the prolonged contact with the melt can partially have a Rc-region to be directly in contact with the melt, unlike a defect distribution of a solid-liquid interface that has been growing. This experimental result contradicts a hypothesis of Voronkov's diffusion model, which always assumes the equilibrium concentrations of Vs and Is as the boundary condition for distribution of point defects on the growth interface. The results were disscussed from a qualitative point of view of temperature distribution and thermal stress by the pulling-stop.

Intrinsic point defects in off-stoichiometric Cu2ZnSnSe4: A neutron diffraction study

NASA Astrophysics Data System (ADS)

Gurieva, Galina; Valle Rios, Laura Elisa; Franz, Alexandra; Whitfield, Pamela; Schorr, Susan

2018-04-01

This work is an experimental study of intrinsic point defects in off-stoichiometric kesterite type CZTSe by means of neutron powder diffraction. We revealed the existence of copper vacancies (VCu), various cation anti site defects (CuZn, ZnCu, ZnSn, SnZn, and CuZn), as well as interstitials (Cui, Zni) in a wide range of off-stoichiometric polycrystalline powder samples synthesized by the solid state reaction. The results show that the point defects present in off-stoichiometric CZTSe agree with the off-stoichiometry type model, assuming certain cation substitutions accounting for charge balance. In addition to the known off-stoichiometry types A-H, new types (I-L) have been introduced. For the very first time, a correlation between the chemical composition of the CZTSe kesterite type phase and the occurring intrinsic point defects is presented. In addition to the off-stoichiometry type specific defects, the Cu/Zn disorder is always present in the CZTSe phase. In Cu-poor/Zn-rich CZTSe, a composition considered as the one that delivers the best photovoltaic performance, mainly copper vacancies, ZnCu and ZnSn anti sites are present. Also, this compositional region shows the lowest degree of Cu/Zn disorder.

19q13.12 microdeletion syndrome fibroblasts display abnormal storage of cholesterol and sphingolipids in the endo-lysosomal system.

PubMed

Zhao, Kexin; van der Spoel, Aarnoud; Castiglioni, Claudia; Gale, Sarah; Fujiwara, Hideji; Ory, Daniel S; Ridgway, Neale D

2018-06-01

Microdeletions in 19q12q13.12 cause a rare and complex haploinsufficiency syndrome characterized by intellectual deficiency, developmental delays, and neurological movement disorders. Variability in the size and interval of the deletions makes it difficult to attribute the complex clinical phenotype of this syndrome to an underlying gene(s). As an alternate approach, we examined the biochemical and metabolic features of fibroblasts from an affected individual to derive clues as to the molecular basis for the syndrome. Immunofluorescence and electron microscopy of affected fibroblasts revealed an abnormal endo-lysosomal compartment that was characterized by rapid accumulation of lysosomotropic dyes, elevated LAMP1 and LAMP2 expression and vacuoles containing membrane whorls, common features of lysosomal lipid storage disorders. The late endosomes-lysosomes (LE/LY) of affected fibroblasts accumulated low-density lipoprotein cholesterol, and displayed reduced cholesterol esterification and increased de novo cholesterol synthesis, indicative of defective cholesterol transport to the endoplasmic reticulum. Affected fibroblasts also had increased ceramide and sphingolipid mass, altered glycosphingolipid species and accumulation of a fluorescent lactosylceramide probe in LE/LY. Autophagosomes also accumulated in affected fibroblasts because of decreased fusion with autolysosomes, a defect associated with other lysosomal storage diseases. Attempts to correct the cholesterol/sphingolipid storage defect in fibroblasts with cyclodextrin, sphingolipid synthesis inhibitors or by altering ion transport were unsuccessful. Our data show that 19q13.12 deletion fibroblasts have abnormal accumulation of cholesterol and sphingolipids in the endo-lysosomal system that compromises organelle function and could be an underlying cause of the clinical features of the syndrome. Copyright © 2018 Elsevier B.V. All rights reserved.

Impaired Lysosomal Function Underlies Monoclonal Light Chain–Associated Renal Fanconi Syndrome

PubMed Central

Luciani, Alessandro; Sirac, Christophe; Terryn, Sara; Javaugue, Vincent; Prange, Jenny Ann; Bender, Sébastien; Bonaud, Amélie; Cogné, Michel; Aucouturier, Pierre; Ronco, Pierre

2016-01-01

Monoclonal gammopathies are frequently complicated by kidney lesions that increase the disease morbidity and mortality. In particular, abnormal Ig free light chains (LCs) may accumulate within epithelial cells, causing proximal tubule (PT) dysfunction and renal Fanconi syndrome (RFS). To investigate the mechanisms linking LC accumulation and PT dysfunction, we used transgenic mice overexpressing human control or RFS-associated κLCs (RFS-κLCs) and primary cultures of mouse PT cells exposed to low doses of corresponding human κLCs (25 μg/ml). Before the onset of renal failure, mice overexpressing RFS-κLCs showed PT dysfunction related to loss of apical transporters and receptors and increased PT cell proliferation rates associated with lysosomal accumulation of κLCs. Exposure of PT cells to RFS-κLCs resulted in κLC accumulation within enlarged and dysfunctional lysosomes, alteration of cellular dynamics, defective proteolysis and hydrolase maturation, and impaired lysosomal acidification. These changes were specific to the RFS-κLC variable (V) sequence, because they did not occur with control LCs or the same RFS-κLC carrying a single substitution (Ala30→Ser) in the V domain. The lysosomal alterations induced by RFS-κLCs were reflected in increased cell proliferation, decreased apical expression of endocytic receptors, and defective endocytosis. These results reveal that specific κLCs accumulate within lysosomes, altering lysosome dynamics and proteolytic function through defective acidification, thereby causing dedifferentiation and loss of reabsorptive capacity of PT cells. The characterization of these early events, which are similar to those encountered in congenital lysosomal disorders, provides a basis for the reported differential LC toxicity and new perspectives on LC-induced RFS. PMID:26614382

Vertical Root Fracture initiation in curved roots after root canal preparation: A dentinal micro-crack analysis with LED transillumination

PubMed Central

Martín-Biedma, Benjamín; Varela-Patiño, Purificación; Ruíz-Piñón, Manuel; Castelo-Baz, Pablo

2017-01-01

Background One of the causative factors of root defects is the increased friction produced by rotary instrumentation. A high canal curvature may increase stress, making the tooth more susceptible to dentinal cracks. The purpose of this study was to evaluate dentinal micro-crack formation with the ProTaper NEXT and ProTaper Universal systems using LED transillumination, and to analyze the micro-crack generated at the point of maximum canal curvature. Material and Methods 60 human mandibular premolars with curvatures between 30–49° and radii between 2–4 mm were used. The root canals were instrumented using the Protaper Universal® and Protaper NEXT® systems, with the aid of the Proglider® system. The obtained samples were sectioned transversely before subsequent analysis with LED transillumination at 2 mm and 8 mm from the apex and at the point of maximum canal curvature. Defects were scored: 0 for no defects; and 1 for micro-cracks. Results Root defects were not observed in the control group. The ProTaper NEXT system caused fewer defects (16.7%) than the ProTaper Universal system (40%) (P<0.05). The ProTaper Universal system caused significantly more micro-cracks at the point of maximum canal curvature than the ProTaper NEXT system (P<0.05). Conclusions Rotary instrumentation systems often generate root defects, but the ProTaper NEXT system generated fewer dentinal defects than the ProTaper Universal system. A higher prevalence of defects was found at the point of maximum curvature in the ProTaper Universal group. Key words:Curved root, Micro-crack, point of maximum canal curvature, ProTaper NEXT, ProTaper Universal, Vertical root fracture. PMID:29167712

Defect states of complexes involving a vacancy on the boron site in boronitrene

NASA Astrophysics Data System (ADS)

Ngwenya, T. B.; Ukpong, A. M.; Chetty, N.

2011-12-01

First principles calculations have been performed to investigate the ground state properties of freestanding monolayer hexagonal boronitrene (h-BN). We have considered monolayers that contain native point defects and their complexes, which form when the point defects bind with the boron vacancy on the nearest-neighbor position. The changes in the electronic structure are analyzed to show the extent of localization of the defect-induced midgap states. The variations in formation energies suggest that defective h-BN monolayers that contain carbon substitutional impurities are the most stable structures, irrespective of the changes in growth conditions. The high energies of formation of the boron vacancy complexes suggest that they are less stable, and their creation by ion bombardment would require high-energy ions compared to point defects. Using the relative positions of the derived midgap levels for the double vacancy complex, it is shown that the quasi-donor-acceptor pair interpretation of optical transitions is consistent with stimulated transitions between electron and hole states in boronitrene.

Accelerated defect visualization of microelectronic systems using binary search with fixed pitch-catch distance laser ultrasonic scanning

NASA Astrophysics Data System (ADS)

Park, Byeongjin; Sohn, Hoon

2018-04-01

The practicality of laser ultrasonic scanning is limited because scanning at a high spatial resolution demands a prohibitively long scanning time. Inspired by binary search, an accelerated defect visualization technique is developed to visualize defect with a reduced scanning time. The pitch-catch distance between the excitation point and the sensing point is also fixed during scanning to maintain a high signal-to-noise ratio of measured ultrasonic responses. The approximate defect boundary is identified by examining the interactions between ultrasonic waves and defect observed at the scanning points that are sparsely selected by a binary search algorithm. Here, a time-domain laser ultrasonic response is transformed into a spatial ultrasonic domain response using a basis pursuit approach so that the interactions between ultrasonic waves and defect can be better identified in the spatial ultrasonic domain. Then, the area inside the identified defect boundary is visualized as defect. The performance of the proposed defect visualization technique is validated through an experiment on a semiconductor chip. The proposed defect visualization technique accelerates the defect visualization process in three aspects: (1) The number of measurements that is necessary for defect visualization is dramatically reduced by a binary search algorithm; (2) The number of averaging that is necessary to achieve a high signal-to-noise ratio is reduced by maintaining the wave propagation distance short; and (3) With the proposed technique, defect can be identified with a lower spatial resolution than the spatial resolution required by full-field wave propagation imaging.

Dextrocardia

MedlinePlus

Cyanotic heart defect - dextrocardia; Congenital heart defect - dextrocardia; Birth defect - dextrocardia ... During the early weeks of pregnancy, the baby’s heart develops. Sometimes, it turns so that it points ...

Characterization of oxygen defects in diamond by means of density functional theory calculations

NASA Astrophysics Data System (ADS)

Thiering, Gergő; Gali, Adam

2016-09-01

Point defects in diamond are of high interest as candidates for realizing solid state quantum bits, bioimaging agents, or ultrasensitive electric or magnetic field sensors. Various artificial diamond synthesis methods should introduce oxygen contamination in diamond, however, the incorporation of oxygen into diamond crystal and the nature of oxygen-related point defects are largely unknown. Oxygen may be potentially interesting as a source of quantum bits or it may interact with other point defects which are well established solid state qubits. Here we employ plane-wave supercell calculations within density functional theory, in order to characterize the electronic and magneto-optical properties of various oxygen-related defects. Besides the trivial single interstitial and substitutional oxygen defects we also consider their complexes with vacancies and hydrogen atoms. We find that oxygen defects are mostly electrically active and introduce highly correlated orbitals that pose a challenge for density functional theory modeling. Nevertheless, we are able to identify the fingerprints of substitutional oxygen defect, the oxygen-vacancy and oxygen-vacancy-hydrogen complexes in the electron paramagnetic resonance spectrum. We demonstrate that first principles calculations can predict the motional averaging of the electron paramagnetic resonance spectrum of defects that are subject to Jahn-Teller distortion. We show that the high-spin neutral oxygen-vacancy defect exhibits very fast nonradiative decay from its optical excited state that might hinder applying it as a qubit.

FIBER OPTICS: Role of point defects in the photosensitivity of hydrogen-loaded phosphosilicate glass

NASA Astrophysics Data System (ADS)

Larionov, Yu V.

2010-08-01

It is shown that point defect modifications in hydrogen-loaded phosphosilicate glass (PSG) do not play a central role in determining its photosensitivity. Photochemical reactions that involve a two-step point defect modification and pre-exposure effect are incapable of accounting for photoinduced refractive index changes. It seems likely that a key role in UV-induced refractive index modifications is played by structural changes in the PSG network. Experimental data are presented that demonstrate intricate network rearrangement dynamics during UV exposure of PSG.

Effects of artificially produced defects on film thickness distribution in sliding EHD point contacts

NASA Technical Reports Server (NTRS)

Cusano, C.; Wedeven, L. D.

1981-01-01

The effects of artificially produced dents and grooves on the elastohydrodynamic (EHD) film thickness profile in a sliding point contact were investigated by means of optical interferometry. The defects, formed on the surface of a highly polished ball, were held stationary at various locations within and in the vicinity of the contact region while the disk was rotating. It is shown that the defects, having a geometry similar to what can be expected in practice, can dramatically change the film thickness which exists when no defects are present in or near the contact. This change in film thickness is mainly a function of the position of the defects in the inlet region, the geometry of the defects, the orientation of the defects in the case of grooves, and the depth of the defect relative to the central film thickness.

Imaging atomic-level random walk of a point defect in graphene

NASA Astrophysics Data System (ADS)

Kotakoski, Jani; Mangler, Clemens; Meyer, Jannik C.

2014-05-01

Deviations from the perfect atomic arrangements in crystals play an important role in affecting their properties. Similarly, diffusion of such deviations is behind many microstructural changes in solids. However, observation of point defect diffusion is hindered both by the difficulties related to direct imaging of non-periodic structures and by the timescales involved in the diffusion process. Here, instead of imaging thermal diffusion, we stimulate and follow the migration of a divacancy through graphene lattice using a scanning transmission electron microscope operated at 60 kV. The beam-activated process happens on a timescale that allows us to capture a significant part of the structural transformations and trajectory of the defect. The low voltage combined with ultra-high vacuum conditions ensure that the defect remains stable over long image sequences, which allows us for the first time to directly follow the diffusion of a point defect in a crystalline material.

Insight into point defects and impurities in titanium from first principles

NASA Astrophysics Data System (ADS)

Nayak, Sanjeev K.; Hung, Cain J.; Sharma, Vinit; Alpay, S. Pamir; Dongare, Avinash M.; Brindley, William J.; Hebert, Rainer J.

2018-03-01

Titanium alloys find extensive use in the aerospace and biomedical industries due to a unique combination of strength, density, and corrosion resistance. Decades of mostly experimental research has led to a large body of knowledge of the processing-microstructure-properties linkages. But much of the existing understanding of point defects that play a significant role in the mechanical properties of titanium is based on semi-empirical rules. In this work, we present the results of a detailed self-consistent first-principles study that was developed to determine formation energies of intrinsic point defects including vacancies, self-interstitials, and extrinsic point defects, such as, interstitial and substitutional impurities/dopants. We find that most elements, regardless of size, prefer substitutional positions, but highly electronegative elements, such as C, N, O, F, S, and Cl, some of which are common impurities in Ti, occupy interstitial positions.

Ferromagnetism induced by point defect in Janus monolayer MoSSe regulated by strain engineering

NASA Astrophysics Data System (ADS)

Meng, Ming; Li, Tinghui; Li, Shaofeng; Liu, Kuili

2018-03-01

The formation and regulation of magnetism dependent on introduced defects in the Janus MoSSe monolayer has attracted much attention because of its potential application in spintronics. Here, we present a theoretical study of defect formation in the MoSSe monolayer and its introduced magnetism under external strain. The tensile deformation induced by external strain not only leads to decreases in defect formation energy, but also enhances magnetic characteristics. However, as compressed deformation increases, the magnetism in the structure induced by Se or S defects remains unchanged because this microstructural deformation adequately spin polarizes unpaired electrons of neighboring Mo atoms. Our results suggest the use of point defect and strain engineering in the Janus MoSSe monolayer for spintronics applications.

Native point defects in GaSb

NASA Astrophysics Data System (ADS)

Kujala, J.; Segercrantz, N.; Tuomisto, F.; Slotte, J.

2014-10-01

We have applied positron annihilation spectroscopy to study native point defects in Te-doped n-type and nominally undoped p-type GaSb single crystals. The results show that the dominant vacancy defect trapping positrons in bulk GaSb is the gallium monovacancy. The temperature dependence of the average positron lifetime in both p- and n-type GaSb indicates that negative ion type defects with no associated open volume compete with the Ga vacancies. Based on comparison with theoretical predictions, these negative ions are identified as Ga antisites. The concentrations of these negatively charged defects exceed the Ga vacancy concentrations nearly by an order of magnitude. We conclude that the Ga antisite is the native defect responsible for p-type conductivity in GaSb single crystals.

Effects of LED phototherapy on bone defects grafted with MTA, bone morphogenetic proteins and guided bone regeneration: a Raman spectroscopic study.

PubMed

Pinheiro, Antonio L B; Soares, Luiz G P; Cangussú, Maria Cristina T; Santos, Nicole R S; Barbosa, Artur Felipe S; Silveira Júnior, Landulfo

2012-09-01

We studied peaks of calcium hydroxyapatite (CHA) and protein and lipid CH groups in defects grafted with mineral trioxide aggregate (MTA) treated or not with LED irradiation, bone morphogenetic proteins and guided bone regeneration. A total of 90 rats were divided into ten groups each of which was subdivided into three subgroups (evaluated at 15, 21 and 30 days after surgery). Defects were irradiated with LED light (wavelength 850 ± 10 nm) at 48-h intervals for 15 days. Raman readings were taken at the surface of the defects. There were no statistically significant differences in the CHA peaks among the nonirradiated defects at any of the experimental time-points. On the other hand, there were significant differences between the defects filled with blood clot and the irradiated defects at all time-points (p < 0.001, p = 0.02, p < 0.001). There were significant differences between the mean peak CHA in nonirradiated defects at all the experimental time-points (p < 0.01). The mean peak of the defects filled with blood clot was significantly different from that of the defects filled with MTA (p < 0.001). There were significant differences between the defects filled with blood clot and the irradiated defects (p < 0.001). The results of this study using Raman spectral analysis indicate that infrared LED light irradiation improves the deposition of CHA in healing bone grafted or not with MTA.

Defect stability in thorium monocarbide: An ab initio study

NASA Astrophysics Data System (ADS)

Wang, Chang-Ying; Han, Han; Shao, Kuan; Cheng, Cheng; Huai, Ping

2015-09-01

The elastic properties and point defects of thorium monocarbide (ThC) have been studied by means of density functional theory based on the projector-augmented-wave method. The calculated electronic and elastic properties of ThC are in good agreement with experimental data and previous theoretical results. Five types of point defects have been considered in our study, including the vacancy defect, interstitial defect, antisite defect, schottky defect, and composition-conserving defect. Among these defects, the carbon vacancy defect has the lowest formation energy of 0.29 eV. The second most stable defect (0.49 eV) is one of composition-conserving defects in which one carbon is removed to another carbon site forming a C2 dimer. In addition, we also discuss several kinds of carbon interstitial defects, and predict that the carbon trimer configuration may be a transition state for a carbon dimer diffusion in ThC. Project supported by the International S&T Cooperation Program of China (Grant No. 2014DFG60230), the National Natural Science Foundation of China (Grant No. 91326105), the National Basic Research Program of China (Grant No. 2010CB934504), and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA02040104).

First-principle calculation on mechanical and thermal properties of B2-NiSc with point defects

NASA Astrophysics Data System (ADS)

Yuan, Zhipeng; Cui, Hongbao; Guo, Xuefeng

2017-01-01

Using the first-principles plane-wave pseudo-potential method based on density functional theory, the effect of vacancy and anti-position defect on the mechanical and thermal properties of B2-NiSc intermetallics were discussed in detail. Several parameters, such as the shear modulus, bulk modulus, modulus of elasticity, C 11-C 11, the Debye temperature and Poisson's ratio, have been calculated to evaluate the effect of vacancy and anti-position defect on the hardness, ductility and thermal properties of B2-NiSc intermetallics. The results show that VNi, ScNi, VSc and NiSc the four point defects all make the crystal hardness decrease and improve plasticity of B2-NiSc intermetallics. The entropy, enthalpy and free energy of VNi, ScNi, VSc and NiSc are monotonously changed as temperature changes. From the perspective of free energy, NiSc is the most stable, while ScNi is the most unstable. Debye temperature of NiSc intermetallics with four different point defects shows VNi, ScNi, VSc and NiSc the four point defects all reduce the stability of B2-NiSc intermetallics. Project supported by the National Natural Science Foundation of China (Nos. 51301063, 51571086) and the Talent Introduction Foundation of Henan Polytechnic University (No. Y-2009).

Canine Models for Copper Homeostasis Disorders.

PubMed

Wu, Xiaoyan; Leegwater, Peter A J; Fieten, Hille

2016-02-04

Copper is an essential trace nutrient metal involved in a multitude of cellular processes. Hereditary defects in copper metabolism result in disorders with a severe clinical course such as Wilson disease and Menkes disease. In Wilson disease, copper accumulation leads to liver cirrhosis and neurological impairments. A lack in genotype-phenotype correlation in Wilson disease points toward the influence of environmental factors or modifying genes. In a number of Non-Wilsonian forms of copper metabolism, the underlying genetic defects remain elusive. Several pure bred dog populations are affected with copper-associated hepatitis showing similarities to human copper metabolism disorders. Gene-mapping studies in these populations offer the opportunity to discover new genes involved in copper metabolism. Furthermore, due to the relatively large body size and long life-span of dogs they are excellent models for development of new treatment strategies. One example is the recent use of canine organoids for disease modeling and gene therapy of copper storage disease. This review addresses the opportunities offered by canine genetics for discovery of genes involved in copper metabolism disorders. Further, possibilities for the use of dogs in development of new treatment modalities for copper storage disorders, including gene repair in patient-derived hepatic organoids, are highlighted.

Canine Models for Copper Homeostasis Disorders

PubMed Central

Wu, Xiaoyan; Leegwater, Peter A. J.; Fieten, Hille

2016-01-01

Copper is an essential trace nutrient metal involved in a multitude of cellular processes. Hereditary defects in copper metabolism result in disorders with a severe clinical course such as Wilson disease and Menkes disease. In Wilson disease, copper accumulation leads to liver cirrhosis and neurological impairments. A lack in genotype-phenotype correlation in Wilson disease points toward the influence of environmental factors or modifying genes. In a number of Non-Wilsonian forms of copper metabolism, the underlying genetic defects remain elusive. Several pure bred dog populations are affected with copper-associated hepatitis showing similarities to human copper metabolism disorders. Gene-mapping studies in these populations offer the opportunity to discover new genes involved in copper metabolism. Furthermore, due to the relatively large body size and long life-span of dogs they are excellent models for development of new treatment strategies. One example is the recent use of canine organoids for disease modeling and gene therapy of copper storage disease. This review addresses the opportunities offered by canine genetics for discovery of genes involved in copper metabolism disorders. Further, possibilities for the use of dogs in development of new treatment modalities for copper storage disorders, including gene repair in patient-derived hepatic organoids, are highlighted. PMID:26861285

Charge Trapping Properties of Ge Nanocrystals Grown via Solid-State Dewetting

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

Johnston, Steven; Jadli, I.; Aouassa, M.

2018-05-04

In the present work, we report on the charge trapping properties of Germanium Nanocrystals (Ge NCs) self assembled on SiO2 thin layer for promising applications in next-generation non volatile memory by the means of Deep Level Transient Spectroscopy (DLTS) and high frequency C-V method. The Ge NCs were grown via dewetting phenomenon at solid state by Ultra-High Vacuum (UHV) annealing and passivated with silicon before SiO2 capping. The role of the surface passivation is to reduce the electrical defect density at the Ge NCs-SiO2 interface. The presence of the Ge NCs in the oxide of the MOS capacitors strongly affectsmore » the C-V characteristics and increases the accumulation capacitance, causes a negative flat band voltage (VFB) shift. The DLTS has been used to study the individual Ge NCs as a single point deep level defect in the oxide. DLTS reveals two main features: the first electron traps around 255 K could correspond to dangling bonds at the Si/SiO2 interface and the second, at high-temperature (>300 K) response, could be originated from minority carrier generation in Ge NCs.« less

Glycosylphosphatidylinositol-anchored proteins are required for cell wall synthesis and morphogenesis in Arabidopsis.

PubMed

Gillmor, C Stewart; Lukowitz, Wolfgang; Brininstool, Ginger; Sedbrook, John C; Hamann, Thorsten; Poindexter, Patricia; Somerville, Chris

2005-04-01

Mutations at five loci named PEANUT1-5 (PNT) were identified in a genetic screen for radially swollen embryo mutants. pnt1 cell walls showed decreased crystalline cellulose, increased pectins, and irregular and ectopic deposition of pectins, xyloglucans, and callose. Furthermore, pnt1 pollen is less viable than the wild type, and pnt1 embryos were delayed in morphogenesis and showed defects in shoot and root meristems. The PNT1 gene encodes the Arabidopsis thaliana homolog of mammalian PIG-M, an endoplasmic reticulum-localized mannosyltransferase that is required for synthesis of the glycosylphosphatidylinositol (GPI) anchor. All five pnt mutants showed strongly reduced accumulation of GPI-anchored proteins, suggesting that they all have defects in GPI anchor synthesis. Although the mutants are seedling lethal, pnt1 cells are able to proliferate for a limited time as undifferentiated callus and do not show the massive deposition of ectopic cell wall material seen in pnt1 embryos. The different phenotype of pnt1 cells in embryos and callus suggest a differential requirement for GPI-anchored proteins in cell wall synthesis in these two tissues and points to the importance of GPI anchoring in coordinated multicellular growth.

Severe epilepsy as the major symptom of new mutations in the mitochondrial tRNA(Phe) gene.

PubMed

Zsurka, G; Hampel, K G; Nelson, I; Jardel, C; Mirandola, S R; Sassen, R; Kornblum, C; Marcorelles, P; Lavoué, S; Lombès, A; Kunz, W S

2010-02-09

To present 2 families with maternally inherited severe epilepsy as the main symptom of mitochondrial disease due to point mutations at position 616 in the mitochondrial tRNA(Phe) (MT-TF) gene. Histologic stainings were performed on skeletal muscle slices from the 2 index patients. Oxidative phosphorylation activity was measured by oxygraphic and spectrophotometric methods. The patients' complete mitochondrial DNA (mtDNA) and the relevant mtDNA region in maternal relatives were sequenced. Muscle histology showed only decreased overall COX staining, while a combined respiratory chain defect, most severely affecting complex IV, was noted in both patients' skeletal muscle. Sequencing of the mtDNA revealed in both patients a mutation at position 616 in the MT-TF gene (T>C or T>G). These mutations disrupt a base pair in the anticodon stem at a highly conserved position. They were apparently homoplasmic in both patients, and had different heteroplasmy levels in the investigated maternal relatives. Deleterious mutations in the mitochondrial tRNA(Phe) may solely manifest with epilepsy when segregating to homoplasmy. They may be overlooked in the absence of lactate accumulation and typical mosaic mitochondrial defects in muscle.

Strong spin-orbit splitting and magnetism of point defect states in monolayer WS2

NASA Astrophysics Data System (ADS)

Li, Wun-Fan; Fang, Changming; van Huis, Marijn A.

2016-11-01

The spin-orbit coupling (SOC) effect has been known to be profound in monolayer pristine transition metal dichalcogenides (TMDs). Here we show that point defects, which are omnipresent in the TMD membranes, exhibit even stronger SOC effects and change the physics of the host materials drastically. In this article we chose the representative monolayer WS2 slabs from the TMD family together with seven typical types of point defects including monovacancies, interstitials, and antisites. We calculated the formation energies of these defects, and studied the effect of spin-orbit coupling (SOC) on the corresponding defect states. We found that the S monovacancy (VS) and S interstitial (adatom) have the lowest formation energies. In the case of VS and both of the WS and WS 2 antisites, the defect states exhibit strong splitting up to 296 meV when SOC is considered. Depending on the relative position of the defect state with respect to the conduction band minimum (CBM), the hybrid functional HSE will either increase the splitting by up to 60 meV (far from CBM), or decrease the splitting by up to 57 meV (close to CBM). Furthermore, we found that both the WS and WS 2 antisites possess a magnetic moment of 2 μB localized at the antisite W atom and the neighboring W atoms. The dependence of SOC on the orientation of the magnetic moment for the WS and WS 2 antisites is discussed. All these findings provide insights in the defect behavior under SOC and point to possibilities for spintronics applications for TMDs.

Computationally-efficient stochastic cluster dynamics method for modeling damage accumulation in irradiated materials

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

Hoang, Tuan L.; Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, CA 94550; Marian, Jaime, E-mail: jmarian@ucla.edu

2015-11-01

An improved version of a recently developed stochastic cluster dynamics (SCD) method (Marian and Bulatov, 2012) [6] is introduced as an alternative to rate theory (RT) methods for solving coupled ordinary differential equation (ODE) systems for irradiation damage simulations. SCD circumvents by design the curse of dimensionality of the variable space that renders traditional ODE-based RT approaches inefficient when handling complex defect population comprised of multiple (more than two) defect species. Several improvements introduced here enable efficient and accurate simulations of irradiated materials up to realistic (high) damage doses characteristic of next-generation nuclear systems. The first improvement is a proceduremore » for efficiently updating the defect reaction-network and event selection in the context of a dynamically expanding reaction-network. Next is a novel implementation of the τ-leaping method that speeds up SCD simulations by advancing the state of the reaction network in large time increments when appropriate. Lastly, a volume rescaling procedure is introduced to control the computational complexity of the expanding reaction-network through occasional reductions of the defect population while maintaining accurate statistics. The enhanced SCD method is then applied to model defect cluster accumulation in iron thin films subjected to triple ion-beam (Fe{sup 3+}, He{sup +} and H{sup +}) irradiations, for which standard RT or spatially-resolved kinetic Monte Carlo simulations are prohibitively expensive.« less

Computationally-efficient stochastic cluster dynamics method for modeling damage accumulation in irradiated materials

NASA Astrophysics Data System (ADS)

Hoang, Tuan L.; Marian, Jaime; Bulatov, Vasily V.; Hosemann, Peter

2015-11-01

An improved version of a recently developed stochastic cluster dynamics (SCD) method (Marian and Bulatov, 2012) [6] is introduced as an alternative to rate theory (RT) methods for solving coupled ordinary differential equation (ODE) systems for irradiation damage simulations. SCD circumvents by design the curse of dimensionality of the variable space that renders traditional ODE-based RT approaches inefficient when handling complex defect population comprised of multiple (more than two) defect species. Several improvements introduced here enable efficient and accurate simulations of irradiated materials up to realistic (high) damage doses characteristic of next-generation nuclear systems. The first improvement is a procedure for efficiently updating the defect reaction-network and event selection in the context of a dynamically expanding reaction-network. Next is a novel implementation of the τ-leaping method that speeds up SCD simulations by advancing the state of the reaction network in large time increments when appropriate. Lastly, a volume rescaling procedure is introduced to control the computational complexity of the expanding reaction-network through occasional reductions of the defect population while maintaining accurate statistics. The enhanced SCD method is then applied to model defect cluster accumulation in iron thin films subjected to triple ion-beam (Fe3+, He+ and H+) irradiations, for which standard RT or spatially-resolved kinetic Monte Carlo simulations are prohibitively expensive.

Epitaxial Growths of m-Plane AlGaN/GaN and AlInN/GaN Heterostructures Applicable for Normally-Off Mode High Power Field Effect Transistors on Freestanding GaN Substrates

DTIC Science & Technology

2011-08-17

cathodoluminescence (CL), and Hall effect measurement. We will disclose how structural and point defects affect the internal quantum efficiency. We have a complete...18. S. F. Chichibu, A. Uedono, T. Onuma, S. P. DenBaars, U. K. Mishra, J. S. Speck, and S. Nakamura, “Impact of Point Defects on the Luminescence...A. Uedono, “Major impacts of point defects and impurities on the carrier recombination dynamics in AlN,” Appl. Phys. Lett. 97(20), 201904 (2010

Native point defects in GaSb

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

Kujala, J.; Segercrantz, N.; Tuomisto, F.

2014-10-14

We have applied positron annihilation spectroscopy to study native point defects in Te-doped n-type and nominally undoped p-type GaSb single crystals. The results show that the dominant vacancy defect trapping positrons in bulk GaSb is the gallium monovacancy. The temperature dependence of the average positron lifetime in both p- and n-type GaSb indicates that negative ion type defects with no associated open volume compete with the Ga vacancies. Based on comparison with theoretical predictions, these negative ions are identified as Ga antisites. The concentrations of these negatively charged defects exceed the Ga vacancy concentrations nearly by an order of magnitude.more » We conclude that the Ga antisite is the native defect responsible for p-type conductivity in GaSb single crystals.« less

Generation and characterization of point defects in SrTiO3 and Y3Al5O12

NASA Astrophysics Data System (ADS)

Selim, F. A.; Winarski, D.; Varney, C. R.; Tarun, M. C.; Ji, Jianfeng; McCluskey, M. D.

Positron annihilation lifetime spectroscopy (PALS) was applied to characterize point defects in single crystals of Y3Al5O12 and SrTiO3 after populating different types of defects by relevant thermal treatments. In SrTiO3, PALS measurements identified Sr vacancy, Ti vacancy, vacancy complexes of Ti-O (vacancy) and hydrogen complex defects. In Y3Al5O12 single crystals the measurements showed the presence of Al-vacancy, (Al-O) vacancy and Al-vacancy passivated by hydrogen. These defects are shown to play the major role in defining the electronic and optical properties of these complex oxides.

A review of defects and disorder in multinary tetrahedrally bonded semiconductors [Defects and disorder in multinary tetrahedrally bonded semiconductors studied by experiment and theory

DOE PAGES

Baranowski, Lauryn L.; Zawadzki, Pawel; Lany, Stephan; ...

2016-11-10

Defects are critical to understanding the electronic properties of semiconducting compounds, for applications such as light-emitting diodes, transistors, photovoltaics, and thermoelectrics. In this review, we describe our work investigating defects in tetrahedrally bonded, multinary semiconductors, and discuss the place of our research within the context of publications by other groups. We applied experimental and theory techniques to understand point defects, structural disorder, and extended antisite defects in one semiconductor of interest for photovoltaic applications, Cu 2SnS 3. We contrast our findings on Cu 2SnS 3 with other chemically related Cu-Sn-S compounds, as well as structurally related compounds such as Cumore » 2ZnSnS 4 and Cu(In,Ga)Se 2. We find that evaluation of point defects alone is not sufficient to understand defect behavior in multinary tetrahedrally bonded semiconductors. In the case of Cu 2SnS 3 and Cu 2ZnSnS 4, structural disorder and entropy-driven cation clustering can result in nanoscale compositional inhomogeneities which detrimentally impact the electronic transport. Therefore, it is not sufficient to assess only the point defect behavior of new multinary tetrahedrally bonded compounds; effects such as structural disorder and extended antisite defects must also be considered. Altogether, this review provides a framework for evaluating tetrahedrally bonded semiconducting compounds with respect to their defect behavior for photovoltaic and other applications, and suggests new materials that may not be as prone to such imperfections.« less

A review of defects and disorder in multinary tetrahedrally bonded semiconductors [Defects and disorder in multinary tetrahedrally bonded semiconductors studied by experiment and theory

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

Baranowski, Lauryn L.; Zawadzki, Pawel; Lany, Stephan

Defects are critical to understanding the electronic properties of semiconducting compounds, for applications such as light-emitting diodes, transistors, photovoltaics, and thermoelectrics. In this review, we describe our work investigating defects in tetrahedrally bonded, multinary semiconductors, and discuss the place of our research within the context of publications by other groups. We applied experimental and theory techniques to understand point defects, structural disorder, and extended antisite defects in one semiconductor of interest for photovoltaic applications, Cu 2SnS 3. We contrast our findings on Cu 2SnS 3 with other chemically related Cu-Sn-S compounds, as well as structurally related compounds such as Cumore » 2ZnSnS 4 and Cu(In,Ga)Se 2. We find that evaluation of point defects alone is not sufficient to understand defect behavior in multinary tetrahedrally bonded semiconductors. In the case of Cu 2SnS 3 and Cu 2ZnSnS 4, structural disorder and entropy-driven cation clustering can result in nanoscale compositional inhomogeneities which detrimentally impact the electronic transport. Therefore, it is not sufficient to assess only the point defect behavior of new multinary tetrahedrally bonded compounds; effects such as structural disorder and extended antisite defects must also be considered. Altogether, this review provides a framework for evaluating tetrahedrally bonded semiconducting compounds with respect to their defect behavior for photovoltaic and other applications, and suggests new materials that may not be as prone to such imperfections.« less

Theoretical model of dynamic spin polarization of nuclei coupled to paramagnetic point defects in diamond and silicon carbide

NASA Astrophysics Data System (ADS)

Ivády, Viktor; Szász, Krisztián; Falk, Abram L.; Klimov, Paul V.; Christle, David J.; Janzén, Erik; Abrikosov, Igor A.; Awschalom, David D.; Gali, Adam

2015-09-01

Dynamic nuclear spin polarization (DNP) mediated by paramagnetic point defects in semiconductors is a key resource for both initializing nuclear quantum memories and producing nuclear hyperpolarization. DNP is therefore an important process in the field of quantum-information processing, sensitivity-enhanced nuclear magnetic resonance, and nuclear-spin-based spintronics. DNP based on optical pumping of point defects has been demonstrated by using the electron spin of nitrogen-vacancy (NV) center in diamond, and more recently, by using divacancy and related defect spins in hexagonal silicon carbide (SiC). Here, we describe a general model for these optical DNP processes that allows the effects of many microscopic processes to be integrated. Applying this theory, we gain a deeper insight into dynamic nuclear spin polarization and the physics of diamond and SiC defects. Our results are in good agreement with experimental observations and provide a detailed and unified understanding. In particular, our findings show that the defect electron spin coherence times and excited state lifetimes are crucial factors in the entire DNP process.

Squalene epoxidase as a target for manipulation of squalene levels in the yeast Saccharomyces cerevisiae.

PubMed

Garaiová, Martina; Zambojová, Veronika; Simová, Zuzana; Griač, Peter; Hapala, Ivan

2014-03-01

Squalene is a valuable natural substance with several biotechnological applications. In the yeast Saccharomyces cerevisiae, it is produced in the isoprenoid pathway as the first precursor dedicated to ergosterol biosynthesis. The aim of this study was to explore the potential of squalene epoxidase encoded by the ERG1 gene as the target for manipulating squalene levels in yeast. Highest squalene levels (over 1000 μg squalene per 10(9)  cells) were induced by specific point mutations in ERG1 gene that reduced activity of squalene epoxidase and caused hypersensitivity to terbinafine. This accumulation of squalene in erg1 mutants did not significantly disturb their growth. Treatment with squalene epoxidase inhibitor terbinafine revealed a limit in squalene accumulation at 700 μg squalene per 10(9)  cells which was associated with pronounced growth defects. Inhibition of squalene epoxidase activity by anaerobiosis or heme deficiency resulted in relatively low squalene levels. These levels were significantly increased by ergosterol depletion in anaerobic cells which indicated feedback inhibition of squalene production by ergosterol. Accumulation of squalene in erg1 mutants and terbinafine-treated cells were associated with increased cellular content and aggregation of lipid droplets. Our results prove that targeted genetic manipulation of the ERG1 gene is a promising tool for increasing squalene production in yeast. © 2013 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd.

Domain disruption and defect accumulation during unipolar electric fatigue in a BZT-BCT ceramic

NASA Astrophysics Data System (ADS)

Fan, Zhongming; Zhou, Chao; Ren, Xiaobing; Tan, Xiaoli

2017-12-01

0.5Ba(Zr0.2Ti0.8)O30.5(Ba0.7Ca0.3)TiO3 (BZT-BCT) is a promising lead-free piezoelectric ceramic with excellent piezoelectric properties (e.g., d33 > 600 pC/N). As potential device applications are considered, the electric fatigue resistance of the ceramic must be evaluated. In this Letter, electric-field in situ transmission electron microscopy is employed to study the microstructural evolution in the BZT-BCT polycrystalline ceramic during unipolar cycling. It is shown that the large ferroelectric domains are disrupted and replaced with accumulated defect clusters and fragmented domains after 5 × 104 unipolar cycles. In this fatigued state, the grain becomes nonresponsive to applied voltages.

Magnifying narrow-band imaging of gastric mucosal morphology predicts the H. pylori-related epigenetic field defect.

PubMed

Tahara, Tomomitsu; Yamazaki, Jumpei; Tahara, Sayumi; Okubo, Masaaki; Kawamura, Tomohiko; Horiguchi, Noriyuki; Ishizuka, Takamitsu; Nagasaka, Mitsuo; Nakagawa, Yoshihito; Shibata, Tomoyuki; Kuroda, Makoto; Ohmiya, Naoki

2017-06-08

DNA methylation is associated with "field defect" in the gastric mucosa. To characterize "field defect" morphologically, we examined DNA methylation of non-neoplastic gastric mucosa in relation to their morphology seen by narrow-band imaging (NBI) with magnifying endoscopy. Magnifying NBI of non-neoplastic gastric body was classified as follows: normal-small and round pits with uniform subepithelial capillary networks; type 1-a little enlarged round pits with indistinct subepithelial capillary networks; type 2-remarkably enlarged pits with irregular vessels; and type 3-clearly demarcated oval or tubulovillous pits with bulky coiled or wavy vessels. Methylation of nine candidate genes (MYOD1, SLC16A12, GDNF, IGF2, MIR 124A1, CDH1, PRDM5, RORA and MLF1) were determined by bisulfite pyrosequencing. Infinium HumanMethylation450 array was used to characterize the methylation of >450,000 CpG sites. Mean Z score methylation of nine genes positively correlated with the changes of mucosal patterns from normal to types 1, 2, and 3 (P < 0.0001). Genome-wide analysis showed that development of mucosal patterns correlated with methylation accumulation especially at CpG islands. Genes with promoter CpG islands that were gradually methylated with the development of mucosal patterns significantly enriched the genes involved in zinc-related pathways. The results indicates that gastric mucosal morphology predicts a "field defect" in this tissue type. Accumulation of DNA methylation is associated with "field defect" in the non-neoplastic gastric mucosa. Endoscopic identification of "field defect" has important implications for preventing gastric cancer. Our results suggest that magnifying NBI of gastric mucosal morphology predicts a "field defect" in the gastric mucosa.

Deleterious effects of neuronal accumulation of glycogen in flies and mice.

PubMed

Duran, Jordi; Tevy, María Florencia; Garcia-Rocha, Mar; Calbó, Joaquim; Milán, Marco; Guinovart, Joan J

2012-08-01

Under physiological conditions, most neurons keep glycogen synthase (GS) in an inactive form and do not show detectable levels of glycogen. Nevertheless, aberrant glycogen accumulation in neurons is a hallmark of patients suffering from Lafora disease or other polyglucosan disorders. Although these diseases are associated with mutations in genes involved in glycogen metabolism, the role of glycogen accumulation remains elusive. Here, we generated mouse and fly models expressing an active form of GS to force neuronal accumulation of glycogen. We present evidence that the progressive accumulation of glycogen in mouse and Drosophila neurons leads to neuronal loss, locomotion defects and reduced lifespan. Our results highlight glycogen accumulation in neurons as a direct cause of neurodegeneration. Copyright © 2012 EMBO Molecular Medicine.

Deleterious effects of neuronal accumulation of glycogen in flies and mice

PubMed Central

Duran, Jordi; Tevy, María Florencia; Garcia-Rocha, Mar; Calbó, Joaquim; Milán, Marco; Guinovart, Joan J

2012-01-01

Under physiological conditions, most neurons keep glycogen synthase (GS) in an inactive form and do not show detectable levels of glycogen. Nevertheless, aberrant glycogen accumulation in neurons is a hallmark of patients suffering from Lafora disease or other polyglucosan disorders. Although these diseases are associated with mutations in genes involved in glycogen metabolism, the role of glycogen accumulation remains elusive. Here, we generated mouse and fly models expressing an active form of GS to force neuronal accumulation of glycogen. We present evidence that the progressive accumulation of glycogen in mouse and Drosophila neurons leads to neuronal loss, locomotion defects and reduced lifespan. Our results highlight glycogen accumulation in neurons as a direct cause of neurodegeneration. PMID:22549942

Molecular dynamical simulations of melting Al nanoparticles using a reaxff reactive force field

NASA Astrophysics Data System (ADS)

Liu, Junpeng; Wang, Mengjun; Liu, Pingan

2018-06-01

Molecular dynamics simulations were performed to study thermal properties and melting points of Al nanoparticles by using a reactive force field under canonical (NVT) ensembles. Al nanoparticles (particle size 2–4 nm) were considered in simulations. A combination of structural and thermodynamic parameters such as the Lindemann index, heat capacities, potential energy and radial-distribution functions was employed to decide melting points. We used annealing technique to obtain the initial Al nanoparticle model. Comparison was made between ReaxFF results and other simulation results. We found that ReaxFF force field is reasonable to describe Al cluster melting behavior. The linear relationship between particle size and melting points was found. After validating the ReaxFF force field, more attention was paid on thermal properties of Al nanoparticles with different defect concentrations. 4 nm Al nanoparticles with different defect concentrations (5%–20%) were considered in this paper. Our results revealed that: the melting points are irrelevant with defect concentration at a certain particle size. The extra storage energy of Al nanoparticles is proportional to nanoparticles’ defect concentration, when defect concentration is 5%–15%. While the particle with 20% defect concentration is similar to the cluster with 10% defect concentration. After melting, the extra energy of all nanoparticles decreases sharply, and the extra storage energy is nearly zero at 600 K. The centro-symmetry parameter analysis shows structure evolution of different models during melting processes.

Theoretical Study of Defect Signatures in III-V and II-VI Semiconductors

DTIC Science & Technology

2006-03-01

collaboration with experimentalists at Linköpin University (Sweden), we identified the recently observed EPR signals in diluted GaPN to be Gallium ...the results from USPP calculations to all electron calculations. o Study NO-Zni complexes and other point defects in ZnO using USPP calculations...parameters for point defects in semiconductors. o Results on stability of NO-Zni complexes in ZnO and preliminary results on their electronic

Chiral photonic crystals with an anisotropic defect layer.

PubMed

Gevorgyan, A H; Harutyunyan, M Z

2007-09-01

In the present paper we consider some properties of defect modes in chiral photonic crystals with an anisotropic defect layer. We solved the problem by Ambartsumian's layer addition method. We investigated the influence of the defect layer thickness variation and its location in the chiral photonic crystal (CPC) and also its optical axes orientation, as well as of CPC thickness variation on defect mode properties. Variations of the optical thickness of the defect layer have its impact on the defect mode linewidth and the light accumulation in the defect. We obtain that CPCs lose their base property at certain defect layer thicknesses; namely, they lose their diffraction reflection dependence on light polarization. We also show that the circular polarization handedness changes from right-handed to left-handed if the defect layer location is changed, and therefore, such systems can be used to create sources of elliptically polarized light with tunable ellipticity. Some nonreciprocity properties of such systems are investigated, too. In particular, it is also shown that such a system can work as a practically ideal wide band optical diode for circularly polarized incident light provided the defect layer thickness is properly chosen, and it can work as a narrow band diode at small defect layer thicknesses.

Distinctive Roles for Periplasmic Proteases in the Maintenance of Essential Outer Membrane Protein Assembly.

PubMed

Soltes, Garner R; Martin, Nicholas R; Park, Eunhae; Sutterlin, Holly A; Silhavy, Thomas J

2017-10-15

Outer membrane protein (OMP) biogenesis in Escherichia coli is a robust process essential to the life of the organism. It is catalyzed by the β-barrel assembly machine (Bam) complex, and a number of quality control factors, including periplasmic chaperones and proteases, maintain the integrity of this trafficking pathway. Little is known, however, about how periplasmic proteases recognize and degrade OMP substrates when assembly is compromised or whether different proteases recognize the same substrate at distinct points in the assembly pathway. In this work, we use well-defined assembly-defective mutants of LptD, the essential lipopolysaccharide assembly translocon, to show that the periplasmic protease DegP degrades substrates with assembly defects that prevent or impair initial contact with Bam, causing the mutant protein to accumulate in the periplasm. In contrast, another periplasmic protease, BepA, degrades a LptD mutant substrate that has engaged the Bam complex and formed a nearly complete barrel. Furthermore, we describe the role of the outer membrane lipoprotein YcaL, a protease of heretofore unknown function, in the degradation of a LptD substrate that has engaged the Bam complex but is stalled at an earlier step in the assembly process that is not accessible to BepA. Our results demonstrate that multiple periplasmic proteases monitor OMPs at distinct points in the assembly process. IMPORTANCE OMP assembly is catalyzed by the essential Bam complex and occurs in a cellular environment devoid of energy sources. Assembly intermediates that misfold can compromise this essential molecular machine. Here we demonstrate distinctive roles for three different periplasmic proteases that can clear OMP substrates with folding defects that compromise assembly at three different stages. These quality control factors help ensure the integrity of the permeability barrier that contributes to the intrinsic resistance of Gram-negative organisms to many antibiotics. Copyright © 2017 American Society for Microbiology.

Long-term preservation of retinal function in the RCS rat model of retinitis pigmentosa following lentivirus-mediated gene therapy.

PubMed

Tschernutter, M; Schlichtenbrede, F C; Howe, S; Balaggan, K S; Munro, P M; Bainbridge, J W B; Thrasher, A J; Smith, A J; Ali, R R

2005-04-01

The Royal College of Surgeons (RCS) rat is a well-characterized model of autosomal recessive retinitis pigmentosa (RP) due to a defect in the retinal pigment epithelium (RPE). It is homozygous for a null mutation in the gene encoding , a receptor tyrosine kinase found in RPE cells, that is required for phagocytosis of shed photoreceptor outer segments. The absence of Mertk results in accumulation of outer segment debris. This subsequently leads to progressive loss of photoreceptor cells. In order to evaluate the efficacy of lentiviral-mediated gene replacement therapy in the RCS rat, we produced recombinant VSV-G pseudotyped HIV-1-based lentiviruses containing a murine Mertk cDNA driven by a spleen focus forming virus (SFFV) promoter. The vector was subretinally injected into the right eye of 10-day-old RCS rats; the left eye was left untreated as an internal control. Here, we present a detailed assessment of the duration and extent of the morphological rescue and the resulting functional benefits. We examined animals at various time points over a period of 7 months by light and electron microscopy, and electroretinography. We observed correction of the phagocytic defect, slowing of photoreceptor cell loss and preservation of retinal function for up to 7 months. This study demonstrates the potential of gene therapy approaches for the treatment of retinal degenerations caused by defects specific to the RPE and supports the use of lentiviral vectors for the treatment of such disorders.

Defects in Amorphous Semiconductors: The Case of Amorphous Indium Gallium Zinc Oxide

NASA Astrophysics Data System (ADS)

de Jamblinne de Meux, A.; Pourtois, G.; Genoe, J.; Heremans, P.

2018-05-01

Based on a rational classification of defects in amorphous materials, we propose a simplified model to describe intrinsic defects and hydrogen impurities in amorphous indium gallium zinc oxide (a -IGZO). The proposed approach consists of organizing defects into two categories: point defects, generating structural anomalies such as metal—metal or oxygen—oxygen bonds, and defects emerging from changes in the material stoichiometry, such as vacancies and interstitial atoms. Based on first-principles simulations, it is argued that the defects originating from the second group always act as perfect donors or perfect acceptors. This classification simplifies and rationalizes the nature of defects in amorphous phases. In a -IGZO, the most important point defects are metal—metal bonds (or small metal clusters) and peroxides (O - O single bonds). Electrons are captured by metal—metal bonds and released by the formation of peroxides. The presence of hydrogen can lead to two additional types of defects: metal-hydrogen defects, acting as acceptors, and oxygen-hydrogen defects, acting as donors. The impact of these defects is linked to different instabilities observed in a -IGZO. Specifically, the diffusion of hydrogen and oxygen is connected to positive- and negative-bias stresses, while negative-bias illumination stress originates from the formation of peroxides.

Basic Study on Term of Warranty Liability for Water Supply, Drainage, and Sanitation Arrangement Work Defect in Apartment Building

NASA Astrophysics Data System (ADS)

Park, Junmo; Seo, DeokSeok

2017-06-01

The defect lawsuit of the apartment which is the representative residential style of Korea continues and becomes a social problem. In the defect lawsuit, the term of warranty liability is a period that can demand the defect repair according to defect occurrence, and the exclusion period of the exercise of rights. However, the term of warranty liability stipulated in relevant laws such as Enforcement Decree of the Housing Act is being changed arbitrarily, without any established grounds. Therefore, a reasonable standard for establishing the term of warranty liability is required. In this study, the defects of water supply, drainage and sanitation arrangement work were studied. As a result of analyzing the number of defect occurrence in the apartment, it was shown that the defects in water supply, drainage and sanitation arrangement work occurred more than 80% in the 1st ∼ 2nd year after completion. However, the occurrence of defects from the 3rd year was extremely slight. On the other hand, it was confirmed that the defect occurrence continued until fairly late point of time as the end point of time of the defects was in the 7th to 9th years.

A coumaroyl-ester-3-hydroxylase Insertion Mutant Reveals the Existence of Nonredundant meta-Hydroxylation Pathways and Essential Roles for Phenolic Precursors in Cell Expansion and Plant Growth1[W][OA

PubMed Central

Abdulrazzak, Nawroz; Pollet, Brigitte; Ehlting, Jürgen; Larsen, Kim; Asnaghi, Carole; Ronseau, Sebastien; Proux, Caroline; Erhardt, Mathieu; Seltzer, Virginie; Renou, Jean-Pierre; Ullmann, Pascaline; Pauly, Markus; Lapierre, Catherine; Werck-Reichhart, Danièle

2006-01-01

Cytochromes P450 monooxygenases from the CYP98 family catalyze the meta-hydroxylation step in the phenylpropanoid biosynthetic pathway. The ref8 Arabidopsis (Arabidopsis thaliana) mutant, with a point mutation in the CYP98A3 gene, was previously described to show developmental defects, changes in lignin composition, and lack of soluble sinapoyl esters. We isolated a T-DNA insertion mutant in CYP98A3 and show that this mutation leads to a more drastic inhibition of plant development and inhibition of cell growth. Similar to the ref8 mutant, the insertion mutant has reduced lignin content, with stem lignin essentially made of p-hydroxyphenyl units and trace amounts of guaiacyl and syringyl units. However, its roots display an ectopic lignification and a substantial proportion of guaiacyl and syringyl units, suggesting the occurrence of an alternative CYP98A3-independent meta-hydroxylation mechanism active mainly in the roots. Relative to the control, mutant plantlets produce very low amounts of sinapoyl esters, but accumulate flavonol glycosides. Reduced cell growth seems correlated with alterations in the abundance of cell wall polysaccharides, in particular decrease in crystalline cellulose, and profound modifications in gene expression and homeostasis reminiscent of a stress response. CYP98A3 thus constitutes a critical bottleneck in the phenylpropanoid pathway and in the synthesis of compounds controlling plant development. CYP98A3 cosuppressed lines show a gradation of developmental defects and changes in lignin content (40% reduction) and structure (prominent frequency of p-hydroxyphenyl units), but content in foliar sinapoyl esters is similar to the control. The purple coloration of their leaves is correlated to the accumulation of sinapoylated anthocyanins. PMID:16377748

Isolation and characterization of a mutant defective in triacylglycerol accumulation in nitrogen-starved Chlamydomonas reinhardtii.

PubMed

Hung, Chun-Hsien; Kanehara, Kazue; Nakamura, Yuki

2016-09-01

Triacylglycerol (TAG), a major source of biodiesel production, accumulates in nitrogen-starved Chlamydomonas reinhardtii. However, the metabolic pathway of starch-to-TAG conversion remains elusive because an enzyme that affects the starch degradation is unknown. Here, we isolated a new class of mutant bgal1, which expressed an overaccumulation of starch granules and defective photosynthetic growth. The bgal1 was a null mutant of a previously uncharacterized β-galactosidase-like gene (Cre02.g119700), which decreased total β-galactosidase activity 40% of the wild type. Upon nitrogen starvation, the bgal1 mutant showed decreased TAG accumulation mainly due to the reduced flux of de novo TAG biosynthesis evidenced by increased unsaturation of fatty acid composition in TAG and reduced TAG accumulation by additional supplementation of acetate to the culture media. Metabolomic analysis of the bgal1 mutant showed significantly reduced levels of metabolites following the hydrolysis of starch and substrates for TAG accumulation, whereas metabolites in TCA cycle were unaffected. Upon nitrogen starvation, while levels of glucose 6-phosphate, fructose 6-phosphate and acetyl-CoA remained lower, most of the other metabolites in glycolysis were increased but those in the TCA cycle were decreased, supporting TAG accumulation. We suggest that BGAL1 may be involved in the degradation of starch, which affects TAG accumulation in nitrogen-starved C. reinhardtii. This article is part of a Special Issue entitled: Plant Lipid Biology edited by Kent D. Chapman and Ivo Feussner. Copyright © 2016 Elsevier B.V. All rights reserved.

Enhanced thermoelectric performance of In2O3-based ceramics via Nanostructuring and Point Defect Engineering

PubMed Central

Lan, Jin-Le; Liu, Yaochun; Lin, Yuan-Hua; Nan, Ce-Wen; Cai, Qing; Yang, Xiaoping

2015-01-01

The issue of how to improve the thermoelectric figure of merit (ZT) in oxide semiconductors has been challenging for more than 20 years. In this work, we report an effective path to substantial reduction in thermal conductivity and increment in carrier concentration, and thus a remarkable enhancement in the ZT value is achieved. The ZT value of In2O3 system was enhanced 4-fold by nanostructuing (nano-grains and nano-inclusions) and point defect engineering. The introduction of point defects in In2O3 results in a glass-like thermal conductivity. The lattice thermal conductivity could be reduced by 60%, and extraordinary low lattice thermal conductivity (1.2 W m−1 K−1 @ 973 K) below the amorphous limit was achieved. Our work paves a path for enhancing the ZT in oxides by both the nanosturcturing and the point defect engineering for better phonon-glasses and electron-crystal (PGEC) materials. PMID:25586762

Many-Body Theory of Proton-Generated Point Defects for Losses of Electron Energy and Photons in Quantum Wells

NASA Astrophysics Data System (ADS)

Huang, Danhong; Iurov, Andrii; Gao, Fei; Gumbs, Godfrey; Cardimona, D. A.

2018-02-01

The effects of point defects on the loss of either energies of ballistic electron beams or incident photons are studied by using a many-body theory in a multi-quantum-well system. This theory includes the defect-induced vertex correction to a bare polarization function of electrons within the ladder approximation, and the intralayer and interlayer screening of defect-electron interactions is also taken into account in the random-phase approximation. The numerical results of defect effects on both energy-loss and optical-absorption spectra are presented and analyzed for various defect densities, numbers of quantum wells, and wave vectors. The diffusion-reaction equation is employed for calculating distributions of point defects in a layered structure. For completeness, the production rate for Frenkel-pair defects and their initial concentration are obtained based on atomic-level molecular-dynamics simulations. By combining the defect-effect, diffusion-reaction, and molecular-dynamics models with an available space-weather-forecast model, it will be possible in the future to enable specific designing for electronic and optoelectronic quantum devices that will be operated in space with radiation-hardening protection and, therefore, effectively extend the lifetime of these satellite onboard electronic and optoelectronic devices. Specifically, this theory can lead to a better characterization of quantum-well photodetectors not only for high quantum efficiency and low dark current density but also for radiation tolerance or mitigating the effects of the radiation.

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

Kozlovski, V. V.; Lebedev, A. A.; Bogdanova, E. V.

The model of conductivity compensation in SiC under irradiation with high-energy electrons is presented. The following processes are considered to cause a decrease in the free carrier concentration: (i) formation of deep traps by intrinsic point defects, Frenkel pairs produced by irradiation; (ii) 'deactivation' of the dopant via formation of neutral complexes including a dopant atom and a radiation-induced point defect; and (iii) formation of deep compensating traps via generation of charged complexes constituted by a dopant atom and a radiation-induced point defect. To determine the compensation mechanism, dose dependences of the deep compensation of moderately doped SiC (CVD) undermore » electron irradiation have been experimentally studied. It is demonstrated that, in contrast to n-FZ-Si, moderately doped SiC (CVD) exhibits linear dependences (with a strongly nonlinear dependence observed for Si). Therefore, the conductivity compensation in silicon carbide under electron irradiation occurs due to deep traps formed by primary radiation defects (vacancies and interstitial atoms) in the silicon and carbon sublattices. It is known that the compensation in silicon is due to the formation of secondary radiation defects that include a dopant atom. It is shown that, in contrast to n-SiC (CVD), primary defects in only the carbon sublattice of moderately doped p-SiC (CVD) cannot account for the compensation process. In p-SiC, either primary defects in the silicon sublattice or defects in both sublattices are responsible for the conductivity compensation.« less

Vacancy-type defects induced by grinding of Si wafers studied by monoenergetic positron beams

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

Uedono, Akira; Yoshihara, Nakaaki; Mizushima, Yoriko

2014-10-07

Vacancy-type defects introduced by the grinding of Czochralski-grown Si wafers were studied using monoenergetic positron beams. Measurements of Doppler broadening spectra of the annihilation radiation and the lifetime spectra of positrons showed that vacancy-type defects were introduced in the surface region (<98 nm), and the major defect species were identified as (i) relatively small vacancies incorporated in dislocations and (ii) large vacancy clusters. Annealing experiments showed that the defect concentration decreased with increasing annealing temperature in the range between 100 and 500°C. After 600–700°C annealing, the defect-rich region expanded up to about 170 nm, which was attributed to rearrangements ofmore » dislocation networks, and a resultant emission of point defects toward the inside of the sample. Above 800°C, the stability limit of those vacancies was reached and they started to disappear. After the vacancies were annealed out (900°C), oxygen-related defects were the major point defects and they were located at <25 nm.« less

Silicon displacement threshold energy determined by electron paramagnetic resonance and positron annihilation spectroscopy in cubic and hexagonal polytypes of silicon carbide

NASA Astrophysics Data System (ADS)

Kerbiriou, X.; Barthe, M.-F.; Esnouf, S.; Desgardin, P.; Blondiaux, G.; Petite, G.

2007-05-01

Both for electronic and nuclear applications, it is of major interest to understand the properties of point defects into silicon carbide (SiC). Low energy electron irradiations are supposed to create primary defects into materials. SiC single crystals have been irradiated with electrons at two beam energies in order to investigate the silicon displacement threshold energy into SiC. This paper presents the characterization of the electron irradiation-induced point defects into both polytypes hexagonal (6H) and cubic (3C) SiC single crystals by using both positron annihilation spectroscopy (PAS) and electron paramagnetic resonance (EPR). The nature and the concentration of the generated point defects depend on the energy of the electron beam and the polytype. After an electron irradiation at an energy of 800 keV vSi mono-vacancies and vSi-vC di-vacancies are detected in both 3C and 6H-SiC polytypes. On the contrary, the nature of point defects detected after an electron irradiation at 190 keV strongly depends on the polytype. Into 6H-SiC crystals, silicon Frenkel pairs vSi-Si are detected whereas only carbon vacancy related defects are detected into 3C-SiC crystals. The difference observed in the distribution of defects detected into the two polytypes can be explained by the different values of the silicon displacement threshold energies for 3C and 6H-SiC. By comparing the calculated theoretical numbers of displaced atoms with the defects numbers measured using EPR, the silicon displacement threshold energy has been estimated to be slightly lower than 20 eV in the 6H polytype and close to 25 eV in the 3C polytype.

Fermi Level Control of Point Defects During Growth of Mg-Doped GaN

NASA Astrophysics Data System (ADS)

Bryan, Zachary; Hoffmann, Marc; Tweedie, James; Kirste, Ronny; Callsen, Gordon; Bryan, Isaac; Rice, Anthony; Bobea, Milena; Mita, Seiji; Xie, Jinqiao; Sitar, Zlatko; Collazo, Ramón

2013-05-01

In this study, Fermi level control of point defects during metalorganic chemical vapor deposition (MOCVD) of Mg-doped GaN has been demonstrated by above-bandgap illumination. Resistivity and photoluminescence (PL) measurements are used to investigate the Mg dopant activation of samples with Mg concentration of 2 × 1019 cm-3 grown with and without exposure to ultraviolet (UV) illumination. Samples grown under UV illumination have five orders of magnitude lower resistivity values compared with typical unannealed GaN:Mg samples. The PL spectra of samples grown with UV exposure are similar to the spectra of those grown without UV exposure that were subsequently annealed, indicating a different incorporation of compensating defects during growth. Based on PL and resistivity measurements we show that Fermi level control of point defects during growth of III-nitrides is feasible.

Modelling of thermal field and point defect dynamics during silicon single crystal growth using CZ technique

NASA Astrophysics Data System (ADS)

Sabanskis, A.; Virbulis, J.

2018-05-01

Mathematical modelling is employed to numerically analyse the dynamics of the Czochralski (CZ) silicon single crystal growth. The model is axisymmetric, its thermal part describes heat transfer by conduction and thermal radiation, and allows to predict the time-dependent shape of the crystal-melt interface. Besides the thermal field, the point defect dynamics is modelled using the finite element method. The considered process consists of cone growth and cylindrical phases, including a short period of a reduced crystal pull rate, and a power jump to avoid large diameter changes. The influence of the thermal stresses on the point defects is also investigated.

Defects in THO/TREX-2 function cause accumulation of novel cytoplasmic mRNP granules that can be cleared by autophagy

PubMed Central

Eshleman, Nichole; Liu, Guangbo; McGrath, Kaitlyn; Parker, Roy; Buchan, J. Ross

2016-01-01

The nuclear THO and TREX-2 complexes are implicated in several steps of nuclear mRNP biogenesis, including transcription, 3′ end processing and export. In a recent genomic microscopy screen in Saccharomyces cerevisiae for mutants with constitutive stress granules, we identified that absence of THO and TREX-2 complex subunits leads to the accumulation of Pab1-GFP in cytoplasmic foci. We now show that these THO/TREX-2 mutant induced foci (“TT foci”) are not stress granules but instead are a mRNP granule containing poly(A)+ mRNA, some mRNP components also found in stress granules, as well several proteins involved in mRNA 3′ end processing and export not normally seen in stress granules. In addition, TT foci are resistant to cycloheximide-induced disassembly, suggesting the presence of mRNPs impaired for entry into translation. THO mutants also exhibit defects in normal stress granule assembly. Finally, our data also suggest that TT foci are targeted by autophagy. These observations argue that defects in nuclear THO and TREX-2 complexes can affect cytoplasmic mRNP function by producing aberrant mRNPs that are exported to cytosol, where they accumulate in TT foci and ultimately can be cleared by autophagy. This identifies a novel mechanism of quality control for aberrant mRNPs assembled in the nucleus. PMID:27251550

Concentration of point defects in 4H-SiC characterized by a magnetic measurement

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

Peng, B.; Jia, R. X., E-mail: rxjia@mail.xidian.edu.cn; Wang, Y. T.

A magnetic method is presented to characterize the concentration of point defects in silicon carbide. In this method, the concentration of common charged point defects, which is related to the density of paramagnetic centers, is determined by fitting the paramagnetic component of the specimen to the Brillouin function. Several parameters in the Brillouin function can be measured such as: the g-factor can be obtained from electron spin resonance spectroscopy, and the magnetic moment of paramagnetic centers can be obtained from positron lifetime spectroscopy combined with a first-principles calculation. To evaluate the characterization method, silicon carbide specimens with different concentrations ofmore » point defects are prepared with aluminum ion implantation. The fitting results of the densities of paramagnetic centers for the implanted doses of 1 × 10{sup 14} cm{sup −2}, 1 × 10{sup 15} cm{sup −2} and 1 × 10{sup 16} cm{sup −2} are 6.52 × 10{sup 14}/g, 1.14 × 10{sup 15}/g and 9.45 × 10{sup 14}/g, respectively. The same trends are also observed for the S-parameters in the Doppler broadening spectra. It is shown that this method is an accurate and convenient way to obtain the concentration of point defects in 4H-SiC.« less

The verification of printability about marginal defects and the detectability at the inspection tool in sub 50nm node

NASA Astrophysics Data System (ADS)

Lee, Hyemi; Jeong, Goomin; Seo, Kangjun; Kim, Sangchul; kim, changreol

2008-05-01

Since mask design rule is smaller and smaller, Defects become one of the issues dropping the mask yield. Furthermore controlled defect size become smaller while masks are manufactured. According to ITRS roadmap on 2007, controlled defect size is 46nm in 57nm node and 36nm in 45nm node on a mask. However the machine development is delayed in contrast with the speed of the photolithography development. Generally mask manufacturing process is divided into 3 parts. First part is patterning on a mask and second part is inspecting the pattern and repairing the defect on the mask. At that time, inspection tools of transmitted light type are normally used and are the most trustful as progressive type in the developed inspection tools until now. Final part is shipping the mask after the qualifying the issue points and weak points. Issue points on a mask are qualified by using the AIMS (Aerial image measurement system). But this system is including the inherent error possibility, which is AIMS measures the issue points based on the inspection results. It means defects printed on a wafer are over the specific size detected by inspection tools and the inspection tool detects the almost defects. Even though there are no tools to detect the 46nm and 36nm defects suggested by ITRS roadmap, this assumption is applied to manufacturing the 57nm and 45nm device. So we make the programmed defect mask consisted with various defect type such as spot, clear extension, dark extension and CD variation on L/S(line and space), C/H(contact hole) and Active pattern in 55nm and 45nm node. And the programmed defect mask was inspected by using the inspection tool of transmitted light type and was measured by using AIMS 45-193i. Then the marginal defects were compared between the inspection tool and AIMS. Accordingly we could verify whether defect size is proper or not, which was suggested to be controlled on a mask by ITRS roadmap. Also this result could suggest appropriate inspection tools for next generation device among the inspection tools of transmitted light type, reflected light type and aerial image type.

Determining oxide trapped charges in Al2O3 insulating films on recessed AlGaN/GaN heterostructures by gate capacitance transients measurements

NASA Astrophysics Data System (ADS)

Fiorenza, Patrick; Greco, Giuseppe; Schilirò, Emanuela; Iucolano, Ferdinando; Lo Nigro, Raffaella; Roccaforte, Fabrizio

2018-05-01

This letter presents time-dependent gate-capacitance transient measurements (C–t) to determine the oxide trapped charges (N ot) in Al2O3 films deposited on recessed AlGaN/GaN heterostructures. The C–t transients acquired at different temperatures under strong accumulation allowed to accurately monitor the gradual electron trapping, while hindering the re-emission by fast traps that may affect conventional C–V hysteresis measurements. Using this method, an increase of N ot from 2 to 6 × 1012 cm‑2 was estimated between 25 and 150 °C. The electron trapping is ruled by an Arrhenius dependence with an activation energy of 0.12 eV which was associated to points defects present in the Al2O3 films.

Single Molecule Investigation of Kinesin-1 Motility Using Engineered Microtubule Defects

NASA Astrophysics Data System (ADS)

Gramlich, Michael W.; Conway, Leslie; Liang, Winnie H.; Labastide, Joelle A.; King, Stephen J.; Xu, Jing; Ross, Jennifer L.

2017-03-01

The structure of the microtubule is tightly regulated in cells via a number of microtubule associated proteins and enzymes. Microtubules accumulate structural defects during polymerization, and defect size can further increase under mechanical stresses. Intriguingly, microtubule defects have been shown to be targeted for removal via severing enzymes or self-repair. The cell’s control in defect removal suggests that defects can impact microtubule-based processes, including molecular motor-based intracellular transport. We previously demonstrated that microtubule defects influence cargo transport by multiple kinesin motors. However, mechanistic investigations of the observed effects remained challenging, since defects occur randomly during polymerization and are not directly observable in current motility assays. To overcome this challenge, we used end-to-end annealing to generate defects that are directly observable using standard epi-fluorescence microscopy. We demonstrate that the annealed sites recapitulate the effects of polymerization-derived defects on multiple-motor transport, and thus represent a simple and appropriate model for naturally-occurring defects. We found that single kinesins undergo premature dissociation, but not preferential pausing, at the annealed sites. Our findings provide the first mechanistic insight to how defects impact kinesin-based transport. Preferential dissociation on the single-molecule level has the potential to impair cargo delivery at locations of microtubule defect sites in vivo.

Starvation induced cell death in autophagy-defective yeast mutants is caused by mitochondria dysfunction.

PubMed

Suzuki, Sho W; Onodera, Jun; Ohsumi, Yoshinori

2011-02-25

Autophagy is a highly-conserved cellular degradation and recycling system that is essential for cell survival during nutrient starvation. The loss of viability had been used as an initial screen to identify autophagy-defective (atg) mutants of the yeast Saccharomyces cerevisiae, but the mechanism of cell death in these mutants has remained unclear. When cells grown in a rich medium were transferred to a synthetic nitrogen starvation media, secreted metabolites lowered the extracellular pH below 3.0 and autophagy-defective mutants mostly died. We found that buffering of the starvation medium dramatically restored the viability of atg mutants. In response to starvation, wild-type (WT) cells were able to upregulate components of the respiratory pathway and ROS (reactive oxygen species) scavenging enzymes, but atg mutants lacked this synthetic capacity. Consequently, autophagy-defective mutants accumulated the high level of ROS, leading to deficient respiratory function, resulting in the loss of mitochondria DNA (mtDNA). We also showed that mtDNA deficient cells are subject to cell death under low pH starvation conditions. Taken together, under starvation conditions non-selective autophagy, rather than mitophagy, plays an essential role in preventing ROS accumulation, and thus in maintaining mitochondria function. The failure of response to starvation is the major cause of cell death in atg mutants.

Influence of crystal orientation on the formation of femtosecond laser-induced periodic surface structures and lattice defects accumulation

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

Sedao, Xxx; Garrelie, Florence, E-mail: florence.garrelie@univ-st-etienne.fr; Colombier, Jean-Philippe

2014-04-28

The influence of crystal orientation on the formation of femtosecond laser-induced periodic surface structures (LIPSS) has been investigated on a polycrystalline nickel sample. Electron Backscatter Diffraction characterization has been exploited to provide structural information within the laser spot on irradiated samples to determine the dependence of LIPSS formation and lattice defects (stacking faults, twins, dislocations) upon the crystal orientation. Significant differences are observed at low-to-medium number of laser pulses, outstandingly for (111)-oriented surface which favors lattice defects formation rather than LIPSS formation.

Interactions of Saprophytic Yeasts with a nor Mutant of Aspergillus flavus

PubMed Central

Hua, Sui-Sheng T.; Baker, James L.; Flores-Espiritu, Melanie

1999-01-01

The nor mutant of Aspergillus flavus has a defective norsolorinic acid reductase, and thus the aflatoxin biosynthetic pathway is blocked, resulting in the accumulation of norsolorinic acid, a bright red-orange pigment. We developed a visual agar plate assay to monitor yeast strains for their ability to inhibit aflatoxin production by visually scoring the accumulation of this pigment of the nor mutant. We identified yeast strains that reduced the red-orange pigment accumulation in the nor mutant. These yeasts also reduced aflatoxin accumulation by a toxigenic strain of A. flavus. These yeasts may be useful for reducing aflatoxin contamination of food commodities. PMID:10347069

Analysis of an optimization-based atomistic-to-continuum coupling method for point defects

DOE PAGES

Olson, Derek; Shapeev, Alexander V.; Bochev, Pavel B.; ...

2015-11-16

Here, we formulate and analyze an optimization-based Atomistic-to-Continuum (AtC) coupling method for problems with point defects. Application of a potential-based atomistic model near the defect core enables accurate simulation of the defect. Away from the core, where site energies become nearly independent of the lattice position, the method switches to a more efficient continuum model. The two models are merged by minimizing the mismatch of their states on an overlap region, subject to the atomistic and continuum force balance equations acting independently in their domains. We prove that the optimization problem is well-posed and establish error estimates.

Effective response theory for zero-energy Majorana bound states in three spatial dimensions

NASA Astrophysics Data System (ADS)

Lopes, Pedro L. e. S.; Teo, Jeffrey C. Y.; Ryu, Shinsei

2015-05-01

We propose a gravitational response theory for point defects (hedgehogs) binding Majorana zero modes in (3 + 1)-dimensional superconductors. Starting in 4 + 1 dimensions, where the point defect is extended into a line, a coupling of the bulk defect texture with the gravitational field is introduced. Diffeomorphism invariance then leads to an S U (2) 2 Kac-Moody current running along the defect line. The S U (2) 2 Kac-Moody algebra accounts for the non-Abelian nature of the zero modes in 3 + 1 dimensions. It is then shown to also encode the angular momentum density which permeates throughout the bulk between hedgehog-antihedgehog pairs.

Self-regulation mechanism for charged point defects in hybrid halide perovskites

DOE PAGES

Walsh, Aron; Scanlon, David O.; Chen, Shiyou; ...

2014-12-11

Hybrid halide perovskites such as methylammonium lead iodide (CH 3NH 3PbI 3) exhibit unusually low free-carrier concentrations despite being processed at low-temperatures from solution. We demonstrate, through quantum mechanical calculations, that an origin of this phenomenon is a prevalence of ionic over electronic disorder in stoichiometric materials. Schottky defect formation provides a mechanism to self-regulate the concentration of charge carriers through ionic compensation of charged point defects. The equilibrium charged vacancy concentration is predicted to exceed 0.4 % at room temperature. Furthermore, this behavior, which goes against established defect conventions for inorganic semiconductors, has implications for photovoltaic performance.

A sharp interface model for void growth in irradiated materials

NASA Astrophysics Data System (ADS)

Hochrainer, Thomas; El-Azab, Anter

2015-03-01

A thermodynamic formalism for the interaction of point defects with free surfaces in single-component solids has been developed and applied to the problem of void growth by absorption of point defects in irradiated metals. This formalism consists of two parts, a detailed description of the dynamics of defects within the non-equilibrium thermodynamic frame, and the application of the second law of thermodynamics to provide closure relations for all kinetic equations. Enforcing the principle of non-negative entropy production showed that the description of the problem of void evolution under irradiation must include a relationship between the normal fluxes of defects into the void surface and the driving thermodynamic forces for the void surface motion; these thermodynamic forces are identified for both vacancies and interstitials and the relationships between these forces and the normal point defect fluxes are established using the concepts of transition state theory. The latter theory implies that the defect accommodation into the surface is a thermally activated process. Numerical examples are given to illustrate void growth dynamics in this new formalism and to investigate the effect of the surface energy barriers on void growth. Consequences for phase field models of void growth are discussed.

Mitochondria drive autophagy pathology via microtubule disassembly

PubMed Central

Arduíno, Daniela M.; Esteves, A. Raquel; Cardoso, Sandra Morais

2013-01-01

Neurons are exquisitely dependent on quality control systems to maintain a healthy intracellular environment. A permanent assessment of protein and organelle “quality” allows a coordinated action between repair and clearance of damage proteins and dysfunctional organelles. Impairments in the intracellular clearance mechanisms in long-lived postmitotic cells, like neurons, result in the progressive accumulation of damaged organelles and aggregates of aberrant proteins. Using cells bearing Parkinson disease (PD) patients’ mitochondria, we demonstrated that aberrant accumulation of autophagosomes in PD, commonly interpreted as an abnormal induction of autophagy, is instead due to defective autophagic clearance. This defect is a consequence of alterations in the microtubule network driven by mitochondrial dysfunction that hinder mitochondria and autophagosome trafficking. We uncover mitochondria and microtubule-directed traffic as main players in the regulation of autophagy in PD. PMID:23075854

Characterization of Point Defects in Lithium Aluminate (LiAlO2) Single Crystals

DTIC Science & Technology

2015-09-17

high-quality neutron detectors since 235U and 239Pu, the two isotopes used to fuel nuclear weapons , both emit neu- trons through spontaneous fission of...dissertation has iden- tified and characterized the major point defects created and induced through x ray and neutron radiation using electron paramagnetic... neutron irradiation is an F+ center; an oxygen vacancy with one trapped electron. This defect has two states, a stable state that survives up to 500 ◦C and

Multiple Surface Regions on the Niemann-Pick C2 Protein Facilitate Intracellular Cholesterol Transport.

PubMed

McCauliff, Leslie A; Xu, Zhi; Li, Ran; Kodukula, Sarala; Ko, Dennis C; Scott, Matthew P; Kahn, Peter C; Storch, Judith

2015-11-06

The cholesterol storage disorder Niemann-Pick type C (NPC) disease is caused by defects in either of two late endosomal/lysosomal proteins, NPC1 and NPC2. NPC2 is a 16-kDa soluble protein that binds cholesterol in a 1:1 stoichiometry and can transfer cholesterol between membranes by a mechanism that involves protein-membrane interactions. To examine the structural basis of NPC2 function in cholesterol trafficking, a series of point mutations were generated across the surface of the protein. Several NPC2 mutants exhibited deficient sterol transport properties in a set of fluorescence-based assays. Notably, these mutants were also unable to promote egress of accumulated intracellular cholesterol from npc2(-/-) fibroblasts. The mutations mapped to several regions on the protein surface, suggesting that NPC2 can bind to more than one membrane simultaneously. Indeed, we have previously demonstrated that WT NPC2 promotes vesicle-vesicle interactions. These interactions were abrogated, however, by mutations causing defective sterol transfer properties. Molecular modeling shows that NPC2 is highly plastic, with several intense positively charged regions across the surface that could interact favorably with negatively charged membrane phospholipids. The point mutations generated in this study caused changes in NPC2 surface charge distribution with minimal conformational changes. The plasticity, coupled with membrane flexibility, probably allows for multiple cholesterol transfer routes. Thus, we hypothesize that, in part, NPC2 rapidly traffics cholesterol between closely appositioned membranes within the multilamellar interior of late endosomal/lysosomal proteins, ultimately effecting cholesterol egress from this compartment. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

Apparatus and method for creating a photonic densely-accumulated ray-point

NASA Technical Reports Server (NTRS)

Park, Yeonjoon (Inventor); Choi, Sang H. (Inventor); King, Glen C. (Inventor); Elliott, James R. (Inventor)

2012-01-01

An optical apparatus includes an optical diffraction device configured for diffracting a predetermined wavelength of incident light onto adjacent optical focal points, and a photon detector for detecting a spectral characteristic of the predetermined wavelength. One of the optical focal points is a constructive interference point and the other optical focal point is a destructive interference point. The diffraction device, which may be a micro-zone plate (MZP) of micro-ring gratings or an optical lens, generates a constructive ray point using phase-contrasting of the destructive interference point. The ray point is located between adjacent optical focal points. A method of generating a densely-accumulated ray point includes directing incident light onto the optical diffraction device, diffracting the selected wavelength onto the constructive interference focal point and the destructive interference focal point, and generating the densely-accumulated ray point in a narrow region.

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.

Box 6: Nanoscale Defects

NASA Astrophysics Data System (ADS)

Alves, Eduardo; Breese, Mark

Defects affect virtually all properties of crystalline materials, and their role is magnified in nanoscale structures. In this box we describe the different type of defects with particular emphasis on point and linear defects. Above zero Kelvin all real materials have a defect population within their structure, which affects either their crystalline, electronic or optical properties. It is common to attribute a negative connotation to the presence of defects. However, a perfect silicon crystal or any other defect-free semiconductor would have a limited functionality and might even be useless.

Point Defects and p -Type Doping in ScN from First Principles

NASA Astrophysics Data System (ADS)

Kumagai, Yu; Tsunoda, Naoki; Oba, Fumiyasu

2018-03-01

Scandium nitride (ScN) has been intensively researched as a prototype of rocksalt nitrides and a potential counterpart of the wurtzite group IIIa nitrides. It also holds great promise for applications in various fields, including optoelectronics, thermoelectrics, spintronics, and piezoelectrics. We theoretically investigate the bulk properties, band-edge positions, chemical stability, and point defects, i.e., native defects, unintentionally doped impurities, and p -type dopants of ScN using the Heyd-Scuseria-Ernzerhof hybrid functional. We find several fascinating behaviors: (i) a high level for the valence-band maximum, (ii) the lowest formation energy among binary nitrides, (iii) high formation energies of native point defects, (iv) low formation energies of donor-type impurities, and (v) a p -type conversion by Mg doping. Furthermore, we uncover the origins of the Burstein-Moss shift commonly observed in ScN. Our work sheds light on a fundamental understanding of ScN in regard to its technological applications.

Role of the charge state of interface defects in electronic inhomogeneity evolution with gate voltage in graphene

NASA Astrophysics Data System (ADS)

Singh, Anil Kumar; Gupta, Anjan K.

2018-05-01

Evolution of electronic inhomogeneities with back-gate voltage in graphene on SiO2 was studied using room temperature scanning tunneling microscopy and spectroscopy. Reversal of contrast in some places in the conductance maps and sharp changes in cross correlations between topographic and conductance maps, when graphene Fermi energy approaches its Dirac point, are attributed to the change in charge state of interface defects. The spatial correlations in the conductance maps, described by two length scales, and their growth during approach to Dirac point, show a qualitative agreement with the predictions of the screening theory of graphene. Thus a sharp change in the two length scales close to the Dirac point, seen in our experiments, is interpreted in terms of the change in charge state of some of the interface defects. A systematic understanding and control of the charge state of defects can help in memory applications of graphene.

Hidden topological constellations and polyvalent charges in chiral nematic droplets

NASA Astrophysics Data System (ADS)

Posnjak, Gregor; Čopar, Simon; Muševič, Igor

2017-02-01

Topology has an increasingly important role in the physics of condensed matter, quantum systems, material science, photonics and biology, with spectacular realizations of topological concepts in liquid crystals. Here we report on long-lived hidden topological states in thermally quenched, chiral nematic droplets, formed from string-like, triangular and polyhedral constellations of monovalent and polyvalent singular point defects. These topological defects are regularly packed into a spherical liquid volume and stabilized by the elastic energy barrier due to the helical structure and confinement of the liquid crystal in the micro-sphere. We observe, for the first time, topological three-dimensional point defects of the quantized hedgehog charge q=-2, -3. These higher-charge defects act as ideal polyvalent artificial atoms, binding the defects into polyhedral constellations representing topological molecules.

Hidden topological constellations and polyvalent charges in chiral nematic droplets

PubMed Central

Posnjak, Gregor; Čopar, Simon; Muševič, Igor

2017-01-01

Topology has an increasingly important role in the physics of condensed matter, quantum systems, material science, photonics and biology, with spectacular realizations of topological concepts in liquid crystals. Here we report on long-lived hidden topological states in thermally quenched, chiral nematic droplets, formed from string-like, triangular and polyhedral constellations of monovalent and polyvalent singular point defects. These topological defects are regularly packed into a spherical liquid volume and stabilized by the elastic energy barrier due to the helical structure and confinement of the liquid crystal in the micro-sphere. We observe, for the first time, topological three-dimensional point defects of the quantized hedgehog charge q=−2, −3. These higher-charge defects act as ideal polyvalent artificial atoms, binding the defects into polyhedral constellations representing topological molecules. PMID:28220770

Fumarate hydratase is a critical metabolic regulator of hematopoietic stem cell functions.

PubMed

Guitart, Amelie V; Panagopoulou, Theano I; Villacreces, Arnaud; Vukovic, Milica; Sepulveda, Catarina; Allen, Lewis; Carter, Roderick N; van de Lagemaat, Louie N; Morgan, Marcos; Giles, Peter; Sas, Zuzanna; Gonzalez, Marta Vila; Lawson, Hannah; Paris, Jasmin; Edwards-Hicks, Joy; Schaak, Katrin; Subramani, Chithra; Gezer, Deniz; Armesilla-Diaz, Alejandro; Wills, Jimi; Easterbrook, Aaron; Coman, David; So, Chi Wai Eric; O'Carroll, Donal; Vernimmen, Douglas; Rodrigues, Neil P; Pollard, Patrick J; Morton, Nicholas M; Finch, Andrew; Kranc, Kamil R

2017-03-06

Strict regulation of stem cell metabolism is essential for tissue functions and tumor suppression. In this study, we investigated the role of fumarate hydratase (Fh1), a key component of the mitochondrial tricarboxylic acid (TCA) cycle and cytosolic fumarate metabolism, in normal and leukemic hematopoiesis. Hematopoiesis-specific Fh1 deletion (resulting in endogenous fumarate accumulation and a genetic TCA cycle block reflected by decreased maximal mitochondrial respiration) caused lethal fetal liver hematopoietic defects and hematopoietic stem cell (HSC) failure. Reexpression of extramitochondrial Fh1 (which normalized fumarate levels but not maximal mitochondrial respiration) rescued these phenotypes, indicating the causal role of cellular fumarate accumulation. However, HSCs lacking mitochondrial Fh1 (which had normal fumarate levels but defective maximal mitochondrial respiration) failed to self-renew and displayed lymphoid differentiation defects. In contrast, leukemia-initiating cells lacking mitochondrial Fh1 efficiently propagated Meis1 / Hoxa9 -driven leukemia. Thus, we identify novel roles for fumarate metabolism in HSC maintenance and hematopoietic differentiation and reveal a differential requirement for mitochondrial Fh1 in normal hematopoiesis and leukemia propagation. © 2017 Guitart et al.

Influence of annealing on the photodeposition of silver on periodically poled lithium niobate

DOE PAGES

Carville, N. Craig; Neumayer, Sabine M.; Manzo, Michele; ...

2016-02-03

Here, the preferential deposition of metal nanoparticles onto periodically poled lithium niobate surfaces, whereby photogenerated electrons accumulate in accordance with local electric fields and reduce metal ions from solution, is known to depend on the intensity and wavelength of the illumination and the concentration of the solution used. Here, it is shown that for identical deposition conditions (wavelength, intensity, concentration), post-poling annealing for 10 h at 200 °C modifies the surface reactivity through the reorientation of internal defect fields. Whereas silver nanoparticles deposit preferentially on the +z domains on unannealed crystals, the deposition occurs preferentially along 180 degrees domain wallsmore » for annealed crystals. In neither case is the deposition selective; limited deposition occurs also on the unannealed -z domain surface and on both annealed domain surfaces. The observed behavior is attributed to a relaxation of the poling-induced defect frustration mediated by Li + ion mobility during annealing, which affects the accumulation of electrons, thereby changing the surface reactivity. The evolution of the defect field with temperature is corroborated using Raman spectroscopy.« less

A cascade method for TFT-LCD defect detection

NASA Astrophysics Data System (ADS)

Yi, Songsong; Wu, Xiaojun; Yu, Zhiyang; Mo, Zhuoya

2017-07-01

In this paper, we propose a novel cascade detection algorithm which focuses on point and line defects on TFT-LCD. At the first step of the algorithm, we use the gray level difference of su-bimage to segment the abnormal area. The second step is based on phase only transform (POT) which corresponds to the Discrete Fourier Transform (DFT), normalized by the magnitude. It can remove regularities like texture and noise. After that, we improve the method of setting regions of interest (ROI) with the method of edge segmentation and polar transformation. The algorithm has outstanding performance in both computation speed and accuracy. It can solve most of the defect detections including dark point, light point, dark line, etc.

Polaronic and ionic conduction in NaMnO2: influence of native point defects

NASA Astrophysics Data System (ADS)

Zhu, Zhen; Peelaers, Hartwin; van de Walle, Chris G.

Layered NaMnO2 has promising applications as a cathode material for sodium ion batteries. We will discuss strategies to improve the electrical performance of NaMnO2, including how to optimize the conditions of synthesis and how impurity doping affects the performance. Using hybrid density functional theory, we explored the structural, electronic, and defect properties of bulk NaMnO2. It is antiferromagnetic in the ground state with a band gap of 3.75 eV. Small hole and electron polarons can form in the bulk either through self-trapping or adjacent to point defects. We find that both Na and Mn vacancies are shallow acceptors with the induced holes trapped as small polarons, while O vacancies are deep defect centers. Cation antisites, especially MnNa, are found to have low formation energies. As a result, we expect that MnNa exists in as-grown NaMnO2 in moderate concentrations, rather than forming only at a later stage of the charging process, at which point it causes undesirable structural phase transitions. Both electronic conduction, via polaron hopping, and ionic conduction, through VNa migration, are significantly affected by the presence of point defects. This work was supported by DOE.

N vacancy, self-interstitial diffusion, and Frenkel-pair formation/dissociation in TiN studied by ab-initio and classical molecular dynamics

NASA Astrophysics Data System (ADS)

Sangiovanni, Davide G.; Alling, Björn; Hultman, Lars; Abrikosov, Igor A.

2015-03-01

We use ab-initio and classical molecular dynamics (AIMD, CMD) to simulate diffusion of N vacancy and N self-interstitial point-defects in B1 TiN. The physical properties of TiN, important material system for thin film and coatings applications, are largely dictated by concentration and mobility of point defects. We determine N dilute-point-defect diffusion pathways, activation energies, attempt frequencies, and diffusion coefficients as a function of temperature. In addition, MD simulations reveal an unanticipated atomistic process, which controls the spontaneous formation of N-self-interstitial/N-vacancy pairs (Frenkel pairs) in defect-free TiN. This entails that a N lattice atom leaves its bulk position and bonds to a neighboring N lattice atom. In most cases, Frenkel-pair NI and NV recombine within a fraction of ns; 50% of these processes result in the exchange of two nitrogen lattice atoms. Occasionally, however, Frenkel-pair N-interstitial atoms permanently escape from the anion vacancy site, thus producing unpaired NI and NV point defects. The Knut and Alice Wallenberg foundation (Isotope Project, 2011.0094), the Swedish Research Council (VR) Linköping Linnaeus Initiative LiLi-NFM (Grant 2008-6572), and the Swedish Government Strategic Research (Grant MatLiU 2009-00971).

Nitrogen vacancy, self-interstitial diffusion, and Frenkel-pair formation/dissociation in B 1 TiN studied by ab initio and classical molecular dynamics with optimized potentials

NASA Astrophysics Data System (ADS)

Sangiovanni, D. G.; Alling, B.; Steneteg, P.; Hultman, L.; Abrikosov, I. A.

2015-02-01

We use ab initio and classical molecular dynamics (AIMD and CMD) based on the modified embedded-atom method (MEAM) potential to simulate diffusion of N vacancy and N self-interstitial point defects in B 1 TiN. TiN MEAM parameters are optimized to obtain CMD nitrogen point-defect jump rates in agreement with AIMD predictions, as well as an excellent description of Ti Nx(˜0.7

A molecular dynamics simulation study of irradiation induced defects in gold nanowire

NASA Astrophysics Data System (ADS)

Liu, Wenqiang; Chen, Piheng; Qiu, Ruizhi; Khan, Maaz; Liu, Jie; Hou, Mingdong; Duan, Jinglai

2017-08-01

Displacement cascade in gold nanowires was studied using molecular dynamics computer simulations. Primary knock-on atoms (PKAs) with different kinetic energies were initiated either at the surface or at the center of the nanowires. We found three kinds of defects that were induced by the cascade, including point defects, stacking faults and crater at the surface. The starting points of PKAs influence the number of residual point defects, and this consequently affect the boundary of anti-radiation window which was proposed by calculation of diffusion of point defects to the free surface of nanowires. Formation of stacking faults that expanded the whole cross-section of gold nanowires was observed when the PKA's kinetic energy was higher than 5 keV. Increasing the PKA's kinetic energy up to more than 10 keV may lead to the formation of crater at the surface of nanowires due to microexplosion of hot atoms. At this energy, PKAs started from the center of nanowires can also result in the creation of crater because length of cascade region is comparable to diameter of nanowires. Both the two factors, namely initial positions of PKAs as well as the craters induced by higher energy irradiation, would influence the ability of radiation resistance of metal nanowires.

Modification of electronic structure, magnetic structure, and topological phase of bismuthene by point defects

NASA Astrophysics Data System (ADS)

Kadioglu, Yelda; Kilic, Sevket Berkay; Demirci, Salih; Aktürk, O. Üzengi; Aktürk, Ethem; Ciraci, Salim

2017-12-01

This paper reveals how the electronic structure, magnetic structure, and topological phase of two-dimensional (2D), single-layer structures of bismuth are modified by point defects. We first showed that a free-standing, single-layer, hexagonal structure of bismuth, named h-bismuthene, exhibits nontrivial band topology. We then investigated interactions between single foreign adatoms and bismuthene structures, which comprise stability, bonding, electronic structure, and magnetic structures. Localized states in diverse locations of the band gap and resonant states in band continua of bismuthene are induced upon the adsorption of different adatoms, which modify electronic and magnetic properties. Specific adatoms result in reconstruction around the adsorption site. Single vacancies and divacancies can form readily in bismuthene structures and remain stable at high temperatures. Through rebondings, Stone-Whales-type defects are constructed by divacancies, which transform into a large hole at high temperature. Like adsorbed adatoms, vacancies induce also localized gap states, which can be eliminated through rebondings in divacancies. We also showed that not only the optical and magnetic properties, but also the topological features of pristine h-bismuthene can be modified by point defects. The modification of the topological features depends on the energies of localized states and also on the strength of coupling between point defects.

Effect of point defects on the amorphization of metallic alloys during ion implantation. [NiTi

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

Pedraza, D.F.; Mansur, L.K.

1985-01-01

A theoretical model of radiation-induced amorphization of ordered intermetallic compounds is developed. The mechanism is proposed to be the buildup of lattice defects to very high concentrations, which destabilizes the crystalline structure. Because simple point defects do not normally reach such levels during irradiation, a new defect complex containing a vacancy and an interstitial is hypothesized. Crucial properties of the complex are that the interstitial sees a local chemical environment similar to that of an atom in the ordered lattice, that the formation of the complex prevents mutual recombination and that the complex is immobile. The evolution of a disordermore » based on complexes is not accompanied by like point defect aggregation. The latter leads to the development of a sink microstructure in alloys that do not become amorphous. For electron irradiation, the complexes form by diffusional encounters. For ion irradiation, complexes are also formed directly in cascades. The possibility of direct amorphization in cascades is also included. Calculations for the compound NiTi show reasonable agreement with measured amorphization kinetics.« less

Anticorrelation between Surface and Subsurface Point Defects and the Impact on the Redox Chemistry of TiO2(110)

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

Yoon, Yeohoon; Du, Yingge; Garcia, Juan C.

2015-02-02

Using combination of STM, DFT and SIMS, we explored the interplay and relative impact of surface vs. subsurface defects on the surface chemistry of rutile TiO2. STM results show that surface O vacancies (VO’s) are virtually absent in the vicinity of positively-charged subsurface point-defects. This observation is consistent with DFT calculations of impact of subsurface defect proximity on VO formation energy. To monitor the influence of such lateral anticorrelation on surface redox chemistry, a test reaction of the dissociative adsorption of O2 is employed, which is observed to be suppressed around them. DFT results attribute this to a perceived absencemore » of the intrinsic (Ti) (and likely extrinsic) interstitials in the nearest subsurface layer beneath “inhibited” areas. We also postulate that the entire nearest subsurface region could be voided of any charged point-defects, whereas prevalent VO’s are largely responsible for mediation of the redox chemistry at reduced TiO2(110) surface.« less

Impaired auxin biosynthesis in the defective endosperm18 mutant is due to mutational loss of expression in the ZmYuc1 gene encoding endosperm-specific YUCCA1 protein in maize.

USDA-ARS?s Scientific Manuscript database

A seed-specific maize mutant, defective endosperm18 (de18), accumulates approximately 40% less dry mass and 10- to 15- fold less auxin (IAA) as compared to the De18; however, a causal basis of these changes is not known. Cellular analyses here showed that the de18 developing endosperm had lower tota...

Autophagy as a melanocytic self-defense mechanism.

PubMed

Setaluri, Vijayasaradhi

2015-05-01

Defects in autophagy have implications for melanocyte survival and manifestations of skin pigmentary disorders. Zhang et al. (2015) show that mouse melanocytes lacking the autophagy protein Atg7 undergo premature senescence in vitro and accumulate products of oxidative damage, despite activation of the redox response. Interestingly, contrary to previous findings, the melanocyte-specific deficiency in autophagy did not cause major defects in melanosome biogenesis, nor did it produce visually striking changes in mouse coat color.

In situ transmission electron microscopy He + implantation and thermal aging of nanocrystalline iron

DOE PAGES

Muntifering, Brittany R.; Fang, Youwu; Leff, Asher C.; ...

2016-10-04

Due to their high density of interfaces, nanostructured material are hypothesized to show a higher tolerance to radiation damage compared to conventional coarse-grained materials and are on interest for use in future nuclear reactors. In order to investigate the roles of vacancies, self-interstitials, and helium during defect accumulation, and the thermal evolution of such defects, a complex set of in situ TEM experiments were performed in nanocrystalline iron.

Study of Te Inclusion and Related Point Defects in THM-Growth CdMnTe Crystal

NASA Astrophysics Data System (ADS)

Mao, Yifei; Zhang, Jijun; Min, Jiahua; Liang, Xiaoyan; Huang, Jian; Tang, Ke; Ling, Liwen; Li, Ming; Zhang, Ying; Wang, Linjun

2018-02-01

This study establishes a model for describing the interaction between Te inclusions, dislocations and point defects in CdMnTe crystals. The role of the complex environment surrounding the formation of Te inclusions was analyzed. Images of Te inclusions captured by scanning electron microscope and infrared microscope were used to observe the morphology of Te inclusions. The morphology of Te inclusions is discussed in light of crystallography, from the crystal growth temperature at 900°C to the melting temperature of Te inclusions using the traveling heater method. The dislocation nets around Te inclusions were calculated by counting lattice mismatches between the Te inclusions and the bulk CdMnTe at 470°C. The point defects of Te antisites were found to be gathered around Te inclusions, with dislocation climb during the cooling phase of crystal growth from 470°C to room temperature. The Te inclusions, dislocation nets and surrounding point defects are considered to be an entirety for evaluating the effect of Te inclusions on CdMnTe detector performance, and an effective mobility-lifetime product (μτ) was obtained.

Investigation of point and extended defects in electron irradiated silicon—Dependence on the particle energy

NASA Astrophysics Data System (ADS)

Radu, R.; Pintilie, I.; Nistor, L. C.; Fretwurst, E.; Lindstroem, G.; Makarenko, L. F.

2015-04-01

This work is focusing on generation, time evolution, and impact on the electrical performance of silicon diodes impaired by radiation induced active defects. n-type silicon diodes had been irradiated with electrons ranging from 1.5 MeV to 27 MeV. It is shown that the formation of small clusters starts already after irradiation with high fluence of 1.5 MeV electrons. An increase of the introduction rates of both point defects and small clusters with increasing energy is seen, showing saturation for electron energies above ˜15 MeV. The changes in the leakage current at low irradiation fluence-values proved to be determined by the change in the configuration of the tri-vacancy (V3). Similar to V3, other cluster related defects are showing bistability indicating that they might be associated with larger vacancy clusters. The change of the space charge density with irradiation and with annealing time after irradiation is fully described by accounting for the radiation induced trapping centers. High resolution electron microscopy investigations correlated with the annealing experiments revealed changes in the spatial structure of the defects. Furthermore, it is shown that while the generation of point defects is well described by the classical Non Ionizing Energy Loss (NIEL), the formation of small defect clusters is better described by the "effective NIEL" using results from molecular dynamics simulations.

Defect classification in sparsity-based structural health monitoring

NASA Astrophysics Data System (ADS)

Golato, Andrew; Ahmad, Fauzia; Santhanam, Sridhar; Amin, Moeness G.

2017-05-01

Guided waves have gained popularity in structural health monitoring (SHM) due to their ability to inspect large areas with little attenuation, while providing rich interactions with defects. For thin-walled structures, the propagating waves are Lamb waves, which are a complex but well understood type of guided waves. Recent works have cast the defect localization problem of Lamb wave based SHM within the sparse reconstruction framework. These methods make use of a linear model relating the measurements with the scene reflectivity under the assumption of point-like defects. However, most structural defects are not perfect points but tend to assume specific forms, such as surface cracks or internal cracks. Knowledge of the "type" of defects is useful in the assessment phase of SHM. In this paper, we present a dual purpose sparsity-based imaging scheme which, in addition to accurately localizing defects, properly classifies the defects present simultaneously. The proposed approach takes advantage of the bias exhibited by certain types of defects toward a specific Lamb wave mode. For example, some defects strongly interact with the anti-symmetric modes, while others strongly interact with the symmetric modes. We build model based dictionaries for the fundamental symmetric and anti-symmetric wave modes, which are then utilized in unison to properly localize and classify the defects present. Simulated data of surface and internal defects in a thin Aluminum plate are used to validate the proposed scheme.

Optical signatures of deep level defects in Ga2O3

NASA Astrophysics Data System (ADS)

Gao, Hantian; Muralidharan, Shreyas; Pronin, Nicholas; Karim, Md Rezaul; White, Susan M.; Asel, Thaddeus; Foster, Geoffrey; Krishnamoorthy, Sriram; Rajan, Siddharth; Cao, Lei R.; Higashiwaki, Masataka; von Wenckstern, Holger; Grundmann, Marius; Zhao, Hongping; Look, David C.; Brillson, Leonard J.

2018-06-01

We used depth-resolved cathodoluminescence spectroscopy and surface photovoltage spectroscopy to measure the effects of near-surface plasma processing and neutron irradiation on native point defects in β-Ga2O3. The near-surface sensitivity and depth resolution of these optical techniques enabled us to identify spectral changes associated with removing or creating these defects, leading to identification of one oxygen vacancy-related and two gallium vacancy-related energy levels in the β-Ga2O3 bandgap. The combined near-surface detection and processing of Ga2O3 suggests an avenue for identifying the physical nature and reducing the density of native point defects in this and other semiconductors.

Plastidial Folate Prevents Starch Biosynthesis Triggered by Sugar Influx into Non-Photosynthetic Plastids of Arabidopsis

PubMed Central

Hayashi, Makoto; Tanaka, Mina; Yamamoto, Saki; Nakagawa, Taro; Kanai, Masatake; Anegawa, Aya; Ohnishi, Miwa; Mimura, Tetsuro; Nishimura, Mikio

2017-01-01

Abstract Regulation of sucrose–starch interconversion in plants is important to maintain energy supplies necessary for viability and growth. Arabidopsis mutants were screened for aberrant responses to sucrose to identify candidates with a defect in the regulation of starch biosynthesis. One such mutant, fpgs1-4, accumulated substantial amounts of starch in non-photosynthetic cells. Dark-grown mutant seedlings exhibited shortened hypocotyls and accumulated starch in etioplasts when supplied with exogenous sucrose/glucose. Similar starch accumulation from exogenous sucrose was observed in mutant chloroplasts, when photosynthesis was prevented by organ culture in darkness. Molecular genetic analyses revealed that the mutant was defective in plastidial folylpolyglutamate synthetase, one of the enzymes engaged in folate biosynthesis. Active folate derivatives are important biomolecules that function as cofactors for a variety of enzymes. Exogenously supplied 5-formyl-tetrahydrofolate abrogated the mutant phenotypes, indicating that the fpgs1-4 mutant produced insufficient folate derivative levels. In addition, the antifolate agents methotrexate and 5-fluorouracil induced starch accumulation from exogenously supplied sucrose in dark-grown seedlings of wild-type Arabidopsis. These results indicate that plastidial folate suppresses starch biosynthesis triggered by sugar influx into non-photosynthetic cells, demonstrating a hitherto unsuspected link between plastidial folate and starch metabolism. PMID:28586467

Poor repair of skeletal muscle in aging mice reflects a defect in local, interleukin-33-dependent, accumulation of regulatory T cells

PubMed Central

Kuswanto, Wilson; Burzyn, Dalia; Panduro, Marisella; Wang, Kathy K.; Jang, Young Charles; Wagers, Amy J.; Benoist, Christophe; Mathis, Diane

2016-01-01

SUMMARY Normal repair of skeletal muscle requires local expansion of a special population of Foxp3+CD4+ regulatory T (Treg) cells. Such cells failed to accumulate in acutely injured muscle of old mice, known to undergo ineffectual repair. This defect reflected reduced recruitment of Treg cells to injured muscle, as well as less proliferation and retention therein. Interleukin (IL)-33 regulated muscle Treg cell homeostasis in young mice, and its administration to old mice ameliorated their deficits in Treg cell accumulation and muscle regeneration. The major IL-33-expressing cells in skeletal muscle displayed a constellation of markers diagnostic of fibro/adipogenic progenitor cells, and were often associated with neural structures, including nerve fibers, nerve bundles and muscle spindles, which are stretch-sensitive mechanoreceptors important for proprioception. IL-33+ cells were more frequent after muscle injury, and were reduced in old mice. IL-33 is well situated to relay signals between the nervous and immune systems within the muscle context. PMID:26872699

Point Defects in Two-Dimensional Layered Semiconductors: Physics and Its Applications

NASA Astrophysics Data System (ADS)

Suh, Joonki

Recent advances in material science and semiconductor processing have been achieved largely based on in-depth understanding, efficient management and advanced application of point defects in host semiconductors, thus finding the relevant techniques such as doping and defect engineering as a traditional scientific and technological solution. Meanwhile, two- dimensional (2D) layered semiconductors currently draw tremendous attentions due to industrial needs and their rich physics at the nanoscale; as we approach the end of critical device dimensions in silicon-based technology, ultra-thin semiconductors have the potential as next- generation channel materials, and new physics also emerges at such reduced dimensions where confinement of electrons, phonons, and other quasi-particles is significant. It is therefore rewarding and interesting to understand and redefine the impact of lattice defects by investigating their interactions with energy/charge carriers of the host matter. Potentially, the established understanding will provide unprecedented opportunities for realizing new functionalities and enhancing the performance of energy harvesting and optoelectronic devices. In this thesis, multiple novel 2D layered semiconductors, such as bismuth and transition- metal chalcogenides, are explored. Following an introduction of conventional effects induced by point defects in semiconductors, the related physics of electronically active amphoteric defects is revisited in greater details. This can elucidate the complication of a two-dimensional electron gas coexisting with the topological states on the surface of bismuth chalcogenides, recently suggested as topological insulators. Therefore, native point defects are still one of the keys to understand and exploit topological insulators. In addition to from a fundamental science point of view, the effects of point defects on the integrated thermal-electrical transport, as well as the entropy-transporting process in thermoelectric materials are thoroughly investigated. Point defects can potentially beat the undesired coupling, often term "thermoelectric Bermuda triangle", among electrical conductivity, thermal conductivity and thermopower. The maximum thermoelectric performance is demonstrated with an intermediate density of defects when they beneficially and multi-functionally act as electron donors, as well as strongly energy-dependent electron and phonon scatterers. Therefore, this is a good example of how fundamental defect physics can be applied for practical devices toward renewable energy technology. Another interesting field of layered nanomaterials is on transition-metal dichalcogenides (TMDs), sensational candidates for 2D semiconductor physics and applications. At the reduced dimensionality of 2D where a far stronger correlation between point defects and charge carriers is expected, it is studied how chalcogen vacancies alter optical properties of monolayer TMDs. A new, sub-bandgap broad emission lines as well as increase in the overall photoluminescence intensity at low temperatures are reported as a result of high quantum efficiency of excitons, i.e., bound electron-hole pairs, localized at defect sites. On electrical transport, both n- and p-type materials are needed to form junctions and support bipolar carrier conduction while typically only one type of doping is stable for a particular TMD. For example, MoS2 is natively n-type, thus the lack of p-type doping hampers the development of charge-splitting p-n junctions of MoS2. To address this issue, we demonstrate stable p-type conduction in MoS2 by substitutional Nb doping up to the degenerate level. Proof-of-concept, van der Waals p-n homo-junctions based on vertically stacked MoS2 layers are also fabricated which enable gate-tuneable current rectification. Various electronic devices fabricated are stable in ambient air even without additional treatment such as capping layer protection, thanks to the substitutionality nature of the doping; this is in stark contrast to the existing approach of using molecular doping, which usually suffers from volatility and reactivity with air and/or water molecules.

Detection of small surface defects using DCT based enhancement approach in machine vision systems

NASA Astrophysics Data System (ADS)

He, Fuqiang; Wang, Wen; Chen, Zichen

2005-12-01

Utilizing DCT based enhancement approach, an improved small defect detection algorithm for real-time leather surface inspection was developed. A two-stage decomposition procedure was proposed to extract an odd-odd frequency matrix after a digital image has been transformed to DCT domain. Then, the reverse cumulative sum algorithm was proposed to detect the transition points of the gentle curves plotted from the odd-odd frequency matrix. The best radius of the cutting sector was computed in terms of the transition points and the high-pass filtering operation was implemented. The filtered image was then inversed and transformed back to the spatial domain. Finally, the restored image was segmented by an entropy method and some defect features are calculated. Experimental results show the proposed small defect detection method can reach the small defect detection rate by 94%.

Influence of chemical disorder on energy dissipation and defect evolution in concentrated solid solution alloys

PubMed Central

Zhang, Yanwen; Stocks, G. Malcolm; Jin, Ke; Lu, Chenyang; Bei, Hongbin; Sales, Brian C.; Wang, Lumin; Béland, Laurent K.; Stoller, Roger E.; Samolyuk, German D.; Caro, Magdalena; Caro, Alfredo; Weber, William J.

2015-01-01

A grand challenge in materials research is to understand complex electronic correlation and non-equilibrium atomic interactions, and how such intrinsic properties and dynamic processes affect energy transfer and defect evolution in irradiated materials. Here we report that chemical disorder, with an increasing number of principal elements and/or altered concentrations of specific elements, in single-phase concentrated solid solution alloys can lead to substantial reduction in electron mean free path and orders of magnitude decrease in electrical and thermal conductivity. The subsequently slow energy dissipation affects defect dynamics at the early stages, and consequentially may result in less deleterious defects. Suppressed damage accumulation with increasing chemical disorder from pure nickel to binary and to more complex quaternary solid solutions is observed. Understanding and controlling energy dissipation and defect dynamics by altering alloy complexity may pave the way for new design principles of radiation-tolerant structural alloys for energy applications. PMID:26507943

Defect silicene and graphene as applied to the anode of lithium-ion batteries: Numerical experiment

NASA Astrophysics Data System (ADS)

Galashev, A. E.; Rakhmanova, O. R.; Zaikov, Yu. P.

2016-09-01

Mechanical properties and stability of two layers of defect silicene supported by graphene sheets, between which the lithium ion passes under an electrostatic field, are studied by the molecular dynamics method. Defects are mono-, di-, tri-, and hexavacansies. Graphene and silicene edges are rigidly fixed. Graphene sheets contacting with silicene take a convex shape, deflecting outward. Mono- and divacancies in silicene tend to a size decrease; larger vacancies exhibit better stability. The ion motion control using an electric field becomes possible only using perfect silicene or silicene with mono- and divacancies. The ion penetrated through larger defects, and its motion in the silicene channel becomes uncontrolled. When the ion moves in the channel, the most strong stress spikes appear in silicene containing monovacancies. In the case of fixed edges, perfect silicene intercalated with a lithium ion is inclined to accumulate larger stresses than silicene containing defects.

Ab initio theory of point defects in oxide materials: structure, properties, chemical reactivity

NASA Astrophysics Data System (ADS)

Pacchioni, Gianfranco

2000-05-01

Point defects play a fundamental role in determining the physical and chemical properties of inorganic materials. This holds not only for the bulk properties but also for the surface of oxides where several kinds of point defects exist and exhibit a rich and complex chemistry. A particularly important defect in oxides is the oxygen vacancy. Depending on the electronic structure of the material the nature of oxygen vacancies changes dramatically. In this article we provide a rationalization of the very different electronic structure of neutral and charged oxygen vacancies in SiO 2 and MgO, two oxide materials with completely different electronic structure (from very ionic, MgO, to largely covalent, SiO 2). We used methods of ab initio quantum chemistry, from density functional theory (DFT) to configuration interaction (CI), to determine the ground and excited state properties of these defects. The theoretical results are combined with recent spectroscopic measurements. A series of observable properties has been determined in this way: defect formation energies, hyperfine interactions in electron paramagnetic resonance (EPR) spectra of paramagnetic centers, optical spectra, surface chemical reactivity. The interplay between experimental and theoretical information allows one to unambiguously identify the structure of oxygen vacancies in these binary oxides and on their surfaces.

Copper intercalation at the interface of graphene and Ir(111) studied by scanning tunneling microscopy

NASA Astrophysics Data System (ADS)

Sicot, M.; Fagot-Revurat, Y.; Kierren, B.; Vasseur, G.; Malterre, D.

2014-11-01

We report on the intercalation of a submonolayer of copper at 775 K underneath graphene epitaxially grown on Ir(111) studied by means of low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) at 77 K. Nucleation and growth dynamics of Cu below graphene have been investigated, and, most importantly, the intercalation mechanism has been identified. First, LEED patterns reveal the pseudomorphic growth of Cu on Ir under the topmost graphene layer resulting in a large Cu in-plane lattice parameter expansion of about 6% compared to Cu(111). Second, large-scale STM topographs as a function of Cu coverage show that Cu diffusion on Ir below graphene exhibits a low energy barrier resulting in Cu accumulation at Ir step edges. As a result, the graphene sheet undergoes a strong edges reshaping. Finally, atomically-resolved STM images reveal a damaged graphene sheet at the atomic scale after metal intercalation. Point defects in graphene were shown to be carbon vacancies. According to these results, a Cu penetration path beneath graphene is proposed to occur via metal aided defect formation with no or poor self healing of the graphene sheet. This work illustrates the fact that Cu intercalation is harmful for graphene grown on Ir(111) at the atomic scale.

Mitochondria drive autophagy pathology via microtubule disassembly: a new hypothesis for Parkinson disease.

PubMed

Arduíno, Daniela M; Esteves, A Raquel; Cardoso, Sandra Morais

2013-01-01

Neurons are exquisitely dependent on quality control systems to maintain a healthy intracellular environment. A permanent assessment of protein and organelle "quality" allows a coordinated action between repair and clearance of damage proteins and dysfunctional organelles. Impairments in the intracellular clearance mechanisms in long-lived postmitotic cells, like neurons, result in the progressive accumulation of damaged organelles and aggregates of aberrant proteins. Using cells bearing Parkinson disease (PD) patients' mitochondria, we demonstrated that aberrant accumulation of autophagosomes in PD, commonly interpreted as an abnormal induction of autophagy, is instead due to defective autophagic clearance. This defect is a consequence of alterations in the microtubule network driven by mitochondrial dysfunction that hinder mitochondria and autophagosome trafficking. We uncover mitochondria and microtubule-directed traffic as main players in the regulation of autophagy in PD.

Grain Boundary Effect on Charge Transport in Pentacene Thin Films

NASA Astrophysics Data System (ADS)

Weis, Martin; Gmucová, Katarína; Nádaždy, Vojtech; Majková, Eva; Haško, Daniel; Taguchi, Dai; Manaka, Takaaki; Iwamoto, Mitsumasa

2011-04-01

We report on charge transport properties of polycrystalline pentacene films with variable average grain size in the range from 0.1 to 0.3 µm controlled by the preparation technology. We illustrate with the organic field-effect transistors decrease of the effective mobility and presence of traps with decrease of the grain size. Analysis of the charge transfer excitons reveals decrease of the mobile charge density and the steady-state voltammetry showed significant increase of oxygen- and hydrogen-related defects. We also briefly discuss accumulation of the defects on the grain boundary and show relation between the defect density and grain boundary length.

Imaging active topological defects in carbon nanotubes

NASA Astrophysics Data System (ADS)

Suenaga, Kazu; Wakabayashi, Hideaki; Koshino, Masanori; Sato, Yuta; Urita, Koki; Iijima, Sumio

2007-06-01

A single-walled carbon nanotube (SWNT) is a wrapped single graphene layer, and its plastic deformation should require active topological defects-non-hexagonal carbon rings that can migrate along the nanotube wall. Although in situ transmission electron microscopy (TEM) has been used to examine the deformation of SWNTs, these studies deal only with diameter changes and no atomistic mechanism has been elucidated experimentally. Theory predicts that some topological defects can form through the Stone-Wales transformation in SWNTs under tension at 2,000 K, and could act as a dislocation core. We demonstrate here, by means of high-resolution (HR)-TEM with atomic sensitivity, the first direct imaging of pentagon-heptagon pair defects found in an SWNT that was heated at 2,273 K. Moreover, our in situ HR-TEM observation reveals an accumulation of topological defects near the kink of a deformed nanotube. This result suggests that dislocation motions or active topological defects are indeed responsible for the plastic deformation of SWNTs.

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

NASA Technical Reports Server (NTRS)

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

1996-01-01

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

Vacancy clustering and its dissociation process in electroless deposited copper films studied by monoenergetic positron beams

NASA Astrophysics Data System (ADS)

Uedono, A.; Yamashita, Y.; Tsutsui, T.; Dordi, Y.; Li, S.; Oshima, N.; Suzuki, R.

2012-05-01

Positron annihilation was used to probe vacancy-type defects in electroless deposited copper films. For as-deposited films, two different types of vacancy-type defects were found to coexist; these were identified as vacancy aggregates (V3-V4) and larger vacancy clusters (˜V10). After annealing at about 200 °C, the defects started to diffuse toward the surface and aggregate. The same tendency has been observed for sulfur only, suggesting the formation of complexes between sulfur and vacancies. The defect concentration near the Cu/barrier-metal interface was high even after annealing above 600 °C, and this was attributed to an accumulation of vacancy-impurity complexes. The observed defect reactions were attributed to suppression of the vacancy diffusion to sinks through the formation of impurity-vacancy complexes. It was shown that electroless plating has a high potential to suppress the formation of voids/hillocks caused by defect migration.

[Forensic medical evaluation of stab-incised wounds caused by knives with point defects].

PubMed

Krupin, K N; Leonov, S V

2011-01-01

The present experimental study allowed to characterize specific signs of stab-incised wounds caused by knives with operational point defects. Diagnostic coefficients calculated for these macro- and microscopic features facilitate differential diagnostics of the injuries and make it possible to identify a concrete stabbing/cutting weapon with which the wound was inflicted..

First-principles study on oxidation effects in uranium oxides and high-pressure high-temperature behavior of point defects in uranium dioxide

NASA Astrophysics Data System (ADS)

Geng, Hua Y.; Song, Hong X.; Jin, K.; Xiang, S. K.; Wu, Q.

2011-11-01

Formation Gibbs free energy of point defects and oxygen clusters in uranium dioxide at high-pressure high-temperature conditions are calculated from first principles, using the LSDA+U approach for the electronic structure and the Debye model for the lattice vibrations. The phonon contribution on Frenkel pairs is found to be notable, whereas it is negligible for the Schottky defect. Hydrostatic compression changes the formation energies drastically, making defect concentrations depend more sensitively on pressure. Calculations show that, if no oxygen clusters are considered, uranium vacancy becomes predominant in overstoichiometric UO2 with the aid of the contribution from lattice vibrations, while compression favors oxygen defects and suppresses uranium vacancy greatly. At ambient pressure, however, the experimental observation of predominant oxygen defects in this regime can be reproduced only in a form of cuboctahedral clusters, underlining the importance of defect clustering in UO2+x. Making use of the point defect model, an equation of state for nonstoichiometric oxides is established, which is then applied to describe the shock Hugoniot of UO2+x. Furthermore, the oxidization and compression behavior of uranium monoxide, triuranium octoxide, uranium trioxide, and a series of defective UO2 at 0 K are investigated. The evolution of mechanical properties and electronic structures with an increase of the oxidation degree are analyzed, revealing the transition of the ground state of uranium oxides from metallic to Mott insulator and then to charge-transfer insulator due to the interplay of strongly correlated effects of 5f orbitals and the shift of electrons from uranium to oxygen atoms.

Demineralized Bone Matrix Scaffolds Modified by CBD-SDF-1α Promote Bone Regeneration via Recruiting Endogenous Stem Cells.

PubMed

Shi, Jiajia; Sun, Jie; Zhang, Wen; Liang, Hui; Shi, Qin; Li, Xiaoran; Chen, Yanyan; Zhuang, Yan; Dai, Jianwu

2016-10-07

The reconstruction of bone usually depends on substitute transplantation, which has drawbacks including the limited bone substitutes available, comorbidity, immune rejection, and limited endogenous bone regeneration. Here, we constructed a functionalized bone substitute by combining application of the demineralized bone matrix (DBM) and collagen-binding stromal-cell-derived factor-1α (CBD-SDF-1α). DBM was a poriferous and biodegradable bone substitute, derived from bovine bone and consisting mainly of collagen. CBD-SDF-1α could bind to collagen and be controllably released from the DBM to mobilize stem cells. In a rat femur defect model, CBD-SDF-1α-modified DBM scaffolds could efficiently mobilize CD34 + and c-kit + endogenous stem cells homing to the injured site at 3 days after implantation. According to the data from micro-CT, CBD-SDF-1α-modified DBM scaffolds could help the bone defects rejoin with mineralization accumulated and bone volume expanded. Interestingly, osteoprotegerin (OPG) and osteopontin (OPN) were highly expressed in CBD-SDF-1α group at an early time after implantation, while osteocalcin (OCN) was more expanded. H&E and Masson's trichrome staining showed that the CBD-SDF-1α-modified DBM scaffold group had more osteoblasts and that the bone defect rejoined earlier. The ultimate strength of the regenerated bone was investigated by three-point bending, showing that the CBD-SDF-1α group had superior strength. In conclusion, CBD-SDF-1α-modified DBM scaffolds could promote bone regeneration by recruiting endogenous stem cells.

Anomalous Dirac point transport due to extended defects in bilayer graphene.

PubMed

Shallcross, Sam; Sharma, Sangeeta; Weber, Heiko B

2017-08-24

Charge transport at the Dirac point in bilayer graphene exhibits two dramatically different transport states, insulating and metallic, that occur in apparently otherwise indistinguishable experimental samples. We demonstrate that the existence of these two transport states has its origin in an interplay between evanescent modes, that dominate charge transport near the Dirac point, and disordered configurations of extended defects in the form of partial dislocations. In a large ensemble of bilayer systems with randomly positioned partial dislocations, the distribution of conductivities is found to be strongly peaked at both the insulating and metallic limits. We argue that this distribution form, that occurs only at the Dirac point, lies at the heart of the observation of both metallic and insulating states in bilayer graphene.In seemingly indistinguishable bilayer graphene samples, two distinct transport regimes, insulating and metallic, have been identified experimentally. Here, the authors demonstrate that these two states originate from the interplay between extended defects and evanescent modes at the Dirac point.

Defective control of pre–messenger RNA splicing in human disease

PubMed Central

Shkreta, Lulzim

2016-01-01

Examples of associations between human disease and defects in pre–messenger RNA splicing/alternative splicing are accumulating. Although many alterations are caused by mutations in splicing signals or regulatory sequence elements, recent studies have noted the disruptive impact of mutated generic spliceosome components and splicing regulatory proteins. This review highlights recent progress in our understanding of how the altered splicing function of RNA-binding proteins contributes to myelodysplastic syndromes, cancer, and neuropathologies. PMID:26728853

Developmental Defects of Caenorhabditis elegans Lacking Branched-chain α-Ketoacid Dehydrogenase Are Mainly Caused by Monomethyl Branched-chain Fatty Acid Deficiency.

PubMed

Jia, Fan; Cui, Mingxue; Than, Minh T; Han, Min

2016-02-05

Branched-chain α-ketoacid dehydrogenase (BCKDH) catalyzes the critical step in the branched-chain amino acid (BCAA) catabolic pathway and has been the focus of extensive studies. Mutations in the complex disrupt many fundamental metabolic pathways and cause multiple human diseases including maple syrup urine disease (MSUD), autism, and other related neurological disorders. BCKDH may also be required for the synthesis of monomethyl branched-chain fatty acids (mmBCFAs) from BCAAs. The pathology of MSUD has been attributed mainly to BCAA accumulation, but the role of mmBCFA has not been evaluated. Here we show that disrupting BCKDH in Caenorhabditis elegans causes mmBCFA deficiency, in addition to BCAA accumulation. Worms with deficiency in BCKDH function manifest larval arrest and embryonic lethal phenotypes, and mmBCFA supplementation suppressed both without correcting BCAA levels. The majority of developmental defects caused by BCKDH deficiency may thus be attributed to lacking mmBCFAs in worms. Tissue-specific analysis shows that restoration of BCKDH function in multiple tissues can rescue the defects, but is especially effective in neurons. Taken together, we conclude that mmBCFA deficiency is largely responsible for the developmental defects in the worm and conceivably might also be a critical contributor to the pathology of human MSUD. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.

Fabrication of a bionic microstructure on a C/SiC brake lining surface: Positive applications of surface defects for surface wetting control

NASA Astrophysics Data System (ADS)

Wu, M. L.; Ren, C. Z.; Xu, H. Z.; Zhou, C. L.

2018-05-01

The material removal processes generate interesting surface topographies, unfortunately, that was usually considered to be surface defects. To date, little attention has been devoted to the positive applications of these interesting surface defects resulted from laser ablation to improve C/SiC surface wettability. In this study, the formation mechanism behind surface defects (residual particles) is discussed first. The results showed that the residual particles with various diameters experienced regeneration and migration, causing them to accumulate repeatedly. The effective accumulation of these residual particles with various diameters provides a new method about fabricating bionic microstructures for surface wetting control. The negligible influence of ablation processes on the chemical component of the subsurface was studied by comparing the C-O-Si weight percentage at the C/SiC subsurface. A group of microstructures were fabricated under different laser trace and different laser parameters. Surface wettability experimental results for different types of microstructures were compared. The results showed that the surface wettability increased as the laser scanning speed decreased. The surface wettability increased with the density of the laser scanning trace. We also demonstrated the application of optimized combination of laser parameters and laser trace to simulate a lotus leaf's microstructure on C/SiC surfaces. The parameter selection depends on the specific material properties.

Effects of chemical alternation on damage accumulation in concentrated solid-solution alloys

DOE PAGES

Ullah, Mohammad W.; Xue, Haizhou; Velisa, Gihan; ...

2017-06-23

Single-phase concentrated solid-solution alloys (SP-CSAs) have recently gained unprecedented attention due to their promising properties. To understand effects of alloying elements on irradiation-induced defect production, recombination and evolution, an integrated study of ion irradiation, ion beam analysis and atomistic simulations are carried out on a unique set of model crystals with increasing chemical complexity, from pure Ni to Ni 80Fe 20, Ni 50Fe 50, and Ni 80Cr 20 binaries, and to a more complex Ni 40Fe 40Cr 20 alloy. Both experimental and simulation results suggest that the binary and ternary alloys exhibit higher radiation resistance than elemental Ni. The modelingmore » work predicts that Ni 40Fe 40Cr 20 has the best radiation tolerance, with the number of surviving Frenkel pairs being factors of 2.0 and 1.4 lower than pure Ni and the 80:20 binary alloys, respectively. While the reduced defect mobility in SP-CSAs is identified as a general mechanism leading to slower growth of large defect clusters, the effect of specific alloying elements on suppression of damage accumulation is clearly demonstrated. This work suggests that concentrated solid-solution provides an effective way to enhance radiation tolerance by creating elemental alternation at the atomic level. The demonstrated chemical effects on defect dynamics may inspire new design principles of radiation-tolerant structural alloys for advanced energy systems.« less

Experimental investigation on the microscopic structure of intrinsic paramagnetic point defects in amorphous silicon dioxide

NASA Astrophysics Data System (ADS)

Buscarino, G.

2007-11-01

In the present Ph.D. Thesis we report an experimental investigation on the effects of gamma- and beta-ray irradiation and of subsequent thermal treatment on many types of a-SiO2 materials, differing in the production methods, OH- and Al-content, and oxygen deficiencies. Our main objective is to gain further insight on the microscopic structures of the E'_gamma, E'_delta, E'_alpha and triplet paramagnetic centers, which are among the most important and studied class of radiation induced intrinsic point defects in a-SiO2. To pursue this objective, we use prevalently the EPR spectroscopy. In particular, our work is focused on the properties of the unpaired electrons wave functions involved in the defects, and this aspect is mainly investigated through the study of the EPR signals originating from the interaction of the unpaired electrons with 29Si magnetic nuclei (with nuclear spin I=1/2 and natural abundance 4.7 %). In addition, in some cases of interest, OA measurements are also performed with the aim to further characterize the electronic properties of the defects. Furthermore, due to its relevance for electronics application, the charge state of the defects is investigated by looking at the processes responsible for the generation of the defects of interest. Once these information were gained, the possible sites that can serve as precursors for defects formation are deduced, with the definitive purpose to obtain in the future more radiation resistant a-SiO2 materials in which the deleterious effects connected with the point defects are significantly reduced.

Ultralow Thermal Conductivity in Diamond-Like Semiconductors: Selective Scattering of Phonons from Antisite Defects

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

Gorai, Prashun; Stevanovic, Vladan; Toberer, Eric

In this work, we discover anomalously low lattice thermal conductivity (<0.25 W/mK at 300 degrees C) in the Hg-containing quaternary diamond-like semiconductors within the Cu2IIBIVTe4 (IIB: Zn, Cd, Hg) (IV: Si, Ge, Sn) set of compositions. Using high-temperature X-ray diffraction, resonant ultrasound spectroscopy, and transport properties, we uncover the critical role of the antisite defects HgCu and CuHg on phonon transport within the Hg-containing systems. Despite the differences in chemistry between Hg and Cu, the high concentration of these antisite defects emerges from the energetic proximity of the kesterite and stannite cation motifs. Our phonon calculations reveal that heavier groupmore » IIB elements not only introduce low-lying optical modes, but the subsequent antisite defects also possess unusually strong point defect phonon scattering power. The scattering strength stems from the fundamentally different vibrational modes supported by the constituent elements (e.g., Hg and Cu). Despite the significant impact on the thermal properties, antisite defects do not negatively impact the mobility (>50 cm2/(Vs) at 300 degrees C) in Hg-containing systems, leading to predicted zT > 1.5 in Cu2HgGeTe4 and Cu2HgSnTe4 under optimized doping. In addition to introducing a potentially new p-type thermoelectric material, this work provides (1) a strategy to use the proximity of phase transitions to increase point defect phonon scattering, and (2) a means to quantify the power of a given point defect through inexpensive phonon calculations.« less

Chronic acetaminophen ingestion resulting in severe anion gap metabolic acidosis secondary to 5-oxoproline accumulation: an under diagnosed phenomenon.

PubMed

O'Brien, L Morgan Nordstrom; Hooper, Michael; Flemmer, Mark; Marik, Paul Ellis

2012-07-03

Anion gap metabolic acidosis is commonly caused by lactic acidosis, ketoacidosis, and ingestion of methanol, salicylates, ethylene glycol or accumulation of organic/inorganic acids. However, rare causes of metabolic acidosis from enzyme defects, such as disturbances in the γ-glutamyl cycle, are being reported in higher frequencies in the adult population. Such disturbances cause an accumulation of 5-oxoproline and ultimately an anion gap metabolic acidosis. These disturbances are often associated with acetaminophen in the setting of certain risk factors such as sepsis, malnutrition, liver disease, female gender, pregnancy or renal failure.

DEFECTIVE TRAFFICKING OF CONE PHOTORECEPTOR CNG CHANNELS INDUCES THE UNFOLDED PROTEIN RESPONSE AND ER STRESS-ASSOCIATED CELL DEATH

PubMed Central

Duricka, Deborah L.; Brown, R. Lane; Varnum, Michael D.

2011-01-01

SYNOPSIS Mutations that perturb the function of photoreceptor cyclic nucleotide-gated (CNG) channels are associated with several human retinal disorders, but the molecular and cellular mechanisms leading to photoreceptor dysfunction and degeneration remain unclear. Many loss-of-function mutations result in intracellular accumulation of CNG channel subunits. Accumulation of proteins in the endoplasmic reticulum (ER) is known to cause ER stress and trigger the unfolded protein response (UPR), an evolutionarily conserved cellular program that results in either adaptation via increased protein processing capacity or apoptotic cell death. We hypothesize that defective trafficking of cone photoreceptor CNG channels can induce UPR-mediated cell death. To test this idea, CNGA3 subunits bearing the R563H and Q655X mutations were expressed in photoreceptor-derived 661W cells with CNGB3 subunits. Compared to wild type, R563H and Q655X subunits displayed altered degradation rates and/or were retained in the ER. ER retention was associated with increased expression of UPR-related markers of ER stress and with decreased cell viability. Chemical and pharmacological chaperones (TUDCA, 4PBA, and the cGMP analog CPT-cGMP) differentially reduced degradation and/or promoted plasma-membrane localization of defective subunits. Improved subunit maturation was concordant with reduced expression of ER stress markers and improved viability of cells expressing localization-defective channels. These results indicate that ER stress can arise from expression of localization defective CNG channels, and may represent a contributing factor for photoreceptor degeneration. PMID:21992067

Defective trafficking of cone photoreceptor CNG channels induces the unfolded protein response and ER-stress-associated cell death.

PubMed

Duricka, Deborah L; Brown, R Lane; Varnum, Michael D

2012-01-15

Mutations that perturb the function of photoreceptor CNG (cyclic nucleotide-gated) channels are associated with several human retinal disorders, but the molecular and cellular mechanisms leading to photoreceptor dysfunction and degeneration remain unclear. Many loss-of-function mutations result in intracellular accumulation of CNG channel subunits. Accumulation of proteins in the ER (endoplasmic reticulum) is known to cause ER stress and trigger the UPR (unfolded protein response), an evolutionarily conserved cellular programme that results in either adaptation via increased protein processing capacity or apoptotic cell death. We hypothesize that defective trafficking of cone photoreceptor CNG channels can induce UPR-mediated cell death. To test this idea, CNGA3 subunits bearing the R563H and Q655X mutations were expressed in photoreceptor-derived 661W cells with CNGB3 subunits. Compared with wild-type, R563H and Q655X subunits displayed altered degradation rates and/or were retained in the ER. ER retention was associated with increased expression of UPR-related markers of ER stress and with decreased cell viability. Chemical and pharmacological chaperones {TUDCA (tauroursodeoxycholate sodium salt), 4-PBA (sodium 4-phenylbutyrate) and the cGMP analogue CPT-cGMP [8-(4-chlorophenylthio)-cGMP]} differentially reduced degradation and/or promoted plasma-membrane localization of defective subunits. Improved subunit maturation was concordant with reduced expression of ER-stress markers and improved viability of cells expressing localization-defective channels. These results indicate that ER stress can arise from expression of localization-defective CNG channels, and may represent a contributing factor for photoreceptor degeneration.

First-principles investigation of point defect and atomic diffusion in Al2Ca

NASA Astrophysics Data System (ADS)

Tian, Xiao; Wang, Jia-Ning; Wang, Ya-Ping; Shi, Xue-Feng; Tang, Bi-Yu

2017-04-01

Point defects and atomic diffusion in Al2Ca have been studied from first-principles calculations within density functional framework. After formation energy and relative stability of point defects are investigated, several predominant diffusion processes in Al2Ca are studied, including sublattice one-step mechanism, 3-jump vacancy cycles and antistructure sublattice mechanism. The associated energy profiles are calculated with climbing image nudged elastic band (CI-NEB) method, then the saddle points and activation barriers during atomic diffusion are further determined. The resulted activation barriers show that both Al and Ca can diffuse mainly mediated by neighbor vacancy on their own sublattice. 3-jump cycle mechanism mediated by VCa may make some contribution to the overall Al diffusion. And antistructure (AS) sublattice mechanism can also play an important role in Ca atomic diffusion owing to the moderate activation barrier.

Defect production in nonlinear quench across a quantum critical point.

PubMed

Sen, Diptiman; Sengupta, K; Mondal, Shreyoshi

2008-07-04

We show that the defect density n, for a slow nonlinear power-law quench with a rate tau(-1) and an exponent alpha>0, which takes the system through a critical point characterized by correlation length and dynamical critical exponents nu and z, scales as n approximately tau(-alphanud/(alphaznu+1)) [n approximately (alphag((alpha-1)/alpha)/tau)(nud/(znu+1))] if the quench takes the system across the critical point at time t=0 [t=t(0) not = 0], where g is a nonuniversal constant and d is the system dimension. These scaling laws constitute the first theoretical results for defect production in nonlinear quenches across quantum critical points and reproduce their well-known counterpart for a linear quench (alpha=1) as a special case. We supplement our results with numerical studies of well-known models and suggest experiments to test our theory.

Stitching h-BN by atomic layer deposition of LiF as a stable interface for lithium metal anode

PubMed Central

Xie, Jin; Liao, Lei; Gong, Yongji; Li, Yanbin; Shi, Feifei; Pei, Allen; Sun, Jie; Zhang, Rufan; Kong, Biao; Subbaraman, Ram; Christensen, Jake; Cui, Yi

2017-01-01

Defects are important features in two-dimensional (2D) materials that have a strong influence on their chemical and physical properties. Through the enhanced chemical reactivity at defect sites (point defects, line defects, etc.), one can selectively functionalize 2D materials via chemical reactions and thereby tune their physical properties. We demonstrate the selective atomic layer deposition of LiF on defect sites of h-BN prepared by chemical vapor deposition. The LiF deposits primarily on the line and point defects of h-BN, thereby creating seams that hold the h-BN crystallites together. The chemically and mechanically stable hybrid LiF/h-BN film successfully suppresses lithium dendrite formation during both the initial electrochemical deposition onto a copper foil and the subsequent cycling. The protected lithium electrodes exhibit good cycling behavior with more than 300 cycles at relatively high coulombic efficiency (>95%) in an additive-free carbonate electrolyte. PMID:29202031

Stitching h-BN by atomic layer deposition of LiF as a stable interface for lithium metal anode

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

Xie, Jin; Liao, Lei; Gong, Yongji

Defects are important features in two-dimensional (2D) materials that have a strong influence on their chemical and physical properties. Through the enhanced chemical reactivity at defect sites (point defects, line defects, etc.), one can selectively functionalize 2D materials via chemical reactions and thereby tune their physical properties. We demonstrate the selective atomic layer deposition of LiF on defect sites of h-BN prepared by chemical vapor deposition. The LiF deposits primarily on the line and point defects of h-BN, thereby creating seams that hold the h-BN crystallites together. The chemically and mechanically stable hybrid LiF/h-BN film successfully suppresses lithium dendrite formationmore » during both the initial electrochemical deposition onto a copper foil and the subsequent cycling. In conclusion, the protected lithium electrodes exhibit good cycling behavior with more than 300 cycles at relatively high coulombic efficiency (>95%) in an additive-free carbonate electrolyte.« less

Stitching h-BN by atomic layer deposition of LiF as a stable interface for lithium metal anode

DOE PAGES

Xie, Jin; Liao, Lei; Gong, Yongji; ...

2017-11-29

Defects are important features in two-dimensional (2D) materials that have a strong influence on their chemical and physical properties. Through the enhanced chemical reactivity at defect sites (point defects, line defects, etc.), one can selectively functionalize 2D materials via chemical reactions and thereby tune their physical properties. We demonstrate the selective atomic layer deposition of LiF on defect sites of h-BN prepared by chemical vapor deposition. The LiF deposits primarily on the line and point defects of h-BN, thereby creating seams that hold the h-BN crystallites together. The chemically and mechanically stable hybrid LiF/h-BN film successfully suppresses lithium dendrite formationmore » during both the initial electrochemical deposition onto a copper foil and the subsequent cycling. In conclusion, the protected lithium electrodes exhibit good cycling behavior with more than 300 cycles at relatively high coulombic efficiency (>95%) in an additive-free carbonate electrolyte.« less

Radiation-modified natural zeolites for cleaning liquid nuclear waste (irradiation against radioactivity)

PubMed Central

Yeritsyan, Hrant; Sahakyan, Aram; Harutyunyan, Vachagan; Nikoghosyan, Sergey; Hakhverdyan, Eleonora; Grigoryan, Norair; Hovhannisyan, Aghasi; Atoyan, Vovik; Keheyan, Yeghis; Rhodes, Christopher

2013-01-01

There have been comparatively few investigations reported of radiation effects in zeolites, although it is known that these materials may be modified substantially by exposure to ionizing radiation. Thus, by exposure to γ-rays or high-energy particles, the charge states of atoms may be changed so to create, and accumulate, lattice point defects, and to form structurally disordered regions. Such a technique may permit the creation, in a controlled fashion, of additionally useful properties of the material while preserving its essential stoichiometry and structure. Accordingly, we present an application, in which the cation-exchange capacity of a natural zeolite (clinoptilolite) is substantially enhanced, for the treatment/decontamination of water contaminated with radionuclides e.g. 134Cs, 137Cs and 90Sr, by its exposure to high-energy (8 MeV) electrons, and to different total doses. PMID:24132177

Point defects in thorium nitride: A first-principles study

NASA Astrophysics Data System (ADS)

Pérez Daroca, D.; Llois, A. M.; Mosca, H. O.

2016-11-01

Thorium and its compounds (carbides and nitrides) are being investigated as possible materials to be used as nuclear fuels for Generation-IV reactors. As a first step in the research of these materials under irradiation, we study the formation energies and stability of point defects in thorium nitride by means of first-principles calculations within the framework of density functional theory. We focus on vacancies, interstitials, Frenkel pairs and Schottky defects. We found that N and Th vacancies have almost the same formation energy and that the most energetically favorable defects of all studied in this work are N interstitials. These kind of results for ThN, to the best authors' knowledge, have not been obtained previously, neither experimentally, nor theoretically.

Estimates of point defect production in α-quartz using molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Cowen, Benjamin J.; El-Genk, Mohamed S.

2017-07-01

Molecular dynamics (MD) simulations are performed to investigate the production of point defects in α-quartz by oxygen and silicon primary knock-on atoms (PKAs) of 0.25-2 keV. The Wigner-Seitz (WS) defect analysis is used to identify the produced vacancies, interstitials, and antisites, and the coordination defect analysis is used to identify the under and over-coordinated oxygen and silicon atoms. The defects at the end of the ballistic phase and the residual defects, after annealing, increase with increased PKA energy, and are statistically the same for the oxygen and silicon PKAs. The WS defect analysis results show that the numbers of the oxygen vacancies and interstitials (VO, Oi) at the end of the ballistic phase is the highest, followed closely by those of the silicon vacancies and interstitials (VSi, Sii). The number of the residual oxygen and silicon vacancies and interstitials are statistically the same. In addition, the under-coordinated OI and SiIII, which are the primary defects during the ballistic phase, have high annealing efficiencies (>89%). The over-coordinated defects of OIII and SiV, which are not nearly as abundant in the ballistic phase, have much lower annealing efficiencies (<63%) that decrease with increased PKA energy.

X-Ray Diffraction and Imaging Study of Imperfections of Crystallized Lysozyme with Coherent X-Rays

NASA Technical Reports Server (NTRS)

Hu, Zheng-Wei; Chu, Y. S.; Lai, B.; Cai, Z.; Thomas, B. R.; Chernov, A. A.

2003-01-01

Phase-sensitive x-ray diffraction imaging and high angular-resolution diffraction combined with phase contrast radiographic imaging are employed to characterize defects and perfection of a uniformly grown tetragonal lysozyme crystal in symmetric Laue case. The fill width at half-maximum (FWHM) of a 4 4 0 rocking curve measured from the original crystal is approximately 16.7 arcseconds, and defects, which include point defects, line defects, and microscopic domains, have been clearly observed in the diffraction images of the crystal. The observed line defects carry distinct dislocation features running approximately along the <110> growth front, and they have been found to originate mostly at a central growth area and occasionally at outer growth regions. Individual point defects trapped at a crystal nucleus are resolved in the images of high sensitivity to defects. Slow dehydration has led to the broadening of the 4 4 0 rocking curve by a factor of approximately 2.4. A significant change of the defect structure and configuration with drying has been revealed, which suggests the dehydration induced migration and evolution of dislocations and lattice rearrangements to reduce overall strain energy. The sufficient details of the observed defects shed light upon perfection, nucleation and growth, and properties of protein crystals.

Fast Estimation of Defect Profiles from the Magnetic Flux Leakage Signal Based on a Multi-Power Affine Projection Algorithm

PubMed Central

Han, Wenhua; Shen, Xiaohui; Xu, Jun; Wang, Ping; Tian, Guiyun; Wu, Zhengyang

2014-01-01

Magnetic flux leakage (MFL) inspection is one of the most important and sensitive nondestructive testing approaches. For online MFL inspection of a long-range railway track or oil pipeline, a fast and effective defect profile estimating method based on a multi-power affine projection algorithm (MAPA) is proposed, where the depth of a sampling point is related with not only the MFL signals before it, but also the ones after it, and all of the sampling points related to one point appear as serials or multi-power. Defect profile estimation has two steps: regulating a weight vector in an MAPA filter and estimating a defect profile with the MAPA filter. Both simulation and experimental data are used to test the performance of the proposed method. The results demonstrate that the proposed method exhibits high speed while maintaining the estimated profiles clearly close to the desired ones in a noisy environment, thereby meeting the demand of accurate online inspection. PMID:25192314

Fast estimation of defect profiles from the magnetic flux leakage signal based on a multi-power affine projection algorithm.

PubMed

Han, Wenhua; Shen, Xiaohui; Xu, Jun; Wang, Ping; Tian, Guiyun; Wu, Zhengyang

2014-09-04

Magnetic flux leakage (MFL) inspection is one of the most important and sensitive nondestructive testing approaches. For online MFL inspection of a long-range railway track or oil pipeline, a fast and effective defect profile estimating method based on a multi-power affine projection algorithm (MAPA) is proposed, where the depth of a sampling point is related with not only the MFL signals before it, but also the ones after it, and all of the sampling points related to one point appear as serials or multi-power. Defect profile estimation has two steps: regulating a weight vector in an MAPA filter and estimating a defect profile with the MAPA filter. Both simulation and experimental data are used to test the performance of the proposed method. The results demonstrate that the proposed method exhibits high speed while maintaining the estimated profiles clearly close to the desired ones in a noisy environment, thereby meeting the demand of accurate online inspection.

On the Enthalpy and Entropy of Point Defect Formation in Crystals

NASA Astrophysics Data System (ADS)

Kobelev, N. P.; Khonik, V. A.

2018-03-01

A standard way to determine the formation enthalpy H and entropy S of point defect formation in crystals consists in the application of the Arrhenius equation for the defect concentration. In this work, we show that a formal use of this method actually gives the effective (apparent) values of these quantities, which appear to be significantly overestimated. The underlying physical reason lies in temperature-dependent formation enthalpy of the defects, which is controlled by temperature dependence of the elastic moduli. We present an evaluation of the "true" H- and S-values for aluminum, which are derived on the basis of experimental data by taking into account temperature dependence of the formation enthalpy related to temperature dependence of the elastic moduli. The knowledge of the "true" activation parameters is needed for a correct calculation of the defect concentration constituting thus an issue of major importance for different fundamental and application issues of condensed matter physics and chemistry.

Influence of point defects on the thermal conductivity in FeSi

NASA Astrophysics Data System (ADS)

Stern, Robin; Wang, Tao; Carrete, Jesús; Mingo, Natalio; Madsen, Georg K. H.

2018-05-01

The unique transport properties of B20 FeSi have been investigated for decades. The progress in theoretical calculations allows the explanation and prediction of more and more of such properties. In this paper we investigate the lattice thermal conductivity of FeSi. Calculation for pristine FeSi severely overestimates the lattice thermal conductivity compared to experiment. We point out that the defect concentration can be considerably larger than indicated by the Hall coefficient. The defect formation energies are calculated and it is found that a substantial amount of iron vacancies can form at thermal equilibrium. These will lead to an increased phonon scattering. To explain the thermal conductivity of FeSi, we consider phonon-phonon, isotope, and phonon-defect scattering to assess possible scattering mechanisms. The calculated thermal conductivities indicate that phonon-defect scattering is important in order to explain the reported experimental values.

Electrically active point defects in Mg implanted n-type GaN grown by metal-organic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Alfieri, G.; Sundaramoorthy, V. K.; Micheletto, R.

2018-05-01

Magnesium (Mg) is the p-type doping of choice for GaN, and selective area doping by ion implantation is a routine technique employed during device processing. While electrically active defects have been thoroughly studied in as-grown GaN, not much is known about defects generated by ion implantation. This is especially true for the case of Mg. In this study, we carried out an electrical characterization investigation of point defects generated by Mg implantation in GaN. We have found at least nine electrically active levels in the 0.2-1.2 eV energy range, below the conduction band. The isochronal annealing behavior of these levels showed that most of them are thermally stable up to 1000 °C. The nature of the detected defects is then discussed in the light of the results found in the literature.

Point defects in hexagonal germanium carbide monolayer: A first-principles calculation

NASA Astrophysics Data System (ADS)

Ersan, Fatih; Gökçe, Aytaç Gürhan; Aktürk, Ethem

2016-12-01

On the basis of first-principles plane-wave calculations, we investigated the electronic and magnetic properties of various point defects including single Ge and C vacancies, Ge + C divacancy, Ge↔C antisites and the Stone-Wales (SW) defects in a GeC monolayer. We found that various periodic vacancy defects in GeC single layer give rise to crucial effects on the electronic and magnetic properties. The band gaps of GeC monolayer vary significantly from 0.308 eV to 1.738 eV due to the presence of antisites and Stone-Wales defects. While nonmagnetic ground state of semiconducting GeC turns into metal by introducing a carbon vacancy, it becomes half-metal by a single Ge vacancy with high magnetization (4 μB) value per supercell. All the vacancy types have zero net magnetic moments, except single Ge vacancy.

Identification of bearing faults using time domain zero-crossings

NASA Astrophysics Data System (ADS)

William, P. E.; Hoffman, M. W.

2011-11-01

In this paper, zero-crossing characteristic features are employed for early detection and identification of single point bearing defects in rotating machinery. As a result of bearing defects, characteristic defect frequencies appear in the machine vibration signal, normally requiring spectral analysis or envelope analysis to identify the defect type. Zero-crossing features are extracted directly from the time domain vibration signal using only the duration between successive zero-crossing intervals and do not require estimation of the rotational frequency. The features are a time domain representation of the composite vibration signature in the spectral domain. Features are normalized by the length of the observation window and classification is performed using a multilayer feedforward neural network. The model was evaluated on vibration data recorded using an accelerometer mounted on an induction motor housing subjected to a number of single point defects with different severity levels.

Motility and Chemotaxis Mediate the Preferential Colonization of Gastric Injury Sites by Helicobacter pylori

PubMed Central

Aihara, Eitaro; Closson, Chet; Matthis, Andrea L.; Schumacher, Michael A.; Engevik, Amy C.; Zavros, Yana; Ottemann, Karen M.; Montrose, Marshall H.

2014-01-01

Helicobacter pylori (H. pylori) is a pathogen contributing to peptic inflammation, ulceration, and cancer. A crucial step in the pathogenic sequence is when the bacterium first interacts with gastric tissue, an event that is poorly understood in vivo. We have shown that the luminal space adjacent to gastric epithelial damage is a microenvironment, and we hypothesized that this microenvironment might enhance H. pylori colonization. Inoculation with 106 H. pylori (wild-type Sydney Strain 1, SS1) significantly delayed healing of acetic-acid induced ulcers at Day 1, 7 and 30 post-inoculation, and wild-type SS1 preferentially colonized the ulcerated area compared to uninjured gastric tissue in the same animal at all time points. Gastric resident Lactobacillus spp. did not preferentially colonize ulcerated tissue. To determine whether bacterial motility and chemotaxis are important to ulcer healing and colonization, we analyzed isogenic H. pylori mutants defective in motility (ΔmotB) or chemotaxis (ΔcheY). ΔmotB (106) failed to colonize ulcerated or healthy stomach tissue. ΔcheY (106) colonized both tissues, but without preferential colonization of ulcerated tissue. However, ΔcheY did modestly delay ulcer healing, suggesting that chemotaxis is not required for this process. We used two-photon microscopy to induce microscopic epithelial lesions in vivo, and evaluated accumulation of fluorescently labeled H. pylori at gastric damage sites in the time frame of minutes instead of days. By 5 min after inducing damage, H. pylori SS1 preferentially accumulated at the site of damage and inhibited gastric epithelial restitution. H. pylori ΔcheY modestly accumulated at the gastric surface and inhibited restitution, but did not preferentially accumulate at the injury site. H. pylori ΔmotB neither accumulated at the surface nor inhibited restitution. We conclude that bacterial chemosensing and motility rapidly promote H. pylori colonization of injury sites, and thereby biases the injured tissue towards sustained gastric damage. PMID:25033386

Motility and chemotaxis mediate the preferential colonization of gastric injury sites by Helicobacter pylori.

PubMed

Aihara, Eitaro; Closson, Chet; Matthis, Andrea L; Schumacher, Michael A; Engevik, Amy C; Zavros, Yana; Ottemann, Karen M; Montrose, Marshall H

2014-07-01

Helicobacter pylori (H. pylori) is a pathogen contributing to peptic inflammation, ulceration, and cancer. A crucial step in the pathogenic sequence is when the bacterium first interacts with gastric tissue, an event that is poorly understood in vivo. We have shown that the luminal space adjacent to gastric epithelial damage is a microenvironment, and we hypothesized that this microenvironment might enhance H. pylori colonization. Inoculation with 106 H. pylori (wild-type Sydney Strain 1, SS1) significantly delayed healing of acetic-acid induced ulcers at Day 1, 7 and 30 post-inoculation, and wild-type SS1 preferentially colonized the ulcerated area compared to uninjured gastric tissue in the same animal at all time points. Gastric resident Lactobacillus spp. did not preferentially colonize ulcerated tissue. To determine whether bacterial motility and chemotaxis are important to ulcer healing and colonization, we analyzed isogenic H. pylori mutants defective in motility (ΔmotB) or chemotaxis (ΔcheY). ΔmotB (10(6)) failed to colonize ulcerated or healthy stomach tissue. ΔcheY (10(6)) colonized both tissues, but without preferential colonization of ulcerated tissue. However, ΔcheY did modestly delay ulcer healing, suggesting that chemotaxis is not required for this process. We used two-photon microscopy to induce microscopic epithelial lesions in vivo, and evaluated accumulation of fluorescently labeled H. pylori at gastric damage sites in the time frame of minutes instead of days. By 5 min after inducing damage, H. pylori SS1 preferentially accumulated at the site of damage and inhibited gastric epithelial restitution. H. pylori ΔcheY modestly accumulated at the gastric surface and inhibited restitution, but did not preferentially accumulate at the injury site. H. pylori ΔmotB neither accumulated at the surface nor inhibited restitution. We conclude that bacterial chemosensing and motility rapidly promote H. pylori colonization of injury sites, and thereby biases the injured tissue towards sustained gastric damage.

Dimensional control of defect dynamics in perovskite oxide superlattices

NASA Astrophysics Data System (ADS)

Bredeson, Isaac; Zhang, Lipeng; Kent, P. R. C.; Cooper, Valentino R.; Xu, Haixuan

2018-03-01

Point defects play a critical role in the structural, physical, and interfacial properties of perovskite oxide superlattices. However, understanding of the fundamental properties of point defects in superlattices, especially their transport properties, is rather limited. Here, we report predictions of the stability and dynamics of oxygen vacancies in SrTi O3/PbTi O3 oxide superlattices using first-principles calculations in combination with the kinetic Monte Carlo method. By varying the stacking period, i.e., changing of n in n STO /n PTO , we discover a crossover from three-dimensional diffusion to primarily two-dimensional planar diffusion. Such planar diffusion may lead to novel designs of ionic conductors. We show that the dominant vacancy position may vary in the superlattices, depending on the superlattice structure and stacking period, contradicting the common assumption that point defects reside at interfaces. Moreover, we predict a significant increase in room-temperature ionic conductivity for 3STO/3PTO relative to the bulk phases. Considering the variety of cations that can be accommodated in perovskite superlattices and the potential mismatch of spin, charge, and orbitals at the interfaces, this paper identifies a pathway to control defect dynamics for technological applications.

Combining the 3D model generated from point clouds and thermography to identify the defects presented on the facades of a building

NASA Astrophysics Data System (ADS)

Huang, Yishuo; Chiang, Chih-Hung; Hsu, Keng-Tsang

2018-03-01

Defects presented on the facades of a building do have profound impacts on extending the life cycle of the building. How to identify the defects is a crucial issue; destructive and non-destructive methods are usually employed to identify the defects presented on a building. Destructive methods always cause the permanent damages for the examined objects; on the other hand, non-destructive testing (NDT) methods have been widely applied to detect those defects presented on exterior layers of a building. However, NDT methods cannot provide efficient and reliable information for identifying the defects because of the huge examination areas. Infrared thermography is often applied to quantitative energy performance measurements for building envelopes. Defects on the exterior layer of buildings may be caused by several factors: ventilation losses, conduction losses, thermal bridging, defective services, moisture condensation, moisture ingress, and structure defects. Analyzing the collected thermal images can be quite difficult when the spatial variations of surface temperature are small. In this paper the authors employ image segmentation to cluster those pixels with similar surface temperatures such that the processed thermal images can be composed of limited groups. The surface temperature distribution in each segmented group is homogenous. In doing so, the regional boundaries of the segmented regions can be identified and extracted. A terrestrial laser scanner (TLS) is widely used to collect the point clouds of a building, and those point clouds are applied to reconstruct the 3D model of the building. A mapping model is constructed such that the segmented thermal images can be projected onto the 2D image of the specified 3D building. In this paper, the administrative building in Chaoyang University campus is used as an example. The experimental results not only provide the defect information but also offer their corresponding spatial locations in the 3D model.

The role of disclinations on the organization and conductivity in liquid crystal nanocomposites

NASA Astrophysics Data System (ADS)

Martinez-Miranda, Luz J.; Romero-Hasler, P.; Meneses-Franco, A.; Soto-Bustamante, E. A.

The structure of TiO2 nanoparticles in a liquid crystal nanocomposite was found to be an oblique structure due to the alignment of the TiO2 with respect to the liquid crystals. This order is anisotropic due to the ordering of the liquid crystals. The particles are highly localized in the nanocomposite, which has consequences in the electrical percolation. We want to obtain an understanding of how the nanoparticles organize in this highly localized fashion. The nanoparticles and the liquid crystals phase separate, with the nanoparticles accumulating in the defects exhibited by the liquid crystal even after being sonicated initially. The liquid crystal is polymerized by the process of electropolymerization that takes place in the isotropic phase of the monomers. The nanoparticles are free to move away from the defects where they phase separate since the defects disappear in the isotropic. We believe the polymerization imposes a limitation in the movement of the nanoparticles. The combination of the accumulation in the disclinations, the polymerization in the isotropic and the formation of the liquid crystal unit side chains can affect the conductivity of the nanocomposite. NSF-OISE-1157589; Fondecyt Project 1130187; CONICYT scholarships 21130413 and 21090713.

Wiskott-Aldrich syndrome protein is required for NK cell cytotoxicity and colocalizes with actin to NK cell-activating immunologic synapses

NASA Astrophysics Data System (ADS)

Orange, Jordan S.; Ramesh, Narayanaswamy; Remold-O'Donnell, Eileen; Sasahara, Yoji; Koopman, Louise; Byrne, Michael; Bonilla, Francisco A.; Rosen, Fred S.; Geha, Raif S.; Strominger, Jack L.

2002-08-01

The Wiskott-Aldrich syndrome (WAS) is a primary immunodeficiency disorder caused by a mutation in WAS protein (WASp) that results in defective actin polymerization. Although the function of many hematopoietic cells requires WASp, the specific expression and function of this molecule in natural killer (NK) cells is unknown. Here, we report that WAS patients have increased percentages of peripheral blood NK cells and that fresh enriched NK cells from two patients with a WASp mutation have defective cytolytic function. In normal NK cells, WASp was expressed and localized to the activating immunologic synapse (IS) with filamentous actin (F-actin). Perforin also localized to the NK cell-activating IS but at a lesser frequency than F-actin and WASp. The accumulation of F-actin and WASp at the activating IS was decreased significantly in NK cells that had been treated with the inhibitor of actin polymerization, cytochalasin D. NK cells from WAS patients lacked expression of WASp and accumulated F-actin at the activating IS infrequently. Thus, WASp has an important function in NK cells. In patients with WASp mutations, the resulting NK cell defects are likely to contribute to their disease.

Increased Phonon Scattering by Nanograins and Point Defects in Nanostructured Silicon with a Low Concentration of Germanium

NASA Astrophysics Data System (ADS)

Zhu, G. H.; Lee, H.; Lan, Y. C.; Wang, X. W.; Joshi, G.; Wang, D. Z.; Yang, J.; Vashaee, D.; Guilbert, H.; Pillitteri, A.; Dresselhaus, M. S.; Chen, G.; Ren, Z. F.

2009-05-01

The mechanism for phonon scattering by nanostructures and by point defects in nanostructured silicon (Si) and the silicon germanium (Ge) alloy and their thermoelectric properties are investigated. We found that the thermal conductivity is reduced by a factor of 10 in nanostructured Si in comparison with bulk crystalline Si. However, nanosize interfaces are not as effective as point defects in scattering phonons with wavelengths shorter than 1 nm. We further found that a 5at.% Ge replacing Si is very efficient in scattering phonons shorter than 1 nm, resulting in a further thermal conductivity reduction by a factor of 2, thereby leading to a thermoelectric figure of merit 0.95 for Si95Ge5, similar to that of large grained Si80Ge20 alloys.

Gamma-rays and heat-treatment conversions of point defects in massive rose quartz from the Borborema Pegmatite Province, Northeast Brazil

NASA Astrophysics Data System (ADS)

Guzzo, Pedro L.; Barreto, Sandra B.; Miranda, Milena R.; Gonzaga, Raysa S. G.; Casals, Sandra A.

2017-11-01

An extensive characterization of trace elements and point defects in rose quartz from the Borborema Pegmatite Province (BPP) in the northeast of Brazil was carried out by complementary spectroscopic methods. The aim here was to document the change in the configuration of point defects into the quartz lattice induced by heat-treatment and ionizing radiation. The samples were extracted from the core of two granitic rare element (REL) pegmatites, Taboa (Carnaúba dos Dantas, RN) and Alto do Feio (Pedra Lavrada, PB). The contents of Al, P, Ti, Ni, Fe, Ge, Li, Be, B and K were measured by laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Polished plates were heat-treated at 500 and 1000 °C and then irradiated with 50 kGy of γ rays. Point defects were characterized by optical (UV-Vis), infrared (IR), and electron paramagnetic resonance (EPR) spectroscopies. In the as-received condition, [AlO4/H]0 centers, Li- and B-dependent OH defects were observed. Point defects related to Al and Li species were significantly affected by heat-treatment at 1000 °C and/or γ radiation. Paramagnetic centers such as [AlO4]0, [GeO4/Li]0, [TiO4/Li]0 and [O2 3-/Li]0 were created by the diffusion of Li+ ions from their original diamagnetic centers related to substitutional Al3+ and OH-species. The smoky color developed after irradiation and the signal intensities of the paramagnetic centers were independent from the original rose color grade. The samples from the Taboa (TB) pegmatite showed the highest concentration of Al, Ti, Fe and Li elements as well as the highest signal intensities for [AlO4]0, [AlO4/H]0, [GeO4/Li]0 and [TiO4/Li]0 centers. Although TB also showed the higher concentration of B element, the intensity of the 3597 cm-1 IR band related to [BO4/H]0 centers was higher for Alto do Feio (AF) samples. This result suggests that the uptake of B into the quartz core of each pegmatite took place through different mechanisms. It was concluded that the change in the point defect configuration was essentially governed by the motion of Li species whose incorporation into the quartz lattice is closely related to Al concentration.

Chondral defect repair after the microfracture procedure: a nonhuman primate model.

PubMed

Gill, Thomas J; McCulloch, Patrick C; Glasson, Sonya S; Blanchet, Tracey; Morris, Elizabeth A

2005-05-01

The extent and time course of chondral defect healing after microfracture in humans are not well described. Although most physicians recommend a period of activity and weightbearing restriction to protect the healing cartilage, there are limited data on which to base decisions regarding the duration of such restrictions. Evaluation of the status of chondral defect repair at different time points after microfracture in a primate model may provide a rationale for postoperative activity recommendations. Descriptive laboratory study. Full-thickness chondral defects created on the femoral condyles and trochlea of 12 cynomolgus macaques were treated with microfracture and evaluated by gross and histologic examination at 6 and 12 weeks. At 6 weeks, there was limited chondral repair and ongoing resorption of subchondral bone. By 12 weeks, the defects were completely filled and showed more mature cartilage and bone repair. In the primate animal model, significant improvements in the extent and quality of cartilage repair were observed from the 6- to 12-week time points after microfracture. The poor status of the defect repair at 6 weeks and the ongoing healing observed from the 6- to 12-week time points may indicate that the repair is vulnerable during this initial postoperative period. Assuming the goal of postoperative weightbearing and activity restriction in patients after microfracture is to protect immature repair tissue, this study lends support to extending such recommendations longer than 6 weeks.

Metabolic states following accumulation of intracellular aggregates: implications for neurodegenerative diseases.

PubMed

Vazquez, Alexei

2013-01-01

The formation of intracellular aggregates is a common etiology of several neurodegenerative diseases. Mitochondrial defects and oxidative stress has been pointed as the major mechanistic links between the accumulation of intracellular aggregates and cell death. In this work we propose a "metabolic cell death by overcrowding" as an alternative hypothesis. Using a model of neuron metabolism, we predict that as the concentration of protein aggregates increases the neurons transit through three different metabolic phases. The first phase (0-6 mM) corresponds with the normal neuron state, where the neuronal activity is sustained by the oxidative phosphorylation of lactate. The second phase (6-8.6 mM) is characterized by a mixed utilization of lactate and glucose as energy substrates and a switch from ammonia uptake to ammonia release by neurons. In the third phase (8.6-9.3 mM) neurons are predicted to support their energy demands from glycolysis and an alternative pathway for energy generation, involving reactions from serine synthesis, one carbon metabolism and the glycine cleavage system. The model also predicts a decrease in the maximum neuronal capacity for energy generation with increasing the concentration of protein aggregates. Ultimately this maximum capacity becomes zero when the protein aggregates reach a concentration of about 9.3 mM, predicting the cessation of neuronal activity.

Recapitulation of premature ageing with iPSCs from Hutchinson-Gilford progeria syndrome.

PubMed

Liu, Guang-Hui; Barkho, Basam Z; Ruiz, Sergio; Diep, Dinh; Qu, Jing; Yang, Sheng-Lian; Panopoulos, Athanasia D; Suzuki, Keiichiro; Kurian, Leo; Walsh, Christopher; Thompson, James; Boue, Stephanie; Fung, Ho Lim; Sancho-Martinez, Ignacio; Zhang, Kun; Yates, John; Izpisua Belmonte, Juan Carlos

2011-04-14

Hutchinson-Gilford progeria syndrome (HGPS) is a rare and fatal human premature ageing disease, characterized by premature arteriosclerosis and degeneration of vascular smooth muscle cells (SMCs). HGPS is caused by a single point mutation in the lamin A (LMNA) gene, resulting in the generation of progerin, a truncated splicing mutant of lamin A. Accumulation of progerin leads to various ageing-associated nuclear defects including disorganization of nuclear lamina and loss of heterochromatin. Here we report the generation of induced pluripotent stem cells (iPSCs) from fibroblasts obtained from patients with HGPS. HGPS-iPSCs show absence of progerin, and more importantly, lack the nuclear envelope and epigenetic alterations normally associated with premature ageing. Upon differentiation of HGPS-iPSCs, progerin and its ageing-associated phenotypic consequences are restored. Specifically, directed differentiation of HGPS-iPSCs to SMCs leads to the appearance of premature senescence phenotypes associated with vascular ageing. Additionally, our studies identify DNA-dependent protein kinase catalytic subunit (DNAPKcs, also known as PRKDC) as a downstream target of progerin. The absence of nuclear DNAPK holoenzyme correlates with premature as well as physiological ageing. Because progerin also accumulates during physiological ageing, our results provide an in vitro iPSC-based model to study the pathogenesis of human premature and physiological vascular ageing.

PROGRESS IN THE STUDY OF ION IRRADIATION IN TUNGSTEN

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

Jiang, Weilin; Kruska, Karen; Henager, Charles H.

2017-02-27

The experimental study intends to generate data to validate the theoretical predictions on defect accumulation and recovery, as well as to investigate microstructural evolution and transmutant precipitation in mono- and poly-crystalline tungsten using ion implantation.

Photoluminescence as a tool for characterizing point defects in semiconductors

NASA Astrophysics Data System (ADS)

Reshchikov, Michael

2012-02-01

Photoluminescence is one of the most powerful tools used to study optically-active point defects in semiconductors, especially in wide-bandgap materials. Gallium nitride (GaN) and zinc oxide (ZnO) have attracted considerable attention in the last two decades due to their prospects in optoelectronics applications, including blue and ultraviolet light-emitting devices. However, in spite of many years of extensive studies and a great number of publications on photoluminescence from GaN and ZnO, only a few defect-related luminescence bands are reliably identified. Among them are the Zn-related blue band in GaN, Cu-related green band and Li-related orange band in ZnO. Numerous suggestions for the identification of other luminescence bands, such as the yellow band in GaN, or green and yellow bands in ZnO, do not stand up under scrutiny. In these conditions, it is important to classify the defect-related luminescence bands and find their unique characteristics. In this presentation, we will review the origin of the major luminescence bands in GaN and ZnO. Through simulations of the temperature and excitation intensity dependences of photoluminescence and by employing phenomenological models we are able to obtain important characteristics of point defects such as carrier capture cross-sections for defects, concentrations of defects, and their charge states. These models are also used to find the absolute internal quantum efficiency of photoluminescence and obtain information about nonradiative defects. Results from photoluminescence measurements will be compared with results of the first-principle calculations, as well as with the experimental data obtained by other techniques such as positron annihilation spectroscopy, deep-level transient spectroscopy, and secondary ion mass spectrometry.

The evolution of interaction between grain boundary and irradiation-induced point defects: Symmetric tilt GB in tungsten

NASA Astrophysics Data System (ADS)

Li, Hong; Qin, Yuan; Yang, Yingying; Yao, Man; Wang, Xudong; Xu, Haixuan; Phillpot, Simon R.

2018-03-01

Molecular dynamics method is used and scheme of calculational tests is designed. The atomic evolution view of the interaction between grain boundary (GB) and irradiation-induced point defects is given in six symmetric tilt GB structures of bcc tungsten with the energy of the primary knock-on atom (PKA) EPKA of 3 and 5 keV and the simulated temperature of 300 K. During the collision cascade with GB structure there are synergistic mechanisms to reduce the number of point defects: one is vacancies recombine with interstitials, and another is interstitials diffuse towards the GB with vacancies almost not move. The larger the ratio of the peak defect zone of the cascades overlaps with the GB region, the statistically relative smaller the number of surviving point defects in the grain interior (GI); and when the two almost do not overlap, vacancy-intensive area generally exists nearby GBs, and has a tendency to move toward GB with the increase of EPKA. In contrast, the distribution of interstitials is relatively uniform nearby GBs and is affected by the EPKA far less than the vacancy. The GB has a bias-absorption effect on the interstitials compared with vacancies. It shows that the number of surviving vacancies statistically has increasing trend with the increase of the distance between PKA and GB. While the number of surviving interstitials does not change much, and is less than the number of interstitials in the single crystal at the same conditions. The number of surviving vacancies in the GI is always larger than that of interstitials. The GB local extension after irradiation is observed for which the interstitials absorbed by the GB may be responsible. The designed scheme of calculational tests in the paper is completely applicable to the investigation of the interaction between other types of GBs and irradiation-induced point defects.

Core-level photoabsorption study of defects and metastable bonding configurations in boron nitride

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

Jimenez, I.; Jankowski, A.F.; Terminello, L.J.

1997-04-01

Boron nitride is an interesting material for technological applications and for fundamental solid state physics investigations. It is a compound isoelectronic with carbon and, like carbon can possess sp{sup 2} and sp{sup 3} bonded phases resembling graphite and diamond. BN crystallizes in the sp{sup 2}-bonded hexagonal (h-BN), rhombohedral (r-BN) and turbostratic phases, and in the sp{sup 3}-bonded cubic (c-BN) and wurtzite (w-BN) phases. A new family of materials is obtained when replacing C-C pairs in graphite with isoelectronic B-N pairs, resulting in C{sub 2}BN compounds. Regarding other boron compounds, BN is exceptional in the sense that it has standard two-centermore » bonds with conventional coordination numbers, while other boron compounds (e.g. B{sub 4}C) are based on the boron icosahedron unit with three-center bonds and high coordination numbers. The existence of several allotropic forms and fullerene-like structures for BN suggests a rich variety of local bonding and poses the questions of how this affects the local electronic structure and how the material accommodates the stress induced in the transition regions between different phases. One would expect point defects to play a crucial role in stress accommodation, but these must also have a strong influence in the electronic structure, since the B-N bond is polar and a point defect will thus be a charged structure. The study of point defects in relationship to the electronic structure is of fundamental interest in these materials. Recently, the authors have shown that Near-Edge X-ray Absorption Fine Structure (NEXAFS) is sensitive to point defects in h-BN, and to the formation of metastable phases even in amorphous materials. This is significant since other phase identification techniques like vibrational spectroscopies or x-ray diffraction yield ambiguous results for nanocrystalline and amorphous samples. Serendipitously, NEXAFS also combines chemical selectivity with point defect sensitivity.« less

The boron implantation in the varied zone MBE MCT epilayer

NASA Astrophysics Data System (ADS)

Voitsekhovskii, Alexander V.; Grigor'ev, Denis V.; Kokhanenko, Andrey P.; Korotaev, Alexander G.; Sidorov, Yuriy G.; Varavin, Vasiliy S.; Dvoretsky, Sergey A.; Mikhailov, Nicolay N.; Talipov, Niyaz Kh.

2005-09-01

In the paper experimental results on boron implantation of the CdxHg1-xTe epilayers with various composition near surface of the material are discussed. The electron concentration in the surface layer after irradiation vs irradiation dose and ion energy are investigated for range of doses 1011 - 3•1015 cm-2 and energies of 20 - 150 keV. Also the results of the electrical active defects distribution measurement, carried out by differential Hall method, after boron implantation are represented. Consideration of the received data shows, that composition gradient influence mainly on the various dynamics of accumulation of electric active radiation defects. The electric active defects distribution analysis shows, that the other factors are negligible.

Nuclear pore complex component MOS7/Nup88 is required for innate immunity and nuclear accumulation of defense regulators in Arabidopsis.

PubMed

Cheng, Yu Ti; Germain, Hugo; Wiermer, Marcel; Bi, Dongling; Xu, Fang; García, Ana V; Wirthmueller, Lennart; Després, Charles; Parker, Jane E; Zhang, Yuelin; Li, Xin

2009-08-01

Plant immune responses depend on dynamic signaling events across the nuclear envelope through nuclear pores. Nuclear accumulation of certain resistance (R) proteins and downstream signal transducers are critical for their functions, but it is not understood how these processes are controlled. Here, we report the identification, cloning, and analysis of Arabidopsis thaliana modifier of snc1,7 (mos7-1), a partial loss-of-function mutation that suppresses immune responses conditioned by the autoactivated R protein snc1 (for suppressor of npr1-1, constitutive 1). mos7-1 single mutant plants exhibit defects in basal and R protein-mediated immunity and in systemic acquired resistance but do not display obvious pleiotropic defects in development, salt tolerance, or plant hormone responses. MOS7 is homologous to human and Drosophila melanogaster nucleoporin Nup88 and resides at the nuclear envelope. In animals, Nup88 attenuates nuclear export of activated NF-kappaB transcription factors, resulting in nuclear accumulation of NF-kappaB. Our analysis shows that nuclear accumulation of snc1 and the defense signaling components Enhanced Disease Susceptibility 1 and Nonexpresser of PR genes 1 is significantly reduced in mos7-1 plants, while nuclear retention of other tested proteins is unaffected. The data suggest that specifically modulating the nuclear concentrations of certain defense proteins regulates defense outputs.

Plastidial Folate Prevents Starch Biosynthesis Triggered by Sugar Influx into Non-Photosynthetic Plastids of Arabidopsis.

PubMed

Hayashi, Makoto; Tanaka, Mina; Yamamoto, Saki; Nakagawa, Taro; Kanai, Masatake; Anegawa, Aya; Ohnishi, Miwa; Mimura, Tetsuro; Nishimura, Mikio

2017-08-01

Regulation of sucrose-starch interconversion in plants is important to maintain energy supplies necessary for viability and growth. Arabidopsis mutants were screened for aberrant responses to sucrose to identify candidates with a defect in the regulation of starch biosynthesis. One such mutant, fpgs1-4, accumulated substantial amounts of starch in non-photosynthetic cells. Dark-grown mutant seedlings exhibited shortened hypocotyls and accumulated starch in etioplasts when supplied with exogenous sucrose/glucose. Similar starch accumulation from exogenous sucrose was observed in mutant chloroplasts, when photosynthesis was prevented by organ culture in darkness. Molecular genetic analyses revealed that the mutant was defective in plastidial folylpolyglutamate synthetase, one of the enzymes engaged in folate biosynthesis. Active folate derivatives are important biomolecules that function as cofactors for a variety of enzymes. Exogenously supplied 5-formyl-tetrahydrofolate abrogated the mutant phenotypes, indicating that the fpgs1-4 mutant produced insufficient folate derivative levels. In addition, the antifolate agents methotrexate and 5-fluorouracil induced starch accumulation from exogenously supplied sucrose in dark-grown seedlings of wild-type Arabidopsis. These results indicate that plastidial folate suppresses starch biosynthesis triggered by sugar influx into non-photosynthetic cells, demonstrating a hitherto unsuspected link between plastidial folate and starch metabolism. © The Author 2017. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists.

Point Defects in Oxides: Tailoring Materials Through Defect Engineering

NASA Astrophysics Data System (ADS)

Tuller, Harry L.; Bishop, Sean R.

2011-08-01

Optimization of electrical, optical, mechanical, and other properties of many advanced, functional materials today relies on precise control of point defects. This article illustrates the progress that has been made in elucidating the often complex equilibria exhibited by many materials by examining two recently well-characterized model systems, TlBr for radiation detection and PrxCe1-xO2-δ, of potential interest in solid-oxide fuel cells. The interplay between material composition, electrical conductivity, and mechanical properties (electrochemomechanics) is discussed, and implications in these relations, for example, enhancing electrical properties through large mechanical strains, are described. The impact of space charge and strain fields at interfaces, particularly important in nanostructure materials, is also emphasized. Key experimental techniques useful in characterizing bulk and surface defects are summarized and reviewed.

Point defects in ZnO: an approach from first principles

PubMed Central

Oba, Fumiyasu; Choi, Minseok; Togo, Atsushi; Tanaka, Isao

2011-01-01

Recent first-principles studies of point defects in ZnO are reviewed with a focus on native defects. Key properties of defects, such as formation energies, donor and acceptor levels, optical transition energies, migration energies and atomic and electronic structure, have been evaluated using various approaches including the local density approximation (LDA) and generalized gradient approximation (GGA) to DFT, LDA+U/GGA+U, hybrid Hartree–Fock density functionals, sX and GW approximation. Results significantly depend on the approximation to exchange correlation, the simulation models for defects and the post-processes to correct shortcomings of the approximation and models. The choice of a proper approach is, therefore, crucial for reliable theoretical predictions. First-principles studies have provided an insight into the energetics and atomic and electronic structures of native point defects and impurities and defect-induced properties of ZnO. Native defects that are relevant to the n-type conductivity and the non-stoichiometry toward the O-deficient side in reduced ZnO have been debated. It is suggested that the O vacancy is responsible for the non-stoichiometry because of its low formation energy under O-poor chemical potential conditions. However, the O vacancy is a very deep donor and cannot be a major source of carrier electrons. The Zn interstitial and anti-site are shallow donors, but these defects are unlikely to form at a high concentration in n-type ZnO under thermal equilibrium. Therefore, the n-type conductivity is attributed to other sources such as residual impurities including H impurities with several atomic configurations, a metastable shallow donor state of the O vacancy, and defect complexes involving the Zn interstitial. Among the native acceptor-type defects, the Zn vacancy is dominant. It is a deep acceptor and cannot produce a high concentration of holes. The O interstitial and anti-site are high in formation energy and/or are electrically inactive and, hence, are unlikely to play essential roles in electrical properties. Overall defect energetics suggests a preference for the native donor-type defects over acceptor-type defects in ZnO. The O vacancy, Zn interstitial and Zn anti-site have very low formation energies when the Fermi level is low. Therefore, these defects are expected to be sources of a strong hole compensation in p-type ZnO. For the n-type doping, the compensation of carrier electrons by the native acceptor-type defects can be mostly suppressed when O-poor chemical potential conditions, i.e. low O partial pressure conditions, are chosen during crystal growth and/or doping. PMID:27877390

Defect interactions with stepped CeO₂/SrTiO₃ interfaces: implications for radiation damage evolution and fast ion conduction.

PubMed

Dholabhai, Pratik P; Aguiar, Jeffery A; Misra, Amit; Uberuaga, Blas P

2014-05-21

Due to reduced dimensions and increased interfacial content, nanocomposite oxides offer improved functionalities in a wide variety of advanced technological applications, including their potential use as radiation tolerant materials. To better understand the role of interface structures in influencing the radiation damage tolerance of oxides, we have conducted atomistic calculations to elucidate the behavior of radiation-induced point defects (vacancies and interstitials) at interface steps in a model CeO2/SrTiO3 system. We find that atomic-scale steps at the interface have substantial influence on the defect behavior, which ultimately dictate the material performance in hostile irradiation environments. Distinctive steps react dissimilarly to cation and anion defects, effectively becoming biased sinks for different types of defects. Steps also attract cation interstitials, leaving behind an excess of immobile vacancies. Further, defects introduce significant structural and chemical distortions primarily at the steps. These two factors are plausible origins for the enhanced amorphization at steps seen in our recent experiments. The present work indicates that comprehensive examination of the interaction of radiation-induced point defects with the atomic-scale topology and defect structure of heterointerfaces is essential to evaluate the radiation tolerance of nanocomposites. Finally, our results have implications for other applications, such as fast ion conduction.

Phonon-defect scattering and thermal transport in semiconductors: developing guiding principles

NASA Astrophysics Data System (ADS)

Polanco, Carlos; Lindsay, Lucas

First principles calculations of thermal conductivity have shown remarkable agreement with measurements for high-quality crystals. Nevertheless, most materials contain defects that provide significant extrinsic resistance and lower the conductivity from that of a perfect sample. This effect is usually accounted for with simplified analytical models that neglect the atomistic details of the defect and the exact dynamical properties of the system, which limits prediction capabilities. Recently, a method based on Greens functions was developed to calculate the phonon-defect scattering rates from first principles. This method has shown the important role of point defects in determining thermal transport in diamond and boron arsenide, two competitors for the highest bulk thermal conductivity. Here, we study the role of point defects on other relatively high thermal conductivity semiconductors, e.g., BN, BeSe, SiC, GaN and Si. We compare their first principles defect-phonon scattering rates and effects on transport properties with those from simplified models and explore common principles that determine these. Efforts will focus on basic vibrational properties that vary from system to system, such as density of states, interatomic force constants and defect deformation. Research supported by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division.

Point-Defect Nature of the Ultraviolet Absorption Band in AlN

NASA Astrophysics Data System (ADS)

Alden, D.; Harris, J. S.; Bryan, Z.; Baker, J. N.; Reddy, P.; Mita, S.; Callsen, G.; Hoffmann, A.; Irving, D. L.; Collazo, R.; Sitar, Z.

2018-05-01

We present an approach where point defects and defect complexes are identified using power-dependent photoluminescence excitation spectroscopy, impurity data from SIMS, and density-functional-theory (DFT)-based calculations accounting for the total charge balance in the crystal. Employing the capabilities of such an experimental computational approach, in this work, the ultraviolet-C absorption band at 4.7 eV, as well as the 2.7- and 3.9-eV luminescence bands in AlN single crystals grown via physical vapor transport (PVT) are studied in detail. Photoluminescence excitation spectroscopy measurements demonstrate the relationship between the defect luminescent bands centered at 3.9 and 2.7 eV to the commonly observed absorption band centered at 4.7 eV. Accordingly, the thermodynamic transition energy for the absorption band at 4.7 eV and the luminescence band at 3.9 eV is estimated at 4.2 eV, in agreement with the thermodynamic transition energy for the CN- point defect. Finally, the 2.7-eV PL band is the result of a donor-acceptor pair transition between the VN and CN point defects since nitrogen vacancies are predicted to be present in the crystal in concentrations similar to carbon-employing charge-balance-constrained DFT calculations. Power-dependent photoluminescence measurements reveal the presence of the deep donor state with a thermodynamic transition energy of 5.0 eV, which we hypothesize to be nitrogen vacancies in agreement with predictions based on theory. The charge state, concentration, and type of impurities in the crystal are calculated considering a fixed amount of impurities and using a DFT-based defect solver, which considers their respective formation energies and the total charge balance in the crystal. The presented results show that nitrogen vacancies are the most likely candidate for the deep donor state involved in the donor-acceptor pair transition with peak emission at 2.7 eV for the conditions relevant to PVT growth.

Defects in the Expression of Chloroplast Proteins Leads to H2O2 Accumulation and Activation of Cyclic Electron Flow around Photosystem I

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

Strand, Deserah D.; Livingston, Aaron K.; Satoh-Cruz, Mio

We describe a new member of the class of mutants in Arabidopsis exhibiting high rates of cyclic electron flow around photosystem I (CEF), a light-driven process that produces ATP but not NADPH. High cyclic electron flow 2 (hcef2) shows strongly increased CEF activity through the NADPH dehydrogenase complex (NDH), accompanied by increases in thylakoid proton motive force (pmf), activation of the photoprotective qE response, and the accumulation of H 2O 2 . Surprisingly, hcef2 was mapped to a nonsense mutation in the TADA1 (tRNA adenosine deaminase arginine) locus, coding for a plastid targeted tRNA editing enzyme required for efficient codonmore » recognition. Comparison of protein content from representative thylakoid complexes, the cytochrome bf complex and the ATP synthase, suggests that inefficient translation of hcef2 leads to compromised complex assembly or stability leading to alterations in stoichiometries of major thylakoid complexes as well as their constituent subunits. Altered subunit stoichiometries for photosystem I, ratios and properties of cytochrome bf hemes, and the decay kinetics of the flash induced thylakoid electric field suggest that these defect lead to accumulation of H 2O 2 in hcef2, which we have previously shown leads to activation of NDHrelated CEF. We observed similar increases in CEF and H 2O 2 accumulation in other translation defective mutants, suggesting that loss of coordination in plastid protein levels lead to imbalances in the photosynthetic energy balance that leads to increased CEF. These results, together with a large body of previous observations, support a general model in which processes that imbalances in chloroplast energetics result in the production of H 2O 2 , which activates CEF, either as a redox signal or by inducing deficits in ATP levels.« less

Rift Valley fever virus NSS gene expression correlates with a defect in nuclear mRNA export.

PubMed

Copeland, Anna Maria; Van Deusen, Nicole M; Schmaljohn, Connie S

2015-12-01

We investigated the localization of host mRNA during Rift Valley fever virus (RVFV) infection. Fluorescence in situ hybridization revealed that infection with RVFV altered the localization of host mRNA. mRNA accumulated in the nuclei of RVFV-infected but not mock-infected cells. Further, overexpression of the NSS gene, but not the N, GN or NSM genes correlated with mRNA nuclear accumulation. Nuclear accumulation of host mRNA was not observed in cells infected with a strain of RVFV lacking the gene encoding NSS, confirming that expression of NSS is likely responsible for this phenomenon. Published by Elsevier Inc.

Chronic acetaminophen ingestion resulting in severe anion gap metabolic acidosis secondary to 5-oxoproline accumulation: an under diagnosed phenomenon

PubMed Central

O’Brien, L. Morgan Nordstrom; Hooper, Michael; Flemmer, Mark; Marik, Paul Ellis

2012-01-01

Anion gap metabolic acidosis is commonly caused by lactic acidosis, ketoacidosis, and ingestion of methanol, salicylates, ethylene glycol or accumulation of organic/inorganic acids. However, rare causes of metabolic acidosis from enzyme defects, such as disturbances in the γ-glutamyl cycle, are being reported in higher frequencies in the adult population. Such disturbances cause an accumulation of 5-oxoproline and ultimately an anion gap metabolic acidosis. These disturbances are often associated with acetaminophen in the setting of certain risk factors such as sepsis, malnutrition, liver disease, female gender, pregnancy or renal failure. PMID:22761219

Point Defects and Grain Boundaries in Rotationally Commensurate MoS 2 on Epitaxial Graphene

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

Liu, Xiaolong; Balla, Itamar; Bergeron, Hadallia

2016-03-28

With reduced degrees of freedom, structural defects are expected to play a greater role in two-dimensional materials in comparison to their bulk counterparts. In particular, mechanical strength, electronic properties, and chemical reactivity are strongly affected by crystal imperfections in the atomically thin limit. Here, ultrahigh vacuum (UHV) scanning tunneling microscopy (STM) and spectroscopy (STS) are employed to interrogate point and line defects in monolayer MoS2 grown on epitaxial graphene (EG) at the atomic scale. Five types of point defects are observed with the majority species showing apparent structures that are consistent with vacancy and interstitial models. The total defect densitymore » is observed to be lower than MoS2 grown on other substrates and is likely attributed to the van der Waals epitaxy of MoS2 on EG. Grain boundaries (GBs) with 30° and 60° tilt angles resulting from the rotational commensurability of MoS2 on EG are more easily resolved by STM than atomic force microscopy at similar scales due to the enhanced contrast from their distinct electronic states. For example, band gap reduction to ~0.8 and ~0.5 eV is observed with STS for 30° and 60° GBs, respectively. In addition, atomic resolution STM images of these GBs are found to agree well with proposed structure models. This work offers quantitative insight into the structure and properties of common defects in MoS2 and suggests pathways for tailoring the performance of MoS2/graphene heterostructures via defect engineering.« less

Pathogenic lysosomal depletion in Parkinson's disease.

PubMed

Dehay, Benjamin; Bové, Jordi; Rodríguez-Muela, Natalia; Perier, Celine; Recasens, Ariadna; Boya, Patricia; Vila, Miquel

2010-09-15

Mounting evidence suggests a role for autophagy dysregulation in Parkinson's disease (PD). The bulk degradation of cytoplasmic proteins (including α-synuclein) and organelles (such as mitochondria) is mediated by macroautophagy, which involves the sequestration of cytosolic components into autophagosomes (AP) and its delivery to lysosomes. Accumulation of AP occurs in postmortem brain samples from PD patients, which has been widely attributed to an induction of autophagy. However, the cause and pathogenic significance of these changes remain unknown. Here we found in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mouse model of PD that AP accumulation and dopaminergic cell death are preceded by a marked decrease in the amount of lysosomes within dopaminergic neurons. Lysosomal depletion was secondary to the abnormal permeabilization of lysosomal membranes induced by increased mitochondrial-derived reactive oxygen species. Lysosomal permeabilization resulted in a defective clearance and subsequent accumulation of undegraded AP and contributed directly to neurodegeneration by the ectopic release of lysosomal proteases into the cytosol. Lysosomal breakdown and AP accumulation also occurred in PD brain samples, where Lewy bodies were strongly immunoreactive for AP markers. Induction of lysosomal biogenesis by genetic or pharmacological activation of lysosomal transcription factor EB restored lysosomal levels, increased AP clearance and attenuated 1-methyl-4-phenylpyridinium-induced cell death. Similarly, the autophagy-enhancer compound rapamycin attenuated PD-related dopaminergic neurodegeneration, both in vitro and in vivo, by restoring lysosomal levels. Our results indicate that AP accumulation in PD results from defective lysosomal-mediated AP clearance secondary to lysosomal depletion. Restoration of lysosomal levels and function may thus represent a novel neuroprotective strategy in PD.

Effect of time-of-flight and point spread function modeling on detectability of myocardial defects in PET

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

Schaefferkoetter, Joshua, E-mail: dnrjds@nus.edu.sg; Ouyang, Jinsong; Rakvongthai, Yothin

2014-06-15

Purpose: A study was designed to investigate the impact of time-of-flight (TOF) and point spread function (PSF) modeling on the detectability of myocardial defects. Methods: Clinical FDG-PET data were used to generate populations of defect-present and defect-absent images. Defects were incorporated at three contrast levels, and images were reconstructed by ordered subset expectation maximization (OSEM) iterative methods including ordinary Poisson, alone and with PSF, TOF, and PSF+TOF. Channelized Hotelling observer signal-to-noise ratio (SNR) was the surrogate for human observer performance. Results: For three iterations, 12 subsets, and no postreconstruction smoothing, TOF improved overall defect detection SNR by 8.6% as comparedmore » to its non-TOF counterpart for all the defect contrasts. Due to the slow convergence of PSF reconstruction, PSF yielded 4.4% less SNR than non-PSF. For reconstruction parameters (iteration number and postreconstruction smoothing kernel size) optimizing observer SNR, PSF showed larger improvement for faint defects. The combination of TOF and PSF improved mean detection SNR as compared to non-TOF and non-PSF counterparts by 3.0% and 3.2%, respectively. Conclusions: For typical reconstruction protocol used in clinical practice, i.e., less than five iterations, TOF improved defect detectability. In contrast, PSF generally yielded less detectability. For large number of iterations, TOF+PSF yields the best observer performance.« less

More on boundary holographic Witten diagrams

NASA Astrophysics Data System (ADS)

Sato, Yoshiki

2018-01-01

In this paper we discuss geodesic Witten diagrams in general holographic conformal field theories with boundary or defect. In boundary or defect conformal field theory, two-point functions are nontrivial and can be decomposed into conformal blocks in two distinct ways; ambient channel decomposition and boundary channel decomposition. In our previous work [A. Karch and Y. Sato, J. High Energy Phys. 09 (2017) 121., 10.1007/JHEP09(2017)121] we only consider two-point functions of same operators. We generalize our previous work to a situation where operators in two-point functions are different. We obtain two distinct decomposition for two-point functions of different operators.

Defective lysosomal proteolysis and axonal transport are early pathogenic events that worsen with age leading to increased APP metabolism and synaptic Abeta in transgenic APP/PS1 hippocampus.

PubMed

Torres, Manuel; Jimenez, Sebastian; Sanchez-Varo, Raquel; Navarro, Victoria; Trujillo-Estrada, Laura; Sanchez-Mejias, Elisabeth; Carmona, Irene; Davila, Jose Carlos; Vizuete, Marisa; Gutierrez, Antonia; Vitorica, Javier

2012-11-22

Axonal pathology might constitute one of the earliest manifestations of Alzheimer disease. Axonal dystrophies were observed in Alzheimer's patients and transgenic models at early ages. These axonal dystrophies could reflect the disruption of axonal transport and the accumulation of multiple vesicles at local points. It has been also proposed that dystrophies might interfere with normal intracellular proteolysis. In this work, we have investigated the progression of the hippocampal pathology and the possible implication in Abeta production in young (6 months) and aged (18 months) PS1(M146L)/APP(751sl) transgenic mice. Our data demonstrated the existence of a progressive, age-dependent, formation of axonal dystrophies, mainly located in contact with congophilic Abeta deposition, which exhibited tau and neurofilament hyperphosphorylation. This progressive pathology was paralleled with decreased expression of the motor proteins kinesin and dynein. Furthermore, we also observed an early decrease in the activity of cathepsins B and D, progressing to a deep inhibition of these lysosomal proteases at late ages. This lysosomal impairment could be responsible for the accumulation of LC3-II and ubiquitinated proteins within axonal dystrophies. We have also investigated the repercussion of these deficiencies on the APP metabolism. Our data demonstrated the existence of an increase in the amyloidogenic pathway, which was reflected by the accumulation of hAPPfl, C99 fragment, intracellular Abeta in parallel with an increase in BACE and gamma-secretase activities. In vitro experiments, using APPswe transfected N2a cells, demonstrated that any imbalance on the proteolytic systems reproduced the in vivo alterations in APP metabolism. Finally, our data also demonstrated that Abeta peptides were preferentially accumulated in isolated synaptosomes. A progressive age-dependent cytoskeletal pathology along with a reduction of lysosomal and, in minor extent, proteasomal activity could be directly implicated in the progressive accumulation of APP derived fragments (and Abeta peptides) in parallel with the increase of BACE-1 and gamma-secretase activities. This retard in the APP metabolism seemed to be directly implicated in the synaptic Abeta accumulation and, in consequence, in the pathology progression between synaptically connected regions.

Exceptional gettering response of epitaxially grown kerfless silicon

DOE PAGES

Powell, D. M.; Markevich, V. P.; Hofstetter, J.; ...

2016-02-08

The bulk minority-carrier lifetime in p- and n-type kerfless epitaxial (epi) crystalline silicon wafers is shown to increase >500 during phosphorus gettering. We employ kinetic defect simulations and microstructural characterization techniques to elucidate the root cause of this exceptional gettering response. Simulations and deep-level transient spectroscopy (DLTS) indicate that a high concentra- tion of point defects (likely Pt) is “locked in” during fast (60 C/min) cooling during epi wafer growth. The fine dispersion of moderately fast-diffusing recombination-active point defects limits as-grown lifetime but can also be removed during gettering, confirmed by DLTS measurements. Synchrotron-based X-ray fluorescence microscopy indicates metal agglomeratesmore » at structural defects, yet the structural defect density is sufficiently low to enable high lifetimes. Consequently, after phosphorus diffusion gettering, epi silicon exhibits a higher lifetime than materials with similar bulk impurity contents but higher densities of structural defects, including multicrystalline ingot and ribbon silicon materials. As a result, device simulations suggest a solar-cell efficiency potential of this material >23%.« less

First-principles investigation of the structural characteristics of LiMO2 cathode materials for lithium secondary batteries

NASA Astrophysics Data System (ADS)

Kim, Yongseon

2015-11-01

The structural features related to the defects of LiMO2 (M = Ni, Co, Mn) cathode materials for lithium secondary batteries were investigated by a simulation of phase diagrams based on first-principle calculations. Crystal models with various types of point defects were designed and dealt with as independent phases, which enabled an examination of the thermodynamic stability of the defects. A perfect phase without defects appeared to be the most stable for LiCoO2, whereas the formation of Li vacancies, O vacancies, and antisites between Li and Ni was thermodynamically unavoidable for LiNiO2. The introduction of both Co and Mn in LiNiO2 was effective in reducing the formation of point defects, but increasing the relative amount of Mn was undesirable because the antisite defect remained stable with Mn doping. The simulation showed good agreement with the experimental data and previous reports. Therefore, the method and the results of this study are expected to be useful for examining the synthesis, structure and related properties of layer-structured cathode materials.

Lattice constant in nonstoichiometric uranium dioxide from first principles

NASA Astrophysics Data System (ADS)

Bruneval, Fabien; Freyss, Michel; Crocombette, Jean-Paul

2018-02-01

Nonstoichiometric uranium dioxide experiences a shrinkage of its lattice constant with increasing oxygen content, in both the hypostoichiometric and the hyperstoichiometric regimes. Based on first-principles calculations within the density functional theory (DFT)+U approximation, we have developed a point defect model that accounts for the volume of relaxation of the most significant intrinsic defects of UO2. Our point defect model takes special care of the treatment of the charged defects in the equilibration of the model and in the determination of reliable defect volumes of formation. In the hypostoichiometric regime, the oxygen vacancies are dominant and explain the lattice constant variation with their surprisingly positive volume of relaxation. In the hyperstoichiometric regime, the uranium vacancies are predicted to be the dominating defect,in contradiction with experimental observations. However, disregarding uranium vacancies allows us to recover a good match for the lattice-constant variation as a function of stoichiometry. This can be considered a clue that the uranium vacancies are indeed absent in UO2 +x, possibly due to the very slow diffusion of uranium.

Raman spectroscopic studies of defect structures and phase transition in hyper-stoichiometric UO(2+x).

PubMed

He, Heming; Shoesmith, David

2010-07-28

A method to determine the defect structures in hyper-stoichiometric UO(2+x) using a combination of XRD and Raman spectroscopy has been developed. A sequence of phase transitions, from cubic to tetragonal symmetry, occurs with increasing degree of non-stoichiometry. This sequence proceeds from a cubic phase through an intermediate t''-type tetragonal (axial ratio c/a = 1) phase to a final t-type tetragonal (c/a not = 1) phase. Four distinct structural defect regions can be identified in the stoichiometry range, UO(2) to U(3)O(7): (i) a random point defect structure (x (in UO(2+x)) < or = 0.05); (ii) a non-stoichiometry region (0.05 < or = x < or = 0.15) over which point defects are gradually eliminated and replaced by the Willis 2:2:2 cluster; (iii) a mixture of Willis and cuboctahedral clusters (0.15 < or = x < or = 0.23); (iv) the cuboctahedral cluster (x > or = 0.23). The geometry and steric arrangement of these defects is primarily determined by the concentration of the excess-oxygen interstitials.

Impact of defects on the electrical transport, optical properties and failure mechanisms of GaN nanowires.

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

Armstrong, Andrew M.; Aubry, Sylvie; Shaner, Eric Arthur

2010-09-01

We present the results of a three year LDRD project that focused on understanding the impact of defects on the electrical, optical and thermal properties of GaN-based nanowires (NWs). We describe the development and application of a host of experimental techniques to quantify and understand the physics of defects and thermal transport in GaN NWs. We also present the development of analytical models and computational studies of thermal conductivity in GaN NWs. Finally, we present an atomistic model for GaN NW electrical breakdown supported with experimental evidence. GaN-based nanowires are attractive for applications requiring compact, high-current density devices such asmore » ultraviolet laser arrays. Understanding GaN nanowire failure at high-current density is crucial to developing nanowire (NW) devices. Nanowire device failure is likely more complex than thin film due to the prominence of surface effects and enhanced interaction among point defects. Understanding the impact of surfaces and point defects on nanowire thermal and electrical transport is the first step toward rational control and mitigation of device failure mechanisms. However, investigating defects in GaN NWs is extremely challenging because conventional defect spectroscopy techniques are unsuitable for wide-bandgap nanostructures. To understand NW breakdown, the influence of pre-existing and emergent defects during high current stress on NW properties will be investigated. Acute sensitivity of NW thermal conductivity to point-defect density is expected due to the lack of threading dislocation (TD) gettering sites, and enhanced phonon-surface scattering further inhibits thermal transport. Excess defect creation during Joule heating could further degrade thermal conductivity, producing a viscous cycle culminating in catastrophic breakdown. To investigate these issues, a unique combination of electron microscopy, scanning luminescence and photoconductivity implemented at the nanoscale will be used in concert with sophisticated molecular-dynamics calculations of surface and defect-mediated NW thermal transport. This proposal seeks to elucidate long standing material science questions for GaN while addressing issues critical to realizing reliable GaN NW devices.« less

Metalworking defects in surgery screws as a possible cause of post-surgical infections

NASA Astrophysics Data System (ADS)

Spector, Mario; Peretti, Leandro E.; Romero, Gustavo

2016-04-01

In the first phase of this work, surface defects (metalworking) in stainless steel implantable prostheses and their possible relation to infections that can be generated after surgery was studied. In a second phase, the results obtained in the aforementioned stage were applied to knee cruciate ligaments surgery screws, considering the fact that a substantial number of Mucormycetes infections have been reported after arthroscopic surgery in Argentina since the year 2005. Two types of screws, transverse and interference screws, were analyzed. The Allen heads presented defects such as burrs and metalworking bending as a result of the machining process. These defects allow the accumulation of machining oil, which could be contaminated with fungal spores. When this is the case, the gaseous sterilization by ethylene oxide may be jeopardized. Cortical screws were also analyzed and were found to present serious metalworking defects inside their heads. To reduce the risk of infection in surgery, the use of screws with metalworking defects on the outer surface, analyzed with stereomicroscope and considering the inside part of the Allen as an outer surface, should be avoided altogether.

Solid State Lighting Program (Falcon)

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

Meeks, Steven

2012-06-30

Over the past two years, KLA-Tencor and partners successfully developed and deployed software and hardware tools that increase product yield for High Brightness LED (HBLED) manufacturing and reduce product development and factory ramp times. This report summarizes our development effort and details of how the results of the Solid State Light Program (Falcon) have started to help HBLED manufacturers optimize process control by enabling them to flag and correct identified killer defect conditions at any point of origin in the process manufacturing flow. This constitutes a quantum leap in yield management over current practice. Current practice consists of die dispositioningmore » which is just rejection of bad die at end of process based upon probe tests, loosely assisted by optical in-line monitoring for gross process deficiencies. For the first time, and as a result of our Solid State Lighting Program, our LED manufacturing partners have obtained the software and hardware tools that optimize individual process steps to control killer defects at the point in the processes where they originate. Products developed during our two year program enable optimized inspection strategies for many product lines to minimize cost and maximize yield. The Solid State Lighting Program was structured in three phases: i) the development of advanced imaging modes that achieve clear separation between LED defect types, improves signal to noise and scan rates, and minimizes nuisance defects for both front end and back end inspection tools, ii) the creation of defect source analysis (DSA) software that connect the defect maps from back-end and front-end HBLED manufacturing tools to permit the automatic overlay and traceability of defects between tools and process steps, suppress nuisance defects, and identify the origin of killer defects with process step and conditions, and iii) working with partners (Philips Lumileds) on product wafers, obtain a detailed statistical correlation of automated defect and DSA map overlay to failed die identified using end product probe test results. Results from our two year effort have led to “automated end-to-end defect detection” with full defect traceability and the ability to unambiguously correlate device killer defects to optically detected features and their point of origin within the process. Success of the program can be measured by yield improvements at our partner’s facilities and new product orders.« less

Defects in Arsenic Implanted p + -n- and n + -p- Structures Based on MBE Grown CdHgTe Films

NASA Astrophysics Data System (ADS)

Izhnin, I. I.; Fitsych, E. I.; Voitsekhovskii, A. V.; Korotaev, A. G.; Mynbaev, K. D.; Varavin, V. S.; Dvoretsky, S. A.; Mikhailov, N. N.; Yakushev, M. V.; Bonchyk, A. Yu.; Savytskyy, H. V.; Świątek, Z.

2018-02-01

Complex studies of the defect structure of arsenic-implanted (with the energy of 190 keV) Cd x Hg 1-x Te ( x = 0.22) films grown by molecular-beam epitaxy are carried out. The investigations were performed using secondary-ion mass spectroscopy, transmission electron microscopy, optical reflection in the visible region of the spectrum, and electrical measurements. Radiation donor defects were studied in n +- p- and n +- n-structures obtained by implantation and formed on the basis of p-type and n-type materials, respectively, without activation annealing. It is shown that in the layer of the distribution of implanted ions, a layer of large extended defects with low density is formed in the near-surface region followed by a layer of smaller extended defects with larger density. A different character of accumulation of electrically active donor defects in the films with and without a protective graded-gap surface layer has been revealed. It is demonstrated that p +- n- structures are formed on the basis of n-type material upon activation of arsenic in the process of postimplantation thermal annealing with 100% activation of impurity and complete annihilation of radiation donor defects.

Distinct functions of the laminin β LN domain and collagen IV during cardiac extracellular matrix formation and stabilization of alary muscle attachments revealed by EMS mutagenesis in Drosophila

PubMed Central

2014-01-01

Background The Drosophila heart (dorsal vessel) is a relatively simple tubular organ that serves as a model for several aspects of cardiogenesis. Cardiac morphogenesis, proper heart function and stability require structural components whose identity and ways of assembly are only partially understood. Structural components are also needed to connect the myocardial tube with neighboring cells such as pericardial cells and specialized muscle fibers, the so-called alary muscles. Results Using an EMS mutagenesis screen for cardiac and muscular abnormalities in Drosophila embryos we obtained multiple mutants for two genetically interacting complementation groups that showed similar alary muscle and pericardial cell detachment phenotypes. The molecular lesions underlying these defects were identified as domain-specific point mutations in LamininB1 and Cg25C, encoding the extracellular matrix (ECM) components laminin β and collagen IV α1, respectively. Of particular interest within the LamininB1 group are certain hypomorphic mutants that feature prominent defects in cardiac morphogenesis and cardiac ECM layer formation, but in contrast to amorphic mutants, only mild defects in other tissues. All of these alleles carry clustered missense mutations in the laminin LN domain. The identified Cg25C mutants display weaker and largely temperature-sensitive phenotypes that result from glycine substitutions in different Gly-X-Y repeats of the triple helix-forming domain. While initial basement membrane assembly is not abolished in Cg25C mutants, incorporation of perlecan is impaired and intracellular accumulation of perlecan as well as the collagen IV α2 chain is detected during late embryogenesis. Conclusions Assembly of the cardiac ECM depends primarily on laminin, whereas collagen IV is needed for stabilization. Our data underscore the importance of a correctly assembled ECM particularly for the development of cardiac tissues and their lateral connections. The mutational analysis suggests that the β6/β3/β8 interface of the laminin β LN domain is highly critical for formation of contiguous cardiac ECM layers. Certain mutations in the collagen IV triple helix-forming domain may exert a semi-dominant effect leading to an overall weakening of ECM structures as well as intracellular accumulation of collagen and other molecules, thus paralleling observations made in other organisms and in connection with collagen-related diseases. PMID:24935095

Defects, optical absorption and electron mobility in indium and gallium nitrides

NASA Astrophysics Data System (ADS)

Tansley, T. L.; Egan, R. J.

1993-04-01

We review the experimental evidence for the origin and location of the four native point defects in the wide gap semiconducting indium and gallium nitrides and compare then with experimental predictions. The donor triplets associated with nitrogen vacancies and the deep compensating centres ascribed to the antisite substitutional defects appear to have the greatest effect on macroscopic properties, apparently including the four luminescent bands in GaN. Calculated mobilities in InN and GaN depend principally on ionised impurity and polar-mode phonon scattering. We reconcile these results with experimental data and point out the consequences for improvements in material growth.

Effect of symmetrical and asymmetrical tilt grain boundaries on radiation-induced defects in zirconium

NASA Astrophysics Data System (ADS)

Singh, Divya; Parashar, Avinash

2018-07-01

In this article, molecular-dynamics-based simulations were used to study the effect of grain boundaries (GBs) on the formation and spatial distribution of radiation-induced point defects. In order to perform this study, two sets of symmetrical and asymmetrical tilt grain boundaries were constructed along [0 0 0 1] and [0   ‑1 1 0] as the tilt axis, respectively. Vacancy, interstitial and Frenkel pair formation energies were estimated as a function of the distance from the GB core for both symmetrical as well as asymmetrical tilt GBs. The trend obtained between GB energies and point defect formation energies helps explain the biased absorption of interstitials over vacancies in most cases, as well as the equal absorption of both kinds of point defects in a few of them. It has already been reported from the experimental work that [0 0 0 1] GB structures closely resemble the polycrystalline texture of hcp materials, which motivates us to study the effect of irradiation on these GBs.

Role of point defects and HfO2/TiN interface stoichiometry on effective work function modulation in ultra-scaled complementary metal-oxide-semiconductor devices

NASA Astrophysics Data System (ADS)

Pandey, R. K.; Sathiyanarayanan, Rajesh; Kwon, Unoh; Narayanan, Vijay; Murali, K. V. R. M.

2013-07-01

We investigate the physical properties of a portion of the gate stack of an ultra-scaled complementary metal-oxide-semiconductor (CMOS) device. The effects of point defects, such as oxygen vacancy, oxygen, and aluminum interstitials at the HfO2/TiN interface, on the effective work function of TiN are explored using density functional theory. We compute the diffusion barriers of such point defects in the bulk TiN and across the HfO2/TiN interface. Diffusion of these point defects across the HfO2/TiN interface occurs during the device integration process. This results in variation of the effective work function and hence in the threshold voltage variation in the devices. Further, we simulate the effects of varying the HfO2/TiN interface stoichiometry on the effective work function modulation in these extremely-scaled CMOS devices. Our results show that the interface rich in nitrogen gives higher effective work function, whereas the interface rich in titanium gives lower effective work function, compared to a stoichiometric HfO2/TiN interface. This theoretical prediction is confirmed by the experiment, demonstrating over 700 meV modulation in the effective work function.

Kibble Zurek mechanism of topological defect formation in quantum field theory with matrix product states

NASA Astrophysics Data System (ADS)

Gillman, Edward; Rajantie, Arttu

2018-05-01

The Kibble Zurek mechanism in a relativistic ϕ4 scalar field theory in D =(1 +1 ) is studied using uniform matrix product states. The equal time two point function in momentum space G2(k ) is approximated as the system is driven through a quantum phase transition at a variety of different quench rates τQ. We focus on looking for signatures of topological defect formation in the system and demonstrate the consistency of the picture that the two point function G2(k ) displays two characteristic scales, the defect density n and the kink width dK. Consequently, G2(k ) provides a clear signature for the formation of defects and a well defined measure of the defect density in the system. These results provide a benchmark for the use of tensor networks as powerful nonperturbative nonequilibrium methods for relativistic quantum field theory, providing a promising technique for the future study of high energy physics and cosmology.

Defect-selective dry etching for quick and easy probing of hexagonal boron nitride domains.

PubMed

Wu, Qinke; Lee, Joohyun; Park, Sangwoo; Woo, Hwi Je; Lee, Sungjoo; Song, Young Jae

2018-03-23

In this study, we demonstrate a new method to selectively etch the point defects or the boundaries of as-grown hexagonal boron nitride (hBN) films and flakes in situ on copper substrates using hydrogen and argon gases. The initial quality of the chemical vapor deposition-grown hBN films and flakes was confirmed by UV-vis absorption spectroscopy, atomic force microscopy, and transmission electron microscopy. Different gas flow ratios of Ar/H 2 were then employed to etch the same quality of samples and it was found that etching with hydrogen starts from the point defects and grows epitaxially, which helps in confirming crystalline orientations. However, etching with argon is sensitive to line defects (boundaries) and helps in visualizing the domain size. Finally, based on this defect-selective dry etching technique, it could be visualized that the domains of a polycrystalline hBN monolayer merged together with many parts, even with those that grew from a single nucleation seed.

Defect-selective dry etching for quick and easy probing of hexagonal boron nitride domains

NASA Astrophysics Data System (ADS)

Wu, Qinke; Lee, Joohyun; Park, Sangwoo; Woo, Hwi Je; Lee, Sungjoo; Song, Young Jae

2018-03-01

In this study, we demonstrate a new method to selectively etch the point defects or the boundaries of as-grown hexagonal boron nitride (hBN) films and flakes in situ on copper substrates using hydrogen and argon gases. The initial quality of the chemical vapor deposition-grown hBN films and flakes was confirmed by UV-vis absorption spectroscopy, atomic force microscopy, and transmission electron microscopy. Different gas flow ratios of Ar/H2 were then employed to etch the same quality of samples and it was found that etching with hydrogen starts from the point defects and grows epitaxially, which helps in confirming crystalline orientations. However, etching with argon is sensitive to line defects (boundaries) and helps in visualizing the domain size. Finally, based on this defect-selective dry etching technique, it could be visualized that the domains of a polycrystalline hBN monolayer merged together with many parts, even with those that grew from a single nucleation seed.

Slow relaxation of cascade-induced defects in Fe

DOE PAGES

Béland, Laurent Karim; Osetsky, Yuri N.; Stoller, Roger E.; ...

2015-02-17

On-the-fly kinetic Monte Carlo (KMC) simulations are performed to investigate slow relaxation of non-equilibrium systems. Point defects induced by 25 keV cascades in α -Fe are shown to lead to a characteristic time-evolution, described by the replenish and relax mechanism. Then, we produce an atomistically-based assessment of models proposed to explain the slow structural relaxation by focusing on the aggregation of 50 vacancies and 25 self-interstital atoms (SIA) in 10-lattice-parameter α-Fe boxes, two processes that are closely related to cascade annealing and exhibit similar time signature. Four atomistic effects explain the timescales involved in the evolution: defect concentration heterogeneities, concentration-enhancedmore » mobility, cluster-size dependent bond energies and defect-induced pressure. In conclusion, these findings suggest that the two main classes of models to explain slow structural relaxation, the Eyring model and the Gibbs model, both play a role to limit the rate of relaxation of these simple point-defect systems.« less

Detecting Submicron Pattern Defects On Optical Photomasks Using An Enhanced El-3 Electron-Beam Lithography Tool

NASA Astrophysics Data System (ADS)

Simpson, R. A.; Davis, D. E.

1982-09-01

This paper describes techniques to detect submicron pattern defects on optical photomasks with an enhanced direct-write, electron-beam lithographic tool. EL-3 is a third generation, shaped spot, electron-beam lithography tool developed by IBM to fabricate semiconductor devices and masks. This tool is being upgraded to provide 100% inspection of optical photomasks for submicron pattern defects, which are subsequently repaired. Fixed-size overlapped spots are stepped over the mask patterns while a signal derived from the back-scattered electrons is monitored to detect pattern defects. Inspection does not require pattern recognition because the inspection scan patterns are derived from the original design data. The inspection spot is square and larger than the minimum defect to be detected, to improve throughput. A new registration technique provides the beam-to-pattern overlay required to locate submicron defects. The 'guard banding" of inspection shapes prevents mask and system tolerances from producing false alarms that would occur should the spots be mispositioned such that they only partially covered a shape being inspected. A rescanning technique eliminates noise-related false alarms and significantly improves throughput. Data is accumulated during inspection and processed offline, as required for defect repair. EL-3 will detect 0.5 um pattern defects at throughputs compatible with mask manufacturing.

Objectively assessed physical activity and sedentary behaviour does not differ between children and adolescents with and without a congenital heart defect: a pilot examination.

PubMed

Ewalt, Lauren A; Danduran, Michael J; Strath, Scott J; Moerchen, Victoria; Swartz, Ann M

2012-02-01

To objectively evaluate and describe physical activity levels in children with a stable congenital heart defect and compare those levels with children who do not have a congenital heart defect. We matched 21 pairs of children for gender and grade in school and gave them an accelerometer-based motion sensor to wear for 7 consecutive days. Physical activity levels did not differ between children with and without a congenital heart defect. During the 7 days of monitoring, children in this study spent most of their time in sedentary behaviours, that is, 6.7 hours of the 13 monitored hours, 54 minutes in moderate-intensity physical activity, and 12 minutes in vigorous-intensity physical activity. Less than one-fifth of all participants, with or without a congenital heart defect, accumulated sufficient physical activity to meet current physical activity recommendations for children and adolescents. Children with a stable congenital heart defect have activity behaviours that are similar to children without a congenital heart defect. Habitual physical activity in children with a congenital heart defect should be encouraged early on in life to develop strong physical activity habits that will hopefully follow them across their lifespan.

Effects of Point Mutations in the Major Capsid Protein of Beet Western Yellows Virus on Capsid Formation, Virus Accumulation, and Aphid Transmission

PubMed Central

Brault, V.; Bergdoll, M.; Mutterer, J.; Prasad, V.; Pfeffer, S.; Erdinger, M.; Richards, K. E.; Ziegler-Graff, V.

2003-01-01

Point mutations were introduced into the major capsid protein (P3) of cloned infectious cDNA of the polerovirus beet western yellows virus (BWYV) by manipulation of cloned infectious cDNA. Seven mutations targeted sites on the S domain predicted to lie on the capsid surface. An eighth mutation eliminated two arginine residues in the R domain, which is thought to extend into the capsid interior. The effects of the mutations on virus capsid formation, virus accumulation in protoplasts and plants, and aphid transmission were tested. All of the mutants replicated in protoplasts. The S-domain mutant W166R failed to protect viral RNA from RNase attack, suggesting that this particular mutation interfered with stable capsid formation. The R-domain mutant R7A/R8A protected ∼90% of the viral RNA strand from RNase, suggesting that lower positive-charge density in the mutant capsid interior interfered with stable packaging of the complete strand into virions. Neither of these mutants systemically infected plants. The six remaining mutants properly packaged viral RNA and could invade Nicotiana clevelandii systemically following agroinfection. Mutant Q121E/N122D was poorly transmitted by aphids, implicating one or both targeted residues in virus-vector interactions. Successful transmission of mutant D172N was accompanied either by reversion to the wild type or by appearance of a second-site mutation, N137D. This finding indicates that D172 is also important for transmission but that the D172N transmission defect can be compensated for by a “reverse” substitution at another site. The results have been used to evaluate possible structural models for the BWYV capsid. PMID:12584348

DNA-damage foci to detect and characterize DNA repair alterations in children treated for pediatric malignancies.

PubMed

Schuler, Nadine; Palm, Jan; Kaiser, Mareike; Betten, Dominik; Furtwängler, Rhoikos; Rübe, Christian; Graf, Norbert; Rübe, Claudia E

2014-01-01

In children diagnosed with cancer, we evaluated the DNA damage foci approach to identify patients with double-strand break (DSB) repair deficiencies, who may overreact to DNA-damaging radio- and chemotherapy. In one patient with Fanconi anemia (FA) suffering relapsing squamous cell carcinomas of the oral cavity we also characterized the repair defect in biopsies of skin, mucosa and tumor. In children with histologically confirmed tumors or leukemias and healthy control-children DSB repair was investigated by counting γH2AX-, 53BP1- and pATM-foci in blood lymphocytes at defined time points after ex-vivo irradiation. This DSB repair capacity was correlated with treatment-related normal-tissue responses. For the FA patient the defective repair was also characterized in tissue biopsies by analyzing DNA damage response proteins by light and electron microscopy. Between tumor-children and healthy control-children we observed significant differences in mean DSB repair capacity, suggesting that childhood cancer is based on genetic alterations affecting DNA repair. Only 1 out of 4 patients with grade-4 normal-tissue toxicities revealed an impaired DSB repair capacity. The defective DNA repair in FA patient was verified in irradiated blood lymphocytes as well as in non-irradiated mucosa and skin biopsies leading to an excessive accumulation of heterochromatin-associated DSBs in rapidly cycling cells. Analyzing human tissues we show that DSB repair alterations predispose to cancer formation at younger ages and affect the susceptibility to normal-tissue toxicities. DNA damage foci analysis of blood and tissue samples allows one to detect and characterize DSB repair deficiencies and enables identification of patients at risk for high-grade toxicities. However, not all treatment-associated normal-tissue toxicities can be explained by DSB repair deficiencies.

Interaction of metronidazole with DNA repair mutants of Escherichia coli.

PubMed

Yeung, T C; Beaulieu, B B; McLafferty, M A; Goldman, P

1984-01-01

It has been proposed that one of metronidazole's partially reduced intermediates interacts either with DNA to exert a bactericidal effect or with water to form acetamide. To test this hypothesis we have examined the effect of metronidazole on several mutants of Escherichia coli that are defective in DNA repair. UV-susceptible RecA- and UvrB- point mutants have an increased susceptibility to metronidazole as manifested by both a decreased minimal inhibitory concentration and a greater bactericidal response to metronidazole in resting cultures. By these criteria, however, we find that UvrB- deletion mutants, which lack the ability to reduce nitrate and chlorate, are no more susceptible to metronidazole than is the wild type. We find, however, that these deletion mutants also lack the ability to reduce metronidazole and thus possibly to form its reactive species. When metronidazole's bactericidal effect is expressed in terms of the concurrent accumulation of acetamide derived from metronidazole, then all RecA- and UvrB- mutants are killed more efficiently than their wild types. The data are consistent, therefore, with metronidazole's lethal effect being mediated by a partially reduced intermediate on the metabolic pathway between metronidazole and acetamide. Defects in other aspects of the DNA repair system do not confer this increased susceptibility to the proposed intermediate. A Tag- mutant, for example, which is defective in 3-methyl-adenine-DNA glycosylase, does not have this increased susceptibility to the presumed precursor of acetamide. Thus, these results provide further support for the hypothesis that the bactericidal effect of metronidazole is mediated by a partially reduced intermediate in the metabolic conversion of metronidazole to acetamide and suggest that this intermediate interacts with DNA to produce a lesion similar to that caused by UV light.

Interaction of metronidazole with DNA repair mutants of Escherichia coli.

PubMed Central

Yeung, T C; Beaulieu, B B; McLafferty, M A; Goldman, P

1984-01-01

It has been proposed that one of metronidazole's partially reduced intermediates interacts either with DNA to exert a bactericidal effect or with water to form acetamide. To test this hypothesis we have examined the effect of metronidazole on several mutants of Escherichia coli that are defective in DNA repair. UV-susceptible RecA- and UvrB- point mutants have an increased susceptibility to metronidazole as manifested by both a decreased minimal inhibitory concentration and a greater bactericidal response to metronidazole in resting cultures. By these criteria, however, we find that UvrB- deletion mutants, which lack the ability to reduce nitrate and chlorate, are no more susceptible to metronidazole than is the wild type. We find, however, that these deletion mutants also lack the ability to reduce metronidazole and thus possibly to form its reactive species. When metronidazole's bactericidal effect is expressed in terms of the concurrent accumulation of acetamide derived from metronidazole, then all RecA- and UvrB- mutants are killed more efficiently than their wild types. The data are consistent, therefore, with metronidazole's lethal effect being mediated by a partially reduced intermediate on the metabolic pathway between metronidazole and acetamide. Defects in other aspects of the DNA repair system do not confer this increased susceptibility to the proposed intermediate. A Tag- mutant, for example, which is defective in 3-methyl-adenine-DNA glycosylase, does not have this increased susceptibility to the presumed precursor of acetamide. Thus, these results provide further support for the hypothesis that the bactericidal effect of metronidazole is mediated by a partially reduced intermediate in the metabolic conversion of metronidazole to acetamide and suggest that this intermediate interacts with DNA to produce a lesion similar to that caused by UV light. PMID:6367636

Neutron irradiation damage of nuclear graphite studied by high-resolution transmission electron microscopy and Raman spectroscopy

NASA Astrophysics Data System (ADS)

Krishna, R.; Jones, A. N.; McDermott, L.; Marsden, B. J.

2015-12-01

Nuclear graphite components are produced from polycrystalline artificial graphite manufacture from a binder and filler coke with approximately 20% porosity. During the operational lifetime, nuclear graphite moderator components are subjected to fast neutron irradiation which contributes to the change of material and physical properties such as thermal expansion co-efficient, young's modulus and dimensional change. These changes are directly driven by irradiation-induced changes to the crystal structure as reflected through the bulk microstructure. It is therefore of critical importance that these irradiation changes and there implication on component property changes are fully understood. This work examines a range of irradiated graphite samples removed from the British Experimental Pile Zero (BEPO) reactor; a low temperature, low fluence, air-cooled Materials Test Reactor which operated in the UK. Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM) have been employed to characterise the effect of increased irradiation fluence on graphite microstructure and understand low temperature irradiation damage processes. HRTEM confirms the structural damage of the crystal lattice caused by irradiation attributed to a high number of defects generation with the accumulation of dislocation interactions at nano-scale range. Irradiation-induced crystal defects, lattice parameters and crystallite size compared to virgin nuclear graphite are characterised using selected area diffraction (SAD) patterns in TEM and Raman Spectroscopy. The consolidated 'D'peak in the Raman spectra confirms the formation of in-plane point defects and reflected as disordered regions in the lattice. The reduced intensity and broadened peaks of 'G' and 'D' in the Raman and HRTEM results confirm the appearance of turbulence and disordering of the basal planes whilst maintaining their coherent layered graphite structure.

A compensating point defect in carbon-doped GaN substrates studied with electron paramagnetic resonance spectroscopy

NASA Astrophysics Data System (ADS)

Willoughby, W. R.; Zvanut, M. E.; Paudel, Subash; Iwinska, M.; Sochacki, T.; Bockowski, M.

2018-04-01

Electron paramagnetic resonance (EPR) spectroscopy was used to investigate a type of point defect present in 1019 cm-3 carbon-doped GaN substrates grown by hydride vapor phase epitaxy. A broad, isotropic resonance at g ˜ 1.987 was observed at 3.5 K, and the EPR intensity increased with illumination at energies greater than 2.75 eV and decreased with photon energies greater than 0.95 eV. The latter is consistent with a deep level of 0.95 eV above the valence band maximum and implies that the associated defect likely participates in donor compensation. The ionization energy for this defect is close to the predicted value for the (-/0) transition level of CN and transition levels associated with Ga vacancies such as VGa and VGa-ON-2H.

Energy conversion modeling of the intrinsic persistent luminescence of solids via energy transfer paths between transition levels.

PubMed

Huang, Bolong; Sun, Mingzi

2017-04-05

An energy conversion model has been established for the intrinsic persistent luminescence in solids related to the native point defect levels, formations, and transitions. In this study, we showed how the recombination of charge carriers between different defect levels along the zero phonon line (ZPL) can lead to energy conversions supporting the intrinsic persistent phosphorescence in solids. This suggests that the key driving force for this optical phenomenon is the pair of electrons hopping between different charged defects with negative-U eff . Such a negative correlation energy will provide a sustainable energy source for electron-holes to further recombine in a new cycle with a specific quantum yield. This will help us to understand the intrinsic persistent luminescence with respect to native point defect levels as well as the correlations of electronics and energetics.

Repair of retropatellar cartilage defects in the knee with microfracture and a cell-free polymer-based implant.

PubMed

Becher, Christoph; Ettinger, Max; Ezechieli, Marco; Kaps, Christian; Ewig, Marc; Smith, Tomas

2015-07-01

To analyze magnetic resonance imaging (MRI) at 3T and the clinical outcome in a short-term pilot study after treatment of retropatellar cartilage defects with microfracturing and subsequent covering with the cell-free chondrotissue(®) polyglycolic acid-hyaluronan implant. Five consecutive patients after microfracturing and defect coverage with the chondrotissue(®) implant immersed with autologous serum were included. After a mean follow-up of 21 months (range 11-31 months), defect fill and repair tissue quality was assessed by 3-T MRI followed by applying established MRI scoring systems. The patients' situation was assessed using the Knee injury and Osteoarthritis Outcome Score (KOOS) and a patients' satisfaction questionnaire. Magnetic resonance imaging showed good to excellent defect fill with complete integration. The mean MOCART score was 61 (range 50-75) points. The mean Henderson score was 7 (range 6-9) points. All patients showed subchondral bone alterations. The KOOS showed good values in all sub-categories in 4 out of 5 patients and a mean overall score of 73 (range 40-90) points. Two patients rated the outcome as excellent, two as good and one as fair. All patients would have the procedure again and recommend it. In this small case series, the coverage of symptomatic retropatellar cartilage defects with the chondrotissue(®) implant after microfracturing was safe and feasible with improvement of the patients' situation at short-term follow-up. IV, case series.

New insights from an old mutant: SPADIX4 governs fruiting body development but not hyphal fusion in Sordaria macrospora.

PubMed

Teichert, Ines; Lutomski, Miriam; Märker, Ramona; Nowrousian, Minou; Kück, Ulrich

2017-02-01

During the sexual life cycle of filamentous fungi, multicellular fruiting bodies are generated for the dispersal of spores. The filamentous ascomycete Sordaria macrospora has a long history as a model system for studying fruiting body formation, and two collections of sterile mutants have been generated. However, for most of these mutants, the underlying genetic defect remains unknown. Here, we investigated the mutant spadix (spd) that was generated by X-ray mutagenesis in the 1950s and terminates sexual development after the formation of pre-fruiting bodies (protoperithecia). We sequenced the spd genome and found a 22 kb deletion affecting four genes, which we termed spd1-4. Generation of deletion strains revealed that only spd4 is required for fruiting body formation. Although sterility in S. macrospora is often coupled with a vegetative hyphal fusion defect, Δspd4 was still capable of fusion. This feature distinguishes SPD4 from many other regulators of sexual development. Remarkably, GFP-tagged SPD4 accumulated in the nuclei of vegetative hyphae and fruiting body initials, the ascogonial coils, but not in sterile tissue from the developing protoperithecium. Our results point to SPD4 as a specific determinant of fruiting body formation. Research on SPD4 will, therefore, contribute to understanding cellular reprogramming during initiation of sexual development in fungi.

Density functional theory study of defects in unalloyed δ-Pu

DOE PAGES

Hernandez, S. C.; Freibert, F. J.; Wills, J. M.

2017-03-19

Using density functional theory, we explore in this paper various classical point and complex defects within the face-centered cubic unalloyed δ-plutonium matrix that are potentially induced from self-irradiation. For plutonium only defects, the most energetically stable defect is a distorted split-interstitial. Gallium, the δ-phase stabilizer, is thermodynamically stable as a substitutional defect, but becomes unstable when participating in a complex defect configuration. Finally, complex uranium defects may thermodynamically exist as uranium substitutional with neighboring plutonium interstitial and stabilization of uranium within the lattice is shown via partial density of states and charge density difference plots to be 5f hybridization betweenmore » uranium and plutonium.« less

Density functional theory study of defects in unalloyed δ-Pu

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

Hernandez, S. C.; Freibert, F. J.; Wills, J. M.

Using density functional theory, we explore in this paper various classical point and complex defects within the face-centered cubic unalloyed δ-plutonium matrix that are potentially induced from self-irradiation. For plutonium only defects, the most energetically stable defect is a distorted split-interstitial. Gallium, the δ-phase stabilizer, is thermodynamically stable as a substitutional defect, but becomes unstable when participating in a complex defect configuration. Finally, complex uranium defects may thermodynamically exist as uranium substitutional with neighboring plutonium interstitial and stabilization of uranium within the lattice is shown via partial density of states and charge density difference plots to be 5f hybridization betweenmore » uranium and plutonium.« less

Mesoscale modeling of solute precipitation and radiation damage

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

Zhang, Yongfeng; Schwen, Daniel; Ke, Huibin

2015-09-01

This report summarizes the low length scale effort during FY 2014 in developing mesoscale capabilities for microstructure evolution in reactor pressure vessels. During operation, reactor pressure vessels are subject to hardening and embrittlement caused by irradiation-induced defect accumulation and irradiation-enhanced solute precipitation. Both defect production and solute precipitation start from the atomic scale, and manifest their eventual effects as degradation in engineering-scale properties. To predict the property degradation, multiscale modeling and simulation are needed to deal with the microstructure evolution, and to link the microstructure feature to material properties. In this report, the development of mesoscale capabilities for defect accumulationmore » and solute precipitation are summarized. Atomic-scale efforts that supply information for the mesoscale capabilities are also included.« less

Atomic scale simulations of pyrochlore oxides with a tight-binding variable-charge model: implications for radiation tolerance.

PubMed

Sattonnay, G; Tétot, R

2014-02-05

Atomistic simulations with new interatomic potentials derived from a tight-binding variable-charge model were performed in order to investigate the lattice properties and the defect formation energies in Gd2Ti2O7 and Gd2Zr2O7 pyrochlores. The main objective was to determine the role played by the defect stability on the radiation tolerance of these compounds. Calculations show that the titanate has a more covalent character than the zirconate. Moreover, the properties of oxygen Frenkel pairs, cation antisite defects and cation Frenkel pairs were studied. In Gd2Ti2O7 the cation antisite defect and the Ti-Frenkel pair are not stable: they evolve towards more stable defect configurations during the atomic relaxation process. This phenomenon is driven by a decrease of the Ti coordination number down to five which leads to a local atomic reorganization and strong structural distortions around the defects. These kinds of atomic rearrangements are not observed around defects in Gd2Zr2O7. Therefore, the defect stability in A2B2O7 depends on the ability of B atoms to accommodate high coordination number (higher than six seems impossible for Ti). The accumulation of structural distortions around Ti-defects due to this phenomenon could drive the Gd2Ti2O7 amorphization induced by irradiation.

Understanding the Irradiation Behavior of Zirconium Carbide

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

Motta, Arthur; Sridharan, Kumar; Morgan, Dane

2013-10-11

Zirconium carbide (ZrC) is being considered for utilization in high-temperature gas-cooled reactor fuels in deep-burn TRISO fuel. Zirconium carbide possesses a cubic B1-type crystal structure with a high melting point, exceptional hardness, and good thermal and electrical conductivities. The use of ZrC as part of the TRISO fuel requires a thorough understanding of its irradiation response. However, the radiation effects on ZrC are still poorly understood. The majority of the existing research is focused on the radiation damage phenomena at higher temperatures (>450{degree}C) where many fundamental aspects of defect production and kinetics cannot be easily distinguished. Little is known aboutmore » basic defect formation, clustering, and evolution of ZrC under irradiation, although some atomistic simulation and phenomenological studies have been performed. Such detailed information is needed to construct a model describing the microstructural evolution in fast-neutron irradiated materials that will be of great technological importance for the development of ZrC-based fuel. The goal of the proposed project is to gain fundamental understanding of the radiation-induced defect formation in zirconium carbide and irradiation response by using a combination of state-of-the-art experimental methods and atomistic modeling. This project will combine (1) in situ ion irradiation at a specialized facility at a national laboratory, (2) controlled temperature proton irradiation on bulk samples, and (3) atomistic modeling to gain a fundamental understanding of defect formation in ZrC. The proposed project will cover the irradiation temperatures from cryogenic temperature to as high as 800{degree}C, and dose ranges from 0.1 to 100 dpa. The examination of this wide range of temperatures and doses allows us to obtain an experimental data set that can be effectively used to exercise and benchmark the computer calculations of defect properties. Combining the examination of radiation-induced microstructures mapped spatially and temporally, microstructural evolution during post-irradiation annealing, and atomistic modeling of defect formation and transport energetics will provide new, critical understanding about property changes in ZrC. The behavior of materials under irradiation is determined by the balance between damage production, defect clustering, and lattice response. In order to predict those effects at high temperatures so targeted testing can be expanded and extrapolated beyond the known database, it is necessary to determine the defect energetics and mobilities as these control damage accumulation and annealing. In particular, low-temperature irradiations are invaluable for determining the regions of defect mobility. Computer simulation techniques are particularly useful for identifying basic defect properties, especially if closely coupled with a well-constructed and complete experimental database. The close coupling of calculation and experiment in this project will provide mutual benchmarking and allow us to glean a deeper understanding of the irradiation response of ZrC, which can then be applied to the prediction of its behavior in reactor conditions.« less

Thermal equilibrium concentration of intrinsic point defects in heavily doped silicon crystals - Theoretical study of formation energy and formation entropy in area of influence of dopant atoms-

NASA Astrophysics Data System (ADS)

Kobayashi, K.; Yamaoka, S.; Sueoka, K.; Vanhellemont, J.

2017-09-01

It is well known that p-type, neutral and n-type dopants affect the intrinsic point defect (vacancy V and self-interstitial I) behavior in single crystal Si. By the interaction with V and/or I, (1) growing Si crystals become more V- or I-rich, (2) oxygen precipitation is enhanced or retarded, and (3) dopant diffusion is enhanced or retarded, depending on the type and concentration of dopant atoms. Since these interactions affect a wide range of Si properties ranging from as-grown crystal quality to LSI performance, numerical simulations are used to predict and to control the behavior of both dopant atoms and intrinsic point defects. In most cases, the thermal equilibrium concentrations of dopant-point defect pairs are evaluated using the mass action law by taking only the binding energy of closest pair to each other into account. The impacts of dopant atoms on the formation of V and I more distant than 1st neighbor and on the change of formation entropy are usually neglected. In this study, we have evaluated the thermal equilibrium concentrations of intrinsic point defects in heavily doped Si crystals. Density functional theory (DFT) calculations were performed to obtain the formation energy (Ef) of the uncharged V and I at all sites in a 64-atom supercell around a substitutional p-type (B, Ga, In, and Tl), neutral (C, Ge, and Sn) and n-type (P, As, and Sb) dopant atom. The formation (vibration) entropies (Sf) of free I, V and I, V at 1st neighboring site from B, C, Sn, P and As atoms were also calculated with the linear response method. The dependences of the thermal equilibrium concentrations of trapped and total intrinsic point defects (sum of free I or V and I or V trapped with dopant atoms) on the concentrations of B, C, Sn, P and As in Si were obtained. Furthermore, the present evaluations well explain the experimental results of the so-called ;Voronkov criterion; in B and C doped Si, and also the observed dopant dependent void sizes in P and As doped Si crystals. The expressions obtained in the present work are very useful for the numerical simulation of grown-in defect behavior, oxygen precipitation and dopant diffusion in heavily doped Si. DFT calculations also showed that Coulomb interaction reaches approximately 30 Å from p (n)-type dopant atoms to I (V) in Si.

[Comparing the ranges of defect measured with standard white on white and Pulsar perimetries].

PubMed

González de la Rosa, M; González-Hernández, M; García-Feijoo, J; Sánchez Méndez, M; García-Sánchez, J

2011-04-01

Normal thresholds on Pulsar perimetry fall faster than those of standard perimetry in the peripheral visual field. Two related studies were performed. Firstly, the frequency distributions of glaucoma defects on standard automated perimetry (SAP) and the relationship of the centre and periphery (Study A) were studied first, followed by an attempt to establish the limits of pulsar perimetry (Study B). A: frequency of defects was calculated in 78.663 SAP perimetries (G1-TOP, Octopus 1-2-3, Haag-Streit). Study B: 204 eyes with mean defect (MD-SAP) lower than 9 dB were examined 8.92 ± 4.19 times with SAP (TOP-32, Octopus 311) and temporal modulation perimetry (T30W, Pulsar Perimeter, Haag-Streit). Study A: 50.7% of the SAP examinations showed MD values lower than 9 dB and 32.7% bellow 6 dB. The MD correlation of the central 20° with the MD of the most peripheral points was r=0.933. Study B: in cases with MD-TOP-32 lower than 6 dB, SAP had the maximum possibility of detecting defect in 0.02% of points and Pulsar in 0.29%. In subjects with MD-TOP-32 between 6 and 9 dB frequencies were 0.38% in SAP and 3.5% in Pulsar (5.1% for eccentricities higher than 20°). Pulsar allows detecting defects, without range limitations, in the initial half of SAP frequencies expected on glaucoma patients. In order to study the progression of deeper defects the examination should focus on the central points, where the dynamic range of both systems is more equivalent. Copyright © 2010 Sociedad Española de Oftalmología. Published by Elsevier Espana. All rights reserved.

Ab initio phonon point defect scattering and thermal transport in graphene

NASA Astrophysics Data System (ADS)

Polanco, Carlos A.; Lindsay, Lucas

2018-01-01

We study the scattering of phonons from point defects and their effect on lattice thermal conductivity κ using a parameter-free ab initio Green's function methodology. Specifically, we focus on the scattering of phonons by boron (B), nitrogen (N), and phosphorus substitutions as well as single- and double-carbon vacancies in graphene. We show that changes of the atomic structure and harmonic interatomic force constants locally near defects govern the strength and frequency trends of the scattering of out-of-plane acoustic (ZA) phonons, the dominant heat carriers in graphene. ZA scattering rates due to N substitutions are nearly an order of magnitude smaller than those for B defects despite having similar mass perturbations. Furthermore, ZA phonon scattering rates from N defects decrease with increasing frequency in the lower-frequency spectrum in stark contrast to expected trends from simple models. ZA phonon-vacancy scattering rates are found to have a significantly softer frequency dependence (˜ω0 ) in graphene than typically employed in phenomenological models. The rigorous Green's function calculations demonstrate that typical mass-defect models do not adequately describe ZA phonon-defect scattering rates. Our ab initio calculations capture well the trend of κ vs vacancy density from experiments, though not the magnitudes. This work elucidates important insights into phonon-defect scattering and thermal transport in graphene, and demonstrates the applicability of first-principles methods toward describing these properties in imperfect materials.

Thermodynamic assessment of oxygen diffusion in non-stoichiometric UO2±x from experimental data and Frenkel pair modeling

NASA Astrophysics Data System (ADS)

Berthinier, C.; Rado, C.; Chatillon, C.; Hodaj, F.

2013-02-01

The self and chemical diffusion of oxygen in the non-stoichiometric domain of the UO2 compound is analyzed from the point of view of experimental determinations and modeling from Frenkel pair defects. The correlation between the self-diffusion and the chemical diffusion coefficients is analyzed using the Darken coefficient calculated from a thermodynamic description of the UO2±x phase. This description was obtained from an optimization of thermodynamic and phase diagram data and modeling with different point defects, including the Frenkel pair point defects. The proposed diffusion coefficients correspond to the 300-2300 K temperature range and to the full composition range of the non stoichiometric UO2 compound. These values will be used for the simulation of the oxidation and ignition of the uranium carbide in different oxygen atmospheres that starts at temperatures as low as 400 K.

Primary radiation damage of an FeCr alloy under pressure: Atomistic simulation

NASA Astrophysics Data System (ADS)

Tikhonchev, M. Yu.; Svetukhin, V. V.

2017-05-01

The primary radiation damage of a binary FeCr alloy deformed by applied mechanical loading is studied by an atomistic molecular dynamics simulation. Loading is simulated by specifying an applied pressure of 0.25, 1.0, and 2.5 GPa of both signs. Hydrostatic and uniaxial loading is considered along the [001], [111], [112], and [210] directions. The influence of loading on the energy of point defect formation and the threshold atomic displacement energy in single-component bcc iron is investigated. The 10-keV atomic displacement cascades in a "random" binary Fe-9 at % Cr alloy are simulated at an initial temperature of 300 K. The number of the point defects generated in a cascade is estimated, and the clustering of point defects and the spatial orientation of interstitial configurations are analyzed. Our results agree with the results of other researchers and supplement them.

Distribution of point defects in Si(100)/Si grown by low-temperature molecular-beam epitaxy and solid-phase epitaxy

NASA Astrophysics Data System (ADS)

Asoka-Kumar, P.; Gossmann, H.-J.; Unterwald, F. C.; Feldman, L. C.; Leung, T. C.; Au, H. L.; Talyanski, V.; Nielsen, B.; Lynn, K. G.

1993-08-01

Positron annihilation in Si is a quantitaive, depth-sensitive technique for the detection of vacancylike defects or voids. A sensitivity of 5×1015 cm-3 for voidlike defects is easily achieved. The technique has been applied to a study of point-defect distributions in thin films of Si grown by molecular-beam epitaxy. A special procedure was developed to remove the influence of the native oxide on the positron measurement. 200-nm-thick films grown at temperatures between 475 and 560 °C show no defects below the sensitivity limit and are indistinguishable from the bulk substrate. So are films grown at 220 °C, provided a 2-min high-temperature anneal to a peak temperature of >=500 °C is executed every ~=30 nm during growth. If TRTA=450 °C, part of the film contains vacancylike defects to a concentration of ~=1018 cm-3. These results correlate well with current-voltage characteristics of p-n junctions grown with different rapid thermal anneal (RTA) temperatures. Ion scattering, with a defect sensitivity of ~=1%, shows no difference between films grown with different TRTA. Recrystallization of amorphous films, deposited at room temperature and annealed in situ at 550 °C, always leaves a significant defect concentration of ~=2×1018 cm-3; those defects are reduced but still present even after a 2-h 800 °C furnace anneal.

Automation of the Image Analysis for Thermographic Inspection

NASA Technical Reports Server (NTRS)

Plotnikov, Yuri A.; Winfree, William P.

1998-01-01

Several data processing procedures for the pulse thermal inspection require preliminary determination of an unflawed region. Typically, an initial analysis of the thermal images is performed by an operator to determine the locations of unflawed and the defective areas. In the present work an algorithm is developed for automatically determining a reference point corresponding to an unflawed region. Results are obtained for defects which are arbitrarily located in the inspection region. A comparison is presented of the distributions of derived values with right and wrong localization of the reference point. Different algorithms of automatic determination of the reference point are compared.

Evaluation of melting point of UO 2 by molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Arima, Tatsumi; Idemitsu, Kazuya; Inagaki, Yaohiro; Tsujita, Yuichi; Kinoshita, Motoyasu; Yakub, Eugene

2009-06-01

The melting point of UO 2 has been evaluated by molecular dynamics simulation (MD) in terms of interatomic potential, pressure and Schottky defect concentration. The Born-Mayer-Huggins potentials with or without a Morse potential were explored in the present study. Two-phase simulation whose supercell at the initial state consisted of solid and liquid phases gave the melting point comparable to the experimental data using the potential proposed by Yakub. The heat of fusion was determined by the difference in enthalpy at the melting point. In addition, MD calculations showed that the melting point increased with pressure applied to the system. Thus, the Clausius-Clapeyron equation was verified. Furthermore, MD calculations clarified that an addition of Schottky defects, which generated the local disorder in the UO 2 crystal, lowered the melting point.

32 CFR 634.47 - Disposition of driving records.

Code of Federal Regulations, 2010 CFR

2010-07-01

... ENFORCEMENT AND CRIMINAL INVESTIGATIONS MOTOR VEHICLE TRAFFIC SUPERVISION Driving Records and the Traffic... accumulation of traffic points. Traffic points for persons being transferred will continue to accumulate as... on the driver record regarding suspensions, revocations, moving violations, or chargeable accidents...

Crystal defect studies using x-ray diffuse scattering

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

Larson, B.C.

1980-01-01

Microscopic lattice defects such as point (single atom) defects, dislocation loops, and solute precipitates are characterized by local electronic density changes at the defect sites and by distortions of the lattice structure surrounding the defects. The effect of these interruptions of the crystal lattice on the scattering of x-rays is considered in this paper, and examples are presented of the use of the diffuse scattering to study the defects. X-ray studies of self-interstitials in electron irradiated aluminum and copper are discussed in terms of the identification of the interstitial configuration. Methods for detecting the onset of point defect aggregation intomore » dislocation loops are considered and new techniques for the determination of separate size distributions for vacancy loops and interstitial loops are presented. Direct comparisons of dislocation loop measurements by x-rays with existing electron microscopy studies of dislocation loops indicate agreement for larger size loops, but x-ray measurements report higher concentrations in the smaller loop range. Methods for distinguishing between loops and three-dimensional precipitates are discussed and possibilities for detailed studies considered. A comparison of dislocation loop size distributions obtained from integral diffuse scattering measurements with those from TEM show a discrepancy in the smaller sizes similar to that described above.« less

Environmental Defects And Economic Impact On Global Market Of Rare Earth Metals

NASA Astrophysics Data System (ADS)

Charalampides, G.; Vatalis, K.; Karayannis, V.; Baklavaridis, A.

2016-11-01

Rare earth elements include the 14 lanthanides as well as lanthanium and often yttrium. Actually, most of them are not very rare and occur widely dispersed in a variety of rocks. Rare earth metals are vital to some of the world's faster growing industries: catalysts, Nd-magnets, ceramics, glass, metallurgy, battery alloys, electronics and phosphors. Worldwide, the main countries for distribution of rare earths deposits include China, USA, Russia, Brasil, India, Australia, Greenland and Malaysia. The mining and processing of rare earth metals usually result in significant environmental defects. Many deposits are associated with high concentrations of radioactive elements such as uranium and thorium, which requires separate treatment and disposal. The accumulation of rare earth elements in soils has occurred due to pollution caused by the exploitation of rare earth resources and the wide use of rare earths as fertilizers in agriculture. This accumulation has a toxic effect on the soil microfauna community. However, there are large differences in market prices due to the degree of purity determined by the specifications in the applications. The main focus of this article is to overview Rare Earth Metals’ overall impact on global economy and their environmental defects on soils during processing techniques and as they are used as fertilizers.

Ciliopathy proteins regulate paracrine signaling by modulating proteasomal degradation of mediators

PubMed Central

Liu, Yangfan P.; Tsai, I-Chun; Morleo, Manuela; Oh, Edwin C.; Leitch, Carmen C.; Massa, Filomena; Lee, Byung-Hoon; Parker, David S.; Finley, Daniel; Zaghloul, Norann A.; Franco, Brunella; Katsanis, Nicholas

2014-01-01

Cilia are critical mediators of paracrine signaling; however, it is unknown whether proteins that contribute to ciliopathies converge on multiple paracrine pathways through a common mechanism. Here, we show that loss of cilopathy-associated proteins Bardet-Biedl syndrome 4 (BBS4) or oral-facial-digital syndrome 1 (OFD1) results in the accumulation of signaling mediators normally targeted for proteasomal degradation. In WT cells, several BBS proteins and OFD1 interacted with proteasomal subunits, and loss of either BBS4 or OFD1 led to depletion of multiple subunits from the centrosomal proteasome. Furthermore, overexpression of proteasomal regulatory components or treatment with proteasomal activators sulforaphane (SFN) and mevalonolactone (MVA) ameliorated signaling defects in cells lacking BBS1, BBS4, and OFD1, in morphant zebrafish embryos, and in induced neurons from Ofd1-deficient mice. Finally, we tested the hypothesis that other proteasome-dependent pathways not known to be associated with ciliopathies are defective in the absence of ciliopathy proteins. We found that loss of BBS1, BBS4, or OFD1 led to decreased NF-κB activity and concomitant IκBβ accumulation and that these defects were ameliorated with SFN treatment. Taken together, our data indicate that basal body proteasomal regulation governs paracrine signaling pathways and suggest that augmenting proteasomal function might benefit ciliopathy patients. PMID:24691443

Effect of thiram on chicken growth plate cartilage

USDA-ARS?s Scientific Manuscript database

Thiram is a general use dithiocarbamate pesticide. It causes tibial dyschondroplasia, a growth plate cartilage defect in poultry characterized by growth plate broadening due to the accumulation of nonviable chondrocytes which lead to lameness. Since proteins play significant roles in all aspects cel...

Using Dice Games to Teach Hazards, Risk, and Outcomes in HACCP Classes

ERIC Educational Resources Information Center

Oyarzabal, Omar A.

2015-01-01

This article describes the incorporation of a dice game (piggy) to teach food safety hazards and risk in an engaging way in HACCP classes. Each player accumulates points by rolling two dice, but loses points in a turn when rolling a 7, or all accumulated points when rolling two consecutive doubles. This game helps explain the difference between a…

Decreased cytochrome-c oxidase activity and lack of age-related accumulation of mitochondrial DNA deletions in the brains of schizophrenics

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

Cavelier, L.; Jazin, E.E.; Eriksson, I.

1995-09-01

Defects in mitochondrial energy production have been implicated in several neurodegenerative disorders, such as Parkinson disease and amyotrophic lateral sclerosis. To study the contribution of mitochondrial defects to Alzheimer disease and schizophrenia, cytochrome-c oxidase (COX) activity and levels of the mtDNA{sup 4977} deletion in postmortem brain tissue specimens of patients were compared with those of asymptomatic age-matched controls. No difference in COX activity was observed between Alzheimer patients and controls in any of five brain regions investigated. In contrast, schizophrenic patients had a 63% reduction of the COX activity in the nucleus caudatus (P<0.0001) and a 43% reduction in themore » cortex gyrus frontalis (P<0.05) as compared to controls. The average levels of the mtDNA{sup 4977} deletion did not differ significantly between Alzheimer patients and controls, and the deletion followed similar modes of accumulation with age in the two groups. In contrast, no age-related accumulation of mtDNA deletions was found in schizophrenic patients. The reduction in COX activity in schizophrenic patients did not correlate with changes in the total amount of mtDNA or levels of the mtDNA{sup 4977} deletion. The lack of age-related accumulation of the mtDNA{sup 4977} deletion and reduction in COX activity suggest that a mitochondrial dysfunction may be involved in the pathogenesis of schizophrenia. 41 refs., 3 figs., 1 tab.« less

Periodic surface structure bifurcation induced by ultrafast laser generated point defect diffusion in GaAs

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

Abere, Michael J.; Yalisove, Steven M.; Torralva, Ben

2016-04-11

The formation of high spatial frequency laser induced periodic surface structures (HSFL) with period <0.3 λ in GaAs after irradiation with femtosecond laser pulses in air is studied. We have identified a point defect generation mechanism that operates in a specific range of fluences in semiconductors between the band-gap closure and ultrafast-melt thresholds that produces vacancy/interstitial pairs. Stress relaxation, via diffusing defects, forms the 350–400 nm tall and ∼90 nm wide structures through a bifurcation process of lower spatial frequency surface structures. The resulting HSFL are predominately epitaxial single crystals and retain the original GaAs stoichiometry.

Influence of processing in mercury and selenium vapor on the electrical properties of Cd /SUB x/ Hg /SUB 1-x/ Se, Zn /SUB x/ Hg /SUB 1-x/ Se solid solutions

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

Gavaleshko, N.P.; Khomyak, V.V.; Makogonenko, V.N.

1985-12-01

In order to determine the predominant intrinsic point defects in Cd /SUB x/ Hg /SUB 1-x/ Se and Zn /SUB x/ Hg /SUB 1-x/ Se solid solutions, the authors study the influence of annealing in mercury and selenium vapor on the carrier concentration and mobility. When the specimens are annealed in selenium vapor the electron concentration at first increases and then becomes constant. A theoretical analysis of the results obtained indicate that selenium vacancies are the predominant point defects in the solutions, and that the process of defect formation itself is quasiepitaxial.

Global analysis of translation termination in E. coli.

PubMed

Baggett, Natalie E; Zhang, Yan; Gross, Carol A

2017-03-01

Terminating protein translation accurately and efficiently is critical for both protein fidelity and ribosome recycling for continued translation. The three bacterial release factors (RFs) play key roles: RF1 and 2 recognize stop codons and terminate translation; and RF3 promotes disassociation of bound release factors. Probing release factors mutations with reporter constructs containing programmed frameshifting sequences or premature stop codons had revealed a propensity for readthrough or frameshifting at these specific sites, but their effects on translation genome-wide have not been examined. We performed ribosome profiling on a set of isogenic strains with well-characterized release factor mutations to determine how they alter translation globally. Consistent with their known defects, strains with increasingly severe release factor defects exhibit increasingly severe accumulation of ribosomes over stop codons, indicative of an increased duration of the termination/release phase of translation. Release factor mutant strains also exhibit increased occupancy in the region following the stop codon at a significant number of genes. Our global analysis revealed that, as expected, translation termination is generally efficient and accurate, but that at a significant number of genes (≥ 50) the ribosome signature after the stop codon is suggestive of translation past the stop codon. Even native E. coli K-12 exhibits the ribosome signature suggestive of protein extension, especially at UGA codons, which rely exclusively on the reduced function RF2 variant of the K-12 strain for termination. Deletion of RF3 increases the severity of the defect. We unambiguously demonstrate readthrough and frameshifting protein extensions and their further accumulation in mutant strains for a few select cases. In addition to enhancing recoding, ribosome accumulation over stop codons disrupts attenuation control of biosynthetic operons, and may alter expression of some overlapping genes. Together, these functional alterations may either augment the protein repertoire or produce deleterious proteins.

First-principles study of structural, electronic, and optical properties of surface defects in GaAs(001) - β2(2x4)

NASA Astrophysics Data System (ADS)

Bacuyag, Dhonny; Escaño, Mary Clare Sison; David, Melanie; Tani, Masahiko

2018-06-01

We performed first-principles calculations based on density functional theory (DFT) to investigate the role of point defects in the structural, electronic, and optical properties of the GaAs(001)- β2(2x4). In terms of structural properties, AsGa is the most stable defect structure, consistent with experiments. With respect to the electronic structure, band structures revealed the existence of sub-band and midgap states for all defects. The induced sub-bands and midgap states originated from the redistributions of charges towards these defects and neighboring atoms. The presence of these point defects introduced deep energy levels characteristic of EB3 (0.97 eV), EL4 (0.52 eV), and EL2 (0.82 eV) for AsGa, GaAs, GaV, respectively. The optical properties are found to be strongly related to these induced gap states. The calculated onset values in the absorption spectra, corresponding to the energy gaps, confirmed the absorption below the known bulk band gap of 1.43 eV. These support the possible two-step photoabsorption mediated by midgap states as observed in experiments.

Characterization of Drosophila Saposin-related mutants as a model for lysosomal sphingolipid storage diseases

PubMed Central

Schulze, Heike; Paradis, Marie; Gosejacob, Dominic; Papan, Cyrus; Shevchenko, Andrej; Psathaki, Olympia Ekaterina; Thielisch, Melanie; Sandhoff, Konrad

2017-01-01

ABSTRACT Sphingolipidoses are inherited diseases belonging to the class of lysosomal storage diseases (LSDs), which are characterized by the accumulation of indigestible material in the lysosome caused by specific defects in the lysosomal degradation machinery. While some LSDs can be efficiently treated by enzyme replacement therapy (ERT), this is not possible if the nervous system is affected due to the presence of the blood-brain barrier. Sphingolipidoses in particular often present as severe, untreatable forms of LSDs with massive sphingolipid and membrane accumulation in lysosomes, neurodegeneration and very short life expectancy. The digestion of intralumenal membranes within lysosomes is facilitated by lysosomal sphingolipid activator proteins (saposins), which are cleaved from a prosaposin precursor. Prosaposin mutations cause some of the severest forms of sphingolipidoses, and are associated with perinatal lethality in mice, hampering studies on disease progression. We identify the Drosophila prosaposin orthologue Saposin-related (Sap-r) as a key regulator of lysosomal lipid homeostasis in the fly. Its mutation leads to a typical spingolipidosis phenotype with an enlarged endolysosomal compartment and sphingolipid accumulation as shown by mass spectrometry and thin layer chromatography. Sap-r mutants show reduced viability with ∼50% survival to adulthood, allowing us to study progressive neurodegeneration and analyze their lipid profile in young and aged flies. Additionally, we observe a defect in sterol homeostasis with local sterol depletion at the plasma membrane. Furthermore, we find that autophagy is increased, resulting in the accumulation of mitochondria in lysosomes, concomitant with increased oxidative stress. Together, we establish Drosophila Sap-r mutants as a lysosomal storage disease model suitable for studying the age-dependent progression of lysosomal dysfunction associated with lipid accumulation and the resulting pathological signaling events. PMID:28389479

Novel association of VACTERL, neural tube defect and crossed renal ectopia: sonic hedgehog signaling: a point of coherence?

PubMed

Vaze, Dhananjay; Mahalik, Santosh; Rao, Katragadda L N

2012-12-01

The present case report describes two patients with a novel combination of VACTERL (vertebral, anorectal, cardiac, tracheoesophageal, renal, limb), neural tube defect and crossed renal ectopia. Though cases of VACTERL associated with crossed renal ectopia have been described, the present case report is the first to describe its combination with neural tube defect. The cases reported here are significant because central nervous system manifestations are scarce in VACTERL syndrome. The role of sonic hedgehog pathway has been proposed in VACTERL association and neural tube defects. Axial Sonic hedgehog signaling has also been implicated in the mediolateral positioning of the renal parenchyma. With this knowledge, the etiopathogenesis of this novel combination is discussed to highlight the role of sonic hedgehog signaling as a point of coherence. © 2011 The Authors. Congenital Anomalies © 2011 Japanese Teratology Society.

Soliton-impurity interaction in two Ablowitz-Ladik chains with different coupling

NASA Astrophysics Data System (ADS)

Kamburova, R. S.; Primatarowa, M. T.

2014-12-01

The interaction of solitons with point defects in a system of coupled Ablowitz- Ladik (AL) chains is studied numerically. The system is a discrete analog of coupled nonlinear Schrodinger equations. Two types of interchain coupling are investigated: one which admits reduction of the system to the standard integrable AL model (dispersive coupling) and one which couples opposite sites of the chains and does not admit reduction to the AL model (nondispersive coupling). The action of the two coupling types is additive and they can compensate each other in some cases. We have obtained that the single-peak bound soliton-defect solution (attractive impurity) is stable against perturbations, while the double-peak bound soliton-defect solution (repulsive impurity) is unstable and can be easily destroyed. Linear point defects do not influence the period of energy transfer and it is close to the period for the homogeneous case.

Application of constrained equilibrium thermodynamics to irradiated alloy systems

NASA Astrophysics Data System (ADS)

Holloway, James Paul; Stubbins, James F.

1984-05-01

Equilibrium thermodynamics are applied to systems with an excess of point defects to calculate the relative stability of phases. It is possible to model systems with supersaturation levels of vacancies and interstitials, such as those found under irradiation. The calculations reveal the extent to which phase compositional boundaries could shift when one phase or both in a two phase system contain an excess of point defects. Phase boundary shifts in the Ni-Si, Fe-Ni, Ni-Cr, and Fe-Cr systems are examined as a function of the number of excess defects in each phase. It is also found that the critical temperature of the sigma phase in the Fe-Cr system and the fcc-bcc transition in the Fe-Ni are sensitive to excess defect concentrations. These results may apply to local irradiation-induced phase transformations in the presence of solute segregation.

Effect of ultrasonic cavitation on the diffusivity of a point defect in the passive film on formed Nb in 0.5 M HCl solution.

PubMed

Li, D G

2015-11-01

This work primarily focused on the influence of ultrasonic cavitation on the transport property of the point defect in the passive film on formed Nb in 0.5M HCl solution via electrochemical techniques based on the point defect model (PDM). The influence of ultrasonic cavitation on the composition and structure of the passive film was detected by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The transport property of a point defect in the passive film was characterized by the diffusivity of the point defect (D0). The influences of the ultrasonic cavitation power, passivated time and the distance between horn bottom and sample surface on D0 were analyzed. The results demonstrated that the passive film formed on Nb was an n-type semiconductor with a donor density (ND) ranging from 10(19) cm(-3) to 10(20) cm(-3) in the case of static state, while the order of ND increased one to two times by applying ultrasonic cavitation during film formation. The diffusivity of the point defect (D0) in the passive film formed on Nb at 0.5 V for 1 h in a 0.5 M HCl solution in the static state was calculated to be 9.704×10(-18) cm(2) s(-1), and it increased to 1.255×10(-16) cm(2) s(-1), 7.259×10(-16) cm(2) s(-1) and 7.296×10(-15) cm(2) s(-1) when applying the 180 W, 270 W and 450 W ultrasonic cavitation powers during film formation. D0 increased with the increment of the ultrasonic cavitation power, and decreased with the increased in formation time and distance between the horn bottom and sample surface. AES results showed the film structure and composition were changed by applying the ultrasonic cavitation. XPS results revealed that the passive film was mainly composed of Nb2O5 in the static state, and the low valence Nb-oxide (NbO) appeared in the passive film except Nb2O5 in the case of applying a 270 W ultrasonic cavitation power. Copyright © 2015 Elsevier B.V. All rights reserved.

A quantitative study on accumulation of age mass around stagnation points in nested flow systems

NASA Astrophysics Data System (ADS)

Jiang, Xiao-Wei; Wan, Li; Ge, Shemin; Cao, Guo-Liang; Hou, Guang-Cai; Hu, Fu-Sheng; Wang, Xu-Sheng; Li, Hailong; Liang, Si-Hai

2012-12-01

The stagnant zones in nested flow systems have been assumed to be critical to accumulation of transported matter, such as metallic ions and hydrocarbons in drainage basins. However, little quantitative research has been devoted to prove this assumption. In this paper, the transport of age mass is used as an example to demonstrate that transported matter could accumulate around stagnation points. The spatial distribution of model age is analyzed in a series of drainage basins of different depths. We found that groundwater age has a local or regional maximum value around each stagnation point, which proves the accumulation of age mass. In basins where local, intermediate and regional flow systems are all well developed, the regional maximum groundwater age occurs at the regional stagnation point below the basin valley. This can be attributed to the long travel distances of regional flow systems as well as stagnancy of the water. However, when local flow systems dominate, the maximum groundwater age in the basin can be located around the local stagnation points due to stagnancy, which are far away from the basin valley. A case study is presented to illustrate groundwater flow and age in the Ordos Plateau, northwestern China. The accumulation of age mass around stagnation points is confirmed by tracer age determined by 14C dating in two boreholes and simulated age near local stagnation points under different dispersivities. The results will help shed light on the relationship between groundwater flow and distributions of groundwater age, hydrochemistry, mineral resources, and hydrocarbons in drainage basins.

Characterization of Deep and Shallow Levels in GaN

NASA Astrophysics Data System (ADS)

Wessels, Bruce

1997-03-01

The role of native defects and impurities in compensating n-type GaN was investigated. From the observed dependence of carrier concentration on dopant partial pressure the compensating acceptor in n-type material is attributed to the triply charged gallium vacancy. This is consistent with recent calculations on defect stability using density functional theory. The interaction of hydrogen and point defects in GaN was also investigated using FTIR. The role of these defects in compensation will be discussed.

Elucidation of Iron Gettering Mechanisms in Boron-Implanted Silicon Solar Cells

DOE PAGES

Laine, Hannu S.; Vahanissi, Ville; Liu, Zhengjun; ...

2017-12-15

To facilitate cost-effective manufacturing of boron-implanted silicon solar cells as an alternative to BBr 3 diffusion, we performed a quantitative test of the gettering induced by solar-typical boron-implants with the potential for low saturation current density emitters (< 50 fA/cm 2). We show that depending on the contamination level and the gettering anneal chosen, such boron-implanted emitters can induce more than a 99.9% reduction in bulk iron point defect concentration. The iron point defect results as well as synchrotron-based Nano-X-ray-fluorescence investigations of iron precipitates formed in the implanted layer imply that, with the chosen experimental parameters, iron precipitation is themore » dominant gettering mechanism, with segregation-based gettering playing a smaller role. We reproduce the measured iron point defect and precipitate distributions via kinetics modeling. First, we simulate the structural defect distribution created by the implantation process, and then we model these structural defects as heterogeneous precipitation sites for iron. Unlike previous theoretical work on gettering via boron- or phosphorus-implantation, our model is free of adjustable simulation parameters. The close agreement between the model and experimental results indicates that the model successfully captures the necessary physics to describe the iron gettering mechanisms operating in boron-implanted silicon. Furthermore, this modeling capability allows high-performance, cost-effective implanted silicon solar cells to be designed.« less

Elucidation of Iron Gettering Mechanisms in Boron-Implanted Silicon Solar Cells

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

Laine, Hannu S.; Vahanissi, Ville; Liu, Zhengjun

To facilitate cost-effective manufacturing of boron-implanted silicon solar cells as an alternative to BBr 3 diffusion, we performed a quantitative test of the gettering induced by solar-typical boron-implants with the potential for low saturation current density emitters (< 50 fA/cm 2). We show that depending on the contamination level and the gettering anneal chosen, such boron-implanted emitters can induce more than a 99.9% reduction in bulk iron point defect concentration. The iron point defect results as well as synchrotron-based Nano-X-ray-fluorescence investigations of iron precipitates formed in the implanted layer imply that, with the chosen experimental parameters, iron precipitation is themore » dominant gettering mechanism, with segregation-based gettering playing a smaller role. We reproduce the measured iron point defect and precipitate distributions via kinetics modeling. First, we simulate the structural defect distribution created by the implantation process, and then we model these structural defects as heterogeneous precipitation sites for iron. Unlike previous theoretical work on gettering via boron- or phosphorus-implantation, our model is free of adjustable simulation parameters. The close agreement between the model and experimental results indicates that the model successfully captures the necessary physics to describe the iron gettering mechanisms operating in boron-implanted silicon. Furthermore, this modeling capability allows high-performance, cost-effective implanted silicon solar cells to be designed.« less

A phase field model for segregation and precipitation induced by irradiation in alloys

NASA Astrophysics Data System (ADS)

Badillo, A.; Bellon, P.; Averback, R. S.

2015-04-01

A phase field model is introduced to model the evolution of multicomponent alloys under irradiation, including radiation-induced segregation and precipitation. The thermodynamic and kinetic components of this model are derived using a mean-field model. The mobility coefficient and the contribution of chemical heterogeneity to free energy are rescaled by the cell size used in the phase field model, yielding microstructural evolutions that are independent of the cell size. A new treatment is proposed for point defect clusters, using a mixed discrete-continuous approach to capture the stochastic character of defect cluster production in displacement cascades, while retaining the efficient modeling of the fate of these clusters using diffusion equations. The model is tested on unary and binary alloy systems using two-dimensional simulations. In a unary system, the evolution of point defects under irradiation is studied in the presence of defect clusters, either pre-existing ones or those created by irradiation, and compared with rate theory calculations. Binary alloys with zero and positive heats of mixing are then studied to investigate the effect of point defect clustering on radiation-induced segregation and precipitation in undersaturated solid solutions. Lastly, irradiation conditions and alloy parameters leading to irradiation-induced homogeneous precipitation are investigated. The results are discussed in the context of experimental results reported for Ni-Si and Al-Zn undersaturated solid solutions subjected to irradiation.

Luminescence from defects in GaN

NASA Astrophysics Data System (ADS)

Reshchikov, M. A.; Morkoç, H.

2006-04-01

We briefly review the luminescence properties of defects in GaN and focus on the most interesting defects. In particular, the blue luminescence band peaking at about 3 eV is assigned to different defects and even different types of transitions in undoped, Zn-, C-, and Mg-doped GaN. Another omnipresent luminescence band, the yellow luminescence band may have different origin in nearly dislocation-free freestanding GaN templates, undoped thin layers, and carbon-doped GaN. The Y4 and Y7 lines are caused by recombination at unidentified point defects captured by threading edge dislocations.

Explosive mutation accumulation triggered by heterozygous human Pol ε proofreading-deficiency is driven by suppression of mismatch repair

PubMed Central

Campbell, Brittany B; Ungerleider, Nathan; Light, Nicholas; Wu, Tong; LeCompte, Kimberly G; Goksenin, A Yasemin; Bunnell, Bruce A; Tabori, Uri; Shlien, Adam

2018-01-01

Tumors defective for DNA polymerase (Pol) ε proofreading have the highest tumor mutation burden identified. A major unanswered question is whether loss of Pol ε proofreading by itself is sufficient to drive this mutagenesis, or whether additional factors are necessary. To address this, we used a combination of next generation sequencing and in vitro biochemistry on human cell lines engineered to have defects in Pol ε proofreading and mismatch repair. Absent mismatch repair, monoallelic Pol ε proofreading deficiency caused a rapid increase in a unique mutation signature, similar to that observed in tumors from patients with biallelic mismatch repair deficiency and heterozygous Pol ε mutations. Restoring mismatch repair was sufficient to suppress the explosive mutation accumulation. These results strongly suggest that concomitant suppression of mismatch repair, a hallmark of colorectal and other aggressive cancers, is a critical force for driving the explosive mutagenesis seen in tumors expressing exonuclease-deficient Pol ε. PMID:29488881

ATG3-dependent autophagy mediates mitochondrial homeostasis in pluripotency acquirement and maintenance

PubMed Central

Liu, Kun; Zhao, Qian; Liu, Pinglei; Cao, Jiani; Gong, Jiaqi; Wang, Chaoqun; Wang, Weixu; Li, Xiaoyan; Sun, Hongyan; Zhang, Chao; Li, Yufei; Jiang, Minggui; Zhu, Shaohua; Sun, Qingyuan; Jiao, Jianwei; Hu, Baoyang; Zhao, Xiaoyang; Li, Wei; Chen, Quan; Zhou, Qi; Zhao, Tongbiao

2016-01-01

ABSTRACT Pluripotent stem cells, including induced pluripotent and embryonic stem cells (ESCs), have less developed mitochondria than somatic cells and, therefore, rely more heavily on glycolysis for energy production.1-3 However, how mitochondrial homeostasis matches the demands of nuclear reprogramming and regulates pluripotency in ESCs is largely unknown. Here, we identified ATG3-dependent autophagy as an executor for both mitochondrial remodeling during somatic cell reprogramming and mitochondrial homeostasis regulation in ESCs. Dysfunctional autophagy by Atg3 deletion inhibited mitochondrial removal during pluripotency induction, resulting in decreased reprogramming efficiency and accumulation of abnormal mitochondria in established iPSCs. In Atg3 null mouse ESCs, accumulation of aberrant mitochondria was accompanied by enhanced ROS generation, defective ATP production and attenuated pluripotency gene expression, leading to abnormal self-renewal and differentiation. These defects were rescued by reacquisition of wild-type but not lipidation-deficient Atg3 expression. Taken together, our findings highlight a critical role of ATG3-dependent autophagy for mitochondrial homeostasis regulation in both pluripotency acquirement and maintenance. PMID:27575019

ATG3-dependent autophagy mediates mitochondrial homeostasis in pluripotency acquirement and maintenance.

PubMed

Liu, Kun; Zhao, Qian; Liu, Pinglei; Cao, Jiani; Gong, Jiaqi; Wang, Chaoqun; Wang, Weixu; Li, Xiaoyan; Sun, Hongyan; Zhang, Chao; Li, Yufei; Jiang, Minggui; Zhu, Shaohua; Sun, Qingyuan; Jiao, Jianwei; Hu, Baoyang; Zhao, Xiaoyang; Li, Wei; Chen, Quan; Zhou, Qi; Zhao, Tongbiao

2016-11-01

Pluripotent stem cells, including induced pluripotent and embryonic stem cells (ESCs), have less developed mitochondria than somatic cells and, therefore, rely more heavily on glycolysis for energy production. 1-3 However, how mitochondrial homeostasis matches the demands of nuclear reprogramming and regulates pluripotency in ESCs is largely unknown. Here, we identified ATG3-dependent autophagy as an executor for both mitochondrial remodeling during somatic cell reprogramming and mitochondrial homeostasis regulation in ESCs. Dysfunctional autophagy by Atg3 deletion inhibited mitochondrial removal during pluripotency induction, resulting in decreased reprogramming efficiency and accumulation of abnormal mitochondria in established iPSCs. In Atg3 null mouse ESCs, accumulation of aberrant mitochondria was accompanied by enhanced ROS generation, defective ATP production and attenuated pluripotency gene expression, leading to abnormal self-renewal and differentiation. These defects were rescued by reacquisition of wild-type but not lipidation-deficient Atg3 expression. Taken together, our findings highlight a critical role of ATG3-dependent autophagy for mitochondrial homeostasis regulation in both pluripotency acquirement and maintenance.

Explosive mutation accumulation triggered by heterozygous human Pol ε proofreading-deficiency is driven by suppression of mismatch repair.

PubMed

Hodel, Karl P; de Borja, Richard; Henninger, Erin E; Campbell, Brittany B; Ungerleider, Nathan; Light, Nicholas; Wu, Tong; LeCompte, Kimberly G; Goksenin, A Yasemin; Bunnell, Bruce A; Tabori, Uri; Shlien, Adam; Pursell, Zachary F

2018-02-28

Tumors defective for DNA polymerase (Pol) ε proofreading have the highest tumor mutation burden identified. A major unanswered question is whether loss of Pol ε proofreading by itself is sufficient to drive this mutagenesis, or whether additional factors are necessary. To address this, we used a combination of next generation sequencing and in vitro biochemistry on human cell lines engineered to have defects in Pol ε proofreading and mismatch repair. Absent mismatch repair, monoallelic Pol ε proofreading deficiency caused a rapid increase in a unique mutation signature, similar to that observed in tumors from patients with biallelic mismatch repair deficiency and heterozygous Pol ε mutations. Restoring mismatch repair was sufficient to suppress the explosive mutation accumulation. These results strongly suggest that concomitant suppression of mismatch repair, a hallmark of colorectal and other aggressive cancers, is a critical force for driving the explosive mutagenesis seen in tumors expressing exonuclease-deficient Pol ε. © 2018, Hodel et al.

Comparison of naturally occurring and ligature-induced peri-implantitis bone defects in humans and dogs.

PubMed

Schwarz, Frank; Herten, Monika; Sager, Martin; Bieling, Katrin; Sculean, Anton; Becker, Jürgen

2007-04-01

The aim of the present study was to evaluate and compare naturally occuring and ligature-induced peri-implantitis bone defects in humans and dogs. Twenty-four partially and fully edentulous patients undergoing peri-implant bone augmentation procedures due to advanced peri-implant infections were included in this study (n=40 implants). Furthermore, peri-implantitis was induced by ligature placement and plaque accumulation in five beagle dogs for three months following implant insertion (n=15 implants). The ligatures were removed when about 30% of the initial bone was lost. During open flap surgery, configuration and defect characteristics of the peri-implant bone loss were recorded in both humans and dogs. Open flap surgery generally revealed two different classes of peri-implant bone defects. While Class I defects featured well-defined intrabony components, Class II defects were characterized by consistent horizontal bone loss. The allocation of intrabony components of Class I defects regarding the implant body allowed a subdivision of five different configurations (Classes Ia-e). In particular, human defects were most frequently Class Ie (55.3%), followed by Ib (15.8%), Ic (13.3%), Id (10.2%), and Ia (5.4%). Similarly, bone defects in dogs were also most frequently Class Ie (86.6%), while merely two out of 15 defects were Classes Ia and Ic (6.7%, respectively). Within the limits of the present study, it might be concluded that configurations and sizes of ligature-induced peri-implantitis bone defects in dogs seemed to resemble naturally occurring lesions in humans.

The very-long-chain hydroxy fatty acyl-CoA dehydratase PASTICCINO2 is essential and limiting for plant development

PubMed Central

Bach, Liên; Michaelson, Louise V.; Haslam, Richard; Bellec, Yannick; Gissot, Lionel; Marion, Jessica; Da Costa, Marco; Boutin, Jean-Pierre; Miquel, Martine; Tellier, Frédérique; Domergue, Frederic; Markham, Jonathan E.; Beaudoin, Frederic; Napier, Johnathan A.; Faure, Jean-Denis

2008-01-01

Very-long-chain fatty acids (VLCFAs) are synthesized as acyl-CoAs by the endoplasmic reticulum-localized elongase multiprotein complex. Two Arabidopsis genes are putative homologues of the recently identified yeast 3-hydroxy-acyl-CoA dehydratase (PHS1), the third enzyme of the elongase complex. We showed that Arabidopsis PASTICCINO2 (PAS2) was able to restore phs1 cytokinesis defects and sphingolipid long chain base overaccumulation. Conversely, the expression of PHS1 was able to complement the developmental defects and the accumulation of long chain bases of the pas2–1 mutant. The pas2–1 mutant was characterized by a general reduction of VLCFA pools in seed storage triacylglycerols, cuticular waxes, and complex sphingolipids. Most strikingly, the defective elongation cycle resulted in the accumulation of 3-hydroxy-acyl-CoA intermediates, indicating premature termination of fatty acid elongation and confirming the role of PAS2 in this process. We demonstrated by in vivo bimolecular fluorescence complementation that PAS2 was specifically associated in the endoplasmic reticulum with the enoyl-CoA reductase CER10, the fourth enzyme of the elongase complex. Finally, complete loss of PAS2 function is embryo lethal, and the ectopic expression of PHS1 led to enhanced levels of VLCFAs associated with severe developmental defects. Altogether these results demonstrate that the plant 3-hydroxy-acyl-CoA dehydratase PASTICCINO2 is an essential and limiting enzyme in VLCFA synthesis but also that PAS2-derived VLCFA homeostasis is required for specific developmental processes. PMID:18799749

First-principles study of uranium carbide: Accommodation of point defects and of helium, xenon, and oxygen impurities

NASA Astrophysics Data System (ADS)

Freyss, Michel

2010-01-01

Point defects and volatile impurities (helium, xenon, oxygen) in uranium monocarbide UC are studied by first-principles calculations. Preliminarily, bulk properties of UC and of two other uranium carbide phases, UC2 and U2C3 , are calculated in order to compare them to experimental data and to get confidence in the use of the generalized gradient approximation for this class of compounds. The subsequent study of different types of point defects shows that the carbon sublattice best accommodates the defects. The perturbation of the crystal structure induced by the defects is weak and the interaction between defects is found short range. Interstitial carbon dumbbells possibly play an important role in the diffusion of carbon atoms. The most favorable location of diluted helium, xenon, and oxygen impurities in the UC crystal lattice is then determined. The rare-gas atoms occupy preferably a uranium substitution site or a uranium site in a U-C bivacancy. But their incorporation in UC is, however, not energetically favorable, especially for xenon, suggesting their propensity to diffuse in the material and/or form bubbles. On the other hand, oxygen atoms are very favorably incorporated as diluted atoms in the UC lattice, confirming the easy oxidation of UC. The oxygen atoms preferably occupy a carbon substitution site or the carbon site of a U-C bivacancy. Our results are compared to available experimental data on UC and to similar studies by first-principles calculations for other carbides and nitrides with the rock-salt structure.

Developmental accumulation of inorganic polyphosphate affects germination and energetic metabolism in Dictyostelium discoideum

PubMed Central

Livermore, Thomas Miles; Chubb, Jonathan Robert; Saiardi, Adolfo

2016-01-01

Inorganic polyphosphate (polyP) is composed of linear chains of phosphate groups linked by high-energy phosphoanhydride bonds. However, this simple, ubiquitous molecule remains poorly understood. The use of nonstandardized analytical methods has contributed to this lack of clarity. By using improved polyacrylamide gel electrophoresis we were able to visualize polyP extracted from Dictyostelium discoideum. We established that polyP is undetectable in cells lacking the polyphosphate kinase (DdPpk1). Generation of this ppk1 null strain revealed that polyP is important for the general fitness of the amoebae with the mutant strain displaying a substantial growth defect. We discovered an unprecedented accumulation of polyP during the developmental program, with polyP increasing more than 100-fold. The failure of ppk1 spores to accumulate polyP results in a germination defect. These phenotypes are underpinned by the ability of polyP to regulate basic energetic metabolism, demonstrated by a 2.5-fold decrease in the level of ATP in vegetative ppk1. Finally, the lack of polyP during the development of ppk1 mutant cells is partially offset by an increase of both ATP and inositol pyrophosphates, evidence for a model in which there is a functional interplay between inositol pyrophosphates, ATP, and polyP. PMID:26755590

Multi-scale simulation of radiation damage accumulation and subsequent hardening in neutron-irradiated α-Fe

DOE PAGES

Dunn, Aaron; Dingreville, Remi; Capolungo, Laurent

2015-11-27

A hierarchical methodology is introduced to predict the effects of radiation damage and irradiation conditions on the yield stress and internal stress heterogeneity developments in polycrystalline α-Fe. Simulations of defect accumulation under displacement cascade damage conditions are performed using spatially resolved stochastic cluster dynamics. The resulting void and dislocation loop concentrations and average sizes are then input into a crystal plasticity formulation that accounts for the change in critical resolved shear stress due to the presence of radiation induced defects. The simulated polycrystalline tensile tests show a good match to experimental hardening data over a wide range of irradiation doses.more » With this capability, stress heterogeneity development and the effect of dose rate on hardening is investigated. The model predicts increased hardening at higher dose rates for low total doses. By contrast, at doses above 10 –2 dpa when cascade overlap becomes significant, the model does not predict significantly different hardening for different dose rates. In conclusion, the development of such a model enables simulation of radiation damage accumulation and associated hardening without relying on experimental data as an input under a wide range of irradiation conditions such as dose, dose rate, and temperature.« less

Small polarons and point defects in LaFeO3

NASA Astrophysics Data System (ADS)

Zhu, Zhen; Peelaers, Hartwin; van de Walle, Chris G.

The proton-conductive perovskite-type LaFeO3 is a promising negative-electrode material for Ni/metal-hydride (Ni-MH) batteries. It has a discharge capacity up to 530 mAhg-1 at 333 K, which is significantly higher than commercialized AB5-type alloys. To elucidate the underlying mechanism of this performance, we have investigated the structural and electronic properties of bulk LaFeO3, as well as the effect of point defects, using hybrid density functional methods. LaFeO3 is antiferromagnetic in the ground state with a band gap of 3.54 eV. Small hole and electron polarons can form through self- or point-defect-assisted trapping. We find that La vacancies and Sr substitutional on La sites are shallow acceptors with the induced holes trapped as small polarons, while O and Fe vacancies are deep defect centers. Hydrogen interstitials behave like shallow donors, with the donor electrons localized on nearby iron sites as electron polarons. With a large trapping energy, these polarons can act as electron or hole traps and affect the electrical performance of LaFeO3 as the negative electrode for Ni-MH batteries. We acknowledge DOE for financial support.

Effects of fO2, fH2O and aoxide on formation and density of extended planar defects in olivine

NASA Astrophysics Data System (ADS)

Burgess, K.; Cooper, R. F.

2011-12-01

Melt inclusions are used in geochemistry to inform our understanding of many physiochemical processes taking place in the mantle, such as melting, melt-rock interactions and magma mixing. Fundamental to this interpretation of melt inclusions is the assumption that they act as closed systems, i.e., they are chemically isolated after trapping and preserve primitive magma compositions. However, recent work indicates that volatiles (e.g., H and F) can be rapidly reset [Portnyagin et al., 2008], and the diffusion mechanisms and rates in tracer diffusion experiments, specifically of REEs, are a matter of some debate [Spandler and O'Neill, 2010; Cherniak, 2010]. The compendium of observations and experiments suggests a role of planar extended defects in effecting and affecting diffusion kinetics in olivine. Planar extended defects are the exothermic condensation of charged point defects into two-dimensional structures, their third dimension insufficient (i.e., sub-unit cell) to describe them as a unique phase. These planar defects, in a manner similar to mechanisms of "pipe" diffusion along dislocations and of grain boundary diffusion, can lead to measured diffusivities far greater than the lattice diffusivity, and their overall effect on flux is proportional to their spatial density [cf. Hart, 1957]. High-resolution TEM and AEM investigation of experimental olivine-basalt samples show the presence of planar defects near the olivine-melt interface, with the area fraction of the high-contrast defects in the images being greatest at high fO2 and/or fH2O while temperature has an effect on the defect dimensions but not total areal density. EDS analysis of the interface regions indicate high Ti/Ca and Ti/Al ratios compared to the glass; the stability of intercalated humite-type defects in olivine, a planar defect type found in some natural olivines [e.g., Risold et al., 2001; Hermann et al., 2007], is increased to higher temperature by the incorporation of Ti. Activities of oxides clearly affect the presence and density of the defects. Olivine-ilmenite experiments were also carried out in varying fO2 and fH2O conditions. Thermodynamic calculations for concentrations of point defects, defect association(s) and defect condensation in olivine can relate experimental data for measured diffusivities to discerning natural conditions where condensed-defect, fast-path diffusion in olivine could be significant. Planar extended defects can potentially play a role in the kinetics of deformation of olivine in the mantle, particularly as the condensation reaction lowers the activity of mobile point defects. Cherniak, Am. Mineral. 95 (2010) 362-368. Hart, Acta Met. 5 (1957) 597. Hermann et al., Contrib. Mineral. Petrol. 153 (2007) 417-428. Portnyagin et al., Earth Planet. Sci.Lett. 272 (2008) 541-552. Risold et al., Contrib. Mineral. Petrol. 142 (2001) 619-628. Spandler and O'Neill, Contrib. Mineral. Petrol. 159 (2010) 791-818.

Mutants of the lactose carrier of Escherichia coli which show altered sugar recognition plus a severe defect in sugar accumulation.

PubMed

Varela, M F; Wilson, T H; Rodon-Rivera, V; Shepherd, S; Dehne, T A; Rector, A C

2000-04-01

Lactose and melibiose are actively accumulated by the wild-type Escherichia coli lactose carrier, which is an integral membrane protein energized by the proton motive force. Mutants of the E. coli lactose carrier were isolated by their ability to grow on minimal plates with succinate plus IPTG in the presence of the toxic lactose analog beta-thio-o-nitrophenylgalactoside (TONPG). TONPG-resistant mutants were streaked on melibiose MacConkey indicator plates, and red clones were picked. These melibiose positive mutants were then streaked on lactose MacConkey plates, and white clones were picked. Transport assays indicated that the mutants had altered sugar recognition and a defect in sugar accumulation. The mutants had a poor apparent K(m) for both lactose and melibiose in transport. One mutant had almost no ability to take up lactose, but melibiose downhill transport was 58% (V(max)) of normal. All of the mutants accumulated methyl-alpha-d-galactopyranoside (TMG) to only 8% or less of normal, and two failed to accumulate. Immunoblot analysis of the mutant lactose carrier proteins indicated that loss of sugar transport activity was not due to loss of expression in the membrane. Nucleotide sequencing of the lacY gene from the mutants revealed changes in the following amino acids of the lactose carrier: M23I, W151L, G257D, A295D and G377V. Two of the mutants (G257D and G377V) are novel in that they represent the first amino acids in periplasmic loops to be implicated with changes in sugar recognition. We conclude that the amino acids M23, W151, G257, A295 and G377 of the E. coli lactose carrier play either a direct or an indirect role in sugar recognition and accumulation.

Branching points in the low-temperature dipolar hard sphere fluid

NASA Astrophysics Data System (ADS)

Rovigatti, Lorenzo; Kantorovich, Sofia; Ivanov, Alexey O.; Tavares, José Maria; Sciortino, Francesco

2013-10-01

In this contribution, we investigate the low-temperature, low-density behaviour of dipolar hard-sphere (DHS) particles, i.e., hard spheres with dipoles embedded in their centre. We aim at describing the DHS fluid in terms of a network of chains and rings (the fundamental clusters) held together by branching points (defects) of different nature. We first introduce a systematic way of classifying inter-cluster connections according to their topology, and then employ this classification to analyse the geometric and thermodynamic properties of each class of defects, as extracted from state-of-the-art equilibrium Monte Carlo simulations. By computing the average density and energetic cost of each defect class, we find that the relevant contribution to inter-cluster interactions is indeed provided by (rare) three-way junctions and by four-way junctions arising from parallel or anti-parallel locally linear aggregates. All other (numerous) defects are either intra-cluster or associated to low cluster-cluster interaction energies, suggesting that these defects do not play a significant part in the thermodynamic description of the self-assembly processes of dipolar hard spheres.

Density Functional Calculations of Native Defects in CH 3 NH 3 PbI 3 : Effects of Spin–Orbit Coupling and Self-Interaction Error

DOE PAGES

Du, Mao-Hua

2015-04-02

We know that native point defects play an important role in carrier transport properties of CH3NH3PbI3. However, the nature of many important defects remains controversial due partly to the conflicting results reported by recent density functional theory (DFT) calculations. In this Letter, we show that self-interaction error and the neglect of spin–orbit coupling (SOC) in many previous DFT calculations resulted in incorrect positions of valence and conduction band edges, although their difference, which is the band gap, is in good agreement with the experimental value. Moreover, this problem has led to incorrect predictions of defect-level positions. Hybrid density functional calculations,more » which partially correct the self-interaction error and include the SOC, show that, among native point defects (including vacancies, interstitials, and antisites), only the iodine vacancy and its complexes induce deep electron and hole trapping levels inside of the band gap, acting as nonradiative recombination centers.« less

Femtosecond pulsed laser micromachining of single crystalline 3C SiC structures based on a laser-induced defect-activation process

NASA Astrophysics Data System (ADS)

Dong, Yuanyuan; Zorman, Christian; Molian, Pal

2003-09-01

A femtosecond pulsed Ti:sapphire laser with a pulse width of 120 fs, a wavelength of 800 nm and a repetition rate of 1 kHz was employed for direct write patterning of single crystalline 3C-SiC thin films deposited on Si substrates. The ablation mechanism of SiC was investigated as a function of pulse energy. At high pulse energies (>1 µJ), ablation occurred via thermally dominated processes such as melting, boiling and vaporizing of single crystalline SiC. At low pulse energies, the ablation mechanism involved a defect-activation process that included the accumulation of defects, formation of nano-particles and vaporization of crystal boundaries, which contributed to well-defined and debris-free patterns in 3C-SiC thin films. The interactions between femtosecond laser pulses and the intrinsic lattice defects in epitaxially grown 3C-SiC films led to the generation of nano-particles. Micromechanical structures such as micromotor rotors and lateral resonators were patterned into 3C-SiC films using the defect-activation ablation mechanism.

Impurity distribution and microstructure of Ga-doped ZnO films grown by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Kvit, A. V.; Yankovich, A. B.; Avrutin, V.; Liu, H.; Izyumskaya, N.; Özgür, Ü.; Morkoç, H.; Voyles, P. M.

2012-12-01

We report microstructural characterization of heavily Ga-doped ZnO (GZO) thin films on GaN and sapphire by aberration-corrected scanning transmission electron microscopy. Growth under oxygen-rich and metal-rich growth conditions leads to changes in the GZO polarity and different extended defects. For GZO layers on sapphire, the primary extended defects are voids, inversion domain boundaries, and low-angle grain boundaries. Ga doping of ZnO grown under metal-rich conditions causes a switch from pure oxygen polarity to mixed oxygen and zinc polarity in small domains. Electron energy loss spectroscopy and energy dispersive spectroscopy spectrum imaging show that Ga is homogeneous, but other residual impurities tend to accumulate at the GZO surface and at extended defects. GZO grown on GaN on c-plane sapphire has Zn polarity and no voids. There are misfit dislocations at the interfaces between GZO and an undoped ZnO buffer layer and at the buffer/GaN interface. Low-angle grain boundaries are the only threading microstructural defects. The potential effects of different extended defects and impurity distributions on free carrier scattering are discussed.

Regulating intestinal function to reduce atherogenic lipoproteins.

PubMed

Hussain, M Mahmood; Leung, Tung Ming; Zhou, Liye; Abu-Merhi, Sarah

2013-08-01

Significant knowledge regarding different molecules involved in the transport of dietary fat into the circulation has been garnered. Studies point to the possibility that accumulation of intestine-derived lipoproteins in the plasma could contribute to atherosclerosis. This article provides a brief overview of dietary lipid metabolism and studies in mice supporting the hypothesis that intestinal lipoproteins contribute to atherosclerosis. Deficiencies in lipoprotein lipase and Gpihbp1, and overexpression of heparanse in mice, are associated with increases in atherosclerosis, suggesting that defects in catabolism of larger lipoproteins in the plasma contribute to atherosclerosis. Furthermore, inositol-requiring enzyme 1β-deficient mice that produce more intestinal lipoproteins also develop more atherosclerosis. Thus, increases in plasma intestinal lipoproteins due to either overproduction or reduced catabolism result in augmented atherosclerosis. Intestinal lipoproteins tend to adhere strongly to subendothelial proteoglycans, elicit an inflammatory response by endothelial cells and activate macrophages, contributing to the initiation and progression of the disease. Thus, molecules that reduce intestinal lipid absorption can be useful in lowering atherosclerosis.

Defective fluid shear stress mechanotransduction mediates hereditary hemorrhagic telangiectasia

PubMed Central

Baeyens, Nicolas; Larrivée, Bruno; Ola, Roxana; Hayward-Piatkowskyi, Brielle; Dubrac, Alexandre; Huang, Billy; Ross, Tyler D.; Coon, Brian G.; Min, Elizabeth; Tsarfati, Maya; Tong, Haibin; Eichmann, Anne

2016-01-01

Morphogenesis of the vascular system is strongly modulated by mechanical forces from blood flow. Hereditary hemorrhagic telangiectasia (HHT) is an inherited autosomal-dominant disease in which arteriovenous malformations and telangiectasias accumulate with age. Most cases are linked to heterozygous mutations in Alk1 or Endoglin, receptors for bone morphogenetic proteins (BMPs) 9 and 10. Evidence suggests that a second hit results in clonal expansion of endothelial cells to form lesions with poor mural cell coverage that spontaneously rupture and bleed. We now report that fluid shear stress potentiates BMPs to activate Alk1 signaling, which correlates with enhanced association of Alk1 and endoglin. Alk1 is required for BMP9 and flow responses, whereas endoglin is only required for enhancement by flow. This pathway mediates both inhibition of endothelial proliferation and recruitment of mural cells; thus, its loss blocks flow-induced vascular stabilization. Identification of Alk1 signaling as a convergence point for flow and soluble ligands provides a molecular mechanism for development of HHT lesions. PMID:27646277

Finite-size versus interface-proximity effects in thin-film epitaxial SrTiO3

NASA Astrophysics Data System (ADS)

De Souza, R. A.; Gunkel, F.; Hoffmann-Eifert, S.; Dittmann, R.

2014-06-01

The equilibrium electrical conductivity of epitaxial SrTiO3 (STO) thin films was investigated as a function of temperature, 950≤ T/K ≤1100, and oxygen partial pressure, 10-23≤ pO2/bar ≤1. Compared with single-crystal STO, nanoscale thin-film STO exhibited with decreasing film thickness an increasingly enhanced electronic conductivity under highly reducing conditions, with a corresponding decrease in the activation enthalpy of conduction. This implies substantial modification of STO's point-defect thermodynamics for nanoscale film thicknesses. We argue, however, against such a finite-size effect and for an interface-proximity effect. Indeed, assuming trapping of oxygen vacancies at the STO surface and concomitant depletion of oxygen vacancies—and accumulation of electrons—in an equilibrium surface space-charge layer, we are able to predict quantitatively the conductivity as a function of temperature, oxygen partial pressure, and film thickness. Particularly complex behavior is predicted for ultrathin films that are consumed entirely by space charge.

Neutron-induced defects in optical fibers

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

Rizzolo, S., E-mail: serena.rizzolo@univ-st-etienne.fr; Dipartimento di Fisica e Chimica, Università di Palermo, Palermo; and Areva Centre Technique, Le Creusot

2014-10-21

We present a study on 0.8 MeV neutron-induced defects up to fluences of 10{sup 17} n/cm{sup 2} in fluorine doped optical fibers by using electron paramagnetic resonance, optical absorption and confocal micro-luminescence techniques. Our results allow to address the microscopic mechanisms leading to the generation of Silica-related point-defects such as E', H(I), POR and NBOH Centers.

Two-stage synergy of electronic energy loss with defects in LiTaO 3 under ion irradiation

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

Sellami, Neila; Crespillo, Miguel L.; Zhang, Yanwen

Understanding energy dissipation in electronic and atomic subsystems and subsequent defect evolution is a scientific challenge. Separate and combined effects of electronic and nuclear energy deposition in z-cut LiTaO 3 have been investigated. Irradiation of pristine LiTaO 3 samples with 2 MeV Ta ions leads to amorphization due to atomic displacement damage, described by a disorder accumulation model. Here, while 21 MeV Si ions do not produce significant damage in pristine LiTaO 3, introduction of pre-existing defects sensitizes LiTaO 3 to the formation of ion tracks from the electronic energy loss by 21 MeV Si ions that induce a synergisticmore » two-stage phase transition process.« less

Two-stage synergy of electronic energy loss with defects in LiTaO 3 under ion irradiation

DOE PAGES

Sellami, Neila; Crespillo, Miguel L.; Zhang, Yanwen; ...

2018-03-27

Understanding energy dissipation in electronic and atomic subsystems and subsequent defect evolution is a scientific challenge. Separate and combined effects of electronic and nuclear energy deposition in z-cut LiTaO 3 have been investigated. Irradiation of pristine LiTaO 3 samples with 2 MeV Ta ions leads to amorphization due to atomic displacement damage, described by a disorder accumulation model. Here, while 21 MeV Si ions do not produce significant damage in pristine LiTaO 3, introduction of pre-existing defects sensitizes LiTaO 3 to the formation of ion tracks from the electronic energy loss by 21 MeV Si ions that induce a synergisticmore » two-stage phase transition process.« less

Combining DFT, Cluster Expansions, and KMC to Model Point Defects in Alloys

NASA Astrophysics Data System (ADS)

Modine, N. A.; Wright, A. F.; Lee, S. R.; Foiles, S. M.; Battaile, C. C.; Thomas, J. C.; van der Ven, A.

In an alloy, defect energies are sensitive to the occupations of nearby atomic sites, which leads to a distribution of defect properties. When radiation-induced defects diffuse from their initially non-equilibrium locations, this distribution becomes time-dependent. The defects can become trapped in energetically favorable regions of the alloy leading to a diffusion rate that slows dramatically with time. Density Functional Theory (DFT) allows the accurate determination of ground state and transition state energies for a defect in a particular alloy environment but requires thousands of processing hours for each such calculation. Kinetic Monte-Carlo (KMC) can be used to model defect diffusion and the changing distribution of defect properties but requires energy evaluations for millions of local environments. We have used the Cluster Expansion (CE) formalism to ``glue'' together these seemingly incompatible methods. The occupation of each alloy site is represented by an Ising-like variable, and products of these variables are used to expand quantities of interest. Once a CE is fit to a training set of DFT energies, it allows very rapid evaluation of the energy for an arbitrary configuration, while maintaining the accuracy of the underlying DFT calculations. These energy evaluations are then used to drive our KMC simulations. We will demonstrate the application of our DFT/MC/KMC approach to model thermal and carrier-induced diffusion of intrinsic point defects in III-V alloys. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE.

The CiCs(SiI)n Defect in Silicon from a Density Functional Theory Perspective.

PubMed

Christopoulos, Stavros-Richard G; Sgourou, Efstratia N; Vovk, Ruslan V; Chroneos, Alexander; Londos, Charalampos A

2018-04-16

Carbon constitutes a significant defect in silicon (Si) as it can interact with intrinsic point defects and affect the operation of devices. In heavily irradiated Si containing carbon the initially produced carbon interstitial-carbon substitutional (C i C s ) defect can associate with self-interstitials (Si I 's) to form, in the course of irradiation, the C i C s (Si I ) defect and further form larger complexes namely, C i C s (Si I ) n defects, by the sequential trapping of self-interstitials defects. In the present study, we use density functional theory to clarify the structure and energetics of the C i C s (Si I ) n defects. We report that the lowest energy C i C s (Si I ) and C i C s (Si I )₂ defects are strongly bound with -2.77 and -5.30 eV, respectively.

Ab initio phonon point defect scattering and thermal transport in graphene

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

Polanco, Carlos A.; Lindsay, Lucas R.

Here, we study the scattering of phonons from point defects and their effect on lattice thermal conductivity κ using a parameter-free ab initio Green's function methodology. Specifically, we focus on the scattering of phonons by boron (B), nitrogen (N), and phosphorus substitutions as well as single- and double-carbon vacancies in graphene. We show that changes of the atomic structure and harmonic interatomic force constants locally near defects govern the strength and frequency trends of the scattering of out-of-plane acoustic (ZA) phonons, the dominant heat carriers in graphene. ZA scattering rates due to N substitutions are nearly an order of magnitudemore » smaller than those for B defects despite having similar mass perturbations. Furthermore, ZA phonon scattering rates from N defects decrease with increasing frequency in the lower-frequency spectrum in stark contrast to expected trends from simple models. ZA phonon-vacancy scattering rates are found to have a significantly softer frequency dependence (~ω 0) in graphene than typically employed in phenomenological models. The rigorous Green's function calculations demonstrate that typical mass-defect models do not adequately describe ZA phonon-defect scattering rates. Our ab initio calculations capture well the trend of κ vs vacancy density from experiments, though not the magnitudes. In conclusion, this work elucidates important insights into phonon-defect scattering and thermal transport in graphene, and demonstrates the applicability of first-principles methods toward describing these properties in imperfect materials.« less

Ab initio phonon point defect scattering and thermal transport in graphene

DOE PAGES

Polanco, Carlos A.; Lindsay, Lucas R.

2018-01-04

Here, we study the scattering of phonons from point defects and their effect on lattice thermal conductivity κ using a parameter-free ab initio Green's function methodology. Specifically, we focus on the scattering of phonons by boron (B), nitrogen (N), and phosphorus substitutions as well as single- and double-carbon vacancies in graphene. We show that changes of the atomic structure and harmonic interatomic force constants locally near defects govern the strength and frequency trends of the scattering of out-of-plane acoustic (ZA) phonons, the dominant heat carriers in graphene. ZA scattering rates due to N substitutions are nearly an order of magnitudemore » smaller than those for B defects despite having similar mass perturbations. Furthermore, ZA phonon scattering rates from N defects decrease with increasing frequency in the lower-frequency spectrum in stark contrast to expected trends from simple models. ZA phonon-vacancy scattering rates are found to have a significantly softer frequency dependence (~ω 0) in graphene than typically employed in phenomenological models. The rigorous Green's function calculations demonstrate that typical mass-defect models do not adequately describe ZA phonon-defect scattering rates. Our ab initio calculations capture well the trend of κ vs vacancy density from experiments, though not the magnitudes. In conclusion, this work elucidates important insights into phonon-defect scattering and thermal transport in graphene, and demonstrates the applicability of first-principles methods toward describing these properties in imperfect materials.« less

Effect of ion velocity on creation of point defects halos of latent tracks in LiF

NASA Astrophysics Data System (ADS)

Volkov, A. E.; Schwartz, K.; Medvedev, N. A.; Trautmann, C.

2017-09-01

Parameters of point defects halos (F-color centers) created due to decays of self-trapped valence holes generated in nanometric vicinities of trajectories of gold ions of 275 MeV and 2187 MeV in LiF are estimated in absorption spectroscopy experiments. Such ions have approximately the same electronic stopping: 24.6 keV/nm and 22.9 keV/nm, respectively. In contrast to the usual concept of the velocity effect that a slower ion produces larger structure changes due to a higher density of the deposited energy, the opposite effect occurs for the defect halo revealing a larger radius and a larger defect concentration for an ion of the higher velocity realizing the same energy loss. Spatial spreading of generated valence holes before their self-trapping (500 fs) forms the size of the defect halos around the trajectories of the applied ions. Simulations with Monte-Carlo code TREKIS show no significant difference in the initial spatial distributions of these valence holes by the times of finishing of ionization cascades (∼10 fs after the projectile passage) within the radii of the defect halos deduced from the experiments. Using these distributions as initial conditions for spatial spreading of generated valence holes and taking into account the difference between the defect halo radii, the diffusion coefficients of these holes near the trajectories of 275 and 2187 MeV Au ions in LiF are estimated showing about six times larger value in tracks of the faster ion for irradiations at room temperatures. Presence of H-color centers changes considerably the kinetics of the created defect ensemble in the defect halo resulting in differences between the defect halo parameters in LiF crystals irradiated at 8 K vs. 300 K.

Thermally promoted evolution of open-volume defects and Cu precipitates in the deformed FeCu alloys

NASA Astrophysics Data System (ADS)

Jin, Shuoxue; Cao, Xingzhong; Cheng, Guodong; Lian, Xiangyu; Zhu, Te; Zhang, Peng; Yu, Runsheng; Wang, Baoyi

2018-04-01

We have studied the effect of isothermal annealing on the evolution of the open-volume defect and the Cu precipitate in deformed Fe0.15Cu, Fe0.3Cu and Fe0.6Cu alloys. Using the coincidence Doppler broadening, positron annihilation lifetime and the S-W couples, the evolution of local electronic circumstance around the annihilation sites, open-volume defects and interaction between open-volume defects and Cu precipitates were measured as a function of the isothermal annealing temperatures. Cold rolling deformation induced an obvious increment in S parameters due to the formation of open-volume defects. Annealing not only resulted in gradual recovery of open-volume defects and Cu thermal precipitation, but also promoted the combination and interaction between defects and Cu precipitates. The interaction between open-volume defects and Cu precipitates was revealed clearly by the view point of S-W relationship. The S-W interaction for the different CumVn complexes was also calculated theoretically by MIKA-Doppler, which supports our experimental observations qualitatively. The results indicate that open-volume defects were formed first after cold rolling, followed by the Cu precipitation and recovery of open-volume defects, Cu precipitates recovered at the end. It is interesting that the trajectory of (S, W) points with increasing annealing temperature formed a similar closed "Parallelogram" shape. It is benefit for revealing the behavior of Cu thermal precipitation and their evolution in various Cu-bearing steels under thermal treatment. In addition, we also investigated the Cu content effect on the Cu precipitation in FeCu alloys, and the Cu precipitate phenomenon was enhanced in higher Cu content alloys.

Ion channeling study of defects in compound crystals using Monte Carlo simulations

NASA Astrophysics Data System (ADS)

Turos, A.; Jozwik, P.; Nowicki, L.; Sathish, N.

2014-08-01

Ion channeling is a well-established technique for determination of structural properties of crystalline materials. Defect depth profiles have been usually determined basing on the two-beam model developed by Bøgh (1968) [1]. As long as the main research interest was focused on single element crystals it was considered as sufficiently accurate. New challenge emerged with growing technological importance of compound single crystals and epitaxial heterostructures. Overlap of partial spectra due to different sublattices and formation of complicated defect structures makes the two beam method hardly applicable. The solution is provided by Monte Carlo computer simulations. Our paper reviews principal aspects of this approach and the recent developments in the McChasy simulation code. The latter made it possible to distinguish between randomly displaced atoms (RDA) and extended defects (dislocations, loops, etc.). Hence, complex defect structures can be characterized by the relative content of these two components. The next refinement of the code consists of detailed parameterization of dislocations and dislocation loops. Defect profiles for variety of compound crystals (GaN, ZnO, SrTiO3) have been measured and evaluated using the McChasy code. Damage accumulation curves for RDA and extended defects revealed non monotonous defect buildup with some characteristic steps. Transition to each stage is governed by the different driving force. As shown by the complementary high resolution XRD measurements lattice strain plays here the crucial role and can be correlated with the concentration of extended defects.

Native defects in Tl 6SI 4: Density functional calculations

DOE PAGES

Shi, Hongliang; Du, Mao -Hua

2015-05-05

In this study, Tl 6SI 4 is a promising room-temperature semiconductor radiation detection material. Here, we report density functional calculations of native defects and dielectric properties of Tl 6SI 4. Formation energies and defect levels of native point defects and defect complexes are calculated. Donor-acceptor defect complexes are shown to be abundant in Tl 6SI 4. High resistivity can be obtained by Fermi level pinning by native donor and acceptor defects. Deep donors that are detrimental to electron transport are identified and methods to mitigate such problem are discussed. Furthermore, we show that mixed ionic-covalent character of Tl 6SI 4more » gives rise to enhanced Born effective charges and large static dielectric constant, which provides effective screening of charged defects and impurities.« less

Enhanced accumulation of adipocytes in bone marrow stromal cells in the presence of increased extracellular and intracellular [Ca{sup 2+}

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

Hashimoto, Ryota, E-mail: hryota@juntendo.ac.jp; Katoh, Youichi, E-mail: katoyo@juntendo-urayasu.jp; Nakamura, Kyoko

2012-07-13

Highlights: Black-Right-Pointing-Pointer High [Ca{sup 2+}]{sub o} enhances adipocyte accumulation in the presence of adipogenic inducers. Black-Right-Pointing-Pointer High [Ca{sup 2+}]{sub o} enhances both proliferation and adipocyte differentiation in BMSCs. Black-Right-Pointing-Pointer High [Ca{sup 2+}]{sub o} induces an increase in [Ca{sup 2+}]{sub o} in BMSCs. Black-Right-Pointing-Pointer An intracellular Ca{sup 2+} chelator suppresses the enhancement in adipocyte accumulation. Black-Right-Pointing-Pointer Controlling [Ca{sup 2+}]{sub o} may govern the balance of adipocyte and osteoblast development. -- Abstract: The bone marrow stroma contains osteoblasts and adipocytes that have a common precursor: the pluripotent mesenchymal stem cell found in bone marrow stromal cells (BMSCs). Local bone marrow Ca{sup 2+}more » levels can reach high concentrations due to bone resorption, which is one of the notable features of the bone marrow stroma. Here, we describe the effects of high [Ca{sup 2+}]{sub o} on the accumulation of adipocytes in the bone marrow stroma. Using primary mouse BMSCs, we evaluated the level of adipocyte accumulation by measuring Oil Red O staining and glycerol-3-phosphate dehydrogenase (GPDH) activity. High [Ca{sup 2+}]{sub o} enhanced the accumulation of adipocytes following treatment with both insulin and dexamethasone together but not in the absence of this treatment. This enhanced accumulation was the result of both the accelerated proliferation of BMSCs and their differentiation into adipocytes. Using the fura-2 method, we also showed that high [Ca{sup 2+}]{sub o} induces an increase in [Ca{sup 2+}]{sub i}. An intracellular Ca{sup 2+} chelator suppressed the enhancement in adipocyte accumulation due to increased [Ca{sup 2+}]{sub o} in BMSCs. These data suggest a new role for extracellular Ca{sup 2+} in the bone marrow stroma: increased [Ca{sup 2+}]{sub o} induces an increase in [Ca{sup 2+}]{sub i} levels, which in turn enhances the accumulation of adipocytes under certain conditions.« less

First-principles study of point defects at a semicoherent interface

DOE PAGES

Metsanurk, E.; Tamm, A.; Caro, A.; ...

2014-12-19

Most of the atomistic modeling of semicoherent metal-metal interfaces has so far been based on the use of semiempirical interatomic potentials. Here, we show that key conclusions drawn from previous studies are in contradiction with more precise ab-initio calculations. In particular we find that single point defects do not delocalize, but remain compact near the interfacial plane in Cu-Nb multilayers. Lastly, we give a simple qualitative explanation for this difference on the basis of the well known limited transferability of empirical potentials.

Method for reducing energy losses in laser crystals

DOEpatents

Atherton, L.J.; DeYoreo, J.J.; Roberts, D.H.

1992-03-24

A process for reducing energy losses in crystals is disclosed which comprises: a. heating a crystal to a temperature sufficiently high as to cause dissolution of microscopic inclusions into the crystal, thereby converting said inclusions into point-defects, and b. maintaining said crystal at a given temperature for a period of time sufficient to cause said point-defects to diffuse out of said crystal. Also disclosed are crystals treated by the process, and lasers utilizing the crystals as a source of light. 12 figs.

Method for reducing energy losses in laser crystals

DOEpatents

Atherton, L. Jeffrey; DeYoreo, James J.; Roberts, David H.

1992-01-01

A process for reducing energy losses in crystals is disclosed which comprises: a. heating a crystal to a temperature sufficiently high as to cause dissolution of microscopic inclusions into the crystal, thereby converting said inclusions into point-defects, and b. maintaining said crystal at a given temperature for a period of time sufficient to cause said point-defects to diffuse out of said crystal. Also disclosed are crystals treated by the process, and lasers utilizing the crystals as a source of light.

Detection of defects in formed sheet metal using medial axis transformation

NASA Astrophysics Data System (ADS)

Murmu, Naresh C.; Velgan, Roman

2003-05-01

In the metal forming processes, the sheet metals are often prone to various defects such as thinning, dents, wrinkles etc. In the present manufacturing environments with ever increasing demand of higher quality, detecting the defects of formed sheet metal using an effective and objective inspection system is the foremost norm to remain competitive in market. The defect detection using optical techniques aspire to satisfy its needs to be non-contact and fast. However, the main difficulties to achieve this goal remain essentially on the development of efficient evaluation technique and accurate interpretation of extracted data. The defect like thinning is detected by evaluating the deviations of the thickness in the formed sheet metal against its nominal value. The present evaluation procedure for determination of thickness applied on the measurements data is not without deficiency. To improve this procedure, a new evaluation approach based on medial axis transformation is proposed here. The formed sheet metals are digitized using fringe projection systems in different orientations, and afterwards registered into one coordinate frame. The medial axis transformation (MAT) is applied on the point clouds, generating the point clouds of MAT. This data is further processed and medial surface is determined. The thinning defect is detected by evaluating local wall thickness and other defects like wrinkles are determined using the shape recognition on the medial surface. The applied algorithm is simple, fast and robust.

Intragenic Suppression of a Trafficking-Defective Brassinosteroid Receptor Mutant in Arabidopsis

PubMed Central

Belkhadir, Youssef; Durbak, Amanda; Wierzba, Michael; Schmitz, Robert J.; Aguirre, Andrea; Michel, Rene; Rowe, Scott; Fujioka, Shozo; Tax, Frans E.

2010-01-01

The cell surface receptor kinase BRASSINOSTEROID-INSENSITIVE-1 (BRI1) is the major receptor for steroid hormones in Arabidopsis. Plants homozygous for loss-of-function mutations in BRI1 display a reduction in the size of vegetative organs, resulting in dwarfism. The recessive bri1-5 mutation produces receptors that do not accumulate to wild-type levels and are retained mainly in the endoplasmic reticulum. We have isolated a dominant suppressor of the dwarf phenotype of bri1-5 plants. We show that this suppression is caused by a second-site mutation in BRI1, bri1-5R1. The bri1-5R1 mutation partially rescues the phenotypes of bri1-5 in many tissues and enhances bri1-5 phenotypes above wild-type levels in several other tissues. We demonstrate that the phenotypes of bri1-5R1 plants are due to both increased cell expansion and increased cell division. To test the mechanism of bri1-5 suppression, we assessed whether the phenotypic suppression in bri1-5R1 was dependent on ligand availability and the integrity of the signaling pathway. Our results indicate that the suppression of the dwarf phenotypes associated with bri1-5R1 requires both BR biosynthesis and the receptor kinase BRI1-ASSOCIATED KINASE-1 (BAK1). Finally, we show that bri1-5R1 partially restores the accumulation and plasma membrane localization of BRI1. Collectively, our results point toward a model in which bri1-R1 compensates for the protein-folding abnormalities caused by bri1-5, restoring accumulation of the receptor and its delivery to the cell surface. PMID:20457881

Hybrid Defect Phase Transition: Renormalization Group and Monte Carlo Analysis

NASA Astrophysics Data System (ADS)

Kaufman, Miron; Diep, H. T.

2010-03-01

For the q-state Potts model with 2 < q <= 4 on the square lattice with a defect line, the order parameter on the defect line jumps discontinuously from zero to a nonzero value while the defect energy varies continuously with the temperature at the critical temperature. Monte-Carlo simulations (H. T. Diep, M. Kaufman, Phys Rev E 2009) of the q-state Potts model on a square lattice with a line of defects verify the renormalization group prediction (M. Kaufman, R. B. Griffiths, Phys Rev B 1982) on the occurrence of the hybrid transition on the defect line. This is interesting since for those q values the bulk transition is continuous. This hybrid (continuous - discontinuous) defect transition is induced by the infinite range correlations at the bulk critical point.

Computer programs for eddy-current defect studies

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

Pate, J. R.; Dodd, C. V.

Several computer programs to aid in the design of eddy-current tests and probes have been written. The programs, written in Fortran, deal in various ways with the response to defects exhibited by four types of probes: the pancake probe, the reflection probe, the circumferential boreside probe, and the circumferential encircling probe. Programs are included which calculate the impedance or voltage change in a coil due to a defect, which calculate and plot the defect sensitivity factor of a coil, and which invert calculated or experimental readings to obtain the size of a defect. The theory upon which the programs aremore » based is the Burrows point defect theory, and thus the calculations of the programs will be more accurate for small defects. 6 refs., 21 figs.« less

Treatment outcomes of ligature-induced recession in the dog model using guided tissue regeneration or coronally positioned flap procedures.

PubMed

Papageorgiou, Athanasios; Vouros, Ioannis; Konstantinidis, Antonios

2009-04-01

The aims of the study were: (1) to determine the quality of the hard and soft tissues formed in segments treated with coronally positioned flaps alone (CPF group) or combined with a polylactic acid resorbable membrane (guided tissue regeneration--GTR group) in wide type defects (canine teeth), and (2) to evaluate the behaviour of the newly regenerated tissues to an experimentally induced inflammation initiated by microbial plaque at the submarginal level in recession type defects (premolar teeth). The randomized block design was used in the study, with each dog receiving both treatments (GTR and CPF). Gingival recession defects were surgically created in the 2nd and 4th mandibular premolars and, after 10 weeks, also in the maxillary canines of three dogs. The defects in the premolar area were created earlier than the defects in the canine teeth so that both areas would be ready for biopsy at the same time. Two months after the creation of the defects the exposed roots in the control group of teeth were surgically covered with coronally positioned flaps only (CPF group), and in the test group of teeth a coronally positioned flap was used in combination with a resorbable membrane (GTR group). In the premolar teeth only, after a healing period of five months, cotton ligatures were placed intrasulcularly and these areas were left without plaque control for 10 weeks. Following this, biopsies were taken from the canines and the premolars in order to examine (1) the quality of the hard and soft tissues formed after five months of healing in the canine teeth and (2) the response of the newly formed tissues to microbial accumulation induced by the subgingival ligature placement. In the wide defects of the canine teeth, the use of the membrane produced a mean new attachment formation of 44%, while the repositioned flap technique produced 22% new attachment. The regeneration of bone was limited to the apical area for both techniques and amounted to 15% and 10%, respectively. In the narrow defects of the premolars both techniques produced comparable mean root coverage percentages. The inflammatory conditions created in the study led to a comparable loss of mean clinical attachment and an increase in tissue recession and the extent of the inflammatory process for both groups. The use of resorbable membranes for the treatment of wide recession type defects in the canine teeth (GTR group) produced significantly better clinical results, with higher mean root coverage and increased regenerative capacity of the periodontal tissues, compared with the coronally positioned flap technique (CPF group). Additionally, the regenerated tissues created after the use of both techniques in narrow recession defects (premolar teeth) demonstrated comparable resistance to the microbial accumulation conditions created.

Experimental study on slow flexural waves around the defect modes in a phononic crystal beam using fiber Bragg gratings

NASA Astrophysics Data System (ADS)

Chuang, Kuo-Chih; Zhang, Zhi-Qiang; Wang, Hua-Xin

2016-12-01

This work experimentally studies influences of the point defect modes on the group velocity of flexural waves in a phononic crystal Timoshenko beam. Using the transfer matrix method with a supercell technique, the band structures and the group velocities around the defect modes are theoretically obtained. Particularly, to demonstrate the existence of the localized defect modes inside the band gaps, a high-sensitivity fiber Bragg grating sensing system is set up and the displacement transmittance is measured. Slow propagation of flexural waves via defect coupling in the phononic crystal beam is then experimentally demonstrated with Hanning windowed tone burst excitations.

Growth of defect-free GaAsSbN axial nanowires via self-catalyzed molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Sharma, Manish; Deshmukh, Prithviraj; Kasanaboina, Pavan; Reynolds, C. Lewis, Jr.; Liu, Yang; Iyer, Shanthi

2017-12-01

Bandgap reduction of 10% by incorporation of a dilute amount of N is reported for the first time, in axial GaAsSb nanowires (NWs) grown on Si (111) via Ga-assisted molecular beam epitaxy. Impact of N incorporation on the surface morphology, NW growth kinetics, and their structural and optical properties were examined. Dilute nitride NWs with Sb composition of 7 at% did not exhibit any noticeable planar defects, as revealed by the absence of satellite twin peaks in the selected-area diffraction pattern and high-resolution transmission electron microscopy imaging. Point defects were also minimal in as-grown dilute nitride NWs, as ascertained from the comparison of low-temperature photoluminescence spectra as well as the shape and shift of Raman modes, with in situ annealed NWs in different ambients. Evidence of enhanced incorporation of N was found in the NWs in situ annealed in N ambient, but with deteriorated optical quality due to simultaneous creation of N-induced defects. The lack of any noticeable defects in the as-grown GaAsSbN NWs demonstrates the advantage of the vapor-liquid-solid mechanism responsible for growth of axial configuration over the vapor-solid growth mechanism for core-shell NWs as well as their thin film counterpart, which commonly exhibit N-induced point defects.

Constructing the GW self-energy of a point defect from the perfect crystal and the near neighborhood of the defect

NASA Astrophysics Data System (ADS)

Skachkov, Dmitry; van Schilfgaarde, Mark; Lambrecht, Walter

The full-potential linearized muffin-tin orbital method allows for a real space representation of the GW or quasi-particle self-consistent (QS)GW self-energy ΣR , L ; R' + T , L'. This can be used to construct the self-energy matrix for a point defect system in a large supercell from that of the perfect crystal in the primitive cell and the self-energy of the defect site and its near neighborhood, obtained self-consistently in a smaller supercell. At the interface between both regions we can average the two types of ΣR , L ; R' + T , L' matrix blocks. The result relies on the limited range of the self-energy matrix in real space. It means that we can calculate the quasiparticle energy levels of the defect system at essentially the cost of a DFT calculation and a few QSGW calculations for relatively small systems. The approach presently focuses on quasiparticle energy levels of band structures of the defect system rather than total energies. We will present test results for AsGa\\ in GaAs, ZnGe in ZnGeN2, NO, VO, VZn, and NO - VZn in ZnO. Supported by the US-DOE-BES under Grant No. DE-SC0008933.

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

Basu, Banasri; Bandyopadhyay, Pratul; Majumdar, Priyadarshi

We have studied quantum phase transition induced by a quench in different one-dimensional spin systems. Our analysis is based on the dynamical mechanism which envisages nonadiabaticity in the vicinity of the critical point. This causes spin fluctuation which leads to the random fluctuation of the Berry phase factor acquired by a spin state when the ground state of the system evolves in a closed path. The two-point correlation of this phase factor is associated with the probability of the formation of defects. In this framework, we have estimated the density of defects produced in several one-dimensional spin chains. At themore » critical region, the entanglement entropy of a block of L spins with the rest of the system is also estimated which is found to increase logarithmically with L. The dependence on the quench time puts a constraint on the block size L. It is also pointed out that the Lipkin-Meshkov-Glick model in point-splitting regularized form appears as a combination of the XXX model and Ising model with magnetic field in the negative z axis. This unveils the underlying conformal symmetry at criticality which is lost in the sharp point limit. Our analysis shows that the density of defects as well as the scaling behavior of the entanglement entropy follows a universal behavior in all these systems.« less

Role of Grain Boundaries under Long-Time Radiation

NASA Astrophysics Data System (ADS)

Zhu, Yichao; Luo, Jing; Guo, Xu; Xiang, Yang; Chapman, Stephen Jonathan

2018-06-01

Materials containing a high proportion of grain boundaries offer significant potential for the development of radiation-resistant structural materials. However, a proper understanding of the connection between the radiation-induced microstructural behavior of a grain boundary and its impact at long natural time scales is still missing. In this Letter, point defect absorption at interfaces is summarized by a jump Robin-type condition at a coarse-grained level, wherein the role of interface microstructure is effectively taken into account. Then a concise formula linking the sink strength of a polycrystalline aggregate with its grain size is introduced and is well compared with experimental observation. Based on the derived model, a coarse-grained formulation incorporating the coupled evolution of grain boundaries and point defects is proposed, so as to underpin the study of long-time morphological evolution of grains induced by irradiation. Our simulation results suggest that the presence of point defect sources within a grain further accelerates its shrinking process, and radiation tends to trigger the extension of twin boundary sections.

Design principles for radiation-resistant solid solutions

NASA Astrophysics Data System (ADS)

Schuler, Thomas; Trinkle, Dallas R.; Bellon, Pascal; Averback, Robert

2017-05-01

We develop a multiscale approach to quantify the increase in the recombined fraction of point defects under irradiation resulting from dilute solute additions to a solid solution. This methodology provides design principles for radiation-resistant materials. Using an existing database of solute diffusivities, we identify Sb as one of the most efficient solutes for this purpose in a Cu matrix. We perform density-functional-theory calculations to obtain binding and migration energies of Sb atoms, vacancies, and self-interstitial atoms in various configurations. The computed data informs the self-consistent mean-field formalism to calculate transport coefficients, allowing us to make quantitative predictions of the recombined fraction of point defects as a function of temperature and irradiation rate using homogeneous rate equations. We identify two different mechanisms according to which solutes lead to an increase in the recombined fraction of point defects; at low temperature, solutes slow down vacancies (kinetic effect), while at high temperature, solutes stabilize vacancies in the solid solution (thermodynamic effect). Extension to other metallic matrices and solutes are discussed.

The influence of point defects on the thermal conductivity of AlN crystals

NASA Astrophysics Data System (ADS)

Rounds, Robert; Sarkar, Biplab; Alden, Dorian; Guo, Qiang; Klump, Andrew; Hartmann, Carsten; Nagashima, Toru; Kirste, Ronny; Franke, Alexander; Bickermann, Matthias; Kumagai, Yoshinao; Sitar, Zlatko; Collazo, Ramón

2018-05-01

The average bulk thermal conductivity of free-standing physical vapor transport and hydride vapor phase epitaxy single crystal AlN samples with different impurity concentrations is analyzed using the 3ω method in the temperature range of 30-325 K. AlN wafers grown by physical vapor transport show significant variation in thermal conductivity at room temperature with values ranging between 268 W/m K and 339 W/m K. AlN crystals grown by hydride vapor phase epitaxy yield values between 298 W/m K and 341 W/m K at room temperature, suggesting that the same fundamental mechanisms limit the thermal conductivity of AlN grown by both techniques. All samples in this work show phonon resonance behavior resulting from incorporated point defects. Samples shown by optical analysis to contain carbon-silicon complexes exhibit higher thermal conductivity above 100 K. Phonon scattering by point defects is determined to be the main limiting factor for thermal conductivity of AlN within the investigated temperature range.

Elementary model of severe plastic deformation by KoBo process

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

Gusak, A.; Storozhuk, N.; Danielewski, M., E-mail: daniel@agh.edu.pl

2014-01-21

Self-consistent model of generation, interaction, and annihilation of point defects in the gradient of oscillating stresses is presented. This model describes the recently suggested method of severe plastic deformation by combination of pressure and oscillating rotations of the die along the billet axis (KoBo process). Model provides the existence of distinct zone of reduced viscosity with sharply increased concentration of point defects. This zone provides the high extrusion velocity. Presented model confirms that the Severe Plastic Deformation (SPD) in KoBo may be treated as non-equilibrium phase transition of abrupt drop of viscosity in rather well defined spatial zone. In thismore » very zone, an intensive lateral rotational movement proceeds together with generation of point defects which in self-organized manner make rotation possible by the decrease of viscosity. The special properties of material under KoBo version of SPD can be described without using the concepts of nonequilibrium grain boundaries, ballistic jumps and amorphization. The model can be extended to include different SPD processes.« less

Effects of Defects in Laser Additive Manufactured Ti-6Al-4V on Fatigue Properties

NASA Astrophysics Data System (ADS)

Wycisk, Eric; Solbach, Andreas; Siddique, Shafaqat; Herzog, Dirk; Walther, Frank; Emmelmann, Claus

Laser Additive Manufacturing (LAM) enables economical production of complex lightweight structures as well as patient individual implants. Due to these possibilities the additive manufacturing technology gains increasing importance in the aircraft and the medical industry. Yet these industries obtain high quality standards and demand predictability of material properties for static and dynamic load cases. However, especially fatigue and crack propagation properties are not sufficiently determined. Therefore this paper presents an analysis and simulation of crack propagation behavior considering Laser Additive Manufacturing specific defects, such as porosity and surface roughness. For the mechanical characterization of laser additive manufactured titanium alloy Ti-6Al-4V, crack propagation rates are experimentally determined and used for an analytical modeling and simulation of fatigue. Using experimental results from HCF tests and simulated data, the fatigue and crack resistance performance is analyzed considering material specific defects and surface roughness. The accumulated results enable the reliable prediction of the defects influence on fatigue life of laser additive manufactured titanium components.

Autophagy Sustains Mitochondrial Glutamine Metabolism and Growth of BRAFV600E–Driven Lung Tumors

PubMed Central

Strohecker, Anne M.; Guo, Jessie Yanxiang; Karsli-Uzunbas, Gizem; Price, Sandy M.; Chen, Guanghua Jim; Mathew, Robin; McMahon, Martin; White, Eileen

2013-01-01

Autophagic elimination of defective mitochondria suppresses oxidative stress and preserves mitochondrial function. Here, the essential autophagy gene Atg7 was deleted in a mouse model of BRAFV600E-induced lung cancer in the presence or absence of the tumor suppressor TRP53. Atg7 deletion initially induced oxidative stress and accelerated tumor cell proliferation in a manner indistinguishable from Nrf2 ablation. Compound deletion of Atg7 and Nrf2 had no additive effect suggesting that both genes modulate tumorigenesis by regulating oxidative stress, revealing a potential mechanism of autophagy-mediated tumor suppression. At later stages of tumorigenesis, Atg7 deficiency resulted in an accumulation of defective mitochondria, proliferative defects, reduced tumor burden, conversion of adenomas and adenocarcinomas to oncocytomas, and increased mouse lifespan. Autophagy-defective tumor-derived cell lines were impaired in their ability to respire, survive starvation and were glutamine-dependent, suggesting that autophagy-supplied substrates from protein degradation sustains BRAFV600E-tumor growth and metabolism. PMID:23965987

USP5/Leon deubiquitinase confines postsynaptic growth by maintaining ubiquitin homeostasis through Ubiquilin.

PubMed

Wang, Chien-Hsiang; Huang, Yi-Chun; Chen, Pei-Yi; Cheng, Ying-Ju; Kao, Hsiu-Hua; Pi, Haiwei; Chien, Cheng-Ting

2017-05-10

Synapse formation and growth are tightly controlled processes. How synaptic growth is terminated after reaching proper size remains unclear. Here, we show that Leon, the Drosophila USP5 deubiquitinase, controls postsynaptic growth. In leon mutants, postsynaptic specializations of neuromuscular junctions are dramatically expanded, including the subsynaptic reticulum, the postsynaptic density, and the glutamate receptor cluster. Expansion of these postsynaptic features is caused by a disruption of ubiquitin homeostasis with accumulation of free ubiquitin chains and ubiquitinated substrates in the leon mutant. Accumulation of Ubiquilin (Ubqn), the ubiquitin receptor whose human homolog ubiquilin 2 is associated with familial amyotrophic lateral sclerosis, also contributes to defects in postsynaptic growth and ubiquitin homeostasis. Importantly, accumulations of postsynaptic proteins cause different aspects of postsynaptic overgrowth in leon mutants. Thus, the deubiquitinase Leon maintains ubiquitin homeostasis and proper Ubqn levels, preventing postsynaptic proteins from accumulation to confine postsynaptic growth.

Evaluation of Guided Bone Regeneration around Oral Implants over Different Healing Times Using Two Different Bovine Bone Materials: A Randomized, Controlled Clinical and Histological Investigation.

PubMed

Kohal, Ralf Joachim; Straub, Lisa Marie; Wolkewitz, Martin; Bächle, Maria; Patzelt, Sebastian Berthold Maximilian

2015-10-01

To evaluate the potential of two bone substitute materials and the influence of different healing periods in guided bone regeneration therapy of osseous defects around implants. Twenty-four edentulous patients received implants in the region of the lost lower incisors. Around two standardized osseous defects were created, treated either with a 50:50 mixture of PepGen P-15® and OsteoGraf®/N-700 (test group) or with BioOss® (control group), and covered with titanium membranes. After healing periods of 2, 4, 6, or 9 months, the implants were removed together with the surrounding bone and subsequently prepared for histological evaluations. Defect depths in both groups showed a clinical reduction after intervention. The histologically measured distance from the implant shoulder to the first point of bone-implant contact (BIC) after treatment did not differ between the two groups. The healing time influenced the level of the first point of BIC, with a longer healing period producing a more coronal first point of BIC. A greater percentage BIC and a higher fraction of mineralized bone were found in the pristine bone area compared with the augmented defect area. It can be concluded that in the treatment of osseous defects around oral implants, both materials were equally effective bone substitute materials when used in combination with guided bone regeneration. © 2014 Wiley Periodicals, Inc.

Gadd45a deletion aggravates hematopoietic stem cell dysfunction in ATM-deficient mice.

PubMed

Chen, Yulin; Yang, Runan; Guo, Peng; Ju, Zhenyu

2014-01-01

Ataxia telangiectasia mutated (ATM) kinase plays an essential role in the maintenance of genomic stability. ATM-deficient (ATM(-/-)) mice exhibit hematopoietic stem cell (HSC) dysfunction and a high incidence of lymphoma. Gadd45a controls cell cycle arrest, apoptosis and DNA repair, and is involved in the ATM-p53 mediated DNA damage response. However, the role of Gadd45a in regulating the functionality of ATM(-/-) HSCs is unknown. Here we report that Gadd45a deletion did not rescue the defects of T-cells and B-cells development in ATM(-/-) mice. Instead, ATM and Gadd45a double knockout (ATM(-/-) Gadd45a(-/-)) HSCs exhibited an aggravated defect in long-term self-renewal capacity compared to ATM(-/-) HSCs in HSC transplantation experiments. Further experiments revealed that the aggravated defect of ATM(-/-) Gadd45a(-/-) HSCs was due to a reduction of cell proliferation, associated with an accumulation of DNA damage and subsequent activation of DNA damage response including an up-regulation of p53-p21 signaling pathway. Additionally, ATM(-/-) Gadd45a(-/-) mice showed an increased incidence of hematopoietic malignancies, as well as an increased rate of metastasis than ATM(-/-) mice. In conclusion, Gadd45a deletion aggravated the DNA damage accumulation, which subsequently resulted in a further impaired self-renewal capacity and an increased malignant transformation in ATM(-/-) HSCs.

Defective lysosomal proteolysis and axonal transport are early pathogenic events that worsen with age leading to increased APP metabolism and synaptic Abeta in transgenic APP/PS1 hippocampus

PubMed Central

2012-01-01

Background Axonal pathology might constitute one of the earliest manifestations of Alzheimer disease. Axonal dystrophies were observed in Alzheimer’s patients and transgenic models at early ages. These axonal dystrophies could reflect the disruption of axonal transport and the accumulation of multiple vesicles at local points. It has been also proposed that dystrophies might interfere with normal intracellular proteolysis. In this work, we have investigated the progression of the hippocampal pathology and the possible implication in Abeta production in young (6 months) and aged (18 months) PS1(M146L)/APP(751sl) transgenic mice. Results Our data demonstrated the existence of a progressive, age-dependent, formation of axonal dystrophies, mainly located in contact with congophilic Abeta deposition, which exhibited tau and neurofilament hyperphosphorylation. This progressive pathology was paralleled with decreased expression of the motor proteins kinesin and dynein. Furthermore, we also observed an early decrease in the activity of cathepsins B and D, progressing to a deep inhibition of these lysosomal proteases at late ages. This lysosomal impairment could be responsible for the accumulation of LC3-II and ubiquitinated proteins within axonal dystrophies. We have also investigated the repercussion of these deficiencies on the APP metabolism. Our data demonstrated the existence of an increase in the amyloidogenic pathway, which was reflected by the accumulation of hAPPfl, C99 fragment, intracellular Abeta in parallel with an increase in BACE and gamma-secretase activities. In vitro experiments, using APPswe transfected N2a cells, demonstrated that any imbalance on the proteolytic systems reproduced the in vivo alterations in APP metabolism. Finally, our data also demonstrated that Abeta peptides were preferentially accumulated in isolated synaptosomes. Conclusion A progressive age-dependent cytoskeletal pathology along with a reduction of lysosomal and, in minor extent, proteasomal activity could be directly implicated in the progressive accumulation of APP derived fragments (and Abeta peptides) in parallel with the increase of BACE-1 and gamma-secretase activities. This retard in the APP metabolism seemed to be directly implicated in the synaptic Abeta accumulation and, in consequence, in the pathology progression between synaptically connected regions. PMID:23173743

Uses of available record systems in epidemiologic studies of reproductive toxicology

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

Polednak, A.P.; Janerich, D.T.

The uses of available record systems in epidemiologic studies of reproductive toxicology are described with reference to New York State. The available record systems (and relevant reproductive end points) described include: a newborn screening program for metabolic diseases and hemoglobinopathies (relevant to point mutations); chromosome registries and prenatal cytogenetics (for chromosome anomalies); live birth certificates (for birth defects, birthweight, sex ratio, etc); fetal death certificates (for spontaneous fetal deaths); and a statewide cancer registry (for childhood cancers and transplacental carcinogenesis). The uses and limitations of these record systems are discussed, along with examples of their use in descriptive and analyticmore » epidemiologic studies. Descriptive studies outlined include investigations of temporal and geographic trends in birth defects, birth weight, and fetal deaths, with reference to environmental questions (eg, Love Canal, nuclear power plants). Analytic studies described concern parental occupation in relation to specific birth defects (neural tube defects and Down syndrome) and maternal use of contraceptive drugs.« less

Atomically resolved structural determination of graphene and its point defects via extrapolation assisted phase retrieval

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

Latychevskaia, Tatiana; Fink, Hans-Werner

Previously reported crystalline structures obtained by an iterative phase retrieval reconstruction of their diffraction patterns seem to be free from displaying any irregularities or defects in the lattice, which appears to be unrealistic. We demonstrate here that the structure of a nanocrystal including its atomic defects can unambiguously be recovered from its diffraction pattern alone by applying a direct phase retrieval procedure not relying on prior information of the object shape. Individual point defects in the atomic lattice are clearly apparent. Conventional phase retrieval routines assume isotropic scattering. We show that when dealing with electrons, the quantitatively correct transmission functionmore » of the sample cannot be retrieved due to anisotropic, strong forward scattering specific to electrons. We summarize the conditions for this phase retrieval method and show that the diffraction pattern can be extrapolated beyond the original record to even reveal formerly not visible Bragg peaks. Such extrapolated wave field pattern leads to enhanced spatial resolution in the reconstruction.« less

Quantifying point defects in Cu 2 ZnSn(S,Se) 4 thin films using resonant x-ray diffraction

DOE PAGES

Stone, Kevin H.; Christensen, Steven T.; Harvey, Steven P.; ...

2016-10-17

Cu 2ZnSn(S,Se)4 is an interesting, earth abundant photovoltaic material, but has suffered from low open circuit voltage. To better understand the film structure, we have measured resonant x-ray diffraction across the Cu and Zn K-edges for the device quality thin films of Cu 2ZnSnS4 (8.6% efficiency) and Cu 2ZnSn(S,Se)4 (3.5% efficiency). This approach allows for the confirmation of the underlying kesterite structure and quantification of the concentration of point defects and vacancies on the Cu, Zn, and Sn sublattices. Rietveld refinement of powder diffraction data collected at multiple energies is used to determine that there exists a high level ofmore » Cu Zn and Zn Cu defects on the 2c and 2d Wyckoff positions. We observe a significantly lower concentration of Zn Sn defects and Cu or Zn vacancies.« less

Research on subsurface defects of potassium dihydrogen phosphate crystals fabricated by single point diamond turning technique

NASA Astrophysics Data System (ADS)

Tie, Guipeng; Dai, Yifan; Guan, Chaoliang; Chen, Shaoshan; Song, Bing

2013-03-01

Potassium dihydrogen phosphate (KDP) crystals, which are widely used in high-power laser systems, are required to be free of defects on fabricated subsurfaces. The depth of subsurface defects (SSD) of KDP crystals is significantly influenced by the parameters used in the single point diamond turning technique. In this paper, based on the deliquescent magnetorheological finishing technique, the SSD of KDP crystals is observed and the depths under various cutting parameters are detected and discussed. The results indicate that no SSD is generated under small parameters and with the increase of cutting parameters, SSD appears and the depth rises almost linearly. Although the ascending trends of SSD depths caused by cutting depth and feed rate are much alike, the two parameters make different contributions. Taking the same material removal efficiency as a criterion, a large cutting depth generates shallower SSD depth than a large feed rate. Based on the experiment results, an optimized cutting procedure is obtained to generate defect-free surfaces.

Theoretical characterisation of point defects on a MoS2 monolayer by scanning tunnelling microscopy.

PubMed

González, C; Biel, B; Dappe, Y J

2016-03-11

Different S and Mo vacancies as well as their corresponding antisite defects in a free-standing MoS2 monolayer are analysed by means of scanning tunnelling microscopy (STM) simulations. Our theoretical methodology, based on the Keldysh nonequilibrium Green function formalism within the density functional theory (DFT) approach, is applied to simulate STM images for different voltages and tip heights. Combining the geometrical and electronic effects, all features of the different STM images can be explained, providing a valuable guide for future experiments. Our results confirm previous reports on S atom imaging, but also reveal a strong dependence on the applied bias for vacancies and antisite defects that include extra S atoms. By contrast, when additional Mo atoms cover the S vacancies, the MoS2 gap vanishes and a bias-independent bright protrusion is obtained in the STM image. Finally, we show that the inclusion of these point defects promotes the emergence of reactive dangling bonds that may act as efficient adsorption sites for external adsorbates.

Origin of the relatively low transport mobility of graphene grown through chemical vapor deposition

PubMed Central

Song, H. S.; Li, S. L.; Miyazaki, H.; Sato, S.; Hayashi, K.; Yamada, A.; Yokoyama, N.; Tsukagoshi, K.

2012-01-01

The reasons for the relatively low transport mobility of graphene grown through chemical vapor deposition (CVD-G), which include point defect, surface contamination, and line defect, were analyzed in the current study. A series of control experiments demonstrated that the determinant factor for the low transport mobility of CVD-G did not arise from point defects or surface contaminations, but stemmed from line defects induced by grain boundaries. Electron microscopies characterized the presence of grain boundaries and indicated the polycrystalline nature of the CVD-G. Field-effect transistors based on CVD-G without the grain boundary obtained a transport mobility comparative to that of Kish graphene, which directly indicated the detrimental effect of grain boundaries. The effect of grain boundary on transport mobility was qualitatively explained using a potential barrier model. Furthermore, the conduction mechanism of CVD-G was also investigated using the temperature dependence measurements. This study can help understand the intrinsic transport features of CVD-G. PMID:22468224

Evidence Accumulator or Decision Threshold – Which Cortical Mechanism are We Observing?

PubMed Central

Simen, Patrick

2012-01-01

Most psychological models of perceptual decision making are of the accumulation-to-threshold variety. The neural basis of accumulation in parietal and prefrontal cortex is therefore a topic of great interest in neuroscience. In contrast, threshold mechanisms have received less attention, and their neural basis has usually been sought in subcortical structures. Here I analyze a model of a decision threshold that can be implemented in the same cortical areas as evidence accumulators, and whose behavior bears on two open questions in decision neuroscience: (1) When ramping activity is observed in a brain region during decision making, does it reflect evidence accumulation? (2) Are changes in speed-accuracy tradeoffs and response biases more likely to be achieved by changes in thresholds, or in accumulation rates and starting points? The analysis suggests that task-modulated ramping activity, by itself, is weak evidence that a brain area mediates evidence accumulation as opposed to threshold readout; and that signs of modulated accumulation are as likely to indicate threshold adaptation as adaptation of starting points and accumulation rates. These conclusions imply that how thresholds are modeled can dramatically impact accumulator-based interpretations of this data. PMID:22737136

Clustered vacancies in ZnO: chemical aspects and consequences on physical properties

NASA Astrophysics Data System (ADS)

Pal, S.; Gogurla, N.; Das, Avishek; Singha, S. S.; Kumar, Pravin; Kanjilal, D.; Singha, A.; Chattopadhyay, S.; Jana, D.; Sarkar, A.

2018-03-01

The chemical nature of point defects, their segregation, cluster or complex formation in ZnO is an important area of investigation. The evolution of a defective state with MeV Ar ion irradiation fluence 1  ×  1014 and 1  ×  1016 ions cm-2 has been monitored here using x-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and Raman spectroscopy. The XPS study shows the presence of oxygen vacancies (V O) in Ar irradiated ZnO. Zn(LMM) Auger spectra clearly identifies a transition involving metallic zinc in the irradiated samples. An intense PL emission from interstitial Zn (I Zn)-related shallow donor bound excitons (DBX) is visible in the 10 K spectra for all samples. Although overall PL is largely reduced with irradiation disorder, DBX intensity is increased for the highest fluence irradiated sample. The Raman study indicates damage in both the zinc and oxygen sub-lattice by an energetic ion beam. Representative Raman modes from defect complexes involving V O, I Zn and I O are visible after irradiation with intermediate fluence. A further increase of fluence shows, to some extent, a homogenization of disorder. A huge reduction of resistance is also noted for this sample. Certainly, high irradiation fluence induces a qualitative modification of the conventional (and highly resistive) grain boundary (GB) structure of granular ZnO. A low resistive path, involving I Zn related shallow donors, across the GB can be presumed to explain resistance reduction. Open volumes (V Zn and V O) agglomerate more and more with increasing irradiation fluence and are finally transformed to voids. The results as a whole have been elucidated with a model which emphasizes the possible evolution of a new defect microstructure that is distinctively different from the GB-related disorder. Based on the model, qualitative explanations of commonly observed radiation hardness, colouration and ferromagnetism in disordered ZnO have been put forward. A coherent scenario on disorder accumulation in ZnO has been presented, which we believe will guide further discussion on this topic.

Deacetylase activity of histone deacetylase 3 is required for productive VDJ recombination and B-cell development

PubMed Central

Stengel, Kristy R.; Barnett, Kelly R.; Wang, Jing; Liu, Qi; Hodges, Emily; Hiebert, Scott W.; Bhaskara, Srividya

2017-01-01

Histone deacetylase 3 (HDAC3) is the catalytic component of NCoR/SMRT corepressor complexes that mediate the actions of transcription factors implicated in the regulation of B-cell development and function. We crossed Hdac3 conditional knockout mice with Mb1-Cre knockin animals to delete Hdac3 in early progenitor B cells. The spleens of Hdac3F/−Mb1-Cre+/− mice were virtually devoid of mature B cells, and B220+CD43+ B-cell progenitors accumulated within the bone marrow. Quantitative deep sequencing of the Ig heavy chain locus from B220+CD43+ populations identified a defect in VHDJH recombination with a severe reduction in productive rearrangements, which directly corresponded to the loss of pre-B cells from Hdac3Δ/− bone marrow. For Hdac3Δ/− B cells that did show productive VDJ rearrangement, there was significant skewing toward the incorporation of proximal VH gene segments and a corresponding reduction in distal VH gene segment use. Although transcriptional effects within these loci were modest, Hdac3Δ/− progenitor cells displayed global changes in chromatin structure that likely hindered effective distal V-DJ recombination. Reintroduction of wild-type Hdac3 restored normal B-cell development, whereas an Hdac3 point mutant lacking deacetylase activity failed to complement this defect. Thus, the deacetylase activity of Hdac3 is required for the generation of mature B cells. PMID:28739911

Novel ethyl methanesulfonate (EMS)-induced null alleles of the Drosophila homolog of LRRK2 reveal a crucial role in endolysosomal functions and autophagy in vivo.

PubMed

Dodson, Mark W; Leung, Lok K; Lone, Mohiddin; Lizzio, Michael A; Guo, Ming

2014-12-01

Mutations in LRRK2 cause a dominantly inherited form of Parkinson's disease (PD) and are the most common known genetic determinant of PD. Inhibitor-based therapies targeting LRRK2 have emerged as a key therapeutic strategy in PD; thus, understanding the consequences of inhibiting the normal cellular functions of this protein is vital. Despite much interest, the physiological functions of LRRK2 remain unclear. Several recent studies have linked the toxicity caused by overexpression of pathogenic mutant forms of LRRK2 to defects in the endolysosomal and autophagy pathways, raising the question of whether endogenous LRRK2 might play a role in these processes. Here, we report the characterization of multiple novel ethyl methanesulfonate (EMS)-induced nonsense alleles in the Drosophila LRRK2 homolog, lrrk. Using these alleles, we show that lrrk loss-of-function causes striking defects in the endolysosomal and autophagy pathways, including the accumulation of markedly enlarged lysosomes that are laden with undigested contents, consistent with a defect in lysosomal degradation. lrrk loss-of-function also results in the accumulation of autophagosomes, as well as the presence of enlarged early endosomes laden with mono-ubiquitylated cargo proteins, suggesting an additional defect in lysosomal substrate delivery. Interestingly, the lysosomal abnormalities in these lrrk mutants can be suppressed by a constitutively active form of the small GTPase rab9, which promotes retromer-dependent recycling from late endosomes to the Golgi. Collectively, our data provides compelling evidence of a vital role for lrrk in lysosomal function and endolysosomal membrane transport in vivo, and suggests a link between lrrk and retromer-mediated endosomal recycling. © 2014. Published by The Company of Biologists Ltd.

GPR-4 Is a Predicted G-Protein-Coupled Receptor Required for Carbon Source-Dependent Asexual Growth and Development in Neurospora crassa

PubMed Central

Li, Liande; Borkovich, Katherine A.

2006-01-01

The filamentous fungus Neurospora crassa is able to utilize a wide variety of carbon sources. Here, we examine the involvement of a predicted G-protein-coupled receptor (GPCR), GPR-4, during growth and development in the presence of different carbon sources in N. crassa. Δgpr-4 mutants have reduced mass accumulation compared to the wild type when cultured on high levels of glycerol, mannitol, or arabinose. The defect is most severe on glycerol and is cell density dependent. The genetic and physical relationship between GPR-4 and the three N. crassa Gα subunits (GNA-1, GNA-2, and GNA-3) was explored. All three Gα mutants are defective in mass accumulation when cultured on glycerol. However, the phenotypes of Δgna-1 and Δgpr-4 Δgna-1 mutants are identical, introduction of a constitutively activated gna-1 allele suppresses the defects of the Δgpr-4 mutation, and the carboxy terminus of GPR-4 interacts most strongly with GNA-1 in the yeast two-hybrid assay. Although steady-state cyclic AMP (cAMP) levels are normal in Δgpr-4 strains, exogenous cAMP partially remediates the dry mass defects of Δgpr-4 mutants on glycerol medium and Δgpr-4 strains lack the transient increase in cAMP levels observed in the wild type after addition of glucose to glycerol-grown liquid cultures. Our results support the hypothesis that GPR-4 is coupled to GNA-1 in a cAMP signaling pathway that regulates the response to carbon source in N. crassa. GPR-4-related GPCRs are present in the genomes of several filamentous ascomycete fungal pathogens, raising the possibility that a similar pathway regulates carbon sensing in these organisms. PMID:16896213

One-point functions in defect CFT and integrability

NASA Astrophysics Data System (ADS)

de Leeuw, Marius; Kristjansen, Charlotte; Zarembo, Konstantin

2015-08-01

We calculate planar tree level one-point functions of non-protected operators in the defect conformal field theory dual to the D3-D5 brane system with k units of the world volume flux. Working in the operator basis of Bethe eigenstates of the Heisenberg XXX 1/2 spin chain we express the one-point functions as overlaps of these eigenstates with a matrix product state. For k = 2 we obtain a closed expression of determinant form for any number of excitations, and in the case of half-filling we find a relation with the Néel state. In addition, we present a number of results for the limiting case k → ∞.

First-principles investigation of thermodynamic and kinetic properties in titanium-hydrogen system and B2-nickel-alminum compound: Phase stability, point defect complexes and diffusion

NASA Astrophysics Data System (ADS)

Xu, Qingchuan

The purpose of this thesis is to show the technique of predicting thermodynamic and kinetic properties from first-principles using density functional theory (DFT) calculations, cluster expansion methods and Monte Carlo simulations instead of experiments. Two material systems are selected as examples: one is an interstitial system (Ti-H system) and another is a substitutional compound (B2-NiAl alloy). For Ti-H system, this thesis investigated hydride stability, exploring the role of configurational degrees of freedom, zero-point vibrational energy and coherency strains. The tetragonal gamma-TiH phase was predicted to be unstable relative to hcp alpha-Ti and fcc based delta-TiH2. Zero point vibrational energy makes the gamma phase even less stable. The coherency strains between hydride precipitates and alpha-Ti matrix stabilize gamma-TiH relative to alpha-Ti and delta-TiH2. We also found that hydrogen prefers octahedral sites at low hydrogen concentration and tetrahedral sites at high concentration. For B2-NiAl, this thesis investigated the point defects and various diffusion mechanisms. A low barrier collective hop was discovered that could mediate Al diffusion through the anti-structural-bridge (ASB) mechanism. We also found an alternative hop sequence for the migration of a triple defect and a six-jump-cycle than that proposed previously. Going beyond the mean field approximation, we found that the inclusion of interactions among point defects is crucial to predict the concentration of defect complexes. Accounting for interactions among defects and incorporating all diffusion mechanisms proposed for B2-NiAl in Monte Carlo simulation, we calculated tracer diffusion coefficients. For the first time, the relative importance of various diffusion mechanisms is revealed. The ASB hop is the dominant mechanism for Ni in Ni-rich alloy and for Al diffusion in Al-rich alloys. Other mechanisms also play a role to various extents. We also calculated the self and interdiffusion coefficients for B2-NiAl. We found in Al-rich alloys that the thermodynamic factor of Al is much greater than that of Ni while in Ni-rich alloys they are very similar. This difference in thermodynamic factors results in a much higher self-diffusion coefficient of Al compared to that of Ni in Al-rich alloys and also causes two different interdiffusion coefficients.

Near band edge photoluminescence of ZnO nanowires: Optimization via surface engineering

NASA Astrophysics Data System (ADS)

Yan, Danhua; Zhang, Wenrui; Cen, Jiajie; Stavitski, Eli; Sadowski, Jerzy T.; Vescovo, Elio; Walter, Andrew; Attenkofer, Klaus; Stacchiola, Darío J.; Liu, Mingzhao

2017-12-01

Zinc oxide (ZnO) nanowire arrays have potential applications for various devices such as ultra-violet light emitting diodes and lasers, where photoluminescence of intense near band edge emission without defect emissions is usually desired. Here, we demonstrate, counter-intuitively, that the near band edge emission may become dominant by introducing certain surface defects to ZnO nanowires via surface engineering. Specifically, near band edge emission (NBE) is effectively enhanced after a low pressure O2 plasma treatment that sputters off surface oxygen species to produce a reduced and oxygen vacancy-rich surface. The effect is attributed to the lowered surface valence band maximum of the reduced ZnO surface that creates an accumulative band bending, which screens the photo-generated minority carriers (holes) from reaching or being trapped by the surface defects.

Near band edge photoluminescence of ZnO nanowires: Optimization via surface engineering

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

Yan, Danhua; Zhang, Wenrui; Cen, Jiajie

Zinc oxide (ZnO) nanowire arrays have potential applications for various devices including ultra-violet light emitting diodes and lasers, where photoluminescence of intense near band edge emission without defect emissions is usually desired. Here, we demonstrate, counter-intuitively, that the near band edge emission may become dominant by introducing certain surface defects to ZnO nanowires via surface engineering. Specifically, near band edge emission (NBE) is effectively enhanced after a low pressure O 2 plasma treatment that sputters off surface oxygen species to produce a reduced and oxygen vacancy-rich surface. The effect is attributed to the lowered surface valence band maximum of themore » reduced ZnO surface that creates an accumulative band bending, which screens the photo-generated minority carriers (holes) from reaching or being trapped by the surface defects.« less

Near band edge photoluminescence of ZnO nanowires: Optimization via surface engineering

DOE PAGES

Yan, Danhua; Zhang, Wenrui; Cen, Jiajie; ...

2017-12-04

Zinc oxide (ZnO) nanowire arrays have potential applications for various devices including ultra-violet light emitting diodes and lasers, where photoluminescence of intense near band edge emission without defect emissions is usually desired. Here, we demonstrate, counter-intuitively, that the near band edge emission may become dominant by introducing certain surface defects to ZnO nanowires via surface engineering. Specifically, near band edge emission (NBE) is effectively enhanced after a low pressure O 2 plasma treatment that sputters off surface oxygen species to produce a reduced and oxygen vacancy-rich surface. The effect is attributed to the lowered surface valence band maximum of themore » reduced ZnO surface that creates an accumulative band bending, which screens the photo-generated minority carriers (holes) from reaching or being trapped by the surface defects.« less

Computational model for living nematic

NASA Astrophysics Data System (ADS)

Genkin, Mikhail; Sokolov, Andrey; Lavrentovich, Oleg; Aranson, Igor

A realization of an active system has been conceived by combining swimming bacteria and a lyotropic nematic liquid crystal. Here, by coupling the well-established and validated model of nematic liquid crystals with the bacterial dynamics we developed a computational model describing intricate properties of such a living nematic. In faithful agreement with the experiment, the model reproduces the onset of periodic undulation of the nematic director and consequent proliferation of topological defects with the increase in bacterial concentration. It yields testable prediction on the accumulation and transport of bacteria in the cores of +1/2 topological defects and depletion of bacteria in the cores of -1/2 defects. Our new experiment on motile bacteria suspended in a free-standing liquid crystalline film fully confirmed this prediction. This effect can be used to capture and manipulation of small amounts of bacteria.

Computational Simulation of Damage Progression of Composite Thin Shells Subjected to Mechanical Loads

NASA Technical Reports Server (NTRS)

Gotsis, P. K.; Chamis, C. C.; Minnetyan, L.

1996-01-01

Defect-free and defected composite thin shells with ply orientation (90/0/+/-75) made of graphite/epoxy are simulated for damage progression and fracture due to internal pressure and axial loading. The thin shells have a cylindrical geometry with one end fixed and the other free. The applied load consists of an internal pressure in conjunction with an axial load at the free end, the cure temperature was 177 C (350 F) and the operational temperature was 21 C (70 F). The residual stresses due to the processing are taken into account. Shells with defect and without defects were examined by using CODSTRAN an integrated computer code that couples composite mechanics, finite element and account for all possible failure modes inherent in composites. CODSTRAN traces damage initiation, growth, accumulation, damage propagation and the final fracture of the structure. The results show that damage initiation started with matrix failure while damage/fracture progression occurred due to additional matrix failure and fiber fracture. The burst pressure of the (90/0/+/- 75) defected shell was 0.092% of that of the free defect. Finally the results of the damage progression of the (90/0/+/- 75), defective composite shell was compared with the (90/0/+/- theta, where theta = 45 and 60, layup configurations. It was shown that the examined laminate (90/0/+/- 75) has the least damage tolerant of the two compared defective shells with the (90/0/+/- theta), theta = 45 and 60 laminates.

Modeling of the interfacial separation work in relation to impurity concentration in adjoining materials

NASA Astrophysics Data System (ADS)

Alekseev, Ilia M.; Makhviladze, Tariel M.; Minushev, Airat Kh.; Sarychev, Mikhail E.

2009-10-01

On the basis of the general thermodynamic approach developed in a model describing the influence of point defects on the separation work at an interface of solid materials is developed. The kinetic equations describing the defect exchange between the interface and the material bulks are formulated. The model have been applied to the case when joined materials contain such point defects as impurity atoms (interstitial and substitutional), concretized the main characteristic parameters required for a numerical modeling as well as clarified their domains of variability. The results of the numerical modeling concerning the dependences on impurity concentrations and the temperature dependences are obtained and analyzed. Particularly, the effects of interfacial strengthening and adhesion incompatibility predicted analytically for the case of impurity atoms are verified and analyzed.

Modeling of the interfacial separation work in relation to impurity concentration in adjoining materials

NASA Astrophysics Data System (ADS)

Alekseev, Ilia M.; Makhviladze, Tariel M.; Minushev, Airat Kh.; Sarychev, Mikhail E.

2010-02-01

On the basis of the general thermodynamic approach developed in a model describing the influence of point defects on the separation work at an interface of solid materials is developed. The kinetic equations describing the defect exchange between the interface and the material bulks are formulated. The model have been applied to the case when joined materials contain such point defects as impurity atoms (interstitial and substitutional), concretized the main characteristic parameters required for a numerical modeling as well as clarified their domains of variability. The results of the numerical modeling concerning the dependences on impurity concentrations and the temperature dependences are obtained and analyzed. Particularly, the effects of interfacial strengthening and adhesion incompatibility predicted analytically for the case of impurity atoms are verified and analyzed.

The role of defects in Fe(II) – goethite electron transfer

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

Andrade de Notini, Luiza; Latta, Drew; Neumann, Anke

Despite accumulating experimental evidence for Fe(II)-Fe(III) oxide electron transfer, computational chemical calculations suggest that oxidation of sorbed Fe(II) is not energetically feasible unless defects are present. Here we used isotope specific 57Fe Mössbauer spectroscopy to investigate whether Fe(II)-goethite electron transfer is influenced by defects. Specifically, we heated the mineral to try to anneal the goethite surface and ground goethite to try to create defects. We found that heating goethite results in less oxidation of sorbed Fe(II) by goethite. When goethite was re-ground after heating, electron transfer was partially restored. X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) ofmore » heated and ground goethite confirm that heating and grinding alter the surface structure of the goethite. We propose that the heating process annealed the surface and decreased the number of sites where electron transfer could occur. Our experimental findings suggest that surface defects play an important role in Fe(II)-goethite electron transfer as suggested by computational calculations. Our finding that defects influence heterogeneous Fe(II)-goethite electron transfer has important implications for Fe(II) driven recrystallization of Fe oxides, as well as X and Y.« less

Nucleation and growth kinetics for intercalated islands during deposition on layered materials with isolated pointlike surface defects

DOE PAGES

Han, Yong; Lii-Rosales, A.; Zhou, Y.; ...

2017-10-13

Theory and stochastic lattice-gas modeling is developed for the formation of intercalated metal islands in the gallery between the top layer and the underlying layer at the surface of layered materials. Our model for this process involves deposition of atoms, some fraction of which then enter the gallery through well-separated pointlike defects in the top layer. Subsequently, these atoms diffuse within the subsurface gallery leading to nucleation and growth of intercalated islands nearby the defect point source. For the case of a single point defect, continuum diffusion equation analysis provides insight into the nucleation kinetics. However, complementary tailored lattice-gas modelingmore » produces a more comprehensive and quantitative characterization. We analyze the large spread in nucleation times and positions relative to the defect for the first nucleated island. We also consider the formation of subsequent islands and the evolution of island growth shapes. The shapes reflect in part our natural adoption of a hexagonal close-packed island structure. As a result, motivation and support for the model is provided by scanning tunneling microscopy observations of the formation of intercalated metal islands in highly-ordered pyrolytic graphite at higher temperatures.« less

Decoupling and tuning competing effects of different types of defects on flux creep in irradiated YBa 2Cu 3O 7-δ coated conductors

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

Eley, S.; Leroux, M.; Rupich, M. W.

YBa 2Cu 3O 7-δ coated conductors (CCs) have achieved high critical current densities (J c) that can be further increased through the introduction of additional defects using particle irradiation. However, these gains are accompanied by increases in the flux creep rate, a manifestation of competition between the different types of defects. In this paper, we study this competition to better understand how to design pinning landscapes that simultaneously increase J c and reduce creep. CCs grown by metal organic deposition show non-monotonic changes in the temperature-dependent creep rate, S(T). Notably, in low fields, there is a conspicuous dip to lowmore » S as the temperature (T) increases from ~20 to ~65 K. Oxygen-, proton-, and Au-irradiation substantially increase S in this temperature range. Focusing on an oxygen-irradiated CC, we investigate the contribution of different types of irradiation-induced defects to the flux creep rate. Specifically, we study S(T) as we tune the relative density of point defects to larger defects by annealing both an as-grown and an irradiated CC in O 2 at temperatures T A = 250 °C–600 °C. Finally, we observe a steady decrease in S(T > 20 K) with increasing T A, unveiling the role of pre-existing nanoparticle precipitates in creating the dip in S(T) and point defects and clusters in increasing S at intermediate temperatures.« less

Decoupling and tuning competing effects of different types of defects on flux creep in irradiated YBa 2Cu 3O 7-δ coated conductors

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

Eley, S.; Leroux, M.; Rupich, M. W.

YBa 2Cu 3O 7-δ coated conductors (CCs) have achieved high critical current densities (J c) that can be further increased through the introduction of additional defects using particle irradiation. However, these gains are accompanied by increases in the flux creep rate, a manifestation of competition between the different types of defects. Here, we study this competition to better understand how to design pinning landscapes that simultaneously increase J c and reduce creep. CCs grown by metal organic deposition show non-monotonic changes in the temperature-dependent creep rate, S(T). Notably, in low fields, there is a conspicuous dip to low S asmore » the temperature (T) increases from ~20 to ~65 K. Oxygen-, proton-, and Au-irradiation substantially increase S in this temperature range. Focusing on an oxygen-irradiated CC, we investigate the contribution of different types of irradiation-induced defects to the flux creep rate. Specifically, we study S(T) as we tune the relative density of point defects to larger defects by annealing both an as-grown and an irradiated CC in O 2 at temperatures T A = 250 °C–600 °C. We observe a steady decrease in S(T > 20 K) with increasing T A, unveiling the role of pre-existing nanoparticle precipitates in creating the dip in S(T) and point defects and clusters in increasing S at intermediate temperatures.« less

Recombination-Enhanced Effect in Green/Yellow Luminescence from BeZnCdSe Quantum Wells Grown by Molecular Beam Epitaxy

NASA Astrophysics Data System (ADS)

Akimoto, Ryoichi

2018-02-01

The recombination-enhanced defect reaction (REDR) effect in single green/yellow emission BeZnCdSe quantum wells (QWs) has been investigated using photoluminescence (PL) microscopy and time-resolved PL measurements. Even though a lattice hardening effect is expected in BeZnCdSe QWs alloyed with beryllium, PL intensity enhancement due to photoannealing as well as subsequent degradation due to generation of dark spot defects (DSDs) and dark line defects (DLDs) were observed. PL microscopy provided insights into the REDR effect during photoannealing. PL images were spatially inhomogeneous in intensity for the as-grown wafer, with the darker areas having size from submicrometer to 1 μm becoming brighter with the progress of photoannealing, revealing a built-in distribution of point defects incorporated in the structure during crystal growth. In addition, we showed that the PL lifetime increased with the progress of photoannealing; hence, the density of point defects decreased due to the REDR effect. A nonradiative decay channel insensitive to the REDR effect was also found in the area free from DSDs and DLDs, suggesting that another type of defect remained in the structure (note that this is not the defect reported in study of slow-mode degradation in long-lived laser diodes). As the degradation progresses, a nonradiative channel such as photocarrier diffusion and subsequent trapping by a patch of DLDs will emerge before radiative recombination.

Mitochondrial β-Cyanoalanine Synthase Is Essential for Root Hair Formation in Arabidopsis thaliana[W

PubMed Central

García, Irene; Castellano, José María; Vioque, Blanca; Solano, Roberto; Gotor, Cecilia; Romero, Luis C.

2010-01-01

Cyanide is stoichiometrically produced as a coproduct of the ethylene biosynthesis pathway and is detoxified by β-cyanoalanine synthase enzymes. The molecular and phenotypical analysis of T-DNA insertion mutants of the mitochondrial β-cyanoalanine synthase CYS-C1 suggests that discrete accumulation of cyanide is not toxic for the plant and does not alter mitochondrial respiration rates but does act as a strong inhibitor of root hair development. The cys-c1 null allele is defective in root hair formation and accumulates cyanide in root tissues. The root hair defect is phenocopied in wild-type plants by the exogenous addition of cyanide to the growth medium and is reversed by the addition of hydroxocobalamin or by genetic complementation with the CYS-C1 gene. Hydroxocobalamin not only recovers the root phenotype of the mutant but also the formation of reactive oxygen species at the initial step of root hair tip growth. Transcriptional profiling of the cys-c1 mutant reveals that cyanide accumulation acts as a repressive signal for several genes encoding enzymes involved in cell wall rebuilding and the formation of the root hair tip as well as genes involved in ethylene signaling and metabolism. Our results demonstrate that mitochondrial β-cyanoalanine synthase activity is essential to maintain a low level of cyanide for proper root hair development. PMID:20935247

A proposed role for selective autophagy in regulating auxin-dependent lateral root development under phosphate starvation in Arabidopsis.

PubMed

Sankaranarayanan, Subramanian; Samuel, Marcus A

2015-01-01

Plants respond to limited soil nutrient availability by inducing more lateral roots (LR) to increase the root surface area. At the cellular level, nutrient starvation triggers the process of autophagy through which bulk degradation of cellular materials is achieved to facilitate nutrient mobilization. Whether there is any link between the cellular autophagy and induction of LR had remained unknown. We recently showed that the S-Domain receptor Kinase (ARK2) and U Box/Armadillo Repeat-Containing E3 ligase (PUB9) module is required for lateral root formation under phosphate starvation in Arabidopsis thaliana.(1) We also showed that PUB9 localized to autophagic bodies following either activation by ARK2 or under phosphate starvation and ark2-1/pub9-1 plants displayed lateral root defects with inability to accumulate auxin in the root tips under phosphate starvation.(1) Supplementing exogenous auxin was sufficient to rescue the LR defects in ark2-1/pub9-1 mutant. Blocking of autophagic responses in wild-type Arabidopsis also resulted in inhibition of both lateral roots and auxin accumulation in the root tips indicating the importance of autophagy in mediating auxin accumulation under phosphate starved conditions.(1) Here, we propose a model for ARK2/AtPUB9 module in regulation of lateral root development via selective autophagy.

Inflammation and Macular Oedema after Pars Plana Vitrectomy

PubMed Central

Romano, Vito; Angi, Martina; del Grosso, Renata; Romano, Davide; Vinciguerra, Paolo; Romano, Mario R.

2013-01-01

Cystoid macular oedema (CMO) is a major cause of reduced vision following intraocular surgery. Although the aetiology of CMO is not completely clarified, intraocular inflammation is known to play a major role in its development. The macula may develop cytotoxic oedema when the primary lesion and fluid accumulation occur in the parenchymatous cells (intracellular oedema) or vasogenic oedema when the primary defect occurs in the blood-retinal barrier and leads to extracellular fluid accumulation (extracellular oedema). We report on the mechanisms of CMO formation after pars plana vitrectomy and associated surgical procedures and discuss possible therapeutic approaches. PMID:24288446

CoFFEE: Corrections For Formation Energy and Eigenvalues for charged defect simulations

NASA Astrophysics Data System (ADS)

Naik, Mit H.; Jain, Manish

2018-05-01

Charged point defects in materials are widely studied using Density Functional Theory (DFT) packages with periodic boundary conditions. The formation energy and defect level computed from these simulations need to be corrected to remove the contributions from the spurious long-range interaction between the defect and its periodic images. To this effect, the CoFFEE code implements the Freysoldt-Neugebauer-Van de Walle (FNV) correction scheme. The corrections can be applied to charged defects in a complete range of material shapes and size: bulk, slab (or two-dimensional), wires and nanoribbons. The code is written in Python and features MPI parallelization and optimizations using the Cython package for slow steps.

Nanometer-scale surface potential and resistance mapping of wide-bandgap Cu(In,Ga)Se2 thin films

NASA Astrophysics Data System (ADS)

Jiang, C.-S.; Contreras, M. A.; Mansfield, L. M.; Moutinho, H. R.; Egaas, B.; Ramanathan, K.; Al-Jassim, M. M.

2015-01-01

We report microscopic characterization studies of wide-bandgap Cu(In,Ga)Se2 photovoltaic thin films using the nano-electrical probes of scanning Kelvin probe force microscopy and scanning spreading resistance microscopy. With increasing bandgap, the potential imaging shows significant increases in both the large potential features due to extended defects or defect aggregations and the potential fluctuation due to unresolvable point defects with single or a few charges. The resistance imaging shows increases in both overall resistance and resistance nonuniformity due to defects in the subsurface region. These defects are expected to affect open-circuit voltage after the surfaces are turned to junction upon device completion.

Optical transitions in two-dimensional topological insulators with point defects

NASA Astrophysics Data System (ADS)

Sablikov, Vladimir A.; Sukhanov, Aleksei A.

2016-12-01

Nontrivial properties of electronic states in topological insulators are inherent not only to the surface and boundary states, but to bound states localized at structure defects as well. We clarify how the unusual properties of the defect-induced bound states are manifested in optical absorption spectra in two-dimensional topological insulators. The calculations are carried out for defects with short-range potential. We find that the defects give rise to the appearance of specific features in the absorption spectrum, which are an inherent property of topological insulators. They have the form of two or three absorption peaks that are due to intracenter transitions between electron-like and hole-like bound states.

Holographic Chern-Simons defects

DOE PAGES

Fujita, Mitsutoshi; Melby-Thompson, Charles M.; Meyer, René; ...

2016-06-28

Here, we study SU(N ) Yang-Mills-Chern-Simons theory in the presence of defects that shift the Chern-Simons level from a holographic point of view by embedding the system in string theory. The model is a D3-D7 system in Type IIB string theory, whose gravity dual is given by the AdS soliton background with probe D7 branes attaching to the AdS boundary along the defects. We holographically renormalize the free energy of the defect system with sources, from which we obtain the correlation functions for certain operators naturally associated to these defects. We find interesting phase transitions when the separation of themore » defects as well as the temperature are varied. We also discuss some implications for the Fractional Quantum Hall Effect and for 2-dimensional QCD.« less

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

Giapintzakis, J.; Lee, W.C.; Rice, J.P.

Single crystals of R{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7-{delta}}, (R=Y, Eu and Gd), have been irradiated with 0.4--1.0 MeV electrons in directions near the c-axis. An incident threshold electron energy for producing flux pinning defects has been found. In-situ TEM studies found no visible defects induced by electron irradiation. This means that point defects or small clusters ({le} 20 {Angstrom}) are responsible for the extra pinning. A consistent interpretation of the data suggests that the most likely pinning defect is the displacement of a Cu atom from the CuO{sub 2} planes.

Determination of defect content and defect profile in semiconductor heterostructures

NASA Astrophysics Data System (ADS)

Zubiaga, A.; Garcia, J. A.; Plazaola, F.; Zúñiga-Pérez, J.; Muñoz-Sanjosé, V.

2011-01-01

In this article we present an overview of the technique to obtain the defects depth profile and width of a deposited layer and multilayer based on positron annihilation spectroscopy. In particular we apply the method to ZnO and ZnO/ZnCdO layers deposited on sapphire substrates. After introducing some terminology we first calculate the trend that the W/S parameters of the Doppler broadening measurements must follow, both in a qualitative and quantitative way. From this point we extend the results to calculate the width and defect profiles in deposited layer samples.

Probing defects in ZnO nanostructures by Photoluminescence and Positron Annihilation Spectroscopy

NASA Astrophysics Data System (ADS)

Ghosh, Manoranjan; Raychaudhuri, A. K.; Chaudhuri, S. K.; Das, Dipankar

2008-03-01

We have investigated defect related emission in the blue green region (2.2 eV -- 2.5 eV) of ZnO nanostructures having spherical (5 nm-15 nm) as well as those with hexagonal platelet and rod like morphologies (20nm-100 nm), synthesized by solvo-thermal route. This emission show anomalous size dependence. Emission energy near 2.2 eV, shifts to higher energy (2.5 eV) for increase in size beyond 20nm when shape of the nanostructures changes. This change in photoluminescence has a close correlation with the size (and shape) induced change in the positron trapping rate which is directly proportional to the defect concentration. The trapping rates show non-monotonous dependence on size. It increases initially as the size increases (5nm-15nm) and then decreases as the size increases beyond 20nm. While increase of the trapping rate on size reduction is expected due to accumulation of more defects at the surface, the initial dependence of the trapping rate on the size (below 20nm) is anomalous. The data are explained by the presence of defects like Zn vacancy and confinement due to size reduction.

28 CFR 100.10 - Definitions.

Code of Federal Regulations, 2011 CFR

2011-07-01

... Judicial Administration DEPARTMENT OF JUSTICE (CONTINUED) COST RECOVERY REGULATIONS, COMMUNICATIONS.... Business unit means any segment of an organization for which cost data are routinely accumulated by the... accumulation system, is one of the final accumulation points. Installed or deployed means that, on a specific...

Disruption of the Arabidopsis CGI-58 homologue produces Chanarin-Dorfman-like lipodystrophy in plants

USDA-ARS?s Scientific Manuscript database

CGI-58 is the defective gene in the human neutral lipid storage disease called Chanarin-Dorfman syndrome. This disorder causes intracellular lipid droplets to accumulate in nonadipose tissues, such as skin and blood cells. Here, disruption of the homologous CGI-58 gene in Arabidopsis thaliana result...

Pollution and contamination of the domestic environment leading to detrimental, long run and possible irreversible effects upon human and animal health and longevity

NASA Technical Reports Server (NTRS)

1975-01-01

Negative impacts of industrial waste disposal into the domestic environment affect human and animal health and longevity, destruct the ecosystem, and accumulate potential harmful substances in the food chain leading to disease and genetic defects in the population.

ICK is essential for cell type-specific ciliogenesis and the regulation of ciliary transport.

PubMed

Chaya, Taro; Omori, Yoshihiro; Kuwahara, Ryusuke; Furukawa, Takahisa

2014-06-02

Cilia and flagella are formed and maintained by intraflagellar transport (IFT) and play important roles in sensing and moving across species. At the distal tip of the cilia/flagella, IFT complexes turn around to switch from anterograde to retrograde transport; however, the underlying regulatory mechanism is unclear. Here, we identified ICK localization at the tip of cilia as a regulator of ciliary transport. In ICK-deficient mice, we found ciliary defects in neuronal progenitor cells with Hedgehog signal defects. ICK-deficient cells formed cilia with mislocalized Hedgehog signaling components. Loss of ICK caused the accumulation of IFT-A, IFT-B, and BBSome components at the ciliary tips. In contrast, overexpression of ICK induced the strong accumulation of IFT-B, but not IFT-A or BBSome components at ciliary tips. In addition, ICK directly phosphorylated Kif3a, while inhibition of this Kif3a phosphorylation affected ciliary formation. Our results suggest that ICK is a Kif3a kinase and essential for proper ciliogenesis in development by regulating ciliary transport at the tip of cilia. © 2014 The Authors.

ICK is essential for cell type-specific ciliogenesis and the regulation of ciliary transport

PubMed Central

Chaya, Taro; Omori, Yoshihiro; Kuwahara, Ryusuke; Furukawa, Takahisa

2014-01-01

Cilia and flagella are formed and maintained by intraflagellar transport (IFT) and play important roles in sensing and moving across species. At the distal tip of the cilia/flagella, IFT complexes turn around to switch from anterograde to retrograde transport; however, the underlying regulatory mechanism is unclear. Here, we identified ICK localization at the tip of cilia as a regulator of ciliary transport. In ICK-deficient mice, we found ciliary defects in neuronal progenitor cells with Hedgehog signal defects. ICK-deficient cells formed cilia with mislocalized Hedgehog signaling components. Loss of ICK caused the accumulation of IFT-A, IFT-B, and BBSome components at the ciliary tips. In contrast, overexpression of ICK induced the strong accumulation of IFT-B, but not IFT-A or BBSome components at ciliary tips. In addition, ICK directly phosphorylated Kif3a, while inhibition of this Kif3a phosphorylation affected ciliary formation. Our results suggest that ICK is a Kif3a kinase and essential for proper ciliogenesis in development by regulating ciliary transport at the tip of cilia. PMID:24797473

Impaired retrograde transport of axonal autophagosomes contributes to autophagic stress in Alzheimer’s disease neurons

PubMed Central

Tammineni, Prasad; Ye, Xuan; Feng, Tuancheng; Aikal, Daniyal; Cai, Qian

2017-01-01

Neurons face unique challenges of transporting nascent autophagic vacuoles (AVs) from distal axons toward the soma, where mature lysosomes are mainly located. Autophagy defects have been linked to Alzheimer’s disease (AD). However, the mechanisms underlying altered autophagy remain unknown. Here, we demonstrate that defective retrograde transport contributes to autophagic stress in AD axons. Amphisomes predominantly accumulate at axonal terminals of mutant hAPP mice and AD patient brains. Amyloid-β (Aβ) oligomers associate with AVs in AD axons and interact with dynein motors. This interaction impairs dynein recruitment to amphisomes through competitive interruption of dynein-Snapin motor-adaptor coupling, thus immobilizing them in distal axons. Consistently, deletion of Snapin in mice causes AD-like axonal autophagic stress, whereas overexpressing Snapin in hAPP neurons reduces autophagic accumulation at presynaptic terminals by enhancing AV retrograde transport. Altogether, our study provides new mechanistic insight into AD-associated autophagic stress, thus establishing a foundation for ameliorating axonal pathology in AD. DOI: http://dx.doi.org/10.7554/eLife.21776.001 PMID:28085665

Persistent activation of Nrf2 through p62 in hepatocellular carcinoma cells

PubMed Central

Inami, Yoshihiro; Waguri, Satoshi; Sakamoto, Ayako; Kouno, Tsuguka; Nakada, Kazuto; Hino, Okio; Watanabe, Sumio; Ando, Jin; Iwadate, Manabu; Yamamoto, Masayuki; Lee, Myung-Shik; Tanaka, Keiji

2011-01-01

Suppression of autophagy is always accompanied by marked accumulation of p62, a selective autophagy substrate. Because p62 interacts with the Nrf2-binding site on Keap1, which is a Cullin 3–based ubiquitin ligase adapter protein, autophagy deficiency causes competitive inhibition of the Nrf2–Keap1 interaction, resulting in stabilization of Nrf2 followed by transcriptional activation of Nrf2 target genes. Herein, we show that liver-specific autophagy-deficient mice harbor adenomas linked to both the formation of p62- and Keap1-positive cellular aggregates and induction of Nrf2 targets. Importantly, similar aggregates were identified in more than 25% of human hepatocellular carcinomas (HCC), and induction of Nrf2 target genes was recognized in most of these tumors. Gene targeting of p62 in an HCC cell line markedly abrogates the anchorage-independent growth, whereas forced expression of p62, but not a Keap1 interaction-defective mutant, resulted in recovery of the growth defect. These results indicate the involvement of persistent activation of Nrf2 through the accumulation of p62 in hepatoma development. PMID:21482715

mTORC1 Coordinates Protein Synthesis and Immunoproteasome Formation via PRAS40 to Prevent Accumulation of Protein Stress.

PubMed

Yun, Young Sung; Kim, Kwan Hyun; Tschida, Barbara; Sachs, Zohar; Noble-Orcutt, Klara E; Moriarity, Branden S; Ai, Teng; Ding, Rui; Williams, Jessica; Chen, Liqiang; Largaespada, David; Kim, Do-Hyung

2016-02-18

Reduction of translational fidelity often occurs in cells with high rates of protein synthesis, generating defective ribosomal products. If not removed, such aberrant proteins can be a major source of cellular stress causing human diseases. Here, we demonstrate that mTORC1 promotes the formation of immunoproteasomes for efficient turnover of defective proteins and cell survival. mTORC1 sequesters precursors of immunoproteasome β subunits via PRAS40. When activated, mTORC1 phosphorylates PRAS40 to enhance protein synthesis and simultaneously to facilitate the assembly of the β subunits for forming immunoproteasomes. Consequently, the PRAS40 phosphorylations play crucial roles in clearing aberrant proteins that accumulate due to mTORC1 activation. Mutations of RAS, PTEN, and TSC1, which cause mTORC1 hyperactivation, enhance immunoproteasome formation in cells and tissues. Those mutations increase cellular dependence on immunoproteasomes for stress response and survival. These results define a mechanism by which mTORC1 couples elevated protein synthesis with immunoproteasome biogenesis to protect cells against protein stress. Copyright © 2016 Elsevier Inc. All rights reserved.

Mechanistic Studies of Superplasticity of Structural Ceramics

DTIC Science & Technology

1992-02-01

green compact, with a higher density and and most of Ine heavier transition-metal fewer defects and agglomerates, has a cations of the third row, is very...between 60% to 65% of the theoretical defects is merely one which mediates the above solid "elec- density. Samples of 2Y-TZP and other TZPs were prepared...trolyte," although any tendency toward binding between similarly, except for a smaller dopant concentration ot 0.6% point defects and dopants to form

Identification of superficial defects in reconstructed 3D objects using phase-shifting fringe projection

NASA Astrophysics Data System (ADS)

Madrigal, Carlos A.; Restrepo, Alejandro; Branch, John W.

2016-09-01

3D reconstruction of small objects is used in applications of surface analysis, forensic analysis and tissue reconstruction in medicine. In this paper, we propose a strategy for the 3D reconstruction of small objects and the identification of some superficial defects. We applied a technique of projection of structured light patterns, specifically sinusoidal fringes and an algorithm of phase unwrapping. A CMOS camera was used to capture images and a DLP digital light projector for synchronous projection of the sinusoidal pattern onto the objects. We implemented a technique based on a 2D flat pattern as calibration process, so the intrinsic and extrinsic parameters of the camera and the DLP were defined. Experimental tests were performed in samples of artificial teeth, coal particles, welding defects and surfaces tested with Vickers indentation. Areas less than 5cm were studied. The objects were reconstructed in 3D with densities of about one million points per sample. In addition, the steps of 3D description, identification of primitive, training and classification were implemented to recognize defects, such as: holes, cracks, roughness textures and bumps. We found that pattern recognition strategies are useful, when quality supervision of surfaces has enough quantities of points to evaluate the defective region, because the identification of defects in small objects is a demanding activity of the visual inspection.

Defect-detection algorithm for noncontact acoustic inspection using spectrum entropy

NASA Astrophysics Data System (ADS)

Sugimoto, Kazuko; Akamatsu, Ryo; Sugimoto, Tsuneyoshi; Utagawa, Noriyuki; Kuroda, Chitose; Katakura, Kageyoshi

2015-07-01

In recent years, the detachment of concrete from bridges or tunnels and the degradation of concrete structures have become serious social problems. The importance of inspection, repair, and updating is recognized in measures against degradation. We have so far studied the noncontact acoustic inspection method using airborne sound and the laser Doppler vibrometer. In this method, depending on the surface state (reflectance, dirt, etc.), the quantity of the light of the returning laser decreases and optical noise resulting from the leakage of light reception arises. Some influencing factors are the stability of the output of the laser Doppler vibrometer, the low reflective characteristic of the measurement surface, the diffused reflection characteristic, measurement distance, and laser irradiation angle. If defect detection depends only on the vibration energy ratio since the frequency characteristic of the optical noise resembles white noise, the detection of optical noise resulting from the leakage of light reception may indicate a defective part. Therefore, in this work, the combination of the vibrational energy ratio and spectrum entropy is used to judge whether a measured point is healthy or defective or an abnormal measurement point. An algorithm that enables more vivid detection of a defective part is proposed. When our technique was applied in an experiment with real concrete structures, the defective part could be extracted more vividly and the validity of our proposed algorithm was confirmed.

Computational modelling of ovine critical-sized tibial defects with implanted scaffolds and prediction of the safety of fixator removal.

PubMed

Doyle, Heather; Lohfeld, Stefan; Dürselen, Lutz; McHugh, Peter

2015-04-01

Computational model geometries of tibial defects with two types of implanted tissue engineering scaffolds, β-tricalcium phosphate (β-TCP) and poly-ε-caprolactone (PCL)/β-TCP, are constructed from µ-CT scan images of the real in vivo defects. Simulations of each defect under four-point bending and under simulated in vivo axial compressive loading are performed. The mechanical stability of each defect is analysed using stress distribution analysis. The results of this analysis highlights the influence of callus volume, and both scaffold volume and stiffness, on the load-bearing abilities of these defects. Clinically-used image-based methods to predict the safety of removing external fixation are evaluated for each defect. Comparison of these measures with the results of computational analyses indicates that care must be taken in the interpretation of these measures. Copyright © 2015 Elsevier Ltd. All rights reserved.

First principles study of intrinsic defects in hexagonal tungsten carbide

NASA Astrophysics Data System (ADS)

Kong, Xiang-Shan; You, Yu-Wei; Xia, J. H.; Liu, C. S.; Fang, Q. F.; Luo, G.-N.; Huang, Qun-Ying

2010-11-01

The characteristics of intrinsic defects are important for the understanding of self-diffusion processes, mechanical strength, brittleness, and plasticity of tungsten carbide, which are present in the divertor of fusion reactors. Here, we use first-principles calculations to investigate the stability of point defects and their complexes in tungsten carbide. Our results confirm that the defect formation energies of carbon are much lower than that of tungsten and reveal the carbon vacancy to be the dominant defect in tungsten carbide. The C sbnd C dimer configuration along the dense a direction is the most stable configuration of carbon interstitial defect. The results of carbon defect diffusion show that the carbon vacancy stay for a wide range of temperature because of extremely high diffusion barriers, while carbon interstitial migration is activated at lower temperatures for its considerably lower activation energy. Both of them prefer to diffusion in carbon basal plane.

Effects of Defects on the Mechanical Properties of Kinked Silicon Nanowires.

PubMed

Chen, Yun; Zhang, Cheng; Li, Liyi; Tuan, Chia-Chi; Chen, Xin; Gao, Jian; He, Yunbo; Wong, Ching-Ping

2017-12-01

Kinked silicon nanowires (KSiNWs) have many special properties that make them attractive for a number of applications. The mechanical properties of KSiNWs play important roles in the performance of sensors. In this work, the effects of defects on the mechanical properties of KSiNWs are studied using molecular dynamics simulations and indirectly validated by experiments. It is found that kinks are weak points in the nanowire (NW) because of inharmonious deformation, resulting in a smaller elastic modulus than that of straight NWs. In addition, surface defects have more significant effects on the mechanical properties of KSiNWs than internal defects. The effects of the width or the diameter of the defects are larger than those of the length of the defects. Overall, the elastic modulus of KSiNWs is not sensitive to defects; therefore, KSiNWs have a great potential as strain or stress sensors in special applications.

Novel application of stem cell-derived factors for periodontal regeneration

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

Inukai, Takeharu, E-mail: t-inukai@med.nagoya-u.ac.jp; Katagiri, Wataru, E-mail: w-kat@med.nagoya-u.ac.jp; Yoshimi, Ryoko, E-mail: lianzi@med.nagoya-u.ac.jp

Highlights: Black-Right-Pointing-Pointer Mesenchymal stem cells (MSCs) secrete a variety of cytokines. Black-Right-Pointing-Pointer Cytokines were detected in conditioned medium from cultured MSCs (MSC-CM). Black-Right-Pointing-Pointer MSC-CM enhanced activation of dog MSCs and periodontal ligament cells. Black-Right-Pointing-Pointer MSC-CM significantly promoted alveolar bone and cementum regeneration. Black-Right-Pointing-Pointer Multiple cytokines contained in MSC-CM promote periodontal regeneration. -- Abstract: The effect of conditioned medium from cultured mesenchymal stem cells (MSC-CM) on periodontal regeneration was evaluated. In vitro, MSC-CM stimulated migration and proliferation of dog MSCs (dMSCs) and dog periodontal ligament cells (dPDLCs). Cytokines such as insulin-like growth factor, vascular endothelial growth factor, transforming growth factor-{beta}1, andmore » hepatocyte growth factor were detected in MSC-CM. In vivo, one-wall critical-size, intrabony periodontal defects were surgically created in the mandible of dogs. Dogs with these defects were divided into three groups that received MSC-CM, PBS, or no implants. Absorbable atelo-collagen sponges (TERUPLUG Registered-Sign ) were used as a scaffold material. Based on radiographic and histological observation 4 weeks after transplantation, the defect sites in the MSC-CM group displayed significantly greater alveolar bone and cementum regeneration than the other groups. These findings suggest that MSC-CM enhanced periodontal regeneration due to multiple cytokines contained in MSC-CM.« less

Genetic mutations in adipose triglyceride lipase and myocardial up-regulation of peroxisome proliferated activated receptor-γ in patients with triglyceride deposit cardiomyovasculopathy

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

Hirano, Ken-ichi, E-mail: khirano@cnt-osaka.com; Department of Cardiovascular Medicine, Graduate School of Medicine, Osaka University, 2-2, Yamadaoka, Suita, Osaka 565-0871; Tanaka, Tatsuya

2014-01-10

Highlights: •Triglyceride deposit cardiomyovasculopathy (TGCV) is a rare severe heart disease. •PPARγ is up-regulated in myocardium in patients with TGCV. •Possible vicious cycle for fatty acid may be involved in pathophysiology of TGCV. -- Abstract: Adipose triglyceride lipase (ATGL, also known as PNPLA2) is an essential molecule for hydrolysis of intracellular triglyceride (TG). Genetic ATGL deficiency is a rare multi-systemic neutral lipid storage disease. Information regarding its clinical profile and pathophysiology, particularly for cardiac involvement, is still very limited. A previous middle-aged ATGL-deficient patient in our institute (Case 1) with severe heart failure required cardiac transplantation (CTx) and exhibited amore » novel phenotype, “Triglyceride deposit cardiomyovasculopathy (TGCV)”. Here, we tried to elucidate molecular mechanism underlying TGCV. The subjects were two cases with TGCV, including our second case who was a 33-year-old male patient (Case 2) with congestive heart failure requiring CTx. Case 2 was homozygous for a point mutation in the 5′ splice donor site of intron 5 in the ATGL, which results in at least two types of mRNAs due to splicing defects. The myocardium of both patients (Cases 1 and 2) showed up-regulation of peroxisome proliferated activated receptors (PPARs), key transcription factors for metabolism of long chain fatty acids (LCFAs), which was in contrast to these molecules’ lower expression in ATGL-targeted mice. We investigated the intracellular metabolism of LCFAs under human ATGL-deficient conditions using patients’ passaged skin fibroblasts as a model. ATGL-deficient cells showed higher uptake and abnormal intracellular transport of LCFA, resulting in massive TG accumulation. We used these findings from cardiac specimens and cell-biological experiments to construct a hypothetical model to clarify the pathophysiology of the human disorder. In patients with TGCV, even when hydrolysis of intracellular TG is defective, the marked up-regulation of PPARγ and related genes may lead to increased uptake of LCFAs, the substrates for TG synthesis. This potentially vicious cycle of LCFAs could explain the massive accumulation of TG and severe clinical course for this rare disease.« less

Effects of point defect concentrations of the reactive element oxides on the oxidation kinetics of pure Ni and Ni-Cr alloys

NASA Astrophysics Data System (ADS)

Yan, Ruey-Fong

The addition of some reactive element oxides, e.g. Ysb2Osb3 or ZrOsb2, has significant effects, e.g. improvement in scale adhesion and reduction in oxidation rate, on the oxidation behavior of chromia and alumina scale forming alloys at high temperatures. However, there is little agreement about how a small addition of an oxygen-active element can cause such profound effects. It was the goal of this project to study the growth kinetics of an oxide scale when different reactive-element oxides were added to pure Ni and Ni-Cr alloys and, consequently, to aid in clarifying the mechanism of reactive element effects. The oxidation kinetics were measured using a thermogravimetric analysis (TGA) method and the material characterization of oxide scale was conducted. The relationship between point defect structures and oxidation kinetics was discussed. The results in this research showed that Ysb2Osb3 and ZrOsb2 exhibited the reactive element effects on the oxidation behaviors of Ni and Ni-Cr alloys. In addition, the point defect concentrations of the reactive element oxide, Ysb2Osb3, were changed by doping of different valent oxides. The modification of point defect concentrations of the reactive element oxide dispersed phases did change the oxidation kinetics of the pure Ni and Ni-Cr alloys containing Ysb2Osb3. These results indicate that the transport properties of the reactive element oxide dispersed phases are one of the important factors in determining the growth rate of an oxide scale.

Association of Lipid Accumulation Product with Cardio-Metabolic Risk Factors in Postmenopausal Women.

PubMed

Namazi Shabestari, Alireza; Asadi, Mojgan; Jouyandeh, Zahra; Qorbani, Mostafa; Kelishadi, Roya

2016-06-01

The lipid accumulation product is a novel, safe and inexpensive index of central lipid over accumulation based on waist circumference and fasting concentration of circulating triglycerides. This study was designed to investigate the ability of lipid accumulation product to predict Cardio-metabolic risk factors in postmenopausal women. In this Cross-sectional study, 264 postmenopausal women by using convenience sampling method were selected from menopause clinic in Tehran. Cardio-metabolic risk factors were measured, and lipid accumulation product (waist-58×triglycerides [nmol/L]) was calculated. Optimal cut-off point of lipid accumulation product for predicting metabolic syndrome was estimated by ROC (Receiver-operating characteristic) curve analysis. Metabolic syndrome was diagnosed in 41.2% of subjects. Optimal cut-off point of lipid accumulation product for predicting metabolic syndrome was 47.63 (sensitivity:75%; specificity:77.9%). High lipid accumulation product increases risk of all Cardio-metabolic risk factors except overweight, high Total Cholesterol, high Low Density Lipoprotein Cholesterol and high Fasting Blood Sugar in postmenopausal women. Our findings show that lipid accumulation product is associated with metabolic syndrome and some Cardio-metabolic risk factors Also lipid accumulation product may have been a useful tool for predicting cardiovascular disease and metabolic syndrome risk in postmenopausal women.

Quasibound states in short SNS junctions with point defects

NASA Astrophysics Data System (ADS)

Bespalov, A. A.

2018-04-01

Using the Green functions technique, we study the subgap spectrum of short three-dimensional superconductor-normal metal-superconductor junctions containing one or two point impurities in the normal layer. We find that a single nonmagnetic or magnetic defect induces two quasibound Shiba-like states. If the defect is located close to the junction edge, the energies of these states oscillate as functions of the distance between the impurity and the edge. In the case of two nonmagnetic impurities, there are generally four quasibound states (two per spin projection). Their energies oscillate as functions of the distance between the impurities, and reach their asymptotic values when this distance becomes much larger than the Fermi wavelength. The contributions of the impurities to the Josephson current, local density of states, and to the normal-state conductance of the junction are analyzed.

First-principles study of point defects in thorium carbide

NASA Astrophysics Data System (ADS)

Pérez Daroca, D.; Jaroszewicz, S.; Llois, A. M.; Mosca, H. O.

2014-11-01

Thorium-based materials are currently being investigated in relation with their potential utilization in Generation-IV reactors as nuclear fuels. One of the most important issues to be studied is their behavior under irradiation. A first approach to this goal is the study of point defects. By means of first-principles calculations within the framework of density functional theory, we study the stability and formation energies of vacancies, interstitials and Frenkel pairs in thorium carbide. We find that C isolated vacancies are the most likely defects, while C interstitials are energetically favored as compared to Th ones. These kind of results for ThC, to the best authors' knowledge, have not been obtained previously, neither experimentally, nor theoretically. For this reason, we compare with results on other compounds with the same NaCl-type structure.

First-Principles Study of Charge Diffusion between Proximate Solid-State Qubits and Its Implications on Sensor Applications

NASA Astrophysics Data System (ADS)

Chou, Jyh-Pin; Bodrog, Zoltán; Gali, Adam

2018-03-01

Solid-state qubits from paramagnetic point defects in solids are promising platforms to realize quantum networks and novel nanoscale sensors. Recent advances in materials engineering make it possible to create proximate qubits in solids that might interact with each other, leading to electron spin or charge fluctuation. Here we develop a method to calculate the tunneling-mediated charge diffusion between point defects from first principles and apply it to nitrogen-vacancy (NV) qubits in diamond. The calculated tunneling rates are in quantitative agreement with previous experimental data. Our results suggest that proximate neutral and negatively charged NV defect pairs can form a NV-NV molecule. A tunneling-mediated model for the source of decoherence of the near-surface NV qubits is developed based on our findings on the interacting qubits in diamond.

Global analysis of translation termination in E. coli

PubMed Central

Baggett, Natalie E.

2017-01-01

Terminating protein translation accurately and efficiently is critical for both protein fidelity and ribosome recycling for continued translation. The three bacterial release factors (RFs) play key roles: RF1 and 2 recognize stop codons and terminate translation; and RF3 promotes disassociation of bound release factors. Probing release factors mutations with reporter constructs containing programmed frameshifting sequences or premature stop codons had revealed a propensity for readthrough or frameshifting at these specific sites, but their effects on translation genome-wide have not been examined. We performed ribosome profiling on a set of isogenic strains with well-characterized release factor mutations to determine how they alter translation globally. Consistent with their known defects, strains with increasingly severe release factor defects exhibit increasingly severe accumulation of ribosomes over stop codons, indicative of an increased duration of the termination/release phase of translation. Release factor mutant strains also exhibit increased occupancy in the region following the stop codon at a significant number of genes. Our global analysis revealed that, as expected, translation termination is generally efficient and accurate, but that at a significant number of genes (≥ 50) the ribosome signature after the stop codon is suggestive of translation past the stop codon. Even native E. coli K-12 exhibits the ribosome signature suggestive of protein extension, especially at UGA codons, which rely exclusively on the reduced function RF2 variant of the K-12 strain for termination. Deletion of RF3 increases the severity of the defect. We unambiguously demonstrate readthrough and frameshifting protein extensions and their further accumulation in mutant strains for a few select cases. In addition to enhancing recoding, ribosome accumulation over stop codons disrupts attenuation control of biosynthetic operons, and may alter expression of some overlapping genes. Together, these functional alterations may either augment the protein repertoire or produce deleterious proteins. PMID:28301469

An analysis of point defects induced by In, Al, Ni, and Sn dopants in Bridgman-grown CdZnTe detectors and their influence on trapping of charge carriers

DOE PAGES

Gul, R.; Roy, U. N.; James, R. B.

2017-03-15

In this paper, we studied point defects induced in Bridgman-grown CdZnTe detectors doped with Indium (In), Aluminium (Al), Nickel (Ni), and Tin (Sn). Point defects associated with different dopants were observed, and these defects were analyzed in detail for their contributions to electron/hole (e/h) trapping. We also explored the correlations between the nature and abundance of the point defects with their influence on the resistivity, electron mobility-lifetime (μτ e) product, and electron trapping time. We used current-deep level transient spectroscopy to determine the energy, capture cross-section, and concentration of each trap. Furthermore, we used the data to determine the trappingmore » and de-trapping times for the charge carriers. In In-doped CdZnTe detectors, uncompensated Cd vacancies (V Cd -) were identified as a dominant trap. The V Cd - were almost compensated in detectors doped with Al, Ni, and Sn, in addition to co-doping with In. Dominant traps related to the dopant were found at E v + 0.36 eV and E v + 1.1 eV, E c + 76 meV and E v + 0.61 eV, E v + 36 meV and E v + 0.86 eV, E v + 0.52 eV and E c + 0.83 eV in CZT:In, CZT:In + Al, CZT:In + Ni, and CZT:In + Sn, respectively. Results indicate that the addition of other dopants with In affects the type, nature, concentration (N t), and capture cross-section (σ) and hence trapping (t t) and de-trapping (t dt) times. Finally, the dopant-induced traps, their corresponding concentrations, and charge capture cross-section play an important role in the performance of radiation detectors, especially for devices that rely solely on electron transport.« less

An analysis of point defects induced by In, Al, Ni, and Sn dopants in Bridgman-grown CdZnTe detectors and their influence on trapping of charge carriers

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

Gul, R.; Roy, U. N.; James, R. B.

In this paper, we studied point defects induced in Bridgman-grown CdZnTe detectors doped with Indium (In), Aluminium (Al), Nickel (Ni), and Tin (Sn). Point defects associated with different dopants were observed, and these defects were analyzed in detail for their contributions to electron/hole (e/h) trapping. We also explored the correlations between the nature and abundance of the point defects with their influence on the resistivity, electron mobility-lifetime (μτ e) product, and electron trapping time. We used current-deep level transient spectroscopy to determine the energy, capture cross-section, and concentration of each trap. Furthermore, we used the data to determine the trappingmore » and de-trapping times for the charge carriers. In In-doped CdZnTe detectors, uncompensated Cd vacancies (V Cd -) were identified as a dominant trap. The V Cd - were almost compensated in detectors doped with Al, Ni, and Sn, in addition to co-doping with In. Dominant traps related to the dopant were found at E v + 0.36 eV and E v + 1.1 eV, E c + 76 meV and E v + 0.61 eV, E v + 36 meV and E v + 0.86 eV, E v + 0.52 eV and E c + 0.83 eV in CZT:In, CZT:In + Al, CZT:In + Ni, and CZT:In + Sn, respectively. Results indicate that the addition of other dopants with In affects the type, nature, concentration (N t), and capture cross-section (σ) and hence trapping (t t) and de-trapping (t dt) times. Finally, the dopant-induced traps, their corresponding concentrations, and charge capture cross-section play an important role in the performance of radiation detectors, especially for devices that rely solely on electron transport.« less

Conditional ablation of the choroideremia gene causes age-related changes in mouse retinal pigment epithelium.

PubMed

Wavre-Shapton, Silène T; Tolmachova, Tanya; Lopes da Silva, Mafalda; da Silva, Mafalda Lopes; Futter, Clare E; Seabra, Miguel C

2013-01-01

The retinal pigment epithelium (RPE) is a pigmented monolayer of cells lying between the photoreceptors and a layer of fenestrated capillaries, the choriocapillaris. Choroideremia (CHM) is an X-linked progressive degeneration of these three layers caused by the loss of function of Rab Escort protein-1 (REP1). REP1 is involved in the prenylation of Rab proteins, key regulators of membrane trafficking. To study the pathological consequences of chronic disruption of membrane traffic in the RPE we used a cell type-specific knock-out mouse model of the disease, where the Chm/Rep1 gene is deleted only in pigmented cells (Chm(Flox), Tyr-Cre+). Transmission electron microscopy (TEM) was used to quantitate the melanosome distribution in the RPE and immunofluorescent staining of rhodopsin was used to quantitate phagocytosed rod outer segments in retinal sections. The ultrastructure of the RPE and Bruch's membrane at different ages was characterised by TEM to analyse age-related changes occurring as a result of defects in membrane traffic pathways. Chm/Rep1 gene knockout in RPE cells resulted in reduced numbers of melanosomes in the apical processes and delayed phagosome degradation. In addition, the RPE accumulated pathological changes at 5-6 months of age similar to those observed in 2-year old controls. These included the intracellular accumulation of lipofuscin-containing deposits, disorganised basal infoldings and the extracellular accumulation of basal laminar and basal linear deposits. The phenotype of the Chm(Flox), Tyr-Cre+ mice suggests that loss of the Chm/Rep1 gene causes premature accumulation of features of aging in the RPE. Furthermore, the striking similarities between the present observations and some of the phenotypes reported in age-related macular degeneration (AMD) suggest that membrane traffic defects may contribute to the pathogenesis of AMD.

On the ab initio calculation of vibrational formation entropy of point defect: the case of the silicon vacancy

NASA Astrophysics Data System (ADS)

Seeberger, Pia; Vidal, Julien

2017-08-01

Formation entropy of point defects is one of the last crucial elements required to fully describe the temperature dependence of point defect formation. However, while many attempts have been made to compute them for very complicated systems, very few works have been carried out such as to assess the different effects of finite size effects and precision on such quantity. Large discrepancies can be found in the literature for a system as primitive as the silicon vacancy. In this work, we have proposed a systematic study of formation entropy for silicon vacancy in its 3 stable charge states: neutral, +2 and -2 for supercells with size not below 432 atoms. Rationalization of the formation entropy is presented, highlighting importance of finite size error and the difficulty to compute such quantities due to high numerical requirement. It is proposed that the direct calculation of formation entropy of VSi using first principles methods will be plagued by very high computational workload (or large numerical errors) and finite size dependent results.

Point defect disorder in high-temperature solution grown Sr6Tb0.94Fe1.06(BO3)6 single crystals

NASA Astrophysics Data System (ADS)

Velázquez, M.; Péchev, S.; Duttine, M.; Wattiaux, A.; Labrugère, C.; Veber, Ph.; Buffière, S.; Denux, D.

2018-08-01

New Sr6Tb0.94Fe1.06(BO3)6 single crystals were obtained from lithium borate high-temperature solution growth under controlled atmosphere. Their average crystal structure was found to adopt the trigonal R-3 space group with lattice parameters a = 12.2164 Å and c = 9.1934 Å. A combined multiscale characterization approach, involving diffuse reflectance, X-ray photoelectron (XPS) and Mössbauer spectroscopies, was undertaken to establish the exact nature of the point defect disorder in this crystal structure. The FeTb× antisite disorder in the Sr6Tb0.94Fe1.06(BO3)6 single crystals is different from the kind of point defect disorder known to exist in the powder phase material counterpart. The absence of Tb4+ cations in the crystal lattice was established by XPS, and that of any phase transition down to 4 K was checked by specific heat measurements. The magnetic susceptibility curve was found to follow a Curie-Weiss behaviour in the 4-354 K temperature range.

Thermal equilibrium concentrations and effects of negatively charged Ga vacancies in n-type GaAs

NASA Astrophysics Data System (ADS)

Tan, T. Y.; You, H.-M.; Gösele, U. M.

1993-03-01

We have calculated the thermal equilibrium concentrations of the various negatively charged Ga vacancy species in GaAs. The triply-negatively-charged Ga vacancy, V {Ga/3-}, has been emphasized, since it dominates Ga self-diffusion and Ga-Al interdiffusion under intrinsic and n-doping conditions, as well as the diffusion of Si donor atoms occupying Ga sites. Under strong n-doping conditions, the thermal equilibrium V {Ga/3-}concentration, C_{V_{_{Ga} }^{3 - } }^{eq} (n), has been found to exhibit a temperature independence or a negative temperature dependence, i.e., the C_{V_{_{Ga} }^{3 - } }^{eq} (n) value is either unchanged or increases as the temperature is lowered. This is quite contrary to the normal point defect behavior for which the point defect thermal equilibrium concentration decreases as the temperature is lowered. This C_{V_{_{Ga} }^{3 - } }^{eq} (n) property provides explanations to a number of outstanding experimental results, either requiring the interpretation that V {Ga/3-}has attained its thermal equilibrium concentration at the onset of each experiment, or requiring mechanisms involving point defect non-equilibrium phenomena.

Defect identification for the As Ga family

NASA Astrophysics Data System (ADS)

Overhof, H.; Spaeth, J.-M.

2003-12-01

The AsGa family consists of at least four distinctly different point defects including the technologically important EL2 defect. While the different members are easily distinguished from their MCDA spectra, the differences of the hf and shf interactions as derived from ODEPR and ODENDOR are rather small. We present ab initio calculations using the LMTO-ASA Green's function method for a variety of defect models that might be relevant for the identification of AsGa-related defects. We confirm the identification of the isolated AsGa and show that the {AsGa-X2} defect must be identified with the nearest-neighbor antistructure pair rather than with the {AsGa-VAs} pair. For the {AsGa-X1} defect a distant antistructure pair is a likely candidate. For the EL2, the most important member of the AsGa family, we have not found a conclusive defect model. The recent ODENDOR data are similar to those of the distant orthorhombic {AsGa-VGa} pair, which, however is a triple acceptor and not a donor.

Functional Characterization of Ice Plant SKD1, an AAA-Type ATPase Associated with the Endoplasmic Reticulum-Golgi Network, and Its Role in Adaptation to Salt Stress1[W

PubMed Central

Jou, Yingtzy; Chiang, Chih-Pin; Jauh, Guang-Yuh; Yen, Hungchen Emilie

2006-01-01

A salt-induced gene mcSKD1 (suppressor of K+ transport growth defect) able to facilitate K+ uptake has previously been identified from the halophyte ice plant (Mesembryanthemum crystallinum). The sequence of mcSKD1 is homologous to vacuolar protein sorting 4, an ATPase associated with a variety of cellular activities-type ATPase that participates in the sorting of vacuolar proteins into multivesicular bodies in yeast (Saccharomyces cerevisiae). Recombinant mcSKD1 exhibited ATP hydrolytic activities in vitro with a half-maximal rate at an ATP concentration of 1.25 mm. Point mutations on active site residues abolished its ATPase activity. ADP is both a product and a strong inhibitor of the reaction. ADP-binding form of mcSDK1 greatly reduced its catalytic activity. The mcSKD1 protein accumulated ubiquitously in both vegetative and reproductive parts of plants. Highest accumulation was observed in cells actively engaging in the secretory processes, such as bladder cells of leaf epidermis. Membrane fractionation and double-labeling immunofluorescence showed the predominant localization of mcSKD1 in the endoplasmic reticulum-Golgi network. Immunoelectron microscopy identified the formation of mcSKD1 proteins into small aggregates in the cytosol and associated with membrane continuum within the endomembrane compartments. These results indicated that this ATPase participates in the endoplasmic reticulum-Golgi mediated protein sorting machinery for both housekeeping function and compartmentalization of excess Na+ under high salinity. PMID:16581876

WRNIP1 accumulates at laser light irradiated sites rapidly via its ubiquitin-binding zinc finger domain and independently from its ATPase domain

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

Nomura, Hironoshin; Yoshimura, Akari, E-mail: akari_yo@musashino-u.ac.jp; Edo, Takato

2012-01-27

Highlights: Black-Right-Pointing-Pointer WRNIP1 accumulates in laser light irradiated sites very rapidly via UBZ domain. Black-Right-Pointing-Pointer The ATPase domain of WRNIP1 is dispensable for its accumulation. Black-Right-Pointing-Pointer The accumulation of WRNIP1 seems not to be dependent on the interaction with WRN. -- Abstract: WRNIP1 (Werner helicase-interacting protein 1) was originally identified as a protein that interacts with the Werner syndrome responsible gene product. WRNIP1 contains a ubiquitin-binding zinc-finger (UBZ) domain in the N-terminal region and two leucine zipper motifs in the C-terminal region. In addition, it possesses an ATPase domain in the middle of the molecule and the lysine residues servingmore » as ubiquitin acceptors in the entire of the molecule. Here, we report that WRNIP1 accumulates in laser light irradiated sites very rapidly via its ubiquitin-binding zinc finger domain, which is known to bind polyubiquitin and to be involved in ubiquitination of WRNIP1 itself. The accumulation of WRNIP1 in laser light irradiated sites also required the C-terminal region containing two leucine zippers, which is reportedly involved in the oligomerization of WRNIP1. Mutated WRNIP1 with a deleted ATPase domain or with mutations in lysine residues, which serve as ubiquitin acceptors, accumulated in laser light irradiated sites, suggesting that the ATPase domain of WRNIP1 and ubiquitination of WRNIP1 are dispensable for the accumulation.« less

Off-stoichiometric defect clustering in irradiated oxides

NASA Astrophysics Data System (ADS)

Khalil, Sarah; Allen, Todd; EL-Azab, Anter

2017-04-01

A cluster dynamics model describing the formation of vacancy and interstitial clusters in irradiated oxides has been developed. The model, which tracks the composition of the oxide matrix and the defect clusters, was applied to the early stage formation of voids and dislocation loops in UO2, and the effects of irradiation temperature and dose rate on the evolution of their densities and composition was investigated. The results show that Frenkel defects dominate the nucleation process in irradiated UO2. The results also show that oxygen vacancies drive vacancy clustering while the migration energy of uranium vacancies is a rate-limiting factor for the nucleation and growth of voids. In a stoichiometric UO2 under irradiation, off-stoichiometric vacancy clusters exist with a higher concentration of hyper-stoichiometric clusters. Similarly, off-stoichiometric interstitial clusters form with a higher concentration of hyper-stoichiometric clusters. The UO2 matrix was found to be hyper-stoichiometric due to the accumulation of uranium vacancies.

Defect generation in amorphous-indium-gallium-zinc-oxide thin-film transistors by positive bias stress at elevated temperature

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

Um, Jae Gwang; Mativenga, Mallory; Jang, Jin, E-mail: jjang@khu.ac.kr

2014-04-07

We report on the generation and characterization of a hump in the transfer characteristics of amorphous indium gallium zinc-oxide thin-film transistors by positive bias temperature stress. The hump depends strongly on the gate bias stress at 100 °C. Due to the hump, the positive shift of the transfer characteristic in deep depletion is always smaller that in accumulation. Since, the latter shift is twice the former, with very good correlation, we conclude that the effect is due to creation of a double acceptor, likely to be a cation vacancy. Our results indicate that these defects are located near the gate insulator/activemore » layer interface, rather than in the bulk. Migration of donor defects from the interface towards the bulk may also occur under PBST at 100 °C.« less

Inversin relays Frizzled-8 signals to promote proximal pronephros development

PubMed Central

Lienkamp, Soeren; Ganner, Athina; Boehlke, Christopher; Schmidt, Thorsten; Arnold, Sebastian J.; Schäfer, Tobias; Romaker, Daniel; Schuler, Julia; Hoff, Sylvia; Powelske, Christian; Eifler, Annekathrin; Krönig, Corinna; Bullerkotte, Axel; Nitschke, Roland; Kuehn, E. Wolfgang; Kim, Emily; Burkhardt, Hans; Brox, Thomas; Ronneberger, Olaf; Gloy, Joachim; Walz, Gerd

2010-01-01

Mutations of inversin cause type II nephronophthisis, an infantile autosomal recessive disease characterized by cystic kidney disease and developmental defects. Inversin regulates Wnt signaling and is required for convergent extension movements during early embryogenesis. We now show that Inversin is essential for Xenopus pronephros formation, involving two distinct and opposing forms of cell movements. Knockdown of Inversin abrogated both proximal pronephros extension and distal tubule differentiation, phenotypes similar to that of Xenopus deficient in Frizzled-8. Exogenous Inversin rescued the pronephric defects caused by lack of Frizzled-8, indicating that Inversin acts downstream of Frizzled-8 in pronephros morphogenesis. Depletion of Inversin prevents the recruitment of Dishevelled in response to Frizzled-8 and impeded the accumulation of Dishevelled at the apical membrane of tubular epithelial cells in vivo. Thus, defective tubule morphogenesis seems to contribute to the renal pathology observed in patients with nephronophthisis type II. PMID:21059920

High throughput, parallel imaging and biomarker quantification of human spermatozoa by ImageStream flow cytometry.

PubMed

Buckman, Clayton; George, Thaddeus C; Friend, Sherree; Sutovsky, Miriam; Miranda-Vizuete, Antonio; Ozanon, Christophe; Morrissey, Phil; Sutovsky, Peter

2009-12-01

Spermatid specific thioredoxin-3 protein (SPTRX-3) accumulates in the superfluous cytoplasm of defective human spermatozoa. Novel ImageStream technology combining flow cytometry with cell imaging was used for parallel quantification and visualization of SPTRX-3 protein in defective spermatozoa of five men from infertile couples. The majority of the SPTRX-3 containing cells were overwhelmingly spermatozoa with a variety of morphological defects, detectable in the ImageStream recorded images. Quantitative parameters of relative SPTRX-3 induced fluorescence measured by ImageStream correlated closely with conventional flow cytometric measurements of the same sample set and reflected the results of clinical semen evaluation. Image Stream quantification of SPTRX-3 combines and surpasses the informative value of both conventional flow cytometry and light microscopic semen evaluation. The observed patterns of the retention of SPTRX-3 in the sperm samples from infertility patients support the view that SPTRX3 is a biomarker of male infertility.

Analysis of oxygen potential of (U 0.7Pu 0.3)O 2±x and (U 0.8Pu 0.2)O 2±x based on point defect chemistry

NASA Astrophysics Data System (ADS)

Kato, Masato; Konashi, Kenji; Nakae, Nobuo

2009-06-01

Stoichiometries in (U 0.7Pu 0.3)O 2±x and (U 0.8Pu 0.2)O 2±x were analyzed with the experimental data of oxygen potential based on point defect chemistry. The relationship between the deviation x of stoichiometric composition and the oxygen partial pressure P was evaluated using a Kröger-Vink diagram. The concentrations of the point defects in uranium and plutonium mixed oxide (MOX) were estimated from the measurement data of oxygen potentials as functions of temperature and P. The analysis results showed that x was proportional to PO2±1/2 near the stoichiometric region of both (U 0.7Pu 0.3)O 2±x and (U 0.8Pu 0.2)O 2±x, which suggested that intrinsic ionization was the dominant defect. A model to calculate oxygen potential was derived and it represented the experimental data accurately. Further, the model estimated the thermodynamic data, ΔH and ΔS, of stoichiometric (U 0.7Pu 0.3)O 2.00 and (U 0.8Pu 0.2)O 2.00 as -552.5 kJ·mol -1 and -149.7 J·mol -1, and -674.0 kJ · mol -1 and -219.4 J · mol -1, respectively.

Characterization and manipulation of individual defects in insulating hexagonal boron nitride using scanning tunnelling microscopy.

PubMed

Wong, Dillon; Velasco, Jairo; Ju, Long; Lee, Juwon; Kahn, Salman; Tsai, Hsin-Zon; Germany, Chad; Taniguchi, Takashi; Watanabe, Kenji; Zettl, Alex; Wang, Feng; Crommie, Michael F

2015-11-01

Defects play a key role in determining the properties and technological applications of nanoscale materials and, because they tend to be highly localized, characterizing them at the single-defect level is of particular importance. Scanning tunnelling microscopy has long been used to image the electronic structure of individual point defects in conductors, semiconductors and ultrathin films, but such single-defect electronic characterization remains an elusive goal for intrinsic bulk insulators. Here, we show that individual native defects in an intrinsic bulk hexagonal boron nitride insulator can be characterized and manipulated using a scanning tunnelling microscope. This would typically be impossible due to the lack of a conducting drain path for electrical current. We overcome this problem by using a graphene/boron nitride heterostructure, which exploits the atomically thin nature of graphene to allow the visualization of defect phenomena in the underlying bulk boron nitride. We observe three different defect structures that we attribute to defects within the bulk insulating boron nitride. Using scanning tunnelling spectroscopy we obtain charge and energy-level information for these boron nitride defect structures. We also show that it is possible to manipulate the defects through voltage pulses applied to the scanning tunnelling microscope tip.

Dual Role for Phospholipid:Diacylglycerol Acyltransferase: Enhancing Fatty Acid Synthesis and Diverting Fatty Acids from Membrane Lipids to Triacylglycerol in Arabidopsis Leaves[C][W

PubMed Central

Fan, Jilian; Yan, Chengshi; Zhang, Xuebin; Xu, Changcheng

2013-01-01

There is growing interest in engineering green biomass to expand the production of plant oils as feed and biofuels. Here, we show that PHOSPHOLIPID:DIACYLGLYCEROL ACYLTRANSFERASE1 (PDAT1) is a critical enzyme involved in triacylglycerol (TAG) synthesis in leaves. Overexpression of PDAT1 increases leaf TAG accumulation, leading to oil droplet overexpansion through fusion. Ectopic expression of oleosin promotes the clustering of small oil droplets. Coexpression of PDAT1 with oleosin boosts leaf TAG content by up to 6.4% of the dry weight without affecting membrane lipid composition and plant growth. PDAT1 overexpression stimulates fatty acid synthesis (FAS) and increases fatty acid flux toward the prokaryotic glycerolipid pathway. In the trigalactosyldiacylglycerol1-1 mutant, which is defective in eukaryotic thylakoid lipid synthesis, the combined overexpression of PDAT1 with oleosin increases leaf TAG content to 8.6% of the dry weight and total leaf lipid by fourfold. In the plastidic glycerol-3-phosphate acyltransferase1 mutant, which is defective in the prokaryotic glycerolipid pathway, PDAT1 overexpression enhances TAG content at the expense of thylakoid membrane lipids, leading to defects in chloroplast division and thylakoid biogenesis. Collectively, these results reveal a dual role for PDAT1 in enhancing fatty acid and TAG synthesis in leaves and suggest that increasing FAS is the key to engineering high levels of TAG accumulation in green biomass. PMID:24076979

Treatment of Inherited Eye Defects by Systemic Hematopoietic Stem Cell Transplantation.

PubMed

Rocca, Celine J; Kreymerman, Alexander; Ur, Sarah N; Frizzi, Katie E; Naphade, Swati; Lau, Athena; Tran, Tammy; Calcutt, Nigel A; Goldberg, Jeffrey L; Cherqui, Stephanie

2015-11-01

Cystinosis is caused by a deficiency in the lysosomal cystine transporter, cystinosin (CTNS gene), resulting in cystine crystal accumulation in tissues. In eyes, crystals accumulate in the cornea causing photophobia and eventually blindness. Hematopoietic stem progenitor cells (HSPCs) rescue the kidney in a mouse model of cystinosis. We investigated the potential for HSPC transplantation to treat corneal defects in cystinosis. We isolated HSPCs from transgenic DsRed mice and systemically transplanted irradiated Ctns-/- mice. A year posttransplantation, we investigated the fate and function of HSPCs by in vivo confocal and fluorescence microscopy (IVCM), quantitative RT-PCR (RT-qPCR), mass spectrometry, histology, and by measuring the IOP. To determine the mechanism by which HSPCs may rescue disease cells, we transplanted Ctns-/- mice with Ctns-/- DsRed HSPCs virally transduced to express functional CTNS-eGFP fusion protein. We found that a single systemic transplantation of wild-type HSPCs prevented ocular pathology in the Ctns-/- mice. Engraftment-derived HSPCs were detected within the cornea, and also in the sclera, ciliary body, retina, choroid, and lens. Transplantation of HSPC led to substantial decreases in corneal cystine crystals, restoration of normal corneal thickness, and lowered IOP in mice with high levels of donor-derived cell engraftment. Finally, we found that HSPC-derived progeny differentiated into macrophages, which displayed tunneling nanotubes capable of transferring cystinosin-bearing lysosomes to diseased cells. To our knowledge, this is the first demonstration that HSPCs can rescue hereditary corneal defects, and supports a new potential therapeutic strategy for treating ocular pathologies.

Microstructural characterization of ultra thin copper interconnects

NASA Astrophysics Data System (ADS)

Yang, Hee-Dong

The present study investigates the defects related to reliability issues, such as physical failures developed during processing and end use. In the first part of this study, kinetic analysis using the Johnson-Mehl-Avrami (JMA) model demonstrates that a self-annealing mechanism in electroplated Cu films depends on the film properties, such as thickness and the amount of crystal defects in an as-deposited state. In order to obtain the evidence of such defects, the microstructural characterization of defects in ultra thin copper interconnects using transmission electron microscopy (TEM) is presented. Examination of the defects using TEM reveals that voids filled with gas form as a lens shape along the {110} habit planes of the copper matrix. In the second part of this study, methodology and results of an electro-thermal-fatigue (ETF) testing, designed for early detection of process defects, are presented. Such ETF testing combines high-density current electrical stressing and thermal cycling to accelerate the evolution of defects in Cu interconnects. In ETF testing, the evolution of defects provides the nucleation sites for voids which open or close during thermal cycling. Then, the accumulation of voids creates the change in resistance when they reach a critical size. As a result of voids evolution, the high current density and high joule heating create a transient resistance increase. ETF testing reveals two failure modes, and the mode-I failure has the importance in detecting defects. The number of cycles to failure in ETF testing decreases with higher current density, but the rate of thermal cycling has no effect. Results from this investigation suggest that impurities in the copper electrodeposition process must be carefully controlled to achieve reliable ultra thin copper interconnects.

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

Yang, Yongsoo; Chen, Chien-Chun; Scott, M. C.

Perfect crystals are rare in nature. Real materials often contain crystal defects and chemical order/disorder such as grain boundaries, dislocations, interfaces, surface reconstructions and point defects. Such disruption in periodicity strongly affects material properties and functionality. Despite rapid development of quantitative material characterization methods, correlating three-dimensional (3D) atomic arrangements of chemical order/disorder and crystal defects with material properties remains a challenge. On a parallel front, quantum mechanics calculations such as density functional theory (DFT) have progressed from the modelling of ideal bulk systems to modelling ‘real’ materials with dopants, dislocations, grain boundaries and interfaces; but these calculations rely heavily onmore » average atomic models extracted from crystallography. To improve the predictive power of first-principles calculations, there is a pressing need to use atomic coordinates of real systems beyond average crystallographic measurements. Here we determine the 3D coordinates of 6,569 iron and 16,627 platinum atoms in an iron-platinum nanoparticle, and correlate chemical order/disorder and crystal defects with material properties at the single-atom level. We identify rich structural variety with unprecedented 3D detail including atomic composition, grain boundaries, anti-phase boundaries, anti-site point defects and swap defects. We show that the experimentally measured coordinates and chemical species with 22 picometre precision can be used as direct input for DFT calculations of material properties such as atomic spin and orbital magnetic moments and local magnetocrystalline anisotropy. The work presented here combines 3D atomic structure determination of crystal defects with DFT calculations, which is expected to advance our understanding of structure–property relationships at the fundamental level.« less

Deciphering chemical order/disorder and material properties at the single-atom level.

PubMed

Yang, Yongsoo; Chen, Chien-Chun; Scott, M C; Ophus, Colin; Xu, Rui; Pryor, Alan; Wu, Li; Sun, Fan; Theis, Wolfgang; Zhou, Jihan; Eisenbach, Markus; Kent, Paul R C; Sabirianov, Renat F; Zeng, Hao; Ercius, Peter; Miao, Jianwei

2017-02-01

Perfect crystals are rare in nature. Real materials often contain crystal defects and chemical order/disorder such as grain boundaries, dislocations, interfaces, surface reconstructions and point defects. Such disruption in periodicity strongly affects material properties and functionality. Despite rapid development of quantitative material characterization methods, correlating three-dimensional (3D) atomic arrangements of chemical order/disorder and crystal defects with material properties remains a challenge. On a parallel front, quantum mechanics calculations such as density functional theory (DFT) have progressed from the modelling of ideal bulk systems to modelling 'real' materials with dopants, dislocations, grain boundaries and interfaces; but these calculations rely heavily on average atomic models extracted from crystallography. To improve the predictive power of first-principles calculations, there is a pressing need to use atomic coordinates of real systems beyond average crystallographic measurements. Here we determine the 3D coordinates of 6,569 iron and 16,627 platinum atoms in an iron-platinum nanoparticle, and correlate chemical order/disorder and crystal defects with material properties at the single-atom level. We identify rich structural variety with unprecedented 3D detail including atomic composition, grain boundaries, anti-phase boundaries, anti-site point defects and swap defects. We show that the experimentally measured coordinates and chemical species with 22 picometre precision can be used as direct input for DFT calculations of material properties such as atomic spin and orbital magnetic moments and local magnetocrystalline anisotropy. This work combines 3D atomic structure determination of crystal defects with DFT calculations, which is expected to advance our understanding of structure-property relationships at the fundamental level.

Production and aging of paramagnetic point defects in P-doped floating zone silicon irradiated with high fluence 27 MeV electrons

NASA Astrophysics Data System (ADS)

Joita, A. C.; Nistor, S. V.

2018-04-01

Enhancing the long term stable performance of silicon detectors used for monitoring the position and flux of the particle beams in high energy physics experiments requires a better knowledge of the nature, stability, and transformation properties of the radiation defects created over the operation time. We report the results of an electron spin resonance investigation in the nature, transformation, and long term stability of the irradiation paramagnetic point defects (IPPDs) produced by high fluence (2 × 1016 cm-2), high energy (27 MeV) electrons in n-type, P-doped standard floating zone silicon. We found out that both freshly irradiated and aged (i.e., stored after irradiation for 3.5 years at 250 K) samples mainly contain negatively charged tetravacancy and pentavacancy defects in the first case and tetravacancy defects in the second one. The fact that such small cluster vacancy defects have not been observed by irradiation with low energy (below 5 MeV) electrons, but were abundantly produced by irradiation with neutrons, strongly suggests the presence of the same mechanism of direct formation of small vacancy clusters by irradiation with neutrons and high energy, high fluence electrons, in agreement with theoretical predictions. Differences in the nature and annealing properties of the IPPDs observed between the 27 MeV electrons freshly irradiated, and irradiated and aged samples were attributed to the presence of a high concentration of divacancies in the freshly irradiated samples, defects which transform during storage at 250 K through diffusion and recombination processes.

Ab initio study of point defects near stacking faults in 3C-SiC

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

Xi, Jianqi; Liu, Bin; Zhang, Yanwen

Interactions between point defects and stacking faults in 3C-SiC are studied using an ab initio method based on density functional theory. The results show that the discontinuity of the stacking sequence considerably affects the configurations and behavior of intrinsic defects, especially in the case of silicon interstitials. The existence of an intrinsic stacking fault (missing a C-Si bilayer) shortens the distance between the tetrahedral-center site and its second-nearest-neighboring silicon layer, making the tetrahedral silicon interstitial unstable. Instead of a tetrahedral configuration with four C neighbors, a pyramid-like interstitial structure with a defect state within the band gap becomes a stablemore » configuration. In addition, orientation rotation occurs in the split interstitials that has diverse effects on the energy landscape of silicon and carbon split interstitials in the stacking fault region. Moreover, our analyses of ionic relaxation and electronic structure of vacancies show that the built-in strain field, owing to the existence of the stacking fault, makes the local environment around vacancies more complex than that in the bulk.« less

Ab initio study of point defects near stacking faults in 3C-SiC

DOE PAGES

Xi, Jianqi; Liu, Bin; Zhang, Yanwen; ...

2016-07-02

Interactions between point defects and stacking faults in 3C-SiC are studied using an ab initio method based on density functional theory. The results show that the discontinuity of the stacking sequence considerably affects the configurations and behavior of intrinsic defects, especially in the case of silicon interstitials. The existence of an intrinsic stacking fault (missing a C-Si bilayer) shortens the distance between the tetrahedral-center site and its second-nearest-neighboring silicon layer, making the tetrahedral silicon interstitial unstable. Instead of a tetrahedral configuration with four C neighbors, a pyramid-like interstitial structure with a defect state within the band gap becomes a stablemore » configuration. In addition, orientation rotation occurs in the split interstitials that has diverse effects on the energy landscape of silicon and carbon split interstitials in the stacking fault region. Moreover, our analyses of ionic relaxation and electronic structure of vacancies show that the built-in strain field, owing to the existence of the stacking fault, makes the local environment around vacancies more complex than that in the bulk.« less

Point defect evolution in Ni, NiFe and NiCr alloys from atomistic simulations and irradiation experiments

DOE PAGES

Aidhy, Dilpuneet S.; Lu, Chenyang; Jin, Ke; ...

2015-08-08

Using molecular dynamics simulations, we elucidate irradiation-induced point defect evolution in fcc pure Ni, Ni 0.5Fe 0.5, and Ni 0.8Cr 0.2 solid solution alloys. We find that irradiation-induced interstitials form dislocation loops that are of 1/3 <111>{111}-type, consistent with our experimental results. While the loops are formed in all the three materials, the kinetics of formation is considerably slower in NiFe and NiCr than in pure Ni, indicating that defect migration barriers and extended defect formation energies could be higher in the alloys than pure Ni. As a result, while larger size clusters are formed in pure Ni, smaller andmore » more clusters are observed in the alloys. The vacancy diffusion occurs at relatively higher temperatures than interstitials, and their clustering leads to formation of stacking fault tetrahedra, also consistent with our experiments. The results also show that the surviving Frenkel pairs are composition-dependent and are largely Ni dominated.« less

A tungsten-rhenium interatomic potential for point defect studies

DOE PAGES

Setyawan, Wahyu; Gao, Ning; Kurtz, Richard J.

2018-05-28

A tungsten-rhenium (W-Re) classical interatomic potential is developed within the embedded atom method (EAM) interaction framework. A force-matching method is employed to fit the potential to ab initio forces, energies, and stresses. Simulated annealing is combined with the conjugate gradient technique to search for an optimum potential from over 1000 initial trial sets. The potential is designed for studying point defects in W-Re systems. It gives good predictions of the formation energies of Re defects in W and the binding energies of W self-interstitial clusters with Re. The potential is further evaluated for describing the formation energy of structures inmore » the σ and χ intermetallic phases. The predicted convex-hulls of formation energy are in excellent agreement with ab initio data. In pure Re, the potential can reproduce the formation energies of vacancy and self-interstitial defects sufficiently accurately, and gives the correct ground state self-interstitial configuration. Furthermore, by including liquid structures in the fit, the potential yields a Re melting temperature (3130 K) that is close to the experimental value (3459 K).« less

A tungsten-rhenium interatomic potential for point defect studies

NASA Astrophysics Data System (ADS)

Setyawan, Wahyu; Gao, Ning; Kurtz, Richard J.

2018-05-01

A tungsten-rhenium (W-Re) classical interatomic potential is developed within the embedded atom method interaction framework. A force-matching method is employed to fit the potential to ab initio forces, energies, and stresses. Simulated annealing is combined with the conjugate gradient technique to search for an optimum potential from over 1000 initial trial sets. The potential is designed for studying point defects in W-Re systems. It gives good predictions of the formation energies of Re defects in W and the binding energies of W self-interstitial clusters with Re. The potential is further evaluated for describing the formation energy of structures in the σ and χ intermetallic phases. The predicted convex-hulls of formation energy are in excellent agreement with ab initio data. In pure Re, the potential can reproduce the formation energies of vacancies and self-interstitial defects sufficiently accurately and gives the correct ground state self-interstitial configuration. Furthermore, by including liquid structures in the fit, the potential yields a Re melting temperature (3130 K) that is close to the experimental value (3459 K).

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

Han, Yong; Lii-Rosales, A.; Zhou, Y.

Theory and stochastic lattice-gas modeling is developed for the formation of intercalated metal islands in the gallery between the top layer and the underlying layer at the surface of layered materials. Our model for this process involves deposition of atoms, some fraction of which then enter the gallery through well-separated pointlike defects in the top layer. Subsequently, these atoms diffuse within the subsurface gallery leading to nucleation and growth of intercalated islands nearby the defect point source. For the case of a single point defect, continuum diffusion equation analysis provides insight into the nucleation kinetics. However, complementary tailored lattice-gas modelingmore » produces a more comprehensive and quantitative characterization. We analyze the large spread in nucleation times and positions relative to the defect for the first nucleated island. We also consider the formation of subsequent islands and the evolution of island growth shapes. The shapes reflect in part our natural adoption of a hexagonal close-packed island structure. As a result, motivation and support for the model is provided by scanning tunneling microscopy observations of the formation of intercalated metal islands in highly-ordered pyrolytic graphite at higher temperatures.« less

Positron annihilation spectroscopy of vacancy-related defects in CdTe:Cl and CdZnTe:Ge at different stoichiometry deviations

PubMed Central

Šedivý, L.; Čížek, J.; Belas, E.; Grill, R.; Melikhova, O.

2016-01-01

Positron annihilation spectroscopy (PAS) was used to examine the effect of defined Cd-rich and Te-rich annealing on point defects in Cl-doped CdTe and Ge-doped CdZnTe semi-insulating single crystals. The as-grown crystals contain open-volume defects connected with Cd vacancies . It was found that the Cd vacancies agglomerate into clusters coupled with Cl in CdTe:Cl, and in CdZnTe:Ge they are coupled with Ge donors. While annealing in Cd pressure reduces of the density, subsequent annealing in Te pressure restores . The CdTe:Cl contains negatively-charged shallow traps interpreted as Rydberg states of A-centres and representing the major positron trapping sites at low temperature. Positrons confined in the shallow traps exhibit lifetime, which is shorter than the CdTe bulk lifetime. Interpretation of the PAS data was successfully combined with electrical resistivity, Hall effect measurements and chemical analysis, and allowed us to determine the principal point defect densities. PMID:26860684

Density functional calculations on structural materials for nuclear energy applications and functional materials for photovoltaic energy applications (abstract only).

PubMed

Domain, C; Olsson, P; Becquart, C S; Legris, A; Guillemoles, J F

2008-02-13

Ab initio density functional theory calculations are carried out in order to predict the evolution of structural materials under aggressive working conditions such as cases with exposure to corrosion and irradiation, as well as to predict and investigate the properties of functional materials for photovoltaic energy applications. Structural metallic materials used in nuclear facilities are subjected to irradiation which induces the creation of large amounts of point defects. These defects interact with each other as well as with the different elements constituting the alloys, which leads to modifications of the microstructure and the mechanical properties. VASP (Vienna Ab initio Simulation Package) has been used to determine the properties of point defect clusters and also those of extended defects such as dislocations. The resulting quantities, such as interaction energies and migration energies, are used in larger scale simulation methods in order to build predictive tools. For photovoltaic energy applications, ab initio calculations are used in order to search for new semiconductors and possible element substitutions for existing ones in order to improve their efficiency.

Modeling of point defects and rare gas incorporation in uranium mono-carbide

NASA Astrophysics Data System (ADS)

Chartier, A.; Van Brutzel, L.

2007-02-01

An embedded atom method (EAM) potential has been established for uranium mono-carbide. This EAM potential was fitted on structural properties of metallic uranium and uranium mono-carbide. The formation energies of point defects, as well as activation energies for self migration, have been evaluated in order to cross-check the suitability of the potential. Assuming that the carbon vacancies are the main defects in uranium mono-carbide compounds, the migration paths and energies are consistent with experimental data selected by Catlow[C.R.A. Catlow, J. Nucl. Mater. 60 (1976) 151]. The insertion and migration energies for He, Kr and Xe have also been evaluated with available inter-atomic potentials [H.H. Andersen, P. Sigmund, Nucl. Instr. and Meth. B 38 (1965) 238]. Results show that the most stable defect configuration for rare gases is within uranium vacancies. The migration energy of an interstitial Xe is 0.5 eV, in agreement with the experimental value of 0.5 eV [Hj. Matzke, Science of advanced LMFBR fuels, Solid State Physics, Chemistry and Technology of Carbides, Nitrides and Carbonitrides of Uranium and Plutonium, North-Holland, 1986].

A tungsten-rhenium interatomic potential for point defect studies

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

Setyawan, Wahyu; Gao, Ning; Kurtz, Richard J.

A tungsten-rhenium (W-Re) classical interatomic potential is developed within the embedded atom method (EAM) interaction framework. A force-matching method is employed to fit the potential to ab initio forces, energies, and stresses. Simulated annealing is combined with the conjugate gradient technique to search for an optimum potential from over 1000 initial trial sets. The potential is designed for studying point defects in W-Re systems. It gives good predictions of the formation energies of Re defects in W and the binding energies of W self-interstitial clusters with Re. The potential is further evaluated for describing the formation energy of structures inmore » the σ and χ intermetallic phases. The predicted convex-hulls of formation energy are in excellent agreement with ab initio data. In pure Re, the potential can reproduce the formation energies of vacancy and self-interstitial defects sufficiently accurately, and gives the correct ground state self-interstitial configuration. Furthermore, by including liquid structures in the fit, the potential yields a Re melting temperature (3130 K) that is close to the experimental value (3459 K).« less

Acid-free co-operative self-assembly of graphene-ZnO nanocomposites and its defect mediated visible light photocatalytic activities

NASA Astrophysics Data System (ADS)

Parameshwari, R.; Jothivenkatachalam, K.; Banks, Craig E.; Jeganathan, K.

2017-02-01

We propose an acid-free and environmental friendly surfactant based approach to anchor zinc oxide (ZnO) nanoparticles on graphene. Herein, liquid-phase exfoliated graphene in water by ultrasonic waves has been used to prepare graphene-ZnO (G-ZnO) nanocomposites that circumvent the use of various toxic acids and chemicals which are generally used in the preparation of graphene-based nanocomposites. Oxygen vacancy related defect peaks observed by Raman and photoluminescence confirm the formation of C-O-Zn bond due to the synergistic interaction of carbon and zinc via oxygen atoms in G-ZnO nanocomposites. The enhanced photocatalytic behavior of G-ZnO under visible light as evaluated using the dye Rhodamine B holds its genesis from the intrinsic oxygen defects in G-ZnO. Furthermore, graphene acts as electron sink for accumulation of charges from defect levels of ZnO, which controls recombination of charge carriers. It is envisaged that the acid-free and facile strategy can be a potential route for the preparation of graphene-based hybrid materials using liquid-phase exfoliation methodology.

Ion irradiation induced defect evolution in Ni and Ni-based FCC equiatomic binary alloys

DOE PAGES

Jin, Ke; Zhang, Yanwen; Bei, Hongbin

2015-09-09

In order to explore the chemical effects on radiation response of alloys with multi-principal elements, defect evolution under Au ion irradiation was investigated in the elemental Ni, equiatomic NiCo and NiFe alloys. Single crystals were successfully grown in an optical floating zone furnace and their (100) surfaces were irradiated with 3 MeV Au ions at fluences ranging from 1 × 10 13 to 5 × 10 15 ions cm –2 at room temperature. The irradiation-induced defect evolution was analyzed by using ion channeling technique. Experiment shows that NiFe is more irradiation-resistant than NiCo and pure Ni at low fluences. Withmore » continuously increasing the ion fluences, damage level is eventually saturated for all materials but at different dose levels. The saturation level in pure Ni appears at relatively lower irradiation fluence than the alloys, suggesting that damage accumulation slows down in the alloys. Here, under high-fluence irradiations, pure Ni has wider damage ranges than the alloys, indicating that defects in pure Ni have high mobility.« less

Irradiation-induced grain growth and defect evolution in nanocrystalline zirconia with doped grain boundaries

DOE PAGES

Dey, Sanchita; Mardinly, John; Wang, Yongqiang; ...

2016-05-27

Grain boundaries are effective sinks for radiation-induced defects, ultimately impacting the radiation tolerance of nanocrystalline materials (dense materials with nanosized grains) against net defect accumulation. However, irradiation-induced grain growth leads to grain boundary area decrease, shortening potential benefits of nanostructures. A possible approach to mitigate this is the introduction of dopants to target a decrease in grain boundary mobility or a reduction in grain boundary energy to eliminate driving forces for grain growth (using similar strategies as to control thermal growth). Here, in this study, we tested this concept in nanocrystalline zirconia doped with lanthanum. Although the dopant is observedmore » to segregate to the grain boundaries, causing grain boundary energy decrease and promoting dragging forces for thermally activated boundary movement, irradiation induced grain growth could not be avoided under heavy ion irradiation, suggesting a different growth mechanism as compared to thermal growth. Furthermore, it is apparent that reducing the grain boundary energy reduced the effectiveness of the grain boundary as sinks, and the number of defects in the doped material is higher than in undoped (La-free) YSZ.« less

Defect-induced change of temperature-dependent elastic constants in BCC iron

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

Gao, N.; Setyawan, W.; Zhang, S. H.

2017-07-01

The effects of radiation-induced defects (randomly distributed vacancies, voids, and interstitial dislocation loops) on temperature-dependent elastic constants, C11, C12, and C44 in BCC iron, are studied with molecular dynamics method. The elastic constants are found to decrease with increasing temperatures for all cases containing different defects. The presence of vacancies, voids, or interstitial loops further decreases the elastic constants. For a given number of point defects, the randomly distributed vacancies show the strongest effect compared to voids or interstitial loops. All these results are expected to provide useful information to combine with experimental results for further understanding of radiation damage.

Geometric Defects in Quantum Hall States

NASA Astrophysics Data System (ADS)

Gromov, Andrey

I will describe a geometric analogue of Laughlin quasiholes in fractional quantum Hall (FQH) states. These ``quasiholes'' are generated by an insertion of quantized fluxes of curvature - which can be modeled by branch points of a certain Riemann surface - and, consequently, are related to genons. Unlike quasiholes, the genons are not excitations, but extrinsic defects. Fusion of genons describes the response of an FQH state to a process that changes (effective) topology of the physical space. These defects are abelian for IQH states and non-abelian for FQH states. I will explain how to calculate an electric charge, geometric spin and adiabatic mutual statistics of the these defects. Leo Kadanoff Fellowship.

Effective defect diffusion lengths in Ar-ion bombarded 3C-SiC

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

Bayu Aji, L. B.; Wallace, J. B.; Shao, L.

Above room temperature, SiC exhibits pronounced processes of diffusion and interaction of radiation-generated point defects. Here, we use the recently developed pulsed ion beam method to measure effective defect diffusion lengths in 3C-SiC bombarded in the temperature range of 25–200 °C with 500 keV Ar ions. Results reveal a diffusion length of ~10 nm, which exhibits a weak temperature dependence, changing from 9 to 13 nm with increasing temperature. Lastly, these results have important implications for understanding and predicting radiation damage in SiC and for the development of radiation-resistant materials via interface-mediated defect reactions.

Effective defect diffusion lengths in Ar-ion bombarded 3C-SiC

DOE PAGES

Bayu Aji, L. B.; Wallace, J. B.; Shao, L.; ...

2016-04-14

Above room temperature, SiC exhibits pronounced processes of diffusion and interaction of radiation-generated point defects. Here, we use the recently developed pulsed ion beam method to measure effective defect diffusion lengths in 3C-SiC bombarded in the temperature range of 25–200 °C with 500 keV Ar ions. Results reveal a diffusion length of ~10 nm, which exhibits a weak temperature dependence, changing from 9 to 13 nm with increasing temperature. Lastly, these results have important implications for understanding and predicting radiation damage in SiC and for the development of radiation-resistant materials via interface-mediated defect reactions.

Classical integrable defects as quasi Bäcklund transformations

NASA Astrophysics Data System (ADS)

Doikou, Anastasia

2016-10-01

We consider the algebraic setting of classical defects in discrete and continuous integrable theories. We derive the ;equations of motion; on the defect point via the space-like and time-like description. We then exploit the structural similarity of these equations with the discrete and continuous Bäcklund transformations. And although these equations are similar they are not exactly the same to the Bäcklund transformations. We also consider specific examples of integrable models to demonstrate our construction, i.e. the Toda chain and the sine-Gordon model. The equations of the time (space) evolution of the defect (discontinuity) degrees of freedom for these models are explicitly derived.