Science.gov

Sample records for stabilizes multimer formation

  1. Multimer Formation Explains Allelic Suppression of PRDM9 Recombination Hotspots.

    PubMed

    Baker, Christopher L; Petkova, Pavlina; Walker, Michael; Flachs, Petr; Mihola, Ondrej; Trachtulec, Zdenek; Petkov, Petko M; Paigen, Kenneth

    2015-09-01

    Genetic recombination during meiosis functions to increase genetic diversity, promotes elimination of deleterious alleles, and helps assure proper segregation of chromatids. Mammalian recombination events are concentrated at specialized sites, termed hotspots, whose locations are determined by PRDM9, a zinc finger DNA-binding histone methyltransferase. Prdm9 is highly polymorphic with most alleles activating their own set of hotspots. In populations exhibiting high frequencies of heterozygosity, questions remain about the influences different alleles have in heterozygous individuals where the two variant forms of PRDM9 typically do not activate equivalent populations of hotspots. We now find that, in addition to activating its own hotspots, the presence of one Prdm9 allele can modify the activity of hotspots activated by the other allele. PRDM9 function is also dosage sensitive; Prdm9+/- heterozygous null mice have reduced numbers and less active hotspots and increased numbers of aberrant germ cells. In mice carrying two Prdm9 alleles, there is allelic competition; the stronger Prdm9 allele can partially or entirely suppress chromatin modification and recombination at hotspots of the weaker allele. In cell cultures, PRDM9 protein variants form functional heteromeric complexes which can bind hotspots sequences. When a heteromeric complex binds at a hotspot of one PRDM9 variant, the other PRDM9 variant, which would otherwise not bind, can still methylate hotspot nucleosomes. We propose that in heterozygous individuals the underlying molecular mechanism of allelic suppression results from formation of PRDM9 heteromers, where the DNA binding activity of one protein variant dominantly directs recombination initiation towards its own hotspots, effectively titrating down recombination by the other protein variant. In natural populations with many heterozygous individuals, allelic competition will influence the recombination landscape. PMID:26368021

  2. Antibody Stabilization of Peptide–MHC Multimers Reveals Functional T Cells Bearing Extremely Low-Affinity TCRs

    PubMed Central

    Tungatt, Katie; Bianchi, Valentina; Crowther, Michael D.; Powell, Wendy E.; Schauenburg, Andrea J.; Trimby, Andrew; Donia, Marco; Miles, John J.; Holland, Christopher J.; Cole, David K.; Godkin, Andrew J.; Peakman, Mark; Straten, Per Thor; Svane, Inge Marie; Dolton, Garry

    2015-01-01

    Fluorochrome-conjugated peptide–MHC (pMHC) multimers are commonly used in combination with flow cytometry for direct ex vivo visualization and characterization of Ag-specific T cells, but these reagents can fail to stain cells when TCR affinity and/or TCR cell-surface density are low. pMHC multimer staining of tumor-specific, autoimmune, or MHC class II–restricted T cells can be particularly challenging, as these T cells tend to express relatively low-affinity TCRs. In this study, we attempted to improve staining using anti-fluorochrome unconjugated primary Abs followed by secondary staining with anti-Ab fluorochrome-conjugated Abs to amplify fluorescence intensity. Unexpectedly, we found that the simple addition of an anti-fluorochrome unconjugated Ab during staining resulted in considerably improved fluorescence intensity with both pMHC tetramers and dextramers and with PE-, allophycocyanin-, or FITC-based reagents. Importantly, when combined with protein kinase inhibitor treatment, Ab stabilization allowed pMHC tetramer staining of T cells even when the cognate TCR–pMHC affinity was extremely low (KD >1 mM) and produced the best results that we have observed to date. We find that this inexpensive addition to pMHC multimer staining protocols also allows improved recovery of cells that have recently been exposed to Ag, improvements in the recovery of self-specific T cells from PBMCs or whole-blood samples, and the use of less reagent during staining. In summary, Ab stabilization of pMHC multimers during T cell staining extends the range of TCR affinities that can be detected, yields considerably enhanced staining intensities, and is compatible with using reduced amounts of these expensive reagents. PMID:25452566

  3. Seed-Specific Expression of Spider Silk Protein Multimers Causes Long-Term Stability.

    PubMed

    Weichert, Nicola; Hauptmann, Valeska; Helmold, Christine; Conrad, Udo

    2016-01-01

    Seeds enable plants to germinate and to grow in situations of limited availability of nutrients. The stable storage of different seed proteins is a remarkable presumption for successful germination and growth. These strategies have been adapted and used in several molecular farming projects. In this study, we explore the benefits of seed-based expression to produce the high molecular weight spider silk protein FLAG using intein-based trans-splicing. Multimers larger than 460 kDa in size are routinely produced, which is above the native size of the FLAG protein. The storage of seeds for 8 weeks and 1 year at an ambient temperature of 15°C does not influence the accumulation level. Even the extended storage time does not influence the typical pattern of multimerized bands. These results show that seeds are the method of choice for stable accumulation of products of complex transgenes and have the capability for long-term storage at moderate conditions, an important feature for the development of suitable downstream processes. PMID:26858734

  4. Seed-Specific Expression of Spider Silk Protein Multimers Causes Long-Term Stability

    PubMed Central

    Weichert, Nicola; Hauptmann, Valeska; Helmold, Christine; Conrad, Udo

    2016-01-01

    Seeds enable plants to germinate and to grow in situations of limited availability of nutrients. The stable storage of different seed proteins is a remarkable presumption for successful germination and growth. These strategies have been adapted and used in several molecular farming projects. In this study, we explore the benefits of seed-based expression to produce the high molecular weight spider silk protein FLAG using intein-based trans-splicing. Multimers larger than 460 kDa in size are routinely produced, which is above the native size of the FLAG protein. The storage of seeds for 8 weeks and 1 year at an ambient temperature of 15°C does not influence the accumulation level. Even the extended storage time does not influence the typical pattern of multimerized bands. These results show that seeds are the method of choice for stable accumulation of products of complex transgenes and have the capability for long-term storage at moderate conditions, an important feature for the development of suitable downstream processes. PMID:26858734

  5. Direct observation of multimer stabilization in the mechanical unfolding pathway of a protein undergoing oligomerization.

    PubMed

    Scholl, Zackary N; Yang, Weitao; Marszalek, Piotr E

    2015-02-24

    Understanding how protein oligomerization affects the stability of monomers in self-assembled structures is crucial to the development of new protein-based nanomaterials and protein cages for drug delivery. Here, we use single-molecule force spectroscopy (AFM-SMFS), protein engineering, and computer simulations to evaluate how dimerization and tetramerization affects the stability of the monomer of Streptavidin, a model homotetrameric protein. The unfolding force directly relates to the folding stability, and we find that monomer of Streptavidin is mechanically stabilized by 40% upon dimerization, and that it is stabilized an additional 24% upon tetramerization. We also find that biotin binding increases stability by another 50% as compared to the apo-tetrameric form. We used the distribution of unfolding forces to extract properties of the underlying energy landscape and found that the distance to the transition state is decreased and the barrier height is increased upon multimerization. Finally, we investigated the origin of the strengthening by ligand binding. We found that, rather than being strengthened through intramolecular contacts, it is strengthened due to the contacts provided by the biotin-binding loop that crosses the interface between the dimers. PMID:25639698

  6. The penC mutation conferring antibiotic resistance in Neisseria gonorrhoeae arises from a mutation in the PilQ secretin that interferes with multimer stability

    PubMed Central

    Zhao, Shuqing; Tobiason, Deborah M.; Hu, Mei; Seifert, H. Steven; Nicholas, Robert A.

    2008-01-01

    The penC resistance gene was previously characterized in a FA19 penA mtrR penB gonococcal strain (PR100) as a spontaneous mutation that increased resistance to penicillin and tetracycline. We show here that antibiotic resistance mediated by penC is the result of a Glu-666 to Lys missense mutation in the pilQ gene that interferes with the formation of the SDS-resistant high-molecular-mass PilQ secretin complex, disrupts piliation, and decreases transformation frequency by 50-fold. Deletion of pilQ in PR100 confers the same level of antibiotic resistance as the penC mutation, but increased resistance was observed only in strains containing the mtrR and penB resistance determinants. Site-saturation mutagenesis of Glu-666 revealed that only acidic or amidated amino acids at this position preserved PilQ function. Consistent with early studies suggesting the importance of cysteine residues on stability of the PilQ multimer, mutation of either of the two cysteine residues in FA19 PilQ led to a similar phenotype as penC: increased antibiotic resistance, loss of piliation, intermediate levels of transformation competence, and absence of SDS-resistant PilQ oligomers. These data show that a functional secretin complex can enhance the entry of antibiotics into the cell and suggest that the PilQ oligomer forms a pore in the outer membrane through which antibiotics diffuse into the periplasm. PMID:16101998

  7. A conserved motif mediates both multimer formation and allosteric activation of phosphoglycerate mutase 5.

    PubMed

    Wilkins, Jordan M; McConnell, Cyrus; Tipton, Peter A; Hannink, Mark

    2014-09-01

    Phosphoglycerate mutase 5 (PGAM5) is an atypical mitochondrial Ser/Thr phosphatase that modulates mitochondrial dynamics and participates in both apoptotic and necrotic cell death. The mechanisms that regulate the phosphatase activity of PGAM5 are poorly understood. The C-terminal phosphoglycerate mutase domain of PGAM5 shares homology with the catalytic domains found in other members of the phosphoglycerate mutase family, including a conserved histidine that is absolutely required for catalytic activity. However, this conserved domain is not sufficient for maximal phosphatase activity. We have identified a highly conserved amino acid motif, WDXNWD, located within the unique N-terminal region, which is required for assembly of PGAM5 into large multimeric complexes. Alanine substitutions within the WDXNWD motif abolish the formation of multimeric complexes and markedly reduce phosphatase activity of PGAM5. A peptide containing the WDXNWD motif dissociates the multimeric complex and reduces but does not fully abolish phosphatase activity. Addition of the WDXNWD-containing peptide in trans to a mutant PGAM5 protein lacking the WDXNWD motif markedly increases phosphatase activity of the mutant protein. Our results are consistent with an intermolecular allosteric regulation mechanism for the phosphatase activity of PGAM5, in which the assembly of PGAM5 into multimeric complexes, mediated by the WDXNWD motif, results in maximal activation of phosphatase activity. Our results suggest the possibility of identifying small molecules that function as allosteric regulators of the phosphatase activity of PGAM5. PMID:25012655

  8. A Conserved Motif Mediates both Multimer Formation and Allosteric Activation of Phosphoglycerate Mutase 5*

    PubMed Central

    Wilkins, Jordan M.; McConnell, Cyrus; Tipton, Peter A.; Hannink, Mark

    2014-01-01

    Phosphoglycerate mutase 5 (PGAM5) is an atypical mitochondrial Ser/Thr phosphatase that modulates mitochondrial dynamics and participates in both apoptotic and necrotic cell death. The mechanisms that regulate the phosphatase activity of PGAM5 are poorly understood. The C-terminal phosphoglycerate mutase domain of PGAM5 shares homology with the catalytic domains found in other members of the phosphoglycerate mutase family, including a conserved histidine that is absolutely required for catalytic activity. However, this conserved domain is not sufficient for maximal phosphatase activity. We have identified a highly conserved amino acid motif, WDXNWD, located within the unique N-terminal region, which is required for assembly of PGAM5 into large multimeric complexes. Alanine substitutions within the WDXNWD motif abolish the formation of multimeric complexes and markedly reduce phosphatase activity of PGAM5. A peptide containing the WDXNWD motif dissociates the multimeric complex and reduces but does not fully abolish phosphatase activity. Addition of the WDXNWD-containing peptide in trans to a mutant PGAM5 protein lacking the WDXNWD motif markedly increases phosphatase activity of the mutant protein. Our results are consistent with an intermolecular allosteric regulation mechanism for the phosphatase activity of PGAM5, in which the assembly of PGAM5 into multimeric complexes, mediated by the WDXNWD motif, results in maximal activation of phosphatase activity. Our results suggest the possibility of identifying small molecules that function as allosteric regulators of the phosphatase activity of PGAM5. PMID:25012655

  9. Formation of multimers of bacterial collagens through introduction of specific sites for oxidative crosslinking.

    PubMed

    Stoichevska, Violet; An, Bo; Peng, Yong Y; Yigit, Sezin; Vashi, Aditya V; Kaplan, David L; Werkmeister, Jerome A; Dumsday, Geoff J; Ramshaw, John A M

    2016-09-01

    A range of non-animal collagens has been described, derived from bacterial species, which form stable triple-helical structures without the need for secondary modification to include hydroxyproline in the sequence. The non-animal collagens studied to date are typically smaller than animal interstitial collagens, around one quarter the length and do not pack into large fibrillar aggregates like those that are formed by the major animal interstitial collagens. A consequence of this for biomedical products is that fabricated items, such as collagen sponges, are not as mechanically and dimensionally stable as those of animal collagens. In the present study, we examined the production of larger, polymeric forms of non-animal collagens through introduction of tyrosine and cysteine residues that can form selective crosslinks through oxidation. These modifications allow the formation of larger aggregates of the non-animal collagens. When Tyr residues were incorporated, gels were obtained. And with Cys soluble aggregates were formed. These materials can be formed into sponges that are more stable than those formed without these modifications. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2369-2376, 2016. PMID:27171817

  10. Double Domain Swapping in Bovine Seminal RNase: Formation of Distinct N- and C-swapped Tetramers and Multimers with Increasing Biological Activities

    PubMed Central

    Gotte, Giovanni; Mahmoud Helmy, Alexander; Ercole, Carmine; Spadaccini, Roberta; Laurents, Douglas V.; Donadelli, Massimo; Picone, Delia

    2012-01-01

    Bovine seminal (BS) RNase, the unique natively dimeric member of the RNase super-family, represents a special case not only for its additional biological actions but also for the singular features of 3D domain swapping. The native enzyme is indeed a mixture of two isoforms: M = M, a dimer held together by two inter-subunit disulfide bonds, and MxM, 70% of the total, which, besides the two mentioned disulfides, is additionally stabilized by the swapping of its N-termini. When lyophilized from 40% acetic acid, BS-RNase oligomerizes as the super-family proto-type RNase A does. In this paper, we induced BS-RNase self-association and analyzed the multimers by size-exclusion chromatography, cross-linking, electrophoresis, mutagenesis, dynamic light scattering, molecular modelling. Finally, we evaluated their enzymatic and cytotoxic activities. Several BS-RNase domain-swapped oligomers were detected, including two tetramers, one exchanging only the N-termini, the other being either N- or C-swapped. The C-swapping event, confirmed by results on a BS-K113N mutant, has been firstly seen in BS-RNase here, and probably stabilizes also multimers larger than tetramers. Interestingly, all BS-RNase oligomers are more enzymatically active than the native dimer and, above all, they display a cytotoxic activity that definitely increases with the molecular weight of the multimers. This latter feature, to date unknown for BS-RNase, suggests again that the self-association of RNases strongly modulates their biological and potentially therapeutic properties. PMID:23071641

  11. Increased Length of Long Terminal Repeats Inhibits Ty1 Transposition and Leads to the Formation of Tandem Multimers

    PubMed Central

    Lauermann, V.; Hermankova, M.; Boeke, J. D.

    1997-01-01

    The Ty1 retrotransposon of Saccharomyces cerevisiae is bounded by long-terminal repeats (LTRs). We have constructed a variety of Ty1 elements in which the LTR length has been increased from the normal length of 334 bp to >2 kb. Although small insertions in the LTR have minimal effects on transposition frequency, larger insertions dramatically reduce it. Nevertheless, elements with long LTRs are incorporated into the genome at a low frequency. Most of these rare insertion events represent Ty1 tandem (head to tail) multimers. PMID:9093846

  12. Ribonucleoprotein multimers and their functions

    PubMed Central

    Bleichert, Franziska; Baserga, Susan J.

    2010-01-01

    Ribonucleoproteins (RNPs) play key roles in many cellular processes and often function as RNP enzymes. Similar to proteins, some of these RNPs exist and function as multimers, either momomeric or heteromeric. While in some cases the mechanistic function of multimerization is well understood, the functional consequences of multimerization of other RNPs remain enigmatic. In this review we will discuss the function and organization of small RNPs that exist as stable multimers, including RNPs catalyzing RNA chemical modifications, telomerase RNP, and RNPs involved in pre-mRNA splicing. PMID:20572804

  13. MULTIMEDIA EXPOSURE ASSESSMENT MODEL (MULTIMED)

    EPA Science Inventory

    The Multimedia Exposure Assessment Model (MULTIMED) for exposure assessment simulates the movement of contaminants leaching from a waste disposal facility. The model consists of a number of modules which predict concentrations at a receptor due to transport in the subsurface, sur...

  14. Cryopreservation of MHC Multimers: Recommendations for Quality Assurance in Detection of Antigen Specific T Cells

    PubMed Central

    Hadrup, Sine Reker; Maurer, Dominik; Laske, Karoline; Frøsig, Thomas Mørch; Andersen, Sofie Ramskov; Britten, Cedrik M; van der Burg, Sjoerd H; Walter, Steffen; Gouttefangeas, Cécile

    2015-01-01

    Fluorescence-labeled peptide-MHC class I multimers serve as ideal tools for the detection of antigen-specific T cells by flow cytometry, enabling functional and phenotypical characterization of specific T cells at the single cell level. While this technique offers a number of unique advantages, MHC multimer reagents can be difficult to handle in terms of stability and quality assurance. The stability of a given fluorescence-labeled MHC multimer complex depends on both the stability of the peptide-MHC complex itself and the stability of the fluorochrome. Consequently, stability is difficult to predict and long-term storage is generally not recommended. We investigated here the possibility of cryopreserving MHC multimers, both in-house produced and commercially available, using a wide range of peptide-MHC class I multimers comprising virus and cancer-associated epitopes of different affinities presented by various HLA-class I molecules. Cryopreservation of MHC multimers was feasible for at least 6 months, when they were dissolved in buffer containing 5–16% glycerol (v/v) and 0.5% serum albumin (w/v). The addition of cryoprotectants was tolerated across three different T-cell staining protocols for all fluorescence labels tested (PE, APC, PE-Cy7 and Quantum dots). We propose cryopreservation as an easily implementable method for stable storage of MHC multimers and recommend the use of cryopreservation in long-term immunomonitoring projects, thereby eliminating the variability introduced by different batches and inconsistent stability. © 2014 International Society for Advancement of Cytometry PMID:25297339

  15. Cyclic Imide Dioxime: Formation and Hydrolytic Stability

    SciTech Connect

    Kang, S.O.; Vukovic, Sinisa; Custelcean, Radu; Hay, Benjamin

    2012-01-01

    Poly(acrylamidoximes) play an important role in the uranium extraction from seawater. The present work reports solution studies of simple analogs to address the formation and stability of two binding sites present in these polymers, open-chain amidoximes and cyclic imide dioximes, including: 1) conditions that maximize the formation of the cyclic form, 2) existence of a base-induced conversion from open-chain to cyclic form, and 3) degradation under acid and base conditions.

  16. Mitochondrial uncoupler carbonyl cyanide M-chlorophenylhydrazone induces the multimer assembly and activity of repair enzyme protein L-isoaspartyl methyltransferase.

    PubMed

    Fanélus, Irvens; Desrosiers, Richard R

    2013-07-01

    The protein L-isoaspartyl methyltransferase (PIMT) repairs damaged aspartyl residues in proteins. It is commonly described as a cytosolic protein highly expressed in brain tissues. Here, we report that PIMT is an active monomeric as well as a multimeric protein in mitochondria isolated from neuroblastoma cells. Upon treatments with mitochondrial uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP), PIMT monomers level decreased by half while that of PIMT multimers was higher. Gel electrophoresis under reducing conditions of CCCP-induced PIMT multimers led to PIMT monomers accumulation, indicating that multimers resulted from disulfide-linked PIMT monomers. The antioxidant ascorbic acid significantly lowered CCCP-induced formation of PIMT multimers, suggesting that reactive oxygen species contributed to PIMT multimerization. In addition, the elevation of PIMT multimers catalytic activity upon treatments with CCCP was severely inhibited by the reducing agent dithiothreitol. This indicated that PIMT monomers have lower enzymatic activity following CCCP treatments and that activation of PIMT multimers is essentially dependent on the formation of disulfide-linked monomers of PIMT. Furthermore, the perturbation of mitochondrial function by CCCP promoted the accumulation of damaged aspartyl residues in proteins with high molecular weights. Thus, this study demonstrates the formation of active PIMT multimers associated with mitochondria that could play a key role in repairing damaged proteins accumulating during mitochondrial dysfunction. PMID:23319267

  17. Antarctic ice rise formation, evolution, and stability

    NASA Astrophysics Data System (ADS)

    Favier, Lionel; Pattyn, Frank

    2015-06-01

    Antarctic ice rises originate from the contact between ice shelves and one of the numerous topographic highs emerging from the edge of the continental shelf. While investigations of the Raymond effect indicate their millennial-scale stability, little is known about their formation and their role in ice shelf stability. Here we present for the first time the simulation of an ice rise using the BISICLES model. The numerical results successfully reproduce several field-observable features, such as the substantial thinning downstream of the ice rise and the successive formation of a promontory and ice rise with stable radial ice flow center, showing that ice rises are formed during the ice sheet deglaciation. We quantify the ice rise buttressing effect, found to be mostly transient, delaying grounding line retreat significantly but resulting in comparable steady state positions. We demonstrate that ice rises are key in controlling simulations of Antarctic deglaciation.

  18. Borehole Stability in High-Temperature Formations

    NASA Astrophysics Data System (ADS)

    Yan, Chuanliang; Deng, Jingen; Yu, Baohua; Li, Wenliang; Chen, Zijian; Hu, Lianbo; Li, Yang

    2014-11-01

    In oil and gas drilling or geothermal well drilling, the temperature difference between the drilling fluid and formation will lead to an apparent temperature change around the borehole, which will influence the stress state around the borehole and tend to cause borehole instability in high geothermal gradient formations. The thermal effect is usually not considered as a factor in most of the conventional borehole stability models. In this research, in order to solve the borehole instability in high-temperature formations, a calculation model of the temperature field around the borehole during drilling is established. The effects of drilling fluid circulation, drilling fluid density, and mud displacement on the temperature field are analyzed. Besides these effects, the effect of temperature change on the stress around the borehole is analyzed based on thermoelasticity theory. In addition, the relationships between temperature and strength of four types of rocks are respectively established based on experimental results, and thermal expansion coefficients are also tested. On this basis, a borehole stability model is established considering thermal effects and the effect of temperature change on borehole stability is also analyzed. The results show that the fracture pressure and collapse pressure will both increase as the temperature of borehole rises, and vice versa. The fracture pressure is more sensitive to temperature. Temperature has different effects on collapse pressures due to different lithological characters; however, the variation of fracture pressure is unrelated to lithology. The research results can provide a reference for the design of drilling fluid density in high-temperature wells.

  19. Group formation stabilizes predator-prey dynamics.

    PubMed

    Fryxell, John M; Mosser, Anna; Sinclair, Anthony R E; Packer, Craig

    2007-10-25

    Theoretical ecology is largely founded on the principle of mass action, in which uncoordinated populations of predators and prey move in a random and well-mixed fashion across a featureless landscape. The conceptual core of this body of theory is the functional response, predicting the rate of prey consumption by individual predators as a function of predator and/or prey densities. This assumption is seriously violated in many ecosystems in which predators and/or prey form social groups. Here we develop a new set of group-dependent functional responses to consider the ecological implications of sociality and apply the model to the Serengeti ecosystem. All of the prey species typically captured by Serengeti lions (Panthera leo) are gregarious, exhibiting nonlinear relationships between prey-group density and population density. The observed patterns of group formation profoundly reduce food intake rates below the levels expected under random mixing, having as strong an impact on intake rates as the seasonal migratory behaviour of the herbivores. A dynamical system model parameterized for the Serengeti ecosystem (using wildebeest (Connochaetes taurinus) as a well-studied example) shows that grouping strongly stabilizes interactions between lions and wildebeest. Our results suggest that social groups rather than individuals are the basic building blocks around which predator-prey interactions should be modelled and that group formation may provide the underlying stability of many ecosystems. PMID:17960242

  20. Update on von Willebrand factor multimers: focus on high-molecular-weight multimers and their role in hemostasis

    PubMed Central

    Stockschlaeder, Marcus; Schneppenheim, Reinhard; Budde, Ulrich

    2014-01-01

    Normal hemostasis requires von Willebrand factor (VWF) to support platelet adhesion and aggregation at sites of vascular injury. VWF is a multimeric glycoprotein built from identical subunits that contain binding sites for both platelet glycoprotein receptors and collagen. The adhesive activity of VWF depends on the size of its multimers, which range from 500 to over 10 000 kDa. There is good evidence that the high-molecular-weight multimers (HMWM), which are 5000–10 000 kDa, are the most effective in supporting interaction with collagen and platelet receptors and in facilitating wound healing under conditions of shear stress. Thus, these HMWM of VWF are of particular clinical interest. The unusually large multimers of VWF are, under normal conditions, cleaved by the plasma metalloproteinase ADAMTS13 to smaller, less adhesive multimers. A reduction or lack of HMWM, owing to a multimerization defect of VWF or to an increased susceptibility of VWF for ADAMTS13, leads to a functionally impaired VWF and the particular type 2A of von Willebrand disease. This review considers the biology and function of VWF multimers with a particular focus on the characterization of HMWM – their production, storage, release, degradation, and role in normal physiology. Evidence from basic research and the study of clinical diseases and their management highlight a pivotal role for the HMWM of VWF in hemostasis. PMID:24448155

  1. Formation, Stability, and Breakup of Nanojets

    NASA Astrophysics Data System (ADS)

    Moseler, Michael; Landman, Uzi

    2000-08-01

    Atomistic molecular dynamics simulations reveal the formation of nanojets with velocities up to 400 meters per second, created by pressurized injection of fluid propane through nanoscale convergent gold nozzles with heating or coating of the nozzle exterior surface to prevent formation of thick blocking films. The atomistic description is related to continuum hydrodynamic modeling through the derivation of a stochastic lubrication equation that includes thermally triggered fluctuations whose influence on the dynamical evolution increases as the jet dimensions become smaller. Emergence of double-cone neck shapes is predicted when the jet approaches nanoscale molecular dimensions, deviating from the long-thread universal similarity solution obtained in the absence of such fluctuations.

  2. Selecting brines and clay stabilizers to prevent formation damage

    SciTech Connect

    Evans, B.; Ali, S.

    1997-05-01

    Although many technical reports have been written about formation damage caused by brine/formation interactions, this article discusses the effects brines and chemical clay stabilizers have on pure samples of kaolinite, smectite, illite and chlorite clays. Analytical chemistry and geochemical models were not employed in this study; instead, capillary suction time tests were used to empirically compare clay migration and swelling characteristics when samples were exposed to certain brine/clay stabilizer combinations. Objective of the study was to determine which type of clay was most damaging in reservoir rocks, and whether one brine or chemical stabilizer could meet the needs of stabilizing all clay types. This information is provided with well completion operations in mind, especially when fluid cost/performance is a major concern. This article compares the unique brine/chemical stabilizer reaction characteristics of each clay type common to oil and gas reservoirs.

  3. Characterization of α-Synuclein Multimer Stoichiometry in Complex Biological Samples by Electrophoresis.

    PubMed

    Killinger, Bryan A; Moszczynska, Anna

    2016-04-01

    The aberrant aggregation of α-synuclein in the brain is a hallmark of Parkinson's disease (PD). In vivo soluble α-synuclein occurs as a monomer and several multimers, the latter of which may be important for the biological function of α-synuclein. Currently, there is a lack of reproducible methods to compare α-synuclein multimer abundance between complex biological samples. Here we developed a method, termed "multimer-PAGE," that combines in-gel chemical cross-linking with several common electrophoretic techniques to measure the stoichiometry of soluble α-synuclein multimers in brain tissue lysates. Results show that soluble α-synuclein from the rat brain exists as several high molecular weight species of approximately 56 kDa (αS56), 80 kDa (αS80), and 100 kDa (αS100) that comigrate with endogenous lipids, detergents, and/or micelles during blue native gel electrophoresis (BN-PAGE). Co-extraction of endogenous lipids with α-synuclein was essential for the detection of soluble α-synuclein multimers. Homogenization of brain tissue in small buffer volumes (>50 mg tissue per 1 mL buffer) increased relative lipid extraction and subsequently resulted in abundant soluble multimer detection via multimer-PAGE. α-Synuclein multimers captured by directly cross-linking soluble lysates resembled those observed following multimer-PAGE. The ratio of multimer (αS80) to monomer (αS17) increased linearly with protein input into multimer-PAGE, suggesting to some extent, multimers were also formed during electrophoresis. Overall, soluble α-synuclein maintains lipid interactions following tissue disruption and readily forms multimers when this lipid-protein complex is preserved. Once the multimer-PAGE technique was validated, relative stoichiometric comparisons could be conducted simultaneously between 14 biological samples. Multimer-PAGE provides a simple inexpensive biochemical technique to study the molecular factors influencing α-synuclein multimerization. PMID

  4. Unique profile of chicken adiponectin, a predominantly heavy molecular weight multimer, and relationship to visceral adiposity.

    PubMed

    Hendricks, Gilbert L; Hadley, Jill A; Krzysik-Walker, Susan M; Prabhu, K Sandeep; Vasilatos-Younken, Regina; Ramachandran, Ramesh

    2009-07-01

    Adiponectin, a 30-kDa adipokine hormone, circulates as heavy, medium, and light molecular weight isoforms in mammals. Plasma heavy molecular weight (HMW) adiponectin isoform levels are inversely correlated with the incidence of type 2 diabetes in humans. The objectives of the present study were to characterize adiponectin protein and quantify plasma adiponectin levels in chickens, which are naturally hyperglycemic relative to mammals. Using gel filtration column chromatography and Western blot analysis under nonreducing and non-heat-denaturing native conditions, adiponectin in chicken plasma, and adipose tissue is predominantly a multimeric HMW isoform that is larger than 669 kDa mass. Under reducing conditions and heating to 70-100 C, however, a majority of the multimeric adiponectin in chicken plasma and adipose tissue was reduced to oligomeric and/or monomeric forms. Immunoprecipitation and elution under neutral pH preserved the HMW adiponectin multimer, whereas brief exposure to acidic pH led to dissociation of HMW multimer into multiple oligomers. Mass spectrometric analysis of chicken adiponectin revealed the presence of hydroxyproline and differential glycosylation of hydroxylysine residues in the collagenous domain. An enzyme immunoassay was developed and validated for quantifying plasma adiponectin in chickens. Plasma adiponectin levels were found to be significantly lower in 8- compared with 4-wk-old male chickens and inversely related to abdominal fat pad mass. Collectively, our results provide novel evidence that adiponectin in chicken plasma and tissues is predominantly a HMW multimer, suggesting the presence of unique multimerization and stabilization mechanisms in the chicken that favors preponderance of HMW adiponectin over other oligomers. PMID:19299452

  5. Single domain antibody multimers confer protection against rabies infection.

    PubMed

    Boruah, Bhargavi M; Liu, Dawei; Ye, Duan; Gu, Tie-Jun; Jiang, Chun-Lai; Qu, Mingsheng; Wright, Edward; Wang, Wei; He, Wen; Liu, Changzhen; Gao, Bin

    2013-01-01

    Post-exposure prophylactic (PEP) neutralizing antibodies against Rabies are the most effective way to prevent infection-related fatality. The outer envelope glycoprotein of the Rabies virus (RABV) is the most significant surface antigen for generating virus-neutralizing antibodies. The small size and uncompromised functional specificity of single domain antibodies (sdAbs) can be exploited in the fields of experimental therapeutic applications for infectious diseases through formatting flexibilities to increase their avidity towards target antigens. In this study, we used phage display technique to select and identify sdAbs that were specific for the RABV glycoprotein from a naïve llama-derived antibody library. To increase their neutralizing potencies, the sdAbs were fused with a coiled-coil peptide derived from the human cartilage oligomeric matrix protein (COMP48) to form homogenous pentavalent multimers, known as combodies. Compared to monovalent sdAbs, the combodies, namely 26424 and 26434, exhibited high avidity and were able to neutralize 85-fold higher input of RABV (CVS-11 strain) pseudotypes in vitro, as a result of multimerization, while retaining their specificities for target antigen. 26424 and 26434 were capable of neutralizing CVS-11 pseudotypes in vitro by 90-95% as compared to human rabies immunoglobulin (HRIG), currently used for PEP in Rabies. The multimeric sdAbs were also demonstrated to be partially protective for mice that were infected with lethal doses of rabies virus in vivo. The results demonstrate that the combodies could be valuable tools in understanding viral mechanisms, diagnosis and possible anti-viral candidate for RABV infection. PMID:23977032

  6. String Stability of a Linear Formation Flight Control System

    NASA Technical Reports Server (NTRS)

    Allen, Michael J.; Ryan, Jack; Hanson, Curtis E.; Parle, James F.

    2002-01-01

    String stability analysis of an autonomous formation flight system was performed using linear and nonlinear simulations. String stability is a measure of how position errors propagate from one vehicle to another in a cascaded system. In the formation flight system considered here, each i(sup th) aircraft uses information from itself and the preceding ((i-1)(sup th)) aircraft to track a commanded relative position. A possible solution for meeting performance requirements with such a system is to allow string instability. This paper explores two results of string instability and outlines analysis techniques for string unstable systems. The three analysis techniques presented here are: linear, nonlinear formation performance, and ride quality. The linear technique was developed from a worst-case scenario and could be applied to the design of a string unstable controller. The nonlinear formation performance and ride quality analysis techniques both use nonlinear formation simulation. Three of the four formation-controller gain-sets analyzed in this paper were limited more by ride quality than by performance. Formations of up to seven aircraft in a cascaded formation could be used in the presence of light gusts with this string unstable system.

  7. Impact of alcohols on the formation and stability of protein-stabilized nanoemulsions.

    PubMed

    Zeeb, Benjamin; Herz, Eva; McClements, David Julian; Weiss, Jochen

    2014-11-01

    Nanoemulsions are increasingly being used for encapsulation, protection, and delivery of bioactive lipids, however, their formation from natural emulsifiers is still challenging. We investigated the impact of alcohol on the formation and stability of protein-stabilized oil-in-water nanoemulsions prepared by high-pressure homogenization. The influence of different alcohols (ethanol, 1-propanol, and 1-butanol) at various concentrations (0-25% w/w) on the formation and stability of emulsions stabilized by sodium caseinate, whey protein isolate, and fish gelatin was investigated. The mean particle diameter decreased with increasing alcohol concentrations from 0 to 10%w/w, but extensive droplet aggregation occurred at higher levels. This phenomenon was attributed to enhanced protein-protein interactions between the adsorbed emulsifier molecules in the presence of alcohol leading to droplet flocculation. The smallest droplets (d<100nm) were obtained when 10%w/w 1-butanol was added to sodium caseinate-stabilized nanoemulsions, but relatively small droplets (d<150nm) could also be obtained in the presence of a food-grade alcohol (ethanol). This study demonstrated that alcohol addition might be a useful tool for producing protein-stabilized nanoemulsions suitable for use as delivery systems of lipophilic bioactive agents. PMID:25129338

  8. Reprint of: Impact of alcohols on the formation and stability of protein-stabilized nanoemulsions.

    PubMed

    Zeeb, Benjamin; Herz, Eva; McClements, David Julian; Weiss, Jochen

    2015-07-01

    Nanoemulsions are increasingly being used for encapsulation, protection, and delivery of bioactive lipids, however, their formation from natural emulsifiers is still challenging. We investigated the impact of alcohol on the formation and stability of protein-stabilized oil-in-water nanoemulsions prepared by high-pressure homogenization. The influence of different alcohols (ethanol, 1-propanol, and 1-butanol) at various concentrations (0-25% w/w) on the formation and stability of emulsions stabilized by sodium caseinate, whey protein isolate, and fish gelatin was investigated. The mean particle diameter decreased with increasing alcohol concentrations from 0 to 10%w/w, but extensive droplet aggregation occurred at higher levels. This phenomenon was attributed to enhanced protein-protein interactions between the adsorbed emulsifier molecules in the presence of alcohol leading to droplet flocculation. The smallest droplets (d<100 nm) were obtained when 10%w/w 1-butanol was added to sodium caseinate-stabilized nanoemulsions, but relatively small droplets (d<150 nm) could also be obtained in the presence of a food-grade alcohol (ethanol). This study demonstrated that alcohol addition might be a useful tool for producing protein-stabilized nanoemulsions suitable for use as delivery systems of lipophilic bioactive agents. PMID:25865241

  9. New Insight into Cataract Formation: Enhanced Stability through Mutual Attraction

    SciTech Connect

    Stradner, A.; Schurtenberger, P.; Foffi, G.; Dorsaz, N.; Thurston, G.

    2007-11-09

    Small-angle neutron scattering experiments and molecular dynamics simulations combined with an application of concepts from soft matter physics to complex protein mixtures provide new insight into the stability of eye lens protein mixtures. Exploring this colloid-protein analogy we demonstrate that weak attractions between unlike proteins help to maintain lens transparency in an extremely sensitive and nonmonotonic manner. These results not only represent an important step towards a better understanding of protein condensation diseases such as cataract formation, but provide general guidelines for tuning the stability of colloid mixtures, a topic relevant for soft matter physics and industrial applications.

  10. A Versatile Simple Capture Assay for Assessing the Structural Integrity of MHC Multimer Reagents

    PubMed Central

    Malo, Courtney S.; Renner, Danielle N.; Van Keulen, Virginia S.; Girtman, Megan A.; Nevala, Wendy N.; Pavelko, Kevin D.; Gil, Diana; Schrum, Adam G.; Johnson, Aaron J.; Pease, Larry R.

    2015-01-01

    Antigen-specific T cell responses can be visualized using MHC:peptide multimers. In cases where robust T cell controls are not readily available to assess the integrity of multimer reagents prior to analyzing limited sample, the ability to assess the structural integrity of MHC multimers before their use in critical experiments would be useful. We present a method to probe the structural integrity of MHC multimers using antibodies specific for conformational determinants. Beads coated with anti-mouse Ig are incubated with conformation-specific mouse monoclonal antibody and then with fluorescently tagged MHC multimer. The ability of the bead to capture the labeled multimer can be measured semi-quantitatively by flow cytometry. In this manner, the correct folding of MHC multimers can be visualized and batches of multimer can be compared for quality control. Because there are multiple conformational epitopes formed by various molecular interactions among heavy chain, peptide, and β2M, this capture assay can assess the fidelity of each aspect of multimer structure, depending on the availability of antibodies. The described approach could be particularly useful for studies using irreplaceable samples, including patient samples collected in clinical trials. PMID:26389800

  11. Detergent Stabilized Nanopore Formation Kinetics of an Anthrax Protein

    NASA Astrophysics Data System (ADS)

    Peterson, Kelby

    2015-03-01

    This summer research project funded through the Society of Physics Students Internship Program and The National Institute of Standards and Technology focused on optimization of pore formation of Protective Antigen protein secreted by Bacillus Anthraces. This experiment analyzes the use of N-tetradecylphosphocholine (FOS-14 Detergent) to stabilize the water soluble protein, protective antigen protein (PA63) to regulate the kinetics of pore formation in a model bilayer lipid membrane. The FOS-14 Detergent was tested under various conditions to understand its impact on the protein pore formation. The optimization of this channel insertion is critical in preparing samples of oriented for neutron reflectometry that provide new data to increase the understanding of the protein's structure.

  12. Characterization of α-Synuclein Multimer Stoichiometry in Complex Biological Samples by Electrophoresis

    PubMed Central

    2016-01-01

    The aberrant aggregation of α-synuclein in the brain is a hallmark of Parkinson’s disease (PD). In vivo soluble α-synuclein occurs as a monomer and several multimers, the latter of which may be important for the biological function of α-synuclein. Currently, there is a lack of reproducible methods to compare α-synuclein multimer abundance between complex biological samples. Here we developed a method, termed “multimer-PAGE,” that combines in-gel chemical cross-linking with several common electrophoretic techniques to measure the stoichiometry of soluble α-synuclein multimers in brain tissue lysates. Results show that soluble α-synuclein from the rat brain exists as several high molecular weight species of approximately 56 kDa (αS56), 80 kDa (αS80), and 100 kDa (αS100) that comigrate with endogenous lipids, detergents, and/or micelles during blue native gel electrophoresis (BN-PAGE). Co-extraction of endogenous lipids with α-synuclein was essential for the detection of soluble α-synuclein multimers. Homogenization of brain tissue in small buffer volumes (>50 mg tissue per 1 mL buffer) increased relative lipid extraction and subsequently resulted in abundant soluble multimer detection via multimer-PAGE. α-Synuclein multimers captured by directly cross-linking soluble lysates resembled those observed following multimer-PAGE. The ratio of multimer (αS80) to monomer (αS17) increased linearly with protein input into multimer-PAGE, suggesting to some extent, multimers were also formed during electrophoresis. Overall, soluble α-synuclein maintains lipid interactions following tissue disruption and readily forms multimers when this lipid–protein complex is preserved. Once the multimer-PAGE technique was validated, relative stoichiometric comparisons could be conducted simultaneously between 14 biological samples. Multimer-PAGE provides a simple inexpensive biochemical technique to study the molecular factors influencing α-synuclein multimerization

  13. Transient colloidal stability controls the particle formation of SBA-15.

    PubMed

    Ruan, Juanfang; Kjellman, Tomas; Sakamoto, Yasuhiro; Alfredsson, Viveka

    2012-08-01

    A hypothesis about (transient) colloidal stability as a controlling mechanism for particle formation in SBA-15 is presented. The hypothesis is based on results from both in situ and ex situ investigations, including cryogenic transmission electron microscopy (cryo-TEM), UV-vis spectroscopy, and dynamic light scattering (DLS). Cryo-TEM images show that particles grow via the formation of silica-Pluronic-water "flocs", which coalesce in a seemingly arbitrary manner. Despite this, the final material consists of well-defined particles with a small size distribution. We argue that the interface between the flocs and surrounding media is covered by Pluronic molecules, which provide steric stabilization. As the flocs grow, the coverage of polymers at the interface is increased until a stable size is reached, and that regulates the particle size. By targeting the characteristics of the Pluronic molecules, during the on-going synthesis, the hypothesis is tested. The results are consistent with the concept of (transient) colloidal stability. PMID:22758927

  14. Transient Colloidal Stability Controls the Particle Formation of SBA-15

    PubMed Central

    2012-01-01

    A hypothesis about (transient) colloidal stability as a controlling mechanism for particle formation in SBA-15 is presented. The hypothesis is based on results from both in situ and ex situ investigations, including cryogenic transmission electron microscopy (cryo-TEM), UV–vis spectroscopy, and dynamic light scattering (DLS). Cryo-TEM images show that particles grow via the formation of silica–Pluronic–water “flocs”, which coalesce in a seemingly arbitrary manner. Despite this, the final material consists of well-defined particles with a small size distribution. We argue that the interface between the flocs and surrounding media is covered by Pluronic molecules, which provide steric stabilization. As the flocs grow, the coverage of polymers at the interface is increased until a stable size is reached, and that regulates the particle size. By targeting the characteristics of the Pluronic molecules, during the on-going synthesis, the hypothesis is tested. The results are consistent with the concept of (transient) colloidal stability. PMID:22758927

  15. Formation, early evolution, and gravitational stability of protoplanetary disks

    NASA Technical Reports Server (NTRS)

    Nakamoto, Taishi; Nakagawa, Yoshitsugo

    1994-01-01

    The formation, viscous evolution, and gravitational stability of protoplanetary disks are investigated. The formation process is parameterized by the angular velocity of the molecular cloud core omega, while the viscous evolution is parameterized by the viscosity parameter alpha in the disk; in this study we consider a range of (0.4-6) x 10(exp -14)/s for omega and from 10(exp -5) to 10(exp -1) for alpha. The axisymmetric gravitational stabilities of the disks are checked using Toomre's criterion. The resulting disk surface temperature distribution, (d log T(sub s)/d log R) approximately = -0.6 (R is the cylindrical radius), can be attributed to two heating sources: the viscous heating dominant in the inner disk region, and the accretion shock heating dominant in the outer disk region. This surface temperature distribution matches that observed in many disks around young stellar objects. During the infall stage, disks with alpha less than 10(exp -1.5) become gravitationally unstable independent of omega. The gravitational instabilities occur at radii ranging from 5 to 40 AU. The ratio of the disk mass to the central star mass ranges from 0.2 to 0.5 at the times of instability, about 4 x 10(exp -5) x (omega/10(exp -14)/s)(exp -0.67) yr. Most disks with low alpha and high omega become gravitationally unstable during their formation phase.

  16. Molecular basis for amyloid fibril formation and stability

    PubMed Central

    Makin, O. Sumner; Atkins, Edward; Sikorski, Pawel; Johansson, Jan; Serpell, Louise C.

    2005-01-01

    The molecular structure of the amyloid fibril has remained elusive because of the difficulty of growing well diffracting crystals. By using a sequence-designed polypeptide, we have produced crystals of an amyloid fiber. These crystals diffract to high resolution (1 Å) by electron and x-ray diffraction, enabling us to determine a detailed structure for amyloid. The structure reveals that the polypeptides form fibrous crystals composed of antiparallel β-sheets in a cross-β arrangement, characteristic of all amyloid fibers, and allows us to determine the side-chain packing within an amyloid fiber. The antiparallel β-sheets are zipped together by means of π-bonding between adjacent phenylalanine rings and salt-bridges between charge pairs (glutamic acid–lysine), thus controlling and stabilizing the structure. These interactions are likely to be important in the formation and stability of other amyloid fibrils. PMID:15630094

  17. Dual degradation signals control Gli protein stability and tumor formation

    PubMed Central

    Huntzicker, Erik G.; Estay, Ivette S.; Zhen, Hanson; Lokteva, Ludmila A.; Jackson, Peter K.; Oro, Anthony E.

    2006-01-01

    Regulated protein destruction controls many key cellular processes with aberrant regulation increasingly found during carcinogenesis. Gli proteins mediate the transcriptional effects of the Sonic hedgehog pathway, which is implicated in up to 25% of human tumors. Here we show that Gli is rapidly destroyed by the proteasome and that mouse basal cell carcinoma induction correlates with Gli protein accumulation. We identify two independent destruction signals in Gli1, DN and DC, and show that removal of these signals stabilizes Gli1 protein and rapidly accelerates tumor formation in transgenic animals. These data argue that control of Gli protein accumulation underlies tumorigenesis and suggest a new avenue for antitumor therapy. PMID:16421275

  18. Pickering emulsions stabilized by oppositely charged colloids: Stability and pattern formation

    NASA Astrophysics Data System (ADS)

    Christdoss Pushpam, Sam David; Basavaraj, Madivala G.; Mani, Ethayaraja

    2015-11-01

    A binary mixture of oppositely charged colloids can be used to stabilize water-in-oil or oil-in-water emulsions. A Monte Carlo simulation study to address the effect of charge ratio of colloids on the stability of Pickering emulsions is presented. The colloidal particles at the interface are modeled as aligned dipolar hard spheres, with attractive interaction between unlike-charged and repulsive interaction between like-charged particles. The optimum composition (fraction of positively charged particles) required for the stabilization corresponds to a minimum in the interaction energy per particle. In addition, for each charge ratio, there is a range of compositions where emulsions can be stabilized. The structural arrangement of particles or the pattern formation at the emulsion interface is strongly influenced by the charge ratio. We find well-mixed isotropic, square, and hexagonal arrangements of particles on the emulsion surface for different compositions at a given charge ratio. The distribution of coordination numbers is calculated to characterize structural features. The simulation study is useful for the rational design of Pickering emulsifications wherein oppositely charged colloids are used, and for the control of pattern formation that can be useful for the synthesis of colloidosomes and porous shells derived thereof.

  19. Polymer Stabilized Nanosuspensions Formed via Flash Nanoprecipitation: Nanoparticle Formation, Formulation, and Stability

    NASA Astrophysics Data System (ADS)

    Zhu, ZhengXi

    Nanoparticles loaded with hydrophobic components (e.g., active pharmaceutical ingredients, medical diagnostic agents, nutritional or personal care chemicals, catalysts, dyes/pigments, and substances with exceptional magnetic/optical/electronic/thermal properties) have tremendous industrial applications. The common desire is to efficiently generate nanoparticles with a desired size, size distribution, and size stability. Recently, Flash NanoPrecipition (FNP) technique with a fast, continuous, and easily scalable process has been developed to efficiently generate hydrophobe-loaded nanoparticles. This dissertation extended this technique, optimized process conditions and material formulations, and gave new insights into the mechanism and kinetics of nanoparticle formation. This dissertation demonstrated successful generation of spherical beta-carotene nanoparticles with an average diameter of 50--100 nm (90 wt% nanoparticles below 200 nm), good size stability (maintained an average diameter below 200 nm for at least one week in saline), and much higher loading (80--90 wt%) than traditional carriers, such as micelles and polymersomes (typically <20 wt%). Moreover, the nanoparticles are amorphous and expected to have a high dissolution rate and bioavailability. To give insights into the mechanism and kinetics of nanoparticle formation, much remarkable evidence supported the kinetically frozen structures of the nanoparticles rather than the thermodynamic equilibrium micelles. Time scales of the particle formation via FNP were proposed. To optimize the material formulations, either polyelectrolytes (i.e., epsilon-polylysine, branched and linear poly(ethylene imine), and chitosan) or amphiphilic diblock copolymers (i.e., polystyrene-b-poly(ethylene glycol) (PS-b-PEG), polycarprolactone-b-poly(ethylene glycol) (PCL-b-PEG), poly(lactic acid)-b-poly(ethylene glycol) (PLA-b-PEG), and poly(lactic-co-glycolic acid)-b-poly(ethylene glycol) (PLGA-b-PEG)) were selectively screened

  20. Formation and Stability of Radiation Products in Europa's Icy Shell

    NASA Technical Reports Server (NTRS)

    Moore, M. H.; Hudson, R. L.; Carlson, R. W.; Ferrante, R. F.

    2004-01-01

    Spectra of Europa reveal a surface dominated by water-ice along with hydrated materials and minor amounts of SO2, CO2, and H2O2. Jovian magnetospheric ions (protons, sulfur, and oxygen) and electrons produce significant chemical modifications of the surface on time scales of a few years at micrometer depths. Our laboratory studies examine the formation and stability of radiation products in H2O-rich ices relevant to Europa. Infrared (IR) spectra of ices before and after irradiation reveal the radiation destruction of molecules and the formation of products at 86 - 132 K. In addition, spectra of ices during warming track thermal evolution due to chemical changes and sublimation processes. IR-identified radiation products in 86 - 132 K irradiated H2O + SO2 ices are the bisulfate ion, HSO4(-), sulfate ion, SO4(2-) and the hydronium ion, H3O(+). Warming results in the formation of a residual spectrum similar to liquid sulfuric acid, H2SO4, for H2O:SO2 ratios of 30:1, whereas hydrated sulfuric acid, H2SO4 4 H2O, forms for ratios of 30:1. Radiation products identified for irradiated H2O + H2S ices at 86 K are H2S2 and SO2. When irradiated at 110 and 132 K, ices with H2O:H2S ratios if either 3:1 or 30:1 show the formation of H2SO4 4 H2O on warming to 175 K. We have also examined the radiation stability of H2SO4. Addition of CO2 to H2O + SO2 ices results in the formation of CO3 at 2046 cm (sup -1) (4.89 m). This is the strongest band from a carbon-containing product in the mid-IR spectral region, and it is also seen when either pure CO2 or H2O + CO2 ice is irradiated. Experiments with CH4 added to H2O + SO2 + CO2 ices addressed the question of methane's use as a marker of methanogens in an irradiated ice environment. New results on the near-IR spectrum of pure H2O2 will be included in this presentation. Interpretations of near-IR water bands, with H2O2 present, will be discussed. Irradiations of H2O2 and H2O + H2O2 mixtures, to examine the possibility of O2 and O3

  1. Purification of α-synuclein from human brain reveals an instability of endogenous multimers as the protein approaches purity.

    PubMed

    Luth, Eric S; Bartels, Tim; Dettmer, Ulf; Kim, Nora C; Selkoe, Dennis J

    2015-01-20

    Despite two decades of research, the structure-function relationships of endogenous, physiological forms of α-synuclein (αSyn) are not well understood. Most in vitro studies of this Parkinson's disease-related protein have focused on recombinant αSyn that is unfolded and monomeric, assuming that this represents its state in the normal human brain. Recently, we have provided evidence that αSyn exists in considerable part in neurons, erythrocytes, and other cells as a metastable multimer that principally sizes as a tetramer. In contrast to recombinant αSyn, physiological tetramers purified from human erythrocytes have substantial α-helical content and resist pathological aggregation into β-sheet rich fibers. Here, we report the first method to fully purify soluble αSyn from the most relevant source, human brain. We describe protocols that purify αSyn to homogeneity from nondiseased human cortex using ammonium sulfate precipitation, gel filtration, and ion exchange, hydrophobic interaction, and affinity chromatographies. Cross-linking of the starting material and the partially purified chromatographic fractions revealed abundant αSyn multimers, including apparent tetramers, but these were destabilized in large part to monomers during the final purification step. The method also fully purified the homologue β-synuclein, with a similar outcome. Circular dichroism spectroscopy showed that purified, brain-derived αSyn can display more helical content than the recombinant protein, but this result varied. Collectively, our data suggest that purifying αSyn to homogeneity destabilizes native, α-helix-rich multimers that exist in intact and partially purified brain samples. This finding suggests existence of a stabilizing cofactor (e.g., a small lipid) present inside neurons that is lost during final purification. PMID:25490121

  2. Twinned silicon and germanium nanocrystals: Formation, stability and quantum confinement

    SciTech Connect

    Yu, Ting; Pi, Xiaodong Ni, Zhenyi; Zhang, Hui; Yang, Deren

    2015-03-15

    Although twins are often observed in Si/Ge nanocrystals (NCs), little theoretical investigation has been carried out to understand this type of important planar defects in Si/Ge NCs. We now study the twinning of Si/Ge NCs in the frame work of density functional theory by representatively considering single-twinned and fivefold-twinned Si/Ge NCs. It is found that the formation of twinned Si/Ge NCs is thermodynamically possible. The effect of twinning on the formation of Si NCs is different from that of Ge NCs. For both Si and Ge NCs twinning enhances their stability. The quantum confinement effect is weakened by twinning for Si NCs. Twinning actually enhances the quantum confinement of Ge NCs when they are small (<136 atoms), while weakening the quantum confinement of Ge NCs as their size is large (>136 atoms). The current results help to better understand the experimental work on twinned Si/Ge NCs and guide the tuning of Si/Ge-NC structures for desired properties.

  3. Interrogating the repertoire: broadening the scope of peptide-MHC multimer analysis.

    PubMed

    Davis, Mark M; Altman, John D; Newell, Evan W

    2011-08-01

    Labelling antigen-specific T cells with peptide-MHC multimers has provided an invaluable way to monitor T cell-mediated immune responses. A number of recent developments in this technology have made these multimers much easier to make and use in large numbers. Furthermore, enrichment techniques have provided a greatly increased sensitivity that allows the analysis of the naive T cell repertoire directly. Thus, we can expect a flood of new information to emerge in the coming years. PMID:21760610

  4. Liquid Crystal Formation from Sunflower Oil: Long Term Stability Studies.

    PubMed

    da Rocha-Filho, Pedro Alves; Maruno, Mônica; Ferrari, Márcio; Topan, José Fernando

    2016-01-01

    The Brazilian biodiversity offers a multiplicity of raw materials with great potential in cosmetics industry applications. Some vegetable oils and fatty esters increase skin hydration by occlusivity, keeping the skin hydrated and with a shiny appearance. Sunflower (Helianthus annus L.) oil is widely employed in cosmetic emulsions in the form of soaps, creams, moisturizers and skin cleansers due to the presence of polyphenols and its high vitamin E content. Liquid crystals are systems with many applications in both pharmaceutical and cosmetic formulations and are easily detected by microscopy under polarized light due to their birefringence properties. The aim of this research was to develop emulsions from natural sunflower oil for topical uses. Sunflower oil (75.0% w/w) was combined with liquid vaseline (25.0% w/w) employing a natural self-emulsifying base (SEB) derivative. The high temperature of the emulsification process did not influence the antioxidant properties of sunflower oil. Fatty esters were added to cosmetic formulations and extended stability tests were performed to characterize the emulsions. Fatty esters like cetyl palmitate and cetyl ester increase the formation of anisotropic structures. O/W emulsions showed acidic pH values and pseudoplastic behavior. The presence of a lamellar phase was observed after a period of 90 days under different storage conditions. PMID:27294894

  5. Formation stability analysis of unmanned multi-vehicles under interconnection topologies

    NASA Astrophysics Data System (ADS)

    Yang, Aolei; Naeem, Wasif; Fei, Minrui

    2015-04-01

    In this paper, the overall formation stability of an unmanned multi-vehicle is mathematically presented under interconnection topologies. A novel definition of formation error is first given and followed by the proposed formation stability hypothesis. Based on this hypothesis, a unique extension-decomposition-aggregation scheme is then employed to support the stability analysis for the overall multi-vehicle formation under a mesh topology. It is proved that the overall formation control system consisting of N number of nonlinear vehicles is not only asymptotically stable, but also exponentially stable in the sense of Lyapunov within a neighbourhood of the desired formation. This technique is shown to be applicable for a mesh topology but is equally applicable for other topologies. A simulation study of the formation manoeuvre of multiple Aerosonde UAVs (unmanned aerial vehicles), in 3-D space, is finally carried out verifying the achieved formation stability result.

  6. Formation, stability, and reactivity studies of neutral iron sulfide clusters

    NASA Astrophysics Data System (ADS)

    Yin, Shi; Wang, Zhechen; Bernstein, Elliot

    2014-03-01

    Different methods are used to generate neutral iron sulfide clusters to study their formation, stability, and reactivity, employing a time of flight mass spectrometer (TOFMS) with VUV (118 nm) radiation single photon ionization (SPI). Neutral FemSn (m = 1-4, n = 1-6), and hydrogen containing FemSnHx (x >0, n > m) clusters are generated by the reaction of seeded H2S in a helium carrier gas with laser ablated iron metal within a supersonic nozzle. The observed strong signal of association products Fe2S2(SH)0,1 M (M = CO, C2H4, C3H6) suggest that the Fe2S2(SH)0,1 clusters have the high activity for interactions with these small molecules. In order to avoid the effect for reactivity from hydrogen containing clusters, pure FemSnclusters are generated through laser ablation of a mixed iron/sulfur target in the presence of a pure helium carrier gas. (FeS)m (m = 1-4) is observed to be the most stable series. Reaction of CO and H2 on neutral (FeS)1,2clusters is farther investigated both experimentally and theoretically. A size dependent reactivity of iron sulfide clusters toward CO is characterized. The reaction FeS + CO --> Fe + OCS is found for the FeS cluster. Products Fe2S 213COH2 and Fe2S 213COH4 are identified for reactions of 13CO and H2 on Fe2S2 clusters: this suggests that the Fe2S2 cluster has a high catalytic activity for hydrogenation reactions of CO to form formaldehyde and methanol. DFT calculations are performed to explore the potential energy surfaces for the two reactions: Fe2S2 + CO + 2H2 --> Fe2S2 + CH3OH; and Fe2S2 + CO + H2 --> Fe2S2 + CH2O.

  7. LMI Based Robust Blood Glucose Regulation in Type-1 Diabetes Patient with Daily Multi-meal Ingestion

    NASA Astrophysics Data System (ADS)

    Mandal, S.; Bhattacharjee, A.; Sutradhar, A.

    2014-04-01

    This paper illustrates the design of a robust output feedback H ∞ controller for the nonlinear glucose-insulin (GI) process in a type-1 diabetes patient to deliver insulin through intravenous infusion device. The H ∞ design specification have been realized using the concept of linear matrix inequality (LMI) and the LMI approach has been used to quadratically stabilize the GI process via output feedback H ∞ controller. The controller has been designed on the basis of full 19th order linearized state-space model generated from the modified Sorensen's nonlinear model of GI process. The resulting controller has been tested with the nonlinear patient model (the modified Sorensen's model) in presence of patient parameter variations and other uncertainty conditions. The performance of the controller was assessed in terms of its ability to track the normoglycemic set point of 81 mg/dl with a typical multi-meal disturbance throughout a day that yields robust performance and noise rejection.

  8. An explanation for minor multimer species in endothelial cell-synthesized von Willebrand factor.

    PubMed Central

    Lynch, D C; Zimmerman, T S; Ling, E H; Browning, P J

    1986-01-01

    Initial synthesis of von Willebrand factor (vWf) by cultured human endothelial cells proceeds by formation of a dimer of pro-vWf subunits. These subunits are found only within the cell and have an apparent molecular weight of 240,000-260,000, as measured by electrophoresis in sodium dodecyl sulfate-polyacrylamide gels. Posttranslational modifications, including proteolytic cleavage, glycosylation, and sulfation, result in the appearance of two additional vWf subunits. The major one migrates with the subunit of plasma vWf at an apparent molecular weight of 220,000-225,000 and the other migrates more slowly than pro-vWf at an apparent molecular weight of 260,000-275,000. These subunits oligomerize to form a set of vWf multimers, which are subsequently secreted into the culture medium. We isolated individual vWf oligomer species from the agarose gel bands and show that vWf minor, or satellite, species differ from major species in subunit composition. Images PMID:3486890

  9. An explanation for minor multimer species in endothelial cell-synthesized von Willebrand factor.

    PubMed

    Lynch, D C; Zimmerman, T S; Ling, E H; Browning, P J

    1986-06-01

    Initial synthesis of von Willebrand factor (vWf) by cultured human endothelial cells proceeds by formation of a dimer of pro-vWf subunits. These subunits are found only within the cell and have an apparent molecular weight of 240,000-260,000, as measured by electrophoresis in sodium dodecyl sulfate-polyacrylamide gels. Posttranslational modifications, including proteolytic cleavage, glycosylation, and sulfation, result in the appearance of two additional vWf subunits. The major one migrates with the subunit of plasma vWf at an apparent molecular weight of 220,000-225,000 and the other migrates more slowly than pro-vWf at an apparent molecular weight of 260,000-275,000. These subunits oligomerize to form a set of vWf multimers, which are subsequently secreted into the culture medium. We isolated individual vWf oligomer species from the agarose gel bands and show that vWf minor, or satellite, species differ from major species in subunit composition. PMID:3486890

  10. Solid-Supported Lipid Membranes: Formation, Stability and Applications

    NASA Astrophysics Data System (ADS)

    Goh, Haw Zan

    This thesis presents a comprehensive investigation of the formation of supported lipid membranes with vesicle hemifusion, their stability under detergents and organic solvents and their applications in molecular biology. In Chapter 3, we describe how isolated patches of DOPC bilayers supported on glass surfaces are dissolved by various detergents (decyl maltoside, dodecyl maltoside, CHAPS, CTAB, SDS, TritonX-100 and Tween20) at their CMC, as investigated by fluorescence video microscopy. In general, detergents partition into distal leaflets of bilayers and lead to the expansion of the bilayers through a rolling motion of the distal over the proximal leaflets, in agreement with the first stage of the established 3-stage model of lipid vesicle solubilization by detergents. Subsequently, we study the partitioning of organic solvents (methanol, ethanol, isopropanol, propanol, acetone and chloroform) into isolated bilayer patches on glass in Chapter 4 with fluorescence microscopy. The area expansion of bilayers due to the partitioning of organic solvents is measured. From the titration of organic solvents, we measured the rate of area expansion as a function of the volume fraction of organic solvents, which is proposed to be a measure of strength of interactions between solvents and membranes. From the same experiments, we also measure the maximum expansion of bilayers (or the maximum binding stoichiometry between organic solvents and lipids) before structural breakdown, which depends on the depth of penetration of solvents to the membranes. In Chapter 5, we investigate the formation of sparsely-tethered bilayer lipid membranes (stBLMs) with vesicle hemifusion. In vesicle hemifusion, lipid vesicles in contact with a hydrophobic alkyl-terminated self-assembled monolayer (SAM) deposit a lipid monolayer to the SAM surface, thus completing the bilayer. Electrical Impedance Spectroscopy and Neutron Reflectivity are used to probe the integrity of stBLMs in terms of their

  11. On the Mechanical Stability of Austenite Matrix After Martensite Formation in a Medium Mn Steel

    NASA Astrophysics Data System (ADS)

    He, B. B.; Huang, M. X.

    2016-04-01

    The present work employs the nanoindentation technique to investigate the effect of prior martensite formation on the mechanical stability of a retained austenite matrix. It is found that the small austenite grains that were surrounded by martensite laths have higher mechanical stability than the large austenite grains that were free of martensite laths. The higher mechanical stability of small austenite grains is due to its higher amount of defects resulting from the prior martensite formation. These defects act as barriers for the later martensite formation and therefore contribute to the higher mechanical stability of small austenite grains. As a result, the present work suggests that the formation of martensite tends to stabilize the surrounding austenite matrix. Therefore, it may explain the lower transformed amount of martensite after quenching as compared to the theoretical calculation using the Koistinen and Marburger (K-M) equation.

  12. On the Mechanical Stability of Austenite Matrix After Martensite Formation in a Medium Mn Steel

    NASA Astrophysics Data System (ADS)

    He, B. B.; Huang, M. X.

    2016-07-01

    The present work employs the nanoindentation technique to investigate the effect of prior martensite formation on the mechanical stability of a retained austenite matrix. It is found that the small austenite grains that were surrounded by martensite laths have higher mechanical stability than the large austenite grains that were free of martensite laths. The higher mechanical stability of small austenite grains is due to its higher amount of defects resulting from the prior martensite formation. These defects act as barriers for the later martensite formation and therefore contribute to the higher mechanical stability of small austenite grains. As a result, the present work suggests that the formation of martensite tends to stabilize the surrounding austenite matrix. Therefore, it may explain the lower transformed amount of martensite after quenching as compared to the theoretical calculation using the Koistinen and Marburger (K-M) equation.

  13. Formation and stability of polychlorinated biphenyl Pickering emulsions

    NASA Astrophysics Data System (ADS)

    Roy-Perreault, Andréanne; Kueper, Bernard H.; Rawson, Jim

    2005-03-01

    An emulsion stabilized by colloidal suspensions of finely divided solids is known as a Pickering emulsion. The potential for polychlorinated biphenyls (PCBs) to form Pickering emulsions ex situ when in contact with powdered solids, such as clays and metal oxides, is investigated here. Bentonite, iron oxide and magnesium oxide dispersions proved to be robust Pickering emulsion stabilizers, whereas manganese oxide dispersions were not. Batch experiments revealed that emulsions can be formed using a moderately low energy input and can be stabilized with solid concentrations as low as 0.5 wt.%. For the base conditions (volumetric oil fraction ( ϕoil)=30 vol.%; solid concentration ( χ)=2 wt.%), the formed emulsions were indefinitely stable and the initial average droplet diameters varied from 80 to 258 μm, depending on the solid used in the colloidal dispersion. The average droplet size varied at early time, but for most conditions stabilized to a steady-state value 1 week after preparation. The effect of Ostwald ripening was limited. At greater than 0.5 wt.% concentration, the efficiency of the solid dispersion as a stabilizer was dependant on the volumetric oil fraction but not on the solid concentration. Generally, systems with volumetric oil fractions outside of the 20-70 vol.% range were unstable. The emulsions' droplet stability, average droplet size and size distribution were observed to vary as a function of the amount of energy provided to the system, the volumetric oil fraction, and the concentration of the solid in the aqueous dispersion. It is hypothesized that drilling through fractured rock in the immediate vicinity of dense, non-aqueous phase liquid (DNAPL) PCBs may provide both the energy and solid material necessary to form Pickering emulsions.

  14. Stability of furosemide polymorphs and the effects of complex formation with β-cyclodextrin and maltodextrin.

    PubMed

    Garnero, Claudia; Chattah, Ana Karina; Longhi, Marcela

    2016-11-01

    The effect of the formation of supramolecular binary complexes with β-cyclodextrin and maltodextrin on the chemical and physical stability of the polymorphs I and II of furosemide was evaluated in solid state. The solid samples were placed under accelerated storage conditions and exposed to daylight into a stability chamber for a 6-month. Chemical stability was monitored by high performance liquid chromatography, while the physical stability was studied by solid state nuclear magnetic resonance, powder X-ray diffraction and scanning electron microscopy. Changes in the physical appearance of the samples were evaluated. The studies showed a significant stabilizing effect of β-cyclodextrin on furosemide form II. Our results suggest that the complex formation is a useful tool for improving the stability of furosemide polymorphs. These new complexes are promising candidates that can be used in the pharmaceutical industry for the preparation of alternative matrices that improve physicochemical properties. PMID:27516309

  15. Explaining Friendship Formation and Friendship Stability: The Role of Children's and Friends' Aggression and Victimization

    ERIC Educational Resources Information Center

    Ellis, Wendy E.; Zarbatany, Lynne

    2007-01-01

    This study examined variation in friendship formation and friendship stability as a function of children's and their friends' victimization, overt aggression, and relational aggression. Participants were 605 pre- and early adolescents in fifth through eighth grades (M age = 12.05) assessed twice over a three-month period. Scores for stability and…

  16. Formation and Stability of Impurity "snakes" in Tokamak Plasmas

    SciTech Connect

    L. Delgado-Aparicio, et. al.

    2013-01-28

    New observations of the formation and dynamics of long-lived impurity-induced helical "snake" modes in tokamak plasmas have recently been carried-out on Alcator C-Mod. The snakes form as an asymmetry in the impurity ion density that undergoes a seamless transition from a small helically displaced density to a large crescent-shaped helical structure inside q < 1, with a regularly sawtoothing core. The observations show that the conditions for the formation and persistence of a snake cannot be explained by plasma pressure alone. Instead, many features arise naturally from nonlinear interactions in a 3D MHD model that separately evolves the plasma density and temperature

  17. von Willebrand Factor multimers profiling with a semi-automated system.

    PubMed

    Pasotti, Fabio; Martini, Giuliana; Caimi, Luigi; Ricotta, Doris

    2013-03-01

    Abnormalities in plasma von Willebrand factor (vWF) concentration and function result in von Willebrand disease (vWD). The diagnosis requires a battery of tests such as screening procedures, confirmatory tests, phenotypic characterization, and genotyping. The phenotypic testing (multimer pattern analysis) is important in order to subclassify the hereditary and the acquired forms of vWD. Only few laboratories are skilled to perform this analysis. The extreme range of protein size from 250 kDa monomer to over 20,000 kDa multimers requires a time-consuming procedure (3-4 days) and presents many technical difficulties. To standardize the method and to overcome technical difficulties, we developed a rapid and sensitive semi-automated method to visualize the multimeric structure of vWF. The semi-automated method we present performs the electrophoresis of patient's plasma in 120 min on a precast gel. Gels are suitable for the G26 Interlab instrumentation. After gel blotting, the method allows visualization of the vWF multimer pattern directly on the membrane. We reduced the time required from 72 to 8 h and we propose this test for the first level screening of vWF multimer deficiency. PMID:23334940

  18. Formation mechanism of silver nanoparticles stabilized in glassy matrices.

    PubMed

    Simo, Anne; Polte, Jörg; Pfänder, Norbert; Vainio, Ulla; Emmerling, Franziska; Rademann, Klaus

    2012-11-14

    In any given matrix control over the final particle size distribution requires a constitutive understanding of the mechanisms and kinetics of the particle evolution. In this contribution we report on the formation mechanism of silver nanoparticles embedded in a soda-lime silicate glass matrix. For the silver ion-exchanged glass it is shown that at temperatures below 410 °C only molecular clusters (diameter <1 nm) are forming which are most likely silver dimers. These clusters grow to nanoparticles (diameter >1 nm) by annealing above this threshold temperature of 410 °C. It is evidenced that the growth and thus the final silver nanoparticle size are determined by matrix-assisted reduction mechanisms. As a consequence, particle growth proceeds after the initial formation of stable clusters by addition of silver monomers which diffuse from the glass matrix. This is in contrast to the widely accepted concept of particle growth in metal-glass systems, in which it is assumed that the nanoparticle formation is predominantly governed by Ostwald ripening processes. PMID:23098252

  19. Protein modification by acrolein: Formation and stability of cysteine adducts

    PubMed Central

    Cai, Jian; Bhatnagar, Aruni; Pierce, William M.

    2010-01-01

    The toxicity of the ubiquitous pollutant and endogenous metabolite, acrolein, is due in part to covalent protein modifications. Acrolein reacts readily with protein nucleophiles via Michael addition and Schiff base formation. Potential acrolein targets in protein include the nucleophilic side chains of cysteine, histidine, and lysine residues as well as the free amino terminus of proteins. Although cysteine is the most acrolein-reactive residue, cysteine-acrolein adducts are difficult to identify in vitro and in vivo. In this study, model peptides with cysteine, lysine, and histidine residues were used to examine the reactivity of acrolein. Results from these experiments show that acrolein reacts rapidly with cysteine residues through Michael addition to form M+56 Da adducts. These M+56 adducts are, however, not stable, even though spontaneous dissociation of the adduct is slow. Further studies demonstrated that when acrolein and model peptides are incubated at physiological pH and temperature, the M+56 adducts decreased gradually accompanied by the increase of M+38 adducts, which are formed from intra-molecular Schiff base formation. Adduct formation with the side chains of other amino acid residues (lysine and histidine) was much slower than cysteine and required higher acrolein concentration. When cysteine residues were blocked by reaction with iodoacetamide and higher concentrations of acrolein were used, adducts of the N-terminal amino group or histidyl residues were formed but lysine adducts were not detected. Collectively, these data demonstrate that acrolein reacts avidly with protein cysteine residues and that the apparent loss of protein-acrolein Michael adducts over time may be related to the appearance of a novel (M+38) adduct. These findings may be important in identification of in vivo adducts of acrolein with protein cysteine residues. PMID:19231900

  20. Formation and stability of hollow MgO nanoshells.

    PubMed

    Krishnan, Gopi; Palasantzas, G; Kooi, B J

    2010-07-01

    High temperature annealing of gas phase synthesized Mg nanoparticles surrounded by an MgO shell leads to formation of hollow MgO nanoshells due to the evaporation assisted Kirkendall effect. Under electron beam exposure in TEM, the (220) MgO facets reduce their high surface energy by forming cube facets, which is followed by nanoshell size reduction and collapse within a few minutes. However, in ambient conditions the nanoshells remain stable for significant periods of time and further degrade by becoming filled with carbon while lossing any MgO identity. Finally, in moderate low vacuum they remained stable for months indicating promise for applications. PMID:21128428

  1. Formation and stability of Vitamin E enriched nanoemulsions stabilized by Octenyl Succinic Anhydride modified starch

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Vitamin E (VE) is highly susceptible to autoxidation; therefore, it requires systems to encapsulate and protect it from autoxidation.In this study,we developed VE delivery systems, which were stabilized by Capsul® (MS), a starch modified with octenyl succinic anhydride. Influences of interfacial ten...

  2. Interface stability and defect formation during crystal growth

    SciTech Connect

    Fabietti, L.M.R.

    1991-01-08

    Unidirectional solidification experiments have been carried out in organic crystals with the aim of improving our knowledge on the effects of constraints on the interface morphology and to increase our understanding of the growth of anisotropic materials. The experimental information shows that lateral constraints such as a sharp change in the cross-sectional area in the solid liquid interface path, can produce important changes in the microstructure if the interface morphology is planar, cellular or dendritic. The study of anisotropic materials cover several topics. It is first shown that slight anisotropy does not influence the dendrite tip selection criterion. This conclusion is obtained from the analysis of the relationship between tip radius and velocity for dendrites growing under the steady state condition for two different materials, CBr{sub 4} and C{sub 2}Cl{sub 6}, which have different surface energy anisotropy values. The values of the dendrite operating parameters {sigma}* are compared with the predictions of the solvability theory and the morphological stability theory. The experiments show better agreement with the latter theory. Critical experiments have been designed and carried out to find the response functions which determine the composition and temperature of the interface as a function of velocity in faceted materials. The experiments, carried out in Napthalene-Camphor system, indicate a strong temperature dependence of the planar interface growth which can be correlated with the step growth mechanism. Experiments on the interface instability show an important dependence on the crystallographic orientation. Unidirectional solidification experiments in zone refined Napthalene confined in very thin cells (gap size {le} 50 {mu}m) have proven to be a good method to study the defect production at the solid liquid interface. 118 refs., 90 figs., 5 tabs.

  3. Formation and stabilization of nanoemulsions using biosurfactants: Rhamnolipids.

    PubMed

    Bai, Long; McClements, David Julian

    2016-10-01

    Nanoemulsions are used in the food, cosmetics, personal care and pharmaceutical industries to provide desirable optical, textural, stability, and delivery characteristics. In many industrial applications, it is desirable to formulate nanoemulsions using natural ingredients so as to develop label-friendly products. Rhamnolipids are biosurfactants isolated from certain microorganisms using fermentation processes. They are glycolipids that have a polar head consisting of rhamnose units and a non-polar tail consisting of a hydrocarbon chain. In this study, the interfacial characteristics of this natural surfactant at medium chain triglyceride (MCT) oil-water interfaces were characterized, and its ability to form nanoemulsions was compared to that of another natural surfactant (quillaja saponins). The influence of rhamnolipid concentration, homogenization pressure, and oil type on the mean droplet diameter of emulsions produced by microfluidization was determined. Rhamnolipids were highly effective at forming small droplets (d32<0.15μm) at low surfactant-to-oil ratios (SOR<1:10) for MCT oil. Rhamnolipids could also be used to form small droplets using long chain triglyceride oils, such as corn and fish oil. Rhamnolipid-coated droplets were stable to aggregation over a range of pH values (5-9), salt concentrations (<100mM NaCl) and temperatures (20-90°C). However, droplet aggregation was observed at highly acidic (pH 2-4) and high ionic strength (200-500mM NaCl) conditions. These effects were attributed to a reduction in electrostatic repulsion at low pH and high salt levels. Rhamnolipid-coated droplets had a high negative charge at neutral pH that decreased in magnitude with decreasing pH. These results indicate that rhamnolipids are effective natural surfactants that may be able to replace synthetic surfactants in certain commercial applications. PMID:27372634

  4. Formation of hydrothermal biochar and char stability in soils

    NASA Astrophysics Data System (ADS)

    Baumert, Julia; Gleixner, Gerd

    2010-05-01

    The use of charcoal as an artificial soil additive is suggested to beneficially modify degraded soil, reduce greenhouse gas emission and improve crop yields. So far research has been mainly done using pyrolysis chars which are produced by dry pyrolysis of biomass. Here we used hydrothermal carbonisation (HTC). In this process wet biomass is converted to char at moderate temperatures (~200°C). Due to the exothermal carbonisation reaction this process is almost energy neutral, i.e. the energy needed to start the carbonisation equals the energy released during carbonisation. Different process parameters have been used to modify the properties of the produced chars. We examined the chemical and morphological properties of hydrothermally synthesized biochar. Cellulose, yeast and sucrose were used as model substances for a range of parent material types like organic and garden waste as well as residues from biogas production. By modifying the process conditions of hydrothermal carbonisation concerning temperature (180°C to 220°C) and duration (6 hours to 24 hours) we produced a variety of different biochars. Our findings suggest that the elemental composition and the thermal stability of resulting chars depend on the feedstock and production conditions. Functional group chemistry determined by NMR shows that the aromaticity of the product increases as a function of temperature whereas the amount of O-alkylic compounds declines, concurrently. Our results show that the properties of the biochar can be manipulated by the modification of process conditions. This opens the opportunity to adjust the charcoal to a given soil type.

  5. The formation and stability of the solid electrolyte interface on the graphite anode

    NASA Astrophysics Data System (ADS)

    Agubra, Victor A.; Fergus, Jeffrey W.

    2014-12-01

    The solid electrolyte interface (SEI) layer plays a critical role in the cycle life of Li-ion batteries. The potential difference across the SEI during charging results in the potential for Li+ intercalation at the graphite-SEI interface to be lower than the potential at the SEI-electrolyte interface, which can prevent electrolyte reduction and decomposition. The stability of the SEI layer at certain critical battery operating conditions remains a challenge in the performance of lithium ion batteries. Electrolyte additives and surface modification of the anode electrode have been shown to improve the formation of an effective SEI layer. However, there is still a need for improving the robustness of the SEI to withstand extreme battery operating conditions. In this paper, the formation and stability of the SEI layer for lithium ion batteries is reviewed. This review includes discussion of the formation, growth and stability of the SEI on graphite anode materials.

  6. Granulocyte proteases do not process endothelial cell-derived unusually large von Willebrand factor multimers to plasma vWF in vivo.

    PubMed

    Phillips, M D; Vu, C; Nolasco, L; Moake, J L

    1991-06-01

    The unusually large von Willebrand factor (ULvWF) multimers present within endothelial cells and platelets are larger than the vWF multimers normally found in adult human plasma. Furthermore, ULvWF multimers are cleared rapidly from the circulation if they are released by intense endothelial cell stimulation. The mechanisms by which the ULvWF multimers are processed to large plasma vWF multimers are not known. It has been demonstrated that granulocyte proteases are capable of decreasing vWF multimer size in vitro, and that some patients with myeloproliferative syndromes have a relative absence of large plasma vWF multimers in sodium citrate-anticoagulated plasma samples. In order to assess the influence of granulocyte proteases on vWF multimer size, we evaluated the vWF multimeric patterns in 94 plasma samples from 60 patients with neutrophil counts that were either considerably elevated or extremely reduced. In 83 of 94 plasma samples, the vWF multimeric patterns were normal. No patients with very low neutrophil counts had ULvWF multimers present. These observations suggest that granulocyte proteases are not likely to be involved in vivo in the processing of ULvWF multimers from endothelial cells to the smaller vWF forms in circulation. PMID:2069167

  7. The Use of Peptide–Major-Histocompatibility-Complex Multimers in Type 1 Diabetes Mellitus

    PubMed Central

    Gojanovich, Greg S; Murray, Sabrina L; Buntzman, Adam S; Young, Ellen F; Vincent, Benjamin G; Hess, Paul R; DVM

    2012-01-01

    Major histocompatibility complex (MHC) class I and MHC class II molecules present short peptides that are derived from endogenous and exogenous proteins, respectively, to cognate T-cell receptors (TCRs) on the surface of T cells. The exquisite specificity with which T cells recognize particular peptide–major-histocompatibility-complex (pMHC) combinations has permitted development of soluble pMHC multimers that bind exclusively to selected T-cell populations. Because the pathogenesis of type 1 diabetes mellitus (T1DM) is driven largely by islet-reactive T-cell activity that causes β-cell death, these reagents are useful tools for studying and, potentially, for treating this disease. When coupled to fluorophores or paramagnetic nanoparticles, pMHC multimers have been used to visualize the expansion and islet invasion of T-cell effectors during diabetogenesis. Administration of pMHC multimers to mice has been shown to modulate T-cell responses by signaling through the TCR or by delivering a toxic moiety that deletes the targeted T cell. In the nonobese diabetic mouse model of T1DM, a pMHC-I tetramer coupled to a potent ribosome-inactivating toxin caused long-term elimination of a specific diabetogenic cluster of differentiation 8+ T-cell population from the pancreatic islets and delayed the onset of diabetes. This review will provide an overview of the development and use of pMHC multimers, particularly in T1DM, and describe the therapeutic promise these reagents have as an antigen-specific means of ameliorating deleterious T-cell responses in this autoimmune disease. PMID:22768881

  8. Lack of multimer organization of von Willebrand factor in an acquired von Willebrand syndrome.

    PubMed

    Casonato, A; Pontara, E; Doria, A; Bertomoro, A; Cattini, M G; Gambari, P F; Girolami, A

    2002-03-01

    We report a case of acquired von Willebrand syndrome (AVWS) in a 20-year-old-woman with systemic lupus erythematosus, in whom severe bleeding complications followed kidney biopsy. Coagulation studies demonstrated undetectable levels of ristocetin-induced platelet aggregation (RIPA), von Willebrand factor antigen (VWF:Ag) and VWF ristocetin cofactor activity (VWF:RCo), associated with significantly prolonged bleeding time; unlike type 3 von Willebrand disease (VWD), platelet VWF was reduced but not undetectable. The plasma VWF multimer pattern was characterized by the presence of only two bands, one of low molecular weight (MW) running as the protomer of plasma VWF in normals, the other of abnormally high MW without detectable intermediate multimers; this pattern resembles that of VWF present in endothelial cells. A search for an anti-VWF antibody demonstrated the presence of an inhibitor at high titre. This anti-VWF antibody did not interfere in the interaction of VWF with platelet glycoprotein (GP) Ib through the A1 domain, and did not react with the A2 domain of VWF; instead, it seemed to modify the relative representation of high and low MW VWF multimers released by normal human umbilical vein endothelial cells (HUVEC). After Azathioprine and corticosteroid treatment, the anti-VWF antibody disappeared and the patient's haemostatic profile normalized, except for the platelet VWF content which still remained decreased. We suggest that the anti-VWF antibody present in the AVWS described compromised both circulating VWF levels and their multimeric organization, inducing the maintenance of the multimer structure that VWF normally has before or in the early phase after secretion from endothelial cells. PMID:11886398

  9. Contribution of plant lignin to the soil organic matter formation and stabilization

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Lignin is the third most abundant plant constituent after cellulose and hemicellulose and thought to be one of the building blocks for soil organic matter formation. Lignin can be used as a predictor for long-term soil organic matter stabilization and C sequestration. Soils and humic acids from fo...

  10. ARHGAP18: an endogenous inhibitor of angiogenesis, limiting tip formation and stabilizing junctions

    PubMed Central

    Chang, Garry HK; Lay, Angelina J; Ting, Ka Ka; Zhao, Yang; Coleman, Paul R; Powter, Elizabeth E; Formaz-Preston, Ann; Jolly, Christopher J; Bower, Neil I; Hogan, Benjamin M; Rinkwitz, Silke; Becker, Thomas S; Vadas, Mathew A; Gamble, Jennifer R

    2014-01-01

    The formation of the vascular network requires a tightly controlled balance of pro-angiogenic and stabilizing signals. Perturbation of this balance can result in dysregulated blood vessel morphogenesis and drive pathologies including cancer. Here, we have identified a novel gene, ARHGAP18, as an endogenous negative regulator of angiogenesis, limiting pro-angiogenic signaling and promoting vascular stability. Loss of ARHGAP18 promotes EC hypersprouting during zebrafish and murine retinal vessel development and enhances tumor vascularization and growth. Endogenous ARHGAP18 acts specifically on RhoC and relocalizes to the angiogenic and destabilized EC junctions in a ROCK dependent manner, where it is important in reaffirming stable EC junctions and suppressing tip cell behavior, at least partially through regulation of tip cell genes, Dll4, Flk-1 and Flt-4. These findings highlight ARHGAP18 as a specific RhoGAP to fine tune vascular morphogenesis, limiting tip cell formation and promoting junctional integrity to stabilize the angiogenic architecture. PMID:25425145

  11. Structural control of nonadiabatic bond formation: the photochemical formation and stability of substituted 4a,4b-dihydrotriphenylenes.

    PubMed

    Snyder, Joshua A; Bragg, Arthur E

    2015-04-30

    Nonadiabatic photocyclization makes bonds and is the first step in the photoinduced cyclodehydrogenation of ortho-arenes to yield polycyclic aromatic hydrocarbons. How molecular structure alters potential-energy landscapes, excited-state dynamics, and stabilities of reactants and intermediates underlies the feasibility of desirable photochemistry. In order to gain insight into these structure-dynamics relationships, we have used femtosecond transient absorption spectroscopy (TAS) to examine photoinduced dynamics of 1,2,3-triphenylbenzene (TPB) and ortho-quaterphenyl (OQTP), phenyl-subsituted analogues of ortho-terphenyl (OTP). Dynamics of TPB and OTP are quite similar: TPB exhibits fast (7.4 ps) excited-state decay with concomitant formation and vibrational relaxation of 9-phenyl-dihydrotriphenylene (9-phenyl DHT). In contrast, photoexcited OQTP exhibits multistate kinetics leading to formation of 1-phenyl DHT. Excited-state calculations reveal the existence of two distinct minima on the OQTP S1 surface and, together with photophysical data, support a mechanism involving both direct cyclization by way of an asymmetric structure and indirect cyclization by way of a symmetric quinoid-like minimum. Temperature-dependent nanosecond TAS was utilized to assess the relative stabilities of intermediates, substantiating the observed trend in photochemical reactivity OTP > OQTP > TPB. In total, this work demonstrates how specific structural variations alter the course of the excited-state dynamics and photoproduct stability that underlies desired photochemistry. PMID:25849258

  12. Conditions for Circumstellar Disc Formation II: Effects of Initial Cloud Stability and Mass Accretion Rate

    NASA Astrophysics Data System (ADS)

    Machida, Masahiro N.; Matsumoto, Tomoaki; Inutsuka, Shu-ichiro

    2016-09-01

    Disc formation in strongly magnetized cloud cores is investigated using a three-dimensional magnetohydrodynamic simulation with a focus on the effects of the initial cloud stability and the mass accretion rate. The initial cloud stability greatly alters the disc formation process even for prestellar clouds with the same mass-to-flux ratio. A high mass accretion rate onto the disc-forming region is realized in initially unstable clouds, and a large angular momentum is introduced into the circumstellar region in a short time. The region around the protostar has both a thin infalling envelope and a weak magnetic field, which both weaken the effect of magnetic braking. The growth of the rotation-supported disc is promoted in such unstable clouds. Conversely, clouds in an initially near-equilibrium state show lower accretion rates of mass and angular momentum. The angular momentum is transported to the outer envelope before protostar formation. After protostar formation, the circumstellar region has a thick infalling envelope and a strong magnetic field that effectively brake the disc. As a result, disc formation is suppressed when the initial cloud is in a nearly stable state. The density distribution of the initial cloud also affects the disc formation process. Disc growth strongly depends on the initial conditions when the prestellar cloud has a uniform density, whereas there is no significant difference in the disc formation process in prestellar clouds with nonuniform densities.

  13. Comparison of different procedures to stabilize biogas formation after process failure in a thermophilic waste digestion system: Influence of aggregate formation on process stability

    SciTech Connect

    Kleyboecker, A.; Liebrich, M.; Kasina, M.; Kraume, M.; Wittmaier, M.; Wuerdemann, H.

    2012-06-15

    Highlights: Black-Right-Pointing-Pointer Mechanism of process recovery with calcium oxide. Black-Right-Pointing-Pointer Formation of insoluble calcium salts with long chain fatty acids and phosphate. Black-Right-Pointing-Pointer Adsorption of VFAs by the precipitates resulting in the formation of aggregates. Black-Right-Pointing-Pointer Acid uptake and phosphate release by the phosphate-accumulating organisms. Black-Right-Pointing-Pointer Microbial degradation of volatile fatty acids in the aggregates. - Abstract: Following a process failure in a full-scale biogas reactor, different counter measures were undertaken to stabilize the process of biogas formation, including the reduction of the organic loading rate, the addition of sodium hydroxide (NaOH), and the introduction of calcium oxide (CaO). Corresponding to the results of the process recovery in the full-scale digester, laboratory experiments showed that CaO was more capable of stabilizing the process than NaOH. While both additives were able to raise the pH to a neutral milieu (pH > 7.0), the formation of aggregates was observed particularly when CaO was used as the additive. Scanning electron microscopy investigations revealed calcium phosphate compounds in the core of the aggregates. Phosphate seemed to be released by phosphorus-accumulating organisms, when volatile fatty acids accumulated. The calcium, which was charged by the CaO addition, formed insoluble salts with long chain fatty acids, and caused the precipitation of calcium phosphate compounds. These aggregates were surrounded by a white layer of carbon rich organic matter, probably consisting of volatile fatty acids. Thus, during the process recovery with CaO, the decrease in the amount of accumulated acids in the liquid phase was likely enabled by (1) the formation of insoluble calcium salts with long chain fatty acids, (2) the adsorption of volatile fatty acids by the precipitates, (3) the acid uptake by phosphorus-accumulating organisms and (4

  14. Tuning the formation and stability of microcapsules by environmental conditions and chitosan structure.

    PubMed

    Ren, Ying; Xie, Hongguo; Liu, Xiaocen; Yang, Fan; Yu, Weiting; Ma, Xiaojun

    2016-10-01

    The goal of this work is to tune the formation and stability of the alginate-chitosan (AC) polyelectrolyte complexes (PECs) and microcapsules. Particularly, we explore the role of the conformation of chitosan on its interaction with alginate to understand the mechanism underpinning their interactions at the molecular level. Reducing the charge density by increasing pH will increase the compactness of chitosan, the values of the enthalpy (H) and stoichiometry (N) of binding between chitosan and alginate. Consequently, chitosan has advantage in being adsorbed on alginate beads to form microcapsules, including the binding rate and binding amount. Though the total heat release remain similar in the range of ionic strength, chitosan diffuses much easier into alginate hydrogels when in higher ionic strength. Increasing pH and ionic strength both help AC microcapsules to have higher stability. The results indicate that the formation and stability of AC microcapsules are related to the rigidity and conformations of chitosan molecules. After increasing acetylation degree (DA) of chitosan, the binding rate of chitosan and mechanical strength of AC microcapsules are both reduced. This work demonstrates the versatility and feasibility of tuning the formation and stability of polysaccharide microcapsules by physical factors and chitosan chemical structures. PMID:27344950

  15. The diskmass survey. VIII. On the relationship between disk stability and star formation

    SciTech Connect

    Westfall, Kyle B.; Verheijen, Marc A. W.; Andersen, David R.; Bershady, Matthew A.; Martinsson, Thomas P. K.; Swaters, Robert A.

    2014-04-10

    We study the relationship between the stability level of late-type galaxy disks and their star-formation activity using integral-field gaseous and stellar kinematic data. Specifically, we compare the two-component (gas+stars) stability parameter from Romeo and Wiegert (Q {sub RW}), incorporating stellar kinematic data for the first time, and the star-formation rate estimated from 21 cm continuum emission. We determine the stability level of each disk probabilistically using a Bayesian analysis of our data and a simple dynamical model. Our method incorporates the shape of the stellar velocity ellipsoid (SVE) and yields robust SVE measurements for over 90% of our sample. Averaging over this subsample, we find a meridional shape of σ{sub z}/σ{sub R}=0.51{sub −0.25}{sup +0.36} for the SVE and, at 1.5 disk scale lengths, a stability parameter of Q {sub RW} = 2.0 ± 0.9. We also find that the disk-averaged star-formation-rate surface density ( Σ-dot {sub e,∗}) is correlated with the disk-averaged gas and stellar mass surface densities (Σ {sub e,} {sub g} and Σ {sub e,} {sub *}) and anti-correlated with Q {sub RW}. We show that an anti-correlation between Σ-dot {sub e,∗} and Q {sub RW} can be predicted using empirical scaling relations, such that this outcome is consistent with well-established statistical properties of star-forming galaxies. Interestingly, Σ-dot {sub e,∗} is not correlated with the gas-only or star-only Toomre parameters, demonstrating the merit of calculating a multi-component stability parameter when comparing to star-formation activity. Finally, our results are consistent with the Ostriker et al. model of self-regulated star-formation, which predicts Σ-dot {sub e,∗}/Σ{sub e,g}∝Σ{sub e,∗}{sup 1/2}. Based on this and other theoretical expectations, we discuss the possibility of a physical link between disk stability level and star-formation rate in light of our empirical results.

  16. Role of the crystal field stabilization energy in the formation of metal(II) formate mixed crystals

    NASA Astrophysics Data System (ADS)

    Balarew, Christo; Stoilova, Donka; Vassileva, Violeta

    A relationship between the distribution coefficient values and the factors determining the isomorphous substitution of some metal(II) formates (Mg, Mn, Fe, Co, Ni, Cu, Zn, Cd) has been found, given by D=[exp⁡{aṡf[ΔR/R]+bṡϕ(Δɛ)+cṡψ(Δs)}/{RT}, where Δ R/R is the relative difference in the ionic radii of the intersubstituting ions, Δɛ is the difference in the Me sbnd O bond energy, Δ s is the difference in the crystal field stabilization energy. The pre-exponential term represents the balance in bonding factors between the ions in the crystal and in the aqueous solution, in the case of ideally mixing in the solid state. The exponential term takes into account the enthalpy of mixing in the solid state. For the isostructural formate salts in which the substitution of a given cation by another one occurs in equivalent octahedral positions, the difference in the crystal field stabilization energy exerts the most important influence on the enthalpy of mixing.

  17. Evaluation of the geological relationships to gas hydrate formation and stability

    SciTech Connect

    Not Available

    1986-01-01

    Although there are many publications pertaining to gas hydrates, their formation and stability in various geological conditions are poorly known. Therefore, for the same reasons and because of the very broad scope of our research, limited amount and extremely dispersed information, the study regions are very large. Moreover, almost without exception the geological environments controlling gas hydrates formation and stability of the studied regions are very complex. The regions studied (completed and partially completed - total 17 locations) during the reporting period, particularly the Gulf of Mexico and the Middle America Trench, are the most important in this entire research project. In the past, both of these regions have been extensively studied, the presence of gas hydrates confirmed and samples recovered. In our investigation it was necessary not only to review all previous data and interpretations, but to do a thorough analysis of the basins, and a critical evaluation of an previously reported and publicly available but not published information.

  18. Formation and thermal stability of amorphous Cu-Zr thin films deposited by coevaporation

    SciTech Connect

    Minemura, T.; van den Broek, J.J.; Daams, J.L.C.

    1988-05-01

    The formation and thermal stability of amorphous thin films have been characterized by comparing them with those of melt-spun ribbons. The various Cu/sub 1-//sub x/Zr/sub x/ thin films were deposited by coevaporation. The amorphous formation range and the crystallization behavior in the films were investigated with x-ray diffraction and differential scanning calorimetry. The amorphous thin films are formed in the composition range x = 0.20--0.75, which is wider than that found for the melt-spun ribbons. The crystallization temperature and the activation energy for crystallization are lower than those of the melt-spun ribbons, although the composition dependencies show tendencies similar to those of the ribbons. These differences in thermal stability between amorphous films and ribbons might be due to a lower degree of the short-range ordering in the films.

  19. Dynamical stability of imaged planetary systems in formation: Application to HL Tau

    NASA Astrophysics Data System (ADS)

    Tamayo, Daniel; Triaud, Amaury H. M. J.; Menou, Kristen; Rein, Hanno

    2015-08-01

    A recent ALMA image revealed several concentric gaps in the protoplanetary disk surrounding the young star HL Tau. We consider the hypothesis that these gaps are carved by planets, and present a general framework for understanding the dynamical stability of such systems over typical disk lifetimes, providing estimates for the maximum planetary masses.We argue that the locations of resonances should be significantly shifted in massive disks like HL Tau, and that theoretical uncertainties in the exact offset, together with observational errors, imply a large uncertainty in the dynamical state and stability in such disks. This may present an important barrier to using systems like HL Tau as a proxy for the initial conditions following planet formation. An important observational avenue to breaking this degeneracy is to search for eccentric gaps, which could implicate resonantly interacting planets. Unfortunately, a massive disk would also induce swift pericenter precession that would smear out any such eccentric features of planetary origin. This motivates pushing toward more typical, less massive disks.For a nominal non-resonant model of the HL Tau system with five planets, we find a maximum mass for the outer three bodies of approximately 2 Neptune masses. In a resonant configuration, these planets can reach at least the mass of Saturn. The inner two planets' masses are unconstrained by dynamical stability arguments. We will consider the implications for the HL Tau system, and discuss the exciting future of the planetary formation studies in the ALMA era.

  20. Understanding and controlling nanoporosity formation for improving the stability of bimetallic fuel cell catalysts.

    PubMed

    Gan, Lin; Heggen, Marc; O'Malley, Rachel; Theobald, Brian; Strasser, Peter

    2013-03-13

    Nanoporosity is a frequently reported phenomenon in bimetallic particle ensembles used as electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells. It is generally considered a favorable characteristic, because it increases the catalytically active surface area. However, the effect of nanoporosity on the intrinsic activity and stability of a nanoparticle electrocatalyst has remained unclear. Here, we present a facile atmosphere-controlled acid leaching technique to control the formation of nanoporosity in Pt-Ni bimetallic nanoparticles. By statistical analysis of particle size, composition, nanoporosity, and atomic-scale core-shell fine structures before and after electrochemical stability test, we uncover that nanoporosity formation in particles larger than ca. 10 nm is intrinsically tied to a drastic dissolution of Ni and, as a result of this, a rapid drop in intrinsic catalytic activity during ORR testing, translating into severe catalyst performance degradation. In contrast, O2-free acid leaching enabled the suppression of nanoporosity resulting in more solid core-shell particle architectures with thin Pt-enriched shells; surprisingly, such particles maintained high intrinsic activity and improved catalytic durability under otherwise identical ORR tests. On the basis of these findings, we suggest that catalytic stability could further improve by controlling the particle size below ca. 10 nm to avoid nanoporosity. Our findings provide an explanation for the degradation of bimetallic particle ensembles and show an easy to implement pathway toward more durable fuel cell cathode catalysts. PMID:23360425

  1. Understanding soil organic matter formation and stabilization (Philippe Duchaufour Medal Lecture)

    NASA Astrophysics Data System (ADS)

    Kögel-Knabner, Ingrid

    2015-04-01

    During the biomass formation/decomposition cycle carbon dioxide (CO2), the main gas driving global warming, is either released from or stabilized in the organic matter of soils. One of the most fundamental functions of soil organic matter is the provision of metabolic energy which drives soil biological processes. In essence, it is the transformation of carbon by plant, micro- and macro-biological processes that provides energy and results in the establishment of a cycle that connects above- and belowground energy transformations. The amount and type of organic matter accumulated in soils is controlled, among other factors by intrinsic soil properties, specifically soil texture and the associated aggregate structures. Soil development leads to the formation of aggregated structures composed of a highly complex mixture of different mineral and organic constituents. The resulting soil type specific carbon sequestration can strongly be affected by soil management, varying greatly with the type and intensity of land use. The processes of formation and stabilization of organic matter through organo-mineral interactions in aggregated soil structures are controlled at the sub-µm scale. Understanding the binding of organic matter in these fine soil structures is thus key to elucidate the biogeochemical soil processes that are part of the carbon cycle as well as to evaluate the effects of soil management on the carbon cycle. I will discuss open questions for understanding these processes and how we can approach them by combining state-of-the-art analytical techniques with innovative experiments.

  2. A model for the formation and stabilization of charged water clathrates

    NASA Technical Reports Server (NTRS)

    Holland, P. M.; Castleman, A. W., Jr.

    1980-01-01

    A model for the formation and stabilization of charged water clathrates is presented which accounts for observed anomalies in H(+)(H2O)n ion distributions. These anomalies are observed in both ion cluster and neutral expansions and are consistent with the sizes expected for clathrate ions. That the same sizes are observed in both ion cluster and neutral expansions strongly suggests that a rapid ionic process is responsible for their formation. The proposed model is based on the high mobility and bonding effects of the excess proton in water. Computer simulations suggest that excess proton movement in a water clathrate would be suitable for stabilizing the clathrate structure as well as giving it access to a large number of nearly degenerate proton configurations. The formation of clathrates in charged water clusters of proper size can be ascribed to the following: rapid excess proton movement, a strong preference of the H3O(+) for a three-coordinate bonding structure (which is compatible with hydrogen bonding), and finally, relatively slow processes leading to thermal disorder.

  3. Stability of synchronized dynamics and pattern formation in coupled systems: Review of some recent results

    NASA Astrophysics Data System (ADS)

    Chen, Yonghong; Rangarajan, Govindan; Ding, Mingzhou

    2006-12-01

    In arbitrarily coupled dynamical systems (maps or ordinary differential equations), the stability of synchronized states (including equilibrium point, periodic orbit or chaotic attractor) and the formation of patterns from loss of stability of the synchronized states are two problems of current research interest. These two problems are often treated separately in the literature. Here, we present a unified framework in which we show that the eigenvalues of the coupling matrix determine the stability of the synchronized state, while the eigenvectors correspond to patterns emerging from desynchronization. Based on this simple framework three results are derived: First, general approaches are developed that yield constraints directly on the coupling strengths which ensure the stability of synchronized dynamics. Second, when the synchronized state becomes unstable spatial patterns can be selectively realized by varying the coupling strengths. Distinct temporal evolution of the spatial pattern can be obtained depending on the bifurcating synchronized state. Third, given a desired spatiotemporal pattern, one is able to design coupling schemes which give rise to that pattern as the coupled system evolves. Systems with specific coupling schemes are used as examples to illustrate the general methods.

  4. Rearrangement of MICU1 multimers for activation of MCU is solely controlled by cytosolic Ca2+

    PubMed Central

    Waldeck-Weiermair, Markus; Malli, Roland; Parichatikanond, Warisara; Gottschalk, Benjamin; Madreiter-Sokolowski, Corina T.; Klec, Christiane; Rost, Rene; Graier, Wolfgang F.

    2015-01-01

    Mitochondrial Ca2+ uptake is a vital process that controls distinct cell and organelle functions. Mitochondrial calcium uptake 1 (MICU1) was identified as key regulator of the mitochondrial Ca2+ uniporter (MCU) that together with the essential MCU regulator (EMRE) forms the mitochondrial Ca2+ channel. However, mechanisms by which MICU1 controls MCU/EMRE activity to tune mitochondrial Ca2+ signals remain ambiguous. Here we established a live-cell FRET approach and demonstrate that elevations of cytosolic Ca2+ rearranges MICU1 multimers with an EC50 of 4.4 μM, resulting in activation of mitochondrial Ca2+ uptake. MICU1 rearrangement essentially requires the EF-hand motifs and strictly correlates with the shape of cytosolic Ca2+ rises. We further show that rearrangements of MICU1 multimers were independent of matrix Ca2+ concentration, mitochondrial membrane potential, and expression levels of MCU and EMRE. Our experiments provide novel details about how MCU/EMRE is regulated by MICU1 and an original approach to investigate MCU/EMRE activation in intact cells. PMID:26489515

  5. Rearrangement of MICU1 multimers for activation of MCU is solely controlled by cytosolic Ca(2.).

    PubMed

    Waldeck-Weiermair, Markus; Malli, Roland; Parichatikanond, Warisara; Gottschalk, Benjamin; Madreiter-Sokolowski, Corina T; Klec, Christiane; Rost, Rene; Graier, Wolfgang F

    2015-01-01

    Mitochondrial Ca(2+) uptake is a vital process that controls distinct cell and organelle functions. Mitochondrial calcium uptake 1 (MICU1) was identified as key regulator of the mitochondrial Ca(2+) uniporter (MCU) that together with the essential MCU regulator (EMRE) forms the mitochondrial Ca(2+) channel. However, mechanisms by which MICU1 controls MCU/EMRE activity to tune mitochondrial Ca(2+) signals remain ambiguous. Here we established a live-cell FRET approach and demonstrate that elevations of cytosolic Ca(2+) rearranges MICU1 multimers with an EC50 of 4.4 μM, resulting in activation of mitochondrial Ca(2+) uptake. MICU1 rearrangement essentially requires the EF-hand motifs and strictly correlates with the shape of cytosolic Ca(2+) rises. We further show that rearrangements of MICU1 multimers were independent of matrix Ca(2+) concentration, mitochondrial membrane potential, and expression levels of MCU and EMRE. Our experiments provide novel details about how MCU/EMRE is regulated by MICU1 and an original approach to investigate MCU/EMRE activation in intact cells. PMID:26489515

  6. Improved methods for the formation and stabilization of R-loops

    PubMed Central

    Kaback, David B.; Angerer, Lynne M.; Davidson, Norman

    1979-01-01

    Improved methods for the formation and stabilization of R-loops for visualization in the electron microscope are presented. The two complementary strands of a duplex DNA are photochemically crosslinked once every 1 to 3 kb using 4, 5', 8 trimethylpsoralen. R-loops are then formed by incubation with RNA in 70% formamide at a temperature above the DNA melting temperature. Finally, the R-loops are stabilized by modifying the free single strand of DNA with glyoxal, thus minimizing the displacement of the hybridized RNA by branch migration. In this manner R-loops can be formed and visualized at a high frequency irrespective of the base composition of the nucleic acid of interest. Images PMID:379821

  7. High-Temperature Stability and Grain Boundary Complexion Formation in a Nanocrystalline Cu-Zr Alloy

    NASA Astrophysics Data System (ADS)

    Khalajhedayati, Amirhossein; Rupert, Timothy J.

    2015-12-01

    Nanocrystalline Cu-3 at.% Zr powders with ~20 nm average grain size were created with mechanical alloying and their thermal stability was studied from 550-950°C. Annealing drove Zr segregation to the grain boundaries, which led to the formation of amorphous intergranular complexions at higher temperatures. Grain growth was retarded significantly, with 1 week of annealing at 950°C, or 98% of the solidus temperature, only leading to coarsening of the average grain size to 54 nm. The enhanced thermal stability can be connected to both a reduction in grain boundary energy with doping as well as the precipitation of ZrC particles. High mechanical strength is retained even after these aggressive heat treatments, showing that complexion engineering may be a viable path toward the fabrication of bulk nanostructured materials with excellent properties.

  8. Stabilization of thylakoid membranes in isoprene-emitting plants reduces formation of reactive oxygen species.

    PubMed

    Velikova, Violeta; Sharkey, Thomas D; Loreto, Francesco

    2012-01-01

    Isoprene is emitted by a significant fraction of the world's vegetation. Isoprene makes leaves more thermotolerant, yet we do not fully understand how. We have recently shown that isoprene stabilizes thylakoid membranes under heat stress. Here we show that heat-stressed, isoprene-emitting transgenic Arabidopsis plants also produce a lower pool of reactive oxygen and reactive nitrogen species, and that this was especially due to a lower accumulation of H2O2 in isoprene emitting plants. It remains difficult to disentangle whether in heat stressed plants isoprene also directly reacts with and quenches reactive oxygen species (ROS), or reduces ROS formation by stabilizing thylakoids. We present considerations that make the latter a more likely mechanism, under our experimental circumstances. PMID:22301981

  9. Formation, levitation, and stability of prominences in the magnetized solar atmosphere

    NASA Technical Reports Server (NTRS)

    Drake, J. F.; Mok, Y.; Van Hoven, G.

    1993-01-01

    The dynamic formation of prominences in the initial magnetothermal equilibrium and their stability to sideward displacements are investigated focusing on the structure of the 2D solar atmosphere in the presence of coronal arcades or loops. A model based on 2D magnetohydrodynamic equations takes into account gravity, compressible flows, heating, radiation, anisotropic thermal conduction, and coupling to a deep chromosphere. It is found that prominences in simple arcades characterized by magnetic field with significant curvature at the apex are unstable to a lateral displacement.

  10. Stability of Galactic Gaseous Disks and the Formation of Massive Clusters

    SciTech Connect

    Escala, Andres; Larson, Richard B.

    2008-08-21

    We study gravitational instabilities in disks, with special attention to the most massive clumps that form because they are expected to be the progenitors of globular-type clusters. The maximum unstable mass is set by rotation and depends only on the surface density and orbital frequency of the disk. We propose that the formation of massive clusters is related to this largest scale in galaxies not stabilized by rotation. Using data from the literature, we predict that globular-like clusters can form in nuclear starburst disks and protogalactic disks but not in typical spiral galaxies, in agreement with observations.

  11. Formation, spin-up, and stability of field-reversed configurations

    DOE PAGESBeta

    Omelchenko, Yuri A.

    2015-08-24

    Formation, spontaneous spin-up and stability of theta-pinch formed field-reversed configurations are studied self-consistently in three dimensions with a multiscale hybrid model that treats all plasma ions as full-orbit collisional macro-particles and the electrons as a massless quasineutral fluid. The end-to-end hybrid simulations for the first time reveal poloidal profiles of implosion-driven fast toroidal plasma rotation and demonstrate three well-known discharge regimes as a function of experimental parameters: the decaying stable configuration, the tilt unstable configuration and the nonlinear evolution of a fast growing tearing mode.

  12. Stabilization of a formate dehydrogenase by covalent immobilization on highly activated glyoxyl-agarose supports.

    PubMed

    Bolivar, Juan M; Wilson, Lorena; Ferrarotti, Susana Alicia; Fernandez-Lafuente, Roberto; Guisan, Jose M; Mateo, Cesar

    2006-03-01

    Formate dehydrogenase (FDH) is a stable enzyme that may be readily inactivated by the interaction with hydrophobic interfaces (e.g., due to strong stirring). This may be avoided by immobilizing the enzyme on a porous support by any technique. Thus, even if the enzyme is going to be used in an ultra-membrane reactor, the immobilization presents some advantages. Immobilization on supports activated with bromocianogen, polyethylenimine, glutaraldehyde, etc., did not promote any stabilization of the enzyme under thermal inactivation. However, the immobilization of FDH on highly activated glyoxyl agarose has permitted increasing the enzyme stability against any distorting agent: pH, T, organic solvent, etc. The time of support-enzyme reaction, the temperature of immobilization, and the activation of the support need to be optimized to get the optimal stability-activity properties. Optimized biocatalyst retained 50% of the offered activity and became 50 times more stable at high temperature and neutral pH. Moreover, the quaternary structure of this dimeric enzyme becomes stabilized by immobilization under optimized conditions. Thus, at acidic pH (conditions where the subunit dissociation is the first step in the enzyme inactivation), the immobilization of both subunits of the enzyme on glyoxyl-agarose has allowed the enzyme to be stabilized by hundreds of times. Moreover, the optimal temperature of the enzyme has been increased (even by 10 degrees C at pH 4.5). Very interestingly, the activity with NAD(+)-dextran was around 60% of that observed with free cofactor. PMID:16529396

  13. Evaluation of the geological relationships to gas hydrate formation and stability

    SciTech Connect

    Krason, J.; Finley, P.

    1988-01-01

    The summaries of regional basin analyses document that potentially economic accumulations of gas hydrates can be formed in both active and passive margin settings. The principal requirement for gas hydrate formation in either setting is abundant methane. Passive margin sediments with high sedimentation rates and sufficient sedimentary organic carbon can generate large quantities of biogenic methane for hydrate formation. Similarly, active margin locations near a terrigenous sediment source can also have high methane generation potential due to rapid burial of adequate amounts of sedimentary organic matter. Many active margins with evidence of gas hydrate presence correspond to areas subject to upwelling. Upwelling currents can enhance methane generation by increasing primary productivity and thus sedimentary organic carbon. Structural deformation of the marginal sediments at both active and passive sites can enhance gas hydrate formation by providing pathways for migration of both biogenic and thermogenic gas to the shallow gas hydrate stability zone. Additionally, conventional hydrocarbon traps may initially concentrate sufficient amounts of hydrocarbons for subsequent gas hydrate formation.

  14. SDS-PAGE/immunoblot detection of Abeta multimers in human cortical tissue homogenates using antigen-epitope retrieval.

    PubMed

    Rosen, Rebecca F; Tomidokoro, Yasushi; Ghiso, Jorge A; Walker, Lary C

    2010-01-01

    The anomalous folding and polymerization of the beta-amyloid (Abeta) peptide is thought to initiate the neurodegenerative cascade in Alzheimer's disease pathogenesis(1). Abeta is predominantly a 40- or 42-amino acid peptide that is prone to self-aggregation into beta-sheet-rich amyloid fibrils that are found in the cores of cerebral senile plaques in Alzheimer's disease. Increasing evidence suggests that low molecular weight, soluble Abeta multimers are more toxic than fibrillar Abeta amyloid(2). The identification and quantification of low- and high-molecular weight multimeric Abeta species in brain tissue is an essential objective in Alzheimer's disease research, and the methods employed also can be applied to the identification and characterization of toxic multimers in other proteopathies(3). Naturally occurring Abeta multimers can be detected by SDS-polyacrylamide gel electrophoresis followed by immunoblotting with Abeta-specific antibodies. However, the separation and detection of multimeric Abeta requires the use of highly concentrated cortical homogenates and antigen retrieval in small pore-size nitrocellulose membranes. Here we describe a technique for the preparation of clarified human cortical homogenates, separation of proteins by SDS-PAGE, and antigen-epitope retrieval/Western blotting with antibody 6E10 to the N-terminal region of the Abeta peptide. Using this protocol, we consistently detect Abeta monomers, dimers, trimers, tetramers, and higher molecular weight multimers in cortical tissue from humans with Alzheimer's pathology. PMID:20418805

  15. Silicate formation and thermal stability of ternary rare earth oxides as high-k dielectrics

    SciTech Connect

    Elshocht, S. van; Adelmann, C.; Conard, T.; Delabie, A.; Franquet, A.; Nyns, L.; Richard, O.; Lehnen, P.; Swerts, J.; Gendt, S. de

    2008-07-15

    Hf-based dielectrics are currently being introduced into complementary metal oxide semiconductor transistors as replacement for SiON to limit gate leakage current densities. Alternative materials such as rare earth based dielectrics are of interest to obtain proper threshold voltages as well as to engineer a material with a high thermal stability. The authors have studied rare earth based dielectrics such as Dy{sub 2}O{sub 3}, DyHfO{sub x}, DyScO{sub x}, La{sub 2}O{sub 3}, HfLaO{sub x}, and LaAlO{sub x} by means of ellipsometry, time of flight secondary ion mass spectroscopy x-ray diffraction, and x-ray photoelectron spectroscopy. The authors show that ellipsometry is an easy and powerful tool to study silicate formation. For ternary rare earth oxides, this behavior is heavily dependent on the composition of the deposited layer and demonstrates a nonlinear dependence. The system evolves to a stable composition that is controlled by the thermal budget and the rare earth content of the layer. It is shown that silicate formation can lead to a severe overestimation of the thermal stability of ternary rare earth oxides.

  16. Formation of disulfide bonds in insect prophenoloxidase enhances immunity through improving enzyme activity and stability.

    PubMed

    Lu, Anrui; Peng, Qin; Ling, Erjun

    2014-06-01

    Type 3 copper proteins, including insect prophenoloxidase (PPO), contain two copper atoms in the active site pocket and can oxidize phenols. Insect PPO plays an important role in immunity. Insects and other invertebrates show limited recovery from pathogen invasion and wounds if phenoloxidase (PO) activity is low. In most insect PPOs, two disulfide bonds are present near the C-terminus. However, in Pimpla hypochondriaca (a parasitoid wasp), each PPO contains one disulfide bond. We thus questioned whether the formation of two sulfide bonds in insect PPOs improved protein stability and/or increased insect innate immunity over time. Using Drosophila melanogaster PPO1 as a model, one or two disulfide bonds were deleted to evaluate the importance of disulfide bonds in insect immunity. rPPO1 and mutants lacking disulfide bonds could be expressed and showed PO activity. However, the PO activities of mutants lacking one or two disulfide bonds significantly decreased. Deletion of disulfide bonds also reduced PPO thermostability. Furthermore, antibacterial activities against Escherichia coli and Bacillus subtilis significantly decreased when disulfide bonds were deleted. Therefore, the formation of two disulfide bond(s) in insect PPO enhances antibacterial activity by increasing PO activity and stability. PMID:24480295

  17. Mechanistic Insights into the Formation of Dodecanethiolate-Stabilized Magnetic Iridium Nanoparticles: Thiosulfate vs Thiol Ligands

    PubMed Central

    2015-01-01

    The synthesis of stable and isolable iridium nanoparticles with an average core size of ∼1.2 ± 0.3 nm was achieved by employing sodium S-dodecylthiosulfate as a ligand precursor during the modified Brust–Schiffrin reaction. Transmission electron microscopy (TEM) of the isolated Ir nanoparticles revealed a high degree of monodispersity. Further characterizations with 1H NMR, FT-IR, UV–vis spectroscopy, thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) confirmed that the synthesized Ir nanoparticles are stabilized by dodecanethiolate ligands produced upon the adsorption/cleavage of S-dodecylthiosulfate on the growing Ir nanoparticle surface. By comparison, synthetic attempts employing dodecanethiol as a stabilizing ligand led to the formation of Ir-thiolate species (Ir(SR)3) as an intermediate and Ir-hydroxide species at the completion of reaction. Mechanistic investigations of these two reactions using S-dodecylthiosulfate and dodecanethiol provided deeper understandings on the novelty of thiosulfate ligands, which allow the successful formation of stable thiolate-capped Ir nanoparticles. Moreover, these Ir nanoparticles were shown to have strong magnetic properties. PMID:25018790

  18. Kinetic simulations of the formation and stability of the field-reversed configuration

    SciTech Connect

    Omelchenko, Yu. A.

    2000-05-01

    The Field-Reversed Configuration (FRC) is a high-beta compact toroidal plasma confined primarily by poloidal fields. In the FRC the external field is reversed on axis by the diamagnetic current carried by thermal plasma particles. A three-dimensional, hybrid, particle-in-cell (zero-inertia fluid electrons, and kinetic ions), code FLAME, previously used to study ion rings [Yu. A. Omelchenko and R. N. Sudan, J. Comp. Phys. 133, 146 (1997)], is applied to investigate FRC formation and tilt instability. Axisymmetric FRC equilibria are obtained by simulating the standard experimental reversed theta-pinch technique. These are used to study the nonlinear tilt mode in the ''kinetic'' and ''fluid-like'' cases characterized by ''small'' ({approx}3) and ''large'' ({approx}12) ratios of the characteristic radial plasma size to the mean ion gyro-radius, respectively. The formation simulations have revealed the presence of a substantial toroidal (azimuthal) magnetic field inside the separatrix, generated due to the stretching of the poloidal field by a sheared toroidal electron flow. This is shown to be an important tilt-stabilizing effect in both cases. On the other hand, the tilt mode stabilization by finite Larmor radius effects has been found relatively insignificant for the chosen equilibria. (c) 2000 American Institute of Physics.

  19. Dynamics, Fluxes, Stability, Succession and Landscape Formation in Cold Environments: The DYNAFLUX / DYNACOLD Network

    NASA Astrophysics Data System (ADS)

    Beylich, Achim A.

    2015-04-01

    Within Europe there is a wide array of high-latitude and high-altitude landscapes, covering a significant proportion of the total land area. These defined cold climate landscapes represent a variety of stages of deglaciation history and landscape formation. We find landscapes at different levels of postglacial stabilization, providing the unique opportunity to study the interactions between geo-, bio-, social and socio-economic systems at the land surface. The DYNAFLUX / DYNACOLD Network (2004 - ) bridges across the geo-, bio-, social and socio-economic sciences in order to investigate the complex dynamics of stabilization, succession and landscape formation during and after ice retreat and under human impact. The Network provides a multidisciplinary forum where research groups come together. It is linking and integrating a number of networks and programs and creates an umbrella program and a forum for sharing knowledge. The focus of this network is relevant for different end users, including risk and vulnerability assessment, sustainable land use, land management and conservation. Also questions closely related to Global Change like, e.g., hazards, permafrost degradation, loss of biodiversity are addressed.

  20. Hillock formation of Pt thin films on single-crystal yttria-stabilized zirconia

    NASA Astrophysics Data System (ADS)

    Galinski, Henning; Ryll, Thomas; Schlagenhauf, Lukas; Gauckler, Ludwig J.; Stender, Patrick; Schmitz, Guido

    2012-03-01

    The stability of metal thin films on a dielectric substrate is conditioned by the magnitude of the interactive forces at the interface. In the case of a nonreactive interface and weak adhesion, the minimization of the free surface energy gives rise to an instability of the thin film. In order to study these effects, Pt thin films with a thickness of 50 nm were deposited via ion-beam sputtering on yttria-stabilized zirconia single crystals. All Pt films were subjected to heat treatments up to 973 K for 2 h. The morphological evolution of Pt thin films has been investigated by means of scanning electron microscopy, atomic force microscopy, and standard image analysis techniques. Three main observations have been made: (i) The deposition method has a direct impact on the morphological evolution of the film during annealing. Instead of hole formation, which is typically observed as a response to a thermal treatment, anisotropic pyramidal-shaped hillocks are formed on top of the film. (ii) It is shown by comparing the hillocks’ aspect ratio with finite element method simulations that the hillock formation can be assigned to a stress relaxation process inside the thin film. (iii) By measuring the quasiequilibrium shapes and the shape fluctuations of the formed Pt hillocks the anisotropy of the step free energy and its stiffness have been derived in addition to the anisotropic kink energy of the hillocks’ edges.

  1. Effect of surface hydrophobicity on the formation and stability of oxygen nanobubbles.

    PubMed

    Pan, Gang; Yang, Bo

    2012-06-01

    The formation mechanism of a nanoscale gas state is studied on inorganic clay surfaces modified with hexamethyldisilazane, which show different contact angles in ethanol-water solutions. As the dissolved oxygen becomes oversaturated due to the decrease in ethanol-water ratio, oxygen nanoscale gas state are formed and stabilized on the hydrophobic surfaces so that the total oxygen content in the suspension is increased compared to the control solution without the particles. However, the total oxygen content in the suspension with hydrophilic surfaces is lower than the control solution without the particles because the hydrophilic particle surfaces destabilize the nanobubbles on the surfaces by spreading and coagulating them into microbubbles that quickly escape from the suspension solution. No significant correlation was observed between the nanobubble formation and the shape or roughness of the surfaces. Our results suggest that a nanoscale gas state can be formed on both hydrophobic and hydrophilic particle surfaces, but that the stability of the surface nanoscale gas state can vary greatly depending on the hydrophobicity of the solid surfaces. PMID:22271703

  2. The DYNAFLUX / DYNACOLD Network: Dynamics, Fluxes, Stability, Succession and Landscape Formation in Cold Climate Environments

    NASA Astrophysics Data System (ADS)

    Beylich, Achim A.

    2016-04-01

    There is a wide range of high-latitude and high-altitude cold climate landscapes in Europe, covering a significant proportion of the total land surface area. This spectrum of defined cold climate landscapes represents a variety of stages of deglaciation history and landscape formation. We can find landscapes at different levels of postglacial stabilization which is providing the opportunity to study the interactions between geo-, bio-, social and socio-economic systems at the land surface. The DYNAFLUX / DYNACOLD Network (2004-) bridges across the geo-, bio-, social and socio-economic sciences in order to analyze the complex dynamics of stabilization, succession and landscape formation during and after ice retreat and under ongoing human influences. The network provides a multidisciplinary forum where researchers come together. In addition, it is linking a number of networks, working groups and programs and creates an umbrella network and a forum for sharing knowledge. The scientific focus of this network is also relevant for different end users, including risk and vulnerability assessment, sustainable land use, land management and conservation. In addition, key questions related to Global Change like, e.g., hazards, permafrost degradation and loss of biodiversity are discussed.

  3. Influence of PEG-12 Dimethicone addition on stability and formation of emulsions containing liquid crystal.

    PubMed

    Andrade, F F; Santos, O D H; Oliveira, W P; Rocha-Filho, P A

    2007-06-01

    Oil/water emulsions, containing liquid crystals, were developed employing Andiroba oil, PEG-12 Dimethicone and Crodafos CES. It was evaluated the influence of silicone surfactants on the emulsions stability and on the formation of liquid crystalline phases and therefore, physicochemical characteristics, such as rheology and zeta potential, were evaluated. Emulsions were prepared by the emulsions phase inversion method. All the formulations presented lamellar liquid crystalline phases. The PEG-12 Dimethicone addition did not change microscopically the liquid crystalline phases. The emulsions containing silicone demonstrated lower viscosity than those without the additive. This is an important feature, as the silicone did not change the rheological profile; however, the addition of silicone still can be used as a viscosity controller. The formulations had their viscosity increased 15 and 150 days after their preparation. This characteristic shows that the emulsions have their organization increased along the storing time. In the analysis of zeta potential, we could verify that all formulations presented negative values between -39.7 and -70.0 mV. Within this range of values, the emulsion physical stability is high (Fig. 10). It was concluded that the addition of PEG-12 Dimethicone kept the liquid crystalline phase of the emulsion obtained with Crodafos CES, influencing in a positive way in the system stability. PMID:18489351

  4. Iron hydroxy carbonate formation in zerovalent iron permeable reactive barriers: Characterization and evaluation of phase stability

    SciTech Connect

    Wilkin, Richard T.; Lee, T.R.

    2010-10-22

    Predicting the long-term potential of permeable reactive barriers for treating contaminated groundwater relies on understanding the endpoints of biogeochemical reactions between influent groundwater and the reactive medium. Iron hydroxy carbonate (chukanovite) is frequently observed as a secondary mineral precipitate in granular iron PRBs. Mineralogical characterization was carried out using X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and X-ray absorption spectroscopy on materials collected from three field-based PRBs in the US (East Helena, MT; Elizabeth City, NC; Denver Federal Center, CO). These PRBs were installed to treat a range of contaminants, including chlorinated organics, hexavalent chromium, and arsenic. Results obtained indicate that chukanovite is a prevalent secondary precipitate in the PRBs. Laboratory experiments on high-purity chukanovite separates were carried out to constrain the room-temperature solubility for this mineral. An estimated Gibbs energy of formation ({Delta}{sub f}G{sup o}) for chukanovite is - 1174.4 {+-} 6 kJ/mol. A mineral stability diagram is consistent with observations from the field. Water chemistry from the three reactive barriers falls inside the predicted stability field for chukanovite, at inorganic carbon concentrations intermediate to the stability fields of siderite and ferrous hydroxide. These new data will aid in developing better predictive models of mineral accumulation in zerovalent iron PRBs.

  5. Iron hydroxy carbonate formation in zerovalent iron permeable reactive barriers: characterization and evaluation of phase stability.

    PubMed

    Lee, Tony R; Wilkin, Richard T

    2010-07-30

    Predicting the long-term potential of permeable reactive barriers for treating contaminated groundwater relies on understanding the endpoints of biogeochemical reactions between influent groundwater and the reactive medium. Iron hydroxy carbonate (chukanovite) is frequently observed as a secondary mineral precipitate in granular iron PRBs. Mineralogical characterization was carried out using X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and X-ray absorption spectroscopy on materials collected from three field-based PRBs in the US (East Helena, MT; Elizabeth City, NC; Denver Federal Center, CO). These PRBs were installed to treat a range of contaminants, including chlorinated organics, hexavalent chromium, and arsenic. Results obtained indicate that chukanovite is a prevalent secondary precipitate in the PRBs. Laboratory experiments on high-purity chukanovite separates were carried out to constrain the room-temperature solubility for this mineral. An estimated Gibbs energy of formation (Delta(f)G degrees) for chukanovite is -1174.4 +/- 6 kJ/mol. A mineral stability diagram is consistent with observations from the field. Water chemistry from the three reactive barriers falls inside the predicted stability field for chukanovite, at inorganic carbon concentrations intermediate to the stability fields of siderite and ferrous hydroxide. These new data will aid in developing better predictive models of mineral accumulation in zerovalent iron PRBs. PMID:20554346

  6. Formation and Stabilization of Raphasatin and Sulforaphene from Radish Roots by Endogenous Enzymolysis

    PubMed Central

    Kim, Jae-Won; Kim, Mi-Bo; Lim, Sang-Bin

    2015-01-01

    The biologically active compounds raphasatin and sulforaphene are formed during the hydrolysis of radishes by an endogenous myrosinase. Raphasatin is very unstable, and it is generated and simultaneously degraded to less active compounds during hydrolysis in aqueous media. This study determined the hydrolysis conditions to maximize the formation of raphasatin and sulforaphene by an endogenous myrosinase and minimize their degradation during the hydrolysis of radish roots. The reaction parameters, such as the reaction medium, reaction time, type of mixing, and reaction temperature were optimized. A stability test for raphasatin and sulforaphene was also performed during storage of the hydrolyzed products at 25°C for 10 days. The formation and breakdown of raphasatin and sulforaphene in radish roots by endogenous enzymolysis was strongly influenced by the reaction medium, reaction time, and type of mixing. The production and stabilization of raphasatin in radishes was efficient in water and dichloromethane with shaking for 15 min at 25°C. For sulforaphene, the favorable condition was water as the reaction medium without shaking for 10 min at 25°C. The maximum yields of raphasatin and sulforaphene were achieved in a concurrent hydrolysis reaction without shaking in water for 10 min and then with shaking in dichloromethane for 15 min at 25°C. Under these conditions, the yields of raphasatin and sulforaphene were maximized at 12.89 and 1.93 μmol/g of dry radish, respectively. The stabilities of raphasatin and sulforaphene in the hydrolyzed products were 56.4% and 86.5% after 10 days of storage in water and dichloromethane at 25°C. PMID:26175999

  7. Formation and Stabilization of Raphasatin and Sulforaphene from Radish Roots by Endogenous Enzymolysis.

    PubMed

    Kim, Jae-Won; Kim, Mi-Bo; Lim, Sang-Bin

    2015-06-01

    The biologically active compounds raphasatin and sulforaphene are formed during the hydrolysis of radishes by an endogenous myrosinase. Raphasatin is very unstable, and it is generated and simultaneously degraded to less active compounds during hydrolysis in aqueous media. This study determined the hydrolysis conditions to maximize the formation of raphasatin and sulforaphene by an endogenous myrosinase and minimize their degradation during the hydrolysis of radish roots. The reaction parameters, such as the reaction medium, reaction time, type of mixing, and reaction temperature were optimized. A stability test for raphasatin and sulforaphene was also performed during storage of the hydrolyzed products at 25°C for 10 days. The formation and breakdown of raphasatin and sulforaphene in radish roots by endogenous enzymolysis was strongly influenced by the reaction medium, reaction time, and type of mixing. The production and stabilization of raphasatin in radishes was efficient in water and dichloromethane with shaking for 15 min at 25°C. For sulforaphene, the favorable condition was water as the reaction medium without shaking for 10 min at 25°C. The maximum yields of raphasatin and sulforaphene were achieved in a concurrent hydrolysis reaction without shaking in water for 10 min and then with shaking in dichloromethane for 15 min at 25°C. Under these conditions, the yields of raphasatin and sulforaphene were maximized at 12.89 and 1.93 μmol/g of dry radish, respectively. The stabilities of raphasatin and sulforaphene in the hydrolyzed products were 56.4% and 86.5% after 10 days of storage in water and dichloromethane at 25°C. PMID:26175999

  8. Magnetic microparticle-based multimer detection system for the detection of prion oligomers in sheep

    PubMed Central

    Lim, Kuntaek; Kim, Su Yeon; Lee, Byoungsub; Segarra, Christiane; Kang, Sungmin; Ju, Youngran; Schmerr, Mary Jo; Coste, Joliette; Kim, Sang Yun; Yokoyama, Takashi; An, Seong Soo A

    2015-01-01

    Transmissible spongiform encephalopathies (TSEs) are zoonotic fatal neurodegenerative diseases in animals and humans. TSEs are commonly known as bovine spongiform encephalopathy in cattle, scrapie in sheep and goats, chronic wasting disease in cervids, and Creutzfeldt–Jakob disease in humans. The putative transmissible agents are infectious prion proteins (PrPSc), which are formed by the conversion of the normal prion protein on the glycoprotein cell surface in the presence of other PrPSc. Reports of the transmission of TSEs through blood raised considerable concern about the safety of blood and blood products. To address this issue, many laboratories attempted to develop a sensitive and accurate blood diagnostic test to detect PrPSc. Previously, we reported that, compared to normal controls, the multimer detection system (MDS) was more efficient in detecting PrPSc in infected hamster brain homogenate, mouse plasma spiked with purified PrPSc from scrapie mouse brain, and scrapie-infected hamster plasmas. MDS differentiates prion multimers from the cellular monomer through the multimeric expression of epitopes on prion multimers, in contrast to the monomeric form. In this study, MDS detected PrPSc in plasma samples from scrapie-infected sheep expressing clinical symptoms, demonstrating 100% sensitivity and specificity in these samples. Plasma samples from asymptomatic lambs at the preclinical stage (8-month-old naturally infected offspring of scrapie-infected parents expressing a highly susceptible genotype) tested positive with 50% sensitivity and 100% specificity. In the first of two coded analyses using clinical scrapie-infected sheep and normal healthy samples, MDS successfully identified all but one of the clinical samples with 92% sensitivity and 100% specificity. Similar results were obtained in the second coded analysis using preclinical samples. MDS again successfully identified all but one of the samples with 87% sensitivity and 100% specificity. The

  9. Magnetic microparticle-based multimer detection system for the detection of prion oligomers in sheep.

    PubMed

    Lim, Kuntaek; Kim, Su Yeon; Lee, Byoungsub; Segarra, Christiane; Kang, Sungmin; Ju, Youngran; Schmerr, Mary Jo; Coste, Joliette; Kim, Sang Yun; Yokoyama, Takashi; An, Seong Soo A

    2015-01-01

    Transmissible spongiform encephalopathies (TSEs) are zoonotic fatal neurodegenerative diseases in animals and humans. TSEs are commonly known as bovine spongiform encephalopathy in cattle, scrapie in sheep and goats, chronic wasting disease in cervids, and Creutzfeldt-Jakob disease in humans. The putative transmissible agents are infectious prion proteins (PrP(Sc)), which are formed by the conversion of the normal prion protein on the glycoprotein cell surface in the presence of other PrP(Sc). Reports of the transmission of TSEs through blood raised considerable concern about the safety of blood and blood products. To address this issue, many laboratories attempted to develop a sensitive and accurate blood diagnostic test to detect PrP(Sc). Previously, we reported that, compared to normal controls, the multimer detection system (MDS) was more efficient in detecting PrP(Sc) in infected hamster brain homogenate, mouse plasma spiked with purified PrP(Sc) from scrapie mouse brain, and scrapie-infected hamster plasmas. MDS differentiates prion multimers from the cellular monomer through the multimeric expression of epitopes on prion multimers, in contrast to the monomeric form. In this study, MDS detected PrP(Sc) in plasma samples from scrapie-infected sheep expressing clinical symptoms, demonstrating 100% sensitivity and specificity in these samples. Plasma samples from asymptomatic lambs at the preclinical stage (8-month-old naturally infected offspring of scrapie-infected parents expressing a highly susceptible genotype) tested positive with 50% sensitivity and 100% specificity. In the first of two coded analyses using clinical scrapie-infected sheep and normal healthy samples, MDS successfully identified all but one of the clinical samples with 92% sensitivity and 100% specificity. Similar results were obtained in the second coded analysis using preclinical samples. MDS again successfully identified all but one of the samples with 87% sensitivity and 100

  10. Dew formation characteristics in a revegetation-stabilized desert ecosystem in Shapotou area, Northern China

    NASA Astrophysics Data System (ADS)

    Pan, Yan-xia; Wang, Xin-ping; Zhang, Ya-feng

    2010-06-01

    SummarySoil moisture in the upper layer plays an important role in arid desert ecosystems. Dew as an additional source of fresh water, may have a positive impact upon the ecosystems in arid and semi-arid zones. Measurements on dew formation amount and duration were carried out in the whole October of 2008 at different condensing surface types (bare dune sands, physical soil crusts and biological soil crusts) associated with different inter-space positions between plants, and at the area under plant canopy in a revegetation-stabilized arid desert ecosystem in Shapotou area, China. The results indicated that there was a positive linear correlation between dew amounts and relative humidity, while mean temperature was negatively linearly related to dew amounts and no significant relationship was found between dew amounts and wind speed. Clear and foggy mornings were characterized by higher dew amounts and longer dew duration, whereas less dew was recorded during cloudy and especially windy mornings. Crusts, especially the biological soil crusts, obtained significantly higher amounts of dew than that of bare moving sand dunes. It was more difficult for dew to condense under the canopy of the plants than on the bare sand dunes. At the first stage of ecological engineering projects, dew can renew the moisture losing through the evaporation of soil and transpiration of leaves, and thus can supply important source of water for xerophytic shrubs. The higher dew amount at the inter-space of re-vegetated plants is an important driving factor for the growth of microorganisms and spore plants, which further accelerate the formation of biological soil crusts and stabilization of moving sand dunes. The presence of biological soil crusts, in turn, helps to facilitate the formation of dew. Therefore, a mutual enhanced effect exists between dew and artificially revegetation ecosystems.

  11. Studies on the formation and stability of triplex DNA using fluorescence correlation spectroscopy.

    PubMed

    Hu, Hongyan; Huang, Xiangyi; Ren, Jicun

    2016-05-01

    Triplex DNA has become one of the most useful recognition motifs in the design of new molecular biology tools, therapeutic agents and sophisticated DNA-based nanomaterials because of its direct recognition of natural double-stranded DNA. In this paper, we developed a sensitive and microscale method to study the formation and stability characterization of triplex DNA using fluorescence correlation spectroscopy (FCS). The principle of this method is mainly based on the excellent capacity of FCS for sensitively distinguishing between free single-strand DNA (ssDNA) fluorescent probes and fluorescent probe-double-strand DNA (dsDNA) hybridized complexes. First, we systematically investigated the experimental conditions of triplex DNA formation. Then, we evaluated the equilibrium association constants (Ka ) under different ssDNA probe lengths, composition and pH. Finally, we used FCS to measure the hybridization fraction of a 20-mer perfectly matched ssDNA probe and three single-base mismatched ssDNA probes with 146-mer dsDNA. Our data illustrated that FCS is a useful tool for the direct determination of the thermodynamic parameters of triplex DNA formation and discrimination of a single-base mismatch of triplex DNA without denaturation. Compared with current methods, our method is characterized by high sensitivity, good universality and small sample and reagent requirements. More importantly, our method has the potential to become a platform for triplex DNA research in vitro. Copyright © 2015 John Wiley & Sons, Ltd. PMID:26377428

  12. Chondroitin 6-Sulfation Regulates Perineuronal Net Formation by Controlling the Stability of Aggrecan

    PubMed Central

    Miyata, Shinji; Kitagawa, Hiroshi

    2016-01-01

    Perineuronal nets (PNNs) are lattice-like extracellular matrix structures composed of chondroitin sulfate proteoglycans (CSPGs). The appearance of PNNs parallels the decline of neural plasticity, and disruption of PNNs reactivates neural plasticity in the adult brain. We previously reported that sulfation patterns of chondroitin sulfate (CS) chains on CSPGs influenced the formation of PNNs and neural plasticity. However, the mechanism of PNN formation regulated by CS sulfation remains unknown. Here we found that overexpression of chondroitin 6-sulfotransferase-1 (C6ST-1), which catalyzes 6-sulfation of CS chains, selectively decreased aggrecan, a major CSPG in PNNs, in the aged brain without affecting other PNN components. Both diffuse and PNN-associated aggrecans were reduced by overexpression of C6ST-1. C6ST-1 increased 6-sulfation in both the repeating disaccharide region and linkage region of CS chains. Overexpression of 6-sulfation primarily impaired accumulation of aggrecan in PNNs, whereas condensation of other PNN components was not affected. Finally, we found that increased 6-sulfation accelerated proteolysis of aggrecan by a disintegrin and metalloproteinase domain with thrombospondin motif (ADAMTS) protease. Taken together, our results indicate that sulfation patterns of CS chains on aggrecan influenced the stability of the CSPG, thereby regulating formation of PNNs and neural plasticity. PMID:27057358

  13. Centlein, a novel microtubule-associated protein stabilizing microtubules and involved in neurite formation.

    PubMed

    Jing, Zhenli; Yin, Huilong; Wang, Pan; Gao, Juntao; Yuan, Li

    2016-04-01

    We have previously reported that the centriolar protein centlein functions as a molecular link between C-Nap1 and Cep68 to maintain centrosome cohesion [1]. In this study, we identified centlein as a novel microtubule-associated protein (MAP), directly binding to purified microtubules (MTs) via its longest coiled-coil domain. Overexpression of centlein caused profound nocodazole- and cold-resistant MT bundles, which also relied on its MT-binding domain. siRNA-mediated centlein depletion resulted in a significant reduction in tubulin acetylation level and overall fluorescence intensity of cytoplasmic MT acetylation. Centlein was further characterized in neurons. We found that centlein overexpression inhibited neurite formation in retinoic acid (RA)-induced SH-SY5Y and N2a cells. Taken together, we propose that centlein is involved in MT stability and neuritogenesis in vivo. PMID:26915804

  14. Generalized Momentum Control of the Spin-Stabilized Magnetospheric Multiscale Formation

    NASA Technical Reports Server (NTRS)

    Queen, Steven Z.; Shah, Neerav; Benegalrao, Suyog S.; Blackman, Kathie

    2015-01-01

    The Magnetospheric Multiscale (MMS) mission consists of four identically instrumented, spin-stabilized observatories elliptically orbiting the Earth in a tetrahedron formation. The on-board attitude control system adjusts the angular momentum of the system using a generalized thruster-actuated control system that simultaneously manages precession, nutation and spin. Originally developed using Lyapunov control-theory with rate-feedback, a published algorithm has been augmented to provide a balanced attitude/rate response using a single weighting parameter. This approach overcomes an orientation sign-ambiguity in the existing formulation, and also allows for a smoothly tuned-response applicable to both a compact/agile spacecraft, as well as one with large articulating appendages.

  15. The DYNAFLUX / DYNACOLD Network: Dynamics, Fluxes, Stability, Succession and Landscape Formation in Cold Environments

    NASA Astrophysics Data System (ADS)

    Beylich, A. A.; Molau, U.

    2012-04-01

    Within Europe there is a wide array of high-latitude and high-altitude landscapes, covering a significant proportion of the total land area. These cold climate landscapes represent a variety of stages of deglaciation history and landscape formation. We find landscapes at different levels of postglacial stabilization providing the unique possibility to study the interactions between geo-, bio-, social and socio-economic systems at the land surface. The DYNAFLUX / DYNACOLD Network (2004 - ) bridges across geo-, bio-, social and socio-economic sciences in order to investigate the complex dynamics of stabilization, succession and landscape formation during and after ice retreat and under human impact. DYNAFLUX / DYNACOLD provides a multidisciplinary forum where research groups come together. The integrated approach provides - in addition to newly generated disciplinary knowledge - the qualitative and quantitative linkages of findings from geo-, bio- and socio-work groups to develop a systems-based holistic level-of-understanding about the dynamics of environmental fluxes in high-latitude and high-altitude geo-ecosystems and landscapes. This knowledge can be used to assess the risks and potentials of the future development with reference to land use intensity / changes and climatic dynamics. DYNAFLUX / DYNACOLD is since 2004 linking and integrating a number of networks and programmes and creates an umbrella programme and a forum for sharing knowledge. The focus of the Network is relevant for different end users, including risk and vulnerability assessment, sustainable land use, land management and conservation. Also questions with regards to Global Change are addressed (hazards, permafrost degradation, loss of biodiversity, etc.).

  16. Dynamical Stability of Imaged Planetary Systems in Formation: Application to HL Tau

    NASA Astrophysics Data System (ADS)

    Tamayo, D.; Triaud, A. H. M. J.; Menou, K.; Rein, H.

    2015-06-01

    A recent Atacama Large Millimeter/Submillimeter Array image revealed several concentric gaps in the protoplanetary disk surrounding the young star HL Tau. We consider the hypothesis that these gaps are carved by planets, and present a general framework for understanding the dynamical stability of such systems over typical disk lifetimes, providing estimates for the maximum planetary masses. We collect these easily evaluated constraints into a workflow that can help guide the design and interpretation of new observational campaigns and numerical simulations of gap opening in such systems. We argue that the locations of resonances should be significantly shifted in massive disks like HL Tau, and that theoretical uncertainties in the exact offset, together with observational errors, imply a large uncertainty in the dynamical state and stability in such disks. This presents an important barrier to using systems like HL Tau as a proxy for the initial conditions following planet formation. An important observational avenue to breaking this degeneracy is to search for eccentric gaps, which could implicate resonantly interacting planets. Unfortunately, massive disks like HL Tau should induce swift pericenter precession that would smear out any such eccentric features of planetary origin. This motivates pushing toward more typical, less massive disks. For a nominal non-resonant model of the HL Tau system with five planets, we find a maximum mass for the outer three bodies of approximately 2 Neptune masses. In a resonant configuration, these planets can reach at least the mass of Saturn. The inner two planets’ masses are unconstrained by dynamical stability arguments.

  17. Trifluoroethanol modulates α-synuclein amyloid-like aggregate formation, stability and dissolution.

    PubMed

    Di Carlo, Maria Giovanna; Vetri, Valeria; Buscarino, Gianpiero; Leone, Maurizio; Vestergaard, Bente; Foderà, Vito

    2016-09-01

    The conversion of proteins into amyloid fibrils and other amyloid-like aggregates is closely connected to the onset of a series of age-related pathologies. Upon changes in environmental conditions, amyloid-like aggregates may also undergo disassembly into oligomeric aggregates, the latter being recognized as key effectors in toxicity. This indicates new possible routes for in vivo accumulation of toxic species. In the light of the recognized implication of α-Synuclein (αSN) in Parkinson's disease, we present an experimental study on supramolecular assembly of αSN with a focus on stability and disassembly paths of such supramolecular aggregate species. Using spectroscopic techniques, two-photon microscopy, small-angle X-ray scattering and atomic force microscopy, we report evidences on how the stability of αSN amyloid-like aggregates can be altered by changing solution conditions. We show that amyloid-like aggregate formation can be induced at high temperature in the presence of trifluoroethanol (TFE). Moreover, sudden disassembly or further structural reorganisation toward higher hierarchical species can be induced by varying TFE concentration. Our results may contribute in deciphering fundamental mechanisms and interactions underlying supramolecular clustering/dissolution of αSN oligomers in cells. PMID:27372900

  18. Oxidation Enhances Human Serum Albumin Thermal Stability and Changes the Routes of Amyloid Fibril Formation

    PubMed Central

    Sancataldo, Giuseppe; Vetri, Valeria; Foderà, Vito; Di Cara, Gianluca; Militello, Valeria; Leone, Maurizio

    2014-01-01

    Oxidative damages are linked to several aging-related diseases and are among the chemical pathways determining protein degradation. Specifically, interplay of oxidative stress and protein aggregation is recognized to have a link to the loss of cellular function in pathologies like Alzheimer's and Parkinson's diseases. Interaction between protein and reactive oxygen species may indeed induce small changes in protein structure and lead to the inhibition/modification of protein aggregation process, potentially determining the formation of species with different inherent toxicity. Understanding the temperate relationship between these events can be of utmost importance in unraveling the molecular basis of neurodegeneration. In this work, we investigated the effect of hydrogen peroxide oxidation on Human Serum Albumin (HSA) structure, thermal stability and aggregation properties. In the selected conditions, HSA forms fibrillar aggregates, while the oxidized protein undergoes aggregation via new routes involving, in different extents, specific domains of the molecule. Minute variations due to oxidation of single residues affect HSA tertiary structure leading to protein compaction, increased thermal stability, and reduced association propensity. PMID:24416244

  19. Emulsification by high frequency ultrasound using piezoelectric transducer: formation and stability of emulsifier free emulsion.

    PubMed

    Kaci, Messaouda; Meziani, Smail; Arab-Tehrany, Elmira; Gillet, Guillaume; Desjardins-Lavisse, Isabelle; Desobry, Stephane

    2014-05-01

    Emulsifier free emulsion was developed with a new patented technique for food and cosmetic applications. This emulsification process dispersed oil droplets in water without any emulsifier. Emulsions were prepared with different vegetable oil ratios 5%, 10% and 15% (v/v) using high frequency ultrasounds generated by piezoelectric ceramic transducer vibrating at 1.7 MHz. The emulsion was prepared with various emulsification times between 0 and 10h. Oil droplets size was measured by laser granulometry. The pH variation was monitored; electrophoretic mobility and conductivity variation were measured using Zêtasizer equipment during emulsification process. The results revealed that oil droplets average size decreased significantly (p<0.05) during the first 6h of emulsification process and that from 160 to 1 μm for emulsions with 5%, 10% and from 400 to 29 μm for emulsion with 15% of initial oil ratio. For all tested oil ratios, pH measurement showed significant decrease and negative electrophoretic mobility showed the accumulation of OH(-) at oil/water interface leading to droplets stability in the emulsion. The conductivity of emulsions showed a decrease of the ions quantity in solution, which indicated formation of positive charge layer around OH(-) structure. They constitute a double ionic layer around oil particles providing emulsion stability. This study showed a strong correlation between turbidity measurement and proportion of emulsified oil. PMID:24315670

  20. Energy approach to rivalry dynamics, soliton stability, and pattern formation in neuronal networks

    NASA Astrophysics Data System (ADS)

    Loxley, P. N.; Robinson, P. A.

    2007-10-01

    Hopfield’s Lyapunov function is used to view the stability and topology of equilibria in neuronal networks for visual rivalry and pattern formation. For two neural populations with reciprocal inhibition and slow adaptation, the dynamics of neural activity is found to include a pair of limit cycles: one for oscillations between states where one population has high activity and the other has low activity, as in rivalry, and one for oscillations between states where both populations have the same activity. Hopfield’s Lyapunov function is used to find the dynamical mechanism for oscillations and the basin of attraction of each limit cycle. For a spatially continuous population with lateral inhibition, stable equilibria are found for local regions of high activity (solitons) and for bound states of two or more solitons. Bound states become stable when moving two solitons together minimizes the Lyapunov function, a result of decreasing activity in regions between peaks of high activity when the firing rate is described by a sigmoid function. Lowering the barrier to soliton formation leads to a pattern-forming instability, and a nonlinear solution to the dynamical equations is found to be given by a soliton lattice, which is completely characterized by the soliton width and the spacing between neighboring solitons. Fluctuations due to noise create lattice vacancies analogous to point defects in crystals, leading to activity which is spatially inhomogeneous.

  1. Stabilization and breakdown of Archean Cratons: Formation of sedimentary basins, mafic magmatism, and metallogenic productivity

    NASA Astrophysics Data System (ADS)

    Rosen, O. M.

    2011-01-01

    The Kenorland supercontinent was created as a result of the ascent of the most powerful mantle plumes in the Earth’s geological history and accompanied by the formation of the continental crust and its subsequent accretion into a supercontinent 2.7 Ga ago. The geological phenomena that occurred at that time in Australia, Canada, and South Africa reflecting its features are considered in this paper. The first sedimentary basins resting upon the sialic basement give evidence for long-existing peneplanes formed in the Early Precambrian, i.e., for stabilization of the underlying cratons; this is also supported by the appearance of rapakivi granite 2.8 Ga ago. The platform regime existed as early as the Mesoarchean 3.5 Ga ago. The platform sedimentary basins developed almost continuously over a billion years. Layered mafic intrusions were frequently emplaced into sedimentary sequences. Unique gold, uranium, PGE, chrome, and other deposits are hosted in sedimentary basins and layered intrusions. The extremely high intensity of plume activity determined the origin and breakdown of the Kenorland supercontinent and the cause of transport of ore elements concentrated in unique deposits. In terms of the intensity of plume-related magmatism and ore formation, the considered period of geological history has no more recent analogues and was critical for the Earth’s evolution.

  2. Stabilization of a β-hairpin in monomeric Alzheimer's amyloid-β peptide inhibits amyloid formation

    PubMed Central

    Hoyer, Wolfgang; Grönwall, Caroline; Jonsson, Andreas; Ståhl, Stefan; Härd, Torleif

    2008-01-01

    According to the amyloid hypothesis, the pathogenesis of Alzheimer's disease is triggered by the oligomerization and aggregation of the amyloid-β (Aβ) peptide into protein plaques. Formation of the potentially toxic oligomeric and fibrillar Aβ assemblies is accompanied by a conformational change toward a high content of β-structure. Here, we report the solution structure of Aβ(1–40) in complex with the phage-display selected affibody protein ZAβ3, a binding protein of nanomolar affinity. Bound Aβ(1–40) features a β-hairpin comprising residues 17–36, providing the first high-resolution structure of Aβ in β conformation. The positions of the secondary structure elements strongly resemble those observed for fibrillar Aβ. ZAβ3 stabilizes the β-sheet by extending it intermolecularly and by burying both of the mostly nonpolar faces of the Aβ hairpin within a large hydrophobic tunnel-like cavity. Consequently, ZAβ3 acts as a stoichiometric inhibitor of Aβ fibrillation. The selected Aβ conformation allows us to suggest a structural mechanism for amyloid formation based on soluble oligomeric hairpin intermediates. PMID:18375754

  3. Theoretical study of polyiodide formation and stability on monolayer and bilayer graphene.

    PubMed

    Tristant, Damien; Puech, Pascal; Gerber, Iann C

    2015-11-28

    The presence of polyiodide complexes have been reported several times when carbon-based materials were doped by iodine molecules, but their formation mechanism remains unclear. By using first-principles calculations that include nonlocal correlation effects by means of a van der Waals density functional approach, we propose that the formation of triiodide (I3(-)) and pentaiodide (I5(-)) is due to a large density of iodine molecules (I2) in interaction with a carbonaceous substrate. As soon as the concentration of surface iodine reaches a threshold value of 12.5% for a graphene monolayer and 6.25% for a bilayer, these complexes spontaneously appear. The corresponding structural and energetic aspects, electronic structures and vibrational frequencies support this statement. An upshift of the Dirac point from the Fermi level with values of 0.45 and 0.52 eV is observed for adsorbed complexes on graphene and intercalated complexes between two layers, respectively. For doped-graphene, it corresponds to a graphene hole density of around 1.1 × 10(13) cm(-2), in quantitative agreement with experiments. Additionally, we have studied the thermal stability at room temperature of these adsorbed ions on graphene by means of ab initio molecular dynamics, which also shows successful p-doping with polyiodide complexes. PMID:26497888

  4. Formation and stability of ridge-ridge-ridge triple junctions in rheologically realistic lithosphere model

    NASA Astrophysics Data System (ADS)

    Gerya, Taras; Burov, Evgueni

    2015-04-01

    Triple junctions are probably the most remarkable features of plate boundaries since their presence constitutes one of the major demonstrations of plate tectonics theory. Divergent (R-R-R) triple junctions (at 120° and T junctions) are particular ones since their stability depends on the exact values of the relative velocities of plate divergence and hence is strongly affected by plate rheology and processes of crustal accretion. The mechanisms of their formation and long-term steadiness are not well understood even though it is commonly accepted, generally based on common sense, that the geometry and stability of triple junctions should be related to the intuitively acceptable geometric considerations that 3-branch configurations should be "stable" over the time on a 3D Earth surface. That said, most plate boundaries are in fact 2D in terms that they involve only two plates, while junctions with 3 and more branches, if even mechanically not excluded, are generally short-lived and hence rarely observed at tectonic scale. Indeed, it has been long-time suggested that triple junctions result from evolution of short-lived quadruple junctions, yet, without providing a consistent mechanical explanation or experimental demonstration of this process, due to the rheological complexity of the lithosphere and that of strain localization and crustal accretion processes. For example, it is supposed that R-R-R junctions form as result of axisymmetric mantle upwellings. However, impingement of buoyant fluid on a non-pre-stressed lithosphere should result in multiple radial cracks, as is well known from previous analog and numerical experiments. In case of uni-directionally pre-stressed lithosphere, it has also shown that linear 2D rift structures should be formed. Therefore, a complete 3D thermos-mechanically consistent approach is needed to understand the processes of formation of multi-branch junctions. With this goal we here reproduce and study the processes of multi

  5. Mechanism of Formation and Stabilization of Nanoparticles Produced by Heating Electrostatic Complexes of WPI-Dextran Conjugate and Chondroitin Sulfate.

    PubMed

    Dai, Qingyuan; Zhu, Xiuling; Yu, Jingyang; Karangwa, Eric; Xia, Shuqin; Zhang, Xiaoming; Jia, Chengsheng

    2016-07-13

    Protein conformational changes were demonstrated in biopolymer nanoparticles, and molecular forces were studied to elucidate the formation and stabilization mechanism of biopolymer nanoparticles. The biopolymer nanoparticles were prepared by heating electrostatic complexes of whey protein isolate (WPI)-dextran conjugate (WD) and chondroitin sulfate (ChS) above the denaturation temperature and near the isoelectric point of WPI. The internal characteristics of biopolymer nanoparticles were analyzed by several spectroscopic techniques. Results showed that grafted dextran significantly (p < 0.05) prevented the formation of large aggregates of WD dispersion during heat treatment. However, heat treatment slightly induced the hydrophobicity changes of the microenvironment around fluorophores of WD. ChS electrostatic interaction with WD changed the fluorescence intensity of WD regardless of heat treatment. Far-UV circular dichroism (CD) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopies confirmed that glycosylation and ionic polysaccharide did not significantly cause protein conformational changes in WD and ChS (WDC) during heat treatment. In addition, hydrophobic bonds were the major molecular force for the formation and stabilization of biopolymer nanoparticles. However, hydrogen bonds slightly influenced their formation and stabilization. Ionic bonds only promoted the formation of biopolymer nanoparticles, while disulfide bonds partly contributed to their stability. This work will be beneficial to understand protein conformational changes and molecular forces in biopolymer nanoparticles, and to prepare the stable biopolymer nanoparticles from heating electrostatic complexes of native or glycosylated protein and polysaccharide. PMID:27329490

  6. Increased von Willebrand factor antigen and high molecular weight multimers in sickle cell disease associated with nocturnal hypoxemia.

    PubMed

    Krishnan, Suba; Siegel, Jamie; Pullen, Gene; Hevelow, Megan; Dampier, Carlton; Stuart, Marie

    2008-01-01

    We evaluated vWF profiles in children and adolescents with SCD and sleep hypoxemia. Mean vWF:Ag levels were significantly elevated in the SCD-hypoxemia group when compared with SCD-normoxia and control groups (p=0.007); and correlated inversely with pulse oximetry (r=-0.54, p=0.01). Densitographic analyses of vWF multimer distribution also showed an inverse correlation between %HMW-multimers and oxygen saturation (r=-0.62, p=0.03). The previously reported association between nocturnal desaturation and SCD vascular complications, including stroke, may be influenced by hypoxemic modulation of vWF as noted in this study. PMID:18230405

  7. Formation, stability, and solubility of metal oxide nanoparticles: Surface entropy, enthalpy, and free energy of ferrihydrite

    NASA Astrophysics Data System (ADS)

    Hiemstra, Tjisse

    2015-06-01

    Ferrihydrite (Fh) is an excellent model for understanding nanoparticle behavior in general. Moreover, Fh is one of the most important Fe (hydr) oxides in nature. Fh particles can be extremely small leading to a very high reactive surface area that changes its chemical potential, strongly affecting the solubility, nucleation, and stability. These characteristics can be coupled to the interfacial Gibbs free energy, being γ = 0.186 ± 0.01 J m-2 for Fh. The surface free energy has a relatively large contribution of surface entropy (-TSsurf = +0.079 ± 0.01 J m-2). The surface entropy is primarily related to the formation of surface groups by chemisorption of water (-17.1 J mol-1 K-1), for Fh equivalent with +0.064 ± 0.002 J m-2 at a surface loading NH2O = 12.6 μmol m-2. The entropy contribution of physisorbed water has been estimated by analyzing, as model, the surface enthalpy, entropy, and Gibbs free energy of the principal interfaces of H2O, i.e. ice-water-gas. It is about 20% of the contribution of chemisorbed water. The surface enthalpy of Fh is exceptionally low (Hsurf = +0.107 ± 0.01 J m-2), which can be explained by surface depletion (SD) of relatively unstable Fe polyhedra, or similarly, by additional surface loading of the non-depleted mineral core with specific Fe polyhedra for stabilization. The experimental enthalpy of Fh formation varies linearly with the surface area and correctly predicts the enthalpy value for the mineral core (-405.2 ± 1.2 kJ mol FeO3/2), being similar to the literature value for Fh as virtual bulk material (-406.7 ± 1.5 kJ mol FeO3/2) obtained with MO/DFT computations. The thermochemical quantities of the mineral core and surface are essentially the same for the entire range of Fh samples, in line with the SD model. The solubility of Fh suspensions as a whole may differ from the behavior of individual particles due to polydispersity. For 2-line Fh, the overall solubility is log Kso ∼ -38.5 ± 0.1 and for prolongedly aged 6

  8. Partial reactivation of a huge deep-seated ancient rock slide: recognition, formation mechanism, and stability

    NASA Astrophysics Data System (ADS)

    Tang, Minggao; Xu, Qiang; Li, Yusheng; Huang, Runqiu; Rengers, Niek; Zhu, Xing

    2016-08-01

    About 18 years ago, a large-scale discontinuous layer in properties and colour was found in the new Fengjie town at the shore of the Three Gorges Reservoir area in China. There are many resettled residents and buildings on the sloping area, the safety of which is potentially affected by this layer, so it has become the focus of attention. Before this study started there were two viewpoints regarding the origin of this layer. One was that is was from a huge ancient slide and the other was that is was from a fault graben. In order to find out how it was formed and to be able to carry out a stability analysis of the slope the authors have carried out a research program, including geological field investigations and mapping, a deep drilling hole, a geotechnical centrifuge model test, and a simulation analysis. The results of the research led to the conclusion that the layer is the sliding plane of a huge deep-seated ancient rock slide, which we called the Sanmashan landslide. An important argument for the conclusion is the recognition of a regional compressive tectonic stress field in this area, which cannot lead to the formation of a fault graben because it needs a tensional tectonic stress field. Moreover, numerous unique geological features, sliding marks, and other relics of the ancient slide have been discovered in the field. The formation process of the ancient slide could be repeated in a large geotechnical centrifuge model test. The test shows that a deformation and failure process of "creep-crack-cut" has occurred. The type of the ancient slide can be classified as a "successive rotational rock slide". Finally, the role of seepage in the stability of the Sanmashan landslide has been analysed. Our final conclusions are that, during rainfall and filling-drawdown cycles in the Three Gorges Reservoir, the Sanmashan landslide as a whole is dormant and stable and the secondary landslides in the toe area of the slope are presently stable but can be reactivated. This

  9. Effect of chain length on the formation and stability of synthetic alpha-helical coiled coils.

    PubMed

    Su, J Y; Hodges, R S; Kay, C M

    1994-12-27

    A series of polypeptides containing 9, 12, 16, 19, 23, 26, 30, 33, and 35 amino acid residues was designed to investigate the effects of peptide chain length on the formation and stability of two-stranded alpha-helical dimers or coiled coils. These peptides were synthesized by the solid-phase method, purified by reversed-phase high-performance liquid chromatography (RP-HPLC), and characterized by RP-HPLC, amino acid composition analysis, and mass spectrometry. The amphipathic alpha-helical peptides were designed to dimerize by interchain hydrophobic interactions at positions a and d and interchain salt bridges between lysine and glutamic acid residues at positions e and g of the repeating heptad sequence of Glu-Ile-Glu-Ala-Leu-Lys-Ala (g-a-b-c-d-e-f). The ability of these peptides to form alpha-helical structures in the presence and absence of a helix-inducing reagent (trifluoroethanol) was monitored by circular dichroism spectroscopy. The helicity of the peptides increased with increasing chain length in a cooperative manner. A minimum of three heptads corresponding to six helical turns was required for a peptide to adopt the two-stranded alpha-helical coiled coil conformation in aqueous medium. The increased stability of the peptides as a result of an increase in hydrophobic interactions (chain length) was demonstrated by the shift in the transitions of the guanidine hydrochloride (Gdn.HCl) denaturation and thermal unfolding profiles. The concentrations of denaturant (Gdn.HCl) required to achieve 50% denaturation are 3.2, 4.9, 6.9, and 7.5 M for peptides 23r, 26r, 30r, and 33r, respectively, in aqueous medium. However, the effect of a chain length increase on coiled-coil stability was not additive. The melting temperature, Tm, at which 50% of the helicity is lost, increased by 34 degrees C in changing the peptide chain length from 23 to 26; however, that shift was only 14 degrees C when the chain length was increased from 30 to 33 residues. These results are

  10. Green rust nanoparticle formation, stability and oxidation, and its role in natural and engineered systems

    NASA Astrophysics Data System (ADS)

    Shaw, S.; Benning, L.; Ahmed, I.; Kakonyi, G.; Sumoondur, A.; Terrill, N.

    2009-12-01

    Highly reactive green rust (GR) nanoparticles are believed to play an important role in the geochemistry of water saturated sediments (e.g. hydromorphic soils) and engineered systems where zero-valent iron is used for decontaminating polluted sites (e.g. permeable reactive barriers). The presence of structural Fe2+ within GR and its high specific surface area make it an effective reductant for many inorganic (e.g. Cr, U, Se) and organic substances (e.g. tetrachloroethene (TCE)). These reduction processes can lead to breakdown of organic molecules or the formation of insoluble reduced inorganic phases (e.g., UO2(s)), thus reducing the bioavailability of these toxic compounds. Understanding the formation and geochemical stability of GR is key to assessing its potential role in natural sediments and engineered environments. However, characterizing GR is difficult due to the rapid oxidation (seconds - minutes) of structural Fe2+ in the presence of air. Thus, to obtain detailed information about the mechanism and kinetics of GR formation, stabilisation and oxidative breakdown, novel synchrotron-based methods have been developed which combine in situ and time-resolved X-ray diffraction/scattering (XRD/SAXS) analysis with controlled anaerobic chemical synthesis. This system allowed the simultaneous quantification of several chemical parameters in the aqueous solution (i.e., pH, Eh) with detailed analysis of the changes in the solid phase crystal structure. In conjunction with this X-ray Absorption Spectroscopy (XAS) was used to characterise the speciation of trace elements (i.e. U, Zn and Se) associated with GR as it crystallised and/or transformed. The formation of green rust (Fe2+/Fe3+ > 1.2) from solution occurs via a 3 stage process. The first stage is the nucleation and growth of ferric hydroxysulfate (schwertmannite) nanoparticles (~5 nm). With increasing pH the schwertmannite transforms into nanogoethite particles (< 50 nm). This process is catalyzed by adsorbed Fe

  11. Modulation of the respiratory supercomplexes in yeast: enhanced formation of cytochrome oxidase increases the stability and abundance of respiratory supercomplexes.

    PubMed

    Cui, Tie-Zhong; Conte, Annalea; Fox, Jennifer L; Zara, Vincenzo; Winge, Dennis R

    2014-02-28

    Yeast cells deficient in the Rieske iron-sulfur subunit (Rip1) of ubiquinol-cytochrome c reductase (bc1) accumulate a late core assembly intermediate, which weakly associates with cytochrome oxidase (CcO) in a respiratory supercomplex. Expression of the N-terminal half of Rip1, which lacks the C-terminal FeS-containing globular domain (designated N-Rip1), results in a marked stabilization of trimeric and tetrameric bc1-CcO supercomplexes. Another bc1 mutant (qcr9Δ) stalled at the same assembly intermediate is likewise converted to stable supercomplex species by the expression of N-Rip1, but not by expression of intact Rip1. The N-Rip1-induced stabilization of bc1-CcO supercomplexes is independent of the Bcs1 translocase, which mediates Rip1 translocation during bc1 biogenesis. N-Rip1 induces the stabilization of bc1-CcO supercomplexes through an enhanced formation of CcO. The association of N-Rip1 with the late core bc1 assembly intermediate appears to confer stabilization of a CcO assembly intermediate. This induced stabilization of CcO is dependent on the Rcf1 supercomplex stabilization factor and only partially dependent on the presence of cardiolipin. N-Rip1 exerts a related induction of CcO stabilization in WT yeast, resulting in enhanced respiration. Additionally, the impact of CcO stabilization on supercomplexes was observed by means other than expression of N-Rip1 (via overexpression of CcO subunits Cox4 and Cox5a), demonstrating that this is a general phenomenon. This study presents the first evidence showing that supercomplexes can be stabilized by the stimulated formation of CcO. PMID:24421313

  12. Stability of formation control using a consensus protocol under directed communications with two time delays and delay scheduling

    NASA Astrophysics Data System (ADS)

    Cepeda-Gomez, Rudy; Olgac, Nejat

    2016-01-01

    We consider a linear algorithm to achieve formation control in a group of agents which are driven by second-order dynamics and affected by two rationally independent delays. One of the delays is in the position and the other in the velocity information channels. These delays are taken as constant and uniform throughout the system. The communication topology is assumed to be directed and fixed. The formation is attained by adding a supplementary control term to the stabilising consensus protocol. In preparation for the formation control logic, we first study the stability of the consensus, using the recent cluster treatment of characteristic roots (CTCR) paradigm. This effort results in a unique depiction of the non-conservative stability boundaries in the domain of the delays. However, CTCR requires the knowledge of the potential stability switching loci exhaustively within this domain. The creation of these loci is done in a new surrogate coordinate system, called the 'spectral delay space (SDS)'. The relative stability is also investigated, which has to do with the speed of reaching consensus. This step leads to a paradoxical control design concept, called the 'delay scheduling', which highlights the fact that the group behaviour may be enhanced by increasing the delays. These steps lead to a control strategy to establish a desired group formation that guarantees spacing among the agents. Example case studies are presented to validate the underlying analytical derivations.

  13. Formation and stability of lanthanide complexes and their encapsulation into polymeric microspheres

    SciTech Connect

    Mumper, R.J.; Jay, M.

    1992-10-15

    The complexation of lanthanides (Ln) with dicarbonyl compounds (acetylacetone, acac; ethyl acetoacetate; 3-ethyl-2,4-pentanedione; 2,4-hexanedione; 3-methyl-2,4-pentanedione; and diethyl malonate) was investigated using a potentiometric titration technique. The ability of a dicarbonyl compound to complex with the lanthanide elements was greatly dependent on its pK{sub a} and on the pH of the titrated solution. Selected lanthanide complexes (Ln complexes) were incorporated into spherical poly(L-lactic acid)(PLA) matrices and irradiated in a nuclear reactor with neutrons to produce short-lived high-energy {Beta}-particle-emitting radioisotopes. The lanthanides investigated (Ho, Dy, Sm, and La) were chosen on the basis of their physical and nuclear properties. A transition element (Re) was also studied. The small decrease in the ionic radii of the lanthanides with increasing atomic number led to (a) greater ability to extract and complex from an aqueous solution with complexing agents, (b) larger formation and stability constants for the Ln complexes, (c) increased solubility of the Ln complexes in chloroform, and (d) increase in the maximum percent incorporation of the stable lanthanides in PLA spheres. Ho(aca) was found to be the most promising candidate of the complexes studied on the basis of the above observations and due to the favorable physical properties of {sup 165}Ho and nuclear properties of {sup 166}Ho. 21 refs., 5 figs., 4 tabs.

  14. Silicon oxide cluster formation and stability in the laser ablation of SiO targets.

    PubMed

    Jadraque, María; Santos, Magna; Díaz, Luís; Alvarez-Ruiz, Jesús; Martín, Margarita

    2009-10-15

    The formation mechanism and stability of silicon oxide clusters observed in the ablation of SiO targets at 266 nm were investigated by time-of-flight mass spectrometry, laser-induced fluorescence (LIF), and DFT calculations. Neutral and positively charged Si(n)(+/0) and Si(n)O(m)H(0,1)(+) clusters were identified in the plume, but neutral Si(n)O(m) could not be observed. The time distribution of SiO in the plume measured by postionization with an ArF laser (Delta lambda approximately 1 nm, tau approximately 14 ns) and mass spectrometric detection was compared with that obtained by LIF with narrowband dye laser selective excitation of one specific rovibronic transition in SiO. Postionization leads to a multicomponent distribution that extends up to times near 100 micros after ablation, whereas LIF measurements obtain time distributions shorter than 20 micros. DFT calculations of several Si(n)O(m)(0/+) were performed, showing that one photon absorption of the postionization laser makes available low-energy dissociation channels of the neutrals, whereas two photon absorption is required for ionization. DFT calculations were carried out for stoichiometric H-containing clusters Si(n)O(n)H(+) (n = 1-4). For n = 1,2, the optimized geometries involve bonding of hydrogen to one oxygen atom in the clusters; for n = 3 and 4, the structures containing H-Si bonds are more stable. PMID:19810756

  15. Stimuli-responsive surfactant/phospholipid stabilized colloidal dispersions and their film formation.

    PubMed

    Lestage, David J; Yu, Min; Urban, Marek W

    2005-01-01

    Methyl methacrylate (MMA) and n-butyl acrylate (nBA) were copolymerized into stable colloidal particles in the presence of micelle forming sodium dioctyl sulfosuccinate (SDOSS) and liposome forming 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) in aqueous media that serve as thermodynamically stable loci for lipophilic monomers and nanostructured templates. These studies show for the first time that hollow colloidal particles may coalesce to form polymeric films and the combination of SDOSS and DLPC dispersing agents provides a stimuli-responsive environment during film formation through which individual surface stabilizing components can be driven to the film-air (F-A) or film-substrate (F-S) interface. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) of p-MMA/nBA colloidal dispersions revealed preferential and enhanced mobility of SDOSS and DLPC lipid rafts to the F-A and F-S interfaces in response to thermal, ionic, and enzymatic stimuli. PMID:15877379

  16. Role of the Filters in the Formation and Stabilization of Semiquinone Radicals Collected from Cigarette Smoke

    PubMed Central

    Maskos, Zofia; Dellinger, Barry

    2013-01-01

    The fractional pyrolysis of Bright tobacco was performed in nitrogen atmosphere over the temperature range of 240 – 510 °C in a specially constructed, high temperature flow reactor system. Electron paramagnetic resonance (EPR) spectroscopy was used to analyze the free radicals in the initially produced total particular matter (TPM) and in TPM after exposure to ambient air (aging). Different filters have been used to collect TPM from tobacco smoke: cellulosic, cellulose nitrate, cellulose acetate, nylon, Teflon and Cambridge. The collection of the primary radicals (measured immediately after collection of TPM on filters), the formation and stabilization of the secondary radicals (defined as radicals formed during aging of TPM samples on the filters) depend significantly on the material of the filter. A mechanistic explanation about different binding capability of the filters decreasing in the order: cellulosic < cellulose nitrate < cellulose acetate < nylon ~ teflon is presented. Different properties were observed for the Cambridge filter. Specific care must be taken using the filters for identification of radicals from tobacco smoke to avoid artifacts in each case. PMID:24265513

  17. Formation, antioxidant property and oxidative stability of cold pressed rice bran oil emulsion.

    PubMed

    Thanonkaew, Amonrat; Wongyai, Surapote; Decker, Eric A; McClements, David J

    2015-10-01

    Cold pressed rice bran oil (CPRBO) is used in foods, cosmetics, and pharmaceuticals due to its desirable health and functional attributes. The purpose of this work was to study the formation, antioxidant property and oxidative stability of oil-in-water emulsion of CPRBO. The influence of oil (10-40 % CPRBO) and surfactant (1-5 % glyceryl monostearate (GMS)) concentration on the properties of emulsions were studied. The lightness (L*) and yellowness (b*) of CPRBO emulsions decreased as GMS concentration increased, which was attributed to a decrease in droplet size after homogenization. The CPRBO emulsion was stable during storage at room temperature for 30 days. Increasing the oil concentration in the CPRBO emulsions increased their antioxidant activity, which can be attributed to the corresponding increase in phytochemical content. However, GMS concentration had little impact on the antioxidant activity of CPRBO emulsions. The storage of CPRBO emulsion at room temperature showed that lipid oxidation markers gradually increased after 30 days of storage, which was correlated to a decrease in gamma oryzanol content and antioxidant activity. These results have important implications for the utilization of rice bran oil (RBO) as a function ingredient in food, cosmetic, and pharmaceutical products. PMID:26396397

  18. Heme stabilization of α-Synuclein oligomers during amyloid fibril formation

    PubMed Central

    Hayden, Eric Y.; Kaur, Prerna; Williams, Thomas L.; Matsui, Hiroshi; Yeh, Syun-Ru; Rousseau, Denis L.

    2015-01-01

    Alpha-Synuclein (αSyn), which forms amyloid fibrils, is linked to the neuronal pathology of Parkinson’s disease, as it is the major fibrillar component of Lewy bodies, the inclusions that are characteristic of the disease. Oligomeric structures, common to many neurodegenerative disease-related proteins, may in fact be the primary toxic species, while the amyloid fibrils exist as either a less toxic dead-end species, or even as a beneficial mechanism to clear damaged proteins. In order to alter the progression of the aggregation and gain insights into the pre-fibrillar structures, the effect of heme on αSyn oligomerization was determined by several different techniques including native (non-denaturing) polyacrylamide gel electrophoresis, thioflavin T fluorescence, transmission electron microscopy, atomic force microscopy, circular dichroism and membrane permeation using a calcein release assay. During aggregation, heme is able to bind the αSyn in a specific fashion, stabilizing distinct oligomeric conformations and promoting the formation of αSyn into annular structures, thereby delaying and/or inhibiting the fibrillation process. These results indicate that heme may play a regulatory role in the progression of Parkinson’s disease; in addition, they provide insights of how the aggregation process may be altered, which may be applicable to the understanding of many neurodegenerative diseases. PMID:26161848

  19. Enigmatic Isovaline: Investigating the Stability, Racemization, and Formation of a Non-biological Meteoritic Amino Acid

    NASA Technical Reports Server (NTRS)

    Hudson, Reggie; Moore, Marla; Lewis, Ariel; Dworkin, Jason

    2008-01-01

    Among the Murchison meteoritic amino acids, isovaline stands out as being both nonbiological (non-protein) and having a relatively high abundance. While approximately equal amounts of D- and L-isovaline have been reported in Murchison and other CM meteorites, the molecule's structure appears to prohibit its racemization in aqueous solutions. We recently have investigated the low-temperature solid-phase chemistry of both isovaline and valine with an eye toward each molecule's formation, stability, and possible interconversions of D and L enantiomers. Ion-irradiated isovaline- and valinecontaining ices were examined by IR spectroscopy and highly-sensitive liquid chromatography/time-of-flight mass spectral methods to assess both amino acid destruction and racemization. Samples were studied in the presence and in the absence of water-ice, and the destruction of both isovaline and valine was measured as a function of radiation dose. In addition, we have undertaken experiments to synthesize isovaline, valine, and their amino acid isomers by solid-phase radiation-chemical pathways other than the oft-invoked Strecker process. This presentation will review and summarize some of our recent findings. -- Our work has been supported by a grant to the Goddard Center for Astrobiology through the NASA Astrobiology Institute. Experiments were performed in the Cosmic Ice Laboratory (RLH, MHM, AL) and the Astrobiology Analytical Laboratory (JPD, DPG) at the NASA Goddard Space Flight Center.

  20. The relationship between nighttime formation of gaseous HONO and nocturnal stability in an urban environment

    NASA Astrophysics Data System (ADS)

    McLaren, Robert; Wojtal, Patryk; Taylor, Peter

    2014-05-01

    Nitrous acid (HONO) is an important radical precursor in the troposphere that accumulates overnight giving rise to a significant photolytic production of the hydroxyl radical, OH, in the boundary layer during early morning hours the next day. It is understood that HONO is formed in the dark through the heterogeneous hydrolysis of NO2 on surfaces (2 NO2+ H2O -> HONO + HNO3) in a first order process, largely dominated by hydrolysis on ground surfaces and a smaller contribution from aerosol surfaces. Despite progress, the dark heterogeneous mechanism of HONO formation is still not well understood, mirroring our lack of consensus on the daytime production of HONO. We have measured HONO at night in an urban area (York University, Toronto, Canada) by DOAS for over one year. This rich dataset was analyzed with a view to understanding the nocturnal formation mechanism, and possible links to the daytime HONO formation mechanism. Frequently, "steady-states" of HONO are observed at night; d[HONO]/dt ~ 0, which follow after a rapid buildup of HONO during sunset at rates of several ppb hr-1. These steady-state levels of HONO are found to be independent of the mixing ratio of NO2 throughout the night. On other occasions, steady-states are not observed and HONO continues to increase throughout the night, highly correlated with the levels of NO2 d([HONO]/[NO2])/dt ~ 0). We have found that a very significant predictor of the type of behavior is the nocturnal stability of the atmosphere, measured by the thermal gradient, ΔT=T9.5m-T1.0m, and wind speed. The steady-state behavior is found to occur almost exclusively on unstable nights with higher wind speeds and ΔT ~ 0, when mixing of air in the lower atmosphere is more efficient. The non steady-state behavior of HONO is observed on stable nights with low wind speeds and large thermal gradients, ΔT > 2oC indicating limited vertical mixing. The observation of NO2 independent steady-states of HONO under conditions of efficient

  1. The formation, transformation, and stability of environmentally relevant uranyl mineral phases

    NASA Astrophysics Data System (ADS)

    Sowder, Andrew Gene

    Characterization of contaminated soils and sediments has identified discrete uranyl minerals as important source terms, controlling the environmental transport and biological uptake of uranium. Fundamental kinetic and thermodynamic data describing the formation, transformation, and stability of uranyl minerals in the environment are incomplete or lacking. This work examines the fate of the uranyl oxide hydrate schoepite (UOL·2H2O) in calcium, phosphate, and silicate bearing systems. Transformation of schoepite to uranyl phosphate phases was rapid and extensive, even at room temperature. The calcium uranyl phosphate autunite (Ca[(UO2)(PO4)]2·xH2O) was the chief alteration product in Ca-PO4 bearing systems. Becquerelite (Ca[(UO2)6O4(OH)6]·8H 2O) was identified as an important metastable weathering product in the presence of calcium and formed in parallel with autunite in certain systems. Uranyl silicates were not observed. Instead, the presence of dissolved silica inhibited the transformation of schoepite to becquerelite. Reaction pathways for the transformation of schoepite to becquerelite and autunite were deduced from structural and topological arguments and from experimental observations. Schoepite transforms to becquerelite via a solid state reaction without dissolution of its sheet structure. In contrast, the formation of autunite requires the complete dissolution of schoepite. Kinetic dissolution studies were conducted to determine the relative impact of four minerals (schoepite, becquerelite, chernikovite, and meta-autunite) on the environmental availability of uranium. Significant variations were observed in the rate and extent of dissolution among the mineral-treatment combinations examined. The uranyl phosphates, chernikovite and meta-autunite, proved to be far more resistant to dissolution than the uranyl oxide hydrates, schoepite and becquerelite. Exceptions to this rule, however, indicate the importance of specific mineral dissolution kinetics in

  2. Assembly and function of AsGlu2 fibrillar multimer of oat beta-glucosidase.

    PubMed

    Kwak, Su-Nam; Kim, Sang-Yeob; Choi, Sa-Ra; Kim, In-Soo

    2009-03-01

    Oat beta-glucosidase in plastid exists as a long fibrillar structure of AsGlu1 homomultimer (type I) and heteromultimer of AsGlu1 and AsGlu2 (type II). In spite of the high amino acid sequence homology of AsGlu1 and AsGlu2, AsGlu1 assembles into the fibrillar multimers but AsGlu2 forms a dimer when expressed in E. coli. A swapping analysis of AsGlu2 cDNA with AsGlu1 cDNA indicated that the C-terminal segment of AsGlu1 was critical for the fibrillar multimerization. A single substitution of glutamic acid-495 of AsGlu2 in the C-terminal region with lysine, an AsGlu1 counterpart amino acid for the glutamic acid-495, assembled the AsGlu2 into fibrillar homomultimers. The mutant AsGlu2 homomultimer was highly stable and had relatively faster electric mobility in native gel than the AsGlu1 homomultimer. Multimerization increased enzyme affinity to substrates. PMID:19100871

  3. Oligomerization of bovine ribonuclease A: structural and functional features of its multimers.

    PubMed Central

    Libonati, Massimo; Gotte, Giovanni

    2004-01-01

    Bovine pancreatic RNase A (ribonuclease A) aggregates to form various types of catalytically active oligomers during lyophilization from aqueous acetic acid solutions. Each oligomeric species is present in at least two conformational isomers. The structures of two dimers and one of the two trimers have been solved, while plausible models have been proposed for the structures of a second trimer and two tetrameric conformers. In this review, these structures, as well as the general conditions for RNase A oligomerization, based on the well known 3D (three-dimensional) domain-swapping mechanism, are described and discussed. Attention is also focused on some functional properties of the RNase A oligomers. Their enzymic activities, particularly their ability to degrade double-stranded RNAs and polyadenylate, are summarized and discussed. The same is true for the remarkable antitumour activity of the oligomers, displayed in vitro and in vivo, in contrast with monomeric RNase A, which lacks these activities. The RNase A multimers also show an aspermatogenic action, but lack any detectable embryotoxicity. The fact that both activity against double-stranded RNA and the antitumour action increase with the size of the oligomer suggests that these activities may share a common structural requirement, such as a high number or density of positive charges present on the RNase A oligomers. PMID:15104538

  4. Expression, purification, and characterization of protective MPT64 antigen protein and identification of its multimers isolated from nontoxic Mycobacterium tuberculosis H37Ra.

    PubMed

    Chu, Teng-Ping J; Yuann, Jeu-Ming P

    2011-05-01

    MPT64, a secreted protein of Mycobacterium tuberculosis (MTB), stimulates the immune reactions within cells and is a protective antigen that is lost by the bacilli Calmette-Guérin (BCG) vaccine during propagation. To minimize the toxicity caused by MTB, we used the MPT64 gene encoded by nontoxic H37Ra MTB to carry out genetic expansion via polymerase chain reaction and gene clone MPT64. The plasmid DNA encoded MPT64 was expressed at 20°C for 22 H, and a large quantity of MPT64 was obtained. In the absence of urea, MPT64 multimers with subunits being covalently connected via disulfide bonds were detected by Western blot showing strong protein-protein interactions, as evidenced by the formation of MPT64 tetramers. Finally, with urea of decreasing concentrations, we refolded MPT64 purified in the presence of urea and determined its secondary structures using circular dichroism. MPT64 was found to contain 2.2% α-helix, 50.9% β-sheet, 19.5% turn, and 27.4% random coil. The molecular weight of MPT64 was determined by a matrix-assisted laser desorption ionization-time of flight mass spectrometer and found to be 23,497 Da, very close to the theoretical molecular weight of MPT64. The results presented here provide a sound basis for future biochemical and biophysical studies of MPT64 or any other proteins encoded by nontoxic H37Ra MTB. PMID:21679242

  5. Studies on chalcone derivatives: Complex formation, thermal behavior, stability constant and antioxidant activity

    NASA Astrophysics Data System (ADS)

    El-Sayed, Yusif S.; Gaber, M.

    2015-02-01

    The chalcone 3-[4‧-dimethylaminophenyl]-1-(2-pyridyl) prop-2-en-1-one (DMAPP) and 3-(4‧-diethylaminophenyl)-1-(2-pyridinyl) prop-2-en-1-one abbreviated as DEAPP have been synthesized and characterized with IR, 1H NMR, 13C NMR spectroscopic techniques as described previously (El-Daly et al., 2008; Gaber et al., 2009; El-Sayed, 2013). By using UV visible spectroscopy method the mole fraction ratio for copper with DMAPP and DEAPP complexes were determined and it was found to be 1:1. The stability constants of this complex have been determined by Job's method. The stability constant (Kf) of copper with DMAPP and DEAPP complexes in universal buffer pH = 3.2 was determined to be 9.9 × 104 and 5.2 × 104 respectively. The effect of Cu(II) ion on the emission spectrum of the free chalcone is also assigned. Adherence to Beer's law and Ringbom optimum concentration ranges are determined. The thermal decomposition of the metal complexes is studied by TGA technique. The kinetic parameters like activation energy, pre-exponential factor and entropy of activation are estimated. The structure of complexes was energetically optimized through molecular mechanics applying MM+ force field coupled with molecular dynamics simulation. The bond lengths and bond angles have been calculated to confirm the geometry of the ligands and their Cu(II) complexes. The mode of interaction of the chalcone to copper nanoparticles was studied. The apparent association constants of the colloidal copper nanoparticles:chalcone complexes in solution were evaluated using the spectral method and compared with the formation constant of the Cu(II) chalcone complexes. Antioxidant activity of these chalcones was evaluated by using 1,1‧-diphenyl-2-picrylhydrazyl (DPPHrad) radicals scavenging method, which showed that the antioxidant activity of DMAPP has higher value than the DEAPP. Semi-empirical study results showed that DMAPP have higher dipole moment than DEAPP [1].

  6. Controlled formation of emulsion gels stabilized by salted myofibrillar protein under malondialdehyde (MDA)-induced oxidative stress.

    PubMed

    Zhou, Feibai; Sun, Weizheng; Zhao, Mouming

    2015-04-15

    This study presented the cold-set gelation of emulsions stabilized by salted myofibrillar protein (MP) under oxidative stress originated from malondialdehyde (MDA). Gel properties were compared over a range of MDA/NaCl concentrations including gel viscoelastic properties, strength, water-holding capacity (WHC), amount of protein entrapped, and microstructure. The oxidative stability of emulsion gels as indicated by lipid hydroperoxide was further determined and compared. Results indicated that emulsion stabilized by MP at swollen state under certain ionic strengths (0.2-0.6 M) was the premise of gel formation under MDA. In the presence of intermediate MDA concentrations (2.5-10 mM), the emulsion gels showed an improved elasticity, strength, WHC, and oxidative stability. This improvement should be mainly attributed to the enhanced protein-protein cross-linkings via MDA, which were homogeneously formed among absorbed and/or unabsorbed proteins, entrapping a greater amount and fractions of protein within network. Therefore, the oil droplets were better adherent to the gel matrix. Nevertheless, addition of high MDA concentrations (25-50 mM) led to the formation of excessive covalent bonds, which might break protein-protein bonds and trigger the desorption of protein from the interface. This ultimately caused "oil leak" phenomena as well as the collapse of gel structure and, thus, overall decreased gel properties and oxidative stability. PMID:25749308

  7. Control of stability of polypeptide multilayer nanofilms by quantitative control of disulfide bond formation

    NASA Astrophysics Data System (ADS)

    Zhong, Yang; Li, Bingyun; Haynie, Donald T.

    2006-12-01

    The crosslinking of polymers in a polymeric material will alter the mechanical properties of the material. Control over the mechanical properties of polyelectrolyte multilayer films (PEMs) could be useful for applications of the technology in medicine and other areas. Disulfide bonds are 'natural' polypeptide crosslinks found widely in wild-type proteins. Here, we have designed and synthesized three pairs of oppositely charged 32mer polypeptide to have 0, 4, or 8 cysteine (Cys) residues per molecule, and we have characterized physical properties of the peptides in a PEM context. The average linear density of free thiol in the designed peptides was 0, 0.125, or 0.25 per amino acid residue. The peptides were used to make 10-bilayer PEMs by electrostatic layer-by-layer self-assembly (LBL). Cys was included in the peptides to study specific effects of disulfide bond formation on PEM properties. Features of film assembly have been found to depend on the amino acid sequence, as in protein folding. Following polypeptide self-assembly into multilayer films, Cys residues were disulfide-crosslinked under mild oxidizing conditions. The stability of the crosslinked films at acidic pH has been found to depend on the number of Cys residues per peptide for a given crosslinking procedure. Crosslinked and non-crosslinked films have been analysed by ultraviolet spectroscopy (UVS), ellipsometry, and atomic force microscopy (AFM) to characterize film assembly, surface morphology, and disassembly. A selective etching model of the disassembly process at acidic pH is proposed on the basis of the experimental data. In this model, regions of film in which the disulfide bond density is low are etched at a higher rate than regions where the density is high.

  8. Preliminary protein corona formation stabilizes gold nanoparticles and improves deposition efficiency

    NASA Astrophysics Data System (ADS)

    Luby, Alexandra O.; Breitner, Emily K.; Comfort, Kristen K.

    2016-08-01

    Due to their advantageous characteristics, gold nanoparticles (AuNPs) are being increasingly utilized in a vast array of biomedical applications. However, the efficacy of these procedures are highly dependent upon strong interactions between AuNPs and the surrounding environment. While the field of nanotechnology has grown exponentially, there is still much to be discovered with regards to the complex interactions between NPs and biological systems. One area of particular interest is the generation of a protein corona, which instantaneously forms when NPs encounter a protein-rich environment. Currently, the corona is viewed as an obstacle and has been identified as the cause for loss of application efficiency in physiological systems. To date, however, no study has explored if the protein corona could be designed and advantageously utilized to improve both NP behavior and application efficacy. Therefore, we sought to identify if the formation of a preliminary protein corona could modify both AuNP characteristics and association with the HaCaT cell model. In this study, a corona comprised solely of epidermal growth factor (EGF) was successfully formed around 10-nm AuNPs. These EGF-AuNPs demonstrated augmented particle stability, a modified corona composition, and increased deposition over stock AuNPs, while remaining biocompatible. Analysis of AuNP dosimetry was repeated under dynamic conditions, with lateral flow significantly disrupting deposition and the nano-cellular interface. Taken together, this study demonstrated the plausibility and potential of utilizing the protein corona as a means to influence NP behavior; however, fluid dynamics remains a major challenge to progressing NP dosimetry.

  9. Formation of Inclusions in Ti-Stabilized 17Cr Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Yin, Xue; Sun, Yanhui; Yang, Yindong; Bai, Xuefeng; Barati, Mansoor; Mclean, Alex

    2016-04-01

    The behavior and formation mechanisms of inclusions in Ti-stabilized, 17Cr Austenitic Stainless Steel produced by the ingot casting route were investigated through systematic sampling of liquid steel and rolled products. Analysis methods included total oxygen and nitrogen contents, optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results indicate that the composition of inclusions was strongly dependent on the types of added alloying agents. During the AOD refining process, after the addition of ferrosilicon alloy and electrolytic manganese, followed by aluminum, the composition of inclusions changed from manganese silicate-rich inclusions to alumina-rich inclusions. After tapping and titanium wire feeding, pure TiN particles and complex inclusions with Al2O3-MgO-TiO x cores containing TiN were found to be the dominant inclusions when [pct Ti] was 0.307 mass pct in the molten steel. These findings were confirmed by thermodynamic calculations which indicated that there was a driving force for TiN inclusions to be formed in the liquid phase due to the high contents of [Ti] and [N] in the molten steel. From the start of casting through to the rolled bar, there was no further change in the composition of inclusions compared to the titanium addition stage. Stringer-shaped TiN inclusions were observed in the rolled bar. These inclusions were elongated along the rolling direction with lengths varying from 17 to 84 µm and could have a detrimental impact on the corrosion resistance as well as the mechanical properties of the stainless steel products.

  10. Preliminary protein corona formation stabilizes gold nanoparticles and improves deposition efficiency

    NASA Astrophysics Data System (ADS)

    Luby, Alexandra O.; Breitner, Emily K.; Comfort, Kristen K.

    2015-09-01

    Due to their advantageous characteristics, gold nanoparticles (AuNPs) are being increasingly utilized in a vast array of biomedical applications. However, the efficacy of these procedures are highly dependent upon strong interactions between AuNPs and the surrounding environment. While the field of nanotechnology has grown exponentially, there is still much to be discovered with regards to the complex interactions between NPs and biological systems. One area of particular interest is the generation of a protein corona, which instantaneously forms when NPs encounter a protein-rich environment. Currently, the corona is viewed as an obstacle and has been identified as the cause for loss of application efficiency in physiological systems. To date, however, no study has explored if the protein corona could be designed and advantageously utilized to improve both NP behavior and application efficacy. Therefore, we sought to identify if the formation of a preliminary protein corona could modify both AuNP characteristics and association with the HaCaT cell model. In this study, a corona comprised solely of epidermal growth factor (EGF) was successfully formed around 10-nm AuNPs. These EGF-AuNPs demonstrated augmented particle stability, a modified corona composition, and increased deposition over stock AuNPs, while remaining biocompatible. Analysis of AuNP dosimetry was repeated under dynamic conditions, with lateral flow significantly disrupting deposition and the nano-cellular interface. Taken together, this study demonstrated the plausibility and potential of utilizing the protein corona as a means to influence NP behavior; however, fluid dynamics remains a major challenge to progressing NP dosimetry.

  11. Stabilization of Wave Formation on a Contact Boundary of Metal Layers at an Oblique Impact during Kelvin - Helmholtz Instability Development

    SciTech Connect

    Drennov, O. B.; Mikhailov, A. L.

    2006-07-28

    The elimination effect of disturbances and mutual mixing on a contact boundaries of metal layers at oblique impact during Kelvin - Helmholtz instability development was established and investigated. Thin layers of metal coatings ({delta}{approx}30 {mu}m) reduce amplitude of disturbance realization in 10 - 100 times and eliminate mutual mixing of contacting materials (eliminate the formation of a welded point). The foils of the same materials and thicknesses are not characterized by the same strong stabilizing properties. This stabilizing effect is explained by physical properties of a metal coating as a whole. Thermophysical limits for coating layers are pointed out.

  12. Magnetic-Activated Cell Sorting of TCR-Engineered T Cells, Using tCD34 as a Gene Marker, but Not Peptide–MHC Multimers, Results in Significant Numbers of Functional CD4+ and CD8+ T Cells

    PubMed Central

    Govers, Coen; Berrevoets, Cor; Treffers-Westerlaken, Elike; Broertjes, Marieke

    2012-01-01

    Abstract T cell-sorting technologies with peptide–MHC multimers or antibodies against gene markers enable enrichment of antigen-specific T cells and are expected to enhance the therapeutic efficacy of clinical T cell therapy. However, a direct comparison between sorting reagents for their ability to enrich T cells is lacking. Here, we compared the in vitro properties of primary human T cells gene-engineered with gp100280–288/HLA-A2-specific T cell receptor-αβ (TCRαβ) on magnetic-activated cell sorting (MACS) with various peptide–MHC multimers or an antibody against truncated CD34 (tCD34). With respect to peptide–MHC multimers, we observed that Streptamer®, when compared with pentamers and tetramers, improved T cell yield as well as level and stability of enrichment, of TCR-engineered T cells (>65% of peptide–MHC-binding T cells, stable for at least 6 weeks). In agreement with these findings, Streptamer, the only detachable reagent, revealed significant T cell expansion in the first week after MACS. Sorting TCR and tCD34 gene-engineered T cells with CD34 monoclonal antibody (mAb) resulted in the most significant T cell yield and enrichment of T cells (>95% of tCD34 T cells, stable for at least 6 weeks). Notably, T cells sorted with CD34 mAb, when compared with Streptamer, bound about 2- to 3-fold less peptide–MHC but showed superior antigen-specific upregulated expression of CD107a and production of interferon (IFN)-γ. Multiparametric flow cytometry revealed that CD4+ T cells, uniquely present in CD34 mAb-sorted T cells, contributed to enhanced IFN-γ production. Taken together, we postulate that CD34 mAb-based sorting of gene-marked T cells has benefits toward applications of T cell therapy, especially those that require CD4+ T cells. PMID:22871260

  13. Molecular dynamics study of calcite, hydrate and the temperature effect on CO2 transport and adsorption stability in geological formations

    NASA Astrophysics Data System (ADS)

    Van Cuong, Phan; Kvamme, Bjørn; Kuznetsova, Tatiana; Jensen, Bjørnar

    2012-06-01

    Molecular dynamics (MD) simulations at several different temperatures were run to investigate the transport, adsorption, and stability of carbon dioxide (CO2) and water phases in contact with a ? calcite surface. All simulated systems showed evidence of CO2 transport and interface stability heavily affected by the presence of calcite and the simulation temperature. The number of CO2 molecules that successfully traversed the water layer and adsorbed on the calcite surface increased with temperature, while the adsorption stability (indicated by the adsorption energy) decreased. It was found that the short-range potential has a significant impact on the preferred CO2 orientation and adsorption selectivity. Carbon dioxide tended to fill partial hydrate cavities at the water-hydrate interface, potentially promoting the formation of new hydrate. These findings indicate the need to consider the implications that CO2 injection will have for reservoirs with pre-existing clathrate hydrates.

  14. Effects of temperature dependent pre-amorphization implantation on NiPt silicide formation and thermal stability on Si(100)

    NASA Astrophysics Data System (ADS)

    Ozcan, Ahmet S.; Wall, Donald; Jordan-Sweet, Jean; Lavoie, Christian

    2013-04-01

    Using temperature controlled Si and C ion implantation, we studied the effects of pre-amorphization implantation on NiPt alloy silicide phase formation. In situ synchrotron x-ray diffraction and resistance measurements were used to monitor phase and morphology evolution in silicide films. Results show that substrate amorphization strongly modulate the nucleation of silicide phases, regardless of implant species. However, morphological stability of the thin films is mainly enhanced by C addition, independently of the amorphization depth.

  15. Effects of temperature dependent pre-amorphization implantation on NiPt silicide formation and thermal stability on Si(100)

    SciTech Connect

    Ozcan, Ahmet S.; Wall, Donald; Jordan-Sweet, Jean; Lavoie, Christian

    2013-04-29

    Using temperature controlled Si and C ion implantation, we studied the effects of pre-amorphization implantation on NiPt alloy silicide phase formation. In situ synchrotron x-ray diffraction and resistance measurements were used to monitor phase and morphology evolution in silicide films. Results show that substrate amorphization strongly modulate the nucleation of silicide phases, regardless of implant species. However, morphological stability of the thin films is mainly enhanced by C addition, independently of the amorphization depth.

  16. Stability constants for the formation of lead chloride complexes as a function of temperature and ionic strength

    NASA Astrophysics Data System (ADS)

    Luo, Yanxin; Millero, Frank J.

    2007-01-01

    The stability constants for the formation of lead (Pb 2+) with chloride Pb+nCl↔PbCln2-nβn(n=1,2,3) have been determined using a spectrophotometric method in NaClO 4 solutions as a function of ionic strength (0-6 m) and temperature (15-45 °C). The results have been fitted to the equations:

  17. High-frequency detection of the formation and stabilization of a radiation-induced defect cluster in semiconductor structures

    SciTech Connect

    Puzanov, A. S.; Obolenskiy, S. V. Kozlov, V. A.; Volkova, E. V.; Paveliev, D. G.

    2015-12-15

    The processes of the formation and stabilization of a radiation-induced defect cluster upon the arrival of a fast neutron to the space-charge region of a semiconductor diode are analyzed. The current pulse formed by secondary electrons is calculated and the spectrum of the signal generated by the diode (detector) under the action of an instantaneous neutron flux of the fission spectrum is determined. The possibility of experimental detection of the picosecond radiation-induced transition processes is discussed.

  18. Formation of a Human Immunodeficiency Virus Type 1 Core of Optimal Stability Is Crucial for Viral Replication

    PubMed Central

    Forshey, Brett M.; von Schwedler, Uta; Sundquist, Wesley I.; Aiken, Christopher

    2002-01-01

    Virions of human immunodeficiency virus type 1 (HIV-1) and other lentiviruses contain conical cores consisting of a protein shell composed of the viral capsid protein (CA) surrounding an internal viral ribonucleoprotein complex. Although genetic studies have implicated CA in both early and late stages of the virus replication cycle, the mechanism of core disassembly following penetration of target cells remains undefined. Using quantitative assays for analyzing HIV-1 core stability in vitro, we identified point mutations in CA that either reduce or increase the stability of the HIV-1 core without impairing conical core formation in virions. Alterations in core stability resulted in severely attenuated HIV-1 replication and impaired reverse transcription in target cells with only minimal effects on viral DNA synthesis in permeabilized virions in vitro. We conclude that formation of a viral core of optimal stability is a prerequisite for efficient HIV-1 infection and suggest that disassembly of the HIV-1 core is a regulated step in infection that may be an attractive target for pharmacologic intervention. PMID:11991995

  19. Formation, characterization, and stability of methaneselenolate monolayers on Au(111): an electrochemical high-resolution photoemission spectroscopy and DFT study.

    PubMed

    Cometto, F P; Calderón, C A; Morán, M; Ruano, G; Ascolani, H; Zampieri, G; Paredes-Olivera, P; Patrito, E M

    2014-04-01

    We investigated the mechanism of formation and stability of self-assembled monolayers (SAMs) of methaneselenolate on Au(111) prepared by the immersion method in ethanolic solutions of dimethyl diselenide (DMDSe). The adsorbed species were characterized by electrochemical measurements and high-resolution photoelectron spectroscopy (HR-XPS). The importance of the headgroup on formation mechanism and the stability of the SAMs was addressed by comparatively studying methaneselenolate (MSe) and methanethiolate (MT) monolayers. Density Functional Theory (DFT) calculations were performed to identify the elementary reaction steps in the mechanisms of formation and decomposition of the monolayers. Reductive desorption and HR-XPS measurements indicated that a MSe monolayer is formed at short immersion times by the cleavage of the Se-Se bond of DMDSe. However, the monolayer decomposes at long immersion times at room temperature, as evidenced by the appearance of atomic Se on the surface. The decomposition is more pronounced for MSe than for MT monolayers. The MSe monolayer stability can be greatly improved by two modifications in the preparation method: immersion at low temperatures (-20 °C) and the addition of a reducing agent to the forming solution. PMID:24645647

  20. Analysis of K-Area core samples for K-Area formation stabilization work

    SciTech Connect

    Langton, C.A.

    1992-05-27

    Foundation stabilization work in K-Area has been recently completed by Bechtel Inc. This effort involved pumping cement and cement-sand grout into unconsolidated sediments under K-Area. Subsequent to stabilization, core samples were collected to document the extent of grout flow in the area. Samples of this core were examined by SRTC personnel in support of the grouting program at the request of Bechtel personnel. This report summarizes the results of the SRTC study.

  1. The effects of pH and PEG 400-water cosolvents on oxytetracycline-magnesium complex formation and stability.

    PubMed

    Tongaree, S; Goldberg, A M; Flanagan, D R; Poust, R I

    2000-01-01

    The effects of pH and PEG 400 on the stoichiometry, conformation, and stability of the magnesium-oxytetracycline (Mg+2-OTC) complex were evaluated. Circular dichroism (CD) and HPLC were used to investigate Mg+2-OTC complex formation and determine the stability of the complexes formed. The stoichiometry of the complex was determined to be a 1:1 molar ratio of Mg+2 to OTC regardless of changes in pH, in the range 7-10, and regardless of the percentage of polyethylene glycol (PEG) 400 in solution. CD showed that the conformation assumed by Mg+2-OTC complex is sensitive to changes in pH, however, little to no effect was found when the PEG 400 concentration was varied. PEG 400 was found to effect the magnitude of complexation as evident by the dependence of CD peak intensity on the cosolvent concentration in solution. The Job's method confirmed that the formation of this complex increased with increasing PEG 400 concentration and was most favored at pH 8. HPLC analyses of OTC solutions at pH 9 revealed the formation of multiple degradation products after storage at 50 degrees C. The incidence and magnitude of OTC degradation products were reduced in the presence of Mg+2 and PEG 400. Despite the HPLC results of maintained OTC stability in magnesium-complexed solutions over time, visual inspection showed these solutions to have darkened, indicating that an oxidative process is responsible for initial degradation of OTC. Therefore, the need for additional measures (i.e., antioxidants) was established to ensure the long-term stability of OTC in solution. PMID:10810749

  2. Stability constants for the formation of rare earth-inorganic complexes as a function of ionic strength

    NASA Astrophysics Data System (ADS)

    Millero, Frank J.

    1992-08-01

    Recent studies have been made on the distribution of the rare earths (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) in natural waters relative to their concentration in shales. These metals have also been used as models for the behavior of the trivalent actinides. The speciation of the rare earths in natural waters is modelled by using ionic interaction models which require reliable stability constants. In this paper the stability constants for the formation of lanthanide complexes ( k mx∗) with Cl -, NO 3-, SO 42-, OH -, HCO 3-, H 2PO 4-, HPO 42-, and CO 32- determined in NaClO 44 at various ionic strengths have been extrapolated to infinite dilution using the Pitzer interaction model. The activity coefficients for free ions ( γM, γx) needed for this extrapolation have been estimated from the Pitzer equations. The thermodynamic stability constants ( KMX) and activity coefficients of the various ion pairs ( γMX) were determined from In ( solK MX∗/γ Mγ x) = In K mx+ In (γ MX). The activity coefficients of the ion pairs have been used to determine Pitzer parameters ( BMX) for the rare earth complexes. The values of BMX were found to be the same for complexes of the same charge. These results make it possible to estimate the stability constants for the formation of rare earth complexes over a wide range of ionic strengths. The stability constants have been used to determine the speciation of the lanthanides in seawater and in brines. The carbonate complexes dominate for all natural waters where the carbonate alkalinity is greater than 0.001 eq/L at a pH near 8.

  3. The role of non-ionizing radiation pressure in star formation: the stability of cores and filaments

    NASA Astrophysics Data System (ADS)

    Seo, Young Min; Youdin, Andrew N.

    2016-09-01

    Stars form when filaments and dense cores in molecular clouds fragment and collapse due to self-gravity. In the most basic analyses of gravitational stability, the competition between self-gravity and thermal pressure sets the critical (i.e. maximum stable) mass of spheres and the critical line density of cylinders. Previous work has considered additional support from magnetic fields and turbulence. Here, we consider the effects of non-ionizing radiation, specifically the inward radiation pressure force that acts on dense structures embedded in an isotropic radiation field. Using hydrostatic, isothermal models, we find that irradiation lowers the critical mass and line density for gravitational collapse, and can thus act as a trigger for star formation. For structures with moderate central densities, ˜103 cm-3, the interstellar radiation field in the Solar vicinity has an order unity effect on stability thresholds. For more evolved objects with higher central densities, a significant lowering of stability thresholds requires stronger irradiation, as can be found closer to the Galactic centre or near stellar associations. Even when strong sources of ionizing radiation are absent or extincted, our study shows that interstellar irradiation can significantly influence the star formation process.

  4. The Role of Non-ionizing Radiation Pressure in Star Formation: The Stability of Cores and Filaments

    NASA Astrophysics Data System (ADS)

    Seo, Young Min; Youdin, Andrew N.

    2016-06-01

    Stars form when filaments and dense cores in molecular clouds fragment and collapse due to self-gravity. In the most basic analyses of gravitational stability, the competition between self-gravity and thermal pressure sets the critical (i.e. maximum stable) mass of spheres and the critical line density of cylinders. Previous work has considered additional support from magnetic fields and turbulence. Here, we consider the effects of non-ionizing radiation, specifically the inward radiation pressure force that acts on dense structures embedded in an isotropic radiation field. Using hydrostatic, isothermal models, we find that irradiation lowers the critical mass and line density for gravitational collapse, and can thus act as a trigger for star formation. For structures with moderate central densities, ˜103 cm-3, the interstellar radiation field in the Solar vicinity has an order unity effect on stability thresholds. For more evolved objects with higher central densities, a significant lowering of stability thresholds requires stronger irradiation, as can be found closer to the Galactic center or near stellar associations. Even when strong sources of ionizing radiation are absent or extincted, our study shows that interstellar irradiation can significantly influence the star formation process.

  5. The Formation and Stability of Carbonic Acid on Outer Solar System Bodies

    NASA Technical Reports Server (NTRS)

    Peeters, Z.; Hudson, R. L.; Moore, M. H.; Lewis, Ariel

    2009-01-01

    The radiation chemistry, thermal stability, and vapor pressure of solid-phase carbonic acid (H2CO3) have been studied with mid-infrared spectroscopy. A new procedure for measuring this molecule's radiation stability has been used to obtain intrinsic IR band strengths and half-lives for radiolytic destruction. Results are compared to literature values. We report, for the first time, measurements of carbonic acid's vapor pressure and its heat of sublimation. We also report the first observation of a chemical reaction involving solid-phase carbonic acid. Possible applications of these findings are discussed, with an emphasis on the outer Solar System.

  6. Phase formation and morphological stability of ultrathin Ni-Co-Pt silicide films formed on Si(100)

    SciTech Connect

    Xu, Peng; Wu, Dongping; Kubart, Tomas; Gao, Xindong; Zhang, Shi-Li

    2014-05-15

    Ultrathin Ni, Co, and Pt films, each no more than 4 nm in thickness, as well as their various combinations are employed to investigate the competing growth of epitaxial Co{sub 1-y}Ni{sub y}Si{sub 2} films against polycrystalline Pt{sub 1-z}Ni{sub z}Si. The phase formation critically affects the morphological stability of the resulting silicide films, with the epitaxial films being superior to the polycrystalline ones. Any combination of those metals improves the morphological stability with reference to their parent individual metal silicide films. When Ni, Co, and Pt are all included, the precise initial location of Pt does little to affect the final phase formation in the silicide films and the epitaxial growth of Co{sub 1-x}Ni{sub x}Si{sub 2} films is always perturbed, in accordance to thermodynamics that shows a preferential formation of Pt{sub 1-z}Ni{sub z}Si over that of Co{sub 1-y}Ni{sub y}Si{sub 2}.

  7. Mesenchymal condensation-dependent accumulation of collagen VI stabilizes organ-specific cell fates during embryonic tooth formation

    PubMed Central

    Mammoto, Tadanori; Mammoto, Akiko; Jiang, Amanda; Jiang, Elisabeth; Hashmi, Basma; Ingber, Donald E.

    2015-01-01

    Background Mechanical compression of cells during mesenchymal condensation triggers cells to undergo odontogenic differentiation during tooth organ formation in the embryo. However, the mechanism by which cell compaction is stabilized over time to ensure correct organ specific cell fate switching remains unknown. Results Here, we show that mesenchymal cell compaction induces accumulation of collagen VI in the extracellular matrix (ECM), which physically stabilizes compressed mesenchymal cell shapes and ensures efficient organ-specific cell fate switching during tooth organ development. Mechanical induction of collagen VI deposition is mediated by signaling through the actin-p38MAPK-SP1 pathway, and the ECM scaffold is stabilized by lysyl oxidase (LOX) in the condensing mesenchyme. Moreover, perturbation of synthesis or cross-linking of collagen VI alters the size of the condensation in vivo. Conclusions These findings suggest that the odontogenic differentiation process that is induced by cell compaction during mesenchymal condensation is stabilized and sustained through mechanically-regulated production of collagen VI within the mesenchymal ECM. PMID:25715693

  8. Comparison of modified starch and Quillaja saponins in the formation and stabilization of flavor nanoemulsions.

    PubMed

    Zhang, Jian; Bing, Lu; Reineccius, Gary A

    2016-02-01

    Modified starch (MS) and Quillaja saponins (QS) were compared to fabricate and stabilize orange oil nanoemulsions using microfluidization. Ester gum (EG) was incorporated in the oil phase at variable proportions (0-60%) as Ostwald ripening inhibitor and viscosity modifier. Optimal viscosity ratios of dispersed to continuous phase (ηd/ηc) were identified as 0.8-3.1 and 2.1-3.3 with MS and QS as emulsifier, respectively. QS was found superior to MS in fabricating nanoemulsion with smallest MDD of 69 nm and turbidity of 102 NTU at 0.05% of dispersed phase. With EG incorporated in the oil phase, QS stabilized nanoemulsions were stable during 2 weeks of storage at 23 °C; whereas MS stabilized nanoemulsions showed significant increases in MDD and turbidity. Zeta potential measurements showed QS imparted higher droplet charge (>-20 mV) than MS (<-5 mV) at pH 3.6 indicating MS stabilized nanoemulsions were destabilized by coalescence due to insufficient interfacial charge. PMID:26304319

  9. Role of stabilized Criegee Intermediate in secondary organic aerosol formation from the ozonolysis of α-cedrene

    NASA Astrophysics Data System (ADS)

    Yao, Lei; Ma, Yan; Wang, Lin; Zheng, Jun; Khalizov, Alexei; Chen, Mindong; Zhou, Yaoyao; Qi, Lu; Cui, Fenping

    2014-09-01

    Atmospheric ozonolysis of sesquiterpenes is an important source of secondary organic aerosols (SOA). The mechanisms by which Criegee Intermediates (CIs) react to form SOA precursors and the influence of environmental conditions, however, remain unclear. On the basis of environmental chamber experiments coupled with detailed characterization of gas-phase and particle-phase products, we present evidence that a significant fraction of CIs from ozonolysis of α-cedrene are stabilized and bimolecular reactions of these stabilized CIs (SCIs) play a key role in the formation of SOA precursors. Ozonolysis experiments were conducted in a 4.5 m3 collapsible fluoropolymer chamber under various conditions in the presence of the OH radical and SCI scavengers. The size and mass of SOA particles produced during ozonolysis were measured directly and used for calculation of particle effective density and mass yield. Gaseous and particulate products were analyzed by several mass spectrometry methods. A total of 14 compounds in gas phase and 17 compounds in particle phase were tentatively identified. The major gas-phase products are secondary ozonides (SOZ) from intramolecular reactions of SCIs. Multifunctional organic acids are dominant particle-phase products. The measured density of aerosol particles is 1.04 ± 0.03 to 1.38 ± 0.03 g/cm3, and the aerosol mass yield is (23.7 ± 0.4)% to (46.4 ± 6.5)%, depending on reaction conditions. The presence of acetic acid, an SCI scavenger, inhibits new particle formation, but leads to increased aerosol mass yield. In contrast, the addition of SO2 dramatically enhances new particle formation and total aerosol yield. The calculated OH formation yield decreases from (62.4 ± 4.9)% to (9.0 ± 1.6)% upon addition of SCI scavengers CH3COOH and SO2, indicating that a large fraction of excited CIs are collisionally stabilized and unimolecular decomposition of SCIs via the hydroperoxide channel can be suppressed by bimolecular reactions. The

  10. Stabilization of simulated lead sludge with iron sludge via formation of PbFe₁₂O₁₉ by thermal treatment.

    PubMed

    Mao, Linqiang; Cui, Hao; An, Hao; Wang, Bing; Zhai, Jianping; Zhao, Yongbin; Li, Qin

    2014-12-01

    This study investigated the feasibility of stabilizing lead sludge by reaction with iron sludge via the formation of PbFe12O19 through a thermal treatment process. Lead hydroxide was used to simulate lead-laden sludge and the sintering procedure was performed by firing a mixture of this simulated sludge together with iron sludge at a Fe/Pb molar ratio of 12 over the temperature range from 650 to 1400 °C. The accompanying phase transformations as well as the surface characteristic of sintered samples were observed by XRD and SEM, while the leaching behavior of the stabilized sludge in an acidic environment was evaluated by a modified Toxicity Characteristic Leaching Procedure (TCLP) test. The results confirmed that PbFe12O19 acts as a stabilization phase for lead, and showed that the formation of a PbFe12O19 phase began at 750 °C with the lead completely incorporated into the PbFe12O19 phase at 1050 °C. Above 1100 °C, the PbFe12O19 phase began to decompose, accompanied by the reappearance of Fe2O3. The volumes of compressed sludge samples were reduced significantly after thermal treatment, with accompanying volume reductions of 40% at 1050 °C. This study compared the leaching of lead from PbO and sintered sludge samples using a prolonged TCLP test, and the data showed that the PbFe12O19 phase was superior to the PbO and that the sintered sludge sample exhibited very high stability under acidic environments. These results suggest a promising and reliable method of reducing lead sludge mobility and toxicity has been identified. PMID:25461943

  11. Artificial soil formation and stabilization of material cycles in closed ecological systems for Mars habitats

    NASA Astrophysics Data System (ADS)

    Borchardt, Joshua D.

    Scientists are increasingly pressured to investigate novel ways in which to feed astronauts for the first mission to Mars in the 2030s. It is the aim of this thesis to conduct a preliminary investigation for soil formation of NASA JSC Mars-1A Regolith Simulant in an environmentally closed ecosystem to simulate plant growth within these initial habitats, and the prospect of soil formation from a Mars parent material for agricultural purposes. The rhizosphere and plant stress will be the main regions of research focus. It is hypothesized rhizosphere activity will determine the rate of stable soil formation adequate to support the agricultural needs of Mars's first human inhabitants. A Brassica rapa (Wisconsin FastPlant(TM)) was grown on several different substrates, and evaluated for plant stress, elemental analysis, soil fertility, and mineralogical analysis to identify the biogeochemical factors related to areas inside and outside of the rhizosphere, which affect soil formation. In addition, multiple plant generations were grown to investigate bioavailability of nutrients within the system, and lay down preliminary approaches for mathematical model development in order to predict & evaluate future conditions and applications under reduced resource availability situations. Overall, the story of early soil formation from a Mars regolith simulant is further defined to aid in the success of our first human adventurers to the red planet.

  12. A BENCHMARKING ANALYSIS FOR FIVE RADIONUCLIDE VADOSE ZONE MODELS (CHAIN, MULTIMED_DP, FECTUZ, HYDRUS, AND CHAIN 2D) IN SOIL SCREENING LEVEL CALCULATIONS

    EPA Science Inventory

    Five radionuclide vadose zone models with different degrees of complexity (CHAIN, MULTIMED_DP, FECTUZ, HYDRUS, and CHAIN 2D) were selected for use in soil screening level (SSL) calculations. A benchmarking analysis between the models was conducted for a radionuclide (99Tc) rele...

  13. Reversible HLA multimers (Streptamers) for the isolation of human cytotoxic T lymphocytes functionally active against tumor- and virus-derived antigens.

    PubMed

    Neudorfer, Julia; Schmidt, Burkhard; Huster, Katharina M; Anderl, Florian; Schiemann, Matthias; Holzapfel, Gerd; Schmidt, Thomas; Germeroth, Lothar; Wagner, Hermann; Peschel, Christian; Busch, Dirk H; Bernhard, Helga

    2007-03-30

    The development of MHC/peptide multimers has facilitated the visualization and purification of antigen-specific T cells. However, the persistence of multimers leads to prolonged T cell receptor signaling and subsequently to altered T-cell function. We have recently developed a new type of MHC/peptide multimers, which can be dissociated from the T cell. Herein, we have generated and tested for the first time reversible HLA/peptide multimers, termed Streptamers, for the isolation of human T cells. The Streptamer technique demonstrates the specificity and sensitivity of conventional HLA/peptide tetramers with regards to the sorting of human T lymphocytes. This is shown for T cells directed against immunogenic peptides derived from viral and tumor-associated antigens. We show that antigen-specific cytotoxic T cells remain functionally active following Streptamer dissociation, whereas lytic function and proliferation of the T cells is impaired in the presence of conventional tetramers. These novel HLA/peptide Streptamer reagents allow the isolation of antigen-specific T cells with preserved function and, therefore, facilitate the development of adoptive T cell transfer regimens for the treatment of patients with cancer or infectious diseases. PMID:17306825

  14. Efficient CO2 capture by tertiary amine-functionalized ionic liquids through Li+-stabilized zwitterionic adduct formation

    PubMed Central

    Yang, Zhen-Zhen

    2014-01-01

    Summary Highly efficient CO2 absorption was realized through formation of zwitterionic adducts, combining synthetic strategies to ionic liquids (ILs) and coordination. The essence of our strategy is to make use of multidentate cation coordination between Li+ and an organic base. Also PEG-functionalized organic bases were employed to enhance the CO2-philicity. The ILs were reacted with CO2 to form the zwitterionic adduct. Coordination effects between various lithium salts and neutral ligands, as well as the CO2 capacity of the chelated ILs obtained were investigated. For example, the CO2 capacity of PEG150MeBu2N increased steadily from 0.10 to 0.66 (mol CO2 absorbed per mol of base) through the formation of zwitterionic adducts being stabilized by Li+. PMID:25246955

  15. Microfluidic EDGE emulsification: the importance of interface interactions on droplet formation and pressure stability

    NASA Astrophysics Data System (ADS)

    Sahin, Sami; Bliznyuk, Olesya; Rovalino Cordova, Ana; Schroën, Karin

    2016-05-01

    The fact that interactions of components with interfaces can influence processes is well-known; e.g. deposit accumulation on heat exchangers and membrane fouling lead to additional resistances against heat and mass transfer, respectively. In microfluidic emulsification, the situation is even more complex. Component accumulation at the liquid/liquid interface is necessary for emulsion stability, while undesired at the solid/liquid interface where it may change wettability. For successful emulsification both aspects need to be controlled, and that is investigated in this paper for o/w emulsification with microfluidic EDGE devices. These devices were characterised previously, and can be used to detect small wettability changes through e.g. the pressure stability of the device. We used various oil/emulsifier combinations (alkanes, vegetable oil, surfactants and proteins) and related droplet size and operational pressure stability to component interactions with the solid surface and liquid interface. Surfactants with a strong interaction with glass always favour emulsification, while surfactants that have week interactions with the surface can be replaced by vegetable oil that interacts strongly with glass, resulting in loss of emulsification. Our findings clearly show that an appropriate combination of construction material and emulsion components is needed to achieve successful emulsification in microfluidic EDGE devices.

  16. Formation and Stabilization of Nano-Sized Pt Clusters on TiO2 Surfaces

    SciTech Connect

    Baer, Donald R.; Liang, Yong; Gan, Shupan

    2000-09-30

    This paper reports experiments related to the stability and size distributions of platinum (Pt) clusters on TiO2 surfaces. Efforts to enhance the efficiency and reliability of microsystems will likely use components or elements with at least one dimension smaller than a micron. The ability to design and fabricate elements at submicron dimensions-nanotechnology-is a rapidly growing area of science and technology. In this paper we describe experiments using newly generated knowledge of surfaces and the nanodimensional information provided by scanning probe microscopy (SPM) that are designed to assist development of a new generation of catalysts for application in microchemical systems. Critical questions for the design of a new catalyst is the ability to fabricate metal clusters of different sizes and their temperature stability. We report on the investigation of nucleation, growth, and temperature stability of self-organized nanoscale Pt clusters on different TiO2 surfaces using scanning tunneling microscopy (STM) and x-ray photoelectron spectroscopy (XPS). Surfaces examined include anatase (001) and rutile (110), both (1x1) and reconstructed (1x2) forms.

  17. Dynamical stability of imaged planetary systems in formation: Application to HL Tau

    NASA Astrophysics Data System (ADS)

    Tamayo, Daniel; Triaud, Amaury H. M. J.; Menou, Kristen; Rein, Hanno

    2015-05-01

    A recent ALMA image revealed several concentric gaps in the protoplanetary disk surrounding the young star HL Tau. We consider the hypothesis that these gaps are carved by planets, and present a general framework for understanding the dynamical stability of such systems over typical disk lifetimes, providing estimates for the maximum planetary masses. We argue that the locations of resonances should be significantly shifted in disks as massive as estimated for HL Tau, and that theoretical uncertainties in the exact offset, together with observational errors, imply a large uncertainty in the dynamical state and stability in such disks. An important observational avenue to breaking this degeneracy is to search for eccentric gaps, which could implicate resonantly interacting planets. Unfortunately, massive disks should also induce swift pericenter precession that would smear out any such eccentric features of planetary origin. This motivates pushing toward more typical, less massive disks. For a nominal non-resonant model of the HL Tau system with five planets, we find a maximum mass for the outer three bodies of approximately 2 Neptune masses. In a resonant configuration, these planets can reach at least the mass of Saturn. The inner two planets' masses are unconstrained by dynamical stability arguments.

  18. Microfluidic EDGE emulsification: the importance of interface interactions on droplet formation and pressure stability

    PubMed Central

    Sahin, Sami; Bliznyuk, Olesya; Rovalino Cordova, Ana; Schroën, Karin

    2016-01-01

    The fact that interactions of components with interfaces can influence processes is well-known; e.g. deposit accumulation on heat exchangers and membrane fouling lead to additional resistances against heat and mass transfer, respectively. In microfluidic emulsification, the situation is even more complex. Component accumulation at the liquid/liquid interface is necessary for emulsion stability, while undesired at the solid/liquid interface where it may change wettability. For successful emulsification both aspects need to be controlled, and that is investigated in this paper for o/w emulsification with microfluidic EDGE devices. These devices were characterised previously, and can be used to detect small wettability changes through e.g. the pressure stability of the device. We used various oil/emulsifier combinations (alkanes, vegetable oil, surfactants and proteins) and related droplet size and operational pressure stability to component interactions with the solid surface and liquid interface. Surfactants with a strong interaction with glass always favour emulsification, while surfactants that have week interactions with the surface can be replaced by vegetable oil that interacts strongly with glass, resulting in loss of emulsification. Our findings clearly show that an appropriate combination of construction material and emulsion components is needed to achieve successful emulsification in microfluidic EDGE devices. PMID:27230981

  19. Microfluidic EDGE emulsification: the importance of interface interactions on droplet formation and pressure stability.

    PubMed

    Sahin, Sami; Bliznyuk, Olesya; Rovalino Cordova, Ana; Schroën, Karin

    2016-01-01

    The fact that interactions of components with interfaces can influence processes is well-known; e.g. deposit accumulation on heat exchangers and membrane fouling lead to additional resistances against heat and mass transfer, respectively. In microfluidic emulsification, the situation is even more complex. Component accumulation at the liquid/liquid interface is necessary for emulsion stability, while undesired at the solid/liquid interface where it may change wettability. For successful emulsification both aspects need to be controlled, and that is investigated in this paper for o/w emulsification with microfluidic EDGE devices. These devices were characterised previously, and can be used to detect small wettability changes through e.g. the pressure stability of the device. We used various oil/emulsifier combinations (alkanes, vegetable oil, surfactants and proteins) and related droplet size and operational pressure stability to component interactions with the solid surface and liquid interface. Surfactants with a strong interaction with glass always favour emulsification, while surfactants that have week interactions with the surface can be replaced by vegetable oil that interacts strongly with glass, resulting in loss of emulsification. Our findings clearly show that an appropriate combination of construction material and emulsion components is needed to achieve successful emulsification in microfluidic EDGE devices. PMID:27230981

  20. Evaluation of the geological relationships to gas hydrate formation and stability. Progress report, June 16--September 30, 1988

    SciTech Connect

    Krason, J.; Finley, P.

    1988-12-31

    The summaries of regional basin analyses document that potentially economic accumulations of gas hydrates can be formed in both active and passive margin settings. The principal requirement for gas hydrate formation in either setting is abundant methane. Passive margin sediments with high sedimentation rates and sufficient sedimentary organic carbon can generate large quantities of biogenic methane for hydrate formation. Similarly, active margin locations near a terrigenous sediment source can also have high methane generation potential due to rapid burial of adequate amounts of sedimentary organic matter. Many active margins with evidence of gas hydrate presence correspond to areas subject to upwelling. Upwelling currents can enhance methane generation by increasing primary productivity and thus sedimentary organic carbon. Structural deformation of the marginal sediments at both active and passive sites can enhance gas hydrate formation by providing pathways for migration of both biogenic and thermogenic gas to the shallow gas hydrate stability zone. Additionally, conventional hydrocarbon traps may initially concentrate sufficient amounts of hydrocarbons for subsequent gas hydrate formation.

  1. Formation and Stability of Ni-Al Hydroxide Phases in Soils

    SciTech Connect

    Peltier, E.; Van Der Lelie, D; Sparks, D

    2010-01-01

    The formation of mixed metal-aluminum hydroxide surface precipitates is a potentially significant uptake route for trace metals (including Co, Ni, and Zn) in environmental systems. This paper investigates the effect of mixed Ni-Al hydroxide precipitate formation and aging on Ni solubility and bioavailability in laboratory contaminated soils. Two Delaware agricultural soils were reacted with a 3 mM Ni solution for 12 months at pH's above and below the threshold for mixed Ni-Al hydroxide formation. Ni speciation was determined at 1, 6, and 12 months using X-ray absorption spectroscopy (XAS). Precipitate solubility was examined through desorption experiments using HNO{sub 3} and EDTA as desorbing agents, whereas metal bioavailability was assessed using a Ni-specific bacterial biosensor. For both soils, the formation of Ni-Al hydroxide surface precipitates resulted in a reduction in the fraction of desorbed and bioavailable Ni. However, precipitate dissolution was greater, particularly with EDTA, than in published studies on isolated soil clay fractions, and less affected by aging processes. These results suggest that mixed Ni-Al hydroxide phases forming in real world environments may be both longer-lasting and more susceptible to ligand-promoted dissolution than previously expected.

  2. Formation and Stabilization of Vertical Hierarchies among Adolescents: Towards a Quantitative Ethology of Dominance among Humans

    ERIC Educational Resources Information Center

    Martin, John Levi

    2009-01-01

    Social psychological investigations of hierarchy formation have been almost entirely confined to the case of task-oriented groups and hence have produced theories that turn on the existence of such a task. But other forms of vertical hierarchy may emerge in non-task groups. One form, orderings of dominance, has been studied among animals using…

  3. Pyromorphite Formation And Stability After Quick Lime Neutralisation In The Presence Of Soil And Clay Sorbents

    EPA Science Inventory

    Soluble Pb is immobilised in pure systems as pyromorphite by adding sources of P, but doubts remain about the efectiveness of this approach in natural soil systems, particularly given the ability of soil humic substances to interfere with Pb-mineral formation. In addition, recen...

  4. The Role of Music Preferences in Early Adolescents' Friendship Formation and Stability

    ERIC Educational Resources Information Center

    Selfhout, Maarten H. W.; Branje, Susan J. T.; ter Bogt, Tom F. M.; Meeus, Wim H. J.

    2009-01-01

    The present study examines the role of similarity in music preferences in the formation and discontinuation of friendships over a 1-year period. Questionnaire data were gathered from 283 Dutch same-sex mutual best friends (mean age = 12.97) in two waves with a 1-year interval. Results show consistent evidence for high similarity in specific music…

  5. Formation rates, stability and reactivity of sulfuric acid - amine clusters predicted by computational chemistry

    NASA Astrophysics Data System (ADS)

    Kurtén, Theo; Ortega, Ismael; Kupiainen, Oona; Olenius, Tinja; Loukonen, Ville; Reiman, Heidi; McGrath, Matthew; Vehkamäki, Hanna

    2013-04-01

    Despite the importance of atmospheric particle formation for both climate and air quality, both experiments and non-empirical models using e.g. sulfuric acid, ammonia and water as condensing vapors have so far been unable to reproduce atmospheric observations using realistic trace gas concentrations. Recent experimental and theoretical evidence has shown that this mystery is likely resolved by amines. Combining first-principles evaporation rates for sulfuric acid - dimethylamine clusters with cluster kinetic modeling, we show that even sub-ppt concentrations of amines, together with atmospherically realistic concentrations of sulfuric acid, result in formation rates close to those observed in the atmosphere. Our simulated cluster formation rates are also close to, though somewhat larger than, those measured at the CLOUD experiment in CERN for both sulfuric acid - ammonia and sulfuric acid - dimethylamine systems. A sensitivity analysis indicates that the remaining discrepancy for the sulfuric acid - amine particle formation rates is likely caused by steric hindrances to cluster formation (due to alkyl groups of the amine molecules) rather than by significant errors in the evaporation rates. First-principles molecular dynamic and reaction kinetic modeling shed further light on the microscopic physics and chemistry of sulfuric acid - amine clusters. For example, while the number and type of hydrogen bonds in the clusters typically reach their equilibrium values on a picosecond timescale, and the overall bonding patterns predicted by traditional "static" quantum chemical calculations seem to be stable, the individual atoms participating in the hydrogen bonds continuously change at atmospherically realistic temperatures. From a chemical reactivity perspective, we have also discovered a surprising phenomenon: clustering with sulfuric acid molecules slightly increases the activation energy required for the abstraction of alkyl hydrogens from amine molecules. This implies

  6. Silver-cemented frit formation for the stabilization of the packing structure in the microchannel of electrochromatographic microchips.

    PubMed

    Park, Jongman; Oh, Hyejin; Jeon, In-Sun

    2011-10-28

    A simple but effective frit formation technique was developed to stabilize the packing structure inside the microchannel of capillary electrochromatographic microchips, utilizing the electroless plating technique. A Ag(NH(3))(2)(+) solution was allowed to diffuse through the colloidal silica packing in the microchannel from the reservoir of the microchip for a limited amount of time, and then it was reduced by an excess amount of formaldehyde solution. A frit structure of ~70 μm in length was formed at the entrance of the microchannel without clogging when treated with 1mM Ag(NH(3))(2)(+) ion and formaldehyde for 30s and 150 s, respectively. The formation of the frit structure was confirmed by a scanning electron microscopy. The stability of the packing structure was tested rigorously and then confirmed by applying alternating electroosmotic flows back and forth with pulsed potential steps on both sides of the frit structure. The effect of the treatment on the electrochromatograms was evaluated after the microchips were repeatedly used and stored for a long period of time. The results indicated that the silver-cemented frit structure extended the lifetime of the fully packed CEC microchips distinctly. PMID:21945197

  7. Release of bioactive volatiles from supramolecular hydrogels: influence of reversible acylhydrazone formation on gel stability and volatile compound evaporation.

    PubMed

    Buchs, Barbara; Fieber, Wolfgang; Vigouroux-Elie, Florence; Sreenivasachary, Nampally; Lehn, Jean-Marie; Herrmann, Andreas

    2011-04-21

    In the presence of alkali metal cations, guanosine-5'-hydrazide (1) forms stable supramolecular hydrogels by selective self-assembly into a G-quartet structure. Besides being physically trapped inside the gel structure, biologically active aldehydes or ketones can also reversibly react with the free hydrazide functions at the periphery of the G-quartet to form acylhydrazones. This particularity makes the hydrogels interesting as delivery systems for the slow release of bioactive carbonyl derivatives. Hydrogels formed from 1 were found to be significantly more stable than those obtained from guanosine. Both physical inclusion of bioactive volatiles and reversible hydrazone formation could be demonstrated by indirect methods. Gel stabilities were measured by oscillating disk rheology measurements, which showed that thermodynamic equilibration of the gel is slow and requires several cooling and heating cycles. Furthermore, combining the rheology data with dynamic headspace analysis of fragrance evaporation suggested that reversible hydrazone formation of some carbonyl compounds influences the release of volatiles, whereas the absolute stability of the gel seemed to have no influence on the evaporation rates. PMID:21380478

  8. Formation and stability of D-limonene organogel-based nanoemulsion prepared by a high-pressure homogenizer.

    PubMed

    Zahi, Mohamed Reda; Wan, Pingyu; Liang, Hao; Yuan, Qipeng

    2014-12-31

    D-limonene organogel-based nanoemulsion was prepared by high-pressure homogenization technology. The organogelator type had a major role on the formation of the formulations, in which stearic acid has given nanoemulsions with the smallest droplet size. The surfactant type and concentration also had an appreciable effect on droplet formation, with Tween 80 giving a mean droplet diameter (d ≈ 112 nm) among a range of non-ionic surfactants (Tween 20, 40, 60, 80, and 85). In addition, high-pressure homogenization conditions played a key role in the nanoemulsion preparation. The stability of d-limonene organogel-based nanoemulsion was also investigated under two different temperatures (4 and 28 °C) through 2 weeks of storage. Results showed a good stability of the formulations, which is maybe due to the incorporation of D-limonene into the organogel prior to homogenization. This study may have a valuable contribution for the design and use of organogel-based nanoemulsion as a delivery system in food. PMID:25514199

  9. Mechanism of oil bank formation, coalescence in porous media and emulsion stability. Annual report, June 1979-May 1980

    SciTech Connect

    Wasan, D.T.

    1981-02-01

    This report presents results of a basic study of coalescence phenomena, emulsion formation and stability, and dynamic interfacial properties when crude oils and pure hydrocarbons are contacted with aqueous solutions of surfactant/polymer and alkaline agents. These measurements are correlated with each other and with observations on oil bank formation and displacement and recovery efficiency by chemical flooding in microwave monitored laboratory core flooding experiments. The scope of this work includes three interrelated tasks: I - Caustic Flooding of Heavy Crude, II - Surfactant/Polymer Flooding, and III - Thin Liquid Films: drainage and stability of foam and emulsion films. Results obtained in each of these three tasks are summarized: Crude oils from Huntington Beach, Wilmington Field, Salem and El Dorado and the hydrocarbon, decane were used. The chemical agents employed were: n-hexanol, Dow Pusher 700, sodium lauryl sulfate, lauryl alcohol, petroleum sulfonate, TRS 10-80, TRS 10-410, iBuOH, NaCl brine, sodium orthosilicate, sodium hydroxide, Petrostep 465, and C/sub 3/ to C/sub 5/ alcohols.

  10. Mitochondrial translocation contact sites: separation of dynamic and stabilizing elements in formation of a TOM-TIM-preprotein supercomplex.

    PubMed

    Chacinska, Agnieszka; Rehling, Peter; Guiard, Bernard; Frazier, Ann E; Schulze-Specking, Agnes; Pfanner, Nikolaus; Voos, Wolfgang; Meisinger, Chris

    2003-10-15

    Preproteins with N-terminal presequences are imported into mitochondria at translocation contact sites that include the translocase of the outer membrane (TOM complex) and the presequence translocase of the inner membrane (TIM23 complex). Little is known about the functional cooperation of these translocases. We have characterized translocation contact sites by a productive TOM-TIM-preprotein supercomplex to address the role of three translocase subunits that expose domains to the intermembrane space (IMS). The IMS domain of the receptor Tom22 is required for stabilization of the translocation contact site supercomplex. Surprisingly, the N-terminal segment of the channel Tim23, which tethers the TIM23 complex to the outer membrane, is dispensable for both protein import and generation of the TOM-TIM supercomplex. Tim50, with its large IMS domain, is crucial for generation but not for stabilization of the supercomplex. Thus, Tim50 functions as a dynamic factor and the IMS domain of Tom22 represents a stabilizing element in formation of a productive translocation contact site supercomplex. PMID:14532110

  11. Formation of a compound flux rope by the merging of two filament channels, the associated dynamics, and its stability

    SciTech Connect

    Joshi, Navin Chandra; Inoue, Satoshi; Magara, Tetsuya E-mail: njoshi98@gmail.com

    2014-11-01

    We present observations of compound flux rope formation, which occurred on 2014 January 1, via merging of two nearby filament channels, the associated dynamics, and its stability using multiwavelength data. We also discuss the dynamics of cool and hot plasma moving along the newly formed compound flux rope. The merging started after the interaction between the southern leg of the northward filament and the northern leg of the southward filament at ≈01:21 UT and continued until a compound flux rope formed at ≈01:33 UT. During the merging, the cool filament plasma heated up and started to move along both sides of the compound flux rope, i.e., toward the north (≈265 km s{sup –1}) and south (≈118 km s{sup –1}) from the point of merging. After traveling a distance of ≈150 Mm toward the north, the plasma cooled down and started to return back to the south (≈14 km s{sup –1}) after ≈02:00 UT. The observations provide a clear example of compound flux rope formation via merging of two different flux ropes and the occurrence of a flare through tether cutting reconnection. However, the compound flux rope remained stable in the corona and had a confined eruption. The coronal magnetic field decay index measurements revealed that both the filaments and the compound flux rope axis lie within the stability domain (decay index <1.5), which may be the possible cause for their stability. The present study also deals with the relationship between the filament's chirality (sinistral) and the helicity (positive) of the surrounding flux rope.

  12. Site-directed Mutagenesis Reveals Regions Implicated in the Stability and Fiber Formation of Human λ3r Light Chains*

    PubMed Central

    Villalba, Miryam I.; Canul-Tec, Juan C.; Luna-Martínez, Oscar D.; Sánchez-Alcalá, Rosalba; Olamendi-Portugal, Timoteo; Rudiño-Piñera, Enrique; Rojas, Sonia; Sánchez-López, Rosana; Fernández-Velasco, Daniel A.; Becerril, Baltazar

    2015-01-01

    Light chain amyloidosis (AL) is a disease that affects vital organs by the fibrillar aggregation of monoclonal light chains. λ3r germ line is significantly implicated in this disease. In this work, we contrasted the thermodynamic stability and aggregation propensity of 3mJL2 (nonamyloidogenic) and 3rJL2 (amyloidogenic) λ3 germ lines. Because of an inherent limitation (extremely low expression), Cys at position 34 of the 3r germ line was replaced by Tyr reaching a good expression yield. A second substitution (W91A) was introduced in 3r to obtain a better template to incorporate additional mutations. Although the single mutant (C34Y) was not fibrillogenic, the second mutation located at CDR3 (W91A) induced fibrillogenesis. We propose, for the first time, that CDR3 (position 91) affects the stability and fiber formation of human λ3r light chains. Using the double mutant (3rJL2/YA) as template, other variants were constructed to evaluate the importance of those substitutions into the stability and aggregation propensity of λ3 light chains. A change in position 7 (P7D) boosted 3rJL2/YA fibrillogenic properties. Modification of position 48 (I48M) partially reverted 3rJL2/YA fibril aggregation. Finally, changes at positions 8 (P8S) or 40 (P40S) completely reverted fibril formation. These results confirm the influential roles of N-terminal region (positions 7 and 8) and the loop 40–60 (positions 40 and 48) on AL. X-ray crystallography revealed that the three-dimensional topology of the single and double λ3r mutants was not significantly altered. This mutagenic approach helped to identify key regions implicated in λ3 AL. PMID:25505244

  13. Formation, Stability, and Mobility of One-Dimensional Lipid Bilayer on High Curvature Substrates

    SciTech Connect

    Huang, J; Martinez, J; Artyukhin, A; Sirbuly, D; Wang, Y; Ju, J W; Stroeve, P; Noy, A

    2007-03-23

    Curved lipid membranes are ubiquitous in living systems and play an important role in many biological processes. To understand how curvature and lipid composition affect membrane formation and fluidity we have assembled and studied mixed 1,2-Dioleoyl-sn-Glycero-3-Phosphocholine (DOPC) and 1,2-Dioleoyl-sn-Glycero-3-Phosphoethanolamine (DOPE) supported lipid bilayers on amorphous silicon nanowires with controlled diameters ranging from 20 nm to 200 nm. Addition of cone-shaped DOPE molecules to cylindrical DOPC molecules promotes vesicle fusion and bilayer formation on smaller diameter nanowires. Our experiments demonstrate that nanowire-supported bilayers are mobile, exhibit fast recovery after photobleaching, and have low concentration of defects. Lipid diffusion coefficients in these high-curvature tubular membranes are comparable to the values reported for flat supported bilayers and increase with decreasing nanowire diameter.

  14. [THROMBIN-MEDIATED EFFECTS OF BLOOD MICROPARTICLES ON FORMATION, STRUCTURE, AND STABILITY OF FIBRIN CLOTS].

    PubMed

    Nabiullina, R M; Mustafin, I G; Ataullakhanov, F I; Litvinov, R I; Zubairova, L D

    2015-07-01

    The effects of blood microparticles (MPs) on the dynamics of fibrin polymerization, clot structure and susceptibility to fibrinolysis were studied. Kinetics of fibrin polymerization, fibrinolysis, thrombin generation in platelet-free, microparticle-depleted and microparticle-depleted plasma replenished with cephalin, from healthy donors were analyzed in parallel. MPs have profound effects on all stages of fibrin formation, decrease its turbidity. All parameters obtained in the absence of MPs were recovered after reconstitution of phospholipids. Thrombin generation rates were reduced in the absence of MPs. In the presence of MPs the fibrin networks had less poro us structures with thinner fibers, while clots formed in the absence of MPs had larger pores and were built of thicker fibers. Clots formed in the presence of MPs were significantly more resistant to fibrinolysis. Results show that normally circulating MPs can support the formation of stable clots at the sites of vascular injury. PMID:26591054

  15. Two Decades of Stability and Change in Age at First Union Formation

    PubMed Central

    Manning, Wendy D.; Brown, Susan L.; Payne, Krista K.

    2014-01-01

    The landscape of union formation has been shifting; Americans are now marrying at the highest ages on record and the majority of young adults have cohabited. Yet little attention has been paid to the timing of cohabitation relative to marriage. Using the National Survey of Families and Households and 4 cycles of the National Survey of Family Growth, the authors examined the timing of marriage, cohabitation, and unions over 20 years. As the median age at first marriage has climbed, the age at cohabitation has remained stable for men and women. The changes in the timing of union formation have been similar according to race/ethnicity. The marked delay in marriage among women and men with low educational attainment has resulted in a near-convergence in the age at first marriage according to education. The authors conclude that the rise in cohabitation has offset changes in the levels and timing of marriage. PMID:25147410

  16. Two Decades of Stability and Change in Age at First Union Formation.

    PubMed

    Manning, Wendy D; Brown, Susan L; Payne, Krista K

    2014-04-01

    The landscape of union formation has been shifting; Americans are now marrying at the highest ages on record and the majority of young adults have cohabited. Yet little attention has been paid to the timing of cohabitation relative to marriage. Using the National Survey of Families and Households and 4 cycles of the National Survey of Family Growth, the authors examined the timing of marriage, cohabitation, and unions over 20 years. As the median age at first marriage has climbed, the age at cohabitation has remained stable for men and women. The changes in the timing of union formation have been similar according to race/ethnicity. The marked delay in marriage among women and men with low educational attainment has resulted in a near-convergence in the age at first marriage according to education. The authors conclude that the rise in cohabitation has offset changes in the levels and timing of marriage. PMID:25147410

  17. Formin-mediated actin polymerization at endothelial junctions is required for vessel lumen formation and stabilization.

    PubMed

    Phng, Li-Kun; Gebala, Véronique; Bentley, Katie; Philippides, Andrew; Wacker, Andrin; Mathivet, Thomas; Sauteur, Loïc; Stanchi, Fabio; Belting, Heinz-Georg; Affolter, Markus; Gerhardt, Holger

    2015-01-12

    During blood vessel formation, endothelial cells (ECs) establish cell-cell junctions and rearrange to form multicellular tubes. Here, we show that during lumen formation, the actin nucleator and elongation factor, formin-like 3 (fmnl3), localizes to EC junctions, where filamentous actin (F-actin) cables assemble. Fluorescent actin reporters and fluorescence recovery after photobleaching experiments in zebrafish embryos identified a pool of dynamic F-actin with high turnover at EC junctions in vessels. Knockdown of fmnl3 expression, chemical inhibition of formin function, and expression of dominant-negative fmnl3 revealed that formin activity maintains a stable F-actin content at EC junctions by continual polymerization of F-actin cables. Reduced actin polymerization leads to destabilized endothelial junctions and consequently to failure in blood vessel lumenization and lumen instability. Our findings highlight the importance of formin activity in blood vessel morphogenesis. PMID:25584798

  18. Substituents on Quinone Methides Strongly Modulate Formation and Stability of Their Nucleophilic Adducts

    PubMed Central

    Weinert, Emily E.; Dondi, Ruggero; Colloredo-Melz, Stefano; Frankenfield, Kristen N.; Mitchell, Charles H.; Freccero, Mauro; Rokita, Steven E.

    2008-01-01

    Electronic perturbation of quinone methides (QM) greatly influences their stability and in turn alters the kinetics and product profile of QM reaction with deoxynucleosides. Consistent with the electron deficient nature of this reactive intermediate, electron-donating substituents are stabilizing and electron-withdrawing substituents are destabilizing. For example, a dC N3-QM adduct is made stable over the course of observation (7 days) by the presence of an electron-withdrawing ester group that inhibits QM regeneration. Conversely, a related adduct with an electron donating methyl group is very labile and regenerates its QM with a half-life of approximately 5 hr. The generality of these effects is demonstrated with a series of alternative quinone methide precursors (QMP) containing a variety of substituents attached at different positions with respect to the exocyclic methylene. The rates of nucleophilic addition to substituted QMs measured by laser flash photolysis similarly span five orders of magnitude with electron rich species reacting most slowly and electron deficient species reacting most quickly. The reversibility of QM reaction can now be predictably adjusted for any desired application. PMID:16953635

  19. Stabilizing Surfactant Templated Cylindrical Mesopores in Polymer and Carbon Films through Composite Formation with Silica Reinforcement

    SciTech Connect

    Song, Lingyan; Feng, Dan; Lee, Hae-Jeong; Wang, Chengqing; Wu, Quanyan; Zhao, Dongyuan; Vogt, Bryan D.

    2010-10-22

    A facile approach to maintain the periodic mesostructure of cylindrical pores in polymer-resin and carbon films after thermal template removal is explored through the reactive coassembly of resol (carbon precursor) and tetraethylorthosilicate (silica precursor) with triblock copolymer Pluronic F127. Without silica, a low porosity, disordered film is formed after pyrolysis despite the presence of an ordered mesostructure prior to template removal. However for silica concentration greater than 25 wt %, pyrolysis at 350 C yields a mesoporous silica-polymer film with well-defined pore mesostructure. These films remain well ordered upon carbonization at 800 C. In addition to the mesostructural stability, the addition of silica to the matrix impacts other morphological characteristics. For example, the average pore size and porosity of the films increase from 3.2 to 7.5 nm and 12 to 45%, respectively, as the concentration of silica in the wall matrix increases from 0 to 32 wt %. The improved thermal stability of the ordered mesostructure with the addition of silica to the matrix is attributed to the reinforcement of the mechanical properties leading to resistance to stress induced collapse of the mesostructure during template removal.

  20. Effects of amphiphilic diblock copolymer on drug nanoparticle formation and stability

    PubMed Central

    Zhu, Zhengxi

    2013-01-01

    This study systematically compares the effects of amphiphilic diblock copolymer (di-BCP) on stabilizing hydrophobic drug nanoparticles formed by flash nanoprecipitation (FNP), and provides a guideline on choosing suitable di-BCPs. Four widely used di-BCPs, i.e., polystyrene-block-poly(ethylene glycol) (PS-b-PEG), polycaprolactone-block-poly(ethylene glycol) (PCL-b-PEG), polylactide-block-poly(ethylene glycol) (PLA-b-PEG), and poly(lactic-co-glycolic acid) (PLGA-b-PEG), and β-carotene as a model drug were used. The study showed that PLGA-b-PEG was the most suitable one, whose hydrophobic block was biodegradable and noncrystallizable as well as had relatively high glass transition temperature (Tg) and a right solubility parameter (δ). The molecular weight of PLGA block over the range from 5k to 15k showed an insignificant effect on controlling the particle size. Amorphous drug particles with a high drug loading of over 83 wt% can be achieved. Much remarkable evidence supported the nanoparticles with kinetically frozen and nonequilibrium packing structures of polymer chains rather than either the micelles or micellar nanoparticles with two well segregated polymer blocks. The thermodynamic effects of the drug and BCP on the particle stability, size and structures were discussed by using solubility parameters. PMID:24070569

  1. Solubilizing and Stabilizing Proteins in Anhydrous Ionic Liquids through Formation of Protein-Polymer Surfactant Nanoconstructs.

    PubMed

    Brogan, Alex P S; Hallett, Jason P

    2016-04-01

    Nonaqueous biocatalysis is rapidly becoming a desirable tool for chemical and fuel synthesis in both the laboratory and industry. Similarly, ionic liquids are increasingly popular anhydrous reaction media for a number of industrial processes. Consequently, the use of enzymes in ionic liquids as efficient, environment-friendly, commercial biocatalysts is highly attractive. However, issues surrounding the poor solubility and low stability of enzymes in truly anhydrous media remain a significant challenge. Here, we demonstrate for the first time that engineering the surface of a protein to yield protein-polymer surfactant nanoconstructs allows for dissolution of dry protein into dry ionic liquids. Using myoglobin as a model protein, we show that this method can deliver protein molecules with near native structure into both hydrophilic and hydrophobic anhydrous ionic liquids. Remarkably, using temperature-dependent synchrotron radiation circular dichroism spectroscopy to measure half-denaturation temperatures, our results show that protein stability increases by 55 °C in the ionic liquid as compared to aqueous solution, pushing the solution thermal denaturation beyond the boiling point of water. Therefore, the work presented herein could provide a platform for the realization of biocatalysis at high temperatures or in anhydrous solvent systems. PMID:26976718

  2. Formation and stability of the dispersed particles composed of retinyl palmitate and phosphatidylcholine.

    PubMed

    Asai, Y; Watanabe, S

    2000-01-01

    The purpose of this study was to develop an intravenous formulation composed of retinyl palmitate (RP) for the treatment of cancer. RP was dispersed with soybean phosphatidylcholine (PC) using sonication and the dispersal mechanism was evaluated by characterizing the dispersed particles using dynamic light-scattering, fluorescence spectroscopy, and surface monolayer techniques. The dispersions in the RP mole fraction range of 0.1-0.8 were stable at room temperature for 3 days. A limited amount of RP was incorporated into PC bilayer membranes (approximately 3 mol%). The excess RP separated from the PC bilayers was stabilized as emulsion particles by the PC surface monolayer. When the PC content was less than the solubility in RP, the PC monolayer did not completely cover the hydrophobic RP particle surfaces and separation into oil/water occurred. The miscibility between RP and PC and the lipid composition were critically important for the stability of the dispersed particles (coexistence of emulsion particles [surface monolayer of PC + core of RP] with vesicular particles [bilayer]) of the lipid mixtures. PMID:10669916

  3. Formation and Stability of Phenylphosphonic Acid Monolayers on ZnO: Comparison of In Situ and Ex Situ SAM Preparation.

    PubMed

    Ostapenko, Alexandra; Klöffel, Tobias; Meyer, Bernd; Witte, Gregor

    2016-05-24

    Self-assembled monolayers (SAMs) enable an electronic interface tailoring of conductive metal oxides and offer an alternative to common transparent electrodes in optoelectronic devices. Here, the influence of surface orientation and pretreatment on the formation and stability of SAMs has been studied for the case of phenylphosphonic acid (PPA) on ZnO single crystals. Using thermal desorption spectroscopy (TDS), X-ray photoelectron spectroscopy (XPS), near-edge X-ray adsorption fine structure spectroscopy (NEXAFS) and density-functional theory (DFT) calculations, the thermal stability and orientational ordering of PPA-SAMs on the polar and mixed-terminated ZnO surfaces were analyzed. On all surfaces, PPA-SAMs remain stable up to 550 K, while at higher temperatures a C-P bond cleavage and dissociative desorption takes place yielding two distinct desorption peaks. Based on DFT calculations, these desorption channels are attributed to protonated and deprotonated chemisorbed PPA molecules, which can be related to tri- and bidentate species, hence allowing to determine their relative abundance from the intensity ratio. Beside immersion, an alternative monolayer preparation based on vacuum deposition in combination with controlled desorption of excess multilayers is demonstrated. This enables a SAM preparation on bare ZnO surfaces without any precoating due to exposure to ambient air, which is further compared with SAM formation on intentionally hydroxylated substrates. Corresponding TDS data indicate that initial hydroxylation favors the formation of tridentate and deprotonated bidentate, while the OMBD preparation on bare surfaces yields a larger fraction of protonated bidentate species. The orientation of PPA molecules adopted in the SAMs was determined from the dichroism of K-edge NEXAFS measurements and reveals an almost upright orientation for the deprotonated species, while a slight tilting is obtained for monolayer films with a large fraction of protonated

  4. Beta-Barrel Scaffold of Fluorescent Proteins: Folding, Stability and Role in Chromophore Formation

    PubMed Central

    Stepanenko, Olesya V.; Stepanenko, Olga V.; Kuznetsova, Irina M.; Verkhusha, Vladislav V.; Turoverov, Konstantin K.

    2013-01-01

    This review focuses on the current view of the interaction between the β-barrel scaffold of fluorescent proteins and their unique chromophore located in the internal helix. The chromophore originates from the polypeptide chain and its properties are influenced by the surrounding protein matrix of the β-barrel. On the other hand, it appears that a chromophore tightens the β-barrel scaffold and plays a crucial role in its stability. Furthermore, the presence of a mature chromophore causes hysteresis of protein unfolding and refolding. We survey studies measuring protein unfolding and refolding using traditional methods as well as new approaches, such as mechanical unfolding and reassembly of truncated fluorescent proteins. We also analyze models of fluorescent protein unfolding and refolding obtained through different approaches, and compare the results of protein folding in vitro to co-translational folding of a newly synthesized polypeptide chain. PMID:23351712

  5. Post-Formation Shrinkage and Stabilization of Microfluidic Bubbles in Lipid Solution.

    PubMed

    Shih, Roger; Lee, Abraham P

    2016-03-01

    Medical ultrasound imaging often employs ultrasound contrast agents (UCAs), injectable microbubbles stabilized by shells or membranes. In tissue, the compressible gas cores can strongly scatter acoustic signals, resonate, and emit harmonics. However, bubbles generated by conventional methods have nonuniform sizes, reducing the fraction that resonates with a given transducer. Microfluidic flow-focusing is an alternative production method which generates highly monodisperse bubbles with uniform constituents, enabling more-efficient contrast enhancement than current UCAs. Production size is tunable by adjusting gas pressure and solution flow rate, but solution effects on downstream stable size and lifetime have not been closely examined. This study therefore investigated several solution parameters, including the DSPC/DSPE-PEG2000 lipid ratio, concentration, viscosity, and preparation temperature to determine their effects on stabilization. It was found that bubble lifetime roughly correlated with stable size, which in turn was strongly influenced by primary-lipid-to-emulsifier ratio, analogous to its effects on conventional bubble yield and Langmuir-trough compressibility in existing studies. Raising DSPE-PEG2000 fraction in solution reduced bubble surface area in proportion to its reduction of lipid packing density at low compression in literature. In addition, the surface area was found to increase proportionately with lipid concentration above 2.1 mM. However, viscosities above or below 2.3-3.3 mPa·s seemed to reduce bubble size. Finally, lipid preparation at room temperature led to smaller bubbles compared to preparation near or above the primary lipid's phase transition point. Understanding these effects will further improve on postformation control over microfluidic bubble production, and facilitate size-tuning for optimal contrast enhancement. PMID:26820229

  6. The Formation and Stability of Recognition Memory: What Happens Upon Recall?

    PubMed Central

    Davis, Sabrina; Renaudineau, Sophie; Poirier, Roseline; Poucet, Bruno; Save, Etienne; Laroche, Serge

    2010-01-01

    The idea that an already consolidated memory can become destabilized after recall and requires a process of reconsolidation to maintain it for subsequent use has gained much credence over the past decade. Experimental studies in rodents have shown pharmacological, genetic, or injurious manipulation at the time of memory reactivation can disrupt the already consolidated memory. Despite the force of experimental data showing this phenomenon, a number of questions have remained unanswered and no consensus has emerged as to the conditions under which a memory can be disrupted following reactivation. To date most rodent studies of reconsolidation are based on negatively reinforced memories, in particular fear-associated memories, while the storage and stability of forms of memory that do not rely on explicit reinforcement have been less often studied. In this review, we focus on recognition memory, a paradigm widely used in humans to probe declarative memory. We briefly outline recent advances in our understanding of the processes and brain circuits involved in recognition memory and review the evidence that recognition memory can undergo reconsolidation upon reactivation. We also review recent findings suggesting that some molecular mechanisms underlying consolidation of recognition memory are similarly recruited after recall to ensure memory stability, while others are more specifically engaged in consolidation or reconsolidation. Finally, we provide novel data on the role of Rsk2, a mental retardation gene, and of the transcription factor zif268/egr1 in reconsolidation of object-location memory, and offer suggestions as to how assessing the activation of certain molecular mechanisms following recall in recognition memory may help understand the relative importance of different aspects of remodeling or updating long-lasting memories. PMID:21120149

  7. Formation and stability of nanoemulsions with mixed ionic-nonionic surfactants.

    PubMed

    Wang, Lijuan; Tabor, Rico; Eastoe, Julian; Li, Xuefeng; Heenan, Richard K; Dong, Jinfeng

    2009-11-14

    A simple, low-energy two-step dilution process has been applied with binary mixtures of ionic-nonionic surfactants to prepare nanoemulsions. The systems consist of water/DDAB-C(12)E(5)/decane. Nanoemulsions were obtained by dilution of concentrates located in bicontinuous microemulsion or lamellar liquid crystal phase regions. The nanoemulsions generated were investigated both by contrast-variation small-angle neutron scattering (SANS) and dynamic light scattering (DLS). The SANS profiles show that C(12)E(5) nanodroplets suffer essentially no structural change on incorporation of the cationic DDAB surfactant, except for increased electrostatic repulsive interactions. Interestingly, SANS indicated that the preferred droplet sizes were hardly affected by the surfactant mixture composition (up to a DDAB molar ratio (m(DDAB)/(m(DDAB) + m(C(12)E(5))) of 0.40) and droplet volume fraction, phi, between 0.006 and 0.120. No notable changes in the structure or radius of nanoemulsion droplets were observed by SANS over the test period of 1 d, although the droplet number intensity decreased significantly in systems stabilized by C(12)E(5) only. However, the DLS sizing shows a marked increase with time, with higher droplet volume fractions giving rise to the largest changes. The discrepancy between apparent nanoemulsion droplet size determined by DLS and SANS data can be attributed to long-range droplet interactions occurring outside of the SANS sensitivity range. The combined SANS and DLS results suggest flocculation is the main mechanism of instability for these nanoemulsions. The flocculation rate is shown to be significantly retarded by addition of the charged DDAB, which may be due to enhanced electrostatic repulsive forces between droplets, leading to improved stability of the nanoemulsions. PMID:19851556

  8. The stability of elastically strained nanorings and the formation of quantum dot molecules

    NASA Astrophysics Data System (ADS)

    Gill, Simon P. A.

    2015-05-01

    Self-assembled nanorings have recently been identified in a number of heteroepitaxially strained material systems. Under some circumstances these rings have been observed to break up into ring-shaped quantum dot molecules. A general non-linear model for the elastic strain energy of non-axisymmetric epitaxially strained nanostructures beyond the small slope assumption is developed. This model is then used to investigate the stability of strained nanorings evolving via surface diffusion subject to perturbations around their circumference. An expression for the fastest growing mode is determined and related to experimental observations. The model predicts a region of stability for rings below a critical radius, and also a region for larger rings which have a proportionally small thickness. The predictions of the model are shown to be consistent with the available results. For the heteroepitaxial InP on In0.5Ga0.5P system investigated by Jevasuwan et al. (2013), the nanorings are found to be stable below a certain critical size. This is in good quantitative agreement with the model predictions. At larger sizes, the rings are unstable. The number of dots in the resulting quantum dot molecule is similar to the mode number for the fastest growing mode. Second order terms show that the number of dots is expected to reduce as the height of the ring increases in proportion to its thickness. The strained In0.4Ga0.6As on GaAs nanorings of Hanke et al. (2007) are always stable and this is in accordance with the findings of the analysis. The Au nanorings of Ruffino et al. (2011) are stable as well, even as they expand during annealing. This observation is also shown to be consistent with the proposed model, which is expected to be useful in the design and tailoring of heteroepitaxial systems for the self-organisation of quantum dot molecules.

  9. Formation and Stabilization of Environmentally Persistent Free Radicals Induced by the Interaction of Anthracene with Fe(III)-Modified Clays.

    PubMed

    Jia, Hanzhong; Nulaji, Gulimire; Gao, Hongwei; Wang, Fu; Zhu, Yunqing; Wang, Chuanyi

    2016-06-21

    Environmentally persistent free radicals (EPFRs) are occasionally detected in Superfund sites but the formation of EPFRs induced by polycyclic aromatic hydrocarbons (PAHs) is not well understood. In the present work, the formation of EPFRs on anthracene-contaminated clay minerals was quantitatively monitored via electron paramagnetic resonance (EPR) spectroscopy, and surface/interface-related environmental influential factors were systematically explored. The obtained results suggest that EPFRs are more readily formed on anthracene-contaminated Fe(III)-montmorillonite than in other tested systems. Depending on the reaction condition, more than one type of organic radicals including anthracene-based radical cations with g-factors of 2.0028-2.0030 and oxygenic carbon-centered radicals featured by g-factors of 2.0032-2.0038 were identified. The formed EPFRs are stabilized by their interaction with interlayer surfaces, and such surface-bound EPFRs exhibit slow decay with 1/e-lifetime of 38.46 days. Transformation pathway and possible mechanism are proposed on the basis of experimental results and quantum mechanical simulations. Overall, the formation of EPFRs involves single-electron-transfer from anthracene to Fe(III) initially, followed by H2O addition on formed aromatic radical cation. Because of their potential exposure in soil and atmosphere, such clay surface-associated EPFRs might induce more serious toxicity than PAHs and exerts significant impacts on human health. PMID:27224055

  10. The formation and stability of He-vacancy clusters within displacement cascades in α-Fe

    SciTech Connect

    Gao, Fei; Heinisch, Howard L.; Kurtz, Richard J.

    2007-10-25

    Molecular dynamics (MD) methods have been utilized to study the formation of vacancy clusters created by displacement cascades in α-Fe containing concentrations of substitutional He atoms varying from 1-5%. These He concentrations are not necessarily intended to represent specific conditions within a fusion reactor (average end-of-life He concentrations in the first wall are expected to be on the order of 0.15%), but they provide an opportunity to investigate the effects of substantial amounts of He on cascade processes and microstructure development under damage producing conditions.

  11. Pyromorphite formation and stability after quick lime neutralisation in the presence of soil and clay sorbents

    SciTech Connect

    Chappell, Mark A.; Scheckel, Kirk G.

    2008-06-16

    Soluble Pb is immobilised in pure systems as pyromorphite by adding sources of P, but doubts remain about the effectiveness of this approach in natural soil systems, particularly given the ability of soil humic substances to interfere with Pb-mineral formation. In addition, recent thermodynamic modelling predicts that pyromorphite formed by the addition of phosphoric acid to Pb-contaminated soils, followed by neutralisation with quick lime (Ca(OH){sub 2}) will destabilise the mineral, reverting the Pb back to more soluble species such as cerussite or anglesite. In this paper, we describe experiments to form pyromorphite in the presence of two different sorbents: a reference smectite called Panther Creek Bentonite, and a commercially available, organically rich potting mixture. We present X-ray diffraction (XRD) evidence suggestive of pyromorphite formation, yet, like similar studies, the evidence is less than conclusive. Linear combination fits of Pb X-ray absorption fine-structure spectroscopy (XAFS) data collected at the Advanced Photon Source at Argonne National Laboratory show that pyromorphite is the major Pb species formed after the addition of phosphoric acid. Furthermore, XAFS data shows that neutralising with quick lime enhances (as opposed to reducing) pyromorphite content in these systems. These results call into question relying solely on XRD data to confirm or deny the existence of minerals like pyromorphite, whose complex morphology give less intense and more complicated diffraction patterns than some of the simpler Pb minerals.

  12. Study of the Stability and Planetary Formation in the System HD98800

    NASA Astrophysics Data System (ADS)

    De Cássia Domingos, Rita; Winter, O. C.

    2009-09-01

    HD 98800 is a quadruple stellar system, with two close stars pairs A and B of the high inclination and eccentricity. A circumbinary disk around the B component was detected. It extends between 1.5 - 2.0 AU and 5.9 - 6.5 AU. In this work we numerically investigate the possibility of the giant planet formation in this complex dynamical environment. We divide our work into two parts. Firstly, we infer the possible stable regions around the B component where particles can survive for 1 Myr. We considered a range of inclinations and eccentricities for the A component. These results are presented in the (a, e) plane for different values of inclination. The results show that in general particles survive between 3 to 9 AU. Now, in the second part, we are working about the possibility of in situ planetary formation in these stable regions. We are numerically investigating the stage of planetary embryo accretion from planetesimals. Acknowledgements: The authors thank FAPESP and CNPq for the financial support.

  13. In situ formation of magnetite reactive barriers in soil for waste stabilization

    DOEpatents

    Moore, Robert C.

    2003-01-01

    Reactive barriers containing magnetite and methods for making magnetite reactive barriers in situ in soil for sequestering soil contaminants including actinides and heavy metals, organic materials, iodine and technetium are disclosed. According to one embodiment, a two-step reagent introduction into soil takes place. In the first step, free oxygen is removed from the soil by separately injecting into the soil aqueous solutions of iron (II) salt, for example FeCl.sub.2, and base, for example NaOH or NH.sub.3 in about a 1:1 volume ratio. Then, in the second step, similar reagents are injected a second time (however, according to about a 1:2 volume ratio, iron to salt) to form magnetite. The magnetite formation is facilitated, in part, due to slow intrusion of oxygen into the soil from the surface. The invention techniques are suited to injection of reagents into soil in proximity to a contamination plume or source allowing in situ formation of the reactive barrier at the location of waste or hazardous material. Mixing of reagents to form. precipitate is mediated and enhanced through movement of reagents in soil as a result of phenomena including capillary action, movement of groundwater, soil washing and reagent injection pressure.

  14. Carbonic Anhydrase Generates CO2 and H+ That Drive Spider Silk Formation Via Opposite Effects on the Terminal Domains

    PubMed Central

    Otikovs, Martins; Landreh, Michael; Nordling, Kerstin; Kronqvist, Nina; Westermark, Per; Jörnvall, Hans; Knight, Stefan; Ridderstråle, Yvonne; Holm, Lena; Meng, Qing; Jaudzems, Kristaps; Chesler, Mitchell; Johansson, Jan; Rising, Anna

    2014-01-01

    Spider silk fibers are produced from soluble proteins (spidroins) under ambient conditions in a complex but poorly understood process. Spidroins are highly repetitive in sequence but capped by nonrepetitive N- and C-terminal domains (NT and CT) that are suggested to regulate fiber conversion in similar manners. By using ion selective microelectrodes we found that the pH gradient in the silk gland is much broader than previously known. Surprisingly, the terminal domains respond in opposite ways when pH is decreased from 7 to 5: Urea denaturation and temperature stability assays show that NT dimers get significantly stabilized and then lock the spidroins into multimers, whereas CT on the other hand is destabilized and unfolds into ThT-positive β-sheet amyloid fibrils, which can trigger fiber formation. There is a high carbon dioxide pressure (pCO2) in distal parts of the gland, and a CO2 analogue interacts with buried regions in CT as determined by nuclear magnetic resonance (NMR) spectroscopy. Activity staining of histological sections and inhibition experiments reveal that the pH gradient is created by carbonic anhydrase. Carbonic anhydrase activity emerges in the same region of the gland as the opposite effects on NT and CT stability occur. These synchronous events suggest a novel CO2 and proton-dependent lock and trigger mechanism of spider silk formation. PMID:25093327

  15. Formation and Stabilization of Single-Crystalline Metastable AuGe Phases in Ge Nanowires

    SciTech Connect

    Sutter, E.; Sutter, P.

    2011-07-22

    We use in situ observations by variable temperature transmission electron microscopy on AuGe alloy drops at the tips of Ge nanowires (NWs) with systematically varying composition to demonstrate the controlled formation of metastable solid phases integrated in NWs. The process, which operates in the regime of vapor-liquid-solid growth, involves a size-dependent depression of the alloy liquidus at the nanoscale that leads to extremely Ge-rich AuGe melts at low temperatures. During slow cooling, these liquid AuGe alloy drops show pronounced departures from equilibrium, i.e., a frustrated phase separation of Ge into the adjacent solid NW, and ultimately crystallize as single-crystalline segments of metastable {gamma}-AuGe. Our findings demonstrate a general avenue for synthesizing NW heterostructures containing stable and metastable solid phases, applicable to a wide range of materials of which NWs form by the vapor-liquid-solid method.

  16. Immobilization-stabilization of proteins on nanofibrillated cellulose derivatives and their bioactive film formation.

    PubMed

    Arola, Suvi; Tammelin, Tekla; Setälä, Harri; Tullila, Antti; Linder, Markus B

    2012-03-12

    In a number of different applications for enzymes and specific binding proteins a key technology is the immobilization of these proteins to different types of supports. In this work we describe a concept for protein immobilization that is based on nanofibrillated cellulose (NFC). NFC is a form of cellulose where fibers have been disintegrated into fibrils that are only a few nanometers in diameter and have a very large aspect ratio. Proteins were conjugated through three different strategies using amine, epoxy, and carboxylic acid functionalized NFC. The conjugation chemistries were chosen according to the reactive groups on the NFC derivatives; epoxy amination, heterobifunctional modification of amino groups, and EDC/s-NHS activation of carboxylic acid groups. The conjugation reactions were performed in solution and immobilization was performed by spin coating the protein-NCF conjugates. The structure of NFC was shown to be advantageous for both protein performance and stability. The use of NFC allows all covalent chemistry to be performed in solution, while the immobilization is achieved by a simple spin coating or spreading of the protein-NFC conjugates on a support. This allows more scalable methods and better control of conditions compared to the traditional methods that depend on surface reactions. PMID:22248303

  17. Composition-dependent stability of the medium-range order responsible for metallic glass formation

    SciTech Connect

    Zhang, Feng; Ji, Min; Fang, Xiao-Wei; Sun, Yang; Wang, Cai-Zhuang; Mendelev, Mikhail I.; Kramer, M. J.; Napolitano, Ralph E.; Ho, Kai-Ming

    2014-09-18

    The competition between the characteristic medium-range order corresponding to amorphous alloys and that in ordered crystalline phases is central to phase selection and morphology evolution under various processing conditions. We examine the stability of a model glass system, Cu–Zr, by comparing the energetics of various medium-range structural motifs over a wide range of compositions using first-principles calculations. Furthermore, we focus specifically on motifs that represent possible building blocks for competing glassy and crystalline phases, and we employ a genetic algorithm to efficiently identify the energetically favored decorations of each motif for specific compositions. These results show that a Bergman-type motif with crystallization-resisting icosahedral symmetry is energetically most favorable in the composition range 0.63 < xCu < 0.68, and is the underlying motif for one of the three optimal glass-forming ranges observed experimentally for this binary system (Li et al., 2008). This work establishes an energy-based methodology to evaluate specific medium-range structural motifs which compete with stable crystalline nuclei in deeply undercooled liquids.

  18. Composition-dependent stability of the medium-range order responsible for metallic glass formation

    DOE PAGESBeta

    Zhang, Feng; Ji, Min; Fang, Xiao-Wei; Sun, Yang; Wang, Cai-Zhuang; Mendelev, Mikhail I.; Kramer, M. J.; Napolitano, Ralph E.; Ho, Kai-Ming

    2014-09-18

    The competition between the characteristic medium-range order corresponding to amorphous alloys and that in ordered crystalline phases is central to phase selection and morphology evolution under various processing conditions. We examine the stability of a model glass system, Cu–Zr, by comparing the energetics of various medium-range structural motifs over a wide range of compositions using first-principles calculations. Furthermore, we focus specifically on motifs that represent possible building blocks for competing glassy and crystalline phases, and we employ a genetic algorithm to efficiently identify the energetically favored decorations of each motif for specific compositions. These results show that a Bergman-type motifmore » with crystallization-resisting icosahedral symmetry is energetically most favorable in the composition range 0.63 < xCu < 0.68, and is the underlying motif for one of the three optimal glass-forming ranges observed experimentally for this binary system (Li et al., 2008). This work establishes an energy-based methodology to evaluate specific medium-range structural motifs which compete with stable crystalline nuclei in deeply undercooled liquids.« less

  19. Gamma-hydroxybutyric acid stability and formation in blood and urine.

    PubMed

    Beránková, Katerina; Mutnanská, Katerina; Balíková, Marie

    2006-09-12

    Gamma-hydroxybutyric acid (GHB) can cause problems in interpretation of toxicological findings due to its endogenous nature, significant production in tissues after death and potential formation in stored samples. Our study was designed to determine the influence of storage conditions on GHB levels and its possible in vitro formation in blood and urine in cases where no exogenous use of GHB or its precursors was suspected. The samples were prepared by validated method based on liquid-liquid reextraction with adipic acid internal standard and MSTFA derivatization and assayed on a GC-MS operating in EI SIM mode. The first part of the study was performed with pooled blood and urine samples obtained from living and deceased subjects stored with and without NaF (1% w/v) at 4 and -20 degrees C over 8 months. In ante-mortem samples (both blood and urine) no significant GHB production was found. After 4 months of storage, the substantial GHB rise up to 100 mg/Lwas observed in post-mortem blood stored at 4 degrees C without NaF with subsequent gradual decrease in following months. The inhibition of GHB production was apparent during storage in NaF treated frozen blood samples. In post-mortem urine only slight temporary GHB levels were ascertained (up to 8 mg/L). The second part of our study was aimed to analyse 20 individual post-mortem blood samples stored at 4 degrees C for 16-27 days between autopsy and analysis without preservation followed by storage at 4 degrees C with NaF for 4 months. The temporary GHB production with maximum of 28 mg/Lwas detected in some samples. PMID:16857333

  20. C-N Bond Formation from a Masked High-Valent Copper Complex Stabilized by Redox Non-Innocent Ligands.

    PubMed

    Jacquet, Jérémy; Chaumont, Pauline; Gontard, Geoffrey; Orio, Maylis; Vezin, Hervé; Blanchard, Sébastien; Desage-El Murr, Marine; Fensterbank, Louis

    2016-08-26

    The reactivity of a stable copper(II) complex bearing fully oxidized iminobenzoquinone redox ligands towards nucleophiles is described. In sharp contrast with its genuine low-valent counterpart bearing reduced ligands, this complex performs high-yielding C-N bond formations. Mechanistic studies suggest that this behavior could stem from a mechanism akin to reductive elimination occurring at the metal center but facilitated by the ligand: it is proposed that a masked high oxidation state of the metal can be stabilized as a lower copper(II) oxidation state by the redox ligands without forfeiting its ability to behave as a high-valent copper(III) center. These observations are substantiated by a combination of advanced EPR spectroscopy techniques with DFT studies. This work sheds light on the potential of redox ligands as promoters of unusual reactivities at metal centers and illustrates the concept of masked high-valent metallic species. PMID:27504607

  1. A Kalman Filter for Mass Property and Thrust Identification of the Spin-Stabilized Magnetospheric Multiscale Formation

    NASA Technical Reports Server (NTRS)

    Queen, Steven Z.

    2015-01-01

    The Magnetospheric Multiscale (MMS) mission consists of four identically instrumented, spin-stabilized observatories, elliptically orbiting the Earth in a tetrahedron formation. For the operational success of the mission, on-board systems must be able to deliver high-precision orbital adjustment maneuvers. On MMS, this is accomplished using feedback from on-board star sensors in tandem with accelerometers whose measurements are dynamically corrected for errors associated with a spinning platform. In order to determine the required corrections to the measured acceleration, precise estimates of attitude, rate, and mass-properties are necessary. To this end, both an on-board and ground-based Multiplicative Extended Kalman Filter (MEKF) were formulated and implemented in order to estimate the dynamic and quasi-static properties of the spacecraft.

  2. Formation of copper aluminate spinel and cuprous aluminate delafossite to thermally stabilize simulated copper-laden sludge.

    PubMed

    Hu, Ching-Yao; Shih, Kaimin; Leckie, James O

    2010-09-15

    The study reported herein indicated the stabilization mechanisms at work when copper-laden sludge is thermally treated with gamma-alumina and kaolinite precursors, and evaluated the prolonged leachability of their product phases. Four copper-containing phases - copper oxide (CuO), cuprous oxide (Cu(2)O), copper aluminate spinel (CuAl(2)O(4)), and cuprous aluminate delafossite (CuAlO(2)) - were found in the thermal reactions of the investigated systems. These phases were independently synthesized for leaching by 0.1M HCl aqueous solution, and the relative leachabilities were found to be CuAl(2)O(4)formation mechanism employed to stabilize copper into CuAl(2)O(4) and CuAlO(2) are extensively discussed here. With a 3h of short sintering, it was found that CuAl(2)O(4) could be effectively formed between 850 and 950 degrees C by the gamma-alumina precursor. Although kaolinite had a lower incorporation capability than gamma-alumina, it was found to transform a considerable amount of copper into CuAl(2)O(4) between 950 and 1000 degrees C. At higher temperatures, CuAlO(2) was produced only in the gamma-alumina system as the occurrence of Cu(2)O-cristobalite solution in the kaolinite system precluded the production of CuAlO(2). The hypothesis that the spinel formation mechanism has two stages was supported by the results of the changing Cu/Al mole ratio in the system, and the rate-limiting step was identified as the diffusion process in the second stage. PMID:20570043

  3. Landfast sea ice formation and deformation near barrow, Alaska: Variability and implications for ice stability

    NASA Astrophysics Data System (ADS)

    Jones, Joshua M.

    Climate change in the Arctic is having large and far-reaching effects. Sea ice is declining in annual extent and thinning with a warming of the atmosphere and the ocean. As a result, sea ice dynamic behaviour and processes are undergoing major changes, interacting with socio-economic changes underway in the Arctic. Near Barrow, Alaska, landfast sea ice is an integral part of native Inupiaq culture and impacts the natural resource extraction and maritime industries. Events known as breakouts of the landfast ice, in which stable landfast ice becomes mobile and detaches from the coast, have been occurring more frequently in recent years in northern Alaska. The current study investigates processes contributing to breakout events near Barrow, and environmental conditions related to the detachment of landfast sea ice from the coast. In this study, synoptic scale sea level pressure patterns are classified in an attempt to identify atmospheric preconditioning and drivers of breakout events. An unsupervised classification approach, so called Self-Organizing Maps, is employed to sort daily sea level pressure distributions across the study area into commonly observed patterns. The results did not point to any particular distributions which favored the occurrence of breakouts. Because of the comparatively small number of breakout events tracked at Barrow to date (nine events between 2006 and 2010), continued data collection may still yield data that support a relationship between breakout events and large scale sea level pressure distributions. Two case studies for breakout events in the 2008/09 and 2009/10 ice seasons help identify contributing and controlling factors for shorefast ice fragmentation and detachment. Observational data, primarily from components of the Barrow Sea Ice Observatory, are used to quantify stresses acting upon the landfast ice. The stability of the landfast ice cover is estimated through the calculation of the extent of grounded pressure ridges

  4. Analytical modelling of wave refraction and convergence on coral reef platforms: Implications for island formation and stability

    NASA Astrophysics Data System (ADS)

    Mandlier, Philipp Georg; Kench, Paul Simon

    2012-07-01

    An analytical model was constructed to simulate the refraction of waves on coral reef platforms comprising an idealised bathymetry of uniform depth and vertical reef faces. Model simulations were conducted to investigate the influence of key parameters such as reef shape and depth as well as wave period on the propagation behaviour of incident waves. Results of the refraction analysis demonstrate that different reef shapes produce characteristic patterns of wave convergence on reef surfaces. The location and stability of focal zones and hence wave convergence is largely controlled by the shape of platforms. Platform configuration further controls the distribution of wave energy across platform surfaces and determines the influence of incident wave forcing on different reef sections. Results have significant implications for sedimentation processes and hence the formation and stability of islands on reef platforms. Wave propagation patterns define sediment transport vectors and subsequently control the transport and deposition of different sized material. Platforms which promote marked wave convergence behaviour, such as elliptical and circular reefs, are more likely to retain sediment on reef surfaces, whereas narrow linear structures have a higher potential for the off-reef evacuation of sediment over leeward reef margins and the subsequent infill of deeper lagoonal areas. The study provides a physical basis for future investigations of reef hydrodynamics and platform sedimentation processes.

  5. Correlated Formation and Stability of SIA Loops and Stacking Fault Tetrahedra in High Energy Displacement Cascades in Copper,

    SciTech Connect

    Voskoboinikov, Roman E; Osetskiy, Yury N; Bacon, David J

    2005-01-01

    Atomistic modeling was conducted for an investigation of primary damage creation, self-interstitial and vacancy clusters formation, and their stability in high energy displacement cascades in copper. The simulations were carried out for a wide range of temperatures (100 K {le} T {le} 900 K) and primary knock-on atom (PKA) energies 5 keV {le} Epka {le} 25 keV. This study of over 400 cascades is the largest yet reported for this metal. At least 20 cascades for each (Epka, T) pair were simulated in order to ensure statistical reliability of the results. The number of surviving point defects for each cascade and the mean value for cascades at the same temperature and PKA energy were found. The corresponding fraction of self-interstitial atoms (SIA) in dislocation loops and vacancies in stacking fault tetrahedron (SFT)-like clusters was calculated. Strong spatial and size correlation of SFTs and SIA clusters at low temperatures were established. In the context of high dose irradiation and the spatial overlap of displacement cascades, the stability of SFTs and dislocation loops inside an overlapping cascade region was investigated. It was observed that an SFT destroyed in the collision phase by a cascade is always recreated. On being completely enveloped by the region of displaced atoms, both SFT and SIA dislocation loops are destroyed with corresponding decrease of the number of residual point defects, whereas partial overlapping leads to increase in size of both types of cluster.

  6. Formation and Stabilization of Combustion-Generated, Environmentally Persistent Radicals on Ni(II)O Supported on a Silica Surface

    PubMed Central

    Vejerano, Eric; Lomnicki, Slawomir M.; Dellinger, Barry

    2013-01-01

    Previous studies have indicated Environmentally Persistent Free Radicals (EPFRs) are formed when hydroxyl- and chlorine-substituted aromatics chemisorbed on Cu(II)O and Fe(III)2O3 surfaces and were stabilized through their interactions with the surface metal cation. The current study reports our laboratory investigation on the formation and stabilization of EPFRs on an Ni(II)O surface. The EPFRs were produced by the chemisorption of adsorbates on the supported metal oxide surface and transfer of an electron from the adsorbate to the metal center, resulting in reduction of the metal cation. Depending on the temperature and the nature of the adsorbate, more than one type of organic radical was formed. A phenoxyl-type radical, with g-value between 2.0029 and 2.0044, and a semiquinone-type radical, with g-value from 2.0050 to as high as 2.0081, were observed. The half-lives on Ni(II)O were long and ranged from 1.5 to 5.2 days, which were similar to what were observed on Fe(III)2O3,. The yields of the EPFRs formed on Ni(II)O was ~ 8x higher than on Cu(II)O and ~50x higher than on Fe(III)2O3. PMID:22831558

  7. Evaluation of the geological relationships to gas hydrate formation and stability

    SciTech Connect

    Not Available

    1985-01-01

    During the reported year we have enhanced our knowledge on and gained considerable experience in assessment of the gas hydrate resources in the offshore environments. Specifically, we have learned and gained experience in the following: Efficiently locating data sources, including published literature and unpublished information. We have established personal communication extremely critical in data accessability and acquisition. We have updated information pertinent to gas hydrate knowledge, also based on thorough study and evaluation of most Russian literature and additional publications in languages other than English. Besides critical evaluation of widely spread literature, in many cases our reports include previously unpublished information (e.g. BSRs from the Gulf of Mexico). The assessment of the gas resources potential associated with the gas hydrates, although in most cases at a low level of confidence, appears also very encouraging for further, more detailed, study. We are also confident that, because of the present reports' format, new data and a concept-oriented approach, the result of our study will be of strong interest to various industries, research institutions and numerous governmental agencies.

  8. CCM2-CCM3 interaction stabilizes their protein expression and permits endothelial network formation

    SciTech Connect

    Draheim, Kyle M.; Li, Xiaofeng; Zhang, Rong; Fisher, Oriana S.; Villari, Giulia; Boggon, Titus J.; Calderwood, David A.

    2015-04-21

    Mutations in the essential adaptor proteins CCM2 or CCM3 lead to cerebral cavernous malformations (CCM), vascular lesions that most frequently occur in the brain and are strongly associated with hemorrhagic stroke, seizures, and other neurological disorders. CCM2 binds CCM3, but the molecular basis of this interaction, and its functional significance, have not been elucidated. Here, we used x-ray crystallography and structure-guided mutagenesis to show that an α-helical LD-like motif within CCM2 binds the highly conserved “HP1” pocket of the CCM3 focal adhesion targeting (FAT) homology domain. By knocking down CCM2 or CCM3 and rescuing with binding-deficient mutants, we establish that CCM2–CCM3 interactions protect CCM2 and CCM3 proteins from proteasomal degradation and show that both CCM2 and CCM3 are required for normal endothelial cell network formation. However, CCM3 expression in the absence of CCM2 is sufficient to support normal cell growth, revealing complex-independent roles for CCM3.

  9. MHD simulations of protostellar jets: formation and stability of shock diamonds

    NASA Astrophysics Data System (ADS)

    Ustamujic, Sabina

    2016-07-01

    The early stages of a star birth are characterised by a variety of mass ejection phenomena, including outflows and collimated jets, that are strongly related with the accretion process developed in the context of the star-disc interaction. After been ejected, jets move through the ambient medium, interacting and producing shocks and complex structures that are observed at different wavelength bands. In particular, X-ray observations show evidence of strong shocks heating the plasma up to temperatures of a few million degrees. In some cases, the shocked features appear to be stationary and have been interpreted as shock diamonds. We aim at investigating the physical properties of the shocked plasma and the role of the magnetic field on the collimation performing 2.5D MHD simulations, including the effects of the thermal conduction and the radiative losses. We modelled the propagation of a jet ramming with a supersonic speed into an initially isothermal and homogeneous magnetized medium. We studied the physics that guides the formation of a stationary shock (for instance a shock diamond) and compared the results with observations, via the emission measure distribution vs. temperature and the luminosity synthesised from the simulations.

  10. [Effect of Increasing Organic Loading Rate on the Formation and Stabilization Process of Aerobic Granular Sludge].

    PubMed

    Liu, Xiao-peng; Wang, Jan-fang; Qian, Fei-yue; Wang, Yan; Chen, Chong-jun; Shen, Yao-liang

    2015-09-01

    In order to evaluate the effect of organic loading rate ( OLR) on the formation of aerobic granular sludge (AGS), a lab-scale cylindrical SBR reactor (sodium acetate as carbon source) was constructed and inoculated with collected sewage sludge. The evolution of morphology, microbial activity and extracellular polymeric substances (EPS) characteristics of sludge samples in the reactor were recorded and analyzed. The results showed that AGS has the highest growth rate under the condition of 3. 20-4. 84 kg.(m3.d)-1 OLR, and a selective discharging strategy of the floccular sludge was suggested to maintain the predominance of AGS in reactor. The accumulated sludge concentration, SVI30, mean granule size, settling velocity and SOUR value of the AGS in steady-state operated SBR was 23. 9 g.L-1, 20 mL.g-1, 1. 4 mm, 102 m.h-1 and 50. 2 mg.(g.h)-1, respectively. The granulation process not only obviously changed the sludge appearance, but also significantly improved the microbial activity. Meanwhile, linear correlation was observed between the variation of protein/polysaccharide concentration and the granule size of AGS. Thus, variation of protein/ polysaccharide concentration of the EPS could be applied as an indicator for optimization of the cultivation method of AGS. PMID:26717698

  11. Evaluation of the formation and stability of hydroxyalkylsulfonic acids in wines.

    PubMed

    de Azevedo, Luciana C; Reis, Marina M; Motta, Luiz F; da Rocha, Gisele O; Silva, Luciana A; de Andrade, Jailson B

    2007-10-17

    The presence of carbonyl compounds (CCs) in wines has sparked the interest of researchers in several countries. The quantification of some of these compounds has been used as a parameter of quality for many fermented beverages. Although present in minute quantities (except for acetaldehyde), they have a strong olfactory impact. In addition, the CCs found in wines have a strong affinity for bisulfite and can form stable adducts, which will also interfere in the characteristics of aroma. The greatest challenge, however, is to predict which CCs have the strongest affinity for S(IV) and what conditions favor this interaction. To better understand the reaction of CC-bisulfite adduct formation (HASA), this study has evaluated the profile of 22 CCs in a "synthetic wine" containing bisulfite and in 10 real samples of different wines from the São Francisco Valley, northeastern Brazil. On the basis of principal component analysis (PCA) and dissociation constants, the results revealed that aliphatic aldehydes form adducts with S(IV), whereas ketones, cyclic aldehydes, and trans-alkenes interact weakly and are found predominantly in their free form. These results revealed also that pH 10 and 11 were defined as the most appropriate for CC-SO 2 adduct dissociation, and the total CCs were quantified reliably. PMID:17877410

  12. CCM2–CCM3 interaction stabilizes their protein expression and permits endothelial network formation

    PubMed Central

    Draheim, Kyle M.; Li, Xiaofeng; Zhang, Rong; Fisher, Oriana S.; Villari, Giulia

    2015-01-01

    Mutations in the essential adaptor proteins CCM2 or CCM3 lead to cerebral cavernous malformations (CCM), vascular lesions that most frequently occur in the brain and are strongly associated with hemorrhagic stroke, seizures, and other neurological disorders. CCM2 binds CCM3, but the molecular basis of this interaction, and its functional significance, have not been elucidated. Here, we used x-ray crystallography and structure-guided mutagenesis to show that an α-helical LD-like motif within CCM2 binds the highly conserved “HP1” pocket of the CCM3 focal adhesion targeting (FAT) homology domain. By knocking down CCM2 or CCM3 and rescuing with binding-deficient mutants, we establish that CCM2–CCM3 interactions protect CCM2 and CCM3 proteins from proteasomal degradation and show that both CCM2 and CCM3 are required for normal endothelial cell network formation. However, CCM3 expression in the absence of CCM2 is sufficient to support normal cell growth, revealing complex-independent roles for CCM3. PMID:25825518

  13. Sol-gel reaction stability studied: Influence in the formation temperature and properties of ferroelectric thin films

    SciTech Connect

    Perez, J. Vilarinho, P.M.; Kholkin, A.L.; Almeida, A.

    2009-03-05

    Lead zirconium titanate (PZT) sol-gel solutions were prepared based on distilled lead acetate precursor solutions. A detailed analysis of the distillation effect on the lead precursor and the final PZT solution were carried out by Infrared and Raman techniques. It was found that the increase in the number of distillation steps experienced by the lead precursor solutions removes the constitutional water and increases the lead acetate-2-methoxyethanol interconnectivity; thus improving stability and avoiding the aging effect of the resulting PZT solutions. The thermal decomposition process of the PZT solutions was analyzed based on the thermogravimetric (TG) and differential thermogravimetric analysis (DTA) measurements. It was found that as the number of distillation steps in the lead precursor solutions increases, the decomposition rate increases and the formation temperature of pure perovskite PZT films decreases. X-ray diffraction (XRD) technique was used to study the film phase formation. A pure perovskite phase at 500 deg. C was found by the XRD analysis after the second distillation step. Scanning electron microscope technique was used to carry out the microstructural analysis. Dense microstructure was found in all analyzed films and an incipient columnar grain growth was revealed in PZT films prepared based on lead precursor solution with more than three distillation steps. The dependence of the dielectric, ferroelectric and piezoelectric properties on the number of distillation steps was revealed and a correlation between the distillation process, film microstructure properties and electrical performance was established.

  14. Diagnostics and modeling of yttria-stabilized zirconia formation in solution-precursor plasma-spray process

    NASA Astrophysics Data System (ADS)

    Ozturk, Alper

    Thermal barrier coatings produced by solution-precursor plasma-spray (SPPS) process have been shown to offer superior thermal properties and durability. The microstructure of these coatings combines favorable properties of conventional air plasma spray (APS) and electron beam physical vapor deposition (EB-PVD) coatings by providing evenly spaced, through-thickness vertical cracks and uniformly distributed porosity resulting in good strain tolerance and low thermal conductivity. This experimental and computational study aims at clarifying some of the key aspects of this process through diagnostics of the actual process, modeling of vaporization and precipitation within droplets and through model experiments which utilize a combustion flame instead of a plasma jet. The work also includes characterization of the combustion flame and study of the possibility of coating formation utilizing combustion processes instead of plasmas. Plasma-extracted sample indicate presence of spherical sintered polycrystalline particles of 100 nm to 1 micron. Characterization of the precursor spray show that the mean droplet size is about 40 micron suggesting droplet disintegration in the process. Modeling of the heat and mass transfer around the droplets and solute precipitation predict formation of shell type structures and ceno-spheres supported by the experimental evidence of shell type structures in the single pass plasma experiments. Combustion flame experiments were found to produce sintered polycrystalline tetragonal yttria-stabilized zirconia particles similar to the plasma-extracted samples. The microstructural and compositional evolution of the ceramic particles was characterized as a function of downstream distance in the flame jet.

  15. Formation and Fragmentation of Unsaturated Fatty Acid [M - 2H + Na]- Ions: Stabilized Carbanions for Charge-Directed Fragmentation

    NASA Astrophysics Data System (ADS)

    Thomas, Michael C.; Kirk, Benjamin B.; Altvater, Jens; Blanksby, Stephen J.; Nette, Geoffrey W.

    2013-12-01

    Fatty acids are long-chain carboxylic acids that readily produce [M - H]- ions upon negative ion electrospray ionization (ESI) and cationic complexes with alkali, alkaline earth, and transition metals in positive ion ESI. In contrast, only one anionic monomeric fatty acid-metal ion complex has been reported in the literature, namely [M - 2H + FeIICl]-. In this manuscript, we present two methods to form anionic unsaturated fatty acid-sodium ion complexes (i.e., [M - 2H + Na]-). We find that these ions may be generated efficiently by two distinct methods: (1) negative ion ESI of a methanolic solution containing the fatty acid and sodium fluoride forming an [M - H + NaF]- ion. Subsequent collision-induced dissociation (CID) results in the desired [M - 2H + Na]- ion via the neutral loss of HF. (2) Direct formation of the [M - 2H + Na]- ion by negative ion ESI of a methanolic solution containing the fatty acid and sodium hydroxide or bicarbonate. In addition to deprotonation of the carboxylic acid moiety, formation of [M - 2H + Na]- ions requires the removal of a proton from the fatty acid acyl chain. We propose that this deprotonation occurs at the bis-allylic position(s) of polyunsaturated fatty acids resulting in the formation of a resonance-stabilized carbanion. This proposal is supported by ab initio calculations, which reveal that removal of a proton from the bis-allylic position, followed by neutral loss of HX (where X = F- and -OH), is the lowest energy dissociation pathway.

  16. H-treatment impact on conductive-filament formation and stability in Ta2O5-based resistive-switching memory cells

    NASA Astrophysics Data System (ADS)

    Goux, L.; Kim, J. Y.; Magyari-Kope, B.; Nishi, Y.; Redolfi, A.; Jurczak, M.

    2015-03-01

    In this article, we evidence the lower formation energy and improved stability of the conductive filament (CF) formed in TiNTa2O5Ta resistive-switching memory cells treated in NH3 atmosphere at 400 °C. This annealing treatment results in (i) lower forming voltage, (ii) lower CF resistance, and (iii) longer retention lifetime of the oxygen-vacancy (Vo) chain constituting the CF. Atomistic insights into these processes are provided by ab initio calculations performed for hydrogen (H) species incorporated in non-stoichiometric Ta2O5 supercells: (i) Vo formation energy is reduced by the presence of H, (ii) Vo-chain CF conductivity is increased by Vo + OH complex formation, and (iii) Vo-chain retention is strengthened by the stable Vo + OH complex. As a result, efficient CF formation and excellent state stability are obtained after 15 days at 250 °C.

  17. Role of the reaction of stabilized Criegee intermediates with peroxy radicals in particle formation and growth in air.

    PubMed

    Zhao, Yue; Wingen, Lisa M; Perraud, Véronique; Greaves, John; Finlayson-Pitts, Barbara J

    2015-05-21

    Ozonolysis of alkenes is an important source of secondary organic aerosol (SOA) in the atmosphere. However, the mechanisms by which stabilized Criegee intermediates (SCI) react to form and grow the particles, and in particular the contributions from oligomers, are not well understood. In this study, ozonolysis of trans-3-hexene (C6H12), as a proxy for small alkenes, was investigated with an emphasis on the mechanisms of particle formation and growth. Ozonolysis experiments were carried out both in static Teflon chambers (18-20 min reaction times) and in a glass flow reactor (24 s reaction time) in the absence and presence of OH or SCI scavengers, and under different relative humidity (RH) conditions. The chemical composition of polydisperse and size-selected SOA particles was probed using different mass spectrometric techniques and infrared spectroscopy. Oligomers having SCI as the chain unit are found to be the dominant components of such SOA particles. The formation mechanism for these oligomers suggested by our results follows the sequential addition of SCI to organic peroxy (RO2) radicals, in agreement with previous studies by Moortgat and coworkers. Smaller particles are shown to have a relatively greater contribution from longer oligomers. Higher O/C ratios are observed in smaller particles and are similar to those of oligomers resulting from RO2 + nSCI, supporting a significant role for longer oligomers in particle nucleation and early growth. Under atmospherically relevant RH of 30-80%, water vapor suppresses oligomer formation through scavenging SCI, but also enhances particle nucleation. Under humid conditions, or in the presence of formic or hydrochloric acid as SCI scavengers, peroxyhemiacetals are formed by the acid-catalyzed particle phase reaction between oligomers from RO2 + nSCI and a trans-3-hexene derived carbonyl product. In contrast to the ozonolysis of trans-3-hexene, oligomerization involving RO2 + nSCI does not appear to be prevalent in the

  18. Copper stabilization via spinel formation during the sintering of simulated copper-laden sludge with aluminum-rich ceramic precursors.

    PubMed

    Tang, Yuanyuan; Chui, Stephen Sin-Yin; Shih, Kaimin; Zhang, Lingru

    2011-04-15

    The feasibility of incorporating copper-laden sludge into low-cost ceramic products, such as construction ceramics, was investigated by sintering simulated copper-laden sludge with four aluminum-rich ceramic precursors. The results indicated that all of these precursors (γ-Al(2)O(3), corundum, kaolinite, mullite) could crystallochemically stabilize the hazardous copper in the more durable copper aluminate spinel (CuAl(2)O(4)) structure. To simulate the process of copper transformation into a spinel structure, CuO was mixed with the four aluminum-rich precursors, and fired at 650-1150 °C for 3 h. The products were examined using powder X-ray diffraction (XRD) and scanning electron microscopic techniques. The efficiency of copper transformation among crystalline phases was quantitatively determined through Rietveld refinement analysis of the XRD data. The sintering experiment revealed that the optimal sintering temperature for CuAl(2)O(4) formation was around 1000 °C and that the efficiency of copper incorporation into the crystalline CuAl(2)O(4) structure after 3 h of sintering ranged from 40 to 95%, depending on the type of aluminum precursor used. Prolonged leaching tests were carried out by using acetic acid with an initial pH value of 2.9 to leach CuO and CuAl(2)O(4) samples for 22 d. The sample leachability analysis revealed that the CuAl(2)O(4) spinel structure was more superior to stabilize copper, and suggested a promising and reliable technique for incorporating copper-laden sludge or its incineration ash into usable ceramic products. Such results also demonstrated the potential of a waste-to-resource strategy by using waste materials as part of the raw materials with the attainable temperature range used in the production of ceramics. PMID:21428386

  19. Formation of H2-He substellar bodies in cold conditions. Gravitational stability of binary mixtures in a phase transition

    NASA Astrophysics Data System (ADS)

    Füglistaler, A.; Pfenniger, D.

    2016-06-01

    Context. Molecular clouds typically consist of 3/4 H2, 1/4 He and traces of heavier elements. In an earlier work we showed that at very low temperatures and high densities, H2 can be in a phase transition leading to the formation of ice clumps as large as comets or even planets. However, He has very different chemical properties and no phase transition is expected before H2 in dense interstellar medium conditions. The gravitational stability of fluid mixtures has been studied before, but these studies did not include a phase transition. Aims: We study the gravitational stability of binary fluid mixtures with special emphasis on when one component is in a phase transition. The numerical results are aimed at applications in molecular cloud conditions, but the theoretical results are more general. Methods: First, we study the gravitational stability of van der Waals fluid mixtures using linearized analysis and examine virial equilibrium conditions using the Lennard-Jones intermolecular potential. Then, combining the Lennard-Jones and gravitational potentials, the non-linear dynamics of fluid mixtures are studied via computer simulations using the molecular dynamics code LAMMPS. Results: Along with the classical, ideal-gas Jeans instability criterion, a fluid mixture is always gravitationally unstable if it is in a phase transition because compression does not increase pressure. However, the condensed phase fraction increases. In unstable situations the species can separate: in some conditions He precipitates faster than H2, while in other conditions the converse occurs. Also, for an initial gas phase collapse the geometry is essential. Contrary to spherical or filamentary collapses, sheet-like collapses starting below 15 K easily reach H2 condensation conditions because then they are fastest and both the increase of heating and opacity are limited. Conclusions: Depending on density, temperature and mass, either rocky H2 planetoids, or gaseous He planetoids form. H2

  20. Formation of a Stabilized Cysteine Sulfinic Acid Is Critical for the Mitochondrial Function of the Parkinsonism Protein DJ-1

    SciTech Connect

    Blackinton, Jeff; Lakshminarasimhan, Mahadevan; Thomas, Kelly J.; Ahmad, Rili; Greggio, Elisa; Raza, Ashraf S.; Cookson, Mark R.; Wilson, Mark A.

    2009-03-02

    The formation of cysteine-sulfinic acid has recently become appreciated as a modification that links protein function to cellular oxidative status. Human DJ-1, a protein associated with inherited parkinsonism, readily forms cysteine-sulfinic acid at a conserved cysteine residue (Cys{sup 106} in human DJ-1). Mutation of Cys{sup 106} causes the protein to lose its normal protective function in cell culture and model organisms. However, it is unknown whether the loss of DJ-1 protective function in these mutants is due to the absence of Cys{sup 106} oxidation or the absence of the cysteine residue itself. To address this question, we designed a series of substitutions at a proximal glutamic acid residue (Glu{sup 18}) in human DJ-1 that alter the oxidative propensity of Cys{sup 106} through changes in hydrogen bonding. We show that two mutations, E18N and E18Q, allow Cys{sup 106} to be oxidized to Cys{sup 106}-sulfinic acid under mild conditions. In contrast, the E18D mutation stabilizes a cysteine-sulfenic acid that is readily reduced to the thiol in solution and in vivo. We show that E18N and E18Q can both partially substitute for wild-type DJ-1 using mitochondrial fission and cell viability assays. In contrast, the oxidatively impaired E18D mutant behaves as an inactive C106A mutant and fails to protect cells. We therefore conclude that formation of Cys{sup 106}-sulfinic acid is a key modification that regulates the protective function of DJ-1.

  1. Foam-stabilizing effects and cling formation patterns of iso-alpha-acids and reduced iso-alpha-acids in lager beer.

    PubMed

    Kunimune, Takeshi; Shellhammer, Thomas H

    2008-09-24

    Foam-stabilizing properties and cling formation patterns of iso-alpha-acids and reduced iso-alpha-acids were investigated using an unhopped lager beer. Unhopped beer was dosed with iso-alpha-acid (Iso), rho-iso-alpha-acid (Rho), tetrahydro-iso-alpha-acid (Tetra), and hexahydro-iso-alpha-acid (Hexa), separately, over a range of concentrations from 2 to 10 ppm. A uniform foam was created by Inpack 2000 Flasher Head and was measured by a NIBEM Foam Stability Tester (NIBEM-TPH) followed by a NIBEM Cling Meter (NIBEM-CLM) to determine the relationship between the concentration and NIBEM-30 and the cling formation ability of each compound. The foam-stabilizing power was determined to be Tetra, Hexa, Iso, and Rho from the strongest to weakest. Linear regression models were created using the NIBEM-TPH data set, and on the basis of 95% confidence intervals, the foam stability of Tetra or Hexa became significantly larger than that of Iso when 2.4 or 4.2 ppm of Tetra or Hexa was used as a replacement for Iso, respectively. Cling formation patterns could be categorized into three groups: "ring", "mesh", and "powdery". The control beer had the lowest foam stability and did not yield any foam cling. PMID:18729457

  2. Effects of biodegradable plastics on the predominant culturable bacteria associated with soil aggregate formation and stability after 9 months of incubation in natural soil

    Technology Transfer Automated Retrieval System (TEKTRAN)

    An in vitro study of the effects of biodegradable plastics on the predominant soil aggregating bacteria associated to soil aggregate formation and stability after 9 months of incubation in soil. Caesar-TonThat TC, Fukui R*, Caesar AJ., Lartey, RT, and Gaskin, JF. USDA-Agricultural Research Service, ...

  3. The identification of goat peroxiredoxin-5 and the evaluation and enhancement of its stability by nanoparticle formation

    PubMed Central

    Feng, Xiaozhou; Liu, Juanjuan; Fan, Shuai; Liu, Fan; Li, Yadong; Jin, Yuanyuan; Bai, Liping; Yang, Zhaoyong

    2016-01-01

    An anticancer bioactive peptide (ACBP), goat peroxiredoxin-5 (gPRDX5), was identified from goat-spleen extract after immunizing the goat with gastric cancer-cell lysate. Its amino acid sequence was determined by employing 2D nano-LC-ESI-LTQ-Orbitrap MS/MS combined with Mascot database search in the goat subset of the Uniprot database. The recombinant gPRDX5 protein was acquired by heterogeneous expression in Escherichia coli. Subsequently, the anti-cancer bioactivity of the peptide was measured by several kinds of tumor cells. The results indicated that the gPRDX5 was a good anti-cancer candidate, especially for killing B16 cells. However, the peptide was found to be unstable without modification with pharmaceutical excipients, which would be a hurdle for future medicinal application. In order to overcome this problem and find an effective way to evaluate the gPRDX5, nanoparticle formation, which has been widely used in drug delivery because of its steadiness in application, less side-effects and enhancement of drug accumulation in target issues, was used here to address the issues. In this work, the gPRDX5 was dispersed into nanoparticles before delivered to B16 cells. By the nanotechnological method, the gPRDX5 was stabilized by a fast and accurate procedure, which suggests a promising way for screening the peptide for further possible medicinal applications. PMID:27074889

  4. Chitosan-mediated formation of biomimetic silica nanoparticles: an effective method for manganese peroxidase immobilization and stabilization.

    PubMed

    Luan, Pan-Pan; Jiang, Yan-Jun; Zhang, Song-Ping; Gao, Jing; Su, Zhi-Guo; Ma, Guang-Hui; Zhang, Yu-Fei

    2014-11-01

    Our work here, for the first time, reported the use of chitosan-mediated biomimetic silica nanoparticles in enzyme immobilization. In order to make clear the relationship among silicification process, silica nanoparticle structure and immobilized enzyme activity, a mechanism of chitosan-mediated silicification using sodium silicate as the silica source was primarily evaluated. Chitosan was demonstrated effectively to promote the silicification not only in accelerating the aggregation rate of sodium silicate, but also in templating the formation of silica nanoparticles. Although the whole biomimetic silicification process contained polycondensation-aggregation-precipitation three stages, the elemental unit in precipitated silica was confirmed to be nanoparticles with 100 nm diameter regardless of the chitosan and silicate concentration used. Furthermore, the effect of enzyme on silicification process was also investigated. The introducing of manganese peroxidase (MnP) to silica precursor solution had no obvious effect on the silicification rate and nanoparticle morphology. The residual activity and embedding rate of immobilized MnP were 64.2% and 36.4% respectively under the optimum conditions. In addition, compared to native MnP, the MnP embedded in chitosan/silica nanoparticles exhibited improved stability against organic solvent and ultrasonic wave. After ultrasonic treatment for 20 min, 77% of the initial activity was remained due to the protective effect of chitosan/silica nanoparticles, while native MnP lost almost all of its original activity. PMID:24913823

  5. The identification of goat peroxiredoxin-5 and the evaluation and enhancement of its stability by nanoparticle formation.

    PubMed

    Feng, Xiaozhou; Liu, Juanjuan; Fan, Shuai; Liu, Fan; Li, Yadong; Jin, Yuanyuan; Bai, Liping; Yang, Zhaoyong

    2016-01-01

    An anticancer bioactive peptide (ACBP), goat peroxiredoxin-5 (gPRDX5), was identified from goat-spleen extract after immunizing the goat with gastric cancer-cell lysate. Its amino acid sequence was determined by employing 2D nano-LC-ESI-LTQ-Orbitrap MS/MS combined with Mascot database search in the goat subset of the Uniprot database. The recombinant gPRDX5 protein was acquired by heterogeneous expression in Escherichia coli. Subsequently, the anti-cancer bioactivity of the peptide was measured by several kinds of tumor cells. The results indicated that the gPRDX5 was a good anti-cancer candidate, especially for killing B16 cells. However, the peptide was found to be unstable without modification with pharmaceutical excipients, which would be a hurdle for future medicinal application. In order to overcome this problem and find an effective way to evaluate the gPRDX5, nanoparticle formation, which has been widely used in drug delivery because of its steadiness in application, less side-effects and enhancement of drug accumulation in target issues, was used here to address the issues. In this work, the gPRDX5 was dispersed into nanoparticles before delivered to B16 cells. By the nanotechnological method, the gPRDX5 was stabilized by a fast and accurate procedure, which suggests a promising way for screening the peptide for further possible medicinal applications. PMID:27074889

  6. Formation and stability of interpenetrating polymer network hydrogels consisting of fibrin and hyaluronic acid for tissue engineering.

    PubMed

    Lee, Fan; Kurisawa, Motoichi

    2013-02-01

    Fibrin gel is widely used as a tissue engineering scaffold. However, it has poor mechanical properties, which often result in rapid contraction and degradation of the scaffold. An interpenetrating polymer network (IPN) hydrogel composed of fibrin and hyaluronic acid-tyramine (HA-Tyr) was developed to improve the mechanical properties. The fibrin network was formed by cleaving fibrinogen with thrombin, producing fibrin monomers that rapidly polymerize. The HA network was formed through the coupling of tyramine moieties using horseradish peroxidase (HRP) and hydrogen peroxide (H₂O₂). The degree of crosslinking of the HA-Tyr network can be tuned by varying the H₂O₂ concentration, producing IPN hydrogels with different storage moduli (G'). While fibrin gels were completely degraded in the presence of plasmin and contracted when embedded with cells, the shape of the IPN hydrogels was maintained due to structural support by the HA-Tyr networks. Cell proliferation and capillary formation occurred in IPN hydrogels and were found to decrease with increasing G' of the hydrogels. The results suggest that fibrin-HA-Tyr IPN hydrogels are a potential alternative to fibrin gels as scaffolds for tissue engineering applications that require shape stability. PMID:22943886

  7. The identification of goat peroxiredoxin-5 and the evaluation and enhancement of its stability by nanoparticle formation

    NASA Astrophysics Data System (ADS)

    Feng, Xiaozhou; Liu, Juanjuan; Fan, Shuai; Liu, Fan; Li, Yadong; Jin, Yuanyuan; Bai, Liping; Yang, Zhaoyong

    2016-04-01

    An anticancer bioactive peptide (ACBP), goat peroxiredoxin-5 (gPRDX5), was identified from goat-spleen extract after immunizing the goat with gastric cancer-cell lysate. Its amino acid sequence was determined by employing 2D nano-LC-ESI-LTQ-Orbitrap MS/MS combined with Mascot database search in the goat subset of the Uniprot database. The recombinant gPRDX5 protein was acquired by heterogeneous expression in Escherichia coli. Subsequently, the anti-cancer bioactivity of the peptide was measured by several kinds of tumor cells. The results indicated that the gPRDX5 was a good anti-cancer candidate, especially for killing B16 cells. However, the peptide was found to be unstable without modification with pharmaceutical excipients, which would be a hurdle for future medicinal application. In order to overcome this problem and find an effective way to evaluate the gPRDX5, nanoparticle formation, which has been widely used in drug delivery because of its steadiness in application, less side-effects and enhancement of drug accumulation in target issues, was used here to address the issues. In this work, the gPRDX5 was dispersed into nanoparticles before delivered to B16 cells. By the nanotechnological method, the gPRDX5 was stabilized by a fast and accurate procedure, which suggests a promising way for screening the peptide for further possible medicinal applications.

  8. Numerical studies of nitric oxide formation in nanosecond-pulsed discharge-stabilized flames of premixed methane/air.

    PubMed

    Bak, Moon Soo; Cappelli, Mark A

    2015-08-13

    A simulation is developed to investigate the kinetics of nitric oxide (NO) formation in premixed methane/air combustion stabilized by nanosecond-pulsed discharges. The simulation consists of two connected parts. The first part calculates the kinetics within the discharge while considering both plasma/combustion reactions and species diffusion, advection and thermal conduction to the surrounding flow. The second part calculates the kinetics of the overall flow after mixing the discharge flow with the surrounding flow to account for the effect that the discharge has on the overall kinetics. The simulation reveals that the discharge produces a significant amount of atomic oxygen (O) as a result of the high discharge temperature and dissociative quenching of excited state nitrogen by molecular oxygen. This atomic oxygen subsequently produces hydroxyl (OH) radicals. The fractions of these O and OH then undergo Zel'dovich reactions and are found to contribute to as much as 73% of the total NO that is produced. The post-discharge simulation shows that the NO survives within the flow once produced. PMID:26170428

  9. The spectrin-based membrane skeleton stabilizes mouse megakaryocyte membrane systems and is essential for proplatelet and platelet formation.

    PubMed

    Patel-Hett, Sunita; Wang, Hongbei; Begonja, Antonija J; Thon, Jonathan N; Alden, Eva C; Wandersee, Nancy J; An, Xiuli; Mohandas, Narla; Hartwig, John H; Italiano, Joseph E

    2011-08-11

    Megakaryocytes generate platelets by remodeling their cytoplasm first into proplatelets and then into preplatelets, which undergo fission to generate platelets. Although the functions of microtubules and actin during platelet biogenesis have been defined, the role of the spectrin cytoskeleton is unknown. We investigated the function of the spectrin-based membrane skeleton in proplatelet and platelet production in murine megakaryocytes. Electron microscopy revealed that, like circulating platelets, proplatelets have a dense membrane skeleton, the main fibrous component of which is spectrin. Unlike other cells, megakaryocytes and their progeny express both erythroid and nonerythroid spectrins. Assembly of spectrin into tetramers is required for invaginated membrane system maturation and proplatelet extension, because expression of a spectrin tetramer-disrupting construct in megakaryocytes inhibits both processes. Incorporation of this spectrin-disrupting fragment into a novel permeabilized proplatelet system rapidly destabilizes proplatelets, causing blebbing and swelling. Spectrin tetramers also stabilize the "barbell shapes" of the penultimate stage in platelet production, because addition of the tetramer-disrupting construct converts these barbell shapes to spheres, demonstrating that membrane skeletal continuity maintains the elongated, pre-fission shape. The results of this study provide evidence for a role for spectrin in different steps of megakaryocyte development through its participation in the formation of invaginated membranes and in the maintenance of proplatelet structure. PMID:21566095

  10. Stability constants for the formation of lead chloride complexes as a function of temperature and ionic strength

    PubMed Central

    Luo, Yanxin; Millero, Frank J.

    2015-01-01

    The stability constants for the formation of lead (Pb2+) with chloride Pb2+=nCl−↔PbCln2−nβn(n=1,2,3) have been determined using a spectrophotometric method in NaClO4 solutions as a function of ionic strength (0–6 m) and temperature (15–45 °C). The results have been fitted to the equations: logβ1∗=logβ1+0.21I−8.61I0.5∕(1+1.2I0.5)+1927.40[I0.5∕(1+1.2I0.5)]∕Tlogβ2∗=logβ2+0.32I−4.67I0.5(1+1.2I0.5)+594.54[I0.5∕(1+1.2I0.5)]∕Tlogβ3∗=logβ3+0.40I−2.68I0.5(1+1.2I0.5)−43.98[I0.5∕(1+1.2I0.5)]∕T with standard errors of 0.05, 0.04 and 0.06, respectively. The thermodynamic values of log β1, logβ2 and logβ3 at 25.0 °C and the enthalpies of formation of PbCl+, PbCl20 and PbCl3− are in good agreement with literature values. We have combined our results with the earlier work of Seward (1984) to yield thermodynamic constants that are valid from 15 to 300 °C: logβ1=44.82+0.031T−21.21logTlogβ2=61.42+0.046T−29.51logTlogβ3=107.97+0.071T−51.46logT with standard errors of 0.05, 0.08 and 0.10, respectively. PMID:26937043