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1

Polymeric nanoparticulate system augmented the anticancer therapeutic efficacy of gemcitabine.  

PubMed

Gemcitabine hydrochloride is an anticancer nucleoside analogue indicated in clinic for the treatment of various solid tumors. Although this drug has been demonstrated to display anticancer activity against a wide variety of tumors, it is needed to be administered at high doses to elicit the required therapeutic response, simultaneously leading to severe adverse effects. We hypothesized that the efficient delivery of gemcitabine to tumors using a biodegradable carrier system could reduce the dose required to elicit sufficient therapeutic response. Thus, we have developed a nanoparticle formulation of gemcitabine suitable for parenteral administration based on the biodegradable polymer poly(octylcyanoacrylate) (POCA). The nanoparticles were synthesized by anionic polymerization of the corresponding monomer. Two drug loading methods were analyzed: the first one based on gemcitabine surface adsorption onto the preformed nanoparticles, and the second method being gemcitabine addition before the polymerization process leading to drug entrapment in the polymeric network. A detailed investigation of the capabilities of the polymer particles to load this drug is described. Gemcitabine entrapment into the polymer matrix yielded a higher drug loading and a slower drug release profile as compared with drug adsorption procedure. The main factors determining the gemcitabine incorporation to the polymer network were the nanoparticles preparation procedure, the monomer concentration, the surfactant concentration, the pH, and the drug concentration. The release kinetic of gemcitabine was found to be controlled by the pH and the type of drug incorporation. The cytotoxicity studies performed on L1210 tumor cells revealed a similar anticancer activity of the gemcitabine-loaded POCA (GPOCA) nanoparticle as free gemcitabine. Following intravenous administration into the mice bearing L1210 wt subcutaneous tumor, the GPOCA nanoparticles displayed significantly greater anticancer activity compared to free gemcitabine; this has been additionally confirmed by histology and immunohistochemistry studies, suggesting the potential of GPOCA for the efficient treatment of cancer. PMID:19694612

Arias, José L; Reddy, L Harivardhan; Couvreur, Patrick

2009-09-01

2

Development and characterization of polymeric nanoparticulate delivery system for hydrophillic drug: Gemcitabine  

NASA Astrophysics Data System (ADS)

Gemcitabine is a nucleoside analogue, used in various carcinomas such as non small cell lung cancer, pancreatic cancer, ovarian cancer and breast cancer. The major setbacks to the conventional therapy with gemcitabine include its short half-life and highly hydrophilic nature. The objectives of this investigation were to develop and evaluate the physiochemical properties, drug loading and entrapment efficiency, in vitro release, cytotoxicity, and cellular uptake of polymeric nano-particulate formulations containing gemcitabine hydrochloride. The study also entailed development and validation of a high performance liquid chromatography (HPLC) method for the analysis of gemcitabine hydrochloride. A reverse phase HPLC method using a C18 Luna column was developed and validated. Alginate and Poly lactide co glycolide/Poly-epsilon-caprolactone (PLGA:PCL 80:20) nanoparticles were prepared by multiple emulsion-solvent evaporation methodology. An aqueous solution of low viscosity alginate containing gemcitabine was emulsified into 10% solution of dioctyl-sulfosuccinate in dichloro methane (DCM) by sonication. The primary emulsion was then emulsified in 0.5% (w/v) aqueous solution of polyvinyl alcohol (PVA). Calcium chloride solution (60% w/v) was used to cause cross linking of the polymer. For PLGA:PCL system, the polymer mix was dissolved in dichloromethane (DCM) and an aqueous gemcitabine (with and without sodium chloride) was emulsified under ultrasonic conditions (12-watts; 1-min). This primary emulsion was further emulsified in 2% (w/v) PVA under ultrasonic conditions (24-watts; 3-min) to prepare a multiple-emulsion (w/o/w). In both cases DCM, the organic solvent was evaporated (20- hours, magnetic-stirrer) prior to ultracentrifugation (10000-rpm for PLGA:PCL; 25000-rpm for alginate). The pellet obtained was washed thrice with de-ionized water to remove PVA and any free drug and re-centrifuged. The particles were re-suspended in de-ionized water and then lyophilized to obtain the dried powdered delivery formulation. Particle size and surface charge of the nano-particles were measured using zeta-sizer. The surface morphology and microstructure were evaluated by scanning electron microscopy The drug loading and entrapment efficiencies were evaluated by a HPLC method (Luna C18 column (4.6 X 250 mm), 95/5 (v/v) 0.04M ammonium acetate/acetonitrile mobile phase (pH 5.5), 1.0 ml/min flow rate and 268 nm UV detection). Differential scanning calorimetry (DSC) was used to determine the physical state of gemcitabine in the nanoparticles. The cytotoxicity in pancreatic cancer cells (BxPC-3) was evaluated by MTT assay. The cellular uptake of gemcitabine solution and gemcitabine loaded alginate nano-particle suspension in BxPC-3 cells was determined for 15, 30 and 60 minutes. The particle-size and surface-charge was 564.7+/-56.5nm and -25.65+/-1.94mV for PLGA:PCL and 210.6+/-6.90nm and -33.21+/-1.63mV for alginate. Both the nano-particles were distinctly spherical and non-porous. The drug load was 5.14% for PLGA:PCL and 6.87% for alginate-particles, and the practical entrapment efficiency was found to be 54.1 % and 22.4% respectively. However, in case of PLGA:PCL particles, a two-fold increase in the entrapment efficiency was observed with the addition of sodium-chloride. The absence of endothermic melting peak of the drug in the DSC thermogram was an indication of the non-crystalline state of gemcitabine in the nanoparticles. In addition, there was no cytotoxicity associated with nanoparticle concentrations at-or-below 5 mg/mL. The uptake of nano-particles was around 4 times higher than the solution with treatment for 15 minutes and increased to almost 7 times following treatment for 60 minutes. Gemcitabine hydrochloride could be successfully formulated into a sustained release nano-particulate formulation using calcium cross-linked alginate and dioctyl sulfo succinate system. The nano-particulate delivery system exhibited better cytotoxic activity and also significantly enhanced the accumulation of the drug in BxPC-3 cell monolayers.

Khurana, Jatin

3

Nano-particulate coating on cotton fabric through DBD  

NASA Astrophysics Data System (ADS)

Plasma polymerization of fluorocarbon was processed through dielectric barrier discharge (DBD). A thin hydrophobic film packed with nano-particulate structure was obtained on cotton fabric surface. The contact angle of the water and 1-bromonaphthalene on coated cotton fabric was 133° and 124° separately. The surface morphology of the coating was observed through SEM (Scanning Electronic Microscope). It was found that cotton fabric surface was tightly adhered to a thin film packed by nano-particles from 10nm to 200nm. This process showed potential applications in continuous coating of textiles with functional nano-particulate polymers, but without changing their softness performance.

Guo, Ying; Zhang, Jing; Xu, Jinzhou; Zhou, Rongming; Yu, Jianyong

2008-02-01

4

Advances in polymeric and inorganic vectors for nonviral nucleic acid delivery  

PubMed Central

Nonviral systems for nucleic acid delivery offer a host of potential advantages compared with viruses, including reduced toxicity and immunogenicity, increased ease of production and less stringent vector size limitations, but remain far less efficient than their viral counterparts. In this article we review recent advances in the delivery of nucleic acids using polymeric and inorganic vectors. We discuss the wide range of materials being designed and evaluated for these purposes while considering the physical requirements and barriers to entry that these agents face and reviewing recent novel approaches towards improving delivery with respect to each of these barriers. Furthermore, we provide a brief overview of past and ongoing nonviral gene therapy clinical trials. We conclude with a discussion of multifunctional nucleic acid carriers and future directions. PMID:22826857

Sunshine, Joel C; Bishop, Corey J; Green, Jordan J

2014-01-01

5

Engineering a Polymeric Gene Delivery Vector Based on Poly(ethylenimine) and Hyaluronic Acid  

PubMed Central

In this work, the effects of primary amines, ligand targeting, and overall charge on the effectiveness of branched poly(ethylenimine)-hyaluronic acid conjugate (bPEI-HA) zwitterionic gene delivery vectors are investigated. To elucidate the relative importance of each of these parameters, the zeta potential, cytotoxicity, and transfection efficiency were explored for a variety of formulations of bPEI-HA. It was found that the length of the hyaluronic acid (HA) oligosaccharide had the most significant effect on cytotoxicity and transfection efficiency with human mesenchymal stem cells. Test groups of bPEI incorporating HA with a length of 10 saccharides had significantly higher transfection efficiency (14.6±2.0%) and lower cytotoxicity than other formulations tested, with the cytotoxicity of the group containing the greatest mass of 10 saccharide showing similar results as the positive controls at the highest polymer concentration (100 ?g/ml). Additionally, molar incorporation of HA, as opposed to the saccharide length and HA mass incorporation, had the greatest effect on zeta potential, but a minor effect on both cytotoxicity and transfection efficiency. This work demonstrates the relative importance of each of these tunable design criteria when creating a zwitterionic polymeric gene delivery vector and provides useful specific information regarding the design of bPEI-HA gene delivery vectors. PMID:22455481

Needham, Clark J.; Williams, Austin K.; Chew, Sue Anne; Kasper, F. Kurtis; Mikos, Antonios G.

2012-01-01

6

Encapsulation of antioxidants in gastrointestinal-resistant nanoparticulate carriers.  

PubMed

Reactive oxygen species (ROS) are known to cause several human pathologies. For this reason, antioxidants have gained utmost importance because of their potential as prophylactic and therapeutic agents in many diseases. Examples of their application include their use in diabetic patients, as aging drugs, in cancer diseases, Parkinson's, Alzheimer's, autoimmune disorders, and also in inflammation. Antioxidants have limited absorption profiles, therefore low bioavailability and low concentrations at the target site. Efforts have been done towards loading antioxidant molecules in advanced nanoparticulate carriers, e.g., liposomes, polymeric nanoparticles, solid lipid nanoparticles, self-emulsifying drug delivery system. Examples of -successful achievements include the encapsulation of drugs and other active ingredients, e.g., coenzyme Q10, vitamin E and vitamin A, resveratrol and polyphenols, curcumin, lycopene, silymarin, and superoxide dismutase. This review focuses on the comprehensive analysis of using nanoparticulate carriers for loading these molecules for oral administration. PMID:23740112

Souto, Eliana B; Severino, Patrícia; Basso, Rafael; Santana, Maria Helena A

2013-01-01

7

Dispersion of nanoparticulate suspensions using self-assembled surfactant aggregates  

NASA Astrophysics Data System (ADS)

The dispersion of particles is critical for several industrial applications such as paints, inks, coatings, and cosmetics. Several emerging applications such as abrasives for precision polishing, and drug delivery systems are increasingly relying on nanoparticulates to achieve the desired performance. In the case of nanoparticles, the dispersion becomes more challenging because of the lack of fundamental understanding of dispersant adsorption and interparticle force prediction. Additionally, many of these processes use severe processing environments such as high normal forces (>100 mN/m), high shear forces (>10,000 s -1), and high ionic strengths (>0.1 M). Under such processing conditions, traditionally used dispersants based on electrostatics, and steric force repulsion mechanism may not be adequate. Hence, the development of optimally performing dispersants requires a fundamental understanding of the dispersion mechanism at the atomic/molecular scale. This study explores the use of self-assembled surfactant aggregates at the solid-liquid interface for dispersing nanoparticles in severe processing environments. Surfactant molecules can provide a feasible alternative to polymeric or inorganic dispersants for stabilizing ultrafine particles. The barrier to aggregation in the presence of surfactant molecules was measured using atomic force microscopy. The barrier heights correlated to suspension stability. To understand the mechanism for nanoparticulate suspension stability in the presence of surfactant films, the interface was characterized using zeta potential, contact angle, adsorption, and FT-IR (adsorbed surfactant film structure measurements). The effect of solution conditions such as pH and ionic strength on the suspension stability, and the self-assembled surfactant films was also investigated. It was determined that a transition from a random to an ordered orientation of the surfactant molecules at the interface was responsible for stability of nanoparticulates. Additionally, the role of the surface in surfactant self-assembly was investigated. Mechanical and thermodynamic properties of the self-assembled layer at the solid-liquid interface were calculated based on experimental results, and compared to the corresponding properties in the bulk solution.

Singh, Pankaj Kumar

8

Vectors  

NSDL National Science Digital Library

This lesson was created by Larry Friesen and Anne Gillis for Butler Community College. It will help physics and calculus students differentiate between the uses of vectors in mathematics vs. physics. This website provides two PDF documents that give detailed lessons about vectors, including an overview of terminology, sample problems, and an HTML worksheet is also provided. For educators or students, this site offers well laid-out lessons and/or practice with vectors.

Friesen, Larry; Gillis, Anne

2008-04-18

9

vectors  

NSDL National Science Digital Library

The word vector comes from the Latin term vehere, to carry. In Biology, a vector is an agent which carries disease, such as a mosquito carrying infected blood from one patient to the next. In physics, a vector is a quantity which has both a magnitude and a direction associated with it. The most commonly used example of vectors in everyday life is velocity. When you drive your car, your speedometer tells you the speed of your car, but it doesn't tell you where you are going. The combination of both where you are going and how fast you are going there is your car's velocity.

David Joiner

10

Vectors  

NSDL National Science Digital Library

This web page introduces vectors as an extension of numbers having both magnitude and direction. The initial motivation is to describe velocity but the material includes a general discussion of vector algebra and an application to forces for the inclined plane. The page contains links to a related lesson plan and further opportunities to explore vectors. This is part of the extensive web site "From Stargazers to Starships", that uses space exploration and space science to introduce topics in physics and astronomy. Translations in Spanish and French are available.

Stern, David

2006-07-16

11

Photosensitive liquid crystals with nanoparticulate internal structure  

NASA Astrophysics Data System (ADS)

Stabilization of thermodynamic relaxation of photoinduced cis isomers of azobenzene liquid-crystal molecules is observed in nanoparticulate networks. The phenomenon permits bistability of the phase state (anisotropic and isotropic) of the material and reversible all-optical switching between those states, resulting in strong changes in the light-scattering properties of the material. Recording of complex optical structures with high spatial resolution with the aid of laser beams of different wavelengths is demonstrated.

Tabiryan, N.; Grozhik, V.; Serak, S.

2002-11-01

12

Rate-programming of nano-particulate delivery systems for smart bioactive scaffolds in tissue engineering  

NASA Astrophysics Data System (ADS)

Development of smart bioactive scaffolds is of importance in tissue engineering, where cell proliferation, differentiation and migration within scaffolds can be regulated by the interactions between cells and scaffold through the use of growth factors (GFs) and extra cellular matrix peptides. One challenge in this area is to spatiotemporally control the dose, sequence and profile of release of GFs so as to regulate cellular fates during tissue regeneration. This challenge would be addressed by rate-programming of nano-particulate delivery systems, where the release of GFs via polymeric nanoparticles is controlled by means of the methods of, such as externally-controlled and physicochemically/architecturally-modulated so as to mimic the profile of physiological GFs. Identifying and understanding such factors as the desired release profiles, mechanisms of release, physicochemical characteristics of polymeric nanoparticles, and externally-triggering stimuli are essential for designing and optimizing such delivery systems. This review surveys the recent studies on the desired release profiles of GFs in various tissue engineering applications, elucidates the major release mechanisms and critical factors affecting release profiles, and overviews the role played by the mathematical models for optimizing nano-particulate delivery systems. Potentials of stimuli responsive nanoparticles for spatiotemporal control of GF release are also presented, along with the recent advances in strategies for spatiotemporal control of GF delivery within tissue engineered scaffolds. The recommendation for the future studies to overcome challenges for developing sophisticated particulate delivery systems in tissue engineering is discussed prior to the presentation of conclusions drawn from this paper.

Izadifar, Mohammad; Haddadi, Azita; Chen, Xiongbiao; Kelly, Michael E.

2015-01-01

13

Treatment of lung cancer via telomerase inhibition: self-assembled nanoplexes versus polymeric nanoparticles as vectors for 2'-O-Methyl-RNA.  

PubMed

Antisense oligonucleotide, 2'-O-Methyl-RNA (OMR), is known as potent telomerase inhibitor for the treatment of lung cancer but limited by poor intracellular uptake. Chitosan-coated polymeric nanoparticles were compared to chitosan solution as non-viral vectors for OMR. The study investigated the role of chitosan properties and concentration in improving the efficiency of the nanocarriers in terms of loading, viability, cellular uptake, and telomerase inhibition in human lung cancer cell lines. Certain concentration of chitosan on nanoparticle surface is necessary to significantly increase the cellular uptake. However, excessive chitosan negatively affected the transfection efficiency. Self-assembled nanoplexes with chitosan polymer are preferentially adsorbed to the cell membrane rather than being internalized. Thus, polymeric nanoparticles proved to be superior to cationic polymers as carrier for antisense oligonucleotides. Charge cannot be considered the principle factor behind improved transfection. Uptake studies carried out on air-interface cell cultures to mimic in vivo conditions supported the results on normal cultures showing enhanced uptake of nanoplexes over naked oligonucleotides. OMR nanoplexes reduced telomerase activity by ?50% in A549 cells concluding the potential of the system as a safe, non-invasive, and efficient treatment for lung carcinoma. These data are prerequisites for the ongoing studies on lung perfusion model and in vivo experiments. PMID:22198416

Nafee, N; Schneider, M; Friebel, K; Dong, M; Schaefer, U F; Mürdter, T E; Lehr, C-M

2012-04-01

14

Extracellular stability of nanoparticulate drug carriers  

PubMed Central

Nanoparticulate (NP) drug carrier systems are attractive vehicles for selective drug delivery to solid tumors. Ideally, NPs should evade clearance by the reticuloendothelial system while maintaining the ability to interact with tumor cells and facilitate cellular uptake. Great effort has been made to fulfill these design criteria, yielding various types of functionalized NPs. Another important consideration in NP design is the physical and functional stability during circulation, which, if ignored, can significantly undermine the promise of intelligently designed NP drug carriers. This commentary reviews several NP examples with stability issues and their consequences, ending in a discussion of experimental methods for reliable prediction of NP stability. PMID:24214175

Liu, Karen C.; Yeo, Yoon

2014-01-01

15

Zn sorption mechanisms onto sheathed Leptothrix discophora and the impact of the nanoparticulate biogenic Mn oxide coating.  

PubMed

Zinc sorption on sheathed Leptothrix discophora bacterium, the isolated extracellular polymeric substances (EPS) sheath, and Mn oxide-coated bacteria was investigated with macroscopic and spectroscopic techniques. Complexation with L. discophora was dominated by the outer membrane phosphoryl groups of the phospholipid bilayer while sorption to isolated EPS was dominated by carboxyl groups. Precipitation of nanoparticulate Mn oxide coatings on the cell surface increased site capacity by over twenty times with significant increase in metal sorption. XAS analysis of Zn sorption in the coated system showed Mn oxide phase contributions of 18 to 43% through mononuclear inner-sphere complexes. The coordination environments in coprecipitation samples were identical to those of sorption samples, indicating that, even in coprecipitation, Zn is not incorporated into the Mn oxide structure. Rather, through enzymatic oxidation by L. discophora, Mn(II) is oxidized and precipitated onto the biofilm providing a large surface for metal sequestration. The nanoparticulate Mn oxide coating exhibited significant microporosity (75%) suggesting contributions from intraparticle diffusion. Transient studies conducted over 7 months revealed a 170% increase in Zn loading. However, the intraparticle diffusivity of 10(-19) cm(2) s(-1) is two orders of magnitude smaller than that for abiotic Mn oxide which we attribute to morphological changes such as reduced pore sizes in the nanoparticulate oxide. Our results demonstrate that the cell-bound Mn oxide particles can sorb significant amounts of Zn over long periods of time representing an important surface for sequestration of metal contaminants. PMID:19268965

Boonfueng, Thipnakarin; Axe, Lisa; Yee, Nathan; Hahn, Dittmar; Ndiba, Peter K

2009-05-15

16

Zn Sorption Mechanisms onto Sheathed Leptothrix Discophora and the Impact of the Nanoparticulate Biogenic Mn Oxide Coating  

SciTech Connect

Zinc sorption on sheathed Leptothrix discophora bacterium, the isolated extracellular polymeric substances (EPS) sheath, and Mn oxide-coated bacteria was investigated with macroscopic and spectroscopic techniques. Complexation with L. discophora was dominated by the outer membrane phosphoryl groups of the phospholipid bilayer while sorption to isolated EPS was dominated by carboxyl groups. Precipitation of nanoparticulate Mn oxide coatings on the cell surface increased site capacity by over twenty times with significant increase in metal sorption. XAS analysis of Zn sorption in the coated system showed Mn oxide phase contributions of 18 to 43% through mononuclear inner-sphere complexes. The coordination environments in coprecipitation samples were identical to those of sorption samples, indicating that, even in coprecipitation, Zn is not incorporated into the Mn oxide structure. Rather, through enzymatic oxidation by L. discophora, Mn(II) is oxidized and precipitated onto the biofilm providing a large surface for metal sequestration. The nanoparticulate Mn oxide coating exhibited significant microporosity (75%) suggesting contributions from intraparticle diffusion. Transient studies conducted over 7 months revealed a 170% increase in Zn loading. However, the intraparticle diffusivity of 10{sup -19} cm{sup 2} s{sup -1} is two orders of magnitude smaller than that for abiotic Mn oxide which we attribute to morphological changes such as reduced pore sizes in the nanoparticulate oxide. Our results demonstrate that the cell-bound Mn oxide particles can sorb significant amounts of Zn over long periods of time representing an important surface for sequestration of metal contaminants.

Boonfueng, T.; Axe, L; Yee, N; Hahn, D; Ndiba, P

2009-01-01

17

Nanoparticulate cellular patches for cell-mediated tumoritropic delivery.  

PubMed

The targeted delivery of therapeutics to tumors remains an important challenge in cancer nanomedicine. Attaching nanoparticles to cells that have tumoritropic migratory properties is a promising modality to address this challenge. Here we describe a technique to create nanoparticulate cellular patches that remain attached to the membrane of cells for up to 2 days. NeutrAvidin-coated nanoparticles were anchored on cells possessing biotinylated plasma membrane. Human bone marrow derived mesenchymal stem cells with nanoparticulate patches retained their inherent tumoritropic properties as shown using a tumor model in a 3D extracellular matrix. Additionally, human umbilical vein endothelial cells with nanoparticulate patches were able to retain their functional properties and form multicellular structures as rapidly as unmodified endothelial cells. These results provide a novel strategy to actively deliver nanostructures and therapeutics to tumors utilizing stem cells as carriers and also suggest that nanoparticulate cellular patches may have applications in tissue regeneration. PMID:20121215

Cheng, Hao; Kastrup, Christian J; Ramanathan, Renuka; Siegwart, Daniel J; Ma, Minglin; Bogatyrev, Said R; Xu, Qiaobing; Whitehead, Kathryn A; Langer, Robert; Anderson, Daniel G

2010-02-23

18

Nanoparticulate-catalyzed oxygen transfer processes  

DOEpatents

Nanoparticulates of oxygen transfer materials that are oxides of rare earth metals, combinations of rare earth metals, and combinations of transition metals and rare earth metals are used as catalysts in a variety of processes. Unexpectedly large thermal efficiencies are achieved relative to micron sized particulates. Processes that use these catalysts are exemplified in a multistage reactor. The exemplified reactor cracks C6 to C20 hydrocarbons, desulfurizes the hydrocarbon stream and reforms the hydrocarbons in the stream to produce hydrogen. In a first reactor stage the steam and hydrocarbon are passed through particulate mixed rare earth metal oxide to crack larger hydrocarbon molecules. In a second stage, the steam and hydrocarbon are passed through particulate material that desulfurizes the hydrocarbon. In a third stage, the hydrocarbon and steam are passed through a heated, mixed transition metal/rare earth metal oxide to reform the lower hydrocarbons and thereby produce hydrogen. Stages can be alone or combined. Parallel reactors can provide continuous reactant flow. Each of the processes can be carried out individually.

Hunt, Andrew T. (Atlanta, GA); Breitkopf, Richard C. (Dunwoody, GA)

2009-12-01

19

Comparative cytotoxicity assessments of some manufactured and anthropogenic nanoparticulate materials  

NASA Astrophysics Data System (ADS)

Due to increasing diversity of newly engineered nanoparticles, it is important to consider the hazards of these materials. Very little is known regarding the potential toxicity of relatively new nanomaterials. However, beginning with several historical accounts of nanomaterials applications---chrysotile asbestos and silver---it was assumed that these examples would provide some awareness and guidelines for future nanomaterial and nanotechnology applications, especially health effects. In this study in vitro assays were performed on a murine alveolar macrophage cell line (RAW 264.7), human alveolar macrophage cell line (THB-1), and human epithelial lung cell line (A549) to assess the comparative cytotoxicity of a wide range of manufactured (Ag, TiO2, Fe2O3, Al2O3, ZrO2, black carbon, two different types of multiwall structures and chrysotile asbestos as the toxicity standard) and anthropogenic nanoparticulates. There are several parameters of nanoparticulates that are considered to trigger an inflammatory response (particularly respiratory) or cause toxicity. These parameters include: particle size, shape, specific surface area, transition metals in particulates, and organic compounds. Therefore, a wide variety of manufactured and anthropogenic nanoparticulates having different morphologies, sizes, specific surface area and chemistries as noted were tested. To determine the nanoparticulates' size and morphology, they were characterized by transmission electron microscopy, where it was observed that the commercial multiwall carbon nanotube aggregate had an identical morphology to chrysotile asbestos and combustion-formed carbon nanotubes, i.e.; those that form from natural gas combustion. Light optical microscopy was used to determine cell morphology upon exposure to nanoparticulates as an indication of cell death. Also, the polycyclic aromatic hydrocarbon (PAH) content of the collected nanoparticulates was analyzed and correlated with cytotoxic responses. For toxicity evaluation, cytokine production, mitochondrial function (MTT assay), reactive oxygen species generation (ROS), were assessed after 48 and 336 hours under control and exposed conditions. A simple, direct-contact assay was developed to evaluate the toxicity of anthropogenic particulate matter (PM), without removing it from high volume filter collections and exposing collected PM by direct contact with the human epithelial (A549) cells in culture. The cell viability data revealed that the manufactured nanomaterials exhibit cytotoxic response for the murine alveolar and human macrophage cell line, but in particular to the human epithelial cell line. Assay results for the direct-contact of filter-collected carbonaceous nanoparticulate, showed toxicity for all PM, but with various natural gas combustion PM being the most toxic. Light optical microscopy examination of affected human epithelial cells confirmed quantitative results. These nanoparticulate soots also produced the most reactive oxygen species (ROS) on the A549 cell culture as well as along with the Fe2O3, MWCNT-N, and black carbon (BC). Comparison of polycyclic aromatic hydrocarbon (PAH) content and concentration for the carbonaceous PM showed no PAH correlation with relative cell viability after 48 h. In addition, there was no correlation of cytotoxic response with specific surface area in the manufactured nanoparticulate materials. In conclusion, the manufactured as well as the anthropogenic nanomaterials were observed to generate large amounts of ROS and cytokines. This study suggests that the mechanism of toxicity is likely due to the generation of reactive oxygen species (ROS). Also, the comparative assessments presented, should be viewed as a precaution when considering the inhalation of the corresponding nanoparticulate materials in concentrations approaching those identified to be dangerous for recognized pathogens such as silica, black carbon, and asbestos. Humans should avoid breathing these nanoparticulate materials, although there are anthropogenic nanoparticulate materials such as MWCNT agg

Soto, Karla Fabiola

20

Multistrain influenza protection induced by a nanoparticulate mucosal immunotherapeutic  

Microsoft Academic Search

All commercial influenza vaccines elicit antibody responses that protect against seasonal infection, but this approach is limited by the need for annual vaccine reformulation that precludes efficient responses against epidemic and pandemic disease. In this study we describe a novel vaccination approach in which a nanoparticulate, liposome-based agent containing short, highly conserved influenza-derived peptides is delivered to the respiratory tract

W Tai; L Roberts; A Seryshev; J M Gubatan; C S Bland; R Zabriskie; S Kulkarni; L Soong; I Mbawuike; B Gilbert; F Kheradmand; D B Corry

2011-01-01

21

Nanotechnology in Biomaterials: Nanoparticulates as Drug Delivery Systems  

E-print Network

227 11 Nanotechnology in Biomaterials: Nanoparticulates as Drug Delivery Systems Birsen Demirbag Delivery Systems A drug delivery system (DDS) can be de ned as the system that achieves the administra the concentration, rate, time, and place of release of drugs in the body.1 The primary purpose of drug delivery

Hasýrcý, Vasýf

22

Surface modified nanoparticulate carrier constructs for oral mucosal vaccine delivery.  

PubMed

Mucosal administration of vaccines is one of the most popular approaches to induce desired immunity against various types of antigen and microbial in central as well as peripheral blood and in most external mucosal surfaces. The oral route is a preferred choice over parenteral route for this purpose mainly due to an ease of administration and therefore, for the possibility of covering large population for mass immunization. Different strategies of mucosal vaccination aimed to prevent colony formation and infection by pathogens and block its development. But a major concern with these vaccines is the degradation of protein components in stomach due to physiological conditions and gastric enzymes. Therefore, surface modified nanoparticles offer a better and stable alternative for efficient delivery and better activation of required immune responses. Natural and synthetic polymers are used to prepare nanoparticulate carrier systems for the development of oral mucosal vaccines. Amongst these, biodegradable polymers based nano-particulate carriers have been explored extensively for the development of delivery systems. Present review summarizes possible approaches and mechanisms for the systemic immunization by oral vaccines and critically discusses various polymers used, different strategies of surface modification to achieve targeting of antigen loaded nanoparticulate carrier at cellular level that are essentially required for a successful mucosal vaccination approach, and future prospects of nanoparticulate system as adjutants in oral mucosal vaccination. PMID:25007830

Mishra, Neeraj; Singh, Devendra; Sharma, Sandeep; Baldi, Ashish

2014-01-01

23

Nanoparticulate bioavailable iron minerals in icebergs and glaciers R. RAISWELL  

E-print Network

Nanoparticulate bioavailable iron minerals in icebergs and glaciers R. RAISWELL 1 , L. G. BENNING 1, Bristol University, Bristol BS8 1SS, UK ABSTRACT Ice-hosted sediments in glaciers and icebergs from by icebergs to the Southern Ocean is comparable to the flux of soluble, bioavailable Fe from aeolian dust

Benning, Liane G.

24

Nanoparticulate magnetite thin films as electrode materials for the fabrication of electrochemical capacitors  

Microsoft Academic Search

Magnetite nanoparticles in stable colloidal suspension were prepared by the co-precipitation method. Nanoparticulate magnetite\\u000a thin films on supporting stainless steel plates were prepared by drop-coating followed by heat treatment under controlled\\u000a conditions. The effects of calcination temperature and atmosphere on the microstructure and electrochemical properties of\\u000a nanoparticulate magnetite thin films were investigated. Nanoparticulate magnetite thin films prepared under optimized conditions

Suh Cem Pang; Wai Hwa Khoh; Suk Fun Chin

2010-01-01

25

Mechanisms of Tumor Vascular Priming by a Nanoparticulate Doxorubicin Formulation  

PubMed Central

Purpose Tumor vascular normalization by antiangiogenic agents may increase tumor perfusion but reestablish vascular barrier properties in CNS tumors. Vascular priming via nanoparticulate carriers represents a mechanistically distinct alternative. This study investigated mechanisms by which sterically-stabilized liposomal doxorubicin (SSL-DXR) modulates tumor vascular properties. Methods Functional vascular responses to SSL-DXR were investigated in orthotopic rat brain tumors using deposition of fluorescent permeability probes and dynamic contrast-enhanced magnetic resonance imaging. Microvessel density and tumor burden were quantified by immunohistochemistry (CD-31) and quantitative RT-PCR (VE-cadherin). Results Administration of SSL-DXR (5.7 mg/kg iv) initially (3–4 days post-treatment) decreased tumor vascular permeability, ktrans (vascular exchange constant), vascular endothelial cell content, microvessel density, and deposition of nanoparticulates. Tumor vasculature became less chaotic. Permeability and perfusion returned to control values 6–7 days post-treatment, but intratumor SSL-DXR depot continued to effect tumor vascular endothelial compartment 7–10 days post-treatment, mediating enhanced permeability. Conclusions SSL-DXR ultimately increased tumor vascular permeability, but initially normalized tumor vasculature and decreased tumor perfusion, permeability, and nanoparticulate deposition. These temporal changes in vascular integrity resulting from a single SSL-DXR dose have important implications for the design of combination therapies incorporating nanoparticle-based agents for tumor vascular priming. PMID:22798260

Chaudhuri, Tista Roy; Arnold, Robert D.; Yang, Jun; Turowski, Steven G.; Qu, Yang; Spernyak, Joseph A.; Mazurchuk, Richard; Mager, Donald E.

2013-01-01

26

Rapid detection of cancer related DNA nanoparticulate biomarkers and nanoparticles in whole blood  

Microsoft Academic Search

The ability to rapidly detect cell free circulating (cfc) DNA, cfc-RNA, exosomes and other nanoparticulate disease biomarkers as well as drug delivery nanoparticles directly in blood is a major challenge for nanomedicine. We now show that microarray and new high voltage dielectrophoretic (DEP) devices can be used to rapidly isolate and detect cfc-DNA nanoparticulates and nanoparticles directly from whole blood

Michael J. Heller; Raj Krishnan; Avery Sonnenberg

2010-01-01

27

Nanoparticulate Coatings with Efficient Up-Conversion Properties.  

PubMed

Nanoparticulate films with high up-conversion emission (UC) properties were prepared by spray-deposition of nanometer-sized YVO4:Yb,Er particles. The optical properties of YVO4:Yb,Er were optimized upon annealing before the film deposition in order to get the highest possible UC signal in the considered type of system. Thanks to a simple model and some time-resolved spectroscopic investigations, the contribution of the scattering to the UC signal could be separated from the intrinsic properties (crystallinity, surface defects) of the material. The films obtained by this technique present the advantages of having both high UC and good transparency. PMID:25409538

Dantelle, Geraldine; Calderón-Villajos, Rocío; Zaldo, Carlos; Cascales, Concepción; Gacoin, Thierry

2014-12-01

28

Kinetic analysis of nanoparticulate polyelectrolyte complex interactions with endothelial cells.  

PubMed

A non-toxic, nanoparticulate polyelectrolyte complex (PEC) drug delivery system was formulated to maintain suitable physicochemical properties at physiological pH. Toxicity, binding, and internalization were evaluated in relevant microvascular endothelial cells. PEC were non-toxic, as indicated by cell proliferation studies and propidium iodide staining. Inhibitor studies revealed that PEC were bound, in part, via heparan sulfate proteoglycans and internalized through macropinocytosis. A novel, flow cytometric, Scatchard protocol was established and showed that PEC, in the absence of surface modification, bind cells non-specifically with positive cooperativity, as seen by graphical transformations. PMID:17560645

Hartig, Sean M; Greene, Rachel R; Carlesso, Gianluca; Higginbotham, James N; Khan, Wasif N; Prokop, Ales; Davidson, Jeffrey M

2007-09-01

29

Concepts and practices used to develop functional PLGA-based nanoparticulate systems  

PubMed Central

The functionality of bare polylactide-co-glycolide (PLGA) nanoparticles is limited to drug depot or drug solubilization in their hard cores. They have inherent weaknesses as a drug-delivery system. For instance, when administered intravenously, the nanoparticles undergo rapid clearance from systemic circulation before reaching the site of action. Furthermore, plain PLGA nanoparticles cannot distinguish between different cell types. Recent research shows that surface functionalization of nanoparticles and development of new nanoparticulate dosage forms help overcome these delivery challenges and improve in vivo performance. Immense research efforts have propelled the development of diverse functional PLGA-based nanoparticulate delivery systems. Representative examples include PEGylated micelles/nanoparticles (PEG, polyethylene glycol), polyplexes, polymersomes, core-shell–type lipid-PLGA hybrids, cell-PLGA hybrids, receptor-specific ligand-PLGA conjugates, and theranostics. Each PLGA-based nanoparticulate dosage form has specific features that distinguish it from other nanoparticulate systems. This review focuses on fundamental concepts and practices that are used in the development of various functional nanoparticulate dosage forms. We describe how the attributes of these functional nanoparticulate forms might contribute to achievement of desired therapeutic effects that are not attainable using conventional therapies. Functional PLGA-based nanoparticulate systems are expected to deliver chemotherapeutic, diagnostic, and imaging agents in a highly selective and effective manner. PMID:23459088

Sah, Hongkee; Thoma, Laura A; Desu, Hari R; Sah, Edel; Wood, George C

2013-01-01

30

An RGD-Modified MRI-Visible Polymeric Vector for Targeted siRNA Delivery to Hepatocellular Carcinoma in Nude Mice  

PubMed Central

RNA interference (RNAi) has significant therapeutic promise for the genetic treatment of hepatocellular carcinoma (HCC). Targeted vectors are able to deliver small interfering RNA (siRNA) into HCC cells with high transfection efficiency and stability. The tripeptide arginine glycine aspartic acid (RGD)-modified non-viral vector, polyethylene glycol-grafted polyethylenimine functionalized with superparamagnetic iron oxide nanoparticles (RGD-PEG-g-PEI-SPION), was constructed as a magnetic resonance imaging (MRI)-visible nanocarrier for the delivery of Survivin siRNA targeting the human HCC cell line Bel-7402. The biophysical characterization of the RGD-PEG-g-PEI-SPION was performed. The RGD-modified complexes exhibited a higher transfection efficiency in transferring Survivin siRNA into Bel-7402 cells compared with a non-targeted delivery system, which resulted in more significant gene suppression at both the Survivin mRNA and protein expression levels. Then, the level of caspase-3 activation was significantly elevated, and a remarkable level of tumor cell apoptosis was induced. As a result, the tumor growth in the nude mice Bel-7402 hepatoma model was significantly inhibited. The targeting ability of the RGD-PEG-g-PEI-SPION was successfully imaged by MRI scans performed in vitro and in vivo. Our results strongly indicated that the RGD-PEG-g-PEI-SPION can potentially be used as a targeted non-viral vector for altering gene expression in the treatment of hepatocellular carcinoma and for detecting the tumor in vivo as an effective MRI probe. PMID:23922634

Shen, Min; Zhu, Kangshun; Cheng, Du; Liu, Zhihao; Shan, Hong

2013-01-01

31

An RGD-modified MRI-visible polymeric vector for targeted siRNA delivery to hepatocellular carcinoma in nude mice.  

PubMed

RNA interference (RNAi) has significant therapeutic promise for the genetic treatment of hepatocellular carcinoma (HCC). Targeted vectors are able to deliver small interfering RNA (siRNA) into HCC cells with high transfection efficiency and stability. The tripeptide arginine glycine aspartic acid (RGD)-modified non-viral vector, polyethylene glycol-grafted polyethylenimine functionalized with superparamagnetic iron oxide nanoparticles (RGD-PEG-g-PEI-SPION), was constructed as a magnetic resonance imaging (MRI)-visible nanocarrier for the delivery of Survivin siRNA targeting the human HCC cell line Bel-7402. The biophysical characterization of the RGD-PEG-g-PEI-SPION was performed. The RGD-modified complexes exhibited a higher transfection efficiency in transferring Survivin siRNA into Bel-7402 cells compared with a non-targeted delivery system, which resulted in more significant gene suppression at both the Survivin mRNA and protein expression levels. Then, the level of caspase-3 activation was significantly elevated, and a remarkable level of tumor cell apoptosis was induced. As a result, the tumor growth in the nude mice Bel-7402 hepatoma model was significantly inhibited. The targeting ability of the RGD-PEG-g-PEI-SPION was successfully imaged by MRI scans performed in vitro and in vivo. Our results strongly indicated that the RGD-PEG-g-PEI-SPION can potentially be used as a targeted non-viral vector for altering gene expression in the treatment of hepatocellular carcinoma and for detecting the tumor in vivo as an effective MRI probe. PMID:23922634

Wu, Chun; Gong, Faming; Pang, Pengfei; Shen, Min; Zhu, Kangshun; Cheng, Du; Liu, Zhihao; Shan, Hong

2013-01-01

32

Nanoparticulate carrier system: a novel treatment approach for hyperlipidemia.  

PubMed

Abstract Hyperlipidemia is a prevailing risk factor that leads to development and progression of atherosclerosis and consequently cardiovascular diseases. Several antihyperlipidemic drugs are having various disadvantages such as low water solubility and poor bioavailabilty due to presystemic gastrointestinal clearance. Thus, there is a considerable need for the development of efficient delivery methods and carriers. This review focuses on the importance and role of various nanoparticulate systems as carrier for antihyperlipidemic drugs in the treatment of hyperlipidemia. Some nanoparticle technology-based products are approved by FDA for effective treatment of hyperlipidemia, namely Tricor® by Abbott Laboratories (Chicago, IL, USA) and Triglide® by Skye Pharma (London, UK). Efforts to address each of these issues are going on, and should remain the focus on the future studies and look forward to many more clinical products in the future. PMID:24904976

Sharma, Kritika; Kumar, Kulyash; Mishra, Neeraj

2014-06-01

33

A TEM analysis of nanoparticulates in a Polar ice core  

SciTech Connect

This paper explores the prospect for analyzing nanoparticulates in age-dated ice cores representing times in antiquity to establish a historical reference for atmospheric particulate regimes. Analytical transmission electron microscope (TEM) techniques were utilized to observe representative ice-melt water drops dried down on carbon/formvar or similar coated grids. A 10,000-year-old Greenland ice core was melted, and representative water drops were transferred to coated grids in a clean room environment. Essentially, all particulates observed were aggregates and either crystalline or complex mixtures of nanocrystals. Especially notable was the observation of carbon nanotubes and related fullerene-like nanocrystal forms. These observations are similar with some aspects of contemporary airborne particulates including carbon nanotubes and complex nanocrystal aggregates.

Esquivel, E.V.; Murr, L.E

2004-03-15

34

Polymeric Actuators.  

PubMed

Actuators are materials and devices that are able to change their shape in response to changes in environmental conditions and perform mechanical work on nano-, micro-, and macroscales. Among the huge variety of different actuators, polymer-based ones are highly attractive because of a number of properties such as sensitivity to a broad range of stimuli and good mechanical properties. The goal of this review is to provide a general picture of different mechanisms and working principles of polymeric actuators as well as to show a palette of their applications. PMID:25386998

Ionov, Leonid

2014-11-11

35

A review of the formation and classification of amphiphilic block copolymer nanoparticulate structures: micelles, nanospheres, nanocapsules and polymersomes  

Microsoft Academic Search

Amphiphilic block copolymers are able to form a range of different nanoparticulate structures. These include micelles, nanospheres, nanocapsules, and polymersomes. This review attempts to clarify some of the terminology used in the literature by providing an overview of the major features of each type of nanoparticle and the factors that influence the formation of particular nanoparticulate formulations.

Kevin Letchford; Helen Burt

2007-01-01

36

Nanoparticulate carriers (NPC) for oral pharmaceutics and nutraceutics.  

PubMed

The introduction of nanoparticulate carriers (NPC) in the pharmaceutic and nutraceutic fields has changed the definitions of disease management and treatment, diagnosis, as well as the supply food chain in the agri-food sector. NPC composed of synthetic polymers, proteins or polysaccharides gather interesting properties to be used for oral administration of pharmaceutics and nutraceutics. Oral administration remains the most convenient way of delivering drugs (e.g. peptides, proteins and nucleic acids) since these suffer similar metabolic pathways as food supply. Recent advances in biotechnology have produced highly potent new molecules however with low oral bioavailability. A suitable and promising approach to overcome their sensitivity to chemical and enzymatic hydrolysis as well as the poor cellular uptake, would be their entrapment within suitable gastrointestinal (GI) resistant NPC. Increasing attention has been paid to the potential use of NPC for peptides, proteins, antioxidants (carotenoids, omega fatty acids, coenzyme Q10), vitamins, probiotics, for oral administration. This review focuses on the most important materials to produce NPC for oral administration, and the most recent achievements in the production techniques and bioactives successfully delivered by these means. PMID:20225647

Lopes, C M; Martins-Lopes, P; Souto, E B

2010-02-01

37

Dynamics of discontinuous coating and drying of nanoparticulate films.  

SciTech Connect

Heightened interest in micro-scale and nano-scale patterning by imprinting, embossing, and nano-particulate suspension coating stems from a recent surge in development of higher-throughput manufacturing methods for integrated devices. Energy-applications addressing alternative, renewable energy sources offer many examples of the need for improved manufacturing technology for micro and nano-structured films. In this presentation we address one approach to micro- and nano-pattering coating using film deposition and differential wetting of nanoparticles suspensions. Rather than print nanoparticle or colloidal inks in discontinuous patches, which typically employs ink jet printing technology, patterns can be formed with controlled dewetting of a continuously coated film. Here we report the dynamics of a volatile organic solvent laden with nanoparticles dispensed on the surfaces of water droplets, whose contact angles (surface energy) and perimeters are defined by lithographic patterning of initially (super)hydrophobic surfaces.. The lubrication flow equation together with averaged particle transport equation are employed to predict the film thickness and particle average concentration profiles during subsequent drying of the organic and water solvents. The predictions are validated by contact angle measurements, in situ grazing incidence small angle x-ray scattering experiments, and TEM images of the final nanoparticle assemblies.

Schunk, Peter Randall; Dunphy, Darren Robert (University of New Mexico, Albuquerque, NM); Brinker, C. Jeffrey; Tjiptowidjojo, Kristianto (University of New Mexico, Albuquerque, NM)

2010-09-01

38

Microstructures and Nanostructures for Environmental Carbon Nanotubes and Nanoparticulate Soots  

PubMed Central

This paper examines the microstructures and nanostructures for natural (mined) chrysotile asbestos nanotubes (Mg3 Si2O5 (OH)4) in comparison with commercial multiwall carbon nanotubes (MWCNTs), utilizing scanning and transmission electron microscopy (SEM and TEM). Black carbon (BC) and a variety of specific soot particulate (aggregate) microstructures and nanostructures are also examined comparatively by SEM and TEM. A range of MWCNTs collected in the environment (both indoor and outdoor) are also examined and shown to be similar to some commercial MWCNTs but to exhibit a diversity of microstructures and nanostructures, including aggregation with other multiconcentric fullerenic nanoparticles. MWCNTs formed in the environment nucleate from special hemispherical graphene “caps” and there is evidence for preferential or energetically favorable chiralities, tube growth, and closing. The multiconcentric graphene tubes (?5 to 50 nm diameter) differentiate themselves from multiconcentric fullerenic nanoparticles and especially turbostratic BC and carbonaceous soot nanospherules (?8 to 80 nm diameter) because the latter are composed of curved graphene fragments intermixed or intercalated with polycyclic aromatic hydrocarbon (PAH) isomers of varying molecular weights and mass concentrations; depending upon combustion conditions and sources. The functionalizing of these nanostructures and photoxidation and related photothermal phenomena, as these may influence the cytotoxicities of these nanoparticulate aggregates, will also be discussed in the context of nanostructures and nanostructure phenomena, and implications for respiratory health. PMID:19151426

Murr, L. E.

2008-01-01

39

Structurally inhomogeneous nanoparticulate catalysts in cobalt-catalyzed carbon nanotube growth  

NASA Astrophysics Data System (ADS)

The structure of nanoparticulate catalysts involved in cobalt-catalyzed chemical vapor deposition growth of carbon nanotubes (CNTs) was investigated by in situ environmental transmission electron microscopy (ETEM). In contrast to previous studies, the analyses of ETEM images showed that the nanoparticulate catalysts were structurally inhomogeneous during CNT growth in the source gas of acetylene at a rate of pressure increase of about 3 Pa/h and at 550 °C. The lattice fringes observed in the nanoparticulate catalysts can be accounted for by not a single crystalline structure but by several possible pairs of structures including pure Co and cobalt carbides. The inhomogeneous structures were unstable with time. The possible origin of the inhomogeneous structures is discussed.

Kohigashi, Y.; Yoshida, H.; Homma, Y.; Takeda, S.

2014-08-01

40

Structure evolution of nanoparticulate Fe2O3.  

PubMed

The atomic structure and properties of nanoparticulate Fe2O3 are characterized starting from its smallest Fe2O3 building unit through (Fe2O3)n clusters to nanometer-sized Fe2O3 particles. This is achieved by combining global structure optimizations at the density functional theory level, molecular dynamics simulations by employing tailored, ab initio parameterized interatomic potential functions and experiments. With the exception of nearly tetrahedral, adamantane-like (Fe2O3)2 small (Fe2O3)n clusters assume compact, virtually amorphous structures with little or no symmetry. For n = 2-5 (Fe2O3)n clusters consist mainly of two- and three-membered Fe-O rings. Starting from n = 5 they increasingly assume tetrahedral shape with the adamantane-like (Fe2O3)2 unit as the main building block. However, the small energy differences between different isomers of the same cluster-size make precise structural assignment for larger (Fe2O3)n clusters difficult. The tetrahedral morphology persists for Fe2O3 nanoparticles with up to 3 nm in diameter. Simulated crystallization of larger nanoparticles with diameters of about 5 nm demonstrates pronounced melting point depression and leads to formation of ?-Fe2O3 single crystals with hexagonal morphology. This finding is in excellent agreement with the results obtained for Fe2O3 nanopowders generated by laser vaporization and provides the first direct indication that ?-Fe2O3 may be thermodynamically the most stable phase in this size regime. PMID:25587689

Erlebach, Andreas; Kurland, Heinz-Dieter; Grabow, Janet; Müller, Frank A; Sierka, Marek

2015-02-01

41

Methylation of Mercury by Bacteria Exposed to Dissolved, Nanoparticulate, and Microparticulate Mercuric Sulfides  

E-print Network

Methylation of Mercury by Bacteria Exposed to Dissolved, Nanoparticulate, and Microparticulate bacteria that methylate Hg(II). In sediment porewater, Hg(II) associates with sulfides and natural organic intermediates of heterogeneous mineral precipitation. Here, we exposed two strains of sulfate-reducing bacteria

42

bacteria driven polymerization  

E-print Network

12/20/2007 1 Motion of bacteria driven by actin polymerization forces Michael C. DeSantis Physics.B. Alberts) Examples of other intracellular pathogens propelled by actoclampins (actin filament (+)-end by actin polymerization. Cell signaling and its influence by actin polymerization transitions

Wang, Yan Mei

43

Cationic additives in nanosystems activate cytotoxicity and inflammatory response of human neutrophils: lipid nanoparticles versus polymeric nanoparticles.  

PubMed

This report compares the effect of lipid and polymeric nanoparticles upon human neutrophils in the presence of cationic surfactants. Nanostructured lipid carriers and poly(lactic-co-glycolic) acid nanoparticles were manufactured as lipid and polymeric systems, respectively. Some cytotoxic and proinflammatory mediators such as lactate dehydrogenase (LDH), elastase, O2 (•-), and intracellular Ca(2+) were examined. The nanoparticles showed a size of 170-225 nm. Incorporation of cetyltrimethylammonium bromide or soyaethyl morpholinium ethosulfate, the cationic surfactant, converted zeta potential from a negative to a positive charge. Nanoparticles without cationic surfactants revealed a negligible change on immune and inflammatory responses. Cationic surfactants in both nanoparticulate and free forms induced cell death and the release of mediators. Lipid nanoparticles generally demonstrated a greater response compared to polymeric nanoparticles. The neutrophil morphology observed by electron microscopy confirmed this trend. Cetyltrimethylammonium bromide as the coating material showed more significant activation of neutrophils than soyaethyl morpholinium ethosulfate. Confocal microscope imaging displayed a limited internalization of nanoparticles into neutrophils. It is proposed that cationic nanoparticles interact with the cell membrane, triggering membrane disruption and the following Ca(2+) influx. The elevation of intracellular Ca(2+) induces degranulation and oxidative stress. The consequence of these effects is cytotoxicity and cell death. Caution should be taken when selecting feasible nanoparticulate formulations and cationic additives for consideration of applicability and toxicity. PMID:25609950

Hwang, Tsong-Long; Aljuffali, Ibrahim A; Lin, Chwan-Fwu; Chang, Yuan-Ting; Fang, Jia-You

2015-01-01

44

Cationic additives in nanosystems activate cytotoxicity and inflammatory response of human neutrophils: lipid nanoparticles versus polymeric nanoparticles  

PubMed Central

This report compares the effect of lipid and polymeric nanoparticles upon human neutrophils in the presence of cationic surfactants. Nanostructured lipid carriers and poly(lactic-co-glycolic) acid nanoparticles were manufactured as lipid and polymeric systems, respectively. Some cytotoxic and proinflammatory mediators such as lactate dehydrogenase (LDH), elastase, O2•?, and intracellular Ca2+ were examined. The nanoparticles showed a size of 170–225 nm. Incorporation of cetyltrimethylammonium bromide or soyaethyl morpholinium ethosulfate, the cationic surfactant, converted zeta potential from a negative to a positive charge. Nanoparticles without cationic surfactants revealed a negligible change on immune and inflammatory responses. Cationic surfactants in both nanoparticulate and free forms induced cell death and the release of mediators. Lipid nanoparticles generally demonstrated a greater response compared to polymeric nanoparticles. The neutrophil morphology observed by electron microscopy confirmed this trend. Cetyltrimethylammonium bromide as the coating material showed more significant activation of neutrophils than soyaethyl morpholinium ethosulfate. Confocal microscope imaging displayed a limited internalization of nanoparticles into neutrophils. It is proposed that cationic nanoparticles interact with the cell membrane, triggering membrane disruption and the following Ca2+ influx. The elevation of intracellular Ca2+ induces degranulation and oxidative stress. The consequence of these effects is cytotoxicity and cell death. Caution should be taken when selecting feasible nanoparticulate formulations and cationic additives for consideration of applicability and toxicity. PMID:25609950

Hwang, Tsong-Long; Aljuffali, Ibrahim A; Lin, Chwan-Fwu; Chang, Yuan-Ting; Fang, Jia-You

2015-01-01

45

Analytical Electron Microscopy for Characterization of Fluid or Semi-Solid Multiphase Systems Containing Nanoparticulate Material  

PubMed Central

The analysis of nanomaterials in pharmaceutical or cosmetic preparations is an important aspect both in formulation development and quality control of marketed products. Despite the increased popularity of nanoparticulate compounds especially in dermal preparations such as emulsions, methods and protocols of analysis for the characterization of such systems are scarce. This work combines an original sample preparation procedure along with different methods of analytical electron microscopy for the comprehensive analysis of fluid or semi-solid dermal preparations containing nanoparticulate material. Energy-filtered transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron energy loss spectroscopy and high resolution imaging were performed on model emulsions and a marketed product to reveal different structural aspects of both the emulsion bulk phase and incorporated nanosized material. An innovative analytical approach for the determination of the physical stability of the emulsion under investigation is presented. Advantages and limitations of the employed analytical imaging techniques are highlighted. PMID:24300401

Klang, Victoria; Valenta, Claudia; Matsko, Nadejda B.

2013-01-01

46

Seeded growth of robust SERS-active 2D Au@Ag nanoparticulate films  

SciTech Connect

We demonstrate herein a novel and versatile solution-based methodology for fabricating self-organized two-dimensional (2D) Au nanoparticle arrays on glass using in situ nucleation at an aminosilane monolayer followed by seeded, electroless growth; subsequent deposition of Ag produced Au{at}Ag core-shell nanoparticulate films which proved highly promising as surface-enhanced Raman scattering (SERS) platforms.

Baker, Gary A [ORNL; Dai, Sheng [ORNL; Hagaman, Edward {Ed} W [ORNL; Mahurin, Shannon Mark [ORNL; Zhu, Haoguo [ORNL; Bao, Lili [Oak Ridge National Laboratory (ORNL)

2008-01-01

47

Nanoparticulate silver increases uric acid and allantoin excretion in rats, as identified by metabolomics.  

PubMed

Metabolomic investigation of rat urine was employed to identify mammalian metabolites affected by ionic or nanoparticulate silver. Female and male Wistar rats were administered silver nanoparticles (2.25, 4.5 or 9.0 mg kg(-1) body weight per day) or ionic silver (silver acetate, 9.0 mg silver kg(-1) bw per day) by oral gavage for 28 days. On day 18, urine was collected for 24 h and subjected to metabolomics with high performance liquid chromatography-quadropole time-of-flight mass spectrometry (HPLC-QTOF-MS)-based separation and detection. Principal component analysis was subsequently applied to the data. Metabolomic differences in urine composition were found in female rats but not in male rats. Several metabolites were identified by the use of elemental composition calculated from the exact mass combined with searches in the Human Metabolome Database.The metabolite identities were eventually verified by co-chromatography with authentic standards. Differences were found in uric acid and its degradation product, allantoin. Administration of nanoparticulate silver increased both metabolites, whereas ionic silver only increased allantoin. In conclusion, metabolomic investigation of rat urine showed that increased levels of uric acid and allantoin were associated with exposure to nanoparticulate silver. PMID:22610381

Hadrup, Niels; Lam, Henrik R; Loeschner, Katrin; Mortensen, Alicja; Larsen, Erik H; Frandsen, Henrik

2012-11-01

48

Water-based nanoparticulate solar cells using a diketopyrrolopyrrole donor polymer.  

PubMed

Organic photovoltaic devices with either bulk heterojunction (BHJ) or nanoparticulate (NP) active layers have been prepared from a 1?:?2 blend of (poly{3,6-dithiophene-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-naphthalene}) (PDPP-TNT) and the fullerene acceptor, ([6,6]-phenyl C71-butyric acid methyl ester) (PC70BM). Atomic force microscopy (AFM) and scanning electron microscopy (SEM) have been used to investigate the morphology of the active layers of the two approaches. Mild thermal treatment of the NP film is required to promote initial joining of the NPs in order for the devices to function, however the NP structure is retained. Consequently, whereas gross phase segregation of the active layer occurs in the BHJ device spin cast from chloroform, the nanoparticulate approach retains control of the material domain sizes on the length scale of exciton diffusion in the materials. As a result, NP devices are found to generate more than twice the current density of BHJ devices and have a substantially greater overall efficiency. The use of aqueous nanoparticulate dispersions offers a promising approach to control the donor acceptor morphology on the nanoscale with the benefit of environmentally-friendly, solution-based fabrication. PMID:24382591

Vaughan, Ben; Williams, Evan L; Holmes, Natalie P; Sonar, Prashant; Dodabalapur, Ananth; Dastoor, Paul C; Belcher, Warwick J

2014-02-14

49

Dielectrophoretic isolation and detection of cfc-DNA nanoparticulate biomarkers and virus from blood.  

PubMed

Dielectrophoretic (DEP) microarray devices allow important cellular nanoparticulate biomarkers and virus to be rapidly isolated, concentrated, and detected directly from clinical and biological samples. A variety of submicron nanoparticulate entities including cell free circulating (cfc) DNA, mitochondria, and virus can be isolated into DEP high-field areas on microelectrodes, while blood cells and other micron-size entities become isolated into DEP low-field areas between the microelectrodes. The nanoparticulate entities are held in the DEP high-field areas while cells are washed away along with proteins and other small molecules that are not affected by the DEP electric fields. DEP carried out on 20 ?L of whole blood obtained from chronic lymphocytic leukemia patients showed a considerable amount of SYBR Green stained DNA fluorescent material concentrated in the DEP high-field regions. Whole blood obtained from healthy individuals showed little or no fluorescent DNA materials in the DEP high-field regions. Fluorescent T7 bacteriophage virus could be isolated directly from blood samples, and fluorescently stained mitochondria could be isolated from biological buffer samples. Using newer DEP microarray devices, high-molecular-weight DNA could be isolated from serum and detected at levels as low as 8-16 ng/mL. PMID:23436471

Sonnenberg, Avery; Marciniak, Jennifer Y; McCanna, James; Krishnan, Rajaram; Rassenti, Laura; Kipps, Thomas J; Heller, Michael J

2013-04-01

50

Superior preclinical efficacy of gemcitabine developed as chitosan nanoparticulate system.  

PubMed

Gemcitabine, an anticancer nucleoside analogue, undergoes rapid enzymatic degradation following intravenous injection. This necessitates the administration of a high order of doses to observe a required therapeutic response, while such high doses result in significant side effects. To improve the intravenous delivery of gemcitabine and simultaneously enhance its antitumor activity, we have investigated its incorporation into a drug nanoplatform based on the biodegradable polymer chitosan. Two gemcitabine loading methods have been investigated: (i) entrapment into the polymeric network (entrapment procedure): drug incorporation prior to the coacervation process that leads to the formation of gemcitabine-loaded chitosan (GemChit) nanoparticles; and (ii) surface deposition onto already formed chitosan nanoparticles after incubation in gemcitabine solution (adsorption procedure). The former method produced much higher gemcitabine loading values and a sustained release profile. The main factors determining the gemcitabine loading and release kinetic have also been analyzed. Following intravenous injection, the GemChit formulation displayed a significantly improved antitumor activity comparatively to free gemcitabine, which was further confirmed by histology and immunohistochemistry studies, suggesting the potential of this chitosan-based gemcitabine nanomedicine for the effective treatment of tumors. PMID:21117615

Arias, José L; Reddy, L Harivardhan; Couvreur, Patrick

2011-01-10

51

Nanoparticulate Adjuvants and Delivery Systems for Allergen Immunotherapy  

PubMed Central

In the last decades, significant progress in research and clinics has been made to offer possible innovative therapeutics for the management of allergic diseases. However, current allergen immunotherapy shows limitations concerning the long-term efficacy and safety due to local side effects and risk of anaphylaxis. Thus, effective and safe vaccines with reduced dose of allergen have been developed using adjuvants. Nevertheless, the use of adjuvants still has several disadvantages, which limits its use in human vaccines. In this context, several novel adjuvants for allergen immunotherapy are currently being investigated and developed. Currently, nanoparticles-based allergen-delivery systems have received much interest as potential adjuvants for allergen immunotherapy. It has been demonstrated that the incorporation of allergens into a delivery system plays an important role in the efficacy of allergy vaccines. Several nanoparticles-based delivery systems have been described, including biodegradable and nondegradable polymeric carriers. Therefore, this paper provides an overview of the current adjuvants used for allergen immunotherapy. Furthermore, nanoparticles-based allergen-delivery systems are focused as a novel and promising strategy for allergy vaccines. PMID:22496608

De Souza Rebouças, Juliana; Esparza, Irene; Ferrer, Marta; Sanz, María Luisa; Irache, Juan Manuel; Gamazo, Carlos

2012-01-01

52

Smart polymeric nanoparticles for cancer gene delivery.  

PubMed

The massive amount of human genetic information already available has accelerated the identification of target genes, making gene and nucleic acid therapy the next generation of medicine. Nanoparticle (NP)-based anticancer gene therapy treatment has received significant interest in this evolving field. Recent advances in vector technology have improved gene transfection efficiencies of nonviral vectors to a level similar to viruses. This review serves as an introduction to surface modifications of NPs based on polymeric structural improvements and target moieties. A discussion regarding the future perspective of multifunctional NPs in cancer therapy is also included. PMID:25531409

Lin, Guimei; Zhang, Hong; Huang, Leaf

2015-02-01

53

Step-Growth Polymerization.  

ERIC Educational Resources Information Center

Following a comparison of chain-growth and step-growth polymerization, focuses on the latter process by describing requirements for high molecular weight, step-growth polymerization kinetics, synthesis and molecular weight distribution of some linear step-growth polymers, and three-dimensional network step-growth polymers. (JN)

Stille, J. K.

1981-01-01

54

Making Polymeric Microspheres  

NASA Technical Reports Server (NTRS)

Combination of advanced techniques yields uniform particles for biomedical applications. Process combines ink-jet and irradiation/freeze-polymerization techniques to make polymeric microspheres of uniform size in diameters from 100 to 400 micrometer. Microspheres used in chromatography, cell sorting, cell labeling, and manufacture of pharmaceutical materials.

Rhim, Won-Kyu; Hyson, Michael T.; Chung, Sang-Kun; Colvin, Michael S.; Chang, Manchium

1989-01-01

55

Thermodynamics of Polymerization. I  

Microsoft Academic Search

I. THE CHILING TEMPERATURE CONCEPT A. Thermodynamic Approach The Gibbs free energy of a system at temperature T is defined as were H is the enthalpy and S the entropy of the system. The free energy change for any polymerization will be, therefore, When the polymer has a lower free energy than the initial monomer, a polymerization can occur spontaneously,

Hideo Sawada

1969-01-01

56

Ferroportin mediates the intestinal absorption of iron from a nanoparticulate ferritin core mimetic in mice  

PubMed Central

The ferritin core is composed of fine nanoparticulate Fe3+ oxohydroxide, and we have developed a synthetic mimetic, nanoparticulate Fe3+ polyoxohydroxide (nanoFe3+). The aim of this study was to determine how dietary iron derived in this fashion is absorbed in the duodenum. Following a 4 wk run-in on an Fe-deficient diet, mice with intestinal-specific disruption of the Fpn-1 gene (Fpn-KO), or littermate wild-type (WT) controls, were supplemented with Fe2+ sulfate (FeSO4), nanoFe3+, or no added Fe for a further 4 wk. A control group was Fe sufficient throughout. Direct intestinal absorption of nanoFe3+ was investigated using isolated duodenal loops. Our data show that FeSO4 and nanoFe3+ are equally bioavailable in WT mice, and at wk 8 the mean ± sem hemoglobin increase was 18 ± 7 g/L in the FeSO4 group and 30 ± 5 g/L in the nanoFe3+ group. Oral iron failed to be utilized by Fpn-KO mice and was retained in enterocytes, irrespective of the iron source. In summary, although nanoFe3+ is taken up directly by the duodenum its homeostasis is under the normal regulatory control of dietary iron absorption, namely via ferroportin-dependent efflux from enterocytes, and thus offers potential as a novel oral iron supplement.—Aslam, M. F., Frazer, D. M., Faria, N., Bruggraber, S. F. A., Wilkins, S. J., Mirciov, C., Powell, J. J., Anderson, G. J., Pereira, D. I. A. Ferroportin mediates the intestinal absorption of iron from a nanoparticulate ferritin core mimetic in mice. PMID:24776745

Aslam, Mohamad F.; Frazer, David M.; Faria, Nuno; Bruggraber, Sylvaine F. A.; Wilkins, Sarah J.; Mirciov, Cornel; Powell, Jonathan J.; Anderson, Greg J.; Pereira, Dora I. A.

2014-01-01

57

Structure and electrical properties of nanoparticulate tungsten oxide prepared by microwave plasma synthesis  

NASA Astrophysics Data System (ADS)

Nanoparticulate WO3 films were prepared using microwave plasma synthesis and studied with respect to the electrical conductivity in dependence of ambient conditions. The WO3 films with a monoclinic structure were made from cluster-assembled nanoparticles (diameter 3 nm) by means of dispersion and spin-coating. Above 100 °C a thermally activated decrease of the electrical resistance due to oxygen vacancy donors is found. A reversible increase of the electrical resistance R due to oxygen uptake is observed. The decrease of R in response to reducing H2S in the ppm range is studied in dependence of temperature and pre-annealing conditions.

Sagmeister, M.; Postl, M.; Brossmann, U.; List, E. J. W.; Klug, A.; Letofsky-Papst, I.; Szabó, D. V.; Würschum, R.

2011-08-01

58

Multiphase Polymeric Materials  

NSDL National Science Digital Library

Developed by a group of PhD students at the University of Southern Mississippi, the Multiphase Polymeric Materials Website presents both general information about composites and current research on multiphase polymeric materials, including information about blends, coatings, and nanocomposites. As the newest addition to Macrogalleria (described in the March 31, 1999 Scout Report for Science & Engineering), the Multiphase Polymeric Materials Website includes information on Composites in General, Composites, Characterization and Analysis, and Application. Most useful to researchers, the Application section introduces the relationship between polymer composites and component level electronics with examples such as PCB Construction, Encapsulation of Integrated Circuits, and Non-Conductive Adhesives.

59

Vector Voyage!  

NSDL National Science Digital Library

In this activity, students will use vector analysis to understand the concept of dead reckoning. Students will use vectors to plot their course based on a time and speed. They will then correct the positions with vectors representing winds and currents.

Jeff White

2004-01-01

60

Rapid detection of cancer related DNA nanoparticulate biomarkers and nanoparticles in whole blood  

NASA Astrophysics Data System (ADS)

The ability to rapidly detect cell free circulating (cfc) DNA, cfc-RNA, exosomes and other nanoparticulate disease biomarkers as well as drug delivery nanoparticles directly in blood is a major challenge for nanomedicine. We now show that microarray and new high voltage dielectrophoretic (DEP) devices can be used to rapidly isolate and detect cfc-DNA nanoparticulates and nanoparticles directly from whole blood and other high conductance samples (plasma, serum, urine, etc.). At DEP frequencies of 5kHz-10kHz both fluorescent-stained high molecular weight (hmw) DNA, cfc-DNA and fluorescent nanoparticles separate from the blood and become highly concentrated at specific DEP highfield regions over the microelectrodes, while blood cells move to the DEP low field-regions. The blood cells can then be removed by a simple fluidic wash while the DNA and nanoparticles remain highly concentrated. The hmw-DNA could be detected at a level of <260ng/ml and the nanoparticles at <9.5 x 109 particles/ml, detection levels that are well within the range for viable clinical diagnostics and drug nanoparticle monitoring. Disease specific cfc-DNA materials could also be detected directly in blood from patients with Chronic Lymphocytic Leukemia (CLL) and confirmed by PCR genotyping analysis.

Heller, Michael J.; Krishnan, Raj; Sonnenberg, Avery

2010-08-01

61

Natural and anthropogenic environmental nanoparticulates: Their microstructural characterization and respiratory health implications  

NASA Astrophysics Data System (ADS)

A wide range of environmental particulate matter (PM) both indoor and outdoor and consisting of natural and anthropogenic PM was collected by high volume air filters, electrostatic precipitation, and thermophoretic precipitation directly onto transmission electron microscope (TEM) coated grid platforms. These collected PM have been systematically characterized by TEM, energy-dispersive X-ray spectrometry (EDS) and scanning electron microscopy (SEM). In the El Paso, TX, USA/Juarez, Mexico metroplex 93% of outdoor PM 1 is crystalline while 40% of PM 1 is carbonaceous soot (including multiwall carbon nanotubes (MWCNTs) and multiconcentric fullerenes) PM. Multiply-replicated cytotoxicity ( in vitro) assays utilizing a human epithelial (lung model) cell line (A549) consistently demonstrated varying degrees of cell death for essentially all PM which was characterized as aggregates of nanoparticulates or primary nanoparticles. Cytokine release was detected for Fe 2O 3, chrysotile asbestos, BC, and MWCNT PM while reactive oxygen species (ROS) production has been detected for Fe 2O 3, asbestos, BC, and MWCNT aggregate PM as well as natural gas combustion PM. Nanoparticulate materials in the indoor and outdoor environments appear to be variously cytotoxic, especially carbonaceous nano-PM such as multiwall carbon nanotubes, black carbon, and soot nano-PM produced by natural gas combustion.

Murr, L. E.; Garza, K. M.

62

Sweating liquid micro-marbles: dropwise condensation on hydrophobic nanoparticulate materials.  

PubMed

Liquid marbles have opened up several potential applications including biochemical batch reaction engineering and gas sensing. To be successful candidates in these applications, the ability to prepare liquid marbles of controlled sizes and in a continuous process is crucial. This has been the missing link in the science leading to these applications. In the current study, we present a remarkably simple process driven by condensation on a nanoparticulate matrix to continuously produce liquid marbles whose mean size can be controlled in the range of diameters from 3 to 1000 ?m, while the distribution width is also controllable independently. We experimentally demonstrate the physics involved in this condensation-driven marble formation process using two fluids-glycerol and ethylene glycol-which span an order of magnitude in viscosity. Hydrophobic fumed silica nanoparticulate material is used as the encapsulating medium owing to its intertwined agglomerate nature. We show that the primary mechanism causing the formation of liquid marbles is droplet nucleation followed by growth driven by condensation. Drop coalescence in dense droplet ensembles is the secondary mechanism, which attempts to destroy the distribution width controllability. From a physics perspective, it will be demonstrated that strong coalescence dominated growth gives rise to a hitherto unreported, significantly higher rate of growth. PMID:22994499

Bhosale, Prasad S; Panchagnula, Mahesh V

2012-10-23

63

Cardiac oxidative damage in mice following exposure to nanoparticulate titanium dioxide.  

PubMed

Nanoparticulate titanium dioxide (nano-TiO2 ) is a widely used powerful nanoparticulate material with high stability, anticorrosion, and photocatalytic property. However, it is possible that during nano-TiO2 exposure, there may be negative effects on cardiovascular system in intoxicated mice. The present study was therefore undertaken to determine nano-TiO2 -induced oxidative stress and to determine whether nano-TiO2 intoxication alters the antioxidant system in the mouse heart exposed to 2.5, 5, and 10 mg/kg body weight nano-TiO2 for 90 consecutive days. The findings showed that long-term exposure to nano-TiO2 resulted in obvious titanium accumulation in heart, in turn led to sparse cardiac muscle fibers, inflammatory response, cell necrosis, and cardiac biochemical dysfunction. Nano-TiO2 exposure promoted remarkably reactive oxygen species production such as superoxide radicals, hydrogen peroxide, and increased malondialdehyde, carbonyl and 8-OHdG levels as degradation products of lipid, protein, and DNA peroxidation in heart. Furthermore, nano-TiO2 exposure attenuated the activities of antioxidative enzymes, such as superoxide dismutase, ascorbate peroxidase, glutathione reductase, glutathione-S-transferase, and levels of antioxidants including ascorbic acid, glutathione, and thiol in heart. Therefore, TiO2 NPs exposure may impair cardiovascular system in mice, and attention should be aroused on the application of nano-TiO2 and their potential long-term exposure effects especially on human beings. PMID:23553934

Sheng, Lei; Wang, Xiaochun; Sang, Xuezi; Ze, Yuguan; Zhao, Xiaoyang; Liu, Dong; Gui, Suxin; Sun, Qingqing; Cheng, Jie; Cheng, Zhe; Hu, Renping; Wang, Ling; Hong, Fashui

2013-11-01

64

Nanoparticulate Transport of Oximes over an In Vitro Blood-Brain Barrier Model  

PubMed Central

Background Due to the use of organophosphates (OP) as pesticides and the availability of OP-type nerve agents, an effective medical treatment for OP poisonings is still a challenging problem. The acute toxicity of an OP poisoning is mainly due to the inhibition of acetylcholinesterase (AChE) in the peripheral and central nervous systems (CNS). This results in an increase in the synaptic concentration of the neurotransmitter acetylcholine, overstimulation of cholinergic receptors and disorder of numerous body functions up to death. The standard treatment of OP poisoning includes a combination of a muscarinic antagonist and an AChE reactivator (oxime). However, these oximes can not cross the blood-brain barrier (BBB) sufficiently. Therefore, new strategies are needed to transport oximes over the BBB. Methodology/Principal Findings In this study, we combined different oximes (obidoxime dichloride and two different HI 6 salts, HI 6 dichloride monohydrate and HI 6 dimethanesulfonate) with human serum albumin nanoparticles and could show an oxime transport over an in vitro BBB model. In general, the nanoparticulate transported oximes achieved a better reactivation of OP-inhibited AChE than free oximes. Conclusions/Significance With these nanoparticles, for the first time, a tool exists that could enable a transport of oximes over the BBB. This is very important for survival after severe OP intoxication. Therefore, these nanoparticulate formulations are promising formulations for the treatment of the peripheral and the CNS after OP poisoning. PMID:21151975

Wagner, Sylvia; Kufleitner, Jürgen; Zensi, Anja; Dadparvar, Miriam; Wien, Sascha; Bungert, Judith; Vogel, Tikva; Worek, Franz; Kreuter, Jörg; von Briesen, Hagen

2010-01-01

65

Polymerization of vegetable oils  

SciTech Connect

The addition of antioxidants and dispersants is not sufficient to eliminate gum formation in vegetable oils. Even with relatively unsaturated oils like rapeseed the extent of unsaturation overwhelms these additives. Fuel deterioration during storage will be minimized in an anaerobic storage environment and, to a lesser extent, with a lower degree of oil unsaturation. Gum formation and carbon coking can also occur immediately preceding and during combustion. Thermal polymerization may be the dominant gum forming reaction under combustion conditions since thermal polymerization has a higher activation energy than oxidative polymerization and anaerobic conditions can occur within atomized fuel droplets. Carbon coking can be reduced with a lower degree of oil unsaturation and with better atomization of the fuel. 4 figures, 1 table.

Korus, R.A.; Mousetis, T.L.; Lloyd, L.

1982-01-01

66

Net methylation of mercury in estuarine sediment microcosms amended with dissolved, nanoparticulate, and microparticulate mercuric sulfides.  

PubMed

The production of methylmercury (MeHg) by anaerobic microorganisms depends in part on the speciation and bioavailability of inorganic mercury to these organisms. Our previous work with pure cultures of methylating bacteria has demonstrated that the methylation potential of mercury decreased during the aging of mercuric sulfides (from dissolved to nanoparticulate and microcrystalline HgS). The objective of this study was to understand the relationship between mercury sulfide speciation and methylation potential in experiments that more closely simulate the complexity of sediment settings. The study involved sediment slurry microcosms that represented a spectrum of salinities in an estuary and were each amended with different forms of mercuric sulfides: dissolved Hg and sulfide, nanoparticulate HgS (3-4 nm in diameter), and microparticulate HgS (>500 nm). The results indicated that net MeHg production was influenced by both the activity of sulfate-reducing microorganisms (roughly represented by the rate of sulfate loss) and the bioavailability of mercury. In the presence of abundant sulfate and carbon sources (supporting relatively high microbial activity), net MeHg production in the slurries amended with dissolved Hg was greater than in slurries amended with nano-HgS, similar to previous experiments with pure bacterial cultures. In microcosms with minimal microbial activity (indicated by low rates of sulfate loss), the addition of either dissolved Hg or nano-HgS resulted in similar amounts of net MeHg production. For all slurries receiving micro-HgS, MeHg production did not exceed abiotic controls. In slurries amended with dissolved and nano-HgS, mercury was mainly partitioned to bulk-scale mineral particles and colloids, indicating that Hg bioavailability was not simply related to dissolved Hg concentration or speciation. Overall, the results suggest that models for mercury methylation potential in the environment will need to balance the relative contributions of mercury speciation and activity of methylating microorganisms. PMID:25007388

Zhang, Tong; Kucharzyk, Katarzyna H; Kim, Bojeong; Deshusses, Marc A; Hsu-Kim, Heileen

2014-08-19

67

In vitro and in vivo evaluation of a nanoparticulate bioceramic paste for dental pulp repair.  

PubMed

Bioactive materials play an important role in facilitating dental pulp repair when living dental pulp is exposed after injuries. Mineral trioxide aggregate is the currently recommended material of choice for pulp repair procedures though has several disadvantages, especially the inconvenience of handling. Little information is yet available about the early events and molecular mechanisms involved in bioceramic-mediated dental pulp repair. We aimed to characterize and determine the apatite-forming ability of the novel ready-to-use nanoparticulate bioceramic iRoot BP Plus, and investigate its effects on the in vitro recruitment of human dental pulp stem cells (DPSCs), as well as its capacity to induce dentin bridge formation in an in vivo model of pulp repair. It was found that iRoot BP Plus was nanosized and had excellent apatite-forming ability in vitro. Treatment with iRoot BP Plus extracts promoted the adhesion, migration and attachment of DPSCs, and optimized focal adhesion formation (Vinculin, p-Paxillin and p-Focal adhesion kinase) and stress fibre assembly. Consistent with the in vitro results, we observed the formation of a homogeneous dentin bridge and the expression of odontogenic (dentin sialoprotein, dentin matrix protein 1) and focal adhesion molecules (Vinculin, p-Paxillin) at the injury site of pulp repair model by iRoot BP Plus. Our findings provide valuable insights into the mechanism of bioceramic-mediated dental pulp repair, and the novel revolutionary ready-to-use nanoparticulate bioceramic paste shows promising therapeutic potential in dental pulp repair application. PMID:25182220

Zhu, Lingxin; Yang, Jingwen; Zhang, Jie; Lei, Dongqi; Xiao, Lan; Cheng, Xue; Lin, Ying; Peng, Bin

2014-12-01

68

Kinetics of Emulsion Polymerization  

Microsoft Academic Search

As a basis for understanding emulsion polymerization, the kinetics of free radical reactions in isolated loci is discussed subject to the condition that the free radicals are supplied to the loci from an external source. Three cases of interest are considered: that in which the average number of free radicals per locus is small compared with unity, that in which

Wendell V. Smith; Roswell H. Ewart

1948-01-01

69

Responsive polymeric delivery systems  

Microsoft Academic Search

This paper discusses the state of the art in a relatively new approach in the field of controlled drug delivery–responsive polymeric drug delivery systems. Such systems are capable of adjusting drug release rates in response to a physiological need. The fundamental principles of externally and self-regulated delivery systems are examined. Special attention is paid to specific clinical settings such as

Joseph Kost; Robert Langer

2001-01-01

70

Vector processing  

SciTech Connect

An apparatus is described for adapting a scalar data processor having a cache memory connected between main memory and a central processing unit, for efficient vector processing including: means for defining separate scalar and vector data areas in the cache memory, vector mode selection means for selectively enabling access to either the vector or scalar data areas of the cache memory, cache memory addressing means including separate vector and scalar addressing means responsive to the vector mode selection means and the central processing unit for accessing either the vector or scalar data areas of the cache memory, wherein the central processing unit includes: a pair of operand registers, and a result register, coupling means for providing a data path from the operand registers to an ALU and a further data path from an ALU to the result register, second coupling means for providing a data path from the cache memory to one of the operand registers and to the result register; an output buffer; third coupling means providing a data path from either of the operand registers to the second coupling means and to the output buffer; fourth coupling means providing a data path from the second coupling means or the output buffer to the cache memory; and fifth coupling means providing a data path from the result register to either of the operand registers.

Drimak, E.G.

1986-06-10

71

Active radar guides missile to its target: receptor-based targeted treatment of hepatocellular carcinoma by nanoparticulate systems.  

PubMed

Patients with hepatocellular carcinoma (HCC) usually present at advanced stages and do not benefit from surgical resection, so drug therapy should deserve a prominent place in unresectable HCC treatment. But chemotherapy agents, such as doxorubicin, cisplatin, and paclitaxel, frequently encounter important problems such as low specificity and non-selective biodistribution. Recently, the development of nanotechnology led to significant breakthroughs to overcome these problems. Decorating the surfaces of nanoparticulate-based drug carriers with homing devices has demonstrated its potential in concentrating chemotherapy agents specifically to HCC cells. In this paper, we reviewed the current status of active targeting strategies for nanoparticulate systems based on various receptors such as asialoglycoprotein receptor, transferrin receptor, epidermal growth factor receptor, folate receptor, integrin, and CD44, which are abundantly expressed on the surfaces of hepatocytes or liver cancer cells. Furthermore, we pointed out their merits and defects and provided theoretical references for further research. PMID:25424700

Yan, Jing-Jun; Liao, Jia-Zhi; Lin, Ju-Sheng; He, Xing-Xing

2015-01-01

72

Particle-Level Modeling of the Charge-Discharge Behavior of Nanoparticulate Phase-Separating Li-Ion Battery Electrodes  

E-print Network

In nanoparticulate phase-separating electrodes, phase separation inside the particles can be hindered during their charge/discharge cycles even when a thermodynamic driving force for phase separation exists. In such cases, particles may (de)lithiate discretely in a process referred to as mosaic instability. This instability could be the key to elucidating the complex charge/discharge dynamics in nanoparticulate phase-separating electrodes. In this paper, the dynamics of the mosaic instability is studied using Smoothed Boundary Method simulations at the particle level, where the concentration and electrostatic potential fields are spatially resolved around individual particles. Two sets of configurations consisting of spherical particles with an identical radius are employed to study the instability in detail. The effect of an activity-dependent exchange current density on the mosaic instability, which leads to asymmetric charge/discharge, is also studied. While we show that our model reproduces the results of...

Orvananos, Bernardo; Yu, Hui-Chia; Bazant, Martin Z; Thornton, Katsuyo

2013-01-01

73

Vector Fields  

NSDL National Science Digital Library

Vector fields are vectors which change from point to point. A standard example is the velocity of moving air, in other words, wind. For instance, the current wind pattern in the San Francisco area can be found at . This site has a 2-dimensional representation; careful reading of the webpage will tell you at what elevation the wind is shown. How would you represent a vector field in 3 dimensions? What features are important? Some simple examples are shown. Each can be rotated by clicking and dragging with the mouse. Explore!

Ay, Tevian

2006-01-01

74

Cloning vector  

DOEpatents

A vector comprising a filamentous phage sequence containing a first copy of filamentous phage gene X and other sequences necessary for the phage to propagate is disclosed. The vector also contains a second copy of filamentous phage gene X downstream from a promoter capable of promoting transcription in a bacterial host. In a preferred form of the present invention, the filamentous phage is M13 and the vector additionally includes a restriction endonuclease site located in such a manner as to substantially inactivate the second gene X when a DNA sequence is inserted into the restriction site. 2 figures.

Guilfoyle, R.A.; Smith, L.M.

1994-12-27

75

Vector quantization  

NASA Technical Reports Server (NTRS)

During the past ten years Vector Quantization (VQ) has developed from a theoretical possibility promised by Shannon's source coding theorems into a powerful and competitive technique for speech and image coding and compression at medium to low bit rates. In this survey, the basic ideas behind the design of vector quantizers are sketched and some comments made on the state-of-the-art and current research efforts.

Gray, Robert M.

1989-01-01

76

Frontal Polymerization in Microgravity  

NASA Technical Reports Server (NTRS)

Frontal polymerization systems, with their inherent large thermal and compositional gradients, are greatly affected by buoyancy-driven convection. Sounding rocket experiments allowed the preparation of benchmark materials and demonstrated that methods to suppress the Rayleigh-Taylor instability in ground-based research did not significantly affect the molecular weight of the polymer. Experiments under weightlessness show clearly that bubbles produced during the reaction interact very differently than under 1 g.

Pojman, John A.

1999-01-01

77

Structure-based rational design of prodrugs to enable their combination with polymeric nanoparticle delivery platforms for enhanced antitumor efficacy.  

PubMed

Drug-loaded nanoparticles (NPs) are of particular interest for efficient cancer therapy due to their improved drug delivery and therapeutic index in various types of cancer. However, the encapsulation of many chemotherapeutics into delivery NPs is often hampered by their unfavorable physicochemical properties. Here, we employed a drug reform strategy to construct a small library of SN-38 (7-ethyl-10-hydroxycamptothecin)-derived prodrugs, in which the phenolate group was modified with a variety of hydrophobic moieties. This esterification fine-tuned the polarity of the SN-38 molecule and enhanced the lipophilicity of the formed prodrugs, thereby inducing their self-assembly into biodegradable poly(ethylene glycol)-block-poly(d,l-lactic acid) (PEG-PLA) nanoparticulate structures. Our strategy combining the rational engineering of prodrugs with the pre-eminent features of conventionally used polymeric materials should open new avenues for designing more potent drug delivery systems as a therapeutic modality. PMID:25196427

Wang, Hangxiang; Xie, Haiyang; Wu, Jiaping; Wei, Xuyong; Zhou, Lin; Xu, Xiao; Zheng, Shusen

2014-10-20

78

Structure-Based Rational Design of Prodrugs To Enable Their Combination with Polymeric Nanoparticle Delivery Platforms for Enhanced Antitumor Efficacy**  

PubMed Central

Drug-loaded nanoparticles (NPs) are of particular interest for efficient cancer therapy due to their improved drug delivery and therapeutic index in various types of cancer. However, the encapsulation of many chemotherapeutics into delivery NPs is often hampered by their unfavorable physicochemical properties. Here, we employed a drug reform strategy to construct a small library of SN-38 (7-ethyl-10-hydroxycamptothecin)-derived prodrugs, in which the phenolate group was modified with a variety of hydrophobic moieties. This esterification fine-tuned the polarity of the SN-38 molecule and enhanced the lipophilicity of the formed prodrugs, thereby inducing their self-assembly into biodegradable poly(ethylene glycol)-block-poly(d,l-lactic acid) (PEG-PLA) nanoparticulate structures. Our strategy combining the rational engineering of prodrugs with the pre-eminent features of conventionally used polymeric materials should open new avenues for designing more potent drug delivery systems as a therapeutic modality. PMID:25196427

Wang, Hangxiang; Xie, Haiyang; Wu, Jiaping; Wei, Xuyong; Zhou, Lin; Xu, Xiao; Zheng, Shusen

2014-01-01

79

Selective electrochemical detection of dopamine in a microfluidic channel on carbon nanoparticulate electrodes.  

PubMed

There is a continuous need for the construction of detection systems in microfluidic devices. In particular, electrochemical detection allows the separation of signals from the analyte and interfering substances in the potential domain. Here, a simple microfluidic device for the sensitive and selective determination of dopamine in the presence of interfering substances was constructed and tested. It employs a carbon nanoparticulate electrode allowing the separation of voltammetric signals of dopamine and common interfering substances (ascorbic acid and acetaminophen) both in quiescent conditions and in flow due to the electrocatalytic effect. These voltammograms were also successfully simulated. The limit of detection of dopamine detected by square wave voltammetry in 1 mM solutions of interfering substances in phosphate buffered saline is about 100 nM. In human serum a clear voltammetric signal could be seen for a 200 nM solution, sufficient to detect dopamine in the cerebral fluid. Flow injection analysis allows a decrease in the limit of detection down to 3.5 nM. PMID:24757708

Rozniecka, Ewa; Jonsson-Niedziolka, Martin; Celebanska, Anna; Niedziolka-Jonsson, Joanna; Opallo, Marcin

2014-06-01

80

Effect of nanoparticulate bioactive glass particles on bioactivity and cytocompatibility of poly(3-hydroxybutyrate) composites  

PubMed Central

This work investigated the effect of adding nanoparticulate (29 nm) bioactive glass particles on the bioactivity, degradation and in vitro cytocompatibility of poly(3-hydroxybutyrate) (P(3HB)) composites/nano-sized bioactive glass (n-BG). Two different concentrations (10 and 20 wt %) of nanoscale bioactive glass particles of 45S5 Bioglass composition were used to prepare composite films. Several techniques (Raman spectroscopy, scanning electron microscopy, atomic force microscopy, energy dispersive X-ray) were used to monitor their surface and bioreactivity over a 45-day period of immersion in simulated body fluid (SBF). All results suggested the P(3HB)/n-BG composites to be highly bioactive, confirmed by the formation of hydroxyapatite on material surfaces upon immersion in SBF. The weight loss and water uptake were found to increase on increasing bioactive glass content. Cytocompatibility study (cell proliferation, cell attachment, alkaline phosphatase activity and osteocalcin production) using human MG-63 osteoblast-like cells in osteogenic and non-osteogenic medium showed that the composite substrates are suitable for cell attachment, proliferation and differentiation. PMID:19640877

Misra, Superb K.; Ansari, Tahera; Mohn, Dirk; Valappil, Sabeel P.; Brunner, Tobias J.; Stark, Wendelin J.; Roy, Ipsita; Knowles, Jonathan C.; Sibbons, Paul D.; Jones, Eugenia Valsami; Boccaccini, Aldo R.; Salih, Vehid

2010-01-01

81

Developing micro-/nanoparticulate drug delivery systems using “design of experiments”  

PubMed Central

Of late, micro and nanoparticluate drug delivery systems have been gaining immense importance primarily attributed to their improved drug release controlling and targeting efficiencies. Also, the small particle size and desirable surface charge associated with these delivery systems render them suitable for specific applications like lymphatic uptake, pulmonary uptake, tumor targeting, brain targeting, etc. For decades, micro and nanoparticulate systems have been prepared by the conventional “trial and error” approach of changing One Variable at a Time (OVAT). Using this methodology, the solution of a specific problematic formulation characteristic can certainly be achieved, but attainment of the true optimal composition is never guaranteed. Thus, the present manuscript provides an updated account of the systematic approach “Design of Experiments (DoE)” as applicable to formulation development of microparticles and nanostructured systems. Besides providing a bird's eye view of the various experimental designs and optimization techniques employed for DoE optimization of such systems, the present manuscript also presents a copilation of the major micro/nano-structuctred systems optimized through DoE till date. In a nutshell, the article will act both as a ready reckoner of DoE optimization of micro/nano drug delivery systems and a catalyst in providing an impetus to young pharmaceutical “nano & micro” researchers to venture into the rewarding field of systematic DoE optimization. PMID:23071925

Singh, Bhupinder; Bhatowa, Rahul; Tripathi, Chandra Bhushan; Kapil, Rishi

2011-01-01

82

Effects of ZnO nanoparticulate addition on the properties of PMNT ceramics  

PubMed Central

This research was conducted in order to study the effect of ZnO nanoparticulate addition on the properties of 0.9 Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 [PMNT] ceramics. The PMNT ceramics were prepared by a solid-state reaction. The ZnO nanoparticles were added into PMNT ceramics to form PMNT/xZnO (x = 0, 0.05, 0.1, 0.5, and 1.0 wt.%). The PMNT/xZnO ceramics were investigated in terms of phase, microstructure, and mechanical and electrical properties. It was found that the density and grain size of PMNT ceramics tended to increase with an increasing amount of ZnO content. Moreover, a transgranular fracture was observed for the samples containing ZnO, while pure PMNT ceramics showed only a intergranular fracture. An addition of only 0.05 wt.% of ZnO was also found to enhance the hardness and dielectric and ferroelectric properties of the PMNT ceramics. PMID:22222049

2012-01-01

83

Nonagonistic Dectin-1 ligand transforms CpG into a multitask nanoparticulate TLR9 agonist.  

PubMed

CpG DNA, a ligand for Toll-like receptor 9 (TLR9), has been one of the most promising immunotherapeutic agents. Although there are several types of potent humanized CpG oligodeoxynucleotide (ODN), developing "all-in-one" CpG ODNs activating both B cells and plasmacytoid dendritic cells forming a stable nanoparticle without aggregation has not been successful. In this study, we generated a novel nanoparticulate K CpG ODN (K3) wrapped by the nonagonistic Dectin-1 ligand schizophyllan (SPG), K3-SPG. In sharp contrast to K3 alone, K3-SPG stimulates human peripheral blood mononuclear cells to produce a large amount of both type I and type II IFN, targeting the same endosome where IFN-inducing D CpG ODN resides without losing its K-type activity. K3-SPG thus became a potent adjuvant for induction of both humoral and cellular immune responses, particularly CTL induction, to coadministered protein antigens without conjugation. Such potent adjuvant activity of K3-SPG is attributed to its nature of being a nanoparticle rather than targeting Dectin-1 by SPG, accumulating and activating antigen-bearing macrophages and dendritic cells in the draining lymph node. K3-SPG acting as an influenza vaccine adjuvant was demonstrated in vivo in both murine and nonhuman primate models. Taken together, K3-SPG may be useful for immunotherapeutic applications that require type I and type II IFN as well as CTL induction. PMID:24516163

Kobiyama, Kouji; Aoshi, Taiki; Narita, Hirotaka; Kuroda, Etsushi; Hayashi, Masayuki; Tetsutani, Kohhei; Koyama, Shohei; Mochizuki, Shinichi; Sakurai, Kazuo; Katakai, Yuko; Yasutomi, Yasuhiro; Saijo, Shinobu; Iwakura, Yoichiro; Akira, Shizuo; Coban, Cevayir; Ishii, Ken J

2014-02-25

84

Modular Modification of Polymeric Microspheres.  

E-print Network

??Die vorliegende Arbeit beschreibt die vielseitige Modifikation von polymeren Mikrokugeln mit Polymeren. Die Polymere, darunter auch Glucopolymere, wurden durch die kontrollierte RAFT-Polymerisation erhalten. Die Funktionalisierung… (more)

Kaupp, Michael

2014-01-01

85

Pipeline vectorization  

Microsoft Academic Search

This paper presents pipeline vectorization, amethod for synthesizing hardware pipelines based on softwarevectorizing compilers. The method improves eciencyand ease of development of hardware designs, particularlyfor users with little electronics design experience. We proposeseveral loop transformations to customize pipelinesto meet hardware resource constraints, while maximizingavailable parallelism. For run-time recongurable systems,we apply hardware specialization to increase...

Markus Weinhardt; Wayne Luk

2001-01-01

86

Living olefin polymerization processes  

DOEpatents

Processes for the living polymerization of olefin monomers with terminal carbon-carbon double bonds are disclosed. The processes employ initiators that include a metal atom and a ligand having two group 15 atoms and a group 16 atom or three group 15 atoms. The ligand is bonded to the metal atom through two anionic or covalent bonds and a dative bond. The initiators are particularly stable under reaction conditions in the absence of olefin monomer. The processes provide polymers having low polydispersities, especially block copolymers having low polydispersities. It is an additional advantage of these processes that, during block copolymer synthesis, a relatively small amount of homopolymer is formed.

Schrock, Richard R. (Winchester, MA); Baumann, Robert (Cambridge, MA)

1999-01-01

87

Living olefin polymerization processes  

DOEpatents

Processes for the living polymerization of olefin monomers with terminal carbon-carbon double bonds are disclosed. The processes employ initiators that include a metal atom and a ligand having two group 15 atoms and a group 16 atom or three group 15 atoms. The ligand is bonded to the metal atom through two anionic or covalent bonds and a dative bond. The initiators are particularly stable under reaction conditions in the absence of olefin monomer. The processes provide polymers having low polydispersities, especially block copolymers having low polydispersities. It is an additional advantage of these processes that, during block copolymer synthesis, a relatively small amount of homopolymer is formed.

Schrock, R.R.; Baumann, R.

1999-03-30

88

Bimorphic polymeric photomechanical actuator  

NASA Technical Reports Server (NTRS)

A bimorphic polymeric photomechanical actuator, in one embodiment using polyvinylidene fluoride (PVDF) as a photosensitive body, transmitting light over fiber optic cables, and controlling the shape and pulse duration of the light pulse to control movement of the actuator. Multiple light beams are utilized to generate different ranges of motion for the actuator from a single photomechanical body and alternative designs use multiple light beams and multiple photomechanical bodies to provide controlled movement. Actuator movement using one or more ranges of motion is utilized to control motion to position an actuating element in three dimensional space.

Sarkisov, Sergey S. (Inventor); Curley, Michael J. (Inventor); Adamovsky, Grigory (Inventor); Sarkisov, Jr., Sergey S. (Inventor); Fields, Aisha B. (Inventor)

2006-01-01

89

In vitro analysis of nanoparticulate hydroxyapatite/chitosan composites as potential drug delivery platforms for the sustained release of antibiotics in the treatment of osteomyelitis.  

PubMed

Nanoparticulate composites of hydroxyapatite (HAp) and chitosan were synthesized by ultrasound-assisted sequential precipitation and characterized for their microstructure at the atomic scale, surface charge, drug release properties, and combined antibacterial and osteogenic response. Crystallinity of HAp nanoparticles was reduced because of the interference of the surface layers of chitosan with the dissolution/reprecipitation-mediated recrystallization mechanism that conditions the transition from the as-precipitated amorphous calcium phosphate phase to the most thermodynamically stable one--HAp. Embedment of 5-10 nm sized, narrowly dispersed HAp nanoparticles within the polymeric matrix mitigated the burst release of the small molecule model drug, fluorescein, bound to HAp by physisorption, and promoted sustained-release kinetics throughout the 3 weeks of release time. The addition of chitosan to the particulate drug carrier formulation, however, reduced the antibacterial efficacy against S aureus. Excellent cell spreading and proliferation of osteoblastic MC3T3-E1 cells evidenced on microscopic conglomerates of HAp nanoparticles in vitro also markedly diminished on HAp/chitosan composites. Mitochondrial dehydrogenase activity exhibited normal values only for HAp/chitosan particle concentrations of up to 2 mg/cm(2) and significantly dropped, by about 50%, at higher particle concentrations (4 and 8 mg/cm(2)). The gene expression of osteocalcin, a mineralization inductor, and the transcription factor Runx2 was downregulated in cells incubated in the presence of 3 mg/cm(2) HAp/chitosan composite particles, whereas the expression of osteopontin, a potent mineralization inhibitor, was upregulated, further demonstrating the partially unfavorable osteoblastic cell response to the given particles. The peak in the expression of osteogenic markers paralleling the osteoblastic differentiation was also delayed most for the cell population incubated with HAp/chitosan particles. Overall, the positive effect of chitosan coating on the drug elution profile of HAp nanoparticles as carriers for the controlled delivery of antibiotics in the treatment of osteomyelitis was compensated for by the lower bacteriostatic efficiency and the comparatively unviable cell response to the composite material, especially at higher dosages. PMID:24382825

Uskokovi?, Vuk; Desai, Tejal A

2014-02-01

90

In Vitro Analysis of Nanoparticulate Hydroxyapatite/Chitosan Composites as Potential Drug Delivery Platforms for the Sustained Release of Antibiotics in the Treatment of Osteomyelitis  

PubMed Central

Nanoparticulate composites of hydroxyapatite (HAp) and chitosan were synthesized by ultrasound-assisted sequential precipitation and characterized for their microstructure at the atomic scale, surface charge, drug release properties, and combined antibacterial and osteogenic response. Crystallinity of HAp nanoparticles was reduced because of the interference of the surface layers of chitosan with the dissolution/reprecipitation-mediated recrystallization mechanism that conditions the transition from the as-precipitated amorphous calcium phosphate phase to the most thermodynamically stable one—HAp. Embedment of 5–10 nm sized, narrowly dispersed HAp nanoparticles within the polymeric matrix mitigated the burst release of the small molecule model drug, fluorescein, bound to HAp by physisorption, and promoted sustained-release kinetics throughout the 3 weeks of release time. The addition of chitosan to the particulate drug carrier formulation, however, reduced the antibacterial efficacy against S aureus. Excellent cell spreading and proliferation of osteoblastic MC3T3-E1 cells evidenced on microscopic conglomerates of HAp nanoparticles in vitro also markedly diminished on HAp/chitosan composites. Mitochondrial dehydrogenase activity exhibited normal values only for HAp/chitosan particle concentrations of up to 2 mg/cm2 and significantly dropped, by about 50%, at higher particle concentrations (4 and 8 mg/cm2). The gene expression of osteocalcin, a mineralization inductor, and the transcription factor Runx2 was downregulated in cells incubated in the presence of 3 mg/cm2 HAp/chitosan composite particles, whereas the expression of osteopontin, a potent mineralization inhibitor, was upregulated, further demonstrating the partially unfavorable osteoblastic cell response to the given particles. The peak in the expression of osteogenic markers paralleling the osteoblastic differentiation was also delayed most for the cell population incubated with HAp/chitosan particles. Overall, the positive effect of chitosan coating on the drug elution profile of HAp nanoparticles as carriers for the controlled delivery of antibiotics in the treatment of osteomyelitis was compensated for by the lower bacteriostatic efficiency and the comparatively unviable cell response to the composite material, especially at higher dosages. PMID:24382825

USKOKOVI?, VUK; DESAI, TEJAL A.

2014-01-01

91

Organometallic Polymeric Conductors  

NASA Technical Reports Server (NTRS)

For aerospace applications, the use of polymers can result in tremendous weight savings over metals. Suitable polymeric materials for some applications like EMI shielding, spacecraft grounding, and charge dissipation must combine high electrical conductivity with long-term environmental stability, good processability, and good mechanical properties. Recently, other investigators have reported hybrid films made from an electrically conductive polymer combined with insulating polymers. In all of these instances, the films were prepared by infiltrating an insulating polymer with a precursor for a conductive polymer (either polypyrrole or polythiophene), and oxidatively polymerizing the precursor in situ. The resulting composite films have good electrical conductivity, while overcoming the brittleness inherent in most conductive polymers. The highest conductivities reported (approximately 4/Scm) were achieved with polythiophene in a polystyrene host polymer. The best films using a polyamide as base polymer were four orders of magnitude less conductive than the polystyrene films. The authors suggested that this was because polyimides were unable to swell sufficiently for infiltration of monomer as in the polystyrene. It was not clear, however, if the different conductivities obtained were merely the result of differing oxidation conditions. Oxidation time, temperature and oxidant concentration varied widely among the studies.

1997-01-01

92

Cytotoxic Responses and Potential Respiratory Health Effects of Carbon and Carbonaceous Nanoparticulates in the Paso del Norte Airshed Environment  

PubMed Central

We have utilized a range of manufactured or commercial nanoparticulate materials, including surrogate carbon nano-PM along with combustion-generated carbonaceous (soot) nano-PM characteristic of environmental nano-PM (both indoor and outdoor) to investigate and compare their cytotoxic response in vitro with an immortalized human epithelial (lung model) cell line (A549). These have included nano-Ag, Al2O3, TiO2, Fe2O3, ZrO2, Si3N4, chrysotile asbestos, BC, 2 types of MWCNT-aggregate PM (MWCNT-R and MWCNT-N), and high-volume glass fiber collected soots: candle, wood, diesel (truck), tire, and 3-types of natural gas kitchen burner-generated soots: yellow (fuel-rich) flame, low-flow blue flame, and normal flow blue flame soot PM. These carbonaceous nano-PM species can be found in either the indoor and outdoor environments or microenvironments. Two-day and two-week in-vitro cultures of A549 showed cell death (or decreased cell viability) for all nanoparticulate materials, but especially significant for all but the TiO2 and candle, wood, and diesel PM. The natural gas kitchen burner combustion PM cell death response was characteristic of BC and MWCNT PM. There was no correlation with total PAH content of the soot PM. Cytokine release (IL-6, IL-8) was detected for the Ag, Fe2 O3, asbestos, BC and the MWCNT PM. Reactive oxygen species (ROS) production was also detected for Ag, Fe2 O3, ZrO2, asbestos, BC, and the MWCNT aggregate PM, as well as the natural gas kitchen burner combustion PM. TEM, FESEM, and optical microscopy examination of these nanomaterials illustrate the wide range in PM morphologies and crystallinities as well as cell morphologies. Taken together, these results illustrate proinflammatory and related respiratory health issues in relation to environmental nanoparticulates. PMID:18441401

Soto, K. F.; Murr, L. E.; Garza, K. M.

2008-01-01

93

Methylation of mercury by bacteria exposed to dissolved, nanoparticulate, and microparticulate mercuric sulfides.  

PubMed

The production of the neurotoxic methylmercury in the environment is partly controlled by the bioavailability of inorganic divalent mercury (Hg(II)) to anaerobic bacteria that methylate Hg(II). In sediment porewater, Hg(II) associates with sulfides and natural organic matter to form chemical species that include organic-coated mercury sulfide nanoparticles as reaction intermediates of heterogeneous mineral precipitation. Here, we exposed two strains of sulfate-reducing bacteria to three forms of inorganic mercury: dissolved Hg and sulfide, nanoparticulate HgS, and microparticulate HgS. The bacteria cultures exposed to HgS nanoparticles methylated mercury at a rate slower than cultures exposed to dissolved forms of mercury. However, net methylmercury production in cultures exposed to nanoparticles was 6 times greater than in cultures treated with microscale particles, even when normalized to specific surface area. Furthermore, the methylation potential of HgS nanoparticles decreased with storage time of the nanoparticles in their original stock solution. In bacteria cultures amended with nano-HgS from a 16 h-old nanoparticle stock, 6-10% of total mercury was converted to methylmercury after one day. In contrast, 2-4% was methylated in cultures amended with nano-HgS that was aged for 3 days or 1 week. The methylation of mercury derived from nanoparticles (in contrast to the larger particles) would not be predicted by equilibrium speciation of mercury in the aqueous phase (<0.2 ?m) and was possibly caused by the disordered structure of nanoparticles that facilitated release of chemically labile mercury species immediately adjacent to cell surfaces. Our results add new dimensions to the mechanistic understanding of mercury methylation potential by demonstrating that bioavailability is related to the geochemical intermediates of rate-limited mercury sulfide precipitation reactions. These findings could help explain observations that the "aging" of mercury in sediments reduces its methylation potential and provide a basis for assessing and remediating methylmercury hotspots in the environment. PMID:22145980

Zhang, Tong; Kim, Bojeong; Levard, Clément; Reinsch, Brian C; Lowry, Gregory V; Deshusses, Marc A; Hsu-Kim, Heileen

2012-07-01

94

Nanospray technology for an in situ gelling nanoparticulate powder as a wound dressing.  

PubMed

In the current study the feasibility of the novel nano spray drying technique for the production of stable nanoparticulate dry powder, able to gel when administered locally on a wound, is explored. Gentamicin sulphate (GS) was loaded into alginate/pectin nanoparticles as highly soluble (hygroscopic) model drug with wide range antibacterial agent for wound dressing. The influence of process variables, mainly spray mesh size and feed concentration, on particle size and morphology, powder wound fluid uptake ability and gelling rate, as well as hydrogel water vapour transmission at wound site were studied. Particles morphology was spherical with few exceptions as slightly corrugated particles when the larger nozzle was used. Production of spherical nanoparticles (d50 ? 350 nm) in good yield (82-92%) required 4 ?m spray mesh whereas 7 ?m mesh produced larger wrinkled particles. Nano spray-dried particles showed high encapsulation efficiency (? 80%), good flowability, high fluid uptake, fast gel formation (15 min) and proper adhesiveness to fill the wound site and to remove easily the formulation after use. Moreover, moisture transmission of the in situ formed hydrogel was between 95 and 90 g/m(2)/h, an optimum range to avoid wound dehydration or occlusion phenomena. Release of the encapsulated GS, monitored as permeation rate using Franz cells in simulated wound fluid (SWF) was related to particle size and gelling rate. Sustained permeation profiles were obtained achieving total permeation of the drug between 3 and 6 days. However, all nano spray-dried formulations presented a burst effect, suitable to prevent infection spreading at the beginning of the therapy. Antimicrobial tests against Staphylococcus aureus and Pseudomonas aeruginosa showed stronger and prolonged antimicrobial effect of the nanoparticles compared to pure GS both shortly after administration and over time (till 12 days). PMID:24979533

De Cicco, Felicetta; Porta, Amalia; Sansone, Francesca; Aquino, Rita P; Del Gaudio, Pasquale

2014-10-01

95

Microparticulated and nanoparticulated zirconium oxide added to calcium silicate cement: Evaluation of physicochemical and biological properties.  

PubMed

The physicochemical and biological properties of calcium silicate-based cement (CS) associated to microparticulated (micro) or nanoparticulated (nano) zirconium oxide (ZrO2 ) were compared with CS and bismuth oxide (BO) with CS. The pH, release of calcium ions, radiopacity, setting time, and compression strength of the materials were evaluated. The tissue reaction promoted by these materials in the subcutaneous was also investigated by morphological, immunohistochemical, and quantitative analyses. For this purpose, polyethylene tubes filled with materials were implanted into rat subcutaneous. After 7, 15, 30, and 60 days, the tubes surrounded by capsules were fixed and embedded in paraffin. In the H&E-stained sections, the number of inflammatory cells (ICs) in the capsule was obtained. Moreover, detection of interleukin-6 (IL-6) by immunohistochemistry and number of IL-6 immunolabeled cells were carried out. von Kossa method was also performed. The differences among the groups were subjected to Tukey test (p???0.05). The solutions containing the materials presented an alkaline pH and released calcium ions. The addition of radiopacifiers increased setting time and radiopacity of CS. A higher compressive strength in the CS?+?ZrO2 (micro and nano) was found compared with CS?+?BO. The number of IC and IL-6 positive cells in the materials with ZrO2 was significantly reduced in comparison with CS?+?BO. von Kossa-positive structures were observed adjacent to implanted materials. The ZrO2 associated to the CS provides satisfactory physicochemical properties and better biological response than BO. Thus, ZrO2 may be a good alternative for use as radiopacifying agent in substitution to BO. PMID:24497271

Silva, Guilherme F; Bosso, Roberta; Ferino, Rafael V; Tanomaru-Filho, Mário; Bernardi, Maria I B; Guerreiro-Tanomaru, Juliane M; Cerri, Paulo S

2014-12-01

96

An aquaporin 4 antisense oligonucleotide loaded, brain targeted nanoparticulate system design.  

PubMed

Aquaporins (AQPs), members of the water-channel protein family, are highly expressed in brain tissue especially in astrocytic end-feet. They are important players for water hemostasis during development of cytotoxic as well as vasogenic edema. Increased expression of AQPs is important in pathophysiology of neurological diseases such as neuroinflammation and ischemia. Unfortunately, there are a few pharmacological inhibitors of AQP4 with several side effects limiting their translation as a drug for use in clinical conditions. Another therapeutic approach is using antisense oligonucleotides (ASOs) to block AQP4 activity. These are short, synthetic, modified nucleic acids that bind RNA to modulate its function. However, they cannot pass the blood brain barrier (BBB). To overcome this obstacle we designed a nanoparticulate system made up of chitosan nanoparticles surface modified with PEG and conjugated with monoclonal anti transferrin receptor-1 antibody via streptavidin-biotin binding. The nanocarrier system could be targeted to the transferrin receptor-1 at the brain endothelial capillaries through monoclonal antibodies. It is hypothesized that the nanoparticles could pass the BBB via receptor mediated transcytosis and reach brain parenchyma. Particle size, zeta potential, loading capacity and release profiles of nanoparticles were investigated. It was observed that all types of chitosau (CS) nanoparticles had positive zeta potential values and nanoparticle particle size distribution varied between 100 and 800 nm. The association efficiency of ASOs into the nanoparticles was between 80-97% and the release profiles of the nanoparticles exhibited an initial burst effect followed by a controlled release. The results showed that the designed chitosan based nanocarriers could be a promising carrier system to transport nucleic acid based drugs to brain parenchyma. PMID:24855824

Kozlu, S; Caban, S; Yerlikaya, F; Fernandez-Megia, E; Novoa-Carballal, R; Riguera, R; Yemisci, M; Gursoy-Ozdemir, Y; Dalkara, T; Couvreur, P; Capan, Y

2014-05-01

97

K-edge ratio method for identification of multiple nanoparticulate contrast agents by spectral CT imaging  

PubMed Central

Objective: Recently introduced energy-sensitive X-ray CT makes it feasible to discriminate different nanoparticulate contrast materials. The purpose of this work is to present a K-edge ratio method for differentiating multiple simultaneous contrast agents using spectral CT. Methods: The ratio of two images relevant to energy bins straddling the K-edge of the materials is calculated using an analytic CT simulator. In the resulting parametric map, the selected contrast agent regions can be identified using a thresholding algorithm. The K-edge ratio algorithm is applied to spectral images of simulated phantoms to identify and differentiate up to four simultaneous and targeted CT contrast agents. Results: We show that different combinations of simultaneous CT contrast agents can be identified by the proposed K-edge ratio method when energy-sensitive CT is used. In the K-edge parametric maps, the pixel values for biological tissues and contrast agents reach a maximum of 0.95, whereas for the selected contrast agents, the pixel values are larger than 1.10. The number of contrast agents that can be discriminated is limited owing to photon starvation. For reliable material discrimination, minimum photon counts corresponding to 140?kVp, 100?mAs and 5-mm slice thickness must be used. Conclusion: The proposed K-edge ratio method is a straightforward and fast method for identification and discrimination of multiple simultaneous CT contrast agents. Advances in knowledge: A new spectral CT-based algorithm is proposed which provides a new concept of molecular CT imaging by non-iteratively identifying multiple contrast agents when they are simultaneously targeting different organs. PMID:23934964

Ghadiri, H; Ay, M R; Shiran, M B; Soltanian-Zadeh, H

2013-01-01

98

Polymerization with freezing  

NASA Astrophysics Data System (ADS)

Irreversible aggregation processes involving reactive and frozen clusters are investigated using the rate equation approach. In aggregation events, two clusters join irreversibly to form a larger cluster; additionally, reactive clusters may spontaneously freeze. Frozen clusters do not participate in merger events. Generally, freezing controls the nature of the aggregation process, as demonstrated by the final distribution of frozen clusters. The cluster mass distribution has a power-law tail, Fk~k-?, when the freezing process is sufficiently slow. Different exponents, ? = 1 and 3, are found for the constant and the product aggregation rates, respectively. For the latter case, the standard polymerization model, either no gels, or a single gel, or even multiple gels, may be produced.

Ben-Naim, E.; Krapivsky, P. L.

2005-12-01

99

Highly transparent and conductive Al-doped ZnO nanoparticulate thin films using direct write processing  

NASA Astrophysics Data System (ADS)

Solution processable Al-doped ZnO (AZO) thin films are attractive candidates for low cost transparent electrodes. We demonstrate here an optimized nanoparticulate ink for the fabrication of AZO thin films using scalable, low-cost direct write processing (ultrasonic spray deposition) in air at atmospheric pressure. The thin films were made via thermal processing of as-deposited films. AZO films deposited using the proposed nanoparticulate ink with further reducing in vacuum and rf plasma of forming gas exhibited optical transparency greater than 95% across the visible spectrum, and electrical resistivity of 0.5 ? cm and it drops down to 7.0 × 10-2 ? cm after illuminating with UV light, which is comparable to commercially available tin doped indium oxide colloidal coatings. Various structural analyses were performed to investigate the influence of ink chemistry, deposition parameters, and annealing temperatures on the structural, optical, and electrical characteristics of the spray deposited AZO thin films. Optical micrographs confirmed the presence of surface defects and cracks using the AZO NPs ink without any additives. After adding N-(2-Aminoethyl)-3-aminopropylmethyldimethoxy silane to the ink, AZO films exhibited an optical transparency which was virtually identical to that of the plain glass substrate.

Vunnam, S.; Ankireddy, K.; Kellar, J.; Cross, W.

2014-05-01

100

Polyelectrolyte-mediated assembly of copper-phthalocyanine tetrasulfonate multilayers and the subsequent production of nanoparticulate copper oxide thin films.  

PubMed

An approach to producing films of nanometer-sized copper oxide particulates, based on polyelectrolyte-mediated assembly of the precursor, copper(II)phthalocyanine tetrasulfonate (CPTS), is described. Multilayered CPTS and polydiallyldimethylammonium chloride (PDADMAC) were alternately assembled on different planar substrates via the layer-by-layer (LbL) procedure. The growth of CPTS multilayers was monitored by UV-visible spectrometry and quartz crystal microbalance (QCM) measurements. Both the UV-visible spectra and the QCM data showed that a fixed amount of CPTS could be attached to the substrate surface for a given adsorption cycle. Cyclic voltammograms at the CPTS/PDADMAC-covered gold electrode exhibited a decrease in peak currents with the layer number, indicating that the permeability of CPTS multilayers on the electrodes had diminished. When these CPTS multilayered films were calcined at elevated temperatures, uniform thin films composed of nanoparticulate copper oxide could be produced. Ellipsometry showed that the thickness of copper oxide nanoparticulate films could be precisely tailored by varying the thickness of CPTS multilayer films. The morphology and roughness of CPTS multilayer and copper oxide thin films were characterized by atomic force microscopy. X-ray diffraction (XRD) measurements indicated that these thin films contained both CuO and Cu2O nanoparticles. The preparation of such copper oxide thin films with the use of metal complex precursors represents a new route for the synthesis of inorganic oxide films with a controlled thickness. PMID:15518398

Chickneyan, Zarui Sara; Briseno, Alejandro L; Shi, Xiangyang; Han, Shubo; Huang, Jiaxing; Zhou, Feimeng

2004-07-01

101

Porphyrin-sensitized nanoparticulate TiO2 as the photoanode of a hybrid photoelectrochemical biofuel cell.  

PubMed

Porphyrin-sensitized nanoparticulate TiO(2) on conducting glass has been investigated as a photoanode material for a new cell that converts light energy into electricity. The cell is a hybrid of a dye-sensitized nanoparticulate semiconductor photoelectrochemical solar cell, and a biofuel cell that oxidizes glucose. Porphyrin molecules excited by light inject electrons into the photoanode, from where they enter the external circuit. The resulting porphyrin radical cations are reduced by NADH in aqueous buffer, ultimately regenerating the photoanode and producing NAD(+). Glucose dehydrogenase oxidizes glucose, and in the process recycles NAD(+) back to NADH. The photoanode is coupled with a suitable cathode to make a functioning cell (Hg/Hg(2)SO(4) was employed for evaluation purposes). The cell produces 1.1 V at open circuit and has a fill factor of 0.61. These values are both significantly higher than those for a previously reported cell of a similar type based on an SnO(2) electrode. PMID:15350115

Brune, Alicia; Jeong, Goojin; Liddell, Paul A; Sotomura, Tadashi; Moore, Thomas A; Moore, Ana L; Gust, Devens

2004-09-14

102

Was Mineral Surface Complexity and Toxicity an Impetus for Evolution of Microbial Extracellular Polymeric Substances?  

NASA Astrophysics Data System (ADS)

Modern ecological niches are teeming with an astonishing diversity of microbial life closely associated with mineral surfaces, highlighting the remarkable success of microorganisms in conquering the challenges and capitalizing on the benefits presented by the mineral-water interface. Such community-living is enabled by an extracellular, polymeric, biofilm matrix developed at cell surfaces. Despite the energetic penalties, biofilm formation capability likely evolved on early Earth because of crucial cell survival functions, of which recognized roles include facilitating cell-attachment at mineral surfaces, intercellular signaling and lateral gene transfer, protection from dessication in tidal pools, and screening toxic UV light and toxic soluble metals. Cell-attachment to mineral surfaces was likely critical for cell survival and function, but the potential toxicity of mineral surfaces towards cells and the complexities of the mineral-water-cell interface in promoting biofilm formation, have not been fully appreciated. We examined the effects of nanoparticulate oxides (amorphous SiO2, anatase ?-TiO2, and ?-Al2O3) on EPS- and biofilm-producing wild-type strains and their isogenic knock-out mutants which are defective in EPS-producing ability. In detail, we used Gram-negative wild-type Pseudomonas aeruginosa PAO1 and its EPS knock-out mutant ?-psl, and the Gram-positive wild-type Bacillus subtilis NCIB3610 and its EPS-knock-out mutant yhxB?. We conducted bacterial growth experiments in the presence of each oxide in order to determine the viability of each cell type relative to oxide-free controls. The amount of EPS generated in the presence of oxides was also quantified and qualitatively analyzed by fluorescent stains. The results indicated a previously unrecognized role for microbial extracellular polymeric substances (EPS) in shielding both Gram-negative and Gram-positive cells against the toxic effects of mineral surfaces. This role is distinct from the protection provided against toxic soluble metals. Furthermore, we found that mineral toxicity is specific to the surface chemistry and particle size of the mineral, and that EPS protect against this mineral-specific toxicity via different mechanisms. Most intriguingly, we determined that EPS production is mineral-induced. By addressing the mechanistic detailed interactions at the mineral-water-cell interface, we provide insight to the potential impact of nanoparticulate mineral surfaces in promoting increased complexity of cell surfaces, including EPS and biofilm formation, on early Earth.

Sahai, N.; Xu, J.; Zhu, C.; Campbell, J.; Hickey, W.; Zhang, N.

2011-12-01

103

High temperature structural, polymeric foams from high internal emulsion polymerization  

SciTech Connect

In 1982, a high internal phase emulsion (HIPE) polymerization process to manufacture microcellular, polymeric foam systems was patented by Unilever. This patent discloses a polymerization process that occurs in a water-in-oil emulsion in which the water represents at least 76% of the emulsion by volume. The oil phase consists of vinyl monomers such as styrene and acrylates that are crosslinked by divinyl monomers during polymerization. After polymerization and drying to remove the water phase, the result is a crosslinked polymer foam with an open cell microstructure that is homogeneous throughout in terms of morphology, density, and mechanical properties. Since 1982, numerous patents have examined various HIPE polymerized foam processing techniques and applications that include absorbents for body fluids, cleaning materials, and ion exchange systems. All the published HIPE polymerized foams have concentrated on materials for low temperature applications. Copolymerization of styrene with maleic anhydride and N-substituted maleimides to produce heat resistant thermoplastics has been studied extensively. These investigations have shown that styrene will free radically copolymerize with N-substituted maleimides to create an alternating thermoplastic copolymer with a Tg of approximately 200{degrees}C. However, there are many difficulties in attempting the maleimide styrene copolymerization in a HIPE such as lower polymerization temperatures, maleimide solubility difficulties in both styrene and water, and difficulty obtaining a stable HIPE with a styrene/maleimide oil phase. This work describes the preparation of copolymer foams from N-ethylmaleimide and Bis(3-ethyl-5-methyl-4-maleimide-phenyl)methane with styrene based monomers and crosslinking agents.

Hoisington, M.A.; Duke, J.R.; Apen, P.G.

1996-02-01

104

Polymeric micelles as new drug carriers  

Microsoft Academic Search

Advances in block copolymer syntheses have led to polymeric micelles that may serve as nanoscopic drug carriers. For drug delivery, micelles were prepared from biocompatible and biodegradable block copolymers. The polymeric micelles display functional groups on their surfaces for attachment of pilot molecules. Researchers are establishing chemical as well as physical routes of loading drugs into polymeric micelles. Notably, polymeric

Glen S. Kwon; Teruo Okano

1996-01-01

105

Organometallic Polymeric Conductors  

NASA Technical Reports Server (NTRS)

For aerospace applications, the use of polymers can result in tremendous weight savings over metals. Suitable polymeric materials for some applications like EMI shielding, spacecraft grounding, and charge dissipation must combine high electrical conductivity with long-term environmental stability, good processability, and good mechanical properties. Recently, other investigators have reported hybrid films made from an electrically conductive polymer combined with insulating polymers. In all of these instances, the films were prepared by infiltrating an insulating polymer with a precursor for a conductive polymer (either polypyrrole or polythiophene), and oxidatively polymerizing the precursor in situ. The resulting composite films have good electrical conductivity, while overcoming the brittleness inherent in most conductive polymers. Many aerospace applications require a combination of properties. Thus, hybrid films made from polyimides or other engineering resins are of primary interest, but only if conductivities on the same order as those obtained with a polystyrene base could be obtained. Hence, a series of experiments was performed to optimize the conductivity of polyimide-based composite films. The polyimide base chosen for this study was Kapton. 3-MethylThiophene (3MT) was used for the conductive phase. Three processing variables were identified for producing these composite films, namely time, temperature, and oxidant concentration for the in situ oxidation. Statistically designed experiments were used to examine the effects of these variables and synergistic/interactive effects among variables on the electrical conductivity and mechanical strength of the films. Multiple linear regression analysis of the tensile data revealed that temperature and time have the greatest effect on maximum stress. The response surface of maximum stress vs. temperature and time (for oxidant concentration at 1.2 M) is shown. Conductivity of the composite films was measured for over 150 days in air at ambient temperature. The conductivity of the films dropped only half an order of magnitude in that time. Films aged under vacuum at ambient temperature diminished slightly in conductivity in the first day, but did not change thereafter. An experimental design approach will be applied to maximize the efficiency of the laboratory effort. The material properties (initial and long term) will also be monitored and assessed. The experimental results will add to the existing database for electrically conductive polymer materials. Attachments: 1) Synthesis Crystal Structure, and Polymerization of 1,2:5,6:9,10-Tribenzo-3,7,11,13-tetradehydro(14) annulene. 2) Reinvestigation of the Photocyclization of 1,4-Phenylene Bis(phenylmaleic anhydride): Preparation and Structure of (5)Helicene 5,6:9,10-Dianhydride. 3) Preparation and Structure Charecterization of a Platinum Catecholate Complex Containing Two 3-Ethynyltheophone Groups. and 4) Rigid-Rod Polymers Based on Noncoplanar 4,4'-Biphenyldiamines: A Review of Polymer Properties vs Configuration of Diamines.

Youngs, Wiley J.

1997-01-01

106

Polymerization of anionic wormlike micelles.  

PubMed

Polymerizable anionic wormlike micelles are obtained upon mixing the hydrotropic salt p-toluidine hydrochloride (PTHC) with the reactive anionic surfactant sodium 4-(8-methacryloyloxyoctyl)oxybenzene sulfonate (MOBS). Polymerization captures the cross-sectional radius of the micelles (approximately 2 nm), induces micellar growth, and leads to the formation of a stable single-phase dispersion of wormlike micellar polymers. The unpolymerized and polymerized micelles were characterized using static and dynamic laser light scattering, small-angle neutron scattering, 1H NMR, and stopped-flow light scattering. Stopped-flow light scattering was also used to measure the average lifetime of the unpolymerized wormlike micelles. A comparison of the average lifetime of unpolymerized wormlike micelles with the surfactant monomer propagation rate was used to elucidate the mechanism of polymerization. There is a significant correlation between the ratio of the average lifetime to the monomer propagation rate and the average aggregation number of the polymerized wormlike micelles. PMID:16430253

Zhu, Zhiyuan; González, Yamaira I; Xu, Hangxun; Kaler, Eric W; Liu, Shiyong

2006-01-31

107

Polymeric phospholipids as new biomaterials.  

PubMed

Phospholipid polymers form a new class of biomaterials with many potential applications in medicine and research. The development of these compounds is based upon the mimicry of cell surfaces and reflects our current understanding of the properties of membrane lipids. Physicochemical characterization of the monomeric, diacetylenic phospholipids illustrates the similarities to naturally occurring lipids, similarities that are confirmed by the capacity to enrich the membranes of A. laidlawii to the level of 90% diacetylenic lipid. Polymerization of diacetylenic phospholipids is easily attained by irradiation and produces a stable, crystalline array. The ability to link membrane lipids covalently permits the isothermal restriction in their motion, and is useful in basic studies of biomembranes. The thromboresistance of polymeric phosphatidylcholines in vitro may be a consequence of the inability of phosphatidylcholines to participate in coagulation. The restricted lateral diffusion of proteins along a polymeric lattice will also inhibit the formation of coagulation complexes. Existing polymers may be altered by a coating of polymeric lipid obtained by the Langmuir-Blodgett method. Polymerized vesicles display significant reductions in permeability and aggregation. Entrapment of soluble materials and reconstitution of membrane proteins may be exploited in controlled and site-directed drug delivery. Polymerization of cells in situ produces "cellular capsules" with entrapped membrane and cellular components. Polymeric hemosomes are capable of gas transport and may function as red cell surrogates. The hybrid qualities of biomembranes (polar surfaces, nonthrombogenic, low antigenic potential, and low permeability) and synthetic polymers (chemical and physical stability) suggest that polymeric phosphatidylcholines may serve as models for biomaterials design. PMID:3860157

Hayward, J A; Johnston, D S; Chapman, D

1985-01-01

108

Nanoparticulate flurbiprofen reduces amyloid-?42 generation in an in vitro blood–brain barrier model  

PubMed Central

Introduction The amyloid-?42 (A?42) peptide plays a crucial role in the pathogenesis of Alzheimer’s disease (AD), the most common neurodegenerative disorder affecting the elderly. Over the past years, several approaches and compounds developed for the treatment of AD have failed in clinical studies, likely in part due to their low penetration of the blood–brain barrier (BBB). Since nanotechnology-based strategies offer new possibilities for the delivery of drugs to the brain, this technique is studied intensively for the treatment of AD and other neurological disorders. Methods The A?42 lowering drug flurbiprofen was embedded in polylactide (PLA) nanoparticles by emulsification-diffusion technique and their potential as drug carriers in an in vitro BBB model was examined. First, the cytotoxic potential of the PLA-flurbiprofen nanoparticles on endothelial cells and the cellular binding and uptake by endothelial cells was studied. Furthermore, the biological activity of the nanoparticulate flurbiprofen on ?-secretase modulation as well as its in vitro release was examined. Furthermore, the protein corona of the nanoparticles was studied as well as their ability to transport flurbiprofen across an in vitro BBB model. Results PLA-flurbiprofen nanoparticles were endocytosed by endothelial cells and neither affected the vitality nor barrier function of the endothelial cell monolayer. The exposure of the PLA-flurbiprofen nanoparticles to human plasma occurred in a rapid protein corona formation, resulting in their decoration with bioactive proteins, including apolipoprotein E. Furthermore, luminally administered PLA-flurbiprofen nanoparticles in contrast to free flurbiprofen were able to modulate ?-secretase activity by selectively decreasing A?42 levels in the abluminal compartment of the BBB model. Conclusions In this study, we were able to show that flurbiprofen can be transported by PLA nanoparticles across an in vitro BBB model and most importantly, the transported flurbiprofen modulated ?-secretase activity by selectively decreasing A?42 levels. These results demonstrate that the modification of drugs via embedding in nanoparticles is a promising tool to facilitate drug delivery to the brain, which enables future development for the treatment of neurodegenerative disorders like AD. PMID:24280275

2013-01-01

109

Stabilization of Nanoparticulate HgS by Thiols and Humic Substances During HgS Precipitation  

NASA Astrophysics Data System (ADS)

In the aquatic environment mercury has a strong affinity for reduced sulfur-containing ligands such as inorganic sulfides and thiolate functional groups in natural organic matter (NOM). Complexation of aqueous Hg(II) is particularly important because coordination to inorganic sulfide and humic compounds governs Hg(II) speciation (and subsequent bioavailability and mobility) in contaminated water and sediment. The purpose of this study was to explore the potential for NOM-coated HgS nanoparticles in the aquatic environment. HgS precipitation experiments were conducted in the presence of natural organic acids that are prevalent in surface water and sediment porewater. Dynamic light scattering was used to the monitor the size of HgS particles precipitating over time. The results indicated that humic substances decreased growth rates of precipitating HgS particles and stabilized particles with aggregate diameters smaller than 0.2 ?m for at least 8 hours. Thiol-containing low molecular weight acids such as cysteine and thioglycolate also decreased growth of HgS particles whereas the hydroxyl-containing acids (serine and glycolate) did not affect particle growth rates. As the humic and thiol concentration increased in solution, growth rates of HgS particles decreased. Growth rates of the aggregates increased in solutions with greater ionic strength. Nanoparticles of HgS would be possible in aquatic environments where HgS precipitation is possible. We conducted equilibrium speciation calculations to determine HgS(s) saturation indices under conditions typical for sediment porewater. The calculations indicated that the metacinnabar saturation index was 1 to 3 orders of magnitude above or below saturation, depending on Hg-(bi)sulfide and Hg-NOM binding constants, which vary by orders of magnitude. These insights suggest that HgS nanoparticles may exist in surface waters and porewater of contaminated sediments as a result of kinetically-hindered mineralization reactions. Hg(II) uptake rates by methylating organisms may be governed by rate-limited mineralization reactions, rather than equilibrium Hg(II) speciation in porewater. However, further studies are needed to directly quantify the bioavailability of nanoparticulate Hg to microbes.

Hsu-Kim, H.; Deonarine, A.

2008-12-01

110

Kinetics of silica polymerization  

SciTech Connect

The polymerization of silicic acid in geothermal brine-like aqueous solutions to produce amorphous silica in colloidal form has been studied experimentally and theoretically. A large amount of high quality experimental data has been generated over the temperature rang 23 to 100{sup 0}C. Wide ranges of dissolved silica concentration, pH, and sodium chloride concentration were covered. The catalytic effects of fluoride and the reaction inhibiting effects of aluminum and boron were studied also. Two basic processes have been separately studied: the formation of new colloidal particles by the homogeneous nucleation process and the deposition of dissolved silica on pre-existing colloidal particles. A rigorous theory of the formation of colloidal particles of amorphous silica by homogeneous nucleation was developed. This theory employs the Lothe-Pound formalism, and is embodied in the computer code SILNUC which quantitatively models the homogeneous nucleation and growth of colloidal silica particles in more than enough detail for practical application. The theory and code were extensively used in planning the experimental work and analyzing the data produced. The code is now complete and running in its final form. It is capable of reproducing most of the experimental results to within experimental error. It is also capable of extrapolation to experimentally inaccessible conditions, i.e., high temperatures, rapidly varying temperature and pH, etc.

Weres, O.; Yee, A.; Tsao, L.

1980-05-01

111

Polymeric materials for neovascularization  

NASA Astrophysics Data System (ADS)

Revascularization therapies have emerged as a promising strategy to treat various acute and chronic wounds, cardiovascular diseases, and tissue defects. It is common to either administer proangiogenic growth factors, such as vascular endothelial growth factor (VEGF), or transplant cells that endogenously express multiple proangiogenic factors. Additionally, these strategies utilize a wide variety of polymeric systems, including hydrogels and biodegradable plastics, to deliver proangiogenic factors in a sophisticated manner to maintain a sustained proangiogenic environment. Despite some impressive results in rebuilding vascular networks, it is still a challenging task to engineer mature and functional neovessels in target tissues, because of the increasing complexities involved with neovascularization applications. To resolve these challenges, this work aims to design a wide variety of proangiogenic biomaterial systems with tunable properties used for neovascularization therapies. This thesis describes the design of several biomaterial systems used for the delivery of proangiogenic factors in neovascularization therapies, including: an electrospun/electrosprayed biodegradable plastic patch used for directional blood vessel growth (Chapter 2), an alginate-g-pyrrole hydrogel system that biochemically stimulates cellular endogenous proangiogenic factor expression (Chapter 3), an enzyme-catalyzed alginate-g-pyrrole hydrogel system for VEGF delivery (Chapter 4), an enzyme-activated alginate-g-pyrrole hydrogel system with systematically controllable electrical and mechanical properties (Chapter 5), and an alginate-g-pyrrole hydrogel that enables the decoupled control of electrical conductivity and mechanical rigidity and is use to electrically stimulate cellular endogenous proangiogenic factor expression (Chapter 6). Overall, the biomaterial systems developed in this thesis will be broadly useful for improving the quality of a wide array of molecular and cellular based revascularization therapies.

DeVolder, Ross John

112

Impact of dissolved silica on arsenite removal by nano-particulate FeS and FeS-coated sand.  

PubMed

This work evaluated the inhibitory effect of dissolved silica on arsenite adsorption to nanoparticulate FeS (NP-FeS) or mackinawite and FeS-coated sand (CS-FeS) sorbents. Arsenite retention by the NP-FeS solid was not affected by dissolved silicate over a wide range in pH, in contrast to the known inhibitory effect of dissolved silica on As(III) uptake by Fe-(hydr)oxide systems. However, some inhibition was observed in CS-FeS system at pH 9. This latter result is attributed to the co-existence of both FeS and small amounts of Fe-(hydr)oxide phases on the sand surface. Given the ubiquitous presence of dissolved Si in groundwater, FeS-based sorbents may have an advantage for As retention compared to those based on Fe-(hydr)oxides in reducing subsurface environments. PMID:23538091

Han, Young-Soo; Demond, Avery H; Hayes, Kim F

2013-07-01

113

Coal and tire burning mixtures containing ultrafine and nanoparticulate materials induce oxidative stress and inflammatory activation in macrophages.  

PubMed

Ultra-fine and nano-particulate materials resulting from mixtures of coal and non-coal fuels combustion for power generation release to the air components with toxic potential. We evaluated toxicological and inflammatory effects at cellular level that could be induced by ultrafine/nanoparticles-containing ashes from burning mixtures of coal and tires from an American power plant. Coal fly ashes (CFA) samples from the combustion of high-S coal and tire-derived fuel, the latter about 2-3% of the total fuel feed, in a 100-MW cyclone utility boiler, were suspended in the cell culture medium of RAW 264.7 macrophages. Cell viability, assessed by MTT reduction, SRB incorporation and contrast-phase microscopy analysis demonstrated that CFA did not induce acute toxicity. However, CFA at 1mg/mL induced an increase of approximately 338% in intracellular TNF-?, while release of this proinflammatory cytokine was increased by 1.6-fold. The expression of the inflammatory mediator CD40 receptor was enhanced by 2-fold, the receptor for advanced glycation endproducts (RAGE) had a 5.7-fold increase and the stress response protein HSP70 was increased nearly 12-fold by CFA at 1mg/mL. Although CFA did not induce cell death, parameters of oxidative stress and reactive species production were found to be altered at several degrees, such as nitrite accumulation (22% increase), DCFH oxidation (3.5-fold increase), catalase (5-fold increase) and superoxide dismutase (35% inhibition) activities, lipoperoxidation (4.2 fold-increase) and sulfhydryl oxidation (40% decrease in free SH groups). The present results suggest that CFA containing ultra-fine and nano-particulate materials from coal and tire combustion may induce sub-chronic cell damage, as they alter inflammatory and oxidative stress parameters at the molecular and cellular levels, but do not induce acute cell death. PMID:23856402

Gasparotto, Juciano; Somensi, Nauana; Caregnato, Fernanda F; Rabelo, Thallita K; DaBoit, Kátia; Oliveira, Marcos L S; Moreira, José C F; Gelain, Daniel P

2013-10-01

114

Absence of systemic toxicity in mouse model towards BaTiO3 nanoparticulate based eluate treatment.  

PubMed

One of the existing issues in implant failure of orthopedic biomaterials is the toxicity induced by the fine particles released during long term use in vivo, leading to acute inflammatory response. In developing a new class of piezobiocomposite to mimic the integrated electrical and mechanical properties of bone, bone-mimicking physical properties as well as in vitro cytocompatibility properties have been achieved with spark plasma sintered hydroxyapatite (HA)-barium titanate (BaTiO3) composites. However, the presence of BaTiO3 remains a concern towards the potential toxicity effect. To address this issue, present work reports the first result to conclusively confirm the non-toxic effect of HA-BaTiO3 piezobiocomposite nanoparticulates, in vivo. Twenty BALB/c mice were intra-articularly injected at their right knee joints with different concentrations of HA-BaTiO3 composite of up to 25 mg/ml. The histopathological examination confirmed the absence of any trace of injected particles or any sign of inflammatory reaction in the vital organs, such as heart, spleen, kidney and liver at 7 days post-exposure period. Rather, the injected nanoparticulates were found to be agglomerated in the vicinity of the knee joint, surrounded by macrophages. Importantly, the absence of any systemic toxicity response in any of the vital organs in the treated mouse model, other than a mild local response at the site of delivery, was recorded. The serum biochemical analyses using proinflammatory cytokines (TNF-? and IL-1?) also complimented to the non-immunogenic response to injected particulates. Altogether, the absence of any inflammatory/adverse reaction will open up myriad of opportunities for BaTiO3 based piezoelectric implantable devices in biomedical applications. PMID:25655497

Dubey, Ashutosh Kumar; Thrivikraman, Greeshma; Basu, Bikramjit

2015-02-01

115

Stereospecific olefin polymerization catalysts  

DOEpatents

A metallocene catalyst system for the polymerization of .alpha.-olefins to yield stereospecific polymers including syndiotactic, and isotactic polymers. The catalyst system includes a metal and a ligand of the formula ##STR1## wherein: R.sup.1, R.sup.2, and R.sup.3 are independently selected from the group consisting of hydrogen, C.sub.1 to C.sub.10 alkyl, 5 to 7 membered cycloalkyl, which in turn may have from 1 to 3 C.sub.1 to C.sub.10 alkyls as a substituent, C.sub.6 to C.sub.15 aryl or arylalkyl in which two adjacent radicals may together stand for cyclic groups having 4 to 15 carbon atoms which in turn may be substituted, or Si(R.sup.8).sub.3 where R.sup.8 is selected from the group consisting of C.sub.1 to C.sub.10 alkyl, C.sub.6 to C.sub.15 aryl or C.sub.3 to C.sub.10 cycloalkyl; R.sup.4 and R.sup.6 are substituents both having van der Waals radii larger than the van der Waals radii of groups R.sup.1 and R.sup.3 ; R.sup.5 is a substituent having a van der Waals radius less than about the van der Waals radius of a methyl group; E.sup.1, E.sup.2 are independently selected from the group consisting of Si(R.sup.9).sub.2, Si(R.sup.9).sub.2 --Si(R.sup.9).sub.2, Ge(R.sup.9).sub.2, Sn(R.sup.9).sub.2, C(R.sup.9).sub.2, C(R.sup.9).sub.2 --C(R.sup.9).sub.2, where R.sup.9 is C.sub.1 to C.sub.10 alkyl, C.sub.6 to C.sub.15 aryl or C.sub.3 to C.sub.10 cycloalkyl; and the ligand may have C.sub.S or C.sub.1 -symmetry. Preferred metals are selected from the group consisting of group III, group IV, group V or lanthanide group elements. The catalysts are used to prepare stereoregular polymers including polypropylene from .alpha.-olefin monomers.

Bercaw, John E. (Pasadena, CA); Herzog, Timothy A. (Pasadena, CA)

1998-01-01

116

Stereospecific olefin polymerization catalysts  

DOEpatents

A metallocene catalyst system is described for the polymerization of {alpha}-olefins to yield stereospecific polymers including syndiotactic, and isotactic polymers. The catalyst system includes a metal and a ligand of the formula shown wherein: R{sup 1}, R{sup 2}, and R{sup 3} are independently selected from the group consisting of hydrogen, C{sub 1} to C{sub 10} alkyl, 5 to 7 membered cycloalkyl, which in turn may have from 1 to 3 C{sub 1} to C{sub 10} alkyls as a substituent, C{sub 6} to C{sub 15} aryl or arylalkyl in which two adjacent radicals may together stand for cyclic groups having 4 to 15 carbon atoms which in turn may be substituted, or Si(R{sup 8}){sub 3} where R{sup 8} is selected from the group consisting of C{sub 1} to C{sub 10} alkyl, C{sub 6} to C{sub 15} aryl or C{sub 3} to C{sub 10} cycloalkyl; R{sup 4} and R{sup 6} are substituents both having van der Waals radii larger than the van der Waals radii of groups R{sup 1} and R{sup 3}; R{sup 5} is a substituent having a van der Waals radius less than about the van der Waals radius of a methyl group; E{sup 1}, E{sup 2} are independently selected from the group consisting of Si(R{sup 9}){sub 2}, Si(R{sup 9}){sub 2}--Si(R{sup 9}){sub 2}, Ge(R{sup 9}){sub 2}, Sn(R{sup 9}){sub 2}, C(R{sup 9}){sub 2}, C(R{sup 9}){sub 2}--C(R{sup 9}){sub 2}, where R{sup 9} is C{sub 1} to C{sub 10} alkyl, C{sub 6} to C{sub 15} aryl or C{sub 3} to C{sub 10} cycloalkyl; and the ligand may have C{sub S} or C{sub 1}-symmetry. Preferred metals are selected from the group consisting of group III, group IV, group V or lanthanide group elements. The catalysts are used to prepare stereoregular polymers including polypropylene from {alpha}-olefin monomers.

Bercaw, J.E.; Herzog, T.A.

1998-01-13

117

Dynamics of nanoparticules detected at 1 AU by S/WAVES onboard STEREO spacecraft  

NASA Astrophysics Data System (ADS)

In order to interpret in detail the S/WAVES data on the interplanetary nanodust discovered by STEREO at 1 AU [Meyer-Vernet et al., 2009], we study the dynamics of nanoparticles in the inner interplanetary medium as well as the distribution of their velocities and directions of arrival, with a model based on [Czechowski and Mann, 2012]. We deduce the charges released by their impacts on the STEREO spacecraft at 1 AU and their dependence on the position of the spacecraft on their orbits. The model studies nanoparticles of size equal or smaller than about 70 nm, assumed to be created via collisional fragmentation of dust grains of larger size moving on keplerian orbits, and sublimation of dust, meteoroids and comets. The nanoparticles are released near the Sun with initial velocities close to keplerian, and mainly subjected to the Lorentz force calculated with a simple solar wind model. A part of the nanoparticles is accelerated to high speeds of the order of 300 km/s, thereby providing impact charges between 10(-14) and 10(-11) Cb [Belheouane, 2014] which enable them to be detected by S/WAVES, whereas another part is trapped within about 0.2 AU from the Sun. We discuss how the fluxes and direction of arrival at 1 AU are expected to change in function of the solar cycle. These results enable us to interpret in detail the STEREO/WAVES observations [Zaslavsky et al., 2012]; [Pantellini et al., 2013]; [Le Chat et al., 2013]. Belheouane, S. (2014). Nanoparticules dans le vent solaire, observations spatiales et theorie. PhD thesis, Pierre and Marie Curie University UPMC. Czechowski, A. and Mann, I. (2012). Nanodust Dynamics in Interplanetary Space, chapter Nanodust Dynamics in Interplanetary Space. Springer Berlin Heidelberg. Le Chat, G., Zaslavsky, A., Meyer-Vernet, N., Issautier, K., Belheouane, S., Pantellini, F., Maksimovic, M., Zouganelis, I., Bale, S., and Kasper, J. (2013). Interplanetary Nanodust Detection by the Solar Terrestrial Relations Observatory/WAVES Low Frequency Receiver. Solar Physics, 286(2):549-559. Meyer-Vernet, N., Maksimovic, M., Czechowski, A., Mann, I., Zouganelis, I., Goetz, K., Kaiser, M., Cyr, O. S., Bougeret, J.-L., and Bale, S. (2009). Dust Detection by the Wave Instrument on STEREO : Nanoparticles Picked up by the Solar Wind? Solar Phys, 256:463-474. Pantellini, F., Le Chat, G., Belheouane, S., Meyer-Vernet, N., and Zaslavsky, A. (2013). On the detection of nano dust using spacecraft based boom antennas. Solar Wind 13: Proceedings of the Thirteenth International Solar Wind Conference, 1539:414-417. Zaslavsky, A., Meyer-Vernet, N., Mann, I., Czechowski, A., Issautier, K., Le Chat, G., Pantellini, F., Goetz, K., Maksimovic, M., Bale, S. D., and Kasper, J. K. (2012). Interplanetary dust detection by radio antennas: Mass calibration and fluxes measured by STEREO/WAVES. J. Geophys. Res., 117.

Belheouane, Soraya; Issautier, Karine; Meyer-Vernet, Nicole; Le Chat, Gaétan; Czechowski, Andrzej; Zaslavsky, Arnaud; Zouganelis, Yannis; Mann, Ingrid

118

Degradation of nanoparticulate-coated and uncoated sulfide-based cathodoluminescent phosphors.  

SciTech Connect

Changes in the cathodoluminescent (CL) brightness and in the surface chemistry of nanoparticulate SiO{sub 2}-coated and uncoated ZnS:Ag, Cl powder phosphor have been investigated using a PHI 545 scanning Auger electron spectrometer (AES), an Oriel optical spectrometer and a JEOL 6400 scanning electron microscope (SEM). The data were collected in a stainless steel UHV chamber with residual gas pressures between 1 x 10{sup -8} and 1 x 10{sup -6} Torr as measured by a Dycor LC residual gas analyzer (RGA). The primary electron current density was 272 {micro}A/cm{sup 2}, while the primary beam energy was varied bwteen 2 and 5 keV. In the presence of a 2keV primary electron beam in 1 x 10{sup -6} Torr of water for both the SiO{sub 2}-coated and the uncoated cases, the amounts of C and S on the surface decreased, that of O increased and the CL intensity decreased with electron dose. This surface chemistry change lead to the development of a surface dead layer and is explained by the electron beam stimulated surface chemical reaction model (ESSCR). The penetration range of the impinging low energy primary electrons is on the order of 10-100 nm creating a reaction region very close to the surface. The ESSCR takes this into account postulating that primary and secondary electrons dissociate physisorbed molecules to form reactive atomic species. These atomic species remove surface S as volatile SO{sub x} or H{sub 2}S. In the case of an oxidizing ambient (i.e. high partial pressure of water), a non-luminescent ZnO layer is formed. this oxide layer has been measured to be on the order of 3-30 nm. In the case where the vacuum of 1 x 10{sup -8} Torr was dominated by hydrogen and had a low water content, there was a small increase in the S signal, no rise in the O Auger signal, but the CL intensity still decreased. This is explained by the ESSCR whereby H removes S as H{sub 2}S leaving elemental Zn, which evaporates due to a high vapor pressure. In the case of ZnS:Ag,Cl coated with SiO{sub 2}, morphological changes were observed on the surface after extended electron beam exposure. Erosion of ZnS occurs more dramatically at an accelerating voltage of 5kV even at the same current density. Uncoated ZnS:Ag,Cl phosphors exhibited similar surface chemical changes to that of SiO{sub 2}-coated ZnS:Ag,Cl but did not degrade to the same extent. Also, no change in the surface morphology was observed. These SEM images as well as reaction rate data suggest that these nanometer sized SiO{sub 2} particles acted as a catalyst for decomposition of the ZnS especially in a reducing ambient (i.e. high hydrogen partial pressure). In order to reduce CL degradation of these and other phosphors, protective coatings were pulse laser deposited onto the phosphor surface. The effectiveness of these coatings was dependent upon both the thickness and the uniformity. Thicknesses of these coatings ranged from 1-5 nm and were uniform as determined using profilometry and TEM.

Abrams, Billie Lynn; Bang, Jungsik S. (University of Florida, Gainesville, FL); Thomes, William Joseph, Jr.; Holloway, Paul H. (University of Florida, Gainesville, FL)

2003-07-01

119

On-demand photoinitiated polymerization  

DOEpatents

Compositions and methods for adjustable lenses are provided. In some embodiments, the lenses contain a lens matrix material, a masking compound, and a prepolymer. The lens matrix material provides structure to the lens. The masking compound is capable of blocking polymerization or crosslinking of the prepolymer, until photoisomerization of the compound is triggered, and the compound is converted from a first isomer to a second isomer having a different absorption profile. The prepolymer is a composition that can undergo a polymerization or crosslinking reaction upon photoinitiation to alter one or more of the properties of the lenses.

Boydston, Andrew J; Grubbs, Robert H; Daeffler, Chris; Momcilovic, Nebojsa

2013-12-10

120

Tunnel magnetoresistance of polymeric chains  

E-print Network

Coherent spin-dependent electronic transport is investigated in a molecular junction made of polymeric chain attached to ferromagnetic electrodes (Ni and Co, respectively). Molecular system is described by a simple Huckel model, while the coupling to the electrodes is treated through the use of a broad-band theory. The current flowing through the device is calculated within non-equilibrium Green's function approach. It is shown that tunnel magnetoresistance of molecular junction can be quite large (over 100 %)and strongly depends on: (i) the lenght of the polymeric chain and (ii) the strength of the molecule-to-electrodes coupling.

Kamil Walczak

2004-10-25

121

Ligand-directed active tumor-targeting polymeric nanoparticles for cancer chemotherapy.  

PubMed

In recent years, polymeric nanoparticles have appeared as a most viable and versatile delivery system for targeted cancer therapy. Various in vivo studies have demonstrated that virus-sized stealth particles are able to circulate for a prolonged time and preferentially accumulate in the tumor site via the enhanced permeability and retention (EPR) effect (so-called "passive tumor-targeting"). The surface decoration of stealth nanoparticles by a specific tumor-homing ligand, such as antibody, antibody fragment, peptide, aptamer, polysaccharide, saccharide, folic acid, and so on, might further lead to increased retention and accumulation of nanoparticles in the tumor vasculature as well as selective and efficient internalization by target tumor cells (termed as "active tumor-targeting"). Notably, these active targeting nanoparticulate drug formulations have shown improved, though to varying degrees, therapeutic performances in different tumor models as compared to their passive targeting counterparts. In addition to type of ligands, several other factors such as in vivo stability of nanoparticles, particle shape and size, and ligand density also play an important role in targeted cancer chemotherapy. In this review, concept and recent development of polymeric nanoparticles conjugated with specific targeting ligands, ranging from proteins (e.g., antibodies, antibody fragments, growth factors, and transferrin), peptides (e.g., cyclic RGD, octreotide, AP peptide, and tLyp-1 peptide), aptamers (e.g., A10 and AS1411), polysaccharides (e.g., hyaluronic acid), to small biomolecules (e.g., folic acid, galactose, bisphosphonates, and biotin), for active tumor-targeting drug delivery in vitro and in vivo are highlighted and discussed. With promise to maximize therapeutic efficacy while minimizing systemic side effects, ligand-mediated active tumor-targeting treatment modality has become an emerging and indispensable platform for safe and efficient cancer therapy. PMID:24798476

Zhong, Yinan; Meng, Fenghua; Deng, Chao; Zhong, Zhiyuan

2014-06-01

122

Segmentation strategies for polymerized volume data sets  

E-print Network

A new technique, called the polymerization algorithm, is described for the hierarchical segmentation of polymerized volume data sets (PVDS) using the Lblock data structure. The Lblock data structure is defined as a 3dimensional isorectangular block...

Doddapaneni, Venkata Purna

2006-04-12

123

Nonlinear optical and conductive polymeric material  

DOEpatents

A polymeric material is described which exhibits nonlinear optical properties if undoped and conductive properties if doped. The polymer is prepared by polymerizing diethynylsilane compositions, the resulting polymeric material having a weight average molecular weight between about 20,000 and about 200,000 grams per mole. The polymer is prepared and catalytically polymerized by exposure to a catalyst, such as MoCl[sub 5] or W(CO)[sub 6].

Barton, T.J.; Ijadi-Maghsooodi, S; Yi Pang.

1993-10-19

124

Nonlinear optical and conductive polymeric material  

DOEpatents

A polymeric material which exhibits nonlinear optical properties if undoped and conductive properties if doped. The polymer is prepared by polymerizing diethynylsilane compositions, the resulting polymeric material having a weight average molecular weight between about 20,000 and about 200,000 grams per mole. The polymer is prepared and catalytically polymerized by exposure to a catalyst, such as MoCl.sub.5 or W(CO).sub.6 /hv.

Barton, Thomas J. (Ames, IA); Ijadi-Maghsoodi, Sina (Ames, IA); Pang, Yi (Ames, IA)

1992-05-19

125

Nonlinear optical and conductive polymeric material  

DOEpatents

A polymeric material which exhibits nonlinear optical properties if undoped and conductive properties if doped. The polymer is prepared by polymerizing diethynylsilane compositions, the resulting polymeric material having a weight average molecular weight between about 20,000 and about 200,000 grams per mole. The polymer is prepared and catalytically polymerized by exposure to a catalyst, such as MoCl[sub 5] or W(CO)[sub 6]/hv.

Barton, T.J.; Ijadi-Maghsoodi, S.; Pang, Y.

1992-05-19

126

Nonlinear optical and conductive polymeric material  

DOEpatents

A polymeric material which exhibits nonlinear optical properties if undoped and conductive properties if doped. The polymer is prepared by polymerizing diethynylsilane compositions, the resulting polymeric material having a weight average molecular weight between about 20,000 and about 200,000 grams per mole. The polymer is prepared and catalytically polymerized by exposure to a catalyst, such as MoCl.sub.5 or W(CO).sub.6 /hv.

Barton, Thomas J. (Ames, IA); Ijadi-Maghsoodi, Sina (Ames, IA); Pang, Yi (Ames, IA)

1993-10-19

127

Polymerization of safflower and rapeseed oils  

Microsoft Academic Search

Rates of polymerization of oils from 2 safflower and 2 rapeseed varieties were measured in the air and under vacuum. Thermal\\u000a polymerization rates showed a stronger dependence on the degree of unsaturation than on oxidative polymerization. Molecular\\u000a weight distributions of polymerized oils were determined by size exclusion chromatography, and the relationship between viscosity\\u000a and weight-average molecular weight was determined.

Roger A. Korus; Traci L. Mousetis

1984-01-01

128

Attempting a classification for electrical polymeric actuators  

Microsoft Academic Search

Polymeric actuators, electroactive polymer actuators, electromechanical polymeric actuators, artificial muscles, and other, are usual expressions to name actuators developed during the last 15-20 years based on interactions between the electric energy and polymer films. The polymeric actuators can be divided into two main fields: electromechanical actuators working by electrostatic interactions between the polymer and the applied electric fields, and electrochemomechanical

T. F. Otero; J. López Cascales; A. J. Fernández-Romero

2007-01-01

129

X-ray absorption and photoelectron spectroscopic study of the association of As(III) with nanoparticulate FeS and FeS-coated sand.  

PubMed

Iron sulfide (FeS) has been demonstrated to have a high removal capacity for arsenic (As) in reducing environments. However, FeS may be present as a coating, rather than in nanoparticulate form, in both natural and engineered systems. Frequently, the removal capacity of coatings may be different than that of nanoparticulates in batch systems. To assess the differences in removal mechanisms between nanoparticulate FeS and FeS present as a coating, the solid phase products from the reaction of As(III) with FeS-coated sand and with suspensions of nanoparticulate (NP) FeS were determined using x-ray absorption spectroscopy and x-ray photoelectron spectroscopy. In reaction with NP FeS at pH 5, As(III) was reduced to As(II) to form realgar (AsS), while at pH 9, As(III) adsorbed as an As(III) thioarsenite species. In contrast, in the FeS-coated sand system, As(III) formed the solid phase orpiment (As(2)S(3)) at pH 5, but adsorbed as an As(III) arsenite species at pH 9. These different solid reaction products are attributed to differences in FeS concentration and the resultant redox (pe) differences in the FeS-coated sand system versus suspensions of NP FeS. These results point to the importance of accounting for differences in concentration and redox when making inferences for coatings based on batch suspension studies. PMID:21911241

Han, Young-Soo; Jeong, Hoon Y; Demond, Avery H; Hayes, Kim F

2011-11-01

130

Outdoor HV composite polymeric insulators  

Microsoft Academic Search

HV composite polymeric insulators are being accepted increasingly for use in outdoor installations by the traditionally cautious electric power utilities worldwide. They currently represent ~60 to 70% of newly installed HV insulators in North America. The tremendous growth in the applications of non-ceramic composite insulators is due to their advantages over the traditional ceramic and glass insulators. These include light

R. Hackam

1999-01-01

131

The Viscosity of Polymeric Fluids.  

ERIC Educational Resources Information Center

To illustrate the behavior of polymeric fluids and in what respects they differ from Newtonian liquids, an experiment was developed to account for the shear-rate dependence of non-Newtonian fluids. Background information, procedures, and results are provided for the experiment. Useful in transport processes, fluid mechanics, or physical chemistry…

Perrin, J. E.; Martin, G. C.

1983-01-01

132

POLYMERIC INTERFACES FOR STACK MONITORING  

EPA Science Inventory

Research has been performed on the use of polymeric interfaces for in situ continuous stack monitoring of gaseous pollutants. Permeabilities of candidate interface materials to SO2 were measured at temperatures from ambient to 200C, and the results were used to design interfaces ...

133

Radiation-hardened polymeric films  

SciTech Connect

This patent describes polymeric dielectric compositions with reduced radiation induced conductivity, containing from about 10/sup 15/ to 10/sup 21/ molecules/cm/sup 3/ of a compatible organic Lewis acid or Lewis base as dopant. The dielectric is a low electronic mobility polymer selected from the group consisting of polyesters, polyolefins, perfluorinated polyolefins, vinyl polymers, vinylidene polymers, polycarbonates, polysulfones, and polyimides.

Arnold, C. Jr.; Hughes, R.C.; Kepler, G.; Kurtz, S.R.

1986-11-11

134

Low vibration polymeric composite engine  

NASA Astrophysics Data System (ADS)

An internal combustion engine is constructed with metallic parts in its regions which are subjected to high stress (temperature, pressure) during combustion and polymeric materials in its regions which are subjected to relatively lower stresses. The integrated construction helps realize increased power densities and reductions on engine noise without compromising engine performance. V-configuration Diesel engines particularly benefit from this construction.

Guimond, David P.; Muench, Rolf K.

1994-12-01

135

Sleeving nanocelluloses by admicellar polymerization.  

PubMed

This investigation reports the first application of admicellar polymerization to cellulose nanofibers in the form of bacterial cellulose, microfibrillated cellulose, and cellulose nanowhiskers using styrene and ethyl acrylate. The success of this physical sleeving was assessed by SEM, FTIR, and contact angle measurements, providing an original and simple approach to the modification of cellulose nanofibers in their pristine aqueous environment. PMID:23921337

Trovatti, Eliane; Ferreira, Adriane de Medeiros; Carvalho, Antonio José Felix; Ribeiro, Sidney José Lima; Gandini, Alessandro

2013-10-15

136

Novel polymeric elastomers for actuation  

Microsoft Academic Search

Efficient actuators that are lightweight, high performance and compact are needed to support telerobotic requirements for future NASA missions. A new class of electrostrictive polymeric materials has been developed in our recent work. The materials are graft elastomers that exhibit not only large electric field-induced strain (4%) but also a relatively high mechanical modulus (560 MPa). Consequently, the materials offer

J. Su; J. S. Harrison; T. St Clair

2000-01-01

137

Metal containing polymeric functional microspheres  

NASA Technical Reports Server (NTRS)

Polymeric functional microspheres containing metal or metal compounds are formed by addition polymerization of a covalently bondable olefinic monomer such as hydroxyethylmethacrylate in the presence of finely divided metal or metal oxide particles, such as iron, gold, platinum or magnetite, which are embedded in the resulting microspheres. The microspheres can be covalently bonded to chemotherapeutic agents, antibodies, or other proteins providing a means for labeling or separating labeled cells. Labeled cells or microspheres can be concentrated at a specific body location such as in the vicinity of a malignant tumor by applying a magnetic field to the location and then introducing the magnetically attractable microspheres or cells into the circulatory system of the subject. Labeled cells can be separated from a cell mixture by applying a predetermined magnetic field to a tube in which the mixture is flowing. After collection of the labeled cells, the magnetic field is discontinued and the labeled sub-cell population recovered.

Yen, Shiao-Ping S. (Inventor); Rembaum, Alan (Inventor); Molday, Robert S. (Inventor)

1979-01-01

138

Polymeric Anti-HIV Therapeutics.  

PubMed

The scope of this review is to highlight the application of polymer therapeutics in an effort to curb the transmission and infection of the human immunodeficiency virus (HIV). Following a description of the HIV life cycle, the use of approved antiretroviral drugs that inhibit critical steps in the HIV infection process is highlighted. After that, a comprehensive overview of the structure and inhibitory properties of polymeric anti-HIV therapeutic agents is presented. This overview will include inhibitors based on polysaccharides, synthetic polymers, dendritic polymers, polymer conjugates as well as polymeric DC-SIGN antagonists. The review will conclude with a section that discusses the applications of polymers and polymer conjugates as systemic and topical anti-HIV therapeutics. PMID:25185484

Danial, Maarten; Klok, Harm-Anton

2014-09-01

139

Polymeric cationic substituted acrylamide surfactants  

SciTech Connect

A new composition of matter comprises a copolymer of a surface active quaternary ammonium monomer salt and from 50 to 97% by wt of acrylamide. The new copolymers can have molecular weights substantially greater than 10,000 and still remain water soluble and surface active. Copolymers are prepared by polymerization techniques known in the art. The quaternary ammonium monomer is dispersed under inert atmosphere in aqueous solution which may additionally contain dissolved therein a low molecular weight alcohol such as ethanol, isopropanol, and the like. Acidic polymerization initiator such as the azo initiators, organic peroxides, or redox initiators such as the sulfite- persulfate system is then added in an amount calculated to yield a polymer product of desired molecular weight. (14 claims.

Nieh, E.C.Y.

1983-11-15

140

Malaria Vector Species  

NSDL National Science Digital Library

A sub-page of the extremely informative VectorBase. This is a worldwide listing of malaria vectors divided into 12 geographic regions following the 1957 classic The Epidemiology and Control of Malaria by MacDonald.

0002-11-30

141

Anti-biofouling polymer-decorated lutetium-based nanoparticulate contrast agents for in vivo high-resolution trimodal imaging.  

PubMed

Nanomaterials have gained considerable attention and interest in the development of novel and high-resolution contrast agents for medical diagnosis and prognosis in clinic. A classical urea-based homogeneous precipitation route that combines the merits of in situ thermal decomposition and surface modification is introduced to construct polyethylene glycol molecule (PEG)-decorated hybrid lutetium oxide nanoparticles (PEG-UCNPs). By utilizing the admirable optical and magnetic properties of the yielded PEG-UCNPs, in vivo up-conversion luminescence and T1 -enhanced magnetic resonance imaging of small animals are conducted, revealing obvious signals after subcutaneous and intravenous injection, respectively. Due to the strong X-ray absorption and high atomic number of lanthanide elements, X-ray computed-tomography imaging based on PEG-UCNPs is then designed and carried out, achieving excellent imaging outcome in animal experiments. This is the first example of the usage of hybrid lutetium oxide nanoparticles as effective nanoprobes. Furthermore, biodistribution, clearance route, as well as long-term toxicity are investigated in detail after intravenous injection in a murine model, indicating the overall safety of PEG-UCNPs. Compared with previous lanthanide fluorides, our nanoprobes exhibit more advantages, such as facile construction process and nearly total excretion from the animal body within a month. Taken together, these results promise the use of PEG-UCNPs as a safe and efficient nanoparticulate contrast agent for potential application in multimodal imaging. PMID:24610806

Liu, Zhen; Dong, Kai; Liu, Jianhua; Han, Xueli; Ren, Jinsong; Qu, Xiaogang

2014-06-25

142

Effect of Ni precursor solution concentration on the magnetic properties and exchange bias of Ni-NiO nanoparticulate systems  

NASA Astrophysics Data System (ADS)

We report on a comparative study of the exchange bias effect and magnetic properties of Ni-NiO nanoparticulate systems synthesized by the chemical reduction of NiCl2 solution of two different molar concentrations—1 M (high) and 0.05 M (low)—followed by annealing of the dried precipitate in the temperature range 400-600 °C in air. Interestingly, the samples derived from the low molarity solution have higher Ni content and larger crystallite size than those prepared from their high molarity counterparts. These molarity dependent features subsequently modulate the magnitude of the exchange bias field in the samples, which is found to be absent or small in the 0.05 M series, but of moderate value in the 1 M samples. The different physical attributes of the particles derived from different concentrations of Ni-precursor solution are explained by invoking different nucleation kinetics and supersaturation degrees surrounding the viable growing nucleus. Furthermore, an observed increase of exchange bias with increasing annealing temperature, in contrast to the reported agglomeration of particles on annealing and subsequent reduction in bias magnitude, has been explained in correlation to the Ni-NiO interface density.

Roy, Aparna; De Toro, J. A.; Amaral, V. S.; Marques, D. P.; Ferreira, J. M. F.

2014-09-01

143

Support vector domain description  

Microsoft Academic Search

This paper shows the use of a data domain description method, inspired by the support vector machine by Vapnik, called the support vector domain description (SVDD). This data description can be used for novelty or outlier de- tection. A spherically shaped decision boundary around a set of objects is constructed by a set of support vectors describing the sphere boundary.

David M. J. Tax; Robert P. W. Duin

1999-01-01

144

Vector Microprocessors Krste Asanovic  

E-print Network

Vector Microprocessors by Krste Asanovi´c B.A. (University of Cambridge) 1987 A dissertation 1998 #12;Vector Microprocessors Copyright 1998 by Krste Asanovi´c #12;1 Abstract Vector Microprocessors microprocessor imple- mentations targeting a much broader range of applications. I present the design

Asanoviæ, Krste

145

Nonintegrating Foamy Virus Vectors?  

PubMed Central

Foamy viruses (FVs), or spumaviruses, are integrating retroviruses that have been developed as vectors. Here we generated nonintegrating foamy virus (NIFV) vectors by introducing point mutations into the highly conserved DD35E catalytic core motif of the foamy virus integrase sequence. NIFV vectors produced high-titer stocks, transduced dividing cells, and did not integrate. Cells infected with NIFV vectors contained episomal vector genomes that consisted of linear, 1-long-terminal-repeat (1-LTR), and 2-LTR circular DNAs. These episomes expressed transgenes, were stable, and became progressively diluted in the dividing cell population. 1-LTR circles but not 2-LTR circles were found in all vector stocks prior to infection. Residual integration of NIFV vectors occurred at a frequency 4 logs lower than that of integrase-proficient FV vectors. Cre recombinase expressed from a NIFV vector mediated excision of both an integrated, floxed FV vector and a gene-targeted neo expression cassette, demonstrating the utility of these episomal vectors. The broad host range and large packaging capacity of NIFV vectors should make them useful for a variety of applications requiring transient gene expression. PMID:20592072

Deyle, David R.; Li, Yi; Olson, Erik M.; Russell, David W.

2010-01-01

146

Ring-expansion metathesis polymerization: catalyst-dependent polymerization profiles.  

PubMed

Ring-expansion metathesis polymerization (REMP) mediated by recently developed cyclic Ru catalysts has been studied in detail with a focus on the polymer products obtained under varied reaction conditions and catalyst architectures. Depending upon the nature of the catalyst structure, two distinct molecular weight evolutions were observed. Polymerization conducted with catalysts bearing six-carbon tethers displayed rapid polymer molecular weight growth which reached a maximum value at ca. 70% monomer conversion, resembling a chain-growth polymerization mechanism. In contrast, five-carbon-tethered catalysts led to molecular weight growth that resembled a step-growth mechanism with a steep increase occurring only after 95% monomer conversion. The underlying reason for these mechanistic differences appeared to be ready release of five-carbon-tethered catalysts from growing polymer rings, which competed significantly with propagation. Owing to reversible chain transfer and the lack of end groups in REMP, the final molecular weights of cyclic polymers was controlled by thermodynamic equilibria. Large ring sizes in the range of 60-120 kDa were observed at equilibrium for polycyclooctene and polycyclododecatriene, which were found to be independent of catalyst structure and initial monomer/catalyst ratio. While six-carbon-tethered catalysts were slowly incorporated into the formed cyclic polymer, the incorporation of five-carbon-tethered catalysts was minimal, as revealed by ICP-MS. Further polymer analysis was conducted using melt-state magic-angle spinning (13)C NMR spectroscopy of both linear and cyclic polymers, which revealed little or no chain ends for the latter topology. PMID:19199611

Xia, Yan; Boydston, Andrew J; Yao, Yefeng; Kornfield, Julia A; Gorodetskaya, Irina A; Spiess, Hans W; Grubbs, Robert H

2009-02-25

147

Structural insights into de novo actin polymerization  

PubMed Central

Summary Many cellular functions depend on rapid and localized actin polymerization/depolymerization. Yet, the de novo polymerization of actin in cells is kinetically unfavorable because of the instability of polymerization intermediates (small actin oligomers) and the actions of actin monomer binding proteins. Cells use filament nucleation and elongation factors to initiate and sustain polymerization. Structural biology is beginning to shed light on the diverse mechanisms by which these unrelated proteins initiate polymerization, undergo regulation, and mediate the transition of monomeric actin onto actin filaments. A prominent role is played by the W domain, which in some of these proteins occurs in tandem repeats that recruit multiple actin subunits. Pro-rich regions are also abundant and mediate the binding of profilin-actin complexes, which are the main source of polymerization competent actin in cells. Filament nucleation and elongation factors frequently interact with Rho family GTPases, which relay signals from membrane receptors to regulate actin cytoskeleton remodeling. PMID:20096561

Dominguez, Roberto

2010-01-01

148

UV-Triggered Dopamine Polymerization: Control of Polymerization, Surface Coating, and Photopatterning.  

PubMed

UV irradiation is demonstrated to initiate dopamine polymerization and deposition on different surfaces under both acidic and basic pH. The observed acceleration of the dopamine polymerization is explained by the UV-induced formation of reactive oxygen species that trigger dopamine polymerization. The UV-induced dopamine polymerization leads to a better control over polydopamine deposition and formation of functional polydopamine micropatterns. PMID:25381870

Du, Xin; Li, Linxian; Li, Junsheng; Yang, Chengwu; Frenkel, Nataliya; Welle, Alexander; Heissler, Stefan; Nefedov, Alexei; Grunze, Michael; Levkin, Pavel A

2014-12-01

149

POLYMER PROGRAM SEMINAR "Targeted polymeric nanoparticles  

E-print Network

systems are polymeric nanoparticles and liposomes. Controlled release polymer technology impacts every drugs for combination therapy. The surface engineering of these nanoparticles may yield them "stealth

Alpay, S. Pamir

150

Ionene modified small polymeric beads  

NASA Technical Reports Server (NTRS)

Linear ionene polyquaternary cationic polymeric segments are bonded by means of the Menshutkin reaction (quaternization) to biocompatible, extremely small, porous particles containing halide or tertiary amine sites which are centers for attachment of the segments. The modified beads in the form of emulsions or suspensions offer a large, positively-charged surface area capable of irreversibly binding polyanions such as heparin, DNA, RNA or bile acids to remove them from solution or of reversibly binding monoanions such as penicillin, pesticides, sex attractants and the like for slow release from the suspension.

Rembaum, Alan (Inventor)

1977-01-01

151

Marketing NASA Langley Polymeric Materials  

NASA Technical Reports Server (NTRS)

A marketing tool was created to expand the knowledge of LaRC developed polymeric materials, in order to facilitate the technology transfer process and increase technology commercialization awareness among a non-technical audience. The created brochure features four materials, LaRC-CP, LaRC-RP46, LaRC-SI, and LaRC-IA, and highlights their competitive strengths in potential commercial applications. Excellent opportunities exist in the $40 million per year microelectronics market and the $6 billion adhesives market. It is hoped that the created brochure will generate inquiries regarding the use of the above materials in markets such as these.

Flynn, Diane M.

1995-01-01

152

Electrically controlled polymeric gel actuators  

DOEpatents

Electrically controlled polymeric gel actuators or synthetic muscles are described capable of undergoing substantial expansion and contraction when subjected to changing pH environments, temperature, or solvent. The actuators employ compliant containers for the gels and their solvents. The gels employed may be cylindrical electromechanical gel fibers such as polyacrylamide fibers or a mixture of poly vinyl alcohol-polyacrylic acid arranged in a parallel aggregate and contained in an electrolytic solvent bath such as salt water. The invention includes smart, electrically activated devices exploiting this phenomenon. These devices are capable of being manipulated via active computer control as large displacement actuators for use in adaptive structure such as robots. 11 figures.

Adolf, D.B.; Shahinpoor, M.; Segalman, D.J.; Witkowski, W.R.

1993-10-05

153

Combustion-Generated Nanoparticulates in the El Paso, TX, USA / Juarez, Mexico Metroplex: Their Comparative Characterization and Potential for Adverse Health Effects  

PubMed Central

In this paper we report on the collection of fine (PM1) and ultrafine (PM0.1), or nanoparticulate, carbonaceous materials using thermophoretic precipitation onto silicon monoxide/formvar-coated 3 mm grids which were examined in the transmission electron microscope (TEM). We characterize and compare diesel particulate matter (DPM), tire particulate matter (TPM), wood burning particulate matter, and other soot (or black carbons (BC)) along with carbon nanotube and related fullerene nanoparticle aggregates in the outdoor air, as well as carbon nanotube aggregates in the indoor air; and with reference to specific gas combustion sources. These TEM investigations include detailed microstructural and microdiffraction observations and comparisons as they relate to the aggregate morphologies as well as their component (primary) nanoparticles. We have also conducted both clinical surveys regarding asthma incidence and the use of gas cooking stoves as well as random surveys by zip code throughout the city of El Paso. In addition, we report on short term (2 day) and longer term (2 week) in vitro assays for black carbon and a commercial multiwall carbon nanotube aggregate sample using a murine macrophage cell line, which demonstrate significant cytotoxicity; comparable to a chrysotile asbestos nanoparticulate reference. The multi-wall carbon nanotube aggregate material is identical to those collected in the indoor and outdoor air, and may serve as a surrogate. Taken together with the plethora of toxic responses reported for DPM, these findings prompt concerns for airborne carbonaceous nanoparticulates in general. The implications of these preliminary findings and their potential health effects, as well as directions for related studies addressing these complex issues, will also be examined. PMID:16823077

Murr, L. E.; Soto, K. F.; Garza, K. M.; Guerrero, P. A.; Martinez, F.; Esquivel, E. V.; Ramirez, D. A.; Shi, Y.; Bang, J. J.; Venzor, J.

2006-01-01

154

Polymerization  

NSDL National Science Digital Library

In this activity, by the Concord Consortium's Molecular Literacy project, students "explore both polymers and copolymers." Upon completion of this activity students should be able to compare linear, branched, and cross-linked polymers; connect the density of polymers with differences in their structure; and connect polymer structures with their reversibility, and consider the importance for recycling." The activity itself is a java-based interactive resource built upon the free, open source Molecular Workbench software. In the activity, students are allowed to explore at their own pace in a digital environment full of demonstrations, illustrations, and models they can manipulate. In addition to the activity, visitors will find an overview of the activity, a test and rubric, central concepts, and their correlation to AAAS standards.

155

21 CFR 870.3650 - Pacemaker polymeric mesh bag.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 false Pacemaker polymeric mesh bag. 870.3650 Section 870.3650 Food... § 870.3650 Pacemaker polymeric mesh bag. (a) Identification. A pacemaker polymeric mesh bag is an implanted device used to hold a...

2010-04-01

156

21 CFR 870.3650 - Pacemaker polymeric mesh bag.  

Code of Federal Regulations, 2011 CFR

...2011-04-01 false Pacemaker polymeric mesh bag. 870.3650 Section 870.3650 Food... § 870.3650 Pacemaker polymeric mesh bag. (a) Identification. A pacemaker polymeric mesh bag is an implanted device used to hold a...

2011-04-01

157

21 CFR 870.3650 - Pacemaker polymeric mesh bag.  

Code of Federal Regulations, 2013 CFR

...2013-04-01 false Pacemaker polymeric mesh bag. 870.3650 Section 870.3650 Food... § 870.3650 Pacemaker polymeric mesh bag. (a) Identification. A pacemaker polymeric mesh bag is an implanted device used to hold a...

2013-04-01

158

21 CFR 870.3650 - Pacemaker polymeric mesh bag.  

Code of Federal Regulations, 2014 CFR

...2014-04-01 false Pacemaker polymeric mesh bag. 870.3650 Section 870.3650 Food... § 870.3650 Pacemaker polymeric mesh bag. (a) Identification. A pacemaker polymeric mesh bag is an implanted device used to hold a...

2014-04-01

159

21 CFR 870.3650 - Pacemaker polymeric mesh bag.  

Code of Federal Regulations, 2012 CFR

...2012-04-01 false Pacemaker polymeric mesh bag. 870.3650 Section 870.3650 Food... § 870.3650 Pacemaker polymeric mesh bag. (a) Identification. A pacemaker polymeric mesh bag is an implanted device used to hold a...

2012-04-01

160

40 CFR 721.10299 - Polymeric MDI based polyurethanes (generic).  

Code of Federal Regulations, 2013 CFR

...2013-07-01 false Polymeric MDI based polyurethanes (generic). 721.10299 Section...721.10299 Polymeric MDI based polyurethanes (generic). (a) Chemical substance...identified generically as polymeric MDI based polyurethanes (PMNs P-00-2,...

2013-07-01

161

40 CFR 721.10299 - Polymeric MDI based polyurethanes (generic).  

Code of Federal Regulations, 2014 CFR

...2014-07-01 false Polymeric MDI based polyurethanes (generic). 721.10299 Section...721.10299 Polymeric MDI based polyurethanes (generic). (a) Chemical substance...identified generically as polymeric MDI based polyurethanes (PMNs P-00-2,...

2014-07-01

162

40 CFR 721.10299 - Polymeric MDI based polyurethanes (generic).  

Code of Federal Regulations, 2012 CFR

...2012-07-01 false Polymeric MDI based polyurethanes (generic). 721.10299 Section...721.10299 Polymeric MDI based polyurethanes (generic). (a) Chemical substance...identified generically as polymeric MDI based polyurethanes (PMNs P-00-2,...

2012-07-01

163

Index Sets and Vectorization  

SciTech Connect

Vectorization is data parallelism (SIMD, SIMT, etc.) - extension of ISA enabling the same instruction to be performed on multiple data items simultaeously. Many/most CPUs support vectorization in some form. Vectorization is difficult to enable, but can yield large efficiency gains. Extra programmer effort is required because: (1) not all algorithms can be vectorized (regular algorithm structure and fine-grain parallelism must be used); (2) most CPUs have data alignment restrictions for load/store operations (obey or risk incorrect code); (3) special directives are often needed to enable vectorization; and (4) vector instructions are architecture-specific. Vectorization is the best way to optimize for power and performance due to reduced clock cycles. When data is organized properly, a vector load instruction (i.e. movaps) can replace 'normal' load instructions (i.e. movsd). Vector operations can potentially have a smaller footprint in the instruction cache when fewer instructions need to be executed. Hybrid index sets insulate users from architecture specific details. We have applied hybrid index sets to achieve optimal vectorization. We can extend this concept to handle other programming models.

Keasler, J A

2012-03-27

164

Nanomechanical testing of polymeric nanofibers  

NASA Astrophysics Data System (ADS)

Biodegradable polymeric nanofibrous scaffold comprises individual nanofibers where their stiffnesses can promote or undermine the various cellular functions as well as structural integrity of the scaffold. As such, there is a need to investigate the nanomechanical properties of these individual nanofibers. However, conducting mechanical tests of individual fibers at the nanometer scale can pose great challenges and difficulties. Here, we present novel techniques to perform nanomechanical testing of individual polymeric nanofibers. For demonstration of the nano tensile tests, polycaprolactone (PCL) nanofibers were produced via electrospinning. These fibers were deposited across two parallel edges of a cardboard frame so that a single nanofiber can be isolated for tensile test using a nano tensile tester. For nanoscale three-point bend test, a Poly (L-lactic acid) (PLLA) nanofiber was suspended across a microsized groove etched on a silicon wafer. An atomic force microscope (AFM) tip was then used to apply a point load on the mid-span of the suspended fiber. Beam bending theory was then used to calculate the elastic modulus of the nanofiber. For nanoindentation test, a PLLA nanofiber was deposited on a mica substrate and an AFM tip used to indent the nanofiber. Modified Hertz theory for normal contact was then used to evaluate the elastic modulus of the nanofiber.

Tan, E. P. S.; Lim, C. T.

2005-04-01

165

Generation of Oxidants From the Reaction of Nanoparticulate Zero-Valent Iron and Oxygen for the use in Contaminant Remediation  

NASA Astrophysics Data System (ADS)

The reaction of zero-valent iron (ZVI) with oxygen can lead to the formation of oxidants, which may be used to transform recalcitrant contaminants including non-polar organics and certain metals. Nanoparticulate iron might provide a practical mechanism of remediating oxygen-containing groundwater and contaminated soil. To gain insight into the reaction mechanism and to quantify the yield of oxidants, experiments were performed with model organic compounds in the presence of nanoparticulate zero-valent iron and oxygen. At pH values below 5, ZVI nanoparticles were oxidized within 30 minutes with a stoichiometry of approximately two Fe0 oxidized per O2 consumed. Using the oxidation of methanol and ethanol to formaldehyde and acetaldehyde, respectively, we found that less than 2% of the consumed oxygen was converted to reactive oxidants under acidic conditions. The yield of aldehydes increased with pH up to pH 7, with maximum oxidant yields of around 5% relative to the mass of ZVI added. The increase of aldehyde yield with pH was attributable to changes in the processes responsible for oxidant production. At pH values below 5, the corrosion of ZVI by oxygen produces hydrogen peroxide, which subsequently reacts with ferrous iron [Fe(II)] via the Fenton reaction. At higher pH values, the aldehydes are produced when Fe(II), the initial product of ZVI oxidation, reacts with oxygen. The decrease in oxidant yield at pH values above 7 may be attributable to precipitation of Fe(II). The oxidation of benzoic acid and 2-propanol to para-hydroxybenzoic acid and acetone, respectively, followed a very different trend compared to the primary alcohols. In both cases, the highest product yields (approximately 2% with respect to ZVI added) were observed at pH 3. Yields decreased with increasing pH, with no oxidized product detected at neutral pH. These results suggest that two different oxidants may be produced by the system: hydroxyl radical (OH-·) at acidic pH and a more selective oxidant such as the ferryl ion [Fe(IV)] at neutral pH. This provides insight into the type of compounds that may be oxidized using the zero-valent iron and oxygen system. The addition of certain compounds such as oxalate and polyoxometalate (POM) may improve contaminant remediation efficiencies by enhancing oxidant yields. The introduction of 1 mM oxalate improved the formaldehyde yield by approximately 20% at neutral pH. Oxalate accelerates the Fenton reaction and limits the passivation of the ZVI surface by increasing iron solubility. The presence of excess POM greatly enhanced the yield of formaldehyde, with maximum yields of 60 and 35% with respect to ZVI added at pH 2 and 7, respectively. The mechanism of POM enhancement is a function of solution pH. At acidic pH, POM acts an electron shuttle by directly transferring electrons from ZVI to oxygen to increase the hydrogen peroxide production. At neutral pH, POM may act by forming soluble iron-complexes and preventing the build-up of an iron oxide layer on the ZVI surface.

Keenan, C. R.; Lee, C.; Sedlak, D. L.

2007-12-01

166

The Production and Export of Bioavailable Iron from Ice Sheets - the Importance of Colloidal and Nanoparticulate Phases  

NASA Astrophysics Data System (ADS)

Glaciers cover approximately 10% of the world's land surface at present, but our knowledge of biogeochemical processes occurring beneath them is still limited, as is our understanding of their impact on downstream ecosystems via the export of nutrients in runoff. Recent work has suggested that glaciers are a primary source of nutrients to near coastal areas(1). For example, macronutrients, such as nitrogen and phosphorus, and micronutrients, such as iron, may support primary production(2,3). Nutrient limitation of primary producers is known to be prevalent in large sectors of the world's oceans and iron is a significant limiting nutrient in Polar waters(4,5). Significantly, large oceanic algal blooms have been observed in polar areas where glacial influence is large(6,7). Our knowledge of iron speciation, concentrations and export dynamics in glacial meltwater is limited due, in part, to problems associated with collecting trace measurements in remote field locations. For example, recent work has indicated large uncertainty in 'dissolved' meltwater iron concentrations (0.2 - 4000 ?M(8,9)). There is currently a dearth of information about labile nanoparticulate iron in glacial meltwaters, as well as export dynamics from large ice sheet catchments. Existing research has focused on small catchment examples(8,10), which behave differently to larger catchments(11). Presented here is the first time series of daily variations in meltwater iron concentrations (dissolved, filterable colloidal/nanoparticulate and bioavailable suspended sediment bound) from two large contrasting glacial catchments in Greenland over the 2012 and 2013 summer melt seasons. We also present the first estimates of iron concentrations in Greenlandic icebergs, which have been identified as hot spots of biological activity in the open ocean(12,13). Budgets for ice sheets based on our data demonstrate the importance of glaciers in global nutrient cycles, and reveal a large and previously under-appreciated component of the global iron cycle. References 1 Hood, E. & Scott, D, Nat Geosci 1, 583-587 (2008) 2 Wadham, J. et al., Earth Env Sci T R So (2013) 3 Gerringa, L. J. A. et al., Deep-Sea Res Pt II 71-76, 16-31 (2012) 4 Martin, J. H. & Fitzwater, S. E., Nature 331, 341-343 (1988) 5 Martin, J. H., Fitzwater, S. E. & Gordon, R. M., Global Biogeochem Cy 4, 5-12 (1990) 6 Perrette, M., Yool, A., Quartly, G. D. & Popova, E. E., Biogeosciences 8, 515-524 (2011) 7 Frajka-Williams, E. & Rhines, P. B., Deep-Sea Res Pt I 57, 541-552 (2010) 8 Statham, P. J., Skidmore, M. & Tranter, M., Global Biogeochem Cy 22 (2008) 9 Mikucki, J. A. et al., Science 324, 397-400 (2009) 10 Bhatia, M. P. et al., Nat Geosci (2013) 11 Wadham, J. L. et al., Global Biogeochem Cy 24 (2010) 12 Smith, K. L. et al., Science 317, 478-482 (2007) 13 Raiswell, R. & Canfield, D. E., Geochemical Perspectives 1, 1-220 (2012)

Hawkings, J.; Wadham, J. L.; Tranter, M.; Raiswell, R.; Benning, L. G.; Statham, P. J.; Tedstone, A.; Nienow, P. W.; Telling, J.; Bagshaw, E.

2013-12-01

167

Micro-CT Based Experimental Liver Imaging Using a Nanoparticulate Contrast Agent: A Longitudinal Study in Mice  

PubMed Central

Background Micro-CT imaging of liver disease in mice relies on high soft tissue contrast to detect small lesions like liver metastases. Purpose of this study was to characterize the localization and time course of contrast enhancement of a nanoparticular alkaline earth metal-based contrast agent (VISCOVER ExiTron nano) developed for small animal liver CT imaging. Methodology ExiTron nano 6000 and ExiTron nano 12000, formulated for liver/spleen imaging and angiography, respectively, were intravenously injected in C57BL/6J-mice. The distribution and time course of contrast enhancement were analysed by repeated micro-CT up to 6 months. Finally, mice developing liver metastases after intrasplenic injection of colon carcinoma cells underwent longitudinal micro-CT imaging after a single injection of ExiTron nano. Principal Findings After a single injection of ExiTron nano the contrast of liver and spleen peaked after 4–8 hours, lasted up to several months and was tolerated well by all mice. In addition, strong contrast enhancement of abdominal and mediastinal lymph nodes and the adrenal glands was observed. Within the first two hours after injection, particularly ExiTron nano 12000 provided pronounced contrast for imaging of vascular structures. ExiTron nano facilitated detection of liver metastases and provided sufficient contrast for longitudinal observation of tumor development over weeks. Conclusions The nanoparticulate contrast agents ExiTron nano 6000 and 12000 provide strong contrast of the liver, spleen, lymph nodes and adrenal glands up to weeks, hereby allowing longitudinal monitoring of pathological processes of these organs in small animals, with ExiTron nano 12000 being particularly optimized for angiography due to its very high initial vessel contrast. PMID:21984939

Boll, Hanne; Nittka, Stefanie; Doyon, Fabian; Neumaier, Michael; Marx, Alexander; Kramer, Martin; Groden, Christoph; Brockmann, Marc A.

2011-01-01

168

Chemodynamics of soft nanoparticulate complexes: Cu(II) and Ni(II) complexes with fulvic acids and aquatic humic acids.  

PubMed

The dynamics of metal complexation by small humic substances (fulvic acid and aquatic humic acid, collectively denoted as “fulvic-like substance”, FS) are explored within the framework of concepts recently developed for soft nanoparticulate complexants. From a comprehensive collection of published equilibrium and dissociation rate constants for CuFS and NiFS complexes, the association rate constant, ka, is determined as a function of the degree of complexing site occupation, ?. From this large data set, it is shown for the first time that ka is independent of ?. This result has important consequences for finding the nature of the rate limiting step in the association process. The influence of electric effects on the rate of the association process is described, namely (i) the accelerating effect of the negatively charged electrostatic field of FS on the diffusion of metal ions toward it, and (ii) the extent to which metal ions electrostatically accumulate in the counterionic atmosphere of FS. These processes are discussed qualitatively in relation to the derived values of ka. For slowly dehydrating metal ions such as Ni(H2O)6 2+ (dehydration rate constant, kw), ka is expected to derive straight from kw. In contrast, for rapidly dehydrating metal ions such as Cu(H2O)6 2+, transport limitations and electric effects involved in the formation of the precursor outer-sphere associate appear to be important overall rate-limiting factors. This is of great significance for understanding the chemodynamics of humic complexes in the sense that inner-sphere complex formation would not always be the (sole) rate limiting step. PMID:22934531

Town, Raewyn M; van Leeuwen, Herman P; Buffle, Jacques

2012-10-01

169

Chemoprevention of pancreatic cancer using solid-lipid nanoparticulate delivery of a novel aspirin, curcumin and sulforaphane drug combination regimen  

PubMed Central

Pancreatic cancer is the fourth largest cause of cancer deaths in the Unites States and the prognosis is grim with <5% survival chances upon diagnosis. The objective of this study was to assess the combined chemopreventive effect of solid lipid nanoparticle (SLN) encapsulated drugs aspirin (ASP), curcumin (CUR) and free sulforaphane (SFN) for the chemoprevention of pancreatic cancer. Experiments were carried out (1) to evaluate the feasibility of encapsulation of these chemopreventive agents within solid lipid systems and (2) to measure the synergistic effects of a combination of ASP with CUR in SLNs mixed with free SFN against cell proliferation and apoptosis in pancreatic cancer cells, MIA PaCa-2 and Panc-1. The SLNs were prepared using a modified solvent evaporation technique and were characterized for particle sizing, encapsulation efficiency and drug release. ASP and CUR SLNs were formulated within the particle size range of 150–250 nm and were found to have an encapsulation efficiency of 85 and 69%, respectively. Sustained release of drugs over a 96 h period from SLNs was observed. The SLNs were stable over a 3-month storage period at room temperature. Cell viability studies demonstrated that combinations of low doses of ASP SLN (25 ?M), CUR SLN (2.5 ?M) and free SFN (5 ?M) significantly reduced cell viability by 43.6 and 48.49% in MIAPaca-2 and Panc-1 cell lines, respectively. Furthermore, increased apoptosis of 61.3 and 60.37% was found in MIA Paca-2 and Panc-1 cell lines, respectively, in comparison to the individual doses administered. Synergistic effects were demonstrated using MTS and apoptosis assays. Thus, this study successfully demonstrated the feasibility of using a solid lipid nanoparticulate system for the first time to deliver this novel combination chemoprevention regimen, providing valuable evidence for the usability of nanotechnology-based drug regimens towards pancreatic cancer chemoprevention. PMID:23007664

SUTARIA, DHRUVITKUMAR; GRANDHI, BALAGANGADHAR KARTHIK; THAKKAR, ARVIND; WANG, JEFFREY; PRABHU, SUNIL

2012-01-01

170

Exchange bias beyond the superparamagnetic blocking temperature of the antiferromagnet in a Ni-NiO nanoparticulate system  

SciTech Connect

We report magnetic and exchange bias studies on Ni-NiO nanoparticulate systems synthesized by a two-step process, namely, chemical reduction of a Ni salt followed by air annealing of the dried precipitate in the temperature range 400–550?°C. Size of Ni and NiO crystallites as estimated from X–ray diffraction line broadening ranges between 10.5–13.5?nm and 2.3–4?nm, respectively. The magneto-thermal plots (M-T) of these bi-magnetic samples show a well developed peak in the vicinity of 130?K. This has been identified as the superparamagnetic blocking temperature “T{sub B}” of NiO. Interestingly, all samples exhibit exchange bias even above their respective NiO blocking temperatures, right up to 300?K, the maximum temperature of measurement. This is in contrast to previous reports since exchange bias requires the antiferromagnetic NiO to have a stable direction of its moment in order to pin the ferromagnet (Ni) magnetization, whereas such stability is unlikely above T{sub B} since the NiO is superparamagnetic, its moment flipping under thermal activation. Our observation is elucidated by taking into account the core-shell morphology of the Ni-NiO nanoparticles whereby clustering of some of these nanoparticles connects their NiO shells to form extended continuous regions of NiO, which because of their large size remain blocked at T?>?T{sub B}, with thermally stable spins capable of pinning the Ni cores and giving rise to exchange bias. The investigated samples may thus be envisaged as being constituted of both isolated core-shell Ni-NiO nanoparticles as well as clustered ones, with T{sub B} denoting the blocking temperature of the NiO shell of the isolated particles.

Roy, Aparna, E-mail: aparna.roy@ua.pt, E-mail: aparnaroy15@gmail.com; Ferreira, J. M. F. [Department of Materials and Ceramics Engineering and CICECO, University of Aveiro, 3810-193 Aveiro (Portugal); De Toro, J. A.; Muniz, P.; Riveiro, J. M. [Departamento de Fisica Aplicada, Universidad de Castilla-La Mancha, 13071 Ciudad Real (Spain); Amaral, V. S. [Department of Physics and CICECO, University of Aveiro, 3810-193 Aveiro (Portugal)

2014-02-21

171

High pinning performance of YBa2Cu3O7?x films added with Y2O3 nanoparticulate defects  

NASA Astrophysics Data System (ADS)

We report the epitaxial growth and superconducting properties of Y2O3-added YBa2Cu3Ox (YBCO) films grown on SrTiO3-buffered MgO substrates by pulsed-laser deposition using surface-modified YBCO targets. Areas of Y2O3 sectors on the YBCO target were increased to 5.44% and 9.22% of the total YBCO pellet in order to find a correlation between the Y2O3 content, morphology, and the pinning properties of YBCO + Y2O3 mixed films. The maximum global pinning forces, FP, at 77 K were 14.3 GN m?3 and 1.15 GN m?3 for the Y2O3 5.44A% and 9.22A%, respectively. The 5.44A% Y2O3-added sample presents a very high value of pinning force at 77 K, approaching the value obtained in YBCO films with added BaZrO3 nanorods, but with less depression in the superconducting critical temperature, Tc. In accordance with scanning transmission electron microscopy (STEM) observations, both films present nanoparticulate Y2O3 dispersed in a YBCO matrix where Y2Ba4Cu8O16 (Y248) intergrowths were also observed. Consistent with the strong pinning theory, the size and distribution of randomly dispersed Y2O3 particles are optimal for the flux pinning of a 5.44A% Y2O3-YBCO film, while in the case of a 9.22A% film, the YBCO matrix is degraded by jam-packed Y248 intergrowth, which leads to a comparatively poor pinning performance. We further used the single-vortex dynamics model to account for vortex pinning in the samples. The 5.44A% Y2O3-YBCO film result shows good agreement with the model fit up to 4 T of the applied magnetic field.

Mele, Paolo; Guzman, Roger; Gazquez, Jaume; Puig, Teresa; Obradors, Xavier; Saini, Shrikant; Yoshida, Yutaka; Mukaida, Masashi; Ichinose, Ataru; Matsumoto, Kaname; Idries Adam, Malik

2015-02-01

172

Chemoprevention of pancreatic cancer using solid-lipid nanoparticulate delivery of a novel aspirin, curcumin and sulforaphane drug combination regimen.  

PubMed

Pancreatic cancer is the fourth largest cause of cancer deaths in the Unites States and the prognosis is grim with <5% survival chances upon diagnosis. The objective of this study was to assess the combined chemopreventive effect of solid lipid nanoparticle (SLN) encapsulated drugs aspirin (ASP), curcumin (CUR) and free sulforaphane (SFN) for the chemoprevention of pancreatic cancer. Experiments were carried out (1) to evaluate the feasibility of encapsulation of these chemopreventive agents within solid lipid systems and (2) to measure the synergistic effects of a combination of ASP with CUR in SLNs mixed with free SFN against cell proliferation and apoptosis in pancreatic cancer cells, MIA PaCa-2 and Panc-1. The SLNs were prepared using a modified solvent evaporation technique and were characterized for particle sizing, encapsulation efficiency and drug release. ASP and CUR SLNs were formulated within the particle size range of 150?250 nm and were found to have an encapsulation efficiency of 85 and 69%, respectively. Sustained release of drugs over a 96 h period from SLNs was observed. The SLNs were stable over a 3-month storage period at room temperature. Cell viability studies demonstrated that combinations of low doses of ASP SLN (25 µM), CUR SLN (2.5 µM) and free SFN (5 µM) significantly reduced cell viability by 43.6 and 48.49% in MIAPaca-2 and Panc-1 cell lines, respectively. Furthermore, increased apoptosis of 61.3 and 60.37% was found in MIA Paca-2 and Panc-1 cell lines, respectively, in comparison to the individual doses administered. Synergistic effects were demonstrated using MTS and apoptosis assays. Thus, this study successfully demonstrated the feasibility of using a solid lipid nanoparticulate system for the first time to deliver this novel combination chemoprevention regimen, providing valuable evidence for the usability of nanotechnology-based drug regimens towards pancreatic cancer chemoprevention. PMID:23007664

Sutaria, Dhruvitkumar; Grandhi, Balagangadhar Karthik; Thakkar, Arvind; Wang, Jeffrey; Prabhu, Sunil

2012-12-01

173

A Novel Nanoparticulate Formulation of Arsenic Trioxide with Enhanced Therapeutic Efficacy in a Murine Model of Breast Cancer  

PubMed Central

Purpose The clinical success of arsenic trioxide (As2O3) in hematological malignancies has not been replicated in solid tumors due to poor pharmacokinetics and dose-limiting toxicity. We have developed a novel nanoparticulate formulation of As2O3 encapsulated in liposomal vesicles or “nanobins” [(NB(Ni,As)] to overcome these hurdles. We postulated that nanobin encapsulation of As2O3 would improve its therapeutic index against clinically aggressive solid tumors, such as triple negative breast carcinomas. Experimental Design The cytotoxicity of NB(Ni,As), the empty nanobin, and free As2O3 was evaluated against a panel of human breast cancer cell lines. The plasma pharmacokinetics of NB(Ni,As) and free As2O3 were compared in rats to measure drug exposure. In addition, the antitumor activity of these agents was evaluated in an orthotopic model of human triple negative breast cancer. Results The NB(Ni,As) agent was much less cytotoxic in vitro against a panel of human breast cancer cell lines than free As2O3. In contrast, NB(Ni,As) dramatically potentiated the therapeutic efficacy of As2O3 in vivo in an orthotopic model of triple negative breast cancer. Reduced plasma clearance, enhanced tumor uptake, and induction of tumor cell apoptosis were observed for NB(Ni,As). Conclusions Nanobin encapsulation of As2O3 improves the pharmacokinetics and antitumor efficacy of this cytotoxic agent in vivo. Our findings demonstrate the therapeutic potential of this nanoscale agent and provide a foundation for future clinical studies in breast cancer and other solid tumors. PMID:20519360

Ahn, Richard W.; Chen, Feng; Chen, Haimei; Stern, Stephan T.; Clogston, Jeffrey D.; Patri, Anil K.; Raja, Meera R.; Swindell, Elden P.; Parimi, Vamsi; Cryns, Vincent L.; O’Halloran, Thomas V.

2010-01-01

174

Exchange bias beyond the superparamagnetic blocking temperature of the antiferromagnet in a Ni-NiO nanoparticulate system  

NASA Astrophysics Data System (ADS)

We report magnetic and exchange bias studies on Ni-NiO nanoparticulate systems synthesized by a two-step process, namely, chemical reduction of a Ni salt followed by air annealing of the dried precipitate in the temperature range 400-550 °C. Size of Ni and NiO crystallites as estimated from X-ray diffraction line broadening ranges between 10.5-13.5 nm and 2.3-4 nm, respectively. The magneto-thermal plots (M-T) of these bi-magnetic samples show a well developed peak in the vicinity of 130 K. This has been identified as the superparamagnetic blocking temperature "TB" of NiO. Interestingly, all samples exhibit exchange bias even above their respective NiO blocking temperatures, right up to 300 K, the maximum temperature of measurement. This is in contrast to previous reports since exchange bias requires the antiferromagnetic NiO to have a stable direction of its moment in order to pin the ferromagnet (Ni) magnetization, whereas such stability is unlikely above TB since the NiO is superparamagnetic, its moment flipping under thermal activation. Our observation is elucidated by taking into account the core-shell morphology of the Ni-NiO nanoparticles whereby clustering of some of these nanoparticles connects their NiO shells to form extended continuous regions of NiO, which because of their large size remain blocked at T > TB, with thermally stable spins capable of pinning the Ni cores and giving rise to exchange bias. The investigated samples may thus be envisaged as being constituted of both isolated core-shell Ni-NiO nanoparticles as well as clustered ones, with TB denoting the blocking temperature of the NiO shell of the isolated particles.

Roy, Aparna; De Toro, J. A.; Amaral, V. S.; Muniz, P.; Riveiro, J. M.; Ferreira, J. M. F.

2014-02-01

175

Enzyme-catalyzed polymerization to functional polymers  

Microsoft Academic Search

In this article, described are our recent advances in enzymatic polymerization, defined as chemical polymer syntheses in vitro (in test tubes) via non-biosynthetic pathways catalyzed by an isolated enzyme. The major target macromolecules formed via the enzymatic polymerizations in this article are polyesters and polyphenols. For synthesis of polyesters, hydrolases are used as catalyst; hydrolases, enzymes catalyzing a bond-cleavage reaction

Hiroshi Uyama; Shiro Kobayashi

2002-01-01

176

Spring-loaded polymeric gel actuators  

DOEpatents

Spring-loaded electrically controllable polymeric gel actuators are disclosed. The polymeric gels can be polyvinyl alcohol, polyacrylic acid, or polyacrylamide, and are contained in an electrolytic solvent bath such as water plus acetone. The action of the gel is mechanically biased, allowing the expansive and contractile forces to be optimized for specific applications.

Shahinpoor, Mohsen (Albuquerque, NM)

1995-01-01

177

Fluidized bed reactor for catalytic olefin polymerization  

Microsoft Academic Search

Due to the continuous improvement of catalysts and processes, polyolefins have become one of the most important plastics in the world. Polyolefins can be produced at low costs with a variety of end-use properties. Nowadays, the most important propylene polymerization processes are executed in the liquid or the gas phase or a combination of both. In contrast to propylene polymerizations

Gerhardus Bernardus Meier

2000-01-01

178

Escalation of polymerization in a thermal gradient  

PubMed Central

For the emergence of early life, the formation of biopolymers such as RNA is essential. However, the addition of nucleotide monomers to existing oligonucleotides requires millimolar concentrations. Even in such optimistic settings, no polymerization of RNA longer than about 20 bases could be demonstrated. How then could self-replicating ribozymes appear, for which recent experiments suggest a minimal length of 200 nt? Here, we demonstrate a mechanism to bridge this gap: the escalated polymerization of nucleotides by a spatially confined thermal gradient. The gradient accumulates monomers by thermophoresis and convection while retaining longer polymers exponentially better. Polymerization and accumulation become mutually self-enhancing and result in a hyperexponential escalation of polymer length. We describe this escalation theoretically under the conservative assumption of reversible polymerization. Taking into account the separately measured thermophoretic properties of RNA, we extrapolate the results for primordial RNA polymerization inside a temperature gradient in pores or fissures of rocks. With a dilute, nanomolar concentration of monomers the model predicts that a pore length of 5 cm and a temperature difference of 10 K suffice to polymerize 200-mers of RNA in micromolar concentrations. The probability to generate these long RNAs is raised by a factor of >10600 compared with polymerization in a physical equilibrium. We experimentally validate the theory with the reversible polymerization of DNA blocks in a laser-driven thermal trap. The results confirm that a thermal gradient can significantly enlarge the available sequence space for the emergence of catalytically active polymers. PMID:23630280

Mast, Christof B.; Schink, Severin; Gerland, Ulrich; Braun, Dieter

2013-01-01

179

Spring-loaded polymeric gel actuators  

DOEpatents

Spring-loaded electrically controllable polymeric gel actuators are disclosed. The polymeric gels can be polyvinyl alcohol, polyacrylic acid, or polyacrylamide, and are contained in an electrolytic solvent bath such as water plus acetone. The action of the gel is mechanically biased, allowing the expansive and contractile forces to be optimized for specific applications. 5 figs.

Shahinpoor, M.

1995-02-14

180

PRION PROLIFERATION WITH UNBOUNDED POLYMERIZATION RATES  

E-print Network

PRION PROLIFERATION WITH UNBOUNDED POLYMERIZATION RATES CHRISTOPH WALKER Abstract. A model for prion replication is studied. We prove global existence of weak solutions for unbounded polymerization Prions are widely regarded as the infectious agent causing fatal diseases known as TSE's including BSE

Walker, Christoph

181

Oxidation-responsive polymeric vesicles  

NASA Astrophysics Data System (ADS)

Vesicles formed in water by synthetic macro-amphiphiles have attracted much attention as nanocontainers having properties that extend the physical and chemical limits of liposomes. We sought to develop ABA block copolymeric amphiphiles that self-assemble into unilamellar vesicles that can be further oxidatively destabilized. We selected poly(ethylene glycol) (PEG) as the hydrophilic A blocks, owing to its resistance to protein adsorption and low toxicity. As hydrophobic B blocks, we selected poly(propylene sulphide) (PPS), owing to its extreme hydrophobicity, its low glass-transition temperature, and most importantly its oxidative conversion from a hydrophobe to a hydrophile, poly(propylene sulphoxide) and ultimately poly(propylene sulphone). This is the first example of the use of oxidative conversions to destabilize such carriers. This new class of oxidation-responsive polymeric vesicles may find applications as nanocontainers in drug delivery, biosensing and biodetection.

Napoli, Alessandro; Valentini, Massimiliano; Tirelli, Nicola; Müller, Martin; Hubbell, Jeffrey A.

2004-03-01

182

Molecular and polymeric ceramic precursors  

SciTech Connect

The development of new methods for the production of complex materials is one of the most important problems in modern solid state chemistry and materials science. This project is attempting to apply the synthetic principles which have evolved inorganic and organometallic chemistry to the production of technologically important non-oxide ceramics, such as boron nitride, boron carbide and metal borides. Our recent work has now resulted in the production of new polymer systems, including poly(B-vinylborazine), polyvinylpentaborane and polyborazylene, that have proven to be high yield precursors to boron-based ceramic materials. Current work is now directed toward the synthesis of new types of molecular and polymeric boron-containing species and on exploration of the solid state properties of the ceramics that have been produced in these studies.

Sneddon, L.G.

1991-08-01

183

Molecular and polymeric ceramic precursors  

SciTech Connect

The development of new methods for the production of complex materials is one of the most important problems in modern solid state chemistry and materials science. This project is attempting to apply the synthetic principles which have evolved in inorganic and organometallic chemistry to the production of technologically important non-oxide ceramics, such as boron nitride, boron carbide and metal borides. Recent work has now resulted in the production of new polymer systems, including poly(B-vinylborazine), polyvinylpentaborane and polyborazylene, that have proven to be high yield precursors to boron-based ceramic materials. Current work is now directed toward the synthesis of new types of molecular and polymeric boron-containing species and an exploration of the solid state properties of the ceramics that have been produced in these studies.

Sneddon, L.G.

1992-06-01

184

Hemocompatibility of Polymeric Nanostructured Surfaces  

PubMed Central

Tissue integration is an important property when inducing transplant tolerance, however, the hemocompatibility of the biomaterial surface also plays an important role in the ultimate success of the implant. Therefore, in order to induce transplant tolerance, it is critical to understand the interaction of blood components with the material surfaces. In this study, we have investigated the adsorption of key blood serum proteins, in vitro adhesion and activation of platelets and clotting kinetics of whole blood on flat polycaprolactone (PCL) surfaces, nanowire (NW) surfaces and nanofiber (NF) surfaces. Previous studies have shown that polymeric nanostructured surfaces improve cell adhesion, proliferation and viability; however it is unclear how these polymeric nanostructured surfaces interact with the blood and its components. Protein adsorption results indicate that while there were no significant differences in total albumin adsorption on PCL, NW and NF surfaces, NW surfaces had higher total fibrinogen and immunoglobulin-G adsorption compared to NF and PCL surfaces. In contrast, NF surfaces had higher surface FIB and IgG adsorption compared to PCL and NW surfaces. Platelet adhesion and viability studies show more adhesion and clustering of platelets on the NF surfaces as compared to PCL and NW surfaces. Platelet activation studies reveal that NW surfaces have the highest percentage of unactivated platelets, whereas NF surfaces have the highest percentage of fully activated platelets. Whole blood clotting results indicate that NW surfaces maintain an increased amount of free hemoglobin during the clotting process compared to PCL and NF surface, indicating less clotting and slower rate of clotting on their surfaces. PMID:23848447

Leszczak, Victoria; Smith, Barbara S.; Popat, Ketul C.

2013-01-01

185

Hyperbranched polysiloxysilane nanoparticles for nonviral gene delivery vectors and nanoprobes  

NASA Astrophysics Data System (ADS)

We report an approach to produce predefined surface charge tunable gene delivery vectors using siloxysilsane-based polymer for gene delivery studies. To obtain nonviral vectors, new series of hyperbranched polysiloxysilane (HBPS) were synthesized, and the end groups in polymer structures have modified with hydrophilic molecules; in other words, carboxylic acid and quaternary ammonium groups were employed into terminal structures to give the amphiphilicity. The novelty of these amphiphilic HBPS polymers lies in the fact that nanoparticles with different zeta potential (surface charge density) can be easily tailored and functionalized. These polymeric nanoparticles which containing various chemical groups on the surface indicated altered surface charge distributions (from -40 to +64mV). Finally, the use of these nanoparticles as efficient gene delivery vectors was demonstrated by means of in vitro transfection study using ?- galactosidase plasmid and pEGFP-N1 plasmid, and the most efficient combination was obtained using HBPS-CN30:70.

Kim, Won Jin; Bonoiu, Adela C.; Lee, Kwang-Sup; Hayakawa, Teruaki; Xia, Cheng; Kakimoto, Masa-aki; Pudavar, Haridas E.; Prasad, Paras N.

2009-08-01

186

Support Vector Data Description  

Microsoft Academic Search

Data domain description concerns the characterization of a data set. A good description covers all target data but includes no superfluous space. The boundary of a dataset can be used to detect novel data or outliers. We will present the Support Vector Data Description (SVDD) which is inspired by the Support Vector Classifier. It obtains a spherically shaped boundary around

David M. J. Tax; Robert P. W. Duin

2004-01-01

187

Vector generator scan converter  

DOEpatents

High printing speeds for graphics data are achieved with a laser printer by transmitting compressed graphics data from a main processor over an I/O (input/output) channel to a vector generator scan converter which reconstructs a full graphics image for input to the laser printer through a raster data input port. The vector generator scan converter includes a microprocessor with associated microcode memory containing a microcode instruction set, a working memory for storing compressed data, vector generator hardward for drawing a full graphic image from vector parameters calculated by the microprocessor, image buffer memory for storing the reconstructed graphics image and an output scanner for reading the graphics image data and inputting the data to the printer. The vector generator scan converter eliminates the bottleneck created by the I/O channel for transmitting graphics data from the main processor to the laser printer, and increases printer speed up to thirty fold.

Moore, James M. (Livermore, CA); Leighton, James F. (Livermore, CA)

1990-01-01

188

Vector generator scan converter  

DOEpatents

High printing speeds for graphics data are achieved with a laser printer by transmitting compressed graphics data from a main processor over an I/O channel to a vector generator scan converter which reconstructs a full graphics image for input to the laser printer through a raster data input port. The vector generator scan converter includes a microprocessor with associated microcode memory containing a microcode instruction set, a working memory for storing compressed data, vector generator hardware for drawing a full graphic image from vector parameters calculated by the microprocessor, image buffer memory for storing the reconstructed graphics image and an output scanner for reading the graphics image data and inputting the data to the printer. The vector generator scan converter eliminates the bottleneck created by the I/O channel for transmitting graphics data from the main processor to the laser printer, and increases printer speed up to thirty fold. 7 figs.

Moore, J.M.; Leighton, J.F.

1988-02-05

189

Free-standing, single-bilayer-thick polymeric nanosheets via spatially confined polymerization.  

PubMed

Polymeric nanosheets organized by molecular building blocks bearing specifically oriented reactive groups provide abundant and versatile strategies for tailoring structure and chemical functionality periodically over extended length scales that complement graphene. Here we report the bulk synthesis of free-standing polymeric nanosheets via spatially confined polymerization from an elaborate 2D supramolecular system composed of two liquid-crystalline lamellar bilayer membranes of a self-assembled nonionic surfactant--dodecylglyceryl itaconate (DGI)--sandwiched by a water layer. By employing a covalent polymerization on the lamellar bilayer membranes, single-bilayer-thick (4.2 nm), and large area (greater than 100 ?m(2)) polymeric nanosheets of bilayer membranes are achieved. The polymeric nanosheets could serve as a well-defined 2D platform for post-functionalization for producing advanced hybrid materials by introducing the reactions on the hydroxyl groups at the head of DGI on the outer surfaces. PMID:24700401

Qin, Haili; Wang, Dong; Xiong, Xiong; Jin, Jian

2014-06-01

190

Fabrication and manipulation of polymeric magnetic particles with magnetorheological fluid  

E-print Network

Fabrication and manipulation of polymeric magnetic particles with magnetorheological fluid Jaime: Magnetorheological fluid Microfluidic Polymeric particle a b s t r a c t Polymeric magnetic microparticles have been in cores of magnetorheological (MR) fluids surrounded by polymeric shells. We demonstrate

191

Polymerization in emulsion microdroplet reactors  

NASA Astrophysics Data System (ADS)

The goal of this research project is to utilize emulsion droplets as chemical reactors for execution of complex polymerization chemistries to develop unique and functional particle materials. Emulsions are dispersions of immiscible fluids where one fluid usually exists in the form of drops. Not surprisingly, if a liquid-to-solid chemical reaction proceeds to completion within these drops, the resultant solid particles will possess the shape and relative size distribution of the drops. The two immiscible liquid phases required for emulsion polymerization provide unique and complex chemical and physical environments suitable for the engineering of novel materials. The development of novel non-ionic fluorosurfactants allows fluorocarbon oils to be used as the continuous phase in a water-free emulsion. Such emulsions enable the encapsulation of almost any hydrocarbon compound in droplets that may be used as separate compartments for water-sensitive syntheses. Here, we exemplify the promise of this approach by suspension polymerization of polyurethanes (PU), in which the liquid precursor is emulsified into droplets that are then converted 1:1 into polymer particles. The stability of the droplets against coalescence upon removal of the continuous phase by evaporation confirms the formation of solid PU particles. These results prove that the water-free environment of fluorocarbon based emulsions enables high conversion. We produce monodisperse, cross-linked, and fluorescently labeled PU-latexes with controllable mesh size through microfluidic emulsification in a simple one-step process. A novel method for the fabrication of monodisperse mesoporous silica particles is presented. It is based on the formation of well-defined equally sized emulsion droplets using a microfluidic approach. The droplets contain the silica precursor/surfactant solution and are suspended in hexadecane as the continuous oil phase. The solvent is then expelled from the droplets, leading to concentration and micellization of the surfactant. At the same time, the silica solidifies around the surfactant structures, forming equally sized mesoporous particles. The procedure can be tuned to produce well-separated particles or alternatively particles that are linked together. The latter allows us to create 2D or 3D structures with hierarchical porosity. Oil, water, and surfactant liquid mixtures exhibit very complex phase behavior. Depending on the conditions, such mixtures give rise to highly organized structures. A proper selection of the type and concentration of surfactants determines the structuring at the nanoscale level. In this work, we show that hierarchically bimodal nanoporous structures can be obtained by templating silica microparticles with a specially designed surfactant micelle/microemulsion mixture. Tuning the phase state by adjusting the surfactant composition and concentration allows for the controlled design of a system where microemulsion droplets coexist with smaller surfactant micellar structures. The microemulsion droplet and micellar dimensions determine the two types of pore sizes (single nanometers and tens of nanometers). We also demonstrate the fabrication of carbon and carbon/platinum replicas of the silica microspheres using a "lost-wax" approach. Such particles have great potential for the design of electrocatalysts for fuel cells, chromatography separations, and other applications. It was determined that slight variations in microemulsion mixture components (electrolyte concentration, wt% of surfactants, oil to sol ratio, etc.) produces strikingly different pore morphologies and particle surface areas. Control over the size and structure of the smaller micelle-templated pores was made possible by varying the length of the hydrocarbon block within the trimethyl ammonium bromide surfactant and characterized using X-ray diffraction. The effect of emulsion aging was studied by synthesizing particles at progressive time levels from a sample emulsion. It was discovered surface pore size increases after just a few hours, with

Carroll, Nick J.

192

Polymeric Coatings for Electrodynamic Tethers  

NASA Technical Reports Server (NTRS)

Two polymeric coatings have been developed for the Propulsive Small Expendable Deployer System (ProSEDS) mission. ProSEDS is designed to provide an on-orbit demonstration of the electrodynamic propulsion capabilities of tethers in space. The ProSEDS experiment will be a secondary payload on a Delta II unmanned expendable booster scheduled for launch in August 2000. A 5-km conductive tether is attached to the Delta 11 second stage and collects current from the low Earth orbit (LEO) plasma to facilitate de-orbit of the spent stage. The conductive tether is attached to a 10-km non-conductive tether, the other end of which is attached to an endmass containing several scientific instruments. A bare metal tether would have the best conductivity but thermal concerns preclude this design. A conductive polymer developed by Triton Systems has been optimized for conductivity and thermo-optical properties. The current design for the ProSEDS conductive tether is seven strands of 28 AWG aluminum wire individually coated with 8.7 micrometers (0.35 mil) of an atomic oxygen-resistant conductive polymer composed of a mixture of 87% Clear Oxygen-Resistant polymer (COR) and 13% polyanaline (PANi), wrapped around a braided Kevlar (TM) 49 core. Extensive testing has been performed at the Marshall Space Flight Center (MSFC) to qualify this material for flight on ProSEDS. Atomic oxygen exposure was performed, with solar absorptance and infrared emittance measured before and after exposure. Conductivity was measured before and after atomic oxygen exposure. High voltage tests, up to 1500 V, of the current collecting ability of the COR/PANi have been completed. Approximately 160 meters of the conductive tether closest to the Delta 11 second stage is insulated to prevent any electron reconnection to the tether from the plasma contactor. The insulation is composed of polyimide overcoated with TOR-BP, another polymeric coating developed by Triton for this mission. TOR-BP acts as both insulator and a protective coating against atomic oxygen erosion. The insulation has been tested to withstand 5000 V.

Vaughn, Jason A.; Kamenetzky, Rachel R.; Finckenor, Miria M.; Schuler, Peter

2000-01-01

193

Hydrogel polymerization in microgravity for contact lenses  

NASA Astrophysics Data System (ADS)

Contact lenses become widely used for vision correction. The modern contact lenses made of polymer materials have to satisfy a number of requirements: biocompatibility and non-toxicity, low elastic module, high oxygen permeability, good wettability, mechanical strength and stable shape. To following all these requirements, special polymer compositions and polymerization techniques are in development. One of the unique technology is based on polymerization process in microgravity. The synthesis of the polymer structures proceeds in low concentration solution and Earth gravity has a great influence on the polymerization kinetics and final properties of the gel. The microgravity conditions give a possibility to get a regular polymer network with specific macromolecular structure. The experiments on board of space station and theoretical models of the polymerization processes are considered for contact lenses application.

Shcherbakova, Oksana; Kostarev, Konstantin; Kondyurin, Alexey

194

Giant vesicles compressed by actin polymerization  

E-print Network

Actin polymerization plays a critical role in generating propulsive force to drive many types of cell motility. The discovery of actin based motility of the bacterial pathogen Listeria monocytogenes has lead to clearer ...

Carrel, Hyman A. (Hyman Andrew), 1979-

2004-01-01

195

Physicochemically functional ultrathin films by interfacial polymerization  

DOEpatents

Interfacially-polymerized ultrathin films containing physicochemically functional groups are disclosed, both with and without supports. Various applications are disclosed, including membrane electrodes, selective membranes and sorbents, biocompatible materials, targeted drug delivery, and narrow band optical absorbers. 3 figs.

Lonsdale, H.K.; Babcock, W.C.; Friensen, D.T.; Smith, K.L.; Johnson, B.M.; Wamser, C.C.

1990-08-14

196

Reverse-osmosis membranes by plasma polymerization  

NASA Technical Reports Server (NTRS)

Thin allyl amine polymer films were developed using plasma polymerization. Resulting dry composite membranes effectively reject sodium chloride during reverse osmosis. Films are 98% sodium chloride rejective, and 46% urea rejective.

Hollahan, J. R.; Wydeven, T.

1972-01-01

197

Aging of polymeric composites : a literature review  

E-print Network

Due to their increased use in today's society, an extensive survey was undertaken in this report to condense what's been, thus far, discovered as to the effects of aging on polymeric composites. Special emphasis was placed ...

Treviño-Garrido, Margie N

2013-01-01

198

Hydrocarbon polymeric binder for advanced solid propellant  

NASA Technical Reports Server (NTRS)

A series of DEAB initiated isoprene polymerizations were run in the 5-gallon stirred autoclave reactor. Polymerization run parameters such as initiator concentration and feed rate were correlated with the molecular weight to provide a basis for molecular weight control in future runs. Synthetic methods were developed for the preparation of n-1,3-alkadienes. By these methods, 1,3-nonadiene was polymerized using DEAB initiator to give an ester-telechelic polynonadiene. This was subsequently hydrogenated with copper chromite catalyst to give a hydroxyl terminated saturated liquid hydrocarbon prepolymer having greatly improved viscosity characteristics and a Tg 18 degrees lower than that of the hydrogenated polyisoprenes. The hydroxyl-telechelic saturated polymers prepared by the hydrogenolysis of ester-telechelic polyisoprene were reached with diisocyanates under conditions favoring linear chain extension gel permeation chromatography was used to monitor this condensation polymerization. Fractions having molecular weights above one million were produced.

Potts, J. E. (editor)

1972-01-01

199

Biorenewable polymeric materials from vegetable oils.  

E-print Network

??This dissertation discusses the synthesis and characterization of novel biorenewable vegetable oil-based polymeric materials, including thermosets and environmentally-friendly waterborne polyurethane dispersions. The thermosets prepared by… (more)

Xia, Ying

2011-01-01

200

Physicochemically functional ultrathin films by interfacial polymerization  

DOEpatents

Interfacially-polymerized ultrathin films containing physicochemically functional groups are disclosed, both with and without supports. Various applications are disclsoed, including membrane electrodes, selective membranes and sorbents, biocompatible materials, targeted drug delivery, and narrow band optical absorbers.

Lonsdale, Harold K. (Bend, OR); Babcock, Walter C. (Bend, OR); Friensen, Dwayne T. (Bend, OR); Smith, Kelly L. (Bend, OR); Johnson, Bruce M. (Bend, OR); Wamser, Carl C. (West Linn, OR)

1990-01-01

201

Dielectric films improve life of polymeric insulators  

NASA Technical Reports Server (NTRS)

Degradation of polymeric insulators may be significantly reduced when polymer surfaces are coated with film having gradation of dielectric constants, larger where it is in contact with polymer and smaller at its exposed surface.

Hudis, M.; Wydeven, T.

1975-01-01

202

Quadratic exponential vectors  

SciTech Connect

We give a necessary and sufficient condition for the existence of a quadratic exponential vector with test function in L{sup 2}(R{sup d}) intersection L{sup {infinity}}(R{sup d}). We prove the linear independence and totality, in the quadratic Fock space, of these vectors. Using a technique different from the one used by Accardi et al. [Quantum Probability and Infinite Dimensional Analysis, Vol. 25, p. 262, (2009)], we also extend, to a more general class of test functions, the explicit form of the scalar product between two such vectors.

Accardi, Luigi; Dhahri, Ameur [Volterra Center, University of Roma Tor Vergata, Via Columbia 2, 00133 Roma (Italy)

2009-12-15

203

MAC^3: Vectors Worksheet  

NSDL National Science Digital Library

This page contains a worksheet on the topic of vectors for beginning physics students. It was developed as a companion to the lecture presentations by the same authors (see Related Items on this page for a link.) A primary goal of the full instructional unit is to help physics and calculus students differentiate the uses of vectors for physics vs. mathematics, a difficulty known as the "vector calculus gap". This resource is part of a collection developed by the NSF-funded Mathematics Across the Community College Curriculum (MAC 3).

Friesen, Larry; Gillis, Anne

2008-12-22

204

Post polymerization cure shape memory polymers  

SciTech Connect

This invention relates to chemical polymer compositions, methods of synthesis, and fabrication methods for devices regarding polymers capable of displaying shape memory behavior (SMPs) and which can first be polymerized to a linear or branched polymeric structure, having thermoplastic properties, subsequently processed into a device through processes typical of polymer melts, solutions, and dispersions and then crossed linked to a shape memory thermoset polymer retaining the processed shape.

Wilson, Thomas S; Hearon, Michael Keith; Bearinger, Jane P

2014-11-11

205

Migration of Monomeric and Polymeric PVC Plasticizers  

Microsoft Academic Search

This paper summarizes current literature on the migration of monomeric and polymeric PVC plasticizers\\u000a from medical materials, food packaging, and toys. Especially highlighted is macromolecular engineering\\u000a as a tool to increase the plasticizing efficiency and migration resistance for polymeric plasticizers.\\u000a The effect of branching, molecular weight, end-group functionality, and polydispersity on plasticizer performance\\u000a was evaluated by quantification of low-molecular-weight hydrolysis products,

Minna Hakkarainen

206

Polymeric micelles: authoritative aspects for drug delivery  

Microsoft Academic Search

The generation of supramolecular architectures with well-defined structures and functionalities is recently garnering attraction. Self-assemblage of amphiphilic polymers leads to the formation of polymeric micelles that demonstrate unique set of characteristics such as excellent biocompatibility, low toxicity, enhanced blood circulation time, and solubilization of poorly water-soluble drugs. In this article, we provide an up-to-date review on important aspects of polymeric

Sushant S. Kulthe; Yogesh M. Choudhari; Nazma N. Inamdar; Vishnukant Mourya

2012-01-01

207

Next-generation polymeric photonic devices  

Microsoft Academic Search

A versatile polymeric waveguide technology is proposed for low-cost high-performance photonic devices that address the needs of both the telecom and the datacom industries. We have developed advanced organic polymeric materials that can be readily made into both multimode and single-mode optical waveguide structures of controlled numerical aperture and geometry. These materials are formed from highly-crosslinked acrylate monomers with specific

Louay A. Eldada; Lawrence W. Shacklette; Robert A. Norwood; James T. Yardley

1997-01-01

208

New ring-opening polymerizations for copolymers having controlled microstructures  

Microsoft Academic Search

Various prestructured cyclic monomers were synthesized and polymerized to construct the copolymers of controlled mer sequence. Vinylcyclopropanes with substituents –CN, –CO2R and –C6H5 were prepared and radically ring-opening polymerized in 1,5-fashion to obtain high molecular weight polymers. Anionic polymerization of these monomers gave 3,5-polymers with vinyl pendent group. 2-Phenyl-3-vinyloxirane polymerized radically by C–C scission. These polymerization behaviors of 3-membered ring

I Cho

2000-01-01

209

Retroviral vectors for gene transfer.  

PubMed

INTRODUCTIONRetroviral vectors from the ?-retrovirus genus were the first retroviral vectors to be developed. They have been called oncoretroviral vectors or simple retroviral vectors because of their derivation from oncogenic retroviruses having a simple gag-pol-env genome structure. Later additions to the retroviral vector family include the lentiviral and foamy viral vectors derived from more complex retroviruses that contain multiple accessory genes in addition to the standard gag-pol-env genes. This article describes the advantages and disadvantages of retroviral vectors for gene therapy. It also discusses the issues that must be considered in designing retroviral vectors and in choosing retroviral packaging cell lines. PMID:21356814

Cornetta, Kenneth; Pollok, Karen E; Miller, A Dusty

2008-01-01

210

The tempered polymerization of human neuroserpin.  

PubMed

Neuroserpin, a member of the serpin protein superfamily, is an inhibitor of proteolytic activity that is involved in pathologies such as ischemia, Alzheimer's disease, and Familial Encephalopathy with Neuroserpin Inclusion Bodies (FENIB). The latter belongs to a class of conformational diseases, known as serpinopathies, which are related to the aberrant polymerization of serpin mutants. Neuroserpin is known to polymerize, even in its wild type form, under thermal stress. Here, we study the mechanism of neuroserpin polymerization over a wide range of temperatures by different techniques. Our experiments show how the onset of polymerization is dependent on the formation of an intermediate monomeric conformer, which then associates with a native monomer to yield a dimeric species. After the formation of small polymers, the aggregation proceeds via monomer addition as well as polymer-polymer association. No further secondary mechanism takes place up to very high temperatures, thus resulting in the formation of neuroserpin linear polymeric chains. Most interesting, the overall aggregation is tuned by the co-occurrence of monomer inactivation (i.e. the formation of latent neuroserpin) and by a mechanism of fragmentation. The polymerization kinetics exhibit a unique modulation of the average mass and size of polymers, which might suggest synchronization among the different processes involved. Thus, fragmentation would control and temper the aggregation process, instead of enhancing it, as typically observed (e.g.) for amyloid fibrillation. PMID:22412873

Noto, Rosina; Santangelo, Maria Grazia; Ricagno, Stefano; Mangione, Maria Rosalia; Levantino, Matteo; Pezzullo, Margherita; Martorana, Vincenzo; Cupane, Antonio; Bolognesi, Martino; Manno, Mauro

2012-01-01

211

The Tempered Polymerization of Human Neuroserpin  

PubMed Central

Neuroserpin, a member of the serpin protein superfamily, is an inhibitor of proteolytic activity that is involved in pathologies such as ischemia, Alzheimer's disease, and Familial Encephalopathy with Neuroserpin Inclusion Bodies (FENIB). The latter belongs to a class of conformational diseases, known as serpinopathies, which are related to the aberrant polymerization of serpin mutants. Neuroserpin is known to polymerize, even in its wild type form, under thermal stress. Here, we study the mechanism of neuroserpin polymerization over a wide range of temperatures by different techniques. Our experiments show how the onset of polymerization is dependent on the formation of an intermediate monomeric conformer, which then associates with a native monomer to yield a dimeric species. After the formation of small polymers, the aggregation proceeds via monomer addition as well as polymer-polymer association. No further secondary mechanism takes place up to very high temperatures, thus resulting in the formation of neuroserpin linear polymeric chains. Most interesting, the overall aggregation is tuned by the co-occurrence of monomer inactivation (i.e. the formation of latent neuroserpin) and by a mechanism of fragmentation. The polymerization kinetics exhibit a unique modulation of the average mass and size of polymers, which might suggest synchronization among the different processes involved. Thus, fragmentation would control and temper the aggregation process, instead of enhancing it, as typically observed (e.g.) for amyloid fibrillation. PMID:22412873

Ricagno, Stefano; Mangione, Maria Rosalia; Levantino, Matteo; Pezzullo, Margherita; Martorana, Vincenzo; Cupane, Antonio; Bolognesi, Martino; Manno, Mauro

2012-01-01

212

Polymeric conjugates for drug delivery  

PubMed Central

The field of polymer therapeutics has evolved over the past decade and has resulted in the development of polymer-drug conjugates with a wide variety of architectures and chemical properties. Whereas traditional non-degradable polymeric carriers such as poly(ethylene glycol) (PEG) and N-(2-hydroxypropyl methacrylamide) (HPMA) copolymers have been translated to use in the clinic, functionalized polymer-drug conjugates are increasingly being utilized to obtain biodegradable, stimuli-sensitive, and targeted systems in an attempt to further enhance localized drug delivery and ease of elimination. In addition, the study of conjugates bearing both therapeutic and diagnostic agents has resulted in multifunctional carriers with the potential to both “see and treat” patients. In this paper, the rational design of polymer-drug conjugates will be discussed followed by a review of different classes of conjugates currently under investigation. The design and chemistry used for the synthesis of various conjugates will be presented with additional comments on their potential applications and current developmental status. PMID:22707853

Larson, Nate; Ghandehari, Hamidreza

2012-01-01

213

Polymeric waveguide Fabry Perot resonators  

NASA Astrophysics Data System (ADS)

Optical microcavities are used in variety of applications ranging from sensors to lasers and signal routing in high volume communication networks. Achieving a high quality factor (Q) is necessary for achieving the higher sensitivity in sensing applications and for narrow linewidth light emission in most lasing applications. In this work, we propose a new way for achieving a higher quality factor in thin film, Fabry-Perot polymeric optical resonators. We show that lateral photon confinement in a vertical Fabry-Perot microcavities can be achieved by optical writing of a refractive index profile utilizing our UV-sensitive polymer. This method can improve the quality factor by one or more orders of magnitudes. In order to demonstrate this improvement, the device has been fabricated. The fabricated device consists of two dielectric Bragg reflectors with a layer of 100 ?m thick polymer layer between them. The polymer is a thiol-ene/methacrylate photopolymer whose optical index can be modified utilizing standard photo-lithography processes. The refractive index of this polymer can be modified utilizing standard photo-lithography processes. The measured finesse of the fabricated device was 692 and the quality factor was 55000. The achieved finesse combined with the flexible polymer layer allows this device to be used as an ultrasound detector in optical micromachined ultrasound transducers (OMUT).

Tadayon, Mohammad Amin; Baylor, Martha-Elizabeth; Ashkenazi, Shai

2014-03-01

214

Targeted adenoviral vectors  

NASA Astrophysics Data System (ADS)

The practical implementation of gene therapy in the clinical setting mandates gene delivery vehicles, or vectors, capable of efficient gene delivery selectively to the target disease cells. The utility of adenoviral vectors for gene therapy is restricted by their dependence on the native adenoviral primary cellular receptor for cell entry. Therefore, a number of strategies have been developed to allow CAR-independent infection of specific cell types, including the use of bispecific conjugates and genetic modifications to the adenoviral capsid proteins, in particular the fibre protein. These targeted adenoviral vectors have demonstrated efficient gene transfer in vitro , correlating with a therapeutic benefit in preclinical animal models. Such vectors are predicted to possess enhanced efficacy in human clinical studies, although anatomical barriers to their use must be circumvented.

Douglas, Joanne T.

215

Light Vector Mesons  

E-print Network

This article reviews the current status of experimental results obtained in the measurement of light vector mesons produced in proton-proton and heavy ion collisions at different energies. The review is focused on two phenomena related to the light vector mesons; the modification of the spectral shape in search of Chiral symmetry restoration and suppression of the meson production in heavy ion collisions. The experimental results show that the spectral shape of light vector mesons are modified compared to the parameters measured in vacuum. The nature and the magnitude of the modification depends on the energy density of the media in which they are produced. The suppression patterns of light vector mesons are different from the measurements of other mesons and baryons. The mechanisms responsible for the suppression of the mesons are not yet understood. Systematic comparison of existing experimental results points to the missing data which may help to resolve the problem.

Alexander Milov

2008-12-21

216

Baculovirus as vaccine vectors.  

PubMed

Application of viral vectors derived from human viruses to mediate immune response in animals and humans has been greatly hampered by the problems associated with pre-existing immunity and associated toxicities. Among few non-human viral vectors, baculovirus has now evolved as a novel tool for vaccine vector development. With broad tissue tropism and expanded bio-safety profile suitably supplemented with intrinsic immunostimulatory properties, baculovirus has now attained a niche position in the arena of vaccine development. Recombinant envelope-modified baculovirus equipped with novel shuttle promoters for in vivo transduction has shown promising results in several animal models. Baculovirus mediated induction of systemic and mucosal immune responses through intranasal or oral administration has now open an entirely new way for the development of new generation vaccines. Gaining additional insight into the baculovirus biology and its interaction with non-native hosts will certainly promote this human-friendly virus as a potential vector for clinical applications. PMID:20394572

Madhan, Selvaraj; Prabakaran, Mookkan; Kwang, Jimmy

2010-06-01

217

Generalizing the Poynting Vector  

NASA Astrophysics Data System (ADS)

A very general energy conservation law derived from a Lagrangian theory of dielectric crystals is presented. It includes energy propagation from electromagnetic, spin, and acoustic waves. Both linear and nonlinear waves are included as well as various polaritonic combinations. Waves involving nonlocal (wave-vector-dispersive) interactions are also included. An example of the latter for which the Poynting vector is invalid, but which is correctly handled by this theory, is presented.

Nelson, D. F.

1996-06-01

218

Bloch vector projection noise  

NASA Technical Reports Server (NTRS)

In the optical measurement of the Bloch vector components describing a system of N two-level atoms, the quantum fluctuations in these components are coupled into the measuring optical field. This paper develops the quantum theory of optical measurement of Bloch vector projection noise. The preparation and probing of coherence in an effective two-level system consisting of the two ground states in an atomic three-level lambda-scheme are analyzed.

Wang, Li-Jun; Bacon, A. M.; Zhao, H.-Z.; Thomas, J. E.

1994-01-01

219

New Core-Shell Nanoparticules for the Intravenous Delivery of siRNA to Experimental Thyroid Papillary Carcinoma  

Microsoft Academic Search

Purpose  Development of efficient in vivo delivery nanodevices remains a major challenge to achieve clinical application of siRNA. The present study refers to the\\u000a conception of core-shell nanoparticles aiming to make possible intravenous administration of chemically unmodified siRNA oriented\\u000a towards the junction oncogene of the papillary thyroid carcinoma.\\u000a \\u000a \\u000a \\u000a \\u000a Methods  Nanoparticles were prepared by redox radical emulsion polymerization of isobutylcyanoacrylate and isohexylcyanoacrylate with

Henri de Martimprey; Jean-Rémi Bertrand; Claude Malvy; Patrick Couvreur; Christine Vauthier

2010-01-01

220

Combustion Synthesis of Nanoparticulate LiMgxMn1-xPO4 (x=0, 0.1, 0.2) Carbon Composites  

SciTech Connect

A combustion synthesis technique was used to prepare nanoparticulate LiMgxMn1-xPO4 (x=0, 0.1,0.2)/carbon composites. Powders consisted of carbon-coated particles about 30 nm in diameter, which were partly agglomerated into larger secondary particles. The utilization of the active materials in lithium cells depended most strongly upon the post-treatment and the Mg content, and was not influenced by the amount of carbon. Best results were achieved with a hydrothermally treated LiMg0.2Mn0.8PO4/C composite, which exhibited close to 50percent utilization of the theoretical capacity at a C/2 discharge rate.

Doeff, Marca M; Chen, Jiajun; Conry, Thomas E.; Wang, Ruigang; Wilcox, James; Aumentado, Albert

2009-12-14

221

Thermal conductivity of a polymerizing liquid  

NASA Astrophysics Data System (ADS)

Thermal conductivity ? of seven polymerizing liquids has been measured in real time at different temperatures, and calorimetry and dielectric spectroscopy of one liquid are performed to help interpret the results. As a covalently bonded linear chain or a network structure in the liquid grows, ? of the Debye equation initially increases with the polymerization time tpolym as the molecular weight, density, and sound velocity increase, as on cooling a liquid. The measured ? reaches a maximum and then decreases, thus showing a peak at a certain tpolym and finally becomes constant, which is not the true behavior of steady state ?. The dielectric relaxation time of the covalently bonded structure at the tpolym for the ? peak is less than 5s and the extent of polymerization is below the vitrification plateau value. The peak height increases when the pulse time for ? measurement is increased. An increase in the liquid's temperature shifts the ? peak to a shorter tpolym. Liquid compositions polymerizing rapidly show a similar shift, and those polymerizing slowly or whose viscosity does not reach a high enough value show a small ? peak or none. The ? peak may be an artifact of the time dependence of heat capacity during the pulse time used for the ? measurement, as proposed for glasses and supercooled liquids, similar to the changes in other properties observed as an artifact of kinetic freezing/unfreezing. For a polymerizing liquid, the peak may additionally arise when the rate of increase in the elastic modulus becomes equal to the rate of decrease in equilibrium Cp. In either case, its appearance does not distinguish the Brownian motions' slowing on polymerization from that on cooling or compressing a liquid.

Venkateshan, K.; Johari, G. P.

2006-08-01

222

A new method to align liquid crystal molecules by linear photo-polymerization for liquid crystal display  

Microsoft Academic Search

A new technique to uniformly align liquid crystal molecules is presented. The technique is based on producing an anisotropic surface on the glass substrate coated with photo-polymers by photo-polymerization of linear polarized UV-light. The orientation of liquid crystal molecules is governed by the direction of the polarized vector of UV-light. Using this method, we have studied the photo-polymer PSi-CM aligning

Liang Zhao-Yan; Fang Kun; Xuan Li; Huang Xi-Min; Ding Bao-Quan; Lu Ran; Zhao Ying-Ying

2000-01-01

223

On noninferior performance index vectors  

Microsoft Academic Search

The noninferior vector index problem of optimal control theory is investigated in an effort to establish some basic properties of the noninferior index surface in the generalN-dimensional index problem. The vector performance index problem is first converted to a family of scalar index problems by forming an auxiliary scalar index as a function of the vector index and a vector

R. W. Reid; S. J. Citron

1971-01-01

224

Generalizing the Poynting Vector  

NASA Astrophysics Data System (ADS)

An examination of the Poynting theorem reveals that the Poynting vector E × H represents energy flow in an electromagnetic wave only when D is proportional to E and B to H. Thus the Poynting theorem does not apply to interactions for which the constitutive relations mix electric and magnetic variables, are nonlinear in the fields, involve derivatives of the fields (nonlocal or wavevector-dispersive interactions), or involve nonelectromagnetic fields such as an acoustic field needed for acoustooptic diffraction. To obtain an energy flow vector that includes all these possibilities it is necessary to treat the material medium as fundamentally as the electromagnetic field, i.e. with equations of motion for all of the longwavelength (continuum) modes of excitation of the medium -- acoustic, optic (ionic and, to a certain degree, electronic) and spin. We have used a Lagrangian theory of dielectric crystals to produce an energy conservation statement whose energy flow vector includes all of the above generalizations. We illustrate the power of the new energy flow vector by applying it to two linear optical interactions (optical activity and exciton-polariton propagation, both wavevector-dispersive interactions) for which the Poynting vector fails.

Nelson, D. F.

1996-05-01

225

Delivery of antibiotics with polymeric particles.  

PubMed

Despite the wide use of antibiotics, bacterial infection is still one of the leading causes of hospitalization and mortality. The clinical failure of antibiotic therapy is linked with low bioavailability, poor penetration to bacterial infection sites, and the side effects of antibiotics, as well as the antibiotic resistance properties of bacteria. Antibiotics encapsulated in nanoparticles or microparticles made up of a biodegradable polymer have shown great potential in replacing the administration of antibiotics in their "free" form. Polymeric particles provide protection to antibiotics against environmental deactivation and alter antibiotic pharmacokinetics and biodistribution. Polymeric particles can overcome tissue and cellular barriers and deliver antibiotics into very dense tissues and inaccessible target cells. Polymeric particles can be modified to target or respond to particular tissues, cells, and even bacteria, and thereby facilitate the selective concentration or release of the antibiotic at infection sites, respectively. Thus, the delivery of antibiotics with polymeric particles augments the level of the bioactive drug at the site of infection while reducing the dosage and the dosing frequency. The end results are improved therapeutic effects as well as decreased "pill burden" and drug side effects in patients. The main objective of this review is to analyze recent advances and current perspectives in the use of polymeric antibiotic delivery systems in the treatment of bacterial infection. PMID:24548540

Xiong, Meng-Hua; Bao, Yan; Yang, Xian-Zhu; Zhu, Yan-Hua; Wang, Jun

2014-11-30

226

Polymeric filament thinning and breakup in microchannels  

E-print Network

The effects of elasticity on filament thinning and breakup are investigated in microchannel cross flow. When a viscous solution is stretched by an external immiscible fluid, a low 100 ppm polymer concentration strongly affects the breakup process, compared to the Newtonian case. Qualitatively, polymeric filaments show much slower evolution, and their morphology features multiple connected drops. Measurements of filament thickness show two main temporal regimes: flow- and capillary-driven. At early times both polymeric and Newtonian fluids are flow-driven, and filament thinning is exponential. At later times, Newtonian filament thinning crosses over to a capillary-driven regime, in which the decay is algebraic. By contrast, the polymeric fluid first crosses over to a second type of flow-driven behavior, in which viscoelastic stresses inside the filament become important and the decay is again exponential. Finally, the polymeric filament becomes capillary-driven at late times with algebraic decay. We show that the exponential flow thinning behavior allows a novel measurement of the extensional viscosities of both Newtonian and polymeric fluids.

P. E. Arratia; J. P. Gollub; D. J. Durian

2007-03-15

227

Structural basis of reverse nucleotide polymerization.  

PubMed

Nucleotide polymerization proceeds in the forward (5'-3') direction. This tenet of the central dogma of molecular biology is found in diverse processes including transcription, reverse transcription, DNA replication, and even in lagging strand synthesis where reverse polymerization (3'-5') would present a "simpler" solution. Interestingly, reverse (3'-5') nucleotide addition is catalyzed by the tRNA maturation enzyme tRNA(His) guanylyltransferase, a structural homolog of canonical forward polymerases. We present a Candida albicans tRNA(His) guanylyltransferase-tRNA(His) complex structure that reveals the structural basis of reverse polymerization. The directionality of nucleotide polymerization is determined by the orientation of approach of the nucleotide substrate. The tRNA substrate enters the enzyme's active site from the opposite direction (180° flip) compared with similar nucleotide substrates of canonical 5'-3' polymerases, and the finger domains are on opposing sides of the core palm domain. Structural, biochemical, and phylogenetic data indicate that reverse polymerization appeared early in evolution and resembles a mirror image of the forward process. PMID:24324136

Nakamura, Akiyoshi; Nemoto, Taiki; Heinemann, Ilka U; Yamashita, Keitaro; Sonoda, Tomoyo; Komoda, Keisuke; Tanaka, Isao; Söll, Dieter; Yao, Min

2013-12-24

228

Mixing in polymeric microfluidic devices.  

SciTech Connect

This SAND report describes progress made during a Sandia National Laboratories sponsored graduate fellowship. The fellowship was funded through an LDRD proposal. The goal of this project is development and characterization of mixing strategies for polymeric microfluidic devices. The mixing strategies under investigation include electroosmotic flow focusing, hydrodynamic focusing, physical constrictions and porous polymer monoliths. For electroosmotic flow focusing, simulations were performed to determine the effect of electroosmotic flow in a microchannel with heterogeneous surface potential. The heterogeneous surface potential caused recirculations to form within the microchannel. These recirculations could then be used to restrict two mixing streams and reduce the characteristic diffusion length. Maximum mixing occurred when the ratio of the mixing region surface potential to the average channel surface potential was made large in magnitude and negative in sign, and when the ratio of the characteristic convection time to the characteristic diffusion time was minimized. Based on these results, experiments were performed to evaluate the manipulation of surface potential using living-radical photopolymerization. The material chosen to manipulate typically exhibits a negative surface potential. Using living-radical surface grafting, a positive surface potential was produced using 2-(Dimethylamino)ethyl methacrylate and a neutral surface was produced using a poly(ethylene glycol) surface graft. Simulations investigating hydrodynamic focusing were also performed. For this technique, mixing is enhanced by using a tertiary fluid stream to constrict the two mixing streams and reduce the characteristic diffusion length. Maximum mixing occurred when the ratio of the tertiary flow stream flow-rate to the mixing streams flow-rate was maximized. Also, like the electroosmotic focusing mixer, mixing was also maximized when the ratio of the characteristic convection time to the characteristic diffusion time was minimized. Physical constrictions were investigated through simulations. The results show that the maximum mixing occurs when the height of the mixing region is minimized. Finally, experiments were performed to determine the effectiveness of using porous polymer monoliths to enhance mixing. The porous polymer monoliths were constructed using a monomer/salt paste. Two salt crystal size ranges were used; 75 to 106 microns and 53 to 180 microns. Mixing in the porous polymer monoliths fabricated with the 75 to 106 micron salt crystal size range was six times higher than a channel without a monolith. Mixing in the monolith fabricated with the 53 to 180 micron salt crystal size range was nine times higher.

Schunk, Peter Randall; Sun, Amy Cha-Tien; Davis, Robert H. (University of Colorado at Boulder, Boulder, CO); Brotherton, Christopher M. (University of Colorado at Boulder, Boulder, CO)

2006-04-01

229

Vector financial rogue waves  

NASA Astrophysics Data System (ADS)

The coupled nonlinear volatility and option pricing model presented recently by Ivancevic is investigated, which generates a leverage effect, i.e., stock volatility is (negatively) correlated to stock returns, and can be regarded as a coupled nonlinear wave alternative of the Black-Scholes option pricing model. In this Letter, we analytically propose vector financial rogue waves of the coupled nonlinear volatility and option pricing model without an embedded w-learning. Moreover, we exhibit their dynamical behaviors for chosen different parameters. The vector financial rogue wave (rogon) solutions may be used to describe the possible physical mechanisms for the rogue wave phenomena and to further excite the possibility of relative researches and potential applications of vector rogue waves in the financial markets and other related fields.

Yan, Zhenya

2011-11-01

230

Self-assembly of DNA-polymer complexes using template polymerization.  

PubMed Central

The self-assembly of supramolecular complexes of nucleic acids and polymers is of relevance to several biological processes including viral and chromatin formation as well as gene therapy vector design. We now show that template polymerization facilitates condensation of DNA into particles that are <150 nm in diameter. Inclusion of a poly(ethylene glycol)-containing monomer prevents aggregation of these particles. The DNA within the particles remains biologically active and can express foreign genes in cells. The formation or breakage of covalent bonds has until now not been employed to compact DNA into artificial particles. PMID:9722638

Trubetskoy, V S; Budker, V G; Hanson, L J; Slattum, P M; Wolff, J A; Hagstrom, J E

1998-01-01

231

Universal metastability of sickle hemoglobin polymerization  

NASA Astrophysics Data System (ADS)

Sickle hemoglobin (HbS) is a natural mutation of the normal hemoglobin (HbA) found in the red blood cells of human body. Polymerization of HbS occurs when the concentration of deoxyHbS exceeds a well-defined solubility, which is the underlying cause of the Sickle Cell Disease. It has long been assumed that thermodynamic equilibrium is reached when polymerization comes to an end. However, in this thesis we demonstrate that in confined volume as well as in bulk solution, HbS polymerization terminates prematurely, leaving the solution in a metastable state. A newly developed Reservoir method as well as modulated excitation method were adopted for the study. This discovery of universal metastability gives us new insights into understanding the mechanism of sickle cell disease.

Weng, Weijun

232

Attempting a classification for electrical polymeric actuators  

NASA Astrophysics Data System (ADS)

Polymeric actuators, electroactive polymer actuators, electromechanical polymeric actuators, artificial muscles, and other, are usual expressions to name actuators developed during the last 15-20 years based on interactions between the electric energy and polymer films. The polymeric actuators can be divided into two main fields: electromechanical actuators working by electrostatic interactions between the polymer and the applied electric fields, and electrochemomechanical actuators, or reactive actuators, working by an electrochemical reaction driven by the flowing electric current. The electromechanical actuators can be classified into electrostrictive, piezoelectric, ferroelectric, electrostatic and electrokinetic. They can include a solvent (wet) or not (dry), or they can include a salt or not. Similitude and differences related to the rate and position control or to the possibility or not to include sensing abilities are discussed.

Otero, T. F.; López Cascales, J.; Fernández-Romero, A. J.

2007-04-01

233

Laser microstructuring for fabricating superhydrophobic polymeric surfaces  

NASA Astrophysics Data System (ADS)

In this paper we show the fabrication of hydrophobic polymeric surfaces through laser microstructuring. By using 70-ps pulses from a Q-switched and mode-locked Nd:YAG laser at 532 nm, we were able to produce grooves with different width and separation, resulting in square-shaped pillar patterns. We investigate the dependence of the morphology on the surface static contact angle for water, showing that it is in agreement with the Cassie-Baxter model. We demonstrate the fabrication of a superhydrophobic polymeric surface, presenting a water contact angle of 157°. The surface structuring method presented here seems to be an interesting option to control the wetting properties of polymeric surfaces.

Cardoso, M. R.; Tribuzi, V.; Balogh, D. T.; Misoguti, L.; Mendonça, C. R.

2011-02-01

234

Bunyavirus-vector interactions.  

PubMed

The Bunyaviridae family is comprised of more than 350 viruses, of which many within the Hantavirus, Orthobunyavirus, Nairovirus, Tospovirus, and Phlebovirus genera are significant human or agricultural pathogens. The viruses within the Orthobunyavirus, Nairovirus, and Phlebovirus genera are transmitted by hematophagous arthropods, such as mosquitoes, midges, flies, and ticks, and their associated arthropods not only serve as vectors but also as virus reservoirs in many cases. This review presents an overview of several important emerging or re-emerging bunyaviruses and describes what is known about bunyavirus-vector interactions based on epidemiological, ultrastructural, and genetic studies of members of this virus family. PMID:25402172

Horne, Kate McElroy; Vanlandingham, Dana L

2014-11-01

235

Fabrication of triazinedithiol functional polymeric nanofilm by potentiostatic polymerization on aluminum surface  

NASA Astrophysics Data System (ADS)

The functional polymeric nanofilm of 6-(N-allyl-1,1,2,2-tetrahydroperfluorodecyl)amino-1,3,5-triazine-2,4-dithiol monosodium (AF17N) was prepared on pure aluminum surface by potentiostatic polymerization at different potentials. The thickness and weight of polymeric nanofilm increased proportionally to electro-polymerization potential following linear equation. The chemical structure of nanofilm was characterized by Fourier transform-infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Adsorption peaks in FT-IR and C1s, N1s, S2p, F1s and Al2p peaks in XPS spectra indicated that the polymeric nanofilm was poly(6-(N-allyl-1,1,2,2-tetrahydroperfluorodecyl)amino-1,3,5-triazine-2,4-disulfide) (PAF17). The morphologies of polymeric nanofilm were also observed by atomic force microscopy (AFM). All the results showed that the optimal electro-polymerization potential and time were 8 V and 20 s, respectively. Uniform and compact nanofilm of PAF17 could be obtained under these conditions. It is expected that this technique will be applied in the preparation of lubricating, dielectric and hydrophobic surface on aluminum substrate.

Wang, Fang; Wang, Yabin; Li, Yanni; Wang, Qian

2011-01-01

236

Polymeric matrix materials for infrared metamaterials  

DOEpatents

A polymeric matrix material exhibits low loss at optical frequencies and facilitates the fabrication of all-dielectric metamaterials. The low-loss polymeric matrix material can be synthesized by providing an unsaturated polymer, comprising double or triple bonds; partially hydrogenating the unsaturated polymer; depositing a film of the partially hydrogenated polymer and a crosslinker on a substrate; and photopatterning the film by exposing the film to ultraviolet light through a patterning mask, thereby cross-linking at least some of the remaining unsaturated groups of the partially hydrogenated polymer in the exposed portions.

Dirk, Shawn M; Rasberry, Roger D; Rahimian, Kamyar

2014-04-22

237

Polymerization Initiated at the Sidewalls of Carbon Nanotubes  

NASA Technical Reports Server (NTRS)

A process has been developed for growing polymer chains via anionic, cationic, or radical polymerization from the side walls of functionalized carbon nanotubes, which will facilitate greater dispersion in polymer matrices, and will greatly enhance reinforcement ability in polymeric material.

Tour, James M.; Hudson, Jared L.

2011-01-01

238

Strategy for construction of polymerized volume data sets  

E-print Network

This thesis develops a strategy for polymerized volume data set construction. Given a volume data set defined over a regular three-dimensional grid, a polymerized volume data set (PVDS) can be defined as follows: edges between adjacent vertices...

Aragonda, Prathyusha

2006-04-12

239

Support vector machines  

NASA Technical Reports Server (NTRS)

Support Vector Machines (SVMs) are a type of supervised learning algorith,, other examples of which are Artificial Neural Networks (ANNs), Decision Trees, and Naive Bayesian Classifiers. Supervised learning algorithms are used to classify objects labled by a 'supervisor' - typically a human 'expert.'.

Garay, Michael J.; Mazzoni, Dominic; Davies, Roger; Wagstaff, Kiri

2004-01-01

240

Vectorizing Cartoon Animations  

Microsoft Academic Search

We present a system for vectorizing 2D raster format cartoon animations. The output animations are visually flicker free, smaller in file size, and easy to edit. We identify decorative lines separately from colored regions. We use an accurate and semantically meaningful image decomposition algorithm, supporting an arbitrary color model for each region. To ensure temporal coherence in the output, we

Song-hai Zhang; Tao Chen; Yi-fei Zhang; Shi-min Hu; Ralph R. Martin

2009-01-01

241

Self-Condensing Vinyl Polymerization: An Approach to Dendritic Materials  

Microsoft Academic Search

Self-condensing vinyl polymerization was used to produce dendritic polymers with both highly branched structures and numerous reactive groups. A vinyl monomer will undergo self-polymerization if it contains a pendant group that can be transformed into an initiating moiety by the action of an external stimulus. The self-polymerization combines features of a classical vinyl polymerization process with those of a polycondensation

Jean M. J. Frechet; Masahiro Henmi; Ivan Gitsov; Sadahito Aoshima; Marc R. Leduc; R. Bernard Grubbs

1995-01-01

242

Probing polymerization forces by using actin-propelled lipid vesicles  

E-print Network

Probing polymerization forces by using actin-propelled lipid vesicles Arpita Upadhyaya, Jeffrey R with the Listeria monocytogenes viru- lence factor ActA are propelled by actin polymerization. The polymerization and Shigella flexneri recruit the host cell's actin to propel themselves through the cytoplasm. Studies

van Oudenaarden, Alexander

243

Stall force of polymerizing microtubules and filament bundles  

E-print Network

OFFPRINT Stall force of polymerizing microtubules and filament bundles J. Krawczyk and J. Kierfeld, 93 (2011) 28006 www.epljournal.org doi: 10.1209/0295-5075/93/28006 Stall force of polymerizing investigate stall force and polymerization kinetics of rigid protofilaments in a microtubule or interacting

Kierfeld, Jan

244

Characterization of Electroinitiated and Radiation Polymerized Poly(Butadiene Sulfone)  

Microsoft Academic Search

Polymerization of butadiene sulfone was accomplished by using two different methods. The first method involves electrochemical polymerization of the monomer using the constant potential electrolysis technique. Oxidation of the monomer under nitrogen atmosphere in an acetonitrile-tetrabutylammonium tetrafluoroborate system yields brown, tarry polymers. On the other hand, the second initiation method, which was radiation polymerization, yields white, powdery polymers. Structural analyses

B. Hacioglu; S. Suzer; U. Akbulut; L. Toppare; P. Aybar; J. H. P. Utley

1991-01-01

245

RNA-Catalyzed RNA Polymerization: Accurate and  

E-print Network

the type of polymerization needed for RNA replication. The ribozyme uses nucleoside triphosphates of the appeal of this hypothesis comes from the realization that ribozymes would have been far easier], replication of a ribozyme requires only a single macromolecular activity: an RNA-dependent RNA polymerase

Bartel, David

246

Biodegradable polymeric nanoparticles as drug delivery devices  

Microsoft Academic Search

This review presents the most outstanding contributions in the field of biodegradable polymeric nanoparticles used as drug delivery systems. Methods of preparation, drug loading and drug release are covered. The most important findings on surface modification methods as well as surface characterization are covered from 1990 through mid-2000.

Kumaresh S Soppimath; Tejraj M Aminabhavi; Anandrao R Kulkarni; Walter E Rudzinski

2001-01-01

247

A capacitively coupled polymeric internal antenna  

Microsoft Academic Search

A capacitively-coupled polymeric internal antenna is introduced for Bluetooth or GPS applications. Such an antenna can be easily fabricated on a flexible film substrate and attached to the inside surface of the plastic housing of a portable wireless device, such as a PDA. The proposed antenna saves critical space on the printed circuit board (PCB) and eliminates the need for

Khan M. Z. Shams; M. Ali

2004-01-01

248

Composite polymeric/ceramic pervaporation membrane reactor  

SciTech Connect

We have investigated the preparation of composite polymeric/ceramic membranes. We have studied the effect of the preparation techniques on the properties of these composite membranes. A model has been developed to describe the transport characteristics. We have used these membranes in pervaporation membrane reactor applications. Our experimental data and modeling results will be presented.

Zhu, Y.; Tsotsis, T.T. [Univ. of Southern California, Los Angeles, CA (United States)

1995-12-01

249

Microwave welding of polymeric-microfluidic devices  

Microsoft Academic Search

This paper describes a novel technique for bonding polymeric-microfluidic devices using microwave energy and a conductive polymer (polyaniline). The bonding is achieved by patterning the polyaniline features at the polymer joint interface by filling of milled microchannels. The absorbed electromagnetic energy is then converted into heat, facilitating the localized microwave bonding of two polymethylmethacrylate (PMMA) substrates. A coaxial open-ended probe

A. A. Yussuf; I. Sbarski; J. P. Hayes; M. Solomon; N. Tran

2005-01-01

250

Thermostatistics of the polymeric ideal gas  

NASA Astrophysics Data System (ADS)

In this paper, we formulate statistical mechanics of the polymerized systems in the semiclassical regime. On the corresponding polymeric symplectic manifold, we set up a noncanonical coordinate system in which all of the polymeric effects are summarized in the density of states. Since we show that the polymeric effects only change the number of microstates of a statistical system, working in this coordinate is quite reasonable from the statistical point of view. The results show that the number of microstates decreases due to existence of an upper bound for the momentum of the test particles in the polymer framework. We obtain a corresponding canonical partition function by means of the deformed density of states. By using the partition function, we study thermodynamics of the ideal gas in the polymer framework and show that our results are in good agreement with those that arise from the full quantum consideration at high temperature, and they coincide with their usual counterpart in the limit of low temperature.

Gorji, M. A.; Nozari, K.; Vakili, B.

2014-08-01

251

Impregnated metal-polymeric functional beads  

NASA Technical Reports Server (NTRS)

Amine containing polymeric microspheres such as polyvinyl pyridine are complexed with metal salts or acids containing metals such as gold, platinum or iron. After reduction with sodium borohydride, the salt is reduced to finely divided free metal or metal oxides, useful as catalysts. Microspheres containing covalent bonding sites can be used for labeling or separating proteins.

Rembaum, Alan (Inventor); Volksen, Willi (Inventor)

1980-01-01

252

Fractal vector measures and vector calculus on planar fractal domains  

Microsoft Academic Search

We define an abstract framework for self-similar vector-valued Borel measures on a compact space X based upon a formulation of Iterated Function Systems (IFS) on such measures. This IFS method permits the construction of tangent and normal vector measures to planar fractal curves. Line integrals of smooth vector fields over planar fractal curves may then be defined. These line integrals

F. Mendivil; E. R. Vrscay

2002-01-01

253

Polymerization of lactams: 97. Anionic polymerization of ?-caprolactam activated by esters  

Microsoft Academic Search

The anionic polymerization of ?-caprolactam initiated with 0.5mol% ethyl magnesium bromide in the presence of cycloaliphatic esters (lactones), such as ?-butyrolactone, ?-valerolactone and ?-caprolactone, has been studied in the temperature range 150–190°C and concentration up to 5mol%. To explain reaction mechanism, the polymerizations carried out in the presence n-butyl acetate and dimethyl terephthalate were also evaluated. The apparent rate constants

Jan Merna; Daniela Chromcová; Ji?í Brožek; Jan Roda

2006-01-01

254

Insect Vectors of Human Pathogens  

NSDL National Science Digital Library

Four orders of insects (Hemiptera, Phthiraptera, Diptera, and Siphonaptera) are covered detailing vector species along with their pathogens of human importance. Links to pathogens as well as vectors are highlighted (some of these are CDC, and WHO).

0000-00-00

255

Probabilistic classification vector machines.  

PubMed

In this paper, a sparse learning algorithm, probabilistic classification vector machines (PCVMs), is proposed. We analyze relevance vector machines (RVMs) for classification problems and observe that adopting the same prior for different classes may lead to unstable solutions. In order to tackle this problem, a signed and truncated Gaussian prior is adopted over every weight in PCVMs, where the sign of prior is determined by the class label, i.e., +1 or -1. The truncated Gaussian prior not only restricts the sign of weights but also leads to a sparse estimation of weight vectors, and thus controls the complexity of the model. In PCVMs, the kernel parameters can be optimized simultaneously within the training algorithm. The performance of PCVMs is extensively evaluated on four synthetic data sets and 13 benchmark data sets using three performance metrics, error rate (ERR), area under the curve of receiver operating characteristic (AUC), and root mean squared error (RMSE). We compare PCVMs with soft-margin support vector machines (SVM(Soft)), hard-margin support vector machines (SVM(Hard)), SVM with the kernel parameters optimized by PCVMs (SVM(PCVM)), relevance vector machines (RVMs), and some other baseline classifiers. Through five replications of twofold cross-validation F test, i.e., 5 x 2 cross-validation F test, over single data sets and Friedman test with the corresponding post-hoc test to compare these algorithms over multiple data sets, we notice that PCVMs outperform other algorithms, including SVM(Soft), SVM(Hard), RVM, and SVM(PCVM), on most of the data sets under the three metrics, especially under AUC. Our results also reveal that the performance of SVM(PCVM) is slightly better than SVM(Soft), implying that the parameter optimization algorithm in PCVMs is better than cross validation in terms of performance and computational complexity. In this paper, we also discuss the superiority of PCVMs' formulation using maximum a posteriori (MAP) analysis and margin analysis, which explain the empirical success of PCVMs. PMID:19398403

Chen, Huanhuan; Tino, Peter; Yao, Xin

2009-06-01

256

Polymerization by classical and frustrated Lewis pairs.  

PubMed

Main-group classical and frustrated Lewis pairs (CLPs and FLPs) comprising strong Lewis acids (LAs) and strong Lewis bases (LBs) are highly active for polymerization of conjugated polar alkenes, affording typically high molecular weight polymers with relatively narrow molecular weight distributions. Especially effective systems are the Lewis pairs (LPs) consisting of the strong LA Al(C6F5)3 and strong LBs, such as achiral phosphines and chiral chelating diphosphines, N-heterocyclic carbenes, and phosphazene superbases, for polymerization of methacrylates and acrylamides as well as renewable ?-methylene-?-butyrolactones. Chain initiation involves cooperative addition of LPs to the monomer to generate zwitterionic active species, and chain propagation proceeds via a bimetallic, activated-monomer addition mechanism. Transition metal nucleophile/electrophile pairs comprising neutral metallocene bis(ester enolate)s and strong LAs E(C6F5)3 (E = Al, B) generate two drastically different polymerization systems, depending on the LA. With E = Al, catalyst activation and chain initiating events lead to dually active ion-pairs, thereby effecting ion-pairing polymerization that affords polymers with unique stereo-multiblock microstructures. With E = B, on the other hand, the FLP-induced catalyst activation generates metallacyclic cations paired with the hydridoborate anion [HB(C6F5)3](-); uniquely, such ion-pairs effect catalytic polymerization of conjugated polar alkenes by an H-shuttling mechanism, with the cation catalyzing chain growth and the anion promoting chain transfer by shuttling the hydride between the cation and anion centers through the neutral borane. PMID:23097029

Chen, Eugene Y-X

2013-01-01

257

Free heme and sickle hemoglobin polymerization  

NASA Astrophysics Data System (ADS)

This work investigates further the mechanism of one of the most interesting of the protein self-assembly systems---the polymerization of sickle hemoglobin and the role of free heme in it. Polymerization of sickle hemoglobin is the primary event in the pathology of a chronic hemolytic condition called sickle cell anemia with complex pathogenesis, unexplained variability and symptomatic treatment. Auto-oxidation develops in hemoglobin solutions exposed to room temperature and causes release of ferriheme. The composition of such solutions is investigated by mass spectrometry. Heme dimers whose amount corresponds to the initial amounts of heme released from the protein are followed. Differences in the dimer peak height are established for hemoglobin variants A, S and C and depending on the exposure duration. The effects of free heme on polymerization kinetics are studied. Growth rates and two characteristic parameters of nucleation are measured for stored Hb S. After dialysis of polymerizing solutions, no spherulites are detected at moderately high supersaturation and prolonged exposure times. The addition of 0.16-0.26 mM amounts of heme to dialyzed solutions leads to restoration of polymerization. The measured kinetic parameters have higher values compared to the ones before dialysis. The amount of heme in non-dialyzed aged solution is characterized using spectrophotometry. Three methods are used: difference in absorbance of dialyzed and non-dialyzed solutions, characteristic absorbance of heme-albumin complex and absorbance of non-dialyzed solutions with added potassium cyanide. The various approaches suggest the presence of 0.12 to 0.18 mM of free ferriheme in such solutions. Open questions are whether the same amounts of free heme are present in vivo and whether the same mechanism operates intracellulary. If the answer to those questions is positive, then removal of free heme from erythrocytes can influence their readiness to sickle.

Uzunova, Veselina V.

258

Lentiviral and Retroviral Vector Systems  

Microsoft Academic Search

Retroviruses have been widely used as gene transfer vectors, and in fact represent the vector system used in the majority\\u000a of clinical gene therapy trials for cancer to date. In an ex vivo setting, conventional replication-defective oncoretrovirus\\u000a vectors can reliably and efficiently achieve permanent gene transfer which is selective for dividing cells; however, successful\\u000a application of these vectors in vivo

Renata Stripecke; Noriyuki Kasahara

259

Vectors from A to B  

NSDL National Science Digital Library

This is an activity about vectors and velocity. It outlines the addition and subtraction of vectors, and introduces the application of trigonometry to describing vectors. The resource is designed to support student analysis of THEMIS (Time History of Events and Macroscale Interactions during Substorms) Magnetometer line-plot data. Learners will complete worksheets consisting of problem sets that allow them to work with vector data in magnetic fields. This is activity 15 from Exploring Magnetism: Earth's Magnetic Personality.

260

Kinematics of vector fields  

E-print Network

Different (not only by sign) affine connections are introduced for contravariant and covariant tensor fields over a differentiable manifold by means of a non-canonical contraction operator, defining the notion dual bases and commuting with the covariant and with the Lie-differential operator. Classification of the linear transports on the basis of the connections between the connections is given. Notion of relative velocity and relative acceleration for vector fields are determined. By means of these kinematic characteristics several other types of notions as shear velocity, shear acceleration, rotation velocity, rotation acceleration, expansion velocity and expansion acceleration are introduced and on their basis auto-parallel and non-isotropic (non-null) vector fields are classified.

S. Manoff

2000-03-02

261

Statistical analysis of cointegration vectors  

Microsoft Academic Search

We consider a nonstationary vector autoregressive process which is integrated of order 1, and generated by i.i.d. Gaussian errors. We then derive the maximum likelihood estimator of the space of cointegration vectors and the likelihood ratio test of the hypothesis that it has a given number of dimensions. Further we test linear hypotheses about the cointegration vectors. The asymptotic distribution

Soren Johansen

1988-01-01

262

Topochemical polymerization of C70 controlled by monomer crystal packing.  

PubMed

Polymeric forms of C60 are now well known, but numerous attempts to obtain C70 in a polymeric state have yielded only dimers. Polymeric C70 has now been synthesized by treatment of hexagonally packed C70 single crystals under moderate hydrostatic pressure (2 gigapascals) at elevated temperature (300 degrees C), which confirms predictions from our modeling of polymeric structures of C70. Single-crystal x-ray diffraction shows that the molecules are bridged into polymeric zigzag chains that extend along the c axis of the parent structure. Solid-state nuclear magnetic resonance and Raman data provide evidence for covalent chemical bonding between the C70 cages. PMID:11474107

Soldatov, A V; Roth, G; Dzyabchenko, A; Johnels, D; Lebedkin, S; Meingast, C; Sundqvist, B; Haluska, M; Kuzmany, H

2001-07-27

263

Vector Magnetograph Design  

NASA Technical Reports Server (NTRS)

This report covers work performed during the period of November 1994 through March 1996 on the design of a Space-borne Solar Vector Magnetograph. This work has been performed as part of a design team under the supervision of Dr. Mona Hagyard and Dr. Alan Gary of the Space Science Laboratory. Many tasks were performed and this report documents the results from some of those tasks, each contained in the corresponding appendix. Appendices are organized in chronological order.

Chipman, Russell A.

1996-01-01

264

Vector representation of tourmaline compositions  

NASA Technical Reports Server (NTRS)

The vector method for representing mineral compositions of amphibole and mica groups is applied to the tourmaline group. Consideration is given to the methods for drawing the relevant vector diagrams, relating the exchange vectors to one another, and contouring the diagrams for constant values of Na, Ca, Li, Fe, Mg, Al, Si, and OH. The method is used to depict a wide range of possible tourmaline end-member compositions and solid solutions, starting from a single point. In addition to vector depictions of multicomponent natural tourmalines, vectors are presented for simpler systems such as (Na,Al)-tourmalines, alkali-free tourmalines, and elbaites.

Burt, Donald M.

1989-01-01

265

Vector ecology of equine piroplasmosis.  

PubMed

Equine piroplasmosis is a disease of Equidae, including horses, donkeys, mules, and zebras, caused by either of two protozoan parasites, Theileria equi or Babesia caballi. These parasites are biologically transmitted between hosts via tick vectors, and although they have inherent differences they are categorized together because they cause similar pathology and have similar morphologies, life cycles, and vector relationships. To complete their life cycle, these parasites must undergo a complex series of developmental events, including sexual-stage development in their tick vectors. Consequently, ticks are the definitive hosts as well as vectors for these parasites, and the vector relationship is restricted to a few competent tick species. Because the vector relationship is critical to the epidemiology of these parasites, we highlight current knowledge of the vector ecology of these tick-borne equine pathogens, emphasizing tick transmissibility and potential control strategies to prevent their spread. PMID:25564746

Scoles, Glen A; Ueti, Massaro W

2015-01-01

266

Generation of stable vector-producing cells for retroviral vectors.  

PubMed

INTRODUCTIONThis procedure describes the generation of clonal vector-producing cells that will provide an unlimited amount of unrearranged retroviral vector. The procedure involves transfection of one packaging cell line to generate a vector that is used to transduce a second packaging cell line. The resultant vector-producing clones generally contain a single integrated copy of the retroviral vector, and virus produced from this integrated vector is as genetically homogeneous as possible. Although the vector produced by a given packaging cell line can sometimes be used to transduce the same cell line, the transduction rate is typically low because of receptor blockage by the Env protein made by the target packaging cells. Indeed, this procedure will select for target cells that express low Env protein levels and thus are less resistant to transduction, but at the same time will ultimately produce less vector because of low Env production. Therefore, to obtain the highest vector titers, it is important to use pairs of packaging cells such that receptor blockage is not an issue. In this example, we use PE501 ecotropic packaging cells for transfection and broad-host-range PT67 packaging cells to make stable vector-producing cells. PMID:21356804

Cornetta, Kenneth; Pollok, Karen E; Miller, A Dusty

2008-01-01

267

Constructing monocrystalline covalent organic networks by polymerization  

NASA Astrophysics Data System (ADS)

An emerging strategy for making ordered materials is modular construction, which connects preformed molecular subunits to neighbours through interactions of properly selected reactive sites. This strategy has yielded remarkable materials, including metal-organic frameworks joined by coordinative bonds, supramolecular networks linked by strong non-covalent interactions, and covalent organic frameworks in which atoms of carbon and other light elements are bonded covalently. However, the strategy has not yet produced covalently bonded organic materials in the form of large single crystals. Here we show that such materials can result from reversible self-addition polymerizations of suitably designed monomers. In particular, monomers with four tetrahedrally oriented nitroso groups polymerize to form diamondoid azodioxy networks that can be fully characterized by single-crystal X-ray diffraction. This work forges a strong new link between polymer science and supramolecular chemistry by showing how predictably ordered covalent or non-covalent structures can both be built using a single modular strategy.

Beaudoin, Daniel; Maris, Thierry; Wuest, James D.

2013-10-01

268

Cooperative polymerization of one-patch colloids  

SciTech Connect

We numerically investigate cooperative polymerization in an off-lattice model based on a pairwise additive potential using particles with a single attractive patch that covers 30% of the colloid surface. Upon cooling, these particles self-assemble into small clusters which, below a density-dependent temperature, spontaneously reorganize into long straight tubes. We evaluate the partition functions of clusters of all sizes to provide an accurate description of the chemical reaction constants governing this process. Our calculations show that, for intermediate sizes, the partition functions retain contributions from two different structures, differing in both energy and entropy. We illustrate the microscopic mechanism behind the complex polymerization process in this system and provide a detailed evaluation of its thermodynamics.

Vissers, Teun; Smallenburg, Frank; Munaò, Gianmarco; Preisler, Zden?k; Sciortino, Francesco [Sapienza, Università di Roma, Piazzale Aldo Moro 2, 00185, Roma (Italy)] [Sapienza, Università di Roma, Piazzale Aldo Moro 2, 00185, Roma (Italy)

2014-04-14

269

Living anionic polymerization using a microfluidic reactor.  

PubMed

Living anionic polymerizations were conducted within aluminum-polyimide microfluidic devices. Polymerizations of styrene in cyclohexane were carried out at various conditions, including elevated temperature (60 degrees C) and high monomer concentration (42%, by volume). The reactions were safely maintained at a controlled temperature at all points in the reactor. Conducting these reactions in a batch reactor results in uncontrolled heat generation with potentially dangerous rises in pressure. Moreover, the microfluidic nature of these devices allows for flexible 2D designing of the flow channel. Four flow designs were examined (straight, periodically pinched, obtuse zigzag, and acute zigzag channels). The ability to use the channel pattern to increase the level of mixing throughout the reactor was evaluated. When moderately high molecular mass polymers with increased viscosity were made, the patterned channels produced polymers with narrower PDI, indicating that passive mixing arising from the channel design is improving the reaction conditions. PMID:19107294

Iida, Kazunori; Chastek, Thomas Q; Beers, Kathryn L; Cavicchi, Kevin A; Chun, Jaehun; Fasolka, Michael J

2009-01-21

270

Chemical characterization of selected LDEF polymeric materials  

NASA Technical Reports Server (NTRS)

Chemical characterization of selected polymeric materials which received exposure on the Long Duration Exposure Facility (LDEF) is reported. The specimens examined include silvered fluorinated ethylene propylene Teflon thermal blanket material, polysulfone, epoxy, polyimide matrix resin/graphite fiber reinforced composites, and several high performance polymer films. These specimens came from numerous LDEF locations, and thus received different environmental exposures. The results to date show no significant change at the molecular level in the polymer that survived exposure. Scanning electron and scanning tunneling microscopes show resin loss and a texturing of some specimens which resulted in a change in optical properties. The potential effect of a silicon-containing molecular contamination on these materials is addressed. The possibility of continued post-exposure degradation of some polymeric films is also proposed.

Young, Philip R.; Slemp, Wayne S.

1991-01-01

271

Chemical characterization of selected LDEF polymeric materials  

NASA Technical Reports Server (NTRS)

The chemical characterization of selected polymeric materials which received exposure on the LDEF is reported. The specimens examined include silvered fluorinated ethylene propylene (FEP) teflon thermal blanket material, polysulfone matrix resin/graphite fiber reinforced composites, and several high performance polymer films. These specimens came from numerous LDEF locations and, thus, received different environmental exposures. The results of infrared, thermal, x ray photoelectron, and various solution property analyses have shown no significant change at the molecular level in the polymer that survived exposure. However, scanning electron and scanning tunneling microscopies show resin loss and a texturing of the surface of some specimens which resulted in a change in optical properties. The potential effect of a silicon containing molecular contamination on these materials is addressed. The possibility of continued post-exposure degradation of some polymeric films is also proposed.

Young, Philip R.; Slemp, Wayne S.

1992-01-01

272

Design, characterization, and aerosolization of organic solution advanced spray-dried moxifloxacin and ofloxacin dipalmitoylphosphatidylcholine (DPPC) microparticulate/nanoparticulate powders for pulmonary inhalation aerosol delivery  

PubMed Central

The aim of this study was to design and develop respirable antibiotics moxifloxacin (MOXI) hydrochloride and ofloxacin (OFLX) microparticles and nanoparticles, and multifunctional antibiotics particles with or without lung surfactant 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) for targeted dry powder inhalation delivery as a pulmonary nanomedicine. Particles were rationally designed and produced by advanced spray-drying particle engineering from an organic solution in closed mode (no water) from dilute solution. Scanning electron microscopy indicated that these particles had both optimal particle morphology and surface morphology, and the particle size distributions were suitable for pulmonary delivery. Comprehensive and systematic physicochemical characterization and in vitro aerosol dispersion performance revealed significant differences between these two fluoroquinolone antibiotics following spray drying as drug aerosols and as cospray-dried antibiotic drug: DPPC aerosols. Fourier transform infrared spectroscopy and confocal Raman microspectroscopy were employed to probe composition and interactions in the solid state. Spray-dried MOXI was rendered noncrystalline (amorphous) following organic solution advanced spray drying. This was in contrast to spray-dried OFLX, which retained partial crystallinity, as did OFLX:DPPC powders at certain compositions. Aerosol dispersion performance was conducted using inertial impaction with a dry powder inhaler device approved for human use. The present study demonstrates that the use of DPPC offers improved aerosol delivery of MOXI as cospray-dried microparticulate/nanoparticulate powders, whereas residual partial crystallinity influenced aerosol dispersion of OFLX and most of the compositions of OFLX:DPPC inhalation powders. PMID:24092972

Duan, Jinghua; Vogt, Frederick G; Li, Xiaojian; Hayes, Don; Mansour, Heidi M

2013-01-01

273

Nanoparticulate Mn3O4/VGCF composite conversion-anode material with extraordinarily high capacity and excellent rate capability for lithium ion batteries.  

PubMed

In this work, highly conductive vapor grown carbon fiber (VGCF) was applied as an electrically conductive agent for facile synthesis of a nanoparticulate Mn3O4/VGCF composite material. This material exhibits super high specific capacity and excellent rate capability as a conversion-anode for lithium ion batteries. Rate performance test result demonstrates that at the discharge/charge current density of 0.2 A g(-1) a reversible capacity of ca. 950 mAh g(-1) is delivered, and when the current rate is increased to a high current density of 5 A g(-1), a reversible capacity of ca. 390 mAh g(-1) is retained. Cyclic performance examination conducted at the current density of 0.5 A g(-1) reveals that in the initial 20 cycles the reversible capacity decreases gradually from 855 to 747 mAh g(-1). However, since then, it increases gradually with cycle number increasing, and after 200 cycles an extraordinarily high reversible capacity of 1391 mAh g(-1) is achieved. PMID:25247688

Ma, Feng; Yuan, Anbao; Xu, Jiaqiang

2014-10-22

274

Biologically produced acid precipitable polymeric lignin  

DOEpatents

A water soluble, acid precipitable polymeric degraded lignin (APPL), having a molecular weight of at least 12,000 daltons, and comprising, by percentage of total weight, at least three times the number of phenolic hydroxyl groups and carboxylic acid groups present in native lignin. The APPL may be modified by chemical oxidation and reduction to increase its phenolic hydroxyl content and reduce the number of its antioxidant inhibitory side chains, thereby improving antioxidant properties.

Crawford, Don L. (Moscow, ID); Pometto, III, Anthony L. (Moscow, ID)

1984-01-01

275

Polymeric assemblies for sensitive colorimetric assays  

DOEpatents

The presently claimed invention relates to polymeric assemblies which visibly change color in the presence of analyte. In particular, the presently claimed invention relates to liposomes comprising a plurality of lipid monomers, which comprises a polymerizable group, a hydrophilic head group and a hydrophobic tail group, and one or more ligands. Overall carbon chain length, and polymerizable group positioning on the monomer influence color change sensitivity to analyte concentrations.

Charych, Deborah (Albany, CA)

2000-01-01

276

Supported polymeric liquid membranes for wastewater treatment  

SciTech Connect

The removal or elimination of organic residues from aqueous waste streams represents a major need in the chemical industry. A class of membrane has been developed called supported polymeric liquid membranes capable of removing and concentrating low molecular weight organic compounds from dilute aqueous solutions, especially those that also contain high concentrations of inorganic salts. These membranes are prepared by filling the pores of microfiltration or ultrafiltration membranes with polymeric (oligomeric) liquids having affinity for the organic compounds of interest. With this approach, membrane`s separation characteristics are decoupled from its mechanical stability and depend primarily on the chemical properties of the liquid polymer used. As a result, membranes of diverse separation capabilities can be conveniently prepared using liquid polymers possessing the appropriate functional groups. Physical properties typical of polymeric liquids such as high viscosity, extremely low volatility and insolubility in water contribute to the observed stability of the membranes under broad operating conditions. This membrane process has been successfully applied to several aqueous waste streams. This paper describes the early development activities for treating a waste stream containing a dilute mixture of C2-C6 carboxylic acids. Feasibility testings were initially carried out with flat sheet membranes in a small stirred cell. Scaleup was then conducted using hollow fiber membranes, first with small modules prepared in the laboratory, then with a much larger commercial module. Attractive features of this membrane process include the ability to recover the contaminants in concentrated form for either recycle or more economical disposal, low pressure (ambient) operation, simple scale-up using commercial hollow fiber modules, and ease of in-situ regeneration of the polymeric liquid.

Ho, S.V. [Monsanto Co., St. Louis, MO (United States)

1997-12-31

277

Biologically responsive polymeric nanoparticles for drug delivery.  

PubMed

Responsive nanoparticles that release their drug cargo in accordance with a change in pH or oxidative stress are of significant clinical interest as this approach offers the opportunity to link drug delivery to a specific location or disease state. This research news article reviews the current state of this field by examining a series of published articles that highlight the novelty and benefits of using responsive polymeric particles to achieve functionally-targeted drug delivery. PMID:22988558

Colson, Yolonda L; Grinstaff, Mark W

2012-07-24

278

In Situ Forming Polymeric Drug Delivery Systems  

PubMed Central

In situ forming polymeric formulations are drug delivery systems that are in sol form before administration in the body, but once administered, undergo gelation in situ, to form a gel. The formation of gels depends on factors like temperature modulation, pH change, presence of ions and ultra violet irradiation, from which the drug gets released in a sustained and controlled manner. Various polymers that are used for the formulation of in situ gels include gellan gum, alginic acid, xyloglucan, pectin, chitosan, poly(DL-lactic acid), poly(DL-lactide-co-glycolide) and poly-caprolactone. The choice of solvents like water, dimethylsulphoxide, N-methyl pyrrolidone, triacetin and 2-pyrrolidone for these formulations depends on the solubility of polymer used. Mainly in situ gels are administered by oral, ocular, rectal, vaginal, injectable and intraperitoneal routes. The in situ gel forming polymeric formulations offer several advantages like sustained and prolonged action in comparison to conventional drug delivery systems. The article presents a detailed review of these types of polymeric systems, their evaluation, advancements and their commercial formulations. From a manufacturing point of view, the production of such devices is less complex and thus lowers the investment and manufacturing cost. PMID:20490289

Madan, M.; Bajaj, A.; Lewis, S.; Udupa, N.; Baig, J. A.

2009-01-01

279

Homogeneous catalysts for stereoregular olefin polymerization  

DOEpatents

The synthesis, and use as precatalysts of chiral organozirconium complexes for olefin polymerization are disclosed, having the structure (C[sub 5]R[prime][sub 4[minus]x]R*[sub x])-A-(C[sub 5]R[double prime][sub 4[minus]y]R[prime][double prime][sub y])-M-Q[sub p], where x and y represent the number of unsubstituted locations on the cyclopentadienyl ring; R[prime], R[double prime], R[prime][double prime], and R* represent substituted and unsubstituted alkyl groups having 1--30 carbon atoms and R* is a chiral ligand; A is a fragment containing a Group 13, 14, 15, or 16 element of the Periodic Table; M is a Group 3, 4, or 5 metal of the Periodic Table; and Q is a hydrocarbyl radical, or halogen radical, with 3 [<=] p [<=] 0. Related complexes may be prepared by alkylation of the corresponding dichlorides. In the presence of methylalumoxane or triarylborane cocatalysts, these complexes form cation-like'' species which are highly active for olefin polymerization. In combination with a Lewis acid cocatalyst, propylene or other [alpha]-olefin polymerization can be effected with very high efficiency and isospecificity. 1 fig.

Marks, T.J.; Eisen, M.S.; Giardello, M.A.

1994-07-19

280

Homogeneous catalysts for stereoregular olefin polymerization  

DOEpatents

The synthesis, and use as precatalysts of chiral organozirconium complexes for olefin polymerization are disclosed, having the structure (C{sub 5}R{prime}{sub 4{minus}x}R*{sub x})A(C{sub 5}R{double_prime}{sub 4{minus}y}R{double_prime}{prime}{sub y})MQ{sub p}, where x and y represent the number of unsubstituted locations on the cyclopentadienyl ring; R{prime}, R{double_prime}, R{double_prime}{prime}, and R* represent substituted and unsubstituted alkyl groups having 1--30 carbon atoms and R* is a chiral ligand; A is a fragment containing a Group 13, 14, 15, or 16 element of the Periodic Table; M is a Group 3, 4, or 5 metal of the Periodic Table; and Q is a hydrocarbyl radical, or halogen radical, with 3{>=}p{>=}0. Related complexes may be prepared by alkylation of the corresponding dichlorides. In the presence of methylalumoxane or triarylborane cocatalysts, these complexes form ``cation-like`` species which are highly active for olefin polymerization. In combination with a Lewis acid cocatalyst, propylene or other {alpha}-olefin polymerization can be effected with very high efficiency and isospecificity. 1 fig.

Marks, T.J.; Eisen, M.S.; Giardello, M.A.

1995-10-03

281

Homogeneous catalysts for stereoregular olefin polymerization  

DOEpatents

The synthesis, and use as precatalysts of chiral organozirconium complexes for olefin polymerization are disclosed, having the structure (C.sub.5 R'.sub.4-x R*.sub.x) A (C.sub.5 R".sub.4-y R"'.sub.y) M Q.sub.p, where x and y represent the number of unsubstituted locations on the cyclopentadienyl ring; R', R", R"', and R* represent substituted and unsubstituted alkyl groups having 1-30 carbon atoms and R* is a chiral ligand; A is a fragment containing a Group 13, 14, 15, or 16 element of the Periodic Table; M is a Group 3, 4, or 5 metal of the Periodic Table; and Q is a hydrocarbyl radical, or halogen radical, with 3.ltoreq.p.ltoreq.o. Related complexes may be prepared by alkylation of the corresponding dichorides. In the presence of methylalumoxane or triarylborane cocatalysts, these complexes form "cation-like" species which are highly active for olefin polymerization. In combination with a Lewis acid cocatalyst, propylene or other .alpha.-olefin polymerization can be effected with very high efficiency and isospecificity.

Marks, Tobin J. (Evanston, IL); Eisen, Moris S. (Evanston, IL); Giardello, Michael A. (Skokie, IL)

1995-01-01

282

Homogeneous catalysts for stereoregular olefin polymerization  

DOEpatents

The synthesis, and use as precatalysts of chiral organozirconium complexes for olefin polymerization are disclosed, having the structure (C.sub.5 R'.sub.4-x R*.sub.x) A (C.sub.5 R".sub.4-y R'".sub.y) M Q.sub.p, where x and y represent the number of unsubstituted locations on the cyclopentadienyl ring; R', R", R'", and R* represent substituted and unsubstituted alkyl groups having 1-30 carbon atoms and R* is a chiral ligand; A is a fragment containing a Group 13, 14, 15, or 16 element of the Periodic Table; M is a Group 3, 4, or 5 metal of the Periodic Table; and Q is a hydrocarbyl radical, or halogen radical, with 3.ltoreq.p.ltoreq.o. Related complexes may be prepared by alkylation of the corresponding dichorides. In the presence of methylalumoxane or triarylborane cocatalysts, these complexes form "cation-like" species which are highly active for olefin polymerization. In combination with a Lewis acid cocatalyst, propylene or other .alpha.-olefin polymerization can be effected with very high efficiency and isospecificity.

Marks, Tobin J. (Evanston, IL); Eisen, Moris S. (Evanston, IL); Giardello, Michael A. (Skokie, IL)

1994-01-01

283

Polymerization initated at sidewalls of carbon nanotubes  

NASA Technical Reports Server (NTRS)

The present invention is directed to aryl halide (such as aryl bromide) functionalized carbon nanotubes that can be utilized in anionic polymerization processes to form polymer-carbon nanotube materials with improved dispersion ability in polymer matrices. In this process the aryl halide is reacted with an alkyllithium species or is reacted with a metal to replace the aryl-bromine bond with an aryl-lithium or aryl-metal bond, respectively. It has further been discovered that other functionalized carbon nanotubes, after deprotonation with a deprotonation agent, can similarly be utilized in anionic polymerization processes to form polymer-carbon nanotube materials. Additionally or alternatively, a ring opening polymerization process can be performed. The resultant materials can be used by themselves due to their enhanced strength and reinforcement ability when compared to their unbound polymer analogs. Additionally, these materials can also be blended with pre-formed polymers to establish compatibility and enhanced dispersion of nanotubes in otherwise hard to disperse matrices resulting in significantly improved material properties. The resultant polymer-carbon nanotube materials can also be used in drug delivery processes due to their improved dispersion ability and biodegradability, and can also be used for scaffolding to promote cellular growth of tissue.

Tour, James M. (Inventor); Hudson, Jared L. (Inventor); Krishnamoorti, Ramanan (Inventor); Yurekli, Koray (Inventor); Mitchell, Cynthia A. (Inventor)

2011-01-01

284

Performance of selected polymeric materials on LDEF  

NASA Technical Reports Server (NTRS)

The NASA Long Duration Exposure Facility (LDEF) provided a unique environmental exposure of a wide variety of materials for potential advanced spacecraft application. This paper examines the molecular level response of selected polymeric materials which flew onboard this vehicle. Polymers include epolyimide, polysulfone, and polystyrene film and polyimide, polysulfone, and epoxy matrix resin/graphite fiber reinforced composites. Several promising experimental films were also studied. Most specimens received 5.8 years of low Earth orbital (LEO) exposure on LDEF. Several samples received on 10 months of exposure. Chemical characterization techniques included ultraviolet-visible and infrared spectroscopy, thermal analysis, x-ray photoelectron spectroscopy, and selected solution property measurements. Results suggest that many molecular level effects present during the first 10 months of exposure were not present after 5.8 years of exposure for specimens on or near Row 9. Increased AO fluence near the end of the mission likely eroded away much environmentally induced surface phenomena. The objective of this work is to provide fundamental information for use in improving the performance of polymeric materials for LEO application. A secondary objective is to gain an appreciation for the constraints and limitations of results from LDEF polymeric materials experiments.

Young, Philip R.; Slemp, Wayne S.; Stein, Bland A.

1993-01-01

285

Formation and polymerization of cyclic disilsesquioxanes  

SciTech Connect

Sol-gel polymerication of {alpha}, {omega}-bis(triethoxysilyl)alkanes normally leads to alkylene-bridged polysilsesquioxanes in the form of insoluble, highly crosslinked polymeric gels. Hydrolysis of the six ethoxide groups on each monomer gives silanols that then condense to form a network of siloxane bonds. Unlike most Sol-gel precursors, these flexible hydrocarbon-bridged monomers can participate not only in intermolecular condensation reactions that lead to polymeric networks, but in intramolecular condensation reactions leading to cyclic disilsesquioxanes as well. Partitioning between these two reaction manifolds should be an important determinant of the manner in which the network polymer is assembled and, be an important determinant of the manner in which the network polymer is assembled and, ultimately, the final morphologies of the crosslinked gels. The relative importance of the two pathways should be dependent on a variety of factors, including the reaction mechanism (acid or base catalysis), the concentration of {alpha}, {omega}(triethoxysilyl)alkane and, most importantly for this study, the length of the alkylene bridging group.

Loy, D.A.; Carpenter, J.P.; Myers, S.A.; Assink, R.A. [Sandia National Labs., Albuquerque, NM (United States); Small, Greaves, J; Shea, K.J. [California Univ., Irvine, CA (United States)

1996-07-01

286

Protein crystallization on polymeric film surfaces  

NASA Astrophysics Data System (ADS)

Polymeric films containing ionizable groups, such as sulfonated polystyrene, cross-linked gelatin films with adsorbed poly- L-lysine or entrapped poly- L-aspartate and silk fibroin with entrapped poly- L-lysine or poly- L-aspartate, have been tested as heterogeneous nucleant surfaces for proteins. Concanavalin A from jack bean and chicken egg-white lysozyme were used as models. It was found that the crystallization of concanavalin A by the vapor diffusion technique, is strongly influenced by the presence of ionizable groups on the film surface. Both the induction time and protein concentration necessary for the crystal nucleation decrease whereas the nucleation density increases on going from the reference siliconized cover slip to the uncharged polymeric surfaces and even more to the charged ones. Non-specific attractive and local interactions between the protein and the film surface might promote molecular collisions and the clustering with the due symmetry for the formation of the crystal nuclei. The results suggest that the studied polymeric film surfaces could be particularly useful for the crystallization of proteins from solutions at low starting concentration, thus using small quantities of protein, and for proteins with very long crystallization time.

Fermani, Simona; Falini, Giuseppe; Minnucci, Massimiliano; Ripamonti, Alberto

2001-04-01

287

Projection Vectors and Fibonacci and Lucas Cubes  

Microsoft Academic Search

Abstract: Projection vectors of subgraphs of Cartesian products are introduced as thecounting vectors of edges that project onto the factors. For several standard constructionstheir projection vectors are computed. It is proved that the projection vectors of Fibonaccicubes are precisely the rows of the Fibonacci triangle and that the projection vectors ofLucas cubes are Fn-1 -constant vectors. Some problems are listed

Sandi Klavzar; Iztok Peterin

288

Aerodynamics of thrust vectoring  

NASA Technical Reports Server (NTRS)

Thrust vectoring as a means to enhance maneuverability and aerodynamic performane of a tactical aircraft is discussed. This concept usually involves the installation of a multifunction nozzle. With the nozzle, the engine thrust can be changed in direction without changing the attitude of the aircraft. Change in the direction of thrust induces a significant change in the aerodynamic forces on the aircraft. Therefore, this device can be used for lift-augmenting as well as stability and control purposes. When the thrust is deflected in the longitudinal direction, the lift force and the pitching stability can be manipulated, while the yawing stability can be controlled by directing the thrust in the lateral direction.

Tseng, J. B.; Lan, C. Edward

1989-01-01

289

Vectoring: Steering a Plane  

NSDL National Science Digital Library

In this two part activity, learners work in pairs or individually to discover how vectoring the thrust from a jet engine affects movement of an airplane. In part one, learners construct an F-15 ACTIVE model with a balloon engine. In part two, learners conduct a series of experiments by changing the angle of the straw to control the direction of the thrust. This activity emphasizes the scientific method including prediction, observation, data collection, and analysis. This lesson plan includes background information, an extension and a sample worksheet.

Nasa

2011-08-20

290

Control vectors for splines  

E-print Network

. Introduction Splines have their roots in the lofting technique used in the shipbuilding and aircraft industries throughout the first half of the 20th century. The first mathematical reference to the notion of splines is accredited to the work of Schoenberg [1... associated with control vectors have been raised to a power of 1, 2, . . . , 10 (coloured from red to blue). Note that this curve cannot be generated using quartic B-splines. (For interpretation of the references to colour in this figure legend, the reader...

Kosinka, Ji?i; Sabin, Malcolm A.; Dodgson, Neil A.

2014-09-03

291

Vector potential photoelectron microscopy  

SciTech Connect

A new class of electron microscope has been developed for the chemical microanalysis of a wide range of real world samples using photoelectron spectroscopy. Highly structured, three-dimensional samples, such as fiber mats and fracture surfaces can be imaged, as well as insulators and magnetic materials. The new microscope uses the vector potential field from a solenoid magnet as a spatial reference for imaging. A prototype instrument has demonstrated imaging of uncoated silk, magnetic steel wool, and micron-sized single strand tungsten wires.

Browning, R. [R. Browning Consultants, 14 John Street, Shoreham, New York 11786 (United States)

2011-10-15

292

Vector control in leishmaniasis.  

PubMed

Indoor residual spraying is a simple and cost effective method of controlling endophilic vectors and DDT remains the insecticide of choice for the control of leishmaniasis. However resistance to insecticide is likely to become more widespread in the population especially in those areas in which insecticide has been used for years. In this context use of slow release emulsified suspension (SRES) may be the best substitute. In this review spraying frequencies of DDT and new schedule of spray have been discussed. Role of biological control and environment management in the control of leishmaniasis has been emphasized. Allethrin (coil) 0.1 and 1.6 per cent prallethrin (liquid) have been found to be effective repellents against Phlebotomus argentipes, the vector of Indian kalaazar. Insecticide impregnated bednets is another area which requires further research on priority basis for the control of leishmaniasis. Role of satellite remote sensing for early prediction of disease by identifying the sandflygenic conditions cannot be undermined. In future synthetic pheromons can be exploited in the control of leishmaniasis. PMID:16778324

Kishore, K; Kumar, V; Kesari, S; Dinesh, D S; Kumar, A J; Das, P; Bhattacharya, S K

2006-03-01

293

Vector wave propagation method.  

PubMed

In this paper, we extend the scalar wave propagation method (WPM) to vector fields. The WPM [Appl. Opt.32, 4984 (1993)] was introduced in order to overcome the major limitations of the beam propagation method (BPM). With the WPM, the range of application can be extended from the simulation of waveguides to simulation of other optical elements like lenses, prisms and gratings. In that reference it was demonstrated that the wave propagation scheme provides valid results for propagation angles up to 85 degrees and that it is not limited to small index variations in the axis of propagation. Here, we extend the WPM to three-dimensional vectorial fields (VWPMs) by considering the polarization dependent Fresnel coefficients for transmission in each propagation step. The continuity of the electric field is maintained in all three dimensions by an enhanced propagation vector and the transfer matrix. We verify the validity of the method by transmission through a prism and by comparison with the focal distribution from vectorial Debye theory. Furthermore, a two-dimensional grating is simulated and compared with the results from three-dimensional RCWA. Especially for 3D problems, the runtime of the VWPM exhibits special advantage over the RCWA. PMID:20360813

Fertig, M; Brenner, K-H

2010-04-01

294

Photothermal determination of thermal diffusivity and polymerization depth profiles of polymerized dental resins  

NASA Astrophysics Data System (ADS)

The degree and depth of curing due to photopolymerization in a commercial dental resin have been studied using photothermal radiometry. The sample consisted of a thick layer of resin on which a thin metallic gold layer was deposited, thus guaranteeing full opacity. Purely thermal-wave inverse problem techniques without the interference of optical profiles were used. Thermal depth profiles were obtained by heating the gold coating with a modulated laser beam and by performing a frequency scan. Prior to each frequency scan, photopolymerization was induced using a high power blue light emitted diode (LED). Due to the highly light dispersive nature of dental resins, the polymerization process depends strongly on optical absorption of the blue light, thereby inducing a depth dependent thermal diffusivity profile in the sample. A robust depth profilometric method for reconstructing the thermal diffusivity depth dependence on degree and depth of polymerization has been developed. The thermal diffusivity depth profile was linked to the polymerization kinetics.

Martínez-Torres, P.; Mandelis, A.; Alvarado-Gil, J. J.

2009-12-01

295

Statistical properties of contact vectors  

NASA Astrophysics Data System (ADS)

We study the statistical properties of contact vectors, a construct to characterize a protein's structure. The contact vector of an N-residue protein is a list of N integers ni, representing the number of residues in contact with residue i. We study analytically (at mean-field level) and numerically the amount of structural information contained in a contact vector. Analytical calculations reveal that a large variance in the contact numbers reduces the degeneracy of the mapping between contact vectors and structures. Exact enumeration for lengths up to N=16 on the three-dimensional cubic lattice indicates that the growth rate of number of contact vectors as a function of N is only 3% less than that for contact maps. In particular, for compact structures we present numerical evidence that, practically, each contact vector corresponds to only a handful of structures. We discuss how this information can be used for better structure prediction.

Kabakçio?lu, A.; Kanter, I.; Vendruscolo, M.; Domany, E.

2002-04-01

296

Statistical properties of contact vectors.  

PubMed

We study the statistical properties of contact vectors, a construct to characterize a protein's structure. The contact vector of an N-residue protein is a list of N integers n(i), representing the number of residues in contact with residue i. We study analytically (at mean-field level) and numerically the amount of structural information contained in a contact vector. Analytical calculations reveal that a large variance in the contact numbers reduces the degeneracy of the mapping between contact vectors and structures. Exact enumeration for lengths up to N=16 on the three-dimensional cubic lattice indicates that the growth rate of number of contact vectors as a function of N is only 3% less than that for contact maps. In particular, for compact structures we present numerical evidence that, practically, each contact vector corresponds to only a handful of structures. We discuss how this information can be used for better structure prediction. PMID:12005870

Kabakçioglu, A; Kanter, I; Vendruscolo, M; Domany, E

2002-04-01

297

Silver nanoparticles and polymeric medical devices: a new approach to prevention of infection?  

Microsoft Academic Search

Objectives: Implantable devices are major risk factors for hospital-acquired infection. Biomaterials coated with silver oxide or silver alloy have all been used in attempts to reduce infection, in most cases with controversial or disappointing clinical results. We have developed a completely new approach using supercritical carbon dioxide to impregnate silicone with nanoparticulate silver metal. This study aimed to evaluate the

Franck Furno; Kelly S. Morley; Ben Wong; Barry L. Sharp; Polly L. Arnold; Steven M. Howdle; Roger Bayston; Paul D. Brown; Peter D. Winship; Helen J. Reid

298

An adaptive vector quantization scheme  

NASA Technical Reports Server (NTRS)

Vector quantization is known to be an effective compression scheme to achieve a low bit rate so as to minimize communication channel bandwidth and also to reduce digital memory storage while maintaining the necessary fidelity of the data. However, the large number of computations required in vector quantizers has been a handicap in using vector quantization for low-rate source coding. An adaptive vector quantization algorithm is introduced that is inherently suitable for simple hardware implementation because it has a simple architecture. It allows fast encoding and decoding because it requires only addition and subtraction operations.

Cheung, K.-M.

1990-01-01

299

Maths Help: Working with Vectors  

NSDL National Science Digital Library

Analysis of a wide range of physical properties such as force, velocity, and acceleration, requires a firm understanding of the mathematics of vectors. This comprehensive Web site covers many aspects of vector algebra and trigonometry. The often-used dot product and cross product are defined, as well as vector representations of lines and planes. Illustrations are used to demonstrate vector analysis and its real-world applications. A few extra sections delve into related topics, including transformation between Cartesian and spherical coordinates. The material is mostly suitable for high school or college students who have taken pre-calculus.

2005-11-08

300

Microwave-assisted radical polymerization of dialkyl fumarates  

NASA Astrophysics Data System (ADS)

Free radical polymerization of dialkyl fumarates (R:isopropyl, cyclohexyl, 2-ethylhexyl, 2-phenylethyl) under microwave irradiation was investigated. The polymerizations were carried out at different powers of irradiation and initiator concentrations (benzoyl peroxide, BP) and the effect of the monomer structure on the conversion, average molecular weights and the polydispersity index ( Mw/ Mn) was analyzed. A significant enhancement of the rates of polymerization was found, as compared with those obtained under thermal conditions.

Cortizo, M. Susana; Laurella, Sergio; Alessandrini, José Luis

2007-07-01

301

Shape of the Polymerization Rate in the Prion Equation  

E-print Network

We consider a polymerization (fragmentation) model with size-dependent parameters involved in prion proliferation. Using power laws for the different rates of this model, we recover the shape of the polymerization rate using experimental data. The technique used is inspired from an article of Zampieri et al. where the fragmentation dependency on prion strains is investigated. Our improvement is to use power laws for the rates whereas Zampieri et al. used a constant polymerization coefficient and linear fragmentation.

Gabriel, Pierre

2010-01-01

302

Solar imaging vector magnetograph  

NASA Technical Reports Server (NTRS)

This report describes an instrument which has been constructed at the University of Hawaii to make observations of the magnetic field in solar active regions. Detailed knowledge of active region magnetic structures is crucial to understanding many solar phenomena, because the magnetic field both defines the morphology of structures seen in the solar atmosphere and is the apparent energy source for solar flares. The new vector magnetograph was conceived in response to a perceived discrepancy between the capabilities of X ray imaging telescopes to be operating during the current solar maximum and those of existing magnetographs. There were no space-based magnetographs planned for this period; the existing ground-based instruments variously suffered from lack of sensitivity, poor time resolution, inadequate spatial resolution or unreliable sites. Yet the studies of flares and their relationship to the solar corona planned for the 1991-1994 maximum absolutely required high quality vector magnetic field measurements. By 'vector' measurements we mean that the observation attempts to deduce the complete strength and direction of the field at the measurement site, rather than just the line of sight component as obtained by a traditional longitudinal magnetograph. Knowledge of the vector field permits one to calculate photospheric electric currents, which might play a part in heating the corona, and to calculate energy stored in coronal magnetic fields as the result of such currents. Information about the strength and direction of magnetic fields in the solar atmosphere can be obtained in a number of ways, but quantitative data is best obtained by observing Zeeman-effect polarization in solar spectral lines. The technique requires measuring the complete state of polarization at one or more wavelengths within a magnetically sensitive line of the solar spectrum. This measurement must be done for each independent spatial point for which one wants magnetic field data. All the measurements need to be done in a time short compared to the time scale for changes of the solar features being observed. Were it possible, one would want to record all the needed data simultaneously, since temporal variation of atmospheric seeing degrades both the image and the polarization sensitivity. Since the measurements must span four dimensions, two spatial plus polarization and wavelength, we had some freedom to design the instrument to favor some dimensions over others in terms of simultaneity. Our earlier instrument, the Haleakala Stokes Polarimeter, records a range of wavelengths spanning two spectral lines in each reading, but requires two seconds to determine the polarization state and obtains spatial information only by assembling a long sequence of measurements at single locations on the sun. The new instrument sacrifices spectral detail and accuracy in favor of greatly improved imaging characteristics. The scientific goals for this instrument were to measure surface magnetic fields with enough accuracy to permit calculations of photospheric currents, but with a field of view covering an entire typical active region, high spatial resolution, and a fast enough temporal cadence for detecting flare-associated changes in magnetic structures.

Canfield, Richard C.

1993-01-01

303

Sorption of organics from aqueous solution onto polymeric resins  

SciTech Connect

The uptake of phenol, toluene, chlorobenzene, and benzoic acid by several polymeric resins and activated carbon was investigated experimentally. Presentation of the sorption data in terms of the number of sorbed monolayers and fractional pore volume filled indicated that, for the polymeric resins, solute uptake cannot be viewed as only a surface adsorption phenomenon. It is suggested that the aqueous phase uptake of phenol, toluene, chlorobenzene, and benzoic acid by the polymeric resins is attributable, in part, to solute absorption. The present study also suggests that solute uptake is affected by the swelling of some of the polymeric resins in water.

Gusler, G.M.; Browne, T.E.; Cohen, Y. (Univ. of California, Los Angeles, CA (United States). Dept. of Chemical Engineering)

1993-11-01

304

Microfluidic approaches to the synthesis of complex polymeric particles  

E-print Network

The synthesis of micron-sized polymeric particles with precise control over shape, monodispersity and chemistry is a technologically important objective. Varied applications including medical diagnostics. designer fabrics ...

Dendukuri, Dhananjay, 1978-

2007-01-01

305

Adjusting the polymerization time of isobutyl-2 cyanoacrylate.  

PubMed

Isobutyl-2 cyanoacrylate (IBCA) polymerizes by an anionic mechanism. The initiation of polymerization depends on an alkaline medium and can be inhibited with the addition of small amounts of acid. Using small amounts of glacial acetic acid (3.7%-7.1% by volume), the polymerization time was prolonged from 2.3 sec to 7.8 sec. In vivo experiments in dogs demonstrated no additional inflammatory reactions to the mixture of IBCA, iophendylate, and tantalum powder when acetic acid was added. Glacial acetic acid offers a safe and effective way, without increase in viscosity, to manipulate the polymerization time of IBCA. PMID:3082125

Spiegel, S M; Viñuela, F; Goldwasser, J M; Fox, A J; Pelz, D M

1986-01-01

306

Preparation of polymeric diacetylene thin films for nonlinear optical applications  

NASA Technical Reports Server (NTRS)

A method for producing polymeric diacetylene thin films having desirable nonlinear optical characteristics has been achieved by producing amorphous diacetylene polymeric films by simultaneous polymerization of diacetylene monomers in solution and deposition of polymerized diacetylenes on to the surface of a transparent substrate through which ultraviolet light has been transmitted. These amorphous polydiacetylene films produced by photo-deposition from solution possess very high optical quality and exhibit large third order nonlinear optical susceptibilities, such properties being suitable for nonlinear optical devices such as waveguides and integrated optics.

Frazier, Donald O. (inventor.); Mcmanus, Samuel P. (inventor.); Paley, Mark S. (inventor.); Donovan, David N. (inventor.)

1995-01-01

307

Design, development, and demonstration of a fully LabVIEW controlled in situ electrochemical Fourier transform infrared setup combined with a wall-jet electrode to investigate the electrochemical interface of nanoparticulate electrocatalysts under reaction conditions.  

PubMed

We present a detailed description of the construction of an in situ electrochemical ATR-FTIR setup combined with a wall-jet electrode to investigate the electrocatalytic properties of nanoparticulate catalysts in situ under controlled mass transport conditions. The presented setup allows the electrochemical interface to be probed in combination with the simultaneous determination of reaction rates. At the same time, the high level of automation allows it to be used as a standard tool in electrocatalysis research. The performance of the setup was demonstrated by probing the oxygen reduction reaction on a platinum black catalyst in sulfuric electrolyte. PMID:23902087

Nesselberger, Markus; Ashton, Sean J; Wiberg, Gustav K H; Arenz, Matthias

2013-07-01

308

Design, development, and demonstration of a fully LabVIEW controlled in situ electrochemical Fourier transform infrared setup combined with a wall-jet electrode to investigate the electrochemical interface of nanoparticulate electrocatalysts under reaction conditions  

NASA Astrophysics Data System (ADS)

We present a detailed description of the construction of an in situ electrochemical ATR-FTIR setup combined with a wall-jet electrode to investigate the electrocatalytic properties of nanoparticulate catalysts in situ under controlled mass transport conditions. The presented setup allows the electrochemical interface to be probed in combination with the simultaneous determination of reaction rates. At the same time, the high level of automation allows it to be used as a standard tool in electrocatalysis research. The performance of the setup was demonstrated by probing the oxygen reduction reaction on a platinum black catalyst in sulfuric electrolyte.

Nesselberger, Markus; Ashton, Sean J.; Wiberg, Gustav K. H.; Arenz, Matthias

2013-07-01

309

Uptake of Nitroaromatic Compounds by Polymeric Tubing  

SciTech Connect

The type of polymeric material used in the manufacturing of tubing determines its strength, elasticity, and durability. Tubing made of polymeric material is commonly used for analytical work because it is readily available, inexpensive and can be relatively inert. Polymeric tubing is used in many sampling applications for explosive compounds. A major concern is the uptake of the explosive compounds into or onto the tubing during sampling. Because of the reactive nature of explosives, it is important that as little of the detectable explosive as possible is lost by tubing uptake. It is also important that nothing leaches out of the tubing to interfere with the detection of explosives. High Performance Liquid Chromatography (HPLC) is commonly used for the analysis of trace levels of explosive compounds in the range of parts per billion (ppb) to parts per million (ppm). This study attempts to determine which types of polymers are most conducive to sampling applications where large volumes of dilute explosive solutions are collected through a length of tubing for analysis. This was determined by analyzing the amount of explosive lost from solution per cm{sup 2} of tubing in solution. It was determined that tubing made of polyethylene, teflon, polypropylene, or KYNAR{reg_sign} is recommended for dilute trinitrotoluene (TNT) solution analyses. Tubing made of polypropylene, PHARMED{reg_sign}, KYNAR{reg_sign}, or polyethylene is recommended for analyses involving dilute explosive solutions of RDX. Tubing made from polyurethane, TYGON{reg_sign}, nylon, vinyl, gum rubber, or reinforced PVC are not recommended because they leach contaminants into solution that may interfere with HPLC analysis of explosive peaks.

BOUNKEUA, VIENGNGEUN; RODACY, PHILIP J.

2001-04-01

310

Light-Driven Polymeric Bimorph Actuators  

NASA Technical Reports Server (NTRS)

Light-driven polymeric bimorph actuators are being developed as alternatives to prior electrically and optically driven actuators in advanced, highly miniaturized devices and systems exemplified by microelectromechanical systems (MEMS), micro-electro-optical-mechanical systems (MEOMS), and sensor and actuator arrays in smart structures. These light-driven polymeric bimorph actuators are intended to satisfy a need for actuators that (1) in comparison with the prior actuators, are simpler and less power-hungry; (2) can be driven by low-power visible or mid-infrared light delivered through conventional optic fibers; and (3) are suitable for integration with optical sensors and multiple actuators of the same or different type. The immediate predecessors of the present light-driven polymeric bimorph actuators are bimorph actuators that exploit a photorestrictive effect in lead lanthanum zirconate titanate (PLZT) ceramics. The disadvantages of the PLZT-based actuators are that (1) it is difficult to shape the PLZT ceramics, which are hard and brittle; (2) for actuation, it is necessary to use ultraviolet light (wavelengths < 380 nm), which must be generated by use of high-power, high-pressure arc lamps or lasers; (3) it is difficult to deliver sufficient ultraviolet light through conventional optical fibers because of significant losses in the fibers; (4) the response times of the PLZT actuators are of the order of several seconds unacceptably long for typical applications; and (5) the maximum mechanical displacements of the PLZT-based actuators are limited to those characterized by low strains beyond which PLZT ceramics disintegrate because of their brittleness. The basic element of a light-driven bimorph actuator of the present developmental type is a cantilever beam comprising two layers, at least one of which is a polymer that exhibits a photomechanical effect (see figure). The dominant mechanism of the photomechanical effect is a photothermal one: absorption of light energy causes heating, which, in turn, causes thermal expansion.

Adamovsky, Gregory; Sarkisov, Sergey S.; Curley, Michael J.

2009-01-01

311

Plasma polymerized silicon oxide primers for aluminum  

SciTech Connect

Plasma polymerized films of hexamethyidisiloxane were deposited onto Al and evaluated as primers for structural adhesive bonding. The films were characterized by X-ray photoelectron spectroscopy, reflection-absorption infrared spectroscopy, and ellipsometry. The properties of the films as primers for adhesive bonding of Al were evaluated by preparing lap joints from primed Al coupons, loading the joints and measuring the time required for failure. The effect of an argon plasma pretreatment of the Al adherends on the initial strength and the durability of the lap joints was also studied.

Taylor, C.E.; Segall, I.; Palmer, L.D.; Boerio, F.J. [Univ. of Cincinnati, OH (United States)] [and others

1996-10-01

312

Shock-induced activation of acrylamide polymerization  

SciTech Connect

We have subjected polycrystalline acrylamide to planar impact loading to peak pressures of 4.8 and 6.7 GPa using an air-driven projectile. In contrast to previous experiments involving explosive loading, postshock chemical analysis shows no formation of polyacrylamide associated with the shock loading. However, the impact shocked acrylamide spontaneously polymerizes when dissolved in tetrahydrofuran. This result implies that the stress history produced by the impact experiment results in the formation of a large density of stable active centers, which become mobile in solution. ESR measurements of the shocked acrylamide samples confirms the presence of substantial densities of free radicals. 2 figures.

Dodson, B.W.; Arnold, C. Jr.

1983-08-04

313

Heat flux concentration through polymeric thermal lenses  

NASA Astrophysics Data System (ADS)

A significant contributor to energy inefficiency is the generation as well as the uneven dissipation of heat. Practical methods to adeptly channel heat flux (Q) would then have widespread applications to improved energy utilization and thermal energy management. It would be beneficial to engineer lens-like composite materials (graded in terms of length or thermal conductivity) with augmented attributes for heat control. Here, we propose and demonstrate polymeric composite based Q focusing lenses, architected through geometrical considerations. We indicate a five-fold enhancement of the Q, at the level of ˜2500 W/m2, enabled through such thermal lenses.

Kapadia, R. S.; Bandaru, P. R.

2014-12-01

314

Functional Lactide Monomers: Methodology and Polymerization  

PubMed Central

Side-chain functionalized lactide analogues have been synthesized from commercially available amino acids and polymerized using stannous octoate as a catalyst. The synthetic strategy presented allows for the incorporation of any protected amino acid for the preparation of functionalized diastereomerically pure lactide monomers. The resulting functionalized cyclic monomers can be homopolymerized, and copolymerized with lactides, then quantitatively deprotected forming new functional poly(lactide)-based materials. This strategy allows for the introduction of functional groups along a poly(lactide) (PLA) backbone that after deprotection can be viewed as chemical handles for further functionalization of PLA, yielding improved biomaterials for a variety of applications. PMID:16768392

Gerhardt, Warren W.; Noga, David E.; Hardcastle, Kenneth I.; García, Andrés J.; M. Collard, David; Weck, Marcus

2008-01-01

315

Polymeric precursors for fibers and matrices  

NASA Technical Reports Server (NTRS)

Candidate polymeric precursors for ceramic fiber and matrix processing are discussed, with a view to the advantages and disadvantages of this approach relative to existing alternatives. The properties of ceramic products thus derived are noted to strongly depend on the molecular weight and structure of the starting polymer; in particular, the ceramic's composition and morphology are dependent on the character and extent of crosslinking, as well as on the path of pyrolysis. While large and complex structural ceramic components may ultimately be obtainable by these means, the polymer-precursor method is still in its developmental infancy.

Hurwitz, Frances I.

1992-01-01

316

Polymeric metallic electrodes for rechargeable battery applications  

NASA Technical Reports Server (NTRS)

A review is presented on the status of plastic metal electrodes, emphasizing the use of polyacetylene as a prototype polymeric material. The electrochemical characteristics of polyacetylene are examined; and the potential use of this material, as well as other types of plastic metal electrodes, in batteries is evaluated. Several problem areas which must be solved before polyacetylene can be widely used in battery applications are discussed, including the problem of electrolyte stability, the problem that the depth of discharge and the energy density is limited by the metal-semiconductor transition, and also the poor electrochemical performance of impure material.

Somoano, R.

1982-01-01

317

Multiphoton polymerization using optical trap assisted nanopatterning  

NASA Astrophysics Data System (ADS)

In this letter, we show the combination of multiphoton polymerization and optical trap assisted nanopatterning (OTAN) for the additive manufacturing of structures with nanometer resolution. User-defined patterns of polymer nanostructures are deposited on a glass substrate by a 3.5 ?m polystyrene sphere focusing IR femtosecond laser pulses, showing minimum feature sizes of ?/10. Feature size depends on the applied laser fluence and the bead surface spacing. A finite element model describes the intensity enhancement in the microbead focus. The results presented suggest that OTAN in combination with multiphoton processing is a viable technique for additive nanomanufacturing with sub-diffraction-limited resolution.

Leitz, Karl-Heinz; Tsai, Yu-Cheng; Flad, Florian; Schäffer, Eike; Quentin, Ulf; Alexeev, Ilya; Fardel, Romain; Arnold, Craig B.; Schmidt, Michael

2013-06-01

318

Studies of molecular properties of polymeric materials  

NASA Technical Reports Server (NTRS)

Aerospace environment effects (high energy electrons, thermal cycling, atomic oxygen, and aircraft fluids) on polymeric and composite materials considered for structural use in spacecraft and advanced aircraft are examined. These materials include Mylar, Ultem, and Kapton. In addition to providing information on the behavior of the materials, attempts are made to relate the measurements to the molecular processes occurring in the material. A summary and overview of the technical aspects are given along with a list of the papers that resulted from the studies. The actual papers are included in the appendices and a glossary of technical terms and definitions is included in the front matter.

Harries, W. L.; Long, Sheila Ann T.; Long, Edward R., Jr.

1990-01-01

319

Polymerization of propylene promoted by zirconium benzamidinates.  

PubMed

New bis(N,N-trimethylsilylarylamidinate) zirconium dichloride complexes with various carbon substituents were prepared, and their solid as well as solution state structures were studied. In the polymerization of propylene, after activation by MAO, these catalysts provided two fractions. Ether soluble polymers were obtained at a low activity as sticky polymers with lower molecular weights, except with the o-OMe substituted complex. The solid fractions were composed of a highly isotactic polymer and a moderately syndiotactic polymer. An interesting linear correlation was found between the rates of the 2,1 and 3,1 insertions for the ether soluble fractions. PMID:24077612

Aharonovich, Sinai; Kulkarni, Naveen V; Zhang, Jia-Sheng; Botoshansky, Mark; Kapon, Moshe; Eisen, Moris S

2013-12-28

320

Microscale polymeric helical structures produced by electrospinning  

NASA Astrophysics Data System (ADS)

Microscale helical coils consisting of a composite of one conducting and one nonconducting polymer were produced using electrospinning. The nonconducting polymer was poly(ethylene oxide) and the conducting polymer was poly(aniline sulfonic acid). The coil structures were studied over a range of processing conditions and fiber composition. The data suggest that the helical structures are formed due to viscoelastic contraction upon partial neutralization of the charged fibers. Polymeric microcoils may find applications in microelectromechanical systems, advanced optical components, and drug delivery systems.

Kessick, Royal; Tepper, Gary

2004-06-01

321

Frontal Polymerization in Microgravity Summary of Research  

NASA Technical Reports Server (NTRS)

The project began with frontal polymerization (FP). We studied many aspects of FP on the ground and performed two successful weeks of flying on the KC-135. The project evolved into the current flight investigation, Transient Interfacial Phenomena in Miscible Polymer Systems (TIPMPS), as we recognized that an essential question could best be studied using a non-frontal approach. We present detailed results from our ground-based work on FP, KC-135 results and the background, justification and numerical work for the TIPMPS project.

Pojman, John A.

2002-01-01

322

A polymeric flame retardant additive for rubbers  

SciTech Connect

Synthesis of a polyphosphonate by the interfacial polymerization of bisphenol-A (BPA) and dichloro-phenyl phosphine oxide (DCPO) using cetyltrimethyl ammonium chloride (TMAC) as phase transfer catalyst (PTC) was reported. The polyphosphonate was characterized by elemental analysis, IR, TGA, DSC and 1H-NMR spectroscopy. The flame retardancy of the polymer was done by OI study. The polymer was used as a fire retardant additive to rubbers such as natural rubber (NR), styrene-butadiene rubber(SBR), nitrile rubber (NBR) and chloroprene rubber (CR). The efficiency of the fire retardant property of this additive was determined by LOI measurements of the various rubber samples.

Ghosh, S.N.; Maiti, S. [Indian Institute of Technology, Kharagpur (India)

1993-12-31

323

Novel hybrid polymeric materials for barrier coatings  

NASA Astrophysics Data System (ADS)

Polymer-clay nanocomposites, described as the inclusion of nanometer-sized layered silicates into polymeric materials, have been widely researched due to significant enhancements in material properties with the incorporation of small levels of filler (1--5 wt.%) compared to conventional micro- and macro-composites (20--30 wt.%). One of the most promising applications for polymer-clay nanocomposites is in the field of barrier coatings. The development of UV-curable polymer-clay nanocomposite barrier coatings was explored by employing a novel in situ preparation technique. Unsaturated polyesters were synthesized in the presence of organomodified clays by in situ intercalative polymerization to create highly dispersed clays in a precursor resin. The resulting clay-containing polyesters were crosslinked via UV-irradiation using donor-acceptor chemistry to create polymer-clay nanocomposites which exhibited significantly enhanced barrier properties compared to alternative clay dispersion techniques. The impact of the quaternary alkylammonium organic modifiers, used to increase compatibility between the inorganic clay and organic polymer, was studied to explore influence of the organic modifier structure on the nanocomposite material properties. By incorporating just the organic modifiers, no layered silicates, into the polyester resins, reductions in film mechanical and thermal properties were observed, a strong indicator of film plasticization. An alternative in situ preparation method was explored to further increase the dispersion of organomodified clay within the precursor polyester resins. In stark contrast to traditional in situ polymerization methods, a novel "reverse" in situ preparation method was developed, where unmodified montmorillonite clay was added during polyesterification to a reaction mixture containing the alkylammonium organic modifier. The resulting nanocomposite films exhibited reduced water vapor permeability and increased mechanical properties. The novel preparation of hybrid films coupling the advantageous properties of organic-inorganic hybrids formed through sol-gel chemistry with polymer-clay nanocomposite technology was also explored. Alkoxysilane-functional copolymer-clay nanocomposites were first synthesized, followed by crosslinking via simultaneous hydrolysis and condensation reactions to create the novel hybrid barrier films. By dispersing organomodified clay throughout the hybrid network, dramatic improvements in several film properties were observed, particularly regarding the viscoelastic properties. Additional studies with the same organic-inorganic preparation technique were performed to incorporate amine-functionality into the hybrid film for potential applications as protective membranes in carbon dioxide capture and separation technologies. Finally, controlled free-radical polymerization techniques were combined with the preparation of the organic-inorganic hybrids.

Pavlacky, Erin Christine

324

Durability of Polymeric Glazing and Absorber Materials  

SciTech Connect

The Solar Heating and Lighting Program has set the goal of reducing the cost of solar water heating systems by at least 50%. An attractive approach to such large cost reduction is to replace glass and metal parts with less-expensive, lighter-weight, more-integrated polymeric components. The key challenge with polymers is to maintain performance and assure requisite durability for extended lifetimes. We have begun evaluation of several new UV-screened polycarbonate sheet glazing constructions. This has involved interactions with several major polymer industry companies to obtain improved candidate samples. Proposed absorber materials were tested for UV resistance, and appear adequate for unglazed ICS absorbers.

Jorgensen, G.; Terwilliger, K.; Bingham, C.; Lindquist, C.; Milbourne, M.

2005-11-01

325

Targeted polymeric magnetic nanoparticles for brain imaging  

NASA Astrophysics Data System (ADS)

The purpose of this study was to develop targeted polymeric magnetic nanoparticle system for brain imaging. Near infrared dye indocyanine green (ICG) or p-gycoprotein substrate rhodamine 123 (Rh123) were encapsulated along with oleic acid coated magnetic nanoparticles (OAMNP) in a matrix of poly(lactide-co-glycolide) (PLGA) and methoxy poly(ethyleneglycol)-poly(lactide) (Met-PEG-PLA). The nanoparticles were evaluated for morphology, particle size, dye content and magnetite content. The in vivo biodistribution study was carried out using three groups of six male Sprague Dawley rats each. Group I received a saline solution containing the dye, group II received dye-loaded polymeric magnetic nanoparticles without the aid of a magnetic field, and group III received dye-loaded polymeric magnetic nanoparticles with a magnet (8000 G) placed on the head of the rat. After a preset exposure period, the animals were sacrificed and dye concentration was measured in the brain, liver, kidney, lungs and spleen homogenates. Brain sections were fixed, cryotomed and visualized using fluorescence microscopy. The particles were observed to be spherical and had a mean size of 220 nm. The encapsulation efficiency for OAMNP was 57%, while that for ICG was 56% and for Rh123 was 45%. In the biodistribution study, while the majority of the dose for all animals was found in the liver, kidneys and spleen, group III showed a significantly higher brain concentration than the other two groups (p < 0.001). This result was corroborated by the fluorescence microscopy studies, which showed enhanced dye penetration into the brain tissue for group III. Further studies need to be done to elucidate the exact mechanism responsible for the increased brain uptake of dye to help us understand if the magnetic nanoparticles actually penetrate the blood brain barrier or merely deliver a massive load of dye just outside it, thereby triggering passive diffusion into the brain parenchyma. These results reinforce the potential use of polymeric magnetically-targeted nanoparticles in active brain targeting and imaging.

Kirthivasan, Bharat; Singh, Dhirender; Raut, Sangram; Bommana, Murali Mohan; Squillante, Emilio, III; Sadoqi, Mostafa

2012-03-01

326

Space environmental effects on polymeric materials  

NASA Technical Reports Server (NTRS)

Polymer-matrix composites have considerable potential for use in the construction of orbiting structures such as the space station and space antennas because of their light weight, high strength, and low thermal expansion. However, they can suffer surface erosion by interaction with atomic oxygen in low-Earth orbit and degradation and/or embrittlement by electrons and ultraviolet radiation especially in geosynchronous orbit. Thus, a study of the effect of these environmental hazards on polymeric materials is an important step in the assessment of such materials for future use in space.

Kiefer, Richard L.; Orwoll, Robert A.

1988-01-01

327

Free radical polymerization of poly(ethylene glycol) diacrylate macromers: impact of macromer hydrophobicity and initiator chemistry on polymerization efficiency.  

PubMed

A series of poly(ethylene glycol)-co-poly(lactide) diacrylate macromers was synthesized with variable PEG molecular weights (10 or 20 kDa) and lactate contents (0 or 6 lactates per end group). These macromers were polymerized to form hydrogels by free radical polymerization using either redox or photochemical initiators. The extent of polymerization was determined by monitoring the compressive modulus of the resulting hydrogels and by quantitative determination of unreacted acrylate after exhaustive hydrolysis of the gel. Polymerization efficiency was found to depend on the lactate content of the macromer, with higher lactate macromers giving more efficient polymerization. For redox-initiated polymerization using ferrous gluconate/t-butyl hydroperoxide initiator, macromers containing approximately six lactate repeats per end group required lower concentrations of initiator to reach high conversion than lactate-free macromers. Photochemical polymerization with ?,?-dimethoxy-?-phenylacetophenone (Irgacure 651(®)) was found to be less efficient than redox polymerization, requiring the addition of N-vinyl-2- pyrrolidone (NVP) as a co-monomer to achieve conversions comparable with redox polymerization. When conditions were optimized to provide near complete conversion for all gels, the presence of lactate repeat units in the hydrogel was generally found to reduce swelling and increase the compressive modulus. Calculated values of molecular weight between cross-links (M(c)) and mesh size using Flory-Rehner theory showed that macromer molecular weight had the greatest impact on the network structure of the gel. PMID:21232638

Dai, Xiaoshu; Chen, Xi; Yang, Laura; Foster, Sarah; Coury, Arthur J; Jozefiak, Thomas H

2011-05-01

328

Incremental Reduced Support Vector Machines  

Microsoft Academic Search

The reduced support vector machine (RSVM) has been proposed to avoid the com- putational difficulties in generating a nonlin- ear support vector machine classifier for a massive dataset. RSVM selects a small ran- dom subset from the entire dataset with a user pre-specified size \\

Yuh-Jye Lee; Hung-Yi Lo; Su-Yun Huang

329

Active set support vector regression  

Microsoft Academic Search

This paper presents active set support vector regression (ASVR), a new active set strategy to solve a straightforward reformulation of the standard support vector regression problem. This new algorithm is based on the successful ASVM algorithm for classification problems, and consists of solving a finite number of linear equations with a typically large dimensionality equal to the number of points

David R. Musicant; Alexander Feinberg

2004-01-01

330

Evolutionary Support Vector Regression Machines  

Microsoft Academic Search

Evolutionary support vector machines (ESVMs) are a novel technique that assimilates the learning engine of the state-of-the-art support vector machines (SVMs) but evolves the coefficients of the decision function by means of evo- lutionary algorithms (EAs). The new method has accom- plished the purpose for which it has been initially devel- oped, that of a simpler alternative to the canonical

Ruxandra Stoean; Dumitru Dumitrescu; Mike Preuss; Catalin Stoean

2006-01-01

331

Vector reconstruction from firing rates  

Microsoft Academic Search

In a number of systems including wind detection in the cricket, visual motion perception and coding of arm movement direction in the monkey and place cell response to position in the rat hippocampus, firing rates in a population of tuned neurons are correlated with a vector quantity. We examine and compare several methods that allow the coded vector to be

Emilio Salinas; L. F. Abbott

1994-01-01

332

Novel Bacteriophage lambda Cloning Vector  

Microsoft Academic Search

A simple method for generating phage collections representing eukaryotic genomes has been developed by using a novel bacteriophage lambda vector, lambda 1059. The phage is a BamHI substitution vector that accommodates DNA fragments 6-24 kilobases long. Production of recombinants in lambda 1059 requires deletion of the lambda red and gamma genes. The recombinants are therefore spi- and may be separated

Jonathan Karn; Sydney Brenner; Leslie Barnett; Gianni Cesareni

1980-01-01

333

A model for treating avian aspergillosis: serum and lung tissue kinetics for Japanese quail (Coturnix japonica) following single and multiple aerosol exposures of a nanoparticulate itraconazole suspension.  

PubMed

Aspergillosis is frequently reported in parrots, falcons and other birds held in captivity. Inhalation is the main route of infection for Aspergillus fumigatus, resulting in both acute and chronic disease conditions. Itraconazole (ITRA) is an antifungal commonly used in birds, but administration requires repeated oral dosing and the safety margin is narrow. We describe lung tissue and serum pharmacokinetics of a nanoparticulate ITRA suspension administered to Japanese quail by aerosol exposure. Aerosolized ITRA (1 and 10% suspension) administered over 30 min did not induce adverse clinical reactions in quail upon single or 5-day repeated doses. High lung concentrations, well above the inhibitory levels for A. fumigatus, of 4.14 ± 0.19 ?g/g and 27.5 ± 4.58 ?g/g (mean ± SEM, n = 3), were achieved following single-dose inhalation of 1% and 10% suspension, respectively. Upon multiple dose administration of 10% suspension, mean lung concentrations reached 104.9 ± 10.1 ?g/g. Drug clearance from the lungs was slow with terminal half-lives of 19.7 h and 35.8 h following inhalation of 1% and 10% suspension, respectively. Data suggest that lung clearance is solubility driven. Lung concentrations of hydroxy-itraconazole reached 1-2% of the ITRA lung tissue concentration indicating metabolism in lung tissue. Steady, but low, serum concentrations of ITRA could be measured after multiple dose administration, reaching less than 0.1% of the lung tissue concentration. This formulation may represent a novel, easy to administer treatment modality for fungal lung infection, preventing high systemic exposure. It may also be useful as metaphylaxis to prevent the outbreak of aspergillosis in colonized animals. PMID:23815436

Rundfeldt, Chris; Wyska, El?bieta; Steckel, Hartwig; Witkowski, Andrzej; Je?ewska-Witkowska, Gra?yna; Wla?, Piotr

2013-11-01

334

A neural support vector machine.  

PubMed

Support vector machines are state-of-the-art pattern recognition algorithms that are well founded in optimization and generalization theory but not obviously applicable to the brain. This paper presents Bio-SVM, a biologically feasible support vector machine. An unstable associative memory oscillates between support vectors and interacts with a feed-forward classification pathway. Kernel neurons blend support vectors and sensory input. Downstream temporal integration generates the classification. Instant learning of surprising events and off-line tuning of support vector weights trains the system. Emotion-based learning, forgetting trivia, sleep and brain oscillations are phenomena that agree with the Bio-SVM model. A mapping to the olfactory system is suggested. PMID:20092978

Jändel, Magnus

2010-06-01

335

Divergence-based vector quantization.  

PubMed

Supervised and unsupervised vector quantization methods for classification and clustering traditionally use dissimilarities, frequently taken as Euclidean distances. In this article, we investigate the applicability of divergences instead, focusing on online learning. We deduce the mathematical fundamentals for its utilization in gradient-based online vector quantization algorithms. It bears on the generalized derivatives of the divergences known as Fréchet derivatives in functional analysis, which reduces in finite-dimensional problems to partial derivatives in a natural way. We demonstrate the application of this methodology for widely applied supervised and unsupervised online vector quantization schemes, including self-organizing maps, neural gas, and learning vector quantization. Additionally, principles for hyperparameter optimization and relevance learning for parameterized divergences in the case of supervised vector quantization are given to achieve improved classification accuracy. PMID:21299418

Villmann, Thomas; Haase, Sven

2011-05-01

336

Microwave-Assisted Nitroxide-Mediated Radical Polymerization of Acrylamide in Aqueous Solution  

E-print Network

1 Microwave-Assisted Nitroxide-Mediated Radical Polymerization of Acrylamide in Aqueous Solution for carrying out a living/controlled polymerization of acrylamide. Reasonable results were obtained after 100% of conversion. Keywords: microwave, acrylamide, controlled/living polymerization, Nitroxide

Paris-Sud XI, Université de

337

40 CFR 721.10568 - Diethanolamine salt of polymeric acid (generic).  

Code of Federal Regulations, 2013 CFR

...2013-07-01 false Diethanolamine salt of polymeric acid (generic). 721...Substances § 721.10568 Diethanolamine salt of polymeric acid (generic). (a...identified generically as diethanolamine salt of polymeric acid (PMN...

2013-07-01

338

40 CFR 721.10568 - Diethanolamine salt of polymeric acid (generic).  

Code of Federal Regulations, 2014 CFR

...2014-07-01 2014-07-01 false Diethanolamine salt of polymeric acid (generic...Chemical Substances § 721.10568 Diethanolamine salt of polymeric acid (generic...substance identified generically as diethanolamine salt of polymeric acid (PMN...

2014-07-01

339

Strong liquid-crystalline polymeric compositions  

DOEpatents

Strong liquid-crystalline polymeric (LCP) compositions of matter are described. LCP backbones are combined with liquid crystalline (LC) side chains in a manner which maximizes molecular ordering through interdigitation of the side chains, thereby yielding materials which are predicted to have superior mechanical properties over existing LCPs. The theoretical design of LCPs having such characteristics includes consideration of the spacing distance between side chains along the backbone, the need for rigid sections in the backbone and in the side chains, the degree of polymerization, the length of the side chains, the regularity of the spacing of the side chains along the backbone, the interdigitation of side chains in sub-molecular strips, the packing of the side chains on one or two sides of the backbone to which they are attached, the symmetry of the side chains, the points of attachment of the side chains to the backbone, the flexibility and size of the chemical group connecting each side chain to the backbone, the effect of semiflexible sections in the backbone and the side chains, and the choice of types of dipolar and/or hydrogen bonding forces in the backbones and the side chains for easy alignment. 27 figures.

Dowell, F.

1993-12-07

340

The polymerization reaction of muscle actin.  

PubMed

Recent advances in the studies of the aggregation of G-actin monomers, containing one molecule of ATP, to long filaments of F-actin, with a concomitant hydrolysis of the nucleotide to ADP, are reviewed. With the aid of omega-ATP, the association and dissociation rate constant of the nucleotide could be determined. The binding of the nucleotide is enhanced by the binding of one Ca++ ion, probably at a different site. The delta G value of the Mg++ or Ca++ induced polymerization has been determined to --39 to--59 kJ/mole, the critical protein concentration for the ATP-G-actin to ADP-F-actin conversion is very strongly influenced by the concentration of bivalent cations. The rate constants of the protein monomers, and the rate and equilibrium constants for the propagation step show the process to be extremely cooperative. Actin shows the interesting phenomenon of translocational head-to-tail polymerization, which may be regulated by ATP. The contact sites between the monomers in F-actin have been labeled by chemical modification. Two tryosine residues, 53 and 69, are probably close to one of the two sites. The ATP binding sites has been labeled by an ATP analog, and there is evidence that it is close to the contact site. PMID:340937

Engel, J; Fasold, H; Hulla, F W; Waechter, F; Wegner, A

1977-11-25

341

Directional growth of metallic and polymeric nanowires  

NASA Astrophysics Data System (ADS)

This work delineates the mechanism by which directional nanowire growth occurs in the directed electrochemical nanowire assembly (DENA) technique for growing nanowires on micro-electrode arrays. Indium, polythiophene, and polypyrrole nanowires are the subjects of this study. This technique allows the user to specify the growth path without the use of a mechanical template. Nanowire growth from a user-selected electrode to within ± 3 µm of the straight line path to a second electrode lying within a ~140° angular range and a ~100 µm radius of the selected electrode is demonstrated. Theory for one-dimensional electrochemical diffusion in the inter-electrode region reveals that screening of the applied voltage is incomplete, allowing a long range voltage component to extend from the biased to the grounded electrode. Numerical analysis of two-dimensional multi-electrode arrays shows that a linear ridge of electric field maxima bridges the gap between selected electrodes but decays in all other directions. The presence of this anisotropic, long range voltage defines the wire growth path and suppresses the inherent tip splitting tendency of amorphous polymeric materials. This technology allows polythiophene and polypyrrole to be grown as wires rather than fractal aggregates or films, establishing DENA as an on-chip approach to both crystalline metallic and amorphous polymeric nanowire growth.

Thapa, Prem S.; Ackerson, Bruce J.; Grischkowsky, Daniel R.; Flanders, Bret N.

2009-06-01

342

Predicting polymeric crystal structures by evolutionary algorithms.  

PubMed

The recently developed evolutionary algorithm USPEX proved to be a tool that enables accurate and reliable prediction of structures. Here we extend this method to predict the crystal structure of polymers by constrained evolutionary search, where each monomeric unit is treated as a building block with fixed connectivity. This greatly reduces the search space and allows the initial structure generation with different sequences and packings of these blocks. The new constrained evolutionary algorithm is successfully tested and validated on a diverse range of experimentally known polymers, namely, polyethylene, polyacetylene, poly(glycolic acid), poly(vinyl chloride), poly(oxymethylene), poly(phenylene oxide), and poly (p-phenylene sulfide). By fixing the orientation of polymeric chains, this method can be further extended to predict the structures of complex linear polymers, such as all polymorphs of poly(vinylidene fluoride), nylon-6 and cellulose. The excellent agreement between predicted crystal structures and experimentally known structures assures a major role of this approach in the efficient design of the future polymeric materials. PMID:25338876

Zhu, Qiang; Sharma, Vinit; Oganov, Artem R; Ramprasad, Ramamurthy

2014-10-21

343

Predicting polymeric crystal structures by evolutionary algorithms  

NASA Astrophysics Data System (ADS)

The recently developed evolutionary algorithm USPEX proved to be a tool that enables accurate and reliable prediction of structures. Here we extend this method to predict the crystal structure of polymers by constrained evolutionary search, where each monomeric unit is treated as a building block with fixed connectivity. This greatly reduces the search space and allows the initial structure generation with different sequences and packings of these blocks. The new constrained evolutionary algorithm is successfully tested and validated on a diverse range of experimentally known polymers, namely, polyethylene, polyacetylene, poly(glycolic acid), poly(vinyl chloride), poly(oxymethylene), poly(phenylene oxide), and poly (p-phenylene sulfide). By fixing the orientation of polymeric chains, this method can be further extended to predict the structures of complex linear polymers, such as all polymorphs of poly(vinylidene fluoride), nylon-6 and cellulose. The excellent agreement between predicted crystal structures and experimentally known structures assures a major role of this approach in the efficient design of the future polymeric materials.

Zhu, Qiang; Sharma, Vinit; Oganov, Artem R.; Ramprasad, Ramamurthy

2014-10-01

344

Radiofrequency plasma polymerized perfluoroionomer membrane materials  

SciTech Connect

Ion exchange membranes have received considerable attention in recent years. Applications of ion exchange membranes have included such electrochemical systems as water and organic electrolyzers, redox-flow batteries, and sensors. This work is a study of radiofrequency plasma polymerization of perfluorinated acid-containing monomers and a perfluorinated {open_quotes}backbone{close_quotes} comonomer as a method for synthesizing novel polyionomer film coatings for use as membranes on electrodes and biomedical sensors. The results indicate that, by altering the deposition conditions, some control can be exercised over the retention of acid functional groups by plasma polymers. Using AC impedance measurements, the ionic conductivity of these films was found to be two to four orders of magnitude higher than their aqueous environments. In addition, several of the acid-containing plasma polymerized films were hydrophilic, having an advancing water contact angle of less than fifteen degrees. The initial results of this study have demonstrated the feasibility of using acid-containing plasma polymers as crosslinked membrane materials suitable for use with electrochemical sensors and biosensors.

Danilich, M.J.; Gervasio, D.F.; Marchant, R.E. [Case Western Reserve Univ., Cleveland, OH (United States)

1993-12-31

345

Stimuli-responsive polymeric nanoparticles for nanomedicine.  

PubMed

Nature continues to be the ultimate in nanotechnology, where polymeric nanometer-scale architectures play a central role in biological systems. Inspired by the way nature forms functional supramolecular assemblies, researchers are trying to make nanostructures and to incorporate these into macrostructures as nature does. Recent advances and progress in nanoscience have demonstrated the great potential that nanomaterials have for applications in healthcare. In the realm of drug delivery, nanomaterials have been used in vivo to protect the drug entity in the systemic circulation, ensuring reproducible absorption of bioactive molecules that do not naturally penetrate biological barriers, restricting drug access to specific target sites. Several building blocks have been used in the formulation of nanoparticles. Thus, stability, drug release, and targeting can be tailored by surface modification. Herein the state of the art of stimuli-responsive polymeric nanoparticles are reviewed. Such systems are able to control drug release by reacting to naturally occurring or external applied stimuli. Special attention is paid to the design and nanoparticle formulation of these so-called smart drug-delivery systems. Future strategies for further developments of a promising controlled drug delivery responsive system are also outlined. PMID:25319803

Crucho, Carina I C

2015-01-01

346

Functionalized nanoparticle interactions with polymeric membranes  

PubMed Central

A series of experiments was performed to measure the retention of a class of functionalized nanoparticles (NPs) onporous (microfiltration and ultrafiltration) membranes. The findings impact engineered water and wastewater treatment using membrane technology, characterization and analytical schemes for NP detection, and the use of NPs in waste treatment scenarios. The NPs studied were composed of silver, titanium dioxide, and gold; had organic coatings to yield either positive or negative surface charge; and were between 2 and 10 nm in diameter. NP solutions were applied to polymeric membranes composed of different materials and pore sizes (ranging from ~2 nm [3 kDa molecular weight cutoff] to 0.2 ?m). Greater than 99% rejection was observed of positively charged NPs by negatively charged membranes even though pore diameters were up to 20 times the NP diameter; thus, sorption caused rejection. Negatively charged NPs were less well rejected, but behavior was dependant not only on surface functionality but on NP core material (Ag, TiO2, or Au). NP rejection depended more upon NP properties than membrane properties; all of the negatively charged polymeric membranes behaved similarly. The NP-membrane interaction behavior fell into four categories, which are defined and described here. PMID:22177020

Ladner, D.A.; Steele, M.; Weir, A.; Hristovski, K.; Westerhoff, P.

2011-01-01

347

Vector-valued automorphic forms and vector bundles  

E-print Network

While vector-valued automorphic forms can be defined for an arbitrary Fuchsian group $\\Gamma$ and an arbitrary representation $R$ of $\\Gamma$ in GL$(n,{\\mathbb C})$, their existence has been established in the literature only when restrictions are imposed on both $\\Gamma$ and $R$. In this paper, we prove the existence of $n$ linearly independent vector-valued automorphic forms for any Fuchsian group $\\Gamma$ and any $n$-dimensional complex representation $R$ of $\\Gamma$. To this end, we realize these automorphic forms as global sections of a special rank $n$ vector bundle built using solutions to the Riemann-Hilbert problem over various noncompact Riemann surfaces and Kodaira's vanishing theorem.

Hicham Saber; Abdellah Sebbar

2014-12-25

348

Nano Polymeric Carrier Fabrication Technologies for Advanced Antitumor Therapy  

PubMed Central

Comparing with the traditional therapeutic methods, newly developed cancer therapy based on the nanoparticulates attracted extensively interest due to its unique advantages. However, there are still some drawbacks such as the unfavorable in vivo performance for nanomedicine and undesirable tumor escape from the immunotherapy. While as we know that the in vivo performance strongly depended on the nanocarrier structural properties, thus, the big gap between in vitro and in vivo can be overcome by nanocarrier's structural tailoring by fine chemical design and microstructural tuning. In addition, this fine nanocarrier's engineering can also provide practical solution to solve the problems in traditional cancer immunotherapy. In this paper, we review the latest development in nanomedicine, cancer therapy, and nanoimmunotherapy. We then give an explanation why fine nanocanrrie's engineering with special focus on the unique pathology of tumor microenvironments and properties of immunocells can obviously promote the in vivo performance and improve the therapeutic index of nanoimmunotherapy. PMID:24369011

Li, Wei; Zhao, Mengxin; Ke, Changhong; Zhang, Ge; Zhang, Li; Li, Huafei; Zhang, Fulei; Sun, Yun; Dai, Jianxin; Wang, Hao; Guo, Yajun

2013-01-01

349

Mechanism of the catalytic polymerization of propene under pressure  

Microsoft Academic Search

Summary 1.It was established that, unlike the polymerization of propene over phosphoric acid (which proceeds by simple stepwise addition of propene), its polymerization over zinc chloride is accompanied by isomeric changes which result in the formation of hydrocarbons containing quaternary carbon atoms.2.It was shown that, apart from trialkylalkenes containing quaternary carbons or three consecutive tertiary carbons, the propene trimers included

L. I. Antsus; A. D. Petrov

1956-01-01

350

Probing polymerization forces by using actin-propelled lipid vesicles  

Microsoft Academic Search

Actin polymerization provides a powerful propulsion force for numerous types of cell motility. Although tremendous progress has been made in identifying the biochemical components necessary for actin-based motility, the precise biophysical mechanisms of force generation remain unclear. To probe the polymerization forces quantitatively, we introduce an experimental system in which lipid vesicles coated with the Listeria monocytogenes virulence factor ActA

Arpita Upadhyaya; Jeffrey R. Chabot; Albina Andreeva; Azadeh Samadani; Alexander van Oudenaarden

2003-01-01

351

Conduction mechanism in plasma polymerized lemongrass oil films  

Microsoft Academic Search

The electrical characteristics of radiofrequency plasma polymerized lemongrass oil is discussed in this paper. In plasma polymerized lemongrass oil film, Schottky conduction is observed and we found that the Schottky barrier height depends on the applied field, the field direction and the electrodes used.

D. Sakthi Kumar; M. G. Krishna Pillai

1999-01-01

352

POLYMERIZATION, MORPHOLOGY, AND CRYSTAL STRUCTURE OF POLY(p-BENZAMIDE)  

Microsoft Academic Search

Isothermal polymerization of acetaminobenzoic acid at various temperatures in bulk and solution was monitored by acetic acid evolution. The polymerization took place initially in a homogeneous phase, but it soon changed to heterogeneous as the polymer precipitated from the melt or solution. The reaction course consisted of a short induction period, followed by a fast second-order reaction and a third

H. Bao; F. Rybnikar; P. Saha; J. Yang; P. H. Geil

2001-01-01

353

Coupling of actin hydrolysis and polymerization: Reduced description with two  

E-print Network

OFFPRINT Coupling of actin hydrolysis and polymerization: Reduced description with two nucleotide of actin hydrolysis and polymerization: Reduced description with two nucleotide states X. Li1,2 , R to the hydrolysis of adenosine triphosphate (ATP), which involves both the cleavage of ATP and the release

Kierfeld, Jan

354

Aquacultural Engineering 19 (1999) 163178 Phosphate binding polymeric hydrogels for  

E-print Network

Aquacultural Engineering 19 (1999) 163­178 Phosphate binding polymeric hydrogels for aquaculture in the aquaculture industry. In this study, novel phosphate binding crosslinked poly(allylamine), PAA · HCl, polymeric hydrogel materials were developed, which efficiently bind phosphate anions in aquaculture

Rubloff, Gary W.

355

Stabilisation of titania pigment particles with anionic polymeric dispersants  

Microsoft Academic Search

The stabilisation of titania pigment in dry water-based paint films with anionic polymeric dispersants containing carboxylate groups was investigated. The results were compared to those obtained from rheological analysis of titania pigment suspensions. The polymeric dispersants chosen were polyacrylic acid and polyacrylamides copolymer modified with carboxylate groups. AFM and TEM were used to assess the distribution of the titania pigment

Saeed Farrokhpay; Gayle E. Morris; Daniel Fornasiero; Peter Self

2010-01-01

356

Anisotropic microporous supports impregnated with polymeric ion-exchange materials  

DOEpatents

Novel ion-exchange media are disclosed, the media comprising polymeric anisotropic microporous supports containing polymeric ion-exchange or ion-complexing materials. The supports are anisotropic, having small exterior pores and larger interior pores, and are preferably in the form of beads, fibers and sheets.

Friesen, Dwayne (Bend, OR); Babcock, Walter C. (Bend, OR); Tuttle, Mark (Bend, OR)

1985-05-07

357

Anisotropic microporous supports impregnated with polymeric ion-exchange materials  

DOEpatents

Novel ion-exchange media are disclosed, the media comprising polymeric anisotropic microporous supports containing polymeric ion-exchange or ion-complexing materials. The supports are anisotropic, having small exterior pores and larger interior pores, and are preferably in the form of beads, fibers and sheets. 5 figs.

Friesen, D.; Babcock, W.C.; Tuttle, M.

1985-05-07

358

Photoswitchable NHC-promoted ring-opening polymerizations.  

PubMed

The UV-induced photocyclization of a dithienylethene-annulated N-heterocyclic carbene precatalyst enabled photoswitchable ring-opening polymerizations of ?-caprolactone and ?-valerolactone. The polymerizations proceeded efficiently in ambient light, however UV irradiation attenuated the reaction rate (k(amb)/k(UV) = 59). Subsequent visible light exposure reversed the photocyclization and restored catalytic activity. PMID:23665923

Neilson, Bethany M; Bielawski, Christopher W

2013-06-18

359

Developments of rare earth metal catalysts for olefin polymerization  

Microsoft Academic Search

This review article describes recent developments in rare earth metal complexes as polymerization catalysts, focusing on the polymerization of ethylene and ?-olefins. Most of this kind of catalysts had been based on metallocene type complexes, and their catalytic behaviors are surveyed. Advanced series of half-metallocene and non-Cp type catalyst systems are also summarized.

Yuushou Nakayama; Hajime Yasuda

2004-01-01

360

Polymerization kinetics in three-dimensional direct laser writing.  

PubMed

By in-situ measuring the scattered light during microstructure formation, the polymerization kinetics of three-dimensional direct laser writing are investigated in detail. Oxygen quenching, oxygen diffusion, and inhibitor depletion are shown to have substantial impact on the kinetic behavior. For typical photoresists based on multifunctional acrylates, the polymerization occurs in less than a millisecond. PMID:25146724

Mueller, Jonathan B; Fischer, Joachim; Mayer, Frederik; Kadic, Muamer; Wegener, Martin

2014-10-01

361

Micropatterned composite membranes of polymerized and fluid lipid bilayers.  

PubMed

Micropatterned composite membranes of polymerized and fluid lipid bilayers were constructed on solid substrates. Lithographic photopolymerization of a diacetylene-containing phospholipid, 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DiynePC), and subsequent removal of nonreacted monomers by a detergent solution (0.1 M sodium dodecyl sulfate (SDS)) yielded a patterned polymeric bilayer matrix on the substrate. Fluid lipid bilayers of phosphatidylcholine from egg yolk (egg-PC) were incorporated into the lipid-free wells surrounded by the polymeric bilayers through the process of fusion and reorganization of suspended small unilamellar vesicles. Spatial distribution of the fluid bilayers in the patterned bilayer depended on the degree of photopolymerization that in turn could be modulated by varying the applied UV irradiation dose. The polymeric bilayer domains blocked lateral diffusion of the fluid lipid bilayers and confined them in the defined areas (corrals), if the polymerization was conducted with a sufficiently large UV dose. On the other hand, lipid molecules of the fluid bilayers penetrated into the polymeric bilayer domains, if the UV dose was relatively small. A direct correlation was observed between the applied UV dose and the lateral diffusion coefficient of fluorescent marker molecules in the fluid bilayers embedded within the polymeric bilayer domains. Artificial control of lateral diffusion by polymeric bilayers may lead to the creation of complex and versatile biomimetic model membrane arrays. PMID:15323525

Morigaki, Kenichi; Kiyosue, Kazuyuki; Taguchi, Takahisa

2004-08-31

362

Polymeric vehicles for topical delivery and related analytical methods.  

PubMed

Recently a variety of polymeric vehicles, such as micelles, nanoparticles, and polymersomes, have been explored and some of them are clinically used to deliver therapeutic drugs through skin. In topical delivery, the polymeric vehicles as drug carrier should guarantee non-toxicity, long-term stability, and permeation efficacy for drugs, etc. For the development of the successful topical delivery system, it is of importance to develop the polymeric vehicles of well-defined intrinsic properties, such as molecular weights, HLB, chemical composition, topology, specific ligand conjugation and to investigate the effects of the properties on drug permeation behavior. In addition, the role of polymeric vehicles must be elucidated in in vitro and in vivo analyses. This article describes some important features of polymeric vehicles and corresponding analytical methods in topical delivery even though the application span of polymers has been truly broad in the pharmaceutical fields. PMID:24643380

Cho, Heui Kyoung; Cho, Jin Hun; Jeong, Seong Hoon; Cho, Dong Chul; Yeum, Jeong Hyun; Cheong, In Woo

2014-04-01

363

Controlled Polymerization by Incarceration of Monomers in Nanochannels  

NASA Astrophysics Data System (ADS)

Porous Coordination Polymers (PCPs) composed of transition metal ions and bridging organic ligands have been extensively studied. The characteristic features of PCPs are highly regular channel structures, controllable channel sizes approximating molecular dimensions, designable surface potentials and functionality, and flexible frameworks responsive to guest molecules. Owing to these advantages, successful applications of PCPs range from molecular storage and separation to heterogeneous catalysts. In particular, use of their regulated and tunable nanochannels in the field of polymerization has allowed multi-level control of polymerization via control of stereoregularlity, molecular weight, etc. In this chapter, we focus on recent progress in polymerization utilizing the nanochannels of PCPs, and demonstrate why this polymerization system is attractive and promising from the viewpoint of precision control of polymeric structures.

Uemura, Takashi; Kitagawa, Susumu

364

Novel plasma polymerized films under dc glow discharge  

SciTech Connect

It has been reported that various dielectric films can be readily prepared by plasma polymerization, but these films have been made using AC glow discharge at a specific frequency (such as RF). in this paper, we examined the plasma polymerization of non-fluorinated and fluorinated aromatic hydrocarbons using a new plasma polymerization system that used DC glow discharge. Features of this DC system are; (1) polymerization proceeds under an isotropic electric field, (2) density of cations around the substrate on the cathode is high, (3) the polymer that accumulates during the initial stage is exposed to the DC discharge for a long period of time, (4) depth profile of the polymer films is isotropic, especially when polar monomers are used. The results of ESCA of plasma polymerized films indicated that the content of fluorine in the polymer films was isotropic with the film depth. Dielectric properties of the films were also examined.

Kakimoto, Masa-aki; Suwa, Toshihiro; Imai, Yoshio [Tokyo Institute of Technology (Japan)

1995-12-01

365

Self-Organized and Cu-Coordinated Surface Linear Polymerization  

PubMed Central

We demonstrate a controllable surface-coordinated linear polymerization of long-chain poly(phenylacetylenyl)s that are self-organized into a “circuit-board” pattern on a Cu(100) surface. Scanning tunneling microscopy/spectroscopy (STM/S) corroborated by ab initio calculations, reveals the atomistic details of the molecular structure, and provides a clear signature of electronic and vibrational properties of the poly(phenylacetylene)s chains. Notably, the polymerization reaction is confined epitaxially to the copper lattice, despite a large strain along the polymerized chain that subsequently renders it metallic. Polymerization and depolymerization reactions can be controlled locally at the nanoscale by using a charged metal tip. This control demonstrates the possibility of precisely accessing and controlling conjugated chain-growth polymerization at low temperature. This finding may lead to the bottom-up design and realization of sophisticated architectures for molecular nano-devices. PMID:23811605

Li, Qing; Owens, Jonathan R.; Han, Chengbo; Sumpter, Bobby G.; Lu, Wenchang; Bernholc, Jerzy; Meunier, V.; Maksymovych, Peter; Fuentes-Cabrera, Miguel; Pan, Minghu

2013-01-01

366

Chikungunya virus-vector interactions.  

PubMed

Chikungunya virus (CHIKV) is a mosquito-borne alphavirus that causes chikungunya fever, a severe, debilitating disease that often produces chronic arthralgia. Since 2004, CHIKV has emerged in Africa, Indian Ocean islands, Asia, Europe, and the Americas, causing millions of human infections. Central to understanding CHIKV emergence is knowledge of the natural ecology of transmission and vector infection dynamics. This review presents current understanding of CHIKV infection dynamics in mosquito vectors and its relationship to human disease emergence. The following topics are reviewed: CHIKV infection and vector life history traits including transmission cycles, genetic origins, distribution, emergence and spread, dispersal, vector competence, vector immunity and microbial interactions, and co-infection by CHIKV and other arboviruses. The genetics of vector susceptibility and host range changes, population heterogeneity and selection for the fittest viral genomes, dual host cycling and its impact on CHIKV adaptation, viral bottlenecks and intrahost diversity, and adaptive constraints on CHIKV evolution are also discussed. The potential for CHIKV re-emergence and expansion into new areas and prospects for prevention via vector control are also briefly reviewed. PMID:25421891

Coffey, Lark L; Failloux, Anna-Bella; Weaver, Scott C

2014-11-01

367

Chikungunya Virus–Vector Interactions  

PubMed Central

Chikungunya virus (CHIKV) is a mosquito-borne alphavirus that causes chikungunya fever, a severe, debilitating disease that often produces chronic arthralgia. Since 2004, CHIKV has emerged in Africa, Indian Ocean islands, Asia, Europe, and the Americas, causing millions of human infections. Central to understanding CHIKV emergence is knowledge of the natural ecology of transmission and vector infection dynamics. This review presents current understanding of CHIKV infection dynamics in mosquito vectors and its relationship to human disease emergence. The following topics are reviewed: CHIKV infection and vector life history traits including transmission cycles, genetic origins, distribution, emergence and spread, dispersal, vector competence, vector immunity and microbial interactions, and co-infection by CHIKV and other arboviruses. The genetics of vector susceptibility and host range changes, population heterogeneity and selection for the fittest viral genomes, dual host cycling and its impact on CHIKV adaptation, viral bottlenecks and intrahost diversity, and adaptive constraints on CHIKV evolution are also discussed. The potential for CHIKV re-emergence and expansion into new areas and prospects for prevention via vector control are also briefly reviewed. PMID:25421891

Coffey, Lark L.; Failloux, Anna-Bella; Weaver, Scott C.

2014-01-01

368

Vector volume and black holes  

NASA Astrophysics Data System (ADS)

By examining the rate of growth of an invariant volume V of some spacetime region along a divergence-free vector field v?, we introduce the concept of a “vector volume” Vv. This volume can be defined in various equivalent ways. For example, it can be given as dV(?)/d?, where v???=d/d? and ? is a parameter distance along the integral curve of v. Equivalently, it can be defined as ?v?d??, where d?? is the directed surface element. We find that this volume is especially useful for the description of black holes, but it can be used in other contexts as well. Moreover, this volume has several properties of interest. Among these is the fact that the vector volume is linear with respect to the the choice of vector v?. As a result, for example, in stationary axially symmetric spacetimes with timelike Killing vectors t? and axially symmetric Killing vectors ??, the vector volume of an axially symmetric region with respect to the vector t?+??? is equal for any value of ?, a consequence of the additional result that ?? does not contribute to Vv. Perhaps of most interest is the fact that in Kerr-Schild spacetimes the volume element for the full spacetime is equal to that of the background spacetime. We discuss different ways of using the vector volume to define volumes for black holes. Finally, we relate our work to the recent widespread thermodynamically motivated study of the “volumes” of black holes associated with nonzero values of the cosmological constant ?.

Ballik, William; Lake, Kayll

2013-11-01

369

Versatile functionalization of gene vectors via different types of zwitterionic betaine species for serum-tolerant transfection.  

PubMed

For ideal polymeric gene vectors, their serum stability is of crucial importance. Polycation vectors usually suffer from colloidal aggregation, which makes them easily cleared from the bloodstream. Recently, we reported a comb-shaped vector (DPD) consisting of a dextran backbone and disulfide-linked cationic poly((2-dimethyl amino)ethyl methacrylate) side chains for efficient gene delivery. In this work, versatile functionalization of DPD (as a model gene vector) was proposed via the introduction of different types of zwitterionic carboxybetaine and sulfobetaine species for improving biophysical properties. The incorporation of zwitterionic betaine did not destroy the DNA condensation capability of vectors. All the zwitterionic betaine-functionalized DPD vectors exhibited lower cytotoxicities than the pristine DPD. The DPD-b-polycarboxybetaine block copolymer (DPDbPC) exhibited better gene delivery abilities than the corresponding DPD-r-polycarboxybetaine random copolymer (DPDrPC). Moreover, in the serum case with a high concentration (30%) of fetal bovine serum, the DPD-b-polysulfobetaine block copolymer (DPDbPS) produced much higher gene transfection efficiencies than DPDbPC. Cellular internalization results indicated that the incorporation of zwitterionic betaine could benefit serum stabilities of vectors and enhance cellular uptake. The present study demonstrated that proper incorporation of zwitterionic betaine into gene carriers was an effective method to produce serum-tolerant transfection vectors. PMID:23571001

Xiu, Ke-Mao; Zhao, Na-Na; Yang, Wan-Tai; Xu, Fu-Jian

2013-07-01

370

Emerging Vector-Borne Diseases – Incidence through Vectors  

PubMed Central

Vector-borne diseases use to be a major public health concern only in tropical and subtropical areas, but today they are an emerging threat for the continental and developed countries also. Nowadays, in intercontinental countries, there is a struggle with emerging diseases, which have found their way to appear through vectors. Vector-borne zoonotic diseases occur when vectors, animal hosts, climate conditions, pathogens, and susceptible human population exist at the same time, at the same place. Global climate change is predicted to lead to an increase in vector-borne infectious diseases and disease outbreaks. It could affect the range and population of pathogens, host and vectors, transmission season, etc. Reliable surveillance for diseases that are most likely to emerge is required. Canine vector-borne diseases represent a complex group of diseases including anaplasmosis, babesiosis, bartonellosis, borreliosis, dirofilariosis, ehrlichiosis, and leishmaniosis. Some of these diseases cause serious clinical symptoms in dogs and some of them have a zoonotic potential with an effect to public health. It is expected from veterinarians in coordination with medical doctors to play a fundamental role at primarily prevention and then treatment of vector-borne diseases in dogs. The One Health concept has to be integrated into the struggle against emerging diseases. During a 4-year period, from 2009 to 2013, a total number of 551 dog samples were analyzed for vector-borne diseases (borreliosis, babesiosis, ehrlichiosis, anaplasmosis, dirofilariosis, and leishmaniasis) in routine laboratory work. The analysis was done by serological tests – ELISA for borreliosis, dirofilariosis, and leishmaniasis, modified Knott test for dirofilariosis, and blood smear for babesiosis, ehrlichiosis, and anaplasmosis. This number of samples represented 75% of total number of samples that were sent for analysis for different diseases in dogs. Annually, on average more then half of the samples brought to the laboratory to analysis for different infectious diseases are analyzed for vector-borne diseases. In the region of Vojvodina (northern part of Serbia), the following vector-borne infectious diseases have been found in dogs so far borreliosis, babesiosis, dirofilariosis, leishmaniasis, and anaplasmosis. PMID:25520951

Savi?, Sara; Vidi?, Branka; Grgi?, Zivoslav; Potkonjak, Aleksandar; Spasojevic, Ljubica

2014-01-01

371

Insecticide resistance and vector control.  

PubMed

Insecticide resistance has been a problem in all insect groups that serve as vectors of emerging diseases. Although mechanisms by which insecticides become less effective are similar across all vector taxa, each resistance problem is potentially unique and may involve a complex pattern of resistance foci. The main defense against resistance is close surveillance of the susceptibility of vector populations. We describe the mechanisms of insecticide resistance, as well as specific instances of resistance emergence worldwide, and discuss prospects for resistance management and priorities for detection and surveillance. PMID:19785227

Brogdon, William G; McAllister, Janet C

2004-01-01

372

Vector statistics of LANDSAT imagery  

NASA Technical Reports Server (NTRS)

A digitized multispectral image, such as LANDSAT data, is composed of numerous four dimensional vectors, which quantitatively describe the ground scene from which the data are acquired. The statistics of unique vectors that occur in LANDSAT imagery are studied to determine if that information can provide some guidance on reducing image processing costs. A second purpose of this report is to investigate how the vector statistics are changed by various types of image processing techniques and determine if that information can be useful in choosing one processing approach over another.

Jayroe, R. R., Jr.; Underwood, D.

1977-01-01

373

Inflation with Massive Vector Fields  

E-print Network

We investigate the coupling between the inflaton and massive vector fields. All renormalizable couplings with shift symmetry of the inflaton are considered. The massive vector can be decomposed into a scalar mode and a divergence-free vector mode. We show that the former naturally interacts with the inflaton and the latter decouples at tree level. The model in general predicts $f_{NL}^\\mathrm{equil} = \\mathcal{O}(1)$, while in some regions of the parameter space large non-Gaussianity can arise.

Liu, Junyu; Zhou, Siyi

2015-01-01

374

Colliders and brane vector phenomenology  

SciTech Connect

Brane world oscillations manifest themselves as massive vector gauge fields. Their coupling to the standard model is deduced using the method of nonlinear realizations of the spontaneously broken higher dimensional space-time symmetries. Brane vectors are stable and weakly interacting and therefore escape particle detectors unnoticed. LEP and Tevatron data on the production of a single photon in conjunction with missing energy are used to delineate experimentally excluded regions of brane vector parameter space. The additional region of parameter space accessible to the LHC as well as a future lepton linear collider is also determined by means of this process.

Clark, T. E.; Love, S. T.; Xiong, C.; Nitta, Muneto; Veldhuis, T. ter [Department of Physics, Purdue University, West Lafayette, Indiana 47907-2036 (United States); Department of Physics, Keio University, Hiyoshi, Yokohoma, Kanagawa, 223-8521 (Japan); Department of Physics and Astronomy, Macalester College, Saint Paul, Minnesota 55105-1899 (United States)

2008-12-01

375

Idea Bank: Vector, Vector--That's Our Cry!  

NSDL National Science Digital Library

There are all kinds of computer-based software programs and websites available to help students understand and manipulate vector quantities. But if you have the time and want to do something different, this Idea Bank describes an easy, low-tech, and fun activity for teaching the "head-to-tail" method of combining vectors and the difference between "distance" and "displacement." All you need for this activity are scissors, some envelopes, metersticks, and a football field.

Brown, Jeremy

2009-04-01

376

Space environmental effects on polymeric materials  

NASA Technical Reports Server (NTRS)

Polymeric materials that may be exposed on spacecraft to the hostile environment beyond Earth's atmosphere were subjected to atomic oxygen, electron bombardment, and ultraviolet radiation in terrestrial experiments. Evidence is presented for the utility of an inexpensive asher for determining the relative susceptibility of organic polymers to atomic oxygen. Kapton, Ultem, P1700 polysulfone, and m-CBB/BIS-A (a specially formulated polymer prepared at NASA Langley) all eroded at high rates, just as was observed in shuttle experiments. Films of Ultem, P1700 polysulfone, and m-CBB/BIS-A were irradiated with 85 keV electrons. The UV/VIS absorbance of Ultem was found to decay with time after irradiation, indicating free radical decay. The tensile properties of Ultem began to change only after it had been exposed to 100 Mrads. The effects of dose rate, temperature, and simultaneous vs. sequential electron and UV irradiation were also studied.

Kiefer, Richard L.; Orwoll, Robert A.

1987-01-01

377

Recent Progresses in Polymeric Smart Materials  

NASA Astrophysics Data System (ADS)

Smart materials can be defined as materials that sense and react to environmental conditions or stimuli. In recent years, a wide range of novel smart materials have been developed in biomaterials, sensors, actuators, etc. Their applications cover aerospace, automobile, telecommunications, etc. This paper presents some recent progresses in polymeric smart materials. Special emphasis is laid upon electroactive polymer (EAP), shape memory polymer (SMP) and their composites. For the electroactive polymer, an analysis of stability of dielectric elastomer using strain energy function is derived, and one type of electroactive polymer actuator is presented. For the shape memory polymer, a new method is developed to use infrared laser to actuate the SMP through the optical fiber embedded within the SMP. Electrically conductive nanocarbon powders are utilized as the fillers to improve the electrical conductivity of polymer. A series of fundamental investigations of electroactive SMP are performed and the shape recovery is demonstrated.

Liu, Yan-Ju; Lan, Xin; Lu, Hai-Bao; Leng, Jin-Song

378

Elastic, Conductive, Polymeric Hydrogels and Sponges  

PubMed Central

As a result of inherent rigidity of the conjugated macromolecular chains resulted from the delocalized ?-electron system along the polymer backbone, it has been a huge challenge to make conducting polymer hydrogels elastic by far. Herein elastic and conductive polypyrrole hydrogels with only conducting polymer as the continuous phase have been simply synthesized in the indispensable conditions of 1) mixed solvent, 2) deficient oxidant, and 3) monthly secondary growth. The elastic mechanism and oxidative polymerization mechanism on the resulting PPy hydrogels have been discussed. The resulting hydrogels show some novel properties, e.g., shape memory elasticity, fast functionalization with various guest objects, and fast removal of organic infectants from aqueous solutions, all of which cannot be observed from traditional non-elastic conducting polymer counterparts. What's more, light-weight, elastic, and conductive organic sponges with excellent stress-sensing behavior have been successfully achieved via using the resulting polypyrrole hydrogels as precursors. PMID:25052015

Lu, Yun; He, Weina; Cao, Tai; Guo, Haitao; Zhang, Yongyi; Li, Qingwen; Shao, Ziqiang; Cui, Yulin; Zhang, Xuetong

2014-01-01

379

Approaches to flame resistant polymeric materials  

NASA Technical Reports Server (NTRS)

Four research and development areas are considered for further exploration in the quest of more flame-resistant polymeric materials. It is suggested that improvements in phenolphthalein polycarbonate processability may be gained through linear free energy relationship correlations. Looped functionality in the backbone of a polymer leads to both improved thermal resistance and increased solubility. The guidelines used in the pyrolytic carbon production constitute a good starting point for the development of improved flame-resistant materials. Numerous organic reactions requiring high temperatures and the techniques of protected functionality and latent functionality constitute the third area for exploration. Finally, some well-known organic reactions are suggested for the formation of polymers that were not made before.

Liepins, R.

1975-01-01

380

Plant formins: membrane anchors for actin polymerization.  

PubMed

In plants, the actin cytoskeleton plays a fundamental role in intracellular transport, cell growth, and morphology. Formins are central regulators of actin polymerization and actin-based processes in many eukaryotes. Plants have a diverse family of formins and this diversity arose early in land plant evolution, probably deriving from family expansion and domain acquisition. Recently, formins from different plant lineages have been studied and the focus of these studies is beginning to shift from biochemical characterization to in vivo function. In vivo studies have shown that distinct biochemical activities confer specific cellular functions. Despite these differences, many plant formins have in common a direct link to the plasma membrane, suggesting that formins in plants are important links between the plasma membrane and actin remodeling. PMID:23317636

van Gisbergen, Peter A C; Bezanilla, Magdalena

2013-05-01

381

NDE of polymeric composite material bridge components  

NASA Astrophysics Data System (ADS)

Rapid advancements with respect to utilization of polymeric composite materials for bridge components is occurring. This situation is driven primarily by the potential improvements offered by these materials with respect to long term durability. However, because of the developmental nature of these materials much of the materials characterization has involved short term testing without the synergistic effects of environmental exposure. Efforts to develop nondestructive evaluation procedures, essential for any wide spread use in critical structural applications, have been consequently limited. This paper discuses the effort to develop NDE methods for field inspection of hybrid glass and carbon fiber reinforced vinyl ester pultruded 'double box' I beams that are installed in a small bridge over Tom's Creek, in Blacksburg, Virginia. Integrated structural element sensors, dormant infrared devices, as well as acousto-ultrasonic methods are under development for detecting and monitoring the occurrence and progression of life limiting deterioration mechanisms.

Duke, John C., Jr.; Horne, Michael R.

1998-03-01

382

Vector meson production at HERA  

E-print Network

The rich experimental landscape of exclusive vector meson production at the high energy electron-proton collider HERA is reviewed, with emphasis on the transition from soft to hard diffraction and QCD interpretations.

Pierre Marage

2008-10-20

383

Exclusive vector meson electroproduction @ CLAS  

E-print Network

We present the results of exclusive electroproduction of vector mesons on the proton at CLAS. We discuss the interpretation of these cross sections in terms of t-channel Reggeon exchanges and in terms of Generalized Parton Distributions (GPDs) formalism.

Ahmed Fradi

2010-09-20

384

Gauge theories of vector particles  

Microsoft Academic Search

The possibility of generalizing the Yang-Mills trick is examined. Thus we seek theories of vector bosons invariant under continuous groups of coordinate-dependent linear transformations. All such theories may be expressed as superpositions of certain \\

Sheldon L. Glashow; Murray Gell-Mann

1961-01-01

385

Formation of polymeric toroidal-spiral particles.  

PubMed

Compared to spherical matrices, particles with well-defined internal structure provide large surface to volume ratio and predictable release kinetics for the encapsulated payloads. We describe self-assembly of polymeric particles, whereby competitive kinetics of viscous sedimentation, diffusion, and cross-linking yield a controllable toroidal-spiral (T-S) structure. Precursor polymeric droplets are splashed through the surface of a less dense, miscible solution, after which viscous forces entrain the surrounding bulk solution into the sedimenting polymer drop to form T-S channels. The intricate structure forms because low interfacial tension between the two miscible solutions is dominated by viscous forces. The biocompatible polymer, poly(ethylene glycol) diacrylate (PEG-DA), is used to demonstrate the solidification of the T-S shapes at various configurational stages by UV-triggered cross-linking. The dimensions of the channels are controlled by Weber number during impact on the surface, and Reynolds number and viscosity ratio during subsequent sedimentation. We anticipate applications of the T-S particle in drug delivery, wherein diffusion through these T-S channels and the polymer matrix would offer parallel release pathways for molecules of different sizes. Polyphosphate, as a model macromolecule, is entrained in T-S particles during their formation. The in vitro release kinetics of polyphosphate from the T-S particles with various channel length and width is reported. In addition, self-assembly of T-S particles occurs in a single step under benign conditions for delicate macromolecules, and appears conducive to scaleup. PMID:22077402

Sharma, Vishal; Szymusiak, Magdalena; Shen, Hao; Nitsche, Ludwig C; Liu, Ying

2012-01-10

386

High temperature, structural, polymeric foams from high internal phase emulsion polymerization  

SciTech Connect

This presentation will discuss our initial work on producing high temperature, polymeric, structural foams using a high internal phase emulsion (HIPE) to copolymerize styrene with maleimide based monomers. In this work, N-ethylmaleimide and a bismaleimide (BMI) monomer, Bis(3-ethyl-5-methyl-4-maleimide-phenyl)methane, were successfully free radically copolymerized with styrene in a water-in-oil HIPE to produce polymeric foams with glass transition temperatures (Tg) ranging from 140-220{degrees}C (284-428{degrees}F) depending on composition. The ethylmaleimide and BMI were uniformly incorporated throughout the polymer, which allowed the thermal performance of the foams to be tailored by controlling the concentration of ethylmaleimide and BMI modifiers. In addition, the thermal oxidative stability of the foam systems increased with increasing concentration of maleimide based monomers. The resulting polymeric foams contained an open cell morphology with cell sizes of approximately 10 {mu}m in diameter. Compression tests of the high temperature foam systems showed that compression strengths of approximately 700-850 kPa (100-125 psi) were obtainable at foam densities under 80 mg/cm{sup 3} (5.0 lb/ft{sup 3}).

Hoisington, M.A.; Duke, J.R.; Aspen, P.G. [Los Alamos National Lab., NM (United States)

1996-10-01

387

Simplified Support Vector Decision Rules  

Microsoft Academic Search

A Support Vector Machine (SVM) is a universal learning machine whose decision surfaceis parameterized by a set of support vectors and by a set of corresponding weights.An SVM is also characterized by a kernel function. Choice of the kernel determines whether the resulting SVM is a polynomial classifier, a two-layer neural network, a radialbasis function machine, or some otherlearning machine.SVMs

Christopher J. C. Burges

1996-01-01

388

Efficient Structured Support Vector Regression  

Microsoft Academic Search

\\u000a Support Vector Regression (SVR) has been a long standing problem in machine learning, and gains its popularity on various\\u000a computer vision tasks. In this paper, we propose a structured support vector regression framework by extending the max-margin\\u000a principle to incorporate spatial correlations among neighboring pixels. The objective function in our framework considers\\u000a both label information and pairwise features, helping to

Ke Jia; Lei Wang; Nianjun Liu

2010-01-01

389

Vector control after malaria eradication  

PubMed Central

In considerable areas now in or near the consolidation phase of malaria eradication, other vector-borne diseases present serious public health problems, even though not susceptible to control on the same world-wide scale as malaria. Several of these areas are already making plans for converting their malaria eradication services to vector control services. While it is possible to use essentially the same personnel and equipment, the methods must be adapted to the biology and habits of the vector. For a smooth and rapid transition, considerable advance planning is therefore needed—preferably well ahead of the consolidation phase. The author gives several examples of the need for flexibility in effecting the changeover and of the problems likely to arise after the completion of malaria eradication programmes. He recommends that epidemiological studies should be extended to vector-borne diseases other than malaria while eradication programmes are still in progress and that vector control programmes should be integrated into the basic health services of the country as soon as possible. He also underlines the importance of water management and other aspects of environmental sanitation in vector control programmes. PMID:20604169

Micks, D. W.

1963-01-01

390

Gene therapy using retroviral vectors.  

PubMed

Gene therapy is a novel approach for treating various congenital and acquired genetic disorders, including cancer, heart disease, and acquired immune deficiency syndrome. Amongst possible gene delivery systems, retroviral vector mediated gene transfer has been the most extensively studied and has been approved for use in over 40 current Phase I/II clinical trials for the treatment of various disorders, primarily cancers. Recent technological improvements include the optimization of vector production by concentration and lyophilization, resulting in high titers of vectors, as well as the large-scale production of vector-produced cells for the treatment of brain cancer. Present clinical protocols require specialized care centers with expertise in molecular biology and cell transplantation. Considerable effort is under way to develop retroviral vectors that can be both injected directly into the body and targeted to specific cell types within the body. Such vectors could be administered to patients by physicians in their offices. Successful development of this new technology would greatly expand the clinical potential of gene therapy. PMID:7765744

Gordon, E M; Anderson, W F

1994-12-01

391

Adaptive neural network vector predictor  

NASA Astrophysics Data System (ADS)

In this paper, an adaptive neural network vector predictor is designed in order to improve the performance of the predictive component of the predictive vector quantizer (PVQ). The proposed vector predictor consists of a set of dedicated predictors (experts) where each predictor is optimized for a particular class of input vectors. In our simulations, we used five multi-layer perceptrons (MLP) to design our expert predictors. Each MLP predictor is separately trained by using a set of training vectors that belong to a particular class. The class identity of each training vector is determined by its directional variances. In our current implementation, one predictor is optimized for stationary blocks and four other predictors are designed for horizontal, vertical, 45 degree and 135 degree diagonally oriented edge blocks. The back-propagation algorithm is used for training each network. The directional variances of the neighboring blocks are used to select the appropriate expert predictor for the current input block. Therefore, no overhead information is transmitted in order to inform the receiver about the predictor selection. Our simulation shows that the proposed scheme gives an improvement of more than 1 dB over the predictor consisting of a single MLP predictor. The perceptual quality of the predicted images are also significantly improved.

Wang, Lin-Cheng; Rizvi, Syed A.; Nasrabadi, Nasser M.; Mirelli, Vincent

1996-03-01

392

Phospholipid vesicle fusion on micropatterned polymeric bilayer substrates.  

PubMed

As an approach to create versatile model systems of the biological membrane we have recently developed a novel micropatterning strategy of substrate-supported planar lipid bilayers (SPBs) based on photolithographic polymerization of a diacetylene phospholipid, 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine. The micropatterned SPBs are composed of a polymeric bilayer matrix and embedded fluid lipid bilayers. In this study, we investigated the incorporation of fluid bilayers into micropatterned polymeric bilayer matrices through the adsorption and reorganization of phospholipid vesicles (vesicle fusion). Total internal reflection fluorescence microscopy observation showed that vesicle fusion started at the boundary of polymeric bilayers and propagated into the central part of lipid-free regions. On the other hand, quartz crystal microbalance with dissipation monitoring revealed that the transformation from adsorbed vesicles into SPBs was significantly accelerated for substrates with micropatterned polymeric bilayers. These results indicate that the edges of polymeric bilayers catalyze the formation of SPBs by destabilizing adsorbed vesicles and also support the premise that polymeric bilayers and embedded fluid bilayers are forming a continuous hybrid bilayer membrane, sealing energetically unfavorable bilayer edges. PMID:16766614

Okazaki, Takashi; Morigaki, Kenichi; Taguchi, Takahisa

2006-09-01

393

Vacuum stability requirements of polymeric material for spacecraft application  

NASA Technical Reports Server (NTRS)

The purpose of this document is to establish outgassing requirements and test guidelines for polymeric materials used in the space thermal/vacuum environment around sensitive optical or thermal control surfaces. The scope of this document covers the control of polymeric materials used near or adjacent to optical or thermal control surfaces that are exposed to the thermal/vacuum environment of space. This document establishes the requirements and defines the test method to evaluate polymeric materials used in the vicinity of these surfaces in space applications.

Craig, J. W.

1984-01-01

394

Rubber-like electrically conductive polymeric materials with shape memory  

NASA Astrophysics Data System (ADS)

This paper presents a heating-responsive shape memory polymeric material, which is not only rubber-like at room temperature and above its shape recovery temperature, but also electrically conductive. This polymeric material is made of silicone, melting glue (MG), and carbon black (CB). The influence of volume fractions of MG and CB on the elasticity, electrical resistivity, and shape memory effect of the polymeric material is systematically investigated. The feasibility of Joule heating for shape recovery is experimentally demonstrated with an electric power of 31 V.

Cui, H. P.; Song, C. L.; Huang, W. M.; Wang, C. C.; Zhao, Y.

2013-05-01

395

Photoinduced atom transfer radical polymerization using semiconductor nanoparticles.  

PubMed

Photoinduced atom transfer radical polymerization of methyl methacrylate initiated by in situ generation of copper (I) complex from higher oxidation state species using neat zinc oxide and iron-doped zinc oxide nanoparticles is investigated. The polymerizations proceed in a well-controlled manner under UV light at room temperature as evidenced by kinetic and light on-off experiments. The evolution of molecular weight with conversion shows good correlations between experimental and theoretical molecular weights, which confirmed good control over polymerization along with a narrow molecular weight distribution. PMID:24277641

Dadashi-Silab, Sajjad; Atilla Tasdelen, Mehmet; Mohamed Asiri, Abdullah; Bahadar Khan, Sher; Yagci, Yusuf

2014-02-01

396

Intrinsic embedded sensors for polymeric mechatronics: flexure and force sensing.  

PubMed

While polymeric fabrication processes, including recent advances in additive manufacturing, have revolutionized manufacturing, little work has been done on effective sensing elements compatible with and embedded within polymeric structures. In this paper, we describe the development and evaluation of two important sensing modalities for embedding in polymeric mechatronic and robotic mechanisms: multi-axis flexure joint angle sensing utilizing IR phototransistors, and a small (12 mm), three-axis force sensing via embedded silicon strain gages with similar performance characteristics as an equally sized metal element based sensor. PMID:24573310

Jentoft, Leif P; Dollar, Aaron M; Wagner, Christopher R; Howe, Robert D

2014-01-01

397

Synthesis of shape memory polyurethane using bulk polymerization  

NASA Astrophysics Data System (ADS)

In this paper, a series of shape memory polyurethanes (SMPUs) containing polycaprolactone diol (PCL4000), 1,4-butanediol (BDO), and 4,4'-diphenylmethane diisocyanate (MDI) were synthesized using bulk polymerization. Their thermal properties, thermomechanical properties were analyzed by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA), and the shape memory effect was also investigated. Moreover, one kind of shape memory polyurethane fiber was spinned by melting method from these prepared SMPUs and its shape memory properties were also investigated. The results showed that synthesis of shape memory polyurethane using bulk polymerization can effectively enhance the properties of polyurethanes, save cost and improve efficiency compared with solution polymerization.

Yang, Ziming; Jiang, Qiongling; He, Guanru; Zhou, Wuyi; Yang, Zhuohong

2009-07-01

398

Finding resultant vectors using a rubber band  

NASA Astrophysics Data System (ADS)

Most students have difficulty finding a resultant vector of graphical vector addition and subtraction. We offer here an alternative and simple way of finding a result of vector addition; using a rubber band, the magnitude and direction of a resultant vector can be shown immediately.

Wutchana, U.; Emarat, N.

2014-03-01

399

Image coding using vector quantization: a review  

Microsoft Academic Search

A review of vector quantization techniques used for encoding digital images is presented. First, the concept of vector quantization is introduced, then its application to digital images is explained. Spatial, predictive, transform, hybrid, binary, and subband vector quantizers are reviewed. The emphasis is on the usefulness of the vector quantization when it is combined with conventional image coding techniques, or

NASSER M. NASRABADI; ROBERT A. KING

1988-01-01

400

Method of preparing water purification membranes. [polymerization of allyl amine as thin films in plasma discharge  

NASA Technical Reports Server (NTRS)

Allyl amine and chemically related compounds are polymerized as thin films in the presence of a plasma discharge. The monomer compound can be polymerized by itself or in the presence of an additive gas to promote polymerization and act as a carrier. The polymerized films thus produced show outstanding advantages when used as reverse osmosis membranes.

Hollahan, J. R.; Wydeven, T. J., Jr. (inventors)

1974-01-01

401

Elliptic-symmetry vector optical fields.  

PubMed

We present in principle and demonstrate experimentally a new kind of vector fields: elliptic-symmetry vector optical fields. This is a significant development in vector fields, as this breaks the cylindrical symmetry and enriches the family of vector fields. Due to the presence of an additional degrees of freedom, which is the interval between the foci in the elliptic coordinate system, the elliptic-symmetry vector fields are more flexible than the cylindrical vector fields for controlling the spatial structure of polarization and for engineering the focusing fields. The elliptic-symmetry vector fields can find many specific applications from optical trapping to optical machining and so on. PMID:25321015

Pan, Yue; Li, Yongnan; Li, Si-Min; Ren, Zhi-Cheng; Kong, Ling-Jun; Tu, Chenghou; Wang, Hui-Tian

2014-08-11

402

Vector description of nonlinear magnetization  

NASA Astrophysics Data System (ADS)

The definition of the nonlinear magnetization, which is usually applied in investigating superconductors is discussed in this paper. The nonlinear magnetization of the superconductor, as the response to the alternating magnetic field, is a periodic time function and is determined by the sequence of complex numbers ?n= ?n'+i ?n?, n=1,2,3,… . The sequence ? n is named harmonic susceptibility. Finding some limits in this definition we propose a new description, substituting the complex sequence ? n with the sequence of real covariant vectors limit??j n. Such a definition of the nonlinear magnetization, using the vectors limit??n, allows to determine function M( t) of an investigated system for an arbitrary initial phase ?o of the inducing magnetic field H ac=h ac sin(?t+? o) . Vector description, in our opinion, is superior to the complex one in respect of explicitness, simplicity, and universality. Circular diagrams are used to illustrate the new vector description. We also show how the vectors of the harmonic susceptibility can be derived from both numeric calculations and experimental data.

Rysak, A.; Korczak, S. Z.

2001-06-01

403

Mechanical behavior of structural polymeric foams  

NASA Astrophysics Data System (ADS)

Polymeric foams, a type of porous material made in large volume and being capable of large recoverable defornation, have long been widely used in non-structural applications. For specific applications in vehicle safety and crashworthiness, the stress-strain relationship of these materials must be well understood so as to provide required inputs for finite element models. It is desirable that the mechanical properties be calculated from a single constitutive equation that describes the complete behavior under various loading conditions. This research is focused on the crushability of polymeric structural foams, under various strain rates (loading conditions). Five topics were covered in this dissertation. (1) Experimental investigation was conducted on the structural foams under uniaxial-stress and uniaxial-strain quasistatic conditions. A nonlinear multi-parameter phenomenological constitutive model, that is continuously differentiable and defined in the entire real domain such that the stress-strain responses can be characterized through a single-variable multi-parameter function, is developed and validated for the foam materials under large deformation. (2) A specialized quasistatic compressive test approach, named multi-step loading was then designed to check the uniformity of deformation in a foam specimen subjected to unixial-strain. A graphical analysis tool, named "crushability map" was developed, which was intended to characterize the crushability of foams completely, to facilitate selection of the appropriate candidates according to specific design criteria, to evaluate the residual crushability of foams. (3) The constitutive model was employed then to parametrically characterize the crushability and residual crushability of foams. The parameters in the model were expressed in terms of initial bulk density and/or porosity. It was demonstrated that the functional form of the parameters could be used to retrieve stress-strain response and crushability map, to parametrically represent the crushability and residual crushability. (4) A new data reduction procedure for high strain rate test on foams using polymer split Hopkinson pressure bar (SHPB) based on a novel iterative deconvolution algorithm to correct attenuation and dispersion including viscoelasticity characterization and data reduction was developed and validated. (5) High strain rate behavior of foams in comparison with quasistatic response was conducted. The failure modes and strain rate sensitivity parameter were analyzed and presented.

Liu, Qunli

404

Supramolecular Polymerization from Polypeptide-Grafted Comb Polymers  

SciTech Connect

The helical and tubular structures self-assembled from proteins have inspired scientists to design synthetic building blocks that can be 'polymerized' into supramolecular polymers through coordinated noncovalent interactions. However, cooperative supramolecular polymerization from large, synthetic macromolecules remains a challenge because of the difficulty of controlling the structure and interactions of macromolecular monomers. Herein we report the synthesis of polypeptide-grafted comb polymers and the use of their tunable secondary interactions in solution to achieve controlled supramolecular polymerization. The resulting tubular supramolecular structures, with external diameters of hundreds of nanometers and lengths of tens of micrometers, are stable and resemble to some extent biological superstructures assembled from proteins. This study shows that highly specific intermolecular interactions between macromolecular monomers can enable the cooperative growth of supramolecular polymers. The general applicability of this strategy was demonstrated by carrying out supramolecular polymerization from gold nanoparticles grafted with the same polypeptides on the surface.

Wang, Jing [ORNL; Lu, Hua [ORNL; Kamat, Ranjan K [ORNL; Pingali, Sai Venkatesh [ORNL; Urban, Volker S [ORNL; Cheng, Jianjun [University of Illinois, Urbana-Champaign; Lin, Yao [ORNL

2011-01-01

405

A highly active, isospecific cobalt catalyst for propylene oxide polymerization.  

PubMed

A highly active cobalt complex ((salph)CoOAc; salph = N,N'-bis(3,5-di-tert-butylsalicylidine-1,2-benzenediamine)) was discovered for the isospecific polymerization of rac-propylene oxide. PMID:16104709

Peretti, Kathryn L; Ajiro, Hiroharu; Cohen, Claire T; Lobkovsky, Emil B; Coates, Geoffrey W

2005-08-24

406

21 CFR 177.2250 - Filters, microporous polymeric.  

Code of Federal Regulations, 2012 CFR

...polymeric matrix of polyvinyl chloride, vinyl chloride-propylene, or vinyl chloride-vinyl acetate, in which finely divided silicon dioxide is embedded. Cyclohexanone may be used as a solvent in the production of the filters. (b) Any substance...

2012-04-01

407

21 CFR 177.2250 - Filters, microporous polymeric.  

Code of Federal Regulations, 2013 CFR

...polymeric matrix of polyvinyl chloride, vinyl chloride-propylene, or vinyl chloride-vinyl acetate, in which finely divided silicon dioxide is embedded. Cyclohexanone may be used as a solvent in the production of the filters. (b) Any substance...

2013-04-01

408

21 CFR 177.2250 - Filters, microporous polymeric.  

Code of Federal Regulations, 2014 CFR

...polymeric matrix of polyvinyl chloride, vinyl chloride-propylene, or vinyl chloride-vinyl acetate, in which finely divided silicon dioxide is embedded. Cyclohexanone may be used as a solvent in the production of the filters. (b) Any substance...

2014-04-01

409

Structural studies of the human polymeric immunoglobulin receptor  

E-print Network

The human polymeric immunoglobulin receptor, pIgR, is a glycosylated type I transmembrane protein expressed on the basolateral surface of secretory epithelial cells. pIgR plays a key role in mucosal immunity and, together ...

Hamburger, Agnes Eva, 1976-

2005-01-01

410

UV and electron beam-induced cationic polymerization  

NASA Astrophysics Data System (ADS)

This paper describes the basic photochemistry which has led to the development of rapid, efficient photoinitiators for UV-induced cationic polymerizations. These polymerizations are now widely employed in UV curing processes for such applications as coatings, adhesives and printing inks. The use of photosensitizers has enabled the extension of light-induced cationic polymerizations to the visible wavelength regions as well. Electron-beam irradiation is also capable of mediating the decomposition of cationic photoinitiators. The mechanism of this reaction involves reduction of the onium salt initiator by radicals generated by e-beam induced primary bond cleavage reactions. Rapid, efficient e-beam induced polymerizations at very low doses can be achieved through the use of specially designed monomers. The use of low energy electron beam radiation for thin film applications and high energy radiation to fabricate high performance carbon fiber reinforced epoxy resin matrix composites are described.

Crivello, James V.

1999-05-01

411

Investigation of potential injectable polymeric biomaterials for bone regeneration  

PubMed Central

This article reviews the potential injectable polymeric biomaterial scaffolds currently being investigated for application in bone tissue regeneration. Two types of injectable biomaterial scaffolds are focused in this review, including injectable microspheres and injectable gels. The injectable microspheres section covers several polymeric materials, including poly(l-lactide-co-glycolide)-PLGA, poly (propylene fumarate), and chitosan. The injectable gel section covers alginate gels, hyaluronan hydrogels, poly(ethylene-glycol)-PEG hydrogels, and PEG-PLGA copolymer hydrogels. This review focuses on the effect of cellular behaviorin vitro andin vivo in terms of material properties of polymers, such as biodegradation, biocompatibility, porosity, microsphere size, and cross-linking nature. Injectable polymeric biomaterials offer a major advantage for orthopedic applications by allowing the ability to use noninvasive or minimally invasive treatment methods. Therefore, combining injectable polymeric biomaterial scaffolds with cells have a significant potential to treat orthopedic bone defects, including spine fusion, and craniofacial and periodontal defects. PMID:23401336

Dreifke, Michael B.; Ebraheim, Nabil A.; Jayasuriya, Ambalangodage C.

2014-01-01

412

Emulsion Polymerization of Butyl Acrylate: Spin Trapping and EPR Study  

NASA Technical Reports Server (NTRS)

The propagating radical in the emulsion polymerization reaction of butyl acrylate was detected by Electron Paramagnetic Resonance spectroscopy using two spin trapping agents, 2-methyl-2nitrosopropane and alpha -N-tert-butylnitrone.

Kim, S.; Westmoreland, D.

1994-01-01

413

The unusual dynamics of parasite actin result from isodesmic polymerization  

PubMed Central

Previous reports have indicated that parasite actins are short and inherently unstable, despite being required for motility. Here, we re-examine the polymerization properties of actin in Toxoplasma gondii (TgACTI), unexpectedly finding that it exhibits isodesmic polymerization in contrast to the conventional nucleation-elongation process of all previously studied actins from both eukaryotes and bacteria. TgACTI polymerization kinetics lacks both a lag phase and critical concentration, normally characteristic of actins. Unique among actins, the kinetics of assembly can be fit with a single set of rate constants for all subunit interactions, without need for separate nucleation and elongation rates. This isodesmic model accurately predicts the assembly, disassembly, and the size distribution of TgACTI filaments in vitro, providing a mechanistic explanation for actin dynamics in vivo. Our findings expand the repertoire of mechanisms by which actin polymerization is governed and offer clues about the evolution of self-assembling, stabilized protein polymers. PMID:23921463

Skillman, Kristen M.; Ma, Christopher I.; Fremont, Daved H.; Diraviyam, Karthikeyan; Cooper, John A.; Sept, David; Sibley, L. David

2013-01-01

414

Polymeric micelles for multi-drug delivery in cancer.  

PubMed

Drug combinations are common in cancer treatment and are rapidly evolving, moving beyond chemotherapy combinations to combinations of signal transduction inhibitors. For the delivery of drug combinations, i.e., multi-drug delivery, major considerations are synergy, dose regimen (concurrent versus sequential), pharmacokinetics, toxicity, and safety. In this contribution, we review recent research on polymeric micelles for multi-drug delivery in cancer. In concurrent drug delivery, polymeric micelles deliver multi-poorly water-soluble anticancer agents, satisfying strict requirements in solubility, stability, and safety. In sequential drug delivery, polymeric micelles participate in pretreatment strategies that "prime" solid tumors and enhance the penetration of secondarily administered anticancer agent or nanocarrier. The improved delivery of multiple poorly water-soluble anticancer agents by polymeric micelles via concurrent or sequential regimens offers novel and interesting strategies for drug combinations in cancer treatment. PMID:25501872

Cho, Hyunah; Lai, Tsz Chung; Tomoda, Keishiro; Kwon, Glen S

2015-02-01

415

Energy dependent polymerization of resin-based composite  

Microsoft Academic Search

Objective: This study explores the relationship between the extent of polymerization and the radiant energy (dose) applied during the photopolymerization of resin-based composites.Method: FTIR was used to measure the 5-min and 24-h conversion of four resin-based composites prepared in a thin film and polymerized under conditions of decreasing intensity and a constant exposure time (30s) using a tungsten halogen curing

Rolf H. Halvorson; Robert L. Erickson; Carel L. Davidson

2002-01-01

416

Photoinitiated polymerization of vinyl ether-based systems  

Microsoft Academic Search

The photoinitiated polymerization of vinyl ether (VE)-based coatings has been studied by real-time infrared (RTIR) spectroscopy. In the presence of diaryliodonium or triarylsulfonium photoinitiators, the cationic polymerization occurs rapidly upon UV-exposure and continues to proceed upon storage in the dark. Increasing the formulation viscosity by introduction of telechelic VE oligomers was found to have a strong slowing down effect on

C Decker; C Bianchi; D Decker; F Morel

2001-01-01

417

Dynamics of Actin Cable Polymerization in Fission Yeast  

Microsoft Academic Search

In fission yeast, formin for3p nucleates actin filament bundles (cables) at cell tips which contribute to polarized cell growth. Actin cables reach a steady state of dynamic turnover involving for3p-mediated actin polymerization at the barbed ends near the plasma membrane, retrograde flow of polymerized actin toward the cell center, and cable disassembly. Formin for3p associates with actin at the cable

Hui Wang; Dimitrios Vavylonis

2008-01-01

418

In stress space charge probing during ageing of polymeric samples  

Microsoft Academic Search

Charge injection is known to occur in the prebreakdown stage in polymeric materials. It has recently been demonstrated that a time-resolved measurement of this charge is possible in a double-needle electrode configuration and under AC voltage using an analog experimental setup with a sensitivity of ≈10-14 C. A critical field for charge injection has been defined in two polymeric materials

T. Lebey; C. Laurent; C. Mayoux

1989-01-01

419

Spatial control of actin polymerization during neutrophil chemotaxis  

Microsoft Academic Search

Neutrophils respond to chemotactic stimuli by increasing the nucleation and polymerization of actin filaments, but the location and regulation of these processes are not well understood. Here, using a permeabilized-cell assay, we show that chemotactic stimuli cause neutrophils to organize many discrete sites of actin polymerization, the distribution of which is biased by external chemotactic gradients. Furthermore, the Arp2\\/3 complex,

Orion D. Weiner; Guy Servant; Matthew D. Welch; Timothy J. Mitchison; John W. Sedat; Henry R. Bourne

1999-01-01

420

Cryptosporidium parvum Infection Requires Host Cell Actin Polymerization  

PubMed Central

The intracellular protozoan parasite Cryptosporidium parvum accumulates host cell actin at the interface between the parasite and the host cell cytoplasm. Here we show that the actin polymerizing proteins Arp2/3, vasodilator-stimulated phosphoprotein (VASP), and neural Wiskott Aldrich syndrome protein (N-WASP) are present at this interface and that host cell actin polymerization is necessary for parasite infection. PMID:11500478

Elliott, David A.; Coleman, Daniel J.; Lane, Michael A.; May, Robin C.; Machesky, Laura M.; Clark, Douglas P.

2001-01-01

421

Polymerization shrinkage and elasticity of flowable composites and filled adhesives  

Microsoft Academic Search

Objectives: The magnitude and kinetics of polymerization shrinkage, together with elastic modulus, may be potential predictors of bond failure of adhesive restorations. This study examined these properties in visible-light-cured resins, in particular new flowable composites and filled adhesives.Methods: Polymerization shrinkage values were obtained by digital video imaging before and after light-curing; shrinkage kinetics were obtained by the “deflecting disk” method

R. Labella; P. Lambrechts; B. Van Meerbeek; G. Vanherle

1999-01-01

422

Polymerization of Pu(IV) in aqueous nitric acid solutions  

Microsoft Academic Search

The polymerization of Pu(IV) in aqueous nitric acid solutions has been studied spectrophotometrically both to establish the influence of large UO(NO) concentrations on the polymerization rates and, more generally, to review the influence of the major parameters on the polymer reaction. Typically, experiments have been performed at 50°C and with 0.05 M Pu in nitric acid solutions that vary in

L. M. Toth; H. A. Friedman; M. M. Osborne

1980-01-01

423

Plasma Polymerization of Aniline on Different Surface Functionalized Substrates  

Microsoft Academic Search

The plasma polymerization of aniline on different surface functionlized low-density polyethylene (LDPE) substrates was investigated, and the resulting polymer was characterized by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and atomic force microscopy. The results showed that the structure of plasma-polymerized polyaniline was rather different from polyaniline synthesized by conventional chemical and electrochemical methods. This difference may

Jinggong Wang; K. G. Neoh; Luping Zhao; E. T. Kang

2002-01-01

424

Thermally crosslinked polymeric compositions and methods of making the same  

DOEpatents

The various embodiments of the present disclosure relate generally to thermally crosslinked polymeric compositions and methods of making thermally crosslinked polymeric compositions. An embodiment of the present invention comprises a composition comprising: a first polymer comprising a first repeat unit, the first repeat unit comprising a carboxyl group, wherein the first polymer crosslinks to a second polymer formed from a second repeat unit, and wherein the first polymer crosslinks to the second polymer without formation of an ester group.

Koros, William John; Kratochvil, Adam Michal

2014-03-04

425

Process for impregnating a concrete or cement body with a polymeric material  

DOEpatents

A process for impregnating cementitious solids with polymeric materials by blending polymeric materials in a grout, allowing the grout to cure, and contacting the resulting solidified grout containing the polymeric materials with an organic mixture containing a monomer, a cross-linking agent and a catalyst. The mixture dissolves the polymerized particles and forms a channel for distributing the monomer throughout the network formed by the polymeric particles. The organic components are then cured to form a substantially water-impermeable mass.

Mattus, Alfred J. (Kingston, TN); Spence, Roger D. (Clinton, TN)

1989-01-01

426

Process for impregnating a concrete or cement body with a polymeric material  

DOEpatents

A process for impregnating cementitious solids with polymeric materials by blending polymeric materials in a grout, allowing the grout to cure, and contacting the resulting solidified grout containing the polymeric materials with an organic mixture containing a monomer, a cross-linking agent and a catalyst. The mixture dissolves the polymerized particles and forms a channel for distributing the monomer throughout the network formed by the polymeric particles. The organic components are then cured to form a substantially water-impermeable mass.

Mattus, A.J.; Spence, R.D.

1988-05-04

427

Prime Vectors in Degenerate Lattices  

NASA Astrophysics Data System (ADS)

In this paper the distribution of prime vectors (i.e., vectors with prime components) in degenerate lattices A{Z}^n+\\bar b is investigated, and asymptotic formulas are obtained for the fraction \\pi(N,\\,A{Z}^n,\\,\\bar b) which are valid under certain restrictions on the matrix A, where A\\in {Z}^{m\\times n}, \\bar b\\in {Z}^m, and \\pi(N,\\,A{Z}^n+\\bar b) is the number of prime vectors of the degenerate lattice A{Z}^n+\\bar b with components not exceeding N.The main idea is to reduce the problem to that of solving systems of linear algebraic equations in prime numbers belonging to given arithmetic progressions. An asymptotic formula for the number of solutions of such systems is calculated with the help of a multidimensional variant of the circle method.Bibliography: 12 titles.

Tulyaganova, M. I.

1986-02-01

428

Toward lattice fractional vector calculus  

NASA Astrophysics Data System (ADS)

An analog of fractional vector calculus for physical lattice models is suggested. We use an approach based on the models of three-dimensional lattices with long-range inter-particle interactions. The lattice analogs of fractional partial derivatives are represented by kernels of lattice long-range interactions, where the Fourier series transformations of these kernels have a power-law form with respect to wave vector components. In the continuum limit, these lattice partial derivatives give derivatives of non-integer order with respect to coordinates. In the three-dimensional description of the non-local continuum, the fractional differential operators have the form of fractional partial derivatives of the Riesz type. As examples of the applications of the suggested lattice fractional vector calculus, we give lattice models with long-range interactions for the fractional Maxwell equations of non-local continuous media and for the fractional generalization of the Mindlin and Aifantis continuum models of gradient elasticity.

Tarasov, Vasily E.

2014-09-01

429

Boosting with Averaged Weight Vectors  

NASA Technical Reports Server (NTRS)

AdaBoost is a well-known ensemble learning algorithm that constructs its constituent or base models in sequence. A key step in AdaBoost is constructing a distribution over the training examples to create each base model. This distribution, represented as a vector, is constructed to be orthogonal to the vector of mistakes made by the previous base model in the sequence. The idea is to make the next base model's errors uncorrelated with those of the previous model. Some researchers have pointed out the intuition that it is probably better to construct a distribution that is orthogonal to the mistake vectors of all the previous base models, but that this is not always possible. We present an algorithm that attempts to come as close as possible to this goal in an efficient manner. We present experimental results demonstrating significant improvement over AdaBoost and the Totally Corrective boosting algorithm, which also attempts to satisfy this goal.

Oza, Nikunj C.; Clancy, Daniel (Technical Monitor)

2002-01-01

430

Bouncing scalar field cosmology in the polymeric minisuperspace picture  

NASA Astrophysics Data System (ADS)

We study a cosmological setup consisting of a FRW metric as the background geometry with a massless scalar field in the framework of classical polymerization of a given dynamical system. To do this, we first introduce the polymeric representation of the quantum operators. We then extend the corresponding process to reach a transformation which maps any classical variable to its polymeric counterpart. It is shown that such a formalism has also an analogue in terms of the symplectic structure, i.e. instead of applying polymerization to the classical Hamiltonian to arrive its polymeric form, one can use a new set of variables in terms of which Hamiltonian retains its form but now the corresponding symplectic structure gets a new deformed functional form. We show that these two methods are equivalent and by applying them to the scalar field FRW cosmology see that the resulting scale factor exhibits a bouncing behavior from a contraction phase to an expanding era. Since the replacing of the big bang singularity by a bouncing behavior is one of the most important predictions of the quantum cosmological theories, we may claim that our polymerized classical model brings with itself some signals from quantum theory.

Vakili, B.; Nozari, K.; Hosseinzadeh, V.; Gorji, M. A.

2014-10-01

431

Bouncing scalar field cosmology in the polymeric minisuperspace picture  

E-print Network

We study a cosmological setup consisting of a FRW metric as the background geometry with a massless scalar field in the framework of classical polymerization of a given dynamical system. To do this, we first introduce the polymeric representation of the quantum operators. We then extend the corresponding process to reach a transformation which maps any classical variable to its polymeric counterpart. It is shown that such a formalism has also an analogue in terms of the symplectic structure, i.e., instead of applying polymerization to the classical Hamiltonian to arrive its polymeric form, one can use a new set of variables in terms of which Hamiltonian retains its form but now the corresponding symplectic structure gets a new deformed functional form. We show that these two methods are equivalent and by applying of them to the scalar field FRW cosmology see that the resulting scale factor exhibits a bouncing behavior from a contraction phase to an expanding era. Since the replacing of the big bang singularity by a bouncing behavior is one of the most important predictions of the quantum cosmological theories, we may claim that our polymerized classical model brings with itself some signals from quantum theory.

B. Vakili; K. Nozari; V. Hosseinzadeh; M. A. Gorji

2014-08-20

432

Two Photon Polymerization of Microneedles for Transdermal Drug Delivery  

PubMed Central

Importance of the field Microneedles are small-scale devices that are finding use for transdermal delivery of protein-based pharmacologic agents and nucleic acid-based pharmacologic agents; however, microneedles prepared using conventional microelectronics-based technologies have several shortcomings, which have limited translation of these devices into widespread clinical use. Areas covered in this review Two photon polymerization is a laser-based rapid prototyping technique that has been recently used for direct fabrication of hollow microneedles with a wide variety of geometries. In addition, an indirect rapid prototyping method that involves two photon polymerization and polydimethyl siloxane micromolding has been used for fabrication of solid microneedles with exceptional mechanical properties. What the reader will gain In this review, the use of two photon polymerization for fabricating in-plane and out-of-plane hollow microneedle arrays is described. The use of two photon polymerization-micromolding for fabrication of solid microneedles is also reviewed. In addition, fabrication of microneedles with antimicrobial properties is discussed; antimicrobial microneedles may reduce the risk of infection associated with formation of channels through the stratum corneum. Take home message It is anticipated that the use of two photon polymerization as well as two photon polymerization-micromolding for fabrication of microneedles and other microstructured drug delivery devices will increase over the coming years. PMID:20205601

Gittard, Shaun D.; Ovsianikov, Aleksandr; Chichkov, Boris N.; Doraiswamy, Anand; Narayan, Roger J.

2010-01-01

433

Development and characterization of lyophilized diazepam-loaded polymeric micelles.  

PubMed

Polymeric micelles were studied as delivery carriers of diazepam, a practically insoluble drug in water, for rectal administration. The diazepam-loaded polymeric micelles were developed by using poloxamer 407 (P407), poloxamer 188, and D-?-tocopheryl poly(ethylene glycol) 1000 succinate (TPGS). Among the used polymers, TPGS resulted in polymeric micelles with good characteristics for encapsulation of diazepam which had the small particle size of 8-12 nm and narrow size distribution (PI 0.053-0.275). Additionally, 7.5% w/v of TPGS could entirely entrap the desired concentration of diazepam (5 mg/mL). To improve the physical stability upon lyophilization, an addition of P407 of 1% w/v prevented aggregation, increased physical stability, and maintained chemical stability of the lyophilized powders of diazepam-loaded polymeric micelles for 3 months storage at 4°C. The rate and amount of diazepam release from TPGS polymeric micelles mainly depended on the concentration of TPGS. The release data were fitted to Higuchi's model suggesting that the drug release mechanism was controlled by Fickian diffusion. In conclusion, 10% w/v TPGS and 1% w/v P407 were the optimum formulation of lyophilized diazepam-loaded polymeric micelles. PMID:24092522

Suksiriworapong, Jiraphong; Rungvimolsin, Tanaporn; A-gomol, Atitaya; Junyaprasert, Varaporn Buraphacheep; Chantasart, Doungdaw

2014-02-01

434

Optical investigations of various polymeric materials used in dental technology  

NASA Astrophysics Data System (ADS)

Dental prosthetic restorations have to satisfy high stress as well as aesthetic requirements. In order to avoid deficiencies of dental prostheses, several alternative systems and procedures were imagined, directly related to the material used and also to the manufacturing technology. Increasing the biomechanical comportment of polymeric materials implies fiber reinforcing. The different fibers reinforcing products made very difficult the evaluation of their performances and biomechanical properties analysis. There are several known methods which are used to assess the quality of dental prostheses, but most are invasive. These lead to the destruction of the samples and often no conclusion could be drawn in the investigated areas of interest. Using a time domain en-face OCT system, we have recently demonstrated real time thorough evaluation of quality of various dental treatments. The aim of this study was to assess the quality of various polymeric materials used in dental technology and to validate the en face OCT imagistic evaluation of polymeric dental prostheses by using scanning electron microscopy (SEM) and microcomputer tomography (?CT). SEM investigations evidenced the nonlinear aspect of the interface between the polymeric material and the fiber reinforcement and materials defects in some samples. The results obtained by microCT revealed also some defects inside the polymeric materials and at the interfaces with the fiber reinforcement. The advantages of the OCT method consist in non-invasiveness and high resolution. In addition, en face OCT investigations permit visualization of the more complex stratified structure at the interface between the polymeric material and the fiber reinforcement.

Negrutiu, Meda Lavinia; Sinescu, Cosmin; Topala, Florin Ionel; Ionita, Ciprian; Goguta, Luciana; Marcauteanu, Corina; Rominu, Mihai; Podoleanu, Adrian Gh.

2011-10-01

435

Inorganic Surface Modification of Nonwoven Polymeric Substrates  

NASA Astrophysics Data System (ADS)

In this study, atomic layer deposition (ALD), a vapor phase inorganic thin film deposition technique, is used to modify the surface of a range of industrially relevant polymers to enhance surface properties or impart additional functionalities. Several unique demonstrations of polymer surface modification are presented including uniform nanomaterial photodeposition to the surface of nonowoven fabrics and the first application of photocatalytic thin film coated nonwovens for advanced filtration of heavy metals from solution. Recent advances in polymer synthesis and processing technologies have resulted in the production of novel polymer systems with unique chemistries and sub-micron scale dimensions. As a result, advanced fiber systems have received much attention for potential use in a wide range of industrially and medically important applications such as advanced and selective filtration, catalysis, flexible electronics, and tissue engineering. However, tailoring the surface properties of the polymer is still needed in order to realize the full range of advanced applications, which can be difficult given the high complexity and non-uniformity of nonwoven polymeric structures. Uniform and controllable inorganic surface modification of nonwovens allows the introduction or modification of many crucial polymer properties with a wide range of application methods.

Halbur, Jonathan Chandler

436

How do entangled polymeric liquids flow?  

NASA Astrophysics Data System (ADS)

This work focused on investigating fundamental questions in polymer dynamics such as how entangled polymeric liquids respond to fast external deformation. By developing an effective particle tracking velocimetric (PTV) method, along with conventional rheometric measurements, new insights can be gained into the phenomenology of entangled polymers in presence of startup shear, step strain and large amplitude oscillatory shear (LAOS). During startup shear of well entangled systems, the shear field becomes inhomogeneous after the stress overshoot for a range of applied shear rates beyond the Newtonian region [1]. The emergence of shear banding after stress overshoot helped us to identify the stress overshoot as indicating yielding, whose characteristics obey some scaling laws. In step shear, contrary to the conventional perception that entangled polymers would undergo quiescent relaxation, the PTV observations reveal macroscopic motions after shear cessation [2]. The recoil-like macroscopic motions appears to reflect an elastic breakdown of the entanglement network due to sufficient build-up of retractive forces. LAOS experiments also demonstrate that entangled polymers cannot sustain a high magnitude of fast deformation without undergoing cohesive failure [3]. [1] Macromolecules 2008, 41, 2663 [2] Macromolecules 2007, 40, 8031 [3] J. Rheol. 2008, 52, 341.

Sundar Ravindranath, Sham; Wang, Shi-Qing

2009-03-01

437

Transition metal-free olefin polymerization catalyst  

DOEpatents

Ethylene and/or propylene are polymerized to form high molecular weight, linear polymers by contacting ethylene and/or propylene monomer, in the presence of an inert reaction medium, with a catalyst system which consists essentially of (1) an aluminum alkyl component, such as trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-octylaluminum and diethylaluminum hydride and (2) a Lewis acid or Lewis acid derivative component, such as B (C.sub.6 F.sub.5).sub.3, [(CH.sub.3).sub.2 N (H) (C.sub.6 H.sub.5)].sup.+ [B (C.sub.6 F.sub.5)4].sup.-, [(C.sub.2 H.sub.5).sub.3 NH].sup.+ [B C.sub.6 F.sub.5).sub.4 ],.sup.-, [C(C.sub.6 F.sub.5).sub.3 ].sup.+ [B(C.sub.6 F.sub.5).sub.4 ].sup.-, (C.sub.2 H.sub.5).sub.2 Al(OCH.sub.3), (C.sub.2 H.sub.5).sub.2 Al(2,6-di-t-butyl-4-methylphenoxide), (C.sub.2 H.sub.5)Al(2,6 -di-t-butylphenoxide).sub.2, (C.sub.2 H.sub.5).sub.2 Al(2,6-di-t-butylphonoxide) , 2,6 -di-t-butylphenol.multidot.methylaluminoxane or an alkylaluminoxane, and which may be completely free any transition metal component(s).

Sen, Ayusman (State College, PA); Wojcinski, II, Louis M. (State College, PA); Liu, Shengsheng (State College, PA)

2001-01-01

438

Switchable Adhesion from Bicomponent Polymeric Brushes  

NASA Astrophysics Data System (ADS)

We investigated the adhesive and wetting properties of bicomponent polymeric brushes made from end functionalized hydrophilic and hydrophobic polymer chains. The molecular organization of the mixed brush could be varied reversibly by exposure to selective solvents for the two polymers. Adhesive properties were tested by debonding a flat ended probe from soft pressure-sensitive-adhesives (hydrophobic & hydrophilic) and wetting properties were tested by contact angle measurements of water & diiodomethane droplets. The bicomponent brushes were chemically grafted on silicon wafers from end-functionalized chains. Wetting experiments were done directly on the wafers while for adhesion experiments, the wafers were glued on the flat end of the probe prior to the tests. In all cases the organization of the bicomponent brush could be modified reproducibly and reversibly by exposure to selective solvents. Following this strategy we succeeded to create remarkably stable adaptive polymer surfaces that can modify their adhesion and wetting reversibly and also tune them by varying the ratio of the bicomponent brush layer.

Retsos, Haris; Gorodyska, Ganna; Creton, Costantino

2005-03-01

439

Oligonucleotide and Long Polymeric DNA Encoding  

SciTech Connect

This report summarizes the work done at Lawrence Livermore National Laboratory for the Oligonucleotide and Long Polymeric DNA Encoding project, part of the Microelectronic Bioprocesses Program at DARPA. The goal of the project was to develop a process by which long (circa 10,000 base-pair) synthetic DNA molecules could be synthesized in a timely and economic manner. During construction of the long molecule, errors in DNA sequence occur during hybridization and/or the subsequent enzymatic process. The work done on this project has resulted in a novel synthesis scheme that we call the parallel pyramid synthesis protocol, the development of a suit of computational tools to minimize and quantify errors in the synthesized DNA sequence, and experimental proof of this technique. The modeling consists of three interrelated modules: the bioinformatics code which determines the specifics of parallel pyramid synthesis for a given chain of long DNA, the thermodynamics code which tracks the products of DNA hybridization and polymerase extension during the later steps in the process, and the kinetics model which examines the temporal and spatial processes during one thermocycle. Most importantly, we conducted the first successful syntheses of a gene using small starting oligomers (tetramers). The synthesized sequence, 813 base pairs long, contained a 725 base pair gene, modified green fluorescent protein (mGFP), which has been shown to be a functional gene by cloning into cells and observing its green fluorescent product.

Miller, E; Mariella Jr., R P; Christian, A T; Gardner, S N; Williams, J M

2003-11-24

440

Polymeric Bladder for Storing Liquid Oxygen  

NASA Technical Reports Server (NTRS)

A proposed system for storing oxygen in liquid form and dispensing it in gaseous form is based on (1) initial subcooling of the liquid oxygen; (2) containing the liquid oxygen in a flexible vessel; (3) applying a gas spring to the flexible vessel to keep the oxygen compressed above the saturation pressure and, thus, in the liquid state; and (4) using heat leakage into the system for vaporizing the oxygen to be dispensed. In a typical prior system based on these principles, the flexible vessel is a metal bellows housed in a rigid tank, and the gas spring consists of pressurized helium in the tank volume surrounding the bellows. Unfortunately, the welds in the bellows corrugations are subject to fatigue, and, because bellows have large ullage, a correspondingly large fraction of the oxygen content cannot be expelled. In the proposed system, the flexible vessel would be a bladder made of a liquid- crystal polymer (LCP). (LCPs are strong and compatible with liquid oxygen.) In comparison with a metal bellows, a polymeric bladder would have less ullage and would weigh less. In experiments involving fatigue cycling at liquid-nitrogen temperatures, two LCPs were found to be suitable for this application.

Walker, David H.; Harvey, Andrew C.; Leary, William

2009-01-01

441

Smart materials based on polymeric systems  

NASA Astrophysics Data System (ADS)

The science and technology of the 21st century will rely heavily on the development of new materials. Such materials are expected to be innovative with regards to structure, functionality, and design. One concept in achieving this goal is what has been termed 'smart materials.' A smart material is defined as a material which has been atomically or molecularly engineered in such a way that the microstructure itself is imbued with embedded sensors, actuators, and control mechanisms, giving it the capability of sensing and responding to external stimuli in a predetermined and controlled fashion. Programs in this area have involved technological advances in a number of scientific disciplines inclusive of materials science, chemistry, biotechnology, molecular electronics, nanotechnology, etc. These have encompassed research themes into the design of polymeric materials which are capable of altering their mechanical and electrical properties when exposed to specific molecular species, the synthesis of amphiphlic molecules with easily modified ferroelectric, photochromic and nonlinear properties, the design of stress sensitive molecules capable of monitoring damage and redistributing stresses in composites, and the merging of biological and chemical technologies to create assemblies with signal transduction properties. This presentation highlights some of these activities.

Crowson, Andrew

1996-02-01

442

Polymerization of glucans by enzymatically active membranes.  

PubMed

Conventional enzyme membrane reactors are not appropriate for a continuous synthesis of macromolecules and simultaneous product release. By immobilizing the enzyme in sufficiently large pores of a membrane an ensemble of miniaturized bioreactors is created. Product molecules are continuously removed from the enzyme by the flow of the reaction mixture across the membrane. Additionally, by varying the flow rate, it ought to be possible to influence the substrate as well as the enzyme-product residence times and thereby the product macromolecule's size. In this paper we present the first results of experiments involving enzymatic 1,4-alpha-glucan synthesis, using sucrose as substrate, maltooligosaccharides (DP 3-6) as primers, and membrane-immobilized amylosucrase. Epoxy groups for a covalent enzyme immobilization were generated on polypropylene microfiltration membranes by heterogeneous photoinitiated graft polymerization of glycidyl methacrylate. The influence of primer concentration and flow rate through the enzyme-membrane on amylosucrase activity, molecule growth, and coupling efficiency for glucose (% of coupled glucose versus free glucose) were investigated. The enzymatically mediated chain elongation of maltooligosaccharides by the successive addition of glucose units was achieved for the first time in a transmembrane process utilizing amylosucrase membranes. PMID:12363346

Becker, Margot; Provart, Nicholas; Lehmann, Ingeburg; Ulbricht, Mathias; Hicke, Hans-Georg

2002-01-01

443

Microwave welding of polymeric-microfluidic devices  

NASA Astrophysics Data System (ADS)

This paper describes a novel technique for bonding polymeric-microfluidic devices using microwave energy and a conductive polymer (polyaniline). The bonding is achieved by patterning the polyaniline features at the polymer joint interface by filling of milled microchannels. The absorbed electromagnetic energy is then converted into heat, facilitating the localized microwave bonding of two polymethylmethacrylate (PMMA) substrates. A coaxial open-ended probe was used to study the dielectric properties at 2.45 GHz of the PMMA and polyaniline at a range of temperatures up to 120 °C. The measurements confirm a difference in the dielectric loss factor of the PMMA substrate and the polyaniline, which means that differential heating using microwaves is possible. Microfluidic channels of 200 µm and 400 µm widths were sealed using a microwave power of 300 W for 15 s. The results of the interface evaluations and leak test show that strong bonding is formed at the polymer interface, and there is no fluid leak up to a pressure of 1.18 MPa. Temperature field of microwave heating was found by using direct measurement techniques. A numerical simulation was also conducted by using the finite-element method, which confirmed and validated the experimental results. These results also indicate that no global deformation of the PMMA substrate occurred during the bonding process.

Yussuf, A. A.; Sbarski, I.; Hayes, J. P.; Solomon, M.; Tran, N.

2005-09-01

444

Smart materials based on polymeric systems  

SciTech Connect

The science and technology of the 21st century will rely heavily on the development of new materials. Such materials are expected to be innovative with regards to structure, functionality, and design. One concept in achieving this goal is what has been termed {open_quotes}smart materials{close_quotes}. A smart material is defined as a material which has been atomically or molecularly engineered in such a way that the microstructure itself is imbued with embedded sensors, actuators, and control mechanisms, giving it the capability of sensing and responding to external stimuli in a predetermined and controlled fashion. Programs in this area have involved technological advances in a number of scientific disciplines inclusive of materials science, chemistry, biotechnology, molecular electronics, nanotechnology, etc. These have encompassed research themes into the design of polymeric materials which are capable of altering their mechanical and electrical properties when exposed to specific molecular species, the synthesis of amphiphlic molecules with easily modified ferroelectric, photochromic and nonlinear properties, the design of stress sensitive molecules capable of monitoring damage and redistributing stresses in composites, and the merging of biological and chemical technologies to create assemblies with signal transduction properties. This presentation will highlight some of these activities.

Crowson, A. [Army Research Office, Research Triangle Park, NC (United States)

1995-12-01

445

Helper-Dependent Adenoviral Vectors.  

PubMed

Helper-dependent adenoviral vectors are devoid of all viral coding sequences, possess a large cloning capacity, and can efficiently transduce a wide variety of cell types from various species independent of the cell cycle to mediate long-term transgene expression without chronic toxicity. These non-integrating vectors hold tremendous potential for a variety of gene transfer and gene therapy applications. Here, we review the production technologies, applications, obstacles to clinical translation and their potential resolutions, and the future challenges and unanswered questions regarding this promising gene transfer technology. PMID:24533227

Rosewell, Amanda; Vetrini, Francesco; Ng, Philip

2011-10-29

446

Requirements for airborne vector gravimetry  

NASA Technical Reports Server (NTRS)

The objective of airborne vector gravimetry is the determination of the full gravity disturbance vector along the aircraft trajectory. The paper briefly outlines the concept of this method using a combination of inertial and GPS-satellite data. The accuracy requirements for users in geodesy and solid earth geophysics, oceanography and exploration geophysics are then specified. Using these requirements, accuracy specifications for the GPS subsystem and the INS subsystem are developed. The integration of the subsystems and the problems connected with it are briefly discussed and operational methods are indicated that might reduce some of the stringent accuracy requirements.

Schwarz, K. P.; Colombo, O.; Hein, G.; Knickmeyer, E. T.

1992-01-01

447

Tandem chain walking polymerization and atom transfer radical polymerization for efficient synthesis of dendritic nanoparticles for bioconjugation.  

PubMed

A tandem polymerization methodology, chain walking polymerization (CWP) followed by atom transfer radical polymerization, was developed for efficient synthesis of nanoparticles for bioconjugation. Using the chain walking palladium-alpha-diimine catalyst (catalyst 1), dendritic polymers bearing multiple initiation sites were synthesized and used as macroinitiators for subsequent Cu(I)-mediated ATRP. Control of molecular weight and size of the water-soluble core-shell polymeric nanoparticles was achieved by tuning reaction conditions. Addition of an N-acryloyloxysuccinamide (NAS) monomer at the end of the ATRP afforded NHS-activated polymer nanoparticles. Conjugation with both small dye molecules and protein (ovalbumin) yielded nanoparticle conjugates with relatively high dye or protein per particle ratio. With the efficient synthesis and good biocompatibility, these nanoparticles may find many potential applications in bioconjugation. PMID:16569005

Chen, Guanghui; Huynh, Devan; Felgner, Philip L; Guan, Zhibin

2006-04-01

448

Testing Studentsâ Understanding of Vector Concepts  

NSDL National Science Digital Library

After four years of research we designed a 20-item multiple choice vector concept test (Test of Understanding of Vectors, TUV). In this article we analyze: 1) the reliability and discriminatory power of the test, and 2) studentsâ understanding of the vector concepts evaluated in the test. The final version of the test was administered in English to 423 students who were finishing an Electricity and Magnetism course at a large private Mexican university. In the first part of the article, we show results indicating that the TUV is a reliable assessment tool. In the second part, we examine studentsâ overall performance on the test and analyze the results of the five most difficult items for students: geometric interpretation of dot product, calculation of dot product of two vectors written in unit-vector notation, graphic representation of a unit vector, calculation of the direction of a vector written in unit-vector notation, and graphical subtraction of vector in 2D.

Barniol, Pablo; Zavala, Genaro

2013-12-21

449

Form Factors and Vector Mesons  

Microsoft Academic Search

The 2pi and 3pi resonances are re-examined from the point of view that they are vector mesons coupled to conserved currents. The theory of unstable mesons is discussed and formulas are then derived for the emission and propagation of these mesons. The connection with electromagnetic form factors is then given, particularly for the simple case of infinite bare mass. The

Murray Gell-Mann; Fredrik Zachariasen

1961-01-01

450

Portfolio Analysis for Vector Calculus  

ERIC Educational Resources Information Center

Classic stock portfolio analysis provides an applied context for Lagrange multipliers that undergraduate students appreciate. Although modern metho